System and method for removing volatile hydrocarbons from water stream

Abstract

A system for separating volatile hydrocarbons from a water stream includes a pre-mixer-injector device that receives an untreated water stream containing volatile hydrocarbons, injects compressed air into the untreated water stream, and mixes the injected air with the untreated water stream to form a first injected fluid stream. The shear mixing device receives a first injection fluid stream from the mixer-injector device and shears bubbles within the received first injection fluid stream, thereby forming a foam stream. A pre-degassing separator receives the foam stream from the shear mixing device and separates it into a volatile hydrocarbon stream and a partially treated water stream according to a density difference. A compressor directs clean and oil-free compressed air to the pre-mixer-injector device.

Description

[0001] Priority declaration

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 305,730, filed on February 2, 2022, the contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to systems and methods for purifying water, and more particularly, to systems and methods for removing volatile hydrocarbons from water. Background Art

[0004] Dissolved gases, including methane and other volatile hydrocarbons, may render groundwater drawn from a well undrinkable due to aesthetic, taste, or health concerns. Additionally, at high concentrations, methane and other dissolved volatile hydrocarbons can rapidly escape from the water, creating an explosion hazard in poorly ventilated or confined areas. Systems and methods for removing methane and other volatile hydrocarbons from water are needed. Summary of the invention

[0005] Various aspects of the subject matter may be embodied individually or together in the devices and systems described and claimed below. These aspects may be used alone or in combination with other aspects of the subject matter described herein, and the common description of these aspects is not intended to exclude the use of these aspects alone or the right to claim these aspects alone or in different combinations, as described in the claims attached hereto.

[0006] In one aspect, a system for separating volatile hydrocarbons from a water stream includes a pre-mixer-injector device that receives an untreated water stream including volatile hydrocarbons, injects compressed air into the pressurized untreated water stream, and mixes the injected air with the untreated water stream to form a first injection fluid stream. The air is injected using a diffuser. A shear mixing device receives the first injection fluid stream from the mixer-injector device and shears bubbles within the received first injection fluid stream to form a foam stream. A pre-degassing separator receives the foam stream from the shear mixing device and separates it into a volatile hydrocarbon stream and a partially treated water stream based on density differences. A compressor directs the compressed air to the pre-mixer-injector device.

[0007] In another aspect, a process for separating volatile hydrocarbons from a water stream includes the steps of injecting compressed air into a pressurized and untreated water stream, mixing the compressed air and the untreated water stream to form a first injected fluid stream, shearing bubbles within the first injected fluid stream to form a foam stream, and separating the foam stream into a volatile hydrocarbon stream and a partially treated water stream based on density differences. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a pipeline and flow chart in an embodiment of the system and method of the present disclosure.

[0009] Figure 2 yes Figure 1 A perspective view of an embodiment of a system.

[0010] Figure 3 yes Figure 2 Floor plan of the system.

[0011] Figure 4 yes Figure 1-3 Side view of an embodiment of a syringe-mixer device of the system.

[0012] Figure 5 Is installed in Figure 4 Syringe-Mixer Figure 1-3 A partial cutaway side view of an embodiment of a diffuser of the system.

[0013] Figure 6 yes Figure 5 An enlarged side view of an embodiment of a solution tube of a diffuser. DETAILED DESCRIPTION

[0014] Although the following disclosure refers to treating a water stream at a wellhead, and to systems that may be retrofitted to a prior wellhead, the systems and methods of the present disclosure may be used at downstream or other stages of water treatment.

[0015] It should be noted herein that lines, conduits, ducts, channels and similar structures and corresponding flows are sometimes indicated by the same reference numerals as shown in the Figures.

[0016] Reference numerals introduced in the specification in relation to a drawing may be repeated in one or more subsequent drawings for common elements or components without additional description in the specification, in order to provide context for other features.

[0017] In the claims, letters are used to identify claim steps (e.g., a., b., and c.). These letters are used to aid in referring to method steps and are not intended to indicate the order in which the steps in the claims are to be performed, unless and only if such an order is explicitly recited in the claims.

[0018] Figure 1 1, a first embodiment of the system of the present invention is generally indicated at 10. Pump 12 is located at the wellhead and provides a pressurized flow of untreated groundwater or well water to a split forming lines 14 and 16. Line 16 is a system bypass line through which untreated groundwater or well water may be directed when a corresponding isolation valve 18 is open and isolation valve 20 in line 14 is closed. In normal operation of the system of the present invention, valve 20 is open and valve 18 is closed.

[0019] Groundwater or well water streams contain dissolved methane or natural gas and may contain entrained methane or natural gas and other volatile hydrocarbons that may be dissolved or entrained (including but not limited to ethane and propane or other volatile hydrocarbons).

