Methods for mechanochemical carbon sequestration of solid feedstocks

Abstract

To provide an improved process for sequestering carbon dioxide in a solid feedstock. The present invention relates to a method for mechanochemically sequestrating or capturing carbon from CO2 in a solid feedstock, comprising contacting a CO2-rich gas with a solid feedstock in a particle size reduction device, such as a mill, at a first controlled moisture content of the solid feedstock, and subsequently increasing the moisture content of the solid feedstock and subjecting the solid feedstock to a second carbon sequestration step. The present invention further relates to an apparatus suitable for mechanochemically sequestrating carbon dioxide in a solid feedstock.

Description

[Technical Field]

[0001] The present invention relates to a method and uses thereof for mechanochemical sequestration or capture of carbon from CO2 in solid feedstocks. The present invention further relates to an apparatus suitable for mechanochemical sequestration of carbon dioxide in solid feedstocks. [Background technology]

[0002] Due to anthropogenic emissions, atmospheric carbon dioxide concentrations have increased by at least 30% compared to pre-industrial levels. Furthermore, future global carbon dioxide emissions are projected to increase from approximately 7.4 GcC (billion tonnes of carbon in the atmosphere) per year in 1997 to 26 GtC per year by 2100. Due to the adverse environmental impacts of increasing carbon dioxide emissions, environmental standards regarding the release of pollutants into the atmosphere are becoming stricter.

[0003] Controlling carbon dioxide emissions can be achieved through increased energy conversion efficiency, the use of low-carbon or carbon-free energy sources, and the capture and sequestration of carbon dioxide emissions. Carbon dioxide sequestration remains the preferred method for addressing carbon dioxide emissions to date.

[0004] Mineral carbonation is a sequestration process in which minerals such as olivine and serpentine, or calcium-rich minerals, react with carbon dioxide to form geologically stable mineral carbonates. These processes mimic the natural weathering of rocks.

[0005] The mineral carbonation approach has several inherent advantages, including the natural abundance of raw materials and the ability to permanently and safely store CO2 in solid form. The primary drawback of mineral carbonation is reaction rate, as these naturally occurring processes occur slowly over geological time frames rather than industrial time scales. Previous studies have suspended minerals in aqueous media, as such systems have shown faster reaction rates than direct carbonation. The aqueous mineral carbonation process involves the leaching of magnesium, calcium, or another suitable metal or combination of metals, followed by reaction with dissolved bicarbonate. A drawback of the aqueous method is the need to use the resulting aqueous product or slurry on-site, avoiding expensive and energy-inefficient transportation or evaporation.

[0006] Solid-state sequestration has been achieved by crushing magnesium-rich minerals to fine particle sizes to promote surface reactions known to control most mineral dissolution reactions. Such processes are hindered by extensive comminution of raw materials, high partial pressures, and long reaction times, all of which make the process energy intensive. Other studies have also reported that preheating serpentine minerals to approximately 650 °C significantly increases their carbonation reactivity, likely due to dehydroxylation, increased surface area, and destabilization of the crystalline structure. However, this pretreatment is extremely energy intensive, requiring approximately 200 kWh per ton of serpentine.

[0007] Therefore, there remains a need to develop an efficient, low-temperature, energy-efficient process that can capture carbon dioxide into CO2-related functional groups across a wide variety of feedstocks and that is carried out in an economically viable timeframe.

[0008] US Patent Application Publication No. 2008277319(A1) discloses a method for sequestrating and converting carbon dioxide produced by anthropogenic sources, which involves size-selecting mineral particles and mixing them with water to form a slurry, which is then reacted with carbon dioxide.

[0009] US Patent No. 6,543,709 (B2) discloses a gravity flow air classifier mill that includes a particle return manifold for returning oversized particles to the mill housing.

[0010] WO2021087606A1 discloses a ball milling method for mechanochemical CO2 sequestration in mineral raw materials.

[0011] JP 2022128429 discloses processing waste concrete sludge from centrifugal casting into a powder that can efficiently immobilize carbon dioxide when exposed to air or exhaust gases. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] US Patent Application Publication No. 2008 / 277319 [Patent Document 2] U.S. Patent No. 6,543,709 [Patent Document 3] International Publication No. 2021 / 087606 [Patent Document 4] Japanese Patent Application Publication No. 2022-128429 Summary of the Invention [Problem to be solved by the invention]

[0013] It is an object of the present invention to provide an improved process for sequestrating carbon dioxide in a solid feedstock.

[0014] It is a further object of the present invention to provide a process for sequestrating carbon dioxide into a solid feedstock that is energy efficient and preferably can be operated as a continuous process.

[0015] It is a further object of the present invention to provide an apparatus suitable for the sequestration of carbon dioxide in solid feedstocks.

[0016] The inventors have discovered that a mechanochemical sequestration method with at least two carbon sequestration steps, when combined with solid-phase moisture content control and applied to solid feedstocks, can sequester CO2 very efficiently for a wide variety of feedstocks, taking into account factors such as energy consumption, carbon sequestration capacity, and reactor throughput capacity. This method can be optimally combined with continuous particle size selection methods as described herein. In particular, the inventors have discovered that an efficient two-step mechanochemical CO2 sequestration method with moisture control as described herein can be obtained that provides consistent results, output, and CO2 sequestration performance, thereby significantly improving process reliability and efficiency. Furthermore, the present method has been found to be easily integrated into existing flue gas streams, such as fossil fuel combustion flue gas streams or cement kiln exhaust gas, and can capture point source emissions. [Means for solving the problem]

[0017] Accordingly, in a first aspect, the present invention provides a continuous method for carbon sequestration comprising: (i) providing a solid feedstock having a first moisture content; (ii) providing a first carbon-rich gas comprising at least 1% CO by volume and a second carbon-rich gas comprising at least 1% CO by volume; (iii) subjecting the solid feedstock of step (i) to a size-reduction operation in a size-reduction device in the presence of the first carbon-rich gas of step (ii) to obtain a first CO2-enriched material; and recovering the first CO2-enriched material; (iv) increasing the moisture content of the first CO2-enriched material to a second moisture content higher than the first moisture content to obtain a moistened CO2-enriched material; (v) subjecting the wetted CO2-enriched material to further CO2-enrichment processing outside the particle size reduction device by contacting the wetted CO2-enriched material with a second carbon-rich gas containing at least 1% CO2 by volume to obtain a second CO2-enriched material, and recovering the second CO2-enriched material.

[0018] The method of the present invention can be applied to a variety of solid feedstocks, including, but not limited to, feedstocks comprising fly ash, clay, silicate minerals, crushed glass, steel slag, natural pozzolans, volcanic rock, biochar, and mine waste, as described in more detail elsewhere herein.

[0019] The inventors have found that the large amount of gas (typically flue gas) used for CO2 enrichment tends to shift the moisture content of the solid feedstock toward levels that are undesirable for either particle size reduction in step (iii) or further CO2 enrichment in step (v), even if controlled prior to entering the process. Too high a moisture content in the particle size reduction step can result in agglomeration, clogging / blockage, inefficient and inconsistent particle size reduction, etc., while too low a moisture content in step (v) can reduce carbon sequestration efficiency. Preferably, the moistened CO2-enriched material is maintained at a moisture content equal to or greater than the second moisture content throughout the further CO2 enrichment process in step (v), and preferably the solid feedstock is maintained at a moisture content equal to or less than the first moisture content throughout the particle size reduction operation in step (iii). The first moisture content is preferably less than 8 wt. % (based on the total weight of the solid feedstock), preferably less than 5 wt. % (based on the total weight of the solid feedstock), and the second moisture content is preferably greater than 10 wt. % (based on the total weight of the wetted CO2-enriched material). The inventors have surprisingly found that the second moisture content is preferably less than 35 wt. % (based on the total weight of the wetted CO2-enriched material), preferably less than 27 wt. % (based on the total weight of the wetted CO2-enriched material), and most preferably less than 20 wt. % (based on the total weight of the wetted CO2-enriched material). This is because, above these levels, a decrease in efficiency is observed, particularly when the CO2-enrichment in step (v) is a process in which no further particle size reduction occurs, as described elsewhere herein. Because the material has been ground or milled in step (iii), for example, to a particle size as described elsewhere herein, a high moisture content, such as the 35 wt. % mentioned above, can be accommodated without forming a slurry (making the material easier to handle). Without wishing to be bound by any theory, the inventors believe that the decrease in efficiency observed when the water content of the solid in step (v) is too high is because too much of the surface of the material is covered with water, creating a diffusion boundary layer for carbonation.

[0020] The temperature of the first carbon-rich gas may be in the range of 20 to 300° C. The temperature of the second carbon-rich gas is preferably less than 120° C., preferably less than 100° C. In some embodiments, the temperature of the first carbon-rich gas is higher than the temperature of the second carbon-rich gas.

[0021] The process of the present invention can be carried out using a gas stream containing a dilute carbon dioxide stream, such as a point source emission from combustion (especially the combustion of fossil fuels) or cement kiln exhaust gas. Alternatively, the process can be carried out using a highly concentrated CO2 stream, such as a gas stream containing at least 80% CO2 by volume, preferably at least 95% CO2 by volume.

[0022] In a highly preferred embodiment of the present invention, the particle size reduction operation of step (iii) is carried out by subjecting the solid feedstock of step (i) to milling, preferably roller milling, such as roller milling, especially in a vertical roller mill, in the presence of a first carbon-rich gas.

[0023] In a highly preferred embodiment of the present invention, step (iii) is carried out by an integrated air classifier or a mill with an air classifier located downstream of the mill, preferably a vertical roller mill. In a preferred embodiment of the present invention, the gas flow through the air classifier comprises, and preferably consists of, the first carbon-rich gas prepared in step (ii). In some embodiments, the air classifier is located downstream of the mill, and the gas flow through the air classifier comprises, and preferably consists of, the first carbon-rich gas of step (ii). In all embodiments, gas typically flows from the mill grinding zone to the air classifier. Those skilled in the art will understand that the term "air classifying mill" is used to refer to equipment commonly known as air classifying mills, and that it is the first carbon-rich gas, not air, that flows through the mill.

[0024] The carbon dioxide sequestration process of the present invention has been found to be energy efficient. In some embodiments, the method is provided wherein the total power consumption represented by steps (iii)-(v) is less than 200 Wh, preferably less than 175 Wh, and more preferably less than 150 Wh per kg of second CO2-enriched material recovered in step (v).

[0025] In some embodiments of the invention, the second CO2-enriched material recovered in step (v) exhibits at least one, preferably two, and most preferably three of the following properties: D10 in the range of 0.005-3 μm; D50 in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 40 μm, more preferably in the range of 1 to 40 μm, and most preferably in the range of 5 to 40 μm; D90 in the range of 0.5-300 μm; 0.5~10,000m 2 BET surface area in the range of / g.

[0026] In another aspect, the present invention provides an apparatus for continuous sequestration of carbon dioxide, comprising a particle size reduction device having a housing, the housing comprising a solid feed inlet for introducing a solid feed into the particle size reduction device and a gas inlet for introducing a gas stream into the particle size reduction device; a particle size sorting means, preferably disposed within the housing and in fluid communication with the particle size reduction device, including an outlet for removing material from the particle size reduction device, configured to separate the material from the particle size reduction device into at least a first portion and a second portion, the first portion having a different average particle size than the second portion, and configured to supply the first portion to the outlet and return the second portion to the particle size reduction device; and wherein the gas supply inlet is fluidly connected to a flue gas outlet of a combustion plant or cement kiln, and the outlet for removing material from the particle size reduction device is connected to a wetting device configured to increase the moisture content of the solid material, preferably by spraying an aqueous composition, preferably water, onto the solid material. The wetting device may be configured to increase the moisture content of the solid material removed through the particle size reduction device outlet while the solid material is entrained in the gas stream or after it has been separated from the gas stream.

