U.S. patent application number 13/642193 was filed with the patent office on 2013-02-07 for bentonite-bound compacts of undersized oxidic iron carriers.
The applicant listed for this patent is Christian Boehm, Hado Heckmann. Invention is credited to Christian Boehm, Hado Heckmann.
Application Number | 20130032005 13/642193 |
Document ID | / |
Family ID | 44122617 |
Filed Date | 2013-02-07 |
United States Patent
Application |
20130032005 |
Kind Code |
A1 |
Boehm; Christian ; et
al. |
February 7, 2013 |
BENTONITE-BOUND COMPACTS OF UNDERSIZED OXIDIC IRON CARRIERS
Abstract
A method for producing compacts containing iron oxide from
undersized oxidic iron carriers may include producing a mixture
which comprises undersized oxidic iron carriers, bentonite as a
binder and water, pressing the mixture and hardening the green
compacts obtained by the pressing, as well as to the compacts
produced by the method and to the use of the compacts as lump iron
carriers. The mixture may be subjected to a kneading process
lasting at least 3 minutes and up to 30 minutes, prior to the
pressing. The compacts may thus be produced without a maturing
process.
Inventors: |
Boehm; Christian; (Thalheim,
AT) ; Heckmann; Hado; (Linz, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Boehm; Christian
Heckmann; Hado |
Thalheim
Linz |
|
AT
AT |
|
|
Family ID: |
44122617 |
Appl. No.: |
13/642193 |
Filed: |
March 21, 2011 |
PCT Filed: |
March 21, 2011 |
PCT NO: |
PCT/EP2011/054214 |
371 Date: |
October 19, 2012 |
Current U.S.
Class: |
75/319 ; 75/415;
75/507; 75/770 |
Current CPC
Class: |
C21C 5/56 20130101; Y02P
10/216 20151101; C21B 13/00 20130101; Y02P 10/20 20151101; C22B
7/02 20130101; C22B 1/243 20130101; C21B 7/002 20130101; C21B
13/0086 20130101; C21B 13/0046 20130101; Y02P 10/25 20151101; C21B
2200/00 20130101; Y02P 10/283 20151101; C21C 5/40 20130101 |
Class at
Publication: |
75/319 ; 75/770;
75/507; 75/415 |
International
Class: |
C22B 1/243 20060101
C22B001/243; C21B 13/00 20060101 C21B013/00; C21B 3/02 20060101
C21B003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 2010 |
AT |
A 636/2010 |
Claims
1. A method for producing compacts containing iron oxide from
undersized oxidic iron carriers, comprising: producing a mixture
that comprises (a) undersized oxidic iron carriers produced by
degradation of lump oxidic iron carriers, lump ore, or pellets and
having a particle size of less than 10 mm, (b) bentonite as a
binder, and (c) water, kneading the mixture using a kneading
process having a duration of at least 3 minutes, and after the
kneading process, pressing the mixture and hardening the green
compacts obtained by the pressing.
2. The method of claim 1, wherein the mixture comprises from 3%
weight to 12% weight of bentonite, relative to the weight of
undersized oxidic iron carriers in the mixture.
3. The method as of claim 1, wherein the mixture also comprises
metallurgical residual materials containing iron selected from the
group consisting of: metalized Fe fines, scale, metallurgical dust,
metallurgical sludge, and material from a steel production
process.
4. The method of claim 1, wherein the mixture also comprises at
least one of finely particulate hematitic material and finely
particulate limonitic material.
5. The method of claim 1, wherein the mixture also comprises finely
particulate material formed during the removal of dust from top
gas, reduction gas, or generator gas of a plant for reducing oxidic
iron carriers using a reduction gas.
6. The method of claim 1, comprising heating the mixture during the
kneading process.
7. A compact obtained by: producing a mixture that, comprises (a)
undersized oxidic iron carriers produced by degradation of lump
oxidic iron carriers, lump ore, or pellets and having a particle
size of less than 10 mm, (b) bentonite as a binder, and (c) water,
kneading the mixture using a kneading process having a duration of
at least 3 minutes, and after the kneading process, pressing the
mixture and hardening the green compacts obtained by the
pressing.
8. A method for producing sponge iron or liquid pig iron,
comprising: producing a compact by: producing a mixture that
comprises (a) undersized oxidic iron carriers produced by
degradation of lump oxidic iron carriers, lump ore, or pellets and
having a particle size of less than 10 mm, (b) bentonite as a
binder, and (c) water, kneading the mixture using a kneading
process having a duration of at least 3 minutes, and after the
kneading process, pressing the mixture and hardening the green
compacts obtained, by the pressing, and producing sponge iron or
liquid pig iron by a process that uses the produced compact as a
lump oxide.
