WO2013156673A1 - Filter bag, method for its production, and its use - Google Patents

Filter bag, method for its production, and its use Download PDF

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Publication number
WO2013156673A1
WO2013156673A1 PCT/FI2013/050395 FI2013050395W WO2013156673A1 WO 2013156673 A1 WO2013156673 A1 WO 2013156673A1 FI 2013050395 W FI2013050395 W FI 2013050395W WO 2013156673 A1 WO2013156673 A1 WO 2013156673A1
Authority
WO
WIPO (PCT)
Prior art keywords
filter bag
filter
fabric
scaling
bag
Prior art date
Application number
PCT/FI2013/050395
Other languages
French (fr)
Inventor
Jarmo LINDFORS
Rauno Enqvist
Original Assignee
Metso Fabrics Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Metso Fabrics Inc. filed Critical Metso Fabrics Inc.
Publication of WO2013156673A1 publication Critical patent/WO2013156673A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
    • B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
    • B01D29/111—Making filtering elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/08—Filter cloth, i.e. woven, knitted or interlaced material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
    • B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
    • B01D29/114—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements arranged for inward flow filtration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
    • B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
    • B01D29/13—Supported filter elements
    • B01D29/23—Supported filter elements arranged for outward flow filtration
    • B01D29/27—Filter bags
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/04—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom
    • C01F7/06—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom by treating aluminous minerals or waste-like raw materials with alkali hydroxide, e.g. leaching of bauxite according to the Bayer process
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
    • C01F7/47—Purification of aluminium oxide, aluminium hydroxide or aluminates of aluminates, e.g. removal of compounds of Si, Fe, Ga or of organic compounds from Bayer process liquors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
    • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
    • B01D2239/0604—Arrangement of the fibres in the filtering material
    • B01D2239/0609—Knitted
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
    • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
    • B01D2239/0604—Arrangement of the fibres in the filtering material
    • B01D2239/0618—Non-woven

