A major cement manufacturer in South America was experiencing transfer chute plugging with a highly cohesive limestone and clay mixture. During rainy periods, the chute would plug every few hours, requiring operators to manually dig out the contents in the chute and wash it down with high-pressure water.
Though flow properties testing of the limestone/clay mixture was performed at multiple moisture contents and a viable chute design was issued to the client, plugging resulted upon startup due to the chute being incorrectly fabricated and installed.
The delivery belt conveyor operated at about 4 m/s and delivered limestone and clay at a rate of 2,000 tph.
Material-handling consultants Jenike & Johanson visited the cement plant to determine the cause of the plugging problem in the transfer chute. This chute was just one of several in a belt conveying system that delivered raw materials from a remote quarry to the plant.
After the visit, a discrete element modeling (DEM) analysis was performed with the problematic chute to best understand the cause of plugging. It was determined that the hood was not properly fabricated and when installed, created a flow impediment when the limestone/clay mixture was wet and sticky.
Additionally, the DEM study showed the stream impact on the bottom of the chute before discharge onto the receiving belt would allow buildup.
With the detailed DEM study, Jenike & Johanson was able to recommend modifications to the chute design to ensure reliable throughput of the cohesive mixture. A new hood and spoon section were implemented to maintain velocity through the transfer.
The new hood and spoon sections were fabricated locally and installed in the problematic chute. Since installation, this chute has been operating reliably and has not experienced plugging. The cohesive mixture maintains velocity through the transfer chute, thereby avoiding buildup, plugging or spillage.
Jenike & Johanson, www.jenike.com