U.S. patent application number 11/009702 was filed with the patent office on 2005-05-05 for method for manufacturing hot metal desulfurizing agent and apparatus for same.
This patent application is currently assigned to NKK Corporation. Invention is credited to Kikuchi, Yoshiteru, Nakai, Yoshie, Shimizu, Hiroshi, Takaoka, Toshio, Tanaka, Shuei, Wakamatsu, Shinichi, Watanabe, Atsushi, Yamase, Osamu.
Application Number | 20050092133 11/009702 |
Document ID | / |
Family ID | 18679773 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092133 |
Kind Code |
A1 |
Nakai, Yoshie ; et
al. |
May 5, 2005 |
Method for manufacturing hot metal desulfurizing agent and
apparatus for same
Abstract
The present invention provides a method of desulfurizing hot
metal, which method utilizes desulfurization slag resulting from a
KR hot metal desulfurizing treatment as a desulfurizing agent for
hot metal again to reduce hot metal desulfurization costs and the
amount of slag generated, thereby solving environmental
problems.
Inventors: |
Nakai, Yoshie; (Tokyo,
JP) ; Shimizu, Hiroshi; (Tokyo, JP) ; Takaoka,
Toshio; (Tokyo, JP) ; Kikuchi, Yoshiteru;
(Tokyo, JP) ; Tanaka, Shuei; (Tokyo, JP) ;
Wakamatsu, Shinichi; (Tokyo, JP) ; Watanabe,
Atsushi; (Tokyo, JP) ; Yamase, Osamu; (Tokyo,
JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Assignee: |
NKK Corporation
Tokyo
JP
Kokan Mining Co. Ltd.
Tokyo
JP
|
Family ID: |
18679773 |
Appl. No.: |
11/009702 |
Filed: |
December 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11009702 |
Dec 13, 2004 |
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10317194 |
Dec 12, 2002 |
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10317194 |
Dec 12, 2002 |
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PCT/JP01/05065 |
Jun 14, 2001 |
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Current U.S.
Class: |
75/526 |
Current CPC
Class: |
C21C 7/0645 20130101;
C21C 7/064 20130101; C21C 1/025 20130101; C21C 1/02 20130101; Y02P
10/20 20151101 |
Class at
Publication: |
075/526 |
International
Class: |
C21C 007/064 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2000 |
JP |
2000-178321 |
Claims
1. A method of manufacturing a hot metal desulfurizing agent, the
method being comprising executing a treatment for creating a new
surface in desulfurization slag resulting from a mechanical
agitation type hot metal desulfurizing treatment.
2. A method of manufacturing a hot metal desulfurizing agent for
use in a mechanical agitation type hot metal desulfurizing
treatment according to claim 1, the method being comprising
executing a treatment for creating a new surface in desulfurization
slag resulting from the mechanical agitation type hot metal
desulfurizing treatment.
3. A method according to claim 1, comprising a step of providing
desulfurization slag resulting from the mechanical agitation type
hot metal desulfurizing treatment and a step of executing the
treatment for creating a new surface in the provided
desulfurization slag.
4. A method according to claim 1, wherein the step of executing the
treatment for creating a new surface includes crushing a
desulfurization slag grain and/or separating an aggregate of a
plurality of desulfurization slag grains into desulfurization slag
grains.
5. A method according to claim 1, wherein the step of executing the
treatment for creating a new surface includes crushing the
desulfurization slag grain and/or separating the aggregate of a
plurality of desulfurization slag grains into desulfurization slag
grains by air-cooling the desulfurization slag and/or applying
mechanical energy to the desulfurization slag.
6. A method according to claim 5, wherein the desulfurization slag
is cooled using one or two methods selected from the group
consisting of air cooling and water cooling.
7. A method according to claim 6, wherein the air cooling is
carried out using one or two methods selected from the group
consisting of natural air cooling and forced air cooling.
8. A method according to claim 6, wherein the step of executing the
treatment for creating a new surface by water cooling comprises a
step of watering the desulfurization slag, and this watering step
controls the amount of water provided so as to maintain the
temperature of the desulfurization slag at 100.degree. C. or higher
at the end of the watering, so that only by means of cooling based
on the watering, the aggregate of desulfurization slag can be
separated into desulfurization slag grains and/or the
desulfurization slag grains can be crushed.
9. A method according to claim 1, wherein the step of executing the
treatment for creating a new surface comprises a step of
water-cooling the desulfurization slag and a step of drying a
recovered desulfurizing agent resulting from the water cooling.
10. A method according to claim 1, wherein the step of executing
the treatment for creating a new surface comprises a step of
cooling the desulfurization slag and a step of adjusting the grain
sizes of the desulfurization slag and the recovered desulfurizing
agent.
11. A method according to claim 10, wherein the step of adjusting
the grain size of the recovered desulfurizing agent using a sieve
is executed at a temperature of 600.degree. C. or higher.
12. A method according to claim 1, wherein the step of executing
the treatment for creating a new surface comprises a step of
executing at least one or two treatments selected from the group
consisting of a treatment for magnetically separating and removing
metal from the desulfurization slag or the recovered desulfurizing
agent, a treatment for removing large masses from the
desulfurization slag or the recovered desulfurizing agent to set
the grain size to 100 mm or smaller, and a treatment for setting
the temperature of the desulfurization slag or the recovered
desulfurizing agent to 200.degree. C. or lower.
13. A method according to claim 1, wherein the step of executing
the treatment for creating a new surface comprises a step of
setting the grain size of the desulfurization slag to 100 mm or
smaller and the temperature thereof to 200.degree. C. or lower.
14-32. canceled
33. The method of manufacturing low-sulfur hot metal, the method
being comprising desulfurizing hot metal by adding, to the hot
metal, a hot metal desulfurizing agent comprising a recovered
desulfurizing agent having a new surface created therein resulting
from a mechanical agitation hot metal desulfurizing treatment.
34. The method of manufacturing low-sulfur hot metal, the method
being comprising desulfurizing hot metal using a mechanical
agitation hot metal desulfurizing treatment by adding, to the hot
metal, a hot metal desulfurizing agent comprising a recovered
desulfurizing agent having a new surface created therein resulting
from the mechanical agitation hot metal desulfurizing
treatment.
35. The method of manufacturing low-sulfur hot metal according to
claim 33, the method being comprising desulfurizing the hot metal
by adding, to the hot metal, the desulfurizing agent comprising the
recovered desulfurizing agent having a new surface created therein
resulting from the mechanical agitation hot metal desulfurizing
treatment.
36. The method of manufacturing low-sulfur hot metal according to
claim 33, the method being comprising desulfurizing the hot metal
by adding, to the hot metal, the desulfurizing agent comprising the
recovered desulfurizing agent having a new surface created therein
which results from the mechanical agitation hot metal desulfurizing
treatment and in which part or all of an aggregate of the recovered
desulfurizing agent is separated into pieces.
37. The method according to claim 33, desulfurizing the hot metal
by adding, to hot metal, the recovered desulfurizing agent having a
new surface created therein resulting from the mechanical agitation
type hot metal desulfurizing treatment and one or more sources
selected from the group consisting of a lime source and a carbon
source.
38. The method according to claim 33, desulfurizing hot metal by
mixing the recovered desulfurizing agent resulting from the
mechanical agitation hot metal desulfurizing treatment with one or
more sources selected from the group consisting of a lime source
and a carbon source, and adding this mixture to hot metal.
39. The method according to claim 33, desulfurizing the hot metal
by separately adding, to the hot metal, the recovered desulfurizing
agent resulting from the mechanical agitation hot metal
desulfurizing treatment and one or more sources selected from the
group consisting of a lime source and a carbon source.
40. The method according to claim 37, wherein when the lime source
is added, the mixing ratio is adjusted so as to obtain a
predetermined amount of pure CaO component.
41. The method according to claim 37, comprising a step of
calculating a bulk density of the recovered desulfurizing agent
resulting from the mechanical agitation hot metal desulfurizing
treatment, a step of calculating an amount of pure CaO component in
the recovered desulfurizing agent from the calculated bulk density,
and a step of adjusting an addition ratio of the crushed recovered
desulfurizing agent to the lime source on the basis of the
calculated amount of pure CaO component in the recovered
desulfurizing agent.
42. The method according to claim 37, comprising a step of
adjusting the grain size of the carbon source to 1 mm or smaller
when the carbon source is added.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation Application of PCT Application No.
PCT/JP01/05065, filed Jun. 14, 2001, which was not published under
PCT Article 21(2) in English.
[0002] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2000-178321, filed Jun. 14, 2000, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a method of manufacturing a
desulfurizing agent for hot metal and a desulfurizing agent, and in
particular, to a method of manufacturing a desulfurizing agent for
hot metal, which method effectively reuses desulfurization slag (KR
slag) resulting from a mechanical agitation type hot metal
desulfurizing treatment step, an apparatus for use in this method,
a desulfurizing agent (flux) for use in this method and apparatus,
and a method of desulfurizing hot metal using this desulfurizing
agent.
[0005] 2. Description of the Related Art
[0006] Hot metal output from a blast furnace contains a high
concentration of sulfur (S), which normally affects the quality of
steel. However, since a converter step is intended to oxidize and
remove impurities, molten steel is not expected to be desulfurized
except for part thereof which is vaporized and desulfurized. Thus,
depending on the desired quality, various hot metal pretreatments
are executed between the blast furnace step and the converter step
or molten steel is desulfurized after the converter step. FIG. 23
shows an example of a hot metal pretreatment. In the illustrated
example, hot metal from the blast furnace is sequentially subjected
to a desiliconizing treatment, a desulfurizing treatment, and a
dephosphorizing treatment. The hot metal is then placed in the
converter, where it is subjected to a decarburizing treatment.
[0007] For desulfurization, a lime-based desulfurizing agent is
often used. A desulfurizing reaction in this case proceeds
according to the reaction formula shown below.
