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WO2009040521A1 - Power storage system wherein the electrolyte comprises acid mine drainage - Google Patents

Power storage system wherein the electrolyte comprises acid mine drainage Download PDF

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Publication number
WO2009040521A1
WO2009040521A1 PCT/GB2008/003231 GB2008003231W WO2009040521A1 WO 2009040521 A1 WO2009040521 A1 WO 2009040521A1 GB 2008003231 W GB2008003231 W GB 2008003231W WO 2009040521 A1 WO2009040521 A1 WO 2009040521A1
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WO
WIPO (PCT)
Prior art keywords
flow battery
amd
battery system
electrolyte
electrodes
Prior art date
Application number
PCT/GB2008/003231
Other languages
French (fr)
Inventor
Anthony John Maxwell
Original Assignee
Anthony John Maxwell
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 Anthony John Maxwell filed Critical Anthony John Maxwell
Publication of WO2009040521A1 publication Critical patent/WO2009040521A1/en

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01GCAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/10Multiple hybrid or EDL capacitors, e.g. arrays or modules
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01GCAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22Electrodes
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01GCAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/54Electrolytes
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/36Accumulators not provided for in groups H01M10/05-H01M10/34
    • H01M10/365Zinc-halogen accumulators
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00Hybrid cells; Manufacture thereof
    • H01M12/08Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • H01M12/085Zinc-halogen cells or batteries
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/46Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/46104Devices therefor; Their operating or servicing
    • C02F1/46109Electrodes
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/46Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/469Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
    • C02F1/4691Capacitive deionisation
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/10Nature of the water, waste water, sewage or sludge to be treated from quarries or from mining activities
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00Specific treatment goals
    • C02F2303/24Separation of coarse particles, e.g. by using sieves or screens
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13Energy storage using capacitors

Definitions

  • the present invention relates to the use of polluting acid mine drainage (AMD) and acid rock drainage (ARD) from the in situ pit lakes, mine shafts and surface streams existing on abandoned mine sites as an electrolyte for large scale electrical energy storage.
  • AMD acid mine drainage
  • ARD acid rock drainage
  • the present invention overcomes problems created by the relatively poor energy-to-electrolyte volume ratio evident in many commercial applications, i.e., the storage and handling of large volumes of corrosive liquid electrolytes necessary to retain multi MWs of electrical energy.
  • a flow battery is a form of battery in which electrolyte containing one or more dissolved electroactive species is flowed through a power cell/reactor and in which chemical energy is converted to electricity. Additional electrolyte is stored externally, generally in tanks, and is usually pumped through the cell (or cells) of the reactor. Gravity flow systems are also known.
  • the flow battery may be contrasted with a fuel cell, where the electrolyte remains at all times within the reactor (e.g., in the form of an ion-exchange membrane).
  • a fuel cell only the electroactive substances, which are non-conducting (e.g., hydrogen, methanol, etc.) flow into the reactor.
  • the electrolyte generally the majority
  • the charged electrolyte is circulated through the electrode collectors. No external fuel source is necessary apart from to charge up the electrolyte.
  • Flow batteries can also be distinguished from fuel cells by the fact that the chemical reaction involved is often reversible, i.e., they are generally of the secondary battery type and so they can be re-charged without replacing the electroactive material.
  • Various classes of flow battery exist including the redox (reduction-oxidation) flow battery, in which all electroactive components are dissolved in the electrolyte. If one or more electroactive components are deposited as a solid layer, the system is a hybrid flow battery.
  • the discharge time of a redox flow battery at full power can be varied, as required, from several minutes to many days, depending on the electrolyte volume.
  • Flow batteries known in the art are generally two electrolyte systems in which two electrolytes are pumped through a cell.
  • a zinc-bromine battery is a known example of a flow battery and is based on the reaction between zinc and bromine.
  • the battery comprises a zinc negative electrode and a bromine positive electrode separated by a microporous separator.
  • An aqueous solution of zinc bromide is circulated through the two compartments of the cell from two separate reservoirs.
  • the other electrolyte stream in contact with the positive electrode contains bromine.
  • the bromine storage medium is immiscible with the aqueous solution containing zinc bromide.
  • AMD and ARD result from metal sulphide minerals, particularly pyrite, coming into contact with water and oxygen.
  • the resulting oxidation causes increased mobility of heavy metals, carbon and other harmful particulate matter.
  • this conductive electrolytic mixture carries a negligible electrical charge.
  • pyrite oxidizes to form iron hydroxide, sulphate and hydrogen irons.
  • the liberation of hydrogen ions causes acidity in water passing over the rock. Every mole of pyrite yields four moles of acidity.
