PCT
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(51) International Patent Classification 7 :
`B01D 53/62
`
`A1
`
`(11) International Publication Number:
`
`WO 00110691
`
`(43) International Publication Date:
`
`2 March 2000 (02.03.00)
`
`(21) International Application Number:
`
`(22) International Filing Date:
`
`18 August 1999 (18,08,99)
`
`(30) Priority Data:
`60/096,846
`09/314,220
`
`18 August 1998 (18.08.98)
`19 May 1999 (19.05.99)
`
`US
`US
`
`PCT/US99/18711 (81) Designated States: AL, AM, AT, AU, AZ, BA, BB, BG, BR,
`BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD,
`GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP,
`KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK,
`MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG,
`SI, SK, SI., TJ, TM, q~, ’lq’, UA, UG, UZ, VN, YU, ZW,
`ARIPO patent (GH, GM, KE, LS, MW, SD, SL, SZ, UG,
`ZW), Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ,
`TM), European patent (AT, BE, CH, CY, DE, DK, ES, FI,
`FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OAPI patent
`(BF, B J, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE,
`SN, TD, TG).
`
`(71) Applicant: UNITED STATES DEPARTMENT OF ENERGY
`[US/US]; 1000 Independence Avenue, S.W., Washington,
`DC 20585-0162 (US),
`
`(72) Inventors: RAU, GregolT, Hudson; 18628 Sandy Road, Castro
`Valley, CA 94546 (I[S). CALDEIRA, Kenneth, George;
`420 Jackson Avenue, Livermore, CA 94550 (US).
`
`(74) Agents: GOTYLIEB, Paul, A. et al.; Unitexl States Depart-
`ment of Energy, Technology Transfer and Intellectual Prop-
`erty, 1000 Independence Avenue, S.W., Washington, DC
`20585-0162 (US).
`
`Published
`With international search report.
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
`(54) Title: METHOD AND APPARATUS FOR EXTRACTING AND SEQUESTERING CARBON DIOXIDE
`
`(57) Abstract
`
`A method and apparatus to extract
`and sequester carbon dioxide (COD from
`a stream or volume of gas (l12a) wherein
`said method and apparatus hydrates CO2,
`and reacts the resulting carbonic acid (144)
`with carbonate (152). Suitable carbonates
`include, but are not limited to, carbonates
`of alkali metals and alkaline earth metals,
`preferably carbonates of calcium and mag-
`nesium. Waste products are metal cations
`and bicarbonate in solution (146), providing
`an effective way of sequestering C02 from
`a gaseous environment.
`
`122
`
`0 / MOISTURE I
`I 8 ~’~IELI~INATOR t
`
`112a
`
`I ~C~at~E I
`
`l12b..~
`
`MONITORING
`
`136b
`
`[ 142b
`
`/
`
`149
`
`Akermin, Inc.
`Exhibit 1007
`Page 1
`
`

`

`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applications under the PCT.
`
`AL
`AM
`AT
`AU
`AZ
`BA
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`CI
`CM
`CN
`CU
`CZ
`DE
`DK
`EE
`
`Albania
`Armenia
`Austria
`Australia
`Azerbaijan
`Bosnia and Herzegovina
`Barbados
`Belglun~t
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`C6te d’Ivoire
`Cameroon
`China
`Cuba
`Czech Republic
`Germany
`Denmark
`Estonia
`
`ES
`FI
`FR
`GA
`GB
`Gli]
`GH
`GN
`GR
`HU
`IE
`IL
`IS
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`LC
`LI
`LK
`LR
`
`Spain
`Finland
`France
`Gabon
`Unitcd Kingdom
`Georgia
`Ghana
`Guinea
`Greece
`Hungary
`Ireland
`Israel
`Iceland
`Italy
`Japan
`Kenya
`Kyrgyzstan
`Democratic People’s
`Republic of Korea
`Republic of Korea
`Kazakstan
`Saint Lucia
`Liechtenstein
`Sri Lanka
`Liberia
`
`LS
`LT
`LU
`LV
`MC
`MD
`MG
`MK
`
`ML
`MN
`MR
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`SD
`SE
`SG
`
`Lesotho
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`The former Yugoslav
`Republic of Macedonia
`Mali
`Mongolia
`Mauritania
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`
`SI
`SK
`SN
`SZ
`TD
`TG
`TJ
`TM
`TR
`TT
`UA
`UG
`US
`UZ
`VN
`YU
`ZW
`
`Slovenia
`S]ovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Turkmenis~an
`Tarkey
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`Viet Nam
`Yugoslavia
`Zimbabwe
`
`Akermin, Inc.
