A Nottingham waste reclamation plant has achieved an eight percent increase in productivity is achieved by installing two ABB variable-speed drives on a waste sorting machine. Waste reclamation and recycling company Wastecycle has recycling plants in Nottingham and Leicester. The company collects and processes 450,000 tonnes of waste annually, and over 200,000 tonnes of it is recycled into fuel products for burning power plants.

The 22 kW ABB variable-speed drives (VSDs) are fitted to a waste sorting machine called a trammel on one of two machines at the site. The trommel is a rotating sieve that spins the waste to separate recyclable material from less usable small particles known as fines. The fines fall through the trommel and are collected underneath.

The trommel is driven through a shaft turned by two motors. The two motors must run at precisely the same speed, as any speed differential would twist the shaft. To achieve this, it was decided run two general purpose drives in a master-follower configuration.

Gary Burton, engineering manager for the Nottingham plant, says: “Previously we had no speed control for this trommel as the motors were run direct-on-line. We were looking for a solution that would help us improve productivity and remove even more of the fines.”

The drive application allows Wastecycle to increase the motor speed to 55 Hz, around 1600 rpm, when processing commercial (business) waste, which makes up 75 percent of the intake of waste from customers. This has improved throughput from 23 tonnes an hour to around 25 tonnes an hour, an increase of around eight percent.

Heavier construction waste from building and demolition sites continues to be run at the standard 50 Hz. This is because the lower rotational speed avoids rubble falling from the top of the trommel and damaging the trommel drum.

“We have had no issues with the application since the drives were installed,” says Burton. “As well as the increased throughput, we are also seeing an increase in the proportion of fines removed when using the higher speed. This is important as we use the commercial waste to produce solid recovered fuel for cement factory power plants and too many fines in the product would reduce its calorific value.” They have since installed the same solution on the single trommel at their Leicester site.

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