After a truckload of tires is added to the shredding system, each tire moves one at a time over a conveyor. Alan Rowley watches as tires move through
the grinding process. By this stage, the tires start to resemble the chips that will eventually help fuel Midlothian’s cement-making process.
www.martinmarietta.com | January/February 2 2020 The Conveyor 9
alternative fuel,” he says. “That rubber
offers a high heat value. It’s as uniform as
natural gas and, in our kiln system, more
uniform than coal.”
Rowley, who, along with his team, spent
the better part of two years investigating
and then installing the new shredding
system, says Midlothian has traditionally
relied on alternative fuel sources to provide
about 10 percent of its total fuel. With the
new system in place, he and the team hope
to dramatically increase that figure in the
next few years, meaning they can rely far
less on coal.
The change also means Midlothian is consuming
more tires than ever before, a fact
the division’s Director of Environmental
Services Michael Meinen and other environmental
professionals truly appreciate.
“While this system is certainly helping us
minimize our dependence on fossil fuels,
it’s also helping the Texas Commission on
Environmental Quality (TCEQ),” Meinen
says. “Managing the tires discarded across
the state is a challenge for the TCEQ, so
they’re constantly seeking safe and efficient
recycling methods.”
According to Rowley’s research, more
than 16 million of those 290 million
annually discarded tires are found in Texas.
With the new shredding system in place,
Midlothian is now positioned to use about
16,000 of those tires each day. Combine
that figure with the shredded tires the site
already purchases separately and the
impact expands greatly; Rowley said the
plant set a record in August when it
consumed 45,000 tires in a single day.
Run those numbers across an entire year
and they become astounding. On an
annual basis, Martin Marietta can now
take millions of discarded tires out of the
environment while drastically reducing the
potential for dangerous fires and the risks
for mosquito-borne illnesses.
Environmental impact aside, the system
is also great for business.
An engineering marvel, the shredding
system takes in whole tires by the truckload,
then runs them to the kiln in a
methodical and controlled manner.
Tires are moved onto a conveyor one at a
time and then pushed through a number of
grinders that shred them into very small
chips. About 15 percent of an average road
tire’s weight comes from the steel lining
beneath the rubber, so the shredding
system involves a series of magnets to
remove that lining.
By the time a tire has passed through
the entire shredding system, the rubber –
now resembling very fine chips – is moved
off to the kiln for use in the
cement-making process. The
metal is collected into a large
bin and later sold for scrap
by the ton.
Rowley says the system
can handle tires of any size
– from large ones like those
used on tractor-trailers to the
small ones you might find on
a standard lawnmower.
While the system works
smoothly now, Del Valle
Favela says its adoption was
not without its challenges.
“There’s nothing like this
anywhere else, so there were growing
pains,” he says. “We had to fine-tune the
system. We had to figure out how to make it
grab one tire at a time at just the right rate.
The grinders generate heat, so we had to
figure out how to prevent fires.”
With a bit of experimentation, the team
was able to quickly conquer the shredding
system’s most significant challenges.
Midlothian then added four new employees,
creating a team of nine – eight operators
and one mechanic – to run the system
nonstop. Now, the plant has an environmentally
friendly fuel source that also helps
maintain high operating standards and
efficiencies.
“It’s helping us control costs while driving
profits,” Del Valle Favela says. “Overall, it’s
been a spectacular investment.” ▼
Once removed from the tires, steel wiring is
collected for sale as scrap metal. This sale is
helping decrease the site’s cost per ton.
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