Study on the Influencing Factors of Syngas Heating Value in Underground Coal Gasification

This study investigates the influence mechanism of key factors on the heating value of syngas during underground coal gasification (UCG) and proposes an optimization path for enhanced energy conversion efficiency based on typical global field test data. Integrating data review and pattern analysis, it systematically explores the influence of core factors, including coal seam characteristics, reactor structure, and gasification agent ratio. It is found that the relationship between syngas heating value and coal rank is not simply linear, with representative heating values ranging from 4.13 to 11.96 MJ/m3. Medium-rank coal, characterized by “medium volatile matter and low ash content”, yields high-heating-value syngas when paired with air/steam as the gasification agent. Shaftless reactor structures demonstrate superior overall performance compared to shaft-based designs, with the representative heating value improving from 3.83 MJ/m3 to 7.8 MJ/m3. The combination of U-shaped horizontal wells with the Controlled Retracting Injection Point (CRIP) technology improves the heating value. Effective control over the syngas heating value can be achieved by optimized composition and ratio of the gasification agent, with representative value of 9.10 MJ/m3 in oxygen-enriched steam gasification compared to 4.28 MJ/m3 in air gasification. Based on an evaluation of data fluctuation characteristics, the significance ranking of the factors is as follows: gasification agent, coal rank, and reactor structure. Consequently, an engineering optimization path for enhancing UCG syngas heating value is proposed: prioritize optimizing the composition and ratio of the gasification agent as the primary means of heating value control; on this basis, rationally select coal rank resources, focusing on process compatibility to mitigate performance fluctuations; and then incorporate advanced reactor structures to construct a synergistic and efficient gasification system. This research can provide theoretical support and data references for engineering site selection, process design, and operational control of UCG projects.