Research on the effects of the fly ash reburning on element migration and ash deposition characteristics of high-alkali coal in a full-scale slag-tapping boiler

•Fly ash reburning can enhance the absorption of alkali metals by liquid slag.•Fly ash reburning can reduce alkali metals in the flue gas.•A novel fly ash sampling method was applied.•This work provides a demonstration for burning high alkali coal in full-scale slag-tapping boilers.