DEM/CFD Simulation in Process Engineering

Abstract

Thermal and chemical treatment of bulk solids and particle systems is a basic unit operation in many industrial sectors. The purpose of the treatment can be either to achieve well-defined product properties or to use solids in gasification processes to produce syngas, synthetic fuels, or to recycle waste products. Typical examples are the calcination of minerals as dolomite or magnesite in the basic materials industry, the direct iron ore reduction with hydrogen in steel industry, coffee bean roasting in the food processing industry, or catalytic reactors and fluidized bed spray coating of tablets in the chemical and medical industries, respectively. Many of these processes are operated at high temperatures and are, therefore, energy-intensive and often associated with high CO2 emissions; a careful layout of the systems is needed. Furthermore, target properties of the solids must be achieved concerning reactivity, specific surface area, calcination or roasting degree, etc. To meet all these challenges and requirements, a detailed knowledge of the underlying physical and chemical processes is needed for predictive design. Fundamental studies are first necessary to understand the properties of particulate flows, e.g., regarding turbulence modulation, collisions between particles and/or with surfaces, and particle dispersion, before going toward practical applications. Typical systems are highly loaded with particles, often passed by a reactive gas flow, and are operated at high temperatures. Therefore, measurements are very challenging in such systems. Hence, appropriate simulation methods are needed to support system and reactor layout. Such a method combines the discrete element method (DEM) with computational fluid dynamics (CFD). DEM/CFD allows to track individual particles and their interactions with other particles, surrounding walls, and the gas phase in-between the particles. Conversion of the particles including intra-particle processes can be described as well as size change or development of adhesive forces associated with the thermal treatment. The current focus issue of Chemical Engineering & Technology entitled “DEM/CFD Simulation in Process Engineering” gives a status on the description of particulate flows with a focus on reactive particle-gas systems using DEM/CFD and presents illustrative examples of its application. A review article on DEM/CFD for reacting systems sets the frame for the further contributions that concentrate on fundamental aspects, specific examples, and important methodological developments. Examples presented are shaft kilns (production of quicklime/production of spinel), waste incineration, combustion of wood pellets, and carbonate looping processes. Novel trends as the usage of machine learning in combination with DEM/CFD, the combination of resolved and unresolved DEM/CFD in one simulation domain, and new approaches regarding the immersed boundary method to describe particle-gas systems are presented. The contributions do not claim to cover all relevant aspects needed for DEM/CFD simulations of reactive particle-gas systems but can be seen as a first overview and starting point for interested readers. This focus issue and the corresponding workshop at the Conference on Modelling Fluid Flow in Budapest 2022 have been organized by the Collaborative Research Centre BULK-REACTION financed by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Project-ID 422037413 – TRR 287. Prof. Dr.-Ing. Viktor Scherer Ruhr-Universität Bochum, Faculty of Mechanical Engineering, Department of Energy Plant Technology Prof. Dr.-Ing. Dominique Thévenin Otto von Guericke University Magdeburg, The Laboratory of Fluid Dynamics and Technical Flows Viktor Scherer Dominique Thévenin