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微型流化床固-固反应与内循环微型流化床流动特性研究
其他题名Solid-solid Reaction Analysis and Internally Circulating Flow Characteristics of Micro Fluidized Bed
姚梅琴
学位类型硕士
导师许光文 ; 刘晓星
2013-05-01
学位授予单位中国科学院研究生院
学位专业化学工程
关键词微型流化床   固-固反应   内循环流化床   反应动力学   流体动力学   气相沉积   氧化铁还原
摘要气固相反应在工业生产工艺中占有很重要的地位,合适的反应动力学测量仪器是获得基础数据的必要条件。鉴于目前常用的反应动力学分析仪器在等温快速反应分析方面存在的不足,中国科学院过程工程研究所创新研制了应用于反应动力学研究的微型流化床反应分析仪(MFBRA)。该仪器具有快速升温和等温微分反应特性,适应于快速复杂反应的测试,且扩散抑制作用低,适用于含水蒸汽等特殊气氛的反应动力学分析,形成了与非等温动力学分析测试互补的反应分析方法和分析仪器。本课题扩展微型流化床反应分析方法和仪器的应用。针对典型的固-固反应(石墨还原氧化铁),分别采用热重分析仪(TGA)与MFBRA进行对比测试,考察MFBRA对固-固反应的适用性。根据程序升温反应失重与气体释放特性推测出的反应机理为:反应初始阶段发生直接固-固反应,生成CO2和Fe3O4;反应主体阶段,石墨与CO2发生气化反应生成的CO继续还原Fe3O4,生成Fe。求得反应初始时刻的活化能为Ex=0=520 kJ?mol-1,机理函数为G(x)=(1-x)2,为二级反应。通过MFBRA中石墨等温还原氧化铁实验,根据温度和气速对气体生成规律的影响,验证了TGA中推测的还原反应机理,求得反应体系整体活化能为222 kJ?mol-1,整体反应的机理模型为成核与生长,动力学方程为 。 为拓宽MFBRA的应用领域,本论文开展了适用于化学气相沉积反应的新型MFBRA前期工作。首先考察射流管和导流管结构对传统MFBRA颗粒流体流动特性的影响,在此基础上开展了内循环微型流化床流动特性研究的冷态基础实验,对操作参数和反应器结构进行了优化。结果表明,当环隙区底部压力大于导流管区底部压力,且环隙区通入足够量的气体松动其中的颗粒床层时,即可实现颗粒的环流循环。初始加料床高为45-75 mm时,可获得较宽的操作气速。当导流管直径为15 mm、进气管高度为30 mm和采用环形分布板结构时,可获得较宽的颗粒循环操作气速与较高的循环量控制范围,且导流管区与环隙区之间的窜气量较小。这些结果为设计适用于化学气相沉积反应的内循环微型流化床反应器奠定了基础。
其他摘要Gas-solid reaction is commonly encountered in industrial processes, and its analysis via suitable approach and instrument provides the only way for the related reaction data required by fundamental studies and application technology development. The so-called micro fluidized bed reaction analyzer (MFBRA) has been developed by Institute of Process Engineering, Chinese Academy of Sciences to implement reaction analysis via in-situ feeding of reactant. Featured by fast heating and minimization of diffusional inhibition, it has been shown that MFBRA provides isothermal-differential characteristics and is suitable of analyzing rapid and complicated reactions. The MFBRA is also easy to tackle the reaction involving steam. Thus, MFBRA provides actually an approach and instrument for gas-solid reaction analysis complementary to the thermogravimetric analysis (TGA). This study is devoted to extending the applications of MFBRA. Taking the reduction of iron oxide by graphite as a typical reaction, the complex solid-solid reaction was first investigated in MFBRA by comparing with the analysis in TGA. The reaction mechanism was first analyzed according to the weight loss and gas release characteristics in TGA during a temperature-programmed reaction procedure. At the initial stage of Fe2O3 reduction it occurs the direct solid-solid reaction to form Fe3O4 and CO2. Then in the main reaction stage graphite is gasified by CO2 to generate CO, and in turn Fe3O4 is reduced by the formed CO. The final product is Fe. The initial reaction had an activation energy of Ex=0=520 kJ?mol-1, and the mechanism formula is G(x)=(1-x)2 to indicate a reaction order of 2. The influence of temperature and gas velocity on gas formation in MFBRA verified the reaction mechanism derived from the tests in TGA. The overall activation energy is estimated to be 222 kJ?mol-1 from the tests in MFBRA, and the reaction mechanism is subject to the model of nucleation and growth so that the kinetic equation becomes . Thus, MFBRA is able to determine the overall reaction kinetic parameters of solid-solid reactions. The study conducted also a preliminary research on the micro fluidized bed reactor for analyzing chemical vapor deposition reaction. A jetting tube and a draft tube are made inside the micro fluidized bed to form an internally circulating micro fluidized bed, and the impacts of both jetting and draft tubes on the flow characteristics of the bed were investigated. Optimizing operating parameters and bed configuration were performed. The internal particle circulation was observed when the pressure at the bottom of the annulus was greater than that at the bottom of the draft tube and a gas stream was into the annulus to loose the particles in the annulus. The range of stable operating gas velocity was found to be wider when the initial particle bed height was 45 to 75 mm. The optimal bed configuration is 15 mm for the draft-tube diameter and 30 mm for the jetting tube height, while the fluidizing gas is distributed only into the annulus. Under these conditions the range of operating gas velocity for stable particle circulation was wider, the realized particle circulation rate was higher and varied in a wider range, and the gas bypass between the draft tube and annulus was lower. These results would provide the basic data for designing the micro fluidized bed reactor for chemical vapor deposition analysis.
页数82
语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/8362
专题研究所(批量导入)
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姚梅琴. 微型流化床固-固反应与内循环微型流化床流动特性研究[D]. 中国科学院研究生院,2013.
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