WO1991008818A1

WO1991008818A1 - Apparatus for filtration of liquid

Info

Publication number: WO1991008818A1
Application number: PCT/SE1990/000803
Authority: WO
Inventors: Sven Anders Samuel HÅKANSON
Original assignee: Haakanson Sven Anders Samuel
Priority date: 1989-12-08
Filing date: 1990-12-05
Publication date: 1991-06-27
Also published as: SE465655C; SE465655B; KR920700737A; SE8904138L; SE8904138D0; JPH03181303A; AU6952591A

Abstract

The present invention discloses an apparatus for filtration of liquid, wherein a granular filter medium forming a filter bed (FB) in a filter tank (1) moves downwards, while the liquid to be filtered is introduced into the lower part of said filter bed and flows upwards, dirty granular filter medium is taken out of the bottom of said filter bed and transported to a counter-current washer (21) by a first transport means (18) and washed with a part of filtered liquid, and washed granular filter medium is returned to the top of said filter bed by a second transport means (28). In the present invention, the first transport means, the counter-current washer and the second transport means are placed outside the filter tank. Further, in the present invention, the liquid to be filtered is introduced into the lower part of the filter bed either on its peripheral part (5) or both on its peripheral and inner parts (17).

Description

Apparatus for Filtration of Liquid

2. Fields of the Invention

The present invention relates to an apparatus for filtration of liquid, characterized by upflow of liquid, and downward movement of the filter bed, wherein granular filter medium moves downwards, and wherein dirty granular filter medium is taken out from the bottom of the filter tank and washed, whereupon the washed granu¬ lar filter medium is returned to the top of the filter bed.

3. Related Background Art

In this description, the term "granular filter medium" is used for all granular materials that can be used as a filter medium, for example, natural sand, crushed mineral, and activated carbon. A number of methods are already known of making upflow continuous filters with moving bed, wherein the granular filter medium form¬ ing the filter bed (for example, sand) moves, and is taken out, washed and returned to the top of the filter bed. For example, U.S. Patent No. 2,057,887 that Elliot and Elliot obtained already inl936 shows an upflow continuous filter with moving bed, wherein the sand is taken out from the bottom of the filter tank with a screw conveyer, washed and returned to the top of the filter bed through a screw feeder or a zigzag conduit. In this filter, the liquid to be filtered is introduced into the filter bed through a hollow sand distributor cone with open base placed in the lower part of the filter bed. The filtered liquid is taken out through a circular outlet channel placed around on the inside wall of the filter tank in the upper part above the filter bed. The filter tank is completely filled with sand. The principle of upflow con tinuous filter with moving bed, in which, as in the filter de¬ scribed above, the liquid to be filtered is introduced into the lower part of the filter bed and the filtered liquid is taken out from the upper part of the filter bed while the sand moves down¬ wards, has proved to be correct, and is used in various filters manufactured now. German Patent No. 2,262,599 (corresponding to French Patent No. 72.46629) shows an upflow contnuous filter with moving bed that has an open-topped filter tank, a filter bed with free top, a washer placed above the filter bed, and a sand lift pipe placed outside the filter tank through which the sand is transported from the bottom of the filter tank to the washer. In this fil¬ ter, the sand returns from the washer placed above the filter bed to the top of the filter bed by free fall. The liquid to be filtered is introduced into the lower part of the filter bed through a feeder placed in the sand in the filter bed, and the filtered liquid is taken out over an overflow weir placed above the filter bed.

To take another exemple known to the public, Swedish Patent App¬ lication No. 7602999-0 (corresponding to Japanese examined Pa¬ tent publication No. 51808/81) shows an upflow continuous filter which has a very similar construction to that described in Ger¬ man Patent No. 2,262,599 mentioned above. In this filter, a sand lift pipe is placed in the center of the filter bed in the filter tank. A washer is placed around the sand lift pipe. The washer is immersed into a liquid phase above the filter bed (hereafter referred to zone of filtered liquid phase) with its lower end above the zone where the filter bed is; (hereafter referred to filter bed zone), and the inlet for wash liquid opens into the zone of filtered liquid phase. Part of filtered liquid is supp¬ lied to the washer as wash liquid. In another respects, the function of this filter is much like the filter disclosed in said German patent.

So far available upflow continuous filters with moving bed have, among others, the following problems:

(1) A filter dosclosed in U.S. Patent No. 2,057,887 has several serious disadvantages. First, the liquid to be filtered is in¬ troduced under a hollow sand distributor cone into the flow of sand that moves downwards along the upper surface of the sand filtered is not always uniform around the base of the sand di¬ stributor cone. Accordingly, there is a risk of nonuniform sand movement, caused by nonuniform feed of the liquid to be filtered, and fluidization of sand. Second, the circular outlet channel for filtered liquid is placed in the filter bed, which involves that the outlet channel must be fitted with screen in order to prevent the sand from flowing out. This results in clogging and a high pressure drop.

Many other continuous filters with moving beds have been put on the market, but they have been too complicated or have had other disadvantages so that they have not come into wide use.

