An initiative has been launched in London aimed at developing ‘liquid air’ technologies which could act as an energy storage system cutting carbon emissions, reducing pollution and creating thousands of jobs while also creating a new ‘cold economy’.
The initiative was launched at a two-day Summit, held this week on the 30 June and the 1 July and organised by the Liquid Air Energy Network, hosted by the Institution of Mechanical Engineers (IMechE). The launch was timed to coincide with the publication of a ground-breaking new IMechE report, A Tank of Cold: Cleantech Leapfrog to a More Food Secure World, which explains how in developing countries up to 50 per cent of perishable food rots before ever reaching a plate because ‘cold chains’ are rudimentary or non-existent.
Where these cold chains are developing - in megacities such as Beijing and Delhi - they are powered by highly polluting diesel Transport Refrigeration Units (TRUs) which contribute to chronic and toxic smog. Outdoor pollution has caused 600,000 premature deaths in India in a single year. A new cold economy utilising liquid air systems would allow developing countries to leapfrog to a more sustainable system alleviating hunger increasing cost effectiveness.
In the UK and other developed countries, the ‘cold economy’ is rapidly emerging as a radically new zero-emission approach to the way cooling is provided in all its forms including air conditioning, data centres, superconducting technologies and the 'cold chain' of refrigerated vehicles and warehouses essential for preserving food from farm to fork. The global demand for cooling is projected to increase by 340GW, or three times the current power output of Brazil, by 2030. If satisfied using current technologies, this demand would create carbon emissions of over 2 billion tonnes and appalling levels of urban air pollution. The cold economy is therefore about providing low-carbon, zero-emission cooling by integrating renewable energy with liquid air power and cooling technologies, and by recycling vast amounts of cold that currently go to waste.
The production of liquid air involves a process in which air can be turned into a liquid by cooling it to around -196C using standard industrial equipment. 700 litres of ambient air becomes about 1 litre of liquid air, which can then be stored in an unpressurised insulated vessel. When heat (including ambient or low grade waste heat) is reintroduced to liquid air it boils and turns back into a gas, expanding 700 times in volume. This expansion can be used to drive a piston engine or turbine to do useful work. Liquid air or liquid nitrogen could therefore be used in a number of emerging technologies including electricity storage, transport and the recovery of waste heat.
A single gasometer-style tank of liquid air could prevent the loss of 5GW of wind power for three hours, equivalent to almost 10 percent of the UK’s electricity needs. Smaller systems can be used to provide zero-emission back-up and reserve services thereby replacing existing diesel backup systems. Grid-scale energy storage could be provided by plants such as the pilot plant currently operated by Highview Power Storage in Slough. This is a plant which generates liquid air using cheaper, off-peak electricity, stores it for some hours or days, and then expands it through a turbine to deliver power back to the grid at times of peak demand. Such plants can also be built from standard industrial equipment, which means they can be rapidly deployed.
The technology could help to increase energy security, cutting greenhouse gases and creating a new industry, potentially worth at least £1 billion per year to the British economy, as well as creating around 22,000 jobs. It could also help to significantly increase the efficiency of road vehicles, particularly in commercial buses, vans and refrigerated trucks. Zero-emission liquid air city cars could potentially be refuelled at road-side forecourts at a fraction of current fuel costs and with lower lifecycle vehicle emissions than either electric or hydrogen powered vehicles.
For these reasons, some £20 million in government grants has been awarded to businesses developing liquid air systems, including £9 million support to develop Liquid Air Energy Storage for storing grid electricity, £6 million for the new Centre for Cryogenic Energy Storage at Birmingham University and £5 million to develop liquid air vehicle engines.
“One in eight people on the planet goes to bed hungry every night” said Dr Tim Fox, Head of Energy and Environment for IMechE, who led the report. “That shocking fact is made worse when you consider that a third to a half of the food produced globally is never eaten. If developing countries had the same level of refrigeration as is typical in the developed economies they could save around a quarter of the annual food wastage arising from these countries. What's even more encouraging is that it would often be cheaper to run the clean renewables based liquid air technology than the polluting diesel one.”
Developing a cold economy would require skills in cryogenics and mechanical engineering in which Britain is currently a world leader. Liquid air technologies rely on piston engines, of which Britain exported 1.6 million in 2012 while the UK cryogenics industry, based largely in Oxfordshire, has a combined turnover of £2 billion. A report published earlier this month by the Liquid Air Energy Network, Liquid Air on the Highway, found that UK exports of liquid air engines could rise to 173,000 by 2025, which would create or maintain a further 2,100 jobs. But this analysis was based largely on sales to developed economies.
Two systems currently being developed to embrace the liquid air technology are the Dearman Engine and the Ricardo split cycle engine. The Dearman Engine is a novel piston engine that runs on liquid air or nitrogen, which could be used either as a prime mover (main engine) or as a secondary unit to recover waste heat from an internal combustion engine (ICE) to raise efficiency. The Ricardo split cycle engine is a novel diesel engine design that incorporates liquid nitrogen to increase efficiency by capturing its own exhaust heat.
The Dearman engine was invented by Peter Dearman, a classic British 'garden shed' inventor. It has been tested and is now being developed by the Dearman Engine Company. The novelty of the engine lies in the use of a heat exchange fluid (HEF - water or water and glycol mix) that promotes extremely rapid rates of heat transfer inside it, allowing a small, single-stage Dearman engine to achieve levels of thermal efficiency that would otherwise require more costly, multi-stage expansion with re-heating. In this way the Dearman engine also reduces the size of bulky and inefficient external heat exchanger that handicapped earlier cryogenic engine designs.
The engine will be inexpensive to build and will also be low maintenance with a low environmental impact. Running on a cryogenic fluid gives the Dearman engine two major advantages. First, the evaporation of liquid air or nitrogen gives off large amounts of valuable cold, which can provide 'free' refrigeration or air conditioning. Secondly, the low boiling point (-196C) means that low grade waste heat of around 100C, harvested from diesel engines or in future hydrogen fuel cells, can be used to boost the cryogen's expansion to produce additional power at practical conversion efficiencies approaching 50 percent.