Renewable energy sources are increasingly contributing more to the world’s energy mix as the race to achieve net zero carbon emissions by 2050 gathers pace. In the UK, for example, 2020 marked the first year that wind, solar, bioenergy and hydroelectric sources contributed more to the national energy grid than fossil fuels.[i]
While this is an undoubtedly significant achievement, renewables are not yet at a point where they can provide sufficient baseload power. In practice, this means that steam turbine power stations remain vital for stable and reliable electricity generation. At the same time, the diversifying energy mix is now forcing changes to the way power stations traditionally operate, placing additional strain on older components designed for altogether different conditions.
Adapting to High-Cycle Operation
Combined cycle power stations now run at higher frequencies. This means they need to power up and down as grid demand fluctuates, filling the supply gaps that renewables cannot meet. Higher cycling does help lower carbon emissions, as power stations only operate when needed and are not left idling when the demand for energy is lower.
The main problem is that they have not been designed to operate in this way. High cycling puts greater operational stress on both power stations and their key components, such as valves. This can lead to higher failure rates, which means more plant downtime and higher operating costs. Potentially, it also increases the number of safety issues for plant workers.
The cooling of superheated steam is one of the most critical operations performed in steam turbine power stations. The cooling is undertaken by the steam conditioning valve, which generally performs well under conventional low-cycling plant conditions. However, with power stations adapting to new demands that generate higher cycling frequencies, conditioning valves are now failing more frequently.
This means that there is a clear need for more robust plant components, not only to maintain the supply of electricity but also to minimise the threat of unplanned outages. Given the intermittent nature of renewable power, the availability of these facilities is now more than ever a key part of keeping decarbonisation on track.
Recognising the challenges customers face, IMI Critical Engineering developed a high-performance steam conditioning valve able to function reliably under the testing conditions of today’s combined cycle power plants. The company’s research and development team began with the existing steam conditioning VLB2 valve which they then modified to manage the greater operational stresses that characterise high cycling. Developing the initial design meant that the manufacturing and installation of the new valve – the VLB3 – was quicker, which helped avoid any unnecessary and costly downtime.
The VLB3’s uniform body thickness allows material to expand and contract at the same rate which reduces fatigue damage. The valve body also has smooth transitions that minimise thermal stresses. Meanwhile, conditioning at the outlet takes place with improved thermal separation of the steam and water flow paths, reducing problems in the critical area of injection. Collectively, these modifications significantly lower any potential failure points that may occur when a plant is cooling steam.
As Jackie Hu, Managing Director at IMI Critical Engineering points out: “It was important to us to develop a conditioning valve capable of withstanding the stresses that come with a high cycle approach. Supporting renewables is a priority for IMI Critical Engineering, and getting the VLB3 into plants quickly shows how we are able to understand plant operators’ needs and provide timely solutions that help them run more efficiently. This valve is a product of the teamwork, communication and problem solving required to bring innovation to an evolving industry like power generation.”
VLB3: Third Generation Steam Conditioning Valve
A compact turbine bypass valve with lightweight trim, optimised for high-cycle power plants such as CCPPs. Modular trim with a range of standardised components.