METHODS AND DEVICES FOR STEAM DRIVEN CARBON DIOXIDE CAPTURE

Abstract

A method for separating gaseous carbon dioxide from a gas mixture by cyclic adsorption/desorption using a sorbent material adsorbing said gaseous carbon dioxide, wherein the method comprises the following sequential and in this sequence repeating steps: (a) an adsorption step; (b) and isolating step; (c) injecting a stream of saturated or superheated steam and thereby inducing an increase in internal pressure of the reactor unit and an increase of the temperature of the sorbent from ambient atmospheric temperature to a temperature between 60 and 110° C., starting the desorption of CO2; (d) extracting at least the desorbed gaseous carbon dioxide from the unit and separating gaseous carbon dioxide from water by condensation in or downstream of the unit, while preferably still injecting; (e) bringing the sorbent material to ambient atmospheric pressure conditions and ambient atmospheric temperature conditions

Claims

1. A method for separating gaseous carbon dioxide from a gas mixture, said gas mixture containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material adsorbing said gaseous carbon dioxide, using a unit containing an adsorber structure with said sorbent material, said unit being evacuable to a vacuum pressure of 400 mbarabs or less, and said adsorber structure being heatable to a temperature of at least 60° C. for desorption of at least said gaseous carbon dioxide and said unit being openable to flow-through of said gas mixture and for contacting said gas mixture with said sorbent material for an adsorption step, wherein said method comprises at least the following sequential and in this sequence repeating steps (a) - (d): (a) contacting said gas mixture with said sorbent material to allow at least said gaseous carbon dioxide to adsorb on said sorbent material under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions in said adsorption step; (b) isolating said sorbent with adsorbed carbon dioxide in said unit from said flow-through while maintaining the temperature in the sorbent and then evacuating said unit to a pressure in the range of 20-400 mbarabs; (c) injecting a stream of saturated or superheated steam and thereby inducing an increase in internal pressure of said unit and an increase of the temperature of the sorbent to a temperature between 60 and 110° C., starting desorption of CO2; (d) extracting at least desorbed gaseous carbon dioxide from said unit and separating gaseous carbon dioxide from steam by condensation in or downstream of said unit; (e) bringing the sorbent material to ambient atmospheric pressure conditions and ambient atmospheric temperature conditions.

2. The method according to claim 1, wherein after step (d) and before step (e) the following step is carried out: (d1) ceasing injection and, if used, partial circulation of steam, and evacuation of the said unit to pressure values between 20 - 500 mbarabs, thereby causing evaporation of water from said sorbent and both drying and cooling the sorbent.

3. The method according to claim 1, wherein in step (b) said unit is evacuated to a pressure in the range of 20-400 mbarabs, or 100-200 mbarabs, while not heating the sorbent, and/or wherein the following step is carried out: (b1) flushing the unit of non-condensable gases by a stream of non-condensing steam while essentially holding the pressure at the end of step (b).

4. The method according to claim 1, wherein step (e) includes breaking of the isolation of the unit to the ambient atmospheric air and drying of the sorbent with a stream of warm air.

5. The method according to claim 1, wherein in step (c), steam is injected in the form of fresh steam introduced by way of a corresponding inlet of said unit, and steam is partially recirculated from an outlet of said unit or from an outlet of another unit to said inlet.

6. The method according to claim 1, wherein in step (c) the sorbent is heated to a temperature in the range of 80-110° C.

7. The method according to claim 1, wherein in step (c) the pressure in the unit is in the range of 700-950 mbarabs.

8. The method according to claim 1, wherein at least a portion of a purge gas flow exiting an adsorber structure in step (d) is passing a heat exchanger in which at least a part of the steam contained in said purge gas flow condenses, before the remaining gas flow continues to a vacuum pump and a CO2 production outlet, while on a cold side of said heat exchanger a flow of water is vaporized, and is compressed and added to a flow of freshly generated steam used for a portion or the entire duration of the same or a next adsorber structure’s desorption heat-up phase and/or a portion of said adsorber structure’s purge phase, and/or wherein at least a portion of a purge gas flow exiting the adsorber structure in step (d) is sent directly to a next adsorber structure that has already been evacuated for a portion or the entire duration of said next adsorber structure’s desorption heat-up phase.

9. The method according to claim 1, wherein in at least one of step (c) and step (d) the flow velocity of the steam in the adsorber structure (15) is above 0.05 m/s.

10. The method according to claim 1, wherein in step (d) the molar ratio of steam to carbon dioxide is in the range of 4:1-40:1, and/or wherein in step (c) steam, either saturated at the current pressure or overheated to between 80° C. to 120° C., is introduced to the sorbent material at a ratio of 1 kg/h to 10 kg/h of steam per kg of sorbent in an given flow direction, until the prevalent pressure lies between 600 mmbar and 950 mbar, such that the sorbent temperature reaches values between 85° C. and 110° C., by adsorption and/or condensation of said steam on the sorbent material.

11. The method according to claim 1, wherein in at least one of step (c) and step (d) steam is injected into the unit to flow-through and contact the sorbent material under saturated steam or superheated steam conditions with a superheated steam temperature of up to 140° C., and wherein at least part of the steam having passed through the unit and carrying at least part of the carbon dioxide desorbed from the sorbent is circulated back into the unit for at least a second flow-through and contact the sorbent material.

12. The method according to claim 11, wherein steam having passed through the unit and circulated back into the unit is subjected to a step of reheating, and/or wherein steam having passed through the unit and circulated back into the unit is subjected to a step of reheating at a heating power at 100° C. of at least 0.05 kW/kg sorbent material, and/or wherein steam having passed through the unit and circulated back into the unit is subjected to a step of active propulsion, and/or wherein during circulation the mass ratio of steam to carbon dioxide in the circulation loop is at least 3:1 or at least 5:1, and/or wherein the saturation temperature of the steam in the circulated steam is less than 40° C. higher than the sorbent temperature in the unit at the pressure of regeneration of the sorbent.

13. A method according to claim 1, wherein step (d) comprises at least one phase S2, in which fresh steam is introduced into the unit and at the same time steam is recirculated without extraction of gas from the unit, and at least one phase (S3) involving extraction of gas from the unit under continued recirculation of steam, and/or wherein at least one of step (c) and step (d) is controlled based on at least one of the following parameters: temperature of the circulated steam at the outlet and/or the inlet of the adsorber structure, pressure of the circulated steam at the outlet or the inlet of the adsorber structure, composition of the circulated steam at the outlet and/or the inlet of the adsorber structure, temperature of the sorbent or a combination thereof.

