The flourishing development of aquaculture owes much to the scientific and precise processes employed in aquatic feed processing factories. These factories not only ensure aquatic animals receive balanced nutrition but also drive the sustainable development of the entire aquaculture industry. The aquatic feed processing technology involves a complete sequence of processes from the arrival of raw materials to the production of the final product. This process includes various steps such as material reception, cleaning, crushing, batching, mixing, conditioning, shaping (pelleting, extrusion expansion, pelleting, block pressing, etc.), drying, cooling, and packaging. The processing technology is primarily based on effectively combining different processing steps according to the requirements of different products.
| 1. Material Reception and Inspection |
|---|
| 2. Material Storage and Distribution System |
| 3. Formulation Design and Metering |
| 4. Crushing and Mixing |
| 5. Drying and Cooling |
| 6. Forming and Packaging |
1.Material Reception and Inspection
The production of aquatic feed begins with the reception of raw materials. Various materials such as fish meal, soy protein, corn, etc., undergo strict inspection to ensure their quality meets production requirements. This precise operation in the initial stage lays a solid foundation for subsequent processing.
2.Material Storage and Distribution System
Through advanced material storage systems, factories can effectively manage and store raw materials, ensuring freshness and stability. Meanwhile, an automated distribution system accurately transports various materials to the processing line based on production plans, enhancing production efficiency.
The silo is an essential device for ensuring continuous feed production, increasing automation, and balancing the production process. According to its purpose, silos can be divided into raw material silos, intermediate silos, and finished product silos. Raw material silos include room-style warehouses for storing packaged materials and cylindrical warehouses for storing bulk materials. Cylindrical warehouses have the advantages of a small footprint, low labor intensity, and ease of automation. Intermediate silos are used to temporarily store intermediate products during the feed production process, ensuring a balanced material flow during processing. Intermediate silos mainly include waiting for crushing silos, batching silos, waiting for granulation silos, waiting for expansion silos, and other buffer silos. Finished product silos are used to store packaged finished products and bulk finished products.
3.Formulation Design and Metering
Based on the scientific design of formulations, the third step in aquatic feed processing is accurate metering. This step not only requires precise control of the proportions of various raw materials but also considers the nutritional needs of different growth stages and species of aquatic animals, ensuring that the feed provides nutrients without wasting any components.
The feed batching metering system mainly consists of batching bins, feeders, batching scales, and control systems, with batching scales being the core. There are various types of batching scales, with electronic batching scales being the most commonly used. In the batching process, materials are weighed by weighing sensors. The automated batching system mainly consists of a multifunctional electronic scale, a controller, a feeder, pneumatic valves, etc. When the electronic batching scale is working, it weighs the materials by type (or bin) one by one according to each batch (or scale). The values are accumulated to obtain the cumulative weighing results. The total weight of the batch is obtained.
4.Crushing and Mixing
After the measurement of raw materials is completed, the feed enters the crushing and mixing stage. Efficient crushing equipment ensures that the raw materials reach the ideal particle size, while advanced mixing techniques ensure even mixing of various components. The success of this step relies on scientific processes and modern equipment.
The structure of the hammer mill mainly includes the feeding device, rotor, screen, and body. Raw materials fall into the crushing chamber from the top of the mill due to gravity. In the crushing zone, the raw materials come into contact with the top of the hammers. Due to the significant speed difference between the two, the hammers strike the materials rapidly, causing the raw materials to break.
Hammer mill
For ultrafine grinding, a vertical shaft ultrafine grinder is used, with a faster rotation speed than the hammer mill. After preliminary cleaning and magnetic separation, the material enters the grinding chamber for grinding. Due to the high-speed rotation of the grinding disc, under the action of centrifugal force, the material is crushed by the impact of the hammers on the grinding disc, and then it is rapidly thrown to the surrounding toothed ring at a very high speed. The airflow between the hammers and the toothed ring undergoes an instantaneous change due to the variation in the tooth surface. The material undergoes sudden stress in this gap and is further crushed under repeated action. The crushed material is carried from under the grinding disc to the airflow between the inner wall and the deflector, then enters the grading chamber. Through the rotating grading wheel, a balance of air power and centrifugal force separates the coarse material, which returns to the grinding chamber for regrinding, and the fine material is sucked into the grading impeller, entering the discharge port and the collecting system.
5.Drying and Cooling
The mixed feed enters the drying system, where temperature and humidity are controlled to reduce the moisture content to an appropriate level, enhancing the feed's shelf life. Subsequently, the feed enters the cooling equipment to ensure its temperature is suitable for ideal conditions in packaging and storage.
For extruded feeds, the moisture content is typically between 22% and 28%, and the temperature ranges from 80°C to 135°C. Such high-moisture products are usually soft and inconvenient for storage and transportation. To lower the moisture content, the feed undergoes drying in a drying machine. After drying, the temperature remains relatively high. Therefore, it must be cooled. If packaging or storing products without cooling, the residual moisture in the product will migrate to the coldest part of the packaging, increasing the moisture content at that location and causing product deterioration.
The feed enters the top inlet of the counterflow cooler and is uniformly piled up in the cooler through the discharger. While the pelletized material stays in the machine for a certain period, a fan draws air from the top, and cool air enters from the bottom of the cooler. The cool air flows vertically through the material layer, carrying away the heat and moisture released by the pellets, cooling them to achieve temperature and moisture reduction goals.
Currently, continuous conveyor dryers are commonly used for drying materials, such as a circulating box dryer. The heat source used can be a boiler or natural gas heating. The granular material to be dried is evenly spread over the entire width of the perforated plate. Several movable perforated plates are connected to form a rotatable drying bed. The granular material is spread on the drying bed and is conveyed from one end of the dryer to the other by the screen plate. The drying bed has 2-4 layers, with more layers resulting in longer running paths for the material throughout the entire drying process. Specific drying temperatures, humidity, and airflow are applied to each drying section. The drying hot air temperature is 90-180 degrees, and it passes through the material layer at a speed of 50-60 m/min. The hot air transfers heat to the material, taking away the evaporated moisture.
6.Forming and Packaging
To facilitate storage and use, feed undergoes shaping into various particle shapes in this step. Advanced forming equipment can produce pellets of different specifications according to market demand, meeting the requirements of different farms. Finally, an automated packaging system packages the feed into various specifications to ensure its quality during transportation and storage.
The process of forcing powdered feedstock or powdered feed through a die hole by water, heat conditioning, and mechanical compression to aggregate and form is defined as pelleting. The material is conveyed to the conditioner, typically with a conditioning time of tens of seconds to a few minutes and a temperature around 90-105°C. After conditioning, the material enters the pelletizer, where the pressing mechanism is the core. The pressing mechanism mainly includes the ring die, rollers, uniform feeding plate, and adjusting mechanism. The motor drives the ring die, and the ring die drives the material. The material, driven by friction, rotates the rollers. Under the squeezing of the rollers and the ring die, the material passes through the die hole in a strip shape and is cut into cylindrical shapes of suitable length by a cutting knife. The position of the cutting knife can be adjusted to obtain feed particles of different lengths.
