WO2006137502A1

WO2006137502A1 - Method and apparatus for dehydrating and drying slurry

Info

Publication number: WO2006137502A1
Application number: PCT/JP2006/312556
Authority: WO
Inventors: Junichi Nomura; Shoichi Goda; Norio Yamada; Hiromi Takayasu; Kanroku Chonan; Michinari Itayama
Original assignee: Ebara Corporation
Priority date: 2005-06-21
Filing date: 2006-06-16
Publication date: 2006-12-28
Also published as: JP2008546511A; TW200708330A; JP5478019B2

Abstract

A dehydrating and drying apparatus has a filter press (1) having filter chambers (130) and filter plates (100, 110). The first filter plate (100) has a diaphragm (102), a filter cloth (103) disposed between the diaphragm (102) and the filter chamber (130), and a heating medium chamber (S2). The second filter plate (110) has a heat transfer member (112) made of metal, a filter cloth (113) disposed between the heat transfer surface of the heat transfer member (112) and the filter chamber (130), and a heating medium chamber (S12). The apparatus includes a heating mechanism (20, 26) operable to heat the slurry to a preset temperature higher than a predetermined saturated vapor temperature and a decompressing mechanism operable to instantaneously introduce the heated slurry to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature.

Description

DESCRIPTION

METHOD AND APPARATUS FOR DEHYDRATING AND DRYING SLURRY

Technical Field The present invention relates to a method and apparatus for dehydrating and drying slurry, and more particularly to a method and apparatus for dehydrating and drying slurry such as sludge discharged from a water supply and drainage system, a waste water treatment system in a rural village, a human waste treatment system, an industrial waste water treatment system, and the like.

Background Art

In order to dehydrate and dry slurry (matter including water) such as sludge, a dehydrating apparatus and a drying apparatus are required to be separately provided, so that initial cost and labor of maintenance are greatly increased. In order to resolve such drawbacks, there has been proposed a dehydrating and drying apparatus having a filter press (pressure dehydrator). For example, such a dehydrating and drying apparatus is disclosed by Japanese laid-open patent publication No. 2001-232109. In this type of dehydrating and drying apparatus, slurry in a filter chamber of a filter press is pressed while being heated by a heating medium. The interior of the filter press is evacuated by a vacuum pump to dehydrate and dry the slurry. The dehydrated and dried slurry is discharged as a cake from the filter press.

However, a conventional dehydrating and drying apparatus has an insufficient evaporation rate for organic sludge. Accordingly, the size of the apparatus is problematically increased. Further, if ease of separation of a cake from a filter cloth is deteriorated, much labor is required to maintain the dehydrating and drying apparatus. Furthermore, it disadvantageously takes much time to reduce a pressure in the filter press to a predetermined degree of vacuum after the vacuum pump is operated.

Disclosure of Invention

The present invention has been made in view of the above drawbacks. It is, therefore, an object of the present invention to provide a method and apparatus for dehydrating and drying slurry which can dehydrate and dry slurry efficiently in a short period of time and can improve ease of separation of a cake.

According to a first aspect of the present invention, there is provided a method of dehydrating and drying slurry which can dehydrate and dry slurry efficiently in a short period of time and can improve ease of separation of a cake. In this method, a first filter plate and a second filter plate are disposed so as to form a filter chamber between the first filter plate and the second filter plate. The first filter plate has a filter cloth, a diaphragm, and a heating medium chamber formed therein. The second filter plate has a filter cloth, a heat transfer member made of metal, and a heating medium chamber formed therein. Slurry is supplied to the filter chamber. The slurry is filtered in the filter chamber through the filter cloths of the first filter plate and the second filter plate. The slurry is pressed in the filter chamber against the diaphragm of the first filter plate by supplying a heating medium to the heating medium chamber of the first filter plate. Heat of a heating medium is transferred to the slurry through the heat transfer member of the second filter plate by supplying the heating medium to the heating medium chamber of the second filter plate. The slurry is heated to a preset temperature higher than a predetermined saturated vapor temperature. The slurry is introduced to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature after the heating process of the slurry so that a temperature difference between the preset temperature and the predetermined saturated vapor temperature causes self-evaporation of water in the slurry. In this case, the slurry may be heated during the filtering process of the slurry or during the pressing process of the slurry. The self-evaporation of water in the slurry may be repeated a plurality of times.

According to a second aspect of the present invention, there is provided a method of dehydrating and drying slurry which can dehydrate and dry slurry efficiently in a short period of time and can improve ease of separation of a cake. In this method, filter plates are disposed so as to form a filter chamber between the filter plates. Each of the filter plates has a filter cloth, a heat transfer member made of metal, and a heating medium chamber formed therein. Slurry is supplied to the filter chamber. The slurry is filtered in the filter chamber through the filter cloths of the filter plates. Heat of a heating medium is transferred to the slurry through the heat transfer members of the filter plates by supplying the heating medium to the heating medium chambers of the filter plates. The slurry is heated to a preset temperature higher than a predetermined saturated vapor temperature. The slurry is introduced to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature after the heating process of the slurry so that a temperature difference between the preset temperature and the predetermined saturated vapor temperature causes self-evaporation of water in the slurry. In this case, the slurry may be heated during the filtering process of the slurry or after the filtering process of the slurry. The self-evaporation of water in the slurry may be repeated a plurality of times.

The term "dehydrating" used in the specification includes dehydration by filtration and dehydration by pressing.

A compressed gas may be passed through the filter chamber during the filtering process of the slurry, during the pressing_s process of the slurry, after the filtering process of the slurry, after the pressing process of the slurry, during the self-evaporation of water in the slurry, or after the self-evaporation of water in the slurry.

The self-evaporation of water in the slurry may be repeated a plurality of times, and the ventilation of the compressed gas may be performed after at least one of the self-evaporations of water in the slurry. At least one of stem, air, dehumidified air, and hot discharge gas may be used as the compressed gas.

The compressed gas may be supplied to the filter chamber through a blow line for blowing the compressed gas into the filter chamber, and discharged from the filter chamber through a filtrate discharge line for discharging a filtrate from the filter chamber. Alternatively, the compressed gas may be supplied to the filter chamber through one of a plurality of filtrate discharge lines for discharging a filtrate from the filter chamber, and discharged from the filter chamber through another of the plurality of filtrate discharge lines.

The self-evaporation of water in the slurry may be repeated a plurality of times by connecting the filter chamber sequentially to a plurality of vacuum tanks. Each of the vacuum tanks is held at a pressure equal to or lower than the pressure corresponding to the predetermined saturated vapor temperature. In such a case, drying can efficiently be completed in a shorter period of time, and the interior of the filter press can instantaneously be introduced into a vacuum atmosphere.

A physical property value reflecting a temperature of the slurry in the filter chamber may be measured to control start and stop of the self-evaporation of water in the slurry based on the measured physical property value. It is desirable to repeat the self-evaporation of water in the slurry.

The physical property value may be a temperature of the slurry in the filter chamber and a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber. In this case, the self-evaporation of water in the slurry may be started when the measured temperature of the slurry in the filter chamber is higher than a predetermined value. The self-evaporation of water in the slurry may be stopped when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value. Alternatively, the physical property value may be a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber. The self-evaporation of water in the slurry may be started and stopped when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value.

The physical property value may be a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber. In this case, the self-evaporation of water in the slurry may be started when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value. The self-evaporation of water in the slurry is stopped a predetermined period of time after the starting the self-evaporation of water in the slurry.

The physical property value may be a temperature of a filtrate discharged from the filter chamber and a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber. In this case, the self-evaporation of water in the slurry may be started when the measured temperature of the filtrate discharged from the filter chamber is higher than a predetermined value. The self-evaporation of water in the slurry may be stopped a predetermined period of time after the starting the self-evaporation of water in the slurry or when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value.

The physical property value may be a temperature of the slurry in the filter chamber. In this case, the self-evaporation of water in the slurry is started when the measured temperature of the slurry in the filter chamber is higher than a predetermined value. The self-evaporation of water in the slurry is stopped a predetermined period of time after the starting the self-evaporation of water in the slurry.

The self-evaporation of water in the slurry may be repeated a plurality of times at a predetermined frequency.

It is desirable that the difference between the preset temperature and the predetermined saturated vapor temperature is in a range of from 20°C to 70°C. In this case, it is desirable that the pressure corresponding to the predetermined saturated vapor temperature is not more than an absolute pressure of 0.03 MPa.

According to a third aspect of the present invention, there is provided an apparatus for dehydrating and drying slurry which can dehydrate and dry slurry efficiently in a short period of time and can improve ease of separation of a cake. The apparatus has a filter press having a first filter plate, a second filter plate, and at least one filter chamber formed between the first filter plate and the second filter plate. The first filter plate has a diaphragm, a filter cloth disposed between the diaphragm and the filter chamber, and a heating medium chamber for pressing the diaphragm to the filter chamber by a supplied heating medium. The second filter plate has a heat transfer member made of metal with a heat transfer surface, a filter cloth disposed between the heat transfer surface of the heat transfer member and the filter chamber, and a heating medium chamber for transferring heat of a supplied heating medium to the slurry through the heat transfer surface. The apparatus includes a heating mechanism operable to heat the slurry to a preset temperature higher than a predetermined saturated vapor temperature. The apparatus also includes a decompressing mechanism operable to instantaneously introduce the slurry heated by the heating mechanism to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature.

The second filter plate may have a body made of resin disposed at a peripheral portion of the heat transfer surface of the heat transfer member. The body may be formed integrally with the heat transfer member of the second filter plate.

According to a fourth aspect of the present invention, there is provided an apparatus for dehydrating and drying slurry which can dehydrate and dry slurry efficiently in a short period of time and can improve ease of separation of a cake. The apparatus has a filter press having filter plates and at least one filter chamber formed between the filter plates. Each of the filter plate has a heat transfer member made of metal with a heat transfer surface, a filter cloth disposed between the heat transfer surface of the heat transfer member and the filter chamber, and a heating medium chamber for transferring heat of a supplied heating medium to the slurry through the heat transfer surface. The apparatus includes a heating mechanism operable to heat the slurry to a preset temperature higher than a predetermined saturated vapor temperature. The apparatus also includes a decompressing mechanism operable to instantaneously introduce the slurry heated by the heating mechanism to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature. Each of the filter plates may have a body made of resin disposed at a peripheral portion of the heat transfer surface of the heat transfer member. The body may be formed integrally with the heat transfer member of the filter plate.

The apparatus may include a ventilation mechanism operable to allow a compressed gas to pass through the filter chamber. At least one of stem, air, dehumidified air, and hot discharge gas may be used as the compressed gas. The ventilation mechanism may be configured to supply the compressed gas to the filter chamber through a blow line for blowing the compressed gas into the filter chamber and to discharge the compressed gas from the filter chamber through a filtrate discharge line for discharging a filtrate from the filter chamber. The ventilation mechanism may be configured to supply the compressed gas to the filter chamber through one of a plurality of filtrate discharge lines for discharging a filtrate from the filter chamber and to discharge the compressed gas from the filter chamber through another of the plurality of filtrate discharge lines. Alternatively, the ventilation mechanism may include a plurality of vacuum tanks connected in parallel to the filter chamber of the filter press. Each of the plurality of vacuum tanks may be held at a pressure equal to or lower than the pressure corresponding to the predetermined saturated vapor temperature. The ventilation mechanism may include a plurality of valves operable to switch connections between the plurality of vacuum tanks and the filter chamber of the filter press. The plurality of vacuum tanks may have a cooling mechanism.

The apparatus may include at least one sensor for measuring a physical property value reflecting a temperature of the slurry in the filter chamber. The decompressing mechanism may be controlled based on the physical property value measured by the at least one sensor.

The at least one sensor may include a sensor for measuring a temperature of the slurry in the filter chamber. Alternatively, the at least one sensor may include a first sensor for measuring an inlet temperature of the heating medium chamber and a second sensor for measuring an outlet temperature of the heating medium chamber. The at least one sensor may include a sensor for measuring a temperature of a filtrate discharged from the filter chamber.

It is desirable that the difference between the preset temperature and the predetermined saturated vapor temperature is in a range of from 2O⁰C to 70⁰C. In this case, it is desirable that the pressure corresponding to the predetermined saturated vapor temperature is not more than an absolute pressure of 0.03 MPa.

^' According to the present invention, slurry is introduced into a decompressed atmosphere after the slurry is heated. Irrespective of types of slurry, self-evaporation of water contained in the slurry is accelerated so as to cause bumping. Accordingly, a cake is cracked so as to increase an evaporation area. Thus, it is possible to efficiently dehydrate and dry the slurry in a short period of time.

Further, since the cake is cracked, it is possible to separate the adhesive cake readily from the filter cloths. Accordingly, it is possible to greatly reduce labor for maintenance of the dehydrating and drying apparatus.

Furthermore, when a filter plate with a diaphragm is not used in the dehydrating and drying apparatus, it is possible to use a filter plate having heat transfer surfaces formed by a heat transfer member made of metal. Accordingly, it is possible to remarkably improve the heat transferability of the filter plate.

Additionally, the filter chamber is connected sequentially to a plurality of vacuum tanks held at a pressure lower than the pressure corresponding to the predetermined saturated vapor temperature. Therefore, the interior of the filter press can immediately be introduced into an atmosphere having a desired pressure. It is possible to reduce the volume of a cooling mechanism or a vacuum pump and operate the dehydrating and drying apparatus efficiently.

