Effect of steel slag bed material on ash deposition and Na migration in circulating fluidised bed during Zhundong lignite combustion

Abstract

AbstractThis study verified the effect of steel slag as alternative bed material on ash deposition in circulating fluidised bed (CFB) burning high‐sodium Zhundong lignite (ZD). Sample of ZD was burned in a lab‐scale CFB at 950°C, and the obtained fly ash and ash deposits were characterised. Results showed that the presence of steel slag bed material leads to the abundance of Na (2.39 wt%) in fly ash. Na‐bearing minerals such as Na2SO4, Na2Si2O5 and NaCl of low melting points had been identified, resulting in severe ash deposition on heat transfer surfaces than that with quartz as bed material. This could be mitigated by incorporating 10 wt% oil shale semi‐coke (SC) into ZD, among which Na was captured by aluminosilicate and retained in the interior of SC as (Na, Ca)Al(Si, Al)3O8 of high melting point. Na in the fly ash thus decreased to 1.05 wt% and in the form of high melting‐point Na(AlSi3O8). In addition, ESEM confirms that the SC particles after capturing Na still had an ash fusion temperature of 1280°C, which were insufficient to induce bed particle agglomeration.