Influence of Tree Species, Harvesting Method and Storage on Energy Demand and Wood Chip Quality When Chipping Poplar, Willow and Black Locust

Ralf Pecenka,Thomas Hoffmann,Hannes Lenz,Simeon Olatayo Jekayinfa

doi:10.3390/agriculture10040116

Ralf Pecenka, Thomas Hoffmann + Show 2 more

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https://doi.org/10.3390/agriculture10040116

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Abstract

The cultivation of fast-growing wood (e.g., poplar, willow or black locust) in short rotation coppices and agroforestry systems presents an opportunity for producing biomass sustainably in the agricultural sector. Cost-efficient agricultural wood production requires the availability of high-performance machinery and methods with which high-quality wood chips can be produced at low cost. It is known from harvesting short rotation coppices in practice that both the wood chip quality and the performance of the harvesting machinery depend on a variety of factors (e.g., harvesting method, weather conditions, tree species). That is why this study examines in detail the influence of the tree species (different varieties of poplar, willow, black locust) and the wood condition (fresh, stored or dried, frozen) on the specific energy demand for comminution in a stationary drum chipper and on the particle size distribution of the wood chips produced. For all the tree species examined, the chipping of dried as well as frozen stems was connected with a significant increase in the specific energy demand for comminution. An increase of 31% has been measured if poplar stems are chipped in frozen conditions (max. 6.31 kWh t−1). Drying led to an increase of 59% for dried willow stems (max. 6.67 kWh t−1). Drying and frost had also an influence on the size and quality of the wood chips, but no globally significant connection could be established for the examined tree varieties.

Highlights

Trees planted on agricultural land present an opportunity for producing biomass sustainably and at the same time improving farm income
Fast-growing tree species such as poplar, willow and black locust cultivated in short rotation coppices (SRC) or agroforestry systems (AFS) offer considerable potential for producing plant biomass, but can at the same time withdraw carbon from the atmosphere and store it in their biomass [1,2,3,4,5,6]
A comparison of the comminution experiments that were conducted with four fresh and distinctly thicker stems in each case reveals that the chipping of poplar of the Max variety requires the least energy at 4.81 kWh t−1, followed by willow (Tordis 5.63 kWh t−1, Inger 5.87 kWh t−1 ), black locust (6.28 kWh t−1 ) and the poplar Hybrid 275 (6.50 kWh t−1 ), see

Summary

Introduction

Trees planted on agricultural land present an opportunity for producing biomass sustainably and at the same time improving farm income. Fast-growing tree species such as poplar, willow and black locust cultivated in short rotation coppices (SRC) or agroforestry systems (AFS) offer considerable potential for producing plant biomass, but can at the same time withdraw carbon from the atmosphere and store it in their biomass [1,2,3,4,5,6]. To be successful in competition with wood products from the forestry sector, various obstacles need to be overcome when expanding the cultivation of fast-growing agricultural timber crops. Such expansion is desirable for ecological reasons. Short rotation coppices are harvested in winter with moisture contents of Agriculture 2020, 10, 116; doi:10.3390/agriculture10040116 www.mdpi.com/journal/agriculture

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