The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

Brief Description of Drawings

FIG. 1 is a schematic view showing a dehydrating and drying apparatus according to a first embodiment of the present invention;

FIG. 2 is a cross- sectional view schematically showing a filter press in the dehydrating and drying apparatus shown in FIG. 1;

FIG. 3 is a side view showing a first filter plate in the filter press shown in FIG. 2; FIG. 4A is a cross-sectional view taken along line A-A of FIG. 3;

FIG. 4B is a cross-sectional view taken along line B-B of FIG. 3;

FIGS. 5A and 5B are cross-sectional views showing a second filter plate in the filter press shown in FIG. 2;

FIG. 6 is a cross-sectional view showing a main portion of a filter press according to a second embodiment of the present invention;

FIGS. 7A and 7B are cross-sectional views showing a second filter plate included in the filter press shown in FIG. 6;

FIGS. 8A and 8B are cross-sectional views showing a filter plate according to a third embodiment of the present invention; FIG. 8C is a partial enlarged view of FIG. 8B;

FIG. 9 is a cross-sectional view showing a main portion of a filter press according to a fourth embodiment of the present invention;

FIG. 10 is a cross-sectional view showing a main portion of a filter press according to a fifth embodiment of the present invention;

FIG. 11 is a cross-sectional view showing a main portion of a filter press according to a sixth embodiment of the present invention;

FIG. 12 is a schematic view showing a dehydrating and drying apparatus according to a seventh embodiment of the present invention; and

FIG. 13 is a schematic view showing a dehydrating and drying apparatus according to an eighth embodiment of the present invention.

Best Mode for Carrying Out the Invention A dehydrating and drying apparatus according to embodiments of the present invention will be described below with reference to FIGS. 1 through 13. Like or corresponding parts are denoted by like or corresponding reference numerals in FIGS. 1 through 13, and will not be described below repetitively.

FIG. 1 is a schematic view showing a dehydrating and drying apparatus according to a first embodiment of the present invention. As shown in FIG. 1, the dehydrating and drying apparatus has a filter press 1 for dehydrating and drying slurry such as sludge. The dehydrating and drying apparatus also has a slurry supply line 10 for supplying slurry into filter chambers formed in the filter press 1, a heating medium circulation line 20 for circulating a heating medium (e.g., hot water) through the filter press 1, a vacuum line 30 for evacuating the filter chambers in the filter press 1, a blow line 40 for blowing compressed air into the filter chambers in the filter press 1, and a slurry discharge line 50 for discharging remaining slurry from the filter press 1. The slurry supply line 10, the heating medium circulation line 20, the vacuum line 30, the blow line 40, and the slurry discharge line 50 are connected to the filter press 1. The filter press 1 includes a filter chamber temperature sensor 2 for detecting a temperature of the filter chambers and a relief valve 3 for discharging a gas accumulated in the heating medium circulation line 20 from the filter press 1.

A slurry supply pump 11 is connected to an end of the slurry supply line 10. The slurry supply pump 11 serves to supply slurry through the slurry supply line 10 into the filter chambers in the filter press 1. The slurry supply line 10 has a slurry supply valve 12 for controlling supply of the slurry to the filter press 1 and a slurry pressure sensor 14 for detecting a pressure of the slurry in the slurry supply line 10. The heating medium circulation line 20 includes a heating medium circulation line 2OA upstream of the filter press 1 and a heating medium circulation line 2OB downstream of the filter press 1. The heating medium circulation line 2OA has a heating medium circulation pump 21 for circulating the heating medium in the heating medium circulation line 20 and a first heating medium temperature sensor 22 for detecting a temperature of the heating medium at an inlet of the filter press 1. The heating medium circulation line 2OB has a second heating medium temperature sensor 23 for detecting a temperature of the heating medium at an outlet of the filter press 1, a heating medium pressure sensor 24 for detecting a pressure of the heating medium at the outlet of the filter press 1, and a back-pressure valve 25 for regulating a pressure of the heating medium flowing through the heating medium circulation line 2OB. The pressure of the heating medium to be supplied to the filter press 1 can be adjusted by operating the back-pressure valve 25. The heating medium circulation line 2OA disposed upstream of the filter press 1 and the heating medium circulation line 2OB disposed downstream of the filter press 1 are connected to a heating tank 26 for heating the heating medium circulated in the heating medium circulation line 20. With such an arrangement, the heating medium is heated by the heating tank 26 and supplied through the heating medium circulation line 2OA into the filter press 1 so as to at least heat slurry in the filter chambers of the filter press 1. Then, the heating medium flows out of the filter press 1 and returns through the heating medium circulation line 2OB to the heating tank 26. Thus, the heating medium circulation lines 2OA and 2OB, the heating medium circulation pump 21, and the heating tank 26 form a heating mechanism for heating the slurry in the filter chambers of the filter press 1. In the present embodiment, the slurry is heated in the filter chambers of the filter press 1 by the heating medium circulated in the heating medium circulation line 20 while the slurry is pressed in the filter chambers of the filter press 1. Thus, the filter press 1 in the present embodiment is formed as a horizontal pressure dehydrating and drying device.

A vacuum pump 31 is connected to an end of the vacuum line 30. The vacuum pump 31 serves to evacuate the filter chambers in the filter press 1 through the vacuum line 30. The vacuum line 30 has a first selector valve (control valve) 32 A, a condenser 33 for condensing steam introduced from the filter press 1, and a vacuum tank 34. The vacuum line 30, the vacuum pump 31, the first selector valve 32A, and the vacuum tank 34 form a decompressing mechanism for decompressing the slurry in the filter chambers of the filter press 1. A coolant is supplied to the condenser 33. Heat is exchanged between steam introduced from the filter press 1 into the condenser 33 and the coolant in the condenser 33. Thus, the steam is condensed and then discharged as a condensate from the condenser 33.

As shown in FIG. 1, a filtrate discharge line 35 is connected to the vacuum line 30. The filtrate discharge line 35 serves to discharge a filtrate from the filter chambers in the filter press 1 during dehydration of the slurry. The filtrate discharge line 35 has a second selector valve (control valve) 32B. When the slurry is pressed in the filter chambers by the heating medium, the volume of the filter chambers is reduced. Thus, the slurry in the filter chambers is dehydrated into a cake. During dehydration of the slurry, a filtrate is discharged from the filter chambers. The filtrate is discharged through the filtrate discharge line 35 to the exterior of the dehydrating and drying apparatus.

When the filter chambers in the filter press 1 are to be evacuated by the vacuum pump 31, the first selector valve 32A is opened while the second selector valve 32B is closed. When the filtrate is to be discharged from the filter chambers, the second selector valve 32B is opened while the first selector valve 32A is closed. Further, the pressure of the filter chambers in the filter press 1 can be increased immediately from vacuum to an atmospheric pressure by opening the second selector valve 32B. A compressor (not shown) is connected to the blow line 40 for generating compressed air. Thus, compressed air is blown from the compressor through the blow line 40 into the filter chambers so that slurry remaining within the filter press 1 and slurry remaining at a slurry supply port of the filter chambers are discharged through the slurry discharge line 50 by the compressed air. The blow line 40 has an air valve 41, and the slurry discharge line 50 has a slurry discharge valve 51.

FIG. 2 is a cross-sectional view schematically showing the filter press 1 shown in FIG. 1. As shown in FIG. 2, the filter press 1 includes first filter plates 100, second filter plates 110, and a pair of clamping plates 120A and 120B for clamping the filter plates 100 and 110 from both sides thereof. The first filter plates 100 and the second filter plates 110 are alternately disposed so as to form filter chambers 130 between the first filter plates 100 and the second filter plates 110. Specifically, the first filter plates 100 and the second filter plates 110 are disposed on both sides of each filter chamber 130 so as to face each other.

A slurry supply pipe 121 is attached to a central portion of the clamping plate 120A and connected to the slurry supply line 10 (see FIG. 1). A slurry discharge pipe 122 is attached to a central portion of the clamping plate 120B and connected to the slurry discharge line 50 (see FIG. 1). The aforementioned filter chamber temperature sensor 2 is disposed near the clamping plate 120A. The temperature of the slurry in the filter chambers 130 is detected by the filter chamber temperature sensor 2. A thermocouple can suitably be used as the filter chamber temperature sensor 2.

As shown in FIG. 2, each of the first filter plates 100 has a body 101 made of resin, a diaphragm 102, and a filter cloth 103 disposed between the diaphragm 102 and the filter chambers 130. Each of the second filter plates 110 has a body 111 made of resin, a heat transfer member 112 made of metal, and a filter cloth 113 disposed between the heat transfer member 112 and the filter chambers 130. Thus, in the present embodiment, the filter press 1 employs two types of filter plates including the first filter plate 100 having the diaphragm 102 and the second filter plate 110 having the heat transfer member 112 made of metal. Accordingly, the filter press 1 serves as a single-side pressing device.

FIG. 3 is a side view showing the first filter plate 100 from which the filter cloth 103 is removed. FIG. 4A is a cross-sectional view taken along line A-A of FIG. 3, and FIG. 4B is a cross-sectional view taken along line B-B of FIG. 3. As shown in FIGS. 3 and 4B, the first filter plate 100 has an opening 104 formed at a central portion of the first filter plate 100 so as to correspond to the aforementioned slurry supply pipe 121. The opening 104 extends through the body 101, the diaphragm 102, and the filter cloth 103. Adjacent filter chambers 130 communicate with each other by the opening 104.

As shown in FIGS. 4A and 4B, the diaphragm 102 has a plurality of projections 105 provided on a surface of the diaphragm 102 facing the filter cloth 103. The projections 105 form a fine filtrate chamber Sl between the diaphragm 102 and the filter cloth 103. As shown in FIG. 4 A, the body 101 has filtrate discharge passages 106 communicating with the filtrate chamber Sl. Thus, the filtrate chamber Sl between the diaphragm 102 and the filter cloth 103 is connected through the filtrate discharge passages 106 to the vacuum line 30 (see FIG. 1). Accordingly, vacuum can be formed in the filtrate chamber Sl by the vacuum pump 31. Water of the slurry passes through the filter cloth 103 into the filtrate chamber Sl and flows through the filtrate discharge passages 106 into the filtrate discharge line 35 (see FIG. 1).

The body 101 has recesses 107 formed in surfaces thereof. Each of the recesses 107 forms a heating medium chamber S2 between the body 101 and the diaphragm 102 covering substantially the entire surface of the body 101. Further, as shown in FIG. 4 A, the body 101 has heating medium supply passages 108 communicating with the heating medium chambers S2 and heating medium discharge passages 109 communicating with the heating medium chambers S2. The heating medium chambers S2 between the diaphragm 102 and the body 101 are connected through the heating medium supply passages 108 to the heating medium circulation line 2OA (see FIG. 1). Thus, the heating medium is supplied from the heating medium circulation line 2OA through the heating medium supply passages 108 to the heating medium chambers S2. Furthermore, the heating medium chambers S2 are connected through the heating medium discharge passages 109 to the heating medium circulation line 2OB (see FIG. 1). Thus, the heating medium supplied to the heating medium chambers S2 is discharged through the heating medium discharge passages 109 into the heating medium circulation line 2OB.

FIGS. 5 A and 5B are cross- sectional views of the second filter plate 110. FIG. 5 A is a cross-section on the same plane as that of FIG. 4A, and FIG. 5B is a cross-section on the same plane as that of FIG. 4B. As shown in FIG. 5B, the second filter plate 110 has an opening 114 formed at a central portion of the second filter plate 110 so as to correspond to the aforementioned slurry supply pipe 121, as with the first filter plate 100. The opening 114 extends through the body 111, the heat transfer member 112, and the filter cloth 113. Adjacent filter chambers 130 communicate with each other by the opening 114.

As shown in FIGS. 5 A and 5B, the heat transfer member 112 has a plurality of projections 115 provided on a surface of the heat transfer member 112 facing the filter cloth 113. The projections 115 form a fine filtrate chamber SIl between the heat transfer member 112 and the filter cloth 113. As shown in FIG. 5 A, the body 111 has filtrate discharge passages 116 formed so as to communicate with the filtrate chamber SIl. Thus, the filtrate chamber SI l between the heat transfer member 112 and the filter cloth 113 is connected through the filtrate discharge passages 116 to the vacuum line 30 (see FIG. 1). Accordingly, vacuum can be formed in the filtrate chamber SI l by the vacuum pump 31. Water of the slurry passes through the filter cloth 113 into the filtrate chamber SI l and flows through the filtrate discharge passages 116 into the filtrate discharge line 35 (see FIG. 1). A support member (not shown) may be provided between portions of the heat transfer member 112 so as to bypass the heating medium.

The heat transfer member 112 made of metal has a hollow portion (heating medium chamber) S 1-2 formed therein. The body 111 made of resin is disposed at a peripheral portion of the heating medium chamber S12. As shown in FIG. 5A, the body 111 has a heating medium supply passage 118 communicating with the heating medium chamber S 12 and a heating medium discharge passage 119 communicating with the heating medium chamber S 12. The heating medium chamber S12 in the heat transfer member 112 is connected through the heating medium supply passage 118 to the heating medium circulation line 20 A (see FIG. 1). Thus, the heating medium is supplied from the heating medium circulation line 2OA through the heating medium supply passage 118 to the heating medium chamber S 12. Further, the heating medium chamber S 12 is connected through the heating medium discharge passage 119 to the heating medium circulation line 2OB (see FIG. 1). Thus, the heating medium supplied to the heating medium chamber S12 is discharged through the heating medium discharge passage 119 into the heating medium circulation line 2OB.

