DESCRIPTION INCINERATION APPARATUS AND GASIFICATION APPARATUS Technical Field The present invention relates to an incineration apparatus, and more particularly to an incineration apparatus for incinerating combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil at a high temperature. The present invention also relates to a gasification apparatus, and more particularly to a gasification apparatus for gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil at a high temperature.

Background Art In an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil, a high-temperature gas is produced by incineration or gasification. Such a high-temperature gas includes a corrosive gas containing hydrogen chlorides, ammonia, cyanide, sulfur oxides, hydrogen sulfides, or the like, which are originated from chlorine contents, nitrogen contents, or sulfur contents contained in combustibles.

In such an environment, metallic materials are intensively corroded, particularly, by chlorine. FIG. 1 shows temperature dependency of a corrosion rate of a metallic material in a high-temperature corrosive gas environment. In FIG. 1, electrochemical corrosion occurs in a region under 150°C of an acid dew-point. In a region above the acid dew-point, a relatively small amount of corrosion occurs in a range of 150 to 320°C. In a region above 320°C, corrosion becomes more intensive as the temperature rises. If dust is included in a high-temperature corrosive gas, for example, in a boiler of a waste incineration furnace or the like, then high-temperature molten salt corrosion occurs so that salts in the dust are melted at 300 to 700°C to promote corrosion. As shown by a solid line A in FIG. 1, a corrosion rate of the material becomes extremely high. Even if dust is not included in a high-temperature corrosive gas, as shown by a broken line B, corrosion becomes conspicuous in a region above 320°C as the temperature rises.

Such corrosion behavior is based on the fact that a protective film against corrosion

cannot be formed when a gas contains chlorine contents or sulfur contents because metallic chlorides produced by corrosion have low melting points and extremely high volatility.

Accordingly, direct use of metallic materials has been avoided for devices used in an environment in which the devices are exposed to a high-temperature corrosive gas, particularly, in an environment which causes high-temperature molten salt corrosion. In a case where metallic materials need to be used, the metallic materials are cooled to improve the durability thereof, or a refractory material is used so as not to bring the metallic materials into direct contact with a high-temperature corrosive gas to protect surfaces of the metallic materials.

However, for example, in a heat transfer pipe of a heat exchanger, metallic materials cannot be cooled because the cooling degrades or eliminates required functions of the device. Further, the use of the refractory materials increases the weight of the device and may cause damage or removal of the refractory materials due to a thermal expansion difference between metallic materials and the refractory materials. Accordingly, the device should be inspected periodically to repair the refractory materials.

It has been attempted to adjust composition of a metallic material to improve the corrosion resistance of the metallic material. For example, a high-grade material such as Alloy 625 has a relatively high corrosion resistance in a corrosive gas environment containing hydrogen chlorides. However, such high-grade materials are considerably expensive and do-not necessarily-have-a sufficient corrosion resistance. Thus, a large amount of high-grade material cannot be used for various devices in an apparatus.

Meanwhile, there have been developed new systems to reduce environmental loads or improve energy efficiency in a field of waste disposal.

One of such new systems is a waste gasification and slagging combustion system, which has already been in practical use and is expected to lead the future waste incineration systems.

While a conventional incineration furnace, particularly a fluidized-bed combustion furnace, has a combustion temperature of about 800 to 900°C, a gasification and slagging combustion apparatus has a combustion temperature of about 1200 to 1500°C or about 1200 to 2000°C. Thus, the temperature of a

slagging combustion furnace becomes about 900 to 2000°C, which is extremely higher than that of the conventional incineration furnace. Accordingly, the gasification and slagging combustion apparatus requires a larger number of devices used at high temperatures than the conventional incineration furnace. Further, from the viewpoint of effective utilization of energy, the gasification and slagging combustion apparatus should include a system to effectively recover heat from an exhaust gas having high temperatures of about 1200 to 1500°C. Thus, there has been desired a metallic material having an excellent strength and corrosion resistance at high temperatures, preferably up to about 1200°C, The inventors have discovered that addition of aluminum is effective in improving corrosion resistance in a high-temperature corrosion atmosphere and developed a nickel base corrosion resisting alloy containing aluminum, which is hereinafter referred to as a conventional alloy. FIG. 2 shows a tendency of variation of corrosion rates of alloys in which aluminum (Al) or silicon (Si) is added to a tritium (T) alloy. Such a nickel base corrosion resisting alloy is disclosed by Japanese laid-open patent publication No. 2002-129267, the entire disclosure of which is incorporated herein by reference. The conventional alloy contains chromium (Cr) in a range of about 25 to 40 mass %, aluminum (Al) in a range of about 1.5 to 2.5 mass %, carbon (C) in a range of about 0.1 to 0.5 mass %, tungsten (W) of about 15 mass % or less, manganese (Mn) of about 2.0 mass % or less, silicon (Si) in a range of about 0.3 to 6 mass %, iron (Fe) of about 5 % or less, nickel (Ni), and inevitable-impurities., If the conventional alloy is used with a cast structure, local corrosion may occur along a continuous deposit such as carbide. Thus, the conventional alloy does not have an excellent strength and corrosion resistance at high temperatures, for example, up to about 1200°C. Accordingly, an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil cannot have improved durability and functions.

Disclosure of Invention The present invention has been made in view of the above drawbacks. It is, therefore, an object of the present invention to provide an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as

coal, or liquid fuel such as heavy oil at a high temperature which includes at least one device made of an alloy having an excellent corrosion resistance at high temperatures. For example, such a device is subjected to an intensive corrosion environment in which chlorination can occur as well as sulfidation at high temperatures. The alloy has a sufficient high-temperature strength and corrosion resistance even in a composite corrosion environment in which chlorination and sulfidation occur together with oxidation at high temperatures. Specifically, the object of the present invention is to provide an incineration apparatus or a gasification apparatus which has improved durability and functions as compared to a conventional apparatus without excessive cooling or surface protection.

In order to eliminate the drawbacks of the conventional alloy, the inventors have studied an alloy having excellent properties such that no local corrosion occurs along a continuous deposit such as carbide. The inventors experimentally produced several alloys having different compositions based on commercial alloys and conventional alloys and formed sample devices made of such alloys. The inventors conducted corrosion experiments in an incineration apparatus and a gasification apparatus including the sample devices.

As a result of analysis of the conventional alloys after the corrosion experiments, local corrosion occurred continuously along chromium carbide or tungsten carbide deposited in a base material. Detailed examination of corrosion formation showed that the deposited chromium carbide was changed into chromium chlorides or chromium oxides in the alloy to thereby cause corrosion. Carbide is required for an alloy because it is effective in providing a high-temperature strength.

When carbide unlikely to be corroded is used for an alloy, it is expected to improve the corrosion resistance of the alloy without lowering the strength of the alloy.

Corrosion of carbide can be reduced by a method of converting the carbide into a compound to form a film more protective than chromium carbide, or by a method of converting the carbide into a compound less likely to react with an oxidizing agent than chromium carbide. Chromium (Cr) reacts with oxygen to form Cr203, which has excellent protective properties. However, because chromium carbide is preferentially corroded in the aforementioned environment, even though a Cr203 scale is formed on the alloy, the Cr203 scale cannot effectively perform an excellent protective function in the corrosive environment.

Accordingly, a different approach has been required to improve the corrosion

resistance of carbide. Chromium (Cr) has a strong affinity to an oxidizing agent and hence a low dissociation pressure. Accordingly, even if an oxidizing agent has a low partial pressure, a corrosion reaction occurs. As an oxidizing agent enters into a deeper portion of an alloy along carbide, the partial pressure of the oxidizing agent becomes smaller. Thus, an element having a high dissociation pressure can prevent the corrosion reaction. Specifically, the corrosion resistance of chromium carbide can be improved by addition of an element that has a dissociation pressure higher than chromium (Cr) and is capable of forming carbide interchanged with chromium (Cr). At that time, it is desirable that the addition of the element is unlikely to lower the strength of the alloy. Because problematic corrosion occurs along continuous carbide, the element may partially be substituted for the chromium carbide. Since the element inhibits an oxidizing agent from entering into the alloy, it is possible to reduce corrosion.

From the above viewpoints, the inventors experimentally added niobium (Nb), which is one of the 5A group elements capable of forming carbide, to a conventional alloy to produce new alloys in addition to commercial alloys and conventional alloys. Corrosion experiments were conducted for these alloys in an environment containing HC1. Results are listed in Table 1 below. As can be seen from Table 1, the amounts of internal corrosion were remarkably reduced in niobium added alloys. Thus, addition of niobium (Nb) is effective in improvement of the corrosion resistance of an alloy. Alloy Content (mass %) Maximum Note Mu c Si Nln Ni Cr W U Fe Nb Other 6000C 9000C Inconel-0. 02 0. 06 0.08 Bal. 21. 92 0. 29 4.36 3.50 8. 85Mo 0. 31 N/A Commercial alloy 625 No. 1 0. 28 0. 68 0.69 Bal. 32. 30 16.82 <0. 1 0. 10 0. 29 1.92 Commercial alloy No. 2 0.25 2. 03 0. 70 Bal. 25. 11 4. 86 2. 12 0. 26 0. 68 0. 99 Conventional alloy No. 3 0. 28 2. 10 0.73 Bal. 25. 70 10.60 1. 86 0. 33 0. 38 0. 86 Conventional alloy No. 4 0. 28 1. 22 0. 71 Bal. 26.70 10.00 2.00 0. 17 0. 41 1. pi Conventional alloy No. 5 0. 27 1. 05 0.74 Bal. 27. 51 10.14 1.84 1.05 3. 12 0. 43 0.83 Comparative alloy No. 6 0. 26 2. 07 0.68 Bal. 24.84 9.95 1. 99 0.82 1. 48 0. 29 0.34 Inventive alloy No. 7 0. 27 0. 64 0.82 Bal. 25. 13 10. 04 1. 78 1. 34 1. 49 0. 38 0.43 Inventive alloy No. 8 0. 29 1. 24 0.82 Bal. 27. 31 10.01 1.82 7. 82 1. 52 0. 42 0.62 Inventive alloy No. 9 0. 28 2. 04 0.74 Bal. 23.02 5.07 1.74 0. 85 1. 54Ti 0.32 0.74 Inventive alloy No. 10 0.24 2.12 0. 74 Bal. 23.16 5.03 1. 92 0. 76 1. 52Zr 0.38 0.76 Inventive alloy No. 11 0. 31 1. 98 0. 81 Bal. 23. 22 5.14 1. 99 0. 82 1. 49V 0. 35 0.71 Inventive alloy Table 1

Typically, in a waste incineration furnace, if chlorine is included in an environment together with alkali metal, then alkalichloride molten salt is formed to adversely cause molten salt corrosion. When alloys according to the present invention were used in a molten salt corrosion environment, corrosion behavior was examined. Because tungsten (W) was deposited as carbide together with chromium, corrosion occurred along a tungsten depletion zone which was formed around the carbide. In such a case, by adding a carbide formation additive for preventing tungsten (W) from being deposited as carbide to thereby prevent the formation of the depletion zone, corrosion resistance is expected to be improved.

Any element other than niobium (Nb) can prevent the depletion zone and contribute to improvement of the corrosion resistance as long as it is capable of forming carbide. For example, elements of the 4A and 5A groups in the periodic table can be added. Addition of such an element can prevent a depletion zone and improve the corrosion resistance of an alloy. In the aforementioned corrosion experiments, titanium (Ti), zirconium (Zr), and vanadium (V) were added, and alloys including these elements also showed an improved corrosion resistance as compared to the conventional alloys.

The present invention has been made in view of the above discussion and the experiments based thereon. According to the present invention, tungsten (W) for improving strength and corrosion resistance, and aluminum (Al) and silicon (Si) for improving corrosion resistance are added to a base material of nickel (Ni) having a relatively high corrosion resistance to chlorine so as to produce an alloy having an excellent corrosion resistance at high temperatures. The alloy may include niobium (Nb) for substitution for carbide or an additional element for preventing formation of a depletion zone. The alloy includes iron (Fe) such that the corrosion resistance of the base material is not deteriorated. The alloy contains carbon (C) and manganese (Mn) required to produce an alloy, and impurities of other elements. In an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil, the alloy is used as a material for a device subjected to an intensive corrosion environment in which chlorination can occur as well as sulfidation at high temperatures.

Specifically, according to the present invention, the aforementioned drawbacks have been solved by the following manner.

(1) In an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil at a high temperature, at least one device is made of a nickel base heat resisting alloy. The nickel base heat resisting alloy includes chromium (Cr) in a range of about 23 to 40 mass %, tungsten (W) in a range of about 5 to 15 mass %, silicon (Si) in a range of about 0.3 to 4 mass %, aluminum (Al) in a range of about 1.5 to 2.5 mass %, Carbon (C) in a range of about 0.1 to 0.5 mass %, manganese (Mn) of about 2.0 mass % or less, iron (Fe) of about 5 % or less, and nickel (Ni) of the balance except inevitable impurities.

(2) The nickel base heat resisting alloy may further include niobium (Nb) in a range of about 0.1 to 5 mass %, preferably about 0.1 to 3 mass %.

(3) In order to recover heat from a high-temperature corrosive gas, the apparatus may have a heat exchanger provided in a gas passage through which the high-temperature corrosive gas flows. The heat exchanger has a heat transfer pipe having a surface exposed to the high-temperature corrosive gas. The heat transfer pipe may be made of the nickel base heat resisting alloy.

In order to substitute other carbide for chromium carbide, which has a low corrosion resistance, or to prevent a depletion zone, niobium (Nb) or an element of the 4A or 5A group for forming carbide may be added to a nickel base corrosion resisting alloy including aluminum (Al). Depending on a required corrosion resistance, the amount of iron (Fe) contained may be increased so as to reduce cost of the alloy.

There will be described reasons why the above composition of the alloy is determined.

Chromium (Cr) is required to improve the high-temperature corrosion resistance of an alloy. When chromium (Cr) is bonded to oxygen in an atmosphere, it forms a Cr203 scale to provide a high corrosion resistance at high temperatures.