The foregoing discussions may be summarized as follows:

1) Since the liquid to be filtered is introduced into the filter bed under a hollow cone which also has the function of distri¬ buting sand, the sand movement becomes non-uniform, and the mo¬ ving sand becomes fluidized.

2) The outlet channel is clogged, resulting in a high pressure drop .

(2) A filter disclosed in German Patent No. 2,262,599 has the following problems:

1) The feeder of the liquid to be filtered placed in the sand of the filter bed disturbs uniform sand movement.

2) The filter tank is high because the washer is placed above the filter tank.

(3) A filter disclosed in Swedish Patent Application No. 760299-0 (corresponding Japanese examined Patent publication No. 51808/81) has the following problems:

In this filter, the washer is placed in the deep liquid phase zone above the filter bed, so that the filter has a large height and a large water volume. In order to inspect the function of the filter and to conduct maintenance work, for example, repair or replacement of the sand lift pipe, there must be above the filter tank a clearance enough to allow one to stand and work

2 there. Accordingly, a filter with a filter area of 5 m , for example, requires a height clearance of approximatel 8 from the floor to the ceiling, and weighs approximately 32 tons. Thus, it is impossible to install the filter in existing rooms, and the construction cost for new buildings is high.

In this filter, since a sand lift pipe (with air injection hole) is placed in the filter bed, it is impossible to inspect the sand lift pipe without taking it up after emptying the filter bed of the sand. If the sand lift pipe is worn out, it is likewise im¬ possible to change it without emptying the filter bed of the sand. This causes long shutdown and expensive repair costs. Furthermore inthis filter, the position of the washer makes it impossible to wash the sand in more than one stage, and also makes it diffi¬ cult to wash the dirty sand with detergent, solvent or hot water, when necessary. This limits the use of the filter to those in¬ stances where the liquid to be filtered is good in the sense that the dirt on the sand after filteration comes off easily.

Another problem with this filter is that the movement of the sand in the filter bed is not uniform, with the result that the sand movement may stop. If this happens, the stationary sand is clog¬ ged by the dirt and does not move any more. As a result, the other part of the filter bed becomes overloaded and the filtration deteriorates, and also the short-cir uits developed in the filter bed may finally cause total breakdown of the filtering function of the filter bed. The non-uniformness in the sand movement is caused, by, amongst other things, the construction of the feeder components for the liquid to be filtered which comprises of a large circular inlet hood and a number of inlet pipes, placed in the sand in the filter bed. Further, the angle^* between the ver¬ tical wall of the cylinder section in the upper part of the fil- ter tank and the wall of the hopper section in the lower part is approximately 150 degrees. Thus, the sand flow, which is vertical in the cylinder section, is changed in its direction at the hopper section and therefore it slows down. The sand lift pipe sucks the sand through its lower end, which is placed somewhat above the bottom of the hopper section, and there is no device that makes the inflow of sand uniform at the suction end of the sand lift pipe. Therefore, a very small defect in manufacture, for example, a sand lift pipe being positioned with a slight incline or slightly eccentric to the filter tank, may cause non-uniformnesses in the sand collection from the fil¬ ter bed .

The hollow sand distributor cone in the lower part of the filter bed may also give rise to considerable problems that may cause shutdown for reparation. Fat, fibrers, etc. may collect under the sand distributor cone and form lumps together with sand, preventing the sand flow partly or completely. If the sand dis¬ tributor cone is filled with air or gas, it may cause trouble when thr integral construction of sand distributor cone, sand lift pipe and washer is lifted up.

The foregoing discussions may be summarized as follows:

1) The filter tank is high because a washer is placed around the sand lift pipe placed in the center of the filter bed and is immersed in the deep liquid phase zone above the filter bed zone .

2) For the same reason, the investment cost is high and the in¬ spection and maintenance are difficult.

3) Since the washer is immersed into the liquid phase zone and its inlet opens into the zone of liquid phase, it is impossible to wash dirty sand with anything other than the filtered liquid in the liquid phase zone and detergent, solvent or hot water, for example, cannot be used. Accordingly, the use of this filter is 1imited .

4) The sand can not be washed in more than one stage. Therefore, it is impossible to apply two-stage washing if the liquid to be filtered is bad and makes the sand very dirty. Accordingly, the use of this filter is limited.

5) The feeder components for the liquid to be filtered (a large circular hood and a number of inlet pipes) placed almost in the middle of the aand in the filter bed disturb uniform sand move¬ ment .

6) The lower end of the sand lift pipe is placed somewhat above the bottom of the hopper section, and at its suction opening is no means through which the sand inflow is made uniform. There¬ fore, if the sand is not sucked uniformly at the bottom of the hopper section, the sand collection from the filter bed becomes non-unifor .

7) Fat, fibers, etc. may collect under the hollow sand distri¬ butor cone and form lumps together with sand, which may disturb uniform sand movement.

It is an object of the present invention to provide a filter that requires a low investment cost and allows for ease of main¬ tenance and inspection by placing the sand lift pipe and the washer outside the filter tank and reducing the height of the filter tank. It is another object of the present invention to provide a filter for liquid with a high filtration efficiency, without feeding devices for the liquid to be filtered which have such structures that they make the movement of the granular filter medium non-uniform in the filter, but to ensure uniform movement of the granular filter medium.

