EXO Dust Monitor for Wet Gases

EXO = EXtractive Optical PM monitor for CEMS

Extractive, isokinetic and temperature controlled continuous particulate measurement for wet processes.

EXO system is designed to continuously measure the concentration of dust particles inside industrial stacks. It is an ideal solution for emission monitoring in wet conditions, for example after wet scrubbers or in condensing environments.

EXO dust monitor consists of a heated sampling probe, optical XO sensor module, and an integrated panel PC, which are housed in a weather-proof powder-coated steel enclosure that is mounted on a frame. In a complete installation, the probe is inserted inside a stack perpendicular to the airflow using a flange. An external sample air blower supplies air to an ejector chamber at the end of the sampling line, creating a vacuum effect that draws flue gas through the internal piping of the device and ejects it back into the stack.

During operation, the probe continuously extracts a gas sample, which is heated to vaporize any moisture. The remaining particles are directed through the measurement chamber of the optical XO sensor module. Light from an LED is directed through the particle stream, which causes the light to scatter. A scattered light detector captures the scattered light and determines the particle concentration in the gas sample from the amount of scattered light. The underlying method is called “optical forward scattering”.

The device must be calibrated to the process conditions after installation using a standard reference method.

The user interface displays the measurement results as mg/m3 or 4-20 mA values.


  • Isokinetic sampling in variable flow conditions
  • Continuous Dust levels as low as 0,1 mg/m³
  • Sample stream isolated with air curtain to keep the optics clean -> long maintenance interval
  • Accurate linear measurement for all kinds of dust
  • Color touch screen for easy parametrization
  • LED light source covers different particle size distributions and is less affected by particulate characteristic

Exo usage and applications

EXO is used in wet processes where the dust particles are bound into water droplets or other liquids. Dust particles are bound into droplets in steam saturated (flue) gases where the temperature is below the dew point.

EXO is often used after Wet scrubbers, such as:

  • Spray Towers
  • Tray towers
  • Packed bed & ionized packed bed
  • Fiber Bed scrubber
  • Venturi scrubber

EXO Wet Gas Dust Monitor can be used in various applications such as:

  • Waste incinerators
  • Chemical Waste Incinerators
  • WtE (Waste to Energy) Power plants
  • Biomass incinerators
  • Petroleum Refineries
  • Desulphurization at coal-fired powerplants
  • Chemical Processing Facilities
  • Acid Manufacturing Plants
  • Metal processes such as foundries and die-cast facilities
  • Producers of Wet scrubbers
  • Producers of biomass boilers

References/ Installation after wet scrubber

  • Waste Incineration plant for contaminated soil
  • Biotechnology plant
  • Producer of battery chemicals
  • Special Waste incinerator for Chemicals

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