Mixed refrigerant-based simplified hydrogen liquefaction process: Energy, exergy, economic, and environmental analysis

Abstract

In current study, process of hydrogen liquefaction was proposed to overcome the transportation and storage issues associated with hydrogen. The proposed model is consisted of three refrigeration cycles which are coupled to liquefy hydrogen. Unique selection of mixed refrigerants was adopted in each refrigeration cycle to reduce the energy consumption of the process. The precooling cycle based on mixed refrigerant stream reduces the H-2 temperature from 25 to -160 degrees C. Whereas, cooling and liquefaction cycles reduce the hydrogen temperature up to -251 degrees C which then is further expanded in an expander to approach the liquefaction temperature (-252.1 degrees C) at 1.3 bar. As of authors' knowledge, this is the first study which demonstrates the 4 E's analysis (Energy, exergy, economic, and environmental) of hydrogen liquefaction process. Result of proposed study reveals that the specific energy consumption of proposed process was calculated as 9.477 kWh kg(-1) LH2 which is less than any commercial scale process. As a result, the exergy efficiency of the proposed process was increased by 34%. In addition, the estimated unit production cost was recorded as 5.54 $ kg(-1) of LH2 at the capacity of 1TPD. Cost estimation of proposed model was evaluated at higher capacities 1 to 50 TPD with cost reduction of up to 3.2 $ kg(-1) LH2. Life cycle assessment of proposed process revealed that the 67.85 kg of CO2eq emissions were observed against unit production of liquefied hydrogen for new plant at day 1 while 0.253 kg of CO2eq emissions at day 2. The simplicity and less energy consumption of proposed model built a basis for its development to commercial scale adoption.