Keeping control in hostile environments

Edited by the Engineeringtalk editorial team May 21, 2004

Moeller's electrical infrastructure hardware has consistently proven its capabilities across many applications and industries.

Moeller's electrical infrastructure hardware has consistently proven its capabilities across many applications and industries.

However, in a recent installation at RTS' commercial building waste recycling plant in East London, it has been working beyond the call of duty in an extremely hostile environment.

Commercial building waste, through attrition and dust generation, can cause havoc with the machinery and controls tasked with its transport, sorting and disposal.

This type of hostile environment can bring the best out of machinery and its control systems, with RTS's new recycling plant being no exception.

Part of a GBP 1 million investment, the plant is designed to combat both the growing costs and environmental problems concerning landfill.

Its new facility is able to sort 60t/h of commercial waste into three grades or fractions, which can then be used in some other way rather than going to landfill.

Phoenix Recycling Technology supplied the hardware to undertake this dusty and dirty separation process, with all of its plant being located along two sides of a large custom-built shed.

The first step, an independently controlled shredder, reduces the particles to less than 250mm in size; these then pass underneath an overhead magnetic conveyor before passing into a trommel screen.

The 8.5m-long, 2.5m-wide trommel, weighing in at 10t, spins at 20rev/min and acts as a giant 40mm-per-hole sieve, removing the smaller fractions.

What is left exits the trommel and enters a unit known as a TriSeparator, this uses three controlled streams of air to perform the final sorting, blowing the light fractions into separate bins; what is left (rubble and stone at this stage) exits and is collected at another point.

The brain behind all of this machinery is a control panel filled with Moeller hardware, supplied by solutions provider and Moeller stockist, WGA.

"Phoenix supplied us with the terms of reference and the sequence which the machinery had to start up, operate and then close down", explains Chris Paterson, Director of WGA.

"We then had to specify all the hardware, design the circuit, create the software and package it all up as a turnkey panel".

The panel contains a PLC, several direct online starters, a 11kW star delta starter for the big fans used in the TriSeparator and standard variable speed drives for one conveyor.

Two DV6 vector drives were employed to handle the variable and high loads encountered by the trommel and its two 22kW motors.

Two 30kW braking resistors had to be designed in to cater for the energy regenerated by the trommel on shutdown.

Paterson adds at this point: "Using control cards, Moeller's drives are particularly suited to regenerative braking".

Although the control system is not that complex and the application is not very glamorous, when you consider that there have been no major faults with any of the control gear since installation, it is testament to the capabilities and robustness of Moeller's hardware.