RU2818188C2 - Biocatalyst-based co2 stripping techniques and similar systems - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: present invention relates to the field of CO₂ trapping based on biocatalysts. Described is a method of stripping CO₂ for stripping CO₂ from a biocatalyst-containing absorbing solution with high content of CO₂ to obtain a biocatalyst-containing absorbing solution with low content of CO₂ and gas with high content of CO₂, including: generating a stripping gas from a portion of said biocatalyst-containing absorbent solution with low content of CO₂ in a stripping gas production unit which is a falling film evaporator, and bringing the biocatalyst-containing absorbent solution with high CO₂ content into contact with a stripping gas in the gas-liquid contactor to produce an absorbent solution with low CO₂ content, and a gas with high CO₂ content. Described is a method of stripping CO₂ for stripping CO₂ from a biocatalyst-containing absorbing solution with high content of CO₂ to obtain a biocatalyst-containing absorbing solution with low content of CO₂ and gas with high content of CO₂, including: generation of stripping gas from biocatalyst-containing absorbing solution containing high content of CO₂, and bringing the biocatalyst-containing absorbent solution with high CO₂ content into contact with the stripping gas in the gas-liquid contactor, which is a falling film evaporator, to obtain an absorbent solution with low content of CO₂, and gas with high content of CO₂. Also described is a method for capturing CO₂ based on a biocatalyst, comprising: bringing CO₂-containing gas into contact with an biocatalyst-containing absorbent solution to obtain a biocatalyst-containing absorbent solution with high content of CO₂, use of the CO₂ stripping method for desorption of CO₂ from a biocatalyst-containing absorbent solution with high content of CO₂, thus obtaining an absorbent solution with low content of CO₂ and gas with high content of CO₂. Disclosed is the use of a falling film evaporator for generating a stripping gas for stripping CO₂ from a biocatalyst-containing absorbent solution with high CO₂ content and obtaining a biocatalyst-containing absorbent solution with low content of CO₂.

EFFECT: reduced operating costs, increased stability and service life of the biocatalyst used in the process of capturing CO₂.

15 cl, 17 dwg, 3 tbl, 7 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

1. The present invention generally relates to biocatalyst-based CO ₂ capture methods and, in particular, to CO ₂ stripping techniques using a gas-liquid contactor.

BACKGROUND OF THE ART

2. Some known methods of CO ₂ capture are based on the use of the enzyme carbonic anhydrase to increase the efficiency of CO ₂ capture by absorbent solutions. These processes consist of two main units: an absorption unit for capturing CO ₂ from the CO ₂ -containing gas, and a stripping unit, where the absorbed CO ₂ is released from the CO ₂ -enriched absorbent solution and hence the absorbent solution is regenerated.

3. A simplified configuration of the CO ₂ capture method is shown in Figure 1. The method includes two zones: an absorption zone operating at a low temperature and a stripping zone operating at a higher temperature. In this method, CO ₂ -containing gas (1) is supplied to the absorption unit (2), where it moves upward, coming into contact with an aqueous absorption solution (4). When the gas comes into contact with the absorbent solution, CO ₂ is absorbed by the solution. The treated gas (3) then leaves the absorption unit and is released into the atmosphere or sent to other installations for further processing or use. The absorbent solution containing absorbed CO ₂ (5) is then pumped (pump 6) through two heat exchangers (7, 8), where its temperature is raised, and then fed to the stripping unit (9), where conditions are selected such that CO ₂ is released from solution and the solution is regenerated. A heat exchanger (8) is often optional. The gas (19) leaving the stripping unit (9) is supplied to the condenser (14), where the steam is condensed. The gas-liquid stream (20d) is then sent to a separator (14a) where the high CO ₂ concentration gas (20b) exits the separator (14a) and is directed to (compressor/vacuum pump 36) for use or further processing (stream 20). Condensed steam (20a) is returned to the process. Part of the absorbent solution with a low CO ₂ content leaving the stripping unit (10) is sent back to the absorption unit using a pump (16), the other part of the absorbent solution (11) with a low CO ₂ content is pumped by a pump (17) to the reboiler (12) . Then the solution is boiled to produce steam, the resulting vapor-liquid mixture (13) is sent to the stripping unit (9). The steam moves upward and acts as a stripping gas, promoting the desorption of CO ₂ from solution. Before being fed into the absorber, the solution (15) is cooled through heat exchangers (7, 18).

4. When used in combination with the above techniques, the absorption solution is usually an alkaline solution characterized by a pH above 9, the absorption unit is operated at temperatures from 10 to 50°C, the high CO ₂ absorption solution is heated to a temperature of 50 to 90°C before entering the stripping unit, which can operate under vacuum or near-atmospheric pressure. Consequently, the enzyme used in such CO ₂ capture processes is exposed to an alkaline pH above 9 and temperatures ranging from 10 to 90° C., and high pH and high temperature conditions are known to negatively affect enzymes.

5. Most of the references describing enzyme-based CO ₂ capture methods (carbonic anhydrase-based) emphasize the catalytic role of the enzyme to increase the efficiency of the CO ₂ capture process. The lifetime of the enzyme in such methods is a key issue, which is solved mainly by increasing the thermal stability of the enzyme in several ways.

6. In the first strategy, the enzyme is applied in the absorption zone of the process, where the process temperature to which the enzyme is exposed is lowest. This strategy is applied in different ways: the enzyme can be immobilized on a packed material, while the gas-liquid contactor is a packed column, in this configuration the enzyme is always in the absorber and thus exposed to low temperatures. The enzyme can also be immobilized on microparticles in suspension in an absorbent solution. In this configuration, once the absorption solution leaves the absorber, the microparticles are separated from the high CO ₂ absorption solution and reintroduced into the absorption solution before being supplied to the absorption unit. The enzyme can be used free or solubilized in an absorbent solution, and the enzyme is filtered from the solution in a manner similar to microparticles. In this first strategy, the enzyme is exposed only to the pH and temperature conditions present in the absorption zone of the process.

7. In the second strategy, increasing enzyme stability is achieved using carbonic anhydrase enzymes that are resistant to process conditions, selected from carbonic anhydrase enzymes from naturally occurring microorganisms, or obtained through genetic modification using directed evolution to develop enzymes that are resistant to specific process conditions. The ultimate goal of this second strategy is to develop an enzyme that is active and stable under operating conditions in both the absorption and stripping zones of the process.

8. The third strategy is to combine the new stable enzymes obtained from the second strategy with immobilization techniques and apply this stable immobilized enzyme only in the absorption zone, or in both the absorption zone and the stripping zone.

9. There is still room for improvements associated with the implementation of a biocatalyst-based CO ₂ capture process that would increase the half-life of the biocatalyst under operating conditions.

DISCLOSURE OF THE INVENTION

10. Options for implementing a biocatalyst-based CO ₂ capture method address the above need by providing process design options to minimize or prevent exposure of a solution containing the biocatalyst to bubble formation conditions, in which new gas-liquid interfaces are created through bubble formation, thereby increasing the service life of the biocatalyst. The conditions for the formation of bubbles are met, for example, when a solution containing a biocatalyst is boiled.

11. The present technical solutions relate to a biocatalyst-based CO ₂ capture method, which may include bringing a biocatalyst-containing absorbent solution high in CO ₂ into contact with a stripping gas from a stripping system to create a driving force that desorbs CO ₂ from the biocatalyst-containing absorbent solution. a solution with a high CO ₂ content, to obtain an absorbent solution containing a biocatalyst with a low CO ₂ content, and a CO ₂ enriched gas.

12. The purification system includes a gas-liquid contactor, which may be a direct-acting gas-liquid contactor. Direct acting gas-liquid contactor refers to a device that provides contact between a gas phase and a liquid phase in the absence of any physical barrier (such as membranes). In some embodiments, the gas-liquid contactor may be selected from, for example, a packed column, a tray column, a spray reactor, a rotating packed bed, and a falling film evaporator.

13. The biocatalyst can be used in soluble form or in immobilized form, for example attached to particles or embedded within a porous matrix. For both forms of biocatalyst delivery, the biocatalyst may be in-stream with the absorption solution in an absorption unit (in a high CO ₂ absorbent solution) and in a desorption unit (in a low CO ₂ absorbent solution).

