CO2 CAPTURE AND UTILIZATION SYSTEM AND METHOD

Abstract

A carbon dioxide (CO2) capture and utilization system captures CO2 from flue gas and utilizes the same to enhance algae or cyanobacteria growth. The system generally comprises a CO2 capture unit and a utilization unit that is in fluid communication with the CO2 capture unit. The CO2 capture unit includes a membrane CO2 absorber that captures CO2 from incoming flue gas to produce a CO2-rich solvent. The utilization unit processes the CO2-rich solvent to produce a product stream that includes CO2 and NH3 in a predetermined CO2:NH3 ratio. The product stream is delivered to a cultivation subsystem of the utilization of the unit including one or more species of algae or cyanobacteria. A method for capturing and utilizing CO2 is also provided herein.

Description

TECHNICAL FIELD

The present disclosure is directed to a CO₂ capture and utilization system and method. In particular, the present disclosure is directed to a CO₂ capture and fixation system and method which utilize dual-function NH₃ looping, an indirect membrane CO₂ absorber, and a solvent regenerator delivering just-in-time CO₂ and NH₃ distribution to reduce CO₂ capture cost and provide improved algae or cyanobacteria production.

INTRODUCTION

In recent years, CO₂ capture and utilization systems that utilize captured CO₂ for algae production have been developed for power plant-related applications in an effort to reduce CO₂ emissions. In some known CO₂ capture and utilization systems, an algae culture is either directly contacted (e.g., through flue gas compression, transport and bubble through, or Venturi induction to algae culture) or indirectly contacted (e.g., through capture, transport and supply of high purity CO₂) by flue gas, with each respective configuration having its advantages and disadvantages with respect to incoming CO₂ supply, heavy metal contamination, operability, energy consumption, capital investment, and life cycle of CO₂ emission.

Although bubbling CO₂ is a tried and tested method for carbon supplementation of algae cultures that has proven effective, the capital (material cost) and operating (pressure drop) expenses have to be considered and balanced. For example, a ceramic sparger produces smaller bubbles, increasing mass transfer efficiency, but generates a higher pressure drop, that proves undesirable after a life cycle analysis (LCA) due to the gas compression energy penalty. As an alternative, CO₂ supply from an aqueous caustic stream (pH>7) pre-saturated with CO₂ shows potential for lowering operating costs and increasing the viable distance between an algae farm and a point source of emissions. Once the aqueous HCO₃⁻ and CO₃²⁻ have been consumed by the algae, the liquid is recycled for CO₂ capture. However, notable technical challenges have to be overcome. First, the high water blowdown with the algae harvest requires significant amine or sodium/potassium makeup if it is not a consumable nutrient for algae growth, which destroys the economics and LCA of such approach. Second, fouling on the absorber internal CO₂ capture packing surface is caused by algae and nutrients in the algae growth media. This fouling is similar to algae fouling commonly seen on cooling tower packing resulting from continued organism growth in the dark. Hence, a CO₂ capture solvent that can also act as a nutrient for algae growth would be ideal.

NH₃ is attractive for CO₂ capture and as an algae nutrient. For CO₂ capture it is inexpensive, has a low regeneration energy, zero degradation and a viscosity near that of water. Numerous studies have shown that the scrubbing capacity of NH₃ is approximately 0.9-1.2 kg of CO₂/kg of NH₃, with a CO₂ removal efficiency of ˜99% and half the solvent regeneration energy than that of 30 wt % MEA. The main drawback is, however, high NH₃ emission. Hydrophobic membranes have been studied for CO₂ capture using an aqueous NH₃ solution.¹² However, despite the fact that significant reduction of the NH₃ slip has been achieved, there is still a critical challenge regarding long-term performance stability in industrial applications due to crystallization of ammonium (NH₄⁺) salts on the lumen side of the membrane due to the reverse permeation of NH₃ from liquid side to gas side then reacting with gaseous CO₂.

Another known problem in CO₂ capture and utilization systems is the inhibition of algae growth due to frequent pH swings in the algae bioreactor due to unbalanced (intermittent) feeding systems for CO₂ and N. Moreover, in larger systems (e.g., 1000s of acres), the distance between gas spargers and an algae bioreactor may adversely affect CO₂ delivery and feed to algae. Additionally, in known systems, short-term planned or unplanned disruptions in flue gas can disrupt CO₂ supply to the algae bioreactor and thus adversely affect algae growth.

Accordingly, there is thus a need for improved CO₂ capture and utilization systems and methods.

SUMMARY

The presently disclosed subject matter meets some or all of the above-identified needs, as will become evident to those of ordinary skill in the art after a study of information provided in this document.

This summary describes several embodiments of the presently-disclosed subject matter, and in many cases lists variations and permutations of these embodiments. This summary is merely exemplary of the numerous and varied embodiments. Mention of one or more representative features of a given embodiment is likewise exemplary. Such an embodiment can typically exist with or without the feature(s) mentioned; likewise, those features can be applied to other embodiments of the presently-disclosed subject matter, whether listed in this summary or not. To avoid excessive repetition, this summary does not list or suggest all possible combinations of such features.

Provided herein is a carbon dioxide (CO₂) capture and utilization system.

The CO₂ capture and utilization system includes: a CO₂ capture unit configured to capture CO₂ from flue gas introduced into the system from an industrial facility, such as coal-fired power plant or natural gas plant, or other source; and a utilization unit which is in fluid communication with the CO₂ capture unit, and which processes the CO₂ captured from the incoming flue gas to improve algae or cyanobacteria production. The CO₂ capture unit includes a membrane CO₂ absorber configured to receive flue gas. The membrane CO₂ absorber includes a first section in which flue gas is received into the membrane CO₂ absorber, a second section through which an ammonium solvent passes, and a membrane that is positioned between the first section and the second section of the membrane CO₂ absorber. In some embodiments, the ammonium solvent includes ammonium hydroxide (NH₄OH). In some embodiments the ammonium solvent includes a chelating agent to reduce NH₃ slip through the membrane of the membrane CO₂ absorber. In some embodiments, the chelating agent is one of triethylene glycol di-2-ethylhexoate (TGDE), amino trimethylene phosphonic acid (AMP), tris(hydroxymethyl)aminomethane (Tris), and ZnCl₂. The membrane of the membrane CO₂ absorber is configured to prevent direct contact between the flue gas and the ammonium solvent but permit the passage of CO₂ within the flue gas from the first section to the second section to interact with the ammonium solvent. The interaction between the ammonium solvent and the CO₂ from the flue gas produce a CO₂-rich solvent.

The utilization unit includes a cultivation subsystem which aids in the cultivation of one or more species of algae or cyanobacteria contained therein. In some embodiments, the cultivation subsystem includes at least one of a photobioreactor and an open raceway pond. In use, the utilization system processes the CO₂-rich solvent to produce a product stream that is provided to the cultivation subsystem and includes CO₂ and NH₃ in a predetermined CO₂:NH₃ ratio. In some embodiments, the predetermined CO₂:NH₃ ratio is about 7:1 to about 16:1. In some embodiments, the predetermined CO₂:NH₃ ratio is about 10:1. In some embodiments, the utilization unit includes a solvent regenerator that is in fluid communication with the membrane CO₂ absorber and is configured to process the CO₂-rich solvent to produce the product stream that is subsequently delivered to the cultivation subsystem. In some embodiments, the solvent regenerator is proximally located to the cultivation subsystem, such that the solvent generator provides just-in-time distribution of the predetermined CO₂:NH₃ ratio to the cultivation subsystem. In some embodiments, the solvent regenerator and/or cultivation subsystem may be solar powered, and, to this end, operably connected to one or more solar cells.

In some embodiments, the CO₂ capture and utilization system further includes conduit in fluid communication with a flue gas supply and the membrane CO₂ absorber. In such embodiments, the conduit and the membrane CO₂ absorber are preferably oriented relative to each other, such that, when flue gas from the flue gas supply is saturated, the conduit delivers the saturated flue gas in a downflow that washes the membrane of the membrane CO₂ absorber. In some embodiments, the membrane CO₂ absorber is a hollow fiber membrane. In one such embodiment, the membrane CO₂ absorber includes a non-porous polymer comprising a fluoride material and a microporous hollow fiber support comprising polyether ether ketone (PEEK). In some embodiments, the membrane CO₂ absorber is a flat sheet membrane. In one such embodiment, the membrane of the membrane CO₂ absorber includes a polyethersulfone (PES) and polytetrafluoroethylene (PTFE).

In some embodiments, a lean solvent corresponding to the portion of the CO₂-rich solvent remaining after NH₃ is removed from the CO₂-rich solvent to produce the product stream is transferred from the utilization unit to the membrane CO₂ absorber.

A method for capturing and utilizing carbon dioxide (CO₂) is also provided herein. The method includes: receiving flue gas into a membrane CO₂ absorber containing an ammonium solvent; processing, by a solvent regenerator, a CO₂-rich solvent received from the membrane CO₂ absorber to produce a product stream including CO₂ and NH₃ in a predetermined CO₂:NH₃ ratio, where the CO₂-rich solvent results from an interaction between the ammonium solvent and CO₂ from the flue gas within the membrane CO₂ absorber; and providing the product stream to one or more species of algae or cyanobacteria. In some implementations, the flue gas is saturated and received into the a membrane CO₂ absorber in a downflow which washes a membrane of the membrane CO₂ absorber. In some implementations, the ammonium solvent includes ammonium hydroxide (NH₄OH). In some implementations, the CO₂ and NH₃ are provided to the one or more species of algae or cyanobacteria in a CO₂:NH₃ ratio of about 7:1 to 16:1.

BRIEF DESCRIPTION OF THE DRAWINGS

The presently disclosed subject matter will be better understood, and features, aspects and advantages other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such detailed description makes reference to the following drawings, wherein:

FIG. 1 is a schematic diagram of an exemplary CO₂ capture and fixation system made in accordance with the present invention and an industrial facility from which the exemplary CO₂ capture and fixation system receives flue gas.

