Compressor Surge Prevention Control Implemented on Yokogawa Stardom
CCS's patented SPC provides two independent control loops - dP and Rc. During normal operations, CCS systems offer a high-select mode and control based on the most efficient variable.
If at any point in the process either measurement becomes unavailable, the system provides true continuous control by taking automatic control, based on the available control loop.
The SPC has two Surge Prevention Control PID loops. One of them controls the surge distance along Rc coordinates, another along dP coordinates. The set points for these loops are calculated using CCS's proprietary Control Safety Margin (CSM) algorithm.
When Surge Line is determined, CCS field engineer sets the CSM values for both Rc and dP coordinates. This defines the distances to the Surge Line which need to be maintained by the control loops.
The surge prevention controller uses a first closed loop PID module to control the operating point of the compressor below pressure ratio at surge limit conditions set point for current speed. The process variable of the PID control module is current pressure ratio (Rc).
The PID loop generates a control signal for controlling the opening of the anti-surge valve. A surge limit line is positioned in the stable operating region and displaced down by the safety margin.
The suggested size of the safety margin is typically 3-5% of Rc span and covers the inaccuracy of 1% on polytropic exponents (σ).
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