BACKGROUND

Golden Cat Co. (formerly Lowe Industries, Inc.) manufactures Kitty Litter® and Tidy Cat 3® brand cat litter at its plants nationwide.

Their clay granules are collected from an open stockpile and screened to 3 sizes before being stored in individual bins. After processing, the final product is directed to one of several downpipes. A slide gate at the bottom of each downpipe is used to control the flow of material to a chute that is designed to remove dust generated during handling. The material is then placed in a surge bin which in turn discharges to a packaging machine.

THE PROBLEM

Particle segregation was causing a large volume of smaller particles ("fines") to discharge toward the end of each run which resulted in several bags of unacceptable product. Only by spot checking was it discovered that some of the out-of-spec bags were not being discarded. To increase product quality, segregation had to be minimized and any discharge of fines at the end of each run had to be accurately predicted, resulting in fewer bags with high quantities of fines which could be easily located and discarded. In Golden Cat's systems, both the downpipes and surge bins were subject to this type of segregation.

The flow pattern of material through equipment such as downpipes and surge bins dictates the extent of the segregation that will occur in the discharged material. Jenike & Johanson observed that both pieces of equipment were discharging in a funnel flow pattern. Because of this flow pattern, a steep flow channel formed above the outlet of each surge bin, with non-flowing material remaining around this flow channel. As the level of material in the bin decreased, layers of the non-flowing material slid into the flow channel.

In the downpipes, the fines collected above a ledge of a partially opened slide gate. The coarse material discharged first, followed by a high concentration of fines. Unfortunately, the design of the downpipes could not be modified, so the segregation that occurred there could not be reduced, leaving only the surge bin for modifications.

THE SOLUTION

Flow properties tests run in Jenike & Johanson’s lab confirmed that the surge bins were providing a funnel flow pattern. Based on our test results, we developed recommendations to minimize the segregation in the surge bins by converting them to mass flow bins.

In a mass flow bin, all of the material is in motion whenever any is withdrawn. Material from both the center and the periphery moves toward the outlet simultaneously. A material which has segregated in a side-to-side manner tends to remix at the outlet.

Mass flow was obtained by the use of our patented BINSERT® (cone-in-cone) design. The walls of the BINSERT® outer cone could be made less steep than would normally be required for mass flow, resulting in a larger capacity plus, with a BINSERT® there is better control over the velocity profile of the material. If the center portion were to flow faster, this would aggravate the problem of fines discharge. Uniform flow of material through the bin would minimize the number of bags with high levels of fines and allow Golden Cat to accurately determine the number of bags to discard at the end of each run.

An integral part of this BINSERT® system is the distributor which was designed to be located at the top of the surge bin. This ensures that both the center cone and outer annulus fill with equal amounts of material, minimizing side-to-side segregation during filling of the bin. The distributor also spreads the final discharge of fines from the downpipe across the top surface of the material, ensuring that the fines will discharge last.

Jenike & Johanson also supplied the equipment which ensured the correct interpretation of our recommendations, and allowed us to offer a performance warranty.

THE RESULT

The equipment was installed and worked as designed and warranted. Jenike & Johanson’s modifications of the manufacturing equipment effectively controlled the fines during production, and enabled Golden Cat to achieve the quality of cat litter it desired.

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