14. The method according to claim 1, wherein in step (c) a unit outlet is opened such that a fraction between 0.1-10% of the injected steam is used to flush the unit by leaving through the unit outlet thus purging the reactor of remaining ambient air while the sorbent material temperature is increasing, and/or wherein in step (a) adsorption of CO2 from said gas mixture occurs by forced convection of said gas mixture at flow rates of 20 m3/h to 200 m3/h per kg of sorbent of ambient air.

15. A for carrying out a method according to claim 1, comprising at least one unit containing an adsorber structure with said sorbent material, the unit being evacuable to a vacuum pressure of 400 mbarabs or less, and the adsorber structure being heatable to a temperature of at least 80° C. for the desorption, comprising means for injecting steam into the unit to flow-through and contact the sorbent material under saturated steam or superheated steam conditions with a superheated steam temperature of up to 140° C. at the pressure level in said unit, the unit being openable to flow-through of the gas mixture across and/or through said sorbent material and for contacting it with the sorbent material for the adsorption step, and comprising no further internal or external heating means for heating the sorbent.

16. The method according to claim 1, wherein step (d) involves extracting at least desorbed gaseous carbon dioxide from said unit and separating gaseous carbon dioxide from steam by condensation in or downstream of said unit, while still contacting the sorbent material with steam by injecting and/or circulating saturated or superheated steam into said unit, thereby flushing and purging both steam and CO2 from the unit at a molar ratio of steam to carbon dioxide between 4:1 and 40:1, while regulating the extraction and/or steam supply to essentially maintain the pressure and/or temperature in the sorbent at the end of the preceding step (c) and/or to essentially maintain the pressure in the sorbent at the end of the preceding step (c).

17. The method according to claim 1, wherein after step (d) and before step (e) the following step is carried out: (d1) ceasing the injection and, if used, partial circulation of steam, and evacuation of the unit to pressure values in the range of 50-250 mbarabs in the unit, thereby causing evaporation of water from the sorbent and both drying and cooling the sorbent.

18. The method according to claim 1, wherein after step (b) and before step (c) the following step is carried out: (b1) flushing the unit of non-condensable gases by a stream of non-condensing steam while essentially holding the pressure at the end of step (b), holding the pressure at the end of step (b) in a window of ± 50 mbarabs of the pressure at the end of step (b) and/or holding the temperature below 70° C. or below 60° C.

19. The method according to claim 18, wherein in step (b1) the unit is flushed with saturated steam or steam overheated by at most 20° C. in a ratio of 1 kg/h to 10 kg/h of steam per kg of sorbent, while remaining at the pressure at the end of step (b), to purge the reactor of remaining ambient air.

20. The method according to claim 1, wherein step (e) includes breaking of the isolation of the unit to the ambient atmospheric air and drying of the sorbent with a stream of warm air, having a temperature in the range of 40-100° C., or in the range of 60-80° C.

21. The method according to claim 1, wherein in step (e) said stream of warm air is at ambient pressure and 10 m3/h to 100 m3/h per kg of sorbent, and at a temperature between 40° C. and 90° C., until the sorbent water content lies below 15-30 weight%.

22. The method according to claim 1, wherein in step (c), steam is injected in the form of fresh steam introduced by way of a corresponding inlet of said unit, and steam is partially recirculated from an outlet of said unit or from an outlet of another unit to said inlet, involving reheating and/or propulsion of recirculated steam.

23. The method according to claim 1, wherein in step (c) the sorbent is heated to a temperature in the range of 85-98° C.

24. The method according to claim 1, wherein in step (c) the pressure in the unit is in the range of 750-850 mbarabs.

25. The method according to claim 1, wherein at least a portion of a purge gas flow exiting the adsorber structure in step (d) is passing a heat exchanger in which at least a part of the steam contained in said purge gas flow condenses, at the saturation temperature of the vapor pressure of the gas flow at the hot side of the heat exchanger, before the remaining gas flow continues to a vacuum pump and a CO2 production outlet, while on a cold side of said heat exchanger a flow of water is vaporized, at lower pressure and condensation temperature than that of the purge gas flow, and is compressed and added to a flow of freshly generated steam used for a portion or the entire duration of the same or a next adsorber structure’s desorption heat-up phase and/or a portion of said adsorber structure’s purge phase, and/or wherein at least a portion of a purge gas flow exiting the adsorber structure in step s sent directly to a next adsorber structure that has already been evacuated for a portion or the entire duration of said next adsorber structure’s desorption heat-up phase and preferably a portion of said adsorber structure’s purge phase, wherein only one of either the direct re-use of purge gas flow in another or the same adsorber structure or alternatively the recovery of latent heat in an external heat exchanger is implemented and the entire purge gas flow is sent only to the respective device.

26. The method according to claim 1, wherein in step (c) and/or in step (d) the flow velocity of the steam in the adsorber structure (15) is in the range of 0.2-0.35 m/s, wherein the high flow velocity of the steam in the adsorber structure is achieved in that the steam takes a different path to the flow of air during adsorption in step (a) in order to increase local steam velocity in the bed during desorption.

27. The method according to claim 26, wherein the overall flow paths of adsorption during in step (a) and during steam injection in step (c) and/or (d) are essentially orthogonal.

28. The method according to claim 1, wherein in step (d) the molar ratio of steam to carbon dioxide is in the range of 10:1-30:1, and wherein the extraction and/or steam supply is regulated to maintain the temperature in the sorbent in a window of ± 10° C., or in the window of ± 5° C. from the temperature at the end of the preceding step, and/or wherein in step (c) steam, either saturated at the current pressure or overheated to between 95° C. and 110° C., is introduced to the sorbent material at a ratio of 1 kg/h to 10 kg/h of steam per kg of sorbent in an given flow direction, until the prevalent pressure lies between 800 mbar and 950 mbar, such that the sorbent temperature reaches values between 90° C. and 105° C. by adsorption and/or condensation of said steam on the sorbent material.

29. The method according to claim 1, wherein in at least one of step (c) and step (d) steam is injected into the unit to flow-through and contact the sorbent material under saturated steam or superheated steam conditions with a superheated steam temperature of up to 140° C., and wherein at least part of the steam having passed through the unit and carrying at least part of the carbon dioxide desorbed from the sorbent is circulated back into the unit for at least a second flow-through and contact the sorbent material, wherein at least one of step (c) and step (d) comprises at least one phase, in which there is full circulation of the steam and no steam exiting the system, but if need be further supplying fresh steam and/or wherein the circulation volume flow is in the range of 20-80 m3/h/kg sorbent, wherein the circulation volume flow is in the range of more than 10 ′000 m3/h.

