Condesation/Fractional distillation of air / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Condesation/Fractional distillation of air

first previous 7 8 9 10 next last

Move Thread

LAN_403

IamSmooth

Sat Dec 08 2012, 09:46PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

So an update on where I have gotten:

Starting at an ambient temperature of 50F, I have gotten down to -78F.

Two problems I need to address right now. First, the "cryogenically" rated needle valve has to constantly get opened more as the temperature falls. This is probably from the contraction of the steel metal. However, I believe I have gotten close to the fully open position, which is an issue.

Second, my 4L dewar flask that acts as the reservoir that the output goes to does not hold the temperature. While the needle valve is at -75F, the flask in the middle is 35F. I would think if the vacuum was intact the temperature should be close. I will most likely need a much smaller one with a better seal.

Any thoughts?

IamSmooth

Thu Dec 13 2012, 01:53PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I've decided on increasing the length of my heat exchanger and the amount of insulation. I have a question that I hope someone will be able to answer.

I am putting tubing around my steel coil. Cold air goes through the tubing. The tubing will be surrounded by insulation in a container. The question: is there any benefit to wrapping aluminum tape around the tubing to keep the cold inside the tube? There is no exposure to light and there will already be insulation surrounding it.

Ash Small

Thu Dec 13 2012, 03:59PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

IamSmooth wrote ...

I've decided on increasing the length of my heat exchanger and the amount of insulation. I have a question that I hope someone will be able to answer.

I am putting tubing around my steel coil. Cold air goes through the tubing. The tubing will be surrounded by insulation in a container. The question: is there any benefit to wrapping aluminum tape around the tubing to keep the cold inside the tube? There is no exposure to light and there will already be insulation surrounding it.

Having thought about this for at least a couple of seconds.....It would appear to come down to 'Does aluminium reflect IR?'

I think your money would be better spent wrapping it in more insulating material, but I'm no expert in these matters.

Aluminium is a very good conductor of heat.

2Spoons

Thu Dec 13 2012, 09:01PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

IamSmooth wrote ...

The question: is there any benefit to wrapping aluminum tape around the tubing

No. Your losses are by conduction , not radiation. Thicker/better insulation is what you need.

klugesmith

Thu Dec 13 2012, 10:18PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

How are you going to prevent the outside of outer tube from frosting up?
The container surrounding your insulation could be purged with dry nitrogen gas.
Or with cold ultra-dry air emerging from warm end of your counterflow heat exchanger.

Many years ago, I learned something about the insulation in a commercial pure nitrogen plant, newly installed across a field from my office window. The "cold box" was a cylindrical tank about 6 feet in diameter and 30 feet high, similar in size to the horizontal LN2 storage tank. Six months after the plant started, some component broke and needed to be replaced.

The space between the apparatus and the outer tank was filled with loose insulation like vermiculite. My guess is that the insulation-filled space was then evacuated. (note 1)
For repair access, they cut out a section about 6 feet square, halfway up the tank. Before the cutting, the insulation was blown or sucked (?) into some enclosed trailers through a very large hose.

Here is a small pure N2 plant:

and a detailed document about a full-blown air separation plant:

[edit] Note 1. With the modern Internet there's no need to guess. I found this document

from a cryogenic cold box maker. The box is filled with perlite, which can be loaded or drained through 6 inch ports. But it's not evacuated, it's purged with nitrogen that flows continuously.
1.3.2 Dehumidification Purge
Prior to start-up, the cold box shall be purged of moisture that may have entered. After installation of the breather valve, emergency vent, and perlite, set the nitrogen flow rate to provide approximately two volume changes of the casing every 24 hours. Maintain this purge at least two days.

IamSmooth

Mon Jan 07 2013, 10:44PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Broke -100F for the first time starting at an ambient temperature of around 50F.
It took about 20 minutes. I had to stop to do other things. I'll have to give myself more time and start on a colder day to save time.

I'm using alumina silica insulation. I have the cover off for the photos. It is good to almost 3000F so I thought it would be good for the cryogenic temperatures. If I give myself enough time I should see -320F soon.

IamSmooth

Wed Jan 09 2013, 08:11PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I got liquid air. The last temp I recorded was -282F. I think the thermometer needs to get calibrated. It just stopped at this temp. I took the collector out, but I could not disassemble it. It was frozen shut. I will have to redesign a collecting chamber with a facet to drain the contents.

Although I could not see the liquid, when I turned the chamber upside down I got a sudden rush of mist hissing out. This was the air vaporizing when it hit the sides of the chamber. After the redesign I will so it again so I can collect the liquid N2 and O2.

klugesmith

Wed Jan 09 2013, 09:00PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Very very cool, indeed.

Strong work! Your perseverance is being rewarded.
Soon we expect to see reports of production rates and progressive improvement -- or is it time to call it done, and start a new quest?

Are you using any separately refrigerated consumables, such as ice ?

-Rich

Ash Small

Wed Jan 09 2013, 11:07PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

klugesmith wrote ...

Soon we expect to see reports of production rates and progressive improvement -- or is it time to call it done, and start a new quest?

I think he's planning to separate the N2 and O2, etc, and use the LN2 for something else, Rich.

Pretty cool stuff, IAS.

IamSmooth

Wed Jan 09 2013, 11:11PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

The calibration on my thermometer is definitely off. I need to fix this.
I am fabricating a better knob to control the throttle as it becomes difficult to move below -100F.
I will make a collection tank with a faucet to drain my product.

The compressor uses air to partially cool the compressed air. It exits at around 300F.
I use ice to cool this down further before it goes to the regenerative tank. I plan to write a whole tutorial so others can duplicate this. I was thinking of using dry ice instead of ice. This would speed up the process, but I don't feel like spending money for it each time I plan to use it.

When I opened up my tank it was really cold. I couldn't keep my hands in there even with gloves.

first previous 7 8 9 10 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob