【作者】 周建军；

【导师】 冉景煜；

【作者基本信息】 重庆大学 ， 动力机械及工程， 2007， 硕士

【摘要】 循环流化床燃烧技术在煤质变化很大时,要稳定燃烧存在一定的困难。为了较好的克服普通的循环流化床锅炉在燃用低劣质煤时存在的种种技术缺陷,可以采用循环流化床复合燃烧技术解决这个问题。但是,目前由于对循环流化床复合燃烧技术中二次进料位置对CFB内流动及稳定高效燃烧的研究和认识还很不够,从而较大地阻碍了该技术的进一步优化和应用。文中针对NG-35/3.82-M型链条炉,对其进行了CFB复合燃烧技术改造主要参数的初步确定。在此基础上,采用双流体模型建立了描述CFB复合燃烧技术床内气固两相流动特性模型,通过有限区域法将微分方程组离散为差分方程,利用SIMPLE算法进行求解。论文重点研究分析了CFB复合燃烧技术中不同二次进料射流位置对炉内气固两相流的流动特性,并得出了CFB复合燃烧技术中优化的二次进料射流布置位置。通过改变二次进料口的布置位置和二次风速以及颗粒粒径研究了床内的流化特性,分析了不同布置方式下的气固流动特性。研究发现虽然二次进料口的布置位置不同,依然能够形成核心-环形流动结构;双侧布置二次进料口的方式优于单侧布置进料口,但是在双侧布置的方式中,以在炉膛2300mm处布置方式为水平面上二次进料口形成错位,这样在炉内的水平面上可以形成环形流,加强了气固混合,从而增加了颗粒在炉内的停留时间。另外粒径越大越容易返混至密相区,在密相区聚集。颗粒速度研究结果也表明,双二次风的布置方式,使得颗粒的加速时间比较长,使得湍动能增加,但这同时也增强了炉内的扰动,增强了气固间的相互作用。研究结果还表明,采用复合燃烧技术的循环流化床,对于燃烧器双侧布置位置为2300mm水平面上二次进料位置偏离中心线700mm水平位置为2300mm处、二次风速为35m/s时,可以使气相速度场形成涡流,加强气固间的混合,延长颗粒在炉内的停留时间,而且双二次风布置时也使得颗粒的湍动能增强,更有利于混合。另外,也能够在密相区上方形成二次高浓度颗粒流。因此此种方式为最佳。文中的研究结果为进一步研究CFB复合燃烧技术打下基础,有重要的参考价值。更多还原

【Abstract】 When the coal quality varied great, the CFB will not combust steadily. In order to solve the limitation of the common CFB which combusted the bad coal, the combined combustion will be added to it. For these years, the combined fluid dynamics of the gas-solid flow in the fluidized beds has been the subject of a great deal of academic research throughout the world. For more reliable and improved design and operation, it is necessary to study the hydrodynamics of two-phase flow in the beds.This paper uses the NG-35/3.82-M chain grate stroke as the subject, which adopted the technology of CFB combined combustion to retrofit and the basic parameters are confirmed. On this condition, the gas-solid flow model is constructed by using the two-phase flow model in the CFB adopted combined combustion to retrofit. The differential equations are converted into algebraic finite volume equations with the aid of discrete assumptions. Then, the simulation about influence of the secondary feeder to the flow characteristics in the CFB is carried out. And at last the optimal position of the secondary feeder is obtained.According to change the disposed positions, velocities of the secondary air and particles diameters, the flow characteristics are studied. Although the disposed positions are different, the core-annular structure still can be formed. The results shows that double disposed positions exceed unilaterally disposed positions. But at different velocities of secondary air and double disposed positions apart from horizontal patch board 2300mm whose positions are stagger, it can form annular flow which strengthen the mix of air and particles, and also can prolong the residue time of the particles in the CFB. In another, the bigger in the particles diameter, the more easily for those return to the dense phase zone. The simulation results of the particles velocities also show that when the double secondary air was used, the accelerated time will be extended, which will make the turbulence energy be strong and the reaction between the air phase and solid phase.In all, the results shows that in the circulating fluidized bed (CFB) reactor which adopted the technology of combined combustion to retrofit, when keep the velocity at 2m/s and the double disposed position at 2300mm and apart from centrosymmetric face about 700mm and also the double secondary air about 35m/s, the air vortex will form. This will strengthen the mixing between air and particle and make the residue time be extended. And also double secondary air makes the turbulence energy strong. In addition, higher particle-concentration will be formed above the dense phase zone,and make the particles combusted at high temperature. So this is the best way for optimum design. The study results in this paper have important reference and application value, and pave the way for the CFB combined combustion.更多还原