WO2014033370A1 - A method of filtering sludges - Google Patents

A method of filtering sludges Download PDF

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Publication number
WO2014033370A1
WO2014033370A1 PCT/FI2013/050842 FI2013050842W WO2014033370A1 WO 2014033370 A1 WO2014033370 A1 WO 2014033370A1 FI 2013050842 W FI2013050842 W FI 2013050842W WO 2014033370 A1 WO2014033370 A1 WO 2014033370A1
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WO
WIPO (PCT)
Prior art keywords
sludge
foam
filtering
solid material
filtering unit
Prior art date
Application number
PCT/FI2013/050842
Other languages
French (fr)
Inventor
Karita Kinnunen
Tuomo Hjelt
Jani LEHMONEN
Pentti Pirkonen
Hannu Mursunen
Original Assignee
Teknologian Tutkimuskeskus Vtt
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 Teknologian Tutkimuskeskus Vtt filed Critical Teknologian Tutkimuskeskus Vtt
Publication of WO2014033370A1 publication Critical patent/WO2014033370A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D37/00—Processes of filtration
    • B01D37/02—Precoating the filter medium; Addition of filter aids to the liquid being filtered
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D33/00—Filters with filtering elements which move during the filtering operation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D37/00—Processes of filtration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D37/00—Processes of filtration
    • B01D37/03—Processes of filtration using flocculating agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/08—Subsequent treatment of concentrated product
    • B03D1/10—Removing adhering liquid from separated materials
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
    • C02F11/147—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using organic substances
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
    • C02F11/148—Combined use of inorganic and organic substances, being added in the same treatment step
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/10—Nature of the water, waste water, sewage or sludge to be treated from quarries or from mining activities
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/26—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof
    • C02F2103/28—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof from the paper or cellulose industry
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/04—Surfactants, used as part of a formulation or alone

