1. Classicality of double cone rotary vacuum dryer
The double-cone rotary vacuum dryer is a widely used equipment for the production of raw materials. This is because during the vacuum drying process, the pressure inside the cylinder is always lower than the atmospheric pressure, the number of gas molecules is small, the density is low, and the oxygen content is low. The ability to dry the production of drugs that are susceptible to oxidative changes can reduce the chance of contamination of materials. Also, since the temperature of the water is proportional to the vapor pressure during the vaporization process, the moisture in the material can be vaporized at a low temperature during vacuum drying to achieve low temperature drying, and is particularly suitable for the production of heat sensitive materials in pharmaceuticals. At the same time, vacuum drying can eliminate the surface hardening phenomenon caused by atmospheric hot air drying. This is because the pressure difference between the vacuum drying material and the surface is large. Under the pressure gradient, the moisture quickly moves to the surface without surface hardening. In addition, when vacuum drying, the temperature gradient between the inside and the outside of the material is small, and the reverse osmosis allows the solvent to move and collect on its own, effectively overcoming the dispersion of the solvent generated by the hot air drying.
From a functional point of view, the double cone rotary vacuum dryer is a drying device that integrates mixing and vacuum drying. It is applied as a classic device with simplicity, convenience and double effect. It has a practical and economical side. It is difficult to replace Other equipment.
2. Discussion on improving the thinking of double cone rotary vacuum dryer
Although the double-cone rotary vacuum dryer is regarded as a classic, it has been diluted by pharmaceutical companies in recent years. The fundamental reason is that the manufacturer lacks research and structural improvements. It is difficult to optimize CIP/SIP and drying performance in structure, so it is necessary to discuss its improvement ideas.
2.1. Discussion on drying speed of double cone rotary vacuum dryer
2.1.1, the concept of vacuum drying speed
According to the literature 1 , the drying process of the material firstly causes the moisture on the surface of the material to be vaporized by heat and removed by the vacuum equipment. The moisture on the surface of the material is gradually reduced by vaporization, and a temperature difference is formed between the inside and the surface of the material. The internal moisture diffuses to the surface under the influence of the temperature difference and vaporizes after reaching the surface. In addition, during the vacuum drying process, there is a pressure difference at the same time, so that the vaporized water molecules accelerate toward the vacuum space. In the vacuum drying process, people always want to speed up the drying rate, shorten the drying time, but drying speed factor affecting 1 are the following:
(1) The condition of the material to be dried (such as material shape, size and size, stacking method), the moisture content, density, viscosity and other properties of the material itself. Generally, when the material particles are fine and uniform, the pile is loosened, and the thickness is thin, the internal moisture is easily diffused. If the initial temperature of the material is increased, the treatment before vacuum filtration, and the moisture content of the material are reduced, the vacuum drying speed can be increased.
(2) The higher the degree of vacuum, the more favorable the vaporization of water at a lower temperature, but the excessive vacuum is unfavorable for heat conduction, which will affect the heating effect on the material. In order to improve the drying speed of the material, the degree of vacuum should be considered comprehensively according to the characteristics of the material. Generally, the degree of vacuum should be not less than 1 × 10 4 Pa.
2.1.2 Factors Affecting Drying Speed ​​of Double Cone Rotary Vacuum Dryer
In the literature 1, the drying process of the double cone rotary vacuum dryer was tested. The vacuum, drying temperature, steam pressure and drying time were taken as parameters. The curve of the test showed that the drying process of the double cone rotary vacuum dryer can be divided into the first heating. The first constant temperature, the second warming, the second constant temperature and the cooling of the five classes. Among them: (1) The first temperature rise is a preheating stage in which the material is heated to raise the temperature. In this stage, the amount of water vaporization in the material is small; (2) The first constant temperature is a constant-speed drying stage in which the free water, surface water, and capillary water of the material are vaporized in a large amount. Therefore, the temperature and the vacuum are in a constant state, and the degree of vacuum is approximately equal to the saturated vapor pressure of the water at the drying temperature; (3) the second temperature rise is a process of heating the internal moisture of the material to the surface of the material, due to the small amount of vaporized water, resulting in The temperature rise and the true degree of the material also increase; (4) the second constant temperature is the stage of vaporized material enveloping water and part of the crystal water, and the dry water mobility is determined by the vaporization rate, so the temperature and vacuum are stable; At the beginning of the cooling phase, the heating steam is turned off, and the cooling water is passed to the jacket jacket, and the cylinder is cooled to lower the temperature of the internal material to discharge the dried product.
