Infrared photoacoustic spectrometry natural gas calorific value analysis system and method

Abstract

The invention discloses an infrared photoacoustic spectrometry natural gas calorific value analysis system and method, and belongs to the technical field of natural gas calorific value analysis. The system comprises an infrared light source generator, a light cutting sheet, a gas chamber, an automatic sampling device, a light filter (with an automatic calibration function), a thin film micro-sound detector, a thermal conductivity type hydrogen sensor, a double-path high-performance phase-sensitive detection circuit, a signal amplification circuit, a data acquisition and processing device, and a data display, remote transmission and output module. A motor in the infrared light source generator is externally arranged, so that the stability of long-term operation of a product can be improved to a great extent, single-light-path multi-component measurement is realized by applying an optical filter, the number of components to be measured is expanded, an automatic calibration gas chamber is designed in the optical filter, and a full-automatic zero point / range calibration function is supported; the measurement precision of long-term online operation of the instrument is ensured, and the technical bottlenecks of frequent calibration, high maintenance cost, limited multi-component detection and the like of the traditional analysis instrument are successfully solved.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas calorific value analysis, and in particular to a natural gas calorific value analysis system and method using infrared photoacoustic spectroscopy. Background Art

[0002] At present, there are two main methods for determining the calorific value of natural gas: direct measurement method and indirect measurement method. The direct measurement method determines the calorific value of natural gas by direct combustion, while the indirect measurement method determines the content of each component in natural gas and then calculates the calorific value (indirect measurement method). The instrument commonly used in the direct measurement method is the water flow calorimeter, but the application of this equipment requires a lot of complicated experimental work and is not convenient for direct measurement of natural gas pipelines. The analyzers based on the indirect measurement method mainly include gas chromatographs and infrared analyzers.

[0003] Gas chromatography is an analytical technology based on separation. It requires carrier gas during the measurement process, and the analysis interval is long. At the same time, the instrument has high requirements for operators. The infrared analyzer based on non-dispersive infrared photoacoustic spectroscopy technology has a simple structure, does not require carrier gas, is easy to operate, and has relatively low requirements for operators. It can realize continuous detection of natural gas pipelines on site. At present, the infrared natural gas calorific value analyzer on the market only measures CH4 and C n H m To calculate the calorific value, the accuracy deviation is large, so a high-precision infrared photoacoustic spectroscopy natural gas calorific value analysis system is needed to improve the above problems.

[0004] Photoacoustic spectroscopy gas detection technology is an important technology that uses the photoacoustic thermal effect to achieve gas detection. This technology is a background-free measurement method that is not affected by light scattering. It also has the advantages of high sensitivity and real-time online monitoring. Therefore, this technology has a broad application market in the field of gas analysis and detection. Summary of the invention

[0005] The purpose of the present invention is to provide a natural gas calorific value analysis system and method using infrared photoacoustic spectroscopy to solve the problems raised in the above-mentioned background technology. The infrared photoacoustic spectroscopy natural gas calorific value analysis system involved in the present invention has a measurement process in which an infrared light source emits stable and continuous infrared light, which is converted into infrared light alternating at a certain frequency after being modulated by a light-cutting plate and enters the measurement side and reference side of the gas chamber in a time-sharing manner. The infrared light is absorbed by the measurement gas and the reference gas in the gas chamber in a time-sharing manner, and then a changing sound pressure signal is generated in the detector, which is converted into a corresponding voltage signal through an acoustic-to-electric conversion module. After conversion, CO, CO2, CH4, C2H6, C n H m The volume fraction (or mole fraction) of the gas is then used to calculate the higher calorific value and lower calorific value of the mixed gas using the weighted average method based on the unit calorific value coefficient corresponding to each combustible component.

[0006] To achieve the above object, the present invention provides the following technical solutions: The first aspect of the present invention provides a natural gas calorific value analysis system using infrared photoacoustic spectroscopy, comprising: an infrared light source generator, a light cutter, an analysis gas chamber, an optical filter, a thin film micro-sound detector, a phase-sensitive detection circuit and a signal amplification circuit, a data acquisition and processor, and a data display, remote transmission and output module; The infrared light source generator emits continuous infrared light, which becomes infrared light alternating with a set frequency after passing through the cutter, enters the measuring side and reference side of the analysis chamber in time, and then becomes monochromatic light through the filter and enters the detection cavity of the thin film micro-acoustic detector. The microphone in the detection cavity detects the photoacoustic signal, and then converts the acoustic signal into an electrical signal through the acoustic-to-electric conversion module. The data is processed by the data acquisition and processor, and the results are displayed and transmitted by the data display, remote transmission and output modules.

