Abstract

Fly ash deposition is an important phenomenon associated with ash/slag handling and discharge in the entrained-flow coal gasification process. Fouling and slagging inside the gasifier may cause reliability and safety problems because they can impose strong negative effects on the gasifier wall in the way of heat transfer and chemical corrosion. For these reasons, this study focuses on investigating the ash deposition distribution inside of a two-stage entrained-flow gasifier. The computational model is developed in order to simulate the gasification process with a focus on modeling ash formation, fly ash, and ash deposition. The Eulerian-Lagrangian approach is applied to solve the reactive thermal-flow field and particle trajectories with heterogeneous reactions. The governing equations include the Navier-Stokes equations, twelve species transport equations, and ten global chemical reactions consisting of three heterogeneous reactions and seven homogeneous reactions. The coal/ash particles are tracked with the Lagrangian method. The effects of different coal/ash injection schemes and different coal types on ash deposition have been investigated. The results show that the two-stage fuel feeding scheme could distribute the ash throughout a larger gasifier’s volume and, hence, could reduce the peak ash deposition rate and make the ash distribution more uniform inside the gasifier. Gasification of a high-ash coal results in a high ash deposition rate, low syngas higher heating value (HHV), and low carbon conversion rate. The result of ash deposition rate in this study can be used as a boundary condition to provide ash particle influx distribution for use in slagging models.

Highlights

  • Gasification is an incomplete combustion process, converting a variety of carbon-based feedstock into cleanHow to cite this paper: Lu, X.J. and Wang, T. (2015) Simulation of Ash Deposition Behavior in an Entrained Flow Coal Gasifier

  • By only injecting a certain amount of dry coal without oxygen in the second gasifier stage, only endothermic gasification reactions will occur, lowering the exit temperature of the syngas compared to a one-stage injection scheme

  • The results show that the carbon conversion rates are the same for each coal feeding scheme: all three cases reach 98% carbon conversion, but the syngas higher heating value (HHV) increases from 205,896 kJ/kmol to 208,726 kJ/kmol when the coal feeding at the second stage increases from 0% to 75%

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Summary

Introduction

Gasification is an incomplete combustion process, converting a variety of carbon-based feedstock into cleanHow to cite this paper: Lu, X.J. and Wang, T. (2015) Simulation of Ash Deposition Behavior in an Entrained Flow Coal Gasifier. Gasification is an incomplete combustion process, converting a variety of carbon-based feedstock into clean. (2015) Simulation of Ash Deposition Behavior in an Entrained Flow Coal Gasifier. Wang synthetic gas (syngas), which is primarily a mixture of hydrogen (H2) and carbon-monoxide (CO) as fuels. The syngas produced can be used as a fuel, usually for boilers or gas turbines to generate electricity. It can be made into a substitute natural gas (SNG), hydrogen gas, and/or other chemical products. As a part of this learning process, the CFD model is utilized to help provide some preliminary understanding of ash deposition behavior in an entrained flow gasifier

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