| With the increasing depletion of coal, oil and other energy resources, biomass energy has been widely used in all aspects of human life as it is the only renewable carbon source; The amount of NOx produced by biomass combustion is not negligible and its efficient conversion and clean utilization has been widely concerned. Biomass briquette fuel is a kind of biomass energy, it is formed by crushing, drying, mixing and extruding of the agricultural and forestry wastes. It has the characteristics of small volume, convenient transportation and stable efficienc combustion. At present, the coal combustion technology utilization in the utilization process of biomass fuel and not pay attention to NOx emissions due to the lack of research on the combustion characteristics and NOx emissions of biomass briquette, then caused problems of low fuel utilization efficiency and environmental pollution. Therefore, it is very important to study the combustion characteristics and NOx emission characteristics of biomass briquette fuel.The TGA experiments and fuel properties analysis of biomass briquette in Guangdong was carried out at different heating rates. The results show that, the obvious weight loss occurs in the range of 450 K to 850 K and is mainly in the stage of pyrolysis. With the increase of heating rate, the maximum weight loss rate point moved to the higher temperature side, the maximum weight loss rate increased, combustion characteristics index increased as well as combustible characteristics index and burnout characteristics index, in favor of ignition and burn-out of biomass briquette. Reaction order of the pyrolysis zone is higher than that of the char combustion zone. Activation energy of the pyrolysis zone is less than that of the char combustion zone and they didn’t changed obviously, they are 88.32~103.80 kJ/mol and 101.31~123.72 kJ/mol, respectively.For moving grate-firing furnace, simulations of biomass briquette were divided into in-bed and out-of-bed models. Modeling in-bed fuel combustion by means of the finite element method combined with fuel characteristic data, and the simulation provide the gas temperature and compositions leaving the bed top, which are then used as the inlet conditions for the out-of-bed simulation of FLUENT. The results show that, it may be useful to improve the combustion efficiency of biomass and reduce the heat loss of flue gas by segmenting air distribution. The combustion of the combustible gas in the chamber forms a high temperature zone of 1000 K. Changing the length and height of the furnace arch, getting the optimized furnace arch structure that is suitable for the combustion of biomass briquette.Establishing an appropriate NOx production and decomposition model is of practical significance to the grate firing of biomass fuel. The CHEMKIN software package is used to simulate the combustion process of biomass pyrolysis and char combustion. Through rate of production(ROP) analysis and simplification based on reaction kinetics model GRI-Mech3.0, the reaction mechanism of volatile-N and char-N converting into NOx were specified. In contrast to previous models, which converts char-N directly into NOx, such as De Soete model, char-N was precipitated as HCN and NH3 in this model. It could be seen that intermediate elementary reaction of biomass fuel-N transfer process and that of coal fuel-N transfer process were different. Modeling a NOx production and decomposition model of the biomass fuel nitrogen in grate furnace firing with the reduction reaction of N2 O and NO by hydrocarbon substances and char. This model could not only describe combustion characteristics accurately, but also saved computation time significantly. |
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