Providing Balance to Fluctuating Renewables
The design team had three key design drivers for the facility: flexibility, reliability, and efficiency. For example, one of important purposes of this plant is to provide electricity during periods when renewable sources such as solar and wind power produce intermittent amounts of electricity due to changing weather conditions.
“Renewable and discontinuous power generation technologies such as wind and solar power are increasingly penetrating the European electric power market,” Balling said. “Renewable resources certainly are leading the way to reduced CO2 emissions in Europe; however, on the other hand, their limited availability and predictability pose a considerable challenge to grid stability.”
Periods of low generation from renewable sources due to weather conditions (low winds, overcast skies, and day/night cycles) have to be covered by other types of power generation such as fossil-fired power plants, explained Balling. As a result, the requirements related to operational flexibility and rapid load response of the existing and new-built fossil fleet, as formulated in grid codes and customer specifications, are constantly increasing. These grid code and customer specification changes drive modern power plant design to place a strong focus on operational flexibility and grid support operation.
Fast Cycling: The Need for Speed
In recent years, the demand for quicker start-ups at CCPPs soon followed the demand for more frequent start-ups, Balling explained. This market demand finally resulted in the launch of a development project by Siemens that combined all the initial engineering ideas into a single integrated plant concept called FACY (derived from FAst CYcling). The aim of the subsequently initiated research and development program was to design a plant for an increased number of starts and to reduce start-up times. If possible, no limits were to be placed on the gas turbine by other power plant components, such as the heat-recovery steam generator or steam turbine, during hot and warm starts.
During the course of the project, potential areas came to light in which further optimization could be achieved, although these had to wait for a second development generation to be implemented. The major improvement offered by this second generation involved the start-up procedure, according to Balling. “Hold points,” which are stages at which plant personnel had to wait until certain steam parameters had been reached before the start-up process could begin, were eliminated as part of the shortened “start on the fly” start-up procedure. With second-generation FACY plants, the steam turbine is started up in parallel with the gas turbine using the first steam that becomes available after a hot start. Whereas the first-generation FACY plants reduced start-up times for a hot start from 100 to 55 minutes, second-generation FACY plants succeeded in pushing start-up times down below the 40-minute mark for an output of 850 MW.
“The Sloe Centrale plant was one of the first plants in commercial operation that incorporated the advantages of both the first and second generations of the FACY concept,” Balling said. “During its acceptance tests that achieved more than 59% net efficiency, the Sloe Centrale plant recorded impressive 30-minute start-up times. Equally good results have been exhibited by other reference plants. This means that the expectations placed on the second generation of FACY have been far surpassed in a number of cases.”
Winning Combination
The Sloe Centrale Power Plant promises to provide an abundant, reliable source of electricity with low emissions to the citizens of Zeeland Province well into the future.
“The new power plant impressively shows how security of supply, cost-effectiveness, and environmental compatibility can be harmonized,” Balling said.
— Angela Neville, JD, is POWER’s senior editor.
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