savin1_20200909_104117论文igu2006pdfigu2006paperpaperadd11167

1、23rd World Gas Conference, Amsterdam 2006A NEW APPROACH FOR MEASURING WATER AND HEAVY HYDROCARBON DEW POINTS OF NATURAL GASES BY USING A THREE-CHANNEL LASER INTERFEROMETERMain authorA.M. DerevyaginS.V. Seleznev, A.R. Stepanov, A.G. Agaltsov NPF Vympel Company, SaratovV.A. Istomin VNIIGAZ, Moscow Reg

2、ionRussiaABSTRACTA novel technology is used for dew points control. Three-channel laser interferometer allows simultaneously detect three phases on an instrument mirror: liquid phase (water or suppercooled water, water solutions), solid phase (ice or gas hydrates) and hydrocarbon phase. Condensation

3、 technique of dewpoint measurement is applied.A new industrial device CONG-Prima 10 was developed. Performance specification of CONG-to +30 oC;Prima 10 Analyzer: measurement range of water dew point temperature from -50Measurement range of HC dew point temperature from -30 to +30 oC; threshold of ad

4、missible absolute error for dew point temperature are 0.25 oC for water and 1 oC for hydrocarbons, maximum allowable working pressure of gas analyzed is 25 MPa; Measurement time is about 10-30 min.The CONG-Prima 10 Analyzer was tested and certified by the State Standard Body of the Russian Federatio

5、n (in the city of Irkuitsk, the State humidity standard is in the State Standard Institute of this city). The tests were conducted with the help of the following reference means: i) humidity gas generator (“Rodnik-2” reference dynamic generator) with an absolute error of dew point reproduction being

6、 0.10C (for measurement of range and error); ii) high-precision unit (UVT 103-A-2001), with an absolute error of dew point reproduction being no more than 0.10C, working pressure being up to 10 MPa (for measurement of working pressure range).The special laboratory test results show that the Analyzer

7、 error does not exceed 0.1 oC. This value is comparable (equal) with the accuracy of reference means. Pressure influence on the analyzers reading has not been found. The difference of 0.2 oC between the readings of the Analyzer in above-zero region without and under pressure can be explained by the

8、fact that the measurements were made on different reference units with an accuracy of 0.1 oC.Industrial CONG-PRIMA 10 Analyzer may be used for dew points control of different compositions natural gases. Brief discussion of industrial and laboratory applications is presented. Also the Analyzer may be

9、 used for research purposes: for studying gas hydrate equilibria, detection methanol content in gas phase, kinetics of condensation from gas phase.TABLE OF CONTENTS1. Abstract2. Body of Paper3. References4. List Tables5. List of FiguresA NEW APPROACH FOR MEASURING WATER AND HEAVYHYDROCARBON DEW POIN

10、TS OF NATURAL GASES BY USING A THREE-CHANNEL LASER INTERFEROMETERA.M. Derevyagin, S.V. Seleznev, A.R. Stepanov, A.G. Agaltsov NPF Vympel Company, Saratov, RussiaV.A. IstominVNIIGAZ, Moscow Region, Russia1 INTRODUCTIONProcess flows of associated oil and natural gases contain different admixtures in s

11、olid (mechanical impurities), liquid (absorbents, compressor oil, etc.) and gaseous state (water, methanol, vapors of absorbents and heavy hydrocarbons) a content of which define quality indices of sales gas.Temperatures of water and heavy hydrocarbon dew points are generally accepted criteria for g

12、as quality assessment. Instruments based on condensation method of dew point measurement are known both in Russia and other countries as reliable instruments for monitoring quality of natural and associated gases. They are one of the basic components being used in systems of automation and optimizat

13、ion of processes in oil and gas industry.Presence of extraneous impurities in gas phase during condensation process very often leads to its accumulation on a sensitive element (mirror) of dew points device. Therefore the correct measurement of dew points temperatures becomes impossible. Various syst

14、ems of gas clearing (filters, splitters, membranes) are used to support sensitive element in operation. In turn the application of such systems can lead to distortion of test gas due to sorption-desorption processes on filtering elements and as a result dew points measurement may be distorted.The an

15、alysis shows that the realization of condensation method for natural gas with some impurities requires a solution of some complicated problems, including i) selective measurement of water dew point at the presence of higher hydrocarbons and glycols condensed at higher temperature in natural gas; ii)

16、 increase in sensibility of track on locating condensed water on an analyzer mirror during simultaneous condensation of other attached foreign materials; iii) complicated and unreliable design, large size and weight and power consumption.So the new approach for measuring of dew points is needed. We

17、present an advanced gas quality control technology by means of both laser interferometer and condensation methods. Practical realization of the technology in industrial device (CONG-PRIMA 10 Analyzer) is discussed. The device may be used for dew points control of different compositions natural gases

18、.2 PHYSICAL PRINSIPLES AND MEASURING PROBLEMS OF GAS DEW POINTSThe analysis of methods for measuring gas humidity has shown that direct measuring procedures, of which the most promising is condensation method or method of gas dew points, are of primary priority. The method lies in measuring temperat

