Experimental research on the countercurrent fixed-bed combustion of biomass

Fixed-bed combustion is the oldest and most flexible method for generating heat from solid fuels with diverse morphological characteristics. This approach consolidates countercurrent fixed-bed burners as the most employed technique for biomass combustion in small- and medium-scale installations. In recent decades, researchers worldwide have generated significant experimental evidence to decipher the complex mechanisms behind reaction front propagation using laboratory-scale burners, which simulate the conditions of fuel in industrial plants. Many experimental results are available in the scientific literature, and the consolidation and discussion of the most relevant data can be useful for better understanding the current state of the art and identifying knowledge gaps on the subject. This paper presents a systematic review of the available literature concerning experimental studies of biomass fixed-bed combustion in laboratory-scale reactors. The central discussion encompasses the definition of the parameters employed to characterize the reaction zone behaviour and their dependence on fuel properties and primary air conditions. The insights gained in this review were addressed to propose criteria for harnessing the abundant availability of agricultural residues as alternative fuels in grate-firing systems.