`Exhibit 1007
`Page 2
`
`

`

`WO 00/10691
`
`PCT/US99/18711
`
`METHOD AND,... APPARATUS FOR EXTRACTING
`
`AND SEOUESTERING CARBON DIOXIDE
`
`STATEMENT OF GOVERNMENT INTEREST
`
`5
`
`The United States Government has rights in this invention pursuant to Contract No. W-
`
`7405-ENG-48 between the U.S. Department of Energy and the University of California.
`
`CROSS-REFERENCE TO RELATED APPLICATIONS
`
`This application claims the benefit of U.S. Provisional Application No. 60/096,846,
`
`10
`
`filed 8/18/98, and U.S. Application No. 09)/314,220, filed 5/19/1999.
`
`TECHNICAL FIELD
`
`The present invention relates generally to a method and apparatus for extracting carbon
`
`dioxide (COz) from a stream or volume of gas, and sequestering said COz from the atmosphere
`
`15
`
`or other gaseous envh’onment. The invention particularly relates to a method and apparatus
`
`that utilize carbonate and water to sequester said CO~_ as bicarbonate.
`
`BACKGROUND ART
`
`A variety of chemical means exist or have been proposed which consume COz
`
`2O
`
`contained in emissions fi’om fossil fuel combustion or other gas streams, thus reducing the
`
`potential atmospheric COz burden (reviews by: H. Herzog and E. Drake, "Carbon Dioxide
`
`Recovery and Disposal From Large Energy Systems’, Annual Reviews of Energy and
`
`Environment Vol. 21, p 145-166, 1996; X. Xiaoding and J.A. Moulijn, "Mitigation of CO2 by
`
`Chemical Reactions and Promising Products", Energy and Fuels, Vol. 10, p 305-325, 1996).
`
`25
`
`Among these chemical approaches, the exposure and reaction of such waste COz to certain
`
`naturally occurring or artificially formed calcium-, magnesium-, sodium-, and/or silica-rich
`
`minerals has been explored as reviewed below. The reaction of certain carbonate and silicate
`
`rninerals with CO,. is a welt-known "rock weathering" phenomenon that plays a major role in
`
`controlling atmospheric CO2 on geologic time scales (R.A. Berner, A.C. Lasaga, and R.M.
`
`3O
`
`Garrels, "The Carbonate-Silicate Geochemical Cycle and its Effect on Atmospheric Carbon
`
`Dioxide Over the Last 100 Million Years", American Journal of Science, Vol. 283, p 42-50,
`
`1983). Over the very long term such process are expected to eventually consume most of the
`
`COz emitted by man’s activities. The problem is that such natural processes occur on the order
`
`of >1,000 year time scales and thus will have little immediate impact on the rapidly increasing
`
`Akermin, Inc.
`Exhibit 1007
`Page 3
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`

`

`WO 00/10691
`
`PCT/US99/! 8711
`
`COx emissions and atmospheric COx burden in the coming centuries. Nevertheless, several
`
`researchers have proposed that certain weathering reactions be used to sequester COs, in
`
`particular those reactions which lead to COs sequestration or storage in the form of solid
`
`carbonates.
`
`For example, fbxation and storage of COx by artificial weathering of waste concrete in
`
`combination with coccolithophorid algae cultures was reported by H. Takano and T.
