| Research Abstract |
As one of the cleanup technologies of fly ash including some heavy metals and chloride compounds, a roasting method is being developed. With the presence of toxic cations (Hg, Cd, Pb, Cr, Ni, and Co), high emissions level of these elements is induced by the recombination with Cl radical. Due to the environment pollution and corrosive problem, the emission of HCl has been a subject of concern in recent years. Most of research contents focus on controlling the emissions of HCl by improving combustion conditions and adding additives, however, a relative little attention is paid on the behavior of Cl_2. The main purpose is to investigate the behaviors of chlorine and chloride compounds. In addition, a detailed kinetic model of this reaction system is developed and validated against experimental results obtained from a flow reactor.
Cl radicals are originally produced from the collision reaction of HCl and O_2, which initiates the overall reaction process. Within a relative limited range of O_2 concentration, Cl2 concentration is increasing with O_2 concentration.
The reaction HC1+O_2→Cl+HO_2 is the main source of Cl radicals which initiate the chain reaction of this system. The Cl radicals generated at high temperature finally form HCl and Cl_2 during the cooling process. The two experimental results, increasing HCl and without H_2O, indicate that the formation of Cl_2 is more likely to proceed than the formation of HCl.
The experiments on heavy metals vaporization and partition with different chlorine content were performed in a drop tube furnace (DTF) with air condition. The chlorine concentration was controlled by the proportion of CaCl_2 in the experimental samples which were composed by SiO_2, Al_2O_3, PbCl_2, ZnO, CuO, CaCl_2 and Fe_2O_3. According to this result, more fraction of Cl makes Pb to vaporize easily and the suitable recovery temperature for Pb compounds is below 973K in this case.
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