A method and device for detecting non-methane total hydrocarbons with high time resolution

Abstract

The present invention discloses a high time resolution non-methane total hydrocarbon detection device and method, which mainly include a metal sintered filter, a sampling probe, a heating pipe sampling pump, a heating pipe, a catalytic furnace, a total hydrocarbon column, an electronic mass flow controller 1, an electronic mass flow controller 2, a proportional valve, a total hydrocarbon FID detector, a methane FID detector, a microcurrent signal processor 1, and a microcurrent signal processor 2; the present invention realizes improvement of the detection accuracy of non-methane total hydrocarbons by redefining the total hydrocarbon response time and the methane response time so that the total hydrocarbon response time and the methane response time are the same.

Description

Technical Field

[0001] The present invention mainly relates to the field of environmental protection equipment, and in particular to a high time resolution non-methane total hydrocarbon detection method and device. Background Art

[0002] Volatile organic compounds (VOCs) are important precursors to the formation of secondary pollutants such as fine particulate matter (PM2.5) and ozone (O3), which in turn cause atmospheric environmental problems such as haze and photochemical smog. Since the hydrogen flame ionization detector (FID) has the characteristics of high sensitivity and wide linear range for organic detectors, gas chromatography (GC-FID) is currently the main method for monitoring VOCs and is widely used in online monitoring equipment. However, due to the lack of comparison equipment in online monitoring equipment, traditional laboratory gas chromatographs are large in size and heavy in weight, making it difficult to perform tests on the platform. Samples are collected in sampling bags or suma cans and sent to the laboratory for testing. The intermediate process will cause sample loss and condensation, and the analysis results are quite different from those of online monitoring equipment. Therefore, in response to the above situation, portable gas chromatographs came into being. Portable gas chromatographs can ensure the timeliness of measurement results, and they are small in size and light in weight, making them easy to monitor on site.

[0003] Due to the characteristics of the GC-FID method, the analysis cycle of non-methane total hydrocarbons (NMHC) is usually 2 minutes through quantitative analysis by quantitative loop, and it is impossible to provide real-time feedback on the changing trend of the current monitoring point. Catalytic-FID effectively makes up for this shortcoming. The catalytic-FID method can achieve the output in seconds, but due to the 3-5s time difference in the response time of the total hydrocarbon and methane systems, generally speaking, due to the small internal resistance of the total hydrocarbon gas path, the response is fast, and the methane gas path passes through the catalytic furnace and the filter device, and the response speed is slow, and thus the sample gas concentration in the same time period cannot be accurately measured, resulting in the difference between the measured non-methane total hydrocarbon concentration and the actual concentration. According to the test results of this research team, the method of simply adjusting the length of the pipeline to make the total hydrocarbon and methane response time the same cannot completely eliminate the delay in the rapid change of total hydrocarbons and methane, resulting in the non-methane total hydrocarbon concentration calculated by the difference between the two often showing negative values. Summary of the invention

[0004] The present invention provides a high-time-resolution non-methane total hydrocarbon detection method and device, which solves the above-mentioned technical problems proposed in the prior art.

[0005] The present invention provides a high time resolution non-methane total hydrocarbon detection device, comprising a sample collection unit and a host;

[0006] The host comprises a gas source supply unit, a catalytic furnace, a flow control unit, a detection unit, and a signal processing unit; the sample collection unit comprises a sampling pump, a heating pipe, and a sampling probe; a metal sintered filter is installed at the sampling probe; the catalytic furnace comprises a catalyst and a heating and heat-insulating material; the flow control unit comprises an electronic mass flow controller 1 and an electronic mass flow controller 2; the detection unit comprises a total hydrocarbon FID detector and a methane FID detector; the signal processing unit comprises a micro-current signal processor 1 and a micro-current signal processor 2; the gas source supply unit comprises a low-pressure hydrogen storage bottle, a sample gas pipeline, and an air pipeline; the sample gas pipeline comprises a total hydrocarbon gas circuit and a methane gas circuit; a proportional valve is built in the total hydrocarbon gas circuit;

[0007] Wherein, the sampling pump is placed at the tail end of the heating pipe; the head end of the heating pipe is connected to the tail end of the sampling probe; a metal sintered filter is installed at the sampling probe; the gas outlet of the sampling pump is connected to the head end of the total hydrocarbon gas path and the head end of the methane gas path through a tee respectively; an electronic mass flow controller 1 and a total hydrocarbon column are installed in the total hydrocarbon gas path; wherein the electronic mass flow controller 1 is connected to the head end of the total hydrocarbon column; a total hydrocarbon FID detector and a micro-current signal processor 1 are arranged in the total hydrocarbon gas path; the micro-current signal processor 1 is electrically connected to the total hydrocarbon FID detector. A high-efficiency hydrocarbon removal filter is installed at the head end of the air duct; a catalytic furnace and an electronic mass flow controller 2 are installed inside the methane gas path; wherein the tail end of the catalytic furnace is connected to the head end of the methane column through an electronic mass flow controller 2; a methane FID detector and a micro-current signal processor 2 are arranged in the methane column; the methane FID detector is electrically connected to the micro-current signal processor 2.

