CA2608790A1 - Cleaning process for impaired membranes - Google Patents
Cleaning process for impaired membranes Download PDFInfo
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- CA2608790A1 CA2608790A1 CA 2608790 CA2608790A CA2608790A1 CA 2608790 A1 CA2608790 A1 CA 2608790A1 CA 2608790 CA2608790 CA 2608790 CA 2608790 A CA2608790 A CA 2608790A CA 2608790 A1 CA2608790 A1 CA 2608790A1
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- Prior art keywords
- acid
- cleaning process
- aqueous acid
- filters
- aqueous
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- 238000000034 method Methods 0.000 title claims abstract description 38
- 238000004140 cleaning Methods 0.000 title claims abstract description 29
- 230000001771 impaired effect Effects 0.000 title claims description 8
- 239000012528 membrane Substances 0.000 title abstract description 14
- 229940043430 calcium compound Drugs 0.000 claims abstract description 13
- 150000001674 calcium compounds Chemical class 0.000 claims abstract description 13
- 239000000463 material Substances 0.000 claims abstract description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910000323 aluminium silicate Inorganic materials 0.000 claims abstract description 6
- 239000011260 aqueous acid Substances 0.000 claims description 29
- 239000002253 acid Substances 0.000 claims description 22
- -1 fluoride ions Chemical class 0.000 claims description 15
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 13
- 150000007524 organic acids Chemical class 0.000 claims description 11
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 9
- 239000000080 wetting agent Substances 0.000 claims description 7
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 6
- AEMRFAOFKBGASW-UHFFFAOYSA-N Glycolic acid Chemical compound OCC(O)=O AEMRFAOFKBGASW-UHFFFAOYSA-N 0.000 claims description 6
- 239000002738 chelating agent Substances 0.000 claims description 6
- 229910052976 metal sulfide Inorganic materials 0.000 claims description 6
- 150000007522 mineralic acids Chemical class 0.000 claims description 6
- 238000011010 flushing procedure Methods 0.000 claims description 5
- 150000004760 silicates Chemical class 0.000 claims description 5
- LNOPIUAQISRISI-UHFFFAOYSA-N n'-hydroxy-2-propan-2-ylsulfonylethanimidamide Chemical compound CC(C)S(=O)(=O)CC(N)=NO LNOPIUAQISRISI-UHFFFAOYSA-N 0.000 claims description 4
- 150000003863 ammonium salts Chemical class 0.000 claims description 3
- 229960004275 glycolic acid Drugs 0.000 claims description 3
- 235000005985 organic acids Nutrition 0.000 claims description 3
- 238000001914 filtration Methods 0.000 abstract description 13
- 239000007788 liquid Substances 0.000 abstract description 8
- 239000000203 mixture Substances 0.000 abstract description 5
- 235000008733 Citrus aurantifolia Nutrition 0.000 abstract description 4
- 235000011941 Tilia x europaea Nutrition 0.000 abstract description 4
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 abstract description 4
- 239000004571 lime Substances 0.000 abstract description 4
- 238000001226 reprecipitation Methods 0.000 abstract description 3
- 239000002655 kraft paper Substances 0.000 abstract description 2
- IJKVHSBPTUYDLN-UHFFFAOYSA-N dihydroxy(oxo)silane Chemical compound O[Si](O)=O IJKVHSBPTUYDLN-UHFFFAOYSA-N 0.000 abstract 2
- 239000003513 alkali Substances 0.000 abstract 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 abstract 1
- 229910052782 aluminium Inorganic materials 0.000 abstract 1
- 150000003377 silicon compounds Chemical class 0.000 abstract 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 9
- 239000000243 solution Substances 0.000 description 8
- 238000005260 corrosion Methods 0.000 description 6
- 230000007797 corrosion Effects 0.000 description 6
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 5
- 150000004673 fluoride salts Chemical class 0.000 description 5
- 239000003112 inhibitor Substances 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 3
- 150000007513 acids Chemical class 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 2
- 239000004327 boric acid Substances 0.000 description 2
- 229910052791 calcium Inorganic materials 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 150000001768 cations Chemical class 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 239000000123 paper Substances 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 239000002195 soluble material Substances 0.000 description 2
