Fuel Characteristics

Wood Energy Data

When using wood and biomass as fuels, important properties are energy content, moisture content and ash content.

Energy Content

Energy content, or heating value is expressed as the amount of energy per physical unit, e.g. joule per kilogram. This is the amount of energy that is released in the form of heat when the fuel is burned completely. The Gross Heating Value (GHV) refers to the total energy released whereas the Net Heating Value (NHV) refers to the energy that is actually available from combustion after accounting for energy losses from water evaporation.

Moisture Content

The moisture content indicates the amount of water in the fuel, expressed as a percentage of the weight. For wood and other biomass, moisture content is the most critical factor determining the amount of heat that can be obtained through combustion. When burning the fuel, the water needs to be evaporated first, before heat becomes available. Therefore, the higher the moisture content, the lower the energy content.

Ash Content

This refers to components that are non-combustible (other than water), which affects the energy content of fuels.

For wood and other biomass that is completely dry and ash free, the GHV is in the order of 20 MJ/kg (±15%).

The table below gives typical values for major fuels. Data are from the Energy and Environment Basics.

	Net Heating Value on wet basis (MJ/kg)	Moisture content on wet basis	Ash content
Bagasse	7.7 - 8	40 - 60	1.7 - 3.8
Coconut shells	18	8	4
Cotton stalks	16	10 - 20	0.1
Maize cobs	13 - 15	10 - 20	2
Rice husks	14	9	19
Straw	12	10	4.4
Wood	8.4 - 17	10 - 60	0.25 - 1.7
Charcoal	25 - 32	1 - 10	0.5 - 6

Apart from these characteristics, biomass fuels show a large variation in other properties such as bulk density, volatile matter content and size. These also influence the choice of conversion technology suitable for a particular fuel. For example, fuelwood can be used with little need of pre-processing, whereas agricultural residues require more pre-treatment to make handling and transport easier, for example briquetting.

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