The encyclopedia · Engineering & Operations · Technical decision · 1895-1910
Carl von Linde made air a cheap liquid by using the cold the gas itself already carried
Linde liquefied air with a counterflow heat exchanger and an expansion valve, then distilled it into cheap oxygen and nitrogen.
Linde · Linde AG
the move
Linde, a Munich professor who had already built refrigeration machines, took up the problem of liquefying air. The hard part was that air is extremely hard to condense, and brutal cooling was too expensive.
His 1895 process compressed air, cooled it, expanded it through a valve, and used a counterflow heat exchanger to let the cold exhaust pre-cool the incoming air. Each circulation made the air colder until it condensed.
In 1902 he completed the separation of liquid air into nitrogen and oxygen by rectification, a distillation-like process, and in 1910 developed the double-column that became the basis of cryogenic air separation, giving cheap industrial oxygen.
why it works
- Counterflow recovers the cold from the exhaust and reuses it to chill the next batch, so the temperature drops each cycle.
- Joule-Thomson expansion cools air during the process, and using recycled cold multiplies the effect.
- Liquefied air can then be separated by distillation on the basis of boiling point, yielding pure gases.
- Cheap oxygen opened up welding, steelmaking and a hundred industrial uses.
what transfers
Make the process feed itself: recycling the cold the system already generates removes the cost that was making the whole approach uneconomic.
what came after
Linde founded the company that became Linde AG, which along with Air Liquide became the first large-scale industrial gas companies. The process supplied oxygen for welding and steel and provided nitrogen for ammonia synthesis and many other industrial gases, and it became one of the most important industrial gas technology platforms.
references
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