Method for treating coal gasification wastewater by single tower alkali injection and pressurization steam stripping

Abstract

The invention discloses a method for treating coal gasification wastewater by single tower alkali injection and pressurization steam stripping, comprising the following steps: the cold and hot coal gasification wastewater respectively enters a single tower from the upper part and middle upper part of a wastewater steam stripping tower, gas ammonia is extracted from the lateral line of the single tower which goes through three-level dephlegmation to obtain high-concentration ammonia, condensate returns to a stock tank; alkali is injected at the position below the lateral line to transform fixed ammonia into ammonia which is to be removed; the mass percentage concentration of alkali liquor is 20-40%, the use level of the alkali liquor is not more than that of mol number of fixed ammonia in the wastewater, and residue is extracted from the tower bottom and is subjected to follow-up extraction and dephenolizing process of coal gasification wastewater. In the method of the invention, the process removing acid gas, free ammonia and fixed ammonia is carried out simultaneously on the coal gasification wastewater in the wastewater steam stripping single tower, as a result, high-concentration ammonia is obtained, the content of carbon dioxide, sulfureted hydrogen, free ammonia and fixed ammonia in tower kettle purified water is extremely low, encrustment is not prone to take place, pH value is reduced to around 6, as a result, fine extraction conditions are created for the follow-up solvent extraction dephenolizing of the coal gasification wastewater. The method of the invention is suitable for the coal gasification wastewater and overall treatment process thereof.

Description

technical field [0001] The invention relates to a treatment and recovery method for coal gasification sewage, in particular to a method for treating coal gasification sewage by single-tower alkali injection and pressurized stripping. Background technique [0002] Coal gasification is an effective way to use coal cleanly and efficiently, and it is widely used in industries such as coal-to-gas, synthetic ammonia, and coal-fired power generation. The Lurgi pressurized gasification process is one of the most widely used gasification processes at present. During the washing, cooling and purification process of coal gas, a large amount of sewage with complex components will be produced, and due to the high concentration of COD and NH 3 -N, making the treatment of such sewage a difficult problem in water treatment, and with the development of the coal gasification industry, it has become one of the main pollution sources of the water environment. The composition of gas sewage is c...

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Problems solved by technology

In the field of coal gasification wastewater, Chinese patent 200610036072.7 discloses a single-tower pressurized stripping method and device for treating coal gasification wastewater. For coal gasification wastewater, three steps are taken: stripping, deacidification and ammonia removal, extraction and dephenolization, and solvent recovery. Improve the removal rate of carbon dioxide and ammonia, reduce the pH value of the extraction to improve the dephenolization effect, but this patented technology does not consider the existence of fixed ammonium, which is caused by the presence of thiocyanate, thiosulfate and nitric acid in coal gasification sewage Root, nitrite, sulfate, cyanide, sulfite and other fatty acid substances are easy to form fixed ammonium with ammonium. This technology is difficult to remove fixed ammonium by pyrolysis, and the purified water from a single tower The content of fixed ammonium exceeds the water quality standard for subsequent biochemical treatment, affecting biochemical treatment

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