Definitions

  • the invention relates to a filter bag, and particularly, to a filter bag designed and provided for liquid filtration.
  • the invention relates to a method for producing a filter bag, and to use of the filter bag.
  • Aluminium is produced in the Bayer process, in which aluminium oxide AI2O3, i.e. alumina, is filtered.
  • filter bags with a closed lower end and an open upper end are used.
  • a typical problem of the Bayer process is that material being filtered adheres to surfaces in contact with the material being filtered. This happens in filter bags as well. Material adhered to the filter bag may crystallize as a very hard layer of dirt, or scale, which is very difficult to remove. The scale accumulated in the filter bag complicates the removal and replacement of the filter bag.
  • An object of the present invention is to provide a novel and improved filter bag, a method for its production, and use of the filter bag.
  • the filter bag of the invention is characterized in that the filter fabric extends from the open end of the filter bag to the closed end, the filter fabric covering the entire length of the filter bag; and that the filter fabric comprises at least one portion treated with an anti-scaling material, the anti-scaling material preventing material being filtered from accumulating at the portion treated with the anti-scaling material.
  • the method of the invention is characterized by treating the filter fabric with an anti-scaling material at least partly.
  • a filter bag is made of filter fabric extending from one end of the bag to the other end and forming the bag's basic structure that receives physical loads and acts as a filtering surface.
  • the filter fabric thus extends over the entire length of the filter bag.
  • the filter bag comprises one or more portions treated with an anti-scaling material.
  • An advantage of the disclosed solution is that the filter bag is strong and steady, because the filter fabric extends from its one end to the other.
  • the structure is also simple and easy to manufacture, since it does not include any separate parts.
  • Another advantage is that the anti-scaling portion may be suited to each case.
  • the anti-scaling material to be used, treatment method, amount of anti-scaling material, and location and extent of the portion treated with an anti-scaling material in the filter bag structure may be selected in each case separately. It is also possible to prefabricate filter bags, which are treated as desired by the client for the client's process.
  • the filter bag comprises a neck portion made of filter fabric.
  • the neck portion extends a desired distance from the open end of the bag towards the closed end.
  • the filter fabric at the neck portion has been treated with an anti-scaling material. This application prevents a layer of scale from accumulating at the upper end of the filter bag, which is typically the most critical place with respect to accumulation of scale, i.e. to contamination.
  • the idea of an embodiment is that the entire filter bag is treated with the anti-scaling material.
  • the anti-scaling material must be permeable to liquid, or alternatively the anti-scaling treatment must be performed in such a manner that no continuous film is formed on the filter fabric as a result.
  • the filter bag comprises two or more portions having different anti-scaling treatments.
  • the anti-scaling material forms a layer of coating on at least one surface of the filter fabric at the filter bag's portion treated with the anti-scaling material.
  • the anti-scaling material has penetrated into the structure of the filter fabric at the portion treated with the anti-scaling material.
  • Such an anti-scaling treatment attaches well to the filter fabric.
  • the treatment may be a coating or impregnation, for example.
  • the anti-scaling treatment is on the side of the outer surface of the filter bag.
  • the anti-scaling treatment is on the side of the outer surface and inner surface of the filter bag.
  • said portion treated with the anti-scaling material is impermeable to liquid.
  • Such an anti-scaling treat- ment may be performed for, for instance, the neck portion at the upper end of the bag or for some other limited portion.
  • the filter bag comprises one single filter fabric with predefined properties in terms of permeability, physical resistance and chemical resistance.
  • the filter fabric extends as one uniform piece from one end of the filter bag to the other end.
  • the filter fabric comprises threads consisting of polyamide PA.
  • the filter fabric comprises threads consisting of polypropylene PP.
  • the filter fabric is a woven fabric.
