The Characteristics Of NO_x Emission And Mechanism Study On NO_x Formation In Cement Precalciner

Large coal consumption in cement industry results in a significant NOx emission, and with the increasing prosperity of the cement industry in recent years, it has come to be one of major sources for NOx emission in addition to thermal power industries and the automobile industry. So how to deduct and control NOx emission in cement prodiction process has become a critical problem affecting the quality of atmospheric environment and the development of cement industry.Cement precalciner is one of the important equipment for NOx emission in cement factories. The objective of this work is to explore the characteristics of NOx emission and the mechanism of NOx formation on account for the special characteristics such as low temperature/high concentration of CO2/complex and astable atmosphere/ pre-decomposition of raw materials in cement precalciner. Experiments have been taken in the desigened gas-solid reactor to investigate the characteristics of NOx emission during coal combustion under cement precalciner condition. The mechanism of nitric oxide (NO) formation from the oxidation of hydrogen cyanide (HCN) during the combustion of volatile from pulverized coal under cement precalciner conditions has been studied in terms of a chemical kinetic model. All studies in this thesis provide the foundation of experiment and theory for the effectual strategy to control and deduct the NO emission in cement factories. The main contents of this thesis are as follows:Firstly, the characteristics of cement industry and the main source of NO emission in cement factories have been introduced. The significance of researches on the characteristics of NOx emission and the mechanism of NOx formation has been analyzed. Than the study situation on the characteristics of NOx emission and the mechanisim of NOx conversion dring coal combustion in ordinary pulverized coal fired boilers has been summarized. All the above contents provide the foundation of experiment and theory for the following experiments studies and kinetic modeling. And the main contents of this paper are put forward.The characteristics of NOx emission from coal combustion in cement precalciner has been investigated in a desigened gas-solid reactor under the suspension and spray condition of industry precalciner. Based on experiments stuies, the release characteristics of NOx emission have been obtained and the effect mechanisms of the special working condition such as high concentration of CO2 and the presence of cement raw meal in cement precalciner on NOx emission have been analyzed.The calculation principles/methods and models of kinetic modeling have been introduced which provide theoretical basis for the studies of detail kinetic modeling of NOx formatin, and the significance of kinetic modeling studies on the process of combustion has been analyzed. The development history of kinetic modeling studies and the main resesrch content of detailed kinetic study on combustion using Chemkin modeling have been summaried.The mechanism of nitric oxide (NO) formation from the oxidation of hydrogen cyanide (HCN) during the combustion of volatile from pulverized coal under cement precalciner conditions has been studied in terms of a chemical kinetic model. By using the rate of production (ROP) and pathway analyses, the detail kinetics modeling of volatile NO formation has been established and the specific chemical effect of high concentration of CO2 in cement precalciner on volatile NO formation was identified in different excess air coefficients during coal volatile combustion. Specifically,the major reaction pathways of volatile NO formation from HCN under cement precalciner conditions are identified. And the numerical results of this study proposed a theoretical guidance for effectual predictive control of NOx emission in cement precalciner.Finally, the whole research work was summarized and the prospects for the further studies on coal analysis were suggested.