Instructional Manual For Clarification Of Startup In Source Categories Affected By New Source Performance Standards - U.s. Environmental Protection Agency - 1979 Page 143
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146 I
current to the limestone, exhausting out the feed end of the kiln.
At the
lower end of the kiln, the quicklime is discharged to a cooling system.
Systems to preheat the limestone prior to introduction to the kiln
are becoming widely used to conserve fuel consumption.
Kilns operated with
preheaters are shorter in length, requiring 60' to 70 percent less space than
kilns without them.
Particulate matter emitted from lime rotary kilns are
usually controlled by cyclones, baghouses, electrostatic precipitators, water
scrubbers, or gravel bed filters.
Hydration
The hydration process is initiated by blending quicklime with water
ina pug mill premixer.
After mixing, the
lime-wa~er
slurry
pa~ses
to an agi-
tator-hydrator.
An exothermic chemical reaction takes place in the hydrator
producing steam, which is vented to the atmosphere along with any air that enters
the hydrator through the charging port.
The most common air pollution control
methods used to treat hydrator emissions are water sprays in the hydrator ex-
haust stack or wet scrubbers.
Pre-Startup Operations
The rotary kiln is the heart of a lime manufacturing operation; all other
unit operations are based o,n the performance of the kiln.
As a result, ancillary
process operations such as crushing, screening, milling, and material and fuel
storage and conveying must be thoroughly tested under operating conditions prior
to the introduction of limestone into the kiln.
Electrical systems and mechani-
cal I!quipment are checked out initially on an individual basis and then as
integral parts of the process operation.
Instrumentation and control panels
are also debugged during
thi~
phase.
Likewise, mechanical equipment are tested
to assure that they are properly installed and aligned, and that they are rota-
ting freely and in the right direction.
During pre-startup, conveyor speeds
are adjusted, feeder rates are monitored and transfer lines are checked for
free passage.
Equipment shakedown of unit operations may occur simultaneously
or in some logical sequence.
The pre-startup shakedown period may last from
one to three months.
In regards to the rotary kiln,. once it has been erected, even before it
has been bolted down, various tests are conducted to check its alignment and
rotation.
Upon paasing inspection, the kiln is then secured to the support
piers and again checked
fo~
alignment and rotation.
A third check is made when
heat is first applied to the kiln.
During this phase, the kiln may stretch
15 to 20 centimeters (6 to 8 inches) in length and 0.6 centimeters (0.25 inches)
in diameter.
One of the most important pre-startup operations is the "seasoning" or
drying out of the kiln.
New refractory brick lining the inner wall of the kiln
contains residual amounts of water which must be driven out of the bricks be-
fore limestone can be fed to the kiln.
The.dryingou
a
process is slow, requir-
ing a gradual warming of the bricks, up to 149 to 204 C (300 to 400
0
F), to
prevent cracking and loosening.
Supplemental gas or oil-fired burners are
131
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