11 replies to this topic

[pathfinder]

Dear fellow Engineers,

 

This forum is/has been helping and benefiting a lot of Engineers around the world. So first of all, A BIG thanks and kudos to the admins and senior members.

 

Now coming to the topic, I believe that there are a lot of graduate engineers like me who have little knowledge on the various processes. I myself am new to oil and gas sector and I am learning things day by day. As for the topic mentioned, I went through a lot of threads in the forum and I saw a lot of expert questions and expert answers. I'd like to understand things in a simpler way. I hope this helps other newbie engineers too.

 

So, the TEG process. Can someone explain us the whole process in simple words? I'v been reading a lot of books (Manning, etc ) and I see different (slightly) PFDs in each. I have also referred to Mr.Art's valued replies and PFD. So here are my doubts in a nutshell:

 

1. The inlet separator before the contactor (Absorber)  is installed as a slug catcher and hence to prevent foaming?

2. What are the major causes of foaming. where else can it occur other than in the contactor?

3. As seen in many PFDs, is the outlet (dry) gas pass through a TEG cooler before connecting to the supply line? If so what should be the ideal temp/pressure for this gas? OR is it a heat exchanger where the lean glycol is cooled before it enters the contactor?

4. According the PFD I have attached herewith, the dry gas passes through a "gas scrubber". What are the advantages of this system?

5. Why is the rich glycol made to pass through the Reflux Condenser before entering the flash vessel?

6. As per Mr.Art's PFD, the rich glycol is again passed through a heat exchanger before reaching the flash vessel, why is that so? whats the advantage and what is the ideal temperature of the liquid during these stages?

7. What is happening in the still column after flashing? why cant it be directly fed to the reboiler?

8. What is stripping column for? What is stripped here and how does it happen?

9. As per the PFD i have attached, a "stripping gas" is provided to the surge drum. I understand the surge drum is a "surge" drum in its literal meaning.so can u explain this design we have? especially the dry gas fed to the drum.

10. The logic of glycol exchanger (E-XXX2). 

11. The flare line, it opens through a PSV whenever a back pressure from main line happens and also during shutdown time...correct me if im wrong. A bit more idea abt flare will be helpful.

12. For this project we have, we r taking the TEG units as a whole from the vendor. So kindly advice any particular and important things(technical) to be reviewed before finalizing the vendor.

 

As for my PFD, the location is Iraq,  Gas input is 150 MMSCFD, 47 bar max. supply temp 40-60 deg cel.

 

I knw its a bit lengthy thread, still Thanks in advance for your valuable replies and views

Attached Files

•  TEG Dehydration -Mr.Art.pdf   46.76KB   215 downloads

Edited by pathfinder, 04 September 2014 - 12:57 AM.

[Art Montemayor]

Nizins:

 

I am working to respond to your 12 questions.  It is a lengthy process.  In the meantime, please furnish specific information regarding your queries.

• The PFD has various notations that are not identified.  Please tell us what they mean.
• The PFD is a unspecific and generalized drawing.  Is this a final or preliminary document?  It is difficult – if not impossible - to refer to a general drawing with specific answers.  Please furnish a specific drawing or description of what you are dealing with.
• You say you are “taking the TEG units as a whole from the vendor”.  This is interesting, but not relevant.  The forum would be more interested in knowing if you are presently in the process of purchasing the process as a complete TEG unit or if you have already purchased it.  If you have already purchased, a lot of forum comments and recommendations may be useless because they will be after the fact.
• Who is designing and supplying the process package?  Who specified the package for the client?
• What are the design specifications for the feed gas and the product gas?  - the pressure, composition, and temperature of the feed gas and the water content of the product gas?
• Is this a land facility or will it be offshore?

 

[Art Montemayor]

 Pathfinder:

 

It's taken some time to answer each one of your numerous questions.  I've added my reply to each in RED, below:

  

1. The inlet separator before the contactor (Absorber) is installed as a slug catcher and hence to prevent foaming?

The purpose of the inlet separator is to remove any contaminants from the humid feed natural gas going to the TEG Contactor.  The role that this separator plays is one of the most important ones in the TEG process because it ensures that process upsets such as foaming, fouling, and TEG contamination will be mitigated.  The proper sizing and efficient operation of this piece of equipment cannot be overstressed.

