Note: Descriptions are shown in the official language in which they were submitted.
CA 02861315 2015-07-15
COMPOSITE BRIQUETTE FOR STEELMAKING OR IRONMAKING
FURNACE CHARGE
Field
PH] The present invention relates generally to ferrous metallurgy and
in
particular, to a composite briquette for a steelmaking or ironmaking furnace
charge.
Background
[00021 In the field of steelmaking, an electric furnace charge is
typically made
from scrap metal, carbon and fluxes such as lime and/or dolime, all in pieces
having a
minimum size of 0.5 inch (about 12.7 mm).
[0003] It is known to add specific materials to a furnace charge in the
form of
briquettes. However, carbon, which is an essential part of the mixture of
materials, is
quite slippery in its powdered or comminuted form. Consequently, carbon is
typically
employed in a non-pulverized state, for example as metallurgical coke. It
would be of
advantage to be able to utilize carbon "fines", for example those recovered
from a
dust collector, and to recycle such fines in their powdered or dust state. A
further
problem relates to the density of carbon, which is quite low compared
generally to the
metals. For example, when carbon is added to the furnace via a charge bucket,
it will
tend to float on top of the liquid metal, thus decreasing the yield of carbon
in solution
in the steel.
[0004] It would also be of advantage to improve the quality of the slag
through the addition of a briquette.
10005] It is an object at least to provide a novel composite briquette
for a
steelmaking or ironmaking furnace charge.
Summary of the Invention
[0006] In one aspect, there is provided a composite briquette for
addition to a
charge in a steelmaking furnace, the briquette comprising: at least 80 % by
weight of
magnesium carbonate; and from 1 to 20 % by weight of a binder, the binder
comprising molasses and lime.
[0007] The briquette may comprise about 90 % by weight magnesium
carbonate and about 10 % by weight of the binder.
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[0008] The briquette may further comprise one or more substances selected
from the group consisting of limestone (CaCO3), dolomite (CaMg(CO3)2), dolime
(Ca0=Mg0), burnt lime (CaO), hydrated lime (Ca(OH)2), and magnesium oxide
(MgO).
[0009] The briquette may further comprise one or more carbonaceous
substances selected from the group consisting of: metallurgical coke, carbon
fines,
anthracite, and non-anthracitic coal.
[00010] The briquette may comprise from 5 to 19 % by weight of the
carbonaceous substances.
[00011] The briquette may further comprise from 1 to 15 % by weight of
magnesium oxide.
[00012] The magnesium carbonate may be powdered magnesium carbonate
ore, and wherein briquette, after calcining, may further comprise one or more
substances selected from the group consisting of: CaO, A1203, Si02, and Fe203.
[00013] The furnace may be an electric arc furnace or a basic oxygen
furnace.
[00014] In one embodiment, there is provided the use of the briquette as
addition to the charge in the steelmaking furnace, the furnace being an
electric arc
furnace or a basic oxygen furnace.
[00015] In another aspect, there is provided a method of improving a slag-
covered charge in a steelmaking furnace, the slag-covered charge comprising a
charge
covered with slag, the method comprising: compressing a quantity of magnesium
carbonate and a binder in a suitable mold to make a briquette, the binder
comprising
molasses and lime, the briquette comprising at least 80 % by weight magnesium
carbonate and from 1 to 20 % by weight of the binder; and introducing said
briquette
to the charge below the slag in the steelmaking furnace, whereby upon
introducing the
briquette to the charge, CO2 is generated, such that the CO,) foams the slag
from
underneath.
[00016] The briquette may comprise about 90 % by weight magnesium
carbonate and about 10 % by weight of the binder.
[00017] The briquette may further comprise one or more carbonaceous
substances selected from the group consisting of: metallurgical coke, carbon
fines,
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anthracite, and non-anthracitic coal. The briquette may comprise from 5 to 19
A by
weight of the carbonaceous substances.
