Coal Preparation » Fine Coal
This project's objective was to assess the applicability of the flotation rate constant-bubble surface area flux (k-Sb) relationship to describe coal flotation, and its use as a means of characterising and optimising fine coal flotation (irrespective of cell technology).
Site work was conducted at Peak Downs and Burton Coal.
The work involved measurements of bubble size, superficial air velocity and air hold-up to determine the value of bubble surface area flux (Sb) in operating cells, combined with sampling of feed to reveal the prevailing rate constant k. Characterisation of the hydrodynamic characteristics of coal flotation cells has not been attempted on this scale before.
The JKMRC 60 litre flotation cell was operated in parallel with the site cell under investigation allowing major changes to be made to the operating conditions of the test cell (as opposed to the site cell) in order in order to investigate the k-Sb relationship.
Attempts were made to measure froth recovery, froth recovery is generally assumed to be 100 percent, but is normally much lower. Difficulties in analysing the results made it impossible to determine froth recovery.
Measurement of bubble size proved very much harder than anticipated. In the Microcel, bubble size was estimated using the drift-flux method, while in the Jameson cell bubble sizes in the cell tank and the downcomer were measured using a photographic method.
The wide range in feed size distribution combined with short-term variations in coal quality (especially at Peak Downs) made it difficult to determine an overall rate constant for the flotation. Consequently the project did not fully achieve its objective of being able to relate flotation performance to coal flotability and cell hydrodynamics.
However a large amount of cell characterisation data relating to plant scale Jameson and Microcels was gathered. The project has gone some way to overcoming the problem noted by Sanders & Williamson (1996) that 'assessment of flotation performance is one of the weakest areas of coal preparation engineering.' The data will be made available in Excel spreadsheets on CD ROM.
Further work in this area is recommended to bring the flotation of coal up to the same level of understanding that is now available for the flotation of metalliferous ores.