Study On Development Of On-line Monitoring Device For Extracting Ultra-low Concentration Dust By Light Forward Scattering

With the rapid development of Chinese economy,the issues of environment have become increasingly prominent.In particular,the intensification of smog has caused continuous concern in all sectors of society in recent years.So as to improve the atmospheric environment and strengthen the supervision of soot concentration emissions in thermal power,steel and other industries,the state has issued a series of standard documents.In order to achieve the concentration of dust emission standards promulgated by the state,the major domestic enterprises to develop the ultra-low emission power generation transformation of coal-fired units.However,the dustcontaining smoke will be low dust,low temperature and high humidity after the reform.Therefore,it has become the main difficulty to accurate and effective monitoring of the concentration of smoke particles in the development of online monitoring devices after the reform.This paper has carried out the following work on the online monitoring of smoke particles concentration after ultra-low emission reform:1.By comparing and analyzing different soot concentration measurement methods,it is clear that the light forward scattering method has advantages in the field of ultralow concentration soot online monitoring.2.To further understand the principle of measuring the concentration of particle by light scattering method,the light scattering theory and the inversion of particle concentration are analyzed.3.The overall design of the online monitoring device is carried out,mainly including the design of the sampling system,the measuring unit and the electrical control system.(1).This paper designed a sampling system with extraction heating and whole heat tracing function.It includes pretreatment unit,heat tracing tube,vacuum pump and return smoke unit.To ensure the representativeness of the sampling and the stability of the measurement,the sampling probe in the pretreatment unit selects a straight tube with 45° slit design,and in order to eliminate the influence of droplets on the measurement,a heating rob is installed inside it.During the sampling process,the heat tracing tube heats the heated dust-containing smoke to prevent condensation of water vapor in it.And the return smoke unit adopts the S-type pitot tube design,and can also measure the flow velocity of the flue gas in the flue while returning the gas.(2).The measuring unit includes measuring instrument,measuring chamber and purging fan.In order to meet the ultra-low concentration measurement requirements,the particle concentration measuring instrument based on the light forward scattering method is used.It also introduces the insulation and purging design for the measuring unit.4.The electrical control system is based on the industrial computer control system and the temperature control system,where in the industrial computer control system is mainly responsible for data acquisition,processing,display,storage,control of isospeed sampling and S-type pitot tube;And the temperature control system is primarily responsible for the heating and insulation control of the sampled smoke.The two systems ensure the stability of the continuous online measurement of the device together.5.Firstly,the simulated low-concentration smoke test was carried out on the device,and compared with the filter weighing method.The accuracy of the measurement results under simulated low-concentration soot conditions was verified.And then,through a series of on-site tests on the measuring device and comparison with the manual sampling method,the device can truly reflect the soot concentration in the flue gas.The feasibility of the online monitoring device designed in this paper is verified.