Compactors are getting more technologically sophisticated—and landfills are utilizing them profitably.
A key component
in operating a profitable landfill is the compactor, a machine that has not only
added brute force but also a great deal of intelligent design and technological
sophistication in recent years. As you might expect, environmental constraints
have driven the need for landfill operators to optimize the available land that
is set aside for these operations.
The more solid
waste that can be compacted into the land area and airspace reserved for
landfilling, the longer the space can be utilized for its intended purpose.
Inefficient use of the space may mean a drawn-out permitting process and all of
the attendant concerns from neighbors and communities—amid an ever-shrinking
quantity of available land to begin with.
It’s the
constraints of quality land that make the compactor such a key piece of
machinery. A more specialized machine than a dozer with wheels on it, the
compactor is equipped with specially designed wheels that use teeth for
shredding, as well as special power-train and wheel guarding, and a trash blade
and wheel cleaners specifically designed for use in landfills. These machines
are significantly different from construction compactors, which use different
wheels designed for soil tamping, as well as cleaner assemblies suited for wet
soils having smaller grain structures than solid waste. While a soil compactor’s
smaller tamping wheels blend and compact smaller soil-grain structures and mix
them with moisture, a solid waste compactor’s wheels must shred and compact
material whether or not moisture, such as rainwater, is present.
With compaction
such a crucial goal in the solid waste industry, landfill managers are becoming
increasingly knowledgeable about the machine components that maximize it. As the
machines have improved their compaction ability with advancements in teeth
design and more weight, managers are turning their attention to such other
design features of compactors as productivity, safety enhancements, and
maintenance-reducing equipment to increase the profitability of their operations
in general.
Compaction Depends on a
Combination
No single
“magic bullet” exists for maximizing compaction. Density of solid waste results
from a combination of machine components and depends on several variables. These
variables include lift thickness, particle size or reduction of particle size,
moisture, the rate at which trash is dumped in the landfill (the more even the
flow, the better the compaction potential), and compaction effort. Among the
machine components and design attributes that work in unison to compact trash
are the sheer weight of the machine, the concentrated pressure on the wheels,
and the teeth of the wheels, which reduce the particle size, facilitating
compaction.
Incorrect usage
of compactors, such as using them like bulldozers to push waste away from the
point of input up or down steep grades to the fill, can cause accelerated tooth
wear and create uneven thickness in the material surface. Controlled placement
of waste to predetermined depths, keeping compactors operating at minimum slopes
to maximize designed weight distribution to the wheels, maintaining top slopes
that allow weather-related moisture to flow across the top of the fill rather
than pool, and measurement of surface profile after compaction can maximize
density.
The importance
of shredding waste in terms of maximizing waste density is easy to understand.
Fill up a wheelbarrow with pea gravel and it weighs more than if you were to
fill it up with larger rocks, the stacking of which creates large voids between
pieces. The longer the teeth on the wheels maintain their shape, the better and
more consistent reduction will be achieved. The maintenance of the tooth pattern
on the wheels has a major impact on the pounds per square inch (psi) or on the
pounds per linear inch of drum contact area. Smooth wheel surfaces would have
the same effect of a track under a dozer, distributing the compactor’s weight
over a wider area and reducing the pounds per linear inch.
No single
design or pattern of teeth ideally suits every landfill—they must be
site-specific. The height, width, and shape of the teeth can vary according to
the physical properties of trash. Generally, teeth should not be rounded but
should maintain a sharp shape as they wear. Rounded teeth not only lose
shredding ability but also lose their grip, which can cause transmission and
differential problems. Machine manufacturers have addressed slippage with
hydrostatic all-wheel drive, which allows the wheels to turn independently and
is electronically timed. One manufacturer offers no-spin differentials on its
machines.
Another
manufacturer argues that teeth with two distinct styles—one for traction and
compaction, the other for demolition (cutting) and stability—can grind and shred
material faster than a one-piece, single-tip design can. The number of teeth and
their cumulative tip surface area affect the psi on the wheels, and the surface
area must be designed based on the size of the tractor and the type of material.
