Enhancement Of Mass Transfer And Absorption In WFGD By Molecular Dynamics Simulation

SO2emissions in coal utilization process is an important environmental factor that restricts China’s stable development. Further study in high-efficiency desulfurization technology is needed urgently to reach China’s latest target of energy saving and emission reduction and develop near zero emission technology. An effective method to optimize the existing limestone-gypsum wet FGD technology is to develop high-efficiency, multi-effect enhancement technology of mass transfer and absorption. Based on this, research on strengthening mechanism of mass transfer and absorption in WFGD was carried out by molecular dynamics simulation in this article.Firstly, both diffusion dynamics and dissolving mechanism of slurry components was studied. Diffusion coefficients of H2O, SO2, Ca2+, CO32-at temperatures between20℃-70℃and diffusion-activated energies were obtained by a series simulations. Radical distribution functions were analyzed to gain insight into the hydration structure and coordination number of SO2, Ca2+, CO32-in slurry and influence of temperature on their dissolving characteristics. The results show that the interaction between SO2and surrounding H2OS becomes greatest at the temperature of40℃and50℃, which means benefit for SO2absorption. Further analysis of interaction energy between SO2and slurry also shows that, slurry’s ability to "constrain" SO2becomes strongest at the temperature near50℃.Secondly, further study on influence of organic acid additive on solution properties was carried out, taking sodium oxalate, sodium malonate, sodium succinate, sodium glutarate, sodium adipate, sodium benzoate as representatives. The strengthening capacity of different additives in solution was compared in three aspects, including influence of additive on diffusing capacity of the components, influence of additive on dissolution of SO2and hydrolyzing capacity of the six additives. It was found that additive could effectively enhance the solution’s ability to "capture" and hydrate SO2.Finally, influencing mechanism of organic acid additive on air/liquid interface was studied, including influence of additive on structure of the air/liquid interface, distribution behavior of SO2and additive and strengthening capacity of additive on dissolution of SO2in the interface area. The results show that the strengthening capacity of additive on absorption of SO2refers to two aspects,(a) the distribution behavior of additive anion,(b) influence of additive anion on the interface thickness. A better one has a stronger feature to distribute in the interface and a smaller interface thickness of its solution.