  • the filter fabric comprises one or more base fabrics and one or more batt fibre layers attached thereto. It may deal with a 'needled felt', in which a batt fibre is attached to the base fabric by needling.
  • the filter fabric is non- woven, such as a fabric made by winding.
  • the fabric may be a knitted fabric, thread assembly, or non-woven fibre fabric, for instance.
  • the open end of the filter bag is provided with at least one connection element.
  • the filter bag may be fixed to a filter apparatus by means of the connection element.
  • the connection element may hold the filter bag vertically from the filter apparatus.
  • the open end of the filter bag is provided with a loop fastened to the filter fabric.
  • the loop forms the connection element, and it may be made of rubber, for example.
  • the open end portion of the filter bag comprises a channel or hem which surrounds the filter bag and is provided with at least one loop that forms the connection element.
  • the channel is made of filter fabric.
  • a predefined portion of the filter fabric may be folded at the open end of the filter bag towards the closed end of the bag, after which the folded portion may be affixed by sewing, for instance, so that said channel is formed.
  • a rod-like rubber member may be inserted into the channel, where it is shaped into a loop-like connection element.
  • the member form- ing the loop may be arranged in its place before the folded portion of the filter fabric is affixed.
  • the open end portion of the filter bag comprises a channel which surrounds the filter bag and to which paste-like material is extruded, cast or otherwise arranged, the paste-like material filling the channel and forming a connection element when it hardens.
  • the filter bag comprises only one layer of filter fabric, with the exception of a potential channel at the open end of the bag, the channel being formed by folding the filter fabric.
  • the open end portion of the filter bag is sealed by means of the anti-scaling material to be impermeable to liquid at a predefined distance from the open end.
  • the anti-scaling material is applied to the filter fabric by brushing.
  • the anti-scaling material is applied to the filter fabric by rolling.
  • the anti-scaling material is applied to the filter fabric by spraying.
  • the anti-scaling material is applied to the filter fabric by immersing.
  • the anti-scaling material is rubber or a rubber mixture.
  • the anti-scaling material is epoxy or the like.
  • the anti-scaling material comprises silicone.
  • the anti-scaling material is a material that renders the surface of the filter bag smooth. A smooth surface does not attract dirt easily.
  • the anti-scaling material may also in some cases clog the filter fabric, and thus dirt cannot penetrate into the structure.
  • the anti-scaling material is a material that forms on the surface of the filter bag an elastic portion to which dirt does not adhere easily.
  • dirt adhered to such an elastic surface is easily removable, since by bending and moving the elastic surface, it is possible to break the scale or a similar layer of dirt and to remove it from the filter bag.
  • the anti-scaling material is a fluoropolymer.
  • the anti-scaling material is polytetrafluoroethylene PTFE.
  • the anti-scaling material comprises nanoparticles.
  • the idea of an embodiment is that at least part of the filter fabric of the filter bag is immersed in an anti-scaling material comprising nanoparticles.
  • the filter bag comprises at least two portions treated with different anti-scaling materials.
  • the first portion may comprise, for instance, a rubber-like anti-scaling material and the second portion may comprise, for instance, epoxy material.
  • a film made of an anti- scaling material is fixed to the filter bag.
  • the anti-scaling film may be fixed to the filter fabric by an adhesive.
  • the anti-scaling film may be fixed by using heat or compression or the combined effect of these. If rubber-like material is used as an anti-scaling film, it may also be vulcanized to the filter fabric.
  • the anti-scaling film itself does not have a sufficient mechanical resistance, but the filter fabric to which the anti-scaling film is fixed provides the entire filter bag with the necessary mechanical properties.
  • the filter bag comprises at least two portions treated with an anti-scaling material and with different applications of anti-scaling material.
  • the first portion may comprise, for instance, an anti-scaling coating on the surface of the filter fabric and the second portion may comprise, for instance, an anti-scaling material that is impregnated to the structure of the filter fabric.
