| Air pollution has become the most serious environmental problem in China and even in the world.Inhalable particulate matter is one of the most important components of air pollutants,which is very easy to be deposited in the human body and cause great harm health problems.As one of the world top coal consumers,coal accounts for more than 50%of primary energy consumption structure of China,particulate matters emitted by coal-fired power plants is one of the important sources of inhalable particulate matter in China.With the transformation of ultra-clean emission of coal-fired power plants,the requirements for particulate matter emission and control of coal-fired power plants are further improved,that is,the mass concentration of particulate matter should not be greater than 10 mg/m3.Tighter emissions standards require more precise measurements to ensure.CEMS is the most often used emission monitoring system in Chinese power station,and optical methods have been used in over 90%CEMSs of coal-fired power stations.Optical methods are usually performed the calibration by the known particles,but the characteristics of the fly ash particle matters are susceptible to boiler operation condition,fuel types and post-treatment processing conditions.Simple periodic calibration has been unable to meet the existing measurement needs,and some scholars have begun to combine different measurement methods to improve the accuracy and reliability of measurement.Based on above problems,light scattering method andβ-ray attenuation method were selected to be carried out the following aspects of research work.Firstly,based on the Mie scattering theory and the basic theory of beta ray,the properties of particles that may affect the measurement results of light scattering method and beta ray attenuation method were analyzed in detail.Furthermore,a series of simulation calculations and experimental measurements were performed in this paper to study the influence of particle size and shape on the light scattering method.The scattering light distribution characteristics of particles with different shapes and different particle sizes were studied.The results of calculation and experiment shows that the influence of particle size and shape and relative error caused by these two properties can be reduced obviously when the scattering angle of10°～15°is chosen for the mass concentration measurement.Secondly,the effects of different particle properties onβ-ray attenuation method were studied experimentally.An experimental system ofβ-ray attenuation method was established,and three kinds of actual fly ash particles and five kinds of pure matter particles of common components in coal ash particles were selected for measurement.The experimental results show that the change of particle size has no significant impact on the accuracy of the experimental results,but when the particle composition changed,it could cause at least 20%-40%measurement error.Therefore,whenβ-ray attenuation method is used in the scene of power plant boiler,it is better to calibrate several times under different conditions to reduce the error.Specially,the experimental results show that the magnetic domain or the magnetic field generated by spontaneous magnetization in the ferromagnetic material,likeγ-Fe2O3,don’t have a significant effect on theβ-rays,which lead to little influence to the results in the measurement of ferromagnetic objects byβ-ray attenuation method.At last,a novel method based on asymmetric factor light scattering method combined withβ-ray attenuation monitor（AFLSM-BAM）was proposed and compared with other three common LSM-BAM methods by simulation calculation and experimental measurement.The simulation and experiment results show that the maximum relative error can be reduced from80.51%to 28.52%compared with other three coupling methods,and the average relative error of AFLSM-BAM can be reduced to 6.80%～8.71%.The Bland-Altman agreement analyses for the four coupling methods and BAM were performed,and show that the AFLSM-BAM is better than the other three methods. |
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