14. In a first aspect, a CO ₂ stripping method is provided, including generating a stripping gas and contacting a high CO ₂ absorption solution with the stripping gas to produce a low CO ₂ absorption solution and a high CO ₂ gas.

15. Optionally, at least part or all of the stripping gas is generated from a portion of the low CO ₂ absorbent solution. In some embodiments of the CO ₂ stripping method, generating the stripping gas includes supplying a portion of the low CO ₂ absorbent solution to a stripping gas generation unit to produce stripping gas, the method further including supplying the stripping gas to a gas-liquid contactor. The boil-off gas generation unit may be a falling film evaporator, and the gas-liquid contactor may be a packed column, tray column, or rotating packed bed.

16. In addition, the stripping gas is optionally generated from a high CO ₂ absorbing solution. In some embodiments of the CO ₂ stripping method, generating the stripping gas involves heating a high CO ₂ absorbent solution in a gas-liquid contactor to produce stripping gas and simultaneously stripping the high CO ₂ absorbing solution. The gas-liquid contactor may be a falling film evaporator.

17. In some embodiments, the absorption solution is an aqueous biocatalyst solution and therefore the resulting stripping gas may include steam.

18. In another aspect, a CO ₂ stripping method is provided, comprising condensing at least a portion of a CO ₂ -rich gas to generate a stripping liquid, generating a stripping gas from the stripping liquid, and bringing a CO ₂ -rich absorbent solution into contact with stripping gas to obtain an absorbent solution with a low CO ₂ content and CO ₂ enriched gas.

19. In some embodiments, the generation of stripping gas from the stripping liquid is carried out in a reboiler, wherein the stripping gas is supplied to a direct gas-liquid contactor. The direct gas-liquid contactor may be, for example, a packed column, a tray column, a spray reactor, or a rotating packed bed.

20. In some embodiments, the stripping liquid is a liquid containing water, which may be water or an aqueous solution such as a salt solution (eg, NaCl, KCl, K ₂ CO ₃ , Ka ₂ CO ₃ ).

21. In other embodiments, the stripping liquid is a liquid organic compound. Optionally, the stripping liquid may be immiscible with water and have a lower density than water. Additionally, the stripping liquid may optionally be immiscible with water and have a higher density than water. For example, the liquid organic compound may be a hydrocarbon CxHy, where x=5 or 6; or a halogenated hydrocarbon derivative including hexane, cyclohexane, cyclopentane, cis-1,2-dichloroethene, 2-methylpentane, trichlorethylene, CHCl ₂ , perfluorohexane or an organosilicon compound such as tetramethylsilane.

22. In some embodiments, the stripping gas is supplied to a plurality of spaced locations, preferably distributed along the height of the gas-liquid contactor. In other embodiments, the high CO ₂ absorbent solution is withdrawn from various sections of the direct gas-liquid contactor for heating and reintroduced into the gas-liquid contactor through heating circuits.

23. In an additional aspect, there is provided a CO ₂ stripping method comprising directly contacting a high CO ₂ absorption solution with a stripping gas to produce a low CO ₂ absorbing solution and a CO ₂ -enriched gas, wherein the stripping gas is a non-condensable gas. It should be noted that direct contact refers to contact between the gas phase and the liquid phase in the absence of any physical barrier (for example, membranes).

24. In some embodiments, direct contact of the high CO ₂ absorbent solution with the stripping gas occurs in a packed column, tray column, or rotating packed bed (acting as a gas-liquid contactor).

25. In some embodiments, the non-condensable gas is air or nitrogen.

26. In an additional aspect, a method of stripping CO ₂ is provided, comprising minimizing or preventing the exposure of a high CO ₂ absorbent solution to bubble formation conditions in which new gas-liquid interfaces are created through the formation of bubbles, and stripping CO ₂ from the high CO 2 absorbent solution. CO ₂ content.

27. In another aspect, a biocatalyst-based CO ₂ capture method is provided, comprising contacting a gas containing CO ₂ with an absorption solution to obtain an absorption solution with a high CO ₂ content, and using any of the above CO ₂ stripping methods to desorption the CO ₂ from a high CO ₂ absorption solution, thereby obtaining a low CO ₂ absorption solution and a high CO ₂ gas.

28. In another aspect, there is provided a method for desorption of CO ₂ from a biocatalyst-containing high-CO ₂ absorption solution in an evaporator, the method comprising supplying a biocatalyst-containing high-CO ₂ absorption solution to the evaporator and heating the biocatalyst-containing high-CO 2 absorption solution ₂ to simultaneously generate a stripping gas and provide a driving force for the desorption of CO ₂ from the biocatalyst-containing absorbent solution with a high CO ₂ content. In some embodiments, the evaporator may be a falling film evaporator or equivalent.

29. In another aspect, it is proposed to use an evaporator to generate a stripping gas for stripping CO ₂ from a biocatalyst-containing absorption solution with a high CO ₂ content, and producing a biocatalyst-containing absorption solution with a low CO ₂ content. In some embodiments, an evaporator is used to generate boil-off gas from a biocatalyst-containing absorption solution with a high CO ₂ content. In other embodiments, an evaporator is used to generate boil-off gas from a biocatalyst-containing low CO ₂ absorbent solution. In some embodiments, the evaporator may be a falling film evaporator.

30. Although the invention will be described in connection with exemplary embodiments, it should be understood that it is not intended to limit the scope of the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents that may be included as defined herein. The objects, advantages and other features of the present invention will become more apparent and understood after reading the following non-limiting description of the present invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

31. Embodiments of a biocatalyst-based CO ₂ capture method and similar units are presented and also understood in connection with the following figures.

32. Figure 1 is a simplified diagram of a biocatalysis-based CO ₂ capture method including an absorption zone and a stripping zone (prior art).

33. Figure 2 is a simplified diagram of a biocatalyst-based CO ₂ capture method in which the reboiler is replaced by a falling film evaporator.

34. Figure 2a is a schematic illustration of a falling film evaporator.

35. Figure 3 is a configuration diagram of a stripper unit in which the stripping gas required for the stripper unit is supplied through a stripper gas loop according to the first embodiment.

36. Figure 3a is a diagram of a stripper configuration where the stripper gas required for the stripper is supplied through a stripper gas loop according to the second embodiment, wherein the stripper gas is introduced through a plurality of injection ports distributed along the height of the stripper.

37. Figure 3b is a configuration diagram of a stripper unit in which the stripper gas required for the stripper is supplied through a stripper gas loop according to a third embodiment in which the absorbent solution is withdrawn from various sections of the stripper unit for heating and reintroduced to the stripper unit through heating circuits.

38. Figure 4 is a diagram of a biocatalyst-based CO ₂ capture method including a stripping gas and an evaporation loop according to the first embodiment.

39. Figure 4a is a diagram of a biocatalyst-based CO ₂ capture method including a stripping gas and an evaporation loop according to a second embodiment.

40. Figure 4b is a diagram of a biocatalyst-based CO ₂ capture method including a flash gas and a flash loop according to an alternative embodiment where the gas used in the flash loop is used in a closed loop system.

41. Figure 5 is a diagram of a biocatalyst-based CO ₂ capture method where the stripping gas required for the stripping unit is supplied through a stripping gas loop, and where the stripping liquid is immiscible with water and has a lower density than water.

42. Figure 5a is a diagram of a biocatalyst based CO ₂ capture process where the stripping gas required for the stripping unit is supplied through a stripping gas loop and where the stripping liquid is immiscible with water and has a higher density than water.

43. Figure 6 is a diagram of a biocatalyst based CO ₂ capture method where the stripping gas required for the stripping unit is a gas supplied from an external source.

44. Figure 6a is a diagram of a biocatalyst-based CO ₂ capture method where the stripping gas required for the stripper is a gas supplied from an external source and where the gas is heated before being supplied to the stripper.

45. Figure 7 is a diagram of a biocatalyst-based CO ₂ capture method where the stripper unit is a falling film evaporator and the stripper gas is vapor evaporated from the absorption solution.

