IMPROVEMENTS RELATING TO CARBON DIOXIDE CAPTURE

Abstract

A method is disclosed for separating compressed dry air to provide carbon dioxide and reduced-carbon dioxide compressed dry air. The method comprises providing a source of compressed dry air and admitting compressed dry air into a first chamber containing a carbon dioxide-adsorbent material at a first temperature. The carbon dioxide-adsorbent material adsorbs carbon dioxide from the compressed dry air to form reduced-carbon dioxide compressed dry air, which is allowed to pass out of the first chamber. The first chamber is closed to the source of compressed dry air. Then the carbon dioxide-adsorbent material is heated to a second temperature. This releases carbon dioxide from the carbon dioxide-adsorbent material, which carbon dioxide is removed from the first chamber. The method may be low cost and low energy, and may be easily integrated into existing compressed dry air systems. A carbon dioxide capture unit and a compressed dry air production system for separating compressed dry air to provide carbon dioxide and reduced-carbon dioxide compressed dry air are also described.

Claims

1. A method of separating compressed dry air to provide carbon dioxide and reduced-carbon dioxide compressed dry air, the method comprising the steps of: a) providing a source of compressed dry air; b) admitting compressed dry air into a first chamber containing a carbon dioxide-adsorbent material at a first temperature in order to adsorb carbon dioxide from the compressed dry air onto the carbon dioxide-adsorbent material and to form reduced-carbon dioxide compressed dry air, and allowing the reduced-carbon dioxide compressed dry air to pass out of the first chamber; c) closing the first chamber to the source of compressed dry air; e) heating the carbon dioxide-adsorbent material to a second temperature in order to release carbon dioxide from the carbon dioxide-adsorbent material; and f) removing the carbon dioxide from the first chamber.

2. The method of claim 1, further comprising, after step c) and before step e), the step of: d) evacuating the first chamber to remove residual dry air from the first chamber.

3. The method of claim 1, wherein step (b) is carried out until the carbon dioxide-adsorbent material is at least 70% saturated with carbon dioxide.

4. The method of claim 1, wherein step (d) and/or step (f) comprises applying a vacuum to the first chamber.

5. The method of claim 1, wherein step (e) comprises sealing the first chamber such that heating the carbon dioxide-adsorbent material to the second temperature increases the pressure of carbon dioxide in the first chamber.

6. The method of claim 5, wherein no other gas contacts the carbon dioxide-adsorbent material in step (e) or step (f.

7. The method of claim 1, wherein the first temperature is ambient and the second temperature is from 50 to 200° C.

8. The method of claim 1, wherein step (f) comprises directing the carbon dioxide removed from the first chamber to a storage vessel.

9. The method of claim 1, further comprising the step of: g) cooling the carbon dioxide-adsorbent material to the first temperature.

10. The method of claim 9, further comprising repeating step (b) following step (g).

11. The method of claim 1, wherein step (b) is carried out for the same period of time as step (c), step (d), step (e), and step (f), and step (g) when present, combined.

12. The method of claim 1, wherein the pressure in the first chamber in at least a part of step (b) is from 1,000 to 20,000 mbar, and the pressure in the first chamber in at least a part of step (d) when present, step (e), and step (f), and step (g) when present, is less than 10 mbar.

13. The method of claim 1, wherein step (b) is carried out in the first chamber while step (c), step (d) when present, step (e), or step (f), or step (g) when present, is carried out simultaneously in a second chamber containing a carbon dioxide-adsorbent material.

14. A carbon dioxide capture unit for removing carbon dioxide from a source of compressed dry air, the carbon dioxide capture unit comprising: at least one chamber comprising a carbon dioxide-adsorbent material, a gas inlet, and a gas outlet; a heater for heating the carbon dioxide-adsorbent material; an input valve in fluid communication with the gas inlet for connection of the gas inlet to a source of compressed dry air; and at least one output valve in fluid communication with the gas outlet for connection of the gas outlet to a reduced-carbon dioxide compressed dry air output and a carbon dioxide output.

