Effect of particle size on the burnout and emissions of particulate matter from the combustion of pulverized agricultural residues in a drop tube furnace

Milling and grinding biomass fuels for pulverized combustion in industrial furnaces can be very expensive. This study aims to evaluate the effect of the particle size on the burnout and emissions of particulate matter from the combustion of agricultural residues (wheat straw and rice husk) in a drop tube furnace. Initially, both agricultural residues were crushed and sieved below 1 mm and the resulting particle size distributions formed one size class here named <1000 μm. In addition to this wide size class, three narrow particle size classes were prepared for each residue; namely, size classes 100-200 µm, 400-600 µm and 800-1000 µm. Subsequently, all size classes of both agricultural residues were burnt in a drop tube furnace at 1100 °C. The data reported include profiles of temperature, particle burnout and particulate matter concentration and size distribution measured along the drop tube furnace. The main conclusions from this study are: (i) for both agricultural residues the size class 100-200 µm presents the highest burnout values, followed by the size classes 400-600 µm and 800-1000 µm; (ii) the burnout values for the rice husk are higher than those for the wheat straw, and the total particulate matter emissions are rather similar for both agricultural residues, regardless of the size class; (iii) during the last stages of the combustion of the wheat straw occur particle fragmentation and the size classes 400-600 µm and 800-1000 µm are those that most contribute to this phenomenon, but particle fragmentation was not observed during the combustion of the rice husk; (iv) the wheat straw size classes 100-200 µm, 400-600 µm and <1000 µm present a bimodal particulate matter size distribution, while the class size 800-1000 µm presents a unimodal one, but the rice husk size classes show all a unimodal particulate matter size distribution.