Optimizing Operations of Finished Water Pumps and Protecting the Distribution
System with Transient Modeling
95TH Annual Conference | November 2015 | Raleigh Convention Center, Raleigh, NC
Authors
Crystal Broadbent, Hazen
and Sawyer
Kelvin Creech, Town of
Cary
Michael Wang, Hazen and
Sawyer
Outline
Project Background
Surge Modeling
Field Work
Model Calibration
Air Release Valve
Analysis
Economic Analysis
Recommendations
Summary
Purpose
Surge Model used
to identify problems
affecting
operations of
finished water
pumps, WTP, and
distribution system
•
Optimize operations
•
Reduce O&M cost
•
Protect critical
infrastructure
Background
Background
Staff suspect
finished water
pumps were
adversely affected
by entrained air
left in the
transmission main
•
•
The WTP:
•
40 mgd WTP
•
9 finished water pumps
•
42-inch transmission main
The challenges:
•
After maintenance, unable to
purge all air out of transmission
main
•
High-pitch sound emanating from
existing air release valves
Surge Model
Surge
Model
2010
MDD
Pumps Operating
at MDD
• Two 1000 hp
Q= 24.3 mgd
Pressure = 161.4
psi
• One 450 hp
High Service Pump Detail
High Service Pumps in Surge Model
Surge Relief Valve
ADAMS Control
Valve, typ.
FWP-7
FWP-6
FWP-5
FWP-4
FWP-3
FWP-8
42-inch Transmission Line Profile
System Profile
500
480
460
Elevation (feet)
440
420
400
380
360
CPZ Zone
340
320
300
0
Pipeline
HSP
2000
4000
6000
8000
Distance (feet)
1.0E+4
1.2E+4
1.4E+4
Field Test
Field Test – Logger Location
Jenks & Apex
Hwy 55
Between
pumps and
ADAMS
valves
Venturi Vault
Green Level
Church Rd
Field Test
• Work performed April 18th, 2013
• Evaluated a series of pump on and off configurations
•
Pump 6 start
•
Pump 5 start while Pump 6 operating
•
Pump 6 off while Pump 5 operating
•
Pump 3 on while Pump 4 operating
•
Pump 3 off while Pump 4 operating
• Measured pressures at hydrants
Pump 6
WTP Meter - Upstream
Green Level Hydrant
Jenks & 55 Hydrant
CPZ Pressure
Green Level Vault Pressure
Jenks/55 Pressure
Jenks/55 Flow
CPZ Flow
Green Level Vault Flow
Pump 6 Start
200
150
100
50
SCADA does not capture the
pressure wave
0
25
20
SCADA does not capture the pump start up
15
10
5
0
11:26:01
11:26:44
11:27:27
11:28:11
Time (h:m:s)
11:28:54
11:29:37
Fow (mgd)
Pressure (psi)
250
Pump 5
Pump 6
WTP Meter - Upstream
Green Level Hydrant
Jenks & 55 Hydrant
CPZ Pressure
Green Level Vault Pressure
Jenks/55 Pressure
Jenks/55 Flow
CPZ Flow
Green Level Vault Flow
250
Pump 5 Start
Pump 6 Operating
25 psi
difference
150
100
A 25 psi difference between Pump 5 and Pump 6 &
WTP Meter. This indicates that the ADAMS valve in
front of Pump 5 is throttling flow and energy is being
consumed.
50
0
25
20
15
10
5
11:40:25
11:40:42
11:41:00
11:41:17
11:41:34
Time (h:m:s)
11:41:51
11:42:09
11:42:26
0
11:42:43
Fow (mgd)
Pressure (psi)
200
Pump 5
Pump 6
WTP Meter - Upstream
Green Level Hydrant
Jenks & 55 Hydrant
CPZ Pressure
Green Level Vault Pressure
Jenks/55 Pressure
Jenks/55 Flow
CPZ Flow
Green Level Vault Flow
Pump 6 Off
Pump 5 Operating
250
150
100
50
0
25
20
15
10
5
0
11:58:51
11:59:34
12:00:17
12:01:00
Time (h:m:s)
12:01:44
12:02:27
Fow (mgd)
Pressure (psi)
200
Pump 3
Pump 4
WTP Meter - Upstream
Green Level Hydrant
Jenks & 55 Hydrant
CPZ Pressure
Green Level Vault Pressure
Jenks/55 Pressure
Jenks/55 Flow
CPZ Flow
Green Level Vault Flow
250
Pump 3 On
Pump 4 Operating
150
100
50
Pressures are the same for Pump 4, Pump 3 and
WTP Meter, as would be expected
0
25
20
15
10
5
0
12:27:22
12:28:05
12:28:48
12:29:31
Time (h:m:s)
12:30:14
12:30:58
Fow (mgd)
Pressure (psi)
200
Pump 3
Pump 4
WTP Meter - Upstream
Green Level Hydrant
