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Turbine revision returned the guaranteed efficiency values

C A S E Jyväskylän Voima Oy

The operating hour-based annual maintenance took

a surprising turn when major damage requiring major

repairs was discovered in the rotors of the high-

pressure (HP) and intermediate-pressure (IP) turbines.

The ten-week project extended to nearly seven

months, but in the end, the machine was started

precisely on the agreed date, and the total expansion

efficiency of the turbine increased by more than 4%.

Alva-yhtiöt Oy©

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The Keljonlahti power plant, commissioned in 2010, is a biofuel power plant in Central Finland, which produces electricity and district heat for the Jyväskylä area. The plant’s fuel power is 500 megawatts, maximum net electric power 210 megawatts, and district heating output 260 megawatts. Wood is used as the main fuel, and peat as an auxiliary fuel.

An overhaul that would involve opening the turbine had already been planned in Keljonlahti since 2015, when certain irregularities were detected in the behaviour of the turbine. Among other things, the vibration measurements and bearing temperatures of the IP rotor were alarmingly high. A misalignment had also already been detected before the periodic maintenance, which was subjected to competitive bidding in late 2018.

Fortum eNext met the requirements of the public bidding and offered the best total price for the work. In only two weeks, the parties proceeded from bidding to negotiations and signing the contract in early 2019.

The assignment consisted of a regular operating hour-based overhaul involving opening the turbine. The unit was dismantled and inspected, its parts were cleaned and repaired where necessary, and finally, the unit was reassembled. Based on the known problems, the assignment also included the balancing of the IP rotor and realignment of the pedestal. Both parties also wished to identify what was causing the turbine’s unusual vibration behaviour.

The project began with dismantling work at the beginning of April, and the entire revision was to be completed by the end of June. However, problems arose in the early stages of the project, when an attempt was made to open the turbine, and its parts could not be removed as usual. Once the IP turbine had been opened, it was already clear that the damage was larger than anticipated, and the overhaul would be significantly prolonged.

As many as 80% of turbine overhauls uncover something surprising.

As the dismantling work progressed, damage requiring major repairs was discovered in the rotors of the HP and IP turbines. Some of the blades had become loose, and deformations were detected in some of the blades. Some seal strips had stuck and become damaged.

While some damage had been predicted, the overall scope of the damage came as a surprise.

”The behaviour of the turbine gave us reason to believe not everything was in order, but we needed an expert to point out all the damage and different types of faults. In any case, the damage had greatly affected productivity; since the overhaul, the total expansion efficiency of the HP turbine has increased by more than 4%”, says Toni Hult, the Maintenance Manager of the Keljonlahti plant.

Turbine revision returned the guaranteed efficiency values

The first weeks did not go as planned

The rotor blade maintenance work was unplanned additional work, which was promptly initiated. Fortum eNext provided descriptions of the damage and recommended measures that should be taken to repair them.

“In our experience, as many as 80% of turbine overhauls uncover something surprising. We apply a technical and customer-based approach in our operations. We do not easily recommend replacement of the entire machine; instead, we work with our customer to find solutions that will repair the faults but keep the costs reasonable”, says Vesa Kylmälä, who is in charge of Fortum’s turbine and generator maintenance service business.

The planning of the repairs and the preparation of the repair plan were initiated immediately through good collaboration between Fortum’s experts and the Keljonlahti plant’s own personnel. The project schedule was updated on 20 June, and 28 October was agreed as the new start-up date. The original ten-week project extended to nearly seven months.

Once a picture of the situation had been outlined and the repair plan drawn, the work progressed without interruptions throughout the summer and into the beginning of the autumn. The rotors were taken to Naantali to be re-bladed and repaired at Fortum’s own workshop specialising in turbines.

The same people should be present at the opening and during the assembly to prevent information gaps.

At the plant, the number of personnel at the site was decreased during the summer, but work was not suspended. Instead, the time was used to conduct clearance measurements, disk fittings and other types of work that could be performed without the rotors. Once the first rotor was returned to the plant, the workers could continue with the actual fitting of internal parts and assembly.

In the maintenance of the HP turbine rotor, one option would have been to re-blade the entire rotor.

“Our solution was to only repair the damaged parts and the cause of the damage. We ended up replacing three stages completely, and we replaced seven to nine blades in five stages. We implemented the realignment of the unit by adjusting the basement springs, which is a very unusual way to carry out alignment work”, says Fortum eNext’s Project Manager Ville Paakkonen.

Overall, the entire project was extensive. Alex Schreckenbach, who is in charge of operations at the Keljonlahti plant, says that he particularly appreciates the fact that the project was completed on schedule and delivered on the previously agreed dates, even though it consisted of several partial deliveries and included many challenges and surprises.

