Technology for wet stack measurement of dust concentration

𝘗𝘳𝘰𝘚𝘤𝘢𝘵𝘵𝘦𝘳™ Extractive

Extractive ProScatter™ technology provides a unique solution to the growing number of challenging applications for wet stack measurement of dust concentration.

By efficiently evaporating any water droplets or vapour in a continuously taken sample of flue gas, reliable and accurate dust concentration measurement can be made in stacks after wet Flue Gas Desulphurisation (FGD) plant or Wet Scrubber systems. Dust concentration is measured by a patented laser scatter technique without interference from water.

The analyser takes a continuous sample from the stack under iso-kinetic conditions in a sampling head which is close coupled to the analyser. On passing into the analyser, water droplets or steam below dew point are evaporated in a cylindrical heated vapourising system to create dry flue gas above dew point. The heated flue gas then passes into a measurement cell, where the particulate concentration is measured using a ProScatter™ laser scatter system. The sampling system is powered by an inbuilt venturi pump meaning there are no moving parts or fans to block or contaminate. Flue gas is returned to the stack by the same sampling port as the sample is taken.

Core Features of the Technology are:

  • The compact and unique cyclonic vaporising system permits a larger more representative flue gas sample to be heated compared to systems using line heating or heated dilution air.
  • The dust measurement sensor is a ProScatter™ laser scatter device with the advantages of cone scatter measurement giving:
    • high signal to noise and stable measurement at particulate concentration levels as low as 0.1mg/m3.
    • an automatic span/contamination check mechanism to challenge the instrument without introducing an exposed moving detector mechanism.
  • The sample pump can be adjusted to different flow rates, allowing iso-kinetic and representative sampling of the stack gas.
  • The system has in-built automatic monitoring of all active components to confirm reliable and correct operation of the complete system (including both sampling system and analyser).
  • Compared to other extractive light scatter probe systems, the extractive ProScatter™ instrument:
    • Has provisions for automatic adjustment to Isokinetic conditions, meaning more accurate and representative measurements
    • Automatic control and function test of all critical components (see QA features)
    • Modular design to facilitate lifting to stack location and ease of assembly
    • Use of ProScatter™ QAL1 approved light scatter probe, providing unique advantages for monitoring according to PS-11 and EN-14181
  • Compared to BETA Attenuation extractive the ProScatter™ technique does not require any radioactivity licensing, provides visibility to short term process variations (BETA is a 15 minute batch measurement) and has far fewer moving parts with inherent reliability and maintenance advantages.
Extractive ProScatter™ technology has automatic zero and span checks on both the measurement instrument and the sample and handling system to ensure good quality measurements and to permit early diagnosis of any deterioration in system performance.

Instrument automatic self-checks involve reference scattering bodies which are periodically automatically rotated into the measurement path hence providing a full check of the instrument’s capability to measure scattered light. Flow rates and heater temperatures are continually monitored in the extractive flow line, to ensure any sample line blockage or problems with insufficient heating are automatically detected and avoided. The system automatically indicates when valid measurements are occurring, hence avoiding any measurement errors during any system warm up. In addition, trace heaters may be added to the intake air to ensure there is no risk of condensation in the pipes.