×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Low pressure gas transfer

Low pressure gas transfer

Low pressure gas transfer

(OP)
Hi all,
I'll really appreciate some help regarding equipment selection.
We are about to design an Associated Petroleum Gas Treatment plant. The plant will be located approximately 1.5 km from Gathering Station, and it is planned to lay two pipelines (high pressure 7 barg and low pressure) from GS to APGT.
Gas pressure at tie-in point to (inside of GS) low pressure pipeline is almost atmospheric (200 - 600 Pa), with max flow 4000 sm3/h. We are now considering the following options to transfer AP gas to the APGT plant.
1. Liquid ring compressor (preferably installed at APGT)
2. Blower or fan installed at GS and screw compressor or sliding vane at APGT
3. Ejector at GS (probably multiple ejectors) and centrifugal at APGT
4. Your option
Any experience sharing in transferring low pressure gas is highly welcomed.

RE: Low pressure gas transfer

What is the flow rate of the hi pressure pipeline?

Lo P gas pipelines are not efficient and will be subject to liquids collecting inside. I hope there is a good reason that the two gas streams cannot be combined by compressing the lo P stress at the GS and then building only one pipeline.

RE: Low pressure gas transfer

(OP)
Hi 1503-44,

Flow rate of the high pressure pipeline is around 9000 scm3/h.

I hope there is a good reason that the two gas streams cannot be combined by compressing the lo P stress at the GS and then building only one pipeline.

Pipelines can be combined, I am proposing option 3 above (ejectors). Is there any other way to combine two different pressure pipelines?

RE: Low pressure gas transfer

Not really. Obviously they must operate at the same pressure.

Do you know what pipeline diameters you are planning to use?
Is it natural gas?
Are there liquids, water, or condensates in the gas stream coming from the GS? How much?
Usually you have liquids in pipes before arriving at the treating facility.

Due to the very poor efficiency of atmospheric pressure gas pipelines, I suggest using the higher pressure 7 barg range, if possible. I have not worked out the gas velocity, as you did not mention pipe diameters, however it is usually very important to have a velocity that will push any liquids along the pipeline, especially in gathering systems where you normally get water and condensates from the wells.

I'm not sure about using ejectors. My impression is that they like higher pressures, but I do not know anything about them.

RE: Low pressure gas transfer

(OP)
Diameter of LP pipeline 20", HP pipeline 10". Actually we are in the design stage and diameters can be changed.

Yes, there is liquids in pipes. During treatment about 250kg/h water will be returned to GS for reinjection.

Probably you right, ejectors will require higher pressure, but we can add something like recycle compressor to increase motive gas pressure.

What about LRV compressor? Any experience using LRV compressors in low pressure pipeline?

RE: Low pressure gas transfer

OK, so you can move your 4000 SCM/H through a 250mm pipeline for 1.5 km with only a 0.1 bar pressure drop at 12m/s.

But I am confused because I thought the 200-600 pressure was kPa, but now I see that you wrote Pa. Can you confirm the pressure unit.





RE: Low pressure gas transfer

(OP)
Yes, that is the problem. There is only just 1.002 bara at the tie-in point.

RE: Low pressure gas transfer

Well let's just call that 0 kPag.
Yeah. Thats a problem.
So you need like a 15 kW compressor.
I dont know about any equipment with that small power.
Maybe someone else can help.

So, why 2 pipelines?

RE: Low pressure gas transfer

A fart has more pressure than that...

Seriously, just compress the LP gas into the high pressure supply at the GS

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Low pressure gas transfer

How about a multistage centrifugal compressor (second preference recip compressor) to inject LP gas into 700kapg HP line at GS - much more efficient than an LR compressor or ejectors, and less troublesome too - see operating map in the GPSA. You can install 2x50% machines ( ie 2x2000sm3/hr machines) running on electric motors with VFD (or gas engines, if you must).
Besides, a dedicated 1.5km LP line at these pressures will be next to impossible to pig.

RE: Low pressure gas transfer

(OP)
1503-44,

There is no pipelines yet, just two tie-ins. We need to increase LP gas pressure after tie-in, and yes you right, inject gas to HP pipeline.

RE: Low pressure gas transfer

(OP)
LittleInch,

just compress the LP gas into the high pressure supply at the GS

That is the area I need you guys expert opinion. I need to know which type compressor will work at 1.002 bara suction pressure and flow of 4000 scm/h.

RE: Low pressure gas transfer

George is saying
1) centrifugal
2) reciprocating compressor

Gas flow is always better at higher pressure so install the compressor at the gathering station if possible.


LI, its great you found your sense of humor, but now I have an image of a really unusual PI that I can't seem to get rid of.

RE: Low pressure gas transfer

(OP)

Georgeverghese,

As per operating map of the GSPA rotary-screw seems the best option for flow of 4000scm/h and discharge pressure 7 barg.

I am not sure about centrifugal compressors, normally they require higher suction pressure. Plus there will be some pressure loses till compressor.

RE: Low pressure gas transfer

(OP)
1503-44,

From control point of view it is preferred to install compressor at APGT, but if there no other option compressor will be installed at GS.

RE: Low pressure gas transfer

Rotary screws may be troublesome to operate in fouling service. Cleaning up the gas upstream would present other disposal and operating issues. Centrifugals would be best from a reliability point of view, but will most likely be higher CAPEX. Recip machines are also troublesome but are lower CAPEX like rotary screws. Project managers may prefer the cheapest option, especially when Big Brother JV partner is watching how you spend their money, but if you can convince them of lowest life cycle cost with centrifugals, that would be better.

