Accurately measure moisture in bulk solids

TEWS Elektronik offers suitable solutions for measuring moisture that meet the complex challenges faced by producers of concrete, cement, ceramics, (quartz) sand and glass, among others. TEWS moisture analyzers guarantee a reliable and accurate measurement. The analyzers measure independently of bulk density, size, color and mass and both at the surface and in the core of the product. These innovative sensors can also measure abrasive materials over long periods.

NIR or microwave analyser

Moisture measurements in bulk flows are often carried out with NIR or microwave analysers. Measuring moisture with microwaves is a contact measurement, which means that the sensors can wear quickly with abrasive materials. A NIR analyser is not, but is sensitive to ambient light, structure and color changes. They also measure moisture mainly on the surface of the product.

The NIR measurement is therefore especially suitable in an environment that hardly changes. The microwave analyser does not experience the disadvantages of an optical (NIR) measurement. A standard microwave analyser measures moisture on the surface as well as the moisture contained in the product. In fact, the amount of water per unit volume is determined. However, this does not yet provide the correct moisture percentage. Namely, the amount of product per unit volume can vary, depending on the bulk density. In order to determine the moisture mass percentage, it is therefore necessary to divide the amount of water per volume unit by the amount of product per volume unit, or the bulk density.

Bulk density of great importance for moisture analysis

Bulk density is determined indirectly in virtually all analyzers. However, many moisture analysers assume that the bulk density is linearly dependent on the amount of moisture. That's where it goes wrong, because this is not the case with many products. With some products, the particles swell at higher moisture percentages, which changes the stack density and thus the bulk density. An example is the behavior of sand; the volume of a particular mass of sand dumped is highly dependent on the moisture content, but without a linear relationship.

This non-linear behavior is a challenge in the concrete industry, for example; a small deviation in the composition can greatly shorten the life of concrete. Bulk density can also vary widely with a wide particle size distribution. Not only on a micro but also on a macro scale. Shards of glass or ceramic can vary greatly in size and shape. As a result, the bulk density is not constant and an indirect measurement is often not representative of the entire batch.

Moisture measurement independent of grain size, bulk density, color and mass

The TEWS Elektronik microwave analyser measures the moisture percentage and bulk density in one measurement, so that it compensates for variations in bulk density. The measurement is independent of the (bulk) density, size (grain or chip size and shape) and mass. This system therefore does not assume that the bulk density is linearly dependent on the amount of moisture. The moisture percentage is also not dependent on the size of the raw materials used or grain size. This allows you to determine the moisture percentage of your products much more accurately, also in-line, and you can better control your process. An important second challenge in measuring moisture in abrasive materials such as concrete, sand and shards is the fact that the concrete mix can very quickly damage the sensors of the analysers. Sand and gravel can cause the sensors to wear out within months. TEWS developed an in-line analyzer, in which the product is poured into a tubular cylindrical sensor and emptied again in a cycle of two to three times per minute. This way the sensor is less stressed by the flow. This sensor is placed in a bypass.

More information about a moisture measurement in the production of cement, concrete, glass or ceramic

For more information about TEWS Elektronik's moisture analysers, please contact Kees van der Sar, Product Manager at Inventech, on telephone number +0031(0)162-460404 or email. Download the brochure here.