46. Figure 7a is a diagram of a biocatalyst-based CO ₂ capture method where the stripper unit consists of two falling film evaporators operating in parallel and the stripping gas is vapor evaporated from the absorption solution.

47. Figure 7b is a diagram of a biocatalyst-based CO ₂ capture process where the stripper unit consists of two falling film evaporators operating in series and the stripping gas is vapor evaporated from the absorption solution.

48. Figure 7c is a schematic of a biocatalyst-based CO ₂ capture method where the stripper unit consists of two falling film evaporators operating in series, and where the stripping gas from the first falling film evaporator is the heat source for the second falling film evaporator.

49. Although the invention will be described in connection with exemplary embodiments, it should be understood that it is not intended to limit the scope of the invention to these embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents that may be included as defined in the appended claims.

IMPLEMENTATION OF THE INVENTION

50. These technical solutions relate to the field of CO ₂ capture based on biocatalysts. The CO ₂ -containing gas may be combustion flue gas, process gas, biogas or natural gas from various sources. In particular, the present invention relates to carbonic anhydrase-based CO ₂ capture methods in which the carbonic anhydrase biocatalyst is present in an absorption solution and flows with that solution through a gas-liquid contactor. More specifically, the present invention discloses methods/processes to increase the life of the biocatalyst and reduce the cost of the biocatalyst technology.

51. Recent studies have clearly demonstrated that, in addition to pH and temperature, a third parameter has a very important influence on the stability of the biocatalytic process: the rate of formation of new gas-liquid interfaces. This phenomenon occurs in the absorption unit, the stripper unit, and, more importantly, in the reboiler attached to the stripper unit, which provides stripping gas, usually steam, by boiling the absorption solution. It has been clearly demonstrated that the rate of loss of biocatalyst activity is directly related to the flow rate of the generated steam in the reboiler. In fact, it is the high boiling rate, which provides a high rate of gas-liquid interface formation, that mainly causes the loss of biocatalyst activity during CO ₂ capture.

52. In the following description, the term "about" means within the acceptable range of error for a particular value, as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e. limitations of the measurement system. It is generally accepted that a measure of accuracy of 10% is acceptable and includes the term "about".

53. In the above description, the embodiment is an example or implementation of the present invention. The various appearances of “one embodiment,” “an embodiment,” “some embodiments,” or “some embodiments” do not necessarily all refer to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, these features may also be provided separately or in any suitable combination. Conversely, although the present invention may be described herein in the context of individual embodiments for the sake of clarity, the present invention may also be practiced in a single embodiment.

54. It is worth mentioning that throughout the following description, when the singular and indefinite form is used to introduce an element, it means “only one,” but rather may mean “one or more.” It should also be understood that while the specification states that a component, feature, structure or characteristic "may", "could", "could" or "could" be included, that particular component, feature, structure or characteristic is not necessarily included.

55. Currently described biocatalyst-based CO ₂ capture techniques involve controlling the rate of gas-liquid interface formation to influence the life of the biocatalyst. In particular, this application provides methods that minimize the formation of new gas-liquid interfaces and increase the life of the biocatalyst in the process.

56. This description should be considered in the light of the following definitions: Absorber or absorption unit.

57. An absorber (also referred to herein as an absorption unit) is a gas-liquid contactor, which may be, for example, a packed column, a tray column, or a rotating packed bed.

Stripping column

58. A stripper (also referred to herein as a stripper) is a gas-liquid contactor that can be a packed column, tray column, spray reactor, rotating packed bed, or falling film evaporator.

Absorbing solution

59. The absorbent solution is an aqueous solution that may include at least one of the following compounds: K ₂ CO ₃ , KHCO ₃ , Na ₂ CO ₃ , NaHCO ₃ , tertiary amines, tertiary alkanolamines, tertiary amino acids. The absorbent solution includes solutions that do not form a carbamate.

Gas with high CO ₂ content

60. The CO ₂ -rich gas is the gas phase leaving the stripping column, prior to any subsequent treatments or process steps.

Biocatalyst

61. Biocatalysts that can be used in the present methods are selected from the group consisting of enzymes, liposomes, microorganisms, animal cells, plant cells, and any combination thereof. The biocatalyst can be used in soluble form or in immobilized form, that is, attached to a particle or embedded within a porous matrix. For both forms of biocatalyst delivery, the biocatalyst is in-line with the absorbent solution in an absorbent block and a stripping block. It should be noted that the biocatalyst may preferably be an enzyme such as carbonic anhydrase. The enzyme may be present in the absorbent solution at an enzyme concentration of about 0-2 g/L, optionally about 0.05-1 g/L, and optionally about 0.1-0.3 g/L.

62. The enzyme carbonic anhydrase, which has a relatively low molecular weight, can be prepared as part of a complex to increase its size. Various types of enzyme complexes can be prepared. Among them there are complexes using whole cells, such as red blood cells. However, when red blood cells are used, enzymes quickly leak and are lost. Carbonic anhydrase may be immobilized on the surface of the microparticle carrier material, embedded in the microparticle carrier material, or a combination thereof. In another optional aspect, the carbonic anhydrase may also be presented in the form of cross-linked enzyme aggregates (CLEA), and the carrier material includes a portion of the carbonic anhydrase and a cross-linking agent. In yet another optional aspect, the carbonic anhydrase is provided in the form of cross-linked enzyme crystals (CLECs) and the carrier material includes a portion of the carbonic anhydrase. The materials and methods selected must stabilize the enzyme to make it more resistant to process conditions, allowing the enzyme to remain immobilized, that is, fixed or entrapped on/in the carrier material when applied to the process. In other words, the materials and chemical bonds (when using a chemical method) must remain stable over a long period of time to ensure long-term stability of the enzyme in the process.

63. The present invention provides methods for reducing the rate of loss of biocatalyst activity in CO ₂ capture processes by providing alternative process configurations in which there is little to no boiling, in which the biocatalyst in the absorbent solution flows through absorption and desorption units. Three options are discussed below.

64. In the first option, steam is produced by sending a low CO ₂ absorbent solution to an evaporator instead of a reboiler. A reboiler is commonly used in CO ₂ capture processes to produce steam from a low CO ₂ absorbent solution. Steam is generated when the absorbent solution is boiled, i.e. when water vapor bubbles form in a solution. The formation of these vapor bubbles results in the formation of new gas/liquid interfaces (vapor bubbles from the absorbent solution), which have been found to be detrimental to the biocatalyst. To minimize the formation of bubbles, the reboiler (12) (Figure 1) can be replaced by an evaporator, in which the operating conditions are selected so that steam is generated by evaporation, that is, water evaporates on the surface of the aqueous solution. Under such operating conditions, the formation of new gas/liquid interfaces is minimal and occurs solely due to the flow of the absorbent solution in the evaporator. In such a device, the formation of bubbles is almost eliminated, and therefore the carbonic anhydrase enzyme is minimally exposed to new gas/liquid interfaces.

65. In the second option, the stripping gas is supplied not after evaporation or boiling of the absorbent solution, but from the external stripping gas circuit, where the stripping gas can condense, for example, water. The absorbent solution is not fed to the reboiler and therefore is not subjected to any boiling conditions. The reboiler (12) (Figure 1) is removed from the process configuration.

66. In a third embodiment, the reboiler (12) (Figure 1) is removed from the process and the stripping gas required for the stripping unit is a non-condensable gas. The absorbent solution is not boiled. The stripping gas is a non-condensable gas such as air or nitrogen.

67. Operating conditions in the absorption unit may include an absorption temperature of about 10-60°C and an absorption pressure of about 1-40 bar. Operating conditions in the stripping unit may include a stripping temperature of about 50-80°C and a stripping pressure of about 0.1-1 atm.

Option 1: Falling Film Evaporator

68. In the first option, it is proposed to replace the reboiler with an evaporator. Evaporators are used in many industries, such as the food, chemical, pharmaceutical and dairy industries, to concentrate solutions or suspensions. In such applications, it is necessary to remove water from these solutions or suspensions to obtain a product of the desired quality. In these applications, the water vapor is removed while the end product is a concentrated solution. For example, to prepare condensed milk, more than 45% of the water is evaporated from natural milk.