“The fact that Fortum was able to repair such major damage within such a short time really proves its strong expertise and flexibility. The delivery and repair times could have been three or four times longer, and that still would have been acceptable. Given the duration of the project and the extent of the repairs, I consider this to be an excellent performance”, he says.

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Start-up exactly as agreed – expertise combined with historical information guaranteed success

The duration of the project tripled

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One important factor contributing to the success was that the same people worked at the plant throughout the project, which extended from weeks to months.

The project was completed on schedule despite the fact that there were many challenges and surprises along the way.

“The plant’s personnel know the history of the plant, and we provide the experts. The same people should be present at the opening and during the assembly to prevent information gaps. This was ensured in the project. Good cooperation is also needed”, Ville Paakkonen describes the project.

The protection system tests were completed in June in accordance with the updated schedule, and the start-up was performed on 28 October 2019 as agreed – almost to the hour.

“The start-up after an overhaul as large as this is always more or less a mystery. The start-up is when we get the final confirmation on whether the decisions made during the project were the right ones. In this case, they were, as the start-up went really well! For me, it was the highlight of the project”, says Toni Hult.

One week after the start-up, it was detected that some control valves were stuck, and the machine had to be shut down. The cause was found to be the seal material of the stuffing boxes, which was the right material according to the drawings and parts lists, but did not actually fit this location. The turbine was shut down and detached from the boiler process for the duration of the four-day repair work. Throughout the repair work, the plant was able to meet its district heat production target without burning coal. The valves were repaired by replacing the seal material, and no problems have been detected since.

Before the maintenance, the plant had been forced to set restrictions on the use of the turbine, and it could not perform a full back-pressure run. Due to the power range and running mode restrictions, the plant produced condensate power, even though the price of electricity was low. It had also been forced to slow down the rates of change of loads because of the turbine’s vibration problems.

Back to guaranteed values

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Since the overhaul, it has been possible to operate the machine without any power range or running mode restrictions. The turbine has operated normally throughout the heating season, and the plant has again reached its guaranteed delivery values.

“I must say that the turbine seems like it’s brand-new. The turbine runs very smoothly, and you can sense this in the turbine hall and everywhere at the plant. The feel in the turbine hall is completely different than what it was before the maintenance”, Alex Schreckenbach says happily.

Both Alex Schreckenbach and Toni Hult emphasise the importance of cooperation and openness in the success of the project.

“I have been involved in many projects, and this was the smoothest of them all. Throughout the project, we worked on the problems and tried to find solutions together. We never found the supplier to be simply dictating our options without hearing us, which does sometimes happen. We became familiar with the Fortum people and could work with them directly, which is not always the case either”, Toni Hult says.

“Our smooth cooperation played an important role, as did Fortum’s ability to view the situation from the customer’s perspective and their genuine understanding of the importance of turbine maintenance to the customer’s business and its overall cost. I had already had positive experiences working with Fortum, and this project significantly reinforced my confidence in the company. They made us feel we were an important customer and that they genuinely wanted to serve their customer’s best interests in the best possible way”, Alex Schreckenbach concludes.

Smooth co-operation played an important role

“‘I would describe the project as a masterful performance: the schedule was redrawn in June, with the parts still undelivered, and four months later, after major repair work, the turbine was started exactly on the agreed date of 28 October!” Toni Hult, Maintenance Manager at Keljonlahti plant

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For further information, please contact:

Teemu HeinonenSenior Product Manager, TurbinesEmail: teemu.heinonen@fortum.comTel: +358 50 454 2134

Customer challenges Solution by Fortum eNext Customer benefits

Conducting regular time-based maintenance for the turbine

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Operational and power limitations due to several issues:

Higher than normal vibration levels

Higher than normal bearing temperatures

Pedestal misalignment

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Initially agreed scope:

Turbine overhaul based on operating hours, including disassembly of the unit, inspections, cleaning the parts and repair if needed, and final assembly

Aligning the pedestal

» Turbine efficiency improved by 4%»

C A S E Jyväskylän Voima Oy

During the overhaul:

Prompt diagnosis of the discovered damages and clear recommendations on actions to be taken

Replacing damaged blades at Fortum eNext’s dedicated turbine workshop in Naantali, Finland

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Regaining full capacity and operational capability – no more limitations to power levels or operational modes

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Scope of works adjusted to cover the exact customer need in a cost-conscious way

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CustomerJyväskylän Voima Oy, Finland

SiteKeljonlahti CHP in Jyväskylä,

Finland, producing electricity and heat for the surrounding community

Prompt and timely delivery – extended scope covered within a short time frame, including production ramp-up according to agreed schedule

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Plant type: combined heat and power (CHP) production

Fuel: 60% wood-based biomass, 40% peat

Boiler: Foster Wheeler

Turbine-generator: LMZ

Commissioned in 2010

Fuel power 500 MW