Method and apparatus for removing carbon dioxide from a gas

Abstract

This application discloses a method and apparatus for removing carbon dioxide from a gas. In one example, the apparatus comprises a vessel to receive a solution, a gas-liquid contactor configured to diffuse a gas or gas mixture into the solution, and a draft tube within the vessel configured to direct a flow of the diffused gas or gas mixture. An impeller circulates the diffused gas or gas mixture in the solution for a period of time sufficient to produce one or more carbon species and is configured to create a down draft which draws a flow of bubbles downward through the draft tube and upward along a circulatory path outside of the draft tube so as to promote mixing of bubbles of the gas or gas mixture with the solution in order to produce the carbon species. The apparatus further comprises a packing material disposed on the circulatory path so as to facilitate contact of the gas or gas mixture with the solution.

Description

Method and apparatus for removing carbon dioxide from a gas Technical Field

[0001] The present disclosure relates to a method and apparatus for removing carbon dioxide from a gas.Background

[0002] Gas from power plants, industrial plants, refineries and so forth are a major source of greenhouse gases, in particular carbon dioxide. There are several chemical processes and scrubbers which are routinely used to treat gas to remove pollutants such as particulates, heavy metal compounds, nitrogen oxides and sulphur oxides to comply with regulations for environmental emissions control. However, there is an ongoing need for technologies directed to methods and systems for capture and storage of carbon dioxide that are economically viable. Additionally, it would be advantageous to convert the massive volume of carbon dioxide being discharged into the atmosphere into multiple by-products to avoid the market glut and disposal problems which might arise if only one product was produced.

[0003] One commercially proven process for the recovery of carbon dioxide from gas uses commercial absorbents comprising monoethanolamine (MEA) and other primary amines. These absorbents are capable of recovering 85-95% of the carbon dioxide in flue gas and produce a 99.95+% pure carbon dioxide product when regenerated.However, these absorbents require regular regeneration which has an energy cost associated therewith, and the absorbents are subject to corrosion and solvent degradation problems over time.

[0004] There is therefore a need for alternative or improved methods and systems for removing carbon dioxide from gases and / or producing one or more commercially useful products from a carbon capture process.

[0005] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.Summary

[0006] A first aspect of the present disclosure provides an apparatus for removing carbon dioxide from a gas, the apparatus comprising: a vessel configured to receive a solution and having a gas inlet to receive a gas or a mixture of gas and ammonia; a gasliquid contactor connected to the second inlet and configured to diffuse said gas or gas mixture into the solution received in the vessel; a draft tube within the vessel to direct flow of the diffused gas or gas mixture; an impeller configured to circulate the diffused gas or gas mixture in the solution for a period of time sufficient to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate; wherein the gas-liquid contactor is disposed in an upper portion of the vessel and connected to the draft tube which is disposed below the gas-liquid contactor; wherein the impeller is configured to create a down draft which draws a flow of bubbles downward through the draft tube and along a circulatory path for bubbles of the gas or gas mixture in said solution for a period of time sufficient to produce carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate; and wherein the apparatus further comprises a packing material disposed on the circulatory path of the bubbles so as to facilitate contact of the gas or gas mixture with the solution.

[0007] A second aspect of the present disclosure provides an apparatus for removing carbon dioxide from a gas, the apparatus comprising: a vessel configured to receive a solution and having a gas inlet to receive a gas or a mixture of gas and ammonia; a hollow perforated annulus connected to the gas inlet and configured to diffuse said gas or gas mixture into the solution received in the vessel; a draft tube extending downward from the hollow perforated annulus for directing a flow of the diffused gas or gas mixture; an impeller to circulate the diffused gas or gas mixture in the solutionfor a period of time sufficient to produce one or more carbon species (e.g. carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate); wherein the impeller is configured to create a down draft which draws a flow of bubbles downward through the draft tube and upward along a circulatory path outside of the draft tube so as to promote mixing of bubbles of the gas or gas mixture with the solution in order to produce the carbon species; and wherein the apparatus further comprises a packing material disposed between outer walls of the draft tube and inner walls of the vessel so as to facilitate contact of the gas or gas mixture with the solution when the bubbles travel on the circulatory path.

[0008] A third aspect of the present disclosure provides a method of removing carbon dioxide from a gas, the method comprising: a) providing a solution in a vessel and b) diffusing a gas or a mixture of gas and ammonia through a gas-liquid contactor into the solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate; wherein a draft tube is supported within the vessel and the gas-liquid contactor comprises a hollow perforated annulus disposed in an upper portion of the vessel above the draft tube and a skirt extends downwardly from the hollow perforated annulus and connects with the draft tube; wherein the method comprises using an impeller to create a down draft which draws a flow of gas or gas mixture bubbles downward through the draft tube and along a circulatory path to disperse the bubbles of the gas or gas mixture in said solution for a period of time sufficient to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate;and wherein a packing material is disposed on the circulatory path of the bubbles so as to facilitate contact of the gas or gas mixture with the solution.

[0009] A fourth aspect of the present disclosure provides a method of removing carbon dioxide from a gas, the method comprising: diffusing a gas or mixture of gas and ammonia into an ammoniated solution under conditions effective to produce an ammonium carbamate containing solution.

[0010] Further aspects and features of the present disclosure are provided in the following description and the appended claims.Brief Description of Drawings

[0011] Examples of the present disclosure will now be described, by way of nonlimiting example only, with reference to the accompanying drawings, in which:

[0012] Fig. 1 A is a schematic diagram showing a method and apparatus according to an example of the present application.

[0013] Fig. IB is a schematic diagram showing a method and apparatus according to another example of the present application.

[0014] Figs. 2A shows an example of an apparatus according to the present application, while Figs. 2B and 2C show internal cross sections of the apparatus.

[0015] Fig. 2D shows a variation of the apparatus of Fig. 2A, in which ammonia is not mixed with gas at the gas inlet at the top of the apparatus, but instead introduced into the solution via a solution recycle path.

[0016] Figs. 3 shows an example of an assembly comprising a liquid gas contactor according to the present application, while Figs. 4 and 5 cross sections of the assembly.

[0017] Fig. 6 is a schematic diagram showing an example of a perforated annulus.

[0018] Fig. 7A is a three dimensional rendering of a perforated annulus; while Fig. 7B is a cross section of the annulus and skrit in the vertical direction.

[0019] Fig. 8 is a schematic diagram showing laminar flow around a perforated annulus.

[0020] Figs. 9A to 9H show examples of a particular type of structured packing.

[0021] Fig. 10 shows the exterior of an apparatus according to an example of the present application, including pipes for recirculating solution.

[0022] Fig. 11 A shows an example bubble dispersion when the impeller speed is below a threshold value and Fig. 1 IB shows an example bubble dispersion when the impeller speed is above a threshold value.

[0023] Figs. 12(a) to 12(f) show examples of different positions for the packing material in the vessel.

[0024] Fig. 13 is a table showing reaction time (carbon dioxide absorption time) for no packing material and two different packing materials at various impeller speeds.

[0025] Fig. 14 is a table showing the percentage reduction in reaction time (carbon dioxide absorption time) for two designs of packing material at various positions compared to an apparatus with no packing material.

[0026] Fig. 15 is a table showing the percentage reduction in reaction time (carbon dioxide absorption time) when a cap is added to the top of the vessel at different impeller speeds.

[0027] Fig 16A is a schematic view of an apparatus used to test reaction time when gas is contacted with an ammoniated solution.

[0028] Fig. 16B is a schematic view of an apparatus which is the same as Fig. 16A, but which also had a packing material disposed in the vessel.

[0029] Fig. 17 is a table showing the results of an experiment conductd with the apparatus of Fig. 16A and 16B using pure carbon dioxide as the gas.

[0030] Fig. 18 is a table showing the results of an experiment conductd with the apparatus of Fig. 16A and 16B using a mixture of carbon dioxide and nitrogen as the gas.

[0031] Fig 19 is a diagram showing different heights of packing material.

[0032] Fig. 20 is a diagram showing different configurations of packing material including various heights with and without gaps.

[0033] Fig. 21 is a graph showing variation in solution pH against time for different packing configurations.

[0034] Fig. 22 is a graph showing variation in solution tempereature against time for different packing configurations.Description of Embodiments

[0035] Throughout this specification, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e. one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms "a", "an" and "the" include plural aspects unless the context clearly dictates otherwise. For example, reference to "a" includes a single as well as two or more; reference to "an" includes a single as well as two or more; reference to "the" includes a single as well as two or more and so forth.

[0036] Each example of the present disclosure described herein is to be applied mutatis mutandis to each and every other example unless specifically stated otherwise. The present disclosure is not to be limited in scope by the specific examples described herein, which are intended for the purpose of exemplification only. Functionally-equivalent products, compositions and methods are clearly within the scope of the disclosure as described herein. The term "and / or", e.g., "X and / or Y" shall be understood to mean either "X and Y" or "X or Y" and shall be taken to provide explicit support for both meanings or for either meaning.

[0037] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a statedelement, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The term "includes" means includes but not limited to, the term "including" means including but not limited to. The term "based on" means based at least in part on. The term "number" means any natural number equal to or greater than one.