The first filter plates 100 and the second filter plates 110 are disposed alternately in parallel so as to form a plurality of filter chambers 130 between the filter cloths 103 of the first filter plates 100 and the filter cloths 113 of the second filter plates 110. These filter plates 100 and 110 are configured to move close to and away from each other. The clamping plate 120A and the clamping plate 120B are fastened to each other by a fastening device (not shown) to fix the filter plates 100 and 110. The slurry is supplied through the slurry supply line 10 (see FIG. 1), the slurry supply pipe 121, and the openings 104 and 114 of the first filter plates 100 and the second filter plates 110 into the filter chambers 130. .

A first example of a dehydrating and drying process of slurry with the above dehydrating and drying apparatus will be described below. The dehydrating and drying process of slurry in this example includes a dehydrating process to dehydrate slurry by filtration and pressing of the slurry, a drying process to dry the dehydrated slurry, and a blowing process to blow the dehydrated or dried slurry. [Dehydrating Process] (1) Filtration Step

First, slurry is supplied to the filter press 1 through the slurry supply line 10, the slurry supply valve 12, and the slurry pressure sensor 14 by the slurry supply pump 11 and is thus filled in the filter chambers 130. When slurry is further supplied to the filter chambers 130, water of the slurry is converted into a filtration filtrate and discharged through the filtrate discharge passages 106 and 116 and the filtrate discharge line 35 from the filtrate chambers Sl and SI l.

It is desirable that the supply pressure of the slurry is set at, for example, a low absolute pressure of 0.15 MPa to 0.20 MPa at the beginning of the filtration. The supply pressure of the slurry may be increased gradually according to the progress of the filtration. Then, eventually, the supply pressure of the slurry may be set at an absolute pressure of at least 0.6 MPa. It is desirable that the period of time of the filtration is selected optimally depending on properties of the slurry.

The slurry may be heated before being supplied to the filter press 1 (preliminary heating filtration). In this case, since the heated slurry is supplied to the filter press 1, the filterability of the slurry can be improved. Further, a heating medium heated in the heating tank 26 may be circulated in the heating medium circulation lines 2OA and 2OB by the heating medium circulation pump 21 and supplied into the heating medium chambers S2 and S 12 in the filter press 1 to heat the slurry during the filtration (heating filtration). In this case, since the slurry is filtered while being heated, the filterability of the slurry can be improved. (2) Pressing Step

Next, a heating medium heated by the heating tank 26 is supplied through the heating medium circulation line 2OA to the heating medium chambers S2 and S 12 in the filter press 1 by the heating medium circulation pump 21. Thus, the slurry in the filter chambers 130 is heated by the heating medium. The heating medium is returned to the heating tank 26 through the heating medium circulation line 2OB, the second heating medium temperature sensor 23, and the heating medium pressure sensor 24. Then, the heating medium is heated by the heating tank 26 and supplied again to the heating medium chambers S2 and S 12 in the filter press 1 through the heating medium circulation line 2OA.

The pressure (pressing pressure) of the heating medium in the heating medium chambers S2 is controlled at a predetermined value by the back-pressure valve 25, which is provided in the heating medium circulation line 2OB. When the heating medium is supplied to the heating medium chambers S2, the diaphragms 102 of the first filter plates 100 are swelled toward the filter chambers 130 to thereby press and heat the slurry in the filter chambers 130. Water in the slurry flows as a pressing filtrate out of the filtrate chambers Sl and SI l. The pressing filtrate is discharged through the filtrate discharge passages 106 and 116 to the filtrate discharge line 35.

When the slurry is filtered and pressed in the above manner, the slurry is dehydrated and gradually converted into a cake. In the dehydrating process, only filtration step may be conducted without the pressing step to dehydrate the slurry. At the beginning of the pressing step, the relief valve 3 (see FIG. 1) may temporarily be opened to discharge an accumulated gas in the heating medium chambers S2 and S 12. Further, it is desirable that the pressing pressure of the slurry is adjustable in a range of from an absolute pressure of 0.1 MPa (atmospheric pressure) to an absolute pressure of 1.6 MPa. It is desirable to increase the pressing pressure gradually to a pressure between the supply pressure of the slurry and 1.6 MPa after starting of the pressing step. Although the temperature of the heating medium should be equal to or more than a saturated vapor temperature corresponding to a vacuum pressure, it is not limited to a specific value. The heating medium should preferably have a temperature of at least 70°C. Thus, the slurry is heated to a preset temperature higher than a predetermined saturated vapor temperature (a saturated vapor temperature corresponding to a vacuum pressure). [Drying Process]

In a drying process, as in a case of the pressing step in the dehydrating process, a heating medium is circulated through the filter press 1. It is desirable that the pressure of the heating medium is adjusted to be lower than the pressing pressure in the pressing step by the back-pressure valve 25. When the drying process is started, the first selector valve 32A is opened to evacuate the filtrate chambers Sl and SI l in the filter press 1 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. Thus, the slurry is introduced to an atmosphere under a vacuum pressure. During the pressing step, the vacuum pump 31 may be operated to decompress the interior of the vacuum tank 34 in advance. In such a case, the filtrate chambers Sl and SI l can instantaneously be decompressed to a vacuum by opening the first selector valve 32A at the beginning of the drying process.

During the pressing step, the slurry is sufficiently heated in the filter chambers 130 by the heating medium. Thus, a large difference is produced between the preset temperature of the slurry and the saturated vapor temperature corresponding to the vacuum pressure. Accordingly, when the slurry in the filter press 1 is instantaneously introduced to an atmosphere under a vacuum pressure in the drying process, thermal energy of the slurry is used for evaporation in addition to heat supplied by the heating medium. As a result, self-evaporation of water contained in the slurry is accelerated so as to cause bumping. The bumping increases a drying rate (evaporation rate) of the slurry.

The efficiency of the vacuum pump 31 can be increased by supplying a coolant to the condenser 33 so that steam produced from the slurry (cake) in the filter chambers 130 is converted into water. It is desirable that the vacuum pressure in the drying process is not more than an absolute pressure of 0.03 MPa. When the preset temperature is at least 100°C, which is a saturated vapor temperature of the atmospheric pressure, the first selector valve 32A may be left closed after the starting of the drying process, and the second selector valve 32B may be opened so that the steam produced from the slurry is discharged through the filtrate discharge line 35, not through the vacuum line 30. In this case, the slurry is sufficiently heated in the filter chambers 130 during the pressing step, and a large difference is produced between the preset temperature of the slurry and a saturated vapor temperature corresponding to an atmospheric pressure. Accordingly, thermal energy of the slurry is used for evaporation to accelerate self-evaporation of water contained in the slurry. Therefore, bumping can be caused to increase a drying rate of the slurry.

As a larger difference is produced between the temperature of the slurry (cake) in the filter chambers 130 and a saturated vapor temperature corresponding to a predetermined vacuum pressure, the drying rate of the slurry becomes higher. However, the temperature of the cake is drastically lowered by evaporation of water after the starting of the drying process. Accordingly, the aforementioned temperature difference is reduced, and the drying rate of the slurry is lowered. From this point of view, operation of introducing the cake to a vacuum atmosphere (decompressed atmosphere) immediately after heating the cake to a predetermined temperature may be repeated a plurality of times so as to maintain an initial drying rate of the slurry in the drying process (repeated drying).

In the case where the drying process is thus repeated, the heating medium is also circulated at a pressure lower than the pressing pressure. The first selector valve 32A is opened to evacuate the filtrate chambers Sl and SIl in the filter press 1 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. After the temperature of the cake in the filter chambers 130 is decreased to a temperature lower than the temperature of the heating medium by a predetermined value, the first selector valve 32A is closed. Then, after the temperature of the cake in the filter chambers 130 is increased to a predetermined temperature, the first selector valve 32A is opened again to evacuate the filtrate chambers Sl and SI l by the vacuum pump 31. Such operation is repeated a predetermined number of times. [Blowing Process] A blowing process may be performed at desired timing (e.g., after completion of the pressing step in the dehydrating process or after completion of the drying process). In the blowing process, the air valve 41 and the slurry discharge valve 51 are opened. Thus, compressed air is supplied to the filter press 1 through the blow line 40, and the slurry is discharged through the slurry discharge line 50.

An end point of the filtration step or the pressing step in the dehydrating process, an end point of the drying process, or timing to proceed to perform a subsequent process may be determined by -a preset period of time. Alternatively, the following methods may be employed to detect end points of the above processes.

(1) An end point of the filtration step in the dehydrating process can be determined by detecting when the amount of a solid material supplied into the filter chambers 130 reaches a predetermined value.

(2) An end point of the pressing step in the dehydrating process can be determined by detecting when the pressure of the filter chambers 130 becomes lower than the pressing pressure of the heating medium, or when a flow rate of the pressing filtrate or the amount of the pressing filtrate reaches a predetermined value, or when the temperature of the cake in the filter chambers 130 reaches a predetermined value.

(3) An end point of the drying process can be determined by detecting a temperature change of the cake in the filter chambers 130, a temperature change of the heating medium, or a temperature change of the filtrate discharge passages 106 and 116.

A second example of a dehydrating and drying process of slurry with the above dehydrating and drying apparatus will be described below. The dehydrating and drying process of slurry in this example includes a dehydrating process to dehydrate slurry by filtration and pressing of the slurry, a drying process to dry the dehydrated slurry, and a blowing process to blow the dehydrated or dried slurry. [Dehydrating Process] (1) Filtration Step

First, slurry is supplied to the filter press 1 through the slurry supply line 10, the slurry supply valve 12, and the slurry pressure sensor 14 by the slurry supply pump 11 and is thus filled in the filter chambers 130. When slurry is further supplied to the filter chambers 130, water of the slurry is converted into a filtration filtrate and discharged through the filtrate discharge passages 106 and 116 and the filtrate discharge line 35 from the filtrate chambers Sl and SIl.

Next, a heating medium heated by the heating tank 26 is supplied through the heating medium circulation line 2OA to the heating medium chambers S2 and S12 in the filter press 1 by the heating medium circulation pump 21. Thus, the slurry in the filter chambers 130 is heated by the heating medium. The heating medium is returned to the heating tank 26 through the heating medium circulation line 2OB, the second heating medium temperature sensor 23, and the heating medium pressure sensor 24. Then, the heating medium is heated by the heating tank 26 and supplied again to the heating medium chambers S2 and S 12 in the filter press 1 through the heating medium circulation line 2OA. The pressure (pressing pressure) of the heating medium in the heating medium chambers S2 is controlled at a predetermined value by the back-pressure valve 25, which is provided in the heating medium circulation line 2OB. When the heating medium is supplied to the heating medium chambers S2, the diaphragms 102 of the. first filter plates 100 are swelled toward the filter chambers 130 to thereby press and heat the slurry in the filter chambers 130. Water in the slurry flows as a pressing filtrate out of the filtrate chambers Sl and SIl. The pressing filtrate is discharged through the filtrate discharge passages 106 and 116 to the filtrate discharge line 35.

When the slurry is filtered and pressed in the above manner, the slurry is dehydrated and gradually converted into a cake. In the dehydrating process, only filtration step may be conducted without the pressing step to dehydrate the slurry.

At the beginning of the pressing step, the relief valve 3 (see FIG. 1) may temporarily be opened to discharge an accumulated gas in the heating medium chambers S2 and S 12. Further, it is desirable that the pressing pressure of the slurry is adjustable in a range of from an absolute pressure of 0.1 MPa (atmospheric pressure) to an absolute pressure of 1.6 MPa. It is desirable to increase the pressing pressure gradually to a pressure between the supply pressure of the slurry and 1.6 MPa after starting of the pressing step. Although the temperature of the heating medium should be equal to or more than a saturated vapor temperature corresponding to a vacuum pressure, it is not limited to a specific value. The heating medium should preferably have a temperature of at least 70°C. Thus, the slurry is heated to a preset temperature higher than a predetermined saturated vapor temperature (a saturated vapor temperature corresponding to a vacuum pressure). [Drying Process]

In a drying process, as in a case of the pressing step in the dehydrating process, a heating medium is circulated through the filter press 1. It is desirable that the pressure of the heating medium is adjusted to be lower than the pressing pressure in the pressing step by the back-pressure valve 25. When the drying process is started, the first selector valve 32A is opened to evacuate the filtrate chambers Sl and SIl in the filter press 1 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. Thus, the slurry is introduced to an atmosphere under a vacuum pressure. During the pressing step, the vacuum pump 31 may be operated to decompress the interior of the vacuum tank 34 in advance. In such a case, the filtrate chambers Sl and SI l can instantaneously be decompressed to a vacuum by opening the first selector valve 32A at the beginning of the drying process.

