An air liquefaction system integrated with organic Rankine cycle for performance enhancement and energy saving

Liquid air energy storage (LAES) is one of the most promising large-scale energy storage technologies that are capable of providing different energy services to ensure the stability and flexibility of the grid with a high renewable penetration. Examples of such services include peak shaving, renewable firming and transmission constraint management. The LAES technology has several advantages relative to other energy storage technologies due to its high energy density, multi-functionalities, no geological constraints, environmental friendliness and scalability. However, the round-trip efficiency (RTE) of a standalone LAES system is around 50-60%, mainly due to the energy-intensive air liquefaction process (i.e., charging process), which, on average, consumes 0.22–0.7 kWh electricity to produce 1 kg liquid air. To reduce this electricity consumption, recycling high-grade cold energy from the liquid air regasification (power recovery) process has been utilized. However, this is not available in some cases, such as at the system start-up stage or when liquid air is used for black start applications. Additionally, partial loss of cold energy during storage, coupled with insufficient utilisation of compression heat, further reduces the RTE. In these cases, a back-up of liquid air produced in an energy-efficient way is need and to address this, we propose an air liquefaction system integrated with an organic Rankine cycle (ORC). This integrated system aims for utilisation of the compression heat by driving an ORC unit. Thermodynamic analyses indicate that the integrated systems allow the operation of air liquefaction unit at a much higher pressure up to 250 bar, leading to increased liquid air yield and reduced energy consumption by 25.36%.