Q&A: Compressor Anti-Surge Control with Compressor Controls Corp. at TPS 2024

Tuesday morning at Turbomachinery & Pump Symposia 2024, speakers from Compressor Controls Corp. (CCC) and Petrobras, including Fabio Zanetti de Souza, Brownfield Account Manager at CCC by Honeywell, presented: Optimizing Compressor Anti-Surge Control to Reduce Power Consumption and Greenhouse Gas Emissions in Oil Production Units.

Decarbonization initiatives are often associated with low-carbon fuel combustion, but a compressor’s anti-surge control system impacts energy efficiency and carbon performance and emissions. According to Zanetti de Souza, an anti-surge control system coupled with performance management helps decarbonize offshore operations by minimizing energy consumption and emissions through precise control and monitoring.

Zanetti de Souza provides details on the panel’s anti-surge control system paper, including key takeaways, the control system’s primary and secondary functionalities, its ability to decarbonize offshore operations, specifically in the Brazilian pre-salt fields, and more.

TURBO: What are you hoping to take away from Tuesday’s paper presentation?

Zanetti de Souza: We aim to demonstrate how fine-tuning control parameters and enabling advanced control strategies, such as derivative response, tight shutoff, etc., can optimize compressor anti-surge control to reduce power consumption and greenhouse gas (GHG) emissions in offshore oil production units. Our goal is to highlight the control theory behind one practical application in a real-case operation with CCC’s control system. We believe that sharing these results can help drive worldwide focus on how relevant the compressor is and its control system as a central contributor to increasing energy efficiency and reducing GHG emissions.

TURBO: What is the primary function of a compressor anti-surge control system, and what are its major components?

Zanetti de Souza: The primary function of the anti-surge control system is to prevent the centrifugal compressor from operating under surge conditions, which is a potentially damaging phenomenon for the compressor. However, the secondary functions of an anti-surge control system are often overlooked or unaddressed by many providers. It can help maintain specific suction pressure in centrifugal compressors through a Ps limit loop or prevent reaching a high discharge pressure through a Pd limit loop. The system also avoids high discharge temperature that could lead to a trip due to high Td or manipulate the anti-surge valve for periodic stroke tests and send operators an alarm if the valve demonstrates some level of stickiness. The anti-surge control can also be used to avoid critical speeds during startup of an expander-recompressor arrangement in natural gas liquids plants or even prevent overspeed.

The major components of an anti-surge control system are:

• Surge Control Valve: Allows for flow recirculation to occur from the discharge side to suction side of the compressor through a recirculation line when opened. This reduces the energy required to compress a certain amount of gas since the discharge pressure is reduced. It is the anti-surge control system vendor’s responsibility to validate anti-surge valve layout and sizing and perform flow measurement device calculation to predict differential pressure readings referencing specific compressor operating points, as well as propose recommended process variable transmitter calibration spans and performance characteristics.
• Measurement Devices/Transmitters: These devices allow the measurement of process variables such as pressure, flow, and temperature in the inlet and outlet of the compressor to be transmitted to the controller.
• Anti-Surge Controller (logic solver): The controller receives the measured process variables from different points in the piping (as mentioned above) and processes them in an anti-surge control loop. The signals’ processing shall be performed in such a way that the anti-surge control loop defines the operating point position in an invariant way when related to suction conditions (invariant to suction flow, pressure, temperature, and Mol weight). This allows the logic solver to plot the operating point position in the compressor map and decide, based on previous programming, which actions should be taken: if the recycle valve should open to prevent the machine from entering surge conditions, if the recycle valve should open to maintain a minimum suction pressure limit condition, etc.)
• Experienced Field Engineering: While the core components of an anti-surge control system—such as the surge control valve, measurement devices, and anti-surge controller—are critical, the expertise of experienced field engineers is equally essential. Their understanding of customer needs, process conditions, and fine-tuning of control logic ensures the system's optimal performance, making them an indispensable component of any effective anti-surge control solution.

TURBO: How does it impact energy and carbon performance?

Zanetti de Souza: A good anti-surge control system can respond quickly to process changes in a way that allows the compressor’s operating envelope to be as big as possible without risking the machine entering excessive surging. If the system is not tuned with the correct control parameters, the operational envelope can be limited, which can result in the unnecessary opening of the surge control valve and waste of energy used to compress the flow passing through the compressor—this increase in energy consumption leads to more emissions. Therefore, a good anti-surge system allows for a safe operation even close to the surge-control line, reducing process upsets and the demand for recycling, therefore cutting unnecessary flaring/emissions and reducing energy consumption.

TURBO: How does combining optimized turbomachinery controls with the appropriate energy and carbon-performance management system help decarbonize offshore operations?

Zanetti de Souza: It helps decarbonize offshore operations by ensuring that energy consumption and emissions are minimized through precise control and monitoring. Optimized controls enhance the efficiency of turbomachinery, reducing the power required for operation, while the performance management system tracks energy use and carbon emissions in real time. This integrated approach allows for continuous adjustments and improvements, ensuring that operations remain as efficient and low-emission as possible, ultimately leading to significant reductions in the carbon footprint of offshore oil production units.