[0008] Accordingly, the present invention proposes a high time resolution non-methane total hydrocarbon detection method, comprising the following steps:

[0009] The sampling pump uses negative pressure to extract the initial sample gas from the external environment, and the initial sample gas is completely vaporized by stabilizing the high temperature through the heating pipe;

[0010] The completely vaporized initial sample gas passes through the metal sintered filter at the sampling probe to obtain pure sample gas;

[0011] After the pure sample gas is processed by positive pressure, it is transported to the total hydrocarbon gas path and the methane gas path in equal amounts through the three-way valve; by changing the length of the total hydrocarbon column, the total hydrocarbon FID response time is made the same as the methane FID response time;

[0012] After the pure sample gas in the total hydrocarbon gas path is transported to the total hydrocarbon column through the electronic mass flow controller, the total hydrocarbon FID detector in the total hydrocarbon column senses the total hydrocarbons in the pure sample gas in the total hydrocarbon column and generates a total hydrocarbon FID micro-current signal; the micro-current signal processor obtains the total hydrocarbon FID micro-current signal and calculates the total hydrocarbon concentration;

[0013] The sample gas in the methane gas path is processed by the catalytic furnace to obtain the catalytic sample gas, and the catalytic sample gas enters the methane FID detector through the electronic mass flow controller 2, and senses the methane in the catalytic sample gas to generate a methane FID microcurrent signal; the microcurrent signal processor 2 obtains the methane FID microcurrent signal and calculates the methane concentration;

[0014] The non-methane total hydrocarbon concentration C (NMHC) is calculated by the methane concentration C (CH4) and the total hydrocarbon concentration C (THC). The calculation method is:

[0015] C(NMHC)=C(THC)-C(CH4).

[0016] Compared with the prior art, the embodiments of the present invention have at least the following technical advantages:

[0017] Analysis of the above-mentioned high time resolution non-methane total hydrocarbon detection method provided by the present invention shows that it is mainly designed with a sampling pump, a heating pipe, a sampling probe, a metal sintered filter, a catalytic furnace, a catalyst, a heating and heat preservation material, an electronic mass flow controller 1, an electronic mass flow controller 2, a total hydrocarbon gas path, a methane gas path, a total hydrocarbon column, a proportional valve, a total hydrocarbon FID detector, a methane FID detector, a micro-current signal processor 1, and a micro-current signal processor 2;

[0018] In specific applications, the heating pipe performs stable high-temperature heating on the quantitative initial sample gas obtained by the negative pressure of the sampling pump to prevent condensation of the sample gas, and filters the particulate matter in the initial sample gas through the metal sintered filter arranged at the sampling probe to obtain a relatively pure sample gas; the example of the present invention fully considers that the initial sample gas contains a large amount of particulate matter, and the sample is prevented from condensing by stable high-temperature heating by the heating pipe, and the particulate matter in the initial sample gas is separated through the metal sintered filter at the top of the sampling probe, thereby obtaining a relatively pure sample gas. At the same time, the heating pipe and the sampling probe adopt inert pipelines to prevent the reaction between the heating pipe and the sampling probe under high temperature conditions from affecting the detection results. Similarly, the metal sintered filter does not react with the sample gas and has a high filtering accuracy, thereby preventing particulate matter from entering the equipment and affecting the detection.

[0019] The pure sample gas after filtration is processed by positive pressure and transported to the total hydrocarbon gas line and the methane gas line in equal amounts through a three-way valve. The pure sample gas in the total hydrocarbon gas line enters the total hydrocarbon column and is responded to by the total hydrocarbon FID detector at the tail end of the total hydrocarbon column, generating a real-time and continuous total hydrocarbon FID microcurrent signal. The microcurrent signal processor 1 obtains the amplified total hydrocarbon FID microcurrent signal, and performs integral quantitative analysis on the signal to calculate the total hydrocarbon concentration C (THC). The pure sample gas in the methane gas line is catalyzed by the catalytic furnace in the methane gas line to obtain a catalytically processed sample gas containing only methane. The catalytically processed sample gas enters the methane FID detector to respond, generating a real-time and continuous methane FID microcurrent signal. The microcurrent signal processor 2 obtains the amplified methane FID microcurrent signal, and performs integral quantitative analysis on the signal to calculate the methane concentration C (CH4), and the non-methane total hydrocarbon concentration C (NMHC) is calculated and measured by over-difference subtraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0021] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings.

