WO1998019972A1

WO1998019972A1 - Method and device for treating organic or inorganic sludge through multi-stage drying process

Info

Publication number: WO1998019972A1
Application number: PCT/KR1997/000216
Authority: WO
Inventors: Hak Jae Kim
Original assignee: Hak Jae Kim
Priority date: 1996-11-07
Filing date: 1997-11-06
Publication date: 1998-05-14
Also published as: KR0177364B1; DK135296A; KR19980034514A

Abstract

A method and device for treating organic or inorganic sludge having a high water content through a multi-stage drying process are disclosed. A multi-layered sludge guide means (200) is arranged in a drying chamber (100) and moves the sludge while heating the sludge by hot air. A hopper (300) is mounted to the device's housing and inputs the sludge into the chamber (100). The sludge input capacity of the hopper (300) is adjustable in accordance with input sludge conditions. A wet vapor exhaust unit (400) forcibly vents wet vapor from the chamber into the atmosphere. A sludge feeding means (600) is arranged on the sludge guide means (200) and continuously feeds the sludge on the guide means while cutting, agitating and crushing the sludge. The method and device of this invention effectively dry the sludge having a high water content of about 80-90 percent, thereby reducing the water content to about 20-30 percent.

Description

METHOD AND DEVICE FOR TREATING ORGANIC OR INORGANIC SLUDGE THROUGH MULTI-STAGE DRYING PROCESS

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates, in general, to a method and device for treating organic or inorganic sludge through a drying process and, more particularly, to a method and device for continuously drying the organic or inorganic sludge generated from, for example, manufacturing plants, filtration plants, sewage disposal plants and stock farms, thus sterilizing the sludge and effectively reducing the water content in the sludge to an appropriate level and lightening the sludge.

Description of the Prior Art

As well known to those skilled in the art, the organic or inorganic sludge generated from manufacturing plants (for example, food processing plants, textile factories and paper mills), filtration plants, sewage disposal plants and stock farms have a water content of about 80 - 90 percent.

When such sludge is buried under the ground, the sludge generates large amounts of toxic water, which contaminates soil and underground water and causes other environmental pollution. Another problem caused by the sludge treatment of burying the sludge under the ground resides in that it is very difficult to find a landfill because of inhabitant's opposition. Therefore, in the near future, it will be almost impossible to treat such sludge by burying. When the total volume and weight of the sludge are remarkably reduced by removing some degree of water from the sludge, it is somewhat easy to treat the sludge. In order to remove water from such sludge, the sludge may be treated by a natural deposition and fermentation process in a sewage disposal plant.

During a natural deposition and fermentation process of sludge in a sewage disposal plant, the sludge is contained in a concrete deposition reservoir for a time, so that the sludge is gradually deposited on the bottom of the reservoir while leaving neutralized water in the upper section inside the reservoir. The neutralized water is sterilized and in turn is discharged into a river. Meanwhile, the concentrated sludge deposited on the reservoir's bottom is collected prior to being fired, buried under the ground or recycled as ferilizer.

However, such a natural deposition and fermentation process for treating the sludge is problematic in that it takes too long and treats only a small quantity of sludge even though it requires large- scaled equipment. Therefore, the above process regrettably limits the amount of sludge to be treated and reduces work efficiency while treating the sludge.

Another problem of the natural deposition and fermentation process resides in that, when various chemicals are added to the sludge in order to ferment and sterilize the sludge, various chemical components may remain in the treated sludge and thereby cause toxic materials, resulting in the disturbance of an ecosystem or environmental pollution such as oil contamination.

It should be understood that it is most preferred to dry the sludge in order to reduce the volume and weight of the sludge while treating the sludge having a high water content. In order to effectively dry the sludge and thereby remove some degree of water from the sludge, an effective sludge drying process has been actively studied recently. In a typical sludge drying device, an adjusting plate is installed in the sludge inlet port of a drying chamber. The sludge inlet port is arranged in the top section of the drying chamber. A plurality of regularly -spaced heating plates are arranged in the drying chamber, while a plurality of screw feeders provided with respective auxiliary vanes are arranged on the heating plates, respectively. In operation of the above device, the sludge is dropped onto the heating plates inside the drying chamber. In the above state, the screw feeders stir up the sludge on the heating plates thereby causing the sludge to be more effectively dried by the heating plates. The above screw feeders also feed the sludge in order to discharge the dried sludge from the drying chamber through an outlet port.