[00018] The magnesium carbonate may be powdered magnesium carbonate
ore, and the briquette, after calcining, may further comprise one or more
substances
selected from the group consisting of: CaO, A1203, Si02, and Fe203.
[000191 The furnace may be an electric arc furnace or a basic oxygen
furnace.
[00020] In another aspect, there is provided a composite briquette for
addition
to a charge in a steelmaking furnace, the briquette comprising: a quantity of
carbon
fines; a quantity of iron powder, the iron powder densifying the briquette and
suppressing the slippery nature of the carbon fines; a quantity of magnesium
carbonate; a quantity of limestone; and a binder.
[00021] The briquette may further comprise one or more selected from the
group consisting of: burnt lime, hydrated lime, dolomite, and dolime.
[00022] 50 % of the total briquette weight may be carbon fines, 25 % of
the
total briquette weight may be iron powder, and the remainder of the total
briquette
weight, apart from the binder, may be magnesium carbonate and limestone.
[00023] The briquette may comprise from 1 to 20 % by weight of the binder.
[00024] The furnace may be an electric arc furnace or a basic oxygen
furnace.
[00025] In one embodiment, there is provided the use of the briquette as
addition to the charge in the steelmaking furnace, the furnace being an
electric arc
furnace or a basic oxygen furnace.
[00026] In another aspect, there is provided a method of improving a slag-
covered charge in a steelmaking furnace, the slag-covered charge comprising a
charge
covered with slag, the method comprising: making a mixture of: a quantity of
carbon
fines, a quantity of iron powder, a quantity of magnesium carbonate, a
quantity of
limestone, and a binder; compressing a portion of said mixture in a suitable
mold to
make a briquette, said iron powder densifying the briquette and suppressing
the
slippery nature of the carbon fines; and introducing said briquette to the
charge below
the slag in the steelmaking furnace so that said iron powder contained in the
briquette
causes the briquette to sink into the charge.
[00027] The mixture may further comprise one or more selected from the
group
consisting of: burnt lime, hydrated lime, dolomite, and dolime.
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[00028] 50 % of the total briquette weight may be carbon fines, 25 % of
the
total briquette weight may be iron powder, and the remainder of the total
briquette
weight, apart from the binder, may be magnesium carbonate and limestone.
[00029] Upon introducing the briquette to the charge, CO2 may be generated
such that the CO2 foams the slag from underneath.
[00030] The mixture may comprise from 1 to 20 % by weight of the binder.
[00031] The binder may comprise molasses and hydrated lime.
[00032] The furnace may be an electric arc furnace or a basic oxygen
furnace.
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Detailed Description of the Embodiments
[00033] The following is directed to a composite briquette for addition to
the
charge in a steelmaking or ironmaking furnace, and which comprises magnesium
carbonate (MgCO3).
[00034] Magnesium carbonate is known to thermally decompose at a lower
temperature than dolomite (CaMg(CO3)2) and limestone (CaCO3). Specifically,
MgCO3 thermally decomposes into magnesium oxide (MgO) and carbon dioxide
(CO2) at about 402 C, while CaMg(CO3)2 and CaCO3 each thermally decompose
into
their constituent oxides at about 730 C and about 825 C, respectively. As a
result,
when added to the charge in a steelmaking or ironmaking furnace, magnesium
carbonate thermally decomposes more quickly, and more readily, than limestone
or
dolomite.
[00035] Table 1 shows a non-limiting example of a mixture from which a
briquette can be fashioned:
TABLE 1:
Carbon C 50%
Powdered iron Fe 25 %
Magnesium carbonate MgCO3 25 %
Total 100 %
1000361 In the table above, deviations from the indicated percentages are
permissible. In this embodiment, the carbon is in the form of loose carbon
fines
recovered from a dust collector, such as a dust collector of an electric arc
furnace, and
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the magnesium carbonate is in the form of powdered magnesium carbonate ore.
