EP4676617A1

EP4676617A1 - Carbon dioxide capturing device

Info

Publication number: EP4676617A1
Application number: EP24703668.4A
Authority: EP
Inventors: James Tonny MANALAL
Original assignee: Technische Universiteit Delft
Current assignee: Technische Universiteit Delft
Priority date: 2023-03-03
Filing date: 2024-02-02
Publication date: 2026-01-14
Also published as: NL2034264B1; WO2024186198A1

Abstract

Method of capturing carbon dioxide from a gas stream, preferably using the carbon dioxide capturing device according to any of the preceding claims, comprising: - cooling a gas stream, containing carbon dioxide and further at least one of nitrogen and oxygen; - capturing carbon dioxide in a solid state from the cooled gas stream, thereby obtaining captured carbon dioxide and a process gas stream having a reduced relative carbon dioxide content; - subjecting the process gas having a reduced relative carbon dioxide content to a gas separation treatment, thereby obtaining at least one coolant gas stream selected from oxygen enriched gas streams, nitrogen enriched gas streams and gas streams enriched in both nitrogen and oxygen; and - using at least one of said coolant gas streams as a cooling medium for the gas stream containing carbon dioxide via a principle heat exchanger.

Description

Carbon dioxide capturing device

The invention relates to a carbon dioxide capturing device and a method of capturing carbon dioxide from a gas stream.

Heavy industry involves the production and manufacturing of goods that typically require significant amounts of energy and raw materials. Examples of heavy industries include the chemical industry, steel and metal production, cement and concrete manufacturing, and power generation.

The chemical industry involves the production of a wide range of products such as plastics, fertilizers, and pharmaceuticals. Many chemical processes involve the use of fossil fuels as a source of energy and raw materials, which results in the production of flue-gas, an exhaust gas that is emitted from a combustion process as a byproduct.

Flue-gas typically comprises a mixture of gases such as carbon dioxide (CO2), water vapor, nitrogen and oxygen. Heavy industry is considered a major contributor of carbon dioxide emissions. As a result, there is increasing pressure on heavy industry to reduce their carbon dioxide footprint, for example by implementing technologies such as carbon capture and storage systems (CCS) to reduce carbon dioxide emissions to the environment.

Cryogenic carbon capture and storage is a process used to capture and store carbon dioxide emissions from large industrial sources. The process involves cooling the flue-gas, to extremely low temperatures, typically around -160 degrees Celsius. Once the carbon dioxide is captured it can be transported to a storage site, where it for example is injected deep underground into geological formations such as depleted oil and gas reservoirs or deep saline aquifers. Cryogenic carbon capture and storage has the advantage of capturing carbon dioxide with high purity and suitability for large-scale industrial sources of carbon dioxide. A major drawback of cryogenic carbon capture and storage is that it is energy-intensive and requires a large amount of energy to cool the flue-gas, which can increase the costs of the process and may render it economically unsustainable.

The invention aims to counteract the above disadvantages, preferably while retaining the advantages. More specifically, the invention aims to reduce external energy supplied to the cryogenic carbon capture and storage, preferably rendering cryogenic carbon capture and storage economically sustainable.

Therefore, the invention provides for a carbon dioxide capturing device, comprising a gas cooling section comprising an inlet arranged to receive a gas comprising carbon dioxide, preferably a waste-gas comprising carbon dioxide, oxygen and nitrogen, in particular a carbon dioxide capturing device according to claim 1.

The gas cooling section is arranged to cool the gas using a principle heat exchanger provided upstream of a cryogenic carbon dioxide capturing unit and arranged to feed the cooled gas from principle the heat exchanger to the cryogenic carbon dioxide capturing unit. The inventor realized that the principle heat exchanger is advantageous to reduce the cooling requirement in the carbon dioxide capturing unit and to reuse some of this cold energy available from the air separation section and thus leading to higher efficiency (in particular energy-wise).

The cryogenic carbon dioxide capturing unit is arranged to produce a carbon dioxide lean gas by capturing carbon dioxide in a solid state in a packed bed from the cooled gas. The inventor realized not only that the use of a packed bed is practically possible, but also that the use of a packed bed facilitates nucleation and increases the rate of solid carbon dioxide deposition, thereby improving efficiency (in particular requiring less energy, increasing capturing capacity per unit of time, or both), especially in combination with the other measures of the method of the present invention. The packed bed in particular allows such improvement by direct phase transition of gaseous carbon dioxide from gaseous carbon dioxide into solid carbon dioxide without passing through a liquid state (deposition).

The cryogenic carbon dioxide capturing unit is arranged to feed the carbon dioxide lean gas to an air separation section. The air separation section is arranged to separate the carbon dioxide lean gas in to at least one process gas and an off gas. Preferably the process gas comprises at least one of oxygen and nitrogen. The carbon dioxide capturing device further comprises a conduit arranged to provide the process gas, via the principle heat exchanger, to an outlet.

The cryogenic carbon dioxide capturing unit comprises a regeneration device arranged to regenerate the packed bed by applying heat to liquify the solid captured carbon dioxide. Thus, in accordance with the present invention capture and regeneration can be accomplished in the same unit, comprising the packed bed. The integration of capture and regeneration unit improves the process efficiency as high pressure increases carbon dioxide capture rate and high pressure favors carbon dioxide regeneration as liquid and also helps to maintain the required operating pressure of the air separation process. So such an integrated approach offers three (synergetic) advantages which substantially helps to improve overall process efficiency (including improved capture rate, reduced energy consumption or both), required equipment and required space for the equipment.

