WO2009041763A2

WO2009041763A2 - Dehydrator

Info

Publication number: WO2009041763A2
Application number: PCT/KR2008/005000
Authority: WO
Inventors: Kyung Deuk Park
Original assignee: Rigen Korea Co., Ltd.
Priority date: 2007-09-28
Filing date: 2008-08-26
Publication date: 2009-04-02
Also published as: KR100812821B1; CN101848870A; WO2009041763A3; CN101848870B

Abstract

A dehydrator using gravity, mechanical compression, electroosmosis is proposed. The dehydrator includes: a gravity dewatering unit dewatering sludge by gravity; a press dewatering unit that is disposed at an outlet of the gravity dewatering unit and presses and dewaters the sludge subjected to the gravity dewatering; and an electroosmotic dewatering unit dewatering the sludge and including an electric drum that is disposed at an outlet of the press dewatering unit and relays or induces current to the sludge,and a caterpillar that is isolated from the electric drum by an insulator disposed along an outer circumference of the electric drum and has a side pressing and contacting the outer circumference of the electric drum.

Description

DEHYDRATOR

Technical Field

[1] The present invention relates to a dehydrator, and more particularly, to a dehydrator using gravity, mechanical compression, and electroosmosis that is capable of dewatering sludge in multiple steps. Background Art

[2] Polymercoagulants are typically used to purify sludge produced in waster water/ sewage treatment plants. Thus, it is difficult to dehydrate the sludge agglomerated using the polymer coagulants. The cost of sludge disposal and a range of recycling greatly vary according to the dehydration rate of sludge. Further, significantly reducing the moisture content of sludge can reduce the disposal cost and allows solid components in the sludge to be recycled into useful fuel, thereby contributing to an increase in economic value. However, a conventional press-type dewatering system suffers from a restriction to dehydration of waste- water sludge. Thus, an electroosmosis sludge dehydrator is gaining popularity due to its high dehydration efficiency.

[3] The electroosmosis sludge dehydrator is designed to remove water from sludge using ionic mobility and includes a rotary drum serving as a cathode or positive electrode, a water permeable compression (press) belt wound around an outer circumference of the rotary drum, and a filter belt overlapping a surface of a dewatering region of the press belt and the rotary drum.

[4] Examples of electroosmosis sludge dehydrators are disclosed in Japanese Patent

Laid-open No. 56-60604 and Korean Patent Application No. 1993-0010856.

[5] According to the disclosed electroosmosis sludge dehydrators, a constant voltage is applied between a drum and a press belt to create an electric field. Water charged in the electric field is separated from sludge for dehydration by moving toward an electrode having an opposite polarity to an electrical charge of sludge particles due to electrophoresis and capillary phenomenon.

[6] Prior to filing this application, the same applicant filed an application for an elec- troosmotic dehydrator under Korean Patent Application No. 2003-39471.

[7] According to the electroosmotic dehydrator, three-phase alternating current (AC) is rectified for each phase (R, S, T) and converted into direct current (DC) voltage pulse in order to prevent a voltage drop. Then, voltages generated by the potential difference are sequentially applied to an electrode so as to maintain a constant voltage without a voltage loss during dehydration. Thus, the electroosmotic dehydrator provides increased dehydration performance.

[8] The present inventor has consistently developed dehydrators to file this application for a high efficiency dehydrator capable of dewatering high-moisture sludge. Disclosure of Invention Technical Problem

[9] To solve the above problems, it is an object of the present invention to provide a dehydrator using gravity, mechanical compression, and electroosmosis designed to provide high dehydration efficiency by dewatering sludge in multiple steps.

[10] It is another objective of the present invention to provide a dehydrator using gravity, mechanical compression, and electrophoresis that provides consistent rinsing of a press belt while preventing oxidation of an electroosmotic drum.

[11] It is another objective of the present invention to provide a dehydrator with high operating efficiency capable of dewatering sludge on both sides of a belt and a drum. Technical Solution

[12] To accomplish the above object of the present invention, there is provided a dehydrator using gravity, mechanical compression, and electroosmosis, the dehydrator comprising: a gravity dewatering unit dewatering sludge by gravity; a press dewatering unit that is disposed at an outlet of the gravity dewatering unit and presses and dewaters the sludge subjected to the gravity dewatering; and an electroosmotic dewatering unit dewatering the sludge and including an electric drum that is disposed at an outlet of the press dewatering unit and relays or induces current to the sludgeand a caterpillar that is isolated from the electric drum by an insulator disposed along an outer circumference of the electric drum and has a side pressing and contacting the outer circumference of the electric drum.

