1. 1 Tom Jenkins JenTech Inc. 6789 N. Elm Tree Road Milwaukee, WI 53217 414-352-5713 tom.jenkins.pe@gmail.com Energy Saving Measures - 2

2. 2 Blower Types and Characteristics Energy Impact of Blower Controls Evaluating the Savings of DO Control Influence of Advanced Control Strategies Understanding Blower Systems, Dissolved Oxygen, and Aeration Process Controls and How they Affect Energy Costs

3. 3 Aeration Energy Concerns Aeration is the Largest Energy Use for most WWTPs

4. 4 Aeration Process Concerns Aeration Supplies O 2 to Bacteria Bacteria Metabolizes Wastes Several Technologies Used Mechanical Surface Aerators Mechanical Brush Aerators Diffused Aeration Diffused Aeration is Most Common Diffused Aeration is Most Efficient If Plant Has Mechanical Aeration Consider Replacement with Diffused Aeration

5. 5 Aeration System Efficiency Controlled Primarily by System Design Aerator Efficiency –SOTE for Diffused Aeration, % –SOTR for Mechanical Aeration, lb O 2 /hp-hr Data: Doctor M. Stenstrom, UCLA

6. 6 It’s all about the bubbles! Diffusers release air at the bottom of the aeration tank to create the bubbles!

7. 7 Blowers Supply Air to the Diffusers Positive Displacement (PD) Blowers Multi-Stage Centrifugal Blowers Single Stage Centrifugal Blowers Turbo Blowers Blower Types and Characteristics

8. 8 Blower Power is a Function of Flow Rate and Pressure Pressure Difference from Inlet to Discharge Determines Power Minimize Inlet Filter Losses and Discharge Pressure to Minimize Power for Given Flow Rate Blower Types and Characteristics

9. 9 The Aeration and Piping System Determines Bower Discharge Pressure Required

10. 10 Positive Displacement (PD) Blowers Constant Flow at Constant Speed Pressure Varies with System Requirements Use VFDs (Variable Frequency Drives) to Modulate Air Flow Turndown is Limited by Blower and Motor Temperature Courtesy Dresser Roots

11. 11 Positive Displacement (PD) Blowers

12. 12 Multistage Centrifugal Blowers Multistage Centrifugal Variable Flow at Defined Pressures and Inlet Conditions Usually Controlled by Inlet Throttling to Modulate Flow Using VFDs to Modulate Air Flow Will Improve Efficiency and Turndown (with appropriate curves) Courtesy Continental Blowers LLC

13. 13 Multistage Centrifugal Blowers

14. 14 Single Stage Centrifugal Blowers Variable Flow, Variable Pressure, High Efficiency Inlet Guide Vanes and/or Variable Discharge Diffusers to Modulate Flow and Improve Turndown - Dual Vane Control Optimizes Efficiency Can Use Variable Speed (Typically Medium Voltage) Courtesy Dresser Roots

15. 15 Single Stage Centrifugal Blowers Inlet Guide Vane (IGV) Control

16. 16 Single Stage Centrifugal Blowers Variable Diffuser Vane (VDV) Control

17. 17 Mechanical Equipment Efficiency

18. 18 Turbo Blowers Variable Flow at Defined Pressures – Characteristic Curve Similar to Multistage Controlled by Built-In Special VFDs to Modulate Flow New Technology - Designed for High Efficiency Courtesy HSI, Inc.

19. 19 Turbo Blower Variations Bearing Types –Magnetic –Air Bearings Combined Control: Variable Speed with Variable Diffuser Vanes Most Manufacturers Limited to 300 hp (for now)

20. 20 Turbo Blowers Courtesy HSI, Inc.

