Trace methane detection device and detection method thereof

Abstract

The invention relates to a trace methane detection device and a detection method thereof, the trace methane detection device comprises: a sampling detection gas circuit formed by sequentially connecting a gas inlet, a three-way solenoid valve I, a quantitative tube, a sampling pump, a three-way solenoid valve II, a trace methane sensor and a gas outlet; the gas phase separation gas circuit comprises a constant flow pump and a chromatographic separation pipe which are connected between other ports of the three-way electromagnetic valve I and the three-way electromagnetic valve II, and the three-way electromagnetic valve I, the quantitative pipe, the three-way electromagnetic valve II, the constant flow pump and the chromatographic separation pipe form the gas phase separation gas circuit; and the signal processing and analyzing module is in signal connection with the trace methane sensor and is used for processing a detection signal of the trace methane sensor to obtain the methane concentration. According to the trace methane detection device and the detection method thereof, the to-be-detected gas sample is separated through the chromatographic separation tube, and the high-sensitivity gas sensor is used for detecting the gas concentration, so that the strong anti-interference performance brought by gas separation in a gas chromatographic analysis method is reserved, and the high-sensitivity detection capability of the gas sensor is combined.

Description

Technical Field

[0001] The invention belongs to the technical field of trace gas detection, and in particular relates to a trace methane detection device and a detection method thereof. Background Art

[0002] Methane is a colorless, odorless, flammable and explosive gas. Because it is very easy to explode in the atmosphere and cause safety accidents, most methane detectors mainly detect the methane explosion limit concentration (4.9%) or the methane power-off concentration (0.5% to 1.5%). However, methane is a common gas existing in nature. It is not only distributed in coal mines, but also exists in the active fault zones of the earth. Studies have shown that the change in the concentration of methane gas escaping from earthquake fault zones can capture information about crustal activity, and its concentration ranges from a few ppm to tens of ppm. In addition, large power transformers are mainly oil-immersed. During operation, due to the effects of electricity and heat, the oil-paper insulation material inside will crack, age or discharge to produce trace amounts of methane gas. By detecting the methane gas content in the transformer insulating oil, the operating status of the transformer can be judged to ensure the economical and safe operation of the transformer.

[0003] Common types of methane sensors include electrochemical sensors, optical sensors, and gas chromatographs. Optical sensors are made based on the spectral absorption principle of methane. Among them, infrared optical methane sensors are the most widely used sensors at present. They have fast response speed and wide measurement range, but their detection limit is high, generally 0.1%, and the cost of optical components is high. The working principle of electrochemical sensors is to measure gas concentration by chemical reaction between devices and the gas being measured, especially the catalytic combustion sensors commonly used in mine alarms. These sensors are low in cost and have high detection accuracy at specific concentrations, but they are very easy to age and have a short lifespan. Using a gas chromatograph to measure gas concentration is currently recognized as a method with high sensitivity, but gas chromatographs are generally large in size, require carrier gas, and have high equipment costs. In addition, semiconductor sensors are generally suitable for low-concentration gas measurements because of their low cost, but semiconductor sensors usually have poor gas selectivity and are easily interfered with, so their use is also limited. Summary of the invention

[0004] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objects of the present invention is to at least solve 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 trace methane detection device and a detection method thereof that meet one or more of the above-mentioned needs.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] A trace methane detection device, comprising:

[0007] The sampling and detection gas circuit is composed of an air inlet, a three-way solenoid valve 1, a quantitative tube, a sampling pump, a three-way solenoid valve 2, a trace methane sensor, and an air outlet connected in sequence; wherein the sampling pump is used to input the gas sample to be tested into the quantitative tube, and the trace methane sensor is used for detection;

[0008] A gas phase separation gas circuit, comprising a constant flow pump and a chromatographic separation tube connected between the remaining ports of the three-way solenoid valve 1 and the three-way solenoid valve 2, wherein the three-way solenoid valve 1, the quantitative tube, the three-way solenoid valve 2, the constant flow pump and the chromatographic separation tube constitute the gas phase separation gas circuit; wherein, by switching the three-way solenoid valve 1 and the three-way solenoid valve 2, the gas in the quantitative tube is input into the chromatographic separation tube by the constant flow pump for gas chromatography separation, and the gas after gas chromatography separation is input into the trace methane sensor for detection;

[0009] The signal processing and analysis module is connected to the trace methane sensor signal and is used to process the detection signal of the trace methane sensor to obtain the methane concentration.

