Improving biomass efficiency at Drax
How can we make renewable power more affordable? It’s a question energy generators never stop asking, among them the owners of the UK’s biggest power station, Drax Power.
A major innovative upgrade that will bring down the cost of biomass
Drax has now converted four of its six power generation units to burn biomass in place of coal and supplies 11 per cent of the country’s renewable energy needs. In 2018, as part of a plan to reduce the cost of biomass generation, it announced a £40 million upgrade to significantly improve the efficiency of three of the units.
The contract with Siemens includes replacing the three HP turbines with a barrel turbine design, as well as a new turbine governing system and control system. The work will start in 2019 and take three years to complete, with one biomass unit being upgraded each year as part of its planned major overhaul.
Efficiencies will come from the new blading and long-life seals within the turbines and the new pipework and valves. “We’re looking at a number of ways to bring down the cost of our biomass generation, and these turbine upgrades are an important part of that work,” confirms Andy Koss, Drax Power CEO.
The idea first took shape during blue-sky discussions between Drax and Siemens. Steve Austin, lead turbine engineer at Drax, sums up the blue-sky approach. “No ideas are off limits. Every suggestion is listened to. It’s a great way of opening up discussions and Siemens is very good at facilitating them. Ninety-five per cent of the ideas on the list won’t make the final cut, but five per cent go onto the shortlist and that’s what we go away and drive forward.
“It helps that we’re a standalone utility. We have more of a free rein to consider innovative improvements than others,” adds Steve. “But this process also works because of our relationship with Siemens. They have a vast network of expertise we can draw upon – centres of excellence in Newcastle, Mulheim and Orlando. There’s a real artery between Drax and Siemens through which we can link to an incredible support network and the latest engineering ideas and designs.”
He emphasises that the blue-sky workshops can’t become talking shops. “We have an action tracker, we agree deadlines and we put in the work. You need a structure.” Stakeholders are essential too. “We have people in both Drax and Siemens who are championing ideas. You need people with vision, who are open-minded, and we have that. Siemens and Drax want to find solutions. We both need to make money, but we’re also teams of engineers who want to make Drax the best available power generator on the grid and a strategic asset to the UK.
“I look at Newcastle as an extension of Drax,” adds Steve. “We’re working in a very collaborative partnership to supply a solution. The fact we can talk very openly about our businesses, without being guarded or stifled, gets us to that solution much more quickly. Simple, open conversations can solve a tremendous amount and really make things happen.”
Barrel turbine design
Over a decade has passed since Siemens last carried out a major upgrade on the HP turbines. Although the barrel turbine design was available then, it was questionable whether it would fit in the space available and it was ruled out for a better value option. But circumstances changed in the intervening years, as the head of mechanical engineering at Drax, Les Lemmon, explains.
“With laser tracking we can now make much more accurate measurements and be confident the barrel turbine will fit into a complex arrangement. We’ve also had time to undertake detailed investigations and data gathering which put us in a much stronger position to make an assessment.
“We know, for example, that the efficiency of the barrel turbine won’t degrade as much as the existing turbine between maintenance intervals, which is worth a lot of money to us. A small improvement in efficiency makes a big difference in the biomass world because the cost of fuel is much higher.
“The other driver is emissions. We want to do all we can to keep emissions to a minimum, plus of course the high carbon price means that any reduction of emissions has a direct impact on our bottom line. This is now also proven technology,” he adds. “Siemens has sold many of these turbines since 2006.”
Innovative financing is enhancing project payback
And there was another important factor that gave the project momentum: finance. The Newcastle team introduced Drax to Siemens Financial Services, whose innovative financing proposal has enhanced the payback of the project.
“It essentially means that we don’t pay anything for the first two years of the project,” explains Gill Danby, procurement projects manager at Drax. “That helps us with our working capital and means we can fund other projects.”
With major projects, a frequent challenge is incurring big upfront costs many months before the financial benefits start coming through. “We’re always looking for the initial payments to be as low as possible, so to start getting benefits two years before any outlay definitely helped push the project forward,” she says. “It moved it up the ranking of other capital investments we were considering, where cash flow is always a major consideration. It was always a viable scheme, but the financing helped improve its appeal.”
Whilst engineers at Drax and Siemens have forged strong relationships over the years, financial relationships were something new. “It was a first for all of us, but the Siemens and Drax finance people gelled really well,” says Gill. “We all had the same understanding and we both got what we needed.”
Les highlights how the financial and engineering worlds talk a different language. “To take just one example, the term ‘taking over’ triggers events like the defects period in our engineering world, but it means something completely different – to do with transferring risk – in the finance world.
“It was very complex but we always found a way through. It wouldn’t have worked if we had a transactional relationship. But as always with Siemens there’s no ‘us and them’ attitude. We’re all driving towards the same goal.”
