PDL's Microdrive-I cuts enerby costs at CHH tissue Mill, Kawerau

APPLICATION BULLETIN - NOVEMBER 1996 | BACK TO INDEX

PDL's Microdrive-I cuts enerby costs at CHH tissue Mill, Kawerau

The PDL Electronics' motor controllers are rapidly becoming a benchmark in energy efficiency for variable speed drives at one of New Zealand's major pulp and paper companies.

The PDL Microdrives have been installed as part of a plant-wide programme to save on motor drive energy costs at Carter Holt Harvey Tissue's large Kawerau mill site.

CHH Tissue is one of the country's largest energy users and established a three-stage programme to improve efficiency of its motor drives, after identifying the important savings available. The CHH Tissue site at Kawerau in the Eastern Bay of Plenty comprises three tissue machines and a pulp mill producing crepe tissue paper and flat paper grades.

Energy saving efforts have traditionally focused on the major parts of the plant, using larger chunks of power within mills, such as pulp and paper refiners.

Don Pedersen, Energy Consultant at the Carter Holt Harvey Tissue site, Kawerau.

However, with traditional motor drive systems using nearly 60 per cent of the total power consumed by New Zealand energy, the potential energy savings of up to 20 per cent on current consumption make motor drives an important target for any energy saving programme.

A specially established energy group carried out an audit of all motor drives on the Kawerau mill site. In an attempt to identify potential savings, each motor drive was examined for potential energy savings using a systems approach.

One of the key areas where motor drives are used at Kawerau is in the wet well effluent plant used to pump sewage from the mill to CHH Tissue's treatment facility. Traditionally, three eddy current couplings drives have been utilised in the plant to move the mill's hourly output of up to 120 cubic metres of effluent. The noise of these motors was so loud and the air so hot it was difficult to talk, let alone work, in the pumproom.

Now, a single PDL "Microdrive-i" quietly and efficiently purrs along handling the same capacity.
Don Pedersen, project manager and principle of Energy and Design Ltd, says that proposals to fit existing motors with AC variable drives in the past had been hampered by the difficulty in assessing actual savings.

"However, if you look at it from a different viewpoint and take into account the efficiency of the whole system, you get a very different result", Don says.
Previously two machines worked full-time, while a third remained as a back-up. Don says currently only one machine runs full-time while a second remains as back-up. The third stands redundant.

Don Pedersen explains to Gary McKinney, Sales Engineer, how only one PDL Microdrive-i now handles the mill's hourly output of 120 cubic metres of effluent.

"So instead of running two inefficiently, we are running just one PDL Microdrive-i very efficiently."

PDL was chosen to supply the variable speed drives primarily because of its excellent service history, the reliability of the company's machines and its local back-up.

"If you buy imported equipment, it's possible that a few years down the track nobody will want to know about it when it comes to service."

PDL has between 70 and 80 drives throughout the CHH Tissue mill, so a good record of supply and service gave PDL the edge when the time came to select a supplier for the pump variable speed drives.

"Energy optimisation is very important in pulp and paper processing," says Don. The PDL Microdrive-i has a 15 per cent energy savings compared with the eddy current coupling.

"But it's not just the energy efficiency factor and you have to look at it more innovatively."

Don has carried out an energy efficiency audit of the Kawerau site and compared the mill's theoretical process requirements with what is actually being used.

"That's where you pick up the difference between the energy waste and extra efficiency in the process."

Using PDL Electronics' Microdrive-i modern variable speed AC drives, the company has been able to achieve not only energy savings and reduce wastage but also lower noise levels in the plant.

The efficiency savings and lower noise levels mean an almost immediate payback for CHH Tissue. It's estimated the payback will be made in a period of 18 months.

Cost savings also stem from a reduction of 988 kW of electrical power compared to 882 kW estimated in the initial capital expenditure. Maintenance costs will also be improved from a predicted reduction in the number of process control valves, improved electric motor overload protection and less wear on equipment generally operating at lower speeds.

The energy saved resulting from the programme makes available power for future site production expansion, such as a pulp mill drying and production upgrade.

Don says the benefits offered by the PDL Electronics' AC variable speed motors means that the Microdrive-i drives have become the CHH Tissue site standard against which others are measured for efficiency and cost.