Numerical Simulation Of Flue Gas Denitrification In Selective Catalytic Reduction (SCR) Of Thermal Power Plant

Nitrogen oxide?NO_x?is one of the most important air pollutants,with the increasingly serious environmental situation in the world,China's environmental standards are increasingly stringent.In recent years,China's environmental protection departments of the thermal power unit NO_x emission requirements continue to increase,thermal power plant environmental protection pressures continue to increase.So the development of efficient,safe and economical denitrification technology has become a thermal power industry imminent problem.Selective catalytic reduction?SCR?flue gas denitrification technology has a high denitrification efficiency?up to 90%?,the impact of safe operation of the unit is small,the system composed of simple characteristics of thermal power units to reduce NO_x emissions of the primary choice.In this paper,the micro-reaction model was established from the micro-reaction mechanism,and the main factors affecting the efficiency of denitrification were analyzed.The reaction temperature,flow field uniformity and ammonia-nitrogen molar ratio had significant influence on denitrification efficiency.Then,600 MW supercritical coal The SCR denitrification system was used as the research object to establish the macroscopic model.The velocity distribution field,pressure distribution field,ammonia concentration distribution field and NO_x removal efficiency of SCR flue gas denitrification reactor of a 600 MW supercritical coal fired unit were established by FLUENT6.3 software,NH₃ escape rate and different particle size of fly ash particles were simulated by numerical simulation.First,the low-speed triangular region,the high-speed scour zone and the low-velocity recirculation zone appear in the reactor are optimized for different shapes of baffles.The simulation results show that the "arc","straight-arc-flat","arc-straight" and "straight" baffles can effectively inhibit flue elbows and variable cross-section flue gas velocity separation phenomenon.The standard deviation of the standard velocity of the first layer catalyst is reduced from 67.34% of the empty tower to 8.60%,which is lower than the design standard requirement of the 15%.Secondly,the NH₃ concentration distribution in the reactor was simulated by spray simulation.The simulation results showed that the concentration of NH₃ was larger due to the lower NH₃ concentration and the influence of the flow field uniformity.influences.When the velocity of the flue gas is low and the disturbance is small,the NH₃ concentration in the near wall is high,and the NH₃ concentration distribution of the first layer catalyst is not ideal.Standard concentration deviation Cn of 23.45%,much higher than the design requirements of 5%,denitrification efficiency is only 80.90%,NH₃ escape rate.In order to reduce the deviation of NH₃ concentration distribution,the denitrification efficiency was improved.In this paper,the ammonia spray was divided into three regions,and the ammonia concentration was adjusted by four kinds of ammonia injection schemes.Finally,The deviation of NH₃ concentration decreased from 23.45% to 4.73%,The NH₃ escape rate at the outlet of the reactor was reduced from 23.44uL/L to 4.57uL/L,and the effect of denitrification increased from 80.90% to 86.77% when the rate was sprayed.The optimized effect was significant.Finally,the motion characteristics and concentration distribution of fly ash particles under different particle sizes are simulated,which has certain guiding significance for rational arrangement of ash hopper and installation of sootblower.