A roll dryer and a drying method thereof

Abstract

The application discloses a roll-type dryer, which comprises a top plate and a bottom plate, a heat exchange body is connected between the top plate and the bottom plate, a receiving hopper and a secondary steam discharge port are connected to the upper end surface of the top plate, the heat exchange body is vertically connected by multiple heat exchange units with the same size, the heat exchange unit comprises a roll-tube heat exchanger and a material-bearing tube heat exchanger, the material-bearing tube heat exchanger is located below the roll-tube heat exchanger, the roll-tube heat exchanger comprises multiple groups of heat exchange rollers, an internal dust collector is connected to the upper end surface of the heat exchange body, the internal dust collector is fixed on the top plate, the inner cavity of the internal dust collector is communicated with the heat exchange body and the secondary steam discharge port, the lower end surface of the heat exchange body is connected with the bottom plate, a discharge port is arranged on the bottom plate and communicated with the heat exchange body, and a discharger is connected to the discharge port. The application can effectively solve the problems of material agglomeration and thick material layer, realize the timely separation of secondary steam from the material, and improve the material drying effect.

Description

Technical Field

[0001] This invention belongs to the field of wet material drying technology, specifically relating to a roller dryer and its drying method. Background Technology

[0002] Wet materials are dispersible materials with high moisture content, generated in large quantities in industrial, agricultural, and daily life processes, such as various industrial sludge, coal slime, tailings sludge, and river silt. Existing wet material drying processes commonly encounter common problems such as material agglomeration, thick material layers, and difficulty in the escape of secondary steam. Wet materials, due to their high moisture content, are prone to agglomeration and have a certain degree of viscosity, leading to scaling on the heat exchange surfaces of equipment during production. This results in insufficient heat exchange and low heat exchange efficiency, as well as impeded material flow, even causing blockages and production shutdowns. Thick material layers increase heat transfer resistance, making it difficult for moisture to escape, ultimately leading to low drying efficiency and increased energy consumption. The timely escape of secondary steam from the material layer is crucial to ensuring the dryness of the wet material; difficulty in the escape of secondary steam and the inability to obtain dry material in a timely manner directly affect product quality and production capacity. Therefore, solving the three major problems in the drying process of wet materials—material sticking to the heat exchange surface and hindering heat exchange, thick material layer hindering mass transfer, and difficulty in the escape of secondary steam affecting the dehydration rate—is the key to improving drying efficiency, increasing drying capacity, and reducing drying investment and costs.

[0003] The patent for "A High-Efficiency Heat Exchanger and Its Working Method" (Patent No.: CN202010743628.6) adopts a vertical multi-layer disturbance drying design, which can effectively solve the problems of material agglomeration and thick material layers. However, it cannot achieve timely removal of secondary steam from the material, resulting in limited material dryness and production capacity, making it difficult to meet market demands for high dryness and large production capacity. The patent for "A Drying Equipment and Drying System" (Patent No.: CN202221882384.0) proposes using a horizontal spiral tube heat exchanger to dry wet materials, which can effectively solve the problems of thick material layers and difficulty in secondary steam escape. However, it is prone to clogging of the spiral grooves by wet materials and is only suitable for drying and dehydrating loose materials with low moisture content, not for drying and dehydrating sticky and wet materials with high moisture content. Summary of the Invention

[0004] The purpose of this invention is to provide a roller dryer and its drying method, which can effectively solve the problems of material agglomeration and thick material layers, realize the timely removal of secondary steam from the material, and improve the drying effect of the material.

[0005] To achieve the above objectives, the present invention provides a roller dryer, comprising a top plate and a bottom plate, the bottom plate being fixedly connected to a support, a heat exchange body being connected between the top plate and the bottom plate, a receiving hopper and a secondary steam outlet being connected to the upper surface of the top plate, and the heat exchange body being formed by vertically connecting multiple layers of heat exchange units of the same specifications and dimensions.

[0006] The upper end face of the heat exchange body is provided with a built-in dust collector, which is fixed on the top plate. Its inner cavity is connected to the heat exchange body and the secondary steam outlet. The lower end face of the heat exchange body is connected to the bottom plate. The bottom plate is provided with a discharge port connected to the heat exchange body, and a discharge device is connected to the discharge port.