When the amount of chromium added is not more than 23 %, the alloy does not provide sufficient effects at temperatures over 1000°C. If chromium (Cr) is excessively added, then the mechanical strength of. the alloy is lowered. When the amount of chromium added is not less than 40 %, a-chromium which has an

adversely influence on the corrosion resistance of the alloy is deposited. Thus, the amount of chromium (Cr) added is preferably in a range of about 23 to 40 %.

Tungsten (W) is required to enhance the high-temperature strength of an alloy. Tungsten (W) contributes to improvement of the corrosion resistance in a molten salt corrosion environment. Accordingly, tungsten (W) of at least 5 % is added to maintain the strength and the corrosion resistance to molten salts.

However, since the corrosion resistance of tungsten (W) is low, if tungsten (W) is added over 15 %, the corrosion resistance is deteriorated at high temperatures.

Thus, the upper limit of addition is set at 15 %. Accordingly, the amount of tungsten (W) added is preferably in a range of about 5 to 15 %.

Although silicon (Si) lowers the high-temperature strength of an alloy, it is effective in improving the castability and the oxidation resistance of an-alloy. The lower limit of addition is set at 0.3 %, at which the castability is improved. When an alloy contains aluminum (Al) and silicon (Si), the corrosion resistance of the alloy can be improved. Accordingly, if the amount of addition of aluminum (Al) and silicon (Si) is increased, the corrosion resistance of an alloy can remarkably be improved. However, at that time, the mechanical properties of the alloy are deteriorated. Thus, from the viewpoint of the mechanical performance, the upper limit is set at 4 %. Therefore, the amount of silicon (Si) added is preferably in a range of about 0.3 to 4 %. When an alloy is required to have a high level of mechanical properties, the amount of silicon (Si) added should preferably be in a range of about 0.3 to 1.5 %.- Aluminum (Al) improves the chlorination resistance of an alloy. When aluminum (Al) of 1.5 % or less is added, the improvement of the chlorination resistance is insufficient. If a large amount of aluminum (Al) is added, the castability is lowered. Thus, from the viewpoint of the castability, the upper limit is set at 2.5 %. Accordingly, the amount of aluminum (Al) added is preferably in a range of about 1.5 to 2.5 %.

Elements of the 4A and 5A groups, such as titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), and tantalum (Ta), are elements capable of forming carbide. Such elements are required to prevent deposition of chromium carbide and formation of a tungsten depletion zone and to improve the corrosion resistance of an alloy. When an element of the 4A or 5A group of at

least 0. 1 % is added, the aforementioned effects can be obtained. However, excessive addition lowers the corrosion resistance of an alloy. Thus, the upper limit is set at 5 %.

It is desirable to use niobium (Nb) as an element for forming carbide.

Addition of niobium (Nb) of 0.1 % can prevent continuous chromium carbide.

However, niobium (Nb) has an extremely low corrosion resistance at high temperatures. Accordingly, excessive addition of niobium (Nb) lowers the corrosion resistance of an alloy. Thus, the upper limit is set at 5 %, at which the corrosion resistance of an alloy is not so influenced. The amount of niobium (Nb) added is preferably in a range of about 0.1 to 5 %, more preferably about 0.1 to 3 %.

It is desirable that the amount of carbon (C) is small in view of the corrosion resistance of an alloy. However, carbon (C) improves the mechanical strength and the castability of an alloy. Accordingly, the amount of carbon (C) is preferably in a range of about 0.1 to 0.5 %.

Manganese (Mn) lowers the oxidation resistance and the high-temperature strength of an alloy. Accordingly, a large amount of manganese (Mn) should not be added. However, manganese (Mn) improves the castability of an alloy and also effectively serves as a deoxidizing agent and a desulfurizing agent. Thus, the amount of manganese (Mn) added is at most about 2 %, preferably at most about 1 %, so as not to largely lower the oxidation resistance and the high-temperature strength of an alloy.

From the viewpoint of the corrosion resistance of an alloy, it is desirable that iron (Fe) is not contained in the alloy. However, when scrap or the like is used as a raw material of an alloy, iron (Fe) may be contained as impurities in an alloy. Accordingly, the upper limit of iron (Fe) contained is set at 5 %.

Preferably, the amount of iron (Fe) contained is at most about 1 %. When the amount of iron (Fe) contained is increased, cost of the alloy can be reduced.

Accordingly, iron (Fe) can be added in a range such that the addition of iron (Fe) does not lower the corrosion resistance of the alloy.

Since an alloy according to the present invention has a high mechanical strength, it is difficult to work the alloy. On the other hand, local corrosion can be reduced without heat treatment in working the alloy. Accordingly, casting is

favorable in cost for working the alloy to produce a mechanical part. Particularly, when the alloy is used to produce a part in the form of a pipe, it is desirable to employ a centrifugal casting method because the centrifugal casting method can reduce manufacturing cost and can form an outer surface of the part so as to have a high corrosion resistance.

There will be described reasons why niobium (Nb) is added in an alloy.

As described above, corrosion occurs in the aforementioned casting alloy under high-temperature oxidation conditions. In this case, chromium carbide, which is continuously deposited, is preferentially corroded. Therefore, in order for the casting alloy to have a sufficient corrosion resistance, preferential corrosion of the chromium carbide should be overcome.

The following three methods can be employed to improve the corrosion resistance of the casting alloy.

1) To prevent deposition of chromium carbide 1-a) The concentration of chromium (Cr) is lowered so as not to deposit chromium carbide.

1-b) The amount of carbon (C) added is decreased, so as not to deposit chromium carbide.

2) To substitute carbide unlikely to be corroded for chromium carbide 3) To change continuously deposited chromium carbide into a discontinuous form 3-a) The shape of the carbide is changed by texture control using heat treatment.

3-b) Other carbide is substituted for a portion of the chromium carbide by addition of an element.

With regard to the method 1), a Cr203 scale is formed to maintain the corrosion resistance. If the amount of chromium (Cr) is insufficient, the corrosion resistance of a base material is lowered. Accordingly, the amount of chromium (Cr) should not be reduced excessively. Further, since the high-temperature strength of the alloy is maintained by carbide, the amount of addition of carbon (C) should not be reduced excessively.

With regard to the method 2), when an element more likely to form carbide than chromium (Cr) is added, the chromium carbide can be replaced with other

carbide. Specifically, elements of the 4A and 5A groups in the periodic table can be used as an element more likely to form carbide than chromium (Cr). However, chromium (Cr) inherently has an excellent oxidation resistance at high temperatures.

Only silicon (Si) and aluminum (Al) are known as elements having a high-temperature corrosion resistance higher than chromium (Cr). Thus, there is not found any additional element that can achieve such effects.

Accordingly, the method 3) of changing chromium carbide into a discontinuous form is effective in a methodology. Texture control using heat treatment is required to change chromium carbide into a discontinuous form.

However, in order to change the form of carbide, it is necessary to reheat the carbide up to an extremely high temperature. Such a reheating process is impracticable in view of the technology level and, mainly, cost.

As a solution of the above, other carbide is substituted for a portion of the chromium carbide so as to change the chromium carbide into a discontinuous form.

Additional elements have various features, and manners of carbide deposition largely differ from one element to another. Niobium (Nb) is suitable for the purpose to change the chromium carbide into a discontinuous form. Other elements cannot change the chromium carbide into a discontinuous form because they are deposited around the chromium carbide or are present together with the chromium carbide. Nevertheless, elements of the 4A and 5A groups can be used for the purpose to prevent a tungsten depletion zone.

From this point of view, niobium (Nb) may be added. However, niobium (Nb) has an extremely low oxidation resistance at high temperatures. Depending on a manner of addition, the corrosion resistance of the alloy may be deteriorated.

Particularly, in a case of a casting alloy, since a cast structure is used as it is without texture control, the corrosion resistance may considerably be lowered depending on a form in which niobium (Nb) is present in the alloy. This is because an oxide film has a tendency to be removed at ultra high temperatures over 1100°C to thereby cause deterioration of the corrosion resistance. When various experiments were conducted to produce alloys in which niobium (Nb) is added, results were better than expected.

One of effects better than expected is that the corrosion resistance was improved in a molten salt corrosion environment. Addition of niobium (Nb) in an

alloy was found effective in preventing the chlorination caused at high temperatures of about 800 to 900°C and in improving the corrosion resistance of the alloy.

However, since niobium (Nb) has a considerably low corrosion resistance, the corrosion resistance of the alloy may be lowered at high temperatures by addition of niobium (Nb). In practical use, it is rare that the operating temperature is limited to 800 to 900°C, and the alloy may possibly be used in a wide temperature range of 500 to 1200°C. Further, when the alloy is used in an incineration furnace or the like, molten salt corrosion or the like may occur in a temperature range of about 600°C.

Thus, in actual use, the alloy is required to have a stable resistance to molten salt corrosion or the like in a wide temperature range. When the corrosion resistance was examined in a molten salt corrosion environment, corrosion was found to occur from a tungsten depletion zone, which was formed around deposited tungsten carbide. According to an alloy in which niobium (Nb) is added, niobium carbide is formed so that tungsten carbide is reduced. Thus, the formation of the tungsten depletion zone can be prevented so that the alloy can provide an excellent corrosion resistance even in a molten salt corrosion environment at about 300 to 700°C in a waste incineration furnace or the like. An alloy according to the present invention has been developed for use in a composite corrosion environment of chlorination and oxidation corrosion at high temperatures. However, an alloy according to the present invention has an excellent corrosion resistance such that it can be used in an environment which may cause molten salt corrosion in various types of waste incineration furnaces, gasification furnaces, and combustion apparatuses.

As described above, an alloy according to the present invention has an excellent corrosion resistance at high temperatures and a high durability in an intensive corrosion environment, such as an environment containing a large amount of chlorine. When the alloy is used for a device which is required to have a corrosion resistance to a high-temperature corrosive gas in an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil, the durability and reliability of the apparatus can be improved, and the cost of the apparatus can be reduced. Alternatively, the functions and performance of the apparatus can be improved by performing a

process that has heretofore been impracticable.

The alloy, which has an excellent corrosion resistance at high temperatures, is used for a device subjected to an intensive corrosion environment in which chlorination can occur as well as sulfidation at high temperatures. Thus, the present invention is applicable to an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil.

The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

Brief Description of Drawings FIG. 1 is a graph showing temperature dependency of a corrosion rate of a general metallic material in a corrosive gas environment; FIG. 2 is a graph showing a tendency of variation of corrosion rates of alloys in which aluminum (Al) or silicon (Si) is added to a tritium (T) alloy; FIG. 3 is a schematic diagram showing a fluidized-bed gasification and slagging combustion apparatus according to a first embodiment of the present invention; FIG. 4 is an enlarged view showing an example of a feeder in the gasification and-slagging combustion apparatus shown in FIG. 3; FIG. 5 is an enlarged view showing an example of a start-up/auxiliary burner in the gasification and slagging combustion apparatus shown in FIG. 3; FIG. 6 is an enlarged view showing a first example of a nozzle port for introducing air, oxygen, steam, or the like into a furnace in the gasification and slagging combustion apparatus shown in FIG. 3; FIG. 7 is an enlarged view showing a second example of a nozzle for introducing air, oxygen, steam, or the like into a furnace in the gasification and slagging combustion apparatus shown in FIG. 3; FIG. 8 is an enlarged view showing a third example of a nozzle for introducing air, oxygen, steam, or the like into a furnace in the gasification and slagging combustion apparatus shown in FIG. 3;

FIG. 9 is an enlarged view showing a fourth example of a nozzle for introducing air, oxygen, steam, or the like into a furnace in the gasification and slagging combustion apparatus shown in FIG. 3; FIG. 10 is an enlarged view showing an example of a thermocouple having a protecting tube in the gasification and slagging combustion apparatus shown in FIG. 3; FIG. 11 is an enlarged view showing a first example of a sampling device having a probe in the gasification and slagging combustion apparatus shown in FIG.

3; FIG. 12 is an enlarged view showing a second example of a sampling device having a probe in the gasification and slagging combustion apparatus shown in FIG. 3; FIGS. 13A and 13B are schematic views showing a slag discharge section in the gasification and slagging combustion apparatus shown in FIG. 3; FIG. 14 is a schematic view showing an example of a slag cooling and granulation device in the gasification and slagging combustion apparatus shown in FIG. 3 ; FIG. 15 is a schematic view showing another example of a slag cooling device for slag in the gasification and slagging combustion apparatus shown in FIG.

3; FIG. 16 is a schematic view showing a bayonet-type heat exchanger in the gasification and slagging combustion apparatus shown in FIG. 3 ; FIG. 17 is a block diagram showing a waste gasification and slagging combustion apparatus having a high-temperature heat exchanger according to a second embodiment of the present invention; FIG. 18 is a block diagram showing a waste gasification and slagging combustion apparatus having a high-temperature heat exchanger according to a third embodiment of the present invention; FIG. 19 is a block diagram showing a waste gasification and slagging combustion apparatus having a high-temperature heat exchanger according to a fourth embodiment of the present invention; FIG. 20A and 20B are schematic views showing boiler heat transfer pipes and a protector in the gasification and slagging combustion apparatus shown in FIG.

3; FIG. 21 is a schematic view showing a kiln-type gasification furnace according to a fifth embodiment of the present invention; FIG. 22 is a schematic view showing a carbonization apparatus according to a sixth embodiment of the present invention; FIG. 23 is a schematic view showing a stoker-type incineration furnace having fire grates according to a seventh embodiment of the present invention; FIG. 24 is a schematic diagram showing a waste gasification power generation system having an internal circulating fluidized-bed gasification furnace and a power generation device according to an eighth embodiment of the present invention; FIG. 25 is a schematic diagram showing a waste gasification power generation system having an internal circulating fluidized-bed gasification furnace and a power generation device according to a ninth embodiment of the present invention; FIG. 26 is a schematic view showing a waste gasification and slagging combustion system according to a tenth embodiment of the present invention; FIG. 27 is a schematic view showing a slagging combustion furnace in the gasification and slagging combustion system shown in FIG. 26; and FIG. 28 is a schematic view showing a waste gasification and slagging combustion system according to an eleventh embodiment of the present invention.

