Numerical Study Of Biomass Combustion Process In A Grate Incinerator

China has abundant biomass resources.According to statistics,the production of crop straw in China is about 600 million tons per year.Utilizing biomass to generate electricity has both environmental and social benefits.In order to solve the common problems in the actual operation of a 130?t/h biomass grate boiler and provide theoretical guidance for the operation of the boiler,computational fluid dynamics?CFD?simulation approach was applied in this research to investigate the effects of the flue gas recirculation technology on improving biomass combustion process and reducing NO_x emissions.CFD simulation results show that flue gas injected with upper secondary air can improve the gas temperature distribution and increase the burnout rate by facilitating the gas flow disturbance in the upper furnace,and mitigate the fouling and slagging issues of the platen superheater by lowering and uniforming the gas temperature.When the lower secondary air is injectd with flue gas,it helps reduce the peak combustion temperature and inhibit the formation of thermal NO_x.As a result,by optimizing secondary air distribution with the flue gas recirculation technology,a more uniform burning condition is obtained and the NO_x emission has decreased by 32.1%compared to the original condition before the optimization.The sensitivity of the biomass fuel properties in the grate furnace was further investigated.The calculation results verify that the boiler has a certain degree of adaptability to the adjustment of the fuel.As the emission of NO_x is greatly affected by fuel nitrogen,it is suggested that biomass fuels with low nitrogen content should be applied in practical applications.Selective Non-catalytic Reduction?SNCR?process was calculated in the biomass grate furnace.The layout of SNCR injectors and the molar ratio of NH₃/NO_x?NSR?affected denitrification efficiency.SNCR simulation results showed that the DeNO_x rate was 34.2%when injectors were installed in the front and back walls of the furnace,while the DeNO_x rate could be increased to 43.2%when the injectors were arranged in the front and both side walls under the condition that NH₃/NO_x was1.5.When NSR increased from 1.0 to 2.0,the effect of NSR on denitrification efficiency decreased,while the of ammonia escape increased,so the recommended value for NSR was 1.5.