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.

Hollow paddle dryer

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.


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.

s-Multilayer paddle dryer

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.

Sludge dryer is a kind of equipment capable of drying sludge. It is an indirect heating low-speed stirring dryer. Because of its clever structure design, it is very good in terms of work efficiency, self-cleaning and drying effect. Yes, but if there are special conditions in the process of use, it will still cause low work efficiency, so let’s take a look at what factors affect the work efficiency of the sludge dryer.

Generally, there are two aspects that can affect the working efficiency of sludge dryers. One is external factors, and the other is internal factors. Let’s take a closer look at them!

External factors affecting the efficiency of sludge dryers

In fact, there are mainly four external factors affecting the sludge dryer’s working efficiency, namely the working environment, material humidity, material supply and heating system.

1. Working environment

The environment also has a great impact on the working efficiency of the sludge dryer. For example, the climate environment in the north of China is very different from the climate environment in the south. The weather in the south is relatively humid and the weather in the north is relatively dry. Then the drying time of the material will be different, and the difference in ambient temperature will also affect the sludge dryer’s working efficiency. The greater the humidity, the lower the drying efficiency and the lower the temperature. It will also be less efficient.

2.Humidity of materials

The material generally depends on the moisture content of the material. If the moisture content of the material is particularly high, the sludge dryer will consume a lot of time and heat during the drying process. The longer the drying time, the more efficient the drying will be. Decreased, so that the humidity of the material will affect the efficiency of the dryer. When the sludge dryer is working, the material should be properly dehydrated, so as to improve the efficiency of the sludge dryer.

3. Supply of materials

If the working efficiency of the dryer is stable, but the supply of materials cannot keep up, this will also affect the working efficiency of the sludge dryer. Therefore, when the sludge dryer is working, it must be ensured by the various departments. The tacit cooperation between them can improve the working efficiency of the sludge dryer.

4.Heating system

During the work of the sludge dryer, heat is very important. If there is no heat, it cannot be dried, so it must be ensured that the sludge dryer is equipped with a reasonable heating installation, and if the fuel is used, the fuel is used. Must be of high quality, high burning value and can be completely extinguished, then the sludge dryer’s working efficiency will be higher, otherwise it will reduce the working efficiency, and the use of power to dry, must ensure the stability of the voltage, dry The machine can be used normally so that it can generate a continuous flow of heat and dry the sludge.

Internal factors affecting the efficiency of sludge dryers

The above are the external factors that affect the efficiency of the sludge dryer. After understanding the external factors, let’s understand the internal factors together. There are four factors that influence the internal factors of the sludge dryer.

1.Stirring leaf quality

When the stirring blades in the sludge dryer are damaged, this will seriously affect the working efficiency of the sludge dryer, because without the stirring blades, it is impossible to move the sludge, and the sludge cannot be fully moved if it cannot move. Integrates with heat, so it can’t dry quickly, which reduces work efficiency.

2.Drying machine failure

When the sludge dryer fails, when the internal water vapor cannot be eliminated, the drying time will be increased, or the water vapor will be re-adsorbed by the material inside, thereby increasing the drying time, so it must be checked during drying. Are the components of the sludge dryer normal?

3.Drying machine speed

In order to speed up the movement of dry materials to the exit, some customers have adjusted the speed of the equipment very low, but this will reduce the number of times that the sludge material in the dryer is thrown away, which constitutes the sludge material. There is very little contact with the hot air state, and the sludge material will not go back and forth repeatedly in the drum, which means that it is passed once, and the sludge material will be sent away quickly, so that the material storage amount is too low to form a material The contact area with hot air is reduced under dynamic and static conditions. Thereby reducing the working efficiency of the sludge dryer.

4. Dryer maintenance

No matter which part is faulty, as long as the sludge dryer fails, the work efficiency will be affected, so the dryer must be inspected and repaired before work and after maintenance to ensure the sludge dryer. The next normal use and the working efficiency of the dryer are normal. Remember to troubleshoot and repair the failure, which is the basic condition to ensure the normal operation of the sludge dryer.

