DE3605971C2 - - Google Patents

Description

The invention relates to a method for gasifying solid, dust-like to lumpy, carbonaceous material with an oxidizing agent and steam under increased pressure in a fluidized bed reactor then complete conversion of the residual carbon to the top discharged solid after separation of product gas in a dust gasification reactor.

In fluidized bed gasification, the fuel is also in the fluidized bed a grain size of up to about 10 mm. The one to maintain of the vortex state required velocity of the vortex fluid determined by the mean grain of the grain mixture supplied. For the coarser portions of the grain mix may make this speed too low become too large for the finer proportions. Therefore, in fluidized bed gasification always a small proportion of the imported fuel is degassed or partially gassed down from the reaction space, a lot however, a larger part with the product gas from the fluidized bed carried upwards.

This portion discharged upwards can be used in fluidized bed gasification processes those working at normal pressure weight about half of the Make out coking carbon. This makes gasification efficiency and Economics of the process significantly impaired.

Known older fluidized bed gasification processes have been improved the yield therefore further gasifying agents above the fluidized bed supplied in order to increase the carbon turnover by increasing the temperature to achieve discharged solid. This is called "Top gasification". (Winkler Gasification; Hydrocarbon processing, April 1975, P. 128). A similar post-gasification with secondary gasifier in single gasifiers is also in H. D. Schilling, Kohlengasgasung, 1981, pages 86 to 95 described. As a rule, the gasification temperature in such processes due to the need to observe the ash softening point  of the solid can only be set about 100 ° C higher than the actual one Fluidized bed gasification temperature. Because of the low available standing time from the exit from the fluidized bed to the exit from the Reactor and the relatively low temperature was only a slight increase of carbon sales reached.

From Freiburger Forschungshefte, A69, 1957, pages 15 to 22 and from the DE-OS 29 29 764 further fluidized bed gasification processes are known, in which the solid discharged from the fluidized bed with the product gas separated from the gas in a downstream cyclone and the separated one Coke dust back into the fluidized bed or into a combustion chamber to be led back. Because those deposited in the cyclone Coke parts are relatively fine-grained Fluid in the fluidized bed also quickly passes through it again carried. Here, too, there was only a moderate improvement in carbon sales can be achieved.

Finally, methods are known in which recycling the deposited Coke dust in the fluidized bed and top gasification take place together, which leads to a further improvement in carbon turnover, however compared to other gasification processes is still not sufficient.

In a newer gasification process described in DE-OS 29 47 222 you have one Fluidized bed and a dust gasification stage combined in a common reactor so that the Solid discharged upward from the fluidized bed after separation from Product gas is returned to a dust gasification stage in a cyclone, to be fully implemented there. The dust gasification products, namely Gas and liquid slag emerge from the dust gasification part below and are directly on or in the fluidized bed below brought in. A heat exchange takes place between the hotter congestion gasification products with the colder parts of the fluidized bed, at the same time, the liquid slag is solidified and in the solid state withdrawn from the bottom of the reactor.

This procedure leads to a very high carbon turnover and a significant increase in gasification efficiency.

The disadvantage, however, is the need for the dust gasification stage arranged in the reactor to cool, creating significant amounts of heat for gas generation get lost. The mechanical stress further limits  the dust gasification level, its volume and thus the free space above the fluidized bed. Furthermore, for the heat exchange between the dust gasification products and the fluidized bed a certain distance between the fluidized bed surface and the dust gasification stage will. The gas velocity becomes due to the gaseous dust gasification products above the fluidized bed compared to a pure fluidized bed system elevated. This can lead to increased dust discharge. Because of these disadvantages, the fluidized bed reactor as such can also be used here are not yet optimally designed, nor is the dust gasification level.

According to another described in DE-OS 34 30 219 Process proposal is therefore provided for fluidized bed and to set up the gasification reactor spatially separated from each other. The fluidized bed reactor can thus be optimally designed for gasification. the fluidized bed surface is no longer fixed to a certain height, A sufficiently large free space is arranged above the fluidized bed. The solid discharged from the fluidized bed is separated off from the Product gas is fed to the dust gasification reactor, advantageously uncooled, from which then the dust gasification products, possibly only the product gas alone, returned to the fluidized bed of the fluidized bed reactor will.

In DE-OS 29 18 859 a dust gasification system is described in which the products obtained from dust gasification reactors in a common waste heat boiler are fed.

The reactors to all of the fluidized bed gasification processes mentioned are there depending on the fluid mechanics, limited in the throughput. The flow conditions necessary to maintain the fluidized bed cannot beyond certain diameters of the fluidized bed reactor be secured more. In addition, with increasing operating pressure fuel used becomes increasingly fine-grained, eventually becoming dusty got to. Therefore, these procedures are only for throughputs of at most ≦ 50 t / h usable. Very high throughput rates are, for. B. in Power plants necessary where combined steam turbine-gas turbine processes the gas required in the gas turbine must be generated from coal. With such plants, coal throughputs of 100 t / h and much more are required.

