Trace methane detection device

Abstract

The utility model relates to a trace methane detection device which comprises a sampling detection gas circuit formed by sequentially connecting a gas inlet, a three-way electromagnetic valve I, a quantitative tube, a sampling pump, a three-way electromagnetic 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 gas sample to be detected is separated through the chromatographic separation tube, and the high-sensitivity gas sensitive sensor is used for detecting the gas concentration, so that not only is the strong anti-interference property brought by gas separation in a gas chromatographic analysis method reserved, but also the high-sensitivity detection capability of the gas sensitive sensor is combined.

Description

Technical Field

[0001] This utility model belongs to the field of trace gas detection technology, specifically relating to a trace methane detection device. Background Technology

[0002] Methane is a colorless, odorless, flammable, and explosive gas. Due to its high flammability and tendency to explode in the atmosphere, it can easily cause safety accidents. Most methane detectors primarily detect the explosive limit concentration (4.9%) or the concentration at the power outage (0.5%–1.5%). However, methane is a common gas found in nature, not only in coal mines but also along active fault lines. Studies have shown that changes in the concentration of methane gas escaping from earthquake fault lines can capture information about crustal activity, with concentration variations ranging from a few ppm to tens of ppm. Furthermore, large power transformers are primarily oil-immersed. During operation, due to electrical and thermal effects, the oil-paper insulation material inside may decompose, age, or discharge, producing trace amounts of methane gas. Detecting the methane gas content in the transformer's insulating oil can help determine the transformer's operating status and ensure its economical and safe operation.

[0003] Common types of methane sensors include electrochemical sensors, optical sensors, and gas chromatographs. Optical sensors utilize the spectral absorption principle of methane. Infrared optical methane sensors are currently the most widely used type, offering fast response and a wide measurement range, but their detection limit is relatively high, typically 0.1%, and the optical components are expensive. Electrochemical sensors work by using a chemical reaction between the device and the analyte gas to measure gas concentration. Catalytic combustion sensors, particularly common in mine alarm systems, are low-cost and offer high accuracy at specific concentrations, but they are prone to aging and have a short lifespan. Gas chromatography is currently recognized as a highly sensitive method for measuring gas concentration; however, gas chromatographs are generally bulky, require carrier gases, and are expensive. Furthermore, semiconductor sensors, due to their low cost, are generally suitable for measuring low-concentration gases, but their gas selectivity is usually poor, making them susceptible to interference, thus limiting their application. Utility Model Content

[0004] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this utility model is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this utility model is to provide a trace methane detection device that meets one or more of the aforementioned requirements.

[0005] To achieve the above-mentioned objectives, this utility model adopts the following technical solution:

[0006] A trace methane detection device, comprising:

[0007] The sampling and detection gas path consists of an inlet, a three-way solenoid valve I, a metering tube, a sampling pump, a three-way solenoid valve II, a trace methane sensor, and an outlet connected in sequence. The sampling pump inputs the gas sample to be tested into the metering tube, and the trace methane sensor detects it.

[0008] The gas phase separation gas path includes a constant flow pump and a chromatographic separation tube connected between the remaining ports of three-way solenoid valve one and three-way solenoid valve two. Three-way solenoid valve one, metering tube, three-way solenoid valve two, constant flow pump and chromatographic separation tube constitute the gas phase separation gas path. By switching three-way solenoid valve one and three-way solenoid valve two, the constant flow pump inputs the gas in the metering tube into the chromatographic separation tube for gas phase separation, and the gas after gas phase 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 chromatographic separation tube is wrapped with an insulation tube, and a heating wire is provided between the insulation tube and the chromatographic separation tube.

[0011] As a preferred embodiment, the chromatographic separation tube is a capillary with an inner wall coated with a graphene film, the inner diameter of the capillary is 400-800 μm and the length is 4-6 meters.

[0012] As a preferred embodiment, the volume of the metering tube is 1 to 3 mL.

[0013] As a preferred embodiment, the trace methane sensor uses multi-walled carbon nanotubes as a substrate and loads tin oxide nanospheres with palladium particles deposited on their surface.

