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News :: 08/23/2018

Increased CEMS reliability with direct measurement of H2O


Axetris, Laser Gas Detection

Pollutant gases such as SO2, NO, CO, HF, HCl and dust are products of combustion that are regulated by national environmental protection agencies. Axetris’ laser gas detection module LGD F200 provides an affordable solution for continuous H2O measurement.

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 H2O as well as H2O combined with NH3 or HCl simultaneously,
thus helping to reduce equipment costs and increase long-term measurement reliability.


When the H2O value is calculated instead of measured, the following types of oxygen
analysers are necessary for the measurement:

  • O2 Wet – Measure with in-situ zirconium oxide analysers
  • O2 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 ×        100        


Compared to the computational method based on O2 wet and dry, the direct moisture
measurement involves less complexity on equipment level leading to increased reliability
over time.


Axetris AG is a designer and OEM manufacturer of Laser Gas Detection (LGD) solutions
based on Tunable Diode Laser Spectroscopy (TDLS). The TDLS technology provides
a valid, cost effective solution to many challenges in environmental gas monitoring and
process control applications involving the measurement of gases such as NH3, HCl, H2O,
CH4, CO2.


The TDLS technology offers many advantages, including:

  • Precise optical, contactless measurements
  • Excellent target gas selectivity
  • Sub ppm-level detectivity
  • Low cost of ownership
  • High stability and reliability in the field


The modules are designed for integration by Original Equipment Manufacturers (OEMs),
operating in the field of gas detection and monitoring in diverse industries.
The LGD F200 series is based on a nearinfrared absorption measurement of the target gas.
The systems are selfcontained, ready-to-use OEM modules, using a flow-through cell
set-up for extractive measurements. The LGD F200 hot version comes with a cell
heated up to 220°C for hot gas measurements in process control and environmental
compliance related applications. The LGD F200 module comes with proprietary digital
signal processing, providing reliable measurements data through an analog and
digital data interface.


Key features of the Axetris LGD F200:

  • Made for easy integration by OEMs
  • Fast response
  • Self-contained
  • Continuous sensor status monitoring
  • Low maintenance
  • 10-30V DC power supply
  • Digital and analog data interfaces
  • Hot-gas measurement up to 220°C


Axetris supports their OEM customers with in-depth technology and application expertise
from feasibilities until product launch. The Axetris team collaborates with their customers
in finding the right product design which best suits their needs in terms of performance and costs.
As an OEM partner, Axetris assists with setting-up the infrastructure and with technical training.


Download the whole success story about increased CEMS reliability.


Environment Protection Agency Office of Environmental Enforcement (OEE),
Air Emissions Monitoring Guidance Note #2 (AG2)

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