The
mixture may be combined with a suitable binder, such as for example industrial
molasses and powdered hydrated lime (Ca(OH)2), and the binder may make up 1 to
20 %, or more, of the total weight of the briquette.
[00037] The example illustrated in Table 1 specifies powdered iron.
However,
this teaching is not intended to be restrictive, as it is possible to use one
or more of
iron, iron oxide, chromium, chromium oxide, nickel, and nickel oxide to
achieve the
same effect. If iron oxide is used, the reaction products will be iron and CO2
gas, as
well as caloric heat that results from burning of the iron oxide. The iron
will revert to
the bath, thus increasing its yield.
[00038] The magnesium carbonate could be combined with limestone and/or
dolomite, each of which will produce CO2 gas. Dolime (CaO MgO), burnt lime
(CaO), hydrated lime (Ca(OH)2), and/or magnesium oxide (MgO) may also be
included.
[00039] The ironmaking furnace may be, for example, a blast furnace. The
steelmaking furnace may be, for example, an electric arc furnace, a basic
oxygen
furnace, and the like. Preferably, the furnace is a blast furnace or an
electric arc
furnace.
[00040] In use, the briquette is added to the charge in a steelmaking or
ironmaking furnace, in such a manner that it is immersed within the charge.
The
briquette dissolves and reacts with the contents of the charge. The powdered
iron
reverts to the bath, thus increasing its yield. The magnesium carbonate
thermally
decomposes into magnesium oxide (MgO) and carbon dioxide (CO2). The MgO
produced is absorbed by the slag. The CO2 produced has the effect of foaming
the
slag from underneath, as the location where the CO2 is generated is buried
within the
charge.
[00041] As will be appreciated, the low decomposition temperature of
magnesium carbonate advantageously allows the slag thickness to be increased
more
rapidly than, and with less energy consumption than, other substances such as
limestone, dolomite, and the like. As will be understood, the rapid formation
of a
thick slag decreases the amount of oxidation of iron in the bath, which
improves the
reaction yield. Additionally, if the steelmaking furnace is an electric arc
furnace, the
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increased thickness of the slag advantageously causes the arc to be more
localized
within the bath and under the slag, which improves efficiency of the electric
arc
furnace and thereby allows melt times to be shortened. These performance
characteristics help mitigate the environmental impact of steelmaking and
ironmaking
operations, and conserve resources.
[00042] As will be appreciated, the accompanying production of CO2 gas
that
occurs upon decomposition of magnesium carbonate causes bubbling under the =
surface of the bath, which advantageously causes mixing and improves the
quality of
the slag, and namely the foaminess, consistency and stability of the slag.
[00043] As will be appreciated, the addition of MgO to the slag
advantageously
results in formation of a protective layer of MgO on the walls of the furnace.
As will
be understood, as the melt is being drained from the furnace, the slag
contacts the wall
surfaces of the furnace and deposits a layer of MgO thereon. As a result, a
new
protective refractory coating is automatically deposited on the walls of the
furnace
with each use, which eliminates the need for separate application of a
protective wall
coating that would otherwise form part of routine furnace maintenance.
[00044] Preferably, the briquette comprises from 20 to 80 % by weight of
the
carbon fines. More preferably, the briquette comprises 30 to 70 % by weight of
the
binder, more preferably 40 to 60 %, most preferably about 45 %.
[00045] Although in the embodiment described above, the carbon is in the
form
of carbon fines, in other embodiments, the carbon may alternatively be in the
form of
one or more other carbonaceous substances, such as for example such as
metallurgical
coke, anthracite, non-anthracitic coal, and the like.
[00046] The briquette is not limited to the composition described above,
and in
other embodiments, the briquette may alternatively have other compositions.
For
example, in another embodiment, magnesium carbonate may be added to the charge
of a steelmaking or ironmaking furnace to improve the quality of the slag.
[00047] For example, powdered magnesium carbonate ore may be combined
with a suitable binder, such as for example industrial molasses and powdered
hydrated lime, and compressed in a suitable mold to make a briquette. The
binder
may make up 1 to 20 %, or more, of the total weight of the briquette.
