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The Jet Process – an innovative
solution to maximise scrap and
HBI rates in converter steelmaking
Fluctuating prices of scrap and direct-reduced hot-briquetted iron (HBI) in recent years – along
with growing pressure from public authorities to further reduce their CO2 footprint – has
heightened the interest of integrated steel producers in increasing the amount of scrap and HBI/
DRI used in converter steelmaking. The new Jet Process by Primetals Technologies is a highly
efficient technological development that allows the portion of solid materials charged into the
converter to be dramatically increased.
Authors: Dr Gerald Wimmer, Krzysztof Pastucha and Dr Erich Wimmer
Primetals Technologies Austria GmbH
H
ot metal, scrap and HBI/DRI are the three primary
iron sources used in steelmaking. The inherent energy
of the hot metal and the heat released during oxygen
blowing, make it possible to charge up to approximately
20% of solid materials in steelmaking converters. If
post-combustion techniques are applied, this rate can be
increased to around 30%. For a higher scrap charging
rate, additional energy for melting and heating is required.
This extra energy can be provided by electrical power or
by taking advantage of the chemical energy of coal. The
generation and use of electricity, however, normally incurs
considerable energy conversion losses and relatively high
costs. The Jet Process was therefore developed to use the
chemical energy of coal in a highly efficient manner to
enable higher portions of scrap/HBI to be used directly in
converter steelmaking.
MILLENNIUM STEEL 2015
PROCESS EQUIPMENT AND DESCRIPTION
60
r Fig 1 Equipment arrangement of the Jet Process
The centerpiece of this process is a converter equipped
with bottom blowing tuyeres for the injection of oxygen,
coal and lime and a hot blast lance system positioned
above the converter mouth for post-combustion purposes.
Figure 1 depicts the main equipment items and Figure 2
the arrangement of tuyeres and piping in the bottom of
the converter.
The coal injected into the hot metal, in addition to the
carbon already in solution, are combusted in two steps:
combustion of C to CO in the bath, and post-combustion
of CO to CO2 above the bath by a hot blast. Two-thirds
of the chemical energy stored in the coal is released in
the second step of this combustion process, hence it is
essential to ensure good post-combustion and an efficient
transfer of the generated heat to the hot metal bath. This
is made possible by air heated to approximately 1,300°C
STEELMAKING AND CASTING
in a pebble heater, enriched with oxygen up to 30% and
blown at near-sonic speed onto the bath surface. A high
impulse is needed to ensure good mixing and is generated
by the high volume blown into the converter. If oxygen
alone were blown, the total volume and total impulse
would be much lower. As a result of this velocity, volume
and momentum of the jet blast, a significant portion of
the surrounding gases with their huge heat content are
conveyed to the bath surface. This leads to a high input
of heat into the liquid metal, intensive bath mixing
and extremely efficient process reactions. An excellent
utilisation rate of the chemical energy contained in the
coal is thus achieved, typically in excess of 50%. This figure
is in contrast to the 36% achieved in electric steelmaking
due to the large energy losses that occur during electrical
power generation.
Oxygen for decarburisation of the hot metal is blown via
tuyeres through the converter bottom into the bath. These
tuyeres act like flame cutters, and large pieces of scrap can
be melted quickly and efficiently. This also intensively mixes
the bath, hence, all reactions are accelerated and rapidly
reach equilibrium. The bottom of the converter looks like a
standard oxygen bottom blown (OBM) converter; the only
difference is that coal can also be injected. Furthermore,
bottom blowing reduces the percentage of iron and iron
oxide lost with the slag, and the tendency for slopping
is decreased compared to standard top-blown converters.
Lime powder blown through tuyeres accelerates
desulphurisation and slag formation, and a smaller slag
volume is generated resulting in increased productivity
and process yield. Typically, yield is 1-2% higher than in a
standard BOF converter operation.
r Fig 2 Converter bottom with tuyeres for oxygen, coal and
lime injection
PROCESS FLEXIBILITY
r Fig 3 Charging scrap
be operated as a typical BOF converter, should this be
required for any reason.
AREAS OF APPLICATION
There are a number of economically attractive market
opportunities for the Jet Process. For example:
` Hot metal : scrap ratio can be adjusted to reflect the
a
MILLENNIUM STEEL 2015
The Jet Process is easily adapted to different scrap or
HBI rates by adjusting the amount of coal injected
and, theoretically, solid charge rates from 0% to 100%
are possible. With up to 30% scrap charge, no coal
injection is required because the heat contained in the
hot blast combined with CO post-combustion provides
enough energy. For scrap rates close to 100%, stepwise or continuous charging in combination with hot
heel operation is necessary. Up to 50-60% scrap is
charged in two loads at the beginning of the process
(see Figure 3). For higher scrap rates not all scrap can be
charged at the beginning so the process has to be stopped
to add additional scrap. Depending on the scrap available
and scrap handling practice, continuous charging might
be beneficial.
To further increase operational flexibility, a modular
converter design has been developed that allows a
conventional converter bottom and an oxygen blowing
lance to be quickly installed so that the converter can
61
STEELMAKING AND CASTING
CONCLUDING REMARKS
variable costs of raw materials.
` Reduced hot metal availability resulting from a blast
furnace blow down, a furnace standstill for revamping
purposes.
` The need to increase total steelmaking output if
converter plant capacity is not a constraining factor.
In such cases the only investment necessary is to
adapt existing converters to the Jet Process, which
is far less expensive than installing added hot metal
capacity and the associated coking and sintering
plant expansions.
` It can contribute to a notable reduction in CO2 emissions.
In a typical integrated plant, huge amounts of CO2 are
generated during hot metal production. Replacing
a portion of the hot metal with scrap considerably
reduces CO2 emissions per tonne of steel. Compared
to standard BOF operations, about 30% of CO2 can
be saved if the scrap rate is increased to 50% by the
application of Jet Technology, even though carbon
is used in the Jet Process as the energy source. Plant
operators can thus reduce CO2 emissions or increase
production while keeping CO2 emissions constant.
The Jet Process is ideally suited for medium to high (2060%) scrap/HBI rates. Below 20%, standard BOF is
better, and above 60%, EAF may be better (depending
on price and availability of electrical energy) in converters
of any size. It represents an attractive upgrading option
for producers to flexibly respond to varying prices for
hot metal, scrap and HBI. Converters equipped with
this solution thus close the gap between conventional
BOF plants and electric arc furnaces. As demonstrated
at the steelworks (100t converter) of one of the world’s
largest producers, the Jet Process is very reliable and
economically promising. Up to 50% of scrap has been
processed successfully. MS
Dr Gerald Wimmer is Head of Technology, Converter
Steelmaking, Krzysztof Pastucha is an expert in stainless
and special steelmaking and Dr Erich Wimmer is an
expert in fluid simulations, all at Primetals Technologies
Austria GmbH, Linz, Austria.
CONTACT: [email protected]
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BLO_AZ_178x125 Millennium Steel_1 1
01.04.2014 18:03:07 Uhr