[0014] As a preferred embodiment, the diameter of the tin oxide nanospheres is no greater than 10 μm.

[0015] Compared with the prior art, the advantages of this utility model are:

[0016] The trace methane detection device of this invention separates the gas sample to be tested through a chromatographic separation tube (i.e. a capillary tube with an inner graphene film), and uses a highly sensitive gas sensor to detect the gas concentration. It retains the strong anti-interference ability brought by gas separation in gas chromatography analysis method, and combines the high sensitivity detection capability of gas sensor. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the trace methane detection device of Embodiment 1 of this utility model. Detailed Implementation

[0018] To more clearly illustrate the embodiments of this utility model, the specific implementation methods of this utility model will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of this utility model. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0019] Example 1:

[0020] 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, a gas 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.

[0021] Specifically, the inlet is sequentially connected to the first three-way solenoid valve 1-1, the metering tube 2, the gas pump 3, the second three-way solenoid valve 1-2, and the trace methane sensor 6, which are then connected to the outlet to form a sampling and detection gas path. This sampling and detection gas path is used to collect the gas to be tested and input it into the metering tube. The trace methane sensor contacts the mixed gas sample to be tested (i.e., the mixed gas) and records the reference signal as the zero-point signal after temperature and pressure interference correction. The second outlet of the first three-way solenoid valve 1-1 is connected to the micro-chromatographic module 4, and the second inlet of the second three-way solenoid valve 1-2 is connected to the constant flow pump 5. The gas phase separation gas path is formed by sequentially passing 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 from the metering tube 2. The constant flow pump 5 inputs the gas in the metering tube 2 into the micro-chromatographic separation module 4 and then into the trace methane sensor 6 for detection. The sensor detection signal is analyzed by the signal processing and analysis module and outputs the methane concentration.

[0022] The gas path control module consists of an air pump, a first three-way solenoid valve, a constant flow pump, and a second three-way solenoid valve. Through single control of the first and second three-way solenoid valves, the device forms two gas paths. The air pump is used to collect the gas to be tested and is only powered on when the gas collection path is working. The constant flow pump uses a miniature diaphragm air pump and a digital flow meter to stably control the flow rate in the gas phase separation path through a program. In order to fully separate methane gas from other gases in the mixed gas, the flow rate is stably controlled at 20 mL / min ± 1 mL / min.

[0023] In this embodiment, the quantitative tube 2 is a fixed-volume gas tube 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, a 1 mL quantitative tube can be used; when the detection range is small, a 3 mL quantitative tube can be used.

[0024] The micro-chromatographic module 4 in this embodiment is based on the principle of gas chromatography separation, separating methane gas from other component gases in a time sequence. The micro-chromatographic module 4 consists of two parts: a thermostatic tube and a chromatographic separation tube. The chromatographic separation tube is wrapped with a thermostatic tube, which contains a resistance heating wire and a temperature controller to precisely control the temperature at 45°C. The chromatographic separation tube is a bundle of capillaries with an inner graphene film, with an inner diameter of 600 μm and a length of 4–6 meters.

[0025] The trace methane sensor 6 in this embodiment is a micro / nano gas sensor. It uses multi-walled carbon nanotubes as a substrate 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 no greater than 10μm. The tin oxide nanospheres loaded with palladium particles are prepared by hydrothermal method, and then mixed with ball-milled and dispersed multi-walled carbon nanotubes and dried to form powder. The powder is then sputtered onto a quartz substrate to form a gas sensor. This micro / nano structure of line-nanosphere combination not only utilizes the good conductivity of linear nanotubes, but also the interlacing of the linear structure forms voids that facilitate the embedding of nanospheres, increasing the contact area between palladium particles and gas.

[0026] In this embodiment, the signal processing and analysis module 7 is connected to the trace methane sensor 6 and is used to measure the sensor's response signal. Specifically, the signal processing and analysis module includes a signal acquisition circuit, an amplification and noise reduction circuit, an automatic calibration circuit, and a reference compensation circuit. The sensor's response signal is sequentially acquired by the signal acquisition circuit, then amplified and denoised by the amplification and noise reduction circuit to output a response value. This response value is then compensated by the reference compensation circuit and converted into a digital signal. When the signal noise is high, the automatic calibration circuit zeroes the signal to reduce noise. The specific structure of the above-mentioned signal processing and analysis module can be found in existing technology and will not be described in detail here.