Table 1 Average drying process parameters of a product 1
stage | Time/min | Vacuum degree / MPa | Drying temperature / °C | Steam pressure / MPa | Saturated vapor pressure / MPa |
First heating First constant temperature Second heating Second constant temperature Cool down | 30 45 30 75 30 | 0.019 0.024 0.018 0.015 0.007 | 46 63 81 93 95~70 | 0.29 0.43 0.44 0.40 0 | 0.01 0.024 0.051 0.081 0.087~0.032 |
Now the average drying process parameters of a product (as shown in Table 1) are listed. It can be seen from Table 1 that the different stages of the drying process of the double cone rotary vacuum dryer have different properties, so different operating parameters should be set according to their different stages, so that the function of the equipment can be utilized more effectively. However, many operating parameters of a realistic double-cone rotary vacuum dryer are constant constant (such as rotational speed) or automatic control (such as working vacuum, drying temperature, etc.), and the following operating parameters for drying different stages of the process to vacuum drying speed The impact of the discussion and recommendations for improvement.
2.1.3. Influence of Rotating Speed ​​of Double Cone Rotary Vacuum Dryer on Vacuum Drying Speed ​​and Discussion
The faster the rotation speed of the double cone rotary vacuum dryer cylinder, the higher the drying speed. However, in the later stage of drying, as the moisture content of the material decreases, the drying speed also decreases. At this time, increasing the rotational speed is not beneficial to the improvement of the drying speed. In addition, in the early stage of drying, the faster rotation speed causes the moisture vaporization to be too fast and the material to bond into a mass. Therefore, a lower rotation speed should be used in the early stage of drying, and the rotation speed should be increased when the surface of the material is dry and not agglomerated, so as to accelerate the drying speed and shorten the drying time.
In this regard, it is recommended to use a variable frequency motor so that the rotation speed of the cylinder can be changed during operation, and a menu can be set to select different cylinder rotation speeds for different time periods (stepless speed regulation within 0~10 rpm) That is, there must be a time-speed relationship setting.
2.1.4. Influence of heating and cooling of double cone rotary vacuum dryer on vacuum drying speed and discussion
The convection heat transfer in the jacket of the double-cone rotary vacuum dryer needs to provide heat and cooling separately, so the jacket will experience the temperature rise by the hot steam method or the cooling by the cooling water method. According to the literature 1 , increasing the temperature of the heat medium can speed up the heating rate and shorten the drying time. For materials with high viscosity, the high temperature of the heat medium is prone to agglomeration. Lowering the cooling water temperature can speed up the cooling and shorten the duty cycle. As the nature of the material is different, an appropriate temperature can be selected, and it is preferred to use a variable temperature drying method, that is, the temperature is low at the initial stage of drying, and the temperature is gradually increased to increase the drying speed.
In this regard, it is recommended to use a temperature sensing element so that the heat or cooling control in the jacket of the double cone rotary vacuum dryer can be changed during operation, and a menu can be set to select the temperature for different time periods, that is, Time-temperature relationship setting.
2.1.5. Influence of vacuum degree on vacuum drying speed of double cone rotary vacuum dryer and discussion
Generally, the double cone rotary vacuum dryer adopts a vacuum degree of 1×10 3 -1×10 4 Pa, the vacuum degree is high, the moisture vaporization temperature in the material is low, and the drying speed is fast. However, if the degree of vacuum is too high, the cost of the pumping system will increase, and the price of the material will increase after drying, which is economically uneconomical. However, as shown in Table 1, the value of the vacuum in the cooling stage is small, so the pressure of the vacuum should be controlled in stages.
In this regard, it is recommended to use a pressure sensing element to make the vacuum control of the double cone rotary vacuum dryer cylinder change during operation, and a menu can be set to select the vacuum degree for different time periods, that is, to have time— The setting of the vacuum degree relationship.
2.1.6. Effect of cone angle and filling amount on vacuum drying speed of double cone rotary vacuum dryer
When the double cone rotary vacuum dryer barrel is stacked with granular or powdery materials, when the angle between the slope of the material pile and the bottom surface increases to a certain angle, the side material will fall down. At this time, the angle between the slope of the material falling off and the bottom is called the slip angle of the material (slip angle is related to material composition, moisture content, particle size and viscosity). Therefore, when the double cone rotary vacuum dryer design choice and should be selected based on the slip angle of the cone angle of a material.
