平焰型粉煤气化炉热态流场分布特性的数值模拟  

Numerical study of hot flow field in an entrained-flow gasifier with flat flame burner

作　　者：冯子洋 刘臻 管清亮 安海泉 方薪晖 彭宝仔 FENG Ziyang;LIU Zhen;GUAN Qingliang;AN Haiquan;FANG Xinhui;PENG Baozai(National Institute of Clean and Low-Carbon Energy,Beijing 102211,China)

机构地区：[1]北京低碳清洁能源研究院,北京102211

出　　处：《煤炭学报》2019年第S02期657-664,共8页Journal of China Coal Society

基　　金：国家重点研发计划资助项目(2017YFB0602603);国家能源集团科技创新资助项目(ST930018SH01)。

摘　　要：目前已有的气流床干粉气化技术所用的工艺烧嘴多为同轴射流形式(氧包煤或煤包氧),射流火焰较长,需要匹配较大高径比的气化炉燃烧室,为保障碳转化率与有效气(CO+H 2)含量,要求其设计的平均停留时间约为4~6 s(按粗合成气计算),这同时需要较大的燃烧室容积去满足要求,因此导致气化炉单体反应器的体积普遍较大,造价较高。为降低气化炉的投资成本,提出了一种顶置平焰型气化烧嘴的气化技术,该技术通过顶置3个烧嘴单元,将传统工艺烧嘴的单一烛形火焰变为较短的平面火焰,降低了火焰长度并提高了径向的反应空间。同时,平焰烧嘴的每个烧嘴单元均为中心1路煤线配合外围3路氧线的对撞流设计,在强化反应速率的同时降低平均停留时间,从而减小设备体积需求。利用CFD模拟软件Fluent分别建立平焰烧嘴和传统顶置同轴射流形式的单烧嘴气化炉三维模型,基于涡耗散概念模型(EDC)的方法对不同烧嘴形式气化炉内的燃烧与气化过程进行模拟,对比分析了包括流场分布、温度分布、平均停留时间、碳转化率等关键特征。结果发现,相比传统单烧嘴,由于3烧嘴单元射流场所拥有的大卷吸率(平焰烧嘴卷吸率Kvmax=3.2,单烧嘴Kvmax=1.3)有助于粉煤颗粒与氧气在燃烧室内的弥散混合,因此平焰型烧嘴的火焰长度降低,炉温分布更加均匀,温度峰值由单烧嘴的2400 K降低至平焰烧嘴的1950 K。更充分的颗粒弥散以及更均匀的温度分布有助于气化炉燃烧室容积的有效利用,同时撞击流形式的烧嘴单元所带来的撞击流可以更快地实现粉煤与气化剂的湍流混合,增加气化反应速率(距离烧嘴0.5 m碳转化率:平焰烧嘴=95.1%,单烧嘴=77.0%)。这些优势可以带来更小的气化炉设计体积或同比更高的处理量。将模拟结果与3 t/d的干粉中试结果进行对比,验证了模型的有效性,对于烧嘴及炉体的优化设Coal burners are considered to be one of the critical units in coal gasification furnaces.Nowadays,as most of the coal burners in entrained-flow gasifiers are designed in the coaxial type(oxygen-encapsulated coal or vice versa),it normally requires a large combustion chamber with a high aspect ratio to keep a good averaged residence time(ART)for the coal particles in order to achieve a good carbon conversion rate(CCR)for the gasifier.As a consequence,the investment of the gasifier has to be increased due to the large combustion/reaction chamber.In this article,a top mounted flat flame burner was proposed to overcome the drawbacks of the coaxial burners.Instead of one,it is designed with three burner units on top of the combustion chamber,which converts the single candle shape flame from the traditional coaxial burner into a shorter and flatter shape flame,so the length of the flame can be reduced in the combustion chamber and extra space for gasification reactions can be created.The combustion characteristics of the flat flame burner were investigated using numerical simulation tools,and the results were compared with a same gasifier but mounted with a coaxial burner,together with the combustion chamber,both of the burners were modeled under the Eddy Dissipation Concept(EDC),the flow field,temperature distribution,CCR,solid particle distribution and the residence time were calculated.The results show that the implementation of flat flame burner leads to more reverse flow(reverse flow rate:flat flame Kvmax=3.2;single Kvmax=1.3)in the upper part of the combustion chamber,which helps the coal particles and oxygen dispersing more evenly in the combustion chamber,and reduces heat concentration near the burner section,therefore,brings a much more uniform temperature and particles distribution along the gasifier.The fuller particle dispersion and more uniform temperature distribution are conductive to the effective utilization of gasifier combustion chamber volume and intensify the mass transfer near the impinging strea

关 键 词：煤气化 平焰烧嘴 对撞流 模拟 FLUENT 实验 

分 类 号：TQ546[化学工程—煤化学工程]