- XOAAWQZATWQOTB-UHFFFAOYSA-N taurine Chemical compound NCCS(O)(=O)=O XOAAWQZATWQOTB-UHFFFAOYSA-N 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- RILZRCJGXSFXNE-UHFFFAOYSA-N 2-[4-(trifluoromethoxy)phenyl]ethanol Chemical compound OCCC1=CC=C(OC(F)(F)F)C=C1 RILZRCJGXSFXNE-UHFFFAOYSA-N 0.000 description 1
- 229910021532 Calcite Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000001506 calcium phosphate Substances 0.000 description 1
- 229910000389 calcium phosphate Inorganic materials 0.000 description 1
- 235000011010 calcium phosphates Nutrition 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- GPGMRSSBVJNWRA-UHFFFAOYSA-N hydrochloride hydrofluoride Chemical compound F.Cl GPGMRSSBVJNWRA-UHFFFAOYSA-N 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 235000006408 oxalic acid Nutrition 0.000 description 1
- 229940116315 oxalic acid Drugs 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 150000003009 phosphonic acids Chemical class 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229920001282 polysaccharide Polymers 0.000 description 1
- 239000005017 polysaccharide Substances 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 102000004169 proteins and genes Human genes 0.000 description 1
- 108090000623 proteins and genes Proteins 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 229960003080 taurine Drugs 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 description 1
Landscapes
- Detergent Compositions (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
A cleaning process using aqueous liquid compositions for cleaning membrane filters used primarily in tubular backpulse liquid filtration systems in Kraft pulp mills for white liquor, green liquor and lime mud filtration and in chlor-alkali processing.
The process removes silicate and aluminosilicate materials that reduce filtration efficiency with minimal damage to the membrane filter. The method consists of a first stage first liquid composition flush to remove soluble calcium compounds followed by a second stage second liquid composition flush that dissolves the silicate and aluminosilicate compounds and prevents reprecipitation of dissolved aluminum and silicon compounds in the filter membrane. The filters are then flushed by water.
The process removes silicate and aluminosilicate materials that reduce filtration efficiency with minimal damage to the membrane filter. The method consists of a first stage first liquid composition flush to remove soluble calcium compounds followed by a second stage second liquid composition flush that dissolves the silicate and aluminosilicate compounds and prevents reprecipitation of dissolved aluminum and silicon compounds in the filter membrane. The filters are then flushed by water.
Description
Title of the Invention Cleaning Process for Impaired Filters Cross-Reference to Related Applications This patent application claims priority from United States Provisional Patent Application 60l857,198 filed in the United States Patent Office on November 7, 2006 and entitled Cleaning Process for Membrane Filters Used in Industrial Liquid Filtration Systems.
Background of the Invention Field of the Invention This invention relates to cleaning processes for impaired filters asid more particularly a cleaning process for impaired tubular backpulse pressure filters used in industrial liquid filtratifln systems.
Description of Prior Art Pressure filters are commonly used in the pulp and paper industry in tubular backpulse liquid filtration systems, These industrial filtration systems are used to filter white Iiquor.
green liquor and lime mud wash fluids. As filtration efficiency decreases, these filters are normally cleaned by acid washing with a buffered acid solution such as sulfaznic acid or dilute hydrochloric acid. Sulfamic acid solution will dissolve acid-soluble material such as calcium carbonate and other carbonate compounds that reduce filtration e#~tciency. An example of this type of filter is the G{?RE~m membrane filter socks used in tubular backpulse liquid filtration systems (Gore & Associates, Inc.}. These membranes are typically made from porous PTFE polymers. Filter material can also be other rnaterials such as woven polypropylene fibers. As filtration efficienc), becomes impaired, these filters must be replaced, incurring significant cost and downtinie.
