Preparation of Clean Coal and Water Mixtures by Efficient Froth Flotation

Deashing of coal by froth flotation with vaporized collectors is studied in combination with preparation of coal water mixtures (CWM). Comparison of deashing performance and flow property of deashed CWM is made between the present method and conventional froth flotation. The effects of coal cleaning on slurry properties are also investigated. It is found that the amount of collector needed to recover carbonaceous matter can be reduced by vaporization of the collector, giving rise to the lower apparent viscosity of deashed CWM. Slurry viscosities of some coals are decreased by cleaning while those of other coals do not change. No increase of slurry viscosity by coal cleaning was observed. Dispersant requirement can be also reduced for some coals because ash, which prevents coal particles from being dispersed, was reduced. Ash erosion and deposition problems can be reduced by the use of cleaned coals, suggesting the possibility of boiler volume reduction.