Mass Transfer And Heat Transfer Of Pressure Swing Adsorption Treatment Process Of Volatile Organic Compounds

This dissertation studies the technologies of the VOCs treatments by Pressure Swing Adsorption (PSA) and the tendency of the technologies. Based on the summarized simulation and experimental theories, this paper mainly focus on mass transfer and heat transfer of the adsorption and PSA treatment of Volatile Organic Compounds (VOCs). In accordance with the characteristic of pressure swing adsorption process, the appropriate mass balance equations, energy balance equation, equation of adsorption equilibrium and mass transfer rate equation for these studies were erected. The coupled mass transfer coefficient equation because of Linear Drive Force (LDF) pricinples was built and the parameters used in the series of equations were calculated and analysed.The adsorption properties of multi-component organic vapor made up of toluene and acetone on activated carbon at different temperature were studied by experiment. The experiment results were compared to the extended Langmuir equation, which showed a good accordance. And the competition adsorption of acetone and toluene was investigated by extended Langmuir equation. The results showed that the activated carbon owned a higher selectivity of toluene and the selectivity was influenced by temperature.A system with two columns was used to study the pressure, temperature, gas phase adsorbate concentration and gas phase adsorbate concentration of two columns five steps PSA treatment, whose cycle time is 606s, of the organic gas made of toluene and acetone.According the erected adsorption and PSA models, programs based on chemical software Athena Visual Studio were developed. The experiment of adsorption and PSA process were simulated by finite difference method. And the experiment results were compared to simulated results. It shows: the pressure of the absorption and desorption steps could be considered as a constant; the pressure changes of pressure-equal steps could be neglected.The height owning greater change is the main zone of mass transfer zone (MTZ).The shifting rates of the MTZ changes as the PSA process going. Temperature curves at different height changes as the cycle numbers change. During the early time of the PSA treatment of VOCs, the shifting rates are slow, then as the PSA process going ,the rates are increasing .It need 260h to make the column (φ50,1200mm height)reach a steady state.As the height of the adsorption columns increase, the gas phase adsorbate concentrations decrease .The concentration cures of acetone of different adsorption moment at different height appear a peak at different time due to the competitive adsorption. And the time of the peak appearing to go forward as the adsorption moment grows until to disappear. Meanwhile, the gas phase adsorbate concentration of different adsorption moment at different height increase.The results show the condensed ratios of desorption gas of acetone and toluene at different desorption moments decrease as the PSA treatment for the mixture of acetone and toluene going, and the ratios of acetone are higher than toluene's; and the condensed ratios of desorption gas of acetone and toluene decrease as the value of desorption moment increase.The purification results of acetone and toluene at different adsorption moment decrease as the PSA treatment for the mixture of acetone and toluene going, and the purification results of toluene are better than the purification results of acetone.Based on the results above, for the specialized PSA proces of specialized working conditions, the best time lengths of different steps of the particular PSA process were confirmed as follows: adsorption step, 200s; blow desorption step, 20s; vacuum desorption step, 180s; pressure equal step, 2s.