Gas Detection Technology Research Articles

The gas-sensing mechanism of Nb2C monolayer for SF6 decomposition based on the DFT study

Abstract In addressing malfunctions in gas-insulated switchgear (GIS) systems, it is imperative to have a real-time tracking system for SF6 decomposition products to guarantee the safety and reliability of the equipment's operation. Although a variety of gas detection technologies are currently available on the market, low-power gas detection devices for SF6 decomposition products are still in the development stage, and technological advances in this area are of great significance for improving the reliability of GIS systems. Based on the density functional theory (DFT), the Nb2C crystal surface structure was established and six adsorption structures of SO2, H2S, SOF2, SO2F2, HF and CO gas molecules on Nb2C crystal surface were constructed by geometrical optimization in this paper. The gas-sensitive properties of each adsorption system were explored in terms of adsorption energy, charge transfer, electron density, density of states and recovery time. The results showed that the Nb2C crystal surface was unfit HF and CO gases detection, both of which showed weak physical adsorption; the adsorption energies of SO2, H2S, SOF2, and SO2F2 on the Nb2C crystal surface were -1.846 eV, -1.081 eV, -5.270 eV, and -10.582 eV, respectively, and all of them were strong chemical adsorption. It was further shown by theoretical recovery time calculations that the Nb2C crystal surface can act as SOF2 and SO2F2 gas scavengers, and are able to desorb H2S (4.69 s) and SO2 (2.26 s) gases by appropriately increasing the temperature, but the Nb2C crystal surface is more suitable for use as a low-power gas-sensitive material for H2S gas detection. Therefore, Nb2C is anticipated to be a promising material for high response, low-power consumption and fast recovery for H2S gas detection in SF6 decomposition gas.

A Review on Photoacoustic Spectroscopy Techniques for Gas Sensing.

The rapid growth of industry and the global drive for modernization have led to an increase in gas emissions, which present significant environmental and health risks. As a result, there is a growing need for precise and sensitive gas-monitoring technologies. This review delves into the progress made regarding photoacoustic gas sensors, with a specific focus on the vital components of acoustic cells and acoustic detectors. This review highlights photoacoustic spectroscopy (PAS) as an optical detection technique, lauding its high sensitivity, selectivity, and capability to detect a wide range of gaseous species. The principles of photoacoustic gas sensors are outlined, emphasizing the use of modulated light absorption to generate heat and subsequently detect gas pressure as acoustic pressure. Additionally, this review provides an overview of recent advancements in photoacoustic gas sensor components while also discussing the applications, challenges, and limitations of these sensors. It also includes a comparative analysis of photoacoustic gas sensors and other types of gas sensors, along with potential future research directions and opportunities. The main aim of this review is to advance the understanding and development of photoacoustic gas detection technology.

Synthesis, analysis and characterization of surfactant-assisted TiO2 nanoparticles for ammonia gas sensor applications

In our study, we focused on gas sensing, particularly ammonia detection. We synthesized and examined three types of nanoparticles: pure and conducting polymer-based TiO2 nanoparticles. The nanoparticles were prepared by an easy sol-gel approach. All of the samples were characterized using XRD, FTIR, UV-vis, FESEM, EDAX and BET. Gas sensing measurements were carried out for each sample. Among them, PEG-TiO2 stood out with remarkable gas sensing abilities, distinguishing it from other gas detection technologies. We thoroughly investigated the sensor performance, focusing close scrutiny to metrics such as response and recovery times. The greatest reduction in response time and recovery time (95 s / 123 s) was achieved at 25 ppm. These metrics provide insights into how quickly the sensor detects and recovers from the presence of the target gas. Our findings offer important insights for optimizing the sensor performance of PEG-TiO2, highlighting its remarkable gas sensing capabilities.

Construction of Solution Processable NUS-8/PANI Nanosheets via Template-Directed Polymerization for Ultratrace Gas Sensing.

