Background Art Conventionally, a wastes heat boiler in an incineration plant comprises a radiation cooling section comprising water tube panels, and a contact cooling section having a number of steam generating tubes or heating tubes across a flow of exhaust gas. In the radiation cooling section, the water tube panels are disposed and surround the exhaust gas flowing in the waste heat boiler for thereby constituting a flow passage of the exhaust gas, so as to recover heat of the exhaust gas flowing therethrough. On the other hand, in the contact cooling section, a number of steam generating tubes or heating tubes are disposed and inserted into the flow passage of the exhaust gas in the waste heat boiler, so as to recover heat of the exhaust gas. In general, the steam generating tubes or the heating tubes are disposed so as to be inserted into the flow passage of the exhaust gas in order to contact the flowing exhaust gas directly, so they have been thought to be disposed at locations where the temperature of the exhaust gas becomes a certain value.

The conventional waste heat boiler in the

incineration plant is operated in such a state that the exhaust gas has a temperature of about 900°C in the inlet of the boiler, and hence any problem does not occur. However, in a gasification and slagging combustion plant, because the temperature of the exhaust gas in the inlet of the boiler is in the range of 1100 to about 1350°C and is higher than that in the conventional incineration plant, if the conventional waste heat boiler in the incineration plant is used as it is, then metals having a low melting point and salts which have been vaporized due to a high temperature are adhered to and deposited on the interior of the waste heat boiler, together with fly ash at a high- temperature range of 900°C or higher, thus causing corrosion caused by the molten salts to progress. Thus, break or damage of boiler tubes is liable to occur, the performance of the waste heat boiler is liable to be lowered due to adhesion and deposition of fly ash onto the boiler tubes, or other malfunction might occur.

Here, the gasification and slagging combustion plant is defined as a system in which wastes are gasified at a relatively low temperature to produce combustible gas in a gasification furnace, and the produced combustible gas is combusted at a relatively high temperature to generate exhaust gas and ash contained in the combustible gas is melted to produce slag in a slagging combustion furnace (combustion fusion furnace).

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 a waste heat boiler in which break or damage of boiler tubes does not occur, the performance of the waste heat boiler is not lowered by adhesion and deposition of fly ash onto the boiler tubes, or other malfunction does not occur.

In order to achieve the above mentioned object of the present invention, according to an aspect of the present invention, there is provided a waste heat boiler comprising: a housing; an inlet section for introducing exhaust gas into the housing; and a first heat exchange section provided in the housing for recovering heat by heat exchange from the exhaust gas which has been introduced through the inlet section; wherein a surface of the first heat exchange section constitutes a flow passage for allowing the exhaust gas to flow therethrough, and refractory is provided on the surface of the first heat exchange section.

According to a preferred aspect of the present invention, the refractory contains SiC as a main component.

According to the present invention, a waste heat boiler 10 has a first heat exchange section 4, and a surface of the first heat exchange section 4 constitutes a flow passage 1 for allowing exhaust gas j introduced through an inlet section 11 to flow therethrough, and refractory 6 containing SiC as a main component is provided on the surface of the first heat exchange section 4 constituting the flow passage 1. Therefore, corrosion of the surface of the first heat exchange section 4 does not occur, dust is hardly adhered to and deposited on or is not adhered to and deposited on the surface of the first heat exchange section 4, and the problem of a lowering of heat transfer coefficient in the first heat exchange section 4 does not occur.

According to a preferred aspect of the present invention, the flow passage has at least two path sections, and a first path section of the at least two path sections is formed by the first heat exchange section.

With this arrangement, since the refractory 6 containing SiC as a main component is provided on the surface of the first heat exchange section 4 constituting a first path

section la, even if the exhaust gas having a high temperature flows through the first path section la, corrosion of the surface of the first heat exchange section 4 does not occur, and dust is hardly adhered to and deposited on or is not adhered to and deposited on the surface of the first heat exchange section 4. Further, the problem of a lowering of heat transfer coefficient in the first heat exchange section 4 does not occur.

According to a preferred aspect of the present invention, a waste heat boiler further comprises a second heat exchange section provided downstream of the first heat exchange section for recovering heat by heat exchange from the combustible gas or the exhaust gas, and a soot blower for removing deposits adhered to a surface of the second heat exchange section by a blow of fluid, and the second heat exchange section and the soot blower are disposed in one of the at least two path sections which is located downstream of the first path section.

