Advances In Aeration Control MWEA Fall Process Seminar November 6, - - PDF document

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Advances In Aeration Control MWEA Fall Process Seminar November 6, 2013

11:15 AM 11:15 AM East Lansing, MI Thomas E. Jenkins President JenTech Inc.

Je JenTe nTech I h Inc. 1

6789 N. Elm Tree Road Milwaukee, WI 53217 414‐352‐5713 info@jentechinc.com

• Importance of Aeration Control
• Advances in Aerators

Diffused

Advances in Aeration Control

• Diffused
• Mechanical
• New Blower Technologies
• Turbo
• Screw Blowers
• Advances in VFDs

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• Advances in VFDs
• Improved Instrumentation & Control Strategies
• DO Control Techniques
• Feedforward Control

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• More Demanding Permit Requirements

Factors Driving Advances in Aeration Control

• More Complicated Processes
• Higher Energy Costs

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• Increased Global Technology Transfer
• Improved Instrumentation Hardware

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• 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

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• Most Municipal WWTPs Operate at 1/3 of Design

Capacity CONSIDER TAKING TANKS OUT OF SERVICE

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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 5

5

11% Aeration

Most Utilities Offer $ Incentives for Reducing Energy Use Rates vary with:

• Time of Day

Energy Consumpon ≠ Energy Cost

• On‐peak, Off‐Peak
• Day of Week
• Size of Costumer
• Demand (kW) and Consumption (kWh)

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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

2.0 2.5 gth

Power

4 0

SAE

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0.0 0.5 1.0 1.5 30 50 70 90 bhp/ft. rotor leng rpm 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!

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New Aeration Technologies:

• Mixing and Aeration

Combined

• Actually Re‐invention of

Older Technology

• Allows Separate Control
• f Oxygen Transfer and

Mixing Energy

ff

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• 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

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• 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

C Q 

 * 20

. 2

Diffused Aeration

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Nominal Power Multiplie

actual

C C Q  

 * 20 . 2

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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)

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• 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

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• Efficiency
• Across Actual Load Spectrum

Blower Considerations

• Control
• Constant Pressure or Flow Based
• Control and Protection Should Be Integrated
• Turndown

f h ff

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• Often More Important Than Efficiency
• Turndown Limits Must Be Included In Control

Strategy

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Example Turbo Blower Characteristics

System Curve

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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 Speed

55 °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

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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

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• 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 umulative Energy

Cumulative Operating Cost

Exisitng Guide Vane Control New 2000 hp motor, 2000 hp VFD

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19 $- $2,000,000 $4,000,000 5 10 15 20 Capital + Cu Years of Operation

DO Control Can Be Very Cost Effective

• Will Save 25% Or More Compared to Manual
• Matches Air Supply To Demand

ll 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

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• a
• e
• 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

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• 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, psig

9.0 8.0 10.0

Pressure Setpoint

• If Pressure Setpoint is Too High Power Is Wasted

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5.0

Flow, SCFM Pressu

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%

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• 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

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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

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• 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

 

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         ngs AnnualSavi

• st

EquipmentC years Payback,

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Over Life of Equipment: Energy Cost is more Significant than Equipment, Installation, or Maintenance Costs Aeration and Energy

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Questions?

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