In the context of the invention, it will be clear to the person skilled in the art that the carbon dioxide lean gas is a gas that has a reduced carbon dioxide content compared to the gas comprising the carbon dioxide, e.g. waste gas or flue-gas, before it has been subjected to a carbon dioxide capturing treatment. In order to capture carbon dioxide from industrial processes, e.g. power plants, chemical plants, combusted biogas from a bioreactor and offgases from bioreactors, an inlet is provided. The carbon dioxide capturing device can be connected to the outlet of an industrial process via a conduit such as industrial piping. Preferably, the conduit is provided such that essentially no gas is emitted to the surrounding of the industrial process without passing through the carbon dioxide capturing device during normal use. The inlet can further comprise safety measures, such as an emergency safety valve, that can insolate the carbon dioxide capturing device from the industrial process, and vice versa, in case of a process irregularity, e.g. an higher than expected pressure.

The gas cooling section is arranged to prepare the gas for, and feeding it to the cryogenic carbon dioxide capturing unit. The principle heat exchanger of the gas cooling section is arranged to cool the gas, preferably to a temperature in the range of -40 to -60 degrees Celsius, more preferably to a temperature in the range of -45 to -50 degree Celsius via the principle heat exchanger. Cooling the gas before feeding it to the cryogenic carbon dioxide capturing unit reduces the cooling that needs to be provided by an external cooling provided by a cooling source in the cryogenic carbon dioxide capturing unit, thereby reducing the total energy required for the carbon dioxide capturing device. Additionally, the gas cooling section can comprise a compressor arranged to pressurize the gas comprising carbon dioxide upstream of the principle heat exchanger, preferably a multistage gas compressor, such that the gas can be pressurized before it is being cooled by the principle heat exchanger. Pressurizing the gas before cooling advantageously results in more efficient cooling, e.g. by reducing the energy needed to cool the gas. More in particular, pressurizing the gas before cooling facilitates the operation of the cryogenic carbon dioxide capturing unit above the triple point of carbon dioxide. Further, pressurizing the gas before cooling can be applied to ensure a sufficient operating pressure of the carbon dioxide lean gas for the air separation unit provided upstream of the cryogenic carbon dioxide capturing unit.

Additionally, the gas cooling section can comprise a gas cleaning arrangement upstream of the principle heat exchanger, preferably to remove water from the gas. The gas cleaning arrangement can comprise a knockout drum and a molecular sieve, each arranged to remove water from the gas. The knockout drum can be used to separate liquid from the gas, making use of a difference in density of the liquid and gas. The gas can be directed to the top of the drum while the liquids settle on the bottom of the drum. The molecular sieve can be used to separate liquid from the gas before it is being pressurized using a porous crystal structure that is able to selectively adsorb molecules on their size and shape, preferably the crystal structure is arranged to filter out water. Removing water from the gas can improve the process efficiency, and can help preventing damage to the equipment due to the presence of ice.

Once the gas is cooled, and preferably after any water present in the gas has substantially been removed by the gas cooling section, the cooled gas can be fed to the cryogenic carbon dioxide capturing unit. The cryogenic carbon dioxide capturing unit can comprise a packed bed to capture carbon dioxide from the cooled gas. The packed bed e.g. comprises Raschig rings (e.g. with a diameter in the range of 5-50 mm, in particular with a diameter of about 10 to about 30 mm) or a structured packing. The packed bed offers an increased effective area for deposition per volume of the vessel wherein the packed bed is present, compared to an empty (unpacked) vessel (such an unpacked tube). Usually, the effective area for deposition per volume of the packed bed is at least about 25 m²/m³ preferably at least about 50 m²/m³, more preferably at least about 100 m²/m³. The upper limit is not critical, albeit that with increasing effective area, the average passage way for the gas/liquid narrows, resulting in increased pressure. Thus, in practice, the packed bed usually provides an effective area for deposition of less than 500 m²/m³, preferably of 400 m²/m³ or less, more preferably of 300 m²/m³ or less, in particular of about 250 m²/m³ or less. The packed bed can be arranged such that the cooled gas can pass through the bed. The solid surface of the packed bed can provide a surface area for ice nucleation, such that the cooled gas, in a state above the triple point of carbon dioxide, comes in contact with a cold metal surface, the carbon dioxide deposits as a solid, such as dry ice, on the metal surface. Once the carbon dioxide has been substantially removed from the cooled gas, the cooled gas is considered to be a carbon dioxide lean gas. Preferably, the carbon dioxide is removed by at least 90 %, more preferably by at least 95 %. For example, if the cooled gas contained 15 vol% carbon dioxide, the carbon dioxide lean gas preferably comprises up to 1.5 vol%, more preferably up to 0.75 vol% carbon dioxide. In principle, essentially all carbon dioxide may be removed, whereby a lean gas containing below ppm levels of carbon dioxide can be obtained. In practice, usually 99.99 % or less, 99.9 % or less, 99 % or less, 98 % or less or 96 % or less or of the carbon dioxide is removed. In an advantageous embodiment, 95 % to 99.99 % of the carbon dioxide is removed. Thus, when carbon dioxide is removed from a gas containing about 15 vol% carbon dioxide, the resultant lean gas contains about 15 to about 7500 ppm carbon dioxide. The cryogenic carbon dioxide capturing unit is further arranged to feed the carbon dioxide lean gas to the air separation section.

