Case study: Problem solving in a minerals process

A minerals manufacturer had been using the same process for 10 years. The manufacturer was confident that the process was highly stable and that Insitec was required only as an on-line QC tool. Since the process was so stable, it was necessary to prove to this customer that the instrument was able to detect changes in the PSD to a tolerance of ±0.3 µm.

When the Insitec was used to measure particle size at the exit of a dynamic classifier in real-time, it was found that certain "blips" occurred from time to time, when the product was completely out of specification. As the mill was running at 20 tonnes/hour this meant that around 15 tonnes of out-of-spec product was being introduced into the product silo.

The cause of this was identified as the feed silo. When the level in the silo fell below a critical value, the powder presented reduced resistance to the vacuum sucking it through the mill. As a result there was a sudden increase in mass flowrate which swamped the dynamic classifier. Following this discovery, plant procedures were re-written to prevent a recurrence of this problem.