CN117405729A - Natural gas hydrocarbon dew point analysis and calibration system and calibration method - Google Patents
Natural gas hydrocarbon dew point analysis and calibration system and calibration method Download PDFInfo
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- 239000004215 Carbon black (E152) Substances 0.000 title claims abstract description 111
- 229930195733 hydrocarbon Natural products 0.000 title claims abstract description 111
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Natural products C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 52
- 238000004458 analytical method Methods 0.000 title claims abstract description 46
- 239000003345 natural gas Substances 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims abstract description 33
- -1 Natural gas hydrocarbon Chemical class 0.000 title claims abstract description 24
- 239000007789 gas Substances 0.000 claims abstract description 112
- 150000002430 hydrocarbons Chemical class 0.000 claims abstract description 87
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 claims abstract description 40
- 239000000126 substance Substances 0.000 claims abstract description 33
- 238000005303 weighing Methods 0.000 claims abstract description 23
- 238000012545 processing Methods 0.000 claims abstract description 19
- 238000004817 gas chromatography Methods 0.000 claims abstract description 8
- 238000004364 calculation method Methods 0.000 claims abstract description 7
- 239000007788 liquid Substances 0.000 claims description 74
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 36
- 229910052697 platinum Inorganic materials 0.000 claims description 18
- 239000003507 refrigerant Substances 0.000 claims description 16
- 230000008569 process Effects 0.000 claims description 9
- 230000008859 change Effects 0.000 claims description 8
- 238000009833 condensation Methods 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 230000005494 condensation Effects 0.000 claims description 4
- 230000001105 regulatory effect Effects 0.000 claims description 3
- 230000007363 regulatory process Effects 0.000 claims description 3
- 238000001514 detection method Methods 0.000 abstract description 7
- 238000004088 simulation Methods 0.000 abstract description 7
- 238000004445 quantitative analysis Methods 0.000 abstract 1
- 239000000523 sample Substances 0.000 description 28
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 12
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- 238000001816 cooling Methods 0.000 description 3
- 238000010992 reflux Methods 0.000 description 3
- 238000013022 venting Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 2
- 238000005057 refrigeration Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000011179 visual inspection Methods 0.000 description 2
- 239000001273 butane Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000010812 external standard method Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000012821 model calculation Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
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- 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
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/62—Detectors specially adapted therefor
- G01N30/64—Electrical detectors
- G01N30/66—Thermal conductivity detectors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/62—Detectors specially adapted therefor
- G01N30/64—Electrical detectors
- G01N30/68—Flame ionisation detectors
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
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- General Health & Medical Sciences (AREA)
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Abstract
The invention relates to a natural gas hydrocarbon dew point analysis and calibration system, which belongs to the technical field of natural gas hydrocarbon dew point analysis and calibration, and comprises a standard substance on-line generating device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point meter to be calibrated, an automatic weighing device and a data processing system; the standard substance on-line generating device is used for generating n-butane gas with the concentration of 10%, and the gas at the outlet is respectively used for the gas source of the standard substance quantitative analysis and calibration device and the standard gas source for the device to be calibrated, and after the method or the structure is adopted, the invention has the following advantages: the method for combining accurate fixed value and dew point calculation simulation of gas chromatography by adopting standard substances on line is adopted, effective tracing and accurate calibration of a natural gas hydrocarbon dew point analysis instrument are realized through the cooperation of a hydrocarbon dew point calibration device and an automatic weighing device, tracing short plates of the natural gas hydrocarbon dew point analysis instrument are supplemented, and the accuracy of hydrocarbon dew point analysis detection values is ensured.
Description
Technical Field
The invention relates to the technical field of natural gas hydrocarbon dew point analysis and calibration, in particular to a natural gas hydrocarbon dew point analysis and calibration system and a calibration method.
Background
In the process of long-distance pipeline transportation of natural gas, the temperature and pressure change can cause the change of the dew point of the natural gas hydrocarbon, and liquid hydrocarbon can be separated out when the critical point is exceeded, so that equipment such as pipelines, compressors and the like are corroded and damaged. Therefore, real-time monitoring of the natural gas hydrocarbon dew point is particularly important; whereas conventional hydrocarbon dew point measurements are made by on-line chromatographs to measure the C1 to C7, C8 content, many measurement devices are in-line with probes in the pipeline and require a specialized technician to operate, combining gas quality/metering parameters into one meter.