Jenks & 55 Hydrant
CPZ Pressure
Green Level Vault Pressure
Jenks/55 Pressure
Jenks/55 Flow
CPZ Flow
Green Level Vault Flow
200
150
100
50
0
25
20
29 second closing: 62 psi pressure
increase
SCADA does not capture the pressure
wave
15
10
5
0
12:45:48
12:46:31
12:47:14
12:47:57
Time (h:m:s)
12:48:40
12:49:24
Fow (mgd)
Pressure (psi)
250
Pump 3 Off
Pump 4 Operating
Model Calibration
Surge Model Calibration to Field Test Results
Analyzed two scenarios
Pump 6 on
Pump 6 turns off while Pump 5 remains on
Graph
Field test results: dashed lines
Surge model results: solid lines
Different color for each location
Pump 6 Start
Model: WTP Meter
Field: WTP Meter
Model: Pump 6
Field: Pump 6
Model: Green Level
Field: Green Level
Model: Jenks & Apex
Field: Jenks & Apex
250
Model Matches Loggers
200
Pressure (psi)
150
100
50
0
350
370
390
410
430
450
Time (sec)
470
490
510
530
550
Pump 6 Off
Model: WTP Meter
Field: WTP Meter
Model: Pump 6
Field: Pump 6
Model: Green Level
Field: Green Level
Model: Jenks & Apex
Field: Jenks & Apex
250
Model Matches Loggers
200
Pressure (psi)
150
100
50
0
20
40
60
80
100
120
Time (sec)
140
160
180
200
Air Valve
Evaluation
Basic Purposes of Air Valves
The Basic Premise
Allow air and gases to be released from a pipe
Allow air into a pipe under negative pressure conditions
Behavior of Air
“Air & Its Impact on a Water and Wastewater System”, Val-Matic; Air Valves Bulletin 1500;
issue 3 volume 52 p 37-44
Installation Guidelines
Air valve connection to the pipe needs to be correctly sized
and located to capture the small air bubbles as well as larger
pockets.
For air-release valves this is particularly important, since
their function is to release these small bubbles and pockets.
Ideal (but not generally practiced in the U.S.):
Connection to Pipe (d) Ratio to Pipe Diameter (D):
d = D for D ≤ 12 inch
d = 0.6D for D inch < D ≤ 60 inch
d = 0.35D for > 60 inch
Orifice Sizing: Air-release Valve
Difficult to predict quantity of air/gases that will come out of
solution
Assume 2% solubility of air in water under standard
conditions
Less is known about dissolved air properties in wastewater
“Choked orifice,” or “sonic flow” occurs when the ratio of low
pressure (absolute) to high pressure (absolute) < 0.528 (for
vacuum, avoid internal pressures below -5 psi gauge)
Orifice Sizing: Air/Vacuum Valve
Pipeline Filling
Fill rate 1ft./sec.
Exhaust air at a rate =
pumping rate or the
design fill rate
Air enters Orifice (3), travels through the
annular space between the cylindrical floats
(4), (5), and (6) and the valve Chamber Barrel
(2) and discharges from the Large Orifice (1)
into atmosphere
Typically vented to
atmosphere a
differential pressure of
< 2 psi.
Valves with anti-slam or
slow-closing may have
a differential pressure
of 5 psi
Orifice Sizing: Air/Vacuum Valve, cont.
Pipeline Draining
Gravity flow based on pipe slope or drain valve
Determine maximum allowable negative pressure (usually -5
psi)
Caution
Improper design of orifice size for an
air/vacuum valve =
Release air too fast “air slam”
Single
stage
2 stage
31
Air Valves for Burst and Draining
Each manufacturer uses its own set of calculations
and some provide free sizing programs
4”
3”
4”
4”
8” 8”
4”
4”
3”
4”
Existing Air Valves are 2 times too
Small
Velocity: 3-3.3 fps
For 42 inch pipe Air
Valve size is between a
4 and 6 inch
Current Size Air Valves
would be for ONLY a 16
to 24 inch pipe
Economic Analysis
Economic Analysis
1.
Evaluated current operations for taking 42” offline and returning it to
service
2.
Determined effectiveness of existing air valves
3.