4. Disclosure of the Invention

In order to achieve the above objects, the following various improvements have been made, which constitute the present inven¬ tion .

First, the height of the filter tank is reduced substantially by placing the washer outside the filter tank and in such a manner that the top of the washer is almost on a level with the top of the filter bed in filter tank. For this purpose, the granular filter medium is transported from the sand collecting box con¬ nected to the bottom of the hopper section of the filter tank to the washer outside the filter tank through a first sand lift pipe likewise placed outside the filter tank. The granular filter medium, washed by the washer, is then transported from the lower part of the washer to the top of the filter bed through a second sand lift pipe. In other words, the granular filter medium is transported in two stages.

Second, in those instances where the liquid to be filtered is bad in the sense so that the granular filter medium becomes very dirty through the filteration of said liquid, two washers, that is, a mechanical prewasher followed by the washer, are provided. The granular filter medium is washed adequately by pre-washing with the mechanical pre-washer and thereafter washing with the washer. Whereupon it is returned to the top of the filter bed. The construction in which the washer is placed outside the filter tank makes the design of a washer very flexible. If the liquid tobe filtered is bad in the sense so that the granular filter medium becomes very dirty through the filteration of said liquid, it is possible to carry out pre-washing with a mechanical pre¬ washer that has a high washing capacity.

Third, the washer and the sand lift pipes are placed outside the filter tank for ease of maintenance and inspection thereof. There is no need for an operator to go up the filter tank to in¬ spect the filter. Accordingly, the height clearance between the top of the filter tank and the ceiling of the building construc¬ tion may be small. It is also possible to inspect or repair the sand lift pipe ithout emptying the filter bed of the granular filter medium. Fourth, no feeder components for the liquid to be filtered are placed inside the filter bed so as to ensure uniform movement of granular filter medium. To achieve this, the liquid to be filtered is introduced into the filter bed via a circular inlet channel placed around the inside wall of the filter tank. The circular inlet channel is formed by placing a funnel-shaped channel wall at an inclination angle of 160 to 170 degrees with the vertical wall of the filter tank. As described above, the large inclination angle minimizes the change in the flow direc¬ tion of tho granular filter medium, and thereby also the slowing- down of the movement of the granular filter medium.

Fifth, in case of filter tanks with an especially large diameter, that is, with an especially large filter area, the liquid to be filtered is introduced Into the filter bed not only through the circular inlet channel but also through a central inlet channel, in order to allow the liquid to be filtered to be supplied uni¬ formly to the filter bed. The central inlet channel is formed as a space between the sand distributor cone and an inlet hood placed in parallel with and somewhat above the sand distributor cone at a required distance. The liquid to be filtered is supp¬ lied to the central inlet channel through a central inlet pipe.

Sijcth, a sand distributor cone is placed in the lower part of the filter bed. The distributor cone has a biconical shape with its underside closed with a reversed cone. A passage for the granular filter medium is formed between the lower cone of the distributor cone and the hopper section. Since the passage has a decreasing horizontal section in the direction of the movement of the granular filter medium, the granular filter medium is accelerated here. The rapid movement of the granular filter me¬ dium ensures uniform movement of the granular filter medium.

Seventh, a ring is mounted at the bottom of the hopper section Under this ring is placed a sand collecting box, from which the granular filter media ia transported to the washer through the first sand lift pipe. The ring is placed in the center of the hopper section .

The present invention provides an apparatus for continuous filt¬ ration of liquid, wherein the liquid to be filtered is introduced into a lower part of filter bed in a filter tank and flows up¬ wards, while the granular filter medium forming said filter bed moves downwards during the filtration, the used granular filter medium is transported from the bottom of said filter bed to the top of a washer and washed ith a part of filtered liquid which moves upwards in said washer, and the washed granular filter me¬ dium is returned to the top of said filter bed from said washer, characterized that, said washer is placed outside the filter tank in parallel and almost level with the filter tank; said used granular filter medium is transported by the exposed transport, means outside the filter tank; and said washed granular filter medium is returned by the another exposed transport, means out¬ side the filter tank.

In this apparatus, said washer includes a washer tank, a cylindri¬ cal separator receiving the down-stream end of the first sand lift pipe and placed above said washer tank, a guide cylinder placed in said washer tank and under said cylindrical separator sur¬ rounding a column with ridges on the inner and outer wall respec¬ tively which gives a labyrinthine passage between said guide cy¬ linder and said column, an outlet opening for washed granular filter medium provided at the lower inside of said washer tank connecting with the top of the filter tank through the second sand lift pipe, an intake opening for a part of filtered liquid provided on the upper part of the side of said washer tan , and a reject water overflow weir provided on said washer tank in such a manner that the water surface level of the overflow weir is below that of the part of filtered liquid which is fluidly connected through said intake opening.

