PDF - Millennium Steel

Danieli converter technology
Danieli Linz Technology, in conjunction with Danieli Corus, offer full design, manufacturing,
installation, process control, automation and commissioning of BOF converters. Examples of
design principles, new products and the benefits obtained are described
Authors: Dr Günther Staudinger, Dr Andreas Hackl, Peter Illecker, Alberto Passon, Edo Engel and Walter Vortrefflich
Danieli Linz Technology and Danieli Corus
D
anieli has established a new business called
Danieli Linz Technology, offering converter design
and engineering from proven Austrian specialists. R&D
researchers based in Italy support developments for
the converter suspension system, tilting drive etc, and
workshops based mainly in Italy and Thailand provide
in-house manufacturing capability. This business is further
complemented by specialists from Danieli Corus who
have decades of experience in BOF process control and
automation systems.
MILLENNIUM STEEL 2013
CONVERTER DESIGN
44
Vessel shell From a metallurgical point of view the
converter has to provide a certain reaction volume, bath
depth and surface area for efficient steelmaking to occur.
In order to optimise the process, the reaction volume
should be as high as possible, with an ideal value for the
specific volume (ratio of inner volume to mass of liquid
steel) of 1.0m3/t.
In greenfield cases this value is easy to achieve, but
restrictions reducing this ratio to 0.8m3/t or even less
are not uncommon, particularly in the revamping
business when, for instance, converter size is increased to
increase output.
The vessel shell acts as an enclosure for the lining and
should have enough stiffness to cope with the weight of
refractory and steel as well as the 360° tilting torques and
dynamic loads during charging, blowing and tapping, etc.
The vessel shape is mostly defined by the need to
maximise the reaction volume. A typical shell has a top
cone, barrel section, bottom cone, dished end and a
flat lip-ring on top. Knuckle sections are not necessary,
but might be applied for other reasons and, in order to
minimise the relining time the converter may be equipped
with a detachable bottom.
Additionally, the shell is exposed to elevated temperatures
of 500°C or more. For instance, during tapping, some parts
of the shell are exposed to heat radiation from the liquid
steel in the ladle and, during slopping, direct contact with
liquid steel or slag is also possible. When too little lining
remains inside the converter, hot spots may appear and, in
the worst case, this can even result in a break-through of
the vessel shell, most likely in the area of the trunnion pins
underneath the trunnion ring.
Thus, material selection for the vessel shell is important
and has to be done carefully to serve the abovementioned
requirements. Based on experience, the most common
material used is a fine grain size unalloyed pressure
vessel steel, such as P275NH, P355NH or A516 Gr.60.
Such material has medium strength and high ductility
and avoids progressive crack growth in cases of serious
damage, but offers enough strength to accommodate the
allowable stress level with a safety margin. Such material
can be repaired relatively easily by welding.
However, since refractory life has increased over the
years, eg, by using Mg-C-bricks and use of slag-splashing
or extended gunning, the temperature of the vessel shell
under normal operations has increased. This increases
the tendency of the material to creep over many years of
operation. As the vessel shell enlarges it gets closer to the
trunnion ring, reducing the natural cooling effect, so further
increasing the temperature and consequently progressively
stimulating the creep effect. Usually the lifetime of the
vessel shell is reached either when its temperature gets too
high to maintain structural integrity or, in the worst case,
the vessel shell touches the trunnion ring.
For higher creep resistance the steels used are P355GH,
A 204 Gr.60, 16Mo3 or even higher grades like 13CrMo44,
A 387 Gr.11. Some cases even require Cr-Mo-alloyed steel
grades like A387 Gr.22 or 10CrMo9-10, but these are very
difficult to weld and post-weld-heat-treatment has to be
applied, which is very difficult in an in-situ weld repair.
Suspension systems The suspension system plays a very
important role. When the shell is exposed to high stresses
and creep, any additional sources of stress should be
avoided as much as possible. To this end, the suspension
system has to be as flexible as possible yet stiff, and there
are a number of different suspension systems in operation
worldwide in an attempt to solve these issues:
`Bracket suspension system (compensation of thermal
expansion by optimised angle of the wedges)
`Disk suspension system Isostatic system – the
converter is supported on two large disks and a link
STEELMAKING AND CASTING
achieves and stabilises tilting the vessel
`Link suspension system Isostatic system – the converter
is supported by five links and a stabiliser
`Lamella type suspension system The converter is
supported by eight elements underneath the trunnion
ring. Each element consists of two relatively thin, high
strength steel plates that act like spring elements.
