LAUSR

Abstract The effect of flue gas recirculation (FGR) on ash deposition and Na migration in a laboratory-scale circulating fluidized bed (CFB) burning Zhundong lignite was investigated. The CFB dense phase was maintained at temperature 950 °C, whereas that of the furnace exit was adjusted to 730 and 680 °C respectively by manipulating the FGR flow rate. Two ash deposition probes maintained at 550 °C were installed in the furnace chamber (P1) and cyclone outlet (P2). The deposited ashes along with the bottom and fly ash were collected and analysed by using XRD, SEM-EDX and ICP-OES. Results showed that the P1 deposit consisted of sintered Ca/Mg/Na sulphates and aluminosilicates at 730 °C, but became granular Na2SO4/CaSO4 at 680 °C. The P2 deposit and fly ash were sintered and rich in CaSO4 and Na2SO4 at 730 °C, but did not show signs of sintering at 680 °C. The bottom ash was enriched in CaSiO3 and NaAlSi3O8 at 730 °C, but were dominated by Na6(AlSiO4)6 at 680 °C. Na in the bottom ash increased from 31.7 to 35.2 mg g−1 as FGR flow rate increased, leading to severe bed particle agglomeration consequently. The FGR thus exerted a trade-off effect on the sintering and deposition propensity of fly ash and agglomeration of bed materials.