Research On Low NO_x Combustion Characteristics Of Gas-fired Steam-Injection Boiler Based On Flue Gas Recirculation

In order to reduce the NO_x emission of YZG22.5-14/360-G Gas-fired Steam-injection Bolier,low nitrogen combustion using flue gas recirculation(FGR)technology has been studied,but little literature has reported that excess oxygen in circulating flue gas will also participate in combustion.In view of the fact that excess oxygen in circulating flue gas using flue gas recirculation technology is also involved in combustion,the volume of oxidant and the volume of flue gas will deviate from the actual situation.Firstly,investigation of YZG22.5-14/360-G gas-fired steam-injection boiler is carried out to obtain the structural parameters and operation status of the boiler.Then,thermodynamic calculation of the boilers was carried out,an iterative method for calculating the volume of oxidizer and the volume of flue gas is proposed in the thermodynamic calculation process.we must analyze these data error of the calculating results of oxidant volume and flue gas volume and total thermodynamic calculations of boilers,we also analyze the effects of FGR on the exhaust gas temperature,combustion efficiency,fuel consumption and theoretical combustion temperature.Finally,based on the investigation data and thermodynamic calculation results,the numerical calculation of the boiler is carried out by using ANSYS simulation software,and the effects of flue gas recirculation rate on combustion temperature,NO_x concentration,free radical concentration and CO generation are analyzed.The conclusions are as follows:the more volume of circulating flue gas,the larger the deviation between the volume of oxidant and the volume of flue gas and the actual situation.When the flue gas recirculation rate rises from 0%to 20%,the number of iterations that the volume of oxidant and the volume of flue gas reaching equilibrium state increases from 0 to 5times,at this time,the relative deviation of oxidant volume before and after iteration is4.29%,and that of flue gas before and after iteration is 3.86%.The fuel consumption without FGR technology is 1850.22 m~3/h,and the investigation data of steam injection station is 1952.71 m~3/h,the error between them is 5.54%,the simulation results of combustion temperature are higher than those of thermodynamic calculation,and the error between them is less than 100 K.FGR technology will result in the rise of flue gas temperature,the increase of combustion efficiency,the decrease of fuel consumption and the decrease of theoretical combustion temperature in the furnace.When the flue gas recirculation rate increases by 5%,the flue gas exhaust temperature increases by about 1?,the fuel consumption decreases by about 1.5 m~3/h,the maximum temperature of combustion in the furnace decreases by 2.9%,and the mass concentration of NO_x at the outlet of the furnace decreases by 11.6%.The volume fraction of CO produced by combustion in furnace is inversely proportional to the mass concentration of NO_x.In order to ensure perfect combustion of fuel in gas-fired steam injection boilers,the optimum cycle ratio of flue gas recirculation should be maintained at 10%~15%.At this time,the concentration of NO_x is 149.45 mg/m~3~129.64 mg/m~3,which less than the current NO_x emission limit of special emission 150 mg/m~3.