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FAQ of Centralized Exhaust Gas Detection (1)



FAQ of centralized exhaust gas detection

1. Conversion and calculation of nitrogen oxides.

The NOx is the mixture of NO and NO2 and is finally expressed by the component content of NO2. Therefore, it is necessary to convert the NO concentration and then add it with the measured NO2 concentration to obtain the final NOX content. If expressed in mass concentration, NOX=NO × 1.53+NO2; If expressed in volume concentration, NOX=NO+NO2;

2. The flue gas data measured by the instrument is abnormal.

Fault judgment: the aging period of the chemical sensor, gas leakage in the gas path, sampling flow, gas pump load, parameter calibration, calibration method, water damage of the chemical sensor or damage of the sensor board, gas cross interference, gas path blockage, pipeline adsorption, uncleaned and forced zero calibration, insufficient vibration and preheating time;

Possible causes:

1. Aging period: if the instrument is a chemical sensor, the expected value of the validity period is two years, but with the frequency of use and the concentration of the gas to be measured, the service life will become lower and lower. Generally speaking, the normal actual service life is about one and a half years. If it is oxygen, the service life may be shorter due to the installation location and air loss;

2. Air leakage: the most intuitive phenomenon is that the oxygen value does not change or changes very little during sampling. It is mainly divided into external gas circuit leakage and internal gas circuit leakage. The external gas circuit shall be checked: sampler, preprocessor, 25 connecting pipe, PTFE pipe, and the inlet of working condition shall be sealed; The internal air circuit shall be checked: the O-ring at the transparent cover bottom of the filter element, all internal pipeline connections, flow pressure sensor, orifice flowmeter, sensor air chamber, including the connection nozzle and O-ring. A simple method can be used to judge whether there is air leakage before and after the pump by blocking the inlet and outlet nozzles of flue gas respectively and observing the change of flue gas sampling flow;

3. Sampling flow: incomplete blockage of gas path (such as foam particles or dust residual particles); The air flow pressure sensor is damaged; The air pump has its own fault (for example, the pump load cannot be reached, the pump head cavity is polluted, etc.); The flow parameters of the air pump are changed; The pipeline of air flow pressure sensor falls off;

4. Load: the negative pressure of flue under working condition is relatively large, which may cause that the power of flue gas pump has been fully loaded, but the set flue gas flow is still not reached. At this time, the load of the front and rear ends of the air pump can be balanced by simultaneously throwing the inlet and outlet ends of the flue gas into the working condition and relying on the static pressure of the working condition itself to achieve normal sampling flow;

5. Parameters: Changes in flue gas parameters will cause differences in flue gas data, which can be corrected by restoring factory settings. Two points need to be paid attention to in flue gas calibration: 1. primary and secondary magnification; 2. Change the measuring range;

6. Debugging method: air bag method and bypass method. It is strictly forbidden to directly connect the outlet of the pressure reducing valve of the standard gas cylinder with the inlet of the flue gas analyzer. Even if the flow is adjusted to the same state, it cannot be directly connected.

7. Sensor damage: due to improper operation or maintenance, water ingress into the gas path or corrosion of the sensor road plate, it is required that the front-end treatment must achieve dehydration effect during sampling, and it should not be placed in a place with high humidity during daily storage, and it should be started regularly;

8. Cross interference: it is inevitable that the chemical sensor will have cross interference with gas, and the target gas can be corrected by filtering the interference gas or data compensation. In addition, the chemical sensor will be poisoned and permanently damaged if it is used beyond the range or there is gas in the use environment that changes the nature of the sensor;

9. Blockage of gas path: the flue gas sampling flow cannot reach the set flow under no-load condition, or the sampling flow always fluctuates and cannot be stabilized under no-load condition. 1. Flue gas filter element. Water ingress, blackening and blockage; 2. Incomplete blocking caused by foam particles in the air inlet nozzle or pipeline; 3. Melting deformation of PTFE pipe in the preprocessor;

10. Pipeline adsorption: water (steam), silicone rubber pipe, rubber pipe and 304 stainless steel have a large adsorption on flue gas (especially SO2), so it is required to improve the pretreatment efficiency and avoid using smoke and dust pipes or dynamic and static pressure pipes for flue gas sampling;

11. Uncleaned and forced zero calibration: when the instrument displays a higher flue gas value, click forced zero calibration, and the current state will be forced to calibrate as the zero state, resulting in the measured value far from the true value; When the flue gas sampling is completed and there is still much residual gas in the instrument gas chamber and pipeline, the sampling is stopped and the machine is shut down for packing without cleaning. The residual gas erodes the chemical sensor for a long time, reducing its accuracy and service life;

12. Vibration and preheating: if it is an optical device, it is not allowed to have a relatively violent vibration at the use site, and vibration will cause errors in the measurement of smoke by the optical device; In addition, optical equipment needs a period of warm-up time before formal sampling. If the warm-up time is not enough, numerical deviation will be caused;


3. The result of manual calculation of sampling volume is inconsistent with the data automatically issued by the instrument.

