Blower Controls for Aeration Efficiency · 2017-05-11 · Common Calculations for All Blowers •...
Transcript of Blower Controls for Aeration Efficiency · 2017-05-11 · Common Calculations for All Blowers •...
Blower Controls for Aeration Efficiency
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Featured Speaker: Tom Jenkins, JenTech Inc.
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Introduction by Rod Smith, Publisher
Blower & Vacuum Best Practices® Magazine
Blower Controls for Aeration Efficiency
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Tom Jenkins, JenTech Inc
• President of JenTech Inc.
• Over 30 years of experience with aeration blowers and blower controls
About the Speaker
For your free subscription, please visit http://www.blowervacuumbestpractices.com/magazine/subscription.
Sponsored by
Blower Controls for Aeration Efficiency
May 11, 2017
1:00 PM CST
Thomas E. Jenkins
President, JenTech Inc.
414-352-573
Topics
• Common characteristics for all blowers
• Wire to air considerations for power evaluation
• PD blower control and evaluation
• Dynamic blower control and evaluation
2
Common Calculations for All Blowers
• Blowers are volumetric flow devices
– m3/hr, ACFM (Actual Cubic Feet per Minute)
– FAD (Free Air Delivery) = volumetric flow at ambient
conditions
• To convert mass flow rate to volumetric flow rate you
must correct for temperature and pressure
– SCFM (Standard Cubic Feet per Minute) typically 68°F 14.7
psia 36% RH is mass flow rate
– Relative humidity may be ignored for most applications
ACFM = SCFM ∙Ta
pa ∙ 35.92Ta = absolute temperature, °Rpa = absolute pressure, psia
3
Common Calculations for All Blowers
• When relative humidity must be considered:
Note: ICFM = Inlet CFM, a special case corresponding
to the actual volumetric flow rate at the blower inlet.
ACFM = SCFM ∙14.58
pb − RH ∙ psat∙
Ta
528∙
pb
pa
Ta = actual absolute temperature, °Rpa = actual absolute pressure, psiapb = barometric pressure, psiapsat = saturation vapor pressure, psia
(a function of temperature)RH = relative humidity, decimal
4
Common Calculations for All Blowers
• Pressure is the second parameter that determines
blower power
• There are several factors contributing to discharge
pressure:
– Static pressure from diffuser submergence
• This is typically the largest component of discharge pressure
• Static pressure is typically 80% to 90% of total discharge
pressure
– Friction losses through the diffusers
– Friction losses through pipe and fittings
– Pressure drop across flow control valves at basins
5
Common Calculations for All Blowers
• Total discharge pressure and system curve can be
calculated from flow:
• The constant kf can be calculated from design or
operating data:
ptotal = d ∙ 0.433 + kf ∙ Q2
ptotal = total discharge pressure, psigd = depth of water at top of diffuser, feetkf = constant of proportionality for friction, psi/SCFM2
Q = flow rate, SCFM
kf =pdes − d ∙ 0.433
Qdes2
pdes = total pressure at design (or actual) flow, psigQdes = flow rate at design (or actual) demand, SCFM 6
Common Calculations for All Blowers
• Blower power can be calculated from flow and
pressure: Pwa =Qs ∙ Ti
ηwa ∙ 3131.6∙ X
X =pd
pi
k−1k
− 1
k − 1
k≈ 0.283
Pwa = wire-to-air power, kWηwa = wire to air efficiency, decimal (includes blower , motor, and VFD)Ti = inlet air temperature, °Rpd, pi = discharge and inlet pressure, psiak = ratio of heat capacity = Cp/Cv, dimensionlessQs = flow rate, SCFM
7
Wire to Air Considerations
• The composite (average) power cost is often used to
estimate operating cost:
• The composite $/kWh is obtained by dividing total
annual power cost by total kWh consumed
• This may not accurately reflect actual operating cost
– On-Peak rate typically for 12 hours per weekday is higher
than Off-Peak rates
– Off-Peak rate for 12 hours per weekday and 24 hours
weekends
– Peak demand charge for highest 15 minute average per
month, is usually 1/3 of total power cost
Annual Cost = ൗ$kWh ∙ kWave ∙ 8760
8
Wire to Air Considerations
• The diurnal flow pattern for wastewater flow rate and
process oxygen demand is similar to the electrical
power demand variations
• If QAve is the air flow rate required to meet process
demand at average daily flow (ADF):
• kW can be calculated from the flow rates and
pressures 9
QOnPeak = QAve ∙ 1.15
QOffPeak = QAve ∙ 0.85
QDemand = QAve ∙ 1.20
Wire to Air Considerations
• Evaluating annual power cost should include time of
day rates and demand charges:
Note that the owner is billed for power and energy, not
efficiency
OnPeakCost = ൗ$kWhOnPeak
∙ kWOnPeak ∙60hr
week∙
52week
year
OffPeakCost = ൗ$kWhOffPeak
∙ kWOffPeak ∙10hr
week∙
52week
year
DemandCost = ൗ$kWDemand
∙ kWDemand ∙12month
year
10
Wire to Air Considerations
• For the most accurate determination of performance
consult the blower manufacturers
• Need to specify:
– barometric pressure
– inlet pressure (barometric less filter and piping losses)
– inlet temperature
– relative humidity
– flow rate (SCFM is best)
– discharge pressure at flow rate
11
1:15 PM
• Positive displacement blowers move a fixed volume of
air for each revolution of the blower shaft
• Control is by variable speed, typically variable
