扭曲片强化裂解炉管多尺度混合特性分析  

Analysis of Multi-scale Mixing Character of Enhanced Cracking Coil with Twisted Tape

作　　者：柏德鸿 宗原[1] 赵玲[1] BAI Dehong;ZONG Yuan;ZHAO Ling(State Key Laboratory of Chemical Engineering,East China University of Science and Technology,Shanghai 200237,China)

机构地区：[1]华东理工大学化学工程联合国家重点实验室,上海200237

出　　处：《华东理工大学学报（自然科学版）》2020年第3期301-309,共9页Journal of East China University of Science and Technology

基　　金：国家自然科学基金(2012CB720501)。

摘　　要：通过耦合丙烷裂解自由基动力学,对装有扭曲片的裂解炉管中的反应流体进行模拟计算,深入分析了流体多尺度混合特性与结焦速率及产物分布之间的相互关系。计算结果表明,相比于空炉管,扭曲片强化炉管虽然压力损失增加5.31%,但在扭曲片下游轴向长度与炉管总长度之比为0.228截面处湍动能提高39.6%,全管特征微观混合时间仅为空炉管时对应值的1.72%,表明扭曲片对裂解过程有较好的介观和微观混合强化作用,该作用提高了管内场分布协同性,使得努赛尔准数(Nu)和史伍德准数(Sh)分别提高7.50%和2.34%,烯烃收率提高5.88%,管壁平均温度下降24.01 K。旋流产生的径向分速度提高了近壁区湍动程度,使得扭曲片强化炉管径向距离(r)与炉管半径(R)之比(r/R)为0.993处的流体停留时间比空管时的对应值降低53.01%,缓解了近壁高温区流体的过度裂解结焦。此外,扭曲片强化炉管微观尺度上的混合强化促使管内达到均匀分子尺度的反应区域比空炉管增大了5.29%,解释了烯烃收率提高的原因。Turbulent mixing enhancement of twisted tape for propane cracking process with detailed radial kinetics was described.Meso-and micro-scale mixing performance were analyzed to reveal the close relationship between turbulent mixing and cracking reaction.Computational fluid dynamics was used to conduct contrast simulations between bare coil and coil with twisted tape in order to present variations of transfer and cracking reaction characteristics.The simulation results show that by paying 5.31%more pressure drop than bare coil,the turbulent kinetic energy at the ratio of axial distance to total length Z/L=0.228 in the downstream of twisted tape is increased by 39.6%,while the overall averaged characteristic micro-mixing time is reduced to 1.72%with respect to bare coil,indicating an effective meso-and micro-mixing enhancement.The intensified turbulent mixing promotes the uniformity of field profiles to improve synergy among temperature,species concentration and velocity distributions,resulting in enhanced heat and mass transfer performance.The Nu and Sh of cracking coil installed twisted tape are increased by 7.50%and 2.34%compared to bare coil,respectively.The overall olefin yield is improved by 5.88%and the averaged coil skin temperature is reduced by 24.01 K.The coking suppression effect can be attributed to the strong swirling flow induced by twisted tape,generating a radial velocity component to accelerate fluid in the wall vicinity.Consequently,the residence time of fluid in the near wall region at the ratio of radial distance to cracking coil radius r/R=0.993 can be reduced by 53.01%.Furthermore,the enhanced turbulent mixing results in better homogenous radial field profiles,enlarging the molecular scale uniform mixed region by 5.29%to extend the reactive zone,which is beneficial for olefin yield improvement.

关 键 词：裂解炉管 过程强化 多尺度混合 抑制结焦 

分 类 号：TQ021.4[化学工程]