The advancement of wireless gas sensing signifies a substantial leap forward in gas detection and intelligent monitoring technologies. This necessitates stringent design criteria for gas sensitive materials with good solution processability, conductivity, and porosity, whose design and synthesis remain challenging yet highly sought-after. Herein, the fabrication of NUS-8/polyaniline (PANI) nanosheets is presented with excellent solution processability, high porosity, triboelectric property, and superior electrical conductivity via a template-directed polymerization strategy. Solution processable NUS-8 nanosheets, synthesized directly by a "one-pot" approach, serve as templates to enhance the "on-site" polymerization of aniline, resulting in the formation of PANI layer on NUS-8 nanosheets with a thickness of 7nm. The resultant NUS-8/PANI nanosheets exhibit outstanding solution processability, and a film conductivity of 8.6 Sm-1. The solution processability enables the facile fabrication of homogeneous and compact NUS-8/PANI films and thus their integration onto electronic devices targeted for multifunctional sensing. The NUS-8/PANI coated sensors demonstrate sensitive and selective detection at room temperature toward ultratrace ammonia with a detection limit of 120 ppb. A wireless sensing system based on the NUS-8/PANI-coated sensor is capable to monitor the spoilage process of meat. This study paves novel avenues for designing and synthesizing gas-sensitive materials for practical applications.

Wearable electro-optical sensor for monitoring of nitrogen dioxide gas in environment

Environmental monitoring for detection of harmful pollutants is a challenge in today’s world. Development of wearable sensors with cost-effectiveness and practicality, while using accessible electronic components can be a solution to this challenge. In the present work ultraviolet light emitting diodes (UV-LEDs) and a Light Dependent Resistor (LDR) pair with carefully designed programmable circuitry is used to detect Nitrogen Dioxide (NO2) in the environment. The sensor is battery operated and rechargeable, making it convenient and eco-friendly. The sensor developed is miniaturized and wearable in nature for the detection of analyte gas in the environment. The sensor is stable and inexpensive as compared to the existing NO2 sensors available, which are electro-chemical, or oxide based. The sensor system is sensitive and selective to its exposure to NO2 gas and has no interference with typical environmental attributes such as humidity and temperature, which is a common challenge in gas detection technologies. The principle of gas detection is absorption based, light falling on the detector absorbed by the test gas present in the environment, thus changing the detector resistance. Absorption-based gas detection is indigenously simple but highly effective technique. This method not only ensures good sensitivity but enhances the selectivity of the electro-optical sensor towards the test gas preventing false triggering in the presence of other interfering gases.

Experimental study on comprehensive detection technology of shallow gas in deep soft soil layer

This study focuses on the underground shallow gas detection project in the Lingkun Island area of the northern entrance tunnel of the Wenzhou City Light Rail S2 line. Based on geological exploration data of shallow gas, we chose the technique of controlled-release gas with static pressure as the experimental foundation, integrating various technologies such as multi-functional in-situ probing, electrical methods, and seismic waves, comprehensively researching shallow gas detection technology in the Lingkun Island area. We conducted field probing experiments to accurately obtain the physical and mechanical properties of gas-rich soil layers and further studied the possibility of determining gas-rich locations. By applying parallel electrical methods, we can accurately identify and distinguish areas of anomalous resistivity in shallow geological structures. Based on abnormal changes in acoustic impedance in strata, we used seismic wave methods, including seismic CT and seismic wave scattering technology, to accurately reveal the presence and depth of shallow gas, providing reliable basis for accurate determination of shallow gas. Finally, we summarized a comprehensive plan for underground shallow gas detection technology, covering on-site data collection, data processing, and image interpretation of results, which will provide valuable references for future shallow gas exploration in relevant areas.

Environmentally friendly gas-filled cabinet trace SF6 gas detection technology based on GA-BP model

In order to build a green and low-carbon power grid, the State Grid takes the SF6 gas content in the low-pressure gas filling cabinet in the small gas chamber as an important detection index. The existing SF6 gas on-site detection technology consumes a lot of gas, and the gas density of the gas chamber decreases significantly after repeated detection in the low-pressure gas filling cabinet, which affects the insulation performance. In order to solve the above problems, a quantitative gas extraction detection technology for tracing SF6 gas in environmentally friendly inflatable cabinets based on a neural network model was proposed. Through theoretical analysis and PCCs calculation, it is verified that the output electrical signal of the pyroelectric probe at different times in the quantitative gas extraction mode has a linear relationship with the SF6 gas concentration. The experimental results show that the two neural network models can accurately output SF6 gas concentration in the quantitative gas intake mode, the main performance indicators of the GA-BP neural network model are good, and the maximum relative error is -2.7%, which is significantly better than the BP neural network model.

