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, including 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 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 providing passage through the wall of said pipeline; b. extending from said housing first and second plates spaced in parallel alignment into said gas stream from said housing, allowing said gas stream to pass therebetween; c. extending from said housing a container structure formed to engage said first and second plates, to contain a fluid sample of said gas stream between said first and second plates, providing a contained fluid sample; d. retracting into said housing said container and said first and second plates 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 said barrier is affixed to a moveable 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 al 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 al 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 an opening providing passage through the wall of said pipeline; first and second aligned plates forming a collection area therebetween, said first and second plates supported by a first vertical support; a container formed to engage said first and second plates to selectively contain fluids situated between said first and second plates when said first and second plates are positioned in said gas stream, said container supported by a second vertical support, said container with said first and second plates formed to selectively fit within said housing; said first and second plates situated for alignment with the flow of said gas stream to minimize disturbance of said flow of said gas stream therebetween; a heater associated with said housing to selectively heat said enclosed sample container engaging said first and second plates, so as to treat any fluids contained 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 so as to selectively block the opening of said housing at said pipeline in association with the positioning of said sample container, so as to provide a streamlined flow thereby.

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 at said sample container, 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. 1A is an end, partially cut-away view of the invention of FIG. 1, wherein the housing is a probe and the sample container is selectively lowered/raised from the probe tip into/from the process gas stream.

(4) FIG. 2 is a 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.

(5) 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.

(6) 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.

(7) 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 lowered from a housing into a source fluid 26 in a pipeline at an approximate 90 degree angle from the direction of fluid flow.

(8) 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 a top plate and bottom plate to form a sample housing, enclosing a sample of the homogenized gas from the gas stream.

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

(10) FIG. 7A is an end, partially cut-away view of the invention of FIG. 5, wherein the housing is a probe and the sample collector is selectively lowered/raised from the probe tip into/from the process gas stream.

(11) FIG. 7B is an end, partially cut-away view of the invention of FIG. 7, wherein the sample housing is selectively lowered/raised from the a probe having a probe tip into/from the process gas stream.

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

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

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

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

(16) 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.

DETAILED DISCUSSION OF THE INVENTION

(17) Referencing FIGS. 1 and 2-3, 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.

(18) 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.

(19) 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.

(20) The sample 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.

(21) Since container 3 is open-ended and in 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.

(22) Referencing FIGS. 1 and 2-4, 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′, closures or the like engaging open ends 41, 41′ respectively, providing a sealed container having the gas/liquid droplet sample situated therein.

(23) 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 47 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 preferably by external actuation means (not shown) attached to support 5.

(24) 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.

(25) 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.

(26) 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.

(27) 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.

(28) 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.

(29) 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.

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

(31) 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.

(32) FIG. 1A illustrates an alternative embodiment of the invention of FIG. 1, wherein container 3 of the sampling cylinder is lowered and raised via sampling support 5 through the probe tip 60 and passageway 61 of a probe 62, in this embodiment, the probe forming the housing 63 or enclosure for the sample cylinder. Other features enumerated in the embodiment of FIG. 1 may likewise be present in this alternative embodiment, such as a heated 10′ probe passageway. Also, a barrier associated with the support 5 may be provided (similar to operation as barrier 1 in the discussion of FIG. 1, infra).

(33) The sampling collection cylinder or container profile as 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-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.

(36) The fluids are heated sufficiently to vaporize and homogenize them thoroughly. Said homogenized, vaporized sample fluid/gas can then be moved to an external location for storage or analysis by a sample conduit, for example.

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

(38) FIGS. 7A and 7B illustrate an alternative embodiment of the invention of FIG. 5, wherein the housing 17 and support structure 24 is lowered and raised through the probe tip 65 and passageway 66 of a probe 67, in this embodiment, the probe forming the enclosure for housing 17. The other elements shown 13, 16, 19, 20, 21 are described infra in the discussion of FIG. 5 et seq. Other features enumerated in the embodiment of FIGS. 5-7 and 8A-8D, may likewise be present in this alternative embodiment, including a heated area 10″, having similar operational principals as heated zone 10 infra.

(39) Continuing with 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.

(40) 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.

(41) 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 FIG. #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.

(42) 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°.

(43) 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.

(44) 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 orifice plate which is equal to D2/D1. Using orifice plate analogy the sample collection zone would probably be in the vena contracta zone.

(45) 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.

(46) 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.

(47) Helmholtz Cavity Dimensions

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

(49) $\mathrm{fr}=\frac{c}{2\pi }\sqrt{\frac{\pi r^2}{l_{\mathrm{eff}}^v}}$
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

(50) 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.

(51) 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.

(52) 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).

(53) TABLE-US-00001 Exemplary Specification Ranges ID of pipe 2″ to 30″ Pressure 30 PSIG to 5,000 PSIG Temperature 50° F. to 120° F. Flow rate 10,000 cubic feet per day to 1 billion cubic feet per day Velocity of gas 10 feet per second to 100 feet per second Ratio of gas to entrained 99:1 to 99.9:1 liquid range Constriction member 0.5 to 0.99 constriction of pipe ID

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

(55) 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

(56) 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 28 pipeline 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

(57) 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.