The efficiency of the vacuum pump 31 can be increased by supplying a coolant to the condenser 33 so that steam produced from the slurry (cake) in the filter chambers 130 is converted into water. It is desirable that the vacuum pressure in the drying process is not more than an absolute, pressure of 0.03 MPa. When the preset temperature is at least 100°C, which is a saturated vapor temperature of the atmospheric pressure, the first selector valve 32A may be left closed after the starting of the drying process, and the second selector valve 32B may be opened so that the steam produced from the slurry is discharged through the filtrate discharge line 35, not through the vacuum line 30. In this case, the slurry is sufficiently heated in the filter chambers 130 during the pressing step, and a large difference is produced between the preset temperature of the slurry and a saturated vapor temperature corresponding to an atmospheric pressure. Accordingly, thermal energy of the slurry is used for evaporation to accelerate self-evaporation of water contained in the slurry. Therefore, bumping can be caused to increase a drying rate of the slurry. As a larger difference is produced between the temperature of the slurry

(cake) in the filter chambers 130 and a saturated vapor temperature corresponding to a predetermined vacuum pressure, the drying rate of the slurry becomes higher. However, the temperature of the cake is drastically lowered by evaporation of water after the starting of the drying process. Accordingly, the aforementioned temperature difference is reduced, and the drying rate of the slurry is lowered. From this point of view, operation of introducing the cake to a vacuum atmosphere (decompressed atmosphere) immediately after heating the cake to a predetermined temperature may be repeated a plurality of times so as to maintain an initial drying rate of the slurry in the drying process (repeated drying). As there is a larger difference between the preset temperature and the saturated vapor temperature, the slurry has a larger quantity of heat so as to enhance the effect of drying the slurry. Therefore, when the drying process is repeatedly performed, timing of starting and stopping the self-evaporation of the slurry have a great influence on an efficiency of the entire system. The temperature of the slurry in the filter chambers is measured to determine this timing. A temperature difference between the temperature of the heating medium at an inlet of the filter press 1 and the temperature of the heating medium at an outlet of the filter press 1 is considered to reflect the temperature of the slurry in the filter chambers. Accordingly, in this example, timing of starting and stopping the self-evaporation of the slurry is determined based on a temperature difference between a temperature of the heating medium at the inlet of the filter press 1, which is detected by the first heating medium temperature sensor 22, and a temperature of the heating medium at the outlet of the filter press 1, which is detected by the second heating medium temperature sensor 23. It is desirable that the preset temperature and the saturated vapor temperature are in a range of from 20°C to 70°C. Further, it is desirable that a pressure corresponding to the saturated vapor temperature is not more than an absolute pressure of 0.03 MPa. For example, when a temperature of the slurry in the filter chambers 130, which is detected by the filter chamber temperature sensor 2, becomes at least a predetermined value, the self-evaporation of water in the slurry may be started. Further, when a temperature difference between an inlet temperature and an outlet temperature of the heating medium, which are detected by the heating medium temperature sensors 22 and 23, respectively, becomes a predetermined value, the self-evaporation of water in the slurry may be stopped. Alternatively, when a temperature difference between an inlet temperature and an outlet temperature of the heating medium, which are measured by the heating medium temperature sensors 22 and 23, respectively, becomes a predetermined value (e.g., less than 2°C), the self-evaporation of water in the slurry may be started. When the temperature difference becomes a predetermined value (e.g., more than 2°C) during the self-evaporation of water in the slurry and then becomes a predetermined value (e.g., less than 2°C), the self-evaporation of water in the slurry may be stopped. Further, when a temperature difference between an inlet temperature and an outlet temperature of the heating medium, which are detected by the heating medium temperature sensors 22 and 23, respectively, becomes a predetermined value (e.g., less than 2°C), the self-evaporation of water in the slurry may be started. Then, the self-evaporation of water in the slurry may be stopped after a predetermined period of time (e.g. several minutes, preferably 3 minutes to 10 minutes). Furthermore, when a temperature of the slurry in the filter chambers 130, which is measured by the filter chamber temperature sensor 2, becomes a predetermined value, the self-evaporation of water in the slurry may be started. Then, the self-evaporation of water in the slurry may be stopped after a predetermined period of time (e.g. several minutes, preferably 3 minutes to 10 minutes). Alternatively, starting and stopping of the self-evaporation may simply be repeated every period of time (e.g., every 3 minutes, preferably 3 minutes to 10 minutes).

In the case where the drying process is repeated, the heating medium is circulated at a pressure lower than the pressing pressure to heat the cake in the filter chambers 130. When a difference between a measured value of the first heating medium temperature sensor 22 and a measured value of the second heating medium temperature sensor 23 reaches a predetermined value, the first selector valve 32A is opened to evacuate the filtrate chambers Sl and SI l in the filter press 1 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. When a difference between a measured value of the first heating medium temperature sensor 22 and a measured value of the second heating medium temperature sensor 23 reaches a predetermined value after the temperature of the cake in the filter chambers 130 is decreased to a temperature lower than the temperature of the heating medium by a predetermined value, the first selector valve 32A is closed. Then, after the temperature of the cake in the filter chambers 130 is increased to a predetermined temperature, the first selector valve 32A is opened again to evacuate the filtrate chambers S 1 and S 11 by the vacuum pump 31. Such operation is repeated a predetermined number of times. A period of time T from start of heating the slurry to a point where the slurry has the preset temperature may be calculated, and the slurry may be heated for this period of time T. The amount S of solid material can be approximated by S = Fl-C where Fl is the amount of sludge supplied, and C is a sludge concentration. The amount W of water in the filter chambers 130 can be approximated by W = Fl - F2 - S where F2 is the total amount of the filtrate. The quantity Ql of heat required to heat a solid material from the predetermined saturated vapor temperature T2 to the preset temperature Tl is defined by Ql = (S-ps + W-pw)"(Tl - T2) where pg is a specific heat of the solid material, and pw is a specific heat of water. The amount Q2 of heat transfer per hour is defined by Q2 = UA(T3 - T4) where T3 is an inlet temperature of the heating medium which is measured by the first heating medium temperature sensor 22, and T4 is an outlet temperature of the heating medium which is measured by the second heating medium temperature sensor 23. Accordingly, a period T (minutes) of time required for heating is defined by t = Q1/Q2-60. The slurry (sludge) is heated for this calculated period T of time, and then the first selector valve 32A is opened to evacuate the filtrate chambers Sl and Sl 1 by the vacuum pump 31. [Blowing Process] A blowing process may be performed at desired timing (e.g., after completion of the pressing step in the dehydrating process or after completion of the drying process). In the blowing process, the air valve 41 and the slurry discharge valve 51 are opened. Thus, compressed air is supplied to the filter press 1 through the blow line 40, and the slurry is discharged through the slurry discharge line 50.

An end point of the filtration step or the pressing step in the dehydrating process, an end point of the drying process, or timing to proceed to perform a subsequent process may be determined by a preset period of time. Alternatively, the following methods may be employed to detect end points of the above processes.

(2) An end point of the pressing step in the dehydrating process can be determined by detecting when the pressure of the filter chambers 130 becomes lower than the pressing pressure of the heating medium, or when a flow rate of the pressing filtrate or the amount of the pressing filtrate reaches a predetermined value, or when the temperature of the cake in the filter chambers 130 reaches a predetermined value. (3) An end point of the drying process can be determined by detecting a temperature change of the cake in the filter chambers 130, a temperature change of the heating medium, or a temperature change of the filtrate discharge passages 106 and 116.

In the above example, a temperature difference between a temperature detected by the first heating medium temperature sensor 22 and a temperature detected by the second heating medium temperature sensor 23 is used as a physical property value reflecting a temperature of the slurry in the filter chambers. Further, in the above example, the first selector valve 32A is opened and closed every certain period of time. However, the physical property value reflecting a temperature of the slurry in the filter chambers is not limited to the above example. For example, temperature sensors may be inserted into the filtrate discharge passages 106 and 116 from the filtrate discharge line 35 near the filter press 1. Temperatures of the filtrate which are detected by these temperature sensors may be used as the aforementioned physical property value. In this case, the self-evaporation of water in the slurry may be started when the detected temperature of the filtrate becomes at least a predetermined value, and stopped when a temperature difference between an inlet temperature and an outlet temperature of the heating medium, which are measured by the heating medium temperature sensors 22 and 23, becomes a predetermined value, or after a predetermined period of time.

FIG. 6 is a cross-sectional view showing a main portion of a filter press 201 according to a second embodiment of the present invention. As shown in FIG. 6, the filter press 201 differs from the filter press 1 according to the first embodiment in that the heat transfer member 112 and the body 111 located at a peripheral portion of the second filter plate 110 are replaced with a heat transfer member 312 integrally made of metal. FIGS. 7 A and 7B are cross-sectional views showing the second filter plate 310. As shown in FIGS. 7 A and 7B, the heat transfer member 312 of the second filter plate 310 is in the form of a hollow doughnut. The hollow portion of the heat transfer member 312 serves as a heating medium chamber S22. Other structures of the filter press 201 are the same as those of the filter press 1 in the first embodiment and will not be described repetitively. FIGS. 8 A and 8B are cross-sectional views showing a filter plate 410 according to a third embodiment of the present invention. FIG. 8C is a partial enlarged view of FIG. 8B. The filter plate 410 shown in FIGS. 8 A through 8 C may be used instead of the second filter plates 110 in the first embodiment. The filter plate 410 differs from the second filter plate 110 of the first embodiment in that the filter plate 410 has an extensible portion 412 formed like bellows at ends of the heat transfer member 112. As shown in FIG. 8C, the heat transfer member 112 is secured to the body 111 by a fastener 112a. Other structures of the filter plate 410 are the same as the second filter plate .110 in the first embodiment and will not be described repetitively.

FIG. 9 is a cross-sectional view showing a main portion of a filter press 501 according to a fourth embodiment of the present invention. The filter plate 100 with the diaphragm 102 may have less heat transferability, and the life of the diaphragm 102 should be considered. Accordingly, in the filter press 501 according to the present embodiment, the filter plates 100 of the first embodiment are replaced with filter plates 110 (see FIGS. 5 A and 5B) each having a heat transfer member 112 made of metal. Filter chambers 130 are formed between the filter plates 110. The filter press 501 in the present embodiment is configured so as not to press slurry in the filter chambers 130. Accordingly, it is not necessary to provide the back-pressure valve 25 in the first embodiment.

An example of a dehydrating and drying process of slurry with the filter press 501 will be described below. The dehydrating and drying process of slurry in this example includes a dehydrating process to dehydrate slurry by filtration of the slurry, a drying process to dry the dehydrated slurry, and a blowing process to blow the dehydrated or dried slurry. [Dehydrating Process (Filtration)]

First, slurry is supplied to the filter press 501 through the slurry supply line 10, the slurry supply valve 12, and the slurry pressure sensor 14 by the slurry supply pump 11 and is thus filled in the filter chambers 130. When slurry is further supplied to the filter chambers 130, water of the slurry is converted into a filtration filtrate and discharged through the filtrate discharge passages 116 and the filtrate discharge line 35 from the filtrate chambers Sl.

It is desirable that the supply pressure of the slurry is set at, for example, a low absolute pressure of 0.15 MPa to 0.20 MPa at the beginning of the filtration. The supply pressure of the slurry may be increased gradually according to the progress of the filtration. Then, eventually, the supply pressure of the slurry may be set at an absolute pressure of at least 1.6 MPa. It is desirable that the period of time of the filtration is selected optimally depending on properties of the slurry. The slurry may be heated before being supplied to the filter press 501

(preliminary heating filtration). In this case, since the heated slurry is supplied to the filter press 501, the filterability of the slurry can be improved. Further, a heating medium heated in the heating tank 26 may be circulated in the heating medium circulation lines 2OA and 2OB by the heating medium circulation pump 21 and supplied into the heating medium chambers S 12 in the filter press 501 to heat the slurry during the filtration (heating filtration). In this case, since the slurry is filtered while being heated, the filterability of the slurry can be improved. [Drying Process]

In a drying process, when the slurry is not heated during the filtration, a heating medium heated in the heating tank 26 is circulated and supplied into the heating medium chambers S 12 in the filter press 501 to heat the slurry to a temperature higher than a saturated vapor temperature corresponding to a predetermined vacuum pressure. When slurry is heated during the filtration, the first selector valve 32A is opened at the beginning of the drying process. Thus, the filtrate chambers SI l in the filter press 501 are evacuated through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31 to introduce the slurry to an atmosphere under a vacuum pressure. During the filtration, the vacuum pump 31 may be operated to decompress the interior of the vacuum tank 34 in advance. In such a case, the filtrate chambers SI l can instantaneously be decompressed to a vacuum by opening the first selector valve 32A at the beginning of the drying process.

The slurry is sufficiently heated in the filter chambers 130 by the heating medium. Thus, a large difference is produced between the preset temperature of the slurry and the saturated vapor temperature corresponding to the vacuum pressure. Accordingly, when the slurry in the filter press 501 is instantaneously introduced to an atmosphere under a vacuum pressure in the drying process, thermal energy of the slurry is used for evaporation in addition to heat supplied by the heating medium. As a result, self-evaporation of water contained in the slurry is accelerated so as to cause bumping. The bumping increases a drying rate (evaporation rate) of the slurry.

As a larger difference is produced between the temperature of the slurry (cake) in the filter chambers 130 and a saturated vapor temperature corresponding to a predetermined vacuum pressure, the drying rate of the slurry becomes higher. However, the temperature of the cake is drastically lowered by evaporation of water after the starting of the drying process. Accordingly, the aforementioned temperature difference is reduced, and the drying rate of the slurry is lowered. From this point of view, operation of introducing the cake to a vacuum atmosphere (decompressed atmosphere) immediately after heating the cake to a predetermined temperature may be repeated a plurality of times so as to maintain an initial drying rate of the slurry in the drying process (repeated drying). In the case where the drying process is thus repeated, the heating medium is also circulated at a low pressure. The first selector valve 32A is opened to evacuate the filtrate chambers SI l in the filter press 501 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. After the temperature of the cake in the filter chambers 130 is decreased to a temperature lower than the temperature of the heating medium by a predetermined value, the first selector valve 32A is closed. Then, after the temperature of the cake in the filter chambers 130 is increased to a predetermined temperature, the first selector valve 32A is opened again to evacuate the filtrate chambers SI l by the vacuum pump 31. Such operation is repeated a predetermined number of times. [Blowing Process]

A blowing process may be performed at desired timing (e.g., after completion of the filtration in the dehydrating process or after completion of the drying process). In the blowing process, the air valve 41 and the slurry discharge valve 51 are opened. Thus, compressed air is supplied to the filter press 501 through the blow line 40, and the slurry is discharged through the slurry discharge line 50.

