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Predicting H2S Corrosion “Hotspot” in Large Sewer Collection System Frank Qiao and Michael Wang

Cost-effective Data Mining from SCADA system to Replace Flow Monitoring. Predicting H2S Corrosion “Hotspot” in Large Sewer Collection System Frank Qiao and Michael Wang March 27, 2018. Outline. Process of H2S Formation First Lesson Case Study Observation and Conclusion.

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Predicting H2S Corrosion “Hotspot” in Large Sewer Collection System Frank Qiao and Michael Wang

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  1. Cost-effective Data Mining from SCADA system to Replace Flow Monitoring Predicting H2S Corrosion “Hotspot” in Large Sewer Collection System Frank Qiao and Michael Wang March 27, 2018

  2. Outline • Process of H2S Formation • First Lesson • Case Study • Observation and Conclusion

  3. Process of H2S Formation Bio/Chemical Bio/Chemical Physical Liquid Pipe Crown Sulfuric Acid Sulfate Sulfide (l) Sulfide (g) Bacteria reduction Bacteria oxidation

  4. First Lesson • Constructed in 1986 to a build out capacity of 8 MGD • ~ 17,000 LF 30" Force Main • ~ 13,000 LF 24" Force Main

  5. Profile

  6. Permanent Dry Area in Transition Zone Most Risky

  7. 24 inch DIP

  8. Polybond Liner Failure

  9. Recent Study 14 mile FM

  10. Typical H2S Gas (ppm)

  11. Higher pH limits H2S-L Formation H2S-G (ppm)

  12. H2S-G to H2S-L Ratio Varies by Location Location Matters a lot More pumping More FM discharge More downstream More H2S formation

  13. H2S-G to H2S-L Ratio

  14. Physics plays a big role • Henry’s Law • Equilibrium needs lots of energy

  15. Henry’s Law Constant

  16. Carbon Can H2S In (ppm)

  17. 14 Mile Long Force Main

  18. FM TRANSITION GRAVITY AV2 AV3 AV8 AV9 AV10 AV11 AV4 AV7 AV5 AV6 AV12 AV14 AV16 AV17

  19. More Extreme Cases

  20. Conclusion • H2S formation is very high in transition zone • H2S-L to H2S-G plays an important role in H2S formation • Long detention time and more turbulence from pumping/hydraulic jump leads to higher H2S-G to H2S-L ratio • Bi-oxide may not be a good treatment strategy • pH adjustment and H2S treatment strategy (H2O2/Fe) may be more effective

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