GB2268265A - Optical detection of liquid dew-point of a gas stream. - Google Patents
Optical detection of liquid dew-point of a gas stream. Download PDFInfo
- Publication number
- GB2268265A GB2268265A GB9312781A GB9312781A GB2268265A GB 2268265 A GB2268265 A GB 2268265A GB 9312781 A GB9312781 A GB 9312781A GB 9312781 A GB9312781 A GB 9312781A GB 2268265 A GB2268265 A GB 2268265A
- Authority
- GB
- United Kingdom
- Prior art keywords
- point
- dew
- liquid
- gas
- ratio
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000007788 liquid Substances 0.000 title claims abstract description 26
- 230000003287 optical effect Effects 0.000 title claims abstract description 12
- 238000001514 detection method Methods 0.000 title claims description 8
- 230000005540 biological transmission Effects 0.000 claims abstract description 11
- 238000005259 measurement Methods 0.000 claims abstract description 7
- 238000000034 method Methods 0.000 claims description 13
- 238000010521 absorption reaction Methods 0.000 claims description 8
- 239000012530 fluid Substances 0.000 claims description 7
- 238000012544 monitoring process Methods 0.000 claims description 5
- 238000005191 phase separation Methods 0.000 claims description 2
- 238000011896 sensitive detection Methods 0.000 claims description 2
- 230000003247 decreasing effect Effects 0.000 claims 1
- 239000007789 gas Substances 0.000 abstract description 31
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 7
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 abstract description 6
- 239000003345 natural gas Substances 0.000 abstract description 3
- 238000009833 condensation Methods 0.000 description 5
- 230000005494 condensation Effects 0.000 description 5
- 230000000007 visual effect Effects 0.000 description 4
- 239000000203 mixture Substances 0.000 description 3
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 2
- 239000002826 coolant Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 239000003570 air Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000000859 sublimation Methods 0.000 description 1
- 230000008022 sublimation Effects 0.000 description 1
- 230000002277 temperature effect Effects 0.000 description 1
- 230000001052 transient effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3554—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for determining moisture content
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/56—Investigating or analyzing materials by the use of thermal means by investigating moisture content
- G01N25/66—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point
- G01N25/70—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point by varying the temperature of the material, e.g. by compression, by expansion
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/26—Oils; Viscous liquids; Paints; Inks
- G01N33/28—Oils, i.e. hydrocarbon liquids
- G01N33/2811—Oils, i.e. hydrocarbon liquids by measuring cloud point or pour point of oils
Landscapes
- Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Immunology (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Pathology (AREA)
- Biochemistry (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Food Science & Technology (AREA)
- Medicinal Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
The liquid dew-point of a gas stream 1 is measured directly. Regular measurements of the dew-point are performed by measuring the optical transmission of an amount of gas tapped from a gas-transport line 9. The ratio of the intensities at two different wavelengths is measured as a function of temperature. The temperature is changed until this ratio abruptly changes, which gives an indication of dew-point. Two narrow-band filters centred on 1.89 mu m and 1.98 mu m we disposed in front of respective modulated sources 3 (or detectors). The temperature of the sample tube 1 is ramped between +3 DEG C to -20 DEG C by a jacket 2. The invention is applicable to measuring the water dew-point of natural gas. <IMAGE>
Description
A METHOD AND APPARATUS FOR IDENTIFYING A CHANGE
IN PHASE OF ONE COMPONENT IN A MULTI COMPONENT
(GAS/LIQUID) FLUID SYSTEM
The present invention relates to a method and apparatus for identifying a change in phase of one component in a multicomponent (gas/liquid) fluid system.
In particular, the invention relates to a method and apparatus for measuring the liquid dew-point of a gas sample.
More in particular, the invention relates to the measurement of the water dew-point or changes in the dew-point properties of a hydrocarbon gas stream, e.g. (high pressure) natural gas.
A variety of devices based upon the principle of detecting the presence of dew on a cooled surface, for example a mirror, by means of light reflection techniques, are currently available for the determination of the water dew-point of gas streams, particularly humid air streams. Humid air is essentially a two-component mixture consisting of a single condensable component in, for all practical purposes, an incondensable carrier. However, it appeared that their performance is not always reliable and accurate.
In order to obtain an accurate indication of the dew-point it is necessary to meet pre-determined requirements as to temperature and pressure and it will be necessary to present a gas sample to be investigated under controlled conditions to the detector.
The most successful of current devices for complex mixtures of gases are those based on the visual observation of condensation or dew on a cooled plane-mirror surface. Their sensitivity is poor, however, and the observation and interpretation of visual condensation formation is subjective and susceptible to operator bias or mis-reading.