69. Various types of evaporators can be used, namely: forced circulation, natural circulation, distributed film, tubular and rising film evaporators, tubular falling film evaporators, tubular rising/falling film evaporators, plate rising film evaporators, falling film plate evaporators and rising/falling film plate evaporators. Among them, falling film evaporators (tubular or plate) are preferred as they provide very short residence times, good heat transfer coefficients and can operate under vacuum conditions where water evaporation occurs at lower temperatures compared to atmospheric pressure or higher pressure. It is widely accepted for concentrating heat-sensitive products in the food industry.

70. A schematic representation of a tubular falling film evaporator is shown in Figure 2a. The tubular falling film evaporator (2a-7) consists of a casing and tubes. The concentrated liquid (2a-3) is supplied to the distributor at the top of the evaporator. The distributor is designed to distribute liquid evenly throughout each tube. This is important to avoid dry spots on the surface of the tubes, which can reduce performance. The liquid is fed inside the walls, where it forms a film. The liquid film falls down under the influence of gravity. The downward flow is enhanced by the parallel downward flow of the resulting steam. This results in a thinner, faster moving film, reducing fluid contact time and improving heat transfer coefficients. A heating fluid (2a-1), which may be steam, hot water, or any hot fluid having the energy to evaporate water from a liquid, is supplied to the shell and provides the thermal energy necessary to heat the liquid to be heated to concentrate and evaporate the water. from liquid. The liquid/steam mixture is removed from the system (2a-4). The heating fluid, now in condensed form and/or at a lower temperature, exits the shell at the bottom (2a-2). Residual film liquid and vapor are separated at the bottom of the shell and in the downstream droplet separator (2a-8). The concentrated liquid (2a-5) comes out at the bottom of the separator, while the steam (2a-6) collects at the top of the separator. Some of the concentrated liquid can be returned back to the evaporator inlet to ensure sufficient wetting of the tubes. The features of the falling film evaporator are gentle evaporation, mainly carried out under vacuum conditions, extremely short residence time of the liquid in the evaporator, low pressure drop, high energy efficiency allowing operation with a small temperature difference between the process and heating fluid, simple process control and automation, flexible management. This type of evaporator is especially suitable for temperature sensitive products. 71. Based on the above advantages of falling film evaporator, the reboiler can be replaced by falling film evaporator. The corresponding configuration of the method is shown in Figure 2. First, CO ₂ -containing gas (1) is supplied to the absorption unit (2). CO ₂ gas is absorbed by the countercurrent of the absorbent solution (4). Purified gas (3) with a low CO ₂ content is removed from the CO ₂ capture process into the atmosphere or sent for use or additional processing. The CO ₂ -rich absorbent solution (5) is pumped (6) and flows through two heat exchangers (7) and (8) to raise its temperature before entering the stripping unit (9). The heat exchanger (8) is optional. In the case where a heat exchanger (8) is used, which allows some of the water from the solution to evaporate, the resulting steam can be recovered and pumped down into the stripper nozzle (9) to act as a stripping gas (not illustrated). An absorbent solution (10) with a low CO ₂ content leaves the stripping unit (9). Part of the stream (10), stream (11), is pumped (17) into the evaporator (21), where the solution is heated and the water evaporates. Flow (22) is formed. Stream (22) contains steam, a low content concentrated absorbent solution, and may also contain CO ₂ gas. The steam stream (22) is collected and sent to the stripping unit (9). The CO ₂ -rich gas (19) leaving the stripper (9) can be fed to a condenser (14) where the steam is condensed. The gas-liquid stream (20d) is then directed to a separator (14a) where the high _CO2 concentration gas (20b) exits the separator (14a) and is directed through a compressor/vacuum pump (36) for further use or processing as a stream (20) . The condensed steam (20a) is returned to the process to be mixed with the regenerated absorbent solution (4). The flow (20 s) represents the process water supply.

72. In an alternative configuration, which is not illustrated, stream (22) may be supplied to a separator in which the gas and liquid phases may be separated and collected separately. The liquid phase (concentrated solution) can be sent back to the reservoir at the bottom of the stripping unit (9) or mixed with the stream (10) or (15) to be directed to the absorption unit (2). The gas phase can then be sent back to the stripping column (9). Unlike the food, dairy, pharmaceutical and chemical industries, the gas and liquid phases are re-injected into the same process unit (stripping unit (9)), while in the food industry the concentrated solution and steam have different purposes. Another difference from the traditional one is that less than 20% (by weight) of the solution must be evaporated.

73. Option 2: Boil-off gas circuit

74. In the second option, the reboiler is removed from the process and replaced with an external boil-off gas loop (Figure 3). The stripping gas loop is a process in which stripping liquid is used to produce stripping gas. The stripping liquid from the reservoir (25) is sent (27) to the reboiler (24) and is boiled to form steam, acting as a stripping gas (28), which is introduced into the bottom of the stripping column (9). The stripping gas passes upward through the stripper column, where it contacts the high CO ₂ absorption solution (stream 5'), desorption of the CO ₂ and evaporation of water from the solution. The stripping steam/steam/CO ₂ mixture (19) leaves the stripping column and is sent to the condenser (14). The stripping gas and water vapor are condensed (26) and moved to a tank (25). The reservoir contains stripping liquid and liquid water. Depending on the nature of the stripping liquid, different process configurations can be adopted, as will be described below. The gas (20b) with a high concentration of CO ₂ is compressed (36) and exits the process (stream 20) for further use or storage. An absorbent solution with a low CO ₂ content leaves the stripping unit (stream 10) and is pumped (pump 16) into the absorption unit (stream 15). Stream (27a) is the feed stream for the stripping liquid.

75. It should also be noted that stream (27) can be heated to a temperature close to that of the reboiler using a heat exchanger before entering the reboiler (not shown in Figure 3).

76. In the first embodiment, stripping steam (28) can be introduced at different heights (from 28a to 28g) along the stripping column, as shown in Figure 3a. This configuration minimizes the temperature gradient throughout the stripper column and increases stripping productivity. The steam, acting as a stripping gas, moves upward through the stripping column and comes into contact with the CO ₂ -rich absorbent solution. As the absorbent solution flows downward, and due to the CO ₂ concentration gradient between the stripping gas and the absorbent solution, the CO ₂ is desorbed. Steam may also condense in the solution. The CO ₂ -rich gas (19) leaving the stripping column (9) contains stripping gas, water vapor and CO ₂ ; and is sent to the condenser (14), where water is condensed and gas (20b) with a high concentration of CO ₂ is formed. The high CO ₂ concentration gas (20b) is then compressed in a compressor (36) and sent as a stream (20) to additional units for use, processing and/or storage.

77. In another embodiment, shown in Figure 3b, stripping steam (28) is introduced into the bottom of the stripping column. However, in different sections of the stripping column, the absorbent solution is withdrawn using a pump, then heated using a heat exchanger, and then returned to the stripping unit. Several heating circuits, such as 29, 30 and 31, may be present along the height of the stripping column. The absorbent solution can be withdrawn from the bottom of the packed bed and reinjected into the top of the same packed bed. Alternatively, the absorbent solution may be withdrawn from the top of the packed bed and reinjected into the bottom of the same packed bed.

78. For both implementations, the number of heating loops or injection ports depends on the height of the column, the energy required for injection, and the economics of the process.

79. The two previous embodiments, i.e. different injection locations and heating circuits, can also be applied to the method configuration shown in Figure 2.

80. Regarding the nature of the stripping liquid, the key properties of the appropriate stripping liquid are the following:

81. It must be in the vapor or gas phase under the conditions of the stripping operation.

82. The vapor or gas phase should condense easily at a temperature slightly below the stripping temperature.

83. Stripping liquids can be selected from water, aqueous solutions and liquid organic compounds having appropriate properties. Liquids or solutions can be divided into two classes: water-miscible and water-immiscible. Depending on the properties of the liquids or solutions, various process configurations are possible, as described below.

