Vacuum Harrow Dryer is a kind of conduction heat transfer dryer. The material is not in direct contact with the heating medium, suitable for drying a small amount of mud, paste-like materials that are not resistant to high temperature and easy to oxidize, with a moisture content of 15% to 90%. The blades of the horizontal rake stirrer in the dryer are made of cast iron or steel, mounted on the square shaft, with half of the blades oriented to the left and the other half to the right. The rotational speed of the shaft is 7~8r/min, which is driven by a motor with a gearbox. At the same time, an automatic steering device is used to change the direction of rotation of the shaft, and the direction of rotation of the agitator at intervals of 5~8min.

When operating, first start the stirrer, add the material to be dried, and close the feeding port. At the same time through the steam heating, heating steam pressure is generally 0.2~0.4Mpa

(table pressure). With a vacuum pump to pump out the water vapor and non-condensable gases, the general drying of materials, the vacuum degree is about 700mmHg. The dryer of the water evaporation intensity, with the nature of the material, humidity, heating steam pressure and vacuum degree of the different and so on. For example, in the vacuum degree of 700mmHg, heating steam pressure of 0.2Mpa

(table pressure), the potato starch from the initial moisture of 40% dry to 20%, the dryer's moisture evaporation intensity of 5~7 kg/m2?h.

Vacuum rake dryer operation than the box dryer labor intensity is low, can recover the useful moisture in the material, the operating condition is good, management is more convenient. Good, more convenient management. Its disadvantages are low production capacity, equipment structure is more complex, easy to damage the stirrer blades and so on. This kind of dryer is applied more in dyestuff and medicine industry. For example, drying of reduced dye intermediates, anthraquinone sulfonic acid, reduced olive green R, salicylic acid intermediates, capron polymer, diamino anthraquinone and other materials. Vacuum harrow dryer equipment structure.

Two, plate dryer

(I) Introduction

Plate dryer, also known as disk dryer, early in the drying monograph published in Japan has been introduced. In recent years, China's Shanghai, Shijiazhuang and other places have been developed successfully. Is in the intermittent stirring conduction dryer on the basis of a series of advanced technology, after continuous improvement and the development of a multi-layer fixed hollow heating disk (also known as loading disk), rotating rake stirring, vertical continuous conduction-based drying device.

This drying process, is the heat carrier into the layers of hollow disc, by means of heat conduction indirectly heating the wet material contacted on the surface of the disc, in the rotary rake leaves under the mechanical action, so that the wetness of the material is constantly moving in the operating temperature evaporation of steam with the equipment exhaust, so as to obtain the qualified drying of finished products at the bottom of the equipment continuously.

The development of plate dryer has a history of several decades. In recent years, many countries will be widely used in the chemical industry, dyes, pesticides, plastics, pharmaceuticals and food and other fields, in the use of continuous improvement. Compared with the traditional drying equipment, it has the advantages of high thermal efficiency, energy saving, uniform drying, good product quality, small footprint, less ancillary equipment, less pollution, continuous production, easy operation and wide range of applications. Therefore, it has a broad development prospect in drying technology, which has attracted more and more people's attention and research. Equipment type and specifications have been serialized, industrialized and large-scale, has developed into an industrial drying device.

(2) equipment structure and operation mechanism

Only one of the type as an example, to illustrate its structure and operation principle. The equipment mainly consists of cylinder and frame, size of the hollow heating plate, spindle, cross arm and rake leaves, disk feeder, the lower disk and finished product outlet, exhaust gas outlet, hot carrier import and export pipe, inspection door, worm gear reducer, stepless transmission and motor and so on. The main component of the equipment is hollow heating plate, the hollow part is welded with folding partition to strengthen, not only to increase the rigidity and strength, but also to improve the heat transfer effect, and give play to the advantages of high utilization rate of heat energy of conduction drying. Each layer of the heating plate are heat carrier import and export tube, generally the upper layers of low-pressure saturated steam or hot water, hot oil series, parallel or series-parallel input heating to control the temperature of each layer; and the bottom two layers of cooling water to reduce product temperature, heat recovery, to ensure quality. The heating plate is fixed on the cylinder frame at a certain spacing, placed horizontally, each layer is equipped with a cross armband, the upper and lower layers are staggered 45 ° staggered fixed in the center of the spindle, and by the worm gear reducer, stepless transmission and motor drive to 0.6 ~ 3.7 (r / min) slowly rotating. Each arm is equipped with a number of detachable plowshare-shaped harrow leaves or flat scrapers, arranged at equal intervals. The rake blade adopts hinged and reed swing structure, so that its bottom edge floats with even on the disk surface, and can be adjusted according to the material properties of the rake blade angle to ensure that the material is constantly pushed forward on the disk surface.

