Wet natural gas sampling method and apparatus therefore

Abstract

A system for on-stream sampling of pressurized process gas such as natural gas or the like, said pressurized process gas having liquid entrained therein, or otherwise referenced as wet. The preferred embodiment of the present invention contemplates a system for obtaining an accurate sample of said wet process gas, as well as providing an apparatus for obtaining same.

Claims

1. The method of sampling a gas stream having entrained liquid therein in a pipeline, comprising the steps of: a. providing a housing having a length and a width, and an opening formed through the wall of said pipeline, so as to provide access to said gas stream having liquid entrained therein; b. extending from said housing first and second spaced plates into said gas stream from said housing, said first and second spaced plates oriented so as to allow said gas stream to pass therebetween in relatively unobstructed fashion to minimize flow disturbance, providing isokinetic flow therebetween; c. extending from said housing a container having an open bottom formed to envelope said first plate and engage said second plate, so as to contain a fluid sample of said gas stream between said first and second plates, providing a contained fluid sample; d. simultaneously retracting into said housing said container and said first and second plates enveloping said fluid sample into said housing, while maintaining said contained fluid sample therein.

2. The method of claim 1, wherein there is further provided after step d the added step e of heating said contained fluid sample to vaporize the sample fluid contents therein, providing a vaporized sample.

3. The method of claim 2, wherein there is further provided after step e the added step f of analyzing said vaporized sample.

4. The method of claim 3, wherein there is further provided after step b the added step b1 of blocking the opening of said housing at said pipeline with a barrier having the profile of the inner diameter of the pipeline, so as to streamline the area for the sampling operation.

5. The method of claim 4, wherein in step b1 there is further provided the step of positioning said barrier utilizing a support.

6. The method of claim 1, wherein said gas stream has a velocity, and wherein there is provided after step a the added step a1 of dispersing entrained liquid in said pipeline into liquid droplets, while utilizing the velocity of said gas stream to suspend said droplets in said gas stream, so as to form a sample zone downstream therefrom.

7. The method of claim 6, wherein in step a1 said entrained liquid is dispersed into liquid droplets by utilizing a plurality of Helmholtz resonator cavities formed in an inner surface in contact with the flowing gas to create sonic energy such that liquid flowing thereover would disperse into droplets suspended by said gas stream.

8. An apparatus for sampling a gas stream having entrained liquid therein in a pipeline, comprising: a housing having a length and a width, and an opening formed through the wall of said pipeline, so as to provide access to said gas stream having liquid entrained therein; first and second aligned plates forming a collection area therebetween, said first and second plates supported by a first vertical support, said first and second aligned plates formed to selectively fit within said housing; a container formed to slidingly envelope said first plate and engage said second plate so as to contain fluids situated between said first and second plates in said gas stream, so as to provide sample containment therebetween; whereby, said container and said first and second plates are formed to be simultaneously repositionable from said fluid stream to said housing, while maintaining sample containment therein.

9. The apparatus of claim 8, wherein there is further provided a barrier having the profile of the inner diameter of the pipeline, said barrier formed to selectively block the opening of said housing at said pipeline, so as to provide a streamlined flow.

10. The apparatus of claim 8, wherein upstream said gas stream from said housing there is provided an apparatus for dispersing entrained liquid into liquid droplets suspended by said gas stream, so as to form a sample zone downstream, comprising: a slope having an end engaging said inner wall of said pipeline, said slope having a plurality of Helmholtz resonator cavities formed thereon in contact with said gas stream so as to facilitate the creation of sonic energy such that liquid flowing thereover would disperse into droplets suspended by said gas stream.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein:

(2) FIG. 1 is an end, partially cut-away view of the first embodiment of the sample collection system present invention, illustrating a cylindrical sample container which has been lowered from a housing into a pipeline containing a process gas stream containing entrained liquid.

(3) FIG. 2 is a first side, partially cut-away view of the invention of FIG. 1, illustrating a sample collection container lowered from a housing into a process gas stream, providing a container having sample gas containing entrained liquid therein.

(4) FIG. 3 is a side, partially cut-away view of the invention of FIG. 1, wherein the container having said sample gas therein is raised into the housing, and sealed via plugs or the like.

