||Technology in Australia 1788-1988
Table of Contents
I The Present Energy Economy
II Australian Energy Consumption
III Research And Development
V Oil And Natural Gas
VI Solar Energy
VII Nuclear Energy
VIII Bagasse Firewood And Other Biomass
IX Electric Power Generation And Distribution electric Power Generation And Distribution
X Manufactured Gas
XI Industrial Process Heat
i The sugar industry
ii General purpose boilers
iii Units used in this chapter
Industrial Process Heat
The sugar industryAustralian sugar mills are generally self-sufficient in their use of bagasse as their primary source of fuel for steam raising; the exceptions occur at the initial start-up, when electricity from the grid is used to get that plant operating and at the beginning of the crushing season, when auxiliary fuels such as wood chips, sawdust, coal, nut shells or oil may be needed to supplement the bagasse carried over from the previous season. Steam is used for generating electricity and for driving prime movers in mills (mainly turbines and some reciprocating engines) and the exhaust steam is used for process heating.
Australian engineers became active in improving the designs to handle local conditions and to improve the performance. Travelling grates were included in the installations, and within 16 years of the first installation of a bagasse suspension fired boiler, a unit of 227 tonne/hour capacity was operating successfully. Some good work was done in computer modelling of boilers by the combined efforts of the Sugar Research Institute (SRI), CSR Ltd., IBM, and the Bureau of Sugar Experiment Stations.
Until this time, the policy of mills in progressively expanding boiler stations by purchasing additional small units, had led to a multiplicity of boilers, with their attendant high cost of maintenance and manning. The present trend in Australia is towards a single large installation.
Bagasse is a difficult material to handle. It chokes readily, does not flow freely in convergent or even parallel conduits and needs divergent chutes for easy flow. It will clog in screw conveyors and its handling behaviour varies with moisture level, cane variety, and growing conditions. Australian engineers have shown great ingenuity in devising methods of conveying, plowing-off belts and reclaiming this difficult material from storage.
Suspension fired boilers' furnace designs have resulted in much taller furnaces, with faced boiler tubes lining the walls. The use of baffles in the path of the flue gases in some designs, to improve the heat transfer from flue gases to the tubes, also introduced tube wear by erosion. Partial re-design and protection of the tubes have been successful in minimising the problem in existing units.
Before the oil crisis of the 1970s, auxiliary oil firing was practised, but the industry was quick to find methods of minimising and almost completely eliminating oil usage. The solutions included: better bagasse firing control and the limited use of extraneous fuels such as coal, woodchips, sawdust, and nutshells.
At the beginning of the crushing season, bagasse may be in short supply due to plant commissioning, wet weather, cane shortage and low levels of fibre in cane at that time. Later in the season it is common for mills to have excess bagasse and some method of disposal is required. A solution adopted by some mills is to incinerate bagasse in their boilers and to use air cooled condensers to condense that quantity of steam which is in excess of the factory's requirements. This gives an efficiency variation as required and saves the cartage and disposal problems of excess bagasse (Levy, 1981). It is disappointing that, in Australia, the electricity generating authorities are not disposed to offer payment which would be adequate to enable the mills to purchase generating plant in excess of their needs in order to supply electricity to the grid.
Organisations in Australian Science at Work - Bureau of Sugar Experiment Stations; Colonial Sugar Refining Company (C.S.R.); I.B.M.; Sugar Research Institute, Mackay
People in Bright Sparcs - Levy, P. W.
© 1988 Print Edition pages 841 - 842, Online Edition 2000
Published by Australian Science and Technology Heritage Centre, using the Web Academic Resource Publisher