[0007] The heat exchange unit includes an outer frame, an inner side plate, a roller tube heat exchanger, a feed tube heat exchanger, a motor, a rotary joint, and a heat exchange medium collection pipe. The outer frame is formed by two side plates and two outer perforated plates joined together. The inner side plate is composed of two inner perforated plates, which are parallel to each other and located inside the two outer perforated plates, and are fixed to the side plates at both ends. A secondary steam flow channel is left between the inner side plate and the outer perforated plate. The secondary steam flow channels of each heat exchange unit are vertically spliced ​​to form a vertical steam channel.

[0008] The outer side of the outer perforated plate is provided with a bearing and a seal for mounting a roller tube heat exchanger. One end of the roller tube heat exchanger is located outside the bearing and connected to a sprocket. The motor is connected to the sprocket via a chain.

[0009] The heat exchanger body has a heat exchange medium outlet connected to the side closer to the motor and a heat exchange medium inlet connected to the side farther from the motor.

[0010] The roller tube heat exchanger includes multiple sets of horizontally arranged heat exchange rollers. Each heat exchange roller passes through an inner side plate and an outer perforated plate at both ends in sequence, and is connected to a heat exchange medium collection pipe through a rotary joint. One side of the heat exchange medium collection pipe is connected to the heat exchange medium inlet, and the other side of the heat exchange medium collection pipe is connected to the heat exchange medium outlet.

[0011] The feed tube heat exchanger is located below the roller tube heat exchanger.

[0012] As a further aspect of the present invention: the heat exchange roller includes a shaft tube, and multiple annular rollers are axially and equally spaced parallel welded to the outer surface of the shaft tube, and the rollers of adjacent heat exchange rollers are arranged in a cross-shaped arrangement on the horizontal plane.

[0013] As a further aspect of the present invention: the outer edge of the roller has a circumferentially distributed sawtooth structure, with three adjacent teeth forming a group, and the tips of the sawtooth teeth in each group being distributed in a tree-branch shape.

[0014] As a further aspect of the present invention: the feed tube heat exchanger includes multiple horizontally closely arranged parallel rectangular tubes and vertical rectangular tubes fixedly connected to both ends of the parallel rectangular tubes. One of the outermost parallel rectangular tubes of the feed tube heat exchanger is fixedly connected to one side plate of the outer frame, and the vertical end face of the other outermost parallel rectangular tube forms a discharge port with the inner end face of another side plate of the outer frame. The discharge ports of each heat exchange unit are alternately distributed. The upper end face of the vertical tube is fixedly connected to the lower end face of the inner side plate. The two vertical tubes are respectively connected to the heat exchange medium collection pipes on both sides through connecting pipes.

[0015] As a further aspect of the present invention: the upper surface of the heat exchanger of the feed tube is welded with multiple heat-conducting fins at equal intervals perpendicular to the parallel rectangular tube. The horizontal distance between adjacent heat-conducting fins on the same parallel rectangular tube is the same as the horizontal distance between the rollers directly above it. Furthermore, the heat-conducting fins on the same parallel rectangular tube are arranged vertically and alternately with the adjacent rollers directly above them at equal intervals.

[0016] As a further aspect of the present invention: the upper end face of the inner side plate is lower than the upper end face of the outer hole plate, but higher than the maximum outer diameter of the roller.

[0017] The present invention also provides a drying method for a roller dryer, comprising the following steps:

[0018] Step 1: Dryer Preheating: The external heat exchange medium enters the heat exchange medium collection pipe from the heat exchange medium inlet. A portion of the heat exchange medium is then fed into the rotary joint, and from there into the shaft tube of the roller tube heat exchanger, preheating the roller tube heat exchanger. The other portion of the heat exchange medium enters a vertical tube of the feed tube heat exchanger and then into a parallel rectangular tube, preheating the feed tube heat exchanger. Once the roller tube heat exchanger and the feed tube heat exchanger reach the set drying temperature, the dryer preheating is complete.