The above is the content of the factors that affect the sludge dryer’s working efficiency. The main factors affecting it are external factors, the environment, materials, and the supply speed of materials, which are related to the quality of fuel for heating and installation. If it is internal, it is related to the failure of sludge dryer Damage, as well as the discharge of water vapor, are related to the speed of operation. These will affect the efficiency of the sludge dryer.

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 a variety of drying equipment on the market. In order to better understand the drying equipment, we will briefly introduce the common types of drying equipment. We all know that the drying process of drying equipment requires a lot of heat energy. In order to save energy, some materials with high moisture content, suspensions or solutions containing solid substances are generally first mechanically dehydrated or heated and evaporated, and then dried in a desiccator. To get a dry solid. In the drying process, the heat and mass (moisture) transfer must be completed at the same time, which can ensure that the moisture partial pressure (concentration) of the material surface is higher than the moisture partial pressure partial pressure in the external space, and then the heat source temperature is higher than the material temperature.

By transferring heat from the high-temperature heat source to the wet material in various ways, the surface of the material can be vaporized and dispersed into the external space, so that the difference in moisture content occurs on the surface and inside of the material. The internal moisture partition diffuses and vaporizes to the surface, so that the moisture content of the material is continuously reduced, and the overall drying of the material is gradually completed. The rate of drying of the material depends on the rate of surface vaporization and the rate of diffusion of the internal moisture. Generally, the drying rate in the early drying stage is controlled by the surface vaporization rate. As long as the external conditions of drying are constant, the drying rate and surface temperature of the material are kept stable. This stage is called the constant-speed drying stage. When the moisture content of the material is reduced to a certain extent. When the internal moisture distribution to the surface is reduced, and the surface vaporization rate is lower than the surface vaporization rate, the drying rate is mainly determined by the internal diffusion rate, and is continuously decreased as the moisture content is lowered. This stage is called the slow-down drying stage. In addition, technological advances will reverse the current export situation of domestic drying equipment.

Drying equipment type

There are many types of drying equipment for drying operations. According to the operating pressure, it can be divided into normal pressure and decompression (also known as vacuum dryer), which can be selected according to your own needs; it can be divided into batch and continuous according to the operation method; Air, flue gas or other drying medium; according to the movement (material movement and drying medium flow) can be divided into co-current, countercurrent and cross-flow, etc., but the common drying equipment mainly has the following categories, let’s take a look at it. .

(1) Slime dryer

The slime sludge of the slime dryer with moisture content of 25~40% is firstly dispersed by the special feeding device and then transported to the feeder by the belt feeder, and then the wet coal slurry is transported by the feeder. In the drying drum, the coal slurry is evenly distributed under the rolling plate of the drying drum, and is evenly dispersed and fully contacted with the hot air to achieve the purpose of drying heat and mass transfer.

(2) Belt dryer

It consists of several independent unit segments. Each unit section includes a circulating fan, a heating unit, a separate or common fresh air intake system, and an exhaust system. The operating parameters of the amount of drying medium, temperature, humidity and exhaust gas circulation can be independently controlled to ensure the reliability of the working with the dryer and the optimization of operating conditions.

(3) Roller scraper dryer

The drum scraper dryer is a continuous operation device for drying a liquid material or a belt material attached to the outer wall of the cylinder by means of a rotating cylinder by 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.

(4) Hollow blade dryer (blade dryer)

The hollow blade dry dryer, also known as the blade dryer, is mainly composed of a W-shaped casing with a jacket and two hollow blade shafts and a transmission device. Hollow blades are arranged on the shaft, and the rotary end of the heat medium is introduced at the shaft end. The heat required to dry the moisture is conducted to the material by the inner wall of the jacketed W-shaped groove and the hollow blade wall.

(5) Vacuum kneading dryer

The dry material is added from the upper part of the top of the vacuum squeezing dryer. When the material is in contact with the shell wall under the stirring of the rotating dent, the surface is continuously updated, and the dried material is subjected to steam (or hot water, heat transfer oil). Indirect heating, but the moisture of the material vaporizes, and the vaporized water is pumped away by the vacuum pump in time. The material to be dried is indirectly heated by the heat carrier to vaporize the water in the material, and the vaporized water is discharged by the vacuum pump in time.

