Experimental Study And Its Process Simulation Of Vacuum Desorption And Pressure Swing Adsorption Processing Of Volatile Organic Gases

The pressure swing adsorption (PSA) is one of the primary methods of treating and recycling volatile organic compound (VOC). The paper researched on the mass and heat transfer of vacuum pressure swing adsorption (VPSA), focusing on the vacuum desorption process which is a difficult point and often simplified as the inverse process of adsorption in the previous documents. The study included two parts. One was building the model coupled with heat and mass transfer to analyze the interreaction of heat and mass transfer and simulating the mass transfer process of acetone desorption from activated carbon. The other one was the experimental research and simulation of VPSA process of multi-component VOC.Firstly, the LDF model and Langmuir model were used to analyze the interreaction of heat and mass transfer coupled with heat and mass transfer and the principle of conservation of quantity and energy. It was found that heat transfer had little influence on mass transfer because of the little change of temperature. The higher desorption vacuum degree and the larger initial adsorption quantity of desorption led to the smaller desorption rate, which was attributed to the affect of capillarity of micropore in the adsorbent and the interreaction of the heat and mass transfer in the process of desorption. The changing process of the desorption concentration contained three phases: vacuum concentration, rapid attenuation and slow attenuation. Because of the little influence caused by the temperature changing, the mass transfer coefficient of LDF was mainly affected by the change rate of adsorption quantity through concentration. The adsorption isotherm showed that the change rate of adsorption quantity through concentration was much different in low concentration and high concentration, but it was nearly linear in low concentration and high concentration respectively. The influence of the coefficient of mass transfer on concentration was various in different phases of desorption, so it made the calculated value of simulation fit the experimental data well by selecting different coefficient of mass transfer or coefficient of axial diffusion. For the same initial adsorption quantity, the greater the partial pressure of acetone led to the larger the coefficient k of mass transfer, and the omission of the coefficient of axial diffusion of desorption was not suitable. Secondly, the dynamic and energetic characteristics of the organic gases of toluene and acetone were analyzed by experimental study and the concentration distribution of the equilibrium state was discussed. It was found that the concentration in the latter half of adsorption bed was not monotonely decreasing, and it was likely to maintain and even increase as desorption time increasing. The results of simulation fit the experimental data of the first half of adsoption bed better than which of the second half. Then the change of the concentration distribution in the bed in steady state was simulated and analyzed. The optimal operation timing of VPSA was obtained by the model. The fixed operating parameters were 21.5℃, the adsorption feed concentration of acetone(58.478g/m³) and toluene (18.014 g/m³), two 5s pressure equalizing time and 10s blowdown time. For 300s adsorption time, the optimal desorption time was 155s. And then for acetone, C_desorption/C_o was 5.53 and C_purify/C_o为0.10. For toluene, C_desorption/C_o was 2.58. For 60s desorption time, the optimal adsorption time was 165s. And then for acetone, C_desorption/C_o was 4.93 and C_purify/C_o为0.10. For toluene, C_desorption/C_o was 2.98.