摘要
燃煤锅炉混氨燃烧是燃煤机组低碳化的主要技术发展方向之一。但由于氨燃料含氮量高,混氨燃烧可能导致锅炉NO_(x)排放的大幅上升,因此,能否实现NO_(x)排放的控制是决定燃煤锅炉混氨燃烧技术可行性的关键之一。为此,对氨–煤混燃实验研究中所观测到的NO_(x)排放随混氨比例(R_(NH_(3)))的不同变化趋势进行了综述,并基于最新实验研究结果给出了这些不同NO_(x)趋势的统一机理解释——NO在炉内的净生成量取决于NH_(3)的NO生成和还原反应在整个炉膛空间不同O_(2)浓度环境下的持续竞争过程。在锅炉运行环境下,NO_(x)排放主要由炉膛主燃区初始燃烧阶段NO的大量生成、还原区NH_(3)对NO的还原和燃尽区残余NH_(3)与燃尽风反应所导致的NO生成这几个阶段所综合决定;不同炉内O_(2)浓度环境下,此NO生成–还原–生成过程可叠加产生多种NO_(x)排放随R_(NH_(3))变化趋势。因此,氨–煤混燃实验中所观测的各种NO_(x)排放趋势不应简单地归因于混氨比例或方式的影响,而应综合考虑不同混氨条件所导致的NH_(3)在炉内燃烧反应环境的变化的影响。基于氨–煤混燃NO生成机制,进一步阐述了开发工程应用燃煤锅炉混氨燃烧NO_(x)预测模型所需考虑的关键因素,重点强调了将对炉内流场和O_(2)分布有直接影响的锅炉设计与关键运行参数转化为模型边界条件和模型参数的必要性。通过对40 MW锅炉和600 MW锅炉混氨燃烧的模拟,对比和验证了不同NO反应模型。结果表明,所提出的修正Østberg机理对NO_(x)排放的预测结果在定性和定量上皆与锅炉试验结果良好吻合。模拟结果还揭示了锅炉混氨燃烧NO生成的一个特殊性质:尽管NH_(3)进入炉膛后会迅速生成大量NO,但其作为气体燃料对O_(2)的快速消耗,将在紧邻NO生成区域的下游形成一个乏O_(2)还原区,使刚刚生成的NO在此区域随即被未燃尽残余NH_(3)大量还原。这一特殊性质大幅降低了锅炉混氨燃烧的NO净生成量。
Ammonia cofiring in coal-fired boilers is one of the promising technical routes for the decarbonization of coal-fired power plants.However,ammonia cofiring could potentially result in drastic increase of NO_(x) emissions due to its high nitrogen content.Effective control of NO_(x) emissions is thus one of the key factors that affect the technical feasibility of ammonia cofiring in coal-fired boilers.Therefore,the divergent trends of NO_(x) emissions with respect to NH_(3) cofiring ratio(R_(NH_(3)))observed in experimental studies were systematically reviewed.A unified mechanism underlying these divergent trends was proposed—the net NO formation is determined by the competition between the NO formation and reduction reactions of NH_(3) in the varying O_(2) environment of the furnace.In a boiler environment,NO_(x) emissions are jointly determined by the NO formation during the initial stage of combustion in the main combustion zone,NO reduction by NH_(3) in the reduction zone,and NO formation by the oxidation reaction of residual NH_(3) with staging air in the burnout zone.The NO formation-reduction-formation processes can add up to generate a variety of NO_(x) emission trends.Therefore,the divergent NO_(x) trends observed in the experiments should not be simply attributed to the effects of NH_(3) cofiring mode or ratio but should comprehensively take into consideration the resultant changes of NH_(3) combustion environment brought about those different NH_(3) cofiring conditions.Based on the above NO formation mechanism of NH_(3)-coal cofiring,the key factors that should be considered in engineering NO_(x) prediction model of NH_(3) cofiring were further elucidated,with particular emphasis on the necessity of converting the key boiler design and operating parameters,which directly affect the furnace flow and O_(2) distributions,to the boundary conditions of the model.By simulating NH_(3) cofiring in a 40 MW boiler and a 600 MW boiler,respectively,the results by different NO models were compared and validated.Results indicated that the modified Østberg mechanism showed good qualitative and quantitative agreement with the testing results.Furthermore,the results revealed a distinctive NO_(x) formation characteristic of NH_(3) cofiring.Although NH_(3) combustion may generate a large amount of NO,due to the rapid combustion consumption of O_(2) by NH_(3),an O_(2)-deficient NO reduction zone is formed adjacent to the high NO formation zone in which the initially formed NO is going to be immediately reduced by the residual NH_(3).This characteristic contributes to a substantial reduction in the net NO production of NH_(3) cofiring.
作者
谢妍
张文振
李明
王西伦
刘欣
初伟
王赫阳
XIE Yan;ZHANG Wenzhen;LI Ming;WANG Xilun;LIU Xin;CHU Wei;WANG Heyang(School of Mechanical Engineering,Tianjin University,Tianjin 300350,China;Yantai Longyuan Power Technology Co.,Ltd.,Yantai 264006,China)
出处
《洁净煤技术》
北大核心
2026年第1期145-160,共16页
Clean Coal Technology
基金
国家资助博士后研究人员计划资助项目(GZC20250426)。
关键词
燃煤锅炉
碳减排
氨煤混燃
NO_(x)排放
数值模拟
coal-fired boiler
carbon reduction
ammonia cofiring
NO_(x)emission
numerical simulation
