September 1, 2010

Top Plant: Langage Combined Cycle Power Plant, Plymouth, Devon, UK

Owner/Operator: Centrica Langage Ltd.

By Dr. Robert Peltier PE

Enviable Features

LPP exhibits many interesting design features that merited its inclusion as a POWER Top Plant. Several are unique to this project yet have much broader application for those seriously considering construction of a combined-cycle plant that has superior baseload efficiency plus the ability to “chase wind” when necessary.

High Reliability and Efficiency. According to Alstom, the thermal efficiency of the €400 million LPP is approximately 58% (LHV), making it one of the highest efficiency air-cooled combined-cycle plants in the world. The NO_x guarantee on natural gas is 40 mg/Nm³ at 15% O₂ dry without supplementary firing. Given Alstom’s long history with designing and building plants of similar design, its reliability guarantee was equally robust: >95% during the first 150 days of operation and 97.5% going forward.

Pleasing Design. LPP is constructed close to a national park, hardly an ideal spot for a power station. Yet its thoughtful architectural design (similar to that of a modern airport—see the cover photo) and strict adherence to environmental constraints has ensured that the plant blends in with the natural surroundings. For example, a green roof (Figure 1) minimizes the plant’s visual impact. Hiding a plant stack is always problematic, so LPP’s was sunk 10 meters into the ground to reduce its height, and the architects made it a key design feature. Today, the stack is a local landmark.

1. Site sensitive. A green roof and a stack sunk 10 meters into the ground minimize the visual impact of Langage Combined Cycle Power Plant. Nearby land is reserved for development of an energy park, a mixed-use industrial area that includes the plant’s administrative building, shown in the upper left corner. The plant design included provisions to add a “steam tail” to supply steam for the park’s district heating system. Courtesy: Alstom

VIP Parking. In the UK’s deregulated electricity markets, the plant offers extremely flexible operation, including the capability to turn down to 40% plant load and below. This turn-down capability is particularly useful for plants that must chase wind or provide spinning reserve as part of their dispatch duties. (See “Flexible Turbine Operation Is Vital for a Robust Grid” in this issue for a complete discussion of how Alstom’s GT24/GT26 sequential combustion design provides rapid response to meet the stringent UK Grid Code while maintaining low-load emissions.) LPP now supplies lucrative frequency support and spinning reserve to the UK grid with a responsive 8 MW/sec ramp rate based on the combined output of the plant.

Quiet Neighbor. Controlling the noise produced by the plant was a key design issue given its location near a residential area. Materials for the colored cladding on the facility’s walls were also selected for their special acoustic properties. The far-field noise limitations at an adjacent neighborhood were kept at a whisper-quiet 35 dBA—the local stream makes more noise than the power station.

Future Growth Option. Land is reserved nearby for development of an energy park, a mixed-use industrial area that includes the plant’s administrative building. The plant design also included provisions to add a “steam tail” to supply steam for district heating the park.