[0007] Preferably, the infrared light source generator comprises: a first broadband infrared light source and a second broadband infrared light source; Two sets of light sources are installed on a light source housing, share a motor and a light cutter, and the motor is external;.

[0008] Preferably, the analysis gas chamber comprises: a first gas chamber and a second gas chamber; the first gas chamber and the second gas chamber are independent of each other and have different lengths, and are used for simultaneously measuring gases with different concentration values.

[0009] Preferably, the optical filter comprises: an optical filter switching device and an automatic calibration structure; The filter switching device is used to switch the filter put into the optical path, and the automatic calibration air chamber realizes automatic calibration of the instrument through the rotation of the calibration air chamber.

[0010] Preferably, the infrared photoacoustic spectroscopy natural gas calorific value analysis system further comprises: an automatic sampling device; The automatic sampling device is controlled according to a program to control the sample gas, the zero point calibration gas and the end point calibration gas to enter the analysis gas chamber in time, thereby controlling the flow rate of the sample injection gas.

[0011] Preferably, the thin film micro-sound detector comprises: a first detector and a second detector; The first detector is filled with CO, CO2, CH4, C n H m Mixed gases, CO, CO2, CH4, C n H m Time-sharing measurement; the second detector is filled with C2H6, and the separate measurement of C2H6 in the fuel gas is achieved by selecting a filter with a suitable passband.

[0012] Preferably, the phase-sensitive detection circuit and signal amplification circuit are dual-path phase-sensitive detection circuit and signal amplification circuit, including: a first pre-stage amplifier circuit, a second pre-stage amplifier circuit, and a signal conditioning and amplification circuit, wherein the first pre-stage amplifier circuit is connected to the first detector, the second pre-stage amplifier circuit is connected to the second detector, the first pre-stage amplifier circuit and the second pre-stage amplifier circuit are both connected to the signal conditioning and amplification circuit; the signal conditioning and amplification circuit is connected to the data acquisition and processor.

[0013] Preferably, the data acquisition and processor adopts a data acquisition control system based on an ARM chip as the core, including: a data acquisition part and a data processing part; The data acquisition part obtains the electrical signals from the phase-sensitive detection circuit and the signal amplification circuit; the data processing part is used to calculate the concentration of various gases in the sample gas with the electrical signals.

[0014] Preferably, the infrared photoacoustic spectroscopy natural gas calorific value analysis system further comprises: a hydrogen sensor; The hydrogen sensor uses a thermal conductivity detector to measure the H2 content in natural gas.

[0015] The second aspect of the present invention provides a method for analyzing the calorific value of natural gas using infrared photoacoustic spectroscopy, based on the aforementioned natural gas calorific value analysis system using infrared photoacoustic spectroscopy, comprising the following steps: Send the sample gas into the analysis gas chamber; The infrared light source generator emits infrared light, and the light is modulated into an infrared beam of a set frequency by the rotation of the light cutter, and then sent to the filter through the analysis gas chamber in turn; The filter switches the filter according to different detection objects and sends the filtered light beam to the thin film micro-sound detector; The thin film micro-sound detector converts the optical signal into an electrical signal, and then sends the amplified electrical signal to the data acquisition and processor through a dual-channel high-performance phase-sensitive detection circuit and a signal amplification circuit; The data acquisition and processor calculates the concentration of various gases in the sample gas and completes the calorific value analysis.

