INJECTION DE GAZ DE REDUCTION CHAUDS DANS UN HAUT FOURNEAU

INJECTION OF HOT REDUCING GASES INTO A BLAST FURNACE

Abrégé anglais

ABSTRACT
Reducing gases heated to a temperature of 1500 to 2800°C are
injected into the main tuyeres of a blast furnace, these gases
mainly containing CO, H2, and possibly N2, and smaller amounts
of CO2 and H2O. The reducing gases are obtained from a solid
fuel, preferably dried and finely crushed, injected into a
reactor in which it is gasified in contact with an oxidising
agent such as air, superoxygenated air, or even recycled throat
gases having a sufficient CO2 content.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A method of injecting hot reducing gases into a blast furnace
with main tuyeres, comprising:
(a) injecting particulate solid fuel into a reactor in
which it is gasified in contact with an oxidising agent and
heating the products of gasification to a temperature of 1500
to 2800°C, to produce reducing gases at 1500 to 2800°C mainly
containing CO and H2 and optionally N2, and smaller amounts
of CO2 and H2O; and
(b) injecting the reducing gases into the main tuyeres.
2. A method as claimed in claim 1, in which the fuel is dried
and finely crushed.
3. A method as claimed in claim 1, in which the particle size
range of the fuel is such that 60 to 100% has a dimension of
less than 75 micrometres.
4. A method as claimed in claim 1, in which additional heat
required to obtain the gases heated to a temperature of 1500
to 2800°C is produced by electrical methods using an arc heater
or a plasma torch which is an integral part of the reactor.
5. A method as claimed in claim 1, in which the solid fuel
is coal.
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6, A method as claimed in claim 19 in which the oxidising
agent is selected from air, superoxygenated air, and recycled
throat gas having a sufficient CO2 content.
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Description

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Iaiection of hot reducinq qases into a blast furnace
The present invention relates to a method of injecting hot
reducing gases produced from solid fuel into a blast furnace.
The applicants have already tested and advocated a method
in which, in order to replace the gases produced at the
main tuyeres of a blast furnace as a result of combustion
of coke with hot air~ known as the hot blast~,reducing
ga~es having a temperature of between 1500 and 2800C are
inJected. '
In this method9 the reducing gases are either produced in
an independent unit and then superheated in a reactor~which
may advantageously be an electrical aPParatUS of the plasma
torch or arc heater type9 or are directly produced in the
reactor where they are simultaneously heated to the required
temperature. These reducing gases may be produced from any
solid~ liquid~or gaseous fuel (hydrocarbor or carbonaceous
material).
The present invention relates to a method of carrying out
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the method described abovs~ and which may be applied to
the particular case in which the reducing~ases injected
into the blast furnace are ~roduced from a solid fuel.
In this respect the term solid fuel includes any material
having a high carbon content, such as fossile material
rangi~g from anthracite to lignite and peat~or even
residues resulting from other industrial operations such
~a~, for example, pitch or petroleum coke.
The production of reducing gases from solid fuel9 including
earbonized residues, is very advantageous in the present
economic situa~ion in which petrol products and natural
ga9es may only be profitably used in a very restricted number
o~ cases. It is ~recisely for this reason that iron and
steel specialists in numerous countries are again using
coal. There have been numerous attempts in various parts
o~ the world to replace a non-ne~ligible portion of the
metallurgical coke by the direct inJection of these coals
into tbe tuyeres of a blast furnace. The research which
has been carried out to date shows that a direct injection
of coal of this type is possible without disturbing the
normal operation of the blast furnace, on condition that
the combustion of this coal takes place to a lar~e ext~nt
in the eddy zone which is produced in the blast furnace
directly in front of the tuyeres through which the hot air
(generally called hot blast) designed for the combustion of
the coke is inJected.
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However,a coal injection of this type poses Particular
problems in the case in which it is desired to use high
rates of injectionp i.e. runs in which the quantity of
coal injected per tonne o~ pig iron is high.
In practice~ this rate of irjection is often expressed
in kg o~ material blasted per tonne of pig iron. However,
the only de~inition which is correct from the technical
and scientific points of view is to express it in grammes
of carbon injected per cubic metre of oxygen available to
convert the coal into CO.
One o~ the problems posed by the lar~e~scale injeGtion of
coal directly into the eddy zone in front of the tuyeres
lies in the fact that the dwell time of the coal in this
zone hardly exceeds one-tenth of a second and~consequently9
that the time available for the combustion o~ the coal is
extremely short. In addition, as the coal injected is cold
it is necessary to heat it above the inflammation temperature
before combustion can commenoe. In addition, the speed
of combustion of the coal is also strongly influenced by
the oxygen potential (resulting from the free C02 and ~2
contents) of the fuel. As the "walls" of the eddy zone into
which the cold coal is injected are formed by coke heated
to a high temperature during its descent in the blast furnace,
the coal competes with the heated coke to obtain the oxygen
required for combustion. In these conditions, it can be

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seen that it is difficult to exceed, without problems,
rate~ of injection of approximately 300 gr-ammes of carbon
per cubic metre of oxygen, i.e. approximately 80 to 120 kg
of coal per tonne of pig iron according to the operating
conditions of the blast furnace.
In addition, the coal injected directly into the eddy zone
may be considered as a cooling injectionp i.e. that the
gases produced by its combustion with the hot blast have
a temperature which is considerably lower than the
temperature obtained by the combustion of the same hot
blast with the coke heated during its passage through the
blast f~rnace before reaching this e~dy zone. Xf this
involves a coolin~ injection at a moderate rate~ the
cooling effect does not cause any problems with respect to
the normal operation of the blast furnace and,in certain
casss~ may even ~e beneficial. However9 for very high
rates of injection and in particular in the case of certain
types of fuel having a considerable cooling effect, this
cooling action may have an extremely detrimental effect
Z and may even prevent normal operation of the furnace. The
visible sians of a run with this excessive cooling effect
are constituted by a very high throat temperature which
shows the de~ective operation of the furnace. It should be
noted that the cooling action of a fuel increases, the more
oxygen and water (moisture or water of crystallisation)
the fuel contains.

