Dynamic compensation method and system for oxygen interference in determination of non-methane total hydrocarbons

Abstract

The present invention belongs to the field of detection and analysis technology, and specifically relates to a method and system for dynamic compensation of oxygen interference in the determination of non-methane total hydrocarbons. The method for dynamic compensation of oxygen interference includes the following steps: S1. In the process of determining non-methane total hydrocarbons, the oxygen concentration of the gas sample to be measured in the sampling gas path is detected in real time; S2. A compensation gas path is set in the gas path at the front end of the inlet of the FID detector nozzle to perform oxygen compensation on the gas sample to be measured, so as to compensate the oxygen concentration of the gas sample to be measured to the target reference oxygen concentration; S3. The gas sample to be measured with the target reference oxygen concentration enters the FID detector for detection. By real-time monitoring of the oxygen concentration in the gas sample to be measured, the oxygen concentration of the FID detector is compensated, so that when the oxygen concentration of the gas sample to be measured changes, the oxygen concentration in the FID detector always remains constant, thereby solving the defect that the change in oxygen concentration has a greater impact on the measured concentration.

Description

Technical Field

[0001] The invention belongs to the technical field of detection and analysis, and in particular relates to a method and system for dynamic compensation of oxygen interference in determination of non-methane total hydrocarbons. Background Art

[0002] At present, the standard determination method of non-methane total hydrocarbons mainly adopts the difference subtraction method, that is, the content of total hydrocarbons and methane in the sample gas is measured separately, and the difference between the two can be used to obtain the content of non-methane total hydrocarbons in the sample gas. Common measurement technologies mainly include gas chromatography and catalytic oxidation. Among them, the principle of gas chromatography is to use double columns with FID detector technology, and methane is separated by methane column and then enters FID detector to measure methane concentration, and the total hydrocarbon column directly measures the total hydrocarbon concentration. The principle of catalytic oxidation method is to use heated catalyst to react hydrocarbons other than methane in the gas to be tested to produce carbon dioxide and water, and then pass the remaining methane in the gas to be tested into FID detector to obtain the methane content, while the total hydrocarbon concentration is directly measured by entering FID detector through another gas path.

[0003] The above two measurement technologies measure the methane concentration by different methods, while the total hydrocarbon concentration is obtained by directly sending the sample gas into the FID detector for measurement, and finally the non-methane total hydrocarbon concentration is calculated by subtraction. However, when the total hydrocarbon concentration is measured using a hydrogen flame ionization detector (i.e., FID detector), due to the synergistic effect of oxygen on the FID detector, the oxygen content will affect the flame combustion state of the detector, thereby affecting the response sensitivity of the FID detector and interfering with the measurement results. In actual measurement applications, the oxygen content varies widely under different working conditions, and the degree of interference caused by oxygen on the detector measurement accuracy will change dynamically with the change of the oxygen content in the gas to be measured.

[0004] In view of the influence of oxygen interference on the accuracy of FID detector measurement results, the following two methods are currently used to correct oxygen interference:

[0005] The first method is to separate the oxygen in the gas to be tested through a chromatographic column and then enter the FID detector to measure the oxygen peak area. When calculating the total hydrocarbon concentration, the oxygen peak area is deducted from the total hydrocarbon peak area to calculate the concentration. This method only considers the fixed effect of oxygen alone on the FID detector, and ignores the synergistic effect of oxygen on other gas components.

[0006] The second method is to measure the total hydrocarbon concentration of standard gases with different concentrations under a single oxygen content background, and to correct the total hydrocarbon measurement concentration of standard gases within all ranges by the difference in the degree of oxygen interference on standard gases with different concentrations under the oxygen background conditions. This method only considers the difference in the influence of oxygen on standard gases with different concentrations and the synergistic effect of sample gas on other gas components, and ignores the large range of oxygen content changes in different working conditions, resulting in different effects of oxygen on the measured concentration under different oxygen content background conditions. When the correction algorithm corresponding to this method is used for correction, the online monitoring instrument needs to be operated for a long time, such as daily maintenance or fault shutdown and repair, which will cause the analysis system status, such as the purity of the gas supply, to change, affecting the long-term stability of the analyzer. Therefore, it is necessary to perform regular quality control calibration and update of the correction algorithm, which is difficult to apply and maintain, and it is difficult to ensure the long-term stability of the correction effect after the status of the analysis system is changed. Summary of the invention