Monitoring and Leak Diagnostics of Sulfur Hexafluoride and Decomposition Gases from Power Equipment for the Reliability and Safety of Power Grid Operation

Sulfur hexafluoride (SF6) is a typical fluorine gas with excellent insulation and arc extinguishing properties that has been widely used in large-scale power equipment. The detection of SF6 gas in high-power electrical equipment is a necessary measure to ensure the reliability and safety of power grid operation. A failure of SF6 insulated electrical equipment, such as discharging or overheating conditions, can cause SF6 gas decomposition, resulting in various decomposition products. The decomposed gases inside the equipment decrease the insulating properties and are toxic. The leakage of SF6 can also decrease the insulating properties. Therefore, it is crucial to monitor the leakage of SF6 decomposed gases from electrical equipment. Quantitative testing of decomposition products allows us to assess the insulation state of the equipment, identify internal faults, and maintain the equipment. This review comprehensively introduces the decomposition formation mechanism of SF6 gas and the current detection technology of decomposition products from the aspects of principle and structure, materials, test effect, and practicability. Finally, the development trends of SF6 and decomposition gas detection technology for the reliability and safety of power grid operation are prospected.

Mixed Potential Type Isoprene Sensor for the Application in Real-Time Monitoring of Biomarker Gases.

Monitoring of isoprene in exhaled breath is expected to provide a noninvasive and painless method for dynamic monitoring of physiological and metabolic states during exercise. However, for real-time and portable detection of isoprene, gas sensors have become the best choice for gas detection technology, which are crucial to achieving the goal of anytime, anywhere, human-centered healthcare in the future. Here, we first report a mixed potential type isoprene sensor based on a Gd2Zr2O7 solid electrolyte and a CdSb2O6 sensing electrode, which enables sensitive detection for isoprene with sensitivities of -21.2 mV/ppm and -65.8 mV/decade in the range of 0.05-1 and 1-100 ppm. The sensing behavior of the sensor follows the mixed potential sensing mechanism and was further verified by the electrochemical polarization curves. The significant differentiation between the sensor response to exhaled breath of healthy individuals and simulated breath containing different concentrations of isoprene demonstrates the potential of the sensor for the detection of isoprene in exhaled breath. Simultaneously, monitoring of isoprene during exercise signifies the feasibility of the sensor in dynamic monitoring of physiological indicators, which is not only of great significance for optimizing training and guiding therapeutic exercise intervention in sporting scenarios but also expected to help further reveal the interaction between exercise, muscle, and organ metabolism in medicine.

Designing an optical gas chamber with stepped structure for non-dispersive infrared methane gas sensor

Compared to traditional semiconductor and electrochemistry gas sensors, the non-dispersive infrared (NDIR) gas detection technology presents notable advantages in terms of stability and selectivity. However, the high-performance NDIR gas sensor generally requires a long optical path, resulting in a large gas chamber. In this short communication, a simple and relatively small stepped optical gas chamber (45 mm × 20 mm × 30 mm) with long optical path (94.92 mm) is designed combining simulation method. Furthermore, the stepped optical gas chamber based on the simulation structure is fabricated by a computer number control technique, and used to fabricate a NDIR gas sensor. The results show that the NDIR gas sensor based on the stepped optical gas chamber can be successfully used for CH4 gas detection with a wide detection range and good repeatability. This work provides an optional reference for developing compact NDIR gas sensor.

