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

摘要

The paper reports on investigations into control methodologies for mitigating ashrelated problems such as particle agglomeration and bed defluidisation during fluidized-bed combustion of low-rank coals. A laboratory scale spouted bed combustor is used to study the effectiveness of control methodologies. In the present work, 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 South Australian low-rank coal. Samples of the same coal subjected to Al pretreatment, water washing and acid washing are also tested in the spouted bed combustor. Experiments showed that both methods are effective to different extents in reducing ash-related problems. Tests with calcined sillimanite and bauxite (as the bed material) showed trouble free operation for longer periods (7-12 hr at 800°C and 3-5 hr at 850°C) 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 of bed particles has been identified as the main 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.