Determination of sulfur dioxide in the exhaust gas from fixed sources of pollution HJ/T 56-2000
The content of sulfur dioxide in exhaust gas is one of the main pollutants that affect urban air quality. According to the technical specification for air pollutants from fixed sources of pollution (HJ/T 56-2000), the determination of sulfur dioxide content in the exhaust gas is commonly measured according to the iodide method.
1 Principle
The so2 in the measured source gas sample reacts with the iodide solution to produce a yellow sulfite liquid (with a maximum absorbance of 430nm) that can be measured by spectrophotometry. According to the Beer-Lambert law, the relationship between absorbance and so2 content is linear, and the so2 concentration in the sample gas can be calculated.
2 Experimental instructions
2.1 Apparatus and materials
(1) Spectrophotometer, with quadratic integrating sphere and wavelength range of 430±2nm.
(2) Distillation tower, condensation chamber and sample funnel with material flow greater than 10L/min.
(3) Water bath heater, reaction vessel and connecting pipes.
(4) Stable reagent: 1.0 mol/L potassium iodide solution.
2.2 Sampling preparation
The sample was diluted with nitrogen by a long tube, and then passed through a series of filters (1μm) placed in a sample funnel, connected the sample tube and the reaction vessel, and then measured directly.
2.3 Determination process
(1) Place 5ml of 1.0mol/L potassium iodide solution into a reaction vessel, add 500ml of nitrogen, and then keep it at 350°C in a water bath.
(2) After the reaction vessel and the sample funnel were connected, adjust the flow of the sample funnel to 10L/min, and the flow of nitrogen to 5L/min.
(3) Put the input light path of the spectrophotometer in the condensation chamber and measure each half minute, until the absorbance is stable, that is, the reading of the absorptivity is not changed more than 0.01, then calculate the value of so2 concentration.
3 Result calculation
According to the ratio of nitrogen and sample, the calculated concentration (C) of so2 in the sample can be obtained. The formula is:
C=A/K*F
Where:
A — the average absorbance value in the stable period of observation
K — the absorption coefficient at a wavelength of 430 nm
F — the flow rate of sample gas,L/min
4 Quality assurance
4.1 Inspection accuracy
The method is suitable for determination of so2 in the exhaust gas from various stationary sources with a concentration range from 0.06mg/m3 to 300mg/m3. The relative standard deviation is below 5%.
4.2 Quality assurance
The quality of all reagents used in the inspection should conform to the requirements of the current national standard. Regular sensitivity calibration and instrument inspection should be carried out to ensure the reliability of the results.
