Coal Preparation » Environmental Improvement
The stated objective of this project was to demonstrate improved operation of the mechanical dewatering of coal tailings based on charge neutralisation of the feed.
The project demonstrated that belt press filter feed charge demand can be measured using a by-line sampling system, with some representivity issues in the sample presentation to the charge analyser unit.
The measured charge demand for all seams tested was highly anionic.
Comparing the charge demand results for different seams showed some broad trends of differentiation but due to the scatter in results definitive seam differential could not be confidently made.
The feed charge demand data is not suitable for input in a feed-forward flocculant addition control system to provide optimum belt press filter performance based on neutralisation of the feed charge. This is primarily because the critical flocculant addition is anionic and the measured charge is also anionic, thus anionic flocculant addition drives the charge further from a neutral state.
Correct anionic flocculant dosing to produce large free draining flocs is believed to be a more critical performance factor than the creation of a neutral feed charge, in a slurry where there are mixed sign charges present on the particle surfaces.
Filtrate charge demand measurements showed that there is generally scope to reduce the cationic flocculant addition levels, compared with the operator set levels based on past experience. However, optimisation (minimisation) of cationic flocculant addition based on filtrate charge demand measurements alone could not be readily determined. This is due to the relatively wide range of charge demand values that provided acceptable filter operation. While the technology did not appear to be suitable for application in a multi-seam environment, it may be functional in a single seam operation with low process variability, provided a reliable reference range could be established.
A simple control system reacting to instances of severe cationic flocculant overdosing could be applied when filtrate charge is highly cationic.