24 replies to this topic

[Dandy Komboris]

Dear My Fellow Engineers

I need some explanation about the work pronciple of reflux coil condenser and Surge Tank in Dehydration Unit (DHU).
First of All My DHU has 60.25 MMSCFD (wet Gas).
I still confuse about the coil condenser?

GLycol reflux condenser (Coil) operating condition :
OP. Temp (Shell/Coil) : 212 F/112 F
OP. Press 9Shell/Coil) : 2.7 PSIG/75 PSIG

Still Colomn operating condition :

OP. Temp : 400 F
OP. Press : 3.0 PSIG

Reboiler operating condition :

OP. Temp : 400 F
OP. Press : 3.0 PSIG

Flash Tank operating condition :
OP. Temp : 112 F
OP. Press : 70 PSIG


Why do we need to install condenser unit since we know that TEG is still in liquid phase ?
I have read some articles about glycol reflux condenser. It said that the function of glycol reflux condenser to heat the glycol temperature. So I assume the condensation occurs in the shell side, that the small amount of TEG entrain with water vapour will condense and go back to reboiler. Am I Right ????

I also confuse in Surge Tank Unit. I have small amount of dry gas to be sent to heating coil in surge tank. That the dry gas will be the heating media in the surge tank. It flows inside the coil
The temperature of dry gas that leaves contactor is around 108 F. But surge tank uperating temperature is 384 Fahrenheit. How do i achieve that temperature since there is no burner system in surge tank.


Please Guys I nedd some explanation and enlightment.
Thank You Very Much For Your Help

Best Regard


Dandy Komboris

[Ceng]

Dandy Komboris

I think you didn't understand the process properly
Lean Glycol will be routed to surge drum with temperature as you said 384 F
Lean Glycol should be cooled before entering the dehydration contactor; you are probably using the dry gas for cooling the lean glycol.

Regards

[Art Montemayor]

Dandy:

Now I am confused. Where do you obtain the temperatures and pressures you cite? Some of these values are not normal or usual. Who designed and built your TEG dehydrating unit? I also do not agree with your process description. It would be much better if you submit a P&ID (or even a PFD) of your TEG unit.

I (nor anyone else, for that matter of fact) cannot furnish any explanations or “enlightenment” if we have no engineering description of your TEG unit – such as a detailed P&ID.

Based on some of the temperatures and pressures you cite, you seem to have a non-conventional version of what I would consider as a normal TEG Unit. I can furnish you a detailed PFD of a typical unit – complete with a detailed heat and mass balance. But you should furnish yours first since you are the one asking the questions. I have complete and detailed responses to each of your questions – but before addressing each one, I need a basis. And that basis is a P&ID or a detailed PFD with heat and mass balance.

I await your reply.

[Dandy Komboris]

Dear Ceng

Thank you very much.
I though the surge tank heats the incoming TEG that come from the reboiler.

[Dandy Komboris]

Dear Art

Here I attach some P&ID. But this P&ID lack of Heat & Mass Balance.
I also need some explanation about The Process that occurs in Glycol Reflux Condenser. Since the TEG boiling point above 500 F I assume that the TEG play the role as cooling media in the Glycol reflux condenser beacuse It's still in liquid phase . Am I Right ? So the Reflux condenser will condense small amount of TEG which is entrained by the hydrocarbon gas. Is That Correct Art ??
This DHP is designed by Cameron Japan Ltd.
Since you are the expert in this field perhaps you know which process that employ in this DHP ?is it Drizzo or Coldfinger.
This DHP Unit is buld in Cilamaya. Indonesia. Now the
Please Enlight Me..
This the inlet gas composition :
C1 = 98.56%
N2 = 0,0085
C2 = 0.0044
CO2 = 0.0015

Dew point = - 11 Celcius
H2O Content = 115 lb/MMSCF
Thank you very much For Your Help.


Best Regard



Dandy Komboris

Attached Files

•  DHP.PDF   909.86KB   398 downloads

[Ceng]

Your welcome
I think it's better for you to study GPSA standard-dehydration part or other references like Kohl's gas purification book.
It will help you understand different type of dehydration processes and also your process.

[Art Montemayor]

Dandy:

Please refer to the attached Excel Workbook for my responses.

Thank you for your submittal of the P&IDs. My personal opinion of your process is that it is a cheap way to put together a TEG unit. I would not accept nor specify such a process. Just about every TEG unit presently operating in the Gulf of Mexico on offshore platforms is very similar to the process I have depicted in my workbook. And there is a sound and good reason for that.