19、ure to which a film of tested gas adjacent to a cooled surface is to be cooled in order to bring it to a state of saturation (by water and other attached foreign materials) under working pressure. This temperature was named as a temperature of dewpoint while the instruments based on this measuring m

20、ethod were named as condensation instruments.Condensation method makes it possible to obtain, normally and in full measure, reliable information about water content in gas. At present there is a spectrum of condensation-type instruments manufactured by different companies in the world market. Howeve

21、r, some instruments are out-of-date and allow only manual measurement thus leading to subjective estimation of dew point (for example, Kharkov-1M and Chandler instruments widely used in Russia). The other instruments are based on physical principles that do not allow measurement of two dew points by

22、 water and hydrocarbons at a time (for instance, Mishel hygrometer). Another instruments have been developed only as experimental models (for example, devices based on microwave registration of water content in gas phase).The analysis shows that the realization of condensation method requires a solu

23、tion of some complicated problems, including1.Selective measurement of water dew point at the presence of higher hydrocarbons and glycols condensed at higher temperature in natural gas;Increase in sensibility of track on locating condensed water on an analyzer mirror during simultaneous condensation

24、 of other attached foreign materials;Complicated and unreliable design, large size and weight and power consumption.2.3.The analysis of the existing physical methods for detecting the presence of condensing moisture on a mirror (i.e. on a sensor) shows that optical method of registration is the most

25、 promising. This choice is based on simplicity of measurement, reliability and stability to real heavy enough operating conditions (i.e. operation in HC gases containing besides water and HC vapors such admixtures as methanol, glycol, compressor oil and mechanical impurities).Usually an optical devi

26、ce includes such components as a source of light (light emitting diode LED), a light receiver (photodiode) and an object for analysis (condensation mirror or sensor). The principle of the method is simple and can be described as follows. Light emitted by LED reflects from the mirror and hits upon th

27、e photodiode. During cooling water condenses on the mirror (as a film and condensation mist near the mirrors surface) leading to the dispersion of light that is fixed by the photodiode. However, this method has one essential disadvantage, namely, rather low sensibility of an optical track to thin fi

28、lms of water. This disadvantage is especially negative when measuring small moisture content in gas (i.e. under high gas pressure and low dew point temperature, below 10 oC). This problem can be solved by two different ways:1. Fiber-optic technology based on the principle of complete disturbance of

29、internal reflection when a film of registered matter appears on the external surface of optical fiber.2. Replacement of LED with laser emitting source and development of laser interference measuring techniques.As for fiber-optic technology, Vympel Company has found an original design option that lie

30、s in using a complete disturbance of internal reflection of light in optical fiber when condensate film appears on the condensation mirror (sensor). The external polished surface of a bend serves as a mirror, with an area of such mirror being 0.25 mm2. This option has allowed to increase sufficientl

31、y sensibility of the optical track. It should be noted that the response of the new optical track is observed at a water film thickness of 0.1 to 0.15 mcm. The unique feature of the design option lies in the fact that quartz optical fiber performs three functions at a time. They include a condensati

32、on mirror, a device registering water film (by decreasing photo signal level when condensate film appears and when a part of light flux comes out from the optical fiber) and a waveguide itself.This physical principle (see, figure 1) has been practically realized in a family of commercial instruments

33、, such as CONG-Prima 2, CONG-Prima 4, CONG-Prima 4P 1, 2.Figure 1. Optoelectronics-based principle of measurement and sensor (condensation mirror) designTEC Peltier thermoelectric cooler; LED light emitting diode; Photodiode light receiver recording a level of optic signal passing through fiber-opti

34、c cableNowadays, more than 300 industrial devices CONG-Prima 2 and 4 are used in Russia and CIS and some ones at Western Europe also. The practical experience show than it will be desirable to improve sensitivity and selectivity of the condensation method when detecting simultaneously both dew point

35、s on water moisture and hydrocarbons in dirty multicomponent natural gases. We choose laser interference technique for realization of the purpose (CONG-Prima 10).In laser interference measuring technique a silicon plate located on the Peltier thermoelectric cooler serves as a sensor (mirror). To reg

36、ister the processes taking place on the sensor during its heating and cooling an optical system (Figure 2) consisting of a source of coherent light (laser) 1, an optical track, a directing prism 2 and photodiodes 3,5 and 6 is used.The latter method is based on the effect of complete polarization dur

37、ing the reflection at interface of media (i.e. the entire light becomes refracted). This effect appears when light falls on the surface at so-called Brewster angle, Figure 3.A laser beam comes out from the directing prism and falls on the sensor (mirror) at Brewster angle. Three photodiodes register

38、 simultaneously changes in the intensity of a reflected beam.In the absence of condensate film on the mirror the entire impinging light becomes refracted. Therefore, values of optical signals coming to the photodiodes are very small. When the condensate film forms, the displacement of media interfac

39、e, change in media refraction coefficient and, as consequence, appearance of two reflected signals that can reinforce or attenuate each others depending on the condensate film thickness take place. The dynamics of this process is fixed by the photodiode installed opposite the directing prism (direct