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[00048] The amount of magnesium carbonate in the briquette
may be selected
according to the particular characteristics of the furnace and to the
particular steel
grade. Preferably, the briquette comprises at least 15 % by weight of
magnesium
carbonate. More preferably, the briquette comprises 50 to 95 % by weight of
magnesium carbonate, still more preferably 70 to 95 %, and most preferably
90%.
1000491 The magnesium carbonate could be combined with one or
more other
substances, if adjustment of slag functionalities (e.g. alumina gettering,
desulphurization, etc.) is desired. Such substances may comprise, for example,
limestone and/or dolomite, each of which will produce CO2 gas upon
decomposition,
and/or any of dolime, burnt lime, hydrated lime, and magnesium oxide. Still
other
substances may be combined with the magnesium carbonate. As will be
understood,
an advantage of using a binder comprising hydrated lime is the efficient and
controlled addition of CaO to the slag for predictable adjustment of slag
functionalities.
1000501 The ironmaking furnace may be, for example, a blast
furnace. The
steelmaking furnace may be, for example, an electric arc furnace, a basic
oxygen
furnace, and the like. Preferably, the furnace is a blast furnace or an
electric arc
furnace.
[00051] In use, the briquette is added to the charge in a
steelmaking or
ironmaking furnace, in such a manner that it is immersed within the charge.
The
briquette dissolves and reacts with the contents of the charge. The magnesium
carbonate thermally decomposes into magnesium oxide (MgO) and carbon dioxide
(CO2). The MgO produced is absorbed by the slag. The CO2 produced has the
effect
of foaming the slag from underneath, as the location where the CO2 is
generated is
buried within the charge.
[00052] In another embodiment, magnesium carbonate ore, in
absence of a
binder, may be added in powdered or granular form to the charge of a
steelmaking or
ironmaking furnace for improving the quality of the slag.
1000531 In still another embodiment, the briquette may
alternatively comprise a
mixture of magnesium carbonate and one or more carbonaceous substances, such
as
metallurgical coke, carbon fines, anthracite, non-anthracitic coal, and the
like. For
example, powdered magnesium carbonate ore and powdered metallurgical coke may
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be combined with a suitable binder, such as for example industrial molasses
and
powdered hydrated lime, and compressed in a suitable mold to make a briquette.
The
binder may make up 1 to 20 %, or more, of the total weight of the briquette.
[00054] The amount of magnesium carbonate in the briquette may be selected
according to the particular characteristics of the furnace and to the
particular steel
grade. Preferably, the briquette comprises at least 15 % by weight of
magnesium
carbonate. Preferably, the briquette comprises 30 to 90 % by weight of
magnesium
carbonate, more preferably 40 to 90 %, most preferably about 50 to about 75 %.
[00055] Preferably, the briquette comprises from 5 to 50 % by weight of
the
one or more carbonaceous substances. More preferably, the briquette comprises
10 to
40 % by weight of the binder, more still preferably 10 to 35 %, most
preferably either
about 14 % or about 30 %.
[00056] One or more other substances could be combined with the powdered
magnesium carbonate ore and powdered metallurgical coke, if adjustment of slag
functionalities (e.g. alumina gettering, desulphurization, etc.) is desired.
Such
substances may comprise, for example, limestone and/or dolomite, each of which
will
produce CO2 gas upon decomposition, and/or any of dolime, burnt lime, hydrated
lime, and magnesium oxide. Still other substances may be combined with the
magnesium carbonate and powdered metallurgical coke.
[00057] The ironmaking furnace may be, for example, a blast furnace. The
steelmaking furnace may be, for example, an electric arc furnace, a basic
oxygen
furnace, and the like. Preferably, the furnace is a blast furnace or an
electric arc
furnace.
[00058] In use, the briquette is added to the charge in a steelmaking or
ironmaking furnace, in such a manner that it is immersed within the charge.
