Research Article Computational Study of Gas-Solid Flow in a Horizontal Stepped Pipeline Zhengquan Li , 1,2 Kaiwei Chu , 3 Renhu Pan, 4 Aibing Yu, 2,4 and Jiaqi Yang 1 1 International Research Institute for Minerals, Metallurgy and Materials, Jiangxi University of Science & Technology, Ganzhou 341000, China 2 Laboratory for Simulation and Modelling of Particulate Systems, Chemical Engineering, Monash University, Clayton, Melbourne, VIC 3800, Australia 3 School of Qilu Transportation, Shandong University, Jinan 250002, China 4 Fujian Longking Corporation, Longyan 364000, China Correspondence should be addressed to Zhengquan Li; qqzhengquan@163.com and Kaiwei Chu; k.chu@sdu.edu.cn Received 5 June 2019; Accepted 19 July 2019; Published 15 September 2019 Academic Editor: Dongmin Yang Copyright©2019ZhengquanLietal.isisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In this paper, the mechanism governing the particle-fluid flow characters in the stepped pipeline is studied by the combined discrete element method (DEM) and computational fluid dynamics (CFD) model (CFD-DEM) and the two fluid model (TFM). emechanismsgoverningthegas-solidflowinthehorizontalsteppedpipelineareinvestigatedintermsofsolidandgasvelocity distributions, pressure drop, process performance, the gas-solid interaction forces, solid-solid interaction forces, and the solid- wall interaction forces. e two models successfully capture the key flow features in the stepped pipeline, such as the decrease of gasvelocity,solidvelocity,andpressuredrop,duringandafterthepassageofgas-solidflowthroughthesteppedsection.Whatis more important, the reason of the appearance of large size solid dune and pressure surge phenomena suffered in the stepped pipelineisinvestigatedmacroscopicallyandmicroscopically.esectioninwhichtheblockageproblemmostlikelyoccursinthe stepped pipeline is confirmed. e pipe wall wearing problem, which is one of the most common and critical problems in pneumaticconveyingsystem,isanalysedandinvestigatedintermsofinteractionforces.Itisshownthatthemostseriouspipewall wearing problem happened in the section which is just behind the stepped part. 1. Introduction In industries, there are always increasing needs to convey large quantities of bulk solids over a long distance (up to 1-2km). In such cases, the long-distance high-pressure dense-phase pneumaticconveyingsystemsareusuallyemployed.issystem mainly consists of storage pumps, conveying pipelines, and cyclone separators. In such a system, the stepped pipeline rather than conventional pipeline is usually used. is is because that, in the conventional pipeline and high-pressure conditions, the gasandsolidvelocitieswillbetoohighattheendofthepipeline due to the compressibility of the gas. High velocity can cause solids attrition, pipe wear, and a large pressure loss. A large pressure loss also means that more power is needed for the transportation. erefore, keeping the conveying air velocity as lowaspossibleisveryimportant.esteppedpipeline(Figure1) provides a solution for this problem. Although the advantages of using stepped pipelines are considerable compared to single-bore pipelines, the use of steppedpipelinesinhigh-pressuresystemshasbeenalongand slow development. Part of this was probably due to the lack of understanding of the mechanisms governing the gas-solid flow characters in the stepped pipeline. ere was very little pub- lished information on the subject, and only a few universities, onaworldwidebasiswereundertakingresearchinthearea[2]. Inthelastdecade,moreandmoreresearcherspaidattentionto this area, but published information is still limited. Generally, studies on gas-solid flows in the stepped pipelines have employed two methods of investigation: experimental and numerical simulation methods [3]. Hindawi Mathematical Problems in Engineering Volume 2019, Article ID 2545347, 15 pages https://doi.org/10.1155/2019/2545347