10 replies to this topic

[Miguel]

hellou

im confused on how to convert from 56 lbh20/MMSCFD too PPMV , i know PPMv is equal to mg/l but i dont know how to convert from mmscfd to Liters

apreciate the feedback

[Art Montemayor]

Miguel:

What you need is a FREE copy of UCONEER.

This is a program that is written and offered for free by one of our Estimeed Forum members, Katmar.

Once you download and install this program you will see how useful and practical it is. Even reknowned pump manufacturers, like Viking Pumps, recommend and offer this program with their logos and propaganda attached to it (with Katmar's blessings and OK, I hope).

Use the Search feature on our Forum and find the Katmar's website to download Uconeer.

[Miguel]

[thank you

Art

[katmar]

Art, thanks for the plug for Uconeer, but I'm afraid Uconeer won't help here. Neither Uconeer nor I have any clue what a lbh20/MMSCFD is. Perhaps Uconeer can help with the elements that make up this strange unit, but it certainly doesn't have it listed. I have used most of the unit conversion programs out there, and I do not recall ever seeing this unit. I would be grateful if Miguel or anyone else could enlighten me on what this unit means.

And yes - Viking bought my blessing ;-)

[gvdlans]

just a guess:

lbh20/MMSCFD means pounds of water per million standard cubic feets per day

and what was meant was

pounds of water per million standard cubic feet

I cannot follow the statement that "i know PPMv is equal to mg/l ". Maybe there is some confusion with ppm(w) (Parts Per Million on Weight basis), where 1 mg/l indeed equals 1 ppm (w), but then only if we are talkin about an aqeous solution.

[Art Montemayor]

Harvey:

I believe that Miguel wants to convert the amount of water vapor existing in a stream of dehydrated natural gas – which is conventionally cited in natural gas contracts as “lbs of water / Million Standard Cubic Feet of natural gas to Parts per Million (volume). The normal abbreviation for the term is Lbs H2O /MMScf, where the “standard” condition is sometimes 14.696 psia & 60 oF. However, the standard conditions can (and often) do change. In past years I have accumulated a bit of grey hairs and face wrinkles writing posts on “Standard Conditions” in Engineering Forums and I was hoping to draw out Miguel and expose him to what is staring him in the face. However, Miguel seems to have smelled a rat and has diplomatically retired. However, now that you have volunteered with the question, I will address what I was hoping to come out of this thread and hope that Miguel comes back to profit from it.

The term “Lbs H2O /MMScf” can, indeed, be transformed to a representative “purity term”, PPM(v). HOWEVER, we are forced to make some engineering and practical decisions that demand us knowing what we are talking about and what is involved in making the conversion.

The mass of water can be converted to moles of water which, in turn, can be converted to volume of water at a base temperature. The volume of natural gas can also be converted to the BASE volume and this allows for the conversion to the required PPM(v).

What I wanted to focus on Miguel is that the natural gas water content is conventionally described in the terms he describes but also as a “dewpoint” reading , or as a “dewpoint depression” – which calls for a more complex and sophisticated “conversion”. This is the first time I have seen a volumetric parts per million concentration used to describe the water content.

[Miguel]

ahahahahha, i didint smell a rat and went away,i just was driving home, i realized what i was saying, i know that the measure of saturated water content in a gas current is Lb H20 /MMSCFD those calculations come from a long algorythm ,if u do not have water content tables and just composition ,you can see where it comes from converting your Volumetric FLOW into molar flow for example 85 MMSCFD (VOLUMETRIC FLOW ) of natural gas , you use the the convertion that says 1lbmol is 379.5Ft and divide that to the 85 MMSCFD and that will give you LBmol or pound mol i dunno how do you say it in english after that you convert your molar flow to water molar flow multyplyng it with the mole fraction and you multiply again with the Molecular weight of water to turn it into mass flow now after that you want to know how much pounds of water (LB) are per each MMSCFD of natural Gas you devide your water mass with your total gass flow, and that will give you a volumetric gass flow LB/MMSCFD some of you just said it is a mass flow, and if im correct MASS/Volume per day its a volumetric flow, mr. Art correct me if im wrong.

