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Key words: Chinese medicine pellets; microwave drying mechanism; drying process; equipment application Chinese herbal medicine pellet production, history has always used the form of manual pan-made pellets, since the emergence of mechanism pills (plastic pellets) in the 1970s, mechanism pills With its uniform size, the diameter of the pill, the weight of the pill is easy to control, and the output is large, it is quickly promoted. At the same time, the Chinese medicine mechanism pill has the ability to be quantitatively weighed, and is in line with the internationally accepted mode of administration. It has the advantages of easy packaging, easy storage, and easy portability, so its development prospect is very broad.
The Chinese medicine pill has a size of a pill, a single pill weighing more than 0.5g, and a pill with a weight below 0.5g. Including water pills, water pill, concentrated pills, honey pills, paste pills, Tibetan pills and so on. For the commonly used pellets, the working principle of the pelletizing machine is to mix the ingredients according to the composition and proportion, and to refine the processed materials through the inner flap of the silo and the screw propeller, and extrude into a round strip. After passing through the stripper, the pellets are cut into pellets and pelletized at high speed. For Da Mi Wan, the above principle also applies. A considerable number of them are also manufactured using a three-roll or five-roll honey pill machine, and the principle is similar to the above.
The main technical requirements of Chinese medicine pellets: (1) The mechanism pellets must be uniform in size, the shape of the pellets is round, and the surface light; (2) there are no double pellets, flat pellets, short cylindrical pellets, large and small pellets, small tails, and Defects such as mouth; (3) Pill weight meets the process requirements.
The process requirements for the drying of small pills: (1) can reach the index of water content after drying; (2) uniform drying, the time limit of disintegration meets the requirements of the Pharmacopoeia; (3) meet the production requirements; (4) consider energy conservation and environmental protection.
The traditional Chinese medicine pellets have traditionally been oven-dried (except for the big honey pill), and then stored separately. At present, there are still many factories in use for this process and equipment. Some manufacturers use vacuum freeze dryers, far infrared dryers, boiling dryers, etc. in the drying equipment of Chinese medicines. These drying equipments account for 40% of the dry production of pills.
In the past 10 years of pill drying, domestically, the microwave drying method and equipment have made great progress, and it has also been recognized by the majority of pharmaceutical companies. In the pharmaceutical machinery industry, microwave drying, microwave sterilization, microwave extraction and other equipment have been introduced, which have shown irreplaceable advantages in improving drug quality, energy conservation, safety and environmental protection.
1 Introduction to Microwave Drying 1.1 Mechanism of Microwave Drying Microwave drying is the use of microwaves to interact with matter molecules in rapidly changing high-frequency electromagnetic fields. Microwaves are absorbed to generate thermal effects, and electromagnetic energy is directly converted into medium heat energy to achieve drying. .
Microwave heating is a type of radiant heating that is carried out under the radiation field of a waveguide, cavity or microwave generator antenna. It is the direct interaction between the microwave and the object, so that the material is heated inside and outside at the same time, without transferring heat through convection or conduction.
Since the microwave energy is directly absorbed by the moisture, the penetration of the microwave electric field to the material, the moisture inside the material and the surface can be simultaneously heated by the microwave, so that the heating is uniform, and the sterilization has the effect of sterilization and insecticide.
1.2 Tunnel type microwave drying equipment When tunnel microwave drying equipment is operated, microwaves are first generated by the microwave generator, and the microwave heater is input through the energy feeding device. The material is sent to the heater by the transmission system. At this time, the moisture in the material is in the microwave energy. Under the action of temperature evaporation, water vapor is discharged through the dehumidification system to achieve the purpose of drying. The bacteria in the material are killed by the biological and thermal effects produced by the microwave electromagnetic field.
2 Advantages of Microwave Drying Chinese Medicine Pellets From the water content before the current pill drying, most of them are between 20% and 40%, such as water pill, water pill, and concentrated pill. After drying, the water content is generally required to be 4%. Between 9% (also about 12%). This water content is very suitable for drying with microwaves.
Since microwave drying is converted from electric energy into heat energy, the microwave energy is directly absorbed by the water, and the moisture inside and inside the material is simultaneously heated by the microwave, and it is not necessary to preheat like the heat conduction heating method. At the same time, the direction of heat conduction is consistent with the direction of wet molecular conduction, which greatly increases the drying rate of the material. Since the heat in the heating is directly derived from the inside of the dried product, the microwave heating device itself does not consume heat, and the thermal efficiency can reach 80% or more. According to the actual test, in the tunnel microwave equipment, only 1.43 kW·h of electric energy is consumed for every 1 kg of water evaporated. These factors allow the microwave-dried pill to fully meet the moisture requirements after drying.
