Research on systems for producing liquid hydrogen and LNG from hydrogen-methane mixtures with hydrogen expansion refrigeration

In industrial production processes, gas mixtures with hydrogen and methane as main useful components are often obtained as by-products, which are often not well utilized. In this paper, an innovative approach is proposed to produce both liquid hydrogen and LNG from industrial by-products with H-2 and CH4 as main components. Taking the purified hydrogen-methane mixtures as the research object, four different separation-liquefaction processes (namely Open Loop-N-2, Open Loop-H-2, Closed Loop-N-2, Closed Loop-H-2) are constructed and optimized, with refrigeration supplied with hydrogen expansion at the cryogenic section and nitrogen or hydrogen expansion at the precooling section. A distillation column is set up before the mixture enters the cryogenic section to facilitate the production of high purity methane and hydrogen products. Every system achieves excellent energy integration, and the load of condenser and reboiler in the column is borne by the hydrogen expansion cycle in the cryogenic section. For each process, the influence of hydrogen mole proportion in feed gas between 10% and 90% on the process performance is analyzed. The results show that the purities of LNG and liquid hydrogen products obtained by the system are higher than 99.99%, and the specific energy consumption of the systems is within 18.01-41.72 kWh.kmol(-1) for different situations. At the same time, an open loop and a closed loop are constructed, respectively, to investigate the necessity of recovering cold energy of boil-off gas. The results suggest recommendation of open loop system with nitrogen precooling. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, a new approach was proposed to produce liquid hydrogen and LNG from industrial by-products containing hydrogen and methane. Different separation-liquefaction processes were optimized to achieve high purity products and energy integration, with the specific energy consumption within a reasonable range. The results suggest the necessity of recovering cold energy of boil-off gas and recommend the use of an open loop system with nitrogen precooling.