Some years ago we got a call from a worried customer saying all the crows in his large detergent plant had turned white.
They did some preliminary investigation and found that the crows were coated with talc powder– maybe preening themselves for a great event ahead!
We had supplied them a couple of pneumatic conveying systems about a year before this unique occurrence. A few days after this call, one of their plant engineers called again and said they had found that the source of this white crow transformation was coming from the filters atop their silos, a part of our supply earlier. Product was passing through the filter bags and out into the atmosphere. So now the worry monkey was squarely on our engineers’ shoulders. We got together in the conference room to diagnose and troubleshoot this phenomenon which was rather baffling since the plant was running fine for more than a year, 24 hours a day.
A sudden filter leakage? We ruled out bag rupture or any other physical free path to the talc powder that this system was handling. So what could it be? We looked at the specifications and the particle size analysis, checked the filter cloth selection and sizing and everything was fine. So how did the leak occur?
Here is where the powder monkey plays its tricks. Turned out that the purchase department of the customer- forever sourcing lower cost raw materials- changed the powder vendor to a new vendor whose specifications had a much finer distribution of the particles than that of the earlier supplier. We asked for the particle size analysis and the distribution curve and lo and behold- the product had much smaller particles than what was given in the original analysis and simply leaked through the pores of the filter cloth which was not sized to handle these finer particles.
Which brings us to the all important input material specifications.
More often than not, most customers send back our Material Properties Data Sheet half filled or unfilled with a request that we figure it out ourselves! Sure we can do a particle size analysis and draw the distribution bell curve. And we select and size the filter accordingly considering the filter velocity and the can velocity (they are both different!) But when comparing prices, we become the gold standard. Why? Because we got into detail and figured things from bottom up.
Moral of the story: Powders are tough to tackle. Ensure you have the technical arsenal to see through them to design your bulk handling system. Work from fundamentals. The simple principles (remember Stokes Law?) and formulae that you learnt in engineering school should always be fresh and sparkling in your minds- never mind if you are customer or vendor. Be a good engineer. Knowledge is Power.