US20160208461A1

US20160208461A1 - Harvesting atmospheric water using natural gas that would typically be flared and wasted

Info

Publication number: US20160208461A1
Application number: US14/995,063
Authority: US
Inventors: Vaibhav Bahadur; Enakshi Wikramanayake
Original assignee: University of Texas System
Current assignee: University of Texas System
Priority date: 2015-01-16
Filing date: 2016-01-13
Publication date: 2016-07-21

Abstract

A method and system for harvesting water from the atmosphere using unwanted combustible gas, where the unwanted combustible gas refers to combustible gas (e.g., natural gas) that would normally be flared off by the oil and gas operator or by a plant (e.g., petrochemical plant). The energy produced by burning the unwanted combustible gas is used to power vapor compression or vapor absorption based refrigeration units which provide the cooling capacity to condense water. The condensers may be coated with specialized condensation promoting coatings that increase the condensation heat transfer performance thereby enabling compact combustible gas powered atmospheric water harvesters. The water collected can be used for oilfield operations, hydraulic fracturing, waterflooding, etc.

Description

TECHNICAL FIELD

The present invention relates generally to natural gas flaring, and more particularly to harvesting atmospheric water using unwanted combustible gas (e.g., unwanted natural gas) that would typically be flared.

BACKGROUND

When petroleum crude oil is extracted and produced from onshore or offshore oil wells, natural gas associated with the oil is produced to the surface as well. Especially in areas of the world lacking gas handling equipment, pipelines and other gas transportation infrastructure, vast amounts of such associated gas are commonly “flared” or burned up as waste or unusable gas. The flaring of associated gas may occur at the top of a vertical flare stack or it may occur in a ground-level flare.
The amount of natural gas that is flared in the world is significant. As per estimates by the U.S. Energy Information Administration (EIA) and the World Bank, the total worldwide flaring in 2011 was about 20% of the annual U.S. domestic gas consumption. This translates to about 10's of billions of dollars' worth of gas flared. Top flaring countries include Russia, Middle East and West African nations; the U.S. ranks 5th in the list. Historically, the ratio of gas flared to gas produced in the U.S. has been low, but flare rates have risen recently from 0.7% in 2010 to 1% in 2013. Locally, the flare rates can be significantly higher. It is estimated that up to a third of the gas produced in the Bakken shale in North Dakota is flared. About 50 sites in North Dakota flare more than 33,980 m³/day (1,200 MCFD) (MCFD: thousand cubic foot per day) and more than 275 sites flare greater than 8,495 m³/day (300 MCFD). In Texas, development of the Eagle Ford shale resulted in a 400% increase in flaring from 2009 to 2012. Recent estimates show that on average, 9,600 m³/day (339 MCFD) of gas is flared per well for newly completed wells in Texas. Flaring represents a significant waste of natural resources, in addition to creating significant environmental, thermal and light pollution near residential areas.
There are no easy solutions to reducing natural gas flaring. Natural gas capture and transportation involves the construction of capital intensive pipelines or liquefaction systems. Many new fields, such as the Bakken shale in North Dakota, are predominantly being developed for oil with gas having a secondary value. Furthermore, gas production from newly developed hydraulically fractured wells declines rapidly, which precludes any infrastructure setup. Lastly, gas production is distributed in producing fields which drives up gas collection costs. At the currently depressed prices and low demand of natural gas, and in the absence of any regulated limits on flaring, the most economical solution for unwanted gas is to flare it off.
Consequently, there is not currently a means for utilizing the unwanted natural gas for some constructive use.

SUMMARY

In one embodiment of the present invention, a method for harvesting atmospheric water comprises receiving an unwanted combustible gas stream that would normally be flared off. The method further comprises purging the unwanted combustible gas stream to remove oxygen from the unwanted combustible gas. The method additionally comprises distributing the combustible gas to a gas conditioning module to condition the combustible gas to be utilized by a gas engine. Furthermore, the method comprises sending the conditioned combustible gas to the gas engine to run a refrigeration cycle. Additionally, the method comprises extracting water from the atmosphere using the refrigeration cycle. In addition, the method comprises storing the extracted water in a water storage unit.
In another embodiment of the present invention, a system for harvesting atmospheric water comprises a gas-based cooling system powered by unwanted combustible gas that would normally be flared, where the unwanted combustible gas is received from a wellhead, a refinery or a plant. The system further comprises a water condenser with a cooling capacity powered by the gas-based cooling system, where the water condenser is configured to condense water vapor from the atmosphere into liquid. The system additionally comprises a water storage unit connected to the water condenser, where the water storage unit is configured to store the water droplets.
The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which:

FIG. 1 illustrates a water harvesting system configured in accordance with an embodiment of the present invention;

FIG. 2 is a flowchart of a method for utilizing unwanted combustible gas (e.g., unwanted natural gas) that would be flared to harvest water from the atmosphere in accordance with an embodiment of the present invention; and

FIG. 3 is a flowchart of a method for storing additional water in the water storage unit of the water harvesting system in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

While the following discusses the present invention in connection with utilizing unwanted natural gas from oil and gas explorations that would typically be flared to harvest water from the atmosphere, the principles of the present invention may be applied to utilizing any unwanted combustible waste gas that would typically be flared to harvest water from the atmosphere. Furthermore, the principles of the present invention may be applied to any unwanted combustible waste gas that would be typically be flared in other industries or plant operations (e.g., petrochemical plant). For example, petrochemical plants typically flare off unwanted natural gas or other combustible gases, which are the byproducts of chemical processes. A person of ordinary skill in the art would be capable of applying the principles of the present invention to such implementations. Further, embodiments applying the principles of the present invention to such implementations would fall within the scope of the present invention.
In the following description, various embodiments are described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the embodiments. It will also be apparent to one skilled in the art that the present invention can be practiced without the specific details described herein. Furthermore, well-known features may be omitted or simplified in order not to obscure the embodiment being described.
As discussed in the Background section, the amount of natural gas that is flared in the world is significant. As per estimates by the U.S. Energy Information Administration (EIA) and the World Bank, the total worldwide flaring in 2011 was about 20% of the annual U.S. domestic gas consumption. This translates to about 10's of billions of dollars' worth of gas flared. Top flaring countries include Russia, Middle East and West African nations; the U.S. ranks 5th in the list. Historically, the ratio of gas flared to gas produced in the U.S. has been low, but flare rates have risen recently from 0.7% in 2010 to 1% in 2013. Locally, the flare rates can be significantly higher. It is estimated that up to a third of the gas produced in the Bakken shale in North Dakota is flared. About 50 sites in North Dakota flare more than 33,980 m³/day (1,200 MCFD) (MCFD: thousand cubic foot per day) and more than 275 sites flare greater than 8,495 m³/day (300 MCFD). In Texas, development of the Eagle Ford shale resulted in a 400% increase in flaring from 2009 to 2012. Recent estimates show that on average, 9,600 m³/day (339 MCFD) of gas is flared per well for newly completed wells in Texas. Flaring represents a significant waste of natural resources, in addition to creating significant environmental, thermal and light pollution near residential areas. There are no easy solutions to reducing natural gas flaring. Natural gas capture and transportation involves the construction of capital intensive pipelines or liquefaction systems. Many new fields, such as the Bakken shale in North Dakota, are predominantly being developed for oil with gas having a secondary value. Furthermore, gas production from newly developed hydraulically fractured wells declines rapidly, which precludes any infrastructure setup. Lastly, gas production is distributed in producing fields which drives up gas collection costs. At the currently depressed prices and low demand of natural gas, and in the absence of any regulated limits on flaring, the most economical solution for unwanted gas is to flare it off. Consequently, there is not currently a means for utilizing the unwanted natural gas for some constructive use.
The principles of the present invention provide a means for utilizing the unwanted natural gas for a constructive use, namely, in harvesting water from the atmosphere. Such a use is especially desired in the oil and gas industry. A significant challenge faced in the oil and gas industry is water procurement for oilfield operations. Fracking is a very water intensive operation typically requiring 5 million gallons of water per well. Sourcing water for hydrocarbon production adds enormous pressure to available resources in water stressed regions, such as Texas, Oklahoma and California in the United States, the Middle East and North and West Africa. In water rich regions like the Marcellus, water sourcing costs (excluding transportation) range from 1 to 2 cents a barrel. However, many major producing fields (e.g., Eagle Ford, Haynesville, Barnett, Bakken) are located in water stressed areas and the costs range from 25 cents-$1 /barrel. Trucking costs range from 2-4 cents/barrel/mile and can be enormous given the huge water requirements and large distances involved. Overall, there is unanimous agreement that sourcing water is a significant challenge to sustain the energy boom in the United States. By utilizing the unwanted natural gas that would typically be flared to harvest water from the atmosphere, as discussed further below in connection with FIGS. 1-3, a significant and sustainable quantity of water could be supplied for oil and gas production operations or personnel consumption at oil and gas production sites. Other benefits include less water trucking traffic, reduced light and thermal pollution and elimination of negative publicity for oil and gas companies.