9. The method of claim 1, wherein the duration of the kneading
process is between 5 minutes and 30 minutes.
10. The method of claim 1, wherein the duration of the kneading
process is between 5 minutes and 20 minutes.
11. The method of claim 1, wherein the duration of the kneading
process is between 5 minutes and 15 minutes.
12. The method of claim 1, wherein the undersized oxidic iron
carriers have a particle size of less than 6.3 mm.
13. The method of claim 1, wherein the undersized oxidic iron
carriers have a particle size of less than 5 mm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. National Stage Application of
International Application No. PCT/EP2011/054214 filed Mar. 21,
2011, which designates the United States of America, and claims
priority to AT Patent Application No. A 636/2010 filed Apr. 19,
2010. The contents of which are hereby incorporated by reference in
their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to a method for producing
compacts containing iron oxide from undersized oxidic iron carriers
by producing a mixture which comprises undersized oxidic iron
carriers, bentonite as a binder and water, pressing the mixture and
hardening the green compacts obtained by the pressing, as well as
to the compacts produced by the method and to the use of the
compacts as lump iron carriers.
BACKGROUND
[0003] In many processes for producing sponge iron which use a
direct reduction shaft with a fixed bed, for example according to
the MIDREX.RTM. or HYL.RTM. processes, or in melt reduction methods
for producing liquid pig iron in which reduction takes place in a
shaft, for example in the COREX.RTM. process, lump oxidic iron
carriers such as lump ore or pellets can be used as starting
material. Owing to transport and handling, the lump oxidic iron
carriers suffer abrasion or may fragment. The products of such
degradation are too fine for use in a direct reduction shaft with a
fixed bed, since they reduce the gas permeability of a fixed bed
overall and increase the risk of poor distribution of the reduction
gases, or channeling with associated incomplete reduction in
certain regions. Before charging into a direct reduction shaft with
a fixed bed, it is therefore necessary to separate an undersize of
oxidic iron carriers due to such degradation from the lump oxidic
iron carriers by screening and/or sifting, for example screening
for a particle size of 6.3 mm and sifting for a particle size of
<200 .mu.m.
[0004] The term undersize is intended to mean particles whose
particle size is less than 10 mm, preferably less than 6.3 mm,
particularly preferably less than 5 mm. These values indicate the
mesh width of the screen used for the screening, through which the
undersize falls. The particle size of an undersize is referred to
as undersized.
[0005] In order to be able to use the undersize, it must be
converted into a lump form, that is to say agglomerated. If
sintering or pelleting systems are present in the vicinity, this
equipment may be used for agglomeration of an undersize. Often,
cold briquetting systems for briquetting the undersize are also
available in the plant assembly. In some cases, the undersize of
the lump oxides is also returned to the ore supplier by return
freight.
[0006] Agglomeration methods for converting finely particulate
material into lump form, such as pelleting or sintering, can only
be operated economically on a large scale. For this reason,
agglomeration is often not carried out and the undersize from
degradation of the lump oxidic iron carriers is stockpiled without
being used.
SUMMARY
[0007] In one embodiment, a method for producing compacts
containing iron oxide from undersized oxidic iron carriers includes
producing a mixture which comprises the undersized oxidic iron
carriers, bentonite as a binder and water, pressing the mixture and
hardening the green compacts obtained by the pressing, wherein the
mixture is subjected after combining its components to a kneading
process lasting at least 3 minutes, preferably at least 5 minutes,
up to 30 minutes, preferably up to 20 minutes, particularly
preferably up to 15 minutes, which is followed by the pressing.
[0008] In a further embodiment, the mixture comprises from 3 to 12
weight % of bentonite, expressed in terms of the amount of
undersized oxidic iron carriers. In a further embodiment, the
mixture also comprises metallurgical residual materials containing
iron,
[0009] preferably at least one member of the group [0010] metalized
Fe fines, [0011] scale, [0012] metallurgical dust, [0013]
metallurgical sludge, [0014] material which comes from a steel
production process, in which recovered sponge iron and/or recovered
pig iron is employed by using compacts produced as disclosed
herein.
