A Simulation Study for Low Rank Coal Gasification in Coal-Water Slurry Gasifier

Abstract

By using a 3-D CFD model, the gasification process of low-rank anthracite coal in a coal-water slurry gasifier was simulated and investigated. The effects of oxygen/coal ratio and inlet slurry temperature on the gasification furnace temperature characteristics, gas composition distribution, carbon conversion and effective gas content were investigated for different kinds of low-rank anthracites. The higher the ash content of anthracite, the lower the gasification efficiency and the lower the effective gas content. Increasing the oxygen/slurry ratio showed no significant change in the effective gas content, but a slight increase in the furnace outlet temperature and CO2 content. Increasing the inlet temperature of CWS enhances both the effective gas yield and gasification efficiency and decreases the CO2 content.

Introduction

Coal–water slurry (CWS) gasifiers are widely used entrained-flow gasifiers due to their simple feeding system, ability to reuse wastewater, and operation at pressures up to 8 MPa. Because CWS-derived syngas contains significant water vapor, no additional steam is required for CO reforming, making this technology attractive for chemical-industry syngas production.

Previous studies on coal gasification have focused on modeling devolatilization, char gasification, and gas-phase reactions, emphasizing detailed kinetic models, turbulence–chemistry interaction, and the effects of water/coal and oxygen/coal ratios. CFD-based simulations have been used to predict temperature, velocity, gas composition, and carbon conversion, and slurry preheating technologies have been proposed to improve cold-gas efficiency and reduce oxygen consumption.

However, most entrained-flow gasifiers use high-rank coals, while DPR Korea primarily has low-rank anthracite with low volatile matter and high ash content. Such coals gasify inefficiently and require higher oxygen/coal ratios, which risks shifting reactions toward complete combustion and increased CO? production. Therefore, this study investigates the gasification behaviors of low-rank anthracites with varying ash and volatile contents.

A validated 3-D CFD model incorporating turbulence (realizable k–ε), radiation (DO model), devolatilization kinetics, and homogeneous/heterogeneous reactions was used to simulate CWS gasification for three types of low-rank anthracite (Cases 1–3) and compare them with a high-rank reference coal (Case 0).

Key Findings

1. Effect of Coal Properties (Ash and Volatile Content)

   • Low-rank coals (Cases 1–3) produced lower outlet temperatures (~1290–1310 °C) and lower effective syngas contents (CO + H? ≈ 70–73%) compared to high-rank coal (Case 0: 1480 °C, 81.8%).

   • Higher ash content reduced gasification efficiency by masking carbon surfaces and increasing unreacted carbon losses.

   • Furnace temperatures for the low-rank coals stayed ~170 °C below ash melting temperatures, indicating the need for flux addition.

2. Effect of Oxygen/Slurry Ratio

   • Increasing O?/slurry ratio (0.62 → 0.72) raised furnace temperature but did not significantly improve effective gas yield.

   • CO generally decreased while CO? increased due to enhanced oxidation.

   • H? trends varied depending on coal ash content, influenced by temperature and available water.

3. Effect of Slurry Inlet Temperature (Preheating)

   • Increasing inlet temperature (20 °C → 250 °C) improved gasification performance:

     • Effective gas content increased by 7.6%.

     • Outlet temperature rose by ~140 °C (1294 °C → 1435 °C).

     • CO? content decreased by 7.5%.

   • Preheating enhances reaction conditions and improves energy efficiency but still requires flux for ash melting.

Conclusion

The higher the ash content of anthracite, the lower the gasification efficiency and the lower the effective gas content. Increasing the oxygen/slurry ratio showed no significant change in the effective gas content, but a trend of increasing the reactor outlet temperature and carbon dioxide content. Also, increasing the inlet temperature of low-rank CWS increases both the gasification temperature, the effective gas yield and the gasification efficiency, and decreases the carbon dioxide content. Credit authorship contribution statement Ri Kwang Jin: Methodology, Investigation. Hong Chol: Conceptualization, Writing original draft. Jon Chol Jin: Data curation Conflict of Interest: The authors declare that they have no conflict of interest.

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Copyright

Copyright © 2025 Kwang Jin Ri, Chol Hong, Chol Jin Jon. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.