Cryogenic energy storage

Cryogenic Energy Storage ( Cryogenic Energy Storage / CES, also Liquid Air Energy Storage / LAES ) refers to the use of low-temperature ( cryogenic ) liquids such as liquid air or liquid nitrogen as an energy store. Both Cryogenic are already being used in vehicle engines. The inventor Peter Dearman developed originally a powered vehicle with liquid air, then took advantage of this technology but also for grid energy storage. The technology is used in a British power station in the pilot operation.

History

Already 1899-1902 powered by a liquid air vehicle with the name Liquid Air was developed. Recently, a vehicle operated with liquid nitrogen, was built. Peter Dearman, a private inventors from Hertfordshire, England, first developed a powered vehicle with liquid air and then used this technology for grid energy storage. Dearman the engine differs from previous nitrogen engines, characterized in that the nitrogen is heated in combination with the heat exchange fluid inside the cylinder.

Power energy storage

Method

In off-peak periods when electricity is particularly cheap (usually at night), this current can be used to air cool down to the ambient temperature with the Claude process to -195 ° C and thus liquefy. Liquid air requires only a thousandth of its original volume and can be stored for a long time in a large vacuum vessel at atmospheric pressure. At high current demand liquid air is pumped at high pressure in a heat exchanger, which serves as a boiler. Ambient temperature air from the atmosphere or hot water from an industrial source of heat used to heat the liquid and bring back into the gaseous state. The associated sharp increase of volume and pressure is used to drive a turbine to generate electricity.

Efficiency

In itself, the method achieves an efficiency of only 25%. This value can, however, significantly increase ( about 50 %) when the method is combined with a cold storage, such as a gravel trap large to accommodate the cold produced on evaporation of the cryogen. The refrigerant may then be reused in the next cooling cycle. To further increase the efficiency of the method can be combined with a power plant or other waste heat source use, ie when heat that would otherwise be emitted to the environment. Highview Power Storage has estimated that a round-trip efficiency ( AC to AC) could be achieved by 70% if you were to have free waste heat at 115 ° C. This number was from independent institutions but not verified and not confirmed. Currently excess of gaseous nitrogen is a by- product in the production of oxygen. This can be liquefied if necessary. The oxygen can be used in coal-fired power plants with oxygen combustion and enables CO2 capture and sequestration. The cryogenic distillation of air is the only current commercially viable technology for oxygen production in large scale.

Pilot plant

A system developed by researchers at the University of Leeds and Highview Power cryogenic energy storage pilot system with 300 kW and a capacity of 2.5 MWh since 2010 to a biomass power plant in the UK Slough in operation. It uses liquid air, the energy storage and heat in order to enhance the thermal re-expansion of the air. From the liquid air carbon dioxide and water were removed because they would freeze at the storage temperature. The efficiency is currently less than 15 percent. But engineers expect an efficiency of about 60% for the next generation of LAES based on intelligence that was obtained by means of the existing plant. The system is based on a proven technology that is safely used in many industrial processes. To produce no rare commodities or expensive components are required. "The system is based on standard industrial components ..., will last for decades and can be serviced by the simplest means ," said Tim Fox, Head of Energy at the Institution of Mechanical Engineers ( IMechE ).

Study " Liquid air in energy and transportation applications "

On 9 May 2013, the Centre for Low Carbon Future a study published with the original title " Liquid Air in the energy and transport systems: Opportunities for industry and innovation in the UK", in which among others Arup, Ricardo, the Messer Group, National Grid and leading UK universities participated. In this study, liquid air is treated as a potential solution to the problem of energy storage and opportunities for the industry in the field of energy and transport systems.