[0015] In a further embodiment, the mixture also comprises finely
particulate hematitic and/or limonitic material. In a further
embodiment, the mixture also comprises finely particulate material
formed during the removal of dust from top gas, reduction gas or
generator gas of a plant for reducing oxidic iron carriers by means
of a reduction gas. In a further embodiment, the mixture is heated
during the kneading process.
[0016] In another embodiment, a compact is obtained by any of the
methods disclosed above. In another embodiment, such a compact is
used as a lump oxidic iron carrier for producing sponge iron or
liquid pig iron.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Example embodiments will be explained in more detail below
with reference to figures, in which:
[0018] FIG. 1 schematically shows an example embodiment of a direct
reduction plant.
[0019] FIG. 2 schematically shows an example embodiment of a melt
reduction plant.
DETAILED DESCRIPTION
[0020] Some embodiments provide a method for converting the
undersize into lump form, which makes the undersize suitable for
economic use in order to produce sponge iron or liquid pig
iron.
[0021] For example, some embodiments provide a method for producing
compacts containing iron oxide from undersized oxidic iron carriers
by producing a mixture which comprises the undersized oxidic iron
carriers, bentonite as a binder and water, pressing the mixture and
hardening the green compacts obtained by the pressing, wherein the
mixture is subjected after combining its components to a kneading
process lasting at least 3 minutes, preferably at least 5 minutes,
up to 30 minutes, preferably up to 20 minutes, particularly
preferably up to 15 minutes, which is followed by the pressing.
[0022] The compacts are agglomerates, produced by pressing, of
finely particulate materials. Examples of forms of compacts are
briquettes, tablets and plates or extrudates, or lump fragments
produced by careful disagglomeration from plates or extrudates.
[0023] An advantage of producing compacts from the undersized
oxidic iron carriers, compared with pelleting, is that compact
production, for example briquetting, can react more flexibly to
variations in the quality and quantity of the materials used, and
it is possible to obviate preparation of the materials used by fine
grinding as well as the firing of green pellets. Compact
production, for example briquetting, is therefore in principle more
suitable for processing an undersize which occurs in amounts of up
to 100 000 t/a.
[0024] Bentonite is used as a binder. Bentonite is intended to mean
a material which is a mixture of various clay minerals and contains
smectitic phyllosilicates, e.g., montmorillonite, as the main
component. The smectitic phyllosilicates, e.g., montmorillonite,
are present in amounts of at least 60%, preferably at least 70% as
a weight percentage. The bentonite may be a naturally occurring
rock, or derivatives of a naturally occurring rock obtained by
providing additives or carrying out method steps.
[0025] The term undersized oxidic iron carriers is also, for
example, meant to include dusts which result from the batching of
lump oxidic iron carriers.
[0026] The mixture may comprise from 3 to 12 weight % of bentonite,
expressed in terms of the amount of undersized oxidic iron
carriers, preferably from 6 to 10 weight %. With less bentonite, it
is not possible to ensure a sufficient binder effect. With more
bentonite, the additional bentonite consumption does not provide
any significant benefit in its effect as a binder in the compact.
Also, further processing of the compacts in a steelworks is made
more difficult owing to the increased slag formation due to the
higher bentonite content. In addition, a higher bentonite component
represents unnecessary ballast during transport of the
compacts.
[0027] The components of the mixture may be combined in one or more
steps. For example, the solid components of the mixture may be
combined and premixed first, before water is added in order to
create a doughy consistency. The doughy mixture of all the
components is then subjected to the kneading process.
[0028] The solid and liquid components of the mixture may, however,
also all be combined in one step.
[0029] The kneading process lasts at least 3 minutes, preferably at
least 5 minutes, up to 30 minutes, preferably up to 20 minutes,
particularly preferably up to 15 minutes, the limit values
respectively being included. With a duration of less than 3
minutes, the properties of the green compacts and compacts obtained
are insufficient. With a duration of more than 30 minutes, no
significant change in the properties of the green compacts and
compacts is achieved, but the time saving compared with maturing
decreases with an increasing duration of the kneading process.
[0030] When using bentonite as a binder, it is conventional to
leave the mixture comprising bentonite and water, and especially
the bentonite, to swell for several hours while storing it at rest
[0031] a process which is also referred to as maturing--in order to
allow the binding ability of the bentonite binder to be exerted.
The duration of the maturing is referred to as the maturing
time.
[0032] The kneading process disclosed herein, to which the mixture
is subjected after combining its components, allows the
time-consuming maturing to be eliminated, without significant
impairment or even with improvement of the properties of the
compacts. For the same throughput, this reduces the storage space
necessary for this treatment step (bunker or pile volume), or with
the same storage size it is possible to achieve a higher
throughput. Furthermore, the mixture--and therefore the structure
of the final product, the compact--is homogenized so that the
amount of binder necessary for a particular compact quality can be
reduced.