  • a filter bag that has already been taken into use earlier is treated with the anti-scaling material.
  • the earlier bags that do not comprise any anti-scaling material may be easily treated with the anti-scaling material.
  • filter bags that have been treated with the anti-scaling material earlier may be treated again after washing and care, if their basic structure allows them to be reused.
  • the filter bag presented in this application is used, instead of the Bayer process, in filtration processes of the food industry.
  • the filter bag presented in this application is used in filtration processes of the pharmaceutical industry.
  • the anti- scaling material refers to a material, which helps to prevent accumulation of material in the filter bag, particularly at its mouth part, during filtration.
  • the accumulating material may be referred to as scale, and the material preventing accumulation may be referred to as anti-scaling material.
  • Figure 1 shows schematically Bayer liquor filtration and a related filter apparatus
  • Figure 2 shows schematically a side view of a filter bag used in the Bayer process, the neck portion of the bag being coated with an anti-scaling material, and
  • Figure 3 shows schematically a side view of a second filter bag used in the Bayer process, the entire bag being treated with an anti-scaling material.
  • FIG. 1 shows the principle of a channel filter apparatus 1 used in Bayer liquor filtration.
  • Liquid to be filtered is introduced to a tank 2.
  • the upper part of the tank 2 comprises outlet pipes 3 comprising a plurality of pipe branches 4, each of which is provided with a filter bag 5.
  • the filter bags 5 are supported on the pipe branches 4 and are suspended downwards from the branches. The filter bags 5 are thus immersed in the liquid being filtered.
  • the filter bags 5 comprise open upper parts, which are in contact with the outlet channels of the pipe branches 4. The liquid that has passed through the filter bag 5 is led away from the filter apparatus 1 along the outlet pipes 3.
  • the filter bag 5 may comprise a plurality of vertical adjacent channels, inside of which support elements may be arranged in such a manner that a filter channel remains open in spite of the difference between the pressure inside the channel and the pressure outside the filter bag.
  • Figure 2 shows a filter bag 5 made of a filter fabric.
  • the filter fabric extends from an open end 6 of the bag to a closed end 7 of the bag, which means that the filter fabric covers the entire length of the filter bag 5.
  • the lower end 7 of the bag may be closed by stiches 8 or an adhesive, for instance.
  • a plurality of parallel filter channels 10 are formed inside the bag 5 by means of stiches 9, for instance.
  • the upper end 6 of the filter bag 5 may comprise a connection element 1 1 , by which the filter bag 5 may be fixed to the filter apparatus.
  • the connection element 1 1 may be formed in such a manner that, at the open end 6, the filter fabric is folded back towards the closed end 7, whereby a channel 12 is provided. This can be seen from the sectional view showing a detail.
  • the channel 12 may be provided with a loop 13 or the like, which forms at the circumference of the open end 6 of the filter bag a fastening protrusion, which can be firmly gripped by fastening elements of the filter apparatus.
  • the loop 13 may be made of, for instance, rubber or a similar material.
  • the free end of the folded filter fabric may be fastened to the bag structure by means of stiches 14, for instance.
  • the filter bag 5 also comprises one or more portions 15 treated with an anti-scaling material.
  • a neck part 16 of the filter bag 5 may comprise such a portion treated with an anti-scaling material, which is marked with diagonal lines in the figure.
  • the reach of the neck part 16 from the open end 6 of the bag may be dimensioned as desired.
  • the anti-scaling material is applied to the filter fabric.
  • FIG 3 shows an alternative filter bag 5, which may otherwise be similar to one shown in Figure 2, except that the open end 6 of the filter bag does not have a connection element 1 1 .
  • the bag 5 is fixed to a filter apparatus by means of a separate fastening member.
  • a further difference is that the entire filter bag 5 is treated with an anti-scaling material, which is illustrated in the figure by diagonal lines. Thus, the anti-scaling material is applied to the filter fabric.
  • the filter bag 5 may have a basic structure similar to Figure 2 and it may be provided with an anti-scaling treatment according to Figure 3, extending from one end of the bag 5 to the other.