Heavy hydrocarbon components in natural gas are easily liquefied to form condensate of liquid hydrocarbon in a natural environment with low temperature and a reducing throttle position of a gas pipeline, so that the pipeline is frozen and blocked and a compressor is failed, and the safety of the natural gas pipeline is seriously influenced. Currently, GB 17820-2018 "Natural gas" requires that no liquid hydrocarbon be present in natural gas under the pressure and temperature conditions of the natural gas junction; GB 50251-2015 "gas pipeline engineering design Specification" requires that the dew point of the gas hydrocarbon entering the gas pipeline should be below the minimum ambient temperature. Due to the composition characteristics of natural gas, the natural gas has physical and chemical characteristics of anti-condensation, and in order to realize the detection of the hydrocarbon dew point of the natural gas, GB/T27895-2011 'determination cooling mirror visual inspection method of the hydrocarbon dew point of the natural gas' and SY/T7484-2020 'determination cooling mirror automatic detection method of the hydrocarbon dew point of the natural gas' respectively adopt a visual inspection method and an automatic method of a cooling mirror analyzer to analyze and detect the hydrocarbon dew point.
Compared with the richer hydrocarbon dew point analysis and detection instruments in the market and the corresponding national/industry standard analysis methods, the hydrocarbon dew point analysis and detection instruments are lack of corresponding standard devices and calibration methods for carrying out magnitude calibration and tracing on the hydrocarbon dew point analysis instruments, so that the accuracy of the detection data of the hydrocarbon dew point analysis instruments cannot be effectively ensured.
In view of the foregoing, it is desirable to provide a natural gas hydrocarbon dew point analysis calibration system and calibration method to solve the above problems.
Disclosure of Invention
The invention aims to solve the technical problems, and provides a natural gas hydrocarbon dew point analysis and calibration system and a calibration method, wherein the method of combining accurate gas chromatography fixed value and dew point calculation simulation of standard substances is adopted, and the effective traceability and accurate calibration of a natural gas hydrocarbon dew point analysis instrument are realized through the cooperation of a hydrocarbon dew point calibration device and an automatic weighing device.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a natural gas hydrocarbon dew point analysis and calibration system comprises a standard substance on-line generation device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point meter to be calibrated, an automatic weighing device and a data processing system;
the standard substance online generating device is used for generating n-butane gas with the concentration of 10%, and an outlet path of the standard substance online generating device is respectively communicated with the gas chromatograph, the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated through a tee joint;
the gas chromatograph analyzes the real concentration of the n-butane gas emitted by the standard substance on-line generating device, predicts the hydrocarbon dew point through a model, and then feeds back to the hydrocarbon dew point calibration device for calibration;
the hydrocarbon dew point calibration device is used for comparing and correcting the dew point of the hydrocarbon dew point meter to be calibrated;
the automatic weighing device is used for carrying out standard control on the n-butane gas, and then feeding the n-butane gas back to the hydrocarbon dew point calibration device through dynamic feedback, and carrying out composition analysis of the discharged gas of the automatic weighing device and inputting the discharged gas into the gas chromatograph.
Preferably, the model predicts the hydrocarbon dew point as a linear equation
y＝0.0024x5-0.0633x4+0.6602x3-3.6449x2+14.833x-48.681。
Preferably, the model predicts that the difference between the hydrocarbon dew points in the pressure range of 0 to 10bar is in the range of-0.12 to 1.54 ℃.
Preferably, the gas chromatograph is one or a combination of two of a flame ionization detector FID and a thermal conductivity detector TCD.
