Study On Combustion And Nox Emission Characteristics Of Gas-fired Boiler With Combustion Stabilizing Device

There is a rich blast furnace gas(BFG)production in steel industry.Effective and rational utilization of BFG is an important part of energy conservation and emission reduction in enterprises.In this paper,numerical simulation is employed together with combustion adjustment test to study problems in a 75t/h BFG and coke oven gas(COG)mixed-fired boiler with combustion stabilizing device,such as instable combustion,low thermal efficiency and high mass concentration of NOx emission.More details are as follow:Firstly,combustion processes of different COG blending ratio were experimentally investigated.Results showed that:when the blending ratio of COG increases,both thermal efficiency and NO_X concentration increase.When completely burning BFG,Thermal efficiency is lower and the mass NO_X concentration at exit is 35mg/m~3.However,it is 431 mg/m~3 when COG blending ratio is 40%.Considering the thermal efficiency and NO_X emission concentration,COG blending ratio to maintain about 20%,the thermal efficiency of the boiler is 88.84%and the concentration of NO_X emission is 152mg/m~3.Meanwhile,combustion processes of different COG blending ratio were numerically simulated.Results showed that:when the blending ratio of COG increases,the furnace temperature will rise.The NO_X concentration also increases with the COG firing rate elevating,which is because of the increase of furnace temperature,and the increasing extent is growing faster.Furthermore,the experimental data for NO_X concentration show a good agreement with the caculated results.Secondly,in the actual operating condition,distribution of velocity field,temperature field and NO_X concentration of the boiler with and without combustion stabilizing device were obtained and discussed.Results showed that:the combustion stabilizing device coupled with burners enables the flame to spun upwards around its side surface.After setting the device,the ignition distance of BFG is closer and furnace radiation capacity is stronger.The combustion stabilizing device can be used as the stable heat source,and strengthen heat exchange in the furnace.Finally,numerical simulations of variable load operation(100%?80%?60%and40%)and different excess air coefficient(?=0.9?1.0?1.1 and 1.2)were respectively carried out in the condition of 20%COG blending ratio.Results showed that:When the load decreases,the temperature level in boiler declines obviously,thus the NO_X generation is reduced.At 40%load,the highest temperature is 1371K,so the ignition and combustion stabilization of BFG need to be considered.The concentration of NO_X emission increases with the increasing of the excess air coefficient,but CO burnout ratio reduces with the decreasing of the excess air coefficient.Under the simulated conditions in this paper,the recommended excess air coefficient is 1.1.