What’s Eating Your Pump?
Selecting Submersible Pumps for
Landfill Leachate and Condensate
Removal Applications
Copyright © 2009 QED Environmental Systems, Inc. All rights reserved. Reproduction or distribution for
commercial purposes, in whole or in part, is prohibited except with written permission from QED.
Today’s presentation will cover:
• Landfill liquids – leachate and condensate
• Typical pumps used in landfill applications
• Operating principles of typical landfill pumps
• Advantages and disadvantages by pump type
• Factors affecting pump selection
• Case history examples
• Questions and answers
Leachate
Liquid from precipitation, waste breakdown, and discarded liquids
•
Volume varies seasonally
and regionally, often widely
•
Elevated temperatures
•
High levels of suspended and
dissolved solids
•
Foaming potential
•
Viscosity can be greater than
water
•
Corrosives and aggressive
organics
•
Extremes of pH at some sites
Condensate
Liquid that condenses from landfill gas in the collection system
•
Variable liquid volume
•
Mostly water and organics
•
Moderate temperatures
•
Relatively low solids
concentrations
•
Viscosity typically close to
water
•
Potentially explosive
environment (landfill gas)
Why Pump?
Leachate
•
•
•
•
Meet regulatory requirements (head against liner)
Prevent liner leakage, side slope seeps and odors
Recirculate leachate to accelerate gas production
Gradient control (unlined cells)
Condensate
• Maximize gas flow from wells and through piping
• Maintain steady operation of power generation systems
• Prevent damage to blowers, generators and flares
Typical pumps used in landfills
• Electric
submersible (centrifugal)
• Air-powered automatic
• Piston
Each is affected differently by site factors
ELECTRIC
SUBMERSIBLE PUMP
AIR-POWERED
AUTOMATIC PUMP
PISTON
PUMP
Electric pump system components
• Control box
• Discharge pipe
• Power and sensor
cables
• Level sensors
• Pump
• Motor
Electric pump – how it works
• AC electric power drives the motor, turning
the shaft and impellers within the pump
chamber.
• Rotating impellers create suction that draws
water over the motor into the pump where it is
pressurized by centrifugal force, pushing it up
the discharge pipe.
• Flow rate is not typically controlled; the pump
runs at maximum output based on operation
conditions.
• Flow can be controlled by a variable
frequency drive, or VFD, but adds significant
cost.
• Level control requires the use of level sensors
in the well wired to the control box.
Electric pump design considerations
• Electric pumps have the highest flow
rate capability, with landfill versions
designed to handle 50-200 GPM or
higher.
• Solids handling is limited due to
close tolerances within the pump
chamber and high speed rotation of
the impellers.
• Impellers can be eroded or pitted by
solids and cavitation. Seals and
bearings can be damaged by solids.
•Metallic components and bearings
can corrode. Shaft corrosion and
rubber hardening can damage motor
shaft seal, resulting in motor failure.
• Level sensors can be blinded or
coated by chemicals and mineral
deposits, resulting in failure to start or
stop pump.
Electric pump strengths and weaknesses
Strengths
• Highest flow rates (200+ GPM) efficiency at lowest initial cost (standard pumps)
• Can pump in slant and horizontal casings if fully submerged
• No air contact with the pumped liquid – lower potential for clogged piping
• Wide availability at local suppliers (water well pump vendors)
Weaknesses
• Limited solids handling capability
• Higher maintenance and greater downtime due to impeller and bearing wear
• Motor failure from corrosion, high temperature, rapid on/off cycling, running dry
and solids clogging (locked rotor)
• Standard warranty coverage doesn’t extend to landfill pumping applications
• Electric power poses safety concerns in potentially explosive environment
• Local suppliers often can’t provide turnkey systems
Air-powered pump system components
• Pressure regulator/filter
• Air supply and discharge tubing
• Pump
• No control box
• No level sensors
• No power and sensor cables
Air-powered automatic pump – how it works
Fill Cycle
• Liquid enters the pump through bottom check
valve.
• As pump fills, air escapes through the exhaust
valve and the internal float rises.
Discharge Cycle
• At the top of its travel, the float opens the air
inlet and closes the exhaust valve.
• Air pressure closes the bottom check valve
and liquid is pushed up the discharge tubing.
• As the liquid level in the pump falls, the float
moves down, closes the air inlet valve and
opens the air exhaust valve, and a new fill cycle
begins.
Air-powered pump design considerations
• High-clearance check valves and
passages maximize solids handling
capability.
• Low-speed moving parts minimizes
wear.
• Built-in on/off level control eliminates
need for level sensors.