CaO+S.fwdarw.CaS+O
[0008] With only CaO, such a desulfurizing reaction involves a high
melting point. Thus, typically, fluorite, alumina-based flux, or
the like is industrially used to facilitate slagging. However,
these slagging agents are generally expensive, so that an increase
in the compounding rate of such a slagging agent leads to an
increase in the costs of the desulfurizing agent. Furthermore, an
increase in the compounding rate of the slagging agent may reduce
the concentration of lime in the desulfurizing agent to degrade
reaction effects.
[0009] Further, slag resulting from a pyrometalurgy step in a blast
furnace or a converter is reused for blast furnace cement, concrete
material, fertilizers, or road material after having contained
metal removed. However, desulfurization slag is characterized by
containing a large amount of CaO and being likely to be weathered.
Accordingly, there is no other way but to use the desulfurizing
slag for cement material by executing a pretreatment that requires
much time and labor. Furthermore, at present, this treatment
involves high cost.
[0010] Jpn. Pat. Appln. KOKAI Publication No. 4-120209 describes a
technique of utilizing converter slag as a slagging agent. This
application states that the grain size of the blast furnace slag is
set at 3 to 50 mm and that this range of grain size serves to
produce a sufficient dephosphorizing effect. However, this
application is not mainly intended for desulfurization, and has no
references to desulfurization.
[0011] Further, Jpn. Pat. Appln. KOKAI Publication No. 10-30115
discloses a technique of cooling and crushing converter slag,
separating and recovering the iron component from the slag, and
compounding lime and fluorite into the slag so that it can be used
as a desulfurizing agent. However, this application has no
references to the recycling of desulfurization slag as in the above
technique.
[0012] As an example of the recycling of desulfurization slag,
there is a report on a process of reusing injection desulfurization
slag containing a large amount of unreacted lime, in a mechanical
agitation type hot metal desulfurizing treatment which allows lime
to be used efficiently (Sumitomo Metals Vol. 45-3 (1993) p. 52 to
58). However, with the treatment (hereinafter referred to as the
"prior art of desulfurization slag recycling") reported in this
document, there is a limit to the improvement of efficiency of
utilization of lime as described later. Further, since this
technique reuses the slag in the process using different addition
and agitation methods, it is not applicable if a plurality of
processes are not available.
[0013] A mechanical agitation type hot metal desulfurization
apparatus desulfurizes hot metal by immersing and rotating an
impeller in hot metal, adding a desulfurizing agent (normally lime)
to the hot metal from above, and rotating the impeller to agitate
the hot metal. A process commonly known as the "KR method" is a hot
metal desulfurizing treatment using this apparatus. FIG. 24 shows
an example of a desulfurizing facility.
[0014] As described above, at present, desulfurization slag
resulting from a hot metal desulfurizing treatment is not
effectively recycled. Further, for desulfurization of hot metal,
there are many points to be improved.
BRIEF SUMMARY OF THE INVENTION
[0015] The inventors examined the efficiency of utilization of a
desulfurizing agent used in the KR desulfurizing step. FIG. 18
shows the ratio of lime effectively used to introduced lime wherein
the case in which desulfurization slag resulting from a mechanical
agitation type hot metal desulfurizing treatment method is used as
a desulfurizing agent for the mechanical agitation type hot metal
desulfurizing treatment method is compared with the case in which
desulfurization slag resulting from an injection method is used as
a desulfurizing agent for the mechanical agitation type hot metal
desulfurizing treatment method. As indicated in FIG. 18, the
inventors have found that the efficiency of utilization of the
desulfurizing agent during a single KR desulfurizing step
corresponds to about 7% of the total desulfurizing agent, with the
remaining 93% unreacted. Accordingly, on the basis of this
knowledge, the inventors expected that the desulfurizing agent that
has been used in the KR desulfurizing step can be reused as an
inexpensive source of lime for the desulfurizing agent because it
still contains about 93% of lime that contributes to
desulfurization in the subsequent treatment.
[0016] The present invention is provided on the basis of this
knowledge. It is an object of the present invention to provide a
method of desulfurizing hot metal, which method effectively reuses
desulfurization slag resulting from a hot metal desulfurizing
treatment in order to reduce the costs of hot metal desulfurization
and the amount of slag generated.
[0017] It is another object of the present invention to
inexpensively carry out a hot metal desulfurizing treatment with a
reduced amount of slag generated and to provide a desulfurizing
agent for use in this treatment.
[0018] It is yet another object of the present invention to provide
a method of transporting desulfurization slag and an apparatus used
to manufacture desulfurization slag.
[0019] The present invention is provided to accomplish these
objects.
[0020] A method of manufacturing a hot metal desulfurizing agent
according to the present invention comprises the following
steps:
[0021] 1. A method of manufacturing a hot metal desulfurizing
agent, the method comprising executing a treatment for creating a
new surface in desulfurization slag resulting from a mechanical
agitation type hot metal desulfurizing treatment.
[0022] 2. A method of manufacturing a hot metal desulfurizing agent
for use in a mechanical agitation type hot metal desulfurizing
treatment, the method comprising executing a treatment for creating
a new surface in desulfurization slag resulting from the mechanical
agitation type hot metal desulfurizing treatment.
[0023] 3. A method comprising a step of providing desulfurization
slag resulting from the mechanical agitation type hot metal
desulfurizing treatment and a step of executing the treatment for
creating a new surface in the provided desulfurization slag.
[0024] 4. A method wherein the step of executing the treatment for
creating a new surface includes crushing a desulfurization slag
grain and/or separating an aggregate of a plurality of
desulfurization slag grains into desulfurization slag grains.
[0025] 5. A method wherein the step of executing the treatment for
creating a new surface includes crushing the desulfurization slag
grain and/or separating the aggregate of a plurality of
desulfurization slag grains into the desulfurization slag grains by
air-cooling the desulfurization slag and/or applying mechanical
energy to the desulfurization slag.
[0026] 6. A method wherein the desulfurization slag is cooled using
one or two methods selected from a group consisting of air cooling
and water cooling.
[0027] 7. A method wherein the air cooling is carried out using one
or two methods selected from a group consisting of natural cooling
and forced air cooling.
[0028] 8. A method wherein the step of executing the treatment for
creating a new surface by water cooling comprises a step of
watering the desulfurization slag, and this watering step controls
the amount of water provided so as to maintain the temperature of
the desulfurization slag at 100.degree. C. or higher at the end of
the watering, so that only by means of cooling based on the
watering, the aggregate of desulfurization slag can be separated
into desulfurization slag grains and/or the desulfurization slag
grains can be crushed.
[0029] 9. A method wherein the step of executing the treatment for
creating a new surface comprises a step of water-cooling the
desulfurization slag and a step of drying the recovered
desulfurizing agent resulting from the water cooling.
[0030] 10. A method wherein the step of executing the treatment for
creating a new surface comprises a step of cooling the
desulfurization slag and a step of adjusting the grain sizes of the
desulfurization slag and the recovered desulfurizing agent.
[0031] 11. A method wherein the step of adjusting the grain size of
the recovered desulfurizing agent using a sieve is executed at a
temperature of 600.degree. C. or higher.
[0032] 12. A method wherein the step of executing the treatment for
creating a new surface comprises a step of executing at least one
or two treatments selected from a group consisting of a treatment
for magnetically separating and removing metal from the
desulfurization slag or the recovered desulfurizing agent, a
treatment for removing large masses from the desulfurization slag
or the recovered desulfurizing agent to set the grain size at 100
mm or smaller, and a treatment for setting the temperature of the
desulfurization slag or the recovered desulfurizing agent at
200.degree. C. or lower.
[0033] 13. A method wherein the step of executing the treatment for
creating a new surface comprises a step of setting the grain size
of the desulfurization slag at 100 mm or smaller and the
temperature thereof at 200.degree. C. or lower.
[0034] 14. A method of transporting a recovered desulfurizing
agent, the method comprising a step of loading a recovered
desulfurizing agent resulting from a mechanical agitation type hot
metal desulfurizing treatment onto a transport vehicle using a pair
of movable basket sections that can be opened and closed and a step
of using the transport vehicle to transport the recovered
desulfurizing agent to a desulfurizing treatment facility.
[0035] 15. A method comprising a step of screening the cooled and
crushed recovered desulfurizing agent to remove large masses before
or simultaneously with the step of using the transport vehicle to
transport the recovered desulfurizing agent.
[0036] 16. A method of transporting a recovered desulfurizing
agent, the method comprising a step of loading a recovered
desulfurizing agent resulting from a mechanical agitation type hot
metal desulfurizing treatment onto a transport vehicle having a
capability of sucking the recovered desulfurizing agent and a step
of using the transport vehicle to transport the recovered
desulfurizing agent to a desulfurizing treatment facility.
[0037] 17. A method wherein the step of loading the recovered
desulfurizing agent is executed while adjusting a height from which
the recovered desulfurizing agent is dropped onto the transport
vehicle, to 1.5 m or less.
[0038] 18. An apparatus which screens a recovered desulfurizing
agent, the apparatus comprising an apparatus main body having a
sieve mesh that screens a crushed recovered desulfurizing agent and
an air sucking hose attached to the apparatus main body to
facilitate suction of the recovered desulfurizing agent into the
apparatus main body.
[0039] 19. An apparatus which screens a recovered desulfurizing
agent, the apparatus comprising a member having a diagonally
arranged sieve mesh, a diagonal plate diagonally arranged below the
member and on which a minus sieve slides down, and a sliding way on
which the minus sieve from the diagonal plate falls and then slides
down, and wherein the apparatus is arranged so that the spacing
between the member having the sieve mesh and the diagonal plate and
the vertical height of drop of a linkage between the diagonal plate
and the sliding way are each 500 mm or less and the height of drop
from the sliding way to a ground surface is 500 mm or less.
[0040] 20. A hot metal desulfurizing agent comprising a recovered
desulfurizing agent resulting from a mechanical agitation type hot
metal desulfurizing treatment.
