Numerical Simulation Of A SCR De-NO_x System In Coal-fired Unit

Nitrogen oxides is one of the main sources of air pollutants.With the increasingly stringent environmental requirements,coal-field need moreefficient denitration technology.Selective Catalytic Reduction is widely used for DeNO_x of flue gas due to its high denitration efficiency and non-secondary-pollution.The inhomogeneous distribution of the parameters before the first catalyst layer,such as flue gas velocity,the concentration of ammonia and fly ash would greatly effect NO_x removal efficiency and NH₃ escape rate.The paper researched a SCR denitration system of 600MW tangentially coal-fired boiler and the flow field,pressure field,the control method of ammonia injection and the motion characteristics of fly ash particles were simulated with the help of numerical simulation software.?1?By optimizing the right angle structure of elbow 2 and installing the guide plate,the speed relative standard deviation of Ammonia Injection Grid is reduced from 19.04%to 13%,the relative deviation coefficient of velocity of the first layer catalystthe is reduced from 19.1%to 8%,which is lower than the design standard requirement of the 15%.?2?The ammonia concentration distribution in the entrance layer of the first layer catalyst is very uneven when the ammonia injection is uniform,and the standard deviation is 11.7%,which is higher than the design standard requirement of the 5%.The appropriate distribution of ammonia molar concentrationcould be gotten by grouping nozzles according to the distribution of NO_x.The ammonia concentration was adjusted by three kinds of ammonia injection schemes.If the non-uniform control method 3 of ammonia injection was adopted,the ammonia deviation coefficient before the first catalyst layer can be reduced to 2.2%,denitration efficiency increased from 85.74%to 87.78%and the ammonia slip decreased from 21.3ppm to 13.8 ppm,which well met the engineering requirements.?3?The lower the load and the decrease of the flue gas temperature,it is not conducive to the removal of NOx.The standard deviation of ammonia concentration in the first layer catalyst is larger,and the denitrification efficiency is lower when the distance between the Ammonia Injection Grid and the bottom of the flue gas is farther.?4?After optimizing the original structure of the SCR denitrification system,the inhomogeneous concentration deviation coefficient of fly ash before the first catalyst layer is reduced from 42%to 32%.The distribution of fly ash concentration and distribution of flue gas flow are a positive correlation?The hopper is arranged in the bottom of the vertical flue can effectively optimize the concentration of fly ash distribution.The ash hopper has better trapping effect on particles of fly.