Analysis and solution to the factors affecting the processing quality of pellets
1 Identification of the quality of pellet feed processing The quality of pellet processing is mainly reflected in the following aspects:
1 Stability of the particles. It mainly refers to the characteristics of the original geometry of the pellets during cooling, classification, transportation and storage.
2 The appearance quality of the particles. Mainly refers to whether the surface of the particles is smooth, whether the color and length of the particles are consistent.
3 hardness of the particles. Feeding different animals requires different hardness requirements for the pellets. For example, the hardness of pig feed is lower, and the hardness of duck and fish feed is higher.
4 degree of aging of the particles. The high degree of ripening of the particles is beneficial to the digestion and absorption of the animals, and is often judged by detecting the degree of gelatinization of the starch.
5 particles of moisture. Reasonable moisture is beneficial to improve the palatability of the feed and the economic benefits of the enterprise; and lower moisture is a necessary condition for safe storage of the feed.
2 Factors affecting the quality of pellet processing According to the research of Dr. Xiong Yiqiang, the feed technology consultant of the American Soybean Association, the formula accounts for 40%, the crushing particle size accounts for 20%, the quenching and tempering effect accounts for 20%, and the granulation process control accounts for 20%. 15%, cooling conditions accounted for 5%. The empirical data we have obtained in production practice basically conforms to this view.
2.1 Formulation is an important factor in ensuring the quality of the pellets. Among them, the influence of moisture, starch, protein and crude fat fiber on the quality of the particles is particularly obvious.
2.1.1 After mixing the water raw materials, the ideal moisture content of the sample is 12% to 14% in summer and 10% to 12% in winter. After absorbing the steam from the quenching and tempering raw materials, the water reaches 15% to 17%. Generally, the steam material with a 1% by weight of the raw material added is raised by 13 to 15 °C. The author uses the “counter-flow cooler†under the climatic conditions in Sichuan. If the steam saturation is high, the grain moisture will be reduced by 0.5% to 1.5% in the summer after granulation cooling. If the conditioner and cooler are not used in winter. The moisture retention will increase by 0.5% to 1.5%. As long as the saturation of the steam is sufficient, no matter whether it is added in winter or in summer, the steam is tempered and the moisture of the finished product is lower than that of the low temperature. Therefore, to control the moisture of the finished product, it is necessary to control the moisture content Excessive moisture in the raw materials can also cause blockage of the ring mold during the granulation process, resulting in a sheet-like casserole mixed into the finished product, and even the production cannot be continuously carried out. If the moisture content of the raw material is too low, the finished product pellets tend to be dry and the powdering rate will increase. At the same time, in order to improve the economic benefits of the enterprise and the palatability of the animal, the water can be artificially added in a conditional manner, which is specified in the “tempering effectâ€. Clarified.
2.1.2 The surface of starch raw starch is rough, the granulation resistance is large, and the bonding performance is poor. However, the starch will be partially gelatinized by steam quenching and tempering. The gelatinized starch has good bonding properties and good particle quality. Therefore, in order to meet the requirements of the process rather than the requirements of nutritional indicators, a certain amount of starch raw materials are also added to the formulation. This is especially important in the formulation of aquaculture materials. For example, in the formulation of juvenile fish, the digestibility of starch in juvenile fish is very low from the nutritional point of view, but it must be added in order to maintain the stability of juvenile fish in water. A certain amount of starch, or other binder. The starch has different bonding properties after gelatinization of different raw materials. For example, barley and wheat have better bonding properties than corn, and drying corn is not as good as naturally drying corn.
2.1.3 When the protein content in the protein formula is appropriate, it is easy to granulate, and the quality of the granules is also good, because the protein is denatured after heating, the viscosity is increased, and the granulator has improved yield and good quality. When the protein content is too high, the ability to absorb steam is seriously degraded, the temperature of quenching and tempering is lowered, and the effect of granulation is lowered.