[0022] Figure 1 It is a schematic diagram of the difference curve of the response time of total hydrocarbons and methane for monitoring the concentration of non-methane total hydrocarbons by the catalytic-FID method in the prior art;

[0023] Figure 2 It is a schematic diagram of the difference curve of the non-methane total hydrocarbon concentration monitored by the catalytic-FID method in the prior art;

[0024] Figure 3 This is a schematic diagram of defining T response time for monitoring total hydrocarbon concentration and methane concentration in a device and method for measuring non-methane total hydrocarbons with high time resolution according to an embodiment of the present invention;

[0025] Figure 4 It is a specific flow chart of the steps in a method for measuring non-methane total hydrocarbons with high time resolution provided by an embodiment of the present invention;

[0026] Figure 5 is a specific processing flow chart of step S20 in a method for measuring non-methane total hydrocarbons with high time resolution provided by an embodiment of the present invention;

[0027] Figure 6 This is an overall architecture diagram of a device for measuring non-methane total hydrocarbons with high time resolution provided by an embodiment of the present invention.

[0028] Reference numerals: sampling pump 10; heating pipe 11; sampling probe 12; metal sintered filter 121; tee 122; catalytic furnace 13; electronic mass flow controller 1 141; electronic mass flow controller 2 142; total hydrocarbon gas line 15; methane gas line 16; total hydrocarbon column 151; total hydrocarbon FID detector 17; methane FID detector 18; micro-current signal processor 1 191; micro-current signal processor 2 192. DETAILED DESCRIPTION

[0029] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0030] Embodiment 1

[0031] The embodiment of the present invention proposes a portable gas chromatograph for measuring non-methane total hydrocarbons with high time resolution. The device adopts the catalytic-FID principle and provides real-time measurement data of total hydrocarbons, methane and non-methane total hydrocarbons with a time resolution as low as 1s. Due to the internal characteristics of the device, the embodiment of the present invention redefines the T response time. The T response time should be divided into two stages, namely T1 and T2. The embodiment of the present invention describes how to control the T1 and T2 times to achieve the same effect of total hydrocarbon and methane response time during the measurement process.

[0032] See also Figure 6 The present invention provides a high time resolution non-methane total hydrocarbon detection device, including a sampling pump 10, a heating pipe 11, a sampling probe 12, a metal sintered filter 121, a catalytic furnace 13, an electronic mass flow controller 141, an electronic mass flow controller 2 142, a total hydrocarbon gas path 15, a methane gas path 16, a total hydrocarbon column 151, a total hydrocarbon FID detector 17, a methane FID detector 18, a micro-current signal processor 191, and a micro-current signal processor 2 192;

[0033] The tail end of the total hydrocarbon gas path 15 is connected to the head end of the total hydrocarbon column 151, and a total hydrocarbon FID detector 17 and a micro-current signal processor 191 are provided at the tail end of the total hydrocarbon column, and the total hydrocarbon FID detector 17 is connected to the micro-current signal processor 191, and an electronic mass flow controller 141 is provided at the tail end of the total hydrocarbon gas path 15;

[0034] The total hydrocarbon FID detector 17 is used to generate a continuous micro-current signal by responding to the total hydrocarbons in the total hydrocarbon column 151 in real time;

[0035] The micro-current signal processor 191 is used to amplify the micro-current signal generated by the total hydrocarbon FID detector 17 and perform integral quantitative analysis on the signal to obtain the total hydrocarbon concentration in the current total hydrocarbon gas path 15;

[0036] The electronic mass flow controller 141 is used to control the total hydrocarbon flow in the total hydrocarbon gas path 15 by adjusting the proportional valve;

[0037] The methane gas line 16 is provided with a catalytic furnace 13 (or the methane gas line 16 is provided with a catalytic furnace 13), and the tail end of the methane gas line 16 is provided with a methane FID detector 18 and a micro-current signal processor 2 192, and the methane FID detector 18 is connected to the micro-current signal processor 2 192, and the head end of the methane gas line 16 is provided with an electronic mass flow controller 2 142;

[0038] The methane FID detector 18 is used to generate a continuous micro-current signal by responding to the methane in the methane gas circuit 16 in real time;

[0039] The micro-current signal processor 2 192 is used to amplify the micro-current signal generated by the methane FID detector 18 and perform integral quantitative analysis on the signal to obtain the methane concentration in the current methane gas circuit 16;

[0040] The electronic mass flow controller 142 is used to control the methane flow in the methane gas line 16.