  • AMD can be characterised by low pH and increased acidity, elevated heavy metals, sulphate and total dissolved solids (TDS).
  • TDS total dissolved solids
  • the AMD is harmful to the environment.
  • Much effort has been put into controlling AMD, including waste segregation, adding basic calcareous material such as limestone to reduce acidity, and capping mine adits and ground surface fissures to prevent uncontrolled discharges.
  • the AMD is collected in pit lakes and treated using active or passive treatment systems, including using reed beds designed to remove contaminants.
  • AMD continues to be a problem, in both active and abandoned mines throughout the world.
  • the Present Invention By exploiting the capacity of different oxidation states in the metallic charged particulate matter of AMD or ARD, almost unlimited electricity storage capacity becomes available. Because a system's electrical energy retention capacity can be increased as the "energy function" is dete ⁇ nined by the volume of electrolyte, the cost per kWh decreases as the energy capacity increases.
  • the present invention accordingly relates to a flow battery system wherein the electrolyte comprises acid mine drainage and/or acid rock drainage from mine sites.
  • the AMD is pumped directly from the mine into containers, each of which forms a battery cell.
  • the "power function" is determined by the size and number of cells, adequate land area is usually available at abandoned or orphan mine sites to install meaningful numbers of large size interconnected flow cell structures housed in transportable modules, for example twelve meter transport containers.
  • Each container is a cell.
  • the cells can be fabricated to a preferred size.
  • the cells can be lined with or be made of fibreglass to prevent unwanted reaction of electrolyte with the cell walls which could occur if the cells are metal containers.
  • the cells have electrodes suspended within them.
  • the electrodes can be of a metal known in the art, e.g., copper, zinc or lead.
  • the electrodes are separated by a microporous polymer membrane.
  • Preferred electrode systems are power cell electrode collectors which are, in effect, electrical double layer capacitor constructions. This means that in addition to electrical energy being stored in the electrolyte, the electrical double layer capacitor electrode configuration will also store electrical energy. As the electrode plate surfaces are so large, storage will be in multi farads, not in micro- or pico- farads as found in most electrical double layer capacitors supplied in conventional tubular configurations.
  • the electrodes used may preferably comprise a carbon/metal mixture compressed to form a solid electrode.
  • the metal is preferably dried particulate metal from mine water used as the electrolyte.
  • the electrode plate collectors are constructed of dried AMD/ARD particulate matter which may have a heavy metallic content, mixed with activated charcoal and compressed into plates to form porous conductive electrodes, each approximately 0.5 mm - 0.7 mm thick.
  • Each electrode plate charge collector will be separated by an approximately 1.0 nm ion permeable polymer dielectric membrane.
  • a number of alternating negative and positive cells, e.g., from 7 - 10, may be assembled into one collector electrode stack. Cell stack modules can then be connected in parallel or series to meet energy requirements.
  • the electrolyte flows into and through the stack modules. As the electrolyte passes over the electrode surfaces, charged particles are stimulated to flow when terminal electrical connectors are connected to an external load. The differing oxidation and reduction states cause an electric current to flow.
  • the preferred double layer capacitors enable instant power to be drawn from the system. Effectively the charged electrolyte flowing over and through a cell forms one electrode, the compressed metal/carbon the other. The positive and negative poles of the charged electrolyte are distributed relative to each other over a very short distance due to the thin dielectric membranes. An external electric field applied during charging creates the electrical double layer at the charcoal/metal/membrane separator/electrode and electrolyte interfaces.
  • the containers may be preferable to earth the containers to ground, e.g. by copper rods connected to the metal and then driven into the ground.
  • the pit lakes themselves which are used to collect the AMD/ARD may be used as large scale giant flow cell batteries.
  • the system may be recharged by mechanically exchanging electrolyte with recharged solution.
  • the electrolyte is either pumped or gravity fed to the array of external battery cells, optionally through filters if required.
  • the electrolyte passes through the cells and is returned to the reservoirs or pit lakes. If it is preferred to circulate positive and negative electrolytes, then one electrolyte from one pit lake can be chemically doped.
  • Figure 1 is a schematic illustration of a flow battery system.
  • Figure 2 is a schematic illustration of a complete system according to the present invention.
  • Figure 3 is a schematic illustration of a double layer capacitor.
  • Figure 4 is a schematic illustration of the system in use in a settlement lake.
  • Figure 5 is a schematic section through an alternative power panel for use in a pit lake system.