Document 1 also considers that the ratio of the actual charge volume to the dry cylinder volume is the fill rate. The filling rate of the double cone rotary vacuum dryer is usually between 30% and 50%, which is also related to the bulk density of the material.
 It can be seen from the above that the angle of the cone of the double cone rotary vacuum dryer is too large or too small, which will affect the turning mixing effect, and the formed dry surface of the material finally affects the drying speed. Similarly, the actual filling volume filling rate will also affect the turning mixing effect, which affects the drying speed.
2.2. Discussion on the structure of double cone rotary vacuum dryer
Although the double cone rotary vacuum dryer has many practical advantages, its structural imperfections hinder its application and development. Especially for the production of aseptic bulk drugs, the imperfections of the equipment that have not been improved are: (1) leakage and cleaning problems of the dynamic and static seals of the vacuum tube empty sleeve rotary shaft; (2) cleaning of the cylinder structure Or sterilization problems; (3) easy to discharge and cleaning problems with the feed/discharge structure.
2.2.1. Discussion on leakage and cleaning of dynamic and static seals of vacuum tube empty sleeve rotary shaft
In the double-cone rotary vacuum shaft dryer, the double-frame shaft sealing structure is adopted. Due to the unreliable sealing of the structure, the leakage of the cylinder is easy to cause leakage, sometimes appearing. The so-called "oil leak" phenomenon. At the same time, because the seal is unreliable, the powder is stored during drying. The balance powder here is difficult to clean by the ordinary rotary dynamic water washing method, which causes cross-contamination during batch change.
Recently, some domestic manufacturers have made some improvements, and some use special seals (such as special mechanical seals, magnetic fluid seals, etc.). Some manufacturers 2 have improved the structure of the vacuum so that the vacuumed part does not protrude into the inside of the cylinder, and only contacts the outside of the rotating cylinder. The metal sintered mesh is used as a filter, which is easy to clean and easy to disinfect and sterilize. It is equipped with a system that uses high-purity nitrogen backflush to prevent dust particles from clogging the filter mesh and ensuring a smooth vacuum.
2.2.2 Discussion on the cleaning and sterilization of the barrel structure
In the cleaning of the cylinder of the partial double-cone rotary vacuum dryer, some of them are switched by the vacuum line, and the cleaning water is rotated to rotate the cylinder, so that the dynamic cleaning method cannot be completely washed, at least in the static and dynamic contact surface and the knot. The material is not washed.
Secondly, some manufacturers did not design and manufacture the cylinder as a pressure vessel. It is difficult to switch the vacuum line to steam to sterilize, so it is impossible to sterilize the steam in place. This of course involves the feed/discharge structure and the sealing structure, the form and pressure properties of which are also related to steam sterilization. The most important requirement for the use of equipment in a sterile environment is sterilization after cleaning. The most effective and direct method of sterilization is usually wet heat and dry heat sterilization. The barrel structure is not removable based on the equipment. It cannot be dry heat sterilized and can only be sterilized by moist heat (steam).
In this regard, it is said that it is easy to clean and sterilize, as long as it can be carried out around this topic. Recently, some manufacturers in the country have made some improvements. In terms of cleaning, the method of switching the vacuum line and putting the pressurized washing water to rotate the cylinder and then releasing the net, although improved, is not very effective. . In terms of sterilization, some manufacturers consider the pressure bearing property in the manufacture of the cylinder and the material valve, and it is also possible to complete the SIP by switching the vacuum line and introducing steam.
2.2.3. Discussion on the easy discharge and cleaning of the feed/discharge structure
 Although this problem is an extension of the above problems, the special requirements for feeding/discharging are easy to put out, easy to operate, easy to clean/detoxify. Some domestic manufacturers have adopted butterfly valves or detachable structures, and have achieved certain results. However, compared with GMP and corresponding process requirements, there are many articles to be developed here.
2.3, double cone rotary vacuum dryer to improve the point of thinking
As for the double-cone rotary vacuum dryer to be improved, there are many ideas that can be developed. The author feels that the following ideas can also be tried. Here are only thinking and suggestive ideas.
