The moisture content of pellet feed is a very important quality index, which directly affects the quality of pellet feed and the economic benefits of feed enterprises. Effective control of it is one of the key technologies to ensure the quality and safety of feed products.
The moisture content of pellet feed is a very important quality index, which directly affects the quality of pellet feed and the economic benefits of feed enterprises. Effective control of it is one of the key technologies to ensure the quality and safety of feed products. If the moisture content exceeds the specified standard, the pellet feed is prone to mildew and deterioration, which is not conducive to preservation, and will also reduce the content of nutrients. The moisture content also causes unstable product quality and affects the brand reputation of the product. In the process of feed processing, appropriate moisture content is beneficial to pelleting, reducing energy consumption and improving production. Therefore, in the production process of compound feed, in order to make the production run more smoothly, the energy consumption is lower, the particles are smoother and more uniform, and the final product meets the specified moisture content standard, it is necessary to carry out moisture control throughout the production process.
Moisture control is to comprehensively control various factors according to different situations in the whole process of production, so that the final moisture content of the product can reach the expected target of the producer. The main factors that affect the final moisture content of feed products are: the moisture content of the feed material itself, the moisture change in the crushing stage, the liquid addition amount in the mixing stage, the moisture content of the steam, the level of conditioning, the size of the die hole and its thickness of the die, The air volume and drying time of the cooler, the packaging quality management, the influence of different climatic and environmental factors, etc.
1. Moisture control of feed ingredients
1. The key to moisture control in the raw material receiving process is to accurately detect the moisture content in the raw material sample
Sampling must represent the overall situation of the whole batch of raw materials. Samples should be taken according to the sampling standard to prevent leakage of sampling. In order to reduce the error, two to three parallel samples can be tested, and the average value can be obtained as the test value.
2. Do a good job in the management and storage of raw materials that are easy to absorb water (rice bran, wheat bran, etc.)
It is not necessary to purchase too many raw materials that are easy to absorb water at one time. At the same time, avoid stacking against the wall, pay attention to warehouse management, prevent moisture, and prevent moisture from entering the warehouse in wet weather. The raw materials should be fed according to the amount of raw materials under normal production conditions, and the raw materials should be shipped out of the warehouse in accordance with the "first-in, first-out" principle, so as to shorten the inventory period of raw materials as much as possible. After testing, cotton rapeseed meal with a moisture content of more than 10% in storage will lose about 1% moisture after six months of storage.
2. Moisture control in the crushing stage
The crushing process is a key link in the processing of feed products, and the loss of moisture in the crushing process cannot be ignored. By comparing the moisture content of the materials before and after pulverization, it is found that with the reduction of the pulverized particle size of the materials, the moisture loss increases significantly. Similarly, for the materials with different gradient moisture contents, the comparison of the moisture content of the materials before and after pulverization shows that with the increase of the moisture content of the materials, the moisture loss of the pulverized powder increases, the maximum moisture loss is close to 1%, and the pulverization efficiency is significantly reduced. Energy consumption has increased significantly. After the shrimp feed is superfinely pulverized, 98% of the particle size can exceed 80 mesh. At present, the most commonly used fish feed is the water drop type hammer mill, and the particle size of the screen is 1.0-1.5mm. For pulverizers equipped with negative pressure suction and damper adjustment device, the air volume can be adjusted. Comparing the moisture loss of materials before and after pulverization, it is found that the air volume has a significant impact on the production efficiency, while the moisture loss has no significant effect, but with the increase of the air volume, the moisture loss still tends to increase. After the corn is crushed, the water loss by mechanical transportation is 0.22%, and the loss by pneumatic transportation is 0.95%. Most of the shrimp feed is crushed without net, and it is transported by air suction.
3. Moisture control in the mixing process
When the moisture content of the powder after mixing is much lower than 12.5%, it can be considered to add atomized water during mixing. But there are many problems in this aspect at present: it cannot exceed 2%; the water retention performance is poor, adding 2% of water only has a water retention rate of 40-50%; it is best to use hot water to prevent mildew; the mixing time and water addition time should be considered (sprayed together) are consistent; in order to ensure uniformity, adjust the position of the nozzle and the size of the nozzle; it is necessary to add a mildew inhibitor; pay attention to cleaning the inner wall of the mixer. A number of factors limit the addition of water to the mixer, and the addition of free water increases the potential for mold in the finished product.
4. Moisture control in the process of conditioning
The conditioning process is the most important process in the processing of feed products. The conditioning moisture, conditioning temperature and conditioning time are the key factors to control the conditioning effect of the final material. In the process of steam conditioning, moisture is the carrier of heat energy. The amount of conditioning moisture affects the temperature of conditioning. The conditioning moisture is adjusted by controlling the amount of steam added, and conditioning time determines the steam Utilization of water and heat energy.