Best Mode for Carrying Out the Invention Embodiments according to the present invention will be described below with reference to FIGS. 3 through 26. In the following embodiments, a nickel base heat resisting alloy is used as a material for a device of an apparatus. The nickel base heat resisting alloy includes chromium (Cr) in a range of about 23 to 40 mass %, tungsten (W) in a range of about 5 to 15 mass %, silicon (Si) in a range of about 0.3 to 4 mass %, aluminum (Al) in a range of about 1.5 to 2.5 mass %, at least one of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), and tantalum (Ta) in a range of about 0.1 to 5 %, carbon (C) in a range of about 0.1 to 0.5 mass %, manganese (Mn) of about 2.0 mass % or less, iron (Fe) of about 5 % or less, and Ni of the balance except inevitable impurities. Devices made of the

nickel base heat resisting alloy having the above composition can have a sufficient corrosion resistance and high-temperature strength. Preferred alloys to be used will be described below.

FIG. 3 is a waste gasification and slagging combustion apparatus (waste gasification and slagging combustion furnace) according to a first embodiment of the present invention. As shown in FIG. 3, the gasification and slagging combustion apparatus includes a fluidized-bed gasification furnace 101 and a swirling-type slagging combustion furnace 102. Wastes A are introduced into a fluidized-bed gasification furnace 101 by a feeder 108. The wastes A are heated to about 500 to 600°C and gasified in an oxygen deficient atmosphere having a smaller amount of oxygen than a theoretical amount of oxygen required for combustion of the wastes. The fluidized-bed gasification furnace 101 includes a fluidized bed having a low temperature, and the interior of the fluidized-bed gasification furnace 101 is under a reducing atmosphere. Accordingly, metals such as iron, copper, and aluminum included in the wastes A can be recovered from incombustibles without being oxidized.

The fluidized-bed gasification furnace 101 produces a pyrolysis gas B containing char, tar, and the like. The pyrolysis gas B is supplied to the swirling-type slagging combustion furnace 102 and combusted therein at high temperatures of about 1200 to 1500°C without an auxiliary fuel. Since combustion of the gas is mainly performed in the swirling-type slagging combustion furnace 102, the gas can be combusted at a low air ratio of about 1.3. An air ratio is defined as a ratio of the amount of supplied air to a theoretical amount of air required for combustion of the wastes. Accordingly, it is possible to reduce the amount of exhaust gas discharged from the swirling-type slagging combustion furnace 102. Further, since the gas is combusted at temperatures of at least about 1200°C, dioxins can completely be decomposed in the swirling-type slagging combustion furnace 102. Furthermore, the swirling-type slagging combustion furnace 102 employs a revolving flow of a gas to effectively separate slag by centrifugal forces. By cooling the slag, heavy metals can be confined in glassy solid slag C.

An exhaust gas D from the swirling-type slagging combustion furnace 102 has a temperature of about 1200 to 1500°C. As shown in FIG. 3, the gasification

and slagging combustion apparatus has a high-temperature heat exchanger 103, a waste heat boiler 104, an economizer 105, an air preheater 106, and a bag filter 107.

The exhaust gas D is discharged from the swirling-type slagging combustion furnace 102 and supplied into the high-temperature heat exchanger 103, the waste heat boiler 104, the economizer 105, and the air preheater 106. As a result, the temperature of the exhaust gas D is lowered. The exhaust gas D is finally introduced into the bag filter 107, where dust is removed from the exhaust gas D, and is released into an atmosphere from a chimney (not shown).

When wastes are pyrolyzed in the fluidized-bed gasification furnace 101, corrosive gas components, such as hydrogen chlorides, ammonia, cyanide, sulfur oxides, or hydrogen sulfides, which are originated from chlorine contents, nitrogen contents, or sulfur contents contained in the wastes, are produced in the fluidized-bed gasification furnace 101. A portion of the corrosive gas components is decomposed or synthesized while passing through the swirling-type slagging combustion furnace 102, the waste heat boiler 104, and the like. Most of the corrosive gas components are neutralized and removed by calcium hydroxide E, which is introduced upstream of the bag filter 107, and then discharged as a portion of bag filter ash F to the exterior of the apparatus.

Thus, the corrosive gas components flow through devices disposed in the fluidized-bed gasification furnace 101 and the bag filter 107 and devices disposed between the fluidized-bed gasification furnace 101 and the bag filter 107.

Accordingly, such devices have portions required to have a corrosion resistance to the corrosive gas components. In the present embodiment, these portions of the devices are made of the inventive nickel base heat resisting alloy described above.

Thus, the gasification and slagging combustion apparatus can have improved durability and functions as compared to a conventional apparatus. In FIG. 3, circular marks represent portions, which are expected to improve the durability and functions of the apparatus when they are made of the inventive nickel base heat resisting alloy. There will be described devices or portions made of the inventive nickel base heat resisting alloy.

In the first embodiment, the inventive nickel base heat resisting alloy is used in the feeder 108 for introducing wastes into the fluidized-bed gasification furnace 101. FIG. 4 shows details of the feeder 108. In the present embodiment,

the inventive alloy is used in the feeder 108 of the fluidized-bed gasification furnace 101. However, the inventive alloy is not limited to use in a feeder of a fluidized-bed gasification furnace. For example, the inventive alloy may be used in a feeder of a fluidized-bed combustion furnace, a kiln-type gasification furnace, or other types of furnaces.

The feeder 108 comprises a screw conveyor feeder attached to the fluidized-bed gasification furnace 101. As shown in FIG. 4, the feeder 108 has a casing 1, a screw shaft 2, and a screw blade 3. The casing 1, the screw shaft 2, and the screw blade 3 are brought into direct contact with the interior of the fluidized-bed gasification furnace 101, which has a high temperature, and thus exposed to a corrosive gas G produced by gasification of the wastes A. The corrosive gas G has a high temperature of about 500 to 700°C. In a conventional feeder, a casing, a screw shaft, and a screw blade are generally made of stainless steel and cooled by cooling water to prevent degradation of materials due to high temperatures. In such a case, cooling water H is introduced into the interior of the rotating screw shaft 2. Accordingly, the conventional feeder has complicated structures at a junction between the screw shaft and cooling water pipes. Further, a large amount of cooling water H is required depending on the size of the apparatus. Furthermore, each of the casing 1, the screw shaft 2, and the screw blade 3 is brought into direct contact with the wastes A, and friction is produced against the wastes A. If the screw shaft 2 is broken by excessive friction or corrosion, then the cooling water H may leak so as to exert an adverse influence on the state of the furnace.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance to a high-temperature corrosive gas having temperatures of about 500 to 700°C. Accordingly, in the present embodiment, the casing 1, the screw shaft 2, and the screw blade 3 are made of the inventive nickel base heat resisting alloy.

Thus, the feeder 108 can have improved durability. Further, the amount of cooling water H is remarkably reduced as compared to the conventional feeder.

Alternatively, it is possible to eliminate cooling water H and to simplify the arrangement of the apparatus.

Specific composition of the alloy may be determined in consideration of corrosion resistance at temperatures of about 500 to 700°C, particularly about 600°C.

In order to maintain the corrosion resistance, the alloy may include chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 5 %, preferably about 0.1 to 3 %, more preferably about 0.1 to 2 %.

The casing 1 is preferably formed by a pipe produced by a centrifugal casting method using the inventive alloy. With regard to the screw shaft 2 and the screw blade 3, the composition of the alloy is preferably determined in consideration of weldability and abrasion resistance to each other. Specifically, the amount of silicon (Si) is preferably reduced to improve the weldability, and tungsten (W) is preferably increased to enhance the high-temperature strength.

More specifically, the alloy preferably includes silicon (Si) in a range of about 0.3 to 1.5 %, and tungsten (W) in a range of about 7 to 15 %. More preferably, the alloy includes silicon (Si) in a range of about 0.3 to 1.0 %, and tungsten (W) in a range of about 10 to 15 %.

As shown in FIG. 3, the fluidized-bed gasification furnace 101 has a start-up/auxiliary burner 109a, and the swirling-type slagging combustion furnace 102 has a start-up/auxiliary burner 109b. The inventive nickel base heat resisting alloy is used in the start-up/auxiliary burners 109a and 109b. FIG. 5 shows details of the start-up/auxiliary burner 109a in the fluidized-bed gasification furnace 101.

Since the start-up/auxiliary burner 109b in the swirling-type slagging combustion furnace 102 has the same-structure as the start-up/auxiliary burner 109a in the fluidized-bed gasification furnace 101, details of the start-up/auxiliary-burner 109b will not be described repetitively.

In the present embodiment, the inventive alloy is used in the start-up/auxiliary burners 109a and 109b of the fluidized-bed gasification furnace 101 and the swirling-type slagging combustion furnace 102. However, the inventive alloy is not limited to use in start-up/auxiliary burners of a fluidized-bed gasification furnace and a swirling-type slagging combustion furnace. For example, the inventive alloy may be used in a start-up/auxiliary burner of a fluidized-bed combustion furnace, a kiln-type gasification furnace, a shaft-type slagging combustion furnace, or any other furnace having a high-temperature corrosive gas environment.

The burner 109a is supplied with fuel J. The fuel J generally comprises fossil fuel such as light oil, heavy oil, propane gas, or natural gas. The burner 109a has a nozzle tip 11 and a flame holder 12. Although the combustion temperature depends on an air-fuel ratio (ratio of air I and fuel J), it becomes a high temperature over about 1000°C. Accordingly, the nozzle tip 11 and the flame holder 12, which have high temperatures, are cooled for protection. However, excessive cooling for improving the durability of materials may exert an adverse influence on the combustion temperature, i. e. , a combustion state. Therefore, in a conventional burner, cooling water H is supplied to cool the materials, and the burner is made of materials having a sufficient mechanical strength at a temperature to which the materials are cooled by the cooling water H. However, a conventional material with a high-temperature strength generally has a low corrosion resistance. Accordingly, when the burner is not operated, it is necessary to supply a purge gas K such as air, steam, or nitrogen so as not to expose the burner to a high-temperature corrosive gas G. Alternatively, the conventional burner is required to be withdrawn from the furnace by a mechanical withdrawal device so as not to expose the burner to the high-temperature corrosive gas G.

The inventive nickel base heat resisting alloy shows not only an excellent corrosion resistance at temperatures of about 900 to 1000°C, but also a high-temperature strength to some extent. Accordingly, in the present embodiment, the nozzle tip 11 and the flame holder 12 of the burner 109a are made of the inventive nickel base heat resisting alloy. Thus, the burner 109a can have longer life. Further, since the amount of purge gas K supplied can be reduced, it is possible to prevent the purge gas K from exerting an adverse influence on the combustion state of the furnace. Furthermore, a mechanical withdrawal device for withdrawing the burner 109a can be eliminated to simplify the arrangement of the apparatus.

Specific composition of the alloy may be determined in consideration of corrosion resistance at temperatures over about 900°C. Thus, the alloy may include chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 5 %, preferably about 0.1 to 3 %, more preferably about 0.1 to 2 %.

Since the burner 109a includes parts having complicated shapes, the

composition of the alloy is preferably determined in consideration of productivity in a casting process. Specifically, the amount of silicon (Si) is preferably reduced in a range such that the corrosion resistance and the high-temperature strength are not influenced. More specifically, the alloy preferably includes silicon (Si) in a range of about 0.3 to 1.5 %, and aluminum (Al) in a range of about 1.8 to 2.2 %. More preferably, the alloy includes silicon (Si) in a range of about 0.3 to 1.0 %.

As shown in FIG. 3, the gasification and slagging combustion apparatus has nozzle ports 110 for blowing a gas such as air, oxygen, or steam into the fluidized-bed gasification furnace 101 and the swirling-type slagging combustion furnace 102. The inventive nickel base heat resisting alloy is used in the nozzle ports 110. FIGS. 6 through 9 show examples of the nozzle port 110. In the present embodiment, the inventive alloy is used in the nozzle ports 110 of the fluidized-bed gasification furnace 101 and the swirling-type slagging combustion furnace 102. However, the inventive alloy is not limited to use in a nozzle port of a fluidized-bed gasification furnace and a swirling-type slagging combustion furnace. For example, the inventive alloy may be used in a nozzle port of a fluidized-bed combustion furnace, a kiln-type gasification furnace, a shaft-type slagging combustion furnace, or any other furnace having a high-temperature corrosive gas environment.

FIG. 6 shows a first example of the nozzle port 110 which is provided in a furnace having no molten slag of ash contents therein, such as the fluidized-bed gasification furnace 101. Gas L such as air is supplied through the nozzle 110 into the furnace. As shown in FIG. 6, the furnace has a wall including a shell or a water tube wall 21 made of steel and a refractory material 22 attached to an inner surface of the shell or the water tube wall 21. The temperature of an upstream portion of the nozzle 110 away from the furnace is substantially equal to that of the gas L to be supplied. However, the temperature of a tip portion 110a of the nozzle 110 is largely increased by the influence from the internal temperature of the furnace.

As shown in FIG. 6, the nozzle 100 has a tip end located at an outer position from an inner surface of the refractory material 22. This configuration can prevent deterioration of strength due to exposure of the tip portion 1 l0a to a high temperature atmosphere and can prevent corrosion due to contact with a

high-temperature corrosive gas G in the furnace. However, the refractory material 22 may have cracks or be broken at corners 22a thereof due to thermal expansion.

FIG. 7 shows a second example of a nozzle port 110, which is provided in a furnace having no molten slag of ash contents therein, such as the fluidized-bed gasification furnace 101. As shown in FIG. 7, the nozzle 110 has a tip end located on the same plane as an inner surface of the refractory material 22. With this configuration, the refractory material 22 can be prevented from being damaged.

However, the temperature of the tip portion 110a of the nozzle 110 is increased.

The tip portion 110a of the nozzle 110 is brought into contact with a high-temperature corrosive gas G in the furnace. Accordingly, if the nozzle 110 does not have a sufficient strength and corrosion resistance at high temperatures, the nozzle 110 is likely to be damaged. Since a conventional nozzle is made of a metallic material such as carbon steel or stainless steel, it does not have a sufficient strength and corrosion resistance at high temperatures.

