There is a growing interest to trade Biomass as fuel based on energy content rather than trade in volume or weight. This makes it more important to know the moisture content of the Biomass. A common method to determine the moisture content is with an oven in a laboratory. However, this method is time consuming and the used samples are not always representative because of their small sizes. The aim of this study was to find out if the system from INADCO Moisture Measurement can be used to determine the moisture content of Biomass online.
The inline measuring system of INADCO Moisture Measurement consists of three parts.
The first part is the sample taker, a horizontal moving plate that takes small samples out of a falling product stream. This sample will be put into a cylinder with a diameter of 315mm and a volume of 20L. The sample taker needs to take several times small samples before the cylinder is completely filled. By this way of filling the cylinder results in a large sample which is representative for the amount of product that has passed during the filling of the cylinder.
The second part is the real-time weighing of the cylinder. The weight is used in the control system to know if the cylinder is completely filled and for the determination of the bulk density, which is the result of dividing that weight by the known volume being 20 liters .
The third part is for the determination of the moisture content. For this the 20 liter cylinder is made double-walled. In between them the measuring probe is mounted. This measuring probe comprises a surface of approximately 85% of the cylinder and has a penetration depth of 8-10cm in the material based on a high-frequency technique. Due to the large volume of the sample in the cylinder, the large measuring probe and the high penetration depth of the measuring probe it is possible to determine the moisture content of almost all the material that has been collected in the cylinder.
Once the cylinder is completely filled, the sampling is stopped which creates a stable environment in order to perform reliable measurement a few seconds later. When the measuring is complete the sample taker will open the bottom of the cylinder so that the collected product goes back into the still passing material stream. When the bottom is closed again the sampling will restart. The cycle time for doing one complete measurement is approximately 1 minute. The results are in absolute values (gr/l) or percentage and will be shown on an Operator Panel and are send to a process computer.
For the study the SLU and Energidalen created 80 different samples of 50 liters in the range of 35%, 50% and 75% of moisture content with different fractions of material. They used different types of material of chipped wood like Spruce, Birch, Pine, stemwood and branchwood and mixes of these materials. In the test they used also Bark and Peat.
Each prepared sample was always measured 2 times with the INADCO system. Because this was a test setup the sample was put on the horizontal plate and then the plate was rotated manually to the cylinder so that the product could be collected in the cylinder until the cylinder was completely filled. From each filled cylinder where 2 samples taken immediately after the measurement for comparison with the drying stove. In this way 160 measuring results and reference points could be compared. All the results were entered into Excel so that a regression line could be determinated in a graph without classification in wood species, moisture content or particle size.
The test concluded that the technique used in the INADCO measuring equipment is at least as reliable and accurate as the drying stove which is used to check the measuring results. The correlation graph showed clearly that the accuracy of the INADCO measurement system will increase significant when classify will be used.
The first results of this test where presented at the ETA Biomass Conference and Exhibition, a scientific conference held in the beginning of June in Copenhagen, Denmark. Many attendees received the results as “remarkable good”.
The results of the test is assessed by Energidalen as extremely positive so they committed themselves to do a next test where the INADCO system will be implemented into a real process installation where again the SLU shall execute the tests and evaluate the results. Apart from that, a “Scientific Paper” will be written by the SLU given the major step which is made with this new technology.