Energy Efficient Drying of Alumina
GREENHOUSE GAS ABATEMENT PROGRAM PROJECT
Project Management: Queensland Alumina Limited (QAL)
Project Details
- Queensland Alumina Limited (QAL) operates the world's largest alumina refinery at Gladstone in Queensland producing around 7% of the world's alumina.
- Calcination is the last step in the processing of bauxite to alumina. The refinery's calcination section was designed with nine rotary kilns and one fluid bed calciner to carry out this process.
- The GGAP project replaced the 9 rotary kilns that were about 30 years old, with three modern and less energy intensive stationary kilns. This provides significant reductions in energy consumption and consequently greenhouse gas emissions.
- Another environmental benefit of the project, in addition to greenhouse gas emission reductions, is reduction of physical dust emissions from the plant. QAL has also been a signatory the Australian Government's Greenhouse Challenge Plus programme since 1997.
GGAP Funding: $11 million under the GGAP.
Total Project Cost: $175.7 million.
Expected Greenhouse Gas Abatement: Up to 1.43 million tonnes of carbon dioxide equivalent over the period 2008-2012, at the time the project was approved.
About the Project
Queensland Alumina Limited (QAL) operates the world's largest alumina refinery near Gladstone in Queensland. QAL produces around 7% of the world's alumina (aluminium oxide Al2O3). Alumina is produced from bauxite, a naturally occurring ore deposit. Alumina produced at Gladstone is smelter grade and used in the production of aluminum. The Bayer process is used in the Gladstone refinery to convert bauxite into alumina.
The Bayer process was developed by the chemist Karl Bayer in 1887 and is an economical method of producing alumina. It consists of 4 stages:
- Digestion of the bauxite;
- Clarification of the liquor stream;
- Precipitation of alumina hydrate; and
- Calcination of alumina.
The calcining stage consists of three steps; washing, calcining and cooling.
Washing: A slurry of coarse hydrate (Al2O3.3H2O) obtained from the precipitation stage of the Bayer process is filtered and washed to remove the process liquor.
Calcining: The resulting filter cake obtained from washing of the coarse hydrate is fed through a series of calcining units, either a circulating fluidised bed calciner or one of nine rotary kilns (each 100m long and 4m in diameter).
During the calcining process both free moisture and chemically combined water is removed by raising the temperatures to more than 1100°C through firing with natural gas. The project's scope involves gaining greenhouse gas emission reductions during the calcination stage by replacing the nine older rotary kilns with three energy-efficient calciners. The resultant energy savings are expected to translate to 1.43 million tonnes of CO2 equivalent in the years 2008 to 2012.
Cooling: Rotary or satellite coolers are used to cool the calcined alumina. Fluidised-bed coolers further reduce alumina temperature to less than 90°C before it is discharged on to conveyor belts which carry it to storage buildings where it is stockpiled for shipment.
Note: Carbon dioxide equivalent (CO2-e) is the basis for comparing the warming effect of a greenhouse gas as compared to carbon dioxide and is calculated by multiplying the mass of a greenhouse gas by its global warming potential.
< Projects
Related information
Key
Links to another web site
Opens a pop-up window