Research On The Test Methods For PM_2.5 In Flue Gas Of Thermal Power Plants

Coal burning is a major source of particulate matter, especially the PM2.5which can go into our lungs and it’s one of the main sources of urban air quality. At present, the coal consumption in thermal power industry accounts for more than half of the country’s total coal consumption and in the next period of time, the coal consumption of thermal power industry and the proportion of total coal consumption will continue to grow. Therefore, the amount of fine particulate matter PM2.5caused by the thermal power industry is very large and we need to figure out the emissions and the emission concentration of fine particulate matter PM2.5. However, we haven’t form the Test Method Standard of the fine particulate matter PM2.5in the flue gas in our country. So the study on the technologies and methods of detection of fine particulate matter PM2.5is meaningful to figure out the emissions of PM2.5from the flue gas and their impact on the ambient air.As the test object, the coal-fired units of three representative domestic thermal power plants were selected in this paper, which are300MW sub-critical coal-fired unit of A power plant in Shanghai,1000MW ultra-supercritical coal-fired units of B power plant in Taizhou, and600MW super-critical coal-fired units of C power plant in Yangzhou. The test time of them are from September10th to17th in2012, from May13th to16th in2013and from April23th to27th in2013.Referring to the widely used current international accurate detection technology (ELPI and Gravimetric Method), the experimental system and the test plan has been established to test PM2.5in flue gas of the three selected thermal power plant. The result in ELPI shows that the reproducibility is poor, the relative error and absolute error are large, wherein, the range of relative error of undiluted sample and the74times diluted sample of plant A are-23.79%～24.91%and-33.93%～34.96%, the range of relative error of8.7times diluted and74-fold dilution sample of B plant are-19.39%～16.88%and-12.87%-36.31%, under the same conditions like B, the range of relative error of plant C are-29.27%～14.52%and-42.62%-34.09%. Correspondingly, the range of absolutely error of A, B, C plant are-2.01mg/m3～3.47mg/m3and-1.32mg/m3～2.80mg/m3,-0.32mg/m3-0.40mg/m3and-0.19mg/m3～0.65mg/m3,-0.12mg/m3-0.09mg/m3and-0.26mg/m3～0.45mg/m3, respectively.While applying ELPI to PM2.5test, gravimetric method is also applied to the testing of PM2.5in corresponding flue gas of coal-fired generating units. The results show that the gravimetric method has better repeatability; relative error and absolute error are relatively small. In which the range of relative error of PM2.5mass concentration of exports in A Power ESP under the two load conditions are-3.66%～2.78%and-4.93%～2.81%, the range of relative error of PM2.5mass concentration in desulfurization system and precipitator outlet of B power plant are-4.99%～4.95%and-2.53%～3.73%, the range of relative error of PM2.5mass concentration in C power plant unit at full load desulfurization system and precipitator outlet are-10.0%～0.22%and-2.81%～2.87%, the range of relative error of PM2.5mass concentration in83%desulfurization system and precipitator outlet which is under load conditions are-2.73%-7.80%and-4.18%～2.38%. The range of corresponding absolute error of A, B and C power plants were respectively-0.317mg/m3～0.257mg/m3and-0.315mg/m3～0.194mg/m3,-0.095mg/m3～0.104mg/m3and-0.124mg/m3-0.195mg/m3, the absolute error C plants were-0.081mg/m3-0.03mg/m3,-0.051mg/m3-0.054mg/m3and-0.027mg/m3-0.086mg/m3,-0.056mg/m3-0.034mg/m3.According to the detecting result, the relative error of ELPI is generally larger which can’t meet the error assessment requirements on China’s "stationary sources CEMS technical specifications"(HJ/T75-2007), nor to meet the regulations of International Organization for Standardization "Stationary source emissions-Determination of PM/10/PM2.5mass concentration in flue gas-relative error Measurement at low concentrations by use of impactors "(ISO23210-2009). While the test results for gravimetric method’s relative error were generally small, repeatability. All the test results of the relative error meet the requirements of HJ/T75-2007and ISO23210-2009. Taking the complexity of the charge method, affected by many factors, and high environmental requirements in instrumentation into account, ELPI is not recommended as the standard method of thermal power plant flue gas PM2.5testing. Instead, with the characteristics which were easy to carry the test instrument, easy to operate, less influential factors, and less demanding on the environment of the instrument of the gravimetric method, we strongly recommend that the gravimetric method been used as a standard method of flue gas PM2.5testing of thermal power plant.