Instructional Manual For Clarification Of Startup In Source Categories Affected By New Source Performance Standards - U.s. Environmental Protection Agency - 1979 Page 123
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146 is then loaded with a 0.2 m
3
(55 gallon) drum of coke (the conductive material).
The electrode cylinder and content is lowered into the coke drum bearing down
with electric power.
The system electrodes are energized with low voltage,
wherein heat is created by electrical resistance from the coke.
This heat
bakes the carbon paste in the upper portion of the cylinder.
Voltage is in-
creased and more coke is added, thus increasing the furnace temperature and
baking more of the carbon mixture in the column.
The bake-in will continue
until about 4.6 meters (15 feet) of carbon mixture in the column is baked to
a hard carbon body.
As the pre-baked electrode is consumed
(-2.5 cm or 1 in.
per hr), the self-baked electrode will slip down bearing on the coke.
More
carbon mixture would then be added to the column to replace the consumed por-
tion of the electrode.
Once the bake-in is completed, pre-baked electrodes
are not used again.
Pre-baked electrodes are only used during bake-in
(startup).
If pre-baked electrodes are not used during bake-in, the entire
electrode column is filled with carbon paste and baked with an
au~iliary
fuel
(oil or gas).
The entire bake-in takes 2 weeks time while curing the furnace
takes another 2 to 3 weeks, and heating the furnace to operating temperatures
takes about I to 2 weeks.
During the bake-in, curing, and heatup, the furnace
will normally be shutdown 5 to 10 times for repair of malfunctions, defects
and especially to tighten the bus bar.
Shutdown and startup will only take
a few hours unless there is a major malfunction.
The total pre-startup opera-
tion may consume a 5 to 7 week period.
Startup Operations
Up to this time, no metal has been introduced into the furnace.
Upon
reaching operating temperatures of 2760 to 33l6°C (5000 to 6000
0
F), metal is
slowly introduced to the furnace.
The furnace is stabilized and then more
charge is added.
The technique will continue until the furnace has attained
rated capacity.
If everything operates smoothly, the furnace should reach
maximum production in six months.
However, in ferroalloy production, there
are numerous units involved where many problems can develop.
Experience has
shown that most plants take 6 to 12 months to reach maximum production.
Two
major problems are the integration of all units and the training of operators.
If any units, systems or operators are not running at rated capacity, the
maximum production rate cannot be reached.
Most furnaces operate at 50 percent
maximum production the first year and in succeeding years production will
increase to about 90 percent.
The first year of operation is usually plagued
with numerous malfunctions and breakdowns.
The official startup date for an
electric submerged arc furnace should begin when metal is first introduced
into the furnace.
111
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