The Problem
A major cake mix manufacturer was experiencing unacceptable variations in several of their final mixes. Jenike & Johanson was called in to solve this segregation (demixing) problem. From our observations and additional plant processing data, we determined the chief source of ingredient demixing was an often-overlooked one: the pneumatic conveying system.
The orientation of the conveying line as it entered the hold bin contributed to the problem. The conveying line entered the top of the bin, and directed the incoming stream of material down into the center of the bin. The kinetic energy of the incoming air/material stream contributed to the tendency of the bed of material in the bin to remain fluidized, allowing fluidization segregation to occur. This resulted in a layer of fines at the surface of the material in the bin.
Jenike & Johanson's Solution
The first part of our recommendation was to revise the sequence of ingredient addition. By adding one of the major ingredients earlier in the process, the blend was made more cohesive (less free flowing). As with many blends, this reduced its tendency to segregate.
To minimize fluidization segregation, we recommended rerouting the conveying line so that it discharged the material vertically up and into a target box. This diffused the energy of the discharge stream and allowed the particles to settle out more gently across the pile's top surface. We also recommended that the hold bin be modified to ensure a mass flow pattern so that the effects of any remaining side to side segregation would be minimized during discharge of the bin.
The Result
Pneumatic conveying is a highly useful technology, but one with problems all its own. Solving – or, more importantly, preventing – these problems requires a thorough understanding of the flow characteristics of the bulk solids being conveyed as well as the effects of air-driven transfer on ingredient mixtures.
Our client implemented our recommendations that yielded immediate cake mix quality improvement.
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