The
briquette dissolves and reacts with the contents of the charge. The magnesium
carbonate thermally decomposes into magnesium oxide (MgO) and carbon dioxide
(CO2). The MgO produced is absorbed by the slag. The CO2 produced has the
effect
of foaming the slag from underneath, as the location where the CO2 is
generated is
buried within the charge.
[00059] As will be appreciated, the combination of a carbonaceous
substance
with one or more denser compounds, such as magnesium carbonate, in briquette
form
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advantageously enables carbon to be introduced into the bath in a more facile
manner,
as compared to adding loose carbonaceous powder, and thereby increases the
carbon
addition efficiency. This higher carbon addition efficiency advantageously
allows the
final carbon composition in the bath and in the slag to be more accurately
predicted.
[00060] Although in the embodiments described above, the binder comprises
industrial molasses and hydrated lime, in other embodiments, the binder may
alternatively comprise dextrin and water, which may for example be combined in
a
7:3 weight ratio. Still other suitable binders may alternatively be used.
[00061] In the embodiments described above, the briquette may comprise
from
1 to 20 % or more, by weight, of the binder. Preferably, the briquette
comprises from
1 to 15 % by weight of the binder. More preferably, the briquette comprises 5
to 15
% by weight of the binder, more preferably 7 to 12 %, most preferably 10 %.
[00062] Although in the embodiments described above, the powdered
magnesium carbonate is in the form of powdered magnesium carbonate ore, in
other
embodiments, other suitable sources of magnesium carbonate may alternatively
be
used.
[00063] The briquette of the embodiments described above may be made from
powders having particle sizes within any suitable range.
[00064] The following examples illustrate various applications of the
above-
described embodiments.
[00065] EXAMPLE 1
[00066] In this example, a briquette having the composition (wt %) shown
in
Table 2, was made:
TABLE 2:
Carbon fines 43.6 %
Fe 22.1 %
Dolomite 24.3 %
Molasses 6.0 %
Lime (hyd.) 4.0 %
[00067] The briquette was formed by providing a mixture of loose carbon
fines
(particle size range of about 0.8 to about 1.0 mm) recovered from a dust
collector of
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an electric arc furnace, powdered iron (particle size range of about 0.4 to
about 0.6
mm), and a powdered dolomite ore (particle size range of about 0.8 to about
4.8 mm),
together with a binder consisting of a mixture of industrial molasses and
powdered
hydrated lime.
[00068] As will be understood, the powdered iron could be replaced with
powdered iron oxide (Fe203), which will produce CO2 gas and contribute to the
foaming effect described above.
[00069] The briquette had the post-calcination composition (wt %) shown in
Table 3:
TABLE 3:
43.7%
Fe 22.5 %
CaO 12.2%
MgO 6.6%
2.9%
L.O.I. 12.1 %
[00070] The L.O.I. is mainly attributed to the decomposition of the
dolomite
and the binder used. The layer of CO and CO2 produced will protect the bath
from
oxidation and enhance the carbon yield.
[00071] The manufacturing process by which the briquette is formed has the
effect of densification, with the following typical values: loose carbon prior
to
compression has a density of approximately 0.63 to 0.65 g/cm3. If a briquette
is
manufactured from the loose carbon only, the density can be raised into the
range of
1.6 to 1.75 g/cm3. However, utilizing the formulation given at the beginning
of this
example, and compressing the formulation, will yield a density in the range of
2.4 to
2.6 g/cm3.
[00072] The densification due to compression has the effect of increasing
the
efficiency of the carbon addition, since the carbon is allowed to penetrate
the bath,
rather than simply floating on top of the bath.
