Numerical Simulation Research On Performance Of A 7MW Biomass Hot-wind Boiler

Grate-firing hot-wind boilers are usually used to produce hot air to dry grain.However,the existing coal-fired drying boilers have features of relatively small in scale,large number,and higher pollutant emissions.It is a general trend to make full use of biomass resources and develop biomass hot-wind boilers.For the chain furnace,its combustion must follow the 3T+E principle,namely Time,Temperature,Turbulence,and Excess air ratio.For the 3T+E principle,it is the furnace arch and the air distribution mode that play an extremely key role,so the air distribution mode and the arch is optimized to improve boiler combustion efficiency.In this thesis,by using FLIC+FLUENT software,a 7MW layer-fired biomass hot-wind boiler is used as the research object for numerical simulation research,the calculation was carried out under different air distribution modes and different shapes of arches:（1）The influence of the air distribution mode on its combustion performance:The calculation was carried out under three different air distribution modes,named as:front-enhanced,uniform and rear-enhanced mode.The flue gas components above the grate,the temperature field in the furnace and the nitrogen oxide concentration at the furnace outlet were analyzed.The calculation results show that the NOx emissions under the conditions of front-enhanced,uniform and rear-enhanced mode correspond to 133.5mg/Nm³,104.4mg/Nm³and76.6mg/Nm³,respectively,and rear-enhanced mode can enlarge the length of the reaction zone,thereby increasing the utilization of the grate,and increase the boiler combustion performance and decrease NOx emission.The results can provide optimization guidance for the actual operation of such boilers for grain drying.（2）The influence of the front arch parameters on its combustion performance:When the coverage length of front arch increases from 0.9a₁ to 1.1a₁,the average temperature of the front arch increases from 1075K to 1084K,and the outlet temperature of the furnace increases from1099K to 1112K.When the height of front arch increases from 0.9h₁ to 1.1h₁,the average temperature of the front arch decreases from 1099K to 1068K,and the average temperature of the furnace outlet decreases from 1121K to 1100K.（3）The influence of the rear arch parameters on its combustion performance:When the cover length of rear arch increases from 0.9a₂ to 1.1a₂,the average temperature of the front and rear arch increases from 1072 K and 1038 K to 1106 K and 1072 K,respectively,while the average temperature of the furnace outlet increases from 1102 K to 1124 K.When the height of the rear arch increased from 0.9h₂ to 1.1h₂,the average temperature of the front and rear arch decreased from 1081K and 1052K to 1073K and 1042K respectively,and the average temperature of the furnace outlet decreased from 1115K to 1101K.