However, the above sludge drying device is problematic in that it is difficult to control the amount of sludge to be fed to the drying chamber. The device also fails to break sludge lumps in the drying chamber, thus reducing work efficiency while agitating and feeding the sludge. When the sludge lumps are heaped in the drying chamber, the screw feeders are inevitably overloaded and damaged thus shortening the expected life span of the sludge drying device.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a method and device for treating organic or inorganic sludge through a multi-stage drying process, in which the above problems can be overcome and which improve work efficiency while drying the sludge.

It is, therefore, an object of the present invention to provide a method and device for treating organic or inorganic sludge through a multi-stage drying process, which not only save the area for installing the sludge drying devic, but also are less likely to cause any secondary environmental pollution.

In order to accomplish the above objects, the present invention provides a device for treating organic or inorganic sludge through a multi-stage drying process. In the device, a multi-layered sludge guide means, which has first- to fifth- stage guide plates, is arranged in a drying chamber of a longitudinal box- shaped housing. The sludge guide means moves the sludge while heating the sludge by hot air inside the chamber. The guide plates are arranged in the chamber in order of the first-, second-, third-, fourth- and fifth- stage plates in a direction from the upper to the lower section. A hopper is mounted to a top end portion of the housing and inputs the sludge into the chamber. The sludge input capacity of the hopper is adjustable in accordance with input sludge conditions. A wet vapor exhaust unit is mounted to the housing at a position in vicinity to the hopper and forcibly vents wet vapor from the chamber into the atmosphere. The exhaust unit has a fan motor and a damper. The damper controls the size of a vent opening of the unit and thereby controls the amount of exhaust wet vapor in accordance with both the drying rate of the sludge and the temperature inside the chamber. A sludge feeding means is rotatably arranged on the sludge guide means and continuously feeds the sludge on the guide means while cutting, agitating and crushing the sludge. A heating means applies the hot air to the sludge guide means and thereby dries the sludge on the guiding means. The heating means comprises a burner generating the hot air, and a nozzle pipe discharging the hot air onto the sludge guide means. The method and device of this invention effectively dry the sludge having high water content of about 80 - 90 percent, thereby reducing the water content to about 20 - 30 percent. The finally-dried sludge can be thus easily treated in a post-treatment process.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a sectional view showing the construction of a sludge drying device in accordance with the primary embodiment of the present invention;

Figs. 2a and 2b are sectional views showing the construction of two types of hoppers selectively installed on the sludge drying device of this invention in accordance with water content of input sludge to be treated by the device; Fig. 3 is a sectional view showing the construction of the sludge inlet part of the drying device provided with the hopper of

Fig. 2a in accordance with the invention; and

Figs. 4a to 4d are perspective and sectional views showing the configuration and consturuction of four types of paddles of a sludge feeding means installed in the drying device of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 is a sectional view showing the construction of a sludge drying device in accordance with the primary embodiment of the present invention. As shown in Fig. 1, the drying device 100 of this invention is encased by a longitudinal box- shaped housing and defines a drying chamber 110. The device 100 also includes a sludge guide means 200, a sludge feeding means 600 and a heating means 700. The sludge guide means 200 comprises five sludge guide plates, that is, first-to fifth- stage guide plates 210, 220, 230, 240 and 250 which are axially arranged in the housing of the device

100, so that organic or inorganic sludge having plenty of water is dried while passing on the above guide plates. The sludge feeding means 600 are arranged on the sludge guide means 200 and continuously feeds the sludge on the guide means 200 while cutting, agitating and crushing the sludge. Meanwhile, the heating means 700 applies hot air to the sludge in order to dry the sludge.

In accordance with the present invention, organic or inorganic sludge is treated by the drying device 100 as follows. When the sludge is input into the drying chamber 110, the sludge is primarily loaded onto the first- stage guide plate 210 and is fed to the second-stage guide plate 220 by the sludge feeding means 600. At a position corresponding to the first-stage plate 210 inside the chamber 110, the temperature inside the chamber 110 is maintained at about 170^°C . The sludge which moves on the first-stage plate 210 is thus preheated to 170 °C . Thereafter, the sludge moves on the second-stage plate 220 in order to be fed to the third-stage guide plate 230 by the sludge feeding means 600. While the sludge moves on the second- stage plate 220, the sludge is heated to about 200 °C and thereby rapidly absorbs latent heat. The sludge is thus brought into a latently -heated state, (the primary drying step of a sludge drying process).