Research on temperature and pressure interference in photoacoustic spectroscopy gas detection

AbstractPhotoacoustic spectroscopy (PAS) is a highly sensitive optical detection technique for trace gases. However, PAS is sensitive to environmental factors such as temperature and pressure during actual measurement. In this paper, we study the interference characteristics of temperature and pressure in PAS gas detection. The influence of pressure and temperature on PAS is theoretically analyzed based on the basic principle of gas photoacoustic spectroscopy. The effect of different pressure and temperature conditions on the resonance frequency and signal amplitude of PAS is studied through COMSOL software simulation and validated through experiments. Results show that changes in temperature and pressure will affect the resonance frequency and signal amplitude of PAS, thereby impacting the system's sensitivity and accuracy. To reduce the impact of temperature on the PAS sensor, a temperature compensation model was derived based on experimental analysis. Real‐time temperature detection is used to compensate for the photoacoustic signal based on temperature changes, which can improve the accuracy and stability of photoacoustic spectroscopy gas detection. For 5% CO2, the photoacoustic signal and experimental temperature data were measured for 3612 s, and after temperature compensation, the detection limit was 0.0192% at an integration time of 365 s, which is 0.0128% higher than before temperature compensation. The system's normalized noise equivalent absorption coefficient is 3.30 × 10−8 cm−1 WHz−1/2. This research improves the accuracy and reliability of photoacoustic spectroscopy gas detection technology and provides useful references for temperature correction in similar gas detection fields.

Simultaneous detection of greenhouse gases CH4 and CO2 based on a dual differential photoacoustic spectroscopy system.

In addition to the atmospheric measurement, detection of dissolved carbon oxides and hydrocarbons in a water region is also an important aspect of greenhouse gas monitoring, such as CH4 and CO2. The first step of measuring dissolved gases is the separation process of water and gases. However, slow degassing efficiency is a big challenge which requires the gas detection technology itself with low gas consumption. Photoacoustic spectroscopy (PAS) is a good choice with advantages of high sensitivity, low gas consumption, and zero background, which has been rapidly developed in recent years and is expected to be applied in the field of dissolved gas detection. In this study, a miniaturized differential photoacoustic cell with a volume of 7.9 mL is designed for CH4 and CO2 detection, and a dual differential method with four microphones is proposed to enhance the photoacoustic signal. What we believe to be a new method increases photoacoustic signal by 4 times and improves the signal to noise ratio (SNR) over 10 times compared with the conventional single-microphone mode. Two distributed feedback (DFB) lasers at 1651 nm and 2004nm are employed to construct the PAS system for CH4 and CO2 detection respectively. Wavelength modulation spectroscopy (WMS) and 2nd harmonic demodulation techniques are applied to further improve the SNR. As a result, sensitivity of 0.44 ppm and 7.39 ppm for CH4 and CO2 are achieved respectively with an integration time of 10 s. Allan deviation analysis indicates that the sensitivity can be further improved to 42 ppb (NNEA=4.7×10-10cm-1WHz-1/2) for CH4 and 0.86 ppm (NNEA=5.3×10-10cm-1WHz-1/2) for CO2 when the integration time is extended to 1000 s.

A Concentration Prediction and Gas Classification Model Based on LSTM-Attention Multi-task Learning Framework Network

The electronic nose (E-nose), a bionic olfactory system, has been widely used in gas identification and concentration prediction. However, these tasks are usually based on separate systems, leading to high detection costs. To address this issue, a multi-task learning network model based on LSTM-Attention (MTL-LSTMA) as a skeleton has been proposed to simultaneously train both species recognition and concentration prediction tasks. The introduction of an attention mechanism greatly reduces interference in gas feature information, improving the electronic nose pattern recognition algorithm’s efficiency. The MTL-LSTMA model was tested through five sets of comparison experiments, showing the best performance in both concentration prediction and species identification. The proposed model has broad application prospects and may revolutionize gas detection technology.

Detection of R290 leaks in RACHP equipment using ultrasonic sensors

There is a growing need for cost-effective leak detection in smaller RACHP equipment that uses R290 and other flammable hydrocarbon refrigerants. Gas detection technology may not be suitable in many cases due to cost and reliability implications whilst detection with system parameters can suffer long response times. Ultrasonic leak detection can be an economical and reliable method. This study presents the development and testing of an ultrasonic leak detector using off-the-shelf components, within a conventional split type wall-mounted air conditioner indoor unit. Depending upon the chosen sensor, a fast and effective response to simulated “small” R290 leaks was achieved. Measurements of potential interference from environmental noise across ultrasonic frequencies suggests false alarms are unlikely. Such a leak detector was found to be potentially effective.

