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Hollow paddle dryer is a type of horizontal stirring dryer. Because the inner hollow stirring blade is similar to a boat paddle, it is called a hollow paddle dryer. It is more suitable for granular materials, powdery and paste materials drying, so the use range is still very wide, in the process of use due to various factors, will reduce the life of the hollow paddle dryer.

First, the factors affecting the life of hollow blade dryers

In order to improve the service life of hollow blade dryers, it is necessary to meet certain requirements. Only when these are met, not only the life can be improved, but also the work efficiency can be improved.

1.Use environment

The use environment of the hollow paddle dryer should be indoors, protected from direct sunlight, and not exposed to wind and rain, and the voltage must meet the normal use of the dryer.

2.Part inspection

Also check whether the various parts of the hollow blade dryer are installed properly and whether they can work normally. In particular, pay attention to check whether the lubricating oil and the inlet are smooth and the outlet is closed.

3.Test run

To carry out trial operation and start the motor in dry running, the blade rotation must meet the specified requirements, and there must be no abnormality, vibration and noise in the blade operation.

4.Materials

The humidity of the material must be controlled, it must not be too wet, and the material must not be doped with foreign materials, especially hard-shaped foreign materials, to prevent damage to the hollow blade dryer by the foreign materials, and the amount of dry materials must be controlled. Do not put too much or too little material into the dryer to dry it, and put it according to the workload of the dryer.

In addition to satisfying the conditions to increase the service life, we can also improve the life of hollow blade dryers through correct and normal use.

Second,the correct use of the dryer

1. When using, drain the condensate in the steam pipe first, and then close the shut-off valve.

2. After that, turn on the air switch of the electric control cabinet to start the circulating fan of each heating chamber.

3. When the temperature in the drying room reaches 145 ° C, set the switch of the speed control motor controller to the “ON” position, and then turn the speed control knob clockwise to bring the pointer to the required position. At the same time adjust the tightness of the conveyor chain, and then start feeding the material to the dryer and drying it.

4. It is also possible to control the humidity in the drying room by adjusting the angles of the inlet and exhaust air valves, so that the materials can be dried to a good state.

5. When all the materials leave the dryer, you can close the steam supply shut-off valve, and then turn off the fans later. Turn off the main drive, then turn the speed control knob counterclockwise to the zero position, and the controller switch is set to the “off” position.

If you want to increase the service life, the correct method of use is also very important, so you must use it according to the instructions to ensure normal work and not cause great wear to the machine. In addition to satisfying the conditions and correct use, maintenance is also very important. Only with good maintenance can the dryer work longer.

Third,precautions for dryer maintenance

1. Before the work is carried out, a comprehensive inspection of each component shall be carried out, and after the work, it shall be inspected to see if there is a fault, and once it is found, it shall be resolved immediately to prevent accidents during use.

2. Pay attention to the delivery of materials during the work, and do not allow overpressure or overload operation.

3. Pay attention to the condition of the bearing, and stop the repair once the problem is found.

4. Pay attention to the use of lubricating oil to prevent problems during use due to lubrication work. Add lubricating oil and pay attention to dust prevention.

5. Clean after use to prevent the inside of the dryer from being corroded and rusted due to uncleanness, especially the door seal strips are cleaned to prevent aging and affect the service life.

6. Periodically check and maintain when not in use for a long time, and clean it well. When cleaning, pay attention not to use a liquid with strong acid and alkaline strength. After cleaning, you should pay attention to dry the water. To prevent corrosion and rust.

The above is all about increasing the life of hollow blade dryers. In fact, we must pay attention to meet the conditions and requirements of hollow blade dryers. In addition, we must operate the dryers correctly to prevent injuries caused by incorrect use. To increase the service life, regular maintenance is required.

Drying is a process of heat and mass transfer. Regarding the definition of “drying”, the important point is energy. Driven by energy, the material is dry and the heat source is critical to the overall drying process and is an important part of the drying equipment. The drying equipment uses a heat source, and the fuel used includes gas, liquid and solid.

