Agglomeration behaviour of various biomass fuels under different air staging conditions in fluidised bed technology for renewable energy applications

The most common technology for thermochemical conversion of solid fuel through the process of gasification, such as coal, varieties of residues from biomass and agriculture are the bubbling fluidised bed or fluidised bed systems. However, there are some disadvantages within these systems including the formation of eutectic mixtures, increased process of melting and bed agglomeration. Hence, the current study aimed to evaluate the agglomeration behaviour of various biomass fuels. Characteristics of five biomass fuels (miscanthus, peanut, straw, domestic wood and industrial wood) in a bubbling fluidised bed (BFB) combustor were studied by SEM-EDX, XRD and XRF analysis of bed materials and ash samples. The influence of bed temperatures on the fuel ash composition and bed particles was evaluated, as well as fuel ash components, their interaction with the particles from the bed sand and morphology of the bed material. The combustion efficiency ranged from 95.5 to 99.5% with the highest value obtained for miscanthus under SA conditions. The peanut and straw had the highest K content, whereas the industrial wood ash contained the highest Ca content compared to other biomasses. The XRF results showed that most of the potassium (K) from the wheat straw biomass was converted to K2O with 19%. No bed agglomeration was noticed without staging-air (WSA) and with staging-air (SA) combustion conditions, even with temperatures up to 850 °C during the testing period. Overall obtained results demonstrated that agglomeration is unlikely expected to be a major problem during fluidised bed combustion of tested biomass fuels.