[0038] REMOVAL OF CARBON DIOXIDE FROM A GAS

[0039] The present application is directed to a method, system and apparatus for removing carbon dioxide from a gas. In some examples, the gas may be an exhaust gas arising from industrial or combustion processes. However, the present application is not limited there to and in other examples, the gas may be any gas or gaseous mixture which includes carbon dioxide. For example, the gas may be supplied in containers, supplied via a pipeline, exhausted to the atmosphere via a pipe or supplied or captured by any other means. In some examples, the gas may be a flue gas, which is a gas exiting to the atmosphere via a pipe for conveying exhaust gases produced by industrial or combustion processes. In still other examples, the gas may be air containing carbon dioxide which is air captured from the environment. In some examples, the gas may be combustion exhaust gas produced at power plants fuelled by fossil fuels, such as coal, oil and gas. In other examples the gas may be a gas containing carbon dioxide produced by other industrial processes such as cement and lime production, steel production, incinerators, and the process furnaces in large refineries, petrochemical and chemical plants, or an exhaust gas from various types of engines including, but not limited to, diesel engines, combustion engines, and gas-turbine engines.

[0040] The composition of the gas depends on the source of the gas and will depend on a combustion fuel or a type of industrial process which generated the gas. In some examples, the gas may comprise one or more gases selected from the group comprising nitrogen, carbon dioxide, carbon monoxide, water vapour, oxygen, hydrocarbons, and pollutants, such as particulate matter, nitrogen oxides (NOx) and sulphur oxides (SOx).

[0041] According to one example of the present disclosure, the method of removing carbon dioxide from the gas comprises:diffusing a gas or a mixture of gas and ammonia into a solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate.

[0042] According to another example of the present disclosure, the method of removing carbon dioxide from the gas comprises:a) providing a solution in a vessel; andb) diffusing a gas or a mixture of gas and ammonia through a gas-liquid contactor into the solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate.

[0043] In the above two examples, the solution may be an ammoniated solution. For instance, solution may be recycled from the vessel and introduced back into the vessel with added ammonia. In some examples, a flow of ammonia may be introduced into a flow of gas to form a mixed gas stream comprising a mixture of gas and ammonia, and the mixed gas stream may be diffused through the gas-liquid contactor.

[0044] Fig. 1 A is a schematic diagram showing how a flow of ammonia 10 is introduced to a flow of gas 20 to form a gas mixture 40 which is diffused into a solution 50 in an apparatus 100. The flows of ammonia 10 and gas 20 may be combined and mixed by a mixing element 30, such as a venturi. In some examples the ammonia may be humidified ammonia. The gas mixture 40 is diffused into the solution by a gas-liquid contactor 140 and reacts with the solution in the vessel to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate. Here and elsewherein the specification, unless context demands otherwise, the term “gas mixture” refers to a mixture of the gas to be treated and ammonia 10.

[0045] Fig. IB is a schematic diagram showing an alternative arrangement in which a flow of gas 20 is diffused into an ammoniated solution 50 in an apparatus 100. The gas may be diffused into the solution by a gas-liquid contactor 140 and reacts with the ammoniated solution in the vessel to produce one or more of carbonic acid, carbonate,bicarbonate, carbamic acid and / or carbamate. The principle of Fig. IB is similar to Fig.1 A, except that instead of mixing ammonia with the gas stream before entry into the vessel, the solution in the vessel is ammoniated by other means.

[0046] In the example shown in dotted lines in Fig. IB, a portion of the solution exiting the vessel is recycled by directing a portion of the recycled solution 122 on a recyle path that re-introduces the solution to the vessel. For instance, the recycled solution may be pumped to a sprinkler system in the headspace of the vessel to sprinkle the recycled solution into the vessel. Ammonia gas may be added to the recycled solution on recycle path as shown by reference numeral 128. In other examples, there may be a separate inlet for introducing ammonia to the solution in the vessel, or the solution may be ammoniated prior to introduction to the vessel, e.g. through a hatch at the top. It is also possible to combine the approaches of both Fig. 1 A and Fig. IB so that ammonia is introduced into a stream of gas 20 via mixing element 30 so that a mixture of gas and ammonia is diffused into the solution, and by adding ammonia to a solution recycle path 122 or by other means.

[0047] Through the processes shown in Fig. 1 A and Fig. IB, the carbon dioxide is removed from the gas and products including one or more carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate are produced. The carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate, which may be dissolved in the solution, can be retrieved through an outlet 60 of the vessel and used downstream to produce further products such as, but not limited to, limestone, urea, ammonium nitrate or fertilizers. In this way the process both removes carbon dioxide, which would otherwise be released into the atmosphere, and produces commercially valuable products which can be sold or used in agricultural or industrial processes.

[0048] The apparatus 100 comprises a vessel 110 for receiving a solution and the gas or gas mixture. The vessel 110 may be referred to as a reaction vessel as it is used as a container for reacting the solution with the gas or gas mixture. In some examples the vessel may be formed of stainless steel. In some examples the vessel may have acircular cross section and / or a generally cylindrical shape. In some examples the vessel may extend vertically between a top end and a bottom end.

[0049] The apparatus 100 includes a vessel 110, a gas-liquid contactor 140 and various features including a draft tube 150, an impeller 160 and a packing material 190 for facilitating and promoting the reaction between the gas or gas mixture and the solution. These are described in more detail below with reference to Figs. 2 to 4.

[0050] CHEMICAL PROCESS

[0051] The method described herein comprises diffusing the gas or gas mixture comprising carbon dioxide or ammonia and carbon dioxide into the solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate.Gas mixture

[0052] The method may comprise introducing a flow of ammonia into a flow of the gas comprising carbon dioxide to form a gas mixture.

[0053] In one embodiment, the flow of the gas comprises a humidified flow of the gas (e.g. humidified flue gas). The term 'humidified' as use herein refers to a gas which is at least partially saturated with water vapour at pressure and temperature.

[0054] The temperature of the gas or gas mixture will depend on the source. For example, gas exiting a flue (e.g. flue gas) may have a temperature in the range of about 300 °C to about 800 °C, depending on the process by which the flue gas is produced, the length of the flue, and other factors as will be understood by those skilled in the art. In view of the advantages described herein provided by keeping the solution described herein at a relatively low temperature, it may be similarly beneficial to cool the gas or gas mixture prior to contacting it with the ammoniated solution.

[0055] Accordingly, prior to contacting the gas mixture with the solution (e.g. the ammoniated solution), the gas mixture may be cooled. In one embodiment, the gasmixture is cooled to less than about 40°C, preferably between about 30 to about 35°C. In one embodiment, the temperature differential between the cooled gas mixture and solution is less than about 35°C, 30°C, 25°C, 20°C, 15°C or 10°C.

[0056] Alternatively, prior to contacting the gas with ammonia, the gas may be cooled. In one embodiment, the gas is cooled to less than about 40°C, preferably between about 30 to about 35°C. In one embodiment, the temperature differential between the cooled gas and solution is less than about 35°C, 30°C, 25°C, 20°C, 15°C or 10°C.

[0057] Cooling the gas or gas mixture may be achieved by expanding the gas or gas mixture through an expander. Additionally, or alternatively, cooling the gas or gas mixture may be achieved by passing the gas or gas mixture through one or more heat exchangers. The heat exchangers may be air-cooled heat exchangers or water-cooled heat exchangers.

[0058] Additionally, or alternatively, cooling the gas may be achieved by mixing the gas with a lower temperature gas. In one embodiment, cooling the gas may be achieved by the mixing of the gas with ammonia gas prior to contacting the gas mixture with the solution.

[0059] Advantageously, in some embodiments or examples, the ammonia in the resulting gas mixture will be absorbed and solubilized in the solution when the gas mixture is passed through the gas-liquid absorption zone, as described above.

[0060] In one embodiment, the gas mixture comprises between about 20% v / w / to about 40% v / v ammonia. The gas mixture may comprise at least about 20%, 25%, 30%, 35% or 40% v / v or more ammonia. The gas mixture may comprise less than about 40%, 35%, 30%, 25% or 20% v / v or less ammonia. The amount of ammonia in the gas mixture may be in a range provided by any two of these upper and / or lower values. The gas mixture may also comprise head space vapour described herein.

[0061] By mixing the gas (e.g. flue gas) with ammonia prior to contacting with the solution in the vessel, some of the carbon dioxide can initially react with the ammonia gas, which increases the removal rate. The unreacted ammonia in the gas mixture can then be absorbed / dissolved in the solution when the gas mixture is diffused therein, which in turn can react with the carbon dioxide containing gas to form the one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate.Solution

[0062] The solution 50 may be any solution which is able to ab sorb / dissolve the ammonia. The solution may be a liquid. In some examples the solution may be an aqueous solution. Such aqueous solutions may comprise any type of water (which may be referred to as a solvent) including but not limited to deionized water, ultrapure water, distilled water, municipal water, produced water, process water, brine, hypersaline water, or seawater, or a mixture thereof, which is capable ofab sorbing / dissolving the ammonia. When absorbed / dissolved in the solution, the ammonia may take the form of ammonium ions and / or dissolved molecular ammonia. Such a solution may also be referred to as an “ammoniated solution” which broadly refers to any type of solution containing ammonia.

