LPG Mass and LPG Volume

It depends on the pressure it is delivered at.
There are gas laws which explain the relationship, but basically if you double the pressure you half the volume.
So in rough terms, if we assume your metered gas is at only a few inches above atmospheric pressure we can call that 1bar pressure, the cylinder is, say at 10bar (I dunno), hmmm you still need the volume of the cylinder or the density of the gas (at STP [standard temperature and pressure])

I think I'll quit while I'm behind, someone can probably give you an explicite answer straight off the top of their head (Probably PWSlack...he know stuff)
Del

Thanks for replying. Few inputs: maximum pressure a typical gas meter can handle is 1 bar, so gas is supplied on, say, 0.8-0.9 bar. If we presume that 80% of the cylinder is filled in liquid form (20% is left for the vapours), the question now remains is that 1 kg of LPG in liquid form, if expanded to vapour at .9 bar, will generate how much volume in cubic meter?

Hello Del

The cylinder pressure is 5 - 10 bar (I haven't got data to hand) but contents are liquid at that pressure. Liquid LPG has SG about 0.55 if I remember right but it's irrelevant as it's sold by weight.

To relate meter reading (m³) to weight of gas, need gas density. At likely pressure and temperature molar volume is ~ 24 m³. I believe LPG is mainly propane C₃H₈ and MW = 44, giving density 1.83 kg/m³. If not OP needs to find out the MW.

Incidentally, LPG for cars is sold by the litre. As the calorific value per kg of common hydrocarbons (including LPG and petrol) is about the same, whereas SG of petrol is about 0.8, LPG for cars isn't as good an idea as it seems at first glance.

Cheers..........Codey

Hi Codemaster,

Thanks for the beautiful explaination. It really solved the issue. Typically, in India (at the point of use) Butane and Propane are supplied in some proportion (80:20 or 60:40, will find out exactly from the gas supplying company). That will provide better MW. With molar volume and MW, I can use gas laws to derive near accurate SG.

In your calculation, 1.83 kg/m3 is the SG at atmospheric pressure (1 bar) at more than 25 deg C. However as the gas is supplied at .8 bar above atmospheric pressure, probably the value will be around 3.5 kg/ m3 at 1.8 bar.

Am I right?

Shailendra

Hello Shailendra

Glad the explanation helped.

Molar volume is 22.4m³ at 0°C and 1 atm (760 mmHg). I prefer to work in bar which is 750 mmHg and molar volume = 22.4*760/750 = 22.7m³. At 1 bar and 15°C (288K) it becomes 22.7*288/273 ~ 24 m³.

You're right, SG is higher at 1.8 bar, I make it closer to 3.3 than 3.5 kg/m³. There was a discussion a few weeks ago about gas metering at higher pressure. Link below is some of it but there was more which I can't find at the moment.

http://cr4.globalspec.com/thread/37577/A-valid-formula-for-calculating-a-customer-s-usage-factor-for-natural-gas

Cheers.......Codey

Found the rest of it, on below

http://cr4.globalspec.com/thread/37569/Calculating-line-loss-for-natural-gas

Codey

<...how to convert, or relate the rate/ kg of LPG to rate/ m3...>

Use the density of the gas: kg/m3.

Density varies with pressure.

Dear Mr.PWSlack,

It is not the Density alone. The Pressure is to be taken in to account.

DHAYANANDHAN.S

The pressure and temperature affect the density, but density alone gives the relationship between mass and volume.

Now, that's a link worth having.

Seriously you get propane through a utility company? We get natural gas that way. Propane here always comes in bulk rate and the customer has a big tank 500 - 1000 US gallons (2000 - 4000 liters) that gets filled with a truck mounted delivery system.

We have the small portable tanks too for camping and cooking but the fill charge on those is a rip off! The cost for the volume in a small tank works out to be around three times Higher than its bulk cost for the big home heating tanks.

Our local bulk rate is $1.30 a gallon. The most common portable tank is called a 20 pound cylinder. (it holds 20 pounds of propane) or just under 5 US gallons. The average fill cost right now is about $17 - $20! or $3 - $3.30 a gallon. Thats $10 - $14 extra for two minutes of work for the local dealer!

Fortunately have my own transfer pump and I do tanks for family and friends for $7.50 flat rate.

Dear,

These totally depend on the density of the said LPG.

Pls refer formula density= mass/volume

for exmp. density is 05660 (LPG), volume is 100ltr

mass = volume*density = 100*.5660 =56.6Kg

hope the answer of quation.

Baig saeed ali

Hi Below is URL to all the info you need to answer your ? LPG Mass verses Volume.

http://www.altenergy.com/Technology/LPGProperties.htm

Hope this Helps.

OLFARTZ