NEW SOUTH WALES Sugar Milling Co-Op is required to operate its Harwood boiler at
low load during the non-crushing season to supply refinery steam demand. Boiler loads
in the slack season typically fall to around 25% of Maximum Continuous Rating
(MCR), resulting in inefficient operation due to the elevated excess air ratios required to
maintain suspension burning. Excess bagasse generated during the crushing season is
insufficient to supply the full refinery off-season demand, resulting in the purchase of
other biomass fuels or coal. As part of Harwood’s EEO (Energy Efficiency
Opportunities) initiatives, trials were designed and undertaken to operate the boiler with
air entering a reduced portion of the grate, with the specific aim of improving low load
boiler efficiency. The successful trials with modified mode of operation gave
significantly lower flue gas losses to produce a 2.7% increase in boiler efficiency and a
4.5% reduction in fuel consumption. This work will form the basis for further extended
operational trials in 2011 designed to establish permanent, lower cost, low risk, reliable
and sustainable low firing operations.