A method for calibrating hydrocarbon dew point analysis of natural gas, comprising the steps of:
the accurate concentration x of the generated gas of the standard substance on-line generating device is determined through analysis of a gas chromatograph;
the precise pressure controller precisely controls the pressure of the generated gas, and the flow of the generated gas is precisely metered to be v through the mass flowmeter;
the temperature in the system is dynamically fed back in real time through a platinum resistance temperature sensor, the result is fed back to a refrigerator, the refrigerating power of the refrigerator is dynamically regulated, and the refrigerator flows back through a refrigerant outlet and a refrigerant; realizing accurate control of temperature; under the condition of x concentration, the hydrocarbon dew point of the sample gas is T0, the temperature is sequentially adjusted from T0+3 ℃ to T0-3 ℃ from high to low, the initial temperature step is 1 ℃, when the liquid dew outflow is found to enter a reference liquid storage container, the temperature T1 is recorded, the temperature is sequentially adjusted from T1+1 ℃ to T ℃ from high to low, the temperature step is 0.1 ℃, in the regulating process, the balance time of each temperature point is 30min, the concentration of n-butane in the discharged air is analyzed through online gas chromatography, when the n-butane concentration is 0, the fact that the n-butane in the sample gas is condensed is proved, and the initial dew condensation temperature T is determined, namely the hydrocarbon dew point of the sample gas;
in the temperature control process, the temperature of the four platinum resistance temperature sensors and the set value are ensured to be within +/-0.01 ℃ so as to ensure that the regulation control is successful;
the platinum resistance temperature sensor is calibrated or identified through a standard platinum resistance, so that the tracing of temperature data to the International measuring unit Kelvin K is realized;
the flow path directions of the generated gas and the refrigerant outlet are opposite to each other, so that the sufficient heat exchange of the sample is ensured;
the condensed liquid of the sample after heat exchange enters a multi-way selector valve, and the sample automatically enters a reference liquid storage container or a standard liquid storage container;
the quality change of the reference liquid storage container or the standard liquid storage container is transmitted into a data processing system through a quality sensor to perform data processing;
when the multi-way selector valve is cut into a standard liquid storage container, the data processing system automatically peels and clears the weighing device, and the hydrocarbon liquid mass of the standard liquid storage container is recorded within the time t;
the reference liquid storage container and the standard liquid storage container are connected with external air discharge through pipelines, and the air discharge pipelines are provided with one-way valves, so that gas or air is prevented from flowing back, and weighing accuracy is affected;
when the vent gas enters the gas chromatograph, real-time online analysis is performed for analyzing whether the vent gas overflows n-butane.
Preferably, the switching principle of the multi-way selector valve is as follows: in the process of determining the hydrocarbon dew point, the samples enter a reference liquid storage container, after the hydrocarbon dew point T of the sample gas is determined, the samples are turned to a standard liquid storage container, the time T is recorded, the theoretical condensate mass is m, and the calculation is carried out according to the following formula;
after the method or the structure is adopted, the invention has the following advantages:
the method for combining accurate fixed value and dew point calculation simulation of gas chromatography by adopting standard substances on line is adopted, effective tracing and accurate calibration of a natural gas hydrocarbon dew point analysis instrument are realized through the cooperation of a hydrocarbon dew point calibration device and an automatic weighing device, tracing short plates of the natural gas hydrocarbon dew point analysis instrument are supplemented, and the accuracy of hydrocarbon dew point analysis detection values is ensured.
The foregoing summary is for the purpose of the specification only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the present invention will become apparent by reference to the drawings and the following detailed description.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the technical descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of the system of the present invention;
FIG. 2 is a connection diagram of the calibration method of the present invention;
FIG. 3 is a simulated dew point plot of 10% n-butane in nitrogen of the present invention.
As shown in the figure: 1. a standard substance on-line generating device; 2. a precision pressure controller; 3. a mass flowmeter; 4. a platinum resistance temperature sensor; 5. a refrigerating machine; 6. a refrigerant outlet; 7. refluxing the refrigerant; 8. condensing the liquid; 9. a multi-way selector valve; 10. a reference reservoir condensate inlet; 11. venting the reference reservoir; 12. a condensate inlet of the standard liquid storage container; 13. venting the standard liquid storage container; 14. a reference reservoir; 15. a standard reservoir; 16. venting air; 17. a data processing system.
Detailed Description
Embodiments of the present application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are exemplary only for the purpose of explaining the present application and are not to be construed as limiting the present application.
In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art as the case may be.
The present invention will be described in further detail in connection with the following.
