Life cycle assessment and optimization analysis of different LNG usage scenarios

This paper aims to compare the environmental impacts of LNG in different life cycle stages and for various usages by applying life cycle assessment (LCA). According to different usage processes, we set three scenarios including S1-hydrogen production, S2-electricity generation, and S3-vehicle fuel to evaluate their environmental impacts. Furthermore, in order to satisfy better city development, an optimization analysis was made to identify the optimal distribution structure of LNG. The environmental impact analysis of LNG was conducted using life cycle assessment and CML2001 method. LCA was performed based on the ISO 14040 standard using GaBi 5.0 software. Four impact categories (i.e., global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), and photochemical ozone creation potential (POCP)) were considered. Sensitivity analysis was also made by means of GaBi 5.0 software. Crystal Ball software was applied to make the optimization analysis for different LNG usage scenarios. The minimum environmental impact factor was taken as the objective function to confirm the optimal distribution structure of LNG. The LCA results indicate that the environmental impacts of the gasification and usage stages far outweigh that of the transportation stage, and the highest environmental impact category for each scenario is GWP. The largest contribution factor to GWP of S1 is the production supply of imported electricity, whereas the largest contribution factor to GWP of S2 and S3 is the emissions. The optimization analysis indicate that when imported LNG is allocated 25% for hydrogen production, 73% for electricity generation and 2% for vehicle fuel, the GWP and cost of the total LNG usage are both minimum. Environmental analysis on different LNG usage scenarios allows the identification and selection of comprehensive LNG usage plans with the minimum environment impacts and lowest cost. For different LNG usage scenarios, the GWP of LNG used for vehicle fuel is the highest and for hydrogen production is the lowest. The production supply of imported electricity and the emissions are the two largest contribution factors to LCA results as well as the sensitivity analysis results of the three scenarios. The optimization analysis method and results can provide technology reference for scientific urban planning of LNG application and allocation.