This invention relates to an apparatus for charging a reactor operated under pressure with carbonaceous solids, in which the solids are gasified with oxygen and/or steam in a fixed bed, wherein the apparatus includes a ring-shaped apron open at the top and at the bottom, to which the solids are supplied through a lock, and furthermore to a reactor for the fixed-bed gasification with this apparatus and to 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) with a gasification medium (oxygen/air, steam) into so-called synthesis gas. As main components, this synthe- sis 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 substances for a plurality of chemical syntheses, based on which longer-chain products, such as gasoline and diesel as so-called CtL fuels (Coal to Liquids), or other valuable materials (SNG = Substitute Natural Gas, H ₂ for ammonia/fertilizers/urea, meth- anol etc.) can then be produced.

The synthesis gas, however, 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 substantially cylindrical vertical reactor with outer water jacket. The solid carbonaceous fuel, in general coal or biomass, is introduced from above through a lock into the coal distributor present in the interior of the reactor, wherein a fixed bed is formed, which rests on a rotary grate arranged in the lower region of the reactor. 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 is effected. Degassing is followed by the actual gasification of the solids according 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.

The lock system for supplying the fuel into the reactor is necessary, since the reactor is operated at a pressure of up to 100 barg, preferably up to 60 barg, particularly preferably at an operating pressure of at least 50 barg, and hence the solids must be introduced under pressure. Introducing via a lock system is effected discontinuously, wherein the fuel first is introduced under atmospheric conditions into the lock terminated by the reactor, then is pressurized in the lock system and is filled into the reactor under this pressure. Subsequently, the reactor is again closed against the lock system. To be able to nevertheless operate the process in the steady state under constant conditions, a further solids reservoir must therefore be provided inside the reactor, which ensures that the fixed bed always has the same height. For this purpose, various internals for example from Lurgi® or VEB PKM Anlagenbau Leipzig, such as so- called coal distributors, are known. Attempts have been made to selectively influence the natural segregation of the coal grain spectrum by various designs of these apparatuses. The results only were suitable to a limited extent to achieve an improved gasification. Grain spectrum and disintegration behavior are very dependent on the type and properties of the coals.

Such apparatus is described for example in DE 1 1 2005 002 983 T5. This is a cylindrical or inwardly tapering, i.e. hollow inversely frustoconical apron with open end, which hangs down from the head of the reactor, so that coal which is drained from the coal lock moves along the inside of the apron, so as to be distributed in the solids bed. The lower end of the apron typically is located inside the fixed bed. Between apron and wall of the gas generator a ring-shaped gas collecting zone is formed, from which the raw gas collected there is withdrawn laterally through a gas outlet.

In the largest plants currently operated, coals mostly are converted to synthesis gas in a fixed-bed gasification process, in which the outlet and reaction end temperatures are so low on average that the synthesis gas obtained is withdrawn from the reactor with temperatures between 200 and 300 °C (for moist lignites) or between 400 and 450 °C (for young hard coals). A distinction must be made here between average temperature and temperature peaks caused by inhomogeneities of the fixed bed. The average temperature is decisive for the corrosion and thus the service life of the component. The temperature peaks determine the thermal and mechanical load and therefore must not exceed limit values. The limit values of a plant for coal gasification in the fixed bed so far had to be defined such that at temperature peaks of 650 or 670 °C power reductions or even a shut-down of the reactor have become necessary, in order to limit the thermal load of the raw gas outlet. Poor coal qualities or properties and high loads increase the amplitude and frequency of such temperature peaks.

Due to the increasing shortage of fossil raw materials, solids gasifiers have to be designed such in the future that not only for example moist lignite or younger hard coals, but also other coals with higher reaction end temperatures and inferior properties can be gasified. In addition, the fixed-bed gasification of re- newable raw materials or secondary raw materials is gaining in importance, which mostly have inferior properties with respect to the fixed-bed gasification. The temperatures resulting there canlead to gas outlet temperatures of at least 700 °C, preferably up to 800 °C, in part even up to 1000 °C. At these temperatures, the apron used 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. As mentioned already, 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 temperatures typically used so far (e.g. moist lignite about 250 °C, young hard coal about 450 °C, compared with older hard coal 450 - 550°C, anthracite 550 - 600°C), this leads to stronger corrosion at the apron. To these typical operating temperatures the temperature peaks also must be added, which depend on the quality and the grain spectrum of the coals. Greatly disintegrating lignites, for example, cause channeling due to the high content of fine grain, which leads to CO2 and temperature peaks. For changing the apron, the plant must be shut down, so that production losses will occur. On the other hand, the apron is so large that the use of high-temperature resistant materials would cause a considerable increase in investment costs and therefore is uneconomic, all the more so as the use of high-temperature resistant materials would prevent corrosion e.g. by hydrogen halides only to a limited extent.

