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Summary: This study mainly focuses on determining the optimal configuration that efficiently utilizes liquefied natural gas (LNG) cold energy in hydrogen precooling for liquid hydrogen production. To achieve this goal, two different configurations are designed: (a) adding LNG cold energy to the existing hydrogen precooling cycle and (b) replacing the existing hydrogen precooling cycle with LNG cold energy. An equilibrium hydrogen model is developed to reflect the thermodynamic property of ortho‐para conversion of hydrogen. Bayesian optimization is performed to determine the optimal operating conditions which minimize the specific energy consumption for all configurations. The specific energy consumption of the configuration involving hydrogen precooling with only LNG is 5.613 kWh/kg‐LH2, and it is reduced by 8.13% and 3.19% from the base case design and the configuration involving hydrogen precooling with both LNG and a mixed refrigerant cycle, respectively. In addition, a techno‐economic analysis is conducted. Compare to the base case design, the capital cost and operating cost of the design replacing hydrogen precooling with LNG are reduced by 31.76% and 11.55%, respectively. This study shows that the proposed design of replacing the hydrogen precooling cycle with an LNG stream can save energy consumption, moreover, it is highly effective for capital investment saving due to its simple configuration. [ABSTRACT FROM AUTHOR]

Summary: This study focuses primarily on improving large‐scale hydrogen liquefaction process by integrating liquefied natural gas (LNG) stream to utilize LNG cold energy. For the hydrogen liquefaction process, a large amount of energy is required for the compression and the cryogenic refrigeration system. LNG is one of the main sources for producing hydrogen, and it can be an opportunity to save energy because LNG cold energy is normally discarded into seawater during regasification. The objective of this study is to reduce the specific energy consumption and specific liquefaction cost. The proposed design which produces 300 ton/day of liquid hydrogen is compared with a base case design comprising two‐stage mixed refrigerant refrigeration cycles. To minimize the specific energy consumption, multiparameter optimization is conducted by connecting simulation results to a genetic algorithm. Through the optimization, the flow rates of LNG and MR in the precooling cycle decrease by 1.08 and 21.00 kg/s, respectively. The specific energy consumption is reduced from 4.36 to 4.07 kWh/kg‐LH2. Particularly, in the precooling cycle where the LNG stream is integrated, it decreases by more than 26.40%. Regarding the specific liquefaction cost of hydrogen liquefaction, the capital expenses are reduced by 15.16%, and annual operating expenses are diminished by 9.05%. Therefore, the total specific cost liquefaction shows a reduction of approximately 7.7%. Overall, an efficient hydrogen liquefaction process will provide a guideline for LNG‐dependent countries by reducing the specific energy consumption and the specific liquefaction cost by recovering the waste cold energy. [ABSTRACT FROM AUTHOR]

A novel power-management-system design coupling liquid air energy storage (LAES) with liquefied natural gas (LNG) regasification is proposed that combines flexibility in responding to power demand, presented high energy efficiency and capacity. The proposed liquefied natural gas-thermal energy storage-liquid air energy storage (LNG-TES-LAES) process uses LNG cold energy via two different mechanisms. During on-peak times, when the proposed process requires no power consumption to meet the relatively higher electricity demand, LNG cold energy is recovered and stored via liquid propane. During off-peak times, the proposed process uses both cold energy from LNG and liquid propane, effectively doubling the cold energy available and enhancing the process flexibility. The liquid propane cold energy is used for air compression to reduce the power input requirement, while LNG cold energy is used mainly to liquefy air. These unique features afforded an electrical round-trip efficiency of 187.4% and an exergy efficiency of 75.1%, which are the highest among recently reported values. The energy capacity for the regasification of 1 MTPA LNG was 12.14 MW, which is adequate for bulk power management systems. By adopting flexibility, LNG cold energy has been distributed efficiently, and where LNG could be continuously regasified in the energy storage/release processes. • The proposed energy storage mechanism operates via multiple time-based modes. • LNG cold energy was effectively used for air liquefaction and air compression. • Electrical round-trip efficiency reached 187.4%, which is the highest recent value. • Exergy efficiency reached 75.1%, and the process is economically feasible. • The proposed process enabled flexible operations depending on energy demand. [ABSTRACT FROM AUTHOR]

Exergoeconomic optimization of the production of liquid air by utilizing the cold energy of liquefied natural gas (LNG) was undertaken for the first time. LNG cold energy, which is generally wasted in commercial regasification, can potentially be harnessed to produce liquid air. By using an exergoeconomic approach, the optimal design for reducing the specific energy consumption in the production of liquid air was determined, affording a 7.45% reduction in the specific energy consumption. Thermodynamic analysis revealed that the specific energy consumption could be minimized by using the optimized portion of LNG cold energy. Economic study indicated that the optimized system also afforded a 4.61% reduction in the total cost. Beyond this, the effects of both increasing and decreasing the energy recovery operations were investigated, from which the most cost effective process flow was determined. In conclusion, the most cost effective strategy for reducing the specific energy consumption for liquid air production does not necessarily require using the largest proportion of LNG cold energy. This is because although adding equipment reduces the energy consumption, it also increases the total costs beyond an optimal point. These are important findings for advancing the effort to efficiently utilize LNG cold energy. • Exergoeconomic aspects were revealed for liquid air production via LNG cold energy. • The use of LNG cold energy was optimized for more efficient liquid air production. • Cost based optimum was found as function of the number of energy recovery stages. • Optimization gave reductions of 7.45% in the energy required and 4.61% total cost. [ABSTRACT FROM AUTHOR]