Granular feed has the advantages of uniform nutrient distribution, high digestibility, easy storage and automatic grading, and is increasingly used in the breeding industry. Granulation is an important part of the process of producing pellets. The quality of the pellets directly affects the quality of the feed. For feed manufacturers, how to reduce machine wear and power consumption, under the premise of reducing production costs, to ensure granulation quality, improve granulation production, has become a goal that feed enterprises are pursuing in the competition. In this paper, a comprehensive analysis of the factors affecting granulation is carried out, and the control methods are described.
1 Different feed ingredients have different chemical compositions and physical properties, which have different effects on granulation and thus have different granulation characteristics.
1.1 The effect of starch starch on granulation is limited by temperature and moisture. In the presence of certain moisture, the starch swells when heated above the gelatinization temperature, the inter-molecular bond breaks, and the starch molecules produce hydration to form α-starch. The higher the temperature, the higher the degree of gelatinization. The starch is easily granulated after gelatinization. Therefore, the feed having a high starch content has a high density of the feed and is easy to be granulated. However, feeds with high starch content tend to contain low protein, which is difficult to gelatinize under low temperature conditions, and is easy to make brittle pellet feed.
1.2 Protein proteins are thermoplastic and adhesive. In the granulation process, after the protein is heated by friction, it is subjected to high temperature and high pressure, and the tertiary and quaternary molecular structures of the protein are broken, and the plasticity of the feed is increased, which is favorable for granulation.
1.3 Fatty fat has a lubricating effect, which can reduce the frictional resistance when the material passes through the die hole, prolong the life of the die, reduce energy consumption and increase production. Its source is the feed itself and the two added from the outside. The fat contained in the raw material itself is infiltrated by the tissue during the granulation process, which is beneficial to granulation. When the high-energy feed is used, when the amount of oil added exceeds 3%, the particles are softened, the quality is lowered, the granulation rate is low, and the wear of the stamper is increased. Therefore, the amount of addition is generally 1 to 3%, and when it is necessary to add a large amount of fat, the excess may be achieved by a method of applying grease after granulation.
1.4 Cellulose cellulose has a certain polymerization force and has a certain bonding effect on the feed. However, when the amount is large, it is difficult to squeeze through the die hole and it is difficult to form particles. This is because a large force is required to push the high-fiber feed into the die hole, which not only shortens the life of the die but also affects the yield, but can Made of hard particles. It is generally considered that the raw material contains 3 to 7% of crude fiber, which can increase the hardness of the granules after granulation and reduce the pulverization rate. However, if the coarse fiber exceeds 10%, the hardness and granulation rate of the granules are lowered due to poor adhesion, and the dies are increased. Mechanical wear of the rolls.
2 Physical properties of feed 2.1 Particle size The size of raw materials can be divided into four types: coarse, medium, fine and ultrafine. It is generally believed that the smaller the particle size for granulation, the better, because: 1 the raw material has a small particle size, the surface area is large, which is favorable for the absorption of heat and moisture, and is easy to be gelatinized; 2 when the pulverized particle size is fine, the density of the granule after pressing is large. It can improve the yield and quality of feed. However, most studies have shown that the suppression of different diameters of pellet feed products should use the corresponding particle size. Generally, the pig feed passes through a 3~3.5mm round-hole sieve, and the chicken feed passes through a 4mm round-hole sieve. In general, the feed particle size distribution is basically uniform (does not contain large particles), and the particle size of the appropriate size group, the granular product has good appearance quality, and the yield can be increased by 10-15%.
2.2 Moisture content The moisture content of the feed before granulation is an extremely important parameter. The highest limit moisture content is 18%. If it exceeds 18%, it will cause blockage of the die hole, so it is generally suitable to control about 16%. The effect of moisture on granulation is closely related to the form of moisture. When the moisture content of the material exceeds a certain amount, the water will exist in the form of free state, and the proper amount of this form of moisture (usually called free water), Adhering to the surface of the material particles to form a water film can reduce the frictional resistance through the die hole and prolong the service life of the die. In addition, it can hydrate the natural binder and help improve the quality of the granulation. However, the free moisture content should not be greater than 6%, otherwise the granulation will become too soft, and the pressure roller will easily "slip", which is difficult to pass through the die hole, but will reduce the yield and quality.
2.3 Materials with different bulk density have different bulk density, materials with small bulk density, high cellulose content, generally not conducive to granulation, small output, and high energy consumption. The material with large capacity can absorb water better, the effect of quenching and tempering is better, it is beneficial to granulation, and the quality of finished product is good.
2.4 The presence of various hard impurities and ropes, such as impurities and sand, will not only affect the quality of the finished feed, but also reduce the feeding effect, and will seriously wear or block the mold roll and reduce the efficiency of feed granulation. In the production process, the raw materials are required to pass through the primary screening and de-ironing devices before entering the granulator.
3 Feed formula composition Different feed types have different requirements for granulation conditions. When producing pellet feed, the granulation conditions should be determined according to the formula composition.
3.1 High protein feed The feed with high protein content will exhibit good thermoplasticity and adhesion when heated, which can increase the hardness of the particles and increase the yield. However, it does not require a large amount of water like high-starch feed, and excessive moisture tends to clog the pores due to gelation. The less the water, the better the cooling and dehydration. Generally, the amount of water added is 1-2%, and it is supplied by steam. Therefore, the steam should meet the conditions of water and temperature.
