Fair exchange: alternative approach to rotor refurbishment
In April this year a Life Time Extension project began at Peterhead, the largest thermal power station in Scotland, to improve its efficiency and extend the asset life. To keep downtime to a minimum, SSE opted for a gas turbine rotor exchange solution which enables Siemens to cut 15 days from a standard outage.
The rotor exchange concept was very attractive to SSE. We wanted to trial it.Tony Thomas, Manager at SSE Peterhead
Tony Thomas has a clear ambition for Peterhead power plant, the site he has managed since 2011 and his seventh station in a 40-year career. “As near as we can, we want to return to the efficiency levels the plant achieved when it was built. That’s very important for SSE. And we’re looking for the same reliability and performance that we’ve had for the last 100,000 hours.”
The Life Time Extension now underway at Peterhead was originally scheduled for 2014. Plans were put on the back burner when difficult market conditions saw the station’s operating hours drop significantly, making the investment uneconomic. But in late 2017 market conditions were favourable once more, and the station has been running at full capacity ever since.
“Two years ago it wouldn’t have greatly mattered how long the outage took,” says Tony. “But in the current climate uptime is really important. The standard 44 day outage for an LTE was acceptable, but the 29 day proposal Siemens put to us was certainly appealing and we wanted to trial it.”
The 15 day reduction is made possible by the Siemens rotor exchange concept. Essentially, rather than remove the gas turbine rotor, refurbish and reinstall it, a previously refurbished rotor – ready and waiting at a Siemens factory – is installed instead. Meanwhile, the original rotor is refurbished ready to take the place of the second rotor, which in turn will be refurbished in time to take the place of the third rotor. The third ‘spare’ rotor is then transported to a Siemens factory where it will be refurbished in readiness for when the next Siemens customer – anywhere in the world – should need it.
“It’s a sensible concept and it worked for us. Part of the appeal is that it reduces risk because there are no issues of emergent work, and since the outage durations are shorter there is less safety risk too,” explains Tony.
SSE’s Kevin Beaumont, lead mechanical asset engineer at Peterhead, agrees. “Another bonus for Peterhead is that the gas turbine rotor which Siemens shipped here to replace the first of our three is a later model, so we’re benefitting from some technology upgrades that may deliver additional power. Plus, Siemens has provided new thermal insulation for the GT that will result in efficiency gains. That’s a real positive for us too.”
Tony believes Siemens has become much more customer-focused in recent years. “Siemens is looking at solutions from the customer’s point of view. They asked us what was important and it was our emphasis on safety, a reduced outage period and efficiency gains that led to this solution.
“It’s in both our interests to run Peterhead as effectively as we can,” he adds, “and that can only happen if Siemens has a close understanding of our challenges. I feel they’ve shown a genuine interest.”
He looks back to a project Siemens undertook at Peterhead in 2016: the upgrade of the Siemens distributed control system for the three gas turbines and boilers, and the migration of the balance of plant control system from an obsolete Schneider system to the Siemens T3000. “We’ve built up a good relationship. It’s not just a contractual arrangement; it works as a partnership.”
The success so far of this latest project has much to do with planning. “Although we didn’t get the green light until December 2017, we started the journey in 2011 so we’d done a lot of advance background work to ensure the people and parts were available,” says Kevin. “To complete the first outage in 28 days and the second in 24 is no mean feat, and it hasn’t happened by accident.” The third and final rotor exchange, scheduled for completion in early September, could also happen within 24 days although is contracted for 29.
He sees the project as a logistical challenge as much as a technical one: “The spare parts, for example, cover an area the size of a football pitch.” Snow was also added to the mix. “The project began during some of the most adverse weather conditions we’ve ever seen in Scotland. Without the goodwill and desire of everyone to make it happen, we could very easily have fallen down. But there’s an open and understanding relationship between SSE and Siemens. We appreciate each other’s needs.”
An early and unexpected challenge occurred in February during the pre-outage build-up. Siemens site manager Dave Heslop happened to be at Peterhead when a major issue with the generator arose, resulting in significant emergent work. Alongside planning a complex first outage for the Life Time Extension he found himself managing the day-to-day challenges of a generator rotor exchange.
“To refurbish a generator rotor in Germany typically takes 30 to 40 days, so it made sense to bring the rotor exchange concept into operation on this occasion too. By shipping over a rotor from Mulheim and by using the same experienced team who had carried out a very similar exchange at Seabank in 2014, we were able to significantly improve on the target date,” explains Dave.
