Simulation Of Structured Catalyst And Reactor For Flue Gas Denitrification

Selective catalytic reduction (SCR) with ammonia is the most widely used due to its efficiency, selectivity and economics in the flue gas denitrification technologies. In this technology, structured catalyst is used due to the several advantages they offer, like low pressure drop, high external geometric surface and resistance to deposition of dust, especially honeycomb-like cordierite structured catalyst. In this study, the three-dimensional SCR structured catalyst and reactor model was established, and simulation was done by used FLUENT software. The relationship between the internals of SCR flow system and mixing performance was investigated for making the flow uniformity and controlling ammonia slip, and the internals of SCR flow system were optimized. The configuration of structured catalyst has prominent influence on transfer and reaction performances of SCR for NO removal. Therefore, this study provides a comprehensive comparison of transfer and reaction performances for traditional pellet packed-bed reactor and two types of structured catalysts with five kinds of channel shapes.Firstly, in the SCR flow section, arranging the flow-guided internals can improve the uniformity of velocity distribution but is unfavorable for the uniformity of NH3 concentration distribution. Therefore, the ammonia injection grids (AIG) with four kinds of nozzle diameters (i.e.1.0mm,1.5mm, 2.0mm and mixed diameters) were investigated, and it is found that the AIG with mixed nozzle diameters in which A3, A4, B3 and B4 nozzles' diameters are 1.0mm and other nozzles' diameters are 1.5mm is the most favorable for the uniformity of NH3 concentration distribution. In the SCR reactor section, the appropriate space length between two catalyst layers is about 100mm, 1000mm and 12mm for honeycomb-like cordierite catalyst, plate-type catalysts with parallel channel arrangement, and with cross channel arrangement, respectively. Therefore, the cross channel arrangement is superior to the parallel channel arrangement in saving the SCR reactor volume.Secondly, the comparisons of transfer and reaction performances for traditional pellet packed-bed reactor and two types of structured catalysts were investigated. It is found that structured catalyst has a much low pressure drop and high effectiveness factor than traditional pellet packed-bed reactor, and coating catalyst seems more suitable than extruded catalyst for SCR for NO removal.The last, the comparisons of transfer and reaction performances for five kinds of structured catalyst channel shapes were also investigated. Although round channel brings the best heat and mass transfer, triangle channel of coating catalyst possesses the highest NO conversion due to chemical reaction being the controlling step for coating catalyst. So the triangle channel should be paid more attention in the coating catalyst design and optimization for flue gas denitrification.