40、 signal). A value of the signal considered depends on a length laser wave and condensate film thickness. These data allow in principle to measure the condensate film thickness in time, at least at its initial stage of formation (given a length of light wave emitted by laser).Figure 2. Laser interfer

41、ence-based principle of measurement and sensor (condensation mirror) design1 Source of coherent light (laser).2 Directing prism serving for exact directing a laser beam on the mirror at the Brewster angle. 3 - Photodiode (rear side) intended to fix scattered light intensity. When water (drops or cry

42、stals) condensates, the light increases its intensity.4 Mirror. Mirror is a silicon plate that absorbs a laser beam when condensate is absent. The mirror temperature is controlled by a thermoelectronic battery (Peltier elements) and measured by a heat- sensing device having a size comparable with a

43、size of the mirror.5 Photodiode (front straight) intended to fix scattered light intensity (direct signal). When HC (film) condensates, the light increases its intensity.6 - Photodiode (front side) intended to fix scattered light intensity. When water condensates (drops or crystals), the light incre

44、ases its intensity.The experiments show that the processes of water and heavy hydrocarbons condensation on the mirror (silicon plate) essentially differ. HC condensate is uniformly distributed on the mirror (sensor), while in the process of water condensation a film of liquid aqueous phase is growin

45、g to a certain level followed by the formation of microdrops (due to high surface tension of water). Later these drops may be crystallized with the formation of ice or gas hydrates (depending on thermobaric conditions). These processes are followed by a sharp increase in scattered light and attenuat

46、ion of reflected light with simultaneous loss of laser emission coherence. The photodiodes 5 and 6 fix the formation of drops or crystals (in case of water freezing or hydrating). They also fix a change in scattered light; therefore, they are located from a side of the directing prism and of the pho

47、todiode that fixes a direct signal.Figure 3. Principle of operation of gas dew-point laser Analyzer1 Impinging light; 2 - Reflected light; 3 - Refracted light.When drops or crystals of liquid appear, the most change occurs on the photodiodes 5 and 6 with a value of signal on the photodiode 3 being d

48、ecreased. When HC film forms and grows, a change of scattered signal on the photodiodes 5 and 6 is insufficient. At the same time a value of direct signal sharply changes depending on a HC film thickness. Thanks to the understanding of physical processes taking place on the mirror and analysis of di

49、rect and scattered signals one can clearly determine what component of gaseous phase (water or HC) condenses on the mirror. Thus, this technique allows simultaneous measurement of gas dew point temperature both by HC and aqueous phases (water, ice and gas hydrates) and precise measurement of gas dew

50、 point temperature by HC being below a temperature of water dew point.Based on the principles of laser interferometry a CONG-Prima 10 Analyzer has been developed. At present the unit has successfully passed laboratory and metrological tests and has been prepared for full-scale production.Figure 4. I

51、nitial information sensing device of KONG-Prima-10 Analyzer1 Shell; 2 Pressure seal; 3 - Heat-sensing device; 4 Directing prism; 5, 6, 7 Photodiodes; 8 Cooler; 9 Silicon plate (mirror); 10 Laser; 11 Optical track.In figure 5 the process of water condensation at mirror ofCONG-Prima-10 Analyzeris pres

52、ented.Figure 5. Kong-Prima-10 Analyzers sensor and condensing mirror during the process of moisture condensation3 NATURAL GAS DEW POINT LASER ANALYZER CONG-PRIMA 10At present, a three-channel laser interference Analyzer has successfully passed laboratory and numerous commercial tests.The CONG-Prima

53、10 Analyzer provides:measurement of gas dew point temperatures by water and/or hydrocarbons;recording of measured dew points and average hour values of pressure and temperature of monitored medium (when additional pressure and temperature transducers are connected to the unit) and entering these dat

54、a into volatile memory of the Analyzer;continuous digital indication of the measured dew points (oC) and values of pressure (MPa), temperature (oC) of monitored gas medium and recalculated humidity values (in mg/m3) (when additional pressure and temperature transducers are connected to the unit);tra

55、nsmission of information on the Analyzers operational state to another information-measuring systems via RS-485 interface;conversion of dew point temperature values (oC) into another humidity units (mg/m3) and conversion of measured dew point values from an actual pressure into contract pressure (e.

56、g.3.92 MPa according to Russian standard of gas quality).The main components of the Analyzer are a dew point transducer and a block performing general control of the Analyzer including a central controlling block and an interface unit (Figure 6).Figure 6. General view of central controlling block (a

57、bove); General view of Analyzer operated by interface unit (below: left - power supply source, in center dew point transducer, and right interface unit)The Analyzer has two design options:1.2.One dew point transducer. The Analyzer is operated by the interface unit;Up to four dew point transducers si

58、multaneously operated by the central controlling block.Dew point transducer is of explosion-proof construction. Interface unit and controlling block aredesigned for operation in explosion-proof zones.Performance specification of CONG-Prima 10 AnalyzerMeasurement range of water dew point temperature Measurement range of HC dew point temperature Threshold of admissible absolute error for dew temperature:-50+30 oC-30+30 oCpoint0.25 oC1 oC (pure propane) 25 MPa10-30 minDigital, according to EIA RS-485;Analog 4-20 mAWater HCM