The sludge under the latently -heated state in turn is fed to the third- stage guide plate 230. On the third- stage plate 230, the sludge feeding means 600 feeds the sludge to the fourth- stage plate 240 while further cutting and crushing the sludge. Therefore, water in the sludge on the third-stage plate 230 is more actively vaporized. On the fourth- stage plate 240, the sludge is finally dried. At a position corresponding to the fourth-stage plate 240 inside the drying chamber 110, the temperature of hot air is maintained at about 400 ^°C which is the highest temperature inside the chamber 110. The sludge on the fourth-stage plate 240 is thus heated to about 400 °C and thereby being finally dried, (the final drying step of the sludge drying process).

The finally-dried sludge is fed from the fourth-stage plate 240 to the fifth-stage plate 250 where the sludge is cooled in order to have an appropriate water content. The sludge in turn is discharged from the device 100. In the above sludge drying device 100, a thermal- insulating layer 120 is interposed between inner and outer walls of the housing in order to effectively reduce heat loss of the device 100.

In the preferred embodiment of this invention, the thermal- insulating layer 120 preferably has a thickness of about 65 - 100 mm.

Mounted to a top end portion of the device 100 is a hopper 300 of which the sludge input capacity is adjustable in accordance with sludge conditions. The device 100 also includes a wet vapor exhaust unit 400, which is provided on the top of the housing at a position in vicinity to the hopper 300 and has a fan motor 410 thereby forcibly venting wet vapor from the chamber 110 into the atmosphere.

The exhaust unit 400 has a damper 420. The damper 420 appropriately controls the size of a vent opening of the unit 400 and thereby controls the amount of exhaust wet vapor in accordance with both the drying rate of the sludge and the temperature inside the drying chamber 110.

The above-mentioned first-stage to fifth-stage guide plates 210, 220, 230, 240 and 250 of the sludge guide means 200 are arranged in the drying chamber 110 into a multi- layered construction, so that the sludge from the hopper 300 orderly moves on the guide plates 210, 220, 230, 240 and 250 while being heated by hot air generated from the heating means 700. In order to the discharge the finally-dried sludge from the deivce 100, a sludge outlet port 500 is formed on one end wall of the device's housing at a position in vicinity to the final end of the fifth- stage plate 250.

Each of the multi-layered guide plates 210, 220, 230, 240 and 250 of the sludge guide means 200 comprises a longitudinal plate member, of which the top surface is regularly waved in order to form a plurality of transverse grooves G having an arcuate configuration. The sludge feeding means 600 is arranged above the arcuate grooves G, thereby continuously feeding the sludge on the plates 210, 220, 230, 240 and 250 while cutting, agitating and crushing the sludge.

The above sludge feeding means 600 comprises several types of paddles: feeding paddles 610, cutting paddles 620, agitating paddles

630 and crushing paddles 640. The feeding paddles 610 effectively feed the sludge on the guide plates. The cutting paddles 620 cut the sludge in order to prevent the sludge from lumping. The agitating paddles 630 agitate the sludge in order to effectively bring the sludge into unifrom contact with hot air inside the chamber 110. Meanwhile, the crushing paddles 640 crush the sludge into small pieces.

As shown in Fig. 1, the feeding paddles 610 are continuously or alternately arranged on the sludge guiding means 200. The cutting paddles 620 are selectively interposed between the alternately-arranged feeding paddles 610. Meanwhile, the agitating and crushing paddles 630 and 640 are mainly arranged on the fifth- stage plate 250 where the sludge is finally dried.

In the present invention, it is preferable to connect the paddles 610, 620, 630 and 640 of the sludge feeding means 600 to one motor through a power transmission mechanism and thereby to cause the paddles 610, 620, 630 and 640 to cooperate with each other in operation of the device 100.

The heating means 700, which generates hot air in order to maintain the high temperature conditions inside the chamber 110, is preferably arranged on both ends of the device's housing.

