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CEMS provides real-time monitoring of smoke, dust, SO2, and NCX concentrations and emissions in the flue gas, which is mainly measured by a turbidity meter for measuring dust concentration, a flue gas analysis system for measuring the concentration of S02, NOt, and O2, and temperature, flow, and humidity measurements. The unit composition is not only the on-line monitoring instrument of the desulfurization system, but also the on-line monitoring instrument of the real-time pollutant emission monitoring system. The sampling probe is installed in the mixed flue or chimney.
CEMS mainly includes particulate monitoring, gaseous pollutant monitoring, smoke emission parameter measurement, data acquisition and transmission and processing subsystems, which measure the concentration of particulates, the concentration of gaseous pollutants, and the temperature of flue gas in the flue gas by sampling and non-sampling methods. , pressure, flow rate (or flow), moisture content, oxygen content (or co2 content), etc., calculate the concentration and emission of pollutants in the flue gas, display and print various parameters, charts and transmissions through data, graphic transmission system To a fixed pollution source monitoring system. The continuous monitoring system for smoke emissions is shown in Figure 1. 
2CEMS data error reasons and solutions (l) CEMS measurement location should avoid flue bends and sharp changes in the site of the section, when the installation location can not meet the requirements, should be as far as possible in the airflow stability section. In the case of unstable flow field in the monitoring section, if the inertial motion will cause the non-uniform distribution of the particle and smoke velocity, it will cause the measured value to deviate from the actual value. In this regard, the CEMS should be installed as far as possible on the long straight vertical flue, so as to avoid the impact of water mist, water droplets and flue diameter and other factors on the measurement; to find the best measurement position in the monitoring section by manual monitoring method. Through the reference manual monitoring data, determine the installation location of CEMS on the monitoring section. If it is difficult to meet the above installation requirements, the actual operation of the desulphurization system of the thermal power plant should be regularly tested and compared with the CEMS monitoring data and the real-time data of the desulfurization DCS to ensure the accuracy of the CEMS monitoring data.
(2) The CEMS of the unit with an installed capacity of more than 300 MW is required to be calibrated by the supplier. Therefore, the calibration period is long and the accuracy of the measured value is greatly affected. In this regard, the thermal power plant shall regularly calibrate, maintain and maintain the CEMS, and record relevant data to ensure the correctness of the CEMS monitoring data.
(3) In some thermal power plants, only one set of CEMS is allocated to multiple units, making the measurement time for a single unit short, and it cannot meet the need for continuous, real-time tracking and measurement of pollutants emitted from fixed sources. In order to meet the requirement that the total number of measured hours for each fixed source is not less than 75% of the total operating hours of the boiler and kiln, the measurement time per hour must not be less than 45 minutes, and one set of CEMS should be installed for each unit.
(4) The CEMS of many units is only equipped with S02, NOx, soot concentration and oxygen sensitive measurement units, and no flue gas measurement unit is configured. This can only measure the concentration of pollutants and cannot measure the total amount of flue gas and thus cannot Unit emissions are monitored. In addition, the CEMS of some units is not equipped with a humidity measurement unit, so that it is impossible to obtain the concentration and emission amount of smoke pollutants at the same time. In this regard, CEMS should be configured for the desulfurization system requirements of the unit.
(5) The standard gas index used for the calibration of the measurement system is not suitable, resulting in inaccurate test results. In this regard, the standard gas designated by the environmental protection department should be selected to ensure the purity of the standard gas.
3Manually modify the identification method of the uploaded data (1) Check the relevant display data of CEMS and desulfurization DCS, and compare the historical trend, query the load of the unit, the opening degree of the induced draft fan, the flow of the flue gas, on the DCS, The historical trend of desulfurization net smoke flow rate, inlet/outlet so2 concentration of flue gas, booster fan current, and the opening degree of its blades, and the desulfurization bypass adjustment damper opening degree, etc., adopt 24-hour monitoring and historical trend positioning and inquiries. Compare the query results with the reported data and reports. Special attention should be paid to the curve segments that are too smooth in the historical trend curve because the real-time parameter curves are jagged or wavy. At the same time, attention should also be paid to historical curves with exactly the same trend of change, because the trend of real-time parameter curves tends to have a certain lag.
(2) According to thermal power plant power generation and coal consumption, desulfurization system power consumption and water consumption, by-product output, desulfurization equipment maintenance records, coal quality into the furnace, desulfurizer dosage and other parameters, using the material balance formula to repeat Calculate the comparison and use the calculation results as a basis for monitoring.
(3) The CEMS is calibrated with precision instruments approved and approved by the national authoritative metrology department to calibrate and determine the reliability of the data. At the same time, inspect the daily inspection, maintenance and regular calibration and verification of CEMS equipment to determine the authenticity and reliability of the CEMS monitoring data.
(4) Emissions of SO2 are estimated based on the changes in parameters such as pH of absorption tower slurry, unit load, flue gas flow rate, slurry supply density in the absorption tower, and density of slurry in the absorption tower. If the absorption tower slurry circulation pump is used to reduce pump operation, SO2 emissions will exceed the standard.
(5) For the case of modifying the actual measurement value into the setup program of CEMS, the method of comparing the monitoring data of CEMS with the real-time value of DCS can be used to check the authenticity of the CEMS monitoring data.
(6) Determine the authenticity of the CEMS monitoring data by checking the historical data of the flue gas desulfurization equipment online.
(7) Check the time and duration of the CEMS fault, compare it with the DCS historical data of this time period, and check the method to determine whether to remove the authenticity of the CEMS monitoring data by exiting the CEMS.
Application and Problems Analysis of Continuous Monitoring System for Smoke Emissions in Thermal Power Plants
1CEMS