The present invention relates to a gas draw for a reactor for the gasification of carbonaceous solids with oxygen and/or steam with a gas inlet opening and a gas outlet opening and a gas discharge duct provided in between, and to a reactor with such gas draw and a method for operating such a reactor. Gasification is understood to be the conversion of a carbonaceous, solid or liquid substance (e.g. coal, biomass or petroleum coke) with a gasification medium (oxygen/air, steam) into so-called synthesis gas. As main components, this synthesis gas contains hydrogen (H ₂ ), water (H ₂ O), carbon monoxide (CO), carbon dioxide (CO ₂ ), and methane (CH ). CO and H ₂ are the starting substanc- es for a multitude of chemical syntheses, based on which longer-chain products can then be produced.

The synthesis gas also contains hydrogen sulfide (H ₂ S), carbon oxide sulfide (COS), hydrochloric acid (HCI), ammonia (NH ₃ ), hydrocyanic acid (HCN), partly hydrogen fluoride (HF) and possibly also higher hydrocarbons and tar oils. The composition of the gas is dependent on the composition of the feedstock, the kind and quantity of the gasification media used, the reaction conditions and the kinetic boundary conditions of the occurring reactions as specified by the chosen gasification process.

In principle, three different types of processes for the gasification of solids are known: The gasification in fluidized beds, the gasification in a fixed bed formed of the solids, and finally the gasification in an entrained-bed reactor. The different gasification technologies impose different requirements on the fuel, which must be taken into account correspondingly in the choice of the fuel or the conception of the fuel processing.

When the actual reactor is designed as fixed-bed reactor, it includes a substan- tially cylindrical vertical reactor with outer water jacket, which is operated under a pressure of up to 60 barg. The carbonaceous fuel, in general coal or biomass, is introduced from above through a lock into the solids distributor present in the interior of the reactor. On a rotary grate arranged in the lower region of the reactor a fixed bed is formed. From this lower region, oxygen and steam are blown into the fixed bed.

These hot gases flow through the fixed bed from the bottom to the top, whereas the solids are refilled from above through the lock system. Therefore, reference is also made to a counterflow fixed-bed gasification. Since the refilled solids have a temperature of about 40 °C, the entire fixed bed has a temperature profile in which the hottest part is located in the vicinity of the rotary grate and the temperature decreases upwards towards the solids supply. Corresponding to this temperature profile, different reactions take place inside the fixed bed. Therefore, reference often is also made to reaction zones, where there is no clear separation into individual regions, but the individual zones merge into each other. In the upper part of the gasifier in the vicinity of the refilled solids, drying and desorption of physisorbed gases are effected. Below the drying zone the so-called reaction zone is located, in whose upper part degassing of the solids takes place. Degassing is followed by the actual gasification of the solids ac- cording to the Boudouard reaction as well as the water gas and water-gas shift reactions. In the succeeding zone, the combustion of the solids is effected.

The ash obtained in particular during the combustion falls through the rotary grate and is further discharged from there. The non-converted gas fractions of the reactants, mainly steam, nitrogen and argon, are withdrawn together with the formed synthesis gas via a gas draw provided above the fixed bed.

Such fixed-bed coal gasifier is described in DE 1 1 2005 002 983 T5. From the lock system the coal is introduced into the reactor via a cylindrical or inwardly tapering apron. The apron serves as solids reservoir, which despite the batch- wise coal supply via the lock system ensures a constant height of the fixed bed. The lower end of the apron typically is located inside the fixed bed. Between apron and wall a ring-shaped gas collecting zone is formed, from which the raw gas is withdrawn through a gas outlet. This gas outlet is an opening in the reactor, which is adjoined by a pipe which is connected with the reactor via a flange. Through this gas outlet, the raw synthesis gas obtained is supplied to the further processing. In general, the first succeeding step is cooling of the gas by quenching with water.

Up to now, coals only were converted into synthesis gas in a fixed-bed gasification process, in which the reaction temperature was so low that the synthesis gas obtained was withdrawn from the reactor with temperatures between 200 and 600 °C, often between 200 and 300 °C for wet lignite. Due to the increasing shortage of fossil raw materials, solids gasifiers will have to be designed such in the future that not only for example moist lignite, but also for less reactive coals which will be gasified at higher "reaction end temperatures". In addition, the fixed-bed gasification of renewable raw materials is gaining in importance. However, the temperature required for this purpose leads to gas outlet temperatures of up to 700 °C, partly even up to 800 °C in part even up to 1000 °C. At these temperatures, the gas outlet is exposed to a distinctly greater material stress.