  • FIG. 1 shows a schematic representation of a flow battery system as known in the art. Electrolyte is contained within tanks and is pumped through the system. There are two electrodes separated by an ion exchange membrane. Connection of terminals to each of the electrodes provides power. Electrolyte can be pumped around the system in continuous flow.
  • FIG 2 shows one application of the flow battery system to the present invention.
  • Acid Mine Drainage is stored in pit lakes. These are the “electrolyte tanks” shown in Figure 1.
  • the AMD is pumped from the lakes, optionally through a filter to remove any large particles which might either block the pump or block the battery cell stack.
  • Two filters are preferably included, one before the pump and one after the pump. If there is sufficient gravity between the pit lakes and the battery cell system, a flow can be accomplished by gravity feed.
  • AMD flows into and through the battery cell stacks which are housed in transport containers.
  • the transport containers are preferably lined with fibreglass.
  • One or more battery cell stacks can be connected in series or parallel. AMD will flow into the multiple cell stacks.
  • the cell stacks comprise a number of electrode pairs. Direct Current (DC) power can be drawn from the electrodes. As required, the DC current can be converted to Alternating Current (AC) by means of an alternator.
  • DC Direct Current
  • AC Alternating Current
  • the AMD Once the AMD has flowed through the battery cell stacks, it is re-circulated to the pit lakes.
  • the AMD can be recharged in the pit lakes, e.g., by electrical input from a wind turbine generator. As necessary, the AMD can be doped when in the pit lakes.
  • FIG 3 is a schematic representation of a double layer capacitor.
  • the electrodes can be made of a compressed mixture of porous charcoal and metal extracted from the Acid Mine Drainage. Each electrode is backed with a collector. The electrode pairs are separated by a thin membrane/separator. A number of the electrodes are connected together to form a battery cell stack.
  • the lake bed will be coated with a sheet which forms a double layer capacitor.
  • Settlement pit lakes usually have a cement faced block or concrete wall bed. This base is then usually lined with a polymer sheet which fo ⁇ ns a wateiproof membrane.
  • the liners are usually ethylene- propylene-diene (EDPE) or butyl rubber and about 1 - 2 mm thick. To these liners can be laminated material to form the double layer capacitor.
  • the electric double layer capacitor is a static and passive electrical energy storage device. EDLCs hold their stored electrical charges in an ionic layer that fo ⁇ ns at the interface between each of the two electrodes and a common electrolyte. Power densities are typically ten times that of most batteries.
  • Preferred EDLCs are made of activated carbon impregnated felts or non-woven polymers, such as may be obtained from Purification
  • an EDLC based on carbon nanotubes is particularly preferred.
  • a matrix of vertically aligned carbon nanotubes can be used as an EDLC to provide very high power density. Examples of carbon nanotubes enhanced EDLCs have been discussed by Riccardo Signorelli of MIT, USA.
  • the base metal foil acts as one electrode which is separated from the flowing AMD by a thin ion permeable membrane separator.
  • This membrane can carry the ELDC.
  • the pit wall will have the following layers:
  • Ion permeable membrane such as woven polymer 4
  • Metal foil electrode such as aluminium
  • a number of prefabricated EDL capacitor strips may be connected in series to increase the emf, or in parallel to increase the capacitance.
  • the AMD can be charged via chargers suspended over the lake on gantries.
  • the chargers are electrodes dipping into the AMD electrolyte, which may be formed of carbon coated or impregnated metal foil or conductive polymer mesh.
  • the charge can be provided by any means such as solar power, the electric grid or wind turbines, etc.
  • these positive electrodes may have the same sandwich construction as the electrode on the lake wall.
  • the suspended block electrodes may be, for example, 2m x Im in size.
  • the positive electrode provides additional charge to the electrolyte, which is stored in the double capacitor.
  • the system is switched so that power can be drawn off from the electrodes, e.g. the electrodes on the lake wall.
  • a stored power supply can be taken from the flow battery, and used to supply power to e.g. the mine pumps or even to the electricity grid.
  • the power output from the container or lake can be drawn off through a metal terminal attached to either the metal foil lining the lake or the charging plate suspended in the electrolytic AMD.
  • FIG 4 shows a schematic version of the flow battery system as applied to a pit lake.
  • a pit lake 41 is made from a concrete wall, optionally surrounded or sunk into the soil.
  • the lake is filled with Acid Mine Drainage (AMD).
  • One or more electrodes 42 are suspended from a gantry 43.
  • the electrodes are connected to a power charging / discharging terminal 44.
  • the terminal 44 may be connected to an array of solar panels, a wind turbine or the electricity grid.
