A method of separatnig co2 from a gas stream

Abstract

The present invention relates to a method of separating carbon dioxide (C02) from a gas stream, the method comprising: providing a C02 containing gas stream to an absorption column; providing a composition comprising at least 20 wt% AMP (2-amino-2-methyl-1 -propanol), and at least 55 wt% DMSO (dimethyl sulfoxide) to the absorption column; contacting the C02 containing gas stream with the composition in the absorption column to thereby form a slurry comprising a solid fraction and a liquid fraction; separating the slurry into a solid-predominated phase and a liquid-predominated phase, the solidpredominated phase comprising at least 85 wt% of the solid fraction, the liquid-predominated phase constituting at least 60 wt% of the slurry, the solid content of the liquid-predominated phase comprising being less than 15 wt% of the solid fraction; and re-circulating the liquid-predominated phase to the absorption column to form at least a part of said composition.

Description

The present invention relates to a method of separating carbon dioxide (CO2) from a gas stream. The present invention also relates to a CO2 separating system.Background of the InventionConventional methods for capturing and separating CO2 from gas streams typically involve the use of absorption columns where CO2 is absorbed by a liquid solvent. The most common techniques employ aqueous solutions of amines, such as monoethanolamine (MEA), which absorb CO2 from the gas stream. Following absorption, the rich solvent containing the absorbed CO2 is directed to a stripper unit where the CO2 is desorbed at elevated temperatures, and the lean solvent is recycled back to the absorption column.These methods, while effective in capturing CO2, are often criticized for their high energy demand, primarily due to the thermal energy required for the regeneration of the solvent in the stripper. Additionally, the degradation of solvents and the large solvent circulation rates contribute to increased operational costs and environmental concerns. Thus, there is a need in the industry for an improved method for separating CO2 from a gas stream.SummaryAn object of the present invention is to overcome at least some of the above mentioned problems, and to provide a method of separating CO2 from a gas stream which is improved compared to prior art solutions. The method includes the using of a composition comprising at least 20 wt% AMP (2-amino-2-methyl-1 -propanol), and at least 55 wt% DMSO (dimethyl sulfoxide) in an absorption column for interacting with a CO2 containing gas stream to form a slurry comprising a solid fraction and a liquid fraction. The use of the specific composition forms a slurry with separable solid and liquid fractions.By separating the slurry into a solid-predominated phase comprising a majority of the solids (in wt%), and a liquid-predominated phase comprising at least 60 wt% of the slurry, the liquid-predominated phase may be recirculated to the absorption column without being subject to the same energyintensive processing used for re-generating the solid-predominated phase. Hereby, an improved method for separating CO2 from a gas stream, typically with regards to energy efficiency, is providedAccording to at least a first aspect of the present invention, a method of separating carbon dioxide (CO2) from a gas stream is provided. The method comprises: providing a CO2 containing gas stream to an absorption column; providing a composition comprising at least 20 wt% 2-amino-2-methyl-1-propanol (AMP) and at least 55 wt% dimethyl sulfoxide (DMSO) to the absorption column; contacting the CO2 containing gas stream with the composition in the absorption column to thereby form a slurry comprising a solid fraction and a liquid fraction; separating the slurry into a solidpredominated phase and a liquid-predominated phase, the solidpredominated phase comprising at least 85 wt% of the solid fraction, the liquid-predominated phase constituting at least 60 wt% of the slurry, the liquid-predominated phase comprising less than 15 wt% of the solid fraction; and re-circulating the liquid-predominated phase to the absorption column to form at least a part of said composition.Hereby, an improved method of separating CO2 from a gas stream is provided. As at least 60 wt% of the slurry is recirculated to the absorption column, and as the solid content of the liquid-predominated phase is less than 15 wt%, an energy efficient method is achieved. That is, by the separation resulting in that at least 85 wt% of the solids from the slurry is comprised in the solid-predominated phase, and that less than 15 wt% of the solids from the slurry is comprised in the liquid-predominated