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The technique proposed by the present invention enables
operation with an extremely high solid fuel consumption
extending up to the vicinity of the theoretical possible
limit (525 grammes of carbon per cubic metre of C02 or
HzO~ which corresPonds to 10S0 grammes of carbon per cubic
metre of 2)~ whilst eliminating ths difficulties or the
problems which are intrinsic to the direct coal injection
technique as described above
The new method proposed therefore has the advantage that
pig iron may be produced whilst using high proportions of
~olid fuels without passing through the coking stage and
without causing the drawbacks of a direct injection into
the blast furnace. In addition, this new technique enables
the use of the intrinsic advantages of the method of
~5 inJection of hot reducing gases already disclosed in the
Belgian Patent Specifications No 748.274, 767.8979 770.
0949 813.118. Moreover, it is emphasised that the use of
solid fuel with gasification in accorclance with the injection
method described above leads to a substantial increase of
the blast furnace output.
The method of the present inventdon in which reducing gases
heated to a temperature of 1500 to 2800~C are inJected into
the main tuyeres, these gases containing chiefly C0 and H2
and possibly N2 and, in smaller quantities, C02 and H20, is
essentially characterised in that these reducing gases are

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obtained from a solid fuel, preferably dried and finely
crushed~ injected in suitable proportions ~0/carbon ratio)
into a rsactor in which it is gasified in contact with
an oxidising agent such as air, superoxygenated air or
even recycled throat gases having a sufficient C02 content.
In an advantageous variant of the invention, which takes
into account that the optimum granular size of the fuel
used varies slightly in accordancewith the nature and the
reactivity of the said fuel~ a material whose granular size
is located in the range of 60 to ~00% of size lower than
75 micrometres ~s used.
The additional heat required to obtain gases heated to a
temperature of between ~500 and 2800C~ as required within
the scope of the method, is advanta~eously provided~ in
accordance with the invention, by electrical methods using
an arc heater or a plasma torch as an integral part of the
reactor.
As a result ofthe use of this new technique, there are
obtained at the nozzles of the tuyeres heated reducing
gases which only contain fuel ash and a comparatively low
proportion of unburnt residue. Their residual ~2 and C02
content is controlled such as to burn a pre-determined
amount of coke (coke rate) selected on the basis of
economic and otber consideratio~s.

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In order to show the advantages of the method o~ the
invention, the detailed examples given below show the
differences in the technical characteristics of a blast
furnace7 in the first instance for a conventional furnace
run with direct coal injection (Case A) and then for a
run in accordance wibh the method comprising the injection
of hot reducing gases produced from coal (Cases ~ and C)4
In Case A, 100 kg of coal per tonne of pig iron were
directly injected into the blast f~rnace through the main
tuyeres. A coke rate of 372 kgft of pig iron was achieved,
which was considerably lower than that of a run without
coal injection. A throat gas temperature of 240C and
a production output of 144.1~t/h were achieved.
In Case B, 1124 Nm /t 0~ pig iron of reducing gases
produced from 200 kg~t pig iron of coal9 i.eO double that
o~ Case A, were injected. 918 Nm /t plg iron of ordinary
air at ~250 C were consumed to produce these reducing gases
in a reactor comprising a plasma furnace. A coke rate
of 247 kg/t pig iron,i.e. substantiall~ lower than that of
Case A (372 kg/t pig iron), was achieved. Furthermore, the
throat gas temperature (200C) was considerably lower than
that of case A (240 C~.- The production output of the
furnace was 161.51 t/h, iOe. much higher than that of case
8 (144.13 t/h)~
Case C is similar to that o~ case B~ with an injection of

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981 Nm3/t pi~ iron of reducing ~ases prodwced from 200 kg/
t pig iron of coal. 739 N~ /t pig iron of air at 1250C
to which had been added 39.4 Nm /t pig iron of 2 were
consumed to produce the reducing gases also in a reactor
comprising a plasma furnaceO With respect to case B,
practically the same coke rate was obtained (248 kg/t pig iron)~
with a throat gas temperature which was much lower (121C
in5tead of 200 C) and a substantially improved production
output (181.86 tJh instead of 161.51 t/h). (Nm - m at
normal temperature and pressure~.

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A B C
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Coke rate (dry ) kg/t pig iron 372 247 248
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Coal
Quanti-ty kg/t pig iron 100
.
Blast
Quantity Nm /t pig iron 1082
Te~perature C 1250
El~ ~ kWlj-~ pig iron 69 61 54
Piro~as
Air at 1250C Nm3/t pig iron 918 739
Coal kg/t pig iron 200 200
Electrical energy k~h,'t pig iron 213 216
Oxygen Nm3/t pig iron --- 39.4
Reducing Gas
CO % 20.79 23.73
C2 % 4.83 5.62
H2 % 3.53 3.72
~2 æ 6.13 7.17
N2 ~ 64.72 59076
~mount Nm3/t pig iron 1124 381
Throat gas
CO % 22.46 22.38 24.97.
C2 Y 20.63 21,48 23.93
H2 ~ 2.33 4~02 4.41
Amount Nm /t pig iron 1571 1398 1259
Temperature C 240 200 121
Production output t~h 144.13 161~51 181~86
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