Carbon dioxide adsorber for aircraft

A system for processing recirculation air recovered from an aircraft cabin includes a mixing chamber and a carbon dioxide removal system. The carbon dioxide removal system has an inlet for recovered recirculation air from the aircraft cabin, an outlet to the mixing chamber; at least two assemblies of carbon dioxide sorbent that are thermally linked, a CO2 outlet valve; and a controller for managing desorption of carbon dioxide from the sorbent depending on aircraft status. The mixing chamber has an inlet from the carbon dioxide removal system, an inlet from an environmental control system, and an outlet connected to the aircraft cabin.

BACKGROUND

Exemplary embodiments pertain to the art of systems and methods for removing carbon dioxide from recirculation air discharged from an aircraft cabin.

The air conditioning system for a modern passenger aircraft includes an air conditioning unit which is supplied with compressed process air from a compressor or bled off from an engine or an auxiliary power unit of the aircraft. Cooled air leaving the air conditioning unit is supplied to a mixing chamber where it is mixed with recirculation air from the aircraft cabin to result in mixed air. The mixed air is supplied to the aircraft cabin.

The carbon dioxide (CO2) content of the recirculated air increases due to human respiration. The carbon dioxide content of the air returned to the aircraft cabin can be reduced by mixing with fresh air from the air conditioning unit, by adsorption, or by a combination thereof. While currently available systems are adequate, there is a need for more efficient systems and methods for reducing the carbon dioxide content of the recirculated air and the air returned to the aircraft cabin.

BRIEF DESCRIPTION

Disclosed is a system for processing recirculation air recovered from an aircraft cabin comprising a mixing chamber and a carbon dioxide removal system, wherein the carbon dioxide removal system has an inlet for recovered recirculation air from the aircraft cabin, an outlet to the mixing chamber; at least two assemblies of carbon dioxide sorbent that are thermally linked, a CO2outlet valve; and a controller for managing desorption of carbon dioxide from the sorbent depending on aircraft status and further wherein the mixing chamber has an inlet from the carbon dioxide removal system, an inlet from an environmental control system, and an outlet connected to the aircraft cabin.

Also disclosed is a method for processing recirculation air recovered from an aircraft cabin comprising supplying recovered recirculation air from the aircraft cabin to a carbon dioxide removal system having at least two thermally linked assemblies of carbon dioxide sorbent; removing carbon dioxide from the recovered recirculation air to form processed recirculation air, removing carbon dioxide from the carbon dioxide sorbent; mixing the processed recirculation air with conditioned fresh air and sending the mixture to the aircraft cabin, wherein the removal of carbon dioxide from the carbon dioxide sorbent is by reduced pressure, elevated temperature or both and is determined by the aircraft status.

DETAILED DESCRIPTION

Carbon dioxide removal from recovered recirculated aircraft cabin air may involve the use of a carbon dioxide sorbent. The carbon dioxide sorbent can be regenerated and used repeatedly. Regeneration can involve exposing the carbon dioxide sorbent to reduced pressure, elevated temperature or both. By using a controller to manage the regeneration conditions efficiency can be maximized depending upon the aircraft status. For example, at cruising conditions (elevated altitude), ambient pressure is less than the pressure of the aircraft cabin and pressurized areas of the aircraft. This low ambient pressure can be employed to provide reduced pressure for regeneration. When the aircraft is on the ground or the ambient pressure is too high for sufficient regeneration alone, elevated temperature can be used for regeneration. The controller monitors the ambient pressure and manages the regeneration method. When the regeneration method involves elevated temperature the thermal linking of the two sorbent beds helps to recover energy from the carbon dioxide adsorption in one bed and use it to facilitate the carbon dioxide desorption in the second bed. Through the use of a controller in combination with a carbon dioxide removal system the need for fresh air from the engine (via the air conditioning system) is reduced. Fresh air is typically provided as bleed air from the engines and the air is conditioned to achieve the desired temperature and pressure. Systems that reduce the demand for fresh air from the air conditioning system offer an opportunity to reduce overall aircraft energy consumption as compared with the current state of art.

According to the systems and methods described herein, process streams include cabin air. These process streams contain carbon dioxide that can be removed from the process stream.