The object of the present invention is to provide a fluidized bed gasification process, with subsequent flue gasification, the with a simplified procedure and reduced expenditure on equipment enables continuous operation of the pigeon dust reactor.

To solve this problem are mentioned in a method of the beginning Generic term discharged from at least two fluidized bed reactors Solids fed together to a dust gasification reactor.

The gasification with an oxidizing agent and water vapor with increased Printing takes place under normal process and printing conditions. For example pressures of 1-80 bar are suitable.

The parallel connection of several fluidized bed reactors and the processing of the solid discharged upward from the fluidized bed reactors in a common dust gasification reactor not only enables optimal Design of each fluidized bed reactor, but also the optimal design of the dust gasification reactor. As fluidized bed reactors can Conventional reactors are used, such as those used for fluidized bed gasification be used with spatially separated dust gasification (see e.g. DE-OS 34 30 219). The fluidized bed reactor can also now a calming room above the fluidized bed receive as it is necessary for the grain used. The fluidized bed surface no longer needs to be kept at a certain height to become, it can migrate depending on the throughput that is currently is required by the reactor. The fluidized bed gasification can also with top gasification, for example as in Hydrocarbon Processing, April 1978, p. 128 described, provided, as well as, for. B. a usual Return of the coarser portion of that discharged from the fluidized bed Solid. In this case, only the finer fraction would go to the dust gasification reactor are fed. So there are all options for optimal Performed fluidized bed gasification.

The dust gasification reactor can be of conventional construction. He can in of a size where the ratio of volume to surface of the reaction space is cheapest. Also the time of stay the dust gasification stage can be optimally adjusted. In fluid bed systems, when operated under pressure, less dust is ejected  than in systems under normal pressure. The amount of discharged can Solid value reach a value that in the known method with the common arrangement of dust gasification level and fluidized bed level operating the dust gasification stage in a reactor is uneconomical does this because too much heat is extracted when this stage is cooled is and a gasification process in the dust gasification stage practically not more can be maintained. This phenomenon occurs in a dust gasification reactor, which is fed by several fluidized bed reactors will not, especially not if this is set up separately Dust gasification reactor is uncooled. That with such reactors used weight of masonry - in contrast to cooled reactors - causes no technical bottlenecks here.

In the process according to the invention, it is also possible to remove the fluidized bed reactors Solid discharged downwards if the residual carbon content is too high after appropriate customary processing in the respective fluidized bed reactor attributed and / or the common dust gasification reactor feed.

The fuel parts are drawn off from the fluidized bed reactors, which were either too coarse for the fluidized bed process or by depleting the carbon content, d. H. Enrichment of the ashes have become too heavy. But there will also be a corresponding one Fine grain fraction discharged, which is due to fluidic, mostly local Conditions in the reactor. Depending on the amount of so after bottom of carbon discharged from the fluidized bed reactor the return to one of the gasification stages can be economical. It must be borne in mind that the coal in the gas generation plant imported ashes can also be removed from the system must if the entire system should not suffocate in its own ashes.

Preparation is necessary for the return. The return takes place into the fluidized bed itself, either the proportion, for example contains more than 80 or 90% ash and the The rest must be brought to the fluidized bed or the entire amount must be sufficient be crushed so that when reintroduced into the fluidized bed no longer sink down. In the latter case, this would be processed ash portion discharged upwards from the fluidized bed and melted down in the dust gasification reactor. Should the from the  Fluid bed discharged downward to the dust gasification reactor be carried out immediately, so it must be crushed to grain size as they are carried upwards from the fluidized bed Solid has to complete it in the dust gasification reactor gasify or melt. The one from the fluidized bed reactors Ashes are discharged upwards through the dust gasification stage taken from the process in the form of slag.

The procedure according to the invention makes it possible to have two or more To combine fluidized bed reactors with a dust gasification reactor. The Number of fluidized bed reactors with a dust gasification reactor is combined is variable. It depends on how high the share of the unreacted solids in those from the fluidized bed reactors discharged solids. Generally 2 to about 8, in particular 2 to 6 and preferably 2 to 4 fluidized bed reactors combined a dust gasification reactor.

Are z. B. fluidized bed reactors on a dust gasification reactor switched, so is in the dust gasification reactor in the form of Coking carbon introduced a chemically bound heat, which is about the Heat quantity corresponds to that with the pure substance of the fuel in a fluidized bed reactor is introduced.

