Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/02—Loose filtering material, e.g. loose fibres

Definitions

• Apparatus for cleaning of liquids comprising a granulated filter material.
• the present application concerns an apparatus for the cleaning of liquids, comprising a filter bed for downstream filtration of the liquid, said filter bed comprising one or more granulated materials.
• the invention also describes the use of the filter material in an apparatus for the cleaning of liquid comprising a filter bed for downstream filtration of the liquid.
• filter beds When removing particles from liquids by means of deep bed filters, it is known that filter beds operates at its optimum when the efficiency of filtration, or the filter coefficient for the filter, increases in the direction of flow of the liquid, and this can be achieved by letting the filter grain size decrease in the direction of flow of the liquid through the filter bed.
• Up- stream filtration has certain disadvantages relating to its operation, and will not be described further.
• Downstream filterbeds are based on a combination of two- or several different filter materials with different grain size and density, such as anthrasite, silica sand and garnet sand. Normally, are one or several relatively thin support layers of coarse material situated underneath the main filter bed. The support layers are not a part of the filter bed and have no function except from keeping the filter bed in place, and to contribute to an even distribution of the backwash water, etc. and will not be further dealt with.
• two- or multimedia filters can be put together and comprise two- or several dissimilar materials (filter layers) where density and grain size are chosen to fulfil two essential criteria of function: firstly, that filter layers must be composed of materials with such a grain size and density that liquid on its way through the filter bed first encounters a filter layer with the largest filter grains, and thereafter layers with reduced filter grain size, and, secondly, that materials (the filter layers) must have dissimilar sinking rates in order to make the materials (layers) maintain their respective place in the filter bed even after many sequences with backwash, expansion and sedimentation of the filter grains.
• the selection of materials for various layers of the filter bed must take place along a line falling towards the right (multilayer), so that grain size and sinking rate differ from layer to layer.
• the optimal and ideal, continuously decreasing grain size from coarse to fine in the direction of flow of the liquid has previously been attempted achieved by using upstream filters or downstream filters with two- or several types of materials (filter media), where the ideal situation is approached by using filter beds comprising two- or several layers with various media.
• the latter filter types are called two- or multimedia filters respectively.
• coarse to fine grain distribution is approached from filter layer to filter layer in the direction of flow of the liquid by using filter materials or filter media of various types, grain size and density, and where each material forms a separate layer.
• the filter bed is designed with an upper of the largest grains with the lowest density, followed by the next layer with somewhat smaller grains and somewhat higher density, and so on. The sum of these layers forms the total depth of the filter bed.
• Typical examples of commonly used filters of this type for the treatment of drinking water, are two-media filter beds with the coarsely grained anthracite (1- 2 mm) with low density (1 ,4 kg/dm 3 ), over finely grained sand (0,5-1 ,0 mm) with higher density (2,7 kg/dm 3 ), or three-media filters where in addition, a layer of coarser and lighter plastic materials is above the anthrasite and the sand.
• a three-media filter may comprise a layer of finely grained garnet sand with high density, placed under the anthrasite and sand layers. Multimedia filter- beds comprising more than three different materials can also be found, but they are still put together according to the same principles.
• the designer of the filters is restricted to the given properties of the materials and must know the relative properties of the materials.
• the selection of the materials and the composition of the filter bed may not be optimal, and this may for instance affect the efficiency of the cleaning, the functionality and capasity of storage, and may necessitate frequent backwash with high consumption of backwash water.
• An unfavourable choice of materials in the filter bed may also result in the backwash having to be performed with larger amounts of liquids to fluidise the filter bed than what is ideally necessary.
• filter media have high density and weight, even as dry, and this can be a disadvantage in terms of freight and handling.
• today's filter materials are manufactured and delivered by several different manufacturers and suppliers, and it is therefore necessary for the designers of the filter plants (consultants, plant owners, etc.) to provide necessary data from several places concerning the various filter materials, in order to select the right material type and combination to design an optimal filter bed, to provide the various materials that are used in the right amount, etc. This poses a challenge to the consultants, the designers, the plant owners and users of this type of filters.