[13] According to another aspect of the present invention, there is provided a dehydrator using gravity, mechanical compression, and electroosmosis, comprising: a frame; first and second guide rollers spaced a predetermined distance apart from each other on the frame; pressing rollers located adjacent to the first and second guide rollers; a dehydrating belt on an endless track that is trained around the first and second guide rollers and the pressing rollers, has a plurality of dehydrating holes or is formed of a mesh material, and forms a gravity dewatering unit that dewaters sludge between the first and second guide rollers by gravity; a press belt that is trained around the pressing rollers and the first idle rollers located below the pressing rollers, overlaps the dehydrating belt so that they are trained around the pressing rollers in an overlapping manner in order to form a press dewatering unit that presses and dewaters the sludge subjected to dewatering by the gravity dewatering unit; and an electroosmotic dewatering unit that is mounted to the frame and performs electroosmotic dewatering on the sludge subjected to press dewatering by the dehydrating belt and the press belt.

[14] In the present invention, the electroosmotic dewatering unit comprises: an electrode roller having partition electrodes on an outer circumference along which a part of the press belt moves; a caterpillar isolated from the electrode roller by overlapping the press belt trained around the second guide rollers and the electrode roller; a current applying unit applying current to the electrode roller and the caterpillar; and an electrode roller rinsing unit that is disposed adjacent to the electrode roller and rinses and polishes the outer circumference of the electrode roller.

[15] The dehydrator may further comprise a suction dewatering unit that is disposed between the gravity dewatering unit and the press watering unit or in the gravity dewatering unit and dries out water from the sludge dewatered by the gravity. Brief Description of the Drawings

[16] FIG. 1 is a perspective view of a dehydrator using gravity, mechanical compression, and electroosmosis according to an embodiment of the present invention;

[17] FIG. 2 is a schematic side view of the dehydrator of FIG. 1;

[18] FIG. 3 is a perspective view of the tension applying unit shown in FIG. 2;

[19] FIG. 4 is a perspective view of a pressing roller or tension applying unit shown in

FIG. 2;

[20] FIG. 5 is a perspective view of a second suction dewatering unit shown in FIG. 2;

[21] FIG. 6 is a perspective view of a press belt rinsing unit shown in FIG. 2;

[22] FIG. 7 is a perspective view of an electrode roller rinsing unit shown in FIG. 2;

[23] FIGS. 8 and 9 are exploded perspective views of electrode rollers according to embodiments of the present invention;

[24] FIG. 10 is a perspective view of the caterpillar shown in FIG. 2;

[25] FIG. 11 is a perspective view of unit electrodes in the caterpillar shown in FIG. 2;

[26] FIG. 12 is a perspective view of a caterpillar according to another embodiment of the present invention;

[27] FIG. 13 is a side view of a dehydrator using gravity, mechanical compression, and electroosmosis according to another embodiment of the present invention; and

[28] FIGS. 14 through 19 illustrate a dehydrator using gravity, mechanical compression, and electroosmosis according to another embodiment of the present invention. Best Mode for Carrying Out the Invention

[29] FIGS. 1 through 3 illustrate a dehydrator 10 using gravity, mechanical compression, and electroosmosis according to an embodiment of the present invention. Referring to FIGS. 1 through 3, the dehyirator 10 includes a gravity dewatering unit 20 that is mounted to a frame 11 and dewaters sludge 200 using gravity, a press dewatering unit 40 that is disposed at an outlet of the gravity dewatering unit 20 and presses the sludge subjected to first dewatering by the gravity dewatering unit 20 for dehydration, and an electroosmotic dewatering unit 60 that is disposed at an outlet of the press dewatering unit 40 and dewaters the sludge subjected to second dewatering by the press dewatering unit 40 using current relay and induction.

[30] The configuration of the dehydrator 10 is described in more detail with reference to

FIGS. 1 through 3.

[31] The gravity dewatering unit 20 in the dehydrator 10 according to an embodiment of the present invention includes first and second guide rollers 21 and 22 disposed to the frame 11 while being spaced apart a predetermined distance from each other and a plurality of pressing rollers 41 through 45 disposed to a portion of the frame 11 adjacent to lower portions of the first and second guide rollers 21 and 22. The dehydrator 10 further includes a dehydrating belt 23 on an endless track, along which the first and second guide rollers 21 and 22 and the plurality of pressing rollers 41 through 45 sequentially move. The dehydrating belt 23 has a plurality of dehydrating holes 24 or formed from a mesh material. The dehydrator 10 further includes a guide wall disposed at either side of the dehydrating belt 23 between the first and second rollers 21 and 22.

