As the maintenance group responsible for all assets in the chemical processing plant, Sitech Manufacturing Services has to ensure ongoing productivity and continued operations in a very competitive market. Proactive maintenance schedules and planned upgrades allow the company to deliver reliability and cost-effective production. In a recent project, Sulzer was called in to offer its design expertise and provide a retrofit solution to overhaul three bad actors that continued to present issues that the OEM was unable to resolve.
Within the vast array of equipment at the processing facility, three pumps, which were originally installed in 1968, are tasked with the onerous job of pumping the ammonia feedstock for the production of nitrogen fertilizer. Two of the between-bearing design, type BB3, twin impeller axial flow pumps are powered by steam turbines and one by a fixed-speed electric motor. In addition to this, an extra pump is kept as a spare.
From the outset, the pumps have suffered from poor reliability, with a mean time between failure of around 12 months, which has incurred high maintenance costs for the plant. The engineers had to deal with high vibration, excessive wear and broken impellers, all of which were causing a loss of performance and annual maintenance costs of around EUR 150,000.
Over the years, several design changes and mechanical improvements have been made to the pumps. In 1996, due to the corrosion that was also being experienced, the OEM suggested all the internal components were changed for parts made using Super Duplex stainless steel.
However, the material change did not address the inherent design issues, and the pumps continued to suffer from jammed wear rings, damaged impellers and excessive wear. The resultant loss of performance and high maintenance costs continued to cause issues, to the point that the pumps were identified as a major cause for concern in the nitrogen process.
Sulzer became aware of the issues being experienced with the pumps and offered to provide an engineered solution that would deliver long-term performance and reliability. Having appreciated the benefits that Sulzer could deliver, Sitech Manufacturing Services supplied the spare pump to the local service centre in the Netherlands, as the impeller was broken and the pump needed to be repaired.
The retrofit process was preceded by a root cause analysis to determine the weak points in the existing design, and enabled Sulzer to establish the best solution for this application.
The first step was to use a laser scanner to create a precision model of the entire pump. Once this was complete, the design work could start on the new impellers and driveshaft. Sulzer’s high-energy pump experts in Leeds supported the project with their extensive equipment knowledge and application experience.
Starting with Sulzer’s own BBT-D pump design as a reference, the engineers focused on the impeller characteristics as well as the wearing parts, which required improved durability. Once complete, the plans were sent to the manufacturing site for this project in Germany, which created the new impellers and shaft.
Ben Lauwerijssen, regional sales manager, Benelux for Sulzer explains: “Back in the Netherlands, the pump was reassembled with the new components before being tested for performance. Once complete, the pump was returned to the chemical plant where it was installed, commissioned and found to run very smoothly. In all, the whole project was completed in 20 weeks.”
Having identified these pumps as a source of concern in the manufacturing process, two more pumps were also scheduled for the same improvements and now, only one pump remains to be completed. The retrofits have been a considerable success and the first has now delivered faultless reliability for over six years, confirming that Sulzer could deliver all of the improvements that were promised.
Frank Sleijpen at Sitech Manufacturing Services concludes: “The continued vibration monitoring has shown that Sulzer’s design modifications have not only greatly improved the MTBF, but readings are significantly lower than those for the original pumps. This is a good indication of continued performance and long-term reliability, which will continue to save the company money year on year.”