1-3, a natural gas hydrocarbon dew point analysis and calibration system comprises a standard substance on-line generation device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point meter to be calibrated, an automatic weighing device and a data processing system;
the standard substance online generating device is used for generating n-butane gas with the concentration of 10%, and an outlet path of the standard substance online generating device is respectively communicated with the gas chromatograph, the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated through a tee joint;
the gas chromatograph analyzes the real concentration of the n-butane gas emitted by the standard substance on-line generating device, predicts the hydrocarbon dew point through a model, and then feeds back to the hydrocarbon dew point calibration device for calibration;
the hydrocarbon dew point calibration device is used for comparing and correcting the dew point of the hydrocarbon dew point meter to be calibrated;
the automatic weighing device is used for carrying out standard control on the n-butane gas, and then feeding the n-butane gas back to the hydrocarbon dew point calibration device through dynamic feedback, and carrying out composition analysis of the discharged gas of the automatic weighing device and inputting the discharged gas into the gas chromatograph.
The linear equation of the model prediction hydrocarbon dew point is that
y＝0.0024x 5 -0.0633x 4 +0.6602x 3 -3.6449x 2 +14.833x-48.681。
The model predicts that the difference between the hydrocarbon dew points in the pressure range of hydrocarbon dew points (0-10) bar is in the range of (-0.12-1.54) deg.c.
The gas chromatograph is one or two of a flame ionization detector FID or a thermal conductivity detector TCD.
A method for calibrating hydrocarbon dew point analysis of natural gas, comprising the steps of:
(1) the accurate concentration x of the generated gas of the standard substance on-line generating device is determined through analysis of a gas chromatograph;
(2) the precise pressure controller precisely controls the pressure of the generated gas, and the flow of the generated gas is precisely metered to be v through the mass flowmeter;
(3) the temperature in the system is dynamically fed back in real time through a platinum resistance temperature sensor, the result is fed back to a refrigerator, the refrigerating power of the refrigerator is dynamically regulated, and the refrigerator flows back through a refrigerant outlet and a refrigerant; realizing accurate control of temperature; under the condition of x concentration, the hydrocarbon dew point of the sample gas is T0, the temperature is sequentially adjusted from T0+3 ℃ to T0-3 ℃ from high to low, the initial temperature step is 1 ℃, when the liquid dew outflow is found to enter a reference liquid storage container, the temperature T1 is recorded, the temperature is sequentially adjusted from T1+1 ℃ to T ℃ from high to low, the temperature step is 0.1 ℃, in the regulating process, the balance time of each temperature point is 30min, the concentration of n-butane in the discharged air is analyzed through online gas chromatography, when the n-butane concentration is 0, the fact that the n-butane in the sample gas is condensed is proved, and the initial dew condensation temperature T is determined, namely the hydrocarbon dew point of the sample gas;
(4) in the temperature control process, the temperature of the four platinum resistance temperature sensors and the set value are ensured to be within +/-0.01 ℃ so as to ensure that the regulation control is successful;
(5) the platinum resistance temperature sensor is calibrated or identified through a standard platinum resistance, so that the tracing of temperature data to the International measuring unit Kelvin K is realized;
(6) the flow path directions of the generated gas and the refrigerant outlet are opposite to each other, so that the sufficient heat exchange of the sample is ensured;
(7) the condensed liquid of the sample after heat exchange enters a multi-way selector valve, and the sample automatically enters a reference liquid storage container or a standard liquid storage container;
(8) the quality change of the reference liquid storage container or the standard liquid storage container is transmitted into a data processing system through a quality sensor to perform data processing;
(9) when the multi-way selector valve is cut into a standard liquid storage container, the data processing system automatically peels and clears the weighing device, and the hydrocarbon liquid mass of the standard liquid storage container is recorded within the time t;
the reference liquid storage container and the standard liquid storage container are connected with external air discharge through pipelines, and the air discharge pipelines are provided with one-way valves, so that gas or air is prevented from flowing back, and weighing accuracy is influenced;
when the vent gas enters the gas chromatograph, real-time online analysis is performed for analyzing whether the vent gas overflows n-butane.