FIG. 2 is an image of a CO₂ capture unit of the exemplary CO₂ capture and fixation system of FIG. 1.

FIG. 3 is an image of a membrane CO₂ absorber of the CO₂ capture unit of FIG. 2 in isolation.

FIG. 4 is an image of a first alternative membrane CO₂ absorber which may be utilized in the CO₂ capture unit of FIG. 2 in place of the membrane CO₂ absorber of FIG. 3.

FIG. 5 is an annotated image of a second alternative membrane CO₂ absorber which may be utilized in the CO₂ capture unit of FIG. 2 in place of the membrane CO₂ absorber of FIG. 3.

FIGS. 6A-6B are images of two cyclic flow photobioreactors (PBRs) which can be utilized in a utilization unit of the exemplary CO₂ capture and fixation system of FIG. 1. (A) 100,000 L cyclic flow PBR. (B) 1,200 L cyclic flow PBR.

FIG. 7 is an image of a 1,100 L open raceway pond which can be utilized in the utilization unit of the exemplary CO₂ capture and fixation system of FIG. 1.

FIG. 8 is another schematic diagram of the exemplary CO₂ capture and fixation system of FIG. 1.

FIG. 9 is a NH₃—CO₂—H₂O ternary phase diagram.⁹

FIG. 10 is a graph showing the minimum fuel selling price (MFSP) in dollars per gallon gas equivalent (GGE) change for various CO₂ sources. All cases assume co-location with the microalgae facility, and algae productivity of 25 g m⁻² day⁻¹.¹³ The blue shaded area shows the optimal bioreactor utilization efficiency of 40-50%, to balance the capital and operational cost of the algae system if compression and distribution of the CO₂ source is required. The red point is the MFSP for CO₂ from a coal-fired power plant achievable with the exemplary CO₂ capture and fixation system.

FIG. 11 is a graph showing NH₃ slip data of 2M NH₃ solution and carbon loaded 2M NH₃+ZNCl₂ solution.

FIG. 12 is an annotated satellite image of a carbon capture and utilization system in which a membrane CO₂ absorber and solar-powered regenerators made in accordance with the present invention are implemented.

FIG. 13 is an image of a tubular PBR system in which Scenedesmus acutus was cultivated using urea (control), ammonium carbonate ((NH₄)₂CO₃), and ammonium bicarbonate (NH₄HCO₃). Left to right: urea (n=3, tubes 1-3), ammonium carbonate (n=3, tubes 3-6), and ammonium bicarbonate (n=3, tubes 7-9).

FIG. 14 is a graph showing ammonium ions as a nitrogen source: culture pH versus time. Error bars represent the standard deviation (n=3).

FIG. 15 is a graph showing ammonium ions as a nitrogen source: culture absorbance at 560 nm versus time. Error bars represent the standard deviation (n=3).

FIG. 16 is a graph showing ammonium ions as a nitrogen source: culture density in g/L (dry mass measurements) versus time. Error bars represent the standard deviation (n=3).

FIG. 17 is an annotated image of a lab-scale CO₂ capture unit.

FIG. 18A is an image of a membrane CO₂ absorber which can be utilized in the lab-scale CO₂ capture unit of FIG. 17.

FIG. 18B is a sectional view of the membrane CO₂ absorber of FIG. 18A.

FIG. 19A is a chart showing the total alkalinity and carbon loading of three batches of 1M NH₄OH+0.5M (NH₄)₂CO₃ solvent utilized in the membrane CO₂ absorber of FIG. 18A in the lab-scale CO₂ capture unit of FIG. 17.

FIG. 19B is a chart showing the total alkalinity and carbon loading of 1M NH₄OH+0.5M (NH₄)₂CO₃+1 wt % TGDE solvent and 0.5M (NH₄)₂CO₃+20 wt % TGDE utilized in the membrane CO₂ absorber of FIG. 18A in the lab-scale CO₂ capture unit of FIG. 17.

FIG. 19C is a chart showing the total alkalinity and carbon loading of three batches of 1M NH₄OH+0.5M (NH₄)₂CO₃+10 wt % AMP solvent utilized in the membrane CO₂ absorber of FIG. 18A in the lab-scale CO₂ capture unit of FIG. 17.

FIG. 20 is a graph showing the CO₂ capture efficiency of the first alternative membrane CO₂ of FIG. 4 over a 50 hour period when implemented in the CO₂ capture unit of FIG. 2 and tested using multiple ammonium solvents, including solvents with and without chelating agents.

FIG. 21 is a graph showing the gas pressure drop of the tested ammonium solvents of FIG. 20 over a 50 hour operation period.

FIG. 22 is a graph showing the CO₂ capture efficiency and carbon loading (mol C/mol N) of the membrane CO₂ absorber of FIGS. 2 and 3 when tested with 2M NH₄OH solvent.

FIG. 23 is a graph showing the CO₂ capture efficiency and carbon loading (mol C/mol N) of the membrane CO₂ absorber of FIGS. 2 and 3 when tested with 2M NH₄OH+10 wt % AMP solvent.

FIG. 24 is a graph showing the CO₂ capture efficiency and carbon loading (mol C/mol N) of the membrane CO₂ absorber of FIGS. 2 and 3 when tested with 2M NH₄OH+10 wt % Tris solvent.

FIG. 25 is a graph showing the NH₃ slip (bars) and carbon loading (mol C/mol N) (trend line with square makers) of the second alternative membrane absorber of FIG. 5 when implemented in the CO₂ capture unit of FIG. 2 and tested using NH₄OH solvent.

FIG. 26 is a graph showing the CO₂ capture efficiency, carbon loading (mol C/mol N), and pH of the second alternative membrane absorber of FIG. 5 when implemented in the CO₂ capture unit of FIG. 2 and tested using NH₄OH solvent, with the CO₂ concentration is set of 5% and gas feed inflow is adjusted to 0.15 CFM, 2.41 CFM, and 3.67 CFM.

FIG. 27 is a graph showing the CO₂ capture efficiency, carbon loading (mol C/mol N), and pH of the of the second alternative membrane absorber of FIG. 5 when implemented in the CO₂ capture unit of FIG. 2 and tested using NH₄OH solvent, with the CO₂ concentration is set of 14% and gas feed inflow is adjusted to 0.15 CFM, 2.41 CFM, and 3.67 CFM.

FIG. 28 is a set of three images showing a front surface, back surface, and cross sectional view of a polyethersulfone (PES) substrate.

FIG. 29 is a set of three images showing a front surface, back surface, and cross sectional view of a PES substrate coated with 0.1 wt % Teflon AF2400 by virtue of being dipped into Teflon AF2400 for a period of 1 minute.

FIG. 30 is a set of three images showing a front surface, back surface, and cross sectional view of a PES substrate coated with 1 wt % Teflon AF2400 by virtue of being immersed into Teflon AF2400 for a period of 10 minute.

FIG. 31 is a pair of two images showing a surface and cross-sectional view of a Sterlitech® PTFE 0.1 μm laminated membrane.

FIG. 32 is a pair of two images showing a surface and cross-sectional view of a Sterlitech® PTFE 0.2 μm laminated membrane.

FIG. 33 is a chart showing the productivity (g/L/day) of algae provided with varying mole ratios of CO₂:NH₃ across different cycles.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure belongs. Any methods and materials similar to or equivalent to those described herein can be used in the practice or testing of the present disclosure, including the methods and materials that are described below.

As used herein, and unless otherwise indicated, the term “flue gas” is understood to mean an exhaust gas which includes carbon dioxide (CO₂) and which is emitted from an industrial facility, regardless of the conduit by which such exhaust gas is emitted from the industrial facility or the type of industrial facility. Accordingly, unless indicated to the contrary, “flue gas” encompasses variations including: in some embodiments, the flue gas is emitted from a power plant, such as a coal-fired power plant or natural gas-fired power plant; in some embodiments, the flue gas is emitted from a chemical plant; in some embodiments, the flue gas is emitted from a utilities plant; and in some embodiments, the flue gas is emitted from a cement plant.

Reference to a first component being in fluid communication with a second component is understood to mean that the first component and the second component are directly or indirectly connected by suitable means as to permit liquid to be transferred from the first component and received by the second component. In this regard, one of skill in the art will appreciate that a first component is still considered to be in fluid communication with a second component in instances where there are one or more intervening components (e.g., a heat exchanger, pump, etc.) which treat or process the fluid or gas directed from the first component prior to being received at the second component.

Following long-standing patent law convention, the terms “a,” “an,” and “the” refer to “one or more” when used in this application, including the claims. Thus, for example, reference to “a cell” includes a plurality of cells, and so forth.

The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently-disclosed subject matter.

As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, concentration, percentage, or the like is meant to encompass variations of in some embodiments ±50%, in some embodiments ±40%, in some embodiments ±30%, in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.

As used herein, ranges can be expressed as from “about” one particular value, and/or to “about” another particular value. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

Where reference is made to a URL or other such identifier or address, it is understood that such identifiers can change and particular information on the Internet can come and go, but equivalent information can be found by searching the Internet. Reference thereto evidences the availability and public dissemination of such information.

As used herein, nomenclature for compounds, including organic compounds, can be given using common names, IUPAC, IUBMB, or CAS recommendations for nomenclature. When one or more stereochemical features are present, Cahn-Ingold-Prelog rules for stereochemistry can be employed to designate stereochemical priority, ElZ specification, and the like. One of skill in the art can readily ascertain the structure of a compound if given a name, either by systemic reduction of the compound structure using naming conventions, or by commercially available software, such as CHEMDRAW™ (Cambridgesoft Corporation, U.S.A.).