Abstract

The invention relates to a filter bag, a method for producing a filter bag, and use. The filter bag (5) is made of a filter fabric and has a longitudinal, substantially tubular form. One end (7) of the bag is closed and the other end (6) is open. Furthermore, the filter fabric is treated with an anti-scaling material (15) partly or completely.

Description

Filter bag, method for its production, and its use
Background of the invention
[0001] The invention relates to a filter bag, and particularly, to a filter bag designed and provided for liquid filtration.
[0002] Furthermore, the invention relates to a method for producing a filter bag, and to use of the filter bag.
[0003] The field of the invention is described in more detail in the preambles of the independent claims of the application.
[0004] Aluminium is produced in the Bayer process, in which aluminium oxide AI2O3, i.e. alumina, is filtered. In the filtration, filter bags with a closed lower end and an open upper end are used. A typical problem of the Bayer process is that material being filtered adheres to surfaces in contact with the material being filtered. This happens in filter bags as well. Material adhered to the filter bag may crystallize as a very hard layer of dirt, or scale, which is very difficult to remove. The scale accumulated in the filter bag complicates the removal and replacement of the filter bag.
Brief description of the invention
[0005] An object of the present invention is to provide a novel and improved filter bag, a method for its production, and use of the filter bag.
[0006] The filter bag of the invention is characterized in that the filter fabric extends from the open end of the filter bag to the closed end, the filter fabric covering the entire length of the filter bag; and that the filter fabric comprises at least one portion treated with an anti-scaling material, the anti-scaling material preventing material being filtered from accumulating at the portion treated with the anti-scaling material.
[0007] The method of the invention is characterized by treating the filter fabric with an anti-scaling material at least partly.
[0008] The use of the invention is characterized by using the filter bag as claimed in the independent claim 1 in the Bayer process for filtering aluminium oxide AI2O3.
[0009] The idea is that a filter bag is made of filter fabric extending from one end of the bag to the other end and forming the bag's basic structure that receives physical loads and acts as a filtering surface. The filter fabric thus extends over the entire length of the filter bag. In addition, the filter bag comprises one or more portions treated with an anti-scaling material. [0010] An advantage of the disclosed solution is that the filter bag is strong and steady, because the filter fabric extends from its one end to the other. The structure is also simple and easy to manufacture, since it does not include any separate parts. Another advantage is that the anti-scaling portion may be suited to each case. The anti-scaling material to be used, treatment method, amount of anti-scaling material, and location and extent of the portion treated with an anti-scaling material in the filter bag structure may be selected in each case separately. It is also possible to prefabricate filter bags, which are treated as desired by the client for the client's process.
[0011] The idea of an embodiment is that the filter bag comprises a neck portion made of filter fabric. The neck portion extends a desired distance from the open end of the bag towards the closed end. The filter fabric at the neck portion has been treated with an anti-scaling material. This application prevents a layer of scale from accumulating at the upper end of the filter bag, which is typically the most critical place with respect to accumulation of scale, i.e. to contamination.
[0012] The idea of an embodiment is that the entire filter bag is treated with the anti-scaling material. In this case, the anti-scaling material must be permeable to liquid, or alternatively the anti-scaling treatment must be performed in such a manner that no continuous film is formed on the filter fabric as a result.
[0013] The idea of an embodiment is that the filter bag comprises two or more portions having different anti-scaling treatments.
[0014] The idea of an embodiment is that the anti-scaling material forms a layer of coating on at least one surface of the filter fabric at the filter bag's portion treated with the anti-scaling material.
[0015] The idea of an embodiment is that the anti-scaling material has penetrated into the structure of the filter fabric at the portion treated with the anti-scaling material. Such an anti-scaling treatment attaches well to the filter fabric. The treatment may be a coating or impregnation, for example.
[0016] The idea of an embodiment is that the anti-scaling treatment is on the side of the outer surface of the filter bag.
[0017] The idea of an embodiment is that the anti-scaling treatment is on the side of the outer surface and inner surface of the filter bag.
[0018] The idea of an embodiment is that said portion treated with the anti-scaling material is impermeable to liquid. Such an anti-scaling treat- ment may be performed for, for instance, the neck portion at the upper end of the bag or for some other limited portion.
[0019] The idea of an embodiment is that the filter bag comprises one single filter fabric with predefined properties in terms of permeability, physical resistance and chemical resistance.
[0020] The idea of an embodiment is that the filter fabric extends as one uniform piece from one end of the filter bag to the other end.
