Pembroke B Combined Cycle Gas Turbine (CCGT) Power Station is the largest power station to be built in the United Kingdom since Drax Power Station was completed in 1986, and is the largest CCGT station in Europe. The station is located on Pennar Gut, a small bay feeding Milford Haven in West Wales and is built on the same site as the original oil-fired station that was closed in 1997.
The new power station is operated by RWE npower and produces 2000 MW from five 400 MW generator units, each using direct seawater cooling abstracted from the original cooling water intake. Milford Haven is surrounded by the Pembrokeshire National Park, and Milford Haven itself falls within the boundary of the Pembrokeshire Marine Special Area of Conservation (SAC). Of particular note in Pembrokeshire SAC are eel, salmonids, lampreys and grey seal, but all fish are considered important at the site since they contribute to the food chain within the SAC.
Even though the original cooling water intake has been used for the new station, it was not designed to modern environmental standards, and the increased emphasis on protecting the marine environment resulted in the need to minimise the impact of water abstraction on the SAC. RWE npower was therefore required to install the Best Available Technology (BAT) to screen the intake in accordance with the Environment Agency’s Best Practice Guide for the Screening of Intakes. The most suitable system for large scale coastal abstractions is deemed to be an acoustic fish deterrent (AFD) system combined with a fish recovery and return (FRR). However, to maximise the effectiveness of the system against European eel (Anguilla anguilla), which are now protected under The Eels (England and Wales) Regulations 2009, the Environment Agency required that ‘strobe’ lights be incorporated into the deterrent system.
Fish Guidance Systems was therefore commissioned to supply a suitable fish deterrent system and FGS proposed a Sound Projector Array (SPA) system should be installed. However, due to the large size of the intake, and the need to install ‘strobe’ lights, the latest MkIII version of the SPA system was proposed, which uses FGS’s patented SILAS® technology.
The MkIII Sound Projectors are based upon the previous MkII units, but each Sound Projector contains a digital signal, amplifier and other electronics required to operate and monitor the projector. In addition, the Sound Projectors incorporate FGS’s High Intensity Lights, which are synchronised to flash with the acoustic signal. This has the benefit of not only deflecting eels, but also of increasing the overall effectiveness of the system for other fish species in the vicinity of the intake.
Since the original intake was to be used the fish deterrent system had to be retrofitted to the original structure, which comprised 17 inlet gates, and in order to maintain an intake velocity of less than 0.3 m/s, the whole of the intake is used to abstract the required water. The projectors could not be located in the main flow as they might impact the flow of water into the intake, and so they were mounted on the buttresses that separate the inlet gates. As a result, there are 18 columns of Sound Projectors, with one column on each buttress.
PrISM modelling was carried out to determine the optimum number of Sound Projectors for the system, which initially indicated that 54 Sound Projectors were required to screen the intake however, the Environment Agency also requested redundancy be incorporated into the system owing to the ecological sensitivity of the site. As a result four Sound Projectors were specified for each column, with a total of 72 Sound Projectors being installed on the intake.
Four drum screens and a fish recovery and return system were installed by EIMCO Water Technologies Ltd (now OVIVO UK Ltd) to complete the screening of the intake.
The design of the deployment system for the Sound Projectors was carried out by EIMCO, based upon designs used by FGS at previous installations. The projectors are bolted to sliders that are mounted upon vertical rails, and a lifting wire runs up to the surface so that the projectors can be raised for cleaning and maintenance. The projectors are raised by using the permanent overhead crane installed for maintenance of the main intake, and a walkway runs in front of the projectors, to enable access from the power station, rather than having to use a boat. In this way, the number of personnel required to access the projectors was reduced, as well as the time required to maintain the system.
The SILAS® Control Unit was set up to provide a ‘Profibus™’ link to the general monitoring system within the power station, so that the system could be monitored remotely from the main Control Room at all times.
Currently no trials have been carried out, due to the need to switch off the system as part of the evaluation, but discussions are on-going with Natural Resources Wales (formerly the Environment Agency) on how best to achieve this, and the results will be reported at a later date.