As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

The details of one or more embodiments of the presently-disclosed subject matter are set forth in this document. Modifications to embodiments described in this document, and other embodiments, will be evident to those of ordinary skill in the art after a study of the information provided in this document. The information provided in this document, and particularly the specific details of the described exemplary embodiments, is provided primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom. In case of conflict, the specification of this document, including definitions, will control.

Provided herein is a carbon dioxide (CO₂) capture and utilization system which provides reduced CO₂ capture cost and improved algae production. Accordingly, the system 10 of the present disclosure may find utility in a variety of environments and applications in which a reduction in the capital cost of CO₂ capture from flue gas or otherwise and/or enhanced algae growth within a bioreactor or raceway system is needed or desired.

FIGS. 1 and 8 are schematic diagrams of an exemplary CO₂ capture and utilization system (or system) 10 made in accordance with the present invention.

FIG. 2 is an image of a CO₂ capture unit 12 of the exemplary system 10 of FIG. 1.

Referring now to FIGS. 1, 2, and 8, the system 10 generally includes: a CO₂ capture unit 12 (identified as “CO₂ Capture Block” in FIG. 1) configured to capture CO₂ from flue gas introduced into the system 10 from an industrial facility; and a utilization unit 30 (identified as “Utilization Block” in FIG. 1) which is in fluid communication with the CO₂ capture unit 12, and which utilizes the CO₂ captured from the incoming flue gas to improve algae production. As shown, the CO₂ capture unit 12 is positioned downstream of, and configured to receive flue gas from, an industrial facility 5 (e.g., a coal- or natural gas-fired power plant), preferably in a saturated condition. In this regard, the CO₂ capture unit 12 includes a membrane CO₂ absorber 14 that is in fluid communication with a flue gas-emitting component of the industrial facility 5, such as sulfide dioxide (SO₂) scrubber 7 (FIG. 1), in this case via conduit 11 (FIG. 1). As shown in FIG. 2, the conduit 11 supplying the inflow of flue gas from the industrial facility 5 and the membrane CO₂ absorber 14 are oriented within the CO₂ capture unit 12 and relative to each other, such that a downflow of flue gas is emitted into the membrane CO₂ absorber 14 while the system 10 is in use. Subsequent to the flue gas entering the membrane CO₂ absorber 14, the flue gas contacts a solvent within the membrane CO₂ absorber 14 in a manner which enriches the solvent with CO₂ from the flue gas. In this exemplary embodiment, the solvent is an ammonium solvent and the membrane CO₂ absorber 14 is a gas-liquid, indirect contact membrane, such that, after entering the membrane CO₂ absorber 14, the downflow of flue gas indirectly contacts the ammonium solvent. That is, the membrane CO₂ absorber 14 prevents the ammonium solvent and flue gas from contacting each other directly, but permits CO₂ within the flue gas to pass through a membrane of the membrane CO₂ absorber 14 to interact with the ammonium solvent. Specifically, in this exemplary embodiment, the ammonium solvent is aqueous ammonia with an ammonium hydroxide (NH₄OH) concentration of about 3-4 wt % and has a carbon/nitrogen mol (C/N mol) loading of about 0.3 to 0.4 C/N mol. Typically, following the absorption of CO₂ from the flue gas, the aqueous ammonium solvent (i.e., the CO₂-rich solvent) will still have an NH₄OH concentration of about 3-4 wt %, but there will be more bicarbonate (HCO₃) and carbonate (NH₄CO₃) species present in the solvent and will have a higher carbon/nitrogen mol (C/N mol) loading of about 0.5 to 0.7 mol depending on the CO₂ capture efficiency. In some embodiments, a chelating compound, such as triethylene glycol di-2-ethylhexoate (TGDE), amino trimethylene phosphonic acid (AMP), tris(hydroxymethyl)aminomethane (Tris) or a chelating compound including zinc, such as ZnCl₂, is utilized within the ammonium solvent to reduce NH₃ slip. In some embodiments, the inclusion of the chelating compound reduces NH₃ by approximately 20% as compared to a control solvent of the same composition except for the presence of the chelating agent.

FIG. 3 is an image of the membrane CO₂ absorber 14 of the CO₂ capture unit of FIG. 2, which, in this case is a Sterlitecth® PTFE membrane.

FIGS. 4 and 5 are images of a first alternative membrane 114 and a second alternative membrane 214, which may be used in place of the membrane CO₂ absorber 14 of FIG. 3 in the CO₂ capture unit of FIG. 2.

Referring now to FIGS. 1-3, in this exemplary embodiment, the membrane CO₂ absorber 14 is a flat sheet membrane, which includes one or more liquid phase sections 14a through which the ammonium solvent passes, a gas phase section 14b in which the flue gas is received, and one or more membrane sections (or membranes) 14c positioned in between the one or more liquid phase sections 14a and the gas phase section 14b. Specifically, in this exemplary embodiment, the membrane CO₂ absorber 14 is a polytetrafluoroethylene (PTFE) membrane manufactured by Sterlitech®, which includes two liquid phase sections 14a and two membrane sections 14c. In some embodiments, each membrane section 14c of the membrane CO₂ absorber 14 may include polyethersulfone (PES), polyethylene terephthalate (PET), polytetrafluroethylene (PTFE), or combinations thereof. It should be appreciated, however, that the membrane CO₂ absorber 14 is not necessarily limited to a flat sheet membrane of the construction described above. For instance, in alternatives embodiments, a hollow fiber membrane, such as a non-porous polymer (e.g., a fluoride material) with a microporous hollow fiber support (e.g., polyether ether ketone (PEEK) membrane 114 (FIG. 4) or a MICRODYN membrane 214 (FIG. 5), may be used.

Referring now again to FIGS. 1, 2, and 8 NH₃ slip occurring as a result of the solvent moving from the liquid side to the gas side of the membrane CO₂ absorber 14 can react with SO₂ and CO₂ present in the flue gas, causing salts to form. However, as a result of the flue gas entering the system 10 being introduced into the membrane CO₂ absorber 14 in a downflow and saturated condition, condensate is formed from the flue gas and continuously washes the gas-side section of the one or more membrane sections 14c, thus removing any salt species, such as ammonium sulfate and ammonium carbonate, formed as a result of NH₃ slip from building upon the membrane and enabling long-term operation of the membrane CO₂ absorber 14 and CO₂ capture unit 12. The foregoing washing action thus eliminates the need for flue gas pretreatment for cooling (for maintaining water balance) and SO₂ removal (for reducing the thermal stable salt formation), which is typically required in known CO₂ capture and utilization systems. By eliminating the need for such flue gas pretreatment, the system 10 of the present disclosure, in turn, also effectively reduces the capital costs associated with CO₂ capture from flue gas as compared to that of known CO₂ capture and utilization systems. Furthermore, in this exemplary embodiment, the condensed water including the dissolved salt species from NH₃ slip is collected within a condensate trap 20, which is in fluid communication and downstream of the membrane CO₂ absorber 14. In addition to the membrane CO₂ absorber 14, the condensate trap 20 is also in fluid communication with one or more cultivation subsystems 32a, 32b (FIG. 1), the importance of which is further described below.

Referring still to FIGS. 1, 2, and 8, in this exemplary embodiment, to reduce or eliminate the release of NH₃ into the atmosphere, the treated flue gas (i.e., the flue gas having passed through the membrane CO₂ absorber 14) is routed through an acid tower 22 configured to remove any NH₃ in the treated flue gas prior to being exhausted into the atmosphere via induced fan 13 and conduit 15.

FIGS. 6A and 6B are various images of example photobioreactors (PBRs) 36 which may be utilized in the utilization unit 30 of the system 10.

FIG. 7 is an image of an example open raceway pond (ORP) 38 which may be utilized in the utilization unit 30 of the system 10.

Referring now again to FIGS. 1, 2, 6A, 6B, 7 and 8, CO₂-rich solvent resulting from the interaction between the ammonium solvent and flue gas within the membrane CO₂ absorber 14 is directed from the CO₂ capture unit 12 and to the utilization unit 30 for subsequent processing. Specifically, in this exemplary embodiment, the CO₂-rich solvent is processed by the utilization unit 30 as to produce (i) a solvent stream which can be recirculated back to and reused within the membrane CO₂ absorber 14 and (ii) a product stream containing CO₂ captured from the flue gas and volatized NH₃ from the solvent, which can be provided in a predetermined CO₂:NH₃ ratio to one or more cultivation subsystems 32a, 32b (FIG. 1) within the utilization unit 30 containing one or more species of algae, such as Scenedesmus acutus (UTEX B72), to enhance algae production. To this end, the utilization unit 30 thus includes one or more solvent regenerators (or strippers) 31a, 31b for solvent regeneration, such as flash/matrix stirppers, which are configured to process the CO₂-rich solvent to produce the product stream and are in fluid communication with one or more cultivation subsystems 32a, 32b, such that the product stream produced by each respective stripper 31a, 31b is provided to the cultivation subsystem 32a, 32b to which it is in fluid communication with. As shown in FIG. 1, each stripper 31a, 31b may be solar powered and, to this end, operably connected to a solar cell 33a, 33b to eliminate the need for steam extraction during the solvent regeneration process, thus further reducing the capital cost associated with CO₂ capture from the flue gas relative to known systems. Each cultivation subsystem 32a, 32b can comprise one or more PBRs 36 (FIGS. 6A and 6B) and/or one or more ORPs 38 (FIG. 7). Each stripper 31a, 31b is preferably installed near the cultivation subsystem 32a, 32b to which it corresponds to provide continuous just-in-time distribution of CO₂:NH₃. The product stream is produced by each respective stripper 31a, 31b is a result of the stripper 31a, 31b heating and pressurizing the CO₂-rich solvent contained therein. In this regard, the CO₂:NH₃ ratio in of the product stream produced by each respective stripper 31a, 31b can be adjusted and controlled by adjusting the stripper pressure and the stripper exit temperature. In some embodiments, each respective stripper 31a, 31b is configured to deliver a product stream with a CO₂:NH₃ molar ratio of about 7 to about 16. In some embodiments, each respective stripper 31a, 31b is configured to deliver a product stream with a CO₂:NH₃ molar ratio of about 10.