Possible causes:

1. The data of the soot meter is measured in real time, while the manual calculation is based on the final average value. There will be some errors in the two calculation methods;

2. Most of the manually calculated environmental parameters are based on the actual parameters measured separately by other standards (such as barometer, thermometer, etc.), while the instrument uses its own internal parameters to calculate. The relative positions of the two algorithms are different, and the results are naturally inconsistent;

3. Manual calculation is mostly calculated by taking integer or fixed number of decimal points, while the instrument is calculated based on the real value of the value, and there will be errors in the retention of the number of significant digits and the way of rounding off the number. To sum up, even if the same formula is used for calculation, there must be some difference between the value calculated manually and the value displayed by the instrument. It is recommended that the value displayed by the instrument should prevail. As long as the operation of the sampling process is correct, the value of the instrument should be more accurate than that calculated manually.


4. The inspection flow of soot meter is unqualified.

Fault judgment: parameters and settings.

Possible causes:

1. Parameters: relevant parameters in the instrument maintenance interface have been changed or have not been calibrated for a long time, such as smoke temperature, humidity, pressure (dynamic pressure, static pressure, gauge pressure, flow pressure, etc.), flow, etc;

2. Setting: when calibrating the flow, all environmental parameters (ambient temperature, atmospheric pressure, etc.) should be consistent with the calibrator and the current calibration conditions, especially the flue gas temperature items that need attention. If it is in the measurement mode, the signal line and the flue gas temperature sensor must be sent for inspection together and correctly connected during the inspection; If the smoke temperature item is in the input mode, it should be manually input to be consistent with the current ambient temperature.


5. The smoke and dust under the working condition can be seen with the naked eye, but the actual sampling results are very low or even can not be collected.

Fault judgment: position, air leakage, setting, parameters and operation.

Possible causes:

1. Location: The location of the points and openings does not meet the sampling requirements, and the distance from the elbow and fan is not enough to cause vortex, so you can try to replace the sampling points or select other openings;

2. Air leakage: check the air tightness of all connecting parts between the filter cartridge (membrane) and the host (including the host itself) by sections, especially whether there is air leakage in the sampling pipe, the air water separator (drying cylinder, buffer), the transparent cover on the host, etc;

3. Setting: The selected sampling method is incorrect, and the constant speed tracking sampling shall be satisfied as far as possible; The flow rate is not predicted, resulting in the sampling flow mismatch;

4. Parameters: relevant parameters in the instrument maintenance interface have been changed or have not been calibrated for a long time, such as smoke temperature, humidity, pressure (dynamic pressure, static pressure, gauge pressure, flow pressure, etc.), flow, etc;

5. Operation: When taking samples after sampling, the loss of samples is caused or all samples are not collected completely, including the samples left in the elbow assembly and the damaged and adhered parts of the filter cartridge (membrane).


6. When the smoke temperature is high, the tracking rate of the instrument cannot meet the sampling requirements.

Possible cause: At present, the modes selected by the soot tester for sampling are smoke temperature and static pressure modes, that is, the selected flow point is the state at the inlet nozzle of the sampling pipe in the flue under working conditions. Therefore, when the temperature is high, the actual flow transmitted to the instrument dust pump may be low or even cannot reach the normal working state of the dust pump, so the tracking rate may not meet the standard. The soot meter of our company includes two calculation modes: smoke temperature and static pressure and temperature and pressure gauge. In case of the above situations, you can select the temperature and pressure gauge mode in the system settings, which can ensure the normal operation of the dust pump without affecting the final sampling concentration;


7. There is no dynamic pressure or flow rate display.
Fault judgment: operation, position, air leakage or blockage, water discharge, working condition and parameters.
Possible causes:
1. Operation;
2. Location: The opening at the location where the sampling pipe is placed does not meet the requirements of the national standard, and the distance from the elbow, fan, etc. is not enough to cause vortex, so the sampling point can be replaced or other openings can be selected;
3. Air leakage or blockage: First, check whether the pitot tube and orange blue connecting tube of the sampling tube have air leakage or blockage. Note: 1. Each tube should be checked separately rather than together; 2. In addition to air tightness, the permeability shall also be checked; Secondly, check whether the dynamic pressure of the host is normal. You can press the △ P+end with your finger to determine whether there is a change in the value. If there is no change, it may be air leakage or blockage in the machine and the pressure sensor is damaged;
4. Water discharge: in one case, the dynamic pressure and flow rate are normal at the initial stage of sampling, but they become lower and lower as time goes by. In this case, the pressure of the main engine should be calibrated again in time. In addition, the sampling pipe and orange blue pipe should be drained in time to avoid pressure deviation caused by the gravity of condensate;
5. Working condition: one working condition is that there is no fan, and the flue gas is naturally discharged by gravity. This working condition itself has no dynamic pressure or the dynamic pressure is very low, so the pitot tube method cannot be used to measure the pressure and flow rate;
6. Parameters: 1. The pressure parameters on the maintenance interface were abnormal, and no effective quality control calibration was carried out; 2. Incorrect setting or measurement of atmospheric pressure, temperature, humidity and other environmental parameters; 3. The flue gas density coefficient is changed to an abnormal value;


