Hammer mill operating and biomass physical conditions effects on particle size distribution of solid pulverized biofuels

Milling is a required pre-treatment for the use of biomass as a pulverized solid biofuel in some thermochemical technologies such as combustion, gasification and bioethanol production, as well as in densification processes. The particle size plays a key role on these energy conversion technologies. Experimental tests for poplar and corn stover were performed to obtain pulverized material at different physical conditions of the biomass (input particle size and moisture content) and operational parameters (opening sizes of the screen and angular speed of hammers). Fourteen parameters related to size central trends, dispersion and shape of particle size distribution (PSD) were calculated and analyzed by a novel data post-processing methodology, combining Artificial Neural Networks and statistical analysis. Results show that the characteristic size of the product (geometric mean size) is mainly influenced by the classification of the screen with values from five to eight times lower than their openings size. The angular speed of the hammer governs the variability and dispersion of sizes. The higher the angular speed, the lower the dispersion on particle size. Physical conditions of the biomass present a negligible effect on PSD.