[0041] The specific design of the high time resolution non-methane total hydrocarbon detection device includes a sample collection unit: the sample collection unit is entirely inert piping, and the main body is composed of a 2m long heating pipe 11 and a sampling probe 12. The temperature of the heating pipe 11 is maintained at 120°C or 20°C higher than the actual sample gas temperature. The sampling probe 12 is provided with a metal sintered filter that does not react with the sample gas, and the filtering accuracy is usually 0.2μm, to prevent particulate matter from entering the device and affecting the detection;

[0042] Gas source supply unit: mainly the gas source required by the FID detector; Hydrogen: Hydrogen is stored in the form of a low-pressure hydrogen storage bottle with a storage capacity of up to 50L, which is safe and convenient to use; Carrier gas: The principle of the portable gas chromatograph mentioned in the embodiment of the present invention is catalytic-FID, and the carrier gas is the sample gas; Air: Air is obtained by filtering ambient air with a high-efficiency hydrocarbon removal filter.

[0043] Catalytic furnace: Catalytic furnace consists of catalyst and heating and heat preservation materials. Catalyst refers to non-methane total hydrocarbon catalyst. Catalyst is mainly composed of precious metals such as palladium and platinum, among which the platinum content ranges from 0.1% to 5%. It is in granular form with a diameter of 3mm (spherical). The operating temperature of the catalytic furnace is 280℃, the catalytic flow rate is about 50ml / min, and the catalytic efficiency is more than 98%.

[0044] Flow control unit: Hydrogen and air are controlled by electronic mass flow controllers. The sample gas is extracted from the external environment by the negative pressure of the sampling pump, and then sent to the total hydrocarbon and methane gas path for analysis under positive pressure. In order to achieve the same T response time for total hydrocarbon and methane detection, the flow control unit makes the following implementation plan:

[0045] Definition: Total hydrocarbon response time T = T11 + T12 Unit: s

[0046] Definition of methane response time T=T21+T22 Unit: s

[0047] The time of T1 and T2 is defined as follows: when the same amount of pure sample gas after physical filtration is introduced and the equipment calibration is completed, the total hydrocarbon responds first. The moment when the total hydrocarbon and methane concentrations are the same is defined as T1, and the moment when the readings are stable after they are the same is defined as T2.

[0048] Define Q1 as the total hydrocarbon gas flow rate, unit: mL / min;

[0049] Define Q2 as the methane gas flow rate, unit: mL / min;

[0050] T1: The first-stage response time of total hydrocarbons and methane. If T1 time is to be the same, that is, T11=T21, then the flow rate of the sample gas must be the same, that is, Q1=Q2. However, due to the influence of the catalytic furnace and the FID detector nozzle aperture in the methane gas path, the rear-end gas resistance is not exactly the same, that is, it cannot be guaranteed that under the same pressure, the total hydrocarbon gas path flow rate Q1 is equal to the methane gas path flow rate Q2, so T1 time cannot be defined to be the same.

[0051] T2: Second-stage response time of total hydrocarbons and methane. To ensure the same T1 time through the above verification, we must first determine the total hydrocarbon T12 and methane T22 time. At this time, by using methane standard gas and adjusting the sampling flow rate, we can achieve that the second response time of total hydrocarbons T12 is equal to the second response time of methane T22, and record the first-stage response time of total hydrocarbons T11 and the first-stage response time of methane T21 when the second-stage response times of the two gas paths are the same.

[0052] An electronic mass flow controller is connected in series in each of the total hydrocarbon and methane gas lines to control and record the total hydrocarbon gas line flow rate Q1 and the methane gas line flow rate Q2 respectively.

[0053] Since the second response time T2 of total hydrocarbon and methane is the same, the total hydrocarbon column length can be changed to achieve the same effect as the first response time of total hydrocarbon and methane. The specific implementation method is to change the length of the total hydrocarbon column to ΔL (mm), and the cross-sectional area of ​​the pipeline is S (cm 2 )

[0054] ΔL=(T11-T21)÷60*Q1÷S;

[0055] After the total hydrocarbon column length is changed, the overall gas path flow Q1 will change. At this time, the built-in proportional valve of the total hydrocarbon gas path is used to adjust the pipeline air resistance so that the flow after adjusting the total hydrocarbon column length is the same as the previous Q1, thereby ensuring that the T response time of the total hydrocarbon and methane is the same.