[0010] As a preferred embodiment, the trace methane sensor is based on multi-walled carbon nanotubes and loaded with tin oxide nanospheres with palladium particles deposited on the surface.

[0011] As a preferred solution, the surface deposition amount of palladium particles in the tin oxide nanospheres is 2.5-3.5 wt %, and the diameter of the tin oxide nanospheres is no more than 10 μm.

[0012] As a preferred solution, tin oxide nanospheres with palladium particles deposited on the surface are prepared by a hydrothermal method, and then mixed with multi-walled carbon nanotubes dispersed by ball milling and dried to form a powder, which is then sputtered onto a quartz substrate to obtain a trace methane sensor.

[0013] As a preferred solution, the chromatographic separation tube is wrapped with a heat preservation tube, and a heating wire is provided between the heat preservation tube and the chromatographic separation tube.

[0014] As a preferred embodiment, the chromatographic separation tube is a capillary tube with an inner wall coated with a graphene film, the inner diameter of the capillary tube is 400 to 800 μm, and the length is 4 to 6 meters.

[0015] As a preferred solution, the volume of the quantitative tube is 1 to 3 mL.

[0016] As a preferred solution, the flow rate of the constant flow pump is stably controlled at 20 mL / min±1 mL / min.

[0017] The present invention also provides a detection method of the trace methane detection device as described in any of the above schemes, comprising the following steps:

[0018] S1. The gas sample to be tested collects a quantitative volume of gas through the sampling and detection gas path, and the detection signal of the trace methane sensor is used as the zero point signal;

[0019] S2. Switch three-way solenoid valve 1 and three-way solenoid valve 2. The gas in the quantitative tube passes through the chromatographic separation tube and then enters the trace methane sensor for detection. The signal processing and analysis module processes the detection signal of the trace methane sensor to obtain the methane concentration.

[0020] As a preferred solution, in step S2, the detection signal of the trace methane sensor is processed, and compensation correction is also performed on the detection signal:

[0021]

[0022] Among them, U 补偿后 is the detection signal after compensation, U 补偿前 is the detection signal of the trace methane sensor, U 零点 is the zero point signal, and α is the correction coefficient.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The trace methane detection device and detection method of the present invention separate the gas sample to be tested through a chromatographic separation tube (i.e., a capillary tube coated with a graphene film), and use a highly sensitive gas sensor to detect the gas concentration, which not only retains the strong anti-interference brought about by gas separation in the gas chromatography analysis method, but also combines the high-sensitivity detection capability of the gas sensor; in addition, the environmental interference problem of the signal is solved through the reference compensation processing of the sensor itself, and there is no need to use a carrier gas, so that the volume of the detection device is greatly reduced and the detection cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural diagram of the trace methane detection device of Example 1 of the present invention. DETAILED DESCRIPTION

[0026] 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.

[0027] Embodiment 1:

[0028] like Figure 1 As shown, the trace methane detection device of this embodiment includes a first three-way solenoid valve 1-1, a quantitative tube 2, an air pump 3, a second three-way solenoid valve 1-2, a micro-chromatographic separation module 4, a constant flow pump 5, a trace methane sensor 6 and a signal processing and analysis module 7.

[0029] Specifically, the air inlet is connected to the first three-way solenoid valve 1-1, the quantitative tube 2, the air pump 3, the second three-way solenoid valve 1-2 and the trace methane sensor 6 in sequence, which are connected to the air outlet to form a sampling and detection air circuit. The sampling and detection air circuit is used to collect the gas to be tested and input it into the quantitative tube. The trace methane sensor contacts the mixed gas sample to be tested (i.e., the mixed gas) and records the reference signal as a zero signal after temperature and air pressure interference correction; the second air outlet of the first three-way solenoid valve 1-1 is connected to the micro-chromatographic module 4, and the second air inlet of the second three-way solenoid valve 1-2 is connected to the constant flow pump 5. The quantitative tube 2 passes through the first three-way solenoid valve 1-1, the micro-chromatographic separation module 4, the constant flow pump 5, and the second three-way solenoid valve 1-2 in sequence to form a gas phase separation air circuit. The gas in the quantitative tube 2 is input into the micro-chromatographic separation module 4 by the constant flow pump 5 and then sent to the trace methane sensor 6 for detection. The sensor detection signal is analyzed by the signal processing and analysis module and then the methane concentration is output.

