Before carrying out CEMS comparison and monitoring, we should first try to understand and grasp as much as possible the basic situation of the pollution source site, the environmental conditions of the site and the basic information of CEMS, which is conducive to more adequate and targeted quasi-work and improve work efficiency.
(1) Grasp the basic situation of the pollution source where the monitoring is located
The geographical location of the pollution source, such as the type of area it belongs to, the relevant emission standards implemented, etc.
Types of polluting enterprises (electricity, chemicals, cement, steel, etc.).
The production situation and recent production plan of the polluting enterprise, normal, full load, low load, shutdown, overhaul, etc., as well as whether there are periodic changes.
The situation of the pollutant treatment facility, the existence of the dust collector, the type (electricity, bag), the operating capacity and the condition;The presence, mode (dry, wet), operational capacity and condition of the desulfurization facility;The existence, mode, operation capacity and condition of denitrification facilities.
The emission of the pollution source under normal production conditions, the type of pollutants discharged, the emission concentration, the emission amount and the relevant approximate emission parameters (flow rate, temperature, static pressure, humidity, etc.).
Types of pollutants: the objects of comparison and monitoring (the main pollutants emitted by different industries are different).
Emission concentration (high, low): determines the selection of the range of the reference instrument to be used, the selection of the reference material during calibration, and the selection of the calibration concentration.
Flow velocity (high, low): The flue gas velocity is too low (<5ms), and the sensitivity of the microdifferential pressure sensor is reduced by the pitot tube method, and the sampling and testing errors are increased.
Temperature (high, low): If the temperature is too high (>500), the cartridge type for particulate sampling will change.
Static pressure (positive, negative, large, small): the positive and negative pressure in the chimney or flue;Positive pressure should pay attention to protection, and excessive negative pressure will increase the requirements for the air pump of the sampler and analyzer, and sometimes a single pump is required.
l Humidity (large and small): There is no heating after wet desulfurization, and the humidity is often very large, so auxiliary dehydration equipment needs to be added.
The basic situation of the discharge port, whether it is standardized, the shape and size of the chimney or flue (circular diameter, rectangular height, width, etc.), area, the path of the flue, the discharge bypass, etc. From the shape and size of the sampling flue, the length of the sampling gun that should be used can be estimated, as well as the working time and initial workload of the comparison monitoring.
The reference method compares and monitors the environmental conditions, the reference monitoring of the straight pipe section of the flue, the reference test hole (the location, number, and size meet the requirements), the sampling platform, the ladder and the guardrail, the platform height, area, and multi-layer platform settings: the ladder situation (the general platform height is 5m, and it should be equipped with a zigzag ladder, spiral ladder, and elevator);Whether the guardrail height is 12m, etc.
Compare and monitor the safety of the site, whether there is a stable power supply, distance;Whether there are hazardous places and facilities around the operating environment;The safety of the operating platform and ladder (stable and sturdy);Compare whether there is any leakage of polluting gas that affects health at the site.
(2) Understand the basic situation of the CEMS installed in the pollution source
Basic information such as the model, brand, manufacturer, basic configuration, and completion time of its installation, commissioning, and acceptance.
The sampling and analysis test principle of CEMS, there are great differences in the status and calculation process of pollutant data displayed and recorded by different sampling and analysis test principles, and the data of CEMS comparison is confirmed**.
The daily operation status of CEMS, normal operation, failure, maintenance and repair;Whether there is daily operation and maintenance, calibration, operation and maintenance methods, as well as on-site data quality control measures and plans taken, etc.
