Jawaharlal Nehru Technological University Hyderabad B.Tech IV GEOLOGICAL AND TECHNOLOGICAL FACTORS OF COAL GASIFICATION CBM, SHALE GAB Previous Question Paper (September 2020 - R15)

Underground Coal Gasification (UCG) is an in-situ industrial process that converts coal seams into combustible gas without the need for mining. The process involves drilling injection and production wells into the coal seam, injecting gasifying agents such as air, oxygen, or steam, and initiating controlled combustion underground. This thermal and chemical reaction breaks down the coal structure, producing a mixture of gases known as syngas, which primarily consists of hydrogen, carbon monoxide, methane, and carbon dioxide. The resulting syngas is then brought to the surface through production wells, where it can be cleaned and utilized for power generation, chemical synthesis, or as a fuel source.

The efficiency and success of Underground Coal Gasification are influenced by several critical geological, technological, and operational factors:

• Coal Seam Characteristics: The thickness, depth, and dip of the coal seam are vital. Thicker seams provide more fuel, while depth influences the pressure and temperature conditions required for gasification. Excessive depth increases drilling costs and structural stability challenges.
• Geological and Hydrogeological Conditions: The presence of faults, fractures, and groundwater flow can lead to gas leakage or water ingress, which cools the reaction zone and reduces syngas quality. The permeability of the surrounding strata must be low to ensure containment.
• Gasifying Agents: The composition and flow rate of the injected agents (air, oxygen, or steam) directly control the reaction temperature and the calorific value of the syngas. Using oxygen instead of air eliminates nitrogen dilution, resulting in a higher heating value gas.
• Well Configuration and Linkage: The distance between injection and production wells and the method of establishing a flow path (linkage) through the coal are critical. Effective linkage ensures uniform gasification and prevents short-circuiting of the gasifying agents.
• Operational Pressure and Temperature: Maintaining optimal pressure is necessary to control the reaction rate and prevent the escape of gases into surrounding formations. Temperature management is essential to ensure complete carbon conversion and minimize the formation of undesirable byproducts.