[0027] The particle size selector is preferably an air classifier. The particle size reducer is preferably a mill, more preferably a vertical roller mill. The particle size reducer is configured to reduce the particle size of the solid feedstock. The zone of the particle size reducer where particle size reduction occurs is in fluid communication with a gas inlet. The solid feedstock inlet and the gas inlet may be the same (e.g., to allow for the use of a gas stream carrying the solid feedstock). [Brief explanation of the drawings]

[0028] [Figure 1] Figure 1 shows a process flow diagram of the method of the present invention, in which step (iii) of the method is carried out by milling in an air classifying mill, and the further CO2-enriched processing step (v) of the method comprises storing the CO2-enriched material in a vessel under continuous exhaust gas flow. Point source emissions such as flue gas or cement kiln exhaust gas are cooled by heat exchange in two steps and provided to an air classifying mill (operating on this cooled exhaust gas) after the first step, and provided to processing in step (v) after the second cooling step. [Figure 2]2 shows a process flow diagram of the method of the present invention, in which step (iii) of the method is carried out by milling in an air classifying mill, and the further CO2-enriched processing step (v) of the method comprises storing the CO2-enriched material in a vessel under a continuous flue gas flow. Point source emissions, such as flue gas or cement kiln exhaust gas, are divided into a first portion and a second portion. The first portion is cooled by mixing with air and provided to the air classifying mill (operating against a combined flow of air and flue gas), while the second portion is cooled by heat exchange and provided to the processing of step (v). DETAILED DESCRIPTION OF THE INVENTION

[0029] As used herein, the word "comprise" and variations thereof, such as "comprises" and "comprising," are to be interpreted in an open and inclusive sense, meaning that the described embodiment includes the recited features, but does not exclude the presence of other features unless doing so would render the embodiment inoperable.

[0030] As used herein, phrases such as "one embodiment," "particular embodiment," "embodiment," and the like should be interpreted to mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the appearances of such phrases in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. For example, particular features of the disclosure that are described herein in the context of separate embodiments are also expressly contemplated in combination in a single embodiment.

[0031] As used herein, the singular forms "a," "an," and "the" should be construed to include plural referents unless the content clearly dictates otherwise. Also, it should be noted that the term "or" is generally used in its broadest sense, i.e., meaning "and / or," unless the content clearly dictates otherwise.

[0032] The term "CO2-enriched material" is used herein to refer to the solid feedstock after contact with CO2 during the particle size reduction operation in step (iii) or the further CO2-enrichment processing in step (v). Depending on the feedstock, the physical and / or chemical mechanisms underlying CO2 sequestration may differ. For example, if the feedstock contains minerals, CO2 is typically converted to carbonates (also referred to as carbonation). If the feedstock contains elemental carbon (e.g., graphite), CO2 is typically attached to the carbon in the form of various functional groups such as carboxylate, epoxide, carbonyl, etc.

[0033] According to the present invention, the BET surface area referred to herein is measured at a temperature of 77 K using a sample mass of 0.1 to 0.5 g. The BET surface area referred to herein is measured using nitrogen. A preferred analytical method for measuring the BET surface area involves heating the sample to 400°C and performing a desorption cycle prior to surface area analysis. A suitable and therefore preferred analytical instrument for measuring the BET surface area is a Micromeritics Gemini VII 2390 Surface Analyzer, preferably equipped with a Micromeritics FlowPrep 060 flow gas degassing unit.

[0034] As used herein, TGA refers to thermogravimetric analysis, a technique known to those skilled in the art. In the context of the present invention, a preferred TGA setup for measuring the CO2 content of raw and carbonated materials is a Setaram TAG 16 TGA / DSC dual chamber balance using 0.1-2 mg of sample. In accordance with the present invention, TGA is performed under an inert atmosphere, such as nitrogen or argon.

[0035] According to the present invention, unless otherwise specified, particle size distribution characteristics such as D10, D50, and D90, as well as specific surface area (unless explicitly stated to be BET surface area) referred to herein are measured using a laser light scattering particle size analyzer utilizing Mie's light scattering theory, such as a Brookhaven laser particle sizer, model Microbrook 2000 LD, or another instrument of equal or greater sensitivity, and the data are reported using the volume-equivalent sphere model. As known to those skilled in the art, D50 is the mass median diameter, i.e., the diameter at which 50% of the mass of the sample is made up of smaller particles. Similarly, D10 and D90 represent the diameter at which 10% or 90% of the mass of the sample is made up of smaller particles.

[0036] The total carbon (TC) content referred to herein is preferably measured according to the method described in Soil Sampling and Methods of Analysis, 2nd Ed., CRC Press (2008), p. 244, which is further incorporated herein by reference. The total carbon (TC) content is always expressed herein as weight percent based on the total weight of the composition being measured. For example, when referring to the total carbon content of a solid feedstock, it is based on the total weight of the solid feedstock, and when referring to the total carbon content of a CO2-enriched material, it is based on the total weight of the CO2-enriched material.

[0037] The moisture content of the solid material referred to herein (e.g., the solid feedstock provided in step (i) of the present method and the moistened CO2-enriched material obtained in step (iv)) refers to the moisture content measured by oven-drying the material at 150°C to constant weight and comparing the initial weight to the dry weight.

[0038] For purposes of this disclosure, the ideal gas law is assumed, whereby mole percent of a gas is considered to be equal to volume percent.

[0039] Process Description In a first aspect, the present invention provides a method for carbon sequestration, comprising: (i) providing a solid feedstock having a first moisture content; (ii) providing a first carbon-rich gas comprising at least 1% CO by volume and a second carbon-rich gas comprising at least 1% CO by volume; (iii) subjecting the solid feedstock of step (i) to a particle size reduction operation in a particle size reduction device in the presence of the first carbon-rich gas of step (ii) to obtain a first CO2-enriched material; and recovering the first CO2-enriched material; (iv) increasing the moisture content of the first CO2-enriched material to a second moisture content higher than the first moisture content to obtain a moistened CO2-enriched material; (v) subjecting the wetted CO2-enriched material to further CO2-enrichment processing outside the particle size reduction device by contacting the wetted CO2-enriched material with a second carbon-rich gas containing at least 1% CO2 by volume to obtain a second CO2-enriched material, and recovering the second CO2-enriched material.

[0040] In some embodiments of the present invention, a method is provided in which at least step (iii), preferably steps (iii) through (v), are carried out in a continuous mode. The term "continuous" is to be interpreted as a process in which the production of the first CO2-enriched material is carried out continuously by continuous processing of the particle size reduction operation. Thus, in a continuous process, the first CO2-enriched material is continuously output over a given period of time. Preferably, steps (iv) and (v) are also carried out continuously, resulting in the process continuously outputting the second CO2-enriched material over a given period of time. This is in contrast to a batch process in which there is no continuous output of CO2-enriched material; instead, individual portions ("batches") are processed for a period of time before the entire batch is completely processed at once. Even when at least step (iii), preferably steps (iii) through (v), are carried out in a continuous mode, some other steps may still be carried out in a batch mode. For example, the solid feedstock of step (i) may be stored in a silo and continuously fed to a particle size reduction device, where it is continuously subjected to steps (iii) through (v).

[0041] Alternatively, individual portions of the solid feedstock may be loaded into the particle size reduction device and then continuously subjected to steps (iii) to (v), resulting in continuous recovery of the second CO2-enriched material over a given period until the individual portions of the feedstock in the particle size reduction device are consumed. A hybrid of these two configurations is also possible, in which individual portions of the solid feedstock are continuously fed to the particle size reduction device (according to a regular or irregular pattern). In all of these described cases, step (iii) is considered continuous because the output of the first CO2-enriched material is continuous over a given period. When only step (iii) is performed in a continuous mode, the continuously produced first CO2-enriched material may be collected in a buffer reservoir, such as a buffer silo, until it is subjected to steps (iv) and (v) in a batchwise manner. Alternatively, steps (iv) and (v) may also be performed continuously. In the latter case, a buffer reservoir, such as a buffer silo, may still be used to absorb the difference in processing capacity between steps (iii) and (v). In some embodiments of the invention, the method is operated such that the first CO2-enriched material is continuously collected for at least 1 minute, preferably at least 10 minutes, and more preferably at least 30 minutes. In preferred embodiments of the invention, the method is operated such that the first CO2-enriched material is continuously collected for at least 1 hour, preferably at least 4 hours, and more preferably at least 8 hours. In more preferred embodiments of the invention, the method is operated such that the first and second CO2-enriched materials are continuously collected for at least 1 minute, preferably at least 10 minutes, and more preferably at least 30 minutes. In more preferred embodiments of the invention, the method is operated such that the first and second CO2-enriched materials are continuously collected for at least 1 hour, preferably at least 4 hours, and more preferably at least 8 hours.

[0042] As will be understood by those skilled in the art, step (iii) is carried out in the presence of the first carbon-rich gas provided in step (ii), which means that the solid feedstock of step (i) is contacted with the first carbon-rich gas provided in step (ii) during the particle size reduction operation of step (iii), which may result in sequestration of CO2 into the solid feedstock, for example by carbonation, oxidation, etc.

[0043] As with any chemical process, appropriate reaction parameters such as residence time, temperature, pressure, etc. within the particle size reduction device will depend largely on the desired degree of CO sequestration, desired surface area, etc., and can be routinely determined by periodically sampling the material and monitoring the reaction progress, for example, by BET analysis, particle size analysis, and total carbon measurements as described herein.

[0044] The first and second carbon-rich gases in step (ii) of the process described herein can be any gas stream containing a significant amount of CO. Those skilled in the art will appreciate that the composition of the gas may change as the reaction progresses, but continuous replenishment can be provided, for example, by a continuous flow of fresh gas through steps (iii) and (v) of the process. This, coupled with a continuous supply of solid feedstock, allows the process to be operated in a continuous mode. Given that CO sequestration occurs throughout the process, the gas following each of steps (iii) and (v) of the process will have a reduced CO concentration compared to the gas entering steps (iii) and (v), respectively. The phrase "in the presence of a first carbon-rich gas" in step (iii) should be interpreted to mean that the atmosphere within the particle size reduction apparatus consists essentially of the first carbon-rich gas provided in step (ii) throughout the operation of the process.

[0045] In an embodiment of the method described herein, the first and second carbon-rich gases provided in step (ii) comprise flue gas, particularly flue gas from the combustion of fossil fuels, wood pellets, biomass, or municipal waste. The fossil fuel combustion can be from the combustion of coal, petroleum coke, oil, natural gas, shale oil, bitumen (asphalt), tar sands oil, or heavy oil, or any combination thereof. The flue gas may optionally have been treated to reduce its water content, SO2 content, and / or NOx content. In an embodiment of the method described herein, the first and second carbon-rich gases provided in step (ii) comprise cement kiln flue gas. Typically, the cement kiln flue gas comprises fossil fuel combustion flue gas because cement kilns are typically heated by the combustion of fossil fuels and is typically further enriched with CO from the calcination of limestone that occurs within the cement kiln for the purpose of producing cement. The cement kiln flue gas may optionally have been treated to reduce its water content, SO content, and / or NO content.

