Method and apparatus for production of iron from iron compounds

A method and apparatus for production of iron from iron compounds is provided. There is a first stage of pre-reducing the iron compounds in a first chamber having a rotationally symmetrical wall, and a second stage of further reducing the iron compounds in a second chamber below the first chamber, fuel and oxygen being supplied to the second chamber. A reducing gas passes upwardly into the first chamber to effect the pre-reduction therein. Oxygen is fed to the first chamber. The iron compounds in the first chamber at least partly melt and then flow downwardly along the wall towards said second chamber. The iron compounds are introduced into the first chamber in particle form and by means of a carrier gas which provides one or more jets. The oxygen is fed into the first chamber at least partly in the form of one or more jets having tangential components. The velocity of introduction of the oxygen is greater than the velocity of introduction of the iron compounds in the jets thereof, while the velocity of introduction of the iron compounds is such that the particles reach the wall of the first chamber in an at least partly molten state.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a method of production of iron, particularly pig 
iron, from iron compounds by a two-stage process of first pre-reducing the 
iron compounds in a first chamber with a rotationally symmetrical wall and 
a vertical axis, and secondly further reducing the iron compounds in a 
second chamber located beneath the first chamber. In the second chamber 
the further reduction of the iron compounds takes place with fuel and 
oxygen being supplied to the second chamber to produce a reducing gas 
which passes upwardly into the first chamber to effect the pre-reduction 
there. Oxygen is supplied to maintain a combustion in the reducing gas in 
the first chamber, so that the iron compounds at least partly melt and 
pass down into the second chamber. The invention also relates to an 
apparatus for carrying out this method. 
2. Description of the Prior Art 
A method and apparatus of this type is known from NL application 257,692 
(to which FR-A-1314435 corresponds). A similar disclosure is in Steel 
Times International, GB, 1993, March No. 2, page 24. The first, upper 
chamber is known as a melting cyclone or cyclone pre-reducer. Other 
two-stage processes for pre-reducing iron compounds are also known, such 
as for example a process in a fluidized bed reactor. However, the 
pre-reduced iron compounds from the fluidized bed in that process are 
introduced in solid state into a metallurgical vessel, the so-called 
melting reactor. This places high demands on the post-combustion of the 
reaction gases in the melting reactor required for creating the necessary 
heat in the melting reactor. The melt is only partly helped by this heat 
which is released above the melt. In the process of the type of the 
present invention, however, the post-combustion can take place in the 
first chamber and the heat released from this transfers directly to the 
iron compounds. 
The present inventors have studied this type of process and have obtained a 
new and deeper insight into this technology. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide an improved and easily practised 
method and apparatus production of iron from iron compounds, and 
particularly for pre-reducing iron compounds in a melting cyclone. 
According to the invention there is provided a method of production of iron 
from iron compounds comprising the two stages of 
(a) pre-reducing the iron compounds in a first chamber having a wall which 
is substantially rotationally symmetrical about an axis, 
(b) further reducing the iron compounds in a second chamber below the first 
chamber, fuel and oxygen being supplied to the second chamber so that 
there is produced therein a reducing gas which passes upwardly into the 
first chamber to effect the pre-reduction, 
wherein said iron compounds and oxygen are introduced into the first 
chamber so that the oxygen maintains a combustion in said first chamber, 
with the effect that the iron compounds in the first chamber at least 
partly melt and then flow downwardly along said wall of said first chamber 
towards said second chamber. 
This process is characterised by 
(i) introducing the iron compounds into the first chamber in particle form 
and by means of a carrier gas which provides one or more jets of the iron 
compounds into the first chamber, 
(ii) introducing the oxygen into the first chamber at least partly in the 
form of one or more jets separately from the jet or jets of the iron 
compounds, 
(iii) the velocity of introduction of the oxygen in the jet or jets thereof 
being greater than the velocity of introduction of the iron compounds, 
(iv) the direction of the jet or jets of oxygen having a tangential 
component so that the reducing gas is given a rotating motion around the 
axis of the first chamber, and 
(v) the velocity of introduction of the iron compounds being such that said 
particles thereof reach the wall of the first chamber in an at least 
partly molten state. 