`
`Matsunaga, "COx Fixation by Artificial Weathering of Waste Concrete and Coccolithophorid
`
`Algae Cultures", Energy Conversion Management, Vol. 36, No. 6-9. p 697-700, 1995. It was
`
`shown that COx can be sequestered into biologically produced carbonate and biomass. Various
`
`10
`
`mechanisms of rock weathering to fix COx was discussed by T. Kojima, "Evaluation Strategies
`
`for Chemical and Biological Fixation/Utilization Processes of Carbon Dioxide", Energy
`
`Conversion Management, Vol. 36, No. 6-9, p 881-884, 1995. Studies of COx fixation by
`
`silicate rock weathering were reported by T. Kojima, A. Nagamine, N. Ueno and S. Uemiya,
`
`"Absorption and Fixation of Carbon Dioxide by Rock Weathering", Energy Conversion
`
`15
`
`Management, Vol. 38, Suppl., p $461-8466, 1997. Sequestering of COx as carbonate by
`
`reaction with minerals rich in calcium and magnesium oxides was reported by K,S. Lackner,
`
`C.H. Wendt, D.P. Butt, E.L. Joyce, D.H. Sharp, "Carbon Disposal in Carbonate Minerals",
`
`Energy, Vol. 20, No. 11, p 1153-1170, 1995. Reacting flue gas CO2 with water and soil to
`
`ultimately precipitate and sequester the COx as carbonate was explored by T, Chohji, M.
`
`20
`
`Tabata, and E. Hirai, "CO~ Recovery From Flue Gas by an Ecotechnological (Environmentally
`
`Friendly) System", Energy, Vol. 22 No. 2/3, p 151-159, 1997. A study by H. Kheshgi
`
`("Sequestering Atmospheric Carbon Dioxide by Increasing Ocean Alkalinity", Energy, Vol. 20,
`
`No. 9, p 912-922, 1995) looked at the option of adding calcium oxide to the ocean as a means
`
`of increasing the COx absorption capacity of the ocean. The preceding approaches often
`
`25
`
`require elevated temperatures or pressures, significant energy, land, or other resource inputs,
`
`and/or have negative environmental impacts. The cost of implementing these technologies is
`
`therefore often prohibitive.
`
`As reviewed by H. Herzog and E. Drake, (Annual Reviews, loc. cir.) several chemical
`
`means exist for separating and concentrating COx from gas streams. U.S. Patent 4,376,101
`
`30
`
`(Sartori et al) discloses the removal of COo from a gaseous streain via use of an aqueous
`
`solution containing an alkali metal salt or hydroxide and an activator or promoter system
`
`comprising an amine compound. While such processes remove or separate COz from a waste
`
`stream, they offer no downstream method of ultimately sequestering the COs from the
`
`Akermin, Inc.
`Exhibit 1007
`Page 4
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`

`

`WO 00/10691
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`PCT/US99/18711
`
`atmosphere. They also often require elevated temperatures or pressures, exotic chemicals,
`
`and/or significant inputs of energy or resources.
`
`Gas/water/calcium carbonate (limestone) reactors have been used in desulfurization of
`
`power plants exhaust as reviewed by H. N. Soud and M. Takeshita, "FGD Handbook, IEA
`
`Coal Research, London, 438p., 1994. Such reactors differ from the present invention in three
`
`important aspects: 1) The volume of SOz in the gas streams to which desulfurization is appfied
`
`is vastly smaller than the COz content in the same gas stream; 2) The hydration step in
`
`carbonate desulfurization involves combining SO,- with H,-O to form the strong acid HzSO3. In
`
`contrast, the hydration of CO2 envisioned here forms carbonic acid HzCO3, a weak acid which
`
`10
`
`has a slower reaction rate with carbonate than does H,-SO3.3) The reaction of HzSO3 with
`
`carbonate (e.g., CaCO3) and oxygen forms a solid, CaSO4, and a gas, CO,., whereas the H2CO~
`
`with carbonate reaction forms cations and bicarbonate in solution, does not require
`
`supplemental oxygen, produces tittle or no sofid waste, and consumes rather than generates
`
`gaseous COs.
