Analysis of moisture control technology for pellet feed processing

Abstract By analyzing the conventional moisture control technology in the processing of pellet feed, the water addition technology and on-line detection and control technology of low-moisture feed were introduced, which helped to improve the quality and uniformity of pellet feed and increase the economic benefits of the enterprise.

Keywords feed processing; moisture; control technology

CLC number S816.9

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 processing enterprises. Effective control of it is one of the keys to ensure the quality and safety of feed products. When the moisture content exceeds the specified standard, the pellet feed is prone to mildew and deterioration, which is not conducive to preservation, and also reduces the content of nutrients and reduces the energy of the feed; if the moisture content is too low, it will affect the taste of the feed and cause excessive weight loss. The economic benefits of processing enterprises have dropped significantly. In the feed processing process, the suitable moisture content is beneficial to granulation, which can improve the processing quality and production efficiency of the pellet feed product and reduce the processing cost. How to control the moisture content of pellet feed has become a common concern of feed processing enterprises.

The source of raw materials and the variety of varieties used in the processing of pellet feeds bring about differences in the moisture distribution of feed processing intermediate products and final products and the variability of water content. Studies have shown that the moisture content of the semi-finished powder after mixing is generally between 9% and 14%; the moisture content of the powder before quenching and tempering is about 12.5%; the moisture content of the mold material after quenching and tempering is between 15.0% and 16.5%. It is reasonable, the quality of processed pellet feed is good, the finish is uniform, the chalking rate is low, and the energy consumption is also low. The moisture content of the final product is also easy to meet the standard requirements (the moisture of the pellet feed after processing should not be higher than 12.5%).

1 moisture control technology

The moisture content of the raw material itself and the amount of water added and cooling during the quenching and tempering process are the main factors affecting the final moisture content of the pellet feed product. In the processing of pellet feed, these factors should be comprehensively controlled according to different conditions to ensure that the final moisture content of the product reaches the expected target.

1.1 moisture control of raw materials

The pellet feed is made up of a variety of raw materials. The moisture of the finished feed is closely related to the raw materials. When the moisture content of the raw materials exceeds the standard, the current pellet feed processing method cannot be solved. Only by controlling the moisture of the raw materials can the water be harvested. Effectively control the moisture of the finished pellet feed. First of all, there must be a sound raw material management system, strict control of raw material procurement and storage, the moisture content of conventional raw materials should not exceed the normal indicators, all materials that do not meet the requirements are not allowed to purchase and enter the warehouse, the raw materials with excessive moisture, generally The finished feed must not be processed. Second, the raw materials that are easy to absorb water should not be crushed as much as possible. They should not be stacked on the wall. The storage time should be set according to the type of raw materials. The moisture content should be re-measured after the storage time. Third, pay attention to warehouse management. The warehouse should be regularly ventilated. Generally, temperature control and humidity control devices should be installed. The raw materials should be discharged in accordance with the principle of “first in, first out” to ensure that the moisture content of the raw materials and other quality indicators are within the specified fluctuation range. Within the limit, the feedstock should be fed according to the amount of raw materials used under normal production conditions, and the stocking period of raw materials should be shortened as much as possible.

1.2 moisture control during quenching and tempering

Quenching and tempering is the hydrothermal treatment of the powdered material before granulation. By quenching and tempering, the digestibility of the feed can be improved, the hardness of the granules can be improved, the pulverization rate of the granules can be reduced, the pathogenic bacteria can be killed, the granulation energy can be saved, and the mold can be improved. Roll life. The amount of steam (moisture) added during quenching and tempering will have a great influence on the quenching effect and the moisture content of the finished pellet feed. If too much steam is added, the material will become too soft, which will easily block the die hole and affect the production. The moisture content of the finished pellet is high; if the steam is insufficiently added, the pellet machine output is low, the stamper and the press roll are worn, and the degree of ripening is low. The surface of the product is rough, the powdering rate is high, and the power consumption is large.

The moisture content of the material after quenching and tempering is one of the important indicators for judging the effect of quenching and tempering. The amount of steam added can be controlled by adjusting the amount of steam entering and the quality of steam. In the production process, the water content of the powder should be adjusted accordingly to achieve the desired temperature and moisture content. For powders with normal moisture content, dry steam is required for quenching and tempering, and water-containing steam will adversely affect quenching and tempering. It is generally reasonable to add steam in an amount of 4% to 6% of the productivity. For powders with lower moisture content, we must find ways to increase the moisture content of the material. The material can be increased after reducing the steam pressure, closing all or part of the steam trap, adding unsaturated steam, increasing the time of quenching and tempering. Moisture content to increase the moisture content of the granules. For powders with high moisture content, high-pressure super-saturated steam should be used to make the temperature of the powder after quenching and tempering meet the requirements and the water content is not too high.

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1.3 moisture control during cooling

Cooling is to reduce the temperature of the pellet feed so that it does not exceed 3 to 5 °C at room temperature, taking away the moisture in the pellets, so that the moisture content of the pellet feed product meets the prescribed standards. After cooling, the temperature and moisture of the pellet feed must meet the requirements before packaging, otherwise the finished product will be mildewed and deteriorated during storage. The cooling air volume and cooling time should be adjusted according to the yield, temperature, moisture, particle size and composition of the pelletized material just released from the mold. The cooling air volume for the dry, smaller pellet feed should be smaller and the cooling time should be shorter. On the contrary, the wet, larger pellet feed should increase the air volume and extend the cooling time. To ensure that all particles receive the same cooling time, they should be operated in strict accordance with the requirements of the cooler to ensure that they are automatically discharged evenly. In the process of granulation start and end, the cooler should work for a few more minutes. Especially after the granulator is stopped, the cooler should work for another 10 minutes to ensure that all the particles are out.

