Direct carbon dioxide recovery

Abstract

The present disclosure provides systems and methods for direct air capture of carbon dioxide or other gases using calcium sorbents in a manner that allows for large-scale, relatively low-cost implementation. Specifically, the calcium sorbents can be provided as substantially thin coating layers on one or more substrates and utilized for direct air capture of carbon dioxide by chemical adsorption. The carbonated sorbents can be disposed of for carbon dioxide sequestration or regenerated with the capture of carbon dioxide released from the carbonated sorbents during a regeneration process.

Description

Technical Field

[0001] The present disclosure relates to systems and methods useful for carbon dioxide recovery. More specifically, the systems and methods can directly recover carbon dioxide from air or another stream using an adsorbent.

Background Art

[0002] There are ongoing global efforts to address the increasing concentrations of greenhouse gases in the atmosphere, particularly carbon dioxide (CO2). Although much work is being done to reduce the amount of such gases emitted into the atmosphere each year, there is a growing understanding that reducing emissions alone may be insufficient to address concerns regarding climate change. Accordingly, research is currently underway on methods not only to reduce greenhouse gas emissions but also to remove such gases that already exist in the atmosphere.

[0003] The large-scale deployment of current methods for recovering CO2 from ambient air has ended unsuccessfully, at least in part, due to the excessive costs associated with known methods considering that the global CO2 emissions are on the order of approximately 37 billion tons per year. Current CO2 removal methods have high capital costs and high operating costs for various reasons. For example, since the total CO2 concentration in ambient air is very dilute compared to the main components (e.g., nitrogen, oxygen, and argon), previously identified removal methods have required high specificity and high efficiency to be cost-effective. Despite the previously identified high-efficiency removal methods, such methods lacked the ability to pass a sufficient volume of ambient air through the recovery system to make the known methods simple enough and cost-effective enough for industrial-scale implementation. As a requirement for achieving high efficiency, known removal methods have required the use of renewable solvents and / or chemicals to offset the high cost of the required materials. Thus, such renewable solvents and / or chemicals used in known recovery methods must be separated from the recovered CO2 for regeneration, and this separation requirement also adds additional cost and energy to the process.

[0004] There is a strong global desire to implement CO2 removal technologies as a means to combat climate change, but unduly high costs have so far hindered such implementation. Without affordable technologies for removing existing CO2 from the atmosphere, the world will continue to struggle to reduce and reverse anthropogenic global warming. Therefore, additional technologies effective for the removal of greenhouse gases, including CO2, from ambient air are still needed in this field. SUMMARY OF THE INVENTION

[0005] In one or more embodiments, the present disclosure can provide systems and methods adapted or configured to directly recover carbon dioxide from ambient air. Advantageously, the systems and methods can maximize the available surface area of the calcium adsorbent to increase the amount of carbon dioxide that can be removed from ambient air. The present disclosure can also be effective in minimizing the associated costs of a production and logistics system integrated with a passive air recovery process while simultaneously reducing the accumulation of carbon dioxide in the atmosphere.

[0006] The systems and methods of the present disclosure can provide relatively low-cost, highly efficient direct removal of carbon dioxide from ambient air, particularly when compared to known carbon dioxide removal systems that require high-cost chemicals that must be continuously regenerated. More specifically, the systems and methods can be adapted or configured to accelerate the carbonation of the calcium adsorbent in ambient air, which, in some embodiments, can be achieved by providing the adsorbent on one or more substrates in a manner that maximizes the available adsorbent surface area and utilizes a thickness designed such that the adsorbent can rapidly and thoroughly carbonate.

[0007] The use of calcium hydroxide for the chemical adsorption of carbon dioxide from air has been previously proposed (see “Carbon Dioxide Extraction From Air: Is It An Option?” Lackner, 1999, as well as “Liquid-Like H2O Adsorption Layers to Catalyze the Ca(OH)2 / CO2 Solid-Gas Reaction and to Form a Non-Protective Solid Product Layer at 20°C” Beruto and Botter, 2000), but no known systems have been shown to be effective in utilizing these properties in a viable direct air capture system with passive carbonation. Rather, previous systems relied on the active acceleration of direct air capture by means of a carbonator, an air contactor, additional solvents, a pellet reactor, as well as additional heat and energy inputs. However, such active processes add significant costs and risks that are beneficially avoided by the systems and methods of the present disclosure. Even known passive calcium direct air capture systems (see Erans et al., 2019) have not been able to provide a practical integrated system. For example, U.S. Patent No. 10,570,018 discloses a passive calcium direct air capture system, but such a system still fails to meet the requirements necessary for practical implementation (i.e., it does not enable the acceleration of carbonation at a sufficiently low cost). However, all of these drawbacks can be overcome according to one or more embodiments of the systems and methods of the present disclosure that provide the acceleration of carbonation at a cost that is sufficiently low for practical implementation.

[0008] The systems and methods of the present disclosure for at least direct air capture of carbon dioxide (i.e., other contaminants may likewise be removed from ambient air using the present disclosure) overcome some of the limitations of known processes for removing carbon dioxide from air. For example, known processes require highly efficient, fast-acting sorbents / chemicals to rapidly remove carbon dioxide from ambient air. Due to excessive material costs, such processes require efficient regeneration of the sorbent / chemicals. Similarly, to achieve rapid turnover, such processes require an active air stream (e.g., using a blower) to achieve rapid turnover. The systems and methods of the present disclosure mitigate or completely overcome such limitations. As further described herein, the systems and methods are low-cost but have been overlooked by the prior art for use in a practicable air capture system due to recognized efficiency limitations, enabling the use of sorbents / chemicals. The lower-cost sorbents / chemicals also enable an integrated sorbent generation and recovery process. The methods and systems can likewise be performed efficiently without complete regeneration of the sorbent / chemicals. Further, the methods and systems can be performed in the absence of any obvious forced air components (e.g., blowers), if desired, because high efficiency can be achieved even when slower reaction times are utilized. More specifically, the systems and methods of the present disclosure provide for the implementation of a high surface area configuration that achieves low-cost, high-efficiency absorption even in the absence of partial or complete sorbent / chemical regeneration and in the absence of applied forced air components.

[0009] In one or more embodiments, the system and method may incorporate the use of a passive calcium chemisorption carbonation process. Exemplary embodiments may utilize one or more circulating and / or stationary suspension substrates that are randomly distributed or can be clearly organized within a closed, semi-closed, or covered structure. The circulating substrate may specifically utilize vertical, horizontal, and / or passive conveyor systems. The calcium adsorbent may be provided in a substantially process-ready state - i.e., in a chemical state where the calcium adsorbent is ready to undergo a carbon dioxide absorption process that is either spontaneously or catalytically driven. In some embodiments, the calcium adsorbent precursor may be treated to provide a process-ready material. For example, calcium carbonate (CaCO3) may be calcined and slaked to form a calcium hydroxide slurry or suspension. Preferably, such treatment is performed with partial, substantially complete, or fully complete recovery of the carbon dioxide driven off from the calcium carbonate. Alternatively or additionally, calcium oxide and / or calcium hydroxide may be provided from further processes that are preferably produced with recovery of any generated carbon dioxide.