2. What are the major causes of foaming.  Where else can it occur other than in the contactor?

The major cause of foaming in a TEG process is oil or heavy hydrocarbons carried into the process by the feed gas or by greases introduced elsewhere in the process.

TEG does not foam by itself.  Any contaminant that affects TEG surface tension will cause foaming.  The most common cause of glycol carryover from the contactor is mass-transfer-induced foaming.  Elevated or fluctuating contactor differential pressures are indicators of foaming with related glycol losses.  Gas entering the contactor must be free of all liquid and fine solid particles to avoid contactor contamination and foaming.  Carryover of hydrocarbon condensate due to scrubber mist eliminator malfunction or high gas velocity in the contactor causes foaming.  Also, TEG inlet temperature to the contactor should be 10 ^oF higher than the gas outlet to avoid liquid hydrocarbon condensation.  A flash tank residence time of at least 5 minutes is needed to separate lighter hydrocarbons from rich TEG.  Foaming inducers should be removed by the sock filter and activated carbon filter.  Particles of 5 microns and larger should be removed by the sock filter.  The activated carbon filter removes organic products like acids and traces of liquid hydrocarbons.  An iron content of 15 ppm or higher in the TEG will increase foaming.

3. As seen in many PFDs, is the outlet (dry) gas pass through a TEG cooler before connecting to the supply line?  If so what should be the ideal temp/pressure for this gas? OR is it a heat exchanger where the lean glycol is cooled before it enters the contactor?

This question is written in bad English and is hard to understand.  If you mean: “is a TEG cooler using product dry gas a requirement?”…. then the answer is no.  Normally, product dry gas is used to cool the warm lean TEG entering the contactor.  However, you can use any other coolant for this purpose – cooling water or atmospheric air.

4. According the PFD I have attached herewith, the dry gas passes through a “gas scrubber”.  What are the advantages of this system?

This is not an “advantage”, but rather a necessity to remove any TEG particles exiting the contactor overheads entrained in the product dry gas.  This is to reduce TEG losses and also avoid product gas contamination downstream.

5. Why is the rich glycol made to pass through the Reflux Condenser before entering the flash vessel?

The rich TEG is being used as a heat sink to cool and condense some of the water vapor rising in the still and also pre-heat itself at the same time.

6. As per Mr. Art's PFD, the rich glycol is again passed through a heat exchanger before reaching the flash vessel, why is that so?  What’s the advantage and what is the ideal temperature of the liquid during these stages?

There is a need to heat the rich TEG and also to cool the lean TEG.  The TEG exchanger is doing a portion of this need.  It also reduces the fuel gas energy input into the reboiler.

7. What is happening in the still column after flashing?  Why can’t it be directly fed to the reboiler?

The still column strips out the bulk of the water content in the rich TEG.  You need approximately 1 ideal stage of separation for this to occur – that why you can’t just dump it into the reboiler.

8. What is stripping column for?  What is stripped here and how does it happen?

In the reboiler the TEG is heated to approximately 400 ^oF to remove enough water vapor to re-concentrate it to 98.8 percent.  However, Low dew points simply cannot be achieved using the maximum 98.8 wt % glycol obtainable with a 400 ^oF reboiler at atmospheric pressure.  These low dew points will need up to 99.9 wt % lean glycol at the absorber top inlet.  Increasing reboiler temperature is not an option due to the thermal decomposition temperature of 404 ^oF for TEG.  Stripping gas has a much greater effect than increasing reboiler temperature.  For maximum efficiency, stripping gas should be introduced in a short column after the hot glycol is removed from the reboiler.

9. As per the PFD I have attached, a “stripping gas” is provided to the surge drum.  I understand the surge drum is a “surge” drum in its literal meaning.so can u explain this design we have?  Especially the dry gas fed to the drum.

