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Transport refrigeration using liquid nitrogen proposed as way to slash emissions and diesel costs

A report from a collaboration of academics and industry proposes nitrogen for cooling and motive power in transport refrigeration as the first step in creating low-emission commercial vehicle fleets

The Liquid Air Energy Network, a collaboaration of academics and industry has released a report suggesting that transport refrigeration can be in the vanguard of a mass conversion of commercial vehicles to run on liquid nitrogen. The Liquid Air on the Highway report contends that by using the cryogenic system to provide the cooling and the motive power, transport refrigeration units are an ideal application, produce zero carbon emissions, as well as significantly reducing diesel.

Transport and commercial refrigeration specialist Hubbard Products is working on making this a reality, working on advanced trials with the Dearman Engine Company to use Dearman’s revolutionary liquid air engine, that produces zero carbon emissions, as the power source for a range of transport refrigeration units.
The Liquid Air on the Highway report concludes that there is a compelling business case for converting commercial vehicles to the liquid nitrogen. It said: “There is a strong financial, air-quality, energy security and carbon reduction case for developing liquid air-equipped commercial vehicles.A projected British fleet that grows to 36,000 vehicles by 2025 could save more than 1 billion litres of diesel, 1.4 million tCO2e well-to-wheel) and £113 million of net investment costs. Promising first applications include refrigerated trucks and trailers and heat hybrid buses and lorries. These could provide major reductions in diesel consumption, local air pollution, well-to-wheel carbon emissions, noise and cost. The strongest coudl repay their investment within months and the rest in a range of two to four years.”

Hubbard said that its transport refrigeration units will for the first time use liquid nitrogen, commonly referred to as ‘liquid air’, as both the motive power and as a subsidiary cooling medium. Liquid Nitrogen is a well-known cryogenic medium and is already used as a coolant in some larger TRUs.
Hubbard Products is the preferred partner for the Dearman Engine Company, working to develop applications for their revolutionary new power source. The firm said: “We have always placed energy efficiency at the top of our list of performance criteria for both static and transport refrigeration units. The Liquid Air on the Highway report states that regulating emissions from TRUs would be a timely and cost-effective way of reducing pollution that causes 29,000 premature deaths in Britain each year, we will be truly proud to help deliver product efficiency that will have a real human impact”.

Dearman said: “The Dearman refrigeration unit is a significant advance on current liquid nitrogen cooling systems because it produces both cooling and shaft power from a single unit of ‘fuel’. The cryogen (either liquid air or liquid nitrogen) is vaporised in a heat exchanger in the refrigeration compartment, so cooling it down; then the high pressure gas is used to drive the Dearman engine, whose shaft power can be used to drive a conventional refrigeration compressor or for auxiliary power. This means it is extremely efficient and cost effective. It is also produces zero exhaust emissions.”

Hubbard said it is using a Dearman Engine running on liquefied air (held in an unpressurised insulated container at -194 deg C) to drive the compressor units of a TRU. “The Dearman Engine injects liquid air with a small amount of antifreeze into the engine cylinder, the liquid air re-gasifies on exposure to the ambient temperature, expanding by 700 times its volume creating a non-percussive (quiet) source of drive for a piston or turbine. The expanded, cold gas is emitted and recovered to be used within the TRU as ‘free-issue’ refrigeration before finally being expelled as air.”

It added “The project is part of Hubbard’s long-term business model and comes at a time when the company is planning a purpose built unit close to its current Suffolk base, that will accommodate new product development, manufacturing and engineering facilities associated with the development of sustainable refrigeration technologies.”

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