2.1.4 Fat: The right amount of fat can reduce the frictional resistance of the material and the ring mold, thereby reducing the ring mold wear; it can also increase the output, reduce the energy consumption, and smooth the surface of the particles. However, if the temperature is too high, the quality of the particles will decrease and the viscosity will be particularly brittle. If the formula requires more than 5% fat, a post-spray process can be used.
2.1.5 Crude fiber: The crude fiber content should not exceed 10% to 15%. Because of its poor adhesion, the binding force between the feed particles is reduced; at the same time, it affects the ability of the feed to absorb steam, so that the hardness of the feed is increased, the molding rate and the yield are reduced, and the wear of the equipment and the vibration of the equipment are seriously increased. .
2.2 Crushing of raw materials Particle size is an important part of the quality and production efficiency. The pulverization fineness determines the surface area of ​​the feed component. The particle size is fine, the surface area is large, the moisture absorbing steam is uniform and rapid, and the degree of starch gelatinization in the raw material is high. The finer the pulverization degree, the more uniform the quality of the granules produced, and the smaller the wear of the ring die and the press rolls. On the contrary, the pulverization of the raw material having a coarse particle size causes the granules to be broken and broken due to the large particles, resulting in an increase in the powder.
2.2.1 Quenching and tempering effect Quenching and tempering is an important link before granulation. Good tempering effect can greatly improve production, reduce granulator vibration, reduce energy consumption and improve particle quality. The quality of the quenching and tempering effect can be reflected by three indicators. First, the temperature of the raw materials after quenching and tempering: generally, the pig material is not lower than 80 ° C; the aquatic material is not lower than 90 ° C; the poultry material is not lower than 65 ° C. According to Dr. Xiong Yiqiang's research: the higher the temperature regulation, the higher the temperature is, the better the quality of the particles is guaranteed, and the nutrients are destroyed as little as possible. The second is moisture: usually with the feed after conditioning, the water can reach 15% to 17%. The absorption capacity of different materials for water is not the same; if the material has poor absorption capacity for water, adding too much steam will become a blocking machine after being converted into free water. Third, time: The material needs to stay in the quenching and tempering room for 30~40s.
There are three factors that affect the effect of quenching and tempering: 1 the characteristics of the material itself; 2 the quality of the steam; 3 the performance and parameter adjustment of the quenching and tempering equipment.
2.3 Ring mold and granulator factors The influence of ring mold on the quality of pellet feed is mainly the compression ratio of the ring mold, the pore diameter, the roughness of the pore wall, the diameter and depth of the pressure relief hole, and the maintenance and use conditions. Different varieties of feed have different compression ratios and die hole diameter requirements. To suppress different types of feed, it is necessary to select the corresponding compression ratio and pore size to obtain the feed pellets of the required quality. The maintenance and use of the ring mold will also affect the quality of the pellet feed. If the following conditions occur, the pellet feed quality will be significantly reduced: uneven wear of the working surface of the ring die, excessive honeycomb holes, effective thickness reduction and inner surface of the die hole. Spots or nicks appear.
The main factor of the granulator is the speed. The linear speed of the ring die on the granulator is generally 4-8 m/s (the linear velocity is measured on the outer diameter), and the granulator which can provide two kinds of die speed can obtain the good effect when producing a wide variety of feed. In general, the higher the rotational speed of the granulator, the worse the quality of the feed pellets.
2.4 Cooling factors The temperature of the pellets leaving the ring mold is 70 ° C ~ 100 ° C, the water content is 15% ~ 18%, in order to safely store and transport, to ensure the durability of the particles, reduce the breakage of particles, the temperature of the pellets should be reduced to no Above 5 ° C above room temperature, Zui is well controlled within 3 ° C. The water is reduced to 10% to 12.5%, which is done by a cooler. Generally, when the air temperature rises by about 11 °C, the water holding capacity can be doubled, so when the moisture content of the semi-finished product is high, the moisture of the finished product can be adjusted by increasing the temperature of the air entering the cooler. Currently used in a wide range of applications with ring die granulators is a counterflow chiller. This chiller is highly automated and has a smooth, non-cracked, smooth appearance.
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