|Siemens and Drax have worked together in a five-year modernisation programme now being completed at the UK’s largest power plant Source: Siemens|
Drax power station is poised to complete what it claims is the largest steam turbine modernisation programme in UK history. The UK’s largest power plant ” which produces 7 per cent of the Britain’s power and has a capacity of 4000 MW ” is putting the finishing touches to replacing all six units at its site in Yorkshire, in the north of England.
The five-year project cost à‚£100 million ($156 million) and will see Drax cut its carbon emissions by 1 million tonnes a year. Drax burns 10 million tonnes a year of solid fuel, of which 1.3 million was biomass last year, making Drax the UK’s largest single renewable generator..
Siemens was awarded the contract to replace the low-pressure (LP) and high-pressure (HP) turbines, and made the parts at its manufacturing centres in Newcastle, UK and Muelheim an der Ruhr in Germany.
The turbines consist of 28 separate turbine rotors, which together weigh more than 2800 tonnes. Each has 80 000 individual turbine blades, which, laid end-to-end, would stretch 42 km.
Drax production director Peter Emery says the company takes “our responsibility to cut carbon emissions seriously and this project marks a significant milestone in our efforts to do that”.
|Peter Emery: this turbine project marks a ‘significant milestone’|
He explains that the decision to go ahead with the modernisation was taken because “it became clear to us that climate was becoming business critical. When we floated the company investors were not too interested in carbon emissions. That has changed.”
He adds that Drax’s high visibility in Yorkshire ” where it covers 750 hectares ” increases the plant’s environmental obligations to its region. “We can be seen for miles around so it’s important that we are viewed as an asset to the neighbourhood”.
Emery, who joined Drax in 2004, claims that the à‚£100 million investment “demonstrates our continued commitment to delivering leading operational performance. The completion of this project makes our turbines amongst some of the most efficient in the world.” He also praises the “excellent collaborative relationship with Siemens in Newcastle and Germany”.
Steve Austin, lead turbine engineer at Drax, said Siemens was chosen because “we wanted someone with a credible record, someone who shared our vision and somebody who knew our turbines”. But he admits the choice presented challenges. “It was a little bit tense at first until we started to trust each other.”
Darren Davidson, head of projects at Siemens Newcastle, agrees: “I wasn’t 100 per cent convinced it would work but I thought it was worth a try.”
As time went by, though, Davidson was won over. “Over the past five years, each unit has been delivered successfully and on schedule. We have worked with Drax from the start of the tendering phase, helping to bring to light issues relating to the sustainability of the plant, and together during the project execution work to deliver improvements in design through to installation to achieve project objectives.”
Throughout the process, “the whole team has demonstrated excellence”, he adds. Conflicts of opinion have also been resolved in unconventional ways. The best example offered by Austin and Davidson came from Siemens’ desire to use Chinese blades for the turbines.
At first, Drax said no: it was specified in the contract that the supplier should be European. But Drax agreed to travel to China with Siemens and the two companies then spent six months validating the Chinese manufacturer. Austin now concedes that Siemens’ faith in the Asian supplier was justified: “By the time we’d finished, the quality was better than some of our other manufacturers.”
HP turbine: The upgraded turbine units supplied were of full arc throttle control design as a retrofit inner module designed to fit into the existing HP outer cylinder. The modules include:
- New inner cylinder giving superior creep strength to original cylinder and designed to interface with existing outer casing;
- Single un-bored monobloc rotor with enhanced material properties;
- Modern 3DS reaction blading;
- Upgraded sealing technology to help longer term performance;
- Re-designed steam inlet sealing arrangement;
- Re-use of existing outer casing, shaft gland housings and journal bearings.
LP turbine: The LP turbine upgrades are of a double flow design having an exhaust area of 8 m2 and were developed to maximise performance at minimum capital cost. The existing exhaust casing was retained to reduce site installation time and costs. The original impulse design was replaced with reaction blading. Features consisted of:
- Fully bladed monobloc rotors with enhanced material properties;
- Modern 3DS reaction blading in first four stages;
- L-0 blades of free standing side entry root design;
- Retention of original low pressure casing;
- New stationary blade carriers located in existing diaphragm grooves;
- Optimised inlet and exhaust flow areas;
- Redesigned radial clearances and sealing;
- Re-use of existing LP shaft seal housings and journal bearings.
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