FIG. 1illustrates one embodiment of carbon dioxide (CO2) removal system10. CO2removal system10includes inlet valve12, first sorbent assembly14A, second sorbent assembly14B, heat exchange system16, gas stream outlet valve18, CO2outlet valve20, and controller24. A process stream enters CO2removal system10via inlet valve12. The process stream is recovered recirculation air from an aircraft cabin. The process stream can be delivered to CO2removal system10by pump or other means. Inlet valve12allows the process air stream to communicate with first sorbent assembly14A and second sorbent assembly14B. Depending on the position of inlet valve12, the process stream is directed to first sorbent assembly14A or second sorbent assembly14B. As shown inFIG. 1, inlet valve12is positioned so that the process stream is directed to first sorbent assembly14A. The process stream contains CO2. Exemplary incoming process streams for CO2removal system10contain between about 0.5% CO2and about 1% CO2by volume.

First sorbent assembly14A includes a solid amine sorbent. Solid amine sorbent26is contained within first sorbent assembly14A. Solid amine sorbent26is a regenerable CO2sorbent. In one exemplary embodiment, solid amine sorbent26includes one of the amine sorbents described in U.S. Pat. No. 6,364,938, which is hereby incorporated by reference in its entirety. Under certain conditions, solid amine sorbent26adsorbs CO2from a process stream flowing through first sorbent assembly14A and in contact with solid amine sorbent26. In this case, CO2is removed from the process stream flowing through first sorbent assembly14A when it is adsorbed by solid amine sorbent26. Under other conditions, solid amine sorbent26desorbs CO2to a process stream flowing through first sorbent assembly14A and in contact with solid amine sorbent26. Here, CO2from solid amine sorbent26is taken up by the process stream and carried away from first sorbent assembly14A. The temperature of and pressure surrounding solid amine sorbent26determines whether solid amine sorbent26adsorbs CO2or desorbs CO2. Second sorbent assembly14B is generally located near and can have identical or similar size and dimensions to first sorbent assembly14A. Second sorbent assembly14B also includes solid amine sorbent26. First sorbent assembly14A and second sorbent assembly14B are designed to generally operate in opposing sorption modes. That is, when first sorbent assembly14A is adsorbing CO2, second sorbent assembly14B is desorbing CO2. When first sorbent assembly14A is desorbing CO2, second sorbent assembly14B is adsorbing CO2.

First sorbent assembly14A and second sorbent assembly14B are thermally linked by a heat exchange system. In the embodiment illustrated inFIG. 1, the heat exchange system includes thermoelectric device16. Thermoelectric device16is positioned between first sorbent assembly14A and second sorbent assembly14B. Thermoelectric devices take advantage of the thermoelectric effect, which describes the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to a thermoelectric device, it creates a temperature difference (i.e. one side is heated while the other side is cooled). For example, when a voltage is applied to thermoelectric device16, one side of thermoelectric device16generates heat and heats adjacent first sorbent assembly14A. At the same time, the other side of thermoelectric device16is cooled and cools adjacent second sorbent assembly14B. The voltage is reversed to cool first sorbent assembly14A and heat second sorbent assembly14B. Thermoelectric device16provides an efficient means of temperature adjustment without requiring a significant amount of power. While the heat exchange system can take forms other than a thermoelectric device, CO2removal system10will be described in greater detail where the heat exchange system is a thermoelectric device.

Gas stream outlet valve18communicates with first sorbent assembly14A and second sorbent assembly14B. Gas stream outlet valve18allows a process stream50that has passed through a CO2adsorbing bed (first sorbent assembly14A or second sorbent assembly14B) to exit CO2removal system10and, as shown inFIG. 6, enter the mixing chamber40via inlet35where it is combined with a process stream33from the environmental control system via inlet37and the combined process stream45leaves the mixing chamber via outlet39and is delivered to the aircraft cabin. At a given time, gas stream outlet valve18communicates with the CO2adsorbing bed but not the CO2desorbing bed.

CO2outlet valve20also communicates with first sorbent assembly14A and second sorbent assembly14B. CO2outlet valve20allows a process stream that has passed through a CO2desorbing bed (first sorbent assembly14A or second sorbent assembly14B) to exit CO2removal system10. The process stream exiting CO2removal system10through CO2outlet valve20generally has a higher concentration than the process stream entering CO2removal system10through inlet valve12. The process stream exiting through CO2outlet valve may communicate directly with the ambient environment or may pass through an ambient outlet valve.

