US20080112869A1

US20080112869A1 - Direct contact liquid air contaminant control system

Info

Publication number: US20080112869A1
Application number: US11/741,686
Authority: US
Inventors: Allen K. MacKnight
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2003-06-30
Filing date: 2007-04-27
Publication date: 2008-05-15
Also published as: US20040265199A1; WO2005005026A1; US7252703B2

Abstract

An integrated environmental control system for cabin air of an aircraft or spacecraft. Humidity and temperature of cabin air are controlled with a direct contact liquid air contaminant control system that revitalizes cabin air by removal of carbon dioxide and other trace gas contaminants through use of a direct contact air, liquid scrubber element and stripper element. The scrubber element has two rotor elements rotatably mounted in a housing first for centrifugal separation of an air flow and liquid absorbent mixture which liquid absorbent has absorbed carbon dioxide and trace gas contaminants. Then second for centrifugal separation of an air flow and acid water wash mixture which acid water wash has liquid absorbent and other contaminants. The processed air is then passed through a charcoal bed filter for further removal of contaminants. A rotary contact processor may also be used to reprocess contaminated liquid absorbent for reuse.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 10/611,490 filed Jun. 30, 2003.

BACKGROUND OF THE INVENTION

The present invention generally relates to an air environment control system (ECS) that revitalizes air and more specifically to the apparatus and methods that control humidity and temperature of cabin air of aircraft and spacecraft while removing carbon dioxide and other trace gas contaminates.
Liquid amine (methanol amine water solutions) based carbon dioxide and trace gas contaminant removal apparatus and processes for regeneration of air have been used in nuclear submarines for over forty years. Such systems are used to remove carbon dioxide for the breathing air and depend on gravity to process the liquid carbon amine or other liquids and air mixture.
An example of a combustion gas carbon dioxide process and apparatus is disclosed in U.S. Pat. No. 5,318,758. This type of gas process involves towers and other structures that depend on gravity, blowers and pumps to process the gas. Such systems are not simple or compact and do not work in reduced gravity environments such as on aircraft and spacecraft.
The use of alternative absorbent solutions has been disclosed in U.S. Pat. Nos. 4,285,918 and 3,632,519. These patents teach that water solutions of 3-amino-1,2-propanediol and ω-aminomethyl alkyl sulfone have improved performance for carbon dioxide removal in closed environments such as submarines. They address only the removal of carbon dioxide whereas there are a number of other contaminants that must be removed in these closed environments.
Centrifugal liquid and gas processors have been explored as described in the article “The Centrifugal Mass Exchange Apparatus in Air-Conditioning System of Isolated, Inhabited Object and Its Work Control”, by P. A. Barabash, et al, in Proceedings of the 4^thEuropean Symposium on Space Environmental and Control Systems, Oct. 21-24, 1991. The article postulates use of a centrifugal apparatus to work with an air-conditioning system in a closed habitat system such as an orbital space station. A single stage system is proposed that keeps air temperature and humidity parameters within limits. The single stage rotor does not anticipate a more staged air process system using contaminant absorbent fluids and acid wash to provide carbon dioxide and other contaminant removal from a cabin air environment. Indeed, present spacecraft and space stations typically employ apparatus dedicated exclusively to contaminant extraction from cabin air. Another apparatus is used for maintaining humidity and temperature of the cabin air. Each of these independent systems adds undesirable weight and consumes valuable space and power in a spacecraft.
As can be seen, there is a need for a simple, compact ECS in which humidity and temperature control are integrated with air regeneration functions for use in aircraft and spacecraft.

SUMMARY OF THE INVENTION

An improved environmental control system and method according to the present invention may comprise a carbon dioxide scrubber, a liquid absorbent stripper, a charcoal filter, and supporting containers, pumps and other elements.
In one aspect of the present invention, method for providing environmental control for cabin air of a vehicle comprises the steps of introducing a portion of the cabin air as air flow into a carbon dioxide scrubber and spraying a liquid mist into the air flow thereby modifying humidity, temperature and carbon dioxide concentration of the cabin air.
In another aspect of the present invention, an environmental control apparatus for cabin air of a vehicle comprises a contaminant scrubber wherein a contamination-control liquid is introduced as a mist into an air flow of a portion of the cabin air through the contaminant scrubber. The contamination-control liquid has a temperature lower than a temperature of the cabin air. Temperature of the cabin air is reduced and humidity of the cabin air is modified.
In another aspect of the present invention, an apparatus for controlling humidity and temperature of cabin air in a vehicle comprises a rotary contact processor for direct contact liquid absorbent and gas contaminant processing.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional block diagram of the invention;

