ISSUE FOCUS 44 FEED & ADDITIVE MAGAZINE April 2024 Hydronix Moisture Sensor Rotary Valve High Level Sensor Low Level Sensor 6. Drying: Pellets dried for durability Measuring at the input to the dryer enables feed-forward calculation of dryer parameters to ensure optimised performance and minimal energy consumption. Pellets must be under 12% internal moisture for maximum pellet durability and storage life. 7. Coating: Fat coating added Measuring before fat coating, at the output of the dryer, enables PID feedback control using the error from the target moisture value to adjust the process appropriately. 8. Cooling: Cool to storage temperature During cooling some moisture is lost, so the pellets finish at ~10% but this is often not monitored. Measuring at the output of the cooler allows control of cooling parameters and also enables a final quality control check prior to packaging or storage. MOISTURE CONTROL IN ACTION Figure 2 shows an example of a moisture control installation on a holding hopper before a fat coater. This holds material at around 60°C and is fed from the dryer. This allows a buffer of material to build up to ensure the coater has a constant feed of material whilst in operation. In this installation, a Hydronix sensor is used to measure the moisture of the dosed material. The sensor has built-in averaging (and filtering) functions making this straight-forward to achieve without needing complex changes to the control system. The average function may be triggered in various ways, in this case starting when the high-level switch is covered during filling and stopping when the low-level switch is uncovered. Additionally, a successful application using a Hydronix sensor after the dryer, in aquafeed, or other applications, is to monitor the dryer output moisture level. This may then be used to control the dryer temperature. This is proven to improve the consistency and repeatability of the final product moisture, and hence improve the final product quality. Figure 2. Moisture control between the dryer and coater
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