30. The method according to claim 11, wherein steam having passed through the unit and circulated back into the unit is subjected to a step of reheating, to a temperature above 95° C., or to a temperature above 100° C., and/or wherein steam having passed through the unit and circulated back into the unit is subjected to a step of reheating at a heating power at 100° C. of at least 0.2 kW/kg sorbent material, and/or wherein during circulation the mass ratio of steam to carbon dioxide in the circulation loop is in the range of 10:1-15:1, and/or wherein the saturation temperature of the steam in the circulated steam is less than 20° C. higher than the sorbent temperature in the unit at the pressure of regeneration of the sorbent, wherein the pressure of regeneration of the sorbent is in the range of 100 and 1500 mbar (a), or between 600 and 1200 mbar (a).

31. The method according to claim 11, wherein step (d) comprises at least one phase S2, in which fresh steam is introduced into the unit and at the same time steam is recirculated without extraction of gas from the unit and under increase of the pressure in the unit, and at least one phase S3 involving extraction of gas from the unit under continued recirculation of steam and under decreasing supply with fresh steam, and/or wherein at least one of step (c) and step (d) is controlled based on at least one of the following parameters: temperature of the circulated steam at the outlet and/or the inlet of the adsorber structure, pressure of the circulated steam at the outlet or the inlet of the adsorber structure, composition of the circulated steam at the outlet and/or the inlet of the adsorber structure, temperature of the sorbent or a combination thereof, and wherein further the composition of the circulated steam is used as a parameter for determining how much fresh steam is introduced, and/or at which moment extraction of gas from the unit is started, and/or to which extent extraction of gas from the unit is taking place in combination with circulation and/or injection of steam.

32. The method according to claim 31, wherein the temperature and/or the pressure of the circulated steam at the inlet of the adsorber structure is controlled, based on at least one of the temperature of the circulated steam at the outlet of the adsorber structure, the composition and/or pressure of the circulated steam at the outlet of the adsorber structure, and the temperature of the of the sorbent, to avoid condensation of the steam and/or drying of the sorbent in the adsorber structure.

33. The method according to claim 32, wherein the temperature and/or the pressure of the circulated steam at the inlet of the adsorber structure is controlled such that the saturation temperature of the steam in the adsorber structure is at least as high as or higher than the temperature of the of the sorbent in the adsorber structure.

34. The method according to claim 33, wherein the saturation temperature of the steam in the adsorber structure is at least as high as or higher than the temperature of the of the sorbent in the adsorber structure, namely at least 5° C. or at least 10° C., higher than the temperature of the of the sorbent in the adsorber structure for avoiding condensation and/or at most 20° C. or at most 15° C. higher than the temperature of the of the sorbent in the adsorber structure for avoiding drying of the sorbent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0158] Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

[0159] FIG. 1 shows a schematic representation of required and optional steps for the method presented to attain CO2 in an economically feasible cyclic adsorption and desorption process;

[0160] FIG. 2 shows exemplary equilibrium water uptake of two different sorbents during exposure to air with varying relative humidity;

[0161] FIG. 3 shows the amount, type and effect of water uptake on an exemplary sorbent;

[0162] FIG. 4 shows the increase in time required to remove CO2 from a sorbent particle with diameter dp, based on a qualitative 1D-model using either the diffusion coefficient for CO2 in steam or for CO2 in liquid water;

[0163] FIG. 5 shows a schematic realization of a reactor with the required inlets and outlets for the method presented;

[0164] FIG. 6 shows the decrease in performance below economically feasible values at high relative humidity of ambient air during adsorption – as measured on a pilot plant with an unsuited prior art process – sorbent combination;

[0165] FIG. 7 shows reactor pressure and reactor temperature as measured during application of embodiment 1 of the method in a pilot prototype;

[0166] FIG. 8 shows steam and CO2 mass flows and product gas CO2 concentration as measured during application of embodiment 1 of the method in a pilot prototype;

[0167] FIG. 9 shows reactor pressure and reactor temperature as measured during application of embodiment 2 of the method in a pilot prototype;

[0168] FIG. 10 shows steam and CO2 mass flows and product gas CO2 concentration as measured during application of embodiment 2 of the method in a pilot prototype;

[0169] FIG. 11 shows reactor pressure and reactor temperature as measured during application of embodiment 3 of the method in a pilot prototype;

[0170] FIG. 12 shows steam and CO2 mass flows and product gas CO2 concentration as measured during application of embodiment 3 of the method in a pilot prototype;

[0171] FIG. 13 shows stabilization of performance at average economically feasible values even at high relative humidity of ambient air during adsorption - as measured on a pilot plant with the presented method

[0172] FIG. 14 shows an analysis of the energetic considerations when choosing between using an individual or both heat recovery methods; further costs are not included in this assessment;

[0173] FIG. 15 shows a schematic arrangement of adsorber structures and peripheral equipment for the proposed process and in particular also for employment of energy optimization by the combined recovery of latent heat and for the direct re-use of desorption purge gas flows for desorption heat-up of the next reactor in line to be desorbed;

[0174] FIG. 16 shows a possible configuration for recirculation of a steam with re-injection into the sorbent regeneration process for the embodiment using direct steam recirculation for one unit;

[0175] FIG. 17 shows experimental process curves for temperature, pressures and flows for a steam circulation desorption of a typical DAC sorbent for the embodiment using direct steam recirculation for one unit;

[0176] FIG. 18 shows equilibrium isotherms of a typical DAC sorbent at ambient atmospheric and elevated temperatures for the embodiment using direct steam recirculation for one unit; and

[0177] FIG. 19 shows uptake capacities of dry and wet sorbents under typical conditions of atmospheric CO2 adsorption for the embodiment using direct steam recirculation for one unit.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0178] The following embodiments are all examples of successful cyclical operation. Differences between embodiments stem from differences in plant output requirements or operational constraints, differences in sorbent characteristics of the material in use – in particular water and CO2 uptake characteristics – and differences in the predominant ambient conditions at which step 1, adsorption, occurs.