Operations staff often have the short end of the stick when it comes to machine selection, and end up having to nurse a troublesome child for 20years, while the design phase project manager gets a feather in his cap for low cost project completed on time and on schedule, and then he runs off in a hurry to mess up the next project.

RE: Low pressure gas transfer

If located at the treater, the gas will expand greatly, especially at near vacuum levels, as pressure reduces along the pipe. At 1Barg, gas volume doubles with only a 1 bar pressure drop, velocity doubles and pressure drop along the pipe is squared, gas density is less so you pay a lot to transport very little gas. It will work for now, but increasing flow rate in the future could become very difficult. Increasing flow often happens with gathering systems. If that is not expected, locating the compressor at the treater station could be OK. You will have to catch any liquids in a slug catcher before they can hit the compressor.

BTW Is the high pressure pipeline the 500mm, or the 250?

RE: Low pressure gas transfer

(OP)
1503-44,

Diameter of LP pipeline is 500mm, HP 250.

4000 scm/h is the maximum expected flow. You right, we need to catch liquids before the compressor.

Separation of liquids from gas is another challenge.

Gents, any idea except slug catcher?


RE: Low pressure gas transfer

Which one depends on what comes out of the well. Water, gas liquids, condensates, sand?
I think you will need a slug catcher for gas with 250kg/h of liquids. Thats like 5-8 m3/day.
Whats the elevation profile of the 1.5 kn run.
Up hill, down hill, both or flat? How many meter difference in elevation?


Some seperator options here,
https://www.youtube.com/watch?v=-xWQMWJD8hg

RE: Low pressure gas transfer

As I understand your project,

You only need 1 pipeline.

You can run 13,000 m3/h through the 500mm line at 0.15 Barg at a velocity of 18m/s and 16kW compression.

Or

You can run 13,000 m3/h through the 250mm line at 3.7 Barg at a velocity of 23m/s and 187kW compression. Any lower pressure than that will increase velocity too high.

RE: Low pressure gas transfer

Rauf,

You need to understand what it is exactly you're transporting.

Is this simply water saturated gas or does it have some free liquid ( water or H/C) in it? Makes a big difference to decide how you're going to transport it.

There may be 250kg/hr coming back but if this is all condensate stripped out of the gas it's a lot different to free water in the pipeline.

If it's a mist type liquid then you might need a coalescer or cyclone or maybe just a good de-mister pad in a separator or Knock out drum upstream your compressor.

If you want to look at types of compressors look at air compressors. They start at atmospheric conditions and compress gas to 7-8 bar very commonly. You can't just use an air compressor to compress hydrocarbons, but the types of compressor are similar. Just be wary of the temperature you will have d/s any compressor.

At 1500m of pipe you're not really looking at a big difference in cost and if there is no space or power at the GS, then you could just lower the pressure at the APGT below atmospheric pressure by using a blower, axial fan or other compressor. A lot depends on what happens to the gas when it gets to your APGT as doing it that way you have no capacity to run the gas through any filters, coalescers etc so you will end up with some liquid in your pipeline.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Low pressure gas transfer

It seems that some low pressure separator will be needed. Maybe something like a very large "drip pipe" separator that can be suctioned out every day or two.

RE: Low pressure gas transfer

(OP)
LittleInch,

Feed gas is water saturated at operating P and T of 60C at tie-in point.

GS do not want to update their design docs, so it preferred to locate any required equipment at APGT.

lot depends on what happens to the gas when it gets to your APGT as doing it that way you have no capacity to run the gas through any filters, coalescers etc so you will end up with some liquid in your pipeline.

Due to low pressure, I have no capacity to run the gas through any equipment even at GS site. That is why I am looking for proper compressor to increase the pressure.

RE: Low pressure gas transfer

A drip pipe, or other type of simple separator won't need much pressure, so you can at least get the liquids and sand out before going into the compressor. At low pressure the bigger the separator the better. It needs low velocities to work properly.

RE: Low pressure gas transfer

The above flow and pressures were for compressor at the GS.

If you place the compressor at the GT, the 4000m3/h through the 250mm pipeline has a high velocity of 47m/s or, going through the 500mm the velocity is 10m/s
Using a compressor discharge pressure of 2 barg at the GT requires around 200kW.

RE: Low pressure gas transfer

(OP)
1503-44,

Thanks you for your calculations. Diameter of pipeline will be calculated on later stage, after decision of compressor type and location.

There is about 10 meter elevation difference sloop to APGT, so liquids in the pipeline theoretically can be collected at APGT area.


RE: Low pressure gas transfer

Oil free rotary screw compressors may work okay at GS only if you are gathering and boosting clean LP casing head gas into HP line, and not production gas. If these are oil flooded screws, you can expect all sorts of mechanical problems with lube oil contamination with heavy hydrocarbons in the gas. Oil free screws have limited life span even when they work well, so you'll need sufficient inline and offline spare machines.

RE: Low pressure gas transfer

You have to know pipeline diameter or you will not know your compressors suction pressure and/or discharge pressure. The items cannot be designed separately. They work together.

RE: Low pressure gas transfer

We had a similar problem which was easily solved by compressing the LP gas to HP value at the GS.

RE: Low pressure gas transfer

(OP)
Hi Sesquipedalianist,

Could you please share a little bit more information? Like suction pressure, compression method and etc.

RE: Low pressure gas transfer



From the process facilities and economics, install a centrifugal compressor at gas station with discharge pressure close to the amine gas plant treatment.

Be aware of the liquid condensation, Is water o c5+ ?????

Horacio 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close