[00073] EXAMPLE 2
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[00074] In this example, a briquette having the post-calcination
composition
(wt %) shown in Table 4 was made:
TABLE 4:
MgO 92.19%
CaO 2.46%
A1203 0.85 %
Si02 2.58 %
TiO2 0.14%
Fe203 0.71 %
Cr203 0.02 %
MnO 0.05%
< 0.001 %
Moisture 1.0%
Total 100%
[00075] The briquette was formed by providing a mixture of powdered
magnesium carbonate ore (particle size range of about 0.8 to about 4.8 mm) and
a
binder, combined in a weight ratio of 90:10, and compressing the mixture in a
suitable
mold. The binder was a mixture of industrial molasses and powdered hydrated
lime,
combined in a weight ratio of 3:2.
[00076] The briquette had a generally square shape and a size of about 40
mm
per side, with a density of 2.18 g/cm3 and a white colour. The briquette had a
L.O.I.
value of 35.0 %, which is mainly attributed to the decomposition of the
magnesium
carbonate and the binder. Notably, the L.O.I. value of the briquette is lower
than the
L.O.I. value of the loose powder of Example 3.
[00077] The briquette was used during reactions in a 125 tonne electric
arc
furnace. A summary of the performance of the briquette ("Briquette A") during
the
reactions is shown in Table 5. For comparison, a summary of the performance of
a
standard conventional additive, namely crushed brick ("standard practice"),
during the
reactions is also shown:
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TABLE 5:
Standard Briquette A difference
Practice
Number of Heats 44 11
Quantity added (lbs) 3500 3500
Actual MgO added (lbs) 3220 2100 -34.78 %
Average MgO in soln. (wt %) 8.79 1.75 9.20 1.88 +4.66 %
Briquette A with 1st charge (wt 10.69 1.80
Briquette A with 2' charge (wt 7.95 0.62
%)
[00078] As may be seen, the use of Briquette A results in a reduction of
the
actual MgO added by about 35 %, while advantageously increasing the average
MgO
in the slag by about 4.5 %. The amount of MgO in the slag is about 34 % higher
when the Briquette A was added with the first charge (i.e. when little or no
slag layer
previously existed) than when the Briquette A was added with the second
charge.
[00079] The decomposition of magnesium carbonate within Briquette A
produces fine, active MgO particles, which are absorbed by the slag. It was
observed
that when Briquettes A were added and the briquettes penetrated the slag so as
to be
buried in the charge, tiny bubbles of CO2 were seen to form.
[00080] The average composition of the slag after the reactions, by weight
percent, is shown in Table 6:
TABLE 6:
Standard Briquette A difference
Practice
CaO 36.07 3.72 36.41 3.04 + 0.93 %
A1203 6.99 1.98 7.68 0.99 + 9.87 %
Si02 11.83 3.75 13.23 1.44 + 11.83%
Fe2O3 27.71 7.32 24.59 5.53 - 11.26%
Mn203 5.46 1.03 5.31 0.37 - 2.82 %
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[00081] As may be seen, the use of Briquette A results in a reduction of
the
iron content of the slag by more than 11 %, as compared to standard practice.
This
may be attributed to the ability of the magnesium carbonate to rapidly
decompose and
contribute to or form the slag, which allows a protective barrier to more
quickly form
on the bath surface. As a result, less of the iron in the bath is oxidized
during the
reaction, which advantageously increases the yield of the reaction.
[00082] During the test, 22 heats were carried out using crushed brick,
followed by 11 heats carried out using Briquette A, followed by 22 heats
carried out
using crushed brick. The operational performance of the 125 tonne electric arc
furnace before, during, and after the addition of Briquette A is shown in
Table 7:
TABLE 7:
Standard Standard Standard Briquette A
Practice Practice Practice
(before test) (after test) (avg)
Power usage 427.0 24.1 428.0 14.4 427.5 420.0 9.9
(KWh/T)
[00083] As may be seen, the amount of power required for the reaction is
lower
when Briquette A is used, as compared to standard practice.