[0063] The solution / ammoniated solution may be prepared by sparging the solvent (e.g. one or more types of water described above) with a source of ammonia, such as anhydrous ammonia gas, to produce an ammonium hydroxide solution. Alternatively, the ammoniated solution may be prepared by mixing an ammonium hydroxide solution and / or the solution comprising one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate described herein (e.g. some of the solution obtained from outlet 60 described herein is recycled back for use as the solution).

[0064] The amount of ammonia in the solution can vary. In one embodiment, concentration of ammonia in the solution may be between about 5% w / v to about 30% w / v. The concentration of ammonia in the solution may be at least about 5, 10, 15, 20, 25 or 30% w / v or more. The concentration of ammonia in the solution may be less thanabout 30, 25, 20, 15, 10 or 5% w / v or more. The concentration of ammonia in the solution may also be in a range provided by any two of these upper and / or lower values.

[0065] The pH of the solution can vary depending on the target species (e.g. whether or not carbamate, carbamic acid, carbonic acid, carbonate and or bicarbonate is being targeted). In one embodiment, the pH of the solution may be alkaline. For example, the pH of the solution may be between about 8 to about 12, between about 9 to about 11, or between 9.5 to about 10.5.

[0066] The temperature of the solution can similarly be varied depending on the target species. In one embodiment, the solution may be maintained at a temperature of less than 35°C. In one embodiment, the solution may be maintained at a temperature of between about 5°C to about 35°C. The solution may be maintained at a temperature (in °C) of at least about 5, 10, 15, 20, 25, 30 or 35. The solution may be maintained at a temperature (in °C) of less than about 35, 30, 25, 20, 15, 10 or 5. The temperature of the solution may be in a range provided by any two of these upper and / or lower values, for example between about 15°C to about 20°C. Such low temperatures can lower the partial pressure of ammonia present in the head space above the solution. Alternatively or additionally, the low temperature of the solution can increase the capacity of the solution to absorb / dissolved carbon dioxide from the gas or gas mixture and in some cases can also maintain the carbon dioxide in the solution as the one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate anions.Diffusing the gas or gas mixture into the solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate

[0067] The gas or gas mixture is diffused into the solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate. Each of these species may be produced in isolation or in various combinations, and in some cases may all be produced. Alternatively the method, apparatus and system described hereincan be tailored to promote the formation of one or more of these species over the other, for example produce a solution comprising large amounts of carbamate.

[0068] The carbamate may be present as ammonium carbamate. The carbonate may be present as ammonium carbonate. The bicarbonate may be present as ammonium bicarbonate.

[0069] It will be appreciated that contacting gas or gas mixture with the solution described herein to produce the carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate facilitates absorption of carbon dioxide in the solution. Absorption may be a physical absorption or chemisorption process.

[0070] In physical absorption processes, some of the carbon dioxide is dissolved in the ammonia gas of the gas mixture and / or the solution. The solubility of the dissolved carbon dioxide in the solution will be dependent, at least in part, on the temperature of the solution.

[0071] The primary chemisorption process relating to absorption of carbon dioxide in the gas mixture and / or solution can be described as follows via the formation of the preferred carbamate species:CO2 + 2NH3+ H2O NH4COONH2 (aq)

[0072] The formation of the carbonic acid, carbamic acid, carbamate and / or carbonate species can be described as follows:CO2 + NH3+ H2O (NH4)HCO3(aq)CO2+NH3H2NCOOH (aq)CO2 + 2NH3+ H2O (NH4)2CO3(aq)CO2 + H2O H2CO3(aq)

[0073] The concentration of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate in the solution can vary, depending on whether one or more of these species are being targeted for production.

[0074] If present, the concentration of carbonate in the solution may be between about 1% w / v to about 25% w / v. The concentration of carbonate in the solution (in % w / v) may be at least about 1, 2, 5, 8, 10, 12, 14, 16, 18, 20. The concentration of carbonate in the solution (in % w / v) may be less than about 20, 18, 16, 14, 12, 10, 8, 5, 2 or 1. The concentration of carbonate may be in range provided by any two of these upper and / or lower values.

[0075] If present, the concentration of bicarbonate in the solution may be between about 10% w / v to about 90% w / v. The concentration of bicarbonate in the solution (in % w / v) may be at least about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or more. The concentration of bicarbonate in the solution (in % w / v) may be less than about 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15 or less. The concentration of bicarbonate may be in range provided by any two of these upper and / or lower values.

[0076] If present, the concentration of carbonic acid in the solution may be between about 10% w / v to about 90% w / v. The concentration of carbonic acid in the solution (in % w / v) may be at least about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or more. The concentration of carbonic acid in the solution (in % w / v) may be less than about 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15 or less. The concentration of carbonic acid may be in range provided by any two of these upper and / or lower values.

[0077] If present, the concentration of carbamic acid in the solution may be between about 10% w / v to about 90% w / v. The concentration of carbamic acid in the solution (in % w / v) may be at least about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or more. The concentration of carbamic acid in the solution (in % w / v) may be less than about 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15 or less. Theconcentration of carbamic acid may be in range provided by any two of these upper and / or lower values.

[0078] If present, the concentration of carbamate in the solution may be between about 25% w / v to about 100% w / v. The concentration of carbamate in the solution (in % w / v) may be at least about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 or 95 or more. The concentration of carbamate in the solution (in % w / v) may be less than about 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30 or 25 or less. The concentration of carbamate may be in range provided by any two of these upper and / or lower values.

[0079] The gas or gas mixture may be diffused through a gas-liquid contactor described herein.

[0080] In some embodiments, at least some of the solution containing the carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate can be recycled for use as the solution at step b).Ammonium carbonate-containing solution

[0081] Ammonium carbamate is a precursor to urea, which is widely used in industry, including in fertilizers as a source of nitrogen. It is also an important raw material for the chemical industry. Ammonium carbamate is typically produced as part of the Bosch-Meiser process via the fast exothermic reaction of liquid ammonia with gaseous carbon dioxide at high temperatures (e.g. 160°C or more) and high pressures (e.g. 110 atm or more). Such operating conditions not only are energy intensive, but also produces vast quantities of carbon dioxide and consumes large amounts of fossil fuels. For example, the Bosch-Meiser process consumes 21-29 million kilojoules of energy and releases an average of 0.7-2.3 tonnes of carbon dioxide. Therefore, it is greatly attractive to develop alternative urea production technologies, directly using carbon dioxide already produced (e.g. flue gas).

[0082] As part of developing the vessel, apparatus and system described herein, the applicant has also surprisingly identified that by using water as the solvent in the solution, carbon dioxide can be removed from gas or gas mixture described herein and converted into ammonium carbamate.

[0083] According to another example of the present disclosure, the method of removing carbon dioxide from the gas comprises:diffusing the gas or a mixture of the gas and ammonia into a solution or an ammoniated solution under conditions effective to produce an ammonium carbamate-containing solution.

[0084] As used herein, the term “ammonium carbamate-containing solution” refers to an aqueous solution of ammonium carbamate containing at least a carbamate species (H2NCOCF) and one or more of the following species in various relative concentrations depending on at least the temperature and pH of the ammoniated solution: carbonate (CO3‘), bicarbonate (HCO3‘), ammonium (NH4+), hydroxide (OH") and / or protons (H+).

[0085] The concentration of ammonium carbamate in the ammonium carbamate-containing solution may be between about 25% w / v to about 100% w / v. The concentration of ammonium carbamate in the ammonium carbamate-containing solution (in % w / v) may be at least about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 or 95 or more. The concentration of ammonium carbamate in the ammonium carbamate-containing solution (in % w / v) may be less than about 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30 or 25 or less. The concentration of ammonium carbamate may be in range provided by any two of these upper and / or lower values.

[0086] The formation of ammonium carbamate over other species can be controlled by adjusting at least the temperature and / or pH of the ammoniated solution, including those described above in relation to the solution. For example, the pH of the ammoniated solution may between about 8 to about 12, between about 9 to about 11, or between 9.5 to about 10.5. For example, the ammoniated solution may be maintained at a temperature of less than 35°C, such as between about 5°C to about 35°C. Suchalkaline pH’s and / or low temperatures can result in the preferential formation of ammonium carbamate over other species.

[0087] In some embodiments, at least some of the ammonium-carbamate solution can be recycled for use as the ammoniated solution at step b).Urea production

[0088] The ammonium carbamate-containing solution can be processed into urea. For example, the ammonium carbamate-containing solution can be processed into urea using the second step of the Bosch-Meiser process, known as urea conversion, which is the slower endothermic decomposition of ammonium carbamate into urea and water.Fertilizer production

[0089] The solution comprising one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate species described herein (e.g. the ammonium carbonate-containing solution, ammonium bicarbonate-containing solution and / or ammonium carbamate-containing solution) can be processed using industrial processes / methods to convert them into one or more products, including for example fertilizers.

[0090] As described below, the applicant has also developed a system and apparatus which facilitates the above chemical processes and in certain implementations may provide quicker reaction time, more complete removal of the carbon dioxide and / or improved yield of the desired end products.

[0091] SYSTEM AND APPARA TUS

[0092] Fig. 2A shows an example of an exterior of an apparatus 100 for removing carbon dioxide from a gas, while Figs 2B and 2C are schematic cross-sections showing an interior of the apparatus.