[0056] Detection unit: equipped with two dedicated micro FID detectors, used to detect the total hydrocarbon and methane concentrations in the sample gas respectively;

[0057] Signal processing unit: By collecting FID micro-current signals, amplifying the micro-current signals, and integrating and quantitatively analyzing the signals, the total hydrocarbon and methane concentrations are calculated.

[0058] Embodiment 2

[0059] See also Figure 4 The present invention also provides a high time resolution non-methane total hydrocarbon detection method, comprising the following steps:

[0060] Step S10: The sample gas is extracted from the external environment by the sampling pump 10 at negative pressure, and the sample gas is completely vaporized by the heat tracing pipe 11 at a stable high temperature. The method of extracting sample gas under negative pressure adopted in the embodiment of the present invention can stably extract a certain amount of sample gas, and the heat tracing pipe 11 is at a stable high temperature to vaporize the sample gas, and the heat tracing pipe 11 is kept at a stable 120°C (i.e., the stable high temperature stated in the above scheme), so as to avoid condensation of components in the sample gas and affect the sampling results.

[0061] Step S11: Filter the particulate matter in the completely vaporized sample gas through the metal sintered filter at the sampling probe 12 to obtain a pure sample gas; the particulate matter generally refers to some dust particles in the air; it should be noted that the heating pipe 11 and the sampling probe 12 both use inert pipelines, and the metal sintered filter does not react with the sample gas to prevent the sample gas detection error caused by the reaction with the sample gas under high temperature conditions, and the filtration accuracy of the metal sintered filter is 0.2μm, which can fully filter the particulate matter and prevent the particulate matter from entering the equipment and affecting the detection accuracy. The metal sintered filter used in the example of the present invention does not react with the sample gas and the metal sintered filter has a high filtration accuracy, which can fully filter the particulate matter in the initial sample gas and prevent the particulate matter from entering the equipment and affecting the detection accuracy, and the sampling probe 12 and the heating pipe 11 are inert pipelines, and the initial sample gas will not react with them, thereby affecting the accuracy of the detection result;

[0062] Step S20: After the filtration, the pure sample gas is positively pressure treated and then transported to the total hydrocarbon gas path 15 and the methane gas path 16 in equal amounts through the tee (it should be noted that the sample gas enters through the negative pressure of the sampling pump and then passes through the tee and is output under positive pressure); the total hydrocarbon FID response time is made the same as the methane FID response time by changing the length of the total hydrocarbon column;

[0063] Step S21: the branched pure sample gas in the total hydrocarbon gas path 15 enters the total hydrocarbon FID detector 17 through the total hydrocarbon column 151, and the total hydrocarbon FID detector 17 responds to the total hydrocarbons in the pure sample gas in the total hydrocarbon column 151 to generate a total hydrocarbon FID microcurrent signal (the above signal refers to the real-time continuous total hydrocarbon FID microcurrent signal obtained by real-time detection);

[0064] The micro-current signal processor 191 obtains the total hydrocarbon FID micro-current signal, amplifies the total hydrocarbon FID micro-current signal, and performs integral quantitative analysis on the signal (the work of the micro-current signal processor 191 is prior art and will not be described in detail here), and calculates the total hydrocarbon concentration;

[0065] Step S22: the pure sample gas after branching in the methane gas path 16 is subjected to catalytic treatment by the catalytic furnace 13 in the methane gas path 16 to obtain catalytic sample gas, wherein the catalytic sample gas is a sample gas formed by catalyzing organic matter other than methane in the pure sample gas in the methane gas path 16 into inorganic matter (the catalytic sample gas contains only methane, a single gas);

[0066] The catalyzed sample gas enters the methane FID detector 18, and the methane FID detector 18 responds to the remaining organic matter in the catalyzed sample gas (at this time, the inorganic matter in the sample gas does not respond to the methane FID, and the organic matter in the sample gas is only methane), generating a methane FID micro-current signal;

[0067] The micro-current signal processor 2 192 obtains the methane FID micro-current signal, amplifies the methane FID micro-current signal, and performs integral quantitative analysis on the signal to calculate the methane concentration.

