Numerical And Simulation On The Optimization Of Gas Solid Two-phase Flows In SCR Denitrification System

Selective Catalytic Reduction?SCR?denitrification technology accounts for about 90%of the denitrification project of coal-fired power boilers.The denitration reactor is the core component of SCR denitrification system.At present,in the design of denitrification system,only the heterogeneity of gas flow field is often taken into account,and the adverse effect of the unevenness of fly ash concentration in the system is neglected.When combusting the high ash content coal,it is likely to cause the catalyst hole blockage due to flue gas concentration in the flue gas in the back wall area of denitrification reactor,one will increase the denitrification system resistance to increase the use of electricity,the second is will increase pore flue gas velocity of the non-clogging catalyst,aggravate the catalyst wear to shorten its service life,and the third will reduce the denitrification efficiency due to the reduction of the effective area of the catalyst.Therefore,it is necessary to research the gas-solid two-phase flow characteristics of SCR denitrification system and optimize the distribution of fly ash concentration in denitrification reactor.According to the design scheme of SCR denitrification system of 2×130 t h^-1 boiler in a power plant,the whole system physical model was established.The gas-solid two-phase flow of the denitrification system was calculated by RANS-DPM method.The layout scheme of the rectifier components in the denitration reactor was obtained.The construction drawings of the rectifier are designed and applied to the project.The actual operation of the denitrification system shows that the system resistance<800Pa,denitrification efficiency>90%,the catalyst does not clog,indicating that the installation of rectifier components to improve the uneven distribution of fly ash.However,through on-site measurements,it was found that the distribution of fly ash at the upper catalyst inlet was still uneven and needed to be further optimized.According to the research experience of the optimization of fly ash distribution in the denitrification system,the cross-sectional dimension of the rectifier is equivalent to the grid scale of the RANS calculation method,and it is difficult to obtain further optimization results.Therefore,the use of grid requirements for more sophisticated LES method to carry out follow-up optimization research work.In order to meet the requirements of the LES method for the grid scale,the actual denitration reactor was reduced to the small scale denitration reactor model.The gas-solid two-phase flow of the small-scale denitration reactor under different gas-solid inlet conditions was studied by LES-DPM The results show that the particle size of fly ash particles is broadly distributed.With the increase of particle size,the particles are weakened by the vortex structure,the effect of their own momentum increases,and the particles with larger particle size are enriched,With the air flow into the back wall of the particles,resulting in increased particle concentration of the back wall;when burning high ash coal,with the increase in particle mass flow,the rigidity of the particles increased,weakened the local area of the vortex structure,The particles tend to be enriched in the back wall.Based on the nonuniform inlet conditions,the gas flow field of the small scale denitration reactor was optimized.Four straight arc diversion plates were added at the inlet of the reactor,and the velocity nonuniformity coefficient of the inlet cross section of the catalyst decreased from 32.6%to 12.92%To meet the requirement of speed uniformity of SCR denitrification system.After optimization of gas phase flow field,the non-uniformity coefficient of fly ash concentration in the inlet cross section of the catalyst is reduced from 53.6%to 46.1%,which indicates that the gas flow field optimization is beneficial to improve the fly ash concentration And the effect of the non-uniformity of the fly ash concentration is reduced to 23.35%,and the effect is very obvious.At this time,the gas phase The velocity nonuniformity coefficient drops to 13%and is further improved.This optimization program will be applied in the subsequent transformation of the project.