21. 21 Blower Flow Control Select Blowers for Efficiency Across Operating Range Evaluate at Realistic Operating Conditions Look at Control Options Look at New Speed for PDs (VFD or Sheaves) Look at New Impellers for Centrifugals Select Blowers for Turndown 2:1 turndown available for most blowers Provide At Least 5:1 Turndown Compared to Design Flow Use 4 blowers @ 33% of Design Flow OR 2 blowers @ 25% plus 2 @ 50% of Design Flow

22. 22 Controlling Flow to Match Demand Reduces Power Flow Control Technique Influences Efficiency Throttling is LEAST Efficient (NEVER with PD) Guide Vanes Next in Efficiency Inlet Guide Vanes (IGV) Variable Diffuser Vane (VDV) Dual Vanes Variable Speed MOST Efficient Variable Frequency Drive - VFD Also Referred to as Inverter Also Referred to Adjustable Speed Drive (ASD) Most Blowers Can Provide 40% to 60% Turndown Blower Flow Control

23. 23 Centrifugal Blowers: VFD Will Typically Save 15% to 20% vs. Throttling VFD Will Typically Save 5% to 10% vs. Guide Vanes Blowers with Flat Curves not Suitable for VFD Control 1.5 psi rise to surge Steadily Increasing Pressure vs. Flow PD Blowers: Flow and Savings Proportional to Speed Minimum Speed Usually 50% of Nominal Speed Blower Flow Control

24. 24 Converts 60 Hz AC Input to Output at Required Hz Typically 3-Phase 480 VAC 4160 VAC In Larger hp Output Voltage Cannot Exceed Input Voltage Rating Actually by Current, not hp Must Confirm Motor FLA (Full Load Amps) Variable Frequency Drives

25. 25 Load Type Variable Torque Centrifugal Pumps and Blowers Constant Torque PD Pumps and Blowers Bypass Contactors Use Only When Required Newer Drives More Reliable Motor dV/dt and Insulation Damage Limit Cable Length VFD to Motor (Typically Req’d Cable < 100 ft.) Depends on Manufacturer and Motor Power Reflective Wave Traps Motor Bearing Damage (Fluting) Uncommon Good Grounding and Close Coupling will Usually Prevent It Insulated Bearings and Shaft Grounding Brushes Available VFD Application Considerations

26. 26 VFD Application Considerations An Example of Motor Bearing Fluting – The VFD was too far from the motor

27. 27 VFDs Can Create Harmonics in Power Supply “Clean Power” is ONLY Referring to Line Side NO Impact on Motor IEEE-519 Intended to Protect Other Utility Customers PCC (Point of Common Coupling) is Utility/Plant Transformer Should Perform Harmonics Study to Verify Need Clean Power Techniques Line Reactors Active Filters 12 and 18-Pulse VFDs All Reduce Efficiency All Increase Equipment Cost VFD Harmonics (Beware of Snake Oil)

28. 28 VFD Power Factor Typically > 95% Motor and VFD Efficiency Vary with Load Must Look at System Efficiency VFD and Motor Efficiency

29. 29 Dissolved Oxygen (DO) Control is The Way to Determine the Process Air Demand the Blowers Must Satisfy DO Control Will Typically Save 25% to 40% Compared to Manual Blower Control Aeration & DO Control

30. 30 DO Control System Objectives: 1.Satisfy the Oxygen Demand of the Treatment Process 2.Achieve Process Requirements at the Lowest Possible Cost – i.e. Lowest Energy use Aeration & DO Control

31. 31 Aeration & DO Control Process Considerations ALWAYS Outweigh Energy Considerations DO (Dissolved Oxygen) concentration is an indirect indicator of proper air flow to the process “Normal” DO concentration means the process is not oxygen limited If you have very low or zero DO you cannot have adequate process performance in an aerobic system You can have high DO and not have adequate process performance

32. 32 Choose Correct DO Concentration –Use minimum DO that gives required process performance –Most operators set DO concentration too high Conventional Wisdom: 2.0 ppm for BOD removal – can be as low as 1.0 ppm Conventional Wisdom: 3.0 ppm for Nitrification – can be as low as 1.0 ppm If BNR use as low DO concentration as possible to avoid “oxygen poisoning” in recycle flow Aeration & DO Control

33. 33 In Most Municipal Facilities Diurnal Load Varies 2:1 Aeration & DO Control