[0030] The air pump, the first three-way solenoid valve, the constant flow pump, and the second three-way solenoid valve constitute an air circuit control module. Through the single control of the first three-way solenoid valve and the second three-way solenoid valve, the device forms two air circuits. The air pump is used to collect the gas to be tested, and is powered on only when the collection air circuit is working. The constant flow pump uses a micro diaphragm air pump and a digital flow meter to stably control the flow rate in the gas phase separation air circuit through a program. In order to fully separate the methane gas from other gases in the mixed gas, the flow rate is stably controlled at 20mL / min±1mL / min.

[0031] The quantitative tube 2 of this embodiment is a fixed volume gas tube, which is used to accurately control the volume of the collected gas for quantitative analysis. The size of the quantitative tube can be determined according to the detection range. When the detection range is large, the quantitative tube can be 1mL; when the detection range is small, the quantitative tube can be 3mL.

[0032] The micro-chromatographic module 4 of this embodiment is based on the principle of gas chromatography separation, and separates methane gas from other components of gas in time sequence. The micro-chromatographic module 4 includes a constant temperature tube and a chromatographic separation tube. The chromatographic separation tube is wrapped with a constant temperature tube, and the constant temperature tube contains a resistance heating wire and a temperature controller to accurately control the temperature at 45°C. The chromatographic separation tube is a bundle of capillaries coated with graphene film, with an inner diameter of 600μm and a length of 4 to 6 meters.

[0033] The trace methane sensor 6 of the present embodiment is a micro-nano gas sensor, which is based on multi-walled carbon nanotubes and tin oxide nanospheres loaded with palladium particles. The surface deposition amount of palladium particles is 2.5wt% to 3.5wt%, and the diameter of the tin oxide nanospheres is not more than 10μm. The tin oxide nanospheres loaded with palladium particles are prepared by a hydrothermal method, and then mixed with multi-walled carbon nanotubes dispersed by ball milling and dried to form a powder, which is sputtered onto a quartz substrate to form a gas sensor; this micro-nano structure of the wire-nanosphere combination not only utilizes the good conductivity of the linear nanotubes, but also the interlacing of the linear structure forms voids that facilitate the embedding of the nanospheres, thereby increasing the contact area between the palladium particles and the gas.

[0034] The signal processing and analysis module 7 of this embodiment is connected to the trace methane sensor 6 by an electrode, and is used to measure the response signal of the sensor. Specifically, the signal processing and analysis module includes a signal acquisition circuit, an amplification and noise reduction circuit, an automatic adjustment circuit, and a reference compensation circuit. The response signal of the sensor is collected by the signal acquisition circuit in turn, and then the amplification and noise reduction circuit performs signal amplification and noise reduction to output a response value. The response value is converted into a digital signal after compensation by the reference compensation circuit. When the signal noise is large, the automatic adjustment circuit performs zeroing to reduce the noise. The specific structure of the above-mentioned signal processing and analysis module can refer to the prior art and will not be repeated here.

[0035] Based on the above-mentioned trace methane detection device, the detection method of the trace methane detection device of this embodiment includes the following steps:

[0036] (1) The gas sample to be tested is passed through the sampling and detection gas path to collect a quantitative volume of gas, and the detection signal of the trace methane sensor is used as the zero point signal;

[0037] (2) Switching three-way solenoid valve 1 and three-way solenoid valve 2, the gas in the quantitative tube passes through the chromatographic separation tube and then enters the trace methane sensor for detection. The signal processing and analysis module processes the detection signal of the trace methane sensor to obtain the methane concentration.

[0038] The processing of the detection signal of the trace methane sensor also includes compensation and correction of the detection signal:

[0039]

[0040] Among them, U 补偿后 is the detection signal after compensation, U 补偿前 is the detection signal of the trace methane sensor, U 零点 is the zero-point signal, α is the correction coefficient;

[0041] Finally, the compensated detection signal is converted into methane concentration. The specific conversion formula can be referred to the prior art and will not be described here.

