The Problem

One of our clients had a problem of packaging different grades of kaolin clay uniformly into bulk bags at high rates. The clay's poor handling characteristics made it very difficult to maintain uniform discharge from the 100 ton silos to the packaging equipment. Discharging from the silos at a high bulk density was also critical for stable bulk bags and efficient packaging.

Jenike & Johanson's Solution

Our first step in the solution was to design silos that ensured mass flow. To overcome the arching capability and frictional characteristics of the clay, we selected a transition hopper, which allowed us to create less steep wall angles than in a cone, thereby saving headroom.

We recommended an oval-shaped, air-assisted discharger. Instead of aerating a large volume of material, this unit fluidizes only a thin layer of material near its walls. This thin layer of material greatly reduces friction at the walls, allowing material to flow along relatively shallow wall angles. Also, the addition of air overcomes the limiting rate problems and increases the packaged density in comparison to a fully-fluidized system.

Scale model tests on the conceptual design confirmed the counterintuitive notion that the addition of air would increase packaging density. We then designed, fabricated, tested, and supplied a full scale discharger.

The Result

Jenike & Johanson's mass flow design met and even exceeded our client's original requirements. It is not only an efficient and successful solution to a troublesome flow problem, but also very cost effective. Our design was one-third the cost of a comparable mechanical feeding technique.

In addition, our design was able to fill a one ton bulk bag in about two minutes—five times faster than the original requirement.

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