Study On Assessment Method Of Compliance With Air Pollutant Emission Limits Of Thermal Power Plant Based On CEMS Data

Pollutants such as SO2,NOx and PM emitted from stationary sources will pollute the atmosphere and endanger human health.Research on the assessment method of compliance with emission limits for stationary sources has great significance to improv-ing the environmental air quality and protecting human health in China.At present,the assessment method of compliance with emission limits in Chinese Emission standards of air pollutants for stationary sources are mostly based on manual monitoring.With the continuous improvement of Chinese ecological and environmental supervision re-quirements and the rapid popularization of Continuous Emissions Monitoring System(CEMS)in key stationary sources,it is necessary to study and formulate assessment method of compliance with emission limits based on CEMS data,and then make the air pollutant emissions can be accurately controlled.As one of the key air pollution sources,to study their assessment method of compliance with emission limits based on CEMS data,which has important guiding significance for the establishment of the system of assessment method of compliance with air pollutant emission limits in stationary sources.This study collected CEMS data of SO2,NOx and PM from more than 2,000 ther-mal power units installed with continuous emission monitoring systems across China in 2015.For each pollutant,select units that meet the data validity conditions based on data missing and data abnormalities,etc.Using statistical methods,analyze the proba-bility distribution characteristics of the emission concentration of thermal power units of different installed scales,and select representative units based on log-normal com-pliance.Analyze the statistical relationship between the daily average values and hourly cumulative frequency,monthly average values and hourly cumulative frequency of rep-resentative units individually.Five scenarios are set up:linear fitting line,95%confi-dence upper and lower limits,and 95%prediction upper and lower limits,to study the correlation between daily average values and hourly average values,and monthly average values and hourly average values corresponding to each scenario.On this basis,the relationship between daily average values and hourly average values,monthly av-erage values and hourly average values is analyzed for SO2,NOx and PM while different proportion of thermal power units compliance with emission limits.The research results show that:①The linear fitting determination coefficient(R2)with the log-normal distribution of the hourly average values about SO2,NOx,and PM of the CEMS data of thermal power plants reflects the log-normal conformity of the emission concentration.The proportions of the three pollutants meeting R2≥0.8 are 86%,66%and 80%,and the proportions meeting R2≥0.9 are 60%,36%and 54%re-spectively.②Using Scenario 5(95%prediction upper limit)to study and formulate emission limits can maximize the proportion of thermal power units that compliance with standard under normal operating conditions,and meet the requirements of the standard in the five scenarios.In this scenario,when the 95%of hourly average values,daily average values and monthly average values of the SO2,NOx and PM compliance with the corresponding emission limits simultaneously in a calendar year:If 90%of the units are required to meet the limit values,the hourly limit values can be set as 1.5 times the daily limit values and 1.8 times the monthly limit values.If 95%of the units are required to meet the limit values,the hourly limit values can be set as 1.6 times the daily limit values and 2.0 times the monthly limit values.If 99%of the units are required to meet the limit values,the hourly concentration limit can be set as 2.0 times the daily limit values and 2.3 times the monthly limit values.③The above-mentioned correla-tion between the emission limits for hourly average values,daily average values and monthly average values are independent of capacity scale of thermal power generation units.The thermal power units of various installation scales can be stipulated by the same assessment method of compliance with emission limits.The result is basically consistent with the corresponding value in the Directive 2010/75/EU on industrial emis-sions,and provide a reference for improving the content of the assessment method of compliance with air pollutant emission limits in Emission standard of air pollutants for thermal power plants of China.In accordance with the management requirements of precise pollution control,sci-entific pollution control and pollution control according to law,the Emission standard of air pollutants for thermal power plants should include the content of assessment method of compliance with emission limits based on CEMS data,and stipulate hourly concentration,daily average values and monthly average values.The method should gradually extend it to other key air pollutant emission sources,making it an important method for the implementation of assessment method of compliance with emission lim-its in stationary air pollution sources.