at the preconditioner, the time delay in seeing a product change is based on 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 and nutrition.
When designing a waste recovery solution, two primary methods normally are 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 Total without any operational changes to the extruder. $123,455
A 1% inclusion rate is typically more than enough to handle most daily wet waste generation. More concentrated solutions can be used, but most likely will result in operational characteristic changes of the extruder, such as needing more DCC or extruder barrel water to accommodate for the increase in added solids.
Table 2: Annual waste recovery
system savings
Water Recovered
savings material
3,844 $116,705
Energy savings
$2,906
A waste recovery system’s payback period typically is between 8-10 months.
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 a production facility with a WRS facilitating wet waste from an extrusion line producing premium dog food.
Our 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 (see Table 2).
Note that these savings numbers are conservative because this client’s operational procedures reduced much of the waste potential. In most cases, the payback period of implementing a WRS is between 8–10 months. ■
September 2008 Extru-Technician 10
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