[0093] The apparatus comprises a reaction vessel 110, as described above, for receiving a solution and into which gas or a mixture of gas and ammonia is to be diffused. The vessel 110 may extend vertically from a top end to a bottom end and may have one or more legs 112.

[0094] The vessel 110 is configured to receive a solution and has a gas inlet 130 for receiving a mixture of gas and ammonia. The vessel may have both a first inlet 120 (“solution inlet”) for receiving the solution and a second inlet 130 (“gas inlet”) for receiving the mixture of gas and ammonia. The solution inlet may be positioned at the top end of the vessel. In some examples the solution inlet may be a hatch in a lid of the vessel. In other examples the solution may be introduced by sprinklers inside a headspace of the vessel, a dedicated inlet pipe or other means. The gas inlet 130 may be a second inlet and may, for example, be a pipe for delivering the gas mixture into the vessel.

[0095] Referring to Figs. 2B and 2C, the apparatus 100 has a gas-liquid contactor 140 disposed within the vessel and in communication with the gas inlet 130. The gas-liquid contactor 140 is configured to diffuse the gas mixture into the solution 50 received in the vessel. In operation, the gas-liquid contactor 140 may be positioned below a surface level 52 of the solution in the vessel. The gas-liquid contactor 140 may take the form of a perforated annulus 142, an example of which is shown in further detail in Figs. 3 to 7.

[0096] The apparatus further comprises a draft tube 150 within the vessel for directing flow of the diffused gas mixture exiting the gas-liquid contactor 140. The draft tube is supported within the vessel and may extend downwardly from the gasliquid contactor 140. The gas-liquid contactor 140 may thus be disposed in an upper portion of the vessel and connected to the draft tube which is disposed below the gasliquid contactor. The apparatus also comprises an impeller 160 configured to circulate the diffused gas or gas mixture in the solution. The impeller may be an axial flow impeller. The impeller is operable to circulate the diffused gas mixture in the solution for a period of time sufficient to produce carbon species including one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate.

[0097] As shown by the arrows in Fig. 2C, the impeller 160 is configured to create a down draft 170 which draws a flow of bubbles of the gas mixture downward through the draft tube 150 and upward along a circulatory path 180 outside of the draft tube. This circulatory path promotes mixing of bubbles of the gas mixture with the solution in order to produce the carbon species. The downdraft and circulatory flow are further illustrated in Fig. 8. The down draft 170 is inside the draft tube 150 and is a down flow of the solution and bubbles 175 in the solution. The upward part of the circulatory path 180 is outside of the draft tube 150 and comprises the upward flow of solution and bubbles 175 floating upward outside of the draft tube.

[0098] Fig. 2D shows a variation of the apparatus, in which like reference numerals denote like parts to Figs. 2A to 2C. The apparatus of Fig. 2D differs in that the gas inlet 130 receives the gas 20 to be treated (a gas comprising carbon dioxide), but does not receive a mixture of gas and ammonia. Rather, ammonia 128 is introduced into the recycled solution path 124 which delivers recycled solution mixed with ammonia into the vessel via sprinklers in the headspace of the vessel. Otherwise, the apparatus operates as described above, except that the liquid-gas contactor and draft tube diffuse and direct the gas from the gas inlet 130, rather than a mixture of gas and ammonia. As will be understood by a person skilled in the art, it is possible to combine the approaches of Fig. 2A and Fig. 2D so that ammonia is introduced both by mixing ammonia with the flow of gas into the vessel and by injecting ammonia into a solution recycle path.

[0099] Referring to Figs. 3-8, the gas-liquid contactor 140 may comprise a hollow perforated annulus 142. The hollow perforated annulus 142 may be disposed in an upper portion of the vessel above the draft tube 150.

[0100] In some examples, a skirt 144 may extend downwardly from the hollow perforated annulus 142 to connect the annulus 142 with the draft tube 150. The skirt 144 may be fixedly attached to the annulus or integrally formed with the annulus. In some examples, the skirt 144 is fixedly attached (e.g. welded) to the draft tube or maybe integrally formed with the draft tube. In the illustrated example, the annulus 142, skirt 144 and draft tube 150 are formed as an integral piece.

[0101] Referring to Figs. 4 and 5, the hollow perforated annulus 142 is coupled to the gas or gas mixture inlet 130 and configured to diffuse the gas or gas mixture into the solution. As shown in Fig. 6 (which is a cross section from above) and Fig. 7A (which is a schematic perspective view from below), an inner wall 146 of the hollow perforated annulus may have a plurality of holes 148. During operation of the apparatus, the gas or gas mixture is diffused through the holes 148 and entrained by the flow of fluid generated by the impeller 160 to flow down through the draft tube. In some examples the holes may have a diameter of between 2mm and 10mm, and in some examples approximately 5mm. This produces a size of bubble which has been found to mix well and promote reaction in the solution to produce carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate. In some examples, there may be 20 or more holes and in some example 40 or more holes. The gas-liquid contactor (e.g. perforated annulus) may have a shield to deflect gas diffused through the holes in the downward direction. In some examples, the skirt 144 may have a portion 144 A which loops over the perforated annulus 142 and is arranged to deflect diffused gas downwards and / or to prevent the diffused gas from immediately rising to the surface of the solution. For example, the shield 144A may extend adjacent and over the holes 148 in the perforated annulus. An example is shown in Fig. 7B which is a cross section of the annulus and the skirt in the vertical direction.

[0102] In some examples, an outer wall 147 of the hollow perforated annulus 142 and / or skirt 144 is shaped to promote laminar flow of bubbles past the outer wall of the annulus on an upward portion of the circulatory path. Fig. 8 shows an example of this laminar flow. In order to promote the laminar flow, the hollow perforated annulus 142 may have an outer diameter which is larger than an outer diameter of draft tube 150. In some examples, as shown in Fig. 3, the skirt 144 may have a funnel shape which tapers from the larger outer diameter of the perforated annulus to the smaller diameter of the draft tube.

[0103] Referring to Figs 2B and 2C, a packing material 190 is disposed on the circulatory path of the bubbles so as to facilitate contact of the gas or gas mixture with the solution. The packing material may be disposed on the circulatory path 180. The packing material may for example be disposed between the outer walls of the draft tube and the inner walls of the vessel so as facilitate contact of the gas or gas mixture with the solution when the bubbles travel upward on the circulatory path 180.

[0104] The packing material may comprise one or more of: Structured Packing (e.g. Metal Gauze Packings, Mesh Packings, Plastic Packings); Saddles (e.g. Intalox saddles, IMTP saddles), Rings (e.g. Pall rings, Raschig rings, Lessing rings), Rotating Disc Contactors, etc. Providing structured packing on the circulatory path has been found to significantly improve the reaction rate.

[0105] The apparatus may comprise a mixer 134 (e.g. a venturi) for mixing the ammonia with the gas to form the gas mixture. The mixer may be positioned upstream of the second inlet 130.

[0106] The impeller 160 and / or the annulus 142 and draft tube 150 are movable vertically within the vessel 110 between a non-operating position and one or more operating positions. In this way by moving the impeller and / or annulus and draft tube the operating conditions may be varied. When in an operating position, the hollow perforated annulus is positioned below a surface of the solution 52 in the vessel. The impeller 160 comprises a shaft 162 and impeller blades or vanes 164. When in an operating position, the vanes or blades 164 of the impeller are positioned within the draft tube or below the draft tube.

[0107] The perforated annulus 142, skirt 144 and draft tube 150 may be part of an assembly 114 which enters the vessel 110 through a top end of the vessel, e.g. as shown in Figs 2A-2C. In the illustrated example, the impeller 160 has a fixed position relative to the vessel, while the assembly 114 is vertically movable. However, in other examples, the impeller could be vertically movable while the assembly is fixed, or both could be vertically movable relative to the vessel. For instance, while in the illustratedexample the draft tube 150 is supported in the vessel 110 from above by a vertically movable assembly 114, in other examples the draft tube may be supported by frame or structural elements connected to the vessel walls, while the impeller may be vertically movable.

[0108] The assembly 114 may be movable vertically between a non-operating position (shown in Fig. 2B) and an operating position (shown in Fig. 2C). The operating position is a position in which the impeller is operated to generate the circulatory flow down through the inside of the draft tube and up around the outside of the draft tube. In some examples, the impeller vanes or blades are at the bottom of the draft tube (as shown in Fig 2C), or just below the draft tube when the apparatus is in the operating position, as this provides a strong circulatory flow.

[0109] Referring to Fig. 3, the assembly 114 may comprise two or more pipes 130A, 130B which enter the top of the vessel and act as gas inlets for delivering the gas or the mixture of gas and ammonia to the perforated annulus. The pipes 130A, 130B may be in fluid communication with and receive the gas or gas mixture from a delivery pipe 132. The delivery pipe or channel 132 may receive a stream of gas 20 including carbon dioxide and include a mixing element 134 (e.g. venturi) for mixing the stream of gas 20 with a stream of ammonia 10 received through a side pipe or channel 136. The assembly may further comprise a motor 138 for moving the assembly vertically with respect to the vessel.

[0110] In use, the apparatus 100 may be used to perform a method of removing carbon dioxide from a gas by:a) providing a solution in a vessel; andb) diffusing the gas or a mixture of gas and ammonia through a gas-liquid contactor into the solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate.