15. A compressed dry air production system comprising: a source of compressed dry air; a carbon dioxide capture unit; a reduced-carbon dioxide compressed dry air output; and a carbon dioxide output; wherein the carbon dioxide capture unit comprises: at least one chamber comprising a carbon dioxide-adsorbent material, a gas inlet, and a gas outlet, a heater for heating the carbon dioxide-adsorbent material, an input valve in fluid communication with the gas inlet and the source of compressed dry air, and at least one output valve in fluid communication with the gas outlet, the reduced-carbon dioxide compressed dry air output, and the carbon dioxide output.

16. The carbon dioxide capture unit of claim 14, wherein the at least one chamber comprises a first chamber and a second chamber which are not in fluid communication with the same input valve.

17. The system of claim 15, wherein the at least one chamber comprises a first chamber and a second chamber which are not in fluid communication with the same input valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0255] For a better understanding of the invention, and to show how example embodiments may be carried into effect, reference will now be made to the accompanying drawings in which:

[0256] FIG. 1 is a diagram of a compressed dry air production system according to the third aspect of the present invention.

[0257] FIG. 2 is a graph showing the evolution of the pressure and temperature in a first chamber during a method according to the first aspect of the present invention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

[0258] FIG. 1 shows a compressed dry air production system according to the third aspect of the present invention comprising a source of compressed dry air (1), a reduced-carbon dioxide compressed dry air output (2), and a carbon dioxide capture unit. The carbon dioxide capture unit comprises a first chamber (3) comprising a gas inlet (3A), a gas outlet (3B), and a carbon dioxide-adsorbent material (3C), a heater (31) for heating the carbon dioxide-adsorbent material (3C), a carbon dioxide output (6), an input valve (32) in fluid communication with the gas inlet (3A) and the source of compressed dry air (1), an output valve (33) in fluid communication with the gas outlet (3B) and the reduced-carbon dioxide compressed dry air output (2), an output valve (34) in fluid communication with the gas outlet (3B) and the carbon dioxide output (6), and a vent valve (35) in fluid communication with the gas outlet (3B). The carbon dioxide capture unit also comprises a second chamber (4) comprising a gas inlet (4A), a gas outlet (4B), and a carbon dioxide-adsorbent material (4C), a heater (41) for heating the carbon dioxide-adsorbent material (4C), an input valve (42) in fluid communication with the gas inlet (4A) and the source of compressed dry air (1), an output valve (43) in fluid communication with the gas outlet (4B) and the reduced-carbon dioxide compressed dry air output (2), an output valve (44) in fluid communication with the gas outlet (4B) and the carbon dioxide output (6), and a vent valve (45) in fluid communication with the gas outlet (4B). The system also comprises a bypass conduit (8) which allows compressed dry air from the source of compressed dry air (1) to flow to the output (2) without passing through the carbon capture unit. The bypass conduit comprises bypass input valve (81) which is a three-port valve in fluid communication with the source of compressed dry air (1), the bypass (8), and the input valves (32, 42), and a bypass output valve (82) which is a three-port valve in fluid communication with the bypass (8), the reduced-carbon dioxide compressed dry air output (2), and the output valves (33, 43). In this example the first chamber (3) and the second chamber (4) each contain 137 kg of SIFSIX-3-Ni as the carbon dioxide-adsorbent material (3C) and (4C).

[0259] The system in FIG. 1 may be used to carry out a method according to the first aspect of the present invention. Arrows in FIG. 1 indicated the direction of gas flow. FIG. 2 shows the evolution of the pressure and temperature in the first chamber (3) during a complete cycle of steps (b) to (g) in a method according to the first aspect of the present invention.

[0260] In step (a) compressed dry air is provided by the source of compressed dry air (1). The bypass input valve (81) is operated to allow compressed dry air to flow from the source of compressed dry air (1) to the input valve (32) of the first chamber (3) and the input valve (42) of the second chamber (4). The pressure, temperature, humidity, and carbon dioxide level of the compressed dry air are controlled with the help of sensors (11).

[0261] The following list highlights the key parameters of a common compressed dry air (CDA) production unit which may be used as a source of compressed dry air: flow: 1500 Nm.sup.3/h, pressure: 10 bar, temperature: 20° C., pressure dew point: −40° C., carbon dioxide concentration: 400 ppm.