In addition, coals which have high contents of sulfur or halogens are gasified to an increasing extent. This leads to compounds such as H ₂ S, COS, HCI and HF in the resulting raw synthesis gas. Together with temperatures which lie above the typical temperatures used so far (e.g. wet lignite about 250 °C, hard coal about 450 °C, compared with older hard coal 450 - 550°C, anthracite 550 - 600°C) this leads to a strong corrosion at the gas outlet. For changing the gas outlet pipe, the plant must be shut down, so that production losses will occur. On the other hand, the use of high-temperature resistant materials would lead to a considerable rise in the investment costs, since the gas outlet is a pressure- loaded plant section (up to 60 barg) and corresponding wall thicknesses must be provided. Therefore, it is the object of the present invention to provide a gas outlet which independent of the carbonaceous solids used will have a long service life and can also be used at temperatures of up to 800 °C or more.

In accordance with the invention, this problem is solved by a gas draw with the features of claim 1 . The tubular gas discharge duct is surrounded by an inner jacket and an outer jacket, between which a cooling gap is formed with at least one inlet and outlet for cooling liquid. At the edge of the preferably rotationally symmetrical body, inner and outer jacket are connected in a liquid-impermeable manner.

One opening of the gas discharge duct is designed such that it can be connected with the reactor in a gas-tight manner. The other opening is designed for connection to further gas treatment systems. Preferably, the gas outlet opens into a cooling device for the hot raw synthesis gas. It often is quenched with water. Such quench cooling can be effected for example in a Venturi cooler.

A straight formation of the gas discharge duct prevents deposits in curvatures. By an angular formation, however, the plant can be constructed more compact. In a preferred embodiment of the invention the gas draw includes at least one inlet and one outlet for the coolant. It can thereby be ensured that the coolant flows from the inlet to the outlet in the cooling gap between inner and outer jacket. To achieve an optimum flow with coolant, inlet and outlet are spaced from each other as far as possible.

Preferably, the gas draw is formed as T-piece, wherein the gas outlet opening is arranged substantially vertical to the gas inlet opening coupled to the reactor. Substantially vertical in the sense of the present invention refers to an angle of 85 to 95°, preferably 90° between the axis of the openings.

A particularly preferred embodiment furthermore provides that in the interior of the inner jacket an insert is arranged, which includes a curved inner tube. The insert is designed such that an inlet opening of the insert terminates parallel to the gas inlet opening and an outlet opening terminates parallel to the gas outlet opening. When gas now is introduced into the gas draw, it flows through the insert and is deflected by the curved inner tube such that it flows out of the gas outlet opening arranged offset by about 90°. In a preferred development of this invention, a space filled with insulating material is formed between inner part and the inner jacket of the gas draw. Preferably, this insulating material is glass wool, as it is inert towards the exiting gases. In principle, other inert insulating materials can also be taken into account. Since the exiting gas almost exclusively flows through the insert surrounded with insulating material, there is no direct contact surface between gas and the surface of the jacket of the gas discharge duct defining the cooling gap. The temperature profile obtained due to cooling is formed over the thickness of the insulating material and extends between the gas temperature and the coolant temperature. When water is used as coolant, the coolant temperature maximally is 275°C at an operating pressure of 60 bara. By omitting a direct contact surface, it can almost be excluded that tars contained in the gas stream will condense out and thus clog the gas draw in the long run. On the other hand, the material stress is reduced distinctly by cooling the gas draw and hot gas corro- sion is avoided. When using water as coolant, proceeding from the maximum coolant temperature of 275 °C (boiling point at 60 bara), the temperature obtained at the inner jacket is about 300 °C and hence lies distinctly below the gas temperatures of 700 °C or even 800 °C. When cooling water is used at an operating pressure of 30 bara, the boiling point is about 234 °C.

Furthermore, the pressure load by the reactor pressure of up to 60 bara lies on the inner and outer jacket of the apparatus, but not on the insert. As a result, the wall thickness of the insert can be designed distinctly smaller. This allows to fabricate the insert of materials resistant to hot-gas corrosion, such as Inconel, without thereby incurring considerably higher investment costs. If this is omitted, or hot-gas corrosion occurs nevertheless, the insert can be replaced quickly and easily, in that it is pulled out of the gas discharge duct on the side facing away from the reactor and is replaced or repaired. In accordance with the invention, a removable cover therefore is provided on an opening of the gas discharge duct opposite the gas inlet opening, to which the insert preferably is connected, in particular screwed or welded.

