Moisture Content

The moisture content of biomass material varies greatly. This has a significant effect on many of the energy conversion processes. As an example, when biogas is obtained from an anaerobic digestion process the percentage of solids present in the digestate affects the gas yields. For dry biomass fuels such as wood, the amount of water present has a considerable effect on the proportion of the total heat content of the material that is able to be recovered during combustion.

For wood, the moisture content depends on a combination of climatic conditions, time of year when harvesting takes place, and the duration and method of storage (Simpson and TenWolde 1999). The following simple formulas can be used to calculate the moisture content of biomass:

moisture content (wet basis) = (total weight of wet wood – oven dry weight)/total weight of wet wood * 100

moisture content (dry basis) = (total weight of wet wood – oven dry weight)/oven dry weight * 100.

Energy yields are often expressed as net caloric values. These values increase as wood moisture content is reduced. Thus, the drier the wood, the greater the amount of energy that can be produced. The percent moisture content of the biomass utilized has a large impact upon the design and selection of technologies ideal for energy production.

Net calorific value of waste wood (Pinus radiata)
as a function of moisture content.