[0007] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objects of the present invention is to solve at least one or more of the above-mentioned problems in the prior art. In other words, one of the objects of the present invention is to provide a method and system for dynamic compensation of oxygen interference for non-methane total hydrocarbon determination that meets one or more of the above-mentioned requirements.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0009] The oxygen interference dynamic compensation method for the determination of non-methane total hydrocarbons comprises the following steps:

[0010] S1. During the determination of non-methane total hydrocarbons, the oxygen concentration of the gas sample to be measured in the sample inlet gas path is detected in real time;

[0011] S2. A compensation gas circuit is set in the gas circuit at the front end of the FID detector nozzle inlet to perform oxygen compensation on the gas sample to be measured, so as to compensate the oxygen concentration of the gas sample to be measured to the target reference oxygen concentration;

[0012] S3. The gas sample with the target reference oxygen concentration enters the FID detector for detection.

[0013] As a preferred solution, in step S2, the compensation gas flow Q for oxygen compensation is:

[0014]

[0015]

[0016] Among them, Q H is the combustion gas flow rate of the FID detector, Q Nis the carrier gas flow rate of the FID detector, V is the injection volume of the gas sample to be tested, T is the peak width of the total hydrocarbon peak, C * is the oxygen reference concentration at the nozzle of the FID detector where the sample gas, fuel gas and carrier gas enter, C0 is the target reference oxygen concentration, and C is the oxygen concentration of the sample gas to be tested.

[0017] As a preferred embodiment, the combustion gas is hydrogen.

[0018] As a preferred embodiment, the carrier gas is nitrogen or helium.

[0019] As a preferred solution, the compensating gas circuit is provided with a flow controller for controlling the compensating gas flow rate.

[0020] As a preferred solution, the target reference oxygen concentration is not less than the maximum oxygen concentration of the gas sample to be tested under the working conditions to be tested.

[0021] The present invention also provides an oxygen interference dynamic compensation system for non-methane total hydrocarbon determination, using the oxygen interference dynamic compensation method described in the above scheme, and the oxygen interference dynamic compensation system comprises:

[0022] The oxygen concentration detection module is used to detect the oxygen concentration of the gas sample to be tested in the sampling gas path in real time;

[0023] The compensation gas circuit is arranged at the gas circuit at the front end of the FID detector nozzle inlet, and the connection point between the compensation gas circuit and the gas circuit at the front end of the FID detector nozzle inlet is located downstream of the oxygen concentration detection module along the flow direction of the gas sample to be measured; the compensation gas circuit is used to perform oxygen compensation on the gas sample to be measured, so as to compensate the oxygen concentration of the gas sample to be measured to the target reference oxygen concentration;

[0024] The FID detector is used to detect the input target reference oxygen concentration of the gas sample to be tested.

[0025] As a preferred solution, the compensation gas flow Q of the oxygen compensation is:

[0026]

[0027]

[0028] Among them, Q H is the combustion gas flow rate of the FID detector, Q N is the carrier gas flow rate of the FID detector, V is the injection volume of the gas sample to be tested, T is the peak width of the total hydrocarbon peak, C * is the oxygen reference concentration at the nozzle of the FID detector where the sample gas, fuel gas and carrier gas enter, C0 is the target reference oxygen concentration, and C is the oxygen concentration of the sample gas to be tested.

[0029] The compensation gas flow Q of the above oxygen compensation is the dynamic oxygen compensation model.

[0030] As a preferred solution, the compensating gas circuit is provided with a flow controller for controlling the compensating gas flow rate.

[0031] As a preferred solution, the target reference oxygen concentration is not less than the maximum oxygen concentration of the gas sample to be tested under the working conditions to be tested.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The oxygen interference dynamic compensation method and system for non-methane total hydrocarbon determination of the present invention compensates for the oxygen concentration of the FID detector by real-time monitoring of the oxygen concentration in the gas sample to be measured, so that when the oxygen concentration of the gas sample to be measured changes, the oxygen concentration in the FID detector always remains constant, thereby solving the defect that the change in oxygen concentration has a large impact on the measured concentration. Compared with other existing methods of correcting measurement results through algorithms, the present invention has high applicability, and a unified correction method can be used between different instruments, and there is no need to establish correction algorithms for different instruments separately and calibrate and update them regularly, which solves the oxygen interference problem more conveniently while meeting the application requirements of complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of a method for dynamic compensation of oxygen interference in the determination of non-methane total hydrocarbons in Example 1 of the present invention;

[0035] Figure 2 It is a structural diagram of the oxygen interference dynamic compensation system for the determination of non-methane total hydrocarbons in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] In order to more clearly illustrate the embodiments of the present invention, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings and other implementation methods can be obtained based on these accompanying drawings without creative work.

