Inhibition of O-containing functional groups in coal on the release of alkali metals during co-pyrolysis of coal and biomass in a visual fixed bed combined with laser-induced breakdown spectroscopy.

• A VFB-LIBS online system was applied for the in-situ detection of released AMs. • The concentration of released AMs in gaseous phase was quantitatively measured. • The temporal release of AMs can be limited in the whole pyrolysis. • The higher content of C = O in coal, the stronger limitation on the release of AMs. • The inhibition of OCFG was not selective for the release of K and Na. Co-pyrolysis of coal and biomass is a promising technology for clean and efficient utilization of these two carbon resources. In this study, a visual fixed bed (VFB) combined with laser-induced breakdown spectroscopy (LIBS) was applied to investigate the effect of O-containing functional groups (OCFG) in coal on the release of alkali metals (AMs) during the co-pyrolysis of coal and biomass. The results showed that low temperature pre-oxidation increased the content of OCFG in coal, especially C=O and O–C=O groups, and limited the release of AMs during the co-pyrolysis. The higher pre-oxidation degree, the stronger limitation on the release of AMs. The increase of OCFG declined the maximum release concentrations of AMs and the temporal release of AMs in the whole pyrolysis process rather than some period. The release ratio of AMs can be maximally reduced about 39% by the OCFG. The relationship between release of AMs and structure of chars during the pyrolysis was also investigated. It was obtained that the layering placement of biomass and coal showed the less volatilization of AMs than the mixing placement of them. This study provided the theoretical basis for mitigating equipment corrosion problems caused by AMs in industrial applications. [ABSTRACT FROM AUTHOR]