[0019] Step 2: Drying and dehydrating wet materials to generate secondary steam: Once the overall temperature of the dryer reaches the set temperature, the motor is turned on. The motor drives all heat exchange rollers in the same layer to rotate in the same direction via chain drive. Feeding begins from the receiving hopper. The wet material enters the outer surface of the uppermost heat exchange roller and the upper surface of the heat exchanger in the receiving tube. Under the action of friction and centrifugal force on the outer surface of the rotating rollers and shaft tube, the wet material rotates synchronously with the heat exchange rollers. When the wet material between the rollers rotates 180°, it is blocked by the rollers of the adjacent heat exchange rollers and pushed by the opposite direction of material movement, realizing online cleaning of the material between the rollers. At the same time, the wet material is relayed forward between adjacent heat exchange rollers, completing the same-layer conveying of wet material. When the material has passed through the first layer, it falls from the discharge port into the next layer by its own weight to continue to be heated, dried and dehydrated, and finally comes out from the bottom discharge port. In addition, since the rollers and shaft tube are good heat conductors, the heat in the heat exchange medium in the shaft tube is quickly transferred to the wet material, accelerating the drying and dehydration of the wet material and generating secondary steam.

[0020] Step 3, Secondary Steam Escape: The secondary steam generated by the drying and dehydration of wet materials in each heat exchange unit escapes from the secondary steam flow channel between the outer perforated plate and the inner side plate, enters the vertical steam channel, and then enters the built-in dust collector through the vertical steam channel. The secondary steam after dust removal is discharged from the secondary steam outlet.

[0021] Step 4: Dry material discharge: Turn on the discharge device to discharge the dry material from the bottom discharge port after drying, thus completing the material drying process.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] Roller tube heat exchangers are both material conveying mechanisms and heat exchange mechanisms. They can simultaneously achieve thin-layer drying of wet materials on the heat exchange surface and online cleaning of materials on the heat exchange surface, causing the materials to continuously tumble and move forward, enhancing heat transfer between materials and between materials and the metal heat exchange surface, thereby improving heat exchange efficiency.

[0024] The secondary steam generated during the drying and dehydration of wet materials rises directly through a vertical steam channel, reducing the residence time of the secondary steam in the dryer, improving the drying mass transfer efficiency, and reducing the resistance to secondary steam escape, thus achieving energy saving and facilitating industrial production applications. Attached Figure Description

[0025] Figure 1 This is a front view of the roller dryer in this invention;

[0026] Figure 2 This is a top view of the heat exchange unit in this invention;

[0027] Figure 3 This is a front view of the heat exchange unit in this invention;

[0028] Figure 4 This is a top view of the feed tube heat exchanger in this invention;

[0029] Figure 5 This is a front view of the feed tube heat exchanger in this invention;

[0030] Figure 6 This is a diagram of the outer edge structure in this invention.

[0031] Among them, 1. receiving hopper, 2. secondary steam outlet, 3. top plate, 4. built-in dust collector, 5. support frame, 6. heat exchange unit, 7. heat exchange medium inlet, 8. heat exchange medium outlet, 9. bottom plate, 10. discharge port, 11. discharge device.

[0032] 6-1. Outer frame; 6-2. Inner plate; 6-3. Heat exchange medium collection pipe; 6-4. Rotary joint; 6-5. Shaft tube; 6-6. Roller; 6-7. Bearing; 6-8. Seal; 6-9. Sprocket; 6-10. Chain; 6-11. Motor; 6-12. Heat-conducting fins; 6-13. Parallel rectangular tube; 6-14. Vertical rectangular tube; 6-15. Connecting pipe.

[0033] 6-1-1, Side plate; 6-1-2, Outer perforated plate;

[0034] 6-6-1, Left-leaning tooth; 6-6-2, Right-leaning tooth; 6-6-3, Upright tooth. Detailed Implementation

[0035] The invention will now be further described with reference to the accompanying drawings.

[0036] like Figures 1 to 3 As shown, a roller dryer includes a top plate 3 and a bottom plate 9. The bottom plate 9 is fixed to a support 5. A heat exchange body is connected between the top plate 3 and the bottom plate 9. A receiving hopper 1 and a secondary steam outlet 2 are connected to the upper end face of the top plate 3. The heat exchange body is formed by vertically connecting multiple layers of heat exchange units 6 with the same specifications and dimensions.

[0037] An internal dust collector 4 is provided on the upper end face of the heat exchange body. The internal dust collector 4 is fixed on the top plate 3. Its inner cavity is connected to the heat exchange body and the secondary steam outlet 2. The lower end face of the heat exchange body is connected to the bottom plate 9. The bottom plate 9 is provided with an outlet 10 connected to the heat exchange body. A discharge device 11 is connected to the outlet 10.

