Air Seal Stops Pulper Leakage
EP Editorial Staff | April 8, 2020
An air seal is at the center of a new pulper configuration that eliminated 20 hr. of annual downtime.
An upstate New York paper mill had an ongoing problem with a leaking pulper. Similar to other pulpers, it had significant shaft runout caused by uneven distribution when paper bales were dumped into it. Many mixers, agitators, and pulpers experience similar shaft leakage. The material weight in the bowls and any other movement, cause packing movement, contamination, and premature failure. If mechanical seals are used in these applications, the same movement, the abrasive stock mixture, contamination, and shock damage the seal faces, again causing premature failure.
Impact of the problem was significant and included:
• paper stock losses, housekeeping issues, and stock disposal
• gearbox-oil contamination
• frequent packing replacement
• belt and shaft wear
• safety issues
• eventual gearbox and shaft replacement
• downtime with lost production.
The pulper leakage was nonstop. The mill’s team estimated the yearly loss at $100,000. As tolerances were affected more by the movement and related shaft wear, losses would only increase. The stock also had to be cleaned up and sent to a disposal service. In addition to the housekeeping labor costs, disposal costs were about $25/ton.
The packing that sealed the pulper was ineffective. To some extent, it helped minimize shaft movement, but it also trapped pulp, which then wore the shaft. The on-site team replaced the packing every three months. The pulper was down for 5 hr. for every packing change.
The gearbox, located below the pulper, also became a victim of the leaking. As the stock fell on it, lubricating oil became contaminated with water and stock particles. The maintenance team estimated that they used about 5 gal. of oil weekly to replace the contaminated oil. Though an oil seal was in place, the contamination breached the seal. As the pulp fell onto the gearbox, it also contaminated the drive belt on the gearbox. The wear resulted in belt replacement, including the cost of the material, labor hours, and downtime.
Because the pulper was installed in a vertical orientation, there was limited workspace and performing the frequent maintenance was difficult and dangerous. Personnel worked in a contaminated space that was essentially full of pulp slurry.
The ongoing damage from the leakage eventually resulted in the need to replace the gearbox. Because of the equipment’s size and orientation, this was a major operation that required a crane to lift and position the components. Clearly, a solution was needed.
The mill team replaced all sealing technology, instead of one item at a time. To seal the pulp process, packing was replaced and two solutions installed in the pulper stuffing box. First, a tight-tolerance, split-cylinder bushing made of bearing-grade PPS was installed to stabilize the shaft. This provided support, especially when paper stock was dumped into the bowl.
The team then installed a SEPCO, Alabaster, AL (sepco.com), noncontact air seal in place of the packing follower. The seal uses air to create a pressure differential between the product and the environment. It completely contained the pulper with zero leakage. The seal also withstood some shaft movement, adding to the protection during stock dumping.
In addition to this seal technology combination, a true noncontact, compound labyrinth bearing isolator was used to replace the existing oil seal in the gearbox. The isolator has a vertical orientation that provides lubrication protection during static and dynamic conditions.
The goal with the bearing isolator was to stem the contamination that caused the failure and ultimate replacement of the former gearbox. It succeeded because of the redundant system of expellers and vertically oriented expulsion chambers backed by static coalescing O-rings that further break down contamination. The configuration formed an effective seal to protect the lubricant and the bearings. EP
For more information, visit sepco.com.