with that said and , said very confusingly, my trouble comes, because ive contacted an adsortion tower vendor PROCEL and they have given me a data sheet they want me to fill with specifications, and one of the specifictiatons is that i have to give them the water content or the Adsorbate requirementes in PPMV and i sinceriley only know how to calculate water content is in lbh20 /MMSCF or iin Kgh20/MMm3D so, i need to know how to take the quantity of water requiired and the one present and convert it into PPMV so i could fill the form


that said i apologize for my redaction and for the mistakes in writing ,english is not my first language

and Art you know my case i wright a lot asking questions about dehydration

Regards

PS: before somebody says " Miguel thinks PPMV is a water content measure, i know it isnt , but i would like to know how can i expresss!! my desired water content in PPMV

[katmar]

Art, thanks for the explanation - now I am on the same page as the rest of you. What threw me was the lower case "h" and the upper case "O" in h2O, plus the fact that the "O" (oh) was actually typed as a "0" (zero). I read it as "lbh twenty" in the same way that we sometimes write "SG60" when the reference temperature for SG is 60 degrees F.

Miguel, you need to be aware that SCF (standard cubic foot) is actually a unit of mass and not a unit of volume. This means you have a double conversion if you want to convert a mass/mass concentration to a volume/volume basis. You will need the molecular mass of your dry natural gas in order to make this conversion.

[Art Montemayor]

Harvey:

Thanks a bunch for continuing to contribute to this thread at least one more time. Your thoughts and comments add to the summary that I want to pass on to Miguel. I believe that Miguel will recognize the importance of your comments and take them to heart.

Miguel:

The point I want to pass on to you for your benefit is that this exposure to units conversion can be rewarding for you - not only because of the free software or the ability to find a quick information source, but primarily because it has exposed you to the fact that it is VERY important to define and understand the units that you are dealing with. For example, note what Harvey has pointed out.

Your established need is to identify the quantity of water vapor contained in a stream of natural gas in order to specify it in a data sheet that will be used for designing an adsorption unit (or a TEG dehydration unit). The accuracy of generating and expressing the needed information is critical if you are to have the proper equipment designed and supplied.

Bear in mind that you are wanting (or being asked) to express the water vapor content as something I call a "purity" level - parts per million (volume/volume). What this means to the recipient of this information is important to keep in mind. Don't just "sling" numbers out at the recipient. Make sure you are talking and writing about the same subject with others. As I said, the water vapor content in natural gas is usually reported as lbs/MM Scf or as a dewpoint or dewpoint depression. The latter two methods are more complex and difficult to derive. What I have outlined for you is the same as what Katmar has detailed. Be aware that you need to have a FULL understanding of what you have to do. You need to:

1) assume that all the water in the natural gas exists as a vapor (actually, a partial vapor);
2) know the molecular weight of the natural gas;
3) have knowledge of the volume occupied by a mole of gas (at a specificed temperature & pressure);
4) convert the mass of gas to moles of gas;
5) convert the moles of gas to volume of gas (again, at a specified temperature & presssure);
6) convert the volumes of the natural gas & the water vapor to the same base temperature & pressure;
7) express the base volume of water vapor contained in a million base volumes of natural gas.

Please bear in mind that the PPM(v) number assumes that the water exists as pure vapor mixed with pure gaseous natural gas - the mixture is totally gaseous. This only works when the gas is LESS than saturated with water vapor.

There are some functions of Uconeer that you can use for this work. But the most important part is that of exposing you to all the functions that Uconeer gives you and also to appreciate what it can do for you in the future. You may not be able to judge it now, but I can tell you from 48 years of experience that Katmar put a LOT of work and useful, profitable information into that program.

P.D. I think you know that a mole of gas occupies 379.49 cf at 60 oF & 14.696 psia (NGPSA source).

[Miguel]

thank you very much, Katmar, Art

this clears everything pretty much


thank you for your time

[hygrometry]

Here are ideal gas calculations
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