at present, there are many methods of governance for vocs, which are summarized as follows:
1) absorption: the use of exhaust gas in the mixed component solubility in the selected sorbents in different, or one or more components and active absorbent in chemical reaction, the harmful substance is separated from the exhaust gas, a gas purification method to. in essence, it is the transfer of gaseous pollutants into the liquid phase in the waste gas, which often produces two pollution. this method is suitable for high gas, low temperature, low concentration of hydrophilic waste gas components and not suitable for non hydrophilic waste gas.
2) the condensation method: according to the nature of the waste gas, the organic waste gas by freezing device cooling to the solidification temperature appropriate, gaseous organic waste gas into the liquid is separated, the high cost, low operation cost, high efficiency, equipment maintenance management strength. in particular, it is especially suitable for high concentration and recovery of gaseous material. low concentration and mixed gas are not applicable.
3) direct combustion (to): using gas or fuel and other auxiliary fuels to burn the mixture, heating it from room temperature to over 750 degrees, so that harmful substances can be decomposed into harmless substances under the action of high temperature.
the advantages of direct combustion method, the outlet temperature is relatively stable, automatic adjustment of combustion and the outlet temperature by using plc program, so as to keep the temperature in the range of stable, especially for the back-end production needs thermal energy and strict occasions of temperature fluctuation; use of combustion heat to to replace the original use of natural gas combustion furnace provides the heat the production process, is the ideal choice. to overcomes the shortcomings of the unstable and continuous change of the rto outlet temperature.
4) regenerative burning method (rto): oxidizing organic waste gas to generate co2 and h2o at high temperature (750--850 c), so as to purify exhaust gas and recover the heat released during decomposition. the heat recovery efficiency is over 95%, and the efficiency of treatment is over 95%. at present, it is the most economical and effective treatment technology, especially for the treatment of organic waste gas with medium and medium high concentration of gas. because of the use of ceramic regenerator, the weight of the device is large and the one-time investment cost is relatively high. the temperature of the outlet is continuously changed.
5) catalytic combustion: transforming waste gas into harmless carbon dioxide and water through catalytic combustion. this method has low ignition temperature, high energy saving, high purification rate, convenient operation, large investment in area and equipment, and is suitable for high temperature or high concentration organic waste gas. but there will be no ingredients in the waste gas, such as halides, heavy metals, s, as, mercury and so on. the operation cost is high, the price of precious metal catalyst is expensive, and the service life of the catalyst must be changed only for 7200 hours.
6) activated carbon adsorption of organic waste gas by activated carbon adsorption, activated carbon, a new beginning of the use of up to 90% and above the purification rate, but with the increase of adsorption saturation, the treatment efficiency of the way down, soon to discharge standard. simple equipment, less investment, but the frequent replacement of activated carbon, the operation cost is huge; activated carbon replaced belong to hazardous waste, professional processing, high processing cost; also increased the handling, transportation, replacement and other procedures, resulting in the increase of operation cost and labor intensity.
7) adsorption - catalytic combustion method: this method has advantages of comprehensive adsorption and catalytic combustion method, using novel adsorption materials (honeycomb activated carbon) adsorption, the hot air introduced in close to saturation after desorption, desorption analysis, gas catalytic combustion bed flameless combustion, the thorough purification, hot gas cycle in the system, greatly reduce the energy consumption. this method has the advantages of stable and reliable operation, low operation cost, convenient maintenance and so on. it is suitable for the treatment of exhaust gas with large air volume and low concentration. but there will be no ingredients in the waste gas, such as halides, heavy metals, s, as, mercury and so on. the operation cost is high, the price of precious metal catalyst is expensive, and the service life of the catalyst must be changed only for 7200 hours. in addition the desorbed activated carbon decreased, the need to replace several times after the desorption of activated carbon, the replaced belong to hazardous waste, treatment by professional solid waste, the treatment cost is high.
8): low temperature plasma discharge process in the electric field, electron energy from the electric field, the inelastic collision energy into pollutants molecular internal energy or kinetic energy, these energy molecules are excited or ionized to form active groups, while oxygen and moisture in the air in the high energy electron effects can be produced a large number of new ecological hydrogen, active oxygen and hydroxyl oxygen and other active groups, these active groups collide each other will lead to a series of complex physical and chemical reaction. but the effect on voc is very low. it is suitable for the decomposition of organic waste gas and oil fumes with ultra-low concentration (<30mg/m3), and the treatment efficiency is only about 30%.
9) uv photocatalytic oxidation under specific irradiation of ultraviolet light, generate ozone, hydroxyl radicals of harmful gas co oxidation decomposition, decomposition of governance is especially suitable for ultra low concentration municipal malodorous gases, the malodorous gases substances into small molecule compounds no odor or completely mineralized, governance efficiency 30%. it is suitable for treatment of harmful substances with low concentration and malodorous ingredients.
in actual operation, especially in open real-time online monitoring of the forthcoming implementation of the selection, real-time and efficient control methods is the main trend of the industrial waste gas treatment process, the traditional method is generally not recommended the use of the employer, in order to avoid the previous high investment, the actual effect is not ideal but later governance operation cost is huge, can not meet the environmental monitoring operation environment need.