Conduction heating dryer


1. Vacuum Dryer Vacuum Dryer is a conductive heat transfer dryer. The material is not directly in contact with the heating medium, and is suitable for drying a small amount of mud-like or paste-like materials which are not resistant to high temperature and easy to be oxidized, and the water content is 15% to 90%. The blades of the horizontal jaw mixer in the dryer are made of cast iron or steel and are mounted on a square shaft with half of the blades to the left and the other half to the right. The shaft speed is 7~8r/min, which is driven by the motor with gearbox. At the same time, the automatic steering device is adopted to change the rotation direction of the shaft and change the rotation direction of the agitator every 5~8 minutes.
In operation, first start the agitator, add the dried material, and close the feed port. At the same time, it is heated by steam, and the pressure of heating steam is generally 0.2~0.4Mpa (gauge pressure). The water vapor and the non-condensable gas are extracted by a vacuum pump, and when the material is generally dried, the degree of vacuum is about 700 mmHg. The moisture evaporation intensity of such a dryer varies depending on the nature of the material, humidity, heating steam pressure, and degree of vacuum. For example, when the degree of vacuum is 700 mmHg and the heating steam pressure is 0.2 MPa (gauge pressure), the potato starch is dried from 40% to 20% of the initial moisture, and the water evaporation intensity of the dryer is 5-7 kg/m2?h.
The operation of the vacuum sputum dryer is lower than the labor intensity of the box dryer, and the useful moisture content in the material can be recovered, the operating conditions are good, and the management is convenient. The disadvantage is that the production capacity is low, the structure of the device is relatively complicated, and the blades of the agitator are easily damaged. Such dryers are used more in the dye and pharmaceutical industries. For example, drying of a vat dye intermediate, an oxime sulfonic acid, a reduced olive green R, a salicylic acid intermediate, a Kupron polymer, a diamino hydrazine, and the like. Vacuum 干燥 dryer machine structure.
Second, the plate dryer (a) Foreword plate dryer, also known as the tray dryer, was introduced in the dry monograph published in Japan in the early years. In recent years, China's Shanghai, Shijiazhuang and other places have been successfully developed. It is a multi-layer fixed hollow heating disc (also known as a loading tray), which is developed on the basis of intermittently stirring and conducting the dryer, and has been comprehensively improved. Conductive-based drying unit.
The drying process is to pass the heat carrier into the hollow disks of each layer, and indirectly heat the wet material contacted on the disk surface by means of heat conduction, and the wetness of the continuously moving material under the mechanical action of the rotary blade The fraction is evaporated at the operating temperature and its vapor is withdrawn from the plant exhaust to continuously obtain a qualified dry product at the bottom of the equipment.
Plate dryers have been in development for decades. In recent years, many countries have applied it to the fields of chemicals, dyes, pesticides, plastics, medicine and food, and have continuously improved and improved in use. Compared with traditional drying equipment, it has the advantages of high thermal efficiency, energy saving, uniform drying, good product quality, small footprint, less auxiliary equipment, less pollution, continuous production, convenient operation and wide application range. Therefore, it has broad prospects for development in drying technology, which has attracted more and more people's attention and research. Equipment types and specifications have been serialized, industrialized and large-scale, and have been developed into an industrial drying device.
(II) Equipment structure and operation mechanism Now only one of the types is taken as an example to illustrate its structure and operation principle. The equipment is mainly composed of a cylinder body and a frame, a hollow hollow heating plate, a main shaft, a cross arm and a rakes blade, a disc feeder, a hopper tray and a finished product outlet, an exhaust gas outlet, a heat carrier inlet and outlet pipe, an inspection door, a worm wheel reducer, A continuously variable transmission and a motor. The main component of the equipment is a hollow heating plate, and the hollow part is welded with a baffle plate to strengthen, which not only increases the rigidity and strength, but also improves the heat transfer effect, and exerts the advantage of high utilization rate of conduction drying heat energy. There are heat carrier inlet and outlet pipes on each layer of heating plate. Generally, the upper layers are made of low-pressure saturated steam or hot water, hot oil in series, parallel or series-parallel input heating to control the temperature of each layer; and the bottom two layers are connected to cooling water. To reduce product temperature, recover heat and ensure quality. The heating plate is fixed on the frame of the cylinder at a certain interval, and is placed horizontally. Each layer is equipped with a cross arm frame, and the upper and lower layers are staggered and fixed at 45° on the central spindle, and the worm wheel reducer and the continuously variable transmission are arranged. And the motor and other drives, slowly rotate at 0.6~3.7 (r/min). Each of the booms is provided with a plurality of detachable hoe-shaped rakes or flat squeegees arranged equidistantly. The 耙 leaf adopts hinged and reed oscillating structure, so that the bottom edge floats evenly on the disk surface, and the angle of the 耙 leaf can be adjusted arbitrarily according to the material properties to ensure that the material is continuously advancing on the disk surface.