phase, a high amount of the slurry (i.e. at least 60 wt%) can be recirculated to the absorption column without further removal of the solids from the liquid-predominated phase. Hereby, the energy efficiency of the method may be improved. It should be understood that the solid-predominated phase is not recirculated to the absorption column together with the liquid-predominated phase. In other words, the solid-predominated phase and the liquid-predominated phase are forming separated process streams, wherein the process stream formed by the liquid-predominated phase is recirculated to the absorption column while the process stream formed by the solid-predominated phase is not recirculated to the absorption column. The temperature of the slurry out from the absorption column and / or the temperature of the slurry in the separation may be in a predetermine range, e.g. between 30 °C and 55 °C. Moreover, the separation of the slurry into a solid-predominated phase and a liquidpredominated phase may be performed isothermally, or at least withing a temperature span of 10 °C.Typically, the solid-predominated phase constitutes less than 40 wt% of the slurry. For example, the solid-predominated phase may comprise less than 15 wt% or less than 10 wt% of the liquid fraction. For such embodiments, the total amount of the liquid fraction is preferably twice the total amount of the solid fraction in the slurry. Typically, at least a majority of the CO2 from the CO2 containing gas stream is trapped in the slurry, and in particular in the solid fraction of the slurry. Preferably, at least 80% or at least 90% of the CO2 from the CO2 containing gas stream is trapped. The combined components used for separating CO2 from the gas stream according to the method of the first aspect may be referred to as a system for separating CO2 from a gas stream. The system may be referred to as a CO2 separating system. The CO2 separating system may thus comprise at least the absorption column, an inlet device configured to provide the composition into the absorption column, a separation unit configured to separate the slurry and a re-circulation arrangement configured to re-circulate the liquid-predominated phase to the inlet device of the absorption column.According to one embodiment, the solid-predominated phase is a solid, or a precipitate. Correspondingly, and according to one embodiment, the liquid-predominated phase is a liquid. However, when separating the slurry into the solid-predominated phase and the liquid-predominated phase, a small amount of liquid from the liquid fraction may adhere to, or go along with, the solid or precipitate.According to one embodiment, the total amount of the liquid fraction is preferably twice the total amount of the solid fraction in the slurry. For example, the solid fraction may constitute 25-35 wt% of the slurry, such as 28-29 wt% of the slurry.According to one embodiment, separating the slurry into the solidpredominated phase and the liquid-predominated phase is performed downstream of the absorption column. Thus, the separation of the slurry into the solid-predominated phase and the liquid-predominated phase may be performed physically separated from the absorption column. The separation may be performed by subjecting the slurry to a separation unit.According to one embodiment, the method further comprises: conveying the solid-predominated phase to a stripper, dissolving solids of the solid-predominated phase in the stripper and thereby obtaining a CO2 stream and a CO2 lean solvent, the stripper being controlled to achieve a temperature of the CO2 lean solvent of less than 98 °C. Thus, instead of recirculating the solid-predominated phase to the absorption column together with the liquid-predominated phase, the solid-predominated phase is conveyed to the stripper to release the majority of the absorbed CO2 from the solid-predominated phase. Hereby, the CO2 from the CO2 containing gas stream is obtained in the CO2 stream. The dissolvement of solids of the solidpredominated phase is typically achieved by thermal heat (heating) in the stripper. For example, the stripper is controlled to achieve a temperature of the CO2 lean solvent of than 95 °C, or less than 90 °C, e.g. between 80 °C and 90 °C.According to one embodiment, the method further comprises: mixing the solid-predominated phase with a fraction of the CO2 lean solvent from the stripper. Thus, the CO2 lean solvent is used for backmixing with the solidpredominated phase, improving the properties of the solid-predominated phase. For example, by adapting the fraction of the CO2 lean solvent used for backmixing, the solid-predominated phase may be liquefied, or at least form a concentrated slurry.According to