With this arrangement, the waste heat boiler has a soot blower SB, and hence deposits adhered to and deposited on the surfaces of the second heat exchange sections 7,26a, 26b, and 26c can be removed by a blow of fluid with the soot blower SB, and the problem of a lowering of heat transfer coefficient in the second heat exchange sections 7,26a, 26b, and 26c hardly occur.

According to a preferred aspect of the present invention, a waste heat boiler further comprises a second heat exchange section provided downstream of the first heat exchange section for recovering heat by heat exchange from the exhaust gas, and the flow passage has at least three path sections, and the second heat exchange section disposed in a final path section of the at least three path sections is constructed in a repetitive meandering manner at a certain pitch in a direction in parallel with a flow direction of the exhaust gas.

With this arrangement, the second heat exchange sections 26a, 26b and 26c disposed in the final path section lc of the at least three path sections are constructed in a repetitive meandering manner at a certain pitch in a direction in parallel with a flow direction of the exhaust gas j.

Therefore, dust is hardly adhered to and deposited on the surfaces of the second heat exchange sections 26a, 26b and 26c, or is not adhered to and deposited on the surfaces of the second heat exchange sections 26a, 26b and 26c, and the problem of a lowering of heat transfer coefficient in the second heat exchange sections 26a, 26b, and 26c hardly occur.

According to another aspect of the present invention, there is provided a gasification and slagging combustion system comprising: a fluidized-bed gasification furnace for gasifying wastes to produce combustible gas; a slagging combustion furnace for combusting the combustible gas and melting solid components contained in the combustible gas to generate exhaust gas; and a waste heat boiler for recovering heat from the exhaust gas, the waste heat boiler comprising: a housing; an inlet section for introducing the exhaust gas into the housing; and a first heat exchange section provided in the housing for recovering heat by heat exchange from the exhaust gas which has been introduced through the inlet section; wherein a surface of the first heat exchange section constitutes a flow passage for allowing the exhaust gas to flow therethrough, and refractory is provided on the surface of the first heat exchange section.

Brief Description of Drawings FIG. 1 is a schematic view showing a fluidized- bed gasification furnace, a swirling-type slagging combustion furnace, and a waste heat boiler according to an embodiment of the present invention;

FIG. 2 is a side cross-sectional view of the waste heat boiler according to an embodiment of the present invention; FIG. 3 is a fragmentary front view of the waste heat boiler; FIG. 4A is a cross-sectional view taken along line X-X of FIG. 2; FIG. 4B is a cross-sectional view taken along line Y-Y of FIG. 2; FIG. 4C is a cross-sectional view taken along line Z-Z of FIG. 2; FIG. 5 is a cross-sectional view of a water tube panel having a surface on which SiC castable is provided; FIG. 6 is a cross-sectional view of a deslagger; and FIG. 7 is a cross-sectional view of a soot blower.

Best Mode for Carrying Out the Invention A waste heat boiler according to embodiments of the present invention will be described below with reference to the drawings. In FIGS. 1 through 7, like or corresponding parts are denoted by like or corresponding reference numerals throughout views, and repetitive description is eliminated.

FIG. 1 is a schematic view showing a gasification and slagging combustion system (gasification and combustion fusion system) comprising a fluidized-bed gasification furnace 5, a swirling-type slagging combustion furnace (combustion fusion furnace) 8, and a waste heat boiler 10 according to an embodiment of the present invention. The waste heat boiler 10 is disposed at a subsequent stage of the fluidized-bed gasification furnace 5 and the swirling-type slagging combustion furnace 8.

FIG. 2 is a side cross-sectional view of the waste

heat boiler 10. FIG. 3 is a front view of the waste heat boiler 10. FIG. 4A is a cross-sectional view taken along line X-X of FIG. 2 (first path section la (described later)), FIG. 4B is a cross-sectional view taken along line Y-Y of FIG. 2 (second path section lb (described later)), and FIG. 4C is a cross-sectional view taken along line Z-Z of FIG. 2 (third path section lc (described later)). In FIGS. 3 and 4A through 4C, a steam system including a steam separator, headers, steam pipes and the like (described later) is not shown.

Next, the waste heat boiler 10 will be described with reference to FIGS. 2,3 and 4A through 4C.