The material to be dried from the top of the disk feeder continuously added to the equipment on the top of the first layer of small heating plate on the inner circle of the disk, in the rotary rake leaves under the mechanical action, while tumbling and stirring, while from the inside to the outside and constantly moving forward, in a serrated shape all over the entire surface of the disk, to get in contact with the heating and drying; and then the material from the outer edge of the second layer of the heating plate below the outer circle of the disk, in the reverse installation of rake Under the action of the rake leaves, and from the outside to the inside of the order to move to the inner edge, falling to the third layer of small heating plate on the inner circle of the disk. And so on, so that the material layer by layer from top to bottom layer by layer to move, continuous heating and drying. The evaporated moisture is mixed with the exhaust gas in the equipment and discharged naturally from the upper outlet, and the final dry material falls onto the lower disk and is continuously discharged by the rake blade scraping to the bottom discharge port to obtain the qualified dry finished product.

According to the product performance, drying requirements and the size of the handling capacity, the plate dryer adopts a series of measures such as stepless speed regulation of the spindle, manual adjustment of the height of the disc feeder regulating sleeve, control of temperature distribution of each layer of the heating disk, cooling down at the end of cooling, etc., which gives play to the superior performance of the plate dryer.

Three, hollow paddle dryer (blade dryer)

(A) paddle dryer overview

As early as the seventies domestic units on the development of paddle dryer, limited to the technical conditions and the design of the hot shaft structure is excessively complex, and therefore stopped halfway. With China's reform and opening up, the continuous introduction of foreign equipment, the domestic information in this regard continues to increase, so the domestic unit of its development, has formed a series of models.

Paddle dryer is a kind of horizontal stirring type dryer which is mainly used for heat conduction. Because of the stirring blade shaped like a paddle, solid people called paddle dryer, also known as foreign tank dryer or stirring dryer. Paddle dryer has been developed abroad for many years, at present this model to Japan Nara Machinery Manufacturing Co., Ltd. as a representative, has developed a double-axis and four-axis structure, more than 10 specifications of the series of products.

Paddle dryer is a kind of horizontal stirring drying equipment with two (or four) axes. It was first successfully developed by the former Federal Republic of Germany, and then Japan introduced the technology and improved it, and developed a series of products with two structures of double-axis and four-axis and more than ten specifications. The heat required for drying relies on indirect heating by heat conduction, so the drying process does not need or only needs a small amount of gas to take away the moisture. This greatly reduces the part of heat loss taken away by the gas and improves the utilization rate of heat, which is a kind of energy-saving drying equipment. It is suitable for drying granular and powder materials, and it can also be used for drying paste materials.

(2) Equipment structure

The double shaft paddle dryer consists of W-shaped shell with jacketed end surface, upper cover, two hollow shafts with blades, two end caps, rotary joints with hot medium, metal hose and transmission mechanism including gears and sprockets.

The core of this equipment is two hollow shafts and hollow stirring paddles welded on the shafts. The shape of the paddles is wedge-shaped hollow semicircular, which can be passed through the heating medium. In addition to the role of stirring, but also the heat transfer body of the equipment, the paddle blade of the two main heat transfer side into a slant, so when the material and the slant contact, with the rotation of the blade, the particles quickly from the slant sliding away, so that the heat transfer surface is constantly updated to strengthen the heat transfer. There is a scraper at the bottom of the triangle of the paddle to scrape up the material deposited at the bottom of the shell to prevent dead space.

The layout of the paddle and the size of each part have certain requirements, and in the feeding area, drying area, discharge area, in addition to the paddle, another auxiliary agencies to ensure stable operation of the whole machine, drying and uniformity. In addition, the residence time can also be adjusted.

The heating medium of this equipment can be used either with steam, thermal oil or hot water, but the phase state of the heat carrier is different, and its hollow shaft structure is also different. When heated with steam, the structure of the hot shaft is simple; when heated with hot water, the shaft structure is more complex, especially when the liquid flow rate in the tube needs to be considered, it is more so.

Large paddle drying equipment, the shaft diameter of about 500mm, so sealing is a big problem. Seventies and eighties introduced equipment, its shaft sealing problem is not well solved, operation often have solid powder leakage to the two end cover phenomenon. Therefore, usually set the discharge port at the bottom of the end cover, and regularly remove the material from the end cover. In addition to the inconvenience caused by the operation, but also due to the leakage of dust, increase the wear and tear of the shaft, affecting the life of the equipment. In addition, flammable and explosive gases often need to be equipped with a backblow at the seal to prevent flammable and explosive gases from leaking. For large shaft sealing problems, foreign countries in recent years to get a better solution, the end cap at the basic material, do not need regular cleaning and blowback gas.

(C) equipment performance and characteristics

1. By the structure of the equipment can be seen, the heat required for drying is relying on the jacket and blade wall indirect heating, therefore, the drying process can be used without or only a small amount of gas in order to carry the material to the evaporation of moisture, heat utilization rate of up to 80% ~ 90%.

2. The heat transfer surface of this equipment is composed of two parts: the blade and the wall, in which the blade heat transfer surface accounts for most of the equipment, so the structure is compact, the heat transfer surface per unit volume is large, and the area is small, so it can save the investment cost.