Recently, Taylor and McGuffie ("Investigation of Non-Process Element Chemistry at Elk Falls Mill - Green Liquor Clarifier and Lime Cycle", presented at the Pulp and Paper Teclinical Association of Canada PACWEST Conference, .lasper, AB, Canada, May 20, 2006) reported that the filtration efficiency of niembrane filters used for white liquor filtradon could be significantly reduced by silicate and aluminosilicate compounds.
These coinpounds are not significantly removed by normal acid washing of the n1enll)rane filters.
In US Patent 5,277,819, a membrane filter cleaning process is outlined that removes protein and polysaccharide compounds from pol_yaanide membranes.
I.n US Patent 4,802,990, a method for dissolving mineral salts is described. A
mixture of phosphonic acids containing either sulfamic acid, oxalic acid, hydroxyacetic acid, 2-amino ethane sulfonic acid or fluoroboric acid and neutralized to pH 7.0, is described. In example IV of that patent, a calcite mineral deposit was quickly dissolved followed by a rapid re-precipitation of a gelatinous material. Such a re-precipitation reaction can cause additional plugging of membrane filter systems.
Background of the Invention Field of the Invention This invention relates to cleaning processes for impaired filters asid more particularly a cleaning process for impaired tubular backpulse pressure filters used in industrial liquid filtratifln systems.
Description of Prior Art Pressure filters are commonly used in the pulp and paper industry in tubular backpulse liquid filtration systems, These industrial filtration systems are used to filter white Iiquor.
green liquor and lime mud wash fluids. As filtration efficiency decreases, these filters are normally cleaned by acid washing with a buffered acid solution such as sulfaznic acid or dilute hydrochloric acid. Sulfamic acid solution will dissolve acid-soluble material such as calcium carbonate and other carbonate compounds that reduce filtration e#~tciency. An example of this type of filter is the G{?RE~m membrane filter socks used in tubular backpulse liquid filtration systems (Gore & Associates, Inc.}. These membranes are typically made from porous PTFE polymers. Filter material can also be other rnaterials such as woven polypropylene fibers. As filtration efficienc), becomes impaired, these filters must be replaced, incurring significant cost and downtinie.
Recently, Taylor and McGuffie ("Investigation of Non-Process Element Chemistry at Elk Falls Mill - Green Liquor Clarifier and Lime Cycle", presented at the Pulp and Paper Teclinical Association of Canada PACWEST Conference, .lasper, AB, Canada, May 20, 2006) reported that the filtration efficiency of niembrane filters used for white liquor filtradon could be significantly reduced by silicate and aluminosilicate compounds.
These coinpounds are not significantly removed by normal acid washing of the n1enll)rane filters.
In US Patent 5,277,819, a membrane filter cleaning process is outlined that removes protein and polysaccharide compounds from pol_yaanide membranes.
I.n US Patent 4,802,990, a method for dissolving mineral salts is described. A
mixture of phosphonic acids containing either sulfamic acid, oxalic acid, hydroxyacetic acid, 2-amino ethane sulfonic acid or fluoroboric acid and neutralized to pH 7.0, is described. In example IV of that patent, a calcite mineral deposit was quickly dissolved followed by a rapid re-precipitation of a gelatinous material. Such a re-precipitation reaction can cause additional plugging of membrane filter systems.
Numerous procedures are know-n for dissolving silicate-containing materials from well bores in the petroleum industry. For example, U.S. Patent 1,990,969 uses solutions of hydrochloric acid and water-soluble fluoride salts. This avoids the surface handling of hydrofluoric acid solution. Cn U.S. Patent 2,001,579 the corrosivity of hydrochloric acid and hydrofluoric acids is reduced by the addition of a corrosion inhibitor_ In U.S. Patent 2,050,931 a water-wetting agent is injected ahead of an aqueous solution of hydrochloric acid and hydrofluoric acid to improve the silicate dissolving ability of the treatment. In U.S. Patent 2,367,354, a hydrochloric acid solution is injected ahead of a solution of hydrofluoric acid to remove multivalent cations from the region containing the silicate materials. This prevents damaging precipitation reactions. In U.S. Patent 2,663,689, boric acid is dissolved in an aqueous hydrochloric acid-hydrofluoric acid solution to avoid precipitation of insoluble fluotide salts, when niultivalent cations are encountered, or precipitation of gelatinous hydrofluorosilic acid, when the acidity of the solution is depleted.