I don’t agree with the design shown in your PFD.  If you refer to my PFD sketch, you will see what I advocate.  Dry stripping gas should be introduced in the bottom of a packed bed that is contacting the lean, hot TEG exiting the reboiler and going to the Surge Drum.

10. The logic of glycol exchanger (E-XXX2).

There is no “logic” here.  There is a specific duty requirement.  Read the response to #6.

11. The flare line, it opens through a PSV whenever a back pressure from main line happens and also during shutdown time ... correct me if I’m wrong.  A bit more idea abt flare will be helpful.

You PFD is not specific, so it is hard to explain exactly what the flare is handling in your design scheme.  We need specific information.

12. For this project we have, we’re taking the TEG units as a whole from the vendor.  So kindly advice any particular and important things (technical) to be reviewed before finalizing the vendor.

I don’t understand what you mean by “we’re taking the TEG units as a whole from the vendor”.  We need to know what stage in the project you are in: have you already purchased the TEG unit or are you presently specifying or talking to vendors?  This is important for us to know so we know what we can do something about and what we can’t do because the unit is already purchased.  We need specific information as to where you are at in the project schedule and what we can help with in order to allow you avoid mistakes or errors.

  

You basically need to study the TEG process in depth.  What you should already have read are such classic documents/books as:

• The GPSA Engineering Databook;
• “Gas Purification”, by Kohl and Nielson (1997);
• Gas Processing by John Campbell
• Glycol Dehydrator Design Manual – 1976 (which you can download for free right here in our website) 

I am attaching some additional information for your reading as well.

 

 Optimize TEG Circulation and Flash Tank.docx   571.75KB   181 downloads

 Design Glycol Units for Maximum Efficiency.docx   128.04KB   176 downloads

[gazepdapi1]

 

7. What is happening in the still column after flashing?  Why can’t it be directly fed to the reboiler?

The still column strips out the bulk of the water content in the rich TEG.  You need approximately 1 ideal stage of separation for this to occur – that why you can’t just dump it into the reboiler.

 

 

Art,

 

Can you please elaborate a little more on this? What do you mean by strips out most of the bulk water? You mean the water in the rich glycol that's being fed into the still column?

[trinhduchanh]

Dear Art,

 

I have a concern related to the glycol system. I wrote my concern in another thread few days ago. After reading this thread as question No 2 from pathfinder I found with the same attention to what I was concern. Now please allow me to rewrite the question in your topic. Could you please help me clarify this concern.

 

http://www.cheresour...r-to-contactor/

 

Quote.

As i known normal practice then temperature of Lean TEG always design higher +5^oC with inlet feed gas from dehydration inlet scrubber. When i refer to some book and previous project document then it is same design with that. But now we are working with new project have  a glycol system with different design. Vendor utilized temperatue from outlet gas glycol contactor below lean TEG temperature inlet gas +5^oC instead for using inlet gas temperature to control TEG temperature inject to gycol contactor. As per my undertanding if they use reference point from gas outlet then margin of lean TEG with gas inlet will be more than +5^oC as i assume that it around 7 to 8 ^oC. If inlet glycol tempeatures greater than 10^oC above the gas inlet temperature result in high glycol losses to gas. Any body have experience with that design can you help me explain why vendor  must design glycol system such that  so it's have more advantages than compared with traditional designs?

Unquote.

[pathfinder]

Thank you for your wonderful and explanatory answers.  

 

Qn. 3 : Apologize for my bad english, I think I got lost somewhere when I wrote that Qn. LOL. Anways, your reply was helpful. But according to my PFD, a separate cooler(air cooled) is being provided for the purpose of cooling the lean glycol entering the contactor. So based on your reply, Can i suggest them to use the dry gas to cool the warm lean glycol? If air-cooled isnt there a chance that the lean TEG will be undercooled during winter? Since the inlet gas is fed at 40-65 deg cel, i believe the lean TEG temp should not be below 45-65 deg cel range.

