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Moisture measurement

franseboomschors Albemarle_ grof houtpellets potgrond houtsnippers slib Schors

MOISTURE MEASUREMENT in more or less inhomogeneous bulk products like Biomass or potting soil substrates

Moisture sensors. For determing the moisture content in rough and inhomogeneus and homogeneus bulkstreams.
Different Moisture sensors.
Flat or Cylinder

Quality Requirements, Economic value, Energy consumption. Just a few words that could increase the importance of knowing the moisture content of your product. The most known existing inline systems are NEAR INFRA RED (NIR) and MICROWAVE. Beautiful systems that unfortunately cannot be used in any application.

It seems to be so easy. A measuring system above or below the product and the correct value is measured. Our experience within the market however learns us that the measured values may not always be considered as reliable and accurate. After analysis of the used techniques and the measurement results, different and mainly explainable causes for the wrong measurement results can be given. Some of these reasons are explained on our website. You can go fast forward to this item with this link.

The Moisture measuring sensor which has been developed by us has been used as an additive in our Bulk Density meter or in the execution of a Flat Plate-sensor for under a conveyor belt if the bulk density is known or constant, or is determined in another way.

With the demand from the Biomass industry is our moisture measurement system now integrated into a newly developed instrument specifically for coarse products. Due to the increasing prices of all kinds of biomass, it becomes increasingly important to measure the Moisture Content of the product. More and more the price of these products is based on its real economical value, the energy content, where the Moisture percentage is a factor which has a huge influence on it. See this link to get more information about this Biomass-Energymeter

Other reasons for measuring the moisture content of your product could be for increasing the quality of the product or for improving or accelerating the process.
For many processes, it is very important to know the moisture content of the processed product. Some examples of those are industrial dryers, burning or pelletizing biomass like woodchips and sawdust and producing bricks in brickworks.

Most types of biomass are inhomogeneous and very compressible products. The distribution of the water in the product is far from even. That makes it very hard and time consuming to prepare a representative sample of the product.

For getting high quality measuring results, you have to fulfill the following requirements:

1. Getting a good representative sample from the product
2. Having a measuring Volume that is much bigger than the biggest structure in your product.
3. Having a very good Bulk Density compensation to compensate for changing compression or flow-properties.

With our measuring equipment, the Moisturemeter I, we fulfill all of these requirements.

Ad1: For getting a good representative sample out of the product stream, we use our Densimeter. This apparatus was developed back in the year 2000, and since then widely spread over Western Europe for measuring the Bulk Density of peat, according to the then new developed standard EN12580 for measuring that Bulk Density for trading purposes.

Ad2: Our measuring cylinder has a volume of 20 liters, required by that previous mentioned standard.

Ad3: Because the Moisturemeter is built as an option on top of our Densimeter, we have perfect Bulk Density compensation for free!. Basically the machine is a Densimeter.

Back in 2005 we developed a high frequency Moisture measuring system being able to measure a thick shell of product (by then: Peat) on the inside of that cylinder. The high frequency system covers most of the wall of the cylinder, and has some 8 centimeters intrusion depth. So the covered volume is much bigger than the very fibrous and rough structure of the peat to be measured.

As a leading supplier of measuring equipment for measuring bulk density and moisture content of rough inhomogeneous bulk products, we continue developing to comply with market demands. Because we develop and produce ourselves, we are also able to adapt our equipment to your needs.

The above-mentioned solution is a fully automated system. No human involvement, no forgetting to take samples any more. Just giving you the requested results.

Our system provides you with not only the Moisture percentage, but also the absolute values of Moisture content and Bulk Density in grams per liter.
In our basic version, we need about one minute to fill the measuring cylinder. The measurement itself only takes some seconds. So basically you can have a new measuring result every one minute.

Measuring systems
There are many ways of determining the moisture content of those substrates and other inhomogeneous products. However, all of those known methods have their own disadvantages.

