Draining LPG from old vehicle tanks

[thanatos1111]

I've got a weird question..... I know of a place that I can get a couple large propane tanks from old cars, and I was thinking about welding a couple together and using a compressor head and an electric motor to make a really big air compressor tank. The only problem is that they're still filled with propane. Not being one to waste this stuff as barbecue season is ahead, what's the best way to reclaim this stuff into my 20lb. tanks? I'm sure there's a process to drain propane cause propane tanks get overfilled all the time...

I don't care about legality issues...

[thanatos1111]

Someone out there has to know something about this....

[triver525]

The whole thing sounds like an accident waiting to happen if you ask me.

[wjjeeper]

use a cutting torch to cut a hole in the bottom and it will drain out real fast like. :burnout:

[alloroc]

You'll have to build some adapter hoses and look into renting a EDIT: flammable vapor recovery pump.

[Darkane]

You need a compressor to suction the propane out into a fresh cylinder. You can't "pump" a vapour. Need to re-compress it. The liquid in the bottom will flash in the tank as the volume is being drawn out. This is not worth it. Just vent it to atmosphere, or burn it.

[benyl]

Just attach the big tanks to your BBQ... hahaha call a bunch of friends over for some ribs!

[alloroc]

Originally posted by Darkane
You need a compressor to suction the propane out into a fresh cylinder.
Correct


Originally posted by Darkane
You can't "pump" a vapour.
False


Originally posted by Darkane
Need to re-compress it. The liquid in the bottom will flash in the tank as the volume is being drawn out.

True, however a refrigeration reclaim pump will move the liquid by sucking vapor off the tank you are filling. Once the liquid is gone from the tank you are evacuating it will switch to vapor mode and 'pump' the remaining vapor into the reclaim tank.


Originally posted by Darkane
This is not worth it.

Probably


Originally posted by Darkane
Just vent it to atmosphere, or burn it.

Danger Danger!!

[Darkane]

Originally posted by alloroc

Correct


False



True, however a refrigeration reclaim pump will move the liquid by sucking vapor off the tank you are filling. Once the liquid is gone from the tank you are evacuating it will switch to vapor mode and 'pump' the remaining vapor into the reclaim tank.



Probably



Danger Danger!!

Lol you absolutly cannot "pump" a vapour. Ever heard of cavitation? Also in refrigeration the reason you can use a pump is because in the Condensor accumulator where they pump the liquid from, the Refrigerent is just liquid. It stays under high enough pressure where it wont flash off. In a propane tank the C3 is pressurized and at the bottom becomes a liquid. Thats why a full propane tank has liquid and empty does not. HOWEVER an empty propane tank still has pressure.

So besides Venting it how do you suggest he gets rid of it? Remember Legality is of no concern here.

[DNSDJS]

well.... the best thing is BBQ
a HUGE ONE!!

DO NOT BURN IT!!

(BIG BOOM)

UNLESS you want to meet GOD realli realli fast.
LMAO

[Darkane]

Originally posted by DNSDJS
well.... the best thing is BBQ
a HUGE ONE!!

DO NOT BURN IT!!

(BIG BOOM)

UNLESS you want to meet GOD realli realli fast.
LMAO

haha, Its fine to burn. I didn't mean strait out of the tanks. Propane at 100F is 172Psi!! that would be an insane flame. Hook up a pressure regulator like a BBQ and burn it that way. By the way the only way to blowup propane tank is to heat it enough to blow on pressure. Every 10 Degrees is 1.5% expansion If I recall

[alloroc]

A second edit: The following recovery procedure if done with a refrigeration pump should be used only with non flammable materials. I just remembered refrigeration pumps allow the gas to pass by the open motor windings.


Originally posted by Darkane


Lol you absolutly cannot "pump" a vapour. Ever heard of cavitation? Also in refrigeration the reason you can use a pump is because in the Condensor accumulator where they pump the liquid from, the Refrigerent is just liquid. It stays under high enough pressure where it wont flash off. In a propane tank the C3 is pressurized and at the bottom becomes a liquid. Thats why a full propane tank has liquid and empty does not. HOWEVER an empty propane tank still has pressure.

So besides Venting it how do you suggest he gets rid of it? Remember Legality is of no concern here.