As evidenced above, the ammonium solvent utilized within the system 10 thus acts as both a CO₂ capture agent within the CO₂ capture unit 12 and as a N nutrient for algae growth in the utilization unit 30. In one preferred embodiment, each respective stripper 31a, 31b is configured to deliver a product stream with a CO₂:NH₃ molar ratio of about 10. The continuous feed of CO₂ and NH₃ to the cultivation subsystems 32a, 32b serves to overcome typical algae growth inhibition problems commonly occurring in CO₂ capture and utilization systems of known construction due to frequent pH swings in the cultivation unit resulting from unbalanced (intermittent) feeding of CO₂ and nitrogen (N). Accordingly, in this way, the continuous feed of CO₂ and NH₃ also provides enhanced algae growth relative to such systems. Furthermore, due to the proximity between the regenerator and the cultivation subsystem, the risk of pressure drop when sparging gas into the algae is significantly reduced.

As shown in FIG. 1, to further promote algae growth, in this exemplary embodiment, the condensed water with dissolved salt species collected within the condensate trap 20 is pumped, via pump 21 to the one or more cultivation subsystems 32a, 32b.

Referring now specifically to FIGS. 1 and 8, following solvent regeneration, the ammonium solvent will typically have a NH₄OH concentration that is less than 3-4 wt % due to some NH₃ being utilized in the product stream to feed the algae in the cultivation subsystems 32a, 32b. In this regard, following solvent regeneration, the ammonium solvent may be characterized as “lean solvent.”. The lean solvent is transmitted from each stripper 31a, 31b and directed into the membrane CO₂ absorber 14 for use therein via conduit 17. Accordingly, in addition to a cultivation subsystem 32a, 32b, each stripper 31a, 31b is also in fluid communication with the membrane CO₂ absorber 14. Preferably, to bring the NH₄OH concentration of the solvent back to about 3-4 wt %, a concentrated NH₄OH solution is added to the lean solvent prior to being introduced into the membrane CO₂ absorber 14, as indicated by the introduction of NH₃ and coolant in FIG. 1.

Referring now specifically to FIG. 8, in this exemplary embodiment, the CO₂-rich solvent exiting the membrane CO₂ absorber 14 is circulated through the utilization unit 30, regenerated to lean solvent back to the membrane CO₂ absorber 14 along the below-described path. As shown, upon exiting the membrane CO₂ absorber 14, the CO₂-rich solvent is first directed into a solvent tank 16 and then pumped, via solvent circulation pump 18 and conduit 19, through first heat exchanger 23, a second heat exchanger 24, and a third heat exchanger 25 prior to being introduced into cultivation subsystem 32a for solvent regeneration. The solvent tank 16 helps to ensure a smooth continuous flow of solvent and that the solvent circulation pump 18 does not run dry. In this exemplary embodiment, the second heat exchanger 24 is regulated by a solar thermo collector. Stripper 31a then directs the solvent into a condenser 35 which is regulated by a fifth heat exchanger 29. The condenser 35 releases a predetermined ratio of CO₂/NH₃ as a product stream to cultivation unit and the resulting condensate (i.e., the lean solvent) is returned to stripper 31a. In this regard, the condenser 35 may be a component of stripper 31a or a separate component which supplements operation of stripper 31a. The lean solvent is then pumped via pump 27 back to the first heat exchanger 23 via pump 27. The lean solvent is then directed from the first heat exchanger 23 through a fourth heat exchanger 28 and into the membrane CO₂ absorber 14. However, as noted above, a concentrated NH₄OH solution is preferably added to the lean solvent prior to being introduced into the membrane CO₂ absorber 14. Although stripper 31b is not shown in FIG. 8, it is appreciated that the CO₂-rich solvent would be, in this exemplary embodiment, delivered to, processed by, and returned from stripper 31b in the same manner as described above for stripper 31a.

Referring now specifically to FIG. 1, in this exemplary embodiment, the utilization unit 30 includes two strippers 31a, 31b (one of which is shown in FIG. 8) and two corresponding cultivation subsystems 32a, 32b (neither of which is shown in FIG. 8). Of course, the system 10 is not limited to such configuration. In this regard, embodiments are contemplated in which only a single stripper and corresponding cultivation subsystem are utilized within the utilization unit 30 as well as embodiments in which more than two strippers and corresponding cultivation subsystems are utilized.

Also provided herein is a method of capturing and utilizing CO₂, which utilizes the above-described system 10. The method of capturing and utilizing CO₂ thus includes method steps which reflect the operation of, functionality provided by, and/or effects resulting from use of the above-described system 10, either as a whole or by individual components thereof. Accordingly, to avoid excessive repetition, where reference is made to the above-described CO₂ capture and utilization system or a specific component thereof as providing some function or operation, it is understood that the method of capturing and utilizing CO₂ includes, at least in some embodiments, a method step which reflects such function or operation. Accordingly, in some embodiments, the method of capturing and utilizing CO₂ provided herein may include the use of some or all of the components of the above-described system 10. Unless specified or context precludes otherwise, the various method steps may be carried out in any order.

Like algae, cyanobacteria are similarly able to fixate captured CO₂ and utilize nitrogen as a nutrient source. Accordingly, although discussed herein primarily with respect to providing enhanced algae growth, one of ordinary skill in the art will appreciate that, in some embodiments or implementations, one or more species of cyanobacteria may alternatively be used in place of algae to fixate CO₂ within the system 10 and method described herein without departing from the spirit or scope of the present invention.

The presently-disclosed subject matter is further illustrated by the following specific but non-limiting examples. The following examples may include compilations of data that are representative of data gathered at various times during the course of development and experimentation related to the presently-disclosed subject matter. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein.

EXAMPLES

Example 1

Ammonium Looping with Membrane Absorber and Distributed Stripper for Enhanced Algae Growth

The present NH₃-based looping integrated CO₂ capture and utilization system (FIGS. 1 and 8) described herein reduces capture capital and operating costs by 50% by eliminating flue gas pretreatment for cooling/SO₂ removal, steam extraction for solvent regeneration and CO₂ compression. It also boosts algae production by 50% by continuously supplying CO₂ and NH₃ in the appropriate growth ratio, compared to intermittent, decoupled feeding systems. To these ends, the current system includes at least three features which are unique to the present CO₂ capture and utilization system. First, the system utilizes a thermally- and oxidatively-stable, dual-function, NH₃ reagent that is both the CO₂ capture absorbent and an algae nutrient. Second, the system utilizes a downward flow, gas-liquid, indirect contact membrane CO₂ absorber, where the capture and biofixation is decoupled and NH₃ slip is minimized by including a chelating compound in the ammonium solvent. Condensate from incoming saturated flue gas continually washes the gas side of the absorber to ensure long-term operation. Third, carbon-rich solvent distributed regenerators installed near algae cultivation units to provide local, just-in-time distribution of CO₂ and NH₃ at the appropriate ratio boosting algae production. Solvent regeneration is powered by solar-thermal energy, thus eliminating the need for steam extraction.

Reduced Cost of CO₂ Captured to Cultivation Unit. Approximately 25% of the cost of aqueous post-combustion (PC) CO₂ capture is associated with flue gas pretreatment, steam extraction, and CO₂ compression, which are all eliminated by the current CO₂ capture and utilization system. Advantage is taken of the flue gas condensate in the indirect-contact low-thermally conducting membrane CO₂ absorber (FIGS. 1, 2, and 8), eliminating the need for a cooling (for maintaining the water balance in the typical aqueous systems) and SO₂ removal pretreatment (for reducing the thermal stable salt formation in the conventional aqueous systems) step. Ammonium solvent regeneration is powered by solar energy, thus eliminating the need for steam extraction. The integrated solvent regenerator with cultivation unit (e.g., photobioreactor or open raceway pond) eliminates the need to compress a CO₂ product stream. A preliminary techno-economic analysis (TEA) conducted by Colorado State University has indicated that 20-50% of the cost of algae production is from CO₂ cost and distribution depending on the source (coal or natural gas (NG), respectively), the way CO₂ is supplied and the distance transported.

Dual-Functional NH₃ Looping. To reduce NH₃ emissions, NH₃ slip within the system is managed in three ways. First, a carbon-loaded low concentration ammonium solvent (e.g., a 2M NH₃ solvent) with additives is employed to lower the NH₃ vapor pressure. The species partial pressure is proportional to the concentration in the liquid. Hence, lowering the concentration will lower the partial pressure. Additionally, previous work has demonstrated that the addition of Zn²⁺ into ammonium solvents to chelate the NH₃ can reduce NH₃ volatility. Second, a downflow flue gas configuration is utilized due to the fact that flue gas is entering the membrane CO₂ absorber at a saturated condition, forming liquid film along the membrane wall due to heat transfer. Experiments performed using water-saturated simulated flue gas showed a benefit to anti-fouling and NH₃ slip recapture from the water condensate liquid phase formed on the gas-side of the membrane. The downflow orientation also allows the condensate to continuously wash ammonium salts from the membrane surface when formed. The collected condensate is fed to the algae as makeup water and supplemental nutrients. Third, a nanoporous, dense membrane is utilized. In an effort to reduce NH₃ slip, a set of chemically resistant composite fibers have been utilized, made of a thin dense layer that is highly permeable to CO₂ but less permeable to NH₃. It was found that fluorinated polymers are effective for this purpose by increasing the NH₃ mass transfer resistance. Further development of the membrane material may be conducted to depress the NH₃ permeability. Optional coatings and membrane materials may, in some instances, be considered with higher CO₂ permeabilities than NH₃, such as polydimethylsiloxne (PDMS), TPX®, or Teflon AF2400®.

