Outokumpu Stainless Limited manufactures stainless steel prime products at their SMACC facility in Sheffield. As part of the process fume extraction from the plant is essential to ensure health, safety and environmental conditions are met. The extraction system is built around four 2.5m Double Inlet Double Width (DIDW) aerofoil bladed fans pulling 520,000cfm each with 1.2MW Variable Speed Drive (VSD) motors.
The fans are operating at temperatures of up to 130oC, and are installed upstream of the main filter plant, so the fans are exposed to dust being extracted from the plant.
Outokumpu carry out regular maintenance and repair on the fans, and during these inspections it was identified that both the impeller and the inlet cones to No 4 unit were excessively worn and possibly uneconomical to be repaired, therefore a replacement fan unit was scheduled.
Based on the decision to replace the impeller, Outokumpu were keen to develop current technologies that would improve value in service and not just a like-for-like replacement. They wanted to have a fan with the improved ability to resist the dust, giving the benefit of improved reliability, performance and reduced costs.
A number of fan companies including Halifax Fan were asked to tender for the project including all installation aspects of the scheme. The high particulate nature of the gases meant that special consideration had to be given to the wear characteristics of the impeller blades and long-term reliability was very much written into the specification.
To address the wear on the impeller, Halifax Fan carried out a detailed on-site survey into the fan geometry, noting existing protection and wear patterns, and used this information to create a direct replacement suitable for the application. As is typical of large fan contracts, Halifax carried out a detailed Finite Element Analysis (FEA) of the impeller. This included assessment of the effect of the wear protection solution on the impeller integrity and life.
To enhance the impeller’s wear characteristics, it was concluded that tungsten carbide was the most suitable material as an overlay for the hardest working wear plate areas of the impeller. With the design confirmed, the next step was to manufacture the impeller, shaft and inlet cones. As Halifax Fans are an international company, a decision was made to exploit the experience of their different operations in the manufacture of the impeller. This resulted in key component manufacture being distributed within the group. They proceeded with the impeller manufacture at their Akron, Ohio (USA) facility, with the manufacture of the inlet cones in the Brighouse UK facility and the manufacture of the new shaft with a local UK supplier. The logistics of this collaborative operation was handled by their Brighouse team.
The impeller was manufactured and balanced prior to assembly onto the main shaft, the assembly operation being carried out by their Brighouse employees. Such was the quality of manufacture that no further balancing was required. The rotating assembly was installed on-site with bearing vibration measurements of only 1.3mm/s RMS, well within the tolerance requirements for a new fan. This was in no small part due to the experience of Halifax’s Large Fan installation team in carrying out rotating assembly replacements of large fans.
Outokumpo’s Capital and Plant Engineer, Charles Bradley-Smith said
We hadn’t known Halifax Fan before the tendering process but were keen to find a new quality supplier that broadened our choices. The company was vetted very thoroughly and only when we were satisfied that they could offer a quality product and meet our tight operational deadlines, did we proceed with the tender process for the replacement impeller. Halifax Fans met all our expectations and the fan is now fully commissioned supporting the melt shop operations. It will be some time before we can fully examine the impeller unit, to determine if the chosen materials do in fact provide the necessary protection to the impeller in what is a very harsh environment. A key deliverable from the scheme is to minimise plant outages, reduce operational and maintenance costs and to improve overhaul plant efficiency and reliability
Halifax is confident that they have achieved this through a combination of design, manufacturing and installation experience. This is very much in-line with Halifax Fan’s aims of Quality - Reliability - Efficiency.