Another feature provided by the present invention is an apparatus for continuosly filtrating liquid, wherein the liquid to be fil¬ tered is introduced into a lower part of filter bed in a filter tank and flows upwards, while the granular filter medium forming the filter bed moves downwards during the filtration, the used granular filter medium is successively taken out of the bottom of said filter bed and transported to the top of a counter- current washer by a sand lift pipe and washed with a part of filtered liquid which is supplied into the lower part of said counter-current washer and moves upwards therein, while the used granular filter medium moves downwards, and the washed granular filter medium is returned to the top of said filter bed, charac¬ terized in that, said filter tank includes a funnel-shaped channel wall hich is provided around the inner wall of the lower part of the filter tank, a lower inlet pipe, through which said liquid to be filtered is introduced, opens into the space defined by the inner wall of the filter tank and outer wall of said fun¬ nel-shaped channel wall, and a distributor cone having a biconical shape which is placed between the center of said funnel-shaped channel walland the lower inside of the filter tank so as to allow a specified space therebetween: said counter-current washer is placed outside the filter tank; said sand lift pipe is the first sand lift pipe connecting between the bottom of the filter tank on the outside and the top of a washer tank of the counter- current washer; and said washed granular filter medium is re¬ turned b the second sand lift pipe connecting between the lower inside of the washer tank and a separator placed above the filter tank, wherein each of said first and second sand lift pipes is provided ith an injection hole for pressurized air or water at near the upstream end.

Yet another apparatus provided by the present invention is an apparatus for continuously filtrating liquid, wherein the liquid to be filtered is introduced into a lower part of filter bed in a filter tank and flows upwards, while the granular filter medium forming the filter bed moves downwards during the filtration, the used granular filter medium is successively taken out of the bottom of said filter bed and transported to the top of a counter- current washer by a sand lift pipe and washed with a part of filtered liquid which is supplied into the lower part of said counter-current washer and moves upwards therein, while the used granular filter medium moves downwards, and the washed granular filter medium is returned to the top of said filter bed, characte¬ rized in that, said filter tank includes a funnel-shaped channel wall which is provided around the inner wall of the lower part of the filter tank, a lower inlet pipe, through which said liquid to be filtered is introduced, opens into the space defined by the inner wall of the filter tank and the outer wall of said funnel- shaped channel wall, a distributor cone having a biconical shape which is placed between the center of said funnel-shaped channel wall and the lo r inside of the filter tank so as to allo a specified space therebetween, an upper inlet pipe, through which said liquid to be filtrered is introduced, is connected to the upper part of the filter tank, a central inlet pipe connected to said upper inlet pipe is placed above said distributor cone, and the lower end of said central inlet pipe is connected to a conical inlet hood placed above and in parallel with said distributor cone; said counter-current washer is placed outside the filter tank; said sand lift pipe is the first sand lift pipe connecting between the bottom of the filter tank on the outside and the top of a washer tan of the counter-current washer; and said washed granular filter medium is returned by the second sand lift pipe connecting between the lower inside of the washer tank and a sepa¬ rator placed above the filter tank, wherein each of said first and second sand lift pipes is provided with an injection hole for pressurized air or water at near the upstream end.

In these apparatus of the present invention the angle Qe ormed by the inner wall of the filter tank and the inner wall of the funnel-shaped channel wall is 160 to 170 degrees, the passage is formed between the side wall of the lower cone of the distributor cone and the inner wall of a hopper section in the lower part of the filter tan , the replaceable ring is mounted in the center of and at the bottom of a hopper section in the lower part of the filter tank, and the upper end of the periphery of said ring is projected from the inner surface of the bottom plate of the hoppe section at their joint, and the mechanical pre-washer is connected before the counter-current washer. The present invention is an apparatus for filtration of liquid constructed, as described above, and in the granular filter medium in the filter bed there are no such feeder components for the liquid to be filtered that may disturb uniform movement of the granular filter medium, so ensuring uniform downward movement of the granular filter medium through the filter bed. When the granular filter medium descends and reaches the hopper section of the filter tank, granular filter medium is accelerated in and passes through the passage formed between the lower cone of the distributor cone and the bottom plate of the hopper sec¬ tion of the filter tank, and gathers uniformly from the entire hopper section to the center of and at the bottom of the hopper section .

Then the used granular filter medium enters the sand collecting box under the hopper section through the ring mounted on the bottom of the hopper section, from which it is transported to the top of the washer through the first sand lift pipe. The used gra¬ nular filter medium is washed in the washer in counter-current to the wash liquid comprises of the filtered liquid. The washed granular filter medium falls to the bottom of the washer tank of the washer, whereupon it is returned to the top of the filter bed through the second sand lift pipe. The wash liquid introduced into the lower space of the washer tank of the washer from the pit for filtered liquid flows upwards against the downward move¬ ment of the used granular filter medium and flows out over the overflow weir. If necessary, detergent, etc. may be added to the wash liquid which is supplied to the washer from the pit for filtered liquid or through the slit for intake of filtered liquid If necessary, in order to wash the dirty granular filter medium effectively, the supply of the wash liquid from the pit for fil¬ tered liquid or through the slit for intake of filtered liquid to the washer may be stopped with a valve or a gate, and deter¬ gent, solvent, or hot water may be supplied to the washer with a separate pump or by another means.