Preferable Growth Media with Just-in-Time C:N Delivery at Appropriate Ratio. In the regenerators, the amount of CO₂ and NH₃ in the resulting product stream is adjusted and controlled by a combination of the stripper pressure and stripper exit temperature. In the system, a pressure of 50 psi and a temperature of 135° F. after the overhead condenser should deliver a product stream with C:N molar ratio of ˜7, as required by the algae culture. The direct connection between the regenerator and the cultivation unit will avoid long distance delivery, and reduce associated capital and gas compression cost. Algae biomass typically contains 45-50% C, 7-8% N, and 1.4% P, varying according to species and growth conditions. Numerous studies have suggested that the effects of N on algae production and composition may depend on the source and chemical composition of N added to the growth medium. Additionally, the thermally compressed CO₂/NH₃ stream from the stripper will facilitate sparging of this stream into the cultivation units for high CO₂ utilization efficiency.

Disruptions of CO₂ Original Source. The ammonium solvent loop of the current technology can continue to circulate with regeneration occurring for short periods during interruption of the flue gas supply. In this case, the solvent is over-stripped, but the algae feed will remain continuous.

Control of NH₃ slip. First, according to thermodynamics, the gaseous partial pressure of a species is proportional to the molar ratio of the species in the solution, in this application, dissolved NH₃; hence, a low dissolved NH₃ concentration in the CO₂ capture solvent via zinc chelating (expressed in Table 1) and the presence of carbon species (carbonate and bicarbonate) will depress the NH₃ partial pressure that is the driving force for slip to the gas-side of the membrane. Second, 30-50 ppm SO₂ present in flue gas could react with NH₃, in a similar pathway as CO₂, if NH₃ slips to form ammonium sulfate or sulfite for further flue gas SOx reduction, with the salts dissolving in the liquid condensate from the saturated flue gas after wet flue gas desulfurization (WFGD).

TABLE 1
Chelation, CO2 Capture and Regeneration Reactions.
Zn2+ + 4NH3 ↔ [Zn(NH3)4]2+
CO2 + H2O ↔ HCO3− + H+
NH3 + H2O ↔ NH4+ + OH−
[Zn(NH3)4]2+ + HCO3− ↔ [Zn(NH2COO)2]2 + 2NH3 + 2H2O
2NH3 + CO2 + H2O ↔ (NH4)2CO3

In-situ Antifouling. As evidenced in the NH₃—CO₂—H₂O ternary phase diagram shown in FIG. 9, ammonium carbanate, a sticky solid, is the only product between NH₃ and CO₂ in the absence of water. However, non-sticky ammonium carbonate, a compound that is very soluble in water, is formed at a saturated gas condition when the CO₂ concentration is much higher than the NH₃ concentration, as it exists in the proposed scenario. Downflow condensed water from the saturated flue gas in the application of coal-fired power plant (FIG. 1) will continuously dissolve and wash away the NH₄⁺ salts as they form and prevent fouling of the membrane. For application at a NG power plant, periodically sprayed water on the membrane wall is required to clean the salts.

Enhanced Algae Growth. Algae is less productive when under chemical stress, which is the practical case resulting from intermittent intake of NH₄⁺, HCO₃⁻ and CO₃²⁻, or when there is an imbalance in the C:N ratio in the algae growth medium, as shown in Table 2. At high C:N ratios, consumption of N by the culture (in parallel with CO₂ consumption) will result in a pH decrease, whereas at low C:N ratios the pH increases. Hence, there is a strong incentive to target the stoichiometric C:N ratio in the solution fed to the culture to minimize fluctuations in pH. To address this, distributed solvent regenerators are operated individually to deliver just-in-time CO₂ and NH₃ to the cultivation unit as needed and at the appropriate ratio. Given that the molar C:N ratio of rich NH₄⁺ solution exiting the membrane contactor is 0.5 (corresponding to ammonium carbonate) without any regeneration, and 147 when the regenerator outlet is set at 210° F. and 59 psi, the stoichiometric C:N ratio (˜7) for Scenedesmus acutus (UTEX B72), the algae strain to be used in the current example, is readily achieved by adjusting the stripper pressure and exhaust temperature.

TABLE 2
NH3 and CO2 Consumption.
NH4+ consumption-excess CO2 present (NH4+ limiting):
(NH4)2CO3 → → H2CO3; NH4HCO3 → → H2CO3
CO2 consumption-excess NH4+ present (CO2 limiting):
(NH4)2CO3 + H2O → → 2NH4OH; NH4HCO3 → → NH4OH

Algae Growth and Integrated Regeneration by Solar Energy. The algae production rate for UTEX B72 depends on the geological location and cultivation system. In Kentucky (KY), the University of Kentucky Center for Applied Energy Research (UK CAER) has achieved productivity of 35 g m⁻² day⁻¹ (dry weight basis) under optimum climatic conditions (cultivation May-September) using a tubular PBR with intermittent CO₂ feeding based on culture pH. For ORPs, areal productivities are much lower. For example, for UTEX B72 grown in KY in September-October 2018, fed with CO₂ on an open loop (no pH control), measured areal productivity averaged 4.8 g m⁻² day⁻¹. With the continuous, just-in-time CO₂ and NH₃ delivery to the cultivation unit to minimize the culture pH swing, significant improvement in productivity (at least 50%) can be achieved. This stems not only from the advantage of operating with improved pH control and an optimized C:N ratio, but also from the standpoint of reduced culture contamination. By maintaining constant basic conditions in the culture, rather than feeding gaseous CO₂ which typically results in operational pH values of 7 or less, since CO₂ dissolves in water to form carbonic acid, invasive organisms are less able to establish themselves in the culture, resulting in reduced instances of culture crashes and improved productivity. In both ORPs and PBRs, pests ranging from grazers to parasites can quickly invade and decrease productivity and yield or decimate entire crops. Although there is no one-size-fits-all approach, increasing the culture pH represents one of the simplest and most effective treatment options, providing the algae strain is sufficiently robust to alkaline conditions.

It should be noted that while ORPs are inherently less productive than PBRs, they are the preferred cultivation system for large-scale algae production due to their significantly lower capital cost. Albeit PBRs do possess specific advantages over ORPs and are preferred for niche applications (high-value, low-volume products), the current system preferably utilizes ORPs as the cultivation unit due to anticipated application of massive power generation.

Finally, it should be noted that based on the annual solar intensity of 5 kWh/m²-day in KY and the heat of regeneration of 120 kJ/mol CO₂ (10 kJ/gram C), 50% of algae as C and 50% CO₂ utilization efficiency in the reactor to produce a targeted max. 50 gram/m²-day, the footprint to collect sufficient solar energy (500 kJ) to heat the rich solvent for CO₂ and NH₃ supply is about 0.028 m², which is only 2.8% of the cultivation unit footprint as the upper limit. Hence, solvent regeneration powered by solar energy is feasible.

Typical sources of CO₂ considered for algae cultivation are waste streams from power or chemical plants. These sources range in concentration from low (3-5 vol %, 12-15 vol % and 20-25 vol % for natural gas-fired power plants, coal-fired power plants, and cement plants, respectively) to high (99 wt % for ethanol, NH₃, or hydrogen plants). Assuming the algae farm is co-located with the CO₂ source, two scenarios for introducing CO₂ into algae cultures and three cases of CO₂ sources were considered for a preliminary economic analysis. The two CO₂ delivery methods considered were: 1) compression and subsequent bubbling of the gas directly into the algae growth system; and 2) producing a concentrated aqueous stream saturated or supersaturated with dissolved C. Assuming the chemical CO₂ is free of charge, the cost of CO₂ with the first delivery option (direct use) derives just from the auxiliary power and balance of the plant associated with compression, transportation and distribution, while the cost of CO₂ with the second delivery option (aqueous stream) covers the capital and operational cost associated with CO₂ separation/enrichment, as well as transportation and distribution.

UK CAER past experience has concluded that utilization efficiencies of 40-50% are optimal to balance the capital and operational cost of the algae system if compression and distribution of the CO₂ source is required. As anticipated, utilizing a dilute CO₂ source requires much higher reselling price (RSP) to achieve economic sustainability (FIG. 10).¹³ For instance, at 40% CO₂ utilization efficiency in the cultivation unit, direct use of CO₂ in flue gas produced from NG combustion (5 vol % CO₂) equates to $3.9/gasoline gallon equivalent (GGE), compared to $1.5/GGE needed for coal flue gas (13.5 vol %) and less than $0.2/GGE for ethanol plants or chemical plants due to high capital and operational cost being required to deliver dilute CO₂ to the algae culture. On the other hand, enriching CO₂ from flue gas to 99⁺% purity could reduce the transport and distribution costs associated with the pure CO₂; however, the cost associated with CO₂ capture could exceed the savings. For example, with 90% CO₂ capture from power production, due to the C intensity of coal (Case B12B, 2190 lb/MWe-hr net),¹⁴ CO₂ preconcentration results in high RSP, $2.1 versus $1.5/GGE. Contrarily, due to the low C intensity of NG (Case B31B, 850 lb/MWe-hr net), capture, transport, and distribution of pure CO₂, instead of compressing flue gas containing 5 vol % CO₂, will result in savings of ˜$1 on RSP.¹³

Success of the current system can significantly reduce the cost of CO₂ capture, transport and distribution in four ways. First, using solar thermal energy for solvent regeneration eliminates the need for excess generation capacity (boiler, turbine and their auxiliary equipment) necessary to provide steam and electricity to the solvent regeneration unit. Direct feed of the CO₂ and NH₃ to the algae eliminates the need for the product CO₂ stream compression. The indirect contact between the flue gas and the aqueous capture solvent, and the low thermal conductivity of the membrane, will eliminate the need for flue gas cooling and pretreatment to prevent the accumulation of water and thermally stable salts in the capture loop. These portions of the cost in DOE/NETL Case B12B¹⁴ are ˜$700/kW in capital and $7/MWh in fuel and fixed cost. Second, the use of NH₃ as the capture reagent and nutrient for algae growth could reduce costs associated with solvent makeup, which account for approximately 5% of the overall cost when an advanced, second-generation solvent is used. Third, solvent pumping, transport and distribution reduces the balance of plant (BOP) cost related to the flue gas duct and boost fan. Fourth, the just-in-time CO₂ and NH₃ delivery to the cultivation unit at close to stoichiometric C:N ratio will boost algae production. A 50% reduction of RSP for CO₂ from coal-fired power plants is achievable, as indicated by the red dot in FIG. 10 (<$1/GGE).