[0021] The idea of an embodiment is that the filter fabric comprises threads consisting of polyamide PA.
[0022] The idea of an embodiment is that the filter fabric comprises threads consisting of polypropylene PP.
[0023] The idea of an embodiment is that the filter fabric is a woven fabric.
[0024] The idea of an embodiment is that the filter fabric comprises one or more base fabrics and one or more batt fibre layers attached thereto. It may deal with a 'needled felt', in which a batt fibre is attached to the base fabric by needling.
[0025] The idea of an embodiment is that the filter fabric is non- woven, such as a fabric made by winding. Furthermore, the fabric may be a knitted fabric, thread assembly, or non-woven fibre fabric, for instance.
[0026] The idea of an embodiment is that the open end of the filter bag is provided with at least one connection element. The filter bag may be fixed to a filter apparatus by means of the connection element. The connection element may hold the filter bag vertically from the filter apparatus.
[0027] The idea of an embodiment is that the open end of the filter bag is provided with a loop fastened to the filter fabric. The loop forms the connection element, and it may be made of rubber, for example.
[0028] The idea of an embodiment is that the open end portion of the filter bag comprises a channel or hem which surrounds the filter bag and is provided with at least one loop that forms the connection element. The channel is made of filter fabric. A predefined portion of the filter fabric may be folded at the open end of the filter bag towards the closed end of the bag, after which the folded portion may be affixed by sewing, for instance, so that said channel is formed. A rod-like rubber member may be inserted into the channel, where it is shaped into a loop-like connection element. Alternatively, the member form- ing the loop may be arranged in its place before the folded portion of the filter fabric is affixed.
[0029] The idea of an embodiment is that the open end portion of the filter bag comprises a channel which surrounds the filter bag and to which paste-like material is extruded, cast or otherwise arranged, the paste-like material filling the channel and forming a connection element when it hardens.
[0030] The idea of an embodiment is that the filter bag comprises only one layer of filter fabric, with the exception of a potential channel at the open end of the bag, the channel being formed by folding the filter fabric.
[0031] The idea of an embodiment is that the open end portion of the filter bag is sealed by means of the anti-scaling material to be impermeable to liquid at a predefined distance from the open end.
[0032] The idea of an embodiment is that the anti-scaling material is applied to the filter fabric by brushing.
[0033] The idea of an embodiment is that the anti-scaling material is applied to the filter fabric by rolling.
[0034] The idea of an embodiment is that the anti-scaling material is applied to the filter fabric by spraying.
[0035] The idea of an embodiment is that the anti-scaling material is applied to the filter fabric by immersing.
[0036] The idea of an embodiment is that the anti-scaling material is rubber or a rubber mixture.
[0037] The idea of an embodiment is that the anti-scaling material is epoxy or the like.
[0038] The idea of an embodiment is that the anti-scaling material comprises silicone.
[0039] The idea of an embodiment is that the anti-scaling material is a material that renders the surface of the filter bag smooth. A smooth surface does not attract dirt easily. The anti-scaling material may also in some cases clog the filter fabric, and thus dirt cannot penetrate into the structure.
[0040] The idea of an embodiment is that the anti-scaling material is a material that forms on the surface of the filter bag an elastic portion to which dirt does not adhere easily. In addition, dirt adhered to such an elastic surface is easily removable, since by bending and moving the elastic surface, it is possible to break the scale or a similar layer of dirt and to remove it from the filter bag. [0041] The idea of an embodiment is that the anti-scaling material is a fluoropolymer.
[0042] The idea of an embodiment is that the anti-scaling material is polytetrafluoroethylene PTFE.
[0043] The idea of an embodiment is that the anti-scaling material comprises nanoparticles.
[0044] The idea of an embodiment is that at least part of the filter fabric of the filter bag is immersed in an anti-scaling material comprising nanoparticles.
[0045] The idea of an embodiment is that the filter bag comprises at least two portions treated with different anti-scaling materials. The first portion may comprise, for instance, a rubber-like anti-scaling material and the second portion may comprise, for instance, epoxy material.
[0046] The idea of an embodiment is that a film made of an anti- scaling material is fixed to the filter bag. The anti-scaling film may be fixed to the filter fabric by an adhesive. Alternatively, the anti-scaling film may be fixed by using heat or compression or the combined effect of these. If rubber-like material is used as an anti-scaling film, it may also be vulcanized to the filter fabric. The anti-scaling film itself does not have a sufficient mechanical resistance, but the filter fabric to which the anti-scaling film is fixed provides the entire filter bag with the necessary mechanical properties.
[0047] The idea of an embodiment is that the filter bag comprises at least two portions treated with an anti-scaling material and with different applications of anti-scaling material. The first portion may comprise, for instance, an anti-scaling coating on the surface of the filter fabric and the second portion may comprise, for instance, an anti-scaling material that is impregnated to the structure of the filter fabric.