[0010] The substrate can be coated with a relatively thin layer of calcium hydroxide (or other calcium adsorbent), which can be in the form of a slurry or suspension in particular. Such coating can be by any suitable means, but in particular can be carried out as further described herein. After coating, the coated substrate can be placed in a desired area of the structure and substantially fixed and maintained. Alternatively, the coated substrate can be circulated through at least a part of the structure. The coated substrate is brought into contact with the ambient air for a time sufficient for evaporation (i.e., release of H2O from calcium hydroxide) and carbonation (i.e., uptake of CO2 from the air) to proceed by a desired amount. The carbonated coating that has absorbed the carbon dioxide content from the atmosphere can be removed from the substrate, and the substantially cleaned substrate can be reused. The removed coating can be carried out of the place for use in different processes, industrial utilization, sale, and / or isolation. In some embodiments, the calcium adsorbent can be regenerated for reuse. For example, the carbonated material can be further carbonated as needed before being processed through a calciner to drive out carbon dioxide, and the carbon dioxide can be recovered for isolation or other uses (such as enhanced oil recovery). Calcination can also regenerate calcium oxide. Then, slaking can be carried out to form calcium hydroxide that is coated on the substrate for direct air capture of further carbon dioxide.

[0011] The system according to the present disclosure may include any combination of individual components and / or units useful for performing process steps. For example, in some embodiments, a suitable system may include a calciner that is preferably adapted or configured to recover at least a portion, substantially all, or completely all of the carbon dioxide released by the calciner. The system may similarly include a quenching device, a conveyor system (which may be adapted or configured to operate in one or both of a vertical segment and a horizontal segment), and one or more substrates that are adapted or configured to be suspended at least partially above the floor. The components of the system may exist in a single structure or multiple structures.

[0012] The aforementioned systems and methods, described in more detail below, provide different advantages over known uses of calcium adsorbents for carbon dioxide recovery. Specifically, the present systems and methods provide for maximizing the surface area of the calcium adsorbent while minimizing energy costs, and thus also maximizing the carbonation efficiency of the calcium adsorbent. In some embodiments, this may be achieved, in particular, by customizing the coating thickness of the adsorbent on the substrate to elicit the most efficient rate of carbon dioxide transfer into the adsorbent. This particular design thus enhances the performance of direct air capture systems and reduces costs.

[0013] The present disclosure provides further advantages over known carbon dioxide capture systems. For example, passive capture of carbon dioxide using high surface area adsorbents, as discussed herein, can reduce, substantially eliminate, or completely eliminate the need for expensive equipment such as air contactors, packed towers, fans, pumps and compressors, carbonators, and / or pellet reactors. This advantageous high surface area arrangement can be achieved, in one or more embodiments, by utilization of a relatively thin layer of calcium adsorbent on one or more substrates used. Exemplary embodiments of suitable layer thicknesses can range from about 1.5 kg or less of calcium adsorbent per square meter of exposed area on the substrate. This thin layer can be arranged at a relatively high vertical density such that it is over 5 feet in height while maintaining the thickness of the individual layers of calcium adsorbent. This combination of high surface area and low layer thickness can provide direct air capture of carbon dioxide over a reasonable time (e.g., on the order of hours to months depending on exact coating parameters and desired process throughput) without requiring excessive land area. Further, this substrate-based deposition method enables a thinner application of calcium adsorbent in a practical and efficient arrangement that solves at least some of the problems and issues not addressed by previous passive direct air capture systems. Thus, the system and method can far outperform previously conceived, faster but more capital and energy intensive direct air capture systems while also providing efficiencies that were previously unattainable with previous passive direct air capture systems.

[0014] In addition to the above, reduction or elimination of any active air capture mechanisms can also reduce the associated equipment and costs for generating the electricity and heat required to operate such equipment. As a result, less carbon dioxide is generated to heat and operate the capture system, and the net carbon removal of the present system can significantly exceed what is achievable by known systems and methods.

[0015] A used calcium adsorbent (i.e., an adsorbent that has already been used to passively recover carbon dioxide) can be calcined in such a way that the absorbed carbon dioxide is separated for storage, thereby regenerating the calcium adsorbent for further air recovery. This regeneration reduces the need for limestone to produce the calcium adsorbent. Although the calcination of calcium oxide (CaO) is a common process, its integration with this passive high-density CaO carbonation process is effective in providing significant improvements in the cost and energy use of the full cycle of adsorbent use and regeneration compared to other direct air recovery systems. Unlike the aforementioned processes, the systems and methods of the present disclosure do not require additional chemicals or materials in the air recovery stage, which can complicate the calcination of the calcium adsorbent after it has been utilized for carbon dioxide recovery.

[0016] Previously disclosed processes for using calcium oxide or calcium hydroxide for direct air recovery have not been able to control the space and time required to scale up the process to an industrial level, even when passive systems have been proposed. Calcium adsorbents have been under consideration for direct air recovery for about 20 years, but no system has been developed that enables the passive recovery of carbon dioxide at a useful scale with that calcium. The present disclosure solves this problem and enables a passive direct air recovery process that operates effectively at an industrial scale through the application of a thin layer of adsorbent to accelerate carbonation and its overall system design for high-density storage and logistics processes that minimize space and cost during the carbonation period.

[0017] In one or more embodiments, the present disclosure can, in particular, provide a method for the direct air capture of carbon dioxide. In an exemplary embodiment, such a method comprises preparing a substantially continuous coating layer of a calcium sorbent material on one or more substrates at a density of less than 10 kilograms per square meter, contacting one or more substrates having the substantially continuous coating layer of the calcium sorbent material with air containing carbon dioxide for a time sufficient for the calcium sorbent to react with the carbon dioxide, thereby recovering at least a portion of the carbon dioxide from the air and converting at least a portion of the calcium sorbent to a carbonated form, removing at least a portion of the carbonated calcium sorbent from the one or more substrates, and treating the carbonated calcium sorbent such that the carbon dioxide recovered from the air is in a state ready for sequestration or other use. In further embodiments, the method can be further defined with respect to one or more of the following descriptions that can be combined in any number and / or order.

[0018] The substantially continuous coating layer of the calcium sorbent material can have a density of from about 0.1 ksm to about 5 ksm.

[0019] The substantially continuous coating layer of the calcium sorbent material can have an average thickness of less than 2.5 cm on one or more substrates.

[0020] The substantially continuous coating layer of the calcium sorbent material can have an average thickness of from about 0.01 mm to about 2 cm on one or more substrates.

[0021] One or more substrates can be configured substantially as a sheet.

[0022] The substantially continuous coating layer of the calcium sorbent material can be configured to exhibit a carbonation rate such that at least 25 wt% of the calcium sorbent material is carbonated within a time of 96 hours or less.

[0023] A substantially continuous coating layer of the calcium adsorbing material can be configured to exhibit a carbonation rate such that at least 50% by weight of the calcium adsorbing material is carbonated within about 1 day to about 14 days.

[0024] Contacting one or more substrates having a substantially continuous coating layer of the calcium adsorbing material with air containing carbon dioxide can include suspending one or more substrates having a substantially continuous coating layer of the calcium adsorbing material at a location where the substantially continuous coating layer of the calcium adsorbing material contacts the air.

[0025] Removing at least a portion of the carbonated form of the calcium adsorbent from one or more substrates can include applying a force to the one or more substrates sufficient to break and remove the substantially continuous coating layer of the calcium adsorbing material from the one or more substrates.

[0026] Processing the carbonated form of the calcium adsorbent can include identifying the carbonated form of the calcium adsorbent for isolation of the carbonated form of the calcium adsorbent.

