Full text of DOI:10.1051/metal:2003177

Experience with using alternative
reducing agents at blast furnace*
J. Buchwalder, T. Fuchs, J. Hunger, T. Siepert
(EKO Stahl)
■
INTRODUCTION
Presently operated blast furnaces 5 and 1 of EKO Stahl,
are equipped for injecting heavy fuel oil while BF 1 is
also equipped for injecting fine-grained or granulated
solid matters.
In the normal operation mode, BF 5 is fed with 100 %
heavy fuel oil. The objective is to operate BF 1 with 100 %
mixed plastics agglomerate, as it had been achieved with
BF 3 until may 2001.
This paper presents the experience that EKO
Stahl has gained with the blast furnace injection
of plastics and animal fats as alternative reducing
agents since 1993. The specific pieces of
equipment that have been designed and
implemented for handling, storing and injecting
these substances into the blast furnace tuyeres
are described.
■
HISTORICAL DEVELOPMENT OF
ALTERNATIVE REDUCING AGENTS
INJECTION AT EKO STAHL
Already in 1993, large-scale industrial tests started on blast
furnace 6 with the injection of plastics in granulated form,
that were continued with other injection materials until
1995, e.g. light shredder fraction, oily mill scale, sedimen-
tation and varnish mud granulate.
The parameters that allow line stability and the
overall effects on blast furnace operation are
reported.
In 1993 and 1994, tests were performed using the above-
mentioned materials. Injection quantities and times have
been correspondingly short (1).
Diagrams (fig. 1, 2) for carbofer (mix of oily mill scale and
flue ash) and light shredder fraction show increased injection
rates and injected quantities of different substances (2, 3).
In 1995 and 1996 during a test period of 12 days, technolo-
gically interesting quantities of the light shredder fraction
and the mix of oily mill scale and flue ash could be injec-
ted into the blast furnace through the tuyeres.
A total amount of 961 tons of carbofer and 795 tons of light
shredder fractions have been injected during the testing periods.
Since 1994, prepared plastics from different preparation
methods have been injected, with a total above 1,200 tons.
Figure 3 shows the discontinuous injection equipment
S.I.T. 2000 that has been used for the tests. Handling of
substances has been performed with big bags (3).
*
Subject of a presentation at the 2001 ATS International Steelmaking
Conference (Paris, December 12-13, 2001, Session 5).
La Revue de Métallurgie 2003.
In parallel to the tests on blast furnace 6, an equipment was
developed for large-scale injection of solid matters with a
©
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289

Expérience d’utilisation
d’agents réducteurs de substitution
au haut-fourneau
J. Buchwalder, T. Fuchs, J. Hunger, T. Siepert
(EKO Stahl)
Les hauts-fourneaux 1 et 5 d’EKO Stahl sont équipés
pour l’injection de fuel lourd. Le haut-fourneau 1 dis-
pose également d’un équipement d’injection de solides.
Injection de plastiques agglomérés
Les taux d’injection sont en augmentation régulière
depuis la mise en service des installations en 1996. Les
paramètres caractéristiques de la qualité des plastiques
injectés, humidité, densité, teneur en chlore et cendres
sont très stables. Pour assurer un bon transport, les spé-
cifications sur la granulométrie sont 0 -10 mm et la
fraction inférieure à 250 µm ne représente que 1 %. Pour
une marche stable, il est préférable d’avoir un matériau à
En marche normale, le haut-fourneau 5 injecte 100 % de
fuel lourd alors que le HF 1 a pour objectif d’injecter
1
00 % de plastiques agglomérés.
Historique du développement des injections
d’agents réducteurs auxiliaires chez EKO Stahl
50 % de fractions supérieures à 6 mm. Le taux d’injection
Dès 1993, des essais à grande échelle d’injection de
granulats de plastiques ont été réalisés sur le haut-
fourneau 6, essais qui se sont poursuivis jusqu’en 1995
avec d’autres matériaux tels que les résidus de broyage,
des boues grasses ou des boues de vernissage.
de plastiques a atteint 65 kg/tf ce qui a permis de réduire
à quasi zéro l’injection additionnelle de fuel lourd.
