| Ultra-supercritical coal-fired power generation is currently the most practical energy-saving and emission-reducing power generation technology.Ultra-supercritical coal-fired generating units are widely used because of their high thermal efficiency,low power consumption,and ultra-low emissions.However,in actual operation,the damper opening is adjusted by the operating personnel according to experience,and there is no effective optimization guidance method.Under some conditions,there is a contradiction between the low NOx combustion technology and the thermal efficiency of the boiler,which will cause the damper opening to deviate from the optimal combination.It is difficult to effectively control the pollutant emission while improving the thermal efficiency.At the same time,the conventional measurement technology can not measure the high temperature area of the furnace,which makes the operation personnel unable to understand the combustion condition in the furnace in time and accurately.Related research on the optimization of air distribution for ultra-supercritical wall tangential boilers this paper is carried out.The aim is to grasp the response characteristics of the secondary air volume of the boiler and the influence of the air distribution on the combustion process and pollutant emission in the furnace.Based on this,the optimization method of damper opening is proposed.A three-dimensional mathematical model of a 660 MW ultra-supercritical wall tangential boiler was established.A complete secondary air duct and each damper baffle are constructed on the physical model to study the influence of the air duct structure and the opening degree of the baffle on the air volume distribution.At the same time,a complete heating surface is constructed on the upper part of the furnace,aiming at accurately calculating the heat exchange amount between the flue gas and the heating surface,and obtaining an accurate flue temperature of the furnace exit.In the mathematical model,the Realizable k-? model is used to simulate the gas flow turbulent flow,the stochastic orbit model is used to describe the movement of pulverized coal particles,the P-1 radiation model is used to describe the radiation,and the two-step competitive reaction reaction model is used to describe the volatile matter.The dynamic-diffusion model simulates coke combustion,and the mixture fraction/PDF model simulates gas phase turbulent combustion.In this paper,the resistance characteristics of the damper baffle and the influence of the baffle opening on the damper flow are studied.On this basis,the damper opening degree is used as a means of adjusting the air distribution.Under the BMCR load,when the coal type is designed and typical commoned,the excess air ratio is 1.10,1.15,1.20 and 1.25,the wind speed of the primary inlet is 20m/s,23m/s,26m/s and 29m/s,the AA damper opening is 10%,40%,70% and 100%,the auxiliary damper opening is pagoda air distribution,equal air distribution,inverted pagoda distribution and air distribution,perimeter wind damper opening is 25%,35%,45% and 55%,coal mill combination is ABCDEF,ABCDE,ABCEF,ABDEF,ACDEF and the load is 660 MW,560MW,460 MW,the these variables affect the combustion characteristics and pollutant emission characteristics of the furnace.Based on the results of numerical simulation,combined with the actual operation of the power plant,100 sets of numerical tests were designed.The distribution of velocity field,temperature field and component concentration field in the furnace under various working conditions,as well as the temperature of the high temperature superheater outlet,the concentration of the components and the carbon content of the fly ash are obtained.Based on the numerical experiments,a method for optimizing the air distribution of boilers with high efficiency and low pollution is proposed.a sample database is constructed that combines actual operational data with numerical experimental data.A neural network model is constructed with variables such as load,excess air coefficient,coal quality characteristics,and air distribution mode as inputs,boiler combustion efficiency and NOx emissions as output boiler combustion characteristics.The genetic algorithm is used to optimize the efficient and low-pollution air distribution of the boiler..Based on numerical experiments,neural network model and genetic algorithm optimization method,the "Boiler Air Distribution Optimization System" is constructed and embedded in the DCS system of the target boiler,which is successfully put into operation at the site.The reliability and effectiveness of the system have been further verified by performing performance test on the target boiler.The results show that at 600 MW,500MW and 400 MW,the thermal efficiency of the boiler after operation is increased by 0.50%,0.51% and 0.52%,respectively,and the NOx emissions are reduced by 10.51%,16.68% and 16.72%,respectively. |
PDF Full Text Request