[0027] Based on the above-described trace methane detection device, the detection method of the trace methane detection device in this embodiment includes the following steps:

[0028] (1) A quantitative volume of gas is collected from the gas sample to be tested through the sampling and detection gas path, and the detection signal of the trace methane sensor is used as the zero point signal.

[0029] (2) Switch between three-way solenoid valve one and three-way solenoid valve two. The gas in the metering tube enters the trace methane sensor for detection after passing through the chromatographic separation tube. The signal processing and analysis module processes the detection signal of the trace methane sensor to obtain the methane concentration.

[0030] The processing of the detection signal from the trace methane sensor also includes compensation and correction of the detection signal.

[0031]

[0032] Among them, U补偿后 For the compensated detection signal, U 补偿前 For the detection signal of the trace methane sensor, U 零点 The signal is at zero point, and α is the correction coefficient;

[0033] Finally, the compensated detection signal is converted into methane concentration. The specific conversion formula can be found in existing technologies and will not be elaborated here.

[0034] Example 2:

[0035] The difference between the trace methane detection device in this embodiment and that in Embodiment 1 is:

[0036] The flow direction of the gas phase separation path can be reversed. From the metering tube, the gas flows sequentially through the second three-way solenoid valve, the constant flow pump, the micro-chromatographic separation module, and the first three-way solenoid valve back to the metering tube, forming a gas phase separation path that can also achieve gas chromatographic separation. Then, the second three-way solenoid valve is controlled again to connect with the trace methane sensor for detection, meeting the needs of different applications. That is, through a single control of the first three-way solenoid valve and two controls of the second three-way solenoid valve, the device forms two gas paths, which can also enable the gas after gas chromatographic separation to be input to the trace methane sensor for detection.

[0037] Other architectures can be found in Example 1.

[0038] The above description is only a detailed explanation of the preferred embodiments and principles of this utility model. For those skilled in the art, there may be changes in the specific implementation methods based on the ideas provided by this utility model, and these changes should also be considered within the protection scope of this utility model.

Claims

1. A trace methane detection device, characterized by, The application relates to a trace methane sensor. The sampling detection gas path is sequentially connected by an air inlet, a three-way electromagnetic valve I, a quantitative tube, a sampling pump, a three-way electromagnetic valve II, a trace methane sensor and an air outlet; wherein the sampling pump is used to input the gas sample to be detected into the quantitative tube, and the trace methane sensor is used for detection; The gas phase separation gas path comprises a constant flow pump and a chromatographic separation tube connected between the remaining ports of the three-way electromagnetic valve I and the three-way electromagnetic valve II, and the three-way electromagnetic valve I, the quantitative tube, the three-way electromagnetic valve II, the constant flow pump and the chromatographic separation tube constitute the gas phase separation gas path; wherein the three-way electromagnetic valve I and the three-way electromagnetic valve II are switched, the constant flow pump is used to input the gas in the quantitative tube into the chromatographic separation tube for gas chromatographic separation, and the gas after the gas chromatographic separation is input into the trace methane sensor for detection; The signal processing and analysis module is connected with the signal of the trace methane sensor, and is used for processing the detection signal of the trace methane sensor to obtain the methane concentration.

2. The apparatus for trace methane detection according to claim 1, wherein, 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.

3. The apparatus of claim 2, wherein, 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 mu m, and the length is 4-6 meters.

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

5. The apparatus for trace methane detection according to any one of claims 1 to 3, wherein The trace methane sensor takes a multi-walled carbon nanotube as a substrate, and loads tin oxide nanospheres with deposited palladium particles on the surface.

6. The apparatus for trace methane detection according to claim 5, wherein, The diameter of the tin oxide nanospheres is not greater than 10 mu m.

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