Definitions

  • the present invention relates to the filtering of sludges.
  • the present invention especially relates to a method of enhancing the filtering of sludges consisting of solid material and a liquid phase, according to the preamble of Claim 1.
  • the sludge is fed to a filtering unit, which separates the liquid from the solids.
  • the present invention also relates to the use of foam, according to Claim 17.
  • Sludges which include inorganic or organic solids are generated, in; among others, chemical industry, paper and wood industry, during the purification of waste waters, and in mining industry.
  • Sludges often need to be concentrated, for example by filtering, to reduce the liquid phase, in order to facilitate transportation of the sludges and subsequent financially viable use of them/ Associated with filtering, the high water retention capacity of the solids in the sludges often generates a problem. Moreover, a layer which is poorly permeable by water is generated onto the surface of the filtrate cake which consists of fines. The filtrate cake may also crack during filtering. These phenomena lead to high energy costs, as the suction power decreases. In addition, the moisture content of the filtrate cake may vary, and the residual moisture may remain high.
  • Organic or inorganic auxiliary agents are commonly used in the filtering, either mixed into the sludge or in order to form a "precoat" layer on the surface of the filtrate cake, in order to prevent excessive compaction of the filtrate cake.
  • auxiliary agents are expensive and thus they must be recycled, which increases the filtering costs.
  • the purpose of the present invention is to eliminate at least some of the disadvantages associated with the known technology and to generate a new solution for filtering sludges.
  • the present invention is based on the idea that the filtering of sludges is enhanced with foam, specifically the sludge is treated with foam either before filtering or during filtering.
  • the foam is prepared separately, typically from water and a surface-active agent, for example by using compressed air.
  • the foam may be mixed into the sludge or applied onto the surface of the sludge suspension, depending on the type of filtering technique used.
  • the present invention thus provides usage of foam, which is prepared from a surface-active agent and air, to enhance the filtering of the sludge.
  • the method according to the present invention is mainly characterized by what is stated in the characterizing part of Claim 1.
  • foam can replace auxiliary agents and, at the same time, the consumption of energy required for suction is substantially reduced.
  • the foam, which is mixed into the sludge forms a passage for the liquid phase through the sludge layer to be filtered, in which case it is possible to efficiently reduce the negative impact of the fines on the dewatering and thereby increase the drainage rate.
  • the present invention enables an increase in the filtering capacity and/or a reduction in the residual moisture of the filtrate cake, and also a reduction in the variations in moisture. Case-specifically, it is possible to leave out thermal drying which is used to achieve adequate residual moisture. In addition, the amount of the dissolved and colloidal material in the filtrate is reduced. Furthermore, the method according to the present invention removes the steps required to recycle the lime.
  • the solution according to the present invention can be easily integrated into continuous processes.
  • sludges are treated, e.g. solid-liquid phase combinations, which are prepared for example by flotation or other separation methods.
  • filtering of such suspensions of sludge is enhanced, in which case the final result is a dry sludge cake and a clean or clear filtrate. In practice, even the smallest particles are retained in the filtrate cake.
  • One preferred embodiment is a use of foam in order to enhance the filtering of mining industry concentrates.
  • a method is generated to enhance the filtering of sludge which consists of solid material and a liquid phase.
  • the sludge which is led onto a filtering screen or a filtering fabric, is treated with foam which is formed from water or an aqueous solution and a surface-active agent or similar foaming agent.
  • the enhancing of flotation is previously known, and, specifically, solutions are described which are intended to maximize the efficient separation of particles from the liquid phase, which is dilute.
  • the sludge and the particles in the foam, which are separated from the sludge are scraped from the surface of the flotation basin in order to be treated in the following stages of the process.
  • air and the flotation chemicals are mixed directly into the sludge suspension, i.e. the foam is generated during the separation process.
  • a foam-assisted filtering is carried out.
  • the sludge which is formed from solid material and a liquid phase, is treated with foam in association with the filtering.
  • the foam is separately rendered to a suitable stiffness and then transferred into the sludge, either before the filtering or by feeding the foam onto the top of the sludge layer in the filter.
  • the foam retains the particles in the filtrate cake, the dry matter of the cake is increased and the water removal is accelerated.
  • the foam is mixed with the sludge prior to the sludge being fed to the filtering unit.
