US 20090232861 A1
The present disclosure provides a method and apparatus for extracting carbon dioxide (CO2) from a fluid stream and for delivering that extracted CO2 to controlled environments for utilization by a secondary process. Various extraction and delivery methods are disclosed specific to certain secondary uses, included the attraction of CO2-sensitive insects, the ripening and preservation of produce, and the neutralization of brine.
1. A system for removing carbon dioxide from a fluid, comprising passing a stream of the fluid in contact with a sorbent to absorb and concentrate carbon dioxide from the fluid stream; releasing the carbon dioxide from the sorbent; and delivering the carbon dioxide for use in a secondary process.
2. The system of
3. The system of
4. The system of
5. The system of
6. The system of
7. The method of
8. The method of
9. A method for removing carbon dioxide from a gas, comprising:
bringing said gas in contact with a resin contained in a plurality of chambers, wherein a plurality of chambers are connected in series;
wetting said resin with water, wherein the water enters a first chamber and exits through a last chamber;
collecting water vapor and carbon dioxide from said resin;
separating said carbon dioxide from said water vapor; and
delivering the carbon dioxide for use in a secondary process.
10. The method of
11. The method of
12. The method as of
13. A system for utilization of carbon dioxide that is substantially carbon neutral, comprising a carbon dioxide capture device that collects carbon dioxide from a fluid stream produced by a process that utilizes carbon dioxide, wherein the carbon dioxide capture device delivers the captured carbon dioxide for utilization by the process.
14. The system of
15. A method of creating tradable carbon credits which comprises extracting CO2 from ambient air at a location adjacent or remote from where the CO2 is generated, using sorbent, selling, trading or transferring the resulting CO2 credits to a third party, and using the extracted CO2 in a secondary process.
16. A method for luring CO2 sensitive insects toward a specific location where a moisture sensitive CO2 sorbent that is partially or fully loaded with CO2 is exposed to moisture usually in excess of that present in the ambient air at the location.
17. The method of
18. The method of
19. The method of
20. The method of
21. The method of
22. An apparatus for extracting a gaseous contaminant from a gas stream using a sorbent employing a humidity swing and for distilling a brine, comprising:
a sorbent for capturing the contaminant;
a capture unit, wherein the sorbent is exposed to the gas stream and becomes substantially saturated with the contaminant;
an evaporation unit, wherein a brine is evaporated forming a concentrated brine and water vapor, and wherein the sorbent is brought in contact with the water vapor causing the sorbent to become substantially depleted of the contaminant according to a humidity swing; and
a condensation unit, wherein the water vapor is separated from the contaminant.
23. The apparatus of
24. The apparatus of
25. An apparatus for stabilizing the level of carbon dioxide in an enclosed environment, comprising:
a filter unit attached to said enclosed environment, containing a sorbent material for carbon dioxide capture; and
a regenerating system for regenerating the sorbent material at least in part.
26. The apparatus of
27. The apparatus of
28. The apparatus of
29. A method for stabilizing the level of carbon dioxide in an enclosed environment using the apparatus of
30. The method of
31. The method of
32. The method of
33. A method for extracting carbon dioxide from a gas comprising bringing a stream of the gas in contact with a sorbent, releasing the carbon dioxide from the sorbent to create a carbon dioxide-enriched gas mixture, and bringing the enriched gas mixture in contact with an aqueous solution, wherein the aqueous solution absorbs carbon dioxide from the gas mixture.
34. The method of
35. The method of
36. The method of
37. The method of
38. An apparatus, constructed to perform the method of
39. The method of
40. The method of
41. The method of
42. The method of
43. A method for adding calcium bicarbonate to seawater without changing the alkalinity of the water, comprising using a sorbent that employs a humidity swing to extract carbon dioxide from the air resulting in a gas mixture, precipitating carbonic acid from the gas mixture to dissolve an amount of limestone, forming calcium bicarbonate, and depositing the calcium bicarbonate in the seawater with any remaining carbonic acid.
44. The method of
45. A method of stabilizing sorbent CO2 levels in storage containers of fresh produce, comprising recovering excess CO2 from the storage containers using a sorbent for CO2.
46. A method for removing a gaseous contaminant from a gas stream, comprising
placing said gas stream in contact with a sorbent, wherein the contaminant from said gas stream becomes loaded on said sorbent;
releasing the gas from said substrate by use of a humidity swing; wherein the humidity swing is performed by evaporating a brine to form concentrated brine and water vapor, and bringing the water vapor in contact with the loaded sorbent;
and condensing the water vapor to separate the water vapor from the contaminant.
47. The method of
48. The method of
49. The method of
50. The method of
51. The method of
52. The apparatus of
53. The apparatus of
54. The apparatus of
55. The apparatus of
This application claims priority from U.S. provisional application Ser. No. 61/029,831, filed Feb. 19, 2008, Ser. No. 61/074,972 filed Jun. 23, 2008 and Ser. No. 61/079,776 filed Jul. 10, 2008.