[0041] 21. A hot metal desulfurizing agent comprising the recovered
desulfurizing agent resulting from the mechanical agitation type
hot metal desulfurizing treatment, the hot metal desulfurizing
agent being used for the mechanical agitation type hot metal
desulfurizing treatment.
[0042] 22. A hot metal desulfurizing agent comprising the recovered
desulfurizing agent resulting from the mechanical agitation type
hot metal desulfurizing treatment and having a new surface created
therein.
[0043] 23. A hot metal desulfurizing agent comprising the recovered
desulfurizing agent which results from the mechanical agitation
type hot metal desulfurizing treatment and in which part or all of
an aggregate of recovered desulfurizing agent grains is separated
into pieces.
[0044] 24. A hot metal desulfurizing agent having a maximum grain
size of 100 mm or smaller.
[0045] 25. A hot metal desulfurizing agent comprising the recovered
desulfurizing agent resulting from the mechanical agitation type
hot metal desulfurizing treatment, the hot metal desulfurizing
agent further containing one or two sources selected from a group
consisting of a lime source and a carbon source.
[0046] 26. A hot metal desulfurizing agent wherein the one or two
sources selected from the group consisting of the lime source and
the carbon source are mixed with the recovered desulfurizing agent
resulting from the mechanical agitation type hot metal
desulfurizing treatment, and this mixture is added to hot
metal.
[0047] 27. A hot metal desulfurizing agent wherein the one or two
sources selected from the group consisting of the lime source and
the carbon source are separated from the recovered desulfurizing
agent resulting from the mechanical agitation type hot metal
desulfurizing treatment, and the one or more sources and the
recovered desulfurizing agent are separately added to hot
metal.
[0048] 28. A hot metal desulfurizing agent wherein the lime source
is at least one or two selected from a group consisting of lime,
calcium carbonate, and calcium hydroxide.
[0049] 29. A hot metal desulfurizing agent wherein the total amount
of calcium carbonate and calcium hydroxide, which are included in
the group of lime sources, corresponds to 40 wt % or less of the
whole hot metal desulfurizing agent.
[0050] 30. A hot metal desulfurizing agent wherein the amount of
carbon source corresponds to 30 wt % or less of the whole hot metal
desulfurizing agent.
[0051] 31. A hot metal desulfurizing agent wherein the carbon
source is powders of grain size 1 mm or smaller.
[0052] 32. A hot metal desulfurizing agent wherein the carbon
source is at least one or two selected from a group consisting of
coal, coke, and pitch.
[0053] 33. A method of manufacturing low-sulfur hot metal, the
method comprising desulfurizing hot metal by adding, to the hot
metal, a hot metal desulfurizing agent comprising a recovered
desulfurizing agent resulting from a mechanical agitation type hot
metal desulfurizing treatment.
[0054] 34. A method of manufacturing low-sulfur hot metal, the
method comprising desulfurizing hot metal using a mechanical
agitation type hot metal desulfurizing treatment, by adding, to the
hot metal, a hot metal desulfurizing agent comprising a recovered
desulfurizing agent resulting from the mechanical agitation type
hot metal desulfurizing treatment.
[0055] 35. A method of manufacturing low-sulfur hot metal, the
method comprising desulfurizing the hot metal by adding, to the hot
metal, the desulfurizing agent comprising the recovered
desulfurizing agent resulting from the mechanical agitation type
hot metal desulfurizing treatment and having a new surface created
therein.
[0056] 36. A method of manufacturing low-sulfur hot metal, the
method comprising desulfurizing the hot metal by adding, to the hot
metal, the desulfurizing agent comprising the recovered
desulfurizing agent which results from the mechanical agitation
type hot metal desulfurizing treatment and in which part or all of
an aggregate of the recovered desulfurizing agent is separated into
pieces.
[0057] 37. A method comprising desulfurizing the hot metal by
adding, to hot metal, the recovered desulfurizing agent resulting
from the mechanical agitation type hot metal desulfurizing
treatment and one or more sources selected from a group consisting
of a lime source and a carbon source.
[0058] 38. A method comprising desulfurizing the hot metal by
mixing the recovered desulfurizing agent resulting from the
mechanical agitation type hot metal desulfurizing treatment with
one or more sources selected from a group consisting of a lime
source and a carbon source, and adding this mixture to hot
metal.
[0059] 39. A method comprising desulfurizing the hot metal by
separately adding, to the hot metal, the recovered desulfurizing
agent resulting from the mechanical agitation type hot metal
desulfurizing treatment and one or more sources selected from a
group consisting of a lime source and a carbon source.
[0060] 40. A method wherein when the lime source is added, the
mixing ratio is adjusted so as to obtain a predetermined amount of
pure CaO component.
[0061] 41. A method comprising a step of calculating the bulk
density of the recovered desulfurizing agent resulting from the
mechanical agitation type hot metal desulfurizing treatment, a step
of calculating the amount of pure CaO component in the recovered
desulfurizing agent from the calculated bulk density, and a step of
adjusting the addition ratio of the crushed recovered desulfurizing
agent to the lime source on the basis of the calculated amount of
pure CaO component in the recovered desulfurizing agent.
[0062] 42. A method comprising a step of adjusting the grain size
of the carbon source to 1 mm or smaller when the carbon source is
added.
[0063] (Definition)
[0064] "Desulfurizing agent" refers to common fluxes used for
desulfurization. It includes slag recovered after a treatment for
creating a new surface.
[0065] "Recovered desulfurizing agent" refers specifically to a
desulfurizing agent comprising slag recovered after the treatment
for creating a new surface, wherein the slag may contain metal.
[0066] "Desulfurization slag" refers to desulfurization slag
containing all of a CaO component, other slag components, and a
metal component and which has not been subjected to the treatment
for creating a new surface.
[0067] "Lime" refers to common CaO components.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0068] FIG. 1 is a graph illustrating the relationship between the
amount of lime added per unit amount of hot metal and
desulfurization rate, for recovered desulfurizing agents resulting
from the first and second recycling operations, respectively,
according to the present invention as well as a conventional lime
desulfurizing agent for comparison.
[0069] FIG. 2 is a graph illustrating the relationship between the
number of times of recycling processes executed on desulfurization
slag and the amount of desulfurizing agent used per unit amount of
hot metal wherein the slag is recycled a number of times according
to the present invention.
[0070] FIG. 3 is a graph illustrating the relationship between the
amount of desulfurizing agent added per unit amount of hot metal
and the desulfurization rate, for the desulfurizing agent according
to the present invention and the conventional desulfurizing agent
for comparison.
[0071] FIG. 4 is a graph illustrating the relationship between the
amount of lime component added per unit amount of hot metal and the
desulfurization rate, for the desulfurizing agent according to the
present invention and the conventional desulfurizing agent for
comparison.
[0072] FIG. 5 is a graph illustrating the relationship between the
amount of lime added per unit amount of hot metal and the
desulfurization rate, for the recovered desulfurizing agent treated
according to the present method and the conventional desulfurizing
agent for comparison.
[0073] FIG. 6 is a graph illustrating the relationship between the
temperature of slag measured at the end of watering and the time
required to cool the slag down to room temperature, wherein a
treatment is executed using a desulfurization slag treatment method
according to the present invention.
[0074] FIG. 7 is a graph illustrating the relationship between the
temperature of the slag measured at the end of watering and the
amount of Ca(OH).sub.2 generated in the recovered desulfurizing
agent, wherein a treatment is executed using the desulfurization
slag treatment method according to the present invention.
[0075] FIG. 8 is a graph illustrating the relationship between the
time required to cool slag with different thicknesses and the
temperature of the slag, wherein a treatment is executed using the
desulfurization slag treatment method according to the present
invention.
[0076] FIG. 9 is a graph showing the relationship between the
amount of lime added per unit amount of hot metal and
desulfurization rate, for the recovered desulfurizing agent treated
according to the present invention and the conventional
desulfurizing agent for comparison.
[0077] FIG. 10 is a graph showing the relationship between the
amount of lime added per unit amount of hot metal and
desulfurization rate, for the recovered desulfurizing agent
recycled according to the present invention and the conventional
desulfurizing agent for comparison.
[0078] FIG. 11 is a view showing an example of a screening jig
according to the present invention.
[0079] FIG. 12 is a view showing a screening facility according to
the present invention.
[0080] FIG. 13A is a view useful in describing an essential part of
a recovered desulfurizing agent loading apparatus, and FIG. 13B is
a schematic view showing the entire recovered desulfurizing agent
loading apparatus.
[0081] FIG. 14 is a graph showing the amount of pure CaO component
in the desulfurizing agent and the amount of material desulfurized
(the amount of sulfur before treatment (S)-the amount of sulfur
after treatment (S)).
[0082] FIG. 15 is a graph showing the bulk density and CaO mass %
of desulfurization slag.
[0083] FIG. 16 is a graph showing the relationship between the
amount of lime added per unit amount of hot metal and the
desulfurization rate, for desulfurizing agents obtained by mixing
the recovered desulfurizing agent recovered according to the
present invention with lime and a conventional desulfurizing agent
as a comparative example.
[0084] FIG. 17A is a view showing a slag treatment pattern
performed by a plant test.
[0085] FIG. 17B is a view showing an example of the slag treatment
pattern in FIG. 17A together with a conventional slag treatment
pattern.
[0086] FIG. 18 is a graph showing the ratio of lime effectively
used for desulfurization to introduced lime, by comparing the case
in which desulfurizing agent resulting from a mechanical agitation
type hot metal desulfurizing treatment method is used as a
desulfurizing agent for the mechanical agitation type hot metal
desulfurizing treatment with the case in which desulfurization slag
resulting from an injection method is used as a desulfurizing agent
for the mechanical agitation type hot metal desulfurizing treatment
method.
[0087] FIG. 19 is a graph showing the relationship between the
amount of lime component added per unit amount of hot metal and the
desulfurization rate at each desulfurization level.
