Product category:
Industrial Drives/Controls
News Release from: Danfoss Motion Controls | Subject: VLT 6000 drives
Edited by the Engineeringtalk Editorial
Team on 19 February 2003
Energy savings go through the roof for
tile maker
The application of variable speed drives to the combustion and cooling control of two new kilns has realised energy savings of up to 60% for Britain's leading independent roof tile manufacturer.
By the application of variable speed drives to the combustion and cooling control of its two new kilns, Sandtoft Roof Tiles, Britain's leading independent roof tile manufacturer, has not only realised energy savings of up to 60% but also dramatically reduced fan noise while at the same time, achieved tighter process control Sandtoft Roof Tiles' Broomfleet Tileries, near Brough, East Yorkshire, manufactures clay roof tiles, a process which demands kiln firing of the dry clay tiles of up to 60h at over 1000C, followed by a lengthy cooling period of up to 28h, depending on the type and number of tiles being fired
Combustion conditions are critical to product quality, and the kiln temperature is increased through a predetermined cycle with the temperature even throughout the kiln.
This necessitates a combustion fan to supply the correct amount of air for efficient burning of the natural or LPG gas fuel.
In addition, an eductor fan ensures even heat distribution through control of the flue gas extraction via kiln pressure control.
Uneven firing or cooling can result in discolouration and distortion of the tiles and a high rejection rate, so close control of temperature gradients throughout the kiln is critical.
On its older kilns, Sandtoft controls the combustion and cooling cycle air demand by opening and closing dampers.
Frequently this means running the fan motors at full speed with the dampers virtually closed.
Not only is this very inefficient but it means that fan noise is significant with the motor constantly at full speed.
So successful has been the application of VSDs that Sandtoft is to refurbish the existing kilns applying the same control system and Danfoss VLT 6000 drives.
When deciding on the specification of the new intermittent kilns, Steve Porter, the Works Electrical Engineer, for a number of reasons decided on Danfoss VLT 6000 drives for both the 37kW combustion fan and the 18.5kW eductor fans using the flexibility of the VLT 6000's multi setup function.
Porter comments: "Fitting VLT 6000 drives to the combustion fan means we can not only utilise it during the firing cycle to provide air for the combustion conditions but now we can use the same fan on a different set of settings to provide PID loop controlled cooling air during the cooling cycle.
We have the combustion and cooling cycles preprogrammed into our PLC; the setup of the drives switches seamlessly between a constant reference for firing and a PID loop control for cooling.
Not only does this give us excellent control over the firing and cooling conditions in the kiln but the fan is now drawing closer to 10kW than its 37kW rating when firing and only using the full 37kW capacity for rapid cooling as required.
Similarly, the eductor fan, controlled via a pressure sensor within the kiln uses two setups; one to control kiln pressure and the other to boost rapid cooling air.
Porter adds: "The energy savings are very welcome in view of the increased costs imposed by the Climate Change Levy.
Energy savings of 60% are being realised over a like for like firing cycle.
Reducing noise levels is also important to Sandtoft's environmental policy and an addition benefit is that fan noise has been reduced so dramatically on long cooling cycles that is has proved necessary on occasion to check visually on fan operation as they are now virtually inaudible".
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