Direct capture of carbon dioxide

Abstract

To provide systems and methods for direct air capture of carbon dioxide or other gases through a calcium sorbent in a manner that allows large-scale, relatively low cost implementation.SOLUTION: A calcium sorbent may be provided as a substantially thin coating layer on one or more substrates and utilized for direct air capture of carbon dioxide through chemisorption. The carbonated sorbent may be disposed of for sequestration of the carbon dioxide or regenerated with capture of carbon dioxide released from the carbonated sorbent during the regeneration process.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to systems and methods useful for capturing carbon dioxide. More specifically, the systems and methods can capture carbon dioxide directly from air or another stream using adsorbents. [Background technology]

[0002] There is an ongoing global effort to address the rising concentrations of greenhouse gases, particularly carbon dioxide (CO2), in the atmosphere. While much work is being done to reduce the amount of such gases being released into the atmosphere each year, there is a growing understanding that reducing emissions alone may not be sufficient to address concerns about climate change. Therefore, research is currently underway into methods for not only reducing greenhouse gas emissions, but also removing such gases that are already present in the atmosphere.

[0003] Large-scale deployment of current methods for capturing CO2 from ambient air has been unsuccessful, at least in part, due to the excessive costs associated with known methods given that global CO2 emissions are on the order of approximately 37 billion tons per year. Current CO2 removal methods suffer from high capital costs and high operating costs for a variety of reasons. For example, because the total CO2 concentration in ambient air is very dilute compared to the major components (e.g., nitrogen, oxygen, and argon), previously identified removal methods required high specificity and high efficiency to be cost-effective. Although highly efficient removal methods have previously been identified, such methods lacked the ability to pass sufficient volumes of ambient air through capture systems to make known methods simple and cost-effective enough for industrial-scale implementation. As a prerequisite for achieving high efficiency, known removal methods required the use of renewable solvents and / or chemicals to offset the high cost of the necessary materials. Therefore, such renewable solvents and / or chemicals used in known capture methods must be separated from the captured CO2 for regeneration, and this separation requirement also adds additional cost and energy to the process.

[0004] Although there is a strong global desire to implement CO2 removal technologies as a means to combat climate change, unreasonably high costs have so far hindered such implementation. Without affordable technologies to remove existing CO2 from the atmosphere, the world will continue to struggle to reduce and reverse anthropogenic global warming. Therefore, there remains a need in this field for additional technologies that are effective in removing greenhouse gases, including CO2, from ambient air. Summary of the Invention

[0005] In one or more embodiments, the present disclosure can provide systems and methods adapted or configured to capture carbon dioxide directly from ambient air. Beneficially, the systems and methods can maximize the available surface area of ​​the calcium sorbent 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 production and logistics systems integrated with passive air capture processes while simultaneously mitigating atmospheric carbon dioxide accumulation.

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

[0007] The use of calcium hydroxide for the chemisorption of carbon dioxide from air has previously been proposed (see, “Carbon Dioxide Extraction From Air: Is It An Option?” Lackner, 1999, and “Liquid-Like HO 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 system has been shown to effectively utilize these properties into a viable direct air capture system with passive carbonation. Rather, previous systems have relied on active acceleration of direct air capture through carbonation equipment, air contactors, additional solvents, pellet reactors, and 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 failed to provide a practical integrated system. For example, U.S. Patent No. 10,570,018 discloses a passive calcium direct air recovery system, but such a system still fails to meet the requirements necessary for practical implementation (i.e., does not allow for accelerated carbonation at a sufficiently low cost). However, all of these drawbacks can be overcome in accordance with one or more embodiments of the presently disclosed systems and methods, which provide accelerated carbonation at a sufficiently low cost for practical implementation.

[0008] The systems and methods of the present disclosure, at least for direct air capture of carbon dioxide (i.e., other contaminants may similarly be removed from ambient air using the present disclosure), overcome some limitations of known processes for removing carbon dioxide from air. For example, known processes require highly efficient, high-rate adsorbents / chemicals to rapidly remove carbon dioxide from ambient air. Due to excessive material costs, such processes require efficient regeneration of the adsorbents / chemicals. Similarly, to achieve rapid turnover, such processes require active airflow (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 present systems and methods enable the use of low-cost adsorbents / chemicals that have been ignored by the prior art for use in viable air capture systems due to recognized efficiency limitations. Lower-cost adsorbents / chemicals also enable integrated adsorbent generation and recovery processes. The present methods and systems can similarly be efficiently performed without full adsorbent / chemical regeneration. Furthermore, the present methods and systems can be performed (if desired) in the apparent absence of any forced air components (e.g., blowers), as high efficiencies can be achieved even when slower reaction times are utilized. More specifically, the present systems and methods provide for the implementation of high surface area configurations that achieve high efficiency absorption at low cost, in the partial or complete absence of adsorbent / chemical regeneration, and even in the absence of applied forced air components.

[0009] In one or more embodiments, the present systems and methods may incorporate the use of a passive calcium chemisorption carbonation process. Exemplary embodiments may utilize one or more circulating and / or fixed hanging substrates, which can be randomly distributed or specifically organized within a closed, semi-closed, or covered structure. The circulating substrates may specifically utilize vertical, horizontal, and / or passive conveyor systems. The calcium sorbent may be provided in a substantially process-ready state—i.e., in a chemical state in which the calcium sorbent is ready to undergo a spontaneous or catalytically driven carbon dioxide absorption process. In some embodiments, the calcium sorbent precursor may be processed to provide a process-ready material. For example, calcium carbonate (CaCO) may be calcined and slaked to form a calcium hydroxide slurry or suspension. Preferably, such processing is performed with partial, substantially complete, or sufficiently complete recovery of the carbon dioxide displaced from the calcium carbonate. Alternatively or additionally, calcium oxide and / or calcium hydroxide may be provided from a further process in which they were produced, preferably with recovery of any produced carbon dioxide.