[0038] The heat exchange unit 6 includes an outer frame 6-1, an inner side plate 6-2, a roller tube heat exchanger, a feed tube heat exchanger, a motor 6-11, a rotary joint 6-4, and a heat exchange medium collection pipe 6-3. The outer frame 6-1 is formed by two side plates 6-1-1 and two outer perforated plates 6-1-2. The inner side plate 6-2 is composed of two inner perforated plates, which are located parallel to each other inside the two outer perforated plates 6-1-2, and their two ends are fixed to the side plates 6-1-1 respectively. A secondary steam flow channel is left between the inner side plate 6-2 and the outer perforated plate 6-1-2. The secondary steam flow channels of each heat exchange unit 6 are vertically spliced ​​to form a vertical steam channel.

[0039] The outer side of the outer perforated plate 6-1-2 is equipped with a bearing 6-7 and a seal 6-8 for mounting the roller tube heat exchanger. The inner ends of the bearing 6-7 and the seal 6-8 are tightly fitted with the outer surface of the shaft tube 6-5, which serves to support and fix the heat exchange roller. One end of the roller tube heat exchanger is located outside the bearing 6-7 and is connected to a sprocket 6-9. The motor 6-11 is connected to the sprocket 6-9 through a chain 6-10. Each heat exchange unit 6 is equipped with a separate motor 6-11, so that the speed of each heat exchange roller is independently adjustable. This speed directly affects the material conveying capacity of the dryer and the residence time of the material in the dryer. In the engineering design, the speed should prioritize meeting the residence time in the dryer to ensure the drying effect of the material.

[0040] The heat exchange body is connected to a heat exchange medium outlet 8 on the side closer to the motor 6-11 and a heat exchange medium inlet 7 on the side farther away from the motor 6-11.

[0041] The roller tube heat exchanger includes multiple sets of horizontally arranged heat exchange rollers. Each heat exchange roller passes through an inner side plate 6-2 and an outer perforated plate 6-1-2 at both ends, and is connected to a heat exchange medium collection pipe 6-3 via a rotary joint 6-4. One side of the heat exchange medium collection pipe 6-3 is connected to the heat exchange medium inlet 7, and the other side of the heat exchange medium collection pipe 6-3 is connected to the heat exchange medium outlet 8. The diameter of the holes on the inner side plate 6-2 and the outer perforated plate 6-1-2 matches the outer diameter of the shaft tube 6-5, which facilitates the heat exchange rollers to fit through.

[0042] The material receiving tube heat exchanger is located below the roller tube heat exchanger and works in conjunction with the roller tube heat exchanger to dry and convey materials.

[0043] To facilitate the cleaning of materials adhering to the heat exchange rollers, the heat exchange rollers further include a shaft tube 6-5, on which multiple annular rollers 6-6 are axially and equally spaced and parallelly welded on the outer surface of the shaft tube 6-5. The rollers 6-6 of adjacent heat exchange rollers are arranged in a cross-shaped horizontal plane, forming an interlocking structure.

[0044] The design principle for the distance between adjacent rollers 6-6 on the same shaft tube 6-5 should be to maximize the heat exchange area while ensuring smooth material removal of rollers 6-6. In this invention, the distance is preferably 10mm-50mm. The design principle for the minimum distance between the outer end face of roller 6-6 and the outer wall of the adjacent shaft tube 6-5 should be to minimize the distance while ensuring smooth material removal of rollers 6-6. In this invention, the distance is preferably 5mm-10mm.

[0045] Furthermore, the outer edge of roller 6-6 has a circumferentially distributed sawtooth structure, with every three adjacent teeth forming a group, and the tips of the teeth in each group distributed in a tree-like pattern. For example... Figure 6 As shown, one is a left-biased tooth 6-6-1 with its tip pointing to the left, another is a right-biased tooth 6-6-2 with its tip pointing to the right, and the third is an upright tooth 6-6-3 with its tip not biased. The design principle for the distance between the tips of the left-biased tooth 6-6-1 and the right-biased tooth 6-6-2 and the center of the roller 6-6 should be increased as much as possible while meeting the requirements of processing mechanical strength and smooth online cleaning of materials between the rollers 6-6. In this invention, it is preferably 5-25mm.