[32] The first and second guide rollers 21 and 22 may be secured to the frame 11 obliquely with respect to a horizontal axis so that the dehydrating belt 23 remains slanted. That is, the second guide roller 22 is disposed above the horizontal axis higher than the first guide roller 21 so that the dehydrating belt 23 between the first and second roller 21 and 22 remains slanted, thereby allowing sludge 200 to be dewatered by way of gravity while moving along the dehydrating belt 23. The dehydrator 10 further includes a dehydrating belt rinsing unit 25 that is disposed adjacent to the first guide roller 21 and rinses the dehydrating belt 23, a first suction dewatering unit 26 that is disposed adjacent to the lower portion of the second guide roller 22 and sucks and dries out water from the sludge dewatered by gravity, and a reservoir 27 storing fluids drained from a bottom of the dehydrating belt 23 between the first and second guide rollers 21 and 22.

[33] The dehydrating belt rinsing unit 25 cleans the dehydrating holes 24 of the dehydrating belt 23 using rinsing water and dries them. The dehydrating belt rinsing unit 25 includes a first cover member 25b that is in contact with a top surface of the dehydrating belt 23 adjacent to the first guide roller 21 and has an opening 25a disposed opposite the dehydrating belt rinsing region so as to define it, and a plurality of nozzles 25c spraying high pressure rinsing water toward the dehydrating belt rinsing region. The rinsing water may be the fluids stored in the reservoir 27 as a result of the de watering operation by the gravity dewatering unit 27.

[34] The first suction dewatering unit 26 is disposed at an outlet of the second guide roller

22 and applies a suction force to the sludge dewatered by gravity on the dehydrating belt 23 for dehydration. The first suction dewatering unit 26 includes a second cover member 26b that contacts a bottom surface of the dehydrating belt 23 and has a second opening 26a defining a suction area and a suction pump (not shown) connecting with the second cover element 26b and applying a suction force to the second opening 26a.

[35] Referring to FIG. 3, a tension applying unit 30 is disposed between the second guide roller 22 and the pressing roller 41 and applies a tension force to the dehydrating belt 23. Referring to FIG. 3, the tension applying unit 30 is rotatably supported by a take- up device (not shown) for fixing a position at which the tension applying unit 30 moves up or down to the frame 11 and includes a tension roller 31 that moves along the dehydrating belt 23.

[36] The press dewatering unit 40 is disposed adjacent to the tension roller 31 moving between the first and second guide rollers 21 and 22 and presses the sludge that has undergone gravity dewatering for dehydration. The press dewatering unit 40 includes a first idle roller 46a disposed adjacent to the second guide roller 22, second through sixth idle rollers 46b through 46e located below or beside the pressing rollers 41 through 45, and a press belt 47 trained around the first idle roller 46a, the tension roller 31, the pressing rollers 41 through 45, and the second through sixth idle rollers 46b through 46e.

[37] Referring to FIG. 4, each of the pressing rollers 41 through 45 includes one of rotary axes 41a through 45 a, one of arms 41b through 45b extending radially from the rotary axis, one of first plate bars 41c through 45c wound in a left-hand screw direction from a center of the arm towards one side of the pressing roller, and one of second plate bars 4 Id through 45d wound in a right-hand screw direction towards the other side thereof. In the same manner, the tension roller 31 includes a rotary axis 31a, an arm 31b extending radially from the rotary axis 31a and first and second plate bars 31c and 3 Id wound in left- and right-hand screw direction from the center of the arm 31b towards one or the other side thereof.

[38] The press belt 47 and the dehydrating belt 23 may be trained around the first idle roller 46a, the tension roller 31, and the pressing rollers 41 through 45 disposed adjacent to the second guide roller 22 in an overlapping manner, so that sludge moving between the overlapping dehydrating belt 23 and press belt 47 can be dewatered by the dehydrating belt 23 and the press belt 47.

[39] The dehydrator 10 further includes a second suction dewatering unit 50 that is disposed on at least one side of each of the dehydrating belt 23 and the press belt 47 contacting each other between the first idle roller 46a and the tension roller 31 and applies a suction force to dewater sludge located between the dehydrating belt 23 and the press belt 47. The second suction dewatering unit 50 also has substantially the same configuration as the first suction dewatering unit 50. That is, referring to FIG. 5, the second suction dewatering unit 50 includes a third cover member 51 that contacts the dehydrating belt 23 and has a third opening 26a defining a suction area and a suction pump (not shown) connecting with the third cover element 52 and applying a suction force to the third opening 51. The third cover member 51 has a hopper shape.

[40] The third idle roller 46c moving along the press belt 47 is supported by a support force exerted by the press belt 46c upon the tension roller 31. In this case, the third idle roller 46c may be configured such that a pillow block supporting a rotary axis is suspended by an elastic member.