frequency drives (VFDs)
• Discharge pressure will inherently rise to meet
restriction to flow
• Must have pressure relief valve to prevent damage
to blower and piping
• Max capacity limit, flow and pressure, is based on
motor power and mechanical limitations
• Min capacity limit (turndown) is based on motor and
blower temperature rise
Positive Displacement Blower Control
1:15 PM
• Positive displacement blowers are of two types
• Older lobe type
• Newer screw type
• Typically more efficient and more turndown, but
more expensive
Positive Displacement Blower Control
Lobe Type PD Blower Screw Type PD Blower
1:15 PM
• Positive displacement performance is typically
presented in tabular form
• New CAGI (Compressed Air and Gas Institute) Data
Sheets are one example
Positive Displacement Blower Control
1:15 PM
• Positive displacement performance is typically
presented in tabular form
• New CAGI (Compressed Air and Gas Institute) Data
Sheets are one example
Positive Displacement Blower Control
1:15 PM
• Lobe type PD performance may be calculated from
manufacturer’s data if available
• Displacement
• Slip rpm (represents internal leakage)
• Slip increases with increasing discharge
pressure
• Friction hp
Positive Displacement Blower Control
ICFM = Nactual − Nslip ∙CFR
bhp = 0.0044 ∙ Nactual ∙ CFR ∙ ∆p +FHP
N = rotational speed, rpmCFR = blower displacement, cubic feet per revolutionFHP = friction horsepower, bhp
1:15 PM
• PD performance is often presented as a family of
“curves”
• Performance is approximately linear
• Typical example for a Lobe Type PD:
Positive Displacement Blower Control
1:15 PM
• PD performance is often presented as a family of
“curves”
• Typical example for a Lobe Type PD:
Positive Displacement Blower Control
1:15 PM
• Screw performance is more complex, and
manufacturer’s calculations are usually proprietary
• Performance is approximately linear
• Typical example for a Screw Type PD:
Positive Displacement Blower Control
• Screw performance is more complex, and
manufacturer’s calculations are usually proprietary
• Performance is approximately linear
• Typical example for a Screw Type PD:
1:15 PM
Positive Displacement Blower Control
1:15 PM
• If preliminary prediction of PD performance is needed
the simplest method is to enter the tabular data in a
spreadsheet and use the Excel “forecast” function
• Use forecast for each tabulated speed to create
“curve” data for the actual pressure
• Use forecast on the new curve data to determine
power for actual flow rate
Positive Displacement Blower Control
1:15 PM
• If preliminary prediction of PD performance is needed
the simplest method is to enter the tabular data in a
spreadsheet and use the Excel “forecast” function
• Use it for each tabulated speed to create “curve”
data for the actual pressure
• Use it on the new curve data to determine power for
actual flow rate
Positive Displacement Blower Control
1:15 PM
• If preliminary prediction of PD performance is needed
the simplest method is to enter the tabular data in a
spreadsheet and use the Excel “forecast” function
• Use it for each tabulated speed to create “curve”
data for the actual pressure
• Use it on the new curve data to determine power for
actual flow rate
Positive Displacement Blower Control
1:15 PM
• If preliminary prediction of PD performance is needed
the simplest method is to enter the tabular data in a
spreadsheet and use the Excel “forecast” function
• Use it for each tabulated speed to create “curve”
data for the actual pressure
• Use it on the new curve data to determine power for
actual flow rate
Positive Displacement Blower Control
Centrifugal (Dynamic) Blowers
• Centrifugal blower performance is more
complex than PD performance
• Centrifugal blowers convert impeller kinetic
energy to pressure and flow
• Performance is influenced by air density
and humidity (molecular weight)
25
Centrifugal (Dynamic) Blowers
• There are three types of centrifugal blowers
applied to wastewater aeration applications
– Multistage
– Geared single stage
– High speed gearless single stage (Turbo)
• There are three principal control techniques
for centrifugal blowers
– Inlet throttling: lease expensive, least efficient
– Guide vanes, inlet and discharge
– Variable speed with VFD - most efficient
26
Centrifugal (Dynamic) Blowers
• For any control technique determining
performance requires:
– Calculating the effect of the control on the
performance curve, flow vs. pressure and flow
vs. power
– Establishing the intersection of the system
curve with the flow vs. pressure performance
curve to establish flow rate
– Determining the power required at that flow
rate
• Both the system curve and the performance
curve are required to determine the flow
rate 27
Centrifugal (Dynamic) Blowers
• Multistage blowers use successive compression
stages to obtain discharge pressure
• Generally controlled by inlet throttling or variable
speed
28
Centrifugal (Dynamic) Blowers
• Example for inlet throttling:
– Calculate pressure drop across valve at several
flow rates
29
∆pv =Qs
22.66 ∙ Cv
2
∙SG ∙ Tu
pu
Where:Δpv = pressure drop across the valve, psiQs = air flow rate, SCFMCv = valve flow coefficient from manufacturer’s data, dimensionlessSG = specific gravity, dimensionless, = 1.0 for airTu = upstream absolute air temperature, °Rpu = upstream absolute air pressure, psia
