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煤粉掺氨燃烧颗粒物生成特性研究

Study on formation characteristics of particulate matter in pulverized coal combustion with ammonia

  • 摘要: 煤粉掺氨燃烧作为一种新型的低碳燃烧策略,逐渐受到广泛关注,但掺氨改变了煤粉的燃烧过程,燃煤颗粒物的生成特性也发生变化。论文基于平焰燃烧器,开展掺氨比和燃烧温度对颗粒物生成特性影响的试验研究,通过ELPI(Electrical Low Pressure Impactor)分级采集了燃烧器上方230 mm处的颗粒物,采用SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer)等检测手段分析了颗粒物的质量粒径分布、微观形貌及元素分布,发现PM10呈双模态分布,不同模态的颗粒物因为生成机理的不同呈现显著差别,细模态颗粒物粒径范围为0.03~0.3 μm,颗粒质量浓度在0.01~0.2 mg/m3,粗模态颗粒物的粒径范围为0.3~10 μm,颗粒质量浓度在0.2~18 mg/m3之间;细模态颗粒物主要由烟气中无机物冷凝形成的絮状物组成,而粗模态颗粒物主要由氨煤掺烧后煤颗粒发生焦炭破碎形成,其形状为球形及类球型颗粒物;细模态颗粒物中富含Ca和Na,且Ca含量大于Na,而粗模态颗粒物主要由Si和Al组成,且Si含量大于Al;降低燃烧温度和增加掺氨比均使颗粒物浓度降低,原因是当燃烧温度降低,煤粉颗粒在燃烧过程中的升温速率放缓,挥发分释放速率变慢,煤粉颗粒不完全燃烧,煤颗粒的热应力和内部压力降低,而随着掺氨比增加,氨燃烧产生的水蒸气与高温焦炭颗粒发生水煤气反应,使得焦炭颗粒表面温度的变化速率降低,二者均降低了焦炭破碎的概率,最终使PM10的生成量降低。

     

    Abstract: As a novel low-carbon combustion strategy, ammonia mixing with pulverized coal combustion has gradually attracted widespread attention. However, the addition of ammonia alters the combustion process of pulverized coal, leading to changes in the generation characteristics of coal-fired particulate matter. This paper conducts an experimental study on the impact of ammonia mixing ratio and combustion temperature on the generation characteristics of particulate matter based on a flat flame burner. Particulate matter at 230 mm above the burner was collected using an ELPI(Electrical Low Pressure Impactor). Analysis of the mass particle size distribution, microscopic morphology, and elemental distribution of the particulate matter was conducted using detection methods such as SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer). It was found that PM10 under operating conditions exhibited a bimodal distribution, with significant differences in particulate matter of different modes due to different generation mechanisms. Fine-mode particulate matter had a particle size range of 0.03-0.3 μm, with a particle concentration ranging from 0.01-0.2 mg/m3. Coarse-mode particulate matter has a particle size range of 0.3-10 μm, with a particle concentration ranging from 0.2-18 mg/m3. Fine-mode particulate matter was primarily composed of floccules formed by the cooling of inorganics in the flue gas, while coarse-mode particulate matter was primarily formed by the coke fragmentation of coal particles after the co-combustion of ammonia and coal, taking the shape of spherical and quasi-spherical particles. Fine-mode particulate matter was rich in Ca and Na, with Ca content greater than Na, while coarse-mode particulate matter was primarily composed of Si and Al, with Si content greater than Al. Both reducing the combustion temperature and increasing the ammonia mixing ratio result in a decrease in particulate matter concentration. This was because reducing the combustion temperature slows down the heating rate of pulverized coal particles during combustion, slowed down the release rate of volatiles, led to incomplete combustion of pulverized coal particles, and reduced the thermal stress and internal pressure of coal particles. As the ammonia mixing ratio increased, the water vapor produced by ammonia combustion reacts with high-temperature coke particles, reducing the rate of change in the surface temperature of coke particles. Both factors reduce the probability of coke fragmentation, ultimately reducing the generation of PM10.

     

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