[0010] The substrate can be coated with a relatively thin layer of calcium hydroxide (or other calcium sorbent), which may be in the form of a slurry or suspension. Such coating can be by any suitable means, particularly as described further herein. After coating, the coated substrate can be placed in a desired area of ​​the structure and maintained substantially stationary. Alternatively, the coated substrate can be circulated through at least a portion of the structure. The coated substrate is contacted with ambient air for a period of time sufficient to allow the desired amount of evaporation (i.e., release of HO from the calcium hydroxide) and carbonation (i.e., uptake of CO from the air) to proceed. The carbonated coating, which has absorbed 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 transported from the site for use in a different process, industrial use, sale, and / or sequestration. In some embodiments, the calcium sorbent can be regenerated for reuse. For example, the carbonated material may optionally undergo further carbonation before being processed through a calciner to drive off carbon dioxide, which can be recovered for sequestration or other uses (e.g., enhanced oil recovery). Calcination can also regenerate calcium oxide, which may then be slaked to form calcium hydroxide, which is coated onto a substrate for further direct air capture of carbon dioxide.

[0011] Systems according to the present disclosure may include any combination of individual components and / or units useful for carrying out a process step. For example, in some embodiments, a suitable system may preferably include a calciner adapted or configured to recover at least a portion, substantially all, or entirely all of the carbon dioxide liberated in the calciner. The system may also include a sludger, a conveyor system (which may be adapted or configured to operate in one or both vertical and horizontal segments), and one or more substrates adapted or configured to be suspended at least partially above a floor surface. The system components may exist in a single structure or multiple structures.

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

[0013] The present disclosure offers additional advantages over known carbon dioxide capture systems. For example, passive carbon dioxide capture utilizing high surface area sorbents 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, carbonation equipment, and / or pellet reactors. This advantageous high surface area configuration can be achieved, in one or more embodiments, by utilizing a relatively thin layer of calcium sorbent on one or more substrates used. Exemplary embodiments of suitable layer thicknesses can range from about 1.5 kg or less of calcium sorbent per square meter of exposed area on the substrate. This thin layer can be deployed at a relatively high vertical density, such as greater than 5 feet in height, while maintaining the thickness of individual layers of calcium sorbent. This combination of high surface area and low layer thickness can provide direct air capture of carbon dioxide over reasonable periods of time (e.g., on the scale of hours to months, depending on the exact coating parameters and desired process throughput) without requiring excessive land coverage. Furthermore, this substrate-based deposition method allows for thinner applications of calcium sorbents in practical and efficient configurations that solve at least some of the challenges and problems not addressed by previous passive direct air capture systems. Thus, the present system and method can far outperform previously conceived faster, but more capital and energy intensive, direct air capture systems while also providing efficiencies previously unattainable with previous passive direct air capture systems.

[0014] In addition to the above, the 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 power such equipment. As a result, less carbon dioxide is produced to heat and power the capture system, and the net carbon removal of the present system can significantly exceed that achievable with known systems and methods.

[0015] Spent calcium sorbent (i.e., sorbent that has already been used to passively capture carbon dioxide) can be calcined in a manner that separates the absorbed carbon dioxide for storage, thereby regenerating the calcium sorbent for further air capture. This regeneration reduces the need for limestone to produce the calcium sorbent. While calcium oxide (CaO) calcination is a common process, its integration with the present passive dense CaO carbonation process is effective in providing significant improvements in the full cycle cost and energy use of sorbent use and regeneration compared to other direct air capture systems. Unlike previously described processes, the disclosed system and method does not require additional chemicals or materials at the air capture stage that can complicate the calcination of calcium sorbent after it has been utilized in carbon dioxide capture.

[0016] Previously disclosed processes for using calcium oxide or calcium hydroxide for direct air capture, even when passive systems were proposed, were unable to control the space and time required to scale up the process to industrial levels. While calcium sorbents have been explored for direct air capture for approximately 20 years, no system has been developed that makes it feasible to passively capture carbon dioxide at a scale that uses calcium. The present disclosure solves this problem by its total system design, which involves the application of a thin layer of sorbent to accelerate carbonation, as well as a high-density storage and logistics process that minimizes space and costs during carbonation, enabling a passive direct air capture process that can operate effectively on an industrial scale.

[0017] In one or more embodiments, the present disclosure may provide, inter alia, a method for direct air capture of carbon dioxide. In an exemplary embodiment, such a method may include preparing a substantially continuous coating layer of calcium-adsorbing material on one or more substrates at a density of less than 10 kilograms per square meter; contacting the one or more substrates bearing the substantially continuous coating layer of calcium-adsorbing material with air containing carbon dioxide for a period of time sufficient to cause the calcium sorbent to react with the carbon dioxide, thereby capturing 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 form of the calcium sorbent from the one or more substrates; and treating the carbonated form of the calcium sorbent such that the carbon dioxide captured from the air is ready for sequestration or other use. In further embodiments, the method may be further defined by one or more of the following statements, which may be combined in any number and / or order:

[0018] The substantially continuous coating layer of calcium-adsorbing material may have a density of from about 0.1 ksm to about 5 ksm.

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

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

[0021] One or more of the substrates may be configured substantially as a sheet.

[0022] The substantially continuous coating layer of calcium-adsorbing material may be configured to exhibit a carbonation rate such that at least 25% by weight of the calcium-adsorbing material is carbonated within 96 hours or less.

[0023] The substantially continuous coating layer of calcium-adsorbing material may be 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.

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

[0025] Removing at least a portion of the carbonated form of the calcium adsorbent from the one or more substrates may comprise applying a force to the one or more substrates sufficient to disrupt the substantially continuous coating layer of the calcium adsorbing material and detach the substantially continuous coating layer of the calcium adsorbing material from the one or more substrates.

[0026] Treating the carbonated form of the calcium sorbent may include identifying the carbonated form of the calcium sorbent for sequestration of the carbonated form of the calcium sorbent.

[0027] Treating the carbonated form of the calcium sorbent may include further exposing the carbonated form of the calcium sorbent to ambient air for a time sufficient to increase the carbonation rate.

[0028] Treating the carbonated form of the calcium sorbent may include calcining the carbonated form of the calcium sorbent to release carbon dioxide therefrom to form calcium oxide, and recovering the carbon dioxide released from the calcium sorbent.

[0029] The method may further include slaking calcium oxide to form a calcium-adsorbing material that is used to prepare the substantially continuous coating layer.

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

[0031] Preparing a substantially continuous coating layer of calcium-adsorbing material may include dipping one or more substrates into a reservoir of calcium-adsorbing material.