8. The flue gas temperature display is abnormal.
Fault judgment: components, settings and parameters.
Possible causes:
1. Component damage: mainly including components in the host, temperature test sensor (on the sampling tube), and smoke temperature signal line. If there are multiple smoke and dust meters of the same model on site, you can choose to cross connect the above three methods to judge the fault. After determining the fault, you can temporarily choose the undamaged part to temporarily replace to complete the sampling; The plugs at both ends of the signal line have poor contact with the corresponding sockets. It is recommended that the locking nuts should be used for fastening each connection. After sampling, the plugs should be perpendicular to the socket plane and should not be pulled too hard; If there is interference of large static electricity or high-power equipment on the site, the sampling pipe shall be well grounded as required during sampling;
2. Incorrect setting: the measurement method of flue gas temperature is incorrect. When entering the status, there should be a "*" note at the temperature. When measuring the status, a temperature test sensor that can work normally should be connected;
3. Incorrect parameters: the smoke temperature parameters in the maintenance interface have been changed or the correct quality control calibration has not been carried out.


9. During sampling, the instrument is in the protection shutdown interface when the sampling pump stops.
Fault judgment: blockage, air leakage, setting, parameters, voltage.
Possible causes:
1. Blocking type: all shutdowns caused by blocking type should be reflected from the pressure and power on the sampling interface, such as the pressure gauge rises to a very high level and the power reaches 100%.
The filter cartridge or membrane is blocked after being soaked; Blockage caused by incorrect placement of filter cartridge or membrane; The connecting pipe between the sampling pipe and the host is bent; Water accumulated in the connecting pipe between the sampling pipe and the host machine causes excessive resistance; The filter screen in the air-water separator or drying cylinder is blocked by foreign matters; The filter element on the host has not been cleaned and replaced for a long time, resulting in dust deposition; The pipeline connecting the air-water separator or drying cylinder and the host machine is bent;
2. Gas leakage type: shutdown protection caused by gas leakage type shall also be reflected from the pressure and power of the sampling interface, such as low pressure display, flow rate not meeting the sampling requirements, and power reaching 100%.
The connecting pipe of the pressure sensor inside the instrument falls off; The pipeline between the inlet of the dust pump and the flowmeter inside the instrument falls off; The air outlet of the instrument dust pump is blocked, and the dust pump fails (the pump is stuck, there is no starting voltage, some pump head blades are not thrown out, and the brush is in poor contact, etc.);
3. Setting class: shutdown caused by improper field operation of the instrument.
Determine whether the sampling method (constant speed, constant current) meets the site requirements; If it is constant velocity tracking sampling, whether the flow rate prediction process is carried out in advance and the correct sampling nozzle is selected according to the process results; If it is constant current sampling, whether the set flow value exceeds or approaches the upper limit of the instrument range; Whether the flue gas temperature setting mode (measurement and input) meets the requirements. When entering the status, there should be a "*" note at the temperature. When measuring the status, a temperature test sensor that can work normally should be connected; Check whether the humidity measurement status and results are correct; The flue gas density parameters are modified;
4. Parameter class: the instrument was not calibrated correctly for quality control before going to the site.
Relevant parameters in the instrument maintenance interface have been changed or have not been calibrated for a long time, such as smoke temperature, humidity, pressure (dynamic pressure, static pressure, gauge pressure, flow pressure, etc.), flow, etc; If the maintenance parameters have been saved during the last calibration, they can be changed by restoring the factory settings;
5. Voltage: the obvious phenomenon is that the dust pump can not work normally, or it can not meet the sampling requirements, but the display interface and normal key operation of the instrument are normal.
The instrument cannot work normally due to the problem of on-site AC voltage; The power supply voltage of the dust pump does not reach the normal working voltage due to the damage of the instrument components; The electric capacity of the external DC power box is insufficient, and the dust pump cannot work normally; The voltage of the external DC power box does not match the voltage normally used by the instrument.


10. The PM2.5 test results at the same location are more than those of PM10.
Possible causes: When collecting samples, the damaged filter membranes were not collected together; Whether the sampling conditions and equipment calibration of the two sampling equipment are unified and meet the requirements; One of the equipment has power failure, shutdown and other abnormal conditions during sampling; If the installation of the sampling head does not meet the requirements, the sampling head of PM2.5 shall be installed and cut step by step by TSP/PM10/PM2.5 and cannot be omitted; The distribution position of the two equipment does not meet the requirements or is not under the same environmental conditions.


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