Depending on the working principle of the drying equipment and the structure of the equipment, it is important to choose the appropriate drying method and fuel. For example, if the flue gas is burned by solid fuel (coal), the gas in the gas is more. Generally, the air can only be heated as an indirect heat source, and then dried by using hot air as a drying medium. This process is applied to flue gas and air heat exchange equipment, and of course also includes finned heat exchangers. The method of heat source in drying equipment is also common.

In the choice of heat source, the following principle is the larger energy consumption. There are many problems with the heat source of drying equipment used by many companies. The problem is mainly concentrated in the fact that the heat in the production cannot be matched to the drying equipment. The heat generated is low, the product moisture is high, the heat generated is high, the energy used in the entire drying equipment is too high, and the product cost increases. The drying equipment manufacturer needs to select a suitable heat source for the dryer; and for the drying method, the drying equipment manufacturer Several commonly used drying methods have also been described in detail below.

(1) Normal pressure drying

That is, the drying under atmospheric pressure is called atmospheric drying. The method is simple, and the box dryer (oven or oven) is used. The disadvantage is that the drying time is long, the heat-resistant component may be destroyed due to overheating, and the knot is easy to knot. Piece.

(2) Drying under reduced pressure

Drying under reduced pressure is a method of drying after evacuating in a closed container. The advantage of this method is that the temperature is low and the product quality is easy to smash. In addition, the adverse effects of air on the product are reduced, which has a certain significance for ensuring product quality. Particularly suitable for materials containing heat sensitive ingredients. Commonly used instruments are vacuum dryers. The drying effect depends on the degree of vacuum and the thickness of the object to be dried.

(3) Spray drying

Spray drying refers to a method in which a liquid material is dispersed into a fine droplet by a argonizer, and hot air is used to dry the fine droplets to obtain a dry product. This method can directly dry the solution, suspension and emulsion into granules or powder, eliminating the need for further evaporation and pulverization. The principle is that the dried liquid material is dispersed into a plurality of fine droplets through the purifier into the flowing hot air stream. Because of its large total surface area, the drying speed is extremely fast, and the water evaporation is completed in a few seconds. It has the characteristics of instant drying.

(4) Boiling drying

Also known as fluidized drying, it is a new development of fluidization technology in drug drying. It is mainly used for drying dry wet granular materials such as tablets, granules and the like. It has high drying efficiency, uniform drying and high output. It is suitable for continuous production of the same variety, and has the advantages of low temperature, convenient operation and small floor space. However, it is not easy to clean in the drying chamber, especially for the drying of colored particles, and the proportion of fine powder after drying is large. The principle of boiling and drying is to use the hot air flow blown from the bottom of the fluidized bed to make the particles float and suspend, and the fluidized roll is like “boiling”. The jumping of the material greatly increases the evaporation surface, and the hot air flow passes between the suspended particles. Heat exchange under dynamic conditions to remove moisture for drying purposes. If the vacuum is used for drying, the drying efficiency is higher.

(5) Freeze drying

It refers to a drying method in which the dried liquid is frozen into a national body, and the sublimation property is utilized at a low temperature and a low pressure to directly remove the ice into a gas to thereby achieve the purpose of drying.

Freeze drying requires a high degree of vacuum and low temperature, and the obtained product is porous, loose and easy to dissolve, and is particularly suitable for drying of some heat-resistant medicines and low-melting medicines. Such as enzymes, antibiotics, vaccines, etc., can also avoid the decomposition of easily oxidizable drugs.

With the development of science and technology in recent years, the types of heat sources for dryers are also increasing. New methods and technologies have been continuously improved, and heat pipe heat exchangers have emerged. In addition, the use of non-electrically heated radiators for heating and drying media is also constantly improving.

There are many types of industrial drying equipment, because the equipment performance required in different working environments is different. For example, vacuum drying equipment is used for pharmaceuticals because powdery chemicals can cause dust pollution. The equipment designed for the problem; the vertical drying equipment and the horizontal drying equipment are caused by the environment available at work, which are due to various factors in the work or working environment and actual operation. Created a new type of machine, let’s compare the performance of these common drying equipment.