The heating means 700 comprises a burner 710 and a nozzle pipe 720. The burner 710 generates hot air, while the nozzle pipe 720 discharges hot air from the burner 710 into the drying chamber 110. The heating means 700 supplies hot air into the chamber 110 from the side of the second-, third-and fourth- stage guide plates 220, 230 and 240. Figs. 2a and 2b are sectional views showing the construction of two types of hoppers 300 in accordance with different embodiments of the present invention. The sludge drying device of this invention may be selectively equipped with either of the two types of hoppers 300 in accordance with the water content of input sludge to be treated by the device 100. That is, when the input sludge has a water content of not higher than 90 percent, the first-type hopper 300 of Fig. 2a is installed on the device 100. Meanwhile, when the input sludge has a water content of higher than 90 percent, the second-type hopper 300 of Fig. 2b is installed on the device 100.

As shown in Fig. 2a, the first-type hopper 300 includes a screw shaft 310 which is arranged in the top section inside the hopper housing in order to uniformly scatter the input sludge. A rotating vane shaft 311 is installed in the hopper housing at a position above the neck portion of the hopper housing in order to continuously guide and drop the input sludge into the chamber 110. The above hopper 300 also has a pair of spline shafts 312, which are arranged in the neck portion of the hopper housing, gear into each other and rotate in order to discharge the input sludge into the chamber 110 at a predetermined constant rate.

As shown in Fig. 2b, the second-type hopper 300 includes a screw shaft 320 and a rotating vane shaft 321 which have the same operational functions as those described for the shafts 310 and 311 of the first-type hopper 300. The above hopper 300 also includes a drum shaft 322. The drum shaft 322 is arranged in the neck portion 325 of the hopper housing and discharges the input sludge into the chamber 110. The hopper 300 further includes a regulating plate 323. The regulating plate 323 is rotatably mounted to a hinge shaft 324 at a position in vicinity to the drum shaft 322 and is selectively rotated about the hinge shaft 324 in order to control the amount of sludge to be input into the chamber 110. Therefore, in the first-type hopper 300, the amount of input sludge of the device 100 can be freely controlled by adjusting the rotating speeds of the screw shaft 310, rotating vane shaft 311 and spline shaft 312. In the second-type hopper 300, the amount of input sludge can be freely controlled by adjusting the rotating speeds of the screw shaft 320, rotating vane shaft 321 and drum shaft 322 and by adjusting the position of the regulating plate 324. In addition, either of the two types of hoppers 300 effectively discharges a constant amount of sludge into the chamber 110. Fig. 3 is a sectional view showing the construction of the sludge inlet part of the drying device 100 provided with the hopper 300 of Fig. 2a. As shown in Fig. 3, the multi- layered guide plates 210, 220, 230, 240 and 250 of the sludge guide means 200 are longitudinally arranged in the drying chamber 110 in a way such that the first-stage plate 210 is arranged in the uppermost position in order to be loaded with input sludge first, while the fifth-stage plate 250 is arranged in the lowermost position. The paddles 610, 620, 630 and 640 of the sludge feeding means 600 are arranged over the respective arcuate grooves G of the guide plates 210, 220, 230, 240 and 250, with a close gap being formed between each paddle and an associated groove G in order to allow each paddle to be freely rotated.

Figs. 4a to 4d are perspective and sectional views showing the configuration and construction of four types of paddles 610, 620, 630 and 640 of the sludge feeding means 600 installed in the drying device of the invention.

When organic or inorganic sludge is input into the chamber 110 through the hopper 300, the sludge is primarily loaded onto the first- stage plate 210 which slowly moves the sludge in order to feed the sludge to the second-stage plate 220. In the above state, the sludge on the plate 210 is preheated to about 170^°C . The sludge in turn is fed onto the second- stage plate 220. While the sludge moves on the second- stage plate 220, the sludge is heated to about 200 °C by hot air from the heating means 700 and thereby rapidly absorbs latent heat. The sludge is thus brought into a latently- heated state. The primary drying step of the sludge drying process is finished.