Stripping liquid: Liquid containing water

84. In the first embodiment, the stripping liquid contains water. It can be pure water or an aqueous solution, for example, saline solution (NaCl, KCl, K ₂ CO ₃ , Na ₂ CO ₃ ). The salt concentration can be adjusted to achieve the desired boiling point. When an aqueous solution is used as stripping liquid, its composition or salt concentration is adjusted so that the boiling point of the solution is slightly higher than the operating temperature of the stripper.

85. The stripping steam leaving the reboiler is at a temperature equal to the stripping temperature or slightly higher to produce superheated steam. Preferably, the temperature of the stripping steam leaving the reboiler is no more than 15°C higher than the stripper temperature, more preferably no more than 10°C higher than the stripper temperature, and most preferably no more than 5°C higher than the stripper temperature steaming. The method is as described in Figures 3, 3a and 3b. Since the stripping process is endothermic, there is a possibility that the stripping steam will condense in the stripping unit. As a consequence, water will mix with the water-based absorbent solution, diluting the absorbent solution and therefore changing the process characteristics. To reduce the effect of water condensation and dilution of the absorbent solution, various process configurations are disclosed, which are shown in Figures 4, 4a and 4b.

86. Referring to Figures 4, 4a and 4b, steam is generated in the stripping gas loop, where the stripping liquid is water or brine. The method further includes an evaporation circuit to maintain the quality of the absorbent solution before entering the absorber.

87. A first configuration of the method is shown in Figure 4. The description focuses on the stripe gas loop and control of the condensed stripe steam in the evaporator loop. At the bottom of the stripping column, the tank is divided into two compartments 9a and 9b. Compartment 9a contains a low CO ₂ absorbent solution, and compartment 9b contains stripping liquid, which may be water or an aqueous solution. The liquid from compartment 9b is pumped (pump 44) to the reboiler (24). The liquid boils, producing water vapor (steam) (47), which is introduced as stripping steam into the bottom of the stripping column (9). The steam temperature depends on the solution composition and the operating temperature of the reboiler. The stripping steam moves upward and comes into contact with the descending absorbent solution containing CO ₂ . When both streams are in contact, CO ₂ is released from the absorbent solution, water can evaporate from the absorbent solution, the stripping steam cools, and a portion of the stripping steam can condense and combine with the absorbent solution. The stripping steam leaves the stripping column along with the evolved CO ₂ gas and water vapor (19). The gas mixture (19) is sent to the condenser (14), where the steam and stripping steam are condensed. The gas/liquid mixture (34) is directed to a reservoir (32), where the liquid and gas phases are separated. The gas phase (35) with a high concentration of CO ₂ leaving the reservoir (32) is compressed (36) and sent (stream 20) to additional processing units, processes or storage units. The liquid phase (40) leaving the tank is then mixed with the stream (45) before it enters the reboiler (24). The low CO ₂ absorbent solution (10), which may have a higher water content due to condensed stripping steam, is pumped (pump 16) and directed to heat exchangers (7) and (18) before being supplied to the absorption unit (2). Part of the stream (15), stream (42), is sent to the evaporation circuit.

88. The purpose of the evaporation loop is to remove water added to the absorbent solution in the stripping column and restore the original composition of the absorbent solution. The evaporation circuit includes an evaporation drum (48) operating at a pressure lower than the pressure in the stripper. Upon entering the evaporation drum (48), part of the water present in the solution evaporates. The liquid phase (58) leaving the flash drum (48), having a reduced water content, is pumped (pump 59) and the stream (60) is mixed with the stream (15'). The steam generated in the evaporation drum (57) is sent to the compressor (49) and then to the cooling unit (50), where the water is partially condensed. The gas/liquid mixture (51) is directed to a reservoir (52), where the gas and liquid phases are separated. The gas phase (53) is released into the atmosphere. Stream (53) consists of CO ₂ and water vapor. The liquid phase (54), mainly consisting of water, is recovered, pumped (stream 56) and ultimately mixed with streams (45) and (40) in the boil-off gas loop. Alternatively, stream (54) may be mixed with stream (15').

89. In an alternative configuration, the evaporation drum can be replaced by a falling film evaporator.

90. A second configuration of the method is shown in Figure 4a. This second embodiment is similar to the embodiment in Figure 4 with respect to the boil-off gas circuit. In this second embodiment, excess water present in the absorbent solution is removed after it has circulated through the heat exchanger (7) but before it enters the refrigerator (18). Part of the flow (15') is directed to a packed column (65). Stream (61) is supplied to the top of the column and flows down through the packing material. As it moves, it comes into contact with dry gas or gas below its water saturation level (63). Some of the water present in the absorbent solution evaporates and exits the packed column with the gas stream (64). Stream (64) may be released to the atmosphere or recovered for further processing. The absorption solution leaving the packed column (62), having a reduced water content, is mixed with the absorption stream (15') with a low CO ₂ content. The mixture (15'') is then cooled and fed into the absorption column (2).

91. A third method configuration is shown in Figure 4b. This third embodiment is similar to the embodiment shown in Figure 4a. As in the previous embodiment, excess water present in the low CO ₂ absorption solution (15) is removed after it circulates through the heat exchanger (7) but before entering the refrigerator (18). A portion (61) of the flow (15') is directed to a packed column (65). Stream (61) is supplied to the top of the column and flows down through the packing material. As it moves, it comes into contact with dry gas or gas below its water saturation level (63c). Some of the water present in the absorbent solution evaporates and exits the packed column with the gas stream (64). Stream (64) can be recovered and sent to heat exchanger (14a) where the gas is cooled and the steam is condensed. The gas/liquid mixture (34a) is sent to a gas/liquid separator (32a). The gas stream (35a) leaving the separator (32a) is supplied to the fan (36a). It may then be partially released into the atmosphere (63a) and/or sent back (63b) to the inlet of the packed column (65). The water stream (40a) leaving the separator (32a) is directed back to the boil-off gas circuit in the tank (32). Alternatively, and not shown, a portion of stream (40a) may be mixed with stream (62) or (15''). The low water content absorbent solution (62) exiting the packed column (65) is mixed with the low CO ₂ absorbent stream (15') to form a mixture (15''). Then the mixture (15'') is cooled in the refrigerator (18) and fed into the absorption column (2). Stream (63) is a feed stream.

Stripping liquid: Liquid organic compound

92. For a liquid organic compound to be considered a suitable stripping liquid, it must satisfy the following criteria:

- be in a vapor or gaseous state under operating conditions of the stripping unit;

- be in a liquid state at temperatures slightly below the operating temperature of the stripping column;

- do not mix with aqueous solutions. This property will facilitate the separation of the organic compound from the aqueous solution and will prevent the compound from dissolving in the aqueous solution.

93. Based on the previous criteria, an organic compound may be:

- hydrocarbon CxHy, where x=5 or 6;

- halogenated hydrocarbon derivative;

- any other compound that meets the above criteria.

94. Some candidate compounds are hexane, cyclohexane, cyclopentane, cis-1,2-dichloroethene, 2-methylpentane, trichlorethylene, CHCl ₂ , perfluorohexane and tetramethylsilane.

95. The implementation of this strategy is shown in Figure 5. The description focuses on the stripper unit and stripper gas loop, as well as the control of the condensed stripper steam. The stripping liquid is stored in a tank (25). It moves (stream 66) to the reboiler (24). The stripping liquid boils and produces steam or stripping steam (47), which is introduced into the bottom of the stripping column (9). The stripping steam temperature is higher than the operating temperature in the stripping column (9). The stripping steam moves upward and contacts the descending absorbent solution (5') containing CO ₂ . When both streams are in contact, CO ₂ is released from the absorbent solution, water evaporates from the aqueous absorbent solution, and the stripping steam is cooled but remains in the system in a gaseous state. The stripping steam does not condense because its boiling point is lower than the temperature in the stripping column. The stripping steam leaves the stripping column along with the evolved CO ₂ gas and water vapor (19). The _CO2 -rich gas (19) is sent to a condenser where the steam and stripping steam are condensed into water and stripping liquid. Water and stripping liquid (26) are transferred to a tank (25). Because the two liquid phases are immiscible, they can be separated and then used separately. In case the stripping liquid has a lower density than water, the stripping liquid (66) is collected at the top of the tank and then fed to the boiler (24). The water is recovered (67) and combined with the low CO ₂ absorbent solution between heat exchangers (7) and (18). The gas (20b) with a high concentration of CO ₂ is compressed (36) and then exits the process (20) for further use, processing or storage. If the stripping liquid is denser than water, the process will be as shown in Figure 5a. In both cases, stream (66a) provides replenishment of the stripping liquid.