(5) FIG. 4 is a side, partially cut-away view of the Invention of FIG. 1, wherein the sealed container having said sample gas therein is positioned within the housing into a heating zone to heat the container and sample gas contained therein so as to vaporize the liquid entrained in said sample gas, rendering the sample entirely in gas phase.

(6) FIG. 5 is an end, partially cut-away view of the second embodiment of the sample collection system of the present invention, illustrating a support structure comprised of vertical support 19, top plate 13 and bottom plate 16 is lowered from a housing into a source fluid 26 in a pipeline at an approximate 90 degree angle from the direction of fluid flow.

(7) FIG. 6 illustrates a homogenized mixture of small liquid droplets 7 suspended in a gas stream at a collection area where the collection device is positioned, the Figure further illustrating a sample housing which is lowered from the housing to engage top plate 13 and bottom plate 15 to form a sample housing, enclosing a sample of the homogenized gas from the gas stream.

(8) FIG. 7 illustrates a frontal close-up view of the sample housing of FIG. 6.

(9) FIG. 8A is an isometric view of the sample housing of FIG. 6.

(10) FIG. 8B is an end view of the sample housing of FIG. 6.

(11) FIG. 8C is a side view of the top plate 13, vertical support 19 and bottom plate 16 of FIG. 5.

(12) FIG. 8D is an end view of the top plate 13, vertical support 19 and bottom plate 16 of FIG. 8C.

(13) FIG. 9 is a side view of a device to break up entrained liquid in the gas stream for use in the system of the present invention, converting same into small liquid droplets, providing an area suitable as a collection zone wherein there is provided a homogenized gas and liquid droplet fluid stream.

(14) FIG. 9A is a side, partially cut-away view of the device of FIG. 9 situated within a first custom fabricated spool piece configured to enhance the disbursing of liquid into small droplets, then homogenize the liquid droplets.

(15) FIG. 10A is a third embodiment of the present invention, incorporating elements of the first and second embodiments supra, the present figure illustrating a side, partially cut-away view of a multi-port configuration sample collection container positioned in a process gas stream having liquid droplets entrained therein, the sample collection ports configured therein for sampling of same, so as to contain the collected sample.

(16) FIG. 10B is a side, partially cut-away view of the invention of FIG. 10A, illustrating the step of positioning a housing into the process gas stream so as to envelope the sample collection container containing the collected sample.

(17) FIG. 10C is a side, partially cut-away view of the invention of FIGS. 10A-10B, illustrating the housing enveloping the sample collection container with sample repositioned into secondary housing exterior the process gas stream for further processing and/or retrieval of the collected sample.

DETAILED DISCUSSION OF THE INVENTION

First Embodiment of the Invention

(18) Referencing FIGS. 1-3, a first embodiment of the collection system of the present invention utilizes an open ended container 3, illustrated in the form of a cylinder 40 having first 41 and second 41 ends, a length 42 having a longitudinal or central axis 42, and a passage 44 formed longitudinally therethrough.

(19) The container 3 is mounted to a support/positioning system (further discussed herein) to selectively extend 45 from housing 9 into pipeline 11, positioning the container to allow the unencumbered passage therethrough of a portion of gas or gas/liquid droplet fluid stream 12 with nominal disturbance, said container central axis of said container in alignment with the direction of gas/liquid flow 4. As shown, the housing 9 is mounted to pipeline 11, providing opening 43 into pipeline 11.

(20) The container 3 is constructed of thin wall material, to provide nominal interference with the gas stream, and is suspended by a thin support 5 which is engages the container slightly downstream from its open entry end 6, so as to provide a streamlined attachment surface and overall profile that will minimize the likelihood of appreciable liquid particle flow disturbance.

(21) The collection cylinder or container 3 volume will range from approximately 0.2 cubic inch to 15 cubic inch, depending on sample size required, source fluid pressure, and pipe ID.

(22) Since container 3 is open-ended and in longitudinal alignment with the flow stream, the gas/liquid flow rate through should be the same as the fluid flowing outside of said container 3. Therefore, the flow can be said to be isokinetic within container 3.