`
`15
`
`U.S. Patent 5,100633 (Morrison) describes a process for scrubbing acid-forming gases
`
`which include SO2 and CO2 from an exhaust gas stream through reactions with alkatine
`
`solutions formed from the waste ash from biomass burning. The resulting alkali metal salts are
`
`then precipitated or dewatered forming solid, possibly useful waste products. This process
`
`does not provide a system for net CO2 sequestration, however, considering that the molar ratio
`
`2O
`
`of carbon to alkali metals or to alkaline earth metals in the end products is many times lower
`
`than that ratio in the original biomass burned to form the alkaline ash. That is, only a very small
`
`fractional equivalent of the CO,- released ha biomass combustion can be sequestered by this
`
`process, and therefore when initial ash and COz formation are considered the overall process is
`
`a net source rather than a net sink for CO~.
`
`25
`
`The chemical reactions involving CO2 gas, water, and carbonate minerals (principally
`
`calcium carbonate) have been extensively studied as reviewed by J.W. Morse and F.T.
`
`Mackenzie ( "Geochemistry of Sedhnentary Carbonates", Cambridge, Amsterdam, 707p.,
`
`1990) and by T. Arakaki and A. Mucci ( "A Continuous and Mechanistic Representation of
`
`Calcite Reaction-Controlled Kinetics in Dilute Solutions at 25°C and 1 Atm Total Pressure",
`
`3O
`
`Aquatic Geochemistry, Vol. 1, p 105-130, 1995). However, the context of these studies has
`
`been to describe the dissolution or precipitation of solid carbonate under various conditions,
`
`not the consumption and sequestration of CO~.
`
`DISCLOSURE OF THE INVENTION
`
`3
`
`Akermin, Inc.
`Exhibit 1007
`Page 5
`
`

`

`WO 00/10691
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`PCT/US99/18711
`
`An object of this invention is a method and apparatus for extracting carbon dioxide
`
`(CO~) contained in a stream or volume of gas, and sequestering this COo ~om the stream of
`
`volume of gas.
`
`A further object is a method and apparatus which accomplishes said CO2 extraction and
`
`sequestration without the requirement of elevated temperatures, pressures, and without
`
`significant expenditures of energy or other resources.
`
`A further object is a method and apparatus which utilizes HzO and carbonate.
`
`A further object is a method and apparatus in which the reactants are relatively
`
`abundant and inexpensive, and the end products and process waste streams are
`
`10
`
`environmentally benign.
`
`A further object is a method and apparatus whose relative simplicity and low cost allow
`
`it to be widely employed, therefore impacting COz emissions potentially at the global scale.
`
`A further object is a method and apparatus which can utilize a wide range of fresh- and
`
`salt-water sources.
`
`15
`
`A further object is a method and apparatus which is flexible in siting requirements
`
`allowing location near COz sources, carbonate, and/or water sources.
`
`It is known that carbonic acid reacts with certain metal carbonates to form metal ions
`
`and bicarbonate in solution. Such a reaction is employed in the invention to provide a means of
`
`extracting and sequestering COz from a stream or volume of gas.
`
`20
`
`One embodiment of the present invention is an integrated apparatus comprising a
`
`reactor vessel containing carbonate. A gas stream containing CO,_ enters the reactor vessel. In
`
`the reactor vessel, CO~. contacts an aqueous solution and becomes hydrated to form carbonic
`
`acid, which in turn reacts with the carbonate to form bicarbonate and metal ions. Waste
`
`streams exiting the reactor vessel comprise a gas stream now depleted of CO~, and an aqueous
`
`25
`
`solution of metal ions and bicarbonate.
`
`Another embodiment of the present invention is a sequential apparatus comprising a
`
`hydration vessel and a carbonate reaction vessel. A gas stream containing COz enters the
`
`hydration vessel. In the hydration vessel, C02 contacts an aqueous solution and becomes
`
`hydrated to form carbonic acid. The carbonic acid is transported to the carbonate reaction
`
`30
`
`vessel where it reacts with carbonate located therein, to form bicarbonate and metal ions.
`
`Waste streams comprise a CO2-depleted gas stream exiting the hydration vessel and an
`
`aqueous solution of metal ions and bicarbonate exiting the carbonate reactor vessel.
