Design And Realization Of Concentration Detecting System Of SO₂ In The Flue Gas Based On Non-dispersive Infrared Technology

With the development of national economy, energy consumption has been increasing. The SO₂ pollution has become more and more serious. It has become the atmospheric pollutants confronting human beings, and did serious harm to the ecological environment and human health. 90 percent of SO₂ being discharged into the atmosphere comes from coal energy. Therefore, it is significant to real-time and continuous detection of SO₂ concentration in the flue gas.This paper makes a detailed analysis of the methods using on the SO₂ concentration detecting and expresses their situation at home and abroad. The author has designed a Non-dispersive infrared SO₂ concentration detecting system. The key research contents are as follows:1) The author summarizes SO₂ concentration detecting methods and their situations at home and abroad. Among the methods, the author wholly introduces the Non-dispersive infrared and differential absorption detecting technology, regard these as theoretical basis of this paper.2) Based on infrared absorption spectrum theory, the author uses differential absorption method of Non-dispersive technology to measure the sulfur dioxide. The SO₂ absorption wavelength is chosen at 3.98μm which is locates in 3-5μm. And the mathematical model of SO₂ concentration has been calculated. The components have been selected, such as infrared light source, photoelectric detector, interference filtering pieces and so on. The circuit design includes illuminant driving circuit and lock-in amplifier circuit. By integrating the differential amplifiers and phase sensitive detectors in the lock-in amplifier circuit, the noise has been wiped off, and the system detection accuracy has been enhanced.3) The author has done some experiments on the system. Through the zero gas calibration and the measurement of standard SO₂ concentration, the corresponding relation between measurement data and gas concentration has been obtained. Then the author has fit out the relation curves of concentration and voltage. After that, the author has done experiments to analyze the repeatability and stability of the system. Meanwhile, the experiment results have been compared with the theoretical derivation results. The influential factors of system measurement accuracy have been analyzed.