[0179] Successful cyclical operation of the method requires the sorbent to maintain an economical cyclical CO2 capacity under all conditions. A central challenge is the operation of the adsorption/desorption cycle in a way that avoids excessive deterioration of the sorbent CO2 uptake capacity, caused by thermal or oxidative degradation of the sorbent or active phase, mechanical disintegration of the sorbent material, excessive water loading that impedes diffusion of CO2 into or out of the capture structure in both the adsorption and desorption steps, leaching and washing out of the active phase by liquid water formation or any combination of the above.

[0180] This is achieved by loading the sorbent with amounts of water that reduce the prevalence of any of the above issues to acceptable levels during the desorption steps 5 and 6, employing the required degree of vacuum cooling in step 7, and any necessary further cooling and drying with steps 8 or 9.

Working Embodiments

[0181] The following working embodiments given below are process variants run on a pilot plant for several months at the end of 2019. The pilot plant comprised six individual adsorber structures as reactor chambers. The reaction chambers had a volume of approximately 5 m.sup.3, were outfitted with a suitable sorbent material (such as ion exchange resin with grafted amines), with each chamber loaded with between 300 kg to 700 kg of sorbent. The steam supply of up to 2000 kg/h was sufficient to allow desorption of one of the six chambers at any moment in time, while the other five were in adsorption. The structure setting the sorbent configuration within the reaction chambers as well as the closing mechanism for this arrangement of reaction chambers have been previously filed for patent application (PCT/EP 2020/059282, EP 19 181 818.6 and EP19 216 398.8). The prototype described, successfully conducted testing under real-life conditions of various sorbent - process variants, amassing a total of more than 250 cycles over all of the six reaction chambers. The first, second and third preferred embodiments described below as well as the results given in figures corresponding to these embodiments stem directly from this prototype series. The embodiments thereafter were subsequently successfully implemented on Climeworks mid-scale testing facility.

[0182] A first preferred embodiment is described in conjunction with FIGS. 7 and 8. In this embodiment there is no step of flushing with steam (step (4)). FIG. 7 shows the reactor pressure and the reactor temperature as a function of time as measured during application of in the pilot prototype detailed further below, and FIG. 8 shows steam and CO2 mass flows and product gas CO2 concentration. The x-axis indicates the time, and represents one cycle of the method, typically a cycle takes between 60-180 minutes.

[0183] In this embodiment 1, sorbent is contacted with ambient air within the adsorption step 1 and then closed off from the ambient in step 2. The evacuation step 3 reduces the pressure with the chamber to below 250 mbar. The evacuation line is closed off and saturated or superheated steam is injected in the heating step 5 until a target temperature/pressure pair is reached within the reactor, between 85° C. and 110° C.

[0184] The reactor outlet is opened and superheated steam is injected into the reactor in step 6 at the target pressure of step 5, between 600 mbar and 1500 mbar, to flush product CO2 out of the sorbent material, with both steam and CO2 leaving the reactor via the reactor outlet in a total molar H2O to CO2 ratio between 4 and 40 to 1 for the entire step 6.

[0185] Once CO2 release has been completed, the reactor is again evacuated to a pressure below 250 mbar in step 7, to remove remaining CO2 and to recover water from the sorbent material and at the same time cool the sorbent material. The reactor is re-pressurized to ambient in step 8, and, subsequently, cyclic operation is resumed with the adsorption step 1.

[0186] Embodiment 1 is apt for sorbent materials and systems that require additional drying in step 7 to operate economically during adsorption. The required evacuation system can then be operated to evacuate the reactor in step 3 with the added benefit of improving CO2 quality by the pre-emptive removal of air prior to desorption and the ability to also use steam at pressures below the ambient pressure.

[0187] A second preferred embodiment is described in conjunction with FIGS. 9 and 10. In this embodiment there is a step 4 of flushing with steam. FIG. 9 shows the reactor pressure and the reactor temperature as a function of time as measured during application of in the pilot prototype detailed further below, and FIG. 10 shows steam and CO2 mass flows and product gas CO2 concentration. The x-axis indicates the time, and represents one cycle of the method, typically a cycle takes between 60-180 minutes.

[0188] In this embodiment 2, sorbent is contacted with ambient air within the adsorption step 1 and then closed off from the ambient in step 2. The evacuation step 3 reduces the pressure with the chamber to below 250 mbar.

[0189] A flushing step 4 then introduces saturated or superheated steam while a similar amount is removed by the reactor outlet, thus maintaining to a degree the pressure attained at the end of the evacuation step 3, in order to remove remaining air from the reactor.

[0190] The evacuation line is closed off and saturated or superheated steam is injected in the heating step 5 until a target temperature/pressure pair is reached within the reactor, between 85° C. and 110° C.

[0191] The reactor outlet is opened and superheated steam is injected into the reactor in step 6 at the pressure of step 5, between 600 mbar and 1500 mbar, to flush product CO2 out of the sorbent material, with both steam and CO2 leaving the reactor via the reactor outlet in a total molar H2O to CO2 ratio between 4 and 40 to 1 for the entire step 6.

[0192] Once CO2 release has been completed, the reactor is again evacuated to a pressure below 250 mbar in step 7, to remove remaining CO2 and recover water from the sorbent material and at the same time cool the sorbent material. The reactor is re-pressurized to ambient in step 8, and, subsequently, cyclic operation is resumed with the adsorption step 1.

[0193] Embodiment 2 is apt for sorbent materials and systems that require additional drying in step 7 to operate economically during adsorption, the required evacuation system can then be operated to evacuate the reactor in step 3 with the added benefit of improving CO2 quality by the pre-emptive removal of air prior to desorption and the ability to also use steam at pressures below the ambient pressure, while the flushing step 4 further improves CO2 quality by the removal of even more air from the reactor, at the cost of increased steam and energy requirement.

[0194] A third preferred embodiment is described in conjunction with FIGS. 11 and 12. In this embodiment the step 4 of flushing with steam is combined with step 5 of heat up with steam.

[0195] FIG. 11 shows the reactor pressure and the reactor temperature as a function of time as measured during application in the pilot prototype detailed further below, and FIG. 12 shows steam and CO2 mass flows and product gas CO2 concentration. The x-axis indicates the time, and represents one cycle of the method, typically a cycle takes between 60-180 minutes.

[0196] In this embodiment 3, sorbent is contacted with ambient air within the adsorption step 1 and then closed off from the ambient in step 2. The evacuation step 3 reduces the pressure with the chamber to below 250 mbar.

