Experimental investigation into the incineration of wool scouring sludges in a novel rotating fluidised bed

Abstract

The main purpose of this research was to investigate the possibility of incineration of wool scouring sludges in a novel vertical axis rotating fluidised bed (RFB). A small-scale RFB was designed and constructed with an internal diameter (ID) of 200 mm and height of 50 mm to carry out the experiments. In phase one of the experiments, a cold test was conducted to investigate the fluidisation performance of the RFB, which eventually led to the optimisation of the operating parameters, i.e., sand particle size, rotation speed and bed loading (bed thickness) which ensures complete fluidisation and minimum particle elutriation. Sand particle size of 0.5 to 0.6 mm, rotation speed of 200 to 400 rpm and bed loading of 1 kg (equivalent to bed thickness of 27 mm) were found optimal. These information generated were useful for the second phase of the experiments, which was the hot test, in investigating the possibility of incinerating wool scouring sludges in the RFB. Nine wool sludges from different process routes generated from the wool scouring industries were analysed for their compositions. Most of these sludges were highly moist, had high volatile matter and high ash content with low level of fixed carbon. These characteristics made incineration difficult. Hence, the effect of varying the moisture content, rotation speed and sludge feed rate on the incineration of the three selected sludges were studied in the hot test. With 5% support methane, all sludges with a maximum moisture up to 70% as-received could be successfully burned in the RFB at rotating speeds of 200 and 300 rpm. The combustion was found to be intense with a high efficiency due to the good turbulence and mixing in the RFB. The combustion gases produced, i.e., CO, CO 2 and NO x were reasonably low due to the high combustion intensity and efficiency. To study the dynamics of the bed and freeboard region in the RFB, the velocity flow field was simulated using a computational fluid dynamics (CFD) model to generate information of the flow pattern. The special advantages of swirling flow would benefit the gas combustion in the RFB. The experimental results obtained have suggested that the incineration was successful and the ash particles elutriated were fine due to the good mixing and turbulence in the RFB. This also reflects the RFB as an effective incinerator.