中温条件下烟气De-NO_x技术的研究现状与发展

The State-of-art and Development of Moderate-temperature-based Flue Gas DeNO_x Technology

中温脱硝(De-NOx)指在炉膛出口以后到尾部受热面之前400～900℃温度区间进行脱硝的技术,具有反应器布置灵活、反应器内温度分布均匀和便于现有装置改造的优点。文中对中温烟气脱硝的研究现状进行了分析、总结与展望。中温烟气脱硝包括中温选择性催化还原(selective catalyticreduction,SCR)法、中温选择性非催化还原(selectivenon-catalytic reduction,SNCR)法、中温干法钙基脱硫剂脱硝技术以及负载金属的活性炭还原法等几种方法。中温SCR法使用分子筛催化剂,依然存在易被H2O、SO2毒化的问题;传统的以氨或尿素作还原剂的SNCR法加入H2、H2O2、烃醇类物质、钠盐或生物质气化气等添加剂可将反应温度降低至中温区,也可用肼类物质、氰尿酸、碳酸氢铵或活化氨基等作还原剂将温度窗口向下移动到中温区;中温干法钙基脱硝需结合脱硫进行,并对还原剂的喷入点有严格要求;中温活性炭还原法负载金属及反应机制尚不明确。综合反应效果及各技术对灰尘的适应性、操作的难易度及经济性,推荐中温SNCR脱硝技术为目前中温脱硝技术工程化方向。

The flue gas DeNOx between outlet of furnace and tail heat recovering surface within a temperature range of 400-900 ℃,known as moderate-temperature-based（MTB） DeNOx technology,is attractive due to its flexible installation in new plants,uniform temperature distribution inside the reactor section and ease of retrofit to existing facilities.This paper presented a review and comparison of the reported MTB DeNOx technologies,including MTB selective catalytic reduction（SCR）,MTB selective non-catalytic reduction（SNCR）,DeNOx based on SOx-reacted calcium oxide sorbents,and DeNOx based on activated carbon loaded with different metals.In MTB SCR technology zeolite catalysts are often used but they are easily deactivated by H2O and SO2.Traditional SNCR technology adopts ammonia or urea as reducing agent,and when additives such as H2,H2O2,organic compounds,alkali salts and biomass are used,the reaction temperature will decrease and shift to a moderate temperature range.Some newly introduced reducing agents,such as hydrazine,cyanuric acid,ammonium bicarbonate and activated ammonia can also be used as reducing agents to shift the temperature window to a moderate temperature range.DeNOx based on SOx-reacted calcium oxide sorbents needs strict control of the injection position and DeNOx based on activated carbon loaded with different metals needs further investigation on its mechanism and suitable metal species.Influence of particulates in the flue gas,operation requirements and economics of these MTB DeNOx technologies were also compared.MTB SNCR De-NOxbased on hydrazine and MTB DeNOx using SOx-reacted lime sorbents are recommended as the potential MTB DeNOx technologies for full scale application.