These are very flexible for radial deformation and stiff
in the longitudinal and circumferential directions. The
horizontal forces in the 90° position are controlled by
horizontal elements.
CONVERTER TILTING DRIVE SYSTEM
The tilting drive has special requirements. The converter
tilting torques are relatively large and vary during tilting
from one side to the other. However, most of the time the a
r Fig 1 Finite element calculation of suspension elements (tie rods)
r Fig 2 Danieli converter tilting drive (left). Example of drive system in
workshop (right)
r Fig 3 General arrangement of the Danieli lance design
MILLENNIUM STEEL 2013
Danieli has developed a new suspension system based on
tie-rods which are arranged at four locations around the
vessel shell. Each location incorporates four vertical tie-rods
which are flexible for radial deformation and stiff in the
longitudinal and circumferential directions. Additionally,
two horizontal supports are arranged underneath the
trunnion pins in order to take most load of the converter in
the 90° tilted position (see Figure 1). The first application
of the tie rod suspension system will be applied on a 350t
converter for ArcelorMittal, Poland, with startup scheduled
for 2014.
Danieli has also developed an alternative suspension
system which is based on lamella type vertical elements
and special horizontal support elements. It is called
the Daniella suspension system and a patent has been
issued (No.MI2013A00019). When the vessel shell gets
to operating temperature (up to 500°C), the trunnion
ring is at approximately 200°C. The stress so caused is
compensated by elastic deformation in lamella-type plates
arranged in the support brackets welded to the trunnion
ring. The horizontal bracket welded to the vessel shell can
expand and does not significantly increase the load on the
support brackets due to elastic deformation. When the
deformation from the thermal expansion is applied, the
mechanical horizontal load of the converter deforms the
lamellae further until solid contact to the centre bracket
welded to the trunnion ring is reached, and the full load
is transferred to the trunnion ring. The lamella plates are
kept in place by holder elements, which means no welding
or other mechanical equipment is involved to keep this
plates in splace. Consequently these plates can be easily
changed when needed. Also a change of the characteristic
of the behaviour of the horizontal element is possible after
a certain time of operation.
The first application of this Daniella system is planned for
a 170t converter for NTMK in Russia.
45
converter is stationary and the tilting drives act only as a
brake. Based on our substantial experience in the design
of large gears (from rolling technology), a suitable tilting
drive was developed. The drive is split into the bull gear and
primary gears, varying from one to six primary gears per
drive system and modern designs have two or four primary
gears and motors (see Figure 2). Additionally, one or two
additional pneumatic motors on the drive are provided so
that in the case of power failure, the drive can be operated
in order to empty the converter if necessary.
The tilting drive ‘rides’ on the trunnion ring axes in
order to follow the elastic and dynamic deformation of
the trunnion ring without creating any additional load.
The suspension system, which acts as a torque support
only, introduces vertical loads in the foundation. A large
horizontal interconnection shaft acts like a spring and
minimises any impact loads to the teeth of the large wheel
during shock loads or shaking of the converter. The drive is
manufactured in Italy.
OXYGEN LANCE SYSTEM
The design of the lance lifting device is based on our
long experience in crane design and is equipped with an
emergency drive for emergency use (see Figure 3). Cooling
MILLENNIUM STEEL 2013
r Fig 4 3D fluid dynamic analysis of the water flow
in the lance tip
46
water and oxygen flow in the lance tip are analysed and
optimised using fluid dynamics software (see Figure 4).
PROJECT REALISATION AND
QUALITY CONTROL
Danieli provides the complete supply chain and hence
is within the full Danieli quality control system. The core
equipment is manufactured in-house, including:
`Shell
`Trunnion ring
`Suspension system
`Tilting drive
`Oxygen lance system
Danieli has a number of production centres in Europe and
Asia and employs highly qualified staff. This is a major
advantage, particularly for the vessel shell and trunnion
ring, as these areas are the most critical and have to be
manufactured to the highest standards (see Figure 5). The
engineering, manufacturing and site assembly of the vessel
shell as well as the trunnion ring is carried out according to
pressure vessel codes and rules.