[0016] Compared with the prior art, the beneficial effects of the present invention include at least: In the present invention, (1) by externally mounting the motor in the infrared light source generator, the long-term operation stability of the infrared product can be greatly improved; (2) the application of the filter realizes the measurement of multiple components in a single optical path, expanding the number of components to be measured; (3) an automatic calibration gas chamber is designed in the filter, which can realize the full-automatic zero point / range calibration function of the instrument, facilitating the long-term continuous and reliable online operation of the instrument, and being more suitable for the continuous online monitoring of natural gas pipelines; (4) the automatic sampling device can ensure that the calibration gas and the sample gas enter the measurement gas chamber according to requirements, ensuring constant flow sampling and ensuring that the calibration gas chamber realizes the automatic calibration function; (5) since the infrared calorific value analyzers on the current market only measure CH4 and C n H m , while the present invention measures CO, CO2, CH4, C2H6, C n H m and H2 simultaneously, improving the accuracy of measuring the calorific value of gas by infrared technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the overall block diagram of the system of the present invention; Figure 2 is the structural diagram of the infrared light source of the present invention; Figure 3 is the structural diagram of the filter (with automatic calibration function) of the present invention; Figure 4 is the structural diagram of the dynamic sampling device of the present invention; Figure 5 is the infrared structure model diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0019] For the convenience of understanding the present invention, the present invention will be described more comprehensively with reference to the relevant accompanying drawings. Several embodiments of the present invention are given in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of this invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0021] Please refer to Figures 1-5 As shown, Embodiment 1 of the present invention provides an infrared photoacoustic spectroscopy natural gas calorific value analysis system, including: an infrared light source generator, a chopper, an analysis gas chamber, an automatic sampling device, a filter, a thin-film microphone detector, a dual-channel high-performance phase-sensitive detection circuit and a signal amplification circuit, a hydrogen sensor, a data acquisition and processor, and a data display, remote transmission and output module.

[0022] The infrared light source generator emits stable and continuous infrared light, which becomes infrared light with an alternating set frequency after passing through the chopper and enters the measurement side and the reference side of the analysis gas chamber in a time-sharing manner. Then it becomes monochromatic light after passing through the filter and enters the detection cavity of the thin-film microphone detector. The highly sensitive microphone in the detection cavity detects the photoacoustic signal, and the acoustic signal is converted into an electrical signal through an acoustic-electric conversion module. The electrical signal is converted into an analog signal that can be recognized by a high-precision AD conversion chip through a signal conditioning and amplification filtering circuit, and the data is processed by a signal processing circuit based on ARM. Finally, the data display, remote transmission and output module displays and remotely transmits the result.

[0023] As Figure 2 shown, the infrared light source generator is used to emit stable and continuous infrared light. The rotatable chopper modulates the light emitted by the light source into an infrared light beam with a set fixed frequency, and the fixed frequency is preferably but not limited to being designed according to the characteristics of the thin-film microphone detector.

[0024] Preferably but not restrictively, the infrared light source generator includes: a first broadband infrared light source and a second broadband infrared light source; the two sets of light sources are installed on a light source housing, sharing a motor and a chopper. Using two light sources can achieve simultaneous measurement of two channels, increasing the number of measured components. More preferably, the motor for driving the light source to move is externally placed.

[0025] It should be noted that sharing a set of chopper, motor and light source housing for two sets of light sources can make the measurement module more compact, simplify the motor drive circuit and reduce the power consumption of the whole machine. At the same time, the light source motor is placed outside to solve the signal drift problem caused by the built-in light source. By rotating the chopper, the stable continuous infrared light emitted by the infrared light source generator is modulated into different infrared light beams, which are alternately sent to the detector through the analysis gas chamber to realize the double optical path in time. The infrared light source generator generates a pulse signal, and the pulse width and phase are adjusted by conditioning the pulse signal. By canceling the support components of the local light source radiation source components, the heat conduction of the light source is reduced, and the energy loss caused by the spectral center frequency shift is reduced; the infrared light source generator adopts the parabolic coating technology that greatly improves the intensity of converging light energy, reducing the light energy loss during the transmission of the light source.

[0026] The analysis gas chamber includes: a first gas chamber and a second gas chamber; the first gas chamber and the second gas chamber are independent of each other and are not restricted by the concentration of the measured components of each other, and gas chambers with different lengths can be used to simultaneously measure gases with large differences in concentration values. For example, but not limited to, the first gas chamber is used for the measurement of CO, CO2, CH4, C n H m measurement, and the second gas chamber is used for the separate measurement of C2H6 in alkanes.

[0027] Such as Figure 3 As shown, in order to ensure the stability of the measurement results of the calorimeter, the present invention designs a new filter structure, which includes: a filter switching device and an automatic calibration structure; the filter switching device is used to switch the filter put into the optical path, and the automatic calibration gas chamber realizes the automatic calibration of the instrument by rotating the calibration gas chamber.

[0028] Preferably but not limitedly, the filter is provided with a disk rotary filter switching device, and the filter is driven by a stepper motor to enter the optical path in turn, so that the single optical path optical component forms optical measurements with different spectral characteristics at different times. Multiple filters are preferably but not limited to, CO infrared filter, CH4 infrared filter, CO2 infrared filter and C n H m infrared filter; the driving mode of the filter includes but is not limited to, pulse driving or triangular wave signal driving, preferably continuous triangular wave signal driving, which improves the smoothness and positioning accuracy of the filter rotation compared with pulse driving.

[0029] Preferably, but not restrictively, the automatic calibration structure includes: a calibration gas chamber and a drive motor, which can realize the automatic calibration function of the instrument during the long-term operation of the instrument, thereby ensuring the long-term operation stability of the instrument. Further, the automatic calibration gas chamber includes: a first calibration gas chamber and a second calibration gas chamber, which are used as a reference gas chamber and a calibration gas chamber respectively, and the calibration gas chamber is filled with CH4, CO2 and C3H8 gases with known set concentrations to realize the CH4, CO2 and C3H8 in the natural gas to be tested. n H m When the calibration time is reached during the operation of the instrument, the calibration chamber rotates to the calibration side to calibrate the instrument. After calibration, the calibration chamber rotates to the measurement side for normal measurement.

[0030] It is worth noting that the technical problem to be solved by the filter is to use a single infrared light source generating device in an infrared photoacoustic spectroscopy gas analyzer to detect multiple gases within a range. It is necessary to accurately switch the filter in the detector front component to achieve a method of detecting up to 4 gases. In order to achieve the detection of multiple gases, the present invention provides a disc rotating filter switching device, which drives the filter to enter the optical path in sequence through a stepper motor, so that the single optical path optical component forms optical measurements with different spectral characteristics at different times. At the same time, an automatic calibration gas chamber is designed in the filter, and the automatic calibration of the instrument is achieved by rotating the calibration gas chamber.

[0031] The automatic sampling device is controlled according to a program to control the sample gas, the zero point calibration gas and the end point calibration gas to enter the measuring gas chamber in time, and can also realize the flow control of the sample gas, thereby ensuring that the instrument can realize the automatic calibration function.

[0032] The thin film micro-sound detector comprises: a first detector and a second detector; wherein the first detector is filled with CO, CO2, CH4, C n H m The mixed gas (pre-filled with C2H6, C3H8) can realize CO, CO2, CH4, C n H m Time-sharing measurement; C2H6 is filled in the second detector, and the separate measurement of C2H6 in the fuel gas is achieved by selecting a filter with a suitable passband to avoid interference of other alkanes on C2H6. The first gas chamber, the filter and the first detector are in the first optical path, and the second gas chamber and the second detector are in the second optical path.

[0033] Each thin-film microphone detector includes two absorption chambers, which are airtight with each other (excluding the balance holes) and are optically in series. The one that first receives the radiation is called the front absorption chamber, and the one behind is called the rear absorption chamber. The front absorption chamber mainly absorbs the energy at the center of the spectral band due to its shorter length, while the rear absorption chamber absorbs the remaining energy on both sides. The volume of the detector is designed so that the energy absorbed by the front and rear is equal, thus causing equal pressure pulses to be generated in the gases in the two gas chambers due to the radiation. When the gas to be analyzed enters the analysis side of the gas chamber, the infrared radiation at the center of the spectral band is first absorbed in the gas chamber, resulting in a weakening of the pressure pulse in the front absorption chamber. Therefore, the pressure balance is disrupted, and the generated pulse is applied to the differential thin-film microphone through a capillary tube and is converted into a change in the electrical signal.

[0034] It should be noted that, as one of the prominent substantive features of the present invention and a significant progress brought to the prior art, the infrared light source generator is equipped with two light sources. The two sets of light sources are installed on a light source housing and share a single motor and a chopper. Using two light sources enables simultaneous measurement of two channels, increasing the number of measured components. At the same time, the two light sources, two sets of gas chambers, and two detectors are independent of each other and are not restricted by the concentration of the measured components of each other. Gas with a large difference in concentration values can be measured simultaneously using gas chambers of different lengths. For example, when measuring the component concentration of natural gas, the separate measurement of C2H6 in alkanes is achieved in this way, improving the accuracy of measuring the calorific value of natural gas by the infrared method.