• Gentle pumping action reduces foaming,
which minimizes discharge line clogging
and improves pump performance.
•Bottom inlet allows for pumping short
liquid columns.
•Wide range of materials handles a range
of applications – low pH, high chlorides,
high temperatures, etc.
Configurations to match the application
• Longer pumps provide
higher flow rates, while short
pumps provide maximum
drawdown in short liquid
columns.
• Larger diameters for
maximum flow in 4-inch and
larger risers.
• Smaller diameters fit inside
2-inch risers or larger risers
with restrictions (deformation
or kinks).
Air-powered pump strengths and weaknesses
Strengths
• Air safer than electricity in wet or potentially explosive environments
• Long-term system reliability in aggressive fluids and high solids
• Pump materials and dimensions configured for specific applications
• Built-in level and flow controls
• Gentle pumping action = little foaming of pumped liquids
• Complete systems available from one source, not multiple vendors
Weaknesses
• Maximum flow rates (13-15 GPM) lower than electric pumps
• Less energy efficient than electric pumps
• Higher initial cost than general-duty water supply pumps
• Drive air contact with liquid could increase discharge line deposits
Piston Pump System Components
Drive cylinder
Stuffing box
Drive rod
Discharge pipe
Piston
Pump cylinder
Piston pump – how it works
Lift Stroke (Discharge)
• With top check valve closed, the liquid above
the piston is lifted up the discharge piping.
• Lift stroke also creates suction in pump
cylinder below the piston, drawing in liquid
through bottom check valve.
Down Stroke (Reset)
Liquid passes through the upper check valve
as the piston moves downward to bottom of
travel.
Piston pump design considerations
Piston pumps have been used for
many years in water supply and oil
wells with long-term reliability.
Piston pumps are designed to
handle:
• Viscous fluids
• Aggressive solvents
• High dissolved solids (no air
contact)
• Flammable/explosive
environments
• Sloped or horizontal wells
• Depths to 500 feet and beyond
Piston pump strengths and weaknesses
Strengths
• Depths to 500 feet or greater
• Pumps high viscosity and high temperature liquids
• Can pump from slant and horizontal wells with minimal submergence
• Key components can be serviced at well head without pulling piping
• No air contact with pumped liquid reduces potential for clogged piping
• Minimal foaming of pumped liquids
Weaknesses
• Flow rates (5+ GPM) lower than electric or air-powered pumps
• Higher initial cost than air-powered pumps and most electric pumps
• Potentially higher O&M costs than air-powered pumps in abrasive
solids
Landfill Pump Selection Factors
1 Flow rates
7 Silt and solids
2 Pump lift
8 Corrosives
3 Well diameter
9 Pumped liquid temperatures
4 Minimum liquid column
10 Gases and foams
5 Viscosity greater
than water
11 Discharge line restrictions
6 Explosive/flammable
environment
12 Air contact
Flow rate
How Much Do You Need?
Designing for high instantaneous flow rates adds to the total system
installation and service costs:
• Higher flow pumps cost more and are heavier to install and service.
• Larger pumps require heavier-duty electric power lines and controls.
• Higher instantaneous flow rates require larger diameter discharge
piping, which costs more and won’t “scour” if flow rates are routinely
lower.
• Pumping too fast can pull solids into leachate riser and dewater the
leachate collection piping, increasing clogging.
Flow rate – how much is too much?
Average Flow
Rate = 3.5 GPM
South Florida Landfill Site – Average Daily Leachate Flow
Pump lift
• Electric submersible pumps: 500 feet or greater for 4-inch wells
• Air-powered automatic pumps: 250 feet standard; 400 feet max
• Piston pumps: up to 500 feet
Air-Powered
Automatic Pumps
Electric and
Piston Pumps
Well diameter
Electric submersible pumps and piston pumps typically 4-inch risers and larger.
Air-powered automatic pumps are capable of fitting 2inch risers at lower flow rates. Higher-flow pumps are
available for 3-inch risers and larger.
If deformed or damaged risers are suspected, run a
diameter test plug down each well before designing the
pumping system!
Minimum liquid column
Affects motor cooling, solids intake, air intake and
cavitation, and pump mechanism activation level
Electric
Piston
Air-Powered
Viscosity
Viscosity is measured in units called centipoise.
water
centipoise value = 1
10W30 oil
centipoise value = 100
90W oil
centipoise value = 300
honey
centipoise value = 3000
toothpaste
centipoise value = 5000
grease
centipoise value = 9000
Viscosity
Electric submersible pumps are designed for pumping water; any
higher viscosity can damage impellers (cavitation) and burn out motor.
Air-powered automatic pumps are designed to handle higher viscosity
liquids without adverse effects. Drive air pushing liquid naturally