3.2 Heat-sensitive feeds Most of the feed composition contains more milk powder, sugar, glucose and lactose, which will be coked when the temperature reaches 60 °C. When using a thick die without water, only the friction heat can reach the above temperature and coke. Therefore, the following methods must be considered: 1 select a thin die; 2 reduce the speed of the die; 3 use high pressure steam, and ensure the temperature of the material Controlled below 60 °C.
3.3 Low-protein and high-fiber feeds These feeds with a protein content of 12-16% and rich in cellulose, in which the proportion of cereal raw materials is small and the protein content is low. Therefore, such feeds are difficult to exhibit gelatinization and viscosity by thermal action alone, and with high cellulose content, their water holding capacity is not good, so the moisture content should not be too much. Generally speaking, such feeds are controlled, the moisture content is controlled at 12-13%, and the feed temperature is maintained at about 55-60 °C. Such conditions are suitable. If the moisture content is too high or the material temperature is too high, cracks may occur due to rapid expansion after pressing and discharging.
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3.4 When the urea content in the urea feedstuff is above 6%, almost no steam can be added, and the urea is easily dissolved in water and is in a thin paste. If the water content of urea reaches 20~30%, this becomes a problem of granulation. In addition, urea is easily decomposed by heat, so the granulation process cannot be overheated. When the moisture and heat are too high, the particles are difficult to pass through the die hole, and even if passed, the coagulation occurs during the cooling process.
3.5 High-starch feed High-starch feed (feed with high grain content), the most difficult problem is the need for high temperature and high moisture. The common problem of high starch feed in granulation is to produce soft granules, and the yield is high. However, if the yield is too high, the fine powder will increase, the quality will decrease, and the return flow will increase. The result is not economical. Starch feed has a low protein content and thus has a low binder effect. Cellulose is almost independent of granulation. Although oil can increase particle yield, it does not function as a binder. The granulation must have a water content of 16 to 17% and a temperature of at least 82 ° C, so that the starch can be gelatinized and dextrinized, and the binder acts as a binder after the particles are cooled. In this way, hard starch can be produced by adding water, increasing steam temperature or using a thick stamper, etc., but it may cause damage to some trace additives and chemicals or mold due to insufficient dehydration. The granulation of high starch feed requires a relatively high level of technology.
3.6 High-fat diet oil can increase the yield of granulation and prolong the life of the stamper. However, when the content is too high, the granules will be softened, which will shorten the life of the stamper. If a liquid vegetable oil is used, the particles become softer, and the unsaturated fatty acid is apt to oxidize, resulting in a decrease in nutritional value.
4 Steam addition steam addition is a difficult factor to control during granulation and is the most important factor in determining granulation cost, production and product quality. The essence of steam addition is that the material is subjected to the moist heat and quenching effect of steam, and the effect is as follows: one is to increase the output; the other is to extend the service life of the die roll; the third is to save power and reduce the production cost; the fourth is to improve product quality and nutrition. value. As for the steam used, the following points should be noted: First, the steam supply must be sufficient. Generally speaking, the required steam quantity (including the steam used for molasses heating) can be determined according to 5% of the output; the second is to maintain stable steam. Pressure, the working pressure of the boiler should be maintained at 0.5~0.7MPa, the steam pressure before input to the granulator should be adjusted to 0.2~0.4MPa; the third is to avoid the use of wet steam, but use dry saturated steam.
5 Material quenching and tempering time conditioner is a key component of granulator. The quality of quenching and tempering is good, except for factors such as material itself and steam. Quenching and tempering time is also an important influencing factor. Ideal quenching and tempering time It is the filling factor of the material in the conditioner is less than 0.5. The general granulator is limited in size, it is impossible to make the diameter and length of the conditioner too large in order to prolong the quenching and tempering time, but the material can be appropriately lengthened or shortened by adjusting the angle of the paddles in the tempering device. The residence time in the massifier to ensure the best quality of the granulation process.
6 Die and press rolls 6.1 Press molds are closely related to the quality of the pellets. Generally, the thicker the stamper, the harder the pellet, but the lower the yield; conversely, the thinner the stamper, the softer the pellet, but the higher the yield. In addition, the smaller the die diameter, the greater the hardness, but the lower the yield; conversely, the larger the die diameter, the softer the particles, but the higher the yield. The quality and yield of the granulation are also related to the pore shape of the stamper, but in order to facilitate the manufacture of the stamper, a cylindrical die type stamper is currently used. In summary, the stamper should be selected based on feed formulation, product requirements and feeding objects, taking into account yield and quality.
6.2 Pressure roller The two main conditions are to withstand the pressure generated during the granulation process and the appropriate pressure roller surface to provide maximum traction to avoid slippage. The die roll gap is one of the important factors affecting the granulation effect. When the gap is increased, the material layer is thickened, the extrusion work is increased, and the power consumption is also increased, resulting in a decrease in the press-in force of the material in the crush zone. The roller slips, thereby reducing the yield; conversely, if the gap is too small, the die roll wear is accelerated, and the amount of material caught is reduced, thereby reducing the yield.
7 The feed flow rate should be adjusted according to the characteristics of the granulation raw materials and the requirements of the finished granules, and kept stable to ensure the normal operation of the granulator and the yield and quality of the granulated products.
In short, there are many factors affecting feed granulation. This article only describes the seven main factors of feed composition, feed physical properties, feed formulation, steam addition, preparation time, mold roll condition and feed flow. Considering various factors together, formulating process parameters suitable for specific conditions can improve the particle efficiency of the granulation mechanism and ensure the quality of the granules, so as to obtain a good granulation effect.
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