Simulation And Measurement Of Flue Gas Composition In The Furnace Of 350MW Tangentially Fired Boiler

In recent years,in order to meet more and more stringent NOx emission standards,power plants have generally implemented low nitrogen transformation on boilers.By strengthening air classification,the burnout air rate is increased and the generation of NOx is reduced.However,although strengthening air classification can reduce the generation of NOx,it will increase the main combustion area and restore its atmosphere at the same time,resulting in high-temperature corrosion of water wall and affecting the safe operation of the unit.To solve the above problems,this paper studies from three aspects:simulating the temperature field,velocity field and component distribution in the furnace before and after low nitrogen transformation of the boiler;Simulate and adjust the air distribution of boiler after low nitrogen transformation to improve the high temperature corrosion of water wall;Actual measurement CO/H₂S and NOx in the boiler.This paper takes a 350MW tangentially fired boiler as the research object,and carries out numerical simulation based on the actual size and on-site operation parameters of the boiler before and after low nitrogen transformation.The results show that increasing the number of burnout air nozzles and increasing the burnout air rate from 27%to 40%through low nitrogen transformation can reduce the oxygen content and temperature in the main combustion area and inhibit the formation of nitrogen oxides,but at the same time,it will increase the concentration of reducing gases CO and H₂S in the main combustion area,resulting in high-temperature corrosion of water wall,Affect the safe operation of the unit.By adjusting the air distribution,the high-temperature corrosion of the water wall can be slowed down to a certain extent.This paper simulates that the burnout air rate of the boiler after low nitrogen transformation is reduced from 40%to 35%and 30%respectively.It is found that decreasing the burn out air rate from 40%to 30%can reduce the reducing gas concentration in the main combustion area,but it will greatly increase the NOx generation.Reducing the burn out air rate from 40%to 35%can reduce the reducing gas concentration in the main combustion area without significantly increasing the NOx generation.Increasing wall attached air is an effective measure to improve the high-temperature corrosion of water wall.Based on the position that the high-temperature corrosion area of the boiler is mainly located between UAP2 nozzle and SOFA3 nozzle,the influence of installing wall attached air nozzles on both sides of UAP2 nozzle on the concentration of reducing gas in water wall area is simulated.Aiming at the common problem of high-temperature corrosion in power plants,this paper designs a set of on-site measurement system of CO near the water-cooled wall.The system extracts the flue gas near the water-cooled wall into the measuring instrument in CEMS room through constant current dilution and extraction sampling technology.The way of constant current dilution and power tracing can reduce the dew point of flue gas and prevent the flue gas from condensing in the extraction pipe.The measurement results show that the concentration of reducing gas in the furnace is related to the boiler load.When the boiler load is high,the concentration of reducing gas in the furnace is high.This paper introduces the NOx instrument developed based on the principle of ultraviolet difference,studies the advantages and disadvantages of the in-situ NOx instrument and the problems encountered on site,and puts forward solutions to the problem that the condensation of ammonia bisulfate at the denitration outlet affects the optical path due to the low flue gas temperature in practical use.The ammonium bisulfate droplets are removed by installing a resistance wire outside the measurement module to ensure the measurement accuracy.