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

[0033] In one or more embodiments, the present disclosure may further provide, inter alia, a system for direct air capture of carbon dioxide. In exemplary embodiments, such a system may include a coating system configured to apply a liquid calcium-adsorbing material to one or more substrates to form a substantially continuous coating layer of the calcium-adsorbing material on the one or more substrates; a storage unit configured to store the one or more substrates for a period of time, wherein the one or more substrates are contacted with air such that carbon dioxide in the air reacts with the calcium-adsorbing material to form a carbonated calcium-adsorbing material; and a collection unit configured to remove and collect the carbonated calcium-adsorbing material from the one or more substrates. In further embodiments, the system may be further defined by one or more of the following statements, which may be combined in any number and / or order:

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

[0035] The coating system may further include a dipping unit configured to dipped the one or more substrates into one or more reservoirs of liquid calcium-adsorbing material.

[0036] The coating system can 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 drip pipes configured to drip the calcium-adsorbing material onto the one or more substrates.

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

[0039] The system may further include a solids separator configured to separate the calcium oxide from the 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 adsorbing material.

[0041] These and other features, aspects, and advantages of the present disclosure will become apparent from a reading of the following detailed description 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-described 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 a specific embodiment herein. This disclosure is intended to be read in its entirety such that any separable features or elements of the disclosed invention, in any of its various aspects and embodiments, should be deemed to be intended to be combinable unless the context clearly dictates otherwise. [Brief explanation of the drawings]

[0042] [Figure 1A] FIG. 1 is a diagram of a substrate coated with a substantially continuous layer of calcium-adsorbing material according to an exemplary embodiment of the present disclosure. [Figure 1B]FIG. 1 is a partial cross-sectional view of a substrate coated with a substantially continuous layer of calcium-adsorbing material according to an exemplary embodiment of the present disclosure. [Figure 2] FIG. 1B is a diagram of a substrate being immersed in a reservoir containing a liquid calcium-adsorbing material to form a substantially continuous layer of the calcium-adsorbing material on the substrate, according to an exemplary embodiment of the present disclosure. [Figure 3] 1 is a flowchart illustrating a system and method for direct air capture of carbon dioxide according to an exemplary embodiment of the present disclosure. [Figure 4] 1 is a flowchart illustrating example details of sorbent coating and removal in a system and method for direct air capture of carbon dioxide according to an exemplary embodiment of the present disclosure. [Figure 5] 10 is a flowchart illustrating further example details of sorbent coating and removal in systems and methods for direct air capture of carbon dioxide according to exemplary embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0043] Various aspects of the present disclosure will now be described in more detail below with reference to the accompanying drawings, in which some, but not all, implementations of the present disclosure are shown. Indeed, various implementations of the present disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these example implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the 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 or atmospheric air. The systems and methods utilize a calcium sorbent, preferably renewable, but optionally configured for non-renewable use. In some embodiments, the calcium sorbent may be configured to undergo repeated carbonation and calcination, such that carbon dioxide can be removed from the atmosphere through absorption by the sorbent and then recovered during sorbent regeneration. By way of example, calcium oxide and / or calcium hydroxide may be utilized as the calcium sorbent. Thus, the calcium sorbent may be adapted or configured to spontaneously or catalytically absorb carbon dioxide from ambient air as needed. Such absorption may be effective to form a carbonated form of the calcium sorbent, which can then be regenerated by calcination to drive off carbon dioxide, which can be recovered in the calcination process.

[0045] To form the initial calcium sorbent and / or regenerate the carbonated form of the calcium sorbent, the carbonate salt (e.g., calcium carbonate—CaCO) can be injected into a calciner, which can preferably be equipped with suitable components for recovering at least a portion of the carbon dioxide driven off during calcination. The limestone utilized in forming the sorbent can be provided in particulate form, ensuring that entrained-flow, rotary-hearth, or fluidized-bed calciners can be used for CaO production. In some embodiments, the particulate limestone / CaCO can have an average size (e.g., the largest measurable dimension of length, width, or thickness of an irregularly shaped particle) of about 1 μm to about 1 mm, about 5 μm to about 750 μm, or about 10 μm to about 500 μm. As discussed further below, the calcium oxide so formed can be further processed before being applied to a 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 liberated from the carbonate salt during calcination. In some embodiments, calcination can be carried out by heating the carbonate salt to a temperature ranging from about 700°C to about 1200°C, from about 750°C to about 1100°C, or from about 800°C to about 1000°C. The liberation of carbon dioxide can be effective to form calcium oxide (CaO). At least a portion of the carbon dioxide recovered from calcination can be utilized in industrial processes, enhanced oil recovery, or sequestration. Non-limiting examples of capture technologies that can be implemented to capture carbon dioxide released in calcination include oxyfuel calcination, calcium-based chemical looping, amine-based solvent technology, and the like. Calcination to provide low-carbon CaO can be carried out on-site at a direct air capture facility and, therefore, can be part of an integrated system for continuous or batch processing. If desired, calcination may be performed off-site or by a third party. Thus, the carbonate content may be transported to a calcination site for calcium sorbent regeneration and carbon recovery, and then returned directly to the air recovery facility.

[0047] The CaO may remain in its anhydrous form, or may be hydrated with water to form calcium hydroxide (Ca(OH)), or may be a mixture of both, all of which are interchangeably referred to as "calcium sorbent" or "lime sorbent." Accordingly, a slaking unit may be used in addition to the calcination unit described above to prepare the initial sorbent and / or regenerate the sorbent from the carbonate product. This calcium hydroxide and / or CaO may be further mixed with additional water to provide the calcium sorbent in a form suitable for addition to one or more substrates. The sorbent prior to addition to the substrate(s) may thus be one or more of a paste, a slurry, a spray, or a suspension. Furthermore, in some embodiments, the calcium sorbent may be prepared in a polymeric form, as a metal-organic framework (MOF), or as another suitable mixture and / or molecular structure. The calcium sorbent is preferably provided in any suitable form that enables the calcium sorbent to capture carbon dioxide from ambient air. For example, calcium hydroxide can capture carbon dioxide from air when the relative humidity is greater than 40%, since it is generally understood that the presence of water is important for calcium hydroxide to capture carbon dioxide and produce calcium carbonate. Carbon dioxide in the air can dissolve in water to form carbonic acid (H2CO3), which is HCO3 - and H + thus allowing reaction with calcium to form calcium carbonate and recovery of carbon dioxide.

