Process selection of acid gas removal routes for CO₂-rich UCG-derived gas: Integrating product specifications, valuable-gas retention and energy consumption

Abstract Acid gas removal (AGR) is a key front-end step for converting CO₂-rich UCG-derived gas from fuel use to product-oriented utilization, but process selection must consider downstream gas specifications, valuable-gas retention and energy consumption simultaneously. In this work, five AGR processes—flash-regenerated Selexol, strip-regenerated Selexol, Rectisol, Ryan–Holmes and modified Ryan–Holmes—were developed in Aspen HYSYS for a unified feed gas and treatment capacity. Their operating windows were screened against the inlet requirements of staged cryogenic purification, methanol synthesis and methanation. In addition to residual CO₂/H₂S contents, CH₄/CO/H₂ losses and system energy consumption, a weighted valuable-gas loss rate (WVGLR) was introduced to quantify the overall loss of CH₄, CO and H₂ on a feed-composition-weighted basis, while the loss-corrected equivalent energy consumption (Eeq) incorporates the chemical-energy loss of these valuable gases into the process energy consumption. The Ryan-Holmes process achieved the best compromise in terms of valuable-gas retention and equivalent energy consumption for staged cryogenic purification, although a supplementary freeze-out assessment identified a localized CO₂ solidification constraint that requires further operating-window optimization, with CH₄, CO and H₂ loss rates of 0.96%, 0.12% and 0, respectively, and a loss-corrected equivalent energy consumption of 6.67 MW. Rectisol showed stronger deep desulfurization and wider CO₂ adjustment capability, making it more suitable for methanol synthesis and methanation. The results provide a product-oriented basis for selecting AGR processes for CO₂-rich UCG-derived gas.