In the above primary step, the arrangement of the feeding and cutting paddles 610 and 620 may be freely changed in accordance with sludge conditions. Of course, the number of the two types of paddles 610 and 620 in the above state may be changed in accordance with sludge conditions. In the primary step, the cutting paddles 620 are rotated at a rotating speed of about of 200 rpm. and cut the viscous contents of the sludge thereby increasing the hot air contact area of the sludge and improving the sludge drying effect of the device 100. The sludge under the latently -heated state in turn is fed to the third-stage plate 230. On the third-stage plate 230, the paddles 610 and 620 arranged on the plate 230 feed the sludge to the fourth-stage plate 240 while further cutting and crushing the sludge. Therefore, water in the sludge on the third-stage plate 230 is more actively vaporized.

On the fourth- stage plate 240, the sludge is finally dried. At a position corresponding to the fourth-stage plate 240 inside the drying chamber 110, the temperature of hot air is maintained at about 400 °C which is the highest temperature inside the chamber 110. The sludge on the fourth- stage plate 240 is thus heated to about 40 0°C . While the sludge moves on the fourth- stage plate 240, the cutting and agitating paddles 620 and 630 arranged on the plate 240 rotate at a rotating speed of about 300 - 500 rpm. and effectively cut and agitate the sludge, thus not only cutting the sludge into small pieces but also uniformly scattering the sludge. The sludge on the fourth- stage plate 240 is thus effectively dried by hot air of about 400 °C thereby being finally dried. In operation of the sludge drying device 100, the second- , third- and fourth-stage plates 220, 230 and 240 are individually heated by hot air generated from the heating means 700. Therefore, it is possible to stepwisely dry the sludge while moving the sludge on the above plates 220, 230 and 240.

The finally-dried sludge of the fourth-stage plate 240 in turn is fed to the fifth-stage plate 250. On the fifth-stage plate 250, the sludge is cooled while being agitated and crushed by the paddles 630 and 640 arranged on the plate 250. The sludge thus has an appropriate water content and in turn is discharged from the deivce 100 through the sludge outlet port 500.

In accordance with repeated experiments, it was most effective to dry the organic or inorganic sludge to a water content of 20 - 40 percent. When the treated sludge has a water content of higher than

40 percent, the treated sludge caused a toxic water extraction and fails to achieve an effective weight reduction, thereby causing several problems during a post- treatment process.

When sludge is dried to a water content of 5 - 20 percent, the weight of the sludge is remarkably reduced. However, the treated sludge in the above state turns into powder that floats in air, causing environmental pollution.

In the drying device 100, it is preferable to installl a temperature sensor on the end wall of the device's housing at a position in vicinity to the sludge outlet port 500. In the above case, the amount of hot air generated from the heating means 700 can be effectively controlled in response to an output signal of the temperature sensor.

In order to check the dried state of sludge outside the chamber 110 during the sludge drying operation of the device 100, it is preferable to form a transparent window on the device's housing. In addition, it is preferable to detachably attach both end walls of the device's housing to the side wall. In the above state, the paddles 610, 620, 630 and 640 of the sludge feeding means 600 can be easily removed from the chamber 110 when it is necessary to repair or exchange the paddles. Two shock absorbing springs are preferably provided on both ends of the rotating shaft of each paddle thereby effectively absorbing mechanical shock generated during a rotating motion of the paddle.

As described above, the present invention provides a method and device for treating organic or inorganic sludge having a high water content through a multi-stage drying process. In accordance with the method and device of this invention, the weight and volume of the sludge are remarkably reduced to appropriate levels, so that the treated sludge can be easily treated in a post-treatment process.

In accordance with the method and device of this invention, hot air is generated from a heating means and dries the sludge while simultaneously sterilizing the sludge, thereby effectively removing bacteria, worms and any bad smell from the sludge. The method and device of this invention thus maintain a clean and agreeable work atmosphere and are less like to cause secondary environmental pollution.

