With the rapid development of aquaculture, traditional farming methods are far from meeting people's needs. The requirements for aquafeeds are not only balanced nutrition, good stability of feed in water, but also the environment in which animals live. - The quality of the water body puts more stringent requirements. The production process of aquatic extruded feed is quite different from the traditional production process of livestock and poultry feed. According to the variety of aquatic feed, large changes in raw materials, high fineness of crushing and poor fluidity of materials, the production process is generally adopted. The secondary pulverization and the secondary compounding are mixed, and then the processing of the aquatic expanded feed is completed by puffing, drying, external spraying, cooling, crushing and screening.
1 Raw material cleaning and a coarse crushing
The raw materials used in the feed mill generally come in two forms: one is a powder and they do not need to be coarsely pulverized. This kind of raw material can be directly passed through the pit and hoist, then enter the cone cleaning screen to remove impurities, and then magnetically selected, directly into the batching bin through the distributor or the screw auger to participate in the first batching; the other is A coarsely pulverized material, pellets, is required. After the material is removed into the cleaning equipment through the blanking pit and the hoisting machine, it is removed into the warehouse to be pulverized, and then coarsely pulverized by the pulverizer, and then enters the batching bin through the hoist and the distributor to participate in the first batching. . For individual raw materials, such as shrimp shells, it can be directly sieved into the warehouse to be pulverized without primary screening. A coarse pulverization is a pre-treatment process for superfine pulverization in aquafeed processing. Its main purpose is to reduce the particle size difference and variation range of the material, improve the working condition of the ultrafine pulverizer, and improve the working efficiency and guarantee of the ultrafine pulverizer. At the same time, in order to improve the working environment of workers and reduce cross-contamination, it is recommended to use an independent dust-removing wind network, that is, the feeding port adopts an independent dust-removing system.
2 The first batching and mixing
The first batching is mainly the preparation of the bulk material, that is, the formulation of the larger material in the formula. This process is mainly done by electronic batching scales. However, special attention should be paid to the arching of the batching bin during the first batching process. This is mainly due to the fact that the raw materials of the aquatic feed, especially the high-quality aquatic feed ingredients, are light in weight and poor in fluidity of the materials. Therefore, the anti-cagging measures should be taken for the batching bin, such as eccentric discharge and vibration motor. For the first mixing, a single-shaft horizontal ribbon mixer can be used, and the grease addition system must be considered on the mixer. The first batching and mixing is also the pre-treatment process of ultra-fine pulverization. It is mainly to reduce the variation range of material particle size, improve the working condition of the pulverizer and improve the working efficiency of the pulverizer to ensure the quality of the product.
3 secondary pulverization and secondary ingredients mixing
Due to the low food intake, short digestive tract and poor digestion ability of aquatic animals, the aquaculture feed requires fine particle size to increase the surface area of ​​the feed, increase the contact area of ​​the digestive juice and feed of aquatic animals, and improve the feed of aquatic animals. Digestibility and feed remuneration; also due to the low intake of aquatic animals, the uniformity of feed mixing can be reflected in a smaller range, which also requires a finer grain size. If the shrimp material is to pass through the 40 mesh sieve, the 60 mesh sieve should be less than 5%, so the micro-grinding process must be used. In the secondary pulverization process, the once mixed material is lifted by the hoist and then enters the pulverized warehouse, and then enters the micro pulverizer. The micro-grinder now uses a vertical-axis micro-grinder in the processing of aquatic feed, and is equipped with powerful air-selection equipment, and then enters the rotary grading screen for screening. The purpose of configuring the rotary grading screen here is mainly to remove the fine fluff formed by the coarse fibers in the feed during the pulverization process, because the presence of these fine fluff easily adheres around the die hole of the puffing machine until the die hole is blocked, resulting in The machine is cleaned up, so it must be removed.
