[0001] This invention is related to a process for improving the reactivity, permeability
and/or similar characteristics of an ore charge being subjected to down-draught sintering,
characterized by including into said charge an active quantity of a micropelletized
product produced by balling a fine-grained ore material with the addition of at least
0.5% and at most 4% by weight of a fine-grained hydraulic binder with a specific surface
area of at least 2000 cm
2/gram consisting of blast furnace slag or a similar metallurgical slag and optionally
up to 50% of cement, up to 50% of said slag and/or cement optionally being replaced
with slaked lime, and water, to an agglomerate size of at least 75% below 5 mm, which
prior to charging onto said sintering device is cured to in average at least 50% of
the cured strength obtainable by curing for 28-30 days at room temperature. The invention
is also related to the micropelletized product defined above. The ore is e.g. iron
ore, especially hematitic or magnetitic iron ore, e.g. with at least 60%, at least
75% or at least 85% of its iron present as magnetite. For curing (bonding) the micropellets
can be spread in a layer of comparatively low height or thickness, e.g. at most 15
metres, preferably at most 10 metres or at most 5 metres or even at most 3 metres
in order to prevent that the agglomerates in the lower part of said layer are crushed,
for the period of time required for hardening or bonding to a strength which permits
subsequent transport by loading into a railway wagon or a similar treatment and charging
into a device for performing a metallurgical process, e.g. a draft sintering device
of the travelling grate type or a similar device, without forming an unacceptably
large amount of fine-grained material, as is defined in the following with reference
to testing methods, such as drop test in free fall or dropping through a tube against
a hard bottom surface or against a layer of the tested material with a drop height
of at least 15 metres, and by treatment in a rotating drum of defined dimensions for
a certain period of time. Curing in said store, also called low store, is performed
preferably for 1 to 14 days, especially from 2 to 7 days. Thereafter further storing
can be performed under conditions which permit continued curing preferably for a total
storing and curing time after the production of at least 15 days, preferably at least
30 days and optionally at least 60 or at least 100 days. Depending upon the conditions
the storing can in some cases be restricted to at most 45 days, particularly at most
30 days or at most 15 days or even at most 7 days prior to transportation from the
production location to the location of use or prior to charging into the metallurgical
device for the intended use if the product is used at the production location. Usually
the transport from the production location to the location of use is performed in
lorries, railroad wagons, transport belts, as a suspension or dispersion in a carrying
gas or liquid in tubes, in ships or in a similar way under conditions which would
cause the micropellets produced without the hydraulic binder or without the curing
in the low store or the final curing after low store treatment to be weared and denuded
at said transport to such an extent that the product does not fulfil the required
test standards, especially those stated above.
[0002] Micropelletizing and micropellets are well known concepts which are explained in
the literature. Thus the EP-Al-4 637 comprises a process for converting fine iron
or manganese ores to a material suited for sintering by pelletizing to a pellet size
below 6 mm and discloses in the example the use of an agglomerating agent consisting
of a combination of 3% by weight of sugar cane molass and 5% by weight of lime.
[0003] The micropellet product according to the instant invention comprises agglomerated
particles of varying size with a largest particle size of 5 mm, under certain conditions
a largest particle size of 4 mm or 3 mm. This means that at least 75%, especially
at least 85% or 90%, optionally at least 95% or 98% or even 100% of the quantity by
weight of agglomerated particles or agglomerated particles and unagglomerated feed
material, which has been subjected to the agglomeration treatment without being agglomerated,
has a particle size within the stated upper limits. The lower limit of the agglomerate
size is especially the grain size of the feed material but it is also possible to
settle a lower limit of the agglomerate size, e.g. by sieving or by controlled agglomeration,
such as not below 0.1 mm, not below 0.5 mm, not below 1 mm, not below 2 mm, not below
3 mm or not below 5 mm. Said limit means that at least 75%, preferably at least 85%
or at least 90%, optionally at least 95% or 98% or even 100% of the quantity by weight
of agglomerated particles or agglomerated particles and unagglomerated feed material
has a size which exceeds the stated lower limit.
[0004] The agglomeration is preferably performed on an agglomerating disc with sloping axis
but also any other suitable agglomerating device, e.g. of agglomerating roll type
of similar devices can be used.
[0005] The agglomerates preferably are of essentially spherical shape which can be achieved
e.g. by rolling. Preferably the particles exhibit a ratio largest diameter: smallest
diameter (through the geometrical centre or middle point of the balls) of at most
2, preferably at most 1.5 and especially at most 1.3 or 1.2, said value being fulfilled
by at least 50% and preferably at least 75% of the particles, based on the weight,
especially within the intermediate 50% range of the agglomerate size interval.