Vacuum dehumidification drying equipment

The main parameter controlled by rapid evaporation of water in the raw material to achieve rapid drying is vacuum; the vacuum drying equipment is placed together with the dehumidifying drying equipment for testing, vacuum drying because the drying principle is to reduce the water at low pressure. The principle of evaporation point. The results show that vacuum drying equipment can save 70%-80% energy. This is mainly because the desiccant of the desiccant drying apparatus consumes a large amount of energy during the regeneration process. The drying time of vacuum drying is usually 1/5-1/6 long-time high-temperature drying of other dehumidifying and drying, which causes hot chemical and physical reaction of raw materials, which causes the quality of materials to decrease, such as fading and melt index to decrease. Affecting the quality of waste products reduces the possibility of material quality degradation.

Taking polycarbon PC drying as an example, the vacuum drying equipment shortens the drying time of the material. Drying at 120 degrees Celsius, under the premise of 0.02% final water content, dehumidification drying usually takes about 4 hours, while vacuum drying requires only 20-25 minutes to dry. This saves the drying time of 3 hours and 35 minutes, and the advantage of vacuum drying equipment in the trial section is particularly obvious! Drying efficiency is of particular importance to precision injection molding manufacturers.

Some resins or high-molecular substances have high sensitivity. If the drying time is too long, stress may occur, leading to baking, embrittlement and discoloration. It is mainly used in the honeycomb type dehumidifying drying equipment series, mainly for moisture absorption. The strong engineering plastics are designed and developed for high-efficiency dehumidification heat pump dehumidification drying equipment. How to strictly control the moisture in the raw materials is the key to processing high-quality plastic products, which are represented by today’s models. The most high-tech Japanese honeycomb fiber-based honeycomb rotor is the core component, so the dry air can easily reach -40 ° C dew point, ideally reach -50 ° C or even lower dew point, and dew point The temperature is stable, ensuring the quality and stability of the formed plastic products. It adopts Japanese PLD temperature control system as standard equipment; it also provides PLC control with LCD touch human-machine interface and dew point meter which can monitor the dehumidification effect of the machine at any time. The maximum dry air volume of this product can reach 3000m3/hr.

Box drying equipment

The box type drying device puts the material to be dried into the movable tray. When the power is turned on, the strong wind wheel starts to force the air entering from the air inlet to blow into the electric heating tube, and the air is heated and heated by the electric heating tube and passes through. The perforated partition wall is evenly blown to the material, and the air carrying the moisture will be taken out of the oven by the top exhaust fan.

Repeated circulation in this way achieves the effect of moisture removal and drying. It is widely used for the drying of any plastic raw materials, and can simultaneously dry materials of different materials and colors. It is especially suitable for drying materials with high temperature accuracy, low dosage and various colors. It is also suitable for preheating or drying treatment in food, pharmaceutical, electronic plating and other industries; using PI temperature control to precisely control drying temperature; integrating temperature and time control, facilitating drying parameter setting of various materials; high quality thermal insulation material High sealing design avoids unnecessary energy loss; adjustable air inlet; motor overload protection, phase sequence protection.

Vacuum drying equipment

Also known as vacuum conveyor, vacuum drying equipment is a dust-free and closed pipeline conveying equipment that transports particles and powder materials by means of vacuum suction. The pressure difference between vacuum and environmental space is used to form the gas flow in the pipeline and drive the powdery materials. Exercise to complete the delivery of the powder. Because it is a pipeline transportation, it takes up a small space and can complete the powder transportation in a narrow space, so that the space in the work space is beautiful; especially, it is not limited by the long distance. At the same time, the vacuum feeder can reduce the labor intensity and improve the working efficiency. It is the first choice for most powder material transportation methods. Its main application areas are chemical, pharmaceutical, food, metallurgy, building materials, agricultural and other light and heavy industries. Vacuum feeder is mainly used to transport powder and granular materials, such as raw material powder, chemical powder, metal oxide powder, explosive powder; capsules, tablets, pills, small food pellets, explosive particles, etc.; not suitable for conveying Too moist, sticky, heavy material.

