Proposal of a new soot quantification method and investigation of soot formation behavior in coal gasification

• A soot quantification method (LD method) for coal gasification was proposed.
• LD method utilizes a laser diffraction particle size analyzer.
• Soot yields in coal gasification tests were successfully measured by the LD method.
• Soot formation behaviors during CO2, H2O or O2 gasification were investigated.

Coal gasification is one of the key technologies for utilization of coal. Coal gasification mainly consists of coal pyrolysis, char gasification, and gas-phase reactions. Soot is made up of fine solid carbon particles formed by volatile matter decomposition and has lower gasification reactivity than char. Since the solid products of coal gasification contain both char and soot, it is difficult to quantify the amount of soot produced by this process. In this study, a novel soot and char quantification method utilizing a laser diffraction particle size analyzer is proposed. Coal gasification experiments were performed using a pressurized drop tube furnace (PDTF). The soot and char yields were quantified by the new method. During CO2 gasification, char was selectively gasified and the amount of soot barely decreased. Hence, the carbon conversion initially increased, but remained around 0.8 even at 1673 K. In the case of other gasifying agents, O2 or H2O, different behavior was found. During O2 gasification, the soot yield considerably decreased as the O2 concentration increased. The main reason was not soot gasification, as presumed, but rather the reaction of tar components with O2. In the H2O gasification, the soot yield slightly decreased as the H2O concentration increased.