Numerical modeling of a coal/ammonia Co-fired fluidized bed: Control and kinetics analysis of nitrogen oxides emissions

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS Journal of The Energy Institute Pub Date : 2024-08-12 DOI:10.1016/j.joei.2024.101777
Liangxu Dai , Yujie Hou , Chang'an Wang , Yongxu Chen , Zixiu Jia , Defu Che
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Abstract

The potential increase in nitrogen oxide emissions in the coal/ammonia co-firing can hinder the large-scale utilization of ammonia to reduce carbon emissions. In this work, a fluidized bed simulation model was established to investigate the NOx and N2O behaviors in the process of coal/ammonia co-firing. The effects of several variables on nitrogen oxides emission characteristics were studied, including the ammonia ratio, temperature, excess air ratio, and air/ammonia distribution strategies. The findings indicate that NOx and N2O concentrations rise and then decline with the NH3 co-firing ratio (CR-NH3) increased, peaking at 10 % and 5 % CR-NH3. The formation of N2O is insensitive to the addition of ammonia, while NOx emissions vary dramatically with different ammonia ratios. Higher temperatures enhance the formation of NOx but inhibit the generation of N2O within 750 °C–950 °C. As the temperature rises, the primary decomposition path of N2O shifts from N2O→N2H2→NNH→N2 to N2O→NO2→NO→N2. The generations of NOx and N2O are both enhanced due to the weakness of the reduced atmosphere with the excess air ratio increased. When the primary air ratio is raised, N2O gradually takes over as the main source of nitrogen oxides instead of NOx. The specific primary air ratio in the fluidized bed should be considered in the priority treatment of NOx or N2O in the process of lowering nitrogen oxides emissions. Ammonia distribution strategies have opposite effects on NOx and N2O emissions. With more NH3 introduced as a secondary fuel, the dilute phase area can change from the main source of NO to the consumption area of NO. The present findings can help control the emissions of nitrogen oxides during coal/ammonia co-combustion in coal-fired circulating fluidized bed power plants.

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煤/氨共燃流化床的数值建模:氮氧化物排放的控制和动力学分析
煤/氨联合燃烧过程中可能增加的氮氧化物排放会阻碍大规模利用氨来减少碳排放。本研究建立了流化床模拟模型,以研究煤/氨联合燃烧过程中氮氧化物和一氧化二氮的行为。研究了多个变量对氮氧化物排放特性的影响,包括氨比例、温度、过量空气比例和空气/氨分配策略。研究结果表明,氮氧化物和一氧化二氮的浓度随着 NH3 联烧比率(CR-NH3)的增加而上升,然后下降,在 CR-NH3 比率分别为 10% 和 5% 时达到峰值。一氧化二氮的形成对氨的添加不敏感,而氮氧化物的排放则随不同的氨比例而变化很大。温度越高,氮氧化物的生成越多,但在 750 °C-950 °C 范围内,氮氧化物的生成受到抑制。随着温度的升高,N2O 的主要分解路径从 N2O→N2H2→NNH→N2 转向 N2O→NO2→NO→N2 。随着过量空气比的增加,由于还原气氛的弱化,NOx 和 N2O 的生成都会增加。当一次空气比提高时,N2O 逐渐取代 NOx 成为氮氧化物的主要来源。在降低氮氧化物排放的过程中,应考虑流化床中具体的一次空气比,优先处理 NOx 还是 N2O。氨分配策略对氮氧化物和一氧化二氮排放的影响相反。当引入更多的 NH3 作为辅助燃料时,稀相区会从氮氧化物的主要来源区变为氮氧化物的消耗区。本研究结果有助于控制燃煤循环流化床发电厂的煤/氨共燃过程中氮氧化物的排放。
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来源期刊
Journal of The Energy Institute
Journal of The Energy Institute 工程技术-能源与燃料
CiteScore
10.60
自引率
5.30%
发文量
166
审稿时长
16 days
期刊介绍: The Journal of the Energy Institute provides peer reviewed coverage of original high quality research on energy, engineering and technology.The coverage is broad and the main areas of interest include: Combustion engineering and associated technologies; process heating; power generation; engines and propulsion; emissions and environmental pollution control; clean coal technologies; carbon abatement technologies Emissions and environmental pollution control; safety and hazards; Clean coal technologies; carbon abatement technologies, including carbon capture and storage, CCS; Petroleum engineering and fuel quality, including storage and transport Alternative energy sources; biomass utilisation and biomass conversion technologies; energy from waste, incineration and recycling Energy conversion, energy recovery and energy efficiency; space heating, fuel cells, heat pumps and cooling systems Energy storage The journal''s coverage reflects changes in energy technology that result from the transition to more efficient energy production and end use together with reduced carbon emission.
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