EP2883942A1 - Method and assembly for gasifying solid, organic feed material - Google Patents

Abstract

The invention relates to a process for the at least partial gasification of solid organic feedstock (A), in which a tar-containing carbonization gas is recovered from the feedstock (A) in a low-temperature gasifier (1) by smoldering, and the carbonization gas (B) is subsequently mixed in a high-temperature gasifier ( 2) is converted by partial oxidation and then partial reduction to a synthesis gas (D), wherein the synthesis gas (D) produced in the high-temperature gasifier (2) dedusted in a dust removal device (4) and in a wet scrubber (5) a wet scrubbing using a Is subjected to washing liquid, wherein in the wet scrubbing from the synthesis gas separated residual coke to assist the reduction of the high-temperature gasifier (2) is supplied.

Description

The invention relates to a method and a plant for the at least partial gasification of solid, organic feedstock, in particular of biomass, with a low-temperature gasifier and a high-temperature gasifier.

State of the art

Processes for the production of synthesis gas from solid, organic feedstock, also referred to for short as gasification processes, are known. Advantageously, coal or biomass are used as starting material for such processes. In biomass gasification processes, for example, used wood and forestry wood or so-called energy wood, but also agricultural residues such as straw or chaff are used.

By gasification of biomass to synthesis gas with downstream process steps (so-called Biomass to Liquids method, BTL), for example, synthetic biofuel can be obtained, the well-known in its physicochemical properties gas-to-liquids (GTL) and coal-to- Liquids (CTL) fuels is similar. An example of a plant for the production of BTL fuels is at Kiener, C. and Bilas, I .: Synthetic biofuel of the second generation. World's first commercial BTL production plant. Energy 2.0, July 2008, pp. 42-44 , shown.

Methods and systems for the at least partial gasification of solid, organic feed are also, for example EP 0 745 114 B1 . DE 41 39 512 A1 and DE 42 09 549 A1 known. The present application relates in this case to such processes or plants which have a low-temperature gasifier and a high-temperature gasifier, as explained below. Compared with other methods, these allow, inter alia, a lower consumption of feedstock and have a higher cold gas efficiency.

In a low-temperature gasifier, the feedstock, such as biomass, by partial gasification with a gasification agent at temperatures between about 300 ° C and 600 ° C to coke (in the case of biomass so-called biococ) and carbonization reacted. The implementation is referred to in this application as "smoldering". Smoldering is known to be characterized by substoichiometric oxygen supply and thus incomplete combustion at a comparatively low temperature.

The carbonization gas is then transferred to a combustion chamber of the high-temperature gasifier and there with an oxygen-containing gas, for example with more or less pure oxygen, but also with air and / or oxygen-containing exhaust gases, e.g. from gas turbines or internal combustion engines, partially oxidized. By this oxidation released heat causes a temperature increase to 1200 ° C to 2000 ° C, for example 1400 ° C. Under such conditions, aromatics, tars and oxo compounds contained in the carbonization gas are completely decomposed. As a result, a synthesis gas is formed, which essentially only contains carbon monoxide, hydrogen, carbon dioxide and water vapor. The synthesis gas can also be referred to as (synthesis) raw gas at this point.

In a further stage, for example in a quench unit integrated in the high-temperature gasifier or in a downstream unit, the synthesis gas produced in this way can be brought into contact with coke from the low-temperature gasifier. The coke may be previously treated separately (e.g., by grinding and sifting) and then introduced into the quench unit. By endothermic reactions between coke and synthesis gas (so-called chemical quench) the latter is cooled to a temperature of for example 800 ° C to 1200 ° C. This also causes partial conversion of the carbon dioxide to carbon monoxide.

The carbon monoxide-rich synthesis gas produced in this way can then be further conditioned. The conditioning includes, for example, a further cooling, a dedusting, a compression and / or the separation of residual carbon dioxide.

During the cooling of the carbon monoxide-rich synthesis gas (raw gas) before dedusting, condensation of gaseous alkalis present in the raw gas takes place on the surface of the coke particles.

As a dedusting device, for example, a cyclone is used. In the dedusting device, the coke (residual coke) which has partially reacted in the quench unit is separated off and can be returned to the oxidation unit of the high-temperature gasifier. In the downstream gas scrubber, the syngas stream is contacted with a scrubbing liquid stream to receive undesirable components of the syngas stream into the liquid. Purified and conditioned synthesis gas is then taken from the plant.

The residual coke separated off from the syngas in the dedusting device is typically cooled by means of cooling screws and discharged via a container lock from the dedusting device or from the pressure atmosphere in which it is located.

In order to avoid an alkali concentration due to recirculated residual coke in the oxidation unit of the high-temperature gasifier, according to the prior art only a part of the residual coke is recycled. Another part of the residual coke must be discarded, d. H. be removed from the system without further use.

This leads to various disadvantages. First, the efficiency of the overall system is reduced due to a partial non-utilization of residual coke. The removal of residual coke from the plant proves to be relatively complicated and prone to failure. Finally, the discarded residual coke must be disposed of, which leads to further cost increases.

