Review of ACARP Dewatering Projects

This report presents a review of the 26 past and current coal dewatering research projects funded by NERDDC and ACARP. It was commissioned by ACARP to:

• summarise the practical outcomes
• highlight any further potential outcomes that could be realised for a relatively small amount of additional funding
• recommend any prospective areas for future research.

All projects were critically reviewed. They were also discussed with key participants and with numerous coal preparation practitioners and equipment suppliers. The body of the report presents a brief summary of relevant projects, arranged according to the dewatering equipment or technique under investigation. No broad review of literature was undertaken. That has been done within the projects under review.

The practical outcomes of ACARP dewatering research have been minimal. It seems that no plant is making routine use of production equipment or techniques that can be traced back to these projects. The CSIRO and University of Queensland developed a bench-scale centrifuge. It is used to treat samples of coarse coal to predict product moisture content following processing of that coal type in an industrial-scale vibrating basket centrifuge. This has been used by a number of producers and plant designers for plant design and optimisation. The University of Queensland sought to have its version of the single leaf laboratory filter adopted as an industry standard. To date, little interest has been shown in that device.

The two R&D issues with most potential for near-to-medium term benefit to producers are:

1. Managing water loss and water uptake from the point of production of saleable product to the point of sampling for sale. This can include drainage from stockpiles and rail wagons and water uptake from rain and dust-suppression sprays.
2. Demonstration projects to assist producers to better utilise existing equipment - particularly filters, vibrating basket centrifuges and scroll centrifuges.

Valuable projects on air-purge dewatering and on extending the life of scroll centrifuge baskets are nearing completion. Other matters with near-to-medium term potential include:

1. Properly-resourced plant trials of high-shear conditioning of filter feed with polyelectrolyte flocculants and with oil.
2. A study to generate guidelines as to what size fractions are worth recovering. Inputs would include contamination levels, associated moisture levels and contract provisions.
3. A brief review of the state-of-the-art of briquetting and of briquette stability. It should consider processes which use binders as well as "binderless" processes which require pre-drying. Applications to filter cake and to coal recovered from tailings dams should be included.

Possible productive avenues for the medium term include:

• Super-absorbent polymers for dewatering of fine coal.
• Super-absorbent polymers to allow dry by-pass of fine coal to product
• Depletion Flocculation, whereby osmotic effects can be utilised to compact and strengthen the sludge in a tailings pond.