Control methods for remediation of ash-related problems in fluidised-bed combustors

Investigations into control methodologies for mitigating ash-related problems such as particle agglomeration and bed defluidisation during fluidised-bed combustion of low-rank coals are conducted using a laboratory scale spouted bed combustor. Two control methods are investigated viz., the use of alternative bed materials and pretreatment of coal. Bauxite and calcined sillimanite are used as alternative bed materials in the spouted bed combustor while burning a South Australian low-rank coal. Samples of the same coal subjected to Al pretreatment, water washing and acid washing are also tested. Experimental results indicated that both methods are effective to different extents in reducing particle agglomeration and bed defluidisation. Tests with calcined sillimanite and bauxite as bed materials showed no agglomeration for longer periods than with sand runs at the same bed temperatures. Al pretreatment and water-washing were also found to be effective and resulted in extended combustion operation. Al enrichment in ash coating on bed particles has been identified as the key mechanism for prevention of agglomeration and defluidisation by these control methodologies. For water-washing, the principal reason behind agglomeration and defluidisation control is the reduction in sodium levels.