The object of the invention is therefore a more efficient utilization of residual coke.

Disclosure of the invention

According to the invention, a method and a plant for the at least partial gasification of solid, organic feedstock, in particular of biomass, with a low-temperature gasifier and a high-temperature gasifier with the features of the independent claims are proposed. Preferred embodiments are subject of the subclaims and the following description.

Advantages of the invention

The invention is based on a known process for the at least partial gasification of solid, organic feedstock, for example biomass. From the feedstock a tar-containing carbonization gas is recovered in a low-temperature gasifier by smoldering, as explained above. The carbonization gas is then reacted in a high-temperature gasifier by partial oxidation and then partial reduction to a synthesis gas and further processed downstream of the high-temperature gasifier in appropriate treatment facilities.

The present invention is characterized in that it allows a more effective recycling and thus recovery of residual coke. By the inventive purification of residual coke in a wet scrubber, and recycling of this wet scrubbing residual Kokses in the high-temperature gasifier z. B. a complete return of the residual coke possible.

Advantageous embodiments of the invention are the subject of the dependent claims

It is particularly preferred that the residual coke separated off in the wet scrubbing is fed to the high-temperature gasifier in the form of a slurry. The term slurry is understood to mean a suspension of residual coke particles in a suitable liquid, in particular water. The handling of such a slurry, in particular the intermediate storage and the return to the high temperature carburetor, prove to be particularly uncomplicated.

Advantageously, alkalis dissolved in the wet scrubbing are at least partially stripped off with an excess washing liquid. Such a removal of excess washing liquid makes it possible to adjust a tolerable alkali content of the slurry in an effective manner.

Expediently, residual coke accumulating in the dedusting device is also separated from the synthesis gas during dedusting and at least partially supplied to the high-temperature gasifier in support of the reduction. The combination of a (dry) residual coke recycle with a (wet) residual coke slurry recycle in the high-temperature gasifier proves to be particularly advantageous, since depending on the specific operating conditions variations are conceivable. For example, it is possible to completely dispense with the dry separation of residual coke from the synthesis gas. In this case, the entire residual coke is then deposited over the slurry and recycled. It is also possible, a large part of the residual coke, in particular most of the residual coke, z. B. 60%, 70%, 80%, 90% or 95%, dry deposit over the cyclone and feed the high temperature carburetor. In this case, the slurry system treats only the amount of residual coke that the cyclone does not deposit. In this variant, the system primarily serves to reduce the coke load of the wastewater.

Advantageously, the residual coke slurry is introduced via a filter into a residual coke slurry container. Such a container can be used in a simple manner for the buffer of residual coke slurry.

A pressure within the residual coke slurry container is adjustable in a particularly simple manner by application of an inert gas, such as nitrogen or carbon dioxide.

Brief description of the drawings

FIG. 1

shows a first preferred embodiment of a system which is adapted to carry out the method according to the invention, in a schematic representation.

Embodiment of the invention

In FIG. 1 a system is shown, which is set up for carrying out the method according to the invention. The plant comprises a low temperature carburetor 1 and a high temperature carburetor 2.

In the low-temperature gasifier 1, a solid organic feedstock A, such as biomass such as wood or corresponding waste, as previously explained, are fed. The low-temperature gasifier 1 is set up to blaze the solid organic feedstock A. For this purpose, the Low temperature carburetor 1 externally, ie allothermic, for example, be heated to 300 to 600 ° C. The provision of the heat can be done for example by the waste heat of the high-temperature gasifier 2. Furthermore, the low-temperature gasifier 1 can also be heated autothermally, for example by partial oxidation of the carbon present in the solid organic feedstock A with a separately supplied oxygen G.

Via a line can be discharged from the low temperature carburetor 1 a carbonization B and transferred to the high-temperature carburetor 2. The high temperature carburetor 2 is formed in two parts. It comprises an oxidation unit 21 and a quench unit 22. In the oxidation unit 21, the carbonization gas B is partially oxidized with a supplied oxygen-containing gas H, resulting in temperatures of, for example, 1400 ° C. to 2000 ° C. In the quench unit 22, the synthesis gas D is brought into contact with pyrolysis coke C from the low-temperature gasifier 10. By endothermic reactions (so-called chemical quench) between this pyrolysis C and the synthesis gas D, the latter is cooled, for example, to a temperature of 800 ° C to 1200 ° C. This also causes partial conversion of carbon dioxide present in the synthesis gas D into carbon monoxide.

The carbon monoxide-rich synthesis gas D produced in this way is subsequently cooled in a cooling device 3 downstream of the quench unit 22, for example to a temperature of 600 to 800 ° C. In such a cooling, there is a condensation of alkalis, which are initially present in the gaseous state in the synthesis gas D, on the surface of the coke still present in the synthesis gas.

Downstream of the cooling device 3 are a dedusting device 4, for example a cyclone, and a wet scrubber 5. In the dedusting device 4, the coke which has partially reacted in the quench unit 22, the so-called residual coke E, is separated and passed to the oxidation unit 21 of the high-temperature gasifier 2.