[0048] In some embodiments, the calcium sorbent added to one or more substrates may comprise, consist essentially of, or consist essentially of the calcium material itself and water. However, in other embodiments, one or more additional chemicals or materials may be included and adapted or configured to improve the carbon dioxide chemisorption properties of the calcium sorbent and / or improve the adhesion of the calcium sorbent to the substrate. Similarly, the calcium sorbent may be provided with a particular morphology that may be adapted or configured to improve the carbon dioxide chemisorption properties of the calcium sorbent. Such improvements may include, for example, any one or more of reactivity, viscosity, porosity, surface area, morphological stability, and electronegativity, as well as other beneficial properties. In an exemplary embodiment, sodium hydroxide may be specifically added to the sorbent. In other embodiments, potassium hydroxide, magnesium hydroxide, fumed silica, zeolite, magnetic particles, and / or recycled regenerated sorbent may be added. In addition to the above mixtures, the calcium sorbent 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, packing, and other such operations may be applied to the sorbent, as they have been demonstrated to affect the reactivity and performance of the calcium sorbent applied to one or more substrates.

[0049] Application of the calcium adsorbent to the substrate(s) can be performed in a coating unit or facility. A calcium adsorbent having the composition and / or form described above can be applied in a relatively thin layer onto one or more substrates. For example, the average adsorbent layer thickness over 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., up to the minimum coating thickness 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. While the foregoing ranges pertain to various useful embodiments according to the present disclosure, 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 adsorbing material may be provided in a substantially porous form, providing increased surface area for reaction with carbon dioxide. In such embodiments, a relatively thick coating layer may be utilized while still providing a high carbonation rate, as discussed further below. For example, when a relatively thick coating layer is utilized, the average layer thickness may 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, further simplifying the process in that additional processing (e.g., to achieve high porosity as described above) may be avoided, and a substantially continuous coating layer may be applied at a relatively small average thickness while still achieving a desired carbonation rate. In such embodiments in which a relatively thin coating layer is utilized, the average layer thickness may 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 may be for a single layer of calcium adsorbent, or may be the total thickness of multiple layers (eg, 2, 3, 4, or 5 layers) applied to the substrate.1A and 1B show a representative substrate 10 having a coating 20 of calcium adsorbent applied thereto. As seen in FIG. 1A, the coating 20 may cover less than the entire surface 11 of the substrate 10, although the coating may cover substantially the entire surface if desired. As seen in FIG. 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 sorbent layer thickness is adapted or configured to provide a calcium sorbent density within a specified range. As noted above, useful calcium sorbent densities can vary based on the average layer thickness utilized. Across the desired range, calcium sorbent densities can range from about 10 kilograms per square meter (ksm) of exposed substrate area or less, less than 5 ksm, less than 2 ksm, or less than 1 ksm (e.g., down to a minimum of at least 0.02 ksm). In some embodiments, calcium sorbent density on the substrate can range from 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. Layer thickness can be controlled using various mechanisms, such as controlling the content of water mixed with the calcium sorbent to form the coating mixture. This (or other factors) can be utilized to control the viscosity of the coating mixture and, therefore, the coating thickness of the coating mixture. In some embodiments, the relatively thin nature of the calcium sorbent layer can be particularly effective in enabling passive carbon dioxide capture. While calcium oxide captures carbon dioxide at ambient conditions, the reaction is rate-limited by the coating thickness, and significantly thicker layers essentially cease reactivity 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, coating thicknesses on the higher end of the aforementioned range can be particularly useful when the coating layer is provided in a relatively highly porous form. Similarly, the substrate may be provided with a three-dimensional structure that allows for greater deposition of the sorbent thereon. In an exemplary embodiment, the calcium sorbent can be prepared in the form of a foam exhibiting at least a partial open-cell structure, which is effective in allowing air to penetrate deeper into the layer thickness for reaction between the sorbent and carbon dioxide in the air.

[0051] The present systems and methods may operate within a specified carbonation rate of the sorbent. In some embodiments, the carbonation rate may be maximized so that about 50% by weight or more, about 60% by weight or more, about 70% by weight or more, or about 80% by weight or more of the sorbent is carbonated before removal from the substrate(s). For example, removal of the carbonated substrate may occur upon achieving about 60% to about 98% by weight, about 65% to about 95% by weight, or about 75% to about 90% by weight of the sorbent. Such high levels of carbonation are not expected to be achievable by optimization of known processes because known processes require the use of other types of sorbents / chemicals or are configured for use with sorbents that cannot achieve such high levels of carbonation due to structural limitations (e.g., required sorbent layer thickness). In other embodiments, if a high-throughput process is desired, the carbonation rate may be minimized to increase system throughput. For example, removal of carbonated substrate may occur upon achieving about 25% to about 75% by weight of the sorbent, about 30% to about 65% by weight, or about 35% to about 60% by weight of carbonation. By utilizing such concentration limits, sorbent turnover can be increased so that the total mass of carbon dioxide that can be removed by a given system can be maximized. This is because chemisorption rates can be significantly faster at lower sorbent carbonation rates, and carbonation rates can be significantly slower as the relative proportion of carbonated sorbent increases.