The inventive nickel base heat resisting alloy shows an excellent mechanical strength and corrosion resistance in a temperature range of about 1000 to 1200°C. Accordingly, in the present embodiment, the nozzle 110 shown in FIG.

7 is made of the inventive nickel base heat resisting alloy. Thus, the aforementioned drawbacks can be solved. Specifically, it is possible to prevent damage of the refractory material 22 and corrosion damage of the nozzle 110.

FIGS. 8 and 9 show third and fourth examples of a nozzle port 110, which is provided in a furnace in which molten slag of ash contents flows down on a wall of the furnace, such as the swirling-type slagging combustion furnace 102. In each example, the nozzle 110 supplies gas such as air into the furnace, and is made of the inventive nickel base heat resisting alloy. In either case, gas L generally has a temperature largely lower than the internal temperature of the furnace. If the air supply nozzle 110 has a tip end 110a located on the same plane as an inner. surface of the refractory material 22 as shown in FIG. 7, then slag M is solidified and developed at the tip end 110a of the nozzle 110. In such a case, the nozzle 110 may be clogged by the slag.

The arrangements shown in FIGS. 8 and 9 can solve such a drawback. As shown in FIGS. 8 and 9, the tip end 110a of the nozzle 100 is projected inward to the furnace to some extent. With these arrangements, the flow of the slag M is

prevented from being brought into contact with the gas L supplied from the tip end 110a of the nozzle 100. In FIG. 8, the refractory material 22 has a portion 23 contacting slag which is brought into contact with the flow of the slag M. The portion 23 contacting slag is formed integrally with the refractory material 22. In FIG. 9, a part 24 contacting slag is attached to the tip end 110a of the nozzle 100.

The portion 23 contacting slag and the tip end 110a of the nozzle 100 are integrated into the part 24 contacting slag in FIG. 9. The part 24 contacting slag is made of the nickel base heat resisting alloy.

In the case of FIG. 8, if the portion 23 contacting slag is deteriorated by erosion of the slag, then the refractory material 22 should be repaired in the furnace.

Thus, large-scale maintenance is required. In the case of FIG. 9, the part 24 contacting slag can be replaced as expendables so as to cope with the erosion of the slag. Thus, maintenance of the furnace can be simplified.

In FIG. 8 or 9, when the nozzle 110 and/or the part 24 contacting slag which is brought into contact with the high-temperature corrosive gas is made of the nickel base heat resisting alloy, the durability of the parts, which has been a drawback of conventional nozzles, can remarkably be improved.

Specific composition of the alloy may be determined in consideration of temperatures of the nozzle 110 and/or the part 24 contacting slag. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % to maintain the corrosion resistance. In a case of use at temperatures of about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1. 8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %. In a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % to maintain the high-temperature strength.

In the present embodiment, a thermocouple for measuring the temperature in the apparatus may be provided in the fluidized-bed gasification furnace 101, the swirling-type slagging combustion furnace 102, the waste heat boiler 104, or the like. Further, a sampling device for measuring properties of a gas in the apparatus

may be provided in the fluidized-bed gasification furnace 101, the swirling-type slagging combustion furnace 102, the waste heat boiler 104, or the like. In such a case, the inventive nickel base heat resisting alloy is used as a material for a protecting tube of the thermocouple and a probe of the sampling device.

In the present embodiment, the inventive alloy is used in the thermocouple and the sampling device in the fluidized-bed gasification furnace 101, the swirling-type slagging combustion furnace 102, or the waste heat boiler 104.

However, the inventive alloy is not limited to use in a thermocouple and a sampling device in a fluidized-bed gasification furnace, a swirling-type slagging combustion furnace, or a waste heat boiler. For example, the inventive alloy may be used in a thermocouple and a sampling device of a fluidized-bed combustion furnace, a kiln-type gasification furnace, a shaft--type slagging combustion furnace ; a chemical synthesis/decomposition apparatus, or any other furnace having a high-temperature corrosive gas environment.

Generally, as materials for a protecting tube of a thermocouple and a probe of a sampling device, metal such as stainless steel has heretofore been used for an environment having temperatures below about 700°C, and ceramic such as alumina has been used for an environment having temperatures over about 700°C.

However, since ceramic is vulnerable to thermal shock, the ceramic material may suddenly be broken by fluctuation of temperatures of the furnace. Thus, it is difficult to predict the life of the ceramic material.

In some cases, high-grade metallic materials such as Alloy 625 are used for an environment having temperatures of about 700 to 1000°C. However, such high-grade materials are extremely expensive and do not necessarily have a sufficient corrosion resistance in an environment containing a large amount of corrosive gas such as hydrogen chloride. Further, the high-grade material should be replaced as expendables because the thickness of the material becomes thinner due to corrosion. Thus, cost for replacement is largely increased.

FIG. 10 shows an example of a thermocouple having a protecting tube 31 provided in the fluidized-bed gasification furnace 101. In the present embodiment, the inventive nickel base heat resisting alloy is used in the protecting tube 31 of the thermocouple. The inventive nickel base heat resisting alloy is expected to have a high corrosion resistance at temperature of about 700 to 1000°C as compared to

conventional materials such as stainless steel and high-grade metallic materials such as Alloy 625. Accordingly, by making the protecting tube 31 of the thermocouple of the inventive nickel base heat resisting alloy, it is possible to reduce replacement cost. Further, since the inventive nickel base heat resisting alloy has a sufficient high-temperature strength up to about 1200°C, the nickel base heat resisting alloy as a metallic material can be used in a temperature range in which a ceramic material has heretofore been used. Accordingly, it is possible to prevent thermocouple wires 32 from being broken down due to sudden breakage of a ceramic material.

FIGS. 11 and 12 show first and second examples of a sampling device having a probe 33 provided in the fluidized-bed gasification furnace 101. In the present embodiment, the inventive nickel base heat resisting alloy is used in the probe 33 of the sampling device. Such a sampling device is used-to measure properties of a high-temperature corrosive gas in an incineration furnace, a gasification furnace, a slagging combustion furnace, or the like. As shown in FIG.

11, one of the easiest ways to measure properties of a gas in a furnace is to draw a high-temperature corrosive gas G out of the furnace through a tubular probe 33 inserted into the furnace. With the structure shown in FIG. 11, the temperature of the probe 33 is substantially equal to that of the gas G in the furnace. Accordingly, when the durability of the probe 33 is problematic because of extremely high temperatures in the furnace, as shown in FIG. 12, the probe 33 may be cooled by a cooling fluid (e. g. cooling water) H to improve the durability of the probe 33. If a ceramic material is used as a material for the probe 33, when the probe 33 is broken, then the high-temperature corrosive gas G may leak into the cooling fluid H, or the cooling fluid H may leak into the furnace. However, the probe 33 made of the inventive nickel base heat resisting alloy can have remarkably improved durability and does not cause such a problem.

Specific composition of the alloy may be determined in consideration of operating temperatures. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % to maintain the corrosion resistance. In the case of use at temperatures of about 700 to 1000°C, the alloy preferably includes

chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0. 1 to 2 %. In a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % to maintain the high-temperature strength.

Referring back to FIG. 3, the slagging combustion furnace 102 has a slag discharge section 111 disposed at a lower portion thereof. In the present embodiment, the inventive nickel base heat resisting alloy is used in the slag discharge section 111. Thus, in the present embodiment, the inventive alloy is used in the slag discharge section 111 of the swirling-type slagging combustion furnace 102. However, the inventive alloy is not limited to use in a slag discharge section of a swirling-type slagging combustion furnace. For example, the inventive alloy may be used in a slag discharge section of a shaft-type slagging combustion furnace, a plasma-type melting furnace, an electric resistance furnace, or other types of slagging combustion furnaces.

In the slagging combustion furnace 102, an ash content is melted into slag, which flows down in a liquid form. The slag is discharged through the slag discharge section 111 at the lower portion of the slagging combustion furnace 102.

Generally, the slag discharge section 111 is formed integrally with walls of the slagging combustion furnace 102 by a monolithic refractory material. In such a case, the refractory material may locally be eroded at a portion of the slag flow.

Accordingly, it is necessary to inspect an erosion state periodically in the slagging combustion furnace 102 and repair the refractory material as needed. When the refractory material is repaired, a large number of processes and much time are required to remove an existing refractory material, repair a support of the refractory material, and mount a new refractory material. Thus, the furnace needs to be stopped for a long term at the time of the repair of the refractory material. Further, although a passage for slag may be provided in the slag discharge section 111 to effectively discharge the slag, it is difficult to form such a passage having a complicated shape in the case of the monolithic refractory material.

In a case of a gasification and slagging combustion apparatus for municipal wastes, a slag discharge section needs to be made of a material having a sufficient mechanical strength up to about 1200°C and a corrosion resistance to a

high-temperature corrosive gas in a furnace because slag generally has a melting point of about 1200°C. The inventive nickel base heat resisting alloy has a sufficient mechanical strength in a temperature range up to about 1200°C and an excellent corrosion resistance at high temperatures. Accordingly, in the present embodiment, the slag discharge section, which has heretofore been made of a refractory material, is made of the inventive nickel base heat resisting alloy in order to solve the above drawbacks.

FIGS. 13A and 13B show the slag discharge section having a chute 41 made of the inventive nickel base heat resisting alloy. The chute 41 is mounted on a furnace wall 43 by support parts 42. The slag M is discharged along a passage formed on an upper surface of the chute 41 to the. exterior of the furnace. The chute 41 is preferably manufactured by casting, which can readily form-a passage at low cost. When the slag discharge section needs to be repaired due to corrosion and degradation of the material, only the chute 41 can be removed and replaced with new one. Thus, large-scale maintenance is not required, but only repair work for a relatively short term is required.

The composition of the nickel base heat resisting alloy is preferably determined in consideration of operating temperatures over about 1200°C and an excellent high-temperature corrosion resistance and an excellent high-temperature strength because nitriding also occurs. For example, the nickel base heat resisting alloy preferably includes tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 1 to 4 %, aluminum (Al) in a range of about 1.5 to 2 %, and niobium (Nb) in a range of about 0.1 to 0.5 %.

As shown in FIG. 3, the gasification and slagging combustion apparatus has a slag cooling and granulation device 112 for slag discharged from the slag discharge section 111. The slag cooling and granulation device 112 is made of the inventive nickel base heat resisting alloy. FIGS. 14 and 15 show details of the slag cooling and granulation device 112. In the present embodiment, the inventive alloy is used in the slag cooling and granulation device 112 of the waste gasification and slagging combustion apparatus. However, the inventive alloy is not limited to use in a slag cooling and granulation device of a gasification and slagging combustion apparatus. For example, the inventive alloy may be used in a slag cooling and granulation device of a shaft-type slagging combustion furnace, a

plasma-type melting furnace, an electric resistance furnace, or other types of slagging combustion furnaces.

The slag discharged from the slagging combustion furnace 102 is generally cooled and granulated as shown in FIG. 14. The slag M is brought into direct contact with cooling water H flowing on an inclined metal plate 51. Thus, the slag M is quenched and granulated into particulate slag (water granulated slag) N, which is discharged to the exterior of the furnace. This method is referred to as a water granulation method. With the water granulation method, since the structure of the slag becomes brittle, the strength of the slag is lowered. Accordingly, it is difficult to reuse the slag as subbase course materials or construction materials.

FIG. 15 shows another example of the slag cooling and granulation device 112. As shown in FIG. 15, the inventors have proposed to flow slag M on a metal plate 51, which is cooled from a lower portion by cooling water H, vibrate the metal plate 51 by a vibration device 52 to indirectly cool the slag and granulate the slag into particulate slag (indirectly cooled slag) O, and discharge the indirectly cooled slag O to the exterior of the furnace. This method is disclosed in Japanese laid-open patent publication No. 11-29161, the entire disclosure of which is incorporated herein by reference. With this method, it is possible to control the temperature of the metal plate 51 and the cooling speed of the slag M by adjusting the temperature and the amount of cooling water H flowing beneath the metal plate 51. The temperature of an upper surface of the metal plate 51 is higher than in the case of the water granulation method. Further, the metal plate 51 is-exposed to an atmosphere including a high-temperature corrosive gas G in the furnace.

Accordingly, the durability of the metal plate 51 may be deteriorated. From the viewpoint of the durability of the metal plate 51, when the metal plate 51 is made of stainless steel, the upper limit of the temperature of the metal plate 51 is as low as about 500°C in practical use. A lower cooling speed is preferred because the structure of the indirectly cooled slag O becomes dense to improve the mechanical strength. For this purpose, the temperature of the metal plate 51 needs to be further increased. Accordingly, in order to use the metal plate 51 for a long term in such an environment, it is desired to provide a material having an excellent corrosion resistance.

The inventive nickel base heat resisting alloy shows an excellent

high-temperature corrosion resistance in a temperature range up to about 1200°C.

Accordingly, in the present embodiment, the metal plate 51 is made of the inventive nickel base heat resisting alloy. Thus, the temperature of the metal plate 51 is remarkably increased, and the durability of the metal plate 51 is improved, as compared to a case where the metal plate 51 is made of stainless steel.

This method has the following additional advantages. The cooling speed of the slag is proportional to a temperature difference between the temperature of the slag M and the temperature of the metal plate 51. For example, when the temperature of the slag M is 1300°C, and the metal plate 51 is made of stainless steel having a heat resistant temperature of 500°C, the temperature difference therebetween is 800°C. However, when the metal plate 51 is made of the inventive alloy, and the operating temperature is 900°C, the temperature difference therebetween is 400°C. Accordingly, it is possible to achieve about one-half of the conventional cooling speed. Specifically, when the metal plate 51 is made of the inventive alloy, it is possible to widen a control range of a cooling speed of the slag M to a large extent.

Specific composition of the alloy may be determined in consideration of a required cooling speed and an operating temperature of the metal plate 51. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium in a range of about 0. 1 to 2 % in order to maintain the corrosion resistance. In a case of use at temperatures of about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0. 1 to 2 %. Further, in a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % in order to maintain the high-temperature strength.

