Propane Line Icing Up

[Jupiter]

Okay, now let me try to really confuse you...or perhaps help to clarify

The propane tank is filled with high PRESSURE liquid. The liquid passes through the regulator which greatly reduces the PRESSURE. When the PRESSURE lowers the liquid propane must (by virtue of the laws of physics)boil into a gas. In order to boil, the propane needs heat. It "collects" this heat from the ambient air which is why the pipe turns very cold and the frost appears because of the moisture in the air. This is a completely normal occurrence.

So, it's similar to what happens in the basic refrigeration cycle. Most folks believe that A/C units add cooling to the air (house or RV) when in fact what they actually do is REMOVE heat from the air by rapidly lowering the indoor coil pressure which then "boils" the liquid refrigerant (liquid back to gas) and then moving that heated or boiled gas to the outdoor coil where it is cooled (heat removed) and eventually condensed back to a high pressure liquid. That's the simplified version of the basic refrigeration cycle.

BTW - compressing gas does not in itself make the gas hotter. The heat sensed from compressing a gas (any gas) is from the mechanical friction in the compressor (or bike pump). And "liquified gas" is actually a misnomer. It's either liquid or gas but cannot be both. Liquid, any liquid, cannot be compressed under any circumstance.

cheers,
Joopy

[TQ60]

Compressing the gas accelerates the molecules generating heat...think diesel.

[Ray,IN]

Originally Posted by Jupiter

Okay, now let me try to really confuse you...or perhaps help to clarify

The propane tank is filled with high PRESSURE liquid. The liquid passes through the regulator which greatly reduces the PRESSURE. When the PRESSURE lowers the liquid propane must (by virtue of the laws of physics)boil into a gas. In order to boil, the propane needs heat. It "collects" this heat from the ambient air which is why the pipe turns very cold and the frost appears because of the moisture in the air. This is a completely normal occurrence.

So, it's similar to what happens in the basic refrigeration cycle. Most folks believe that A/C units add cooling to the air (house or RV) when in fact what they actually do is REMOVE heat from the air by rapidly lowering the indoor coil pressure which then "boils" the liquid refrigerant (liquid back to gas) and then moving that heated or boiled gas to the outdoor coil where it is cooled (heat removed) and eventually condensed back to a high pressure liquid. That's the simplified version of the basic refrigeration cycle.

BTW - compressing gas does not in itself make the gas hotter. The heat sensed from compressing a gas (any gas) is from the mechanical friction in the compressor (or bike pump). And "liquified gas" is actually a misnomer. It's either liquid or gas but cannot be both. Liquid, any liquid, cannot be compressed under any circumstance.

cheers,
Joopy

Almost right. For appliances, liquid LP turns to a gas IN the tank as gas pressure is lowered from use, and passes through the regulator as a gas. The regulator reduces tank pressure to 11" water column/ .5 psi. There are different configurations, like engines, that plumb liquid LP to the carb, where it is converted to a gas.

[Jupiter]

Originally Posted by Ray,IN

Almost right. For appliances, liquid LP turns to a gas IN the tank as gas pressure is lowered from use, and passes through the regulator as a gas. The regulator reduces tank pressure to 11" water column/ .5 psi. There are different configurations, like engines, that plumb liquid LP to the carb, where it is converted to a gas.

Thanks for the correction, Ray. You're right on the money

TQ60 - No doubt that at the pressures we're speaking of, there is minor heat gain from the excited molecules. But I stand by the statement that the significant portion of the sensible heat gain in compressed gas is from mechanical friction of a compressor or pump.

cheers,
Joopy

[Murf2u]

Originally Posted by Ray,IN

Almost right. For appliances, liquid LP turns to a gas IN the tank as gas pressure is lowered from use, and passes through the regulator as a gas. The regulator reduces tank pressure to 11" water column/ .5 psi. There are different configurations, like engines, that plumb liquid LP to the carb, where it is converted to a gas.

Maybe I'm misunderstanding your statement Ray, but the pressure in a propane tank can raise and lower from using propane, but NOT unless it's very cold and you're using a LOT of propane.

The gas itself creates the pressure in the tank by boiling off the liquid propane. The warmer it gets, the more pressure it makes, up to about 200 PSIG at roughly 100 deg. F. If however the temp. drops to -44 deg. F. the pressure in the tank will be 0 PSIG.

The use of propane has no bearing on how much vapour and pressure is in the tank. That is purely based on temperature.

[AbdRahim]

TeJay. You have a point. I took calculus in college but never knew what some of that stuff was used for until I was 40 years old. Application?

[Jupiter]

Originally Posted by Murf2u

Maybe I'm misunderstanding your statement Ray, but the pressure in a propane tank can raise and lower from using propane, but NOT unless it's very cold and you're using a LOT of propane.

The gas itself creates the pressure in the tank by boiling off the liquid propane. The warmer it gets, the more pressure it makes, up to about 200 PSIG at roughly 100 deg. F. If however the temp. drops to -44 deg. F. the pressure in the tank will be 0 PSIG.