FIG. 2 illustrates a functional block diagram of the major elements according to an embodiment of the invention;

FIG. 3 illustrates a functional cross-sectional view of a rotary liquid contact processor apparatus according to an embodiment of the invention; and

FIG. 4 is a flow chart of a method for providing environmental control for cabin air of a vehicle according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Referring to FIGS. 1 and 2, an environmental control system (ECS) 10 has an absorber element 20 and a stripper element 80 in fluid communication and in control/data communication. Support elements such as a control and data processor and an electric power source, not shown, are provided by existing platform equipment as is found on spacecraft and aircraft. The ECS 10 may be connected to the cabin air system of a vehicle to process the return air from use in a vehicle human environment, to decontaminate, cool and dehumidify the air, and to return cold clean air for use in a continuing cycle.
The current system absorber element 20 uses a rotary process scrubber 30 and charcoal bed filter 26 to remove contaminants. Both liquid absorbent (such as an amine) and acid water are used in the scrubber 30 for direct contact liquid/vapor phase separation of contaminants. The stripper 80 may also use a rotary processor for liquid/vapor phase separation of liquid absorbent and carbon dioxide. The use of rotary processors allows operation in variable gravity environments such as experienced in aircraft and spacecraft and provides compact, light weight and reliable apparatus as compared to current art bulky, inefficient apparatus. In addition, the use of direct contact liquid/vapor processing allows more efficient heat transfer as compared to current technology, which relies on use of condensing heat exchangers, slurpers, and rotating centrifugal phase separators. A cold contamination-control liquid such as an acid water spray may be used in the air contaminant control system to remove absorbent vapor from the air and for temperature and humidity control. As cabin air is introduced into the ECS 10, and passes through the cold spray the air temperature may be reduced. The air may become saturated as it is cooled toward the temperature of the acid water and some of the moisture conveyed in the air may condense and mix with the acid water. Thus moisture content of the air may diminish. If the air does not become saturated with water as it is cooled to the temperature of the acid water spray, water may evaporate from the cold acid water spray and add the water content of the air. Additionally, cabin air may be cooled as it passes through the cold water spray. These humidity adjustment and cooling functions may be an integral part of the direct liquid contact system and not a separate system. For the present inventive ECS 10 control of humidity may be the design limiting function of the system. The ECS 10 may be sized to process enough air to control the humidity. By doing so, the other functions, such as temperature control and contamination control, may be easily satisfied.
Cabin air may be drawn through the scrubber 30 by a fan that may be used to aid vehicle cabin ventilation air flow. In the scrubber 30 carbon dioxide and other contaminates may be removed from the air through direct contact with a cool liquid absorbent. The liquid absorbent removes carbon dioxide to form a carbonate complex. The term liquid absorbent as commonly understood in the art relates to carbon dioxide liquid absorbents, as for example, water solutions of methanol amine, ethanol amine, isopropyl amine, cesium carbonate, magnesium carbonate and similar solutions. The choice of liquid absorbent may be based on system operational factors such as carbon dioxide pressure, temperature, humidity, regeneration temperature and energy sources.
The amines have a low vapor pressure at absorption conditions; however, without treatment some amine vapor may remain in the processed air to be introduced into the vehicle cabin as a contaminant. To inhibit this event an acid water scrubber 60 may be included in the scrubber 30 to maintain amine pressure at acceptable levels, for example, about 1 ppm. The same process may absorb other basic trace gases such as ammonia. A mild acid, such as, citric, acetic, or hypo-phosphoric acid, may reduce the amine vapor pressure to the desired levels. Additionally, the acid water may serve as an anti-microbial with the potential for reducing bacterial contamination or spread of pathogens. The acid water solution may become very diluted, but the pH should be maintained relatively low, i.e., less than about 2 value. Additional acid may be added to the acid water scrubber 60 to maintain a low pH. For a fully closed system acetic acid, vinegar, may be produced onboard a vehicle using well known biological processes.
