The new ECOtwin enables the cooking degree and the bulk density of extruded products to be accurately selected and controlled.
The ECOtwin system also ensures optimal matching of the performance parameters to the specific needs of the pet food and aquatic feed industries.
In addition, a large portion of the thermal energy can be recovered. This may reduce the steam requirement for preconditioning by as much as 30percent, depending on the particular application.
The new SME and Density Control Modules allow separate selection and online control of the cooking degree and bulk density of the pellets. To achieve this, the extruder is divided into two process sections or areas.
In the first section, the specific mechanical energy (SME) is specified for optimising the texture and cooking degree; in the second section, the precise product temperature at the die and therefore the expansion degree or bulk density of the pellets is selected.*
The module consists of a throttling device with two distribution cylinders. Closing of the valve cylinders increases the length of material backed up ahead of the throttle. As a result, the filling degree and dwell (retention) time increase. This in turn increases the SME. When the cylinders are opened, the opposite happens.
The Density Control Module consists of an open housing attached to the end of the SME Module (degassing housing).
The opening is provided with a socket and a retaining mechanism. It prevents the product particles from being carried along by the steam discharged.
The product temperature at the die and therefore the bulk density can be selected independently of the SME introduced into the first process section.
This is accomplished either by adding positive-pressure steam
(low-density product), by returning neutral-pressure steam to the precooker (medium-density product) or by generating a vacuum (high-density product).
Bühler AG , Extrusion Systems, is based in Uzwil, Switzerland. www.buhler.ch