The waste heat boiler 10 comprises an inlet section 11 from which exhaust gas j is introduced into the boiler, an outlet section 12 from which the exhaust gas j is discharged, external walls 13, a first partition wall 14, a second partition wall 15, and a hopper section 16. The external walls 13, the first partition wall 14, the second partition wall 15, and the hopper section 16 jointly constitute a flow passage 1 for allowing the exhaust gas j to flow through the waste heat boiler 10. The flow passage 1 has such a structure that the exhaust gas j flows through the flow passage 1 in the three path manner.

Specifically, the flow passage 1 has three paths in parallel with each other, and the exhaust gas j flows through the three paths successively by changing a flow direction twice. The external walls 13 comprise a front wall 18 shown at the right of FIG. 2, a backside wall 19 shown at the left of FIG. 2, a side wall 20 shown at the right of FIGS. 4A through 4C, a side wall 17 shown at the left of FIGS. 4A through 4C, and a top wall 21 shown at the top of FIGS. 4A through 4C. The external walls 13 constitute a housing for allowing the exhaust gas j to be contained therein.

The inlet section 11 is connected to an outlet section 51 of the swirling-type slagging combustion furnace

8 (see FIG. 1). The exhaust gas j flows upwardly in a vertical direction through the outlet section 51 and enters the inlet section 11. The flow passage 1 comprises a first path section la, a second path section lb, and a third path section lc arranged in parallel with each other (described later in detail).

The first path section la serves as a first path of the flow passage 1 provided in the waste heat boiler 10 for allowing the exhaust gas j to flow therethrough first, and comprises a portion 17a of the side wall 17 (shown in FIG. 4A), the front wall 18, a portion 14a of the first partition wall 14 (a piece of the first partition wall 14 located at the right side in FIG. 2), a portion 20a of the side wall 20 (shown at the right of FIG. 2), and a portion 2 la of the top wall 21 (shown at the right of FIG. 2).

The second path section 1b of the flow passage 1 serves as a subsequent-stage path of the first path, and comprises a portion 17b of the side wall 17 (shown in FIG. 4B), a portion 14b of the first partition wall 14 (a piece of the first partition wall 14 located at the left side in FIG. 2), a portion 15a of the second partition wall 15 (a piece of the second partition wall 15 located at the right side in FIG. 2), a portion 20b of the side wall 20 (shown at the central part of FIG. 2), a portion 21b of the top wall 21 (shown at the central part of FIG. 2), and a portion of the hopper section 16 (a piece of the hopper section 16 located at the right side in FIG. 2).

The third path section lc of the flow passage 1 serves as a subsequent-stage path of the second path and a final path at the same time, and comprises a portion 17c of the side wall 17 (shown FIG. 4C), the backside wall 19, a portion 15b of the second partition wall 15 (a piece of the second partition wall 15 located at the left side in FIG. 2), a portion 20c of the side wall 20 (shown at the left of FIG. 2), a portion 21c

of the top wall 21 (shown at the left of FIG. 2), and a portion of the hopper section 16 (a piece of the hopper section 16 located at the left side in FIG. 2).

The exhaust gas j which has entered the inlet section 11 flows mainly upwardly through the first path section la shown in FIG. 2, passes through an opening 22 formed in the upper portion of the first partition wall 14, and then flows mainly downwardly through the second path section lb shown in FIG.

2. Thereafter, the exhaust gas j passes through an opening 23 formed in the hopper section 16 located below the second partition wall 15, and flows mainly upwardly through the third path section lc shown in FIG. 2, and then passes through the outlet section 12 and flows leftward in FIG. 2 toward an air heater (not shown). The air heater (not shown) serves to heat combustion air bl (see FIG. 1) to be delivered to the fluidized-bed gasification furnace 5 (see FIG. 1) and the swirling-type slagging combustion furnace 8 (see FIG. 1), which is preferable because improvement of thermal efficiency will be shown.

Water tube panels 4 (see FIG. 5) serving as a first heat exchange section or a radiation cooling section are attached to the inside of the side wall 17 (exhaust gas (j) side, hereinafter the same), the inside of the front wall 18, the inside of the side wall 20, the inside of the top wall 21, both sides of the first partition wall 14, and both sides of the second partition wall 15. In FIGS. 2 and 4A through 4C, the walls to which the water tube panels 4 are attached include a wall W1 whose cross-section is shown by two kinds of oblique lines having different widths, a wall W2 whose cross-section is shown by oblique lines including broken lines, a wall WP which is hatched by broken lines having a small pitch, a wall WQ which is hatched by broken lines having a pitch larger than the pitch of the broken lines in the wall WP, and a wall WR

which is hatched by broken lines having a pitch larger than the pitch of the broken lines in the wall WP.

