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Air Quality Conference Agenda
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Abstract Title: Combination of OFCEAS Spectroscopy and Low Pressure sampling, an advantage for low concentration measurements for CEMS
Abstract Type: Oral
Session Choice: Emission Monitoring
Presenter Name: Mr etienne smith
Company/Organisation: AP2E
Country: France

Abstract Information :

OFCEAS or Optical Feedback Cavity Enhanced Absorption Spectroscopy, is a gas analysis technology developed by the University Joseph Fourier. OFCEAS essentially differs from the older technology enhanced-cavity TDLAS by its feedback principle: a part of the emitted radiation is returned from the chamber to the laser, enabling the tuning of the laser and the cavity, creating a resonance phenomenon. The measuring cavity in which the sample is analyzed is equipped with high reflectivity mirrors gt;99,99, providing an optical path up to 20 km. The consequence of this phenomenon is the identification of intense absorption peaks with narrow spectral width. The system presents very high measurement stability: there is no zero and no span drift and no need for new calibrations. rnrnLPS or Low Pressure Sampling, is a patented sampling technique. The pressure is maintained under 100mbar absolute from the sampling point to the exhaust of the analyzer. Given that the transfer time is reduced, the dew point is decreased below ambient temperature, the interferences between absorption picks is minimized.rnrnThe combination of OFCEAS and LPS was implemented in gas analyzers. At the beginning the goal was to use it for research purposes by the University Joseph Fourier, to measure very low concentration of gases in ambient air. But quickly the technology attracted the interest of the industry, and the technology is now used word wild in CEMs and process applications. rnrnFor Continuous Emission Monitoring, OFCEAS and LPS provide many advantages.rnrnOFCEAS allows very low levels of detection, and measurement range can be from parts per billion to percentage. It can measure standard gas species NOx, SO2, CO, CO2, H2O, but also gases with growing interest in emission HCHO, H2S, HCl, CH4, NH3 even at low concentration. The technology is also self-referenced, and not deviating system, so there is no need of regular calibration. A direct measurement of all gas species is made every 100msec, without calculation treatment.rnrnLPS below 100mbar absolute, reduces the dew point in the sampling which is a critical point for wet gases like in CEMs conditions. For CEMs, lines dont need to have a regular heating at 180C, LPS will allow usage of lines traced at 40C to 80C, and will avoid problems of cold spots in winter. The low pressure also has an impact on the absorption spectrums. The lower the pressure is the thinner are the absorption picks, which allows discrimination of gas species in a same spectrum. The cross-interferences becomes very limited, and trace measurement becomes possible even with high concentration of CO, CO2, hydrocarbons, and H2O. Finally, the low pressure uses limited amount of sampled gas, around 20Lh for CEMs. A low flow of emission gas sampled also means a low amount of particles sampled. The accumulation of dust in the filters of the analyzer is reduced by ten, and the cost of spare parts is therefor reduced.rn

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