Ranjit Rao, Jon Gillam, and Jim Nyenhuis presented Maximize your Combined Cycle Plant’s Performance with 5 Advanced Applications that Provide the Quickest ROI at the 2023 Ovation Users Group Conference.
They opened by sharing some statistics about the challenges with global electrification.
Advance control enables greater power plant flexibility to help address some of these challenges. Jim noted a paradox that the more advanced the automated system, the more crucial the contribution of the human operator becomes to the successful operation of the system.
Advanced control is a wide range of control technologies designed to augment or replace simple PID or logic-based control which executes natively in a redundant controller. Model Predictive Control (MPC) is one of the more universal advanced control techniques. It incorporates a model of the process being controlled and inherently considers time delays. MPC handles multivariable interactions in a systematic fashion and can provide more responsive control actions and better setpoint following than simple PID-based control. Advanced sequence control simplifies control logic, decreases startup times and enables consistent operation.
Some applications where advance control is applied is steam temperature, drum level, coordinated ramp rates, and sequence control.
For combined-cycle power generation plants advanced control application can approve operations in several areas.
The five advanced applications that can generate the quickest ROI in combined-cycle plants include procedural integration, model-based steam temperature control, advanced drum level control, advanced bypass control, and response optimization.
Procedural integration enables faster and more consistent startups, reduced fuel usage, and increased startup reliability and robustness. Ovation has flowchart-based programming that can minimize operator variability for an optimal start and powerful building blocks for a unit single pushbutton start. Manual procedures can be automated capturing existing operations experience and displaying this experience visually for the operations staff.
Applying model-based steam temperature control can return a faster ramp rate, improved heat rate, and increased startup reliability. It drives consistency in operations.
Improving drum level control can yield faster ramp rates, improved bypass control (pressure & attemperator), and a reduction of trip events associated with pressure upsets. It’s important to have properly functioning measurement instrumentation and final control elements.
Response optimization enables faster ramp rates, improved heat rates, and enhanced spinning reserve capability. Typically, one takes a combined mass and volumetric approach to drum level control. It encapsulates geometric impact on level rates into control strategies. This approach allows for density compensation on volume vs. level relationships.
Cycling-related applications ensure automatic management of startup drum-level management and model predictive control is used for dynamic compensation of dP/dL effects during rapid pressure changes.
Advanced bypass control provides better resilience associated with managing significant load rejections from the steam turbine. It supports an expanded range of pressures and increased reliability during blending and un-blending. This approach better manages piping thermal conditions reducing stress on critical bypass piping. Important considerations are proper sizing of the bypass valve and attemperator. The control strategy is based on attemperation energy balance. The MPC model needs to be able to be bypassed in plant upset and leak conditions. Finally, bypass attemperator control is based on optimal temperature & enthalpy control for the protection of condenser and piping per HEI and EPRI recommendations.
Visit the Ovation Power Plant Optimization Software section on Emerson.com for more on Ovation advanced process control capabilities and applications.