An Innovative Review on Thermal Hydraulic Enhancement Techniques for High Pressure Syngas Cooling in Underground Coal Gasification Systems

Abstract

Underground Coal Gasification (UCG) is an important technology for using deep and unmineable coal reserves with less impact on the surface environment. One of the main technical challenges in UCG systems is the safe cooling and handling of synthesis gas produced at very high temperature and pressure inside underground coal seams. If this gas is not cooled properly, it can cause high thermal stresses, large pressure losses, damage to equipment, and safety problems. Conventional heat exchangers often do not perform well under such severe conditions, which has led to the development of improved heat exchanger designs for highpressure gas cooling.

This review presents a detailed overview of augmented and membrane-based heat exchanger technologies developed for cooling high-pressure syngas in underground coal gasification systems. The paper discusses how different heat transfer enhancement methods work, how heat exchanger geometries have evolved, and how design parameters affect heat transfer and pressure drop. Both numerical and experimental studies reported in the literature are reviewed and compared. Material selection and long-term reliability issues are also considered. The review identifies important gaps in current research, especially the lack of experimental data under realistic operating conditions, and suggests future research directions to support the safe, efficient, and reliable use of advanced heat exchangers in industrial UCG applications.