Calibration and maintenance of manual reference instruments
The calibration and maintenance of manual reference instruments and equipment is an important preparation before carrying out CEMS comparison monitoring. Because the CEMS comparison monitoring is based on the results of the manual reference test, it is compared with the continuous monitoring data of the CEMS;Therefore, in the daily management of instruments, the analytical instruments for sampling pollution sources should be maintained regularly to ensure that they maintain their normal working capacityBefore each CEMS comparison and monitoring, the instruments and equipment used in the monitoring should be checked and calibrated as necessary to ensure that the manual reference test data is accurate and reliable, and to ensure the smooth completion of the comparison and monitoring work. (1) Preparation of sampling and testing supplies
The on-site supplies (consumables) to be prepared for CEMS comparison monitoring and manual reference sampling and analysis mainly include the following items.
Cartridges and silica gel used for particulate sampling
The selection and pre-treatment of the cartridge material and the accurate weighing process are key to quality control. Generally, when the flue gas temperature of the on-site pollution source is lower than 500, the filter cartridge made of glass fiber is usedIf you encounter a special emission source (e.g. steel blast furnace exhaust) and the flue gas temperature is high, you should choose a filter cartridge made of corundum;In addition, the drying and weighing requirements for filter cartridges of different materials are slightly different, which should be carried out in accordance with the relevant operating procedures in the GB 161571996, and the same pretreatment steps and control conditions need to be used for the air filter cartridge before sampling and the load particulate matter filter cartridge after sampling to ensure the comparability of data. In addition, since the current smoke sampler needs to use dry silica gel for dehumidification, enough dry silica gel should be prepared for on-site use.
Standard gas for calibration
Zero and range standard gases used in the calibration of gaseous pollutant analyzers. Zero point gas:It is required that the sulfur dioxide and nitrogen oxides contained in zero gas shall not exceed 01μmol/mol。The concentration of other gases contained in the zero gas must not interfere with the readings of the instrument or produce readings of sulfur dioxide and nitrogen oxides.
Range Standard Gas:The uncertainty does not exceed 2% within the validity period of the national standard gas.
Range standard gas concentration:A country approved by the National Metrology Administration.
Class I and Class II standard gases, the uncertainty of which does not exceed 20%。For general range calibration, single-point calibration should be selected, and the standard gas within the existing range of the analytical instrument and slightly higher than the normal emission concentration of the pollution source should be selected for calibration (the concentration is close to the on-site emission value).
Absorption bottles and absorbent liquids for gaseous contaminant sampling
If the flue gas sampler is used to monitor the gaseous pollutants in the flue gas emitted from the pollution source site (which has been rarely used at present), a clean liquid absorption bottle (50ml) should be prepared, and the standard absorption solution required for sampling different pollutants should be prepared, and the specific preparation methods, steps, chemical reagents, and storage conditions and on-site use requirements should be carried out with reference to the relevant standard analysis methods in Table 20-2.
(2) Maintenance and calibration of soot (flue gas) sampler
Air tightness check of the sampler
Due to the long-term use of the smoke (flue) sampler at the site of the pollution source, it is very likely that the pipeline or joint will be aged, the seal is not tight, and there will be air leakage, so the air tightness should be checked.
Generally, the operation of the air tightness inspection method of the sampler in the laboratory is cumbersome, and it is necessary to use special components to seal the sampling population, and connect the negative pressure gauge on the pipelineCheck whether there is air leakage in the pipeline by observing and recording the pressure changes of the negative pressure gauge before and after the start and stop of the sampler pumping pumpThis method is difficult to operate in the field. Therefore, because the sampler sampling flowmeter currently used in China is generally set in front of the sampling pump, some simple and effective on-site methods can be used for inspection, such as after starting the air pump, block the sampling population with your hands, and observe the change of the flow rate of the sampling flowmeter.
Calibration of flow metering devices
The core components of the smoke and dust sampler and flue gas sampler of the flow metering device, due to the long-term use of the sampler at the pollution source site, the related temperature and pressure sensors may drift and ageThe calibration parameters of the internal flow meter are subject to change;On the other hand, the pitot tube coefficient also changes due to the change in the surface finish due to wear. Therefore, these systematic errors must be corrected by regular and effective calibration of the flow metering device.
