Visual Investigation of the Growth of Ash Deposits and Characteristics of Fly Ash with CaO Additives

Experiments were conducted in a pilot-scale test furnace to investigate the influence of CaO additive on the growth of ash deposits and the characteristics of fly ash. The amounts of CaO additive mixed with Datong coal were 0 and 3.5 wt %, and the operating temperature of the furnace was 1573 K. An oil-cooled probe was inserted in the furnace, and a charge coupled device (CCD) monitoring system was equipped with a water-cooling system to obtain the variation of thickness of the deposits with time. This system was used to evaluate the buildup of the deposits. Online monitoring of flue gas was carried out for the emissions of NOx and SO2 using the flue gas analyzer. The fly ash was collected from the bottom of the cyclone separator, and its characteristics were determined using a range of analytical techniques, including polarization microscopy, physisorption analysis, X-ray diffraction (XRD), and X-ray fluorescence (XRF). Frequent shedding of ash deposits was observed for pure coal. Nevertheless, under the condition with additive, serious slagging with a thickness of the deposits up to 66 mm occurred. The addition of CaO resulted in a reduction of SO2 but an increase of NOx emission. The fly ash produced by burning pure coal had a greater specific surface area (SSA). The XRD and XRF analysis results revealed that the CaO additive had a significant impact on the mineral and chemical composition of the fly ash.