Underground Coal Gasification (UCG) is an advanced technology that converts deep coal reserves into synthesis gas for power generation and chemical production. The produced syngas exits the gasification cavity at extremely high temperatures and pressures, requiring efficient cooling before further processing. Conventional heat exchanger designs often experience significant thermodynamic inefficiencies under such severe operating conditions. Therefore, advanced heat exchanger configurations capable of improving energy efficiency and reducing thermodynamic irreversibility are required.
The present study investigates the exergy performance and sustainability characteristics of a membrane helical coil heat exchanger designed for high-pressure syngas cooling in underground coal gasification systems. A three-dimensional Computational Fluid Dynamics (CFD) model was developed using ANSYS Fluent to simulate turbulent compressible flow and heat transfer inside the helical tube. Temperature-dependent thermo physical properties of syngas were incorporated to improve the accuracy of numerical predictions.
The thermodynamic performance of the heat exchanger was evaluated using exergy analysis to quantify energy losses and irreversibilities occurring during heat transfer. The effects of Reynolds number, coil diameter, and pitch ratio on exergy destruction and exergy efficiency were systematically analyzed. Results indicate that the helical coil configuration significantly enhances heat transfer performance due to the formation of curvature-induced secondary flows. The exergy efficiency of the system increases with Reynolds number and reaches a maximum value of approximately 72% under optimal operating conditions.
The analysis reveals that heat transfer irreversibility represents the dominant contributor to exergy destruction in the system. However, appropriate selection of geometric parameters can significantly reduce thermodynamic losses and improve overall system efficiency. The findings of this study demonstrate that membrane helical coil heat exchangers offer a promising solution for sustainable thermal management in underground coal gasification and other high-temperature industrial energy systems.