[0006] The agglomeration can be performed in one or more steps, e.g. for building up micropellets
of different composition within different parts, e.g. with a larger or smaller quantity
of binder and/or combustible material, especially carbonaceous material, mixed into
the outer part of the agglomerates, in relation to the inner part. Said division into
layers can preferably be performed with agglomerates within the upper 50% range of
the agglomerate size range. The outer part of the agglomerates may especially comprise
up to 50% of the weight of the agglomerate and optionally comprise at least 10% or
at least 25% of said weight, and e.g. at least 50% of the particles showing said layers
of different composition may fulfil said request.
[0007] The material used as feed material for agglomeration consists of a finely divided
ore material, especially metal ore material. The agglomerated material consists preferably
of a metal ore, e.g. essentially oxidic or sulphidic metal ore, preferably comprising
one or more of the metals iron, chromium, copper, lead, zinc, tin, cobalt, tungsten,
manganese, titanium.
[0008] Preferably the material consists of oxidic or hydroxidic iron ore, especially hematite
and/or magnetite. Especially preferred is iron ore which to at least 50%, especially
at least 75% or at least 85% or even at least 90-95% or 100% consists of magnetite
as an iron carrier. Especially suitable is a benefication concentrate of the iron
ores stated above as well as other ores which have been disintegrated by grinding.
Preferably the grain size of the material prior to agglomeration may be at most 0.5
mm, especially at most 0.2 mm or at most 0.1 mm and optionally at most 0.05 mm. This
is intended to mean that at least 75%, preferably at least 90% and especially at least
95% or 100% of the metal ore material or similar material has a grain size below said
upper limit. The lower limit of the particle size is normallly the particle size obtained
by grinding, but it is also possible to separate a fine-grained part falling below
a certain limit value prior to agglomeration by sieving or by similar methods. Thus,
the lower limit may be selected to 0.05 mm or to 0.01 or 0.04 mm so that e.g. at least
75%, optionally at least 80% and possibly at least 90 or 95% and under certain conditions
at least 100% of the quantity by weight has a grain size exceeding a stated lower
limit value.
[0009] For the ores mentioned above, especially for iron ores such as hematite and/or magnetite,
a grain size of 8Fr-100% below 0.1 mm and a specific surface area of at least 500,
preferably at least 1000, at least 1200 or at least 1400, under certain conditions
at least 1500 or even at least 2000 cm
2/g is suitable. The upper limit of the specific surface area can usually be selected
arbitrarily and may e.g. amount to 6000, up to 5000 or up to 4000 or even up to 3000
and in some cases lower, such as up to 2800 or up to 2500 cm
2/ g. Usual ranges of the ores stated above is e.g. 1500-2800 or 550-2200 cm
2/g, said values of the specific surface area being calculated according to the "Svensson-method"
disclosed in "Jernkon- torets Annaler", vol. 133, issue 2, 1949, pages 33-86.
[0010] The bonding of the micropellet material is performed with hydraulic binder in finely
divided shape, said binder being mixed into the agglomerates, preferably by mixing
the binder material with the inorganic feed material, especially iron ore, prior to
supplying the ore to the pelletizing equipment, e.g. in a mixing drum or mill being
arranged prior to the pelletizing equipment. The binder may also be grinded together
with the inorganic starting material with simultaneous mixing with said material.
Suitable binders which can be used alone or together with portland cement and similar
are metallurgical slags, such as blast-furnace slag, e.g. acid or basic blast-furnace
slag, slag from the LD-process, the Kaldo-process, Martin-furnace slag, Thomas slag,
slag obtained when performing refining in electric steel furnaces for steel production,
as well as slag derived or obtained from melting other metals, such as processes for
producing lead, copper, zinc, tin, etc., starting e.g. from oxidic and sulphidic ores.
The metallurgical slag may also be used in slag cements. Cement materials of various
types can be used as hydraulic binders together with the slag, such as portland cement
which is produced by intimately mixing lime- and clay-containing products or other
feed materials comprising Si0
2, A1
20
3 and CaO in suitable quantities, said materials being fired and sintered. One may
use a so-called cement clinker or a further treated grinded clinker which optionally
is mixed with further binders, such as up to 2-4% of gypsum. An embodiment of portland
cement is quicksetting cement or special cement which quickly reaches high physical
strength values, usually by comprising a higher content of tri- calciumsilicate or
a lower content of dicalcium- silicate than a corresponding normal portland cement
and optionally being more finely disintegrated or grinded. Other binders are pozzolanic
cement, slag cement and aluminate cement. Slag cement is preferably based on blast-furnace
slag, preferably in combination with lime or lime-supplying materials, such as lime
slag cement produced from blast-furnace slag and lime, eisenportland cement (iron
portland cement) made from about 70% of portland cement and about 30% of blast-furnace
slag, and blast-furnace cement (Hochofenzement) made from about 30-70% of blast-furnace
slag and 70-30% of portland cement. One may also use aluminate cement prepared by
firing to melting of a mixture of lime and bauxite and finely grinding of the molten
product. One may also use non- portland cement, e.g. lime and hydraulic limes obtained
by burning limestone, preferably at about 1000°C or limestones comprising substantial
or effective quantities of A1
20
3, Si0
2 and Fe
20
3 as impurities which after burning can be cured with water without interaction of
carbon dioxide from the air. Said products are also called hydraulic limes.