[0042] Embodiment 2:

[0043] The difference between the trace methane detection device of this embodiment and that of embodiment 1 is as follows:

[0044] The flow direction of the gas phase separation gas path can be reversed, from the quantitative tube through the second three-way solenoid valve, the constant flow pump, the micro-chromatographic separation module, the first three-way solenoid valve in sequence back to the quantitative tube, forming a gas phase separation gas path, and also realizing gas chromatography separation; then the second three-way solenoid valve is controlled again to be connected with the trace methane sensor to realize detection, meeting the needs of different applications; that is, through the single control of the first three-way solenoid valve and the double control of the second three-way solenoid valve, the device forms two gas paths, and the gas after gas chromatography separation can also be input to the trace methane sensor for detection;

[0045] For other structures, please refer to Example 1.

[0046] 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 trace methane detection device, characterized in that: include: The sampling and detection gas circuit is composed of an air inlet, a three-way solenoid valve 1, a quantitative tube, a sampling pump, a three-way solenoid valve 2, a trace methane sensor, and an air outlet connected in sequence; wherein the sampling pump is used to input the gas sample to be tested into the quantitative tube, and the trace methane sensor is used for detection; A gas phase separation gas circuit, comprising a constant flow pump and a chromatographic separation tube connected between the remaining ports of the three-way solenoid valve 1 and the three-way solenoid valve 2, wherein the three-way solenoid valve 1, the quantitative tube, the three-way solenoid valve 2, the constant flow pump and the chromatographic separation tube constitute the gas phase separation gas circuit; wherein, by switching the three-way solenoid valve 1 and the three-way solenoid valve 2, the gas in the quantitative tube is input into the chromatographic separation tube by the constant flow pump for gas chromatography separation, and the gas after gas chromatography separation is input into the trace methane sensor for detection; The signal processing and analysis module is connected to the trace methane sensor signal and is used to process the detection signal of the trace methane sensor to obtain the methane concentration.

2. The trace methane detection device according to claim 1, characterized in that: The trace methane sensor is based on multi-walled carbon nanotubes and loaded with tin oxide nanospheres with palladium particles deposited on the surface.

3. The trace methane detection device according to claim 2, characterized in that: The surface deposition amount of palladium particles in the tin oxide nanospheres is 2.5-3.5wt%, and the diameter of the tin oxide nanospheres is no more than 10μm.

4. The trace methane detection device according to claim 3, characterized in that: Tin oxide nanospheres with palladium particles deposited on the surface were prepared by a hydrothermal method, and then mixed with multi-walled carbon nanotubes dispersed by ball milling and dried to form powder, which was sputtered onto a quartz substrate to obtain a trace methane sensor.

5. The trace methane detection device according to any one of claims 1 to 4, characterized in that: The chromatographic separation tube is wrapped with a heat preservation tube, and a heating wire is arranged between the heat preservation tube and the chromatographic separation tube.

6. The trace methane detection device according to claim 5, characterized in that: The chromatographic separation tube is a capillary tube with a graphene film plated on the inner wall. The inner diameter of the capillary tube is 400-800 μm and the length is 4-6 meters.

7. The trace methane detection device according to any one of claims 1 to 4, characterized in that: The volume of the quantitative tube is 1 to 3 mL.

8. The trace methane detection device according to any one of claims 1 to 4, characterized in that: The flow rate of the constant flow pump is stably controlled at 20 mL / min±1 mL / min.

9. The detection method of the trace methane detection device according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. The gas sample to be tested collects a quantitative volume of gas through the sampling and detection gas path, and the detection signal of the trace methane sensor is used as the zero point signal; S2. Switch three-way solenoid valve 1 and three-way solenoid valve 2. The gas in the quantitative tube passes through the chromatographic separation tube and then enters the trace methane sensor for detection. The signal processing and analysis module processes the detection signal of the trace methane sensor to obtain the methane concentration.

10. The detection method according to claim 9, characterized in that: In the step S2, the detection signal of the trace methane sensor is processed, and compensation correction is also performed on the detection signal: Among them, U 补偿后 is the detection signal after compensation, U 补偿前 is the detection signal of the trace methane sensor, U 零点 is the zero point signal, and α is the correction coefficient.

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