Nowadays, the most common way of determining the moisture contents, is to take a sample from the produced soil, put that in a stove, and determine the decrease in weight after having heated this sample for several hours, in some cases even 24 hours.
The main disadvantages of this method are, that you only get the result many hours after production, and that it is very labor-intensive. In most cases the product has already left the premises or is already processed by the time the results of the test becomes available. So there is less possibility to use the result for quality control, or for preventing wrong products being delivered to your customer. Because the volume of the sample used in this method is relatively small, this is in mostly cases not representative for the total batch. When producing a product which contains different sorts of raw materials, and probably are wetted also, field tests have shown that such a small sample certainly does not represent the production. This is also the case in for instance brickworks, because there a raw mixture of sand and clay has to be sampled

There exists many measuring methods which can be operated on-line. The best known are the following two:

The most commonly used measuring method, Near Infra Red - shortly: NIR -, in many cases gives a very poor result. This is because this method measures only the surface of the product stream, and the measuring result are very vulnerable to changes in color, temperature and structure of the product. Furthermore the dust that is always present in excess in such processes disturbs the measurement. But the biggest issue is that the outside of the product is not representative for the internal moisture. That can happen because the product is not homogeneous, but also because the outside dries when transported on the belt, and it is more moist when it has rained.

The other known measuring system, the Microwave sensor, has the advantage compared to Near Infra Red, that is does not only measure the outside, but it measures a volume inside the product flow. However, this method cannot be used because the bulk density of the product changes in many cases from one moment to the other. Some Microwave sensors do have bulk density compensation but they determine the bulk density by analyze the high frequency signal instead of weighing the product divided by the volume. Furthermore the measured volume is way too small compared to the structure of the product.

Vochtmeten ongecomprimeerd

Situation A: result = 5

Vochtmeten gecomprimeerd

Situation B: result = 8

Blue areaMeasuring sensor (in this example a Microwave sensor)
Green areaMeasuring area
Brown areaProduct
White areaAir
H2O (blue)Water particle

Every sensor has its own measuring area (the green area).
In situation A a standard microwave sensor is measuring in an uncompressed product. The sensor determines 5 water particles.
In situation B the volume of the product used in situation A is now compressed. The bulk density of this product is increased (same weight, less volume). The same sensor with the same measuring area is now measuring 8 water particles.

All the enumerated previous problems in measuring the moisture content of your product, was for us the reason to develop a system that does not have any of those before described disadvantages.

THE INADCO MOISTUREMETER I compared to other measuring techniques

We already had a broad experience in the potting soil production, because of our Densimeter, our Belt Weighers and our Quantity Checker. Especially for inhomogeneous and fibrous products like biomass and peat, there are many challenges to overcome when you want to measure the moisture content of these inline. When measuring woodchips, straw fibers or other compressible products with rough structures, the same issues as mentioned for measuring peat have to be solved, because they are compressible, have changing surfaces and sizes, and their color changes from time to time.

After investigating all systems available on the market, it became clear that there was no commercial system available that could fit all of our requirements. Having ended this survey, we decided that we had to develop one ourselves!!.

The technical requirements we had by then were that our Moisturemeter should:

Moisturesensors. For determing the moisturecontent in rough and inhomogeneus and homogeneus bulkstreams.
New moisturesensors.
For use in the field

The result is an INADCO Moisturemeter I as an option built on the INADCO Densimeter. We measure a big shell of product inside the measuring cylinder. So our measured volume is very big compared to the structure of the product. And we have a perfect Bulk density compensation, because the system is built on top of the Densimeter. So our Moisturemeter I is not measuring only the surface, but it measures also far inside the product. Influences from drying through the flow on the belt, or rain which wetted the outside, have no disturbing influence on the measurement. With its high frequency measuring system it measures the Moisture content of the product in grams per liter. The Densimeter measures the Bulk Density in grams per liter. So the combined results give the percentage of Moisture.

While determining the Bulk Density of the product in our cylinder, we do measure the Moisture contents of that same product at the same moment. We developed a special probe, which is able to measure that moisture content without making any contact with the sample to be measured. In this way we cannot disturb the sample while measuring. Our probe measures a very big sample, so that the inaccuracy of any small sample, does not play a role any more.
Field tests have proven that we do meet the above set of requirements.

You can view some test results in the graph below.

grafiek moisture

As you will notice, the results of our automated measurements do not always exactly correspond with the ones resulting from drying in an oven. Study of the differences showed, that in many cases these differences can be explained as a result of the "manual" sample not representing the measured soil, because of the "manual" sample simply being too small.

Recently our second generation Moisturemeter, the Moisturemeter II, is on the market. It allows to measure the Moisture content of products in a "streaming" process. Of course, some requirements have to be met to achieve reliable results.