Attached Files

•  TEG Dehydration - 70MMScfd.xlsx   162.1KB   378 downloads

[ColinR33]

I would like to add a few comments to Arts response. He has covered most of your questions very well, but I'm not sure he answered everything. There seems to be a misunderstanding about hot, lean TEG being in the flash drum. Looking at your PIDs it appears the fabricator combined the surge and flash drums in a two compartment vessel - same shell but totally separated internally. A way to save space and cost. The fuel gas coils you mention in the surge tank are the stripping gas going to the stripping and still columns and as fuel gas to the burners, the gas is just being preheated as it flows through the surge tank coils. As far as having an internal stripping column, that is a perfectly acceptable design, I have designed and built a numbere of these, as well as ones with external stripping columns. As Art points out, it is a more cost effective way of doing things, but not everyone accepts it, especially in Gulf of Mexico platforms ( been there, done that) or North Sea platforms. Interesting that there is a secong stripping gas injection point below the still column.

Cheers,
Colin

[Dandy Komboris]

Dear Art.

I've seen your DHP P&ID. I am interesting about the TEG flow come out of Flash drum. In My DHP we send the TEG to Sock filter firtst and then send it to Charcoal filter. Is there any different result for this situation ?
Another difference is that In my DHP we use Hot,Lean TEG inside Surge Tank but in your desigh you use Cool,Lean TEG. You said that you wouldn't design TEG unit that way. Do you think there will be much TEG losses in my Surge Tank compare to your design ?

After All..
I would want to say Thank You very much for your cooperation and you've given me such enlightment about DHP.
I am very gratefull for that.

Best Regard


Dandy Komboris

[Dandy Komboris]

Dear Colling

Thanks for the addtitional Information from you.
Yes we inject stripped gas from the second stripping column into the base of reboiler. We do it in order to lower dew point of treated gas.
Do u have any comment or suggestion for that ?

I would be thankfull for all your help


Best Regard



Dandy Komboris

[ColinR33]

Yes, the stripping gas helps reduce the water dew point of the treated gas by helping strip more water out of the lean TEG. The concentration of the lean TEG has the biggest effect on the achievable water dew point as the water content of the gas is determined by equilibrium with the water content of the lean TEG at the top of the contactor (top-tray equilibrium). Without stripping gas you can only get to about 99.1wt% TEG, but with stripping gas you can get to 99.85wt% TEG, which will reduce your treated gas water dewpoint substantially.

Regarding the filtration order, I prefer to have the particulate filter first so the carbon filter does not get plugged off by particulates. Depending on the type of carbon filter, installing the particulate filter downstream may make more sense. If bulk carbon is used in a vessel you definitely want a filter downstream to catch any carbon fines. I would still put one upstream as well. If a carbon canister/cartridge is used, put the particulate filter upstream to protect it from getting plugged off. Bulk media carbon offers the best performance, but results in a much larger, more expensive vessel due to the residence time required to work properly. Most on-shore (and many offshore) installations (that I have seen/designed/installed anyway) use the carbon canister/cartridge because of this. If money is not a concern, bulk media is the way to go.

As for the hot vs cool TEG in the surge drum, it is better to have the lean side of the L/R exchanger between the reboiler and the surge drum. Smaller units just use coils inside the surge drum to cool the lean TEG and preheat the rich TEG. The unit you have is an "unusual" design, first time I have seen TEG booster pumps as well.

Cheers,
Colin

[Dandy Komboris]

Dear Collin

The reason why there are two booster pumps because we use it for loading TEG into the system. We do not have storage tank for TEG instead of that TEG is stored in plenty of drums in our Gas Station.
About "hot vs cool TEG in the surge drum", are you saying that it's better to have cooler TEG in the Surge drum ? So that you suggest I put Heat exchanger before the surge drum?
For additional info, This DHP is located near to Gas Station. We have 6 compressores ( 3 units of 1st stage compressor & 3 units of 2nd stage compressor)


Best Regards



Dandy Komboris

[ColinR33]

As long as it is working I would not change it. One other advantage of having the L/R exchanger between the reboiler and surge drum is you get some added hydraulic head to flow through the hot side of the exchanger which is important as it is essentially gravity flow. That would be my interpretation of why they have the booster pumps P-990/995 there on the line from the surge drum through the exchanger to the circulation pumps P-945/950, but if you are running without them, great.

Cheers,
Colin

[Dandy Komboris]

Dear Colling

L/R exchanger ..
Can u tell me what is it?
Whats does The "L" and "R" stand for?
I never heard about it.
Forgive me

Best Regards

Dandy

[Art Montemayor]

Dandy;

L/R = Lean TEG-to-Rich TEG heat exchanger.

[Dandy Komboris]

Dear All

I have a question about Water Dew Point in Natural gAs.
Our Natural Gas has 98% Methane.
my operator has checked the water dew point temperature in 2 spot (Inlet Glycol contactor and outlet Glycol Contactor) but the result is the different compare to the Water Content of Hydrocarbon From GPSA Engineering Data Book 12th Edition.

