Comparison About Particles Samplers For Coal-fired Pollution Sources And Its Application In Power Plants

Recently,the pollution of fine particles in ambient air has been serious in China.The effect on ambient air quality from fine particles that were emitted from stationary pollution sources,especially coal-fired boilers,as one of the primary sources,cannot be ignored.Although so far there is no standard sampling method and the related emission limits of the fine particles from coal-fired pollution sources in China or abroad,size-classification samplings of fine particles emitted from pollution sources have been carried out in a large scale in many researches.Thus,based on the two aspects of laboratory simulation and field test,it was significant to study their respective characteristics of particles-classified samplers commonly used in coal-fired pollution and the possible problems when sampling.Moreover,the test results of all sampling methods were mutually verified when we study the characteristics of the particle size distributions from coal-fired plants.In this thesis,the testing stability,the instrument operability,the accuracy of test data of four types of samplers(virtual impactors,cyclone samplers,total dust sampler and ELPI)were preliminarily assessed by a small coal stove combed with a self-designed flue gas collection system.The influence of coal quality,combustion temperature and oxygen content on the ratio of fine particles emission was further studied.Based on a coal-fired power plant in Hebei province,the effect of the different sampling methods on test results was studied,and the test results from simultaneous field monitoring by different samplers were compared and analyzed.According to the preliminary research results and test requirements,the emission characteristics of fine particle size distribution from a coal-fired plant in Zhejiang province were studied.The main conclusions are as follows:1)The results of the emission experiments from small coal stove showed that,the fitting degree of test results from ELPI/ELPI+ was lower than the other particles-classified samplers among the four samplers based on the determination coefficient R-square and residual sum of squares.The data points were relatively scattering.95%confidence zone was widest.2)For particles with different sizes in flue gas,the Pearson correlation coefficient of the test results from different samplers indicated that the correlation between the dilution sampling method(ELPI/ELPI+ combined with FPS-4000)and direct sampling method was slightly low,less than 0.9.While,the test results from direct sampling methods were highly corrected with each other,with the correlation coefficient of 0.99.3)For the flue gas with room temperature and lower particles concentration,the superimposed effect of weighing error for different concentration levels was predominant when ELPI/ELPI+ combined with FPS-4000 dilution systems were used.It resulted in a larger error in the test results.Thus,the direct sampling method is recommended.The effect resulted from weighing errors were reduced much for the flue gas with high particles concentration.4)For the flue gas with high temperature,the condensable particulate matters formed during dilution and cooling process could be collected with dilution sampling method.Only the filterable particles could be trapped with the direct sampling methods(including the total smoke test method in the GB/T 16157-1996).To some extent,there is a negative deviation in the measurement of condensable particles in flue gas.5)In the direct sampling methods,the measured mass concentration data of total particulate matter by using cyclone samplers was close to the test results from the total smoke sampling method adopt by national standard in China.The messured PM concentration by virtual impactors showed that the mass concentration of PM2.5 accounted for a high ratio of the mass concentration of PM10.6)The test results of different samplers show that relatively more submicron particles were produced by burning bituminous coal than by using honeycomb briquette;and increasing combustion temperature also promoted the formation of submicron particles as well.7)Based on the experiments taken in a coal-fired plant,the measured mass concentrations of PM2.5 were at the order of magnitude and had a good correlation between a PM2.5 impactor and a two-stage virtual impactors.The measured mass concentration data from dilution sampling method is less relevant to the data from direct sampling method,and they were in conformity with the conclusion from laboratory simulation.8)The comparison of the measured mass concentrations between the dilution sampling method and the direct sampling method,showed that the concentrations of condensable particles and filterable particles in the flue gas emitted from the coal-fired plant were considerable.The proportion of condensable particles in the flue gas was increased after the WESP(wet electric precipitator).Comparing to the results by using an electrostatic precipitator,the mass concentration of PM0.2 rebounded after using a wet desulfurization device.9)The test results from a coal-fired plant in Zhejiang province showed that,under the different operating condition,the particle number concentrations from the outlet of an electrostatic precipitator and the cross section of the chimney(60m)were mainly concentrated in submicron mode(aerodynamic diameter smaller than 1?m)and rapidly decreased with particle size increasing.10)According to the test results from a coal-fired plant in Zhejiang province,when the flue gas temperature was 120? at the outlet of the smoke cooler and using test coal as fuel under the working condition,both original and at the diluted(7 times and 10 times ratio)flue gas,number concentration of particles in the flue gas showed a unimodal distributions.And the particle sizes corresponding to the number concentration peaks gradually reduced with the dilution times increasing,peaking at 0.072 ?m,0.027 ?m,0.009 ?m respectively.In addition,when the dilution ratio of original flue gas increased from 7 to 10 times,the number concentrations of particles with aerodynamic diameter between 6nm and 27nm were increased exponentially.