(6) Double cone rotary vacuum dryer

Double cone rotation The vacuum drying body is slightly olive-shaped with a cover at both ends and two shafts in the middle to support the body. The body has a jacket for heating, and the body can be rotated when dry, so that the material and the wall are frequently replaced, which overcomes the disadvantage that the material in the vacuum oven is mainly guided by the heating cylinder and has low thermal efficiency.

(7) Vacuum oven

Since the evaporation temperature of the volatiles contained in the evaporation of the material can be reduced after decompression, it is suitable for drying various heat-sensitive and easily oxidizable materials. This device is usually a cylinder or other vacuum-operated outer casing. It is heated by electric heating or hot water or heat-conducting oil through a heating plate or a heating pipe, and is suitable for batch production in small batches.

(8) Freeze dryer

In the freeze dryer, the liquid is first cooled and frozen, and then the pressure is reduced to sublimate the ice to obtain a dry material. Since the whole process is carried out below freezing point, it is often used for drying of heat sensitive articles. It is difficult to heat the frozen material under vacuum, and a large refrigeration system is required to condense the sublimated water vapor under reduced pressure, so the drying cost is large.

The moisture in the highly heat sensitive material is frozen and will be maintained at a temperature below freezing below under high vacuum. The water is sublimed to separate from the material. There is less loss of active ingredient in the material, but the drying rate is low.

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.

Structure design and drying characteristics of paddle dryer

1, structural design

The paddle dryer is a new type of energy-saving dryer with a jacket on the outside. Two vane shafts rotate inside each other, and the shaft and the blades are hollow. The heat medium is fed into the shaft, the vanes and the jacket through the swivel joint and the flange. The whole body, shaft and blade can transfer heat and dry materials. The blades on the shaft are radially arranged in a spiral, which realizes the stirring and conveying of the paste material. When the axis is symmetrical, the blades are interlaced to each other, and the materials are cleaned from each other. The outer edge of each blade has an auxiliary blade, and the outer end of the blade has a small distance from the casing. The function is to eliminate the dead angle and fully stir the material to make the axial movement of the material close to the piston flow. Both the shaft and the blade are pressure members, and the thickness design should consider wear resistance and pressure. The layout of the blade should take into account the transport and self-cleaning action of the viscous paste material, and also ensure that it cannot interfere in the hot state. The heat carrier can be hot water, hot oil or water vapor, and the temperature range is 50-320 ° C, and the pressure range is 0.4-1.5 MPa.

2, drying characteristics

The general drying process of the paddle dryer: the wet material enters from the feeding port and rotates in the two-axis mutual rotation, conduction heating, and drying to the discharge port. The material vapor is taken by the hot air introduced from the hot air inlets at both ends to the upper vent. The whole process is completed once from the feed to the dry discharge.

The dryer features as follows

(1) Wide applicability, can be used for drying of the following materials in chemical, pharmaceutical, food, brewing, metallurgical and other industries: organic materials, inorganic materials, viscous materials, non-stick materials, granular materials, powder materials, and The amount of moisture can be dried;

(2) The shaft, the blade and the shell can all transfer heat, the drying area is large, the drying speed is fast, the thermal efficiency is more than twice that of the ordinary drying equipment, and the thermal efficiency can reach more than 80%;

(3) Various operation methods, which can be operated intermittently or continuously, can be pressurized or vacuum operated, and also suitable for heat sensitive materials;

(4) The shaft speed can be adjusted (generally 3~25r/min, peripheral speed 0.03~1.5 m/s), which can control material drying temperature, drying time, final moisture content, output, etc., and the material is evenly mixed and evenly dried. ;

(5) Because it is conduction heating, the amount of gas required for drying is small, energy saving is remarkable, 40% steam is saved compared with similar products, and electricity saving is 30%;

(6) There is very little dust entrainment, and the discharged gas is easy to handle, and the subsequent processing equipment such as the powder object collection system and the material vapor recovery system have small load, or may be omitted;

(7) The structure of the paddle is special, and the heating surface has self-cleaning function;

(8) When an inert gas is used as the carrier, the organic solvent can be recovered;

(9) The rotation of the two shafts at low speed, the amount of wear of the blades and the shaft is small;

(10) There are few wearing parts, and the operation and maintenance cost is low. Only the inner static ring of the bearing bush and the rotary joint is a wearing part.