Due to the microwave heating and drying, it is heated and dried from the inside of the material, and has automatic balance performance. Its volumetric thermal effect will result in uniform heating, avoiding large temperature gradients in conventional heating systems. This is of greater significance for materials that are prone to surface hardening during conventional heat drying.
According to the Pharmacopoeia regulations on the time limit for disintegration, the Chinese medicine Xiaomiwan, Shuimi Pill and Water Pill should be dissolved in 1H; the concentrated pill should be dissolved in 2h. After microwave drying, we can get some of the reactions we expect, such as fine puffing of the pill, so that the disintegration time limit can be greatly shortened.
At the same time, in the drying process, due to high thermal efficiency and short heating time, the surface temperature does not become very high, and the biological effect of electromagnetic waves can kill bacteria at a lower temperature. Therefore, the color, taste, and organic components of the product are not damaged.
3 microwave drying uniformity requires microwave to be a dielectric heating method. In the processing of material heating uniformity, it is necessary to fully consider the arrangement of the microwave feed port and the waveguide deployment by means of calculation, experiment and computer simulation. At the same time, there are more standardized requirements for the form of cloth.
3.1 Distribution of the feed port The distribution of the feed port is not only perpendicular to each other, but also distributed in a star shape. The purpose is to make the microwave in the heating cavity form a resonance in multiple modes. Because in a heating box, the more modes the microwave forms, the more uniform the heating. However, the number of formation modes is related to the size of the cavity, the shape of the cavity, the position and number of the kneading ports, the thickness of the material to be laid, and the water content. In general, the heated materials in the same plane have the opportunity to obtain uniform illumination of the microwaves in equal time. The arrangement of the feed port is shown in Figure 1. Taking the tunnel type microwave drying equipment as an example, the arrangement of the feed ports is not the same in each heating box in the entire tunnel heating box.
3.2 Cloth 3.2.1 Fabric Requirements The traditional Chinese medicine pellets that have just been prepared usually have a large humidity or viscosity. Taking tunnel microwave drying equipment as an example, when feeding materials, it is required to evenly lay the pills on the conveyor belt. Because the thickness of the laid pills is uniform, the density of the edges and the middle is uniform, and the uniformity of drying is guaranteed.
Uniform density (thickness) between the edges and the middle means that the microwave drying is selective. The local material is thick, the relative humidity is large, the absorption capacity for microwave is large, the temperature at this place rises rapidly, and the difference with the thin place may cause uneven drying.
3.2.2 Fabric Thickness (1) After the microwave enters the material, the material absorbs the microwave energy and converts it into heat energy. The field strength and power of the microwave are continuously attenuated, that is, the microwave will penetrate into the decay state after being penetrated into the material.
The absorption and attenuation capacities of different materials for microwave energy are different, depending on the dielectric properties of the materials. The attenuation state determines the penetration ability of the microwave to the medium. When the microwave enters the material, the energy density of the surface of the material is large. As the microwave penetrates into the material, its energy is exponentially attenuated, and the energy of the microwave is released to the material.
The penetration depth can indicate the amount of attenuation of the material by microwave energy. Generally it has two definitions, and only one of them is used in this article. The penetration depth is the distance at which the microwave power decays from the surface of the material to 1/e (36.8%) of the surface value, denoted by De:
Where e is the natural logarithmic base value;
Λ0——free space wavelength;
Εr——dielectric constant;
Tgδ - dielectric loss.
(2) Since the pellet contains water, its relative dielectric constant is 80. At 2450 MHz, the depth of penetration of microwaves into water is 2.3 cm. Therefore, we should fully consider this factor when laying the pellets. Do not increase the thickness of the paving material only by considering the yield, and do not pursue the drying strength and reduce the feed amount.
4 Factors that restrict the drying of microwave drying In the microwave drying of tunnels, since the production of Chinese medicine pellets is continuous, after the power matching is achieved, the production requirements should be well met. The factors that restrict production are as follows:
4.1 The conveyor belt runs in the tunnel type microwave drying equipment, and the microwaves are modular long structures. At present, the domestically produced tunnel-type microwave equipment zui short heating box also has 3 sections, each section is 1m long, adding up to a total length of 6 to 7m, and the tunnel-type microwave equipment of Zui can reach more than tens of meters. The conveyor belt is a PTFE belt. When the conveyor belt is bonded into a ring shape, the joints are mostly hand-bonded, which makes it difficult to avoid the problem of conveyor belt deviation during the working process. The deviation of the conveyor belt will cause the pill to fall into the drying chamber, causing the burning of the drug, etc., which will seriously hinder the work, causing downtime and affecting production.
