Seismic Hazard Assessment Software in Python by Prof. Dr. Costas Sachpazis
You can't throttle me! Controlling blowers with valve and VFDs - v.04
1. You Can't Throttle Me!
Brian Gongol
DJ Gongol & Associates, Inc.
November 4, 2021
NWEA Fall Conference
Kearney, Nebraska
2. Ben Franklin on aeration
"Beware of little expenses;
a small leak will sink a great ship."
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
12. 4. Temperature
How hot or cold is the available air?
How hot or cold is the receiving water?
13. Must size for the worst-case scenario
Hot input air at low density
going into warm water
that doesn't hold DO very well
14. 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
Is anyone's WWTP budget too big for them to spend?
16. Warm weather
Air is less dense
Water holds less dissolved oxygen
More air needed
17. Efficiency means modulating airflow
Matching the air supply to the process needs
prevents energy from going to waste
18. Option #1: Valve throttling
Simple
Inefficient
Manual throttling requires multivariate operator
judgment
Limited by butterfly valve control range
19. 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
20. Big temperature swings complicate throttling
Air temperatures swing quickly
Water temperatures change slowly
Manual throttling can be labor-intensive
25. Step 1: Energy audit
How much energy is being used?
How much does it cost?
Are any cost changes ahead?
26. 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?
27. 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?
28. 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?
29. Step 4: Equipment audit
Is the right equipment in place to meet system needs?
34. 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
35. 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
36. Affinity laws
Reductions in speed have magnified results in
reductions in power
VFDs only effective with at least 1 psi rise to surge
37. Rise to surge
Same condition, but
the lower option
offers far more useful
range to the VFD
38. 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
39. 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
42. 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
43. 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
44. 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
45. 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
46. 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
47. 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
48. Sources
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
Graphs provided courtesy of Hoffman & Lamson/Gardner-Denver
Blower photos provided courtesy of Hoffman & Lamson/Gardner-
Denver