As a new type of energy-saving dryer, the paddle dryer is widely used in the background of energy saving and environmental protection because of its energy saving, good operating environment and wide applicability. Moreover, the equipment manufacturing trend is becoming larger and higher. The development of the finish.

Therefore, the market prospects for paddle dryers are broad and require intensive research and design. In this paper, the finite element method is used to analyze the stress levels of the main components of the dryer for various designs of the specific design, in order to provide some suggestions for the optimization of the strength of the dryer.

Stress calculation

In view of the complexity of the structure and working conditions of the dryer, this paper uses the large finite element software ANSYS to calculate the stress distribution of the main part of the equipment and the hollow blade, and then evaluate the strength of the equipment. To this end, combined with the actual initial design dimensions and structural features, the dryer body uses a three-dimensional mechanical model, while the blades use an axisymmetric two-dimensional model.

The design pressure and design temperature of the dryer were 1.3 MPa and 180 °C, respectively. The boundary condition of the main body of the dryer: select either side as the symmetrical boundary condition, the other side of the head period coupling constraint and the end force load; the upper end face limits the normal displacement of the end face; the pressure is applied to the pressed part of the whole structural model; Close the symmetry boundary. Dryer blade boundary conditions: The lower section of the central axis and the lower section of the blade are symmetric boundaries, and the end face force load is applied to the section on the central axis; the pressure load is applied correspondingly at the pressed part.

The stress of the main structure of the dryer is larger: the connection between the support pipe and the jacket; the greater stress of the hollow blade is the connection between the blade and the central axis (on the blade).

Structure Stress classification Stress value Assessment Result
Dryer body Partial film stress 176 <1.5*125 Failed
Primary + secondary stress 524.9 > 3*125
Hollow paddle (a) Partial film stress 43 <1.5*125 Failed
Primary + secondary stress 422.5 > 3*125
Hollow paddle (b) Partial film stress 42.31 <1.5*125 Failed
Primary + secondary stress 404.3 > 3*125

Optimization design of paddle dryer

In view of the unsatisfactory strength of the above initial design structure, some improvements are needed. At the same time, due to the complicated structure of the main body of the dryer and the large number of design parameters, it is necessary to study the degree of the inferiority of the influence of these parameter changes on the equipment stress, and finally provide some suggestions for the optimization design of the strength of the dryer.

1. Optimized design of the main structure of the dryer

By comparing the second and third schemes with the scheme one, it can be found that the scheme 2 is the best, that is, increasing the wall thickness of the support pipe is more effective than increasing the wall thickness of the jacket to effectively improve the main body strength of the dryer.

2. Improved design of hollow blade of dryer

The improvement scheme and finite element calculation results of the two hollow blade structures of the dryer can be found that the increase of the thickness of the blade plays a major reinforcing role, and the thickness of the central axis can be reduced within a certain range.

In conclusion

As a new type of energy-saving dryer, the hollow blade dryer has been paid more and more attention, and the application field has expanded rapidly. It has prompted designers to deeply study the optimization design of the dryer structure and further develop the reliability, rationality and economy of the equipment.

In this paper, the finite element method is used to analyze the stress intensity of the main components of the hollow blade dryer, such as the main body and the blade section, and the optimization design of the equipment strength is preliminarily carried out. Some useful suggestions are put forward:

(1) Increasing the wall thickness of the support pipe to increase the wall thickness of the jacket can more effectively improve the strength of the dryer body.

(2) The increase in the thickness of the blade plays a major reinforcing role, and the thickness of the central axis is correspondingly reduced under the permission conditions.