 

 

For the information u asked:

1. This is what is given to us from client as of now. We are free to suggest changes if necessary and then the PFD can be revised like wise.

2. What notions are not identified?  The legend on the top of the sheet covers all I guess.

3. We are at the very initial stage of the project and the process team is working on detailed drawings. It was decided to buy the dehydration package as skid units and we are in the process of communicating with various vendors regarding this. 

5. This is a land facility in Iraq.

4. Design Specs:

   The inlet gas water content for various cases is provided in the following Table.

 

Cases               Supply Temp(°C)       Inlet water content(lb H₂O/MMscfd )     Outlet water content(lb H₂O/MMscfd)

Case 1 (Rich)            60                                   757                                               7

Case 2 (Lean)            48                                   392                                              7

 

Inlet gas temperature may vary from 40°C to 60°C. 

 

TEG  dehydration unit is designed to achieve 7 lb H₂O/MMscfd in the dry outlet gas stream, this equates to -2^oC @ 35 barg for Case 1 (Rich) and 0^oC @ 41 barg for Case 2 (Lean) to prevent hydrate formation in the downstream pipeline.

 

 

Your PFD was pretty helpful in understanding the process. Now if u have another one as u mentioned with latest design, pls share with us

 

 

Thanks:

Pathfinder

[Art Montemayor]

 

Pathfinder, gazepdapi, & Trinh:

 

Guys, you have to do your share of the load.  Do your homework by taking the time and studying (not just reading) all the materials I have submitted as well as all the literature and texts that I have recommended.  If you are dealing with gas treating or involved in upstream processes, you should be spending a lot of your time in dominating this field of engineering.  For example:

 

Pathfinder,

It is totally impractical to consider feeding a gas stream to a TEG contactor at a temperature of 65 ^oC.  This temperature is so hot, you can’t keep your hand on the pipe carrying this temperature!  The obvious thing is that equilibrium dewpoint existing between 99.9 % wt. lean TEG at this temperature is too high.  Read my prior posts on the topic of practical operating temperatures for TEG and Amine contactors.  It is common sense to operate the absorber or contactor as cool as you can – WITHIN PRACTICAL LIMITS.  The usual, practical operating temperature range for a TEG contactor is 70 to 100 ^oF.  You can operate higher, but at a cost of capital and higher dewpoints.

 

Why the concern of ambient winter air conditions?  There are temperature controls readily available for air-cooled units.  I have used these systems at sites close to the Canadian border at -25 ^oF and still controlled the outlet temperature.  With a TEG unit you are limited by the TEG viscosity – read the submitted material.  If you need to maintain a product gas with 7.0 lb H₂O/MMScf of gas, then you need to design for approximately 4-5 lb H₂O/ MMScf of gas.  Read the attached document revision.

 

If you are supervising the specifications for design by a supplier, then you have to focus on issues such as:

• What types of internals are to be used in the contactor and stills;
• What is to be the specifications for emissions with regards to BTX and the stripping gas?
• What TEG operating losses will be tolerated?
• How will the flash gas be handled coming from the flash drum?
• What type of dew point analyzer will be used and how will its accurate operation be maintained?  Will this be the controlling element for the TEG contactor?
• If direct-fired reboilers are to be used, what will be the design heating flux used in the tube bundle?
• How will the Stripping column still be designed?

 Gazepdapi1,

The answer to your question has been answered many times in the past and in the documents submitted.  Read the submitted materials.  The answer is very simple.

 

Trinh,

I didn’t address your other post because I frankly couldn’t understand your writing.  Additionally, pathfinder’s #2 question has nothing to do with your topic of lean TEG temperature.  I believe what you are referring to has already been discussed and answered many times, but I would be glad to review the topic once again.  However, you must make an effort in the matter by at least reading all the materials I have furnished now and in the past.  As I mention above, the topic of best feed gas temperature and the related lean TEG inlet temperature has a practical answer and has a simple solution.