In one embodiment of CO2removal system10, CO2outlet valve20is positioned between first sorbent assembly14A, second sorbent assembly14B and the ambient outlet valve22. Ambient outlet valve22opens to the ambient environment when the ambient pressure is less than that of the pressurized cabin and CO2removal system and reduces pressure on the outlet side of first sorbent assembly14A and second sorbent assembly14B to increase the rate of CO2removal (desorption) from the desorbing bed. As discussed in greater detail below, ambient outlet valve22allows CO2removal system10to produce an exiting process stream rich in CO2. The ambient outlet valve is controlled by controller24.

In the embodiment of CO2removal system10shown inFIGS. 1 and 2, controller24communicates with inlet valve12, thermoelectric device16, gas stream outlet valve18, CO2outlet valve20and ambient outlet valve22. Controller24controls the valves and heat exchange system of CO2removal system10to cycle the first sorbent assembly14A and second sorbent assembly14B between CO2adsorption and CO2desorption. The role of controller24and how the valves, heat exchange system and pump operate during the CO2removal process are discussed in additional detail below.

As shown inFIGS. 1 and 2, first sorbent assembly14A and second sorbent assembly14B may be thermally linked by thermoelectric device16. During operation of CO2removal system10, a voltage may be applied to thermoelectric device16such that the CO2adsorbing bed is cooled while the CO2desorbing bed is heated. Thermoelectric device16generally maintains the CO2desorbing bed at a higher temperature than the CO2adsorbing bed. The controller24controls when the desorption is driven by reduced pressure via the ambient outlet valve22, temperature differential via the thermoelectric device16, or a combination thereof. The controller23can direct the system based on the aircraft status. For example, when cruising at altitude the reduced ambient air pressure can provide reduced pressure to facilitate desorption.

As shown inFIG. 1, CO2removal system10is operating in a state where first sorbent assembly14A is the adsorbing bed. A process stream enters CO2removal system10through inlet valve12. Inlet valve12is positioned to allow the process stream to enter first sorbent assembly14A. CO2is adsorbed to solid amine sorbent26in first sorbent assembly14A. Solid amine sorbent26has a defined capacity for CO2adsorption. The temperature of solid amine sorbent26and the CO2pressure within first sorbent assembly14A determine how much CO2can be loaded onto solid amine sorbent26. As the temperature of solid amine sorbent26decreases, the loading capacity for CO2adsorption increases. As the partial pressure of CO2within first sorbent assembly14A increases, the loading capacity for CO2adsorption also increases. The adsorption of CO2by solid amine sorbent26is exothermic. Thus, as CO2is adsorbed by solid amine sorbent26, the temperature of solid amine sorbent26increases, reducing its capacity to adsorb CO2until it reaches an equilibrium state where the temperature of solid amine sorbent26prevents further CO2adsorption. Thermoelectric device16may operate to cool first sorbent assembly14A and, hence, solid amine sorbent26contained within first sorbent assembly14A. By actively cooling first sorbent assembly14A, the CO2loading capacity of solid amine sorbent26may be increased allowing additional CO2adsorption within first sorbent assembly14A. Since first sorbent assembly14A is cooled by thermoelectric device16as CO2is adsorbed by solid amine sorbent26, a temperature-related pressure increase is generally not observed during CO2adsorption. After passing through first sorbent assembly14A, the process stream30is removed from CO2removal system10via gas stream outlet valve18. The process stream removed through gas stream outlet valve18has a lower amount of CO2than the process stream that entered CO2removal system10through inlet valve12.