[0011] The slag used, especially blast-furnace slag, may especially be vitreous, water-granulated
blast-furnace slag or blast-furnace slag which in other ways has achieved corresponding
characteristics, especially reactivity and hydraulic curing and bonding power. The
slag should preferably be basic, especially with a basicity CaO/ Si0
2 = 1.0-2.0 or above, e.g. 1.0-1.5. Examples of compositions or analysis values is
28-40%, e.g. 35--40% Si0
2, 5-17%, e.g. 8-12% AI
20
3, 29―48%, e.g. 35―45% CaO and 2-13%, e.g. 4-8% MgO. The slag as well as other hydraulic
binder constituents should preferably have a low content of Na
20 + K
20, especially when producing agglomerates intended for charging in blast-furnaces
and steel- furnaces, such as a content of said compounds below 2%, preferably below
1% or 0.5%, especially below 0.1 or 0.05%. Examples of suitable binders are calcium
aluminate cement, CA- cement and calcium ferrit cement (C,AF), having the arbitrary
composition 4CaO.AI
20
3-Fe
2O
3.
[0012] The quantity of hydraulic binder should be restricted to the lowest quantity which
gives the desired strength. The upper limit is at most 4%, in some cases at most 3%
or even at most 2% based on the weight of the agglomerated solid materials.
[0013] Combinations of the two or more hydraulic binders used are e.g. portland cement,
slag cement, aluminate cement, etc. plus blast-furnace slag or a similar metallurgical
slag, lime plus blast-furnace slag, and cement plus blast-furnace slag plus lime.
A suitable combination is about 10-50% of cement and about 90-50% av slag, such as
blast-furnace slag, preferably about 1/3 cement plus about 2/3 slag, especially blast-furnace
slag. Said slag and/or cement may also up to 50% be substituted with lime (slaked
lime), e.g. up to 50% of the cement may be substituted with slaked lime and/or up
to 50% of the slag, especially blast-burnace slag, may be substituted with slaked
lime. A particular type of blast-furnace slag is blast-furnace slag which has been
purified from sulphur.
[0014] A suitable mixture is 10-20% cement, 10-20% lime (burned or slaked), 60-80% slag,
such as blast-furnace slag. The hydraulic binder is grinded to a fine particle size,
corresponding to a specific surface area, according to the definition above, of at
least 2000, preferably at least 3000 and especially at least 5000 cm
2/g. Usually reactivity is improved with increasing specific surface area and therefore
also an even larger specific surface area, such as at least 6000 and even at least
7000 cm
2/g or even at least 8000 or 10000 cm
2/g may be preferable. As regards suitable hydraulic binders which can be used according
to the invention and the characteristics of said binders reference is also made to
the Swedish Published Application No. 324 166 and the Swedish Patent No. 226 608.
[0015] Fuel can also be included into the agglomerates, preferably coke powder, anthracite
powder or similar carbonaceous materials, preferably with a relatively low content
of volatile constituents. When producing micropellets of iron ore for down draft sintering,
e.g. on a travelling sinter grate or a similar device, the entire quantity of fuel
required in the process can be included into the agglomerate, preferably in finely
disintegrated state of essentially the same grain size range as the inorganic agglomerated
material and/or the binder. Also a minor part of the total required quantity of fuel,
e.g. 25-75% of said quantity, can be included in the agglomerates and the remainder
may conventionally be included as particles, especially as somewhat coarser particles,
e.g. particles with a size of essentially above 1 mm, e.g. 1-5 mm or 1-3 mm, which
are mixed with the agglomerates and optional other charged constituents.
[0016] The agglomeration of the fine-grained inorganic material with the binder and optionally
other constituents is performed in a wet state, usually with a water content of 5-15%,
e.g. 7-10%, whereof a minor quantity is usually sprayed onto the surface of the agglomerated
charge when rolling the micropellets on an agglomerating disc or similar device.
[0017] In the micropelletizing treatment it is also possible to introduce cores (nuclei),
preferably particles, e.g. recirculated agglomerates, having a particle size above
about 1-2 mm which grow in size through repeated passage through the pelletizing device.
Optionally balling (rolling, pelletizing) may be performed in several steps, e.g.
two or more steps, with increased binder addition in the last step, e.g. to the contents
stated above. Optionally at least 2/3 or the entire quantity of the binder may be
added in the last step.