one embodiment, the method further comprises: controlling the temperature of the fraction of the CO2 lean solvent to a temperature of at least 70 °C, or at least 80 °C. Hereby, the mixing with the solid-predominated phase may be improved.According to one embodiment, the method further comprises: conveying the liquid-predominated phase to a buffer tank prior to recirculating the liquid-predominated phase to the absorption column. The buffer tank may e.g. be sized and dimensioned to hold the complete composition of the AMP and DMSO of the system. For example, for a medium sized power plant generating around 100000 m3 flue gases per hour, the flue gases having a CO2 of 10 vol%, a suitable volume for the buffer tank may be 35 m3. Thus, the re-circulation arrangement may comprise the buffer tank.According to one embodiment, the method further comprises: mixing the CO2 lean solvent from the stripper with the liquid-predominated phase in the buffer tank to form said composition. Hereby, a suitable mixing of the CO2 lean solvent and the liquid-predominated phase, forming said composition, can be achieved. Hence, the stripper may be a component of the CO2 separating system.According to one embodiment, the stripper comprises an indirect heat exchanger, preferably a falling film or a thin film heat exchanger. For example, the stripper may comprise, or be comprised of, a horizontal falling film stripper. Hereby, the solid-predominated phase, preferably mixed with the fraction of the CO2 lean solvent to form said concentrated slurry, can be brought into contact with heated pipes causing the CO2 to be released from the slurry. The heated pipes are preferably low to moderately heated, e.g. at a temperature of between 70 °C and 100 °C or between 85 °C and 100 °C.According to one embodiment, the composition comprises 20-30 wt% AMP, 0-10 wt% water, 0-1 wt% additives and 55-80 wt% DMSO. Hereby, a composition with preferred processability characteristics is provided.According to one embodiment, a majority of the solid fraction is a carbamate. For example, all of the solid fraction is carbamate, or at least 75 wt%, or at least 80 wt%, or at least 85 wt%, or at least 95 wt%, or at least 98 wt% is carbamate. However, a portion of the solid fraction may be carbonate. Thus, by using the above mentioned composition comprising 20-30 wt% AMP, 0-10 wt% water, 0-1 wt% additives and 55-80 wt% DMSO, and contacting the CO2 containing gas stream with the composition in the absorption column, the resulting solid fraction in the slurry is carbamate, or at least a majority of the solid fraction is carbamate.According to one embodiment, separating the slurry into a solidpredominated phase and a liquid-predominated phase includes filtration. Hereby, a high amount of solids in the solid-predominated phase can be achieved. Thus, the previously mentioned separation unit may comprise a filtration stage including one or more filters. The filter(s) may have an air permeability of 3,6 dm3 / dm2 / min (EN ISO 9237) and a differential pressure of 200 Pa.According to one embodiment, the filtration comprises or consists of belt filtration and / or vacuum filtration, such as vacuum belt filtration. Thus, the filtration is achieved by using a belt filter and / or a vacuum filter, such as a vacuum belt filter. For example, by using a belt filter, the slurry is distributed on a movable or moving filter cloth, why the need for pumping the slurry between the absorption column and the separation unit may be reduced, or even omitted. Moreover, by using a vacuum filter, the need for (high) pressures which can cause blow-outs is reduced, or even omitted. When using a vacuum belt filter for the filtration, the slurry is typically distributed on a movable or moving filter cloth, and a vacuum (a pressure below atmospheric pressure) is applied to the filter cloth from below.It is believed, without being bound by any theory, that the use of a vacuum belt filter provides several advantages when used with the specific composition of the current disclosure. For example, the vacuum belt filter includes few moving parts, which is particularly suitable when used with the slurry of the current disclosure as damage of components, e.g. gaskets, may be reduced or even prevented, even if the composition of the current disclosure may be corrosive. Furthermore, a vacuum belt filter typically does not contain a separate drying stage, and the absence of such drying stage is beneficial from an energy consuming perspective and as drying may lead to undesired ventilation of chemicals from the composition.In other embodiments, alternative filtering techniques may be used, such as a filter press, tower filter press or belt filter press.For