Carbon-dioxide-precooled hydrogen liquefaction process: An innovative approach for performance enhancement–Energy, exergy, and economic perspectives

Abstract Hydrogen is an important clean energy carrier that can facilitate and promote clean energy production and mitigate greenhouse gas emissions. However, long-term storage and long-distance transportation of hydrogen are challenging owing to its low energy density, which can be effectively enhanced via liquefaction, an energy- and cost-intensive process. Commercial hydrogen liquefaction processes exhibit specific energy consumptions in the range of 12.0–15.5 kWh/kg with an exergy efficiency of 19.0%–23.6%. This study presents an energy-efficient and cost-effective process configuration for producing liquid hydrogen through stepwise cooling and subsequent ortho–para conversion. The energy intensive precooling cycle is divided into two sub-cycles employing carbon dioxide as a refrigerant. This process exploits the benefits of carbon dioxide in a simple yet efficient configuration. A specific energy consumption of 7.63 kWh/kg was achieved, along with an exergy efficiency of 31.4%. The coefficient of performance and figure of merit of this study was 0.16 and 0.31, respectively. Economic evaluation yielded total equipment and total annualized costs of $12.3 million and $24.2 million/year, respectively. The proposed process can assist in achieving a sustainable and green energy economy by enhancing the overall hydrogen value chain through competitive and efficient hydrogen storage and transportation.