The overall control, safety and energy efficiency of production and
effluent treatment facilities at Glanbia's dairy operation in Kilkenny,
Ireland, have been gretaly improved thanks to the application of drives
technology in various key areas of the plant
The effluent plant at Glanbia's huge food processing facility in
Kilkenny, Ireland is designed to handle a biochemical oxygen demand (BOD)
of 15,000 to 20,000kg per day, and is big enough to serve the needs of a
medium sized town. The target is to reduce the final BOD to negligible
levels of just 10mg/litre and suspended solids to just 15mg/litre before
discharging the treated water into the nearby River Nore. According to
effluent plant foreman Matt Brennan, this is considerably better quality
than the river water itself.
The effluent is passed to a bio-tower with honeycomb filter that removed
some 50% of the BOD, then to a settlement tank to remove more solids,
through an oxidation tank with full nitrification and denitrification
capabilities and finally to a membrane tank that removes final small
particles. Three Control Techniques 132kW Unidrive variable speed drives
and two soft starters power the blowers that control the dissolved oxygen
controlling PLC, which ensures that oxygen levels are maintained between
20% and 40% by increasing or decreasing speed demand to the three drives.
Further blowers, controlled by 75kW Unidrives keep the water agitated in
the membrane tanks to prevent the filters becoming clogged with solids.
Each membrane pack has 150 filter sheets, providing fine filtration of
the effluent prior to discharge. There are ten packs per tank. This
effluent scheme has now been running for five years without problems. The
throughput capacity has been increased from 6,000 to 9,000m3 per day and
final discharge limits have been reduced by 50%.
It was around three years ago that Glanbia standardised on Control
Techniques drives throughout the Kilkenny facility. In addition to their
use within the effluent plant, they are also used to control production
lines and sprayer-dryers. For example, two Unidrives have replaced an
inefficient damper system to improve control of a 4tonne/h sprayer drier
in the powdered milk and whey powder production area. A 180kW Control
Techniques soft starter is also employed to bring the 15,000rpm atomiser
gently up to speed
Both productivity and safety have improved tremendously, says Glanbia's
maintenance manager, Michael Dooley. Production on this machine has
increased from 3.5 to 4.4tonne/h, quality and consistency have improved
and downtime has been drastically cut he says. Before, we couldn't run
the machine for more than 24 hours because of the risk of explosion,
because of dust build up.
A 160kW Unidrive controls the flow of air at 212°C into the dryer, and
this is exhausted via a fan, controlled by a larger 300kW Unidrive. The
damper control was poor, recalls Mr Dooley. It is crucial to both
quality and safety that both vacuum and temperature within the cyclones
are maintained to tight tolerances. Too much air flow and the temperature
drops, increasing the chance of powder being expelled to atmosphere. Too
little flow and there is an increased explosion risk and dust build-up.
There is a substantial payback from energy saving, now that the fans are
no longer run at a constant full speed, and air flow is controlled by fan
speed rather than by mechanical damping. This alone has achieved a
payback of just two years. But the payback from increased production is
even more significant, adds Mr Dooley. The installation of the drives
has virtually eliminated the fire and explosion hazard and has been a
huge success.