example, separating the slurry into a solid-predominated phase and a liquid-predominated phase excludes sedimentation using a sedimentation tank. Using a sedimentation tank may lead to a compact solidpredominated phase, which is undesired from a processability aspect.However, according to one embodiment, separating the slurry into a solidpredominated phase and a liquid-predominated phase includes filtration and sedimentation. In such case, the sedimentation separating step is preferably arranged upstream of the filtration separating step. Thus, any solids separated by the filtration can be brought back to the sedimentation step. Hereby, an efficient separating of the solids and liquids can be achieved. The sedimentation step may be performed using a sedimentation tank.According to one embodiment, the re-circulated composition comprises less than 0.1 mol CO2 / mol AMP. Thus, the previously described steps of separation and subjecting the solid-predominated phase to a stripper may result in a low amount of re-circulated CO2.For example, the solubility of CO2 may be measured at 100 kPa for the current composition (e.g. between 20 wt% and 30 wt% AMP) at a temperature of 30 °C.According to one embodiment, the method further comprises: controlling the temperature of the composition entering the absorption column to a maximum temperature of 40 °C. Hereby, the temperature of the slurry out of the absorption column can be kept low, preferably below 55 °C. Hereby, the risk of re-dissolvement of solids is reduced. Moreover, by controlling the temperature of the composition entering the absorption column to a maximum temperature of 40 °C, the use of supplementary cooling, e.g. by an intercooler in the absorption column may be reduced, or even omitted. The method preferably comprises heat exchanging the composition prior to entering the absorption column, typically by cooling the composition. According to one embodiment, the method comprises: controlling the temperature of the slurry exiting the absorption column to a maximum temperature of 55 °C. According to one embodiment, the absorption column does not comprise an intercooler.According to one embodiment, the method further comprises: cooling the CO2 lean solvent prior to providing it to the buffer tank. Preferably, the CO2 lean solvent is cooled by heat exchanging or other heat utilization means. Thus, heat energy from the CO2 lean solvent may be utilized, prior to providing it to the buffer tank. By cooling the CO2 lean solvent prior to providing it to the buffer tank, heat utilization occurs at a higher temperature compared to after the buffer tank. The CO2 lean solvent is preferably cooled to the same, or substantially the same, temperature as the liquid predominated phase entering the buffer tank. For example, the CO2 lean solvent is cooled to a temperature within 0 °C and 10 °C of the temperature of the liquid predominated phase entering the buffer tank. It should be noted that prior to the buffer tank may be referred to as upstream of the buffer tank, and after the buffer tank referred to as downstream of the buffer tank.According to one embodiment, the size of the buffer tank is adapted to hold the entire amount of the composition during shutdown. Hereby, the various components of the CO2 separating system, such as e.g. the absorption column, the separation unit and the stripper, may be emptied from the composition, e.g. due to maintenance reasons. Thus, the CO2 separating system may be operated in a way in which no composition is allowed to exit the buffer tank, while the other components of the CO2 separating system is operated until they are emptied of the composition, or constituents of the composition, until all of the composition is held within the buffer tank.According to one embodiment, the buffer tank is adapted to prevent ingress of water into the buffer tank. Hereby, water can be prevented from being mixed with the composition when water is being flushed through the CO2 separating system, such as during cleaning of the CO2 separating system. For example, the buffer tank comprises valves for closing the inlets and outlets of the buffer tank, such as e.g. a first inlet providing the liquidpredominated phase to the buffer tank, a second inlet providing the CO2 lean solvent to the buffer tank and the outlet providing the composition to the absorption column. Moreover, a by-pass may be provided to the buffer tank, e.g. extending from upstream of the first and / or second inlets to downstream the outlet of the buffer tank. Hereby, water being flushed through the CO2 separating system may be by-passed the buffer tank in an efficient way.According to one embodiment, the absorption column comprises random packing