`
`Due to its relative simpficity, low-cost, and low environmental impact, it is befieved
`
`that the invention herein disclosed offers distinct advantages over other methods for the
`
`4
`
`Akermin, Inc.
`Exhibit 1007
`Page 6
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`

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`WO 00/10691
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`PCT/US99/18711
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`combined process of extracting CO~. from waste gas streams and sequestering this COz from
`
`the atmosphere.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`These and other features, aspects, and advantages of the present invention will become
`
`better understood with regard to the following description, appended claims, and accompanying
`
`drawings wherein:
`
`FIG. 1 illustrates one embodiment of the present invention comprising an integrated
`
`configuration that extracts and sequesters COx from a gas stream in which COx is hydrated and
`
`10
`
`reacted with carbonate in an integrated hydration carbonate reactor vessel;
`
`FIG. 2 illustrates another embodiment of the present invention comprising a sequential
`
`configuration that extracts and sequesters COx from a gas stream in which COx is first hydrated,
`
`then the resulting carbonic acid solution is sepmately reacted with carbonate;
`
`FIG. 3 illustrates further embodiments of the present invention comprising various
`
`15
`
`means to enhance COz hydration;
`
`FIG. 4 illustrates further etnbodiments of the present invention comprising various
`
`means to enhance the carbonate - carbonic acid reaction;
`
`FIG. 5 illustrates further embodiments of the present invention comprising various
`
`means to handle the carbonate.
`
`20
`
`Definitions
`
`BEST MODES FOR CARRYING OUT TIlE INVENTI.QN
`
`alkali metals -- elements found in column IA of the periodic table of elements
`
`alkaline earth metals -- elements found in column IIA of the periodic table of elements
`
`25
`
`carbon dioxide -- COx
`
`carbonate -- metal carbonate
`
`carbonate group-- CO3
`
`carbonate ion -- CO_~x
`
`carbonate solution -- carbonate particles in suspension or slurry, and/or dissolved in solution
`
`30
`
`COz-depleted gas stream -- a gas stream where some or all of its initial COz has been removed
`
`dissolved carbonate -- metal ions and carbonate ions in solution
`
`metal carbonate -- chemical compound of the form X(CO~)m where X is any element or
`
`combination of elements that can chemically bond with a carbonate group or its multiple,
`
`wherein at least one element is a group IA, IIA, IIIA, IVA, IB, IIB, IIIB, IVB, VB, VIB,
`
`Akermin, Inc.
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`Page 7
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`WO 00/10691
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`PCT/US99/18711
`
`VIIB, or VIIIB element of the periodic table, and m is a stoichiometrically determined
`
`positive integer. Examples of X include but are not limited to alkali metals and alkalhae
`
`earth metals.
`
`metal ion -- one of~the resulting cations formed when metal carbonate X(l~O3)m has reacted
`
`with carbonic acid, wherein the cation is found in solution with bicarbonate, and m is a
`
`stoichiometrically determined positive integer.
`
`wetted carbonate -- static or moving bed, pile, or aerosol composed of carbonate particles
`
`wetted by an aqueous solution
`
`Abbreviations
`
`10
`
`aq -- aqueous
`
`Ca -- calcium
`
`CO2-- carbon dioxide
`
`CO~ -- a carbonate group
`
`CO32 -- carbonate ion
`
`15
`
`HCO3 -- bicarbonate ion
`
`HzCO~ -- carbonic acid
`
`H20 -- water
`
`Mg -- magnesium
`
`Na- sodium
`
`2O
`
`pCO~ -- the partial pressure of COz gas
`
`pH -- the negative logarithm of the hydrogen ion concentration
`
`SOz -- sulfur dioxide
`
`SO3 -- sulfite
`
`SO42- sulfate
`
`25
`
`X -- any element or combination of elements that can chemically bond with a carbonate group
`
`or its multiple, wherein at least one said element is a group IA, IIA, IIIA, IVA, IB, IIB,
`
`IIIB, IVB, VB, VIB, VIIB, or VIIIB element of the periodic table.
