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As an important foundation of the manufacturing industry in China and even in the world, the production of pollution in the production process is relatively similar to that of general industrial production enterprises, mainly including water pollution, air pollution, solid waste and other major aspects (namely "industrial three wastes": waste water, waste gas, waste residue), followed by environmental problems such as noise, waste heat, energy consumption, greenhouse gas emissions and so on. The newly released "Implementation Plan for the Control of Pollutant Discharge Permit System" focuses on the water pollution discharge and air pollution discharge of production enterprises. Therefore, it focuses on which links of foundry enterprises may produce water pollution and air pollution discharge.

l Water pollution discharge

The main process of foundry production does not involve the use of water resources, so the waste water problem of foundry enterprises is often ignored. However, in fact, the foundry enterprises generally exist sewage discharge. Major sources of wastewater discharge may include:

(1) For enterprises that use processes such as hydraulic sand cleaning, water explosion sand cleaning or electro-hydraulic sand cleaning in the sand cleaning department, this department discharges part of the wastewater.

(2) For the production process using cupola, water quenching slag produces some waste water.

(3) A small number of foundry enterprises use a small amount of water and gas furnaces to produce a relative amount of wastewater.

(4) For the process of wet regeneration of old sand, a large amount of water resources are used and a large amount of wastewater is discharged. For example, an enterprise that produces 5 tons of waste sand every day can produce 10 tons of sand recycling wastewater every day according to the sand water ratio of 1:2.

(5) The dust removal system in the production workshop of some enterprises adopts wet dust removal equipment, which captures dust and harmful gases and is discharged in waste water.

(6) heat treatment quenching process consumes a lot of water resources, quenching water contains metal oxide skin and other impurities, direct emissions will cause pollution. In addition, some enterprises in the heat treatment water to add chemicals or the use of oil for heat treatment, the sewage problem is more serious.

(7) equipment (including smelting equipment, dust removal equipment, etc.) cooling circulating water, although this part of the water quality is better and recycling, but long-term circulation caused by poor water quality and even microbial growth and other issues; at the same time part of the circulating water to add antifreeze and other chemicals, discharge all cause water pollution.

(8) A small amount of water for other equipment or sections, such as pickling wastewater, electroplating wastewater, wastewater containing mechanical oil flowing out of die casting machines, air compressors and other machinery, and wastewater discharged by fluorescent immersion inspection for non-destructive inspection, etc.

(9) in the lost wax precision casting, hardening process need to add ammonium chloride and calcium chloride hardening agent, and in the process of dewaxing, also need to add the relative concentration of ammonium chloride solution, this part of the liquid contains a higher concentration of ammonia nitrogen and total nitrogen, if the emission is a serious source of pollution.

(10) Rainwater on the surface and roof of the plant area: some foundry enterprises have some open-air operation areas, some enterprises have more dust and garbage on the ground and roof all the year round, and some enterprises have more dust and garbage that cannot be cleaned in time. In addition, the construction of some factory areas lacks perfect, reasonable and effective drainage design, resulting in cross-flow of sewage, which not only receives pollution in the factory area, but also affects the daily production and life of other enterprises and residents around the factory area.

l Emission of air pollutants

At present, the production workshop of domestic foundry enterprises generally poor working environment, especially the indoor air is turbid, dust and smoke from time to time. Even if the company has used some dust removal equipment in the production workshop, the effect is very limited. At the same time, suspended aerosols (PM2.5 and finer particulate pollutants) and gaseous organic pollutants are still very serious, which not only seriously pollutes the environment, but also threatens the health of operators. The main sources of air pollution and indoor air pollution within foundry enterprises include:

(1) Dust caused by foundry sand: mainly occurs in the sand-related operations such as the Ministry of Modeling, the Ministry of Falling and Sand Clearing, and the Ministry of Sand Reuse. Dust is caused by some ash in the sand. At present, some enterprises have set up dust collection devices in these industrial departments to uniformly treat the dust, thus improving the problem of unorganized emission of dust.

(2) Smelting equipment and other combustion waste gas: especially cupola combustion waste gas emissions are more serious, the main composition of dust in the flue gas is metallurgical soot, carbon soot and dust, in addition to sulfur dioxide, nitrogen oxides and other gases air pollutants. Although the use of electric furnace smelting has greatly reduced the combustion exhaust gas, the metal smelting process itself still produces a small amount of exhaust gas. In addition, a small number of foundry enterprises use a small amount of water gas furnace, resulting in a relative amount of waste water and waste gas.

(3) waste gas produced by casting: because the sand contains relative ash, and the binder and coating contain relative amounts of organic matter, so the re-pouring process produces obvious flue gas, escape to the plant environment, causing air pollution.

(4) Waste gas generated by coating spraying: At present, the sand mold surface coating of China's foundry enterprises mostly use the spraying operation mode. Although the process effect is better, it also causes a large number of coatings to be sprayed directly in the air, which not only wastes but also causes air pollution and threatens the health of operators. In addition, the paint contains a high concentration of alcohol, which is dispersed in the factory and also has a relative safety hazard.

(5) for the use of lost foam process, after pouring EPS "disappeared" when a large number of organic waste gas, such waste gas become more toxic and harmful organic matter such as stupid, toluene, causing serious air pollution, need to be unified collection and purification treatment.

(6) Unorganized emissions in other plants, such as a small amount of dust generated during the crushing, screening, and transportation of raw materials, and a small amount of escape in the use of organic binders.

The above lists some foundry enterprises may produce water pollution and air pollution emissions of the Ministry and section. Some of these are concentrated emissions and some are unorganized emissions to be collected. If foundry enterprises can reduce or even avoid these pollution by improving the process and strengthening management, it is believed that it will be beneficial to the enterprise's pollution emission permit declaration work!