Water tube panels 7 serving as a second heat exchange section or a contact cooling section are disposed in the second path section lb. The water tube panels 7 recover heat by heat exchange from the exhaust gas j. The six water tube panels 7 are juxtaposed in parallel with a flow of the exhaust gas j flowing through the second path section 1b, and also in parallel with the sheet of FIG. 2. Each of the water tube panels 7 has an opening 58 providing space for allowing a soot blower SB to be inserted or taken out. Each of the water tube panels 7 has a lower header 29 and an upper header 30.

Feed water is fed to a steam separator 25, and then fed from the steam separator 25 through a supply pipe 31 to a lower header 28 (shown by two-dot chain lines in FIG. 2).

A part of the feed water flows from the lower header 28 to water tubes 4a (see FIG. 5) of the water tube panels 4 in which the feed water is heated, and then flows into upper headers 24.

A part of the remaining feed water flows from the lower header 28 to the lower headers 29 of the water tube panels 7, and then flows through water tubes (not shown) of the water tube panels 7 in which the feed water is heated. Thereafter, the feed water flows through the upper headers 30 of the water tube panels 7, and then flows into the upper headers 24 where the feed water joins a part of the above-mentioned feed water.

The feed water which has been fed from the water tube panels 4 and the water tube panels 7 to the upper headers 24 is fed through a steam pipe 32 to the steam separator 25, and then steam from the steam separator 25 is fed through a <BR> <BR> steam pipe 33 to a heating tube 26a in which steam is superheated.

The superheated steam which is produced by and discharged from the heating tube 26a is fed through a steam pipe 34 in the third path section lc to a heating tube 26b, and then the superheated

steam discharged from the heating tube 26b is fed through a steam pipe 35 disposed outside the third path section lc to a heating tube 26c in which the superheated steam come out of the heating tube 26b is further superheated. The superheated steam which has been superheated in the heating tube 26c is led through a steam pipe 48 to the outside of the third path section lc, and then fed through a steam pipe (not shown) to a steam turbine (not shown). The heating tubes 26a, 26b and 26c constitute the second heat exchange section of the present invention.

The heating tubes 26a, 26b and 26c serving as the contact cooling section comprise tubes which are mainly arranged in parallel with a flow of the exhaust gas j, and are arranged in a repetitive meandering manner in a flow direction of the exhaust gas j with an appropriate pitch. Because the heating tubes 26a, 26b and 26c are arranged in the repetitive meandering manner in a flow direction of the exhaust gas j, dust such as fly ash is hardly adhered to and deposited on the heating tubes 26a, 26b and 26c.

Each of the portion 17a of the side wall 17 (forming the first path section la), the front wall 18 (see FIG. 3) and the portion 20a of the side wall 20 (forming the first path section la) has six insertion openings 36, and hence the total number of the insertion openings 36 is eighteen. A deslagger (a removing apparatus) DS (see FIG. 6) for ejecting steam is inserted into each of the insertion openings 36. Incidentally, the symbols DS are shown in parentheses near the insertion openings 36 in FIG. 2, and this means that the insertion openings 36 are provided for the deslaggers DS.

Each of the portion 17b of the side wall 17 (forming the second path section lb), the portion 17c of the side wall 17 (forming the third path section lc), the portion 20b of the <BR> <BR> side wall 20 (forming the second path section lb) and the portion

20c of the side wall 20 (forming the third path section lc) has four insertion openings 37, and hence the total number of the insertion openings 37 is sixteen. Further, each of the portion 17a of the side wall 17 (forming the first path section la) shown at the upper part in FIG. 2 and the portion 20a of the side wall 20 (forming the first path section la) shown at the upper part in FIG. 2 has one insertion opening 37, and hence the total number of the insertion openings 37 is two.

Incidentally, the symbols SB are shown in parentheses near the insertion openings 37 in FIG. 2, and this means that the insertion openings 37 are provided for the soot blowers SB.

