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UCC is produced in a chemical leaching process with some similarities to the Bayer process for refining alumina. The process works through a series of steps that convert the minerals to soluble forms and then remove them to a point where the total ash content is less than 0.2%. The dissolved minerals are then precipitated predominantly as calcium sulphates and calcium aluminium silicates, for safe disposal or utilisation in other industries such as building materials and ceramics. A simplified schematic of the process and a typical analysis of UCC and its parent coal are given below.
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Property
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Feed Coal
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UCC (Laboratory)
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Total ash
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8.3%
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0.15%
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Ash particle size
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-
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< 5µm
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Inorganic Content of the Coal
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(ppm)
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(ppm)
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Si
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24,800
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35
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Al
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12,300
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8
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Ti
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733
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477
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Fe
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3,383
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34
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Ca
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437
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22
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Mg
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431
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5
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Na
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919
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58
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K
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464
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9
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P
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86
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3
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Mn
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13
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0
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V
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29
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12
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Ash Fusion Temperature IDT
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> 1500 ºC
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> 1500 ºC
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Greenhouse Gas (GHG) Abatement
The proposed development program for UCC production and UCC fired turbines in Australia envisages approximately 1,750 MW of UCC fired turbine capacity being installed in Australia by 2030, in a combined-cycle configuration. The efficiency increases alone would result in a reduction of 3.5 million tonnes of CO2 emissions from the generators each year or, on a full life-cycle basis, a reduction of 2.5 million tonnes of CO2 annually. If CO2 sequestration becomes an accepted and economic process, then the annual reduction could be around 11 million tonnes of CO2 annually. Detailed costing of power generated using UCC-fired turbines has not yet been made for an Australian installation. However, a Japanese study indicates that initial costs in Australia would be around 5 to 8 cents per kilowatt hour. As with all new technologies, the cost will reduce further as it is commercially developed. The benefits of UCC direct-fired turbines for greenhouse gas reductions in Australia, can also be realised in countries like Japan, China and the USA, but with the vastly greater size of the power generation industry in these countries the impact could be orders of magnitude greater.
UCC offers these countries many advantages including:
- Reduction in greenhouse gas emissions from the generator of 20-30% when compared to a modern conventional PC fired power plant, and 10-20% on a complete lifecycle basis.
- Provision of a coal based generating system that achieves high efficiency power generation from smaller gas turbine combinedcycle units that can be remotely located or used in a distributed energy configuration.
- A system where the UCC fuel can be produced in large plants placed close to the mines, where the fuel can be stockpiled so that any disruptions to the fuel production do not disrupt the generator (unlike IGCC where the gasifier and turbine are closely linked), and where the cost of the fuel is based on the relatively low and stable price of coal compared to the high and unstable price of natural gas.
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