[0027] Processing the carbonated form of the calcium adsorbent can include further exposing the carbonated form of the calcium adsorbent to ambient air for a time sufficient to increase the carbonation rate.

[0028] Processing the carbonated form of the calcium adsorbent can include calcining the carbonated form of the calcium adsorbent to release carbon dioxide therefrom to form calcium oxide and recovering the carbon dioxide released from the calcium adsorbent.

[0029] The method can further include slaking the calcium oxide to form the calcium adsorbing material used to prepare the substantially continuous coating layer.

[0030] The method may further include removing a portion of the calcium sorbent in carbonated form before calcination and adding make-up limestone during calcination.

[0031] Preparing a substantially continuous coating layer of the calcium sorbent material may include immersing one or more substrates in a reservoir of the calcium sorbent material.

[0032] Preparing a substantially continuous coating layer of the calcium sorbent material may include dripping or spraying the calcium sorbent material onto one or more substrates.

[0033] In one or more embodiments, the present disclosure can further provide, in particular, a system for the direct air capture of carbon dioxide. In an exemplary embodiment, such a system includes a coating system configured to apply a liquid calcium sorbent material to one or more substrates to form a substantially continuous coating layer of the calcium sorbent material on the one or more substrates, and a storage unit configured to dispose the one or more substrates for a period of time such that the one or more substrates are in contact with air, and as a result, carbon dioxide in the air reacts with the calcium sorbent material to form a carbonated calcium sorbent material, and a collection unit configured to remove and collect the carbonated calcium sorbent material from the one or more substrates. In further embodiments, the system can be further defined with respect to one or more of the following descriptions that can be combined in any number and / or order.

[0034] The coating system may include one or more reservoirs of the liquid calcium sorbent material.

[0035] The coating system may further include an immersion unit configured to immerse one or more substrates in one or more reservoirs of the liquid calcium sorbent material.

[0036] The coating system may include a suspension unit configured to hold one or more substrates in a substantially vertical position.

[0037] The coating system may further include one or more dropping pipes configured to drop a calcium adsorption material onto one or more substrates.

[0038] The system may further include a calciner configured to receive the carbonated calcium adsorption material and convert the carbonated calcium adsorption material into calcium oxide and carbon dioxide.

[0039] The system may further include a solid separator configured to separate calcium oxide from carbon dioxide.

[0040] The system may further include a lime slaking unit configured to receive calcium oxide and form calcium hydroxide for use as a calcium adsorption material.

[0041] These and other features, aspects, and advantages of the present disclosure will become apparent from reading the following detailed description of the invention in conjunction with the accompanying drawings, which are briefly described below. The present invention includes any combination of two, three, four, or more of the above embodiments, and any combination of two, three, four, or more features or elements described in this disclosure, regardless of whether such features or elements are explicitly combined in the description of the specific embodiments herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosed invention are combinable in any of its various aspects and embodiments, unless the context specifically dictates otherwise.

Brief Description of the Drawings

[0042]

Fig. 1A

Fig. 1B

Fig. 2

Fig. 3

Fig. 4

Fig. 5

[0043] Next, various aspects of the present disclosure will be described in more detail below with reference to the accompanying drawings, which show some but not all implementations of the present disclosure. In fact, the various implementations of the present disclosure may be represented in many different forms and should not be construed as limited to the implementations described herein. Rather, these exemplary implementations are provided to make the present disclosure thorough and complete and to fully convey the scope of the present disclosure to those skilled in the art. As used in this specification and the appended claims, the singular forms "a," "an," and "the" include the plural unless the context clearly dictates otherwise.

[0044] In one or more embodiments, the present disclosure provides systems and methods for the direct capture of carbon dioxide from ambient air or the atmosphere. The systems and methods utilize a calcium adsorbent that is preferably renewable but can be configured for use that is not renewable if desired. In some embodiments, the calcium adsorbent can be configured to undergo repeated carbonation and calcination such that carbon dioxide is removed from the atmosphere through absorption by the adsorbent and can then be recovered during regeneration of the adsorbent. By way of example, calcium oxide and / or calcium hydroxide may be utilized as the calcium adsorbent. Thus, the calcium adsorbent can be adapted or configured to absorb carbon dioxide from ambient air either spontaneously or catalytically as needed. Such absorption can be effective to form the carbonated form of the calcium adsorbent, which can then be regenerated by calcination to expel the carbon dioxide, which can be recovered in the calcination process.

[0045] To form the initial calcium adsorbent and / or to regenerate the carbonated form of the calcium adsorbent, a carbonate (e.g., calcium carbonate - CaCO3) can be injected into a calciner that can comprise suitable components for recovering at least a portion of the carbon dioxide that is preferably expelled during calcination. The limestone utilized to form the adsorbent can be provided in particulate form, ensuring that a co-current flow type, rotary kiln type, or fluidized bed type calciner can be used for CaO production. In some embodiments, the particulate limestone / CaCO3 can have an average size of from about 1 μm to about 1 mm, from about 5 μm to about 750 μm, or from about 10 μm to about 500 μm (e.g., the maximum measurable dimension of the length, width, or thickness of the irregularly shaped particles). As further discussed below, the calcium oxide thus formed can be further processed before being applied to the substrate used in the carbonation reaction.

[0046] The recovery components associated with the calciner are preferably effective to recover at least 75%, at least 85%, at least 90%, at least 95%, at least 99%, or at least 99.9% of the carbon dioxide released from the carbonate during calcination. In some embodiments, the calcination can be performed by heating the carbonate to a temperature in the range of about 700 °C to about 1200 °C, about 750 °C to about 1100 °C, or about 800 °C to about 1000 °C. The release of carbon dioxide can be effective to form calcium oxide (CaO). At least a portion of the carbon dioxide recovered from the calcination can be utilized in industrial processes, enhanced oil recovery, or sequestration. Non-limiting examples of recovery techniques that can be implemented to recover the carbon dioxide released during calcination include oxy-fuel calcination, calcium-based chemical looping, amine-based solvent technology, and the like. The calcination to provide low-carbon CaO can be performed on-site, at a direct air capture facility, and thus can be part of an integrated system for continuous or batch processing. Optionally, the calcination can be performed off-site or by a third party. Accordingly, the carbonate content can be transported to a calcination location for regeneration of the calcium sorbent and carbon recovery and then returned to the direct air capture facility.

[0047] CaO may remain in its anhydrous form, or may be hydrated with water to form calcium hydroxide (Ca(OH)2), or may be a mixture of both, all of which are interchangeably referred to as "calcium adsorbent" or "lime adsorbent". Thus, in addition to the above-mentioned calcination unit, a slaking unit can be used for the preparation of the initial adsorbent and / or the regeneration of the adsorbent from the carbonate product. This calcium hydroxide and / or CaO can be further mixed with additional water to provide a calcium adsorbent in a form suitable for addition to one or more substrates. The adsorbent before addition to the substrate(s) can thus be any one or more of a paste, slurry, spray, or suspension. Further, in some embodiments, the calcium adsorbent may be prepared in polymeric form, as a metal-organic framework (MOF), or as another suitable mixture and / or molecular structure. The calcium adsorbent is preferably provided in any suitable form in which the calcium adsorbent can recover carbon dioxide from the ambient air. For example, calcium hydroxide can recover carbon dioxide from the air when the relative humidity is above 40%, which is because the presence of water is generally understood to be important for calcium hydroxide to recover carbon dioxide to result in calcium carbonate. Carbon dioxide in the air can dissolve in water to form carbonic acid (H2CO3), which can dissociate into HCO3 - and H + and can thus react with calcium to form calcium carbonate and enable the recovery of carbon dioxide.