[0018] The formed agglomerates, optionally after sieving to remove undersized particles
and/or oversized particles or for separating cores or nuclei intended to be recirculated,
are transferred to a store for curing, preferably a store in which the pelletized
material is laid down in a low layer thickness in order to prevent crushing of the
agglomerates in the lower part of said layer, e.g. a layer thickness of at most 15
m, at most 10 m, at most 5 m or even at most 3 m, preferably at least 2 m. The uncured
(unhardened) micropelletized material can be spread in said layer from a conveyor
belt, e.g. as an elongated or annular heap, e.g. by scraping off from an elongated
conveyor belt and spreading out in a direction transverse to said conveyor belt so
that an elongated heap is gradually formed. The elevation from which the material
is dropped is preferably restricted to at most 15 m, preferably at most 10 or at most
5 m. The uncured or green agglomerates may prior to storing be mixed with starting
material which is free from binder or with cured or partly cured agglomerates, optionally
after separation of a finer or coarser fraction of said materials, in order to prevent
a tendency of the uncured or green material to form lumps in the curing treatment.
Preferably up to 40% or up to 30% of such materials are added, e.g. at least 5% or
at least 10%, e.g. 10-20%, based on the weight of the uncured or green material. The
storing time in the low store should be at least sufficient for giving a curing strength
which permits further transportation and handling of the agglomerates, e.g. at least
1-2 days up to 5 or 10 days, preferably so that the agglomerated material when dropped
in free fall from an elevation of 15 m through a tube against a layer of said material
or against a concrete floor shows an increase of the quantity of material with a particle
size below 0.42 mm and/or below 0.15 mm of at most 20%, preferably at most 15% or
at most 10%, said values being obtained after dropping four times with a height of
fall of 15 m. After the agglomerates have achieved said strength they can be transported
from the store and/or stored for a further period of time prior to the final use in
an intended process, especially draft sintering.
[0019] The curing temperature is suitably ambient temperature or room temperature, or about
10-40°C.
[0020] The strength of the agglomerates can also be stated or measured as the compression
strength of separate micropellets when crushing the agglomerates between flat surfaces.
Suitable values for fraction of a diameter size of 4-6 mm is e.g.: minimum strength
after storing in a low store: at least 0.2, preferably at least 0.5, at least 1, at
least 2 or at least 5 kilograms. Compressive strength after final storing prior to
use: at least 0.3, preferably at least 0.5, at least 1, often at least 2 or at least
5 kilograms, preferably at least 0.2 or at least 0.5 or 1 kilograms higher strength
when after the storing in the low store.
[0021] After curing the agglomerates to the stated strength values and/or for the stated
minimum period of time the agglomerates are used in the metallurgical process, especially
downdraught sintering of iron ore on a travelling sinter grate or similar device.
The cured micropellet material may according to the invention comprise up to 100%
of the quantity of charged iron carrier, especially together with recirculated material
from downdraught sintering in e.g. commonly used quantities or may comprise up to
80% and often up to 60% or up to 40% or 20% of the iron carrier in the charge. The
lower limit for achieving the desired effect may e.g. amount to 5% or 10% or even
20% or more.
[0022] Cured micropellet material can according to the invention be arranged homogeneously
distributed in the charge bed of a downdraught sintering device or arranged in one
or more layer in said bed, e.g. with at least 60% or at least 75% or even at least
90% of the quantity of the cured micropellet material distributed in the lower half
or one third of said bed or alternatively in the upper half or one third of the bed
or in the central half or one third of the bed height in order to control or improve
the carrying capacity, resistance against disintegration in the heating step and the
reactivity so that optimum values are obtained within different parts of the bed thickness.
Improved permeability and reactivity makes possible an increase of the bed thickness,
e.g. to above 30 cm, preferably above 35 cm and optionally to above 40 or 50 cm and/or
a reduction of the sintering time to a corresponding degree, said comparison especially
being made with the same starting material when being micropelletized without addition
of the hydraulic binder.
[0023] The following is an example of the invention: In a process comprising sintering on
a sintering band the charge in run A comprised 63.8% fine-grained magnetite concentrate,
27.2% iron ore having a grain size which was suitable for sintering, 1.1% iron sponge
ash, 1.5% LD-slag, 2.7% gabbro, 3.7% burnt lime, together 100%, and furthermore 5.0%
coke breeze, 4.0% limestone and 30.0% recycled material from the sintering process.
[0024] In a run B the magnetite concentrate was substituted with a mixture of 20% by weight
of said concentrate and 80% by weight of cured micropellets of said concentrate bonded
with 1% of portland cement clinker and 2% of blast-furnace slag which were grinded
to a specific surface area of about 6000 cm
2/g.
[0025] In a run C said magnetite concentrate was substituted entirely with the cured micropellet
material.