[0048] The idea of an embodiment is that a filter bag that has already been taken into use earlier is treated with the anti-scaling material. The earlier bags that do not comprise any anti-scaling material may be easily treated with the anti-scaling material. Furthermore, filter bags that have been treated with the anti-scaling material earlier may be treated again after washing and care, if their basic structure allows them to be reused.
[0049] The idea of an embodiment is that the filter bag presented in this application is used, instead of the Bayer process, in filtration processes of the food industry. [0050] The idea of an embodiment is that the filter bag presented in this application is used in filtration processes of the pharmaceutical industry.
[0051] It is to be noted that, in the present application, the anti- scaling material refers to a material, which helps to prevent accumulation of material in the filter bag, particularly at its mouth part, during filtration. The accumulating material may be referred to as scale, and the material preventing accumulation may be referred to as anti-scaling material.
Brief description of the figures
[0052] Some embodiments are explained in more detail in the accompanying drawings, in which
Figure 1 shows schematically Bayer liquor filtration and a related filter apparatus,
Figure 2 shows schematically a side view of a filter bag used in the Bayer process, the neck portion of the bag being coated with an anti-scaling material, and
Figure 3 shows schematically a side view of a second filter bag used in the Bayer process, the entire bag being treated with an anti-scaling material.
[0053] For the sake of clarity, the figures show some embodiments in a simplified manner. Like reference numerals identify like elements in the figures.
Detailed description of some embodiments
[0054] Figure 1 shows the principle of a channel filter apparatus 1 used in Bayer liquor filtration. Liquid to be filtered is introduced to a tank 2. The upper part of the tank 2 comprises outlet pipes 3 comprising a plurality of pipe branches 4, each of which is provided with a filter bag 5. The filter bags 5 are supported on the pipe branches 4 and are suspended downwards from the branches. The filter bags 5 are thus immersed in the liquid being filtered. The filter bags 5 comprise open upper parts, which are in contact with the outlet channels of the pipe branches 4. The liquid that has passed through the filter bag 5 is led away from the filter apparatus 1 along the outlet pipes 3. The filter bag 5 may comprise a plurality of vertical adjacent channels, inside of which support elements may be arranged in such a manner that a filter channel remains open in spite of the difference between the pressure inside the channel and the pressure outside the filter bag. [0055] Figure 2 shows a filter bag 5 made of a filter fabric. The filter fabric extends from an open end 6 of the bag to a closed end 7 of the bag, which means that the filter fabric covers the entire length of the filter bag 5. The lower end 7 of the bag may be closed by stiches 8 or an adhesive, for instance. Furthermore, a plurality of parallel filter channels 10 are formed inside the bag 5 by means of stiches 9, for instance. The upper end 6 of the filter bag 5 may comprise a connection element 1 1 , by which the filter bag 5 may be fixed to the filter apparatus. The connection element 1 1 may be formed in such a manner that, at the open end 6, the filter fabric is folded back towards the closed end 7, whereby a channel 12 is provided. This can be seen from the sectional view showing a detail. The channel 12 may be provided with a loop 13 or the like, which forms at the circumference of the open end 6 of the filter bag a fastening protrusion, which can be firmly gripped by fastening elements of the filter apparatus. The loop 13 may be made of, for instance, rubber or a similar material. The free end of the folded filter fabric may be fastened to the bag structure by means of stiches 14, for instance.
[0056] The filter bag 5 also comprises one or more portions 15 treated with an anti-scaling material. A neck part 16 of the filter bag 5 may comprise such a portion treated with an anti-scaling material, which is marked with diagonal lines in the figure. The reach of the neck part 16 from the open end 6 of the bag may be dimensioned as desired. Thus, the anti-scaling material is applied to the filter fabric.
[0057] Figure 3 shows an alternative filter bag 5, which may otherwise be similar to one shown in Figure 2, except that the open end 6 of the filter bag does not have a connection element 1 1 . In this case, the bag 5 is fixed to a filter apparatus by means of a separate fastening member. A further difference is that the entire filter bag 5 is treated with an anti-scaling material, which is illustrated in the figure by diagonal lines. Thus, the anti-scaling material is applied to the filter fabric.
[0058] Furthermore, the filter bag 5 may have a basic structure similar to Figure 2 and it may be provided with an anti-scaling treatment according to Figure 3, extending from one end of the bag 5 to the other.
[0059] In some cases, features disclosed in this application may be used as such, regardless of other features. On the other hand, when necessary, features disclosed in this application may be combined in order to provide various combinations. [0060] The drawings and the relating description are only intended to illustrate the idea of the invention. Details of the invention may vary within the scope of the claims.

