a fun little project in nead of professionals :)

[Ray80]

Hello all,
I would like some help with a project of mine, an air liquefaction plant. With the capability to produce in quantity liquid oxygen and liquid nitrogen the LOX will be used in amateur rocketry.
Now so you know I will discuss the spirit of this project. I really enjoy making things my self, the heat exchanger, turbo expander, Dewar flasks, everything but the compressor, valves etc.
materials would include PVC, copper, steel, and brass

my heat exchanger may be made by constructing the outer shell with two PVC pipes arranged in such a way as to create a vacuum insulated jacket (with vermiculite filling), and copper coils wound in the inner chamber. The warm air 32C enters the inner chamber at 77 PSI and is cooled to -168C thereby removing the H2O and CO2 in the form of ice. Then some of the dry air exits the top of the said heat exchanger and goes threw a turbo expander after which it enters the tubes of the heat exchanger and is used to cool the said chamber threw said copper coils and is recycled threw the main compressor. The rest of the cooled dry air leaving the heat exchanger at 72psi

the condensation column is made the same way as the heat exchanger. The cooled dry air entering at -168C, 72psi enters the coil inside the column terminating at an expander valve at the bottom of the column, producing liquid oxygen, and gaseous nitrogen at 7psi which enters a second column and is condensed into LN.

The compressor stage is an ordinary air compressor with a regulator fixed onto the air outlet and a HEPA filter on the inlet.

After the compressor stage the air is passed threw a condenser/precooler made like a laboratory condenser
The storage vessel is constructed with PVC and evacuated with vermiculite filling the vacuum. its capacity will hopefully be 500lbs

Some questions I have are.
Can schedule 40 PVC hold up to a vacuum at -183C or would I need to construct the inner wall out of steel?
Does anyone think it will work?
Do I need psychiatric help?
Has anyone herd of a Tesla turbine and what are your thoughts on using one as an expander.
Are there any issues with the heat exchanger?
What is the density of LOX per cubic foot or meter?
How would I remove Hydrocarbons from the air?

I am sure I will have more questions when I start making it.
This is all privately funded and therefor my budget is extremely small.

Thank you for spending the time to read this question.

Raymundo D. Rocha

 

[Helios]

pychiatric help is needed. Creating LOx on a budget will lead you down a dangerous road of using used equipment....if this is not cleaned absolutely thouroughly of all residual hydrocarbons it poses a danger to you and anyone around. LOx is dangerous to the untrained and must be treated as such. I wish you luck and safe construction.

 

[Ray80]

Thank you for that professional warning, I do know the dangers of LOX very well and rest assured I am making nearly every part of it and can therefore have control over every little aspect. I don’t have to sub anything out either. I see that you are an expert on materials perhaps you could tell me if the following would work.

Heating the equipment to 450F and running Gaseous oxygen threw it to reduce and remove any residual Hydrocarbons.

Also help with the removal of hydrocarbons in the air as the plant is running would be appreciated. I am worried about it since my compressor uses 10W30 to lubricate itself. I think that the pre-stage of the heat exchanger will remove the oil by freezing it out of the air along with the CO2 and H2O . But I don’t know.

Also I don’t know where Argon, and other rare gasses, get removed temperature wise.

 

[amjad02]

Hello,I'll try to answer some of these problems depending on my young epxerience:

1.For Oil removal, you may want to consider isntalling an oil purging unit right after the compressor.This can be one or two cylinders containing rasching rings or other packing materials,I know that stones are enough!

2.For dehydrating and adsorbing material containing cylinder may be used(sieve molecule)unit!

3.As for the hydrocarbons,I can only suggest installing a cylinder with silica gel that adsorbs and gaseous hydrocarbons from liquid oxygen.For the same matter I don't think there's a seriuos amount of that in the air anways!

The toughest part would be material selection.you need pretty thick and tough steel for the cylinders and elbows.If you install the air dryer right after the oil purger then you dont have to worry about oil reaching the coulmn.Now designing the column,this may need seriuos work . Good luck

 

[JOHNPIA2]

Helios is right, the hydrocarbon-oxygen combination is TROUBLE! It has caused a number of explosions in professionaly built commercial plants. The only materials good for cryogenic environment(320 deg. F), are stainless steel or non-ferrous. Why don't you just buy your LOX, and save your life, as well as the lives of a few others?

 

[briggsy]

I'm with JOHNPIA2 here. Even at list price commercially available LOX is running in the neighborhood of $5 per gallon. Add another $50 per month for the rental of the container. You stated that your budget is small; save yourself a lot of money, time, and maybe your life and that of others - BUY THE STUFF!