FILTRATION PROCESS AND APPARATUS

Abstract: It is known to filter a suspension or emulsion in a filter bed of particulate filter medium (1) by allowing the suspension to flow upwards through the filter bed simultaneously as the medium (1) flows downwards through a filtering tank (2) wherein filtration takes place. Filtration thus takes place during counterflow between suspension and filter medium. The supply of suspension takes place in the lower part (4) of the filter bed and the filtered liquid phase is taken away from a zone (8) above the filter bed. The polluted filter medium close to the bottom of the filter tank is taken out for conveyance to a washing apparatus (13) above the filter bed and after washing is returned to the upper side of the filter bed. For providing a filter which has a considerably lower construction height than previously for a given and unchanged volume of the filter medium, the washing apparatus (13) is now lowered so that its lower part is at a level below the upper surface of the filter bed.

Description: FILTRATION PROCESS AND APPARATUS. The present invention relates to a method of filtering a suspension or emulsion, and also relates to a filtering apparatus for carrying out the method in accordance with the preamble to the following claims. It may be read from the Swedish patent specification 396 552 that filtering a suspension or emulsion in a filter bed comprising particulate filter material may be carried out by allowing the suspension to flow upwards through the filter bed, simultaneously as the filter medium flows downwards through a filtering tank in which the filtration takes place. Filtering thus takes place during counter flow between suspension and filter medium. The suspension is supplied at a lower part of the filter bed and the filtered liquid phase is taken away from a zone above the filter bed. The polluted filter medium close to the bottom of the filter tank is taken out and conveyed to a washing apparatus above the filter bed, and after washing it is returned to the upper side of the filter bed. By continuous supply of suspension to the filter bed, continuous extraction of filtered liquid phase as well as continuous conveyance of polluted filter medium to the washing apparatus and washed filter medium back to the filter bed results in that the filtering apparatus operates completely continuously, and does not normally need to be taken out of operation. Such filtering apparatus may reach considerable dimensions in order to receive large suspension flows. In large installations there may be a plurality of filtering units, which are placed side by side and work in parallel, this being more practical or more suited to the available space. A method of arranging a large installation of this kind is illustrated in figure 3 of the previously mentioned patent specification 396 552. A normal circular shape of the filtering units has been departed from here, and a hexagonal shape has been adopted to achieve compaction of the units. Since conveyance of the filter medium to the washing apparatus takes place through the filter bed, and the washing apparatus is also within the outer shell of the unit, there is nothing to prevent such compaction of such filtering units. A number of factors affect the selection of the filter apparatus size, such as type of suspension or emulsion, desired purification degree, type of filter medium and, as previously mentioned, the magnitude of the suspension flow that is to be filtered. These factors determine the area and height of the filter bed body or bodies. The filtering apparatus is then designed from these dimensions, e.g. as is illustrated in fig. 1 of the mentioned patent specification 396 552. Although this figure is only a principle sketch, the proportions of the figure do not differ from reality to any notable degree. Accordingly, the observation may be made that a considerable portion of the height of the filtering apparatus has been used to make room for the polluted filter medium washing apparatus. In the case where the available height is limited in the space where the filter units are to be placed, the height of these tanks will cause some limitations in the design. The present invention has come about to provide a filter, which has a considerably lower construction height for a given and unchanged volume of the filter medium. In accordance with the invention this has been arranged by sinking the lower part of the washing apparatus to a level under the upper surface of the filter bed, but with retention of a characteristic method of carrying out washing. This method of washing involves the provision of an upward current of washing liquid, constituting the ready-filtered liquid phase, in a washing path where the polluted filter medium is caused to fall downwards against the washing liquid flow. Since the washed filter medium comes in at a level which is to low in relation to the filter bed, due to sinking the level of the washing apparatus, extra conveying equipment for the filter medium up to the upper side of the filter bed will be required. The invention is characterised in the accompanying claims, and in the following it will be described in the form of a preferred embodiment and with reference to the accompanying drawing figure. The latter illustrates a filtering apparatus in vertical section. In the illustrated embodiment, the particulate filter medium 1 is enclosed in a container with walls 2 and a bottom 3 having a conical or pyramidical shape with the apex downwards. The base of the cone or pyramid should suitably conform to the shape of the container as defined by the walls 2. Sand is well suited as particulate filter medium, although other materials, such as plastics may be used, or mixtures of several materials. After trials, one skilled in the art will find the most suitable material and particle size in each