Ready for anything
For operational flexibility, the KA26-1 combined-cycle system can be run at loads that are less than 40% of its maximum rating. This ability is important not just for backing up wind farms; given the system’s fuel efficiency, it also enables HC Energía to turn a profit from Castejon when market conditions reduce the need for regional generation (Figure 3).
3. Works well with others. A key project requirement was excellent part-load performance, to facilitate the plant’s dispatching on a grid that seeks to maximize wind power production. Courtesy: Alstom Power
The KA26-1’s excellent part-load efficiency and operational flexibility also allow the utility to earn extra revenue by maximizing the time that Castejon spends feeding its full load into the local grid. For example, after an eight-hour shutdown, full-load operation can be resumed in less than one hour. From the low load point, full load can be reached in a matter of minutes.
Just as importantly, thanks to the GT26’s two combustion chambers, Castejon 2 meets or exceeds regional air emission standards, even at partial load. Commissioning tests produced values that are well below the required levels at 100% load for NOx (50 mg/m3), volatile organic compounds (2 ppmv), and CO (10 ppmv). At 70% load, CO emissions were 40 ppmv.
Construction challenges
Alstom’s ability to design and build all of Castejon 2’s main systems in-house offered a number of advantages. The main one was the possibility of integrating the gas and steam turbines, the HRSG, and other key equipment in a way that maximizes the plant’s operational and fuel flexibility while minimizing its emissions.
Because it was Castejon 2’s engineering/procurement/construction (EPC) firm as well as its systems supplier, Alstom was also able to overcome other project challenges, such as reducing equipment lead time. This is the main benefit of the company’s “Plant Integrator” approach.
The main challenge for Castejon 2 was timely project completion, and it met that challenge in just 24.5 months. The schedule allowed for only week between signing of the EPC contract and awarding of the project’s notice to proceed. It also made no provision for a pre-engineering phase. Meeting the fast-track deadlines required Alstom engineers to think long and hard about constructability during the design phase. During that phase, several system designs were optimized with an eye to implementing and commissioning them easily and quickly.
For example, the HRSG chosen has a 10-module heat exchanger that usually requires a lot of piping work to be done on-site. To save time, Alstom prefabricated the 10 modules prior to delivering them to Castejon. Similarly, most control and electrical systems also were supplied as prefabricated modules that had only to be interconnected on-site. All gas turbine and steam turbine internal piping also was prefabricated to the maximum possible extent.
Another tenet of Alstom’s Plant Integrator approach is to tackle civil works—especially underground infrastructure—early. Doing so minimizes interference with construction and erection activities performed later in the project.
To save additional time and money, Alstom made several interfaces to the existing Castejon 1 plant. Those interfaces enabled the use of common systems (such as the balance-of-plant gas system and the raw water and wastewater systems) and made it possible to use medium-voltage boards for both plants (enabling separate panels to be used for each). In designing the interfaces, a key goal was to minimize the time that Castejon 1 had to be shut down while those interfaces were installed. In fact, all of the interfaces were implemented during a planned outage of the older plant, so there was no impact on its commercial operation.
Another important enabler of fast-track execution was a system-oriented approach to work that allowed the erection and commissioning of different systems at the same time. Safety was another focus of construction activities. The Castejon 2 project was completed while meeting all the demanding health and safety requirements of both HC Energía and Alstom, without any serious accidents during more than 1 million man-hours of work.
The new plant’s noise was yet another consideration. Alstom minimized it during the design phase by increasing the surface area of the Castejon 2’s air intake system and optimizing its air duct design.
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