several times each year. Likewise, the company supports and participates in a number of organizations, which monitor constantly changing regulations and compliances, and which also participate in EPA and industry quality control audits throughout each year.
When lime leaves the recovery boiler, it is in a sludge-like state. This lime “mud” is sent to a lime kiln where, in a complicated chemical reaction process, quick-moving combustion gases provide heat as high as 1200° F to remove moisture. The dried lime is returned into the papermaking process. As with other kraft mills, induced draft (I.D.) fans suck air through the kiln and into the scrubbers. In the case of Port Townsend, a 10-ft diameter fan is used.
According to Terry Rohring, maintenance planner
at Port Townsend, “With lime dust in the air and high
operating temperatures, lime kilns need to be taken
care of. These issues can lead to problems that can get
out of hand if not watched. This is especially impor-
tant as lime kilns are such an integral part of the kraft
papermaking process that when a lime kiln is down for
repairs, the entire mill may have to be shut down. And
the biggest problem we had was bearing failure from
contamination. This is a problem we had for years.”
The bearing contamination problem tied into the
lime dust and the need for a long-lasting means to
protect the fan shaft bearing. The bearing assembly
for the fan shaft is a hydrodynamic bearing type to
accommodate the high heat. Due to the close proxim-
ity of the bearing to the fan housing seal and the lack
of an effective, long-lasting shaft seal, lime dust would
leak through the seal and enter the bearing housing
over a relatively short period of time, eventually burying
the pillow block in lime dust. Worse, the lime dust was
allowed to migrate around to additional equipment
(electric motors). In other words, Port Townsend was
dealing with an unpredictable 100% failure rate. What
they needed was an effective, long-lasting shaft seal that
could hold up under their harsh operating conditions.
INEFFECTIVE SEALING METHODS
With lime dust in the air
and high operating
temperatures, lime kilns
need to be taken care of
“Over the years we tried all types of sealing methods,” Rohring continues. “Until we installed Inpro/Seal’s Air Mizer™, nothing worked. The original OEM seal that came with the lime kiln failed many years ago. Over the years, I know my predecessors tried many types of seals. In a search for a solution, we developed our own sealing system consisting of a box, an air nozzle, an aluminum impeller and a sealing device.
“Though better than what we had, it still was not the solution. Even with our own design, we still needed a means to keep lime out of the fan housing. We tried a number of sealing methods, but our high operating temperatures and axial shaft movement made them ineffective and only temporary. Packing did not last, as they would compress and create a leak path. Plus, it would soften to the point where it could leak. Adjustments to the packing were only temporary. Any type of seals that used elastomers would not last either, due to the high temperatures. Contact seals were subject to wear and so were also temporary solutions.”
When lime kilns need maintenance, it is not a simple on-and-off process. Because they work at such high temperatures, they need to be cooled down for at least 24 hours before any maintenance can be performed. Then, to return to operation, another 24 hours are required to heat back up again. Add in the time needed to replace the bearings and one can see
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