[41] Returning to FIG. 2, the dehydrator 10 further includes a press belt rinsing unit 55 that is disposed adjacent to the fourth idle roller 46c and rinses the press belt 47 using air and water. Referring to FIG. 6, in order to rinse the press belt 47 having a plurality of dehydrating holes or mesh shape, the press belt rinsing unit 55 includes a fourth cover member 57 having a fourth opening 56 defining a region in which the press belt 47 is to be rinsed and providing an interior space from which rinsing water is discharged through the fourth opening 56. The press belt rinsing unit 55 further includes an air spray nozzle 58 for spraying high pressure air toward the press belt 47, a compressor (not shown) supplying high pressure air to the air spray nozzle 58, and a connecting tube 59 supplying water stored in the reservoir 27 as a result of dewatering by the gravity dewatering unit 20 to the interior space of the fourth cover member 57. Although not shown in FIG. 2, the connecting tube 59 may include a pump.

[42] Referring to FIGS. 2 and 7, the electroosmotic dewatering unit 60 includes an electrode roller 61 secured to the frame 11 and relays or induces a three-phase AC, a plurality of support rollers 62 through 65 disposed on either side of or below the electrode roller 61, a caterpillar 70 that is trained around the support rollers 62 through 65 and contacts a portion of an outer circumference of the electrode roller 61 (See FIG. 1), and a power applying unit 80 supplying power to the electrode roller 61 and the c aterpillar 70. The press belt 47 is trained around the electrode roller 61 so as to isolate the caterpillar 70 from the electrode roller 61. That is, as shown in FIGS. 1 and 2, the press belt 47 and the caterpillar 70 are trained about the electrode roller 61 in an overlapping manner. Thus, sludge dewatered between the dehydrating belt 23 and the press belt 47 in the press dewatering unit 40 is introduced between the press belt 47 and the electrode roller 61 and then dewatered by the rotating press belt 47 and electrode roller 61 contacting the caterpillar 70. In this case, the press belt 47 may not necessarily be interposed between the electrode roller 61 and the caterpillar 70.

[43] Referring to FIG. 8, the electrode roller 61 includes partition electrodes 61a disposed at regular intervals along an outer circumference thereof and insulated from each other. The electrode roller 61 further includes channel- shaped electrode holders 61c that is disposed along an outer circumference of a support drum 61b or a support frame (not shown) and fixes the corresponding partition electrodes 61a. As shown in FIG. 9, the electrode holders 6 Ie may be support bars arranged along the outer circumference of the support drum 61b at regular intervals. In this case, both ends of each electrode holder 61b are fixed with a fastening member 61f. Each of the partition electrodes 61a may be an iron alloy containing 14 weight% S and 0.1 weight% Mg. When the partition electrode 61a is an iron alloy containing 14 weight% S and 0.1 weight% Mg, applied current density is 2.16A/m² that is higher than applied current density of l.O9A/m² when the partition electrode 61a is formed of a stainless material.

[44] If an inside of the partition electrode 61a corresponding to an outer circumference of the electrode roller 61 may be formed of high content of copper (Cu), aluminum (Al), and alloy containing Cu or Al. A coating layer containing a non-magnetic material such as Cu or Al or a non-magnetic pad may be formed on the inside of the partition electrode 61a.

[45] Referring to FIGS. 2 and 10, the caterpillar 70 includes a plurality of connecting chains 71 on an endless track and a plurality of unit electrodes 72 arranged at regular intervals along the connecting chains 71. Each of the plurality of unit electrodes 72 has a plurality of dehydrating through holes 73. Alternatively, the caterpillar 70 may be a metallic mesh belt. As shown in FIG. 11, a channel- shaped bar may be used as the unit electrode 72 in order to reduce the weight thereof.

[46] Referring to FIG. 12, in another embodiment, the caterpillar 70 includes unit elements 75 having the shape of a bent plate. Each unit element 75 includes a fixing portion 75a fastened to the connecting chain 71, vertical support portions 75b and 75c bent upward from two longitudinal ends of the fixing portion 75a to the outer circumference of the electrode roller 61, horizontal pressing portions 75d and 75e that are bent inwards from ends of the horizontal support portions 75b and 75c and parallel to the fixing portion 75a, and vertical reinforcements 75f and 75g bent from edges of the horizontal pressing portions 75d and 75e toward the fixing portion 75a.

[47] This configuration can reduce the weight of the unit element 75 while improving structural strength. The configuration also allows dehydration between horizontal pressing portions 75d and 75e, thereby increasing dehydration efficiency.

[48] The power applying unit 80 supplies power to the electrode roller 61 and the caterpillar 70. To achieve this purpose, the power applying unit 80 may include a DC power applying unit applying positive and negative voltages to the partition electrode 61a of the electrode roller 61 and the caterpillar 70, respectively. Alternatively, the power applying unit 80 may include an AC voltage applying unit applying a three- phase AC voltage that is greater than 40 Hz or high frequency greater than 40 Hz to the partition electrode 61a of the electrode roller 61 and the caterpillar 70. The power applying unit 80 may further include a brush contacting the unit electrode 72 or caterpillar 70.