In summary, industrial drying equipment is widely used in various industries. They are constantly developing and improving in daily production. In the current technological development, many different working environments have been added.

The core components of the paddle dryer are hollow shafts (which can be divided into single shaft, double shaft, and four shafts) and hollow agitating blades welded to the shaft. Generally, the double shaft is selected in the sludge drying process. The shape of the blade is a wedge-shaped hollow semicircle, and the inside can be heated into the heating medium. In addition to stirring, it is also the main heat transfer body of the device. The two main heat transfer sides of the blade are beveled. When the material is in contact with the inclined surface, as the blade rotates, the particles quickly slide away from the inclined surface, so that the heat transfer surface is continuously updated.

The paddle dryer is a continuous operation device. In the case of two spindle configurations, the direction of rotation is reversed, the spindle speed is lower, and the line speed is less than 2 m/s. The main shaft, the blades and the W-shaped grooves are hollow, and the middle can be heated by hot fluid.

The upper dome of the dryer is not heated and is used to open inspection windows and connect air ducts, pipelines, etc. An air suction port is provided in the middle of the top cover to extract the evaporated water vapor in a micro-negative pressure manner. The heat exchange mode is heat conduction, and only a small amount of ambient air flows when the negative pressure is extracted, and the moving direction of the gas and the material is a cross flow. The residence time of the material in the dryer is long, the process loop is open loop, and the treated exhaust gas is no longer returned.

Since the main shaft is both a rotating part and a main heat exchange surface, considering the equipment sealing and mechanical deformation, the process requires that the working temperature should not exceed 200 degrees. The heat transfer oil only releases sensible heat due to the latent heat released by the steam, and the steam working medium is generally selected in the use process. At this time, the hot runner for transporting the hot fluid is small and easy to arrange. Typical saturated steam temperatures are 150-200 degrees, pressures 5-7 bar, and up to 14 bar.

Design and analysis of paddle dryer

1. Dryer tilting arrangement

The paddle dryer is arranged horizontally, generally with a certain angle of inclination. It feeds from one side and discharges on the other side. The material moves forward in the dryer mainly by gravity. This is due to the blade itself. The inclined surface does not have an axial pushing action, and the squeegee at the top end of the blade is arranged at 90 degrees with the blade, and only serves as a radial copying and stirring, and does not constitute an axial advancement, so the material needs to be advanced. It is done by the angle of inclination of the dryer.

The improved dryer can adjust the angle of the blade bevel to generate the axial driving force, realize the material displacement, and adjust the drying time by using the rotation speed.

2. The setting of the overflow weir

Due to the barrier effect of the blade, the movement of the material in the dryer from the feeding port to the discharge port is in the form of a plug flow, and the distribution of the residence time is narrow, so that the product can be processed for a sufficient time and the heat exchange surface is fully obtained. Use, the material must be filled with the dryer, that is, the material level should be “immersed” the upper edge height of the blade. At the start-up operation, the outlet at the end of the dryer must be closed to achieve the “water storage” effect. At the same time, an overflow weir that blocks the material and maintains a high level is required. In theory, the overflow should be slightly higher than the material. Blade height. The weir is located at the end of the dryer, above the dry mud discharge, and it should have a mechanical structure similar to the “lifting gate” to maintain the required level of the process.

3. Heating shaft type

The heating medium of the equipment can be either steam or heat transfer oil or hot water, but the heat carrier has different phase and the hollow shaft structure is different. When heated by steam, the diameter of the hot shaft is small, and the structure is relatively simple; when heated with hot water or heat transfer oil, the structure of the hot shaft is more complicated, and the liquid flow rate in the tube needs to be considered; the thicker the pipe diameter, the more difficult the rotary joint and the seal are. Big.

