Combustion Mechanism Of Super Fine Coal And Its Surface Chemical Research

Pollutant NOx emission is an increasing threat to environment and human health, which becomes an urgent problem to be solved. Coal combustion in power plant is a major source of NOx. Many control methods have emerged as the times require for solving the NOx emission problem. One of these is fuel returning. In this paper, micronized coal powder returning technology is brought forward and a series of exploring research work is carried out aiming at the key issues of fuel returning such as NOx reduction efficiency and burnout rate.First research on physics,surface, pyrolysis and combustion characteristic of super fine coal is processed in this paper. The results of the change tendency of pulverized coal character with particle size are got from particle size determining test, hole structure analysis test and TG analysis test, which provide theory basis for NOx reduction research with super fine coal returning. The coal pyrolysis can be divided into two main stages(lower and higher temperature stage). The two stage had a great difference in kinetic parameters and mechanism function.. The experimental results show that the coal pyrolysis is strongly affected by heating rate and particle size. As the particle size decreases, the temperature of volatile matter initiation of the coal sample decreases and the maximum rate of mass loss increases.As the heating rate increases, the temperature of volatile matter initiation increases, the total volatile matter evolved decreases and the DTG peak shift to higher temperature. The combustion process of different size coal samples was studied by Thermogravimetric analysis, the refining of coal particle have better ignition and burnout. The combustion process was divided into high and low temperature two regions to analysis, and find that activation energy of high and low temperature region decrease with the refining of coal particle, and decrease ratio is related to coal itself and its surface texture. Moreover, by analying TG,DTG curve of different heating rate from the same particle size, this paper find that with the heating rate increase the activation energy of combustion creation decrease and the samples have lower ignition temperature, but there is some difficulties in burnout of the pulverized-coal.Fixed bed was used to study the effect of particle size and temperature on NO absorption characteristic on coal char surface. Meanwhile, in the adsorption process, using the method of fixed bed penetration curve, adsorption experimental equipment has been set up to gain adsorption equilibrium and experimental data. A Theoretical model was based on mass transfer and sorbent surface reaction process and developed to predict NO adsorption characteristics on coal char surface as determined in laboratory fixed-bed reactor tests at different conditions.After a lot of survey and careful design work, a one-dimensional test system with fuel rebuming is built up. The temperature is controllable and resultant and reductive process of NOx can be simulated in furnace, which provide test basis for NOx reduction research with superfine coal reburning. Using this system, research on NOx emission of the test facility are carried out. The results of influence on NOx emission by coal particle size, furnace temperature, excess air and O2 concentration are reached through tests. Then super fine coal reburning tests are processed, which show a remarkable effect results on NOx reduction. The finer the pulverized coal were, the more NO reduction was. The NO reduction efficiency is increased with increasing burning-fuel rate. The primary oxygen concentration obviously affected NO reduction. As the primary oxygen concentratio is increased, the reburning efficiency is decreased. The reburning zone temperature had more obvious effect on NO reduction. In our experimental condition, with the increase of the reburning zone temperature, more NO could be reduced by pulverized coal.The evolution of functional groups and chemical changes on coal char surface structure and Quantum Chemistry theory was used to study NO adsorption on the char surface . The particle size has a noticeable effect on the magnitude of the changes and this effect was observed in the nitrogen functional group on the surface of the coal char. The surface of the coal char after reaction increases its N-5, N-6,–NO, pyridine-N-oxide, and -NO2 functional group content with decreasing particle size. The heterogeneous mechanism on the NO reduction during pulverized coal returning was analyzed and studied on the basis of the chemical reaction mechanism at molecular level. Two processing ways of N2 generation and the heterogeneous mechanism on the NO reduction were contained, also the dominating reactions were summerized. One process for the formation of the N2 is the reaction between NO molecule adsorption on coal char and following NO molecule; another process is the reaction between NO molecular and N-6 functional group on the coal char surface. Based on Quantum Chemistry theory and Organic Chemistry mechanism of organic sulfur in coal through pyrolysis is studied in this theory, the release paper by Quantum Chemistry Calculation, hoping to establish theoretic base for coal reburning mechanism.