Design Of Flue Gas Monitor Base On Differential Optical Absorption Spectroscopy

The past decades years has witnessed a huge development of industry in China,bring some problems as the same time,environment problems especially the air pollution being the foremost.Real time monitoring of gaseous pollutants emitted by enterprises is a priority and an important prerequisite to control air pollution.Therefore,an urgent need for a product to monitor the composition and concentration of exhaust gas.Under this background,this paper studied the application of Differential Optical Absorption Spectroscopy?DOAS?technology deeply and apply it to the design of flue gas monitoring.Study the Beer�Lambert law and the gas characteristic of pollution gas main ingredients,such as SO₂ and NO_x.This paper focuses on the hardware design and software design of the flue gas monitor.The hardware design consists of flue gas pretreatment module,gas path system and data acquisition and control circuit.In the flue gas pretreatment module,eliminated the water vapor in the gas by using the Nafion tube in the flue gas pretreatment module.STM32F303 has been used as data acquisition and control chip.In the hardware circuit design,in addition to the pressure,temperature acquisition circuit and isolated communication module circuit.The 220V AC detection circuit is designed by using the optical coupling module ISP620-1,and the FRAM is used to design the power down storage circuit MB85RS256A to improve the stability of the equipment;design of ultraviolet light source driving circuit by using LMV321AS5X operational amplifier chip and 2 MOS tubes.The software design is composed of algorithm design and function design.In the algorithm design,least square method has been used to fit experimental data.In order to repair the nonlinear absorption of gas problem,according to the experimental data,the compensation formula of nonlinear absorption is designed.And the temperature compensation formula of the differential absorption cross section is added.In functional design,the whole software development process is divided into several tasks which include:Data reading,power down detection and storage,Modbus communication,temperature compensation calculation of absorption cross section and nonlinear absorption compensation calculation.The communication,synchronization and resource sharing among tasks can be achieved by using event flags,message mailboxes,semaphores and interrupt service functions in RTX system.Test the performance of gas monitor prototype which based on the UV DOAS,the concentration deviation of a single component gas is about 3%,and the concentration deviation is less than 5%.The communication cycle of Modbus under RTX system is100ms,and the cycle jitter<14ns.The test results proved that the technology parameters of gas monitor which based on the DOAS completely satisfy the requirements of environmental protection.