[0197] The flushing step 4 is incorporated in the heat-up step 5, by introducing saturated or superheated steam while a much lower flow is removed from the reactor outlet, thus causing an increase in reactor pressure and temperature until a target temperature/pressure pair is reached within the reactor, between 85° C. and 110° C.

[0198] During the purge step 6, the reactor outlet flow is increased such that the same flow superheated steam is injected into and removed from the reactor, so maintaining the pressure at the end of step 5, between 600 mbar and 1500 mbar, while flushing product CO2 out of the sorbent material, with both steam and CO2 leaving the reactor via the reactor outlet in a total molar H2O to CO2 ratio between 4 and 40 to 1 for the entire step 6.

[0199] Once CO2 release has been completed, the reactor is again evacuated to a pressure below 250 mbar in step 7, to remove remaining CO2 and recover water from the sorbent material and at the same time cool the sorbent material. The reactor is re-pressurized to ambient in step 8, and, subsequently, cyclic operation is resumed with the adsorption step 1.

[0200] Embodiment 3 is apt for sorbent materials and systems that require additional drying in step 7 to operate economically during adsorption, the required evacuation system can then be operated to evacuate the reactor in step 3 with the added benefit of improving CO2 quality by the pre-removal of air prior to desorption and the ability to also use steam at pressures below the ambient pressure, while the flushing incorporated into heat-up further improves CO2 quality by the removal of even more air from the reactor prior to CO2 release. Embodiment 3, by combining the flushing and heating step, prevents introduction of steam into a closed reactor and any associated increase in pressure at any stage of the process and can therefore have an impact on safety considerations and future reactor design considerations.

[0201] FIG. 13 shows the overall CO.sub.2-capture performance of the prototype for the successful embodiments described over a multitude of cycles and ambient relative humidity during adsorption. In contrast to FIG. 6, the overall CO.sub.2-capacity was retained at an average value above 0.8 mmol/g even at high relative humidity, rather than dropping to values around 0.4 mmol/g as in FIG. 6.

Process and Device Including Heat Recovery

[0202] The proposed process requires substantial amounts of steam, both for the heat-up phase as well as for the purge phase with the instantaneous steam to CO2 ratio during purge from 4:1 to 40:1. The heat of vaporization of water means this steam is generated at a high energetic and therefore financial cost. Economically feasible operation of this process therefore entails the re-use and recovery of the energy input into the steam. The novelty of this process is also given by the following analysis, as to when each of the variants is feasible.

[0203] FIG. 15 schematically illustrates the setup used here. The setup comprises multiple main units (15), each consisting of multiple adsorber structure subunits, which are operated sequentially, with all but one subunit in adsorption, while an individual subunit is in desorption. The same is valid for the next main unit, but at a slight temporal offset, such that one subunit of the initial main unit is in purge mode, and the one subunit of the next main unit is in heat-up mode. In the illustration, 15a illustrates an adsorber in purge mode, and 15b an adsorber in heat up mode.

[0204] Steam can be supplied to the adsorber by way of a liquid water source, the output of which is converted to steam in a fresh steam generation unit 11. The fresh steam generation unit 11 comprises a sensible heat exchanger 12 as well as a latent heat exchanger 13, the elements can also be combined in one heat exchanger. The steam is transported to the adsorber structures 15 by way of steam injection lines 27, entering the corresponding adsorber structure by way of the inlets 16.

[0205] Downstream of the adsorber structures 15 and connected to the outlet 17 thereof there are steam outlet lines 29 for taking out the steam/carbon dioxide mixture. By way of a switch valve 19, this exiting steam can either be directed to the process of recovery of carbon dioxide, but it can also be recirculated either to the same adsorber structure (not illustrated), or it can be recirculated to another adsorber structure which is in heat up mode as illustrated by steam reuse line 20. In this steam reuse line, heating elements and propulsion elements can be provided to make sure that at the inlet of the corresponding adsorber structure the recirculated steam has the proper temperature and/or pressure adapted to the process control. For the recirculation aspect a more elaborate description is given in the context of FIGS. 16-19 further below.

[0206] For the purge outlet steam and carbon dioxide not recirculated and directed by switching valve 19 to the actual take out there is first provided a latent heat recovery unit 21. In this latent heat recovery unit 21 in a crossflow liquid water provided by unit 10 (which can be the same as the above-mentioned one) is heated and converted to steam. The corresponding steam is further compressed in compressor 18, and the resulting steam of adapted pressure and/or temperature is introduced by way of the mixing valve 14 with the fresh steam.

[0207] The take-out stream exiting the latent heat recovery unit 21 is then passed by a low temperature condenser 22, passes the main vacuum system 23 to lead to the product carbon dioxide 24.

[0208] As an option it is possible to redirect at least a fraction of the take-out stream exiting the latent heat recovery unit 21 for potential condensate reuse as illustrated by line 25.

[0209] A low-temperature condenser 22 is thus generally employed before the vacuum pump 23 in order to attain high purity CO2 and lower volume flows requiring less energy to be pumped. Energy efficient recovery of the energy in the purge gas flow is obtained with an upstream heat exchanger 21 operating at higher temperature. The outlet purge gas 29 condenses at high pressure on the hotter side of the heat exchanger 21, while a flow 31 of water vaporizes at a lower pressure on the colder side to produce a fresh flow of steam 28 at this lower pressure. The different pressure levels result in different condensation temperatures on either side of the heat exchanger 21, allowing heat to be transferred across the temperature difference. This newly-evaporated flow 28 of steam is compressed in unit 18 to the required pressure and mixed at 14 with fresh steam to provide the steam 27 for the desorption of the same or next reactor 15.

[0210] The required temperature gradient, pressure difference and energy needed for compression limits the flow of steam that can be generated in this fashion as well as the range of operating conditions under which this provides a net benefit. The viability of this concept is given if substantial amounts of steam can be generated in this manner per unit CO2 attained, which is generally the case for high desorption steam to CO2 purge ratios.

[0211] The direct re-use of purge gas is an efficient manner to work around the losses and costs associated with the latent heat recovery concept. The desorption purge gas consisting of steam and CO2 is fed directly into the next reaction chamber as it enters the desorption phase. The purge gas outlet flow from the initial reactor then accounts for all or a portion of the steam required for heat-up of the next reactor, and none or a portion of the steam required for purge, depending on the amount of steam for and the duration of the heat-up and purge phases respectively. An “indefinite” number of reactors can be connected in series in this way. This concept is however normally only viable, if the CO2 content of the purge gas flow is sufficiently far from equilibrium conditions to induce additional release of CO2. If this were not the case, the required duration or amount of purge with fresh steam in the second reactor would simply have to be increased to remove the additional CO2 introduced by the steam re-usage, thus essentially negating any benefit from the steam re-usage.