[0046] like Figure 4 and Figure 5As shown, the feed tube heat exchanger includes multiple horizontally arranged parallel rectangular tubes 6-13 and vertical rectangular tubes 6-14 fixedly connected to both ends of the parallel rectangular tubes 6-13. One of the outermost parallel rectangular tubes 6-13 is fixedly connected to one side plate 6-1-1 of the outer frame 6-1, and the vertical end face of the other outermost parallel rectangular tube 6-13 forms a discharge port with the inner end face of the other side plate 6-1-1 of the outer frame 6-1. The discharge ports of each heat exchange unit 6 are alternately distributed to make full use of the heat exchange area of ​​each layer, extend the drying time of the material, ensure that the material is fully dried, and prevent the material from falling short-circuited between layers. The upper end face of the vertical rectangular tube 6-14 is fixedly connected to the lower end face of the inner side plate 6-2. The two vertical rectangular tubes 6-14 are respectively connected to the heat exchange medium collection pipes 6-3 on both sides through connecting pipes 6-15.

[0047] Furthermore, multiple heat-conducting fins 6-12 are welded at equal intervals perpendicular to the parallel rectangular tubes 6-13 on the upper surface of the heat exchanger to further improve heat exchange efficiency. The horizontal distance between adjacent heat-conducting fins 6-12 on the same parallel rectangular tube 6-13 is the same as the horizontal distance between the corresponding rollers 6-6 directly above it, and the heat-conducting fins 6-12 on the same parallel rectangular tube 6-13 are vertically staggered at equal intervals with the corresponding adjacent rollers 6-6 directly above them.

[0048] To facilitate the escape of secondary steam, the horizontal distance between the adjacent surfaces of the inner side plate 6-2 and the outer perforated plate 6-1-2 should be designed to meet the requirements for the escape of secondary steam, preferably 50-200mm in this invention; the upper end face of the inner side plate 6-2 is lower than the upper end face of the outer perforated plate 6-1-2, and this distance should be designed to meet the requirements for the escape of the amount of secondary steam generated by the heat exchange unit 6, preferably 30-150mm in this invention; the upper end face of the inner side plate 6-2 should be higher than the maximum outer diameter of the roller 6-6 by a certain distance to prevent material from escaping, preferably 50-100mm in this invention.

[0049] The present invention also provides a drying method for a roller dryer, comprising the following steps:

[0050] Step 1: Dryer Preheating: External heat exchange medium enters the heat exchange medium collection pipe 6-3 from the heat exchange medium inlet 7. A portion of the heat exchange medium is then fed into the rotary joint 6-4, and from there into the shaft tube 6-5 of the roller tube heat exchanger, preheating the roller tube heat exchanger. The remaining heat exchange medium enters a vertical rectangular tube 6-14 of the feed tube heat exchanger, and from there into the parallel rectangular tube 6-13, preheating the feed tube heat exchanger. Once both the roller tube heat exchanger and the feed tube heat exchanger reach the set drying temperature, the dryer preheating is complete.

[0051] Step 2: Drying and dehydrating the wet material to generate secondary steam: Once the overall temperature of the dryer reaches the set temperature, motor 6-11 is turned on. Motor 6-11 drives all heat exchange rollers in the same layer to rotate in the same direction via chain 6-10. Feeding begins from hopper 1. The wet material enters the outer surface of the uppermost heat exchange roller and the upper surface of the heat exchanger in the receiving tube from hopper 1. Under the action of friction and centrifugal force on the outer surface of the rotating rollers 6-6 and the shaft tube 6-5, the wet material rotates synchronously with the heat exchange rollers. When the wet material between rollers 6-6 rotates 180°, it is absorbed by the adjacent heat exchange rollers. The rollers 6-6 act as blocks and apply a pushing force in the opposite direction of material movement, achieving online cleaning of material between rollers 6-6. At the same time, wet material relays forward between adjacent heat exchange rollers, completing the same-layer conveying of wet material. When the material has passed through the first layer, it falls from the discharge port into the next layer by its own weight to continue being heated, dried, and dehydrated, and finally comes out from the bottom discharge port 10. In addition, since both rollers 6-6 and shaft tube 6-5 are good heat conductors, the heat in the heat exchange medium in shaft tube 6-5 is quickly transferred to the wet material, accelerating the drying and dehydration of the wet material and generating secondary steam.

