March 1981 issue of HYDROCARBON PROCESSING

[patrickraj]

Dear members,

In March 1981 issue of HYDROCARBON PROCESSING page 135, an example is given for partial condensers. Some-one could clarify what is the dry gas flow and dry gas molecular weight. The gas stream is being natural gas how molecular weight could be 36.7 against natural gas molecular weight of about 18.0 kg/kg-moles.

Thanks in advance

 

[jsummerfield]

Perhaps the issue pertains to the liquids as compared to the dry mostly methane gas. I have not looked for the article and lack a good understanding of your issue. However, that never stopped me from anything before.

Lets call dry natural gas mostly methane with some ethane and other components. Natural gas comes out of the ground saturated with water and heavier hydrocarbons, perhaps carbon dioxide and other stuff like hydrogen sulfide. Condensers can knock out some liquids.

Gas processing equipment removes the undesirable stuff and other stuff that has commercial value. The ethane, propane, iC3, butane, iC4, C5, C6 and heavier can be extracted and sold. The dry gas can be sold provided that the heating value still meets pipeline specifications. I do not know what component or mixture represents the molecular weight of 36.7.

Please advise if this line of thought appears consistent with the article or clarify.

Thanks,

John

 

[TD2K]

I looked up the term dry gas in some of my reference materials.

Bland and Davidson, Petroleum Processing Handbook
dry gas - a gas which does not contain fractions that may easily condense under atmospheric conditions

Although I believe it's primarily a refining term, none of my other reference books lists it. Will check another reference site on the Net I know.

 

[patrickraj]

Thanks for the replies.
If the natural gas contains heavier hydrocarbons also as liquid alongwith water, molecular weight of 36.7 may workout.

 

[25362]

I don't have access to the mentioned article but while looking at "unassociated" natural gas compositions taken from so far away places as N.W. Australia, Algeria, New Zealand, North Sea, and Abu Dhabi, I'd say that the major contributor to a higher MW is CO₂. See, for example, NZ Kapuni's field with up to 45% CO₂.

For "associated" natural gas (having less than 75% methane) the higher MW HCs are indeed the major contributors. The North Sea Forties field gas has a MW in the range mentioned by patrickraj, since it contains less than 47% methane.