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You can't control me! Throttling blowers and with valves and VFDs

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You can't control me! Throttling blowers and with valves and VFDs

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Aeration is achieved by getting the right amount of oxygen into the water for the capacity of the water to handle it. How best to achieve that complicated, multi-variable outcome?

Aeration is achieved by getting the right amount of oxygen into the water for the capacity of the water to handle it. How best to achieve that complicated, multi-variable outcome?

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You can't control me! Throttling blowers and with valves and VFDs

  1. 1. You Can't Throttle Me! Brian Gongol DJ Gongol & Associates, Inc. January 26, 2022 LONM/NWOD Snowball Conference Kearney, Nebraska
  2. 2. Ben Franklin on aeration "Beware of little expenses; a small leak will sink a great ship."
  3. 3. Aeration uses 50% to 70% of WWTP energy  Can't really treat without it  Best bet is to conserve through efficiency  Move just enough air to achieve treatment
  4. 4. One size does not fit all
  5. 5. One size does not fit all Even at the same plant, inputs and outputs will vary over the course of a year
  6. 6. That's because density varies with temperature As temperature goes down, density goes up
  7. 7. Are you good at weather forecasting?
  8. 8. Are you good at weather forecasting? You don't actually have to read a "Skew-T" chart to get the main point
  9. 9. Warm fronts are squishy
  10. 10. Cold fronts have sharp edges
  11. 11. Warm fronts ride over the top Lower density causes them to float
  12. 12. Cold fronts wedge under from below Greater density causes them to sink
  13. 13. Blowers are selected on four dimensions
  14. 14. 1. Flow How much air is needed?
  15. 15. 2. Location Where is the air being obtained? Where is the blower itself being placed?
  16. 16. 3. Pressure How hard must the air be pushed?
  17. 17. 4. Temperature How hot or cold is the available air? How hot or cold is the receiving water?
  18. 18. Must size for the worst-case scenario Hot input air at low density going into warm water that doesn't hold DO very well
  19. 19. But pushing too much air is wasteful  If you're using 10% too much, then that's 5% to 7% of plant energy going to waste  Wasted energy means higher operating costs
  20. 20. Is your budget too big to spend? If so, please see me after this presentation
  21. 21. Cold weather  Air is denser  Water holds more dissolved oxygen  Less air needed
  22. 22. Warm weather  Air is less dense  Water holds less dissolved oxygen  More air needed
  23. 23. Efficiency means modulating airflow Matching the air supply to the process needs prevents energy from going to waste
  24. 24. Think of blower operation like riding a bike
  25. 25. Think of blower operation like riding a bike Sometimes you have to shift gears to go uphill, but you'd be crazy to pedal going downhill
  26. 26. Option #1: Valve throttling  Simple  Inefficient  Manual throttling requires multivariate operator judgment  Limited by butterfly valve control range
  27. 27. Option #2: Speed throttling  More complex: Requires integrating controls  Temperature-based feedback  Automation can account for changes in air temperature and water temperature  Limited by blower turndown potential  May deliver electrical savings
  28. 28. Big temperature swings complicate throttling  Air temperatures swing quickly  Water temperatures change slowly  Manual throttling can be labor-intensive
  29. 29. I was told there would be no math Here's the Streeter-Phelps equation for working out dissolved oxygen concentrations: Ss - O = [kd/(ko - kd)] Du [e-(kd/v)x - e-(ko/v)x ] + (Ss - O0) e-(ko/v)x
  30. 30. Kearney air temperature
  31. 31. It just isn't as easy as "Summer" and "Winter" Here's a case of both within a 48-hour period
  32. 32. Throttling is threefold  Process adaptation  Motor protection  Blower protection (rise to surge)
  33. 33. Knowing your system
  34. 34. Step 1: Energy audit  How much energy is being used?  How much does it cost?  Are any cost changes ahead?
  35. 35. Step 2.a.: System audit  Are plant loads as designed?  Has the process changed?  Is the treatment sufficient?  Is the system harmonized with local climate conditions?
  36. 36. Step 2.b.: Breaking out the power bill  What is the utility rate structure in effect?  Are prices fixed and flat?  Do prices vary with consumption (block pricing)?  Do prices vary with demand?  Do prices vary with time of day?  Do penalties or surcharges apply to high loads?