The present invention relates to a method and apparatus for the removal of selected gases from an environment and the disposal of the selected gases in another environment.
The present invention in one aspect relates to removal of selected gases from the atmosphere. The invention has particular utility in connection with the extraction of carbon dioxide (CO2) from the atmosphere and subsequent sequestration of the extracted CO2 or conversion of the extracted CO2 to useful or benign products and will be described in connection with such utilities, although other utilities are contemplated, including the extraction, sequestration or conversion of other gases from the atmosphere including NOx and SO2.
There is compelling evidence of a strong correlation between the sharply increasing levels of atmospheric CO2 with a commensurate increase in global surface temperatures. This effect is commonly known as Global Warming. Of the various sources of the CO2 emissions, there are a vast number of small, widely distributed emitters that are impractical to mitigate at the source. Additionally, large-scale emitters such as hydrocarbon-fueled power plants are not fully protected from exhausting CO2 into the atmosphere. Combined, these major sources, as well as others, have lead to the creation of a sharply increasing rate of atmospheric CO2 concentration. Until all emitters are corrected at their source, other technologies are required to capture the increasing, albeit relatively low, background levels of atmospheric CO2. Efforts are underway to augment existing emissions reducing technologies as well as the development of new and novel techniques for the direct capture of ambient CO2. These efforts require methodologies to manage the resulting concentrated waste streams of CO2 in such a manner as to prevent its reintroduction to the atmosphere.
The production of CO2 occurs in a variety of industrial applications such as the generation of electricity from coal at power plants and in the use of hydrocarbons that are typically the main components of fuels that are combusted in combustion devices, such as engines. Exhaust gas discharged from such combustion devices contains CO2 gas, which at present is simply released to the atmosphere. However, as greenhouse gas concerns mount, CO2 emissions from all sources will have to be curtailed. For mobile sources such as motor vehicles and airplanes the best option is likely to be the collection of CO2 directly from the air rather than from the mobile device in the motor vehicle or airplane. The advantage of removing CO2 from air is that it eliminates the need for storing CO2 on the mobile device.
Extracting carbon dioxide (CO2) from ambient air would make it possible to use carbon-based fuels and deal with the associated greenhouse gas emissions after the fact. Since CO2 is neither poisonous nor harmful in parts per million quantities, but creates environmental problems simply by accumulating in the atmosphere, it is possible to remove CO2 from air in order to compensate for equally sized emissions elsewhere and at different times.
The present disclosure provides a system, i.e. a method and apparatus for extracting a contaminant from a flow stream, such as ambient air or an exhaust stack, and for delivering the extracted contaminant for use in a secondary process. The present disclosure is described primarily in regards to the removal and sequestration of CO2, though the apparatus and method of the present disclosure may be used with various other contaminants.
In accordance with one aspect of the present disclosure, CO2 is extracted from air and the extracted CO2 is delivered to a secondary process where the CO2 is transformed into an useful or benign product. The CO2 is delivered in whatever form is required for the secondary process, which may be gaseous, solid, or liquid CO2. The secondary process may be any manufacturing, food processing, or other industrial process that uses CO2, such as, machining coolant and lubricant, grit blasting, e.g. for smoothing and paint removal, cryogenic cleaning, quick freeze processes, production and use of R744 refrigerant, CO2 based dry cleaning solvents, perishable shipping container pre-cooling, perishable shipping inert environment maintenance, beverage carbonation, fire suppression, plant fertilization, horticulture, agriculture, silvaculture, aquatic algae production, enhanced oil recovery, water softening, Solvay process, propellant, pressurizing gas, e.g. for aerosol cans, inflation gas, e.g. for life rafts, supercritical CO2 extraction, semi conductor manufacturing, organic solvent, perfume aromatics, decaffeinating beverages, e.g. coffee and tea, supramics, pharmaceutical manufacturing, chemical production such as for urea, methanol, inorganic carbonates, organic carbonates, polyurethanes, paint pigments, foaming agents, carbon based fuels, i.e. synthetic fuels, fumigation, e.g. of grain elevators, neutralization of alkaline water, gas shield, e.g. for welding, which are given as exemplary.
A further aspect of the present disclosure provides a method and apparatus for luring CO2 sensitive insects toward a specific location where a moisture sensitive CO2 sorbent that is partially or fully loaded with CO2 is exposed to moisture usually in excess of that present in the ambient air at the location. The sorbent may be held in place by an open basket that is protected with a roof and a floor against accidental wetting by rain.
Another aspect of the present disclosure is directed to the control of the concentration of specific gases in a closed environment. While the method and apparatus of this aspect of the present disclosure will be described with specific reference to the control of carbon dioxide in the storage, for example, of bananas, but other fruits and vegetables are also contemplated by this disclosure. The present invention provides a atmosphere-controlled environment for storing produce, wherein other parameters as well as carbon dioxide such as humidity may also be controlled, and a plurality of filters attached to the temperature controlled environment.
Yet another aspect of the present disclosure provides a system, i.e. a method and apparatus for extracting carbon dioxide (CO2) from ambient air or an exhaust stack and for delivery, sequestration or conversion of the extracted CO2 into useful or benign products.
