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Will This Control Scheme Work Properly?

control valve pressure control process scheme valve gas

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#1 james.corrobro@gmail.com


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Posted 28 October 2020 - 11:06 AM

Evaluating whether this process scheme (attachd pdf) is ok or not. I have high pr. Scrub which is operating at 15 barg and low pr. Scrub at 1.9 barg. On low pr. Scrub I have pressure control valve with split range which maintain pr. At 1.9 barg in scrub. Down strm of the compressor I am mixing high pr gas with compressed gas. The PC2 takes pr. Reading from high pr. Gas and maintains same pr. For compressed gas so that they mix. The pc3 is an upset scenario case. The pc3 control valve will open when system is at 18.5 barg.

Will pc3 in any way interfere with pressure at high pressure scrub? Will it increase high pressure scrub pr. To 18.5 barg?

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#2 Pilesar


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Posted 28 October 2020 - 01:02 PM

If I understand correctly, in an upset scenario, the PC3 valve to flare will not begin to open until pressure reaches 18.5 barg. In that scenario, the high pressure scrubber would be at a higher pressure than 18.5 barg. The PC2 valve would close which would leave no outlet for the compressed gas. I suggest you develop a cause and effect table for determining what would happen at each feasible scenario.

#3 james.corrobro@gmail.com


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Posted 28 October 2020 - 01:25 PM

hi pilesar, thanks, the pc2 valve is trying to maintain same pr. downstream of pc2 valve for compressed gas as the high pr. gas. hence the function of pc2 is that compresed gas pr. d/s of pc2 valve = high pr. gas pressure. in case of upset when high pr. gas increase to 18.5 barg, will the pc2 valve open more to maintain more pressure or will it close? please guide me

#4 Bobby Strain

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Posted 28 October 2020 - 06:34 PM

Your control scheme is all screwed up. You should be able to find instances for control of similar operations.



#5 Jiten_process


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Posted 31 October 2020 - 11:36 PM

To comment on control scheme, we need to understand the objective of the process. That is the first information. Anyways, the apparent additional requirement to me is, provide compressor recycle line with PCV and PC. PC shall be installed on scrubber and that set point shall be in between PC2 and PC3. 


To me, scheme is not grossly wrong. Need to align with objective of the process which is unknown at the moment and needs to be studied with different scenario. 


Good luck.  

#6 breizh


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Posted 01 November 2020 - 12:51 AM


Share with us the philosophy of the process which is what you are supposed to bring to E&I engineer for him/her to draw/set  the instrument part .

My view


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