[0037] Embodiment 1:

[0038] In this embodiment, under different oxygen background conditions, by adding oxygen gas dynamic compensation to the FID detector, the oxygen content in the FIF detector is compensated to be the same as the target reference point, so that the oxygen content in the FID detector does not change with the change of oxygen concentration in the gas sample to be measured and always remains constant.

[0039] Because the oxygen concentration of the FID detector remains constant, the impact of oxygen on the measured factor always remains consistent with the target reference point. There is no need to regularly update the correction model for quality control, which fundamentally solves the defect of inaccurate measurement results caused by changes in oxygen content in the gas sample to be measured.

[0040] Specifically, Figure 1 As shown, the oxygen interference dynamic compensation method for non-methane total hydrocarbon determination in this embodiment includes the following steps:

[0041] S1. During the determination of non-methane total hydrocarbons, the oxygen concentration of the gas sample to be measured in the sample inlet gas path is detected in real time;

[0042] S2. A compensation gas circuit is set in the gas circuit at the front end of the FID detector nozzle inlet to perform oxygen compensation on the gas sample to be measured, so as to compensate the oxygen concentration of the gas sample to be measured to the target reference oxygen concentration;

[0043] Among them, according to the actual working conditions of the analytical detection system, the oxygen compensation reference point, that is, the target reference oxygen concentration, is selected. The reference point is the maximum typical value of the oxygen concentration in the gas sample to be tested, that is, when the oxygen content in the gas sample to be tested changes, the oxygen concentration in the gas sample to be tested is compensated to the highest oxygen concentration value that may actually occur through the compensation gas; therefore, the target reference oxygen concentration is not less than the highest oxygen concentration of the gas sample to be tested under the working conditions to be tested.

[0044] Specifically, the dynamic oxygen compensation model, that is, the compensation gas flow Q of oxygen compensation is:

[0045]

[0046]

[0047] Among them, Q H is the combustion gas flow rate of the FID detector, Q N is the carrier gas flow rate of the FID detector, V is the injection volume of the gas sample to be tested, T is the peak width of the total hydrocarbon peak (unit: min), C * It is the oxygen reference concentration at the place where the sample gas, fuel gas and carrier gas enter the nozzle of the FID detector (i.e. the proportion of oxygen after the sample gas, fuel gas and carrier gas are mixed), C0 is the target reference oxygen concentration, and C is the oxygen concentration of the sample gas to be tested.

[0048] In this embodiment, the combustion gas is hydrogen, and the carrier gas is nitrogen or helium.

[0049] S3. The gas sample with the target reference oxygen concentration enters the FID detector for detection.

[0050] In addition, the compensation gas circuit of this embodiment is provided with a flow controller for dynamically controlling the compensation gas flow rate to adapt to different working conditions.

[0051] Based on the above oxygen interference dynamic compensation method of this embodiment, Figure 2As shown, this embodiment also provides a dynamic compensation system for oxygen interference in non-methane total hydrocarbon determination, which is based on the existing non-methane total hydrocarbon determination and analysis system and includes an oxygen concentration detection module, a compensation gas circuit and a FID detector.

[0052] Specifically, an oxygen concentration detection module is added to the sample inlet gas path of the analysis system to measure the oxygen concentration of the gas sample to be tested entering the analysis system in real time. In addition, a compensation gas path is added to the gas path at the front end of the FID detector nozzle inlet of the analysis system to perform oxygen compensation, so that the gas sample to be tested is mixed with the compensation gas (i.e., oxygen) and then enters the FID detector for analysis, and the flow rate of the compensation gas is controlled by the flow controller of the compensation gas path.

[0053] The oxygen concentration detection module of this embodiment is used to detect the oxygen concentration of the gas sample to be tested in the sampling gas path in real time;

[0054] The compensation gas circuit of this embodiment is arranged at the gas circuit at the front end of the FID detector nozzle inlet, and the connection point between the compensation gas circuit and the gas circuit at the front end of the FID detector nozzle inlet along the flow direction of the gas sample to be measured is located downstream of the oxygen concentration detection module; the compensation gas circuit is used to perform oxygen compensation on the gas sample to be measured, so as to compensate the oxygen concentration of the gas sample to be measured to the target reference oxygen concentration;

[0055] The FID detector is used to detect the input target reference oxygen concentration of the gas sample to be tested.