Danieli operates workshops that are certified according
to ISO 9001:208, ISO 14000, ISO 18000 as well as ASME
boiler and pressure vessel code (U2 and U for production
of pressure vessels as well on site, PP for production of
pressure piping and S for power boilers). Delivery time is
minimised by careful workshop planning and optimisation
of manufacturing in terms of engineering adapted to
workshop capabilities. This minimises, for instance, the
number of welding seams and weld sizes in order to
reduce residual stress. All manufacturing steps can be
done in-house such as the pressing of the bottom dish end
or knuckle sections, stress relieving of complete trunnion
rings, local stress relieving and developing special welding
procedures. All non-destructive testing is performed inhouse with qualified personnel (Level 2 and 3). The quality
control plan (QCP) is issued by the engineering department
and directly implemented. Following manufacturing, preassembly and erection on site are also done by Danieli, and
r Fig 5 Examples of large vessel shells manufactured within Danieli Thailand
STEELMAKING AND CASTING
preparation can be optimised for customer requirements.
With proprietary workshops, it is also possible to provide
additional services such as stocks of spares for emergency
cases like break-outs or other unforeseeable events.
FROM PROCESS CONTROL TO
AUTOMATIC STEELMAKING
BOF steelmaking is a rapid process which requires stateof-the-art process control and, over many decades, many
improvements have been made, such as the use of a sublance,
waste gas analysis and slag control. All of these tools depend
on a solid, well-tuned process model to be successful.
The Automatic Steelmaking System developed by
Danieli Corus integrates all available tools and combines
them within the BOF static-dynamic process model. This
model was first developed at the IJmuiden steel plant and
further improved during implementation in other plants
worldwide. It has been consistently successful with high
hitting rates and substantially reduced tap-to-tap times.
The Danieli Corus process control system consists of a
set of hardware and software components that can be
implemented individually or combined. After the initial
installation, a system can be upgraded with additional
modules.
A comprehensive process model is at the core of the
system. The system integrates operation and exchange of
information with plant systems varying from raw material
ordering to the plant’s planning and manufacturing
systems ( see Figure 6). The converters can be operated in
full computer mode, but the system also accepts manual
intervention.
The system can be fine-tuned to any plant and optimised
to follow existing operational procedures. A typical operator
screen is shown in Figure 7.
r Fig 6 Danieli Corus process control system
Sublance Danieli Corus is a market leader in this area,
with more than 100 systems in operation. The sublance
automatically takes the selected probe (for measuring
temperature, oxygen, carbon and phosphorous) from
a conditioned storage chamber and, after moving over
the converter, is lowered into the steel bath through the
entrance port on top of the hood. Measurement data is
fed to the process model and the sublance is retracted.
The probe is removed automatically and deposited in a
collection chamber on the converter floor, making a sample
available for analysis within seconds.
a
MILLENNIUM STEEL 2013
Waste gas analysis For additional on-line process
control, a gas analysis system can be installed. This system
is based on mass spectrometry to measure the levels of
carbon monoxide, carbon dioxide, oxygen, hydrogen,
nitrogen, water and argon in the waste gas. This provides
valuable information on the decarburisation rate and
r Fig 7 Typical operator screen
47
bath. The system consists of a pressure reducing system
and a flow control system, capable of controlling the flow
for each individual line. This achieves the desired rate of
agitation and prevents damage and clogging. Flow control
is split over two parallel banks. One has a fixed flow
controller which is always in operation for safety reasons;
the second has an adjustable flow controller which will
be switched on and off depending on the desired steel
grade or process moment. A unique feature of the Danieli
design is that the nozzles can be drilled, allowing for tuyere
replacement during the converter campaign.
r Fig 8 P content measured by the sublance system
versus laboratory analysis of steel sample
oxygen content in the slag and is used to generate
information on the steel carbon content and helps update
decision support information for oxygen blowing.
Since the system provides on-line information on
converter off-gas composition, it is invaluable in
monitoring explosion risk, and either the operator will be
informed or the system will interrupt the blowing process
automatically.
MILLENNIUM STEEL 2013
Advanced slag control (ASCON) In converter
steelmaking, a dry slag leads to increased lining erosion,
whereas a foamy slag induces a risk of slopping, and both
can affect converter availability. This system is based on
a number of measurement modules based on techniques
such as ultrasonics and acoustics for on-line, real-time slag
monitoring and control through closed-loop input into
the oxygen lance control and bottom agitation system.
This module offers automated lance height control for
an optimum balance between slag foaming and process
performance without slopping.
48
Bottom agitation This offers a significant increase in
oxygen blowing efficiency. It is applied to enhance the
reaction between slag and liquid steel and to lower the
oxygen content, and allows the steel maker to produce
low carbon contents without excessive yield, alloy and
refractory losses and a better control of end-point nitrogen
is achieved. Slag will contain reduced amounts of ferrous
elements.
