Technical Sales Engineer
“The moisture affects the costs and the quality of the products. Knowing and subsequently controlling the water content of the material in every step of the process is necessary to improve efficiency, to reduce carbon footprint, and to save money. To achieve these results, sampling the material is not enough because the samples may not be representative of the full batch and the speed of the feedback process is not adequate. It is possible to achieve real-time control in the process with inline sensors.”
Imagine a world where moisture does not matter, a world where you can harvest when you want, where mycotoxins do not affect stored products, where mills always operate at maximum efficiency, and final products are perfect.
It sounds fabulous, but as is well-known in the agricultural, feed, and related industries, moisture is a determining factor in every process. Let us take a few steps back and have a brief overview of all the steps where it is possible to increase profits and efficiency by controlling the moisture.
HARVESTING AND THRESHING
Harvesting is the procedure where ripe crops are cut and picked up to then proceed with the extraction of the grains by another mechanical process called threshing. Depending on the destination of the yield, the crops need harvesting at precise moisture. For example, harvesting and threshing grains when it is too dry (water content below 20% – 25%) can lead to loss, waste, and breakage of material.
Contrary to that, if crops are too wet, it is possible to get mechanical issues requiring additional adjustment of the harvesting equipment. Wet crops will also limit the weight capacity of the machinery and cause problems with the threshing action.
The water content of the yield can be measured inline directly inside the combine harvester to calculate the dry weight as well as provide additional information about spatial variability in the field.
Depending on the location and the weather, the first 48h are crucial for the yield, as mycotoxins can contaminate the product before the storage and drying operations. Knowing the moisture during the harvest will also allow the farmer to plan quickly ahead.
STORAGE AND DRYING
After the previous operations, the crop needs to be stored and preserved accordingly to prevent mycotoxins, spoilage, or heat spots. These often give problems that are directly related to the moisture contents of the grain.
Monitoring moisture during storage is fundamental to be able to regulate the storage operations and to react timely to problems. Drying is a common practice to store grains safely, and it is a delicate process to reach the perfect moisture. By missing the target, the crop is still prone to mycotoxins and spoilage, on the other hand, over-drying is not just an expensive waste of energy but can cause damage and breakage to the grain’s skin, making it prone to mycotoxins and insect attacks.
Excessive drying can also cause the grains to shrink in size, causing yield loss. The material entering the drier has variable water content, and this makes it challenging to regulate the amount of time the material needs to be exposed to the heat or to regulate the temperature. In this process, the inline moisture control is used to automate the dryer to save money and improve the quality.
After drying, depending on the material and system requirements, it may be necessary to reintroduce water into the product by conditioning. This process can be done before the grinding mill and before pelleting operations. Depending on the final application, the conditioning can also heat the material to kill germs, to cook ingredients, and to gelatinate starch.
In the same way that moisture control enhances the drying phase, it also improves the conditioning process by monitoring the target moisture to react timely to changes in the input material.
Grinding is one of the most energy-consuming transformations in many food processes. Through mechanical action, it reduces the size of food materials such as grains, seeds, fruits, and many more to achieve different chemical and microbiological stability.Results vary based on machines and methods used, as well as toughness and moisture of the material processed.
The toughness is the ability of a material to resist breakage; therefore, tougher material will need more mechanical energy to be reduced in size. The plasticity or ductility of a material determines the amount of energy absorbed before breaking down as well as the final size. More plastic or ductile material will need more energy to break, but it will maintain a more regular final shape. In contrast, less plastic or ductile material will shatter into finer and irregular shards like particles.
The elasticity of the material is defined by its water content: therefore, by controlling the moisture of the material, it is possible to determine the energy consumption of the process, the final size of the powder particles, and the product yield and loss.
For these reasons, the initial moisture of many food materials is the most important element to regulate before the grinding process.
TRANSPORT AND FLOWABILITY
After the grinding process, the moisture remains very important as it determines the flowability of the particles as the bonds between water molecules affect the stickiness and caking effect of the powder.
Pelletising is the process of extruding the formulation into cylindric shapes that are more easily consumed by animals. The content of the mix is extremely variable between the various applications and recipes. However, even in this process and after all the other steps, the water content is still an important factor to measure the quality of pellets. Additionally, the pellets may need to be dried for storage.
CONTROL AND SENSORS
In summary, the moisture affects the costs and the quality of the products. Knowing and subsequently controlling the water content of the material in every step of the process is necessary to improve efficiency, to reduce carbon footprint, and to save money.
To achieve these results, sampling the material is not enough because the samples may not be representative of the full batch and the speed of the feedback process is not adequate. It is possible to achieve real-time control in the process with inline sensors.
As water content is an indirect measurement, this means the value is attainable only by calculating it from another measured characteristic; therefore, it is necessary to keep as constant as possible all other variables such:
• Material composition (mix recipe)
• Particles size
• Pressure on the sensor
• Flow speed
For this reason, it is key to calibrate the sensors for each recipe or formulation, only after the system installation. The calibration must be realized by accurate lab tests, calibrating any sensor with another different sensor can cause a sum of errors resulting in incorrect calibrations, defeating the initial objective completely.
Independently from the method used in the process, whilst calibrating any sensor, during the lab test it is critical to completely “cook” away the moisture of the sample to reach the dry weight, as this is what will be used to define the moisture reported by the sensor.
There are many moisture sensors available on the market, and we can summarise the different technology used in five categories:
An essential, often overlooked, difference in the digital microwave technology is the linearity and stability of the output. Resistive, capacitive, and analogue microwave sensors have a nonlinear output making them very difficult to calibrate as they require numerous points to design the curve. Nonlinearity also implies low accuracy at the wet and dry end of the scale (Figure 1).
Sensors with a digital measurement technique have a linear output, the sensor reading, and water content are directly and proportionally related. This method allows systems to achieve optimal calibration with a few points. In theory with a linear system, it is possible to achieve calibration with only two points.
After these considerations, it is possible to define the ideal requirements of the moisture sensor:
• In line with multiple readings per second, providing quick feedback for the control to adjust on every batch.
• Robust, made with high-quality materials to withstand tough industry conditions.
• Linear output, stable over time, accurate in every condition and easy to calibrate.
• Store multiple calibrations to be used with different materials.
• Ability to measure into the flow of the material.
• Unaffected by dust or colours.
• Unaffected by salt and minerals content.
• Self-contained and easy to integrate into a pre-existing system.
• Low maintenance and cost-effective.
• Able to monitor from any device for full connectivity and remote analysis.
• High-temperature resistance may also be required.
• Some applications could also require ATEX or IECEx certificate.
Thanks to the expert research and development team at Hydronix, all the above characteristics can be found in the microwave sensors with unique digital microwave technology made for the grain industry.