Mathematical Simulation Of Adsorption Separation Of Benzene Onto Activated Carbon

Treatment of volatile organic compounds has become a hot issue in today's environmental protection field. Using adsorption technique, organic waste gases can be deeply purified; in addition, adsorption technique has the advantages of simple equipment, simple operation, and low energy consumption. Adsorption technique has been widely applied in purification and recovery of low concentration volatile organic compounds. Because of the complexity and the parameters'coupling of adsorption process, some key parameters are difficult to be accurately obtained through theoretical calculation, except being identified by experiment. This method is both time-consuming and uneconomic. Based on the premise, this work established the mathematical model, using numerical method to simulate the process of adsorption.According to the mass and heat transfer mechanisms of adsorption, mathematical models of adsorption and purging desorption processes of benzene on fixed activated carbon (GH-6A) bed were established. The axial dispersed plug flow model was applied to establish material and energy conservation equation; the Langmuir equation was used to define the adsorption isotherm model; the linear driving force (LDF) model was used to define the mass transfer rate model.Above-mentioned models were applied to simulate atmospheric adsorption and atmospheric, vacuum purging desorption processes of benzene on fixed activated carbon bed, exploring the dynamic distribution of benzene concentration and temperature on the bed and effects on benzene concentration distribution of different operating conditions. The results turned out that:At the atmospheric adsorption process, with higher inlet benzene concentration, higher temperature and quicker gas velocity, the column will be penetrated faster; the change of bed temperature with time was in normal distribution with the maximum temperature of 3K. At the atmospheric adsorption process, with higher temperature and quicker purging velocity, the benzene will be desorbed faster; the change of bed temperature with time was in normal distribution with the maximum temperature of 1K. At the atmospheric adsorption process, gaseous-phase benzene concentration distribution contained three phases:vacuum concentration, rapid attenuation and slow attenuation.In this part, hot purging desorption process was simulated. It explored the dynamic distribution of benzene concentration, the temperature on the bed, and the effects on desorption result of purging gas temperature and velocity. The results turned out that:At the condition of the purging temperature as 473.15K, the desorption rate of benzene reached 94.9%at 10000s; with higher purging temperature and quicker purging velocity, the benzene will be desorbed faster and the desorption rate of benzene will be higher.In this part, temperature swing adsorption process of benzene separation, which contained three phases of adsorption, hot purging desorption and cold purging, was simulated. It explored the dynamic distribution of benzene concentration, the temperature on the bed of different phases when the TSA process reached circulation steady-state, and the effects on TSA result of different operating time at different phases. The results turned out that:Main function of cold purge phase was to lower the bed temperature. With longer hot purging time, the benzene desorption rate will be higher, but the average benzene concentration in desorption gas will be reduced. With longer adsorption time, the benzene desorption rate will be higher, and the average benzene concentration in desorption gas will not be effected.The mathematical models consisted of a series of partial differential equations, which were calculated by method of line using software Matlab. Axial dispersion, heat effect and mass transfer resistance were taken into account in the models and they made the models more realistic.Using the mathematical models and solution Method, we could describe the general rules of adsorption and desorption processes clearly. It indicated that the mathematical models and solution Method are reasonable and they are instructive to the theoretical study of adsorption method.