The carbon dioxide scrubber 40 may act to absorb acidic trace gases. The combination of the carbon dioxide scrubber 40 and acid water scrubber 60 results in substantial removal of water soluble trace gases. There may also be hydrocarbon trace gasses in the air that may not be absorbed in the scrubber 30. These gases may be removed by a charcoal bed filter 26 downstream of the scrubber 30. The charcoal bed filter 26 may be a single use or regenerable device depending on the mission requirements. Generally large portions of the trace contaminants are removed in the scrubber 30 thereby reducing the contaminant load to be processed by the charcoal bed filter 26. Such action may allow for a relatively small charcoal bed filter 26.
The acid water wash sprayed into the acid water scrubber 60 may act to control temperature and humidity by the use of a cold acid water wash in the temperature range of about 40 to 60° F. The cooling occurs due to direct thermal contact when cool acid water is sprayed into the air flow. The large surface area of the spray that may be effective for mass transfer may also be effective for heat transfer. Water vapor in the air may condense in the cold acid water spray and then be separated by the centrifugal action of the acid water scrubber 60 to adjust the humidity.
The resultant dilute acid water may then be accumulated in acid water tank 62. As part of the process water may be removed from the acid water tank and acid may be added to maintain proper pH for reuse in the acid water scrubber 60. The removed dilute acid water may have salts and dissolved trace gasses. It may be processed in a water recovery system in the host vehicle for reuse in the water cycle. Processed acid water may be cooled at acid water cooler 64 and introduced to the acid water scrubber 60.
The carbon dioxide rich liquid absorbent solution may also be processed for reuse in the carbon dioxide scrubber 40. The liquid absorbent solution may be heated and processed through the stripper element 80 to separate carbon dioxide from the liquid absorbent solution. The carbonate complexes formed in the scrubber during the absorption of carbon dioxide are thermally unstable, for example, methanol amine carbonate decomposes at 270° F. Approximately five percent of the flow of liquid absorbent used to treat the air in the scrubber 30 may be heated in liquid absorbent heater 44 and introduced into the stripper 80. The stripper 80 may be a rotary contact processor similar to the rotary contact processor 32.
The stripper 80 permits evolution of the carbon dioxide and the separation of the liquid phase. The method for the process using a rotary contact processor comprises the steps of heating the carbonate rich liquid absorbent to its decomposition temperature in a flow through liquid absorbent heater, communicating the heated liquid absorbent into a first stage scrubber and spraying the heated liquid absorbent onto a rotating heat and mass transfer surface thereby separating the liquid absorbent from the evolved carbon dioxide gas through centrifugal action, accumulating the carbonate lean liquid absorbent and removing it from the transfer surface using pitot pumps, and passing the carbon dioxide gas through a plurality of mist separators for removal of droplets prior to being output.
The carbon dioxide gas may be further processed by introduction into a second stage scrubber to remove water and absorbent vapors. The carbon dioxide gas may be washed by a spray of a cold liquid absorbent that may then be sprayed onto a rotating mass and heat transfer surface, the liquid absorbent separation from the carbon dioxide may be caused by centrifugal action, the liquid absorbent may then be accumulated and then removed by pitot pumps, and the carbon dioxide may be passed through a plurality of mist separators for removal of droplets prior to being output.
In each case of the liquid absorbent and the carbon dioxide processing, more process stages may be used to obtain desired absorbent regeneration and product carbon dioxide purity.
The liquid absorbent may be first processed by a stripper element 80 to remove carbonate complexes present in the solution. The heated liquid absorbent may be sprayed into the stripper element 80, which may be a rotary contact processor wherein the small droplets formed provide a large surface area permitting efficient carbon dioxide transfer. The pressure of the carbon dioxide may be controlled as for example by using a back-pressure regulating valve. Depending on the liquid absorbent used, the pressure can be set in the range of 40 to 70 psi. The rotary stripper element 80 centrifugal action functions to separate the liquid and gas phases similar to the scrubber 30.
The resultant carbon dioxide vapor may be hot and contain water vapor and absorbent vapor. The vapors are removed in a stripper element 80 by cooling the carbon dioxide and condensing the liquid. The cool liquid absorbent solution may be returned to the liquid absorbent tank 42 and the carbon dioxide may be compressed, dried and stored for further use or disposal.