Initial work using this principle, but with electronic detection of the change in light reflectance, showed that the signal obtained was noisy, transient and unreliable. Condensed water is relatively easy to detect as it condenses in a drop-wise manner, but complex mixtures of gases that condense with much lower contact angles quickly form a film on the surface thus restoring reflection.
Further, it has already been proposed to use prismatic devices involving visible or infra-red light which rely on the principle of total internal reflection in the absence of a liquid or other medium on the surface. The presence of liquid or other medium on the surface allows light to escape and reduces the intensity of the return beam. Such an imbalance can be used to signal dew-point when condensed liquid forms on the surface and the change in light intensity can be amplified to drive suitable indicating recorders and relays.
Thus, it is an object of the invention to provide a method and an apparatus for detecting directly water dew-point of gas streams which gives reliable and reproducible results, thus avoiding the influence of contamination e.g. by glycol.
The invention therefore provides a method for identifying a change in phase of one component in a multicomponent (gas/liquid) fluid system by direct regular measurement of liquid dew-point of a gas sample, comprising the steps of:
supplying a gas sample, tapped from a flow line, to an optical dew-point detection device based upon the transmission of a light beam to a detector and monitoring the optical transmission for the reduction associated with absorption by the intervening gas atmosphere;
measuring the intensity I of light of two specific different wavelengths (X1, 2) and doing this simultaneously and regularly at numerous different temperatures;
thereby measuring regularly the ratio I(A11 at several
I(A2) temperatures; and
deriving the indication of liquid dew-point from an abrupt change of said determined intensity ratio.
The invention further provides an apparatus for identifying a change in phase of one component in a multicomponent (gas/liquid) fluid system by direct regular measurement of liquid dew-point of a gas sample, comprising:
means for supplying a gas sample from a flow line to an optical dew-point detection means based upon transmission of a light beam to a detector and monitoring the optical transmission for the reduction associated with absorption by the intervening gas atmosphere;
means for measuring the intensity I of light of two specific different wavelengths (A 2) and doing this simultaneously and regularly at numerous different temperatures;
means for measuring regularly the ratio I(A1) at several 1(A2) temperatures; and
means for deriving the indication of liquid dew-point from an abrupt change of said determined intensity ratio.
The method and apparatus of the invention are based upon the principle of transmission of a light beam from a light source to a remote detector and monitoring the optical transmission for the reduction associated with absorption by the intervening gas atmosphere and the identification of a reduction in the absorption by the species whose condensation is being monitored, e.g. water.
The principle of such detection is known as such to those skilled in the art and will not be described in detail.
The invention will now be described by way of example in more detail with reference to the accompanying drawings in which:
fig. 1 represents schematically the principle of the method and apparatus of the invention;
fig. 2 represents an advantageous embodiment of the invention; and
fig. 3 represents a graph of the results obtained by the invention.
Referring to fig. 1, a gas sample (e.g. natural gas) is taken in any way suitable for the purpose from a flow line (not shown for reasons of clarity) and flows (e.g. at a pressure of about 100 bar) into the tube 1 (shown in longitudinal section) which is provided with a temperature control jacket 2. On completion of the measurement the gas sample is vented or re-injected in any suitable manner to the flow line (not shown for reasons of clarity).
Advantageously, the tube 1 has a length of 1 metre and a diameter of 2.5 cm.
A (modulated) light source 3 transmits light through the tube 2 to two detectors 4a and 4b respectively, which are provided with wavelength selection narrow band filters 5a and 5b respectively.
The optical signals measured by the detectors 4a, 4b are processed further in any suitable processing equipment 6, which is also suitably connected to the light source 3, a heater/chiller unit 7 and the temperature control jacket 2 (for temperature measuring purposes).
The heater/chiller unit 7 is also connected to the temperature control jacket 2 in order to enable heating or cooling of the gas sample contained by the tube 1.
It will be appreciated that advantageously the detectors 4a, 4b could be reduced to one detector to avoid differential temperature effects on the sensitivity of detection. In that case the single light source 3 is replaced by two light sources with the wavelength selection (narrow band) filter being transferred from the detectors to the light sources. Advantageously, the light intensity signals are obtained by phase sensitive detection, with the two sources operated in a phase separation.
The operation of the apparatus of the invention is as follows:
While the gas sample is contained by the tube 1, the light source 3 transmits a modulated light beam to the detectors 4a, 4b.
The quantities measured by the detectors are proportional to the light intensities at two specific wavelengths (X1 and A2 respectively). Advantageously, A1 is 1.89 Hm and A2 is 1.98 pm.