[0052] Step 3, Secondary Steam Escape: The secondary steam generated by the drying and dehydration of the wet material in each heat exchange unit 6 escapes from the secondary steam flow channel between the outer perforated plate 6-1-2 and the inner side plate 6-2, enters the vertical steam channel, and then enters the built-in dust collector 4 through the vertical steam channel. The secondary steam after dust removal is discharged from the secondary steam outlet, and the dust generated by the built-in dust collector 4 falls onto the upper surface of the top heat exchange roller and falls down from the feed port to the discharge port 10 along with the material.

[0053] Step 4: Dry Material Discharge: The discharge device 11 is activated to discharge the dry material from the bottom outlet 10 after drying, completing the material drying process. After heat exchange, the heat exchange medium exits from the parallel rectangular tube 6-13 and enters another vertical rectangular tube 6-14, then exits from this vertical rectangular tube 6-14 and enters another heat exchange medium collection pipe 6-3, finally entering the heat exchange medium outlet 8 from the heat exchange medium collection pipe 6-3. The heat exchange medium includes, but is not limited to, high-temperature flue gas, high-temperature steam, and high-temperature heat transfer oil.

Claims

1. A roller dryer, comprising a top plate (3) and a bottom plate (9), the bottom plate (9) being fixedly connected to a support (5), a heat exchange body being connected between the top plate (3) and the bottom plate (9), and a receiving hopper (1) and a secondary steam outlet (2) being connected to the upper end face of the top plate (3), characterized in that, The heat exchange body is formed by vertically connecting multiple layers of heat exchange units (6) of the same specifications and dimensions; The upper end face of the heat exchange body is provided with a built-in dust collector (4), which is fixed on the top plate (3). Its inner cavity is connected to the heat exchange body and the secondary steam outlet (2). The lower end face of the heat exchange body is connected to the bottom plate (9). The bottom plate (9) is provided with a discharge port (10) connected to the heat exchange body. A discharge device (11) is connected to the discharge port (10). The heat exchange unit (6) includes an outer frame (6-1), an inner side plate (6-2), a roller tube heat exchanger, a feed tube heat exchanger, a motor (6-11), a rotary joint (6-4), and a heat exchange medium collection pipe (6-3). The outer frame (6-1) is formed by two side plates (6-1-1) and two outer perforated plates (6-1-2) joined together. The inner side plate (6-2) is formed by two inner perforated plates, which are located parallel to each other inside the two outer perforated plates (6-1-2) and are fixed at both ends to the side plates (6-1-1). A secondary steam flow channel is left between the inner side plate (6-2) and the outer perforated plate (6-1-2). The secondary steam flow channels of each heat exchange unit (6) are vertically spliced ​​to form a vertical steam channel. The outer perforated plate (6-1-2) is provided with a bearing (6-7) and a seal (6-8) for mounting a roller tube heat exchanger. One end of the roller tube heat exchanger is located outside the bearing (6-7) and connected to a sprocket (6-9). The motor (6-11) is connected to the sprocket (6-9) via a chain (6-10). The heat exchange body is connected to a heat exchange medium outlet (8) on the side closer to the motor (6-11) and a heat exchange medium inlet (7) on the side farther away from the motor (6-11). The roller tube heat exchanger includes multiple sets of horizontally arranged heat exchange rollers. Each heat exchange roller passes through an inner side plate (6-2) and an outer perforated plate (6-1-2) at both ends, and is connected to a heat exchange medium collection pipe (6-3) through a rotary joint (6-4). One side of the heat exchange medium collection pipe (6-3) is connected to the heat exchange medium inlet (7), and the other side of the heat exchange medium collection pipe (6-3) is connected to the heat exchange medium outlet (8). The feed tube heat exchanger is located below the roller tube heat exchanger. The heat exchange roller includes a shaft tube (6-5), and multiple annular rollers (6-6) are axially and parallelly welded at equal intervals on the outer surface of the shaft tube (6-5), and the rollers (6-6) of adjacent heat exchange rollers are arranged in a cross pattern on the horizontal plane. The outer edge of the roller (6-6) has a circumferentially distributed sawtooth structure, with three adjacent teeth forming a group, and the tips of the teeth in each group of sawtooths are distributed in a tree-branch shape.

