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The Analysis of VOC Emissions by Mass Spectrometry for Activated Carbon Bed Control

The Analysis of VOC Emissions by Mass Spectrometry for Activated Carbon Bed Control. Robert G. Wright Thermo ONIX, Winsford, Cheshire, UK. Introduction. Outline of talk:- activated carbon plant multiple bed switching VOC analysis by process MS analysis set-up calibration verification

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The Analysis of VOC Emissions by Mass Spectrometry for Activated Carbon Bed Control

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  1. The Analysis of VOC Emissions by Mass Spectrometry for Activated Carbon Bed Control Robert G. Wright Thermo ONIX, Winsford, Cheshire, UK

  2. Introduction • Outline of talk:- • activated carbon plant • multiple bed switching • VOC analysis by process MS • analysis set-up • calibration • verification • example data • benefits of process MS • controlled bed switching (lower costs) • improved accuracy

  3. Activated Carbon Adsorption Plant

  4. Previous Mode of Operation - Switching Adsorption Beds at Maximum Rate

  5. Previous Operation • switching adsorption beds at maximum rate - wasteful • on-line - FID analyzer - limitations:- • multiple components (13 VOC’s) • different responses for cpds with halogens and oxygen • therefore accuracy poor • off-line laboratory analysis by GC-MS • slow

  6. Why Process MS? • new method of operation was possible • real-time multi-component monitoring • improved sensitivity and accuracy • can predict when bed changeover is required • more efficient steam use • prevents over-limit emissions • emission sources can be traced • network visualization of data • ability to alert operations to limit solvent use • continuous and complete log of all emissions at this site

  7. Process MS • VG Prima (Thermo ONIX) • scanning magnetic sector • Faraday/SEM dual detector • features • speed • multi-stream • high precision • dynamic range • multi-component • cost effective • low maintenance

  8. Principle of Magnetic Sector Process MS • electron impact ionisation • 1000 eV ion acceleration • mass separation in variable magnetic field m/z = B2R2/2V • flat-topped peaks give excellent long term stability

  9. Masses used for Analysis of VOCs in Air

  10. Tail of O2 at mass 31

  11. Method of Calibration • calibration:- • air and 13 cylinders each with a different VOC component at a level of 100 ppm in a balance of nitrogen. • the relative response of the SEM compared with the Faraday detector is calibrated using the mass 34 peak in air (16O18O 800 ppm in air)

  12. Check of Calibration Gases - Cross Interferences

  13. Stability of System

  14. Conclusions about Stability • re-calibration every 2 weeks • Accuracy +/- 5% (at the 100 ppm level) • 1 hour reproducibility +/- 1% • longer term fluctuations, day-to-day, are due to the changes in the SEM gain.

  15. Communication between MS and Control System • relay indicates which Stream: inlet or outlet • 4-20 mA signals represent each VOC • relays also to indicate:- • concentration Alarms • MS status • Analysing/Calibrating/Standby • stream flow failure • MS hardware fault

  16. Process MS Applications Software • GasWorks software • PC used for • configuring Analysis • numeric display and logging • trend display • results via DDE • results via HTML

  17. Example Inlet Data

  18. Example Outlet Data

  19. Inlet MeCl, DCM and Chloroform

  20. Outlet DCM, MeCl and Chloroform

  21. Unnecessary Bed Switching

  22. 24 Hour Statistical Report

  23. Check on method: MS for VOC analysis • MS stable • analysis gave good agreement with GC/MS for average values

  24. Implementation of MS for Control • Adsorption bed is switched based on on-line MS analysis data • Daily cal check • if outside tolerance complete re-calibration performed • digital status from MS to control system suspends analysis based control

  25. Controlled Bed Switching Fixed Switching Controlled Switching

  26. Conclusions • new mode of operation • real-time multi-component monitoring • improved sensitivity and accuracy • bed changeover is controlled • lower energy costs (steam) • over-limit emissions are prevented • emission sources are being traced • network visualization of data • operations can be alerted to limit solvent use • continuous and complete log of all emissions at this site

  27. Results After implementation of Process MS on Activated Carbon Plant… • Reduced Costs • Improved Control of Emissions

  28. Thank You for Listening! Any Questions?

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