Study On Effects Of Biomass Addition On Formation Of Particulate-bounded Mercury From Coal Combustion

Mercury, the only metal in liquid form at room temperature, is volatile but chemically stable at normal conditions of ambient temperature and pressure. Usually, in oxidized or amalgam forms, mercury presents in earth crust with an average crustal abundance of0.08ppm. But in the past few decades, anthropogenic mercury emissions into atmosphere have been widely observed in large quantities. Mercury released into the environment is a persistent and toxic pollutant that may accumulate in food chain and finally cause health problems to humans, and more severe problems to nervous system of a child. Therefore, it is necessary for mercury emission control. In order to promote formation of particulate-bounded mercury during coal combustion process and to facilitate mercury emission control by particle control facilities, this study begins with the key reaction chains for homogenous and heterogeneous oxidation of mercury related to chlorine, and chlorine concentrations in a coal were adjusted through adding biomass so as to reestablish chemical balance between fly ash and gas generated by coal combustion. In this study, three kind of biomass including soybean straw, saw dust, and cotton stalk were added into a lean coal and two bituminous coals. These mixtures were then sent into a one dimensional electric heated entrained flow reactor, in the exit of which the generated fly ash was collected and its carbon content, BET surface area and mercury content were measured. Concentrations of mercury, chlorine and ash particles in the flue gas were also calculated. Experimental results showed a clear N shape curve in each different kind of coals. Maximum capacity for mercury adsorption of a generated fly ash is determined by the coal itself not the added biomass. Bituminous coal has a relative larger capacity and as large as80%of the mercury that entered into the reaction system is transformed into particulate-bounded mercury Lean coal usually has a two times larger carbon content than bituminous coal as well as concentrations of particle, however its total capacity is limited and less mercury is capture by its fly ash and the value of the maximum portion of particulate-bounded mercury in the total mercury is nearly70%. In the view of chemical kinetics, different convert efficiency is probably to be the profile of the final result of the competition-between chlorine relative reactions that have different temperature windows. High proportion of particulate-bounded mercury can be only obtained when biomass and coal is perfectly matched.