REALISING their future depended on the mill producing more than raw sugar the Proserpine Cooperative Sugar Milling Association board in 2002 decided to find a way of value-adding its under utilised cane fibre (bagasse).
Their investigations turned up furfural (plant resins) which could be extracted from the bagasse before it was used to fire the boilers.
The study found it would be profitable at the existing value of $800/tonne, so the cooperative purchased the patent to the SupraYield extraction process from its South African inventors.
Not only was SupraYield the lowest cost and highest yielding extraction process available but being a closed system it overcame the environmental problems that limited furfural production to Third World countries.
Owning the patent also gave the cooperative the opportunity to license other businesses to use the process.
As furfural is a flammable and toxic liquid, getting the local and State Government approvals to operate a furfural plant took a number of years and the $35 million plant was not installed until late last year for operation by the start of the 2010 crushing season.
It is designed to process 100,000 tonnes of bagasse - a third of the mill's annual production - and during the crushing season make 5000 tonnes of liquid furfural. As it now has a value of $1200-$1250/tonne it is worth 50 percent more than the figure on which the feasibility study was based.
Furfural is used in the manufacture of plastics; food flavouring; furfural alcohol; paint; golf balls; as a nematicide; to replace chemicals currently derived from fossil fuels; to blend with ethanol to enable it to dissolve in dieseline to produce Ecodiesel and by infusing it into pine give the wood the durability of teak.
The SupraYield process is a very low cost production system as the bagasse, which has a 48 percent moisture content leaving the crushers, is dried to 30pc using hot exhaust fumes from the boiler and the steam added to the digester during the 45-minute furfural extraction process lifts the moisture content back to 48pc so it is able to be put straight back onto the conveyor belt to feed the boilers.
Construction of the plant was completed during 2009 with commissioning of each section progressively carried out in the last quarter of the year.
The mill's CEO, John Power, told the North Queensland Register an early finish to the crush limited the ability of the mill to carry out extensive trials, but during the past three weeks 15,000 tonnes of bagasse was stockpiled and during November batch trials were put through the plant to produce xylose - the non-flammable precursor to furfural - and all systems operated successfully and passed the regulatory requirements.
The manually operated batch trials were used to develop process parameters for the system. For instance, it was necessary to establish the volume of loading and speed of the conveyor feed to optimise the bagasse pour rate into the digester; how fast the spin spreader inside the digester needed to run to distribute the bagasse evenly and how much steam needed to be added during the process.
In three hours, the first batch loaded the digester to only 40pc capacity while the third batch loaded to 90pc in one hour.
The engineers are now analysing the huge amount of data that was collected so the system can operate automatically.
The only section of the plant still remaining to be tested is the distillation plant - the section where xylose is converted to furfural.
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