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A Methodology To Design and/or Assess Baffles for Floatables Control

Thomas L. Newman II, P.E. HydroQual, Inc. A Methodology To Design and/or Assess Baffles for Floatables Control. Introduction. Interest in Baffles EPA CSO Control Policy / 9 Minimum Controls Municipalities seek cost-effective alternatives Advantages of Baffles

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A Methodology To Design and/or Assess Baffles for Floatables Control

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  1. Thomas L. Newman II, P.E. HydroQual, Inc. A MethodologyTo Design and/or AssessBaffles for Floatables Control

  2. Introduction • Interest in Baffles • EPA CSO Control Policy / 9 Minimum Controls • Municipalities seek cost-effective alternatives • Advantages of Baffles • Low Cost (capital and maintenance) • Simple Design • Easy to Retrofit • Usable with Other Technologies • Disadvantages of Baffles • Not much information available • Limited analytical tools to assess performance HydroQual, Inc.

  3. Objective Develop an Improved Method to Assess the Floatables-Removal Efficiency of Baffles HydroQual, Inc.

  4. Application of Baffles For Floatables Control • Typical Regulator (Without Baffle) • Dry Weather: • 100% capture of • Flow • Floatables Plan View Section View HydroQual, Inc.

  5. Application of Baffles For Floatables Control • Typical Regulator (Without Baffle) • Wet Weather: • CSO Discharge of • Flow • Floatables Plan View (continued) Section View HydroQual, Inc.

  6. Application of Baffles For Floatables Control (continued) Baffle • Typical Regulator With Baffle Installed • Wet Weather: • CSO Discharge of • Flow • Fewer Floatables Plan View Baffle Section View HydroQual, Inc.

  7. Application of Baffles For Floatables Control (continued) Baffle • Typical Regulator With Baffle Installed • Wet Weather: • CSO Discharge of • Flow • Fewer Floatables Plan View Baffle Section View HydroQual, Inc.

  8. Previous Analytical Approaches • Non-turbulent-Flow Case - Floatables: rise velocity, Vz - Minimum Vz for capture (from given release point): Vz,min = Zo Vx / Xo(Dalkir, 1996; Cigana, 1998, 1999) - Laminar streamlines - Neutrally buoyant items follow streamlines, Vx - Capture if trajectory intercepts baffle Baffle Zo Xo Channel HydroQual, Inc.

  9. Baffle Previous Analytical Approaches (continued) - Minimum Vz must also compensate for downward turb. component Vz,min = Zo Vx / Xo + C V* (C factor 0.4 - 1.6) (Dalkir, 1996; Cigana, 1998, 1999) - Minimum Vz (compensating for extra required rise, Zd) Vz,min = (Zo + Zd) Vx / Xo + C V* (C = 0.4 - 1.6) (Dalkir, 1996) • Turbulent-Flow Case • Mixing between streamlines • reduces effective Vz by the RMS velocity component of the vertical turbulence, V* = Vx (n g Rh1/3 )1/2 Drawdown Zone Zd Channel HydroQual, Inc.

  10. Previous Analytical Approaches (continued) • Determine Removal Efficiency from Rise Velocity • Use distribution curve • Laboratory tests on 2,000 items from 2 Montreal CSOs Example: Vz,min = 10 cm/s Efficiency = 20 % HydroQual, Inc.

  11. Shortcomings of Previous Approach (and the solutions!) • Requires multiple calculations: • for overall performance (each release point over the depth) • for each change in baffle position, flow rate, water level, etc. HydroQual, Inc.

  12. Shortcomings of Previous Approach (and the solutions!) (Continued) • Solution: • Spreadsheet Model • inputs standardized • automatic integration (gives overall efficiency) • easy for sensitivity runs • compare results using different approaches HydroQual, Inc.

  13. Shortcomings of Previous Approach (and the solutions!) (Continued) • Does Not Account for Effect of Flow Path: • only release point and baffle position • ignores downward velocity component of flow • predicts 100% capture if baffle extends below inlet invert level • overpredicts capture! Section View HydroQual, Inc.

  14. Shortcomings of Previous Approach (and the solutions!) (Continued) • Solution: • Assume A Simple Flow Path • accounts for effect of baffle position and regulator geometry on flowstream • Example... Section View HydroQual, Inc.

  15. Shortcomings of Previous Approach (and the solutions!) (Continued) • Example: • Item in top streamline must rise a small distance. • Item in bottom streamline must rise full distance (Zs+Zd) before traveling the distance S: • Therefore: • Vz,min = (Zs+Zd)Vs / S ( + C V* ) • where Vs is speed along streamline Zd S Zs Section View HydroQual, Inc.

  16. Shortcomings of Previous Approach (and the solutions!) (Continued) • Does Not Account for Underflow Capture: • some floatables captured in the underflow • model not applicable to “pre-baffle” condition • cannot determine Net Effectiveness of Baffle Installation Section View HydroQual, Inc.

  17. Shortcomings of Previous Approach (and the solutions!) (continued) • Solution: • Account for “Escape Velocity” • Example… • Underflow = 20% of Inflow, • Bottom 20% of streamlines to underflow • Floatables that can rise out of underflow streamlines “escape” but remaining are captured • Add underflow capture to baffle capture for overall capture. Section View HydroQual, Inc.

  18. Efficiency based on 2 Montreal CSOs, but these appear to differ from NYC composition fewer on high and low end of spectrum cause under- or over-estimate of performance NYC tests coming... Shortcomings of Previous Approach (and the solutions!) (continued) HydroQual, Inc.

  19. Comparison / Verification of Results • Previous Approaches Predict Higher Removal Efficiency Than New Model • New Model Still Predicts Relatively High Performance • Comparison to Lab Data is Favorable, but • Not “Apples to Apples” Percent Capture HydroQual, Inc.

  20. Conclusions • New, Improved Model to Assess the Floatables-Removal Efficiency of Baffles • Fully Compatible with Previous Approaches • Spreadsheet format • Considers flow path • Accounts for underflow capture • Enables assessment of “pre-baffle condition” and the net effectiveness of the installation • Awaiting experimental data to further verify model HydroQual, Inc.

  21. Tom Newman HydroQual, Inc. tnewman@hydroqual.com www.hydroqual.com (201) 529-5151 For More Information HydroQual, Inc.

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