Air Down Under: Controlling the costs of compressed air in underground mining
Written by Marc Carrière
Compressed
air can comprise up to 20 percent of the costs of underground mining,
according to the Ontario Mining Association (OMA), and 20 to 40 percent
of energy costs at mines can be attributed to compressed air systems.
Given that up to 70 percent of that air is wasted through leaks, the
problem of leaks in compressed air lines is one of the most costly and
inefficient draws on the bottom line.
The numbers are staggering. The OMA’s compressed air leak management
program report, “Implementing a Sustainable Compressed Air Leak
Program,” demonstrates just how costly leaks can be: a single
1/2-inch-diameter leak, assuming energy costs of $0.10/kWh, can total
to $12,820 throughout the course of a year for a one-shift operation
and as much as $47,850 for a three-shift operation. Even the tiniest of
leaks can add up: a single 1/16-inch-diameter leak can cost up to $200
over a year for a one-shift operation and up to $750 for a three-shift
operation.
In a typical mining operation, leaks in compressed air lines can number
into the hundreds, resulting in wasted energy costs upwards of $100,000
a year. The costs alone should be enough to consider a leak management
program, but leaks also create other problems. Fluctuating system
pressure can lead to inconsistent performance of the tools and
equipment that operate on compressed air. Operation time may need to be
increased to make up for the lower pressure, which can increase
maintenance costs and reduce the service life of compressors due to
excess load.
Problem Areas
Leaks can occur at any point in a compressed air system and are blamed
on a number of factors. Through regular mining activities, compressed
air piping is exposed to vibration, impact and harsh materials, all of
which could lead to leaks. Compressed air lines in the mining industry
are typically joined using grooved mechanical piping due to the joining
method’s ease of installation and maintenance, strength and ability to
quickly adapt to changing mine geography. If the joints of a grooved
system aren’t properly assembled, however, the gasket contained within
the coupling housings can be a leak source. During its study, the OMA
determined that pipe couplings are the most common source of leaks;
approximately 60 to 80 percent of the air loss can be attributed to
couplings.
Fortunately, the solution isn’t as drastic as replacing grooved piping
systems, which mines rely upon to decrease installation and maintenance
downtime and reduce total installed costs. The two primary causes of
couplings as a leak source, pinched gaskets and incompatible gasket
material, are easily fixed.
During coupling installation, a gasket can pinch, creating a leak path,
if it’s not properly lubricated. Lubricating a gasket takes only a few
seconds, but this step is often skipped to save time. If coupling
gaskets are not pre-lubricated, personnel should take the time to
lubricate the gaskets prior to installation, and managers should
educate pipe installers as to the importance of doing so and the
economic ramifications that result from leaks.
Mine maintenance personnel will try just about anything to save time,
so adding a step to the pipe installation process may not be a welcomed
idea. Installation-ready couplings, an alternative to traditional
couplings, require fewer installation steps and decrease installation
time compared to traditional couplings; they also reduce the chances of
pinching a gasket upon assembly. Installation-ready couplings do not
require disassembly prior to installation. The pre-assembled coupling
is simply “stabbed” onto the pipe ends, and the bolts are tightened,
like typical couplings, until the housing bolt pads meet
metal-to-metal. Installation-ready couplings are offered in flexible
and rigid styles in sizes up to 8 inches/200 millimeters.
The benefit of installation-ready couplings is twofold. First, they can
reduce pinched gaskets during installation because the coupling is kept
assembled and installed as a single unit, rather than piece-by-piece.
Second, they can be installed in as little as half the time it would
take to install traditional pipe couplings. As a result,
installation-ready couplings meet owners’ goal to reduce costs and
miners’ goal to save time.
Another cause of leaks at pipe couplings is gasket deterioration, which
can occur when the gasket material is incompatible with, and not
approved for the piping service. For example, when grade “E,” or EPDM,
gaskets are used on compressed air lines, oil vapors present in the
system can degrade the compound, eventually leading to a leak. EPDM is
a commonly specified gasket grade, and is suitable for water services,
but using this grade on air services can be problematic.
Oil separating filters are generally not used on compressed air
systems, so the lines may carry oil vapors. As a result, grade “T,” or
nitrile, gaskets should be used. This gasket grade is designed to stand
up to air with oil vapors and will not degrade with exposure over time.
Nitrile gaskets should not be used on water services, however, so mines
will need to use two types of gaskets: EPDM for water services and
nitrile for air services.
Replacing EPDM gaskets with nitrile gaskets on compressed air lines is
not a quick maintenance procedure, but the cost savings that can be
achieved through this method is significant. The OMA suggests
conducting gasket replacement during maintenance to repair existing
gasket leaks, and during installation of new compressed air systems.
Study Outcome
Three mines participated in the OMA’s air leak management project as
pilot sites. The mines saw almost immediate results in energy savings.
In fact, two of the mines saved about $100,000 in annual operating
costs just by fixing major air leaks. The project report, which
includes lessons learned and best practices, is a must-read for every
mine.
Fixing leaks attributed to gaskets within pipe couplings will not solve
all challenges involving compressed air systems. After all, leaks can
occur at multiple points along the line, and a big-picture leak
management program is necessary to ensure long-term commitment to
locating and repairing leaks. Such a plan, according to the OMA, should
include recognition of the role of people and leadership, uses of
equipment and instrumentation, and the development of new procedures
and processes.
Nevertheless, proper selection and installation of pipe couplings play
a major role in reducing downtime associated with leaks. Repairing
leaks can reduce air loss to less than 10 percent of the mine’s
compressed air output, resulting in immediate and significant cost
savings.
Marc Carrière is the global mining market manager with Victaulic, a
producer of mechanical pipe joining systems. For more information,
visit www.victaulic.com.
Compressed
air can comprise up to 20 percent of the costs of underground mining,
according to the Ontario Mining Association (OMA), and 20 to 40 percent
of energy costs at mines can be attributed to compressed air systems.
Given that up to 70 percent of that air is wasted through leaks, the
problem of leaks in compressed air lines is one of the most costly and
inefficient draws on the bottom line.
Problem Areas
