二次氧量对分级气化炉气化特性影响的分析和比较

第63卷第2期化工学报Vol. 63 No. 2CirsIour20122012年2月CIESC JournalFebruary研 究论文资二次氧量对分级气化炉气化特性 影响的分析和比较吴玉新，蔡春荣，张建胜，岳光溪，吕俊复(清华大学热能工程系，热科学与动力工程教育部重点实验室，北京100084)摘要:分级给氧气流床气化炉具有炉内混合过程强烈、喷嘴附近温度较低等优点。采用CFD数值方法研究了二次氧量变化对气化炉运行特性的影响，分析比较了不同二次给氧量下相交射流火焰特性的变化。当二次给氧量较低时，二次火焰在回流区的作用下明显向上偏斜，其射流动量不足以影晌主射流产生的宏观流场。二次氧量大于总氧量的8%时，回流区在二次射流的卷吸作用下收缩，但颗粒停留时间有所增加。二次氧量为16%时，与二次氧量为2%的工况相比，气化炉上游的平均温度降低约20C，二次射流高度处的平均温度提高约300C.由于总的氧煤质量比不变，二次氧量的变化对气化炉下游的影响并不显著。关键词:数值模拟;分级气流床气化炉;二次给氧;气化炉流场DOI: 10. 3969/j. issn. 0438-1157. 2012.02. 005中图分类号: TQ171.6+ 25; TQ 54文献标志码: A文章编号: 0438- 1157 (2012) 02- -0369 - -06Numerical investigation of effects of secondary oxygen ratio onperformance of staged-entrained flow coal gasifierWU Yuxin, CAI Chunrong, ZHANG Jiansheng, YUE Guangxi, LU Junfu(Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department ofThermal Engineering , Tsinghua University, Beijing 100084, China)Abstract: The staged oxygen entrained flow coal-slurry gasifier has such advantages as higher carbonconversion rate, stronger turbulent mixing inside gasifier and lower temperature near coal slurry nozzle. Inthis paper, the effects of secondary oxygen mass flow rate (SOMFR) on gasification performance werenumerically investigated through CFD simulation. The CFD model was based on the Euler-Lagrangianmethod. Realizable ke model was used to acquire the turbulent information in the gasifier. Presumed PDFmethod was adopted to consider interactions between turbulence and homogeneous reactions. Thecharacteristics of the gasification flames were analyzed as well as the flow field under different SOMFR inthe staged gasifier. As SOMFR decreased, the secondary gasification flame curved up with backflow nearthe wall. At the same time, dome wall temperature increased as well. When SOMFR was less than 8% ofthe total oxygen mass flow rate, the momentum flux of the secondary oxidizer is too low to change themacro flow field. When SOMFR was larger than 8% of the total oxygen mass flow rate, the recirculationregion shrank due to the entrainment of secondary flow. However, particle residence time increased, sincethe velocity in back-flow region increased. Particle gasification process would be benefited from thischange. As SOMFR increased, the down-flow flame length decreased as well as the average temperature inthe top furnace region. The result showed that the average temperature decreased by 20C when SOMFR2011- 08-03收到初稿.2011- 10- 10收到修改稿.Receved date; 2011-08- 03.联系人及第一作者，吴玉新(1979-). 男，博士.