[49] Meanwhile, the dehydrator 10 further includes an electrode roller rinsing unit 90 cleaning the outer circumference of the electrode roller 61 in order to prevent difficulties with power supply due to oxidation of electrode caused by sludge. The electrode roller rinsing unit 90 includes an arm 91 that is rotatably mounted to the frame and elastically biases the outer circumference of the electrode roller 61, a polishing brush 92 that is rotatably disposed to the arm 91 and polishes the outer circumference of the electrode roller 61, and a motor (not shown) driving the polishing brush 92. Of course, a non-rotating polishing brush may be fixed to the arm 91. When the electrode roller 61 is rinsed using the polishing brush 92,

[50] a diluted acetic acid may be used as rinsing water.

[51] Referring to FIG. 13, the electroosmotic dewatering unit 60 may be disposed on an endless track as shown in FIG. 13. The caterpillar 70 trained around the electrode roller 60 is supported by an auxiliary roller in order to form an oval-shaped endless track. The press belt 47 contacting the caterpillar 70 is supported by auxiliary rollers to form a substantially oval-shaped endless track.

[52] Reference numeral 100 denotes a dehydrating belt driving the first guide roller 21 with a driving motor driving the press belt. The dehydrating belt 100, the press belt 47, the caterpillar 70, or rotary drum may be driven by a separate driving unit.

[53] The operation of a dehydrator having the above-mentioned configuration is described in more detail with reference to FIGS. 1 through 13.

[54] When the dehydrator 10 is driven by the motor, sludge 200 to be dewatered is fed onto the dehydrating belt 23 between the first and second guide rollers 21 and 22. The sludge is dewatered by gravity through the plurality of dehydrating holes 24 in the dehydrating belt 23 while water obtained by dewatering the sludge is stored in the reservoir 27. Since the dehydrating belt 23 supported by the first and second guide rollers 21 and 22 is slanted toward the second guide roller 22, the sludge dewatered by gravity is separated from water as the dehydrating belt 23 moves.

[55] Sludge conveyed by the dehydrating belt 23 is then subjected to suction dewatering by the first suction dewatering unit 26 located adjacent to the second guide roller 22. That is, the first suction dewatering unit 26 exerts a suction force on the sludge being conveyed on the dehydrating belt 23 having the plurality of dehydrating holes 24 through the first opening 26a of the first cover member 26b, thereby achieving suction dewatering.

[56] Thereafter, the press dewatering unit 40 dewaters the sludge that has undergone dewatering by the gravity dewatering unit 20 as the dehydrating belt 23 rotates while being in contact with the press belt 47. In this case, water is drained from the pressed sludge through a plurality of dehydrating holes in the dehydrating belt 23 and the press belt 47. In particular, since the third idle roller 46c rotates while being pressed by the tension roller 31, dehydration efficiency can be improved by pressing sludge between the press belt 47 and the dehydrating belt 23. Further, as shown in FIG. 4, each of the pressing rollers 41 through 45 and the tension roller 31 respectively include one of first plate bars 41c through 45c and the first plate bar 31c wound in a left-hand screw direction from the center of one of the arms 41b through 45b and the arm 31b and one of the second plate bars 4 Id through 45d and the second plate bar 3 Id wound in a right-hand screw direction from the center of the arm. Thus, it is possible to prevent the pressing rollers 41 through 45 or the tension roller 31 from peeling off the dehydrating belt 23 or the press belt 47 during the dewatering operation.

[57] The sludge dewatered by the press dewatering unit 40 is transported to the elec- troosmotic dewatering unit 60 for dehydration. More specifically, the electroosmotic dewatering unit 60 dewaters sludge introduced between the outer circumference of the electroosmotic dewatering unit 60 and the press belt 47 using electroosmosis. During the dewatering operation, the partition electrodes 61a arranged along the outer circumference of the electrode roller 61 may be contaminated or oxidized by sludge. To prevent degradation in dehydration performance due to the contamination or oxidation of the electrode roller 61, the electrode roller rinsing unit 90 can rinse and polish a surface of the electrode roller 61 as the polishing bush 92 thereof rotates along the outer circumference of the electrode roller 61. Further, the unit electrode 72 of the caterpillar 72 being in contact with the electric roller 61 has a plurality of through holes 73 through which water can be smoothly pressed out. In particular, when the unit element 75 of the caterpillar 70 has the shape of a bent plate as shown in FIG. 12, the electrode roller 61 substantially makes a contact with the horizontal press portions 75d and 75e, thereby reducing a contact area between the press belt 47 and the electrode roller 61 as well as frictional resistance with the press belt 47. The reduction in frictional resistance may alleviate occurrence of magnetism, thereby reducing power dissipation. The vertical support portions 75b and 75c are spaced a predetermined distance apart from each other, thereby reducing dehydration resistance upon mechanical compression.