In the meantime, the liquid to be filtered is introduced into the lower part of the filter bed in the filter tank through the circular inlet channel, the liquid flows upwards against the downward movement of the granular filter medium during the fil¬ tration thereof, and the filtered liquid flows into the pit for filtered liquid over the overflow weir provided above the filter bed and flows out of the filter tank through discharge pipe.

As described above, in the present invention, the washed granular filter medium washed with the washer is transported through the second sand lift pipe, after the second stage, and returned to the top of the filter bed. Therefore, the top of the washer and the top of the filter bed may be on a level, thus making it pos¬ sible to reduce the height of the filter tank substantially.

In those instance here the liquid to be filtered is bad in the sense that the granular filter medium becomes very dirty after the filtration, the dirty sand is first transported to the me¬ chanical pre-washer through the first sand lift pipe and washed therein effectively. The mechanical pre-washer is supplied with wash liquid, detergent, solvent, or hot water, transported with a separate pump or by other means. The granular filter medium washed with the mechanical pre-washer is fed to the succeeding washer and ashed there again, whereupon the washed granular filter medium is transported through the second sand lift pipe and returned to the top of the filter bed.

5. Advantageous Effects of the Invention

Since, in an apparatus for filtration of liquid of the present invention, the granular filter medium to be washed is taken out of the filter tank, that is, out of the filter bed zone and the zone of filtered liquid phase, and is caused to move in counter- current to the filtered liquid, the filtering process is not restricted by the washing process and therefore the washing pro-, cess may be designed and modified independently. Further, since the liquid to be filtered is introduced into the filter bed either on its peripheral part or on its pheripheral and inner parts, the liquid to be filteted is distributed and moves upwards through the filter bed almost uniformly, providing a high filte¬ ring efficiency.

Since, in an apparatus for filtration of liquid of the present invention, the dirty granular filter medium which has been used for filtration is washed with a washer placed outside the filter tank, it may be combined with another washer suited for the dirt of the liquid to be filtered. For the same reason, detergent, solvent, or hot water may be used to wash the dirty granular fil¬ ter medium. Since the washed granular filter medium is transpor¬ ted and returned to the top of the filter bed as a separate stage itis possible to reduce the height of the filter tank substanti¬ ally. Further, the feeder components for the liquid to be fil¬ tered do not disturb uniform movement of the granular filter medium, providing a high filtering efficiency.

Since, in an apparatus for filtration of liquid of the present invention, the washer is placed outside the filter tank, it is possible to reduce the height of the filter tank substantially.

For example, if t o filter tanks with a horizontal section of

2

5 m and with the same filtering capacities are made as shown in Fig. , a filter tank according to the present invention weighs approximately 20 tons and is approximately 3.9 m high, while a conventional filter weighs approximately 32 tons and is approximately 5.9 m high. The difference in heigh of the two filters with attached equipment is approximately 3 m. Accor¬ dingly, it is considered to have significant practical effects to be able to provide a low filter. In the present invention, it is evident that the equipment height can be reduced substan¬ tially.

6. Brief Description of the Drawings

Fig. 1 is a view in vertical section illustrating an embodiment of an apparatus for filtration of liquid of the present invention Fig. 2 is a partial view in vertical section illustrating an embodiment of an apparatus for filtration of liquid equipped with a mechanical pre-washer. Fig. 3 is a detailed view in vertical section illustrating the bottom- of the hopper section in Fig. 1. Fig. 4 illustrates difference in heigh between an apparatus for filtration of liquid of the present invention and a conventional filter of the same type.

7. Description of the Preferred Embodiments

(Embodiment 1 )

Reffering to the drawings , pre erred embodiments of the present invention are described in the following.

Fig. 1 shows an embodiment of a filter to be used in application for filtering ordinary liquid. A filter tank 1, which may have a circular or polygonal horizontal section, is open upward. An overflow weir 3 is provided in the upper part of the filter tank 1. A lower inlet pipe 4 for the liquid to be filtered is connec ted to the lower part of the filter tank 1. In the lower part o the filter tank 1 there is provided a circular inlet channel 5 which is formed by a vertical wall 1A of the filter tank 1, a bottom plate 9Λ of a hopper section 9 thereunder, and a funnel- shaped channel wall 6. The circular inlet channel 5 may be fitt with a distributor plate 8 with holes (or slits) 7 so as to allo for more uniform inflow of the liquid to be filtered into the filter bed. It is preferred that the angle θi formed by the funnel-shaped channel wall 6 and the vertical wall 1A of the fil ter tank 1 is 160 to 170 degrees. The angle V kf ffoorrmr ed by the bottom plate 9A and the vertical wall 1A of the filter tank 1 is approximately 150 degrees. The bottom plate 9A in the upper par of the hopper section 9 is inclined by approximately 60 degrees out of level to ensure smooth movement of the granular filter medium (hereinafter referred to as sand). In order to reduce th heigh of the filter tank 1, the inclination angle of the bottom plate 9B in the lower part of the hopper section 9 out of the level may be somewhat less than that of the bottom plate 9A in the upper part. In other words, the inclination angle of the lower bottom plate 9B may be approximately 45 degrees from the level .

