Research On High Precision Carbon Dioxide Detection System Based On TDLAS Technology

Since the industrial revolution,human activities have led to massive greenhouse gas emissions,which have intensified the greenhouse effect and triggered global climate change.Serious consequences such as rising sea levels,increased extreme weather events,and ecosystem collapse posing a great threat to humans and the earth.Global emission reduction and response to climate change have become a common global concern.Therefore,accurate measurement of CO₂ emissions is of great significance for developing and implementing mitigation strategies.Tunable Diode Laser Absorption Spectroscopy（TDLAS）,with the advantages of high detection accuracy,fast response time and high sensitivity,which is widely used in the field of gas detection.According to the policy and realistic requirements,this thesis designs and realizes a high precision CO₂ detection system based on TDLAS.The real-time online detection design enables the display and storage of CO₂ gas concentration and enables timely feedback on the working of the system.The main contents of this paper include:In this thesis,the principle and its advancement of TDLAS technology was described.The spectral intensity,absorption line shape function and TDLAS detection technique were also introduced.According to the characteristics of gas molecules absorption and lasers luminescence,the absorption spectrum of CO₂ at 2004 nm was selected.The overall design of CO₂ detection system based on TDLAS was completed,including the main control module,the light source module,the gas absorption cell module,the photodetector module,the data acquisition module and the communication module.In particular,an adjustable optical path gas absorption cell was designed based on a multi-reflective structure.It can meet the requirements of the system in different detection environments.The gas absorption cell can be adjusted by a variety of light ranges through the adjustment lever,which improves the detection accuracy of the system.The software design process is also given on the basis of hardware design.For the interference problem of interference fringe noise in TDLAS system,a method combining CEEMDAN and wavelet threshold denoising was proposed.Firstly,the decomposition of CEEMDAN is used to extract the gas absorption signal features.And the noise components are identified by the mutual correlation function.Then the noise components are processed and the original signal is reconstructed by wavelet threshold denoising method.The results show that the CEEMDAN-wavelet threshold denoising algorithm has the best effect on the suppression of interference fringes.Finally,the CEEMDAN-wavelet threshold denoising algorithm was integrated into the detection system to process the CO₂ spectra measured by the direct absorption method.In addition,the CO₂ detection system was calibrated.The system was experimentally evaluated for detection response time,detection limit,detection accuracy,and stability.The experiments show that the CO₂ detection system developed in this paper has good performance and meets the requirements of high precision and high-performance detection.The research results in this thesis have some reference significance for exploring the improvement of the detection performance of TDLAS system and expanding technical approaches of CO₂ detection.