(23) Referencing FIGS. 3 and 4, a short time after the container 3 is suspended in the gas/liquid flow, it is withdrawn or retracted 46 into housing 9, whereupon the open ends 41, 41 of container 3 are sealed, for example via plugs 8, 8 engaging open ends 41, 41 respectively, providing a sealed container having the gas/liquid droplet sample situated therein.

(24) The sealed container is then heated by a heater (for example, electric resistance or thermoelectric heater, or hydrocarbon fueled heater, or the like) in heating zone 10 in the housing so as to vaporize all entrained liquid in the sealed container, so as to render the sample into a single (gas) phase. The gas is then made to flow 48 via a sample line or the like (not shown) into an external analyzer and/or sample storage container 49 for analysis. Insertion and retraction of container 3 is by external actuation means (not shown) attached to support 5.

(25) To obtain a second sample, the container 3 is unsealed to open its first and second ends (by removing plugs 8, 8, in this example) and container 3 is again extended 50 into the flowing fluid stream 12 to be sampled, where the container thermally interacts with the gas stream to reach temperature equilibrium with same, to refill with a fresh sample of gas/liquid droplets before being withdrawn to begin a new cycle.

(26) Referring to FIG. 1, when fully extended into the fluid source, the sampling support 5 can be formed so as to provide a barrier 1 emanating therefrom, positioned so as to close off the opening of the pipe at the housing, so as to minimize fluidic disturbance/turbulence while providing a streamlined fluid flow path through the sample area in the pipeline during sampling.

(27) Referring to FIG. 1, the opening where housing 9 meets the pipeline may be selectively blocked via a barrier 1 having the profile 2 (in the present example, a radial profile) of the pipeline 11, so as to minimize disturbance in the process stream during the sampling operation when the barrier is in place. The barrier 1 may be affixed to the support 5 to raise or lower same as it is raised or lowered, as above, or may be provided in the form of a trap door which is pivotally affixed to the inner walls of the housing, for example.

(28) The present system thereby provides an static isokinetic process wherein the container obtains a sample under isokinetic fluid flowing conditions, but the sampled fluid flow ceases as the cylinder is withdrawn from the flowing fluid stream and sealed in the sample container. The static sample is then made into a single phase (gas) by heating under the existing static condition, as discussed above.

(29) This static isokinetic sampling process differs from other forms of isokinetic sampling. Conventional dynamic isokinetic sampling is designed to insure an isokinetic fluid flow into the opening of a probe and thereon to an external location. The fluid stream velocity (in dynamic systems) must be known and the fluid velocity entering the probe must be controlled, an impractical approach for traditional field sampling of fluids.

(30) In contrast, in the static isokinetic sampling process, as a volume of the source fluid flowing through a conduit or pipeline is captured by a container suspended in said source fluid, and as the flow rate during capture remains unchanged, no flow rate measurement or control is required. Said container and trapped source fluid is then withdrawn and isolated in a location outside of the source fluid flowing stream. The fluid is thus isokinetically sampled and withdrawn from the source in a static mode.

(31) The present system insures that container 3 will always be filled isokinetically, even when pipeline velocities are rapidly changing.

(32) This apparatus may also be utilized to advantage even when HC liquids are present. High HC dew point gases are difficult to sample dynamically due to phase changes and resulting composition changes which can be triggered by flow, pressure, and/or temperature.

Second Embodiment of the Invention

(33) The profile of the sampling cylinder of the first embodiment illustrated is round, but other geometric shapes would not alter the underlying concept. Accordingly, said static isokinetic sampling method may also be executed by other means.

(34) For example, in FIGS. 5, 6, 7, 8a, 8b, 8c, 8d, a support structure 24, comprised of vertical support 19, top plate 13 and bottom plate 16 is extended 51 into the source fluid 26 at an approximate 90 degree angle from the direction of fluid flow.

(35) After a brief period sample housing 17, refer to FIGS. 5, 6, and 7, is extended 52 to envelope the area between the first 13 and second 16 plates of support structure 24, with lateral edge 22 engaging the side of first plate 13 distal second plate 16, so as to trap a sample of fluid 26 containing a proportion of liquid droplets 7 therein, providing a contained sample 53. The sample housing 17 and support structure 24 are then retracted 54 into heated zone 10 located in housing 27. The fluids are heated sufficiently to vaporize and homogenize them thoroughly. Said homogenized sample fluid can then be moved to an external location for storage or analysis by a sample conduit, for example.

