【作者】 李涛；

【导师】 程乐鸣； 施正伦；

【作者基本信息】 浙江大学 ， 工程热物理， 2010， 硕士

【摘要】 低热值气体是指发热量小于6.28MJ/m3的气体燃料,由于热值低、成分复杂,难以被处理而直接排放。这些低热值气体中含有甲烷,甲烷的温室效益是二氧化碳的21倍,将甲烷高效转化为二氧化碳将产生巨大的环境和经济效益。本文利用燃烧段与蓄热段分离往复多孔介质燃烧技术处理此类低热值气体,并研究拓展系统燃烧极限、增大系统处理低热值气范围的方法。低热值气体是由可燃成分和不参与燃烧的惰性成分组成的无氧混合气,本文将利用氮气稀释天然气模拟低热值气体,并研究此类气体在往复多孔介质燃烧器中的燃烧和污染物排放特性。本文研究工作主要包括两个部分：第一部分,低热值气体在往复多孔介质燃烧器中燃烧极限拓展实验研究。主要考察蓄热段对系统温度波动和分布特性的影响,系统由稳定燃烧过渡到过滤燃烧轴向温度分布的变化特性,以及系统燃烧极限特性。结果表明,蓄热段能显著的降低系统温度波动,提高系统燃烧温度和燃烧效率；当量比降低使得轴向温度分布形状从“马鞍形”、“梯形”、“椭圆形”,变化到系统达到燃烧极限时形成的“三角形”分布；在实验研究范围内,半周期缩短,热负荷降低、截面流速增大,系统燃烧极限先降低后升高,蓄热段蓄热能力增大能较小幅降低系统燃烧极限。系统贫燃极限为当量比0.07,混合气热值264kJ/m3。第二部分,无氧低热值气体往复多孔介质燃烧实验研究。主要考察混合燃气(指天然气与氮气混合气)热值、氧含量和空气当量比对燃烧特性和污染物排放特性的影响,并与单向多孔介质燃烧技术相对比,分析往复多孔介质燃烧技术的优势。研究结果表明：混合燃气热值降低,高温段长度缩短,平均温度和燃烧温度升高；氧含量、空气当量比降低,燃烧温度先升高后降低,排烟温度降低,且不同空气当量比使最大燃烧温度对应的氧含量不同,空气当量比越高对应氧含量越低；相比单向燃烧系统,往复式燃烧系统T/Tad=1对应空气当量比低于单向多孔介质燃烧系统,T/Tad随空气当量比变化的变化趋势大于单向系统,且NOx和CO排放浓度都要低于单向燃烧系统,更加适合低热值混合气燃烧。燃烧效率主要由天然气与氧气接触的几率和高温区宽度决定,随着氧含量、空气当量比降低而降低。空气当量比降低,混合燃气极限热值先降低后升高,系统稳定燃烧极限对应氧含量不断升高。系统混合燃气极限热值为447.35kJ/m3,氧化气氧含量为3.5%,预混气热值为373.2 kJ/m3。在较佳的燃烧工况下,CO排放浓度低于15ppm,NOx排放浓度低于5ppm。更多还原

【Abstract】 Due to low heat value and complex composition, low calorific gases whose heat value is below 6.28MJ/m3 are not exploited and directly discharged. They contain large amounts of methane, greenhouse effects of which are 21 times more than carbon dioxide. The efficient transformation of methane to carbon dioxide will bring us huge environmental and economic benefits. In this thesis, combustion technology in porous media with reciprocating is used to deal with these low calorific gases, and some studies have been done to expend the system’s flammability limit. Some low calorific gases are made up of combustible components and inert components, and don’t contain oxygen. In order to study these gases’combustion and pollutant emission characteristics in porous media combustor with reciprocating flow, the mixture of nitrogen and natural gas is used to simulate these gases. The work done by this article mainly includes two parts:First, experimental studies of flammability limit of low calorific gases combustion in porous media with reciprocating flow system. Effects of regenerator section on temperature fluctuation and distribution, variation characteristics of axial temperature distribution and flammability limits were investigated experimentally. The results show that adding regenerative sections leads to reduction of temperature fluctuation amplitude and increase of combustion temperature and efficiency; With the increasing of equivalence ratio, the shape of axial temperature distribution has continuous changes, from saddle-shaped, ladder-shaped, oval-shaped to triangle-shaped when the system works on flammability limit; With the reducing of half-period, thermal load and inlet gas velocity, the system’s flammability limit firstly decreases and then increases; With increasing of heat storage capacity of regenerator section, the flammability limit is slight lower. The flammability limit can be extended to the low equivalence ratio of 0.07, corresponding to the heat value of 264kJ/m3.Second, experimental studies of anaerobic gases in porous media with reciprocating flow system. The effects of the heat value of mixed fuel gases (the mixture of nitrogen and natural gases)、oxygen content and air equivalence ratio on combustion and pollutant emission characteristics are investigated experimentally; Compared with simple porous media burner, analysis the advantages of reciprocating flow system. The results show that:With the reducing of heat value of mixed fuel gases, the length of high-temperature zone shortens, the average temperature and combustion temperature increases; with the reducing of oxygen content and air equivalence ratio, the combustion temperature firstly increases and then decreases, the exhaust gas temperature decreases, and oxygen contents of the maximum combustion temperature on certain air equivalence ratio are different, the air equivalence ratio higher, the oxygen content lower; Compared with simple porous media burner, the air equivalence ratio is lower when T/Tad=1, and the emission concentration of NOx and CO is lower; With the reducing of air equivalence ratio, the heat value of flammability mixed fuel gases firstly decreases and then increases, the oxygen content of flammability limit rise. The flammability limit can be extended to the mixed fuel gases heat value of 447.35kJ/m3, the oxygen content of the oxidizer of 3.5%, corresponding to the premixed gases heat value of 373.2 kJ/m3. In better combustion condition, the CO emission concentration is below 15ppm and the NOX mission concentration is below 5ppm.更多还原