Next, the deslagger (a removing apparatus) DS will be described in detail with reference to FIG. 6. The deslagger DS has a pipe-like deslagger body 38, and the forward end portion 40 of the deslagger body 38 has a plurality of nozzles 42 provided circumferentially at equal angles of 180°. The deslagger DS is housed horizontally in a casing 46, and the forward end portion 40 of the deslagger DS is inserted into the first path section la (see FIG. 2) through the insertion opening 36.

The steam is ejected from the nozzles 42 at an angle of several degrees to the radial direction toward the wall, and impinges on the walls W2 and WP for thereby removing deposits such as dust adhered to and deposited on the walls W2 and WQ.

The inclined angle of ejection of steam is preferably determined by an area over which the deslagger DS should eject steam, steam condition of the ejected steam, the distance of insertion in the forward end portion 40 of the deslagger body 38 from the insertion opening 36 into the first path section la, characteristics of adhesion of deposits on the surfaces of the walls W2 and WP, and the like.

The deslagger DS is rotatable about a central axis by a drive mechanism (not shown) while ejecting steam, and is

movable axially inwardly in an inserting direction from the insertion opening 36 and outwardly in a withdrawing direction toward the insertion opening 36 while being rotated. The deslagger DS is movable horizontally in a reciprocating manner such that the nozzles 42 are located from a position away from the wall to farther position away from the wall.

The deslagger body 38 has a purge port 44 from which air is supplied to the interior of the casing 46 so as to purge the interior of the casing 46. The purge air flows from the interior of the casing 46 through a gap formed between the insertion opening 36 and the deslagger body 38 to the first path section la for thereby preventing the exhaust gas j (see FIG.

2) from flowing back into the casing 46. In the case where the deslagger body 38 is taken out from the insertion opening 36 into the casing 46, instead of steam, seal air is ejected from the nozzles 42 for thereby sealing the interior of the casing 46 by the seal air, thus preventing the exhaust gas j from flowing back into the casing 46.

Next, the soot blower SB will be described in detail with reference to FIG. 7. The soot blower SB has a pipe-like soot blower body 39 (a part of the soot blower body 39 is not shown), and the forward end portion 41 of the soot blower body 39 has a plurality of nozzles 43 provided circumferentially at equal angles of 180°. The soot blower SB is housed horizontally in a casing 47 (shown in FIG. 7 in partly), and the forward end portion 41 of the soot blower SB is inserted into the second path section 1b (see FIG. 2) and the third path section lc (see FIG. 2) through the insertion opening 37.

The steam is ejected from the nozzles 43 at an angle of several degrees to the radial direction toward the direction away from the walls WP, WQ and WR, and impinges on the water tube panels 7 and the heating tubes 26a, 26b and 26c for thereby removing deposits such as dust adhered to and deposited on the

water tube panels 7 and the heating tubes 26a, 26b and 26c. The inclined angle of ejection of steam is preferably determined by an area over which the soot blower SB should eject steam, steam condition of the ejected steam, the distance of insertion in the forward end portion 41 of the soot blower body 39 from the insertion opening 37 to the second and third path sections lb and lc, characteristics of adhesion of deposits to the surfaces of the walls WP, WQ and WR, and the like.

The soot blower SB is rotatable about a central axis by a drive mechanism (not shown) while ejecting steam, and is movable axially inwardly in an inserting direction from the insertion opening 37 and outwardly in a withdrawing direction toward the insertion opening 37 while being rotated. The soot blower SB is movable horizontally in a reciprocating manner such that the nozzles 43 are located from a position away from the walls WP, WQ and WR to farther position away from the walls WP, WQ and WR.

The soot blower body 39 has a purge port 45 from which air is supplied to the interior of the casing 47 so as to purge the interior of the casing 47. The purge air flows from the interior of the casing 47 through a gap formed between the insertion opening 37 and the soot blower body 39 to the second path section 1b and the third path section lc for thereby preventing the exhaust gas j (see FIG. 2) from flowing back into the casing 47. In the case where the soot blower body 39 is taken out from the insertion opening 37 into the casing 47, instead of steam, seal air is ejected from the nozzles 43 for thereby sealing the interior of the casing 47 by the seal air, thus preventing the exhaust gas from flowing back into the casing 47.