[0068] Preferably, the catalytic furnace 13 performs catalytic treatment to obtain the catalytic sample gas, specifically including: setting the working temperature of the catalytic furnace 13, controlling the working temperature to a high temperature of 280°C (generally, the temperature of methane combustion is 538°C) and controlling the catalytic flow rate to 50ml / min for fine catalysis, so as to catalyze the organic matter (or organic matter gas) other than methane in the pure sample gas in the methane gas path 16 into inorganic matter;

[0069] Step S23: Measure the concentration of non-methane total hydrocarbons by subtraction method: C(NMHC)=C(THC)-C(CH4);

[0070] Where, C(NMHC) is the concentration of non-methane total hydrocarbons; C(THC) is the concentration of total hydrocarbons; C(CH4) is the concentration of methane;

[0071] See also Figure 5, wherein, during the execution of step S20, an equal amount of pure sample gas is introduced into the total hydrocarbon gas line 15 and the methane gas line 16 at the same time to obtain the total hydrocarbon concentration and the methane concentration. In order to ensure that the total hydrocarbon FID detector response time of the total hydrocarbon gas line is consistent with the methane FID detector response time of the methane gas line, and the total hydrocarbon flow rate of the total hydrocarbon gas line is also consistent with the methane flow rate of the methane gas line, the flow controller executes the following steps:

[0072] Step S201: the flow controller obtains the response time of the total hydrocarbon FID detector 17 in the total hydrocarbon gas line 15 and the response time of the methane FID detector 18 in the methane gas line 16, and then calculates the total hydrocarbon concentration when the total hydrocarbon FID detector 17 in the total hydrocarbon gas line 15 responds to the total hydrocarbon (i.e., the response time is recorded as the response time) and the methane concentration when the methane FID detector 18 in the methane gas line 16 responds to the methane;

[0073] Define total hydrocarbon response time T=T11+T12; unit: s;

[0074] Define the methane response time T=T21+T22; unit: s;

[0075] Among them, the first response time of total hydrocarbons is recorded as T11, and the time of the stabilization instant after the second response of total hydrocarbons is recorded as T12;

[0076] Among them, the first response time of methane is recorded as T21, and the time of the stabilization moment after the second response of methane is recorded as T22;

[0077] Wherein, in the case where the length of the total hydrocarbon column 151 is not changed, the above T12 and T22 are the second response times of the total hydrocarbon and methane, that is, T12=T22, and the subsequent operation needs to achieve the same T11 and T21 by changing the length of the total hydrocarbon column 151;

[0078] Step S202: the flow control unit defines the moment when the total hydrocarbon concentration is equal to the methane concentration according to the total hydrocarbon concentration at the response time of the total hydrocarbon FID detector 17 and the methane concentration at the response time of the methane FID detector 18 as T1, and the moment when the total hydrocarbon concentration is equal to the methane concentration until the reading is stable as T2, at which time T12=T22;

[0079] Step S203: The flow control unit controls the total hydrocarbon gas line 15 flow rate Q1 to be the same as the methane gas line 16 flow rate Q2 by changing the length of the total hydrocarbon column 151, so that the first response time of the total hydrocarbon is the same as the first response time of the methane (that is, T11 is the same as T21). The formula for changing the length of the total hydrocarbon column 151 is as follows:

[0080] ΔL=(T11-T21)÷60*Q1÷S;

[0081] Where ΔL is the total hydrocarbon column 151 changed length, in mm;

[0082] S is the cross-sectional area of ​​the pipeline, in cm 2 ;

[0083] T11 is the first response time of total hydrocarbons;

[0084] T21 is the first response time of methane;

[0085] Q1 is the total hydrocarbon gas flow rate in mL / min.

[0086] After changing the length of the total hydrocarbon column 151, the total hydrocarbon gas path flow rate Q1 will change. At this time, the built-in proportional valve of the total hydrocarbon gas path is used to adjust the pipeline air resistance so that the flow rate after adjusting the total hydrocarbon column 151 is the same as the previous Q1, which can ensure that the T response time of the total hydrocarbons and the T response time of methane are the same, thereby ensuring the accuracy of the sample measurement concentration; it should be noted that under normal circumstances, the first response time of the total hydrocarbons will be relatively early, so increasing the length of the total hydrocarbon column 151 is of great significance. By increasing the length of the total hydrocarbon column 151, the value of the first response time of the total hydrocarbons recorded as T11 can be increased, so as to finally achieve the first response time of the total hydrocarbons T11 being the same as the first response time of methane T21. Since T12 (the time of the stabilization moment after the second response of the total hydrocarbons) and T22 (the time of the stabilization moment after the second response of the methane) after stabilization are always the same, the technical purpose of achieving the same response time of the total hydrocarbons T and the T response time of methane can be achieved by changing the length of the total hydrocarbon column 151, thereby ensuring the accuracy of the sample measurement concentration.