[0033] Table 1 shows the evaluation of tests of the production of
compacts in relation to the drop shatter resistance (SF) and the
point pressure strength (PDF) of the compacts in the scope of a
test campaign. For this, the compacts are produced by the disclosed
method with a kneading process, or according to conventional
maturing processes. The compacts are briquettes.
[0034] The drop shatter resistances of green compacts and compacts
produced according to the disclosed method, and of green compacts
and compacts produced with maturing--respectively with the same
starting materials and under otherwise identical conditions--are of
the same order of magnitude, both for green compacts and for
air-dried and thermally dried compacts.
[0035] In comparison to compacts and green compacts produced with
maturing--respectively with the same starting materials and under
otherwise identical conditions--compacts and green compacts
produced by the method according to the disclosed method exhibit an
increase in point pressure strength, particularly in the case of
compacts produced by thermal drying.
[0036] The behavior of the compacts in relation to point pressure
strength after thermal drying is regarded as an indication of the
behavior of the compacts after charging into a reduction zone.
Particularly owing to their point pressure strength properties, the
compacts produced according to the disclosed method are much more
suitable for use in an industrial reduction process than compacts
produced with maturing.
[0037] Sinter feed from the Fabrica mine in Minas Gerais
State/Brazil (FERTECO) was used as undersized oxidic iron carrier
for all the tests shown in Table 1. The particle size used for
producing the compacts was 0-8 mm with a d50 of 0.75 mm and a d95
of 3.15 mm. In order to set up constant test conditions, the sinter
feed was thermally dried to a moisture content of <1% before the
tests.
[0038] The following commercially available bentonites were
used:
[0039] IK=IKO Bond D.RTM. (activated calcium bentonite from IKO
Erbsloh containing about 90% montmorillonite)
[0040] VO=VOLCLAY.RTM. (natural sodium bentonite from Sud-Chemie
containing about 70-80% montmorillonite)
[0041] TI=TIXOTON.RTM. (activated calcium bentonite from Sud-Chemie
containing about 70% montmorillonite)
[0042] CA=CALCIGEL.RTM. (natural calcium bentonite from
Sud-Chemie)
[0043] The mixtures were produced in a batch mixer of the type
FM130D from Lodige.
[0044] The kneading mechanism from Koppern which was used for the
kneading processes consisted of a vertically standing cylindrical
container, through which a centrally rotating shaft with kneading
arms is passed.
[0045] Heating of the kneading mechanism, which could be carried
out in order to supply heat to the mixture during the kneading
process, took place through the housing, to which end saturated
steam at 6 to 8 bar was available.
[0046] The green compacts were produced by means of a test roll
press of the type 52/10 from Koppern. The cushion-shaped format
selected for the green compacts had a nominal volume of 20
cm.sup.3. The material to be pressed was delivered by means of
gravity feeders. Composites consisting of a plurality of green
compacts were produced by the test roll press. These composites
contain green compacts both in the edge region of the composites
and in the central region of the composites.
[0047] In order to obtain individual green compacts or individual
compacts for determination of the drop shatter resistance and the
point pressure strength, the composites are broken up along the
dividing seams between the individual green compacts. Generally,
the composites break up into individual green compacts during
extraction from the test roll press.
[0048] For the compacts produced according to Table 1, the
bentonite (Bent) and subsequently water (W) were initially added to
the undersized oxidic iron carrier--the mixing time was 2 minutes
in each case. The percentages indicated for bentonite and water are
percentages by weight; the percentage by weight refers to the
amount of undersized oxidic iron carriers used in the respective
test.
[0049] Following the mixing process, the mixture was kneaded in the
kneading mechanism in order to produce compacts according to the
disclosed method. The kneading mechanism was heated in some cases,
specifically with indirect heating through the housing. Results
obtained in this way are indicated in Table 1 by the entries Knd+H
in the Treatment column, H standing for heating. Entries Knd-H in
the Treatment column mean that the kneading mechanism was not
heated.
[0050] In order to produce compacts with maturing, the mixture was
left to rest in a maturing container after the mixing process.
[0051] After the kneading process in the kneading mechanism, or the
maturing in the maturing container, the mixtures as material to be
pressed were subjected to pressing in the test roll press, in order
to produce green compacts.