着金项目:国家重点基础研究发展计划项目(2010C227006).Foundation item:_ supported by the National Basic ResearchProgram of China (20中国煤化工MHCNMH G .●370●化工学报第63卷increased from 2% to 16% of the total oxygen mass flow rate. At the height where secondary oxygen wasintroduced, the average temperature increased by 300C as well. In all cases, the temperature flow field atthe down-section of the gasifier did not change, since the oxygen coal mass ratio was kept constant.Key words: numerical simulation; staged-entrained flow coal gasifier; secondary oxygen; flow field ingasifier引言1研究对象及数值模型煤的气化是煤清洁利用的重要过程之一，在该1.1研究对象描述过程中，煤被转化为易于处理的气体并被分离净化模拟对象为一台水煤浆分级给氧气化炉[23],后直接用作气体燃料或者化工原料[1。分级气流床气化炉主喷嘴内环和外环分别通人12. 5%和75%煤气化炉采用分级给氧技术，将大部分氧气和水煤的O2和CO2气体混合物，在保证雾化效果同时降浆从主喷嘴送入炉体，而将剩余氧气在炉体侧壁以低主喷嘴氧煤比和主喷嘴附近温度，延长主喷嘴使对冲形式给人[2。该技术主喷嘴氧煤比低，气化火用寿命。剩余氧化剂从距炉顶约为1/3炉高的对冲焰温度不高，对主气化喷嘴形成有效的保护作.喷嘴引人，二次氧提高了该区域的气化温度，进而用;二次氧气的给人在提高气化温度同时增强了弥补了主火焰区温度降低带来的不利因素.炉内湍流混合过程，因此该气化炉具有稳定运行时本文中，气化炉水煤浆浓度为59. 1%，氧煤间长、碳转化率高等特点[4]。质量比为0.92 [约合0.64 m'O2●(kg煤)-'],气在分级气化炉中，一次给氧量和二次给氧量间化用煤为神府煤，其工业分析及元素分析见表1.的配比是- -个重要参数，合理优化两者的配比，能煤颗粒粒径分为30、60、 110、175 μm四档，其够得到最佳运行工况。二次氧是通过射流的方式在质量分数分别为50%、15%、30%、5%。气化炉侧壁面横向给人，类似于煤粉锅炉中的二次表1水煤浆 原料煤的工业分析和元素分析风。这种给氧方式属于典型的横向湍流射流，在达Table 1 Primary and ultimate analysis of coal for slurry到一定的刚度条件下，会对局部流场产生重要影Primary analysis(D)/%Ultimate analysis(DAF)/%响。高伟等[5]研究了横向射流火焰的特性，发现随V FC A QHv/MJ.kg-iC HO N S33.3957.97 6.74 26. 16374.394.36 13.08 0.92 0.51着射流动量降低，横向火焰沿主流方向弯曲明显，穿透深度逐渐减小。吴海玲等[0]采用数值模拟方法为分析二次氧气体流量变化对二次火焰以及整比较了二维横向射流的平均流动和湍流特性，并分体气化效果的影响，分别取二次氧份额为总气体流析了二次射流回流区对下游壁面换热特性的影响。量的16%、13%、8%、4%和2%进行比较，相应郭婷婷等[']对湍流横向射流的流动特性进行数值模地，通过调整主喷嘴中心给氧量以保证各工况下的拟，发现横向射流与主气流速度是影响横向射流特气化炉氧煤质量比保持恒定。性的重要参数。1.2模型假设和数值模拟方法这些学者的成果对气化炉二次给氧的火焰特性基于简化PDF模型建立的三维CFD模型已对研究有很好的参考价值，但一方面，横向射流气化分级给氧气化炉进行了数值模拟[34),并与实验结火焰在气化炉壁面回流以及主射流的共同影响下，果进行了详细比较，证明了该三维模型的准确性。其形态不同于典型的横向射流[1;另一方面，氧气详细的CFD模型介绍和验证见文献[4, 10]， 在射人气化合成气氛围将产生反扩散湍流火焰，这一这 里仅对主要模型方法做简单介绍。火焰特性与传统的扩散火焰也存在明显差异[89]。本文采用EulerLagrangian方法描述气固湍流为掌握二次氧流量变化对气化过程的影响，本文对反应过程。对气相分别求解连续方程、动量方程和.一台 分级气流床气化炉进行三维数值模拟，在不同能量方程，采用Realizablek-e模型预测气化炉的二次给氧量条件下分别预测气化炉运行特性，并详湍流特性1;为:中国煤化工考虑湍细比较炉内流场以及气化火焰的变化趋势.流脉动对化学反应MHCNMHG化PDF374●化工学报第63卷47: 3119-3129 .References[9] Wu Kuang-Tsai， Robert T Essenhigh Mapping anstructure ofof inverse diffusion flames of methane//20thInverse .m ”Symposium ( International) on Combustion [C]. 1984:New York; John Wiley & Sons Inc，19811925-1932F)。Y。[2] Zhang jiansheng (张建胜)，Wu Yuxin[10] Wu Yuxin (吴玉新), Zhang Jiansheng (张建胜)，WangGuangxi (岳光溪), et al. 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