Anti-Surge Control Theory and Quench Control Theory of Compressor
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Anti-Surge Control Theory
The anti-surge controller must meet some certain process conditions to:
• Prevent the compressor from operating in surge line, thereby saving from any surge related compressor damage.
• Reduce process upsets.
• Maximize the compressor and total train efficiency through utilization of control parameters.
• Assist the station or total compressor process control strategy.
In order to perform these tasks, the controller must monitor the current operating point, generate a Surge Control Line (SCL), and compare the two to determine if movement of the anti-surge valve is necessary.
The compressor performance map describes the relationship between speed, pressures, temperatures, gas properties, and inlet flow. This map will also describe the operating limits of the compressor in terms of a Surge Limit Line (SLL) or surge region. Several variations are possible on how this information is presented, each describing the compressor with a different set of variables. The CCS accommodates two such compressor map definitions, Standard and Universal.
Quench Control Theory
Quench control is used in close loop refrigerant applications (e.g. Propane/Propylene) where cooling of the hot recycle gas is achieved by liquid injection. The liquids used for quenching are produced by the refrigeration compressor operation itself and available through the discharge main condenser. Applications where a quench system is in place do not require any cooler for the ASV loop. Typical piping schematic for quench control relative to a single casing compressor with one side stream is depicted in Figure.
In its simplest form, a quench controller is a standard PID loop that maintains a given suction temperature SP by acting on liquid injection valve.