[0056] As a preferred solution, the compensation gas flow Q of the oxygen compensation is:

[0057]

[0058]

[0059] Among them, Q H is the combustion gas flow rate of the FID detector, Q N is the carrier gas flow rate of the FID detector, V is the injection volume of the gas sample to be tested, T is the peak width of the total hydrocarbon peak, C * is the oxygen reference concentration at the nozzle of the FID detector where the sample gas, fuel gas and carrier gas enter, C0 is the target reference oxygen concentration, and C is the oxygen concentration of the sample gas to be tested.

[0060] This embodiment selects an oxygen compensation reference point, i.e., a target reference oxygen concentration, according to the actual working conditions of the analytical detection system. The reference point is the maximum typical value of the oxygen concentration in the gas sample to be measured, i.e., when the oxygen content in the gas sample to be measured changes, the oxygen concentration in the gas sample to be measured is compensated to the highest possible oxygen concentration value through the compensation gas; therefore, the target reference oxygen concentration is not less than the highest oxygen concentration of the gas sample to be measured under the working conditions to be measured.

[0061] Specifically, the dynamic oxygen compensation model (i.e., the oxygen interference dynamic compensation model), i.e., the compensation gas flow Q of oxygen compensation is:

[0062]

[0063]

[0064] Among them, Q H is the combustion gas flow rate of the FID detector, Q N is the carrier gas flow rate of the FID detector, V is the injection volume of the gas sample to be tested, T is the peak width of the total hydrocarbon peak (unit: min), C * It is the oxygen reference concentration at the place where the sample gas, fuel gas and carrier gas enter the nozzle of the FID detector (i.e. the proportion of oxygen after the sample gas, fuel gas and carrier gas are mixed), C0 is the target reference oxygen concentration, and C is the oxygen concentration of the sample gas to be tested.

[0065] In this embodiment, the combustion gas is hydrogen, and the carrier gas is nitrogen or helium.

[0066] The following is a performance test comparison of the oxygen interference dynamic compensation method and system of this embodiment. Propane standard gas with oxygen content of 0%, 5%, 10%, 15%, and 20% and total hydrocarbon concentration of 1ppm, 2ppm, 5ppm, 10ppm, and 20ppm is respectively introduced into the FID detector to calculate the relative error of the measured concentration of the standard gas under the background of different oxygen content concentrations relative to the measured concentration of the standard gas when the oxygen content is the compensation reference point of 20%. Through the oxygen interference dynamic compensation model, the oxygen concentration at the nozzle of the FID detector in the samples with different oxygen contents is compensated to the reference value through the compensation gas, and the relative error of the measured concentration of the standard gas under the background of different oxygen content concentrations after compensation by the oxygen interference compensation model is calculated relative to the measured concentration of the standard gas when the oxygen content is the compensation reference point of 20%. The calculation results are as follows:

[0067] Table 1 Difference in indication error of sample gas concentration before and after correction

[0068]

[0069] As can be seen from Table 1 above, the measured concentration of the sample gas has a large deviation from the actual concentration before correction, and oxygen has a greater impact on the accuracy of the measurement results. After correction by the oxygen interference compensation model, the relative deviation between the measured concentration and the theoretical concentration is greatly reduced, reducing the impact of the oxygen content in the sample gas on the measurement results, ensuring the accuracy of the measurement results under different oxygen background conditions, and the indication error between the corrected measured concentration and the theoretical concentration can meet the indicator requirement of the standard HJ 1013-2018 that the indication error of oxygen influence is less than or equal to 2% FS.

[0070] In summary, the oxygen interference dynamic compensation method and system of the present invention corrects the oxygen interference in the gas sample to be measured, and has the following advantages:

[0071] 1. The present invention is based on the technology of measuring non-methane total hydrocarbons by gas chromatography in combination with an FID detector. In combination with the characteristics of the influence of oxygen on the FID detector in this technology, an oxygen interference dynamic compensation model is formulated to independently correct the gas samples to be measured with different oxygen content backgrounds, which effectively solves the problem of different interference degrees of different oxygen concentrations on the measurement results in actual measurements, and greatly improves the accuracy of the measured concentration.

[0072] 2. The oxygen interference dynamic compensation model established by the present invention can select the compensation reference point according to different working conditions, and can compensate the sample gas under different oxygen concentration conditions to a uniform concentration, thereby minimizing the problem of poor accuracy of the measurement results caused by changes in the oxygen content in the gas sample to be measured, and has a wide correction range, which can meet the accurate correction of the measurement of the gas sample to be measured under more working conditions in different oxygen content backgrounds.