Summary of the Invention This invention can be applied to tubular backpulse pressure filters with or v;rithout a surface membrane present. Tubular backpulse pressure filters come in two types - one has a surface membrane, the other does not. Both are made from woven polypropylene fibers. This invention applies to both types of filters.
Summary of the Invention This invention can be applied to tubular backpulse pressure filters with or v;rithout a surface membrane present. Tubular backpulse pressure filters come in two types - one has a surface membrane, the other does not. Both are made from woven polypropylene fibers. This invention applies to both types of filters.
To resolve the problems identified with the prior art methods, this invention proposes a cleaning process for filters impaired by materials such as acid-soluble calcium compounds, acid insoluble calcium compounds, silicates, aluminosilict,es and rnet:al sulfides. In one embodiment of the invention the process comprises a first stage of treatment comprising a step where the filters are flushed with a first aqueous acid at a first predetermined temperature and for a first predetermined period of time.
The first step results in the removal of acid-soluble divalent ions and calcium compounds. A
second step is added comprising the step of flushing the filters with water for cleansing.
ln another embodiment of the invention, the process is a multi-step process comprising the steps of flushing the filters with a first aqueous acid at a first predetennined temperature and for a first predeterniined period of time. This results in the removal of acid-soluble calciuni coinpounds. A second step comprises flushing the filters with a second aqueous acid at a second predetermined teinperature for a second period of time.
This second step results in the removal of silicates, aluminosilicates and metal sulfides.
Then a third step comprises flushing the filters with water for cleansing.
In one embodiment of the inven.tion said first aqueous acid is an organic acid or an inorganic acid.
The first step results in the removal of acid-soluble divalent ions and calcium compounds. A
second step is added comprising the step of flushing the filters with water for cleansing.
ln another embodiment of the invention, the process is a multi-step process comprising the steps of flushing the filters with a first aqueous acid at a first predetennined temperature and for a first predeterniined period of time. This results in the removal of acid-soluble calciuni coinpounds. A second step comprises flushing the filters with a second aqueous acid at a second predetermined teinperature for a second period of time.
This second step results in the removal of silicates, aluminosilicates and metal sulfides.
Then a third step comprises flushing the filters with water for cleansing.
In one embodiment of the inven.tion said first aqueous acid is an organic acid or an inorganic acid.
In another embodiment of the invention the second aqueous acid is an organic acid containing fluoride ions. The fluoride ions may have a concentrationn of between 0.1% by wt. and 20% by In yet another embodiment of the invention the second aqueous acid is an inorganic acid containing fluoride ions having a concentration of between 0.1% by wt. and ?0 lo by wt.
The fluoride ions may be derived froni an aninionium salt of hydrofluoiic acid or from fluoboric acid.
In one embodiment of the invention the first aqueous acid or the second aqueous acid may be an emulsified acid.
In another enibodiment of the inventlon there may be added a further step of adding a chelating agent to the first or the second aqueous acid for removing acid insoluble calcium compounds.
In yet another embodiment of the invention there may be added a further step of adding a wetting agent to improve contact between the first and aqueous acids and materials.
In one embodiment of the invention the first and second acids are organic derived from a group of organic acids comprising sulfamic acid, acetic acid, hydroxyacetic acid and citric acid. The first and second acids may have a concentration. between 0.5%
by -%vt, and 1 S% by wt.
S
In yet another embodiment of the invention the first and second acids comprise t7u.oboric acid at a concentration of between 1% by wt_ and 20% by wt.