  • the lake wall is coated with the laminate sandwich and electric double layer capacitor (45) as described above. This laminate covers the whole wall of the lake and acts as a negative anode. When the lake has been charged, power is stored in the EDLC. This can be discharged from the system through the terminal 44.
  • FIG. 5 shows an example of a power panel, 42, as described above.
  • This shows the sandwich system used to form the electrode.
  • Aluminium foil 51 has laminated to it a woven polymer 52 which is impregnated with activated carbon.
  • the layer of the sandwich is separated from the next layer by a porous membrane 53.
  • the two layers of the sandwich are then connected together to form a block electrode
  • a small cylindriform aluminium metal container was lined with a micro-epoxy resin coating and filled with acid mine drainage water taken from The Bowden Close mine near Newcastle, United Kingdom.
  • the AMD was tested and found to have a pH of 5.8 and conductivity estimated at approximately 1950 ⁇ S/cm.
  • the container constitutes the anode electrode.
  • the container was then connected to the negative terminal of a small 0.5 vdc solar panel.
  • Active carbon powder was laminated to a piece of aluminium foil (1 10mm x 70 mm) and the foil connected to the positive terminal of the small solar panel.
  • the laminated carbon coated Aluminium foil was then immersed in the AMD in the container to form the cathode (positive) collector electrode.
  • the assembly was placed in sunlight for 7 hours to charge the AMD. After the 7 hours had elapsed a digital voltmeter o/c reading indicated 0.760 vdc between the electrodes
  • the o/c voltage charge remaining in the container of AMD 12 hours later was 0.650 vdc.
  • the charge was restarted and after a further 6 hours of exposure to sunlight, the o/c vdc was 1.256 vdc.
  • the available electrical energy derived from polluting acid mine or acid rock drainage from abandoned or orphan mining sites, following power disconnection of a mine from a national grid provides a cost effective solution for resumption where required, of continuous mine de- watering.
  • the UK Coal Authority spends over £ million pounds each year on removing water from old abandoned mine systems.
  • the electricity derived from the in-situ systems of the present invention can considerably reduce or even eliminate the costs by providing an electricity power source derived from the waste mine water itself.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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  • Electric Double-Layer Capacitors Or The Like (AREA)

Abstract

The present invention relates to the use of polluting Acid Mine Drainage (AMD) and Acid Rock Drainage (ARD) from pit lakes, mine shafts and surface streams existing on abandoned mine sites have electrolyte for use in flow battery systems. The flow battery systems may preferably include double layer capacitors to store the charge prior to discharge.

Description

MINE POWER STORAGE
Field of Invention The present invention relates to the use of polluting acid mine drainage (AMD) and acid rock drainage (ARD) from the in situ pit lakes, mine shafts and surface streams existing on abandoned mine sites as an electrolyte for large scale electrical energy storage.
Utilizing a variation of redox flow battery technology, in which electrical energy is stored in charged electrolytes, the present invention overcomes problems created by the relatively poor energy-to-electrolyte volume ratio evident in many commercial applications, i.e., the storage and handling of large volumes of corrosive liquid electrolytes necessary to retain multi MWs of electrical energy.
Prior Art and Background
A flow battery is a form of battery in which electrolyte containing one or more dissolved electroactive species is flowed through a power cell/reactor and in which chemical energy is converted to electricity. Additional electrolyte is stored externally, generally in tanks, and is usually pumped through the cell (or cells) of the reactor. Gravity flow systems are also known.
The flow battery may be contrasted with a fuel cell, where the electrolyte remains at all times within the reactor (e.g., in the form of an ion-exchange membrane). In a fuel cell only the electroactive substances, which are non-conducting (e.g., hydrogen, methanol, etc.) flow into the reactor. This is in contrast to a flow battery in which at least some of the electrolyte (generally the majority) is flowed through the reactor. In a flow cell battery the charged electrolyte is circulated through the electrode collectors. No external fuel source is necessary apart from to charge up the electrolyte. Flow batteries can also be distinguished from fuel cells by the fact that the chemical reaction involved is often reversible, i.e., they are generally of the secondary battery type and so they can be re-charged without replacing the electroactive material. Various classes of flow battery exist, including the redox (reduction-oxidation) flow battery, in which all electroactive components are dissolved in the electrolyte. If one or more electroactive components are deposited as a solid layer, the system is a hybrid flow battery. The discharge time of a redox flow battery at full power can be varied, as required, from several minutes to many days, depending on the electrolyte volume.
