Derrick Stack Sizer In-plant Evaluation

Across the industry, millions of tonnes of saleable quality ultrafine coal are ultimately discarded into tailings dams along with the high ash slimes material. While a classifying cyclone is widely considered to be a size separating unit there is also a substantial density separation occurring simultaneously. Consequently, regardless how efficient the hydrocyclones are operated, the separation of particles will vary according to both density and particle size. As a result, there will always be a significant amount of coarse low-density particles reporting to the overflow stream.  

Based purely on the principle of size classification, the Derrick Stack Sizer is a small footprint high capacity technology capable of recovering coal from fine waste streams and reducing the ash value of existing fine product streams. The Stack Sizer can be used as a replacement for classifying cyclones, to recover coal from thickener underflow, to scavenge flotation tailings or even to replace flotation. Effective ultrafine size separation may be a viable alternative to flotation for a thermal coal mine. Even if the hydrocyclone overflow is beneficiated by flotation, a significant proportion of the coal may be lost due to inherent process inefficiency. A Derrick Stack Sizer could be used to recover coal lost in the flotation tailings. It therefore has the potential to be a 'gamechanger' and revolutionise the industry for both thermal and coking coal mines.

There are >100 Derrick Stack Sizers installed in the coal industry world wide. However, there are currently no Derrick Stack Sizers installed in the Australian coal industry. The objective of this project was to provide the Australian coal industry with useful performance of Derrick Stack Sizers across a range of operating conditions. Plant trials will allow sites to properly assess the benefits of Derrick Stack Sizers across a range of site specific circumstances, without requiring each site to individually assess the technology.

A single-deck Stack Sizer was tested at two sites in NSW and one in Qld. The trial unit installation was managed by WPE Process Equipment, while its performance at each site was independently audited. The data collected during the site trials included: feedrate, % solids and ash by size for each stream and float-14 sink and laser sizing of the feed. The Stack Sizer operating variables included screen aperture, feedrate, repulp water flowrate and feed % solids.