Moisture content woodchips - survey TFZ Straubing

Moisture measurement for wood chips – a study by TFZ Straubing

Study TFZ Straubing: “Quick determination of the water content of wood chips.” The fluctuations of the water content of wood chips is a challenge for producers and traders of wood fuels and for the operators of wood chips furnace. A precise and quick determination of the water content is decisive at many intersections of production and distribution of combustible material. The standard method (mostly used) is the determination of water content by drying the combustible in a drying cabinet (according to DIN EN ISO 18134-2). It is a very precise method but time-consuming and labor-intensive. New developed gravimetric and electric measuring procedures could be reasonable alternatives for a quick and accurate determination of the water content. The TFZ report is focused on analyzing the measuring accuracy of the quick determination of the water content of wood chips. Manually operated measuring devices were tested (designed for field use) as well as in-line determination instruments meant to measure within the continuous material flow. The results of the report have also influenced the development of the “ENplus Certification Program for Wood Chips”.

Results of tested online moisture measurement for wood chips

The study has been divided into two main parts. On one hand they have been analyzing manual moisture measuring devices (handheld devices and laboratory measuring devices) for the determination of the water content of wood chips. On the other hand they have been testing online moisture measuring devices (also called process moisture measurement or in-line moisture measurement).

Tested material:

• wood chips out of energy roundwood
• wood chips out of forest residues

Tested moisture sensors:

• ACO Automation Components: Moisture sensor AMMS-0-1-2-0 (capacitive high frequency moisture measurement)
• Schaller GmbH: Moisture sensor Himimeter BLO (electrical conductivity)
• Franz Ludwig GmbH: FL-DIGI Smart (microwave moisture measurement)
• SWR Engineering Messtechnik GmbH: Moisture sensor M-Sens 2 (capacitive high frequency moisture measurement)

Experimental set-up:

Test construction (a) analyses wood chip ranges: Wood chips made of residual forest wood (front) and power wood logs (background), (b) measurement channel filled with wood chips, (c) mounting of sensors into the measurement channel, (d) closed measurement channel with stamp and (e) schematic layouts of the test --> illustration 27 from “Rapid determination of the water content of wood chips” by TFZ Straubing

Summary: ONLINE Moisture Measuring Methods for Wood Chips

The study by TFZ reveals that the measuring accuracy depends on the moisture level and the specific range that has to be measured. The highest accuracy in the described study had the moisture sensor AMMS-0-1-2-0 (Power log wood) and the humimeter BLO (Residual Forest Wood). The research team found out (analog to the manual measurement devices) that regarding online moisture measuring methods beside a high number of repeated measurements a good calibration is decisive to get a good measuring result. Advisable is a calibration right to the actual material. Furthermore, the TFZ Straubing Team has worked out that the devices can even be used for billing purposes at a high number of measurements, provided, that single batch of the material is clearly definable. Especially for the regulation of the combustion management of the tank these kind of devices are suitable. Detailed report from TFZ Straubing “Quick determination of the water content of wood chips”.

Detailed report by TFZ Straubing – “Rapid determination of the water content of wood chips” from Theresa Mendel, Dr. Daniel Kuptz, Andreas Überreiter und Dr. Hans Hartmann. Only the summary of the survey is available in english (page 73 ... 74).

The study has been promoted by the German Ministry of Nutrition and Agriculture (BMEL). The allocation of funds has been realized by the specialist agency of renewable resources (FNR).

Helpful tips and examples about how to find the right measuring position and how to integrate a moisture sensor into a production process you will find here: Case studies - moisture measurement biomass