FIG. 10 is a cross-sectional view showing a main portion of a filter press 601 according to a fifth embodiment of the present invention. As shown in FIG.

10, the filter press 601 differs from the filter press 501 of the fourth embodiment in that the second filter plates 310 (see FIGS. 7A and 7B) of the second embodiment are used instead of the filter plates 110 of the fourth embodiment. Other structures of the filter press 601 are the same as the filter press 501 in the fourth embodiment and will not be described repetitively.

FIG. 11 is a cross-sectional view showing a main portion of a filter press 701 according to a sixth embodiment of the present invention. As shown in FIG.

11, the filter press 701 differs from the filter press 501 of the fourth embodiment in that the filter plates 410 (see FIGS. 8 A and 8B) of the third embodiment are used instead of the filter plates 110 of the fourth embodiment. Other structures of the filter press 701 are the same as the filter press 501 in the fourth embodiment and will not be described repetitively.

FIG. 12 is a schematic view showing a dehydrating and drying apparatus according to a seventh embodiment of the present invention. As shown in FIG. 12, the dehydrating and drying apparatus has a similar structure to the dehydrating and drying apparatus shown in FIG. 1. However, the dehydrating and drying apparatus shown in FIG. 12 differs from the dehydrating and drying apparatus shown in FIG. 1 as follows. A filtrate is discharged from the filter chambers in the filter press 1 through a filtrate discharge line 35. The filtrate discharge line 35 includes a first filtrate discharge line 35 A connected to a portion of a plurality of filtrate chambers and a second filtrate discharge line 35B connected to the rest of the plurality of filtrate chambers. The second filtrate discharge line 35B has a third selector valve (control valve) 32C. When the slurry is pressed in the filter chambers by the heating medium, the volume of the filter chambers is reduced. Thus, the slurry in the filter chambers is dehydrated into a cake. During dehydration of the slurry, a filtrate is discharged from the filter chambers. The filtrate is discharged through the first filtrate discharge line 35 A and the second filtrate discharge line 35B to the exterior of the dehydrating and drying apparatus.

When the filter chambers in the filter press 1 are to be evacuated by the vacuum pump 31, the first selector valve 32 A and the third selector valve 32C are opened while the second selector valve 32B is closed. When the filtrate is to be discharged from the filter chambers, the second selector valve 32B and the third selector valve 32C are opened while the first selector valve 32A is closed. Further, when the pressure of the filter chambers in the filter press 1 can be increased from vacuum to an atmospheric pressure by opening the second selector valve 32B and the third selector valve 32C.

A compressor (not shown) is connected to the blow line 40 for generating compressed air. Thus, compressed air is blown from the compressor through the blow line 40 into the filter chambers so that slurry remaining within the filter press 1 and slurry remaining at a slurry supply port of the filter chambers are discharged through the slurry discharge line 50 by the compressed air. The blow line 40 is branched into a first blow line 40A connected to the filter press 1 and a second blow line 4OB connected to the second filtrate discharge line 35B. The first blow line 4OA has a first air valve 4 IA, and the second blow line 4OB has a second air valve 41B. The slurry discharge line 50 has a slurry discharge valve 51.

An example of a dehydrating and drying process of slurry with the above dehydrating and drying apparatus will be described below. The dehydrating and drying process of slurry in this example includes a dehydrating process to dehydrate slurry by filtration and pressing of the slurry, a drying process to dry the dehydrated slurry, a blowing process to blow the dehydrated or dried slurry, and a ventilation process to allow compressed air to pass through the filter chambers. [Dehydrating Process] (1) Filtration Step

Next, a heating medium heated by the heating tank 26 is supplied through the heating medium circulation line 2OA to the heating medium chambers S2 and S 12 in the filter press 1 by the heating medium circulation pump 21. Thus, the slurry in the filter chambers 130 is heated by the heating medium. The heating medium is returned to the heating tank 26 through the heating medium circulation line 2OB, the second heating medium temperature sensor 23, and the heating medium pressure sensor 24. Then, the heating medium is heated by the heating tank 26 and supplied again to the heating medium chambers S2 and S 12 in the filter press 1 through the heating medium circulation line 20 A.

In a drying process, as in a case .of the pressing step in the dehydrating process, a heating medium is circulated through the filter press 1. It is desirable that the pressure of the heating medium is adjusted to be lower than the pressing pressure in the pressing step by the back-pressure valve 25. When the drying process is started, the first selector valve 32A and the third selector valve 32C are opened to evacuate the filtrate chambers Sl and Sl 1 in the filter press 1 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. Thus, the slurry is introduced to an atmosphere under a vacuum pressure. During the pressing step, the vacuum pump 31 may be operated to decompress the interior of the vacuum tank 34 in advance. In such a case, the filtrate chambers Sl and SI l can instantaneously be decompressed to a vacuum by opening the first selector valve 32A and the third selector valve 32C at the beginning of the drying process.

The efficiency of the vacuum pump 31 can be increased by supplying a coolant to the condenser 33 so that steam produced from the slurry (cake) in the filter chambers 130 is converted into water. It is desirable that the vacuum pressure in. the drying process is not more than an absolute pressure of 0.03 MPa. When the preset temperature is at least 100°C, which is a saturated vapor temperature of the atmospheric pressure, the first selector valve 32A may be left closed after the starting of the drying process, and the second selector valve 32B and the third selector valve 32C may be opened so that the steam produced from the slurry is discharged through the filtrate discharge line 35, not through the vacuum line 30. In this case, the slurry is sufficiently heated in the filter chambers 130 during the pressing step, and a large difference is produced between the preset temperature of the slurry and a saturated vapor temperature corresponding to an atmospheric pressure. Accordingly, thermal energy of the slurry is used for evaporation to accelerate self-evaporation of water contained in the slurry. Therefore, bumping can be caused to increase a drying rate of the slurry.

In the case where the drying process is thus repeated, the heating medium is also circulated at a pressure lower than the pressing pressure. The first selector valve 32A and the third selector valve 32C are opened to evacuate the filtrate chambers Sl and SIl in the filter press 1 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. After the temperature of the cake in the filter chambers 130 is decreased to a temperature lower than the temperature of the heating medium by a predetermined value, the first selector valve 32A is closed. Then, after the temperature of the cake in the filter chambers 130 is increased to a predetermined temperature, the first selector valve 32A is opened again to evacuate the filtrate chambers Sl and SIl by the vacuum pump 31. Such operation is repeated a predetermined number of times. [Blowing Process] A blowing process may be performed at desired timing (e.g., after completion of the pressing step in the dehydrating process or after completion of the drying process). In the blowing process, the first air valve 41A and the slurry discharge valve 51 are opened while the first selector valve 32 A, the second selector valve 32B, the third selector valve 32C, and the second air valve 4 IB are closed. Thus, compressed air is supplied through the first blow line 4OA to the filter press 1, and the slurry is discharged through the slurry discharge line 50. [Ventilation Process]

A ventilation process may be performed at desired timing (e.g., after completion of the filtration step or the pressing step in the dehydrating process, or during the drying process, or after the drying process). A ventilation process may be performed several times during the drying process. A ventilation process after completion of the filtration step in the dehydrating process serves to discharge water remaining in the slurry within the filter chambers 130. A ventilation process after completion of the drying process serves to further dry a cake that has been dried mainly in the filter chambers 130 and cracked so as to increase its surface area. One of steam, air, dehumidified air, and hot discharge gas may be used as compressed air to be supplied. Ventilation of compressed air in the ventilation process is classified into the following two types.

(A) Compressed air is supplied from the first blow line 4OA into the filter chambers 130. Water or steam in the filter chambers 130 is discharged through the filtrate discharge passages 106 and 116. At that time, the first air valve 4 IA, the second selector valve 32B, and the third selector valve 32C are opened while the second air valve 41B, the first selector valve 32A, and the slurry discharge valve 51 are closed. Specifically, the first blow line 4OA and the filtrate discharge line 35 form a ventilation mechanism for allowing compressed air to pass through the filter chambers 130. (B) Compressed air is supplied from the second blow line 4OB through the second filtrate discharge line 35B to the filtrate chambers Sl and SI l. The compressed air is supplied through the filter cloths into the filter chambers 130. Water or steam in the filter chambers 130 is discharged through the first filtrate discharge line 35 A. At that time, the second air valve 4 IB and the first selector valve 32A are opened, and the first air valve 41A, the second selector valve 32B, the third selector valve 32C, and the slurry discharge valve 51 are closed. The vacuum pump 31 is operated to evacuate the filtrate chambers Sl and SI l. Specifically, the second blow line 4OB, the second filtrate discharge line 35B, and the first filtrate discharge line 35A form a ventilation mechanism for allowing compressed air to pass through the filter chambers 130.

In a case where the vacuum pump 31 is not operated, the second air valve 4 IB and the second selector valve 32B may be opened, and the first air valve 4 IA, the third selector valve 32C, and the slurry discharge valve 51 may be closed. An end point of the filtration step or the pressing step in the dehydrating process, an end point of the drying process, or timing to proceed to perform a subsequent process may be determined by a preset period of time. Alternatively, the following methods may be employed to detect end points of the above processes.

The filter press described in the second to sixth embodiments may be used instead of the filter press 1 in the present embodiment.

An example of a dehydrating and drying process of slurry with the above dehydrating and drying apparatus using the filter press 501 shown in FIG. 9 will be described below. The dehydrating and drying process of slurry in this example includes a . dehydrating process to dehydrate slurry by filtration of the slurry, a drying process to dry the dehydrated slurry, a blowing process to blow the dehydrated or dried slurry, and a ventilation process to allow compressed air to pass through the filter chambers. [Dehydrating Process (Filtration)]

It is desirable that the supply pressure of the slurry is set at, for example, a low absolute pressure of 0.15 MPa to 0.20 MPa at the beginning of the filtration. The supply pressure of the slurry may be increased gradually according to the progress of the filtration. Then, eventually, the supply pressure of the slurry may be set at an absolute pressure of at least 1.6 MPa. It is desirable that the period of time of the filtration is selected optimally depending on properties of the slurry.

The slurry may be heated before being supplied to the filter press 501 (preliminary heating filtration). In this case, since the heated slurry is supplied to the filter press 501, the filterability of the slurry can be improved. Further, a heating medium heated in the heating tank 26 may be circulated in the heating medium circulation lines 20 A and 2OB by the heating medium circulation pump 21 and supplied into the heating medium chambers S 12 in the filter press 501 to heat the slurry during the filtration (heating filtration). In this case, since the slurry is filtered while being heated, the filterability of the slurry can be improved. [Drying Process]

In a drying process, when the slurry is not heated during the filtration, a heating medium heated in the heating tank 26 is circulated and supplied into the heating medium chambers S 12 in the filter press 501 to heat the slurry to a temperature higher than a saturated vapor temperature corresponding to a predetermined vacuum pressure. When slurry is heated during the filtration, the first selector valve 32A and the third selector valve 32C are opened at the beginning of the drying process. Thus, the filtrate chambers SIl in the filter press 501 are evacuated through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31 to introduce the slurry to an atmosphere under a vacuum pressure. During the filtration, the vacuum pump 31 may be operated to decompress the interior of the vacuum tank 34 in advance. In such a case, the filtrate chambers SIl can instantaneously be decompressed to a vacuum by opening the first selector valve 32A and the third selector valve 32C at the beginning of the drying process.

In the case where the drying process is thus repeated, the heating medium is also circulated at a low pressure. The first selector valve 32A and the third selector valve 32C are opened to evacuate the filtrate chambers SI l in the filter press 501 through the condenser 33, the vacuum tank 34, and the vacuum line 30 by the vacuum pump 31. After the temperature of the cake in the filter chambers 130 is decreased to a temperature lower than the temperature of the heating medium by a predetermined value, the first selector valve 32A is closed. Then, after the temperature of the cake in the filter chambers 130 is increased to a predetermined temperature, the first selector valve 32A is opened again to evacuate the filtrate chambers SI l by the vacuum pump 31. Such operation is repeated a predetermined number of times. [Blowing Process]

A blowing process may be performed at desired timing (e.g., after completion of the filtration in the dehydrating process or after completion of the drying process). In the blowing process, the first air valve 41 A and the slurry discharge valve 51 are opened, and the first selector valve 32A, the second selector valve 32B, the third selector valve 32C, and the second air valve 41B are closed. Thus, compressed air is supplied to the filter press 501 through the first blow line 4OA, and the slurry is discharged through the slurry discharge line 50. [Ventilation Process]

A ventilation process may be performed at desired timing (e.g., after completion of the filtration in the dehydrating process, or during the drying process, or after the drying process). A ventilation process may be performed several times during the drying process. Either of the aforementioned methods (A) and (B) may be employed for the ventilation process.