Repeated contact with the material from different angles provides ideal
compaction.
Key variables
of tooth integrity include shape and hardness. However, fitting the teeth to the
size and weight of the unit is crucial, too. Some customers prefer a smaller
foot design to aid shredding, whereas others value longevity. Because compaction
is site-specific to a large extent, the landfill manager should work closely
with the dealer to specify an optimal tooth pattern.
Michael Franck,
landfill operations manager with The Stanislaus County (CA) Department of
Environmental Resources operates one compactor on a single active 96-acre
landfill. The department recently began using heavy-duty wheel teeth from Caron
Compactor Co. “They’re thicker, heavier, and add more weight to the machine so
we get a better chop,” says Franck. “I know there are a lot of sites that still
do a three-to-one slope, and they’re pushing garbage up a slope, whereas what we
do is work a flat path from the bottom up, so the equipment is always working on
a flat surface. That way, you’re getting more pressure down on the center of the
wheel than you do going up a slope, plus less slippage.”
Tracking tooth
wear is a key maintenance function in a landfill operation, says Jerry Libecki,
disposal site supervisor with the Fresno County (CA) Department of Public Works
and Planning. The county operates seven compactors on two active landfills. “You
have to find your ‘happy spot,’” he says. “It’s easy to tell in the operation.
If you cover your trash with dirt and you’re running scrapers over the trash to
cover it, that scraper operator can definitely tell if the pile is hard enough,
based on what it looks like after he runs over it.”
Some landfills
have recently upgraded their compaction ability by specifying machines with more
sheer weight, among other features. One manufacturer claims that substituting a
120,000-pound, 500-horsepower unit for an 80,000-pound, 340-horsepower machine
with the same wheel and blade design can yield a 15%–20% increase in density.
Some manufacturers, arguing that compaction is more a function of wheel-drum
force than ability of the teeth to shred material, offer narrower, high-density
wheels.
Libecki notes
that the industry has learned a great deal about what maximizes compaction. “I
have seen improved compaction; there’s no doubt about that,” he says. “Eight
years ago, you might have been able to achieve 1,200 pounds per cubic yard.
Today, a lot of places are easily getting 1,800 pounds. One of the important
things when you look at the weight of the machine is if you have a tooth and a
wheel that can handle the weight of the machine, because with the added weight
of the machine comes added stress and wear to the components.”
Matching wheel
to machine is also critical, Libecki adds. “You’re also going to want to make
sure that your wheel has added strength and that it’s also going to work well
with the running gear of the equipment of the wheel,” he says. A wheel that is
too small, Libecki explains, can cause the machine’s underside to contact the
trash, causing maintenance problems. “You really need to make sure, in my
opinion, that you get a wheel that matches the tractor,” he says. “There are a
lot of people who sell wheels and [teeth] who aren’t necessarily manufacturers
of the tractor; you’re going to want to make sure that the add-on matches the
tractor.”
Another
potential problem with wheels occurs when wire or other debris in the trash
wraps around the axles. In recent years, machine manufacturers have addressed
this problem with two design alterations: adding wheel guarding systems or
keeping the area between the inside of the wheels and the compactor frame open
for easy detection and removal of debris.
Most machine
manufacturers install the wheels on their machines very close to the frame and
add cable traps or wire guards to deflect materials from threading tightly
around the axles. Some wheel designs also incorporate either a continuous row of
teeth on the inside wheel edge or additional guards on the inside of the wheels
to reduce material wrapping. Bomag adds two wire cutters per wheel to protect
against wire wraparound and subsequent damage to seals. Occasional maintenance
should still be performed on debris that can work its way into the wheel axles.
Al-jon designs its compactors with the area between the wheels and the frame
open to make debris visible and easy to remove.
