Improving performance in rotating machinery
Published by John Williams,
Keeping important assets such as turbines, generators, pumps, electric motors and compressors in optimum working condition is an important step in maximising reliability and productivity.
Using expert advice and taking advantage of the latest maintenance techniques can deliver significant improvements in performance and reduced downtime for these large-scale pieces of rotating equipment - used throughout the hydrocarbon sector.
Harald Grossmann, Head of Service Contracts, Germany, at Sulzer, looks at modern maintenance techniques and their benefits for the hydrocarbon processing industry.
Hydrocarbon processing delivers hundreds of products that define everyday life. All the processes employed to create these essential products rely heavily on rotating equipment, so investing in the maintenance of these assets is an important step to preserving plant performance and efficiency.
Rerating pumps improves efficiency following a change in application specifications.
Refineries depend on thousands of pumps of all shapes and sizes to increase pressure and flow in many types of media and keep the complex processes moving. High temperatures and aggressive chemicals combine to create a very challenging environment that can cause erosion and corrosion, which lead to reductions in efficiency and productivity over time.
Changes in the flow or head requirements of a pumping application can also have a significant effect on energy efficiency and reliability. In some cases, without expert intervention, pumping assets can be damaged by cavitation erosion caused by the pump working outside of its preferred operating parameters.
The design of the impeller and casing can be modified to accommodate changes in the application and ensure optimum performance and efficiency. In some cases, alternative parts for older assets may not be available, but it is possible to take advantage of the latest scanning and CAD technology in combination with new manufacturing techniques to create one-off parts cost effectively.
Reverse engineering using laser scanners and additive manufacturing has greatly reduced the time required to create new components. Flow geometry can be checked using computational fluid dynamics (CFD) while 5-axis milling, and rapid prototyping techniques have delivered massive improvements in turnaround times.
The complex and varied equipment used throughout the hydrocarbon refining process all needs power, hence power generation equipment including steam turbines and generators is critical. Any process that involves gas streams is at risk from particulate fouling, caused by small particles in the intake media. Fouling can cause an increase in the surface roughness of the critical flow path components leading to a reduction in efficiency. This is a particularly serious issue where sticky hydrocarbon aerosols are constantly present.
In such an environment, the effects of the particle fouling need to be minimised and this can be achieved by applying specialised, anti-fouling coatings. These can be tailor-made to specific applications and consist of an aluminium base coat for corrosion protection, an inorganic sealer and a specialised non-stick top layer. The coating can be applied to turbines, pumps and compressors to protect both rotating and stationary blades, guide vanes, rotors and impellers.
Dynamic balancing of rotating equipment is essential following a repair.
As with many things, prevention is better than cure, and implementing a robust condition monitoring program is important in establishing the operational status of essential equipment such as compressors and high energy pumps. Vibration analysis can identify imminent bearing failure while thermal imaging offers an insight into poor electrical connections and any imbalance of phase loadings.
For large pieces of electrical equipment, especially high-voltage assets and those without full redundancy systems, testing of the electrical windings, especially partial discharge analysis, can provide important information on the overall condition of the machine and a projected lifetime. This information can be used to plan repairs and refurbishments, which can not only avoid any unplanned downtime, but often deliver design upgrades and improved efficiency.
Condition monitoring gathers and records operational and maintenance data to enable planned repairs to coincide with regular shutdown or outages. This allows new parts, such as windings and impellers to be designed and manufactured ahead of time, reducing project duration and improving reliability at the same time.
Electrical efficiency has a huge impact on running costs and legacy equipment can benefit significantly from improvements in electrical winding technology and correctly matching the equipment’s optimum efficiency performance parameters to the application.
Stator coils from legacy drive motors could have delivered decades of reliable service, but in that time insulation technologies have progressed significantly. Using enhanced designs, modern coils can be manufactured with thinner insulation, allowing a greater copper content compared to the original parts, reducing heat build-up and improving energy efficiency.
At the same time, matching the motor and the driven equipment, such as a pump or a compressor, is equally important. As processes evolve, so the equipment needs to change also; re-rating pumps to ensure they continue to operate around the best efficiency point (BEP). Such work requires specialist knowledge as well as experienced design and manufacturing facilities to deliver reliable and efficient assets.
Communication is improved with customer acceptance visits.
By looking at the wider application, maintenance staff are more likely to reach the root cause of an issue. For example, pumps are inextricably linked to the pipework and the performance of both the impellers and the pump seals can be affected by the design and installation of the pipes and valves. This becomes even more prevalent where high temperatures are involved, and thermal expansion factors must be carefully considered.
Within every hydrocarbon processing plant there is a wide variety of complex assets that need to be managed effectively to optimise performance. Reliability can be achieved by using a robust planned maintenance strategy that is supported by an experienced maintenance provider. Taking advantage of cutting-edge design and manufacturing facilities reduces downtime and delivers extended reliability and improved efficiency.
High capacity machine tools are essential for repairs to large-scale equipment.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/27092019/improving-performance-in-rotating-machinery/
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