individual case, depending on what is to be filtered and how effectivly filtration shall take place. The suspension or emulsion which is to be filtered is taken, as illustrated by the arrow A into the container via the inlet 4, e.g. through the bottom of the container. The inflow of the suspension in the filter bed takes place at the lower part of the bed via a plurality of pipes 5 with pipe openings 6. Above each of the pipe openings there is a shield 7 for preventing direct contact of the filter medium with the pipe openings and for exposing a larger surface of the filter medium to the incoming suspension. Alternatively, the suspension can be taken in from above through unillustrated pipes and under the shields 7. The risk of clogging the filter due to heavy instantaneous pollution of the filter medium adjacent the pipe openings is thus reduced. By the shields having a V-shape, and by placing the pipe openings under shields, there is achieved the least possible obstruction to the downward passage of the filter medium. Placing the inlet pipe openings 6 in the lower part of the filter bed results in the advantage that the most polluted part of the filter material, i.e. that which goes past the shields and the pipe openings, continues downwards and is not utilized further for filtration. Blockage at the inlets is thus prevented, and new filter medium is continuously exposed to the incoming suspension. The latter flows upwards in a direction counter to that of the filter medium through a zone of the filter bed towards an increasingly cleaner medium. The filtered liquid phase, obtained as a result of the upward flow of the suspension through the filter bed zone, is maintained as a zone 8 of filtered liquid phase above the filter bed, and in the illustrated embodiment example, its level is determined by the filtered liquid phase being taken out from the filtering apparatus via an overflow 9 to an outlet (arrow B) . The opening of some suitable elevating means 10 is situated in the conically or pyramidically shaped portion 3 of the container down which flows the filter medium polluted during filtration. As will be seen from the illustrated embodiment example, the elevating means extends centrally through the apparatus and can be such as a so-called mammoth pump. This type of pump uses air as conveying medium, and the air is supplied from above and down a conduit 11 extending along a conveyer pipe 12 included in the elevating means. Air is supplied through the conveyer pipe via unillustrated holes at the lower end of the conduit. The filter medium is conveyed (arrow C) by the air through the pipe 12 to a washing apparatus 13 situated in the filter bed. The filter medium to be washed comes out from the upper part of the conveyer pipe 12, changes direction (arrow D) , and runs downwards in a washing path formed between the elevating means 10 and an outer shell 14 of the washing apparatus. The outer shell 14 is suitably concentrically formed around the elevating means 10. Due to its being polluted, the filter medium may contain cohesive aggregats. These are broken down when they meet obstacles 15 in the washing path. The obstacles 15 are formed such that they force the filter medium to change direction somewhat, at the same time as its fall rate changes. All the time it is in the washing path the filter medium meets a washing medium moving in a counter direction. The filtered liquid phase in the zone 8 above the filter bed is used as washing liquid. This zone 8 is in communication with the lower part of the washing path via a space 16 between the washing apparatus and an outer casing 17 forming a shield against the bed. The washing liquid is thus taken in at the lower part of the- washing path, as illustrated by the arrow E in the embodiment example. The washing liquid, or reject, polluted by washing, is taken from the washing path, as illustrated by the arrow F and is taken out via an overflow 18 and discharged from the apparatus, e.g. as illustrated by the arrow G. This overflow 18 should be adjustable in height and possibly in its width as well, to enable regulation of the washing liquid amount through the washing path. If the overflow is lowered, the washing liquid amount increases. This amount can also be affected by the clear solution level in the zone 8 being regulated by the overflow 9. It is the difference in level between the clear solution level in the zone 8 and the washing water level in the zone 8a above the washing apparatus that determines the washing liquid amount. The filter medium, that has been washed during its passage along the washing path, is taken down to a lowest point with the aid of an oblique bottom 19 under the washing apparatus. Immediately above this lowest point there is the opening of a further conveying means 20 for the filter medium. In the embodiment example illustrated here, this also comprises a mammoth pump, e.g. with air as the conveying medium. The pipe of the conveying means 20 extends up to a level at a height above the upper side of the filter bed such that, with the aid of a distribution plate 21 provided with a roof it is possible to distribute the filter medium over the upper side of the filter bed. Within the framework of given premises, i.e. the method and apparatus for carrying out filter medium washing, there has been achieved with the aid of the present invention a variant of the filtering unit, which has a considerably reduced construction height. In the described, and perhaps the most advantageous embodiment, the washing apparatus is still within the same configuration of the filtering unit since it has been sunk into the space for the filter medium itself. The filtering unit is consequently given the least possible space, not only in height but also laterally. The possibility still remains of compactly placing a plurality of filtering units side by side.