Advantageously, during capturing of the carbon dioxide, the packed bed is cooled using a multiple stage cascade refrigeration system, such as a three-stage cascade refrigeration system (TCRS). A multiple stage refrigeration comprises a plurality of (single stage) refrigeration cycles: a high-temperature cycle (HTC), one or more medium temperature cycles (MTC) and a low-temperature cycles. The skilled person will be able to select different refrigerants for the different stages, dependent on the boiling points of the refrigerants. Preferred examples of refrigerants are methane, ethane, propane and hydrofluorocarbon refrigerants (such as R-134a). The multistage configuration, in particular the TCRS improves the refrigeration cycle efficiency compared to a single stage refrigeration cycle.

In the packed bed, the temperature of the cooled gas is further cooled, preferably to about -140 degrees Celsius or less, via a first auxiliary heat exchanger. The use of the principle heat exchanger reduces the cooling duty required for the first auxiliary heat exchanger/refrigeration cycle and thus leads to higher overall process efficiency. In a preferred embodiment, the product gas is used as a coolant for the first auxiliary heat exchanger. Optionally, in order to facilitate better cooling of the cooled gas, the cryogenic carbon dioxide capturing unit can further comprise an external refrigeration cycle arranged to at least partially further cool the cooled gas, preferably to a temperature of about -140 degrees Celsius or less, via the first auxiliary heat exchanger.

During the further cooling of the cooled gas, the gas is preferably kept above a pressure corresponding to the triple point of carbon dioxide, i.e. 0.5180 MPa. If the pressure of the cooled gas is kept above the pressure of the triple point of carbon dioxide, and if the cooled gas is further cooled, preferably to about - 140 degrees Celsius or less, the carbon dioxide will go from a gaseous state to a solid state without going through a liquid phase due to the partial pressure of carbon dioxide in the cooled gas. This may further increase the process efficiency of capturing carbon dioxide from the cooled gas as less energy is required since there is only one phase-change, i.e. from a gaseous state to a solid state.

The cryogenic carbon dioxide capturing unit can further comprise a regeneration unit arranged to regenerate the packed bed. Preferably, the regeneration unit is arranged to heat a saturated packed bed, i.e. a packed bed in which the solid deposition rate is no longer considered sufficient due to the presence of removed carbon dioxide on the surface of the solid packed bed material. When the saturated packed bed is heated, the captured carbon dioxide will release in from the surface of the solid adsorbent material in a liquid state. When the carbon dioxide in the packed carbon bed subsequently can be heated, e.g. using an external heating cycle or residual heat generated otherwhere in the process, the captured carbon dioxide can reach a liquid state, preferably in a temperature range between -60 and -40 degree Celsius. Once the liquified carbon dioxide has been removed from the packed bed, a cooling source may be used to cool the packed bed again such that it is arranged to capture carbon dioxide from the cooled gas in a solid state again. By providing the captured carbon dioxide in a liquid state, as opposed to e.g. a gaseous or solid state, the captured carbon dioxide can be conveniently, and energy efficiently, transported at a relatively high mass rate, e.g. using a pump. Additionally, if the captured carbon dioxide is subsequently used in a liquid phase, e.g. when the captured carbon dioxide is stored in an empty gas field, it is more energy efficient to supply the carbon dioxide in the same physical state, since no additionally energy needs to be provided to further change the temperature of and the pressure on the liquified carbon dioxide.

The cryogenic carbon dioxide capturing unit can further comprise a pump to pressurize the liquified carbon dioxide and a heating source to heat the liquified carbon dioxide, preferably to transport conditions, more preferably in a pressure range of 30 - 80 bar gauge and a temperature range of 10 - 40 degrees Celsius. The heating source may be an external heating cycle, such as a second auxiliary heat exchanger, or making use of residual heat from elsewhere in the process, for example the external cooling cycle of the packed bed. Getting the liquified carbon dioxide in transport condition allows for the relatively easy transportation from the production site, for example transporting it to a storage field or onto transportation vessels such as vessels, trucks or trains.

The air separation section is arranged to separate the carbon dioxide lean gas into at least one process gas and an off gas. Preferably, the carbon dioxide lean gas is first further cooled, preferably in the range of -150 to -180 degrees Celsius, by a secondary heat exchanger. The cooled carbon dioxide lean gas is subsequently fed to a distillation arrangement in which the carbon dioxide lean gas is separated in to the off gas and the at least one process gas, based on their boiling points. Preferably, the process gases comprise nitrogen and oxygen and are more preferably separated in an oxygen rich stream and a nitrogen rich stream. The oxygen rich stream, the nitrogen rich stream and the off gas are preferably in a gaseous state, having a maximum temperature of -180 degrees Celsius.

