Research On Key Technologies Of Optical Fiber Gas Sensor And Its Application In Safety Engineering

Energy is an important material foundation for the survival and development of mankind, and it is related to the national economy and national security. In the process of exploitation and utilization of energy, production safety has become an important issue in economic development. In recent years, the state has paid great attention to the safety production, the total amount of safety production accidents is a downward trend, but heavy and special events are frequent and serious harm.In China's coal field, gas and spontaneous combustion are two major disasters in coal mine safety production. For the gas disaster, the monitor and control system of gas is the main means of monitoring and early warning. The main problems of the current coal mine monitoring and control system are the poor reliability, frequent calibration, short life span and small scale for the catalytic combustion sensor. The traditional infrared sensors are susceptible to background gas interference and cannot be used normally in high dust and high humidity environment, Olefin gas cross-interference is serious, power consumption and other problems; these sensors cannot meet the needs of mine safety.The prediction and early warning of coal spontaneous combustion mainly adopts the analysis and forecast method of gas index. The trace gas detection equipment used in traditional spontaneous combustion is chromatographic analysis system, which has many problems such as complex equipment, complex operation, slow analysis speed, and On-line monitoring cannot be achieved, which limits its application range. With the technical progress, the improved beam tube system using infrared analyzer to replace part of the chromatographic analyzer, to speed up the detection speed, but there are shortcomings of the measurement of gas species is less, cannot achieve the presence of large cross-interference olefins trace gas detection. Therefore, the shortcomings of the existing detection technology limit the development of fire forecasting technology.The optical fiber gas detection technology based on laser spectroscopy has the advantages of high resolution, high selectivity, multi-component and low power consumption etc. It has become an effective tool for industrial harmful gas detection, can effectively solve the existing problems of coal mine safety field gas detection, to provide reliable data protection for coal mine disaster prediction.This subject comes from the actual demand of coal mine safety, combining with the development status of mine safety especially the demand of coal mine gas detection technology; this paper puts forward the application of tunable laser spectroscopy to solve the gas-sensing products Demand problem, Which are urgently needed in major disasters such as coal mine gas and fire. Based on the investigation and analysis, starting from the main contradiction of the overall design of the instrument, discusses the laser wavelength shift of the optical fiber gas sensing, interference of optical noise in trace gas detection, cross-interference problems in multi-component detection; A method of detecting trace gases based on preset background gas and a method of removing cross-interference based on multi-variables is proposed. A detector with low optical noise and a long-path air chamber coupled with optical fiber are developed. Optical fiber methane sensor and fiber multi-component gas sensor are developed; The performance of the sensor was tested and analyzed; the results show that the developed optical fiber gas sensor has a good performance to meet the application requirements of the field of coal mine safety.This paper mainly studies the following aspects:1. Through research and analysis, to determine the direction of research topics. The basic theoretical knowledge of laser spectroscopy is studied in depth. Based on the general theory of spectral absorption technique and theoretical analysis of laser absorption spectrum, the theoretical basis for the development of the sensor is provided.2. Development of optical fiber methane sensor based on laser absorption spectroscopy. Based on the direct absorption spectroscopy, a new self-calibration scheme based on the reference optical path and the reference gas chamber is proposed to solve the problem of poor stability and big measurement errors for the optical fiber methane sensor, which is susceptible to the intensity disturbance and laser drift, thus effectively eliminating the influence of the laser wavelength drift. A calibration method based on least squares method is proposed, which improves the measurement precision of the large measurement range by damping least squares method. A detailed performance and reliability test of the developed sensor is carried out.3. The problems in the analysis of trace gases in laser absorption spectroscopy are analyzed. Aiming at the existing optical noise in optical components, developed a low noise photoelectric detector; Based on Herriott long path cell theory, an optically coupled long-path detection chamber is developed. Different noise processing algorithms are studied. Fourier transform filter algorithm is used to suppress the optical interference noise. Kalman filter algorithm is used to improve the stability of the measurement.4. Due to background fluctuation caused by the optical element, limits the system to enhance the detection limit, in order to further improve the system detection limit, we propose a background optimization of trace gas detection method based on zero preset, combined with the least squares fitting algorithm to achieve accurate and stable ppm level of carbon monoxide gas detection.5. According to the requirements of multiple gas detection, a multi-gas detection technology scheme based on wavelength division multiplexing laser array is proposed. Aiming at the problem of cross-interference between different gases, combined with multicomponent detection, a multivariate analysis method based on gas concentration and spectrum is proposed, which effectively eliminates cross-interference.6. According to the requirement of coal mine safety, the detection of trace gases such as carbon monoxide, ethylene and acetylene was studied, the system was tested, and the detection of high sensitivity and high accuracy is realized.7. Combined with the needs of the field, the application research of optical fiber gas sensor in coal mine safety is carried out, which verifies the feasibility of sensor application in field measurement.Through the research of this topic, we mainly do the following aspects of innovative work:1. A fiber methane sensor was developed. According to the existing laser methane sensor is easily affected by intensity disturbance and laser drift,which can cause the poor stability and measurement error problem, the proposed self calibration scheme based on reference light path and the reference gas chamber eliminates the influence of laser wavelength drift. The reliability test of optical fiber methane sensor is carried out for the first time, which lays a good foundation for the practical application of the sensor in the future.2. The optical interference is analyzed, and a low-noise photo detector is proposed for the first time, which solves the background drift problem caused by the optical noise of the detector.3. Based on the principle of Herriott long-path-length cell, a fiber-coupled long-path detection chamber is developed for the first time. The gas chamber can be used as a stand-alone element or can be cascaded by fiber to form a longer light path, greatly facilitates the study of trace gas detection technology.4. A method of background optimization gas detection based on preset zero point is proposed for the first time. The background of the sensor signal is enhanced by cascading the reference gas chamber and the sensing gas chamber, and the noise background is eliminated effectively. Combined with least squares fitting and Kalman filtering algorithm to achieve the ppm level of carbon monoxide gas accurate and stable detection.5. The multi-component gas detection technology based on WDM is realized for the first time, and the influence of gas crosstalk on the detection results is effectively reduced by multivariate analysis. Fiber multi-component gas detector was developed.