[0111] The gas 20 may be compressed to a pressure between the range of about 5 psi to about 15 psi before being received by the apparatus (e.g. by receiving pipe 132). The gas may have a flow rate of 1-50 kg / hour. The ammonia may have a flow rate of 3-20 kg / hour.

[0112] As explained above, a draft tube 150 is supported within the vessel 110 and the gas-liquid contactor 140 may comprise a hollow perforated annulus 142, disposed in an upper portion of the vessel above the draft tube, while a skirt 144 may connect the hollow perforated annulus 142 with the draft tube 150.

[0113] The impeller 160 is used to create a down draft which draws a flow of gas or gas mixture bubbles downward through the draft tube and along a circulatory path 170 to disperse the bubbles of the gas or gas mixture in the solution for a period of time sufficient to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate. The packing material 190 is disposed on the circulatory path of the bubbles 180 so as to facilitate contact of the gas or gas mixture with the solution.

[0114] PACKING MATERIAL

[0115] The packing material may comprise one or more of: Structured Packing (e.g. Metal Gauze Packings, Mesh Packings, Plastic Packings); Saddles (e.g. Intalox saddles, IMTP saddles), Rings (e.g. Pall rings, Raschig rings, Lessing rings), Rotating Disc Contactors, etc. Providing packing material on the circulatory path has been found to significantly improve the reaction rate. The packing may be formed of a material which does not chemically react with, nor have a catalytic effect, on the solution or the gases diffused into the solution. Rather, the purpose of the packing material is to enhance the mixing of gas with liquid and thus improve the reaction rate.

[0116] In some examples, the packing material may be a structured packing.Structured packing is packing which comprises relatively larger pieces of material with holes, grooves, corrugation or other textured elements to provide an increased surface area, rather than many small separate pieces. The structured packing may providecontrolled flow paths which improve gas-liquid contact. The structured packing may, for example, be formed of corrugated sheets, gauze or knitted wire structures etc.Structured packing offers several advantages over loose or random packing. Compared to loose or random packing, structured packing is easier to install and has a defined shape and extent. For example, structured packing may have a defined bottom position, in contrast to loose packing which falls to the bottom of any container it is put in.Further, compared to loose packing, structured packing allows gas and liquid to move more evenly through the system, which improves contact between the gas and liquid phases and leads to better mass-transfer efficiency. Structured packing also creates less pressure drop, performs more consistently when scaled up, and stays stable during operation. In practice, structured packing is easier to remove, clean, and put back, which helps maintain reliable long-term performance and reduces maintenance effort.

[0117] In some examples, the structured packing may be of a type which comprises a body having an axis and a plurality of sheets, wherein adjacent sheets of the plurality of sheets define a curved fluid flow path that rotates around the axis as the sheets extend from one end of the body towards another end of the body. The structured packing may have a single axis or a plurality of axes around which the sheets define a curved flow path. Examples of structured packing of this type are shown in Figs. 9A to 9H. Further details of this type of structured packing are described in US Patent No. 11,602,726 which is incorporated herein by reference. It is being understood that this type of structured packing is just one example and other types of structured packing could be used.

[0118] The structured packing in Fig. 9A has a single twisted axis (one centre of rotation), while the structured packing shown in Fig. 9B has six independently rotating axes (6 centres of rotation). Figs. 9C and 9D show structured packing with eight and ten centres of rotation, respectively. Fig. 9E shows a structured packing with six centres of rotation, similar to Fig. 9B, but with four times the channel density. Figure 9F shows a structured packing with six centres of rotation, similar to Fig 9B, but a twist of 360 degrees or one full turn which results in a less dense structure.

[0119] The packing material 190 may include a portion disposed between an inner wall of the vessel 110 and an outer wall of the draft tube 150 as shown in Figs 2B and 2C. For example, there may be no packing material in the central passage defined by the draft tube, but rather packing material may be provided in an annular arrangement around the draft tube 150. In this way the bubbles are not obstructed when travelling downward through the draft tube, but the time that bubbles spend on the upward part of the circulatory path is increased thereby increasing the reaction rate. In some examples, there may be one or more apertures in the packing material to allow passage of probes as shown in Fig. 9G. In some examples, a portion of the packing material may be disposed within the draft tube. Fig. 9H shows an example of a packing material which comprises a first portion 190A which is to be disposed between the inner wall of the vessel and an outer wall of the draft tube, and a second portion 190B which is to be disposed within the draft tube and which may substantially occupy the whole width of the draft tube. In this way the centre of the draft tube is substantially filled with the packing material. In this way the packing material cuts across both the downward flow 170 and the upward flow 180 of the circulatory path thereby further promoting gas liquid contact and increasing the reaction rate. The packing material may include one or more apertures to allow passage of a shaft of the impeller and / or one or more probes. The packing material may include a portion disposed below a bottom end of the draft tube. This increases the reaction rate, by increasing the time that the bubbles spend to travel from the bottom to the top of the vessel.

[0120] The packing material has a height extending between an uppermost position and lowermost position of the packing material. In some examples the packing material may extend continuously between the uppermost position and the lowermost position. In other examples, the packing material may comprise several non-continuous sections with vertical gaps between the sections.

[0121] In some examples, the packing material has a height equal to at least 8% of a height of the vessel. In some examples there is a space between the lowermost portion of the packing material and the bottom of the vessel. In some examples the lowermost position of the packing material is at a height of at least 15% of the height of the vesselfrom the bottom of the vessel. In this way there is room for small vortexes to form and for the bubbles to disperse in the space between the bottom of the packing material and the bottom of the vessel.

[0122] In some examples, the uppermost position of the packing material is at a height of between 30% and 60% of a height of the vessel.

[0123] The apparatus may be configured to drive the impeller at a speed of at least 300 revolutions per minute (rpm). When performing the method to remove carbon dioxide from the gas or gas mixture, the impeller may be driven at this speed or greater. In experiments it was found that at least this speed was needed to effectively promote mixing of the gas and fluid and create the desired circulatory path when packing material is present.

[0124] Referring back to Figs. 2A-2C, the apparatus may comprise a first outlet 126 for outlet of the end products of the reaction (e.g. carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate. This first outlet corresponds to outlet 60 in Fig. 1 and may be at a lower portion of the vessel. The apparatus may comprise a second outlet 122 at a lower portion of the vessel for recirculating solution to another portion of the vessel (e.g. to an upper portion of the vessel) via a recycled solution line 124.

[0125] In some examples ammonia may injected into recirculated solution. For example, the outlet 126 may include a side channel for recycling a portion of the solution via a second re-circulation line 129 (shown in Fig. 10). The second recirculation line 129 may go through a heat exchanger 137 (shown in Fig. 10) to a recirculation manifold and sprinklers or another delivery mechanism at the top of the vessel. Ammonia may be injected into the second recirculation line 129 through an ammonia delivery line 128. In this way, at a beginning of the process ammonia gas 10 may be injected into the solution in the vessel through the ammonia inlet 136 at the top and ammonia may be injected into the recirculated solution which is delivered by the sprinklers. For example, a source of ammonia may be arranged to deliver ammonia to the ammonia inlet 136 at the top where it mixes via the mixer 134 with the gas 20comprising carbon dioxide, and a source of ammonia may be arranged to deliver ammonia to a portion of the solution which is diverted from the outlet 126 to second recirculation line 129 through heat exchanger 137 to the re-circulation manifold and sprinklers 116 at the top. Meanwhile, the first re-circulation line 124 may deliver recirculated solution which is not mixed with ammonia to the the re-circulation manifold and sprinklers 116 at the top. In some examples outlets 122 and 126 may be below the lowermost position of the packing material 190.

[0126] As mentioned above, the apparatus may comprise one or more sprinklers 116 at an upper portion of the vessel for spraying the recirculated solution into the vessel. In some examples, a pump may be provided for circulating the solution extracted from the recirculation outlet 122 at the bottom portion of the vessel, via a recirculation line 124 back into the vessel through the sprinklers 116 at the top.

[0127] Fig. 10 shows an example of the apparatus 100 in further detail, in which the like reference numerals indicate the same parts as in Fig. 2A. The apparatus has a pump 139 for pumping recirculated solution from the outlet 122 at the bottom of the vessel along a first re-circulation path 124 to the re-circulation manifold and sprinklers 116 as the top of the vessel. In addition the outlet 126 for end products may also be used for recirculating a portion of the solution. A branch of the outlet 126 is injected with ammonia at a second ammonia inlet 128 and then routed on a second re-circulatioon path 129 through a heat exchanger 137 on the outside of the vessel and to the re-circulation manifold and sprinklers 116 as the top of the vessel. In this way once the desired end products have been extracted, heat can be extracted and the solution recirculated with additional ammonia. Unreacted vapours from the headspace of the vessel may be allowed to escape through an exhaust pipe 135. Exhaust pipe 135 may be connected to a scrubber to capture any escaped gas in a separate vessel before the exhaust gas is vented to the atmosphere. Additionally or alternatively, vapours such as water vapour, escaped carbon dioxide and ammonia from the headspace at the top of the vessel may be recirculated via line 131 into the gas input line 132 for delivery back through inlet 130 at the top of the vessel.