[0088] FIG. 20 is a graph showing the relationship between the
amount of lime component added per unit amount of hot metal and the
desulfurization rate at each desulfurization level.
[0089] FIG. 21 is a photograph showing how an aggregate of
desulfurization slag resulting from the mechanical agitation type
hot metal desulfurizing treatment was observed using an SEM, and a
view showing the results of line analysis of an S element in the
aggregate.
[0090] FIG. 22 is a view schematically showing differences between
agitating type hot metal desulfurization slag and hot metal
desulfurization slag obtained by the injection method.
[0091] FIG. 23 is a view showing an example of a hot metal
pretreatment.
[0092] FIG. 24 is a view showing an example of a desulfurizing
facility, shown in FIG. 23.
DETAILED DESCRIPTION OF THE INVENTION
[0093] (Recycling of Desulfurization Slag)
[0094] According to a hot metal desulfurizing method of the present
invention, desulfurization slag resulting from mechanical agitation
type hot metal desulfurizing treatment (hereinafter referred to as
the "KR method") is reused as a desulfurizing agent for another hot
metal desulfurizing treatment (for example, desulfurization slag
resulting from the KR method is reused as a desulfurizing agent for
the KR method, or desulfurization slag resulting from the KR method
is reused as a desulfurizing agent for an injection method). The
hot metal desulfurizing treatment for which desulfurization slag is
reused is not limited-but refers to a commonly executed one.
According to the present invention, desulfurization slag can also
be reused for the same process that results in the desulfurization
slag. Accordingly, the method of the present invention is effective
even in steel manufacturing facilities provided with only hot metal
desulfurizing treatment processes that use the same addition method
and agitation method. The present invention allows desulfurization
slag to be particularly efficiently and effectively recycled if the
recycling operation is applied to the KR method.
[0095] That is, with the injection method, fine lime powders are
added to a bath at a deep position thereof, and thus react while
floating in the bath. Consequently, the fine powders are expected
to react for only a short time, and a desulfurization product is
formed in front layers of the fine powders to only a small
thickness. After the fine powders have come floating to the bath
surface, they are not expected be agitated again so as to be caught
in waves of hot metal. Thus, a reaction surface area does not
increase, and there are substantially no possibilities of
desulfurizing reaction. Further, at this stage, aggregation starts,
so that desulfurization products on the surfaces of the individual
fine powders are aggregated.
[0096] On the other hand, with the KR method, lime powders are
added to the bath surface. Accordingly, the lime powders are caught
in waves of hot metal in so as to go down from the surface to
interior of the bath. Further, at the beginning of the addition,
desulfurizing agent powders start to be aggregated near the
surface. As a result, the lime powers become "undissolved masses"
with substantially unreacted lime contained therein. Even when
aggregation starts, surface areas of the powders which come into
contact with metal react, and desulfurization products are formed
thereon. This reaction continues over the treatment time, and
long-time reaction is thus possible. With the above reaction
mechanism, after desulfurization, the surfaces of the aggregated
coarse grains are covered with desulfurization products to a fixed
thickness. There are only a small amount of desulfurization
products inside the grains. That is, unreacted lime, which is
similar to fresh lime, is present inside the grains. The inventors
used an SEM to observe an aggregate of desulfurization slag
resulting from the mechanical agitation type hot metal
desulfurizing treatment, took photographs thereof, and
line-analyzed an S element therein. As a result, the inventors
confirmed that the above knowledge is correct, as shown in FIG.
21.
[0097] Thus, desulfurization slag resulting from the KR method
contains coarse grains and thus requires only a simple pretreatment
for recycling, thereby reducing recycling treatment costs. Further,
in most cases, unreacted lime grains are aggregated and can thus be
recycled without using any additional special methods of crushing
material or adjusting grain size.
[0098] On the other hand, desulfurization slag resulting from the
injection method, the individual fine grains are enclosed by
desulfurization products. Accordingly, a special crushing operation
or the like is required to make the fine grains much finer. This
increases the number of steps and the treatment time.
[0099] As described above, the KR method accomplishes a high
reaction efficiency during recycling. The surface of an unreacted
lime component can be used directly for reaction for recycling, and
is expected to achieve a reaction efficiency equivalent to that
attained using fresh lime. If KR slag is recycled, it can be
desulfurized with the amount of lime component added per unit
amount of hot metal, unreacted. In contrast, with injection slag, a
complicated pretreatment is required, or the use of a simple
pretreatment requires at least double the amount of lime
component.
[0100] Further, the use of KR slag reduces the treatment time (down
to the same amount as that required for a fresh agent) and
effectively reduces the amount of slag generated. The KR slag
serves to reduce the amount of slag generated, for example, by 50%
after one recycling process and to allow recycling to be carried
out a number of times.
[0101] On the other hand, with the injection method,
desulfurization products on the surfaces of individual fine grains
are aggregated. Thus, for recycling, the individual grains (primary
grains) must be crushed. After recycling, the grains are very fine
(their grain size is half or smaller of that of the primary grain
size). Thus, during recycling based on the KR method, a large
number of grains are likely to scatter. Consequently, additional
lime is required to make up for the loss of the scattered lime
component. For example, if only a conventional desulfurizing agent
resulting from the first recycling operation is used, about 7 kg/t
of desulfurizing agent (about 90% of lime component: 6.3 kg/T of
substantial lime component) is required. In contrast, if a
recovered desulfurizing agent is used, 10 kg/t of desulfurizing
agent (about 66% of lime component: 6.6 kg/T of substantial lime
component)+3 kg/t of conventional desulfurizing agent resulting
from the first recycling operation (about 90% of lime component:
2.7 kg/T of substantial lime component) is required. That is, 9.3
kg/T of lime component is present in the recovered desulfurizing
agent, but because of insufficient formation of effective new
surfaces or a loss resulting from scattering, about 3 kg/T of
desulfurizing agent may not effectively contribute to
desulfurization. That is, an effective lime component takes up only
about 55% of the recovered desulfurizing agent, so that a
supplementary desulfurizing agent must be added, as described in
the previously described document (Sumitomo Metals Vol. 45-3 (1993)
p. 52 to 58).
[0102] With the KR method, as described above, the surface of
coarse grains are covered with desulfurization products to some
degree, with only a small amount of desulfurization products
present inside the grains. That is, unreacted lime similar to fresh
lime is present. Thus, desulfurization is possible if weathering
products are positively generated for recycling and even if the
grains after recycling are as large as or larger than the primary
grains. Furthermore, during recycling based on the KR method, the
amount of grains scattered is equal to or smaller than that
observed when lime is used. For example, if a recovered
desulfurizing agent is used, the amount of recovered desulfurizing
agent used is 14 kg/t (about 50% of lime), and the amount of
effective lime component in the added recovered desulfurizing agent
is similar to that observed if fresh lime is added.
[0103] FIG. 18 shows a summary of the above relationships. If
desulfurization slag resulting from the KR method, an example of
the present invention, is reused as a desulfurizing agent for the
KR method, about 7% of the lime component added for one treatment
is used for desulfurization. Effective utilization rate increases
consistently with the number of times that the desulfurizing agent
is used. In contrast, if desulfurization slag resulting from the
injection method, a conventional technique for desulfurization slag
recycling, is reused as a desulfurizing agent for the KR method,
the total utilization efficiency only slightly exceeds the
utilization efficiency accomplished by one KR process.
[0104] Further, to help make the reader understand the above
description, the specification is accompanied by FIG. 22
schematically showing differences between hot metal desulfurization
slag resulting from the mechanical agitation type method and hot
metal desulfurization slag resulting from the injection method.
FIG. 22 shows how an aggregate of desulfurization slag grains
resulting from the mechanical agitation type hot metal
desulfurizing treatment is separated into pieces to create new
surfaces and how each grain of aggregate of desulfurization slag
grains resulting from the injection method is crushed into pieces.
In the figure, the desulfurization slag grains resulting from the
injection method have substantially the same grain size as the
desulfurization slag grains resulting from the mechanical agitation
type hot metal desulfurizing treatment. However, the
desulfurization slag grains resulting from the injection method are
actually finer.
[0105] (Specific Treatment for Desulfurization Slag)
[0106] FIG. 17A shows a slag treatment pattern performed by a plant
test, and FIG. 17B shows an example of the slag treatment pattern
in FIG. 17A together with a conventional slag treatment
pattern.
[0107] According to the present invention, an arbitrary method is
used to create new surfaces in desulfurization slag resulting from
a desulfurizing step, and the slag obtained is reused as a
desulfurizing agent. In this case, an unreacted lime component must
be exposed as a desulfurization reacting surface so that the slag
can be used as a desulfurizing agent for the next process. The
method used to achieve this is not limited. If a natural cooling
process or a watering and cooling process is executed to create new
surfaces, CaCO.sub.3 and Ca(OH).sub.2 are generated. The residual
CaCO.sub.3 and Ca(OH).sub.2 do not hinder desulfurization reaction,
but an appropriate amount of these components are expected to serve
to improve this reaction. Further, a metal component of a larger
diameter can be removed by magnetic separation or screening, so
that a recovered desulfurizing agent is mainly composed of a lime
component. Furthermore, the grain size of this recovered
desulfurizing agent is restricted by a supply apparatus in a
desulfurizing facility where the agent is used. Accordingly, no
problems occur provided that an appropriate grain size is used. On
the other hand, residual metal of a smaller diameter may remain in
the recovered desulfurizing agent. However, this metal can be
reused as an iron source for the subsequent hot metal pretreatment
step, thereby significantly contributing to increasing the yield of
iron. Various specific examples will be illustrated below.