34. 34 In Most Municipal Facilities Diurnal Load Varies 2:1 Hours/DayDuty Cycle Weighting Factor (% of Time) Flow Factor (% ADF) Totalization Factor (%Time x %ADF) 520.8%70.0%14.58% 312.5%90.0%11.25% 28.3%100.0%8.33% 833.3%107.5%35.83% 625.0%120.0%30.00% 24100.0%100.00% Aeration & DO Control

35. 35 With Manual Control Air Flow is Set to Handle Peak Load Power is Wasted by Excess Aeration During Most Of the Day Aeration & DO Control

36. 36 The Relationship of DO and Air Flow Is Complex and Non-Linear, Making DO Control Difficult OTE & DO Control Example: Response of DO to 20% Load Increase with System Set to Maintain 3.0 ppm DO

37. 37 Low DO can cause undesirable organisms to develop High DO can cause poor settling, undesirable organisms to develop Excess DO does not usually result in more biological activity Bugs don’t work twice as hard at 4.0 ppm DO than they do at 2.0 ppm DO High DO just wastes power Aeration & DO Control

38. 38 Aeration Energy Cost Excess DO means significantly more aeration power.

39. 39 Aeration Energy Savings Excess DO means significantly more aeration power.

40. 40 Additional System Control Considerations: In Many Cases Mixing Limits Dictate Minimum Air Flow, Not DO –Most Plants Operate at 1/3 of Design Capacity –For Fine Pore System Convention is 0.12 CFM/sq. ft. –0.08 CFM/sq. ft. Has Been Adequate in Field Testing –Consider Taking Some Basins Out of Service To Eliminate Mixing Constraints If Blowers Are at Minimum Flow –Consider Adding Smaller Blowers or Changing Impellers (Centrifugal) –Consider VFD or Sheave Change (Positive Displacement) Aeration & DO Control

41. 41 Additional System Control Considerations: Increased MCRT (Mean Cell Retention Time) results in Increased OTE (Process Permitting) Denitrification Can Recover 25% of O 2 Used for Nitrification Proper Diffuser Maintenance Is Necessary to Keep OTE Near Design Values Aeration & DO Control

42. 42 Aeration Process Control: A System Approach is Required Energy Efficiency Optimization Includes Equipment and Controls Aeration Basins Blowers

43. 43 Basin Air Flow Control Pressure Control Most-Open-Valve Control Additional Aeration Control Techniques

44. 44 Basin Flow Control DO Concentration is Controlled by Controlling Air Flow Total System Air Flow is Controlled by the Blowers Flow Control Valves at Each Aeration Basin are Used to Balance Air Between Basins –Air flow distribution not inherently uniform –Influent flow distribution not inherently uniform –RAS flow distribution not inherently uniform –All vary with diurnal and seasonal loading Flow Control Valves at Each Drop Leg are Used to Balance Air Within a Basin

45. 45 Basin Flow Control For Many Facilities Manual Control of Basin Air Flow Balancing is Adequate (Typically Blowers < 200 hp) DO Concentration will Typically Differ by 0.5 ppm to 1.5 ppm Between Basins Automatically Controlling Basin Air Flow Balance to Eliminate the Difference Will Typically Add 5% to the Savings –Example: 25% Savings will Increase to 30% Savings If the Additional Savings Will Pay for the Extra Valves and Flow Meters, then Automatic Flow Control for Each Basin is Justified

46. 46 Basin Flow Control In Very Large Facilities Automatic Control of Each Drop Leg MAY be Justified (Typically Blowers > 500 hp) Drop Leg Control Allows Tapered DO Setpoints –Typical 1.0 ppm @ Influent to 2.0 ppm @ Effluent End of Basin –If BNR Process Effluent DO Setpoint May Be Lower Savings Should be Estimated to Justify the Extra Hardware Expense

47. 47 Pressure Control Pressure Control is NOT Required for Blower Control Pressure Control is a Device Used to Minimize Interaction Between Parallel Basins Pressure Control is Used Indirectly for Matching Total Blower Air Flow to Basin Air Flow Demand Pressure Control is a Historical Artifact Necessitated by Independent PID Loop Control Algorithms

48. 48 Pressure Control In an Old House What Happens When Someone Flushes a Toilet When You’re Taking a Shower? Manipulating Parallel Air Flow Control Valves has the Same Effect!

