Study On The Adsorption Of High Concentration VOCs In Industrial Exhaust Gas With A Pilot-scale Multi-layer Fluidized

Volatile organic compounds(VOCs),which come from the waste gas in petroleum chemical processes,pharmaceutical processes,printing processes and transportation,is one of the main pollutants.VOCs endanger human health and can irritate eyes,nose,respiratory tract,and be harmful to lung,liver and other organs and nervous system,and even cause acute poisoning when one breathe too much.Meanwhile,VOCs are the resources for producing PM2.5 particles.Therefore,research on the removal of VOCs from industrial waste gas is of great significance.At present,many ways for removal of VOCs from industrial waste gas are given.Among them,fixed-bed activated carbon adsorption technology is the most simple method,and has been widely used.However,when waste gas with high VOCs concentration is treated,fire often happen in the fixed-bed due to too concentrated adsorbing heat.This problem can be solved by using fluidized bed adsorption instead,because of its good heat transfer by fluidization of gas and particles.But the adsorption efficiency is low with fluidized bed adsorption due to the severe backmixing of gas and particles in it.In order to solve the problems,multi-layer fluidized bed adsorption is adopted and studied in this paper for treating high VOCs concentration waste gases.The main research contents and conclusion are as follows:1)Eight activated carbons with different shape,and size of 0.5 ～ 1 mm from different companies,were selected as adsorption materials.Four kinds of organic solvents,xylene,ethyl acetate,butanone and carbon tetrachloride,were selected as adsorbates.Saturation adsorption,equilibrium desorption in industrial conditions,under different temperatures and with different adsorbates were measured.The results show that the same activated carbon capacity has different adsorption capacity for different adsorbates,and the highest adsorption capacity was reached for carbon tetrachloride.Spherical active carbon from Japan gives the best adsorption ability,followed by the activated carbon made from apricot shell in Ningxia.The latter gave the most stable adsorption performance and was selected as the candidate adsorption material for the experiment of pilot-scale multilayer fluidized bed.2)Pilot-scale multilayer fluidized bed with internals was designed.The minimum fluidization velocity of the candidate actavited carbon powder is 0.05m/s,and its taking out speed is 11.6m/s.The operating gas velocity was selected between the minimum fluidization velocity and the taking out speed.Gas distribution plate with tapered cowl type and the built-in overflow were selected.Interlayer distribution boards are sieve plate with hole of 5mm diameter,and the aperture ratio is 13%.Meanwhile screw feeder and cyclone separator are chosen to ensure the fluidized bed can be operated stably.3)The hot mold experiments were made with the candidate activated carbon powder in the pilot-scale multilayer fluidized bed.The results show that gas velocity of 0.46m/s and interlayer built-in overflow weir of 2 cm are the best conditions.The temperature decreases from bottom to top.With the increase of inlet concentration,the absorption capacity of the activated carbon increases.And the adsorption efficency reaches above 97%.