Methods for size classification of wood chips

Abstract

Methods for size classification of wood chips were analysed in an international round robin using 13 conventional wood chip samples and two specially prepared standard samples, one from wood chips and one from hog fuel. The true size distribution of these two samples (according to length, width and height) had been determined stereometrically (reference method) using a digital calliper gauge and by weighing each of the about 7000 wood particles per sample. Five different horizontal and three rotary screening devices were tested using five different screen hole diameters (3.15, 8, 16, 45, 63 mm, round holes). These systems are compared to a commercially available continuously measuring image analysis equipment.The results show that among the devices of a measuring principle-horizontal and rotary screening-the results are quite comparable, while there is a severe incompatibility when distributions are determined by different measuring principles. Highest conformity with the reference values is given for measurements with an image analysis system, whereas for all machines with horizontal screens the median value of the size distribution only reached between one-third to half of the reference median value for the particle length distribution. These deviations can be attributed to a higher particle misplacement, which is particularly found in the larger fractions. Such differences decrease when the particle's shape is more roundish (i.e. sphericity closer to one). The median values of length distributions from screenings with a rotary classifier are between the measurements from an image analysis and horizontal screening devices. r

Computer and Experimental Simulation of Biomass Production Using Drum Chipper

“…The size for the wood fibers was determined using a calliper gauge. The share of the wood fibers constant fraction was determined using a sieving method, which is the most appropriate procedure for defining the consistency of a fraction [17,23]. Individual fractions were thus sieved through different sieves with different openings (Fig.…”

Automated determination of poplar chip size distribution based on combined image and multivariate analyses

“…Typically, the result of this analysis is presented in size distribution curves, which are not based on the cumulative percentage mass, as it is for sieve analysis, but refer to the percentage of the total particle projection area (or particle number). Dynamic online image analysis systems are considered particularly interesting because they can sort the particle sizes according to more than just one size parameter [8]. Hartmann et al [8] suggested it would be useful to launch a standardization process in order to include the image analysis method to the scope of applicable standard laboratory principles for biofuels, too, so as to overcome the drawbacks of the screening methods.…”

“…Dynamic online image analysis systems are considered particularly interesting because they can sort the particle sizes according to more than just one size parameter [8]. Hartmann et al [8] suggested it would be useful to launch a standardization process in order to include the image analysis method to the scope of applicable standard laboratory principles for biofuels, too, so as to overcome the drawbacks of the screening methods. Following this suggestion, the aim of this study is to analyze how image analysis combined with multivariate modeling methods can be used to construct cumulative size distribution curves based on chip mass (or weight), which can be compared with the sieving results required by EN standards.…”

Determining wood chip size: image analysis and clustering methods

“…On average, reproducibility is better for horizontal screenings than for rotary screening. However, if different measuring principles are applied, particle size analysis of biofuels is associated with high measuring uncertainties (Hartmann et al, 2006).…”

“…On average, reproducibility is better for horizontal screenings than for rotary screening. However, if different measuring principles are applied, particle size analysis of biofuels is associated with high measuring uncertainties (Hartmann et al, 2006).Since the chip form (shape and size) influences the sieve results, the image analysis could provide a method which is sensitive to the geometrical shape for determining a more accurate measure of size integrated with shape (Fernlund, 1998).Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di ricerca per l'ingegneria agraria (CRA-ING) is conducting a research activity for developing a new method, based on the image analysis, for the classification of wood particles, depending on both size and shape. …”