(36) Retraction and insertion of the actuation members 20, 21 positioning sampling housing 17 and support structure 24 is by external actuation means (not shown).

The Conditioning Apparatus

(37) Referring to FIG. 9, where the gas stream contains liquid not in droplet form, such as liquid flowing along the inner wall or at the bottom of the pipeline, the system of the present invention requires that, prior to collection of the sample via the above apparatus, this liquid must be broken into small droplets, in order to provide a collection zone wherein there is provided the desired gas and liquid droplet mixture.

(38) Traditional static mixers are not well suited for this task. The liquid must first be divided into small droplets, suspended into a flowing gas stream and directed away from the inner wall surface of the pipeline. Under those conditions a sample taken across the cross-section of the pipeline will represent both the gas and liquid phases. It is important that liquid is not flowing along the inner pipe wall or at the bottom of the pipeline in the sample area.

(39) Where the gas stream to be sampled requires conditioning to break up the entrained liquid into small droplets, the present invention provides a conditioning apparatus which is provided upstream of the collection area, situated in line with the gas stream to receive the gas stream, and having a downstream exit having a sloped constriction 29 and 29 (Refer to Figure #9) wherein the fluid flows in direction 4, said constriction 29 terminating with a sharp lip 30 and 30 to break up entrained liquids 32 and 33 into droplets 7 by the force and turbulence of the flowing gas. In the present example, the lip is at a 90 angle relative to the fluid flow and will range from 0.05 to 0.5 in height.

(40) Said lip 30 may be geometrically shaped or having a surface composition (via coating for example) to enhance droplet 7 formation. Sloped constriction of conduit wall 35 of the conditioning apparatus will force liquid 32 and 33 away from the inner pipe wall 35 downstream from said lip 30. The constriction member slope relative to the inner pipe wall will range from 5 to 45.

(41) By breaking up the entrained fluid into suspended droplets to homogenize same into the gas stream, even if within a limited sampling zone 31, one is able to obtain a sample within that sampling zone 31 containing the correct proportion of liquid.

(42) In comparing the constriction to orifice plate flow measurement the maximum constriction ID would be D2 and the pipe ID would be D1. The fractional constriction referenced above is equal to the Beta ratio of an orfice plate which is equal to D2/D1. Using orfice plate analogy the sample collection zone would probably be in the vena contracta zone.

(43) Droplets which are already suspended in the flowing gas before entering sloped constriction 29 and 29 flow into the sampling zone 31 without alteration. Sampling is preformed in sampling zone 31 at an optimum distance downstream of the droplet formation area. Other techniques may be utilized to achieve droplet formation of entrained liquid.

(44) An example is utilizing a plurality of Helmholtz resonator cavities 37 formed in an inner surface in contact with the flowing gas to create sonic energy sufficient to promote droplet formation. Said sonic energy of ultrasonic frequency is a well known method for breaking up a flowing liquid into small droplets. Other types of cavities and methods for producing sonic energy by using the flowing fluid may also be employed in that manner. An external source for vibrating the inner pipe wall, not shown, may also be utilized to aid in droplet formation.

Helmholtz Cavity Dimensions

(45) The following formula will be utilized to produce ultrasonic energy in the range of 20 KHz to 100 KHz.

(46) $\mathrm{fr}=\frac{c}{2}\sqrt{\frac{r^2}{l_{\mathrm{eff}}^v}}$
Where:
fr=resonance frequency of each cavity
c=speed of sound
r=radius of the cavity neck
leff=effective length of the neck
v=volume of the cavity

(47) Helmholtz cavities have a neck and a cavity which may be constructed by overlaying perforated plates in which the holes in a first plate comprises the cavity neck and the holes in a second place comprise the cavity volume. When two such plates are in alignment and placed over a third plate which is unperforated, a plurality of Helmholtz cavities are created.

