1 Cleaning Large Diameter Water Lines by Ice Pigging · PDF fileCleaning Large Diameter Water...
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Cleaning Large Diameter Water Lines by Ice Pigging
NC AWWA-WEA 2015 Spring Conference
Wilmington, NC
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John Collett
336-292-7490
Kevin Eason, PE
336-349-1042
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Overview
• History of previous
distribution system issues
• Overview of ice pigging
technology
• Results from initial ice
pigging
• Plans for continued work
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City of Reidsville
• Water system has over
16,000 connections
• 3.28 mgd average day
demand
• Water treatment plant
supplied from Lake
Reidsville
• High seasonal
manganese and iron in
source water
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Distribution System Buildup
• In past years poor
treatment practices
contributed to
aluminum &
manganese deposits
• Received valid
criticism from industrial
customers regarding
water quality
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This contamination is nearly impossible to
clean from the membranes and, to this
point, require replacement of the
membranes. This is a cost of approximately
$16,000.00 per occurrence. To date since
October 2009 at least 4 known occurrences
have been noted.
In the past 6 months we have had an
unusual number of dirty water
occurrences. As you are aware clean
water for dyeing yarn is critical to providing
a quality product. The affects of dirty
water: additional costs for water due to
softener, backwash frequency increase,
labor costs for redyes of the affected yarn,
etc. The yarn dyed in our facility acts like a
filter and the sediment in the dirty water
attaches itself to the yarn causing off shade
dyeing among other quality issues.
Correspondence from May 2010
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Distribution System Flushing
• Residents customers also affected
• Began unidirectional flushing
program in 2013 for water mains
12-in and smaller
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Buildup in Large Mains Found
• Heavy manganese
buildup noticed in
16-in pipe during
recent construction
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• City decided to explore options to
clean the larger diameter pipes in City
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Cleaning Methods Considered
• Unidirectional Flushing
– Not effective for larger diameter pipes
• Mechanical Pigging
– Increased risk
– Install launch and
retrieval stations
– Butterfly valve removal
• Ice Pigging
– Lower risk, impact, and cost
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What is Ice Pigging?
• Cleaning technique that is operationally
similar to unidirectional flushing with the
impact of solid pigging
• Developed by the University of Bristol in
England
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• Utility Service Group
is sole rights holder
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How Does It Work?
• Ice slurry is injected
into water main and
used to scour inside
of pipe
• Can be pumped like
a liquid but forms
into a semi-solid pig
once in the pipe
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Ice Production
• Ice produced on
location
• Food grade salt
used to control
consistency
• Additional chlorine
may be added as
disinfectant
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Ice Delivery – 10 Ton Load
• Ice delivery
truck brings
ice to site
• Slurry is
pumped into
pipe through
hydrant or
tap
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Ice Discharge
• System pressure used
to push ice pig
• Discharge flow
controlled using
monitoring box
• Pressure maintained
above 20 psi
• Temperature, turbidity,
conductivity measured
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Discharge Sampling
• Samples taken once ice pig arrives downstream
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Waste Handling14
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Ice Pigging Site Schematic15
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Specifics
• Cleaned 2” to 18” diameter pipe (so far)
• Target velocity = 0.5 fps
• Maximum length of run dependent on:
– Pipe diameter and material
– Water temperature
– Number of ice trucks used
• Can pass through fittings and butterfly
valves
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Reidsville Plan
• Deposits expected to
be heaviest leaving
the WTP and in the
southern portion of
system
• City decided to clean
24” pipe leaving WTP
and portions of 16”
pipe on Freeway
DriveBuildup Found
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Ice Pigging Preparation
• Allowable length of runs determined by diameter of pipe, volume of ice per truck, and number of ice trucks available
• Layout runs and locate taps for ice injection and removal
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Hydraulic Model Used During Planning19
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Expected Demand During Pigging
• Average daily
demand Nov
2013 = 2.80
MGD
• Perform pigging
from noon to
5pm
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Predicted Time Reidsville Tanks Can
Supply System Demand
Vance Street Tank Is First To Empty
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1st Phase Of Work Complete22
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1st Phase Of Work Complete
• Ice pigging complete
for 16” pipe
• Estimated 121 lbs
sediment removed
from 1,050’ of
16” pipe
• Lab analysis showed
significant amounts
of iron and
manganese removed
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2nd Phase Planned for May
• 10,500 LF of 24-inch pipe
• 2nd ice truck will double length of run
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Acknowledgements
• Kevin Eason – Public Works Director
• Scott Jewell – WTP Superintendent
• Scotty Wilkins & Paul Treloar – Utility Service Group
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Questions?26