Abstract
Higher air-pollutant (CO2, SO2, particulates, etc.) emission from coal burning prohibits the direct use of coal. The demand for clean and sustainable energy is increasing with the growth of population and living standards. Considering the current energy challenges, coal-enriched countries have focused on the green utilization of coal by converting it to a clean energy source, such as synthetic natural gas (SNG). To fulfill the global clean energy demand, liquefaction is a promising and feasible approach enabling safe storage and transportation. However, the liquefaction of SNG is an energy- and cost-intensive process, primarily owing to the presence of low-boiling impurities such as hydrogen and nitrogen. This paper describes the major challenges and issues associated with the SNG liquefaction process for its commercialization and attempts to solve the issues inherent to the SNG liquefaction industry. The optimal energy-efficient single-loop mixed-refrigerant-based liquefaction schemes, with the separation of low-boiling impurities (hydrogen and/or nitrogen), are presented as a major contribution of this study. The proposed SNG liquefaction schemes are analyzed in comparison with the latest SNG liquefaction study. Liquefied SNG can be produced with energy savings of up to 30.4% compared to the published base case. (C) 2018 Elsevier Ltd. All rights reserved.