[0052] By applying a specified calcium adsorbent coating layer thickness, coating layer density, and desired carbonation rate, the calcium adsorbent layer applied to one or more substrates can be configured or adapted to provide a carbonation rate within specified parameters. Because the carbonation rate is a function of the above factors, such a carbonation rate is not expected to be specific to the calcium adsorbent. In some embodiments, the calcium adsorbent coating formed on one or more substrates can be configured or adapted to exhibit a carbonation rate such that at least 25%, at least 30%, at least 35%, at least 40%, or at least 45% by weight of the calcium adsorbent coating is carbonated within 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). More specifically, calcium sorbent coatings formed on one or more substrates can be configured or adapted to exhibit a carbonation rate such that about 25% to about 50%, about 25% to about 45%, or about 30% to about 45% by weight of the calcium sorbent coating is carbonated within a time period 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. Such carbonation rates can be achieved by controlling one or more of the factors discussed above, such that relatively high throughput systems and methods can be achieved. This can be advantageous when the calcium sorbent is regenerated, and such high throughput can increase the total volume or mass of carbon dioxide removed from the air in 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., sequestered in the form of calcium carbonate that is removed from the substrate without calcination to release carbon dioxide) or when the space for the system is large enough to allow for longer carbonation times. Thus, in such embodiments, the calcium adsorbent coating formed on one or more substrates may be configured or adapted to exhibit a carbonation rate such that at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% by weight of the calcium adsorbent coating 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. Evaluation of the carbonation rate can be performed by taking samples of the calcium adsorbent coating at various times after formation of the coating layer and performing chemical analysis of the adsorbent (e.g., via mass spectrometry or similar analytical method effective to identify chemical composition).

[0054] Application of the calcium adsorbent to one or more substrates can be accomplished by any one or combination of suitable methods. In some embodiments, application can be achieved by directly dipping the substrate in the calcium adsorbent or by spraying the calcium adsorbent onto the substrate. In other embodiments, application can be achieved by using a brush, doctor blade, spray mechanism, dipping, pouring, or any method suitable for applying a thin layer of adsorbent to a substrate. For example, as shown in FIG. 2, substrate 10 can be immersed in a reservoir 30 (e.g., in the form of a tank) containing calcium adsorbent 25. A clamp 40 is attached to substrate 10 to manipulate the substrate through the immersion process. Alternatively, substrate 10 can be passed over reservoir 30 so that as calcium adsorbent 25 is dipped or sprayed onto the substrate, excess adsorbent falls into the reservoir for recirculation to the application component (e.g., a sprayer). 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 applied adsorbent. While the method of applying the calcium sorbent to the substrate can be varied as desired to improve throughput, certain modes of applying the calcium sorbent may be preferred with respect to improving the reactivity of the calcium sorbent with carbon dioxide. For example, spraying the sorbent onto the substrate may be effective in achieving a coating layer with increased porosity, which may improve the ability to utilize thicker layers for chemisorption, as described above. In some embodiments, the calcium sorbent coating 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, or the like. A "substantially" continuous coating indicates that, while some imperfections in the coating or layer (e.g., cracks, pits, and similar defects) are accounted for, the coating is not present in the form of separate pieces or particles present as individual elements (even when individual elements are in physical contact with one another). Rather, the coating or layer extends along the length of the substrate surface as an intact thin film, sheet, membrane, or the like.In certain embodiments, the coatings of the present disclosure may explicitly exclude pelletized lime-based sorbents or other lime-based sorbents in particulate form. The use of such particulate or pelletized sorbents may be undesirable due to the added complexity of forming the particles or pellets, which may require mixing the sorbent with fillers, binders, etc., and then spray-drying or otherwise processing the mixture to form discrete solid particles or pellets. Such particulate materials may also require additional processing to adhere to a substrate and more complex processing to remove the adhered particles for regeneration. Alternatively, such particles or pellets must be placed in a packed-bed reactor so that carbon dioxide-containing air can be processed through the packed bed, which again introduces complexity not present according to the methodology of the present disclosure.

[0055] The substrate itself may be bare or may have adhesives, anti-adherents, catalysts, polymers, and other additives applied prior to application of the calcium sorbent to improve the performance, life, surface area, and / or processability of the calcium sorbent. The substrate surface may be two-dimensional (i.e., substantially flat) or three-dimensional (i.e., sheared, textured, molded, curved, etc.) to improve application, performance, reactivity, surface area, and processability of the calcium sorbent. Increasing the surface area may be desired to accelerate the carbonation reaction, and increasing the volume of sorbent per unit of substrate material may be desired to reduce the costs associated with the substrate material. Plastic is one possible substrate material due to its low cost, structural flexibility, durability, and lack of reactivity with calcium. Other embodiments include wood products, foam board, steel, or any other suitable substrate.

[0056] The substrate may be adapted or configured to be substantially flat when placed on a flat surface or in a suspended configuration. In other embodiments, the substrate may be intentionally adapted or configured to have a three-dimensional shape as described above. For example, the substrate may be formed into a cylindrical, conical, or other shape, which is advantageous for all exposed sides of the substrate to be coated with the calcium sorbent, increasing the surface area per unit of substrate material. In some exemplary embodiments, the substrate may be configured in a rolled configuration to have a substantially spiral cross-section. In other embodiments, the substrate may be adapted or configured to have a porous network in which the pores are large enough to allow the liquid sorbent to flow therethrough and coat the surface of the substrate, but also large enough to allow the carbonated sorbent to be removed from the substrate. For example, a honeycomb structure, such as those 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 to allow efficient removal of the carbonated sorbent. Such structures are commonly formed from ceramic, although metal honeycomb may also be utilized to improve durability.

[0057] The substrate may be rotated, moved, spun, aerated, or otherwise manipulated to affect the drying of the calcium sorbent on the substrate material. Similarly, a blower or the like may be utilized to remove excess sorbent from the coated surface and ensure a substantially even and suitably thin coating of sorbent on the substrate surface. The substrate may be replaced with a rod, tray, board, or another substrate that allows for a thin application of calcium sorbent. In some embodiments, the calcium sorbent may be deposited so that it has sufficient structural integrity to hang, stand, or rest on itself without the aid of another substrate or material. Multiple such substrates may be combined into a system to maximize its performance and minimize waste or loss of sorbent material.

[0058] After coating the sorbent onto one or more substrates, the coated substrate(s) may be moved to a storage unit or facility. The calcium sorbent-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 sorbent, as described above. This time may be referred to as the reaction or carbonation period. In some embodiments, the reaction period may range from as little as a few hours to as long as several months, or longer as needed. During the reaction period, the sorbent 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 sorbent and the water liberated from the reaction of calcium hydroxide with carbon dioxide to produce calcium carbonate and water. The sorbent layer will exhibit an initial weight loss during evaporation of the water used to form the substrate mixture, followed by a weight gain due to carbonation.

