Higher quality and more valuable feed with moisture control

Knowing and controlling the moisture content of your materials from the introduction of the raw materials to the packaging of the final product is key to maximising efficiency, optimising yield and producing a high-quality, consistent product.

Variation in the moisture content of the raw materials has historically presented a challenge to feed processors. The raw ingredients’ moisture content varies depending on the prevailing environmental conditions during harvest, transportation, and storage. Traditional offline tests are time-consuming, subject to error and unrepresentative of the material flowing through the process.

The perfect solution is to constantly measure the flowing materials’ moisture content and correct moisture variations in real-time. In the past, such systems have been complicated to use and have required ongoing complex and expensive maintenance. Modern, sophisticated, reliable and affordable moisture sensors are now available that can simply and economically control the moisture content throughout the entire process.

The use of online moisture measurement sensors enables the control system to automatically react to changes and adjust the process to achieve a continuous and precise moisture level in the material, whether for storage, further processing, or final packaging.

Raw materials vary in moisture content, and this variation leads to weighing discrepancies. The weight of usable material will vary dependent on the moisture content. An increase in moisture content means that there is less usable material. A reduction in moisture content gives more usable material for the given weight. Without compensation, this leads to different proportions of usable material being added to a formulation. This affects both the final yield and causes variation in the nutritional value.

Accurate control of the moisture during the drying process prevents under-drying and over-drying. Over-drying material uses excessive energy, reduces the yield, and can damage the material being dried (for example, becoming brittle if dried too quickly). Under-drying leads to potential mycotoxin growth and reduces the storage life of the material.

The accuracy of the moisture measurement system will affect the final moisture target of the dryer as the material being dried will need to be below a maximum allowed value. If you use a moisture sensor that can get as close as possible to the maximum value, you reduce the amount of extra drying needed, which reduces the energy being wasted.

Although this is often regarded as a small reduction, reducing the distance from the target will lead to more significant savings in energy.

Choosing to rely on a moisture sensor that can measure to a precision of +/-0.5% instead of 1.0% seems a slight improvement. Still suppose you consider a process that is drying material from 20.0% to a maximum of 14.0%. In that case you can see from Figure 2 that the 0.5% improvement in the sensor precision yields a much more considerable 7.15% energy saving if the energy input is proportional to the moisture loss.

Moisture control throughout the process allows the production of higher quality, balanced and more valuable feed:

Measuring online in real-time offers significant benefits over offline measurements.

Periodic offline sampling is time-consuming and subject to:

As Figure 3 shows, the real-time average of the material flow is 12%. The three samples taken at 60, 120, and 180 seconds give an average of 14%, which is a 2% error.

With care, proper equipment, and good technique, it is possible to scientifically calculate an accurate value for the moisture, but it will only ever be valid for that sample.

Installing and integrating an online sensor to measure the moisture continuously gives a much better method for monitoring the material flow.

When selecting a sensor, it is essential to ensure that it is fully temperature stable and completely linear over the working range at which you wish to operate.

A sensor utilising an underlying digital measurement technique that can guarantee linearity allows a much simpler calibration process than one that has a complex relationship, as shown in Figure 4.

An online sensor will still need to be calibrated during commissioning to the specific material flow being measured by taking samples whilst recording the average sensor value and testing in the laboratory.

A sensor using a linear measurement technique only needs two accurate points to derive the calibration line coefficients. By having multiple calibration points and using a linear regression technique, as shown in Figure 5, it is possible to reduce the effects of individual errors on the calibration coefficients.

Once the equipment has been properly installed and set up, the control system can then use the measured value to adjust the process in real-time to give excellent results limited only by the accuracy of the calibration.

A good quality instrument will provide a stable measurement improving reliability and removing the need for constant recalibrations after commissioning.

This repeatable measurement also allows the control system to automatically switch between different calibrations when measuring different materials or formulations in the same location.

Moisture sensors need to be installed in contact with a stable and consistent material flow. Different sensor models are available, which ease different mechanical installations, allowing straightforward installation into mixers and screw or belt conveyors on an existing plant to improve every part of the process, reducing waste, improving quality, saving time and effort.

The sensor should be a self-contained unit offering maximum flexibility of installation and communication using analogue control loop outputs, and common protocols such RS485 and MODBUS allow simple connection to standard process automation systems.

By controlling the moisture during the weighing up of the raw materials, it is possible to correctly control the protein content of the final pellet and guarantee superior product quality. There are also cost benefits of water control ranging from an increase in the yield from a raw material, a reduction in spoiled material and optimisation of the energy input into the processes.

For dryer control, one often overlooked advantage is the ongoing impact of not using the optimal drying rate. By drying with too high a temperature for the moisture in the material, you can increase the damage being done to the husk, which then becomes apparent during either milling or de-husking.

One producer using a moisture control system in their parboiled rice production reported a reduction in broken rice of 2.5%, equivalent to an increase in their yield of premium quality product of 4,000 kg per week. By looking solely at this extra yield at current market rates, this would be an additional USD 1,668.00 per week giving a return on investment of only a few months.

By calculating the energy input needed to dry the material and how much extra energy is input when missing the final target value, it is possible to show extra savings.