The extraction of the contaminant from a gas stream in any of the aspects of the present disclosure discussed above may be accomplished by using one of a number of methods such as disclosed in the several patent applications listed in Appendix A, the contents of which are incorporated herein by reference, as well as other extraction processes described in the literature and patent art, including processes which capture CO2 at the stack.
Further features and advantages of the present invention will be seen from the following detailed description, taken in conjunction with the accompanying drawings, wherein
Various methods and apparatus have been developed for removing CO2 from air. For example, we have recently disclosed methods for efficiently extracting carbon dioxide (CO2) from ambient air using sorbents that either physically or chemically bind and remove CO2 from the air. A class of practical CO2 capture sorbents include strongly alkaline hydroxide solutions such as, for example, sodium or potassium hydroxide, or a carbonate solution such as, for example, sodium or potassium carbonate brine. See for example published PCT Application PCT/US05/29979 and PCT/US06/029238. See also published PCT Application PCT/US07/802,229 which describes the use of solid sorbents such as ion exchange resins for removing CO2 from the air.
In broad concept, the present invention in one aspect extracts carbon dioxide from ambient air using a conventional CO2 extraction method or one of the improved CO2 extraction methods disclosed in our aforesaid PCT Applications, or disclosed herein, and releases at least a portion of the extracted CO2 to a secondary process employing CO2. The CO2 also may be extracted from an exhaust at the exhaust stack.
In our co-pending U.S. application Ser. No. 11/866,326, assigned to a common assignee and incorporated by reference herein, there are provided methods and apparati for extracting carbon dioxide (CO2) from ambient air and for delivering that extracted CO2 to controlled environments. Specifically, the aforementioned applications disclose the delivery of CO2 collected from ambient air or from exhaust gases for use in greenhouses or in algae cultures. The CO2 is extracted from the gas stream by an ion exchange material that when exposed to dry air absorbs CO2 that it will release at a higher partial pressure when exposed to moisture. In this process we can achieve concentration enhancements by factors of from 1 to 100.
In a first exemplary embodiment shown in
The secondary process preferably is connected directly to the CO2 capture apparatus to minimize transportation costs and potential losses associated therewith. Depending on the intended secondary process, the CO2 may be transformed into a solid or liquid state. The CO2 may further be conditioned to a specified pressure and/or temperature.
The secondary process may be any manufacturing, food processing, or other industrial process that uses CO2, such as for example, machining coolant and lubricant, grit blasting, e.g. for smoothing and paint removal, cryogenic cleaning, quick freeze processes, R744 refrigerant, dry cleaning solvent, perishable shipping container pre-cooling, perishable shipping inert environment maintenance, beverage carbonation, fire suppression, plant fertilization, horticulture, agriculture, silvaculture, aquatic algae production, enhanced oil recovery, water softening, Solvay process, propellant, pressurizing gas, e.g. for aerosol cans, inflation gas, e.g. for life rafts, supercritical CO2 extraction, semi conductor manufacturing, organic solvent, perfume aromatics, decaffeinating beverages, e.g. coffee and tea, supramics, pharmaceutical manufacturing, chemical production such as for urea, methanol, inorganic carbonates, organic carbonates, polyurethanes, paint pigments, foaming agents, carbon based fuels, i.e. synthetic fuels, fumigation, e.g. of grain elevators, neutralization of alkaline water, gas shield, e.g. for welding, Many other processes utilizing CO2 are also possible and are deemed to be within the scope of this disclosure.
Our aforementioned commonly owned applications disclose several potential primary sorbents that may be used to capture and remove CO2 from the air. In one approach to CO2 capture, the sorbent is a strong base ion exchange resin that has a strong humidity function, that is to say, an ion exchange resin having the ability to take up CO2 as humidity is decreased, and give up CO2 as humidity is increased. Such resins may be regenerated by contact with water, humid air, or pulses of steam. In this approach the CO2 is returned to a gaseous phase in a more concentrated form, and no liquid media are brought in contact with the collector material.
Other primary sorbents may be regenerated by a secondary sorbent such as weak liquid amine. This amine must be capable of pulling the CO2 content of gas mixture down so that the CO2 partial pressure drops to about e.g., 20 to 30 mbar. Thus it can be far weaker sorbent than the primary sorbent and this allows the use of very weak amines.
Still other sorbent materials may be regenerated by the application of heat (utilizing a thermal swing), or vacuum pressure.
In another example, CO2 is captured and removed from air on a solid phase ion-exchange resin which is placed in a plurality of chambers connected in series. See
The following conceptually describes a CO2 washing system that is based on immersing the resin into liquid water and moving the water over the resin into a separate chamber where the CO2 is allowed to be released from the water.