Calibration mainly includes:a.Calibration of the sampler-related pressure sensor (hydrostatic, dynamic, flowmeter pre-pressure, etc.);b.Calibration of the sampler-related temperature sensor (flue gas temperature, pre-flowmeter temperature, etc.);c.Sampling flow calibration of the sampler flow meter (also suitable for flue gas samplers);d.Calibration of the sampler S-type pitot tube velocity measurement.
The calibration of the flow metering device requires the use of instruments and equipment, mainly including pressure detection instruments, potentiometers or resistance boxes, dry or wet gas accumulation flow meters or standard rotameters, compensating micromanometers or low-speed wind tunnels, and standard pitot tubes.
The above-mentioned calibration of the flow metering device is a large workload, but if any one of the parameters is not tested accurately, the flow rate of the sample, the volume of the gas production, the flue gas temperature and the related calculation will be incorrect, and the data volume will be seriously affected. However, due to the current monitoring of pollution sources at all levels of monitoring stations is very heavy, so in terms of the current domestic instrument stability level, this part of the calibration work can be considered to be carried out 1 2 times a year, if some of the experimental calibration conditions are not available, it can also be considered in the regular measurement and verification process of the instrument and equipment at the same time for the relevant calibration of the flow.
(3) On-site portable flue gas analyzer (electrochemical, optical) calibration
The air tightness inspection operation and requirements of the instrument sampling test gas path are basically the same as those of the aforementioned smoke and dust sampler.
Gas analyzer calibration field portable flue gas analyzer regardless of the principle of electrochemical or optical instrument, the internal detector is affected by environmental conditions and long-term test use, etc., which will cause a certain test system error, so that when testing zero point and range standard gas, the measurement drift will occur due to systematic error, so that the test results are inaccurate, so it needs to use standard gas (including O2) to calibrate it. This calibration process may seem easy, but there are two things that should be taken into account in practice.
The first is to calibrate the standard gas inlet flow control. In the on-site testing and the applicability test of the instrument, it is found that the change of the sampling flow rate of the flue gas analyzer (electrochemical, optical) (imported and domestic) currently used in China has a certain impact on the gas concentration test results, and the general impact is about 5%, and some domestic instruments are affected by the change of inlet flow rate by nearly 10%;Therefore, in the calibration project of this kind of instrument, the injection flow of the calibration standard gas should be controlled to be consistent with or as close as possible to the sampling flow rate in the actual detection, so as to overcome the systematic error and ensure that the calibrated instrument is more accurate in the field test.
The second is the selection of calibration operation process. The calibration process of the on-site portable flue gas analyzer used for reference is generally divided into two types: the calibration of the analyzer and the calibration of the test analysis system (the system includes sampling probes, sampling tubes, air ducts, and analyzers). At present, the requirements for the calibration of CEMS installed in China are all system-wide calibration (standard gas from the sampling probe), mainly to overcome the loss of gas (especially SO2 gas) in various links (filtration, dehydration, etc.) before entering the analyzer. Therefore, for the reference on-site portable flue gas analysis instrument, the whole system calibration process of the test and analysis system should be selected as much as possible during the on-site comparisonIn particular, the whole process calibration of the reference test system must be carried out for the long pipeline path at the front end of the sampling (sampling gas conduction process), which may cause gas adsorption and other losses, so as to improve the accuracy of the test.
As a portable monitoring instrument, it is very common for the on-site portable flue gas analyzer to have drift and fluctuation in the zero point and range in the analysis test, so the calibration of the flue gas analyzer should be calibrated 1 time before each CEMS comparison and monitoring or calibrated before a long interval of useIn addition, the reference flue gas analyzer, whether electrochemical or optical, is mainly used to achieve direct testing (on-site output) at the pollution source comparison monitoring site, so if the site conditions are available (there is a corresponding concentration and qualified and effective standard gas), this part of the calibration work should be considered to be completed at the comparison monitoring site as much as possible.