Therefore, it is the object of the present invention to design the apron also referred to as annular gas collector such that even at gasification temperatures above 450 °C and/or when using fuels containing sulfur and/or halogens long service lives of the plant become possible. At the same time, frequent temperature peaks have to be tolerated without enforcing a load reduction or a brief or longer-term shut-down of the reactor. In accordance with the invention, this object is solved with a charging device according to claim 1 . The apron is cooled and for this purpose includes an inner jacket and an outer jacket, between which a cooling gap is formed with at least one inlet and outlet for the supply and discharge of a cooling medium. In accordance with a development of the invention, the apron is formed rotation- ally symmetrical, in particular cylindrical, conical or partly conical. A cylindrical shape has the advantage that the fuel introduced through the lock system is spread over the entire cross-section of the fuel bed. In addition, the volume of the coal feeder chute thus can be maximized, so that with equal filling volume the same has a comparatively short length and the effective reactor height is not reduced decisively. Nevertheless, it is possible to take up that amount of coal which is required to bridge the time between two coal locking operations and possible irregularities of gasification and feeding.

When the apron jacket is conical, the charging device should taper towards the fixed bed. This has the advantage that the free exit surface for the raw gas from the fixed bed is as large as possible. By providing an exit surface as large as possible, the respective gas velocity and hence the entrained amount of dust can be minimized. In addition, the resulting gas collecting space has a volume as large as possible, so that the flow velocity of the raw gas also is decreased in the gas collecting space and the dust retention is improved. Finally, the exit surface must be designed as large as possible, so that the raw gas can flow over the entire cross-section of the fuel bed more uniformly and the entrainment of coal particles is minimized. Cross flows should be reduced, in order to ensure homogeneous reaction conditions in the entire fixed bed.

A partly conical formation, which is mounted on a cylindrical part, combines the advantages of both designs.

In ongoing operation, the cooling gap is charged with coolant, preferably boiler feed water. If water is used, the water must satisfy the guidelines for steam generators, in order to prevent deposits of carbonate or boiler scale. In principle, the cooling gap must be designed such that the inflow of the coolant is provided at one edge and the outflow of the coolant at the opposite edge. Pref- erably, however, the cooling gap is designed liquid-impermeable at one edge, in that inner and outer jacket here are connected in a liquid-tight manner. Preferably, this edge faces the fixed bed, i.e. is arranged at the bottom in the reactor. Charging the cooling gap with coolant can be effected via a common supply and discharge conduit, or at least one inlet and one outlet are provided.

At the edge of the apron facing away from the fixed bed, i.e. at the upper edge, the cooling gap is closed by a preferably ring-shaped cover in which numerous openings are provided for introducing and discharging the cooling medium. Cooling medium then can be introduced into the cooling gap over the entire circumference of the apron. When the cooling medium, e.g. water, is heated by the hot synthesis gas ascending past the outside of the apron, it is evaporated and rises to the top, in order to escape in vaporous form from the cooling gap through the openings of the cover.

Preferably, inner and outer jacket extend in parallel, since the apparatus thus can be fabricated easily and the resulting cooling gap has the same width at each point. In the same way, it is also conceivable here to form the cooling gap such that at those points at which the volume flow of the gas along the apron and thus the heat quantity to be dissipated is particularly high it has a greater width than at points traversed little. For example, the region facing the gas outlet is subjected to a great load. Hence, it can be ensured that actually the entire apron is cooled sufficiently. In a particularly preferred aspect of the invention a bulkhead is provided between inner and outer jacket of the apron, which preferably extends parallel to the inner and outer jacket, in order to provide for uniform charging with cooling liquid. By the bulkhead, an inner and an outer cooling gap are formed, which are connected with each other at least at one point, preferably over the entire cir- cumference of the apron. The connection between the inner and the outer cooling gap is accomplished particularly easily in that between the bulkhead and a jacket portion connecting the inner jacket with the outer jacket a free space is provided, i.e. the bulkhead does not extend down to the bottom of the apron. With this design it can be achieved that the coolant flows through the apron without a pump being required: The outer cooling gap adjoins the outer jacket of the apron, which is in direct contact with the gas collecting space and is exposed to the temperature of the ascending hot raw synthesis gas, so that it is heated up correspondingly. Via the inner jacket, the coolant in the inner cooling gap is connected with the re- filled solids which only have a temperature of about 40 °C. The coolant in the outer cooling gap therefore is exposed to a distinctly higher heat transfer than the coolant in the inner cooling gap, so that a directional flow through the cooling gap occurs due to convection. When water now is used as cooling liquid, the boiling point of the water lies below the temperature of the hot raw synthesis gas. This also is the case when the cooling system is operated under pressure (30 bara: boiling point 234 °C; 51 bara: 265 °C). The resulting steam always will flow upwards to the outlet. In a particularly preferred aspect, the coolant is supplied to the inner cooling gap and withdrawn from the outer cooling gap. Thus, the introduced cooling water passes through the inner cooling gap, is slightly heated up by contact with the bulkhead, and passes this heat on to the refilled solids in the interior of the apron, which to a minor extent even leads to a decrease in the cooling water temperature, and then gets into the outer cooling gap. As a result of the contact with the hot outer jacket of the apron, the water is evaporated there and thus withdraws heat from the system. The resulting steam flows out of the steam outlet provided in the outer cooling gap. Due to the escape of the steam, new cooling water continuously is conveyed from the inner cooling gap into the outer cooling gap. In this system, inner and outer cooling gap thus are traversed by natural convec- tion. The natural convection is defined by the density difference of the water column in the inlet and the steam-water column in the outlet. This results in a so-called circulation number as quotient of steam generation and water circulation, which is limited by the pressure loss with a given geometry. The apparatus operates particularly effectively when inflow and outflow of the cooling water are effected at the upper edge of the apron with a vertical construction of the reactor.

