|
MIDLOTHIAN, TEXAS - Fugitive
particulate emissions from
the melt shop at a large
steel mill near Dallas
can run but they can't
evade capture with a new
high-efficiency Fugitive
Emission Filtration (FEF-50)
system from Busch International.
Augmenting the melt shop’s
primary 1.65 million ACFM
baghouse collection systems,
twenty (20) 50,000-CFM
packaged FEF collectors
were added to remove fine,
micron-sized particles
from plant air previously
vented through roof monitors.
Designed by the Busch International
unit of CECO Environmental,
the packaged FEF collectors
enabled the plant to add
controls for 30+% less
than the cost of using
a standard baghouse.
The steel mill , with
1.8 million tons of melting
capacity and 1.9 million
tons of rolling capacity,
primarily produces structural
I-beams and H-beams, and
specialty-bar-quality (SBQ)
products, using 100 percent
recycled steel from scrap.
The plant’s
800,000-ton/year shredder,
the largest in the world,
which can shred an auto
and reduce it to fist-sized
pieces in about 15 seconds,
meets about 40 percent of the recycled steel needs.
The remainder of the plant's scrap requirements is
supplied by outside vendors.
After shredding and melting,
molten steel from two electric
arc furnaces with a combined
capacity of 300-tons is
cooled and shaped by continuous
casters into useable billet
for the rolling process.
One continuous caster feeds
the plant’s workhorse
900,000-ton/year medium section mill, which rolls
the bulk of the facility’s structural products,
while the other two feed the 500,000-ton/year bar
mill and 500,000-ton/year large section mill, where
products up to 24” are rolled.
Dust from the
electric arc furnaces is collected by a three baghouse
system installed in various stages since the plant
was built in 1974. The conventionally designed
baghouses use vertically
mounted fabric filter tubes,
and are capable of capturing
from 400,000 to 650,000
ACFM each. Two of the baghouses
combine to pull the EAF
emissions directly from canopy hoods over the furnaces,
while the third provides direct evacuation.
To supplement
the primary collection
system, the steel manufacturer
had committed to the State
to capture the permitted
fugitive emissions that
were generated by natural
draft convection through
the shop. “The
process of controlling,
and ultimately eliminating,
fugitive emissions from
the shop has always been
a goal for the Company,” said
the company's senior manager – plant
engineering at the plant.
Finding the
proper equipment to handle
the light particulate loading
of the fugitive emissions,
which are typically less than 0.02 grains per ACFM
of primarily micron sized particles, was a requisite
for the project. Several options were explored,
before the senior manager-engineer
suggested that Busch collection units be examined,
based on his experience with a former employer. “We
contacted Busch, ran a test against a cartridge
filter, and decided that the FEF system was a better
choice because of its modular design and suitability
for our application. Another advantage was that
the FEF units, including ductwork, support structures
and the collection units, would save us about $2.5
million, compared to adding conventional baghouse
capacity,“ he said.
The FEF-50 system is
a new concept that utilizes horizontally mounted,
high-efficiency polyester fabric filter tubes. “This
system is designed to be run with lighter dust
loadings, compared to the primary collection
system," said
Bill Frank, President, Busch International. "Busch
FEF units deliver long filter life with the lower
dust loading found in fugitive emissions."
Initial
plans called for the FEF-50 system to be installed
on the roof of the 88,000 sq. ft. melt shop,
replacing the existing monitors. "We found
we simply didn’t have enough structural
support and roof area for the building to accommodate
this,” Frank
noted.
The most cost-effective
alternative was to build
structural steel platforms
at roof height next to
the melt shop, above the
plant’s
scrap yard and scrap cranes. Due to the FEF-50
systems modularity, two banks of ten (10)
50,000-cfm units could
be mounted on platforms
on either side of the building. “We
put the FEF units up, replaced the roof monitors
with collection boxes, and connected the
two with ductwork,” said
Frank, “It
has proved an excellent solution.”
Like
a standard dust collector, the FEF-50 system
uses a pulse-jet cleaning cycle to clear
collected material from
the filters, based on increased
differential pressure. The plant has developed
a creative method of eliminating disposal
costs for the collected
dust. “The
cleaning cycle dumps dust into a hopper,
where it’s
collected with screw conveyors and deposited
into super sacks. Then we recycle the sacks
into the melt furnaces. Though the fugitive
dust is very fine, it still contains iron
units and metallic elements.
So we place the super sacks
back into the charge of
scrap going into the furnaces,” the
client reports .
The melt shop’s
FEF-50 system was jointly
designed by the Busch International
and kbd/TECHNIC units of
CECO Environmental, Frank
noted. Installation spanned
about 18 months, from placing
of the order with Busch
in January 2002 to start-up
in July 2003.
“Since
we installed the new system,
we've had no major operational
issues,” Balbo said.
We're especially pleased,
too, that the solution
was significantly less
costly than expanding our
conventional baghouse systems.
|
