Coldry Process

Coldry Process is a patented coal upgrading technology being developed in Victoria, Australia by Environmental Clean Technologies Limited based on 'brown coal densification'. It has been developed specifically to beneficiate low-rank brown coal (lignite) and some forms of sub-bituminous coal by removing the majority of the naturally occurring moisture content; harden and densify the coal; raise the calorific value of the coal; and transform the coal into a stable (lower spontaneous combustion risk), exportable black coal equivalent product for use by black coal fired power generators to produce electricity or as a feedstock for downstream processes such as coal-to-gas, oil and other high value chemicals. The Coldry Process is currently developed to pilot scale (as at October 2012).

Essentially, brown coal is sheared and attritioned reducing the mean particle size and releasing water naturally held in the porous coal microstructure forming a plastic mass. This dispersal of surface and physically trapped moisture lends itself to evaporative removal at or near ambient temperatures. Shearing also opens fresh coal surfaces exposing reactive molecular species, which participate in new bond-forming reactions and liberate some chemically trapped moisture. As the pellets densify, the newly formed structure shrinks, resulting in a significantly more compact microstructure compared to the original coal. This new structure significantly reduces the propensity to self-heat to that of a typical bituminous coal. When applied to lignite and some sub-bituminous coals, the Coldry process produces a feedstock in the form of densified pellets that significantly reduce CO₂ emissions compared to its original brown coal state, when combusted to generate electricity. A key feature of the technology is its use of low-grade 'waste' heat from a co-located power station to provide the evaporative drying energy. Typically, power stations shed that energy via cooling towers, drawing significant water from local river systems. The Coldry plant is designed to act as a heat sink for the power station, offsetting or replacing water taken from the environment for cooling. The temperature range for drying is between 35°C and 45°C. This forms the basis for the synergy with existing mine-mouth power stations and avoids the need to incur increased operational expense by generating high-grade process heat, or by calling on high-grade heat from other processes, that may have higher value in other applications.

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