Continuous Emissions Monitoring with Quantum Cascade Laser Technology

by , | Apr 5, 2023 | Analytical, Energy & Emissions

At the 4C Health, Safety & Environmental Conference, Emerson’s Keith Linsley presented, New Developments in CEMS Analysis using Quantum Cascade Laser Spectroscopy. Here’s the session abstract:

The application of Quantum Cascade Laser based analyzers to CEMS [Continuous Emissions Monitoring Systems] provides improved analyzer availability and reduced maintenance.  The stability of QCL and TDL semiconductor Lasers and the inherent nature of analyte spectral absorption is the foundation of this improved performance.  The added capability of operating at temperatures up to 190C and running Hot/Wet adds further simplicity and lower operational costs.  This talk will explain the technology and the benefits of QCL/TCL spectroscopy for CEMS.

The hybrid Quantum Cascade Laser/Tunable Diode Laser Analyzers is ideal in CEMS applications. Keith shared the advantages of this hybrid approach.

  • Laser modules provide specific wavelengths
  • Absorption Spectroscopy for simplicity
  • Multiple Lasers
  • Laser stability with 10 – 15 year life
  • High Temperature Operation
  • Little or no drift
  • No moving parts, no consumables
  • Fast update rate of 1 second

The QCL/TDL analyzer is used in many chemical and refinery applications:

  • CEMS – cold/dry or hot/wet
  • DeNOx – Ammonia slip/NOx
  • FCCU Regen – O2, CO, CO2, CH4
  • CO Boiler – CO, CO2, O2
  • Impurities in finished Hydrogen, Nitrogen, Ethylene
  • Reformer trace moisture
  • Dryer Vent Gas – ppm CO, CO2
  • O2 in Flare/ Fuel Gas
  • Acetylene converter
  • PSA
  • Natural Gas – trace H2O and CO2
  • Trace CO2 in syngas
  • Air Monitoring

Rosemount Quantum Cascade Laser / Tunable Laser Diode CEMS analyzersWith a sample present, the lasers chirp sequentially through the sample, and a Harriet cell of known path length light to a detector to give absorption data for the fluid component. TDL excites the electron, and the electron emits a photon, and the energy drops. The QCL extends this process to excite the electron multiple times to emit multiple photons, creating a much higher energy reference.

For CEMS applications, the hybrid QCL/TDL analyzer can be used for Cold/Dry and Hot/Wet applications. The majority of systems are required to report a cold/dry measurement. This is where hot flue gas is brought to the sample system chiller to condense and remove H2O from the sample. The measurement is reported on a dry basis.

For Hot/Wet applications, the flue gas is at 110 degC or higher to keep above dew point to remain in the vapor phase. This temperature will be higher if sulfur dioxide is present. Water measurements are performed to convert wet- to dry-basis values. This method eliminates problems and routine maintenance due to the chiller and NOx converters.

Keith summed up the advantages of this technology. It has excellent low-concentration resolution and operation at high temperatures. Reliability and analyzer availability are high and maintenance needs are low because the lasers are extremely stable and the absorption areas of analytes are fixed in the laws of physics. There are no moving parts and calibration is not needed under normal circumstances. Validation of measurements is typically performed monthly. Also, one analyzer replaces many with multiple QCL and TDL capabilities.

Visit the Quantum Cascade Laser Analyzers section on Emerson.com for more on the technology and how it can improve your emissions management.

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