Post on 09-Dec-2018
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Advances In Aeration ControlMWEA Fall Process Seminar
November 6, 201311:15 AM11:15 AM
East Lansing, MI
Thomas E. Jenkins
President JenTech Inc.
JenTech Inc.
1
6789 N. Elm Tree Road
Milwaukee, WI 53217
414‐352‐5713
info@jentechinc.com
• Importance of Aeration Control
• Advances in AeratorsDiffused
Advances in Aeration Control
• Diffused
• Mechanical
• New Blower Technologies• Turbo
• Screw Blowers
• Advances in VFDs
2
• Advances in VFDs
• Improved Instrumentation & Control Strategies• DO Control Techniques
• Feedforward Control
2
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• More Demanding Permit Requirements
Factors Driving Advances in Aeration Control
• More Complicated Processes
• Higher Energy Costs
3
• Increased Global Technology Transfer
• Improved Instrumentation Hardware
3
• Process Performance Comes First!
Improved Control Means More Stable Processes
• Adapting Automatically to Upsets and Changes Can Improve Performance
• Control Strategies Must Integrate Process Equipment Characteristics
4
• Most Municipal WWTPs Operate at 1/3 of Design Capacity
CONSIDER TAKING TANKS OUT OF SERVICE4
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Aeration is the Most Significant Energy Use in a WWTP
Energy Is A significant Concern, and Can Be Used To Justify Systems
WWTP
34%
55%Pumping and Other
HVAC
55
11% Aeration
Most Utilities Offer $ Incentives for Reducing Energy Use
Rates vary with:
• Time of Day
Energy Consump on ≠ Energy Cost
•On‐peak, Off‐Peak
•Day of Week
• Size of Costumer
•Demand (kW) and Consumption (kWh)
66
The First Goal of an ECM (Energy Conservation Measure) is to Reduce Cost While Maintaining or Improving Process Performance
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Variable Speed or On/Off Mechanical Aerators
Mechanical Aerators
2.02.5
gth
Power
4 0
SAE
7
0.00.51.01.5
30 50 70 90
bhp/ft. rotor leng
rpm
0
5
10
30 50 70 90
OTR
lb/hr/ft rotor
length
rpm
SOTR
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
30 40 50 60 70 80 90
SAE lb/hp hr
rpm
Coarse Bubble
Diffused Aeration
Changing to Fine Pore Diffusers Should Always Be Examined!
88
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New Aeration Technologies:
• Mixing and Aeration Combined
• Actually Re‐invention of Older Technology
• Allows Separate Controlof Oxygen Transfer and
Mixing Energy
ff
99
• New Diffuser Geometries and Materials
• Fouling Resistance
•Improved OTE
• Proportional to Submergence
• Deeper is Better
Diffused Aeration Energy
• Also Requires Higher Blower Power
• Proportional to Air Flow per Diffuser
• Flux Rate (1 to 10 SCFM/ft2 Typical)
• Lower is better
P ti l t A t l DO C t ti
1010
• Proportional to Actual DO Concentration
• Lower is Better
• DO Control is Significant
• Most Plants Are Too Conservative In DO Setpoint
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4.00
4.50
er
Blower Power Ratio (Compared to 2.0 ppm DO)
actual CQ *
20 0.2
Diffused Aeration
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50Nominal Power M
ultiplie
actualCCQ
*
200.2
1111
Excess DO means significantly more aeration power.