In one embodiment of the invention the first predetermined temperature and said second predetermined teniperature are between 24 C and 95C. In a preferred embodiment the first and second predeterniined temperatures are between 25 C and 60 C.
In another einbodinient of the invention the first and second predeternrined times are between 0.1 hours auid 0.5 liairs.
In still another enabodinient of the invetrtion first step and the second step fuirther comprise the step of adding a corrosion inhibitor.
Detailed Description The folloNving description is provided for the purpose of describing examples and specific embodiments of the invention oilly and is not intended to exhaustively describe all possible examples and embodiments of the invention.
This irtvention defines a cleaning process for industrial tubular backpulse pressure filters used primarily in Kraft pulp mills for white liquor, green liquor and lime mud filtration, and in chlor-aikali processing. The invention prolongs the use of the porous filter membranes by permitting non-destructive cleaning to remove silicate and aluminosilicate materials that reduce filtration efficiency. This invention can be applied to tubular backpulse filters with or without a surface membrane present_ The process can be a single stage treatnient comprising a first stage treatment followed by a water flush or a two stage treatment comprising a first and second stage treatment. The purpose of the first stage treatment is to remove any acid-soluble divalent ions (such as calcium). If a second stage treatment is also used, then the removal of the acid-soluble divalent ions prevents the formation of insoluble fluoride salts during the second stage of the treatment.
The first stage contains an aqueous solution containing an inorganic acid or an organic acid present in sufficient quantity to remove acid-soluble material. Acid concentrations are 0.1 to 30 wt ro but more preferably 1 to 15 wt %. An organic acid such as sulfarnic acid at a concentration of 5 to 1.0 wt%o is preferred. Treatment tenlperature is frorn 20 to 95T but niost preferably from 20 to 60 C. The first stage may contain corrosion inhibitors, chelating agents or water-wetting agents. The purpose of the corrosion inhibitor is to reduce corrosion in the process equipnient. The chelating agent is required to remove calcium-containing compounds that are not readily soluble in the acid itself.
These include hydroxyiapatite (calcium phosphate) and metal sulfides. A water-wetting agent is used to improve the contact between the acid and the solids present in the filter.
The second stage is identical in composition to the first stage but also contains from 0.1 to 10 wt % fluoride in the form of Hl~' or a fluoride salt. The fluoride ion concentration is most preferably I to 5 wt%, In a preferred embodiment, the fluoride salt is an ammonium salt of hydrofluoric acid. However, it can comprise one or more of substantially any fluoride salt that is relatively water-soluble. The second stage may also contain the organic acid citric acid or boric acid to reduce the precipitation of aluminum-cont:aining compounds_ Treatment temperature is from 25 to 95 C but most preferably from 25 to 60 C. The second stage may contain corrosion inhibitors, chelating agents or water-wetting agents as detailed in the previous paragraph. Following the treatment, the filter is flushed with water.
Although this description has much specificity, these sliould not be construed as lirniting the scope of the invention but as merely providing illustrations of some of examples of the invention. Thus the scope of the invention should be detennined by the appended claims and their legal ecluivalents rather than by the examples given herein.
The fluoride ions may be derived froni an aninionium salt of hydrofluoiic acid or from fluoboric acid.
In one embodiment of the invention the first aqueous acid or the second aqueous acid may be an emulsified acid.
In another enibodiment of the inventlon there may be added a further step of adding a chelating agent to the first or the second aqueous acid for removing acid insoluble calcium compounds.
In yet another embodiment of the invention there may be added a further step of adding a wetting agent to improve contact between the first and aqueous acids and materials.
In one embodiment of the invention the first and second acids are organic derived from a group of organic acids comprising sulfamic acid, acetic acid, hydroxyacetic acid and citric acid. The first and second acids may have a concentration. between 0.5%
by -%vt, and 1 S% by wt.
S
In yet another embodiment of the invention the first and second acids comprise t7u.oboric acid at a concentration of between 1% by wt_ and 20% by wt.