[0020] After entering the pipeline 14, the water from the pump 12 flows through a reducer 22, whereby the diameter of the pipe is reduced, thereby increasing the water flow velocity to promote downstream mixing. By way of example only, the reducer 22 may reduce the pipeline diameter from 10 inches to 8 inches. The water then flows into a pre-mixer-injector device 24, which, by way of example only, may include a static mixer, as will be described in more detail below.

[0021] In the pre-mixer-injector device 24, the water stream enters a static inline mixer having blades or other mixing structures and an injector port, whereby a stream of compressed air 26 is injected into the liquid water and mixed, thereby forming small bubbles in the liquid water. By way of example only, the mixer-injector may be a device as disclosed in U.S. Pat. No. 4,123,800 or U.S. Pat. No. 5,863,128, both issued to Mazzei, the contents of which are incorporated herein by reference.

[0022] By way of example only, the pre-mixer-injector device 24 may be a static inline mixer that brings water and air into intimate contact by introducing small bubbles of air into the water. The resulting turbulence provides an air scrubbing or stripping process that physically removes dissolved gases from the solution, thereby forming methane bubbles in the water.

[0023] The efficiency of the washing or stripping process depends at least in part on the amount of surface contact between air and water, which is primarily controlled by the size of the bubbles (the smaller the bubbles, the higher the efficiency), the water flow rate, and the time of mixing in situ. Therefore, the mixer-injector device 24 is equipped with a diffuser ( Figure 1 28 in the figure), which may include a structure covering the air flow path and having many small openings / holes or grids. Therefore, smaller bubbles are formed in the liquid water flow.

[0024] Figure 4 An example of a suitable syringe-mixer assembly is shown generally at 24. The mixer-syringe assembly 24 includes an injection port 25, such as Figure 5 As shown, the injection port 25 receives the diffuser 28. Figure 5 The diffuser 28 includes a valve body 29 fixed to the mixer-injector device 24 and a solution tube 30 extending into a fluid passage 31 of the mixer-injector. The valve body 29 and the solution tube 30 receive Figure 1 The compressed air flow 26 is shown. Figure 6As shown, the solution tube includes a closed bottom 33 and a plurality of openings 35. The air flow 26 is injected into the water flow through the mixer-injector device through the openings 35. By way of example only, the mixer-injector device 24 can be an SMP series inline static mixer available from Storm Mixer (www.stormmix.com), and the diffuser 28 can be a Model 5721 diffuser available from Inyo Process (www.inyoprocess.com).

[0025] The injected fluid flows from the pre-mixer-injector device 24 through a shear mixing device, such as flash reactors 34a-34c. Although three flash reactors are shown in the figure, the system may include one or another different number of flash reactors. Each flash reactor includes a mixing chamber, the structure of which promotes redirection and shearing of the incoming gas and liquid water mixture. This will produce foam or froth, thereby promoting mass transfer of methane as it emerges from the water for downstream separation. By way of example only, a suitable shear mixing device is a reactor disclosed in U.S. Patent No. 6,730,214 to Mazzei, the contents of which are hereby incorporated herein by reference.

[0026] The foaming stream from the flash reactors 34a-34d then optionally flows through an expander 32, thereby increasing the diameter of the pipe. By way of example only, the expander can increase the diameter of the pipe from eight inches to ten inches. The foaming stream then flows through line 36 to an optional reducer 38, where, by way of example only, the pipe diameter is reduced from ten inches to eight inches. The foaming stream from the reducer 38 then enters a pre-degassing separator 42, which is equipped with a pre-degassing pressure relief valve 43. The removed gas is discharged to the atmosphere 44 through the pressure relief valve 43.

[0027] In the pre-degassing separator 42, methane is separated from the incoming froth stream and leaves the tower as a tower overhead stream 44 through the pre-degassing relief valve 43. The degassing relief valve allows air to escape, while water remains in the separator 42. The pre-degassing separator separates the entrained and stripped methane (and other volatile hydrocarbons if present) from the water based on the density difference between the gas and the liquid. The tower overhead stream 44 can be pure methane or a gas containing a high concentration of methane and is transferred to the air phase through the degassing relief valve. A partially treated water liquid stream 46 leaves the bottom of the pre-degassing separator 42.