  • the sludge and the pre-prepared foam are mixed together to form a mixture.
  • This mixture of solids, which include foam, is led to the filtering unit, wherein the liquid is separated from the solids by using for example gravity or pressure.
  • foam forms from large pores a uniform route through the sludge layer to be filtered, in which case the water-removing effect of the fines material decreases.
  • foam is utilized in filtering the sludge by spreading the foam onto the surface of the sludge web.
  • foam layer which is spread for example onto the surface of the sludge that is fed onto the top of the filtering unit, forms a "cap" on the surface of the sludge being filtered, which prevents cracking of the filtrate cake, and the subsequent increase in suction energy, an increase of the residual moisture and an increase of the distribution of moisture in the filtrate cake.
  • the foam is brought to the filtering unit for example simultaneously with the sludge, or the sludge is first brought to the filtering unit, after which the foam is spread onto the surface of the sludge.
  • the solid material of the sludge is flocculated before the filtering, in order to facilitate the separation of the solid material.
  • inorganic flocculants such as aluminium or iron salt, or organic flocculants, in particular a synthetic or natural polymer, such as a polymer including acrylamide, acrylic acid or styrenesulphonic acid monomers, or a polysaccharide such as starch or cellulose, or a derivative thereof, are used in the flocculation.
  • the surface-active agent used for foaming may be anionic, cationic or non-ionic.
  • suitable surface-active agents are alkyl sulphonates, alkylbenzene sulphonates, such as products marketed under the trademark Tween®, and other commercial compounds, fatty acid soaps, lignosulphonates, sarcosinates, fatty acid amines, and polyoxyethylene alcohols and wood and plant extractives.
  • Tween® alkyl sulphonates
  • fatty acid soaps such as products marketed under the trademark Tween®
  • lignosulphonates such as products marketed under the trademark Tween®
  • sarcosinates such as fatty acid soaps, lignosulphonates, sarcosinates, fatty acid amines, and polyoxyethylene alcohols and wood and plant extractives.
  • foam stabilisers and solid surface-active agents such as CMC, gelatine, pectin, wood extractive substances and similar compounds.
  • the foam typically 0.01 to 10 %, in particular approximately 0.05 to 5 % of the material to be foamed, is used.
  • the foam can be produced in a foam generator, having a static mixer or a mixer which generates turbulence, or a combination thereof, i.e. by using a rotor-stator mixer.
  • Any gas can be used in the foaming, such as air, in particular compressed gases. In one embodiment, compressed air is used.
  • the generated foam is essentially stable during treatment and has a density in the range of 0.5 to 0.95 kg/1, especially 0.7 to 0.9 kg/1 (i.e., the gas/air content of the foam is approximately 50 to 95 % by volume, in particular 70 to 90 % by volume).
  • the average bubble size is in the range of 0.005 to 0.3 mm, in particular 0.01 to 0.1 mm.
  • the amount of the foam used can be freely selected, depending on the sludge to be treated.
  • the foam percentage of the sludge volume is 0.1 to 1000, in particular approximately 0.5 to 200, most suitably approximately 1 to 100 % by volume.
  • the filtering unit is for example a perforated film or filter fabric or filter screen.
  • the present method is applied in filtering carried out using a suction filter. In a more preferable embodiment, the method is applied in continuous suction filtering.
  • the present invention is suitable for use, among others, with such filters which are widely used for example in the mining industry and waste water purification plants. Suction filters are also used in the manufacture of fibre-based products, for example in the paper and cardboard industry.
  • the solution according to the present invention is also suitable in industrial sectors which utilise foam in their production processes, such as chemical industry companies.
  • the sludge to be filtered includes inorganic or organic solids, such as fibre or particles sourced from biomaterial, or fines sourced from stone material.
  • the solids content of the sludge to be treated can vary within wide limits, depending on where the sludge comes from. In general, the solids content of the sludge is 1 mg to 100 g/1, for example approximately 10 mg to 10 g/1, but these are not absolute limits.
  • the sludge is generated by flotation or a similar separation method.
  • a drier filtrate cake is advantageous for sludge transport and further processing.
  • a drier filtrate cake needs less additional fuel, and, on the other hand, a reduced moisture content of the fuel improves the efficiency of the boiler :
  • a change of one percentage unit in the boiler efficiency of a 400 MWth boiler leads to the need for ⁇ 40 GWh more or, correspondingly, less fuel (equivalent to € 500 000 per year).
  • foam may also affect the need for flocculation chemicals; it is possible to reduce the consumption of them, in which case an approximately 1 kg/tDS reduction of chemical consumption corresponds to € 3 to 4/tDS savings.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Hydrology & Water Resources (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Dispersion Chemistry (AREA)
  • Treatment Of Sludge (AREA)

