The abstract article introduces new developments in extrusion technology for the food and feed industries. The emphasis on quality technology is an effective method to increase the output of the extruder. The steady flow shearing technology of the extrusion process and the steady flow technology concept of the discharge process are proposed. The combination of modular screws is used to optimize the extrusion process parameters. The research progress of supercritical carbon dioxide extrusion technology in the food industry.
Keywords extrusion; emphasis on quality; steady flow; modular; supercritical
CLC number S817.12+4
Extrusion technology has been widely used in the food industry as well as in the feed industry. In recent years, some new technologies have emerged in the field of extrusion and expansion. The application of these new technologies has made the extrusion equipment greatly developed in terms of efficiency, energy consumption, reliability, quality of processed products and processing range.
1 High maturity emphasizes quality technology
The material needs to be quenched and tempered before entering the extruder. The purpose of quenching and tempering is to make the material pre-gelatinized. The quality of the gelatinization directly affects the working performance and product quality of the extruder. Therefore, quenching and tempering is an important key technology of the extrusion system.
The common quenching and tempering technique is to simply mix the materials with water and steam. Simple mixing does not allow water and heat to penetrate into the material evenly; for materials, especially some oily materials, it is difficult to make water penetrate into the particles due to the surface tension of water during the quenching and tempering process. The degree of gelatinization inside the particles is increased. This will inevitably require more steam and longer time to improve the conditioning effect.
High maturity emphasizes that quality technology is no longer a simple blending, emphasizing the relative speed of movement and the speed of penetration of heat and mass transfer during quenching and tempering. The rate of penetration of heat and mass transfer depends on factors such as temperature gradient, velocity gradient, humidity gradient, material properties (density, particle size, water content) of the interior and interface layers of the steam and powdered particulate material. The high-speed quenching and tempering improves the temperature gradient, the velocity gradient, and the humidity gradient, thereby improving the quenching and tempering effect.
High maturity emphasizes that the quality technology sets the sub-function blades, which allows the material and mass transfer to form a certain relative movement speed in the body, forming strong contact, strong penetration, reducing quenching time and reducing the use of steam. At the same time, since the material does not completely settle the bottom of the casing during the quenching and tempering process, a part of the material is suspended inside the casing, which further improves the fullness of the material in the casing of the conditioner, thereby prolonging the quenching and tempering time.
High maturity emphasizes the quality technology to increase the fullness of the conditioner from 30% to 35% to 55% to 60%. For the same effective volume regulator, the quenching time can be 40 from the original production. From ~45 s to 180-200 s, the degree of gelatinization increased from 35% to 40% to 50% to 55%, and the steam consumption decreased by about 20%.
As the material is stressed and fully pre-cooked, the new technology can increase the output of the extruder by 10% to 15% compared with the ordinary quenching and tempering, which reduces the energy consumption of the extruder. At the same time, the pre-gelatinization degree of the material is improved. The extruder runs smoothly, significantly reduces the wear on the bushings of the screw and the expansion chamber, and reduces the cost of replacing the wearing parts, thereby achieving the energy-saving and high-efficiency green quenching effect in the extrusion and puffing technology.
2 Steady-state shear extrusion technology
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2.1 Steady flow and steady-state shearing technology of extrusion process
The extrusion process is the core process in extrusion equipment. From the perspective of improving efficiency and reducing energy consumption, the research and development personnel of the shepherd extrusion equipment proposed the idea that the steady flow of the flow in the extrusion chamber is conducive to improving the quality of the extruded product, and at the same time put forward the theory of steady-state shearing, and then pass the test. This theory was verified. The application of this theory can effectively improve the output of the extruder, reduce energy consumption, reduce the wear of the screw and the cavity, and improve the quality of the extruded product. At the same time, the application of this technology expands the processing range of the expanded product, enabling the single-screw extruder to process small particles of 1.0 mm, and even processing smaller particles, which can stabilize long-term production.
