Development and modification of large-scale hydrogen liquefaction process empowered by LNG cold energy: A feasibility study

Abstract

Hydrogen (H2) is considered a promising fuel and an energy carrier for carbon neutrality, but H2 has an issue in transportation and storage due to its low volumetric density. H2 liquefaction is an important technology in H2 supply that can overcome the low density issues, but the system has a serious challenge of high energy consumption. Thus, an improved energy efficient 50 ton day−1 of H2 liquefaction system comprising 4 mixed refrigeration cycles is proposed in this study. Especially, liquefied natural gas (LNG) was mainly used in the replacement of the precooling cycle, and the energy was saved by using the cold energy of LNG and generating electricity through vaporization. The specific energy consumption (SEC) of the proposed system was obtained as 3.996 kWh kg−1, however, particle swarm optimization (PSO) was implemented to increase energy efficiency of proposed process. As a result, the SEC of the optimized process was reduced to 2.917 kWh kg−1 where the LNG-cold energy control during the optimization was crucial to improve the energy efficiency. In addition, the economic and environmental feasibility were investigated. For the optimized process, the cost of the liquefied H2 (LH2) model was calculated as 1.37 $ kg-1, and 1.14 kgCO2 kg−1LH2 emissions were recorded as a result of environmental assessment. Moreover, the uncertainty analysis was implemented to assess the degree of the cost variance and the possibility of H2 production from water electrolysis was quantified. Unfortunately, electrolysis-based LH2 was hard to be economically better than steam methane reforming-based H2, however, alkaline water electrolysis-based LH2 showed the potential to overcome that of steam methane reforming in the future through technological advancement and reduction in production cost. The proposed H2 liquefaction process has a highly improved energy consumption rate, and this process can contribute to developing the H2 economy and become the potential candidate to overcome storage and transportation issues.