Theoretical And Experimental Study Of SCR DeNO_x For Coal-fired Flue Gas

Catalyst is the key part of selective catalytic reduction (SCR) deNO_X process of flue gas and thepreparation technology of catalyst affects the deNO_X effect. In this work, the preparation of TiO₂and its effect on the deNO_X were studied. A series of TiO₂ gel were made under differentconditions as the support of catalysts. WO₃ and V₂O₅ were then loaded on as-prepared TiO₂ in turn.The rusults showed that the treatment temperature of TiO₂ gel had an impact on the structure andactivity of catalyst significantly. Lower drying temperature of the TiO₂ gel improves the deNO_Xactivity of V₂O₅-WO₃/TiO₂ and the NO conversion could reach to 98.3%.The adsorption of NH₃ and H₂O on different sites of deNO_X catalyst has been studiedtheoretically with the density functional theory and cluster model. The calculated results indicatethat ammonia could adsorb on both the Lewis and Bronsted sites of V₂O₅ surface, while theadsorption on the Bronsted sites more favorable energetically. At higher surface loadings of V₂O₅,NH₄⁺ specie, which plays an important role in SCR reaction, formed on O(1)H site with-128kJ/mol adsorption energy. Water could adsorb at the same site stably with-97 kJ/mol adsorptionenergy. On the V₂O₅ surface, adsorption energy of water is the same as that of ammonia.Competitive adsorption of water and ammonia restrains the SCR reaction.The design essentials of large, heavy and high temperature SCR reactor were illustrated withthe 600MW Coal Fired Boiler. The structure and arrangement of the outlet and inlet, the guidingvanes and the ammonia-injecting device were schemed out and verified by hydrodynamicsanalysis to meet the distribution requirement of flue gas velocity and NH₃/NO_X mole ratio, whichensured the optimal effect of catalyst. Based on stress, deflection and thermal effect analysis byCAE method, the wall ribs, beams and supports were designed and optimized to decrease weightand thermal stress. The inner components were constructed to prevent ash from settling down andash-removing devices were employed to remove ash deposit periodically.NH₃/NO_X mixing is one of the intractable challenges during the SCR project. Under the ideaof "making use of nonuniformity actively" instead of the idea of "getting absolute uniformity",the satisfied NH₃/NO_X mixing was achieved in the short and straight inlet to SCR reactor.Furthermore, the space problem was solved which is usual for the SCR retrofits to existingcoal-fired power plants. Based on this method, the high gas deNO_x efficiency was reached withthe limited catalyst cube and low ammonia slip at the same time. This application shows aneffective way for the development of China's own SCR technology and equipment.