Elemental mercury adsorption characteristics and its kinetics over biomass chars

摘要

Four kinds of biomass (called peanut shell (PS), corn stalk (CS), wheat straw (WS) and wood chips (WC)) chars werernprepared by pyrolysis, impregnation with solutions of KCl, KBr and KI, and steam activation. The mercury adsorption was carriedrnout in a fixed-bed reactor with a quartz tube to study the effects of biomass species, pyrolysis temperature (T_p = 573~1173 K),rnsuperficial velocity (V = 9554~31847 h~(-1)), impregnation reagents (KCl, KBr, KI) and steam activation on elemental mercury (Hg~0)rnadsorption characteristics. The results indicated that the mercury adsorption capacity of unit mass of pyrolyzed biomass charsrnshows the pattern of decrease first and then increase with increasing adsorption temperature, and biomass chars pyrolyzed at 873 Krnbehaves the best adsorption characteristics. Mercury adsorption capacity of pyrolyzed char impregnated with solutions of KCl, KBrrnand KI was enhanced significantly. Steam activation can further improve the pore structure and promote the mercury adsorption.rnThe mercury adsorption capacities of the same biomass are ordered as: all-modified char > impregnated char > steam activatedrnchar > pyrolyzed biomass char. The maximum mercury capacity of all-modified biomass char (PS873-KI(3%)-A) at T_a = 413 K andrnV = 19108 h~(-1) is 29.14 μg/g. The kinetic parameters during mercury adsorption process were obtained by pseudo-first order model,rnpseudo-second order model, Fick’s intra-particle diffusion model and Elovich model based on fitting the mercury adsorptionrncurves.