A simple implementation is a set of chamber organized (at least logically into a circle). All but one chamber are filled with water. One chamber (n) is empty and filled with air. Initially chamber n is filled with air, and chamber n+1 is filled with water. Now water is pumped against a minimal pressure drop from chamber k to k+1. This will work for all values of k, except that k=n−1, n, n+1 are special cases which need further consideration. The water in chamber n−1 flows into chamber n, thereby pushing the air inside this chamber out. It is either released to the outside or channeled into chamber n+1 whose water content is moving into chamber n+1. The water pouring into chamber n will inundate the resin that has been replaced into this chamber. The water in chamber n+1 flows into chamber n+2, but rather than obtaining water from chamber n, it pulls in air, which may be the air that resided in chamber n, or fresh air taken from the outside.
At this point we renumber all chambers by replacing n with n−1. Thus it is again chamber n that is filled with air. We now open chamber n, and remove the regenerated resin and replace it with fully loaded resin. Before we load up chamber n, we pump the water from station n−1 to a degassing station and from there to station n+1. This water flow bypasses the currently open chamber n.
This procedure could be used with pure water, in which the process is a simple degassing, but it could also be performed with a carbonate solution which is turned into a bicarbonate and where the CO2 is removed by other means. CO2 removal could be based on an evacuation (which could be achieved by operating an inverted siphon), or based on electrodialysis, or involve a secondary sorbent that is far more compact and thus allows for an easier regeneration option. It also could involve precipitation of bicarbonate from the solution in a thermal swing or a thermal swing for CO2 release from the mixture. The basic layout is independent of these ideas.
A variation of this idea has all chambers evacuated with the exception of chamber n−1 which is filled with water, n which is open to the air, and n+1 which is again filled with water. The nominally evacuated chambers are filled with a mixture of water vapor and CO2. In this case, we pump water from chamber n−1 into n, displacing the air to the outside and immersing the resin in water. The pump does not need to do much work, because at the same time the water in chamber n+1 is sucked into chamber n+2, while chamber n+1 fills itself with air. At the end of this process chamber n+1 is filled with air and open to the outside. Chamber n is filled with water and at vacuum pressure. Chamber n+2 is filled with water and at vacuum pressure, and all other chambers are still under vacuum conditions. No net work was done, but all chambers moved by one. We can now renumber all chambers, and repeat the cycle.
In this case we use the water to stimulate the gas release and the freshly wetted resin in the last chamber is now topping off the CO2 which is pumped out of this chamber, letting gas flow from all other chambers into this one. The CO2 content of the water is likely to be high, however, it remains more or less constant over time as we do not extract this CO2, so after some initial transients, this CO2 reservoir will remain constant and not remove CO2 from the resin (we ignore here some small losses to the outside air which are not completely avoidable) check valves can be installed to prevent backward flow. As a result we have a water driven implementation of the CO2 release which his significantly simpler than a water vapor driven system.
Optionally, some of the water vapor may be recovered from the system during the compression stage. This will provide sufficient heat that the system can operate at slightly elevated temperatures. Indeed it is possible to use the last step of pumping out of the gas to severely cool the resin and remove all excess water.
Yet other possibilities exist. For example, it is possible to create a buffer storage for the water which makes it possible to slowly withdraw water from chamber n−1 and in a second step fill chamber n very rapidly so as to minimize the amount of time the water is in contact with air and thus can exchange gas with the outside air. The buffer itself must be able to change volume. It takes on an additional volume as it takes on the fluid from chamber n−1. It then contracts again as it pushes the same volume into chamber n.
Again mechanical work is related to friction losses, inertial losses, and losses to slight pressure mismatches between the various chambers. This can be adjusted for with careful thermal management.
In yet another example CO2 is captured and removed from air by employing hydrophobic activated carbon materials with strong base ion exchange resins. See
The same ion exchange resins may be used to remove excess CO2 build-up from closed containers such as storage containers for fresh fruit or vegetables, e.g., bananas, in order to maintain a maximum level of CO2 in the container and avoid excessive ripening or spoilage, as will be described in greater detail below.
In another aspect of the present invention shown in
In another exemplary embodiment shown in
The invention also may be used to generate carbon credits. Thus, a manufacturer may extract CO2, and obtain a carbon credit which may be traded or sold, and then use the extracted CO2 in a secondary process, eliminating the cost of purchasing or generating CO2 for the secondary process.
Another aspect of the present disclosure provides an apparatus and method for using captured CO2 to attract CO2 sensitive insects, such as mosquitoes. It is known that certain insect pests like mosquitoes are attracted to sources of CO2, which for them is a way to find a potential victim. In recent years lures have been developed for mosquitoes that release CO2 in the environment in order to attract mosquitoes and potentially other insects. A drawback of most of these devices is that they require gas cartridges of CO2 or natural gas, propane or butane to produce CO2. In related applications it has been shown how certain ion exchange materials can be used to absorb CO2 when they are in a dry state and release it again when they get wet. Here an application of such a material is described wherein the controlled CO2 release is used to attract mosquitoes to a device at certain times while at other times the device recharges its CO2 stores.