In operation of the sludge drying device of this invention, the sludge input, sludge drying and sludge output steps are automatically carried out, so that the device can save labor, save time and improve work efficiency while drying the sludge. In the device, heating equipment may be selectively arranged in series or parallel, so that the sludge drying capacity of the device can be easily adjusted. Another advantage of the invention resides in that the sludge drying device may be installed in a limited area thereby saving space. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A method for treating organic or inorganic sludge through a multi-stage drying process, comprising the steps of: preheating the sludge in a drying chamber to a predetermined temperature by hot air generated by heating means while moving the sludge on a first- stage guide plate in order to feed the sludge to a second- stage guide plate, and heating the sludge to about 200 °C thereby bringing the sludge into a latently-heated state while moving the sludge on said second- stage guide plate in order to feed the sludge on a third-stage guide plate; gradually heating the latently-heated sludge while simultaneously cutting and crushing the sludge into small pieces thereby actively vaporizing water of the sludge while moving the sludge on said third- stage guide plate in order to feed the sludge to a fourth-stage guide plate; finally heating the sludge by hot air of about 400 °C while moving the sludge on said fourth- stage guide plate in order to feed the sludge to a fifth- stage guide plate; and cooling the finally-dried sludge while moving the sludge on said fifth-stage guide plate thereby allowing the sludge to have a predetermined water content, and discharging the sludge from the drying chamber.

2. The method according to claim 1, wherein said finally - dried sludge has a water content of about 20 - 40 percent.

3. A device for treating organic or inorganic sludge through a mulit-stage drying process, comprising: multi-layered sludge guide means having first- to fifth- stage guide plates and arranged in drying chamber of a longitudinal box-shaped housing, and adapted for moving the sludge while heating the sludge by hot air inside said chamber, said guide plates being arranged in said chamber in order of the first-, second-, third-, fourth- and fifth-stage plates in a direction from the upper to the lower section; a hopper mounted to a top end portion of said housing and adapted for inputting the sludge into said chamber, the sludge input capacity of said hopper being adjustable in accordance with input sludge conditions; a wet vapor exhaust unit mounted to the housing at a position in vicinity to said hopper and adapted for forcibly venting wet vapor from said chamber into the atmosphere, said exhaust unit having a fan motor and a damper, said damper controlling the size of a vent opening of said unit and thereby controlling the amount of exhaust wet vapor in accordance with both a drying rate of the sludge and a temperature inside the chamber; sludge feeding means rotatably arranged on said sludge guide means and adapted for continuously feeding the sludge on the guide means while cutting, agitating and curshing the sludge; and heating means for applying the hot air to said sludge guide means and thereby drying the sludge, said heating means comprising a burner generating the hot air and a nozzle pipe discharging the hot air onto the sludge guide means.

4. The deivce according to claim 3, further comprising a thermal-insulating layer interposed between inner and outer walls of said housing in order to effectively reduce heat loss of the housing, said thermal-insulating layer having a thickness of about 65 - 100 mm.

5. The device according to claim 3, wherein said hopper comprises: a screw shaft adapted for uniformly scattering input sludge; a rotating vane shaft adapted for continuously guiding and dropping the input sludge into said drying chamber; and a pair of spline shafts gearing into each other and rotating in order to discharge the input sludge into said chamber at predetermined constant rate.

6. The device according to claim 3, wherein said hopper comprise: a screw shaft adapted for uniformly scattering input sludge; a rotating vane shaft adapted for continuously guiding and dropping the input sludge into said drying chamber; a drum shaft arranged in a neck portion of a hopper housing and adapted for discharging the input sludge into the chamber; and a regulating plate rotatably mounted to a hinge shaft at a position in vicinity to said drum shaft, said regulating plate being selectively rotated about said hinge shaft in order to control the amount of the input sludge.

7. The device according to claim 3, wherein said box- shaped housing is provided with a sludge outlet port for discharging treated sludge from the housing, said outlet port being formed on said housing at a position in vicinity to a final end of siad fifth- stage plate.

8. The device according to claim 3, wherein said sludge feeding means comprises: a plurality of feeding paddles adapted for feeding the sludge on siad sludge guide means; a plurality of cutting paddles adapted for cutting the sludge thereby preventing the sludge from lumping; a plurality of agitating paddles adapted for agitating the sludge thereby effectively bringing the sludge into uniform contact with the hot air inside the chamber; and a plurality of crushing paddles adapted for crushing the sludge into small pieces.

9. The deivce according to claim 8, wherein said feeding paddles are continuously or alternately arranged on the sludge > guiding means, said cutting paddles are selectively interposed between the alternately -arranged feeding paddles, and said agitating and crushing paddles are selectively arranged on the fifth- stage plate where the sludge is finally dried.