Abstract

A method of filtering a sludge, which consists of solid material and a liquid phase. In the method, the sludge is fed to a filtering unit, such as a suction filter, with which the solid material is separated from the liquid. According to the present invention, the sludge is treated with foam in association with the filtering, for example by mixing a pre-prepared foam into the sludge or by spreading a foam layer onto the surface of the filtrate cake. By the present invention, it is possible to increase the filtering capacity and to reduce the residual moisture of the filtrate cake and the moisture variations in the filtrate cake. It is also possible to leave out thermal drying which is used to achieve the desired residual moisture. In addition, the amount of dissolved and colloidal substance in the filtrate is reduced.

Description

A method of filtering sludges
The present invention relates to the filtering of sludges. The present invention especially relates to a method of enhancing the filtering of sludges consisting of solid material and a liquid phase, according to the preamble of Claim 1.
In such method, the sludge is fed to a filtering unit, which separates the liquid from the solids.
The present invention also relates to the use of foam, according to Claim 17.
Sludges which include inorganic or organic solids are generated, in; among others, chemical industry, paper and wood industry, during the purification of waste waters, and in mining industry.
Sludges often need to be concentrated, for example by filtering, to reduce the liquid phase, in order to facilitate transportation of the sludges and subsequent financially viable use of them/ Associated with filtering, the high water retention capacity of the solids in the sludges often generates a problem. Moreover, a layer which is poorly permeable by water is generated onto the surface of the filtrate cake which consists of fines. The filtrate cake may also crack during filtering. These phenomena lead to high energy costs, as the suction power decreases. In addition, the moisture content of the filtrate cake may vary, and the residual moisture may remain high. Organic or inorganic auxiliary agents are commonly used in the filtering, either mixed into the sludge or in order to form a "precoat" layer on the surface of the filtrate cake, in order to prevent excessive compaction of the filtrate cake. During the filtering of concentrations, for example in the mining industry, attempts are made to prevent cracking of the filtrate cake by using liquid materials (lime), which are pumped onto the surface of the filtrate layer. Auxiliary agents are expensive and thus they must be recycled, which increases the filtering costs.
The purpose of the present invention is to eliminate at least some of the disadvantages associated with the known technology and to generate a new solution for filtering sludges. The present invention is based on the idea that the filtering of sludges is enhanced with foam, specifically the sludge is treated with foam either before filtering or during filtering.
The foam is prepared separately, typically from water and a surface-active agent, for example by using compressed air. The foam may be mixed into the sludge or applied onto the surface of the sludge suspension, depending on the type of filtering technique used.
The present invention thus provides usage of foam, which is prepared from a surface-active agent and air, to enhance the filtering of the sludge.
More specifically, the method according to the present invention is mainly characterized by what is stated in the characterizing part of Claim 1.
The usage according to the present invention, in turn, is characterized by what is stated in Claim 17.
Considerable advantages are achieved with the present invention. Thus, in many cases, foam can replace auxiliary agents and, at the same time, the consumption of energy required for suction is substantially reduced. The foam, which is mixed into the sludge forms a passage for the liquid phase through the sludge layer to be filtered, in which case it is possible to efficiently reduce the negative impact of the fines on the dewatering and thereby increase the drainage rate.
The present invention enables an increase in the filtering capacity and/or a reduction in the residual moisture of the filtrate cake, and also a reduction in the variations in moisture. Case-specifically, it is possible to leave out thermal drying which is used to achieve adequate residual moisture. In addition, the amount of the dissolved and colloidal material in the filtrate is reduced. Furthermore, the method according to the present invention removes the steps required to recycle the lime.
The solution according to the present invention can be easily integrated into continuous processes. In the present invention, sludges are treated, e.g. solid-liquid phase combinations, which are prepared for example by flotation or other separation methods. In the present technology, filtering of such suspensions of sludge is enhanced, in which case the final result is a dry sludge cake and a clean or clear filtrate. In practice, even the smallest particles are retained in the filtrate cake.
One preferred embodiment is a use of foam in order to enhance the filtering of mining industry concentrates.
In the following, the present invention is examined more closely with the help of a detailed description.
As described above, in the present invention a method is generated to enhance the filtering of sludge which consists of solid material and a liquid phase. The sludge, which is led onto a filtering screen or a filtering fabric, is treated with foam which is formed from water or an aqueous solution and a surface-active agent or similar foaming agent.
The enhancing of flotation is previously known, and, specifically, solutions are described which are intended to maximize the efficient separation of particles from the liquid phase, which is dilute. In the flotation, the sludge and the particles in the foam, which are separated from the sludge, are scraped from the surface of the flotation basin in order to be treated in the following stages of the process. In the flotation, air and the flotation chemicals are mixed directly into the sludge suspension, i.e. the foam is generated during the separation process. In the present invention, however, a foam-assisted filtering is carried out.