[0052] The green compacts thereby obtained are still soft--which is
indicated in technical terminology by the prefix "green"--and are
subjected to hardening, in order to obtain the finished compact.
This hardening may be carried out for example by at least partial
drying by storage in air and/or a heat treatment.
[0053] After the pressing, individual green compacts were
respectively studied immediately, in technical terminology while
green, in terms of drop shatter resistance (SF) and point pressure
strength (PDF). The results of these studies are shown in the
columns SF green and PDF green. The measurements of drop shatter
resistance and point pressure strength were respectively repeated
after 1 h of hardening in air and after 24 h or 72 h of hardening
in air. The results of these studies are shown in the columns "SF
24 h (72 h)*" and "PDF 24 h (72 h)*".
[0054] A subset of the green compacts obtained in the respective
tests were dried over 30 min at 290.degree. C., and likewise
studied for drop shatter resistance and point pressure strength
after cooling in air. The results of these studies are shown in the
columns "SF dry" and "PDF dry".
[0055] For the drop shatter test (based on ASTM D440) in order to
establish the drop shatter resistance, a sample weighing 4 kg of
green compacts, or compacts hardened by drying in air or by thermal
drying, is dropped four times through a drop tube from a height of
2 m into a collection container, the bottom of which is made in the
form of a solid steel plate. The drop tube has a diameter of 200 mm
and the collection container has a diameter of 260 mm. The
thickness of the steel plate is 12 mm. Evaluation of the drop
shatter test by screening analysis is carried out after the second
and fourth drops. The numerical values in Table 1 respectively
indicate the proportion of the particle size fraction >20 mm
after four drops.
[0056] In order to determine the point pressure strength, a test
machine of the type 469 from ERICHSEN was used. In this test
method, individual green compacts, or compacts hardened by drying
in air or by thermal drying, are clamped between two holders, the
lower of which is coupled to a force transducer and the upper is
continuously adjusted by means of a spindle drive in order to apply
a gradually increasing pressure load. The lower holder is formed by
a round plate with a diameter of 80 mm and the upper by a
horizontal metal rod with a diameter of 10 mm. The forward
increment rate for the upper holder is 8 mm/min. The point pressure
strength is registered as the maximum load recording of a green or
hardened compact before fracture--the entries in Table 1 indicate
the average point pressure strength at fracture as a result of
point pressure loading in newtons. Six green compacts or compacts
from the central region and six green compacts or compacts from the
edge region of the composites obtained in the test roll press were
respectively studied. Average values were calculated from the data
obtained in these studies, the minimum and maximum values
respectively being ignored. The average values are indicated in
Table 1.
TABLE-US-00001 TABLE 1 Bent W SF PDF Test [wt [wt Treat- SF 24 h SF
PDF 24 h PDF No. %] %] ment green (72 h)* dry green (72 h)* dry 1
10% 5% Knd + H 94 90 95 494 821 2188 IK 30 min 2 10% 5% Matu. 92 96
89 159 331 941 IK 120 min 3 10% 5% Matu. 89 96 91 139 287 797 IK
240 min 4 10% 5% Knd - H 93 94 91 209 441 1056 IK 30 min 5 10% 5%
Knd + H 94 92 94 640 783 2129 VO 15 min 6 10% 5% Matu. 93 97 92 112
191 784 VO 60 min 7 10% 5% Knd + H 95 93 93 555 859 1987 TI 15 min
8 10% 5% Matu. 91 97 80 147 295 722 TI 60 min 9 10% 5% Knd + H 95
93* 93 261 835* 1551 CA 15 min 10 10% 5% Matu. 85 95* 76 97 447*
1385 CA 60 min
[0057] Some embodiments provide a compact obtained by the disclosed
method and the use of a compact obtained by the disclosed method as
a lump oxidic iron carrier for producing sponge iron or liquid pig
iron. Sponge iron may for example be produced in a reduction shaft,
a rotary furnace or a rotary tube, in which case the sponge iron
may constitute an intermediate product for the production of liquid
pig iron in a melt reduction process by means of a melt-down
gasifier. This may also involve combined melt reduction/direct
reduction plants or combined direct reduction/coal gasification
plants. For this use, the compacts are employed in the same way as
other types of lump oxidic iron carriers are employed.
[0058] According to one embodiment of the method, the mixture also
comprises metallurgical residual materials containing iron, for
example metalized Fe fines, scale, for example roll scale,
metallurgical dust, for example blast furnace dust or converter
dust or BOF ejections or fine metallic slag dust or EAF ejections
or EAF dust, metallurgical sludge, for example blast furnace sludge
or BOF sludge or hot rolling mill sludge, fine iron, iron
swarf.
