Moisture control is to comprehensively control various factors according to different situations during the entire production process, so that the final moisture content of the product reaches the manufacturer's expected goal. The main factors that affect the final moisture content of the feed product are: the moisture content of the feed raw material itself, the moisture change in the crushing stage, the amount of liquid added in the mixing stage, the moisture content of the steam, the conditioning level, the die hole size and thickness of the die, Cooler air volume and drying time, packaging quality management, the influence of different climate 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 raw material samples. Sampling must represent the overall situation of the entire batch of raw materials. Samples should be taken according to sampling standards to prevent missed sampling. At the same time, sensory detection of raw material moisture in the sampling process high and low.
In the process of raw material moisture detection, accuracy must be ensured. In order to reduce errors, two to three parallel samples can be tested, and the average value can be calculated as the detection value.
2. Do a good job in the management and storage of water-absorbing raw materials (rice bran, wheat bran, etc.)
Raw materials that are easy to absorb water do not need to be purchased too much at one time, and at the same time avoid stacking against the wall, pay attention to warehouse management, moisture-proof, and prevent moisture from entering the warehouse in humid weather. The raw materials should be imported according to the amount of raw materials under normal production conditions, and the raw materials should follow the "first in, first out" principle to shorten the storage period of raw materials as much as possible. After testing, the moisture in the storage is more than 10% cottonseed meal, and the moisture loss is about 1% after six months of storage.
2. Moisture control in the crushing stage
Comparative testing and analysis of the moisture content of the materials before and after crushing were performed on the crusher screen and it was found that as the particle size of the materials decreased, the moisture loss increased significantly. Similarly, for materials with different gradient moisture contents, comparative testing and analysis of the moisture content of the materials before and after crushing found that as the moisture content of the materials increased, the moisture loss of the powder after crushing increased. The maximum moisture loss was close to 1%, and the crushing efficiency was significantly reduced. , the energy consumption increases significantly. After the shrimp material is ultra-finely crushed, 98% of the particle size can pass 80 mesh. Currently, water droplet-type hammer crushers are commonly used for fish feed, and the particle size of the screen is 1.0-1.5mm. For crushers equipped with negative pressure air suction and air door adjustment devices, the air volume can be adjusted. Comparative testing of the moisture loss of materials before and after crushing found that the air volume has a significant impact on production efficiency, while moisture loss has no significant impact. However, as the air volume increases, moisture loss still tends to increase. After corn is crushed, the water loss during mechanical transportation is 0.22%, and the water loss during pneumatic transportation is 0.95%. Most of the shrimp feed is ultra-finely pulverized without a net and transported by air suction pneumatically. Most of the fish feed is crushed and mechanically transported using augers.
3. Moisture control in the mixing process
When the moisture content of the mixed powder is much lower than 12.5%, you can consider spraying atomized water during mixing. However, there are currently many problems in this regard: it cannot exceed 2%; the water retention performance is poor, adding 2% 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 must be considered (sprayed together); to ensure uniformity, adjust the position of the nozzle and the size of the water nozzle; add antifungal agent; pay attention to cleaning the inner wall of the mixer. Many factors limit the addition of water to the mixer, and the added free water will increase the potential moldiness of the finished material.
4. Moisture control during conditioning process
The conditioning process is the most important process in the processing of feed products. Conditioning moisture, conditioning temperature, and conditioning time are key factors that control the conditioning effect of the final material. In the steam conditioning process, moisture is the carrier of heat energy. The amount of conditioning moisture affects the conditioning temperature. The conditioning moisture is adjusted by controlling the amount of steam added, and the conditioning time determines the steam. Utilization efficiency of water and heat energy.
By analyzing the interrelationships between factors in the tempering process, some factors can be adjusted to control other factors. 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 coefficient of the material in the conditioner. This change can increase or decrease the conditioning moisture content by 0.5-1% while keeping the amount of steam added.
1. Steam quality Under normal circumstances, the steam pressure of boilers used in feed mills is 6-9kg/cm2, and the production pressure is 3-4kg/cm2.
