Gas Compression HP / LP Production Stages ??

[JonnyWill]

Hi All,
I'm involved in the front end design of a platform, and I have a question to all you readers. The onset years, gas export is not a problem, after it goes through a series of recompressors it meets the export pressure of the grid. … But after the gas pressure decreases in the well we have to reconfigure the design to meet the demands for the gas export pressure. We are considering adding an extra Compressor to increase the gas pressure.
No assumptions have been made; however consider that the machines are will running to their capacity.
Option 1. Installing another machine as Future, as to booster the pressure.
Option 2. If the Gas Export Compressor, driven by Gas turbine is run at reduced capacity and there after run at a higher load ?
Option 3. Install a LP turbine coupled to the HP on the Gas turbine?

I have to think of the most viable solution…. Taking in consideration, LCC, weight, engineering advances over the coming years, etc
Any suggestions….
Thanks in advance…

 

[zdas04]

This is a very normal design consideration. Many people solve it by assuming that when the additional compression is needed, the wells production will have declined substantially and put in piping with spectacle blinds to allow the number of stages to be changed in the field (i.e. fewer stages early when the wells can buck high line pressure and more stages later when you need to draw them down further).

David

 

[tgmcg]

I would look at several different configurations. You've not mentioned anything about the design flow, MW and pressure requirements, so presumably recips are also a possibility, or a combination of centrifs plus recips. The more info you can provide, the better.

You might try to identify the minimum cost system capable of meeting the future requirement, and then figure out how to meet the interim conditions with it. For example, the future head requirement may require a total of 24 impellers...assuming 10,000 ft of head per wheel. This will probably require three centrif compressor casings in series. However, the near term might only require 19 impellers, which could possibly be done in two casings. It may be cheaper in the long run to install the three casings now, but with fewer wheels in each casing, but totalling 19. You can then re-rate the compressors later on as process conditions change, with minimal piping modifications. Adding a 3rd machine later on can be a very expensive proposition. Much cheaper to add it while the topside facility is in the yard, and size all common/auxilliary systems for the worst case.

Variable speed drive would provide significant additional operational flexibility.