FIG. 13 is a schematic view showing a dehydrating and drying apparatus according to an eighth embodiment of the present invention. As shown in FIG. 13, the dehydrating and drying apparatus has a similar structure to the dehydrating and drying apparatus shown in FIG. 1. However, the dehydrating and drying apparatus shown in FIG. 13 differs from the dehydrating and drying apparatus shown in FIG. 1 as follows. The filter chambers in the filter press 1 are evacuated through a vacuum line 30 having a first selector valve (control valve) 32A and three vacuum tanks 34A, 34B, and 34C. Although three vacuum tanks are provided in parallel in FIG. 13, the number of the vacuum tanks is not limited to three. At least two vacuum tanks may be provided. The vacuum line 30, the vacuum pump 31, the first selector valve 32 A, and the vacuum tanks 34 A, 34B, and 34C form a decompressing mechanism for decompressing the slurry in the filter chambers of the filter press 1.

As shown in FIG. 13, a cooling mechanism 33 is provided for cooling the vacuum tanks 34A, 34B, and 34C. A coolant is supplied to the cooling mechanism 33. Heat is exchanged between steam introduced from the filter press 1 to the cooling mechanism 33 and the coolant in the cooling mechanism 33. Thus, the steam is condensed and then discharged as a condensate from the cooling mechanism 33.

The vacuum tank 34A has a vacuum pump valve 36A disposed between the vacuum pump 31 and the vacuum tank 34A, a filter press valve 37A disposed between the filter press 1 and the vacuum tank 34 A, and a condensate discharge valve 38A for discharging a condensate produced by the cooling mechanism 33. Similarly, the vacuum tank 34B has a vacuum pump valve 36B, a filter press valve 37B, and a condensate discharge valve 38B. The vacuum tank 34C has a vacuum pump valve 36C, a filter press valve 37C, and a condensate discharge valve 38C. Each of the vacuum pump 31 and the vacuum tanks 34A, 34B, and 34C has a pressure sensor (not shown). It is desirable that the volume of the vacuum tanks 34A, 34B, and 34C is about 5 to 20 times, more preferably about 5 to 10 times, the volume of the piping from the filter press 1 to the first selector valve 32A.

As shown in FIG. 13, a filtrate discharge line 35 is connected to the vacuum line 30. The filtrate discharge line 35 serves to discharge a filtrate from the filter chambers in the filter press 1 during dehydration of the slurry. The filtrate discharge line 35 has a second selector valve (control valve) 32B. When the slurry is pressed in the filter chambers by the heating medium, the volume of the filter chambers is reduced. Thus, the slurry in the filter chambers is dehydrated into a cake. During dehydration of the slurry, a filtrate is discharged from the filter chambers. The filtrate is discharged through the filtrate discharge line 35 to the exterior of the dehydrating and drying apparatus. When the filtrate is to be discharged from the filter chambers, the second selector valve 32B is opened while the first selector valve 32A is closed. Further, the pressure of the filter chambers in the filter press 1 can be increased immediately from vacuum to an atmospheric pressure by opening the second selector valve 32B.

A compressor (not shown) is connected to the blow line 40 for generating compressed air. Thus, compressed air is blown from the compressor through the blow line 40 into the filter chambers so that slurry remaining within the filter press 1 and slurry remaining at a slurry supply port of the filter chambers are discharged through the slurry discharge line 50 by the compressed air. The blow line 40 has an air valve 41, and the slurry discharge line 50 has a slurry discharge valve 51. An example of a dehydrating and drying process of slurry with the above dehydrating and drying apparatus will be described below. The dehydrating and drying process of slurry in this example includes a dehydrating process to dehydrate slurry by filtration and pressing of the slurry, a drying process to dry the dehydrated slurry, and a blowing process to blow the dehydrated or dried slurry. [Dehydrating Process] (1) Filtration Step

First, slurry is supplied to the filter press 1 through the slurry supply line 10, the slurry supply valve 12, and the slurry pressure sensor 14 by the slurry supply pump 11 and is thus filled in the filter chambers 130. When slurry is further supplied to the filter chambers 130, water of the slurry is converted into a filtration filtrate and discharged through the filtrate discharge passages 106 and 116 and the filtrate discharge line 35 from the filtrate chambers Sl and SI l. It is desirable that the supply pressure of the slurry is set at, for example, a low absolute pressure of 0.15 MPa to 0.20 MPa at the beginning of the filtration. The supply pressure of the slurry may be increased gradually according to the progress of the filtration. Then, eventually, the supply pressure of the slurry may be set at an absolute pressure of at least 0.6 MPa. It is desirable that the period of time of the filtration is selected optimally depending on properties of the slurry.

The slurry may be heated before being supplied to the filter press 1 (preliminary heating filtration). In this case, since the heated slurry is supplied to the filter press 1, the filterability of the slurry can be improved. Further, a heating medium heated in the heating tank 26 may be circulated in the heating medium circulation lines 2OA and 20B by the heating medium circulation pump 21 and supplied into the heating medium chambers S2 and S 12 in the filter press 1 to heat the slurry during the filtration (heating filtration). In this case, since the slurry is filtered while being heated, the filterability of the slurry can be improved. (2) Pressing Step Next, a heating medium heated by the heating tank 26 is supplied through the heating medium circulation line 2OA to the heating medium chambers S2 and S 12 in the filter press 1 by the heating medium circulation pump 21. Thus, the slurry in the filter chambers 130 is heated by the heating medium. The heating medium is returned to the heating tank 26 through the heating medium circulation line 2OB, the second heating medium temperature sensor 23, and the heating medium pressure sensor 24. Then, the heating medium is heated by the heating tank 26 and supplied again to the heating medium chambers S2 and S 12 in the filter press 1 through the heating medium circulation line 2OA.

The pressure (pressing pressure) of the heating medium in the heating medium chambers S2 is controlled at a predetermined value by the back-pressure valve 25, which is provided in the heating medium circulation line 2OB. When the heating medium is supplied to the heating medium chambers S2, the diaphragms 102 of the first filter plates 100 are swelled toward the filter chambers 130 to thereby press and heat the slurry in the filter chambers 130. Water in the slurry flows as a pressing filtrate out of the filtrate chambers Sl and SI l. The pressing filtrate is discharged through the filtrate discharge passages 106 and 116 to the filtrate discharge line 35. When the slurry is filtered and pressed in the above manner, the slurry is dehydrated and gradually converted into a cake. In the dehydrating process, only filtration step may be conducted without the pressing step to dehydrate the slurry.

It is desirable that the pressing pressure of the slurry is adjustable in a range of from an absolute pressure of 0.1 MPa (atmospheric pressure) to an absolute pressure of 1.6 MPa. It is desirable to increase the pressing pressure gradually to a pressure between the supply pressure of the slurry and 1.6 MPa after starting of the pressing step. Although the temperature of the heating medium should be equal to or more than a saturated vapor temperature corresponding to a vacuum pressure, it is not limited to a specific value. The heating medium should preferably have a temperature of at least 70°C. Thus, the slurry is heated to a preset temperature higher than a predetermined saturated vapor temperature (a saturated vapor temperature corresponding to a vacuum pressure). [Drying Process]

In a drying process, as in a case of the pressing step in the dehydrating process, a heating medium is circulated through the filter press 1. It is desirable that the pressure of the heating medium is adjusted to be lower than the pressing pressure in the pressing step by the back-pressure valve 25. It is desirable that the vacuum tanks 34A, 34B, and 34C are decompressed to a predetermined pressure, preferably at most an absolute pressure of 0.03 MPa, more preferably at most 0.02 MPa during the pressing step in the dehydrating process. For example, the vacuum tanks 34 A, 34B, and 34C and the vacuum pump 31 may be operated as shown in Table 1.

o: Open x: Close

Table 1

As shown in Table 1, the vacuum pump valves 36 A, 36B, and 36C and the filter press valves 37A, 37B, and 37C of the vacuum tanks 34A, 34B, and 34C are opened, and the first selector valve 32A and the condensate discharge valves 38 A, 38B, and 38C of the vacuum tanks 34A, 34B, and 34C are closed. In this state, the vacuum pump 31 and the cooling mechanism 33 are operated (preparation). After the pressure of the vacuum pump 31 or each of the vacuum tanks 34A, 34B, and 34C reaches a predetermined value, the vacuum pump valves 36 A, 36B, and 36C and the filter press valves 37A, 37B, and 37C of the vacuum tanks 34A, 34B, and 34C are closed, and the vacuum pump 31 is stopped (preset pressure). Vacuum 1 listed in table 1 is established immediately after starting of the drying process. Then, Vacuum 2 to Vacuum 5 are repeated. The vacuum pump 31 may continuously be operated to decompress the filter press 1 without switching the respective valves.

The efficiency of the vacuum pump 31 can be increased by supplying a coolant to the cooling mechanism 33 so that steam produced from the slurry (cake) in the filter chambers 130 is converted into water. When the preset temperature is at least 100°C, which is a saturated vapor temperature of the atmospheric pressure, the first selector valve 32A may be left closed after the starting of the drying process, and the second selector valve 32B may be opened so that the steam produced from the slurry is discharged through the filtrate discharge line 35, not through the vacuum line 30. In this case, the slurry is sufficiently heated in the filter chambers 130 during the pressing step, and a large difference is produced between the preset temperature of the slurry and a saturated vapor temperature corresponding to an atmospheric pressure. Accordingly, thermal energy of the slurry is used for evaporation to accelerate self-evaporation of water contained in the slurry. Therefore, bumping can be caused to increase a drying rate of the slurry.

In the case where the drying process is thus repeated, the heating medium is also circulated at a pressure lower than the pressing pressure. The first selector valve 32A is opened to evacuate the filtrate chambers Sl and SIl in the filter press 1. After the temperature of the cake in the filter chambers 130 is decreased to a temperature lower than the temperature of the heating medium by a predetermined value, the first selector valve 32A is closed. Then, after the temperature of the cake in the filter chambers 130 is increased to a predetermined temperature, the first selector valve 32A is opened again to evacuate the filtrate chambers Sl and SI l by the vacuum pump 31. Such operation is repeated a predetermined number of times.

[Blowing Process]

A blowing process may be performed at desired timing (e.g., after completion of the pressing step in the dehydrating process or after completion of the drying process). In the blowing process, the air valve 41 and the slurry discharge valve 51 are opened. Thus, compressed air is supplied to the filter press

1 through the blow line 40, and the slurry is discharged through the slurry discharge line 50. An end point of the filtration step or the pressing step in the dehydrating process, an end point of the drying process, or timing to proceed to perform a subsequent process may be determined by a preset period of time. Alternatively, the following methods may be employed to detect end points of the above processes. (1) An end point of the filtration step in the dehydrating process can be determined by detecting when the amount of a solid material supplied into the filter chambers 130 reaches a predetermined value.

As described above, three vacuum tanks 34A, 34B, and 34C are provided in the present embodiment. However, the number of the vacuum tanks is not limited to three. Two vacuum tanks can also achieve the above effects if a condensate is not discharged from the vacuum tanks.

The filter press described in the second and third embodiments may be used instead of the filter press 1 in the present embodiment. As described above, according to the present invention, a dehydrating process and a drying process of slurry can be performed with minimum energy consumption in a short period of time. Further, ease of separation of a cake can be improved. In the above embodiments, the slurry supply pipe 121 is connected to the central portion of the clamping plate 120A, and each of the filter plates has an opening located at a central portion thereof. However, the present invention is not limited to the illustrated examples. For example, the filter press may be configured such that slurry is supplied from above or blow the filter plates. [Example 1]

Experiments were carried out with use of the dehydrating and drying apparatus shown in FIG. 1. Experiment conditions and results are listed in Table 2. The experiments will be described with reference to Table 2 to show a drying effect when slurry having a predetermined temperature was introduced to an atmosphere under a low pressure and a drying effect when heating and drying under decompression were repeated.

Absolute Pressure

Table 2 As shown in Table 2, sludge including a large amount of organic matter having a concentration of 33 g/1 and an ignition loss of 68 %.was used as test slurry. Drying time was calculated based on a time point at which a water content of a dried cake became 40 % in experiments.

In Experiment 1, hot water was used as a heating medium, and the vacuum pump 31 and the condenser 33 were operated only during a drying process. In Experiment 2, hot water was used as a heating medium, and the vacuum pump 31 and the condenser 33 were operated only during a drying process. Further, the first selector valve 32A was opened and closed several times during the drying process to intermittently disconnect the filter press 1 from the vacuum line 30. In the comparative experiment, hot water was used as a heating medium, and the vacuum pump 31 and the condenser 33 were operated during a dehydration pressing process and a drying process. In the comparative experiment, since vacuum drying was conducted during the dehydration pressing process and the drying process, the slurry (cake) had a low temperature of 53°C. Drying was conducted under conditions in which a saturated vapor temperature corresponding to a vacuum pressure was 48°C, and in which a temperature difference between a cake temperature and the saturated vapor temperature was 5°C. Drying time at which a water content of a dried cake became 40 % was 52 minutes, and a filtration rate was 0.64 kg-m^-h^"1.

In Experiment 1, since vacuum drying was not conducted during the dehydration pressing process, the temperature of the slurry (cake) reached 89°C after completion of the dehydration pressing process. During the drying process, since vacuum drying was conducted, the temperature of the cake was lowered from 89°C to 53°C. Drying was conducted under conditions in which a saturated vapor temperature corresponding to a vacuum pressure was 48°C, and in which a temperature difference between a cake temperature and the saturated vapor temperature was in a range of from 5⁰C to 41°C. Drying time at which a water content of a dried cake became 40 % was 46 minutes, and a filtration rate was 0.67 kg-m^-h^"1. Thus, the filtration rate became 1.05 times that in the comparative experiment. Further, a power of the vacuum pump 31 and the condenser 33 during the drying process was equal to 64 % of that in the comparative experiment.