The combination of these measures is of importance to the method. The iron 
compounds and the oxygen must be introduced separately into the first 
chamber so that they are able to have different velocities. The velocity 
of introduction of the oxygen is preferably at least 50 m/s and more 
preferably at least 100 m/s. By contrast the velocity of the iron 
compounds is preferably in the range from 5 to 40 m/s. At a lower velocity 
of the iron compounds, a larger part of the iron compounds may not reach 
the wall of the first chamber, while at a higher velocity of the iron 
compounds the life of the wall may be excessively shortened. However, the 
velocity of the oxygen must be higher and have a tangential component in 
order to put the reducing gas in a rotating motion by momentum transfer. 
This rotating motion is not of equal importance to all iron compound 
particles alike. The larger and largest particles do reach the wall of the 
first chamber simply under their own weight. However the smaller and 
smallest particles tend to be carried along by the reducing gas in an 
upward axial direction. The rotating motion in the gas centrifuges these 
particles out so that they are kept in the first chamber. This ensures 
that the iron compounds are captured very efficiently. 
In order to make the process run optimally, the iron compounds and the 
oxygen are preferably each introduced into the first chamber as a 
plurality of jets preferably distributed over the height of the first 
chamber. This ensures intensive utilisation of the volume of the first 
chamber. 
Furthermore, it is preferable that a jet of iron compounds and a jet of 
oxygen are caused to cross close to or intersect one another in the first 
chamber, such that, at the crossover point or intersection of the jets of 
oxygen and iron compounds, there is a hot spot in the combustion of the 
reducing gas for the jet of iron compounds, where combustion heat is 
transferred at least in part to the iron compounds, so that the iron 
compounds melt at least partly. This enhances the pre-reduction of the 
iron compounds both by chemical reduction of the iron compounds, and 
possibly also by thermal decomposition. 
The mean axial velocity of the reducing gas in its upward passage through 
the first chamber is preferably at least 5 m/s. The pressure (absolute 
pressure) in the first chamber is preferably in the range 1-6 bar(0.1 to 
0.6 MPa). This intensifies the process in the first chamber. 
Preferably no extra fuel is supplied to the first chamber. It has been 
found that, although extra fuel supplied to the first chamber in addition 
to the reducing gas does combust in the first chamber, the degree of 
combustion of the process gas from the second chamber tends to drop. 
Therefore, on balance, the extra fuel does not contribute any benefit to 
the pre-reduction process. 
The iron compounds preferably have an average grain size in the range 0.05 
to 5 mm. The advantage of this is that natural ore concentrate as supplied 
by ore mines may be used, and not a particular fraction of the 
concentrate. 
The carrier gas for the iron compounds is preferably oxygen. This enhances 
the pre-reduction process. 
It is preferable to introduce the iron compounds low down in the first 
chamber, for example so that more of the iron compounds are introduced 
into the bottom half of the first chamber than into the top half. This 
keeps the capture efficiency high. 
The invention also provides apparatus for production of iron, particularly 
for use in carrying out the method described above, having 
(i) a first chamber having a wall which is substantially rotationally 
symmetrical about a substantially vertical axis, 
(ii) means for supplying iron compounds and oxygen into the first chamber, 
(iii) a discharge conduit for discharging process gases from the first 
chamber, 
(iv) a second chamber arranged beneath the first chamber and in open 
communication therewith for upward flow of process gases into the first 
chamber and downward passage of molten iron compounds from the wall of the 
first chamber into the second chamber, 
(v) means for supplying fuel and oxygen into the second chamber. 
This apparatus is characterised in that the means for supplying iron 
compounds and oxygen into the first chamber comprises a plurality of first 
nozzles for providing jets of the iron compounds in the form of particles 
entrained by carrier gas and a plurality of second nozzles for providing 
jets of oxygen separately from said jets of iron compounds, the first and 
second nozzles being located in the wall of said first chamber, and at 
least one of the second nozzles providing a jet of oxygen having a 
tangential component, relative to the first chamber axis. 
This construction ensures high utilisation of the first chamber. 