[0128] EXPERIMENTAL INVESTIGATIONS

[0129] Experiments were conducted to assess the impact of impeller speed and the use of packing material on the reaction.

[0130] In a first experiment, a lab rig was set up to investigate the fluid and reaction dynamics of a simplified version of the apparatus. In addition, a theoretical model of the apparatus design and fluid dynamics was constructed using ANSYS. The lab rig comprised a vessel of height 425mm and diameter 200mm, with a draft tube extending from 140mm to 240mm. An impeller was provided co-centric with the draft tube and extended down to height 170mm. The vessel was filled with solution to height 310mm.

[0131] Initially, water was used as the solution and the impeller was operated to generate one or more vortexes in the solution and air bubbles travelling on the circulatory path. It was found that a speed of at least 2,400 rpm was needed to generate the desired circulatory flow. When the impeller speed was below this threshold, the downforce was not large enough to overcome the buoyancy force of the bubbles. As a result, at lower speeds, the generated bubbles floated upward through the draft tube and the vessel above the draft tube to the surface of the solution.

[0132] Fig. 11 A shows the air dispersion (i.e. bubble density or volume fraction of air) when the impeller speed is below 2,400 rpm. It can be seen the bubbles all float upwards. Fig. 1 IB shows the air dispersion when the impeller speed is at or above 2,400 rpm threshold.

[0133] As shown in Fig. 1 IB, when the impeller speed was at or above the 2,400 rpm threshold, bubbles are dispersed into the annular region outside of the draft tube.Specifically, bubbles start to be entrained into the solution by the downdraft generated by the impeller, travel to the bottom of the draft tube and then float upwards around the sides of the draft tube. When reaching the top of the draft tube a portion of the bubbles may be drawn back into the down draft while others may float to the surface.

[0134] While the ANSYS simulation predicted this bubble dispersion, it predicted a threshold impeller speed of 1,500 rpm, whereas in the experimental testing it was found that the threshold was 2,400 rpm. At or above the threshold a horizontal vortex generated by the impeller was observed in the draft tube and two vertical vortexes were observed outside of the draft tube.

[0135] The air bubble velocity, size and air density was measured using an optical probe at heights of 60mm, 170mm and 280mm with water as the solution. The bubble velocity, speed and density is relevant as the reaction proceeds by mixing of bubbles with the solution and small bubble size, long residence time and greater density of bubbles can therefore increase the reaction efficiency of the apparatus.

[0136] As shown in Table 1, it was found that the closer to the bottom of the vessel, the faster the bubbles' velocity and the smaller their size. This was thought to be due to higher hydraulic pressure at lower heights (e.g. 60mm) compressing the bubbles; shear forces imposed by the impeller further reducing the bubble size and increasing the bubble velocity, particularly at lower heights; and bubbles colliding and agglomerating into large bubbles when travelling to a higher water level (e.g., 280 mm), leading to increased bubble size and lower bubble velocity.Table 1 : Comparison of Samples from Different Liquid Depths (tank without packings)

[0137] As shown in Table 2, it was found that bubble velocity increased with increased impeller speed (referred to in the table as stirring speed). Bubble size also increased with impeller speed. While, it was previously expected that bubbles would besmaller under higher speeds, the observation of larger bubbles at faster speeds may be due to bubbles coalescing when travelling upwards outside of the draft tube.Table 2: Comparison of Different Stirring Speeds

[0138] The first experiment of Fig. 11 A and Tables 1 and 2 above was carried out without packing. In a second experiment, the impact of packing material was also investigated. Single centre packing of the type shown in Fig 9A was tested at the six different positions shown in Fig. 12. Six centre packing of the type shown in Fig. 9B was also tested in the same positions. In each case there were two sections of packing of 75mm height each, with the first piece positioned such that the upper surface was at height hi above the bottom of the vessel and the second piece with the upper surface at height 112 above the bottom of the vessel. Thus, in the positions shown in Figs. 12 (a), (b), (d) and (e), there was a gap between the first and the second sections, while in Figs.12 (c) and (f), there was no gap, so the packing was continuous from the lowermost to the topmost ends of the packing. Each packing section was of an annular shape so as to fill the space between the inner wall of the vessel and the outer wall of the draft tube (i.e. with a central aperture approximately equal to the outer diameter of the draft tube).

[0139] As shown in Table 3, it was found that packing at lower heights (i.e. closer to the bottom of the vessel) produced lower bubble velocity and smaller bubble sizes. Lower bubble velocity and smaller bubble size were also found when there was no gap between the sections (i.e. continuous packing), compared to when there was a gap between the two sections. The six centre packing design produced lower bubble velocity and smaller bubble size compared to the single centre packing design.Table 3: Packing in different positions

[0140] The above second experiment tested the entrainment of air bubbles in water through action of the impeller, draft tube and packing. As the first and second experiments simply tested the formation of air bubbles and a circulatory path in water, but did not test carbon dioxide absorption, a third experiment was then conducted to test the reaction rate of carbon dioxide in a solution. The third experiment used the same set up as the second experiment, but instead of water, sodium hydroxide (NaOH) at a concentration of 0.02M was used as the solution and carbon dioxide was supplied through a gas sparger at a flow rate of 6 litres per minute (LPM), with an impeller stirring speed of 2550 rpm. Phenolphthalein was used as an indicator in the solution, as it appears red when PH > 8.2 and colourless when PH < 8.2.

[0141] With this set up, mixing of the carbon dioxide with the sodium hydroxide promoted the following chemical reaction and related change in colour of the phenol:2 NaOH + CO2 Na2CO3+ H2OPhenol: PH>8.2 (red) — PH <8.2 (colorless)

[0142] Therefore, the reaction time could be ascertained by measuring the time taken for the solution to change from red to colourless. Tests were carried out for the apparatus with no packing, single centre packing and six centre packing at various stirring speeds, with the results shown in Fig. 13. As can be seen, increased stirring speed led to reduced reaction time (as indicated by the time for colour change). The presence of packing significantly reduced the reaction time compared to the apparatus with no packing. The six centre design reduced the reaction time more than the single centre design. For stirring speeds and packings the reaction time was reduced by as much as 50%, which was a much greater reduction than expected.

[0143] The same tests were then carried out to measure the reaction time with no packing and at different positions of the single centre and six centre packing with a stirring speed of 2550 rpm, with the results shown in Fig. 14. The final column of Fig.14 shows the percentage reduction in reaction time compared to the case with no packing. It was found that a relatively lower position of the packing worked better and that continuous packing also reduced the reaction time further compared to packing with gaps. Another way to interpret this result is that the reaction time is reduced further when the packing is thicker (from top to bottom). The greatest reduction was found with the positioning shown in Fig. 12 (f) and the six centre design. In that case the reduction in reaction time was 57.69%.

[0144] Tests were also carried out with a lid or cap on top of the vessel to prevent or minimize escape of carbon dioxide through the top end of the vessel. The results are shown in Fig. 15 and indicate that the presence of a lid or cap reduced the reaction time.

[0145] While the third experiment tested absorption of carbon dioxide in a sodium hydroxide solution, it did not test absorption of carbon dioxide in an ammoniatedsolution. Therefore, a fourth experiment was conducted to investigate the effect of packing and impeller speed on carbon dioxide absorption in the presence of ammonia.

[0146] Apparatus as shown in Fig. 16A and 16B were set up. The apparatus of Fig.16A comprised a vessel 110 partially filled with an ammoniated aqueous solution 50 and with a headspace 52 between the surface of the solution 50 and a cap 54 at the top of the vessel. The cap has an inlet 130 allowing for injecting gas into the solution, e.g. through a tube which extends through the cap. The cap has a gas exhaust outlet 135 through which gas can be exhausted from the headspace 52, e.g. via a tube. A mass flow controller 220 regulates the injection of gas, while a CO2 sensor 210 monitors the amount of CO2 in the exhaust gas. A further aperture in the cap 54 allows for taking a liquid sample 230, e.g. through a tube extending into the solution. To regulate the temperature at which the reaction is carried out, the vessel 110 was held in a container 300 filled with a water coolant, such as water. By circulating the cooling water through the container 300 via a cooling water inlet 310 and cooling water outlet 320 excess heat could be extracted in order to cool or maintain a temperature of the vessel 110 and solution 50 during the reaction.

[0147] The apparatus of Fig 16B was the same as the apparatus of Fig. 16A except that it included a packing material 190 in the vessel 110. The packing material was positioned below the surface of the solution 50 and slightly above the impeller 160. The packing material 190 was structured packing with a defined top end and bottom end. Structured packing of the type shown in Fig. 9G or Fig. 9H was used. The structured packing had 6 centres, a corrugation of 3.65mm, a gap size of 1.83mm, and an angle of 45 degrees. The vessel had a height of 307mm and a diameter of 180 mm.

[0148] Where packing was present, the bottom of the packing was positioned just above the impeller with a small clearance between the impeller and the packing. The bottom of the packing was positioned near the impeller so that gas bubbles generated by the agitation would be directed straight through the packing. This proximity helps promote proper gas-liquid interaction and helps to prevent gas pockets from forming below the packing.

