Abstract
This study investigated a new technique for obtaining wood powders from whole logs (Pinus sylvestris L.) in a single-step operation. The performance of a prototype multi-blade shaft mill (MBSM) was evaluated using a designed series of experiments including three input parameters, i.e., the moisture content of the log, milling blade speed and log feeding speed, combined with multilinear regression (MLR) analysis. The milling performance was characterised by specific milling energy, particle size distribution and bulk density of powder. For MBSM powders (80 to 95% particles <1.0 mm), the specific milling energy ranged from 99 to 232 kWh t−1 DM. The mass per cent of particles <0.5 mm in MBSM powders ranged from 55 to 80% compared to 41% from hammer-milled powders. Powder bulk density varied from 138 to 264 kg m−3 DM and the moisture content of the milled log was the only significant (p < 0.05) factor affecting the bulk density of resulting powders (dried). MLR models show that the milling energy is inversely proportional to the moisture content, which indicates that moisture influences MBSM milling in a similar way as in the sawing of wood and opposite to that of impact-based mills (i.e. hammer mills).
Highlights
Wood is an abundant and widely available renewable material, whose utilisation in industry fulfils political and societal aims for greater sustainable development [1]
A hammer-milling procedure was used as a comparison and the performance of the multi-blade shaft mill (MBSM) milling technology was investigated with respect to specific energy consumption, particle size distribution and bulk density for produced powders
A total of 27 MBSM experiments were performed at nine different settings according to the experimental design
Summary
Wood is an abundant and widely available renewable material, whose utilisation in industry fulfils political and societal aims for greater sustainable development [1]. In Sweden, the wood supply continues to grow and there is a large supply potential of small-diameter trees from the thinning of young forests [2]. As a structurally complex and multipurpose raw material, wood has excellent potential in industrial applications and products. Wood powders (i.e. wood particulates with a diameter less than approximately 1 mm) are the starting point for many thermal conversion and biorefining applications including combustion [3], chemical, enzymatic [4] and thermochemical processes for energy and chemical production (e.g. gasification). Wood is a product of living trees and after falling and delimbing, the stem wood (i.e. log) is a convenient and compact form in which to store wood before utilisation. When the time comes for size reduction, there are many technologies for producing wood powders [6] and new ones continue to be developed (e.g. Kobayashi et al [7])
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