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VSDs, PLCs and HMIs save £120,000 of energy per year

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A plant-wide energy efficiency installation is already saving £120,000 a year in the woodworking shops at door and mouldings company BLP in Doncaster. The new system is based on variable speed drives, PLCs and HMIs from Mitsubishi Electric.

BLP UK Ltd is believed to be the UK's largest volume manufacturer of MDF wrapped mouldings and membrane pressed cabinet doors for the furniture manufacturing and related industries. Over 400 people are employed on three-shift, seven-day production.

The market is fiercely price-competitive, so reducing operating costs is critical to the company's on-going success. Engineering Manager Dave White explains the origins of the energy efficiency drive: "In a 24x7 manufacturing environment a lot of emphasis is put on maintaining production - keeping the machines going, the materials flowing, the goods going out the door.

"But a while ago I stepped back a bit and started to evaluate our systems from a wider perspective. Many of our major costs were pretty much fixed, but energy looked like it had potential to be better managed."

Energy-hungry dust extraction

Investigation showed the dust extraction system that served all three production buildings was energy hungry and had a rather simplistic control strategy.

"There was the best part of 1000kW of installed motor power, and this basically ran constantly, eating power day and night. We had to devise a project strategy that let us improve the existing system whilst not compromising standards nor disrupting production. Effective dust extraction is critically important to our business for health and safety and maintaining product quality."

Each moulding machine has eight cutting spindles with individual forced-draught extraction heads feeding a series of manifolds into the central air handling system. However, it is notable that the machines do not run continuously; most have 30-40 per cent downtime, so a first step was to find a way to isolate the suction at idle machines.

It was also realised that often when a machine is running, not all spindles are required, so the next objective was to ensure that extraction heads are individually controllable.

Expert advice

At this point Dave White called in energy experts from Mitsubishi Electric, and began working on an approach based on a number of variable speed drives controlling fan motors around the system.

The Mitsubishi team ran a series of trials based on blanking off nozzles and ramping down the motor speeds. The results demonstrated that speeds could be reduced from their normal 50Hz full-power operation to 37Hz without any lose of operational performance. This equated to savings of about 50 per cent of the energy and, therefore, running costs. This, coupled with the switched isolation of extraction heads to idle moulding machines, suggested that significant energy saving could be made.

It was not long until the BLP Board gave Dave White the go-ahead for a pilot scheme on a pair of moulding machines.

"We used pneumatic valves to close off individual suction heads and the Mitsubishi drive to reduce the motor speeds or even isolate the entire machines' extraction, yet maintaining full operational requirements," says Dave White. "We saved £10k of energy expenditure in the first 12 months, which more than paid for the capital costs, so I was confident when I went back to the Board suggesting that we implement the scheme across all three buildings."

Enhanced control systems

As the installation grew and the number of drives increased, greater control was going to be required. Mitsubishi suggested a simple yet powerful control architecture based on four supervisory PLCs and three HMIs for local control, which has potential for further development in the future. Communications around the system are based on CC-link, an open protocol system originally developed by Mitsubishi but placed in the public domain so that complementary products can be developed by any company.

"We have almost completed installation in our two moulding shops and the savings already exceed expected projections. Upgrading the door pressing shop is now a priority, as the energy savings are keenly anticipated, helping maintain future competitiveness."

19 December 2006

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