`
`X(aq) -- any element or combination of elements in solution that can chemically bond with a
`
`carbonate group or its multiple, formed when X(CO~)m dissolves in a solution.
`
`30
`
`X(CO~)m-- carbonate composed of X bonded to one or more carbonate groups, where m is a
`
`stoichiometrically determined positive integer.
`
`The inventive method and apparatus utilize a process comprising two main steps. In
`
`6
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`Page 8
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`step l, gaseous CO2 is hydrated to form carbonic acid, as shown in equation 1:
`
`CO~.(gas) + H20 => Ho-CO.~(aq).
`
`(1)
`
`In step 2, the hydrated COs is reacted with a metal carbonate, hi solid or dissolved form,
`
`to form metal cations and bicarbonate in solution. When the hydrated CO~. or carbonic acid is
`
`reacted with a metal carbonate in solid form, this reaction may be represented as shown in
`
`equation 2a:
`
`mH2CO~(aq) + X(CO~)m(solid) --> X(aq) + 2mHCO3-(aq).
`
`(2a)
`
`When the hydrated COo. or carbonic acid is reacted with a metal carbonate in dissolved form,
`
`this reaction may be represented as shown in equation 2b:
`
`10
`
`HzCO3(aq) + CO32-(aq) => 2HCO~-(aq).
`
`(2b)
`
`Equation 2b implies that the metal carbonate has akeady undergone a dissolution reaction,
`
`which may be represented by equation 3:
`
`X(CO~)m(solid) => X(aq) + mCOs~-(aq). (3)
`
`In step 2, X may represent any element or combination of elements that can chemically
`
`15
`
`bond with the CO32- or its multiple, and wherein at least one element is a group IA, IIA, IIIA,
`
`IVA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIIIB element of the periodic table. Because of
`
`thek natural abundance and reactivity, X would be preferably represented by a member or
`
`members of the group IA and group IIA elements. Carbonates relevant to such a reaction
`
`include but are not limited to CaCO3, CaMg(CO3)~., MgCO3, and NazCO3. For large scale
`
`20
`
`applications X represented by Ca would be preferred because of the relatively high natural
`
`abundance and low cost of Ca(203 (for example, as contained in limestone). Other sources of
`
`cai:bonates include, but are not lhnited to, calcite, dolomite and aragonite. X(aq) represents one
`
`or more ions in solution containing the. elements composing X.
`
`COz Hydration
`
`25
`
`In the present invention, COz in a gas stream may be hydrated in various ways: by
`
`passing the gas stream through an aqueous solution whose surface area is enhanced, preferably
`
`by spraying or atomizing, by bubbling the gas stream into an aqueous solution, and/or by
`
`passing the gas stream over or through wetted carbonate. The gas stream may encounter the
`
`aqueous solution or wetted carbonate vertically, horizontally, or at some other angle. This gas
`
`3O
`
`introduction may be assisted by a compressor or other means well known in the art. This may
`
`be particularly relevant when the gas stream is bubbled into an aqueous solution, or passed
`
`through wetted carbonate that is submerged, where resistance to gas flow from the aqueous
`
`solution and/or carbonate particles is expected. Introduction of gas below wetted carbonate
`
`may serve to partially or completely fluidize the particle bed, enhancing gas-aqueous solution-
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`Page 9
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`carbonate contact. In this configuration the COz hydration occurs in close proximity to the
`
`carbonate-carbonic acid reaction, and both reactions are facilitated by the flow of gas and acid
`
`solution around the carbonate. The incoming gas is thus exposed to a large surface area of
`
`aqueous solution in the form of droplets and wetted carbonate surfaces, facilitating hydration of
`
`CO2 to form a carbonic acid solution within the reactor.
`
`Carbonate Forms
`
`In the present invention, the carbonate may be presented to the carbonic acid in solid
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`phase form, or in liquid phase form. Preferred carbonate forms include: i) pile or bed of
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`particles (or chunks, slabs or blocks), ii) liquid slurry or suspension of particles, iii) solution of
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`dissolved carbonate, or iv) solution or particle aerosol; over or through which the carbonic acid
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`solution from step 1 is passed.