[0108] (i) Crushing Based on Watering Treatment
[0109] In this example, desulfurization slag resulting from a
desulfurizing step is simultaneously cooled and crushed using a
watering treatment, and is then dried and reused as a desulfurizing
agent. Specifically, a watering facility is used to excessively
water hot slag resulting from the desulfurizing process until the
slag is fully impregnated with water. Subsequently, a drying
apparatus is used to completely dry this water-containing slag to
obtain a desulfurizing agent having a reduced grain size of 100 mm
or smaller. However, a smaller grain size is more preferable, and
the maximum grain size is preferably substantially 30 mm or smaller
and more preferably 5 mm or smaller. A mechanical crushing
operation may be performed before or after the watering and drying
steps. Further, in an actual process, mechanical vibration causes
at least part of desulfurization slag to be crushed during
transportation. Specifically, an apparatus used for drying may be a
dryer, or a rotary kiln or the like may be used to perform a
large-scale drying operation. The size of the apparatus and the
like can be set depending on a required throughput or the like. Any
apparatus and method may be used provided that water impregnated
into the cooled slag can be sufficiently removed. The thus recycled
desulfurization slag is used as a desulfurizing agent.
[0110] (ii) Crushing Based on Watering and Agitating Treatment
[0111] In this example, desulfurization slag resulting from the
desulfurizing step is simultaneously cooled and crushed using an
appropriate watering and agitating treatment, and is then reused as
a desulfurizing agent. That is, a watering facility is used to
uniformly water hot slag resulting from the desulfurizing
treatment, while using heavy equipment such as a shovel to agitate
the slag. Specifically, a watering operation is performed until the
hot slag is cooled down to a temperature of about 100.degree. C.
The slag is then left cooled to obtain a desulfurizing agent of a
reduced grain size of about 100 mm or smaller. However, a smaller
grain size is more preferable, and the maximum grain size is
preferably substantially 30 mm or smaller and more preferably 5 mm
or smaller. A mechanical crushing operation may be performed before
or after the watering step. The cooling target temperature is not
limited to a particular value, but may be set depending on the
required throughput or the like. An appropriate amount of water
supplied and agitation reduces the time required to cool the slag.
However, if the watering operation is continued even after the
temperature decreases below 100.degree. C., then a drying treatment
is required. Thus, the watering operation is desirably stopped
before the temperature reaches 100.degree. C. Further, the
agitation is carried out in order to increase cooling speed and
make the watering uniform, so that its frequency may be varied
depending on the required treatment time or throughput. The
agitation may be omitted.
[0112] (iii) Crushing Based on Natural Cooling
[0113] In this example, desulfurization slag resulting from the
desulfurizing step is simultaneously cooled and crushed by
executing natural cooling. The resultant slag is reused as a
desulfurizing agent. That is, hot slag resulting from the
desulfurizing step is left as it is so as to maximize the area of
that part of the slag which contacts with air. The slag is then
agitated using heavy equipment such as a shovel. Specifically, a
recovered desulfurizing agent of temperature 200.degree. C. or
lower and a sufficiently reduced diameter can be obtained in three
days by spreading the hot slag so that its thickness is 0.5 m or
smaller and agitating it about one to three times a day. The
thickness of the slag during cooling is not limited to this value,
but the target thickness can be set depending on the required
treatment time or throughput, the area of a place that is available
for the recycling treatment, or the like. Further, the agitation is
carried out in order to increase the cooling speed, so that its
frequency may also be varied depending on the required treatment
time or throughput. The agitation may be omitted if much treatment
time and throughput are available. Furthermore, a recovered
desulfurizing agent is similarly obtained if the slag is left as it
is without reducing its thickness.
[0114] The cooled and crushed desulfurization slag grains have a
maximum grain size of 100 mm or smaller, preferably 30 mm or
smaller, and more preferably 5 mm. Thus, these grains have a
surface area sufficient to be involved in a desulfurizing reaction
and can be advantageously handled because they do not scatter upon
addition owing to their larger size. In addition, a mechanical
crushing operation may also be used.
[0115] (iv) Screening Hot Slag
[0116] In this example, while hot at 900 to 1,200.degree. C.,
desulfurization slag resulting from the desulfurizing step is
screened using a sieve (30.times.30 mm to 100.times.100 mm) and is
thus separated into metal of a larger diameter containing a slag
component and desulfurization slag of a smaller diameter. The
criterion for the screening is restricted by the supply apparatus
operated when the slag is used as a recovered desulfurizing agent.
Typically, the above ranges are appropriate.
[0117] After the screening, the desulfurization slag of a reduced
diameter is naturally cooled and reused as it is. Even after the
screening, about 20 to 30% of Fe component (T.Fe from the slag and
metallic Fe) remains. However, this Fe component is introduced into
hot metal when it is used for the next desulfurizing step, thereby
increasing the yield of iron.
[0118] When the metal of a larger diameter containing the above
slag components is cooled, an unreacted lime component in the slag
component causes the following reaction:
CaO+H.sub.2O=Ca (OH).sub.2
CaO+CO.sub.2=CaCO.sub.3
[0119] i.e. so-called "powdering" reaction, thereby disintegrating
the slag component in the desulfurization slag into a metal
component and a slag component. After this step, the above
screening operation may be performed again, so that the
desulfurization slag can be efficiently separated into large masses
of a metal component (containing a small amount of slag component)
and a recovered desulfurizing agent (containing a metal component
of a smaller diameter). As a result, about 90% of the unreacted
lime component in the desulfurization slag is recovered as a
recovered desulfurizing agent.
[0120] In this case, any sieve can be used without creating any
problems provided that it can be operated over a temperature range
from 900 to 1,200.degree. C.; a sieve made of iron is sufficient.
The shape, specification, and the like of this sieve are not
limited provided that it can be operated in a desulfurization slag
treatment field. Further, the mesh of the sieve is restricted by
the supply apparatus in the desulfurizing facility where the slag
is used as a recovered desulfurizing agent. An appropriate mesh can
be used without creating any problems.
[0121] As described above, desulfurization slag can be recovered as
an inexpensive lime source by exposing an unreacted lime component
and separating large masses of metal from the desulfurization slag
without magnetic separation. Furthermore, a recovered desulfurizing
agent mainly composed of the desulfurization slag recovered after
screening still has a sufficient desulfurizing capability.
Therefore, lime can be more effectively utilized by reusing the
desulfurization slag a number of times.
[0122] (v) Suppression of Dust
[0123] Dried desulfurization slag is very likely to produce dust.
However, the inventors note that since desulfurization slag is hot
immediately after being produced, most of the slag pieces are
massive. That is, a large amount of dust generated can be prevented
by properly handling the desulfurization slag, e.g. screening it
while it is hot after being generated. A higher temperature is more
advantageous to suppression of dust. Slag was actually dropped from
a drop height of 3 m with its temperature varied, and the amount of
dust generated was measured. Then, it was found that the amount of
dust increases rapidly at a temperature of 600.degree. C. Further,
in connection with an incidental effect of screening at high
temperature, by exposing desulfurization slag to the atmosphere at
high temperature, the desulfurization slag can be cooled rapidly
and thus powdered. This reduces the subsequent cooling load.
[0124] Further, in connection with a facility used for screening,
the amount of dust produced can be reduced using a facility that
serves to reduce the height from which desulfurization slag is
dropped vertically. FIG. 12 shows the configuration of this
facility.
[0125] This facility is composed of a diagonally arranged net (12),
a diagonal plate on which an undersize slides down, and a sliding
way (16). This facility is characterized in that the spacing (13)
between the net (12) and the diagonal plate (14) is set at 500 mm
or smaller in order to reduce the drop height from which
desulfurization slag is dropped. Further, the spacing (15) between
the diagonal plate (14) and the sliding way (16) is set at 500 mm
or smaller. Furthermore, the facility is configured so that the
drop height from the sliding way (16) to the ground (18) is set at
1,500 mm or less. This configuration serves to drastically reduce
the amount of dust produced. Thus, the amount of dust produced
during the treatment can also be reduced by using the above
configuration to adjust the grain size (e.g. 70 mm or smaller) of
dried desulfurization slag using the simple facility and low
operation costs and further screening the slag while it is at a
temperature of 600.degree. C. or higher.
[0126] Further, if the desulfurization slag having its grain size
adjusted as described above is cooled and then loaded onto a dump
truck for recycling, then naturally, it is powdered faster and is
very likely to produce dust. Thus, desulfurization slag is loaded
using a facility such as the one shown in FIG. 13. A movable basket
section (21) is opened in opposite directions and picks up a
recovered desulfurizing agent (22). The movable basket section (21)
is then closed and carries the picked-up recovered desulfurizing
agent to immediately above a carrier (23) of a dump truck, where
the movable section (21) is opened. In this case, the drop height
(24) is 1.5 m or less so that the desulfurization slag can be
loaded onto the dump truck while significantly reducing the amount
of dust produced.
[0127] (vi) Suppression of Other Dust
[0128] If a recovered dry desulfurizing agent is loaded onto a
transport vehicle such as a dump truck for recycling as described
above, then naturally, it is powdered faster and is very likely to
produce dust. However, the amount of dust produced can be minimized
by using a vehicle with a sucking capability instead of the dump
truck to transport the recovered desulfurizing agent. Further, the
recovered desulfurizing agent can concurrently be sieved by
installing a mesh at a suction port during suction, thereby
enabling efficient handling and transportation with a reduced
amount of dust produced.
[0129] Specifically, a suction hose is connected to the vehicle
with the sucking capability to suck and load a recovered
desulfurizing agent obtained by cooling and crushing
desulfurization slag resulting from the hot metal desulfurizing
step. At this time, by installing a jig having a mesh for screening
at the suction port, the desulfurizing agent can concurrently be
sieved so that the required grain size can be obtained. In this
case, the jig attached to the suction port during suction may be
selected on the basis of the required level of the sieve, i.e. the
desired grain size of the recovered desulfurizing agent.
[0130] Furthermore, if no screening operation is required during
suction, the mesh need not be installed at the suction port, and
the desulfurizing agent may be sucked using only the hose.
