燃煤电站锅炉掺氨燃烧与排放特性综述

Review on combustion and emission characteristics of coal-fired utility boilers ammonia/coal co-firing

近年来,氨作为一种无碳、富氢的燃料,多被用作内燃机、燃气轮机和其他工业用途的无碳燃料。为了降低燃煤电厂CO_(2)排放,燃煤掺氨燃烧受到广泛关注。介绍了现有燃煤电厂锅炉碳减排的途径,论述了氨煤掺烧研究的最新进展,分析了燃煤掺氨燃烧过程中可能存在的问题,揭示了燃煤掺氨燃烧特性与污染物排放规律。针对氨在燃煤锅炉中的燃烧特性与燃煤掺氨燃烧过程中高NO_(x)排放特性,在一台燃烧炉中实现了0~100%掺氨比例的燃煤掺氨燃烧试验,并将空气分级燃烧技术应用于燃煤掺氨燃烧,通过试验进一步研究了不同掺氨比例和分级工况(温度、掺氨位置)对燃煤掺氨燃烧产物的影响。燃煤锅炉提供的高水平预热条件及炉内高温热环境均有利于强化氨气燃烧,氨燃烧特性差不会成为制约其在燃煤锅炉掺烧的主要因素。通过调整燃煤混氨方式、优化空气分级燃烧工况可大幅降低NO_(x)排放浓度。延后燃尽风的通入位置,可延长还原区长度,有利于还原区NH_(3)与NO选择性非催化还原反应和煤热解产物(挥发分和焦炭)与NO异相和同相还原反应的进行,有效降低尾气NO浓度。根据试验煤种,空气分级燃烧工况下,燃尽风中、高位布置且燃尽风占总风量30%以上,燃煤掺氨比例控制在20%~30%(按热值)时,燃烧炉尾部烟气中NO_(x)排放浓度可控制在与煤空气分级燃烧相当的水平。空气分级燃烧工况下,随掺氨比例的提高,燃煤掺氨燃烧还原区H_(2) S峰值浓度呈下降趋势,可能缓解水冷壁管的腐蚀;燃煤掺氨燃烧还会大幅促进还原区CO_(2)/H_(2) O和煤焦气化反应进行,造成大量CO生成。燃煤掺氨燃烧技术是燃煤电厂实现低碳和低氮排放极具应用前景的技术发展方向。

In recent years,as a carbon-free,hydrogen-rich fuel,ammonia is mostly used as a carbon-free fuel for internal combustion engines,gas turbines and other industrial applications.Ammonia/coal co-firing has also attracted a lot of attention in order to reduce CO_(2) emissions from coal-fired power stations.The methods for reducing carbon emissions from existing coal-fired power plant boilers were introduced,and the latest progress in ammonia/coal co-firing research was briefly described,and the potential problems in the ammonia/coal co-firing combustion process were analyzed,and the combustion characteristics and pollutant emission rules of ammonia/coal co-firing were revealed.In view of the combustion characteristics of ammonia in coal-fired boilers and the high NO_(x) emission characteristics in the process of ammonia/coal co-firing,a test with 0-100%ammonia co-firing ratio was realized in a combustion furnace,and air-staged combustion technology was applied to ammonia/coal co-firing.The influence of different ammonia co-firing ratios and air-staged techniques(combustion ambient temperature,ammonia addition position)on ammonia/coal co-firing combustion products was examined further.The coal-fired boiler′s strong preheating conditions and high combustion ambient temperature in the furnace promote increase ammonia combustion.As a result,ammonia′s weak combustion properties will not be a significant barrier to ammonia/coal co-firing in coal-fired boilers.NO_(x) emission concentration can be greatly reduced by adjusting the co-firing approach and modifying the air-staged combustion strategies.The length of the reduction zone can be extended by delaying the addition position of the burnout air,which is conductive to the selective non-catalytic reduction reaction between NH_(3) and NO in the reduction zone and the heterogeneous and homogeneous reduction reaction between coal pyrolysis products(volatile and char)and NO,effectively reducing NO_(x) emissions.With a medium and high burnout air addition position and a burnout air ratio of 30%or more of the total air volume,the NO_(x) emission concentration may be regulated at a level comparable to that of coal air-staged combustion if the ammonia co-firing ratio is managed at 20%-30%(calorific value).The peak concentration of H_(2)S in the reduction zone of ammonia/coal co-firing lowers with increasing ammonia co-firing ratio under air-staged combustion circumstances,which may have a moderating trend on the corrosion of water-cooled wall pipes.Ammonia/coal co-firing will also considerably increase the gasification reaction of CO_(2)/H_(2)O and coal char in the reduction zone under air-staged combustion circumstances,resulting in the creation of huge volumes of CO.The utilization of ammonia/coal co-firing technology is a very potential technological advancement path toward achieving low carbon and low nitrogen emissions in coal-fired power plants.