Flow batteries known in the art are generally two electrolyte systems in which two electrolytes are pumped through a cell. A zinc-bromine battery is a known example of a flow battery and is based on the reaction between zinc and bromine. The battery comprises a zinc negative electrode and a bromine positive electrode separated by a microporous separator. An aqueous solution of zinc bromide is circulated through the two compartments of the cell from two separate reservoirs. The other electrolyte stream in contact with the positive electrode contains bromine. The bromine storage medium is immiscible with the aqueous solution containing zinc bromide. When the zinc-bromine battery is completely discharged, all the metal zinc plated on the negative electrodes is dissolved in the electrolyte and again produced the next time the battery is charged. In the fully discharged state the zinc-bromine battery can be left indefinitely.
AMD and ARD result from metal sulphide minerals, particularly pyrite, coming into contact with water and oxygen. The resulting oxidation causes increased mobility of heavy metals, carbon and other harmful particulate matter. As metallic and carbon particulate matter are involved, this conductive electrolytic mixture carries a negligible electrical charge.
In the case of iron sulfide (pyrite/marcasite), the chemical reaction in the acid-generating process can be simplified to:
FeS2 + 15/4 02 + 7/2 H2O >» Fe(OH)3 +2SO4 + 4H In the presence of oxygen and water, pyrite oxidizes to form iron hydroxide, sulphate and hydrogen irons. The liberation of hydrogen ions causes acidity in water passing over the rock. Every mole of pyrite yields four moles of acidity.
AMD can be characterised by low pH and increased acidity, elevated heavy metals, sulphate and total dissolved solids (TDS). The AMD is harmful to the environment. Much effort has been put into controlling AMD, including waste segregation, adding basic calcareous material such as limestone to reduce acidity, and capping mine adits and ground surface fissures to prevent uncontrolled discharges. Most usually, the AMD is collected in pit lakes and treated using active or passive treatment systems, including using reed beds designed to remove contaminants. AMD continues to be a problem, in both active and abandoned mines throughout the world.
Further background to AMD/ARD can be found in the Environmental Protection Agency Seminar Publication no EPA/625/R-95/007 "Managing Environmental Problems at inactive and Abandoned Metals Mine Sites"
Cheng, Dempsey and Logan have published a paper discussing an approach to AMD treatment using fuel cell technologies to generate electricity. Using a microbial fuel cell, an AMD fuel cell was created which was capable of abiotic electricity generation. The work is discussed in Environ Sci. Technol. 2007, vol. 41 , 8149 -8153, published on the web on 19 October 2007.
The Present Invention By exploiting the capacity of different oxidation states in the metallic charged particulate matter of AMD or ARD, almost unlimited electricity storage capacity becomes available. Because a system's electrical energy retention capacity can be increased as the "energy function" is deteπnined by the volume of electrolyte, the cost per kWh decreases as the energy capacity increases. The present invention accordingly relates to a flow battery system wherein the electrolyte comprises acid mine drainage and/or acid rock drainage from mine sites.
Flow battery technology as described above, while not generally suitable for mobile applications, is ideally suited for mass energy storage on abandoned or orphan mine sites.
In one embodiment of the present invention, the AMD is pumped directly from the mine into containers, each of which forms a battery cell. As the "power function" is determined by the size and number of cells, adequate land area is usually available at abandoned or orphan mine sites to install meaningful numbers of large size interconnected flow cell structures housed in transportable modules, for example twelve meter transport containers. Each container is a cell. Alternatively, the cells can be fabricated to a preferred size.
The cells can be lined with or be made of fibreglass to prevent unwanted reaction of electrolyte with the cell walls which could occur if the cells are metal containers.
The cells have electrodes suspended within them. The electrodes can be of a metal known in the art, e.g., copper, zinc or lead. The electrodes are separated by a microporous polymer membrane.
Preferred electrode systems are power cell electrode collectors which are, in effect, electrical double layer capacitor constructions. This means that in addition to electrical energy being stored in the electrolyte, the electrical double layer capacitor electrode configuration will also store electrical energy. As the electrode plate surfaces are so large, storage will be in multi farads, not in micro- or pico- farads as found in most electrical double layer capacitors supplied in conventional tubular configurations.
The electrodes used, either in a conventional flow battery arrangement or in the double capacitor system, may preferably comprise a carbon/metal mixture compressed to form a solid electrode. The metal is preferably dried particulate metal from mine water used as the electrolyte.
Preferably the electrode plate collectors are constructed of dried AMD/ARD particulate matter which may have a heavy metallic content, mixed with activated charcoal and compressed into plates to form porous conductive electrodes, each approximately 0.5 mm - 0.7 mm thick. Each electrode plate charge collector will be separated by an approximately 1.0 nm ion permeable polymer dielectric membrane. A number of alternating negative and positive cells, e.g., from 7 - 10, may be assembled into one collector electrode stack. Cell stack modules can then be connected in parallel or series to meet energy requirements.