The cleared material is subjected to secondary compounding and mixing. Since the fineness of the material entering the secondary batch mixing chamber is above 60 mesh and the density is small, special attention should be paid to the arching phenomenon. In order to eliminate this phenomenon, on the one hand, eccentricity can be used to expand the hopper. On the other hand, all the ultra-finely pulverized material discharge machines adopt the impeller feeder, which not only has a broken arch mechanism, but also can flexibly adjust the flow rate. the size of. After the various ingredients are sub-batched, they enter the secondary mixer. There is a manual feeding port on the top of the secondary mixer, which is mainly used for the addition of trace additives, and a liquid adding mechanism is provided on the mixer for the addition of oil and fat; one is for the addition of water. In the secondary mixing process, various materials must be thoroughly mixed, and the coefficient of variation CV is less than 7%, which is the key to ensure product quality. Therefore, the mixer must use a model with excellent performance, such as a double-shaft horizontal blade mixing. The machine has high mixing uniformity, high output and fast mixing speed. After the secondary pulverization and secondary compounding, the material enters the subsequent process---expansion granulation process.
4 puffing granulation process
In the extrusion process, the material actually undergoes a cooking process under high temperature, high humidity and high pressure conditions. In this process, the physical and chemical properties of the material change strongly, and at the moment when the material is extruded from the die hole, the pressure in the feed is immediately converted from the liquid to the gaseous state from the feed, as the pressure suddenly drops from the high pressure to about 100 kPa. Thereby the material is puffed to form a so-called puffed feed. Because this kind of feed not only has the advantages of general hard pellet feed - good palatability, avoiding automatic grading of products, facilitating transportation, helping digestion, reducing waste during feeding, etc., but also has unique advantages: in feed The starch has a high degree of gelatinization, the protein is more digestible, and the utilization rate of the animal is improved; the floating property is excellent, the fish feeding condition can be easily observed, and the water pollution can be controlled to the maximum extent. These are also the main reasons why expanded feeds are widely used.
After the material is extruded by a puffing machine, it forms wet and soft particles (water content is 25%~30%). At this time, it is better to use pneumatic conveying instead of lifting machine. Because the lifting machine is easy to cause the particle to break and improve the powdering rate; the pneumatic conveying method can not only form a layer of colloidal coating quickly on the surface of the particle, reduce the particle breakage, but also can shape the particle. . Due to its high moisture content, the material transported by pneumatic force must be dried in a dryer to reduce the moisture content of the material to about 13%. There are many kinds of dryers. I believe that when the diameter of the particles is less than 4mm, a vibrating fluidized bed dryer can be used. When the diameter of the particles is larger than 4mm, a belt dryer can be used, or horizontal float drying can be used directly. machine. Because the dryer allows the material to be semi-suspended throughout the screen surface, both the drying effect and the damage to the particles can be minimized. After the material has been dried, it enters the external spray system. The external spraying of the particles is mainly to meet the energy requirements of the fish and to reduce the loss of heat sensitive substances during processing. The nutrients that are not suitable for addition in the previous process can be supplemented by spraying, and the palatability of the feed can be improved and the powder content can be lowered. The optimum operating temperature for this process is around 80 °C. After the material passes through the external spray system, it can enter the counterflow cooler for cooling.
5 Finished product processing and packaging
The cooled material is lifted by a hoist and then crushed into a flat rotary screen for classification. The grading sieve is generally a two-layer sieve, and the lower sieve sieve is a finished product, which can directly enter the finished product warehouse, and then weigh and pack. The upper sieve screen needs to be returned to the crusher for crushing. The undersize sieve is generally a finely pulverized material which can be returned to the batching bin as waste. The above-mentioned production process is a conventional configuration of the current aquatic product expansion feed processing technology, and the process can produce dry feed, slow feed and floating feed. Although the expanded feed processing technology has been recognized by many manufacturers as a new type of processing technology, its investment has not been widely used because it is much larger than the processing technology of hard pellet feed. Nevertheless, the expansion process is the future development of the feed processing industry, especially in the application of aquatic animal feed and pet feed, will replace the traditional hard pellet feed processing technology.
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