The product of the system, in the present example, is a microalgae biomass. Specifically, UTEX B72 was selected as the organism of choice, due its high productivity, robust nature, and high protein content. The latter characteristic renders UTEX B72 biomass an excellent feedstock for the production of bioplastics. Our study shows that the cultivation of UTEX B72 in ORPs using power plant flue gas is commercially viable for an n^th plant if the whole, dried biomass is used as a feedstock for the production of bioplastics with a minimum selling price of $970/tonne, which falls within the profitable feedstock price range.¹² While algae biomass could potentially be used as animal feed, bioplastics represent a more valuable application. Biomass is typically purchased for $800-$1,200/tonne, which allows for profitability in the bioplastic industry. Equally important, LCA results reveal a decrease in greenhouse gas (GHG) emissions of between 67% and 116% (cultivation system and biomass process scheme dependent) through the direct substitution of petroleum-derived plastic resins with algae-based bioplastic feedstock, showing a clear path to improve sustainability of the plastics market. Currently, around 1% of the global plastics market is occupied by bioplastics, the majority of which are made with food products. The global bioplastics market is forecast to grow at a compounded annual growth rate (CAGR) of not less than 20% over the period 2019-2024.¹⁶ In 2019, global bioplastics production was about 2.11 million tonnes.¹⁷ Finally, it should be noted that a variety of other products can be obtained from algae, ranging from low-value products such as fuels (economically unfeasible at present) to high-value products such as nutraceuticals and specialty foods. While such high value products are economically attractive, the small size of these markets means that they are unable to utilize significant amounts of CO₂.

Algae biomass from UTEX B72 typically contains 45-50% C, 7-8% N, and 1.4% P, albeit the elemental composition can vary significantly according to the species of algae and growth conditions. This composition is consistent with the Redfield molar elemental ratio (106:16:1 C:N:P) on a mass basis (40:7:1 C:N:P). Nearly 50% of the final dry product corresponds to the CO₂ feedstock.

The CO₂ capture and utilization system receives flue gas exiting an industrial facility, which, in this case, is a coal-fired plant, after WFGD, at ˜125° F. (coal and plant location dependent) and 15 psi, and is comprised of 11-14 vol % CO₂, 5-7 vol % O₂, 15-17 vol % H₂O, <1 vol % Ar, 20-50 ppm SO₂, 40-60 ppm NOx, and trace amounts of metals, with the balance being N₂. Without concerns about condensate in the gas and thermally stable salts accumulating in the capture solvent, the flue gas enters the membrane reactor directly without the cooling/SO₂ polishing step required by most aqueous post-combustion systems.

Membrane CO₂ Absorber. Several things happen in the membrane CO₂ absorber. CO₂ and SO₂ in the flue gas penetrate to the liquid side, and form carbonate, bicarbonate and sulfite. In parallel, a small portion of the dissolved NH₃, at the ppm level, will slip from the liquid side to the gas side and could react with SO₂ or CO₂ to form salts. Adiabatic expansion cooling occurs as CO₂ is absorbed along the membrane, resulting in condensation of water from the flue gas. This liquid water dissolves the NH₄⁺ salts and prevents surface fouling. The flue gas down-flow drains the liquid to the sump by gravity and prevents membrane flooding. Because aqueous NH₃ is not a preferred agent (compared to amines) for the accumulation of trace metals such as As, Se, and others, the heavy metals most likely will remain in the flue gas.

Testing of Zinc Ammonium Solvent. Zinc-ammonium solvent was tested at the UK CAER large bench CO₂ capture facility. ˜30% reduction in NH₃ slip was observed with tests using ˜7 wt % NH₃ concentration. The membrane, in this example, is a custom built membrane supplied by Compact Membrane Systems of Newport, Del. It is a nanoporous amorphous fluoropolymer membrane and has been demonstrated with other dissolved gas applications.²⁷ Preliminary study using a UK CAER bench-scale membrane device (FIG. 11) revealed that NH₃ slip for the proposed concentrations and chemical additives for membrane absorber is manageable and controllable (FIG. 12). NH₃-based solvent regeneration has been tested by UK CAER (bench), Alstom (large pilot), and SRI (bench and pilot-scales).

System Integration. The CO₂ capture and utilization system, in the present example, integrates UK CAER's existing CO₂ capture system (replacing the absorber and implementing solar-powered regenerator) and cultivation unit (FIG. 12) to demonstrate CO₂ capture and utilization from coal-, NG-, or other industrial-flue gas with 50% algae growth improvement and more than 20% cost reduction. Located in close proximity, these UK CAER facilities have been separately utilized for CO₂ capture and algae growth for many years. Replicating the commercial-scale approach, the final integrated capture and utilization UK CAER system will include real flue gas generators (coal and NG), a hydrophobic membrane CO₂ absorber, a packed-bed stripper, cultivation units, auxiliary pumps, NH₃ and water make-up systems, heat exchangers, valves, instrumentation and controls. A 2M ammonium solvent is used as both the capture agent and N nutrient for algae growth.

Process Description. The CO₂ capture and utilization system uses 15 cfm flue gas produced from either coal or NG combustion and a spiral-wound polymeric membrane for CO₂ preconcentration to simulate an industrial CO₂ source. Other process equipment includes: the membrane CO₂ absorber; solar powered regenerator, such as a flash/matrix stripper; cultivation units, such as ORPs; auxiliary pumps; NH₃ and water make-up systems; heat exchangers; valves; and instrumentation and controls. Flue gas enters a WFGD for SO₂ removal. A fan is then used to boost the pressure before flowing downward through the membrane CO₂ absorber. Treated flue gas flows through a water-wash column to remove any NH₃ slip prior to stack emission. The CO₂-rich solution exited from the absorber will flow through a pump, a heater powered by solar energy, and a solvent regenerator followed by a rich-lean heat exchanger, be pressurized by a pump and recirculate through a lean solvent temperature polisher to CO₂ membrane absorber. The product stream at the solvent regenerator exhaust is injected to the cultivation unit via sparging under just-in-time supply control strategy. A 2 M ammonium solvent is used as a capture agent and N nutrient for algae growth. A membrane absorber with flow capacity of 15 cfm supplied by Compact Membrane System of Newport, Del. is used for CO₂ capture and NH₃ slip study. A modularized cultivation unit with approximate 10 m² is used to evaluate the performance of system integration.

Absorber Performance Evaluation. Operation with 10 ft³ min⁻¹ coal- and NG-derived and industrial flue gas is conducted to establish baseline performance of the membrane CO₂ absorber in terms of CO₂ capture and mass transfer enhancement, NH₃ slip and operation stability due to NH₃ salt formation. The solvent formulation may be adjusted by adding a chelating agent and the C5C catalyst to evaluate effect on mass transfer enhancement and NH₃ slip. The solvent regeneration heat input and operating parameters (temperature and pressure) is studied for CO₂:NH₃ regeneration ratio and solar heater specification. Rejection rate and flux change over time is also measured.

Algae Production Evaluation. UTEX B72 is cultured in a 1,200 L PBR and continuously fed with the appropriate CO₂:NH₃ ratio. The focus of this activity is on optimizing the CO₂:NH₃ introduction control system, based on pH. The algae culture ability to self-buffer, means that optimization is likely iterative. Algae productivity is determined based on regular gravimetric culture density measurements and the algae harvest. Culturing and harvesting follows standard practices. Measured productivity is compared with the modeled productivity for the same period/climatic conditions, using the UK CAER model.

Membrane Modeling. A module-scale model for a counter-current flow membrane absorber using a gas-permeation membrane with selective transport of CO₂ over NH₃ is used. Model inputs include the flue gas stream CO₂ partial pressure, influent concentration of NH₄⁺ in CO₂-lean aqueous stripping stream, and conditions (P, T and flow) of both streams. System parameters include the experimentally measured permeabilities for CO₂ and NH₃ and membrane area. The model outputs the spatial distributions of the CO₂ partial pressure in flue gas stream, the NH₄HCO₃ concentration in the stripping stream, and the trans-membrane fluxes of CO₂ and NH₃ along the membrane module. This facilitates system optimization by balancing the membrane area and the solvent flowrate that strongly influences regeneration energy.

Example 2

Cultivation of Scenedesmus acutus Using Ammonium Ions as the Nitrogen Source

Experiments were conducted to assess the feasibility of culturing Scenedesmus acutus using ammonium ions as the nitrogen source. Aqueous ammonia could be an interesting option for scrubbing CO₂ from flue gas (as ammonium carbonate/bicarbonate), the resulting carbon- and nitrogen-rich stream being used for the cultivation of algae. Indeed, ammonia is a lower-cost source of N than other commonly used sources such as sodium nitrate and urea. However, while some organisms appear able to use aqueous ammonia as a N-source, for other organisms high concentrations of ammonium ions appear to be toxic.