In the hopper section 9, a distributor cone 11 that has a bi¬ conical shape (upwars cone and downward invert cone) rests on supports 10. The nose angle ( of ) of the upper cone 11A of the distributor cone 11 may be 60 to 90 degrees, and the nose angle ( β ) of the lower cone 11B may be somewhat larger, than the nose angle ( '/ ) of the upper cone 11A. Since the nose angle ( Of ) of the upper cone 11Λ of the distributor cone 11 highly affects uniformness in the movement of the granular filter medi¬ um, it may be varied according to the size of the filter tank 1.

At the bottom of the hopper section 9, a replaceable ring 12 is mounted. If the upper end 12T of the ring 12 projects, as shown in Fig. 3, Slightly over the lower end 9C of the bottom plate 9B, a thin layer of sand 42 is formed around the ring 12. This layer of sand, which lies between the moving sand and the bottom plate 9B, protects bottom plate 9B from abrasion.

At the bottom of the hopper section 9, a sand collecting box 13 is mounted, and in its side a drain pipe 14 in which valve 15 is mounted, which is used to drain the water in the filter tank 1. Further, a screen 16 is placed in order to prevent the sand fol¬ lowing with the water.

The upstream end of the first sand lift pipe 18 is connected to the sand collecting box 13 as shown in Fig. 1. The sand lift pipe 18 has near the upstream end an injection hole 19 for pressu¬ rized air or water to transport the sand with pressurized air or water. The downstream end of the first sand lift pipe 18 is connected to a separator 20 above a washer tank 22 of a washer 21 In the washer 21 of the embodiment shown in Fig. 1, a column 24 with ridges 24A on the outer wall is inserted in a guide cylinder 23 with ridges 23A on the inner wall in such a manner that a labyrinthine passage 21A is formed between the guide cylinder 23 and the column 24. Dirty sand and wash water flow through the passage 21Λ in counter-current, that is, downward and upward respectively. In the upper part of the washer tank 22, a reject water overflow weir 25 for adjusting the overflow level of reject water is placed in order to determine the water head of the ash water. A pit 40 for filtered liquid is placed outside the overflow weir 3 provided in the upper part of the filter tank 1 and connected to the washer tank 22 with a wash water pipe 41 (or a communicating hole, if the pit 40 is conti¬ guous to the washer tank 22) . So the part of filtered liquid flowing out of the filter tank 1 is introduced, through the pit

40 for filtered liquid, into the lower space of the washer tank 22 of the washer 21. Λ position 41A, in Fig. 1, shows the up¬ stream end of the wash water pipe 41 on the side of the pit 40 for filtered liquid. If the sand in the filter bed flows over the overflow weir 3, it may settle and collect in the pit 40. Or, if the washer tank 22 is placed directly on the vertical wall 1Λ of the filter tank 1 and the vertical wall 1A of the filter tank 1 above the filter bed is provided with a slit (or a hole) 27 for intake of filtered liquid that feeds the part of filtered liquid from the filter tank 1 to the washer tank 22, then the part of filtered liquid is introduced through the slit 27 into the asher tank 22 and flows to the underside thereof. In the case where the slit 27 is provided, the wash water pipe

41 may be omitted, and also the pit for filtered liquid. The bottom of the washer tank 22 slants down to one side, and the upstream end of a second sand lift pipe opens at some distance from the bottom 30. The second sand lift pipe 28 has an injec¬ tion hole 29 for pressurized air or water near its upstream end to transport the sand with pressurized air or water. The down¬ stream end of the second sand lift pipe 28 is connected to a separator 31 placed in the center of and above the filter bed. A central inlet channel 46 provided in the center of the filter tank 1 is formed between the upper cone 11A of the distributor cone 11 and a conical inlet hood 17 placed in parallel with and above the upper cone 11Λ at a required distance. The liquid to be filtered is introduced through an upper inlet pipe 44 and a central inlet pipe 45 into the central inlet channel 46. A regulator 34 has a function of regulating the sand distribution so as to prevent the sand that falls by free fall from the sepa¬ rator 31 and returns to the top of the filter bed from being disturbed by the upper inlet pipe 44 and central inlet pipe 45.

