Life cycle assessment of liquefied natural gas production from coke oven gas in China

Abstract

Producing liquefied natural gas (LNG) from coke oven gas (COG) is a promising option to partly alleviate the shortage of natural gas supply and effectively utilize the byproduct of coking production in China. In order to systematically evaluate the energy consumption and environmental impact of COG-based LNG process, the life cycle assessment (LCA) method was introduced in this study. Two synthesized approaches were considered and compared, namely decarbonization process and methanation process. Besides, whether with or without H2 extraction in methanation process is also discussed. Inventory data are obtained from onsite investigations of representative enterprises in China. The results indicate that, LNG production stage is the dominated unit in the overall environmental impacts of decarbonization process, next is LNG evaporation stage, while coking stage only contributes 2.38%. The reason is that COG is only responsible for less upstream environmental burdens as a byproduct. In LNG production stage, medium pressure steam, COG and electricity are the key substances. Comparative LCA shows that methanation process shows better environmental performance than decarbonization process in COG-based LNG production since more LNG product are produced. It is suggested that methanation process with H2 extraction is more desirable considering economic performance. This work intends to provide useful insights on the sustainability development of COG utilization in coking industry.