As Balfour Beatty decommissions its Hinkley Point C Marine Works concrete batching plant at Avonmouth, two-and-a-half years after their installation and commissioning, we look at the processes and arduous operating conditions that the three Fulton VSRT steam boilers (amongst the first to be delivered and installed in the UK) have endured.
Embarking on one of the most complex marine engineering projects in the world at the time, Balfour Beatty excavated and constructed three cooling water tunnels under the seabed (two 3.5km intake tunnels and one 1.8km outfall tunnel) that will supply EDF’s two nuclear reactors at the 3,200 MWe Hinkley Point C with cooling water from the Bristol Channel.
In 2017 Balfour Beatty took ownership of a large, purpose-built concrete batching facility at Avonmouth Docks, which saw the beginning of a multi-year contract to supply 38,000 concrete tunnel segments destined for the nuclear facility. The batching plant is responsible for producing concrete segments for the reactor tunnels, with each tunnel ring consisting of six 6m x 4m sections and each of the two 3.5km intake tunnels comprising approximately 2,300 rings and 14,000 segments each.
To meet the target of producing the huge number of segments for the tunnels within the contracted period, a 24h concrete batching process was required, with steam from Fulton’s VSRT vertical steam boilers used to expedite the process by reducing the concrete curing time from a typical 24 hours to just 8 hours per segment. This allowed for 120 segments to be manufactured per day, all of which are cured in four, steam-filled automated curing chambers.
Consistency and quality are paramount in the manufacture of the tunnel segments, with engineers working on the high-performance concrete mixes since 2012. And while the design of the nuclear mix is itself not particularly special, the way it must be handled during the moulding and curing of each segment is extremely important.
The Fulton designed steam boiler system, which was specified by Avon Combined Electrical Services of Bristol and installed and commissioned by Fulton in February 2019, consists of three skid-mounted VSRT boilers packaged with feedwater tank, water treatment and chemical dosing plant and automatic blowdown.
The steam system uses over 45m3 of treated feedwater and operates at 7.5 bar to provide steam for the four curing chambers at between 55°C and 60°C. Gas from six large liquid gas tanks is piped to the gas-fired Fulton VSRT steam boilers, which use 4,500 litres of liquid gas per day and are located in a plant room adjacent to the batching plant.
To ensure the boilers operate in accordance with manufacturer guidelines throughout the contract, Balfour Beatty also has water treatment and service contracts in place with Fulton who, given the Avonmouth-based location of the batching plant, can respond to any demands and be on site extremely quickly.
The VSRT steam system has operated throughout the entire batching contract on an N+1 configuration (one boiler on, one on setback and one boiler off), ensuring two of the three boilers are always operational in any 24h period.
The VSRT is the first steam boiler to emerge from Fulton’s new ‘PURE Technology’ approach, an initiative that’s resulted in a world-first design that is durable, long-lasting and boasts the highest efficiencies and ultra-low NOx emissions as standard.
With over 15 patents pending in three continents, the VSRT’s spiral-rib heat exchanger is a world first. It attains industry-leading heat transfer rates thanks to its unique spiral design, which achieves low stack temperatures by passing the flue gases through a spiral-wound heat exchanger that is fully immersed in water.
Commenting, Fulton’s Carl Knight says: “PURE Technology aims to enhance heat transfer, provide class-leading efficiencies, improve steam quality and reduce NOx emissions.
“Rather than further-improve products like our J Series to achieve these goals, PURE Technology – the culmination of Fulton’s clean slate approach to design – challenges the industry status quo on conventional boiler design by engineering solutions that are fit-for-purpose and fully-optimised for all applications.” says Carl.