The heat is supplied to the hollow blade. If the steam medium is used, the diameter of the inlet and outlet pipes is small due to the release of latent heat. If a heat transfer oil is used, the diameter of these lines may become larger in order to obtain a sufficient heat flow rate, which may reduce the structural strength of the spindle. Since the spindle itself has multiple functions (supporting the blade, transporting the hot fluid, transferring heat transfer, etc.), it needs to overcome the viscous force of the material, the friction between the material and the blade, and the wear of the material itself on the surface of the spindle. The stresses that need to be overcome are large. When designing, it is necessary to ensure its mechanical strength, but also to ensure its heat transfer performance, while also taking into account the material strength, etc. These contradictory conditions will make the design complicated, such as increasing the heat exchange area, the blade needs to be increased. Quantity and diameter, but this will result in an increase in the stress of the spindle. If you want to increase the spindle strength, you need to increase the spindle diameter, but this will reduce the heat transfer area of ​​the blade.

For different heating media, the choice of spindle type and structure are different. For example, if the steamer is used as the working medium, the heat flow channel will be completely different when the heat transfer oil is used as the heat medium, and the heat transfer capacity is also very good. Great changes, so you can’t simply copy and use the original process parameters.

4. Stay time

Theoretically, the residence time of sludge drying can be adjusted by feeding rate, rotation speed, storage amount, etc., and can be arbitrarily selected between several hours and several hours, wherein the overflow weir is to adjust the sludge retention in the dryer. The main means.

In order to make full use of the heat exchange area, the sludge retention in the dryer is required to be high, and the material level should exceed the upper edge height of the blade, that is, the so-called “effective volume” needs to be utilized 100%. If the volume of the entire dryer barrel is calculated according to the steam cover, the effective volume may account for 70-80% of the total volume of the dryer. The high retention rate of the material in the dryer will make the actual residence time of the sludge in the dryer correspondingly longer, up to 3-7 hours.

5. Dry mud back mixing

In theory, since the hollow blades on the main shaft mesh with each other and have self-cleaning effect, the hollow blade dryer can perform semi-drying and full-drying operation of the sludge without performing dry mud back mixing. However, in fact, the self-cleaning of the material shear formed by the mutual engagement of the blades still requires certain preconditions, that is, the meshing precision in the device is sufficiently high, the mechanical gap is small enough, and the shear force between the materials is sufficient to overcome the product. Adhesion on the heat exchange surface. When we analyze the internal structure of the hollow blade dryer, it is not difficult to notice that there is a large gap between the mechanical structures. It is impossible to completely clean the dead zone by mechanical occlusion, which means that the hot surface of the hollow blade is truly realized. The means of self-cleaning and renewal is the mutual friction between the materials, ie the shearing force between the metal surface and the material and between the material and the material. To achieve mutual friction between materials, the method of increasing the packing density of materials can be used to maintain the height of the material level, which can improve the mutual contact chance between the materials, and the self-cleaning of some heat exchange surfaces can be realized by the extrusion of the blade blades.

Due to the nature of the wet mud, there is a tendency to agglomerate, form a ball and bridge during the drying process. It is impossible to overcome the pure material level because the shearing force between the wet mud particles may cause the wet mud to be incapable. The updated gap is “compacted” without causing looseness and fluidity between the particles. Only the dry mud has a characteristic of poor rehydration in a short time due to the complete loss of water on the surface of the particles, and the particle gap is large. When it encounters mechanical shearing force, it has the possibility of sliding off the metal surface. Therefore, in actual engineering, dry slurry back-mixing is considered for the drying of hollow blades. The practice is to screen the dry mud, and the fine dry sludge is pre-mixed with the wet mud.

