【作者】 李钦朋；

【导师】 张力；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2008， 硕士

【摘要】 煤矸石是目前排放量最大的工业固体废弃物之一,具有低挥发分、高灰分、低热值和难燃烧等特点。煤层气是煤炭开采活动中释放出的甲烷,温室效应很强,且易燃易爆,给煤炭开采活动带来隐患。煤矸石和煤层气的排放既污染环境,又浪费了资源。循环流化床燃烧技术现己被公认为一种清洁高效的燃烧技术,因此煤矸石和煤层气在循环流化床中混烧为综合利用煤矸石和煤层气提供了一种新途径,不仅能节约能源,还有利于环保,具有很高的经济和社会效益。本文以采用循环流化床锅炉燃烧技术改造的NG-35/3.82-M型35t/h链条锅炉在为研究对象,对流化床中煤层气燃烧器不同布置位置对炉内气固两相流的流动特性进行数值模拟以及优化设计,并探讨了煤矸石煤层气不同掺混比例对炉内流动特性的影响。通过改变煤层气入口位置和二次风速以及颗粒粒径研究了床内的流化特性,分析了不同设计方式下的流体动力特性。颗粒速度模拟结果表明,煤层气燃烧器布置位置的改变不影响炉内颗粒轴向的速度分布趋势,颗粒的运动形式为中心处向上、近壁面处向下的内循环流动结构。煤层气燃烧器四种不同的布置中,四角切圆布置在炉墙、高度为4m的方式中,在不同的炉膛高度下,颗粒速度波动最小,较其他相对比较平稳。且煤层气入口高度为4m时,可以使入口水平截面气相速度场形成涡流,加强了气固间的混合。因此此种煤层气燃烧器的布置方式为最佳。颗粒空隙率模拟结果表明,煤层气燃烧器布置方式和二次风速对炉膛内颗粒轴向浓度分布有重要的影响。煤层气入口位置为高4m、二次风速35m/s时,能够在密相区上方形成二次高浓度颗粒流。炉内煤矸石煤层气掺混比例对炉内流动特性有重要影响。加入煤层气的比例变大,会使炉内气相扰动变强,这样会加快颗粒的速度,从而缩短在炉内的停留时间,这样不利于炉膛颗粒的燃烧。故存在一个最佳的掺混比例,当掺混比例8/2时,床内颗粒的湍动能力强于其它掺混比例时的湍动能力,炉内速度场和浓度场分布最为合理。文中的研究结果为进一步研究开发煤矸石和煤层气循环流化床混烧技术打下基础,有重要的参考和应用价值。更多还原

【Abstract】 Coal gangue with the characteristics of lower valotile, high ash, lower heat value and hard-to-burn is one of the most quantity industrial solid residues. Coal bed methane with the characteristics of strong greenhouse effect and easy-to-burn and explode, is released methane in the process of exploitation of coal, and it is harmful to the coal exploitation.Emission of coal residue and coal bed methane not only cause environmental pollution, but also waste the resources. The gas-solid combustion technology in the fluidized beds has been considered clean and efficient. So it is a new way for synthetically utilizing coal residue and coal bed methane. It has very high economic and social benefits.CFB combined combustion technology is adopted to retrofit NG-35/3.82-M chain grate stroke in the paper. The influence of the gas burner height to the flow characteristics in the CFB is simulated, and the mixed combustion ratio of the two fuels influence to flow characteristics in the CFB is also investigated. According to different entrance of coal bed methane, different velocity of the secondary air and different particle size, the flow characteristics are studied.According to changing different disposed position and different velocities of the secondary air, the flow characteristics are studied. Distribution of velocity field shows that different entrance of coal bed methane doesn’t influence axial velocity field, particles in the centre of the boiler move upward and particles near the wall move downward. Among four layout formations, when the gas burner layout corner tangentially and the height of the burner is 4m, fluctuations of the particles are the smallest in different height of the boiler, air vortex is formed in the level cross-section of gas entrance. This will strengthen the mixing between air and particle, so this layout formation is the best. Distribution of particle-concentration field shows that, layout formation of the gas burner and velocity of the secondary air will influence axial velocity field of the particles. When the height of the burner is 4m, the secondary air is about 35m/s, higher particle-concentration will be formed above the dense phase zone.The proportion of the two fuels influences flow characteristics in the boiler. When amount of coal bed methane increases, disturbance in the boiler increases and particle velocity increases, then stay time of the particles in CFB decreases. When the mixed proportion is 8:2, turbulent kinetic energy of the particles are the biggest, the distribution of velocity field and concentration field are the best. The study results in this paper have important reference and application value, and pave the way for exploring the mixed combustion technology of coal residue and coal bed methane in CFB.更多还原