96. For both configurations, a heat exchanger (8) (as shown in Figures 1 and 2) can be added to heat the high content absorbent solution fed to the stripping column (9). A heating loop similar to that shown in Figure 3b can be added to the bottom of the stripper column to heat the low content absorbent solution located in the tank below the packing material. These additives may be required to maintain proper temperature conditions in the stripper. These additional steps and associated equipment may be combined with various process embodiments disclosed herein in which the stripping column is a packed column.

Option 3: External boil-off gas

97. In this third embodiment, the reboiler (12) (Figure 1) is removed from the process. The stripping gas is supplied using external non-condensable gas (under process conditions). Examples of suitable non-condensable gases are air and nitrogen. The process configuration corresponding to this embodiment is shown in Figure 6. First, CO ₂ -containing gas (1) is supplied to the absorption unit (2). CO ₂ gas is absorbed by the countercurrent of the absorbent solution (4). Purified gas (3) with a low CO ₂ content is removed from the CO ₂ capture process into the atmosphere or sent for use or additional processing. The absorbent solution (5) with a high CO ₂ content is pumped (pump 6) and sent to the first heat exchanger (7). The heated solution with a high CO ₂ content containing the biocatalyst (5') is heated in the heat exchanger (8) and then fed to the stripping column (9). Heat exchanger (8) is optional. The solution flows down, contacts the stripping gas, leaves the stripping column (10) and is pumped (pump 16) to the heat exchanger (7) and then to the heat exchanger (18), and then the stream (4) is fed to the absorption column (2). Stripping gas (68) is introduced into the bottom of the stripping column packing. The gas flows upward, comes into contact with the absorbing solution, due to the presence of a concentration gradient between the gas phase and the liquid phase, CO ₂ is desorbed from the solution, and water evaporates. The gas (19) leaving the stripping column (9) consists of CO ₂ , water and stripping gas. The stream (19) is then fed to a condenser (14) where the water vapor is condensed and sent back to the process (70). Gas (69), containing CO ₂ and stripping gas, is released into the atmosphere, sent for storage or used in various processes.

98. As shown in Figure 6a, in another embodiment, the temperature of the stripping gas (68) can be increased to increase the concentration gradient between the liquid and gas phases in the stripper column and promote CO ₂ desorption (Figure 6a). In this case, the stripping gas (68) is supplied to the heat exchanger (72) to heat it, and then the stream (71) is supplied to the stripping column (9). In a second embodiment, the stripping unit can be operated under vacuum conditions. Steam (70a) provides the supply of process water. In a further embodiment, the stripping gas may be supplied to various locations along the stripping unit, as shown in Figure 3a.

Option 4: Falling film evaporator as stripper (gas-liquid contactor)

99. The gas-liquid contactor in the stripper unit may also be a falling film evaporator having a plate or tubular configuration. The stripper unit may also consist of several falling film evaporators installed in series or parallel. In this case, the packed column, tray column or rotating packed bed will be removed. The corresponding process configurations are shown in Figure 7, 7a (for evaporators installed in parallel) and 7b (for evaporators installed in series). These embodiments are described below.

100. The first configuration of the method is shown in Figure 7 and is described as follows: First, CO ₂ -containing gas (1) is supplied to the absorption unit (2). CO ₂ gas is absorbed by the countercurrent of the absorbent solution (4). Purified gas (3) with a low CO ₂ content is removed from the CO ₂ capture process into the atmosphere or sent for use or additional processing. An absorbent solution (5) with a high CO ₂ content is pumped (6) and flows through the first heat exchanger (7), and the heated stream (5') is fed into the second heat exchanger (8) to increase its temperature before entering the stripping unit, which is falling film evaporator (73). Heat exchanger (8) is optional. The heat source provides the energy necessary to evaporate some of the water present in the aqueous absorbent solution. When steam (water vapor) is generated, it acts as a stripping gas and provides a driving force that causes CO ₂ to be desorbed from the absorbent solution. The liquid/vapor mixture (74) is directed to a reservoir (75) where the gas phase and liquid phase are separated. The liquid phase, that is, the absorbent solution (15) with a low CO ₂ content, is pumped (pump 16) into the heat exchanger (7) and then into the refrigerator (18). The gas phase exits the reservoir (75), the stream (76) is then sent to a condenser where the water vapor is condensed and then sent back to the process (67). The high CO ₂ concentration gas (20b) leaving the condenser is compressed (36) as a stream (20) which is sent to other units for processing, processing or storage. Stream (67a) supplies water to the process.

101. A process configuration in which the stripper unit consists of two falling film evaporators operating in parallel is shown in Figure 7a. The method is as follows: CO ₂ -containing gas (1) is supplied to the absorption unit (2). CO ₂ gas is absorbed by the countercurrent of the absorbent solution (4). Purified gas (3) with a low CO ₂ content is removed from the CO ₂ capture process into the atmosphere or sent for use or additional processing. An absorbent solution (5) with a high concentration of CO ₂ is pumped (6) and flows through the first heat exchangers (7), and then the heated solution (5') is fed into the second heat exchanger (8) to increase its temperature before entering the stripping unit, which consists of two parallel-connected falling film evaporators (73a and 73b). Heat exchanger (8) is optional. The heat source provides the energy necessary to evaporate some of the water present in the aqueous absorbent solution. When steam (water vapor) is generated, it acts as a stripping gas and provides a driving force that causes CO ₂ to be desorbed from the absorbent solution. The liquid/vapor mixtures exiting the blocks (73a) and (73b), streams (74a and 74b) are directed to a reservoir (75) where the gas phase and liquid phase are separated. In an alternative configuration, streams (74a) and (74b) may be supplied to two separate reservoirs. The liquid phase, that is, the absorbent solution (15) with a low CO ₂ content, is pumped (pump 16) into the heat exchanger (7) and then into the refrigerator (18). The gas phase exits the reservoir (75), the stream (76) is then sent to a condenser where the water vapor is condensed and then sent back to the process (67). The high CO ₂ concentration gas (20b) leaving the condenser (14) is compressed (36) and the stream (20) is then sent to other units for processing, processing or storage. Stream (67a) supplies water to the process.102. A process configuration in which the stripper unit consists of two falling film evaporators operating in series is shown in Figure 7b. The method is as follows: CO ₂ -containing gas (1) is supplied to the absorption unit (2). CO ₂ gas is absorbed by the countercurrent of the absorbent solution (4). Purified gas (3) with a low CO ₂ content is removed from the CO ₂ capture process into the atmosphere or sent for use or additional processing. The _CO2- rich absorbent solution (5) is pumped (6) and flows through the first heat exchanger (7), and then the stream (5') is directed to the second heat exchanger (8) to raise its temperature before entering the first falling film evaporator ( 73a). The heat source provides the energy necessary to evaporate some of the water present in the aqueous absorbent solution. When steam (water vapor) is generated, it acts as a stripping gas and provides a driving force that causes CO ₂ to be desorbed from the absorbent solution. The liquid/vapor mixture leaving (73a) is directed to a reservoir (75a) where the gas phase and liquid phase are separated. The liquid phase (77) is supplied to a second falling film evaporator, the heat source providing the energy necessary to evaporate a portion of the water present in the aqueous absorbent solution. When steam (water vapor) is generated, it acts as a stripping gas and creates a driving force that causes CO ₂ to be desorbed from the absorbent solution. The exiting liquid/vapor mixture (73b) is directed to a tank (75b) where the gas phase and liquid phase are separated, i.e. an absorbent solution (15) with a low CO ₂ content is pumped using a pump (16) into a heat exchanger (7) and then into a refrigerator (18). The gas streams leave the reservoirs, with streams (76a and 76b) then combined (stream 76) and sent to a condenser (14) where the water vapor is condensed and then sent back to the process (67). The high CO ₂ concentration gas (20b) leaving the condenser is compressed (36) and then the gas stream (20) is directed to other units for processing, processing or storage. Stream (67a) supplies water to the process.103. An alternative configuration to that shown in Figure 7b is found in Figure 7c. The difference between both configurations lies in the two falling film evaporators (73a) and (73b). The method is as follows: CO ₂ -containing gas (1) is supplied to the absorption unit (2). CO ₂ gas is absorbed by the countercurrent of the absorbent solution (4). Purified gas (3) with a low CO ₂ content is removed from the CO ₂ capture process into the atmosphere or sent for use or additional processing. The _CO2- rich absorbent solution (5) is pumped (6) and flows through the first heat exchanger (7), and then the stream (5') is directed to the second heat exchanger (8) to raise its temperature before entering the first falling film evaporator ( 73a). The heat source provides the energy necessary to evaporate some of the water present in the aqueous absorbent solution. When steam (water vapor) is generated, it acts as a stripping gas and provides a driving force that causes CO ₂ to be desorbed from the absorbent solution. The liquid/vapor mixture leaving the evaporator (74a) is directed to a tank (75a) where the gas phase and liquid phase are separated. The liquid phase (77) is supplied to a second falling film evaporator, the gas phase (78) is supplied to a second falling film evaporator operating at a lower pressure than the first evaporator, where it is used as a heat source to provide the energy required for evaporation part of the water present in the aqueous absorbent solution. When its heat is transferred to stream (77) in the falling film evaporator, the steam is condensed, recovered and sent back to the process (stream 80). Residual steam and CO ₂ (stream 79) are combined with stream (76). When steam (water vapor) is generated, it acts as a stripping gas and provides a driving force that causes CO ₂ to be desorbed from the absorbent solution. The liquid/vapor mixture leaves the evaporator (73b), the stream (74b) is directed to the tank (75b), where the gas phase and liquid phase are separated, i.e. an absorbent solution (15) with a low CO ₂ content is pumped into the heat exchanger (7) and then into the refrigerator (18). The gas stream (76) leaving the reservoir (75b) is then directed to the condenser (14), where the water vapor is condensed and then sent back to the process (67). The high CO ₂ concentration gas (20b) leaving the condenser is compressed (36) and the stream (20) is then sent to other units for processing, processing or storage. Stream (67a) supplies water to the process.