At least one of the oxygen rich stream, the nitrogen rich stream and off gas stream can be used as a coolant for the principle and secondary heat exchangers. By providing a conduit, e.g. piping, at least one of the streams can be provided to the principle and secondary heat exchangers. The principle and secondary heat exchanger can comprise a first passage way for the gas comprising carbon dioxide from which carbon dioxide is to be captured (carbon dioxide rich gas) and the carbon dioxide lean gas respectively, and at least one additional passage way for at least one of the streams. In the principle heat exchanger, the passages are arranged to transfer heat from the gas comprising carbon dioxide to the at least one process gas, i.e. to cool the carbon dioxide containing gas using the at least one process gas. In the secondary heat exchanger, the passages are arranged to transfer heat from the carbon dioxide lean gas to the at least one process gas, i.e. to cool the carbon dioxide lean gas using the at least one process gas. Using the process gases as coolant reduces the need for an external cooling source, thereby further reducing the overall energy needed by the carbon dioxide capturing device.

The invention furthermore provides for a method of capturing carbon dioxide from a gas stream, preferably using the carbon dioxide capturing device according to any of the claims, comprising: - cooling a gas stream, containing carbon dioxide and further at least one of nitrogen and oxygen;

- capturing carbon dioxide in a solid state from the cooled gas stream, thereby obtaining captured carbon dioxide and a process gas stream having a reduced relative carbon dioxide content;

- subjecting the process gas having a reduced relative carbon dioxide content to a gas separation treatment, thereby obtaining at least one coolant gas stream, or process stream, selected from oxygen enriched gas streams, nitrogen enriched gas streams, gas streams enriched in both nitrogen and oxygen and an off-gas stream; and

- using at least one of said coolant gas streams as a cooling medium for the gas stream containing carbon dioxide via a principle heat exchanger. The off-gas stream can comprise a relatively low oxygen and nitrogen content compared to the oxygen enriched gas stream, nitrogen enriched gas stream and the gas stream enriched in both nitrogen and oxygen.

The method according to the invention in particular is a method according to claim 10.

The gas containing carbon dioxide can be fed into the principle heat exchanger at a pressure in the range of 5-10 bar gauge. It is in particular preferred to feed the gas into the principle heat exchanger at a pressure exceeding the triple point, when aiming to carry out the carbon capturing above the triple point (as is generally preferred), as this allows subsequent feeding the gas from which carbon dioxide is to be removed into the carbon dioxide capturing unit at a pressure above the triple point. Thus, it is particularly preferred to feed the gas containing the carbon dioxide into the principle heat exchanger at a pressure in the range of 5.5-10 bar gauge, more preferably in the range of 6.0 to 10 bar gauge. By pressurizing the gas containing the carbon dioxide, the carbon dioxide can be more efficiently captured from the gas stream by taking advantage of the pressure value of the triple point of carbon dioxide at the temperature of the cooled gas stream and the operating pressure of the air separation unit. In particular, it allows increased carbon dioxide deposition rate (as dry -ice) compared to a pressure close to atmospheric conditions. More specifically, by pressurizing the cooled gas, it can be achieved that the cryogenic carbon dioxide capturing device can be operated at a pressure at which the cooled gas stream entering the cryogenic carbon dioxide capturing device is above the triple point of carbon dioxide while also being at the operating pressure of the air separation unit, reducing the need for additional pressurizing steps. The carbon dioxide can be captured as a solid in a packed bed. The method can comprise regeneration of the packed bed containing captured carbon dioxide, during which regeneration the carbon dioxide is removed from the packed bed as a liquid.

Advantageously, the capturing of carbon dioxide and the regeneration of the packed bed both take place at a super-atmospheric pressure, preferably about the same pressure. The term “about” as used in the present disclosure for pressures in particular includes a deviation of up to 1 bar gauge, more in particular up to 0.5 bar gauge. Advantageously, both the capturing of the carbon dioxide and the regenerating of the packed bed take place at a pressure in the range of 5-10 bar gauge, preferably at a pressure above the carbon dioxide triple point, in particular at a pressure in the range of 5.2-10 bar gauge, more in particular at a pressure in the range of 5.4-10 bar gauge. Preferably both the capturing of the carbon dioxide and the regenerating of the packed bed take place at about the same super- atmospheric pressure. It is advantageous energy-wise, time-wise and spacewise that the present invention allows both capturing and regeneration to take place efficiently at about the same super-atmospheric pressure, since changing pressure from high pressure to low pressure takes time and costs energy. Further, not having to change pressure allows the same vessel to be used for capturing and regeneration. Furthermore, it such super- atmospheric conditions can more closely match typical air separation process operating conditions, such as for the production of industrial grade oxygen and nitrogen. The inventor reahzed that the super-atmospheric capturing pressure, in particular a pressure in the range of 5-10 bar gauge is particularly advantageous for an increased dry ice deposition rate, but also for liquification of the solid carbon dioxide captured in the packed bed.

In a preferred method of the invention, the cryogenic carbon dioxide capturing device is operated (at least during capturing and regeneration) at a pressure at which the cooled gas stream entering the cryogenic carbon dioxide capturing device is above the triple point of carbon dioxide while also being at the operating pressure of the air separation.

The method can further comprise the steps of:

- heating the captured carbon dioxide at least until the captured carbon dioxide is in a liquid state, typically at a constant pressure; and

- further pressurizing and heating the liquid captured carbon dioxide until it reaches transport conditions. The transport conditions can be in the range 30 - 80 bar gauge and can be in the range of 10 - 40 degree Celsius.

The gas stream containing carbon dioxide can be fed in a cryogenic carbon dioxide capturing unit, in particular a cryogenic packed bed, at a bed operating temperature in the range of -140 to -50 degrees C.

