Controlled drives

As part of a strategy to improve productivity and energy efficiency at its pharmaceutical intermediates 11-acre site at West Bromwich in the West Midlands, Robinson Brothers has been upgrading its control systems and electrical equipment over the past two years.

An integral part of the process involves fluid bed drying, where powdered chemicals are drawn into the dryers, fluidised and dried, 24 hours a day, 360 days a year.

As part of the upgrade, Rockwell supplied Robinson with Allen-Bradley PowerFlex 700 ac drives to replace ageing star-delta starters on two of the plant's dryers. Before the variable speed drives were fitted, engineers had to stop the 22kW dryer motors regularly to clean the filters.

'Our old starters caused us quite a few problems because of the frequent stopping and starting, which they're not really designed to do,' says Tom Rutter, Robinson Brothers' site development manager.

'Around six starts an hour is the norm but we were often making more than six starts in 35-40 minutes. It took its toll on the motors and eventually destroyed them.'

'The filter socks on top of the dryer units getting blocked was a major problem,' he explains. 'Every 10 minutes the dryer had to be shut down completely to allow the socks to be blown free. By using the Allen-Bradley drives, we can slow the dryers down rather than stopping the motor completely. We can then clean the filter and speed it up again.'

Each of the dryer motors previously ran at around 14kW during the drying cycle, but Robinson's engineers found that by using the PowerFlex VSDs they could run the motors constantly at a lower speed and still achieve their production targets. With the drives installed, the dryers run at only 10-11kW, some 22% less energy. 'It's now far less expensive to run,' says Rutter. 'Since the installation we've also had to carry out less maintenance because there are fewer problems with the motors. As reliability increases, so does our productivity. Even the overall noise level has been reduced.'

The actual savings amount to up to 24MWh and around £650 per dryer each year. Another incentive, according to Rutter, is the associated tax benefit. The PowerFlex drives are included in the Carbon Trust's Enhanced Capital Allowance (ECA) scheme, enabling firms to claim 100% first year capital allowances on the equipment.

These savings also contribute towards targets outlined in the Climate Change Levy (CCL). Robinson Brothers is an energy intensive business using around 11GWh each year and is eligible for discounts by reducing energy use over ten years.

Following the success of the first two drives, the company has recently finished upgrading a third dryer and is planning a range of other projects over the next year.

Mark Daniels is product manager for drives with Rockwell Automation.