Using model and field test
•
Determined existing restrictions in 42” transmission main
•
Energy cost due to restrictions in 42” transmission main
Current 42” Operation
Normally: 42” feeds CPZ (641’); 30” feeds
WPZ (540’)
Taking out of service
Operate valves to switch 30”
from WPZ to CPZ
Drain 42” through blow off
valves
Supply WPZ through PRVs
from CPZ
Supply CPZ using
3 WPZ pumps 400hp; 5.5 mgd @ 305 ft
1 Swing pump 1000 hp; 9 mgd @ 450 ft
Supplement with Durham water
Placing back into service
24-72 hrs to refill 42” Main
Refill from NC 55 & Old Jenks
Rd
30” Main still providing supply
to CPZ
Operate valves to switch 30”
from CPZ to WPZ
Flush through hydrants
Return 42” Main to service
Hydraulic Model Analysis*
Evaluating 30” TM
Supplying WPZ (typical
operation)
Supplying CPZ (when 42”
offline)
Average Day Demand for WPZ: 3.4
mgd
Average Day Demand CPZ: 16.2 mgd
1 WPZ Pump: 3 hrs a day
6.3 MGD @ 271 ft; 78%
Calculated HP: 384
Davis Drive & Waldo Rood Blvd PRV
between CPZ and WPZ
2.7 mgd
Setting 78 psi
* hydraulic model received from CH2M’s
Swing Pump: operates 2 to 3 times a day:
~ 14hrs each day
9.6 MGD @ 424 ft; 85%
Calculated HP: 840
WPZ Pumps operating: 1, 2 and 9 –
operates continuously
Each: 4.2 mgd @ 380 ft; 78%
Calculated HP: 359 per pump
Together, the WPZ pumps and swing
pump can continue to meet average day
demands
WPZ Pump
Pumping
to CPZ
Pumping
to WPZ
Cost Difference Between Supplying
CPZ with 42” vs. 30”: Average Day Demand
42” Supply CPZ
Pump 3: 384 hp,
8.4hrs/day,
30days/month
Pump 5: 835 hp,
9.4hrs/day,
30days/month;
827 hp,
14.6hrs/day,
30days/month
Pump 6: 835 hp,
9.4hrs/day,
30days/month
Total : 720,000
kwh/month
30” Supply CPZ
3 WPZ pumps
each: 359hp,
24hrs/day,
30days/month
Swing Pump: 840
hp, 14hrs/day,
30days/month
Total : 841,000
kwh/month
Difference
121,000 kwh/month
kWh cost
$0.0535/kwh for all
over 140,000 kWh
per month, per kWh
(duke energy)
Cost for using 30”
verses 42” to supply
CPZ
$1,600 cost/week
$6,500 cost/month
Effectiveness of Existing Air Valves
Cumulative Volume from Air Valves: Power Loss Simulation
90
Proposed Air Valves
Existing Air Valves
80
70
Positive slope: The rate air is entering air valves
60
Volume (cf)
Surge model power
loss result: Existing
valves let in a greater
volume of air and take
longer to expel it than
the proposed valves.
Negative slope: The rate air is being expelled through
the air valves
50
40
30
Larger volume of air is
directly proportional to
the headloss.
20
10
0
0
10
20
30
40
50
60
70
80
Time (seconds)
90
100
110
120
130
140
Comparing Field Test to Model
Field –
Pump 6
ModelWithout
Restrictions
Flow, mgd
10.75
10.75*
Discharge
Pressure, psi
148
140
Discharge HGL, ft
656
637
Suction HGL Range,
ft
290
290
TDH, ft
366
347
Efficiency, %
80
80
Calculated HP
862
818
* Forcing the model to provide the exact flow as the field test
Pumps are operating below the 20.2 inch impeller curve
(shown in the next slides)
Pump 6
Field Test
Model
42" Transmission Main - HGL
Field Test at 10.75mgd
Pump at 10.75mgd
660
Model with Restrictions
Elevation
Possible Restrictions:
Throttled valve
Air pocket
Corrosion buildup*
Biofilm*
*City staff confirmed this is not the case
HGL, ft
650
640
630
450
350
250
0
1000
2000
3000
4000
5000
6000
7000
8000
Distance, ft
9000 10000 11000 12000 13000 14000 15000
Ground Elevation, ft
550
Reduction of Pump Capacity –
Air Pocket
Air pockets in the pipeline add
additional head loss and restrict flow
Head loss is directly proportional to the
size of air pocket
As high as 16% additional head loss
Extremely difficult to predict exact head
loss
Determine entrained air by comparing
the design capacity and actual capacity
Another way is to determine the actual
friction value through field work and
then recalculate capacity with new
friction value to see if entrained air is
an issue
S J van Vuuren, M van Dijka and J N Steenkamp, Quantifying the Influence of Air on the Capacity of Large
Diameter Water Pipelines and Developing Provisional Guidelines for Effective De-aeration. WRC Report
No. 1177/2/03
Potential Energy Savings: One Pump
Evaluation
862 hp,
24hrs/day,
30days/month
818 hp,
24hrs/day,
30days/month
24,000
kwh/month
difference
463,000
kwh/month
439,000
kwh/month
Savings
Field Test
Model with No
Restrictions
$15,400
saving/yr
Difference
Recommendation
Suggested Sizing for 15 and 20 MGD
from Manufacture Software
3”/6” & 3”
4”
4”
4”
8” 8”
4”
4”
4”
3”
New Locations
Hazen Recommendation
Remains the same
4”
4”
4”
6” 6”
4”
3”
4”
3”
New Locations
Various Construction Cost Estimate for
Valve Upgrade
Item
Description
Total Cost
Tee Connection (42”x20”)
$110,000
Tapping Saddle (42” x 12”)
$18,000
Existing Tapping Saddle
(42”x8”)
$13,000
Air Valve
New Manhole
Tee (42”x20”)
$120,000
New Manhole
Tapping Saddle
(42” x 12”)
$29,000
Recommended Modifying
Pump Control Valves
Replace Actuators
More control of
open/close times
Reduce operational cost
by removing headloss
through malfunctioning
valve
ADAMS Valve
50
Summary
Summary
Calibrated Surge Model Optimized Operations
Improved Air Release Protected Critical
Infrastructure
Reduces O&M Cost
52