Title:
Evaluation of Methods for the Determination of Pellet Length
Author(s):
Hartmann, H., Mack, R., Tomaschko, F., Härtl, S., Zelinski, V.
Document(s):
Paper
Abstract:
The existing reference method for determining pellet length (ISO 17829) has demonstrated incon-sistencies in pellet length definitions and apparatus requirements. Consequently, the method is currently being revised by ISO TC 238. The revised standard describes a new device for determining pellet length. Additionally, the standard now unmistakably defines length as the distance between the outer edges of a pellet. However, this research also considers the measurement from midpoint to midpoint, as has also happened in practice. These measurements were compared with those obtained using the conventional hand-held calliper method described in the current standard. A measurement campaign was launched using 25 different 6 mm and 8 mm diameter pellet types, produced using ring or flat die presses and various biomass materials. When the lengths of 6 mm pellets from a research pellet assortment were measured from midpoint to midpoint, the average length was 2.0 mm shorter than that measured from the outer edges of the same pellets. With a second assortment of eight pellet types that had been randomly purchased from the market, the mean difference was 2.9 mm. The mean difference was also 2.9 mm for a third group of five pellet types with a diameter of 8 mm. No noticeable differences were found when comparing the original hand-held calliper method to the new apparatus, provided that the length was determined over the outer edges of each pellet in both cases. The size of a test portion was also varied between 50 and 200 g in four steps. It can be shown that the accuracy increases with the sample size, but between 150 and 200 g the differences in mean pellet length become negligible. The coefficient of variation of the mean pellet length between the four 50 g sub-portions varied between 1.5 % and 3.6 % for 6 mm pellets but could rise up to 16.7 % for few cases of 8 mm pellets. The definition of pellet length (midpoint to midpoint versus outer edges) is also particularly important for determining the proportion of pellets below 10 mm in length, as set out in the ENplus certification scheme. Moreover, the frequency of occurrence of long pellets (mass fraction >40 mm) can quadruple in some cases when measurements are taken from the outer edges compared to the midpoints. The revised standard method using the new measurement device considerably shortens the time required for each sample assess-ment. This enables larger quantities of samples to be processed and therefore leads to greater accuracy.
Keywords:
wood pellets, fuel quality, fuel standards
Topic:
Biomass, Bio-based Products and Bioenergy Integration
Subtopic:
Market implementation, investments & financing
Event:
33rd European Biomass Conference and Exhibition
Session:
3CV.10.16
Pages:
606 - 611
ISBN:
978-88-89407-25-7
Paper DOI:
10.5071/33rdEUBCE2025-3CV.10.16
Price:
FREE
