Research On Ammonia Detection Based On Tunable Diode Laser Absorption Spectroscopy

As one of the harmful gas, ammonia not only has great harm to the environment and human health, but also make contribution to PM2.5. In the field of industry, the total NOx can be decreased effectively by flue gas denitrification with Ammonia. Selective catalytic reduction(SCR) system is one of the main sources of ammonia emissions. Therefore, It is important to realize fast and high-precision ammonia detection.Tunable Diode Laser Absorption Spectroscopy(TDLAS) is a fast online detection technology with high seletectivity? sensitivity and high accuracy and it has been widely used in the field of environment and atmosphere detection?In this paper, the relevant research on ammonia detection of selective catalytic reduction(SCR) system is conducted.Based on the theory of absorption spectroscopy theory, a in-depth theoretical research on TDLAS detection is presented and the harmonic expression of the absorption signal are derived. Based on the wavelength modulation spectroscopy and harmonic detection technology, we built the NH3 detection system and describe the main components. The experimentation research and optimization of the paramenters of laser controller and lock-in amplifier are conducted, and we also analyzed the effects of relevant parameters on second harmonic.Through the experimental study on ammonia detection, we analyze the transition time of the TDLAS system. The components that may cause this phenomenon in the system are improved, and we also validate the effect to the transition time of the TDLAS system. On the basis of experiment,We improve the structure of the system and short the system transition time And improve the system detection accuracyIn the continuous detection experiment, the second harmonic background signal drift in gas continuous detection based on tunable diode laser absorption spectroscopy, a new method of background elimination is proposed by changing center current of the laser. This method can eliminated the effects of concentration inversion by background signal drifting. Second harmonic background signal components and the factors that affect it are described. The absorption center current searches are the method to search background center current is designed. The experimental results show that this method realizes background signal extraction ? reduces the concentration of inversion error and the effects of concentration inversion by background signal. Thus it improves the detection accuracy of the concentration. This method provides an effective background drifting elimination way for continuous high-precision gas detection...