Secondary comminution of wood pellets in power plant and laboratory-scale mills

Abstract

This study aims to determine the influence of mill type and pellet wood composition on particle size and shape of milled wood. The size and shape characteristics of pellets comminuted using power plant-scale roller-and hammer mills were compared with those obtained by using a laboratory-scale roller mill. A 2D dynamic imaging device was used for particle characterization. It was shown that mill type has a significant impact on particle size but an almost negligible effect on the shape of milled wood. Comminution in the pilot plant using a Loesche roller mill requires less energy than using a hammer mill, but generates a larger fraction of coarse particles. The laboratory-scale roller mill provides comparable results with the power plant roller mill with respect to particle size and shape.

One way of representing the size and shape of biomass particles in combustion modeling

“…The Feret maximal diameter, representing the length, is greater than the width. Therefore, the Martin minimal (x Ma min ) and Feret maximal (x Fe max ) diameters are suitable parameters to represent the width and length of biomass particles, confirming previous results of Trubetskaya et al [29]. The most suitable descriptor of particle size, when characterized using sieving and 2D dynamic imaging, is the smallest maximal chord (x c min ) [19].…”

Wood pellet milling tests in a suspension-fired power plant

“…The Camsizer ® definition of the circularity is the ISO 9276-6:2008 standard definition squared [35]. Both shape factors are commonly used for describing comminuted wood particle shapes [12,17]. The aspect ratio (AR) ranging between zero and one is defined as follows:…”

“…Regarding the particle shape, Trubetskaya et al [12] found no difference between roller-milled and hammer-milled particles. However, roller mills required less power for grinding than hammer mills [12,13]. The energy needed for milling biomass depends on the feed moisture, particle size reduction ratio, feedstock characteristics [14], feed rate and mill operating parameters [15].…”

“…The size reduction of solid particles is a significant process in suspension-fired power plants and is commonly performed in hammer mills or roller mills [8,10] to achieve a homogenous fuel distribution that is pneumatically transported to the burners. Previous studies [11][12][13] showed that roller mills were not capable of producing a product as fine as hammer mills. Regarding the particle shape, Trubetskaya et al [12] found no difference between roller-milled and hammer-milled particles.…”

“…Previous studies [11][12][13] showed that roller mills were not capable of producing a product as fine as hammer mills. Regarding the particle shape, Trubetskaya et al [12] found no difference between roller-milled and hammer-milled particles. However, roller mills required less power for grinding than hammer mills [12,13].…”