The coating industry overview
Coating refers to metal and non-metallic surface protective layer or decorative layer. Coating process can be summarized as: simple pretreatment, spraying, drying or curing. Before processing generally includes oil removal, rust removal, passivation (phosphate) process, according to different coating and corrosion resistance requirements. In pre-treatment cleaning process, sand blasting, blasting or grinding process, different departments in different industries also choose to use as needed. With the rapid development of coating technology, electrostatic spraying, electrophoresis paint, powder coating technology has been widely used.
According to the coating process, coating waste gas mainly comes from the pretreatment, spraying, drying and curing process, the pollutant emissions, mainly: pretreatment process of dust or mist, spray paint when the fog and organic solvent, drying and curing of the organic solvent. Paint fog mainly comes from the air spray flying solvent-based coating part of the job, its composition and the paint used. Organic solvents mainly comes from in the process of using paint, thinner, most volatile emissions, its main pollutants into three benzene, resin, etc. The biggest belongs to the spray paint process, coating industry emissions with spray paint room, drying room, and among them the main placing signage at dry room, etc for the exhaust gas.
Summary of textile printing and dyeing industry
Textile printing and dyeing industry exhaust contributed 8.8% of VOCs, the 2011-2020 unconventionality control pollutant emission inventory analysis and prediction research report, according to 2008 statistics our country textile dyeing VOCs (volatile organic compounds) emissions accounted for 8.8% of the total emission sources of various VOCs, account for more than 30% of industrial process emissions of VOCs.
Textile printing and dyeing industry emissions come mainly from two aspects: one is chemical fiber spinning process, the second is textile pretreatment and functional finishing processes.
Viscose fiber spinning technology of chemical fiber, for example, needs to make raw materials as spinning dope, and in the process of manufacturing spinning dope need to join a large number of carbon disulfide, so spinning process will release with hydrogen sulfide, carbon sulfide, sulfur dioxide, give priority to the harmful gas of substances.
Part 1) pretreatment process - drift, drift machine weaving cooked this is drifting on the production line or in the jig dyeing machine in the open. Open the device will have a certain amount of exhaust gas, bleached boiled additives including penetrating agent, wetting agent, etc. Cook the ingredients in bleaching auxiliaries were sulfating sesame oil, sodium alkyl sulfate, secondary alkyl sulfate, sodium alkyl benzene sulfonic acid sodium and so on
2) dyeing production process - drying, the drying process, the dyeing process in organic matter can be released, because the fabric in dyeing and finishing process of adsorption of fertilizer and chemicals, drying flue gas are mainly organic volatile VOCs, including benzene series derivatives and naphthalene derivatives.
3) the heat setting machine processing, one of the most important aspects of the textile pretreatment process. The exhaust pollutants produced during the heat setting is also the main pollutants, various dyes on the textile auxiliaries, coating additives will be released, so there will be a large amount of VOCs eventually exhaust apertures (organic volatile) release. These organic gases are mainly formaldehyde, benzene, aromatic hydrocarbons and other organic gases.
4) printing production, the process of major air pollutants from solvent, in the configuration sizing agent in the printing process to join agents released in the back of the drying, paste the basic not volatilize, main is to configure the solvent used in the pulp and ingredients.
5) functional finishing of textiles, polyester hot melt of disperse dye in the dyeing process, high temperature lead to small molecular dye sublimation for emissions. Cotton fabrics no-iron, flame retardant finishing through baking link, because of the added some chemical agents, baking the aldehyde gas such as formaldehyde and ammonia release occurs.
Waste gas treatment
Coating dyeing and printing waste gas governance mainly to prevent, cure in parallel.
Primary prevention is to reduce the pollution source of emissions: reducing the use of organic solvents; Or change process, and encourage the use of water, high solid, powder, uv-curable coatings such as environmental protection coating with low content of VOCs, restrict the use of solvent-based coating (based on the volatile organic compounds pollution treatment project in zhejiang province, relevant requirements); Or the introduction of a high degree of automation equipment, environmental protection equipment; Pollution source closed as far as possible, to reduce emissions.
Governance is mainly for waste gas treatment.
1) direct combustion method: using the auxiliary fuels such as gas or fuel combustion heat release will mixed gas heated to a certain temperature (700 ~ 800 ℃), reside a certain amount of time, make the flammable harmful material for high temperature decomposition into harmless substance. The law does not apply to cannot combustion and low concentration of exhaust gas, large energy consumption, higher technical requirements, not easy to control and mastery.
2) adsorption concentration + catalytic combustion method/catalytic combustion method: using activated carbon or molecular sieve adsorption concentration low concentration organic waste gases, stripping out again into the catalytic oxidation bed combustion purification. Exhaust gas heating to 200 ~ 300 ℃ after catalytic bed catalytic combustion carbon dioxide and water into harmless odourless, purpose of purification.
3) absorption, absorption can be divided into chemical absorption and physical absorption, most of the organic waste gas should not be used chemical absorption. Physical absorption using appropriate absorbent (such as diesel oil, water, etc.) in the absorption tower to absorb, to absorb a certain concentration after separation of solvent or in sewage treatment, the method is suitable for the high concentration of VOCs, do not apply in low concentrations.
4) activated carbon adsorption method: using porous activated carbon and activated carbon fiber adsorption of organic waste gas, after saturated with low pressure steam regeneration, regeneration when solvent exhaust fumes after condensation, water separation recycling solvent. The running cost is higher, and will produce certain waste water, under normal circumstances, the method is suitable for the occasion of VOCs have recycling value.
Method: 5) ozone ultraviolet ozone method has the advantage that does not produce NOX and CO oxidation process, at the same time can remove paint fog particles and organic solvent, disadvantage is the need to increase the production of ozone equipment and processing to absorb water.
6) the low temperature plasma method: using high energy electron, free radicals and other reactive particles and pollutants in the exhaust, the pollutant molecules decomposition happens within a very short time, and the subsequent reactions to achieve the goal of decomposition of pollutants. Suitable for low concentration, high concentrations is not appropriate.
7) molecular sieve adsorption method
Zeolite molecular sieves with crystal structure and characteristics, the internal cavity can have the effect of adsorbed molecules, due to the crystallization properties of the cavity, molecular sieve pore size distribution is very uniform. Using zeolite molecular sieve adsorption of organic waste gas, after saturated with hot air regeneration, regeneration of the high concentration of solvent exhaust fumes after condensing recovered solvents or incineration process.

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