104. It should be understood that any of the above-mentioned additional aspects of each process, method, system and unit may be combined with any other aspect thereof, unless the two aspects clearly cannot be combined due to mutual exclusivity.

EXPERIMENTAL RESULTS

105. The following examples are provided to demonstrate the effect of boiling an absorbent solution containing the carbonic anhydrase enzyme on the half-life of the enzyme in the process, and how a change in process configuration, such as the use of air as a stripping gas, affects the half-life of the enzyme in the process. These examples describe experimental laboratory tests. Protreat® software from Optimized Gas Treatment Inc was used where process modeling was required.

Example 1: Determination of the Half-Life of Carbonic Anhydrase 1T1 in a Laboratory CO ₂ Capture Unit Including a Reboiler to Produce Steam from a Low CO ₂ Absorbing Solution Containing the 1T1 Enzyme (Reference Process)

106. Tests were conducted to determine the half-life of carbonic anhydrase in a laboratory capture unit. The configuration of the method is shown in Figure 1. The absorbent solution is a 1.45 M K ₂ CO ₃ solution with a CO ₂ content of 0.7 mol C/mol K+. The enzyme carbonic anhydrase 1T1 was used at a concentration of 0.5 g/l. The CO ₂ concentration at the absorber inlet was 12% (v/v) dry matter, and the gas temperature was 30°C. The fluid flow rate was 0.34 liters per minute. The absorber operated at a L/G ratio of 15 g/g. The temperature of the solution in the absorber was 30°C. The high content absorbent solution was heated to 60° C. before entering the stripping column. The stripping column was operated at an absolute pressure of 30 kPa. The low content absorbent solution leaving the stripping column was at a temperature of 65°C and was divided into two streams: the first stream was sent to the absorber at a flow rate of 0.34 L/min. The second stream was fed into the reboiler at a rate of 0.76 liters per minute. The reboiler was a plate heat exchanger. A stream of hot water at 80°C at a flow rate of 5 liters per minute provided the energy required to heat and boil the low CO ₂ absorbent solution and produce steam. The test was carried out over several days. During the test, samples were taken to determine enzyme activity at different times. The half-life of the enzyme was then determined.

107. For the present process conditions, the steam production rate was 4.5 kg/h and the half-life of the 1T1 enzyme was determined to be 12 hours.

Example 2: Effect of operating conditions in the reboiler on the rate of steam generation and half-life of the 1T1 enzyme with the same process configuration as in example 1

108. To determine the effect of steam generation rate on the half-life of the 1T1 enzyme, additional tests were carried out. The test conditions were changed around the reboiler, other conditions were the same as described in Example 1. These are shown in Table 1. For each condition, the steam generation rate is presented as the corresponding half-life of the 1T1 enzyme.

109. As can be seen from Table 1, the half-life of the enzyme is affected by the rate of steam generation. The higher the rate of steam generation, the shorter the half-life of 1T1.

Example 3: Half-life of 1T1 in a laboratory unit for CO ₂ capture, in which the stripping gas is air. The unit operated in the process configuration shown in Figure 6a, where there is a heating circuit to heat the low content absorbent solution present in the tank at the bottom of the stripping column and maintain adequate temperature conditions. BY. Tests were conducted to determine the half-life of carbonic anhydrase in a laboratory capture unit where the stripping gas is air. The absorbent solution is a 1.45 M K ₂ CO ₃ solution with a CO ₂ content of 0.7 mol C/mol K+. The enzyme carbonic anhydrase 1T1 was used at a concentration of 0.5 g/l. The schematic diagram of the plant is as shown in Figure 6a, where there is an additional heat exchanger for heating the liquid present in the tank at the bottom of the stripping column. The CO ₂ concentration at the absorber inlet was 13.5% (v/v) and the gas temperature was 30°C. The fluid flow rate was 0.35 liters per minute. The absorber operated at a L/G ratio of 15 g/g. The temperature of the absorber solution was 30°C, and the high content absorbent solution was heated to 60°C before entering the stripping column. The stripping column was operated at an absolute pressure of 45 kPa. The solution leaving the stripping column had a temperature of 65°C, then was cooled and fed into the absorber. Air with a temperature of 60°C was supplied at a speed of 30 g/min to the bottom of the stripping column. The initial CO ₂ capture efficiency was 75%. Under the same conditions, but without the use of an enzyme, the efficiency of CO ₂ capture was 15%. This confirms the influence of the 1T1 enzyme on the efficiency of CO ₂ capture. The test was carried out over several days. During the test, enzyme activity determinations were performed at different sampling times. The half-life of the enzyme was then determined.

111. Under these process conditions, the half-life of 1T1 was 13 days (312 hours). Compared to the base case presented in Example 1, this represents an increase of 2500%. Compared to the other cases presented in Example 2 (Table 1), this represents an increase of 225 to 1735%. This clearly demonstrates that minimizing enzyme exposure to high gas/liquid interfaces is a key process parameter for increasing enzyme half-life in CO ₂ capture.

Example 4: Simulation of a CO ₂ stripping unit, including a stripping gas circuit, where the stripping liquid is water and where the generated steam was introduced at different heights of the packed stripping column - the influence of the number of injection points (Figure 3a).

112. An absorbent solution containing 1.45 M K ₂ CO ₃ , which contains the enzyme 1T1 at a concentration of 0.5 g/l, was fed at a flow rate of 6.46×10 ⁴ kg/h into a CO ₂ stripping unit consisting of a packed column . The packed column has a height of 25 m and a diameter of 1.11 m. The purification unit operated at a temperature of 66°C and a pressure of 30 kPa. The stripping gas was water vapor, which was supplied through the stripping gas loop. The temperature of the high content absorbent solution supplied to the stripping unit was 65° C. and the pressure was 150 kPa. Steam was supplied at a pressure of 30 kPa and at a temperature of 71°C.

