Technical Note #32 Energy Efficient Technologies - VSD Fan

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The EECB facilitated a targeted Energy Systems Optimisation (ESO) Assessment at Algoa Brick as part of the National Cleaner Production Centre (NCPC) programme. The audit report evaluated 9 of the approximately 50 fans in operation at Algoa Brick for the fitment of VSD’s (Variable Speed Drives).

Of the potential estimated savings of 565,000 kWh / annum due to the fitment of VSD’s, the 37kW exhaust fan at Plant 2 was listed as having the highest potential saving of approximately 127 000 kWh per annum. For this reason and the potential for replication of the project at other brick manufacturers, the EECB undertook to co-fund the fitment of a Variable Speed Drive onto Algoa Brick’s Plant 2 exhaust fan.

The baseline electrical consumption was measured via a PowerStar electrical meter installed in advance of the existing star-delta starter. Secondly, the installation of the VSD was intended to obviate the need for damper control and modulation of the fan. For this reason, the actual influence of the fan on the kiln needed to be measured by means of a draught monitoring system.

Results

At first, the kiln draft was set to maintain a relatively high draft value. This resulted in an average daily electrical consumption of only about 6.8% lower than the baseline. Notwithstanding, it became clear from the varying speed of the VSD that another factor – air leakage – was influencing kiln draught rather than only the speed of the exhaust fan.

Unfortunately, air leaks can come from a number of sources such as the intercar seals on kiln cars, poor kiln car decks, kiln inner door leaks and also leaks into the flues and ducting. Dealing with these air leaks necessitated work on a number of fronts including repairs to intercar seals and kiln car decks (ongoing as there are 90 kiln cars), replacement of the kiln inner door and also changing the kiln pushing regime. Additionally, the exhaust fan and sections of corroded ducting were replaced.

Following these further interventions, the draft setting on the kiln was “walked downwards” whilst maintaining acceptable kiln performance. Further measurement of power consumption now shows a daily average consumption by the Plant 2 exhaust fan of approximately 64.5% lower than the baseline. This equates to an annual energy saving of approximately 120 695 kWh per annum worth approximately R109 205 per annum at AB’s weighted average electricity cost. The project cost R92 610 (including M & V and reporting) giving a simple payback period of 0.85 years or a little over 10 months.

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