Chemical Gas Telemetry System Based on Multispectral Infrared Imaging.

Environmental monitoring, public safety, safe production, and other areas all benefit greatly from the use of gas detection technologies. The infrared image of a gas could be used to determine its type from a long distance in gas detection. The infrared image can show the spatial distribution of the gas cloud and the background, allowing for long-distance and non-contact detection during safety production and hazardous chemical accident rescue. In this study, a gas detection system based on multispectral infrared imaging is devised, which can detect a variety of gases and determine the types of gas by separating the infrared radiation. It is made up of an imaging optical system, an uncooled focal plane detector, a filter controller, and a data gathering and processing system. The resolution of the infrared image is 640 × 512 and the working band of the system is 6.5~15 μm. The system can detect traces of pollutants in ambient air or gas clouds at higher concentrations. Ammonia, sulfur hexafluoride, methane, sulfur dioxide, and dimethyl methyl phosphonate were all successfully detected in real time. Ammonia clouds could be detected at a distance of 1124.5 m.

Simulation and experimental study on adsorption of SF6 decomposition components and optical gas cell materials

Fourier transform infrared spectroscopy (FTIR) is widely used in gas detection of SF6 decomposition components. A gas cell is an important element in the detection system, which can directly affect the accuracy and sensitivity of detection. During the long-term use of the gas cell, SF6 decomposition components may be adsorbed on the inner wall of the gas cell, which affects the detection results and the life of the gas cell. Therefore, the study on the adsorption between the gas cell material and the SF6 decomposition component is of great significance for improving the accuracy of detection. In this paper, based on the density functional theory, the adsorption process and adsorption degree of SF6 decomposition components (SOF2, SO2F2, CO, SO2, and H2S) with three typical main gas cell materials (Al, Cu, and Fe) and two gas cell coating materials (Teflon and Au) were simulated. It was found that the adsorption of Teflon and Au with gas was weak in the five materials and that of Teflon was the weakest. The adsorption energy of the three main gas cell materials was 2.65–6.31 times that of Teflon. The simulation results were also verified by FTIR and the GC-Materials Studio (MS) method. FTIR results showed that Teflon and Au had the weakest influence on the infrared spectral absorption peak and the effect of the two materials on SOF2 and SO2F2 gas absorption peaks is only less than 0.1. The results of gas chromatograph-mass spectrometer (GC-MS) showed that the effects of Teflon materials and Au on gas concentration were 2%–9.41% and the effects of Cu, Fe, and Al on gas concentration were 4.48%–65.43%. Therefore, Au and Teflon are suitable as coating materials for gas cells, which can reduce the adsorption of gas and improve the accuracy of infrared spectroscopy measurement. The results of this paper provide a reference for the development of application of optical gas detection technology in SF6 decomposition component detection.

Miniaturized anti-interference cantilever-enhanced fiber-optic photoacoustic methane sensor

To realize all-optical passive detection of CH 4 in narrow spaces and harsh environments, a compact cantilever-enhanced fiber-optic photoacoustic sensor (CEFPS) resistant to electromagnetic and ambient noise interference is proposed. Through theoretical analysis and finite element simulation, a miniaturized photoacoustic cell (PAC) with diffusion holes has been designed and fabricated. The diffusion holes are used for the circulation of the gas to be measured and attenuate the external noise coupled into the PAC. The concentration information of CH 4 is obtained by demodulating the vibration amplitude of the built-in cantilever generated by the photoacoustic pressure. The design of the built-in cantilever structure avoids the possibility of mechanical damage and reduces the interference of external noise in the detection of photoacoustic signals. The experimental results and the Allan-Werle deviation analysis of the CH 4 signal show that the minimum detection limit (MDL) is 0.32 ppm with an integration time of 60 s. The normalized noise equivalent absorption (NNEA) coefficient is calculated as 2.44 × 10 −8 cm −1 W/Hz 1/2 . The developed CEFPS achieves performance comparable to conventional resonant photoacoustic spectroscopy CH 4 detectors, although the volume is two orders of magnitude lower. • A miniaturized all-optical anti-interference cantilever-enhanced photoacoustic methane sensor is presented. • The cantilever acoustic-sensitive element and miniaturized photoacoustic cell (PAC) adopt a built-in design. • The direct effect of environmental noise interference, wind disturbance and mechanical damage on the cantilever is avoided. • The sensitivity of the sensor reaches the traditional resonant photoacoustic spectroscopy trace gas detection technology. • At the same time, the volume of the built-in miniaturized non-resonant PAC is reduced by about two orders of magnitude.

