Characterization of biomass using instruments – Measurement of forest and crop residues - Biomass as Energy Source: Resources, Systems and Applications - page 56

Volume measurement has a long tradition. Amajor advantage is that volume is simple and easy
tomeasure and verify by all parties. Abuyer or seller can easily challenge an existingmeasurement
by replicating it. However, the measurement result depends e.g. on how compressed the material
is. A shipment of fresh branches and tops will not have the same volume is if the material is
collected after three months in the forest. Further, the density is also likely to increase during
transport. During the last decade, the industry has lesser attention on measuring the volume of
forest residue. Today, weight is the dominating measure.
Weight is a more objective measure in the sense that weight is less affected by transport. There-
fore, weight is increasingly accepted for shipment control as the scale technology has improved.
Further, weight is used as the basis for calculation of transportation costs. Assuming that the
moisture content is constant, the weight would also give a good indication of the amount of dry
biomass. However, reasons cited in section 3.3 indicate that this assumption should not be trusted.
Volume andweight might be combined in order to calculate density. For a given type of material,
densitymight be used in order to calculate approximate moisture content. Unfortunately, the result
is affected by the type of material, the degree of compression and of its fractional distribution.
However, a scale mounted on a front-end loader might e.g. provide useful information when
biomass is to be mixed according to a recipe before it enters the boiler.
A third parameter of great importance is the moisture content ( MC ) since it determines the
amount of dry mass in a certain shipment. Moisture content is important because it affects the
energy content, price and combustion properties.

dry mass = total mass × (1 − MC )

3.2.2 Calorific value
The above measures may all be used in order to estimate the energy content. Assuming that the
energy content in dry biomass is constant, information about weight and moisture content can be
used in order to calculate the energy content of the biomass. However, the energy content of dry
biomass varies depending on the type of material and on its storage time. Therefore, it would be
desirable to measure the energy content itself.
Energy content is traditionally determined through manual sampling followed by the use of
a calorimeter in order to estimate the energy content. Since this process is tedious and time-
consuming, it is impractical for everyday measurement.

3.2.3 Other parameters
Ash content and fractional distribution are other parameters with an economic relevance. The
term ash content often refers to the weight ratio of organically bound elements such as Na or
K. The term is also used as a general expression for various impurities such as dirt. While the
presence of dirt also affects the energy content, high sodium and potassium levels will have an
impact on the plant and its wearing.
Fractional distribution refers to the size distribution of the biomass. Two extremes are sawdust
and branches. The parameter is of interest because the size distribution of the biomass affects the
combustion process. Large differences or changes in size complicates boiler control and decreases
the overall efficiency of a boiler. An example is that fine fraction might be carried away by the
exhaust gases and burn in the upper part of the boiler while large pieces of fuel might not burn
through entirely.
Ash content and fractional distribution might be determined in a laboratory but these methods
are less practical for everyday measurement. Since determination of such parameters requires
manual labor, the sampling intensity will be a trade-off between utility and measurement costs.
There are several types of strategies depending on preferences of the buyer. One might for example
take reference samples from the different biomass types of each respective supplier and then
assume that the measured properties will be representative for a large number of shipments