freezing point of Propane

[Patf]

I think this has been discussed before but thought I could ask again as it's topical. I rang Antargaz to order some more propane and the man asked me what the minimum temperature was here at the moment. I said about -5 at night. At what temp. does propane freeze?  Our tank is buried anyway.

[Bugsy]

Propane (C3H8)is a colourless, odourless, easily liquefied, gaseous hydrocarbon (compound of carbon and hydrogen),the third member of the paraffin series following methane and ethane. It is separated from light crude oil, natural gas, and is a by-product of petroleum refining. Propane is commercially available as liquefied propane or as a major constituent of liquefied petroleum gas (LPG).

Although a gas at atmospheric pressure, propane has a boiling point of -42.1 C (-43.8 F) and thus is liquefied under elevated pressures. It therefore is transported and handled as a liquid in cylinders and tanks. In this form, alone or mixed with liquid butane, it has great importance as a fuel for domestic and industrial/commercial uses and for internal-combustion engines.

The following properties and combustion data have been taken from various sources and the values shown are for an average commercial grade of propane. It should be kept in mind that the commercial grades can vary and, therefore, the values in the tables will also vary.

Extracted from CAN/CGA-B149.2-M95 Propane Installation Code.

Chemical Formula	C3H8
Molecular Weight	44.06
Freezing Point (F)	-310
Freezing Point (C)	-190
Boiling Point (F)	-44
Boiling Point (C)	-42
State at atmospheric pressure (60 f, 15 c)	Vapour
Relative Density (gas)	1.52
Relative Density (water)	0.51
Mass per gallon of liquid at 60 F	5.1 lbs
Mass per litre of liquid at 15.5 C	0.51
BTU/cu.ft. Vapourized	2520
kJ/cubic meter Vapourized	93,800
BTU/lb. Vapourized	21,622
kJ/kg. Vapourized	49,700
Cubic ft. of vapour from 1 lb. of liquid at 60 F.	8.5
Cubic meters of vapour from 1 kg of liquid at 15 C	0.53
Cubic ft. of vapour from 1 gal. of liquid at 60 F.	44
Cubic meters of vapour from 1 litre of liquid at 15 C	0.265
Latent heat of vapourization at boiling point, BTU/gal.	944
Specific enthalpy, kJ/L	219
Cubic feet (meters) of air required to burn 1 cubic ft. (meter) of gas	23.5
Cubic feet (meters) of oxygen required to burn 1 cubic ft. (meter) of gas	5
Cubic feet of air required to burn 1 lb. of gas.	200
Cubic meters of air required to burn 1 kg. of gas.	12.3
Ignition temperature F. (C)	920-1020 (493-549)
Maximum flame temperature F (C)	3600 (1982)
Percentage of gas in air for maximum flame temperature	4.4
Lower and upper limits of flammability (percentage of gas in air)	2.4 to 9.5
Octane number (iso-octane 100)

[Colonel Mustard]

It won't "freeze", ie turn solid, but as Bugbear pointed out, at -42.1 it won't vapourize from liquid to gas - this is its boiling point..

[Pierre ZFP]

Butane on the other hand can be a bit more of a problem as its boiling point is only -0.5 deg C and so can easily freeze up, especially if large amounts are drawn from the tank which will also lower the temperature.

I've had no problem with a Primagaz above ground tank when the temperature has dropped as low as  -12C

[Gluestick]

Always remembering, of course, that a gas under pressure is subject to Boyle's and Charles's and Gay-Lussac's laws and also ............................

Oh boy! We've done this one before!

http://en.wikipedia.org/wiki/Equation_of_state#Boyle.27s_law_.281662.29

http://en.wikipedia.org/wiki/Gas_laws

 

[Patf]

Can't pretend to understand most of your post Bugbear, except that it's very unlikely that propane will freeze. Perhaps the Antargazman was just being sociable. Thanks for the replies.

[Bugsy]

[quote user="Patf"]Can't pretend to understand most of your post Bugbear, except that it's very unlikely that propane will freeze. Perhaps the Antargazman was just being sociable. Thanks for the replies.[/quote]

You can't understand it , neither can I, [:)], bit of click and paste exercise I'm afraid.

Gary

[Gluestick]

PatF:

Your tank is buried: the temp at 1.5 metres below surface is sufficient to operate a  very efficient ground source heating system! Also remember that there is no wind chill.

So don't worry: unless you are in Siberia, no problem.

 

[sid]

[quote user="Gluestick"]

....Also remember that there is no wind chill.

[/quote]

Gluestick

I was under the impression that only living creatures are affected by windchill; isn't it just a sensation we have that it feels colder than it it actually is? [blink]

Sid

[Gluestick]

No, don't believe so.

Wind extracts specific heat since it absorbs radiated relative heat.

If the wind temperature is lower than ambient - which unless it's a Mistral, e.g. - it tends to be, then the wind can take out heat.

An undergound tank tends to at a higher temperature.

 

[PaulT]

Now caravanners know, or at least the all year ones do, Butane in Summer, Propane in Winter.

However, as far as I know, the Butane is the better option as it has a higher calorific value than Propane so, unless it is going to be low temperatures Butane is the better option.

Paul

[Gluestick]

Actually, the Calorific Values are about equal.

http://www.e-lpg.com/lp_gas.asp

The Latent Heat of Proane however is somewhat higher.