[0059] The disclosed systems and methods advantageously provide for the storage and transportation of sorbent-coated substrates during the carbonation period in a manner that achieves particularly desirable results. One or more substrates having calcium sorbent applied thereto may be arranged vertically, attached to a conveyor system, suspended from above, supported by other substrates, or held by the sides or bottom of the substrate. This use of vertical space minimizes land area usage without significant additional infrastructure and allows for drying on two or more sides, such as with a conveyor system. In some embodiments, the conveyor system may be adapted or configured to move the substrates through the storage unit for at least a portion or the entire 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 substrates may also be used, in addition to or instead of vertically suspended storage, either within or outside the conveyor system during and after the initial drying process.

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

[0061] The storage unit or facility may include a suitable cover adapted or configured to protect the calcium sorbent from weather (e.g., rain) that may interfere with the carbonation process. The storage unit or facility may or may not be airtight, depending on the local climate. The temperature, relative humidity, and airflow of the storage space may be controlled to optimize carbonation, or they may be left to fluctuate with ambient conditions. Accordingly, the storage unit or facility may include suitable climate control elements, air intakes, 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 air circulation within the storage unit or facility and ensure that the carbon dioxide concentration in the air near the calcium sorbent does not fall below a range that may reduce process efficiency (e.g., −5%, −10%, −15%, or −20% of the average ambient air CO2 content of the air entering the facility). As another example, the storage unit or facility may include one or more heaters and / or one or more coolers configured or adapted to regulate the temperature within a desired range to improve process efficiency. As yet another example, the storage unit or facility may include one or more humidity regulators that may be 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., greater than 40% RH, greater than 50% RH, or greater than 60% RH, e.g., a range of about 45% RH to about 90% RH, about 45% RH to about 80% RH, or about 50% RH to about 75% RH, etc.). Additionally, excess carbon dioxide (or other gases) beyond that present in the ambient air may be supplied to the storage unit in some embodiments to accelerate carbonation. In some embodiments, the storage unit or facility may incorporate natural topographical features, such as canyons, waterways, cliffs, or caves, to tailor airflow, air temperature, and / or air humidity to better suit process performance.

[0062] After the calcium sorbent has achieved sufficient carbonation within the desired range, the recovered carbon dioxide can be further processed for storage. In some embodiments, the carbonated sorbent 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 sorbent, or the substrate may be suitable for processing through a calciner with the carbonated sorbent. Thus, the substrate may be reusable or disposable. If removal is utilized, removing at least a portion of the carbonated form of the calcium sorbent from the one or more substrates may include applying a force to the one or more substrates sufficient to fracture the coating layer of the calcium sorbent material and detach the coating layer of the calcium sorbent material from the one or more substrates. The fracture may refer to breaking into multiple pieces to facilitate processing, and the fracture of the coating layer may improve the ability to easily detach the coating layer from the substrate.

[0063] A flexible substrate may be utilized, such that bending / flexing the substrate may be sufficient to remove the substantially brittle carbonated sorbent. Accordingly, applying a force to the substrate sufficient to break and dislodge the coating layer may include any force that will bend and / or flex the substrate. Alternatively or additionally, forces that may be applied to the substrate may include shaking, scraping, spraying, vibration, rolling, squeeze rolling, impact impulse, electrostatic impulse, electromagnetic impulse, magnetic, and / or various other methods for removing the carbonated sorbent from the substrate material. Mechanical force may be desirable in some embodiments because various forms of mechanical force can be applied in a cost-effective manner. In other embodiments, sonic or impact force / impulse may be more easily applied. In some embodiments, removal of the sorbent may be enhanced by various compositional and / or surface treatments of the substrate. Following removal, the sorbent material may be given additional time to carbonate, given the newly exposed additional surface area, or the sorbent material may be processed substantially immediately.

[0064] The carbonated sorbent may be regenerated for reuse by passing it through a calciner in substantially the same manner as described above to prepare the original calcium sorbent material. After carbonation, the sorbent material, originally of a first chemical composition (e.g., as calcium hydroxide and / or calcium oxide), has been converted to a different chemical composition—i.e., calcium carbonate. The calcium carbonate may be processed through a calciner with carbon recovery. By reheating the calcium carbonate to temperatures above about 800°C, carbon dioxide is released, which is then recovered for sequestration and utilization. The recovered carbon dioxide is substantially or entirely carbon dioxide removed from ambient air. Additionally, calcium oxide is re-formed, which can again be provided as input to the calcium sorbent, reducing the need for additional limestone input.

[0065] This recalcination (or regeneration) portion of the process is similar to calcium looping. Unlike calcium looping, carbonation occurs through prolonged exposure to air and does not require a carbonator. The behavior of calcium during looping is well understood, and calcium oxide continues to chemisorb carbon dioxide during looping from calcium oxide to calcium carbonate and back to calcium oxide, but it is also known to lose its reactivity after several loops. For example, carbonation conversion may drop below 50% after only five looping cycles in a sequential calciner and carbonator. However, the disclosed system and method can mitigate such sorbent deactivation. Specifically, by at least partially slaked calcium oxide, water can promote the reaction between calcium oxide and carbon dioxide. Furthermore, the elimination of a carbonation reactor (typically operating at approximately 650°C) reduces wear and sintering problems. Furthermore, the residence time of the reaction between calcium hydroxide and carbon dioxide in the present system and method is significantly longer than the residence time of calcium oxide and carbon dioxide in a typical high-temperature carbonator. The cycle between carbonation and calcination can be from a few to hundreds of cycles, reducing the cost of limestone.

[0066] Deactivation of the calcium sorbent may occur, resulting in a reduction in efficiency to a specified level, and such deactivated sorbent may be disposed of in the form of one or more of CaO, Ca(OH)2, and CaCO3. The waste may 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 may be processed for material disposal. To the extent that CaCO3 is disposed of, it also serves as a mineral sequestration of carbon dioxide from the air, retaining it in the form of stone for thousands of years. Therefore, 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 sorbent may be immediately stored in the ground as the stable, non-toxic mineral CaCO3 formed during carbonation, bypassing the recalcination step after the initial carbonation. Because of the passive, low-input system 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] An exemplary embodiment of an overall system and method according to the present disclosure is provided in Figure 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., "dip tank") containing liquid calcium sorbent (e.g., in the form of calcium hydroxide) as the substrates are transported on a vertical conveyor. The substrates are suspended from the ceiling, and the conveyor transports them during carbonation until the carbonated sorbent is removed for further processing.