• the present invention therefore comprises, according to the independent claim, an apparatus for the cleaning of liquids, comprising a filter bed for downstream filtration of said liquid where the filter bed comprises one or several granulated materials. At least one of the granulated materials comprises grains with varying density and size.
• This material may be haydite or light clinker of expanded clay or plastic material with properties such as density and a grain size of the filter material can be adapted during production so that the density of the filter grains is reduced with increasing grain size.
• a filter bed can be designed with one single raw material with substantially continuous or stepwise (stratified) gradation or size from large to smaller grains in the direction of flow of the liquid.
• the invention is intended to encompass filter beds with the above material alone or in combination with other filter media such as sand or anthrasite.
• the filter material can be supplied from one single manufacturer, it can be adapted to various filtration purposes, and the filter designer or plant owner can design and compose of the filter bed.
• the filter bed can be delivered mixed prepacked as a unit from one supplier, with grain sizes, densities and quantity specially adapted for various types of use, such as cleaning of water, sewage water or other liquids.
• the filter medium can be backwashed and then sedimented in place in the filter bed by the filter operator.
• the backwash (cleaning) of the filter bed can be performed with lower flushing velocities and less backwash water than what is normally used, and this is achieved by letting the filter bed comprise easily fluidised material with low density and low a sinking rate.
• Fig. 1 shows the sinking rate of grains of various filter media, with an example of a composition of multimedia (Mehr Anlagen/multilayer) filters, where the sinking rate of the filter grains is given as a function of grain size and density.
• Fig. 2 shows a typical deep bed filter with a granulated material according to the invention.
• Table 1 shows an example of the results achieved with direct filtration of coagulated drinking water in partial filters comprising a filter medium according to the invention and with a traditional two-layer anthrasite sand filter as reference.
• Fig. 1 shows how it is possible to assemble multimedia filters in terms of grain size and type of material (density) to achieve proper sedimentation of the filter material after backwash, so that coarse grains stratifiy over (i.e. as a lower sinking rate) the finer grains.
• On fig. 2, is a two-media filter 1 according to the invention shown with an inlet 4 and an outlet 5.
• the liquid 6 that is to be filtered is on top of the filter.
• the filter comprises a filter medium with coarse grains with low density 2 over finer grains with higher density 3.
• the grains are made of one single material, such as expanded clay or plastic.
• the filter has two thin support layers 7 in the bottom.
• the plastic material can be expanded to foam with various densities.
• Table 1 shows an example of results after direct filtration of drinking water containing humus in two partial filters with filter beds comprising the granulated grain material of expanded clay (LK) according to the invention in two fractions of grain sizes and densitites, and a traditional two-media filter bed with anthrasite over sand (A/S) respectively.
• the table shows that the LK filter gives results that fulfil the quality standards according to the Norwegian drinking water regulations with a good margin, and furthermore that results from the LK filter can be compared with a parallelly run traditional anthrasite sand filter in otherwise similar conditions.
• the filter beds have the same total depth whereas the grain sizes are as follows:
• Two layers of material according to the invention where the first has a grain diameter of 1 to 2 mm above a layer with 0,8 to 1 mm grain diameter, and where the grains in the two layers have different densitites, such as 1 ,2 and 2,0 kg/dm 3 .
• the filter medium is made of expanded clay.
• the used two-media filter according to the state of the art has a layer of anthrasite with a codiameter of 0,8 to 1 ,6 mm over a layer of sand with a grain size of 0,4 to 0,8 mm. Table 1

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Filtering Materials (AREA)
• Filtration Of Liquid (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1999
  • 1999-04-13 NO NO19991750A patent/NO314291B1/no not_active IP Right Cessation
• 2000
  • 2000-04-13 WO PCT/NO2000/000120 patent/WO2000061260A1/en not_active Application Discontinuation
  • 2000-04-13 CA CA002367516A patent/CA2367516A1/en not_active Abandoned
  • 2000-04-13 EP EP00917501A patent/EP1194209A1/en not_active Withdrawn
  • 2000-04-13 AU AU38461/00A patent/AU3846100A/en not_active Abandoned

Non-Patent Citations (1)

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