Conceptual design and analysis of a novel process for hydrogen liquefaction assisted by absorption precooling system

Hydrogen liquefaction processes have effective function in the hydrogen supply chain. However low efficiency and high liquefaction costs are still the most important concerns about the liquefaction plants. In this study a new configuration for a hydrogen liquefier process is proposed and energy-exergy analyzed. The production rate of the liquid hydrogen (LH2) is 90 tons per day that can supply the required LH2 of at least 90 k-180 k hydrogen vehicles in an urban area that results in the reduction of pollutions caused by carbon dioxide emission. The process is simulated in Aspen HYSYS simulator. In addition, it is optimized thorough a trial and error approach that is a functional and simple method of complicated systems analysis. The process includes a mixed refrigerant (MR) refrigeration cycle that precools feed gas hydrogen from 25 degrees C temperature to -199.9 degrees C temperature. A new MR is used in a cascade Joule-Brayton cycle that deep-cools the low-temperature gaseous hydrogen from -199.9 degrees C temperature to -252.2 degrees C temperature in the cryogenic section of the plant. The novel process involves also an absorption refrigeration system (ARS) that cools some hydrogen streams in the precooling and cryogenic sections of the process. The consumed energy per kilogram of produced LH2 is achieved as 6.47 kWh. This quantity is 2.89 kWh in the ideal conditions. The exergy efficiency of the plant is evaluated to be 45.5% that is significantly more than the exergy efficiency of the in operating hydrogen liquefiers in the world. The energy analysis reveals that the coefficient of performance (COP) of the overall system is 0.2034. The achieved COP is a higher amount in compare to the other similar processes. A sensitivity analysis is done to show the effect of the various operation conditions of the process on the features of the plant. Accordingly, the optimum mass flow of the ARS is determined as 207 kg/s for the proposed configuration. As well as, the effect of the change in the temperature approach of the heat exchangers and the changes in the adiabatic efficiency of the compressors and expanders on the SEC, COP, and the exergy efficiency of the overall plant is discussed. Furthermore, financial analysis of the plant estimates the capital expenditures (CAPEX), energy expenditures (EEX), and operational and maintenance expenditures (OMEX) as 25413 2000, 7370 ez000, and 2033 2000 respectively. These can be specially improved be improving of the exergy efficiency of the plant. The results implicates that the proposed configuration has better performance indicators than the in-service liquefiers. Therefore, LHL plant manufacturer can be considered it in the design and development of new plants. As well as, researchers may utilize its operating conditions to improve the proposed processes. (C) 2018 Elsevier Ltd. All rights reserved.