[0046] The CO2 concentration in the first and second carbon-rich gases prepared in step (ii) is preferably at least 2% by volume, more preferably at least 3% by volume. Typical CO2 concentrations in flue gas and cement kiln exhaust gas range from 1 to 20% by volume, e.g., 2 to 15% by volume, 2 to 5% by volume, or 5 to 15% by volume. Consequently, the first and second carbon-rich gases prepared in step (ii) preferably have a CO2 concentration in the range of 1 to 20% by volume, e.g., 2 to 15% by volume, 2 to 5% by volume, or 5 to 15% by volume. In alternative embodiments of the present invention, the first and second carbon-rich gases prepared in step (ii) contain at least 80% by volume of CO2, preferably at least 95% by volume. In some preferred embodiments of the present invention, the CO2 content of the first carbon-rich gas is lower than the CO2 content of the second carbon-rich gas. This can be achieved, for example, by using a flue gas as described herein as the first carbon-rich gas and a high-concentration gas containing at least 30% CO by volume, for example at least 80% CO by volume, as the second carbon-rich gas. This can also be achieved by the embodiments described in the following sections, which are preferred as they result in significant energy savings and optimize CO utilization. In any embodiment of the present invention, the first and second carbon-rich gases are not in a supercritical state.

[0047] In a preferred embodiment of the present invention, step (ii) comprises (ii)a providing a gas stream comprising at least 1% by volume of CO2 and having a temperature above 120°C, the gas stream being preferably flue gas or cement kiln exhaust gas; (ii)b dividing the gas stream of step (i)a into a first portion and a second portion; (ii)c cooling the first portion, which includes mixing the first portion with air, thereby obtaining a first carbon-rich gas; (ii)d cooling the second portion, preferably involving heat exchange, thereby obtaining a second carbon-rich gas; the CO2 content of the first carbon-rich gas is lower than the CO2 content of the second carbon-rich gas; the temperature of the second carbon-rich gas is preferably less than 100°C; Steps (ii)c and (ii)d each optionally include adjusting the humidity of the gas.

[0048] This embodiment results in significant energy savings and optimizes CO2 utilization, especially when combined with air classifier milling, which requires high gas flow rates, as described elsewhere herein. In this way, the amount of cooling energy expended on the air classifier gas stream is limited, since cooling is provided at least in part by mixing with air, while the gas stream of step (v) avoids dilution with air, thereby maintaining its CO2 concentration and improving carbonation efficiency. Another advantage is that by mixing the first substream with air to provide the first carbon-rich gas, a lower flue gas flow rate is required to operate the same particle size reduction device (e.g., an air classifier mill), thereby reducing the space and cost required to construct piping from an existing flue gas source to the particle size reduction device and facilitating the retrofit of existing plants. In these embodiments, additional flow rates to step (iii) can be easily provided, which is important when an air classifier mill is used. Although not required, to balance the process, the second portion can be further mixed with other gas streams to provide a second carbon-rich gas, such as the gas recovered from the particle size reduction device of step (iii), air, or a concentrated gas containing at least 30% CO by volume, e.g., at least 80% CO by volume. Step (ii) preferably does not include mixing the second portion with air. Preferably, at least 70% by volume, more preferably at least 80% by volume, and more preferably at least 95% by volume of the second carbon-rich gas constitutes the second portion of gas, optionally after adjusting the humidity of the gas. In some embodiments, the second carbon-rich gas contacted with the moistened CO2-enriched material consists essentially of the second portion of gas, optionally after adjusting the humidity of the gas. Step (ii)c preferably comprises mixing the first portion with air such that less than 95% by volume of the first carbon-rich gas constitutes the gas of the first portion, more preferably less than 90% by volume, more preferably less than 85% by volume, optionally after adjusting the humidity of the gas.Depending on the temperature of the exhaust gas provided in step (ii)a and the desired temperature of the first carbon-rich gas, a larger portion of air may be mixed, for example, so that less than 80% by volume, less than 70% by volume, or less than 60% by volume of the first carbon-rich gas constitutes the first portion of gas, optionally after a step of adjusting the humidity of the gas. Typically, at least 30% by volume, preferably at least 40% by volume, of the first carbon-rich gas constitutes the first portion of gas. Since the air mixing is performed for cooling purposes, it will be clear that the temperature of the air provided in step (ii)c for mixing with the first portion will be lower than the temperature of the gas stream provided in step (ii)a, for example having a temperature of less than 80°C, preferably less than 40°C.

[0049] In some embodiments of the present invention, preparing a second carbon-rich gas comprising at least 1% by volume CO in step (ii) comprises withdrawing gas from the particle size reduction device in step (iii), optionally after adjusting the humidity of the gas, and preparing the gas to form at least a portion of the second carbon-rich gas in step (v). In such embodiments, the first carbon-rich gas prepared in step (ii) of the methods described herein is first used in step (iii) of the method and then used in step (v) of the method. Typically, for example, when a mill equipped with an air classifier is used in step (iii), the flow rate of gas through step (iii) of the process is much higher than the amount (or flow rate) of gas required for step (v) of the process, and as a result, not all of the gas withdrawn from the particle size reduction device in step (iii) is used in step (v). Furthermore, the gas withdrawn from the particle size reduction device can be mixed with other gas streams to optimize its composition for the CO enrichment process in step (v). For example, it may be mixed with a gas having a higher CO content than the gas recovered from the particle size reduction apparatus in step (iii) to provide a second carbon-rich gas. In some embodiments, the gas is not mixed with another gas and is used in step (v) at the same composition as when recovered from step (iii), optionally after adjusting the humidity of the gas. In a preferred embodiment of the invention, preparing a second carbon-rich gas comprising at least 1 vol.% CO in step (ii) comprises recovering gas from the particle size reduction apparatus in step (iii), optionally after adjusting the humidity of the gas, and preparing the gas to form at least a portion of the second carbon-rich gas in step (v), wherein at least 30 vol.%, more preferably at least 50 vol.%, of the second carbon-rich gas comprises the gas recovered from the particle size reduction apparatus. In some embodiments, the second carbon-rich gas consists essentially of the gas recovered from the particle size reduction apparatus, optionally after adjusting the humidity of the gas.

[0050] In a preferred embodiment of the method described herein, step (ii) comprises providing a hot combustion exhaust gas or cement kiln exhaust gas having a temperature above 120°C, preferably above 150°C, preferably above 190°C, and cooling the hot exhaust gas. The cooling can be achieved by any cooling means known to those skilled in the art, including a heat exchanger (e.g., using ambient air or a cooling liquid), passive cooling, and / or jacket cooling. Passive cooling means that the piping transporting the exhaust gas allows sufficient heat exchange with the ambient air to cool the hot exhaust gas. In practice, this can be achieved, for example, by increasing the length of the piping, reducing the diameter of the piping, or not insulating the piping. Jacket cooling can comprise flowing a cooling fluid through a jacket disposed around the piping transporting the exhaust gas. The cooling fluid used in the heat exchanger or jacket can be any known cooling liquid, including ordinary water or a cooling liquid having a freezing point below -5°C, preferably below -10°C (typically, a water-based cooling liquid containing one or more glycols and one or more corrosion inhibitors). Cooling is preferably carried out by a heat exchanger and / or jacket cooling. Cooling is preferably carried out to a temperature of less than 120°C, preferably less than 100°C, preferably less than 90°C, more preferably less than 80°C, and most preferably less than 70°C. In some embodiments, as described herein above, the cooling process comprises steps (ii)a to (ii)d, wherein the cooling in step (ii)d comprises at least one cooling means different from the cooling in step (ii)c (which may comprise, or even consist essentially of, cooling by mixing with air). For example, the cooling in step (ii)d preferably comprises cooling by heat exchange and / or jacket cooling (techniques that do not substantially affect the gas composition). After cooling, it may be desirable to carry out a further step of subjecting the cooled flue gas to a liquid-gas separation step (e.g., using a dehumidifier, de-misting pad, or similar device) to remove water droplets and / or reduce the moisture content of the cooled flue gas, or (depending on the humidity of the flue gas source and the composition of other gases that are mixed to prepare the first and second carbon-rich gases) to carry out a humidification step.In some embodiments of the present invention, step (ii) comprises providing a high-temperature combustion exhaust gas or cement kiln exhaust gas having a temperature above 120°C and cooling the high-temperature exhaust gas to a temperature below 100°C, the cooled exhaust gas being subjected to a gas-liquid separation step, and the liquid being collected and used in step (iv) to increase the moisture content of the first CO2-enriched material, preferably by spraying it onto the first CO2-enriched material. In either case, the temperature of the gas supplied to the particle size reducer is preferably at least 1°C higher than the dew point in the particle size reducer, preferably 1-20°C higher than the dew point. This allows for easier control of the moisture content of the solid phase.

[0051] Thus, in some preferred embodiments of the present invention, there is provided a method for carbon sequestration, comprising: (i) providing a solid feedstock having a first moisture content; (ii) providing a first carbon-rich gas comprising at least 1% CO by volume and a second carbon-rich gas comprising at least 1% CO by volume; (iii) subjecting the solid feedstock of step (i) to a particle size reduction operation in a particle size reduction device in the presence of the first carbon-rich gas of step (ii) to obtain a first CO2-enriched material; and recovering the first CO2-enriched material; (iv) increasing the moisture content of the first CO2-enriched material to a second moisture content higher than the first moisture content to obtain a moistened CO2-enriched material; (v) subjecting the wetted CO2-enriched material to further CO2-enrichment processing outside the particle size reduction device by contacting the wetted CO2-enriched material with a second carbon-rich gas comprising at least 1% CO2 by volume to obtain a second CO2-enriched material; and recovering the second CO2-enriched material; the gas provided in step (ii) is flue gas or cement kiln exhaust gas, in particular cement kiln gas, or exhaust gas from the combustion of fossil fuels, the combustion of wood pellets, the combustion of biomass or the combustion of municipal waste, A method is provided wherein step (ii) comprises providing a hot flue gas or cement kiln exhaust gas having a temperature above 120°C, preferably above 150°C, preferably above 190°C, and cooling the hot flue gas to a temperature below 120°C, preferably below 100°C, preferably below 90°C, more preferably below 80°C, and most preferably below 70°C. In some embodiments, the hot flue gas or cement kiln exhaust gas is provided at a temperature above 120°C and cooled to a temperature below 80°C, most preferably below 70°C.

[0052] When one or both of the carbon-rich gases provided in step (ii) comprise flue gas or cement kiln exhaust gas, the particle size reduction device preferably comprises a gas inlet fluidly connected to a flue gas outlet of a combustion plant. In some embodiments, step (ii) comprises obtaining a hot flue gas having a temperature above 120°C, preferably above 150°C, preferably above 190°C, by combustion of a fuel as described elsewhere herein. When one or both of the carbon-rich gases provided in step (ii) comprise cement kiln exhaust gas, the particle size reduction device preferably comprises a gas inlet fluidly connected to a cement kiln exhaust gas outlet of a cement plant. In some embodiments, step (ii) comprises obtaining a hot flue gas having a temperature above 120°C, preferably above 150°C, preferably above 190°C, by calcining limestone.