The material to be dried is continuously fed from the top disc feeder to the inner ring surface of the small heating plate on the top of the machine. Under the mechanical action of the rotary rakes, while tumbling and stirring, the product is continuously moved forward from the inside to the outside. It is zigzag covered on the entire surface of the plate and heated by contact; then the material falls from the outer edge to the outer surface of the outer layer of the second heating plate below, and is moved from the outside to the inside under the action of the reversely mounted raft leaves. The inner edge falls to the inner ring surface of the third heating plate. By analogy, the materials are moved layer by layer from top to bottom, and are continuously heated and dried. The evaporated moisture is mixed with the exhaust gas in the equipment and naturally discharged from the upper outlet. The final dry material of the Zui falls onto the lower tray, and is continuously discharged from the raking blade to the bottom discharge opening to obtain a qualified dry product.
According to product performance, drying requirements and processing capacity, the plate dryer adopts a series of steps such as stepless speed regulation of the spindle, manual adjustment of the height of the disc feeder to adjust the height of the heating plate, control of the temperature distribution of each layer of the heating plate, and final cooling and cooling. The superior performance of the plate dryer.
Third, hollow blade dryer (blade dryer)
(I) Overview of the paddle dryer As early as in the 1970s, the development of the paddle dryer was carried out by the unit. The technical conditions and the designed hot shaft structure were too complicated, so they stopped halfway. With the reform and opening up of China and the continuous introduction of foreign equipment, the domestic information in this area has been increasing. Therefore, some units in China have developed it, and a series of models have been formed.
The paddle dryer is a horizontal agitating dryer with heat conduction. Because the agitating blade is shaped like a paddle, the solid is called a paddle dryer, and the foreign is also called a trough dryer or a stirring dryer. The paddle dryer has been developed abroad for many years. At present, this model is represented by Nara Machinery Co., Ltd. of Japan Co., Ltd., and has developed two-axis and four-axis structures and more than 10 specifications.
The paddle dryer is a two-axis (or four-axis) horizontal mixing and drying device. Zui was developed by the former Federal Republic of Germany. After that, Japan introduced the technology and improved it. It has developed two-axis and four-axis structures and more than ten specifications. The heat required for the drying of the device is indirectly heated by heat conduction, so that the drying process does not require or require a small amount of gas to carry away the moisture. This greatly reduces the heat loss caused by the gas and improves the heat utilization rate. It is an energy-saving drying device. It is suitable for the drying of granules and powder materials, and can also be dried for paste materials.
(II) Equipment structure The double-shaft paddle dryer consists of a W-shaped shell with an end face with a jacket, an upper cover, two hollow shafts with blades, end caps at both ends, a rotary joint with a heat medium, and a metal soft The tube and the transmission mechanism including the gear and the sprocket are composed of components.
The core of the device is two hollow shafts and hollow mixing blades welded to the shaft. The blade shape is a wedge-shaped hollow semicircle, which can pass through the heating medium. In addition to stirring, it is also the heat transfer body of the equipment. The two main heat transfer sides of the blade are inclined. Therefore, when the material is in contact with the inclined surface, the particles will quickly slide away from the inclined surface to make the heat transfer. The surface is constantly updated to enhance heat transfer. A scraper is provided at the bottom of the triangle of the blade to scrape the material deposited on the bottom of the shell to prevent a dead angle.
The layout of the blade and the size of each part have certain requirements, and in addition to the blade in the feeding zone, drying zone and discharge zone, an auxiliary mechanism is also provided to ensure stable operation and uniform drying. In addition, the residence time can also be adjusted.
The heating medium of the device can be either steam or hot oil or hot water, but the heat carrier has different phase states, and the hollow shaft structure is also different. When heated by steam, the hot shaft has a simple structure; when heated with hot water, the shaft structure is complicated, especially when it is necessary to consider the flow rate of the liquid in the tube.
Large paddle drying equipment has a shaft diameter of about 500 mm, so sealing is a big problem. In the 1970s and 1980s, the sealing problems of the shafts were not well solved. In the operation, solid powders often leaked to the two end caps. Therefore, a discharge opening is usually provided at the bottom of the end cap to periodically remove the material from the end cap. This not only causes inconvenience to the operation, but also increases the wear of the shaft due to the leakage of dust, which affects the life of the equipment. In addition, for flammable and explosive gases, it is often necessary to provide a reverse blower at the seal to prevent leakage of flammable and explosive gases. For the sealing problem of large shafts, foreign countries have been better solved in recent years. There is basically no accumulation of material at the end cover, and there is no need for regular cleaning and back blowing.
(3) Equipment performance and characteristics 1. It can be known from the structure of the equipment that the heat required for drying is indirectly heated by the jacket and the wall surface of the blade. Therefore, the drying process can use no or only a small amount of gas to carry the moisture fraction of the material evaporation, and the heat utilization rate can reach 80% to 90%.
2. The heat transfer surface of the device is composed of two parts: a blade and a wall surface, wherein the heat transfer surface of the blade occupies a large part, so the device has a compact structure, a large heat transfer surface per unit volume, and a small floor space, which can save investment costs.
