In-Line Filter Eliminates Unwanted Oil
Our CHDA (1,4-cyclohexanedicarboxylic acid) production plant
experienced a significant decrease in conversion efficiency due to oil
contamination of a fixed bed reactor catalyst. The source of the oil proved
to be a pneumatic convey system blower. A specialty filter was installed
to prevent the possibility of future catalyst contamination.
After noticing
the decline in conversion efficiency of the reactor, samples of the used
catalyst were analyzed and found to be contaminated with oil. A process
review yielded several potential sources, which were narrowed down by
inspection. The culprit turned out to be a pneumatic convey blower used
to transfer
PTA (purified terephthalic acid) from dry bulk pneumatic trailers to
a mixing tank. Oil was found coating the inside of the discharge piping
of
the Roots rotary lobe blower, and had contaminated the PTA as it was
conveyed from the trailer to the tank.
PTA
Unloading Blower Package The area lubricator
confirmed that he had been topping-off the
oil reservoir on the blower for several months due to low oil levels. A
review of the CMMS system revealed that the blower had no maintenance
performed on it in the last 8 years. The blower was removed from service
and replaced with a spare. Teardown of the blower showed that the mechanical
seals which separate the oil-lubricated bearings from the process gas side
of the blower had leaked allowing oil to enter the process gas side of
the blower.
Because the cost to change out the catalyst exceeded $150,000,
area operations management wanted a solution that would prevent this
from happening again. Alternatives included a close-coupled
regenerative
blower with permanently sealed bearings, a different lobe-style positive
displacement blower with improved seals, and a filter to capture any
oil leakage that might occur.
Filter
Installation The most cost-effective solution
from a life
cycle cost standpoint proved to be the use of a ZC filter from Rail
Barge Truck Services. The filter has a 1-micron rated media that will
handle
the 800 cfm of hot 20 psig nitrogen with very little pressure drop
and is advertised to capture 100 percent of hot oil or oil mist from
blower bearing
or seal failures. We also initiated a preventive maintenance program
for the blower that includes monthly vibration readings, periodic oil
changes and inspection for leaks, and filter inspection. In addition,
all area
lubricators have been informed to notify maintenance when they notice
equipment requiring abnormal oil replenishment.
Installation of the
filter involved
a simple change to the blower discharge piping, and a differential
pressure gauge was installed to allow operations to monitor the filter
element.
Cost of the filter was less than $1,000, with the total project costing
approximately $3,000. No contamination has been found in the discharge
since the filter has been installed.
By Kevin G. Bellamy, PE, Principal Reliability Engineer,
Eastman Chemical Company
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