Referring now to the Figures in detail, FIG. 1 is a water harvesting system 100 utilizing the unwanted combustible gas (e.g., unwanted natural gas) to be flared in accordance with an embodiment of the present invention. System 100 includes a purging unit 101 connected to the unwanted gas stream (e.g., unwanted natural gas that would typically be flared), from a wellhead, refinery or a production plant (e.g., petrochemical plant), to remove the oxygen/air from the gas in order to eliminate combustion. “Unwanted combustible gas,” as used herein, refers to gas, such as natural gas, that would normally be flared by the oil and gas operator or by a refinery or plant (e.g., petrochemical plant).
Knockout drum 102 (also known as a “vapor-liquid separator”) is configured to remove any large amounts of liquid that may accompany the gas stream. The liquid will then settle on the bottom of knockout drum 102 and the purged combustible gas (e.g., purged natural gas) will be distributed by gas distribution manifold 103.
Previously, unwanted combustible gas (e.g., unwanted natural gas) would be flared in a flare stack 104. However, system 100 utilizes gas distribution manifold 103 (includes flow control device, such as control valves, sensors, seals, etc. that are not shown) to distribute the unwanted combustible gas (e.g., unwanted natural gas) to a gas conditioning module 105 to condition the combustible gas (e.g., natural gas) to be utilized by gas engine 106.
However, there may be times when a surge of unwanted combustible gas (e.g., unwanted natural gas) is received by gas distribution manifold 103 that gas conditioning module 105 and gas engine 106 cannot handle. In such situations, the excess combustible gas (e.g., natural gas) could be flared in flare stack 104. Alternatively, such excess unwanted combustible gas (e.g., natural gas) could be stored in a combustible gas (e.g., natural gas) storage unit 107.
As discussed above, gas conditioning module 105 conditions the unwanted combustible gas (e.g., unwanted natural gas) to be utilized by gas engine 106. In particular, gas conditioning module 105 may include a further knockout drum to further separate any liquids in the unwanted combustible gas stream (e.g., unwanted natural gas stream). Additionally, gas conditioning module 105 may include seals to prevent oxygen/air from mixing with the unwanted combustible gas (e.g., unwanted natural gas). Furthermore, gas conditioning module 105 may include a scrubber configured to remove any impurities in the unwanted combustible gas (e.g., unwanted natural gas) so that gas engine 106 can operate smoothly.
Gas engine 106 is configured to supply the power for the refrigeration cycle (which can be a “vapor compression cycle” or a “vapor absorption cycle”). The vapor compression cycle is driven by a compressor 108 (which is part of the cycle). Compressor 108 is configured to compress hot refrigerant vapor which is condensed by condenser 109 which first cools and removes the superheat via a fan 110 powered by gas engine 106 and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. The liquid then travels through expansion valve 111 (also called a “throttle valve”) which decreases the pressure. The refrigerant then evaporates in the insides of an evaporator 112; the heat required for evaporation is provided by the atmospheric water which condenses on the outside of evaporator 112. Evaporator 112 of the vapor compression cycle thus also acts as the water condenser. The outside of evaporator 112 is configured to condense the water vapor into water droplets on a surface which are then rolled off exposing fresh moisture-laden air to the cold surface. In one embodiment, the surface of the water condenser is coated with hydrophobic/superhydrophobic coatings to facilitate dropwise condensation and roll-off thereby achieving high heat transfer to ensure compact water condensers. The water condensed by the water condenser is collected in a water storage unit 113.
In the refrigeration cycle described above, the air from the atmosphere flows over evaporator 112 via a fan 114 powered by gas engine 106.
In one embodiment, the exhaust of gas engine 106 is scrubbed for impurities (e.g., toxic pollutants) by scrubber 115. In one embodiment, after the exhaust of gas engine 106 is scrubbed, it is released to the atmosphere.
Alternatively, the exhaust (high temperature flue gas) of gas engine 106 which includes carbon dioxide and water vapor is captured in a carbon dioxide capture module 116. In one embodiment, a flue gas water harvesting system 117 is configured to extract water from the water vapor in the flue gas. The extracted water is then stored in water storage unit 113.
In one embodiment, system 100 may be implemented as a mobile system, such as on a flatbed of a truck, thereby increasing the utility of the present invention as it could be easily utilized at various sites (e.g., oil wells) by simply traveling from site to site.