[58] FIGS. 14 through 19 illustrate a dehydrator 300 using gravity, mechanical compression, and electroosmosis according to another embodiment of the present invention.

[59] Referring to FIG. 14, the dehydrator 300 according to the present embodiment includes a gravity dewatering unit 310 that is mounted to a frame 301 adjacent to an outlet of a hopper 302 and has first and second dewatering rollers 311 and 312 combined with each other so as to create a gap for dehydration, a press dewatering unit 320 that is mounted to the frame 301 in close proximity to the gravity dewatering unit 310 and has upper press dewatering rollers 321 combined with each other to form a gap for dehydration and lower press dewatering rollers 322 arranged consecutively from the first and second dewatering rollers 311 and 312 and combined with each other to form a gap for dehydration, and an electroosmotic dewatering unit 340 that is disposed at an end of the press dewatering unit 320 and dewaters the sludge subjected to dewatering by the press dewatering unit 320 using current relay and induction.

[60] More specifically, the gravity dewatering unit 311 is mounted to the frame and drains water from the sludge to be dehydrated using gravity. The gravity dewatering unit 311 includes a plurality of first and second dewatering rollers 311 and 312 disposed below the hopper 302 and combined with each other. The first and second dewatering rollers 311 and 312 have substantially the same configuration. Each of the first dewatering rollers 311 has alternating first disc 311a with a large diameter and second disc 31 Ib with a diameter less than the diameter of the first disc 311a.

[61] The first and second dewatering rollers 311 and 312 contacting each other are disposed in such a way that a first disc 312a of the second dewatering roller 312 is inserted between the first discs 31 Ia of the adjacent first dewatering rollers 311 to contact the second disc 31 Ib, thereby creating a mesh having a small gap. The first and second dewatering rollers 311 and 312 are driven by a first driver (not shown) in the same direction. Idle sprockets mounted on drive axes of the first and second dewatering rollers 311 and 312 are connected to a drive sprocket mounted on a drive axis of the motor by a chain so that the first driver rotates in the same direction as the motor.

[62] The press dewatering unit 320 includes the plurality of upper and lower press dewatering rollers 321 and 322 that are vertically spaced apart by a predetermined distance and press the sludge subjected to dewatering by the gravity dewatering unit 310 for dehydration.

[63] Referring to FIGS. 14 through 16, the lower press dewatering rollers 322 are arranged obliquely upwards from the second dewatering rollers 312. The upper press dewatering rollers 321 are arranged so as to have a progressively decreasing gap with the lower press dewatering rollers 322. The upper and lower press dewatering rollers 321 and 322 have the same configuration as the first and second press dewatering rollers 311 and 312. That is, the upper (lower) press dewatering roller 321 (322) has alternating first disc 321a (322a) and second disc 321b (322b).

[64] Like the first and second dewatering rollers 311 and 312, the upper and lower press dewatering rollers 321 and 322 each are disposed such that the first disc 321a (322a) of the upper (lower) press dewatering roller 321 (322) is inserted between the first discs 321a (322a) of the upper (lower) press dewatering rollers 321 (322) to contact the second disc 321b (322b). The upper and lower press dewatering rollers 321 and 322 are driven by a second driver 330 in the same direction. Referring to FIG. 17, the second driver 330 includes idle sprockets 331 mounted on rotary axes of the upper and lower press dewatering rollers 321 and 322, a drive sprocket 333 mounted on a rotary axis of a motor 332, and a chain 334 trained around the idle and drive sprockets 331 and 333. In this case, the upper press dewatering roller 321 rotates in an opposite direction to that of the lower press dewatering roller 322. When the upper and lower press dewatering rollers 321 and 322 are driven by the second driver 330, the second driver 330 may further include more idle sprockets 331 for converting a rotational force. The first and second dewatering rollers 311 and 312 and the upper and lower press dewatering rollers 321 and 322 are formed of an insulating material such as synthetic resin.

[65] The electroosmotic dewatering unit 340 dewaters sludge subjected to dewatering by the press dewatering unit 320. The electroosmotic dewatering unit 340 includes conducting rollers 341 disposed between lower press dewatering rollers 322 that are additionally installed in the press dewatering unit 320, electrode rollers 342 and 343 spaced apart from each other by a predetermined distance on a sub-frame 345, and a caterpillar 344 trained around the electrode rollers 342 and 343. Snce the caterpillar 344 has substantially the same structure as described with reference to FIG. 10, a detailed explanation thereof will not be given. The sub-frame 345 further includes a means for pressing the caterpillar 344 toward the conducting roller 341. Of course, the conducting rollers 341, the electrode rollers 342 and 343, and the caterpillar 344 are formed of conductive materials.