3. The drying process uses less gas, has a lower flow rate, and less dust is carried away by the gas. Therefore, the gas dust is easily recovered after drying, and the recycling equipment is simple, saving equipment investment. For the drying process with solvent recovery, the solvent concentration in the gas can be increased, the solvent recovery equipment can be reduced or the process can be shortened.
4. Due to the special structure of the blade, the material is alternately squeezed and relaxed during the drying process, enhancing the drying. In addition, when the two blades are reversely rotated in a staggered manner, they have a self-cleaning action, and thus can be applied to viscous and paste materials.
5. The material retention rate in the dryer is very high, and the residence time is adjusted by the feeding rate, the rotation speed, the storage amount, etc., and is arbitrarily selected between several minutes and several hours, so that it is suitable for materials that are easy to dry and difficult to dry. In addition, although there are many stirring blades in the dryer, the material flows in the plug from the feeding port to the discharging port in the dryer, and the residence time is narrow, so the product is evenly dried.
In addition, the mixing and mixing make the material violently turn, thereby obtaining a high heat transfer coefficient, generally reaching 120-350 W/m2k, so the floor space and space are small, saving the capital cost of the plant. The amount of gas used in the drying process is small, the flow rate is low, and the amount of dust carried away by the gas is small, so that the gas dust is easily recovered after drying, and the recycling equipment is small in size, which can save equipment investment. For a drying process that requires recovery of the solvent, the solvent concentration can be greatly increased.
The disadvantage of the paddle dryer is that the structure is complicated, the processing is difficult, and the design of the large dryer is difficult.
(3) Dry materials such as alcohol slag, oxytetracycline slag, erythromycin slag, fly ash, skin powder, clay, kaolin, phosphogypsum, red gypsum, iron oxide yellow, magnesium trisilicate, Alumina, H acid, mycelium, nitroaniline, sodium cyanide, chlordane, indigo, ASN resin, 1010 antioxidant, DM accelerator, and the like.
4. Roller Scraper Dryer The drum scraper dryer is a continuous operation device for drying liquid material or strip material attached to the outer wall of the cylinder by means of a rotating cylinder by means of heat conduction. The liquid to be dried is flowed from the high level tank into the receiving tank of the drum dryer. The drying drum is driven by the transmission and rotates at a specified speed. The material is formed by a film coating device to form a film on the wall surface of the drum. The cylinder is continuously fed into the heating medium to heat the cylinder body, and the moisture of the film is vaporized by the heat transfer of the cylinder wall, and then the material that meets the drying requirement is scraped off by a scraper, and is spirally conveyed into the storage tank for packaging. The moisture removed by evaporation, depending on its nature, can be introduced into the corresponding treatment device through a closed hood; typically water vapor, which can be directly discharged into the atmosphere by an exhaust pipe at the top of the hood.
The drum is an internal heating conduction rotating drying device of the dryer. The wet material obtains the heat transferred by the heat conduction method on the outer wall of the drum, removes the moisture, reaches the required moisture content, and the heat is transmitted from the inner wall of the cylinder to the outer wall of the cylinder, and then passes through. The film has high thermal efficiency and can be operated continuously, so it is widely used in the drying of liquid materials or strip materials, and is more suitable for paste and viscous materials.
The drum scraper dryer has the following features:
(1) High thermal efficiency The heat supplied in the cylinder, except for a small amount of heat radiation and heat loss of the end cover of the cylinder, most of the heat is used for moisture separation, and the thermal efficiency can be as high as 70~80%.
(2) Drying rate The heat transfer and mass transfer process of the wet film on the wall of the large cylinder, from the inside to the outside, the direction is the same, the temperature gradient is large, so that the surface of the film maintains a high evaporation intensity, generally up to 30~70kgH2O/ M2.h
(3) The dry quality of the product is stable. The heating mode of the drum is easy to control. The temperature inside the cylinder and the heat transfer rate of the partition wall can be kept relatively stable, so that the film can be dried under stable heat transfer conditions, and the quality of the product can be guaranteed.
(4) Wide application range The liquid material used for drum drying must have fluidity, adhesion and stability to heat. The form of the material may be a solution, a heterogeneous suspension, an emulsion, a sol or the like. It can also be used for belt materials such as pulp, textiles and celluloid.
(5) The production capacity of a single machine is limited by the size of the cylinder. The dry area of ​​the drum dryer should not be too large. The dry area of ​​a single cylinder rarely exceeds 12 m2. The ability of the same specification equipment to process the liquid is also affected by factors such as the nature of the liquid, the control of the moisture content, the thickness of the film, and the rotation speed of the drum. The variation range is large, generally 50~2000kg/h.
(6) Convenient heating medium Commonly used saturated water vapor, the pressure range is 2~6kgf/com2, rarely exceeding 8kgf/cm2. For some materials that require drying at low temperatures, hot water can be used as the heat medium; for materials to be dried at higher temperatures, heat medium or high-boiling organic matter can also be used as the heat medium.

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