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00
Actual DO Concentration, ppm
Based on 500' ASL, 55 °F, 9.9 ppm Csat
• Lower Air Flow Rates• Reduce Valve Sizes
R S l R l Fl T itt
Impact on Control Systems
• Re‐Scale or Replace Flow Transmitters
• Mixing Limits
• Impact on Blowers• Turndown May Become an Issue
• Verify Pressure Capacity (More Submergence)
1212
•DO Control• Maximizes Savings Opportunity
• Over‐Aeration More Common
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Efficiency Varies with Blower Type
Range is 60% to 80%
Aeration Blowers and Energy
1313
• Efficiency
• Across Actual Load Spectrum
Blower Considerations
• Control
• Constant Pressure or Flow Based
• Control and Protection Should Be Integrated
• Turndown
f h ff
1414
• Often More Important Than Efficiency
• Turndown Limits Must Be Included In Control Strategy
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Example Turbo Blower Characteristics
System Curve
1515
Example Screw Blower Characteristics
65.0%
66.0%
67.0%
68.0%
25.0
30.0
35.0
40.0
fficiency
kW
Typical Screw Blower Performance at Constant Speed55 °F Ti 14.4 pi
60.0%
61.0%
62.0%
63.0%
64.0%
0.0
5.0
10.0
15.0
20.0
5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0
Adiabatic Ef
SCFM
/k
psig Discharge
SCFM/kW
Wire to Air Efficiency
1616
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• Blower Control Usually Included In Packages
• Screw Blowers
Blower Control Considerations
• Typically More Turndown
• Control Simpler
• Turbo Blowers
• Often More Efficient and Lower Cost (CHANGING)
d l d d l
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• Turndown Limits Must Be Included In Control Strategy – Surge Is a Concern
• VFDs Are More Reliable And Less Costly
VFD Applications Have Changed
• Many Utilities Offer “Automatic” VFD Incentives
• Can Be Applied to ALL Types of Blowers
• Proper Selection and Engineering is Required
1818
• Medium Voltage (> 600 Volts) Now Cost Effective
• Increased Competition, Lower Prices
• Typically Greater Than 750 hp
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Payback on Medium Voltage Drives Can Be Good
$6,000,000
$8,000,000
$10,000,000
$12,000,000
$14,000,000
um
ula
tive
En
erg
y
Cumulative Operating Cost Exisitng Guide Vane Control
New 2000 hp motor, 2000 hp VFD
1919
$-
$2,000,000
$4,000,000
0 5 10 15 20Cap
ital
+ C
u
Years of Operation
DO Control Can Be Very Cost Effective•Will Save 25% Or More Compared to Manual
• Matches Air Supply To Demandll S bili• Usually Improves Process Stability
• DO Is An Indirect Indicator of Process Performance
• Low Capital Cost May Make Payback Shorter Than Other Changes
• Control Complexity Should Be Matched to System• Total Blower Air Flow Only
2020
o a o e o O y• Individual Basin Flow Control• Separate Grid DO and Flow Control Within Basins
• New Strategies Improve Efficiency• Most‐Open‐Valve• Direct Flow Control Eliminates Pressure Control
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• MOST‐Open‐Valve (MOV) Control is NOT Necessary for DO Control or Blower Control
Most‐Open‐Valve Control
•Technique for Minimizing System Pressure by Keeping at Least One Basin Valve at Max Position at All Times
2121
• Older Systems Work By Adjusting Pressure Setpoint
• Newer Strategies Work Directly With Flow Control
Pressure Control
• If Constant Pressure Is Maintained Changes in One Valve Won’t Affect Other Basin’s Air Flows
Typical Centrifugal Blower & System Curves
re, p
sig
9.0
8.0
10.0
Pressure Setpoint
• If Pressure Setpoint is Too High Power Is Wasted
2222
5.0
Flow, SCFM
Pre
ss
u
0 500 1000 1500 2000 2500 3000 3500 4000 4500
7.0
6.0
Pressure Setpoint
Wasted Power
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Direct Flow Control• Is Simpler and More Stable
• Typically Reduces Blower Power 5% to 10%
2323
• Optical DO Probes Replacing Membrane Types
• Multi‐Channel and Remote Transmitters
New Analytic Instruments for Control
• New Nutrient Analysis Instruments
• Chiefly for Nutrients – Nitrification/Denitrification
• Many Still Maintenance Intensive
• Most Ammonia Control Strategies Used In Conjunction with DO Control
2424
Conjunction with DO Control
• New Feedforward Controls Based on Measuring Process Demand
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Offgas Based Feed Forward Control• Determines Air Demand By Measuring OUR and OTE
• More Stable and Precise
2525
• Process Requirements Come First!
Use Simple Payback To Calculate Cost Effectiveness
• Use Present Worth for Longer Time Periods
• Implementation for Energy Conservation Should Be Justified By Best Payback
2626
ngsAnnualSavi
ostEquipmentCyearsPayback,