Development of a coupled CFD-DEM multi-grain model

Student thesis: Master

Abstract

Hydrogen is an essential chemical feedstock used in the synthesis of chemicals critical to the global economy. With steam methane reforming accounting for 95% of the production of hydrogen with a production rate of 80 million tonnes of pure hydrogen using natural gas as a feedstock, steam methane reforming is responsible for around 830 million tonnes of CO2 emissions. On the road towards sustainable pathways to create renewable intermediates and transportation fuels with the reduction of greenhouse gas emissions a novel pathway on producing hydrogen on a large scale is thermocatalytic decomposition of methane into hydrogen gas and carbon nanomaterials.
The main advantage of this production method is the reduction of CO2 emitted by supplying heat to the thermocatalytic decompostion reaction of methane compared to steam methane reforming, in case of burning natural gas to provide the heat for the moderately endothermic reaction. Another advantage utilizing this reaction is the production of a valuable byproduct being carbon nanomaterials next to the desired hydrogen.The objective of this project is to couple heat and mass transfer phenomena in the discrete particle model and couple the discrete particle model with a multi-grain model to in a later stage simulate TCD reaction of methane in a lab-scale fluidized bed reactor to improve the understanding of the hydrodynamic behaviour of the fluidized particles. To simulate a lab-scale fluidized bed reactor, an Eulerian-Lagrangian Discrete Particle Model is used. The discrete particle model is coupled with a Multi-Grain model to account for individual intra-particle phenomena based on local conditions in the fluidized bed reactor.
During this project heat and mass transfer phenomena between the CFD-DEM models in DPM have been coupled and verified with simplified analytical solutions. Next to coupling of the models in DPM, the DPM model is coupled with a multi-grain model developed by Hadian et al.[18]. To be able simulate the phenomena occuring in a FBR utilizing TCD of methane it is critical to couple these CFD-DEM-MGM models. The cases used to prove implementation and coupling are described in chapter 3, where the simulation results give accurate comparison with the analytically obtained solutions confirming correct implementation. Critical to obtaining insight in the hydrodynamic behaviour of the fluidized bed due to the polydispersity of the particles by adherence of carbon on the catalyst particles, a polydisperse drag force correlation is implemented. During this thesis the implementation of the drag force correlation developed by Cello et al. has not been verified by experimental data due to extensive simulation times required to obtain results for a credible and exclusionary validation [10]. A preliminary test has been preformed to compare the results with already implemented drag force correlation present in the model.
At the end of the thesis, the main results, conclusions and further extensions to the DPMMGM are summarized to be able to simulate a FBR with TCD of methane together with other research and modelling topic which could utilize implemented and coupled phenomena during thesis.
Date of Award2021
Original languageEnglish
SupervisorMorteza Hadian (Supervisor 1), Martijn J.A. de Munck (Supervisor 1), Kay A. Buist (Supervisor 1) & J.A.M. (Hans) Kuipers (Supervisor 1)

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