[0059] Such material coming from dedusting devices or scrubbers is
optionally subjected to a preparation step for iron enrichment,
before it is used for the production of compacts.
[0060] The mixture may comprise at least one member of the group
[0061] metalized Fe fines, [0062] scale, [0063] metallurgical dust,
[0064] metallurgical sludge, [0065] material which comes from a
steel production process, in which recovered sponge iron and/or pig
iron is employed by using compacts produced as disclosed
herein.
[0066] This, for example, also includes the use of undersized
material screened from the sponge iron.
[0067] For example, it also includes the use of material obtained
after screening during a shutdown, carried out for example for
maintenance reasons, of a unit for obtaining sponge iron and/or pig
iron--for example a direct reduction shaft or a melt-down gasifier.
The term metalized Fe fines is intended to mean fine-grained
metalized iron (Fe) carriers, fine-grained meaning a particle
diameter of up to 6 mm. The metallurgical residual materials
containing iron preferably have a combined content of iron and
carbon which is more than 50 weight %. The combined content of iron
and carbon above that is economically viable, however, depends on
the relevant amount of metallurgical residual materials containing
iron and the dumping costs for such metallurgical residual
materials containing iron. It may be preferable to use material
which comes from a steel production process in which sponge iron
and/or pig iron obtained by using compacts produced according to
the disclosed method is employed. In this way, these metallurgical
residual materials can be recycled into the process leading to
their production. Such recycling is beneficial since metallurgical
residual materials--for example metalized Fe fines, scale,
metallurgical dust, metallurgical sludge--contain large proportions
of iron and/or carbon, and the recycled materials do not need to be
dumped expensively. During the reduction process, the iron
contained in the metallurgical residual materials leads to a saving
on iron ore and the carbon leads to a saving on reducing agent.
[0068] Certain metallurgical residual materials, in particular
scale, fine iron, iron swarf, owing to their granular shape or
their mechanical properties, act as structurally reinforcing
components in the compact by increasing--mechanically by internal
friction--the force which needs to be exerted in order to destroy
the compacts. The greater this force is, the greater is the
strength of the compact. The structurally reinforcing effect is
manifested by an increased strength of the compacts. The strength
is conventionally considered differently according to cold
strength, which indicates the strength at room temperature, and hot
strength, which indicates the strength at a temperature--defined by
the test conditions respectively set up--higher than room
temperature. Besides improving the cold strength of compacts by
metallurgical residual materials containing iron, the hot strength
of compacts--particularly under the conditions existing during the
reduction--can also be improved by metallurgical residual materials
containing iron. The carbon contained in many metallurgical
residual materials may, for example, initiate reduction reactions
inside the compacts when heating the compact, which in turn leads
to reinforcement of the hot strength of the compact.
[0069] When using undersized oxidic iron carriers and metallurgical
residual materials together in order to produce compacts,
additional strength is therefore imparted to the compacts. It is
thus possible to save on binder--which is in fact present in the
compact in order to provide strength--and therefore limit the
introduction of inert substances or slag-forming agents into the
compact.
[0070] In quantitative terms, the mixture may comprise up to 100
weight % of the metallurgical residual materials containing iron,
expressed in terms of the amount of undersized oxidic iron
carriers.
[0071] According to another embodiment, the mixture also comprises
finely particulate hematitic and/or limonitic material, finely
particulate being intended to mean a particle diameter of less than
6 mm. If oxidic material which is difficult to reduce by a
reduction method is present--particularly in the form of
magnetite--then problems of reduction kinetics associated with such
material can be overcome by mixing the material which is difficult
to reduce--present for example in the form of magnetite--with
finely particulate material which is easy to reduce by the same
reduction method--in particular present in the form of hematite or
limonite. In accordance with the Austrian patent AT399887, an
improvement of the reduction kinetics is to be expected from this
mixture.
[0072] Finely particulate reducible material is formed in plants
for the reduction of oxidic iron carriers by means of a reduction
gas, for example plants for carrying out sponge iron production
processes, in which a direct reduction shaft with a fixed bed is
used, for example according to the MIDREX.RTM. or HYL.RTM.
processes, or in melt reduction methods for producing liquid pig
iron, inter alia in the form of dust or sludge from dedusting
devices or scrubbers for removing dust from top gas, reduction gas
or generator gas.
