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Converting Gasses into Liquids

D

David G

Well-known Member
I work a lot with natural gas in both gas and liquid form, there were some questions on how it stays in each form.

The (gas) natural gas is transported via pipelines, with pressures varying between 400 and 2500 PSI. Gasses will not change state unless the pressures are appropriate and you either provide or take away the latent heat of vaporization by heating or chilling. So in essence it behaves just like the AC in your car. Methane, which is the most common component in NG, will not liquify until it it dropped to -250F, and will remain there at almost no pressure, less than a PSI until you give it enough energy to change back to gas, where it expands about 900 times. The LNG systems use the heavies, i.e. propane, pentane and hexane as refrigerants to cool the methane so it will condense, they then use natural gas in heaters to vaporize it and put back on the line.
 
Someone told me once that he could put liquid propane in an open bucket and it would remain a liquid for a short while as it evaporated off the top.

True or...?
 
Yes, that is true.

If "perfectly" insulated, it would remain liquid forever.

The LNG tanks have 15-20' of foam underneath, and the walls are double with that much foam between.
 
Yes, each of the gasses has a liquid point at the appropriate pressure.

This is like looking at dewpoint, it cannot get colder than dew point with rain, fog or snow.
 
We have a propane vaporizer at work and have all the lines insulated and heat traced to keep it vapor till it reaches the engine.
 
That is correct, putting liquid propane in a pail. had to drain a L P tractor tank to weld on it. The welder guy drained the L P into a 5 gal pail and it sat out in the yard for well over a hour till it was all gone. clint
 
(quoted from post at 16:53:59 09/29/18) I work a lot with natural gas in both gas and liquid form, there were some questions on how it stays in each form.

The (gas) natural gas is transported via pipelines, with pressures varying between 400 and 2500 PSI. Gasses will not change state unless the pressures are appropriate and you either provide or take away the latent heat of vaporization by heating or chilling. So in essence it behaves just like the AC in your car. Methane, which is the most common component in NG, will not liquify until it it dropped to -250F, and will remain there at almost no pressure, less than a PSI until you give it enough energy to change back to gas, where it expands about 900 times. The LNG systems use the heavies, i.e. propane, pentane and hexane as refrigerants to cool the methane so it will condense, they then use natural gas in heaters to vaporize it and put back on the line.
Click to expand...

Ah i remember this stuff from school.
We have a H2S line that comes onto site underground, then enters a piperack. Somehow, it liquifies in the line once above ground no matter the ambiant conditions and screws with processes.
 
Propane makes an excellent refrigerant. But it is a little flammable, however refineries routinely use propane refrigeration cycles. They're used to handling flammable products, it seems. Lube plants, for making lubricating oils have giant propane chillers operating at a vacuum.

Do you ever deal with hydrates? Water in pipelines can for hydrates with methane under the right temperatures and pressures. It looks like snow, usually dirty snow. Once formed, the hydrates are very persistent and do not change back to vapors readily. They have been known to plug off high pressure pipelines.
 
R-134a is not propane it is
tetraflourethane one component no
additional refrigerant in it's form.
Not flammable and boils around -15f.
 
Converting any gas into a liquid is done all the time in refrigeration and AC. Only difference is what type of refrigerant they are using.

I remember when ammonia was used in the old ice makers before all the modern refrigerants came about. Wasn't too hard to tell when there was a leak.

Some even experimented with propane blend as a substitute R12 or R22, don't remember if it was R22a or R12a.

It all has to do with ideal gas laws of Pressure, temp and volumes.
 
BMW had a few more or less experimental hydrogen powered cars a few years ago. Even with high pressure & all the insulation they could pack in there, the result was that if you left it in the airport parking lot (or your garage) for a few days, all the hydrogen was gone. Only a water spot under the rear bumper might remain, as the gaseous hydrogen the must be released before tank rupture was burned off in a catalytic process, leaving only water behind. I guess it was" drive it or lose it". :(
 
The manufacturer had this to say, so apparently there is some form propane in this....plus other similar ingredients:
"[i:53301f0aee]It is a blended mix of hydrocarbons - not just "propane"[/i:53301f0aee]."
 
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