[0035] Since the instrument signal of the dual-channel high-performance phase-sensitive detection circuit and signal amplification circuit has a wide dynamic range and the electrical signal is quite weak, a high-performance phase-sensitive detection technology is adopted. The main process of demodulation can perform full-wave rectification on the amplitude-modulated signal and distinguish the phase of the modulation signal from the output of the detector, thereby distinguishing the carrier frequency and improving the anti-interference ability of the entire circuit. At the same time, in order to achieve the detection of an ultra-low range dual-channel, a signal processing circuit with two channels, 4-level programmable amplification, and 3-level filtering is designed.

[0036] The dual-channel high-performance phase-sensitive detection circuit and signal amplification circuit include: a first pre-stage amplification circuit, a second pre-stage amplification circuit, and a signal conditioning and amplification circuit. The first pre-stage amplification circuit is connected to the first detector, the second pre-stage amplification circuit is connected to the second detector, and both the first pre-stage amplification circuit and the second pre-stage amplification circuit are connected to the signal conditioning and amplification circuit; the signal conditioning and amplification circuit is connected to the data acquisition and processing device.

[0037] The data acquisition and processor adopt a data acquisition control system with an ARM chip as the core. The data acquisition part of the data acquisition and processing device realizes passing the sample gas component to be measured through the gas chamber, then converting the optical signal into an electrical signal by the thin-film microphone detector, and then sending the amplified electrical signal into the signal acquisition system with 100k synchronous 24-bit high-precision sampling through a multi-stage high-precision filtering and amplifying circuit; the data processing part of the data acquisition and processing device processes the digital signal collected by the data acquisition system through the ARM processor to calculate the concentration of various gases in the sample gas, and realizes functions such as data storage, table or graphic display, fault warning and printing through the interaction between data processing and peripherals.

[0038] The hydrogen sensor adopts a high-precision thermal conductivity detector, which can measure the H2 content in natural gas and is more suitable for applications in natural gas hydrogen blending projects. Its corrosion-resistant sensitive element has good stability and long life. The basic principle of the thermal conductivity hydrogen sensor works is to determine its composition according to the thermal conductivity of the gas, that is, to determine the content of a certain gas in the mixed gas by measuring the thermal conductivity of the mixed gas. When the background gas (such as N2, etc.) or other components in the mixed gas are basically constant, the thermal conductivity of the mixed gas basically depends on the amount of the component to be measured. In this way, according to the different thermal conductivities of the mixed gas, the amount of the component to be measured can be measured. The thermal conductivity hydrogen sensor is connected to the signal conditioning and amplifying circuit.

[0039] The data display, remote transmission and output module can display and remotely transmit the results.

[0040] Embodiment 2 of the present invention provides a method for analyzing the calorific value of natural gas by infrared photoacoustic spectroscopy. The method is based on the infrared photoacoustic spectroscopy natural gas calorific value analysis system described in Embodiment 1. It includes the following steps: Send the sample gas into the analysis gas chamber; The infrared light source generator emits infrared light. By rotating the chopper, the light is modulated into an infrared light beam with a set frequency and alternately sent to the filter through the analysis gas chamber. The filter switches the filter film for different detection objects and sends the filtered light beam into the thin-film microphone detector. The thin-film microphone detector converts the optical signal into an electrical signal, and then sends the amplified electrical signal into the data acquisition and processor through a dual-channel high-performance phase-sensitive demodulation circuit and a signal amplification circuit. The data acquisition and processor calculates the concentration of various gases in the sample gas, and then completes the calorific value analysis.

[0041] In a further embodiment, the method includes the following detection operation steps: S1. The light source emitted by the infrared light source generator is modulated into an infrared light beam with a fixed frequency (designed according to the characteristics of the detector) by the rotation of the chopper, and is sent to the detector through the analysis cell in turn to achieve a double optical path in time. The light source generates a pulse signal, and the pulse width and phase are adjusted by conditioning the pulse signal. By removing the support components of the local light source radiation source element, the heat conduction of the light source is reduced; the energy loss caused by the spectral center frequency shift is reduced; the parabolic coating technology that greatly improves the intensity of converging light energy is adopted, and the light energy loss during the transmission of the light source is reduced.

