Earlier this year the Cochwillan GoFlo scheme was given the green light, as GoFlo was commissioned to design, manufacture and install two self-cleaning screens to be installed as part of the Cochwillan hydro project.
Carter Jonas land agents (acting on behalf of Penrhyn Energy Ltd) commissioned Gloucestershire based Renewables First for consultancy, design and installation procurement works for the hydro scheme. GoFlo undertook the design, manufacture and installation of the self-cleaning screens. In collaboration, both Renewables First and GoFlo project managed the installation of the hydro turbine and Cochwillan GoFlo screens respectively, each through to commissioning.
The Cochwillan GoFlo self-cleaning travelling water screens will significantly increase energy production and income from the hydro scheme, as well as considerably reducing the time-wasting task of removing screen blockages. Screen blockages and reduced flow are the primary cause of turbine downtime or poor performance at most hydro sites.
The GoFlo scheme involved the installation of two GoFlo self-cleaning screens on the Afon Ogwen, at the water intake of the hydro scheme. The screen assemblage comprises a modular system, consisting of two travelling water screens located directly next to each other. The Cochwillan hydro scheme is very close to the sea and therefore requires an eel screening system that is compliant with the strictest screening rules under the Eel Regulations – hence the 3 mm bar-spacing was specified. The total screened area at the Cochwillan site is 13.5 m2. Each of the two screens measure 1.5 metres in width by 4.5 metres in length.
For ease of installation, the screen package incorporates the purpose-designed GoFlo hinged (pivoting) mounting frames. These are securely fixed to the concrete inlet structure and enable the screens to be lowered into the pivoting frames from a vertical position (as designed). Once secure within the frames, the screens were then tilted to their specified running position at 45 degrees. To hold them securely in position at this angle, the screen frames rest on large steel joists. Interestingly, despite their size, the screens are remarkably lightweight, with each unit weighing less than a tonne respectively.
How is debris removed from the self-cleaning screen? As the screen rotates, it deposits debris into a collection trough, located on the lee-side of the top of the screen. To ensure that debris does not stick to the screen mesh, a spray bar located inside the screen blasts a jet of water, forcing debris into the trough. Once in the trough the debris has to be removed. Although this can be achieved in a number of ways, at Cochwillan it is drawn away from the trough via an automatic sluice gate and into a flushing pipe.
The base of the debris trough is submerged below the normal operating water level. The trough has holes in its base, allowing it to fill with water. Sensors on the screen are able to detect the build up of debris by measuring subtle changes in the water level on each side of the screen. When a build up of debris is detected, an alarm is triggered which activates the debris removal process. Simultaneously the screen will begin to rotate, the spray bar is activated and the debris collection trough sluice gate opens. As the screen deposits debris into the trough, it is then drawn through the sluice and exits the system via the flushing pipe and deposited downstream of the fish bypass. Once the sensors detect that the water levels have returned to normal, the screen will stop rotating, the sluice will close and the spray bar will stop. This all happens automatically and is tied into the control system.
The motors used to power the self-cleaning screens at Cochwillan are located well above the level of the screen. However, they are fully rated to withstand full submersion in the event of flood conditions. Although the screen motors are always located to be above the predefined flood level, they are rated to operate at up to 3 metres below water, without damage.
GoFlo self-cleaning screens can be controlled both manually (in-situ) or remotely. The scheme at Cochwillan incorporates the sophisticated GoFlo monitoring and control feature and includes a camera for remote viewing. The control and monitoring system is equipped with a mobile device web interface, meaning that it can be controlled from anywhere. The Cochwillan control system communicates purely via the 4G network so that it can be controlled remotely. The images below show example screenshots of the monitoring screen interface.
The entire project, including the GoFlo screens and the hydropower system, should be up and running before the end of the year.