A method for recycling waste water from coal gasification production

Abstract

The invention relates to a method for recycling coal gasification production sewage and belongs to the technical field of comprehensive utilization of industrial production. The technical scheme adopted is follows: a temperature increasing tower (3) and a matched vacuum flashing tank (4) are arranged at the gas inlet of a gas cooling tower (1), water is in direct countercurrent contact with the gas in the temperature increasing tower for heat exchanger, after the temperature of the water is increased, the water is delivered into the vacuum flashing tank for flashing, and then the bottom water is returned to the temperature increasing tower to be heated, and therefore, a circulating heating loop is formed; an air heater is arranged at the inlet of a gas furnace, water vapor separated out by the vacuum flash tank enters the air heater, and condensate water is recovered in a gas furnace jacket or a waste boiler to produce the water vapor instead of soft water, and used as a gasifying agent of the gas furnace. The equipment adopted in the method is long in service life and low in operating cost; for the production of every 1 ton of alcohol amine, the dosage of the circulating cooling water of the gas cooling tower is reduced by 10-20m<3>, the amount of sewage recovered is increased by 50-300kg, the dosage of the soft water is reduced by 50-300kg and the consumption of coal is reduced by 5-30kg, and therefore, zero emission of gas washing sewage is realized, and environment-friendly, water-saving and energy-saving benefits are all very remarkable.

Description

technical field [0001] The invention relates to a method for recycling sewage produced by coal gasification, and belongs to the technical field of comprehensive utilization of industrial production. Background technique [0002] Coal chemical industry has become an important part of the chemical industry. Coal gasification occupies a very important position in coal chemical industry. Coal gasification is used to produce city gas and various gases, and is also used to produce synthetic gas. The raw material of chemical products; the process of coal gasification is to use coal (coke) as raw material, air (oxygen or oxygen-enriched), water vapor as gasification agent, and convert the organic matter in coal into The process of combustible gas; the gas obtained from coal gasification is called coal gas, semi-water gas, raw material gas, and the equipment for coal gasification is called coal gas generator, coal gas furnace or gasifier. The temperature of the gas at the outlet of ...

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Problems solved by technology

[0004] One is that the gas washing water is acidic and dusty sewage, with a pH value of 3-5, high COD, high content of harmful substances, many types, and complex components, which cannot be treated and recycled through simple precipitation, filtration, neutralization, etc.;

[0005] Second, the amount of steam that actually participates in the gasification reaction per 1 ton of alcohol ammonia is only 900-1000kg. A large amount of unreacted water vapor is condensed by the gas washing water during the process of gas washing and cooling, and a large amount of condensation heat is released into the gas washing. In sewage, the heat load of gas washing increases greatly, the amount of circulating water increases, the energy consumption and operating costs of gas production increase greatly, and at the same time, a large amount of waste of heat is caused. For each ton of alcohol ammonia produced, the circulating cooling water used for gas washing and cooling Consumption up to 70-100m 3 ;

[0006] Third, when the gas furnace is in good condition, the water vapor decomposition rate reaches more than 50%, the summer temperature is high, and the cooling water tower evaporates a large amount of water loss in dry seasons, the gas washing circulating water system can achieve zero sewage discharge; but it is rainy in summer And in winter when the temperature is low, the water evaporation loss of the cooling water tower is very small, and the problem of water swelling in the system is very prominent, and some sewage is forced to be discharged; when the gas furnace is in poor condition, the steam decomposition rate is below 50%, and the summer temperature is high, The gas scrubbing circulating water system has obvious flooding in the dry season, and the flooding problem will be more serious in the rainy summer and the low temperature season in winter, and the sewage discharge will increase significantly; therefore, it is necessary to build a sewage treatment plant, because this part of the sewage The treatment is difficult, the treatment cost is too high, the treatment is not up to standard, and the phenomenon of illegal sewage pollution occurs from time to time; the annual output of 200,000 tons of alcohol ammonia fixed bed coal gasification device, the annual discharge of gas washing sewage volume is as high as 10,000m 3 Above, there are major environmental issues;

[0007] Fourth, the coal gasification process uses air at normal temperature as the gasification agent. The normal temperature refers to the natural temperature of the outdoor air. There is a big difference between the air temperature in winter and summer, especially in northern my country. The temperature difference between day and night on the same day is sometimes as high as 15°C or more. The change of the air temperature of the gasification agent is extremely unfavorable to the stable operation of the gas furnace, which often causes problems such as increased coal consumption and serious flooding of the gas washing sewage system.

[0008] In response to the above problems, someone proposed a scrubber (cooling tower) with a two-stage structure, as described in Chinese Patent Nos. 200910014146.0 and 201020211741.1. The lower section is equipped with a heat exchanger for heating soft water, and the upper section is used for gas cooling; Patent No. 200910014146.0 is set in the lower section Heat pipe heat exchanger, patent No. 201020211741.1, a bellows tube heat exchanger is installed in the lower section, which solves the problem of recovering part of the low-temperature waste heat, but the problem of water swelling in the gas washing cooling water system has not been solved; the main problem is: heat exchanger The heat exchange tube is directly in contact with the gas, and the dew point corrosion is very serious. The service life of the heat exchanger is very short, generally about 1 year or less than 1 year. Once the heat exchanger leaks, the soft water will leak due to the high pressure of the heated soft water. Into the gas washing cooling water system, resulting in a more serious problem of rising water in the gas washing sewage, poor practicability and economy, not suitable for use in actual production

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