GB1572731A - Top feed endless belt filter apparatus - Google Patents

Description

(54) TOP FEED ENDLESS BELT FILTER APPARATUS (71) We, KANEBO ENVIRONMENT CO., LTD., of 1 Yamaguchicho 325, Higashiyodogawa-ku, Ohsaka-shi, Ohsaka, Japan, a company organised and existing under the laws of Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which is it to be performed, to be particularly described in and by the following statement: This invention relates to a top feed apparatus for continuously dehydrating a slurry, for example in which a muddy residue obtained by coagulating particles resulting from the chemical treatment of faeces and urine of livestock is fed on to the top surface ("top feed") of a continuously travelling filter element for the application thereto of a high degree of dehydration action to facilitate post-treatment.

Conventional top feed continuous dehydrating systems include (a) vacuum systems, (b) vacuum and pressure systems, (c) vacuum and gravity systems, (d) gravity and pressure systems, and (e) pressure systems, the most practical of which are the vacuum and gravity systems (c) because the slurry generally contains viscous fluids which are hard to separate and render filtration extremely difficult. Devices utilising gravity are less expensive but relatively low in efficiency, and on the other hand, devices utilising vacuum pose problems in that it is difficult to completely seal the clearance between the filter-element and the vacuum device and in that it is expensive to produce a vacuum.

In accordance with the present invention, the action of gravity on the slurry itself is utilised during dehydration in a zone where the slurry is fed, optionally assisted by a low degree of vacuum, in other words mere suction onto the travelling filter element; in addition, the inclination of the filter element to the horizontal is chosen to achieve the good filtration and dehydration under gravity.

The invention provides a top feed apparatus for the continuous dehydration of slurry in which an endless filter belt passes over part of its run through a supply zone where in operation slurry to be dehydrated is supplied to the belt surface from above to be filtered by the belt under the action of gravity, the filter belt passing through the supply zone at an inclination of 25 to 500 to the horizontal and means being provided for advancing the filter belt around its endless path so that it moves upwardly at said inclination through the supply zone.

Coagulated particles ("flock") contained in slurry within a slurry supply vessel are linked with each other, and the slurry may be dehydrated efficiently in this condition. However, the flock is generally of low mechanical strength, and when a vacuum suction is applied to the flock, the linking is broken and as a consequence the filter element is blocked. If an excessively strong vacuum is applied, the flock passes through the meshes of the filter element, resulting in failure to achieve the object of solid liquid separation. If the slurry supply vessel is deeper to provide a greater depth of the slurry in an effort to enhance gravity dehydration, the filter element must be advanced under high pressure, and as a consequence sealing problems and mechanical problems such as friction between the filter element and a sealing member occur; the depth of the slurry supply vessel is thus subject to practical limitation.

The invention will be better understood from a reading of the following detailed description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic illustration showing in section the structure of an apparatus in accordance with the present invention; Figs. 2, 3 and 4 explain the principle of the essential part of the Fig. 1 apparatus and its operation; and Fig. 5 is a graphic representation showing operating data of the Fig. 1 apparatus.

Referring now to Fig. 1, the reference numeral 1 indicates a raw liquid transport pipe, 2 a coagulation and reaction vessel, 3 an agitator, 4 a motor for the agitator, and 5 a slurry supply vessel, the coagulation and reaction vessel 2 being normally positioned apart from the slurry supply vessel 5 so that slurry obtained by coagulation in vessel 2 is agitated by the agitator 3 and then transported to the slurry vessel 5 through a conduit 31.

A filter cloth, a filter element in the form of an endless belt, indicated as at 6 is passed over a roller 7 which prevents zigzag movement of the filter cloth, a guide roller 8, a drum 9, one or more pressing rollers 10 and 10', a drive roller 11, and a guide roller 12. The inclination of belt 6 to the horizontal between the roller 7 and the guide roller 8 is set at from 250 to 50".

The pressing rollers 10, 10' and drive roller 11 are conveniently coated with rubber or other resilient material so as to exhibit pressing action and frictional driving action, respectively.

The reference numeral 13 indicates a variable speed motor for driving the drive roller 11 through a chain 32, 14 is a device for adjusting the tension of the filter cloth, 15 is a scraper, 16 is a frame, 17 is a chute, and 33, 33' are pressing arms for retaining the respective pressing rollers 10, 10', the arms being pivotally supported on a shaft 34 extending through opposite side plates of a frame 16 and abutting against cams 18, 18'. which are fixedly mounted on respective shafts 35, 35' extending rotatably through the opposite side plates of the frame.