Cultivation of Scenedesmus acutus was conducted using (NH₄)₂CO₃ (ammonium carbonate) (FIG. 13, tubes 4-6) and NH₄HCO₃ (ammonium bicarbonate) (FIG. 13, tubes 7-9) as the N-sources, as a surrogate for CO₂-enriched aqueous ammonia. In parallel, an experiment was performed using urea as a control (FIG. 13, tubes 1-3). The amounts of the N-containing compounds were adjusted to give the same molar concentration of nitrogen in all cases (urea=140 mg L⁻¹, (NH₄)₂CO₃=256 mg L⁻¹, NH₄HCO₃=422 mg L⁻¹) while the concentrations of the other nutrients were fixed according to the recipe of the urea-containing medium.²⁶

Experiments were conducted in a temperature controlled (20-27° C.) 10 L tubular photobioreactor system (FIG. 13). An artificial light system set to a 16:8 light/dark cycle (T5 cool white fluorescent bulbs) delivered 500 micromole m⁻² s⁻¹ PAR of photoactive radiation. CO₂ was delivered as 3% CO₂/nitrogen balance from gas cylinders. The experiments ran for 21 days.

Three times a week pH, UV-vis absorbance and dry mass measurements were made. As shown in FIG. 14, the pH of all media were very similar and remained close to the initial culture pH of 6.3.

FIG. 15 depicts the measured UV-vis absorbance of the samples measured at 560 nm as a function of run time. These results clearly indicate that the cultures provided with (NH₄)₂CO₃ and NH₄HCO₃ were significantly more productive than the control. This result is confirmed by the corresponding dry mass measurements (FIG. 16): algae growth rates were significantly higher than for the control, there being no statistically significant difference between the rates for (NH₄)₂CO₃ and NH₄HCO₃. Evidently, the organism is able to utilize ammonium ions as a nutrient more efficiently than urea.

Overall, the above results confirm the suitability of ammonium ions as a N-source for Scenedesmus acutus and lend support to the viability of a process scheme in which CO₂ is scrubbed from flue gas using aqueous ammonia, the resulting C- and N-rich stream functioning as a nutrient stream for algae production.

Example 3

Indirect, Gas-Liquid Membrane CO₂ Absorber Performance

Lab-Scale Hollow Fiber Indirect, Gas-Liquid Membrane

A lab-scale CO₂ capture unit (FIG. 17) employing a hollow fiber membrane 314 (FIGS. 17 and 18A) as the membrane CO₂ absorber was provided with a downflow of water saturated feed gas to mimic flue gas inflow for testing periods ranging from 50 hrs (FIGS. 19B and 19C) to 100 hrs (FIG. 19A) to assess viability of prolonged operation of the membrane CO₂ absorber in conditions in which ammonium salt buildup on the gas-side of the membrane CO₂ absorber was possible. The hollow fiber membrane 314 included a non-porous CMS polymer 316 with fluoride material (FIG. 18B) and a microporous hollow fiber support with polyether ether ketone (PEEK) 318 (FIG. 18B) and was 8 inches in length with a surface area of 0.015 ft² (FIG. 18A). The hollow fiber membrane also exhibited a N₂ flow rate of 0.013 at 20 psig/cfm. Batches of ammonium solvent, both with (1M NH₄OH+0.5 M (NH₄)₂CO₃+1 wt % TGDE, 1M NH₄OH+0.5 M (NH₄)₂CO₃+20 wt % TGDE) and without chelating agents (1M NH₄OH+0.5 M (NH₄)₂CO₃)), were utilized within the hollow fiber membrane. Total alkalinity/(mol/kg) and carbon loading/(mol/kg) for the different batches was assessed using acid titration and total organic carbon method, respectively.

The total alkalinity/(mol/kg) and carbon loading/(mol/kg) of the solvent batches without chelating agent are shown in FIG. 19A. The total alkalinity/(mol/kg) and carbon loading/(mol/kg) of the solvent batches TGDE chelating agent are shown in FIG. 19B. The total alkalinity/(mol/kg) and carbon loading/(mol/kg) of the solvent batches with AMP chelating agent is shown in FIG. 19C. Ammonia slip of the tested batches is indicated in Table 3 below.

TABLE 3
Ammonia slip in ammonium solvent batches
with and without chelating agent.
		Testing time	Ammonia
Batch	Solvent	(hr)	slip (ppm)
1	1M NH4OH + 0.5M (NH4)2CO3	100	6345
2	1M NH4OH + 0.5M (NH4)2CO3	100	5409
3	1M NH4OH + 0.5M (NH4)2CO3	100	5795
4	1M NH4OH + 0.5M (NH4)2CO3 + 1 wt %	50	5953
	TGDE
5	1M NH4OH + 0.5M (NH4)2CO3 + 20	50	5049
	wt % TGDE
6	1M NH4OH + 0.5M (NH4)2CO3 + 10	50	4826
	wt % AMP

The findings of the tests demonstrated that prolonged operation of an indirect gas-liquid membrane for flue gas CO₂ capture is possible as a result of any ammonium salts formed on the gas side of the membrane being washed by flue gas condensate. The findings also indicate that ammonia slip of ammonium solvent from the liquid side to the gas-side of the membrane can be reduced significantly with the use of chelating agents, in some cases up to 20%.

Bench-Scale Hollow Fiber Indirect, Gas-Liquid Membrane

The CO₂ capture unit of FIG. 2 was modified as to include a four-inch indirect, gas-liquid hollow membrane (FIG. 20) (i.e., in place of the flat sheet membrane shown in FIG. 3). The membrane (FIG. 20) was 20 inches in length with a surface area of 14 ft² and exhibited an N₂ flow rate of 1.907 at 20 psig/cfm. Multiple ammonium solvents, both with and without various chelating agents, were utilized within the membrane to facilitate CO₂ capture. With each solvent, the membrane was provided with a downflow of saturated flue gas for a period of 50 hours and tested for CO₂ capture efficiency and gas pressure drop over such period. CO₂ capture efficiency was tested via mass balance and gas pressured drop was measured by determining differential pressure. NH₃ slip and outlet CO₂% output percentage were also measured with respect to the solvents of 2M NH₄OH and 2M NH₄OH+8.9 wt % Tris at different carbon loading C/N ratios.

The CO₂ capture efficiency using the tested ammonium solvents over the 50 hour operation period are shown in FIG. 20. The gas pressure drop of the tested ammonium solvents over the 50 hour operation period are shown in FIG. 21. Ammonia slip of, and % CO₂ exhausted following interaction with of 2M NH₄OH and 2M NH₄OH+8.9 wt % Tris is indicated in Table 4 below.

TABLE 4
	Total	Carbon	Carbon	Outlet	NH3
	alkalinity	loading	loading (mol	CO2	slip
Solvent	(mol/kg)	(mol/kg)	C/mol N)	(%)	(ppm)
2M NH4OH	1.718-1.706	1.26-1.36	0.733-0.797	6.77-8.39	1001
2M	2.295-2.281	1.36-1.39	0.592-0.609	6.94-7.76	1050
NH4OH + 8.9
wt % Tris

The findings of the tests indicated that with the hollow fiber membrane of FIG. 20, 1000 ppm NH₃ slip can be achieved at a carbon loading of 0.6 C/N (higher free amine concentration) with the addition of Tris instead of 0.8 C/N (lower free amine concentration) in 2M NH₄OH.

Flat Sheet Indirect, Gas-Liquid Membrane

The CO₂ capture unit of FIG. 2, including the flat-sheet membrane of FIG. 3 with Sterlitech® PTFE membrane, was tested for CO₂ capture efficiency when provided with various ammonium solvents, both with (2M NH₄OH+10 wt % AMP and 2M NH₄OH+10 wt % Tris) and without (2M NH₄OH) various chelating agents, and supplied with saturated flue gas for periods ranging from 8 hrs to 16 hrs. NH₃ slip, carbon loading mol C/mol N, and total alkalinity were also measured with respect to each solvent at different carbon loading C/N. CO₂ capture efficiency was measured by mass balance. NH₃ slip was measured via sampling the flue gas post interaction with the respective solvents. Carbon loading was measured via total organic carbon method. Total alkalinity was measured via acid titration.

The CO₂ capture efficiency and carbon loading with the 2M NH₄OH solvent is shown in FIG. 22 and Table 5 below. The total alkalinity and NH₃ slip with the 2M NH₄OH solvent is shown in Table 5 below. The CO₂ capture efficiency and carbon loading with the 2M NH₄OH+10 wt % AMP solvent is shown in FIG. 23 and Table 5 below. The total alkalinity and NH₃ slip with the 2M NH₄OH+10 wt % AMP solvent is shown in Table 5 below. The CO₂ capture efficiency and carbon loading with the 2M NH₄OH+10 wt % Tris solvent is shown in FIG. 24 and Table 5 below. The total alkalinity and NH₃ slip with the 2M NH₄OH+10 wt % Tris solvent is shown in Table 5 below. In FIGS. 23-24 the trend line with square markers corresponds to carbon loading (mol C/mol N).

TABLE 5
	Total	Carbon	Carbon	Outlet	NH3
	alkalinity	loading	loading (mol	CO2	slip
Solvent	(mol/kg)	(mol/kg)	C/mol N)	(%)	(ppm)
2M NH4OH	1.273-1.115	0.30-0.35	0.238-0.299	4.79-4.81	1925
2M	1.892-1.832	0.48-0.50	0.254-0.270	4.77-4.79	1559
NH4OH + 10
wt % AMP
2M	1.598-1.568	0.39-0.41	0.242-0.260	4.79-4.83	1364
NH4OH + 10
wt % Tris

The findings of the tests indicated that, with the flat sheet membrane (FIG. 3), 1000 ppm NH₃ slip can be demonstrated at ˜0.25 C/N with the addition of 10 wt % Tris. During the course of testing the flat sheet membrane (FIG. 3) it was also observed that the flat sheet membrane achieved a 0.7 kPa pressure drop on the gas side between the membrane inlet and outlet for the flat sheet membrane at 5 cfm feed flow rate as compared to a 15 kPa pressure drop for the hollow fiber membrane of FIG. 20 at 0.2 cfm.

