Numerical Simulation Of Flow And Combustion Characteristics For Down-fired Boilers With OFA

The 660 MW power plant boiler in the study object of this paper is the production of Beijing Babcock & Wilcox company.This paper uses the FLUENT commercial software to study the furnace flow conditions,combustion and NO_x formation.The effect of OFA on hydridyanmics and combustion is simulated.For the calculation conditions,the OFA rate is different,the total air volume remained unchanged.By comparing the simulation results of the three cases: when the OFA ratio increased,the combustion of pulverized coal is getting worse;The oxygen concentration decreased,while the concentration of CO increased,NO_x emission concentration decreased;At the same time,fly ash combustible content increased gradually.We should consider the NO_x emission concentration decreasing,but also should take into account to fly ash combustible content,as well as the efficiency of the boiler and the operation of economy.Considering the analysis results of three conditions,the final selection of the OFA wind rate of 17% is the best program.The effect of blade angle on flow behavior and burning of pulerized coal is simulated.For the calculation conditions,the blade angle of the second air is different.By comparing the simulation results: when changing the blade angle of the second air,the oxygen,the CO in the furnace has small change,basically it does not change the furnace exit NO_x emissions;when the blade angle of the second air is increasesd,flame sweeping wall situation has improved,it is beneficial to reduce the coking in the down fired boiler;At the same time,flame center is getting near the furnace bottom hopper,it is useful for adjusting the furnace temperature.The adjustment of the blade angle of the second air,is usually used in the actual operation of the boiler,it should be setted different on each burner according to the actual situation.Finally,the research boiler of this paper has been put into commercial operation.By comparing field test data and simulate result,the model and simulation results is verified correct and reliable.