Ultra-wide range and wavelength fixed trace gas detection technology based on single chamber multiplexing

The all-fiber photo-thermal interference (PTI) system based on hollow-core photonic crystal fiber (HC-PCF) has the advantages of wide dynamic range, ultra-sensitivity, and small volume, which is of great significance in gas trace analysis. Most of the previous PTI systems obtain the relationship between gas concentration and phase modulation by wavelength scanning and extracting the second harmonic signal absorbed by the gas. However, the residual modulation caused by the asynchronism between wavelength and modulation signal seriously affects the signal-to-noise ratio (SNR) and dynamic detection range of the system. In addition, wavelength scanning has limitations for detecting gas with irregular absorption lines. This paper proposes an all-fiber photo-thermal interference system with pump intensity external modulation. The system is not limited by the gas absorption line and has a high SNR. The factors affecting the dynamic range of the system are analyzed theoretically and experimentally. It is verified that increasing the injection gas pressure can significantly increase the detection limit of the system compared with increasing the pump light power. The redshift of the pump light can dramatically increase the detection limit of the system. A C2H2 gas trace system with the pump wavelength redshifted to 1530.41 nm was demonstrated. The detection lower limit of 9.24 ppm and an extensive dynamic detection range of five orders of magnitude were obtained.

Research and Simulation of Oil and Gas Pipeline Leak Detection Based on Optical Fiber Sensors

<p>This subject mainly researches and simulates the detection method of gas environment by TDLAS gas detection technology. At present, the design of the underground pipe network is relatively complex, which often requires a lot of manpower and financial resources to maintain, and occasionally the corresponding leaked data cannot be detected or transmitted in time. However, if the gas concentration can be detected by TDLAS technology, the corresponding leak points can be found in time. It is directly transmitted to the corresponding host computer through the optical fiber perception, so that the inspectors can find the leakage in time. This subject mainly studies and simulates the application of TDLAS direct absorption method for gas detection, which can accurately measure the methane concentration in the gas environment. Corresponding coordination is mainly carried out through the semiconductor laser, the adjusted signal is injected into the gas chamber environment, and the concentration of the gas in the corresponding environment is calculated by comparing the changes of the light intensity before and after, so that the concentration change of a corresponding gas environment can be fed back.</p> <p> </p>

The effect of the photoacoustic Field-Photoacoustic cell coupling term on the performance of the gas detection system

The optimization of the photoacoustic cell (PAC) has always been a research hotspot in the photoacoustic spectroscopy (PAS) based gas detection technology. Herein, a new influential factor of the PA signals intensity, photoacoustic field (PAF)-PAC coupling term was proposed. In addition, the simulation of the sound pressure distribution in the PAC and the PAS gas detection experiment were carried out. The results show that: the length LC and radius RC of the resonator both have an impact on the sound pressure distribution, the strongest sound pressure intensity appears when LC = 95 mm. Besides, when LC is in the range of 35 ∼ 65 mm, the sound pressure intensity decreases with the increased RC, whereas it increases with RC when LC is in the range of 80 ∼ 125 mm. With the shortening of the focal length F0, the dimension of the light beam and the maximum light intensity reduces and enhances, respectively. In particular, when F0 = 16 mm, the integral value along the major axis of the light spot has the peak value, which also changes with the distance l2 from the laser head to the convex lens, and the peak value appears when l2 = 4 mm. In addition, the optimal response of the gas detection system (GDS) occurs when l1 = 0 mm, l2 = 2 mm, l3 = 2 mm. LC has a significant impact on the representative signal intensity(RSI), and the influence is mainly result from the PAF-PAC coupling term. However, the effect of the RC on the RSI can be approximately negligible.