Le refroidissement résultant de l’injection de plastiques
à faible température de vent est compensé par une forte
suroxygénation qui améliore par ailleurs la productivité
et permet une production annuelle de 550 kt de fonte.
L’utilisation du gueulard à géométrie variable et d’un
modèle de chargement contribue également à l’obten-
tion de ce niveau de productivité.
Depuis 1994, plus de 1 200 t de plastiques préparés
selon diverses méthodes ont été injectées. Une installa-
tion d’injection de 5 t/h sur 13 tuyères a été construite
au haut-fourneau 3 et a démarré fin août 1996.
Injection de graisses animales
Mise au point de l’équipement d’injection
Depuis mars 2001, des graisses animales sont injectées
en mélange au fuel lourd sur le haut-fourneau 5. Avec
Pour utiliser une large gamme de matériaux, EKO Stahl
a développé un système capable d’injecter à la fois des
matériaux fins et des matériaux grenus ainsi que de les
répartir de manière fiable entre les tuyères.
une teneur en carbone de 76,5 % et une teneur en H de
2
1
1,9 % , les graisses animales ont un PCI de 39 MJ/kg
ce qui les rend très proches du fuel pour l’injection au
haut-fourneau. Par ailleurs, leurs caractéristiques phy-
siques (densité, viscosité, température d’inflammation)
sont elles aussi très proches de celles des fuels auxquels
elles se mélangent très facilement à une température de
Deux systèmes d’injection permettent l’alimentation en
phase dense de produits fins, en utilisant le système
Koste validé pour le charbon pulvérisé, et une alimenta-
tion en phase diluée de matériaux grenus. Les solutions
mises en œuvre permettent d’alimenter un nombre quel-
conque de tuyères, les lignes d’injection pouvant être
mises en service indépendamment les unes des autres.
8
0°C, ce qui permet de les utiliser sans préparation
complémentaire. La faible teneur en chlore et la très
faible teneur en soufre des graisses animales contribuent
à la qualité de la fonte et à la régularité de marche du
haut-fourneau. Les graisses animales représentent envi-
ron 25 % de la quantité totale d’agents réducteurs
liquides injectés quotidiennement.
Chaque système possède 13 lignes de 70 m pour alimen-
ter 13 des 15 tuyères du haut-fourneau, les deux tuyères
proches du trou de coulée n’étant pas équipées.
Développements futurs
Afin de permettre une marche en continu, le silo de
dosage est alimenté par un silo de pressurisation lui-
même relié à un silo de stockage intermédiaire relié au
silo de stockage primaire par une ligne de 120 m de
transport en phase diluée. Des extracteurs à vis transfè-
rent les granulats du silo de stockage sur des cribles qui
éliminent les fractions supérieures à 10 mm. Les granu-
lats criblés se déversent dans la trémie de chargement
dont ils sont extraits au moyen d’un extracteur alvéo-
laire qui alimente la ligne de transport.
L’utilisation d’agglomérats de plastiques revêt une
grande importance pour la compétitivité future de la pro-
duction de fonte chez EKO Stahl. La sidérurgie sera appe-
lée à jouer un rôle de plus en plus actif dans le recyclage
des véhicules usagés. En conséquence, on peut prévoir
une augmentation de l’utilisation des résidus organiques
provenant du recyclage des automobiles. Notre expé-
rience d’injection au haut-fourneau montre que cette
solution est viable mais une bonne préparation de ces
matériaux, en particulier l’élimination du cuivre et du
zinc qui sont valorisables par ailleurs reste indispensable.
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HAUT-FOURNEAU
Fig. 1 – Alternative reducing agents
injection of carbofer 1993-1995.
Fig. 1 – Substitution d’agents réducteurs
par injection de carbofer, 1993-1995.
Fig. 2 – Alternative reducing agents
injection of light shredder fraction
1
994-1996.
Fig. 2 – Substitution d’agents réducteurs
par injection de résidus de broyage,
1
994-1996.
nominal capacity of 5 t/h through 13 tuyeres. At the end of
august 1996, injection operation on BF 3 started-up with
this system.