Nitrogen or argon is introduced at the bottom of the
converter through special nozzles, so agitating the steel
AUTOMATIC STEELMAKING CONCEPTS
BOF process control and process automation have now
reached such levels of sophistication that it has become
possible to fully automate the process from charge to
tap. Some aspects, however, may be more attractive to
control semi-automatically with the information provided
by a decision support system. This option is becoming
increasingly attractive now that critical parameters with
respect to liquid steel quality can be measured on-line that
in the past could only be measured by taking a sample and
waiting for lab analysis.
Phosphorous measurement and safe tapping®
Controlling steel P levels, particularly with the increased
use of high P iron ores, continues to be of interest because
of its impact on steel quality. BOF slag is complex in
nature and contains several oxides including CaO, SiO2,
P2O5, MgO, MnO, and FeO. Towards the end of blow, the
kinetics of the different reactions slow down such that
the slag composition approaches a pseudo equilibrium
with the steel, and application of thermodynamic models
alone for direct estimation of P distribution does not
yield sufficiently reliable information for deciding to
start tapping, hence a delay is incurred awaiting the
laboratory results of the turn down sample.
Danieli Corus has successfully implemented P measurement
into the Static–Dynamic Model, so shortening tap-to-tap
times. Measurements are taken with a dedicated, newly
invented sublance TSOP (temperature, sulphur, oxygen and
phosphorus) probe. Figure 8 shows the results from recent
measurements at a steel plant in China comparing predicted
P from the probe versus laboratory analysis of the solidified
sample. It should be mentioned that no alterations were
made to the converter operation to produce more favourable
conditions for P measurement, and no precautions were
taken with respect to converter addition material quality,
quantities or other process control parameters.
It was possible to limit the standard deviation of the
measurement to 24.6ppm with a P content in the steel
bath of <300ppm.
STEELMAKING AND CASTING
q Fig 9 Safe Tapping
probability graph
Operating the converter in full computer
mode Modern BOF process control systems have reached
a level of sophistication allowing for fully computerised
operation. With our static–dynamic process model, after
the hot metal and scrap have been charged (in automatic
mode) the operator can start the heat with one click
of a mouse. Oxygen lance control, converter material
additions systems and all process control equipment,
then work together in computer mode until it is ready
for tapping.
This proprietary model has been constantly improved for
over 40 years and can be fine-tuned to any BOF plant and,
with this level of automation, energy consumption, tap-totap times and additives consumption are further reduced.
More than 25 systems capable of running multiple
converter plants have been installed so far.
ENVIRONMENTAL TECHNOLOGY
In cooperation with GEA Bischoff (Germany), Danieli
has also full capabilities to handle the primary off-gases
coming from the converter. GEA Bischoff has equipped
more than 200 plants with wet (annular gap scrubber)
and dry (electrostatic precipitator) systems, fulfilling the
highest environmental standards. Danieli also cooperates
with Oschatz (Germany) as the preferred sub supplier
for primary cooling stack systems, giving additional
convenience with respect to safe and reliable operation
and maximised energy recovery via high sophisticated
steam production.
Regarding secondary fume emissions Danieli
Environment, with more than 150 references for bag filter
systems, provides sophisticated solutions tailor made to
process and customer needs.
SUMMARY
Danieli now offers full design, manufacturing, installation,
process control, automation and commissioning of BOF
converters. We have established a new business called
Danieli Linz Technology, offering converter design and
engineering which is further complemented by Danieli
Corus, who has decades of experience in BOF process
control and automation systems.
All core components are developed, engineered and
manufactured within the Danieli quality control system,
providing assurance from start to finish. MS
Dr Günther Staudinger, Dr Andreas Hackl, Peter Illecker
and Alberto Passon are with Danieli Linz Technology,
Linz, Austria. Edo Engel and Walter Vortrefflich are with
Danieli Corus, Ijmuiden, The Netherlands
Contact: [email protected]
MILLENNIUM STEEL 2013
A great benefit for the operator in the converter control
room in deciding whether to start tapping the heat or
not is the addition of a decision support system. Rather
than showing the measured data on the operator screen and
letting the operator interpret the data, process conditions
are presented through a newly developed concept called
Safe Tapping®. This is a graphical information tool that
informs the operator through a multi-colour graph whether
or not it is safe (from the point of view of meeting the steel
P specification) to start tapping the heat (see Figure 9).
After each measurement, a marker is shown on the Safe
Tapping® operator screen.
Although the Safe Tapping® decision support system was
built for P measurement, it can be customised to include
any set of process parameters (such as carbon content and
bath temperature windows) that are regarded essential for
tapping. This gives the operator control of the BOF process
at high levels of confidence.
49