The SiC castable 6 (see FIG. 5) of refractory material containing SiC as a main component, fireclay brick, roseki fire brick, mullite refractory, alumina-silica

refractory, sillimanite refractory, or the like is provided on the surfaces, at the side of the exhaust gas j, of the water tube panels 4 (see FIG. 5) attached to the inside of the portion 17a of the side wall 17, the inside of the front wall 18, the inside of the portion 21a of the top wall 21, the inside of the portion 14a of the first partition wall 14, and the inside of the portion 20a of the side wall 20, i. e. the surfaces, at the side of the exhaust gas j, of the water tube panels 4 attached to the walls constituting the first path section la. In FIGS.

2 and 4A through 4C, the walls which have the water tube panels 4 having the SiC castable 6, fireclay brick, roseki fire brick, mullite refractory, alumina-silica refractory, sillimanite refractory, or the like at the side of the exhaust gas j are the walls W2 and WP.

The SiC castable 6, fireclay brick, roseki fire brick, mullite refractory, alumina-silica refractory, sillimanite refractory, or the like is provided on the surfaces, at the side of the exhaust gas j, of the water tube panels 4 attached to the inside of the portion of the top wall (in FIG, 2, the area located at the left of the opening 22 and at the right of the left side end of the second upper header 24 from the right) and portions of the side wall 17 and the side wall 20 (in FIG. 2, the area located at the upper side of the upper end of the first partition wall 14 and at the right of the left side end of the second upper header 24 from the right), i. e. the surfaces of the water tube panels 4 attached to the wall portions constituting the second path section lb.

The SiC castable 6 (see FIG. 5), fireclay brick, roseki fire brick, mullite refractory, alumina-silica refractory, sillimanite refractory, or the like may be provided on the surfaces, at the side of the exhaust gas j, of all of the water tube panels 4 (see FIG. 5) attached to the portion 17b of the side wall 17, the portion 21a of the top wall 21,

the portion 14b of the first partition wall 14, the portion 15a of the second partition wall 15, and the portion 20b of the side wall 20, i. e. the surfaces of all of the water tube panels 4 attached to the wall portions constituting the second path section lb. Further, the SiC castable 6, fireclay brick, roseki fire brick, mullite refractory, alumina-silica refractory, sillimanite refractory, or the like may be provided on the surfaces, at the side of the exhaust gas j, of the water tube panels 4 attached to the portion 17c of the side wall 17, the portion 21c of the top wall 21, the portion 15b of the second partition wall 15, and the portion 20c of the side wall 20, i. e. the surfaces of the water tube panels 4 attached to the wall portions constituting the third path section lc.

Fireclay brick is made of chamotte clay or roseki (contains pyrophyllite (Al2034Si02-H2O) as a main component) or the like, and is a widely used fire brick. The roseki fire brick has a dense texture, and thus an excellent corrosion resistance to slag. The mullite refractory comprises high alumina refractory containing 3A'203-2S'02 as a main component, is dense, and is durable to rapid heating and rapid cooling.

Alumina-silica refractory is composed mainly of alumina and silica, and has a high heat resistance.

SiC refractory is composed mainly of SiC (silicon carbide) which is a kind of ceramics, and contains at least 50% SiC, preferably at least 85% SiC. Such SiC refractory includes shaped refractory such as fire brick or unshaped refractory such as castable. In the present invention, SiC castable made of unshaped material is used as an example. The SiC castable has a high heat transfer coefficient, an excellent erosion resistance having a low porosity, an excellent wear resistance, and an excellent property for preventing clinker to be adhered.

Next, a method for providing the SiC castable 6 on

the surface of the water tube panel 4 will be described below with reference to FIG. 5. Y anchors 27 having Y-shape are fixed to the water tube panel 4 by welding at positions where the SiC castable 6 is to be provided, and then the SiC castable 6 is applied to the water tube panel 4. The castable 6 may comprise chromium-base material, or high alumina-base material.

Further, as another method, instead of the Y anchors 27, studs (not shown) of ceramics (SiC) are fixed to the water tube panel 4, caps (not shown) of ceramics slightly larger than the studs are attached to the studs, and then the SiC castable 6 is applied to the water tube panel 4.

Next, operation of the waste heat boiler will be described below with reference to FIGS. 1,2 and 4A through 4C.