sections. Hereby, clogging of the absorption column may be reduced as compared to e.g. an absorption column comprising structured packing sections. For example, a majority of the absorption sections in the absorption column is random packing sections.According to a second aspect of the present invention, a CO2 separating system is provided. The system comprises:an absorption column configured to receive a CO2 containing gas stream, the absorption column comprising an inlet device configured to provide a composition comprising at least 20 wt% AMP (2-amino-2-methyl-1-propanol), and at least 55 wt% DMSO (dimethyl sulfoxide) to the absorption column, and absorption sections configured to bring the CO2 containing gas stream in contact with the composition in the absorption column to thereby form a slurry comprising a solid fraction and a liquid fraction,a separation unit configured to separate the slurry into a solidpredominated phase and a liquid-predominated phase such that the solidpredominated phase comprises at least 85 wt% of the solid fraction, the liquid-predominated phase constitutes at least 60 wt% of the slurry, and the liquid-predominated phase comprises less than 15 wt% of the solid fraction, anda re-circulation arrangement configured to re-circulate the liquidpredominated phase to the inlet device of the absorption column to form at least a part of the composition.Effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspect of the invention. Embodiments mentioned in relation to the first aspect of the invention are largely compatible with the second aspect of the invention, of which some are exemplified below.Thus, during use of the CO2 separating system, the method of the first aspect of the invention may be implemented. Thus, during use, the composition may be provided into the absorption column by the inlet device. In the absorption column, the CO2 containing gas stream is brought into contact with the composition by the absorption sections of the absorption column to thereby form the slurry comprising the solid fraction and the liquid fraction. In the separation unit, the slurry is separated into the solidpredominated phase and the liquid-predominated phase such that the solidpredominated phase comprises at least 85 wt% of the solid fraction, the liquid-predominated phase constitutes at least 60 wt% of the slurry, and the liquid-predominated phase comprises less than 15 wt% of the solid fraction. Thereafter, the liquid-predominated is re-circulated by the re-circulation arrangement to the inlet device of the absorption column to form at least a part of the composition.Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.Brief Description of the DrawingsThese and other aspects of the present inventive concept will now be described in more detail, with reference to the appended drawings showing an example embodiment of the inventive concept, wherein:Fig. 1 is a schematic view of a CO2 separating system according to the present invention.Fig. 2 is a schematic view of a filter unit according to an embodiment of the present invention.Fig. 3 is a flow chart illustrating a method according to the present invention.Detailed Description of Example EmbodimentsIn the present detailed description, various embodiments of the invention are described.Fig. 1 is a schematic view of a CO2 separating system 10 according to an embodiment of the present invention. The CO2 separating system 10 comprises an absorption column 12. The absorption column 12 is configured to receive a CO2 containing gas stream 14 to absorb CO2 from said gas stream 14, thus allowing a CO2 lean gas stream 15 to be released from the absorption column 12.The absorption column 12 comprises an inlet device 16 configured to provide a composition 18 to the to the absorption column 12. The composition 18 comprises at least 20 wt% AMP (2-amino-2-methyl-1 -propanol), and at least 55 wt% DMSO (dimethyl sulfoxide). In one example, the composition comprises 20-30 wt% AMP, 0-10 wt% water, 0-1 wt% additives and 55-80 wt% DMSO.The absorption column 12 comprises a plurality of absorption sections 20. The absorption sections 20 are configured to bring the CO2 containing gas stream 14 into contact with the composition 18 inside the absorption column 12. The absorption sections 20 may be random packing sections. When the CO2 containing gas stream 14 contacts the composition 18, a slurry 22 comprising a solid fraction and a liquid fraction is formed. A majority of the solid fraction, such as at least 75 wt%, or at least 80 wt%, or at least 85 wt%, or at least 95 %, or at least 99 wt% of the solid fraction, may be a carbamate.A separation unit 28 is arranged downstream of the absorption column 12 to receive the slurry 22. The