[0073] Using this material increases the economic viability of a
process for producing sponge iron or liquid pig iron owing to the
recycling of material into the process circuit. For reasons of
process economy, it may be preferable that the mixture for
producing compacts containing iron oxide also comprises finely
particulate material formed during the removal of dust from top
gas, reduction gas or generator gas of a plant for the reduction of
oxidic iron carriers by means of a reduction gas.
[0074] Here, top gas is intended to mean a gas which, after having
performed its reduction task in relation to the oxidic iron
carriers, is extracted from the unit filled with oxidic iron
carriers in which it has performed its reduction task. In the case
of direct reduction in a direct reduction shaft, for example, top
gas is the gas which is fed out of the direct reduction shaft.
[0075] Generator gas is intended to mean a gas which is formed in a
melt-down gasifier--or in a coal gasifier for producing a gas to be
used for direct reduction of iron ore--by gasifying carbon carriers
in the presence of oxygen. For melt reduction processes, such a
generator gas is cooled to an optimal reduction temperature and
scrubbed before it is used as a reduction gas for reducing oxidic
iron carriers.
[0076] Reduction gas is the gas with the aid of which the oxidic
iron carriers are reduced, while itself being oxidized.
[0077] Sludge obtained by means of scrubbers from the gases is
formed by treating the waste water of the scrubbers, with dust
washed out settling as sludge. This sludge is extracted and
prepared by at least partial dewatering for the use as disclosed
herein. Optionally, the dewatering may also comprise thermal
drying.
[0078] If sludge is present in the mixture of the disclosed method
comprising undersized oxidic iron carriers, bentonite as a binder
and water, at least some of the water of the mixture may be
introduced into the mixture by means of the sludge. The degree of
dewatering of the sludge will then be selected accordingly.
[0079] According to one embodiment, the mixture is heated during
the kneading process. This may for example be done as indirect
heating through the housing of the kneading mechanism, or as direct
steam heating.
[0080] A comparison of tests No. 1 and No. 4 in Table 1 shows that
heating the mixture during the kneading process has positive
effects in respect of a significantly increased point pressure
strength.
[0081] In principle, the disclosed method can make the undersize,
and finely particulate material formed in process steps during
production of steel from pig iron material--for instance DRI,
suitable for the production of pig iron and steel. By recycling
material, a larger proportion of the raw materials is converted
into an end product and therefore they effectively become cheaper.
Dumping, or return freight costs, which have previously had to be
counted in for undersize and other materials from DRI, pig iron or
steel producers, which are used in the disclosed production of
compacts, may be obviated.
[0082] Furthermore, the disclosed method may be used to obtain the
compacts more rapidly than by maturing.
[0083] FIG. 1 schematically shows an example embodiment of a direct
reduction plant. Lump components of oxidic iron carriers 1 are
reduced in a direct reduction shaft 2 with a fixed bed by a
reduction gas 3 to form direct reduced iron (DRI). After passing
through a compaction device 4, the DRI is delivered as hot
briquetted iron (HBI) to a consumer. Top gas extracted from the
direct reduction shaft 2 has its dust load removed in a dedusting
device 10, here a gas scrubber. Before charging their lump
components la into the direct reduction shaft 2, the oxidic iron
carriers 1 have an undersized fraction lb, which is unsuitable for
use in the direct reduction shaft 2, removed from them by screening
on a screen 5. In FIG. 1, the screen is arranged immediately before
the direct reduction shaft 2; in principle, of course, it may be
located at any desired position of the input path for oxidic iron
carriers. Optionally after a breaking process in a breaking device
(not represented in FIG. 1 for the sake of clarity), this
undersized fraction 1b is delivered to a mixing device 6. In the
mixing device 6, the undersized fraction lb is mixed with bentonite
as a binder 12, with undersized material 7 which is formed in the
HBI screening device 8 downstream of the compaction device 4, with
residual materials from a steelworks 9--in the present case
metalized Fe fines and scale--and with sludge 19 from the dedusting
device 10, as well as with water 11. The listed components of the
mixture produced in the mixing device 6 are combined in two steps.
Specifically, the solid components of the mixture--bentonite as a
binder 12, undersized material 7, residual materials from a
steelworks 9, sludge 19 from the dedusting device 10--are initially
combined and premixed in a first step, before water 11 is added in
a second step in order to create a doughy consistency. The sludge
19 from the dedusting device 10 is dewatered and thermally dried
before being combined, this not being graphically represented
separately for the sake of clarity. After combination of the solid
components of the mixture in a first mixer of the mixing device 6,
water 11 is added in a second mixer downstream of the first mixer.