[0048] In some embodiments, the calcium adsorbent added to one or more substrates may consist essentially of, consist of, or consist only of calcium material itself and water. However, in other embodiments, one or more additional chemicals or materials may be included and may be adapted or configured to improve the carbon dioxide chemisorption properties of the calcium adsorbent and / or improve the adhesion of the calcium adsorbent to the substrate. Similarly, the calcium adsorbent may be provided in a particular morphology that may be adapted or configured to improve the carbon dioxide chemisorption properties of the calcium adsorbent. Such improvements may include any one or more of, for example, reactivity, viscosity, porosity, surface area, morphological stability, and electronegativity, as well as other beneficial properties. In an exemplary embodiment, sodium hydroxide may in particular be added to the adsorbent. In other embodiments, potassium hydroxide, magnesium hydroxide, fumed silica, zeolite, magnetic particles, and / or recycled regenerated adsorbent may be added. In addition to the above mixtures, the calcium adsorbent may be formed as a powder, pellet, flake, slurry, gel, honeycomb, and / or provided in other beneficial geometries. Aging, drying, rehydrating, bending, flowing, vibrating, rolling, squeezing, filling, and other such operations may be applied to the adsorbent, as they have been demonstrated to affect the reactivity and performance of the calcium adsorbent when applied to one or more substrates.

[0049] The application of the calcium adsorbent to the substrate(s) can be carried out in a coating unit or facility. The calcium adsorbent in the composition and / or form as described above can be applied as a relatively thin layer on one or more substrates. For example, the average adsorbent layer thickness in a representative area of the substrate can be less than 2.5 cm, less than 2 cm, less than 1.5 cm, or less than 1 cm (e.g., down to the minimum thickness coating achievable by conventional coating methods). In some embodiments, the average layer thickness can range from about 0.01 mm to about 2.25 cm, about 0.01 mm to about 2 cm, about 0.01 mm to about 1.5 cm, about 0.01 mm to about 1 cm, about 0.01 mm to about 7 mm, about 0.01 mm to about 5 mm, about 0.02 mm to about 1 mm, or about 0.03 mm to about 0.5 mm. The foregoing ranges are relevant to various useful embodiments according to the present disclosure, but it is understood that more specific ranges can be implemented based on the exact physical properties of the adsorbent coating material. For example, in some embodiments, the calcium adsorbent material can be provided in a substantially porous form that provides an increased surface area for reacting with carbon dioxide. In such embodiments, a relatively thick coating layer may be utilized, but as further discussed below, a high carbonation rate is still provided. For example, when a relatively thick coating layer is utilized, the average layer thickness can range from about 0.5 mm to about 2.25 cm, about 0.75 mm to about 2 cm, about 1 mm to about 1.5 cm, or about 1.5 mm to about 1 cm. In further exemplary embodiments, a relatively thin coating layer may be utilized, which can further simplify the process in that additional processing (e.g., to achieve a high porosity as described above) can be avoided, and a substantially continuous coating layer can be applied with a relatively small average thickness while still achieving the desired carbonation rate. In such embodiments where a relatively thin coating layer is utilized, the average layer thickness can range from about 0.01 mm to about 2 mm, about 0.05 mm to about 1.5 mm, or about 0.1 mm to about 1 mm. The average thickness can relate to a single layer of the calcium adsorbent or can be the total thickness of multiple layers (e.g., 2, 3, 4, or 5 layers) applied to the substrate.Figures 1A and 1B show a representative substrate 10 having a coating 20 of a calcium adsorbent applied thereto. As seen in Figure 1A, the coating 20 may cover a range smaller than the entire surface 11 of the substrate 10, although the coating may, if desired, cover substantially the entire surface. As seen in Figure 1B, the coating 20 may have a thickness less than the thickness of the substrate, although the thickness of the substrate may vary based on the particular material used to form the substrate.

[0050] Preferably, the average adsorbent layer thickness is adapted or configured to provide a calcium adsorbent density within a defined range. As noted above, the useful calcium adsorbent density can vary based on the average layer thickness utilized. Across the desired range, the calcium adsorbent density can be in a range such as about 10 kg (ksm) or less, less than 5 ksm, less than 2 ksm, or less than 1 ksm per square meter of exposed substrate area (e.g., down to a minimum of at least 0.02 ksm). In some embodiments, the calcium adsorbent density on the substrate can be in the range of about 0.05 ksm to about 10 ksm, about 0.1 ksm to about 5 ksm, about 0.2 ksm to about 2 ksm, or about 0.25 ksm to about 1 ksm. The layer thickness can be managed using various mechanisms such as control of the water content mixed with the calcium adsorbent to form the coating mixture. This (or other elements) can be utilized to control the viscosity of the coating mixture and thus the coating thickness of the coating mixture. In some embodiments, this relatively thin nature of the calcium adsorbent layer can be particularly effective in enabling passive capture of carbon dioxide. Calcium oxide captures carbon dioxide under ambient conditions, but the reaction is rate-limited by the coating thickness, and a fairly thick layer will essentially stop being reactive below a certain depth. However, in some embodiments, the coating layer thickness can be increased by controlling one or more physical properties of the coating layer. For example, a coating thickness on the higher side of the aforementioned range can be particularly useful when the coating layer is provided in a form with a relatively high porosity. Similarly, the substrate can be provided in a three-dimensional structure that allows for more deposition of the adsorbent thereon. In an exemplary embodiment, the calcium adsorbent can be prepared in the form of bubbles that exhibit at least a partially continuous pore structure that is effective to allow air to penetrate deeper within the layer thickness for reaction of the adsorbent with carbon dioxide in the air.

[0051] The present system and method can operate within a defined carbonation rate of the adsorbent. In some embodiments, the carbonation rate can be maximized such that about 50 wt% or more, about 60 wt% or more, about 70 wt% or more, or about 80 wt% or more of the adsorbent is carbonated before being removed from the substrate(s). For example, removal of the carbonated substrate may be performed when carbonation of about 60 wt% to about 98 wt%, about 65 wt% to about 95 wt%, or about 75 wt% to about 90 wt% of the adsorbent is achieved. Known processes are configured to be used with adsorbents that require the use of other types of adsorbents / chemicals or cannot achieve such high levels of carbonation due to structural limitations (e.g., required adsorbent layer thickness), and thus such high levels of carbonation are not expected to be achievable by optimization of known processes. In other embodiments, when a high throughput process is desired, the carbonation rate can be minimized to improve the throughput of the system. For example, removal of the carbonated substrate may be performed when carbonation of about 25 wt% to about 75 wt%, about 30 wt% to about 65 wt%, or about 35 wt% to about 60 wt% of the adsorbent is achieved. By utilizing such concentration limits, the turnover of the adsorbent can be increased such that the total mass of carbon dioxide that can be removed by a given system is maximized. This is because the chemisorption rate can be significantly faster at lower carbonation rates of the adsorbent, and the carbonation rate can be significantly slower as the relative proportion of the carbonated adsorbent increases.