Whilst pleased with the successful completion of the unscheduled generator rotor exchange and with the first two GT rotor outages, he’s very disappointed by the safety record. During the de-stack of the first GT rotor there were two safety incidents within 24 hours.
When a rotor is de-stacked during a Life Time Extension outage, the compressor blades have to be destructively removed. The UK Field Service team typically uses a 14 lb hammer to remove the blades, having found it to be the most effective method. But the Peterhead rotor’s compressor blades had been blasted and re-coated in 2007, making the removal extremely difficult.
“Although it’s an operation that’s been carried out for years, it’s clear with hindsight that we shouldn’t still have been doing it this way,” says Dave. “We need to constantly challenge our processes to ensure they’re as safe as possible and I should have more carefully considered the safety risks. I feel I’ve personally failed the team and it’s a lesson I’ll certainly never forget.”
Immediately after the incidents, the team sat down to agree a new approach. They devised various improvements to the process including the development of a dolly to sit the blade upon so that a second team member no longer needed to stand close to the operation. The team also looked to reduce the potential fatigue risk by limiting the operators’ time and a safe zone was established to restrict access.
As they approached the second de-stack, they consulted the wider Siemens network and undertook some further brainstorming. Two further options were trialled, including the use of a tool supplied from Germany. Since this was only successful on three rows of blades, a new technique involving a jack hammer was developed. The effectiveness of this method surprised everyone.
“Sometimes it feels as if there’s only one way to do a job, but clearly we hadn’t exhausted all the options,” reflects Dave. “We found another way, and it’s the way we’ll use at all sites from now on. There are safety considerations when using jack hammers too of course – hand and arm vibration issues – so we’ll need to carefully look at those. We’ve found a solution but we can still better it. One clear lesson is that we must take more time, outside of the pressures of an outage, to challenge the way we do things.”
Tony is open about his disappointment too. “Safety is our number one value at SSE and we want everyone to get home safely, so to have two incidents happening close together was especially frustrating. Fatigue can set in when a team is working within tight time constraints, and that’s when accidents happen. Areas also get very congested near the end of an outage which adds to the safety risks.
“But on the positive side, together the team devised a new method and I applaud them for that. And when I asked Siemens MD Darren Davidson for a step change in safety performance during the second outage, he responded very tangibly. He stood people down, refocused the team, and we saw a change of mindset.”
All other aspects of the project have gone very well says Tony. He points to the “excellent control of the work areas and PPE compliance” and more generally the rigorous adherence to programme and the openness of the Siemens team, highlighting “the honesty and willingness to share facts”.
“We want technical expertise, absolutely, but also the right mindset and an understanding of how we do things in the UK. The Field Service supervisors are very specialised and that’s definitely a strength. Some of them have been coming here since the machines were built. They know us and they know the site.”
Kevin agrees: “You sense their genuine affiliation with the station. They understand every machine. This is a unique project and people really want to make it work.”
You sense their genuine affiliation with the station. They understand every machine. This is a unique project and people really want to make it work.Kevin Beaumont, Lead Mechanical Asset Engineer at SSE Peterhead
Soon it will be time to focus on the third outage. Tony acknowledges it will be a challenge for everyone – SSE staff as well as Siemens – to stay sharp. “We need to maintain the momentum, and that gets tough towards the end of the outage season. I hope the lads will get some time off before they return, because the human dimension – and the safety performance – is the most important of all.”
His message to the team? “Let’s achieve a 100 per cent record. And then we should celebrate as a group when we finish. So much effort has gone into this project by the outage team, and we should recognise their achievement before we all move on. It’ll be an important chance to say thank you, because it’ll be another four years and 25,000 hours before the team is together again.”
PETERHEAD FACT FILE
- Peterhead power station is a CCGT plant owned and operated by SSE. Situated in Aberdeenshire, it is the largest thermal power station in Scotland.
- Peterhead began operating in 1982. It was originally designed as an oil-fired station but the boilers were converted to also burn gas.
- In 2000, the station completed a major repowering project to increase its efficiency and capacity. Siemens won a £180 million contract to install three gas turbines which were used in an innovative manner to provide steam to one of the original steam turbines. It was the first re-powering of a major power station in the UK and increased the station’s efficiency by 50 per cent.
- In June 2018, SSE submitted a planning application to install a ‘black start’ facility at Peterhead.
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