[0026] The production amounted in run A to 31.8, in run B to 35.5 and in run C to 35.9 tons/square
meter.24 hours. The product quality was in all said runs satisfactory.
[0027] Corresponding experiments were performed with the addition of 1% cement and 1% blast-furnace
slag with similar results.
[0028] Further experiments were performed with the same binder additives but with micropellets
of hematite ore concentrates and mixtures of magnetite and hematite ore concentrates
with similar improvements of production results.
[0029] Corresponding experiments with hematitic ores, especially such ores with more than
80% hematite or tropical hematitic ores give similar good results. Examples of such
tropical or subtropical hematite ores are South American-ores, e.g. hematites from
Brasilia, e.g. from Minas Gerais, hematites from Venezuela, e.g. hematites of the
orinoco-type. Other examples are West African-hematites, e.g. from Liberia and the
Mauretania, e.g. from the Nimba-mine, and Australian hematites, e.g. from the North-West
Territory. Such hematites may in addition to hematite also comprise e.g. martite.
Thus, the invention can with good result be used also for hematitic ores, e.g. such
ores comprising at least 70%, at least 80%, at least 90% or even at least 95% of the
Fe as Fe
20
3.
[0030] For measuring the physical strength of the micropelletized material according to
the invention one may preferably use a device of the type denoted "ISO-Tumbler", i.e.
a drum with the diameter 1000 mm and length 500 mm comprising two internal lifters
with a height (breadth) of 50 mm. Said drum is charged with 15 kg of dry material
and is rotated 200 revolutions at a speed of 25 revolutions/minute. The micropelletized
material should preferably be cured to a physical strength at which after the treatment
in the ISO-Tumbler stated above the fraction of the material with a grain size below
0.15 mm shows an increase with less than 30%, preferably less than 20% and optionally
also less than 15% or 10%, based on the weight of the material being tested in the
drum. Said increase values are also suitable limit values at the test disclosed above
which comprises dropping two or four times with a fall height of 15 m mentioned above.
[0031] It is often preferable to expedite the bonding (curing) or the hydraulic binder,
especially during the first part of the bonding (curing) reaction, and/ or to achieve
a supplementary bonding (curing) especially during the first part of bonding after
forming the micropellet material. This can be achieved in several ways, e.g. by
a) adding a binding accelerator (curing accelerator) to the hydraulic binder, e.g.
chlorides, such as calcium chloride or sodium chloride, sodium carbonate and water
glass. The quantity of said additives may e.g. amount to up to 5% of the weight of
the binder, e.g. 0.5―4% and specially 1-3%, said ranges being valid especially for
chlorides, such as calcium chloride, CaCI2.2H20, and a preferred amount of said and other chlorides is about 2%;
b) by decreasing the quantity of calcium sulphate in the cement, e.g. to at most 50%
or at most 20% of the quantity of calcium sulphate normally present in portland cement;
c) by adding light burnt MgO, preferably in the quantities stated for the accelerator
according to a) above, e.g. about 2%;
d) by adding so called "silica dust" from e.g. electro steel furnaces or ferro silicon
furnaces, i.e. mainly from the gas phase separated silicon oxide, especially silica.
The quantity of said additive can likewise be selected within the limits stated for
the accelerator according to a) above;
e) by subjecting the binder to fine-grinding to a large specific surface area, e.g.
at least 6000 cm2/g or at least 8000 or 10,000 cm2/g or above, e.g. at least 12,000. preferably at least 15,000 or even at least 20,000
cm2/g;
f) by adding residual liquor from cellulose digesting processes, e.g. residual liquor
from the sulphite process or inorganic constituents obtained from treating said liquor;
g) by increasing the temperature in the binding step, e.g. by preheating one or more
of the constituents used in the agglomerating step. Grinding of the binder to a fine
particle size may contribute and give a preheating of the binder, e.g. to about 200°C.
Furthermore, the ore concentrate or the micropellets may be heated prior to, during
or after the agglomerating treatment, e.g. with hot combustion flue gases. A suitable
temperature increase is at least 10° and preferably at least 20° or at least 30°C
above the ambient temperature or the temperature of the starting materials;
h) by carbonate hardening through a reaction with C02, especially a reaction with C02 in combustion flue gases used for heating the material.
[0032] The measures for expediting curing or hardening may of course also be combined so
that two or more such measures are used simultaneously.
[0033] It is also possible to add to the agglomerates other constituents which increase
the thermal stability, such as coal in various forms, e.g. coke, dolomite, A1
20
3 in various forms, bauxite, limestone etc. The agglomerates may also be neutral, acid
or basic, calculated e.g. from the ratio CaO + MgO/Si0
2 which especially for iron ore agglomerates may be within the ranges below 1, 0.5
to 1.5, 1 to 2 or 1.5 to 2.5 or above 2.