[0053] The particle size reduction operation of step (iii) may comprise grinding, milling, mixing, stirring (such as slow or high speed stirring), shearing (such as high torque shear), shaking, blending, pulverizing, pulverizing, crushing, disintegrating, fluidized bed or sonication, preferably grinding, milling, mixing, stirring (such as slow or high speed stirring), shearing (such as high torque shear) or sonication.

[0054] In a preferred embodiment of the present invention, the particle size reduction operation of step (iii) is carried out by subjecting the solid feedstock of step (i) to milling, preferably ball milling, roller milling, basket milling, hammer milling, rotor-stator milling, pin milling, jet milling, and / or rod milling, preferably ball milling or roller milling, most preferably roller milling, in the presence of the gas of step (ii). Thus, in a preferred embodiment, the particle size reduction device is a mill. In a highly preferred embodiment, the particle size reduction device is a ball mill or roller mill, preferably a roller mill. The roller mill is typically a vertical roller mill. Thus, in a highly preferred embodiment of the present invention, the particle size reduction operation of step (iii) is carried out by subjecting the solid feedstock of step (i) to roller milling, preferably in a vertical roller mill, in the presence of the first carbon-rich gas of step (ii). Roller mills are known to those skilled in the art and typically comprise a housing having a substantially cylindrical or conical section, in which one or more rollers are disposed adjacent to the housing, such that upon rotation of the rollers, the feedstock in the mill is crushed and / or pulverized between the rollers and the housing. The feedstock may be provided, for example, to any of the mills described herein (particularly vertical roller mills) as a solid that is simply dropped into the mill (e.g., using a conveyor belt or similar system), or, if the particle size of the feedstock is sufficiently small, as a solid that is carried by the first carbon-rich gas provided in step (ii). In a vertical roller mill, the action of centrifugal force moves the material to the end of the mill where it is crushed and / or broken down.

[0055] In some embodiments of the present invention, particularly in the case of ball milling, the particle size reduction operation can be carried out by rotating a particle size reduction device containing the solid feedstock and gas in the presence of grinding or milling media (e.g., balls or beads). Preferred materials are stainless steel or aluminum oxide. For example, the grinding or milling media can be made from steel (e.g., AISI H13, modified H10), aluminum oxide, chrome white cast iron (e.g., ASTM A532), molybdenum steel (e.g., AISI M2, M4, M-42), chromium-based steel (e.g., H11, H12, H13 CPM V9, ZDP-189), or other media with a hardness of 60 HRC or higher. Such grinding media can be used with or without surface treatments such as nitriding and carburizing. This can be conveniently carried out in a rotating drum.

[0056] The inventors have further found that the particle size reduction operation of step (iii) described herein can be advantageously carried out without the use of an additional oxidizing agent, such as an acid. Thus, the mechanochemical carbon sequestration method described herein is preferably carried out without the use of a strong acid, and preferably without the use of any additional oxidizing agent other than the gas provided in step (ii).

[0057] In embodiments of the process described herein, to promote carbonation, step (v) is carried out at a temperature below 120°C, preferably below 100°C, preferably below 90°C, and more preferably below 85°C. In a preferred embodiment of the present invention, steps (iii) and (v) are carried out at a temperature of at least 30°C, preferably at least 35°C, and preferably at least 38°C. The inventors have found that even when the particle size reduction operation of step (iii) is carried out at a higher temperature, good carbonation can still be achieved, so long as the temperature during step (v) is optimized. Thus, in a particularly preferred embodiment, step (v) is carried out at a temperature in the range of 30-85°C, preferably 30-55°C, and most preferably 35-50°C, for example, 35-45°C or about 40°C. As shown in the accompanying examples, these temperatures allow for improved carbonation efficiency, particularly when slag as described herein is used as the solid raw material. The particle size reduction operation in step (iii) can be carried out at any temperature, for example, in the range of 20 to 300°C, including temperatures above 120°C or even above 150°C. Such high temperatures can occur when very hot exhaust gas is used or when temperature rise due to friction is significant. In some embodiments, the temperature during step (iii) is also less than 120°C, preferably less than 100°C, preferably less than 90°C, and more preferably less than 85°C. In preferred embodiments of the present invention, no active heating is used; any temperature rise is due to the temperature of the inlet gas, friction due to the particle size reduction operation, or the exothermic reaction occurring during mechanochemical carbonation. Temperatures are preferably measured against solid material during processing. In some embodiments, active cooling is provided to the particle size reduction apparatus, for example, by providing a cooling jacket around the housing of the particle size reduction apparatus. The cooling fluid used in the jacket can be any known coolant, including ordinary water or a coolant with a freezing point below -5°C, preferably below -10°C (typically, a water-based coolant containing one or more glycols and one or more corrosion inhibitors).In all embodiments of the present invention, it is preferred that the second carbon-rich gas, when contacted with the moistened CO2-enriched material in step (v), has a temperature in the range of 30 to 85°C, preferably in the range of 30 to 55°C, most preferably in the range of 35 to 50°C, for example in the range of 35 to 45°C or about 40°C.

[0058] The low temperature requirements of the process of the present invention mean that no fossil fuels are required, and where friction caused by the particle size reduction operation and / or the temperature of the gas supply are insufficient to reach the desired temperature, it is practical to use electrical heating means (or a low calorific value green fuel source) to provide heat. In this way, fossil fuels can be avoided throughout the entire production process.

[0059] As will be apparent from the present specification, steps (iii) and (v) are substantially dry processes. The inventors have found that solid phase moisture control offers unique advantages, while steps (iii) and (v) are not performed on an aqueous solution or slurry. The inventors have found that this significantly improves energy efficiency (since there is no need to subsequently remove water) and imparts unique properties to the resulting mechanochemically carbonated solid feedstock, resulting in a material that is substantially different from, for example, aqueous carbonated materials.

[0060] A common premise for moisture control in operations using flue gas for carbon sequestration is that the flue gas temperature needs to be maintained above the dew point (to prevent condensation). The inventors have surprisingly found that the moisture content of the solid feedstock is determinative of the overall efficiency of the operation. In particular, when the two-step (or more) carbon sequestration process described herein is practiced, it is desirable to specifically control the moisture content during the first carbon sequestration and particle size reduction step to be lower than the moisture content during the second carbon sequestration step.

[0061] The first water content is preferably less than 8 wt% (based on the total weight of the solid feedstock), preferably less than 5 wt% (based on the total weight of the solid feedstock), and the second water content is preferably more than 10 wt% (based on the total weight of the moistened CO2-enriched material). The inventors have surprisingly found that the second water content is preferably less than 35 wt% (based on the total weight of the moistened CO2-enriched material), preferably less than 27 wt% (based on the total weight of the moistened CO2-enriched material), and most preferably less than 20 wt% (based on the total weight of the moistened CO2-enriched material), because above these levels, a decrease in efficiency is observed, especially when the CO2-enrichment of step (v) is a process in which no further particle size reduction occurs, as described elsewhere herein.

[0062] Step (iv) of increasing the moisture content of the first CO2-enriched material to a second moisture content higher than the first moisture content to obtain a moistened CO2-enriched material can be carried out by any means known to those skilled in the art. Preferably, step (iv) comprises spraying an aqueous composition, such as water, onto the first CO2-enriched material, and / or step (iv) comprises controlling the humidity of the second carbon-rich gas so that it can increase the moisture content of the first CO2-enriched material upon contact with the first CO2-enriched material. It is highly preferred that step (iv) comprises spraying an aqueous composition, such as water, onto the solid first CO2-enriched material. The inventors have found that such surface wetting is beneficial to CO2 sequestration efficiency. The humidity of the first carbon-rich gas fed to the particle size reduction device is preferably controlled so that the moisture content of the solid feedstock in step (iii) is kept low. However, even if the solid feedstock is moistened by spraying in step (iv), if a dry gas is used in step (v), the solid feedstock may dry out rapidly, resulting in the need for an additional moisture control step to maintain the moisture content of the solid phase in step (v) at or above the second moisture content. To reduce or eliminate the need for such an additional moisture control step, it is preferable to control the humidity of the first carbon-rich gas used in step (v) following the water spraying in step (iv) so that the moisture content of the moistened CO2-enriched material in step (v) is at or above the second moisture content. In all of the embodiments described herein, it is preferred that the second carbon-rich gas has a relative humidity (RH) of at least 70%, preferably at least 85%, more preferably at least 95%, e.g., about 100%.

[0063] The inventors have also found that the large amount of gas (typically flue gas) used for CO2 enrichment tends to cause the moisture content of the solid feedstock, even when controlled, to shift toward levels that are undesirable for either particle size reduction in step (iii) or further CO2 enrichment in step (v). Too high a moisture content in the particle size reduction step can result in agglomeration, clogging / blockage, inefficient and inconsistent particle size reduction, etc., while too low a moisture content in step (v) can reduce carbon sequestration efficiency. Therefore, it is preferred that the moistened CO2-enriched material be maintained at a moisture content equal to or greater than the second moisture content throughout the further CO2 enrichment process in step (v), and preferably the solid feedstock is maintained at a moisture content equal to or less than the first moisture content throughout the particle size reduction operation in step (iii). For purposes of this disclosure, maintaining a target moisture content includes situations in which the solid feedstock deviates from the target moisture content and such deviation is detected or calculated and corrected. Generally, maintaining a particular moisture content throughout a process step should be interpreted to mean that the moisture content is within the desired range for at least 50% of the duration of the step, preferably at least 80% of the duration of the step, and especially throughout the entire duration of the step.

[0064] Maintaining the moisture content of the moistened CO2-enriched material at or above the second moisture content throughout the further CO2-enrichment processing of step (v) can be carried out by (re)wetting the solid phase by spraying with an aqueous composition such as water, or by humidifying the second carbon-rich gas that contacts the solid feedstock. As will be understood by those skilled in the art based on the present disclosure, in some preferred embodiments, there is provided a process of the present invention, wherein step (iv) comprises spraying an aqueous composition such as water onto the first CO2-enriched material to obtain a moistened CO2-enriched material having a second moisture content higher than the first moisture content, and step (v) comprises maintaining the moistened CO2-enriched material at a moisture content equal to or greater than the second moisture content throughout the further CO2-enrichment processing of step (v). The moisture content of the wetted CO2-enriched material can be maintained at or above the second moisture content throughout the further CO2-enrichment processing of step (v), for example, by spraying the wetted CO2-enriched material with an aqueous composition, such as water, one or more times throughout step (v) and / or by humidifying the gas contacting the wetted CO2-enriched material. Thus, in some embodiments of the invention, step (iv) comprises spraying an aqueous composition, such as water, onto the first CO2-enriched material, and step (v) comprises spraying an aqueous composition, such as water, onto the wetted CO2-enriched material. Maintaining the moisture content of the solid feedstock at or below the first moisture content throughout the particle size reduction operation of step (iii) can be accomplished by removing moisture from the gas before it is fed to the particle size reduction device (as described herein above), optionally in combination with temperature control of the particle size reduction operation (as described herein above). Humidification of a gas stream is within the routine capabilities of one skilled in the art and can be accomplished by any means, such as bubbling or sparging the gas through an aqueous composition (e.g., water), membrane-driven water-to-gas humidification, mixing the gas stream with water vapor, etc.

