【作者】 祝媛；

【导师】 张济宇；

【作者基本信息】 福州大学 ， 化学工程， 2004， 硕士

【摘要】 热等离子体煤裂解制乙炔下行床反应器工艺的严重结焦是制约该过程稳定操作与连续运行的瓶颈。当采用适量惰性颗粒与原料粉煤一起通过下行床时，惰性颗粒在煤裂解过程中作为结焦前驱体的载体并不断地冲刷管壁可抑制并减缓反应器的结焦。于是，下行床中将出现二元组分颗粒系统（惰性颗粒与反应颗粒）混合流动的新问题；遗憾的是，迄今几乎所有下行床的报道都是关于单组分颗粒运动与气体混合的研究，因此系统地进行二元组分颗粒流动与混合特性、速度分布与预测、流型演变与发展等研究工作，对拓展下行床的工业应用与解决热等离子体煤热解反应器严重结焦瓶颈问题是非常重要而又十分急需的。本文采用PV-4A光导纤维测速仪在高2m、直径Φ30mm的半圆形下行床反应器中较系统地测定了FCC催化剂（模拟反应颗粒）及不同粒径玻璃珠（模拟惰性颗粒）在6个截面8个径向位置的局部颗粒速度的轴向及径向分布。同时测定与预测了试验颗粒的近似颗粒群沉降速度，进而与理论计算的颗粒群自由沉降速度进行了分析对比。接着考察了流动分区，确定了气固流在下行床中的运动状态。用4种不同物性粒子考察了颗粒物性对颗粒速度轴、径向分布的影响；研究了两种分配器（直管式与环隙式）及操作条件对不同物料局部颗粒速度径向分布的影响。根据本实验和文献中不同下行床结构特征与不同物料体系的实验数据，综合地得出具有一定普适性的无因次局部颗粒速度经验关联式。最后将FCC催化剂和玻璃珠物料同时进入下行床中，考察了不同混合比组成的二元混合组分的颗粒速度径向分布特点。本冷模实验得出以下重要结论：（1）颗粒群自由沉降速度的实验值与理论计算值具有相似的规律，随粒径与密度的增加而逐渐增加，在很低气速时测定的局部颗粒速度及截面平均速度可表示该颗粒群的近似自由沉降速度（即：近似颗粒群沉降速度）。（2）在不同运动阶段时，颗粒速度径向分布相差较大，在第一加速段，分布波动较大，更加陡峭，而在第二加速段及恒速段则趋于稳定，速度分布较均匀。颗粒物性是引起颗粒速度径向分布变化的主要因素，在相同操作条件下密度愈大，粒径愈大的粒子径向分布愈易均匀。（3）局部衰减颗粒速度值反映了颗粒速度径向分布的均匀程度，采用高<WP=3>径比H/D、无因次局部颗粒速度vp*、雷诺数Re0、曳力系数Cds及无因次截面平均颗粒速度的关联式，并包括了不同物料颗粒群沉降速度的修正，可用来预测出表观气速及固体循环速率以及颗粒物性对颗粒速度径向分布的影响，该无因次局部颗粒速度关联式适用于不同结构特征及不同物性参数物料体系，具有一定的普适性。（4）从均匀布气与混合均匀入手设计的环隙式分配器，通过两个不同缝隙使粗、细两种颗粒在分配器中分别得以均匀分配与固体循环量的灵活控制，使细颗粒的局部速度径向分布更为均匀，同时在整个截面的速度相差不大，能有效地在等离子高温反应区进行快速反应；而粗颗粒在下行床管壁附近速度相对増大，能更好地冲刷管壁结焦物，有利于抑制结焦与热等离子体煤裂解制乙炔的生产过程。（5）惰性粒子粒径不同，其清焦的效果并不相同；二元组分混合颗粒速度径向分布较单一组分趋于均匀，其中粗颗粒粒径愈大，颗粒速度径向分布愈均匀，该混合组分速度分布可用来进行加和；二元混合组分的固体循环量比值M*对颗粒速度径向分布的影响不大，从满足实际生产需求与提高生产能力出发，M*值应控制在10％以下。更多还原

【Abstract】 The key problem of coking seriously restricts the stable and continuous operation in thermal plasma downer reactor for the coal cracking process to produce acetylene production. When injecting appropriate amount of inertia particles and coal into downer, the problem of coking could be prohibited or alleviated since the inert particles can carry the coking precursor of coal and also will continually scour the downer wall to draw the coking matter off. However, a binary particle mixture system composed of inert and reaction particles will occur in downer and cause some changes in flow behavior, which become a new unclear problem. Unfortunately almost the past studies were focused mostly on single particle and gas mixing flow behavior in downers. Therefore in order to expand the industrial application scope of downer and resolve the coking problem for the process of acetylene production from coal cracking in thermal plasma downer, It is necessary to have a special and systematic study on the solid flow behavior, redial and axial distributions of local particle velocity and flow development along the downer for the binary particle mixture system.The axial and radial distributions of the local particle velocity at different radial positions on various axial levels along a downer were systematically measured by using a PV-4A fiber-optic particle velocity probe in a half-column downer of 2m-height and Φ30 mm I.D. The approximate particles settling velocities were measured and predicted, and also compared with theoretically calculated ones. Then the flow regions in downer were determined and the flow patterns of gas and solids were examined. Four kinds of solid materials with different physical properties were used to study the effects of particle properties on the axial and radial distributions of the local particle velocity. And the influences of distributor geometry configuration, dealing with both orthogonal tube and annular styles, and operation conditions on radial distributions of the local particle velocity were also investigated in this paper. Based on the concept of dimensionless local particle velocity, a new correlations for predicting the local particle velocity distribution was developed by regressing experimental data from different geometrical downers <WP=5>and different material systems in both present work and literatures, which can be used in a relatively wider range. Finally, the radial distributions of binary mixture particle velocity，formed by respectively and simultaneously injecting fine-FCC catalysts and coarse-glass beads in downers，were examined at different composition ratios of FCC catalysts to glass beads. The main results are shown as below:(1) The approximate particles settling velocities determined by experiments appear in the similar variation rule as the calculated ones, i.e. these velocities are increased with the increasing of particle sizes; In this study, the local particle and mean particle velocities, measured at very low gas flow-rate, can be taken as the approximate particles settling velocities.(2) The gas and solids flow development in downer and the radial distributions of local particle velocity are varied significantly with the physical properties of particle. In the first acceleration region, the radial distributions of local particle velocity fluctuate more often and are more steeped, while in the second acceleration region they are more stable and uniform. The key factor for the great change of radial distributions of local particle velocity is the particle properties, and at the same operation conditions, the large the particle size and the high the particle density, the more even the radial distributions of local particle velocity.(3) The reduced particle velocity () can reflect the even level of the radial distributions of local particle velocity. Five dimensionless numbers, standing for the bed geometrical characteristics, physical properties of particle, and others, i.e., H/D、vp*、Re0、Cds and were employed to develop a new correlation for predicting the更多还原