Development Of Diesel Engine NH₃-SCR Simulation Response Evaluation System And Performance Study Of Commercial SCR Catalysts

With global warming intensifing,greenhouse gas control is urgently needed.As one of the greenhouse gases,N₂O is about 310 times warming potential than CO₂.The N₂O emission limit will be added to the"Light Vehicle Pollutant Limits and Measurement Methods?China Stage 6?"?GB 18352.6-2016?,which will be implemented from July 1,2020.It can be seen that the state attaches importance to N₂O pollutants.Research on N₂O emission reduction is a forward-looking research topic.This paper develops the NH₃-SCR reaction simulation evaluation test bench including the simulation reaction system and the test system.Through the evaluation system,the"National Six"copper base and"National Five"vanadium-based commercial catalysts of various formulations provided by Weichai Power Co.,Ltd.were evaluated.The effects of temperature,space velocity,ammonia-nitrogen ratio and oxygen concentration on the N₂O production and NOx conversion efficiency of the catalysts were investigated.The results showed that,in the temperature range of 150°C⁶50°C,the N₂O production of copper-based catalysts increases first and then decreases with temperature increasing.When the vanadium-based catalyst is in the low temperature range of 100°C⁴00°C,the N₂O formation is close to 0,and the N₂O production increases with the increase of temperature when the temperature is over 400°C.Copper-based catalysts have higher N₂O generation than vanadium-based catalysts in a wide SCR temperature range of 150°C to 500°C.Below a certain airspeed limit,the amount of N₂O produced by the copper-based and vanadium-based catalysts is hardly affected by the space velocity.When the space velocity limit is exceeded,the N₂O production decreases with the increase of the space velocity.The copper-based catalyst has almost no change in the amount of N₂O produced in the range of 0.85-1 ammonia-nitrogen ratio.When the ammonia-nitrogen ratio is greater than 1,the amount of N₂O produced increases with the increase of ammonia-nitrogen ratio.While ammonia-nitrogen ratio is in the range of 0.85 to1.15,the N₂O production amount of the vanadium-based catalyst increases almost linearly with the increase of ammonia-nitrogen ratio.In the range of 0%¹0%O₂ concentration,the N₂O production of copper-based catalysts showed a linear decrease with the increase of O₂concentration,while the N₂O production of vanadium-based catalyst increased with the increase of O₂ concentration.The low-temperature denitration performance of copper-based catalysts is higher than that of vanadium-based catalysts,but at high temperatures,vanadium-based catalysts have more advantages in denitrification than copper-based catalysts.The copper-based catalyst has lower space velocity requirements than the vanadium-based catalyst,and can achieve higher denitration performance at higher space velocities.The optimum ammonia nitrogen ratio for denitration efficiency of copper-based catalysts is 1.05,while that of vanadium-based catalysts is 1.0.The demand for ammonia in copper-based catalysts is slightly higher than that of vanadium-based catalysts.Both the copper-based and vanadium-based catalysts have a denitration efficiency that reaches a maximum after the O₂ concentration is greater than 6%.When the concentration of O₂ is less than 6%,the denitration efficiency of copper-based and vanadium-based catalysts increases with the increase of O₂ concentration.The denitration efficiency of copper-based catalyst increases uniformly with the increase of O₂concentration,while the denitration efficiency of vanadium-based catalyst appears a spike window in the 4%⁶%O₂ concentration range.