Inlet Glycol Contactor
Pressure = 100.4 Psig
Temp = 78.3 F
Flow = 62.652 MMSCFD
Water Content = 79 Lb/MMSCF

Outlet Glycol COntactor
Pressure = 96.1 Psig
Temp = 76.3 F
Flow = 62.652 MMSCFD
Water COntent = 59 Lb/MMSCF

We use SHAW MOISTURE METER to measure water dew point.

When I use the Chart from GPSA Engineering Data Book for Water COntent of Hydrocarbon Gas Fig 20.4
I have different result.

If I use data from the Oulet Glycol COntactor
Temp = 76.3 F
Pressure = 96.1 Psig
I plotted the data then i have 240 Lb/MMSCF for the water content..

Should I calibrate my Meter Device or I was wrong for reading the chart ??

Pleae Help Me

[RockDock]

I think you must be reading the chart incorrectly or doing some type of miscalculation.

The whole point of the Dehydration unit is to remove the water. If you have 240 lb/MMSCF of water, you must have some serious hydrate issues downstream. What unit do you have downstream? Compression?

I suspect the graph you are looking at shows you the saturated water content, not the dehydrated water content. You won't have a simple graph to tell you this. The best thing to do is get lab results to substantiate your meter. Or even easier, look at your ProMax model's prediction of water content. See if that agrees with your meter.

[RockDock]

Here's the model I created in five minutes using some of the data you supplied. I don't know what your dry gas spec is, but your unit can be performing much better.

Here is a .pdf of the model.

Attached Files

•  Basic Dehydration Unit.pdf   188.14KB   279 downloads

[Dandy Komboris]

Dear RockDOck


Is That Hysys simulation ???

[Dandy Komboris]

Dear RockDOck


Thanks for your input..
Is it possible If I want to recycle TEG in water vapour ???
From design Basis Our Glycol Losses is 20 Litre/Day.
So I Assume that we can get 500-550 litre/ month.
But I still don't know what would be the method to get The Glycol.
Reboiler Pressure is around 3 psi.
I Have two vessels in my plant.
Can I Use Vacuum system in the vessel to lower vapour pressure so that I can separate smaal amount of TEG in water Vapour ??

Best Regards



Dandy Komboris

[RockDock]

Dandy,

 

Sorry for the delay. I've been traveling a good deal.

 

To answer your question, that was a ProMax model. I never use Hysys for TEG units anymore.

 

That is a lot of TEG loss. Here are some ways to reduce the TEG in the Water Vapor:

    Reduce the regeneration pressure

    inject stripping gas into the reboiler

    reduce the reboiler T

[Dandy Komboris]

Dear All 

 

Can Two Phase Separator reduce water dew point in Natural Gas Stream ??

in the inlet stream i have nat. gas stream (136.5 Psig, 95.04 Fahrenheit, and water content is 138 lbs/MMSCF)

After the shore separator (2 phase separator) the outlet stream (132.20 PSIG, 83,84 Fahrenheit and water content is 87 Lbs/MMSCF)

Is this because there is a temperature decline so that the water content is reduced ??

 

Please help me.

[Art Montemayor]

Dandy:

 

You need to learn phase equilibria and the saturated state of vapors and gases.   A separator - no matter how efficient - is not capable of reducing the amount of water vapor contained in a volume of water-saturated gas.  All a separator does is separate out the liquid particles entrained in the water-saturated gas stream.   Lowering the gas stream temperature will reduce the amount of water vapor that can saturate the same stream.   This is in accordance with Dalton's Law of partial pressures and should be something you already know and understand before you start using a simulation program.

 

The water content in a gas stream within a pipeline can be in two phases: a liquid phase entrained with the gas and a vapor phase that is the amount of water saturating the gas phase at the temperature and pressure of the flowing stream.  When you say "water content" I am assuming you mean the amount of water vapor saturating the gas.

[Dandy Komboris]

Dear Art

 

You are correct Art.

When I Said "Water Content", meaning amount of water vapour saturating the gas.
In My DHU we have a big loss of glycoll.

Have You Ever found glycol losse in Reboiler Section ??

I mean there is a color change in my DHU because of glycol.

It can be seen now that many equipments in my DHU has "Yellowish Color".

The color is exactly same like Glycol spill in my DHU.

The reboiler operating Temp is 370 F.

Is there any chance that Stripping gas could carry some of the glycol or there is a leakage in my Coil Condenser 9Located in Top of my Still Column) ?
Thank You For Your Kindness Art.

[ColinR33]

If you are injecting too much stripping gas you can flood your packing and carry over glycol, and if you have insufficient reflux there can be excessive glycol losses as well. The questions I would ask are:

1) How much stripping gas are you injecting (scf/gal TEG)?
2) What lean TEG concentration are you trying to achieve?
3) What is your still column diameter and what type of packing?
4) What is the temperature of the vapour leaving the top of the still column?
5) What is the pressure of the regenerator?

Cheers,