2.1.1 Logistics steady flow technology during extrusion
In the extrusion process, due to the pressure difference, the material has various flow forms in the screw, as shown in Figure 1, where the presence of leakage and cross-flow has the greatest impact on the quality of the material. There is a big difference in the residence time between the leakage and cross-flow in the extrusion chamber and the downstream flow in the extrusion chamber, which directly causes the difference in the expansion coefficient of the feed or food after extrusion, which ultimately affects Extrusion product quality, such as uneven particles, inconsistent degree of gelatinization.
In the new technology, through the configuration of the screw, the “zero†gap between the screw and the extrusion puff is designed at the same time. On the one hand, the leakage of the material is reduced as much as possible, and the subdivided mixed structure is used to fully mix the leaked logistics with other logistics. The extruded material is homogenized uniformly, and the particles after extrusion cutting are uniform and beautiful, effectively saving energy waste caused by excessive residence time of the leakage material in the extrusion cavity.
2.1.2 Steady-state shearing technique during extrusion (see Figure 2)
In the extrusion technology of feed and food, material ripening generally requires increasing the degree of shear in the extrusion chamber. In the current technology, the feeding of materials from the inlet of the extrusion main body to the discharge of the formwork is a rapid shearing process, and the rapid shearing is accompanied by high pressure, high energy consumption, high wear and tear, and at the same time brings instability of the logistics, so The technical requirements for the extrusion die of the extruder are very high. Only a good discharge mold can alleviate the instability of the logistics, in order to make the logistics into a uniform pellet of expanded particles.
Steady-state shearing emphasizes a shearing process and is a process of smooth shearing. In this process, the shearing peak is smaller than the rapid shearing, but the reasonable setting of the screw configuration keeps the gelatinization degree of the steady-state shearing and the rapid shearing uniform, and can even further improve the gelatinization degree.
Since the steady-state shear peak during the shearing process is much smaller than the rapid shear, the wear of the screw and the cavity is reduced. It not only improves the service life of the wearing parts, but more importantly, improves the safety and reliability of the extruded food. Since the steady-state shearing is a process in which the change of the front-back drop is not very large, the leakage of the material is relatively reduced throughout the process, the material in the extrusion chamber is uniform, the equipment operation is more stable, and the extruded product is finally extruded. Particle uniformity and aesthetics are better. Practice has proved that steady-state shearing is also a kind of shear that saves energy. The steady-state shearing extruder can increase the output by about 15%, and the power consumption of the extruder system can be reduced by about 12%. Therefore, steady-state shearing is an economical, stable, and energy-saving way.
2.2 steady flow technology in the discharge process
Discharge mold technology is one of the core technologies in the field of food and feed extrusion. This is directly related to the application range of the expanded product and affects the quality of the expanded product.
At the end of the screw extrusion, the material rotates at a certain speed and is unstable. Such a stream directly enters the mold, which is not conducive to molding, and is not conducive to the uniformity of the expanded particles. Steady flow technology is a technology to solve this unstable logistics, and its structure is shown in Figure 3.
By adding a flow-regulating device with a guide type between the end of the extrusion chamber and the discharge die, the rotating stream is first stopped from rotating, and then the stream is formed into an annular pressing zone, and the torus of this region is consistent with the area of ​​the mold. After that, the binding force of the logistics is slowly amplified, the flow rate is slowed down, and the final stream is smoothly and evenly distributed to the front of the opening area of ​​the mold. Such a flow ensures that the material can be uniformly introduced into the discharge mold, ensuring uniformity of material formation. At the same time, since the flow is squeezed out from the screw and first enters the annular extrusion zone, the impact force of the flow on the mold is greatly reduced, the damage degree of the mold is minimized, and the service life of the mold is improved.
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3 Modular, flexible screw combination and process parameter optimization technology
3.1 Modularity and flexibility of the screw combination
The screw combination is another core technology of the extrusion equipment. For different raw materials and different extrusion requirements, different types of screws should be arranged according to the physical properties of the materials. At the same time, the screw configuration must be combined with the processing parameters of the extruder to jointly produce high-quality expanded products (see figure). 4).
In order to adapt to the physical properties of different raw materials and to adapt to the different expansion requirements of various puffed products, the screw elements are designed in a standard form that can be freely combined and modularized. In this way, by adjusting the screw configuration in production and then using different processing parameters, the same extruder can be adapted to the expansion of different product requirements in different occasions in the food and feed industry.