[0034] Calcium hydroxide or calcium oxide in various forms, e.g. burnt lime, slaked lime,
is not used alone as a binder but may form a constituent of the hydraulic binder together
with e.g. a slag which is reactive with the lime.
1. A process for improving the reactivity, permeability and/or similar characteristics
of an ore charge being subjected to down-draught sintering, characterized by including
into said charge an active quantity of a micropelletized product produced by balling
a fine-grained ore material with the addition of at least 0.5 percent and at most
4 percent by weight of a fine-grained hydraulic binder with a specific surface area
of at least 2000 cm2/g, said hydraulic binder consisting of blast furnace slag or a similar metallurgical
slag, and optionally up to 50 percent of cement, up to 50 percent of said slag and/or
cement optionally being replaced with slaked lime, and water, to an agglomerate size
of at least 75 percent by weight below 5 mm, which prior to charging onto said sintering
device is cured to in average at least 50 percent of the cured strength obtainable
by curing for 28-30 days at room temperature.
2. A process according to claim 1, characterized in that the quantity of hydraulic
binder in the cured micropelletized material is at least 1 percent and at most 3 percent,
based on the weight of the agglomerated material.
3. A process according to claim 1 or 2, characterized in that the hydraulic binder
comprises about 80-50 percent slag and 90-50 percent cement, optionally partly replaced
by lime.
4. A process according to any of claims 1-3, characterized in that the hydraulic binder
comprises about 10-20 percent cement, 10-20 percent lime and at least 60 percent slag.
5. A process according to any of the preceding claims, characterized in that the hydraulic
binder comprises slag cement.
6. A process according to any of the preceding claims, characterized in that the ore
consists of iron ore.
7. A process according to any of the preceding claims, characterized by subjecting
the micropelletized material immediately after pelletizing to storing in a layer with
a layer height of at most 10 m for at least 1 day until the increase of the quantity
of material with an agglomerate size below 0.42 mm when subjected to free fall four
times from a fall height of 15 m is below 20 percent, said storing being performed
prior to transportation of the micropelletized material to and charging on a down-draught
sintering device.
8. A process according to any of the preceding claims, characterized in that the micropellets
in one or more steps are formed with a larger or smaller quantity of the hydraulic
binder mixed into the outer part of the agglomerates in relation to the inner part,
said outer part comprising up to 50 percent of the weight of the agglomerate.
9. A process according to any of the preceding claims, characterized by including
into the micropellets coke powder anthracite powder or similar carbonaceous materials.
10. A process according to any of the preceding claims, characterized in that the
bonding of the pellets is improved by carbonate hardening through a reaction with
C02.
11. A process according to any of the preceding claims, characterized in that the
hydraulic binder has a specific surface area of at least 3000 cm2/g.
12. A process according to any of the preceding claims, characterized by curing the
pellets at a temperature of 10-40°C or at ambient temperature.
13. A process according to any of the preceding claims, characterized by charging
the micropelletized material in said down-draught sintering process with a bed height
of above 35 cm and in a quantity of at least 10% of the charged iron carrier.
14. A micropelletized product suited for carrying out the process according to any
of the preceding claims, characterized by comprising a fine-grained ore material balled
to a micropellet size of at least 75 percent below 5 mm, said micropelletized product
being bonded with at least 0.5 percent and at most 4 percent by weight of a fine-grained
hydraulic binder with a specific surface area of at least 2000 cm2/g consisting of blast furnace slag or a similar metallurgical slag, and optionally
up to 50 percent by weight of cement, up to 50 percent of said slag and/or cement
optionally being replaced with slaked lime, and cured to in average at least 50 percent
of the cured strength obtainable by curing for 28-30 days at room temperature.
15. A micropelletized product according to claim 14, characterized in that the ore
consists of iron ore.
16. A micropelletized product according to claim 14 or 15, characterized by comprising
at most 3 percent by weight of the hydraulic binder.