Propane provides a higher burn temperature than Butane; which is why it's preferred for blowlamps.

In fact, Propane can be used in combination with Oxygen (Oxy-Propane) for cutting mild steels; it gives a much cleaner cut than Oxy-Acetylene.

 

[bejay]

[quote user="Gluestick"]

Always remembering, of course, that a gas under pressure is subject to Boyle's and Charles's and Gay-Lussac's laws and also ............................

[/quote]

People do seem very fond of Boyles Law!

Propane in a cylinder is a vapour in equilibrium with its liqid phase and Boyles law does not apply.

The pressure inside a cylinder remains fairly constant which is why you can't measure the contents with a simple pressure gauge. It is however dependent on temperature.

bj

 

 

 

[Gluestick]

[quote]

The pressure inside a cylinder remains fairly constant which is why you can't measure the contents with a simple pressure gauge. It is however dependent on temperature.[/quote]

So.....................................why does one need a regulator?

 

[Michael]

To set the outlet pressure Uh--------------------

[Gluestick]

But if the pressure "Remained fairly constant", then all one would need is a pressure reducer.

The whole point of a Regulator is that it maintains a constant outlet pressure as the cylinder pressure reduces as the gas is consumed.

I've been using industrial gases for over forty years: and the reason we all tend to have two gauges is one to set the outlet pressure, accurately to ensure that the process is controlled reasonably accurately: and two to know how much gas is left in the cylinder. It also helps to ensure one has not been shortchanged on the refill: a not unknown reality with a certain large industrial gas supplier in the UK!

 

[bejay]

A pressure gauge is fine for measuring the contents of an oxygen cylinder because this is a true gas which does obey the simple gas laws.

Butane and propane can of course be used in small devices without a regulator because of the constant pressure. The fine tuning is done with a needle valve,

bj

[Gluestick]

Well, most people use a pressure regulator on propane bottles and a gauge as I stated before. Indeed, I use multi-stage regs on Oxygen, Accetylene, Argon, Argon-CO2 mix and straight C02, as well as propane. And my main propane bottles enjoy two gauges: one for cylinder pressure: and the second for low pressure at the delivery side of the regulator.

However what you said earlier was:

[quote] The pressure inside a cylinder remains fairly constant which is why you can't measure the contents with a simple pressure gauge.[/quote]

Apart from the fact that I don't agree, since the effective pressure reduces in direct proportion to the contents, your earlier statement - as above - disagrees with your last post!

 

[Colonel Mustard]

No-one has mentioned Graham's Law of Diffusion of Gases. So I will.

[bejay]

[quote user="Gluestick"]

Apart from the fact that I don't agree, since the effective pressure reduces in direct proportion to the contents, your earlier statement - as above - disagrees with your last post!

[/quote]

I am not sure that I understand why you say that. Perhaps you have not read it fully.

You are correct in one respect. The presure will of course drop as the cylinder becomes nearly empty. But this does not alter the fact that the pressure in the tank does not follow the inverse proportionality required by Boyles Law.Which is why it shouldn't be used.

May I respectfully suggest that you read the wikipedia link you posted,.this may help.

But, I suppose, enough of 17 th century Physics!

Regards.

bj

 

[Gluestick]

Actually, bj, I originally mentioned the gas laws rather tongue in cheek!

If you search back, regular posters herein enjoyed a spirited, confusing and wonderfully arcane thread on this quite some time ago, wherein everyone was scratching their thatches (or bald spot!) and trying desperately to recall rusty memories of A level physics and various rules of thermo-dynamics and gas-dynamics!

Quite entertaining, actually. [:D]

 

[Patf]

So what is the practical application of these theories to my buried gas tank?  eg Does it mean that when the amount of gas in the tank is very low the pressure goes down? And when the amount is low the meter reading is inaccurate?

[Gluestick]

The pressure in your tank will reduce, PatF as the amount of gas reduces.

However, the pressure delivered to (e.g.) your heating will be fine: until the tank has almost run out: that's the whole point of the regulator.

Don't know what the meter reads: probably gas pressure in the tank. You should see this gradually reducing as you use gas: monitor it and you will be aware of when is the time to call your friendly gasman for a new delivery.

Unfortunately, when the tank is nearly empty, it will run out very quickly and the meter reading is not much use.

 

[bejay]

 

1)  You cannot measure the contents of an LPG cylinder by measuring pressure. The only accurate way to do it is by weight.

This is not exactly a practical procedure with  an underground tank. So......

2) A gauge is fitted to the tank which measures the liquid level in the tank, very like a petrol gauge except that it is mechanical..I assume that the gauge is calibrated to allow for the cylindrical shape of the tank but that, PatF you would need to confirm with your supplier.

bj

 

 

 

[napoleon]

[quote user="sid"][quote user="Gluestick"]

....Also remember that there is no wind chill.

[/quote]

Gluestick

I was under the impression that only living creatures are affected by windchill; isn't it just a sensation we have that it feels colder than it it actually is? [blink]

Sid

[/quote]

Sorry Sid,

I have only just spotted your posting (and the following one). Your impression concerning the term "windchill" is absolutely correct. Windchill describes the physiological effect of an increase in loss of body heat due to forced convection. It gives the subject the sensation that the temperature is lower than it is.

Alistair