[0065] The inventors have found that many materials tend to agglomerate when wet, which is undesirable as it reduces the surface area available for further CO2 enrichment in step (v) and deactivates the material. Step (iv) may further comprise the optional step of deagglomerating the wetted CO2-enriched material. Thus, in some embodiments, step (iv) further comprises the step of deagglomerating the wetted CO2-enriched material before it is subjected to the further CO2-enrichment process of step (v).

[0066] In some embodiments, particularly when step (iii) of the method, or steps (iii) through (v) of the method, are carried out sequentially, step (iii) comprises: (iii)a. continuously separating the first CO2-enriched material into at least one first portion and a second portion, wherein the first portion has a different average particle size than the second portion; (iii)b continuously recovering a first portion of the CO2-enriched material and returning a second portion to the particle size reduction operation of step (iii).

[0067] Steps (iii)a and (iii)b can be carried out by any suitable means known to those skilled in the art, including dynamic image analysis (DIA), laser diffraction (SLS), dynamic light scattering (DLS), and / or particle size measurement devices based on sieve analysis, coupled with means for continuous separation of the CO2-enriched material into different fractions. However, the inventors have found that an air classifier allows for full integration of the process with the treatment of flue gas or cement kiln exhaust gas streams, as described elsewhere herein. Thus, in a highly preferred embodiment of the present invention, step (iii) of the method of the present invention is carried out by an air classifier. Step (iii) can be carried out using a particle size reduction device (preferably a mill, more preferably a vertical roller mill) with an integrated air classifier. Step (iii) can also be carried out using an air classifier located downstream of the particle size reduction device (preferably a mill, preferably a vertical roller mill). The operating principle of an air classifier is known to those skilled in the art, i.e., a forced gas stream (preferably consisting of the first carbon-rich gas prepared in step (ii)) lifts the milled and / or ground material from the milling zone and circulates it to the classification zone, where particles smaller than the classification cut diameter pass through the classifier, while oversized particles are sent back to the milling zone. In a preferred embodiment of the present invention, the gas stream through the air classifier comprises, and preferably consists of, the first carbon-rich gas of step (ii). Typically, the gas flows from the milling zone to the air classifier. This generates a gas stream that carries a first portion of the CO2-enriched material away from the particle size reduction device. After removing the CO2-enriched material from the gas stream exiting the air classifier, the gas stream can be partially recycled to the particle size reduction device used in step (v) of the method described hereinabove, subjected to further purification (e.g., scrubbing), or vented. Thus, step (iii)b preferably further comprises a solid-gas separation step to separate the first CO2-enriched material from the gas stream. Such solid-gas separation can be carried out by any means known to those skilled in the art.In practice, it is sufficient to design the process equipment so that the gas velocity slows after leaving the classifier and the particles fall out of the gas stream unentrained, for example by using a conventional dust collector. The particles can then be moved further downstream in the process, for example by a conveyor belt or screw conveyor, to steps (iv) and (v) of the process.

[0068] Suitable air classifiers in the context of the present invention include gravity air classifiers, gravity-inertia air classifiers, centrifugal air classifiers, cyclonic air classifiers, and / or gyrator air classifiers. The air classifier may include additional means for separating the first and second portions of the CO2-enriched material, including, but not limited to, a rotating rejector or selector blade, a filter unit, and / or an adjustable secondary air system for capturing particles of similar size. As known to those skilled in the art, air classifiers do not strictly separate particles based on particle size, but rather separate particles by a combination of size, shape, and density. In practice, this results in a portion of particles having a first average particle size and another portion of particles having a second average particle size. The difference in average particle size between the first and second portions referred to throughout this specification can be conveniently determined by finding the difference between the D50 of the first portion and the D50 of the second portion, which is considered to represent the difference in average particle size for purposes of the present invention.

[0069] As will be appreciated by those skilled in the art, steps (iii)a and (iii)b are carried out substantially simultaneously, in other words, the particle size reduction operation and the continuous separation of the CO2-enriched material into the first and second fractions are carried out simultaneously and continuously.

[0070] In a preferred embodiment of the invention, step (iii) is carried out using a vertical roller mill with an integral air classifier or an air classifier located downstream of the vertical roller mill, and the gas of step (ii) is supplied to the bottom region of the vertical roller mill below the bottom roller of the mill, the bottom being the lowest part of the mill as viewed in the direction of gravity.

[0071] Generally, step (iii) can be carried out at atmospheric, subatmospheric, or superatmospheric pressure. Thus, in some embodiments, step (iii) is carried out at a pressure greater than about 100 kPa (e.g., at least 101.325 kPa). In some embodiments of the present invention, step (iii) is carried out at a pressure greater than about 300 kPa (e.g., 303.975 kPa), preferably greater than about 600 kPa (e.g., 607.95 kPa). In alternative and preferred embodiments of the present invention, particularly when an air classifying mill is used, step (iii) is carried out at a pressure less than atmospheric pressure, for example less than about 100 kPa (e.g., less than 101.325 kPa), for example less than 50 kPa or less than 10 kPa. Step (v) can also be carried out at atmospheric, subatmospheric, or superatmospheric pressure. However, step (v) is preferably carried out at a pressure above atmospheric pressure, for example above about 100 kPa (e.g., at least 101.325 kPa), preferably above about 300 kPa (e.g., 303.975 kPa), preferably above about 600 kPa (e.g., 607.95 kPa).

[0072] In highly preferred embodiments of the invention in which steps (iii)a and (iii)b are performed, particularly when an air classifier is used in the process (as described elsewhere herein), step (iii) is carried out in the presence of a continuous flow comprising, preferably consisting of, the first carbon-rich gas of step (ii). In preferred embodiments, the continuous flow of gas in the particle size reduction device of step (iii) is achieved by providing a pressure differential between the gas entering the particle size reduction device (preferably a mill, e.g., a vertical roller mill) and the gas exiting the air classifier of at least 20 kPa, more preferably 50 kPa, and most preferably 100 kPa. In some embodiments, the entering gas stream has a pressure greater than 101 kPa, preferably greater than 150 kPa, more preferably greater than 300 kPa, and the exiting gas stream has a pressure less than 80 kPa, preferably less than 50 kPa, and more preferably less than 20 kPa.

[0073] In a highly preferred embodiment of the method described herein, steps (iii) and (v) are carried out at a pressure below the critical pressure of carbon dioxide. Furthermore, the inventors have discovered that very high pressures are not required to prepare the CO2-enriched material in the process of the present invention, and as a result, the method can be carried out in a very energy-efficient manner. It is therefore preferred that steps (iii) and (v) are carried out at a pressure below 10,000 kPa, preferably below 5,000 kPa, more preferably below 2,500 kPa, and most preferably below 1,000 kPa.

[0074] In some embodiments of the present invention, the methods described herein are provided under conditions such that the temperature and pressure during step (iii) are less than the saturated vapor pressure of water at the temperature in the particle size reduction operation unit.

[0075] Step (v) is carried out outside the particle size reduction device after a step of increasing the moisture content of the first CO2-enriched material to a second moisture content higher than the first moisture content, for example by spraying an aqueous composition such as water onto the material, as described elsewhere herein. The further CO2-enrichment treatment of step (v) can be any treatment that increases the total carbon (TC) content of the moistened CO2-enriched material. This therefore means that step (v) can also be a multi-stage process in which multiple CO2-enrichment steps are performed, for example using multiple reactors arranged in series. In an embodiment of the invention, step (v) comprises: placing the moistened CO2-enriched material in a holding means or container in contact with a second carbon-rich gas, preferably under a continuous flow of the second carbon-rich gas, wherein the contacting is preferably for at least 15 minutes, at least 30 minutes, or at least 1 hour; storing the moistened CO2-enriched material in contact with a second carbon-rich gas, preferably in an airtight container, wherein the storage is preferably for at least 15 minutes, at least 30 minutes, or at least 1 hour; feeding the moistened CO2-enriched material into a fluidized bed maintained using a second carbon-rich gas; contacting the wetted CO2-enriched material with a second carbon-rich gas in a reactor comprising a substantially airtight hollow housing and mechanical agitation means configured to contact the solid material during operation, such that an agitated bed of solid material is formed within the reactor during operation; and / or passing a gas stream comprising the moistened CO2-rich material entrained in a second carbon-rich gas through the catalyst bed one or more times.

[0076] In step (v), contacting the wetted CO2-enriched material with the gas can be carried out with moderate agitation, for example by using a continuous stirred tank reactor (CSTR), i.e., a reactor as described in more detail below, or a reactor as in the case of a fluidized bed.

[0077] A preferred method for carrying out step (v) utilizes a reactor having a substantially airtight hollow housing and mechanical agitation means configured to contact the solid material during operation, thereby forming an agitated bed of solid material within the reactor during operation. The reactor includes mechanical agitation means disposed within the housing. The mechanical agitation means is configured to form an agitated bed of solid material within the reactor during operation. Thus, step (v) of the present method preferably includes operating the reactor to provide an agitated bed of solid material. The mechanical agitation means can be provided in the form of any means known to those skilled in the art capable of forming an agitated bed. Such a reactor is not a fluidized bed reactor, which uses a high velocity gas flow to fluidize the solid bed. Thus, at any time during step (v) of the present method, the gas velocity within the reactor is less than the minimum fluidization velocity of the solid feed, preferably less than 80% of the minimum fluidization velocity of the solid feed. Examples of mechanical stirring means include lifting flights attached to the interior of the rotating drum (e.g., attached to the housing of the rotating drum), milling media (such as inert balls or beads) inside the rotating drum, static paddles attached to the interior of the rotating drum, and rotary shaft-driven stirring devices (e.g., screws or mixers) located within the reactor housing. In a preferred embodiment of the present invention, the mechanical stirring means is a rotary shaft-driven stirrer such as a screw (preferably a shaftless screw, or a screw with helical flights attached to the outer surface of the screw shaft), a plow mixer, a ribbon mixer, or a paddle mixer (e.g., a pug mill), preferably a screw. The reactor is preferably configured to move the feedstock from the solid feed inlet to the solid material outlet of the reactor. The solid feed inlet and outlet are preferably located at both ends of the reactor. During operation, a stirred bed of solid material is present in the reactor, and the reactor is preferably configured to move particles contained in the stirred bed from the reactor inlet to the reactor outlet. Those skilled in the art will understand that during normal operation, in which the reactor is continuously fed with solid material, there will always be an agitated bed within the apparatus, but the individual particles contained within the bed will move from the inlet to the outlet of the apparatus according to their average residence time within the apparatus.Thus, step (v) preferably includes operating the reactor so that individual particles of the solid feedstock move from the inlet to the outlet of the apparatus. In a preferred embodiment, the rotary shaft-driven agitator comprises a substantially horizontally disposed rotary shaft. In the case of a shaftless screw, typically, a shaft portion supporting the screw is disposed along the screw axis and connects the screw to a motor. In a highly preferred embodiment of the present invention, the mechanical agitation means comprises a screw disposed within the reactor housing, the screw supported for rotational movement about a first axis, and comprising helical flights. The screw may be a shaftless screw, or a screw in which the helical flights are attached to the outer surface of the screw shaft. As will be understood by those skilled in the art, a shaftless screw is a rotary shaft-driven agitator because a rotary shaft is still used to rotate the screw even if the shaft does not extend axially with the flights. The screw may be single-flighted or double-flighted. The screw may have a constant pitch or a variable pitch. The screw may have tapered flights. The screw may further comprise paddles attached to the shaft between the flights. The helical flights may be made from a single continuous metal sheet wound with multiple blades, or from individual blades or blade sections joined by welding or the like. It is highly preferred that the screw comprises stirring means protruding from the surface of the helical flights and one or more gas passages radially disposed between the first axis and the outer diameter of the screw. The inventors have found that such a screw provides an optimized stirred bed and solid-gas interaction, further improving carbon sequestration efficiency. The stirring means may comprise cut and folded flights.

