Type of Suitable Compressor

[Khansahib]

Gentlemen,
The gas is wet, water saturated and a heavy gas, right out from Production Separator. The Separator is to be operated at 75 psig. The produced gas is transmitted to another Gas compression Platform. The Gas Mol weight is around 20.4, amount of the gas is in between 30 and 50 mmscfd, the pipeline is 18" and the line pressure drops is 50-55 psi.A booster compressor is required that can boost the pressure from 20 psig to a maximum of 100 psig in order to feed the existing compressors. The existing compressor (3 of them) are run by Solar Turbines.

Could anybody advise from the experience as to what type of compressor will be suitable, van, jet, screw or any other type. It is an offshore existing facility and compressor can not be accommodated on the same platform where the production separator is and hence the new compressor will be installed on the compression platform, dedicated for compression.

 

[pmover]

any possibility of restaging the existing gas compressors for the new inlet conditions? you will need to investigate any HP limitations.

otherwise, since plot space is limited, an electric motor driven rotary screw unit is suitable for this application. there are packagers that can assist you with this application; assuming, a packaged unit can be installed/fitted in the location.

good luck.
-pmover

 

[zdas04]

You are a long way from providing enough information for someone to do a competent design, but there are several similar examples of keeping the mother compressor at the same suction conditions and using a bit of the discharge gas to drive an ejector that sucks on the distant platform. There is an SPE paper on this at CalTec that is a bit self serving, but should give you a feel for what they did. You might also look at thread124-250612

David

 

[dcasto]

in my book, the low pressure low differential puts you in the screw package. add in the wet (hydrocarbon liquid and water) and they will perform well, a 408 screw will do 25 MMSCFD with 2000 HP.

 

[Khansahib]

pmover: I have not explored the restaging of existing compressor but my guess is there is no room for using the existing compressor at low pressure. It is based on assumption that if there had been the production people have long ago done it to increase the production from low pressure wells. The other challenge is use of electric driven screw compressor. The satellite platform does not have electricity and what will be approximate size of the compressor (rough estimate) for compressing 40-50 mmscfd gas.

David: I agree that it will require a lot of design input before one can design a compression package. Meantime, I am thinking on the same lines to put multistage eductor (ejector) to reolve this issue but the challenge I have is the minimum pressure of the careir gas? Please keep in mind the amount of gas is 40-50 mmscfd and the low pressure of the low pressure gas is to be raised from 25 psig to 70 psig, if I install a package at Production Platform which is about 1.5 KM from the satellite platform.

In case the eductor is installed at the source satellite platform then I need to raise the pressure from 75 psig to 115 psig of the low pressure gas. To drive the compressor lift gas at 300+ psig is available. I am not sure if this can do the job?

dcasto: I have noted ur response too and looking into the merit based on the conditions and will get back to u.

Last but not the least, you people are wonderful and I thank you for sharing your experiences and providing guideline.

 

[zdas04]

Just to make this thread complete. An "ejector" is a thermocompressor with a compressible power fluid (sonic or supersonic power fluid). An "eductor" is a thermocompressor with an incompressible power fluid (liquid doesn't exhibit choked behavior and velocities are a fraction of the speed of sound).

I was one of the people who's sloppy use of language in a couple of articles and presentations in the early '90's that have created the eductor/ejector confusion. I try to be more careful today.

David

 

[Khansahib]

Gentlemen: As mentioned in the beginning of my thread that around 30 to 50 mmscfd gas from the separator (operating at 20-30 psig) needs to be pressurized to about 100 psig for transportaion to other platform. I need to know how Coleman equation can be used to predict the amount of carrier gas required, the carrier gas is available at 300 psig. Excuse my ignorance I have not worked with jet compressor and now it became a requirement therefore needs to be guided.
It is also advantageous to know merit of jet compressor (eductor)over the screw compressor.

 

[zdas04]

"Coleman Equation?" The only arithmetic I can find by that name is also called the "Exxon Equation" that was developed by a guy who is now at EOG Resources. This "Coleman Equation" describes the critical velocity of a gas stream in a vertical conduit. I have a set of equations that I use to size ejectors and none of the equations even has a name.

You've reached the point in this cycle where you need to hire someone to do the feasibility work. The link I provided above to CalTec will get you to someone who will design and build equipment to do what you want, they'll probably work with you to do the design engineering if they think you are going to purchase equipment from them. If you aren't comfortable with a vendor doing your engineering for you you need to find someone who has done this kind of analysis before and has a clue. They tend to be a bit scarce on the ground but they can be found.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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