Biomass, as a renewable fuel, is now indispensable for generating energy. Professional moisture measurement ensures the quality of the valuable raw material, because the water content largely determines the calorific value. The water content also influences the storage life, the emissions released, the ash and the bulk density.

The test laboratory at Schaller Messtechnik, which is accredited according to EN/ISO 17025, answers which practical measurement methods are suitable for determining the water content of biomass.

Measurement in the laboratory
In the laboratory method, the fuel is dried in a drying cabinet according to DIN EN ISO 18134-2 for at least 12 hours at a defined temperature until the fuel's remaining mass is constant. The water content of the fuel is calculated from the mass loss due to oven drying. This method is used in accredited testing laboratories and is usually used as a reference for quick measurement procedures. Due to its high complexity, this method is prone to errors. It should also be noted that not only water evaporates, but also other ingredients - such as resins.

Electrical measurement methods
Electrical measuring methods are sensible alternatives for a much faster yet accurate water content determination. In practice, a quick determination of the water content is of great advantage.

The two most important electrical processes are:

• Conductance based methods

With this method, the material to be measured is not changed. The method measures the water content based on the electrical conductivity, which increases with higher water content. The more water there is, the more conductivity arises and the electrical resistance decreases. This measurement happens very quickly because only the probe needs to be brought into contact with the biomass. However, the conductance is strongly dependent on temperature. Therefore, it is necessary to carry out an accurate and correct temperature compensation of the measurement result.

• Dielectric processes

In the dielectric process, the water content is calculated by measuring the dielectric constant of water in the biomass. By irradiating the measuring frequency into the material, it is possible to analyze larger quantities of biomass. In addition, the method is less temperature dependent than the conductance method.

Conclusion

Each of the measurement methods described has its advantages and disadvantages. Correct and professional application is crucial. Measuring in the laboratory requires a lot of expertise - with rapid measuring methods, this expertise is already packed into the measuring device. Laboratory measurement should be the reference method for all moisture meter manufacturers. It is therefore advisable to pay attention to the standards when it comes to measuring devices. These guarantee that a standardized measurement procedure is used and that comparisons are therefore possible.

Accredited testing laboratory 

humimeter-devices in the biomass sector