It is possible to expose an amount of resin to air so as to load it with CO2. When the device is activated, e.g. in the evening the resin is exposed to humid air, or is directly wetted for example by a small water spray. As a result the resin will begin releasing CO2 therefore creating an environment that will attract mosquitoes. One implementation, for example, would be a small container filled with polymer strands of the ion exchange resins and similar materials that can be used to absorb CO2. The purpose of the CO2 release is to attract certain insects, like mosquitoes that are attracted by CO2.
The device exposes resin to the air, and containing the resin in a way that is protected from water and rain. During times the device is inactive, it is dry and the resin will collect CO2. The device includes a means of applying moisture to the resin material. Moisture application could be achieved by spraying water onto the resin surface, by wicking water into a woven wick that contains the resin material, or by any other means known in the art.
The device acts as a lure to attract mosquitoes away from people. In this case the device can be completely open, because no part needs to be kept away from people. In another implementation the device includes means of killing the pest once it enters the device. This includes but is not limited to electric discharges, or by contact insecticides embedded into the resin matrix.
It is possible to combine the CO2 lure with other means of attracting insects, including insects that do not respond to the presence of CO2. These means include, but are not limited to light and heat sources, sounds, odors or pheromones. Devices of this nature can be designed for indoor and outdoor use. Indoor use in malaria regions may help suppress the incidence of mosquitoes and hence malaria.
Another aspect of the present disclosure relates to the capture and release of gases generated by the ripening and preservation of fruits and vegetables. Many produce items, i.e., fruits and vegetables, are often stored in a temperature-controlled environment in order to control the ripening process. Methods for the packaging and shipping of such fruits and vegetables have been developed to maximize the amount of time that the produce may be stored. Many methods for storing and ventilating produce are known that provide various types of bags and containers, including gas permeable membranes, that allow some control of the exposure of the produce to gases such as oxygen, ethylene, and carbon dioxide. However, these methods do not provide optimal storage conditions and long-term storage options are still desired.
U.S. Patent Publication No. 2008/0008793, incorporated by reference herein, discloses a method for storing bananas in a controlled environment where oxygen and carbon dioxide levels are optimized in addition to the temperature. Longer periods of storage may be achieved in this environment and improved flavor characteristics may be achieved. The reference fails, however, to discuss how such levels would be reached and maintained.
This aspect of the present disclosure provides a method for to stabilizing the CO2 in a room at any level between 5 ppm and 100,000 ppm. The invention also serves to achieve a low absolute humidity (usually below 25 ppt of water vapor, preferably below 15 ppt, with improved performance as the absolute humidity drops even lower).
Once the resin is loaded the air intake is closed or the resin filter may be moved into a separate chamber. A humidity swing regeneration step follows. Regeneration is accomplished by a change in temperature and absolute humidity, or by wetting the resin, e.g., as described, for example, in U.S. Pat. No. 4,711,645; U.S. Pat. No. 5,318,758; U.S. Pat. No. 5,914,455; U.S. Pat. No. 5,980,611; U.S. Pat. No. 6,117,404; and co-pending U.S. application Ser. No. 11/683,824, and PCT Application Serial No. PCT/US08/82505. Wetting can be accomplished by either dipping the resin into DI or condensation water; by spraying or flowing such water over the resin, (such condensation water may be available from the refrigeration unit operating the storage facility, and may be augmented by condensation water recovered from our unit); by generating steam in a blast of warm air that results in water condensation on the resin material; or by exposing the resin to warm moist air (such warm air may be available from the hot side of the refrigeration unit, it may already be moist or need additional moisture.) If the moisture is added as humidity or by generating steam, it is not necessary to use DI or condensation water.
The moist air loaded with CO2 is then purged from the unit. Heat and water may be recovered in a heat exchange unit that reduces heating demand and water consumption.
The present disclosure as discussed above may be used to cover a range of applications from extremely low levels of CO2 to extremely high levels of CO2. It is in principle possible to remove CO2 from a gas stream that contains CO2 far in excess of the levels discussed above. Levels around 1 to 10 volume percent could easily be accommodated, and operating above about 10 volume percent CO2 is also possible. It is advantageous for this design to operate at temperatures below about 15° C., because the loading and unloading characteristics of the resin improve under these conditions.
Alternative options at elevated levels of CO2 include the use of activated carbon, the use of zeolites, the use of weak based amine, or other physical sorbents such as actuated alumina for CO2 capture instead of ion exchange resin.
In broad aspect the present invention provides a method and apparatus for the extraction of a contaminant from a gas stream. The present invention will be described in reference to a method and apparatus for capturing CO2 from ambient air; however, the invention is also applicable to handling exhaust air or other gas streams and may be used to capture hydrogen sulfide, ammonia, or other common contaminants from such gas streams.
In co-pending PCT International Patent Application Serial No. PCT/US07/84880; U.S. Provisional Patent Application Ser. No. 60/985,586, assigned to a common assignee and incorporated by reference herein, we discuss a CO2 capture process that utilizes a humidity swing to regenerate a sorbent, releasing a mixture of CO2 and water vapor. The water vapor may be removed from the mixture by compression or cooling, either of which will cause the water vapor to condense and precipitate out of the mixture.