2 water addition technology

When the water content of the raw material itself is low, so that the moisture content of the mixed powder is much lower than 12.5%, spraying the atomized water by mixing the materials can improve the granulation efficiency and the quality of the pellet feed, reduce the power consumption, and reduce the product. The weight loss increases economic efficiency.

In order to add moisture to the powder, the moisture of the incoming materials, mixed powders and final products must be monitored in real time. Only when the mixed powder and the final product have a moisture content below 12.5% ​​can the moisture addition be considered. The amount of water added is set manually according to the test results. The target moisture should be set at 2 percentage points higher than the initial moisture, but the maximum moisture should not exceed 13%. If the initial moisture of the mixed powder is 11.2%, the target moisture should be 13%; if the initial moisture of the mixed powder is 9.2%, the target moisture should be 11.2%.

Due to the fluctuation of the moisture content of the powder, when the water is added by manual testing, the final moisture of the pellet feed product must be detected at all times. In the initial stage of each batch of feed production, it is necessary to check diligently. According to the test results, the amount of water added and the feed are cooled. The residence time in the device allows the final moisture of the product to reach the target moisture. For most granulated products, the target moisture is preferably set at 12.5%, and should not exceed 13% at any time, otherwise it is prone to mold and deterioration.

At present, the commonly used water adding equipment is an automatic water adding system, which is suitable for adding water to the mixer, increasing the moisture of the powder, solving the problem that the raw material of the feed mill is too low, and the production cost is too high. The water addition system is mainly composed of stainless steel water storage tank, anti-rust electromagnetic valve, water pump, anti-rust flow meter and intelligent flow meter. The spray quantity and spray delay time can be set on the intelligent flow meter. The system adopts advanced microcomputer automatic control technology, which has the characteristics of high degree of automation, accurate addition ratio, reliable control and convenient operation. However, the requirements of the nozzle in the mixer are very high, and it is necessary to achieve complete atomization to ensure uniform addition. The main problem of this technology is that the amount of water added is relatively fixed, and it cannot be adjusted according to the changes of raw materials and processing processes, which tends to cause the moisture content of the finished pellets to be high.

Another method of adding water is to spray water in the compression chamber of the granulator, where the sprayed water has the effect of evaporating and cooling, which can effectively inhibit the escape of steam, so that the product retains more original moisture, and the moisture of the product can be increased. The amount is the same as the amount of water added here. A large number of test results show that the water addition amount of this method is up to 0.5%, above which the product quality will decrease. The safe way to use this system is to use a moisture on-line detection device to adjust the amount of spray in real time to prevent excessive moisture in the final product.

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3 moisture online detection and control technology

During the processing of pellet feed, the moisture of the material is constantly affected by factors such as pulverization, liquid additives such as water and steam, quenching and tempering, granulation and cooling. Even if the same batch of raw materials, the water change in each process is not the same, the water content of the product is nonlinearly related to the moisture content of the material in the process, and the moisture content of the final product cannot be predicted at all. Therefore, the most ideal moisture measurement and control method in feed processing should be online real-time monitoring and control, dynamic prediction of product moisture content, and the purpose of optimal control of feed product moisture.

There are two control schemes for on-line detection and control of granular feed moisture, one is feedback control and the other is feedforward control. The feedback control is to detect the moisture of the pellet feed after cooling, and the feedforward control detects the moisture of the powder before quenching and tempering. Both of them compare the detected value with the set value of the moisture of the pellet feed product, and control according to the comparison result. The amount of tempered steam (moisture) added and the amount of water sprayed in the compression chamber of the granulator. Compared with the feedback, the feedstock and the ready-to-add water are closer in time and more real-time, so the feedforward control is generally used. On-line control of granular feed processing moisture is a qualitative leap, keeping the water content of the finished product in the narrowest standard area, which is conducive to the stability of the moisture content of the product and improve economic benefits.

Online moisture measurement is an indirect method that obtains the moisture content of a material by measuring changes in physical properties related to moisture, especially changes in electrical properties. In addition to ensuring measurement accuracy and meeting the real-time nature of measurement, online moisture measurement requires attention to the repeatability of measurement data, the fidelity of measurement information, and the intelligence of measurement and measurement data processing. By analyzing and comparing the online measurement method of moisture developed today, the microwave method has proved to be an ideal online measurement method for moisture, which has been successfully applied in many aspects and has been applied to feed moisture measurement in foreign countries.

The error of microwave moisture measurement is less than ±0.4%, and the repeatability error is less than ±0.2%. The instantaneous sampling reading is 10 times/s. The precision is high, the performance is stable, the anti-interference and impact resistance are strong, and the whole process of feed processing can be provided. The moisture monitoring, which maximizes the efficiency of the plant and minimizes the loss, is a safe, observable and controllable system. It is the best choice for real-time monitoring and control of feed moisture online. In practical applications, the microwave moisture measurement and control system includes a microwave detecting unit, a measuring signal processing unit, a system logic control unit, a water and water quantity control unit, a display and monitoring unit, and the like.

4 summary

The moisture content of the finished pellet feed is affected by each link in the raw material, storage and feed processing process, and the moisture control of the processed object is enhanced during the processing, which can improve productivity and increase economic benefits, especially by controlling the moisture content of the powder online. It can improve the quality and uniformity of pellet feed, which is of great significance for ensuring product quality.