Preferably, the bulkhead is to be designed such that the inner cooling gap has a smaller width than the outer cooling gap. This has the advantage that when using water as coolant, the resulting steam provides sufficient volume in the outer cooling gap. Thus, an optimum circulation number of water/steam can be made possible and the pressure loss can be minimized.

Subject-matter of the invention also is a reactor for gasifying carbonaceous solids with oxygen and steam with the features of claim 7. Such reactor includes a rotary grate in the vicinity of the bottom and a solids lock at the head of the reactor, which is followed by the apron described above.

Advantageously, the reactor is formed such that the inlet and/or the outlet of the cooling gap of the apron is connected with a cooling system of the reactor itself. This has the advantage that for cooling the apron no separate cooling circuit must be installed and investment costs thus can be lowered, and in addition the reliability and operational safety of the cooling system are increased. Preferably, the reactor itself likewise has a cooling jacket into which the cooling jacket of the apron is integrated.

Furthermore, apron and reactor preferably are welded to each other. This becomes possible in that by cooling the apparatus the temperature of inner and outer jacket can be lowered distinctly as compared to an uncooled apron. When water below 51 bara is used as cooling liquid, the boiling temperature is about 265 °C and thus lies distinctly below the critical temperature of 300 °C, from which hot gas corrosions progressively occur for carbon steel. In that due to cooling the apron is protected against corrosion, but also against erosion as a result of the coal moving downwards, it no longer must be replaced regularly, so that expensive, releasable connections are not necessary.

Finally, the idea according to the invention also extends to a method for gasifying carbonaceous solids with oxygen and steam with the features of claim 10. The gasification is carried out in a fixed bed, wherein the solids are introduced into the fixed bed of a reactor batch-wise via a lock and then continuously through the charging device according to the invention. A cooling medium is introduced into the jacket in liquid form and withdrawn at least partly in vaporous form. By such cooling, the apparatus can effectively be protected against corrosion and at the same time a slight first cooling of the hot raw synthesis gas can be effected, so that the succeeding components also are loaded less.

Such cooling is particularly advantageous when the steam withdrawn can be reused energetically inside the process as reactant/gasification medium. Inside the fixed-bed gasification, the steam acts as "moderator", in order to limit the combustion temperature such that the coal ash is not molten. The steam must be added in the excess.

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 reactant, 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 lowered, 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 total steam quanti- ty can be saved by the collected recirculation of the steam from all cooled components.

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 a fixed-bed reactor operated in counterflow,

Fig. 2 shows an annular gas collector according to the invention,

Fig. 3 shows a cover of the annular gas collector according to the invention.

Fig. 1 schematically shows the reactor 10. It is a vertical fixed-bed reactor oper- ated in counterflow, which includes a rotary grate 1 1 in the vicinity of the bottom. On this rotary grate 1 1 a solids bed 12 is built up in operation. Via a feeder 13, steam and/or an oxygen-containing medium, such as air, oxygen-enriched air or also pure oxygen is introduced and injected into the bed 12 from below evenly distributed. Ash which is formed by reactions in the fixed bed 12 is discharged through the rotary grate 1 1 and removed via an ash draw 14 with succeeding ash lock. The reactor 10 is water-cooled and includes a cooling gap 17 between an outer jacket 18 and an inner jacket 19 (Figure 2).

Above the reactor 10 a lock 20 is provided, via which coal or other carbona- ceous solids are supplied. The lock 20 is followed by an apron 30 displayed in Figure 2, which serves as solids reservoir, so that the fixed bed 12 in the reactor 10 has a uniform and sufficient filling level, although charging with coal is effected discontinuously through the lock 20. Above the fixed bed 12 a free space is provided around the apron 30, in which reaction gases as well as unused steam are collected. The gases collected in this gas collecting space 15 are withdrawn via a gas draw 16.

