Sorbent technology for trace metal emission control during the combustion of coal

摘要

Experimental studies were carried out to examine the effectiveness of sorbents (TiO_2, calcium hydroxide and calcium carbonate) on the emission control of arsenic during the combustion of three Chinese coals. The effectiveness of these sorbents was tested on an electrically heated drop tube furnace at temperatures ranging from 850～1250℃. The concentrations of As and collected submicronmeter particles size distributions were measured at different operating conditions. The observed experimental results indicate that all three sorbents tested are capable of effectively capturing arsenic, whereas different sorbent have different capture capacity and the capture mechanisms are different. The injection of TiO_2 sorbent is demonstrated to decrease the nucleation rates and increase the resultant mean size of coal combustion aerosol by promoting condensation on agglomerated aerosol particles and to be a relatively effective sorbent in capturing of trace metals. The capture mechanism of calcium-based sorbents seeme to be controlled by chemical reaction of Ca with vapours of trace metal compounds. In addition to the experimental investigations, potential arsenic-sorbent reactions were also identified through chemical equilibrium calculations based on the minimization of system free energy. Results from thermodynamic equilibrium simulations suggest the formation of metal-sorbent compounds such as calcium arsenate.