[0042] S2. For the gas analyzer using a single infrared light source generator in infrared photoacoustic spectroscopy to detect multiple gases within a range, it is necessary to accurately switch the filter in the front component of the thin-film microphone detector to detect up to 4 gases; in order to detect multiple gases, a disc-rotating filter switching device is invented. The filter is driven by a stepper motor to enter the optical path in turn, so that the single optical path optical component forms optical measurements with different spectral characteristics at different times. At the same time, an automatic calibration cell is designed in the filter. The automatic calibration cell consists of a reference cell and a calibration cell. The calibration cell is filled with a certain concentration of CH4, CO2 and C3H8 gases to achieve the automatic calibration of CH4, CO2 and C n H m in the natural gas to be measured. During the operation of the instrument, when the set calibration time arrives, the calibration cell rotates to the calibration side to calibrate the instrument, and after calibration, the calibration cell rotates to the measurement side for normal measurement.

[0043] S3. The automatic sampling device is controlled according to the program to control the sample gas, zero calibration gas and end calibration gas to enter the measurement cell at different times, and at the same time, the flow rate of the sampled gas can be controlled, so as to ensure that the instrument can achieve the automatic calibration function.

[0044] S4. The thin-film microphone detector consists of two absorption cells, which are airtight with each other (ignoring the balance holes) and are optically in series. The one that enters the radiation first is called the front absorption cell, and the one behind is called the rear absorption cell. The front absorption cell mainly absorbs the energy at the center of the absorption band due to its short length, while the rear absorption cell absorbs the remaining energy on both sides. The volume design of the detector makes the energy absorbed by the front and rear equal, so that the gases in the two cells generate equal pressure pulses under radiation. When the gas to be analyzed enters the analysis side of the cell, the infrared radiation at the center of the absorption band is first absorbed in the cell, resulting in a weakening of the pressure pulse in the front absorption cell. Therefore, the pressure balance is destroyed, and the generated pulse is applied to the differential thin-film microphone through the capillary and is converted into a change in the electrical signal; S5, dual-channel high-performance phase-sensitive detection circuit and signal amplification circuit: Since the instrument signal has a wide dynamic range and the electrical signal is quite weak, a high-performance phase-sensitive detection technology is used to enable the main process of demodulation to perform full-wave rectification on the amplitude modulated signal and identify the phase of the modulated signal from the output of the detector, thereby distinguishing the carrier frequency and improving the anti-interference ability of the entire circuit; S6, the data acquisition and processor's data acquisition part realizes passing the sample gas to be tested through the gas chamber, and then the thin film micro-sound detector converts the optical signal into an electrical signal, and then the amplified electrical signal is sent to the 200k synchronous 16-bit high-precision sampling signal acquisition system through a multi-stage high-precision filtering and amplifying circuit. The data processing part processes the digital signal collected by the data acquisition system through the ARM processor to calculate the concentration of various gases in the sample gas. The data processing interacts with the peripherals to realize data storage, table or graphic display, fault warning and printing functions; the results can be displayed and transmitted remotely.

[0045] Embodiment: The infrared light source emits a stable and continuous infrared light, which is converted into infrared light of a certain frequency alternating after passing through the cutter and enters the measuring side and the reference side of the gas chamber in a time-sharing manner, and then is converted into monochromatic light through the filter and enters the detection cavity. The high-sensitivity microphone in the detection cavity detects the photoacoustic signal, and then the acoustic signal is converted into an electrical signal through the acoustic-electric conversion module. The electrical signal is converted into an analog signal that can be recognized by a high-precision AD conversion chip through signal conditioning and amplification and filtering circuits, and the data is processed by STM32, and finally the result is displayed and remotely transmitted; Detector 1 is filled with CO, CO2, CH4, C n H m The mixed gas (pre-filled with C2H6, C3H8) can realize CO, CO2, CH4, C n H m Time-sharing measurement, detector 2 is filled with C2H6, and the separate measurement of C2H6 in the fuel gas is achieved by selecting a filter with a suitable passband, avoiding interference of other alkanes on C2H6; The infrared light source generator is equipped with two light sources. The two sets of light sources are installed on a light source housing and share a motor and a cutter. The two light sources can realize two-way simultaneous measurement, increasing the number of measured components. At the same time, the two light sources, two sets of gas chambers and two detectors are independent of each other and are not limited by the concentration of each measured component. Gas chambers of different lengths can be used to achieve simultaneous measurement of gases with large concentration differences. For example, when measuring the concentration of natural gas components, this method can achieve the separate measurement of C2H6 in alkanes, improving the accuracy of infrared measurement of natural gas calorific value.