In the downstream wet scrubber 5, the synthesis gas stream is brought into contact with a washing liquid stream, in particular water, in order to take up undesired components of the synthesis gas stream into the liquid. Sufficient Purified and conditioned synthesis gas F can then be taken from the plant and fed to downstream processes, for example for the production of synthetic biofuels.

By contacting contaminated synthesis gas with scrubbing liquid (for example water, in the wet scrubber 5, a contaminated scrubbing liquid is obtained, in addition to the purified synthesis gas, alkalies which are condensed on the remaining coke particles are dissolved in the scrubbing liquid, thus particularly containing the contaminated scrubbing liquid Residual coke particles, dissolved alkalis and other water-soluble constituents of the crude synthesis gas.

Furthermore, a circuit for washing liquid is provided, via which washing liquid can be withdrawn at an outlet 5a of the wet scrubber and, after passing through the circuit at an inlet 5b, can again be introduced into the wet scrubber. In this cycle, a circulation pump 6, a backwashable filter 8 and a circulation cooler 10 is provided.

This detergent circuit serves for the extraction of washing liquid, which, as mentioned, in particular contains dissolved alkalis and residual coke. By means of the filter 8, residual coke present in the scrubbing liquid is filtered out, and fed to a residual coke slurry container 12. The washing water with the alkalis dissolved therein passes through the filter 8, and can either be withdrawn from the system as excess water via a valve 14, or returned to the wet scrubber 5 via the circulation cooler 10 and the inlet 5b.

The residual coke slurry container 12 can be acted upon to provide a slurry of a desired viscosity with a corresponding liquid, for example water. The residual coke slurry container is provided with a mixing device 13 which can be driven by a motor 15. An inert gas can be supplied to the residual coke slurry container 12 via a valve 18, whereby a desired pressure in the container can be provided. If necessary, residual coke slurry G is withdrawn from the residual coke slurry container via an outlet 12a and fed to the high-temperature gasifier 2. The connection between the output 12a and the oxidation unit 21 of the high-temperature gasifier is not shown in detail.

The optional dedusting device 4 is partially or completely bypassable by means of a bypass line 20, in which a valve 22 is provided. In particular, with complete circumvention of the dedusting 4 (for example, by complete opening of the valve 22) can be completely dispensed with a dry deposition of residual coke by means of dedusting, in which case all the residual coke through line 20 (together with the synthesis gas) in the wet scrubber 5 is introduced. For example, by adjusting the valve 22, it can be determined in a simple manner what proportion of synthesis gas is to be introduced directly into the wet scrubber 5 via the dedusting device and which part of synthesis gas, bypassing the dedusting device.

With complete closure of the valve 22, for example, the largest part of the residual coke is still deposited via the dedusting device 4. In this case, the slurry system treats only the amount that the dedusting device 4 does not deposit. With this setting, the system is primarily used to reduce the coke load of the wastewater.

The slurry residual coking system described can be made considerably less expensive than residual coking systems according to the prior art. In particular, such a residual coking system has substantially fewer mechanical moving parts, and therefore proves to be more reliable in practice. The illustrated slurry residual coking system enables a reduction of the load of the waste water with coke, whereby a simplified wastewater treatment is provided. The overall efficiency of the carburetor increases because no coke needs to be discarded. It turns out that such a slurry residual coking system requires less electrical energy than solutions according to the prior art.

Claims (8)

Process for the at least partial gasification of solid organic feedstock (A), in which from the feedstock (A) in a low-temperature gasifier (1) by smoldering a tar-containing carbonization gas is recovered, and the carbonization gas (B) in a high-temperature gasifier (2) by partial Oxidation and then partial reduction to a synthesis gas (D) is reacted, wherein the synthesis gas (D) produced in the high-temperature gasifier (2) dedusted in a dedusting (4) and in a wet scrubber (5) is subjected to a wet scrubbing using a washing liquid, wherein in the wet scrubbing residual coke separated from the syngas is fed to the high temperature gasifier (2) to assist the reduction. A method according to claim 1, characterized in that in the wet scrubbing separated residual coke is fed to the high-temperature gasifier in the form of a slurry. Method according to one of claims 1 or 2, characterized in that in the wet scrubbing alkalis are at least partially withdrawn with an excess washing liquid. Method according to one of the preceding claims, characterized in that during dedusting in the dedusting (4) resulting residual coke separated from the synthesis gas and at least partially to support the reduction of the high temperature gasifier (2) is supplied. Method according to one of the preceding claims 2 to 4, characterized in that the residual coke slurry via a filter (8) in a residual coke slurry container (12) is introduced. A method according to claim 5, characterized in that the pressure within the residual coke slurry container (12) is adjustable by means of an inert gas. Plant for carrying out a method according to one of the preceding claims, comprising a low-temperature gasifier (1), a high-temperature gasifier (2), a gas cooling device (3), a dedusting device (4) and a wet scrubber (5), wherein a device (8, 12) is provided is, by means of the separated in the wet scrubbing of the synthesis gas residual coke to support the reduction of the high-temperature gasifier can be supplied. Plant according to claim 7, characterized in that the device (8, 12) is designed to provide a residual coke-containing slurry.

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