Claims: C L A I M S 1. Method in filtering apparatus for filtering a suspension or emulsion, which is supplied to a zone of particulate filter medium forming a filter bed, said suspension or emulsion flowing upwards through the filter bed during filtration and departing from the bed as filtered liquid phase, the filter medium flowing during filtration in a direction downwards through the filter bed zone in counter flow to the suspension past its point of entry for subsequent conveyance separate from the filter bed to a washing path for washing the filter medium polluted by filtration, washing taking place during counter flow with respect to a washing liquid along the washing path, after which the washed filter medium is returned to the filter bed zone at its upper side, c h a r a c t e r i z e d in that polluted filter medium is taken from a low point in the filter bed via a substantially vertical washing path and leaves this at a level below that of the filter bed surface, at which level the washing liquid is supplied, the latter thus flowing in at the lower end of the washing path and departing in a polluted state at a level above the inlet to the path, the cleaned filter material being conveyed from a point below the outlet of the path up to a level above the filter bed surface, where a zone of filtered liquid phase is maintained. 2. Method as claimed in claim 1, c h a r a c t e r i z e d in that the filter medium is subjected to changes in flow rate during its passage along the washing path. 3. Method as claimed in claim 1, c h a r a c t e r i z e d in that a part of the filtered liquid above the filter bed is used as washing liquid. 4. Method as claimed in claim 1, c h a r a c t e r i z e d in that the polluted washing liquid is taken from the washing path at a level below the level of the filtered liquid. 5. Filtering apparatus for carrying out the method in accordance with any one of the preceding claims, and including: a zone of a particulate filter medium forming a filter bed (1) extending vertically in the filtering apparatus; an inlet (4) for the suspension or emulsion which is to be filtered, said inlet being situated in the lower part of the filter bed zone, the suspension flowing in a direction upwards through the filter bed during filtration; a space situated under the inlet (4) and in free communication with the filter bed zone, the filter medium continuously being supplied to this space by the medium flowing in a direction downwards through the filter bed zone; a conveying means (11,12) opening out into the space for elevating filtration-polluted filter medium which has been supplied to this space, and which the means (11,12) conveys to (also included) washing apparatus (13) separate from the filter bed in the filtering apparatus; said washing apparatus being arranged and formed for washing with counter-flow between the filter medium and a washing liquid, the washed filter medium being taken from it and returned to the upper side of the filter bed zone; and an outlet (18) for washing licpiid polluted by washing arranged at the upper part of the washing apparatus, c h a r a c t e r i z e d in that the washing apparatus includes a vertical cylinder (14) , the lower end of which is situated at a level lower than the upper surface of the filter bed, but at a given distance above the intake of the conveying means (11, 12) for the polluted filter medium, there being under the cylinder a reception space (19) for washed filter medium, the intake of a second conveying means (20) being situated in this space, the outlet of said means (20) being above the upper surface of the filter bed, the washing liquid having its inlet to the cylinder at the lower end thereof, and having its outlet (18) from the washing apparatus above the upper end of the cylinder. 6. Filtering apparatus as claimed in claim 5, c h a r a c t e ¬ r i z e d in that the outlet (18) of the washing liquid is lower than the level of the filtered phase (8) above the filter bed (1) . 7. Filtering apparatus as claimed in claim 6, c h a r a c t e ¬ r i z e d in that the height difference between said outlet (8) and said level is regulatable. 8. Filtering apparatus as claimed in any one of preceding claims, c h a r a c t e r i z e d in that the washing apparatus is situated inside the filter bed and is surrounded by a chamber (17) with an opening upwards towards the zone (8) of filtered liquid phase, the lower end of the cylinder (14) being in communication with the bottom portion of the chamber (17) , where said second conveying means (20) has its intake. 