[0068] In the embodiment of FIG. 3 , the coating system 32 may include a dipping unit 35 for dipping the substrates 10 (e.g., hanging sheets) into a reservoir 30 (e.g., a "dipping tank"). The dipping unit 35 may include a portion of a vertical conveyor 50 angled to allow the substrates 10 to move downward into the reservoir 30 and then upward out of the reservoir. In addition to the reservoir 30, the coating system 32 may include additional components, such as a sprayer or dripping element, for applying the calcium adsorbent by methods other than dipping. In other embodiments, the dipping unit 35 may include additional components configured to individually lower individual substrates 10 into the reservoir 30. The substrates 10 exiting the dipping unit are in the form of coated substrates 52 (e.g., lime-coated sheets) having a layer of calcium adsorbent coated thereon. The coated substrates 52 are then placed in a storage unit 54. The storage unit 54 can consist essentially of a conveyor 50 in a shielded location between the soaking unit 35 and the collection unit 60. Alternatively, the storage unit 54 can be a building or room(s) within a building where the coated substrate 52 can undergo carbonation, in which ambient CO from the air reacts with the calcium sorbent and water evaporates from the calcium sorbent. After sufficient carbonation has occurred, the coated substrate 52 moves to a collection unit 60 (e.g., a descaling unit), where the carbonated calcium sorbent is removed from the substrate 10. The substrate 10 is released for reuse in the soaking unit 35, and the carbonated calcium sorbent (which may include CaCO and unreacted Ca(OH)) moves along a horizontal conveyor 65, during which time the partially carbonized calcium sorbent undergoes further carbonation, resulting in the carbonatedization of at least a portion of the unreacted calcium hydroxide. All or a portion of the carbonated calcium sorbent can be removed for disposal, such that the carbon dioxide removed from the air is sequestered in the form of calcium carbonate.All or a portion of the carbonated calcium sorbent can likewise be sent to calciner 70 where carbon dioxide can be liberated to reform calcium oxide, which can be removed in solids separator 75 to provide calcium oxide to lime slaker 80 to form calcium hydroxide slurry for input to reservoir 30 for use as a calcium sorbent.

[0069] While Figure 3 illustrates a fully implementable system and method for carbon dioxide capture, it is understood that only some of the illustrated components and steps may be implemented to perform different embodiments of the present disclosure. Thus, Figure 3 is provided so that those skilled in the art having access to this disclosure may readily recognize various combinations of the illustrated components and steps to achieve different embodiments. For example, in one or more embodiments, the method and system illustrated in Figure 3 may be implemented under one or more of the following conditions: The calciner 70 and solids separator 75 may be absent from the system. Instead, calcium oxide may be input directly to the lime slaker 80. In such an embodiment, lime removed from the substrate in the collection unit 60 may be transported for sequestration and / or delivery to a third party for recalcination with carbon recovery. Similarly, the lime slaker 80 may be absent, and calcium hydroxide may be sourced directly for input to the reservoir 30. The reservoir 30 may be replaced by any further component suitable for applying a calcium adsorbent to the substrate 10. "Sheet" may be replaced with any other suitable substrate material as described elsewhere herein. The lime coated sheets 52 may be circulated through a vertical conveyor for carbonation without intermediate treatment in a collection unit 60. The CaCO3 and Ca(OH)2 removed from the collection unit 60 may be sent directly to recalcination without undergoing further carbonation. The process may be substantially continuous in that application of the calcium sorbent, treatment of the coated substrate for carbonation, and removal of the carbonated sorbent in collection unit 60 may occur without interruption other than required maintenance or scheduled downtime. For example, the system may be large enough so that a single substrate may be cycled only once from exiting coating system 32 to re-entering the coating system, taking a time sufficient for the desired level of carbonation to occur, which may be on the order of hours to days. Thus, the system may 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 manner, coated substrates 52 may be unloaded at the stop station for carbonation to occur while other substrates are processed through the system. The stop station may be intermittently emptied, fully or partially, of coated substrates already undergoing carbonation and loaded with newly coated substrates. The process may operate in a batch mode where the substrate is coated as a batch, stored for carbonation as a batch, and then processed for descaling as a batch. The process may operate through multiple coating and carbonation steps without removing the coating layer from the substrate. For example, a substrate may be coated with a relatively thin layer of calcium-adsorbing material, treated to cause carbonation, and recoated such that additional relatively thin layers of calcium-adsorbing material are added on top of the carbonized layer, etc., until a relatively thick coating of multiple separately carbonized layers is present on the substrate. The coated substrate may then have the coating layer removed.

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

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

[0072] The present system and method can achieve net carbon removal from the atmosphere because the net recovery of CO from the air by the calcium sorbent exceeds any CO emissions from the process. The net carbon flow in an exemplary embodiment of the present disclosure is shown in the table below for a system with a 90% carbon recovery calciner and an 85% calcium sorbent carbonation rate. [Table 1]

[0073] Experimental data demonstrated the ability to achieve >70% carbonation in approximately three days with 0.3 kg of calcium sorbent per square meter of exposed area. This rate and conversion rate would result in a net direct air capture of approximately 100,000 metric tons (MT) using less than 25 acres of land. This land use intensity is far below that required to enable billions of tons of CO2 to be captured from the air, without impacting other land uses or depleting suitable sites nearby limestone and CO2 storage.

[0074] Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the accompanying drawings. It is to be understood, therefore, that the invention is not to be limited to the specific embodiments disclosed, and that modifications 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" herein is understood to mean that a value described as "about" or "substantially" a particular value may vary by an industry-accepted tolerance level for the specified value. Where an industry-accepted tolerance range is not available, it is understood that such terms may indicate that the tolerance may vary by ±3%, ±2%, or ±1% from the specifically described value. Similarly, in some embodiments, the described value may be as precise as necessary, and variations above or below the described value may be expressly excluded.

