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[ashetty]

I’m presently doing some compressor settle out pressure calculations (verification of licensor specified value).I’m having problems in understanding the situation.
My problem begins with finding the limits of settle out pressure. Once the limits are firmed up I can ask for the relevant iso`s and start doing the actual calculations.
For your reference, I have attached a typical compressor circuit with the limits marked out. Here, when the compressor shuts down or trips the suction and discharge SDVs close and the anti-surge valve opens, equalizing the pressure between the compressor inlet shutdown valve and the compressor discharge check valve (or shutdown valve). Settle out pressure then, is the equilibrium pressure which the combined suction and discharge sides of the compressor reach. An ideal settle out assumes that the inlet valve to the compressor unit closes instantaneously with no back flow through the inlet valve.
I have also attached my compressor circuit. It is a 2 stage compression circuit. The relevant gas train has been marked orange.
My first question is should there not be 2 settle out pressures based on which the design pressures of the suction KOD for each compression stage can be decided. The licensor has specified only one value of settle out pressure in the spec sheet, which corresponds to the design pressure of the suction KOD for the first stage of compression. The design pressure of the inter stage suction drum is obviously higher.
My second question is regarding the location of the limits for my settle out pressure calculations.
The end point will be at the compressor discharge SDV (SDV 4), that I have figured out but the starting point is not very clear. In fact the isolation philosophy for the compressors itself is not very clear.
To start with there is no shut down valve upstream of the 1st stage suction KOD. Then the recycle line from ASV1 is routed all the way back to the main column receiver instead of somewhere between where the inlet SDV should have been and the 1st stage suction KOD.
I have two options for my limit 1.The inlet SDV (SDV 1) or at the point where ASV 1 terminates. In the first place I am confused about the location of the SDVs and the termination point of the recycle lines from the ASVs.
If some one can explain the reasoning behind this and more importantly suggest the limits for my calculations I would be grateful.

Attached Files

•  Compressor_circuit.xls   69KB   233 downloads