[0046] Using a single set of chopper, motor, and light source housing for two sets of light sources can make the measurement module more compact, simplify the motor drive circuit, and reduce the power consumption of the whole machine. At the same time, placing the light source motor outside the instrument solves the signal drift problem caused by an internal light source. By rotating the chopper, the light emitted by the light source is modulated into different infrared light beams, which alternately pass through the analysis gas chamber and are sent to the detector, realizing a dual optical path in time. The light source generates a pulse signal, and the pulse width and phase are adjusted by conditioning the pulse signal. By removing the support components of the local light source radiation source element, the heat conduction of the light source is reduced, and the energy loss caused by the spectral center frequency shift is decreased; a parabolic coating technology that greatly improves the intensity of converged light energy is adopted, reducing the light energy loss during the transmission of the light source; It can be understood that calorific value calculation means that the heat released by a certain volume or mass of gas is called the calorific value of the gas, also known as the heat value of the gas; the calorific value is divided into the higher calorific value and the lower calorific value; the higher calorific value refers to the total heat released when the sample gas of unit gas is completely burned and cooled to the initial temperature, and the water vapor is discharged in the state of condensed water; the lower calorific value refers to the total heat released when the sample gas of unit gas is completely burned and cooled to the initial temperature, and the water vapor is discharged in the state of vapor; according to the measured gas concentration values of each component, the calorific value of the gas to be measured is calculated under the standard conditions of 1 atm and 0 °C. According to different display requirements of users, the instrument is equipped with a high and low calorific value display switching function, and the calorific value unit has kilocalorie per standard cubic meter (kcal / Nm 3 ), and megajoule per standard cubic meter (MJ / Nm 3 ) for selection; A comparative test of the natural gas prototype was carried out in the Nanjing Metrology Verification Laboratory and with a chromatograph: The test results are shown in the following table: The comparative test in the metrology verification laboratory is shown in Table 1.

[0047] Table 1 Comparative test in the metrology verification laboratory (Unit: % mole fraction)

[0048] As can be seen from the above table, in the concentration range greater than 90%, the maximum absolute deviation is 0.28%. Therefore, when measuring the methane content by photoacoustic spectroscopy in the concentration range greater than 90%, a test deviation within 0.28% can be obtained; The comparative test results of the ethane component in the metrology verification laboratory are shown in Table 2.

[0049] Table 2 Comparative test in the metrology verification laboratory (Unit: % mole fraction)

[0050] As can be seen from the above table, the maximum absolute deviation is 0.19% within the concentration range of (0~3)%. Therefore, when measuring the ethane content by infrared spectroscopy within the concentration range of (0~3)%, a test deviation within 0.19% can be obtained.

[0051] As one of the prominent substantive features of the present invention and the significant progress brought to the prior art, the infrared natural gas calorific value analyzer proposed in the present invention can realize the measurement of CO, CO2, CH4, C2H6, C n H m and H2, improve the measurement accuracy of the calorific value of the gas, and at the same time expand the application range of the instrument, such as being applied to the measurement of gas components such as coalbed methane calorific value measurement, biogas fermentation, and biogas pyrolysis; gas sampling analysis for various combustion tests in universities, scientific research institutes, etc.

[0052] The present invention supports the full-automatic zero / range calibration function to ensure the measurement accuracy of the instrument during long-term online operation, successfully solves the technical bottlenecks such as frequent calibration, high maintenance cost, and limited multi-component detection of traditional analytical instruments, and provides a high-precision and high-reliability spectral online analysis solution for natural gas energy metering. It is applicable to the needs of continuous online monitoring of calorific value in scenarios such as long-distance natural gas pipelines and urban gate stations.

