Separation of unburned carbon from fly ash using a concurrent flotation column

Abstract

In this study. a new concurrent flotation column that simulates the plug flow reactor was designed with the use of a static mixer, a froth separator column and an optional additional bubble generator for fly ash beneficiation. The objective was to improve the efficiency and effectiveness of unburned carbon removal from fly ash by minimizing energy costs. Cleaning tests were performed with and without the additional bubble genarator. Without the additional bubble generator unburned carbon in the ash product could be reduced to only 2.53%. Incidental loss of carbon particles and insufficient bubble generation were the main causes of poor carbon separation performance. By turning on the additional bubble generator it was aimed to assist bubble generation, to compensate bubble rupture and to recapture the detached or free carbon particles leaving the froth phase. With the additional bubble generator and under optimized conditions a froth product with 95% carbon recovery and a cleaned ash product with less than 1% unburned carbon was obtained. The separation process through the static mixer (feeder) and the separator column and the energy consumption of the unit were analyzed. It was seen that around 80% energy could be saved with the concurrent flotation column compared to conventional flotation. (C) 2009 Elsevier B.V. All rights reserved.