Ask a Powder Pro: What is the most challenging powder that you have ever experienced?

While some powders are more resistant to flow than others, once you have measured a material’s fundamental flow properties, which include its cohesive strength, compressibility, and wall friction, you can design or select reliable storage and handling equipment for any material. Also, an easy-flowing material can be very challenging to handle if the wrong bin and feeder are used.

As an independent consultant specializing in bulk solids handling, storage and processing, I sometimes face more significant challenges from clients who question the science behind bulk solids handling than from the materials being handled. For example, I once had a client who asked me to design a bin. I measured his material’s flow properties. The material had high wall friction, but it was noncohesive. I recommended a simple pyramidal or conical hopper with 30-degree walls and a 4-in. diameter outlet. The hopper would discharge in funnel flow, but any ratholes that formed would collapse and the bin would fully empty.

Rather than follow my recommendation, the client decided to purchase a bin equipped with a cone valve, which is an inverted cone that moves up and down vertically and vibrates to promote flow. I explained to him that, since he was planning to procure several of these bins, this was an unnecessarily expensive choice and that a simple funnel-flow bin would be much more economical.

He said that, during a trial using the cone valve at a supplier’s facility, his material had discharged completely. I explained that Andrew Jenike’s hopper design methods, upon which I based my recommendations, have been used for more than 50 years, and I assured him that a simpler bin would also reliably discharge his material.

To illustrate my point, I told him that, when you celebrate your birthday, after everyone finishes singing and you’ve made your wish, you could opt to put out the candles by grabbing a fire hose and aiming the nozzle at the cake, or you could simply blow out the candles with your breath. Both options will extinguish the candles, but one is a lot simpler than the other.

Because my client didn’t trust or understand proven bulk solids handling system design methods, he went with the fire hose.