Since the bonding of the conveyor belt is done manually, the following conditions may occur during the adjustment process: (1) After the conveyor belt is closed into a ring shape, the side is slightly larger or smaller than the other side, and is bell-shaped; (2) The two drive rollers are not parallel between the horizontal and vertical planes; (3) the feed and discharge frames are not parallel.
4.1.1 Analysis of the normal deviation of transportation The experience of the company's production of microwave equipment for many years, the conveyor belt deviation type can be summarized into the following:
(1) Since the conveyor belt sticks into a bell mouth type or the horizontal direction of the front and rear rollers is not parallel, the conveyor belt will run away toward the small end, and this deviation is irreversible.
(2) The front and rear rollers are on the left side and the other side is on the right side: the front and rear rollers are in the shape of a diamond. Under the action of the tight belt, an axial force will occur, which is offset to one side, and this offset is also irreversible.
(3) Conveying belt back swinging offset: This situation generally belongs to the fact that the conveyor belt sticks into a horn type and the drum is not parallel in the vertical plane. When the conveyor belt runs to one side due to the horn, it can't run any more than the drum Zui, forcing it to run in the opposite direction, so that it runs back and forth, forming a swing form.
(4) The pleats in the middle, such cases are generally rare, belonging to the conveyor belt in the middle of the roller, or the middle of the depression, resulting in the pleats, and the pleats are prone to tearing.
(5) The deviation caused by the operation. When the microwave equipment conveyor belt is partially installed and debugged to the zui state, the working condition is very stable. After a period of operation, some materials fall into the nip between the drum and the conveyor belt, and stick to the surface of the drum. When pasted to a certain amount, the geometry of the surface of the drum changes significantly, resulting in a very stable conveyor belt having to run. Partial phenomenon. In addition, the material contains oily, sugary, dilute and other viscous substances, which penetrate into the surface of the drum, causing the belt to rub while being slipped.
4.1.2 Solution of conveyor belt deviation The conveyor belt deviation is plagued by users and equipment manufacturers. Because manual adjustment of the correction is not only time-consuming, but also difficult to adjust in place. In view of the deviation of the microwave conveyor belt, we have successfully solved this problem by using photoelectric switches and pneumatic devices. Specifically, there are two types: mandatory and non-mandatory:
(1) Mandatory solutions. Mandatory correction of the deviation is also called hard correction. The solutions are as follows: 1) Add a guide bar on the conveyor belt and add a guide groove on the drum. The conveyor belt guide bar forcibly pulls the conveyor belt in the roller guide groove, and does not exceed the rated range; 2) Pneumatic automatic deviation correction: When the conveyor belt runs out a certain distance, the photoelectric probe receives the signal and sends it to the correcting mechanism to make the cylinder piston Movement, pushing the two drive rollers to keep parallel, so that the conveyor belt runs back in the opposite direction, achieving the purpose of smooth work.
(2) Non-mandatory solutions. Mainly: 1) by adjusting the screw to adjust the parallelism between the rollers; 2) adding the sealing member of the material to prevent the material from falling into the heating box.
After various corrective measures have been taken on the conveyor belt, the equipment can be operated normally to meet the production requirements.
4.2 Other factors (1) Cooling system cycle failure. Since the magnetron does not operate normally, the input power is reduced, so the drying speed becomes slow. Since the magnetron has two cooling methods, namely air cooling and water cooling. In the work of air-cooled magnetron, it is necessary to check the reliability of the fan operation frequently, so as to prevent the magnetron from being burnt out when the fan is not working. For the water-cooled magnetron, it is necessary to ensure circulation. The waterway is unimpeded, and there must be no fouling and water leakage in each pipeline. If the cooling is not good, the magnetron and other electronic components will be burned out.
(2) First, the microwave power is not changed and the moisture of the wet pellet is increased, and the second is that the actual input microwave power is reduced (also caused by the aging of the magnetron). During the microwave use of the tunnel, when the microwave power is working under full load, the microwave tube whose power is reduced due to aging of the magnetron should be inspected, and the new magnetron should be replaced in time.
