The Partitional Behavior of sulfur and minerals in the thermal fragmentation char during pyrolysis of lignite

Abstract

In the lignite pyrolysis process, the pulverization of char due to thermal fragmentation are not considered a positive phenomenon. However, we found that the thermal fragmentation effect was beneficial to the desulfurization of char. It was investigated that the yield, total sulfur, and different forms of sulfur distribution of thermal fragmentation char (TFC) with different particle sizes at 300–900 °C. Sulfur tended to be concentrated in the pulverization char by thermal fragmentation. Compared with the total sulfur content of raw coal of 1.69%, the lowest sulfur content of char with the same particle size range after pyrolysis and screening treatment reached 0.86%. The enrichment of total sulfur in the low-temperature stage was derived from sulfate and sulfide sulfur as well as in medium and high temperature stage was mainly derived from sulfide and organic sulfur. Further, the mechanism of mineral transformation and sulfur partitional behavior was explored. The minerals composition, apparent morphology, and surface chemical state of TFC were characterized by X-ray diffraction (XRD), scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). It was found that Fe-S minerals with coarse-size were concentrated in the pulverization char in the form of active distribution. Organic sulfur was also enriched in pulverization char in medium and high temperature stages.