Extruder & Expander to Process Aquatic Feed
by Wala Li Marketing & SalesExtruder & Expander to Process Aquatic Feed
The aquafeed manufacturing industry is widely recognised as one of the
fastest expanding agricultural industries in the world and it is the
wide application of aquatic feed extruder
& expander that contributes a great share for the huge step
forward. Extrusion technology is the most efficient way of turning
various fishmeal, fish oil, soyabean meal, cereals, some slaughterhouse
by-products into palatable feed for aquacultural organisms.
Extruder & Expander basic structure and classifications
From an engineering point of view, an extruder is simply a pump
providing the necessary pressure so as to force the process feed mash
through a restrictive die. It is a high-temperature short-time
bio-reactor that transforms a variety of raw ingredients into feed pellets.
Extrusion equipment is mainly composed of power transmission device,
feeding device, pre-conditioner extruder barrel and discharging cutting
device, etc. The barrel of the extruder is comprised of barrel heads,
screws, flow restrictors (called shearlocks) and a die.
1.1 Wet extruder & Dry extruder
According to whether there is pre-conditioning of feed ingredients with
steam or moisture before entering the extruder barrel, extrusion devices
falls into two categories: dry extruder and wet extruder. During dry
extursion process, all the heat produced is generated by the friction
and mechanical energy. It’s suitable for processing low moisture and
high fat feed material like full-fat soybean expansion. While wet
cooking extruder is a piece of more complex equipment with precision
metering systems for steam or water injection into either the
conditioner and/or the extruder barrel. Preconditioning is a very
important step in wet extrusion process for chemical or physical
reactions to take place.
1.2 Single screw extruder VS Twin screw extruder
Generally in accordance with the number of screw in extruder barrel,
extrusion device is divided into single screw extruder and twin screw
extruder. In contrast to twin screw extruder, recently widespread used
single screw extruder possesses the advantages of less investment and
simple operation. Currently, single-screw extruders produce over 90% of
expanded pet foods, which represent the greatest volume of extruded
products on the market. It has simple structure and constant spindle
speed generally by belt drive. The barrel of a single screw extruder can
be divided into three separate zones:feeding zone,melting zone and
molding zone. In the feeding zone, feed mash is simply received from the
conditioner and transported forward in the barrel, go through solid
conveying and melting process, making feedstocks from a powder to an
elastic dough. Then it will be formed into pellets by flat plate
shaping.
Twin-screw extruder has more priority in quality control and processing
flexibility, which can deal with sticky, multiple oil or very wet raw
material. It develops on the basis of single screw extrusion machine and
has been installed double screw side by side in the barrel. Fully
meshed co-rotating (both screws turn same direction) extruder greatly
improved material conveying, pumping and mixing characteristics. Ideal
twin screw extruder has a much wider operating range in terms of use of
moisture, internal fat, mechanical energy input and product size.
1.3 The advantages of extruder & expander in aquafeed production
☞Wide adaptability: the capability of an extruder enhances the feed
manufacturer’s flexibility to produce fish feed pellets for shrimp,
crab, eel, catfish, carp, frogs, etc. as well as process full-fat
soybean, dogs and cats feed, pet food, ornamental animal feed and
others.
☞High starch gelatinization: feed material goes through the processing
of HTST, starch gelatinization degree increase can reach 80-99% for
Aquatic animals easily digest.
☞Improved water stability: aquatic feed water stability is an important
indicator. Our extruded aquatic feed pellets can soak in the water for
more than 12 hours without decomposition for fish bite.
☞Convenient for density control: it is entirely feasible for an extruder
to produce floating feed, sinking feed and slow sinking feed by density
control; that is more conducive to different fish species.
☞Fine mechanical properties: puffed fodder has good mechanical
performance and less dust, unbreakable. It can reduce feed waste, water
and air pollution.
☞Good to aquatic organism health: extrusion cooking provides hygienic
feed processing and destroys the pathogens & other most viruses to
avoid animal illness.
2. Extrusion technology overview
Extrusion cooking is a process involving feed ingredients plasticizing
and cooking in the extruder barrel by the combination force of
pressure, heat and friction. Feed materials actually go through the
cooking process under the condition of high temperature, high humidity
and high pressure; thus their physical and chemical properties are
changed. When feed material is squeezed out from the die hole, moisture
in the feed immediately changes from liquid into gas form owing to
pressure sharply drop to 100 kpa, so that the particle is expanded and
forms the so-called puffed feed. Extrusion technology is the ideal
choice to process aqua feed because of the benefits it offers to fish
farmers. Extruded feed has also become much popularity due to its
advantages such as high starch gelatinization degree, easily digestible
proteins, high feed utilization rate and good floatability,etc.
2.1 Characteristics analysis on floating feed pellets & sinking feed pellets
Commercial fish diets are manufactured in either floating form or
sinking form. Floating,sinking, and slow sinking aquatic feed can be
produced by adjusting feed formulation and related parameters of
expander.
--Floating feed pellets can float on the surface of the water for a long
time; its feeding method is conducive to raising management, saving
labor and reducing water pollution; especially make it convenient to
observe fish ingestion condition and adjust feeding amount. Generally,
fish farming adopting puffed feed can save 5%-10% aquatic feed compare
to mash and pressure-pelleted feed.
--Puffed sinking pellets absorb water and become soft easily. It is
endowed with the properties of high ripening degree and water stability;
thus is suitable to crabs and other benthic animals; Twin-screw wet
extruder is ideal for sinking aquatic feed production. Pellets expanding
degree is closely related to modulation conditions, operation process
and feedstocks moisture content.
For fish farmers, how to choose the suitable fish pellets is crucial. In fact, the options of loating or sinking pellets mainly depends on fish species that you raise. If you have bottom feeders like shrimp pleco and catfish, it would make perfect sense to give them sinking pellets. While,catfish, carp, tilapia top as well as middle dwelling fish like floating feed. Besides, salmon, trout, sea bass/sea bream, and cod like to eat the slow-sinking feed pellets.
Conclusion: Extrusion technology has more technical and economical advantages in the production of pelleted feed owing to its flexibility and reliability production. In general, single screw extruders provide adequate operating ranges and are more economical to operate; Whereas twin screw extruder with high good material adaptability enables fish farmers to adopt wider ranges of ingredients. Pre-conditioning in wet cooking extrusion can enhance pellet quality greatly. There is no doubt that extruder & expander has a broad prospect in the aquaculture feed industry development and will result in usage of new extrusion technology.
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Created on Dec 31st 1969 18:00. Viewed 0 times.