[0052] By application of a defined calcium adsorbent coating layer thickness, coating layer density, and desired carbonation rate, a calcium adsorbent layer applied to one or more substrates can be configured or adapted to provide a carbonation rate within defined parameters. Since the carbonation rate is a function of the above elements, such a carbonation rate is not expected to be inherent to the calcium adsorbent. In some embodiments, a calcium adsorbent coating formed on one or more substrates is such that at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, or at least 45 wt% of the calcium adsorbent coating is carbonated within a time of 96 hours or less, 84 hours or less, 72 hours or less, 60 hours or less, 48 hours or less, 36 hours or less, or 24 hours or less (e.g., with a minimum carbonation time of 1 hour), and can be configured or adapted to exhibit such a carbonation rate. More specifically, a calcium adsorbent coating formed on one or more substrates is such that about 25 wt% to about 50 wt%, about 25 wt% to about 45 wt%, or about 30 wt% to about 45 wt% of the calcium adsorbent coating is carbonated within a time of about 2 hours to about 96 hours, about 4 hours to about 84 hours, about 6 hours to about 72 hours, about 8 hours to about 60 hours, about 10 hours to about 48 hours, or about 12 hours to about 36 hours, and can be configured or adapted to exhibit such a carbonation rate. Such a carbonation rate can be achieved by controlling one or more of the elements discussed above so that relatively high throughput systems and methods can be achieved. This can be advantageous when the calcium adsorbent is regenerated, and such high throughput can increase the total volume or mass of carbon dioxide removed from the air over a given period of time.

[0053] In some embodiments, it may be desirable to provide more complete carbonation of the calcium adsorbent coating layer before removing the coating layer from the substrate. Such embodiments may be advantageous when the carbonated calcium adsorbent is not regenerated (i.e., isolated in the form of calcium carbonate removed from the substrate without calcination to release carbon dioxide), or when the space for the system is large enough to allow for a longer carbonation time. Thus, in such embodiments, the calcium adsorbent coating formed on one or more substrates may be configured or adapted such that at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, or at least 90 wt% of the calcium adsorbent coating exhibits a carbonation rate such that it is carbonated within a time period of about 0.5 days to about 14 days, about 1 day to about 12 days, about 1.25 days to about 10 days, or about 1.5 days to about 8 days. The carbonation rate can be evaluated by taking samples of the calcium adsorbent coating at various times after the formation of the coating layer and performing a chemical analysis of the adsorbent (e.g., via mass spectrometry or a similar analytical method effective for identifying the chemical composition).

[0054] The application of the calcium adsorbent to one or more substrates can be achieved by any one or combination of suitable methods. In some embodiments, the application can be achieved by directly immersing the substrate into the calcium adsorbent or spraying the calcium adsorbent onto the substrate. In other embodiments, the application can be achieved by using any method suitable for coating a thin layer of the adsorbent onto the substrate, such as a brush, doctor blade, spraying mechanism, dipping, injection, or adsorption. For example, as shown in FIG. 2, the substrate 10 can be immersed in a reservoir 30 (e.g., in the form of a tank) containing the calcium adsorbent 25. A clamp 40 is attached to the substrate 10 to manipulate the substrate through the immersion process. Alternatively, the substrate 10 can pass over the reservoir 30 such that excess adsorbent falls into the reservoir for recirculation to the application component (e.g., the sprayer) when the calcium adsorbent 25 is immersed or sprayed onto the substrate. One or more layers can be applied to the substrate. The application method can be adapted or configured to affect the physical properties of the adsorbent being applied. The method of applying the calcium adsorbent to the substrate can be varied as desired to improve throughput, although a particular mode of applying the calcium adsorbent may be preferred with respect to improving the reactivity of carbon dioxide with the calcium adsorbent. For example, spraying the adsorbent onto the substrate can be effective in achieving a coating layer with increased porosity that can improve the ability to utilize a thicker layer for chemisorption, as described above. In some embodiments, the coating of the calcium adsorbent can be specifically characterized in terms of being a substantially continuous layer (s) on the substrate. Thus, the coating may be referred to as being in the form of a thin film, sheet, membrane, etc. A "substantially" continuous coating accounts for some imperfections (e.g., cracks, depressions, and similar defects) in the coating or layer, but indicates that the coating does not exist in the form of discrete pieces or particles existing as individual elements (even if the individual elements are in physical contact with other of the individual elements). Rather, the coating or layer extends along the length of the substrate surface as an intact thin film, sheet, membrane, etc.In certain embodiments, the coatings of the present disclosure may expressly exclude pelletized lime-based adsorbents or other lime-based adsorbents in particulate form. The use of such particulate or pelletized adsorbents may be undesirable because it adds the complexity of forming particles or pellets, which may require mixing the adsorbent with fillers, binders, etc., and then treating the mixture by spray drying or other means to form discrete solid particles or pellets. Such particulate materials may similarly require additional processing to adhere to the substrate and more complex processing to remove the adhered particles for regeneration. Alternatively, such particles or pellets would have to be placed in a packed bed reactor so that air containing carbon dioxide can be processed through the packed bed, which again introduces complexities not present according to the methodology of the present disclosure.

[0055] The substrate itself may have no coating or may have adhesives, anti-adhesion agents, catalysts, polymers, and other additives applied prior to application of the calcium adsorbent to improve the performance, lifespan, surface area, and / or processability of the calcium adsorbent. The substrate surface can be two-dimensional (i.e., substantially flat) or three-dimensional (i.e., sheared, textured, shaped, curved, etc.) to improve the application, performance, reactivity, surface area, and processability of the calcium adsorbent. An increase in surface area may be desired to accelerate the carbonation reaction, and an increase in the volume of adsorbent per unit of substrate material may be desired to reduce the cost associated with the substrate material. Plastics are one possible substrate material due to their low cost, structural flexibility, durability, and lack of reactivity with calcium. In other embodiments, the substrate is a wood product, foam board, steel, or any substrate suitable for the purpose.

[0056] The substrate can be adapted or configured to be substantially flat when placed on a flat surface or in a suspended configuration. In other embodiments, the substrate can be intentionally adapted or configured to have a three-dimensional shape as described above. For example, the substrate can be shaped into a cylindrical, conical, or other shape, which is advantageous in that all exposed sides of the substrate coated with the calcium adsorbent increase the surface area per unit of substrate material. In some exemplary embodiments, the substrate can be in a wound configuration having a substantially helical cross-section. In other embodiments, the substrate is adapted or configured to have a porous network where the pores are large enough for the liquid adsorbent to flow through and coat the surface of the substrate, and also large enough for the carbonated adsorbent to be removed from the substrate. For example, a honeycomb structure such as commonly used in catalytic converters (e.g., for exhaust systems in the automotive or power plant industries) may be utilized, and the pore size in the honeycomb structure may be suitably sized up to allow for efficient removal of the carbonated adsorbent. Such structures are generally formed from ceramics, although metal honeycombs may be utilized to improve durability.

[0057] The substrate may be manipulated by rotation, movement, spinning, ventilation, or other means so as to affect the drying of the calcium adsorbent on the substrate material. Similarly, a blower or the like may be utilized to remove excess adsorbent from the coated surface and ensure a substantially flat and suitably thin coating of the adsorbent on the substrate surface. The substrate may be replaced with a rod, tray, board, or another substrate that allows for a thin application of the calcium adsorbent. In some embodiments, the calcium adsorbent may be deposited so as to have sufficient structural integrity to hang, stand, or rest on its own without the use of other substrates or materials. A plurality of such substrates may be combined in a system to maximize their performance and minimize waste or loss of the adsorbent material.

