【作者】 王素娟；

【导师】 孙锐；

【作者基本信息】 哈尔滨工业大学 ， 热能工程， 2007， 硕士

【摘要】 随着环保问题的严峻化,降低锅炉的污染物排放日益受到关注,因此北京高井电厂2号炉进行了低NOX燃烧系统改造,在燃烧器上部加装燃尽风,并采用水平浓淡煤粉燃烧器作为主燃烧器,利用二次风分级配风燃烧方式来降低NOX排放。本文采用FLUENT6.2为平台,以高井电厂2号炉一台220t/h四角切圆燃烧方式的锅炉为研究对象,对二次风均等配风和分级配风方式下炉内流动、传热、燃烧和NO生成过程进行了数值计算,得到了炉膛内烟气温度场和燃烧产物的组分浓度分布。在炉内数值模拟过程中,气相湍流流动采用可实现的k-ε双方程模型,气固两相流动采用随机颗粒轨道模型,辐射换热采用P-1辐射模型,挥发分析出采用双竞争反应热解模型,挥发分燃烧模型采用混合分数PDF法,焦炭燃烧采用扩散-动力模型。采用有限差分法来离散微分方程,对控制方程的求解采用SIMPLEC算法,在直角坐标系下的非均匀交错网格系统中求解。模拟结果与热态试验结果进行了对照,两者吻合较好,验证了数学模型的可靠性和精确度,同时也表明将水平浓淡燃烧器和分级燃烧相结合的技术可以更有利于发挥水平浓淡燃烧器的稳燃、低污染排放的性能。通过计算和工业试验可见,分级配风后,煤粉进入炉膛燃烧迅速消耗掉低于理论燃烧的氧气量,同时炉膛中间区域生成了大量的CO,形成还原性气氛,对于有效抑制NOX生成非常有效。二次风倒塔配风方式更有利于NOX排放量的降低,且降低幅度较大;炉膛出口氧量对NOX排放影响较大,随着炉膛出口氧量的降低,氮氧化物的排放量也是降低的。同时,试验和计算均表明飞灰可燃物含量一直保持较低水平,保持了较高的燃烧效率,没有对锅炉的经济性运行产生负面影响。更多还原

【Abstract】 As the problems of environment protection become serious, the emission ofcontamination is regarded more and more. So thenumber 2 boiler in GaoJing powerplant was retrofitted for the second time. OFA was equipped on the upside of theburner, and Horizontal Bias Combustion burner (HBC burner) became main burners.The method of changing secondary air proportion was adopted to lower the NOXemission.This thesis numerically simulates flow, heat transfer, combustion and NOemissionprocessina220t/htangentiallyfiredboilerusingaCFDsoftware FLUENT6.2.Two operation cases are simulated.The first case is under uniform secondaryairdistribution.The other case is under staged secondaryair distribution.The numericalresults showed the temperature field and the concentration distributions of thecombustion species in the furnace. In the numerical simulation of furnace process,the turbulence is accounted for Realizable k-εtwo equations turbulent model. Thestochastic tracking model is applied to analyze the gas-solid flow field. Radiationuses the P-1 model. The devolatilization process is modeled by two competingreaction model. The combustion of volatiles is modeled by the Probability DensityFunction (PDF). Char combustion is modeled by diffusion-kinetics model. Thegoverningequations are discreted over a non-uniform staggered grid in the Cartesiancoordinate using the finite difference method and the equations are solved bySIMPLEC algorithm. The simulation and the measurement of hot test are comparedand they agree with the other fundamentally. It shows that the technology whichcombined the Horizontal Bias Combustion burner (HBC burner) with Air stagecombustiontechnologycanhelptoHBCburnerplayingitsadvantagesasgoodflamestabilityandlowNOemission.Bythe way of numerical simulation and experiment, after air staging, when thepulverized coal is fed into the furnace, it is burned in reductive atmosphere and agreatdealofCOisproduced,whichcanrestraintheproductionofNOXeffectively.The inverse-tower air supply manner of secondary air is more helpful inreducing the emission of NOX, and the reduction amplitude is larger. The content ofO2 at the furnace exit influence a lot on the emission of NOX; the emission of nitrogen oxide reduces when the content of O2 at the furnace exit reduces.Meanwhile, both experiment and calculation results indicated that the calculatedburnout of coal particles kept in a low level all the time, and a high combustionefficiency was kept, which brings none bad influence on the economic character oftheboiler.更多还原