Linking
an annex melter to the existing
melters' pollution control
system takes pressure off
production demands, and saves
$62,000 over an independent
air filtration system.
Pressure balance is key
to a turnkey expansion
of the exhaust air filtration
ductwork at the Mason,
OH, facility of a regional
die caster. When growing
sales of cast aluminum
wheels to the Big Three
automakers called for production
in excess of 5000 pieces
per day, the caster designed
an annex to the 275,000
sq. ft. facility, to make
room for a third production
melt furnace. To marry
the new melter to the pollution
control system of the original
two, the caster turned
to process ventilation
specialist Kirk & Blum,
the company that had designed,
built and installed the
original ductwork system,
in addition to the plant's
graphite dust filtration
system and 23 rooftop stacks,
when the facility was built
in 1990.
"The challenge was
rebalancing the air pressure," says
the client's project engineer. "Because
the new melter is located
so far from the other two,
we hd to double the length
of ductwork just to add
it to the system. However,
all three melters still
have to see identical static
pressure for the system
to work despite the large
pressure drop across the
new ductwork sections."
The original plan for
the annex had assumed that
such a rebalance was impossible.
The company first asked
Kirk & Blum to quote
the price for an entirely
new and independent system
of ductwork, collector
and fan supporting only
the new melter. Allowing
the existing system to
support the annex instead
saved over $61,000.
Duct
resizing
The new melter is located
130 ft. from the closest
of the original two melters,
which are spaced 60 ft.
apart. On the opposite
side of the original melters,
another 120 ft. of ductwork
connects the melters to
a baghouse, and to the
fan that all of the melters
share.
The friction across the
130 ft. of ducting to the
new melter added 2.2" w.g.
of pressure to the system
pressure which required
Kirk & Blum to increase
the speed and horsepower
of the fan to compensate.
However, because this change
increased negative static
pressure throughout the
system, thereby increasing
air flow, Kirk & Blum
also had to retrofit modifications
to the original ductwork
to ensure continued optimal
operation of the existing
melters.
Static pressure is proportional
to flow cross-section the
smaller the cross-section,
the higher the pressure.
To return each of the melter
connections to its proper
operating static pressure,
Kirk & Blum designed
orifice plates to decrease
the cross-sectional area
of the ducts. Its engineers
analyzed the air flow throughout
the system, then resized
each connection point cross-section
to an accuracy of ñ1
sq. in.
Cleaning
contaminants
Each melter is open to
the system only when it
is being cleaned approximately
three times per melter
per week. Employing a chemical
reactant flux, the cleaning
process gives off smoke,
particulate and fumes.
The ductwork carries all
of this to the baghouse,
which removes the contaminants
from the air stream, sending
them to drums for disposal
per EPA regulations. According
to Beach, air reaches the
baghouse at 180øF,
flowing through it at 17,000
cfm. (The baghouse is also
connected to the plant's
remelt furnace, which is
open even during normal
melting, due to contaminants
liberated when scrap parts
are melted.)
To prevent contaminants
from one melter from accidentally
being vented into another,
Kirk & Blum retrofitted
automatic controls to the
existing melter electronics,
ensuring that no two melters
are ever open to the system
simultaneously. |