1. Verfahren zur Verbesserung der Reaktionsfähigkeit, der Permeabilität und/oder ähnlicher
Eigenschaften einer Erzcharge, die einer Unterwind-Sinterung unterworfen wird, dadurch
gekennzeichnet, daß der Charge eine aktive Menge eines mikropelletisierten Produkts
einverleibt wird, das hergestellt worden ist durch Agglomerieren eines feinkörnigen
Erzmaterials unter Zugabe von mindestens 0,5 und höchstens 4 Gew.-% eines feinkörnigen
hydraulischen Bindemittels mit einer spezifischen Oberflächengröße von mindestens
2000 cm2/g, wobei das hydraulische Bindemittel besteht aus Hochofenschlacke oder einer ähnlichen
Hüttenschlacke und gegebenenfalls bis zu 50 % Bindemittel (Zement), wobei bis zu 50
% der Schlacke und/oder des Bindemittels (Zements) gegebenenfalls durch gelöschten
Kalk ersetzt sind, und Wasser, bis mindestens 75 Gew.-% des Agglomerats eine Größe
unter 5 mm haben, die vor dem Einführen in die Sintervorrichtung getrocknet (gehärtet)
worden ist bis auf durchschnittlich mindestens 50 % der Trocknungs- bzw. Härtungsfestigkeit,
die durch 28- bis 30-tägiges Trocknen bzw. Härten bei Raumtemperatur erzielbar ist.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Menge des hydraulischen
Bindemittels in dem getrockneten (gehärteten) mikropelletisierten Material mindestens
1 und höchstens 3 Gew.-%, bezogen auf das Gewicht des agglomerierten Materials, beträgt.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das hydraulische
Bindemittel etwa 90 bis 50 % Schlacke und 10 bis 50 % Zement, der gegebenenfalls teilweise
durch Kalk ersetzt ist, umfaßt.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß das hydraulische
Bindemittel etwa 10 bis 20 % Zement, 10 bis 20 % Kalk und mindestens 60 % Schlacke
umfaßt.
5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
das hydraulische Bindemittel Schlackenzement umfaßt.
6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
das Erz aus Eisenerz besteht.
7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
das mikropelletisierte Material unmittelbar nach dem Pelletisieren gelagert wird in
Form einer Schicht mit einer Schichthöhe von höchstens 10 m für mindestens einen Tag,
bis die Zunahme der Menge des Materials mit einer Agglomeratgröße unter 0,42 mm, wenn
es viermal dem freien Fall aus einer Fallhöhe von 15 m unterworfen worden ist, unter
20 % liegt, wobei die Lagerung vor dem Transport des mikropelletisierten Materials
zu der und vor der Einführung in eine Unterwind-Sintervorrichtung durchgeführt wird.
8. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
die Mikropellets in einer oder mehreren Stufen gebildet werden, wobei eine größere
oder kleinere Menge des hydraulischen Bindemittels dem äußeren Teil derAgglomerate,
bezogen auf den inneren Teil, zugemischt wird, wobei der außere Teil bis zu 50 Gew.-%
des Agglomerats ausmacht.
9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
den Mikropellets Kokspulver, Anthrazitpulver oder ähnliche kohlenstoffhaltige Materialien
zugesetzt werden.
10. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
das Binden der Pellets verbessert wird durch Carbonathärtung durch Umsetzung mit CO2.
11. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
das hydraulische Bindemittel eine spezifische Oberflächengröße von mindestens 3000
cm2/g hat.
12. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
die Pellets bei einer Temperatur von 10 bis 40°C oder bei Umgebungstemperatur getrocknet
bzw. gehärtet werden.
13. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
das mikropelletisierte Material in den Unterwind-Sinterprozeß eingeführt wird in einer
Betthöhe von mehr als 35 cm und in einer Menge von mindestens 10 % des eingeführten
Eisenträgers.
14. Mikropelletisiertes Produkt, das geeignet ist für die Durchführung des Verfahrens
nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß es umfaßt ein
feinkörniges Erzmaterial, das bis zu einer Mikropelletgröße von mindestens 75 % unter
5 mm agglomeriert worden ist, wobei das mikropelletisierte Produkt gebunden ist mit
mindestens 0,5 und höchstens 4 Gew.-% eines feinkörnigen hydraulischen Bindemittels
mit einer spezifischen Oberflächengröße von mindestens 2000 cm2/g, das besteht aus Hochofenschlacke oder einer ähnlichen Hüttenschlacke, und gegebenenfalls
bis zu 50 Gew.-% Bindemittel (Zement), wobei bis zu 50 % der Schlacke und/oder des
Bindemittels (Zements) gegebenenfalls durch gebrannten Kalk ersetzt sind, und getrocknet
(gehärtet) ist bis zu durchschnittlich mindestens 50 % der Trocknungs- bzw. Härtungsfestigkeit,
die durch 28- bis 30- tägiges Trocknen bzw. Härten bei Raumtemperatur erzielbar ist.
15. Mikropelletisiertes Produkt nach Anspruch 14, dadurch gekennzeichnet, daß das
Erz aus Eisenerz besteht.
16. Mikropelletisiertes Produkt nach Anspruch 14 oder 15, dadurch gekennzeichnet,
daß es höchstens 3 Gew.-% hydraulischen Bindemittels enthält.