(48) A combination of methods may be utilized for breaking up entrained liquid into small droplets. Droplet size requirement will depend upon the gas velocity. Gas velocity should be sufficient to maintain suspension of the liquid droplets beyond the static isokinetic sampling point.

(49) Accordingly, prior to specimen collection, the entrained liquid is first broken into small droplets 7 then homogenized into the gas stream 12 (as discussed above).

The Spool Piece

(50) Referring to FIG. 9A, a spool piece may be provided to further enhance the disbursing of liquid into small droplets, as well as homogenizing same. This spool piece may have customized dimensions, or may be standardized, depending upon the installation.

(51) As shown, the spool piece has first 81 and second 81 ends with a main body 83 therebetween. The first end 81 is frustoconical, tapering from a wide diameter commensurate with the process gas pipe so as to engage same so that the gas flow enters via said first end, said first end then narrowing to a lesser diameter to that of the main body having the conditioning apparatus C therein.

(52) The configuration of the first end tapering to the lesser diameter main body thereby increases the velocity of the fluid flowing therein, so as to facilitate enhanced operation of the conditioning apparatus and more effective break-up or disbursement of liquid droplets therein.

(53) As shown, the second end 81 of the spool piece may taper in frustoconical fashion from narrow at the main body to wide at the second end so as to engage the downstream passage, or alternatively, a collection system such as that described herein, at the appropriate diameter.

Third Embodiment

(54) Referencing FIGS. 10A-10C, a third embodiment 61 of the collection system of the present invention has a flow through portion comprising first 81 and second 81 ends, the first 81 end for receiving the flow and the second forming the exit back to the pipeline or other containment means, the first end shown tapering from wide to narrow in frustoconical fashion so as to increase velocity where necessary, the second 81 end shown tapering from narrow to wide to allow egress of the gas stream to the destination pipeline or the like. The tapered or frustoconical or tapered ends 81, 81 may not be required for all situations, such as where an increase in fluid velocity is undesirable or where the diameter of the pipeline to be interfaced is uniform with the present system.

(55) The collection system of the present embodiment comprises a sample unit 62 having sample ports 63, 63, 63 situated along its length, the sample unit 62 shown in the form of a rod 65 having a width 66 and a length 66, with lateral bores 64, 64, 64 therethrough forming sample ports 63, 63, 63 respectively having a central axis 72, each forming a passage formed in axial alignment with the flow 67 of the process gas 68 passing therethrough (when positioned in the process gas for sampling), so as to minimize turbulence.

(56) Like the first embodiment, the sample unit is integrated with a insertion/retraction system (further discussed herein) to selectively extend 69 the sample unit 62 into the process gas 68 flow stream, positioning the sample unit to facilitate the selective sampling of the process gas.

(57) The sample port 63, 63, 63 volume will range from approximately 0.2 cubic inch to 1.0 cubic inch, for example, depending on sample size required, source fluid pressure, and pipe ID.

(58) Since each sample port 63, 63, 63 has a flow through configuration wherein each port's central axis is in longitudinal alignment with the flow stream, the gas/liquid flow rate of the process gas flow stream through each sample port should be about the same as the fluid flowing outside of said sample unit. Therefore, the flow can be said to be isokinetic through said sample ports forming said sample unit.

(59) Continuing with FIGS. 10A-10B, during sampling, after the sample unit has been extended into the gas stream for a period of time to collect the sample, a cylindrical housing 70, shown (in phantom) in FIG. 10A situated in an outer housing 73 outside of the flow stream, is configured to extend 69 into the flow stream and about sample unit, via compressed spring 76 in spring housing 77, selectively released via latching solenoid 78. The housing 70 is thus extended into the fluid source (as shown in FIG. 10B) and about sample 62 unit so as to envelope and provide sealed containment about said sample unit 62 (shown in phantom in FIG. 10B).

(60) A base 71 may be provided at the end of the sample unit distal the retracted housing, said base formed to engage the end of the housing 70 so as to form an enclosure contain the sample ports and any sample fluid associated therewith.