Preferably the first chamber is substantially circular cylindrical with a 
height to diameter ratio of at least 1 and preferably at least 2. It has 
been found that, particularly when the axial velocity of the reducing gas 
in the first chamber is high, a greater height to diameter ratio leads to 
a better capture efficiency. 
Preferably the first nozzles for supplying iron compounds are placed at 
different heights in the wall of the first chamber. At each height level 
there is preferably a group consisting of two first nozzles which are 
located at diametrically opposed places of the wall of the first chamber 
and provide jets whose directions are substantially horizontal, are in the 
same rotational direction with respect to the axis of the first chamber 
and are tangential to an imaginary circle having a diameter in the range 
0.25 to 0.75 times the diameter of the first chamber. Thus the first 
nozzles may be arranged along a plurality of imaginary helices on the wall 
of the first chamber. The first nozzles of each group are preferably 
circumferentially staggered around the axis by 120.degree. with respect to 
the first nozzles of each neighbouring group. 
This pattern of the nozzles for the iron compounds means that a large 
quantity of iron compounds can be introduced into the first chamber, the 
jets do not interfere, and a pre-reduction with a high production output 
is obtained. 
Preferably the second nozzles for supplying oxygen are likewise distributed 
at different heights in the wall of the first chamber. The second nozzles 
are preferably arranged in groups at a plurality of height levels and 
respectively associated with the above-mentioned groups of first nozzles, 
with each group of the second nozzles located in the wall of the first 
chamber at the same height level or slightly lower than the associated 
group of first nozzles. Likewise also each group of second nozzles 
preferably consists of two second nozzles which are located at 
diametrically opposed places of the wall of the first chamber and provide 
jets whose directions are substantially horizontal, are in the same 
rotational direction with respect to the axis of the first chamber and are 
tangential to an imaginary circle having a diameter in the range 0.25 to 
0.75 times the diameter of the first chamber. 
The imaginary circle for the second nozzles is preferably smaller than the 
imaginary circle for the first nozzles. 
Harmonising the supply pattern of the oxygen with the supply pattern of the 
iron compounds in this manner achieves a good transfer of heat to the iron 
compounds, a good degree of pre-reduction and a good capture efficiency. 
Discharge of the process gases is preferably through a discharge conduit 
substantially coaxial with the first chamber. This prevents blockages. 
The first and second chambers are preferably substantially coaxial. This 
makes the construction of the installation simple. 
Conventional iron ore concentrates in particle form may be used as the iron 
compounds. Other iron-containing material, such as dusts produced in the 
steel industry, may be added.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the melting cyclone 1 of FIG. 1 iron compounds are introduced via 
nozzles 2 in particle form entrained by oxygen as a carrier gas. The iron 
compounds are pre-reduced in the melting cyclone 1 and flow down along the 
wall 3 of the melting cyclone 1 and drip into the lower metallurgical 
vessel 4, which is for example a converter. In this vessel 4, oxygen is 
supplied by means of a lance 5 and fuel, for example coal, is supplied 
through the opening 6, and the iron compounds are further reduced into pig 
iron which is then tapped off through an opening 7 together with the slag 
formed. During the further reduction of the iron compounds in the 
metallurgical vessel 4 a hot gas containing CO (and H.sub.2) is produced, 
which passes to the melting cyclone 1. In the melting cyclone, with oxygen 
supplied through the nozzles 8, a combustion takes place, whereby the iron 
compounds are pre-reduced. The process gas is then discharged through a 
conduit 9 on the top of the melting cyclone. A small part of the iron 
compounds is unavoidably carried along with the gas. FIG. 1 also shows the 
possibility of agitating the melt at the bottom of the metallurgical 
vessel 4 by bottom bubbling by introducing an inert gas such as argon 
through openings 10 in the bottom of the vessel. 