Treatment of products exiting the dust gasification reactor Gas and liquid slag can take various forms. once can, as in known methods, the liquid slag from the product gas be separated and granulated in a water bath while the palpable Heat of the product gas in downstream steam generators Steam generation is used. Next, the dust gasification reactor Radiation cooler must be connected immediately in which the product gas and the liquid slag is cooled, the liquid slag is also solidified and deposited while the product gas continues to Cooling flows through the contact heating surfaces of a steam generator.

The sensible warmth of the dust gasification products can also be immediate be supplied to the gasification process in that the dust gasification products Gas and liquid slag in the fluidized bed of one or more of the fluidized bed reactors connected in parallel  with a part of the sensible heat of the dust gasification gas in released into the fluidized bed and at the same time solidified the liquid slag and is excreted downwards or that only the dust gasification gas after separating the liquid slag and its Granulation in a water bath, for example, to the fluidized bed or beds is returned.

Another option is to use a dust gasification reactor to combine another fluidized bed stage in a common reactor, the dust gasification products directly entering this fluidized bed and there the heat exchange and solidification of the liquid Slag occurs; such a dust gasification reactor combined with a fluidized bed stage is described for example in DE-OS 29 47 222. Furthermore, the dust gasification reactor with an inert fluidized bed can be combined, the sensible heat of the product gas and that of liquid slag transferred to this inert fluidized bed and liquid Slag is solidified at the same time. The heat introduced serves the Steam generation or heating of other gasification media, why in the Inert fluidized bed cooling surfaces installed to remove the sensible heat are.

Business considerations on the interplay between availability of a plant and gasification efficiency determine which Way the gasification products are treated.

The product gas emerging from the fluidized bed reactors, including the Dust gasification gas are supplied to dedusting devices which are in capable of under pressure and at high temperatures - in hard coal gasification about 950-1100 ° C - the product gas from the carried To separate solids. Come according to the current state of the art practically hot gas cyclones in question. The separated solid is fed to the dust gasification reactor, the pre-cleaned gas the reactors a common waste heat boiler. The cooling takes place there of the product gas, the heat extracted being used to generate steam is, possibly also partially to warm up in the gasification process needed additional media.  

The waste heat boiler is followed by fine dust removal before that cleaned gas enters the common gas scrubber. Fine dust removal can also be done in the gas scrubber itself. The one in the waste heat boiler Solid matter separated out in fine dust removal or in gas scrubbing is returned to the gasification process; if the recovery economically worthwhile or z. B. environmental requirements do.

For large plants with a very large coal throughput, it may be necessary Combination of z. B. 3 fluidized bed reactors with a dust gasification reactor to be placed side by side several times. In this case too expediently the product gas from each combination group common line of waste heat recovery and gas cleaning fed.

The advantages of the present invention are:

• 1) Each coal throughput can be represented;
• 2) Optimal design of fluidized bed reactors and dust gasification reactor;
• 3) Operation of the fluidized bed reactors possible, even if the dust gasification reactor has failed;
• 6) Complete implementation of the fuel introduced into the system;
• 5) Maximum gasification efficiencies;
• 6) Use of tried and tested reactors in combination, thus maximum availability the individual systems, and therefore the combination;
• 7) Use of the sensible product gas heat of all reactors or combination groups in a plant for the use of waste heat (e.g. waste heat boiler) and subsequent cleaning of the product gases in a gas cleaning system.

Claims (9)

1. A process for the gasification of solid, dusty to lumpy carbonaceous material with an oxidizing agent and steam under increased pressure in a fluidized bed reactor with subsequent complete conversion of the residual carbon of the solid discharged upward after separation of product gas in a dust gasification reactor, characterized in that the from at least Two fluidized bed reactors discharged solids are fed together to a dust gasification reactor. 2. The method according to claim 1, characterized in that that the solid discharged from the fluidized bed reactors downwards if the residual carbon content is too high after appropriate processing returned to one or more fluidized bed reactors and / or the common dust gasification reactor is supplied. 3. The method according to claim 1, characterized in that the product gas from the dust gasification reactor in one or several fluidized bed reactors is recycled. 4. The method according to claim 1, characterized in that the product gas and the slag from the dust gasification reactor returned to one or more of the fluidized bed reactors will. 5. The method according to claim 1, characterized in that the dust gasification reactor with a further fluidized bed stage is combined in a common reactor, the Dust gasification products for heat exchange directly into them Enter the fluidized bed.   6. The method according to claim 1, characterized in that the dust gasification reactor to use the sensible heat which combines dust gasification products with an inert fluidized bed is. 7. The method according to claims 1-6, characterized in that the combination of several fluidized bed reactors with one Dust gasification reactor is operated several times in parallel. 8. The method according to claims 1-7, characterized in that the product gas from the reactors of a combination in a common Waste heat recovery plant is used, for example Steam generation. 9. The method according to claims 1-8, characterized in that the waste heat recovery is a fine dedusting and Gas cleaning or a gas cleaning including fine dust removal for the Product gas from the reactors of the combination connects.