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[processengbd]

We have been designing a glycol reboiler for a 20 MMSCFD dehydration plant.

 

1. According to different vendor table like Sivall's the reboiler duty is much higher then what we calculate from different literature.(see bellow)

 

2. We used heat flux of 6000 Btu/ft sq to find the area of fire tube. If we calculate length and diameter according to Sivall's duty we had to use higher heat flux.

 

 so if we use circulation rate 110 gal/hr then reboiler heat duty form sivalls table is 0.175MMBTU/hr. But size of the reboiler does not match. Size is much greater in Sivalls then other reference.

 

 

Now

According to API 12 GDU The heat duty is 0.1342 MMBTU/ hr

According to Gas Dehydration Field Manual (Arnold) is 0.1 MMBTU/hr

According to GPSA 0.11 MMBTU/hr

 

But the thing is that according to Sivall's table,

it is about 0.175MMBTU/hr according to our glycol flow rate of 110 Gallon /hr

 

For glycol circulation rate calculation we used 3 gal/lb of water removed.

According to HYSYS inlet gas to contactor tower contains 42 lb/hr of water means 50.8 lb/MMSCF. outlet gas contains 7 lb/MMSCF

 

We are concerned that the reboiler will be able to perform the operation. means will it be possible to raise the glycol temperature to 396 deg F.

 

I have attached a snapshot of my HYSYS file so that temperature of different straems can be known.

 

 Untitled 71.jpg   46.09KB   43 downloads

 

I will very much appreciate any suggestion.

 

Processengbd

[Art Montemayor]

 

Processengbd:

 

My suggestions to you are that you first tell us EXACTLY ALL that you are trying to do.  Are you trying to fabricate a TEG dehydration unit in a developing country?  WHO is “we” in “We have been designing a glycol reboiler..”? 

 

We can’t tell if you are calculating the TEG reboiler duty correctly according to the different “methods”.  Why don’t you furnish your detailed calculations instead of your results?   Are we supposed to trust you to do them correctly?

 

It is fairly obvious that you have no expertise or knowledge of designing or fabricating a TEG unit.  A reboiler heat flux of 6,000 Btu/hr-ft² is a good and conservative value.  If existing fabricators use a higher value it is because they are being cheap and trying to maximize their profit.  That is common engineering sense.  Why don’t you understand that?

 

Do you honestly expect to produce pipeline quality natural gas (7 lb H₂0/MMScf) using only 396 ^oF in the Reboiler and NO stripping gas?  Please explain this.

 

You fail to tell us the basic data for your “design”, such as the glycol used (I know it is probably TEG, but you MUST state it), the stripping gas used, and what is the reboiler temperature you are establishing?

 

Your PFD “sucks” – like all HySys flow diagrams.  Why don’t you generate a REAL PFD that shows all the equipment – like the reflux coil, the TEG cooler, the flash drum, the surge drum, the stripping gas heating coil, the stripping gas column, etc., etc.????

 

I have furnished a considerable amount of detailed and explicit information on TEG dehydration design, fabrication, and operation within our Forums in past threads.  This includes detailed, PFDs with completed heat and material balances.  All this information is available to you and all members if you us our SEARCH engine.  Additionally, I have contributed a complete and detailed glycol design manual that can be found in our Forum library.   This manual was preserved by me from an original document prepared by no other than Richard Sivalls.  Have you read, studied, and used this information?   You can design a TEG unit using nothing more than this manual – No HySys simulation is required.  Thousands of TEG units were designed and built using this method before an Simulation program was invented – and all these units worked (most are still operating successfully).  This only bears out and quantifies the value that a simulation program contributes to a TEG design.

 

Please furnish the Sivall’s Table that you refer to as well as other references that you are comparing.  This can all be compiled in an Excel workbook (as any good process engineer should organize his/her produced work) and uploaded.

 

With the above required information, we (those of us on the Forum) can address your queries and check what you claim.