The gas stream containing carbon dioxide can be a flue-gas, and I or a methane rich gas. Additionally or alternatively, the gas stream containing carbon dioxide can have a carbon dioxide content in the range of 5-50 vol%, preferably in the range of 5 - 15 vol% and I or have an excess oxygen content in the range of 2-50 vol%, preferably in the range of 5-15 vol%.

Further advantageous aspects of the invention are set out in the description and appended claims. The technical features described in the paragraphs and sentences above can be isolated from the context, and the isolated technical features from the different paragraphs and sentences can be combined. Such combinations are herewith specifically disclosed in this description.

The invention will further be elucidated on the basis of an exemplary embodiment which is represented in the drawings. The exemplary embodiment is given by way of non-limitative illustrations of the invention.

In the drawings:

Fig. 1 shows a process-flow diagram of a process according to the invention;

Fig. 2 A shows a process-flow diagram of the process of according to the invention of section A of Fig. 1;

Fig. 2B shows a process-flow diagram of the process of according to the invention of section B of Fig. 1;

Fig. 3 shows a process-flow diagram of a cryogenic carbon dioxide capturing unit comprising multiple packed beds for continuous operation.

It is noted that the figures are only a schematic representation that is given by way of non-limited examples. In the figures, the same or corresponding parts are designated with the same reference numerals. Roman numerals are used to indicate the state of the various gases and liquids in the various stages of the embodiment.

Referring to Figs. 1, 2A and 2B, a carbon dioxide capturing device 1 according to an embodiment of the invention is depicted. The carbon dioxide capturing device 1 comprises a gas cooling section 10 comprising an inlet 11 arranged to receive a gas comprising carbon dioxide I, in the shown example a flue-gas comprising carbon dioxide, oxygen and nitrogen. The cooling gas section 10 is arranged to cool the flue-gas I using a principle heat exchanger 12 provided upstream of a cryogenic carbon dioxide capturing unit 20. The principle heat exchanger 12 is arranged to feed the cooled flue-gas II from the principle heat exchanger 12 to the cryogenic carbon dioxide capturing unit 20. The cryogenic carbon dioxide capturing unit 20 is arranged to produce a carbon dioxide lean gas Ill-a, Ill-b by capturing carbon dioxide in a solid state in a packed bed 21 from the cooled flue-gas II. The cryogenic carbon dioxide capture unit 20 is further arranged to feed the carbon dioxide lean gas Ill-a, Ill-b to an air separation unit 30. Said air separation unit 30 is arranged to separate the carbon dioxide lean gas Ill-a, Ill-b in to at least one process gas IV and an off-gas V, in the shown embodiment the air separation unit 30 separates the carbon dioxide lean gas III in to two process gases: an oxygen rich gas IV-a and a nitrogen rich gas IV-b. The carbon dioxide capturing device 1 further comprises a conduit 2, in the shown example piping, arranged to provide the process gases IV-a, IV-b and the off-gas V, via the principle heat exchanger 12 to an outlet 3. In the principle heat exchanger 12, the process gases IV-a, IV-b and the off-gas V is used to cool the flue-gas such that it is closer to the operating temperature of the cryogenic carbon capturing unit 20.

In the shown embodiment, the inlet 11 and outlet 3 is a battery limit of the carbon capturing device 1, i.e. the physical border between the carbon capturing device 1 and its surrounding. In other embodiments, the outlet 3 may be a facility to load liquified carbon dioxide VI on a shipping vessel or may be an empty gas field arranged for storing liquified carbon dioxide.

Upstream of the principle heat exchanger 12 the process gases IV- a, IV-b and the off-gas V are fed to a secondary heat exchanger 27, where the process gases IV-a, IV-b and the off-gas V are used to cool the carbon dioxide lean gas Ill-a to a cooled carbon dioxide lean gas Ill-b.

The gas cooling section 10 comprises a gas cleaning section 13, provided upstream of the principle heat exchanger 12, and a compressor 14, provided upstream of the principle heat exchanger 12 and downstream of the gas cleaning section 13. The gas cleaning section 13 may be used to first remove any remaining water in the flue-gas I, using a knock-out drum 15 and a molecular sieve 16, before being pressurized by the compressor 14. The removed water VII, or waste water, can be stored and purified or released into a sewer or open water if not contaminated severely. Removing water and pressurizing the gas is done to prepare the flue-gas I for the principle heat exchanger 12, to further facilitate the cooling of the flue-gas I.

The cryogenic carbon capturing unit 20 comprises a regeneration device 22 arranged to regenerate the packed bed 21 by applying sufficient heat to liquify the solid captured carbon dioxide via a first auxiliary heat exchanger 24. The liquified carbon dioxide VI is pressurized by a pump 23 in a range of 30-80 bar gauge, allowing for transportation at a sufficient mass flow rate and further heated via a heating source to a temperature range of 10-40 degrees Celsius. In these pressure and temperature ranges, the liquified carbon dioxide VI is in a state which is suitable for transportation.

Additionally, the cryogenic carbon dioxide capturing unit 20 comprises an external refrigeration cycle 25 arranged to further cool the cooled gas II to a temperature of -140 degrees Celsius via a second auxiliary heat exchanger 26. At this temperature, the carbon dioxide of the cooled gas II will solidify and attach to the surface of the contents of the packed bed 21 via deposition and nucleation of carbon dioxide in to dry ice, i.e. solid carbon dioxide. The other primary components of the cooled gas II, will remain in a gaseous state, more specifically as the carbon dioxide lean gas III.