In one embodiment of the invention the first predetermined temperature and said second predetermined teniperature are between 24 C and 95C. In a preferred embodiment the first and second predeterniined temperatures are between 25 C and 60 C.
In another einbodinient of the invention the first and second predeternrined times are between 0.1 hours auid 0.5 liairs.
In still another enabodinient of the invetrtion first step and the second step fuirther comprise the step of adding a corrosion inhibitor.
Detailed Description The folloNving description is provided for the purpose of describing examples and specific embodiments of the invention oilly and is not intended to exhaustively describe all possible examples and embodiments of the invention.
This irtvention defines a cleaning process for industrial tubular backpulse pressure filters used primarily in Kraft pulp mills for white liquor, green liquor and lime mud filtration, and in chlor-aikali processing. The invention prolongs the use of the porous filter membranes by permitting non-destructive cleaning to remove silicate and aluminosilicate materials that reduce filtration efficiency. This invention can be applied to tubular backpulse filters with or without a surface membrane present_ The process can be a single stage treatnient comprising a first stage treatment followed by a water flush or a two stage treatment comprising a first and second stage treatment. The purpose of the first stage treatment is to remove any acid-soluble divalent ions (such as calcium). If a second stage treatment is also used, then the removal of the acid-soluble divalent ions prevents the formation of insoluble fluoride salts during the second stage of the treatment.
The first stage contains an aqueous solution containing an inorganic acid or an organic acid present in sufficient quantity to remove acid-soluble material. Acid concentrations are 0.1 to 30 wt ro but more preferably 1 to 15 wt %. An organic acid such as sulfarnic acid at a concentration of 5 to 1.0 wt%o is preferred. Treatment tenlperature is frorn 20 to 95T but niost preferably from 20 to 60 C. The first stage may contain corrosion inhibitors, chelating agents or water-wetting agents. The purpose of the corrosion inhibitor is to reduce corrosion in the process equipnient. The chelating agent is required to remove calcium-containing compounds that are not readily soluble in the acid itself.
These include hydroxyiapatite (calcium phosphate) and metal sulfides. A water-wetting agent is used to improve the contact between the acid and the solids present in the filter.
The second stage is identical in composition to the first stage but also contains from 0.1 to 10 wt % fluoride in the form of Hl~' or a fluoride salt. The fluoride ion concentration is most preferably I to 5 wt%, In a preferred embodiment, the fluoride salt is an ammonium salt of hydrofluoric acid. However, it can comprise one or more of substantially any fluoride salt that is relatively water-soluble. The second stage may also contain the organic acid citric acid or boric acid to reduce the precipitation of aluminum-cont:aining compounds_ Treatment temperature is from 25 to 95 C but most preferably from 25 to 60 C. The second stage may contain corrosion inhibitors, chelating agents or water-wetting agents as detailed in the previous paragraph. Following the treatment, the filter is flushed with water.
Although this description has much specificity, these sliould not be construed as lirniting the scope of the invention but as merely providing illustrations of some of examples of the invention. Thus the scope of the invention should be detennined by the appended claims and their legal ecluivalents rather than by the examples given herein.
Claims (16)
1. A cleaning process for filters impaired by materials comprising acid-soluble calcium compounds, acid insoluble calcium compounds, silicates, aluminosilicates and metal sulfides, said cleaning process comprising the following:
a. A first step wherein said filters are flushed with a first aqueous acid at a first predetermined temperature and for a first predetermined period of time, said first step resulting in the removal of said acid-soluble calcium compounds; and, b. A second step wherein the filters are flushed with water for cleansing.
a. A first step wherein said filters are flushed with a first aqueous acid at a first predetermined temperature and for a first predetermined period of time, said first step resulting in the removal of said acid-soluble calcium compounds; and, b. A second step wherein the filters are flushed with water for cleansing.