  37. 37. Step 3: Site audit  What do we know about performance data?  What data do we have on blowers, motors, and controls?  What site conditions constrain our options?
  38. 38. Step 4: Equipment audit  Is the right equipment in place to meet system needs?
  39. 39. Step Pre-5: A question Can you be rewarded, recognized, or promoted for improving processes and saving money?
  40. 40. Step 5: Survey the incentives
  41. 41. State incentives: dsireusa.org
  42. 42. State energy programs: naseo.org
  43. 43. Local utility rebates (Or just net savings for the municipal water & power utility)
  44. 44. Automatic controls cost money up-front  Capital expense must be justified  Energy savings are the main bucket of value  Even with cheap power, process optimization makes sense  Automatic controls can save on labor costs (or simply take dumb work off the to-do list)  Payback periods under 5 years are common
  45. 45. What makes a VFD applicable?  Positive-displacement blowers may benefit from VFD controls  Centrifugal blowers (including multi-stage and turbo) obey the same affinity laws as pumps
  46. 46. Affinity laws  Reductions in speed have magnified results in reductions in power  VFDs only effective with at least 1 psi rise to surge
  47. 47. Rise to surge Same condition, but the lower option offers far more useful range to the VFD
  48. 48. Effects of temperature change Slight reduction in speed as VFD adapts to temperature change HP Change From 193.91 to 173.48 Reduction of 20.43 HP
  49. 49. Other benefits  VFDs can reduce inrush current  Adding a PLC opens up integration with SCADA  PLCs can support algorithm- based flow control  Sensor-based operation does away with manually hunting the best condition  Can't do any of the above with valve-based throttling
  50. 50. Sample condition
  51. 51. Cost savings  Design condition at 95°F: 200 hp  At 75°F: 188 hp  At 50°F: 176 hp  At 25°F: 166 hp
  52. 52. Do you know how much 1 horsepower costs?
  53. 53. Do you know how much 1 horsepower costs?  1 hp = 0.7457 kilowatts  0.7457 kW for 24 hours over 365 days = 6,532 kWh  At $0.10 per kWh, 1 hp costs $653.20 per year
  54. 54. Lower horsepower means less electricity  1 hp equals 0.7457 kilowatts  200 hp equals 149.14 kilowatts  Dropping to 188 hp (75° condition) uses 140.91 kilowatts  Dropping to 176 hp (50° condition) uses 131.24 kilowatts  Dropping to 166 hp (25° condition) uses 123.79 kilowatts
  55. 55. Less electricity means lower costs  Normal daily temperature variations would put this one blower in the range to vary by 10 kilowatts just between high and low daily temperatures
  56. 56. Less electricity means lower costs  Normal daily temperature variations would put this one blower in the range to vary by 10 kilowatts just between high and low daily temperatures  If you can save just 10 kilowatts for 12 hours of each day, that's 43,800 kilowatts of energy saved per year
  57. 57. Less electricity means lower costs  Normal daily temperature variations would put this one blower in the range to vary by 10 kilowatts just between high and low daily temperatures  If you can save just 10 kilowatts for 12 hours of each day, that's 43,800 kilowatts of energy saved per year  Then, scale that up to the potential savings across seasonal variations that could be saving 25 to 30 kilowatts for months at a time
  58. 58. Less electricity means lower costs  Normal daily temperature variations would put this one blower in the range to vary by 10 kilowatts just between high and low daily temperatures  If you can save just 10 kilowatts for 12 hours of each day, that's 43,800 kilowatts of energy saved per year  Then, scale that up to the potential savings across seasonal variations that could be saving 25 to 30 kilowatts for months at a time  It's not hard to achieve tens of thousands of dollars in savings by automating speeds on a single blower
  59. 59. Questions?  Thank you for your time and attention  This presentation will be available through gongol.net/presentations  Brian Gongol DJ Gongol & Associates  brian@gongol.net  515-223-4144  @djgongol on LinkedIn, Facebook, and Twitter
  60. 60. Sources  Skew-T chart from the National Weather Service:  https://www.spc.noaa.gov/exper/soundings/22012512_OBS/  Water temperature vs DO graph:  https://www.usgs.gov/special-topic/water-science-school/science/dissolved-oxygen-and- water  Kearney air temperature records:  https://www.weather.gov/wrh/Climate?wfo=gid  Kearney forecast graph:  https://forecast.weather.gov/MapClick.php?lat=40.7008&lon=- 99.0846&lg=english&&FcstType=graphical&menu=1  Streeter-Phelps equation:  http://ponce.sdsu.edu/onlinedostph.html  Graphs provided courtesy of Hoffman & Lamson/Gardner-Denver  Blower photos provided courtesy of Hoffman & Lamson/Gardner-Denver

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