air separation power used 1

[loside]

There may be a better forum for this question but I am uncertain which it would be...
I am interested to get a general breakdown of the energy required/used for industrial air separation plants. A little more specifically, how much electricity is used to get the rare gas Krypton? I think it is true that the rare gases are generally "made" as a by-product of the oxygen separation process. If so, then how much electricity is used to get oxygen and then how much additional electricity is needed to get Krypton?
Any insight would be greatly appreciated.

 

[controlnovice]

I don't have a specific answer for you, but a general one:

The electrical cost difference between getting Oxygen and any other gas is very low.

The main drive is generally one huge electric motor driven compressor. Depending on the plant size, these can be anywhere from 8,000hp to 20,000hp, and I've seen them as high as 35,000hp. There are some refrigeration units an possibly a heater associated with the units, but the compressor is bar far the biggest user.

This one compressor compresses the air into liquid. This liquid is sent to a fractionation column where the different gases are seperated from the liquid.

If the needed gas, in your case Krypton, can be used as a gas, then very little electrical energy is required for pumping the gas or storage of the gas. If you want it as a liquid or high pressure, then another smaller compressor may be needed to turn your gas into a liquid or store at high pressures. This would probably be around 10-20hp, depending on your volume.

Someone may have exact values of energy cost for each gas. I suppose you could find the % of each gas natually found in air, and use those %'s to divide the main compressor's energy use. Should be very close (maybe?).

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[MJCronin]

Google: krypton and gas

Go to the "Wikipedia website"....

"Krypton has an important role in production and usage of the krypton fluoride laser. The laser has been important in the nuclear fusion energy research community in confinement experiments. The laser has high beam uniformity, short wavelength, and the ability to modify the spot size to track an imploding pellet" (from Wikipedia)

Please explain to us why are you so interested in Krypton ?

-MJC

 

[loside]

I appreciate the input.
MJC, I am interested in Krypton for cryogenic cooling. A system that uses tetrafluoromethane could maintain it's performance using krypton as a substitute. My issue is that if the reason to stop using the "freon" is because it is a greenhouse gas then it would be important to know the effect (carbon footprint if you will) of isolating the krypton gas to know if there is really a benefit from a net perspective. Because oxygen and nitrogen are the largest part of the air separation process (the most demand and most common reason to separate air...it will happen whether I use krypton or not) I wish to isolate the power used for O2/N2 production and only look at the energy needed to get the krypton proper. The input I received from controlnovice suggests I had a misunderstanding as it looks as though getting krypton doesn't require a second compression stage to cool the xenon/krypton mix. If this is correct then krypton production could probably be considered to have less of a "footprint" than tetrafluoromethane. Certainly there is energy used but, without a compressor, it is hard for me to imagine a gross energy use here. Being an engineer, I would be interested to see it quantified but I could be somewhat satisfied if I knew krypton was more environmentally friendly from a global or net standpoint. The business plan is to reduce our footprint and I want to understand and make sure that a krypton substitute for tetrafluromethane actually achieves the goal of the company in the end. And...yes...I am aware the cost of krypton!
Thanks

 

[controlnovice]

There may be a second compression stage required.

Separating all of the gases in a single column would require an extremely tall column. The lighter gases may be taken off and recompressed (at grade level), then sent through another fractionation column.

It's due to the height required in the column though, not necessarily the extra compression required.

I did install a unit that had a large capacity Argon separator. It was a smaller column placed near the top, and next to, the 'standard O2/N2' column. I don't think there was another compressor for it. It's been about 15 years, though, so this is old knowledge from an old guy. Not very accurate.


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