Drives drive down dairy's energy bill

The power requirement for the water management system at Milklink dairy has been reduced by up to 173kW/h based on a new control solution from Mitsubishi Electric.

The power requirement for the water management system at Milklink dairy has been reduced by up to 173kW/h, giving a payback period of only 19 months for the entire system, based on a new control solution from Mitsubishi Electric.

The engineering team at Milklink's dairy in Crediton, Devon, prides itself on constantly improving efficiency.

The latest energy saving project involving the site's water management system, has shown what careful planning and implementation can achieve.

The site has its own two bore holes that can produce all their water requirements, but can also connect onto mains water if required.

Water is an essential commodity at the dairy and is used for a host of water services such as wash downs, cooling etc.

The water is softened before use to avoid leaving any residue on the production surfaces.

The old water control system had inherent problems such as water wastage due to leaks, lack of capacity to meet new production demands (the dairy produces 2 million litres of UHT milk per week) and high energy expenditure.

Raw water was stored in a large 38kl Braithwaite tank and fed via a water softening system to two other Braithwaite tanks for use by the boiler house and the factory production lines (these being 38 and 135kl capacity).

The tanks on the system were not able to hold enough water to meet peak demands, such as the wash down periods which happen each night between 0200 and 0500.

Therefore, the water extracted from the boreholes had to be supplemented with mains connected water, which considerably increased costs.

Head pressure from the old system was also very low and to compound everything the old system used DOL starting for the pumps which, due to the huge initial startup pressures and torques, required large 15kW motors.

After careful examination of the shortfalls of the old system, Ken Mason, Electrical Systems Manager for the dairy, and his team put the plans for their new water management solution into practice based around Mitsubishi Electric's latest energy saving variable speed drives (VSDs).

Ken stated: "The objective of the project was to simplify the operation of the system, save energy and operating costs, reduce downtime, reduce water wastage, improve leak detection and to be as environmentally friendly as possible".

First they installed two new raw water silos (69kl each), a soft-water silo with 145kl capacity and replaced the entire water supply piping.

The new storage tanks capacities allow the stored water to match all the production requirements, with the tanks being constantly topped up when required.

To improve the pumping of the water around the entire site and to achieve controlled measurement and control to pumping requirements, Milklink used Mitsubishi's F540 drives and a Q series PLC to control the whole operation.

The pumps motors are now down from 15 to 7.5kW because of the drives' controlled starting.

Using the F540's advanced flux optimisation technology means extra energy savings can be achieved as the drives ramp down the voltage when the load reduces.

Flux optimisation works by calculating and controlling the voltage applied to the motor, so that the motor is working at its maximum efficiency the whole time, using the least possible power.

A Mitsubishi Q series PLC acts as a master controller to automatically measure water demand points, collate data and work out appropriate pumping solutions.

The PLC communicates to the VSDs and line PTY pressure transmitters (used to measure water pressure in the pipes) using the latest global fieldbus, CC-Link.

All the line pressure sensors are 4-20mA analogue output, which connect directly to the Q PLC.

The line pressure of the water system is between 0-4bar, but for optimised use it is held at 3bar to an accuracy of 0.1bar.

All the pumps speeds are controlled by PID loops in the Q PLC with data sent to the drives via the 10Mbyte/s high speed CC-Link connection.

The reaction time of the whole CC-Link network is a mere 15ms, giving instantaneous control of the entire water management system.

Connected to the PLC is a Mitsubishi E700 HMI which is used as the operator interface.

From the interactive HMI screens the operator can change any of the PID control values and settings for any of the pumps and, if required, manually override any elements of the automatic water control system.

All the variables of the VSDs are also shown on the system including frequencies, voltages, and operating currents.

The HMI also displays the line pressure transducers values, all alarms (which are historically logged on the HMI) and time out errors.

Historical trend graphs of soft-water storage and raw water storage flow rates are also managed by the HMI, which are critical in evaluating trends on peak water usage.

The actual changeover from the old to the new water management system took only three months, with all panel building and installation implemented on site by the Milklink engineering team.

Assistant Project Engineer John Bater stated, "Using the latest energy saving drives from Mitsubishi allows us to not only save running costs, but to down rate the pump motors considerably, saving material costs.

Also the CC-Link network made the whole installation much easier.

We now have remote control and programming of the entire system and were surprised how quickly we managed the entire changeover".

The power requirement for the water management system is now reduced by up to 173kW/h, giving a payback period of only 19 months for the entire system, with the extra benefit of reduced water costs, less actual water wastage and increased ease of maintenance.

Ken Mason stated that: "Mitsubishi Electric's automation equipment was chosen as it has been the site standard since 1984 because they have had a zero failure on their PLCs, even in the most testing of environments.

Also, excellent technical service and localised support was provided by Mitsubishi's Melsmart distributor LC Automation".

The system has been so well received by the senior managers of the dairy that the company will soon be expanding the system to connect the water system to upper levels of the management network, via an Ethernet connection to the sites Mitsubishi Master A2AS PLC system, which acts as a communications hub for all other automation on the large dairy site.

Back to top