New Addition To The Pellet Line Reduces Dryer Downtime
Conscientious thermoplastic pellet manufacturers are always on the lookout for ways to operate flawlessly. FINA Oil and Chemical Company found one way to reduce the downtime that their centrifugal dryer was experiencing. When FINA expanded, they installed a Kason Double Deck Cross-Flo Sieve to keep agglomerates out of the dryer. On other lines, agglomerates caused problems leading to downtime of up to 12 hours. Weighing from approximately 1 to 10 pounds and flowing fast, these chunks of plastic can cause havoc in a dryer. Since meeting customer delivery schedules is an important part of FINA' s service, FINA decided to take another step to prevent agglomerates from reaching the dryer.
In August 1988, FINA brought its new train on stream. Since then the 72 inch wide Double Deck Cross-Flo Sieve has successfully diverted agglomerates from the dryer. Approximately 1000 GPM of water, pellets, clusters, and agglomerates flow across the decks.
The new Double Deck Cross-Flo Sieve has a scalping deck above the pellet deck. As the mixture of discrete pellets, water, clustered pellets and agglomerates overflow the headbox, agglomerates slide down the scalping deck, individual pellets and clusters are recovered on the lower deck, and the bulk of the water passes rapidly through the profile wire deck. The water from the sieve is recycled to the underwater pelletizer, the agglomerates go to scrap, and the clusters and pellets to the centrifugal dryer where all the water is removed. Clusters and pellets then go to a screen classifier which removes the clusters.
The 72 inch scalping deck of the new Cross-Flo Sieve consists of longitudinal tubes aligned parallel to the flow and spaced 1/2 inch apart to separate agglomerates. The deck is designed to keep agglomerates flowing to scrap without ever accumulating at the bottom of the scalping deck itself.
The uniquely shaped profile wire of the lower pellet deck is oriented
perpendicular to the flow. The profile wire shape is triangular in section with rounded shoulders or edges. These shoulders are typically tilted to rise slightly above the line of descent to intercept more water than a conventional screen would. With this design, a thin layer of water clings to the preceding bar before accelerating through the screen slots. These wires are spaced 1/16 inch apart.
The Double-Deck Cross-Flo Sieve offers high reliability and trouble-free operation because there are no moving parts. As a result, maintenance requirements are minimal and there is no need for spare parts. After determining the optimum spacing between the scalping deck tubes to optimize the amount of agglomerates diverted, there has been no need to adjust the unit in any way.
All parts in contact with water and pellets being dewatered are made of Type 304 stainless steel, which does not corrode or erode due to abrasion.
The Sieve stands 92 inches tall and extends 92-1/2 inches front to back.
With more than seven months of continual use, the Double-Deck Cross-Flo Sieve has proven to be a valuable addition to the train, significantly reducing dryer downtime.
Screen Tips - Volume 4, Number 2 Summer 1989
Kason Double-Deck Cross-Flo Sieve reduces centrifugal dryer downtime at FINA Oil & Chemical Company's polypropylene plant in Deer Park, TX.