Water harvesting system 100 is not to be limited in scope to the depicted elements. Instead, the principles of the present invention are to include other technology options that may be now or in the future commercially available for harvesting water from the atmosphere. For example, the principles of the present invention may utilize a steam turbine driven chiller system for harvesting water from the atmosphere using unwanted natural gas by utilizing a boiler that is heated by the unwanted natural gas which produces steam which turns a turbine which drives the vapor compression cycle discussed above. In another example, the principles of the present invention may utilize a single-effect vapor absorption chiller system for harvesting water from the atmosphere using unwanted natural gas by utilizing a gas burner/boiler operated by the unwanted gas which produces steam which drives a vapor absorption cycle (refrigerant-lithium bromide) that provides cooling to condense water. In a further example, the principles of the present invention may utilize a direct-fired double-effect vapor absorption chiller system for harvesting water from the atmosphere using unwanted natural gas by utilizing a high temperature generator operated by the unwanted gas which drives a vapor absorption cycle (refrigerant-lithium bromide) that provides the cooling to condense the water. In another example, the principles of the present invention may utilize a micro turbine or gas turbine system for harvesting water from the atmosphere, where the unwanted natural gas is used to run a gas turbine engine that uses the Brayton cycle to run a generator which drives the vapor compression cycle discussed above. In a further example, the principles of the present invention may utilize a co-generation with absorption chilling system for harvesting water from the atmosphere using the waste head from a micro turbine or a gas engine operated by the unwanted gas. This waste heat is used to operate the single-effect absorption chiller or steam turbine driven chiller discussed above. In another example, the principles of the present invention may utilize a desiccant dehumidification system where a desiccant absorbs moisture from the air and a gas-fired burner, operated by the unwanted natural gas, is used to perform desiccant dehydration to collect water from the absorbed moisture.
A description of a flowchart of a method for utilizing unwanted combustible gas (e.g., unwanted natural gas) to harvest water from the atmosphere utilizing water harvesting system 100 is discussed below in connection with FIG. 2.
FIG. 2 is a flowchart of a method 200 for utilizing unwanted combustible gas (e.g., unwanted natural gas) to harvest water from the atmosphere in accordance with an embodiment of the present invention.
Referring to FIG. 2, in conjunction with FIG. 1, in step 201, system 100 receives an unwanted combustible gas stream (e.g., unwanted natural gas stream), such as from a wellhead, a refinery or a plant, that would normally be flared.
In step 202, system 100 purges the unwanted combustible gas stream (e.g., unwanted natural gas stream) by preventing air/oxygen ingress in order to eliminate combustion.
In step 203, gas distribution manifold 103 of system 100 distributes the unwanted combustible gas stream (e.g., unwanted natural gas stream) to gas conditioning module 105 to condition the gas to be used by gas engine 106.
In step 204, system 100 sends the conditioned gas (e.g., conditioned natural gas) to gas engine 106 to run the refrigeration cycle discussed above.
In step 205, evaporator 112 of system 100 extracts water from the atmosphere using the cooling capacity generated by the refrigeration cycle discussed above.
In step 206, system 100 stores the extracted water in water storage unit 113.
In some implementations, method 200 may include other and/or additional steps that, for clarity, are not depicted. Further, in some implementations, method 200 may be executed in a different order than presented. Additionally, in some implementations, certain steps in method 200 may be executed in a substantially simultaneous manner or may be omitted.
The foregoing discusses utilizing unwanted combustible gas (e.g., unwanted natural gas) for extracting water from the atmosphere which is stored in water storage unit 113. Further water may be stored in water storage unit 113 utilizing a flue gas water harvesting system 117 of FIG. 1 as discussed below in connection with FIG. 3.
FIG. 3 is a flowchart of a method 300 for storing additional water in water storage unit 113 of FIG. 1 in accordance with an embodiment of the present invention.
Referring to FIG. 3, in conjunction with FIG. 1, in step 301, scrubber 115 of system 100 removes impurities (e.g., toxic pollutants) from the exhaust of gas engine 106.
In step 302, carbon dioxide capture module 116 of system 100 captures carbon dioxide from the exhaust (high temperature flue gas).
In step 303, flue gas water harvesting system 117 of system 100 extracts water from the water vapor of the flue gas (high temperature waste gas).
In step 304, system 100 stores the extracted water in water storage unit 113.
In some implementations, method 300 may include other and/or additional steps that, for clarity, are not depicted. Further, in some implementations, method 300 may be executed in a different order than presented. Additionally, in some implementations, certain steps in method 300 may be executed in a substantially simultaneous manner or may be omitted.
As a result of the principles of the present invention, combustible gas, such as natural gas, that would normally have been wasted may now be utilized to produce a very useful commodity, namely, water from the atmosphere. The energy produced by burning the unwanted combustible gas (e.g., unwanted natural gas) is used to power vapor compression or vapor absorption based refrigeration units which provide the cooling power to condense water. The condensers may be coated with specialized coatings that increase the efficiency of water condensation leading to compact combustible gas (e.g., natural gas) powered water harvesters. The water collected can be used for oilfield operations or personnel consumption at oil and gas production sites.
The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for harvesting atmospheric water, the method comprising:

receiving an unwanted combustible gas stream that would normally be flared off;

purging said unwanted combustible gas stream to remove oxygen from said unwanted combustible gas;

distributing said combustible gas to a gas conditioning module to condition said combustible gas to be utilized by a gas engine;

sending said conditioned combustible gas to said gas engine to run a refrigeration cycle;

extracting water from the atmosphere using said refrigeration cycle; and

storing said extracted water in a water storage unit.

2. The method as recited in claim 1, wherein said unwanted combustible gas stream is received from a wellhead, refinery or a plant.

3. The method as recited in claim 1 further comprising:

removing impurities from an exhaust of said gas engine.

4. The method as recited in claim 3 further comprising:

capturing carbon dioxide from said exhaust comprising flue gas.

5. The method as recited in claim 4 further comprising:

extracting water from water vapor of said flue gas; and

storing said extracted water in said water storage unit.

6. A system for harvesting atmospheric water, the system comprising:

a gas-based cooling system powered by unwanted combustible gas that would normally be flared, wherein said unwanted combustible gas is received from a wellhead, a refinery or a plant;

a water condenser with a cooling capacity powered by said gas-based cooling system, wherein said water condenser is configured to condense water vapor from the atmosphere into liquid; and

a water storage unit connected to said water condenser, wherein said water storage unit is configured to store said water droplets.

7. The system as recited in claim 6, wherein a surface of said water condenser is coated with hydrophobic or superhydrophobic coatings.

8. The system as recited in claim 6, wherein said gas-based cooling system comprises:

a gas distribution manifold configured to condition said unwanted combustible gas to be utilized by a gas engine configured to power a refrigeration cycle that utilizes said water condenser for condensing water from the atmosphere.

9. The system as recited in claim 8, wherein said gas distribution manifold comprises a knockout drum configured to separate liquids in said unwanted combustible gas.

10. The system as recited in claim 8, wherein said gas distribution manifold comprises a scrubber configured to remove impurities from said unwanted combustible gas.

11. The system as recited in claim 6, wherein said gas-based cooling system further comprises:

a carbon dioxide capture module configured to capture carbon dioxide from an exhaust of said gas engine comprising flue gas.

12. The system as recited in claim 11, wherein said gas-based cooling system further comprises:

a flue gas water harvesting system connected to said carbon dioxide capture module, wherein said flue gas water harvesting system is configured to extract water from water vapor of said flue gas, wherein said extracted water is stored in said water storage unit.

13. The system as recited in claim 6, wherein said gas-based cooling system comprises:

a purging unit configured to remove oxygen from said unwanted combustible gas.

14. The system as recited in claim 13, wherein said gas-based cooling system further comprises:

a knockout drum configured to remove liquids accompanying said unwanted combustible gas.

15. The system as recited in claim 6, wherein said gas-based cooling system comprises a steam turbine driven chiller.

16. The system as recited in claim 6, wherein said gas-based cooling system comprises a single-effect absorption chiller.

17. The system as recited in claim 6, wherein said gas-based cooling system comprises a direct-fired double-effect absorption chiller.

18. The system as recited in claim 6, wherein said gas-based cooling system comprises a gas turbine.

19. The system as recited in claim 6, wherein said gas-based cooling system comprises a desiccant dehumidification system.