One
manufacturer recommends that, if the wheels are located close to the frame and
the axles are not visible, guarding is necessary and the landfill should plan
downtime for periodic removal of the wheels and inspection and removal of
debris. If the wheels are mounted away from the frame and the machine utilizes
hydrostatic drive—and thus is not equipped with turning axles and the area can
be easily inspected and maintained daily—supplemental guarding is not required.
The manufacturer also recommends that the landfill specify warranty coverage for
such components as wheels, axles, or planetaries that may be damaged by
wire.
Several
landfill managers say that they have begun adopting Global Navigation Satellite
System (GNSS) technology for the purpose of further optimizing their compaction.
These systems use a base-station antenna that receives and retransmits satellite
signals via radio transmission to a rover antenna mounted on the compactor. This
process pinpoints the compactor’s location within the landfill area and measures
the elevation and slope of the landfill in a given location. The use of this
technology can help the operator determine, in real time, if the slope or
elevation of a given lift or cell is within specification and allows the
operator to minimize the number of passes necessary to achieve the desired
compaction. GeoLogic Computer Systems, a GNSS hardware and software provider
specializing in the MSW industry, supplies the GNSS antennae, radio units,
in-cab color monitors, and software providing views of cell slope and elevation
throughout the entire site, as well as daily data collection that can be used in
such reports as density monitoring, cost tracking, and work analysis.
Bill Rabbia,
deputy executive director of the Oneida-Herkimer Solid Waste Authority in Utica,
NY, notes that, since it was adopted in late 2006, the authority’s GNSS is being
used as an important managerial information system for its 23-acre landfill that
took 12 years and $12 million to site. “We understand the value of the
airspace—that’s for certain,” Rabbia says. “The very reason was that we were
using the airspace as efficiently as possible. Even considering the cost of the
system, it was a small investment to ensure that we were using the airspace
consistently.”
The authority
has mounted an antenna onto the cab of one of its two compactors at the
landfill. The operator can view elevation and slope from inside the cab while
working and a view of the entire landfill is also available on a computer inside
the office. “The operator inputs information if he wants to spread the waste in
1- or 2-foot lifts. It feeds the information back to them on whether that waste
continues to be compacted, so that if you’re driving over a concrete block,
you’re not going to waste fuel—you’re only going to drive over it once,” Rabbia
says. “There’s also a screen where they can see where they are in relation to
the liner and final cap—that comes in awfully handy when you’re filling to a
final slope.
“On a final
exterior slope, you can make sure you pack that to a full waste limit and pack
it as densely as possible so that you have as little settlement after the fact
as possible. On a lot of those landfills, the outer slope is the tough part.
This is to assist the operator so that you don’t have to peel your intermediate
cover off later and add more waste; you really try to maximize the density of
waste on those outer slopes. We can also look at the computers at our office and
read in real time what the compactor is doing. It tracks a variety of data,
whether it’s hours of idle time per day or hours of run time, so you can
fine-tune your operations.”
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| Photo: Caterpillar |
| Tooth designs and patterns must be site-specific, according to landfill. |
The authority
took location data from the as-built landfill survey and had a three-dimensional
model of the site developed in the GNSS. “In New York state, it’s a permit
requirement that you record locations of any asbestos waste disposed of, so we
use the [GNSS] when we dig an asbestos trench,” he says. “And on a daily basis,
we also need to record where we’re depositing waste in a particular cell. You
can use your coordinates in your [GNSS] for that—there are a bunch of uses
besides the compaction. We’ve had cases where law enforcement has wanted to look
through waste from a particular date, so it’s helpful in that regard. Another
thing is whenever we put in gas-collector piping, the location can be entered
into the system so the operators know to avoid a particular place when we put
asbestos there.”
“Not only can
the operator see, but supervisors can see when you’re wasting your fuel by going
over the same area more times than necessary,” points out Braulio Welch,
mechanic supervisor in the Brevard County (FL) Solid Waste Department, which
operates a single 180-acre landfill and four compactors among its three
facilities. “I think it’s a good advancement in that regard.” Adds Libecki, “It
measures compaction, and it also tells us when we’re not going to get more
compaction out of a pass. You might find that you’re on a lift only three or
four times instead of five.”
