For coal-to-gas wastewater, certain treatment must be carried out according to environmental protection requirements, and the discharge standard is only allowed to be discharged. If the wastewater produced by coal-to-gas enterprises is directly discharged without advanced treatment, it will cause great harm to the atmosphere, soil and rivers.
The distribution of water resources and coal resources in my country is in an inverse relationship. For some areas with rich coal resources, water resources are relatively scarce. This paper will analyze the technical problems faced by the current coal-to-gas wastewater treatment, and propose an optimization plan for the Provide reference for the sustainable development of coal-to-gas enterprises.
The main source of coal-to-gas wastewater
Coal-to-gas production process is to convert coal into gaseous, liquid, solid products and various chemical products through chemical production processes such as coking, coal gasification, coal liquefaction, tar chemical industry, calcium carbide acetylene chemical industry, and chemical product recycling.
The wastewater produced in the production process mainly includes coking wastewater, gasification wastewater and liquefaction wastewater. Coking wastewater refers to the ammonia water formed after coal is coked by high temperature dry distillation, and the circulating cooling water of coal gas in the purification process will also produce induLiquefaction wastewater is industrial wastewater produced by coal liquefaction process. The liquefaction process is divided into direct and indirect liquefaction.strial wastewater containing aminophenol and cyanide pollutants, and coal-to-gas products will also be produced during the refining process. Industrial waste.
Gasification wastewater is a combustible gas generated by the gasification and decomposition of coal in a series of chemical reactions in the reactor. The evaporated gas is condensed water and washing wastewater produced by spray cooling. The wastewater contains a large amount of aminophenol and NH3. and other pollutants.
Liquefaction wastewater is industrial wastewater produced by coal liquefaction process. The liquefaction process is divided into direct and indirect liquefaction.
Direct liquefaction is a process in which coal is hydrogenated in a high temperature and high pressure environment to decompose coal from macromolecules into small molecular organic liquid hydrocarbons. The industrial wastewater produced is rich in NH3 and Al2S3; indirect liquefaction is the product of coal gasification synthesis By adding a catalyst, in the process of producing synthetic oil through a series of chemical reactions, industrial wastewater rich in organic pollutants such as acetic acid, alcohol and ketone will be produced.
Characteristics of Coal-to-Gas Wastewater Treatment
Because the composition of coal-to-gas wastewater is very complex and there are various pollutants, it is very difficult to completely treat these harmful substances. Organic pollutants in wastewater are difficult to degrade, and these organic pollutants are often chemically inactive and difficult to treat by traditional chemical methods.
During the production process, chemical reactions will occur between pollutants in wastewater, which makes the original chemically active pollutants become more stable pollutants after chemical reaction, and continuously deepens the color of wastewater, resulting in wastewater Decolorization treatment is more difficult.
In addition, due to the variety of pollutants contained in wastewater, more treatment methods are required for treatment, such as a combination of chemical and physical methods.
Application analysis of coal-to-gas wastewater treatment technology
3.1 Biochemical treatment
Conventional biochemical treatment adopts anoxic and aerobic biological treatment (A/O process). Due to the complex composition of wastewater containing polycyclic and heterocyclic compounds, the stability of COD indicators in the treated effluent is poor.
With the development of science and technology, some new treatment technologies have emerged, such as: PACT method, carrier fluidized bed biofilm method (CBR), up-flow anaerobic sludge bed treatment (UASB), anaerobic-aerobic combined biological method, etc. The three-phase separation of gas, liquid and solid is achieved. The PACT method uses the adsorption effect of activated carbon on organic matter and dissolved oxygen, and adds activated carbon powder in the activated sludge aeration tank to provide food for the growth of microorganisms to improve the oxidative decomposition efficiency of organic matter. At the same time, activated carbon can also be regenerated by wet air oxidation.
The carrier fluidized bed biofilm method (CBR) is an organic integration of the activated sludge method and the biofilm method in the same biological treatment unit, thereby improving the treatment efficiency and impact resistance of the reaction tank, effectively degrading the pollutants in the wastewater, and reducing the effluent. COD concentration. The Upflow Anaerobic Sludge Bed (UASB) makes the coal-to-gas wastewater pass through the reactor from bottom to top. During this process, most of the organic matter is converted into CH4 and CO2 by microorganisms at the top of the reactor.
The installed three-phase separator realizes the three-phase separation of gas, liquid and solid. Effectively remove phenols and heterocyclic compounds from wastewater. In view of the single use of aerobic or anaerobic treatment technology, it is difficult to achieve satisfactory treatment results. The anaerobic-aerobic combined biological method can effectively degrade the organic compounds naphthalene, quinoline and pyridine in the wastewater, so that the removal rate of CODcr in aerobic biological treatment can reach more than 85%.
3.2 Deep processing
Advanced oxidation and reverse osmosis are the most commonly used advanced treatment technologies. The former mainly utilizes the free radical OH to react with nitrogen, phenols and other substances present in the wastewater to generate carbon dioxide gas and other harmless substances. The reverse osmosis method is mainly used to effectively remove the dissolved salts in the wastewater.
Reverse osmosis technology is based on the pressure difference applied by the water solvent on both sides of the membrane, so as to achieve the filtration or retention of a specific substance present in the wastewater. The technology can be carried out in normal temperature environment, and is obviously superior to other methods in terms of target removal ability, harmful substance recovery effect and environmental friendliness.
In addition, the realization equipment of this technology is relatively small, the input cost is lower, and it can realize fully automatic operation based on advanced technology, which greatly reduces labor costs, so it has irreplaceable advantages in terms of economic, social and environmental benefits. .
The treatment of coal-to-gas wastewater is difficult, but if it is discharged without treatment, it will not only cause serious pollution to the environment, but also seriously affect the growth of organisms in the discharge area. Using more advanced and scientific technology for wastewater treatment is not only a necessary behavior to protect the ecological environment, but also allows water resources to be reused. It is important for the clean development of coal-to-gas companies and the sustainable development of the country. significance.