基于连续方法的气固循环流化床全回路模拟及稳定性分析_贾博宇.pdf

第 23 卷第 2 期2023年 2月过 程 工 程 学 报The Chinese Journal of Process EngineeringVol.23 No.2Feb.2023Full-loop simulation and stability analysis of a gas-solid circulating fluidized bedBoyu JIA1,2,Xinhua LIU2,Ge WANG2,3,Huaiyu SUN1,Bona LU2,4*1.School of Chemical Engineering,Shenyang University of Chemical Technology,Shenyang,Liaoning 110142,China2.Institute of Process Engineering,Chinese Academy of Sciences,Beijing 100190,China3.Sinopec Lubricant Company,Beijing 100085,China4.School of Chemical Engineering,University of Chinese Academy of Sciences,Beijing 100049,ChinaAbstract:The gas-solid fluidized bed has wide application in industry such as refinery,metallurgy,and ore calcination.In the practical operation,it is usually combined with other units like conveying pipe,cyclone,downer and valves to run in a full-loop way.Compared to simulation of a single operating unit,the full-loop simulation of the gas-solid circulating fluidized bed system can reveal interactions between different operating components and diagnose the sudden change of operation,thus being of greater importance in industrial operation.In this study,the full-loop simulation and stability analysis of a gas-solid circulating fluidized bed of virtual process engineering(VPE)are carried out under the framework of two fluid model and kinetic theory of granular flow.The simulation shows that there exists periodic fluctuation of solids volume fraction and pressure drop in the riser where two distinct fluidization states,i.e.,dilute fluidization and dense fluidization,appear alternatively,because of the occurrence of gas bypassing.To figure out the underlying cause,the influence of model factors(mainly refer to gas-solid drag)and operating parameters(i.e.,solid inventory and superficial velocity)on the periodic fluctuation phenomenon is numerically investigated.It is found that changing the drag model cannot eliminate the fluctuation,while reducing the gas velocity and increasing the solid inventory are conducive to the stability of particle circulating transportation and avoiding the occurrence of gas bypassing because of the increase in pressure drop of the Loop-seal.On this basis,the Loop-seal valve which is reported to be closely related to particle conveying is focused on.The simulation with adding a virtual valve in the middle of the inclined pipe is performed and shows that the resistance of particle conveying increases thus ensuring the enough pressure drop of the Loop-seal to operate the full-loop system steadily.The time-averaged axial profile of pressure drop predicted by the simulation agrees with the experimental data.This method is found to be helpful to improve the stability of the full-loop simulation.Key words:full-loop simulation;dense flow transport;circulating fluidized bed;multi-scale structure;particle transporting resistance TFM+KTGFRegulate model factorsand operating parametersRegulate particle transporting resistanceStability achievedTimeSolid volume fractionSolid volume fractionTime研究论文DOI:10.12034/j.issn.1009-606X.222080收稿：2022-03-15，修回：2022-04-30，网络发表：2022-06-10；Received:2022-03-15,Revised:2022-04-30,Published online:2022-06-10基金项目：国家自然科学基金资助项目(编号：22078331)作者简介：贾博宇，硕士研究生，化学工程专业，E-mail:；通讯联系人，鲁波娜，研究员，化学工程专业,E-mail:引用格式引用格式：贾博宇,刘新华,王各,等.基于连续方法的气固循环流化床全回路模拟及稳定性分析.过程工程学报,2023,23(2):226234.Jia B Y,Liu X H,Wang G,et al.Full-loop simulation and stability analysis of a gas-solid circulating fluidized bed(in Chinese).Chin.J.Process Eng.,2023,23(2):226234,DOI:10.12034/j.issn.1009-606X.222080.第 2 期贾博宇等：基于连续方法的气固循环流化床全回路模拟及稳定性分析基于连续方法的气固循环流化床全回路模拟及稳定性分析贾博宇1,2，刘新华2，王 各2,3，孙怀宇1，鲁波娜2,4*1.沈阳化工大学化学工程学院，辽宁 沈阳 1101422.中国科学院过程工程研究所，北京 1001903.中国石化润滑油有限公司，北京 1000854.中国科学院大学化工学院，北京 100049摘要：相比对单个操作单元的模拟，气固循环流化床的全回路模拟能全面揭示各单元之间的联系、诊断操作突变等现象，对实际工业生产更具指导意义。本研究在连续介质模型结合颗粒动理论的框架下，对一套虚拟过程工程(VPE)的气固循环流化床装置进行了全回路模拟和稳定性分析。模拟发现了提升管中的颗粒浓度及压降发生大幅度的周期性震荡现象，两种完全不同的操作状态，即稀相输送和浓相输送，交替式地出现。为分析该现象产生的原因，考察了模型因素(主要是气固相间曳力)和操作因素(颗粒藏料量和提升管表观气速)对周期性震荡现象的影响。研究发现，将考虑非均匀结构影响的曳力替换成均匀曳力，仍不能消除周期震荡现象，其颗粒输送返回装置(Loop-seal)压头不足以保证颗粒从下降管平稳输送到提升管，而降低气速和增大藏料量都有利于颗粒循环输送的稳定性，防止“窜气”现象的发生。结合上述现象，进一步聚焦影响颗粒输送的关键点，即Loop-seal气动阀，采用引入虚拟阀门的方式提高Loop-seal输送管中的输送阻力，从而有效改进了全回路模拟的稳定性，其预测得到的提升管轴向压降分布与实验值基本吻合。关键词：全回路模拟；密相输送；循环流化床；多尺度结构；颗粒应力中图分类号：TQ051.13 文献标识码：A 文章编号：1009-606X(2023)020226091 前 言 气固循环流化床常作为关键操作单元，如反应器、再生器等广泛用于石化、冶金、矿物加工等领域。在实际生产过程中，它通常不是独立操作，而是与其他单元耦合成为连续循环回路系统，常称之为全回路系统。以石油催化裂化(FCC)反应-再生系统为例，整个全回路系统由反应器、沉降器、多级旋风分离器、再生器及各种输送管等多个操作单元构成，各个单元彼此影响，通过调控催化剂颗粒输送达到整个回路的压力和能量平衡。颗粒作为催化介质、热介质或反应原料1，其在整个回路系统中的稳定输送成为保持系统安全操作的关键，而各个操作单元间的联动则是影响其稳定输送的主要因素，因此深入了解全回路系统之间的各单元间的相互作用规律对工业操作具有重要意义。随着气固两相流理论以及计算软硬件的高速发展，计算流体力学(CFD)模拟已成为研究气固复杂流动行为的强大工具。目前，气固两相流模拟研究主要集中于单个操作单元。由于单个操作单元抽离于整个回路系统，因此断面处(单元的出入口)往往需要简化或近似处理，而忽略了回路中相邻单元间的联系。如对旋风分离器的模拟2,3，通常固定入口速度，颗粒出口处或封住或设为单一的负颗粒速度，其模拟得到的旋风效率只代表指定气速下的效率。而全回路中的旋风分离器的入口处速度处于不断变化之中，且受制于相邻反应器的运行情况以及出口结构，因而统计得到的旋风效率是综合值，更符合实际运行情况。对提升管反应器的模拟4-7，通常在出口处设为常压，床内初始堆积一定颗粒物料，而气体入口处给定固定气速，在颗粒入口设为固定的颗粒输送速度，或让颗粒入口颗粒流率等于出口流率从而保持反应器内的存料量不变，由此预测到的流动行为是指定操作条件下的情况，难以反映操作过程中由于参数调整引起的流动结构