 

All:  I have gone to lengths to explain and describe the TEG process and what represents good, current, practical design and operating techniques and practices in the revised copy of Sivall’s Design Manual of 1976 - which you are free to download from our website.  I have added/included my private notes and comments to his writings.  Please take note that I am not criticizing Sivall’s methods or recommendations.  He wrote what he thought was best in the 1970’s; I have the privilege of having worked with his designs and products in the field as well as most of the current TEG process designs of today and can, therefore, add revisions to his writing AS I SEE THEM TODAY based on my experience.  Today we are working under a different design environment and under a different set of rules.  We also enjoy a considerable amount of improvement in design tools, materials of construction, methods of operating, a greatly improved instrumentation capability with very sophisticated measuring and controlling elements.  However, the basic process has NOT CHANGED.  The basic teachings all of you have probably received in Unit Operations Design still apply!  Therefore to understand the process better, you should go back to the basics of Unit Operations Design and concentrate on the principles and teachings found there.

 

I hope this experience helps you all out.

 

NOTE: I cannot upload the revised copy of the Sivall's Manual because it is too large.   I have to ask you to wait while I cut and paste the revised sections in a smaller document that I will post here.

 

[Neelakantan]

kudos ART!

 

I would suggest we pin this so that new engineers need not repeatedly ask the questions about such an established process and the almost "unchanged" flow sheet.

I am wondering if

 

1) the new engineers don't have necessary background skill to read a book and study a process before asking such basic questions (example why we need a stripper, why the feed gas has to be around 35 deg c, why there is a still column, etc) STUDY, STUDY...

2) how the interaction between peers  as well as junior / senior guys happens in the industry nowadays? why ask such questions in the forum (it is not student forum but industrial professionals forum!); are the juniors not able to approach the seniors or do the juniors think the seniors are not skilled? (I am really worried and surprised...; I am sure my juniors would always approach me and I would definitely spend time for them!)

 

regards

neelakantan

[pathfinder]

Thanks Mr. Art. Im studying the books you have suggested. Will come back if I have any further doubts... Thanks a lot

 

Mr. Neekantan,

Sir, We prefer not to bug seniors with "basic" qns like this. So before we go to the senior, we make sure what we r going to ask/suggest/discuss are valid points. We have just started the career and we are learning. We seek help in the forum to get knowledge and to learn. Some stuffs may sound "basic" or stupid to some members as they are well experienced and has a strong knowledge in the subject, but there are many out there like me who have just started their career and learn stuffs their way. I asked those questions when I still had doubts even after reading a lot of books and doing online researches for weeks and now with this forum I got most of my doubts cleared.Thanks to Mr. Art. I think a healthy discussion like this with industry experts are much more helpful than reading a 100 books. So pls dont consider this only as an "industrial professionals forum".

And your proposal to Pin this post would be a great idea and helpful for new engineers

 

 

Thanks & regards:

Pathfinder

[Neelakantan]

my apologies if you think my statement was hurting about "professionalism"; but my idea and inherent question is if you approached your company seniors and do they take time to explain or not; I don't mind your approaching this forum with basic questions ( I do tend to revisit basics all the time) but my tip was to see the forum postings to see if they have been already analysed and answered.

 

I do understand interactive learning (as in a class or forum and training / teaching session in the company or plant) is more efficient way of learning as it goes with differential way of analysing the things rather than reading books which normally go in the quantum way of presenting the things.

 

once again sorry if it offended professionals.

 

regards

neelakantan

[Art Montemayor]

All:

 

Here are my comments to the Sivall's Design Manual on TEG Units.  I have made my comments in RED.  As I explained, these are not critiques to Sivall's document, but my input based on personal experience to date with TEG units.

 

 Glycol Dehydrator Design Manual Comments Rev0.docx   595.86KB   190 downloads

[pathfinder]

Thx Mr. Art. Appreciate ur work in helping us with the best answers.

 

Mr. Neelakantan, No hard feelings here I said my opinion... thats all. And sometimes when we have a busy schedule, we always dont have access to seniors and discuss silly things. Thats the main reason.