Experimental Study and Modeling for In-Duct Mercury Capture by Sorbent Injection

摘要

In order to evaluate mercury capture performance of raw and bromine treated activated carbon, and investigate the influences of particle size, temperature, inlet mercury concentration, residence time, and sorbent feed rate on in-duct mercury capture efficiency, experimental studies on mercury capture by sorbent injection were carried out in an entrained flow reactor. The results show that in-duct mercury capture efficiency of bromine treated activated carbon is higher at 120 "C compared to raw activated carbon. This is owing to the increase of active site (Br) on activated carbon surface that improves chemisorption at higher temperature. Reducing sorbent particle size or increasing inlet mercury concentration can both speed up film mass transfer rate of mercury from gas to surface of the sorbent and rise intraparticle diffusion rate of mercury from surface to internal pores, which then improves mercury capture efficient. Longer residence time is beneficial to the mercury deposition on the inner pores. Due to sorbent residence time is far less than the adsorption equilibrium time, so mass transfer during mercury adsorption progress is recognized as adsorption rate controlling step. Higher temperature reduces physisorption ability leading to mercury removal capacity lowered. Increase of sorbent feed rate results in higher mercury capture, but reduces the mercury accumulative adsorption capacity per unit quality of sorbent. A comprehensive mathematical model, based on mass balance equation, mass transfer model and surface isothermal adsorption model, was established for predicting mercury capture efficient by sorbent injection. Sensitivity analysis of the model parameters was also conducted. The simulation results indicate that the model is capable of forecasting the mercury capture efficient and a good agreement between the modeled curves and the experimental data is obtained. So the mathematical model can be used to provide assistance in analyzing mechanisms for process of sorbent injection. The sensitivity analysis points out that sorbent feeding rate, particle size, adsorption constant K and sorbent residence time exert dominant impacts on mercury capture.