A two stage centrifugal compressor for NG is driven with Siemens Gas Turbine (SGT-500). The anti surge control system is provided by Siemens.

Query is whether, density input from density analyzer at 2nd stage process gas outlet is required as input for controlling anti surge valve for both 1st & 2nd stage or only pressure, temp input is required.

What equation is used to derive set point for anti surge control valve?

 

Generally, anti-surge control does not need gas density involved. It requires suction & discharge pressure, suction&discharge temperature and gas flow differential pressure.