The life of the magnetron can reach 5000 hours per day and the efficiency can reach over 90%. In the process of using microwave equipment, it should be strictly in accordance with the requirements of the use of magnetrons. When the magnetron is used for a considerable period of time, since the electrical components are all operated at high temperatures, an "aging" phenomenon occurs, resulting in a decrease in power. Do not blindly increase the output so that the microwave equipment does not stop working for a long time.
5 Equipment development of microwave drying Chinese medicine pellets 5.1 Tunnel type microwave equipment Tunnel type microwave equipment is suitable for continuous production. It is particularly worth noting that it does not affect the main components of Chinese medicine pills and decoction pieces, etc. after drying, and the drying speed Fast, uniform, low temperature, high drying efficiency, good product quality, good color and disintegration after processing. The application of such equipment has matured and corresponding industry standards have been established. Since the efficiency and environmental protection of this type of equipment have been recognized by the market, the development speed is relatively fast.
5.2 Multi-layer tunnel microwave dryer In order to improve the efficiency of microwave equipment, a multi-layer tunnel microwave dryer dedicated to pill drying was designed, as shown in Figure 2. The working process: after the upper layer of the dried pellets is run, it falls onto the conveyor belt of the lower layer, so that the material has an automatic rearrangement process on the belt, and is again heated by the microwave in the drying box, so that the cycle is repeated several times. The uniformity of the Chinese medicine pills after drying is better. At the same time, the bottom layer of the device is provided with a cooling layer, so that the temperature of the pill is close to room temperature. With the automatic correcting device of the conveyor belt, this type of equipment has been well used in major pharmaceutical companies.
5.3 Pill Drying for Small Batches The microwave oven is suitable for batch production. The dried drug is placed on a rotating disk in a dry box and dried by microwave radiation. The output of box microwave dryers is limited by the tray and power, but it is suitable for small batch production, or for pharmaceutical companies that need to change varieties frequently. Pills with special requirements, such as peppermint, borneol and valuable herbs containing heat-sensitive raw materials, biologically active biological products, and pills that require drying at low temperatures are more suitable after adding vacuum to the box microwave working chamber.
Generally speaking, at room temperature, a batch of pills is dried in an oven for 12 to 16 hours, while microwave vacuum drying requires 45 to 60 minutes, and the drying temperature is 60 to 70 ° C or even lower. The tunnel microwave dryer has a drying temperature of 70 to 90 ° C and a drying time of 30 to 45 minutes. Therefore, it is obvious that the pellet is dried by microwave.
Microwave vacuum drying technology is a transformation technology combining microwave technology with vacuum technology. It has a series of advantages of microwave drying and vacuum drying. It is more suitable for the low-temperature drying of traditional Chinese medicines and biological products, and also suitable for the drying of traditional Chinese medicine extracts.
6 Conclusion Microwave drying Whether vacuum microwave drying, atmospheric microwave drying or tunnel type single-layer or multi-layer dryer, etc., can be applied to program control, and its parameters are input into the program controller to be automated, thus simplifying the operation process. Especially the tunnel type microwave dryer can realize continuous production, which can greatly reduce labor intensity, improve production efficiency and facilitate production management. The production process, because there is no need to preheat or preheat, the power can be dried when the power is turned on. If the power is turned off, the heat source disappears immediately, so the operation is simple, easy to operate, control, and the production cycle is short.
In order to better serve us, we must understand the characteristics of microwaves in use. When drying materials, you should also pay attention to the following aspects: (1) materials of different traits, or the same kind of materials with different water content, should not be dried together; (2) different products have different quality standards, that is There are different water content requirements, according to the actual exploration of the drying curve suitable for the product, for later use; (3) for heat sensitive materials, or fat-containing materials, should consider vacuuming at low temperature; (4) For the drying of food and medicine, their process requirements and characteristics should be summarized separately and treated differently.
It can be seen from the above comparison and analysis that the energy saving and high efficiency of the microwave drying equipment are more obvious. At the same time, it is also an environmentally friendly device, which is the development direction of drying equipment for Chinese medicine pellets.
Analysis of Chinese medicine pellets microwave drying process equipment
Abstract: From the drying of traditional Chinese medicine pellets, the microwave drying method and process of Chinese medicine pellets were analyzed. Some problems appeared in the application of equipment, and some suggestions were given for the microwave drying Chinese medicine pellets, pointing out the design of microwave drying equipment. Some key points that should be considered in terms of aspects.