At the same time that first sorbent assembly14A is adsorbing CO2, second sorbent assembly14B is desorbing CO2. Second sorbent assembly14B includes solid amine sorbent26that contains adsorbed CO2from an earlier CO2adsorption cycle. The desorption of CO2by solid amine sorbent26is endothermic. As noted above, as the temperature of solid amine sorbent26decreases, the loading capacity for CO2adsorption increases. Thus, as CO2is desorbed by solid amine sorbent26, the temperature of solid amine sorbent26decreases, making it more difficult to desorb CO2until it reaches an equilibrium state where the temperature of solid amine sorbent26prevents further CO2desorption. At the same time that thermoelectric device16operates to cool first sorbent assembly14A, thermoelectric device16heats second sorbent assembly14B. By actively heating second sorbent assembly14B, the CO2loading capacity of solid amine sorbent26is decreased making it easier to desorb CO2from solid amine sorbent26within second sorbent assembly14B.

Ambient outlet valve22operates to reduce the partial pressure of CO2at second sorbent assembly14B when the ambient air pressure is less than the pressure of the CO2removal system10(which is typically equivalent to the pressure of the aircraft cabin). As noted above, as the partial pressure of CO2within second sorbent assembly14B increases, the loading capacity for CO2adsorption also increases. Ambient outlet valve22communicates with the CO2desorbing bed—second sorbent assembly14B in the system shown inFIG. 1. Thus, as ambient outlet valve22opens to allow fluid to move away from CO2removal system10, the partial pressure of CO2at second sorbent assembly14B is reduced, thereby reducing the CO2loading capacity of solid amine sorbent26within second sorbent assembly14B. Since the CO2loading capacity of the desorbing bed is reduced, CO2present in second sorbent assembly14B is more easily removed from solid amine sorbent26. A process stream containing high levels of CO2is removed from second sorbent assembly14B and exits CO2removal system10via CO2outlet valve20. The process stream removed through CO2outlet valve20has a higher amount of CO2than the process stream that entered CO2removal system10through inlet valve12. In exemplary embodiments the removed process stream contains at least about 90% CO2by volume. In more exemplary embodiments the removed process stream contains at least about 95% CO2by volume.

FIG. 2illustrates the CO2removal system10ofFIG. 1where the CO2adsorbing and CO2desorbing beds are reversed. Having adsorbed CO2according to the description above and shown inFIG. 1, first sorbent assembly14A is now desorbing CO2inFIG. 2. Likewise, having given up its adsorbed CO2according to the description above and shown inFIG. 1, second sorbent assembly14B is now adsorbing CO2inFIG. 2. Controller24adjusts inlet valve12, thermoelectric device16, gas stream outlet valve18, CO2outlet valve20and ambient outlet valve22so that the process and output streams are flowing through the proper sorbent assemblies. Inlet valve12is positioned to allow the process stream to enter second sorbent assembly14B. Thermoelectric device16operates to cool second sorbent assembly14B and heat first sorbent assembly14A. After passing through second sorbent assembly14B, the process stream is removed from CO2removal system10via gas stream outlet valve18. Ambient outlet valve22operates to reduce the partial pressure of CO2at first sorbent assembly14A. A process stream containing high levels of CO2is removed from first sorbent assembly14A and exits CO2removal system10via CO2outlet valve20.

The descriptions of the CO2adsorbing bed (first sorbent assembly14A) and the CO2desorbing bed (second sorbent assembly14B) inFIG. 1above illustrate a snapshot of adsorption and desorption. Between adsorption and desorption modes, each bed can enter a transitional state. For example, in the case of the adsorbing bed, once solid amine sorbent26of first sorbent assembly14A has reached its CO2adsorption capacity, first sorbent assembly14A is no longer adsorbing CO2. First sorbent assembly14A can now be heated to increase the CO2partial pressure within first sorbent assembly14A. By heating first sorbent assembly14A, the CO2loading capacity of solid amine sorbent26within first sorbent assembly14A is reduced, preparing it for the CO2desorption cycle. The voltage applied to thermoelectric device16is reversed to accommodate the heating change in this transitional state. At the same time, solid amine sorbent26of second sorbent assembly14B has released all of the CO2it is capable of desorbing to the low pressure process stream. Second sorbent assembly14B can now be cooled to increase the CO2loading capacity of solid amine sorbent26within second sorbent assembly14B. By cooling second sorbent assembly14B, the CO2loading capacity of solid amine sorbent26within second sorbent assembly14B is increased, preparing it for the CO2adsorption cycle.

