Does anyone know where I can find some documentation of a real-world liquification process, and the energy costs?

I can calculate the heat that must be removed from O2 gas to get to liquid, but how would this translate to an amount of electricity (kWh) required to operate the cooling equipment?

I hope that my basic thermodynamics calculation are correct?

Attached shows the heat that must be removed 1 mol O2 to liquify

  • $\begingroup$ electricity costs vary by country, location and even time of day. $\endgroup$ – Solar Mike Apr 10 at 13:07
  • $\begingroup$ I mean how much electrical energy in kWh is required... e.g per mol O2 when you start with O2 at standard conditions @SolarMike I edited to clarify $\endgroup$ – dlight Apr 10 at 13:15
  • $\begingroup$ Ok, so what particular process and therefore cooling equipment are you using? $\endgroup$ – Solar Mike Apr 10 at 13:18
  • $\begingroup$ I'm not tied to a particular system, but rather looking at it from a theoretical perspective for modeling. So, I would start with the simplest available options. I read a bit online but could not easily find info. Basically, I need a reasonable approximate electrical energy requirement for this liquification step so I can plug it into a model of a larger system. $\endgroup$ – dlight Apr 10 at 13:27
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    $\begingroup$ There's a bit more to it than that - en.wikipedia.org/wiki/Cryogenic_oxygen_plant $\endgroup$ – Phil Sweet Apr 10 at 17:32

From a physics standpoint, you need to consider your full cycle.

If you increase pressure by pumping in more molecules to a given volume or take a given set of molecules and reduce the volume makes a difference. (Usually high pressure applications like this will end up on the given volume route due to space constraints.) Pressure losses over check valves can have more than an insignificant bearing on easily compressible fluids such as gasses. Compressing very slowly can be efficient but your industrial process will likely need to sacrifice a bit of efficiency to get a desired throughput.

Next up the actual removal of heat. The compression causes the oxygen to increase in temperature. Increased temperature means heat will naturally flow out into a reservoir of the pre-compression temperature, but this is usually too slow for industrial processes. A heat pump of some sort would incur the remaining losses in bringing the compressed oxygen down to condensation temp for your pressure and removing energy at the rate desired for your process (this is where that kWh calculation comes in, but with the energy you put in for compression also included!).

Put both processes together and optimize to find an efficient target pressure and temperature. (One determines the other from Oxygen's phase diagram).

  • $\begingroup$ thanks for the insight. I think in my case the rate limiting step will not be compression. So a slow compression is okay, to some extent. in terms of temperature and pressure, I have no constraint, just needs to be liquid. Indeed I have to calculate how the cooling system will work. I'm still not sure how to calculate it but will keep working on it. $\endgroup$ – dlight Apr 10 at 21:36
  • $\begingroup$ The need to be liquid is the constraint- it makes the necessary pressure a function of temperature or the necessary temperature the function of pressure. You can search for a "Oxygen phase diagram" - the curve between gas and liquid is what you are interested in. $\endgroup$ – Abel Apr 11 at 0:11
  • $\begingroup$ yes I'm aware of phase diagrams. I tried to say that any point in liquid state is equivalent to me, I will want the minimal energy cost to liquefy. $\endgroup$ – dlight Apr 11 at 4:23

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