From the perspective of heat transfer efficiency, dry mud backmixing should be one of the necessary means. According to the water loss condition of the sludge, the evaporation rate of the hollow blade dryer has obvious peak-to-valley changes. When the solid content is less than 25%, the sludge has obvious liquid properties under heating, and the heat transfer condition is better, but the material is easy to form an adhesion layer, which leads to a decrease in evaporation strength, and the sludge is polymerized. The effect is that it has a tendency to form agglomerates, and the contact rate with the heat exchange surface is reduced. When the solid content is between 25% and 75%, the sludge may have surface viscosity, obvious tendency to agglomerate, and poor heat exchange effect. . When the solid content is greater than 75%, the evaporation rate rises because the fine and loose particles regain good contact with the heat exchange surface. The hollow blade drying process generally adopts the method of returning partially dried sludge (dry mud back mixing) according to the purpose of drying, so that the dry mud plays a certain “lubrication” role, obtains better fluidity, avoids adhesion, and its return flow only A small part of the dry mud for export. The proportion of the hollow blade dryer back to the dry mud is not high, generally about 40% (far less than the general requirement of 65%, such as the drum machine), the presence of this dry mud powder is enough to be on the hot surface To the role of “lubrication” and “cleaning”.

6. The dryer does not empty

Any sludge drying process that requires dry mud back mixing has strict requirements for the feeding of wet mud. Before the wet mud is fed, it must be carried out under the condition that the dryer has a large amount of dry “bed material”. Avoid the wet mud as soon as it gets in, it will stick to the heat exchange surface and cause scaling. Therefore, the typical practice is to maintain the returning system to continue working when the drying system is stopped, stop the feeding device, and the dry product is fully refilled. At the same time, the system is cooled. When the system temperature is lower than 60 °C, the whole line is stopped. No clearing is carried out inside, and the material is started directly when driving, which means that the dryer is filled with dry mud when the machine is stopped. In the shutdown process and the boot process, there is always the characteristics of high dust and low humidity, but at this time, it is necessary to pay attention to the problems of dryness and safety.

7.The blade top scraper

Any machine has tolerance gaps, and the hollow blade dryer with spindle engagement is no exception. Wet mud has a viscosity at a certain solid content, and may cause a sticky wall between these gaps, and any adhesion on the hot surface will reduce the heat exchange efficiency. In order to avoid the thickening of the sludge scale layer, mechanical scraping is often used, and it is necessary to use the scraper at the tip of the blade to scrape the sludge. From the action of the squeegee, it is known that with long-term operation, the squeegee pair acts only on the material falling between the blade and the W-shaped groove heat exchange surface, and also on the material attached to the W-shaped groove wall. There is a scraping action, whether it is scraping or scraping, because the moving speed of the scraper is about 2 to 5 m / s, the moving direction of the sludge at the outer edge of the scraper at this speed during the process of picking up or scraping There are two, one is outward extrusion (grinding W-shaped groove) and the other is backward movement (grinding plate).

8. Metal surface hardening treatment

Wear can be one of the important challenges facing hollow blade dryers. The sludge contains abrasive particles. The hollow blade dryer is a typical conductive contact heat transfer. Repeated and long-term contact between the metal and the abrasive particles is inevitable. Coating and hardening can reduce the speed of abrasion, but it is limited by the surface of the abraded metal and also the heat exchange surface (such as W-shaped groove, blade, spindle, etc.), and there are not many hardening measures (spraying silicon carbide, etc.) ), under the heating condition, the adhesion of the wear layer, the actual hardness, etc. are not ideal, and can only play a role in slowing the abrasion.

Because the dry mud particles have a prominent effect on the metal surface, the latter half (15~25%) of the blades are usually heat treated, but for the dry mud back mixing process, the abrasion is the whole process. The existence of the abrasive tendency will undoubtedly affect the material selection of the dryer.
In the heat exchange metal surface of the paddle dryer, the W-shaped groove has a small pressing gap with the scraper, and has a significant pressing effect during the hot surface renewal process. When such a squeeze gap is present, the general abrasion is strongly a relatively “soft” metal surface, which means that it is necessary to protect the W-shaped groove as a heat exchange surface, the scraper can be hardened, but not hardened. The life of the scraper will also be limited.

9. Mechanical dead angle

Mechanical dead angle is one of the design challenges that must be solved by the paddle dryer. It can be divided into three categories:

1) the outer edge of the metal without surface mechanical cleaning;

2) There is surface cleaning but there are inaccessible tolerances;

3) Increased inaccessible tolerance due to abrasion.

