Research Of HBr Modified Fly Ashes On Elemental Mercury Adsorption Properties And Mechanism

Coal-fired power plants are deemed to be one of the main anthropogenic mercury pollution emission sources which can do great harm to people and the ecology health. In this thesis, the hazards of mercury pollution to huaman body and the ecological environment, the main emission resourcesand and conditon are briefly introduced. Mercury emmission technology both in domestic and abroad. Activated carbon injection technology is proved to be an efficient method to control the mercury emmission in flue in coal-fired power plants.However, the cost of injection and the reuseof the of bypruducts hamper its application. Currently, a large number of studies point that fly ash may be a potential,low cost mercury adsorbents. Fly ash mercury removal technology has been widely studied.This article sumrized the adsorption theories and progress about fly ash. Based on these knowledge, this thesis decided to exploit fly adsorbents by modified different kinds of fly ashes with hydrogen bromide in the method of impregination. Adsorption experiments of this adsorbents were conducted in the fixed bed apparatus to evalute the adsorption properites. Temperature programmed decomposition desorption system which was refited from Lumex RA915 was occupied to analyze the mercury speciation in the original fly ash samples and the modified fly ash after adsorption experiment, so the mercury transmission process in the flue and the oxidation and adsorption mechanism by the modified fly ash could be studied.Five kinds of fly ashes were used in this thesis, three kinds of pulverized bituminous coal ash and two kind of circulating fluidized bed furnace bituminous coal ash. All collected samples used in this study were ground in a ball mill for 2-3 minutes, and then sieved to less than 200-mesh. The impregnation method was utilized to modify the fly ash samples. Lots of analysis were conduct to the samples such as SEM/EDS, BET,IC and TGA to exmine changes in microstructure and stability.The adsoption results revealed that, of all the five kinds of original fly ash samples FA0008 and FA0011 had higher mercury. The adsorption properities significantly correlated with the content of the unburned carbon. Adsorpton capacity of the modified fly ashes had positive correlation with HBr modified concentration,but not exactlya liner relationship. The adsorption performance of FA0008 and FA0011 modified fly ashes had improved significantly, especially FA0008, whose adsorption capacity could research 104479ng/g, nearly 100 times higher than that of the original. Thus it could be an potential alternative for activate carbon. The mercury speciation in original fly ash samples were mainly HgCl2,HgS and HgO, part of the fly ash contains only one or two of the forms. The mercury speciation the HBr modofied fly ashes adsorped depended on the boiler type.Speciation in modified ash obtained from PC boiler were mainly HgBr2 and HgO, in proportion of 2:1, the adsorption process was in accordance with Langmuir-Hinshelwood and Eley-Rideal mechanism; speciation in modified ash obtained from CFB boiler were mainly HgS and HgO, the adsorption was in accordance with Mars-Maessen lattice oxidation theory.