Drying effects and dry matter losses during seasonal storage of spruce wood chips under practical conditions

doi:10.1016/j.biombioe.2017.03.022

Biomass and Bioenergy

Volume 111, April 2018, Pages 196-205

https://doi.org/10.1016/j.biombioe.2017.03.022 Get rights and content

Highlights

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Storage of forest wood chips and unchipped wood was examined in extensive field trials.
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Trials were conducted during winter and summer and with and without rain cover.
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Influencing factors on drying and dry matter loss were detected using factorial ANOVA.
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Drying can compensate dry matter loss regarding energy content under certain conditions.
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Storage before chipping can increase quality of wood chips (fine and ash content).

Abstract

The storage of wood chips is important for the biomass supply chain as it compensates for temporal differences in production and consumption. Typical storage-related problems are dry matter and energy losses due to microbial activity.

In extensive field trials, we investigated the storage of spruce wood chips from forest residues (FRC) and from energy roundwood (ERC) with and without rain protection under Central European conditions. Additionally, we examined the storage of unchipped piles.

The results indicate that the investigated factors, i. e. storage duration, season, assortment and rain protection, have a statistically significant influence on moisture content and dry matter loss of wood chips. During five months of storage, the highest decline in moisture content was 22.6 %-points, the highest dry matter loss 11.1 %. In winter, energy losses reached up to 11.3 %. In summer, energy contents did not change or even increased slightly (max. 4.7 %). Pile temperature and dry matter losses were significantly positively correlated in FRC. Formation of different layers within the piles could be detected. Storage performance was better in unchipped than in chipped energy roundwood. Storage of unchipped forest residues was not beneficial concerning energy content, but fuel quality increased due to reduced ash and fine particle content.

Clear best practice recommendations could be drawn regarding wood chip storage under Central European conditions. During winter, FRC should be stored with rain protection or as short as possible while during a dry and warm summer, wood chips can be stored with only few restrictions.

Section snippets

Introduction and aim

Consistent development and efficient use of renewable energy sources are essential to achieve national and international climate protection targets and to reduce the dependency on finite energy sources. Solid biofuels, mainly woody biomass, are important for the German energy supply, especially for heat production. In 2016, 13.4 % of the total final heat energy consumption in Germany were covered by renewable energy sources, primarily by solid biofuels (68.1 %) [1].

Wood chips from forest

Material and methods

Storage experiments were carried out from November 2014 to April 2015 (winter trial) and from May 2015 to October 2015 (summer trial) on a storage site of a biomass supplier in Bavaria (South Germany, 48.96° N, 11.18° E). The experimental setup was identical for both periods. Four wood chip piles of approx. 200 m³ each were built up next to each other, including two piles of forest residue chips (FRC, crown biomass) and two piles of energy roundwood chips (ERC, thin delimbed stem sections of

Characterization of the raw material

Mean moisture content of wood chips ranged from 47.9 to 56.8 % at the beginning of the storage periods. This range is typical for freshly cut green forest biomass [24]. Since the crown biomass had high shares of needles and fine twigs, FRC had a considerably higher fine content (particles ≤ 3.15 mm diameter) and higher ash content compared to ERC. Interestingly, ash content of FRC in winter strongly exceeded 3 %, i. e. the typical range for forest residues [24] (Table 1). This might indicate

Conclusions

The investigations in this study have shown that for wood chips which are stored under practical conditions in Bavaria:

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changes in moisture content and dry matter losses are significantly dependent on storage duration, season, assortment and rain protection (fleece),
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development of the usable energy content is primarily influenced by changes in moisture content and dry matter losses,
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in winter only a small loss of usable energy occurs, except for uncovered forest residue chips; in summer even

Acknowledgements

This research was funded by the Bavarian State Ministry of Food, Agriculture and Forestry under the project no. EW/13/53. We thank our cooperation partners Bavarian State Forest Enterprise and Biomassehof Breitenhuber for supporting this project.

