LNG (Liquefied Natural Gas) shares in the global energy market is steadily increasing. One possible application of LNG is as a fuel for transportation. Stricter air pollution regulations and emission controls have made the natural gas a promising alternative to liquid petroleum fuels, especially in the case of heavy transport. However, in most LNG-fueled vehicles, the physical exergy of LNG is destroyed in the regasification process. This paper investigates possible LNG exergy recovery systems for transportation. The analyses focus on “cold energy” recovery systems as the enthalpy of LNG, which may be used as cooling power in air conditioning or refrigeration. Moreover, four exergy recovery systems that use LNG as a low temperature heat sink to produce electric power are analyzed. This includes single-stage and two-stage direct expansion systems, an ORC (Organic Rankine Cycle) system, and a combined system (ORC + direct expansion). The optimization of the above-mentioned LNG power cycles and exergy analyses are also discussed, with the identification of exergy loss in all components. The analyzed systems achieved exergetic efficiencies in the range of $20\%$ to $36\%$ , which corresponds to a net work in the range of 214 to 380 kJ/kg ${}_{LNG}$ .

Cryogenic Energy Storage (CES) systems are able to improve the stability of electrical grids with large shares of intermittent power plants. In CES systems, excess electrical energy can be used in the liquefaction of cryogenic fluids, which may be stored in large cryogenic vessels for long periods of time. When the demand for electricity is high, work is recovered from the cryogen during a power cycle using ambient or waste heat as an upper heat source. Most research is focused on liquid air energy storage (LAES). However, natural gas can also be a promising working fluid for the CES system. This paper presents a natural gas-based CES system, coupled with a low temperature packed bed cold storage unit. The cold, which is stored at a low temperature level, can be used to increase the efficiency of the cryogenic liquefiers. The model for the packed bed in a high grade cold storage unit was implemented and then compared with the experimental data. The impact of cold recycling on the liquefaction yield and efficiency of the cryogenic energy storage system was investigated

Nitrogen is by-product from cryogenic air separation processes used for oxygen production for metallurgy and oxygen-enriched combustion purposes. If the gases are delivered from air separation unit (ASU) in liquid phase, liquid nitrogen (LN₂) can be used as energy accumulator for stabilization of electrical grid system with large share of renewable energy sources. When the energy demand is high and not enough electricity is generated in power plants, energy accumulated inLN₂may be recovered in a cryogenic power cycle. In this research complete exergy analysis of liquid nitrogen direct expansion cycle and combined direct expansion/Brayton cycle was performed.