CFD Analysis of Coal and Heavy Oil Gasification for Syngas Production

Vikram Sreedharan

Research output: Book/ReportPh.D. thesis

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Abstract

This work deals with the gasification of coal and heavy oil for syngas production using Computational Fluid Dynamics (CFD). Gasification which includes complex physical and chemical processes such as turbulence, multiphase flow, heat and mass transfer and chemical reactions has been modeled using a discrete phase model. In this model, the continuous phase is described by Eulerian conservation equations and the discrete phase is described by tracking individual particles in a Lagrangian framework. A two-way coupling accounts for momentum, heat and mass transfer between the continuous and discrete phases. Gasification consists of the processes of passive heating, devolatilization, volatiles oxidation, char gasification and gas phase reactions. Attention is given here to the chemical kinetics of the gasification processes.
The coal gasification model has been validated for entrained-flow gasifiers of different scale, using different feedstock and under different operating conditions. Two different chemical kinetics schemes have been used. The first scheme was taken directly from the literature and the second improved scheme was proposed in the present work. The predictions of axial temperature profiles through the gasifier and species mole fractions at the outlet of the gasifier show good agreement with experimental and numerical data found in the literature. A general observation is that the outlet species mole fraction of hydrogen and carbon monoxide is underestimated and water vapour and carbon
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dioxide is overestimated. The deviation is fairly small, particularly for the improved chemical kinetics scheme.
The heavy oil gasification model has been validated for a pilot-scale entrained-flow gasifier operating under different oxygen ratios. A gasification model similar to that developed for coal gasification is proposed for heavy oil gasification, using a single chemical kinetics scheme. Predictions of heavy oil gasification are rare in the literature, so that the present work holds some significance. The predictions of the temperature along the gasifier centerline and the species mole fractions at the outlet of the gasifier show good agreement with experimental data found in the literature.
Original languageEnglish
Number of pages118
Publication statusPublished - 2012

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