The shown embodiment depicted in Figs 1, 2A and 2B can be used in a method to capture carbon dioxide from a gas stream. First, the gas stream I, preferably a stream containing carbon dioxide and further at least one nitrogen and oxygen, e.g. flue-gas, is pressurized to a pressure of 6 bar gauge and subsequently cooled by the primary heat exchanger 12 to a temperature of -57 degrees Celsius in the gas cooling section 10.

The cooled gas II is fed to the cryogenic carbon capturing unit 20. The cryogenic carbon capturing unit 20 has during an active phase a temperature of -140 and a pressure of 6 bar gauge. At this temperature and pressure, the carbon dioxide present in the cooled gas II deposits, going from a gaseous state to a solid state, while the other components of the cooled gas II remain in a gaseous state. This allows the cryogenic carbon capturing unit 20 to capture carbon dioxide in a solid state in a packed bed 21, thereby obtaining captured carbon dioxide and a process gas stream Ill-a, Ill-b that has a reduced relative carbon dioxide content.

Once the packed bed 21 is saturated with solid captured carbon dioxide, the bed can be regenerated using a regeneration device 22. The regeneration device applies sufficient heat to the saturated packed bed 21 such that the temperature in the saturated packed bed 21 reaches a temperature of -57 degree and a pressure 6 bar gauge. The liquified carbon dioxide VI is further pressurized and heated, via a pump 23 and an external heating source 24 respectively, such that the liquified carbon dioxide VI is in suitable conditions for transportation.

The process gas Ill-a, Ill-b, having a relatively low carbon dioxide content compared to the flue-gas I and being at a temperature of -140 degrees Celsius and a pressure of 6 bar gauge, is being fed to the air separation unit 30 via the secondary heat exchanger 27. Secondary heat exchanger 27 is arranged to further cool the process gas Ill-a to a process gas Ill-b of -171 degrees Celsius, to facilitate the air separation unit 30. The process gas Ill-b is subjected to a gas separation treatment, thereby obtaining at least one coolant gas stream. In the shown example, the coolant gas stream is a stream of oxygen enriched gas IV-a, a stream of nitrogen IV- b enriched gas and a stream of off-gas V. These coolant gas streams are first used as a cooling medium for the process gas Ill-a in the secondary heat exchanger 27 and subsequently used as a cooling medium in the principle heat exchanger 12. After passing both heat exchangers, the coolant gas streams have been brought from -180 degrees Celsius to 30 degrees Celsius. The oxygen enriched gas and the nitrogen enriched gas can be used or sold as feedstock for other chemical processes.

Advantageously, the carbon dioxide capturing device according to the invention usually comprises at least two cryogenic carbon dioxide capturing units, each containing a packed beds 21, in parallel (a multibed configuration), in particular three to twenty cryogenic carbon dioxide capturing units, each containing a packed bed 21. This allows subsequent stages of a method according to the invention to be carried out in parallel. Thus, a first carbon dioxide capturing unit 21a can be used for an deposition I CO2-capture stage whilst a second packed bed 21b - that contains captured CO2 (from a previous deposition I CO2-capture stage) can be subjected to one or more further stages to recover CO2 from the second packed bed 21b and regenerate it for a further use in another deposition I CO2-capture stage.

Thus, in accordance with the invention it is possible to continuously capture carbon dioxide, thereby also allowing the use of the present invention advantageously to capture carbon dioxide formed in continuous industrial processes wherein carbon dioxide is formed or otherwise released, such as such continuous chemical processes, such continuous fermentative processes or such continuous energy production processes.

A further advantage of a multibed configuration, is that it allows to capture gaseous carbon dioxide formed during regeneration of carbon dioxide; typically, during regeneration of carbon dioxide a part of the solid carbon dioxide becomes liquid and a part becomes gas. The gaseous carbon dioxide can be redirected back to a bed operating in capture stage, e.g. as shown in Fig 3 (21b to 21a). This configuration helps to further improve the overall CO2 capture efficiency as the gaseous CO2 during regeneration step is captured in a simultaneously operating bed. Accordingly, in a particularly preferred embodiment, the carbon dioxide capturing device, comprising a plurality of carbon dioxide capturing units in parallel comprises one or more gas conduits provided between at least a first and at least a second cryogenic carbon dioxide capturing unit, arranged to pass - when the device is in use - gaseous carbon dioxide from a cryogenic carbon dioxide capturing unit wherein regeneration takes place to a cryogenic carbon dioxide capturing unit wherein capturing takes place.

In a highly advantageous embodiment, the carbon dioxide capturing device according to the invention comprises at least four packed beds 22 in parallel, whereby at least a first 21a can be used for (i) deposition I CO2-capture, whilst at least a second packed bed 21b is used for (ii) CO2 purge I pressurization, whilst at least a third packed bed 21c is used for (iii) CO2- melting I recovery and whilst at least a fourth packed bed 2 Id is used for (iv) cooling I bed preparation. A schematic drawing of an apparatus respectively method with a plurality of packed beds units is shown in Figure 3. Having four packed beds 22 (or more) in parallel is particularly advantageous for a continuous removal of carbon dioxide from a gas stream.

