Table 2.4.1 gives the data for moisture content, organic matter content, ash content, and heating value of representative types of biomass.

atmospheric pressure.

** Ash content is determined from the weight of residue (metal oxides) left after heating at about 800°C.

Moisture content differs considerably depending on the kind of biomass, for example, 3% in paper and 98% in sludge. With most biomass types, water content exceeding two-thirds makes the available heat negative (-). Therefore, even if the heating value of the biomass itself is high, if it has a high moisture content in its natural state, it is not suitable for combustion. For example, water hyacinth and sewage sludge have high heating values, when they are dried, but moisture content is about 95% at the sampling, and they are unsuitable for combustion actually.

Total organic matter is left when the ash content subtract from total dry matter. Because the value of ash as energy is zero, a large amount of organic matter means a higher heating value, which is desirable as an energy source. Additionally, organic substances have different heating values depending on the kinds and ratios of their constituent elements (see 2.3 Biomass Composition). Table 2.4.2 presents the elemental analysis results and heating values of representative biomass types and other organic fuels. Because biomass contains more oxygen and less carbon and hydrogen than coal or petroleum, it has a lower heating value per unit weight. Woody and herbaceous biomass types have carbon contents of 45%-50% and hydrogen contents of 5%-6%, giving them an H:C molar ratio of about 2, with little variation. This is because they are affected by their composition, the main components of which are cellulose and lignin.