John Crane’s Warren Smith, mining market director, and Steve Taylor, mining market segment manager, Canada, discuss how customers can improve reliability, bottom line, and water reduction with the latest evolutions in sealing technology.
Warren: There are multiple options for sealing slurry pumps. We find that the geographical location, and economic and environmental issues play a key role in choosing the best option. Spray Nozzle
Packing remains the go-to solution for sealing slurry pumps that both the pump OEM (Original Equipment Manufacturer) and the operators embrace. Today’s mine operators can choose from third generation packing technologies through engineered heavy-duty single and double slurry seals. Packing and mechanical seals offered today are constantly evolving to meet the economic and environmental issues operators face.
Warren: Packing yarn technology is constantly changing. We have moved away from first generation base yarns like cotton, jute, and flax, which typically include PTFE and graphite, as the sacrificial lubricant or graphite packing consumes high levels of energy and requires a leak rate of up to 60 drops per second per inch of shaft outside diameter for cooling and lubricating. This means a typical 30-mm or five-inch shaft would need to leak at a rate of 300 drops per second.
With second generation yarns, we saw the introduction of both Aramid (Kevlar) and ePTFE (gore fiber) packings in the market and still play an important part in our packing portfolio today. Now, our go-to products would be carbon yarns and graphite yarn packings, possibly even supported by hybrid technologies. We can combine packing styles to offer solutions that reduce shaft wear, energy consumption and solutions that leak as low as eight to 10 drops per outside diameter inch of shaft.
Steve: The single biggest sealing technology option available to the mining industry to improve pump reliability and the bottom line is to upgrade mechanical seals on the pumps that are critical to operations and require elevated levels of maintenance. Filter feed and tailing pumps are typical examples. By simply transitioning from gland packing to mechanical seals, mining operations have been able to do away with daily and weekly maintenance schedules on tailing lines and run uninterrupted for 12-18 months, or even enjoy multi-year runs on the filter feeds. This results in significant maintenance cost savings, reduced equipment downtime, and potential water savings. In some cases, this can save 120 L/min per pump.
Steve: Mechanical seal technology relies on a very thin film of lubricant between a rotating and stationary set of flat wear faces. Whether lubrication is provided by the fluid being pumped or by an introduced liquid, the consumption of this medium is extremely low. It is this set of faces that prevents what is inside a pump from escaping into the atmosphere. Along with these faces, there are support components such as springs, O-rings, and drive mechanisms that all work together to allow the seal to do its sealing job. Correct design choices and proper engineering can minimize or eliminate the need for external fresh water.
Steve: There are a few general observations about how slurry pump design may affect mechanical seal performance.
> Sleeve material: It is standard practice to replace the old worn packing sleeve when you are converting to a mechanical seal. It is important that your seal supplier knows about the sleeve material, including what the material is made from.
> Slurry pump wear liners: Many slurry pumps allow for an open or closed liner in the area between the mechanical seal and impeller. Deciding which type should be used for the best seal reliability varies depending on the specific seal and application. Physical space requirements, erosion effects, heat removal and water use are all factors that should be discussed between the mine, the pump OEM, and the seal manufacturer.
> Impellers: The importance of choosing an impeller depends on the specific application and should be discussed between the mine, the pump OEM, and the seal manufacturer.
Steve: It is recognized that a typical seal specification requires tight equipment tolerances, but we also know that slurry pumps are rugged and require the surrounding equipment to be strong as well. Slurry seals are tougher and more forgiving than refinery seals, but we would like to see dial indicators used and a fresh set of bearings for the initial installment. Barrel alignment and the pump frame being square with the shaft are important.
Another factor for consideration is whether the pumps are being routinely adjusted or not touched again until the next overhaul. Well-designed slurry seals can handle a lot of impellers adjusting, but it is important to know about them before settling on a final seal design.
Steve: While the goal is to reduce water use, preferably to zero, there are many times insignificant amounts of water are needed to maximize seal reliability. Part of the seal application procedure is finding out upfront what water, if any, is available and how reliable it is. Unique designs and materials have unique needs, and it is important to keep the primary goals of improving reliability and decreasing water use at the forefront.
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