Prediction of ash composition and agglomerating compounds formed during OXY-CFB combustion of Victorian brown coals

Oxy-fuel based circulating fluidized bed (Oxy-CFB) combustion is an emerging technology that combines the advantage of Oxy-fuel systems for easier CO2 capture and traditional advantages of CFB systems - fuel flexibility, uniform temperature distribution, reduced unit size and operating cost. However, bed agglomeration is a potential problem in an Oxy-CFB system that may lead to a lengthy and expensive unscheduled shutdown. Therefore, there is a need to know the composition of the potential agglomerate forming compounds during Oxy-CFB combustion of coal, through model predictions and experiments. In this paper, we make these predictions using the FactSage software for three major Victorian brown coals at temperatures 800-1000 degreesC. The simulation indicates that no molten phases are formed at temperatures below 900 degreesC. At temperatures beyond 900 degreesC, less than 4.5% of the total ash forms a molten phase. Hence, it is expected that agglomeration is unlikely to be a major problem during Oxy-fuel CFB combustion of Victorian brown coals, if the operating temperature is kept below the melting points of the predicted ash components. These results may serve as a guideline for selecting the conditions for agglomeration-free operation during Oxy-CFB combustion of Victorian brown coal. However, experiments are required to validate the predictions and are in progress.