compensates for the greater resistance to flow of thicker fluids. Very high
viscosities will reduce flow rates (slower filling).
Piston Pumps have the best capability for pumping high viscosity fluids
due to suction at intake. Piston pumps are commonly used for pumping
materials as thick as grease, toothpaste and concrete.
Explosive/flammable environment
Safety regulations, such as National Electric Code and ATEX standards in
the European Union affect the types of pumps that can be used at landfills
in potentially explosive environments.
• Electric pumps have power supply, control box, wiring and motor that
pose potential hazards. Full explosion protection adds thousands of
dollars to each pump.
• Air-powered pumps are inherently safer due to their lack of an ignition
source. Air-powered pumps are the only pumps that are ATEX-certified
for use in explosive environments at landfills.
• Piston pumps using air drivers (not electric drivers) also inherently
safer than electric pumps, but are not yet ATEX-certified.
Silt and solids
• Electric pumps are specifically
designed to pump "clear liquids”; a
50-ppm solids concentration limit is
typical. Impellers, seals, shaft and
bearings are all prone to solids
damage, can result in pump failure.
• Air-powered pumps and piston
pumps have much higher solids
handling capability. Wear is minimal
compared to electric pumps. Air
pumps often require only cleaning;
piston pumps can require repair if
solids are extremely abrasive.
Corrosives
Corrosion in landfill pumps is often the result of elevated chloride levels
(1,000 ppm), especially at temperatures > 75° F, and low pH, which can
be as low as 1.5 in landfill leachate.
• Electric pumps are made of metal, with few options for upgrade. Even
slight corrosion of the motor shaft can erode the seal and lead to motor
failure.
• Air-powered automatic pumps are available in a range of corrosionresistant materials. The pump mechanism is not adversely affected by
moderate corrosion.
• Piston pumps have some metallic
components, but are available in a
corrosion-resistant materials. Shaft seals
at the wellhead are subject to wear if the
shaft surface is corroded.
Pumped liquid temperatures
Landfill leachate and condensate temperatures are typically 100-160° F,
and can be as high 200° F.
Electric pumps use the pumped liquid to cool the motor to prevent
damage. Standard motors are commonly rated for 86°-104° F maximum,
with special motors rated to 140°-170° F maximum. Frequent motor
starts create more heat in the motor than continuous operation. Failure to
meet these operating conditions can void the manufacturers warranty.
Air pumps and piston pumps can operate at higher temperatures since
no cooling is needed. Down-well temperatures over 212° F have been
successfully handled with these pumps.
Gases and foams
• Electric pumps can be damaged due to cavitation; manufacturers
specify that no air or gases be present in the liquid. Foam in leachate
risers can falsely trigger level control sensors to activate the pump,
resulting in failure due to overheating if it runs dry.
• Air-powered automatic and piston
pumps are not damaged by the
presence of foam and gases, but
pump output may be reduced.
Impeller pitting caused by cavitation
Discharge line restriction
Caused by:
• Solids deposition in the piping due to silt build-up and/or precipitation of
dissolved solids.
• Crimping due to shifting of the fill or heavy equipment operation.
• Discharge valve closure due to operator error or vandalism.
Electric pumps can suffer impeller wear from cavitation or motor failure
due to overheating if the discharge lines are blocked, the reason their
manufacturers warn against flow shutoff.
Air-powered automatic and piston pumps are not damaged by
discharge line blockage. The pumps simply slow down or stop, then
returns to full output capacity when the discharge line restriction is
removed.
Air contact
Air contact with leachate may contribute to hardened mineral deposits
and bacterial growth in piping. Preventing the formation of such deposits
is an evolving science. In some cases, pumps with air-to-liquid contact
could add to the problem.
• Electric pumps and piston pumps may have an advantage at sites
with a history of developing solids deposits since there is no air contact
with the pumped liquid.
• Air-powered pumps rely on direct air-to-liquid contact, which could
contribute to solids deposition. Maintaining a higher scouring velocity
through piping sizing could help to minimize this concern.
Leachate piping blockage caused by
solids deposits
Pump Selection Factor
Electric
Air Pump
Piston
1
Flow rate capability, GPM
200+
13-15
5-7
2
Pump lift capability, feet
500+
250-400
500
3
Well diameter, minimum
4”
2”
4”
4
Minimum liquid column, inches
120”
12”
6”
5
Viscosity greater than water



