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HJ 693-2014: Stationary source emission. Determination of nitrogen oxides. Fixed potential by electrolysis method
HJ 693-2014
HJ
NATIONAL ENVIRONMENTAL PROTECTION STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
Stationary Source Emission -
Determination of Nitrogen Oxides -
Fixed Potential by Electrolysis Method
ISSUED ON: FEBRUARY 07, 2014
IMPLEMENTED ON: APRIL 15, 2014
Issued by: Ministry of Environmental Protection of PRC
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative References ... 4
3 Terms and Definitions ... 4
4 Method Principle ... 5
5 Interference and Elimination ... 6
6 Reagents and Materials ... 6
7 Apparatus ... 6
8 Sampling Position and Sampling Point ... 7
9 Analysis Procedures ... 7
10 Results Calculation and Expression ... 9
11 Precision and Accuracy ... 9
12 Quality Assurance and Quality Control ... 11
13 Precautions ... 12
Appendix A (Informative) Instrument Performance Review Table before and
after Measurement ... 13
Stationary Source Emission -
Determination of Nitrogen Oxides -
Fixed Potential by Electrolysis Method
1 Scope
This Standard specifies the fixed potential by electrolysis method for determination of
nitrogen oxides in stationary source emission.
This Standard is applicable to the determination of nitrogen oxide in the stationary
source emission.
The detection limit of tis Standard method is 3mg/m3 for nitrogen oxide (calculated by
NO2); 3mg/m3 for nitrogen dioxide; lower limit of determination is 12mg/m3 for nitrogen
oxide (calculated by NO2); 12mg/m3 for nitrogen dioxide.
2 Normative References
The contents of this Standard refer to the following documents or their terms. For the
undated references, only the valid version applies to this Standard.
GB/T 16157 The Determination of Particulates and Sampling Methods of Gaseous
Pollutants Emitted from Exhaust Gas of Stationary Source
HJ/T 76 Specification and Test Procedures for Continuous Emission Monitoring
Systems of Flue Gas Emitted from Stationary Sources (on Trial)
HJ/T 373 Technical Specifications of Quality Assurance and Quality Control for
Monitoring of Stationary Pollution Source
HJ/T 397 Technical Specifications for Emission Monitoring of Stationary Source
3 Terms and Definitions
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 δ. Therefore, under certain range, the magnitude of the limiting
diffusion current, i, is proportional with the concentration (ρ) of NO or NO2.
5 Interference and Elimination
The particulate matter and moisture in the measured exhaust gas are easily
condensed on the surface of the permeable membrane of the sensor; so that influence
the determination of the NO and NO2. Thus, this method uses a dust filter device and
a dehumidification cooling device, etc. to pretreat the particulate matter and moisture
in the exhaust gas to remove the influence.
The following gases, such as CO2, NH3, CO, SO2, H2, HCl, CH4, C2H4, shall influence
the determination of NO and NO2 in difference degree; interference between NO and
NO2 shall also occur, if the inference is obvious, it shall be corrected in the calculation
program of the instrument.
6 Reagents and Materials
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 Apparatus
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...