FIG. 2 shows that the melting cyclone has a height to diameter ratio of 
over 2. The melting cyclone has a circular cylindrical chamber which is 
oriented vertically and coaxially on the metallurgical vessel 4. The 
melting cyclone has a coaxial outlet 1t forming the discharge conduit 9, 
has a water-cooled shell 12 and is provided internally with a refractory 
lining 13. The metallurgical vessel 4 also has a refractory lining 14. The 
cooling water for the melting cyclone is supplied and discharged by means 
of nozzles 15 and 16. The melting cyclone is considered to be divided into 
sections, of which sections 17, 18 and 19 are provided with the nozzles 
for supplying iron compounds and oxygen. 
First nozzles 20 for supplying iron compounds are located in the wall of 
the melting cyclone in section 17 in plane III as shown in FIG. 3. In the 
plane III.sup.1 slightly below the plane III, second nozzles 21 for 
supplying oxygen are located in the wall of the melting cyclone as also 
shown in FIG. 3. Below the planes III-III.sup.1, further nozzles 20 and 21 
for supplying iron compounds and oxygen are placed in the planes 
IV-IV.sup.1 and V-V.sup.1 respectively as shown in FIGS. 4 and 5 
respectively. The pattern of the input nozzles for iron compounds and 
oxygen of sections 18 and 19 is identical to that of section 17. 
FIG. 3 shows that the two first nozzles 20 for supplying iron compounds, 
also termed a group herein, are placed at diametrically opposed positions 
in the wall and are aimed in directions, which have tangential components 
and are in the same rotational direction and both to touch an imaginary 
circular cylinder 22 coaxial with the melting cyclone. This pattern is 
repeated in FIGS. 4 and 5, it being understood that the nozzles of FIGS. 4 
and 5 are staggered through 120.degree. around the axis relative to the 
nozzles at the next level above or below. In this way the first nozzles 
for supplying the iron compounds can be seen to be placed on helices up 
the wall of the melting cyclone. 
The pattern of the second nozzles 21 for supplying oxygen corresponds with 
this. However, the nozzles 21 are placed slightly lower than the nozzles 
20 because the oxygen is subject to more lift than the iron compounds due 
to the axial velocity of the reducing gas in the melting cyclone. The 
nozzles 21 are likewise aimed in directions which touch an imaginary 
coaxial circular cylinder 23, which, however, is larger than the imaginary 
circular cylinder 22. 
A jet of iron compounds 24 coming out of a nozzle 20 and a jet of oxygen 2S 
coming out of nozzle 21 cross or intersect each other at 26 where the 
oxygen there causes the reducing gas to combust, so that the combustion 
heat is transferred to the iron compounds and the iron compounds are 
pre-reduced and melted at least in part, before they reach the vessel 
wall. 
Test Example 
The test apparatus of FIG. 6 consists of the melting cyclone 1 as described 
above, a combustion chamber 27 and a collecting tank 28 for the reduced 
iron compounds 29. There is no second metallurgical vessel 4 in this test 
arrangement, which is used to simulate the conditions of the two-stage 
reduction process of the invention. In the combustion chamber 27 natural 
gas and oxygen introduced through openings 3 is combusted to produce a 
reducing gas with a temperature of approximately 1,500.degree. C. and a 
composition which is comparable with that produced in the second 
metallurgical vessel in an actual process. In the melting cyclone iron 
compounds and oxygen are introduced through the nozzles 2 and 8. 
Dust-charged waste gas is discharged according to arrow 31. The waste gas 
is burned up in a combustion chamber 32 and then cooled with water and 
cooler 33 and discharged to a gas scrubber according to arrow 34. 
The test arrangement of FIG. 3 was used to test the operation of the 
melting cyclone in accordance with FIG. 2. The dimensions of the melting 
cyclone were 2,000 mm net internal diameter by a height of some 4,000 mm. 
The axial velocity of the reducing gas in the smelting cyclone was 5 m/s. 
Carol Lake iron ore concentrate with an iron content of 66% wt. and a 
particle size of 50-500 .mu.m was supplied at a velocity of 10 m/s and 
oxygen at a velocity ranging from 100 to 200 m/s. The degree of reduction 
defined as 
##EQU1## 
was 10 to 30%. 
The capture efficiency defined as 
##EQU2## 
was 90 to 95%. 
The output of the melting cyclone was approximately 20 ton/h.