The electrolyte flows into and through the stack modules. As the electrolyte passes over the electrode surfaces, charged particles are stimulated to flow when terminal electrical connectors are connected to an external load. The differing oxidation and reduction states cause an electric current to flow.
The preferred double layer capacitors enable instant power to be drawn from the system. Effectively the charged electrolyte flowing over and through a cell forms one electrode, the compressed metal/carbon the other. The positive and negative poles of the charged electrolyte are distributed relative to each other over a very short distance due to the thin dielectric membranes. An external electric field applied during charging creates the electrical double layer at the charcoal/metal/membrane separator/electrode and electrolyte interfaces.
It is envisaged that numbers of flow battery modules can be factory fabricated, pre-assembled, installed and interconnected on abandoned mine sites to provide far greater storage capacity than is currently available from conventional lead acid battery storage installations.
It may be preferable to earth the containers to ground, e.g. by copper rods connected to the metal and then driven into the ground. In an alternative embodiment, the pit lakes themselves which are used to collect the AMD/ARD may be used as large scale giant flow cell batteries.
Pit lakes continually filled or filling with naturally charged particulate matter comprising AMD/ARD electrolytes may be re-charged from wind turbine generators, voltaic solar arrays, the national grid or from conventional battery electrolysis also installed on mine sites. This macro version of flow battery technology also presents opportunities for multi MW electrical energy storage for grid load levelling. The lakes can be lined with a double layer capacitor, the AMD itself forming the positive electrode. The flow cell part of the action is created by AMD / ARD moving over the capacitive sheet structure, either by natural current flow (due to temperature or level gradients) or by a small pump system. Power panel electrodes are suspended in the AMD / ARD. These can be semi-rigid laminated fabrications suspended from solar panels which also serve to charge the electrolyte.
In a yet further embodiment, the system may be recharged by mechanically exchanging electrolyte with recharged solution. The electrolyte is either pumped or gravity fed to the array of external battery cells, optionally through filters if required. The electrolyte passes through the cells and is returned to the reservoirs or pit lakes. If it is preferred to circulate positive and negative electrolytes, then one electrolyte from one pit lake can be chemically doped.
Figures
Figure 1 is a schematic illustration of a flow battery system.
Figure 2 is a schematic illustration of a complete system according to the present invention.
Figure 3 is a schematic illustration of a double layer capacitor.
Figure 4 is a schematic illustration of the system in use in a settlement lake.
Figure 5 is a schematic section through an alternative power panel for use in a pit lake system.
Detailed Description
Figure 1 shows a schematic representation of a flow battery system as known in the art. Electrolyte is contained within tanks and is pumped through the system. There are two electrodes separated by an ion exchange membrane. Connection of terminals to each of the electrodes provides power. Electrolyte can be pumped around the system in continuous flow.
Figure 2 shows one application of the flow battery system to the present invention. Acid Mine Drainage (AMD) is stored in pit lakes. These are the "electrolyte tanks" shown in Figure 1. The AMD is pumped from the lakes, optionally through a filter to remove any large particles which might either block the pump or block the battery cell stack. Two filters are preferably included, one before the pump and one after the pump. If there is sufficient gravity between the pit lakes and the battery cell system, a flow can be accomplished by gravity feed. AMD flows into and through the battery cell stacks which are housed in transport containers. The transport containers are preferably lined with fibreglass. One or more battery cell stacks can be connected in series or parallel. AMD will flow into the multiple cell stacks. The cell stacks comprise a number of electrode pairs. Direct Current (DC) power can be drawn from the electrodes. As required, the DC current can be converted to Alternating Current (AC) by means of an alternator.
Once the AMD has flowed through the battery cell stacks, it is re-circulated to the pit lakes. The AMD can be recharged in the pit lakes, e.g., by electrical input from a wind turbine generator. As necessary, the AMD can be doped when in the pit lakes.
Figure 3 is a schematic representation of a double layer capacitor. The electrodes can be made of a compressed mixture of porous charcoal and metal extracted from the Acid Mine Drainage. Each electrode is backed with a collector. The electrode pairs are separated by a thin membrane/separator. A number of the electrodes are connected together to form a battery cell stack.
In a system where the actual pit lake is used as the "container" for the battery, the lake bed will be coated with a sheet which forms a double layer capacitor. Settlement pit lakes usually have a cement faced block or concrete wall bed. This base is then usually lined with a polymer sheet which foπns a wateiproof membrane. The liners are usually ethylene- propylene-diene (EDPE) or butyl rubber and about 1 - 2 mm thick. To these liners can be laminated material to form the double layer capacitor.