1. Procédé pour améliorer la réactivité, la perméabilité et/ou des caractéristiques
semblables d'une charge de minerai soumise à un frittage à tirage inférieur, caractérisé
par l'inclusion dans ladite charge d'une quantité active d'un produit sous forme de
microboulettes préparé par boulettage d'un minerai à grains fins avec addition d'au
moins 0,5% et d'au plus 4% en poids d'un liant hydraulique à grains fins dont la surface
spécifique est d'au moins 2 000 cm2/g, ledit liant hydraulique consistant en laitier de haut fourneau ou en laitier métallurgique
similaire, et éventuellement en ciment à raison de jusqu'à 50%, jusqu'à 50% dudit
laitier et/ou dudit ciment étant éventuellement remplacés par de la chaux éteinte,
et d'eau, jusqu'à une taille des agglomérés inférieure à 5 mm pour au moins 75% en
poids, cette charge étant durcie, avant d'être introduite dans ledit dispositif de
frittage, pour atteindre jusqu'à au moins 50% en moyenne de la résistance à l'état
durci qui peut être obtenue par durcissement pendant 28 à 30 jours à la température
ambiante.
2. Procédé selon la revendication 1, caractérisé en ce que la quantité de liant hydraulique
dans le matériau sous forme de microboulettes durci est d'au moins 1% et d'au plus
3% par rapport au poids du matériau aggloméré.
3. Procédé selon les revendications 1 ou 2, caractérisé en ce que le liant hydraulique
comprend environ 90 à 50% de laitier et 10 à 50% de ciment, éventuellement remplacés
en partie par de la chaux.
4. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que le liant hydraulique
comprend environ 10 à 20% de ciment, 10 à 20% de chaux et au moins 60% de laitier.
5. Procédé selon l'une des revendications précédentes, caractérisé en ce que le liant
hydraulique comprend un ciment de laitier.
6. Procédé selon l'une des revendications précédentes, caractérisé en ce que le minerai
consiste en du minerai de fer.
7. Procédé selon l'une des revendications précédentes, caractérisé en ce que le matériau
sous forme de microboulettes est soumis, juste après le boulettage, à un stockage
en une couche dont la hauteur est de 10 m au plus pendant au moins 1 jour jusqu'à
ce que l'accroissement de la quantité de matériau présentant une taille d'agglomérés
inférieure à 0,42 mm lorsqu'il est soumis quatre fois à une chute libre d'une hauteur
de chute de 15 m soit inférieur à 20%, ledit stockage ayant lieu avant le transport
du matériau sous forme de microboulettes et son chargement dans un dispositif de frittage
à tirage inférieur.
8. Procédé selon l'une des revendications précédentes, caractérisé en ce que les microboulettes
sont formées en une ou plusieurs étapes, une quantité plus grande ou plus faible du
liant hydraulique étant mélangée à la partie externe des agglomérés par rapport à
la partie interne, ladite partie externe comprenant jusqu'à 50% du poids de l'aggloméré.
9. Procédé selon l'une des revendications précédentes, caractérisé par l'inclusion
de poudre de coke, de poudre d'anthracite ou de matières carbonées similaires dans
les microboulettes.
10. Procédé selon l'une des revendications précédentes, caractérisé en ce que la cohésion
des boulettes est améliorée par durcissement au carbonate grâce à une réaction avec
C02.
11. Procédé selon l'une des revendications précédentes, caractérisé en ce que le liant
hydraulique a une surface spécifique d'au moins 3 000 cm2/g.
12. Procédé selon l'une des revendications précédentes, caractérisé en ce que les
boulettes sont durcies à une température de 10 à 40°C ou à la température ambiante.
13. Procédé selon l'une des revendications précédentes, caractérisé en ce que le matériau
sous forme de microboulettes est chargé dans ledit processus de frittage à tirage
inférieur avec une hauteur de lit supérieure à 35 cm et en une quantité d'au moins
10% par rapport à la charge contenant du fer.
14. Produit sous forme de microboulettes convenant à la mise en oeuvre du procédé
selon l'une des revendications précédentes, caractérisé en ce qu'il comprend un minerai
à grains fins sous forme de microboulettes dont au moins 75% ont une taille inférieure
à 5 mm, ledit produit sous forme de microboulettes étant rendu cohérent par au moins
0,5% et au plus 4% en poids d'un liant hydraulique à grains fins dont la surface spécifique
est d'au moins 2 000 cm2/g et qui consiste en laitier de haut fourneau ou en laitier métallurgique similaire,
et éventuellement en ciment à raison de jusqu'à 50% en poids, jusqu'à 50% dudit laitier
et/ou dudit ciment étant éventuellement remplacés par de la chaux éteinte, et ledit
produit étant durci pour atteindre jusqu'à au moins 50% en moyenne de la résistance
à l'état durci qui peut être obtenue par durcissement pendant 28 à 30 jours à la température
ambiante.
15. Produit sous forme de microboulettes selon la revendication 14, caractérisé en
ce que le minerai consiste en minerai de fer.
16. Produit sous forme de microboulettes selon les revendications 14 ou 15, caractérisé
en ce qu'il comprend au plus 3% en poids du liant hydraulique.