Moisture Analyzer DewTector

The DewTector Story

THE ISSUE

Customers frequently approach Coperion with concerns about product moisture.
•    Plastic manufacturers often face the issue of moisture entering the final product. There are many causes for this: insufficient drying, defective water separators, leaking wash nozzles, condensation, rain, etc. If this goes unnoticed and the product is delivered, it leads to complaints that are associated with high costs and loss of reputation.
•    Processors must adhere to a maximum moisture content to produce high-quality products.
•    In the recycling sector, contaminants are removed through washing, but dry product is needed in the further process.
Nevertheless, product moisture is often not measured or only sporadically, for example, through manual measurement of relative humidity in bags, big bags, etc. This approach is always labor-intensive, mostly non-standardized, and unreliable in detecting moisture.

THE CHALLENGE

Therefore, Coperion has intensively examined the technologies available on the market for automated moisture measurement in the process. These are still not widely used. Here’s why:

→  Established methods such as capacitive moisture measurement or microwave resonance methods are complex and expensive. These indirect methods measure properties such as the dielectric constant and determine the moisture content indirectly through calibration functions that must be determined carefully beforehand.

→ The problem is also that these properties change not only due to moisture, but also, for example, when the composition of the additives in plastics changes. Therefore, a separate calibration would need to be created for each formulation – an unacceptable expense. If the additive content fluctuates, as is particularly the case with surface-applied additives, reliable measurement becomes impossible.

The result was sobering: There is no simple, reliable, and affordable measuring system available on the market that meets the requirements of the plastics industry.

THE SOLUTION

Coperion has therefore decided to develop its own measuring system – focusing on applicability and reliability. The solution is as simple as it is brilliant: Removing moisture by a flow of pressurize air and water-specific detection using a moisture sensor, along with a sophisticated algorithm for analyzing the drying process and determining the amount of moisture – the birth of the Coperion DewTector!

The DewTector Principle

A continuous partial flow for measurement is supplied to the DewTector via a simple branch from a gravity pipe or a higher container. The bulk solid is introduced into a product chamber, which can be pressure-tight separated from the feed and discharge lines by butterfly valves at both the top and bottom.
During the measurement process, a defined amount of air flows through the product chamber and absorbs moisture from the product, which is thereby dried. Thanks to the patented design of the product chamber, the flow is efficiently guided through the product. The air stream exiting the product chamber is directed to the analysis unit, where the moisture content of the air is determined using a hygrometer.
The analysis of the moisture profile over the duration of the measurement allows for the quantification of the amount of moisture removed from the product. Thus, the moisture content of the product in the measurement chamber volume can be reliably determined. With known bulk density, the mass-related moisture content in ppm is obtained.
Unmeasured product and the measured sample are gravimetrically returned to the process.