separation unit 28 is arranged to separate the slurry 22 into a solid-predominated phase 30 and a liquid-predominated phase 32. The solid-predominated phase 30 may be a solid, or a precipitate. The separation unit 28 is preferably a vacuum belt filter, but is should be mentioned that other filtering techniques, such as a filter press or tower filter press may be used.The solid-predominated phase 30 leaving the separation unit 28 comprises at least 85 wt% of the solid fraction, while the liquid-predominated phase 32 leaving the separation unit 28 comprises less than 15 wt% of the solid fraction. The liquid-predominated phase 32 constitutes at least 60 wt% of the slurry 22. The liquid-predominated phase 32 is arranged to be recirculated to the inlet device 16 of the absorption column 12, to form at least a part of the composition 18, by a re-circulation arrangement 34. The composition 18 being recirculated to the absorption column 12 may comprise less than 0.1 mol CO2 / mol AMP.The CO2 separating system 10 may further comprise a stripper 36 for receiving the solid-predominated phase 30 from the separation unit 28. The stripper 36 is configured to dissolve the solids of the solid-predominated phase 30, to obtain a CO2 stream 38 and a CO2 lean solvent 40. CO2 may thus be removed from the CO2 separating system 10 by conveying the CO2 stream 38 away from the stripper 36.The stripper 36 may comprise an indirect heat exchanger 42, such as a falling film or a thin film heat exchanger. Hereby, the solid-predominated phase 30 can be brought into contact with heated pipes causing the CO2 to be released. The heated pipes are preferably low to moderately heated, e.g. at a temperature of between 85 °C and 100 °C. The stripper 36 may control the temperature of the CO2 lean solvent 40 to achieve a temperature of less than 98 °C, e.g. less than 88 °C.The CO2 separating system 10 may further be arranged such that the solid-predominated 30 phase is allowed to be mixed with a fraction of the CO2 lean solvent 40a leaving the stripper 36. Thus, the fraction of the CO2 lean solvent 40a is allowed to be backmixed with the solid-predominated phase 30 to improve the properties of the solid-predominated phase 30. For example, by adapting the fraction of the CO2 lean solvent used for backmixing, the solid-predominated phase 30 may be liquefied, or at least form a concentrated slurry. The temperature of the fraction of the CO2 lean solvent 40a may be controlled to a temperature of at least 70 °C, or at least 80 °C, to improve the mixing with the solid-predominated phase 30.The CO2 separating system 10 may further comprise means for cooling the CO2 lean solvent 40 after leaving the stripper 36. For example, the CO2 may be cooled to the same temperature as the liquid-predominated phase 32, such as to a temperature of 50-60 °C.The re-circulation arrangement 34 in Fig .1 comprises a buffer tank 44. The buffer tank 44 is configured to receive the liquid-predominated phase 32 before it is re-circulated. The buffer tank 44 is further configured to receive the CO2 lean solvent 40 from the stripper 36, whereby the CO2 lean solvent 40 is allowed to be mixed with the liquid-predominated phase 32 in the buffer tank 44 to form the composition 18. The size of the buffer tank 44 may be adapted to hold the entire amount of the composition 18 during shutdown of the CO2 separating system 10, such as during cleaning of the CO2 separating system 10. The buffer tank 44 may further comprise valves and a bypass, such that ingress of water to the buffer tank 44 can be prevented during flushing of the CO2 separating system 10.The CO2 separating system may further comprise a temperature regulating device 46 for controlling the temperature of the composition 18 before entering the absorption column 12. The temperature regulating device 46 may be configured to control the temperature of the composition 18 to a maximum temperature of 30 °C or 40 °C.Fig.2 is a schematic view of the separation unit 28. The separation unit 28 is illustrated as a vacuum belt filter unit. In other embodiments, other and / or additional separation methods and devices may be used.In the disclosed vacuum belt filter, the slurry 22 from the absorption is distributed on a filter cloth 281. The filter cloth 281 is moving in a forward direction relative to the distribution of the slurry 22 onto the filter cloth 281 , that is, from left to right in the figure. The movement may include rotation of the belt around a pair of rollers 282. A vacuum is applied to the filter cloth 281 from below the filter cloth 281. The vacuum may be produced by a vacuum pump 283.The filter cloth 281 comprises a first section 281a and a second section 281b. During separation, the slurry 22 is distributed on the first section 281a. A so-called mother liquid 284 may then be produced, which may be recirculated from the first section 281a through a recirculation line 285. At the second section 281b, the actual filtrate 286 is produced together with a filter cake 288. The filtrate 286 constitutes the liquid pre-dominated phase 32. The filter cake 288 is removed from the belt, such as by scraping. The filter cake 288 may then be conveyed to the stripper 36 as the solid pre-dominated phase 30.The filtrate 286 may also be sprayed onto the filter cake 288 to increase the efficiency of the filter. The filtrate 286 may further be used to clean the filter cloth 281 after the filter cake 288 has been removed, by being supplied through a cleaning line 287.Fig.3 is a flowchart describing a method of separating carbon dioxide (CO2) from a gas stream. The method may be implemented in the CO2 separating system 10 described with reference to Fig. 1. Thus, the same reference numerals are used for like features.In a first step, S101, a CO2 containing gas stream 14 is provided to an absorption column 12.In a second step, S102, a composition 18 comprising at least 20 wt% AMP (2-amino-2-methyl-1 -propanol), and at least 55 wt% DMSO (dimethyl sulfoxide) is provided to the absorption column 12. The composition 18 is typically provided to the absorption column 12 by an injection device 16 as described with reference to Fig. 1.In a third step, S103, occurring subsequently to the first and second steps S101, S102, a slurry 22 is formed by contacting the CO2 containing gas stream 14 with the composition 18 in the absorption column 12. The formed slurry 22 comprises a solid fraction and a liquid fraction.In a fourth step, S104, the slurry 22 is separated into a solidpredominated phase and a liquid-predominated phase. The solidpredominated phase comprises at least 85 wt% of the solid fraction, the liquid-predominated phase constitutes at least 60 wt% of the slurry 22, and the liquid-predominated phase comprises less than 15 wt% of the solid fraction. For example, the solid-predominated phase comprises at least 90 wt% of the solid fraction, the liquid-predominated phase constitutes at least 60 wt% of the slurry 22, and the liquid-predominated phase comprises less than 10 wt% of the solid fraction.In an optional fifth step, S105, the solid-predominated phase is conveyed to a stripper 36. In the stripper 36, the solids of the solidpredominated phase are dissolved, and a CO2 stream together with a CO2 lean solvent are obtained. The stripper 36 may be controlled to a achieve a temperature of the CO2 lean solvent of less than 98 °C, e.g. of less than 90 °C, e.g. between 80 °C and 90 °C.In an optional sixth step, S106, the solid-predominated phase is mixed with a fraction of the CO2 lean solvent from the stripper 36.In an optional seventh step, S107, the liquid-predominated phase is conveyed to a buffer tank 44, prior to being re-circulated to the absorption column 12 (described later).In an optional eight step, S108, the CO2 lean solvent from the stripper 36 is mixed with the liquid-predominated phase in the buffer tank 44, to form the composition 18. Optionally, the temperature of the CO2 lean solvent may be lowered before entering the buffer tank 44.In a ninth step, S109, the liquid-predominated phase 32 is re-circulated to the absorption column 12 to form at least part of the composition 18. The liquid-predominated phase 32 may thus either be recirculated directly from the separation unit 28, or via the optional buffer tank 44. Optionally, the temperature of the composition 18 may be controlled before entering the absorption column 12. For example, the temperature of the composition may be controlled to a maximum temperature of 40 °C.Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A method of separating carbon dioxide (CO2) from a gas stream, the method comprising:providing a CO2 containing gas stream to an absorption column, providing a composition comprising at least 20 wt% AMP (2-amino-2-methyl-1 -propanol), and at least 55 wt% DMSO (dimethyl sulfoxide) to the absorption column,contacting the CO2 containing gas stream with the composition in the absorption column to thereby form a slurry comprising a solid fraction and a liquid fraction,separating the slurry into a solid-predominated phase and a liquidpredominated phase, the solid-predominated phase comprising at least 85 wt% of the solid fraction, the liquid-predominated phase constituting at least 60 wt% of the slurry, the liquid-predominated phase comprising less than 15 wt% of the solid fraction, andre-circulating the liquid-predominated phase to the absorption column to form at least a part of said composition.

2. The method according to claim 1 further comprising: conveying the solidpredominated phase to a stripper, dissolving solids of the solid-predominated phase in the stripper and thereby obtaining a CO2 stream and a CO2 lean solvent, the stripper being controlled to a achieve a temperature of the CO2 lean solvent of less than 98 °C.

3. The method according to claim 2 further comprising: mixing the solidpredominated phase with a fraction of the CO2 lean solvent from the stripper.

4. The method according to any one of claims 1-3, wherein separating the slurry into a solid-predominated phase and a liquid-predominated phase includes filtration.

5. The method according to claim 4, wherein the filtration comprises or consists of belt filtration and / or vacuum filtration, such as vacuum belt filtration.

6. The method according to any one of claims 1 -5 further comprising: conveying the liquid-predominated phase to a buffer tank prior to recirculating the liquid-predominated phase to the absorption column.

7. The method according to claim 6 further comprising: mixing the CO2 lean solvent from the stripper with the liquid-predominated phase in the buffer tank to form said composition.

8. The method according to any one of claims 2-7, wherein the stripper comprises an indirect heat exchanger, preferably a falling film or a thin film heat exchanger.

9. The method according to any one of claims 1-8, wherein the composition comprises 20-30 wt% AMP, 0-10 wt% water, 0-1 wt% additives and 55-80 wt% DMSO.

10. The method according to any one of claims 1-9, wherein a majority of the solid fraction is a carbamate.

11. The method according to any one of claims 1 -10, wherein the recirculated composition comprises less than 0.1 mol C02 / mol AMP.

12. The method according to any one of claims 1-11, further comprising: controlling the temperature of the composition entering the absorption column to a maximum temperature of 40 °C.

13. The method according to any one of claims 1 -12, further comprising: cooling the CO2 lean solvent prior to providing it to the buffer tank.

14. The method according to any one of claims 1 -13, wherein the size of the buffer tank is adapted to hold the entire amount of the composition during shutdown.

15. The method according to any one of claims 1 -14, wherein the buffer tank is adapted to prevent ingress of water into the buffer tank.

16. The method according to any one of claims 1-15, wherein the absorption column comprises random packing sections.

17. A CO2 separating system comprising:an absorption column configured to receive a CO2 containing gas stream, the absorption column comprising an inlet device configured to provide a composition comprising at least 20 wt% AMP (2-amino-2-methyl-1-propanol), and at least 55 wt% DMSO (dimethyl sulfoxide) to the absorption column, and absorption sections configured to bring the CO2 containing gas stream in contact with the composition in the absorption column to thereby form a slurry comprising a solid fraction and a liquid fraction,a separation unit configured to separate the slurry into a solidpredominated phase and a liquid-predominated phase such that the solidpredominated phase comprises at least 85 wt% of the solid fraction, the liquid-predominated phase constitutes at least 60 wt% of the slurry, and the liquid-predominated phase comprises less than 15 wt% of the solid fraction, anda re-circulation arrangement configured to re-circulate the liquidpredominated phase to the inlet device of the absorption column to form at least a part of the composition.