Claims

ΐ?η53ηρπ WO 2013/156673 PCT/FI2013/050395 9 Claims
1. A filter bag (5) which:
is an elongated member mainly consisting of a filter fabric;
comprises an open end (6) and an opposite, closed end (7);
and comprises at least two parallel longitudinal channels (10);
characterized in that
the filter fabric extends from the open end (6) of the filter bag to the closed end (7), the filter fabric covering the entire length of the filter bag (5); and
the filter fabric comprises at least one portion (15) treated with an anti-scaling material, the anti-scaling material preventing material being filtered from accumulating at the portion (15) treated with the anti-scaling material.
2. The filter bag as claimed in claim 1, characterized in that the filter bag (5) comprises a neck part (16) made of a filter fabric and extending at least a predefined distance from the open end (6) towards the closed end (7) of the filter bag; and
the neck part (16) is provided with said anti-scaling treatment.
3. The filter bag as claimed in claim 1 or 2, characterized in that
the portion treated with the anti-scaling material is permeable to liq- uid; and
the filter bag (5) is provided with the anti-scaling treatment along its entire length.
4. The filter bag as claimed in any one of the preceding claims, characterized in that
the anti-scaling material has penetrated at least partly into the surface layer of the material of the filter fabric.
5. The filter bag as claimed in any one of the preceding claims, characterized in that
the filter fabric extends as one uniform piece from one end of the filter bag to the other end.
6. The filter bag as claimed in any one of the preceding claims, characterized in that
the anti-scaling material comprises nanoparticles.
7. A method for producing a filter bag, the method comprising:
providing a filter fabric; ΐ?η53ηρπ
WO 2013/156673 PCT/FI2013/050395
10
forming the filter fabric into a tubular elongated member with side surfaces;
closing one end of the formed tubular member and leaving the other end open; and
fixing the side surfaces at longitudinal fastening points to one another and thus forming at least two longitudinal channels (10) in the filter bag (5);
characterized by
treating the filter fabric with an anti-scaling material at least partly.
8. The method as claimed in claim 7, characterized by coating the filter fabric with the anti-scaling material at least at the open end (6) portion of the filter bag, thus providing the filter bag (5) with a neck part (16) treated with the anti-scaling material and extending a distance towards the closed end (7).
9. The method as claimed in claim 7 or 8, characterized by impregnating the filter fabric with the anti-scaling material partly or completely.
10. The method as claimed in any one of the preceding claims 7 to
9, characterized by
folding the free end of the filter fabric at the open end (6) of the filter bag towards the closed end (7) and fixing the free end to the structure of the filter bag (5), thus forming a channel (12) surrounding the open end (6) of the filter bag; and
arranging in said channel (12) at least one loop (13), which forms a connection element (11 ) for fixing the filter bag (5) to a process apparatus.
11. The method as claimed in any one of the preceding claims 7 to
10, characterized by
immersing at least part of the filter fabric of the filter bag in an anti- scaling material comprising nanoparticles.
12. Use of a filter bag for filtration, characterized by using the filter bag (5) as claimed in the independent claim 1 in the Bayer process for filtering aluminium oxide AI2O3.
PCT/FI2013/050395 2012-04-17 2013-04-11 Filter bag, method for its production, and its use WO2013156673A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20125414 2012-04-17
FI20125414A FI20125414L (en) 2012-04-17 2012-04-17 Filter bag, method of its manufacture and use

Publications (1)

Publication Number Publication Date
WO2013156673A1 true WO2013156673A1 (en) 2013-10-24

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105263596A (en) * 2013-06-05 2016-01-20 瑟法Bdh有限公司 Closure for leaf filter in alumina production
CN110202875A (en) * 2019-07-09 2019-09-06 江苏瀚霆环保滤材有限公司 A kind of blast furnace gas Nomex for steel production

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5639369A (en) * 1995-07-14 1997-06-17 W. L. Gore & Associates, Inc. Filter element
US20040132373A1 (en) * 2001-02-20 2004-07-08 Mueller Hans Rudolf Filter cloth
WO2010091515A1 (en) * 2009-02-13 2010-08-19 SEFAR FYLTIS une société par actions simplifiée Filter bag for bayer liquor filtration

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5639369A (en) * 1995-07-14 1997-06-17 W. L. Gore & Associates, Inc. Filter element
US20040132373A1 (en) * 2001-02-20 2004-07-08 Mueller Hans Rudolf Filter cloth
WO2010091515A1 (en) * 2009-02-13 2010-08-19 SEFAR FYLTIS une société par actions simplifiée Filter bag for bayer liquor filtration

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105263596A (en) * 2013-06-05 2016-01-20 瑟法Bdh有限公司 Closure for leaf filter in alumina production
CN105263596B (en) * 2013-06-05 2017-08-25 瑟法Bdh有限公司 It is used for the closure member of leaf filter in alumina producing
CN110202875A (en) * 2019-07-09 2019-09-06 江苏瀚霆环保滤材有限公司 A kind of blast furnace gas Nomex for steel production
CN110202875B (en) * 2019-07-09 2024-03-29 江苏瀚霆环保滤材有限公司 Needled felt for blast furnace gas for steel production

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