OT - Calibrating Propane Gas Meter

We just installed a volumetric propane gas meter (temperature-compensated) installed on a boiler supply line. One pulse = 0.5 cubic meters. Our system runs @ 10PSI.

The boiler condition monitoring PLC that already measures steam flow rate will be used to determine how many pounds of steam is generated per unit of propane burnt.

Since we purchase propane by the liter (liquid), I would like to convert cubic meters @ 10 PSI to liters, but can't find a conversion table or formula. I did find one that says "Specific volume (1.013 bar and 21 °C (70 °F)) : 0.543 m3/kg". It's easy to convert kg to L, but how do I allow for the pressure differential? This formula is for 14.7PSI (1.013 bar), but I need 10 PSI.

Can anyone help me out with this?

Bear with me here...


Based on this:



4.8 Pressure or compressibility correction factors (Cpl) can be calculated using data compiled in the table in chapter 11.2.2 M of the American Petroleum Institute's (API) Manual of Petroleum Measurement Standards and the equation below.

Where:

• P = Mean pressure at the meter in kPa gauge.
• PE = Equilibrium vapour pressure in kPa at the measurement temperature of the liquid. PE is "0" for liquids which have an equilibrium vapour pressure less than 101.325 kPa at 15 °C.
• F = Compressibility factor for hydrocarbons from chapter 11.2.2 M (350 to 637 kg/m3) and chapter 11.2.1 (638 to 1074 kg/m3) of the API.

4.9 The correction factors for propane (density = 505 kg/m3 @ 15 °C) have been calculated and can be found in Table 2.
4.10 The Cpl is then multiplied by the temperature-compensated net meter reading to provide a net "corrected to reference conditions of 15 °C and vapour pressure at 15 °C" reading.


found at: http://www.ic.gc.ca/eic/site/mc-mc.nsf/eng/lm00102.html



You can go to: http://publications.api.org/


and access a read-only version of the tables/formulas (for free?)


You can also do a google search for:


Compressibility Factor Tables for Hydrocarbons

And the link that includes:

"www.uic.edu/labs/trl/1.../RiaziMansooriSentToSPE.pdf"

Which gives you the math, and one heck of a headache.

Or you can just go here:

http://pipeng.com/index.php/ts/itdmotflup004b
http://pipeng.com/index.php/gsts/itdmotflup004b/itdtoflup00444

To start with do all your calculations in metric or "English". Do not mix the two. At the end you can convert final number to the other system.

One cubic meter = 1 million cubic centimeters
One liter = 1,000 cc or ml
Therefore one cubic meter = 1,000 liter.
You should be able to do this calc using PVT = PVT. Temperature is going to be the tricky part here. I believe you will have to deal with temp in degree Kelvin ie C + 273.

Your specific volume is at atmospheric ie 1013 Bar and at 21 C these are Standard Temp and Pressure. STP in English is 14.7 psia (absolute) so your pressure in psia for 10 psig is 24.7 and in Bar is
1,702.1

Assuming constant temp your gas volume at 1702 should be about .323 cubic meter per kg. Divide this into your meter reading to yield total kg then using liquid density dervie total liters liquid.

I sure hope I got this all correct. Been uhh a couple decades since I messed around with these calcs.

Dan Bentler

Thanks for the help, guys. Here's what I did:

• 1 LIQUID liter of propane @ 0 PSIG = 265.2 liters of propane GAS @ 0 PSIG (I've seen it stated from 260 to 270)
• 1 liter of GAS @ 10 PSIG (our operating pressure) = 1.68 liters of GAS @ 0 PSIG
• 1 cubic meter = 1000 liters
• 500 liters = 1 pulse

(1L LIQUID Propane / 265.2L propane GAS @ 0 PSIG) * (1L propane GAS @ 10 PSIG / 1.68 L propane gas @ 0 PSIG) * (1 cubic meter / 1000L) * (500L / 1 pulse) = 3.167L LIQUID propane / pulse

Yeah, your problem was a bit sticker than it first appeared. Geez...

I was going to (flippantly) suggest you run a tankful through your new meter and figure out the conversion that way. It sounds like it would be a good way to back check your calculations after all.

It appears that your meter is a volume type. I suggest you convert the volume flow rate to mass, which requires correction for temperature and pressure. Note that these corrections require absolute temp and absolute pressure.

Once you have the mass flow rate you can accurately convert that to volume of liquid.

Tom
After reading his post I am not sure if he has a gaseous ie vapor or a liquid propane meter. Either way it is volumetric for sure.

CHeck my numbers and thinking - been so long I am not sure I thunk it out correct. They were made assuming gas at 10 psi and standard temp ie 21 C.

Dan Bentler

leitmotif said:

Tom
After reading his post I am not sure if he has a gaseous ie vapor or a liquid propane meter. Either way it is volumetric for sure.

Dan Bentler

Click to expand...

Sounds to me like it is a diaphragm type gas meter.