MICRODYN Hollow Fiber Indirect, Gas-Liquid Membrane

The CO₂ capture unit of FIG. 2 was modified as to include and utilize a MICRODYN hollow fiber membrane (FIG. 5) with a membrane diameter of 1.8 mm, a membrane area of 0.75 m², and a free flow area of 5 cm² (i.e., instead of using the flat sheet membrane shown in FIG. 3). NH₃ slip at different carbon loading (mol C/mol N) ratios was first measured for the MICRODYN membrane (FIG. 5) provided with 2M NH₄OH and supplied with saturated flue gas for a period of approximately 27 hrs, the results of which are evidenced in FIG. 25 and Table 6 below.

TABLE 6
Carbon loading NH3 slip
(mol C/mol N)  (ppm)
0.588-0.591    603
0.599-0.619    565
0.638-0.656    585
0.656-0.681    492
0.681-0.697    397

The effect of gas feed flow rate with respect to CO₂ Efficiency and pH at different carbon loading (mol C/mol N) levels using the MICRODYN membrane was also tested by (i) setting the inlet CO₂ concentration to 5% and adjusting the gas feed flow to 1.15 CFM, 2.41 CFM, and 3.67 CFM (FIG. 26) and (ii) setting CO₂ concentration to 14% and adjusting the gas feed flow to 1.15 CFM, 2.41 CFM, and 3.67 CFM (FIG. 27). In both instances, the liquid inlet pressure was 1 psig and the gas inlet pressure was ˜0.5 psig.

Testing of the MICRODYN membrane revealed that the increased inner diameter of the membrane dramatically decreased pressure drop and that residence time is the main impact on CO₂ capture efficiency.

Advanced Membrane Development

To determine which membrane compositions best serve to reduce NH₃ slip, various membranes were tested using the lab-scale CO₂ capture unit of FIG. 17. Specifically the following membranes were tested: a polyethersulfone (PES) substrate (FIG. 28); a PES substrate coated with 0.1 wt % Teflon AF2400 by virtue of being dipped into Teflon AF2400 for a period of 1 minute (FIG. 29); a PES substrate coated with 1 wt % Teflon AF2400 by virtue of being immersed into Teflon AF2400 for a period of 10 minutes (FIG. 30); a Sterlitech® PTFE 0.1 μm laminated membrane (FIG. 31); and a Sterlitech® PTFE 0.2 μm laminated membrane (FIG. 32). All membranes were tested with 1M NH₄OH+0.5 M (NH₄)₂CO₃ to simulate solvent circulated back from the utilization unit (i.e., lean solvent provided with concentrated NH₄OH). The NH₃ slip observed for each of the tested membranes is shown in Table 7 below.

TABLE 7
	Contact Angle		Run	Ammonia
Membrane	(°)	Solvent	time (h)	Slip (ppm)
PES substrate	81	1M NH4OH +	3	559
		0.5M
		(NH4)2CO3
PES coated with	118	1M NH4OH +	3	65
0.1 wt % Teflon		0.5M
AF2400 for 10		(NH4)2CO3
min
PES coated with 1	125	1M NH4OH +	6	40
wt % Teflon		0.5M
AF2400 for 1 min		(NH4)2CO3
Sterlitech PTFE	134	1M NH4OH +	5	80
0.1 μm laminated		0.5M
		(NH4)2CO3
Sterlitech PTFE	130	1M NH4OH +	6	734
0.2 μm laminated		0.5M
		(NH4)2CO3

Example 4

Algae Production

To Examine the effect CO₂:NH₃ mole ratios on Scenedesmus acutus culture health and productivity, experiments were conducted in 800 mL bioreactors with constant gas sparging and different CO₂:NH₃ mole ratios (ranging from 7:1 up to 18:1) (FIG. 33). The “cycles” indicated in FIG. 33 refer to growth cycles of algae. In this regard, each bioreactor is normally inoculated with algae at a low concentration (e.g., 0.1 g/LO and the algae are allowed to grow until a concentration of 1 g/L is obtained. At this point, the algae are harvested until a concentration of 0.1 g/L is left in the bioreactor (with the addition of fresh nutrients and water). The algae are allowed to grow again until a concentration of 1 g/L is again reached, followed by harvesting. Each period of growth up to harvesting is characterized as a growth cycle.

As shown in FIG. 33, test revealed that the optimal CO₂:NH₃ mole ratio lines in the range of 10:1-16:1. As shown in Table 8 below, the growth rate of 10:1 CO₂:NH₃ ratio is higher than that obtained using traditional nitrogen sources, such as NaNO₃. For 10:1 CO₂:NH₃, NH₃ utilization was found to be approximately 100% and CO₂ utilization was found to be approximately 70%.

TABLE 8
Urea	NaNO3	CO2/NH3 (10:1)
0.11 ± 0.04	0.13 ± 0.05	0.17 ± 0.05

One of ordinary skill in the art will recognize that additional embodiments and implementations are also possible without departing from the teachings of the present invention. This detailed description, and particularly the specific details of the exemplary embodiments and implementations disclosed herein, is given primarily for clarity of understanding, and no unnecessary limitations are to be understood therefrom, for modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit or scope of the invention.

All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference, including the references set forth in the following references list:

REFERENCES

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Claims

1. A carbon dioxide (CO2) capture and utilization system, comprising: a CO2 capture unit including a membrane CO2 absorber for receiving a flue gas, the membrane CO2 absorber including a first section in which the flue gas is received into the membrane CO2 absorber,a second section through which an ammonium solvent passes, anda membrane positioned between the first section and the second section, the membrane configured to prevent direct contact between the flue gas and ammonium solvent but permit the passage of CO2 within the flue gas from the first section to the second section, whereby the interaction between the ammonium solvent and the CO2 in the second section produce CO2-rich solvent; anda utilization unit in fluid communication with the CO2 capture unit and including a cultivation subsystem for cultivating one or more species of algae or cyanobacteria;wherein, in use, the utilization unit processes the CO2-rich solvent to produce a product stream that is provided to the cultivation subsystem and includes CO2 and NH3 in a predetermined CO2:NH3 ratio.

2. The CO2 capture and utilization system of claim 2, wherein the ammonium solvent includes ammonium hydroxide (NH4OH).

3. The CO2 capture and utilization system of claim 1, wherein the ammonium solvent includes a chelating agent.

4. The CO2 capture and utilization system of claim 3, wherein the chelating agent is one of triethylene glycol di-2-ethylhexoate (TGDE), amino trimethylene phosphonic acid (AMP), tris(hydroxymethyl)aminomethane (Tris), and ZnCl2.

5. The CO2 capture and utilization system of claim 3, wherein the chelating agent reduces NH3 slip corresponding to NH3 from the ammonium solvent traveling through the membrane to the first section of the membrane CO2 absorber as compared to a control ammonium solvent without the chelating agent.

6. The CO2 capture and utilization system of claim 1, and further comprising: a conduit in fluid communication with a flue gas supply and the membrane CO2 absorber, wherein the conduit and the membrane CO2 absorber are oriented relative to each other, such that, when flue gas from the flue gas supply is saturated, the conduit delivers the saturated flue gas in a downflow that washes the membrane of the membrane CO2 absorber.

7. The CO2 capture and utilization system of claim 1, wherein the membrane CO2 absorber is a hollow fiber membrane.

8. The CO2 capture and utilization system of claim 7, wherein the membrane CO2 absorber includes a non-porous polymer comprising a fluoride material and a microporous hollow fiber support comprising polyether ether ketone (PEEK).

9. The CO2 capture and utilization system of claim 1, wherein the membrane CO2 absorber is a flat sheet membrane.

10. The CO2 capture and utilization system of claim 9, wherein the membrane of the membrane CO2 absorber includes a polyethersulfone (PES) and polytetrafluoroethylene (PTFE).

11. The CO2 capture and utilization system of claim 1, wherein the utilization unit includes a solvent regenerator in fluid communication with the membrane CO2 absorber and configured to process the CO2-rich solvent to produce the product stream.

12. The CO2 capture and utilization system of claim 11, wherein the solvent regenerator is proximally located to the cultivation subsystem, such that the solvent generator provides just-in-time distribution of the predetermined CO2:NH3 ratio to the cultivation subsystem.

13. The CO2 capture and utilization system of claim 12, wherein the cultivation subsystem includes at least one of a photobioreactor and an open raceway pond.

14. The CO2 capture and utilization system of claim 1 wherein the predetermined CO2:NH3 ratio is about 7:1 to about 16:1.

15. The CO2 capture and utilization system of claim 1, wherein the predetermined CO2:NH3 ratio is about 10:1.

16. The CO2 capture and utilization system of claim 1, wherein a lean solvent corresponding to the portion of the CO2-rich solvent remaining after NH3 is removed from the CO2-rich solvent to produce the product stream is transferred from the utilization unit to the membrane CO2 absorber.

17. A method for capturing and utilizing carbon dioxide (CO2), the method comprising: receiving flue gas into a membrane CO2 absorber containing an ammonium solvent; processing, by a solvent regenerator, a CO2-rich solvent received from the membrane CO2 absorber to produce a product stream including CO2 and NH3 in a predetermined CO2:NH3 ratio, the CO2-rich solvent resulting from an interaction between the ammonium solvent and CO2 from the flue gas within the membrane CO2 absorber; andproviding the product stream to one or more species of algae or cyanobacteria.

18. The method of claim 17, wherein the flue gas is saturated and received into the a membrane CO2 absorber in a downflow which washes a membrane of the membrane CO2 absorber.

19. The method of claim 17, wherein the ammonium solvent includes ammonium hydroxide (NH4OH).

20. The method of claim 17, wherein the predetermined CO2:NH3 ratio is about 7:1 to about 16:1.