[0078] Preferably, the stirring means comprises one or more lifting bars connecting two adjacent blades of the helical flight. Preferably, two adjacent blades of the helical flight are connected to each other by two or more lifting bars, and / or a majority of the blades are connected to two adjacent blades by one or more lifting bars. The lifting bars may be closed or may comprise one or more openings. The lifting bars are preferably arranged substantially perpendicular to the helical flight. When the screw comprises helical flights attached to the outer surface of the screw shaft (as opposed to a shaftless screw), the one or more gas flow passages are preferably formed by one or more openings extending through the blades of the helical flight.

[0079] In some preferred embodiments of the present invention, step (v) comprises: storing the moistened CO2-enriched material in a holding means or container by contacting the moistened CO2-enriched material with a second carbon-rich gas, preferably under a continuous flow of the second carbon-rich gas, while agitating the moistened CO2-enriched material or rotating the holding means or container, wherein the storage is preferably for at least 15 minutes, at least 30 minutes, or at least 1 hour; contacting the moistened CO2-enriched material with a second carbon-rich gas in a reactor comprising a substantially airtight hollow housing and mechanical agitation means configured to contact the solid material during operation so as to form an agitated bed of solid material in the reactor during operation, and preferably operating the reactor to provide an agitated bed of solid material with a residence time of the feedstock in the reactor of at least 30 seconds, preferably at least 1 minute, more preferably at least 5 minutes; and / or Storing the moistened CO2-enriched material in contact with a second carbon-rich gas, preferably in an airtight container, while stirring the moistened CO2-enriched material or rotating the container, preferably for at least 15 minutes, at least 30 minutes, or at least 1 hour.

[0080] However, it is highly preferred that step (v) does not result in a significant reduction in particle size. Without stirring or gentle agitation, some agglomeration may occur. Therefore, recovering the second CO2-enriched material in step (v) optionally includes a deagglomeration step. In a preferred embodiment of the present invention, the ratio of the D50 of the first CO2-enriched material recovered in step (iii) to the D50 of the second CO2-enriched material recovered in step (v) is in the range of 0.8 to 1.2, preferably in the range of 0.9 to 1.1, and more preferably in the range of 0.95 to 1.05.

[0081] In some embodiments of the present invention, step (iii) and / or step (v) comprise contacting the feedstock with a catalyst, preferably a metal oxide catalyst, such as a transition metal oxide catalyst. Examples of suitable catalysts are selected from the group consisting of iron oxide, cobalt oxide, ruthenium oxide, titanium oxide, nickel oxide, aluminum oxide, and combinations thereof. The catalyst should be suitable for increasing CO2 sequestration of the feedstock. In some embodiments, the catalyst is selected from the group consisting of TC cat The metal oxides are selected from those having a TC:TC ratio of greater than 1.01, preferably greater than 1.05. cat is the increase in the total carbon content of the feedstock when the CO2 sequestration capacity test is conducted. In this test, a 10 gram sample of the solid feedstock is loaded into a pressure cell with a 500 gram stainless steel ball (12 mm diameter) coated with a catalyst, then the cell is pressurized to 1 MPa and rotated at 5000 RPM for 48 hours. The test is conducted at an ambient temperature of 20°C without heating or cooling. TC o is the increase in the total carbon content of the feedstock when subjected to a CO2 sequestration capacity test. In this test, a 10 gram sample of the solid feedstock is loaded into a pressure cell with a 500 gram uncoated stainless steel ball (12 mm diameter), the cell is then pressurized to 1 MPa, and the pressure cell is rotated at 5000 RPM for 48 hours. The test is conducted at an ambient temperature of 20°C without heating or cooling.

[0082] The catalyst may, for example, be mixed with the solid feedstock or may be immobilized on the interior surface, preferably the lining, of the particle size reduction apparatus of step (iii) or the apparatus used in step (v) (e.g., the tank of a continuous stirred tank reactor). The catalyst may also be immobilized on a porous support or bed that is not subject to particle size reduction but is fixed to the particle size reduction apparatus in a manner that allows contact with the solid feedstock, or on a porous support or bed that is fixed to the apparatus used in step (v) (e.g., a catalyst bed disposed in piping configured to convey a gas stream comprising moistened CO2-enriched material entrained in the gas recovered from the particle size reduction apparatus).

[0083] According to a preferred embodiment of the present invention, the total power consumption represented by steps (iii) to (v) is less than 200 Wh, preferably less than 175 Wh, more preferably less than 150 Wh per kg of second CO2-enriched material recovered in step (v).

[0084] The process of the present invention preferably comprises a further step (vi) of drying the second CO2-enriched material recovered in step (v). This avoids clumping / agglomeration of the material during long-term storage. Drying can be carried out by any means known to those skilled in the art. Drying preferably comprises drying the second CO2-enriched material recovered in step (v) to a moisture content of less than 8 wt. % (based on the total weight of the dried second CO2-enriched material), preferably less than 5 wt. % (based on the total weight of the dried second CO2-enriched material), more preferably less than 2 wt. % (based on the total weight of the dried second CO2-enriched material). Drying is preferably carried out by contacting the second CO2-enriched material with a dry gas stream (preferably a continuous flow of dry gas stream) having a temperature of less than 400°C, preferably less than 300°C, preferably less than 250°C, and preferably having a relative humidity (RH) of less than 50%, preferably less than 30%, most preferably less than 10%. By keeping the temperature of the drying gas below the above values, loss of sequestered CO from the CO2-enriched material is avoided. The drying gas stream is preferably a combustion gas or cement kiln exhaust gas as previously described herein, optionally treated to reduce humidity.

[0085] In some embodiments, the dry gas stream comprises a first carbon-rich gas that was obtained as a stream separated from the first carbon-rich gas prior to step (iii) and / or as part or all of the first carbon-rich gas recovered from the particle size reduction device. According to preferred embodiments of the present invention, the second carbon-rich gas is a wet gas, and therefore, by using the first carbon-rich gas before or after use in the particle size reduction device, additional moisture removal from the gas stream can be avoided.

[0086] Solid feedstock characteristics, preconditioning and pretreatment The method of the present invention is not particularly limited with respect to the raw material used. To achieve significant carbon sequestration, the solid raw material prepared in step (i) is preferably a material that exhibits an increase in CO content of at least 1%, preferably at least 4%, when subjected to a CO sequestration capacity test. In this test, a 10-gram sample of the solid raw material is loaded into a pressure cell containing 500 grams of titanium dioxide-coated stainless steel balls (12 mm diameter), and the cell is then pressurized to 1 MPa and rotated at 5,000 RPM for 48 hours. The test is conducted at an ambient temperature of 20°C without heating or cooling. The CO content is determined as the mass loss above 200°C, measured by TGA using a temperature trace in which the temperature is increased from room temperature to 800°C at a rate of 10°C / min and then decreased to room temperature at a rate of 10°C / min. Alternatively, the solid raw material prepared in step (i) is preferably a material that exhibits an increase in total carbon content of at least 1%, preferably at least 4%, when subjected to a CO sequestration capacity test. In this test, a 10 gram sample of the solid material is loaded into a pressure cell containing 500 grams of titanium dioxide coated stainless steel balls (12 mm diameter), the cell is then pressurized to 1 MPa, and the pressure cell is rotated at 5000 RPM for 48 hours. The test is conducted at an ambient temperature of 20°C without heating or cooling.

[0087] In preferred embodiments of the present invention, the solid feedstock provided in step (i) comprises minerals and / or elemental carbon. In some embodiments, the feedstock comprises CaO and / or Ca(OH), preferably the feedstock comprises at least 0.1 wt. % (based on the total weight of the feedstock) of CaO and / or Ca(OH), preferably at least 0.5 wt. % (based on the total weight of the feedstock) of CaO and / or Ca(OH).

[0088] In some embodiments, the solid feedstock provided in step (i) is selected from the group consisting of coal combustion products (especially fly ash or bottom ash), graphene, graphite, clay, shale, silicate minerals, glass (especially soda-lime glass or borosilicate glass), iron or steel slag, wood, limestone, calcite, amosa asbestos, hydrotalcite, natural pozzolana, volcanic rock, biochar, pyroxene, hydrous magnesium silicate, talc, serpentine, serpentinite, peridotite, borosilicate glass, volcanic ash, perlite, pumice, obsidian, volcanic slag, tuff (e.g., rhyolitic tuff, dacite tuff, basaltic tuff, trachytic tuff, phonolitic tuff, diagenetic tuff, etc.). tuff), andesite, clinoptilolite, heulandite, augite, apatite, titanite, biotite, glaucoma, sapphire, sodalite, magnetite, muscovite, chabazite, analcime, hematite, cristobalite, tripolitite, stilite, illite, mica, amphibole, mordenite, andesite, basalt, diatomite, tripolitite, flint, dolomite, forsterite, monticelloide, wollastonite, diopside, enstatite, lizardite, potassium and sodium feldspars, slate, schist, milky shale, hydraulic cement, hydrated lime, concrete, mafic or ultramafic mine wastes and The slag may include one or more of zeolites, preferably selected from serpentinite, peridotite, basalt, volcanic rock, perlite, zeolite, soda-lime glass, bottom ash, coal fly ash, oil fly ash, coal fly ash, subbituminous coal fly ash, anthracite fly ash, bituminous coal fly ash, blast furnace (BF) slag (e.g., air-cooled blast furnace (ACBF) slag or water-cooled blast furnace slag), granulated blast furnace (GBF) slag, basic oxygen furnace (BOF) slag, ladle furnace basic slag (LS), electric arc furnace (EAF) slag, and mafic or ultramafic mine waste. The furnace slag may be from ferrous metals production, non-ferrous metals production, or phosphorus production, preferably from ferrous metals production. Most preferred is the slag raw material described herein.

[0089] In a preferred embodiment of the present invention, the feedstock is not pretreated with an acid.

[0090] In some embodiments of the present invention, step (i) includes preconditioning the solid feedstock by contacting it with the first or second carbon-rich gas of step (ii). In preferred embodiments, preconditioning is performed without simultaneous particle size reduction of the feedstock. For example, the feedstock can be stored with a continuous flow of gas. Alternatively, the feedstock can be stored in an airtight container in the presence of gas. Preconditioning of the solid feedstock can be performed with gentle agitation that does not significantly reduce the particle size of the solid feedstock, for example, in a continuous stirred tank reactor (CSTR).

[0091] The solid raw material is typically a granular material such as aggregate or powder. In a preferred embodiment of the present invention, the solid raw material of step (i) fed to step (iii) has a D95 of less than 20 mm, preferably less than 15 mm, more preferably less than 10 mm, and most preferably less than 4 mm before particle size reduction in step (iii). For example, the D95 may be in the range of 3 to 7 mm. In some embodiments of the present invention, the D95 before particle size reduction in step (iii) is in the range of 1 to 20 mm, preferably in the range of 2 to 15 mm, more preferably in the range of 3 to 10 mm, for example, 3 to 7 mm. The D95 described in this section relates to a mass-based D95 ​​measured by sieve analysis.