Fig. 2 shows the right half of the charging device 1 according to the invention schematically and in section. The gas draw 16 mostly is provided on one side of the reactor only.

The charging device 1 includes a double-walled apron 30 with an inner jacket 31 and an outer jacket 32, between which a cooling gap 33 is formed. At the lower end of the apron 30 facing the fixed bed 12, the inner jacket 31 and the outer jacket 32 are connected in a liquid-tight manner by a jacket portion 35. Inside the apron 30, a bulkhead 34 is provided between the inner jacket 31 and the outer jacket 32. This bulkhead 34 divides the cooling gap 33 formed between inner jacket 31 and outer jacket 32 into an inner cooling gap 33i and an outer cooling gap 33a. In ongoing operation, the inner cooling gap 33i adjoins the solids retained in the apron 30 via the inner jacket 31 , while the outer cooling gap 33a adjoins the gas collecting space 15 and the fixed bed 12 via the outer jacket 32.

Between the bulkhead 34 and the jacket portion 35 connecting the inner jacket 31 and the outer jacket 32 a free space 36 is provided, by which the inner cooling gap 33i and the outer cooling gap 33a are connected with each other at the lower end of the apron 30.

The cooling liquid, preferably water, is introduced between bulkhead 34 and inner jacket 31 , flows downwards by gravity and is in heat exchange with the cold coal (about 40 °C) provided inside the apron. Since the bulkhead 34 does not terminate flush with the jacket portion 35, the water can enter into the outer cooling gap 33a at the lower edge of the apron 30. In the outer jacket 32, the cooling liquid is in direct heat exchange with the hot gas in the gas collecting space 15. Due to the temperature of the gas of up to 700 °C, preferably up to 800 °C, the water is heated to temperatures of the respective boiling point (at an operating pressure of 51 bara about 265 °C) and evaporated. Due to its distinctly lower density, the steam rises upwards (convection) in the outer cooling gap 33a and can be withdrawn at the upper end of the cooling gap 33a. The surface temperature of the outer jacket 32 will be higher than the cooling water temperature by up to 30° (depending on gas temperature and load), since the heat transfer is high on the gas side. At the outer jacket 32, there will still be obtained a temperature slightly below 300 °C, which lies distinctly below the temperature obtained in an uncooled annular gas collector, which substantially corresponds to the gas temperature. A hot gas corrosion of carbon steel can be avoided or at least greatly reduced.

When the reactor 10 itself likewise comprises a water-cooled jacket, the cooling gap 33 of the apron 30 preferably is connected with the cooling system of the reactor 10 such that the cooling water from the cooling gap 17 between outer jacket 18 and inner jacket 19 of the reactor 10 can also be utilized for charging the cooling gap 33 of the apron 30.

Fig. 3 shows a ring-shaped cover 40 which is mounted on the charging device 1 , preferably welded to the same, and at the same time represents the inflow and outflow of the coolant as well as the connection to the reactor 10.

In the center of the cover 40 a circular opening 41 is provided, through which the solids can get from the lock system 20 into the charging device 1 . Offset to the outside and associated to the jacket of the apron 30, two rows of openings 42, 43 are provided on concentric circles, via which the coolant is introduced into the inner cooling gap 33i and withdrawn from the outer cooling gap 33a, respectively. Via a circumferential projection 44, the cover 40 can be connected, e.g. welded to the inner jacket 19 of the reactor 10 (cf. Fig. 2).

In the cooled annular gas collector according to the invention, the abrasion at the inner jacket due to the coal constantly passing by is greatly reduced by the lower wall temperature, and the possible service life thereby is prolonged. Due to the lower temperature, hot gas corrosions at the outer jacket are avoided or greatly reduced independent of the concentration of the corrosive components in the raw gas. The corrosive components in the raw gas are determined by the coal composition.

In addition, the gas is slightly cooled at the outer jacket of the annular gas col- lector, which results in a lower temperature load of the succeeding plant sections. By cooling the gas at the annular gas collector, heat is withdrawn from the process at one point and the coolant is evaporated.

When water is used as coolant, the steam formed subsequently can be fed into the system as steam for the gasification, whereby the costs for the reactants to be provided can be lowered.

List of Reference Numerals:

1 charging device

10 reactor

1 1 rotary grate

12 fixed bed

13 feeding of oxygen-containing gas and/or steam

14 ash draw

15 gas collecting space

16 gas draw

17 cooling gap

18 outer jacket of the reactor

19 inner jacket of the reactor

20 lock

30 apron

31 inner jacket

32 outer jacket

33 cooling gap

33a outer cooling gap

33i inner cooling gap

34 bulkhead

35 jacket portion

36 free space

40 cover

41 opening

42 openings

43 openings

44 projection