Referring to FIGS. 2 and 3, the scrubber 30 rotary contact processor 32 functions to provide direct liquid contact between air and two separate liquids, to separate the liquids and air, and to pump the liquids. The rotary contact processor 32 may be a dual rotor ambient pressure air scrubber that washes the air in the carbon dioxide scrubber rotor 104 with a carbon dioxide absorbent and washes the air with mild acid in the liquid absorbent scrubber rotor 107 as air flows through the device. It is supplied with a liquid absorbent solution, cooled acid wash water, atmospheric air, and electrical power. Electrical power is used for a drive motor, not shown. The advantage of this device is that it operates at atmospheric pressure, it is gravity independent and it provides a simple, rugged device.
The contact processor 32 consists of a rotor assembly comprised of carbon dioxide scrubber rotor 104 and liquid absorbent scrubber rotor 107 mounted in a housing 116 on bearings 120. Scrubbing and separation occur within the rotor. Liquid absorbent solution may be circulated through connections 102, 118 in the stationary hub 122 at one end and cooled acid wash water may be circulated through connections 105, 114 in a stationary baffle 115 located in the middle of the housing.
The two rotors 104, 107 are mounted on shaft 110 and are separated by stationary baffle 115. The first rotor 104 is in the carbon dioxide scrubber chamber 124 and may be used to remove carbon dioxide from the air stream. The second rotor 107 is in the acid wash scrubber chamber 126 and may be used to wash the air and to condense water from the air stream. Mist separators 111 and baffles 115 are used to isolate the two fluids. The air may be moved through the rotary contact processor 32 by a built-in fan 112. An external blower, not shown, may also be used.
The rotary contact processor 32 operates in the following manner: atmospheric air flows in the inlet 101 past the carbon dioxide scrubber rotor 104, through air passage tubes 109 and mist separators 111, past the liquid absorbent scrubber rotor 107, through second air passage tubes 109 and second mist separators 111, and through the fan 112, to the air exhaust 108. The fan 112 moves the air through the rotary contact processor 32 and the drive motor, not shown, keeps the rotors and fan moving at constant speed.
Carbon dioxide is removed from the air stream in the carbon dioxide scrubber chamber 124. Liquid absorbent enters at connection 118 and is sprayed into the air stream near the axis of rotation 128. It forms droplets and a thin layer on the carbon dioxide scrubber rotor 104 heat and mass transfer surface 117. The liquid flows by centrifugal action to the outside of the carbon dioxide scrubber chamber 124. This direct contact promotes the rapid absorption of carbon dioxide by the liquid absorbent. A mist separator 111 keeps liquid absorbent from entering the next chamber. The liquid absorbent forms a layer on the periphery of the chamber 124 and is pumped by the liquid absorbent pitot pump 103 through the liquid absorbent outlet 102 to an external liquid absorbent tank 42. The return liquid absorbent enters through liquid absorbent inlet 118.
The air is washed, cooled and humidity condensed in the acid wash scrubber chamber 126. Cold acid wash enters through the acid water wash inlet 114 and is sprayed into the air stream near the axis of rotation 128. It forms droplets and a thin layer on the liquid absorbent scrubber rotor 107 transfer surface 117. The liquid flows by centrifugal action to the outside of the acid wash scrubber chamber 126 and a portion of the humidity in the air stream condenses. The air stream is cooled below the dew point by the cold acid water wash. A mist separator 111 keeps water droplets from entering the exhaust stream at air exhaust 108. The condensate liquid forms a layer on the periphery of the chamber 126 and is pumped by the acid water pitot pump 106 through the acid water wash outlet 105 to the external circuit. The return cold acid water wash enters through the acid water wash inlet 114.
While one embodiment is described in terms of a two stage scrubber 30 having a carbon dioxide scrubber 40 and a liquid absorbent scrubber 60 having a common rotor shaft and housing, these two elements may also be contained in separate housings with fluid communication therebetween. In such an instance, the baffle 115 would be separated in structure such that the carbon dioxide scrubber 40 would have an outlet enclosed side and the liquid absorbent scrubber 60 would have an inlet enclosed side. Also, more than two stages may be used depending on the purity of the output desired by the user.
An inventive method 200 is illustrated in a flow chart of FIG. 4. In a step 202, a flow of cabin air is introduced into a carbon dioxide scrubber. In a step 204, a liquid mist is sprayed into the introduced air in order to modify its temperature, humidity and carbon dioxide concentration.
It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. A method for providing environmental control for cabin air of a vehicle comprising the steps of:

introducing a portion of the cabin air as air flow into a carbon dioxide scrubber; and

spraying a liquid mist into the air flow thereby modifying humidity, temperature and carbon dioxide concentration of the cabin air.

2. The method of claim 1 wherein the liquid mist is an acid wash.

3. The method of claim 1 comprising the further steps of:

rotating a carbon dioxide scrubber rotor to separate liquid absorbent containing absorbed carbon dioxide and trace contaminants from the air flow;

accumulating the liquid absorbent on a first heat and mass transfer surface for extraction from the carbon dioxide scrubber rotor;

passing the air flow downstream of the carbon dioxide scrubber rotor through a plurality of first air passages and a plurality of first mist separators to a liquid absorbent scrubber rotor.

4. The method of claim 3 comprising the further steps of;

rotating the liquid absorbent scrubber rotor to separate the liquid absorbent containing carbon dioxide and trace contaminants from the air flow;

accumulating the acid wash on a second heat and mass transfer surface for extraction from the liquid absorbent scrubber rotor; and

passing air flow downstream of the liquid absorbent scrubber rotor through a fan to an air exhaust.

5. The method of claim 3 wherein extracted liquid absorbent is processed in a stripper element for reuse.

6. The method of claim 3 wherein contaminated liquid absorbents are reconditioned by performing the steps of:

heating a liquid absorbent containing a carbonate to a decomposition temperature in a liquid absorbent heater whereby carbon dioxide is separated from the liquid absorbent.

7. The method of claim 6 wherein the liquid absorbent is processed through a subsequent scrubber.

8. The method of claim 6 further comprising the steps of:

communicating the carbon dioxide which is separated from the liquid absorbent into a second scrubber;

washing the carbon dioxide using a spray of cold liquid absorbent;

accumulating the cold liquid absorbent for extraction from the second scrubber; and

passing the carbon dioxide through a plurality of mist separators for output from the second scrubber.

9. An environmental control apparatus for cabin air of a vehicle comprising:

a contaminant scrubber wherein a contamination-control liquid is introduced as a mist into an air flow of a portion of the cabin air through the contaminant scrubber;

the contamination-control liquid having a temperature lower than a temperature of the cabin air; and

wherein temperature of the cabin air is reduced and humidity of the cabin air is modified.

10. The environmental control apparatus as in claim 9 wherein the contaminant scrubber is comprised of at least one carbon dioxide scrubber in fluid communication with a liquid absorbent scrubber.

11. The environmental control apparatus as in claim 10 wherein the at least one carbon dioxide scrubber comprises a rotary contact processor.

12. The environmental control apparatus as in claim 11 further comprising a stripper element which comprises a rotary contact processor.

13. The environmental control apparatus as in claim 9 wherein:

a carbon dioxide scrubber rotor is connected to a liquid absorbent scrubber rotor by a rotor shaft;

the carbon dioxide scrubber rotor is in communication with an air inlet and a liquid absorbent inlet wherein a liquid absorbent is introduced as a mist into an air flow through the air inlet, the air flow introduced into a carbon dioxide scrubber chamber having a first heat and mass transfer surface therein of the carbon dioxide scrubber rotor;

the air flow passes through the carbon dioxide scrubber rotor through a plurality of first air passage tubes and a plurality of first mist separators to be introduced downstream into an acid wash scrubber chamber having a second heat and mass transfer surface therein;

the acid wash scrubber is separated from the carbon dioxide scrubber rotor with a baffle;

the baffle has an acid water wash inlet for introduction of a liquid acid water wash as a mist in the air flow; and

the air flow passes through the liquid absorbent scrubber rotor through a plurality of second air passage tubes and a plurality of second mist separators to a fan causing the air flow to exit through an air exhaust.

14. Apparatus for controlling humidity and temperature of cabin air in a vehicle comprising:

a rotary contact processor for direct contact liquid absorbent and gas contaminant processing.

15. The apparatus of claim 14 wherein the rotary contact processor comprises:

a first scrubber rotor in communication with a gas inlet and a liquid absorbent inlet, wherein a liquid absorbent is introduced as a mist into a gas flow through the gas inlet.

16. The apparatus of claim 15 wherein the liquid absorbent inlet and a liquid absorbent outlet are in communication with a liquid absorbent tank, a liquid absorbent heater and a stripper element.

17. The apparatus of claim 16 wherein an acid water wash inlet and an acid water wash outlet are in communication with an acid water tank and an acid water cooler.

18. The apparatus of claim 14 wherein:

a first scrubber rotor is in serial communication with a second scrubber rotor each assembled on a rotor shaft rotatably mounted on a plurality of bearings in a housing; and

gas flow passes through the first scrubber rotor through a plurality of first gas passage tubes and a plurality of first mist separators to be introduced downstream into a second scrubber chamber in fluid communication therewith and having a second heat and mass transfer surface therein.

19. The apparatus of claim 18 wherein:

the second scrubber chamber has a liquid absorbent wash inlet for introduction of a liquid absorbent wash as a mist in the gas flow; and

the gas flow passes through the liquid absorbent scrubber rotor through a plurality of second gas passage tubes and a plurality of second mist

separators to a fan causing the gas flow to exit the rotary contact processor through a gas exhaust.

20. The apparatus of claim 19 further comprising a first pitot pump in a first scrubber chamber for liquid absorbent wash circulation and exit through a liquid absorbent outlet.