April 23, 2012

Liquid Air Production

Liquid air and nitrogen are cryogenic liquids produced by a process called liquefaction.The process is mature (invented over 100 years ago) and forms the basis of the industrial gas industry. Large companies like Air Products, Air Liquide, BOC and Praxair supply millions of tons of cryogenic products to industrial users each year all over the world.


Liquid air simply needs to be kept cold and therefore can be safely and easily stored in insulated containers at atmospheric pressure or at a few bar if required. Containers are available from a few litres up to thousands of cubic metres.

Mobile cryogenic liquid containers are used in the distribution of cryogenic liquids to industrial customers. Liquid air is safer to store and handle than diesel.

The Engine

Because the working fluid is at cryogenic temperatures (very cold i.e. sub minus 160’C), ambient temperatures can superheat it and return it to gaseous air.

When the piston is at the top of the cylinder, some heat exchange fluid is admitted to the engine cylinder. Immediately after this a small quantity of cryogenic liquid is sprayed into the cylinder; it comes into contact with the ambient (but in relative terms to the cryogenic temperatures, superhot) heat exchange fluid and boils very rapidly.

The cryogenic liquid quickly turns to gas building up pressure in the confined space of the engine pushing the piston down the cylinder.

At the bottom of the stroke the exhaust valve opens. As the piston returns to the top of the cylinder the heat exchange fluid and now gaseous air are pushed out of the engine.

Afterwards, the cold air can be exhausted and the heat exchange fluid can be recovered for reheating and use in another cycle.

At the top of the stroke a new cycle begins.