Claims

1. 1. A method for direct air capture (DAC) of carbon dioxide, comprising: preparing a layer of calcium-adsorbing material on a substrate at a density of less than 10 kilograms per square meter; contacting the substrate having the layer of the calcium adsorbing material with air containing carbon dioxide within a storage unit or facility such that at least a portion of the carbon dioxide from the air converts at least a portion of the calcium adsorbent to a carbonated form; controlling carbonation conditions within the storage unit or facility while the substrate having the layer of calcium adsorbing material is in contact with air containing carbon dioxide; A method comprising:

2. 10. The method of claim 1, further comprising removing at least a portion of the calcium converted to carbonated form from the substrate by applying a force to the substrate sufficient to break at least a portion of the calcium converted to carbonated form and dislodge it from the substrate.

3. 3. The method of claim 2, further comprising processing the calcium converted to a carbonated form so that the carbon dioxide recovered from the air is ready for sequestration or other use.

4. 10. The method of claim 1, wherein the carbonation condition is the circulation of air near the calcium adsorbing material.

5. 2. The method of claim 1, wherein the carbonation condition is the carbon dioxide concentration in the air adjacent to the calcium adsorbing material.

6. 6. The method of claim 5, wherein the carbon dioxide concentration in the air adjacent the calcium adsorbent material is controlled to be no more than 5% lower than the carbon dioxide concentration of the average ambient air entering the storage unit facility.

7. 2. The method of claim 1, wherein the carbonation condition is the temperature of the air adjacent the calcium adsorbing material.

8. 10. The method of claim 1, wherein the carbonation condition is a percentage of relative humidity (RH%) within the storage unit or facility.

9. 9. The method of claim 8, wherein the % RH within the storage unit or facility is maintained at a value greater than about 40% RH.

10. 9. The method of claim 8, wherein the % RH within the storage unit or facility is maintained within a range of about 45 to about 90% RH.

11. 1. A method for direct air capture (DAC) of carbon dioxide, comprising: applying a calcium-adsorbing material onto a substrate to define a layer of said calcium-adsorbing material on said substrate at a density of about 0.1 kilograms per square meter to about 5 kilograms per square meter; contacting the substrate having the layer of calcium adsorbing material with air containing carbon dioxide within a storage unit or facility such that at least a portion of the carbon dioxide from the air converts at least a portion of the calcium adsorbent to calcium carbonate; controlling carbonation conditions within the storage unit or facility while the substrate having the layer of calcium adsorbing material is in contact with air containing carbon dioxide; A method comprising:

12. 12. The method of claim 11, further comprising removing at least a portion of the carbonated calcium from the substrate by applying a force to the substrate sufficient to break at least a portion of the carbonated calcium from the substrate.

13. 13. The method of claim 12, further comprising processing the carbonated calcium so that the carbon dioxide captured from the air is ready for sequestration or other use.

14. 12. The method of claim 11, wherein the carbonation condition is the circulation of air near the calcium adsorbing material.

15. 12. The method of claim 11, wherein the carbonation condition is the carbon dioxide concentration in the air adjacent to the calcium adsorbing material.

16. 16. The method of claim 15, wherein the carbon dioxide concentration in the air adjacent the calcium adsorbent material is controlled to be no more than 5% lower than the carbon dioxide concentration of the average ambient air entering the storage unit facility.

17. 12. The method of claim 11, wherein the carbonation condition is the temperature of the air in the vicinity of the calcium adsorbing material.

18. 12. The method of claim 11, wherein the carbonation condition is a percentage of relative humidity (RH%) within the storage unit or facility.

19. 20. The method of claim 18, wherein the % RH within the storage unit or facility is maintained at a value greater than about 40% RH.

20. 20. The method of claim 18, wherein the % RH within the storage unit or facility is maintained within a range of about 45 to about 90% RH.

21. 1. A method for direct air capture (DAC) of carbon dioxide, comprising: contacting a layer of calcium adsorbing material with air containing carbon dioxide within a storage unit or facility, such that at least a portion of the calcium adsorbing material reacts with carbon dioxide from the air to cause carbonation and conversion to carbonated calcium, wherein the layer of calcium adsorbing material is present on one or more substrates at a density of from about 0.1 kilograms per square meter to about 5 kilograms per square meter; controlling carbonation of the calcium sorbent material by controlling one or more properties of the carbon dioxide-containing air within the storage unit or facility; A method comprising:

22. 22. The method of claim 21, wherein the one or more properties of the carbon dioxide-containing air are circulation of the air near the calcium adsorbing material.

22. The method of claim 21, wherein the one or more properties of the carbon dioxide-containing air are the carbon dioxide concentration in the air adjacent the calcium adsorbing material.

23. 22. The method of claim 21, wherein the one or more properties of the carbon dioxide-containing air are the concentration of carbon dioxide in the air adjacent the calcium adsorbing material.

24. 24. The method of claim 23, wherein the concentration of carbon dioxide in the air adjacent the calcium adsorbent material is controlled to be no more than 5% lower than the carbon dioxide concentration of the average ambient air entering the storage unit facility.

25. 22. The method of claim 21, wherein the one or more properties of the carbon dioxide-containing air is the temperature of the air in the vicinity of the calcium adsorbing material.

26. 22. The method of claim 21, wherein the one or more properties of the carbon dioxide-containing air is a relative humidity percentage (RH%) of the air within the storage unit or facility.

27. 27. The method of claim 26, wherein the % RH within the storage unit or facility is maintained at a value greater than about 40% RH.

28. 27. The method of claim 26, wherein the % RH within the storage unit or facility is maintained within a range of about 45 to about 90% RH.

29. 22. The method of claim 21, further comprising removing at least a portion of the carbonated calcium from the substrate by applying a force to the substrate sufficient to break at least a portion of the carbonated calcium from the substrate.

30. 30. The method of claim 29, further comprising processing the carbonated calcium so that the carbon dioxide captured from the air is ready for sequestration or other use.

31. 1. A method for direct air capture of carbon dioxide, comprising: preparing a substantially continuous coating layer of a calcium-adsorbing 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 adsorbing material with air containing carbon dioxide and having a relative humidity (RH) of 40% RH or greater for a time sufficient to cause the calcium adsorbent 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 adsorbent 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 carbonated form of the calcium sorbent so that the carbon dioxide recovered from the air is ready for sequestration or other use; A method comprising:

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