Many variations will be apparent to the skilled person in the art. Such variations are understood to be comprised within the scope of the invention as defined in the appended claims. For example, it is clear to the person skilled in the art that the various external cooling and I or heating cycles to cool or heat the gas, cooled gas, carbon dioxide lean gas, liquified carbon dioxide, nitrogen rich gas, oxygen rich gas and I or the off-gas can be replaced by an internal cooling and I or heating cycle if there is sufficient cooling I heating capacity available. For example, the oxygen rich gas can be used to cool the packed bed of the cryogenic carbon capture section. Reducing the need for external heating I cooling cycles may further improve the energy efficiency and economical feasibility of cryogenic carbon capture and storage. EXAMPLES

Example 1: comparison of heat transfer efficiency for cryocondensation in a packed bed in accordance with the invention compared to the use of a pipe exchanger.

A simple double pipe heat exchanger with a diameter of 470 mm & length of 2400 mm has a specific surface area of ~8.5 m²/m³.

Filling the pipe with a Raschig Super-Ring No-05 random packing with a nominal diameter of 20 mm results in an effective area of about 100- 200 m²/m³. Thus packed bed provides more surface area for the same volume, leading to higher heat transfer and more surface area for ice deposition. Therefore, as heat transfer rate is proportional to the surface area, a much higher deposition rate is possible for the same volume, with a packed bed in accordance with the invention.

Example 2: effect of integration of capture and regeneration

Using Aspen process simulation data: When two gas streams at 6 bar and 1.2 bar containing 80 % N2, 15 % O2 and 5 % CO2 is cooled to -140 degree C, the CO2 capture efficiencies are 97 % and 87 % respectively in an open flash vessel. Thus, an increased CO2 capture efficiency is achieved at higher pressure as the increase in pressure shifts the solid-gas phase equilibrium composition to favour higher solid/liquid formation.

Example 3: effect of integration of air separation

Using Aspen process simulation: The air separation process and the cryogenic carbon capture occurs at the same pressure of 6 bar, only an extra 4 % increase in electricity is used for compressing the flue gas compared to clean air at the same boundary conditions. Thus the integration saves energy as two highly energy intensive units are coupled and operated at the same pressure.

Example 4: effect of the feed of cooled gas from the air separation unit to the outlet via the principle heat exchanger

Example based on Aspen process simulation: The total cold energy need after the compressor to capture 14 kt CC /year from a flue gas stream containing 3-4 vol% CO2 is about -1604 kW. Out of this 686 kW cold energy is provided by the Air separation unit. Thus because of this energy integration between a cryogenic carbon capture and air separation unit, about 43 % of total energy need is saved which would have been otherwise provided by an external cold gas or refrigeration cycle.

Claims

1. Carbon dioxide capturing device comprising: a gas cooling section comprising an inlet arranged to receive a gas comprising carbon dioxide, preferably a waste-gas comprising carbon dioxide, oxygen and nitrogen; wherein the gas cooling section is arranged to cool the gas using a principle heat exchanger provided upstream of a cryogenic carbon dioxide capturing unit and arranged to feed the cooled gas from the principle heat exchanger to the cryogenic carbon dioxide capturing unit; wherein the cryogenic carbon dioxide capturing unit is arranged to produce a carbon dioxide lean gas by capturing carbon dioxide in a solid state in a packed bed from the cooled gas and wherein the cryogenic carbon dioxide capturing unit is arranged to feed the carbon dioxide lean gas to an air separation section; wherein the air separation section is arranged to separate the carbon dioxide lean gas in to at least one process gas and an off gas, wherein preferably the process gas comprises at least one of oxygen and nitrogen; wherein the carbon dioxide capturing device further comprises a conduit arranged to provide the process gas, via the principle heat exchanger, to an outlet. wherein the cryogenic carbon dioxide capturing unit comprises a regeneration device arranged to regenerate the packed bed by applying heat to liquify the solid captured carbon dioxide.

2. Carbon dioxide capturing device according to claim 1, wherein the cryogenic carbon dioxide capturing unit further comprises a pump to pressurize the liquified carbon dioxide and a heating source to heat the liquified carbon dioxide, preferably to transport conditions, more preferably in a range of 30 - 80 bar gauge and temperature range of 10 - 40 degrees Celsius.

3. Carbon dioxide capturing device according to any of the preceding claims, wherein the gas cooling section comprises a compressor arranged to pressurize the gas comprising carbon dioxide upstream of the principle heat exchanger.

4. Carbon dioxide capturing device according to any of the preceding claims, wherein the gas cooling section comprises a gas cleaning arrangement upstream of the principle heat exchanger, said gas cleaning arrangement comprises a knockout drum and a molecular sieve, each arranged to remove water from the gas.

5. Carbon dioxide capturing device according to any of the preceding claims, wherein the cryogenic carbon dioxide capturing unit further comprises a first auxiliary heat exchanger arranged to further cool the cooled gas, preferably to a temperature of about -140 degrees Celsius.

6. Carbon dioxide capturing device according to claim 5, wherein the cryogenic carbon dioxide capturing unit further comprises an external refrigeration cycle arranged to at least partially further cool the cooled gas, preferably to a temperature of about -140 degrees Celsius, via the first auxiliary heat exchanger.

