Underground Coal Gasification Processes and Applications

Underground coal gasification (UCG) is an in situ conversion technique that transforms non-minable coal seams into combustible synthesis gas or syngas by injecting oxidants and steam through boreholes. A high-temperature cavity is formed as heat and chemical reactions drive pyrolysis, combustion and gasification in a controlled combustion zone. The produced syngas—comprising hydrogen, carbon monoxide, methane and carbon dioxide—can be brought to surface for power generation, chemical feedstock or hydrogen production. Integration with carbon capture and storage offers a pathway to reduce greenhouse-gas emissions, while the avoidance of traditional mining mitigates surface disruption and enhances resource recovery. Key challenges include cavity growth control, subsurface permeability management, and minimising contamination of groundwater. Advances in numerical modelling, process monitoring and well-pair configuration are broadening the commercial feasibility of UCG on a global scale, with pilots and field trials underway in several coal-rich regions.

Research from Nature Portfolio

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Research from all publishers

Recent reviews of UCG for decarbonised hydrogen production highlight the growing focus on optimising steam-oxygen ratios, reactor pressure and seam geometry to maximise H₂ yields. Researchers report that coal rank and in situ gasification parameters critically influence hydrogen selectivity, and they advocate coupling UCG with water-gas-shift reactors and advanced separation technologies for clean H₂ delivery. Large-scale laboratory experiments under varying pressure regimes have demonstrated that methane-rich gas yields increase with higher gasification pressures and depend strongly on coal rank, achieving energy efficiencies above 70 per cent in semi-anthracite seams at elevated pressures. Complementary thermochemical equilibrium modelling has been employed to predict syngas composition across a range of deposit-specific temperatures, pressures and oxidant compositions; validation against field and laboratory data confirms its utility for design optimisation and process control, enabling rapid assessment of gas quality for diverse end-uses.

Underground Coal Gasification Processes and Applications publication trend

The graph below shows the total number of articles in underground coal gasification processes and applications across all publications each year (not limited to Nature Index journals).

Technical terms

Syngas: A combustible mixture of hydrogen, carbon monoxide, methane and carbon dioxide produced by gasification of coal.

Pyrolysis: Thermal decomposition of coal in the absence of oxygen, releasing volatile compounds and chars.

Cavity growth: The expansion of the gasification zone within the coal seam as coal is consumed and void space develops.

Permeability: A measure of the ease with which gases or fluids can flow through the coal seam and surrounding strata.

Water-gas-shift reaction: A reversible reaction converting carbon monoxide and water to carbon dioxide and hydrogen, used to enhance H₂ yield from syngas.

Carbon capture and storage (CCS): Techniques for separating CO₂ from syngas and securely storing it underground to mitigate emissions.

References

1. Review of underground coal gasification technologies and carbon capture. International Journal of Energy and Environmental Engineering (2012).
2. Coal decarbonization: A state-of-the-art review of enhanced hydrogen production in underground coal gasification. Energy Reviews (2022).
3. Large-scale Experimental Investigations to Evaluate the Feasibility of Producing Methane-Rich Gas (SNG) through Underground Coal Gasification Process. Effect of Coal Rank and Gasification Pressure. Energies (2020).
4. Synthesis Gas Composition Prediction for Underground Coal Gasification Using a Thermochemical Equilibrium Modeling Approach. Energies (2020).