[0149] A small clearance between the impeller and the bottom of the packing is desirable so as to prevent contact between the impeller and packing during vibration or movement. The clearance can thus be thought of as a mechanical safety gap. The actual clearance between the impeller tip and the bottom of the lowest packing layer can vary depending on the reactor geometry and operating conditions. In the conducted experiments a 48mm gap (about 15% of the vessel height) was used. This worked well as the bottom of the packing was close the impeller flow zone, allowing for efficient bubble dispersion, while being far enough away to avoid mechanical interference. It is envisaged that a clearance between the impeller and the lowermost position of the packing material of between 3% and 10% of the height of the vessel will be suitable for avoiding mechanical interference, while facilitating contact of the bubbles with the solution and avoiding large packets of trapped gas beneath the packing material.

[0150] The fourth experiment was run with various configurations of packing and impeller speeds. Each time the injected gas was pure CO2. The results are shown in Table 4 which is part of Fig. 17. The experiment was run at ambient or room temperature.

[0151] The packing configuration types are shown in Figs. 19 and 20. Fig. 19 shows how a single piece of packing (1 pack) had a height of 53mm. Two pieces of packing together (2 pack) had a height of 106mm. A half piece of packing (0.5 pack) had a height of 26.5mm and by combining a half pack and full pack (1.5 pack) a piece of packing having a height of 79.5mm could be constructed. Fig. 20 shows an example of a 1 pack configuration 610, a 1.5 pack configuration 620, a 2 pack configuration 630, a 2 piece 1.5 pack configuration with a single 20mm gap 640 and a 3 piece 1.5 pack configuration with two 15mm gaps 650.

[0152] As shown in the first row 410 of Table 4 in Fig. 17, the fourth experiment was initially run with an impeller speed of 300 revolutions per minute (rpm) and no packing. The experiment was run until salt was observed indicating that the solution had become saturated with carbon species products. The starting pH of the solution was10.22 and the finish pH was 8.37. The starting temperature was 15.0 degree Celsius and as the reaction is exothermic the finish temperature was 15.4 degrees Celsius.

[0153] It was known from previous experiments that increasing the impeller speed increased the speed of the reaction. However, when the speed was increased beyond 300 rpm with no packing, this produced a noticeable amount of CO2 and ammonia in the off-gas (exhaust gas 135 as shown in Figs 16A and 16B). This relatively high level of CO2 in the off gas indicated that the gas-liquid contact was poor at higher impeller speeds and that the reaction wasn’t proceeding as intended, so no higher-speed trials were conducted without packing.

[0154] Referring to the second row 420 of Table 4, the same experiment was run with 1 piece of packing (height 53mm). Again, salt was observed indicating saturation at the end of the reaction, but due to the presence of packing the duration of the reaction was reduced from 140 minutes to 110 minutes (a reduction of 21.43% in reaction time with the same impeller rpm). This indicated a significant benefit to the use of structured packing, as the reduction in processing time lowers operating costs while improving carbon capture efficiency.

[0155] It was noticed that without packing a single vortex formed at the centre, while with packing multiple fine vortices formed which will have enhanced the gas liquid mixing leading to the faster reaction time as observed.

[0156] As shown in rows 430 and 440, the experiment was run again with 1 piece of packing (height 53mm or 17% of the vessel height) and 2 pieces of packing (height 106mm or 35% of the vessel height) with no gap between them and an rpm of 1400. The higher rpm significantly reduced the reaction time to 27 minutes. This showed that the presence of packing made it possible to run the reaction at much higher rpm, which was not possible without packing. The experiment was terminated when the solution pH reached a level similar to that of the previous tests and salt formation commenced, indicating that the reaction was almost complete.

[0157] The experiment was then repeated with 0.5 packing (height 26.5mm or about 8% the vessel height) at 1400 rpm as shown in row 450, but in this case significant ammonia was detected in the off gas, indicating that the reaction was incomplete and not proceeding as desired. From this the conclusion was drawn that it is better to have a certain height of packing in order to ensure a proper reaction at higher impeller speeds. As shown in row 460 the experiment was then repeated with 1.5 packing (height 79.5mm). In this case salt was observed indicating saturation.

[0158] Finally, the experiment was run with 1.5 packing in two pieces separated by a gap of 20mm. Salt was observed indicating saturation, but the reaction time reduced further to 22 minutes. This was a reduction of 19% compared to the case with no gap (row 460), indicating that the presence of a gap in the packing facilitated the gas liquid mixing and improved the reaction time in the presence of ammonia. Overall, the set up in row 470 provided an 84% reduction in reaction time compared to the setup in row 410.

[0159] A fifth experiment was then conducted using the same set up as the fourth experiment, but with a blended gas comprising 19% carbon dioxide and 81% nitrogen, instead of pure carbon dioxide. This blended gas better reflects that actual exhaust gas composition from industrial processes, as exhaust gases are rarely pure carbon dioxide but rather contain a portion of carbon dioxide. As the nitrogen (N2) does not react and carbon dioxide forms a smaller portion of the gas, it was expected that the reaction would take longer and this was borne out by the experimental results shown in Fig. 18 and Table 5.

[0160] When the blended gas was used in a set up without packing, significant carbon dioxide and ammonia were detected in the off gas, indicating that the system was not capturing the gases effectively. Accordingly, full runs were only performed with packing.

[0161] For blended gas trials, the endpoint of each run was based on the CO2 concentration in the off-gas stream. The target for CO2 in the off-gas was below 5 vol%during the run (and generally remained in the range 2-4%). Each run was terminated when the CO2 concentration rose above 10%. In general, the CO2 concentration remained steady until right at the end of the run where it rose rapidly. Therefore, by observing the CO2 concentration and using it as a cut off, it was possible to make a consistent comparison between runs with different packing configurations.

[0162] In the run shown in row 510 of Table 5, 2 packing was used (height 106mm) with no gap. In row 520, two packing sections with no gaps were used the same as for row 510, but with a lower rpm of 1000, instead of 1400. This resulted in a faster reaction, however the concentration of carbon dioxide in the off-gas exceeded 10% much earlier, before reaching a similar endpoint pH to the other configurations. As a result, subsequent experiments were conducted only at 1400 rpm and focused on optimizing packing height and gap size. In row 530, the experiment was conducted with a two piece 1.5 packing having a 20mm gap between the two pieces. This reduced the duration of the reaction time from 110 minutes to 85 minutes. Further iterations were tried with different numbers of gaps and gap sizes as shown in rows 540 to 570.

[0163] It was determined that the optimum configuration, of those tested, was a 3-piece packing with 2 gaps. While the duration was the same for rows 540 to 560 at 80 minutes, row 560 with 1.5 pack height in three pieces with two 15mm gaps was considered to be the most effective as the off gas carbon dioxide concentration at the end was lower, the rise in temperature relatively small and the temperature profile during the reaction relatively stable. A lower temperature rise and stable temperature profile mean that less cooling is needed, which will significantly simplify the industrial scale design and avoid costs associated with more complicated cooling systems able to accommodate a larger range of temperatures. The configuration of row 570 was the same as for row 560 except that there was a middle part inside the draft tube, e.g. as shown in Fig. 9H. This further reduced the concentration of carbon dioxide in the off gas at the end of the run, indicating that the middle part contributed to a better mixing and a more complete reaction.

[0164] The graphs in Figs. 21 and 22 show the profile of the solution pH and solution temperature over the duration of the trial run for different packing configurations. It can be seen that trial 10 which was for 1.5 pack height with two gaps has a more stable temperature profile.

[0165] It is thought that presence of one or more gaps in the vertical extent of the packing material improves the performance by allowing better circulation and gas movement through the packing. The gap or gaps act like small flow breaks that help redistribute bubbles and liquid, reducing channelling and preventing areas of poor contact. This creates a more even gas-liquid interaction and keeps the temperature and reaction rate steadier across the reactor. Without a gap, it is believed that some of the gas got trapped in the packing, while introducing one or more gaps allowed the gas bubbles to escape and re-enter the liquid, improving both stability and mass transfer. While the earlier experiment shown in Fig. 12 performed better without a gap, that was with a smaller scale design and sodium hydroxide rather than ammoniated solution. The fourth and fifth experiments, having a larger scale and ammoniated solution, better reflect the industrial reactor design, indicating that one or more gaps in the packing will be advantageous in an industrial reactor. In terms of gap size, based on experiments conducted it is believed that a gap size of between 10% and 20% of the total packing height (including the gaps) would be suitable. The total packing height is defined as the distance between the lowermost position and topmost position of the packing material.

[0166] As discussed above, the top of the packing material is kept below the surface of the solution, so that all packing elements stay fully submerged for consistent gasliquid contact throughout operation. The fourth and fifth experiments did not include a draft tube, as a draft tube was not needed to direct the gas in the relatively small scale laboratory set up. Under these conditions, the impeller alone was sufficient to maintain uniform flow and direct the gas through the packing. However, in a full size industrial reactor, a draft tube would be used to better direct the flow of the diffused gas or gas mixture exiting the gas-liquid contactor. The draft tube would be positioned within the vessel, preferably centrally around the axis of the vessel, and the packing material would be installed around the bottom of the draft tube and extend at least partway upthe draft tube. In this way, the gas-liquid mixture exiting the draft tube will flow upward through the packing material.

