Relative density vs specific gravity = ? pressure
Relative density vs specific gravity = ? pressure
(OP)
One of the previous posts reminds me of a situation I ran into last week. Is there a chart which could at least loosely suggest a nominal density of propane based on visual indicators of pressure and specific gravity. I am for the 1st time testing a mass flow meter, we can not get repeatability after making changes to correct the errors seen in a volumetric, small volume or loop/ballistic test. I am suggesting the counter (registering indicator) is at fault, just my gut instinct and 32 years of meter calibration an repair. My experience tells me that 99.8 % -+ .505 specific gravity propane at 35 Deg. F. should be approx. 60 PSIG. If this isn't enough information, let me know and I will try to give better examples to anyone in the refining industry.





RE: Relative density vs specific gravity = ? pressure
I would approach this as a simple saturation problem and get the temp and use a saturation table to get pressure. Or measure pressure and use the table to get temperature. One thing is pretty certain, at most ambient temperatures propane is going to be saturated.
David
RE: Relative density vs specific gravity = ? pressure
You can calculate a density at a given temperature and pressure for propane. How accurate that would be depends on the equation of state you use and the 0.2% of the gas you don't know what it is, so I would think density would be better supplied by an explicit measurement from a sample.
What's the question?
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Relative density vs specific gravity = ? pressure
RE: Relative density vs specific gravity = ? pressure
Losing inventory? That's a good question. As compared to what? Are they reading input to the plant with volume? With mass, or volume to corrected mass, or mass to corrected volume and are they calibrating properly. Are they comparing to weight measurements and mass from an actual sample? Is the inlet reading really any better than your outlet reading?
Not to mention propane systems leak, so it's not uncommon to lose inventory from somewhere, either from inlet-outlet measurements, or from two different meters, or from process losses to valve and pump packings, etc. The question is how much are you losing ... relatively speaking.. to what goes into the plant and how you determine the accuracy of each meter in the mass balance equation for the plant. I doubt that checking your meter by calculating the density is a good place to begin. Get samples and measure them first. Compare enough samples with actually tested densities with the density meter's reading and you'll know how accurate and repeatable your meter is straight away. Balancing against another meter is a waste of time. As I always say, a man with two watches never knows what time it is. It is better to have confidence in a (one) watch.
Plant losses are another story. First get some confidence in the inlet and outlet meter readings first.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Relative density vs specific gravity = ? pressure
is probably better than just any old equation of state method, and definitely is a lot handier.
http://webbook.nist.gov/chemistry/fluid/
gives for pure propane,
35.000 F
75.000 PSIA (NOTE THE ABSOLUTE PRESSURE)
32.864 LBM/FT3
0.030429 FT3/LBM
Density of pure propane would be about 0.5267 when compared to water at 60F
If the other was 0.2% by weight Butane(?) that would make SG around 0.5268
http
So, your mass density meter reading looks high, while your experienced value sounds low. We have added another "watch" to the soup.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Relative density vs specific gravity = ? pressure
RE: Relative density vs specific gravity = ? pressure
Now if we have some specific gravity of propane, say 0.505, that propane's density is 0.505 * 62.37 lbs/ft3 or 31.50 lbs/ft3.
If you know the value of the propane's density, then divide that by 62.37 to get its specific gravity relative to water at 60F.
Density: You first weigh when empty, then fill a sampling cylinder of a known volume and weigh it again when completely full of liquid. Subtract the weight of the cylinder to get the weight of propane alone and divide that weight by the known volume of the cylinder at whatever pressure and temperature it has at that time. It must then be converted to the standard reference pressure and temperature.
I agree it is hard to tell where you're leaks are when the stuff turns to gas and disappears as soon as it gets away from you.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Relative density vs specific gravity = ? pressure
RE: Relative density vs specific gravity = ? pressure
David
RE: Relative density vs specific gravity = ? pressure
Unfortunately my predictions are based on the product shipped by the refiner, IE: BOL. Thanks I'll look at the link you sent. Thanks to all of you.