JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III COAL GASIFICATION, COAL BED METHANE AND SHALE GAS Previous Question Paper (November/December - 2020 - R16)

Underground Coal Gasification (UCG) is an in-situ gasification process that converts coal seams into combustible gas without the need for mining. The process involves drilling two wells into the coal seam: an injection well for supplying gasification agents (air, oxygen, or steam) and a production well for extracting the resulting product gas.

The working principle relies on the controlled combustion of coal underground. The injection of gasification agents initiates a reaction zone where coal is converted into a mixture of hydrogen, carbon monoxide, methane, and carbon dioxide. The reaction proceeds through four main stages: drying, devolatilization, combustion, and gasification. The product gas is then brought to the surface through the production well for processing and utilization.

Merits:

• Eliminates the need for conventional mining, reducing surface disturbance and occupational hazards.
• Allows access to deep or thin coal seams that are technically or economically unfeasible to mine.
• Lower capital expenditure compared to traditional surface gasification plants.
• Reduces waste disposal issues associated with coal ash and tailings.

Demerits:

• Risk of groundwater contamination due to potential leakage of gasification products into aquifers.
• Potential for surface subsidence as the coal seam is consumed.
• Difficulty in controlling the reaction front and maintaining consistent product gas quality.
• Extensive site characterization is required to ensure geological stability and environmental safety.

A typical UCG sketch would show an injection well connected to a production well via a channel created within the coal seam, with the combustion zone located between the two wells, surrounded by the overburden and underburden rock layers.

Underground Coal Gasification (UCG) technology has evolved significantly over the past few years, shifting from experimental pilot projects to more sophisticated, commercially oriented operations. The primary technological advancements include the transition from simple vertical well configurations to Controlled Retraction Injection Point (CRIP) technology, which allows for better control over the gasification front and improved cavity management. Modern UCG now integrates advanced directional drilling, real-time seismic monitoring, and sophisticated process control systems to enhance energy recovery efficiency and minimize environmental risks such as groundwater contamination and surface subsidence.

The global scenario of UCG technology is characterized by a strategic focus on energy security and the utilization of deep, unmineable coal seams. Key regional developments include:

1. China: Currently the global leader in UCG, China has successfully operated numerous commercial-scale projects, focusing on integrating UCG with chemical production and power generation.
2. Australia: Despite facing regulatory and environmental challenges in the past, Australia remains a hub for UCG research, focusing on high-efficiency gasification and stringent site monitoring protocols.
3. India: Recognizing the vast reserves of deep-seated coal, India has initiated several pilot studies and policy frameworks to explore UCG as a viable alternative to conventional mining, particularly for energy-starved regions.
4. Europe and North America: Research in these regions has largely transitioned toward the integration of Carbon Capture and Storage (CCS) with UCG, aiming to transform coal into a low-carbon energy source, though commercial deployment remains limited by economic and regulatory hurdles.

Overall, the global trend is moving away from basic combustion toward a refined, multi-product approach where UCG serves as a feedstock for hydrogen production, synthetic natural gas, and liquid fuels, reflecting a broader shift toward cleaner coal utilization technologies.