[0058] After coating the adsorbent onto one or more substrates, the coated substrate(s) may be moved to a storage unit or facility. The calcium adsorbent-coated substrate material may be stored or otherwise placed in contact with ambient air for a time sufficient to achieve the desired carbonation rate of the adsorbent as described above. This time may be referred to as the reaction period or carbonation period. In some embodiments, the reaction period may range from as short as a few hours to up to several months, or longer as needed. During the reaction period, the adsorbent chemisorbs carbon dioxide from the ambient air or other concentrated carbon dioxide source. Evaporation will also occur from both the water added to the calcium adsorbent and the water liberated from the reaction of calcium hydroxide and carbon dioxide to produce calcium carbonate and water. The layer of adsorbent will exhibit an initial weight loss during evaporation of the water used in forming the substrate mixture, followed by a weight gain due to carbonation.

[0059] The systems and methods of the present disclosure beneficially provide for the storage and transport of the adsorbent-coated substrates during the carbonation period in a manner that particularly achieves desirable results. One or more substrates having a calcium adsorbent coated thereon may be attached to a conveyor system, suspended from above and fixed, supported by other substrates, or held by the sides or bottom of the substrate and arranged vertically. The use of this vertical space minimizes the land area used without significantly adding infrastructure and enables drying of two or more sides, such as with a conveyor system. In some embodiments, the conveyor system may be adapted or configured to move the substrate through a storage unit for at least a portion or all of the duration of the carbonation period. This may be constructed as one continuous conveyor line, a branched conveyor system, or multiple separate conveyor systems. Horizontal stacking of the substrates may also be used, either in addition to or instead of vertical suspended storage, inside or outside of the conveyor system, during and after the initial drying process.

[0060] In one exemplary embodiment, the calcium adsorbent may first be applied onto a substrate hanging substantially vertically that allows for double-sided coating (see Figure 2), and after an initial period of carbonation, the partially carbonated adsorbent may be removed and placed on a substantially horizontal conveyor system, which can be effective in exposing the surface area of the adsorbent that was attached to the substrate material to the ambient air and thus accelerating carbonation. In another exemplary embodiment, the calcium adsorbent may be applied alone to a vertical substrate, and after the carbonation period has sufficiently ended, the at least partially carbonated adsorbent may be removed and proceed to calcination for regeneration of the adsorbent.

[0061] The storage unit or facility may include a suitable covering adapted or configured to protect the calcium adsorbent from weather (e.g., rain) that may interfere with the carbonation process. The storage unit or facility may or may not block air, depending on the local climate. The temperature, relative humidity, and air flow in the storage space may be controlled to optimize carbonation, or they may be left to vary with ambient conditions. Thus, the storage unit or facility may include suitable climate control elements, air inlets, etc., adapted or configured to provide an inflow of ambient air for carbon dioxide removal. For example, the storage unit or facility may include one or more air movers (e.g., fans, blowers, etc.) configured or adapted to increase the circulation of air within the storage unit or facility and ensure that the carbon dioxide concentration in the air near the calcium adsorbent does not fall below a range that could reduce process efficiency (e.g., the average ambient air CO2 content of the air entering the facility - 5%, - 10%, - 15%, or - 20%). As another example, the storage unit or facility may include one or more heaters and / or one or more coolers configured or adapted to adjust the temperature to a desired range to improve process efficiency. As yet another example, the storage unit or facility may include one or more humidity regulators configured or adapted to maintain the relative humidity (RH) within the storage unit or facility within a desired range suitable for improving process efficiency (e.g., above 40% RH, above 50% RH, or above 60% RH, such as in the range of about 45% RH to about 90% RH, about 45% RH to about 80% RH, or about 50% RH to about 75% RH). In addition, in some embodiments, excess carbon dioxide (or other gases) in amounts exceeding those present in the ambient air may be supplied to the storage unit to accelerate carbonation. In some embodiments, the storage unit or facility may incorporate natural topographical features such as canyons, waterways, cliffs, or caves to make the air flow, air temperature, and / or air humidity more suitable for process performance.

[0062] After the calcium adsorbent has achieved sufficient carbonation within the desired range, the recovered carbon dioxide can be further processed for storage. In some embodiments, the carbonated adsorbent may be removed from the substrate material for further processing. In other embodiments, the substrate material may be adapted or configured to be geologically stored with the carbonated adsorbent, or the substrate may be suitable for being processed through a calciner with the carbonated adsorbent. Thus, the substrate can be reusable or disposable. When removal is utilized, removing at least a portion of the calcium adsorbent in its carbonated form from one or more substrates may include breaking the coating layer of the calcium adsorbent material and applying to the one or more substrates a force sufficient to remove the coating layer of the calcium adsorbent material from the one or more substrates. Breaking may indicate cutting into multiple pieces to facilitate processing, and breaking of the coating layer may improve the ability to easily remove the coating layer from the substrate.

[0063] A flexible substrate may be utilized, such that bending / bowing the substrate may be sufficient to remove the substantially brittle carbonated adsorbent. Thus, applying to the substrate a force sufficient to break and remove the coating layer may include any force that causes the substrate to bend and / or bow. Alternatively or in addition, the force that may be applied to the substrate may include shaking, scraping, spraying, vibration, rolling, squeeze rolling, impact impulse, electrostatic impulse, electromagnetic impulse, magnetism, and / or various other methods for removing the carbonated adsorbent from the substrate material. Since various forms of mechanical force can be applied in a cost-effective manner, mechanical force may be desirable in some embodiments. In other embodiments, sound or impact force / impulse may be more easily applied. In some embodiments, removal of the adsorbent may be enhanced by various compositional and / or surface treatments of the substrate. After removal, additional carbonation time may be given to the adsorbent material considering that additional surface area has been newly exposed, or the adsorbent material may be processed substantially immediately.

[0064] The carbonated adsorbent may be regenerated for reuse by passing it through a calciner in substantially the same manner as described above for preparing the original calcium adsorbent material. After carbonation, the adsorbent material, which was originally of a first chemical composition (e.g., as calcium hydroxide and / or calcium oxide), has been converted to a different chemical composition - namely calcium carbonate. Calcium carbonate can be processed through a calciner with carbon recovery. By reheating the calcium carbonate to a temperature above about 800 °C, carbon dioxide is released and then recovered for sequestration and utilization. The recovered carbon dioxide is substantially or completely carbon dioxide removed from ambient air. Further, calcium oxide is reformed and can be resupplied as an input to the calcium adsorbent, reducing the need for additional limestone input.

[0065] This recalcination (or regeneration) part of the process is similar to calcium looping. Unlike calcium looping, since carbonation occurs by long-term exposure to air, a carbonation device is not required. The behavior of calcium during the loop is well understood, and calcium oxide continues to chemisorb carbon dioxide and return to calcium oxide during the loop from calcium oxide to calcium carbonate, but it is also known to lose its reactivity after several loop cycles. For example, the carbonation conversion can drop below 50% after only 5 looping cycles in a continuous calciner and carbonation device. However, the systems and methods of the present disclosure can mitigate such deactivation of the adsorbent. Specifically, by at least partially slaking the calcium oxide, water can facilitate the reaction between calcium oxide and carbon dioxide. Further, the elimination of the carbonation reactor (which typically operates at about 650 °C) reduces problems of wear and sintering. Further, the residence time of the reaction between calcium hydroxide and carbon dioxide in the present systems and methods is significantly longer than the residence time of calcium oxide and carbon dioxide in a typical high-temperature carbonation device. The cycle between carbonation and calcination can be from a few cycles to several hundred cycles, reducing the cost of limestone.

