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    Home > Active Ingredient News > Drugs Articles > Application of double cone rotary vacuum machine in pellet drying

    Application of double cone rotary vacuum machine in pellet drying

    • Last Update: 2012-02-08
    • Source: Internet
    • Author: User
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    Drying is the operation of removing moisture or other volatile components from materials It involves a wide range of drying equipment According to the pressure of the material environment in the process, it can be divided into atmospheric drying and vacuum drying The former is used more, relatively simple, and has been used since ancient times; the latter is developed later, relatively complex However, vacuum drying has many advantages of its own and has been widely used in recent years, especially in pharmaceutical, food and chemical industries As a dosage form in pharmaceutical industry, the drying method of pellets can be ordinary drying under normal pressure or double cone rotary vacuum drying However, the drying effect of the two methods is different, and the quality of the pellets produced by vacuum drying is obviously better The advantages of vacuum drying are as follows: (1) in vacuum environment, the boiling point of water is reduced and low temperature drying can be realized, which provides favorable conditions for the drying of heat sensitive materials, such as some vitamins, which will decompose and deteriorate as soon as they encounter high temperature; (2) In the process of vacuum drying, the pressure in the drying chamber is always lower than the atmospheric pressure, the number of gas molecules is small, the partial pressure of oxygen is reduced, the oxidation deterioration phenomenon of the material in the drying process is avoided, the quality of the dried material is guaranteed, some bacteria can be killed and the reproduction and growth of some bacteria can be inhibited under the condition of anoxia; (3) Vacuum drying can eliminate the surface hardening phenomenon easily under normal pressure; (4) some poisonous and harmful gases can be recovered in the vacuum drying process to prevent environmental pollution When the double cone rotary vacuum drying machine is used in the operation of drying pellets, the container is easy to clean, the dried pellets are clean and sanitary, the surface of the pellets is solid, the sphericity is high, the size is consistent, the content is uniform, the moisture content is qualified, the color is bright and consistent, the fine powder is small, the quality of the medicine is stable, and the storage time is long The working principle of vacuum drying vacuum refers to the gas state in which the molecular density of the gas is lower than that of the gas under atmospheric pressure in a given container The rarity of the gas under vacuum is called vacuum degree Vacuum drying is the process of indirectly heating the material under the condition of lower than atmospheric pressure, and vaporizing the moisture in the material under the corresponding temperature, so as to reduce the moisture content in the material The basic principle of vacuum drying: the saturated vapor pressure of water is closely related to the temperature In the vacuum state, the boiling point of water will be reduced, so the water in the material can be vaporized at low temperature during vacuum drying, which can realize low-temperature drying As you know, at atmospheric pressure, if the temperature reaches 100 ℃, the water begins to boil and vaporize Why is it not easy to cook rice or other food in plateau area? This is because of the low atmospheric pressure in plateau area and the lower boiling point of water If the pressure of the vessel keeps decreasing, when the pressure drops to 613.28pa, the boiling point of water will become 0 ℃ Keeping different vacuum degree can change the drying temperature of materials Usually, the vacuum degree of vacuum drying should be determined by the thermal sensitivity of materials As the vacuum degree of the vacuum pump tends to 0, its gas flow is obviously reduced and tends to 0, which is not conducive to the flow of gas and the discharge of moisture, so the reading of the vacuum gauge is generally controlled below 0.095mpa in production Vacuum drying is the free water in drying materials, which can be divided into gap water, surface water, capillary water and wrapping water In the drying process, first, the heat source transmits the heat energy to the material to raise the temperature and vaporize the moisture content; second, the vaporized moisture content migrates to the drying chamber space to make the moisture content separate from the material surface and discharge from the drying chamber; third, the moisture content in the material moves to the material surface in liquid state to facilitate the vaporization on the surface The three processes of vacuum drying are carried out in a coordinated way The good and bad coordination directly affects the speed of vacuum drying and the quality of materials