2. The roller dryer according to claim 1, characterized in that, The heat exchanger for the feed tube includes multiple horizontally arranged parallel rectangular tubes (6-13) and vertical rectangular tubes (6-14) that are fixedly connected to both ends of the parallel rectangular tubes (6-13). One of the outermost parallel rectangular tubes (6-13) of the heat exchanger is fixedly connected to one side plate (6-1-1) of the outer frame (6-1). The vertical end face of the other outermost parallel rectangular tube (6-13) forms a discharge port with the inner end face of the other side plate (6-1-1) of the outer frame (6-1). The discharge ports of each heat exchange unit (6) are alternately distributed. The upper end face of the vertical rectangular tube (6-14) is fixedly connected to the lower end face of the inner side plate (6-2). The two vertical rectangular tubes (6-14) are respectively connected to the heat exchange medium collection pipes (6-3) on both sides through connecting pipes (6-15).

3. A roller dryer according to claim 2, characterized in that, The upper surface of the heat exchanger is welded with multiple heat-conducting fins (6-12) at equal intervals perpendicular to the parallel rectangular tube (6-13). The horizontal distance between adjacent heat-conducting fins (6-12) on the same parallel rectangular tube (6-13) is the same as the horizontal distance between the corresponding rollers (6-6) directly above it. The heat-conducting fins (6-12) on the same parallel rectangular tube (6-13) are vertically staggered at equal intervals with the adjacent rollers (6-6) directly above them.

4. A roller dryer according to claim 1, characterized in that, The upper end face of the inner side plate (6-2) is lower than the upper end face of the outer hole plate (6-1-2) and higher than the maximum outer diameter of the roller (6-6).

5. A drying method using a roller dryer, characterized in that, The roller dryer according to any one of claims 2-4 includes the following steps: Step 1: Dryer preheating: The external heat exchange medium enters the heat exchange medium collection pipe (6-3) from the heat exchange medium inlet (7), and then a part of the heat exchange medium is fed into the rotary joint (6-4) through the heat exchange medium collection pipe (6-3), and then enters the shaft tube (6-5) of the roller tube heat exchanger through the rotary joint (6-4) to preheat the roller tube heat exchanger; the other part of the heat exchange medium enters a vertical rectangular tube (6-14) of the material receiving tube heat exchanger, and enters the parallel rectangular tube (6-13) from the vertical rectangular tube (6-14) to preheat the material receiving tube heat exchanger; when the roller tube heat exchanger and the material receiving tube heat exchanger reach the set drying temperature, the preheating of the dryer is completed; Step 2: Drying and dehydrating wet materials to generate secondary steam: When the overall temperature of the dryer reaches the set temperature, the motor (6-11) is turned on. The motor (6-11) drives all the heat exchange rollers in the same layer to rotate in the same direction through the chain (6-10). The wet material is fed from the receiving hopper (1) into the outer surface of the uppermost heat exchange roller and the upper surface of the receiving tube heat exchanger. Under the action of friction and centrifugal force on the outer surface of the rotating rollers (6-6) and the shaft tube (6-5), the wet material rotates synchronously with the heat exchange rollers. When the wet material between the rollers (6-6) rotates 180°, it is heated by the adjacent heat exchange rollers. The rollers (6-6) of the hot roller block and apply a pushing force in the opposite direction of the material movement to achieve online cleaning of the material between the rollers (6-6). At the same time, the wet material is relayed between adjacent heat exchange rollers to complete the same-layer conveying of the wet material. When the material has passed the first layer, it falls into the next layer by its own weight from the discharge port to continue to be heated, dried and dehydrated, and finally comes out from the bottom discharge port (10). In addition, since the rollers (6-6) and the shaft tube (6-5) are both good heat conductors, the heat in the heat exchange medium in the shaft tube (6-5) is quickly transferred to the wet material, accelerating the drying and dehydration of the wet material and generating secondary steam. Step 3, Secondary Steam Escape: The secondary steam generated by the drying and dehydration of wet materials in each heat exchange unit (6) escapes from the secondary steam flow channel between the outer perforated plate (6-1-2) and the inner side plate (6-2), enters the vertical steam channel, and then enters the built-in dust collector (4) through the vertical steam channel. The secondary steam after dust removal is discharged from the secondary steam outlet. Step 4: Dry material discharge: Turn on the discharge device (11) to discharge the dry material from the bottom discharge port after drying, thus completing the material drying process.

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