Computational modeling of pyrolysis and combustion in a fixed‐bed waste gasifier

Johnny Chung‐Yin Tsai (Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, USA)
Hong G. Im (Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, USA)
Taig‐Young Kim (Department of Mechanical Engineering, Korea Polytechnic University, Si‐Heung, Korea)
Jaeho Kim (Korea Institute of Energy Research, Daejeon, Korea)

International Journal of Numerical Methods for Heat & Fluid Flow

ISSN: 0961-5539

Publication date: 26 October 2012

Abstract

Purpose

The purpose of this paper is to present a three‐dimensional CFD model that simulates the pyrolysis, combustion and heat transfer phenomena in a refuse‐derived fuel (RDF) gasifier. Correlations between different operation conditions and the waste stack morphology are also investigated. Parametric studies are conducted to optimize operating conditions to achieve an even stack surface minimal the local oxidation in the waste stack.

Design/methodology/approach

This paper proposes a Lagrangian pyrolysis submodel which can be applied to determine the local pyrolysis rate and porosity field by introducing the local characteristic diameter of the waste solid sphere. The flow field is described by a single‐phase porous flow model using the SIMPLE algorithm with momentum extrapolation. A one‐step global reaction was adapted for the chemical reactions inside the gasifier.

Findings

Computational results produced three‐dimensional distribution of the flow field, temperature, species concentration, porosity and the morphology of the waste stack under different operation conditions. Some parametric studies were conducted to assess the effects of the inlet temperature and the feeding rate on the waste stack shape. The results demonstrated that the model can properly capture the essential physical and chemical processes in the gasifier and thus can be used as a predictive simulation tool.

Research limitations/implications

Due to the lack of accurate reaction rate information, the computational results have not been directly compared against experimental data. Additional refinement and subsequent validation against prototype gasifier experiment will be reported in future work.

Originality/value

A full three‐dimensional computational model is developed for the complex two‐phase flow based on porous medium representation of the solid stack. A Lagrangian pyrolysis model based on the characteristic diameter of the solid waste material was proposed to describe the pyrolysis rate history. The developed model reproduces correct physical and chemical behavior inside gasifier with adequate computational efficiency and accuracy.

Keywords

Citation

Chung‐Yin Tsai, J., Im, H., Kim, T. and Kim, J. (2012), "Computational modeling of pyrolysis and combustion in a fixed‐bed waste gasifier", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 22 No. 8, pp. 949-970. https://doi.org/10.1108/09615531211271808

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Publisher

:

Emerald Group Publishing Limited

Copyright © 2012, Emerald Group Publishing Limited

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