At the dew-point, condensation of liquid on the walls of the tube is manifest by the reduction in absorption at the characteristic wavelength and thus the liquid dew-point is indicated by the abrupt change in the relative transmitted intensity of two distinct wavelengths, occurring as the (high pressure) gas is temperature ramped through the liquid dew-point temperature, causing a reduction in liquid vapour concentration in the gas sample as result of liquid condensing out of the gas onto the tube walls, for a downward temperature ramp. Advantageously, the temperature range is from +30 "C to -20 "C.
The intensities are determined and the ratio thereof is measured as a function of temperature. This ratio is advantageously represented on a visual display.
Referring to fig. 2, the same reference numerals as in fig. 1 have been used.
In fig. 2 one detector 4 and two light sources provided with narrow band filters are arranged. In this embodiment the supply 8a from the flow line 9 (partially shown for reasons of clarity) via a valve to the tube 1 and the re-lnjection'line 8b from the tube 1 via a valve to the flow line 9 have been shown.
As already described in the foregoing the gas sample may be vented, if necessary, rather than re-injected to the flow line.
A suitable computer 6a provided with a visual display has been connected to signal conditioning unit 6. Reference numeral 6b represents the light source drivers and phase generator.
Reference numerals lOA, lOb, lOc represent the connections for temperature measurements of gas, coolant and air respectively.
The light sources and the detector are suitably arranged in explosion-proof housings lla and llb.
In fig. 3 the horizontal axis represents coolant temperature in C whereas the vertical axis represents the intensity ratio.
The graph shows the behaviour of the intensity ratio as temperature is ramped downwards at 1/2 C per minute; the sample is air at atmosphere pressure; and the dew-point is detected at just below 22 "C (arrow A).
It will be appreciated by those skilled in the art that the invention is not restricted to measuring water dew-point in a gas sample, but can be applied to measure the temperature at which any component of a fluid (gas/liquid) is preferentially removed (whether by evaporation, boiling, condensation, sublimation or chemical reaction) provided that the component of interest possesses a distinguishable absorption feature from those of the containing medium.
Various modifications of the invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings.
Such modifications are intended to fall within the scope of the appended claims.
Claims (8)
1. A method for identifying a change in phase of one component in a multicomponent (gas/liquid) fluid system by direct regular measurement of liquid dew-point of a gas sample, comprising the steps of:
supplying a gas sample, tapped from a flow line, to an optical dew-point detection device based upon the transmission of a light beam to a detector and monitoring the optical transmission for the reduction associated with absorption by the intervening gas atmosphere;
measuring the intensity I of light of two specific different wavelengths (A1, 2) and doing this simultaneously and regularly at numerous different temperatures;
thereby measuring regularly the ratio I(A1i at several
I(A2 temperatures; and
deriving the indication of liquid dew-point from an abrupt change of said determined intensity ratio.
2. The method as claimed in claim 1 wherein the dew-point is indicated by decreasing the temperature until the ratio increases.
3. The method as claimed in claim 1 wherein the dew-point is indicated by increasing the temperature until the ratio ceases to change rapidly.
4. The method as claimed in any one of claims 1-3 wherein the temperature range is from +30 C to -20 C.
5. The method as claimed in any one of claims 1-4 wherein
A1 is 1.89 m and A2 is 1.98 pm.
6. An apparatus for identifying a change in phase of one component in a multicomponent (gas/liquid) fluid system by direct regular measurement of liquid dew-point of a gas sample, comprising:
means for supplying a gas sample from a flow line to an optical dew-point detection means based upon transmission of a light beam to a detector and monitoring the optical transmission for the reduction associated with absorption by the intervening gas atmosphere;
means for measuring the intensity I of light of two specific different wavelengths (A 2) and doing this simultaneously and regularly at numerous different temperatures;
means for measuring regularly the ratio I(A1) at several
I(A2) temperatures; and
means for deriving the indication of liquid dew-point from an abrupt change of said determined intensity ratio.
7. The apparatus as claimed in claim 6 comprising one detector and two light sources, each light source being provided with a narrow band filter.
8. The apparatus as claimed in claim 6 wherein the light intensity signals are obtained by phase sensitive detection, with the two sources operated with a phase separation.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP92305766 | 1992-06-23 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9312781D0 GB9312781D0 (en) | 1993-08-04 |
| GB2268265A true GB2268265A (en) | 1994-01-05 |
Family
ID=8211411
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9312781A Withdrawn GB2268265A (en) | 1992-06-23 | 1993-06-21 | Optical detection of liquid dew-point of a gas stream. |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2268265A (en) |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2121960A (en) * | 1982-06-07 | 1984-01-04 | Gca Corp | Cloud point analyzer |
-
1993
- 1993-06-21 GB GB9312781A patent/GB2268265A/en not_active Withdrawn
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2121960A (en) * | 1982-06-07 | 1984-01-04 | Gca Corp | Cloud point analyzer |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9312781D0 (en) | 1993-08-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |