China Quench Cooler Used in Waste Incineration Industry to Avoid Dioxin by Swift Cooling Flue Gas

What is dioxin?
Molecular structure of dioxins:
DIOXIN (DXN) is the polychlorinateddibenzo-p-dioxins, which is abbreviated as PCDDs.To put it simply, PCDDs is produced by the combination of two benzene nuclei with two oxygen atoms and the replacement of a part of hydrogen atoms in the benzene nuclei with chlorine atoms. According to the number and location of chlorine atoms, there are a total of 75 substances, among which the most toxic one is 2,3,7, 8-tetrachlorodibenzo-dioxins TCDDs(2,3,7, 8-TCDDS).In addition, there are 135 kinds of dibenzofuran PCDFs produced together with PCDDs.Dioxins and dioxins are commonly referred to as dioxins, so dioxins are not one substance, but as many as 210 substances (isomers).
Features of Dioxin:
Dioxins are solid in the standard state, and their melting point is about 303~305ºC.Dioxins are very difficult to dissolve in water, and their solubility in water is only 7.2x10-6mg/L at room temperature.Also at room temperature, its solubility in dichlorobenzene is as high as 1400mg/L, which means that dioxins are easily soluble in fats, so they tend to accumulate in organisms and are difficult to expel.Dioxins are fairly stable below 705ºC, above which they begin to decompose.In addition, the vapor pressure of dioxins is very low, below 1.33x 10-8pA under standard conditions. Such a low vapor pressure indicates that dioxins are not easily volatilized from the surface at general ambient temperatures.This, combined with thermal stability and low solubility in water, is an important property in determining where dioxins go in the environment.
The flue gas generated by waste incineration and hazardous waste treatment process system contains dioxin. Dioxin is a kind of highly toxic substance, which is seriously harmful to environment and human health. Moreover, it will polymerize at low temperature at 250~650ºC, so it is necessary to cool down the smoke and gas in a short time from 550 to 200ºC in less than 1s to prevent the production of dioxins.
The dioxin quench cooler developed by our company uses ambient air as the cooling medium, which can be designated into two working conditions:
1.When the flue gas in combustor passes through the heat recovery boiler, its temperature is lowered to be around 500ºCand then enters into swift cooling device. The swift cooling device can be designed into all welded plate structure which has the advantages of compact design, high heat transfer efficiency and low flow resistance. The flow rate of flue gas is limited within 10m/s so that the residence time in heat exchanger is less than 0.5s.
2.When the outlet temperature of combustor flue gas is at about 1000 ºC and flue gas enters the swift cooling device directly,the device structure has to be designed as silica glass tubular type.The application temperature of silica glass is at around 1200 ºC,and is resistant to temperature shock at 1000 ºC. This will ensure that flue gas will be cooled within 1s. If there is any damage,the silica glass can be easily and timely replaced, thus extend the service life of the equipment.
The dioxin quench cooler designed by our company completely separates the cold and hot fluids without changing the flue gas composition or affecting other equipments during flue gas reprocessing projects.Meanwhile the ambient air,which is taken as the cooling medium, is heated to higher temperature and can heat the flue gas entering into the denitrification device, saving the process of reheating flue gas by hot blast furnace, achieving recycling and reusing of waste heat.

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