2.3.1, expand the function of the double cone rotary vacuum dryer to adapt to larger applications
(1) Increase the stirring and granulation function. A nozzle-equipped tube (which can spray the adhesive) can be inserted into the vacuum tube of the double-cone rotary vacuum dryer, and a vacuum mixing tube is added to the inside of the cylinder to add a fixed stirring blade. During the rotation of the cylinder, the agitating blades are fixed on the vacuuming tube to force the material to flow from both sides thereof, so that the radial movement is increased while the material slides along the cylinder wall. Therefore, the effect of mixing and agitating the material can be effectively improved, the moisture vaporization is accelerated, and the drying speed is improved. Thereafter, at the end of the powder material process, the powdery dry material can be formed into a granulated product by spraying a corresponding adhesive through a nozzle (a tube capable of spraying an adhesive).
(2) Increase the stirring and pulverizing function. Some domestic manufacturers use the crushing device 2 , which has four combined overall structures, which are arranged in a crisscross pattern, from short to long, and sequentially welded. The cutters adopt different lengths and different angles. Ensure that it can fully contact the material during rotation to ensure the crushing effect. In this way, the material is continuously turned in the double-cone rotary cylinder and exchanges heat with the cylinder wall (the outer half of the cylinder wall is heated by circulating hot water). When the double cone cylinder rotates, the crushing knife rotates at the same time. When the cylinder rotates once, the material contacts the crushing knife once. Since the speed of the crushing knife is relatively fast (up to 250 rpm) and the rotation speed of the cylinder is slow (generally 3 rpm), the crushing effect is very obvious whenever the material comes into contact with the cutter, and the cylinder system operates under vacuum.
2.3.2. Construct the concept of double cone rotary vacuum dryer system design to adapt to productivity improvement
If the double cone rotary vacuum dryer can be effectively used in production, it must be a system concept, in which the organic solvent recovery system is a key process. When supplying double-cone rotary vacuum dryer equipment, manufacturers should not only provide a single machine, but should provide a system. The recovery of organic solvents should be considered. Because the boiling point of the solvent is low, condensed cooling is used to ensure solvent recovery. Use to avoid contamination of the atmosphere after being pumped away by the vacuum pump.
2.3.3. Develop CIP/SIP structure to accommodate aseptic production
The CIP/SIP structure of the double cone rotary vacuum dryer should be changed to develop its structure. In addition to the ideas mentioned above, it can also be connected to the cylinder through a quick-open external spray cleaning device. Form a cleaning loop system. It is also conceivable that the cylinder of the entire double-cone rotary vacuum dryer can be disassembled (for example, a clamp-type square cone mixer structure), so that the entire cylinder can enter the cleaning station for cleaning and sterilization, which is of course too difficult. This point is also the basis for the upgrade of the double-cone rotary vacuum dryer, so that it can adapt to the production of aseptic grade.
3. Optimized combination of double cone rotary vacuum dryer
The optimized combination of the double-cone rotary vacuum dryer of a domestic manufacturer is shown in Figure 1. It is pumped by vacuum port 1, feed quick opening interface 2, explosion-proof box 3, spray device 4, and sintered mesh. Vacuum filter rod 5, inner liner, jacket and insulation material 6, quick-opening valve for single suction filtration, sintering net 8 for suction filtration, hot water inlet 9, hot water outlet 10, explosion-proof control panel 11, explosion-proof motor 12, The speed reducer 13, the pressure gauge 14, the stirring blade 15, the can body 16, the main shaft 17, and the base bracket 18 are composed of the like.
The double cone rotary vacuum dryer optimizes the combination equipment to use the tank rotation, static at different positions, and then equipped with a stirring blade, a sintered mesh vacuum filter rod and a suction mesh for suction filtration, and different combinations are used to complete the traditional reaction. Basic functions of crystallization, concentration, suction filtration, washing and drying equipment.
Our Calcium Channel Inhibitor products is good in quality and competitive in price.
We are manufacturer and supplier of Calcium Channel Inhibitor products following your specific requirement.
We are looking forward to your E-mail and establishing cooperative relationship with you.
We would provide professional Calcium Channel Inhibitor products with good services for you.
Calcium Channel Inhibitor
Manidipine Inhibitor, Ranolazine Inhibitor, Amlodipine Besylate Antagonists
Taizhou Crene Biotechnology Co., Ltd. , http://www.crenelab.com