During the same period, with Deutschen Gesellschaft für
Kunststoffrecycling (German Association for plastics recy-
cling) continuous supply of mixed plastics agglomerate
was agreed upon.
■
DEVELOPMENT OF SUITABLE
EQUIPMENT OF INJECTING COARSE
AND FINE-GRAINED SUBSTANCES
INTO BLAST FURNACE TUYERES
For being able to utilize a broad spectrum of potential
additional reducing agents, the aim was to develop injec-
tion equipment that could dose and feed fine-grained and
granulated waste products equally to all the tuyeres with a
high reliability.
Fig. 3 – Scheme of the test injection installation
at blast furnace 6.
Fig. 3 – Schéma du pilote d’injection au HF 6.
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291

The developed technical solutions allow pro-
viding practically any number of tuyeres. In
this connection, any number of feeding lines
can be switched on and off independently
from each other.
In this special case, two separate systems with
1
3 feeding lines each to 13 of totally 15 tuyeres
were implemented with a length of 70 m. Thus,
each tuyere, but for the tuyeres next to the tap
hole of the blast furnace, could be provided
with powdered materials in dense-phase
conveying (e.g. coal dust) or coarse-grained
materials in dilute-phase conveying. This espe-
cially applies to different prepared residuals.
For providing continuous conveying, the feeder
hopper gets filled with the help of a lock hop-
per that in turn is fed from an intermediate bun-
ker. The latter is fed by means of a 120 m long
dilute-phase feeding line from a storage bunker
system (fig. 4).
Fig. 4 – Scheme of the installation for injection of granulates and powders.
Fig. 4 – Schéma du pilote d’injection de poudres et granulats.
For this purpose, in one feeder hopper, two conveying sys-
tems were installed, a dense-phase conveying system accor-
ding to the proven KOSTE method for coal dust injection
This storage bunker system is designed specifically for
coarse-grained granulates and it is at present used for mixed
plastics granulates. The storage bunker is supplied by closed
roll containers, that are parked at a storage place (fig. 5).
(1) and a dilute-phase system for conveying coarse-grained
materials. In this connection, the problem had to be solved
to feed and dose the coarse-grained materials (grain size up
to 10 mm) symmetrically and with a satisfactory distribu-
tion. For this purpose, relatively small conveying volumes
per feeding line (300-500 kg/h) have to be fed into a large
number of feeding lines.
On request, by means of special vehicles, the roll containers
are put onto a tipping device, that simultaneously and inde-
pendently from each other empties two containers into the
storage bunker (fig. 6). From the storage bunker by means of
screw feeders, the granulate is fed onto a vibrating screen,
where the coarse constituents, above 10 mm in size, are
screened out (fig. 7). Screened granulate falls into a charging
hopper, from where a cellular wheel lock feeds the granulate
into the mentioned dilute-phase line.
For avoiding any wear problem during dosing, pneumatic
dosing and conveying principles have been utilized
exclusively.
Fig. 5 – Storage of agglomerated mixed plastics container
parking place.
Fig. 6 – Plastics unloading station at blast furnace 1,
container tipping station.
Fig. 5 – Aire de stockage des containers de mélanges
de plastiques agglomérés.
Fig. 6 – Poste de déchargement et de déversement
des plastiques au HF 1.
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HAUT-FOURNEAU
To maintain the pneumatic conveyability of agglomerated
mixed plastics, grain size distribution is of great importance
(
fig. 10). According to the specification, the grain size
ranges from 0 to 10 mm. In our experience, the proportion
of particles below 250 µm is limited to 1 %.
For a stable injection under the EKO Stahl conditions, it has
been proved that about 50 % of the injected material has an
upper grain size of 6 mm. Therefore, additional preparation
measures have to be taken.
Along with the blow-in of blast furnace 1 in May 2001, the
switching-over of the injection equipment to blast furnace 1
was performed.
This gave the opportunity to introduce important technical
improvements and extensions. In addition to the renewal of
pressure vessels, the complete replacement of electrical and
automation equipment was executed (fig. 11). The control
Fig. 7 – Plastics unloading station, coarse grain segregation.