The electric double layer capacitor (EDLC) is a static and passive electrical energy storage device. EDLCs hold their stored electrical charges in an ionic layer that foπns at the interface between each of the two electrodes and a common electrolyte. Power densities are typically ten times that of most batteries. Preferred EDLCs are made of activated carbon impregnated felts or non-woven polymers, such as may be obtained from Purification
Products Ltd., of Shipley, West Yorkshire. Such carbon impregnated sheets can provide capacitance in the order of many thousands of farads, and can be laminated to the EPDE lake liner. Maxwell Technologies Inc., of San Diego, USA, is a major producer of EDLCs using activated carbon felt laminated onto metal foil. An ion permeable membrane is preferably placed on the sandwich layers and is in contact with the AMD / ARD electrolyte.
Particularly preferred is an EDLC based on carbon nanotubes. A matrix of vertically aligned carbon nanotubes can be used as an EDLC to provide very high power density. Examples of carbon nanotubes enhanced EDLCs have been discussed by Riccardo Signorelli of MIT, USA.
The base metal foil acts as one electrode which is separated from the flowing AMD by a thin ion permeable membrane separator. This membrane can carry the ELDC. Thus, the pit wall will have the following layers:
1 - Waterproof liner such as EPDE
2 - Polymer liner, such as PVC, preferably sealed onto the waterproof liner
3 - Ion permeable membrane such as woven polymer 4 - Metal foil electrode, such as aluminium
5 - Activated carbon powder
6 - Ion permeable membrane
In one option, a number of prefabricated EDL capacitor strips may be connected in series to increase the emf, or in parallel to increase the capacitance.
If pit lakes are used as the "containers", then the AMD can be charged via chargers suspended over the lake on gantries. The chargers are electrodes dipping into the AMD electrolyte, which may be formed of carbon coated or impregnated metal foil or conductive polymer mesh. The charge can be provided by any means such as solar power, the electric grid or wind turbines, etc. Preferably these positive electrodes may have the same sandwich construction as the electrode on the lake wall. The suspended block electrodes may be, for example, 2m x Im in size. In use, the positive electrode provides additional charge to the electrolyte, which is stored in the double capacitor. When a power supply is required, the system is switched so that power can be drawn off from the electrodes, e.g. the electrodes on the lake wall. Thus a stored power supply can be taken from the flow battery, and used to supply power to e.g. the mine pumps or even to the electricity grid. The power output from the container or lake can be drawn off through a metal terminal attached to either the metal foil lining the lake or the charging plate suspended in the electrolytic AMD.
Figure 4 shows a schematic version of the flow battery system as applied to a pit lake. A pit lake 41 is made from a concrete wall, optionally surrounded or sunk into the soil. The lake is filled with Acid Mine Drainage (AMD). One or more electrodes 42 are suspended from a gantry 43. The electrodes are connected to a power charging / discharging terminal 44. The terminal 44 may be connected to an array of solar panels, a wind turbine or the electricity grid. The lake wall is coated with the laminate sandwich and electric double layer capacitor (45) as described above. This laminate covers the whole wall of the lake and acts as a negative anode. When the lake has been charged, power is stored in the EDLC. This can be discharged from the system through the terminal 44.
Figure 5 shows an example of a power panel, 42, as described above. This shows the sandwich system used to form the electrode. Aluminium foil 51 has laminated to it a woven polymer 52 which is impregnated with activated carbon. There is then a gap, 54, which when the panel is suspended in the lake fills with AMD. The layer of the sandwich is separated from the next layer by a porous membrane 53. The two layers of the sandwich are then connected together to form a block electrode
Examples
The invention will now be described with reference to the following non-limiting examples.
Example 1 - Pilot Scale Test
A small cylindriform aluminium metal container was lined with a micro-epoxy resin coating and filled with acid mine drainage water taken from The Bowden Close mine near Newcastle, United Kingdom. The AMD was tested and found to have a pH of 5.8 and conductivity estimated at approximately 1950μS/cm. The container constitutes the anode electrode. The container was then connected to the negative terminal of a small 0.5 vdc solar panel. Active carbon powder was laminated to a piece of aluminium foil (1 10mm x 70 mm) and the foil connected to the positive terminal of the small solar panel. The laminated carbon coated Aluminium foil was then immersed in the AMD in the container to form the cathode (positive) collector electrode.