The switching principle of the multi-way selector valve is as follows: in-process sample for determining hydrocarbon dew pointThe method comprises the steps of entering a reference liquid storage container, turning to a standard liquid storage container after the hydrocarbon dew point T of sample gas is determined, recording time T, and calculating a theoretical condensate mass m according to the following formula;
standard substance on-line generating device:
(1) the device principle can be a dynamic dilution generation principle or a permeation tube generation principle, and n-butane gas with the theoretical concentration of 10% is generated;
(2) the gas pressure at the outlet of the generating device is continuously adjustable within (1-10) bar, so that the selection of a plurality of calibration pressure points is ensured;
(3) the outlet of the generating device is provided with a tee joint, so that simultaneous sample injection of the hydrocarbon dew point meter to be calibrated and the hydrocarbon dew point calibration device can be realized;
(4) the normal butane and nitrogen used for generation are both national standard substances with evidence, so that traceability is ensured, wherein the normal butane is a high-purity butane gas standard substance GBW (E) 060061; the nitrogen is an ultra-high purity nitrogen standard substance GBW06343;
gas Chromatograph (GC):
(1) the gas chromatograph is used for analyzing the true concentration of n-butane gas with the theoretical concentration of 10% of dynamic occurrence;
(2) in order to prevent analysis errors linearly introduced by an analysis instrument, the used gas standard substance is a normal butane gas standard substance GBW (E) 062325 which is consistent with or close to the concentration of generated gas;
(3) the detector of the gas chromatograph can be one or two of a flame ionization detector FID and a thermal conductivity detector TCD, and is used for analyzing the composition of the high-concentration normal butane gas standard substance and the discharged air which occur on line;
(4) the concentration of the generated gas adopts a single-point accurate matching method (external standard method) to determine the value;
model predicts hydrocarbon dew point:
(1) performing model calculation on the hydrocarbon dew point according to the concentration of the generated gas analyzed by the gas chromatograph;
(2) hydrocarbon dew point prediction is based on physical state equations established by Peng-Robinson;
(3) table 1 and fig. 1 are dew point simulation data and simulated linear plot, respectively, of 10% n-butane in nitrogen, fitting simulated point data to a linear equation of y=0.0024 x 5 -0.0633x 4 +0.6602x 3 -3.6449x 2 +14.833x-48.681；
(4) The difference between the fitting equation and the hydrocarbon dew point of the simulation data in the pressure range of (0-10) bar is in the range of (-0.12-1.54);
(5) to avoid the influence of simulated error, the hydrocarbon dew point is ensured to be accurate and reliable, and the temperature input value of the downstream hydrocarbon dew point calibration device is used for calculating the dew point T 0 On the basis of (C) from (T) 0 +3)℃～(T 0 -3) performing a change in DEG C to determine an accurate value, as shown in FIG. 3 and Table 1;
TABLE 1 dew point simulation data for 10% n-butane in nitrogen
As shown in fig. 2, the standard substance online generating device 1 is sequentially communicated with a precision pressure controller 2 and a mass flowmeter 3 of the automatic weighing device, the temperature in a real-time dynamic feedback system is fed back to the refrigerator 5 through a platinum resistance temperature sensor 4, the accurate control of the temperature and the line closed loop are realized through a refrigerant outlet 6 and a refrigerant reflux 7, condensed liquid 8 after heat exchange of the refrigerator 5 can respectively enter a reference liquid storage container condensed liquid inlet 10 of a reference liquid storage container 14 and a standard liquid storage container condensed liquid inlet 12 of a standard liquid storage container 15 through a multi-way selector valve 9, the mass change of the reference liquid storage container 14 and the standard liquid storage container 15 is transmitted into a data processing system through a mass sensor for data processing, a reference liquid storage container vent 11 and a standard liquid storage container vent 13 are connected with external vent air 16, and real-time online analysis is performed after entering the gas chromatograph for analyzing whether n-butane overflows.