[0092] In some embodiments of the present invention, the solid feedstock may contain large solid pieces that may require a pre-treatment step to achieve a particle size suitable for feeding into the particle size reduction device, e.g., a vertical roller mill, used in step (iii). Such suitable particle size is determined primarily by the presence of oversized particles as reflected by the D95 (e.g., mass basis as measured by sieve analysis) discussed above. Thus, in a preferred embodiment of the present invention, step (i) comprises: (i)a providing a solid material having a first D95; (i)b subjecting the solid material of step (i)a to a particle size reduction operation, thereby obtaining a solid feedstock having a second D95 ​​that is smaller than the first D95.

[0093] In such embodiments, the particle size reduced material of step (i)b is the solid feedstock provided to step (iii). In some embodiments, the solid material provided in step (i)a has a D95 of greater than 10 mm, for example greater than 15 mm or greater than 20 mm. The particle size reduction operation of step (i)b is preferably carried out using a particle size reduction device that is different from the particle size reduction device of step (iii). Step (i)b is preferably carried out by hammer milling, while step (iii) is preferably carried out by vertical roller milling.

[0094] The D95 mentioned in this section relates to mass-based D95 ​​determined by sieve analysis.

[0095] Properties of the obtained CO2-enriched material In a preferred embodiment of the invention, the method described herein is provided wherein the second CO2-enriched material recovered in step (v) has one, two, three, or four, preferably four, of the following properties: D10 in the range of 0.005-3 μm; D50 in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 40 μm, more preferably in the range of 1 to 40 μm, and most preferably in the range of 5 to 40 μm; D90 in the range of 0.5-300 μm; 0.5~10,000m 2 / g, preferably 1 to 2000m 2 BET surface area in the range of / g.

[0096] In all embodiments, D50 and / or D90 are preferably as specified above, as these are the most important particle size characteristics affecting overall performance. The second CO2-enrichment treatment of step (v) is preferably carried out without significant particle size reduction (maintaining maximally gentle agitation to avoid agglomeration, as previously described herein). The first CO2-enriched material recovered in step (iii) preferably meets the same particle size and surface area characteristics as defined herein for the second CO2-enriched material recovered in step (v).

[0097] In other words, it is preferred that the first CO2-enriched material recovered in step (iii) has one, two, three or four, preferably four, of the following properties: D10 in the range of 0.005-3 μm; D50 in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 40 μm, more preferably in the range of 1 to 40 μm, and most preferably in the range of 5 to 40 μm; D90 in the range of 0.5-300 μm; 0.5~10,000m 2 / g, preferably 1 to 2000m 2 BET surface area in the range of / g.

[0098] Therefore, it is preferred that the first CO2-enriched material recovered in step (iii) and the second CO2-enriched material recovered in step (v) each have one, two, three or four, preferably four, of the following properties: D10 in the range of 0.005-3 μm; D50 in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 40 μm, more preferably in the range of 1 to 40 μm, and most preferably in the range of 5 to 40 μm; D90 in the range of 0.5-300 μm; 0.5~10,000m 2 / g, preferably 1 to 2000m 2 BET surface area in the range of / g.

[0099] It is particularly preferred that the first CO2-enriched material recovered in step (iii) and the second CO2-enriched material recovered in step (v) each have a D50 in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 40 μm, more preferably in the range of 1 to 40 μm, and most preferably in the range of 5 to 40 μm.

[0100] In some embodiments, the BET surface area of ​​the second CO2-enriched material recovered in step (v) is between 50 and 2000 m 2 In an alternative embodiment, the BET surface area of ​​the second CO2-enriched material recovered in step (v) is in the range of 1 to 50 m 2 / g.

[0101] Without being bound by any theory, the inventors believe that the isolation method of the present invention, when applied to materials such as graphite, can maintain the platelet morphology. This is observed by maintaining the platelet thickness. Thus, in embodiments of the present invention (particularly those in which the feedstock of step (i) includes or is graphite), the CO2-enriched material recovered in step (v) has a platelet morphology and a platelet thickness of greater than 10 nm, preferably greater than 20 nm, and more preferably greater than 50 nm. The platelet thickness referred to herein is preferably measured by calculating the average platelet thickness, as measured by transmission electron microscopy, for all particles for which the platelet thickness can be measured in a random 25 x 25 micron field recorded from a random sample of the homogenized material batch.

[0102] The process of the present invention is preferably carried out such that the ratio of the CO2 content of the second CO2-enriched material recovered in step (v) to the CO2 content of the solid feedstock of step (i) is at least 1.5:1, preferably at least 3:1, more preferably at least 10:1, where the CO2 content is determined as the mass loss above 200°C measured by TGA using a temperature trace in which the temperature is increased from room temperature to 800°C at a rate of 10°C / min and then decreased to room temperature at a rate of 10°C / min. Similarly, the carbon sequestration treatment of steps (iii)-(v) is preferably carried out such that the ratio of the total carbon content of the second CO2-enriched material recovered in step (v) to the total carbon content of the solid feedstock of step (i) is at least 1.05:1, preferably at least 1.1:1, more preferably at least 1.2:1, particularly when the feedstock is selected from non-carbonaceous materials such as minerals, slags, and glasses as described hereinbefore.

[0103] Without being bound by any theory, the inventors believe that the increase in BET surface area resulting from the carbon sequestration process can be largely attributed to the increase in the number of pores observed due to the decrease in average pore width and the increase in total pore surface area. Accordingly, in embodiments of the present invention, the process is preferably carried out such that the BJH desorption cumulative surface area of ​​the pores of the CO2-enriched material recovered in step (v) is at least 110%, preferably at least 120%, more preferably at least 150% of the BJH desorption cumulative surface area of ​​the pores of the solid feedstock of step (i), and the desorption average pore width (4V / A by BET) of the second CO2-enriched material recovered in step (v) is 90% or less, preferably 85% or less, more preferably 80% or less of the desorption average pore width (4V / A by BET) of the feedstock of step (i). Without being bound by any theory, the inventors believe that the increase in the number of pores, achieved primarily in step (iii), increases the rate of CO diffusion into the solid feedstock, making it more susceptible to further CO enrichment in step (v). In other words, step (iii) of the present invention is believed to activate the feedstock, thereby increasing the effectiveness of further CO enrichment in step (v).

[0104] In an embodiment of the invention, the ratio of the CO content of the second CO2-enriched material recovered in step (v) to the CO2 content of the first CO2-enriched material recovered in step (iii) is at least 1.5:1, preferably at least 3:1, more preferably at least 10:1, where the CO2 content is determined as the mass loss above 200°C measured by TGA using a temperature trace in which the temperature is increased from room temperature to 800°C at a rate of 10°C / min and then decreased to room temperature at a rate of 10°C / min. Similarly, step (v) described herein is preferably carried out such that the ratio of the total carbon content of the further CO2-enriched material recovered in step (v) to the total carbon content of the first CO2-enriched material recovered in step (iii) is at least 1.05:1, preferably at least 1.1:1, more preferably at least 1.2:1.

[0105] Continuous carbon sequestration device In another aspect, the present invention provides an apparatus for continuous sequestration of carbon dioxide, comprising a particle size reduction apparatus having a housing, the housing comprising a solid feed inlet for introducing a solid feed into the particle size reduction apparatus and a gas inlet for introducing a gas stream into the particle size reduction apparatus; particle size selection means, preferably disposed within the housing and in fluid communication with the particle size reduction apparatus, comprising an outlet for removing solid material entrained in the gas stream from the particle size reduction apparatus, the particle size selection means being configured to separate material from the particle size reduction apparatus into at least one first portion and a second portion, the first portion having a different average particle size from the second portion, and configured to feed the first portion to the outlet and return the second portion to the particle size reduction apparatus; the gas supply inlet being fluidly connected to a flue gas outlet of a combustion plant or cement kiln, and the solid material removal outlet being connected to a wetting device configured to increase the moisture content of the solid material, preferably configured to increase the moisture content of the solid material by spraying an aqueous composition, preferably water, onto the solid material.

[0106] The wetting device may be configured to increase the moisture content of the solid material removed through the outlet of the particle size reduction device while the solid material is entrained in the gas stream or after it has been separated from the gas stream.

[0107] The wetting device preferably comprises one or more spray nozzles configured to spray an aqueous composition, such as water, onto the solid material after it has been removed via the solid material removal outlet.

[0108] The particle size selector is preferably an air classifier. The particle size reducer is preferably as described elsewhere herein, in particular a vertical roller mill. The particle size reducer is configured to reduce the particle size of the solid feedstock. The particle size reducer's zone where particle size reduction occurs is in fluid communication with a gas inlet. The solid feedstock inlet and the gas inlet may be the same (e.g., to allow for the use of a gas stream carrying the solid feedstock). [Example]

[0109] Example 1 A specific implementation of the process according to the invention is shown in Figure 1 and is described below. This example relates to a method according to the invention for producing a CO2-enriched material, in which step (iii) of the method is carried out by grinding in an air classifying mill, followed by a further CO2-enrichment treatment step (v) which comprises storing the CO2-enriched material in a vessel under a continuous flow (bubbling) of exhaust gas.

[0110] First, solid raw materials (e.g., aluminosilicate, fly ash, steel slag, natural pozzolana, volcanic rock, clay, or glass) are fed through the feed inlet (1) into the feed hopper (2). Between the feed inlet (1) and the feed hopper (2), a continuous mechanical crushing step (e.g., using a hammer mill) followed by an optional step (not shown) of removing oversized material by screening can be performed. The raw materials fed into the feed hopper have a D95 (mass basis, measured by sieve analysis) of less than 4 mm. The raw materials are transferred via the screw auger (3) to a continuous mill (vertical roller mill with an integrated air classifier) ​​equipped with a classifier (4). The mill is equipped with a dynamic swirl cage classifier. Exhaust gas enters the process through the inlet (5) at a temperature ranging from 150 to 200 °C. The exhaust gas passes through a cooler (6) and is cooled to below 100°C by heat exchange with ambient air before entering a first gas-liquid separator (7), where the water content of the exhaust gas is reduced. The feedstock from the screw auger (3) is then milled in a continuous mill (4), using the exhaust gas exiting the gas-liquid separator (7) to drive an air classifier mill. A cooled glycol loop (8), equipped with an air-cooled heat exchange unit (9), a surge tank (10), and a glycol pump (11), controls any heat generated during the milling process. The classifier continuously returns a portion of the CO2-enriched material to the continuous mill (4) for further milling. The portion of the CO2-enriched material passing through the classifier, with a particle size characterized by a D50 in the range of 20-30 microns, is carried by the exhaust gas stream to a solid-gas separator (12) (dust collector). The CO2-enriched material is sent from the dust collector via a screw auger (14) to a bubbling tower (13) for further CO2 enrichment outside the mill. The screw auger is equipped with a spray bar (20) to increase the surface moisture, so that the overall moisture content of the material for further CO2 enrichment is in the range of 12-15% by weight. The exhaust gas used in the bubbling tower (13) comes from the first gas-liquid separator (7) and passes through a compressor (15), a second cooler (16), and a second gas-liquid separator (17). The residence time of the CO2-enriched material in the bubbling tower is at least one hour. The CO2-enriched material is then stored in a storage silo (18) and discharged as needed.The exhaust gases exit the process through exhaust gas outlet (19) and are ultimately collected for further processing or vented to the atmosphere.