[0131] Moreover, if only large masses of a several tens of cm level
must be removed, a simple jig may be used for suction, jig simply
having partitions arranged at the tip thereof and formed of metal
bars as shown in FIG. 11. An example of such a jig is shown in FIG.
11. This jig is simply composed of a cylinder (1) having the same
diameter as that of the hose and metal bars (2) attached to the tip
of the cylinder so as to form a cone. The size of the mesh of the
sieve and the shape of the jig are not limited and are determined
depending on the required grain size, pretreatment step, or The
like. Furthermore, to facilitate suction, a nozzle (3) is attached
to the jig to suck air. This sucking jig is used to suck the
recovered desulfurizing agent, thereby simultaneously achieving the
loading and screening operations.
[0132] The cooled and crushed recovered desulfurizing agent grains
obtained as described above can solely constitute a desulfurizing
agent according to the present invention or by being combined with
another component as required. That is, the desulfurizing agent
according to the present invention may be composed of only the
recovered desulfurizing agent grains obtained through the above
described steps or may be formed by combining these grains with
another component such as lime or fluorite, as required. In the
latter case, the amount of another component mixed can be properly
determined on the basis of the amount of lime component contained
in the recovered desulfurizing agent or the required
desulfurization rate. A preferred determining method will be
described later.
[0133] (Manufacture of Optimum Desulfurizing Agent)
[0134] Now, description will be given of a method of manufacturing
the optimum desulfurizing agent using a recovered desulfurizing
agent obtained from desulfurization slag. Even with the same
recovered desulfurizing agent, the desulfurization rate varies
significantly depending on the amount of material added per unit
amount of hot metal. However, it has been found that the amount of
pure CaO component in the recovered desulfurizing agent has a clear
correlationship with the amount of material desulfurized (the
amount of S before treatment-the amount of S after treatment).
[0135] Thus, even if the components of the recovered desulfurizing
agent change, a stable desulfurization rate is obtained by also
introducing a pure CaO component into the desulfurizing agent.
Then, the ratio of CaO to the recovered desulfurizing agent must be
determined. To achieve this, the means described below can be used.
Desulfurization slag is roughly divided into a metal component and
a slag component. The inventors note that the ratio of the metal
component to the slag component varies significantly, whereas the
ratio of CaO to the slag component does not vary significantly.
That is, the amount of CaO contained can be estimated by
determining the ratio of the metal component to the slag component
in the recovered desulfurizing agent. Furthermore, the metal has a
relatively large specific gravity of about 7, whereas the slag has
a specific gravity of only 2 to 3.
[0136] This indicates that bulk density increases in proportion to
the amount of metal contained. On the basis of this nature, it is
easy to cut out a specified volume of recovered desulfurizing agent
immediately before use and then weigh it. This weight can be easily
reflected in the amount of material introduced. Thus, according to
the present invention, the amount of CaO contained in the recovered
desulfurizing agent can be estimated promptly and precisely to
determine the amount of recovered desulfurizing agent required for
desulfurization.
[0137] It has been found that when a desulfurizing agent obtained
from desulfurization slag is used, even if the components of the
recovered desulfurizing agent change, a stable desulfurization rate
is obtained by also introducing a pure CaO component into the
desulfurizing agent. Accordingly, if the recovered desulfurizing
agent contains only a small amount of pure CaO component, the
amount of this component added may increase. Consequently, the hot
metal temperature becomes inappropriate, the amount of slag
discharged increases, and other adverse effects are produced.
[0138] Thus, the amount of desulfurizing agent can be reduced by
using a desulfurizing agent containing a mixture of a recovered
desulfurizing agent with at least one or two of lime (CaO), quick
lime (calcium carbonate CaCO.sub.3), and slaked lime (calcium
hydroxide Ca(OH).sub.2). If calcium carbonate (CaCO.sub.3) and
calcium hydroxide (Ca(OH).sub.2) are added, fine fluxes are
generated in molten metal owing to the decomposition reaction shown
below. Thus, the reaction surface area increases to improve the
desulfurization reaction rate. On the other hand, this
decomposition reaction is of an endothermal type and causes oxides
to be generated, which hinder desulfurization reaction, which is of
a reducing type. Accordingly, addition of a large amount of calcium
carbonate and calcium hydroxide may reduce the hot metal
temperature or hinder the desulfurization reaction. Thus, the
amount of these components added must be 40 wt % or less.
[0139] Further, the calcium carbonate component may be added by
adjusting, when lime is calcined, the level of the calcination so
as to leave the calcium carbonate component in the lime. Also in
this case, the calcium carbonate component is mixed with the
desulfurizing agent so that the total amount of calcium carbonate
in the desulfurizing agent is 40 wt % or less. If two or more
components are mixed with the desulfurizing agent, the total amount
of calcium carbonate component, quick lime, and slaked lime is 40
wt % or less of the total amount of desulfurizing agent. The amount
of lime added is not limited and can be freely adjusted depending
on the temperature of the hot metal to be treated.
[0140] Furthermore, if these components are added, the same effects
are produced whether predetermined amounts of these components are
mixed together before addition or are separately added to the hot
metal. In particular, if the amount of material desulfurized is to
be increased in a short time, addition of CaO or the like is more
effective if for example, the temperature of the hot metal to be
treated is low.
[0141] Further, the desulfurizing capability of the desulfurizing
agent can further be improved by adding a C source to this
recovered desulfurizing agent.
[0142] If a C source is added, it acts as a reducing agent to
effect the reaction shown below. This facilitates desulfurization
to increase desulfurization reaction efficiency.
CaO+S+C.fwdarw.CaS+CO (1)
[0143] Further, part of the C source dissolves in the hot metal to
increase the amount of heat source that increase the temperature in
connection with decarbonization in a converter. Addition of an
excessive amount of C source may cause an extra amount of C source
to remain, the extra amount exceeding the amount of C source that
is required for the above reduction reaction or that needs to
dissolve in the hot metal. Consequently, the amount of slag may
increase to degrade the quality of operations or the environment.
Therefore, the amount of C source added to the desulfurizing agent
is desirably 30 wt % or less. Further, the C source used may
contain a sulfur component, so that the concentration of S in the
hot metal may increase depending on the amount of C source added.
In particular, the amount of C source dissolving in the hot metal
varies with the temperature of the hot metal. Accordingly, the
amount of C source added can be adjusted on the basis of the type
of the C source used, the temperature of the hot metal to be
treated, the concentration of S in the hot metal, the required
amount of material desulfurized, the treatment time, or the like.
The C source added is not limited, but any C source may be used
such as coal, coke, pitch coke, or plastic.
[0144] Furthermore, if these C sources are added, the same effects
are produced whether predetermined amounts of these C sources are
mixed together before addition or are separately added to the hot
metal. The C source can be added whether it is massive, granular,
or powdery. However, to easily dissolve in the hot metal, the C
source is preferably composed of powders of grain size about 1 mm
or smaller.
[0145] (Method of Desulfurizing Hot Metal)
[0146] A desulfurizing agent is applied to a hot metal
desulfurizing process, the desulfurizing agent containing the
recovered desulfurizing agent obtained as described above and the
lime source and/or carbon source added as required. The recovered
desulfurizing agent can be applied irrespective of the
configuration of the hot metal desulfurizing facility or the hot
metal desulfurizing method.
[0147] The desulfurizing facility using the recovered desulfurizing
agent may be based on mechanical agitation (KR method), the
injection method (torpedo), or a converter. The main chemical
components of the hot metal are [mass % C]=3.5 to 5.0, [mass %
Si]=0 to 0.3, [mass % S]=0.02 to 0.05, and [mass % P]=0.1 to 0.15.
The temperature of the hot metal is between 1,250 and 1,450.degree.
C. For a treatment, 5 to 300 tons of hot metal is loaded into a
refining container. To mix the desulfurizing agent into the hot
metal, the recovered desulfurizing agent may be mixed with a lime
component before addition, or the recovered desulfurizing agent and
the lime component may be cut out from separate hoppers before
addition. However, to ensure a certain degree of freedom for
operations, it is effective to have a plurality of hoppers. With
any refining container, the method used has only to allow the
recovered desulfurizing agent and the lime component to be
effectively supplied to a bath surface. The amounts of recovered
desulfurizing agent and lime component introduced are varied
depending on the concentrations of Si, S, and P in the hot metal.
The total amount is desirably at most 20 kg/t.
[0148] Now, examples of the present invention will be
described.
EXAMPLE 1
Example in Which Desulfurization Slag Resulting From a Hot Metal
Pretreatment Based on the KR Method is Reused as a Desulfurizing
Agent for a Hot Metal Desulfurizing Process Based on the KR
Method
[0149] In this example, desulfurization slag resulting from a
desulfurizing step based on the KR method is positively cooled and
crushed by the optimum treatment method, and is then reused as a
desulfurizing agent for a desulfurizing process based on the KR
method. For a recycling treatment, a mechanical crushing treatment,
a natural cooling treatment, and a watering treatment are properly
combined together. Specifically, the recycling treatment is
executed by the following method:
[0150] Desulfurization slag resulting from a hot metal pretreatment
based on the KR method is first mechanically crushed while hot.
Specifically, the desulfurization slag can be crushed using heavy
equipment such as a shovel. Furthermore, the hot slag is watered to
facilitate cooling and disintegration. Specifically, a watering
facility is used for cooling.
[0151] Alternatively, the desulfurization slag may be cooled by
leaving it as it is without watering. In this case, to facilitate
cooling, the desulfurization slag may be spread as thin as possible
to increase the contact area thereof which contacts with the
atmosphere. Furthermore, reaction of the desulfurization slag with
steam or carbon dioxide in the atmosphere may be promoted to
facilitate disintegration of a lime component and generation of a
compound such as calcium carbonate or calcium hydroxide. Moreover,
it is possible to crush the hot slag and then pass it through a
sieve to separate large masses such as metal therefrom.
