What you need to know about wood as a fuel?
What you need to know about wood as a fuel?
Wood as a fuel comes in many forms:
| • | logs (chopped wood), |
| • | wood chips, |
| • | sawdust and shavings, |
| • | kora, |
| • | briquettes, |
| • | pellets. |
The multiform nature of wood as a fuel makes it difficult to adopt unambiguous and identical units of measurement for the comparison of different types of wood fuel.
In order to standardize the nomenclature and facilitate the use of wood as a fuel, it is proposed to adopt the following definitions of units:
| 1 m³ | one cubic meter of solid wood volume (the thickness of the wood) – e.g.. 1 m³ cut from a thick tree trunk |
| 1 mp | one cubic meter of wood volume, including the air between the pieces of wood |
| 1 mp of wood chips, shavings or sawdust depending on their density |
<=> | ok. 0,4 m³ of wood |
| 1 m³ of wood | <=> | ok. 2,5 mp of wood chips, shavings or slightly compacted sawdust |
| 1 mp firewood stacked |
<=> | 0,65-0,85 m³ of wood depending on on the size and shape of the rollers |
| 1 mp branch stacked |
<=> | 0,25-0,45 m³ of wood |
| 1 lump wood in the form of logs |
<=> | 0,45-0,65 m³ of wood |
The use of units of mass is also ambiguous, because 1 kg of dry wood and 1 kg of wet wood also means completely different amounts of wood.
The same m³ of solid wood saturated with water can weigh 2 times or more than m³ dry wood.
| 1 kg m.s. | one kilogram of dry wood mass, i.e. one kilogram of wood, from which all the water content was evaporated |
| w [%] | wood moisture content as a fuel expressed as a percentage and determined by the formula
w = [mw / (ms + mw)] × 100% where: mw – mass of water |
Wood is a porous material and, depending on the tree species, has a different density:
| Type wood |
Density kg m.s./m³ |
| buk, oak | 570 |
| Birch | 510 |
| larch | 460 |
| pine, Alder | 420 |
| spruce | 400 |
| poplar, wierzba | 350 |
The most appropriate way to assess the amount of wood according to its volume is to convert from cubic meters to cubic meters of wood, which, with the knowledge of the type of wood and its moisture content, will allow to estimate its calorific value using the table:
| The calorific value of wood [GJ/m³] | ||||||
| Humidity [%] |
beech and oak | Birch | wierzba | larch | pine and alder | spruce |
| 0 | 10,83 | 9,69 | 6,65 | 8,74 | 7,98 | 7,60 |
| 15 | 10,59 | 9,47 | 6,50 | 8,55 | 7,80 | 7,43 |
| 20 | 10,49 | 9,38 | 6,44 | 8,46 | 7,73 | 7,36 |
| 25 | 10,37 | 9,28 | 6,37 | 8,37 | 7,64 | 7,28 |
| 30 | 10,24 | 9,17 | 6,29 | 8,27 | 7,55 | 7,19 |
| 35 | 10,09 | 9,03 | 6,20 | 8,15 | 7,44 | 7,08 |
| 40 | 9,92 | 8,87 | 6,09 | 8,00 | 7,31 | 6,96 |
| 45 | 9,71 | 8,69 | 5,96 | 7,84 | 7,16 | 6,81 |
| 50 | 9,46 | 8,47 | 5,81 | 7,64 | 6,97 | 6,64 |
| 55 | 9,16 | 8,19 | 5,62 | 7,39 | 6,75 | 6,43 |
| 60 | 8,78 | 7,85 | 5,39 | 7,08 | 6,47 | 6,16 |
