STEEL + TECHNOLOGY 04/2019 EXTRACT

STEEL TECHNOLOGY | 55
high productivity leading to low cost production.
• simple and reliable equipment,
• focus on consistency of efficiency,
• the “human factor”,
• continuous improvement and investment
in people,
• environmentally friendly production,
• optimum logistics and material flow,
• clear and integrated investment program.
Beside continuous investment in people
and major investment steps in new technology,
it is crucial for any steel plant to
continuously find ways to increase efficiency,
reliability and maintainability of
existing technology and keeping an eye on
the safety improvement overall. For decades,
BSE and BSW have been following
this strategy, having developed various
innovative solutions all around the electric
arc furnace in combination with the safety
philosophy of the Badische group itself.
Very often melt shops intend these
days to install dedicated additional safety
equipment or systems with the target to
improve working safety with big emphasize
of state-of-the-art “machine safety”
in the execution of these additional systems,
but disregard the status of the main
process equipment and the related process
safety.
The electric arc furnace (EAF) as a main
process unit for melting of “un-virgin”
material, like scrap or DRI, is a very good
example for the fact, that the condition and
set-up of the main equipment according to
production environment and pre-conditions
is essential for the process safety and reliability.
By ensuring a high level of process
safety and reliability of the EAF, automatically
a relative high level of working safety
is reached, because one of the main hazards
of the EAF is its product, liquid steel,
in undefined conditions.
By applying this fact, the following 3
levels for overall safety of an EAF can by
defined:
• right set-up and condition of the EAF
main equipment and sections,
• set-up of operational standards and procedures,
• installation and use of dedicated additional
safety equipment.
Steady and consequent realization of the
first 2 levels leads additionally to higher
process efficiency and optimized consumption
figures because delay rates will
be minimized.
Figure 2. Thermo-scan of BSW-EAF #2 after tapping (Picture: BSE)
Set-up of main process equipment
(safety degree 1)
By analyzing the set-up of an EAF as main
plant for melting of “un-virgin” metallic raw
material, first of all state-of-the-art technical
and safety principles and rules according to
the applied physical and technical principles
need to be implemented. Briefly, the following
physical and technical principles and
requirements need to be fulfilled:
• efficient electric power input through
the arc,
• efficient chemical power input by the
oxygen technology system,
• set-up of EAF shell according to tap
weight and hot heel, as well as shell
volume for charging,
• set-up of EAF movements for charging,
de-slagging, tapping, etc.
• implementation of the EAF in the melt
shop layout by respecting aspects like
internal material flow, connection to
power and utilities supply, connection
to de-dusting system, etc.
During a modernization project 2 forty
years old EAFs were substituted by one
state-of-the-art 145-t EAF to fulfil production
requirements of the mini mill. The
modernized EAF has been installed at the
place of one of the outdated EAFs in the
melt shop. The existing internal buildings,
such as transformer house, control and
hydraulic rooms were re-used. The old
foundations were substituted by completely
new foundations.
One of the main important topics of the
modernization was to guarantee a consecutive
2-bucket-charge with 0.6 t/m³ scrap
density. This requirement led to a shell setup
with an inner diameter of 7,800 mm of
the lower shell and 7,500 mm of the watercooled
panels. The overall height of the
upper shell resulted in 3,400 mm. This
shell layout resulted in an overall required
electrode stroke of 6,000 mm.
Now the question was how to set up
the EAF according to the production target
within the existing melting bay and to comply
with state-of-the-art safety principles
and rules. The following explanation will
highlight briefly the engineering solutions
regarding the aspects of reliability and
safety for operation and maintenance within
the life-cycle of the EAF.
As a first example the required electrode
stroke of 6,000 mm shall be mentioned.
That big electrode stroke was realized by
really rigid and stable design of the electrode
lifting system. A main aspect of this
is a stiff design of the gantry, as well as
electrode lifting columns and electrode
arms combined with self-centering column
guiding units, also designed for good maintainability.
Another important safety aspect of the
EAF is the implementation of fail-safe-principle
in case of complete power failure.
The hydraulic system design features, that
the EAF can be carried into safe condition
even by a complete power failure. Safe
condition of the EAF means:
• EAF in horizontal position,
• all 3 electrodes in upper position,
• roof in upper position and swivelled out.
Furthermore, the height of the upper shell
of 3,400 mm shall by analyzed regarding
safety aspects of the design. The design
of the water-cooled sidewall panels can by
summarized as following:
• overall height 3,400 mm,
• 3 individual cooling circuits,
STEEL + TECHNOLOGY 1 (2019) No. 4