Mixing it up
24 Jun 2014
Effective process control is a key ingredient when mixing solids.
There is much more to the industrial mixing process than blending up a batch of ingredients and hoping for the best.
Without a good dose of scientific expertise in the mix, your process might well come unstuck, say blending technology experts.
Making mineral applications such as ceramics, coatings and composites are core processes for global chemical company Imerys.
Nevertheless, its chief process engineer, Jarrod Hart, says mixing solids together is notoriously difficult.
“It is not just about how well you mix things up, but how well you ensure it stays mixed up,” he says.
To ensure this happens, many process plants opt to mix products at the point of use.
Hart, who is also a member of the Particle Technology special interest group (SIG) at the Institution of Chemical Engineers (IChemE), says there are two different methods for validating the quality of mixed products.
The first is to track the process itself, and the second is to check the products after the fact.
“You are best off having a process in place to make products right the first time,” he says. “The first step is having well-designed machines with no nooks and crannies, and then ensuring you have a well-designed process.”
Within a continuous process, the object of the exercise is to continuously and precisely measure the flow according to the product formula within a very short window of time.
Integrating flow-metering systems that can offer traceability will confirm whether the mixing process has been successfully completed.
“We have one tap on the right and one tap on left and can monitor the flow rate to ensure our mix has right proportions,” he says.
“If you are always recording in a closed feedback loop, then you know your products will always be right.”
The benefit of using computerised flow meters is that unlike humans, they are built to handle continuous monitoring.
“Some machines cost a million dollars a day to run,” says Hart.
“If you measure and control everything then the product will also be consistent, which can prevent costly mistakes”.
However, when it comes to batch processing, mixing processes can be far more difficult to quantify.
“Say, for example, you are doing a batch process and you mix ingredient A and B together for four hours, and then notice stuff stuck on the walls of the drum. You are aiming for a 50/50 mix, but how do you verify it?” he asks.
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