    When vacuumizing and heating is started, the drying speed is slow When the material is heated above the vaporization temperature of water, the drying speed will suddenly speed up The material is heated to the vaporization temperature under the corresponding pressure within the allowable temperature range and vaporized in large quantities At this time, the material temperature remains unchanged The added heat is used as the latent heat of vaporization and various heat losses The vacuum system continuously discharges the vaporized steam Keep the pressure difference between the evaporation surface and the space, so that the drying can continue The moisture content of the material decreases to a certain extent, and the water evaporated from the material decreases Under the condition of constant heating capacity, the temperature of the material begins to rise, the pressure difference between the evaporation surface and the space decreases, and the drying process turns to the deceleration stage The drying rate gradually decreased to zero In the process of vacuum drying, people always want to speed up the drying speed and shorten the drying time However, there are many factors that affect the drying speed, such as the condition of the dried material, wet content, density, viscosity and so on If the initial temperature of the material is increased and the wet content of the material is reduced, the speed of vacuum drying will be improved; if the temperature is too fast and the water is too late to be discharged, the pellets are easy to agglomerate and stick on the wall of the boiler Therefore, the working vacuum of the drying chamber is high, which is conducive to the vaporization of water at a lower temperature However, with a high vacuum, the fluidity of air will become poor, and the water will not be easily discharged out of the container, and the requirements of the vacuum equipment will be improved Therefore, we should consider the influence of vacuum degree comprehensively according to the characteristics of materials In addition, the structure of vacuum drying equipment, heating mode, operator's experience and so on will affect the speed of vacuum drying The system of double cone rotary vacuum drying is mainly composed of double cone rotary vacuum dryer, condenser, dust remover, vacuum extraction system, heating system, cooling system, electric control system, etc When drying pellets, because the temperature cannot be too high, the heating system is suitable for heating with water The cooling system and the water heating system can share a group of water pipes to reduce investment If the moisture in the pellets is water, the condenser may not be used in the equipment; if there is not much dust, the dust remover can be simply replaced by a buffer tank For the double cone rotary vacuum dryer body, the cone jacket is wrapped with an insulating layer to reduce the room temperature The heating water in the jacket firstly transfers the heat to the inner wall of the cylinder, and then the inner wall transfers the heat to the pellets contacting with the cylinder wall, and the wet steam produced is extracted by the vacuum extraction pipe While the cone is rotating, the pellets roll continuously in the cylinder body, and get full mixing The material out is very even in water and color The example of the application of double cone rotary vacuum dryer in the drying of pellets is taking a pellet drying operation as an example The parameters of the pellet are: dry material density 0.70g/cm3, initial moisture content 15%, final moisture content 2% ~ 3%; double cone rotary vacuum dryer parameters: Volume 500L, rotating speed 4 ~ 6R / min; heating temperature: water heating, below 100 ℃ Put pellets into the double cone pot, and the charging amount shall be controlled below 50% (or the material surface shall not be higher than the horizontal pipe position of the air extraction pipe) Close the lid, start to rotate the double cone body, adjust the rotation speed to 4-6r / min, the pellets flow in the double cone body, and get full mixing However, pellet drying can not be steam heated like other materials for two reasons: first, the high temperature of steam will affect the performance of materials; The second is to directly heat the material at high temperature, and the moisture in the pellets will quickly migrate to the surface The moisture on the surface is too late to vaporize, which causes the pellets to adhere to each other, unable to flow, and easy to form caking The whole wall of the pot will also be stuck with a thick layer of powder, unable to conduct heat Therefore, the heating effect of water is better According to the characteristics of the material, select an initial water temperature, then slowly raise the temperature, and vacuum the inside of the double cone boiler body The water generated in the boiler body should be discharged in time, or it will agglomerate The drying of pellets can be divided into four stages: the first stage is the initial stage, and the materials are gradually heated up Because the vaporization temperature has not been reached, the water on the surface of pellets vaporizes little and the drying is slow; when the material temperature reaches the vaporization temperature, it is called the second stage, when the water vaporizes in large amount, the drying speed is fast, the temperature rise will become less obvious and the vacuum degree will drop Strictly speaking, the vaporization temperature in this stage can not be a point, it should be said to be a small range Because the material is always in the heating state, vaporization will take away a lot of heat, both of which will cause the temperature fluctuation, and vaporization will cause the change of vacuum degree, which in turn will cause the change of vaporization temperature, which is a dynamic process If the reading of the vacuum gauge fluctuates at about 0.093mpa, the vaporization temperature will fluctuate at about 40 ℃; in the third stage, as the moisture content of the pellets becomes less, the moisture transferred to the surface becomes less, the material temperature rises obviously, the vacuum degree rises again, and the drying speed becomes slower and slower; in the fourth stage, when the moisture content of the pellets reaches the set requirements, the materials should be cooled Turn off the heating system, put tap water into the jacket, cool the pellets and prepare for discharging Conclusion this paper starts with the advantages and working principle of vacuum drying, discusses the factors that affect the drying speed, and expounds the application of double cone vacuum drying equipment in the field of pellet drying combined with the practical application of the company.
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