Regulation of pre-pyrolysis on the release of alkali metals during the co-gasification of coal and biomass in visualized fixed-bed coupled with laser-induced breakdown spectrometer system

Abstract

The release of alkali metals during the co-gasification of coal and biomass can cause the deposition, slagging, and corrosion of equipment. In this work, the pretreatment of Yangchangwan coal and rice straw via low-temperature pyrolysis was performed to regulate both the release behavior and the release amount of volatiles. The correlation mechanism between the release of volatile matter, the evolution of char physicochemical properties, and the real-time release characteristics of alkali metals during gasification was further investigated using a self-designed visualized fixed-bed coupled with a laser-induced breakdown spectrometer. The results showed that pre-pyrolysis treatment at 300 °C and 450 °C changed the content of volatiles and properties of chars and thus affected the release time and concentration of alkali metals during gasification. The release of volatiles via the short-term (below 15 min) pre-pyrolysis treatment declined the content of C–O–C and CO bonds, thereby promoting the release of alkali metals. When the pre-pyrolysis time exceeded 15 min, the more oxygen-containing groups and the higher structure disorder degree of pre-pyrolysis chars inhibited the release of alkali metals during gasification, reducing the release rate by 8 %. The release of the volatile and the break of oxygen-containing functional groups (C–O–C and CO) were key factors increasing the maximum release concentration of alkali metals during gasification.