[0152] The desulfurization slag resulting from this method was
positively treated to facilitate cooling and crushing of the
desulfurization slag, thereby generating recovered desulfurizing
agent grains of maximum grain size 30 mm or smaller. The grains may
further be mechanically crushed.
[0153] Since the recovered desulfurizing agent obtained has a
maximum grain size of 30 mm or smaller, a surface area is obtained
which is enough to be involved in the desulfurization reaction.
[0154] Since the grains are appropriately fine, production of dust
can be prevented. Further, during reuse with the KR method, a
decrease in yield caused by scattering can be prevented.
Furthermore, the grains can be properly caught in waves in a
bath.
[0155] Moreover, generation of a compound such as calcium carbonate
or calcium hydroxide can be facilitated by positively promoting
cooling and disintegration as described above. When added to the
hot metal, these compounds are decomposed while undergoing
dehydrating and degassing reaction, to facilitate agitation of the
hot metal. Further, the decomposition increases the reaction
surface area, thereby improving the desulfurization efficiency.
[0156] The above recycling method efficiently provides a
desulfurizing agent of grain size 30 mm or smaller having a new
surface with a desulfurizing capability. This desulfurizing agent
was used in the example.
[0157] For comparison, a conventional desulfurizing agent was used
which contained 90% of lime and about 5% of fluorite. Table 1 shows
the average compositions of the conventional desulfurizing agent as
a comparative example and the recovered desulfurizing agent as this
example.
[0158] These desulfurizing agents were applied to a mechanical
agitation type desulfurizing apparatus under the conditions shown
in Table 2 to carry out a hot metal desulfurization
pretreatment.
[0159] After the hot metal desulfurization, the desulfurization
rate achieved by the mechanical agitation type desulfurizing
apparatus was checked for each of the desulfurizing agents. FIG. 3
shows the relationship between the amount of additives (fluxes) per
unit amount of hot metal and the desulfurization slag rate. In the
graph of FIG. 3, a curve a indicates results for the
desulfurization slag of the present invention, while a curve b
indicates results for the conventional desulfurizing agent as a
comparative example.
[0160] The graph of FIG. 3 indicates that with an equal amount of
desulfurizing agent added per unit amount of hot metal, the
desulfurization rate of the recovered desulfurizing agent is about
50 to 90% of that of the comparative desulfurizing agent.
Furthermore, FIG. 4 shows comparison based on the amount of lime
component added per unit amount of hot metal. This graph indicates
that in terms of a contained lime component, the recovered
desulfurizing agent has a desulfurizing capability substantially
equivalent to that of the comparative desulfurizing agent. Thus, a
treatment with the recovered desulfurizing agent is expected to
produce a desulfurizing effect equivalent to that of a
desulfurizing treatment with lime provided that the amount of lime
added per unit amount of hot metal, in the recovered desulfurizing
agent added, is estimated to be equivalent to the amount of lime
required for the desulfurization reaction.
[0161] Table 3 shows changes in the amount of lime used before and
after introduction of the present process. The table indicates that
the reuse of desulfurization slag reliably reduced the amount of
lime used, thereby reducing treatment costs by about 40% compared
to the costs required before introduction.
[0162] Table 4 shows changes in the amount slag generated before
and after introduction of the present process. The amount of slag
generated decreased by 3,000 t/month, thereby demonstrating that
the present process reduces not only desulfurization costs but also
the amount of slag to solve environmental problems.
[0163] This example produces significant effects. For example, it
reduces the desulfurization costs, allows desulfurization slag to
be reused, and reduces the amount of slag generated to solve
environmental problems. Therefore, this example has a high
industrial value.
EXAMPLE 2
Example Relating to the Desulfurization Rate of Recycled
Desulfurization Slag and the Number of Times That the
Desulfurization Slag is Recycled
[0164] In this example, desulfurization slag resulting from a
desulfurizing step was cooled and crushed by a natural cooling or
watering treatment and then reused as a desulfurizing agent during
the same process. A recovered desulfurizing agent of grain size 100
mm or smaller and temperature 200.degree. C. or lower was obtained
without mechanical crushing, and was used as a desulfurizing agent
according to this example. Furthermore, the recovered desulfurizing
agent was used to carry out desulfurization. The resultant slag was
recovered again, and the above method was used to set its size and
temperature at 100 mm or smaller and 200.degree. C. or lower,
respectively. Then, the slag was reused as a desulfurizing agent
according to this example.
[0165] For comparison, the conventional desulfurizing agent was
used which contained 90% of lime and about 5% of fluorite. Table 1
shows the average compositions of the recovered desulfurizing agent
and conventional desulfurizing agent used (all tables are shown at
the end of the specification).
[0166] These desulfurizing agents were applied to the mechanical
agitation type desulfurizing apparatus under the conditions shown
in Table 2 to carry out a hot metal desulfurization
pretreatment.
[0167] FIG. 1 shows the relationship between the amount of lime
added per unit amount of hot metal and the desulfurization rate at
each desulfurization level. This figure indicates that the
recovered desulfurizing agents resulting from the first and second
recycling operations had a desulfurizing capability equal to 80% or
more of that of the comparative desulfurizing agent. Thus, even
with a treatment using the recovered desulfurizing agent resulting
from the second recycling operation, properly increasing the amount
of lime added is expected to serve to produce a desulfurizing
effect equivalent to that of a desulfurizing treatment with
lime.
[0168] FIG. 2 shows changes in the amount of desulfurizing agent
used before and after introduction of the present process, in
connection with the number of desulfurizing agent recycling
operations and changes in the amount of recovered desulfurizing
agent used. The figure indicates that recycling the desulfurizing
agent a number of times served to drastically reduce the amount of
recovered desulfurizing agent used. When a recycling operation was
preformed about three times, the amount of desulfurizing agent used
decreased by about 75% compared to the amount measured before
introduction. At the same time, the amount of slag generated
decreased drastically, thereby demonstrating that the present
process is also effective on environmental problems.
[0169] Thus, according to this example, the use of the
desulfurizing agent of the present invention reduces
desulfurization costs, allows desulfurization slag to be recycled a
number of times, and reduces the amount of waste to solve
environmental problems.
EXAMPLE 3
Cooling and Crushing Based on a Watering Treatment
[0170] In this example, desulfurization slag resulting from a
desulfurizing step is simultaneously cooled and crushed by a
watering treatment, and is then dried and reused as a desulfurizing
agent. Specifically, a watering facility is used to excessively
water the hot slag subjected to the desulfurizing treatment until
the slag is completely impregnated with water. Subsequently, a
drying apparatus is used to completely dry the water-containing
slag to obtain a desulfurizing agent of a sufficiently reduced
grain size of about 5 mm or smaller. Specifically, the apparatus
used for drying may be a dryer, or a rotary kiln or the like may be
used to perform a large-scale drying operation. The size of the
apparatus and the like can be set depending on the required
throughput or the like. Any apparatus and method may be used
provided that water impregnated into the cooled slag can be
sufficiently removed.
[0171] The thus recycled desulfurization slag was used as a
desulfurizing agent according to this example.
[0172] For comparison, the conventional desulfurizing agent was
used which contained 90% of lime and about 5% of fluorite. Table 5
shows the average compositions of the recovered desulfurizing agent
and conventional desulfurizing agent used.
[0173] These desulfurizing agents were applied to the mechanical
agitation type desulfurizing apparatus under the conditions shown
in Table 2 to carry out a hot metal desulfurization
pretreatment.
[0174] FIG. 5 shows the relationship between the amount of lime
added per unit amount of hot metal and the desulfurization rate at
each desulfurization level. This figure indicates that with an
equal amount of lime introduced per unit amount of desulfurization
slag, the recovered desulfurizing agent (indicated by a solid line)
has a desulfurizing capability equal to about 70% of that of the
comparative desulfurizing agent (indicated by a broken line).
EXAMPLE 4
Cooling and Crushing Based on a Watering Treatment
[0175] In this example, desulfurization slag resulting from a
desulfurizing step is simultaneously cooled and crushed by a
watering treatment, and is then reused as a desulfurizing agent.
That is, the watering facility is used to uniformly water the hot
slag resulting from the desulfurizing treatment, while using heavy
equipment such as a shovel to agitate the slag. Specifically, the
watering treatment is continued until the hot slag is cooled down
to a temperature of 80 to 150.degree. C. Subsequently, the slag is
left and cooled until its temperature reaches the room temperature.
Thus, a desulfurizing agent is obtained which has a sufficiently
reduced grain size of 5 mm or smaller. This target cooling
temperature is not limited to a certain value, but can be set
depending on the required throughput or the like.
[0176] For comparison, the conventional desulfurizing agent was
used which contained 90% of lime and about 5% of fluorite. Table 7
shows the average compositions of the recovered desulfurizing agent
and conventional desulfurizing agent used.
[0177] These desulfurizing agents were applied to the mechanical
agitation type desulfurizing apparatus under the conditions shown
in Table 2 to carry out a hot metal desulfurization
pretreatment.
[0178] FIG. 9 shows the relationship between the amount of lime
added per unit amount of hot metal and the desulfurization rate at
each desulfurization level. This figure indicates that with an
equal amount of lime added per unit amount of hot metal, the
desulfurizing agent recovered by watering the slag until its
temperature reaches 150.degree. C. has a desulfurizing capability
substantially equivalent to that of the comparative desulfurizing
agent.
[0179] However, even with the same recovered desulfurizing agent
subjected to the watering treatment, the desulfurizing capability
varies depending on whether the watering treatment is stopped or
continued after the temperature reaches 100.degree. C. This is
assumed to be because the amount of calcium hydroxide generated in
the recovered desulfurizing agent increases significantly if the
slag is cooled even after its temperature reaches 100.degree. C.
and because such an excessive increase in the amount of calcium
hydroxide affects desulfurization, as shown in FIG. 7.
[0180] In this regard, FIG. 6 shows the relationship between the
temperature of the slag measured at the end of watering and the
time required to cool 40 T of desulfurization slag down to the room
temperature. This figure indicates that more time is required to
cool the slag down to the room temperature as the temperature of
the slag is higher at the end of watering.