6
Explosive/flammable environment use



7
Silt and solids handling capability



8
Corrosives in pumped liquid



9
Pumped liquid temperatures over 140°F



10 Gases and foams in pumped liquid



11 Damage if discharge line becoming restricted



12 Air/liquid contact inside pump



KEY:
Good
Acceptable
Not Recommended
Winnebago County Landfill
Winnebago County Landfill Background
• Closed 110 acre municipal/industrial waste landfill in
Wisconsin
• Gas collection system installed in 1990
• 34 electric submersible pumps installed in dual-use
leachate/gas collection wells
Winnebago County Experience
with Electric Submersible Pumps
• In less than one year, 100% pump failure due to
corrosion, clogging, overheating and level control
malfunction due to leachate foaming
• High maintenance and replacement costs forced
County to seek alternatives
• In 1995, after a comparison study of various pumps,
the County replaced electric pumps with air-powered
automatic pumps
Winnebago County Results with
Air-Powered Automatic Pumps
• Automatic pneumatic pumps dramatically reduced
leachate levels in wells, by 62%
• Greatly improved pumping system reliability and
maintenance record, achieved through longer pump
life and simplicity of design
Winnebago County Methane Production
Improvements with Air-Powered Pumps
• Methane gas production flow rates increased 20-25%,
increasing electricity generation
• Less moisture in methane gas
• Methane gas system compressor station reliability
increased due to prevention of flooding in dropout
tanks
• Improved flow and drier gas has reduced downtime of
electric generation facility
Puente Hills Landfill
Los Angeles
Puente Hills Landfill
Los Angeles County Sanitation District
• Largest operating landfill in US
- 1,500 acres
- Over 3.5 million tons per year
- Gas collection system has over 30 miles of collection pipe
• Extreme leachate conditions of high temperature, well
depth and corrosivity
• Flow rates starting around 8 gpm, tapering to < 1 gpm
• Over 100 stainless steel automatic air-powered leachate
pumps installed in 2003
Puente Hills Landfill Experience with
Automatic Pneumatic Pumps
• Performed very well in most wells, averaging 10+
gallons each per day with little maintenance
• Some wells presented problems with corrosion and
mineral deposits (encrustation) at liquid surface
• Piston pumps were purchased for problem wells, to
avoid air contact and ease removal through crust in
riser at liquid surface
Liquid Surface Encrustation
Puente Hills Landfill
Liquid Surface Crust
Conventional Pump
Piston Pump
Puente Hills Landfill Pump Application
Lessons Learned
• Fluid chemistry and well conditions need to be
considered to select the best pump for each well.
• Pilot tests of pumps are advisable for sites without
extensive experience.
• Supplier’s ability to provide a range of system
designs, materials and technical support are key to
a successful project.
Summary
• Landfill liquids are challenging to pumps – conventional
water well pumps often can’t handle these applications.
• Air driven pumps are simple by design, resulting in better
service life and routine operation than electric pumps in
many landfill pumping applications.
• Air driven and mechanical pumps are safer in wells with
potentially explosive landfill gas.
• Knowledge of liquid chemistry and care in pumping system
design will greatly enhance overall system reliability.
• Some ongoing maintenance is expected for any landfill
liquids pumping system, regardless of pump design.
Submersible
Pump
Selection
Guide
QED’s latest Web tool lets
you determine the best type
of submersible pump for
your application based on
flow rate, lift, temperature,
solids handling, and nine
other parameters. We’ll tell
you if an air-powered pump
will work best for you, or if a
traditional electric pump is a
better choice.
www.submersiblepumpguide.com
Questions?
David Kaminski
QED Environmental Systems, Inc.
Tel: 800-366-7610
E-mail: [email protected]
WEB:
www.qedenv.com
www.submersiblepumpguide.com