injection. The use of water injected at the extruder inlet renders a fast-reacting process, meaning that when the injection level is adjusted, a change in the product is seen almost immediately.
Conversely, if the water injection level is changed at the preconditioner, the time delay in seeing a product change is due to the retention time configuration of the preconditioner. However, added moisture at the extruder may reduce the temperature of the incoming feed and extend the warm-up time of the extrusion process, most likely generating an off-spec product until the system reaches the optimum temperature levels.
After implementing the most efficient operational procedures, a plan for the most effective method of waste recovery can be designed. An important step in determining an appropriate waste recovery solution is to calculate the amount of waste rework that can be reintroduced into the raw ingredient stream without creating more waste or off-spec product.
This calculation is based on the extrusion capacity rates and the product formulation. When reviewing the product formulation and specifications, all aspects are considered, including, but not limited, to:
■ Starch gelatinization;
■ Appearance;
■ Durability;
■ Density; ■ Nutrition.
When designing a waste recovery solution, two primary methods are normally used. Each is specific to the type of waste being reintroduced into the process. Waste product is divided into two categories, dry and wet.
Dry waste consists of dry fines generated in the system with moisture less than 13%. This waste is best recycled by grinding and adding back to the raw material recipe batch mixer at rates of 0-5%.
Wet waste typically is the wet product collected from the preconditioner downspout and the extruder die as generated during system startup, shutdown or process interruptions. Through the use of a system such as the proprietary Waste Recovery System (WRS), this material is continuously conveyed, liquefied and injected as slurry directly into the extruder’s preconditioner. The WRS is designed to easily handle up to 1% of the extrusion rate per hour without any operational changes to the extruder.
Designing and implementing an appropriate waste recovery system such as the WRS has an immediate return on investment.
As proof, a case study was developed in an actual production facility of a premium petfood producer with high annual tonnage. The facility had a WRS facilitating wet waste from an extrusion line producing premium dog food. ETI’s findings showed a collective annual savings of $123, 455. Energy savings were $2,906; water savings were $3,844; and recovered materials were worth $116,455.
And every dollar saved correlates with a healthier environment. ■
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