In a case of repair, the time in which the reactor cannot be utilized thus can be minimized. This is the case particularly easily when the cover is screwed to the side facing away from the reactor. Since the outer jacket of the gas draw is not exposed to the reaction gases, it has a very long service life. It can therefore be welded to the reactor, whereby complicated and expensive flange connections, which also must be gas-tight under the existing high pressure of up to 60 barg, can be omitted at this point. In accordance with a development of the invention, a scraper is located in the interior of the gas draw, which extends from the gas inlet opening to the opening of the gas discharge duct located opposite the same and removes deposits. The use of the scraper is necessary in particular when solids are gasified, in which side reactions lead to the formation of tars which will condense out by contact with the cooled inner jacket. The scraper can be removed, if necessary, and be cleaned or replaced. It can also be inserted into the gas discharge duct instead of the insert only for cleaning purposes.

According to the invention, the gas draw also includes a compensator for compensating temperature-related expansions. Thus, the load of the component as a result of thermal stresses can be reduced. Subject-matter of the invention also is a reactor for the gasification of carbonaceous solids with oxygen and/or steam with the features of claim 9. In this reactor, the gas outlet is connected with the above-described gas draw in a gas-tight manner. It was found to be particularly favorable when the inlet and/or the outlet of the cooling gap is connected with a cooling system of the reactor. This is expedient in particular when the reactor itself includes a jacket cooling with an inner reactor jacket and an outer reactor jacket, and into a reactor cooling gap formed in between a coolant, preferably water, is introduced. When the gas draw is con- nected with the cooling system of the reactor, a separate coolant circuit can be omitted, and the apparatus design is simplified.

Finally, the idea according to the invention also extends to a process for gasifying carbonaceous solids with oxygen and/or steam in a fixed bed according to claim 10. The cooling medium is introduced into the gas draw in liquid form and is withdrawn at least partly in vapor form.

The use of the steam turns out to be quite particularly advantageous when water is used as cooling liquid and the cooling water withdrawn in vaporous form itself can be used as educt, i.e. that steam stream which is required for gasifying the solids in the fixed bed is partly fed with the steam generated in the cooling. The steam requirement of the process thereby can be reduced, which lowers the operating costs. When the reactor itself also includes a water-cooled jacket and steam is formed here as well, about 20 vol-% of the required steam quantity can be saved by the collected recirculation of the steam.

Further features, advantages and possible applications of the invention can also be taken from the following description of an exemplary embodiment and the drawings. All features described or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-references.

In the drawings:

Fig. 1 schematically shows the construction of a reactor for the gasification of carbonaceous solids in a fixed bed

Fig. 2 shows a section of the gas draw according to the invention without insert

Fig. 3 shows a section of the insert according to the invention shows a section of the gas draw according to the invention with insert. Fig. 1 schematically shows the reactor 100. It is a fixed-bed reactor operated in counterflow, which includes a rotary grate 101 in the vicinity of the bottom. On this rotary grate 101 a solids bed 102 is built up in operation. Via a feeder 103, steam and/or an oxygen-containing medium, such as air, oxygen-enriched air or also pure oxygen is introduced and injected into the bed from below evenly distributed. Ash which is formed by reactions in the fixed bed falls through the rotary grate 101 and removed via the ash draw 104. The reactor 100 is water- cooled and includes a cooling gap 105 (cf. Fig. 2) between an outer jacket 106 and an inner jacket 107.

Above the reactor 100 a lock 108 is provided, via which coal or other carbonaceous solids are supplied. The lock 108 is adjoined by an apron 109 disposed thereunder, which serves as solids reservoir, so that the fixed bed 102 in the reactor 100 has a uniform filling level, although charging with coal is effected discontinuously through the lock 108. Above the fixed bed 102 a free space is provided around the apron 109, in which reaction gases as well as unused steam and oxygen or oxygen-containing gas are collected. The gases collected in this gas collecting space 1 10 are withdrawn via a gas outlet 1 1 1 .

Figure 2 shows a section through a gas draw 1 according to the invention. The same is formed as T-piece and includes a gas inlet opening 2, a gas outlet opening 3 arranged substantially vertical to the same and a gas discharge duct 4 provided in between. Opposite the gas inlet opening 2 a withdrawal opening 5 is provided at the other end of the gas discharge duct 4. The gas outlet opening 3 is adjoined by an outlet port 6.

The gas draw 1 is double-walled and includes an outer jacket 1 1 and an inner jacket 12, between which a cooling gap 13 is formed. Preferably in the region of the withdrawal opening 5, the cooling gap 13 is closed by a liquid-tight connec- tion 14 between inner jacket 12 and outer jacket 1 1 . Furthermore, the cooling gap 13 also extends into the outlet port 6 and is likewise closed there in a liquid- tight manner via a connection 15. Preferably, the cooling gap 13 also is connected with the cooling gap 105 of the reactor 100.