2. A cleaning process for filters impaired by materials comprising acid-soluble calcium compounds, acid insoluble calcium compounds, silicates, aluminosilicates and metal sulfides, said cleaning process comprising the following:
a. A first step wherein said filters are flushed with a first aqueous acid at a first predetermined temperature and for a first predetermined period of time, said first step resulting in the removal of said acid-soluble calcium compounds;
b. A second step comprising flushing the filters with a second aqueous acid at a second predetermined temperature for a second period of time, the additional step resulting in the removal. of said silicates and said aluminosilicates; and, c. A third step wherein the filters are flushed with water for cleansing.
a. A first step wherein said filters are flushed with a first aqueous acid at a first predetermined temperature and for a first predetermined period of time, said first step resulting in the removal of said acid-soluble calcium compounds;
b. A second step comprising flushing the filters with a second aqueous acid at a second predetermined temperature for a second period of time, the additional step resulting in the removal. of said silicates and said aluminosilicates; and, c. A third step wherein the filters are flushed with water for cleansing.
3. The cleaning process of claim 1 or 2, wherein said first aqueous acid is an organic acid.
4. The cleaning process of claim 3, wherein the first aqueous acid is an inorganic acid.
5. The cleaning process of claim 2, wherein the second aqueous acid is an organic acid containing fluoride ions having a concentration of between 0.1% by wt. and 20%
by wt., and wherein said fluoride ions are derived from an ammonium salt of hydrofluoric acid.
by wt., and wherein said fluoride ions are derived from an ammonium salt of hydrofluoric acid.
6. The cleaning process of claim 2, wherein the second aqueous acid is an organic acid containing fluoride ions having a concentration of between 0.1% by wt. and 20%
by wt., and wherein said fluoride ions are derived from fluoboric acid.
by wt., and wherein said fluoride ions are derived from fluoboric acid.
7. The cleaning process of claim 2, wherein the second aqueous acid is an inorganic acid containing fluoride ions having a concentration of between. 0.1% by wt. and 20% by wt., and wherein said fluoride ions are derived from an ammonium salt of hydrofluoric acid.
8. The cleaning process of claim 2, wherein the second aqueous acid is an inorganic acid containing fluoride ions having a concentration of between 0.1% by wt. and 20%
by wt., and wherein said fluoride ions are derived from fluoboric acid.
by wt., and wherein said fluoride ions are derived from fluoboric acid.
9. The cleaning process of claim 1, further comprising the addition of a chelating agent to said first aqueous acid for removing said calcium compounds and metal sulfides.
10. The cleaning process of claim 2, further comprising the addition of a chelating agent to said first aqueous acid for removing said calcium compounds and metal sulfides.
11. The cleaning process of claim 1, further comprising the addition of a wetting agent to the first aqueous acid to improve contact between the first aqueous acid and said materials.
12. The cleaning process of claim 2, further comprising the addition of a wetting agent to the aqueous acid to improve contact between the aqueous acid and said materials.
13. The cleaning process of claim 3, wherein the first aqueous acid and the second aqueous acid are organic acids derived from a group of organic acids comprising sulfamic acid, acetic acid, hydroxyacetic acid and citric acid, and further wherein the first aqueous acid and the second aqueous acid have a concentration between 0.0% by wt. and 15% by wt.
14. The cleaning process of claim 1, wherein said first predetermined temperature is between 20°C and 95°C.
15. The cleaning process of claim 2, wherein the first and second predetermined temperatures are between 20°C and 95°C.
16. The cleaning process of claim 2, wherein said first predetermined time and said second predetermined time are between 0.1 hours and 0.5 hours.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US85719806P | 2006-11-07 | 2006-11-07 | |
| US60/857,198 | 2006-11-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2608790A1 true CA2608790A1 (en) | 2008-05-07 |
Family
ID=39367207
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2608790 Abandoned CA2608790A1 (en) | 2006-11-07 | 2007-10-24 | Cleaning process for impaired membranes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2608790A1 (en) |
-
2007
- 2007-10-24 CA CA 2608790 patent/CA2608790A1/en not_active Abandoned
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