The mixture with a doughy consistency is kneaded intensively in a
kneading device 13 for a period of 15 minutes.
[0084] The kneaded mixture is then delivered to a pressing device
14. The product of the pressing carried out in the pressing device
14 is green compacts which are still soft. These green compacts are
hardened by storing in air on a storage site 15, while being at
least partially dried and therefore hardened to form compacts.
After their hardening carried out in this way, the compacts
obtained by the hardening are delivered to the direct reduction
shaft 2. In the direct reduction shaft 2, the compacts produced
according to the disclosed method are converted in the same way as
the lump components la of the oxidic iron carriers.
[0085] FIG. 2 schematically shows an example embodiment of a melt
reduction plant. Elements of FIG. 2 which are comparable to FIG. 1
are provided with the same references as in FIG. 1. Lump components
of oxidic iron carriers 1 are charged into a melt reduction unit
16. The melt reduction unit 16 comprises a melt-down gasifier, in
which carbon carriers are gasified in the presence of oxygen 20 in
order to obtain a reduction gas. The reduction gas is fed into a
shaft which contains the lump components of the oxidic iron
carriers 1. During flow through this shaft, at least partial
reduction of the lump components of the oxidic iron carriers takes
place. The material prereduced in this way is subsequently
introduced into the melt-down gasifier, where it is fully reduced
and melted. The resulting liquid pig iron 17 is removed from the
melt-down gasifier. Top gas 18 extracted from the melt reduction
unit 16 has its dust load removed in a dedusting device 10, here a
gas scrubber. Sludge formed during wet dedusting of generator gas
from the melt-down gasifier, which is carried out in order to
produce cool gas, is used in a similar way to the sludge 19,
although this is not represented for the sake of clarity. Before
charging their lump components la into the melt reduction unit 16,
the oxidic iron carriers 1 have an undersized fraction lb, which is
unsuitable for use in the melt reduction unit 16, removed from them
by screening on a screen 5. Optionally after a breaking process in
a breaking device (not represented in FIG. 2 for the sake of
clarity) , this undersized fraction 1b is delivered to a mixing
device 6. In the mixing device 6, the undersized fraction lb is
mixed with bentonite as a binder 12, with residual materials from a
steelworks 9--in the present case metalized Fe fines and scale--and
with sludge from the dedusting device 10, as well as with water 11.
The listed components of the mixture produced in the mixing device
6 are combined in two steps. Specifically, the solid components of
the mixture--bentonite as a binder 12, undersized material 23,
residual materials from a steelworks 9, sludge 19 from the
dedusting device 10--are initially combined and premixed in a first
step, before water 11 is added in a second step in order to create
a doughy consistency. The sludge 19 from the dedusting device 10 is
dewatered and thermally dried before being combined, this not being
graphically represented separately for the sake of clarity. After
combination of the solid components of the mixture in a first mixer
of the mixing device 6, water 11 is added in a second mixer
downstream of the first mixer. The mixture with a doughy
consistency is kneaded intensively in a kneading device 13 for a
period of 15 minutes.
[0086] The kneaded mixture is then delivered to a pressing device
14. The product of the pressing carried out in the pressing device
14 is green compacts which are still soft. These green compacts are
hardened by storing in air on a storage site 15, where they are at
least partially dried and therefore hardened to form compacts.
After their hardening carried out in this way, the compacts
obtained by the hardening are delivered to the melt reduction unit
16. In the melt reduction unit 16, the compacts produced according
to the disclosed method are converted in the same way as the lump
components la of the oxidic iron carriers.
LIST OF REFERENCES
[0087] 1 oxidic iron carriers
[0088] 2 direct reduction shaft
[0089] 3 reduction gas
[0090] 4 compaction device
[0091] 5 screen
[0092] 6 mixing device
[0093] 7 undersized material 7 (which is formed in the HBI
screening device 8 downstream of the compaction device 4)
[0094] 8 HBI screening device
[0095] 9 residual materials from a steelworks
[0096] 10 dedusting device
[0097] 11 water
[0098] 12 binder (bentonite)
[0099] 13 kneading device
[0100] 14 pressing device
[0101] 15 storage site
[0102] 16 melt reduction unit
[0103] 17 liquid pig iron
[0104] 18 top gas
[0105] 19 sludge
[0106] 20 oxygen
* * * * *