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Couplings, Seals, Gaskets
News Release from: Meco Shaft Seals | Subject: Meco custom-engineered shaft seals
Edited by the Processingtalk Editorial
Team on 11 January 2005
Shaft seals stop solvent leaks in oil
mill
A soybean oil extraction plant reports a marked reduction in hexane loss after replacing the packing glands on its extractor, feeder and discharge screw shafts with Meco custom-engineered shaft seals
A soybean oil extraction plant in Alabama reports a marked reduction in hexane loss after replacing the packing glands on its extractor, feeder and discharge screw shafts with custom-engineered shaft seals from Meco The process at this soybean extraction mill is typical: soybeans are ground to a fine pulp known as miscella and mixed with hexane, which causes the oil to be separated from the cellulose in the beans
This article was originally published on Processingtalk on 19 Jan 2004 at 8.00am (UK)
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The oil is heated to the point where all of the hexane evaporates off and just the oil is left.
This plant operates continuously, 24 hours per day, processing 130,000 bushels of soybeans each day.
The problem they wanted to solve was a common one to all oilseed extraction mills that use hexane in the process: hexane in vapour form escapes from the equipment around the drive shafts.
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Hexane is a costly and volatile solvent, which converts quickly from a liquid to a gas at room temperature.
Federal regulations have established a maximum emissions standard for hexane vapours in oil mills.
The production line includes a feeder screw, which delivers the miscella into the extractor, turning at 68 rpm.
At this stage, the product in the conveyor is at 225deg F.
Inside the extractor itself, the temperature drops to around 130-140deg F.
After the extraction process, the pulp is discharged via another screw conveyor, at approximately the same temperature and turning at 75 rpm.
By the inherent nature of screw conveyors, their long shafts tend to run out, i.e they rotate on an elliptical rather than a circular path.
It is this shaft run-out that causes packing in the stuffing boxes around the shafts to eventually become compressed and create a leak path for the product inside, in this case hexane vapors.
Maintenance workers at this plant were scheduling monthly outages to repack the stuffing boxes, which took two workers two hours each time.
Several years ago, the plants maintenance superintendent decided to try an alternative solution to seal the extractor shaft: Meco custom shaft seals.
He had seen them used successfully at another oil mill where he had worked previously and contacted the Meco distributor for the region.
This distributor came into the plant to provide assistance with the exact measuring of the extractor shaft and also was there to help install the first seal.
This process took the team less than one day because the seal was built fully-split so that the bearing would not have to be removed.
In the following year, Meco seals were installed on both ends of the feeder screw and in the next they were installed on the discharge screws.
The Meco distributor helped out with seal installations and rebuilds until plant workers were trained; now they work on them without assistance.
The patented EAS seal design is based on the use of a driving elastomer, which wraps around and grips the shaft.
This both protects the shaft from abrasion damage and blocks product migration along the shaft, even if it is scored or pitted.
Through friction, the elastomer turns with the shaft and drives sacrificial rotors to turn against stator plates, forming the seal interface.
No relative movement takes place between the shaft and any of the rotating seal components, so all wear is limited to the seal interfaces between rotors and stators.
When enough rotor wear occurs, the seals can be quickly rebuilt by replacing only the rotating parts.
The seals are able to accommodate thermal growth of the shaft during the process, as well as shaft run-out of 6mm TIR and more.
The Meco seals are designed to be run with a nitrogen purge in the seal cavity.
This serves to maintain consistent seal face pressures and to keep product out of the seal.
The plant did not have a good supply of nitrogen when they first installed the seals; when they tried to use bottled nitrogen, they found that each bottle only lasted 3 days and soon ceased using the purge.
Running in this manner, the seals failed inside of a year due to excess wear on the internal rotating components.
When the company built a refinery next to the extraction mill they installed a large nitrogen tank to supply both plants.
Since the seals have been purged with nitrogen, they have been running for up to two years between rebuilds.
The Meco seals have saved the company between 4-6 hours of labour per month (They still schedule monthly outages but can use the downtime for other repairs instead of repacking the stuffing boxes).
The largest single benefit of the seals in the maintenance superintendents mind, though, is the elimination of the release of hexane from the process.
The conservation of hexane has meant enormous cost savings for the company.
MSA meter readings at the extractor shaft dropped from 100% before the Meco seals were installed to 0% afterward.
This brought the plant to well below the maximum emissions standard set by federal regulations, a fact which has everyone breathing a little easier. Request a free brochure from Meco Shaft Seals ...
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