Many characteristics of fine coal flotation are analogous to sulphide cleaner flotation where the emphasis is on handling high mass recoveries and rapid kinetics.
“Froth management is one of the key considerations in obtaining an optimal float circuit design,” Outotec said.
“Additionally, there are a number of options in retrofitting or modifying an existing CHPP float circuit. Strategies such as retrofitting of new froth crowders, improved circuit control through using froth cameras, and split feeding can all help improve froth recovery and the flotation cell performance, with minimal operator input even when encountering feed variations.”
A critical factor in coal flotation is froth management. Over the last four years, Outotec has undertaken pilot flotation work and sampling of existing mechanical cells within Australian CHPPs.
One of the key observations was the large variation in the amount of froth being recovered down the bank.
This typical yield profile can be looked upon as two flotation extremes occurring in a single bank of cells: high yield on first cells, with rapid kinetics; and yield falling off rapidly down the bank – with substantial froth crowding required to maintain the product ash content.
The majority of coal comes off the first cell due to the rapid coal flotation kinetics. After this there is a large drop off in mass yield.
The first cell in the bank recovers around 60% to 70% of the mass in the feed, and then falls off in the remaining cells.
Though they are all in the same bank, the individual cells have to operate under very different duties in terms of froth handling and also solids concentration in pulp. This calls for a tailored approach to the cell design.