Fig. 7 – Poste de déchargement des plastiques,
séparation des fractions grossières.
■
USE OF ALTERNATIVE
ADDITIONAL REDUCING
AGENTS IN PRESENT
OPERATION MODE
Agglomerated mixed plastics
Starting the injection at blast furnace 3 at mid
1
996, injection rates could be increased conti-
nuously step by step over the years (fig. 8).
This gradual increase is directly connected with
the extension of collection activities of the Dual
System Germany and the improvement of agglo-
meration capacities in Germany.
Fig. 8 – Monthly injection quantity of agglomerated mixed plastics and
development of the reducing agent consumption.
Fig. 8 – Taux mensuel d’injection de plastiques et évolution
de la consommation d’éléments réducteurs.
About half of the 30,000 tons per year of agglo-
merated mixed plastics required by EKO Stahl is
produced in a preparation plant in Eisenhütten-
stadt that belongs to Alba Recycling Ltd. The
second half is supplied by different firms of the
Federal Republic.
Figure 9 documents the development of quality
parameters (according to the DKR specification)
of the agglomerated mixed plastics, e.g. humidity,
bulk density, chlorine content and ignition residue
over a 2 years period from July 1999 to July 2001.
Except for the increase of ignition residue by
about 0.6 %, a high constancy of parameters can
be seen, e.g. for the chlorine content. This could
be reduced from high values in the years before to
a technically acceptable value of 1.2 % by efforts
of the preparation plants.
Fig. 9 – Evolution of the properties of mixed plastics for injection
from June 1999 to July 2001.
Fig. 9 – Évolution des caractéristiques des mélanges de plastiques injectés
entre juin 1999 et juillet 2001.
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293

of the injection facility is performed
with a software user interface. The main
important extension is the improvement
of nominal line performance to 8 t/h.
These modifications resulted in a fur-
ther improvement of the line stability.
Following a sharp start-up curve during
commissioning of the injection equip-
ment, the agglomerated plastics injec-
tion rate was increased to 65 kg/t of hot
metal (fig. 8). Due to this measure, the
additionally injected quantity of heavy
oil could practically be reduced to
zero. With this injection rate, a monthly
quantity of mixed plastics of 3,000 tons
was reached.
Fig. 10 – Example of particle size distribution of agglomerated
mixed plastics at EKO Stahl.
The significant improvement of line
Fig. 10 – Exemple de distribution de la granulométrie des plastiques injectés à EKO Stahl.
stability is also documented in figure 12.
Already on blast furnace 3, a line availability of about 95 %
could be achieved.
It is the objective for the line on blast furnace 1, to increase
this value to 97 %. This stability has also a significant
impact on the parameters of blast furnace 1 (tabl. I).
To compensate for the effect of high plastics injection rates
and low hot blast temperature, it is possible to operate with
relatively high oxygen enrichment.
This results in the performance-increasing effect that
enables an annual production of 550,000 tons.
Additional support is also given by using movable armour
and a burden distribution model for the double-bell top.
Fig. 11 – Complete replacement of electrical and
automation equipment.
Animal fat
Fig. 11 – Remplacement complet de l’équipement électrique
et des automatismes.
Since March of 2001, in addition to heavy oil, animal fats
from animal body utilization are injected into the blast fur-
nace as reducing agents through the oil injection equipment
of blast furnace 5.
With a carbon content of 76.5 % and a H content of
2
1
1.9 %, animal fats show a calorific value of 39,000 kJ/kg
(tabl. II). Therefore, from the point of view of utilization as
reducing agent in the blast furnace, their material properties
are near to that of heavy oil.
As animal fat can be mixed easily with heavy oil at an opera-
tion temperature of 80°C and as the physical properties, like
density, viscosity and ignition point also are in good confor-
mity, animal fat mixed with fuel oil can be used without any
further preparation. Some problems may appear in the case of
animal fat that contains solid impurities. Additionally instal-
led filters avoid failures of the injection equipment and keep
a smooth injection operation.
Fig. 12 – Comparison of availability of agglomerated mixed
plastics injection facility, BF 3 (2000) and BF 1 (2001).
