The foundry industry is an important foundation of the manufacturing industry in my country and even in the world. The 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 (ie "industrial pollution"). Three wastes": waste water, waste gas, waste residue), followed by environmental problems such as noise, waste heat, energy consumption, and greenhouse gas emissions. 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, there is widespread sewage discharge in foundry enterprises. Major sources of sewage discharge may include:
(1) For enterprises that use hydraulic sand cleaning, water blasting 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 quenched slag produces some waste water.
(3) A small number of foundries use water gas furnaces in a small amount, producing a relative amount of waste water.
(4) For the process of wet regeneration of old sand, a large amount of water resources are used and a large amount of waste water is discharged. For example, an enterprise that produces 5 tons of waste sand per day can regenerate wet sand according to the sand-water ratio of 1:2, which can produce 10 tons of sand regeneration wastewater per day.
(5) The dust removal system in the production workshop of some enterprises adopts wet dust removal equipment, which traps dust and harmful gases and discharges them in the wastewater.
(6) The process of heat treatment and quenching consumes a lot of water resources. The water after quenching contains impurities such as metal oxide scale, and direct discharge will cause pollution. In addition, some enterprises add chemicals to the heat treatment water or use oil for heat treatment, the sewage problem is even more serious.
(7) Cooling circulating water for equipment (including smelting equipment, dust removal equipment, etc.), although the water quality of this part of the water is good and recycled, but the long-term circulation causes problems such as poor water quality and even microbial growth; at the same time, some circulating water is added with antifreeze, etc. Chemicals and efflux all cause water pollution.
(8) A small amount of water used in other equipment or sections, such as pickling wastewater, electroplating wastewater, wastewater containing mechanical oil from machinery such as die-casting machines and air compressors, and wastewater discharged from fluorescent penetrant inspection for non-destructive inspection. etc.
(9) In lost-wax precision casting, hardeners such as ammonium chloride and calcium chloride need to be added during the hardening process, and in the dewaxing process, a relative concentration of ammonium chloride solution needs to be added, and this part of the liquid contains high The concentration of ammonia nitrogen and total nitrogen is a serious pollution source if discharged.
(10) Rainwater on the surface and roof of the factory area: some foundry enterprises have some open-air operation areas, and some enterprises have a lot of dust and garbage on the ground and roof all year round, which cannot be cleaned in time. . In addition, the construction of some plant areas lacks a sound, reasonable and effective drainage design, resulting in cross-flow of sewage, which not only causes pollution in the plant area, but also affects the daily production and life of other enterprises and residents around the plant area.
l Air pollutant emissions
At present, the production workshops of domestic foundry enterprises generally have a poor working environment, especially the indoor air is turbid, the dust is diffused, and the smoky situation occurs 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 is not only serious pollution The environment also threatens the health of operators. The main sources of air pollution and indoor air pollution in foundries include:
(1) Dust caused by sand turning: It mainly occurs in the sand-related operations such as the modeling department, the sand removal department and the sand recycling department. The dust is caused by the partial ash contained in the sand. At present, some enterprises have set up dust collection devices in these industrial departments to deal with the fugitive dust in a unified manner, which has improved the fugitive emission of fugitive dust.
(2) Exhaust gas generated by the combustion of smelting equipment: especially the combustion exhaust gas of cupola furnaces is more serious. The main components of dust in the flue gas are metallurgical soot, carbon soot and dust, and also contain sulfur dioxide, nitrogen oxides and other gases. Air pollution thing. Although the use of electric furnace smelting greatly reduces the combustion exhaust gas, the metal smelting process itself still produces a small amount of exhaust gas. In addition, a small number of foundry companies use water gas furnaces in small quantities, producing a relative amount of waste water and waste gas.
(3) Exhaust gas generated by casting casting: Since the molding sand contains relative ash, and the binder and coating contain a relative amount of organic matter, obvious flue gas is generated during the re-casting process, which escapes into the workshop environment, causing air pollution .
(4) Exhaust gas generated by paint spraying: At present, the sand mold surface paint of foundry enterprises in my country mostly uses the spraying operation method. Although the technological effect is better, it also causes a large amount of paint to be directly sprayed into the air, which is not only wasteful but also causes air pollution. At the same time, it threatens the health of operators. In addition, the paint contains a high concentration of alcohol, which is also a relative safety hazard when dispersed in the factory.
(5) For those using the lost foam process, a large amount of organic waste gas is generated when the EPS "disappears" after pouring. Such waste gas becomes mostly toxic and harmful organic compounds such as stupid and toluene, causing serious air pollution, which needs to be uniformly collected and purified. deal with.
(6) Other unorganized emissions in the factory, such as a small amount of dust generated in the process of crushing, screening, transportation and processing of raw materials, and a small amount of escape from the use of organic binders.
The above lists some ministries and sections of foundries that may produce water pollution and air pollution emissions. Some of these are concentrated emissions and some are fugitive emissions to be collected. If foundry enterprises can reduce or even avoid the generation of these pollutions by improving processes and strengthening management, I believe it will be beneficial for enterprises to apply for pollution discharge permits!
(This article is an original article on the official account of the Wear-resistant Materials and Castings Branch of the China Foundry Association, please indicate when reprinting.)
Henan Aoudi Casting Co., Ltd.
Add：No. 90, Industrial Road, Tiexi District,
Qi County, Hebi, Henan
Tel：+86-0392-7275525
Email：ryan_shi@aoudi.cn
Copyright：© 2021 Henan Aoudi Casting Co., Ltd. 豫ICP备15009732号 Power by： 300.cn SEO
+86-0392-7275525
Email 