(61) As shown in FIGS. 10B and 10C after the housing 70 has been extended 69 to contain the sample unit and any fluid sample associated therewith, the contained sample unit 62 with housing 70 engaging base 71 is retracted, for example, via threaded rod 74 engaging sample unit 62, which threaded rod is rotated utilizing a motor (not shown) engaging worm gear shaft 75. The retracting sample unit 62 with base 71 retracts the housing 70 out of the fluid stream and into outer housing 73, while compressing spring 76, which is latched via latching solenoid 78 for selective deployment at a later time.

(62) The outer housing includes a heater cylinder 80 formed to heat the sample contained in housing 70 so as to vaporize all entrained liquid in the sealed container formed by housing 70 engaging sample unit 62 via and base 71, so as to render the sample into a single (gas) phase. The gas is then made to flow via a sample line or the like (not shown) into an external analyzer and/or sample storage container for analysis.

(63) Referencing FIGS. 10A and 10C, in an alternative embodiment of the invention, the sample unit 62, after being situated in the gas stream for a period of time so as to collect as gas/liquid droplet sample therein, is retracted 69 out of the gas stream and into housing 70, so that base 71 seals the open end 79 of housing, providing a sealed container having the gas/liquid droplet sample situated therein.

(64) The sealed container is then heated by a heater 80 (for example, electric resistance or thermoelectric heater, or hydrocarbon fueled heater, or the like) in so as to vaporize all entrained liquid in the sealed container, so as to render the sample into a single (gas) phase. The gas is then made to flowed via a sample line or the like (not shown) into an external analyzer and/or sample storage container for analysis. Insertion and retraction of sample unit is via threaded rod 74 and worm gear 75 as discussed supra.

(65) Once the housing containing the sample unit and sample is heated and the sample is obtained in gas phase, to obtain a second sample, the sample unit is extended 69, the base 71 disengaging from the end 79 of housing 70, providing the uncontained sample unit 62 into the flowing fluid stream to be sampled, where the container thermally interacts with the gas stream to reach temperature equilibrium with same, to refill with a fresh sample of gas/liquid droplets into sample ports 63, 63, 63 before being withdrawn to begin a new cycle.

Exemplary Specification of the Invention

(66) ID of pipe 2 to 30

(67) Pressure 30 PSIG to 5,000 PSIG

(68) Temperature 50 F. to 120 F.

(69) Flow rate 10,000 cubic feet per day to 1 billion cubic feet per day

(70) Velocity of gas 10 feet per second to 100 feet per second

(71) Ratio of gas to entrained liquid range 99:1 to 99.9:1

(72) Constriction member 0.5 to 0.99 constriction of pipe ID

(73) Vertical supports are constructed of steel, typically stainless steel and range in thickness from 0.02: to 0.10.

(74) The leading edge of the cylinder, upper and lower plates, and supports may be sharpened so as to minimize fluid flow disturbances.

LISTING OF ELEMENTS

(75) 1 barrier 2 radial profile 3 container 4 direction of flow 5 support 6 open entry end 7 small droplets 8 plugs 9 housing 10 heating zone 11 pipeline 12 fluid stream 13 top plate 14 lowered 16 bottom plate 17 sample housing 18 pipe wall 19 vertical support 20 actuation member 21 actuation member 22 lateral edge 24 support structure 26 source fluid, fluid sample (added verify) 27 housing 29, 29 sloped constriction 30, 30 sharp lip 31 sampling zone 32 entrained liquid 33 entrained liquid 35 pipe wall 36 droplets 37 helmholtz resonator cavities 40 cylinder 41 first end 41 second ends 42 length 42 central axis 43 opening 44 passage 45 external 46 retract 47 gas 48 flow 49 container 50 extended 51 extended 52 extended 53 contained sample 54 retracted 61 third embodiment 62 sample unit 63,, sample ports 64,, lateral bores 65 rod 66, length, diameter 67 flow 68 process gas 69, extend, retract 70 housing 71 base 72 central axis 73 outer housing 74 threaded rod 75 worm gear 76 compressed spring 77 spring housing 78 latching solinoid 79 end of housing 80 heater cylinder 81 first second ends 82 spool piece

(76) The invention embodiments herein described are done so in detail for exemplary purposes only, and may be subject to many different variations in design, structure, application and operation methodology. Thus, the detailed disclosures therein should be interpreted in an illustrative, exemplary manner, and not in a limited sense.