To perform the humidity swing, it often is useful to expose the sorbent to low pressure water vapor. In order to achieve the required minimum water vapor pressure, it is may be necessary to operate above ambient temperatures as the maximum water vapor pressure is significantly dependent on temperature. To that end, the aforementioned co-pending applications discuss how to transfer heat to loaded sorbents that need to be inserted into an environment that is at a higher temperature.
In regenerating the sorbent it is necessary to dry the resin material. This opens an opportunity to combine such system with a vacuum distillation system, and use the heat of evaporation that is released when the material is drying to remove heat from the condenser inside the vacuum distillation system. Whereas the recovery of the CO2 in most applications requires entering the resin material into a vacuum chamber, the present invention also may be used to drive a complimentary distillation process.
As explained in the aforementioned co-pending applications, the CO2 sorbent is often an anionic exchange resin, but here we intend to consider all humidity-sensitive CO2 sorbents that can absorb carbon dioxide from the air when they are dry and release carbon dioxide when they have been exposed to humidity in the form of liquid water and/or partial pressures of water vapor which exceed those at ambient conditions. We will generally refer to such materials as water-sensitive CO2 sorbents.
Vacuum distillation is a standard method of creating fresh water from a brine, such as seawater, brackish water or other salt rich brines pumped from underground. For purposes of this disclosure, brine is also used to refer to contaminated water that is otherwise unsuitable as fresh water, such as for example, waters contaminated with biological waste materials. Thus, the term “brine” encompasses all waters contaminated with materials from which water can be separated by vacuum distillation.
Vacuum distillation begins with a chamber that has been at least partially evacuated. Brine is introduced into the chamber and is separated into two components: concentrated brine and fresh water product. There are many ways to supply a fluid into a vacuum chamber that are known to practitioners of the state of the art. By adding and subtracting from the vacuum chamber equal volumes of incompressible fluid it is possible to design a continuous flow system that requires only minimum amount of mechanical work.
The apparatus comprises a vacuum chamber that is divided into at least two parts; an evaporator unit and a condenser unit. As brine is introduced into the evaporator unit, it is allowed to evaporate. In this manner the water vapor becomes separated from the contaminants in the brine. The water vapor is then passed to a condenser unit, where it is allowed to condense. It is necessary to remove heat of condensation to keep from impeding further condensation in the condenser unit. This heat may be passed to the evaporator unit, enabling the evaporation to occur, by counterflow or some other method.
The evaporator unit, which is initially evacuated, fills with water vapor. The equilibrium partial pressure over the brine in the evaporator unit is a function of the temperature and of the salt content of the brine. The equilibrium partial pressure over the condensate in the condenser unit is a function of the temperature. At equal temperature, the equilibrium partial pressure over the condensate is slightly higher than over the brine. Thus, in a system with constant temperature the brine would gradually dilute itself with water extracted from the condensate. The system left to itself would operate in reverse, just as saltwater will become more dilute when it is separated from fresh water with a semi-permeable osmotic membrane.
One way to condense the water vapor in the condenser unit is to raise the pressure, wherein the water vapor will condense at ambient temperatures. This may be accomplished using a compressor to drive up the pressure. The heat of condensation will cause the temperature to rise in the condenser unit, wherein the heat deposited by the condensation can then be transferred to the evaporator unit. The compression acts in effect as a heat pump which transfers heat from the brine to the condensate, and a return heat flow balances out the total heat fluxes inside the system.
Where compression is used to condense the water out of the resulting gas mixture, the heat produced by that process can be transferred to the sorbent to raise its temperature as required. Alternatively, the heat required to drive the sorbent to the requisite temperature can also be derived from the condensation of water that has been allowed to evaporate at ambient conditions.
Another approach is to maintain by some other system a temperature gradient between the evaporator unit and the condenser unit, which is enough to cause a gradient in the equilibrium partial pressure that causes vapor to flow from the evaporator unit to the condenser unit. In order to maintain such a temperature differential, it is necessary to provide the heat of evaporation on the evaporator unit, and remove the heat of condensation on the condenser unit of the chamber. The required temperature differences are small; a few degrees between the evaporator and the condensate are sufficient. Operational temperatures can be low and could be well within the range of ambient temperatures, particularly in warmer climates.
One way of establishing the temperature gradient is to generate heat and transfer it to the evaporator. Another way of establishing the temperature gradient is to actively remove heat on the condenser unit. This requires a heat exchange system that removes heat from the condensate. In such an operation of the device, the temperature of the brine is higher than that of the condenser unit the heat is passed through and cannot be recovered within the system. In principle it is possible to couple one or more additional heat pumps to the system, which pumps the heat removed at the condenser unit and returns it to the evaporation side.
In combination with the CO2 capture system described above, the water vapor is evaporated from the brine and is partly absorbed onto the resin. This will release a substantial portion of the CO2 or other targeted contaminant from the sorbent. When this step is performed in a vacuum chamber, the atmosphere of the chamber will be filled primarily with water vapor and CO2. The vacuum chamber will also aid in the evaporation of the water vapor in the brine. The concentrated brine is then removed and the water is then condensed out of the CO2. Thus, the present invention produces a distilled water stream as well as concentrated CO2.
