INNOVATION IN AQUAFEED PROCESSING TECHNOLOGY

Clextral new Preconditioner + and twin screw

extruder EVOLUM+

by Clextral

World 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 twin-screw extruders with advanced control.

Process flexibility and improved efficiency

In twin-screw extrusion of fish-feed 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

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

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

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EXTRUSION

industrial applications, in particular because of the increased flexibility provided by the AFC. This variable speed device enables adjustments of the residence time as required to adapt the equipment to different types of recipes and to respond to the needs of multi-product extrusion lines. Moreover, this convenient design allows the system to start up when fully charged, even after prolonged downtime with a full tank, thanks to the new kinematic feature.

In terms of hygiene and food safety, the Preconditioner+ is designed with minimal retention areas to facilitate cleaning. This feature is further enhanced by an integrated ‘quick recipe change-over’ function through the reversible AFC system, used here as a conveying screw that enables the entire tank to be emptied. These improvements in equipment cleaning capabilities and hygienic design are important advantages for food processing applications.

Finally, the intensification of Clextral’s Preconditioner + offers improvement in the overall process, energy savings and enhanced quality of finished products, as well as greater flexibility and better control of operating parameters, whatever the recipe.

Clextral continues to innovate with twin-screw extrusion systems that produce aquatic feed with a precise balance of proteins, oils and carbohydrates, processed for optimum digestibility with reduced waste. Clextral’s systems process a wide selection of recipes and raw materials and accurately control pellet density for specific product attributes, such as sinking and floating properties. With these innovations in preconditioner and extruder technologies, Clextral is helping aquafeed processors meet the process challenges of today and the future.

ANDRITZ Feed & Biofuel A/SEurope, Asia, and South America: andritz-fb@andritz.comUSA and Canada: andritz-fb.us@andritz.com www.andritz.com

Your global technology process supplier for the aqua feed industry

ANDRITZ is one of the world’s leading suppliers of techno­logies, systems, and services relating to advanced indu­stri al equipment for the aqua feed industry. With an in-depth knowledge of each key pro-cess, we can supply a compa-tible and homogeneous solution from raw material intake to finis­hed feed bagging.

Improved response time and stability thanks to Advanced Thermal Control

(ATC) proprietary innovation.

New range of twin-screw extruders

A daily task of aquafeed processors is ensuring the perfectly stable quality of the finished product despite daily variation in the characteristics of the raw materials. Clextral’s new EVOLUM + twin-screw extruders offer advanced technology that gives processors new levels of throughput, flexibility, and control while ensuring maximum product quality and process stability.

A major innovation, the Advanced Thermal Control (ATC) is a self-learning, proprietary software solution to ensure absolute precision in temperature control. ATC continuously monitors production and adjusts to changes in parameters (characteristics of raw materials, recipes, throughput, etc.) to ensure process and product consistency. ATC is proven to enhance process stability up to 70 percent, with energy savings averaging 20 percent by eliminating excess heating/cooling to maintain process temperature set points in any circumstances.

The EVOLUM+ range has also been specifically built for more hygienic processing and food safety with ergonomic designs and open profiles that allow full machine access.

January-February 2015 | INTERNATIONAL AQUAFEED | 17

EXTRUSION

Extrusion is a cooking process that typically uses high temperature and high pressure for a short period of time. The first extruder was developed in the 1930s for pasta; extrusion was later modified for the production of pet food and fish feeds as well as human foods like snacks, breakfast cereals and sweets. The extru-sion process begins with preconditioning the meal using steam and water to form a hot, moist mash. The process has the flexibility to produce diets with a wide range of fat levels, densities, shapes and sizes. It also has the capability to produce floating, semi-sinking and sinking pellets for shrimp and pelagic fish. Extrusion has been used to manufacture shrimp feed since the early 1970s, but not widely adopted due to a persistent tendency for expansion in extruded feeds, which leads to undesirable flotation.

Expansion is exacerbated by the use of smaller die open-ings. To minimise flotation, feed manufacturers were forced to limit inclusion levels of starch, which tended to increase raw mate-rial costs. These constraints have been virtually eliminated through recent advances in extrusion technology, such as adjustments in screw design and speed, changes in die configuration and vacuum venting of the extruder barrel. It is now possible to produce 100 percent sinking extruded shrimp feeds with densities equivalent to those of pelleted feeds.

Extruded feed has the advantage of reducing raw material expenses, achieved by the substitution of high levels of wheat flour with lower levels of less expensive starch. This is possible due to the high moisture, temperature

and pressure within extruders, which lead to nearly complete gelatinisation of a wide range of starches. Extruded feeds utilise relatively high levels of moisture, which can be added in the form of flavors and palatability enhancers such as fish, dried solubles and flavorful enzymatic digests of seafood waste. This offers the potential to produce a new generation of highly palatable shrimp feeds without reliance on expensive marine protein such as

squid meal and krill meal. The rate of swelling of extruded feeds can also be manipulated to deliver feeds of varying ‘softness’. The swelling is a function of starch fragmentation, also known as dextrinisaton, which can be controlled by the degree of shear exerted by the extruder screw. The 1995 study Physiochemical properties of extruded pelleted shrimp feeds with various wheat flours conducted by GH Ryu and coauthors at Kansas state university in Kansas, USA showed an 89 percent correla-tion between the extent of starch gelatinisation and the water stability of 10 Asian shrimp feeds. Other studies on conventional single-pelleted feeds for terrestrial animals reported that only about 20 percent of the starch is gelatinised. This explains why typical poultry feed disintegrates in water within minutes of immersion.

In addition, pelleting systems for shrimp feed use advanced manufacturing techniques such as fine grinding of raw materials, multiple steam conditioners, higher moisture levels, pelleting dies with higher compression ratios, post-pelleted conditioning and drying. These techniques increase the starch gelatinisation levels of extruded shrimp feeds to 80 – 95 percent compared with conventional pelleted shrimp feeds.

In a 12-week study in 2000, Albert Tacon and co-workers at the Oceanic Institute in Hawaii, USA compared single feed formulation in pelleted or extruded forms and two different sizes; results reported in February 2003 showed higher shrimp survival and weight gain and greater feed efficiency from extruded feed. These results are being validated on a commercial scale in Korea, Malaysia and Brazil. Compensation for the vitamin losses thought to be slightly higher in extrusion than in pelleting can be easily accomplished by slight fortification of premixes.

Finally, recent developments in extrusion processing allow the production of sophisticated 100 percent sinking diets with lower cost and better performance than conventional pelleted feeds. Its advantages are expected to become more apparent, since the additional benefits of higher liquid addition, greater control of swelling and greater pasteurisation further contribute to higher performance.

Extruded feed for warm water finfish and shrimpby Prof Mohammed Y Al-Saiady

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