[0087] In summary, the embodiment of the present invention proposes a portable gas chromatograph for measuring non-methane total hydrocarbons with high time resolution. The device adopts the catalytic-FID principle and collects samples through negative pressure of a high-temperature sampling pump. The sample gas is then divided into two paths through a three-way connection. One path of the sample gas enters the total hydrocarbon FID detector to measure the total hydrocarbon concentration (THC) in the sample gas; the other path of the sample gas passes through the catalytic furnace and enters the methane FID detector. The function of the catalytic furnace is to catalyze the organic matter in the sample gas into inorganic matter other than methane. The inorganic matter does not respond on the methane FID detector, and the methane concentration (CH4) in the sample gas is measured; the non-methane total hydrocarbon concentration is then measured by subtraction: C(NMHC)=C(THC)-C(CH4), and the time resolution is as low as 1s. Due to the internal characteristics of the device, the embodiment of the present invention redefines the T response time. The T response time should be divided into two stages, namely T1 and T2 (see Appendix). Figure 3 ), the embodiment of the present invention describes how to achieve the same response time of total hydrocarbons and methane during the measurement process by controlling the T1 and T2 times.

[0088] In summary, the technical solutions of the embodiments of the present invention have the following beneficial effects: 1. The portable gas chromatograph can realize on-site monitoring, and can detect the content of total non-methane hydrocarbons in the sample gas with high time resolution; 2. The portable chromatograph can effectively solve the problem of large data deviation caused by the timeliness of samples caused by third-party detection. 3. The same system response time for total hydrocarbons and methane can ensure the accuracy of the measurement data, that is, the total hydrocarbon and methane concentrations at the same time point are obtained, and then the accurate concentration of total non-methane hydrocarbons in the sample gas in the same period is calculated. 4. The catalytic method-FID method can be used in the factory boundary and the field of mobile vehicles to capture the concentration value of total non-methane hydrocarbons in real time and draw a concentration trend curve. 5. High time resolution measurement of total non-methane hydrocarbons to achieve second-level measurement; the response time of total hydrocarbons and methane remains the same at all times to avoid measurement concentration differences caused by response time differences.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. A person skilled in the art may modify the technical solutions described in the above embodiments, or replace part or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high time resolution non-methane total hydrocarbon detection method, characterized in that: The detection process is realized based on the high time resolution non-methane total hydrocarbon detection device, including the following steps: The sampling pump uses negative pressure to extract the initial sample gas from the external environment, and the initial sample gas is completely vaporized by stabilizing the high temperature through the heating pipe; The completely vaporized initial sample gas passes through the metal sintered filter at the sampling probe to obtain pure sample gas; After the sample gas is treated with positive pressure, it is transported to the total hydrocarbon gas line and methane gas line in equal amounts through the three-way valve; By changing the length of the total hydrocarbon column, the total hydrocarbon FID response time is made the same as the methane FID response time; After the sample gas in the total hydrocarbon gas path is transported to the total hydrocarbon column through the electronic mass flow controller, the total hydrocarbon FID detector in the total hydrocarbon column senses the total hydrocarbons in the pure sample gas in the total hydrocarbon column and generates a total hydrocarbon FID micro-current signal; The micro-current signal processor 1 obtains the total hydrocarbon FID micro-current signal and calculates the total hydrocarbon concentration; The sample gas in the methane gas path is processed by the catalytic furnace to obtain the catalytic sample gas. After the catalytic sample gas enters the methane column through the electronic mass flow controller 2, the methane FID detector in the methane gas path senses the methane in the catalytic sample gas and generates a methane FID micro-current signal; the micro-current signal processor 2 obtains the methane FID micro-current signal and calculates the methane concentration; The non-methane total hydrocarbon concentration C (NMHC) is calculated by the methane concentration C (CH4) and the total hydrocarbon concentration C (THC). The calculation method is: C(NMHC)=C(THC)-C(CH4); The method of changing the length of the total hydrocarbon column to make the total hydrocarbon FID response time the same as the methane FID response time specifically includes the following steps: The controller obtains the total hydrocarbon FID detector response time in the total hydrocarbon gas path and the methane FID detector response time in the methane gas path, and then calculates the total hydrocarbon concentration when the total hydrocarbon FID detector in the total hydrocarbon gas path responds to the total hydrocarbons and the methane concentration when the methane FID detector in the methane gas path responds to the methane; Define the total hydrocarbon response time T = T11 + T12; Unit: s; Define the methane response time T=T21+T22; Unit: s; Among them, the first response time of total hydrocarbons is recorded as T11, and the time from the first response of total hydrocarbons to the moment of stability is recorded as T12; Among them, the first response time of methane is recorded as T21, and the time from the first response of methane to the moment of stabilization is recorded as T22; By using methane standard gas and adjusting the sampling flow rate, T12 is equal to T22, and the first response time T11 of total hydrocarbons and the first response time T21 of methane are recorded when T12 is equal to T22; The flow control unit controls the total hydrocarbon gas flow Q1 to be the same as the methane gas flow Q2 by changing the total hydrocarbon column length, so that the first response time of the total hydrocarbon is the same as the first response time of the methane, that is, T11=T21; the total hydrocarbon column length change formula is as follows: ΔL=(T11-T21)÷60*Q1÷S; Where ΔL is the total hydrocarbon column change length, in mm; S is the cross-sectional area of ​​the pipeline, in cm 2 ; T11 is the first response time of total hydrocarbons; T21 is the first response time of methane; Q1 is the total hydrocarbon gas flow rate, in mL / min.