[0066] Deactivation of the calcium adsorbent can occur, and as a result, as long as the efficiency drops below the specified level, such deactivated adsorbent may be disposed of in any one or more forms of CaO, Ca(OH)2, and CaCO3. The waste can be utilized as a product for industries such as cement, agriculture, or road aggregates where chemically similar CaO and limestone are used as inputs. Alternatively, the waste can be processed for disposal of the material. As long as CaCO3 is disposed of, it will also serve as a mineral sequestration of carbon dioxide from the air, holding the carbon dioxide in stone form out of the atmosphere for thousands of years. Thus, at least a portion of the calcium carbonate removed from the substrate(s) after carbonation may be disposed of in a manner that sequesters the recovered carbon dioxide. In some embodiments, the calcium adsorbent may skip the re-calcination step after the first carbonation and be immediately stored underground as the stable and non-toxic mineral CaCO3 formed during carbonation. For the passive low-input systems developed herein, this mineral carbon dioxide storage is potentially attractive in areas with low-cost limestone and unsuitable geology for traditional carbon dioxide sequestration.

[0067] Exemplary embodiments of the overall system and method according to the present disclosure are provided in FIG. 3. As shown in the figure, the exemplary system and method can utilize relatively tall substrates (e.g., "sheets") that are immersed in a reservoir (i.e., a "dip tank") containing a liquid calcium adsorbent (e.g., in the form of calcium hydroxide) because the substrates are transported by a vertical conveyor. Those substrates are suspended from the ceiling and the conveyor transports them during carbonation until the carbonated adsorbent is removed for further processing.

[0068] In the embodiment of FIG. 3, the coating system 32 may include an immersion unit 35 for immersion of the substrate 10 (e.g., a hanging sheet) into a reservoir 30 (e.g., a “dip tank”). The immersion unit 35 may include a part of a vertical conveyor 50 that is angled so that the substrate 10 can move downward into the reservoir 30 and then move upward out of the reservoir. In addition to the reservoir 30, the coating system 32 may include additional components such as a sprayer or a drip component for applying the calcium adsorbent by methods other than immersion. In other embodiments, the immersion unit 35 may include additional components configured to individually lower the individual substrates 10 into the reservoir 30. The substrate 10 emerging from the immersion unit is in the form of a coated substrate 52 (e.g., a lime-coated sheet) having a layer of calcium adsorbent coated thereon. The coated substrate 52 is then placed in a storage unit 54. The storage unit 54 may consist essentially of a conveyor 50 in a sheltered location between the immersion unit 35 and the collection unit 60. Alternatively, the storage unit 54 may be a building or a room(s) within a building where the coated substrate 52 can undergo carbonation where ambient CO2 from the air reacts with the calcium adsorbent and water evaporates from the calcium adsorbent. After sufficient carbonation has occurred, the coated substrate 52 moves to a collection unit 60 (e.g., a lime removal unit). There, the carbonated calcium adsorbent is removed from the substrate 10. The substrate 10 is released for reuse in the immersion unit 35, and the carbonated calcium adsorbent (which may contain CaCO3 and unreacted Ca(OH)2) moves along a horizontal conveyor 65, during which time the partially carbonated calcium adsorbent undergoes further carbonation, resulting in at least a portion of the unreacted calcium hydroxide being carbonated. All or part of the carbonated calcium adsorbent can be removed for disposal such that carbon dioxide removed from the air is sequestered in the form of calcium carbonate.All or part of the carbonated calcium adsorbent can similarly be sent to the calciner 70, where carbon dioxide can be released and calcium oxide can be reformed again. The carbon dioxide is removed by the solid separator 75, and calcium oxide is provided to the lime slaker 80 to form a calcium hydroxide slurry for input to the reservoir 30 for use as a calcium adsorbent.

[0069] Figure 3 shows a fully implementable system and method for carbon dioxide recovery, but it is understood that only some of the components and steps shown may be implemented to carry out different embodiments of the present disclosure. Thus, Figure 3 is provided so that those skilled in the art using the present disclosure can immediately recognize various combinations of the components and steps shown and achieve different embodiments. For example, in one or more embodiments, the method and system shown in Figure 3 may be implemented under one or more of the following conditions. · The calciner 70 and the solid separator 75 may not be present in the system. Instead, calcium oxide may be input directly into the lime slaker 80. In such an embodiment, the lime removed from the substrate by the collection unit 60 may be carried out for isolation and / or delivery to a third party for recalcination with carbon recovery. Similarly, the lime slaker 80 may not be present, and calcium hydroxide may be procured directly for input to the reservoir 30. · The reservoir 30 may be replaced with any additional component suitable for applying the calcium adsorbent to the substrate 10. · The "sheet" may be replaced with any other suitable substrate material as described elsewhere in this specification. · The lime-coated sheet 52 may circulate through the vertical conveyor for carbonation without intermediate processing in the collection unit 60. · The CaCO3 and Ca(OH)2 removed from the collection unit 60 may be sent directly to recalcination without further carbonation. · The process may be substantially continuous in that the application of the calcium adsorbent, the process for carbonation of the coated substrate, and the removal of the carbonated adsorbent in the collection unit 60 can be carried out without interruption other than necessary maintenance or scheduled downtime. For example, the system may be large enough such that a single substrate can circulate only once, taking enough time for the desired level of carbonation to occur, from exiting the coating system 32 until re-entering the coating system. This can be on the order of several hours to several days. Thus, the system can operate continuously. · The vertical conveyor may include a stop station at some point between the coating system 32 and the collection unit 60. In this way, the coated substrate 52 may be dropped at the stop station for carbonation to occur while other substrates are being processed through the system. The stop station may intermittently, completely or partially remove and empty the coated substrate that has already undergone carbonation and load a newly coated substrate. · The process may operate in a batch mode in which substrates are coated as a batch, stored as a batch for carbonation, and then processed as a batch for lime removal. · The process may operate through multiple coating and carbonation steps without removing the coating layer from the substrate. For example, the substrate may be coated with a relatively thin layer of calcium adsorbent material, processed to cause carbonation, and recoated such that additional relatively thin layers of calcium adsorbent material are added on top of the carbonated layers, etc., until a relatively thick coating of multiple separately carbonated layers is present on the substrate. The coated substrate may then have the coating layer removed.

[0070] Further exemplary embodiments are shown in FIGS. 4 and 5. Referring to FIG. 4, the core system as shown in FIG. 3 can remain substantially unchanged, but the vertical conveyor system can be replaced by a stationary sheet. In such an embodiment, the calcium adsorbent can be applied by a pipe and drip system, such that the substrate remains stationary while the calcium adsorbent moves through the system, first in the form of calcium hydroxide and then in the form of carbonated lime. In FIG. 4, the calcium adsorbent can be pumped or otherwise conveyed from reservoir 30 through one or more lines 100 to one or more drip pipes 110 that include one or more perforations 115 for dripping fresh calcium adsorbent onto substrate 200. After the calcium adsorbent has undergone carbonation, the carbonated lime can be removed from substrate 200 (e.g., via a shaking system 155 integrated with a suspension unit 150) such that the carbonated lime falls onto horizontal conveyor 165. The conveyor can be configured to include carbon recovery or deliver the carbonated lime to calciner 70, and as in FIG. 3, connect the calciner to solid separator 75 and lime slaker 80 to deliver the calcium adsorbent to reservoir 30. Although the carbon dioxide and material flows are not shown in FIG. 4, it is understood that such material flows can be substantially the same as those described in connection with FIG. 3.