A method for calibrating hydrocarbon dew point analysis of natural gas, comprising the steps of:
(1) the accurate concentration x (mol/mol) of the generated gas of the standard substance on-line generating device 1 is determined by analysis of a gas chromatograph;
(2) the pressure of the generated gas is precisely controlled by the precise pressure controller to be 101.325kPa, and the flow of the generated gas is precisely measured to be v (L/min) through a mass flowmeter;
(3) the temperature in the system is dynamically fed back in real time through a platinum resistance temperature sensor 4, the result is fed back to a refrigerator 5, the refrigerator 5 dynamically adjusts the refrigeration power, and the refrigeration power is fed back through a refrigerant outlet 6 and a refrigerant reflux 7; realizing accurate control of temperature; under the condition of x (mol/mol) concentration, the hydrocarbon dew point of the sample gas is T0, the temperature is sequentially adjusted from T0+3 ℃ to T0-3 ℃ from high to low, the initial temperature step length is 1 ℃, when the liquid dew outflow is found to enter the reference liquid storage container 14, the temperature T1 is recorded, the temperature is sequentially adjusted from T1+1 ℃ to T ℃ from high to low, the temperature step length is 0.1 ℃, in the adjustment process, the balance time of each temperature point is 30min, the concentration of n-butane in the discharged air is analyzed through online gas chromatography, when the n-butane concentration is 0, the fact that n-butane in the sample gas is all condensed is proved, and the initial condensation temperature T is determined dew The hydrocarbon dew point of the sample gas;
(4) in the temperature control process, the temperature of the four platinum resistance temperature sensors 4 and the set value are ensured to be within +/-0.01 ℃ so as to ensure that the regulation control is successful;
(5) the platinum resistance temperature sensor 4 is calibrated or identified through a standard platinum resistance, so that the tracing of temperature data to the International measuring unit Kelvin K is realized;
(6) the flow path direction of the generated gas and the refrigerant outlet 6 are opposite to each other, so that the sufficient heat exchange of the sample is ensured;
(7) the condensed liquid of the sample after heat exchange enters a multi-way selector valve 9, and the sample automatically enters a reference liquid storage container 14 or a standard liquid storage container 15;
(8) the mass change of the reference liquid storage container 14 or the standard liquid storage container 15 is transmitted into a data processing system 17 through a mass sensor for data processing;
(9) the switching principle of the multi-way selector valve is as follows: in the process of determining the hydrocarbon dew point, the samples enter a reference liquid storage container, after the hydrocarbon dew point T of the sample gas is determined, the samples are turned to a standard liquid storage container, the time T is recorded, the theoretical condensate mass is m, and the calculation is carried out according to the following formula;
wherein: the mass of the m-n-butane condensate is expressed as g; the relative molecular mass of M-n-butane is 58.12g/mol; p-sample inlet pressure, in Pa; t-time of the sample entering the standard liquid storage container, wherein the unit is min; v-flow of sample gas in L/min; x-n-butane component content in moles per mole (mol/mol); r-gas constant, the value is 8.314510 Pa.m3/(mol.K); t-the inlet temperature of the sample in units of on (K).
When the multi-way selector valve 9 is cut to the standard liquid storage container 15, the data processing system 17 automatically peels and clears the weighing device, and records the hydrocarbon liquid mass of the standard liquid storage container within the time t;
the reference liquid storage container air discharge 11 and the standard liquid storage container air discharge 13 are connected with the external air discharge 16, the external air discharge 16 is connected through a pipeline, and the pipelines are all provided with one-way valves to prevent gas or air from flowing back and influence the weighing accuracy;
when the vent gas 16 enters the gas chromatograph, real-time on-line analysis is performed to analyze whether the vent gas has n-butane spills.
The method for combining accurate fixed value and dew point calculation simulation of gas chromatography by adopting standard substances on line in the patent realizes effective traceability and accurate calibration of a natural gas hydrocarbon dew point analysis instrument through the cooperation of a hydrocarbon dew point calibration device and an automatic weighing device.
The invention and its embodiments have been described above with no limitation, and the actual construction is not limited to the embodiments of the invention as shown throughout. In summary, if one of ordinary skill in the art is informed by this disclosure, a structural manner and an embodiment similar to the technical solution should not be creatively devised without departing from the gist of the present invention.
Claims (6)
1. The natural gas hydrocarbon dew point analysis and calibration system is characterized by comprising a standard substance online generation device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point meter to be calibrated, an automatic weighing device and a data processing system;
the standard substance online generating device is used for generating n-butane gas with the concentration of 10%, and an outlet path of the standard substance online generating device is respectively communicated with the gas chromatograph, the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated through a tee joint;
the gas chromatograph analyzes the real concentration of the n-butane gas emitted by the standard substance on-line generating device, predicts the hydrocarbon dew point through a model, and then feeds back to the hydrocarbon dew point calibration device for calibration;
the hydrocarbon dew point calibration device is used for comparing and correcting the dew point of the hydrocarbon dew point meter to be calibrated;
the automatic weighing device is used for carrying out standard control on the n-butane gas, and then feeding the n-butane gas back to the hydrocarbon dew point calibration device through dynamic feedback, and carrying out composition analysis of the discharged gas of the automatic weighing device and inputting the discharged gas into the gas chromatograph.