As shown in FIG. 3, the high-temperature heat exchanger 103 is disposed in a high-temperature corrosive exhaust gas at an outlet of the slagging combustion furnace 102. In the present embodiment, the inventive nickel base heat resisting alloy is used in the high-temperature heat exchanger 103. FIG. 16 shows details of

the high-temperature heat exchanger 103. In the present embodiment, the inventive alloy is used in the high-temperature heat exchanger 103 of the fluidized-bed gasification and slagging combustion apparatus. However, the inventive alloy is not limited to use in a high-temperature heat exchanger of a fluidized-bed gasification and slagging combustion apparatus. For example, the inventive alloy may be used in a high-temperature heat exchanger of a kiln-type gasification and slagging combustion apparatus, a shaft-type slagging combustion furnace, other types of gasification and slagging combustion apparatuses, a stoker-type incineration furnace, or a fluidized-bed combustion furnace.

In the waste gasification and slagging combustion apparatus, the exhaust gas discharged from the outlet of the furnace generally has an extremely high temperature of about 1200 to 1500°C, which is substantially equal to a combustion temperature of the slagging combustion furnace 102. By recovering the thermal energy of the high-temperature exhaust gas so as to be circulated to an upstream side of the process or used for power generation or the like, many advantages can be obtained in view of energy balance including reduction of an auxiliary fuel supplied from the exterior, and improvement of generation efficiency.

Various efforts have heretofore been made to devices for directly recovering heat in such an environment. However, practical heat exchangers have not been developed yet because of intensive corrosion caused in a high-temperature corrosive gas environment.

-Such devices for directly recovering heat in such an environment include a heat regenerator having a heat reservoir such as ceramic through which a heating fluid and a fluid to be heated flow alternately to exchange heat therebetween.

Small amounts of the heating fluid and the fluid to be heated are inevitably mixed with each other. Thus, it is necessary to provide a mechanism such as a valve for switching exhaust gas passages in a high-temperature corrosive environment.

Accordingly, the heat regenerator has a large number of problems such as complicated arrangements.

As another example of the devices for directly recovering heat, there has been proposed a heat exchanger having a metallic heat transfer pipe disposed in an exhaust gas passage. A surface of the heat transfer pipe, which is brought into contact with a corrosive gas, is covered with a refractory material to protect the

metal of the heat transfer pipe. However, in order to absorb a thermal expansion difference between the metallic heat transfer pipe and the refractory material and to reliably hold the refractory material, the refractory material requires a support having an extremely complicated structure. Further, the refractory material generally has a heat conductivity considerably lower than that of a metallic material and lowers an efficiency of heat transfer in the heat exchanger to a large extent.

Accordingly, a heating surface area needs to be increased to a large extent.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance to such a high-temperature corrosive gas. Accordingly, by using the nickel base heat resisting alloy, it is possible to provide a heat exchanger having excellent durability with a simple structure.

FIG. 16 shows an example of a high-temperature heat exchanger using the inventive material having a high-temperature corrosion resistance. The high-temperature heat exchanger shown in FIG. 16 comprises a bayonet-type heat exchanger. The bayonet-type heat exchanger has a heat exchanging section having a large number of double pipes. FIG. 16 shows only one double pipe of the heat exchanging section for purposes of illustration. The double pipe of the heat exchanging section includes a cylindrical outer tube 61 having an opening at an end thereof and a wall at the other end thereof, and a cylindrical inner tube 62 having openings at both ends thereof. A fluid P to be heated, such as air having a low temperature, is introduced from an end of the inner tube 62. Then, the fluid P flows from the other end of the inner tube 62 into an annular space defined between the outer tube 61 and the inner tube 62. The fluid P flows out from an end of the outer tube 61. In this manner, the fluid P is heated so that heat is exchanged between the fluid P to be heated, such as air, and a combustion exhaust gas G, which is a high-temperature corrosive gas.

The fluid P to be heated may flow in a reverse direction to the direction shown in FIG. 16. In such a case, the fluid P flows through the annular space between the outer tube 61 and the inner tube 62 while it is heated. Then, the fluid P reaches the end of the outer tube 61 and flows through the interior of the inner tube 62 while it is cooled. The fluid P is discharged from the end of the inner tube 62.

In the following embodiments, the fluid P, to be heated, having a low

temperature is a gas such as air. However, the fluid P is not limited to air. For example, oxygen, steam, nitrogen, and mixture thereof may be selected as the process requires. Alternatively, the heat exchanger may heat a combustion exhaust gas having a low temperature with a combustion exhaust gas having a high temperature.

In a heat exchanger used in such high temperatures, a temperature difference between the combustion exhaust gas G and the fluid P such as air is so large that necessary measures should be taken against thermal expansion when the heat transfer pipes are fixed at both ends thereof. Accordingly, the structure of the heat exchanger becomes complicated. On the other hand, the bayonet-type high-temperature heat exchanger shown in FIG. 16 has a cantilever structure such that one end thereof is open. Therefore, it is not necessary to consider measures against thermal expansion, and hence the bayonet-type heat exchanger can have a simple structure.

The outer tube 61 has an outer surface which is brought into contact with a combustion exhaust gas G, which is a high-temperature corrosive gas.

Accordingly, in the present embodiment, the outer tube 61 is made of the inventive nickel base heat resisting alloy. A preferred method of producing an outer tube 61 is to weld a cap which has been produced as a sand casting or a permanent mold casting to a straight pipe which has been produced as a centrifugal casting pipe.

However, the outer tube 61 may be produced as an integrally formed casting or produced from a straight pipe and a cap which have been produced by forging.

If the fluid P is a non-corrosive gas such as air, oxygen, steam, nitrogen, or mixture thereof, then the inner tube 62 may be made of carbon steel or stainless steel. If the fluid P is a corrosive gas such as a combustion exhaust gas, then it is desirable to make the inner tube 62 of the inventive nickel base heat resisting alloy.

Specific composition of the alloy may be determined in consideration of operating temperatures of the outer tube 61 and the inner tube 62. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance. In a case of use at temperatures of

about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1. 8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %. Further, in a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % in order to maintain the high-temperature strength.

When the outer tube 61 is made of the inventive nickel base heat resisting alloy, it is desirable to produce a pipe as a straight pipe by a centrifugal casting method, produce a cap as an end portion by sand casting or permanent mold casting, and weld the pipe and the cap so as to form the outer tube 61. In consideration of the castability by sand casting or permanent mold casting, the end portion, i. e. , a cap, may includes a smaller amount of silicon (Si) added within a range in which the corrosion resistance and the high-temperature strength are not problematic, preferably in a range of about 0.3 to 2 %, more preferably about 0.3 to 1 %.

It is desirable to use the inventive alloy in a temperature range up to about 1200°C. Even if the combustion exhaust gas G has a temperature of about 1500°C, the temperature of the outer tube 61 can readily be lowered below about 1200°C by lowering the temperature of the fluid P to some extent because the outer tube 61 is cooled by the fluid P. Thus, the inventive alloy can be used without any problems even in such conditions.

When there is expected adhesion of ash contents contained in the combustion exhaust gas as in the present embodiment, it is practically important to avoid a low temperature region from 300 to 700°C at which molten salt corrosion occurs. Accordingly, it is necessary to maintain the outer tube 61 at a high temperature by, for example, preheating a fluid P prior to introduction of the heat exchanger. Alternatively, it is necessary to arrange the heat transfer pipes in the duct so as to prevent the temperature of the heat transfer pipes from being lowered at local portions due to channeling of the exhaust gas. Even if these measures are taken, intensive molten salt corrosion may be likely to occur because of a temperature range at which the heat transfer pipes are used or characteristics of the adhered ash to the heat transfer pipes. In such a case, it is desirable to increase the amount of niobium (Nb) added up to 0.1 to 3 % so as to produce a material having an improved resistance to molten salt corrosion.

The bayonet-type heat exchanger shown in FIG. 16 has been described as an example of the high-temperature heat exchanger to which the inventive alloy is applied. However, the inventive alloy may be used in a shell-and-tube heat exchanger as long as the inventive alloy is applied to a portion which is brought into contact with a high-temperature corrosive gas.

Heat recovered by the high-temperature shown in FIG. 16 can be utilized in various manners. FIGS. 17 through 19 show examples of utilization of recovered heat. In FIGS. 17 through 19, the waste gasification and slagging combustion apparatus includes a gasification furnace 101 and a slagging combustion furnace 102. As shown in FIGS. 17 through 19, the high-temperature heat exchanger 103 described above is used in the waste gasification and slagging combustion apparatus.

Specifically, the high-temperature heat exchanger 103 is provided right after the slagging combustion furnace 102 downstream of the gasification furnace 101.

Heat is exchanged between a corrosive exhaust gas G having a temperature over about 1200°C and air Ri having a temperature of an ordinary temperature to about 250°C so as to produce high-temperature air R2 having a temperature of about 400 to 800°C.

The high-temperature heat exchanger 103 may not be provided separately right after the slagging combustion furnace 102. The high-temperature heat exchanger 103 may be disposed near the outlet of the slagging combustion furnace 102 so as to be integrated with the slagging combustion furnace 102.

Alternatively, the high-temperature heat exchanger 103 may be disposed-in the subsequent boiler 104 so as to be integrated with the boiler 104.

FIG. 17 shows a gasification and slagging combustion apparatus according to a second embodiment of the present invention in which the high-temperature air R2 obtained by the high-temperature heat exchanger 103 is used as combustion air in the slagging combustion furnace 102. When such high-temperature air is used as combustion air in the slagging combustion furnace 102 instead of air having a relatively low temperature of an ordinary temperature to about 250°C, it is not necessary to introduce an auxiliary fuel or otherwise the amount of auxiliary fuel can considerably be reduced even if the wastes have a low heating value.

FIG. 18 shows a gasification and slagging combustion apparatus according to a third embodiment of the present invention in which the high-temperature heat

exchanger is used as a high-temperature air heater in a waste combustion power generating system, which has been proposed by the inventors. The waste combustion power generating system is disclosed in International patent publication No. W099/19667, the entire disclosure of which is incorporated herein by reference.

High-temperature air R2 having a temperature of about 700°C is obtained by the high-temperature air heater 103 as the high-temperature heat exchanger. The high-temperature air R2 is utilized for a steam heater 113 to reheat superheated steam S1 having a temperature of about 400°C, which is obtained by the subsequent boiler 104. With this configuration, superheated steam S2 having a temperature of about 500°C can be obtained so that high-efficient power generation from wastes can be performed with an efficiency of about 30 to 32 % at generating ends. Air R2 after heating steam is cooled to about 400 to 500°C, but it has a higher temperature as compared to air having a relatively low temperature of an ordinary temperature to about 250°C, which is generally used as combustion air in a slagging combustion furnace 102. Accordingly, the air R2 is used as combustion air in the slagging combustion furnace 102 so as to reduce an auxiliary fuel as with the second embodiment shown in FIG. 17.

FIG. 19 shows a gasification and slagging combustion apparatus according to a fourth embodiment of the present invention in which the gasification furnace 101 comprises a kiln-type gasification furnace utilizing high-temperature air obtained by the high-temperature air heater 103 as a heat source to maintain a proper-gasification temperature in the kiln-type gasification-furnace 101. The gasification temperature in the gasification furnace is generally in a range of about 400 to 1000°C, preferably about 500 to 600°C. However, in order to maintain the interior of the furnace in these ranges, air for indirect heating should have a temperature sufficiently higher than these ranges. If air for heating has a higher temperature, a temperature difference between the air and an atmosphere in the gasification furnace is larger so as to improve the efficiency of heat transfer. Thus, it is possible to reduce a heating surface area.

According to the fourth embodiment shown in FIG. 19, high-temperature air R2 having a temperature of about 400 to 800°C, which is suitable for the above purpose, can readily be obtained so as to heat the gasification furnace effectively.

In FIG. 19, air R3 which has heated the gasification furnace 101 is illustrated as

being used as combustion air in the slagging combustion furnace 102. However, the air R3 may be reused for other purposes such as reheating of the exhaust gas to prevent white smoke or heating of boiler water. Alternatively, the fourth embodiment shown in FIG. 19 may be combined with the second embodiment shown in FIG. 17 so that a portion of the high-temperature air R2 obtained by the high-temperature air heater 103 is utilized to heat the gasification furnace 101 while the rest of the high-temperature air R2 is utilized as combustion air in the slagging combustion furnace 102.

In the embodiment shown in FIG. 3, the waste heat boiler 104 has a boiler heat transfer pipe 104a and a steam superheater heat transfer pipe 104b. The boiler heat transfer pipe 104a, the steam superheater heat transfer pipe 104b, heat transfer pipe support members, and protectors are made of the inventive nickel base heat resisting alloy. FIGS. 20A and 20B show details of the waste heat boiler 104.

In the above embodiments, the waste heat boiler 104 is provided at a downstream portion of the fluidized-bed gasification and slagging combustion apparatus.

However, the waste heat boiler 104 may be provided in a kiln-type gasification and slagging combustion apparatus, a shaft-type slagging combustion furnace, other types of gasification and slagging combustion apparatuses, a stoker-type incineration furnace, or a fluidized-bed combustion furnace.

Heat transfer pipes in a waste heat boiler or a steam superheater are generally made of carbon steel. When the heat transfer pipes are used in a high-temperature-corrosive exhaust gas in a waste incineration-furnace, intensive corrosion occurs due to molten salt corrosion as described in connection with FIG.

1. Thus, the heat transfer pipes are used in a state such that surfaces of the heat transfer pipes have a temperature lower than about 300°C. The temperatures of the boiler heat transfer pipes become 30 to 50°C higher than the temperature of steam in the pipes. Accordingly, the upper limit of the temperature of the steam in the waste incineration boiler is about 350°C.

Recently, there has been developed a waste power generation system in which heat transfer pipes are made of a high-grade metal such as stainless steel or Alloy 625 to improve the corrosion resistance of the heat transfer pipes and increase the temperature of the steam up to about 400°C. However, in the case where such a high-grade material is used, cost for materials is increased to produce a heat

transfer pipe.

The inventive material having a high-temperature corrosion resistance can be produced at lower cost as compared to the high-grade materials. Further, the inventive material has an excellent high-temperature corrosion resistance.

Accordingly, by making the heat transfer pipes of the waste heat boiler or the steam superheater of the inventive material, the boiler can have excellent durability at low cost.

In the waste heat boiler 104 shown in FIG. 3, the inventive material having a high-temperature corrosion resistance can be used at portions including the boiler heat transfer pipe 104a and the steam superheater heat transfer pipe 104b. When these portions are made of the inventive nickel base heat resisting alloy, the durability of the waste heat boiler 104 can be improved, and the cost-of the heat transfer pipes can be reduced.

Specific composition of the alloy may be determined in consideration of operating temperatures of the heat transfer pipes 104a and 104b. The upper limit of the temperature of superheated steam is generally in a range of about 400 to 500°C in a corrosive environment. Thus, the operating temperatures of the material can be assumed to be, for example, in a range of about 500 to 700°C.

Accordingly, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % in order-to maintain the corrosion resistance. In consideration of--compressive strength to pressurized water or pressurized steam, it is desirable to add a small amount of aluminum (Al) in a range in which corrosion resistance is not problematic, preferably in a range of about 1.5 to 2.0 %.

Further, if intensive molten salt corrosion is likely to occur because of a temperature range at which the heat transfer pipes are used or characteristics of the adhered ash to the heat transfer pipes, it is desirable to increase the amount of niobium (Nb) added up to 0.1 to 3 % so as to produce a material having an improved resistance to molten salt corrosion.

The inventive alloy can be applied to support parts for supporting the boiler heat transfer pipe 104a and the steam superheater heat transfer pipe 104b. The support parts are not cooled by steam or saturated water unlike the heat transfer

pipes 104a and 104b. Thus, the temperatures of the support parts are generally higher than those of the heat transfer pipes 104a and 104b. Accordingly, support parts made of a conventional material is problematic in the corrosion resistance.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance in a temperature range of about 800 to 1200°C as compared to conventional materials. Accordingly, by making the support parts of the inventive alloy, it is possible to achieve high reliability and durability.

In the waste heat boiler, the heat transfer pipe may become thinner at specific portions due to wear by erosion effect of ash particles introduced together with a combustion exhaust gas. In such a case, metallic protectors are attached so as to protect surfaces of the heat transfer pipes and prevent wear of the heat transfer pipes. The protectors are generally made of stainless steel. Depending on temperature conditions in the boiler, the protectors become thinner due to intensive corrosion. In such a case, replacement and repair should be necessary frequently.

FIGS. 20A and 20B show a protector 66 made of the inventive nickel base heat resisting alloy in order to solve the above drawbacks. As shown in FIGS.

20A and 20B, the protector 66 made of the inventive nickel base heat resisting alloy is attached so as to protect one of the heat transfer pipes 65. In FIGS. 20A and 20B, the protector 66 is in the form of a semicylinder. However, the protector 66 may be in the form of a flat plate so as to protect a plurality of heat transfer pipes 65.

The support parts and the protectors are not required to have a high compressive strength. Accordingly, it is desirable that specific composition of the alloy is determined in consideration of operating temperatures of the support parts and the protectors, and the corrosion resistance corresponding to the corrosion environment. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % to maintain the corrosion resistance. In a case of use at temperatures of about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %. In a case of use at temperatures over

1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % to maintain the high-temperature strength. In any case, when welding is conducted to mount the support parts and the protectors, the amount of silicon (Si) added should preferably be about 0.3 to 1 % in consideration of the weldability.

Further, if intensive molten salt corrosion is likely to occur because of a temperature range at which the support parts and the protectors are used or characteristics of the adhered ash to the support parts and the protectors, it is desirable to increase the amount of niobium (Nb) added up to 0.1 to 3 % so as to produce a material having an improved resistance to molten salt corrosion.

The application of the nickel base heat resisting alloy according to the present invention has been described in connection with the fluidized-bed gasification and slagging combustion apparatus as shown in FIG. 3. There will be described below embodiments in which the inventive nickel base heat resisting alloy is applied to other types of incineration apparatus or gasification apparatus.

FIG. 21 shows a kiln-type gasification and slagging combustion apparatus having a kiln-type gasification furnace according to a fifth embodiment of the present invention. The kiln-type gasification furnace has a heat transfer pipe 71 made of the inventive nickel base heat resisting alloy.

In the kiln-type gasification furnace of the gasification and slagging combustion apparatus, introduced wastes A are heated by a high-temperature fluid U flowing through the-heat-transfer pipe 71. Thus, the wastes A are pyrolyzed-and gasified to produce a pyrolysis gas B. The pyrolysis gas B mainly contains steam, hydrogen, carbon monoxide, hydrocarbon, and the like. The pyrolysis gas B also contains corrosive components caused by hydrogen chloride and hydrogen sulfide, which are originated from chlorine contents and sulfur contents contained in the wastes A. Thus, the heat transfer pipe 71 needs to be made of a material having a sufficient corrosion resistance. If the heat transfer pipe 71 is made of a material having an insufficient corrosion resistance, then the heat transfer pipe 71 needs to be replaced frequently. Since the kiln-type gasification furnace is generally huge, a large space and much labor are required to replace the heat transfer pipe 71, so that problems arise in view of a site area of the furnace and operating cost.

Although the optimum temperature for pyrolysis and gasification of wastes

depends on properties of the wastes, it is generally in a range of about 400 to 1000°C, preferably about 400 to 600°C If the gasification temperature is 500°C, and the temperature of the high-temperature fluid U flowing through the heat transfer pipe 71 is about 700°C, the heat transfer pipe 71 has an average temperature of about 600°C. Thus, if the heat transfer pipe 71 is made of a conventional material such as carbon steel or stainless steel, it is subjected to an extremely intensive high-temperature corrosion as shown in FIG. 1. Accordingly, the surface of the heat transfer pipe 71 may be covered with a refractory material so as to prevent the surface of the heat transfer pipe 71 from being exposed to a corrosive gas. Alternatively, a protector may be attached to the surface of the heat transfer pipe 71, or an operating temperature may be lowered. However, since these measures lower the efficiency of heat transfer, a heating surface area-needs to be increased, so that the size of the apparatus becomes extremely large.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance in a high-temperature corrosive gas environment of about 600°C as compared to conventional materials. Thus, by making the heat transfer pipe 71 of the inventive alloy, it is possible to eliminate a refractory material or a protector, or improve the operating temperature so as to improve the efficiency of heat transfer.

Accordingly, the apparatus can be made compact in size, and an installation space can be reduced. Further, since the durability of the heat transfer pipe 71 can be improved, replacement of the heat transfer pipe 71 is unnecessary, or otherwise the number of-replacements of-the heat transfer pipe 71 can remarkably be reduced.

Specific composition of the alloy may be determined in consideration of corrosion resistance at temperatures of about 600°C. For example, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and niobium (Nb) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance.

FIG. 22 shows a fluidized-bed combustion furnace or gasification furnace according to a sixth embodiment of the present invention. The fluidized-bed combustion furnace or gasification furnace has a device to produce a carbonized material which is disposed at a freeboard of the furnace 101. The device heats and carbonizes organic wastes such as wood in an atmosphere having a small amount of oxygen, and recovers the organic wastes as carbide. The inventive nickel base

heat resisting alloy is used in the device to produce a carbonized material.

The inventors have proposed a device to produce a carbonized material which is disposed at a freeboard of a furnace for heating and carbonizing organic wastes such as wood in an atmosphere having a small amount of oxygen, and recovering the organic wastes as carbide. Such a device is disclosed by International patent publication No. WO00/24671, the entire disclosure of which is incorporated herein by reference. FIG. 22 shows an example of such a device.

As shown in FIG. 22, a raw material V for carbonization of organic wastes such as wood is introduced into a carbonization drum 72 provided at a freeboard 101a in a fluidized-bed gasification furnace 101. The raw material V is heated and carbonized by a pyrolysis gas B in the gasification furnace 101. Since the pyrolysis gas B is produced by combustion of the wastes, it contains a large amount of corrosive components such as hydrogen chlorides.

The pyrolysis gas B generally has a temperature of about 600 to 1000°C, preferably about 700 to 900°C. Accordingly, the carbonization drum 72 needs to be made of a material having a sufficient corrosion resistance to such a high-temperature corrosive gas atmosphere. Further, a pyrolysis gas W is produced when the raw material V is carbonized in the carbonization drum 72.

The pyrolysis gas W is cooled indirectly by cooling water H so that a portion of the pyrolysis gas W is condensed. In order to recover pyroligneous acid or the like from the condensed liquid, a pyroligneous acid recovery device 75 is provided downstream of the carbonization drum 72. Properties of the pyrolysis gas W vary according to the kind of the raw material V. The pyrolysis gas W may include corrosive components such as chlorine contents or sulfur contents. Thus, if the carbonization drum 72 is made of an improper material, then corrosion occurs inside of the carbonization drum 72 as well as outside of the carbonization drum 72.

The inventive nickel base heat resisting alloy is suitable for use in such a high-temperature corrosive gas atmosphere. By making the carbonization drum 72 of the inventive nickel base heat resisting alloy, the durability of the carbonization drum 72 can remarkably be improved as compared to cases where the carbonization drum 72 is made of a general material such as stainless steel.

Heat deformation of the carbonization drum 72 has an influence on operation of a screw 74 rotating about a screw shaft 2. Accordingly, specific

composition of the alloy may be determined so that the carbonization drum 72 has a high-temperature strength to prevent heat deformation of the carbonization drum 72 and a corrosion resistance at temperatures of about 700 to 1000°C. Thus, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, niobium (Nb) in a range of about 0.1 to 2 %, and tungsten (W) in a range of about 8 to 15 %, preferably about 10 to 15 %. It is desirable to form the carbonization drum 72 with a pipe produced by a centrifugal casting method.

FIG. 23 shows a stoker-type incineration furnace according to a seventh embodiment of the present invention. The inventive nickel base heat resisting alloy is used in fire grates in the stoker-type incineration furnace. As shown in FIG. 23, the stoker-type incineration furnace has fire grates 81 arranged in a stepped manner and a cylinder 82 for actuating the fire grates 81. The cylinder 82 mechanically moves the fire grates 81 to sequentially move wastes A introduced onto the fire grates 81 between a drying process, a gasification process, and a combustion process. In this manner, the wastes are incinerated.

The combustion temperature of the stoker-type incineration furnace is averagely about 900°C. The fire grates 81 have an air cooling structure or a water cooling structure to cool the fire grates 81 to about 400 to 500°C, so that the durability of the fire grates 81 is improved. However, the above temperatures are average. Accordingly, the fire grates 81 may include local portions having a temperature as high as about-600 to 700°C because of unevenly combustion of the wastes.

The fire grates 81 are generally made of heat resistant cast steel or heat resistant alloy. The fire grates 81 are required to have a sufficient mechanical strength in a maximum temperature range of about 600 to 700°C. Further, the fire grates 81 are required to have a high-temperature corrosion resistance to a high-temperature corrosive gas G produced by combustion. Furthermore, the fire grates 81 are required to have a resistance to wear with the wastes A because the wastes A are moved in a direct contact manner on the fire grates 81. Thus, the fire grates 81 are used in an extremely severe environment. Accordingly, the fire grates 81 are generally replaced as expendables at portions that are intensively damaged with new ones at the time of periodic inspection of the furnace. Thus, it

is desirable to make the fire grates 81 of an inexpensive material having an excellent durability. If the durability is slightly degraded, operating cost of the furnace is considerably increased.

Recently, there has been used a stoker furnace having a water cooling structure for cooling fire grates with water from a lower portion of the fire grates.

However, efficient supply of cooling water to the fire grates and simple replacement of the fire grates does not necessarily conform to each other. For this reason, the stoker furnace has a complicated structure.

The inventive nickel base heat resisting alloy shows an excellent high-temperature corrosion resistance in a maximum temperature range of about 800 to 1200°C as compared to heat resistant cast steel or heat resistant alloy.

Accordingly, by making the fire grates 81 of the inventive alloy, it is-possible to considerably improve the durability of the fire grates 81 and reduce operating cost of the furnace.

Specific composition of the alloy may be determined in consideration of abrasion resistance in addition to corrosion resistance at operating temperatures of the fire grates 81. For example, in a case of use at temperature of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % to maintain the corrosion resistance. In a case of use at temperatures of about 700 toP 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %. In a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % to maintain the high-temperature strength. It is desirable that the amount of silicon (Si) added is in a range of about 1 to 4 %, preferably about 2 to 4 % in view of the wear resistance. If the amount of silicon (Si) added is increased, the alloy can be hardened so as to improve the abrasion resistance. In this case, the weldability and the castability are degraded. Accordingly, it is desirable to examine the castability of the fire grates 81 according to shapes of the fire grates 81 and determine the amount of silicon (Si) to be added.

FIG. 24 is a schematic diagram showing a waste gasification power generation system having an internal circulating fluidized-bed gasification furnace and a power generation device 200 according to an eighth embodiment of the present invention. The internal circulating fluidized-bed gasification furnace includes a gasification chamber 101 for pyrolyzing and gasifying a raw material and a combustion chamber 102 for combusting a pyrolysis residue, which has not been pyrolyzed or gasified in the gasification chamber 101. The power generation device 200 generates power by using a gas B produced in the gasification chamber 101 after cooling and cleaning the gas B.

A combustible raw material A such as wastes or sludge is dried in a drier 202 so that moisture is substantially removed. from the material A. The combustible material A is introduced into the gasification chamber-101 of the internal circulating fluidized-bed gasification furnace by a feeder 108. The gasification chamber 101 is maintained at about 300 to 900°C. The material receives heat from a fluidized medium so as to be pyrolyzed and gasified. Thus, a produced gas B and a pyrolysis residue mainly containing fixed carbon of the material and ash are produced in the gasification chamber 101. The temperature of pyrolysis and gasification is higher than a temperature at which combustibles begin to be pyrolyzed and is lower than heat resistant temperatures of materials. The temperature of pyrolysis and gasification is preferably in a temperature range in which the pyrolysis and gasification are maintained by heat from the combustion chamber-102 and the amount of gas produced is large.

The produced gas B is supplied from the gasification chamber 101 to a heat recovery device 203, where the sensible heat is recovered so as to lower the temperature of the produced gas B to about 50 to 300°C, preferably about 50 to 250°C. It is desirable that the produced gas B is lowered in temperature to about 50°C or less to reduce moisture in the gas. On the other hand, it is desirable that the produced gas has a temperature at which tar is not considerably deposited in the heat exchanger. Thus, the temperature of the produced gas B is preferably lowered to about 50 to 300°C, more preferably about 50 to 250°C. Then, the produced gas B is supplied to a gas cooling device 204 so as to be lowered in temperature to about 40 to 50°C, preferably about 40 to 45°C to reduce the amount of moisture. Thereafter, the produced gas B is supplied to a gas cleaning device

205. The gas cleaning device 205 removes corrosive components or toxic components such as hydrogen chlorides, ammonia, cyanide, sulfur oxides, and hydrogen sulfides from the produced gas. The produced gas from which toxic components have been removed is supplied to the power generation device 200 such as a gas turbine and utilized for power generation. The produced gas may be mixed with external fuel such as city gas, and the mixture may be supplied to the power generation device 200. When external fuel is supplied to the power generation device 200, a heating value of a gas to be supplied to the power generation device 200 can be controlled at a constant value by adjusting the amount of external fuel to be mixed even if the heating value of the produced gas varies.

Accordingly, it is possible to maintain the amount of power generation stably in the power generation device 200. In the power generation device 200, the produced gas and the fuel are combusted at temperatures of about 500 to 1800°C, preferably about 800 to 1500°C, so as to produce a combustion gas 206 having a temperature of about 400 to 1500°C. The combustion gas 206 is introduced into a heat exchanger 207, where the sensible heat of the combustion gas 206 is recovered by a heating medium gas. The temperature of the heating medium gas becomes about 150 to 500°C, preferably about 200 to 300°C. The combustion gas preferably has a temperature at which it can be released to the exterior of the system, e. g. about 100 to 200°C. Then, a portion of the combustion gas 206 is supplied as a fluidizing gas into the gasification chamber 101 of the internal circulating fluidized-bed gasification furnace, and an excessive portion is discharged from a chimney 208.

It is desirable that the temperature of the fluidizing gas is as high as possible. The high-temperature heating medium gas which has recovered the sensible heat of the combustion gas 206 is supplied to the heat recovery device 203 so as to recover the sensible heat of the produced gas B. Thus, the temperature of the heating medium gas is further increased to about 200 to 500°C, preferably about 250 to 350°C to quickly dry the raw material A. Then, the heating medium gas is supplied into the drier 202.

In the drier 202, the raw material A is brought into direct contact with the heating medium gas and dried by heat of the high-temperature heating medium gas.

Moisture produced by drying the raw material is discharged from the drier 202 together with the heating medium gas and cooled to about 40 to 50°C by a

dehumidifier 209 so that the moisture and water content in the heating medium gas are condensed and recovered. Thus, the heating medium gas is circulated in the system. The amount of heating medium gas is adjusted by supplying an additional heating medium upstream of the dehumidifier 209. The moisture recovered in the dehumidifier 209 is discharged as waste water.

The pyrolysis residue produced in the gasification chamber 101 is introduced into the combustion chamber 102 together with the fluidized medium and combusted at temperatures of about 500 to 1000°C by combustion air, which is supplied to the combustion chamber 102. The combustion temperature is higher than an ignition temperature of the pyrolysis residue and is lower than heat resistant temperatures of materials. Thus, the temperature of combustion is preferably in a temperature range in which pyrolysis and gasification are performed by heat obtained by combustion of the pyrolysis residue. The combustion of the pyrolysis residue produces a combustion exhaust gas 210 and ash. The combustion exhaust gas 210 and ash are supplied into a heat recovery device 211, where the combustion exhaust gas 210 and ash exchange heat with air to be supplied to the combustion chamber 102 and the power generation device 200. Thus, the temperature of the combustion gas 210 and ash is lowered in the heat recovery device 211. Then, the combustion gas 210 and ash are supplied into a dust collector 212, which removes ash contents, and discharged from the chimney 208. In the heat recovery device 211, the combustion gas 210 having a high temperature of about 400 to 1000°C is lowered in temperature to about 200 to 400°C in consideration of conditions of an inlet of the dust collector 212, whereas the combustion air is heated to about 200 to 500°C, preferably about 250 to 350°C In the eighth embodiment, the inventive nickel base heat resisting alloy can be applied to various portions including the feeder 108, burners 109a and 109b, a sampling device, nozzle ports 110, and the like, as with the aforementioned embodiments.

FIG. 25 is a schematic diagram showing a gasification power generation system having an internal circulating fluidized-bed gasification furnace and a power generation device 200 such as a gas turbine according to a ninth embodiment of the present invention. This gasification power generation system is used for processing combustibles such as wastes or sludge. In the gasification power

generation system, heat transfer pipes for heat recovery devices are made of the inventive nickel base heat resisting alloy.

The internal circulating fluidized-bed gasification furnace includes a gasification chamber 101 for pyrolyzing and gasifying a raw material and a combustion chamber 102 for combusting a pyrolysis residue, which has not been pyrolyzed or gasified in the gasification chamber 101. The power generation device 200 generates power by using a gas B produced in the gasification chamber 101 after cooling and cleaning the gas B.

A combustible raw material A such as wastes or sludge is dried in a drier 202 at temperatures of about 80 to 180°C, preferably about 80 to 120°C, so that moisture is substantially removed from the material A. The combustible material A is introduced into the gasification chamber 101 of the internal circulating fluidized-bed gasification furnace by a feeder 108. The gasification chamber 101 is maintained at about 300 to 900°C, preferably about 400 to 700°C. The material receives heat from a fluidized medium so as to be pyrolyzed and gasified. Thus, a produced gas B and a pyrolysis residue mainly containing fixed carbon of the material and ash are produced in the gasification chamber 101. The temperature of pyrolysis and gasification is higher than a temperature at which combustibles begin to be pyrolyzed and is lower than heat resistant temperatures of materials. The temperature of pyrolysis and gasification is preferably in a temperature range in which the pyrolysis and gasification are maintained by heat from the combustion chamber 102 and the amount of gas produced is large The produced gas B is supplied from the gasification chamber 101 having a temperature of about 300 to 900°C to a heat recovery device 203, where the sensible heat is recovered so as to lower the temperature of the produced gas B to about 50 to 300°C, preferably about 50 to 250°C. It is desirable that the produced gas B is preferably lowered in temperature to about 50°C or less to reduce moisture in the gas. On the other hand, it is desirable that the produced gas preferably has a temperature at which tar is not considerably deposited in the heat exchanger. Thus, the temperature of the produced gas B is preferably lowered to about 50 to 300°C, more preferably about 50 to 250°C. Then, the produced gas B is supplied to a gas cooling device 204 so as to be lowered in temperature to about 40 to 50°C, preferably about 40 to 45°C to reduce the amount of moisture. Thereafter, the

produced gas B is supplied to a gas cleaning device 205. The gas cleaning device 205 removes corrosive components or toxic components such as hydrogen chlorides, ammonia, cyanide, sulfur oxides, and hydrogen sulfides from the produced gas.

The produced gas from which toxic components have been removed is supplied to the power generation device 200 such as a gas turbine and utilized for power generation. The produced gas may be mixed with external fuel such as city gas, and the mixture may be supplied to the power generation device 200. When external fuel is supplied to the power generation device 200, a heating value of a gas to be supplied to the power generation device 200 can be controlled at a constant value by adjusting the amount of external fuel to be mixed even if the heating value of the produced gas varies. Accordingly, it is possible to maintain the amount of power generation stably in the power generation device 200. In the power generation device 200, the produced gas and the fuel are combusted at temperatures of about 500 to 1800°C, preferably about 800 to 1500°C, so as to produce a combustion gas 206 having a temperature of about 500 to 1500°C. The combustion gas 206 is introduced into a heat exchanger 207, where the sensible heat of the combustion gas 206 is recovered by a heating medium gas. The temperature of the heating medium gas becomes about 150 to 500°C, preferably about 200 to 300°C. The combustion gas preferably has a temperature at which it can be released to the exterior of the system, e. g. about 100 to 200°C. Then, a portion of the combustion gas 206 is supplied as a fluidizing gas into the gasification chamber 101 of the internal circulating fluidized-bed gasification furnace, and an excessive portion is discharged from a chimney 208. It is desirable that the temperature of the fluidizing gas is as high as possible. The high-temperature heating medium gas which has recovered the sensible heat of the combustion gas 206 is supplied to the heat recovery device 203 so as to recover the sensible heat of the produced gas B. Thus, the temperature of the heating medium gas is further increased to about 200 to 500°C, preferably about 250 to 350°C to quickly dry the raw material A. Then, the heating medium gas is supplied into the drier 202.

In the drier 202, the raw material A is brought into direct contact with the heating medium gas and dried by heat of the high-temperature heating medium gas.

Moisture produced by drying the raw material is discharged from the drier 202

together with the heating medium gas and cooled to about 40 to 50°C by a dehumidifier 209 so that the moisture and water content in the heating medium gas are condensed and recovered. Thus, the heating medium gas is circulated in the system. The amount of heating medium gas is adjusted by supplying an additional heating medium upstream of the dehumidifier 209. The moisture recovered in the dehumidifier 209 is discharged as waste water.

The pyrolysis residue produced in the gasification chamber 101 is introduced into the combustion chamber 102 together with the fluidized medium and combusted at temperatures of about 500 to 1000°C, preferably about 800 to 900°C by combustion air, which is supplied to the combustion chamber 102. The combustion temperature is higher than an ignition temperature of the pyrolysis residue and is lower than heat resistant temperatures of materials. Thus, the temperature of combustion is preferably in a temperature range in which pyrolysis and gasification are performed by heat obtained by combustion of the pyrolysis residue. The combustion of the pyrolysis residue produces a combustion exhaust gas 210 and ash. The combustion exhaust gas 210 and ash are supplied into a heat recovery device 211, where the combustion exhaust gas 210 and ash exchange heat with air to be supplied to the combustion chamber 102 and the power generation device 200. Thus, the temperature of the combustion gas 210 and ash is lowered in the heat recovery device 211. Then, the combustion gas 210 and ash are supplied into a dust collector 212, which removes ash contents, and discharged from the chimney 208. In the heat recovery device 211, the combustion gas 210 having a high temperature of about 400 to 1000°C is lowered in temperature to about 200 to 400°C in consideration of conditions of an inlet of the dust collector 212, whereas the combustion air is heated to about 200 to 500°C, preferably about 250 to 350°C.

The pyrolysis gas B produced by pyrolysis and gasification mainly contains hydrogen, carbon monoxide, hydrocarbon, and the like as well as steam. In addition to these components, the pyrolysis gas B contains corrosive components caused by hydrogen chloride and hydrogen sulfide, which are originated from chlorine contents and sulfur contents contained in the raw material A.

Accordingly, a heat transfer pipe 213 of the heat recovery device 203 needs to be made of a material have a sufficient corrosion resistance. If the heat transfer pipe

213 has an insufficient corrosion resistance, frequent replacement of the heat transfer pipe 213 is required, resulting in increased operating cost of the system.

Although the optimum temperature for pyrolysis and gasification of the raw material such as wastes or sludge depends on properties of the raw material, it is generally in a range of about 400 to 1000°C, preferably about 400 to 600°C. If the gasification temperature is 500°C, and the temperature of the high-temperature fluid flowing through the heat transfer pipe 213 is about 700°C, the heat transfer pipe 213 has an average temperature of about 600°C. Thus, if the heat transfer pipe 213 is made of a conventional material such as carbon steel or stainless steel, it is subjected to an extremely intensive high-temperature corrosion as shown in FIG.

1. Accordingly, the surface of the heat transfer pipe 213 may be covered with a refractory material so as to prevent the surface of the heat transfer pipe 213 from being exposed to a corrosive gas. Alternatively, a protector may be attached to the surface of the heat transfer pipe 213, or an operating temperature may be lowered.

However, since these measures lower the efficiency of heat transfer, a heating surface area needs to be increased, so that the size of the apparatus becomes extremely large.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance in a high-temperature corrosive gas environment of about 600°C as compared to conventional materials. Thus, by making the heat transfer pipe 213 of the inventive alloy, it is possible to eliminate a refractory material or a protector, or improve the operating temperature so as to improve the efficiency of heat transfer. Accordingly, the apparatus can be made compact in size, and an installation space can be reduced. Further, since the durability of the heat transfer pipe 213 can be improved, replacement of the heat transfer pipe 213 is unnecessary, or otherwise the number of replacements of the heat transfer pipe 213 can remarkably be reduced.

Specific composition of the alloy may be determined in consideration of corrosion resistance at temperatures of about 600°C. For example, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and niobium (Nb) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance.

Further, if intensive molten salt corrosion is likely to occur because of a

temperature range at which the heat transfer pipe is used or characteristics of the adhered ash to the heat transfer pipe, it is desirable to increase the amount of niobium (Nb) added up to 0. 1 to 3 % so as to produce a material having an improved resistance to molten salt corrosion.

Since the pyrolysis residue produced by pyrolysis and gasification of the raw material is combusted at temperatures of about 500 to 1000°C, the combustion gas 210 has temperatures of about 400 to 1000°C. Further, chlorine or sulfur of the raw material is also contained in the pyrolysis residue. Thus, the combustion gas contains hydrogen chlorides or sulfur oxides and is thus corrosive.

Furthermore, since the combustion gas includes ash, a heat transfer pipe 214 of the heat recovery device 211 is subjected to molten salt corrosion due to attachment of the ash. Accordingly, the heat transfer pipe 214 of the heat recovery device 211 needs to be made of a material have a sufficient corrosion resistance. If the heat transfer pipe 214 has an insufficient corrosion resistance, frequent replacement of the heat transfer pipe 214 is required, resulting in increased operating cost of the system.