Providing heat to the drying resin is advantageous and one can therefore integrate a heat exchange system operating between the drying resin collector and the condenser inside the vacuum system. In a typical implementation the evaporation of the water from the resin would not produce quite enough water to make up the water losses from the system; therefore it would have to be augmented by additional brine evaporation.
Another aspect of the present disclosure provides a different process whereby ambient environmental temperatures are used to maintain a constant temperature at the condenser unit, i.e. by flowing ambient air, or ambient water through the heat exchanger on the brine evaporation side, and we use additional brine, e.g. seawater, to operate an evaporative cooler that creates the temperature drop necessary to force the condensation of clean water inside the vacuum chamber. The amount of seawater that needs to be evaporated on the outside of the chamber to maintain a low temperature is approximately equal to the amount of brine that is converted in the vacuum distiller.
The system disclosed herein comprises a vacuum chamber with means of introducing and removing a brine, with means for removal of clean water condensate, with internal surfaces on which the brine is allowed to evaporate, and surfaces of a lower temperature where the water vapor is allowed to condense. The surfaces on which the brine is evaporating are in close contact with a heat exchanger that provides the necessary heat to maintain evaporation. It is advantageous to use free heat, i.e., heat from the ambient environment, which may have been augmented by heat, e.g. from sunshine, or, e.g. waste heat. The surfaces on which water vapor is allowed to condense are in close contact with a heat exchanger that uses additional brine to provide evaporative cooling required to force the condensation.
In the above embodiment, brine is consumed both inside and outside the chamber. The maximum acceptable concentration of the discharge brine will limit the amount of evaporation that is acceptable. The rate of consumption in both cases is similar. The two waste streams can be combined and mixed for return to the ocean or brine reservoir. The returned concentrated brine is slightly cooler than ambient temperatures.
Where ocean water or any water from a large body of water is used, it is not unusual for the input water is already cooler than ambient temperatures. In this case, it is possible to take advantage of the additional cooling power derived from the cool water that is in the system.
In addition, one might use a CO2 membrane that separates CO2 from nitrogen and oxygen. One option would be to use a carbonic anhydrase based membrane separation technology. Of particular utility are membranes with similar properties to the ion exchange resin discussed more fully in our other applications, (see Appendix A). The thin resin membrane would transfer CO2 according to a pressure gradient in CO2 and against a pressure gradient in water vapor. The two combined create a net flow of CO2 across the membrane and thus by keeping the outside of the membrane wet or in high humidity one would create two chemical potentials that will drive CO2 across the membrane.
Finally, there is a great synergy with the climate control of the current chamber. The CO2 management is preferably integrated with de-humidification, or humidification of the air as the case may be, and it may also be integrated with the temperature control and AC handling of the air. The CO2 stabilization unit, shares the air handling and blowing equipment with the other tasks, and it may be built into the same set of ducts. It can take advantage of heat and condensation water produced in the refrigeration unit.
The present disclosure in another aspect provides an additional use for extracted CO2. According to the present invention, the extracted CO2 is employed to neutralize carbonic acid. The present invention takes advantage of the fact that in sequestration, if one can drive the partial pressure of CO2 up by about a factor of about 100, the concentrated CO2 may then be injected into alkaline brines, to neutralize the brine.
The resins disclosed in our previous U.S. Provisional Patent Appln. 60/985,586 and PCT International Patent Appln. Serial No. PCT/US08/60672, assigned to a common assignee, make it possible to capture CO2 from the air and drive it off the sorbent with no more than excess water vapor. It also is possible to wet the resin directly with liquid water and form a carbonate, and transfer the carbonate in a second step through a membrane between the two fluids. However, in most cases, it is preferable to create a concentrated CO2 gas that then can be transferred directly into a more alkaline brine. Here again we can make direct contact between the gas and the brine, or keep them separated by a hydrophobic, porous membrane.
There are many applications where one has access to alkaline underground brines that can be used to drive a humidity swing with ionic exchange sorbents, even if their ion content make them unsuitable for direct contact with the resin. The present invention takes advantage of the humidity swing and transfers the CO2 through the gas phase. Alternatively, hydrophobic membranes may be used to create a gas phase interface between two liquids, or between a liquid and a gas. If the brine covers one side of the membrane it is possible to pull CO2 gas through the membrane without bringing contaminant ions in contact with the sorbent resin.
A particular application of this technology can be realized where some other industrial process has created a highly alkaline waste stream that needs to be neutralized before disposal. In that case, we can introduce carbonic acid, which will either cause the precipitation of insoluble carbonates, or produce soluble but neutral carbonate salts. Similar processes are disclosed in (PCT) Publication Number WO/2005/047183. As an example, consider waste streams from bauxite processing, e.g. in the Bayer process, which produces “red mud” at pH 13. According to the PCT Application cited above, between 1990 and 2003 six to seven million tons of red mud have been produced. Another example mentioned in the reference is the reprocessing or disposal of potassium hydroxide solutions from alkaline batteries. The process of the present invention would create potassium carbonate or bicarbonate producing materials that are indeed quite harmless.