2. A high time resolution non-methane total hydrocarbon detection method according to claim 1, characterized in that: The high time resolution non-methane total hydrocarbon detection device comprises a sample collection unit and a host; The host comprises a gas source supply unit, a catalytic furnace, a flow control unit, a detection unit, and a signal processing unit; the sample collection unit comprises a sampling pump, a heating pipe, and a sampling probe; a metal sintered filter is installed at the sampling probe; the catalytic furnace comprises a catalyst and a heating and heat-insulating material; the flow control unit comprises an electronic mass flow controller 1 and an electronic mass flow controller 2; the detection unit comprises a total hydrocarbon FID detector and a methane FID detector; the signal processing unit comprises a micro-current signal processor 1 and a micro-current signal processor 2; the gas source supply unit comprises a low-pressure hydrogen storage bottle, a sample gas pipeline, and an air pipeline; the sample gas pipeline comprises a total hydrocarbon gas circuit and a methane gas circuit; Wherein, the sampling pump is placed at the tail end of the heating pipe; the head end of the heating pipe is connected to the tail end of the sampling probe; the gas outlet of the sampling pump is connected to the head end of the total hydrocarbon gas path and the head end of the methane gas path through a tee respectively; an electronic mass flow controller 1, a total hydrocarbon column and a proportional valve are installed in the total hydrocarbon gas path; wherein, the electronic mass flow controller 1 is connected to the head end of the total hydrocarbon column; the proportional valve is connected to the tail end of the total hydrocarbon column; a total hydrocarbon FID detector and a microcurrent signal processor 1 are arranged in the total hydrocarbon gas path; the microcurrent signal processor 1 is electrically connected to the total hydrocarbon FID detector; a high-efficiency hydrocarbon removal filter is installed at the head end of the air duct; a catalytic furnace and an electronic mass flow controller 2 are installed inside the methane gas path; wherein, the tail end of the catalytic furnace is connected to the electronic mass flow controller 2; a methane FID detector and a microcurrent signal processor 2 are arranged in the methane gas path; the methane FID detector is electrically connected to the microcurrent signal processor 2; The proportional valve is used to adjust the air resistance of the pipeline and thus adjust the total hydrocarbon flow in the total hydrocarbon column; The total hydrocarbon FID detector is used to generate a continuous micro-current signal by responding to the total hydrocarbons in the total hydrocarbon gas path in real time; The micro-current signal processor 1 is used to amplify the micro-current signal generated by the total hydrocarbon FID detector and perform integral quantitative analysis on the signal to obtain the total hydrocarbon concentration in the current total hydrocarbon gas path; The electronic mass flow controller 1 is used to adjust the total hydrocarbon flow in the total hydrocarbon gas path; A catalytic furnace is provided in the methane gas circuit, and the tail end of the methane gas circuit is connected to the head end of the catalytic furnace. A methane FID detector and a micro-current signal processor 2 are installed at the tail end of the catalytic furnace, and the methane FID detector is connected to the micro-current signal processor 2; The methane FID detector is used to generate a continuous micro-current signal by responding to the methane in the methane gas path in real time; The micro-current signal processor 2 is used to amplify the micro-current signal generated by the methane FID detector and perform integral quantitative analysis on the signal to obtain the methane concentration in the current methane gas path; The second electronic mass flow controller is used to adjust the methane flow in the methane gas path; The heating pipe is 2m long and its temperature is maintained at 120°C.

3. A high time resolution non-methane total hydrocarbon detection method according to claim 2, characterized in that: The heating pipe and the sampling probe both use inert pipelines.

4. The high time resolution non-methane total hydrocarbon detection method according to claim 2, characterized in that: The filtration accuracy of the metal sintered filter is 0.2 μm.

5. The high time resolution non-methane total hydrocarbon detection method according to claim 2, characterized in that: The catalytic furnace performs catalytic treatment to obtain catalytic sample gas, specifically comprising: The working temperature of the catalytic furnace is set to be controlled at a high temperature of 280° C. and the catalytic flow rate is controlled to be 50 ml / min for high-efficiency catalysis.

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