As with the heat transfer pipe 213 of the heat recovery device 203, the heat transfer pipe 214 has an average temperature of about 600°C. Thus, if the heat transfer pipe 214 is made of a conventional material such as carbon steel or stainless steel, it is subjected to an extremely intensive high-temperature corrosion as shown in FIG. 1. Accordingly, the surface of the heat transfer pipe 214 may be covered with a refractory material so as to prevent the surface of the heat transfer pipe 214 from being exposed to a corrosive gas. Alternatively, a protector may be attached to the surface of the heat transfer pipe 214, or an operating temperature may be lowered. However, since these measures lower the efficiency of heat transfer, a heating surface area needs to be increased, so that the size of the apparatus becomes extremely large.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance in a high-temperature corrosive gas environment of about 600°C as compared to conventional materials. Thus, by making the heat transfer pipe 214 of the inventive alloy, it is possible to eliminate a refractory material or a protector, or improve the operating temperature so as to improve the efficiency of heat transfer. Accordingly, the apparatus can be made compact in size, and an

installation space can be reduced. Further, since the durability of the heat transfer pipe 214 can be improved, replacement of the heat transfer pipe 214 is unnecessary, or otherwise the number of replacements of the heat transfer pipe 214 can remarkably be reduced.

Further, the heat recovery device 203 can preheat air sufficiently with the heat transfer pipe 213 made of the inventive alloy. Accordingly, preheated air having a high temperature can be supplied to the power generation device 200 such as a turbine. Thus, generation efficiency can be improved in the power generation device 200 so as to achieve high-efficient power generation from a raw material having a low heating value, such as wastes or sludge, which has been impracticable.

Specific composition of the alloy may be determined in consideration of corrosion resistance at temperatures of about 600°C. For example, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and niobium (Nb) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance.

Further, if intensive molten salt corrosion is likely to occur because of a temperature range at which the heat transfer pipe 213 is used or characteristics of the adhered ash to the heat transfer pipe 213, it is desirable to increase the amount of niobium (Nb) added up to 0.1 to 3 % so as to produce a material having an improved resistance to molten salt corrosion.

Similarly, since the inventive alloy is used in the heat transfer pipe 214 of the heat recovery device 211 for recovering heat from the corrosive combustion gas, the heat transfer pipe 214 can have an excellent corrosion resistance as compared to conventional materials. Accordingly, the efficiency of. heat transfer can be improved. The apparatus can be made compact in size, and an installation space can be reduced. Further, since the durability of the heat transfer pipe 214 can be improved, replacement of the heat transfer pipe 214 is unnecessary, or otherwise the number of replacements of the heat transfer pipe 214 can remarkably be reduced.

Thus, operating cost can be reduced.

Specific composition of the alloy may be determined in consideration of corrosion resistance at temperatures of about 600°C. For example, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and niobium

(Nb) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance.

Further, if intensive molten salt corrosion is likely to occur because of a temperature range at which the heat transfer pipe 214 is used or characteristics of the adhered ash to the heat transfer pipe 214, it is desirable to increase the amount of niobium (Nb) added up to 0.1 to 3 % so as to produce a material having an improved resistance to molten salt corrosion.

There will be described a tenth embodiment of the present invention in which the inventive nickel base heat resisting alloy is used as a material for a pipe or a duct through which a high-temperature corrosive gas flows. A pipe or a duct is generally made of carbon steel for use at temperatures up to about 300°C or made of stainless steel for use at temperatures in a range of about 300 to 700°C. There are no inexpensive metallic materials that can be used for a pipe or a duct at temperatures over about 700°C, for example, in a range of about 700 to 1000°C.

In such a case, a refractory material or a heat insulating material is generally attached onto an inner surface of the pipe or the duct to prevent the material from being increased in temperature and lowered in strength.

Specifically, when a handled fluid is a high-temperature corrosive gas containing a large amount of hydrogen chlorides or the like, intensive corrosion occurs as the temperature of the gas is increased. Thus, the refractory material or the heat insulating material is attached onto the inner surface of the pipe made of carbon steel or stainless steel so as to prevent the pipe from being brought into direct contact with the high-temperature corrosive gas. When the refractory material or the heat insulating material is attached onto the inner surface of the pipe, the diameter of the pipe becomes larger by the thickness of the refractory material or the heat insulating material. Accordingly, the cost of the pipe is increased, and an installation space for the pipe is also increased. Further, in a case where the refractory material is attached to the pipe, the weight of the pipe increases.

Accordingly, it is necessary to enhance the strength of support parts or frames for supporting the pipe. Thus, the construction cost of the entire plant is increased.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance and high-temperature strength to a high-temperature corrosive gas having a temperature of about 700 to 1200°C as well as in a range of about 300 to 700°C.

Thus, with use of the inventive alloy, it is possible to form a pipe capable of

handling a high-temperature corrosive gas without any refractory material or heat insulating material being attached to an inner surface of the pipe. In order to prevent an internal high-temperature corrosive gas from being lowered in temperature due to heat radiation, it is desirable to attach a heat insulating material to the inner surface of the pipe. In order to prevent the pipe from being increased in temperature, a heat insulating material may be attached to an outer surface of the pipe. In this case, attachment, repair, or replacement of the heat insulating material can be performed during use easier than in the case where a heat insulating material is attached to an inner surface of a pipe.

Specific composition of the alloy may be determined in consideration of operating temperatures of the pipe. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance. In a case of use at temperatures of about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %.

Further, in a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % in order to maintain the high-temperature strength.

It is desirable to produce a pipe by a centrifugal casting method because the pipe having a good quality can readily be obtained at low cost. However, sand casting or permanent mold casting is suitable for producing pipe components such as curved pipes and branch pipes because sand casting or permanent mold casting prevents an increase of cost due to machining.

The inventive nickel base heat resisting alloy can be used as a material for a flow regulating valve or a damper in a passage handling a high-temperature corrosive gas. A valve or damper is generally made of cast iron or brass for use at temperatures up to about 300°C and made of stainless casting for use at temperatures in a range of about 300 to 700°C. A high-grade material is required for use in a high-temperature gas having temperature over about 700°C, for example, in a range of about 700 to 1000°C.

When a handled fluid is a high-temperature corrosive gas containing a large amount of hydrogen chlorides or the like, intensive corrosion occurs as the temperature of the gas is increased. Accordingly, even if a valve or a damper is made of a high-grade material such as Alloy 625, it is considerably difficult to use the valve or the damper for a long term.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance to a high-temperature corrosive gas having a temperature of about 700 to 1200°C as well as in a range of about 300 to 700°C. By making a valve or a damper of the inventive alloy, it is possible to regulate a flow rate of a high-temperature corrosive gas having a temperature of about 1200°C, which has been impracticable.

Specific composition of the alloy may be determined in consideration of operating temperatures of the valve or the damper. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance. In a case of use at temperatures of about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %. Further, in a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % in order to maintain the high-temperature strength. For example, in a case of a part having a complicated shape, such as a valve component, it is desirable to determine the amount of silicon (Si) to be added in consideration of the castability at the time of production. Specifically, the amount of silicon (Si) to be added is preferably in a range of about 0.3 to 1 %.

Generally, a body of a valve or a damper is produced by casting, and principle parts inside of the body are produced by machining after casting or by forging. In either case, a portion which is brought into contact with a high-temperature corrosive gas should be made of the inventive nickel base heat resisting alloy.

The inventive nickel base heat resisting alloy can be used as a material for

a fan or a blower in a passage handling a high-temperature corrosive gas. A portion of a fan or a blower which is brought into contact with a handled gas, such as a casing or an impeller, is generally made of cast iron or the like for use at temperatures up to about 300°C and made of stainless casting for use at temperatures in a range of about 300 to 700°C. A high-grade material is required for use in a high-temperature gas having temperature over about 700°C, for example, in a range of about 700 to 1200°C.

When a handled fluid is a high-temperature corrosive gas containing a large amount of hydrogen chlorides or the like, intensive corrosion occurs as the temperature of the gas is increased. Accordingly, even if a fan or a blower is made of a high-grade material such as Alloy 625, it is considerably difficult to use the fan or the blower for a long term.

The inventive nickel base heat resisting alloy shows an excellent corrosion resistance to a high-temperature corrosive gas having a temperature of about 700 to 1200°C as well as in a range of about 300 to 700°C. By making a fan or a blower of the inventive alloy, it is possible to use the fan or the blower in a high-temperature corrosive gas having a temperature of about 1200°C, which has been impracticable.

Specific composition of the alloy. may be determined in consideration of operating temperatures of the fan or the blower. For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance. In a case of use at temperatures of about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %. Further, in a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % in order to maintain the high-temperature strength. For example, in a case of a part having a complicated shape, such as an impeller of a blower, it is desirable to determine the amount of silicon (Si) to be added in consideration of the castability at the time of production. Specifically,

the amount of silicon (Si) to be added is preferably in a range of about 0.3 to 1 %.

The above examples have been described for general pipes handling a high-temperature corrosive gas, which has heretofore been difficult to be handled.

These pipes can be combined with each other to achieve a process that has heretofore been impracticable. There will be described combinations of the above examples with reference to FIGS. 26 through 28.

FIG. 26 shows a waste gasification and slagging combustion apparatus including two gasification furnaces 101a and 101b and a swirling-type slagging combustion furnace 102 according to a tenth embodiment of the present invention.

The inventive alloy is used in a damper provided in the gasification and slagging combustion apparatus.

When wastes include a considerable amount of matter unsuitable for combustion, such as incombustibles, the matter is selected in the gasification furnaces 101a and 101b and discharged from lower portions of the gasification furnaces 101a and 101b. Accordingly, the slagging combustion furnace 102 has a load smaller than the gasification furnaces 101a and 101b. In this case, if a load on the slagging combustion furnace 102 is excessively small, then a ratio of radiation loss to heat produced by combustion is increased so as to require a large amount of auxiliary fuel for stably melting ash.

When the gasification furnaces 101a and 101b is stopped because the matter unsuitable for combustion, such as a metal wire, clogs a discharge port, the slagging combustion furnace 102 also needs to be stopped.

From this point of view, as shown in FIG. 26, the gasification and slagging combustion apparatus has two gasification furnaces 101a and 101b and one slagging combustion furnace 102. Thus, it is possible to properly balance loads on the gasification furnaces 101a and 101b and the slagging combustion furnace 102.

If one of the gasification furnaces 101a and 101b should be stopped, wastes can continuously be processed by the other of the gasification furnaces 101a and 101b.

In this case, dampers 85a and 85b for pressure regulation are required upstream of an inlet of the slagging combustion furnace 102 to absorb a pressure difference between the two gasification furnaces Ida and 101b. The dampers 85a and 85b are also required to separate a stopped gasification furnace from an operating gasification furnace when one of the gasification furnaces is stopped while the other

is operated.

Pyrolysis gases B at outlets of the gasification furnaces 101a and 101b have temperatures of about 400 to 1000°C, preferably about 800 to 900°C. The pyrolysis gases include ash contents. It has heretofore been difficult to provide a damper that can be used in such an environment. The inventive nickel base heat resisting alloy shows an excellent corrosion resistance even in such an environment.

As shown in FIG. 27, by discharging the pyrolysis gases to a downstream portion of the slagging combustion furnace 102, a slag discharge section 111 can be prevented from being cooled. In FIG. 27, a blower 87 and pipes around the blower 87 are exposed to a high-temperature corrosive gas D2, which is a mixture of a combustion exhaust gas D1 and steam X. Thus, the blower 87 and the pipes around the blower 87 are problematic in corrosion resistance when they are made of conventional metallic materials.

The inventive nickel base heat resisting alloy has an excellent high-temperature corrosion resistance in a maximum temperature range of about 800 to 1200°C as compared to conventional heat resistant cast steel or heat resistant alloy. By making the blower 87 and the pipes around the blower 87 of the inventive nickel base heat resisting alloy, the durability of the blower 87 can remarkably be improved.

As shown in FIG. 27, the slagging combustion furnace 102 has a damper 85d and a nozzle 110 for reintroducing the high-temperature corrosive gas D2 discharged from the blower 87 into the slagging combustion furnace 102-. The nozzle 110 may have the same structure as shown in FIG. 8 or 9 to improve the durability of the nozzle 110 and prevent clogging due to solidified slag. The damper 85d may be made of the inventive alloy having a high-temperature corrosion resistance.

As described above, the high-temperature corrosive gas D2 is a mixture of the combustion exhaust gas D1 having a high temperature and steam X.

Accordingly, the temperature of the high-temperature corrosive gas D2 varies to a large extent depending on the amount of steam X produced, i. e. , the amount of slag C discharged. Therefore, it is desirable that the amount of slag C discharged and the amount of steam X discharged are calculated according to properties of the wastes so as to calculate the temperature of the high-temperature corrosive gas D2.

Specific composition of the alloy for the blower 87, the pipes around the blower 87, and the nozzle 110 may be determined based on the calculated temperature of the high-temperature corrosive gas Dz.

For example, in a case of use at temperatures of about 500 to 700°C, the alloy preferably includes chromium (Cr) in a range of about 23 to 27 %, tungsten (W) in a range of about 10 to 15 %, silicon (Si) in a range of about 0.3 to 1 %, and one of niobium (Nb), titanium (Ti), zirconium (Zr), and vanadium (V) in a range of about 0.1 to 2 % in order to maintain the corrosion resistance. In a case of use at temperatures of about 700 to 1000°C, the alloy preferably includes chromium (Cr) in a range of about 25 to 27 %, aluminum (Al) in a range of about 1.8 to 2.5 %, and niobium (Nb) in a range of about 0.1 to 2 %. Further, in a case of use at temperatures over about 1000°C, the alloy preferably includes tungsten (W) in a range of about 10 to 15 % and silicon (Si) in a range of about 0.3 to 1 % in order to maintain the high-temperature strength. For example, in a case of a part having a complicated shape, such as an impeller of the blower 87, it is desirable to determine the amount of silicon (Si) to be added in consideration of the castability at the time of production. Specifically, the amount of silicon (Si) to be added is preferably in a range of 0.3 to 1 %.

FIG. 28 shows a waste gasification and slagging combustion apparatus according to an eleventh embodiment of the present invention. The inventive alloy is used in a damper 85c and/or a blower 86 provided in the gasification and slagging combustion apparatus.

Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Industrial Applicability The present invention is suitable for use in an apparatus for incinerating or gasifying combustibles such as wastes, sludge, solid fuel such as coal, or liquid fuel such as heavy oil at a high temperature.