[0212] Both concepts, direct re-use and latent heat recovery, are employable if overall optimization of energy usage is wanted, and this variant is shown in FIG. 14. However, considering the equipment and investment costs associated with these re-use and recovery concepts, there are certain operating regions where one or the other may be more appropriate.

[0213] Here one must distinguish between whether both steam re-use and latent heat recovery are installed on a plant, or, assuming both variants are installed, when each is to be used. This can be discussed as a function of the overall average steam purge ratio, and is shown in FIG. 13. In general, steam re-use is favorable, but at some stage CO2-product is to be extracted, and it is here where latent heat recovery is selectable. If the overall average steam purge ratio is low, steam re-use will be used for the instantaneous higher purge ratio, while the purge ratio will be too low during product extraction to warrant installation of latent heat recovery, which is shown in FIG. 13. If the overall average purge ratio is high and instantaneous purge ratio covers a large range, then the highest purge ratios go towards direct steam re-use, while the lower steam ratios are still adequate to employ latent heat recovery.

Process and Device Including High Speed Steam Purge

[0214] Another implementation of the introduction of steam sees the reactor designed in such a way that the steam passes the adsorber structure at particularly high speed, which can be implemented in that the steam does not take the path of air during adsorption, but rather a path showing increased flow speeds and favorable purge behavior. The design of the adsorber structure minimizes local adsorption air through-flow velocity in order to attain reasonable pressure drops across the adsorber and high through-flows, to maximize CO2 uptake for a given total adsorption flow. However, such low velocities are detrimental to an efficient purge during desorption. Therefore, the flow conditions and/or the adsorber structure as such or rather the flow path through the adsorber structure can be designed in such a way, that the closed and isolated reactor forces the steam through the reactor bed in a path with substantially lower through-flow area and correspondingly higher velocities inducing beneficial purge conditions. While under conventional conditions the flow velocity of the steam is in the range of 0.01 m/s, this high-speed steam purge is carried out at steam velocities in the range of 0.1-0.4 m/s, preferably in the range of 0.2-0.35 m/s. Typically and preferably this high-speed is achieved at the same volume flow as in the conventional process.

[0215] The following are a series of examples in which the herein disclosed circulation loop was realized and analyzed for a steam desorption process of DAC sorbent materials, preferably (but not necessarily) for the specific process as described above and as claimed for the embodiment using direct steam recirculation for one unit.

[0216] FIG. 16 shows a possible configuration of a circulation loop connected to a DAC unit 101 containing a sorbent material structure 102 for capturing and releasing CO2 in a cyclic process, undergoing regeneration, i.e. for release of the CO2 bound in the capture phase for collection and for preparation of the next capture phase.

[0217] Fresh steam 103 can be supplied and enters the DAC unit 101 at the connection 104 or is aspirated by a circulation device 105 into a circulation conduit 106, passing further to a heat exchanger 107 before (re)entering the DAC unit at the inlet 108.

[0218] As the purpose of the circulation is to achieve far higher effective purge ratios than would otherwise be possible with single pass operation, the volume flow of steam in the circulation loop is much higher than that of the fresh steam injection 103. A rather small flow of fresh steam 103 is aspirated into the circulation loop 106 without passing first into the DAC unit 101. The remainder of the flow difference is given by steam in mixture with desorbed CO2 aspirated out of the DAC unit at connection 104 and passed into the circulation conduit 106. For realizing the process control in order to avoid drying and to optimize desorption, there is a temperature sensor 109 for sensing the temperature of the exiting gases at the connection 108 to the DAC unit, there is a sensor 111 for the sorbent temperature T-11 in the DAC unit and a sensor 110 for the pressure P-10 in the DAC unit.

[0219] Based on these parameters the heat input (e.g. heating temperature) of heat exchanger 107 as well as the extraction of gas from the DAC unit 101 through the conduit 112 by a vacuum extraction device 113 can be adapted to reach the desired steam conditions ideal for desorption while avoiding or limiting drying. The gas composition Q-14 and flow rate F-15 of the extracted gases are measured at the composition and flow sensors 114 and 115, respectively, which support hereby the heating and pressure control of the heat exchanger 107, vacuum system 113 and circulation device 105.

[0220] For the capture of CO2 from atmospheric air, first a gas flow of said air is contacted with the sorbent material structure contained in the unit where said gas flow can have ambient atmospheric conditions. Upon the saturation of the sorbent - typical duration between 60 and 180 min, the unit is isolated from the gas flow and evacuated for example to a nominal pressure of 100 mbarabs.

[0221] A saturated steam flow of 1000 kg/h is then applied to the evacuated and isolated unit where in this example additionally the circulation loop is operational (see more details below). Hereby the temperature is allowed to rise to 90° C. and the pressure to 850 mbarabs. The unit is then again attached to the vacuum system whereby the released CO2 and the applied steam are extracted while the circulation loop is continuing the herein described circulating steam flow. In this example, a fresh steam flow of 200 kg/h is applied to the unit. Upon completion of release of CO2, the fresh steam flow and the circulation loop are stopped and the pressure of the unit is rapidly reduced by the vacuum system to 120 mbarabs provoking a re-evaporation of liquid water from the sorbent material and thereby a cooling to ca. 50° C. The unit is thereafter repressurized to atmospheric conditions and opened to the flow of ambient atmospheric air to restart the adsorption.

[0222] FIG. 17 shows experimental results of the operation of the device in FIG. 16 operating a ‘continuous fill/continuous pass’ sorbent regeneration procedure, wherein the phase S1 pressure P-10 measured by the sensor 110 in the DAC unit 101 is ca. 100 mbarabs (thin solid line) and the sorbent temperature T-11 is at a nominal ambient environmental temperature of 20° C. (thin dashed line).

[0223] In phase S2, fresh steam 103 is injected into the DAC device at a constant flow rate with an operating circulation loop having a heating power at 100° C. of 2 kW and a circulation flow rate of 780 m3/h. No gas is extracted in phase S2, and under the influence of steam condensation and sensible heat exchange with superheated steam the temperature T-11 of the sorbent in the DAC unit and the pressure P-10 in the DAC unit material rise to a nominal value of ca. 85° C. and 900 mbarabs respectively, which is well within the range of desorption for a typical amine functionalized solid sorbent. The difference to the saturation pressure of steam at 900 mbarabs stems from both a small portion of air in the system, which reduces the effective partial pressure as well as the presence of desorbed CO2.