[0028] Merely by way of example, the pre-degasifier 42 may include the technology disclosed in U.S. Pat. No. 6,866,703 to Mazzei, U.S. Pat. No. 5,622,545 to Mazzei et al., and / or U.S. Pat. No. 5,338,341 to Mazzei et al., the contents of each of which are incorporated herein by reference. In such a degasifier, the flow from the reducer 37 enters the top of the degasifier 42 tangentially, which causes it to rotate. The rotating water flows downward through the degasifier 42 and is discharged at the bottom as a liquid stream 46. Methane (and possibly other volatile hydrocarbons) gases are collected at the vortex, where they pass through a collector and flow out of the top of the degasifier 42 through a degassing relief valve 43.

[0029] The partially treated aqueous stream 46 , which may still contain some methane or other volatile hydrocarbons, flows into a post mixer-injector assembly 50 , which is similar in construction and operation to the lead mixer-injector assembly 24 .

[0030] As with the front mixer-injector device 24, in the rear mixer-injector device 50, the water flow enters a second inline mixer and diffuser combination having a mixer and an injector port, whereby a compressed air flow 52 is injected into the liquid water and mixed, thereby forming small bubbles in the liquid water. As previously described, given that methane and other VOC compounds prefer the air phase rather than the water phase, the resulting turbulence causes methane bubbles to form in the water due to air scrubbing. As with the front mixer-injector device 24, the rear mixer-injector device 50 is provided with a diffuser 53, including a structure covering the fluid flow path and having many small openings / holes or a grid.

[0031] After leaving the post mixer-injector device 50, the mixed phase fluid stream 54 enters the pre-degassing separator 56, which is provided with a post-degassing pressure relief valve 58. The post mixer-injector device 50 and the post-degassing pressure relief valve 58 both have similar structures and operations to the pre-degassing separator 56 and the pre-degassing pressure relief valve 43.

[0032] As with the pre-degassing separator 42, in the post-degassing separator 56, methane is separated from the stream 54 and exits the tower through the post-degassing relief valve 58 as the overhead stream 62. A treated water liquid stream 64 exits from the bottom of the post-degassing separator 56.

[0033] A throttling valve may optionally be provided to reduce the pressure of stream 64 before it enters expander 68, thereby increasing the diameter of the pipe. By way of example only, the expander may expand the diameter of the pipe from 8 inches to 10 inches. Treated water stream 72 exits expander 68 and the system through valve 74.

[0034] although Figure 1The embodiment shown shows front and rear mixer-injector devices and front and rear degassing separators, but alternative embodiments of the system of the present disclosure may include one of each component or more than two of each component.

[0035] Compressed air streams 26 and 52 are filtered, clean and oil-free before use and are provided to the pre-mixer-injector assembly 24 and the post-mixer-injector assembly 50 by compressor 82. Compressed air from the compressor and air receiving tank combination and appropriate oil coalescing filter 82 flows through air line 84, throttle valve 86 and rotameter 88 to form stream 26. Compressed air from compressor 82 also flows through air line 94, throttle valve 96 and rotameter 98 to form stream 52.

[0036] The compressor 82 is designed to operate in an automatic mode and deliver air at the desired pressure and flow rate as needed. The adjustable air rotameters 88 and 98 measure the air flow rate in cubic feet per minute (CFM). By way of example only, the compressor can achieve a flow rate of 200-300 CFM at 100 psi.

[0037] Compressor 82 may optionally be equipped with a storage tank 83 (eg, 240 gallons), a coalescing oil filter, or an oil / water separator (not shown) to manage drain line waste water and / or to help minimize cycling of the compressor and save energy.

[0038] Figure 2 and 3 They are shown separately Figure 1 Perspective and plan views of example equipment layouts of the system, where common reference numerals are used. Figure 2 and 3 Also shown is a wet well 102 to which water may be directed from the pump 12 when the pump is activated.

[0039] Figure 1-3 The test results of the system shown for degassing remediation at various air to water ratios provided by each of the front and rear mixer-injector devices 24 and 50 at water flow rates of 280-300 gallons per minute (gpm) are shown in Table 1 below. In Table 1, "Raw Methane" is the methane content in the raw untreated water in micrograms per liter (ug / L), while "Treatment Methane" is the methane content in the treated water in micrograms per liter (ug / L). In addition, the diffusers of the front and rear mixer-injector devices 24 and 50 each provide a back pressure of 10 psi.

[0040]

[0041] Table 1 – Methane removal at various air to water ratios at 10 psi diffuser back pressure

[0042] Table 2 below lists Figure 1-3 The system in is tested at different air to water ratios for a system with a flow rate of 280-300 gpm of deaerated remediation water, where the diffusers of the pre- and post-mixer-injector devices 24 and 50 provide different back pressures.

[0043]

[0044] Table 2 – Methane removal efficiency at different air to water ratios and back pressures

[0045] As shown in the table above, the preferred ratio of air to water provided by each of the front and rear mixer-injector devices 24 and 50 is in the range of 0.80 to 1.50.