According to Experiment 1, slurry was heated during the dehydration pressing process, and the interior of the filter press 1 was immediately introduced into a vacuum atmosphere at the drying process. As a result, it was possible to provide sufficient thermal energy to the slurry so as to accelerate self-evaporation of water in the slurry. Accordingly, drying could be completed in a short period of time.

In Experiment 2, since vacuum drying was not conducted during the dehydration pressing process, the temperature of the slurry (cake) reached 89°C after completion of the dehydration pressing process. During the drying process, in order to prevent the temperature of the cake from being lowered by vacuum drying, the vacuum line 30 was closed by the first selector valve 32A when the temperature of the cake was lowered to 78°C, and the vacuum line 30 was opened by the first selector valve 32A when the temperature of the cake was increased to 88°C. Opening of the vacuum line 30 was repeated 8 times, and the vacuum line 30 was opened each time for 2 minutes. Closing of the vacuum line 30 was repeated 7 times, and the vacuum line 30 was closed each time for 2 minutes.

By repeating heating and vacuum drying of the cake, the temperature of the cake was maintained in a range of from 78°C to 88°C. When a saturated vapor temperature corresponding to a vacuum pressure was 48°C, drying was conducted in a state in which a temperature difference between the temperature of the cake and the saturated vapor temperature was in a range of from 30°C to 40°C. Drying time at which a water content of a dried cake became 40 % was 30 minutes, and a filtration rate was 0.78 kg-m^~2-h^"\ Thus, the filtration rate became 1.22 times that in the comparative experiment. Further, a power of the vacuum pump 31 and the condenser 33 during the drying process was equal to 42 % of that in the comparative experiment.

According to Experiment 2, the cake was heated even during the drying process, and operation of immediately introducing the filter press 1 to a vacuum atmosphere was repeated a plurality of times. As a result, it was possible to maintain acceleration of the self-evaporation due to sufficient thermal energy of the cake. Accordingly, drying could be completed in a shorter period of time. [Example 2]

Experiments were carried out with use of the dehydrating and drying apparatus having the filter press 501 shown in FIG. 9. In a comparative experiment, a filter press having a plurality of filter plates 100 shown in FIGS. 4 A and 4B and arranged in parallel was used.

Sludge including a large amount of organic matter having a concentration of 28 g/1 and an ignition loss of 78 % was used as test slurry. The filter press used in the experiment for the present invention had a filtration area of 3.45 m² and a filter chamber volume of 34 liters. The filter press used in the comparative experiment had a filtration area of 3.45 m² and a filter chamber volume of 50 liters.

These experiments were carried out under the following basic conditions. [Dehydrating Process (Filtration)] Comparative experiment:

Sludge supply pressure: 0.6 MPa Filtration time: 30 minutes

Sludge supply amount: 210 liters Experiment for the present invention:

Sludge supply pressure: Gradually increased from 0.1 MPa to 1.6 MPa

Filtration time: 45 minutes Sludge supply amount: 210 liters

[Pressing Process] Only comparative experiment:

Pressing pressure: 1.6 MPa

Pressing time: 30 minutes [Drying Process]

Comparative experiment:

Heating medium pressure: 0.13 MPa

Vacuum pressure: 0.01 MPa Experiment for the present invention: Heating medium pressure: 0.13 MPa

Vacuum pressure: 0.01 MPa

In the comparative experiment, drying time was calculated based on a time point at which a water content of a dried cake became 55 % in a continuous operation. As a result, the drying time at which a water content of a dried cake became about 55 % in a continuous operation was 70 minutes. At that time, a filtration rate was 0.68 kg/m^2>h.

In a repeated operation of experiment for the present invention, a preset temperature of slurry was 80°C. The first selector valve 32A was opened, and the filter chambers were maintained at 0.01 MPa for 5 minutes. Then, the first selector valve 32A was closed. This operation was repeated 6 times. Operation results are listed in Table 3.

Table 3

In the experiment for the present invention, a heat transfer rate was improved because each of the filter chambers had metal heat transfer surfaces on both sides thereof. As can be seen from the results shown in Table 3, although a filtration time in the experiment for the present invention became 15 minutes longer than that in the comparative experiment, a drying time was shortened by 11 minutes due to improvement of a drying rate, which was caused by repeated self-evaporation. Further, a period of time required for the entire process was shortened by 26 minutes because pressing time was eliminated. As a result, the filtration rate became higher than that in the comparative experiment. Specifically, the filtration rate became 1.32 times as high as that in the comparative experiment. The reasons why the filtration pressure was gradually increased from 0.1 MPa to 1.6 MPa and why the filter chamber volume was 34 liters were to increase the concentration of the slurry after completion of the filtration. Further, by circulating a heated medium during the filtration to heat the slurry to the preset temperature, it is possible to shorten heating time in the drying process by 10 minutes so as to further increase the filtration rate.

Organic sludge having a high compressibility was used as test sludge. Inorganic sludge having a low compressibility may shrink due to drying. The cake should be brought into continuous contact with heat transfer surfaces in order to maintain heat transfer. In such a case, an extensible portion 412 may be provided on the heat transfer member 112 of the filter plate 410 in the sixth embodiment shown in FIG. 11 to bring heat transfer surfaces into continuous contact with the cake. Thus, the dehydrating and drying apparatus can be operated without a lowered efficiency. [Example 3]

Experiments were carried out with use of the dehydrating and drying apparatus shown in FIG. 1. Sludge including a large amount of organic matter having a concentration of 28 g/1 and an ignition loss of 78 % was used as test slurry.

The filter press used in the experiment had a filtration area of 3.45 m² and a filter chamber volume of 50 liters.

These experiments were carried out under the following basic conditions. [Dehydrating Process (Filtration)]

Sludge supply pressure: 0.6 MPa Filtration time: 30 minutes Sludge supply amount: 210 liters

[Dehydrating Process (Pressing)]

Pressing pressure: 1.6 MPa Pressing Time: 30 minutes [Drying Process]

Heating medium pressure: 0.13 MPa

In the experiment, drying time was calculated based on a time point at which a water content of a dried cake became 55 % in a continuous operation. As a result, the drying time at which a water content of a dried cake became about 55 % in a continuous evacuation operation was 70 minutes. At that time, a filtration rate was 0.68 kg/m²-h.

In an experiment for the present invention, a preset temperature Tl was set to be 80°C. The first selector valve 32A was opened when Tl = 8O⁰C. The first selector valve 32A was closed when a temperature difference between an inlet temperature T3 and an outlet temperature T4 of a heating medium was 1°C. Operation results are listed in Table 4.

Table 4

As can be seen from the results shown in Table 4, a drying time at which a water content of a dried cake became about 55 % in the experiment for the present invention was 34 minutes, which was 36 minutes shorter than that in a case where vacuum was continuously produced in the drying process. A filtration rate was 0.90 kg/m²-h. According to the experiment for the present invention, the filtration rate became 1.32 times as high as that in the case where vacuum was continuously produced in the drying process. Efficient and energy-saving operation could be achieved. [Example 4]

The first selector valve 32A was opened and closed at a certain frequency under the same conditions as in Example 3 to perform self-evaporation of slurry. Operation results are listed in Table 5.

Table 5

As can be seen from the results shown in Table 5, a drying time in the case the first selector valve 32 A was opened and closed at a certain frequency was 41 minutes, which was 29 minutes shorter than that in a case where vacuum was continuously produced in the drying process. A filtration rate was 0.78 kg/m^2-h. According to the experiment for the present invention, the filtration rate became 1.14 times as high as that in the case where vacuum was continuously produced in the drying process. Efficient and energy-saving operation could be achieved. [Example 5]

Experiments were carried out with use of the dehydrating and drying apparatus shown in FIG. 12. Experiment conditions and results are listed in Table 6. The experiments will be described with reference to Table 6 to show a drying effect when slurry having a predetermined temperature was introduced to an atmosphere under a low pressure and a drying effect when heating and drying under decompression were repeated.

Absolute pressure

Table 6

As shown in Table 6, sludge including a large amount of organic matter having a concentration of 33 g/1 and an ignition loss of 68 % was used as test slurry. The filter press used in these experiments had a filtration area of 3.45 m². Drying time was calculated based on a time point at which a water content of a dried cake became 40 % in experiments. These experiments were carried out under the following basic conditions.

[Dehydrating Process]

Sludge supply pressure: 0.6 MPa

Filtration time: 30 minutes

Sludge supply amount: 136 liters [Pressing Process]

Pressing pressure: 1.6 MPa

Pressing time: 20 minutes [Drying Process]

Heating medium pressure: 0.13 MPa [Ventilation Process]

In the experiment for the present invention, a compressed gas was supplied from the second blow line 4OB through the second filtrate discharge line 35B into the filtrate chambers Sl and SI l after completion of the drying process. The compressed gas was supplied to the filter chambers 130 through the filter cloths. Water or steam in the filter chambers 130 was discharged through the first filtrate discharge line 35 A. At that time, the second air valve 4 IB and the first selector valve 32A were opened, and the first air valve 4 IA, the second selector valve 32B, the third selector valve 32C, and the slurry discharge valve 51 were closed. Further, the vacuum pump 31 was operated to evacuate the filtrate chambers Sl and SI l. The compressed air was supplied at a flow rate of the 100 1/min for 4 minutes.

In Comparative Experiment 1, hot water was used as a heating medium, and the vacuum pump 31 and the condenser 33 were operated during the dehydration pressing process and the drying process. In Comparative Experiment 2 and the experiment for the present invention, hot water was used as a heating medium, and the vacuum pump 31 and the condenser 33 were operated only during the drying process. The first selector valve 32A was opened and closed several times during the drying process to intermittently disconnect the filter press 1 from the vacuum line 30.

In Comparative Experiment 1, since vacuum drying was conducted during the dehydration pressing process and the drying process, the slurry (cake) had a low temperature of 53°C. Drying was conducted under conditions in which a saturated vapor temperature corresponding to a vacuum pressure was 48°C, and in which a temperature difference between a cake temperature and the saturated vapor temperature was 5°C. Drying time at which a water content of a dried cake became 40 % was 52 minutes, and a filtration rate was 0.64 kg-m^-h^'1. Further, the dried cake was attached to the filter cloths and the metal heat transfer members and was not separated from the filter cloths and the heat transfer members by its own weight.

In Comparative Experiment 2, since vacuum drying was not conducted during the dehydration pressing process, the slurry (cake) had a high temperature of 89°C after completion of the dehydration pressing process. In order to prevent the temperature of the cake from being lowered by vacuum drying, the vacuum line 30 was closed by the first selector valve 32A when the temperature of the cake was lowered to 78°C, and the vacuum line 30 was opened by the first selector valve 32A when the temperature of the cake was increased to 88°C. Opening of the vacuum line 30 was repeated 8 times, and the vacuum line 30 was opened each time for 2 minutes. Closing of the vacuum line 30 was repeated 7 times, and the vacuum line 30 was closed each time for 2 minutes.

By repeating heating and vacuum drying of the cake, the temperature of the cake was maintained in a range of from 78°C to 88°C. When a saturated vapor temperature corresponding to a vacuum pressure was 48°C, drying was conducted in a state in which a temperature difference between the temperature of the cake and the saturated vapor temperature was in a range of from 30°C to 40°C. Drying time at which a water content of a dried cake became 40 % was 30 minutes, and a filtration rate was 0.78 kg-m^-h^"1. Thus, the filtration rate became 1.22 times that in Comparative Experiment 1. Further, a power of the vacuum pump 31 and the condenser 33 during the drying process was equal to 42 % of that in Comparative Experiments.

According to the experiment for the present invention, the cake was heated even during the drying process, and operation of immediately introducing the filter press 1 to a vacuum atmosphere was repeated a plurality of times. As a result, it was possible to maintain acceleration of the self-evaporation due to sufficient thermal energy of the cake. Accordingly, drying could be completed in a shorter period of time. Further, the dried cake was not attached to the filter cloths and the heat transfer members and could be separated from the filter cloths and the heat transfer members by its own weight.

In the experiment for the present invention, the behavior during the drying process was the same as that in Comparative Experiments 1 and 2 because the experiment for the present invention was conducted under the same conditions as those of Comparative Experiments 1 and 2. Further, in the experiment for the present invention, a drying time at which a water content of a dried cake became 40 % was 20 minutes. A ventilation time was 4 minutes, and a filtration rate was 0.83 kg-m^-h^"1. Thus, drying could be completed in a period of time shorter than the drying time in Comparative Experiment 2 by 30 minutes. In a case of sludge including a large amount of organic matter, as the sludge was dried, heat transfer was lessened so as to lower a drying rate. Accordingly, by performing the ventilation process when the drying rate began to be lowered, effective drying could be achieved. [Example 6] Experiments were carried out with use of the filter press 501 shown in FIG.

9 in the dehydrating and drying apparatus shown in FIG. 12. Experiment conditions and results are listed in Table 7. Sludge including a large amount of organic matter having a concentration of 28 g/1 and an ignition loss of 78 % was used as test slurry. The filter press used in these experiments had a filtration area of 3.45 m² and a filter chamber volume of 34 liters.