Uptime and Productivity
When discussing
machine productivity, landfill managers say they value a compactor that stays in
service in the first place. “We count productivity in terms of uptime versus
downtime,” says Welch. “Very seldom does it happen, but you have a cooling
system that is integrated where it cools the oils and fluids that flow to the
different coolers. If you pick up a lot of debris in front of the coolers, it
prevents the air from flowing, and that is what creates the overheating.
The
second issue we used to battle was wire wrapping on the wheels. Manufacturers
have made great strides in [preventing] wire wrapping. It had gotten to the
point to where it was causing damage to the seals or the drive train, causing
the machine to be down for a lengthy period of time.”
“You want
somebody who’s going to support that product,” Libecki adds. “You can have
different variations of compactors, but it’s almost a feature to consider the
support you’re going to have for the machine. You want some kind of response
time to have a mechanic to come out and diagnose an issue. Twenty-four hours is
a pretty good turnaround time, and you’re going to want a turnaround time on a
repair. We ask for three days.”
Operator
comfort and safety are also major factors in productivity, managers say. Welch
notes that the operators ride higher in the cabs on Brevard County’s newer
compactors and the air-filtration system keeps contaminants out of the cab. “Now
the operator doesn’t have to worry too much about the air itself and doesn’t
have to open a window in order to create an unsafe situation.” They previously
had steering wheels, and now they are using joysticks, which means that now they
have even more space in the cab for the operator’s comfort. “We also use
air-ride seats which, again, contribute to the operator’s comfort because the
operator is not sitting on a hard surface or springs that don’t cushion the ride
as well,” Welch says.
Franck notes
that driver comfort has come a long way in recent years. “It’s like going from a
Volkswagen to a Cadillac,” he says of today’s cabs, compared with ones of years
past. “It seems like it’s designed for the operator now,” he says, listing the
option of using a steering wheel or a joystick, shift-on-the-fly transmissions,
more comfortable seating, air conditioning, and windshield wipers as key
upgrades for the operator.
Safety and Maintenance
While uptime is
crucial to compactors, the machines have also grown more intelligent in recent
years, reducing maintenance time and keeping the machines out in the field.
Electronic systems that monitor such operating conditions as lubricant levels
and engine temperatures are often equipped with automatic shutdown capabilities
that warn of problems before they lead to catastrophes.
Libecki says
that his department has invested in two optional features to improve safety.
“We’ve installed cameras so that operators can see better what’s behind the
tractor in case you have a flagger or customer behind the tractor,” says
Libecki. “An added safety feature we have is a fire-suppression system. At our
regional site, a typical compactor is going to switch from forward to reverse on
a three-to-one slope probably 700 to 800 times a day. When that tractor’s moving
all day long, fibers and materials from the trash are going to get around the
engine compartment and eventually, if you don’t keep that area clean, you’re
going to have a fire. I would say that in a year we’ll set off those systems
five to seven times. They have a push-button system inside the cab in case a
fire starts on the unit, and there are also automatic switches with sensors in
the critical areas of the tractor so that if they hit a certain temperature it
automatically puts the fire out. It’s a comfort factor for the operator to know
it’s there.”
An
automatic lubrication system is another feature that landfill managers might
consider adding to their machines. “We normally specify a central lubrication
system for the wear items that do require it,” says Welch. “You obviously have
areas where it’s not feasible to put a lubrication line, because no matter how
much you try to guard it there will be a piece of debris that will cut the line
and defeat the purpose. At the front of the machine, where the blade is, some
manufacturers have gone with ‘lube-for-life bushings or connections at the end
of the cylinders.” Libecki, on the other hand, prefers to have the operator or
maintenance staff routinely check lubrication points manually, because this
practice is thought to keep these individuals vigilant in regard to other
operating conditions on their machines.