Centrifugal and axial compressors are at the heart of many production processes. Effective compressor automation and turbomachinery control not only impacts efficiency, but also safety, reliability, production throughput and energy usage. A complete turbomachinery control system consists of measurement devices, high speed controllers, control valves, guide vane drives, turbine governors and more.
I spoke with Emerson’s Mikhail Ilchenko about compressor control. He noted that it’s important to treat this control not as a standalone black box, but as an integrated component in the plant control system.
When well integrated, it provides:
- Safe and efficient antisurge control
- Steam and gas turbine control
- Load sharing between parallel compressors
- Auxiliary device control
- Mechanical state monitoring and diagnostics
- Modifications of pilots and actuators
- Antisurge valve optimization
- Valves and instrumentation diagnostics
- Maintenance procedures optimization
If you’re unfamiliar with compressor surge, it is a phenomenon where flow oscillations inside the compressor are created when the pressure ratio across the compressor becomes so high that it is restricting the gas flow sufficiently to cause a stall. When this occurs, the pressure ratio drops and the compressor recovers the flow direction. If no action is taken, this process repeats again and again.
The flow direction in the compressor reverses at the moment of surge so the shaft experiences cyclical load changes in the axial direction. At the same time, the imbalance of the acting forces on the rotor cause chaotic movement of the shaft in the radial direction. All of this can cause damage to the seals, bearings, shaft, blades and internally-mounted sensors.
The challenge is to operate the compressor in its maximum zone of efficiency which can be close to this surge line without going in destructive surge conditions. A damaged compressor that causes a shutdown in a refinery catalytic cracking unit can cost the refiner more than $1 million per day in lost production.
The most efficient way to decrease the compressor energy use is precise antisurge control, from the measurement to the control algorithm to the antisurge valve. Knowing where the compressor is operating relative to surge and how fast it can respond sets the required safety margin. A quick response allows safe operation closer to the surge line. Also, energy consumption is minimized by compressors performance control or load control. This is done by stabilizing the main process parameter (e.g. discharge pressure or flow) in the optimum way.
Mikhail highlighted this total Emerson solution including the DeltaV distributed control system combined with Rosemount digital transmitters performing high-speed calculations for surge detection along with specially designed antisurge Fisher valves with air boosters and cushioned seats. These compressor control components are configured and tuned specific to the application by Emerson experts to deliver optimal performance and precise antisurge control. These controls combined with vibration and health monitoring improve safe operations, reliability, production performance and energy efficiency.
For example, precise regulation of the turbomachinery parameters to safely operate closer to the surge zone can provide energy savings of up to 25% by decreasing recycled gas and stabilizing the process parameters surrounding the compressor.
You can connect and interact with Mikhail and compressor control experts and/or visit the DeltaV group in the Emerson Exchange 365 community.