Wow so many misconceptions I don't know where to start.
Please don't be mad I can teach you a few things here. - Its what I do.


Vapor is nothing more than molecules in a saturated or semi gaseous state. You can pump a vapor, you can pump a gas. If not your car would not run.

Type "vapor recovery pump" in google ... see how many products there are.

Now type in "refrigerant recovery pump"

Robinair Brand25200B Robinair Refrigerant Recovery Machine - Designed for the recovery medium and high-pressure refrigerants, including R-410A - Automatically switches from liquid to vapor recovery - Provides continuous recovery without the need to change the hose or flip a switch - Automatic high pressure cut-out switch for safety - Direct liquid recovery without damaging the compressor - Oil-less compressor allows rapid transfer of large amounts of liquid - more


Propane is a refrigerant, a pretty good one. The formula is C3H8 (the refrigerant nomenclature is R290)

In any refrigeration circuit that does not have a pump down cycle (cars, and packaged HVAC units) when the pump is shut off, the pressure equalizes throughout the system. In time the liquid will actually migrate to the coldest point. This is why most HVAC units have compressor heaters, to keep the liquid from forming in the compressor on cold days.

A condensor accumulator is not one object they are two separate items. The condenser is where the refrigerant is pumped to, not from. An accumulator (if used not all HVAC systems have one, however most cars do) is used to trap any liquid in the suction line. Not to prevent cavitation but to prevent liquid lock. A refrigeration compressor pumps ... gas or ... vapor .. taking the low pressure low temperature gas ( or vapor ) and turning it into a high pressure high temperature gas ( or vapor )

Cavitation happens when a pump is moving a liquid and the pressure drop at the impeller is too great. Recovery pumps don't work this way....

Lets say we wish to remove what is a half full tank of 'some LP gas' and move it to another. The stuff in the half full tank is in what is known as a 'saturate' condition. In theory it is at a temperature/pressure equilibrium neither truly liquid or vapor (gas) but we know from practical experience you can shake a small tank and know that it is 'half full' Some tanks only have one outlet, liquid. Refrigeration tanks have two. for a tank with only one outlet we would first hook up the liquid recovery line up to a refrigeration gauge and ensure the line is shut off. Ok now we hook the recovery pump discharge vapor line up to our gauge set and make sure it is shut off.

Now connect the recovery pump high pressure outlet (liquid) line to the tank we wish to put the fluid into. Then we hook up the vacuum (vapor line) up to the LP tank and flip it (the tank) upside down. Now the liquid outlet is a vapor outlet.

Plug the pump in
Open the tank valves
Turn the pump on.
Wait for the 'fully recovered' light to come on.
Close the tank valves
Turn the pump off.

Hose removal is opposite of install.

The EMPTY tank is now likely in a VACUUM and not pressurized.

Edit:
Venting propane is REALLY dangerous, it is heavier than air and can sit for long periods. It sits in a state that leaves it in a perfect stoichiometric condition. This is why propane vehicles are not allowed in parkades. Vent enough and you can actually make a cloud that on a calm day can run down your street and fill the nearest sewer drain with explosive gas. Not good.

[Schwa]

Your knowledge of propane and propane accessories is amazing! Good post though, really, Hank :thumbsup:

[thanatos1111]

Yeah, I know venting to atmosphere is out of the question..... I work for CP Rail and I've seen the vids of tanker cars going blivvy.... (in rail terms, that's like the Hindenburg disaster except for a couple miles..)

As for the barbecue idea, it's not a bad one, I was hoping to save some of the gas to hook up to the BBQ but I don't think I could afford the massive amounts of meat required to use up the gas. I DID want to use a bunch to heat my hot tank when I dip some engine parts (Don't even ask about that one).

The way I figured, is that propane in a pressurized state is in liquid form. If I hooked up a 20 lb tank somehow and let the liquid from the big tank flow into the little one (using a scale to figure out the amount of fill) in theory the liquid would flow out of the big tank into the little tank. Simple plumbing here, right? The next big question is how to hook up the valves....

I don't want to call the propane company to ask if they could drain the tank for me, that's just asking for problems..... might be my only option....

[thanatos1111]

Hmm... flammable liquid recovery pump you say... wonder how exotic that is. I don't think I can find that at Princess Auto.... Probably is muy expensive...

