HJ 1240-2021Stationary source emission - Determination of gaseous pollutants (SO2, NO, NO2, CO, CO2) - Portable Fourier transform infrared spectroscopy method (English PDF)

7.1 Fourier Transform Infrared Gas Analysis System

7.1.1 System Composition

Fourier transform infrared gas analysis system is generally composed of sampling unit, preprocessing device, analyzer and data processing unit.

Among them, the sampling unit includes a sampling tube (including a particulate filter, with heating and heat preservation functions), an air duct, an air pump, etc.; pretreatment the device can choose a constant temperature heating device with a heating temperature of >=180 °C; the analyzer consists of an infrared light source, an interferometer, a sample chamber and a detector;

The data processing unit includes computer, analysis software and reference spectrum.

7.1.2 Performance requirements

7.1.2.1 Indication error. when SO2, NO, NO2 and CO are in the calibration range > 60 µmol/mol, the relative error is within ±5%;

When the range is less than or equal to 60 µmol/mol, the absolute error is within ±3 µmol/mol; the relative error of CO2 is within ±5%.

7.1.2.2 System error. when the calibration range of SO2, NO, NO2, and CO is greater than 60 µmol/mol, the relative error is within ±5%;

When the range is less than or equal to 60 µmol/mol, the absolute error is within ±3 µmol/mol; the relative error of CO2 is within ±5%.

7.1.2.3 Zero drift. within ±3%.

7.1.2.4 Range drift. within ±3%.

7.1.2.5 Analyzer. the wavenumber range should include at least 900 cm-1 to 4000 cm-1; the total optical path length should meet the requirements of each target compound in this standard.

The minimum detection limit is required; the spectral resolution should ensure that the target compound in the gas sample can be separated from the infrared absorption peaks of other coexisting substances.

7.1.2.6 The particulate filter and other properties of the instrument shall meet the technical requirements of HJ 1011 for Type II instruments. Airway and preconditioning the material should be high temperature resistant, anti-corrosion and non-adsorbing, non-reacting with the target compound.

7.2 Standard gas cylinders

Equipped with adjustable pressure reducing valve, adjustable rotameter and air pipe made of polytetrafluoroethylene, the material of each component should avoid compounding with the target Physical adsorption or chemical reaction occurs.

9.1 General requirements

On-site measurement of portable Fourier transform infrared spectroscopy includes steps such as instrument debugging and calibration, sample measurement and so on.

9.2 Instrument debugging

Connect the analyzer, sampling tube, airway, pretreatment device and other parts according to the instrument instruction manual, turn on the instrument, and connect the sampling unit, After the pretreatment device and the analyzer have reached the working state specified in the instrument manual, the system shall be air-tight in accordance with the provisions of GB/T 16157.

sex check. If the inspection fails, it should be checked for leaks and maintained until the inspection is qualified.

9.3 Calibration

9.3.1 Zero check

After the instrument runs stably, introduce the zero-point gas into the analyzer to fully purge the sample chamber, and follow the instructions specified in the instrument manual.

Steps to perform a zero check.

9.3.2 Span Calibration

Introduce the standard gas of the target compound to be measured into the analyzer at the flow rate specified by the instrument for measurement. If the indication error meets the requirements in 7.1.2.1 If required, the analyzer is available; otherwise, it is necessary to perform span calibration according to the steps specified in the instrument manual.

9.4 Sample determination

9.4.1 Place the front end of the sampling pipe in the exhaust cylinder and as close to the center as possible, and seal the gap around the sampling hole tightly to make it airtight.

9.4.2 Start the air pump, take samples at the sampling flow specified by the instrument, and save the measurement data in minutes after the instrument indication is stable.

The measurement was continued for 5 min to 15 min, and the average value was taken as the value of one measurement.

9.4.3 After the measurement of the sample at the same point, clean the analysis system with zero point gas, so that the indication value of the instrument returns to the vicinity of the zero point and remains stable.

9.4.4 Before shutting down, clean the analysis system with zero-point gas, so that the instrument's indication value returns to the vicinity of zero-point and remains stable, and then shuts down the air pump first.

Then turn off the analyzer and the preprocessing device, and finally disconnect all parts of the analysis system to end the measurement.

10.1 Result calculation

The determination results of the target compounds are expressed as the mass concentration of the dry exhaust gas under the standard state (273 K, 101.325 kPa). in, the NOx concentration is calculated as NO2.The formula for calculating the mass concentration of each target compound is.

a) When the instrument indication is expressed in mole fraction (µmol/mol, CO2 is %), SO2, CO and CO2 are converted according to formula (1) is the mass concentration rho (mg/m3, CO2 is g/m) of the dry base exhaust gas in the standard state

22.4 1

= x x x

In the formula. rho--mass concentration of target compound, mg/m3 (CO2 is g/m

M -- the molar mass of the target compound, g/mol;

22.4 -- molar volume of gaseous molecules in standard state, L/mol;

x--molar fraction of target compound in wet-base exhaust gas, µmol/mol (CO2 is %);

sw --the volume fraction of moisture in the exhaust gas, %;

f--unit conversion factor, it is 1 when calculating the mass concentration of SO2 and CO, and 10 when calculating the mass concentration of CO2.

b) When the indicated value of the instrument is expressed in mole fraction (µmol/mol), NOx is converted into dry exhaust gas in standard state according to formula (2) the mass concentration rho of NOx (mg/m3).

NO NO NO

2.05

In the formula. rho

NOX

--NOx mass concentration, mg/m 3;

2.05 -- The conversion factor of the NOx mole fraction calculated as NO2 to the dry basis exhaust gas mass concentration under the standard state, g/L;

NOx --The mole fraction of NO in the wet base exhaust gas, µmol/mol;

2NOx --The mole fraction of NO2 in the wet base exhaust gas, µmol/mol;

sw --The volume fraction of moisture in the exhaust gas, %.

c) When the indication value of the instrument is in mass concentration (mg/m3, CO2 is g/m

3) When expressed, SO2, CO and CO2 are converted according to formula (3) Change to the mass concentration rho (mg/m3, CO2 is g/m) of the dry base exhaust gas in the standard state

In the formula. rho--mass concentration of target compound, mg/m3 (CO2 is g/m

rho'--mass concentration of target compound in wet base exhaust gas, mg/m3 (CO2 is g/m

sw --The volume fraction of moisture in the exhaust gas, %.

d) When the indicated value of the instrument is expressed in terms of mass concentration (mg/m3), NOx is converted into the dry base exhaust gas in the standard state according to formula (4).

Mass concentration rho NOx (mg/m3).

NO NO NO

1.53

In the formula. rho

NOX

--NOx mass concentration, mg/m 3;

1.53 --Conversion coefficient of mass concentration of NO and NO2;

NO --The mass concentration of NO in the wet base exhaust gas, mg/m 3;

2NO --The mass concentration of NO2 in the wet base exhaust gas, mg/m 3;

sw --The volume fraction of moisture in the exhaust gas, %.

10.2 Result representation

When the concentration of SO2, NO, NO2, and CO results in