[66] Meanwhile, a method for applying an electric field to the electrode rollers 342 and

343 and the conducting rollers 341 is described in detail with reference to FIG. 14, 18, and 19. Referring to FIG. 14, in one embodiment, a first common terminal commonly connected to cathodes in diodes independently coupled for three phase power lines R, S, and T is coupled to electrode rollers 342 and 343. One 341a of the three spaced- apart conducting rollers 341 opposing the caterpillar 344 is coupled to an anode terminal Rl of the R-phase power line R, the conducting roller 341b is coupled to an anode terminal Sl of the S-phase power line S, and the conducting roller 341c is coupled to an anode terminal Tl of the T-phase power line T.

[67] In another embodiment, referring to FIG. 18, as described above, an electric field is applied to the electrode rollers 342 and 343 through the first common terminal connected to the diodes independently coupled for the three phase power lines R, S, and T. Then, a second common terminal C commonly connected to cathodes (output terminals) in diodes coupled to the conducting rollers 341 is divided into three terminals C that are respectively coupled to R-, S, and T-phase power lines R, S, and T.

[68] In another embodiment, referring to FIG. 19, three-phase power lines R, S, and T may be coupled separately and directly to three spaced- apart conducting rollers 341 disposed opposite a caterpillar. [69] In the dehyirator 300 having the above-mentioned configuration, the first and second dewatering rollers 311 and 312 in the gravity dewatering unit 310 dewater the sludge 200 fed thereinto through the hopper 302. During the gravity dewatering operation, water is drained from the skφe between the first discs 311a and 312a or the second discs 31 Ib and 312b. The first driver and the second driver 330 rotate the first and second dewatering rollers 311 and 312 and the lower press dewatering rollers 322 clockwise while rotating the upper press dewatering rollers 321 counterclockwise, so that the skφe is transported to the electroosmotic dewatering unit 340.

[70] The sludge that has undergone gravity dewatering is subjected to press dewatering as it moves between the upper and lower press dewatering rollers 321 and 322. During the press dewatering, water is discharged through a gap between the first discs 311a and 312a or the second discs 31 Ib and 312b because the upper and lower press dewatering rollers 321 and 322 have the same configuration as the first and second dewatering rollers 311 and 312.

[71] The sludge that has undergone press dewatering is dewatered using electroosmosis as it passes between the caterpillar 344 and the conducting rollers 341. A dehyirator using gravity, mechanical compression, and electroosmosis according to the present invention is configured to sequentially perform gravity dewatering, press dewatering, and electroosmotic dewatering, thereby allowing multi-step dewatering of high- moisture sludge while providing high dehydration performance.

[72] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

[73] Therefore, it is to be understood that the above-described embodiments have been provided only in a descriptive sense and will not be construed as placing any limitation on the scope of the invention. Industrial Applicability

[74] A dehyirator using gravity, mechanical compression, and electroosmosis according to the present invention having the above-mentioned configuration can be widely used in various applications. Same examples are dewatering of sludge produced in sewage and wastewater terminal treatment plants, disposal of various industrial wastes, coals dug from a mine and food wastes, and manufacturing of diverse products requiring dewatering.

Claims

[1] A dehydrator using gravity, mechanical compression, and electroosmosis, comprising: a gravity dewatering unit dewatering sludge by gravity; a press dewatering unit that is disposed at an outlet of the gravity dewatering unit and presses and dewaters the sludge subjected to the gravity dewatering; and an electroosmotic dewatering unit dewatering the sludge and induing an electric drum that is disposed at an outlet of the press dewatering unit and relays or induces current to the sludge and a caterpillar that is isolated from the electric drum by an insulator disposed along an outer circumference of the electric drum and has a side pressing and contacting the outer circumference of the electric drum.

[2] The dehyirator of claim 1, wherein the gravity dewatering unit includes first and second guide rollers that are spaced a predetermined distance apart from each other on a frame and have a height difference therebetween and a dehydrating belt on an endless track that is trained around the first and second guide rollers and has a plurality of dehydrating holes or is formed of a mesh material.

[3] A dehydrator using gravity, mechanical compression, and electroosmosis, comprising: a frame; first and second guide rollers spaced a predetermined distance apart from each other on the frame; pressing rollers located adjacent to the first and second guide rollers; a dehydrating belt on an endless track that is trained around the first and second guide rollers and the pressing rollers, has a plurality of dehydrating holes or is formed of a mesh material, and forms a gravity dewatering unit that dewaters sludge between the first and second guide rollers by gravity; a press belt that is trained around the pressing rollers and the first idle rollers located below the pressing rollers, overlaps the dehydrating belt so that they are trained around the pressing rollers in an overlapping manner in order to form a press dewatering unit that presses and dewaters the sludge subjected to dewatering by the gravity dewatering unit; and an electroosmotic dewatering unit that is mounted to the frame and performs electroosmotic dewatering on the sludge subjected to press dewatering by the de- hyirating belt and the press belt.

