8 replies to this topic

[BABU]

Is there any website that gives the link to convert PPM moisture in natural gas to pound/SCF?

Or any guidance to perform the same as a manual calculation.

Thanks in advance

[DRS]

1ppm is 1 mg/l, do the conversion. If the gas at non standard conditions, calculate the moisture content at standard conditions and do the conversion.

[gvdlans]

1ppm is 1 mg/l, do the conversion. If the gas at non standard conditions, calculate the moisture content at standard conditions and do the conversion.

NO!!!

1 ppm only equals 1 mg/l if the ppm refers to ppm (weight) and 1 liter of the the "solvent" weighs 1 million mg (=1 kg). Here we may be dealing with ppm (volume), although not specified, and 1 liter of natural gas definitely doesn't weigh 1 kg...

I refer to the recent thread on "How to convert MMscfd to..." started by Sharif for a method on how to do the conversion.

[djack77494]

There are several conventions for expressing concentrations of contaminants, and you should attempt to be specific. In gas/vapor systems, molar (or volume) concentrations are the most common; in liquid systems, mass concentrations prevail. Less common (thankfully) would be mixed concentrations.

You may see your contaminant's concentration expressed as ppmv or ppmw. I greatly prefer specifying it that way over just plain ppm so as to avoid confusion. ppmv means parts per million by volume, which is identical to molar concentration; ppmw means parts per million by weight (really mass).

Once you know what "brand" of ppm you're dealing with, write it out fully and then do the units conversion. Let me illustrate by example:

Say you have 100 ppmv of moisture in natural gas (let's call it N.G.).
This means you have 100 moles of water per 1,000,000 moles of N.G.

Convert as follows:
100 mol H2O/1,000,000 mol CH4 * 18 lb H2O/mol H2O =
1800 lb H2O/1,000,000 mol N.G.
Now, 1800 lb H2O/(1,000,000 mol N.G./379 SCF/mol) =
1800 lb H2O/2639 SCF N.G.
or 0.682 lb H2O/SCF

HTH,
Doug

[BABU]

The denominator can be written as

1,000,000 mol N.G. * 379 SCF/mol
=> 379 MMSCF
=> 1800 lb / 379 MMSCF
= 4.75 lb/MMSCF
i.e. 100 ppmv H2O in N.G. = 4.75 lb/MMSCF

Thanks Doug
Babu

Say you have 100 ppmv of moisture in natural gas (let's call it N.G.).
This means you have 100 moles of water per 1,000,000 moles of N.G.

Convert as follows:
100 mol H2O/1,000,000 mol CH4 * 18 lb H2O/mol H2O =
1800 lb H2O/1,000,000 mol N.G.
Now, 1800 lb H2O/(1,000,000 mol N.G./379 SCF/mol) =
1800 lb H2O/2639 SCF N.G.
or 0.682 lb H2O/SCF

HTH,
Doug
[/quote]

[djack77494]

Babu got it right. If I hadn't been in a hurry, I would have caught the ridiculous value for the answer and realized the error.
Doug

[eostre81]

Hi all,
I have a question related to moisture content in gas using formula coming from UOP 213. did anyone ever hear of it???????
the formula % mol water = R * W * (460+T) * 6.78
V * A
R = volume in mL
W is in g mol
A in mmHg
t is in Fahreinheit
V is in cu ft
can anyone give me clue where 6.78 is coming from????????
Thanx B4

[Art Montemayor]

eostre81:

If you feel you have a legitimate and important query, please originate your own thread with your query. Do not "skyjack" this thread from Babu.

It will be much more efficient and orderly if you start your own thread.

I recommend you be specific as to what you are asking. We don't know what "UOP 213" is or could be. Kindly define all your references in order to make sense of your data.

Basically, your "equation" seems to be a mixture of units - both USA and metric. This is not the usual way to write an equation, so I highly suspect it is flawed.

Always identify your variables. What do the variables represent? Don't just tell us the units of the variable. If you can't do this, you won't get much of a response since readers won't know what the equation is for and how it works.

[hygrometry]

Converting PPMv moisture content to LBS-H2O/MMSCF in Natural Gas


Assume you have 150 ppmv of moisture in natural gas [mostly methane] (CH4)
Thus you have 150 moles of H2O per 1,000,000 moles of CH4
We know that H2O has 18.02 g/mol
conversion 1g = 0.0022 lbs
or H2O has 18.02 * 0.0022= 0.03973 lbs/mol

from PV=nRT ideal gas occupies 22.711 liters/mol at STP
conversion 1 liter= 0.03531467 cubic-feet
or ideal gas occupies 0.80203 SCF/mol

THEN:
(150 mol-H2O/1,000,000 mol-CH4) * 0.03973 lbs-H2O/mol-H2O = 5.9595 lbs-H2O/1,000,000 mol-CH4
THEN:
5.9595 lb-H2O/(1,000,000 mol-CH4 * 0.80203 SCF/mol-CH4) =
( 5.9595 lbs-H2O / 0.80203 SCF/mol-CH4 ) / (1,000,000 mol-CH4) =
7.43 lbs-H2O / 1,000,000 SCF = 7.43 LBS-H2O/MMSCF

or 0.04954 times the PPMv is the LBS-H2O/MMSCF

Note that Natural Gas is not pure methane nor does it behave perfectly like an ideal gas therefore there are two sources of accepted standards for this conversion.
1) The Institute of Gas Technology IGT derived LBS-H2O/MMSCF in Natural Gas from empirical measurements at different gas wells and published them in the 1950’s
2) ASTM has some equations for this but they do not agree with the IGT tables for low moisture levels.
in the IGT tables 150 PPMv = 7.33 LBS-H2O/MMSCF
with the ASTM equations 150 PPMv = 7.48 LBS-H2O/MMSCF

You can download a freeware calculator from www.phymetrix .com that will perform all of these conversions.

Hope this helps!