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Converting Density to Standard Density

  1. Mar 3, 2014 #1
    I have an application where I need to find the density of a substance at standard conditions (101.325kPA, 15°C) from the density at recorded conditions (varies).

    The first application is for natural gas at approximately 11Barg (160 psi, 1100kPA), 80°C (176°F).

    The second application is for crude oil at approximately 11Barg (160psi, 1100kPA), 80°C (176°F).

    There are standard functions available published by API/AGA to do this but I need a more fundamental thermodynamic description of how to do this.

    If somebody can provide a brief explanation I can go away and study in more detail. A description for ideal gases and real gases would be appreciated as well. Obviously in this application the ideal gas theory will be inaccurate.

    Last edited: Mar 3, 2014
  2. jcsd
  3. Mar 3, 2014 #2


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  4. Mar 3, 2014 #3


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    It's not clear that 'crude oil' is a gas, especially at such conditions as described in the OP. In any event, 'crude oil' is a rather complex mixture of various hydrocarbons.
  5. Mar 4, 2014 #4
    This is where I get stuck because the there are several equations of state each with their own advantages/disadvantages. The question is for natural gas under these conditions which equation should be used?

    Also, crude oil is a liquid and obviously will obey a different law. The question is how to find the corrected density for crude oil?
  6. Mar 4, 2014 #5


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    You need to start with tables/equations that have already been developed for your substances.

    A complete table will show all of the phases: solid, liquid, gas.
    It will show this for all temperatures and pressures which have been studied.

    For example, start by looking at water:
    "Wagner and Pruss, The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use, 1995"

    These results are _not_ found via the "Ideal Gas Law" or any other law - they are measured properties of the materials. Hunting up the data is your job.
  7. Mar 4, 2014 #6
    Are you sure you have posed the problem correctly? "find the density of a substance at standard conditions (101.325kPA, 15°C) from the density at recorded conditions (varies)," or is it the other way around. If it is only to find the density at standard conditions, then you can certainly use the ideal gas law for natural gas (methane). And the density of typical crude oil should be readily available at standard conditions.

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