How low can you go? That’s the question owners of gas turbine combined cycle plants are asking these days as they are being called upon to operate those units for rapid response in markets where load following is becoming the norm. The resulting cyclic operation introduces challenges that can result in damage to steam cycle components if you aren’t careful.
Originally, the modern combined cycle gas turbine (CCGT) unit was developed to act as a largely base load source of generation due to its high thermal efficiency and low initial capital cost. But as markets developed for independent power, the service requirements changed. Many markets were essentially energy only (MWh) and while high-efficiency CCGT plants were competitive during peak daytime hours, their limited turndown capability and high part-load heat rates were uneconomic at night. The result was that most new CCGT units were required to do overnight shutdowns (two-shift cycling) during the work week and longer shutdowns over weekends. As natural gas prices have dropped in North America, and renewables with significant tax credits and take-or-pay contracts expanded, markets have had to change to a combination of energy and capacity supply plus related ancillary services. This has increased the need for operational flexibility in CCGT units...
Read the full article in Power Magazine.
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