Back in 2020, UK hydro-turbine manufacturer Gilkes was enlisted to refurbish components of a damaged 90-year-old Francis turbine situated at the New Lanark World Heritage Site along the scenic River Clyde in Scotland. Here we learn from Gilkes how the company pieced back together the turbine into a working machine, and why it was necessary to modernise aspects with up-to-date materials and components.  

What were the most significant challenges encountered during the restoration of the 1931 Boving twin runner Francis turbine at New Lanark Mills?

As with all modernisation projects there is an element of unknown until the equipment is stripped down.  

On this occasion when opening the turbine case it was found that key parts of the machine were damaged beyond repair.  A guide vane had badly corroded resulting in it hitting one of the runners, shattering the cast iron guide vane and damaging the runner. As a result, a large amount of refurbished and replacement components were required. However, because of the age of the machine, quality drawings, particularly of the runner and guide vane profiles, were not available.  The lack of drawings meant that we had to create new drawings and models.

How did Gilkes overcome these challenges with innovative or unique solutions?

Gilkes engineers carried out reverse engineering, including 3D scanning techniques, CAD modelling and machining using a five axis machine. To initiate the process of creating a 3D model, Gilkes performed a visual inspection of the two available runners to identify the one in better condition. Given the debris, corrosion, and damage to multiple blades, a decision was made to scan 180° of the best runner, with a focused scan on two blades with minimal visible damage. This strategic approach ensured accuracy in replicating the existing blade geometry.

The large size of the runner combined with the relatively small space between the blades presented challenges for the scanning process.  To overcome these, Gilkes employed various techniques, including the use of matt white paint to enhance laser projection, adjusting shutter speeds, and employing finer scanner movements. These measures were crucial in overcoming the challenges posed by the physical constraints of the scanning process.

The output of the scanning process was a mesh generated from the collected data points. Gilkes then utilized a combination of scan post-processing software and CAD software to create a 3D model from the surfaces developed from the mesh. The cleaning process involved removing small spikes, narrow gaps, and noise created during the scan, resulting in a base for blade profile sketches.

Given the thin blade thickness in some areas (as low as 1mm), Gilkes implemented a meticulous process to create a smooth and accurate blade surface. This involved producing a flow path of the meridional plane, capturing crown and hub profiles, and importing a scanned mesh of a single blade into the 3D model. The blade profile sketches derived from this process were used in a surface lofting approach, allowing precise control over contours and curvature. The final step included patterning the single blade 18 times and combining it with the crown and hub profiles to complete the 3D model.

How did these technologies contribute to the restoration process and the overall performance of the turbine?

The above techniques were used to create replacement parts, allowing the machine to be reassembled to a working state.  

The use of modern engineering techniques throughout this project enabled Gilkes to bring the machine back to life, whilst extending the lifespan of the equipment and reducing future maintenance requirements. 

The commissioning process, completed in June 2022, marked a milestone as the refurbished turbine now delivers approximately 12% more power. This enhanced output is directed towards powering the visitor center and hotel, with surplus electricity exported to the grid.

The decision to scan the runner played a crucial role in achieving these outcomes. By accurately replicating the proven runner geometry, Gilkes eliminated the need to develop a new runner design from scratch. This not only expedited the restoration process but also ensured that modern materials and parts were seamlessly integrated, contributing to the turbine’s long-term smooth operation. Importantly, the utilization of these modern technologies allowed Gilkes to address pre-existing issues that had contributed to the turbine’s catastrophic failure, effectively designing out those challenges.

Despite encountering various challenges throughout the project, including discovering initial damage, creating a new CAD model, and overcoming access and installation difficulties, Gilkes successfully delivered the project within a customer-acceptable timeframe. The refurbishment stands as a testament to the enduring link between New Lanark and the River Clyde, ensuring that the mills at New Lanark continue to harness the power of the river for generations to come. The modern engineering techniques not only resurrected a historic turbine but also positioned it as a sustainable and efficient source of power for the foreseeable future.

How did Gilkes ensure that the restoration maintained the historical authenticity of the 1931 turbine while incorporating modern materials and technologies?

By reusing the same turbine case and as much of the other remaining external components as possible, to maintain the overall heritage appearance.

Rather than replace all parts as per the original design, the decision was made to modernise aspects with up-to-date materials and components.  This approach offered improvements in performance and durability while maintaining the look and operation of the 90-year-old turbine.

Were there any specific considerations or challenges in blending historical preservation with operational efficiency?

Yes, following initial discussions that the project was to maintain as much of the original equipment as possible, allowance was made for certain components to be upgraded where this would enhance the operation of the machine. 

Hard-wearing, corrosion-resistant materials were not prevalent when the machine was initially designed in 1931. Seizing the opportunity to enhance longevity and reduce maintenance, Gilkes opted to replace some worn components with modern alternatives. Original components, such as guide vane supports and operating ring bearings, were prone to corrosion and wear. For instance, carbon steel guide vane supports rusted heavily, leading to the seizing of guide vane bushes. The operating ring bearings, separated by steel rollers, faced challenges related to limited access for relubrication, resulting in frequent seizing. Additionally, the original shaft bearings, constructed with white metal shells, posed concerns due to potential damage and extended replacement lead times.

The solution was to make much more use of stainless steel. This included guide vanes, shafts and operating ring parts. This would prevent the parts from corroding and seizing, however it did not remove the internal greasing issue. For this problem, the rollers were removed altogether and replaced with a stainless steel filler segment. This was then separated by a modern metal-backed polymer liner. The liner has excellent low friction and maintenance free properties which eradicated the need for grease within 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.  

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.

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.