Experiments And Study On Chemistry Kinetic Mechanism Of NO Reduction By Pulverized Coal And Char Reburning

An experimental system had been developed which could simulate pulverized coal reburning process, equipments that was used to prepare char were designed and fabricated. Various size of pulverized coal and char were prepared for experiments, also their physical and chemical characters were experimentally analyzed.Various factors that affected the NO reduction efficiency at different reburning conditions were systematically and experimentally studied when blended coal char, blended coal, Datong bituminous, Xingtai lean coal were used as reburning fuel. The mechanism that how these factors acted on the reburning process was explained by using chemical kinetics theory, and the effect of char on NO reduction was analyzed. The main results of experimental studies and the innovations in the thesis were summarized as follows.1.When the primary oxygen concentration was in the range of 4%~6% and the reburning-fuel rate was in the range of 20%~25%, particle size of pulverized coal obviously affected the NO reduction efficiency; while for char reburning, when the primary oxygen concentration was in the range of 2%~4% and the reburning-fuel rate was in the range of 20%~25%, the particle size obviously affectes the NO reduction efficiency. At the same conditions, the finer the pulverized coal and char were the more NO reduction was.2.The best residence time of pulverized coal and finer char reburning was about 0.8s, but the bigger size char still had some NO reduction potential after 0.8s.3.With the increase of the reburning zone temperature, more NO could be reduced by char(1100℃~1400℃)and pulverized coal(1100℃~1300℃). For coals that contained more volatiles, reburning zone temperature had more obvious effect on NO reduction. For the same kind of coal, with the increase of reburning fuel fraction, temperature had more obvious effect on NO reduction.4.The primary oxygen concentration obviously affected NO reduction, especially when the reburning coal and char had bigger size.The main results of theory studies and the innovations in the thesis were summarized as follows.1.Kinetic equation that described the process of NO reduction by char reburning was developed, it showed that reaction rate of NO reduction by char was in inverse proportion to the square of particle diameter, and this was consistent with the experimental results.2.The NO reduction process during pulverized coal reburning was analyzed and studied on the basis of the chemical reaction mechanism at molecular level. Accurate models that describes the whole NO reduction process by pulverized coal reburning were brought forwarded, and 270 elementary reactions were contained in the model, also the dominating reactions were summerized.3.The mathematic models that comprehensively described the NO reduction process in entrained flow reactor using blended coal were developed. Energy equations about flue gas and pulverized coal, comprehensive chemical reactions models and the relative kinetic models were involved in the models, the NO reduction process is simulated in entrained flow reactor at the temperature below 1300℃, and the consistence between simulated and experimental results indicated the model was reasonable and reliable.