【作者】 欧阳子区；

【导师】 吕清刚； 朱建国；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 热能工程， 2014， 博士

【摘要】 我国是以煤炭为主要能源的国家,其中难燃的无烟煤占了煤炭总产量的17%。由于煤炭资源的短缺,越来越多的无烟煤被直接用来进行发电,最近几年其份额仍在不断增加。同时,低阶煤梯级利用技术产生大量的几乎不含挥发分的半焦也有待于燃烧发电利用。然而,由于无烟煤和半焦挥发分含量低、固定碳含量高,在燃用上述燃料的一些煤粉电站锅炉中,普遍存在着火困难、低负荷条件下燃烧稳定性差、飞灰含碳量高以及氮氧化物排放高等问题。本论文依据预热强化燃烧的基本理论,建立无烟煤粉循环流化床预热燃烧系统,揭示无烟煤粉预热机制,探索预热燃料高效燃烧方式,实现无烟煤粉稳定、高效燃烧和低污染物排放的统一。在无烟煤粉循环流化床预热燃烧实验台上,对无烟煤粉的预热特性、预热燃料的燃烧特性、煤氮向氮氧化物的转化过程和脱硫特性进行了实验研究,并研究了循环流化床主要运行参数和下行燃烧室配风方式对无烟煤粉预热、燃烧及氮氧化物排放的影响。无烟煤粉在循环流化床中,在较低的空气当量比的条件下,发生部分热解、气化和燃烧,可将自身温度加热到800℃以上。无烟煤粉经循环流化床预热后粒径减小、比表面积和孔容积增大,煤焦颗粒变得疏松多孔,预热燃料的物理特性得到了很大的改善。煤中氮元素在预热过程中发生了析出和转化,析出的煤N主要被还原为NH3和N2,煤N的还原对NOx的减排较为有利。煤中各组分的转化率随预热温度和循环流化床空气当量比的增加而增加。无烟煤粉在循环流化床中的预热温度超过800℃,预热燃料和高温煤气进入下行燃烧室后,与空气相遇发生快速、高效燃烧反应。无烟煤粉预热后燃烧稳定,下行燃烧室温度分布均匀,预热燃料的燃烧不存在着火延迟,燃烧速率处于扩散燃烧控制区,无烟煤粉预热后燃烧效率最高可达97.5%。无烟煤粉经过预热后,其燃烧特性和燃尽特性得到了较大的改善。煤粉循环流化床预热技术和空气分级燃烧技术相结合,在提高煤粉燃烧稳定性和燃尽效率的同时,在降低氮氧化物排放上也有明显的优势。尤其对无烟煤,在没有尾部脱硝装置的情况下,NOx的排放最低可达到103mg/m3(6%O2),接近国家排放法规的限值。NOx排放和煤粉中燃料N向NOx的转化率随煤粉粒径的增加而减小：随着预热温度的升高先降低后升高,在预热温度为900℃时达到最低值；随着循环流化床空气当量比的增加而降低。随还原区空气当量比和总过量空气系数的增加,和还原区停留时间的减少,NOx排放增加。在循环流化床中加入石灰石,对系统的SO2减排有明显的作用,脱硫效率可达到50%以上。脱硫反应发生在循环流化床中,最主要的脱硫反应为H2S和CaO间的反应。循环流化床中加入石灰石对NOx的排放的影响和煤种有重要关系。在东胜褐煤和大同烟煤的预热燃烧中,石灰石的加入对NOx的减排有较大的促进作用；而在阳泉无烟煤和神木半焦的预热燃烧中,石灰石的加入对NOx的排放基本没有影响。研究结果表明,无烟煤粉循环流化床预热燃烧技术可以实现以无烟煤粉为主的低挥发分燃料的稳定、高效和清洁燃烧。研究结果为难燃的无烟煤及低阶煤提质后的半焦在燃烧领域的广泛应用提供了理论基础和技术方案。更多还原

【Abstract】 Coal is the main energy source in china with anthracite accounting for17%of total production. Due to the shortage of coal resource, anthracite is generally used for power generation directly. Meanwhile, large substantial semi-coke with almost no volatile produced by low rank coal utilization technologies also needs to be burned to generate electricity. However, due to the low volatile and high fixed carbon contents, there are some problems in the power plants burning anthracite and semi-coke, such as difficult ignition, unstable combustion at low load, high carbon content in fly ash, and high nitrogen oxide emission. Based on the theory of preheating strengthening combustion, a system for preheating pulverized anthracite in a circulating fluidized bed (CFB) is established. In this thesis, the preheating mechanism of pulverized anthracite is revealed, and the combustion characteristic is explored to achieve stable and efficient combustion and low pollutant emission of preheated pulverized anthracite.In order to explore the preheating and combustion characteristics of pulverized anthracite, the transformation process of coal-nitrogen to NOx, and the desulfurization characteristics, experiments are carried out on a bench scale rig of pulverized anthracite combustion preheated in a circulating fluidized bed. The effects of operating conditions in CFB and the down-fired combustor on the preheating and combustion characteristics of pulverized anthracite and NOx emission are also investigated.The experimental results show that, the preheated pulverized anthracite with a temperature higher than800℃can be obtained steadily and continuously by partial pyrolysis, gasification, and combustion of anthracite coal at a low air equivalence ratio in CFB. After being preheated, the mean particle size of pulverized anthracite significantly decreases, the specific surface area and pore volume increase, and the surface becomes rough with a well-developed pore structure, all of which leads to the improvement of physical structure of the pulverized anthracite. In the preheating process, coal nitrogen mainly converts into NH3and N2, and coal nitrogen reduction in CFB is favorable to reduce NOx emission. The conversion rate of the components in pulverized anthracite increases with the increase in the preheating temperature and the air equivalence ratio in CFB. After the preheated pulverized anthracite and high temperature coal gas with the temperature higher than800℃enter the down-fired combustor encountering with air, fast and efficient combustion occurs. The combustion of the preheated anthracite is steady, and the temperature profile in the down-fired combustor is uniform. There is no any difficulty in ignition in the down-fired combustor. The combustion rate of preheated pulverized anthracite is controlled by both the chemical reaction rate and the diffusion rate. The highest combustion efficiency in the experiments can reach97.5%, which indicates that the combustion and burning-out performance of pulverized anthracite are greatly improved after being preheated.In addition, combing the technology of pulverized coal preheating and air-staging can significantly reduce NOx emission. Especially for pulverized anthracite, the minimum NOx emission is103mg/m3(6%O2) without equipping SCR, which basically reaches the limits of national emission regulations. The NOx emission and fuel-N conversion ratio decrease with the increase in the pulverized coal size and air equivalence ratio in CFB; initially decrease and then increase with the increase in the preheating temperature, reaching a minimum at the preheating temperature of900℃. The NOx emission increases with the increase in the air equivalence ratio in the reducing zone and the excess air ratio, and the decrease in the residence time of preheated anthracite in the reducing zone.SO2emission decreases significantly after the addition of limestone to CFB, and the desulphurization efficiency can reach50%. The desulfurization reaction occurs in CFB, mainly between H2S and CaO. The effect of limestone addition on NOx formation is closely related with the coal type. It is observed that adding limestone to CFB has little effect on NOx emission for Yangquan anthracite coal and Shenmu semi-coke, while it is obviously effective for Dongsheng lignite coal and Datong bituminous coal.The results show that the technique of preheating pulverized anthracite in a CFB can achieve stable, efficient, and clean combustion for the fuels with low volatile content mainly of anthracite coal. The research results in this work provide theoretical basis and technical solution for the utilization of anthracite and smei-coke in the field of combustion.更多还原