In operation, the shafts 35,35' are rotated by a driving device (not shown) and the pressure of the pressing rollers 10, 10' on the drum 9 is adjusted through the cams 18, 18" and pressing arms 33, 33'. This pressure may be varied depending on the kind and quantity of slurry, and the speed of filter cloth.

The reference numeral 19 indicates avacuum box, 20 is a filtrate tray, 21 and 21' are upper and lower filter cloth washing showers, 22 is a filtrate tray, 23 is a filtrate separator, 24 is a blower, 25 is a filter cloth washing pump, 26 is a circulation vessel, 27 is a filtrate drain pipe, and 28 is a cake tray. The filtrate separator 23, the blower 24, the filter cloth washing pump 25 and the circulator 26 are similar to those used in conventional top feed continuous dehydrating apparatus. The roller 7 for preventing zigzag movement of the filter cloth, the guide rollers 8 and 12, the drum 9, and the pressing rollers 10, 10', are driven rollers so that the filter cloth 6 will not go slack during its travel.

The slurry, from which a large amount of filtrate is drawn by the vacuum box, is further compressed, filtered and dehydrated between the drum 9 and the pressing rollers 10, 10' into a cake, which is transferred onto the drum 9 and thence scraped by the scraper 15 into the chute 17 and finally received in the cake tray 28.

Referring to Fig. 2, the slurry supplying zone extends from edge B at the bottom of the slurry supply vessel to edge D of the vacuum box, the portion where the weight of slurry within the slurry supply vessel 5 substantially extends to the filter cloth 6 being represented by A ABC, the length of slurry in contact with the filter cloth 6 by BC, and the depth of slurry by AB. Let 8 be the inclination of the filter cloth to the horizontal, AB BC = sin @, 8, = BC 9 - sin 0 and hence, if the liquid depth AB is constant in the case of 8 = 0 then BC = Since the filter cloth 6 is merely passed over the roller 7 and the guide roller 8, the amount of slurry A ABC that may be placed thereon is limited. In other words, in the case where the area of A ABC is constant, if the value of 8 is made small, the apparatus becomes large and hence expensive, and conversely if the value of f is increased, the apparatus becomes smaller and hence cheaper.

Turning now to Fig. 3, the filter cloth 6 in contact with the lower surface BC of the slurry immediately after having been washed is not loaded with solids. However, as the filter cloth moves upwards to the right, it again effects filtration and rapidly becomes loaded with consequent decrease in its filtration efficiency. The greater the angle 0 the greater the liquid depth AB to increase the liquid pressure, so that considerable filtration may be performed with good filtration efficiency. Another P-Q curve below A ABC indicates variation of filtration along the contact length BC.

In Fig. 4, in the case where the weight of slurry is constant but the angle o varies, that is, let MN and M' N' be the average liquid depth when A ABC and A A' B' C' are the same in area and 0 > B',then MN > M' N'.Thus, it is found that the liquid pressure is increased when the angle o is large and the filtration efficiency per unit contact length of the filter cloth is enhanced.

Referring again to Fig. 2, the vaccum box 19 is positioned adjacent to the lower surface of the filter cloth BD to attract the cloth uniformly under the mild vacuum (200 to 400 mmAq).

Conventional top feed continuous dehydrating apparatuses have used high vacuum, e.g. 600 mm Hg. Areas X, Y and Z below BD, BC and CD represent the slurry supplying area, gravity dehydration area and suction dehydration area, respectively; in the gravity dehydration area Y, gravity dehydration utilising an acute inclination of the filter cloth 6 predominates and suction dehydration is of minor importance. In this case, the suction is small so that dregs from the flock within A ABC as previously mentioned are not loaded onto the filter cloth. In the suction dehydration area Z where gravity is exerted on only a thin layer of slurry, the gravity dehydration assumes a minor role and suction dehydration predominates.

In the manner described above, the slurry is highly dehydrated within the slurry supply zone X but not to a sufficient degree to give the low water content cake required for post-treatment. Therefore a large-diameter drum 9 is disposed downstream of the slurry supply zone X in such a manner that substantially the lower half of its peripheral surface comes in contact under pressure with the filter cloth 6, the drum being frictionally driven by drive roller 11 rotated by variable speed motor 13, and one or more pressing rollers 10, 10' are brought into contact under pressure with the filter cloth 6 on the bottom of the drum 9 to forcibly squeeze and dehydrate the slurry to produce a good cake. It is convenient for the pressing rollers to be independently adjustable in position relative to the drum depending on the raw material being treated and the operating conditions, and in addition the pressure of the rollers on the drum may be adjusted by the cams.