In one aspect of the neutralization process according to the present disclosure, we propose to use an alkaline brine which is preferably in a temperature range between 40 and 60° C., and use the water vapor to recover CO2 from our resins. We then wash the CO2 out of the gas mixture with the help of the alkaline brine. The heated alkaline brine will provide a high level of moisture which induces the resin to give off CO2 while it at the same time prevents the CO2 level from rising substantially. If operated in a vacuum the process should not be transport limited. In the presence of atmospheric pressures, however, the process could be transport limited.
One possible approach is to have the liquor be soaked up in open cell foams such as AQUAFOAM® floral retention foam as described in our PCT Published Application No. WO2006/084008. Another is to have it trickle through a packed bed that is installed parallel to the resin recovery unit and cycles gas from the recovery unit through it. Another option is to contain the resins in a tube whose outside is covered with a material that soaks up the brine. In such a design heat transfer between inside and outside the tube is optimized.
The resin, which has been saturated with CO2 in ambient air, is brought into a chamber connected to a second chamber containing wetted surfaces over which the brine flows. The brine will establish a high level of humidity and the resulting high humidity air is blown over the sorbent material. In one aspect of this invention this exchange will occur with humid air entering the chamber. In another aspect, residual air in the chamber is at least partially removed by evacuation prior to running water vapor through the chamber. As the water vapor is circulated between the wetted surfaces and the sorbent material, it carries CO2 that is released to the alkaline brine where it is absorbed into the brine. In this implementation the resinfunctions to speed up the transfer of CO2 from ambient air into the alkaline brine. Further acceleration of the transfer of CO2 may be achieved with other materials, such as, for example, with carbonic anhydrase that thereby would open the use of brines with relatively low levels of alkalinity e.g with a pH of 8-11. In this range one could even use seawater, even though the accelerated acidification of seawater would in many cases be counter-productive. However, this would not be the case, for example, where the source of an alkaline brine is an underground aquifer, from which brine is removed and to which it is returned once the CO2 is absorbed. The brine could also be water that has been exposed to alkaline mineral rocks such as basalt or peridotite or serpentinite rock. For example, one could percolate the water through a pile of serpentine tailings or other tailings that can release alkalinity.
The use of serpentine tailings to increase alkalinity is known in the art. Alternatively, the serpentine could be mined for this purposes It also is possible in some formations to inject water into alkaline underground systems for the purpose of enriching it with base cations. The presence of CO2 in the water may speed up this process.
In the case of serpentine and olivine as well as basalt, this particular use of mineral sequestration would likely result in the precipitation of magnesium and/or calcium carbonate. The advantage of this method over previous attempts to directly sequester CO2 from the atmosphere is that the CO2 concentrations can be enriched by about a factor of 100, which will greatly help with the reaction kinetics.
Another source of alkalinity could be Mg(OH)2 that has resulted from the processing of serpentine and olivine.
It is also possible to use the CO2 to dissolve calcium carbonate rock that then can be put into the ocean as calcium bicarbonate. In this example it is possible to directly use seawater to drive the dissolution, and the presence of carbonic anhydrase may speed up this process dramatically. See, e.g. PCT International Patent Appln. Serial No. PCY/US08/60672, assigned to a common assignee, for a discussion of the use of carbonic anhydrase to accelerate the CO2 capture process.
The dissolution of limestone with air captured CO2 is analogous to a process in which the CO2 comes from a power plant. The present invention provides a substantial advantage over a power plant in that we do not have to bring enormous amounts of lime stone to a power plant, or distribute the CO2 from a power plant to many different processing sites, but that we can instead develop a facility where seawater, lime and CO2 from the air come together more easily. One specific implementation would be to create a small basin that is periodically flushed with seawater. The CO2 is provided by air capture devices located adjacent to or even above the water surface. Of particular interest are sites where limestone or other forms of calcium carbonate (such as empty mussel shells) are readily available as well. If we have calcium carbonate, seawater and air capture devices in one place, we can provide a way of disposing of CO2 in ocean water without raising the pH of the water.
Indeed, it is possible to install such units adjacent a coral reef area by bringing additional limestone to the site or by extracting limestone debris near the reef. If the units operate in a slight ocean current upstream of the reef, they can generate conditions that are more suitable to the growth of the coral reef. Growth conditions can be improved by raising the ion concentration product of Ca++ and CO3 −−. This product governs the rate of coral reef growth.
It should be emphasized that the above-described embodiments of the present device and process, particularly, and “preferred” embodiments, are merely possible examples of implementations and merely set forth for a clear understanding of the principles of the invention. Many different embodiments of the invention described herein may be designed and/or fabricated without departing from the spirit and scope of the invention. All these and other such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. Therefore the scope of the invention is not intended to be limited except as indicated in the appended claims.