Numerical Investigation For Syngas Co-firing Characteristics And NO_x Emissions In A Coal-fired Boiler

Syngas co-firing with pulverized coal power generation technology not only can reduce the consumption of fossil energy,but also improve the utilization of clean renewable energy.Based on a 330 MW tangentially coal-fired boiler of Junlong power plant in China,the process of syngas co-firing with coal is studied and the co-firing characteristics are analyzed.The main research contents are as follows:(1)The process of syngas co-firing with coal is devised according to the thermal performance parameters and structural dimension of a 330MW coal-fired boiler.The model construction and process of grid and boundary conditions are completed using Gambit software.And under the conditions of air staged combustion,SOFA reverse tangent and variable load operation,the processes of pure coal combustion and co-firing are simulated using Fluent.Moreover,the flow of syngas is treated as secondary combustion flow under co-firing conditions.Ultimately,the combustion characteristics of the furnace under different conditions are obtained,and the accuracy of the simulation results is verified according to relevant experimental data.(2)Based on the combustion conditions of pure coal without SOFA,the effects of increasing SOFA air ratio and co-firing syngas on boiler combustion characteristics and products are studied.The five conditions are as follow:coal-fired boiler without separated over-fire air(SOFA),with SOFA(15%and 20%air ratio),with SOFA(15%and 20%air ratio)and co-firing pine syngas meanwhile.The results show that,in cases without SOFA and with15%SOFA,the flow field in furnace stays stable.In the case with 20%SOFA,however,SOFA tangential circles become worse.At the outlet,compared with coal-fired cases without SOFA,the emissions of NO_x decrease by 10.76%and 13.28%in coal-fired with SOFA cases,as well as 26%and 28.4%in co-firing with SOFA cases.(3)In order to overcome the problem of residual flue gas rotation caused by the tangential round burning method,the effects of different SOFA reverse tangent angles on boiler combustion process and outlet cross-section flue gas temperature,velocity and thermal deviation in cases co-firing pine syngas are studied.The main four cases are as follow:the reverse tangent angles of SOFA are 0°10°,15°,20°.The results show that,variable reverse angle has little effect on combustion region.When the SOFA begins to reverse,the residual tangential circle of flue gas dramatically reduces at the outlet.Moreover,the distribution of flue gas at the outlet section is the most uniform and the speed deviation and thermal deviation are minimized under the angle is 15°.(4)Under the condition staying the intake volume of pine syngas constant,the effects of co-firing pine syngas on the combustion characteristics and NO_x emissions under the variable load are studied.The three cases studied are as follow:330 MW load case,300 MW load case,250 MW load case.The results show that,with the load decreasing,the co-firing ratio of pine syngas will increase and the combustion of the furnace stays stable.At the outlet,compared with 330 MW load case,the NO_x emissions decrease respectively by 12.61%and 26.89%under 300 MW case and 250 MW case,and the uniformity of flue gas distribution is improved.