If the moisture content exceeds the specified standard, the pellet feed is prone to mold and deterioration, which is not conducive to preservation, and will also reduce the content of nutrients; but if the moisture content of the product is too low, it will cause unnecessary losses to the enterprise, and the unevenness The moisture content also causes the instability of product quality and affects the brand reputation of the product. In the process of feed processing, proper moisture content is conducive to pelleting, reducing energy consumption and improving production. Therefore, in the production process of compound feed, in order to make the production go on smoothly, the energy consumption is lower, the particles are smoother and more uniform, and the final product meets the specified moisture content standards, the moisture control in the whole production process must be carried out.
Moisture control is to comprehensively control various factors according to different situations during the whole production process, so that the final moisture content of the product can reach the expected goal of the producer. The main factors affecting the final moisture content of the feed product are: the moisture content of the feed 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 level of tempering, 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
Crusher sieve, comparative detection and analysis of the moisture content of the material before and after crushing found that as the particle size of the crushed material decreases, the water loss increases significantly. Similarly, for materials with different gradient moisture content, the comparative detection and analysis of the moisture content of the material before and after crushing shows that with the increase of the moisture content of the material, the moisture loss of the powder after crushing increases, the maximum loss of moisture is close to 1%, and the crushing efficiency is significantly reduced. Energy consumption increases significantly. After the shrimp material is ultra-finely crushed, 98% of the particle size can pass 80 mesh. At present, the water drop type hammer mill is mostly used for fish feed, and the particle size of the screen is 1.0-1.5mm. For the pulverizer equipped with negative pressure suction and air door adjustment device, the air volume can be adjusted. A comparative test of the moisture loss of the material before and after crushing found that the air volume has a significant impact on the production efficiency, while the water loss has no significant impact, but with the increase of the air volume, the water 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 ultra-fine grinding without net, which is transported by air suction. Most of the fish feed is crushed and then mechanically transported by auger.
3. Moisture control in the mixing process
When the moisture content of the mixed powder is much lower than 12.5%, it may be considered to spray 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% 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 (spray together) are consistent; in order to ensure uniformity, adjust the position of the nozzle and the size of the water nozzle; it is necessary to add anti-fungal 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 mold of the finished material.
4. Moisture control in conditioning process
The conditioning process is the most important process in the processing of feed products. Conditioning moisture, conditioning temperature, and conditioning time are the key factors to control the final material conditioning effect. In the process of steam conditioning, moisture is the carrier of heat energy, the amount of conditioning water affects the level of conditioning temperature, the conditioning moisture is adjusted by controlling the amount of steam added, and the conditioning time determines the steam Utilization of water and heat energy.
Through the analysis of the interrelationship of various factors in the tempering process, some factors can be adjusted to control other factors. For example, the tempering water can be controlled by adjusting the amount of steam added and the length of conditioning time, and the length of conditioning time can be adjusted by changing the filling coefficient of the material in the conditioner. This change can increase or decrease the tempering moisture by 0.5-1% under the condition that the amount of steam added remains unchanged. 1. Steam quality Under normal circumstances, the steam pressure of the boiler used in the feed mill is 6-9kg/cm2, and the production pressure is 3-4kg/cm2.
The higher the pressure, the lower the water content of the steam; conversely, the lower the pressure, the higher the humidity, the higher the water content of the steam. If the gas distribution drum and steam supply pipeline are installed effectively and reasonably, and the condensed water in the steam transmission pipeline can be completely removed, the moisture 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 molded material can reach the ideal moisture content. In the dry and hot season of summer and autumn or when the moisture content of the raw materials used in the formula is low, it is necessary to find a way 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 steam supply pressure of the boiler can be Adjust it to 3-5kg/cm2, the production pressure can be adjusted to 2kg/cm2, close all or part of the steam traps to increase the water content of the steam, so as to achieve the purpose of increasing the water content of the material after conditioning. Due to the low moisture content of the raw material and the low moisture content of the steam, it is difficult for the moisture content of the material after conditioning to reach 16% (it is not easy for the shrimp feed to reach 14%), so closing the trap will not cause a blockage.
2. Conditioning time Under normal circumstances, the longer the material stays in the conditioner, the more fully it will be mixed with the steam, and the moisture absorbed from the steam will 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 increase the conditioning time to absorb more moisture. To increase the conditioning time, methods such as increasing the effective length of the conditioner, reducing the speed of the conditioner, and adjusting the angle of the blades of the conditioner can be adopted. In addition, filling the conditioner with the material as much as possible is also beneficial for the material to absorb more water, but the main function of the conditioner to condition the material should not be ignored blindly pursuing the improvement of the filling coefficient.
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 size 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, 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 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 room temperature by 3-5°C, and take away the moisture in the pellets so that the moisture content of the pellet feed product 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. For dry and small pellet feed, the cooling air volume 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. The granulated (or post-cured) feed pellets must be fully cooled by the cooler before they can be packaged. Generally, the temperature of the finished feed should not be higher than room temperature by 3°C, and the standard can only be met if there is no warm feeling when touched by hands. 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 temperature, which will increase the humidity in these places and the feed products will be more prone to mildew.
8. The influence of environmental temperature and humidity on the moisture content of feed products
For every 11.1°C increase in air temperature, the water retention capacity of the air can be doubled. Thanks to this air heating process it is possible to dry the pellets inside the cooler even in high humidity weather. Hot particles raise the temperature of the air, allowing the air to carry more moisture. In summer, the moisture content of the raw material is low and the moisture content of the finished material will be even lower, so some processing parameters may need to be changed. Ambient humidity will slightly increase moisture content.