Axetris AG

Axetris` laser gas detection module LGD F200 provides affordable H2O measurement - Case study

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Increased CEMS Reliability with Direct Measurement of H2O

Axetris' laser gas detection module LGD F200 provides an affordable solution for continuous H20 measurement.
Pollutant gases such as S02, NO, CO, HF, HCI and dust are products of combustion that are regulated by national environmental protection agencies.

Continuous Emission Monitoring Systems (CEMS) are used to permanently measure pollutants. All gases have to be corrected and reported at standard conditions defined as 0°C, atmospheric pressure 1013 mbar, and dry gas. In order to have the concentration values at standard conditions, pressure, temperature and moisture measurements are required. The presence of humidity in a gas stream takes up space that would otherwise be occupied by pollutant. Therefore, the pollutant concentration expressed on a dry gas basis is higher compared to the value expressed on a wet gas basis.

All emission measurements must be reported on dry gas basis. Axetris Laser Gas Detection modules are able to measure H20 and H20 combined with NH3 or HCI simultaneously, thus helping to reduce equipment costs and increase long-term measurement reliability.

When the H20 value is calculated instead of measured, the following types of oxygen analysers are necessary for the measurement:

  • 02 Wet - Measure with in-situ zirconium oxide analysers
  • 02 Dry - Measure with extractive paramagnetic analysers or electrochemical cells

Emissions of stack gases are usually expressed on a dry gas basis so that variation in the moisture of stack gas does not affect the assessment of the emissions.

To convert concentration values from wet gas to dry gas the following formula is used:

Dry gas concentration = Wet gas concentration x     100/(100-H2O%)

Compared to the computational method based on 02 wet and dry, the direct moisture measurement involves less complexity on equipment level leading to increased reliability over time.

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