To achieve a natural convection inside the cooling gap 13, it was found to be favorable when the cooling gap 13 has a further inlet and outlet for coolant 17, which is provided on the side of the gas discharge duct 4 facing away from the reactor 100 and preferably is connected with the cooling system of the reactor 100. In principle, it is also possible to effect the supply and discharge of the coolant on one side of the gas draw or also through a common connection opening. Due to its lower density, the evaporated cooling medium automatically rises to the top and can be withdrawn. On the side facing away from the reactor 100, the gas draw 1 also includes a flange 16 for attachment of a cover 51 (Fig. 4) with which the withdrawal opening 5 can be closed in a gas-tight manner. At the gas inlet opening 2, however, means 18 are provided, in order to weld the gas draw 1 to the reactor 100. The outlet port 6 surrounding the gas outlet opening 3 is connected with a non- illustrated gas cooling, preferably a Venturi quench. This connection can be flanged or welded.

Figure 3 shows a section through an insert 50 formed according to the invention. In a preferred embodiment, the insert 50 is connected with the cover 51 and via the same can be attached to the flange 18 of the gas draw 1 , when it is pushed into the same. The insert 50 itself has two preferably tubular portions, wherein the first portion 62 includes an inlet 53 which via a curved inner tube 54 is connected with an outlet 55 offset by about 90°. The second portion 56 is the re- maining part of the insert 50 and lies between the curved inner tube 54 and the cover 51 .

Figure 4 finally shows the gas draw according to the invention with inserted insert 50. The insert 50 approximately has the same length as the gas draw 1 , so that the inlet 53 of the insert 50 terminates substantially flush with the gas inlet opening 2. The outlet 55 however terminates substantially flush with the gas outlet opening 3. The diameters of inlet 53 and gas inlet opening 2 or of outlet 55 and gas outlet opening 3 each are adjusted to each other. Possibly, appropriate seals are provided, in order to prevent an exit of gas.

The outside diameter of the insert 50 is slightly smaller than that of the gas discharge duct 4, so that between the inner jacket 12 of the gas draw 1 and the insert 50 a space 60 is formed, which is filled with insulating material. As a result, the outflowing hot gas does not directly get in contact with a surface traversed by coolant, so that a condensation of tars contained in the gas stream is avoided.

Preferably, the insert 50 is fabricated of a nickel-base alloy, since such alloys largely are hot corrosion resistant. The use of such expensive alloys becomes possible in that the inner part is no pressure-loaded component and thus must only have a small wall thickness.

In the same dimension as the insert 50 a non-illustrated scraper can be formed, which is pushed into the gas discharge duct 4 instead of the insert, in order to remove deposits which have formed on the inner wall of the inner jacket 1 1 . This is expediently effected when replacing the insert 50.

In operation, the insert 50 is pushed into the gas draw 1 in the manner shown in Fig. 4. From the reactor 100, hot gas (up to 800 °C or more) enters into the gas outlet opening 3 of the gas draw 1 . To save the pressure-bearing parts of the gas draw 1 , the same are cooled by introducing cooling water through the inlet 17 into the cooling gap 13 between inner jacket 12 and outer jacket 1 1 of the gas draw. When flowing through the cooling gap 13 in direction of the reactor, the cooling water is heated up to its boiling temperature (at 60 bara operating pressure about 265 °C), is evaporated and thereby withdraws heat from the system. The steam then enters into the cooling gap 105 of the reactor 100 and can be recirculated to the gasification as educt. The hot gas does not get in direct contact with pressure-bearing parts of the gas draw 1 , but flows through the insert 50 and is passed through the same to the succeeding gas wash.

The present invention allows to work with gas outlet temperatures of up to 700 °C, preferably even up to 800 °C, in part even up to 1000 °C whereby fuels with lower reactivity can be used. At the same time, the service life of the reactor can be prolonged. Due to the cooling, according to the invention, a hot corrosion at the gas draw can be avoided completely, or only occurs at the insert, it no longer is necessary to design the connection between gas outlet and reactor as flange connection. The use of welded connections increases the reliability of the reactor. In addition, the heat transfer between reactor and gas draw is improved.

List of Reference Numerals:

1 gas draw

2 gas inlet opening

3 gas outlet opening

4 gas discharge duct

5 withdrawal opening

6 outlet port

1 1 outer jacket of the gas draw

12 inner jacket of the gas draw

13 cooling gap

14 liquid-tight connection

15 liquid-tight connection

16 flange

17 inlet or outlet for coolant

18 weld with the reactor

50 insert

51 cover

52 first portion of the insert

53 inlet

54 curved inner tube

55 outlet

56 second portion of the insert

60 space

100 reactor

101 rotary grate

102 fixed bed

103 feeding of steam and/or oxygen

104 ash draw 105 cooling gap

106 outer jacket of the reactor

107 inner jacket of the reactor

108 lock

109 apron

1 10 gas collecting space

1 1 1 gas outlet