Popular Science: Common Types of Dryers and Working Principles of Dryers

- May 08, 2019 -

Dryers are generally divided into two types according to their uses: industrial dryers and civil dryers. In industry, dryers are also called dryers or drying equipment. The emergence of dryer has gone through many stages. With the technology of dryer becoming more and more mature, from drying a single material to now can basically meet the needs of all walks of life.

In the use of dryer, due to the different shapes and properties of the dried materials, the requirements for the dried products are also different. The appropriate drying methods and equipment should be selected according to the properties of the medicinal materials and the requirements of the products. Drying process involves almost all sectors of the national economy and is widely used in production and life. The purpose of drying is to remove water or solvents from some raw materials, semi-finished products and finished products so as to facilitate processing, use, transportation and storage. The general drying methods are mechanical method, chemical method and heating (freezing) method. These methods either have huge equipment, high drying costs, or slow drying speed and small processing capacity. With the development of science and technology, such as biological products, new materials (multi-phase composite materials, nano-materials, intelligent materials and biomedical materials), advanced ceramics, new advanced food and new pharmaceutical products, the traditional drying technology and dryer are not necessarily suitable. Microwave drying technology and microwave dryer have been widely used in light industry, chemical materials industry, food and agricultural products processing industry, and show remarkable advantages. Microwave drying is undoubtedly a new technology to meet the requirements of new products. Microwave drying

< P > 1, microwave drying

< P > microwave drying is different from traditional drying method, and its heat conduction direction is the same as water diffusion direction. Compared with traditional drying methods, it has many advantages, such as high drying rate, energy saving, high production efficiency, uniform drying, clean production, easy to realize automatic control and improve product quality. Therefore, more and more attention has been paid to drying in various fields. As early as the 1960s, a lot of research on the application and theory of microwave drying technology has been carried out abroad, and it has been further developed in recent decades. The research of microwave drying technology in our country started late, and there is a certain gap compared with foreign countries, but it has also made good achievements, and there are many research and application results. Microwave drying technology in China has been used in food industry, material chemical industry, pharmaceutical industry, mineral mining industry, ceramic industry, laboratory analysis, wet natural rubber processing and so on. Drying at atmospheric pressure

< P > 2, drying at atmospheric pressure

< P > I, drying means that the material is placed in a drying plate under atmospheric pressure and dried by hot air. Drying equipment is oven and drying room. Because the material is in a static state, the drying speed is slow. This method is suitable for drying hot and stable wet solid materials, such as medicinal materials, solid powder, wet particles and pellets. In order to speed up the drying process, the materials in the drying tray should not be too thick to be accumulated. It is necessary to cooperate with turning over materials and remove the wet air in time. Drum drying is also called drum drying or drum film drying. The material is coated on the heated metal drum and dried by means of heat conduction. The dried product is thin and easy to crush. This method can be continuously produced and is suitable for the drying of Chinese herbal extracts and the preparation of film agents. The drying equipment includes single drum type and double drum type film dryer.

III. Belt drying refers to the method of drying wet materials by placing them on conveyor belts and heating them with hot and dry air flow or infrared ray. This method is often used for drying Chinese herbal slices and tea preparations.

P>3, vacuum drying

P>also known as vacuum drying. It refers to a method of putting materials in a drying tray, vacuum pumping in an airtight drying box and heating and drying. It is an intermittent operation. Its characteristics are: low drying temperature, fast speed; reduced material and air contact opportunities, can reduce drug pollution or oxidative deterioration; the product is crisp sponge, easy to crush. This method is suitable for the drying of thick extracts and oxidizable materials at high temperature or heat sensitivity. In vacuum drying of thick extract, the quantity of plate, vacuum degree and heating steam pressure should be well controlled so as to avoid material blistering and overflowing, resulting in waste and pollution. The drying equipment is vacuum drying box. Fluidized bed drying

4, fluidized bed drying

I, boiling drying is also called fluidized bed drying. The hot air passes through the drying chamber at a certain speed, and the wet material is dried in a suspended fluidized state in the hot air stream. The contact area between material and air flow is large, which strengthens heat and mass transfer. The drying speed is fast and the product quality is good. This method can be used for continuous production of wet granular materials, such as wet granules and pellets, but not for materials with high moisture content and easy to bond into pellets. There are vertical and horizontal boiling drying equipment. At present, horizontal boiling dryer is widely used.

II and spray drying spray the drug solution or suspension into the drying chamber by nebulizer. The droplets are heat exchanged with the hot air stream in the drying chamber, and the dry powder or fine particles are obtained after evaporation of the solvent. After the atomization, the surface area is increased, the heat and mass transfer is fast, and the drying speed is very fast. It usually takes only a few seconds. Therefore, spray drying has the characteristics of instant drying, especially for the liquid containing thermosensitive ingredients. The method can be continuously produced, and the dried product is loose powder or fine particle with good solubility. Spray drying is one of the best drying technologies in traditional Chinese medicine. Drying equipment is spray dryer.

< P > 5, infrared drying

< P > is a method of drying objects by using infrared radiator to irradiate them. When the infrared emission frequency matches the molecular motion frequency in the material, it will cause the strong vibration and rotation of the material molecules, and the fierce collision and friction between the molecules will generate heat, which will vaporize the water in the material. Because the infrared absorption spectra of materials are mostly distributed in the far infrared region, the drying efficiency of far infrared is higher than that of near infrared. Because the material is heated rapidly and uniformly, and the drying speed is fast, it is suitable for drying of heat-sensitive solid materials and surface drying of some objects. The drying equipment includes vibration far infrared dryer and tunnel infrared dryer. Freeze-drying

6, freeze-drying

will first cool the dried liquid material below freezing point, freeze it into solid state, and then sublimate the ice to water vapor under vacuum conditions to get the dried product, also known as sublimation drying. The characteristics of this method are: materials are dried under high vacuum and low temperature, especially for thermosensitive materials (such as serum, antibiotics and other biological products); porous products are easy to dissolve; low water content is conducive to long-term storage of drugs. Freeze drying can be used to prepare sterile powder for injection. But the equipment investment is large and the production cost is high. The drying equipment is freeze dryer.

for the choice of dryer must be careful, once the machine failure, production will not be able to proceed normally, which is very distressing for enterprises.

Henan Microwave Equipment Liability Co., Ltd. focuses on microwave drying equipment, microwave official website:

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