We greatly acknowledge the technical assistance of our colleagues Albert Maierhofer, Anja Rocktäschel, Mirjana Bubalo, Jens Enke, Benedikt Haas, Alexander Marks, Simon Lesche, Stephan Winter, Thomas Kieslinger and Andreas Lermer from TFZ and Sabrina

References (40)

M.D. Casal et al.
Influence of storage time on the quality and combustion behaviour of pine woodchips
Energy
(2010)
F. Ferrero et al.
A mathematical model to predict the heating-up of large-scale wood piles
J. Loss Prev. Proc.
(2009)
O. Gislerud
Drying and storing of comminuted wood fuels
Biomass
(1990)
T. Thörnqvist
Drying and storage of forest residues for energy production
Biomass
(1985)
H. Lenz et al.
Open-air storage of fine and coarse wood chips of poplar from short rotation coppice in covered piles
Biomass Bioenerg.
(2015)
M. Barontini et al.
Storage dynamics and fuel quality of poplar chips
Biomass Bioenerg.
(2014)
R. Pecenka et al.
Development of bio-physical properties during storage of poplar chips from 15 ha test fields
Biomass Bioenerg.
(2014)
H. Lenz et al.
Continuous weighing of a pile of poplar wood chips – a comparison of methods to determine the dry matter losses during storage
Biomass Bioenerg.
(2017)
R. Jirjis
Storage and drying of wood fuel
Biomass Bioenerg.
(1995)
P. Lehtikangas
Quality properties of pelletised sawdust, logging residues and bark
Biomass Bioenerg.
(2001)

T. Filbakk et al.

Modelling natural drying efficiency in covered and uncovered piles of whole broadleaf trees for energy use

Biomass Bioenerg.

(2011)

R. Jirjis

Effects of particle size and pile height on storage and fuel quality of comminuted Salix viminalis

Biomass Bioenerg.

(2005)

M.A. Brand et al.

Storage as a tool to improve wood fuel quality

Biomass Bioenerg.

(2011)

Bundesministerium für Wirtschaft und Energie (BMWi) et al.

Zeitreihen zur Entwicklung der erneuerbaren Energien in Deutschland

(Dessau-Roßlau, 2017)

H. Weimar et al.

Standorte der Holzwirtschaft – Holzrohstoffmonitoring: Einsatz von Holz in Biomasse-Großfeuerungsanlagen 2011

(2012)

L. Eltrop et al.

Leitfaden Feste Biobrennstoffe

(2014)

M.T. Afzal et al.

Storage of comminuted and uncomminuted forest biomass and its effect on fuel quality

BioResources

(2010)

Ö. Bergman et al.

An Experiment on Outdoor Storage of Whole-tree Chips

(1979)

N. Heding

Exploitation of Marginal Forest Resources for Fuel

(1990)

V. Scholz et al.

Lagerung von Feldholzhackgut: Verluste und Schimmelpilze

Agrartech. Forsch-Agr

(2005)

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Research paperDrying effects and dry matter losses during seasonal storage of spruce wood chips under practical conditions

Highlights

Abstract

Section snippets

Introduction and aim

Material and methods

Characterization of the raw material

Conclusions

Acknowledgements

Energy

J. Loss Prev. Proc.

Biomass

Biomass

Biomass Bioenerg.

Biomass Bioenerg.

Biomass Bioenerg.

Biomass Bioenerg.

Biomass Bioenerg.

Biomass Bioenerg.

Biomass Bioenerg.

Biomass Bioenerg.

Biomass Bioenerg.

Zeitreihen zur Entwicklung der erneuerbaren Energien in Deutschland

Standorte der Holzwirtschaft – Holzrohstoffmonitoring: Einsatz von Holz in Biomasse-Großfeuerungsanlagen 2011

Leitfaden Feste Biobrennstoffe

Storage of comminuted and uncomminuted forest biomass and its effect on fuel quality

BioResources

An Experiment on Outdoor Storage of Whole-tree Chips

Exploitation of Marginal Forest Resources for Fuel

Lagerung von Feldholzhackgut: Verluste und Schimmelpilze

Agrartech. Forsch-Agr

Research paper
Drying effects and dry matter losses during seasonal storage of spruce wood chips under practical conditions