Study Of Evolution Behavior Of Fuel Bound Nitrogen During Biomass Gasification

Biomass is a kind of very important renewable clean energy. With the worse and worse situation of energy and environmental crisis, the effective utilization of waste biomass has become a key issue for the research and application of present renewable energy development in China. Fuel bound nitrogen (FBN) in biomass can be converted to molecular nitrogen or gas phase pollutants and pollutant precursors such as ammonia (NH3), hydrogen cyanide (HCN), and oxides of nitrogen (NOx) during the high temperature gasification, which have complex influences on the optimal design of biomass gasification systems and their pollution control. Therefore, the evolution behavior of FBN during gasification is becoming a hot topic that merits academic attention.In the present work, an extensive investigation on the evolution behavior of FBN during gasification is performed experimentally and theoretically. Firstly, a small-scale experimental equipment for fluidized biomass gasification is built, where·N2 content is analyzed based on the principle of nitrogen balance method. Based on elementary analysis, industrial analysis and GC analysis, the patterns of FBN existed in different biomass are obtained. Further, the experiment of biomass gasification under different operation parameters including gasification temperature, equivalence ratio, and biomass types is performed. The concentration of nitrogenous contents in gasification gas is obtained, based on which the main approach to the evolution behavior of FBN during gasification is summarized. Especially, the contribution of the conversion reaction between NH3 and N2 to the final process of the evolution of FBN is revealed.Secondly, a small-scale pyrolysis experiment of biomass is built. Based on an extensive pyrolysis experiment, the variations of the major nitrogenous volatilizezing contents are obtained under different operation conditions including the reaction temperature and biomass types. Further, the effect of the difference on the chemical structure of FBN in biomass is analyzed and compared with the results of the conventional coal pyrolysis. An important mechanism of the effect of the fact that the nitrogenous contents in biomass come mainly from the amino acid (the weaker C-N bound) on the evolution of FBN is revealed. In addition, the contribution of the formation of HCN and HCNO on the evolution of FBN is discussed. Considering the results mentioned above, a complete mechanism of the evolution of FBN during the gasification and pyrolysis is presented for the first time, which is of great significance to the application of biomass gasification systems.Finally, a preliminary reaction dynamic model on the evolution of FBN during the gasification and pyrolysis is presented, where 6 total chemical reactions including 31 kinds of components based on 70 elementary chemical reactions are considered. In order to improve the convergence of the whole calculation process, a self-adaptive fourth order variable-step-length Runge-Kutta method is introduced to make a numerical solution. A comparative analysis between simulated and experimental results is made aiming at some typical operation conditions and parameters. Then, the relationship between the nitrogenous contents, reaction temperature and equlivant ratio during the gasification and pyrolysis is analyzed. Further, a comparison of the evolution of FBN between oxygen and air is performed, and its differences in the nitrogenous contents as well as influencing mechanisms, such as the reduction of chemical reaction velocity caused by the decrease of concentrations of the component contents, the reduction of the surface activity of coal, and the prolong of the lagging time in O2, are discussed in detail. This is helpful to further understand the ultimate evolution behavior of FBN during the gasification and pyrolysis.