[0224] In phase S3, the extraction of gases is started by the vacuum compression device 113 and the flow profile F-15 of extracted gases (thick dashed line) is measured by the flow sensor 115 with the fraction of CO2 Q-14 being measured by the composition Q sensor 114 (thick dotted line). In this experiment, the flow of fresh steam is gradually reduced in phase S3 from an initial value of 20 kg/h to 5 kg/h and is correspondingly far lower than the volume flow rate of steam in the circulation loop. At first, in Q-14 a peak of released CO2 is found which stems from the CO2 released in the heating phase of S2. Thereafter a more or less constant to decreasing flow of 1 - 0.5 kg/h is recorded. The temperature T-11 of the sorbent material rises constantly in S3 to about 100° C. owing to the exchange of sensible energy with the superheated steam and desorbed CO2 existing in the circulation gas. Simultaneously, the pressure stays substantially constant. This combination of pressure and temperature lies well within the range of superheated steam and therefore drying of the sorbent can be assumed to have taken place.

[0225] This is supported by the fact that the pressure P-10 in the DAC unit 101 remains constant despite a reducing fresh steam supply and a reducing flow rate F-15 as measured by the flow meter 115 and the composition sensor Q-14, respectively. The release of water from the sorbent therefore is responsible for maintaining the pressure P-10.

[0226] The flow F-15 of the product gas mirrors the peak in CO2 and tends to match the supply of fresh steam flow 103 with a small additional portion owing to water stemming from drying. The total ratio of steam supplied to the released CO2 in this experiment was 18:1 whereas the composition of steam to CO2 lay between 2:1 (50%) and 32:1 (3.2%) at the beginning and end of phase S3, respectively.

[0227] In the next phase S4, the system is re-pressurized and the sorbent is allowed to cool off bringing it to a state ready for the next adsorption of CO2.

[0228] Important in these results is the interplay of pressure, temperature of circulating gases consisting of steam and CO2 and flow composition. These three factors influence the drying of sorbent but also the release of CO2 from a particular sorbent as dictated by the isotherms of that material as will be shown by the next figure.

[0229] FIG. 18 illustrates the impact of desorbate accumulation in the circulating steam and the importance of maintaining a minimum steam to CO2 ratio in the circulation loop.

[0230] A DAC sorbent is shown with two equilibrium isotherms: at ambient atmospheric conditions 116 characterized by ambient atmospheric temperatures and an adsorbate partial pressure Pads and an elevated temperature isotherm 117 at 100° C.

[0231] Between these two curves, there exists a maximum partial pressure of desorbate Pdes on the line 117 which can be accepted to give a minimum cyclic adsorption-desorption capacity Δq needed for economically feasible operation. At higher Pdes, the cyclic capacity cannot be reached thermodynamically. It has been experimentally found that for a typical amine functionalized solid sorbent with CO2 adsorption equilibrium capacity of 1.5 mol/kg at ambient atmospheric conditions and a desired cyclic capacity Δq at 100° C. desorption temperature of 1 mol/kg, the maximum allowable CO2 partial pressure Pdes can be at most 8%. Correspondingly, desorbate in mixture with steam must have a steam to CO2 ratio over the entire process of at least 12.5 : 1.

[0232] At lower steam to CO2 ratios and therefore lower energy demand, the desorption equilibrium point shifts right to higher Pdes and lower cyclic capacities Δq. Further, the lower steam ratio drives lower water partial pressures, which strengthens drying processes at the temperatures required for desorption of CO2.

[0233] At higher steam to CO2 ratios, higher cyclic capacities Δq can be reached, but more fresh steam must be injected to the process. Although the generation of fresh steam is thermally on a parity with drying of water from the sorbent, drying is in circulation significantly slower as will be shown. While it is tempting from an energy standpoint to conduct the aforementioned “single-fill” desorption variant, this example demonstrates that at least for the indicated sorbent it cannot be economically done and that fresh steam must always be injected.

Example 1 - Dimensioning of Process Equipment in Circulation and Estimates of Process Duration

[0234] This example explains the practical limitations for operation of circulation consisting of superheated steam and CO2 for DAC applications and addresses an interplay between capital costs for gas conduits and operation costs for gas propulsion.

[0235] Cost wise, there is a sharp increase in the costs of gas conduits suitable for vacuum applications and isolation valves above a diameter of about 350 mm. Correspondingly, it is necessary to remain below 350 mm piping diameter.

[0236] The second limitation involves gas propulsion devices which become increasingly complex, expensive and limited in their volume throughput above 1000 Pa maximum pressure difference. The pressure difference that a gas propulsion device would need to overcome in a circulation loop would be composed of the pressure drop across the sorbent material structure 102, the circulation conduits 106 and heat exchanger 107. Respecting this pressure limit and assuming a sorbent material structure such as that mentioned in the prior art containing 500 kg of sorbent, piping lengths for circulation conduits of 10 m, and a 2 m long heat exchanger having 2 mm plate spacing, a sweep gas volume flow of 14000 Nm3/h is determined. Such flow propulsion devices are firmly in the region of radial blowers.

[0237] There are two further practical temperature limitations imposed by the sorbent and process which are not encountered in the prior art. Firstly, amine functionalized solid sorbents typical and suitable in DAC applications are irreversibly damaged above 120° C., which caps the steam temperature. Secondly, assuming a 12.5:1 (steam to CO2 ratio) and desorption pressure of 900 mbar (a), the temperature of the steam must stay above 94.5° C. to avoid condensation and loss of the steam in the sweep gas altogether. Correspondingly, the useable temperature difference is 25.5° C. and the available thermal energy for desorption under circulation is 104 kW. This thermal energy must be supplied by a corresponding heat exchanger, which on the gas side is assumed to have a heat transfer coefficient of 50 W/m2/K and a gas side contact surface area of 83.3 m2.

[0238] Considering a possible energy demand for the desorption process as can be found in the prior art of 2578 kWh/ton CO2 with a yield of 1 mol CO2/kg and a water release of 3 mol H2O/kg, the process of this example has a thermal energy demand of 56 kWh and a duration therefore of 32 min. The mechanical energy demand for circulation is 2.1 kWh.