[0262] In step (b) the input valve (32) and the output valve (33) are open and allow compressed dry air to flow through the gas inlet (3A) into the first chamber (3). The temperature of the carbon dioxide-adsorbent material (3C) is held at a first temperature, for example 20° C. The pressure in the first chamber (3) is for example 10,000 mbar. The temperature of the carbon dioxide-adsorbent material (3C) and the pressure in the first chamber (3) are controlled with the help of sensors (36). Carbon dioxide is captured from the compressed dry air and reduced-carbon dioxide compressed dry air flows out of the first chamber (3), through the gas outlet (3B), the output valve (33), and the bypass output valve (82) to the reduced-carbon dioxide compressed dry air output (2). The output valve (34) and the vent valve (35) are closed to isolate the first chamber (3) from the atmosphere (7) and a vacuum pump (5). Step (b) is completed when the carbon dioxide-adsorbent material (3C) is saturated with carbon dioxide, for example after 8 hours.

[0263] In step (c) the input valve (32) and the output valve (33) are closed in order to close the first chamber (3) to the source of compressed dry air (1). At this stage the carbon dioxide-adsorbent material (3C) is saturated with carbon dioxide, but the gas phase in the first chamber (3) still contains residual air. In order to provide high purity carbon dioxide when the adsorbed carbon dioxide is recovered, residual air is first removed by opening the vent valve (35) to the atmosphere (7), allowing the pressure in the first chamber (3) to decrease to atmospheric pressure, for example 1,000 mbar.

[0264] In step (d) the vent valve (35) is closed and the output valve (34) is opened. The vacuum pump (5), which is for example a dry pump, reduces the pressure in the first chamber (3) to the partial pressure of the carbon dioxide, for example to 4 mbar, and the remaining dry air in the first chamber (3) flows through the output valve (34), the vacuum pump (5) and the vacuum pump valve (51) to be released to the atmosphere (7). A pressure sensor (52) is used to determine the pressure in the vacuum pump (5).

[0265] The temperature of the carbon dioxide-adsorbent material (3C) in steps (c) and (d) is the first temperature, for example 20° C. The combined duration of steps (c) and (d) is for example 90 seconds.

[0266] In step (e) the first chamber (3) is sealed by closing the output valve (34) when the pressure in the first chamber (3) is sufficiently low, for example 4 mbar. The saturated carbon dioxide-adsorbent material (3C) is heated to a second temperature, for example to 80° C., using the heater (31) in order to release carbon dioxide from the material (3C). This increases the carbon dioxide pressure in the first chamber (3), for example to 150 mbar. Increasing the temperature of the saturated carbon dioxide-adsorbent material (3C) may increase the equilibrium pressure of the carbon dioxide because adsorption is an exothermic phenomenon. The heating may be achieved using waste operational heat associated with the compressor unit of the source of compressed dry air (1), green energy or carbon-emitting energy. The duration of step (e) is for example 1 hour.

[0267] In step (f) the first chamber (3) is connected to the vacuum pump (5) by opening the outlet valve (34) while the carbon dioxide-adsorbent material (3C) is maintained at the second temperature, for example 80° C. The position of the vacuum pump valve (51), which is a three-port valve, is set such that carbon dioxide flows from the first chamber (3) to the carbon dioxide output (6) through the output valve (34) and the vacuum pump (5). The percentage of recovered carbon dioxide is selected to ensure economical capture, as an ideal 100% recovery of the carbon dioxide will result in unfavourably increased costs. For example step (f) is completed once 80% carbon dioxide recovery is reached after 4 hours, during which the pressure in the first chamber (3) decreases to 9.2 mbar.

[0268] Step (g): When the carbon dioxide release is completed, the first chamber (3) is sealed by closing the output valve (34). The carbon dioxide-adsorbent material (30) is cooled to the first temperature, for example 20° C. This is achieved passively (using the heat loss) or actively using a cooling system (not shown). Step (g) for example lasts for 3 hours, during which time the pressure in the first chamber (3) decreases to 0.24 mbar due to the modification of the adsorption equilibrium. Once step (g) is completed a new capture cycle may be commenced starting with step (b).

[0269] The operating conditions of the above method are summarised in Table 1.

TABLE-US-00001 TABLE 1 Example operating conditions of the carbon dioxide capture method. Temperature Pressure Steps (° C.) (mbar) Duration Step (b): Carbon dioxide capture 20 10 000 8 h Carbon Steps (c) and (d): 20 10 000 .fwdarw. 4 1.5 min dioxide Evacuation of residual air release Step (e): Closed system 20 .fwdarw. 80 4 .fwdarw. 150 1 h heating Step (f): Carbon dioxide 80 150 .fwdarw. 9.2 4 h release Step (g): Cooling 80 .fwdarw. 20 9.2 .fwdarw. 0.24 3 h

[0270] Step (b), step (c), step (d), step (e), step (D) and step (g) are carried out in the second chamber (4) in the same way as in the first chamber (3), except that the gas inlet (4A), gas outlet (4B3), carbon dioxide-adsorbent material (4C), heater (41), input valve (42), output valves (43, 44), vent valve (45), and sensors (46) are used instead of the gas inlet (3A), gas outlet (3B3), carbon dioxide-adsorbent material (3C), heater (31), input valve (32), output valves (33, 34), vent valve (35), and sensors (36).

[0271] The system is designed in such a way that the time periods of the capture and the release steps are substantially equal. This enables the first chamber (3) to capture carbon dioxide while the second chamber (4) releases carbon dioxide and undergoes regeneration, and vice versa.

[0272] For example, step (b) is carried out in the first chamber (3) while step (c), step (d), step (e), step (f, and step (g) are carried out in the second chamber (4), and step (b) is carried out in the second chamber (4) while step (c), step (d), step (e), step (f, and step (g) are carried out in the first chamber (3).

[0273] The relative timing and order of the steps is presented in Table 2.

TABLE-US-00002 TABLE 2 Steps of the method used by the carbon dioxide capture unit First chamber (3) Step (b): carbon dioxide Carbon dioxide release capture steps (c + d) (e) (f) (g) Second chamber Carbon dioxide release Step (b): carbon dioxide (4) steps capture (c + d) (e) (f) (g)

[0274] The beginning of step (b) involving the first chamber (3) coincides with the beginning of step (c) involving the second chamber (4). The end of step (g) involving the second chamber (4) coincides with the end of step (b) involving the first chamber (3), whereby the carbon dioxide-adsorbent material (3C) is saturated with carbon dioxide. Then, the input valve (32) and the output valve (33) are closed and the first chamber (3) undergoes the carbon dioxide release process. At the same time, the input valve (42) and the output valve (43) are opened and the second chamber (4) begins capturing carbon dioxide from the compressed dry air, coinciding with the beginning of step (b) involving the second chamber (4).

[0275] The cost and energy required to capture carbon dioxide from air have up to now prevented widespread commercialisation of direct air capture technologies. These problems may be addressed by the example embodiments as described herein, which provide low cost and low energy methods for capturing carbon dioxide from air.

[0276] In summary a method is disclosed for separating compressed dry air to provide carbon dioxide and reduced-carbon dioxide compressed dry air. The method comprises providing a source of compressed dry air and admitting compressed dry air into a first chamber containing a carbon dioxide-adsorbent material at a first temperature. The carbon dioxide-adsorbent material adsorbs carbon dioxide from the compressed dry air to form reduced-carbon dioxide compressed dry air, which is allowed to pass out of the first chamber. The first chamber is closed to the source of compressed dry air. Then the carbon dioxide-adsorbent material is heated to a second temperature. This releases carbon dioxide from the carbon dioxide-adsorbent material, which carbon dioxide is removed from the first chamber. The method is low cost and low energy, and can easily be integrated into existing compressed dry air systems. A carbon dioxide capture unit, a compressed dry air production system, and a use of a first chamber containing a carbon dioxide-adsorbent material for separating compressed dry air to provide carbon dioxide and reduced-carbon dioxide compressed dry air are also described.

[0277] Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0278] Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of” or “consists essentially of” means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention.

[0279] The term “consisting of” or “consists of” means including the components specified but excluding addition of other components.

[0280] Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to encompass or include the meaning “consists essentially of” or “consisting essentially of”, and may also be taken to include the meaning “consists of” or “consisting of”.

[0281] The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments.

[0282] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0283] All of the features disclosed in this specification (including any accompanying claims, and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0284] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0285] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.