BAGASSE is becoming increasingly valuable, both as a fuel and as a biomass
source for new products. Most of the bagasse produced in a sugar factory is used
by the boiler station. Typically, between 50% and 70% of the energy in the
bagasse supplied to the boiler station is transferred to the steam produced; most
of the remaining energy is lost as sensible and latent heat in the boiler exhaust
gases. To recover heat from boiler exhaust gases and reduce the final flue gas
temperature, most Australian boilers use air heaters and/or economisers. Both
these heat recovery devices are major capital cost items, especially when the
costs of the changes to the boiler duct work required for the installation of an air
heater or economiser are taken into account. For several years, Harwood Mill
has been looking at ways to reduce auxiliary fuel use and has considered options
such as increasing the number of gas and air passes. During the 2005
maintenance season, Harwood Mill installed swirl inserts at the top of the air
heater tubes, installed turning vanes in the air heater air inlet plenum, and
replaced some plugged and leaking air heater tubes. This paper investigates the
effects of these modifications and has concluded that the swirl inserts have
significantly increased air heater heat transfer and have reduced bagasse
consumption of the Harwood Mill boiler.