DD224611A5 - COAL GASIFICATION PROCESS - Google Patents

Abstract

The invention relates to a process for the preparation of methane-containing gases. The object of the invention is to provide an improved process which provides economic and ecological advantages. According to the invention, in an ash-slag gasification of carbonaceous materials with steam and oxygen over a fixed bed, at least a portion of the vapor is replaced by an aqueous condensate. The condensate may be water per se, z. As boiler feed water or a drain condensate containing condensed organic compounds and unreacted steam and solubilized salts. This condensate is obtained in the treatment of the product gas. According to the invention, up to 50% of the water required for the gasification reaction can be replaced by the aqueous condensate. The aqueous condensate can be a carrier for suspended materials, such as small particles of coal.

Description

Process for the preparation of methane-containing gases Field of application of the invention

The invention relates to a process for the preparation of methane-containing gases. In general, the invention relates to coal gasification processes.

Characteristic of the known technical solutions

During the gasification of coal with steam and oxygen, an aqueous condensate is formed, consisting mainly of soluble phenolic compounds, ammonia, hydrogen sulphide , hydrogen cyanide, alkali metals and salts. This wastewater can not be discharged without purification, as the biological oxygen demand is far too large for the environment, without any serious ecological consequences. The problem with ash-slag processes is even greater than with dry-ash processes, since the requirement for steam in the process is generally low and the by-produced effluent condensates tend to be more concentrated.

Usually these drainage condensates can be treated prior to biological measures in such a way that phenols and ammonia are removed. Alternatively, the untreated or partially treated condensate can be incinerated to produce a solid residue. "All of these wastewater treatment processes have many disadvantages and disadvantages

to technological difficulties »

The recycling of aqueous condensates obtained in the steam / oxygen gasification of the coal is already known. For example, in PCT Publication WO 80/00974, a process is described in which aqueous condensates resulting from coal dry bed solid bed gasification are fed to an ash slag gasifier with a fluidized bed. Similarly, U.S. Patent 3,971 636 the recycling of an aqueous condensate which has been separated from the synthesis gas of an ash-slag fluidized bed gasification of coal. In the examples of this invention, the aqueous condensate is used as a carrier for the feeding of fine particles of coal in the form of a slurry into the gasifier. »

Although in these publications the primary gasifier is an ash-slag gasifier, it has a completely different operation. In no case does the ash-slag gasifier have a fixed bed construction, which obviously has advantages, since an arrangement with a non-fixed bed allows rapid heating of the condensate and thus precludes any risk of the reactions being quenched,

As can be seen from the statements of the publication WO 80/00974, 'the effluent obtained from the Fsbbett phase is in fact only recycled to the entrained phase.'

From the point of view of the prior art it was not too

expect a recycle condensate feed to be successfully applied to fixed bed ash-slag gasifiers.

Object of the invention

The object of the invention is to provide an improved process for the production of methane-containing gases, which provides economic and ecological advantages,

Explanation of the essence of the invention

The object of the invention is to return at least part of the condensate from the product gas treatment.

It has surprisingly been found that an effective operation of a coal gasification fixed bed can be achieved by the ash-slag process by directly feeding (injecting) an aqueous condensate with other materials to be gasified, wherein if such a condensate is a drain condensate is, the problem of the final shipment of this waste product is mitigated ·

Thus, the present invention is a process for producing methane-containing gases wherein a solid carbonaceous material-containing starting material is gasified in the presence of steam and oxygen as a gasifying agent under fixed bed and ash slag conditions.

and the product gas is treated to remove unreacted steam, water-soluble compounds and condensable organic compounds * characterized in that at least part of the steam demand for the reaction is covered by the addition of an aqueous condensate mixed with the other gasifying agents.

The aqueous condensate is preferably the effluent condensate resulting from the treatment of the product gas. However, the aqueous condensate may also contain purer forms of water, such as those used for refrigeration purposes or as boiler feed water.

The recycled condensate is injected at the point where the other gasification agents are added, e.g., through tuyeres into the stream. In practice constitute steam guide and nozzles can be modified to provide condensate or water at the point of steam injection.

The addition of aqueous substances brings with it a number of surprising advantages, although it was expected that such addition would have a detrimental effect on either the operation of the gasifier or on the slag withdrawal operations. In no case, however, have any difficulties been noticed. The oxygen consumption (based on the amount of carbonaceous material consumed) was slightly increasing, but this was more than offset in terms of cost savings as steam heating was eliminated. In addition, there was a considerable advantage in Oa ₁ when the condensate is an aqueous effluent condensate

only considerable savings are made by the possibility of reusing the water, but also that the dissolved and suspended materials are brought into the reactor. The organic substances are of course useful as reactants.

Thus, by the recirculation condensate in this way, the required amounts of steam are substantially reduced, for example, about 50 % of substantially all the condensate is returned * which is normally obtained in bituminous coal. Up to 50% of the total water used for the gasification reaction can be covered by the aqueous condensate "namely par se as water or as recycled condensate. Another advantage is that the inorganic materials contained in the drain condensate and absorbed by the Schlakke thereby be removed together with the slag from the system »The heavy metal content of the slag, z. B, zirconium, grows, relative to the lack of condensate injection. Deduction of a large portion of the condensate may be desirable for the treatment to remove chlorides and other salts if accumulation of these compounds in the recycled condensate begins to occur. The aqueous condensate may contain some organic constituents dissolved or emulsified therein. In addition, the condensate can serve as a carrier for conveying-suspended solid materials, such as small particles of coal, to the reactor.

embodiment

The invention will now be elucidated with reference to the following examples.

A solid-bed ash-slag coal gasification plant, such as the "3rd Coal Gasification Industry", 2, Supplementary Volume, "1981, Dohn Wiley and Sons, Inc., was modified to include the injection of liquid aqueous materials below the steam To allow oxygen tuyeres. The plant was put into operation by known measures of steam / oxygen gasification of Markam Main coal at a working pressure of 24.73 bar (g). The feed rate of the reactants and the rate of gls are summarized in the following table. Column A lists the rate of reactants prior to the condensate injection. The condensate injection was increased stepwise, corresponding to columns B, C and D, over a period of 21 hours *

A 3 C D Coal feed rate (locks / hr) 3.89 3.90 3.83 3.76 Steam flow rate (ar / stcu) 5418 4827 4482 4182 Condensate injection rate (kg / h) O 440.38 708.24 817,2C

Total H-0 / Oo-encryption

ratio * 1.16 1.17 1.18 1.16

Gas flow (i5 ³ / hr.) 21165 21672 20961 20482 '

Claims (6)

Erfindunqsanspruch A process for the preparation of methane-containing gases, wherein a starting material containing a solid, carbon-containing
Material is gasified in the presence of steam and oxygen as a gasifying agent under fixed bed ash-slag conditions, and the product gas is treated to remove therefrom unreacted steam, water-soluble compounds and condensable organic compounds, characterized in that at least one
Part of the steam demand for the reaction is covered by the addition of an aqueous condensate mixed with the other gasification agents. 2 "Process according to item 1, characterized in that the aqueous condensate is water per se. 3 «method according to item 1, characterized in that the aqueous condensate is a drain condensate, the konden-r
contains unreacted steam, water-soluble compounds and condensed organic compounds, and is produced during the treatment of the product gas. " 4. Method according to item 2 or 3, characterized by
that up to 50 % of the water required for the gasification reaction is replaced by the aqueous condensate is. 5. The method according to item 1, characterized in that the aqueous condensate is a carrier for suspended materials. 6. The method according to item 5, characterized in that the suspended materials are small carbon particles.