Instructional Manual For Clarification Of Startup In Source Categories Affected By New Source Performance Standards - U.s. Environmental Protection Agency - 1979 Page 121
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146 Seventy-five percent of all ferroalloys are produced in electric smelting fur-
naces, of which electric submerged-arc open type is the oldest, simplest and
most widely used.
The alloys are made in the electric furnaces by reduction
of suitable oxides.
For example, in the production of ferrochromium, the charge
may consist Of chrome ore, limestone, quartz coal, wood chips, and scrap iron.
The production of ferroalloy requires a number of steps from materials handling
to smelting to shipment.
Figure 24, illustrates a schematic diagram of the
system involved.
Experts in the electric submerged arc furnace industry indicated that there
are no new plants presently under construction and that there are none planned
for the next 5 to
10
years.
Pre-Startup Operations
The pre-startup operation of a ferroalloy facility involves the coordina-
tion of numerous systems.
Each unit must undergo its own pre-startup checks and
startup procedures before it can be integrated with the rest of the system.
Very often minor malfunctions and defects in units are. the primary reason for
delays in meeting the startup and maximum production dates.
Some of the units
which may have problems are crushers, scales, feeders, castings and pollution
control units .. At this time in the pre-startup proced.ure, most of the units are
checked-out without a material load.
The primary unit used in the production
of ferroalloy is the electric submerged arc furnace.
The furnace ranges in
size from 6.1 to 12.2 meters (20 to 40 feet) in diameter with a height of
4.6 to 6.1 meters (15 to 20 feet).
The furnace has a 5 cm (2 in.) thick steel
shell and is lined with brick refractory.
Between the refractory brick and
the steel shell is a carbon liner.
Electrical power transmitted through
electrodes bearing down on resistant coke provides the heat for smelting in
the furnace.
Systems and components that are given special attention relative
to the electric furnace pre-startup operations are:
water cooling, water
treatment, roof and wall structures, air pollution controls, electrode
rigging, electrode slipping and backing machanisms, tapping, lattle, crane
movement, and all electrical, mechanical and hydraulic subsystems.
The first major step in pre-startup of an electric submerged arc furnace
depends on the type of electrodes used.
Internationally, there are two types
of electrodes that may be used in producing ferroalloys:
prebaked and
self-baked~
The pre-baked electrode, which is usually manufactured elsewhere, is a hard
rod-shaped baked carbon/silicon body ranging in size from 0.3 to 61 cm (1/8 to
24 in.) in diameter and lengths up to 244 cm (96 inches).
The self-baked
electrode is a pasty mixture of carbon and silicon which is baked into a hard.
rod-shaped carbon body within the electric submerged arc furnace (this report
examines only the self-baked electric submerged arc furnace because they are
primarily used in the United States).
The first pre-startup step is the baking of the pasty carbon-silicon mix-
ture into .a hard, rod-shaped body.
This step is called <bake-in.
The carbon
material is contained in a thin gauge, hollow electrode steel cylinder 15 to
18 meters (50 to 60 feet) in height.
At bake-in, a pre-baked electrode is
inserted Into the cylinder followed by a homogeneous mixture composed of coal,
metAllurgical coke, lampblack, coal tar pitch, and petroleum coke.
The furnace
109
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