Industry trends of using finer ingredients like starches, fillers and flow agents — also regrind and recycle materials — in greater percentages can result in ingredient separation and segregation, affecting your final product.
Brand Insights from Horizon Systems
When it comes to pet food, your customers expect a consistent final product every time they purchase your products. Industry trends of using finer ingredients like starches, fillers and flow agents — also regrind and recycle materials — in greater percentages can result in ingredient separation and segregation, affecting your final product. Smaller particle size ingredients can be easily suspended in an air stream, but different sizes and densities will tend to separate when handled.
Separation and segregation can result in issues like poor product quality and ingredient flow and can also create discharge issues from hoppers and silos, leading to the rejection of finished product. If you have noticed any of those issues taking place in your process, consider the following areas to evaluate to help identify where separation and segregation occurs:
- Blending performance
- Changes in ingredients/formulation
- Material handling/storage designs
Sampling
It is critical to determine the process steps where the separation and segregation occur when evaluating your system. You should take samples at each major step in the process to locate the area of occurrence directly after mixing. Take enough samples over a period of time from the same sampling points to ensure statistically significant results and to rule out sampling error.
Ensuring Blending Performance
Before searching for the causes of ingredient separation and segregation, verify that the starting blend quality is acceptable. This can be done by monitoring material fill levels in the heat mixer to ensure the proper mixing. Samples need to be taken and evaluated at the mixer discharge before any handling of the product blend occurs.
Pneumatic Conveying, Filters and Discharge
Pneumatic conveying is one of the two main processes where your product blend is exposed between blending and processing. During pneumatic conveying, the product blend encounters high velocities that can naturally separate particles. Larger particles (sugars, salts, whole grain) typically have high horizontal conveying velocity requirements, while fine particles within a blend (stearates, starches) can be conveyed at much lower velocities. If a transfer system’s velocity is designed incorrectly, separation and segregation can occur within the conveying line.
The area of a transfer system with the highest potential for separation and segregation is typically at the end or exit of a conveying pipe. The air flow direction to exhaust from the vessel is upward, causing particles to suspend in the air stream if it is too high. If the flow of air and product into the filter receiver is continuous, this effect can cause the filter media to blind over and cause damage to the cartridges or bags.
Filter and extruder receiver designs with small housing diameters and tightly packed filter media have higher can and interstitial velocities. The common traditional designs have been driven to minimize space requirements and cost but can have more issues with separation of finer ingredients used in larger percentages within blends.
Separation will occur during the convey cycle of a receiver with too high can/interstitial velocity. Once the airflow stops there is nothing to hold the fine particles up and they are pulsed off the filters, creating a layer on top of the coarse product that fell into the hopper. These layers of product then discharge to the extruder.
Silo/Bin Fill and Discharge
Storage in silos and hoppers is the second main process where your product blends are exposed during handling and processing. Product separation can occur when filling and emptying storage silos because different size and density particles will travel various distances before they settle. The two discharging flow patterns that can contribute to separation are Mass Flow and Funnel Flow.
Mass Flow
- Causes the entire cross section of product to move at the same rate toward the discharge
- Results in first-in/first-out performance discharging of material
- Results in steep cone angles in hopper slopes and more internal devices to interrupt a funnel flow pattern
Funnel Flow
- Pattern where center product in the vessel moves toward the outlet at a higher velocity
- Product on the perimeters of the vessel moves much slower or not at all until the center is empty
- Results in last-in/first-out performance discharging of material
- Can cause separation as product discharges
- May help to remix separated product
- Silos need to be fully or nearly emptied regularly
Next Steps
Once you’ve identified where separation and segregation occur, it’s time to evaluate your equipment for functionality. With the help of Horizon Systems’ knowledgeable and skilled team of experts, you can develop operation parameters and design changes to remedy your separation issue. At Horizon Systems, our experts have more than 40 years of experience diagnosing material segregation and separation issues, as well as engineering solutions that deliver consistent results.