Combustion air bl is supplied at a low air ratio (The low air ratio is defined as a ratio lower than the ratio of the amount of supplied air to the amount of air, which is set to 1.0, required to completely combust combustibles in the supplied wastes.) to the bottom of the fluidized-bed gasification furnace 5 to form a fluidized bed of silica sand over a diffuser plate 5a formed in the fluidized-bed gasification furnace 5. Wastes are supplied into the fluidized-bed gasification furnace 5, and dropped into the fluidized bed of silica sand which is kept at a low temperature of 450 to 650°C. Thus, the wastes are brought into contact with the heated silica sand and the combustion air bl, and pyrolyzed and gasified rapidly, thus producing combustible gas m, tar and solid carbon. The produced combustible gas m produced in the fluidized-bed gasification furnace 5 is supplied to the swirling-type slagging combustion furnace 8 in which the produced gas m is combusted and solid components (ash, or the like) contained in the produced gas m are melted. On the other hand, solid carbon is pulverized into fine char by a vigorous

stirring motion in the fluidized bed, and the fine char is supplied to the swirling-type slagging combustion furnace 8, together with the produced gas. In comparison with the bubbling-type fluidized-bed, forming a fluidized-bed is better in view of operation of swirling-type combustion furnace due to its slower speed of gasification of wastes. Further, combustion air bl may be supplied to a freeboard 5b formed in the upper portion of the fluidized-bed gasification furnace 5 for thereby gasifying tar and solid carbon at a relatively high temperature of 650 to 850°C.

The produced gas m accompanied by fine solid carbon and discharged from the fluidized-bed gasification furnace 5 is supplied to the swirling-type slagging combustion furnace 8, and the produced gas m and the solid carbon are mixed with the combustion air bl in a swirling flow created in a primary combustion chamber 8a and combusted rapidly at a high temperature of 1200 to 1500°C.

Thus, ash content in the solid carbon is entirely converted due to a high temperature into slag mist which is mostly trapped by molten slag phase on an inner wall of the primary combustion chamber 8a under a centrifugal force of the swirling flow. The trapped slag mist then flows down on the inner wall of the primary combustion chamber 8a and enters a secondary combustion chamber 8b, and is then discharged from a bottom of a slag separation chamber 8c. Unburned combustibles remaining in the gas are completely combusted in a tertiary combustion chamber 8d by combustion air bl supplied into the tertiary combustion chamber 8b.

The exhaust gas j discharged from the swirling-type slagging combustion furnace 8 contains a large quantity of salts which have been being vaporized, and is then led from the inlet section 11 to the first path section la of the waste heat boiler 10. The temperature of the exhaust gas j is in the range of 1100

to 1400°C atthe inlet section 11. While the exhaust gas j passes through the first path section la, the exhaust gas j heats feed water flowing through the water tubes 4a of the water tube panels 4 (see FIG. 5) to allow thermal energy in the exhaust gas j to be recovered.

As the temperature of the exhaust gas j is being lowered, fly ash which contains salts having a high concentration is being deposited. The fly ash containing salts having a high concentration is solid solution containing some components, and hence gas phase, liquid phase and solid phase are concurrently generated. Thus, ash has sticky property of high viscosity like paste. Therefore, if such ash contacts inner walls, the ash is liable to be adhered to the inner walls and corrodes components or members to which the ash is adhered.

However, since the SiC castable 6 (see FIG. 5), fireclay brick, roseki fire brick, mullite refractory, alumina-silica refractory, sillimanite-refractory, or the like is provided on the surfaces of the water tube panels 4 in the first path section la, the surfaces of the water tube panels 4 are hardly corroded, and hence break or damage of the water tube panels 4 does not occur and dust is hardly adhered to and deposited on the surfaces of the water tube panels 4. Therefore, even if maintenance interval of the waste heat boiler is long, the problem of a lowering of heat transfer coefficient in the water tube panel 4 hardly arises.

The exhaust gas j which has passed through the opening 22 flows through the second path section lb, and similarly, the exhaust gas j heats the feed water flowing through the water tubes 4a of the water tube panels 4 (see FIG. 5) to allow thermal energy in the exhaust gas j to be recovered. The temperature of the exhaust gas j is intherange of700to 1000°C, preferably 700 to 900 C at the opening 22 serving as the inlet of the second path section lb, and hence the problem of corrosion

of the surface of the water tube panel 4 and the problem of adhesion and deposition of dust hardly arise.