[0046] Embodiments of the present disclosure remove entrained and dissolved methane and other volatile hydrocarbons from water without observing significant changes in non-methane water quality parameters of the treated water stream.

[0047] Additionally, embodiments of the present disclosure provide an in-line process that does not "break" the head pressure of the untreated water stream. Embodiments of the present disclosure also do not have an outlet to discharge the treated water stream at atmospheric pressure. Such embodiments are in contrast to conventional air purge systems and processes and therefore can be used while maintaining pressure in a "closed" system. This reduces energy and equipment costs.

[0048] While the preferred embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications can be made thereto without departing from the spirit of the invention.

Claims

1. A system for separating volatile hydrocarbons from an aqueous stream, comprising: a. a pre-mixer-injector device configured to receive an untreated water stream including volatile hydrocarbons, inject compressed air into the untreated water stream, and mix the injected air with the untreated water stream to form a first injection fluid stream; b. a shear mixing device configured to receive a first injection fluid stream from the mixer-injector device and shear bubbles within the received first injection fluid stream to form a foam stream; c. a pre-degassing separator configured to receive the foam stream from the shear mixing device and separate it into a volatile hydrocarbon stream and a partially treated water stream based on density differences; d. A compressor configured to direct clean, oil-free compressed air to the pre-mixer-injector assembly.

2. The system according to claim 1, further comprising: e. a post-mixer-injector device configured to receive compressed air and a partially treated water stream from a pre-degassing separator, inject the compressed air into the partially treated water stream, and mix the injected air with the partially treated water stream to form a second injection fluid stream, wherein the partially treated water stream from the pre-degassing separator contains residual volatile hydrocarbons; f. A post-degassing separator configured to receive the second injection stream from the post-mixer-injector and separate it into a second volatile hydrocarbon stream and a treated water stream based on density differences.

3. The system of claim 2, wherein the pre-mixer-injector device and the post-mixer-injector device each have a diffuser including a plurality of openings or a grid.

4. The system of claim 2 further comprising a first line reducer located upstream of the pre-mixer-injector device, a first line expander located downstream of the pre-mixer-injector device, a second line reducer located upstream of the pre-degassing separator, and a second line expander located downstream of the post-degassing separator.

5. The system according to claim 2, wherein: The front degassing separator includes a front degassing pressure relief valve, which is configured to open when the pressure of volatile hydrocarbons in the front degassing separator increases, and the rear degassing separator includes a rear degassing pressure relief valve, which is configured to open when the pressure of volatile hydrocarbons in the rear degassing separator increases to above a predetermined level.

6. The system of claim 2, wherein the post mixer-injector device receives compressed air from a compressor.

7. The system of claim 1, wherein the shear mixing device comprises a plurality of flash reactors.

8. The system of claim 1, further comprising a pump configured to direct an untreated water flow to the pre-mixer-injector device.

9. The system of claim 1, further comprising a line reducer located upstream of the pre-mixer-injector device and a line expander located downstream of the pre-mixer-injector device.

10. The system of claim 1, wherein the front degassing separator comprises a front degassing pressure relief valve configured to open when the pressure of the volatile hydrocarbons in the front degassing separator increases.

11. The system according to claim 1, wherein: The pre-mixer-injector device includes a diffuser having a plurality of openings or grids.

12. The system of claim 1 further comprising a throttle valve located downstream of the front gas separator.

13. A method for separating volatile hydrocarbons from an aqueous stream, comprising the steps of: a. Injecting compressed air into an untreated water stream; b. mixing the compressed air with the untreated water stream to form a first injection fluid stream; c. shearing the bubbles within the first injected fluid flow, thereby forming a foam flow; d. Separating the foam stream into a volatile hydrocarbon stream and a partially treated water stream based on density differences.

14. The method according to claim 13, further comprising the steps of: e. injecting compressed air into a portion of the treated water stream; f. mixing the compressed air and the partially treated water stream to form a second injection fluid stream; g. Separating the second injection fluid stream into a volatile hydrocarbon stream and a treated water stream based on density differences.

15. The method of claim 14, wherein the ratio of air to water in step a. and step e. is in the range of 0.80 to 1.

50.

16. The method of claim 13, wherein the volatile hydrocarbon comprises methane.

17. The method of claim 13, further comprising the step of throttling the treated water stream.

18. The method of claim 13, further comprising the step of pumping untreated water prior to step a.

19. The method of claim 18, wherein the untreated water is well water or ground water.

20. The method of claim 13, wherein the ratio of air to water in step a. is in the range of 0.80 to 1.50.

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