The direction of rotation of the wedge-shaped blade itself is constant, that is, both spindles rotate inward, when the narrow side of the wedge-shaped blade is in front, the blade is behind, and the blade has no mechanical action from the narrow and wide heat-exchange surface. Cleaning up needs to be updated by the shear force of the material itself. The portion of the squeegee that is larger than the wedge-shaped portion of the wide heat exchange surface will always scrape the sludge and form a squeezing on the W-shaped groove. In addition, the squeegee and the main shaft only have a “tangent intersection” at a certain point (ie, the center of the scalloped notch) (actually close, the cleaning effect is minimal), and the spindle has no mechanical cleaning on the surface in most cases. All of the above are metal outer edges without surface mechanical cleaning, which account for 70-80% of the total heat exchange area.

There are mechanically cleaned heat exchange surfaces. According to the arrangement rules of the wedge-shaped blades, there are the following dead angles due to inaccessible tolerances: the gap between the scraper of the first row and the last row of blades and the outside of the heating spindle, between the dryers Between the paddle and the spindle packing seal. The gap between the axial squeegees, which is clearly visible.

Due to the aforementioned abrasion problem, especially the increase of the radial blade gap, that is, the blade is thinned by abrasion, and the inaccessible tolerance of the heat exchange surface of the blade and the W-shaped groove is increased. At this time, the scraping action of the scraper is reduced, and when the shear force between the materials is insufficient to overcome the adhesion of the wet mud on the heat exchange surface, the stock and scale on the heat exchange surface are generated. When a certain thickness is formed, it will cause shaft jump, vibration, noise, and the like.

Heat exchange surfaces that cannot be cleaned can be called “mechanical dead angles”. Based on the above factors, the part where the hollow blade dryer cannot be mechanically cleaned accounts for most of the heat exchange area. Therefore, the core problem for this process is how to avoid the stickiness of the product.

10. Heat transfer coefficient

Since the blade is perpendicular to the main shaft, the blade is parallel to the main shaft, and the heat exchange surfaces at both ends of the blade are not pushed but only heat exchange, the radial mixing of the material is sufficient, and the contact frequency between the material and the heat exchange surface is high. , long residence time, theoretically should achieve better heat transfer, the overall heat transfer coefficient should be between 80 ~ 300W / m2.K. In the application of sludge drying, due to the different viscosity of different sludges, the solid content of the dried product also affects the process (such as whether low dryness and semi-drying can be carried out), and the heat transfer coefficient given in the actual project. It may be a big difference.

11. Heat transfer area

The wedge-shaped blades and the main shaft on the hot shaft of the paddle dryer are the main heating surfaces, and the heat exchange area accounts for more than 70% of the total heat exchange area. The design has high requirements on its manufacturing precision, spindle type and hot runner layout. It is generally considered that the dryer is “complex in structure and difficult to process”, and the design of large dryers is more difficult. In foreign countries, a hollow blade dryer with a heat exchange area of ​​1.5 to 295 square meters and a theoretical evaporation capacity of 12 tons per hour has been manufactured. In the field of sludge drying, the heat exchange area of ​​the large installed machine is about 300 square meters. The capacity is less than 5000 kg / hour. The current series design in China is 110 square meters high. The heat exchange area of ​​the commonly used hollow blade dryer is 25-100 square meters, and the height is 160 square meters.

12. The amount of air purged

The blade dryer is a typical conduction dryer. The heat transfer and evaporation are realized by the hot wall instead of the gas convection. In practical applications, the water vapor generated by the drying process needs to be discharged into the dryer in time, and the sludge is dried. In order to prevent odor from overflowing into the environment, it is generally necessary to use a micro-negative pressure operation mode, and there is a necessity to use “purge air”. The extraction of negative pressure will inevitably cause ambient air to enter the circuit from the gap between the dryer and the circuit (shaft joint, wet mud inlet, dry mud outlet, overflow weir seal, etc.), in order to prevent the purge air from causing water vapor in the dryer. Condensation, this gas needs to be heated. The amount of purge air is related to the process itself, measured by the amount of ambient dry air required for water evaporation, generally between 0.1 and 1.2 kg/kg. H2O. The height of this value has an important influence on the net heat consumption of the drying system. A typical hollow blade dryer generally considers the amount of dry air around 0.5 kg/kg.H2O.