[0073] 3. The present invention uses an oxygen concentration detection module to perform real-time measurement and correction of the oxygen concentration in the gas sample to be measured in each analysis cycle, which can accurately correct the measurement results when there is a real-time dynamic change in the oxygen concentration under complex working conditions, and has stronger adaptability to working conditions.

[0074] 4. Compared with other methods of correcting the measurement result values ​​through algorithms, the present invention is more convenient in practical application and does not require regular quality control updates of the correction algorithm, thus ensuring the long-term stability and effectiveness of the correction method.

[0075] The above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, according to the ideas provided by the present invention, there will be changes in the specific implementation methods, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A dynamic compensation method for oxygen interference in the determination of non-methane total hydrocarbons, characterized in that: The following steps are involved: S1. During the determination of non-methane total hydrocarbons, the oxygen concentration of the gas sample to be measured in the sample inlet gas path is detected in real time; S2. A compensation gas circuit is set in the gas circuit at the front end of the FID detector nozzle inlet to perform oxygen compensation on the gas sample to be measured, so as to compensate the oxygen concentration of the gas sample to be measured to the target reference oxygen concentration; S3, the gas sample to be tested with the target reference oxygen concentration enters the FID detector for detection; In step S2, the compensation gas flow rate of oxygen compensation Q for: in, Q H is the combustion gas flow rate of the FID detector, Q N is the carrier gas flow rate of the FID detector, V is the injection volume of the gas sample to be tested, T is the peak width of the total hydrocarbon peak, C * It is the oxygen reference concentration at the nozzle of the gas sample, fuel gas and carrier gas entering the FID detector. C 0 is the target baseline oxygen concentration, C is the oxygen concentration of the sample gas to be tested.

2. The method for dynamic compensation of oxygen interference in determination of non-methane total hydrocarbons according to claim 1, characterized in that: The combustion gas is hydrogen.

3. The method for dynamic compensation of oxygen interference in determination of non-methane total hydrocarbons according to claim 1, characterized in that: The carrier gas is nitrogen or helium.

4. The method for dynamic compensation of oxygen interference in determination of non-methane total hydrocarbons according to claim 1, characterized in that: The compensation gas circuit is provided with a flow controller for controlling the compensation gas flow rate.

5. The method for dynamic compensation of oxygen interference in the determination of non-methane total hydrocarbons according to any one of claims 1 to 4, characterized in that: The target reference oxygen concentration is not less than the maximum oxygen concentration of the gas sample to be tested under the working conditions to be tested.

6. A dynamic compensation system for oxygen interference in non-methane total hydrocarbon determination, using the dynamic compensation method for oxygen interference as claimed in claim 1, characterized in that: The oxygen interference dynamic compensation system comprises: The oxygen concentration detection module is used to detect the oxygen concentration of the gas sample to be tested in the sampling gas path in real time; The compensation gas circuit is arranged at the gas circuit at the front end of the FID detector nozzle inlet, and the connection point between the compensation gas circuit and the gas circuit at the front end of the FID detector nozzle inlet is located downstream of the oxygen concentration detection module along the flow direction of the gas sample to be measured; the compensation gas circuit is used to perform oxygen compensation on the gas sample to be measured, so as to compensate the oxygen concentration of the gas sample to be measured to the target reference oxygen concentration; FID detector, used to detect the input target reference oxygen concentration of the gas sample to be tested; The compensation gas flow rate of oxygen compensation Q for: in, Q H is the combustion gas flow rate of the FID detector, Q N is the carrier gas flow rate of the FID detector, V is the injection volume of the gas sample to be tested, T is the peak width of the total hydrocarbon peak, C * It is the oxygen reference concentration at the nozzle of the gas sample, fuel gas and carrier gas entering the FID detector. C 0 is the target baseline oxygen concentration, C is the oxygen concentration of the sample gas to be tested.

7. The oxygen interference dynamic compensation system for non-methane total hydrocarbon determination according to claim 6, characterized in that: The compensation gas circuit is provided with a flow controller for controlling the compensation gas flow rate.

8. The oxygen interference dynamic compensation system for non-methane total hydrocarbon determination according to any one of claims 6-7, characterized in that: The target reference oxygen concentration is not less than the maximum oxygen concentration of the gas sample to be tested under the working conditions to be tested.

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