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  • Cover photo: Nike Krajnc

  • iii

    WOOD FUELS HANDBOOK

    Prepared by: Dr. Nike Krajnc

    FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS

    Pristina, 2015

  • iv

    The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products of manufacturers, whether or not these have been patented, does not imply that these have been endorsed or recommended by FAO in preference to others of a similar nature that are not mentioned. The views expressed in this information product are those of the author(s) and do not necessarily reflect the views or policies of FAO. ISBN 978-92-5-108728-2 © FAO, 2015 FAO encourages the use, reproduction and dissemination of material in this information product. Except where otherwise indicated, material may be copied, downloaded and printed for private study, research and teaching purposes, or for use in non-commercial products or services, provided that appropriate acknowledgement of FAO as the source and copyright holder is given and that FAO’s endorsement of users’ views, products or services is not implied in any way.

    All requests for translation and adaptation rights and for resale and other commercial use rights should be made via www.fao.org/contact-us/licence-request or addressed to copyright@fao.org.

    FAO information products are available on the FAO website (www.fao.org/publications) and can be

    purchased through publications-sales@fao.org.

    http://www.fao.org/contact-us/licence-request mailto:copyright@fao.org http://www.fao.org/publications mailto:publications-sales@fao.org

  • v

    LIST OF CONTENTS ABBREVIATIONS AND SYMBOLS .....................................................................................................viii INTRODUCTION..................................................................................................................................1 1 WOOD FUELS – DEFINITIONS......................................................................................................2

    1.1 Major traded forms of wood fuels ......................................................................................................... 2

    1.2 The main sources of wood fuel .............................................................................................................. 3

    2 UNITS OF MEASUREMENT FOR WOOD FUELS ........................................................................... 4 2.1 Volume ................................................................................................................................................... 4

    2.2 Weight .................................................................................................................................................... 6

    2.3 Density ................................................................................................................................................... 6

    3 MAIN CHARACTERISTICS OF WOOD FUELS ................................................................................ 8 3.1 Moisture content ................................................................................................................................... 8

    3.2 Units of measurement for thermal energy .......................................................................................... 10

    3.2.1 Calorific value ............................................................................................................. 10

    3.2.2 Theoretical calculation of caloric value ...................................................................... 12

    3.2.3 Energy equivalents ...................................................................................................... 15

    3.3 Ash content and ash melting point ...................................................................................................... 17

    3.4 Biomass chemical composition ............................................................................................................ 18

    4 BIOMASS PRODUCTION CHAINS ............................................................................................. 20 4.1 Machines for producing wood fuels ..................................................................................................... 20

    5 STORAGE OF QUALITY WOOD FUELS ....................................................................................... 22 5.1 Log wood and firewood ....................................................................................................................... 22

    5.1.1 Quality requirements .................................................................................................. 22

    5.1.2 How to store firewood correctly ................................................................................ 23

    5.2 Wood Chips .......................................................................................................................................... 25

    5.2.1 Buying wood chips ...................................................................................................... 25

    5.2.2 Quality requirements .................................................................................................. 26

    5.2.3 How to store wood chips correctly ............................................................................. 27

    5.3 Wood pellets ........................................................................................................................................ 28

    5.3.1 How to select the right pellets .................................................................................... 28

    6 LIST OF STANDARDS FOR SOLID BIOFUELS MENTIONED IN THIS HANDBOOK ................. 30 7 REFERENCES..............................................................................................................................31

  • vi

    LIST OF TABLES AND FIGURES

    Figure 1 - Basic conversion factors ...................................................................................................... 5 Table 1 - Conversion factors for different wood fuels ......................................................................... 5 Table 2 - Conversion factors for selected wood residues .................................................................... 5 Table 3 - Units of measurement .......................................................................................................... 6 Table 4 - Basic density of selected tree species – air dry wood ........................................................... 6 Table 5 - Basic density of selected tree species oven dry wood (wood free of moisture) .................. 7 Table 6 - Typical values of bulk density for selected wood fuels ......................................................... 7 Table 7 - Mass and bulk density of main tree species ......................................................................... 7 Table 8 - Conversion between moisture and water content ............................................................... 9 Table 9 - Conversion factors of thermal energy units ........................................................................ 10 Table 10 - Caloric value and ash content for selected wood fuels .................................................... 11 Table 11 - Weight and calorific value relative to volume and water content ................................... 12 Table 12 - Calorific value of wood depending on water content....................................................... 12 Table 13 - For practical purposes the following average values are used for wood fuels ................. 12 Table 14 Caloric value as function of water content (M %) ............................................................... 13 Table 15 - Conversion factor for firewood- Broad-leafs with water content 20 %............................ 14 Table 16 - Conversion factor for firewood - coniferous with water content 20 % ............................ 14 Table 17 - Conversion factor for wood chips – mixed wood with water content 35 % ..................... 14 Table 18 - Caloric value of selected fuels ........................................................................................... 15 Table 19 - Chemical composition of solid biomass ............................................................................ 18 Figure 2 - Test of monthly measurements of drying of four different piles of log wood .................. 23 Table 20 - Energy content of different types of log wood (with moisture content 20 %) ................. 23 Table 21 - Comparison of storage requirements ................................................................................ 25 Figure 3 - Comparison of storage size for different wood fuels ........................................................ 25 Table 22 - Weight and calorific value depending on weight and water content ............................... 26 Table 23 - Mean values for quantification ......................................................................................... 26

  • vii

    Acknowledgements

    P