[0053] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An infrared photoacoustic spectroscopy natural gas calorific value analysis system, characterized in that Including: An infrared light source generator, a chopper, an analysis gas chamber, a filter, a thin-film microphone detector, a phase-sensitive demodulation circuit and a signal amplification circuit, a data acquisition and processor, and a data display, remote transmission and output module; The infrared light source generator emits continuous infrared light, which becomes infrared light with an alternating set frequency after passing through the chopper and enters the measurement side and reference side of the analysis gas chamber at different times. Then it becomes monochromatic light after passing through the filter and enters the detection cavity of the thin-film microphone detector. The microphone in the detection cavity detects the photoacoustic signal, converts the acoustic signal into an electrical signal through an acoustic-electric conversion module, and the data acquisition and processor processes the data. The data display, remote transmission and output module displays and remotely transmits the result.

2. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to claim 1, characterized in that: The infrared light source generator includes: a first broadband infrared light source and a second broadband infrared light source; The two sets of light sources are installed on a light source housing, sharing a motor and a chopper, and the motor is externally placed.

3. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to claim 1, characterized in that: The analysis gas chamber includes: a first gas chamber and a second gas chamber; the first gas chamber and the second gas chamber are independent of each other and have different lengths for simultaneous measurement of gases with different concentration values.

4. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to claim 1, characterized in that: The filter includes: a filter slice switching device and an automatic calibration structure; The filter slice switching device is used to switch the filter slice put into the optical path, and the automatic calibration gas chamber realizes the automatic calibration of the instrument through the rotation of the calibration gas chamber.

5. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to any one of claims 1 to 4, characterized in that: The infrared photoacoustic spectroscopy natural gas calorific value analysis system further includes: an automatic sampling device; The automatic sampling device is controlled according to a program to control the sample gas, zero calibration gas and end calibration gas to enter the analysis gas chamber at different times and control the flow rate of the sampled gas.

6. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to any one of claims 1 to 4, characterized in that: The thin-film microphone detector includes: a first detector and a first detector; Among them, the first detector is filled with a mixed gas of CO, CO2, CH4, C n H m Time-division measurement of CO, CO2, CH4, C n H m is achieved by switching the filter in the filter; the second detector is filled with C2H6, and the separate measurement of C2H6 in the fuel gas is achieved by selecting a filter with a suitable passband.

7. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to any one of claims 1 to 4, characterized in that: The phase-sensitive demodulation circuit and the signal amplification circuit are a dual-channel phase-sensitive demodulation circuit and signal amplification circuit, including: a first pre-stage amplification circuit, a second pre-stage amplification circuit, and a signal conditioning and amplification circuit. The first pre-stage amplification circuit is connected to the first detector, the second pre-stage amplification circuit is connected to the second detector, and both the first pre-stage amplification circuit and the second pre-stage amplification circuit are connected to the signal conditioning and amplification circuit; the signal conditioning and amplification circuit is connected to the data acquisition and processor.

8. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to any one of claims 1 to 4, characterized in that: The data acquisition and processor adopt a data acquisition control system with an ARM chip as the core, including: a data acquisition part and a data processing part; The data acquisition part acquires the electrical signals of the phase-sensitive demodulation circuit and the signal amplification circuit; the data processing part is used to calculate the concentrations of various gases in the sample gas based on the electrical signals.

9. An infrared photoacoustic spectroscopy natural gas calorific value analysis system according to any one of claims 1 to 4, characterized in that: The infrared photoacoustic spectroscopy natural gas calorific value analysis system further includes: a hydrogen sensor; The hydrogen sensor adopts a thermal conductivity detector and is used to measure the H2 content in natural gas.

10. A method for analyzing the calorific value of natural gas by infrared photoacoustic spectroscopy, based on an infrared photoacoustic spectroscopy natural gas calorific value analysis system according to any one of claims 1 to 9, characterized in that, It includes the following steps: Send the sample gas into the analysis gas chamber; The infrared light source generator emits infrared light. By using the rotation of the chopper, the light is modulated into an infrared light beam with a set frequency and alternately sent to the filter through the analysis gas chamber; The filter switches the filter film for different detection objects and sends the filtered light beam into the thin-film microphone detector; The thin-film microphone detector converts the optical signal into an electrical signal, and then the amplified electrical signal is sent into the data acquisition and processor through the dual-channel high-performance phase-sensitive demodulation circuit and the signal amplification circuit; The data acquisition and processor calculate the concentrations of various gases in the sample gas, and then complete the calorific value analysis.

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