Adsorption/desorption Behaviors Of Two Types Of Fixed-beds For Toluene

VOCs pollution has become one of the main problems of environmental pollution. Fixed-bed adsorption technology is the most widely used one of VOCs treatment technologies, because of its simple equipment and large elasticity of operation. This work is mainly involved with study working adsorption capacity of toluene on two types of fixed beds separately packed with honeycomb activated carbon (HAC) and granular activated carbon (GAC) and the relationship between bed pressure drop of the two types beds and superficial velocity of gas.A pilot fixed-bed adsorber was designed, and breakthrough curves of toluene in the fixed bed packed with HAC were measured at different adsorption conditions for estimation of working adsorption capacity of toluene. The results showed that the working adsorption capacity of HAC for toluene decreased rapidly with an increase in relative humidity (RH). At RH of 26%, the working adsorption capacity was about 7 times more than that at RH of 90%. And, both of bed thickness of HAC and superficial velocity of gas had great influence on its working adsorption capacity. As the bed thickness increased and the superficial velocity decreased, the working adsorption capacity increased, due to an increase in contact time between toluene and HAC. To achieve the maximum adsorption capacity, the contact time should be above 0.4 s.Breakthrough curves and working adsorption capacity of toluene on the fixed bed packed with GAC were measured at different adsorption conditions, and the similar results like the fixed bed with HAC were obtained. But, the working adsorption capacity of GAC for toluene increased first and then decreased with an increase in superficial velocity of gas.The relationship between pressure drop of the fixed beds and superficial velocity of gas was also discussed. The results showed that the bed pressure drop of fixed bed packed with GAC increased rapidly from 400 Pa to 3000 Pa, while the superficial velocity increased from 0.05 m/s to 0.3 m/s. However, the bed pressure drop of fixed bed packed with HAC increased slowly from 50 Pa to 300 Pa, while the superficial velocity increased from 0.4 m/s to 1.2 m/s. At flow rate of 30 m3/h, the breakthrough time and adsorption capacity of toluene in the fixed bed packed with GAC were separately 1.4 times and 2 times more than that in the fixed bed with HAC, when the bed pressure drops of the two types of activated carbon bed were at the same level.The effects of temperatures on regeneration efficiency of the fixed bed packed with GAC were investigated. The results showed that regeneration efficiency increased with an increase in desorption temperature. The regeneration efficiency of the fixed bed was up to 88% when desorption temperature was 195℃. And, the regeneration efficiency increased with an increase in gas flow rate.