1. General

[GLOSS]Biomass[/GLOSS] fuels follow the same sequence of [GLOSS]pyrolysis[/GLOSS], [GLOSS]devolatilisation[/GLOSS] and [GLOSS]combustion[/GLOSS] as low rank coal. However, there are significant differences between coals and biomass
combustion:

• Coal densities range typically from 1100 kg/m3 for low rank coals to 2330 kg/m3 for high-density pyrolytic graphite.
• Biomass densities range from 100 kg/m3 for straw to 500 kg/m3 for forest wood.
• The typical [GLOSS]volatile matter[/GLOSS] content of biomass is 60-80% while the coal consists of 10-50% volatile matter.
• The calorific values (see [GLOSS]Calorific Value[/GLOSS]) of biomass fuels are appreciably lower than that of coals. [1]

2. Estimation – HCV

The [GLOSS]higher calorific value[/GLOSS] (HCV) of coal is most precisely determined by using a bomb calorimeter, as defined for example in the British Standard Methods (BS: 1016:part 5: 1977).

However, good estimates can be obtained using the results of the [GLOSS]ultimate analysis[/GLOSS] of the [GLOSS]fuel[/GLOSS]. There are several relations; a commonly used relationship is Boie’s formula which gives the following calculation method [ibid.]:

HCV (MJ/kg) = 35.160 C + 116.225 H – 11.090
O + 6.280 N + 10.465 S.

where each elemental analysis is expressed as a mass fraction.

The given relation resulted in good agreement with the experimental results of 62 types of biomass, reported in [2] referred in [1]. See also CF24.

Keywords:

Biomass, estimate, higher calorific value.

Source:

[1] Sami, M., Annamalai, K. & Wooldridge, M. (2001): Co-firing of coal and biomass fuel blends. Progress in Energy and Combustion Science, Vol. 27, pp. 171-214.
[2] Ebling, J.M. & Jenkins, B.M. (1985): Physical and chemical properties of biomass. Transaction ASAE, Vol. 23(3), pp.898-902.