The assembly was placed in sunlight for 7 hours to charge the AMD. After the 7 hours had elapsed a digital voltmeter o/c reading indicated 0.760 vdc between the electrodes
The o/c voltage charge remaining in the container of AMD 12 hours later was 0.650 vdc. The charge was restarted and after a further 6 hours of exposure to sunlight, the o/c vdc was 1.256 vdc. With charging disconnected the AMD retained, 5 hours later, an o/c voltage of 1.089 vdc. 14 hours later the o/c vdc was 0.986 vdc, and 72 hours later the reading was 0.684 vdc. Much later (120 hours) the reading was 0.614 vdc and after 360 hours the reading was 0.438 vdc.
This test proves that AMD can hold an electric charge. It was also noted that at the beginning of the test, the AMD was turbid with carbon, heavy metals and iron hydroxide. During charging the mix of iron hydroxide, carbon and heavy metals settled out, leaving much cleaner water which on a larger scale could be easily treated through a reedbed system. Advantages
In conventional energy storage systems solid state electrode reactions are employed for example, in lead acid batteries. In contrast, in redox flow cells the redox couples are all soluble solution species that exist in the drainage water passing through each half cell. Exceptional flow battery life cycles with related savings are evident, as without the need for frequent replacement of sacrificial electrodes, or manual replenishment of electrolytes, the maintenance of large scale flow battery cell installation is cost effective.
The available electrical energy derived from polluting acid mine or acid rock drainage from abandoned or orphan mining sites, following power disconnection of a mine from a national grid provides a cost effective solution for resumption where required, of continuous mine de- watering. In the United Kingdom, The UK Coal Authority spends over £3 million pounds each year on removing water from old abandoned mine systems. The electricity derived from the in-situ systems of the present invention can considerably reduce or even eliminate the costs by providing an electricity power source derived from the waste mine water itself.
Power grid disconnection from an abandoned mine can easily result in catastrophic environmental pollution. When naturally flowing aquifers are disrupted during active mining, sub-surface water pressure can increase to critical levels following cessation of pumping. Protective barriers and concrete plugs are installed to block water exit from adits and fissures. However water volume and pressure often ruptures protective barriers. The Wheal Jane Mine in Cornwall attracted mass European media attention in 1992, when large volumes of acid rich water burst from the mine into the Carnon River and Falmouth Bay.
The continuing availability of electrical energy and abundant clean water from abandoned mine sites presents opportunities for site redevelopment similar to the Eden Project in Cornwall, which was built over an old disused stone quarry. Abandoned or orphan mine sites offer opportunities for local or regional government development, to convert sites into sports and leisure complexes, or agriculture of aquaculture research facilities to fully capitalize on the available low cost energy and clean unpolluted water.

Claims

1. A flow battery system comprising electrolyte and electrodes, wherein the electrolyte comprises Acid Mine Drainage (AMD) and/or Acid Rock Drainage (ARD).
2. A flow battery system as claimed in Claim 1 wherein the electrodes comprise double layer capacitors laminated to a metal.
3. A flow battery system as claimed in Claim 2 wherein the electrodes comprise a compressed porous mixture of carbon particles and metal particles.
4. A flow battery system as claimed in Claim 3 wherein the metal particles are extracted from Acid Mine Drainage and/or Acid Rock Drainage.
5. A flow battery system as claimed in any preceding claim wherein the electrodes are assembled into one or more battery modules.
6. A flow battery system as claimed in Claim 5 wherein the battery modules are assembled within transport containers lined with a liner selected from polymer or fibreglass.
7. A flow battery system as claimed in any preceding claim wherein the electrolyte is circulated from the pit lakes through the battery modules and then back to the pit lakes.
8. A flow battery system as claimed in claim 1 , wherein a pit lake lined with an electrode acts as the container for the battery cell.
9. A flow battery system as claimed in claim 8, wherein an electrode is suspended in the AMD in order to charge the AMD.
10. A flow battery as claimed in claim 1 or claim 8, wherein additional charge to the AMD is provided from any one of one or more solar arrays, a wind turbine or the main electricity grid.
11. A flow battery system as claimed in any Claim 1 wherein the electrodes comprise a laminate of a polymer, a metal foil, and a polymer impregnated with activated carbon.
12. A flow battery system as claimed in claim 12, wherein the laminate additionally comprises an ion permeable membrane.
PCT/GB2008/003231 2007-09-25 2008-09-24 Power storage system wherein the electrolyte comprises acid mine drainage WO2009040521A1 (en)

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WO2021052782A1 (en) * 2019-09-19 2021-03-25 Rwe Gas Storage West Gmbh Hybrid cavern store
US11577979B1 (en) 2021-07-28 2023-02-14 The University Of British Columbia Processes for treatment of wastewater

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