In the present solution, the sludge, which is formed from solid material and a liquid phase, is treated with foam in association with the filtering. The foam is separately rendered to a suitable stiffness and then transferred into the sludge, either before the filtering or by feeding the foam onto the top of the sludge layer in the filter.
In the present solution, the foam retains the particles in the filtrate cake, the dry matter of the cake is increased and the water removal is accelerated. Preferably, the foam is mixed with the sludge prior to the sludge being fed to the filtering unit. In this case, the sludge and the pre-prepared foam are mixed together to form a mixture. This mixture of solids, which include foam, is led to the filtering unit, wherein the liquid is separated from the solids by using for example gravity or pressure.
In this first embodiment of the present invention, foam forms from large pores a uniform route through the sludge layer to be filtered, in which case the water-removing effect of the fines material decreases. In another embodiment, foam is utilized in filtering the sludge by spreading the foam onto the surface of the sludge web. Such a foam layer, which is spread for example onto the surface of the sludge that is fed onto the top of the filtering unit, forms a "cap" on the surface of the sludge being filtered, which prevents cracking of the filtrate cake, and the subsequent increase in suction energy, an increase of the residual moisture and an increase of the distribution of moisture in the filtrate cake.
In this embodiment, the foam is brought to the filtering unit for example simultaneously with the sludge, or the sludge is first brought to the filtering unit, after which the foam is spread onto the surface of the sludge.
It is also possible to directly foam the sludge, for example by mixing surface-active agents into it, and then introducing gas into it, possibly by simultaneously stirring the sludge, in order to generate a foam. In all the above embodiments, most suitably the solid material of the sludge is flocculated before the filtering, in order to facilitate the separation of the solid material. For example inorganic flocculants, such as aluminium or iron salt, or organic flocculants, in particular a synthetic or natural polymer, such as a polymer including acrylamide, acrylic acid or styrenesulphonic acid monomers, or a polysaccharide such as starch or cellulose, or a derivative thereof, are used in the flocculation.
The surface-active agent used for foaming may be anionic, cationic or non-ionic. Examples of suitable surface-active agents are alkyl sulphonates, alkylbenzene sulphonates, such as products marketed under the trademark Tween®, and other commercial compounds, fatty acid soaps, lignosulphonates, sarcosinates, fatty acid amines, and polyoxyethylene alcohols and wood and plant extractives. Naturally, it is possible to use several foaming agents or a mixture of foaming agents. To generate and improve foam stability, it is possible to use foam stabilisers and solid surface-active agents, such as CMC, gelatine, pectin, wood extractive substances and similar compounds.
To generate the foam, typically 0.01 to 10 %, in particular approximately 0.05 to 5 % of the material to be foamed, is used.
The foam can be produced in a foam generator, having a static mixer or a mixer which generates turbulence, or a combination thereof, i.e. by using a rotor-stator mixer. Any gas can be used in the foaming, such as air, in particular compressed gases. In one embodiment, compressed air is used.
Preferably, the generated foam is essentially stable during treatment and has a density in the range of 0.5 to 0.95 kg/1, especially 0.7 to 0.9 kg/1 (i.e., the gas/air content of the foam is approximately 50 to 95 % by volume, in particular 70 to 90 % by volume). The average bubble size is in the range of 0.005 to 0.3 mm, in particular 0.01 to 0.1 mm.
The amount of the foam used can be freely selected, depending on the sludge to be treated. In particular, the foam percentage of the sludge volume is 0.1 to 1000, in particular approximately 0.5 to 200, most suitably approximately 1 to 100 % by volume.
The filtering unit is for example a perforated film or filter fabric or filter screen.
In a preferred embodiment, the present method is applied in filtering carried out using a suction filter. In a more preferable embodiment, the method is applied in continuous suction filtering.
The present invention is suitable for use, among others, with such filters which are widely used for example in the mining industry and waste water purification plants. Suction filters are also used in the manufacture of fibre-based products, for example in the paper and cardboard industry. The solution according to the present invention is also suitable in industrial sectors which utilise foam in their production processes, such as chemical industry companies. The sludge to be filtered includes inorganic or organic solids, such as fibre or particles sourced from biomaterial, or fines sourced from stone material.
The solids content of the sludge to be treated can vary within wide limits, depending on where the sludge comes from. In general, the solids content of the sludge is 1 mg to 100 g/1, for example approximately 10 mg to 10 g/1, but these are not absolute limits.
As mentioned above, in one embodiment, the sludge is generated by flotation or a similar separation method. Example:
Based on preliminary tests, the use of foam has been found to enhance the drainage process: 1) by reducing the drainage time, 2) by generating a drier filtrate cake, and 3) by enhancing adhesion of dissolved and colloidal materials to the filtrate cake.
Shortening of the drainage time allows sludge treatment capacity to be raised, and on the other hand allows the use of shorter filtering equipment, i.e. it reduces investment costs. A drier filtrate cake is advantageous for sludge transport and further processing. When the sludge which is treated as described is burned, a drier filtrate cake needs less additional fuel, and, on the other hand, a reduced moisture content of the fuel improves the efficiency of the boiler :
A change of one percentage unit in the boiler efficiency of a 400 MWth boiler leads to the need for ~ 40 GWh more or, correspondingly, less fuel (equivalent to€ 500 000 per year).
Use of foam may also affect the need for flocculation chemicals; it is possible to reduce the consumption of them, in which case an approximately 1 kg/tDS reduction of chemical consumption corresponds to€ 3 to 4/tDS savings.

