Study On High Temperature Coal Gas Cleaning

The integrated coal gasification combined cycle (IGCC) is a new power-generation scheme and a promising technology of coal cleaning technology (CCT). High temperature coal gas cleaning is one of key links to realize its higher efficiency and less pollution. The HCl-removal and the removal of alkali metal vapor from high temperature coal gas are not only a significant part of high temperature coal gas cleaning but also an important subject of new fired-power generation technologies into the 21-st century.In this paper, a new type of HCl-removal sobent GH1 for high temperature cleaning of coal gas was self-made in the lab. The sorbent made of a natural mineral, Ca(OH)2, Na2CO3 and NaHCO3 has high breakthrough chlorine content of 37.2% (in the condition of 650℃,2500 h-1 space velocity and 1800 ppm HCl input concentration) and high mechanical strength. It can be applied to practical industry. In addition, the effects of process factors were investigated. The experimental data obtained from HCl-removal were analyzed by a model based on fixed-bed reactor and shrinking core models. It was found that reaction between sorbent and HCl vapor is of first-order with respect to initial HCl concentration and the apparent activation energy is 10.9 kJ/mol. The adsorption process is governed mainly by chemical reaction, but the effect of the product layer diffusion cannot yet be neglected. Results of the distribution of chlorine in the sorbent bed indicated that sorbent in the upstream end of the bed is nearly saturated with the chlorine whereas sorbent in the downstream end only contains less than 1wt% chlorine.Six nature minerals and six self-made sorbents were used to remove alkali metal vapor in a self-made alkali metal vapor removing apparatus. Results found that kaolinite, activated alumina and self-made sorbent GM6 are very efficient for alkali metal vapor removal. The effects of temperature and gas volume of flow on sodium content were examined. Based on fixed-bed reactor model, adsorption process of alkali metal vapor on kaolinite and activated alumina under N2 without water vapor was found to be influenced by both adsorption reaction and diffusion of a sodium resultant layer from the kinetics. The adsorption of GM6 under N2 without water vapor is a physical adsorption controlled mainly by the product layer diffusion and under N2 with water vapor it is mainly a chemical adsorption controlled by both chemical control and the product layer diffusion. Results of XRD and SEM also indicated that the adsorption process of activated alumina under N2 is physical adsorption with multi-molecular layers. The adsorption process of GM6 is physical adsorption under N2 and is chemical fixation in the presence of water vapor based on the information of XRD. Results of atom absorbing spectrum and electric potential titration proved that the adsorption process of kaolinite, activated alumina and GM6 is physical adsorption under coal gas.