3. The drying process uses less gas, low flow rate, less dust is taken away by the gas, so it is convenient to recover the dust after drying, and the recovery equipment is simple and saves the equipment investment. For the drying process with solvent recovery, can improve the concentration of solvent in the gas, so that the solvent recovery equipment to reduce or shorten the process.

4. Due to the special structure of the paddle, the material is alternately squeezed and loosened in the drying process, which strengthens the drying. In addition, when the two blades reverse staggered rotation, has a self-cleaning effect, so the viscous and paste materials can also be applied.

5. The material retention rate in the dryer is very high, and the residence time can be adjusted by charging rate, rotating speed, and the amount of stored material, which can be selected arbitrarily between a few minutes and a few hours, so it is suitable for the materials which are easy to be dried and not easy to be dried. In addition, although there are many stirring paddles in the dryer, but the material in the dryer basically from the feeding port to the discharge port is piston flow, residence time distribution is very narrow, so the product drying is uniform.

In addition, stirring and mixing make the material flip violently, so as to obtain a very high heat transfer coefficient, generally can reach 120 ~ 350W/m2k, so the floor space and space are very small, saving the plant infrastructure costs. Drying process gas dosage is less, the flow rate is low, the amount of dust taken away by the gas is less, so the drying gas dust recovery is convenient, the recovery equipment is small, can save equipment investment. For the drying process which needs to recover solvent, the concentration of solvent can be greatly improved.

The disadvantage of paddle dryer is the complex structure, high processing difficulty, the design of large-scale dryer has some difficulty.

(C) paddle dryer has dried materials

Alcohol residue, hygromycin residue, erythromycin residue, fly ash, skin powder, clay, kaolin, phosphogypsum, red gypsum, iron oxide yellow, magnesium trisilicate, alumina, H acid, mycelium, nitroaniline, sodium cyanide, fenitrothanol, indigo, ASN resins, 1010 antioxidant, DM accelerator and so on.

Four, drum scraper dryer

Drum scraper dryer is through the rotation of the cylinder, by way of heat conduction, will be attached to the outer wall of the cylinder liquid phase materials or band materials, drying a continuous operation of the equipment. The material to be dried and processed flows into the receiving trough of the drum dryer from the high level trough. The drying drum is driven by the transmission device and rotates according to the specified speed. Material by the film device, in the drum wall to form a film. Cylinder continuous through the heating medium, heating cylinder, heat transfer from the cylinder wall so that the film of moisture vaporization, and then through the scraper will meet the drying requirements of the material scraped, through the spiral conveyor to the storage tank, packaging. The moisture removed by evaporation, depending on its nature, can be introduced into the corresponding treatment device through the closed cover; generally water vapor, can be released directly to the atmosphere by the exhaust pipe at the top of the cover.

The drum is a dryer within a heat transfer rotating drying equipment, wet materials in the outer wall of the drum to obtain thermal conductivity to transfer heat, moisture removal, to achieve the required moisture content, heat from the inner wall of the cylinder to the outer wall of the cylinder, and then through the film, the heat efficiency is high, and can be operated continuously, so it is widely used in the drying of liquid materials or strip materials, paste and viscous materials are more suitable.

The drum scraper dryer has the following characteristics:

(1)High thermal efficiency The heat supplied in the cylinder, in addition to a small amount of heat radiation and part of the end cover of the cylinder heat loss, most of the heat is used in the wet part of the gasification, and the thermal efficiency can be as high as 70~80%.

(2) drying rate of the cylinder wall of the wet material film of heat and mass transfer process, from inside to outside, the direction of the same, the temperature gradient is larger,

so that the surface of the material film to maintain a higher evaporation intensity, generally up to 30 ~ 70kgH2O/m2.h

(3) the drying of the product quality is stable drum heating mode is easy to control the temperature inside the cylinder and the wall heat transfer rate can be kept relatively stable, so that the material film can be dried with stable quality, and the temperature and heat transfer rate can be maintained relatively stable, so that the material film can be dried with stable quality. The temperature inside the cylinder and the heat transfer rate between the walls can be kept relatively stable, so that the material film can be dried in a stable state of heat transfer, and the quality of the product can be guaranteed.

(4) Wide range of application

The liquid-phase materials to be dried by drum must have fluidity, adhesion and stability to heat. The form of the material can be solution, non-homogeneous suspension, emulsion, sol and so on. For pulp, textile, celluloid and other band materials, can also be used.

(5) the production capacity of a single machine, limited by the size of the cylinder

General drying area of the drum dryer, should not be too large. Single cylinder drying area, rarely more than 12m2. The same specification of the equipment, the ability to deal with the liquid material, but also by the nature of the liquid material, moisture content control, the thickness of the material film, drum speed and other factors, the magnitude of the change is large, generally in the range of 50 to 2000kg/h.

(6) the heating medium is easy Commonly used saturated water vapor, the pressure range of 2 to 6kgf/com2, seldom more than 8kgf/cm2. More than 8kgf/cm2

. For some of the materials required to be dried at low temperatures, hot water can be taken as the heat medium; to be dried at higher temperatures of the material, can also be used as a heat medium or high boiling point of organic materials as a heat medium.