【作者】 张欢；

【导师】 钮根林； 赵辉；

【作者基本信息】 中国石油大学 ， 化学工艺， 2008， 硕士

【摘要】 气固两相流态化渗透在石化、能源、冶金等各个领域,提升管工艺在石油加工中应用尤其广泛。对于多产低碳烯烃的过程,传统的提升管反应器很难同时满足大剂油比、适宜接触时间的目的,而变径提升管则可以较好地实现这两大目标。本文应用计算流体力学(CFD)商业软件,对重质油加工国家重点实验室内3m高的变径提升管冷模装置进行了数值模拟,摸索到一套能够描述该系统气固两相流动的计算模型及相关设置。此外,本文还对大庆炼化公司多产低碳烯烃工业装置内的气固两相的流动行为进行了模拟计算,给出气固两相在提升管内的分布状况,并依据计算的结果对比了不同结构对装置操作造成的影响。由冷模实验测得的固含率可知,提升管变径段内颗粒浓度非常高,团聚现象非常明显,在数值模拟中需要考虑这种团聚作用的影响,杨宁根据能量最小多尺度模型得到的曳力系数简化公式可以描述颗粒团聚的影响;对于固相采用颗粒动理学理论进行封闭,固相进口采用“进口固体通量=出口固体通量”的UDF设置,颗粒碰撞恢复系数取0.85。将模拟结果与相同工况下的实验值进行对比发现,除了轴线上一些位置存在较大的偏差外,其他位置尤其是在提升管边壁处吻合得较好,并且三维网格的计算结果比二维计算结果更准确。本文认为二维计算误差较大的原因主要在网格划分上,由于二维模型中的变径段面积扩大不够明显,导致轴线处气体速度偏大,因而固含率降低。大庆炼化两段提升管多产低碳烯烃(TMP)装置也采用变径提升管技术,并进行了部分装置的改造。本文着重对改造前后的装置的变径段部分进行气固两相流动模拟,同时对相同管径的传统提升管内气固流动状况进行了计算。通过计算结果的对比可以发现,改造后提升管内轴向上的催化剂分布比传统提升管要好,在主要反应区催化剂浓度高;径向上催化剂分布也比较均匀,环-核结构得到一定的弱化;有效避免了催化剂的高速碰撞,因而减小了催化剂磨损的量;催化剂的返混现象减小,可以减小催化剂的结焦,提高产品的结构;同时,变径段以上气固速度急剧增大,可以减少二次反应的发生。更多还原

【Abstract】 Fluidized bed technology was widely encountered in petro-chemical, energy and metallurgy industry. Riser reactor has become one of the most ordinary used equipment in solid catalytic process because of the great success of Fluid Catalytic Cracking process. Enhanced propylene production through catalytic pyrolysis of heavy oil has become a promising technology to promote economic performance of enterprise. While, innovations should be introduced to archive high catalyst-oil ratio and appropriate residence time simultaneously, riser reactor with changing-diameter could be a probable solution. Ideal riser reactor for thus purpose should be made up of several sections with different diameter. Numerical simulations based on computational fluid-dynamic (CFD) technique have been performed to investigate the hydrodynamics of gas-solid two phase flow in a bench scale experiment. Commercial code FLUENT was used in the research and a suitable model was developed .Flow pattern of the gas-solid two phase flow in an industry scale reactor also has been simulated. Effect of different nozzle configuration and its influence on catalyst distribution in reactor were investigated and discussed.Experimental measurement on bench scale equipment indicates that the volume fraction of the catalyst in the larger diameter section of the riser was much higher comparing with the traditional riser, so the catalyst aggregating should have more evidence to influence whole flow pattern. Improved drag model based on EMMS (Energy-Minimization Multi-scale) model should have better ability to predict the dense solid flow behavior in the riser. Constant solid reserve was keep by setting solid inlet velocity according to the solid outlet flux. Kinetic Theory for Granular Flow (KTGF) model was used for solid phase. A value of 0.85 was used for particle restitution coefficient in the simulation. It was noticed that, CFD simulations results basically agree well with the measured experimental measurements. 3D CFD simulation gave better precision than 2D cases due to the more accurate description of real equipment in 3D simulation.Different configurations of nozzles and reactor structure on an industry scale reactor have been investigated by CFD simulation also. According to the numerical simulation, extra notice should be paid to the large-diameter zones, where the main reactions zone. By suitable retrofit, the axial distribution of catalyst particles could be improved significantly, in nozzle zones the solid volume fraction was higher and the catalyst radial distribution was well-proportioned. Ordinary core-annual structure was very weak and the collision between high velocity catalysts was avoided, so the attrition of the catalyst could be eliminated. High gas velocity could be gained in following small diameter riser section, so the undesired by-pass products could be controlled reasonably.更多还原