Effect of temperature on the sintering behavior of Zhundong coal ash in oxy-fuel combustion atmosphere

• Digital image technique was used to monitor the morphology of sintered ash samples under oxy-fuel combustion atmosphere.
• The change in height and area of sintered ash samples with time was obtained through image processing system.
• Layer structure of the sintered samples with different colors was analyzed.
• Mineralogy, chemical compositions, and microstructure of layer structure of sintered samples were analyzed.

This paper was addressed to evaluate the sintering behavior of coal ash at different temperatures under oxy-fuel combustion (O2/CO2 combustion) atmosphere. A lignite (Zhundong coal) characterized by high sodium level has been applied as the fuel material. The raw ash was heat treated at four different temperatures: 1350, 1300, 1250, and 1200 °C, respectively. In addition, two atmospheres has been applied to as the reaction atmosphere: (1) 30 vol.% O2/70 vol.% CO2 (oxy-firing); (2) air (reference). Meanwhile, the shape of the sintered ash samples during the sintering process was monitored by charge coupled device (CCD). The shrinkage of height and area of sintered samples can be obtained by the image processing system. In addition, the microstructure and chemical compositions of the sintered samples were analyzed by a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometry (EDX). Moreover, the distribution of mineral phases in the sintered samples was identified by X-ray diffraction (XRD). The results show that the sintering degree of the samples increases with temperature. In addition, all the samples are characterized by layer structure with different colors. Meanwhile, the XRD results reveal that the oxy-fuel combustion atmosphere did not change dramatically the kinds of mineral phases, but did influence the relative amount of crystalline phases.