Ensuring Reliability: Protecting Steam Cycle Components in Low-Load Operations of CCGT Plants

As the energy market evolves, combined cycle gas turbine (CCGT) plants are increasingly required to operate under low-load conditions to provide rapid response and load-following capabilities. This shift from their original design as baseload power sources introduces several challenges, particularly for the steam cycle components of these plants.

Adapting to Market Demands

Historically, CCGT units were designed for high thermal efficiency and low capital costs, making them ideal for baseload operation. However, the rise of renewable energy sources and fluctuating natural gas prices have demanded greater operational flexibility. Modern CCGT plants must now accommodate frequent starts and stops, as well as extended periods of low-load operation.

Challenges in Low-Load Operation

Operating at low loads can strain various components of the steam cycle, including the heat recovery steam generator (HRSG), power piping, steam turbine generator, and condenser. Issues can include:

• Heat Recovery Steam Generators (HRSGs): At low loads, the reduced steam production and lower operating pressures can lead to overheating of heat exchange surfaces. This is aggravated by increased exhaust gas temperatures from the gas turbine, which can exceed design limits and cause damage to superheater and reheater tubes.
• Steam Turbine Generators (STGs): Frequent cycling and low-load operation can result in thermal fatigue and mechanical wear. Maintaining optimal steam temperatures and pressures is crucial to prevent damage to turbine blades and other components.
• Power Piping and Condensers: These components must handle varying thermal loads and pressures, which can lead to stress and potential failures if not properly managed.

Solutions

To mitigate these challenges, plant operators can implement several strategies:

• Enhanced Turndown Capability: Modifying gas turbines to operate efficiently at lower loads can help maintain steam cycle stability. For example, some designs can achieve good emissions performance at 20% to 30% of design power.
• Optimized Control Systems: Advanced control systems can help manage steam temperatures and pressures more effectively, reducing the risk of overheating and thermal fatigue.
• Regular Maintenance and Inspections: Frequent inspections and proactive maintenance can identify and address potential issues before they lead to significant damage.

Conclusion

As CCGT plants continue to adapt to the demands of modern energy markets, protecting steam cycle components during low-load operation is essential. By understanding the challenges and implementing effective solutions, plant operators can ensure reliable and efficient performance, even under varying load conditions.

Tetra Engineering has been performing HRSG Inspections for over 30 years with 1000s of Inspections to date. We provide an integrated service that supports Owners and Operators throughout the full HRSG life-cycle. In addition to the HRSG Inspections we also perform HRSG Condition Assessments, in which we review not only the present condition of the HRSG Unit but also how historical operation has affected its integrity.

For more information: tetra-eng.com

To find out more on this topic read our article in PowerMag