A filter of the present invention functions in the following way: The initial position is that the filter tank 1 and the washer tank 22 are filled with liquid up to the reject water, over flow weir 25, and the filter tank 1 is filled with sand so that the top of sand, forming into a hill, is slightly below the separator 31. The movement of sand is initiated by supplying pressurized air or water to the injection hole 19 for pressurized air or water of the first sand lift pipe 18 and to the injection hole 29 for pressurized air or water of the second sand lift pipe 28. First, as the first stage, the dirty sand enters the sand collec¬ ting box 13 from the bottom of the hopper section 9 through the ring 12, and is transported to the separator 20 above the washer 21 with the first sand lift pipe 18 as shown by the arrow 47. The sand separated from air or water by this sepatator 20 falls down to the top of the column 24 of the washer 21. Then, the sand passes through the labyrinthine passage 21A formed between the guide cylinder 23 and the column 24 and falls down to the bottom 30 of the washer tank 22 as shown by the arrow 48. Then, as the second stage, the sand is transported to the separator 31 with the second sand lift pipe 28 as shown by the arrows 49 and 50, falls down by free fall as shown by the arrow 51 and returns to the top of the filter bed. The sand returned to the top of the filter bed moves downwards as shown by the arrow 35. When it reaches the hopper section 9 it moves through the passage formed between the lower cone 11B of the distributor cone 11 and the bottom plate 9B of the hopper section 9 as shown by the arrow 32, and then it gathers uniformly from the entire hopper section in the sand collecting box 13 through the ring 12 moun¬ ted inthe center of and at the bottom of the hopper section. In the meantime, the liquid to be filtered is supplied to the lower inlet pipe 4 as shown by the arrow 54, passes through the circlar inlet channel 5 as shown by the arrow 55, and is introd¬ uced into the filter bed (FB) . During the above process, the top of the sand has almost a conical shape as shown by the dotted line 52. In case of a large filter with a large filter area, the liquid to be filtered may be introduced into the filter bed not only through the circular inlet channel 5 but also through the central inlet channel 46 as described previously. The in¬ troduced liquid to be filtered spreads out in the filter bed uniformly, and flows upwards as shown by the arrows 56 and 57. The suspended solids in the liquid to be filtered are collected by the sand, and the filtered liquid comes out of the filter bed. Then, the filtered liquid enters the pit 40 for filtered liquid over the overflow weir 3 as shown by the arrow 58, and flows out of the tank though a discharge pipe 2 as shown by arrow 59. The pit 40 for filtered liquid is connected to the washer tank 22 of the washer 21 with a wash water pipe 41 (or communicating hole) . Therefore, part of the filtered liquid taken out of the filter tank 1 enters the washer tank 22 as wash water through the pit 40 for filtered liquid 40. The wash water flows upwards through the labyrinthine passage 21A in the washer 21, while the dirty sand moves downwards and is washed in counter-current. The reject water flows out over a reject water overflow weir 25 as shown by the arrow 60, and is taken out of the tank through the discharge pipe 26 as shown by the arrow 61. As regards the levels at different locations, it is adjusted so that the level L2 in the pit 40 for filtered liquid is higher than the level L3 at the reject water overflow weir 25, and the level LI at the overflow weir 3 of the filter tank 1 is higher than the level L2 in the pit 40. (Embodiment 2)

Fig. 2 shows an embodiment of an apparatus for filtration of liquid equipped with two washers, that is, a counter-current washer 21, as described above, and a mechanical pre-washer 35. As a mechanical pre-washer, a most common screw type washer is shown, but a washer consisting of a drum with helical blades on the inside mav be used instead. The mechanical pre-washer 35 is equipped ith a screw 36 that blends and at the same time transports the sand upwards as shown by the arrow 62. The mechanical pre-washer 35 is driven by a geared motor 37. The dirty sand is, as the first stage, transported from the bottom of the hopper section 9 via a sand collecting box 13 to the lower part of the mechanical pre-washer 35 through a first sand lift pipe 18 as shown by the arrow 47. Filtered liquid, deter¬ gent, or other wash liquid transported with a pump or by other means is supplied to the top of the mechanical pre-washer 35 through a feed pipe 38, and washes in counter-current the sand which is blended and at the same time transported upwards by a screw 36. The reject water from the mechanical pre-washer 35 flows over a weir 33 in the direction shows by the arrow 64, and is collected in a reject water pan 39, and is taken out from the tank through a drain pipe 26 in the direction shown by the arrow 61. The mechanical pre-washer to the counter-current washer 21. The sand pre-washed by the mechanical pre-washer 35 then enters the counter-current washer 21 through a chute 43 as shown by the arrow 42. The sand is washed here again and then falls down to the bottom 30 of a washer tank 22 as shown by the arrow 48, whereupon the v.ashed sand is transported to a separator 31, as the second stage, with a second sand lift pipe 28 and returned to the top of the filter bed as shown by the arrows 49 and 50. Supply of wash liquid from the pit 40 for filtered liquid to the washer tank 22 may be stopped by closing a valve 63 on wash water pipe 41. Supply of wash liquid from above the filter bed to the washer tank 22 may be stopped by closing a gate 65 on a slit 27. The bottomedge of slit 27 may be posi¬ tioned at the same level as overflow 3 or slightly lower. The result of this is that the wash liquid flow through tne washer will, with some delay, cease when the supply of liquid to the filter is stopped. Unnecessary loss of filtered liquid is prevented .