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`If the carbonate used is relatively insoluble in water, e.g., the calcium carbonate
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`contained in limestone, then its reaction with carbonic acid in the aqueous solution will occur
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`largely as a reaction between a liquid (carbonic acid containing solution) and a solid
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`(15nestone). Because of the abundance and relative low cost of the latter type of carbonate, the
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`use of this carbonate type seems preferred for large scale applications.
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`In such applications relatively water-insoluble carbonate will be presented to the gas aad
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`aqueous solution in the reaction as a bed, pile, slurry, suspension, or aerosol of carbonate
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`particles. The particulate carbonate may be of homogeneous or heterogeneous size and shape
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`2O
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`ranging from very fine particles to large chunks. Prior to reaction with the carbonic acid, the
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`original size and shape of the carbonate may be modified by crushing, etching, drilling, sawing,
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`or otherwise forming the carbonate into sizes and shapes advantageous for step 2. Because the
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`overall rate of step 2 will be a function of the surface area of the particles exposed to the
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`aqueous solution, the greatest surface area and hence greatest reaction rate per unit reactor
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`volume will be achieved with the smallest sized carbonate particles. In such cases the particles
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`in contact with the aqueous solution may form a suspension or slurry of particles depending oa
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`the size of the particles and the agitation or flow of the solution into which they are immersed.
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`The size of such particle might be less than 0.1 mm. At the other extreme would be carbonate
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`particle sizes, e.g., >10 cm whose individual mass would preclude prolonged suspension in air
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`or solution and whose collective mass would then form a static bed, pile, or other configuration
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`of carbonate particles. The aqueous solution, CO2, and carbonic acid solution would then flow
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`in or through the porous carbonate particle mass, facilitating carbonic acid-carbonate contact
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`and possibly gaseous CO2-aqueous solution contact. The advantage of such a scheme would be
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`that less carbonate particle size reduction and associated cost by crushing (or other means
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`common in the art) would be required. It would also preclude the added complexity of handling
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`and pumping solutions containing suspended carbonate particles. With the bed/pile approach, a
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`greater volume of particles and hence a larger reactor vessel size would be needed to attain an
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`equivalent carbonate particle surface area within the reactor. Because it is unlikely and
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`impractical that strict homogeneous particle sizes will be introduced into the reactor and
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`because particle size reduction will occur in the reactor as particles of any size react with
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`carbonic aci& it is likely that some intermediate between a static bed/pile and a dynamic
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`suspension/slurry of carbonate will form in the reactor. The inclusion of carbonate particles in
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`the reactor solution requires attention with regard to solution handling and pumping as will be
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`discussed later.
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`If the form of the carbonate used is soluble in water, e.g. sodium carbonate, then a large
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`portion ff not all of the carbonate will be in ionic, dissolved form in aqueous solution. This
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`means that the carbonic acid - carbonate reaction to form bicarbonate will occur mostly if not
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`entirely in aqueous solution. In addition to the various modes of presenting the carbonic acid to
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`the carbonate described earlier for solid phase carbonate, liquid phase carbonate may be
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`presented to the carbonic acid via means well known in the art, such as spraying, atomizing,
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`blowing, and presentation on wetted structures, or as a pool of liquid into which the gas stream
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`is bubbled.
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`Introduction, Handling, and Removal of Water and Aqueous Solution
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`As step 2 proceeds, the aqueous mixture in proximity to the carbonate will become
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`increasingly satuxated with bicarbonate and the rate of bicarbonate formation will subsequently
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`decline. It may be advantageous to bleed off or remove part of the mixture and replace this
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`removed volume with aqueous solution which is relatively unsaturated with bicarbonate. The
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`amount and timing of such removal will be dictated by the status of the solution chemistry and
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`the desired reaction rates. By means well known in the art, monitoring of one or more solution
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`chemistry parameters such as pH, pCOz, conductivity, alkalinity, and/or metal ion
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`concentration, either in the reactor solution or in the recirculating solution, is therefore desired.