The higher the pressure, the lower the moisture content of the steam; conversely, the lower the pressure, the higher the humidity, and the higher the moisture content of the steam. If the gas distribution bag and steam supply pipeline are installed effectively and reasonably, and the condensed water in the steam transportation pipeline can be completely eliminated, the moisture content of the steam entering the conditioner will be low. During the production process, adjustments must be made according to the actual situation so that the materials entering 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 material. In this case, as long as the production needs are met, the lower the pressure, the better. The boiler steam supply pressure can Adjust it to 3-5kg/cm2, and the production pressure can be adjusted to 2kg/cm2. Close all or part of the traps to increase the moisture content of the steam, thereby achieving the purpose of increasing the moisture content of the conditioned materials. Since the moisture content of the raw material is low and the moisture content of the steam is also low, it is difficult for the moisture content of the conditioned material to reach 16% (it is not easy for the shrimp feed to reach 14%). Therefore, closing the trap will not cause blockage.
2. Conditioning time Under normal circumstances, the longer the material stays in the conditioner, the more fully it will be mixed with steam, and the moisture absorbed from the steam will also increase accordingly, and the higher the moisture content of the material will be. During the production process, if the moisture content of the material is low, more moisture must be absorbed by increasing the conditioning time. To increase the conditioning time, you can increase the effective length of the conditioner, reduce the speed of the conditioner, and adjust the angle of the conditioner blades. In addition, try to fill the conditioner with the material as much as possible, which will also help the material absorb more water. However, you cannot blindly pursue the improvement of the filling coefficient and ignore the main function of the conditioner to condition the material.
5. Die hole size and thickness of die
1. Aperture of the die The pore size of the die is different, and the moisture content of the pellet feed products produced is also different. The feed pellets produced by the die with small pore diameter are small in diameter, and the cooling air can easily penetrate the pellets, so more moisture is taken away during cooling, and the moisture content of the product is lower. On the contrary, the die with large hole diameter has a larger diameter of feed particles, and the cold wind is not easy to penetrate the particles, so less moisture is taken away during cooling, and the product moisture is higher.
2. The effective thickness of the die. The die with a larger effective thickness has a larger friction resistance during the granulation process, and it is difficult for the material to pass through the die hole. The friction temperature is higher, the water loss is larger, and the moisture content of the granule product is lower. Conversely, thinner stampers produce products with higher moisture content.
6. Moisture control in the cooling process
Cooling is the final step in the process of controlling product moisture. In this process, the first thing is to ensure that the moisture content of the product does not exceed the product quality control index, and the second is to control the product temperature 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. In cooling, the decrease of moisture is related to the decrease of temperature, just as in the modulator, the increase of moisture corresponds to the increase of temperature. Generally, every time the temperature increases (or decreases) by 10°C, the moisture content of the material will increase (or decrease) by 0.6%.
Cooling is to reduce the temperature of the pellet feed so that it does not exceed the room temperature by 3-5°C, and take away the moisture in the pellets so that the moisture content of the pellet feed products meets 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 pellet feed just released from the mold or from the post-curing equipment. The cooling air volume used for dry and small pellet feed should be smaller , the cooling time should be shorter; on the contrary, the wetter and larger pellet feed should increase the air volume and prolong the cooling time.
7. Finished product management
Finished product management is also very important. Pelleted (or post-cured) feed pellets must be fully cooled by a cooler before packaging. Generally, the temperature of the finished feed should not be higher than room temperature by 3°C, and it must not feel warm when touched by hand to meet the standard. It is best to avoid sun exposure after packaging, 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 susceptible to mildew.
8. The influence of environmental temperature and humidity on the moisture content of finished feed products
For every 11.1°C increase in air temperature, the water holding power of the air doubles. It is precisely because of this air heating process that pellet feed can be dried in the cooler even in high-humidity weather. Hot particles increase the temperature of the air, allowing the air to take away more moisture. In summer, when the moisture content of raw materials is low, the moisture content of finished materials will be even lower, so some processing parameters may need to be changed. Ambient humidity will increase moisture slightly.