13. Evaporation intensity

The evaporation capacity of a conductive dryer is generally measured in terms of evaporation per square meter and hour, and it theoretically achieves an evaporation of 10 to 60 kg/m2.h. However, in the practice of sludge drying, the value of the design value is generally between 6 and 24 kg/m2.h, and the value of 14 to 18 kg/m2.h is mostly. Refer to other conductive drying (such as disc players, discs), the typical values ​​are between 8 ~ 14 kg / m2.h, consider the heat transfer conditions of the hollow blade dryer is very similar to other conductive dryers The more reliable actual evaporation intensity should be between 8 and 14 kg/m2.h.

14. Product outlet temperature

Since the sludge stays in the dryer for a long time, the outlet temperature of the sludge when leaving the dryer is relatively high, and should be about 90 to 100 °C.

The paddle dryer is a device with high thermal efficiency, low operating cost and cost saving. a jacket is arranged on the dryer cylinder, a hollow blade is arranged on the hollow shaft, and the jacket and the blade are inserted into the intercept body, and the sludge and the hot surface of the blade are fully exchanged under the stirring of the stirring blade to To achieve the purpose of drying. In terms of specific types, it is horizontal, vertical, and biaxial or quadruple. In addition, it can be divided into hot air and conductive.

The wedge-shaped blade heat transfer surface has a self-cleaning function, which can wash away the sludge adhering to the wedge surface, so that the clean heat transfer surface is maintained during operation.

Paddle dryer working principle

A hollow hollow blade is densely arranged on the hollow shaft, and the heat medium flows through the blade through the hollow shaft. The heat transfer area in the effective volume per unit is large, and the temperature of the heat medium is from -40 ° C to 320 ° C. It can be water vapor or liquid type: such as hot water and heat transfer oil. Indirect conduction heating, no air is carried away to remove heat, and heat is used to heat the material. The heat loss is only the heat dissipation to the environment through the insulation of the body. The wedge-shaped blade heat transfer surface has a self-cleaning function. The relative movement of the material particles and the wedge surface produces a scrubbing action, which can wash away the adhering material on the wedge surface, so that a clean heat transfer surface is maintained during operation. The shell of the paddle dryer is of the omega type, and two to four hollow agitating shafts are generally arranged in the casing. The housing has a sealed end cover and an upper cover to prevent material dust from leaking out and fully functioning.

The heat transfer medium passes through the rotary joint and flows through the casing jacket and the hollow agitating shaft. The hollow agitating shaft has different internal structures according to the type of the heat medium to ensure a good heat transfer effect.

The blade dryer is structurally composed of two to four blade shafts, a base, a transmission portion, and a jacketed W-shaped housing.

Paddle dryer features

(1) Since the entire drying process of the material in this type of dryer is carried out in a closed environment, organic volatile gases, odorous gases, etc. generated during the drying process can be sent to the exhaust gas treatment device for treatment. It is then discharged to the atmosphere so that it can avoid polluting the air.

(2) The paddle dryer has a compact structure, a small footprint, and a large heat transfer area per unit volume, so that the basic investment can be effectively reduced and the equipment cost can be reduced.

(3) This kind of dryer has high heat energy utilization rate, because it can effectively reduce heat loss, so it can reach more than 90% in heat utilization.

(4) In the paddle dryer, the blade is a wedge-shaped blade, so it has the function of self-cleaning, and can effectively improve the heat transfer performance and heat transfer effect of the blade. In addition, since the blade can be reverse-rotated and alternately staged, and expanded and agitated, uniformity can be achieved in heat transfer, thereby improving the heat transfer effect of the paddle dryer and improving the drying of the dryer effect.