[0111] Example 2 The process of Example 1 is carried out, and instead of a bubbling tower, a gently stirred tank or silo containing the exhaust gas atmosphere is used for further CO2 enrichment processing outside the mill.

[0112] Example 3 The process of Example 1 or 2 is carried out, and a preconditioning step is carried out in which raw material having a D95 (by mass as measured by sieve analysis) of less than 4 mm (i.e., after an optional crushing step if the raw material is too large) is fed into a gently stirred tank or silo containing an exhaust gas atmosphere.

[0113] Example 4 A specific implementation of the process according to the present invention is shown in Figure 2 and described below. First, solid raw materials (e.g., aluminosilicate, fly ash, steel slag, natural pozzolana, volcanic rock, clay, or glass) are fed through a feed inlet (1) into a feed hopper (2). Between the feed inlet (1) and the feed hopper (2), a continuous mechanical crushing step (e.g., using a hammer mill) can be performed, followed by an optional step (not shown) for removing oversized material by screening. The raw materials fed into the feed hopper have a D95 (mass basis, measured by sieve analysis) of less than 4 mm. The raw materials are transferred via a screw auger (3) to a continuous mill (vertical roller mill with an integrated air classifier) ​​equipped with a classifier (4). The mill is equipped with a dynamic swirl cage classifier. Exhaust gas enters the process through an inlet (5) at a temperature ranging from 150 to 200 °C. The flue gas is split into two parts: a first part, which is mixed with 15-25% ambient air by volume and fed to the mill, and a second part, which passes through a cooler (6), which exchanges heat with ambient air to reduce the temperature of the flue gas to below 100°C without mixing with the air. The cooled second part then enters a first gas-liquid separator (7), which reduces the water content of the flue gas. The feedstock from the screw auger (3) is then milled in a continuous mill (4), using the flue gas exiting the gas-liquid separator (7) to drive an air classifier mill. A cooled glycol loop (8), comprising an air-cooled heat exchange unit (9), a surge tank (10), and a glycol pump (11), controls any heat generated during the milling process. The classifier continuously returns a portion of the CO2-enriched material to the continuous mill (4) for further milling. A portion of the CO2-enriched material passing through the classifier has a particle size characterized by a D50 in the range of 20-30 microns and is carried by the exhaust gas stream to a solid-gas separator (12) (dust collector). From the dust collector, the CO2-enriched material is sent via a screw auger (14) to a bubbling tower (13) for further CO2-enrichment processing outside the mill.

[0114] The screw auger is equipped with a spray bar (20) to increase the surface moisture, resulting in an overall moisture content of the material for further CO2 enrichment processing in the range of 12-15% by weight. The exhaust gas used in the bubbling tower (13) originates from the first gas-liquid separator (7) and passes through a compressor (15), a second cooler (16), and a second gas-liquid separator (17). The residence time of the CO2-enriched material in the bubbling tower is at least one hour. The CO2-enriched material is then stored in a storage silo (18) and discharged as needed. The exhaust gas exits the process through the exhaust gas outlet (19) and is ultimately collected for further processing or discharged to the atmosphere.

[0115] Example 5 The effects of solid-phase moisture content and second carbon-rich gas humidity on the carbonation efficiency of basic oxygen furnace slag (BOF) were investigated. BOF was ball-milled in a fossil fuel flue gas atmosphere (4% CO2 by volume, 100% RH; "First Treatment") to a D50 in the range of 20-30 microns. The milled material was placed in a temperature-controlled vessel under continuous flue gas flow (4% CO2 by volume, temperature and humidity controlled as per the table below; "Second Treatment"). No agitation was performed. Particle size and moisture content were measured according to the methods previously described herein. CO2 uptake was measured by comparing the CO2 content after the first CO2-enrichment treatment but before the second CO2-enrichment treatment to the CO2 content after the second CO2-enrichment treatment, which was determined as the mass loss above 200°C as measured by TGA using a temperature trace in which the temperature was increased from room temperature to 800°C at a rate of 10°C / min and then decreased to room temperature at a rate of 10°C / min. All parameters not stated were held constant.

[0116] [Table 1]

[0117] Similar tests were carried out at a flue gas temperature of 60°C and the carbonation efficiency of the second treatment (measured by CO2 uptake) was found to be similar to that achieved at 80°C.

[0118] Example 6 The effect of temperature on the carbonation efficiency of shale was investigated. Shale was milled in a fossil fuel flue gas atmosphere (4% CO2 by volume). CO2 uptake was determined as the mass loss above 200 °C, measured by TGA, using a temperature trajectory in which the temperature was increased from room temperature to 800 °C at a rate of 10 °C / min, then decreased to room temperature at a rate of 10 °C / min. All parameters not specified were held constant.

[0119] [Table 2]

Claims

1. 1. A method for carbon sequestration, comprising: (i) providing a solid feedstock, the solid feedstock being a particulate material having a first moisture content; (ii) at least 1% by volume of CO ２ and at least 1% by volume of CO ２ providing a second carbon-rich gas comprising: (iii) subjecting the solid feedstock of step (i) to a particle size reduction operation in a particle size reduction device in the presence of the first carbon-rich gas of step (ii), ２ obtaining a first CO enriched material; ２ recovering the enriched material; (iv) the first CO ２ increasing the moisture content of the enriched material to a second moisture content greater than the first moisture content to provide a wetted CO ２ obtaining an enriched material; (v) the moistened CO ２ The enriched material is added to a solution containing at least 1% by volume of CO ２ and contacting the second carbon-rich gas containing ２ The second CO ２ Obtaining the enriched material and ２ and recovering the enriched material.

2. The wetted CO ２ The enriched material is ２ 10. The method of claim 1, wherein the water content is maintained at or above the second water content throughout the enrichment process.

3. Step (iv) comprises adding an aqueous composition, such as water, to the first CO ２ 3. The method of claim 1 or 2, comprising spraying the enriched material.

4. Step (ii) is (ii) a at least 1% by volume of CO ２ providing a gas stream having a temperature above 120°C, the gas stream being preferably a flue gas or a cement kiln exhaust gas; (ii)b. dividing the gas stream of step (i)a. into a first portion and a second portion; (ii)c. cooling the first portion, the step comprising mixing the first portion with air, thereby obtaining the first carbon-rich gas; (ii)d cooling the second portion, thereby obtaining the second carbon-rich gas; the first carbon-rich gas CO ２ the second carbon-rich gas has a CO content of ２ Lower than the content the temperature of the second carbon-rich gas is preferably less than 100°C; 4. The method of claim 1, wherein steps (ii)c and (ii)d each optionally comprise adjusting the humidity of the gas.

5. In step (ii), at least 1 vol. % CO ２ 4. The method of claim 1, wherein preparing a second carbon-rich gas comprising: recovering the gas from the particle size reduction apparatus in step (iii), optionally after adjusting a humidity of the gas; and preparing the gas to form at least a portion of the second carbon-rich gas in step (v).

6. Step (ii) comprises providing a hot combustion exhaust gas or cement kiln exhaust gas having a temperature above 120°C; and cooling the hot exhaust gas to a temperature below 100°C, wherein the cooled exhaust gas is subjected to a gas-liquid separation step, and the liquid is collected; and in step (iv), the first CO ２ To increase the moisture content of the enriched material, preferably said first CO ２ The method according to any one of claims 1 to 5, which is applied by spraying onto the enriched material.

7. In step (v), the second CO ２ Recovering the enriched material optionally includes a deagglomeration step, and ２ D50 of the enriched material and the second CO recovered in step (v). ２ 7. The method according to any one of claims 1 to 6, wherein the ratio of the enriched material to D50 is in the range of 0.8 to 1.2, preferably in the range of 0.9 to 1.1, more preferably in the range of 0.95 to 1.

05.

8. The further CO of step (v) ２ The enrichment process is The wetted CO ２ placing the enriched material in a holding means or container in contact with said second carbon-rich gas, preferably under a continuous flow of second carbon-rich gas, said contacting preferably occurring for at least 15 minutes, at least 30 minutes, or at least 1 hour; The wetted CO ２ storing the enriched material in contact with the second carbon-rich gas, preferably in an airtight container, wherein the storage is preferably for at least 15 minutes, at least 30 minutes, or at least 1 hour; The wetted CO ２ feeding the enriched material to a fluidized bed maintained using said second carbon-rich gas; The optionally wetted CO ２ contacting the enriched material with the second carbon-rich gas in a reactor comprising a substantially airtight hollow housing and mechanical agitation means configured to contact the solid material during operation, such that an agitated bed of solid material forms in the reactor during operation; and / or the humidified CO entrained in the second carbon-rich gas. ２ A method according to any one of claims 1 to 7, comprising passing the gas stream containing the enriched material through a catalyst bed one or more times.

9. The first moisture content is less than 8 wt. % (based on the total weight of the solid feedstock) and the second moisture content is greater than 10 wt. % (based on the total weight of the wetted CO ２ 9. The method according to claim 1, wherein the total weight of the enriched material is 0.1 wt.

10. The second water content is less than 35% by weight (the moistened CO ２ % by weight of the wetted CO ２ % by weight of the wetted CO ２ 10. The method of claim 9, wherein the total weight of the enriched material is 0.1 wt.

11. 11. The method of any one of claims 1 to 10, wherein the solid feedstock is maintained at a moisture content less than or equal to the first moisture content throughout the particle size reduction operation of step (iii).

12. 12. A process according to any one of claims 1 to 11, wherein step (iii) is carried out at a temperature below 120°C, preferably below 100°C, preferably below 90°C, more preferably below 85°C, and step (v) is preferably carried out at a temperature in the range of 30 to 85°C, preferably 30 to 55°C, most preferably 35 to 50°C, for example 35 to 45°C or about 40°C.

13. 13. The method according to any one of claims 1 to 12, wherein the particle size reduction operation of step (iii) is carried out by subjecting the solid feedstock of step (i) to milling, preferably ball milling, roller milling, basket milling, hammer milling, rotor-stator milling, pin milling, jet milling and / or rod milling, preferably roller milling, in the presence of the first carbon-rich gas.

14. 14. The method of claim 13, wherein step (iii) is carried out by a mill with an integral air classifier or by a mill with an air classifier located downstream of said mill, and wherein the gas flow through said air classifier comprises, preferably consists of, said second carbon-rich gas, and said gas flows from said mill to said air classifier.

15. Step (iv) is a further step of step (v) ２ Before being subjected to the enrichment treatment, the wetted CO ２ 15. The method of any one of claims 1 to 14, further comprising the step of deagglomerating the enriched material.

16. The first CO recovered in step (iii) ２ the enriched material and the second CO recovered in step (v). ２ 16. The method of any one of claims 1 to 15, wherein the enriched materials each have a D50 in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 40 μm, more preferably in the range of 1 to 40 μm, and most preferably in the range of 5 to 40 μm.

17. The first CO recovered in step (iii) ２ D50 of the enriched material and the second CO recovered in step (v). ２ 17. The method according to any one of the preceding claims, preferably claim 16, wherein the ratio of the enriched material to D50 is in the range of 0.8 to 1.2, preferably in the range of 0.9 to 1.1, more preferably in the range of 0.95 to 1.05.

Images