ZL50活性炭吸附烟气脱硫过程的内扩散机制及其动力学模型

Intraparticle Diffusion Mechanism and Kinetic Models of Adsorptive Flue Gas Desulphurization by ZL50 Activated Carbon

为考察扩散在炭法烟气脱硫中的机制和规律,用基于扩散的表观吸附动力学模型对烟气中不同SO2体积分数时动态吸附中的扩散过程进行了模拟和扩散机制分析。结果表明,SO2在ZL50脱硫脱硝活性炭内的扩散系数在10^-16-10^-13m^2·s^-1的范围内,扩散可能以构型扩散为主。颗粒内扩散模型随SO2体积分数增大和吸附时间推移预测性能提高;这说明SO2体积分数增加和吸附时间推移使得努森扩散比重增大,构型扩散比重减小,导致SO2扩散阻力比在催化氧化反应中克服更多活化能能垒阻力增加快,使扩散阻力在扩散反应总阻力中的比重增加。吸附过程的一种可能机制是从吸附前期的表面反应控制过渡到后期的扩散与表面反应联合控制。

In order to investigate the effect and rule of diffusion in the dynamic carbonaceous adsorption process of flue gas desulphurization, the SO2 dynamic adsorption process of artificial flue gas with different inlet SO2 volume fractions were modeled and analyzed by diffusion-controlled apparent adsorption kinetic models. The results show that, during the desulphurization and denitrification process, the values of effective diffusion coefficients of SO2 adsorbed by ZL50 activated carbon fall in the region of 10^–16-10^–13 m^2·s^–1, which indicates that these diffusions mainly belong to configuration diffusions. The results also show that the prediction ability and precision of those quoted intraparticle diffusion models increase with the increase of inlet SO2 volume fraction and the time evolution of adsorption; they are caused by the increase of the ratio of Knudsen diffusion part in the whole diffusion process and decrease of the ratio of configurational diffusion part. The above mentioned results indicate that the ratio of diffusion resistance in total diffusion-reaction resistances increases with the increase of inlet SO2 volume fraction and the time evolution of adsorption, which is caused by the decrease of active sites of ZL50 activated carbon and the phenomena of the increasing rate of diffusion resistance for overcoming the diffusion barriers in activated carbon particle pores faster than the increasing rate of the activation energy resistance for overcoming the activation barriers of the catalytic oxidative surface reaction at active sites of ZL50 activated carbon during SO2 chemisorption process. It may be concluded that the possible mechanism of the adsorption process discussed above is that, in the earlier adsorption stage, the rate-controlled step is surface reaction and in the final adsorption stage, the rate-controlled step transits to the combination of diffusion process and surface reaction