[0167] The method and apparatus of the present application capture carbon dioxide and produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate, which may be used as precursors for various different agricultural and / or industrial chemicals. It is thus capable of removing carbon dioxide gas in an environmentally sustainable manner and producing multiple high value products, thereby providing an economic incentive for carbon capture. The apparatus may be retrofitted to existing plants where large volumes of carbon dioxide are produced and can be realized in a relatively small volume of space.

[0168] All of the features of the various example apparatus disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the blocks of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or blocks are mutually exclusive.

[0169] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. An apparatus for removing carbon dioxide from a gas, the apparatus comprising: a vessel configured to receive a solution and having a gas inlet to receive a gas or a mixture of gas and ammonia;a gas-liquid contactor connected to the gas inlet and configured to diffuse said gas or gas mixture into the solution received in the vessel;a draft tube within the vessel to direct flow of the diffused gas or gas mixture; an impeller configured to circulate the diffused gas or gas mixture in the solution for a period of time sufficient to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate;wherein the gas-liquid contactor is disposed in an upper portion of the vessel and connected to the draft tube which is disposed below the gas-liquid contactor;wherein the impeller is configured to create a down draft which draws a flow of bubbles downward through the draft tube and along a circulatory path for bubbles of the gas or gas mixture in said solution for a period of time sufficient to produce carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate; and wherein the apparatus further comprises a packing material disposed on the circulatory path of the bubbles so as to facilitate contact of the gas or gas mixture with the solution.

2. The apparatus of claim 1 wherein the gas-liquid contactor comprises a hollow perforated annulus disposed in an upper portion of the vessel above the draft tube and a skirt that extends downwardly from the hollow perforated annulus and connects with the draft tube.

3. The apparatus of claim 1 or claim 2 wherein the packing material comprises a structured packing.

4. The apparatus of claim 3 wherein the structured packing comprises a body having an axis and a plurality of sheets, wherein adjacent sheets of the plurality of sheets define a curved fluid flow path that rotates around the axis as the sheets extend from one end of the body towards another end of the body.

5. The apparatus of any one of the above claims wherein a portion of the packing material is disposed within the draft tube.

6. The apparatus of 5, wherein the portion of the packing material within the draft tube substantially occupies the whole width of the draft tube with one or more apertures to allow passage of a shaft of the impeller and / or one or more probes.

7. The apparatus of any one of the above claims wherein the packing material includes a portion disposed between an inner wall of the vessel and an outer wall of the draft tube.

8. The apparatus of any one of the above claims wherein the packing material includes a portion disposed below a bottom end of the draft tube.

9. The apparatus of any one of the above claims wherein the packing material has a height extending between an uppermost position and a lowermost position of the packing material.

10. The apparatus of claim 9, wherein the height between the uppermost and lowermost positions of the packing material is equal to at least 8% of a height of the vessel.

11. The apparatus of claim 9 or 10 wherein there is a space between the lowermost position of the packing material and a bottom of the vessel, the lowermost position is preferably at a height of at least 15% of the height of the vessel from the bottom of the vessel.

12. The apparatus of any one of claims 9 to 11, wherein the uppermost position of the packing material is at a height of between 30% and 60% of a height of the vessel.

13. The apparatus of any one of claims 8 to 12 wherein the packing material extends continuously between the uppermost position and the lowermost position. 14 The apparatus of any one of claims 8 to 12 wherein the packing material comprises at least one gap between adjacent packing sections (in the vertical or height direction).

15. The apparatus of any one of claims 8 to 12 wherein the packing material comprises at least two gaps between adjacent packing sections.16 The apparatus of claim 14 or 15 wherein each gap has a height of between 10% and 20% of the total packing height (including the gaps).

17. The apparatus of any one of the above claims wherein, when in an operating position, the impeller is positioned within or below the draft tube.

18. The apparatus of any one of claims 1 to 16 wherein in an operating position, the impeller is positioned below the lowermost position of the packing material.

19. The apparatus of claim 18 wherein in the operating position, the impeller is positioned between 3% and 10% of the vessel height below the lowermost position of the packing material.

20. The apparatus of any one of the above claims, wherein the impeller and / or the gas-liquid contactor and draft tube are movable vertically within the vessel between a non-operating position and an operating position.

21. The apparatus of any one of the above claims wherein the apparatus is configured to drive the impeller at a speed of at least 300 revolutions per minute.

22. The apparatus of any one of the above claims wherein the gas-liquid contactor comprises a plurality of holes having a diameter of between 2mm and 10mm.

23. The apparatus of any one of the above claims wherein the gas-liquid contactor is a hollow perforated annulus comprising a plurality of holes on an inner wall thereof, whereby in use the gas or gas mixture is diffused through said holes and entrained by the flow of fluid generated by the impeller to flow down through the draft tube.

24. The apparatus of claim 2 wherein an outer wall of the hollow perforated annulus and / or skirt is shaped to promote laminar flow of bubbles past the outer wall of the annulus on an upward portion of the circulatory path.

25. The apparatus of claim 2 wherein the hollow perforated annulus has an outer diameter which is larger than an outer diameter of draft tube.

26. The apparatus of claim 2, wherein the skirt has a funnel shape which tapers from the larger outer diameter of the perforated annulus to the smaller diameter of the draft tube.

27. The apparatus of claim 2 wherein the skirt is fixedly attached to the draft tube.

28. The apparatus of claim 2 wherein the skirt is integral with the annulus and attached to or integral with the draft tube.

29. The apparatus of any one of the above claims further comprising a mixer for mixing the ammonia with the gas, the mixer being positioned upstream of the gas inlet.

30. The apparatus of any one of the above claims further comprising an outlet at a lower portion of the vessel for recirculating solution to another part of the vessel, and optionally for receiving ammonia gas to be injected into the recirculated solution.

31. The apparatus of any one of the above claims further comprising one or more sprinklers at an upper portion of the vessel for spraying recirculated solution into the vessel.

32. The apparatus of any one of the above claims wherein the gas-liquid contactor and draft tube are part of an assembly which enters the vessel through a top end of the vessel, the assembly being movable vertically between an operating position and a nonoperating position.

33. The apparatus of any one of the above claims wherein there are two gas inlets in the top end of the vessel and the assembly comprises two pipes which are configured to deliver the gas or the mixture of gas and ammonia from a gas delivery pipe to the two gas inlets.

34. An apparatus for removing carbon dioxide from a gas, the apparatus comprising:a vessel configured to receive a solution and having a gas inlet to receive a gas or a mixture of gas and ammonia;a hollow perforated annulus connected to the gas inlet and configured to diffuse said gas or gas mixture into the solution received in the vessel;a draft tube extending downward from the hollow perforated annulus for directing a flow of the diffused gas or gas mixture;an impeller to circulate the diffused gas or gas mixture in the solution for a period of time sufficient to produce one or more carbon species (e.g. carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate);wherein the impeller is configured to create a down draft which draws a flow of bubbles downward through the draft tube and upward along a circulatory path outside of the draft tube so as to promote mixing of bubbles of the gas or gas mixture with the solution in order to produce the carbon species; andwherein the apparatus further comprises a packing material disposed between outer walls of the draft tube and inner walls of the vessel so as to facilitate contact of the gas or gas mixture with the solution when the bubbles travel on the circulatory path.

35. The apparatus of claim 34 wherein the perforated annulus is connected to the draft tube by a skirt.

36. The apparatus of any one the above claims further comprising a shield to deflect gas diffused from the gas-liquid contactor or hollow perforated annulus in a downward direction.

37. A method of removing carbon dioxide from a gas, the method comprising:a) providing a solution in a vessel;b) diffusing a gas or a mixture of gas and ammonia through a gas-liquid contactor into the solution to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate;wherein a draft tube is supported within the vessel and the gas-liquid contactor comprises a hollow perforated annulus disposed in an upper portion of the vessel above the draft tube and a skirt extends downwardly from the hollow perforated annulus and connects with the draft tube;wherein the method comprises using an impeller to create a down draftwhich draws a flow of gas or gas mixture bubbles downward through the draft tube and along a circulatory path to disperse the bubbles of the gas or gas mixture in said solution for aperiod of time sufficient to produce one or more of carbonic acid, carbonate, bicarbonate, carbamic acid and / or carbamate;and wherein a packing material is disposed on the circulatory path of the bubbles so as to facilitate contact of the gas or gas mixture with the solution.

38. The method of claim 37 wherein the gas is compressed to a pressure between the range of about 5 psi to about 15 psi.

39. The method of claim 37 or 38 wherein the flow of gas has a flow rate of 1-50 kg / hour and a flow of ammonia to be mixed with the gas has a flow rate of 3-20 kg / hour.

40. The method of any one of claims 37 to 39 wherein when in an operating position, the hollow perforated annulus is positioned below a surface of the solution in the vessel.

41. A method of removing carbon dioxide from a gas, the method comprising:diffusing the gas or a mixture of gas and ammonia into a solution or an ammoniated solution under conditions effective to produce an ammonium carbamate.

42. The method of claim 41, wherein the pH of the ammoniated solution is between about 8 to about 12, between about 9 to about 11, or between 9.5 to about 10.5.

3. The method of claim 41 or claim 42, wherein the temperature of the ammoniated solution is between about 15°C to about 20°C.

44. The method of any one of claims 41 to 43, wherein the ammonium carbamate-containing solution is processed into urea.

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