Content area
Full Text
Simple procedure can be used to help determine piping and equipment design pressures into process loops
HEYDARI GORJI * and H. KALAT JARI, Sazeh Consultants, Tehran, Iran
Comments? Write:
Ehen a compressor compresses gas from one system at P 1 and T 1 to another system at P 2 and T 2 and stops during the maximum pressure drop case, a differential pressure is developed. After a compressor shutdown, the gas is trapped between the upstream and downstream discharge check valve and the pressure is equalized out. This equalized pressure throughout compressor loops is called settle-out pressure. The maximum settle-out pressure is calculated from coincident high-trip pressures on both suction and discharge sides of the compressor.
In some situations, a single pressure safety valve is desirable to protect equipment in a process loop. In this regard, and also to establish the design pressure for piping and equipment installed in the process loop, the settle-out pressure is required. Therefore, it is desired to reduce the settle-out pressure as much as possible. Settle-out pressure will decrease if the discharge-side volume of centrifugal compressors is minimized, for instance gas precooling is preferable to compressor discharge cooling.
A simple procedure has been developed to determine the settle-out pressure into compressor loops (for instance, a reaction recycle-gas loop in which a compressor continuously recycles the process gas) or centrifugal compressor stations including knock-out drums, inter coolers and antisurge lines.
Calculation procedure. To calculate the settle-out pressure, isobar sections of the system should be identified. The system volume and confined masses need to be determined and the lumped mass and enthalpy should be distributed in...