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Influence of wood pellets properties on their grinding performance

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Abstract

This study investigates the influence of wood pellet properties on the grindability of pellets in a lab-scale disc mill. The pellet properties investigated included wood type, moisture content, internal pellet particle size distribution, particle density, and durability. Two pellet qualities for industrial use (designated I1 and I2 as per ISO 17225-2:2014) and two types of semi-industrial pellets (beech and pine) were used and grinding was performed on as-received and oven-dried pellets. The grinding performance was assessed by measuring the grinding energy and analyzing the changes in particle morphology (size and shape) with respect to the internal pellet particle morphology. Von Rittinger’s comminution law was used to characterize the pellet grindability. Drying pellets increased their brittleness and improved their grindability, resulting in both grinding energy savings and a higher milled product fineness, and the impact of drying was larger for industrial pellets. Beech pellets had a better grindability (kWh mm t-1 dry wood) than pine pellets (kWh mm t-1 dry wood). The moisture content of pellets did not influence the shape of the milled particles in terms of circularity and elongation ratio. The study also showed that the proposed disc mill has the potential to quickly determine the relative grindability characteristics of various pellet qualities.

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Abbreviations

A Particle :

particle projection area (mm2)

P Particle :

particle perimeter (mm)

m Pellet :

amount of wood pellets (t)

ar:

as-received

C :

circularity (dimensionless)

d :

particle size (mm)

D :

pellet diameter (mm)

d* :

RRBS characteristic particle size (mm) corresponding to 63.2% of the R(d)

D10 :

particle size at 10th percentile of the cumulative undersize distribution (mm)

D25 :

particle size at 25th percentile of the cumulative undersize distribution (mm)

D50 :

particle size at 50th percentile of the cumulative undersize distribution (mm)

D75 :

particle size at 75th percentile of the cumulative undersize distribution (mm)

D90 :

particle size at 90th percentile of the cumulative undersize distribution (mm)

d c , min :

shortest maximum chord (mm)

d f :

RRBS characteristic particle size (mm) of the feed

d Fe,max :

maximum Feret diameter (mm)

d p :

RRBS characteristic particle size (mm) of the product

DW:

oven-dried wood basis

ER :

particle elongation ratio (dimensionless)

K R :

Von Rittinger’s constant (kWh mm t-1 DW)

L :

pellet length (mm)

n :

RRBS uniformity constant (dimensionless)

P :

absorbed mill power (kW)

PSD:

particle size distribution

R(d) :

cumulative undersize distribution (%)

RRBS:

Rosin-Rammler-Bennet-Sperling

SD:

standard deviation

SGEC :

specific grinding energy consumption (kWh t-1 DW)

vol.% :

volume percent

w.b. :

wet basis

wt.% :

weight percent

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Acknowledgements

The authors thank Energiteknologiske Udviklings- og Demonstrationsprogram (EUDP) for the financial support received as part of the ForskEL project “AUWP – Advanced Utilization of Wood Pellets” (Project number: 12325).

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Funding

Research was supported by the Energiteknologiske Udviklings- og Demonstrationsprogram (EUDP) as part of the ForskEL project “AUWP – Advanced Utilization of Wood Pellets” (Project number: 12325).

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Authors and Affiliations

  1. Department of Energy Conversion and Storage, Technical University of Denmark, 2800, Kgs. Lyngby, Denmark

    Marvin Masche

  2. Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800, Kgs. Lyngby, Denmark

    Maria Puig-Arnavat, Peter A. Jensen, Sønnik Clausen, Jesper Ahrenfeldt & Ulrik B. Henriksen

  3. Bioenergy and Thermal Power, Ørsted, Nesa Allé 1, 2820, Gentofte, Denmark

    Jens Kai Holm

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  1. Marvin Masche
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Correspondence to Maria Puig-Arnavat.

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Highlights

• Milling of industrial and semi-industrial wood pellets in a disc mill.

• Milling of dried pellets results in narrower and finer product size distribution.

• Milling of dried pellets reduces grinding energy consumption.

• RRBS model is suitable to describe the internal pellet particle size distribution

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Masche, M., Puig-Arnavat, M., Jensen, P.A. et al. Influence of wood pellets properties on their grinding performance . Biomass Conv. Bioref. 13, 2985–3000 (2023). https://doi.org/10.1007/s13399-021-01559-x

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