Example 2 - Implications of Significant Drying on Desorption Processes

[0239] In this example, the dimensioning of example 1 is again considered. Certain classes of amine functionalized sorbents tend to capture significantly more water than the 3 mol H2O/kg mentioned. Further, steam processes relying on latent heating by steam condensation such as that shown in FIG. 17 will apply much more liquid water to the sorbent than the temperature vacuum swing process of the prior art considered in Example 1. A more realistic water loading may be 15 molH2O/kg. Drying this water amount from the sorbent would represent an additional 84 kWh of energy, which would need to be supplied by the circulation loop. Due to the aforementioned power limitations of 104 kW, the time for this drying alone would be 48 min producing a desorption process time of minimum 80 min. Such processes are in no ways competitive in terms of output or energy demand against processes in which thermal energy is applied through heat exchangers integrated into the sorbent material structure. For this reason, significant drying of the sorbent should be avoided in circulation sweep gas desorption.

Example 3 - Kinetic Limitations Associated With Water

[0240] While the previous example showed that significant drying should be avoided, FIG. 19 shows that certain kinetic limitations associated with water introduction in sorbent materials can be thusly overcome with a small amount of drying. Water introduction has been identified in as a major kinetic resistance to adsorption and is particularly a challenge for steam desorption processes utilizing the latent heating of steam condensation with prolonged purge settings. The adsorption kinetics were investigated on the same DAC amine functionalized solid sorbent desorbed in a saturated steam purge and with a superheated circulating sweep gas at 100° C. and 850 mbar (a). As such, the latter sorbent experienced a certain exposure to conditions, which would dry adsorbed or otherwise accumulated water. In the subsequent adsorptions of CO2 from ambient atmospheric air, it was found that the dried sorbent 118 had a faster uptake of CO2 than the sorbent which did not see drying conditions 119 (0.61 vs. 0.48 molO2/kg in 3 hours). Secondly, the equilibrium capacity of the dried sorbent 18 was higher. Both observations are consistent with previous results, which show that liquid water removal is beneficial to sorbent performance. While the exact amount of water to be dried depends on the sorbent characteristics as well as the process requirements, the circulation loop with superheated steam offers the functionality of tuning the water content to optimize process output and sorbent performance.

Example 4 - Process Control to Avoid Steam Loss in Circulation Loop

[0241] In this example, the process control for the steam recirculation is explained and how it can be used to optimize the balance of drying and desorption in a regeneration process comprising the first two phases of FIG. 17. At the beginning of stage S3, the steam to CO2 ratio may be 2:1 at a total pressure of 900 mbarabs producing a partial steam pressure of 600 mbarabs with a corresponding saturation temperature of 86° C. which is substantially the same as the sorbent temperature at this moment. The heat exchanger 107 of the recirculation loop is therefore set such that the temperature 109 of the gases at the reinjection point of the unit 108 achieves 96° C., which affords a good heat transfer temperature difference to the sorbent to support desorption while limiting the drying potential of the circulation gases and avoiding condensation. In the depicted process, the CO2 content as measured gradually decreases under the influence of slowing desorption and the continuously introduced steam. At some point, a value of 15:1 may be reached still at a total pressure of 900 mbarabs, producing a partial steam pressure of 843 mbarabs and a corresponding saturation temperature of 95° C. that is substantially the sorbent temperature at this moment. In such a case, the described process control increases the temperature 109 of the gases at the reinjection point of the unit 108 beyond the previously mentioned 96° C. – for example to 106° C. – in order to avoid undesired condensation of the steam.

Example 5 - Process Control to Prevent Excessive Drying

[0242] In this example, the disclosed process control for the steam recirculation is used to avoid excessive drying of the sorbent. Again, the first two stages of the process of FIG. 17 (S1 and S2) are common. However, for a particular sorbent, no CO2 is present in the gas phase of the until the beginning of S3. Therefore, at 900 mbarabs, the temperature of the sorbent is substantially equal to the saturation temperature of the steam (96° C.). At the beginning of circulation, the temperature 109 of the gases at the reinjection point of the unit 108 can be set at for example 120° C. to drive strong heat transfer to the sorbent material for the start of desorption. In one possible process variant, the injection of fresh steam is not used and once the circulation of stage S3 is started, CO2 is gradually released and accumulates in the circulation gases reaching 20% in the circulation gases or a steam to CO2 ratio of ca. 4:1. The corresponding partial pressure of steam in the circulation gases is therefore 720 mbarabs with a saturation temperature of 90.7° C., which corresponds substantially to the sorbent temperature. The herein disclosed process control hereby reduces the temperature 109 of the gases at the reinjection point of the unit 8 from 120° C. to 100° C. thereby maintaining a sufficient temperature difference for driving desorption while not excessively drying the sorbent materials.

TABLE-US-00001 LIST OF REFERENCE SIGNS 1 adsorption step (a) 2 isolation step (b) 3 evacuation step (b) 4 step involving flushing with steam (b1) 5 step involving heat up with steam (c) 6 purge step with steam (d) 7 vacuum cool/dry step (d1) 8 step of breaking isolation and re-pressurisation (e) 9 step of air drying (e1) 10 liquid water source recirculated/preheated steam 19 switching valve 20 steam reuse line 21 latent heat recovery unit 22 low temperature condenser 23 main vacuum system 24 product CO2 25 optional condensate reuse 26 valve 27 steam injection line 28 fresh/recovered steam line 29 steam outlet line 30 take out line 31 fresh water line 101 DAC Unit 102 sorbent material structure 103 fresh steam 104 connection for extraction of gas on DAC unit 105 propulsion device 106 circulation conduit 107 heat exchanger 108 re-injection point of sweep gas into DAC unit 109 injection point temperature sensor 110 DAC unit pressure measurement sensor 111 sorbent material temperature measurement sensor 112 product gas extraction conduit 113 vacuum compression device 114 composition sensor 115 flow measurement sensor 116 adsorption condition equilibrium isotherm 117 desorption condition equilibrium isotherm 118 adsorption capacity curve of dried sorbent 119 adsorption capacity curve of wetted sorbent F-15 flow measured in 115 Q-14 CO2 fraction in flow measured in 114 S1-S4 phases of a process involving circulation T-11 sorbent material temperature value measured in 111 T temperature measurement P pressure measurement P-10 DAC unit pressure measured in 110 Q composition measurement F flow measurement q adsorption capacity Δq cyclic capacity t time