Fig. 12 – Comparaison du taux de marche de l’injection
de plastique au HF 3 (2000) et au HF 1 (2001).
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HAUT-FOURNEAU
TABLE I : Current values for blast furnace 1.
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FUTURE DEVELOPMENT
TABLEAU I : Paramètres actuels du haut-fourneau 1.
The use of agglomerated mixed plastics as
reducing agents will be of great importance
for the efficiency of hot metal production in
Eisenhüttenstadt in the future.
June
July
August
Sept.
Oct.
Production Itlmonth)
42,124
46,810
1,584
394
68
39,634
1,487
423
67
48,339 47,258
Average daily production (t/d) 1,530
1,627
409
66
1,639
423
66
It has to be expected that the steel industry,
in co-operation with the automotive sector,
will participate more actively in the recy-
cling of end of life vehicles. Therefore, it
has to be assumed that the problem of utili-
zing organic materials from vehicle recy-
cling will play a more important role. Our
experience with injection indicates that the
utilization in the blast furnace is a feasible
Coke consumption (kg/thm)
Plastic [kg/thm)
419
65
Oil (kg/thm)
4
2
3
0
3
3
O -addition (m /thm)
28
36
35
30
36
2
O -enrichement (%)
1.87
2.48
2.28
2.08
2.49
2
solution. However, careful preparation of light shredder
fraction, especially the separation of copper and zinc,
being valuable raw materials themselves, is an important
prerequisite.
TABLE II : Comparison of characteristic data
for animal fat and heavy oil.
TABLEAU II : Comparaison des propriétés des huiles
lourdes et des graisses animales.
Animal fat
Oil
Calorific value
39,000 kJ/kg
40,000 kJ/kg
Density (15°C) 0.92 - 0.93 g/cm3 0.85 - 1.02 g/cm3
Flash point
S-content
Cl-content
> 180°C
< 0.004%
< 0.002 %
> 100°C
2.2 %
< 0.005 %
The low chlorine content and significantly lower sulphur
content of animal fat bring advantages for the hot metal
production.
Fig. 14 – Oil and animal fat consumption at blast furnaces
of EKO Stahl from March to October 2001.
Analogous to a part of the heavy fuel oil, the fat is sup-
plied in tanker trucks and filled into feeder tanks (fig. 13).
Every day, 25 % of the used liquid reducing agents at the
blast furnaces is animal fat (fig. 14).
Fig. 14 – Injection de graisses animales et d’huiles lourdes aux
hauts-fourneaux d’EKO Stahl entre mars et octobre 2001.
■
REFERENCES
By the end of August 2001, already 10,800 tons of animal
fat could be injected as reducing agent.
(
1) HUNGER (J.) – Einsatz ostdeutscher Braunkohlenbrenn-
stäube und Reststoffe über die Windformen des Hochofens.
Dr.-Ing. Diss., TU Bergakademie Freiberg (1997).
(
2) JANKE (D.), KRÜGER (W.), KALINOWSKI (W.),
SCHWAGER (M.) – Verwertung von ölkontaminierten
Walzzunderschlämmen und Shreddermüll über Hochöfen.
Abschlußbericht, Freiberg, Deutsche Bundesstiftung
Umwelt (february 28, 1997).
(
3) JANKE (D.), BUCHWALDER (J.), HUNGER (J.),
KRÜGER (W.), KALINOWSKI (W.), LETZEL (D.) –
Verwertung ölhaltiger Walzzunderschlämme und der
Shredderleichtfraktion von Altautos im Hochofen. Tagungs-
band XLVI. Berg und Hüttenmännischer Tag, Freiberg
(1995), p. 120-133.
Fig. 13 – Un-loading of heavy oil and animal fat feeder tanks
of the oil injection facility.
(
4) SCHEIDIG (K.) – 6 Jahre KOSTE-Verfahren in der Maxhütte
Unterwellenborn. Betriebserfahrungen und internationaler
Vergleich beim Kohleeinblasen in den Hochofen. Neue
Hütte 35 / 7 (1990), p. 241-245.
Fig. 13 – Déchargement et stockage des huiles lourdes et
des graisses animales pour l’injection.
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