9. Filtering apparatus as claimed in claim (8), c h a r a c ¬ t e r i z e d in that above the cylinder (14) there is a collection chamber (8a) for the polluted washing liquid. AMEMDED CLAIMS [received by the International Bureau on 26 October 1992 (26.10.92); original claims 1 and 5 amended; remaining claims unchanged (3 pages)] 1. Method in filtering apparatus for filtering a suspension or emulsion, which is supplied to a zone of particulate filter medium forming a filter bed, said suspension or emulsion flowing upwards through the filter bed during filtration and departing from the bed as filtered liquid phase, the filter medium flowing during filtration in a direction downwards through the filter bed zone in counter flow to the suspension past its point of entry for subsequent conveyance separate from the filter bed to a washing path for washing the filter medium polluted by filtration, washing taking place during counter flow with respect to a washing liquid along the washing path, after which the washed filter medium is returned to the filter bed zone at its upper side, c h a r a c t e r i z e d in that polluted filter medium is taken from a low point in the filter bed via a substantially vertical washing path inside the filtering apparatus and leaves this at a level below that of the filter bed surface, at which level the washing liquid is supplied, the latter thus flowing in at the lower end of the washing path and departing in a polluted state at a level above the inlet to the path, the cleaned filter material being conveyed from a point below the outlet of the path up to a level above the filter bed surface, where a zone of filtered liquid phase is maintained. 2. Method as claimed in claim 1, c h a r a c t e r i z e d in that the filter medium is subjected to changes in flow rate during its passage along the washing path. 3. Method as claimed in claim 1, c h a r a c t e r i z e d in that a part of the filtered liquid above the filter bed is used as washing liquid. 4. Method as claimed in claim 1, c h a r a c t e r i z e d in that the polluted washing liquid is taken from the washing path at a level below the level of the filtered liquid. 5. Filtering apparatus for carrying out the method in accordance with any one of the preceding claims, and including: a zone of a particulate filter medium forming a filter bed (1) extending vertically in the filtering apparatus; an inlet (4) for the suspension or emulsion which is to be filtered, said inlet being situated in the lower part of the filter bed zone, the suspension flowing in a direction upwards through the filter bed during filtration; a space situated under the inlet (4) and in free communication with the filter bed zone, the filter medium continuously being supplied to this space by the medium flowing in a direction downwards through the filter bed zone; a conveying means (11,12) opening out into the space for elevating filtration-polluted filter medium which has been supplied to this space, and which the means (11,12) conveys to (also included) washing apparatus (13) separate from the filter bed in the filtering apparatus; said washing apparatus being arranged and formed for washing with counter-flow between the filter medium and a washing liquid, the washed filter medium being taken from it and returned to the upper side of the filter bed zone; and an outlet (18) for washing liquid polluted by washing arranged at the upper part of the washing apparatus, c h a r a c t e r i z e d in that the washing apparatus includes a vertical cylinder (14) inside the filtering apparatus, the lower end of which is situated at a level lower than the upper surface of the filter bed, but at a given distance above the intake of the conveying means (11, 12) for the polluted filter medium, there being under the cylinder a reception space (19) for washed filter medium, the intake of a second conveying means (20) being situated in this space, the outlet of said means (20) being above the upper surface of the filter bed, the washing liquid having its inlet to the cylinder at the lower end thereof, and having its outlet (18) from the washing apparatus above the upper end of the cylinder. 6. Filtering apparatus as claimed in claim 5, c h a r a c t e ¬ r i z e d in that the outlet (18) of the washing liquid is lower than the level of the filtered phase (8) above the filter bed (1) . 7. Filtering apparatus as claimed in claim 6, c h a r a c t e ¬ r i z e d in that the height difference between said outlet (8) and said level is regulatable. 8. Filtering apparatus as claimed in any one of preceding claims, c h a r a c t e r i z e d in that the washing apparatus is situated inside the filter bed and is surrounded by a chamber (17) with an opening upwards towards the zone (8) of filtered liquid phase, the lower end of the cylinder (14) being in communication with the bottom portion of the chamber (17) , where said second conveying means (20) has its intake. 9. Filtering apparatus as claimed in claim (8), c h a r a c ¬ t e r i z e d in that above the cylinder (14) there is a collection chamber (8a) for the polluted washing liquid. Statement under Article 19 References EP, Al 0 343 980 and WO, Al 9 108 818 have been considered by us. These two references teach that the entire washing apparatus and thus the washing path is placed outside the filtering apparatus. Claims 1 and 5 of our application are hereby amended so that it is stated that the "vertical washing path" and "the vertical cylinder 14" respectively are inside the filte¬ ring apparatus. These two features are mentioned in the description, page 4, last 15 lines and page 5, lines 1-3. The invention so stated makes it possible place the filtering apparatuses very close to each other. Contrary to what is described in the cited references, our invention diminishes the need of space not only upwards but also so that the occupied floor area will be less.

Inventors: HAAKANSSON SVEN, HJELMNER ULF, LARSSON HANS F, HAAKANSSON, SVEN, HJELMNER, ULF, LARSSON, HANS, F.
Applicants: NORDIC WATER PROD AB, NORDIC WATER PRODUCTS AB
Application year: 1992
Main classification: B01D24
IPC codes: B01D24