113. Simulations were carried out for the same CO ₂ desorption efficiency (47%) to determine the effect of the number of steam injection points on two parameters: the rate of steam condensation into the absorbent solution, the required total steam flow. The simulation results are presented in Table 2. The positions of the injection holes are given as height in (m). The 0 m position corresponds to the top of the stripping unit.

114. Simulation results show that under process conditions, increasing the number of steam injection points makes it possible to reduce the rate of steam condensation in the stripping unit. Another advantage is that the required steam consumption is significantly reduced.

115. In a process in which steam is condensed in the absorption solution exiting the stripping column, process configurations such as those shown in Figures 4, 4a and 4b should be used to evaporate the condensed steam and bring the composition of the absorption solution to its characteristics.

Example 5: Simulation of a CO ₂ stripper unit including a stripping gas circuit in which the stripping liquid is water and the generated steam was introduced at 9 different injection points - influence of the temperature of the high content absorbent solution supplied to the stripper unit.

116. Additional modeling was carried out to determine the feasibility of steam injection without addressing the steam condensation problem. One strategy being considered is to heat the high content absorbent solution fed to the stripper to a higher temperature. A case considered to illustrate the effect of higher solution temperature is described in Example 4, where steam is injected through 9 different injection ports. The simulation results are presented in Table 3.

117. The simulation results shown in Table 3 clearly show that as the temperature of the high content absorbent solution entering the stripping unit increases, the steam condensation rate decreases to the required steam flow rate. In particular, the simulation results show that process conditions can be adjusted to avoid steam condensation and hence the need for an evaporation loop to control the solution composition.

Example 6: Injecting steam through the boil-off gas circuit at the bottom of the stripper and adding two heating circuits (process configuration, Figure 3b)

118. Simulations were carried out to determine the effect of adding two heating circuits to a stripper unit where steam was introduced into the bottom of the packing. The process conditions are as described in Example 4. As for the two heating circuits into which 15% of the absorbent solution was pumped, they include one pump and one heat exchanger. The absorbent solution enters the primary circuit at 5 m and exits at 5.5 m. The temperature of the solution increases from 60 to 70°C. The liquid enters the second heating circuit at 10 m and exits at 10.5 m. The solution temperature rises from 63 to 70 ° C.

119. The simulation results show that under these process conditions the steam condensation rate is reduced from 740 to 294 kg/h, while the required steam flow is reduced from 2100 to 1850. However, an additional heat load of 0.85 GJ/h will be required. Additional modeling by adjusting the proportion of solvent flow passing through the 2 loops to 25 and then to 35% shows that the steam condensation rate can be reduced to 86 kg/h and steam flow to 1700 kg/h, while an additional thermal regime of 1.24 GJ/h is required.

Example 7: Simulation of air purification

120. Flue gas containing 15% CO ₂ (v/v) must be treated to capture 90% of the CO ₂ it contains. The flue gas had a temperature of 30°C and a pressure of 111 kPa and was supplied at a flow rate of 3250 kg/h to the CO ₂ capture unit at a rate of 15 tons per day. The absorbent solution supplied to the absorption unit is 1.45 M K ₂ CO ₃ with a CO ₂ content of 0.7 mol C/mol K ⁺ . The absorption unit operated at a L/G ratio of 10 kg/kg. The design of the stripping column, which used air as stripping gas, was carried out using Protreat® software (method configuration shown in Figure 6a). If the stripping unit operates at 30 kPa and 70°C, an air flow of 75 kg/h provides sufficient solvent regeneration to obtain 90% of the recovery unit's productivity. If the stripping unit operates at a pressure of 101 kPa and a temperature of 70°C, an air flow of 700 kg/h is required. In both cases, the stripping column will have a diameter of 1.15 m and a height of 10 m, the same dimensions as for the case where CO ₂ capture is carried out using a reboiler and where the stripping conditions will be a pressure of 30 kPa and a temperature of 70 ° C .

121. These results show that air purification is technically feasible and is an interesting alternative to using a reboiler to generate boil-off gas. Moreover, the fact that the enzyme is not exposed to the reboiler in this process configuration will result in an increased half-life of the enzyme and therefore lower operating costs.

Claims (21)

1. A CO ₂ stripping method for stripping CO ₂ from an absorbent solution containing a biocatalyst with a high CO ₂ content to obtain an absorbent solution containing a biocatalyst with a low CO ₂ content and gas with a high CO ₂ content, including: generating a boil-off gas from a portion of said biocatalyst-containing low CO ₂ absorbent solution in a boil-off gas generating unit comprising a falling film evaporator, and bringing the biocatalyst-containing absorbent solution high in CO ₂ into contact with the stripping gas in a gas-liquid contactor to produce an absorbent solution low in CO ₂ and gas high in CO ₂ . 2. The method according to claim 1, characterized in that the gas-liquid contactor is a direct-acting gas-liquid contactor. 3. The method according to claim 2, characterized in that the gas-liquid contactor is a packed column, a tray column, a spray reactor or a rotating packed bed. 4. A CO ₂ stripping method for stripping CO ₂ from an absorbent solution containing a biocatalyst with a high CO ₂ content to obtain an absorbent solution containing a biocatalyst with a low CO ₂ content and a gas with a high CO ₂ content, including: generating boil-off gas from the biocatalyst-containing absorbent solution with a high CO ₂ content, and bringing the biocatalyst-containing absorbent solution high in CO ₂ into contact with the stripping gas in a gas-liquid contactor comprising a falling film evaporator to produce a low CO ₂ absorbing solution and a high CO ₂ gas. 5. The method according to claim 4, characterized in that the generation of boil-off gas includes heating an absorbent solution containing a biocatalyst with a high content of CO ₂ in a gas-liquid contactor, which is a falling film evaporator, with simultaneous generation of a boil-off gas and stripping of CO ₂ from the absorbent containing a biocatalyst solution with a high CO ₂ content in a gas-liquid contactor. 6. Method according to any one of paragraphs. 1-5, characterized in that the biocatalyst-containing absorption solution with a high CO ₂ content is an aqueous solution, and the generated stripping gas contains steam. 7. Method according to any one of paragraphs. 1-6, characterized in that the stripping gas is supplied to a plurality of places spaced apart from each other, preferably distributed along the height of the gas-liquid contactor. 8. Method according to any one of paragraphs. 1-7, characterized in that the biocatalyst-containing absorbent solution with a high CO ₂ content is withdrawn from various sections of the gas-liquid contactor for heating and reintroduced into the gas-liquid contactor through heating circuits. 9. Method according to any one of paragraphs. 1-8, including minimizing or preventing the exposure of the biocatalyst-containing high CO ₂ absorption solution and the biocatalyst containing low CO ₂ absorption solution to bubble formation conditions in which new gas-liquid interfaces are created through the formation of bubbles. 10. A method for capturing CO ₂ based on a biocatalyst, including: bringing the CO ₂ -containing gas into contact with a biocatalyst-containing absorption solution to produce a biocatalyst-containing absorption solution with a high CO ₂ content, application of the CO ₂ stripping method according to any one of claims. 1-9 to desorb CO ₂ from the biocatalyst-containing high CO ₂ absorption solution, thereby obtaining a low CO ₂ absorption solution and a high CO ₂ gas. 11. Application of falling film evaporator to generate stripping gas for CO stripping₂ from an absorbent solution containing a biocatalyst with a high content CO₂ and obtaining a biocatalyst-containing absorption solution with a low CO content₂. 12. Application according to claim 11, characterized in that the falling film evaporator is used to generate boil-off gas from the biocatalyst-containing absorption solution with a high CO ₂ content. 13. Method according to any one of paragraphs. 1-9, the method according to claim 10 and use according to any one of paragraphs. 11, 12, characterized in that the biocatalyst-containing absorbent solution with a high CO ₂ content contains biocatalysts in soluble form or in immobilized form, which are in the flow in the boil-off gas generating unit and/or in the gas-liquid contactor. 14. The process, method or use of claim 13, wherein the biocatalysts are attached to particles or enclosed within a porous matrix. 15. Method, method or use according to claim 13 or 14, characterized in that the biocatalyst is carbonic anhydrase or its analogues.