[00084] EXAMPLE 3
[00085] Magnesium carbonate may alternatively be added to the charge in
the
form of a loose powder. A loose, powdered magnesium carbonate ore (particle
size
range of about 0.8 to about 4.8 mm) having the post-calcination composition
(wt %)
shown in Table 8 was used:
TABLE 8:
MgO 97.0%
CaO 2.0%
A1203 0.2 %
SiO2 0.3 %
Fe203 0.5 %
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Total 100%
[00086] The loose powder had a density of 2.28 g/cm3 and a white colour.
[00087] The loose powder was used during a reaction in a 125 tonne
electric
arc furnace.
[00088] The loose powder had a L.O.I. value of 51.1 %. Notably, the L.O.I.
value of the loose powder is greater than the L.O.I. value of the briquette of
Example
2.
[00089] EXAMPLE 4
[00090] In this example, a briquette having the composition (wt %) shown
in
Table 9 was made:
TABLE 9:
Metallurgical 30.3 %
coke
MgO 9.1%
MgCO3 51.6%
Molasses 5.4 %
Lime (hyd.) 3.6%
[00091] The briquette was formed by providing a mixture of powdered
metallurgical coke (particle size range of about 0.8 to about 1.0 mm),
powdered
magnesium oxide (particle size range of about 0.4 to about 0.6 mm), and
powdered
magnesium carbonate ore (particle size range of about 0.8 to about 4.8 mm),
together
with a binder consisting of a mixture of industrial molasses and powdered
hydrated
lime.
[00092] The briquette had a generally square shape and a size of about 54
mm
per side, with a density of about 2.0 g/cm3 and a black colour.
[00093] The briquette had the post-calcination composition (wt %) shown in
Table 10:
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TABLE 10:
C 28.7%
Fe 0.5%
CaO 3.5%
MgO 35.3%
A1203 0.5 %
Si02 1.7%
N 0.1%
L.O.I. 29.7 %
[00094] The briquette had a L.O.I. value of 29.7 %, which is mainly
attributed
to the decomposition of the magnesium carbonate and the binder.
[00095] The density of the briquette, namely 2.0 g/cm3, is greater than
that of
loose powdered metallurgical coke, which has a density of about 0.5 g/cm3. As
will
be appreciated, the higher density of the briquette has the effect of
increasing the
efficiency of the carbon addition, since the carbon is allowed to penetrate
the bath,
rather than simply floating on top of the bath.
[00096] EXAMPLE 5
[00097] In this example, a briquette having the composition (wt %) shown
in
Table 11 was made:
TABLE 11:
Metallurgical 14.0 A
coke
MgCO3 76.0 %
Molasses 6.0%
Lime (hyd.) 4.0 %
[00098] The briquette was formed by providing a mixture of powdered
metallurgical coke (particle size range of about 0.8 to about 1.0 mm) and
powdered
magnesium carbonate ore (particle size range of about 0.8 to about 4.8 mm),
together
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with a binder consisting of a mixture of industrial molasses and powdered
hydrated
lime.
[00099] The briquette had a generally square shape and a size
of about 54 mm
per side, with a density of about 2.0 g/cm3 and a black colour.
[000100] The briquette had the post-calcination composition (wt
%) shown in
Table 12:
TABLE 12:
14.1%
FeO 0.2 %
CaO 3.4%
MgO 38.7%
A1203 0.1 %
Si 02 0.6 %
0.1%
L.O.I. 42.8 %
[000101] The briquette had a L.O.I. value of 42.8 %, which is
mainly attributed
to the decomposition of the magnesium carbonate and the binder.
[000102] The density of the briquette, namely 2.0 g/cm3, is
greater than that of
loose powdered metallurgical coke, which has a density of about 0.5 g/cm3. As
will
be appreciated, the higher density of the briquette has the effect of
increasing the
efficiency of the carbon addition, since the carbon is allowed to penetrate
the bath,
rather than simply floating on top of the bath.
[000103] Although embodiments have been described above, those
of skill in the
art will appreciate that variations and modifications may be made without
departing
from the scope thereof as defined by the appended claims.