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 sludge paddle dryer is used in printing and dyeing, paper making, biological, electroplating, thermoelectric, chemical and sewage treatment plants. The content and requirements of structural design are also very different, but all have the same commonality. The functional design meets the functional requirements of the main sludge dryer and is technically specific. Such as the realization of the working principle, the reliability of the work, the process, materials and assembly.

Quality design takes into account various requirements and limitations, improving product quality and price/performance ratio, and it is a feature of modern engineering design. Specifically, there are many other requirements and restrictions such as operation, aesthetics, cost, safety, and environmental protection. In modern design, quality design is very important and often determines the competitiveness of the product. The design era of sludge-specific dryers that only meet the requirements of major technical functions has passed, and the overall consideration of various requirements and improvement of product quality is the key to the design of modern sludge dryers.

Sludge paddle dryer features

1. The material retention time is adjustable, it can process high water content materials, and can also obtain very low water content materials;
2. Typical conduction drying method, energy saving, large transmission coefficient, high thermal efficiency;

3. Since the required heat is all supplied by the hollow blades and the jacket, in order to reduce the humidity of the exhaust gas, a small amount of hot air is added, the dust entrainment is low, the exhaust gas is easy to handle, and auxiliary equipment such as dust removal is not required;

4. The blade has self-cleaning ability. The blades rotate in opposite directions, and the two inclined surfaces of the blade repeatedly stir, compress, relax and propel the material, so that the page has a unique byte capacity, the heating surface is continuously updated, and the heat transfer coefficient of the sludge paddle dryer is higher than other Any conduction drying method.

Manufacturing material of sludge paddle dryer

The sludge paddle dryer system is one of the thermal technologies we use to develop industrial process systems to meet your application needs. A series of pitch-adjustable blades are produced for high-speed rotation to keep the material constant, agitated contact, and prevent heat transfer wall contamination. All parts in contact with the product are made of AISI 316L stainless steel, but other weldable materials such as Alloy C-22 and AISI 904L are available upon request.

The drying chamber wall, the agitator shaft and the inlet and outlet are heated by a circulating heat transfer fluid to prevent cold spots that may cause solvent condensation or product build-up. The inner surface of the drying chamber is ground or electropolished to optimize corrosion resistance, reduce product adhesion and friction, improve powder flow behavior and facilitate cleaning operations.

A double-layer mechanical sealing system is installed on the shaft of the agitator. The purpose of the research is to ensure the vacuum tightness of the ^ and the purity of the dried material to avoid the risk of contamination of the product. The mechanical seal can be a conventional type of wet rinse or nitrogen transfer dry.

Manufacturing process of sludge paddle dryer

(1) Parts processing to ensure penetration and welding.

(2) Large-scale equipment is processed after welding to ensure the running accuracy.

(3) Manufacture and X-ray, airtightness and water pressure test according to the pressure vessel manufacturing standards.

(4) Sand blasting, rust removal, and paint.

Sludge paddle dryer design process

The advanced state of the sludge paddle dryer is inextricably linked with the market demand. Therefore, in the initial stage of market research, relevant technical personnel should develop an effective equipment research and development plan for the actual situation, and then send some professionals to the market to fully understand. The current level of technology and the problems faced by sludge dryers on the market, and the evaluation and analysis of the economic benefits brought about by equipment development, for the design of the later sludge paddle dryer fully prepared.

The effective heating area of ​​the sludge paddle dryer is the highest, theoretically up to 100%. However, if the design and selection of the rakes are improper, the actual effective heating area will be reduced, and some may even be as low as 50%. The bare area seriously affects the normal performance of the sludge dryer. Through theoretical analysis and graphical analysis method, some guidelines for the design of the blade of the sludge dryer are given, which can eliminate the exposed area of ​​the disk surface, improve the comprehensive heat and mass transfer coefficient of the dryer, and ensure the energy saving advantage of the sludge dryer.

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.