The use of propane has no bearing on how much vapour and pressure is in the tank. That is purely based on temperature.

If I understand correctly, I believe what Ray is saying is that the regulator reduces the tank pressure (regardless of actual tank PSI) to approximately 11"WC or 0.5lb PSI.

Your point about the relationship of the OAT temp & tank pressure is well taken, but should have little impact on line pressure downstream of the regulator.

cheers,
Joopy

[Murf2u]

Originally Posted by Jupiter

If I understand correctly, I believe what Ray is saying is that the regulator reduces the tank pressure (regardless of actual tank PSI) to approximately 11"WC or 0.5lb PSI.



Your point about the relationship of the OAT temp & tank pressure is well taken, but should have little impact on line pressure downstream of the regulator.



cheers,

Joopy

I'm not sure I can read it that way at all.

Originally Posted by Ray,IN

Almost right. For appliances, liquid LP turns to a gas IN the tank as gas pressure is lowered from use, and passes through the regulator as a gas. The regulator reduces tank pressure to 11" water column/ .5 psi. There are different configurations, like engines, that plumb liquid LP to the carb, where it is converted to a gas.

The statement seems clear ".......liquid LP turns to a gas IN the tank as gas pressure is lowered from use.......".

[TeJay]

AbdRahim,

Why thank you for the support on my point. I've seen that happen many, many times. The ability to demonstrate how the world of science and math actually relates to everyday stuff is IMHO directly related to how well both the teacher and the student do or will understand the concepts.

I had a very successful great career in teaching automotive and still can not demonstrate any application for Algebra. I do understand the basics but survived my teaching career and now as an accomplished woodworker without ever finding a single application for it. I guess the teachers could have shown me how to apply the concepts but again, they didn't.

In all reality Geometry applied a great deal more to what I did over my life. Building houses, laying concrete pads and working on engine cylinders. I doubt the average Geometry teacher could discuss how to figure rafters and pitch of a roof but it's nothing more than basic geometry.

TeJay

[Ray,IN]

Originally Posted by Murf2u

I'm not sure I can read it that way at all.






The statement seems clear ".......liquid LP turns to a gas IN the tank as gas pressure is lowered from use.......".

Thank you!
That's what I meant, and said. Regardless of ambient temperature, LP liquid reaches a point where vessel pressure prevents further vaporization if pressure is not relieved by venting or using gas. To reach the 80% full, liquid volume, an LP tank must be vented/lower gas pressure.

[Murf2u]

Ok, now I'm even more confused by your statements.

At or below -44 deg. F. propane ceases to boil and becomes a relatively inert liquid, you could in theory, walk around with a pail full of it and it would behave much like water would in warmer situations.

The 80% 'fill valve' only indicates, by its physical location in the tank at the 80% full point, where the liquid / vapour line is. That's why they have it, so somebody doesn't pump the tank full to 100%. On smaller cylinders they use weight to determine the maximum it should be filled to.

The last 20% is required, other than for safety, to leave enough 'head space' for the propane to boil off enough vapour to ensure liquid propane isn't 'burped up' into the regulator.

[palehorse89]

Some reading:

Quote:
Once a propane appliance is actively in use, the liquid propane in a tank or cylinder begins to boil. The propane vapor, as boiled off the top of the liquid begins its journey downstream to the point at which it is used. Before making its way to the LP Gas system piping, it passes through the regulator where its pressure is reduced to a usable level. Keep in mind that the regulator will only deliver a constant pressure on the outlet side while inlet pressures can significantly vary. As the propane passes through the regulator, it expands (resulting in sub zero temperatures) and causes the regulator to gradually reach the extremely cold temperature of the propane vapor passing through it. Depending on the temperature and humidity of the surrounding air, the regulator will produce condensation, much like that of a frozen mug or glass taken out of a freezer.
This is why, under normal operation in hot and humid climates, the external surface of a regulator will freeze and appear to be frozen or frosted. The rate at which propane is being withdrawn from the tank or cylinder will also cause the container to display a visible frost line, which indicates the liquid level of the propane within the tank.


Propane Regulator Freezing - Frost Forming on Regulator

[twinboat]

On smaller cylinders they use weight to determine the maximum it should be filled to.

The above statement was the case back in the 80s.

With the popularity of backyard grills and poor training, causing over filled tanks venting in mom's trunk, the OPD ( Overfill Protection Device ) valve was mandated on 20 lb cylinders. Other sizes were phased in over time.

[Murf2u]

Originally Posted by twinboat

On smaller cylinders they use weight to determine the maximum it should be filled to.

The above statement was the case back in the 80s.

With the popularity of backyard grills and poor training, causing over filled tanks venting in mom's trunk, the OPD ( Overfill Protection Device ) valve was mandated on 20 lb cylinders. Other sizes were phased in over time.

So you're saying they don't weigh cylinders with OPD's to determine when they're full anymore?