The modular and flexible screw combination can save a lot of resources, enabling a production line to process multiple forms of expanded products and avoiding duplication of investment.
3.2 Process parameter control and optimization technology
A suitable screw configuration is only one of the important requirements for processing high quality puffed products. Suitable processing is another important requirement.
The wide application range of the extruder and the different technical parameters required for the expanded product determine that the extruder needs to use different processing parameters. In each manufacturer, regardless of the food industry or the feed industry, the formula for processing the expanded product is always based on the market. The requirements are constantly adjusted, which requires timely adjustment of the processing parameters of the extruder; even sometimes the raw materials of different origins will have a certain impact on the expanded products, so all this determines the processing parameters of the extruder vary widely.
At present, the control of the processing parameters of the extruder generally depends on the experienced operators. The level of the operator directly affects the quality of the expanded product. This is also the case for many extruder manufacturers who use the same extruder manufacturer. The same type of extruder equipment, but the root cause of the different manufacturers use different effects.
The process parameter control and optimization technology first provides a standard record method for this wide variety of process parameters. This standard data enables the control system of the extruder to be read and can be squeezed under the execution of the extruder operator. The press is standardized for production.
The process parameter control and optimization technology includes a data library. The data in the data base is first derived from an optimized data obtained after the adjustment and exploration of the test process, which is obtained under the premise of processing a certain formula and the technical requirements of the expanded product. Secondly, the data from the best data is obtained. Analysis of formula components and analysis of technical parameters of expanded products. Formula composition analysis, such as starch content, oil content, protein content in the formula, wherein the vegetable protein and animal protein in the protein account for each other; the analysis of technical parameters of the expanded product, such as expansion coefficient, gelatinization degree, discharge temperature, out Material moisture and so on. Linking these data with the processing parameters to form "group data", the formulas that form different physical properties through the accumulation of experiments correspond to different "group data", thus forming a complete database of processing parameters.
In the application process, when encountering a new formula, firstly through the testing and analysis of the components, find the similar formula in the database, obtain a suitable processing parameter through the data optimization technology, and guide the extruder under the control of the process parameters. Production is carried out, completely avoiding the influence of subjective factors of the operator, and the quality of the expanded product can be consistently stable for a long time.
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4 Supercritical carbon dioxide extrusion technology
The traditional extrusion is steam expansion, and the expansion of the material is formed by rapid evaporation of water vapor under a certain pressure. High temperature (130 ~ 170 °C or higher), high pressure, low moisture (13% ~ 24%) and high shear in extrusion can cause heat sensitive ingredients (such as flavors, vitamins, amino acids, etc.) in food materials. The loss of the degree.
By improving the current twin-screw extruder, supercritical carbon dioxide is injected into the cooling section of the expansion chamber at a pressure higher than the cylinder, and is uniformly mixed with the material. When the material is extruded into the die, the expansion of the carbon dioxide is performed. The material is expanded to obtain a porous, bulky structure with a more uniform texture.
Supercritical carbon dioxide is used in food extrusion technology, and the processing temperature is lower than the conventional extrusion temperature based on steam expansion. And carbon dioxide is an inert medium, which has almost no destructive effect on various components in food, and can better protect heat sensitive ingredients, vitamins, flavor substances, natural pigment components, etc., so that the product has a better water solubility index. (WSI) and water absorption index (WAI) values. At present, the application of this processing technology in China's food industry is still in the research and development stage, and has a very broad development prospect.
5 Conclusion
During the “Eleventh Five-Year Plan†period, China's food (feed) industry will focus on key technologies such as texture reorganization and physical modification technology, bioengineering technology, quality and safety control technology. With the wide application of extrusion equipment, extrusion technology will be developed more rapidly.
Fan Wenhai, Jiangsu Muyang Group, Senior Engineer, 225127, No. 1 Muyang Road, Yangzhou City, Jiangsu Province.
Ma Liang, Zhang Guiyang, Gao Ruibin, unit and mailing address are the same as the first author.
Commercial Laminate,Compact Laminate Doors,Commercial Architectural Internal Doors,Commercial Compact Laminate
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