EXTRUSION
INNOVATION IN AQUAFEED PROCESSING TECHNOLOGY
Clextral new Preconditioner + and twin screw extruder EVOLUM+
by Clextral
W
orld leading aquafeed technology expert Clextral has played a pioneering role in the innovation and development of twin-screw extrusion for aquafeed since the 1970s. To respond to new challenges and increase the capacity of existing systems, Clextral is introducing two innovations this year: a new preconditioner and a new range of twinscrew extruders with advanced control.
Process flexibility and improved efficiency
In twin-screw extrusion of fishfeed pellets, preconditioners are recognised by industry experts for their production benefits. The new Clextral Preconditioner+ integrates two horizontal, intermeshing, counter-rotating shafts that provide tangible production benefits: improving the overall process and the quality of the finished food products and enabling energy savings, while providing greater flexibility and more precise control over the operating parameters, whatever the recipe. The key innovation of Clextral’s Preconditioner that improves heat and mass transfer to the product is the
Advanced Filling Control device (AFC) which interacts directly with the material inside the mixing chamber and enables the filling ratio to be adjusted. The AFC system uses an exclusive conveying screw inside the tank and adjusts the flow by enabling a partial and controlled recycling of the material being processed, from the outlet to the entry point, thus intensifying the specific preconditioning functions. In addition to increasing the filling ratio, the AFC system also generates better product distribution, in particular in the first third of the mixing chamber which is the preferential zone for steam injection. The adjustable water and steam injection ports have been optimally positioned to enhance absorption and product exposure time during the mixing stage. Extensive experimental trials have been carried out on the Preconditioner+ to verify the processing improvements generated by its AFC system on the twin-screw extrusion process. In this case a standard fish-feed recipe (basic salmon feed) was used, not to gauge optimal performance but to set an objective benchmark compared to traditional preconditioning systems. The first significant observation was a lowering of the SME (Specific Mechanical
Advanced Filling Control (AFC) system: key innovation of Clextral new preconditioning system
16 | INTERNATIONAL AQUAFEED | January-February 2015
Energy) required in the extruder – an average of 3 percent with equal extrusion parameters – mainly due to the increase in preconditioning time, and largely compensating for the additional consumption of the Preconditioner+. As mentioned previously, this efficient pre-cooking reduces the shear and the torque requirements in the extruder, which results in less wear of the screws and barrels. By focusing exclusively on the Preconditioner+, the experiment also demonstrated that the new filling ratio (up to 75 percent) achieved with AFC made it possible to increase residence time by 60 percent for an equivalent fish-feed flow and therefore to exceed the average of three minutes. At the same time, the combination filling/steam distribution made it possible to increase the product temperature by 3-4°C at the outlet of the Preconditioner+, using comparable steam injection. It is even possible to achieve a product temperature of over 96°C with optimised steam injection, while limiting energy loss due to the new design. Following the improvements on the pre-cooking stage, a significant increase in starch gelatinisation before product feed into the extruder was witnessed and measured. Finally, on the finished product after extrusion, granulation and drying, these upstream modifications resulted in an increased hardness of the pellets of at least 10 to 15 percent, an essential quality criterion required for their use in fish farms. Beyond the process benefits on product quality, it is important to note that this equipment is designed to facilitate