*: Absolute pressure

Table 7

Sludge supply pressure: Gradually increased from 0.1 MPa to 1.6 MPa

Filtration time: 45 minutes

Sludge supply amount: 153 liters [Drying Process]

Heating medium pressure: 0.13 MPa Heating medium temperature: 8O⁰C

Vacuum pressure: 100 MPa [Ventilation Process]

In the comparative experiment, no ventilation process was performed. In the experiment for the present invention, dehumidified air was supplied through the second filtrate discharge line 35B to the filtrate chambers at a flow rate of 100 1/min for 4 minutes. The dehumidified air was discharged through the first filtrate discharge line 35 A.

In the comparative experiment, a drying time was 60 minutes, a water content of a cake was 55 %, and a filtration rate was 0.60 kg-m^-h^"1. In the experiment for the present invention, a drying time was 40 minutes, a ventilation time was 4 minutes, a water content of a cake was 54 %, and a filtration rate was 0.68 kg-m^-h^"1. Thus, by performing the ventilation process, the sludge could be dried in a shorter period of time. [Example 7]

Experiments were carried out with use of the dehydrating and drying apparatus shown in FIG. 13. The experiments were carried out under the following conditions. ^•Filtration area: 3.5 m² -Filter chamber volume: 50 liters ^•Piping volume: 6 liters ^•Discharge amount of vacuum pump: 50 1/min

^• Vacuum tank(s):

60 litters x 3 in the experiment for the present invention 60 litters x 1 in the comparative experiment

^•Preset pressure of vacuum tanks: 5 kPa ^•Pressure corresponding to predetermined saturated vapor temperature: 10 kPa

Experiments were carried out in the following manner. ^• Sludge concentration: 30 g/1 -Ignition loss: 23 %

^•Filtration: 0.6 MPa, 30 minutes

^• Supplied solid material: 4.5 kg ^•Pressing: 1.6 MPa, 20 minutes Under the above conditions, a period of time (drying time) at which a water content of a cake became 40 % in the drying process was measured. In both of the experiment for the present invention and the comparative experiment, the vacuum tanks were decompressed at the pressing step in the dehydrating process. In the experiment for the present invention, the first selector valve 32A was opened and closed at a frequency of 1 minute as shown in Table 8. The vacuum pump was continuously operated after Vacuum 3 in Table 8. In the comparative experiment, the vacuum pump was continuously operated from the pressing step in the dehydrating process, and the first selector valve 32A was opened and closed at a frequency of 1 minute. Operation results are listed in Table 8.

Continued until a water content became a desired value.

Table 8

In the comparative experiment, a drying time at which a water content of a cake became 40 % was 46 minutes, and water of 2.5 kg was recovered from the vacuum tank. In the comparative experiment, since water condensed in the vacuum tank could not be discharged because there was one vacuum tank. The vacuum tank could not sufficiently be decompressed in a predetermined period of time. Accordingly, the interior of the filter press could not be decompressed sufficiently. As a result, a drying time became long.

In the experiment for the present invention, a drying time at which a water content of a cake became 40 % was 30 minutes. In the experiment for the present invention, decompression of the filter press, discharge of a condensate, and decompression of the three vacuum tanks were simultaneously performed for each of the three vacuum tanks, and these processes were repeated. Accordingly, the filter press could sufficiently be decompressed, and drying could be completed in a shorter period of time.

Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Industrial Applicability The present invention is suitably used for a dehydrating and drying apparatus for dehydrating and drying slurry such as sludge discharged from a water supply and drainage system, a waste water treatment system in a rural village, a human waste treatment system, an industrial waste water treatment system, and the like.

Claims

1. A method of dehydrating and drying slurry, said method comprising: disposing a first filter plate having a filter cloth, a diaphragm, and a heating medium chamber formed therein and a second filter plate having a filter cloth, a heat transfer member made of metal, and a heating medium chamber formed therein so as to form a filter chamber between said first filter plate and said second filter plate; supplying slurry to said filter chamber; filtering the slurry in said filter chamber through said filter cloths of said first filter plate and said second filter plate; pressing the slurry in said filter chamber against said diaphragm of said first filter plate by supplying a heating medium to said heating medium chamber of said first filter plate; transferring heat of a heating medium to the slurry through said heat transfer member of said second filter plate by supplying the heating medium to said heating medium chamber of said second filter plate; heating the slurry to a preset temperature higher than a predetermined saturated vapor temperature; and introducing the slurry to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature after said heating the slurry so that a temperature difference between the preset temperature and the predetermined saturated vapor temperature causes self-evaporation of water in the slurry.

2. The method as recited in claim 1, wherein said heating the slurry comprises heating the slurry during said filtering the slurry or during said pressing the slurry, wherein said introducing the slurry comprises repeating the self-evaporation of water in the slurry a plurality of times.

3. A method of dehydrating and drying slurry, said method comprising: disposing filter plates each having a filter cloth, a heat transfer member made of metal, and a heating medium chamber formed therein so as to form a filter chamber between said filter plates; supplying slurry to said filter chamber; filtering the slurry in said filter chamber through said filter cloths of said filter plates; transferring heat of a heating medium to the slurry through said heat transfer members of said filter plates by supplying the heating medium to said heating medium chambers of said filter plates; heating the slurry to a preset temperature higher than a predetermined saturated vapor temperature; and introducing the slurry to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature after said heating the slurry so that a temperature difference between the preset temperature and the predetermined saturated vapor temperature causes self-evaporation of water in the slurry.

4. The method as recited in claim 3, wherein said heating the slurry comprises heating the slurry during said filtering the slurry or after said filtering the slurry, wherein said introducing the slurry comprises repeating the self-evaporation of water in the slurry a plurality of times,

5. The method as recited in any one of claims 1 through 4, further comprising allowing a compressed gas to pass through the filter chamber during said filtering the slurry, during said pressing the slurry, after said filtering the slurry, after said pressing the slurry, during the self-evaporation of water in the slurry, or after the self-evaporation of water in the slurry.

6. The method as recited in claim 5, wherein said allowing the compressed gas to pass through the filter chamber comprises: supplying the compressed gas to the filter chamber through a blow line for blowing the compressed gas into the filter chamber, and discharging the compressed gas from the filter chamber through a filtrate discharge line for discharging a filtrate from the filter chamber.

7. The method as recited in claim 5, wherein said allowing the compressed gas to pass through the filter chamber comprises: supplying the compressed gas to the filter chamber through one of a plurality of filtrate discharge lines for discharging a filtrate from the filter chamber, and discharging the compressed gas from the filter chamber through another of the plurality of filtrate discharge lines.

8. The method as recited in any one of claims 1 through 4, wherein said introducing the slurry comprises repeating the self-evaporation of water in the slurry a plurality of times by connecting the filter chamber sequentially to a plurality of vacuum tanks each held at a pressure equal to or lower than the pressure corresponding to the predetermined saturated vapor temperature.

9. The method as recited in any one of claims 1 through 4, further comprising measuring a physical property value reflecting a temperature of the slurry in the filter chamber; and controlling start and stop of the self-evaporation of water in the slurry based on the measured physical property value.

10. The method as recited in claim 9, wherein said measuring the physical property value comprises measuring a temperature of the slurry in the filter chamber and a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber, wherein said controlling the start and stop of the self-evaporation of water in the slurry comprises: starting the self-evaporation of water in the slurry when the measured temperature of the slurry in the filter chamber is higher than a predetermined value, and stopping the self-evaporation of water in the slurry when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value.

11. The method as recited in claim 9, wherein said measuring the physical property value comprises measuring a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber, wherein said controlling the start and stop of the self-evaporation of water in the slurry comprises starting and stopping the self-evaporation of water in the slurry when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value.

12. The method as recited in claim 9, wherein said measuring the physical property value comprises measuring a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber, wherein said controlling the start and stop of the self-evaporation of water in the slurry comprises: starting the self-evaporation of water in the slurry when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value, and stopping the self-evaporation of water in the slurry a predetermined period of time after said starting the self-evaporation of water in the slurry.

13. The method as recited in claim 9, wherein said measuring the physical property value comprises measuring a temperature of a Filtrate discharged from the filter chamber and a temperature difference between an inlet temperature of the heating medium chamber and an outlet temperature of the heating medium chamber, wherein said controlling the start and stop of the self-evaporation of water in the slurry comprises: starting the self-evaporation of water in the slurry when the measured temperature of the filtrate discharged from the filter chamber is higher than a predetermined value, and stopping the self-evaporation of water in the slurry a predetermined period of time after said starting the self-evaporation of water in the slurry or when the measured temperature difference between the inlet temperature of the heating medium chamber and the outlet temperature of the heating medium chamber is equal to a predetermined value.

14. The method as recited in claim 9, wherein said measuring the physical property value comprises measuring a temperature of the slurry in the filter chamber, wherein said controlling the start and stop of the self-evaporation of water in the slurry comprises: starting the self-evaporation of water in the slurry when the measured temperature of the slurry in the filter chamber is higher than a predetermined value, and stopping the self-evaporation of water in the slurry a predetermined period of time after said starting the self-evaporation of water in the slurry.

15. The method as recited in any one of claims 1 through 4, wherein said introducing the slurry comprises repeating the self-evaporation of water in the slurry a plurality of times at a predetermined frequency.

16. The method as recited in any one of claims 1 through 4, wherein the difference between the preset temperature and the predetermined saturated vapor temperature is in a range of from 20⁰C to 70°C, wherein the pressure corresponding to the predetermined saturated vapor temperature is not more than an absolute pressure of 0.03 MPa.

17. An apparatus for dehydrating and drying slurry, said apparatus comprising: a filter press having a first filter plate, a second filter plate, and at least one filter chamber formed between said first filter plate and said second filter plate, said first filter plate having a diaphragm, a filter cloth disposed between said diaphragm and said filter chamber, and a heating medium chamber for pressing said diaphragm to said filter chamber by a supplied heating medium, said second filter plate having a heat transfer member made of metal with a heat transfer surface, a filter cloth disposed between said heat transfer surface of said heat transfer member and said filter chamber, and a heating medium chamber for transferring heat of a supplied heating medium to the slurry through said heat transfer surface; a heating mechanism operable to heat the slurry to a preset temperature higher than a predetermined saturated vapor temperature; and a decompressing mechanism operable to instantaneously introduce the slurry heated by said heating mechanism to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature.

18. The apparatus as recited in claim 17, wherein said second filter plate has a body made of resin disposed at a peripheral portion of said heat transfer surface of said heat transfer member, said body being formed integrally with said heat transfer member of said second filter plate.

19. An apparatus for dehydrating and drying slurry, said apparatus comprising: a filter press having filter plates and at least one filter chamber formed between said filter plates, each of said filter plate having a heat transfer member made of metal with a heat transfer surface, a filter cloth disposed between said heat transfer surface of said heat transfer member and said filter chamber, and a heating medium chamber for transferring heat of a supplied heating medium to the slurry through said heat transfer surface; a heating mechanism operable to heat the slurry to a preset temperature higher than a predetermined saturated vapor temperature; and a decompressing mechanism operable to instantaneously introduce the slurry heated by said heating mechanism to an atmosphere having a pressure corresponding to the predetermined saturated vapor temperature.

20. The apparatus as recited in claim 19, wherein each of said filter plates has a body made of resin disposed at a peripheral portion of said heat transfer surface of said heat transfer member, said body being formed integrally with said heat transfer member of said filter plate.

21. The apparatus as recited in any one of claims 17 through 20, further comprising a ventilation mechanism operable to allow a compressed gas to pass through said filter chamber.

22. The apparatus as recited in claim 21, wherein said ventilation mechanism is configured to supply the compressed gas to the filter chamber through a blow line for blowing the compressed gas into the filter chamber and to discharge the compressed gas from the filter chamber through a filtrate discharge line for discharging a filtrate from the filter chamber.

23. The apparatus as recited in claim 21, wherein said ventilation mechanism is configured to supply the compressed gas to the filter chamber through one of a plurality of filtrate discharge lines for discharging a filtrate from the filter chamber and to discharge the compressed gas from the filter chamber through another of the plurality of filtrate discharge lines.

24. The apparatus as recited in any one of claims 17 through 20, wherein said decompressing mechanism includes:

(i) a plurality of vacuum tanks connected in parallel to said filter chamber of said filter press, each of said plurality of vacuum tanks being held at a pressure equal to or lower than the pressure corresponding to the predetermined saturated vapor temperature, and

(ii) a plurality of valves operable to switch connections between said plurality of vacuum tanks and said filter chamber of said filter press, said plurality of vacuum tanks having a cooling mechanism.

25. The apparatus as recited in any one of claims 17 through 20, further comprising at least one sensor for measuring a physical property value reflecting a temperature of the slurry in the filter chamber, said decompressing mechanism being controlled based on the physical property value measured by said at least one sensor.

26. The apparatus as recited in claim 25, wherein said at least one sensor includes a sensor for measuring a temperature of the slurry in said filter chamber.

27. The apparatus as recited in claim 25, wherein said at least one sensor includes a first sensor for measuring an inlet temperature of said heating medium chamber and a second sensor for measuring an outlet temperature of said heating medium chamber.

28. The apparatus as recited in claim 25, wherein said at least one sensor includes a sensor for measuring a temperature of a filtrate discharged from said filter chamber.

29. The apparatus as recited in any one of claims 17 through 20, wherein the difference between the preset temperature and the predetermined saturated vapor temperature is in a range of from 20°C to 70°C, wherein the pressure corresponding to the predetermined saturated vapor temperature is not more than an absolute pressure of 0.03 MPa.