The exhaust gas which has passed through the opening 23 of the hopper section 16 flows through the third path section lc, and similarly, the exhaust gas j heats the feed water flowing through the water tubes 4a of the water tube panels 4 (see FIG.

5), and superheats steam in the heating tubes 26a, 26b and 26c disposed in the flow passage, thus allowing thermal energy of the exhaust gas j to be recovered. Superheated steam superheated by the heating tubes 26a, 26b and 26c is fed to a steam turbine (not shown). Because the temperature of the exhaust gas in the third path section lc is lower than that in the second path section lb, the problem of corrosion of the surface of the water tube panel 4 and the problem of adhesion and deposition of dust hardly occur.

The steam is ejected from the deslagger DS, and the ejected steam impinges on the walls WP and W2 in the first path section la to remove dust on the walls WP and W2. The deslaggers DS adjacent to each other are disposed at predetermined intervals or less, and the deslaggers DS are movable horizontally in a reciprocating manner while rotating, and the ejection direction of the steam is inclined at an angle of several degrees to the radial direction of the forward end portion of the deslagger DS toward the wall. Therefore, the steam can be ejected over an entire area of the walls WP and W2 in the first path section la, and then dust adhered to and deposited on the walls WP and W2 in the first path section la can be removed. Therefore, the heat transfer coefficient of the water tube panels 4 in the first path section la can be prevented from being lowered, and the performance of the waste heat boiler can be prevented from being lowered.

The steam is ejected from the soot blowers SB, and the ejected steam impinges on the water tube panels 7 and the

heating tubes 26a, 26b and 26c to remove dust on the water tube panels 7 and the heating tubes 26a, 26b and 26c. It is desirable that the soot blow is performed one time per three hours. The soot blowers SB adjacent to each other are disposed at predetermined intervals or less, and the soot blowers SB are movable horizontally by the distance slightly shorter than the distance of the flow passage in a horizontal direction in a reciprocating manner while rotating. Therefore, the steam can be ejected over entire areas of the water tube panels 7 and the heating tubes 26a, 26b and 26c, and dust adhered to and deposited on the water tube panels 7 and the heating tubes 26a, 26b and 26c can be removed. Therefore, the heat transfer coefficient in the water tube panels 7 and the heating tubes 26a, 26b and 26c can be prevented from being lowered, and the performance of the waste heat boiler can be prevented from being lowered.

Dust removed by the soot blow in the first path section la is dropped into or introduced into the swirling-type slagging combustion furnace 8. Dust removed by the soot blow in the second path section lb and the third path section lc is dropped into the hopper section 16, and is then discharged to the outside through a discharge device (not shown) for discharging dust and the like while sealing between the inside and outside of the system by a double discharge valve such as a double damper, a discharge device such as a screw feeder for discharging the dust and the like continuously, and a crusher (not shown) for crushing large ash or slag-like ash.

In the above embodiments, although the waste heat boiler 10 performs heat recovery by introducing the exhaust gas j discharged from the swirling-type slagging combustion furnace 8 therein, the produced gas m comprising combustible gas and discharged from the fluidized-bed gasification furnace 5 may be introduced into the waste heat boiler 10 to perform heat recovery.

As described above, according to the present invention, the first heat exchange section is provided, and the surface of the first heat exchange section constitutes a flow passage in which the introduced combustible gas or the introduced exhaust gas flows, and SiC castable, fireclay brick, roseki fire brick, mullite refractory, alumina-silica refractory, sillimanite-refractory, or the like is provided on the surface of the first heat exchange section constituting the flow passage. Therefore, corrosion of the surface of the first heat exchange section hardly occur, thus eliminating the problem of break or damage of the boiler tubes. Further, dust is hardly adhered to and deposited on the surface of the first heat exchange section, or is not adhered to and deposited on the surface of the first heat exchange section, and the problem of a lowering of heat transfer coefficient in the first heat exchange section does not arise.

Industrial Applicability The present invention is applicable to a waste heat boiler for recovering thermal energy from high-temperature exhaust gas. The waste heat boiler is provided in a treatment apparatus for combusting and treating wastes such as municipal wastes, refuse-derived fuel (RDF), plastic wastes, waste FRP, biomass wastes, automobile wastes and waste oil, and recovers thermal energy from the exhaust gas.