What is CVAF and why to choose it for mercury monitoring

CVAF is an extremely sensitive technology for mercury measurement with zero SO₂ interference. But what does CVFAF mean and what makes it a superior and unparalleled technology for mercury monitoring systems? This article answers these and many other questions about CVAF, our mercury monitoring technology. Read on to learn more.

1. What does the abbreviation CVAF mean?

CVAF stands for Cold Vapor Atomic Fluorescence. It is an extremely sensitive and selective measurement principle for the measurement of trace mercury levels.

2. How does CVAF in Mercury Monitoring work?

CVAF measurement principle is explained below via the main parts of the mercury analyzer.

1. Mercury vapor lamp: Lamp acts as a UV light source. Lamp emits UV light at a wavelength specific for mercury. The light is directed to the sample cell.
2. Sample cell: Mercury atoms in sample gas are excited by UV light. The excited atoms then start to re-radiate the absorbed energy (fluorescence).
3. Photon-counting detector: Fluorescence light is detected by a photon-counting detector, mounted at 90° to the UV lamp.

 

 

The UV detector does not see the light from the lamp, because of the 90° measurement geometry and light traps for stray light. The only signal picked up by the detector is the fluorescent light coming from the mercury atoms in the sample gas.

Thanks to the CVAF principal’s high sensitivity and Gasmet’s special design, sample pre-concentration is not needed. Gasmet’s optimized integrated thermal converter converts all gaseous mercury compounds to elemental mercury, in order to measure total gaseous mercury. This way, no mercury derivatives are left undetected.

3. How are cross-interferences handled?

The cross-interference effects are eliminated by the use of the Atomic Fluorescence measurement principle, (see question 2).

The CMM withstands for example high concentrations of SO₂ (see question 4).

4. Is there any interference from SO₂?

Other UV absorbing gases such as SO₂ does not interfere with CVAF measurement technique as the light source is selective to mercury, which means that only the fluorescent light from the mercury atoms in the sample gas are detected.

The CMM system has been used in mercury monitoring in a sulphuric acid production process with 5–10 vol-% SO₂ present, and even in this extreme gas matrix, the SO₂ interference does not affect the results.

5. CVAF or CVAA?

In comparison with the CVAA (Cold Vapor Atomic Absorption) measurement technique, the atomic fluorescence used in our systems offers superior sensitivity and reduced cross-interference effects, thanks to the very specific nature of the fluorescence effect.

This is a particular advantage in applications where the concentration of mercury is low and the concentration of other UV absorbing gases such as SO₂ is high. CVAF is therefore the best technology for example for coal-fired power plants and cement kilns.

When compared with other atomic fluorescence analyzers, Gasmet’s solutions are the most compact and cost-effective mercury monitoring solutions with minimized number of moving parts ensuring several accuracy and reliability advantages:

• Sample probe has a unique two-stage blowback mechanism for removing dust from filter surfaces in dusty conditions. This ensures that the filter stays clean.
• Clean filters prevent analyte loss in the probe and minimize memory effects
• CVAF offers superior sensitivity & selectivity
• No recombination of mercury compounds after the converter
• The system is very independent and works well on its own without continuous monitoring or surveillance

Careful design and the preciseness of the structure enables secure to use and low maintenance costs
The unique design enables representative sampling and reliable results, as all the special qualities of mercury have been taken into consideration holistically.

6. What are the key advantages of CVAF?

• The most accurate, sensitive and selective technique on the market:
  The Cold Vapor Atomic Fluorescence technique is an extremely selective technique with a high sensitivity, which ensures accurate measurement of extremely low mercury levels.
• Future-proof technique → the world’s lowest EN 15267 certified range:
  Gasmet CMM system has successfully completed the EN 15267-3 testing with the world’s lowest EN 15267 certified range (0 to 5 µg/m³) for continuous mercury measurement. This new world record makes our CMM future-proof for declining emission limits.

 

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Mercury Emission Monitoring – CMM & CMM AutoQAL Continuous Mercury Monitoring systems CMM AutoQAL and CMM are the perfect solutions for monitoring mercury continuously from hot, wet and corrosive gas streams. These future-proof systems have the lowest certified range in the world (0-5 µg/m3) and CMM AutoQAL has an automatic and integrated QAL3 validation tool.