Through the analysis of the correlation of various factors in the tempering process, it is possible to adjust some of these factors to control some other factor. For example, the conditioning moisture can be controlled by adjusting the amount of steam added and the conditioning time. The conditioning time can be adjusted by changing the filling factor of the material in the conditioner. This change can increase or decrease the conditioning moisture by 0.5-1% without changing the amount of steam added.
1. Steam quality Under normal circumstances, the steam pressure of the boiler used in the feed factory is 6-9kg/cm2, and the production pressure is 3-4kg/cm2. The higher the pressure, the lower the steam moisture content; conversely, the lower the pressure, the higher the humidity, the higher the steam moisture content. If the gas distribution drum and the steam supply pipeline are installed effectively and reasonably, and the condensed water in the steam transmission pipeline can be completely eliminated, the water content of the steam entering the conditioner will be low. In the production process, corresponding adjustments should be made according to the actual situation, so that the material into the mold can reach the ideal moisture content. In the dry and hot seasons of summer and autumn or when the moisture content of the raw materials used in the formula is low, it is necessary to find ways to increase the moisture content of the materials. In this case, as long as the production needs are met, the lower the pressure, the better, and the boiler steam supply pressure can be Adjusted to 3-5kg/cm2, the production and use pressure can be adjusted to 2kg/cm2, close all or part of the steam traps to increase the moisture content of the steam, so as to achieve the purpose of increasing the moisture content of the conditioned material. Due to the low moisture content of the raw material and the low moisture content of the steam, the moisture content of the conditioned material is difficult to reach 16% (the shrimp feed is not easy to reach 14%), so closing the trap will not cause the machine to block.
2. Conditioning time Under normal circumstances, the longer the residence time of the material in the conditioner, the more fully mixed with the steam, the moisture absorbed from the steam will also increase accordingly, and the moisture content of the material will be higher. In the production process, if the moisture content of the material is low, it is necessary to absorb more moisture by increasing the conditioning time. To increase the conditioning time, methods such as increasing the effective length of the conditioner, reducing the rotational speed of the conditioner and adjusting the angle of the conditioner blades can be adopted. In addition, try to make the material fill the conditioner as much as possible, which is also conducive to the material to absorb more water, but cannot blindly pursue the improvement of the filling coefficient and ignore the main function of the conditioner to condition the material.
5. The size and thickness of the die hole of the die
1. The pore size of the die The pore size of the die is different, and the moisture content of the pellet feed product produced is also different. A die with a small hole diameter produces a smaller diameter of feed pellets, and the cooling air can easily penetrate the pellets, so more moisture is taken away during cooling and the product moisture is lower. Conversely, for the die with large aperture, the diameter of feed particles is larger, the cold air is not easy to penetrate the particles, and the moisture taken away during cooling is less, and the moisture content of the product is higher.
2. The effective thickness of the die For a die with a larger effective thickness, the frictional resistance during the granulation process is larger, so it is difficult for the material to pass through the die hole, the friction temperature is higher, the water loss is larger, and the water content of the granulated product is lower. Conversely, thinner stampers have higher moisture content in the product.
6. Moisture control in cooling link
Cooling is the last step in the process to control product moisture. In this process, the first is to ensure that the moisture of the product does not exceed the product quality control index, and the second is to control the temperature of the product within an appropriate range to ensure that the product will not be adversely affected by excessive temperature. At present, most of the counter-flow coolers are used, and the effect is very good. During cooling, the decrease in moisture is related to the decrease in temperature, just as in the modulator, the increase in moisture corresponds to the increase in temperature. Usually, the moisture content of the material will increase (or decrease) by 0.6% for every 10°C increase (or decrease) in temperature.
Cooling is to reduce the temperature of the pellet feed so that it does not exceed the room temperature of 3-5°C, take away the moisture in the pellet, and make the moisture content of the pellet feed product meet the specified standards. Adjust the cooling air volume and cooling time in time according to the output, temperature, moisture, particle size and composition of the pellets that have just been demolded or come out of the post-curing equipment. The cooling air volume used for drier and smaller pellets should be smaller. , the cooling time should be shorter; on the contrary, the wetter, larger pellet feed should increase the air volume and prolong the cooling time.
7. Finished product management
Finished product management is also very important. The pelleted (or post-cured) feed pellets should be fully cooled by the cooler before packaging. Generally, the temperature of the finished feed should not be higher than room temperature 3°C, and the temperature of the finished feed should not be warm to the standard. After packaging, it is best to avoid sun exposure, otherwise the residual moisture in the product will migrate to places with lower packaging and storage temperatures, which will increase the humidity in these places and make the feed products more prone to mildew.
8. The influence of environmental temperature and humidity on the moisture content of finished feed
For every 11.1°C increase in air temperature, the water-holding force of the air can be doubled. It is because of this air heating process that pellets can be dried in the cooler even in high humidity weather. The hot particles raise the air temperature so that the air can carry more water. In summer, the moisture content of the raw material is low, and the moisture content of the finished product will be lower, so some processing parameters may need to be changed. Ambient humidity will increase the water content slightly.
