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Mechanical Conveying Q&A

  •   We have two silos of pigments – one is Bayferrox yellow and another is Cathay coat yellow – both are silo connected with one weigh hopper. The Cathay coat yellow is conveying with a conveying rate of 40 tn/hr but Bayferrox is conveying at 3 tn/hr. Please suggest check points.

    Answered October 20th, 2015 by Expert: Bill Mecke, P.E.

    The flow characteristics of bulk materials can vary greatly and depend on the design of the silos and transitions to the weigh hopper. It appears that the Cathay Coat Yellow pigment flows better than the Bayferrox Yellow pigment. The Bayferrox Yellow pigment is probably bridging in the silo or transition to the weigh hopper resulting in poor bulk material flow and reduced feed rate. I would suggest having both materials tested by Jenike & Johanson to determine their flow characteristics. Jenike & Johanson is the premier bulk material engineering firm with expertise in powder and bulk solids storage, handling, conveying, and processing. Also, the shape of the silos as well as the transition to the weigh hopper needs to be examined to determine if bulk materials are not flowing properly. The bottoms of the silos and the transition to the weigh hopper may need to be redesigned to promote mass-flow, the movement of bulk materials all at once.

    You can check for mass-flow by visually monitoring the pigment in the silos. If the level in the silos decreases in height at an even rate across the width of the silo, then you have mass flow. If only the center of the silo decreases in height as the pigment is discharged, then you have funnel-flow. You can also monitor the discharge of pigment at the transition for the weigh hopper. The flow of pigment should be even and consistent. If not, then you have bridging of the pigment in the transition to the weigh hopper.

    The problems you have described are easily solved with bulk material testing and a possible redesign of your silo bottoms and the transition to the weigh hopper.