2. A natural gas hydrocarbon dew point analysis calibration system according to claim 1, wherein: the linear equation of the model predicted hydrocarbon dew point is y=0.0024x 5 -0.0633x 4 +0.6602x 3 -3.6449x 2 +14.833x-48.681。
3. A natural gas hydrocarbon dew point analysis calibration system according to claim 1, wherein: the model predicts that the difference between the hydrocarbon dew points in the pressure range of 0-10 bar is in the range of-0.12-1.54 ℃.
4. A natural gas hydrocarbon dew point analysis calibration system according to claim 1, wherein: the gas chromatograph is one or two of a flame ionization detector FID or a thermal conductivity detector TCD.
5. A natural gas hydrocarbon dew point analysis and calibration method is characterized in that: the method comprises the following steps:
(1) the accurate concentration x of the generated gas of the standard substance on-line generating device is determined through analysis of a gas chromatograph;
(2) the precise pressure controller precisely controls the pressure of the generated gas, and the flow of the generated gas is precisely metered to be v through the mass flowmeter;
(3) the temperature in the system is dynamically fed back in real time through a platinum resistance temperature sensor, the result is fed back to a refrigerator, the refrigerating power of the refrigerator is dynamically regulated, and the refrigerator flows back through a refrigerant outlet and a refrigerant; realizing accurate control of temperature; under the condition of x concentration, the hydrocarbon dew point of the sample gas is T0, the temperature is sequentially adjusted from T0+3 ℃ to T0-3 ℃ from high to low, the initial temperature step is 1 ℃, when the liquid dew outflow is found to enter a reference liquid storage container, the temperature T1 is recorded, the temperature is sequentially adjusted from T1+1 ℃ to T ℃ from high to low, the temperature step is 0.1 ℃, in the regulating process, the balance time of each temperature point is 30min, the concentration of n-butane in the discharged air is analyzed through online gas chromatography, when the n-butane concentration is 0, the fact that the n-butane in the sample gas is condensed is proved, and the initial dew condensation temperature T is determined, namely the hydrocarbon dew point of the sample gas;
(4) in the temperature control process, the temperature of the four platinum resistance temperature sensors and the set value are ensured to be within +/-0.01 ℃ so as to ensure that the regulation control is successful;
(5) the platinum resistance temperature sensor is calibrated or identified through a standard platinum resistance, so that the tracing of temperature data to the International measuring unit Kelvin K is realized;
(6) the flow path directions of the generated gas and the refrigerant outlet are opposite to each other, so that the sufficient heat exchange of the sample is ensured;
(7) the condensed liquid of the sample after heat exchange enters a multi-way selector valve, and the sample automatically enters a reference liquid storage container or a standard liquid storage container;
(8) the quality change of the reference liquid storage container or the standard liquid storage container is transmitted into a data processing system through a quality sensor to perform data processing;
(9) when the multi-way selector valve is cut into a standard liquid storage container, the data processing system automatically peels and clears the weighing device, and the hydrocarbon liquid mass of the standard liquid storage container is recorded within the time t;
the reference liquid storage container and the standard liquid storage container are connected with external air discharge through pipelines, and the air discharge pipelines are provided with one-way valves, so that gas or air is prevented from flowing back, and weighing accuracy is influenced;
when the vent gas enters the gas chromatograph, real-time online analysis is performed for analyzing whether the vent gas overflows n-butane.
6. A natural gas hydrocarbon dew point analysis calibration system according to claim 5, wherein: the switching principle of the multi-way selector valve is as follows: in the process of determining the hydrocarbon dew point, the samples enter a reference liquid storage container, after the hydrocarbon dew point T of the sample gas is determined, the samples are turned to a standard liquid storage container, the time T is recorded, the theoretical condensate mass is m, and the calculation is carried out according to the following formula;
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