The transitional states described above can be isolated from the adsorbing and desorbing operations or integrated within the adsorbing and desorbing operations. For example, first sorbent assembly14A can be isolated from CO2removal system10using valves12,18and20to prevent process stream flow through first sorbent assembly14A. First sorbent assembly14A can then be heated to increase the pressure within first sorbent assembly14A. Once first sorbent assembly14A has been heated to an appropriate temperature, valves12,18and20can be positioned to allow first sorbent assembly14A to transition to the desorption mode. Alternatively, first sorbent assembly14A can transition to the desorption mode followed by heating and application of negative pressure to increase the rate of CO2desorption. Whether the transitional states are isolated or integrated within CO2removal system10will depend on application or efficiency requirements and design considerations for CO2removal system10.

FIG. 3illustrates an alternative embodiment of a CO2removal system (CO2removal system10B) in which thermoelectric device16has been replaced by heat exchange system28. In one embodiment, heat exchange system28operates as a vapor-compression refrigeration cycle. Heat exchange system28includes heat pump30, expansion device32and reversing valve34. First sorbent assembly14A is adsorbing CO2and functions as the evaporator. Heat is transferred from first sorbent assembly14A to a refrigerant within heat exchange system28. The refrigerant is delivered to reversing valve34, where it is directed to heat pump30. Heat pump30functions as the compressor and delivers the refrigerant to second sorbent assembly14B. Second sorbent assembly14B is desorbing CO2and functions as the condenser. Heat is transferred from the refrigerant to second sorbent assembly14B. The refrigerant is delivered to expansion device32where it expands. The refrigerant is then delivered to first sorbent assembly14A to repeat the process. The flow of refrigerant is reversed using reversing valve34when the adsorbing and desorbing beds are cycled.FIG. 4illustrates CO2removal system10B where second sorbent assembly14B is adsorbing CO2and first sorbent assembly14A is desorbing CO2. Here, second sorbent assembly14B functions as the evaporator and first sorbent assembly14A functions as the condenser. Reversing valve34can adjust the flow of refrigerant within heat exchange system28so that heat pump30only pumps refrigerant in a single direction.

FIG. 5shows an embodiment wherein the first sorbent assembly14A and the second sorbent assembly14B are thermally linked passively by interleaving the two sorbent assemblies.

A wide range of temperatures are suitable for first sorbent assembly14A and second sorbent assembly14B during the CO2removal process. CO2removal system10generally operates most effectively at temperatures between about 15° C. and about 80° C. In an exemplary embodiment, the desorbing bed is heated to a temperature between about 35° C. and about 80° C. while the adsorbing bed is cooled to a temperature between about 15° C. and about 25° C. In one exemplary embodiment, the desorbing bed is heated to a temperature between about 55° C. and about 80° C. Due to the energy required to actively heat and cool first sorbent assembly14A and second sorbent assembly14B, keeping the temperature difference between the desorbing bed and the adsorbing bed small is desirable. Determination of ideal temperature differences depends upon the particular application CO2removal system10is designed for in addition to CO2removal rate requirements. In exemplary embodiments, the temperature difference between the desorbing bed and the adsorbing bed is between about 10° C. and about 65° C. In one exemplary embodiment, the temperature difference between the desorbing bed and the adsorbing bed is between about 10° C. and about 35° C. The low temperature difference between the desorbing and adsorbing beds generally allows CO2removal system10to operate with much greater efficiency than liquid amine and molecular sieve systems.

A wide range of pressures can be drawn on the desorbing bed. CO2removal system10generally operates most effectively where low ambient pressure generates a low pressure on the desorbing bed between 3.5 kPa (0.5 psi) and 100 kPa (14.5 psi). In an exemplary embodiment, a low pressure of between 20 kPa (3.0 psi) and 55 kPa (8.0 psi) is drawn on the desorbing bed.

CO2removal system10can employ a wide range of cycle times between bed transitions from CO2adsorption to CO2desorption and vice versa. As is the case with the temperature difference between the adsorbing bed and the desorbing bed, determination of ideal cycle times depends upon the particular application CO2removal system10is designed for in addition to CO2removal rate requirements. In exemplary embodiments, the adsorbing and desorbing beds cycle at an interval no greater than about 30 minutes. In one exemplary embodiment, the adsorbing and desorbing beds cycle at an interval no greater than about 20 minutes.