[0071] Modifying the embodiment of FIG. 3 can result in further exemplary embodiments for implementation of the systems and methods described herein. For example, as shown in FIG. 5, the elements of the drip system from FIG. 4 remain the same, but a gravity-based collection system 190 is utilized to replace the horizontal conveyor. After the carbonated adsorbent is removed from substrate 200, it falls onto the sloped surface of the gravity-based collection system 190, such that the solid product is collected at a density high enough to allow for easy transport to calciner 70.

[0072] This system and method can achieve net carbon removal from the atmosphere because the net recovery of CO2 from air by the calcium sorbent exceeds any CO2 emissions from the process. The net carbon flows in exemplary embodiments of the present disclosure are shown in the following table for a system with a 90% carbon capture calciner and an 85% calcium sorbent carbonation rate.

Table 1

[0073] The experimental data demonstrated the ability to achieve >70% carbonation in a period of about 3 days with 0.3 kg of calcium sorbent per square meter of exposed area. At this pace and conversion rate, it would result in a net direct air capture of approximately 100,000 metric tons (MT) using less than 25 acres of land. This land utilization is far below what is required to enable billions of tons of CO2 to be recovered from the air, and it will not impact other land uses or exhaust suitable locations close to limestone and CO2 storage sites.

[0074] Many variations and other embodiments of the invention that will be apparent to those of ordinary skill in the art to which this invention pertains will have the benefits of the teachings presented in the foregoing description and the accompanying drawings. Accordingly, it is to be understood that the invention is not limited to the specific embodiments disclosed, and that variations and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0075] The use of the terms "about" and "substantially" in this specification is understood to mean that a value described as "about" a particular value or "substantially" a particular value may vary by only an industrially acceptable tolerance of the specified value. If no industrially acceptable tolerance is available, such terms may be understood to indicate that the acceptable value may vary by ±3%, ±2%, or ±1% from the specifically recited value. Similarly, in some embodiments, the recited value may be exact as necessary, and variations above or below the recited value may be explicitly excluded as required.

Claims

1. A method for direct air capture of carbon dioxide, comprising: preparing a substantially continuous coating layer of a calcium sorbent material on one or more substrates at a density of less than 10 kilograms per square meter; contacting the one or more substrates having the substantially continuous coating layer of the calcium sorbent material with air containing carbon dioxide for a time sufficient for the calcium sorbent to react with the carbon dioxide, thereby recovering at least a portion of the carbon dioxide from the air and converting at least a portion of the calcium sorbent to a carbonated form; removing at least a portion of the calcium sorbent in the carbonated form from the one or more substrates; treating the calcium sorbent in the carbonated form so that the carbon dioxide recovered from the air is ready for sequestration or other use; and a method comprising the steps of:

2. The method according to claim 1, wherein the substantially continuous coating layer of the calcium sorbent material has a density of about 0.1 kilogram per square meter to about 5 kilograms per square meter.

3. The method according to claim 1, wherein the substantially continuous coating layer of the calcium sorbent material has an average thickness of less than 2.5 cm on the one or more substrates.

4. The method according to claim 1, wherein the substantially continuous coating layer of the calcium sorbent material has an average thickness of about 0.01 mm to about 2 cm on the one or more substrates.

5. The method according to claim 1, wherein the one or more substrates are substantially configured as a sheet.

6. The method according to claim 1, wherein the substantially continuous coating layer of the calcium sorbent material is configured to exhibit a carbonation rate such that at least 25% by weight of the calcium sorbent is carbonated within a time of 96 hours or less.

7. The method according to claim 1, wherein the substantially continuous coating layer of the calcium adsorbing material is configured to exhibit a carbonation rate such that at least 50% by weight of the calcium adsorbing material is carbonated within a time period of about 1 day to about 14 days.

8. Contacting the one or more substrates having the substantially continuous coating layer of the calcium adsorbing material with air containing carbon dioxide includes suspending the one or more substrates having the substantially continuous coating layer of the calcium adsorbing material at a location where the substantially continuous coating layer of the calcium adsorbing material contacts the air. The method according to claim 1.

9. Removing at least a portion of the calcium adsorbent in the carbonated form from the one or more substrates includes applying to the one or more substrates a force sufficient to break the substantially continuous coating layer of the calcium adsorbing material and remove the substantially continuous coating layer of the calcium adsorbing material from the one or more substrates. The method according to claim 1.

10. Treating the calcium adsorbent in the carbonated form includes treating the calcium adsorbent to be in the form of particles configured for isolation after carbonation. The method according to claim 1.

11. Treating the calcium adsorbent in the carbonated form includes further exposing the calcium adsorbent in the carbonated form to ambient air for a time sufficient to increase the carbonation rate. The method according to claim 1.

12. Treating the calcium adsorbent in the carbonated form includes calcining the calcium adsorbent in the carbonated form to release carbon dioxide therefrom to form calcium oxide, and recovering the carbon dioxide released from the calcium adsorbent and includes the method according to claim 1.

13. The method according to claim 12, further comprising forming the calcium adsorption material used to slake calcium oxide to prepare the substantially continuous coating layer.

14. The method according to claim 12, further comprising removing a part of the calcium adsorbent in the carbonate form before calcination and adding make-up limestone during calcination.

15. The method according to claim 1, wherein preparing the substantially continuous coating layer of the calcium adsorption material comprises immersing the one or more substrates in a reservoir of the calcium adsorption material.

16. The method according to claim 1, wherein preparing the substantially continuous coating layer of the calcium adsorption material comprises dropping or spraying the calcium adsorption material onto the one or more substrates.

17. A system for direct air capture of carbon dioxide, comprising: A coating system configured to apply a liquid calcium adsorption material to one or more substrates to form a substantially continuous coating layer of the calcium adsorption material on the one or more substrates at a coating density of less than 10 kilograms per square meter; A storage unit configured to dispose of the one or more substrates for a period of time, wherein the one or more substrates are in contact with air, such that carbon dioxide in the air reacts with the calcium adsorption material to form a carbonated calcium adsorption material; A collection unit configured to remove and collect the carbonated calcium adsorption material from the one or more substrates and a system.

18. The system according to claim 17, wherein the coating system comprises one or more reservoirs of the liquid calcium adsorption material.

19. The system according to claim 17, wherein the coating system further comprises an immersion unit configured to immerse the one or more substrates into one or more reservoirs of the liquid calcium adsorbing material.

20. The system according to claim 17, wherein the coating system comprises a suspension unit configured to hold the one or more substrates in a substantially vertical position.

21. The system according to claim 20, wherein the coating system further comprises one or more dropping pipes configured to drop the calcium adsorbing material onto the one or more substrates.

22. The system according to claim 20, further comprising a calciner configured to receive the carbonated calcium adsorbing material and convert the carbonated calcium adsorbing material into calcium oxide and carbon dioxide.

23. The system according to claim 22, further comprising a solid separator configured to separate calcium oxide from carbon dioxide.

24. The system according to claim 23, further comprising a lime slaking unit configured to receive calcium oxide and form calcium hydroxide for use as the calcium adsorbing material.

Images