With apparatus according to the present invention, e.g. comprising a first dehydration device which principally utilises gravity and a second dehydration device which principally utilises compression in the slurry supply zone X, high performance dehydration may be achieved merely by proper choice of the inclination of the filter cloth to the horizontal. For example, in the case of waste water from drinks as exemplified in Table I, the amount treated when the inclination of the endless belt is set at 300 is double than when it is 15 , and further, the degree of suction has been decreased showing that an expensive vacuum device is not required, thus affording an economical and efficient top feed continuous dehydrating apparatus.

Data illustrating effects obtained in accordance with the present invention are given in Table I and Fig. 5: TABLE I (Fig. 5) Examples of Amount of Slurry Treated with Different Filter Cloth Inclinations Slurry charge width: 1,000 mm Speed of filter cloth: 3.6 m/min.

Percentage of water content of cakes obtained by samPles are: (1) ... 84% (2) ... 82% (3) ... 85%

Inclination of filter lot to horizontal 15 30 40 50 Sample ~ Treated quantity (M3/H) (1) Activated sludge from waste water of drinks 1.50 3.00 3.20 3.40 (7,900-8,500 PPM*) (2) Activated sludge from waste water of pig *) 0.96 2.23 2.41 2.50 raising (5,800 PPM*) (3) Activated sludge from waste water of night 1.09 1.52 1.64 1.73 soil (26,200 PPM*) * Suspended solid density.

It is noted that the inclination of the filter cloth within the slurry supply zone in conven tional top feed continuous dehydrating apparatus is below 15". Values and curves indicated in Table I and Fig. 5 represent relationship of the amount of the slurry treated to the inclination of the filter cloth for various raw slurries in obtaining cakes of constant percentage water content under a predetermined degree of vacuum and a predetermined travel speed of filter cloth; as may be seen, the treatment capacity may be increased materially by employing inclinations in the range of from 25 to 500 as compared with a conventional inclination of 15".

WHAT WE CLAIM IS: 1. A top feed apparatus for the continuous dehydration of slurry in which an endless filter belt passes over part of its run through a supply zone where in operation slurry to be dehydrated is supplied to the belt surface from above to be filtered by the belt under the action of gravity, the filter belt passing through the supply zone at an inclination of 25 to 50 to the horizontal and means being provided for advancing the filter belt around its endless path so that it moves upwardly at said inclination through the supply zone.

2. Apparatus according to claim 1 including means for applying suction to the belt from below at and/or after the supply zone so that the slurry is filtered partially under the action of gravity and partially under the action of suction.

3. Apparatus according to claim 1 or 2 including, downstream of the supply zone, a rotatable drum around part of whose circumference the filter belt is trained, means being provided for pressing the filter belt against the drum for the expression of further liquid from slurry on the belt.

4. Continuous dehydrating apparatus substantially as hereinbefore described with reference to Figs. 1 to 4 of the accompanying drawings.

5. Continuous dehydrating apparatus as claimed in claim 1 operated substantially as hereinbefore described with reference to Table 1 and Fig. 5 of the accompanying drawings.

6. A continuous dehydration process using an apparatus as claimed in claim 1 substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. tional top feed continuous dehydrating apparatus is below 15". Values and curves indicated in Table I and Fig. 5 represent relationship of the amount of the slurry treated to the inclination of the filter cloth for various raw slurries in obtaining cakes of constant percentage water content under a predetermined degree of vacuum and a predetermined travel speed of filter cloth; as may be seen, the treatment capacity may be increased materially by employing inclinations in the range of from 25 to 500 as compared with a conventional inclination of 15". WHAT WE CLAIM IS:

1. A top feed apparatus for the continuous dehydration of slurry in which an endless filter belt passes over part of its run through a supply zone where in operation slurry to be dehydrated is supplied to the belt surface from above to be filtered by the belt under the action of gravity, the filter belt passing through the supply zone at an inclination of 25 to 50 to the horizontal and means being provided for advancing the filter belt around its endless path so that it moves upwardly at said inclination through the supply zone.

2. Apparatus according to claim 1 including means for applying suction to the belt from below at and/or after the supply zone so that the slurry is filtered partially under the action of gravity and partially under the action of suction.

3. Apparatus according to claim 1 or 2 including, downstream of the supply zone, a rotatable drum around part of whose circumference the filter belt is trained, means being provided for pressing the filter belt against the drum for the expression of further liquid from slurry on the belt.

4. Continuous dehydrating apparatus substantially as hereinbefore described with reference to Figs. 1 to 4 of the accompanying drawings.

5. Continuous dehydrating apparatus as claimed in claim 1 operated substantially as hereinbefore described with reference to Table 1 and Fig. 5 of the accompanying drawings.

6. A continuous dehydration process using an apparatus as claimed in claim 1 substantially as hereinbefore described.