Post on 26-Mar-2015
transcript
A MethodologyA MethodologyTo Design and/or AssessTo Design and/or Assess
Baffles for Floatables Control Baffles for Floatables Control
Thomas L. Newman II, P.E.
HydroQual, Inc.HydroQual, Inc.
HydroQual, Inc.
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.
Objective
Develop an Improved Method
to Assess the
Floatables-Removal Efficiency
of Baffles
HydroQual, Inc.
Application of Baffles
For Floatables
Control
Typical Regulator (Without Baffle)
Dry Weather: 100% capture of
– Flow– Floatables
Section View
Plan View
HydroQual, Inc.
Application of Baffles
For Floatables
Control
Typical Regulator (Without Baffle)
Wet Weather: CSO Discharge of
– Flow– Floatables
Section View
Plan View
(continued)
HydroQual, Inc.
Application of Baffles
For Floatables
Control
(continued)
Typical Regulator With Baffle Installed
Wet Weather: CSO Discharge of
– Flow– Fewer Floatables
Section View
Plan View
Baffle
Baffle
HydroQual, Inc.
Application of Baffles
For Floatables
Control (continued)
Typical Regulator With Baffle Installed
Wet Weather: CSO Discharge of
– Flow– Fewer Floatables
Section View
Plan View
Baffle
Baffle
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- Laminar streamlines
- Neutrally buoyant items follow streamlines, Vx
Previous Analytical Approaches Non-turbulent-Flow Case
Channel
Baffle
- Floatables: rise velocity, Vz
Xo
- Capture if trajectory intercepts baffle
Zo
- Minimum Vz for capture (from given release point):
Vz,min = Zo Vx / Xo (Dalkir, 1996; Cigana, 1998, 1999)
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Turbulent-Flow Case– Mixing between streamlines
– reduces effective Vz by the RMS velocity component of the vertical turbulence, V* = Vx (n g Rh
1/3 )1/2
Previous Analytical Approaches
Channel
Baffle
Drawdown Zone
- 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)
(continued)
Zd
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Previous Analytical Approaches
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 %
(continued)
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Shortcomings of Previous Approach (and the solutions!)
1 Requires multiple calculations: – for overall performance
(each release point over the depth)
– for each change in baffle position, flow rate, water level, etc.
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Shortcomings of Previous Approach (and the solutions!)
Solution: Spreadsheet Model
inputs standardizedautomatic integration
(gives overall efficiency)easy for sensitivity runscompare results using
different approaches
(Continued)
HydroQual, Inc.
Shortcomings of Previous Approach (and the solutions!)
2 Does Not Account for Effect of Flow Path: – only release point and
baffle position – ignores downward velocity
component of flowpredicts 100% capture
if baffle extends below inlet invert level
overpredicts capture!
(Continued)
Section View
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Shortcomings of Previous Approach (and the solutions!)
Solution: Assume A Simple Flow Path
accounts for effect of baffle position and regulator geometry on flowstream
Example...
(Continued)
Section View
HydroQual, Inc.
Shortcomings of Previous Approach (and the solutions!)
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
(Continued)
SZs
Section View
Zd
HydroQual, Inc.
Shortcomings of Previous Approach (and the solutions!)
3 Does Not Account for Underflow Capture: – some floatables captured in
the underflow – model not applicable to
“pre-baffle” conditioncannot determine
Net Effectiveness of Baffle Installation
(Continued)
Section View
HydroQual, Inc.
Shortcomings of Previous Approach (and the solutions!)
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.
(continued)
Section View
HydroQual, Inc.
Shortcomings of Previous Approach (and the solutions!)
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...
Quiescent Rise-Velocity DistributionFor CSO Floatables
0
20
40
60
80
100
0.1 1 10 100
Rise Velocity (cm/s)
Pe
rce
nt
Gre
ate
r T
ha
n
Sp
ec
ifie
d V
elo
cit
y
CEGEO /Meunier
Alden Labs(estimated)
(continued)
HydroQual, Inc.
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”
0
20
40
60
80
100
No BaffleTest 1
Baffle Test 1
. No BaffleTest 5
BaffleTest 5
Dalkir+
Cigana+
New
Data(Alden)P
erc
en
t C
ap
ture
HydroQual, Inc.
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.
For More Information
Tom Newman
HydroQual, Inc.
tnewman@hydroqual.com
www.hydroqual.com
(201) 529-5151