Compressor is used to flow gas from a lower pressure to a higher pressure system. Compressor are used to compress the gas for sale or on long pipelines to restore pressure drop lost to friction.
Usually the compressor is centrifugal compressor which takes gas from the suction scrubber out oulet and compress is to adjustable pressure. usually the compressor is driven by gas turbine. Suction pressure controller within the package unit control panel will maintain the pressure at suction scrubber by regulating the compressor turbine speed control.
Typical gas turbine cycle
Turbine works with Brayton cycle principle and the main energy is used to drive air compressor and driven equipment. The driven equipment is a series of rotating impellers to impart velocity head to the gas, then converted to pressure head as the gas is slowed in the compressor case.
Process Control utilizing compressor speed
A PIC controls the suction pressure of the compressor train.
The gas turbine speed is modulated to control the suction pressure (PV) to the desired set point. The PIC increase the turbine speed when the pressure is above the set point. the PIC decrease the turbine speed if the pressure is below the setpoint.
The SIC (speed controller) selects the PIC Setpoint that will be used to control the fuel actuator. Tthe output of these two modes are inputs to the SIC fuel control.
The following control block diagram shows the specific I/O used in SIC
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