Claims

Claims of the Invention

1. An apparatus for continuous filtration of a liquid, wherein the liquid to be filtered is introduced into a lower part of the filter bed in a filter tank and flows upwards, while the granular filter medium forming said filter bed moves downwards durin the filtration, the used granular filter medium is tran¬ sported from the bottom of said filter bed to the top of a washer and washed with a part of filtered liquid which moves upwards in said washer, and the washed granular filter medium is returned to the top of said filter bed from said washer, characterized in that, said washer is placed outside the filter tank in parallel and almost the same level as the filter tank; said used granular filter medium is transported by the exposed transport means outside the filter bed; and said washed granu¬ lar filter medium is returned by another exposed transport means outside the filter bed.

2. An apparatus for filtration of liquid as claimed in claim 1 characterized in that, said washer includes a washer tank, a cylindrical separator receiving the downstream end of the first sand lift pipe and placed above said washer tank, a guide cylinder placed in said washer tank and under said cylindrical separator surrounding a column with ridges on the inner and outer wall respectively in such a manner that a labyrinthine passage is formed between said guide cylinder and said column, an outlet for washed granular filter medium provided at the lower inside of said washer tank connecting with the top of the filter tank through the second sand lift pipe, an intake opening for a part of fil¬ tered liquid provided on the upper part of the side of said washer tank, and a reject water overflow weir provided on said washer tank in such a manner that the water surface level of the over¬ flow weir is lower than that of the part of filtered liquid which is fluidly connected through said intake opening.

3. An apparatus for continuous filtration of a liquid, wherein the liquid to be filtered is introduced into a lower part of filter bed in a filter tank and flows upwards, while the granu¬ lar filter mediu forming the filter bed moves downwards during the filtration, the used granular filter medium is successively taken out of the bottom of said filter bed and transported to the top of a counter-current washer by a sand lift pipe and washed with a part of filtered liquid which is supplied into the lower part of said counter-current washer and moves upwards ther¬ ein, while the used granular filter medium moves downwards, and the washed granular filter medium is returned to the top of said filter bed, characteriz d in that; said filter tank includes a funnel-shaped channel wall which is provided around the inner wall of the lower part of the filter tank, a lower inlet pipe, through which said liquid to be filtered is introduced, opens into the space defined by the inner wall of the filter tank and the outer wall of said funnel-shaped channel wall, and a distri¬ butor cone which is placed between the center of said funnel- shaped channel wall and the lower inside of the filter tank so as to allow a specified space therebetween; said counter-current washer is placed outside the filter tank; said sand lift pipe is the first sand lift pipe connecting between the bottom of the filter tank on the outside and the top of a washer tnak of the counter-current washer; and said washed granular filter medium is returned by the second sand lift pipe connecting between the lower inside of the washer tank and a separator placed above the filter tank, wherein each of said first and second sand lift pipes is provided with an injection hole for pressurized air or water at near the upstream end.

4. An apparatus for continuous filtration of a liquid, wherein the liquid to be filtered is introduced into a lower part of filter bed in a filter tank and flows upwards, while the granu¬ lar filter medium forming the filter bed moves downwards during ^' the filtration, the used granular filter medium is successively taken out of the bottom of said filter bed and transported to the top of a counter-current washer by a sand lift pipe and washed with a part of filtered liquid is supplied in to the lower part of said counter-current washer and moves upwards therein, while the used granular filter medium moves downwards, and the washed granular filter medium is returned to the top of said filter bed, characterized in that; Sid filter tank includes a funnel- shaped channel wall which is provided around the inner wall of the lower part of the filter tank, a lower inlet pipe, through which said liquid to be filtered is introduced, opens into the space defined by the inner wall of the filter tank and the outer wall of said unnel-shaped channel wall, a distributor cone which is placed bet en the center of said funnel-shaped channel wall and the lower inside of the filter tank so as to allow a speci¬ fied space therebetween, an upper inlet pipe, through which said liquid to be filtered is introduced, is connected to the upper part of the filter tank, a central inlet pipe connected to said upper inlet pipe is placed above said destributor cone, and the lower end of said central inlet pipe is connected to a conical inlet hood placed above and in parallel with said distributor cone; said counter-current washer is placed outside the filter tank; said sand lift pipe is the first sand lift pipe connecting between the bottom of the filter tank on the outside and the top of a washer tank of the counter-current washer; and said washed granular filter medium is returned by the second sand lift pipe connecting between the lower inside of the washer tank and a separator placed above the filter tank, wherein each of said first and second sand lift pipes is provided with an injection hole for pressurized air or water at near the upstream end.

5. An apparatus for filtration of liquid as claimed in claim 3 or 4, wherein the angle Q formed by the inner wall of the filter tank and the inner wall of the funnel- shaped channel wall is 160 to 170 degrees.

6. An apparatus for filteration of liquid as claimed in claim

3 or 4, wherein a passage is formed between the side of the lower cone of the distributor cone and the inner wall of a hopper section in the lower part of the filter tank.

7. An apparatus for filtration of liquid as claimed in claim 3 or 4, wherein a replaceable ring is mounted in the center of and at the bottom af a hopper section in the lower part of the filter tank, and the upper end of the periphery of said ring is projected from the inner surface of the bottom plate of the hopper section at their joint.

8. An apparatus for filtration of liquid as claimed in claim 3 or 4, wherein a mechanical pre-washer is connected before the counter-current washer.