First, introduction
As the urban sewage treatment rate increases year by year, sludge production also increases dramatically. According to the “Environmental Statistics Annual Report 2010” of the Ministry of Environmental Protection, at the end of 2010, there were 2,881 urban sewage treatment plants in China with a designed processing capacity of 123.31 million t/d, and a total of 33.62 million tons of wastewater was treated throughout the year. Based on this calculation, the annual sludge production in Chinese cities is estimated to be nearly 30 million tons (80% water content). Effective reduction and disposal of sludge has become an important task for environmental protection.

Sludge drying is an intermediate link in the final disposal of sludge. After drying, the sludge can obtain low calorific value that reaches the level of self-sustaining combustion, and can reach a certain level of hygiene and harmlessness. Disposition provides conditions.

Second, the blade dryer

The paddle dryer is a horizontal agitating continuous drying device mainly based on heat conduction. It is mainly composed of a jacketed cylinder, a hollow blade shaft and a driving device. It is imported and exported from the rotary joint of the shaft end, and the heating medium is respectively Enter the inner casing of the dryer casing and the inner cavity of the blade shaft, heat the inner wall of the dryer, the hollow blade and the hollow shaft, and dry the material by means of heat conduction. The material continuously enters the dryer, and is continuously turned over under the continuous rotation and stirring of the hollow blade, so that the material can be fully and uniformly heated. The inclined blade conveys the dried material to the discharge port while rotating.

The paddle dryer has the characteristics of low energy consumption, high heat utilization rate, safety and reliability, low equipment occupation and investment, low operation and maintenance cost, self-purification ability and strong regularity of dry particles.

Third, engineering application

A total treatment capacity of 300t / d sludge drying treatment project, covering an area of ​​2800m <sup> 2 </sup>, drying sludge containing 75% ~ 85% water to 10% ~ 30% water; drying equipment Three paddle dryers are used, each with a processing capacity of 100t/d; the heat source is steam generated by the waste incineration power plant, and the sludge is dried into a waste incineration power plant to achieve sludge decontamination. Targets for reduction, stabilization, and resource utilization. The sludge treated by the project comes from the urban sewage treatment plant. Due to the imperfect rainwater and sewage diversion pipelines in the project service area, the sludge has a large amount of sand and low organic matter content.

(1) Process Description

The sludge drying treatment process of the project mainly includes the following systems: wet sludge storage and transportation system, drying system, dry sludge storage and transportation system, odor processing system, electrical system, automatic control system; wherein the drying system is 3 oars The leaf type sludge drying production line, each blade type sludge drying production line mainly includes one paddle type dryer, one carrier gas washing tower, and one carrier gas circulation fan. The operation of the paddle sludge drying production line is described below.

(1) The sludge entering the dryer is subjected to intense agitation and vibration under the action of the blades, and the heating at the heating interface, the moisture content is quickly evaporated;

(2) Under the action of the circulating fan, the air as the carrier gas flows through the dryer quickly, carrying moisture, ensuring the evaporation rate and diffusion speed of the sludge moisture;

(3) The carrier gas is discharged from the dryer and treated by the washing tower to remove a large amount of water vapor and a small amount of dust contained in the carrier gas;

(4) Most of the treated carrier gas is passed to the dryer for recycling, and the other part enters the deodorization system.

(2) Operation cost analysis

Analysis of resources and energy demand in the operation of the drying process shows that the resource and energy consumption costs are 49,210 yuan / d, and the dry sludge resources and energy consumption cost per ton are 164 yuan.

Fourth, the conclusion

Through the successful application of the paddle dryer in the sludge miniaturization project, it is concluded that it has great technical and economic advantages as a sludge drying technology:

(1) The paddle-type sludge drying process is safe, stable and reliable, and can be minimized, and the pollutant discharge can meet the discharge standard requirements;

(2) Low engineering investment and operating costs, small floor space and low energy consumption;

(3) The management is simple, convenient, and flexible in operation mode. The operation mode and parameters can be adjusted according to the nature and quantity of sludge in different seasons;

(4) Facilitate automatic control of sludge treatment and disposal process and improve management level;

(5) The paddle dryer uses steam as a heat source, which is operated in conjunction with waste incineration power generation equipment. With the concept of circular economy, it can maximize resource conservation and reduce energy consumption.