natural gas water and H.C dewpointing

A C5+ in itself is a little vague, are you going to consider it as pentane, hexane, higher? For dewpoint calculations, the heavy ends are all important, thus this is a major point. Plus, I have my doubts about lab analyses for accuracy of the heavy ends. I've rarely seen a lab analyses that when back calculated for the dew-point, the calculation matches the process stream it is coming off of (for example, if I'm taking a gas stream off a 2 phase separator at 500 psig and 60F, the lab analyses back calculated for the dew point is rarely match 60F. This is just because of the problems of measuring very low concentations of trace components and the calculation accuracies).

If you don't have access to a process simulator, this is a basic dewpoint calculation. Look in your engineering texts, the GPSA engineering data books also walk you through doing this.

Dear TD2k,
thank you very much for your reply.
As you truly mentioned back calculation will not end up to an exact dewpoint due to the errors involved during sampling and the chromotographs as well as the uncertainaties involved in equation of states. However my question is not relevant to dewpoint calculation of the gas . I have proII and Hysys process simulators . The question is concerned with the design of dehydration plants. There is a target value for the amount of heavy hydrocarbons no matter how heavy they are which is called the GPM (gallons of heavy ends (C5+)in the gas phase per 1000 cubic feet of the gas where the simple mechanical refrigeration process may seem more attractive than silica gel adsorption processpurely from the point of economy and may need furthur economic evaluation for process screening. My question is not the economy even it is the amount of GPM where the silica gel adsorption in gas plants can be applied without the problems of coking and lack of good reactivation during regeneration cycle.
Thank you again and waiting any comments.

Sorry, I thought you were asking how much C5+ you could handle to achieve the HC dewpoint of -10C.

I have no experience with silica gels so I can only suggest you talk to the vendors and see what information they have.

In order to determine the water and hydrocarbon dewpoint, I would need to know the complete gas analysis, inlet temperature, inlet pressure, flow configuration, tower size, bed depth, cycle length, regeneration flow rate, heat duty (regeneration), cooler duty, etc.
This is not an analysis that you can get for free. If you are interested in retaining my services, contact me at ggstewar@telusplanet.net.

G. Gordon Stewart, P.Eng.
Gas & Oil Process Engineering Consultant
ggstewar@telusplanet.net

Dear Mr. Stewart,
Many thanks for your reply.
Pls. review my design question. As I requested I am not asking for a cost estimate and detail configuration of a HC and water dewpointing with silica gel adsorption nor a dewpoint calculation studies . The question is simple : how much is the maximum C5+ content of a natural gas where the silica gel adsorption plants find applications (can operate without defficulties)? There have been some papers printed in engineering magazines like OGJ
where I have find somefinger tip figures for considering these plants for economic evaluation when compared to other alternative processes based on capital cost point of view. However my question is relevant to the maximum tollerable C5+ content of the gas where silica gel can work.Asking the vendor as MR.TD2K proposes may not be as reliable as asking the process experts since the silica gel vendors tend to exaggerate about their products.
Thank you.

I need to source a large amount of Mobil Sorbead R, preferably in the UK,

Is there any one who can help??

Paul

Dear Sparkster,
The Mobil in Europe is operating under the name of
ENGELHARD PROCESS CHEMICHALS GMBH located in Honover,Germany. The fax no. is + 49 511 2886-760
Phone +49 511 2886-60
Anyway if you are interested in other generic Mobil-R
products you may contact GRACE ITALIANA in Italy or
CECA in France.
Hope might be of help.
Regards,
M.Sadra

Dear Sadra,

I think what you're looking for is really the breakthrough calcs for C5+ in the sorbead bed. This may call for some data particularly from the vendor for that adsorbent. Then you need to do some design calc to estimate the volume of bed reqd over and above the MTZ considering the no. of years you want to operate without a changeout. My advice is to rely on vendor calcs who'll give you a process guarantee.

Samiran

Dear Samiran,
As I have said my problem is not a design calculation!!to find bed hight, cycle time, reg. flowrate,breakthru time MTZ etc..
In Natural gas industry, the open cycle- cooling- heating is the workhorse configuration because of the simplicity
and effectiveness. If the natural gas contains high amount of heavy hydrocarbons (to a certain limit)the problem of attaining the spec. dew point due to lack of proper reactivation coking etc is experienced with the above configuration.(This subject needs a lot of discussion and the time here is limited). I have faced practically this situation in one of our gas dehydration plant when switching to high C5+ content gas taken from a
dome gas reservoir years ago. Even the shortest feasible cycling could not solve the problem although calculations showed fine results!!!
I think this question calls for a process expert with practical field experience having sound knowledge.One thing more When the process perfomance guarantee comes every body put the blame on the others. The plant designer on the dessicant vendor and vice versa, the operation group on both, the both on operation group,then the switching valve manufacturer for leaking valves , dewpoint analyzers and at last on the nature!!that is the change in gas composition,pressure temperature etc.. So lets be real. Now I hope you understand what I am looking for as the other gentlemen did.
Regards.
M.Sadra

How much C5+ in a gas stream can a short cycle silca dehydrator handle.

The gas stream must be in above the hydrocarbon dewpoint entering the column.
The operating conditions of the regeneration loop must be such that enough of the C5+ condenses so that the liquids are removed.

Typically stream with more than 2.0% C3 in the gas have a composition such that the relative volitilty of the c5+ is nor sufficient to allow economic operation with an non refridgerated regeneration loop.