[4] The dehyirator of claim 3, wherein the electroosmotic dewatering unit comprises: an electrode roller having partition electrodes on an outer circumference along which a part of the press belt moves; a caterpillar isolated from the electrode roller by overlapping the press belt trained around the second guide rollers and the electrode roller; a current applying unit applying current to the electrode roller and the caterpillar; and an electrode roller rinsing unit that is disposed adjacent to the electrode roller and rinses and polishes the outer circumference of the electrode roller.

[5] The dehyirator of claim 4, wherein the electrode roller rinsing unit is installed on the outer circumference of the electrode roller and includes a brush for polishing and rinsing the outer circumference.

[6] The dehyirator of claim 3, further comprising a suction dewatering unit that is disposed between the gravity dewatering unit and the press watering unit or in the gravity dewatering unit and dries out water from the sludge dewatered by the gravity.

[7] The dehyirator of claim 3, further comprising a tension roller that applies a tension force to the dehyirating belt and the press belt that overlap each other as they move between the gravity dewatering unit and the press dewatering unit and is slidably mounted on the frame and along which the overlapping dehyirating belt and press belt move, wherein one of the first idle rollers is pressed by the tension roller in order to press the overlapping and rotating dehyirating belt and press belt.

[8] The dehyirator of claim 3 or 7, wherein each of the pressing rollers or the tension roller includes a rotary axis, an arm extending radially from the rotary axis, a first plate bar wound in a left-hand screw direction from a center of the arm toward one side of the pressing roller or tension roller, and a second plate bar wound in a right-hand screw direction from the center of the arm toward the other side thereof.

[9] The dehyirator of claim 3, further comprising a press belt rinsing unit dewatering the press belt using water drained from the skφe by the gravity dewatering unit.

[10] The dehyirator of claim 4, wherein the current applying unit applies three-phase alternating current (AC) power greater than 40 Hz or AC to the electrode roller.

[11] The dehyirator of claim 4, wherein the current applying unit includes a direct current (DC) power supply that applies positive and negative voltages to the electrode roller and the caterpillar, respectively.

[12] The dehyirator of claim 3, wherein partition electrodes disposed along the outer circumference of the electrode roller are combined or separated by electrode holders.

[13] The dehyirator of claim 4, wherein the caterpillar comprises: a plurality of connecting chains on an endless track; and a plurality of unit electrodes arranged at regular intervals along the connecting chains.

[14] The dehyirator of claim 4, wherein the caterpillar comprises: a plurality of connecting chains on an endless track; and a plurality of unit electrodes each induing a fixing portion fastened to the connecting chain, vertical support por tions bent upward from two longituinal ends of the fixing portion to the outer circumference of the electrode roller, horizontal pressing portions that are bent inwards from ends of the horizontal support portions and parallel to the fixing portion, and vertical reinforcements bent from edges of the horizontal pressing portions toward the fixing portion.

[15] The dehyirator of claim 4, wherein each of the partition electrodes is an iron alloy containing 14 weight% S and 0.1 weight% Mg.

[16] A dehyirator using gravity, mechanical compression, and electroosmosis, comprising a gravity de watering unit that is mounted to a frame adjacent to an outlet of a hopper and has first and second dewatering rollers combined with each other so as to create a gap for dehydration; a press dewatering unit that is mounted to the frame in close proximity to the gravity dewatering unit and has upper press dewatering rollers combined with each other to form a gap for dehydration and lower press dewatering rollers arranged consecutively from the first and second dewatering rollers and combined with each other to form a gap for dehydration; and an electroosmotic dewatering unit that is disposed at an end of the press dewatering unit and dewaters the sludge subjected to dewatering by the press dewatering unit using current relay and induction.

[17] The dehyirator of claim 16, wherein each of the first and second dewatering rollers includes a first disc spaced a predetermined distance apart from a rotary axis and a second disc having a diameter less than that of the first disc and inserted between the first discs.

[18] The dehyirator of claim 16, wherein each of the upper and lower dewatering press dewatering rollers includes a first disc spaced a predetermined distance apart from a rotary axis and a second disc having a diameter less than that of the first disc and inserted between the first discs.

[19] The dehyirator of claim 16, wherein the electroosmotic dewatering unit includes conducting rollers disposed between lower press dewatering rollers that are additionally installed in the press dewatering unit, electrode rollers spaced apart from each other by a predetermined distance on a sub-frame, and a caterpillar trained around the electrode rollers.