[Lexxan]

Saudi Arabia and everywhere else out east burns off all their natural gas as it's useless to them. Who cares about a propane tank.. drain it into the atmosphere. Do it in a big field or something on a windy day lol

[thanatos1111]

Originally posted by Lexxan
Saudi Arabia and everywhere else out east burns off all their natural gas as it's useless to them. Who cares about a propane tank.. drain it into the atmosphere. Do it in a big field or something on a windy day lol


Like I said before, I don't want to waste it. I could get into a big flame war here but I don't have time for it. Please offer something a little more constructive next time.

[Darkane]

Originally posted by alloroc
A second edit: The following recovery procedure if done with a refrigeration pump should be used only with non flammable materials. I just remembered refrigeration pumps allow the gas to pass by the open motor windings.



Wow so many misconceptions I don't know where to start.
Please don't be mad I can teach you a few things here. - Its what I do.


Vapor is nothing more than molecules in a saturated or semi gaseous state. You can pump a vapor, you can pump a gas. If not your car would not run.

Type "vapor recovery pump" in google ... see how many products there are.

Now type in "refrigerant recovery pump"



Propane is a refrigerant, a pretty good one. The formula is C3H8 (the refrigerant nomenclature is R290)

In any refrigeration circuit that does not have a pump down cycle (cars, and packaged HVAC units) when the pump is shut off, the pressure equalizes throughout the system. In time the liquid will actually migrate to the coldest point. This is why most HVAC units have compressor heaters, to keep the liquid from forming in the compressor on cold days.

A condensor accumulator is not one object they are two separate items. The condenser is where the refrigerant is pumped to, not from. An accumulator (if used not all HVAC systems have one, however most cars do) is used to trap any liquid in the suction line. Not to prevent cavitation but to prevent liquid lock. A refrigeration compressor pumps ... gas or ... vapor .. taking the low pressure low temperature gas ( or vapor ) and turning it into a high pressure high temperature gas ( or vapor )

Cavitation happens when a pump is moving a liquid and the pressure drop at the impeller is too great. Recovery pumps don't work this way....

Lets say we wish to remove what is a half full tank of 'some LP gas' and move it to another. The stuff in the half full tank is in what is known as a 'saturate' condition. In theory it is at a temperature/pressure equilibrium neither truly liquid or vapor (gas) but we know from practical experience you can shake a small tank and know that it is 'half full' Some tanks only have one outlet, liquid. Refrigeration tanks have two. for a tank with only one outlet we would first hook up the liquid recovery line up to a refrigeration gauge and ensure the line is shut off. Ok now we hook the recovery pump discharge vapor line up to our gauge set and make sure it is shut off.

Now connect the recovery pump high pressure outlet (liquid) line to the tank we wish to put the fluid into. Then we hook up the vacuum (vapor line) up to the LP tank and flip it (the tank) upside down. Now the liquid outlet is a vapor outlet.

Plug the pump in
Open the tank valves
Turn the pump on.
Wait for the 'fully recovered' light to come on.
Close the tank valves
Turn the pump off.

Hose removal is opposite of install.

The EMPTY tank is now likely in a VACUUM and not pressurized.

Edit:
Venting propane is REALLY dangerous, it is heavier than air and can sit for long periods. It sits in a state that leaves it in a perfect stoichiometric condition. This is why propane vehicles are not allowed in parkades. Vent enough and you can actually make a cloud that on a calm day can run down your street and fill the nearest sewer drain with explosive gas. Not good.

You seem fairly Stubborn so I'll keep this short.

-Accumulators ARE attached to Condensors yes.
-your recovery "pumps" are actually compressors. Sorry dude.

http://www.vaporrecovery.com/exptech1d1.html

http://www.productionpump.com/vapor.htm

I'm sure you know the standard symbol for a compressor and pump. Tell me if that is a pump in the sketch.

Venting is dangerous yeah, But he doesn't care. Legallity isn't an issue. I'm giving solutions.

Last but not least how does a car work? Where is the fuel pump in a tank. Top? no. Bottom yes. What in the bottom of a gas tank? Liquid right on. I'm sure with your propane and refrigeration knowledge you know about pressure Atomization right? Fuel is atomized through the injectors for a burn. Same way an expansion valve works.

But I'm done with cluttering up this guys thread. PM me if you'd like.