7. Carbon dioxide capturing device according to any of the preceding claims, wherein the device comprises a three-stage cascade refrigeration system, arranged to cool the packed bed of the carbon dioxide capturing device in subsequently a high-temperature cycle, a medium-temperature cycle and a low-temperature cycle.

8. Carbon dioxide capturing device according to any of the preceding claims, wherein the carbon dioxide capturing device comprises two or more cryogenic carbon dioxide capturing units, each containing a packed bed, which cryogenic carbon dioxide capturing units are arranged in parallel (with respect to the gas flow from which carbon dioxide is to be captured), arranged to allow at least a first of said cryogenic carbon dioxide capturing units to capture carbon dioxide, whilst at least a second of cryogenic carbon dioxide capturing units is subjected to regeneration.

9. Carbon dioxide capturing device according to claim 8, wherein a gas conduit is provided between said first and said second cryogenic carbon dioxide capturing unit, arranged to pass - when the device is in use - gaseous carbon dioxide from said second cryogenic carbon dioxide capturing unit wherein regeneration takes place to said first cryogenic carbon dioxide capturing unit wherein capturing takes place.

10. Method of capturing carbon dioxide from a gas stream, comprising:

- cooling a gas stream, containing carbon dioxide and further at least one of nitrogen and oxygen, using a principle heat exchanger provided upstream of a cryogenic carbon dioxide capturing unit;

- capturing carbon dioxide in a solid state from the cooled gas stream, which capturing is performed in the cryogenic carbon dioxide capturing unit and which cryogenic carbon dioxide contains a packed bed, thereby obtaining captured carbon dioxide and a process gas stream having a reduced relative carbon dioxide content;

- subjecting the process gas having a reduced relative carbon dioxide content to a gas separation treatment, thereby obtaining at least one coolant gas stream selected from oxygen enriched gas streams, nitrogen enriched gas streams and gas streams enriched in both nitrogen and oxygen;

- using at least one of said coolant gas streams as a cooling medium for the gas stream containing carbon dioxide via the principle heat exchanger; and - regenerating the packed bed by applying heat, thereby liquefying the solid captured carbon dioxide.

11. Method of capturing carbon dioxide from a gas stream according to claim 10, wherein the carbon dioxide capturing device according to any of the claims 1-9 is used.

12. Method of capturing carbon dioxide from a gas stream according to claim 10 or 11, wherein the gas containing carbon dioxide is fed into the principle heat exchanger at a pressure in the range of 5-10 bar gauge, preferably in the range of 5.5-10 bar gauge, more preferably in the range of 6.0 to 10 bar gauge.

13. Method of capturing carbon dioxide from a gas stream according to any of the claims 10, 11 or 12, wherein the carbon dioxide is removed from the packed bed as a liquid.

14. Method of capturing carbon dioxide from a gas stream according to claim 13, comprising:

- further pressurizing and heating the liquid captured carbon dioxide until it reaches transport conditions.

15. Method of capturing carbon dioxide from a gas stream according to claim 14, wherein said transport conditions comprise a pressure in the range 30 - 80 bar gauge and a temperature in the range of 10 - 40 degree Celsius.

16. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-15, wherein the gas stream containing carbon dioxide is fed in the cryogenic carbon dioxide capturing unit at a bed operating temperature in the range of -140 to -50 degrees Celcius.

17. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-16, wherein the gas stream containing carbon dioxide is a flue-gas.

18. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-17, wherein the gas stream containing carbon dioxide has a carbon dioxide content in the range of 5-50 vol%, preferably in the range of 5 - 15 vol%.

19. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-18, wherein the gas stream containing carbon dioxide has an excess oxygen content in the range of 2-50 vol%, preferably in the range of 5-15 vol%.

20. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-19, wherein both the capturing of the carbon dioxide and the regenerating of the packed bed take place at about the same pressure, which pressure is a super-atmospheric pressure.

21. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-20, wherein both the capturing of the carbon dioxide and the regenerating of the packed bed take place at a super-atmospheric pressure, preferably at a pressure in the range of 5.2 to 10 bar gauge.

22. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-21, wherein the capturing and regenerating are carried out at a pressure at which the cooled gas stream entering the cryogenic carbon dioxide capturing device is above the triple point of carbon dioxide while also being at the operating pressure of the air separation unit.

23. Method of capturing carbon dioxide from a gas stream according to any of the claims 10-22, wherein, the method is carried out in a carbon dioxide capturing device comprises two or more cryogenic carbon dioxide capturing units, each containing a packed bed, which cryogenic carbon dioxide capturing units are arranged in parallel, wherein the gas stream is passed through at least a first of said cryogenic carbon dioxide capturing units and carbon dioxide present in the gas stream is captured in the packed bed of said first cryogenic carbon dioxide capturing unit, whilst at least a second of cryogenic carbon dioxide capturing units is subjected to the regeneration of carbon dioxide captured in the packed bed of said second cryogenic carbon dioxide, the regeneration comprising melting of the solid carbon dioxide, thereby forming liquid carbon dioxide.

24. Method of capturing carbon dioxide from a gas stream according to claim 23, wherein during the regeneration also gaseous carbon dioxide is formed in said second cryogenic carbon dioxide capturing unit and said gaseous carbon dioxide is fed to the said first cryogenic carbon dioxide capturing unit, where the gaseous carbon dioxide is captured.