HJ 693-2014Stationary Source Emission - Determination of Nitrogen Oxides - Fixed Potential by Electrolysis Method (English PDF)

3.1 Nitrogen oxides

It refers to the nitrogen oxides in the form of nitrogen oxide (NO) and nitrogen dioxide (NO2) in a stationary source emission.

conditions, the following numbers shall be constant numbers such as electron transfer number Z, farad constant F, gas diffusion area S, diffusion constant D, and diffusion layer thickness delta. Therefore, under certain range, the magnitude of the limiting diffusion current, i, is proportional with the concentration (rho) of NO or NO2.

6.1 Standard gases of nitrogen oxide and nitrogen dioxide

The certified environmental standard gas has an uncertainty of no more than 2%; or the uncertainty currently achievable. Check the standard gas concentration for the calibration error and system bias shall be 40%~60% C.S. or equal to C.S.

6.2 Nitrogen

Purity greater than 99.99%.

7.1 Nitrogen oxide analyzer by fixed potential electrolysis method

7.1.1 Composition

The nitrogen oxide analyzer by fixed potential electrolysis method (hereinafter referred to as: instrument) consists of: main unit (including flow control device, air pump, NO and NO2 sensors, etc.), sampling tube (including dust filter and heating device), air pipe, dehumidifying cooling device, portable printer, etc.

rate of the instrument. Use the standard gas to fill with the clean air-collecting bag, then drain it; repeat for 3 times; then fill with it again for later-use. Calibrate according to the calibration steps specified in the instrument instruction manual.

(2) Steel cylinder method: Firstly, use the gas flow meter to calibrate the sampling flow of the instrument. CONNECT the standard gas steel cylinder equipped with pressure reducing valve, adjustable rotameter, air guiding tube WITH sampling tube; open the cylinder gas valve; adjust the rotameter; inject the gas into the inlet of the instrument according to the flow rate specified by the instrument; the indicated value and the specified value of the sampling flow rate of the instrument shall be consistent. Pay attention that each joint shall not leak. Calibrate according to the calibration steps specified in the instrument instruction manual.

9.2 Determination

9.2.1 Zero calibration

(1) According to the instruction manual of the instrument, correctly connect the instrument’s main unit, sampling tube (including dust filter device and heating device), air guiding tube, dehumidifying cooling device, and other devices.

(2) Turn on the power to the heating device, dehumidifying cooling device, and other devices to meet the conditions specified in the instrument’s instruction manual.

(3) Turn on the power to the main unit; take the clean ambient air or nitrogen gas as the zero gas to conduct the zero calibration of the instrument.

9.2.2 Sample determination

After the zero-point calibration is completed, place the front end of the sampling tube of the instrument in the exhaust pipe; block the sampling hole, so that it does not leak gas. After the instrument indication is stable, record the indication value; record the monitoring result at least once per minute. Take the average value of 5min~15min as one measurement value. During the measurement period, in order to protect the sensor, after a period of measurement, clean the ambient air or nitrogen cleaning sensor according to the instruction manual of the instrument.

9.3 End of determination

9.3.1 After obtaining the determination results, place the sampling tube int the clean

ambient air or nitrogen to bring the indication value of the instrument back to near zero.

9.3.2 Shut down; cut off the power supply; disassemble the parts of the instrument, the measurement is over.

The relative standard deviations in the laboratory are: 0~1.7%, 0.3%~1.4%,

0.1%~0.7%;

The relative standard deviations among laboratories are: 3.2%, 2.0%, 1.3%;

The repeatability limits are: 2.7mg/m3, 9.2mg/m3, 11.9mg/m3;

The reproducibility limits are: 8.4mg/m3, 20.5mg/m3, 35.1mg/m3.

(2) Determination of NO2 standard gases at concentrations of 99mg/m3, 201mg/m3,

419mg/m3 in 6 laboratories:

The relative standard deviations in the laboratory are: 0~1.6%, 0%~2.0%,

0.2%~1.1%;

The relative standard deviations among laboratories are: 3.5%, 2.6%, 1.8%;

The repeatability limits are: 2.7mg/m3, 6.4mg/m3, 8.2mg/m3;

The reproducibility limits are: 8.4mg/m3, 13.8mg/m3, 19.7mg/m3.

(3) Six laboratories simultaneously measure the concentration of NO in the exhaust gas from 4#, 6# nits of a power plant. The concentration of NO in the exhaust gas from 4# unit is 611mg/m3~646mg/m3; the average value is 631mg/m3; while concentration of NO in the exhaust gas from 6# unit is 168mg/m3~193mg/m3; the average value is 178mg/m3.

The relative standard deviations in the laboratory are: 0.8~2.4%, 1.6%~4.3%;

The relative standard deviations among laboratories are: 2.1%, 4.9%;

The repeatability limits are: 35.5mg/m3, 16.2mg/m3;

The reproducibility limits are: 33.3mg/m3, 22.2mg/m3.

(4) Six laboratories simultaneously measure the concentration of NO2 in the exhaust gas from certain glass kiln. The concentration of NO2 in the exhaust gas is

170mg/m3~199mg/m3; the average value is 183mg/m3.

The relative standard deviations in the laboratory are: 3.6%~12.8%;

The relative standard deviations among laboratories are: 6.5%;

The repeatability limits are: 33.3 mg/m3;

The reproducibility limits are: 30.4mg/m3.

11.2 Accuracy

12.7 The instrument with the negative pressure resistance greater than the negative

pressure of the exhaust cylinder shall be selected; avoid the reduction of the sampling flow of the instrument, which results in the low r undetectable test results.

12.8 The service life of a fixed potential electrolysis sensor is generally 1~2 years; it shall be replaced in time after expiration. When calibrating the sensor, if the dynamic range is found to be small, the upper limit of the determination does not reach the full- scale value; or when re-inspecting the calibration span of the instrument, the calibration error exceeds the value specified in item (2) in 7.1.2, indicating the sensor has failed.

It shall be replaced in time and re-verified before use.

13.3 During the measurement process, when the sampling flow rate of the instrument

is lower than the specified value of the instrument, it can be solved by means of an external air pump.

13.4 Timely discharge the condensed water from the dehumidification cooling device

to prevent the measurement results from being affected.

13.5 Clean the dust filter in time to prevent the blockage of the air circuit.

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