Maintenance & rehabilitation | the machine. The opportunity was also taken to
replace the bushings in the guide vanes with a grease free alternative, further reducing the maintenance required.
Above: Old and new runners
Since a new shaft was being manufactured, it was the perfect opportunity to redesign the machine to have modern rolling element bearings. The bearings selected were standard off the shelf products with much shorter lead times. Cost is also important, and the price of a replacement bearing is less than the cost of re-metalling the old bearing shells. Pillow block housings and adapter plates were selected and designed to allow the reuse of existing pedestals. The new bearings were self-aligning, which was important to allow for any misalignment and shaft bending. The new bearings also have reduced maintenance requirements.
Below: Lowering runners and shaft assembly into the shaft
Acknowledging the unique challenges posed by the turbine’s design, particularly the long, slender shaft, Gilkes conducted Finite Element Analysis (FEA) to assess potential bending. Concerns about contact between rotating and static components prompted the need for a detailed analysis to determine minimum clearances. The analysis informed an efficient design that balanced clearances to prevent contact while maximizing power generation and efficiency. The original turbine runners, with 3mm thick
sheet metal blades, required thoughtful redesign when machining new runners from solid blocks. To ensure both historical accuracy and performance, Gilkes utilized Computational Fluid Dynamics (CFD) analysis. Adjustments to blade thickness and leading- edge profiles were made, resulting in a 0.5% increase in maximum turbine efficiency, as predicted by CFD. Furthermore, CFD was employed to map the
expected turbine output across a range of flow rates, providing insights into operational variations. This mapping allowed Gilkes to confidently proceed with commissioning, ensuring the turbine’s robust performance under different operating conditions.
Can you walk us through the step-by-step process of dismantling, refurbishing, and reinstalling the 90-year-old turbine within the constraints of an 18th Century building? Gilkes arrived on site during January 2021 to dismantle the turbine, discovering the guide vane mechanism had so much wear that a guide vane had come into contact with a runner, damaging the runner and guide vanes beyond repair. A lot of internal components had corroded and seized. This meant that the turbine would require additional components including new guide vanes, guide vane mechanism, turbine shaft, runners, and refurbished chambers. Following the initial site assessment, Gilkes returned
to site in October 2021 to remove the remaining failed components including the 5.5m shaft and runner assembly in one piece. The equipment was crane lifted out of the access hatch with the use of temporary scaffolding to help with lifting operations. Only the empty shell of the case was left on site. Once removed full inspection could take place at our workshop to enable a condition assessment report to be compiled. Once the equipment was remanufactured and ready for installation, the reverse installation procedure was carried out. The turbine is installed in the basement of mill number 3. When the turbine was modified to power a generator, a new access hatch approximately 4m2
was built on the side
of the mill to provide access to the turbine hall. This proved problematic for removal and delivery of turbine parts, in particular the shaft assembly, complete with pre-installed runners. Due to the assembly length, it required a complex two position lift utilising both the turbine hall crane and a lorry mounted
crane.All parts were successfully lowered in without a scratch, the order being critical as space below was limited. As the turbine was out of commission at the time
Gilkes became involved, there was no requirement to decommission the existing equipment.
How did the initial contract in 2020 evolve, and were there any changes or additions to the scope of work throughout the project? The project was Initially a smaller scope of work, following an approach by the consultants for Gilkes to assist with the mechanical refurbishment. Following on from the initial strip down an early warning was raised with the customer / consultant. The project was then put-on hold until the mill owners decided what to do.
Following a review of the project with the Scottish government, an extra grant was given to cover the extras required to complete the project.
14 | February 2024 |
www.waterpowermagazine.com
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