Centrifugal (Dynamic) Blowers
• Example for inlet throttling:
– Calculate new actual inlet pressures and
approximate flow vs. pressure performance at
several flow rates
30
pda=pc∙Tic
Tia∙
pia
pic
Where:pda = actual discharge pressure, psigpc = discharge pressure from curve, psigTic,ia = inlet temperature for curve and actual, °Rpic,ia = inlet pressure for curve and actual, psia
Centrifugal (Dynamic) Blowers
• Example for inlet throttling:
– Calculate approximate flow vs. power
performance at several flow rates
31
Pa=Pc∙Tic
Tia∙
pia
pic
Where:Pa = actual blower power, hpPc = blower power from curve, hp
Centrifugal (Dynamic) Blowers
• Example for inlet throttling:
– Plot new performance and system curves
32
Centrifugal (Dynamic) Blowers
• Geared single stage use gears and high impeller
speed to obtain required discharge pressure
• Generally controlled by guide vanes or variable speed
33
Centrifugal (Dynamic) Blowers
• The configuration and effect of guide vanes on geared
single stage blowers is usually proprietary
• Performance must be obtained by interpolating
manufacturer’s curves
34
Centrifugal (Dynamic) Blowers
• The configuration and effect of guide vanes on geared
single stage blowers is usually proprietary
• Performance must be obtained by interpolating
manufacturer’s curves
35
Centrifugal (Dynamic) Blowers
36
• Turbo blowers use impeller direct coupled to high
speed motors to obtain required discharge pressure
• Always variable speed with VFD in package, most of
efficiency gains are from variable speed
Centrifugal (Dynamic) Blowers
37
• For all centrifugal blowers, including turbos,
performance prediction for variable speed is based on
affinity laws: Qa=Qc∙Na
Nc
Xa=Xc∙Na
Nc
2
Pa=Pc∙Na
Nc
3
pd = pi ∙ Xa + 1k
k−1
Where:Qa,c = actual and curve volumetric flow rate, ICFMNa,c = actual and curve rotational speed, rpmPa,c = actual and curve blower power, hppi,d = inlet and discharge pressure, psia
See Slide 7
Centrifugal (Dynamic) Blowers
38
• For all centrifugal blowers, including turbos,
performance prediction for variable speed is based on
affinity laws
Summary
39
• All blower energy analysis depend on using correct
input data
• Analysis should always include blower performance
curves and system curves
• Calculations for determining energy demand depend
on the blower technology
• Variable speed is becoming common for all blower
types and often results in the lowest life cycle cost
Stephen Horne,Kaeser Compressors
•Blower Product Manager for Kaeser Compressors
About the Speaker
For your free subscription, please visit http://www.blowervacuumpractices.com/magazine/subscription.
Blower Master Controllers:
How the IIoT Can Optimize
Blower Station Performance
Stephen Horne
Product Manager—Blowers
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 2
WWTP Requirements
o Plant air requirements vary hourly, daily, and
yearly
o Plant design must accommodate the community
for 20-30 years
o Plant air demand and plant growth rate is not
linear
o Blowers must be sized to accommodate plant full
capacity
o Designers must consider both investment cost and
operational cost
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 3
Overview
o Specific Performance
o Levels of Controls
o Package vs. System Efficiency
o Satisfying Air Demand
o Evaluating and Selecting Blowers
o Dedicated vs. Centralized System Controls
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 4
The Industrial Internet of Things (IIoT)
“… the IoT promotes a heightened level of awareness about our
world, and a platform from which to monitor the reactions to the
changing conditions that said awareness exposes us to.”
— Brendan O’Brien, Chief Architect & Co-Founder, Aria Systems
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 5
Overview of WWTP Air Requirements
Variations in plant demand = Variations in blower output
o As the plant load varies, blower output must be
altered to meet plant needs.
o Too little air supply results in insufficient
oxygen levels in the basin
o Too much air supply results in excessive
energy cost
(producing air that is not required
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 6
Two Levels of Control
System Package
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 7
Two Levels of Control
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 8
Two Levels of Control
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 9
Blower Station Controls and Communications
Modem
SCADA
Blower
Blower
Blower
ServicePackage
health
Flow required AlgorithmMaster
Controller
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 10
Think in Terms of System Efficiency
System efficiency includes:
o All blower packages
o Ancillary equipment
o Master controller
Factors in:
o How equipment meets
changing application demands
Closest match to your power bill
How IIoT Can Optimize Blower Station Performance
© 2017 Kaeser Compressors, Inc., USA • V1.0 us.kaeser.com 11
Thank you. Questions?
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May 2017 Webinar:
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