Method for detecting the occurrence of surge in a centrifugal compressor

Abstract

A method for detecting the occurrence of surge in a centrifugal compressor includes the step of calculating a time rate of change of a discharge pressure of the fluid discharged from the compressor. In one preferred embodiment, the time rate of change of the discharge pressure is calculated by initially setting PREV PRESS and RATE PRESS variables equal to zero (0), and commencing a RATE PRESS subroutine having a time limit for cycling therethrough. The RATE PRESS subroutine includes the steps of obtaining a discharge pressure reading for the fluid discharged from the compressor, subtracting the discharge pressure reading from the PREV PRESS variable to establish the RATE PRESS variable, and resetting the PREV PRESS variable equal to the value of the discharge pressure reading. After the RATE PRESS variable has been determined, the RATE PRESS is compared with an acceptable set time point rate of change for the discharge pressure. If the calculated value of the time rate of change of the discharge pressure is greater than or equal to the acceptable set point time rate of change for the discharge pressure, then a surge detection subroutine having a time limit for cycling therethrough is commenced. The surge detection subroutine may include the steps of calculating a time rate of change of a temperature of the fluid discharged from the compressor, and comparing the calculated time rate of change of the temperature of the fluid discharge from the compressor with an acceptable set point time rate of change for the temperature of the fluid discharged from the compressor. If both calculated time rates of change for the discharge pressure and the discharge temperature are greater than or equal to the respective set point time rates of change for the discharge pressure and the discharge temperature, then the system generates a signal indicating the occurrence of surge.