49. 49 Pressure Control Typical DO Control System with Pressure Control

50. 50 Pressure Control The Blower Curve is the Blower Capability in Terms of Pressure as a Function of Air Flow

51. 51 Pressure Control The System Curve is the System Back Pressure as a Function of Air Flow

52. 52 Pressure Control When the Two Curves Are Combined the Intersection Defines the Actual Operating Point

53. 53 Pressure Control If Constant Pressure Is Maintained Changes in One Valve Won’t Affect Other Basin’s Air Flows If Pressure Setpoint is Too High Power Is Wasted

54. 54 Direct Flow Control Some Systems Eliminate Pressure Control and Use Direct Flow Control for Basins and Blowers

55. 55 Most-Open-Valve Control Most-Open-Valve (MOV) Control is NOT Necessary for DO Control or Blower Control MOV is a Technique for Minimizing System Pressure by Keeping at Least One Basin Valve at Max Position at All Times. MOV Control for Most Systems Works by Modifying the Pressure Setpoint

56. 56 Most-Open-Valve Control (Pressure Based System) If the valve that is at maximum position (the most open valve) is MORE than 75% open, the pressure setpoint will be periodically increased by 0.05 psig The pressure control loop forces the blower output air flow higher, which forces the basin flow control valves to move to a less open position to restore air flow to setpoint The back pressure increases and causes the pressure control loop to decrease blower air flow The logic goes through several iterations. At the new point of equilibrium the basin air flow is the same, but with valves less open (underlined values are typical)

57. 57 Summary: Aeration Control is Critical to WWTP Energy Blower Control is Dependent on Blower Type Control Technique Impacts Blower Power Aeration Basin Control Should Include DO Control Aeration Basin and Blower Control Must be Integrated to Obtain Optimum Efficiency Aeration Process Control: DO and Blowers

58. 58 Aeration Process Control: DO and Blowers Questions and Answers

59. 59 Useful Formulae Ignoring Relative Humidity: For all Blowers RH = relative humidity, decimal PVa = saturated vapor pressure of water at actual temperature, psi Ta = actual air temperature, °F pa = actual air pressure, psia pb = barometric pressure, psia Q= air flow SCFM eff motor = motor efficiency, decimal PF = motor Power Factor, decimal I = current, Amps V = Voltage

60. 60 For PD Blowers Curve Adjustments For Variable Speed Centrifugal Blowers Q = volumetric air flow rate, ICFM Disp = blower displacement, Cubic Feet per Revolution N = blower rotational speed, rpm Slip = slip corrected for actual operating conditions, rpm bhp = blower shaft power required, horsepower Fg = gas power constant from manufacturer (typically 0.00436) ΔPb = total pressure rise across blower, psi FP = friction power corrected for actual operating conditions, horsepower Q1, Q2= air flow at original and new operating speed, ICFM P1, P2=gauge pressure at original and new operating speed, psig p1, p2= power at original and new operating speed, horsepower N1, N2= original and new operating speed, rpm

61. 61 Useful Formulae ΔP = pressure drop through valve, psi Q = air flow rate, SCFM Cv = valve flow coefficient from manufacturer’s data SG = specific gravity of gas, dimensionless (air = 1.0) Tu = upstream temperature, °R Pu = upstream pressure, psia

62. 62 Aeration ECM Evaluation Procedure

63. 63 Aeration ECM Evaluation Procedure

64. 64 Aeration ECM Evaluation Procedure

65. 65 Aeration ECM Evaluation Procedure

66. 66 Aeration ECM Evaluation Procedure

67. 67 Aeration ECM Evaluation Procedure

68. 68 Aeration ECM Evaluation Procedure