“On occasion we’d tell our legal team they were asking for something that wasn’t fair on Siemens, and Siemens would do the same if they felt their people were setting conditions that weren’t fair on Drax,” adds Gill, highlighting the trust and maturity in the relationship. “A lot of companies go into negotiations and don’t give on anything,” says Les. “They don’t prioritise and everything is precious. But we were clear what we could and couldn’t give on.”
Combining old and new
With the first upgrade due to get underway in July 2019, just a year after the contract award, a lot of engineering design work had to happen in both companies before the deal was signed. “We committed a huge amount of resource upfront, as did Siemens,” confirms Les. “It was a leap of faith for us both, but we couldn’t achieve what we’re doing without it.”
He explains one challenge for the Newcastle team is that they’re also taking responsibility for the complex pipework and electrical control system. To keep costs down, rather than invest in a new site-wide control system, Drax is buying part of a Siemens control module and plugging it into its existing system.
“It’s a little like buying a Tesla and getting it to talk to an Austin Morris,” says Les. “We’ve bought a really new hi-tech control system that has to communicate with technology designed and built in the 1960s. That’s the really clever bit.”
He admires the Siemens engineers for taking on the challenge. “They realised it was the only way to get the price down and worked really hard to eliminate the risks. When it came to the detailed design work we also agreed who had the best experience in different areas. Siemens have never been precious.”
The need for innovation extends beyond the control system. “That same innovative thinking has been required to get the barrel turbine to fit within the existing steelwork, and to modify the pipework from four pipes to two. The original solution lost quite a bit of efficiency, so we took it back to Siemens. They spent a lot of time on the redesign and they’ve cracked it.”
The first outage will be the biggest ever undertaken at Drax and includes a number of other companies. “The Siemens element is by far the biggest and most intensive; everything else will fit around it. Siemens has worked with us long enough to know how we do things, our approach to safety and quality. We need to make sure everyone understands that. Communication will be absolutely key.”
Co-ordination is vital too. At Drax, the control and instrumentation team now sits in the same office as the turbine team, a subtle but important change believes Les. He expects to see the same unity in Siemens. “We want to forge the same relationship with other parts of Siemens as we have with the Newcastle team, and we want a cohesive approach from Siemens all the way through. It can’t feel like we’re dealing with 50 different companies.”
He’s impressed with what he’s seen so far. “There’s unique bespoke technology in this contract. It’s much more complex than a new installation. Siemens knew from day one they’d have to be very innovative and that off-the-shelf solutions wouldn’t work. We’ve seen some really pioneering thinking and they’ve really worked with us. We’re all driving towards the same goal.”
The technical challenge
Dave Henery has worked on modernisations for 15 years in his time as a steam turbine engineer at Siemens and has never seen a project to match the scale of the one now underway for Drax.
“With most modernisations, the outside of the turbine remains and the inner components are replaced. With this project, everything is being removed including the valves. It’s halfway between a new build and a modernisation,” says Dave. “I’ve never worked on a scheme of this size and complexity, which is occupying a team of around 10 engineers in Newcastle alone. It’s a really interesting project with a lot of challenging engineering.”
The HP turbine in Drax units 1, 2 and 3 is being replaced with an HP barrel turbine used in new build projects. The standard design is being modified to be shorter axially, to fit within the Drax foundation block, and has modified support palms and keys to interface to the existing bearing pedestals. Replacement main steam admission valves are mounted directly onto the barrel turbine, replacing the existing HP steam chests and interconnecting pipes to the turbine.
“By eliminating the interconnecting loop pipes, we can eliminate the inlet pressure drop and give a permanent performance improvement,” says Dave. The design of the barrel turbine will also provide a higher performance: “Thermal distortion is lower than for the original HP design, which allows for tighter clearances to be used and therefore a consequent improvement in performance.” Another bonus is reduced maintenance. “The first major overhaul is designed to be after 100,000 operating hours – over 10 years – whereas the current turbines are dismantled for overhaul on a four-year cycle.”
Designing new pipework has proved one of the project’s major challenges. “The current HP turbine has four inlets and four exhaust pipes, whereas the new barrel turbine has two inlets and two exhausts. We’ve therefore had to modify the main steam admission pipes from the boiler, and the cold reheat pipes back to the boiler, to reduce the number of connections.”
The pipework engineering is being carried out by Siemens colleagues in Erlangen. “Drax has sent them digital scans of the turbine hall, so they can walk through the station on screen,” explains Dave. “With digital modelling they can see what will work before any physical changes get underway. They can digitally remove old pipes and put in new, and look for clashes.”
A new turbine tripping and governing system will be supplied to control the new HP valves, which will also interface with the remaining IP steam control valves. The new tripping system will replace the original mechanical and hydraulic system with a state-of-the-art electronic trip system. The T3000 digital control system will be provided by Siemens teams in Manchester and Germany.
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