Claims

Claims:
1. A method of filtering a sludge, which consists of solid material and a liquid phase, according to which method the sludge is fed to a filtering unit, which is used to separate the solid material from the liquid, characterized in that the sludge is treated with foam in association with the filtering.
2. The method according to Claim 1, characterized in that the foam is mixed with the sludge before the sludge is fed to the filtering unit.
3. A method according to Claim 1 or 2, characterized in that
- the sludge and the pre-prepared foam are mixed together, or the sludge is foamed, and
- the foamed mixture thus generated is led to the filtering unit, where the solid material and the liquid are separated from each other.
4. A method according to any of the Claims 1 to 3, characterized in that the foam is spread onto the surface of the sludge in association with the filtering.
5. The method according to Claim 4, characterized in that the foam is spread onto the surface of the sludge in the filtering unit.
6. The method according to Claim 5, characterized in that the foam is brought to the filtering unit simultaneously with the sludge, or the sludge is first brought to the filtering unit, after which the foam is spread onto the surface of the sludge.
7. A method according to any of the preceding claims, characterized in that the solid material of the sludge is flocculated before the filtering, in order to facilitate the separation of the solid material from the liquid.
8. The method according to Claim 7, characterized in that an inorganic flocculant, such as aluminium or iron salt, or an organic flocculant, in particular a synthetic or natural polymer, such as a polymer which includes acrylamide, acrylic acid or styrenesulphonic acid monomers, or a polysaccharide or a derivative thereof, is used in the flocculation.
9. A method according to any of the preceding claims, characterized in that the foam is generated from water or an aqueous solution and one or more surface-active agents.
10. The method according to Claim 9, characterized in that the surface-active agent used is alkyl sulphonate, alkylbenzene sulphonate, fatty acid soap, lignosulphonate, sarcosinate, fatty acid amine, or polyoxyethylene alcohols or such.
11. A method according to any of the preceding claims, characterized in that the foam is generated from a mixture of water or an aqueous solution and a surface-active agent or surface-active agents, by feeding a compressed gas into this mixture and possibly by stirring the mixture, in particular by feeding the compressed gas and simultaneously stirring the mixture.
12 A method according to any of the Claims 9 to 11, characterized in that the foam is generated in a foam generator, having a static mixer or a mixer which creates turbulence.
13. A method according to any of the preceding claims, characterized in that the foam percentage of the sludge volume is 0.1 to 1000, in particular approximately 0.5 to 200, most suitably approximately 1 to 100 % by volume.
14. A method according to any of the preceding claims, characterized in that the filtering unit is a perforated film or a filter fabric or a filter screen.
15. A method according to any of the preceding claims, characterized in that the filtering is carried out as suction filtering.
16. A method according to any of the preceding claims, characterized in that the sludge to be filtered includes an inorganic or organic solid material, such as fibre or particles sourced from biomaterial, or fines material sourced from stone material.
17. Use of foam, which is produced from water and a surface-active agent, for enhancing the filtering of sludge.
18. The use according to Claim 17, characterized in that the foam is mixed into the sludge, or the foam is spread onto the surface of the sludge suspension, either before or in association with the filtering.
19. The use according to Claim 17 or 18 in waste water purification plants or,
correspondingly, in filtering of concentrates in the mining industry.
PCT/FI2013/050842 2012-08-31 2013-09-02 A method of filtering sludges WO2014033370A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3053761A (en) * 1957-05-22 1962-09-11 Horace A Bradt Process for separation of liquid from liquid-solid mixtures of fine solid particle size
US4244813A (en) * 1979-08-08 1981-01-13 Bethlehem Steel Corporation Method of increasing fine coal filtration efficiency
JPS56130203A (en) * 1980-03-18 1981-10-13 Dowa Mining Co Ltd Dehydration accelerating method in vacuum filter
WO2011123922A1 (en) * 2010-04-09 2011-10-13 David Bromley Nanoflotation

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3053761A (en) * 1957-05-22 1962-09-11 Horace A Bradt Process for separation of liquid from liquid-solid mixtures of fine solid particle size
US4244813A (en) * 1979-08-08 1981-01-13 Bethlehem Steel Corporation Method of increasing fine coal filtration efficiency
JPS56130203A (en) * 1980-03-18 1981-10-13 Dowa Mining Co Ltd Dehydration accelerating method in vacuum filter
WO2011123922A1 (en) * 2010-04-09 2011-10-13 David Bromley Nanoflotation

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