I got a book wrote in 1902 ( I think it was called Liquid Air, Nitogen Oxygen) that describes how Georges Claude, a french scientist, made liquid air for the first time by adiabatic expansion. The first guy to make it was Linde ( of the Linde gas company fame), but he used very high pressure air and a throttling valve to make the cold.
I also wanted to make liquid oxygen and nitrogen so that is why I bought this book. To make it you have to start off with liquid air, then you run it thru a fractional distillation column to break the air down into oxygen nitrogen and argon.
Linde's process is simple, but uses very high pressure. For every atm you compress air, it drops a 1/4C in temperature when you expand it. That is the basic process. You remove the moisture from air and then compress it to about 200 atm of pressure ( about 3000 psi). You cool the compressed air back to ambient temp (20C). When you expand that gas thru a valve it drops the gas temp 1/4C per atm , which is about 50C. This first expansion gets you from ambient at 20C down to about -20C with losses included. Air doesn't liquidfy until -195C.
So you got to run that -20C air thru a countercurrent heat exchanger which takes the cold from this air and runs it past the incoming air to the compressor so that the air enters the compressor at about 0C. You run this in a loop a few times until the temperature drops down to liquidfying temperatures.
Then you still aren't done, because you have to run that liquid air into a distillation column. At the bottom of the column you run a heat exchanger pipe thru the liquid air and the liquid air cools down the air further before entering the expansion valve.
Making liquid air is all about recycling your cold production over and over so that you don't have to compress your air so much for every cycle. Plus the recycling of the cold brings the temperature way down for the incoming charge so eventually the air can be expanded one time and forms liquid air.
I also wanted to make liquid oxygen and nitrogen so that is why I bought this book. To make it you have to start off with liquid air, then you run it thru a fractional distillation column to break the air down into oxygen nitrogen and argon.
Linde's process is simple, but uses very high pressure. For every atm you compress air, it drops a 1/4C in temperature when you expand it. That is the basic process. You remove the moisture from air and then compress it to about 200 atm of pressure ( about 3000 psi). You cool the compressed air back to ambient temp (20C). When you expand that gas thru a valve it drops the gas temp 1/4C per atm , which is about 50C. This first expansion gets you from ambient at 20C down to about -20C with losses included. Air doesn't liquidfy until -195C.
So you got to run that -20C air thru a countercurrent heat exchanger which takes the cold from this air and runs it past the incoming air to the compressor so that the air enters the compressor at about 0C. You run this in a loop a few times until the temperature drops down to liquidfying temperatures.
Then you still aren't done, because you have to run that liquid air into a distillation column. At the bottom of the column you run a heat exchanger pipe thru the liquid air and the liquid air cools down the air further before entering the expansion valve.
Making liquid air is all about recycling your cold production over and over so that you don't have to compress your air so much for every cycle. Plus the recycling of the cold brings the temperature way down for the incoming charge so eventually the air can be expanded one time and forms liquid air.
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