Numerical Simulation Of Combustion And Reversion In A Tangential Pulverized Coal-Fired Boiler

According to the present situation of large residual rotation at the exit of the furnace on tangentially pulverized coal-fired boiler,using the reversed tangential technology to improve the outlet gas temperature and gas velocity deviation has become an important research topic.Along with the development of numerical simulation technology,using numerical simulation software to study the flow,heat transfer,combustion and NO_x emission of the boiler is becoming more and more mature.In order to provide a theoretical reference for the design and modification of tangentially fired boiler,this paper uses numerical simulation software Fluent to simulate the calculation of a power plant in a 350 MW supercritical power unit,to study the different load of the boiler and the influence of over fire air reversed on the outlet gas temperature and gas velocity deviation on the tangentially fired boiler.The main research contents are as follows:1、Based on the structural characteristic and combustion characteristic of the 350 MW tangential firing boiler,the simulation object is simplified to build the numerical simulation model.The BMCR（boiler maximum continuous rating）conditions of aerodynamic characteristics,combustion characteristics and NO_x emission characteristics were simulated,and the air dynamic field,temperature field,concentration field and NO_x concentration field were analyzed.2、Considering the influence of platen superheater on the flow field in furnace,the platen superheater was simplified to build a numerical model with platen superheater.Using porous model to process the platen superheater.Simulation of flow field in furnace showing that gas flow through the platen superheater has additional momentum loss,which can improve the velocity and temperature deviation at the exit of the furnace.3、Based on the current situation of the variable load operation in power plant and combined with the operation parameters of power plant,analysis and comparison of the combustion and NO_x emission characteristics of four different kinds of load.It is concluded that with the boiler load decreasing,the furnace temperature and the outlet NO_x concentration are all decreased,the mass fraction of CO₂ is slightly decreased,but the change of the CO mass fraction is not obvious.As the low temperature condition in the boiler,ignition and stabilization of combustion problems need to be considered under 30% load.4、According to the present situation of large residual rotation at the exit of the furnace on tangentially pulverized coal fired boiler,using the over fire air reversed tangential technology to simulate the furnace combustion characteristics of different tangential angles.By comparing the characteristic parameters of the furnace relative tangential circle diameter,uneven index of the velocity distribution at the exit of the furnace and the rotation strength of outlet flow,etc.It is concluded that when the over fire air were 15° tangential reversed,it can effectively reduce the residual rotation of the airflow,decreased the uneven velocity distribution degree,weaken the deviation of the flue gas temperature at the exit of furnace.The research of this paper is beneficial to the design,operation and transformation of the tangentially fired boiler,at the same time it provides some reference for the variable load operations in power plant and the application of over fire air reversed tangential technology in tangential firing boiler.