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`Water may be added to, and solution effluent removed from, the reactor by pump,
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`gravity feed, or other means well known in the art for liquid handling. Water addition may
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`occur directly into the reactor or indirectly via addition to and rrfixture with recirculating
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`aqueous solution prior to this mixture’s introduction into the reactor. Also, carbonate solution
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`may be added directly into the reactor or indirectly via addition to and mixture with
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`recirculating aqueous solution prior to this mixture’s introduction into the reactor.
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`The amount of water added to the reactor per unit time relative to the removal of waste
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`solution effluent from the reactor will determine the solution level within the reactor. In various
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`embodiments reactor solution may be maintained or varied at levels ranging from significantly
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`above to significantly below the top level of the particulate carbonate bed/pile within the
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`reactor. The liquid level will dictate the maximum height above the reactor base where solution
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`can be withdrawn for recirculation or removal. For purposes of allowing carbonate particles to
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`settle and for minimiziag particulate load in the recirculated/removed waste solution, it would
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`be advantageous to maintain the solution level and hence the solution outlet or outlets above
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`the carbonate bed/pile level. On the other hand, maintaining liquid levels below the top of the
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`carbonate bed/pile would expose the C02 gas within the reactor to a large wetted surface area
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`formed by the exposed carbonate bed/pile as wetted by the aqueous solution spray, facilitating
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`carbonic acid formation. In either case some carbonate particles may be entrained in the
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`solution outflow which, if deleterious to pumps or other solution handling equipment, could be
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`removed by filtration, settling, or other means well known in the art for liquid/solid separation.
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`Process Parameters
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`Certain process parameters which affect steps 1 and 2 may be varied to maximize the
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`cost/benefit of a reactor’s operation. For example, since high temperatures adversely affect the
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`COz-hydration and carbonate-carbonic acid reactions, low temperatures are preferred within
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`the range between the freezing and boiling points of water for a given operating pressure.
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`Cooling means include those well known in the art for cooling liquids and gases; such may be
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`2O
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`passive (including radiator fins or heat sinks attached to the reactor vessels or process lines),
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`active (indirect via heat exchanger or direct refrigeration), or a combination of the two. Such
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`cooling means may be used to pre-cool the incoming gas stream, or to cool process particular
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`process components including the recirculated gas stream, the gas contained in the reactor
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`vessel, the aqueous solution, the carbonic acid, and!or such liquid as may be pooled in the
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`reactor vessel. In addition, cooling may be achieved by having water recharge or replenishing
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`carbonate at a lower temperature than the components in the reactor vessels. Higher total
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`process pressures above ambient also benefit the hydration and carbonate reactions, serving to
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`increase COz solubility and carbonate reactivity with carbonic acid, and may be cost effective.
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`Pressurizing means include those well known in the art such as a compressor to increase the
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`3O
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`pressure of the incoming gas stream or the gas contained within the reactor vessel. It is
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`preferred that the highest possible concentration of carbonic acid solution be presented to the
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`largest possible carbonate surface area, with the pH of the carbonic acid solution being as low
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`as allowed by the operating temperature, the incoming gas stream’s pCOz, the water volume
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`with which CO2 is hydrated, and the effects of chemical additives (if any). Since the solution
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`streams in the reactor will likely range from concentrated H2CO3 to concentrated HCO3", pH
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`variation (probably 4 to 8) will need to be considered ha designing the reactor bed container,
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`and the solution and gas handling and transport systems. Other parameters to consider include:
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`i) the CO2 concentration, flow rate, and chemical composition of the gas stream entering the
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`reactor, ii) the particle size and total amount of carbonate and thus the total carbonate surface
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`area within the reactor, iii) the rate of physical movement or agitation (if any) of the carbonate
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`and carbonic acid solution, iv) the reactor temperature and/or pressure, and v) the chemical
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`properties, flow rate, and recirculation of solution within the reactor.
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`Various embodiments according to the present invention are described hereunder with
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`reference to FIG. 1. In these embodiments, the H20 hydration aud carbonate reactions occur
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`together in one integrated reactor vessel 100 ("integrated configuration"). The reactor vessel
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`100 comprises two regions: an upper region, and a lower region. An aqueous solution 132 is
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`introduced into