[0181] The desulfurization treatment method of this example enables
desulfurization slag to be efficiently treated, reduces the time
and cost required to recover a desulfurizing agent, and allows a
large amount of desulfurization slag to be recycled to reduce the
amount of slag, thereby helping solve environmental problems.
EXAMPLE 5
Cooling and Crushing Based on a Natural Cooling Treatment
[0182] In this example, desulfurization slag resulting from a
desulfurizing step is simultaneously cooled and crushed by a
watering treatment, and is then reused as a desulfurizing agent.
Specifically, the hot slag subjected to the desulfurization
treatment is left as it is so as to maximize the contact area
thereof which contacts with the atmosphere, and is then agitated
using heavy equipment such as a shovel. Specifically, a recovered
desulfurizing agent of temperature 200.degree. C. or lower and a
sufficiently reduced diameter can be obtained in three days by
spreading the hot slag so that its thickness is 0.5 m or smaller
and agitating it about one to three times a day. The thickness
during cooling is not limited to this value, but the target
thickness can be set depending on the required treatment time or
throughput, the area of a place that is available for the recycling
treatment, or the like. Further, the agitation is carried out to
increase the cooling speed, so that its frequency may also be
varied depending on the required treatment time or throughput. The
agitation may be omitted if much treatment time and throughput are
available. This desulfurizing agent was used as one according this
example.
[0183] Furthermore, a recovered desulfurizing agent is similarly
obtained if the slag is left as it is without reducing its
thickness. This is also shown as a desulfurizing agent according to
this example.
[0184] Further, for comparison in terms of the cooling method,
mechanically crushed desulfurization slag (a mechanically crushed
agent) was used.
[0185] Furthermore, for comparison in terms of desulfurizing
behavior, the conventional desulfurizing agent was used which
contained 90% of lime and about 5% of fluorite. Table 8 shows the
average compositions of the recovered desulfurizing agent and
conventional desulfurizing agent used.
[0186] These desulfurizing agents were applied to the mechanical
agitation type desulfurizing apparatus under the conditions shown
in Table 2 to carry out a hot metal desulfurization
pretreatment.
[0187] FIG. 10 shows the relationship between the amount of lime
added per unit amount of hot metal and the desulfurization rate at
each desulfurization level. This figure indicates that with an
equal amount of lime added per unit amount of hot metal, the
desulfurizing agent recovered by executing natural cooling has a
desulfurizing capability substantially equivalent to that of the
comparative desulfurizing agent.
[0188] Further, even with the same non-watering treatment, the
desulfurization capability of the mechanically crushed recovered
desulfurizing agent is inferior to that of the recovered
desulfurizing agent which has been naturally cooled. This is
assumed to be because the recovered desulfurizing agent which has
been naturally cooled contains several percent of calcium carbonate
generated therein as shown in Table 8 and because during the
desulfurizing treatment, decomposition of calcium carbonate
facilitates agitation of the hot metal and increases the reaction
surface area to improve the desulfurization efficiency.
[0189] Comparison of the desulfurizing capability of the recovered
desulfurizing agent and the time required for the recycling
treatment will be shown below in connection with the different
methods of recovering desulfurization slag shown in Examples 3 to
5.
[0190] Even with the same recovered desulfurizing agent, a higher
desulfurization capability is obtained by crushing slag by watering
(at 150.degree. C.) than by mechanically crushing it. This is
assumed to be because the recovered desulfurizing agent crushed by
watering contains several percent of calcium carbonate generated
therein and because during the desulfurizing treatment,
decomposition of calcium carbonate facilitates agitation of the hot
metal and increases the reaction surface area to improve the
desulfurization efficiency.
[0191] However, with the same recovered desulfurizing agent
subjected to the watering treatment, the desulfurization capability
varies depending on whether the watering operation is controlled
(150.degree. C.) or is continued until the desulfurizing agent is
completely impregnated with water. This is assumed to be because
cooling the desulfurization slag down to a temperature of
100.degree. C. or lower significantly increases the amount of
calcium hydroxide (Ca(OH).sub.2) generated in the recovered
desulfurization slag and because such an excessive increase in the
amount of calcium hydroxide affects desulfurization.
[0192] Further, Table 6 shows a comparison of the treatment
conditions for the desulfurization slag and the time required to
treat about 40 T of desulfurization slag. This table indicates that
the watered desulfurization slag is cooled much faster than that
left as it is without undergoing watering. The table also indicates
that the watering-based treatment allowed the slag to be perfectly
crushed within the time required for cooling. Furthermore,
controlling the amount of water supplied eliminates the need for a
drying treatment after the watering treatment, thereby saving the
facilities, cost, and time required for crushing and drying.
Further, watering during the treatment prevents production of dust
from the desulfurization slag being treated.
[0193] On the other hand, with the natural cooling treatment for
the slag without watering, the required treatment Lime is 170 hours
if the thickness of the desulfurization slag is 1.5 m but decreases
dramatically down to 70 hours if the thickness is 0.4 m. In this
regard, FIG. 8 shows the relationship between the treatment time
and the temperature for the different thicknesses for the
respective treatments (the solid line indicates a thickness of 0.4
m, while the broken line indicates a thickness of 1.5 m). The
treatment speed increases with decreasing thickness. However, the
thickness is determined on the basis of the required cooling speed,
the area of a place available for cooling, or the like. The
non-watering treatment method according to the present invention
requires slightly more time than the watering treatment, but does
not require any watering facilities. Further, with the watering
treatment, it is difficult to uniformly water the slag in the case
of bulk treatment, possibly resulting in water-containing slag. It
is thus difficult to provide such control that such slag is not
generated. Problems with the water-containing slag are that it is
difficult to handle after the recovery treatment, that flame is
generated when it is introduced, that it has an inadequate
desulfurizing capability, and the like. On the other hand, the
non-watering natural cooling treatment method allows the slag to be
easily uniformly treated even in the case of bulk treatment. This
method also causes the lime component in the slag to be "powdered"
(part of the lime component in the slag reacts with moisture or
carbon dioxide in the atmosphere during the natural cooling
operation to change the volume of the slag, which thus becomes
powdery), so that the grain size of the slag decreases as the time
elapses. This eliminates the need for mechanical crushing after the
cooling treatment. Furthermore, part of the lime component in the
slag reacts with carbon dioxide in the atmosphere to generate
calcium carbonate, which is effective in improving the
desulfurization reaction efficiency.
[0194] As described above, by effectively using the desulfurization
slag treatment method of this example according to the conditions
such as the amount of desulfurization slag to be recovered and the
available facilities, the desulfurization slag can be inexpensively
and efficiently treated to reduce the time and cost required to
recover the desulfurization slag. This in turn allows a large
amount of desulfurization slag to be recycled and drastically
reduces the amount of slag to solve environmental problems.
EXAMPLE 6
Screening Desulfurization Slag After Separation of Metal
[0195] In this example, while hot at 900 to 1,200.degree. C.,
desulfurization slag resulting from a desulfurizing step is
screened using a screening apparatus 12 with a .quadrature.70-mm
mesh, and is thus separated into desulfurization slag of a smaller
diameter containing a large amount of unreacted lime and metal of a
larger diameter. In this case, any sieve can be used without
creating any problems provided that it can be operated over a
temperature range from 900 to 1,200.degree. C.; a sieve made of
iron is sufficient. The shape, specification, and the like of this
sieve are not limited provided that it can be operated in a
desulfurization slag treatment field. Further, the mesh of the
sieve is restricted by the supply apparatus in the desulfurizing
facility where the slag is used as a desulfurizing agent. An
appropriate mesh can be used without creating any problems.
[0196] The sieved desulfurization slag of a small diameter is
cooled and then transported, as a recovered desulfurizing agent, to
the supply apparatus on the desulfurizing facility, where it is
used.
[0197] On the other hand, the residual metal can be easily
recovered using the above described method. Further, this metal can
then be reused as an iron source for the hot metal pretreatment
step, thereby significantly contributing to increasing the yield of
iron.
[0198] In this example, desulfurization slag was recovered under
conditions such as those shown in Table 9. The sieve was angularly
installed relative to a horizontal surface. Hot slag was screened
by dropping it from the top of the sieve. Table 10 shows the mass
balance of a desulfurizing agent during its recovery process. It
has been confirmed that even if the desulfurization slag resulting
from the desulfurizing step is sieved, about 90% of CaO in the
desulfurization slag is recovered, with the metal component
effectively removed. That is, the method of the present invention
has proved to enable the slag component in the desulfurization slag
to be effectively recovered without magnetic separation.
[0199] The recovered desulfurizing agent and the lime were applied
to the desulfurizing treatment, and desulfurizing behavior was
checked. For some levels, the mixture of the recovered
desulfurizing agent with the lime was carried out in two manners.
That is, these components were mixed together and then loaded into
a hopper and then a certain part of the mixture was cut out, or a
recovered desulfurizing agent and a lime component were cut out
from the respective hoppers. Table 17 also shows the average
composition of a lime-based desulfurizing agent as a conventional
example. These desulfurizing agents were applied to the mechanical
agitation type desulfurizing apparatus under the test conditions
shown in Table 11 to carry out hot metal desulfurization.
[0200] FIG. 16 shows the relationship between the amount of lime
added per unit amount of hot metal and the desulfurization rate.
The concentration of the lime component in the recovered
desulfurization slag is lower than that of the comparative example,
so that the amount of desulfurizing agent introduced is larger in
this example than in the comparative example. However, the
desulfurizing capability of this example is equivalent to that of
the comparative example, thereby demonstrating the effectiveness of
the present invention.
[0201] Then, to examine the effects of the temperature of the
desulfurization slag on dust, the hot slag was left as it was for
30 minutes to 4 hours and was then passed through the screening
apparatus 12, previously described. Then, it was checked how dust
was produced and how the temperature changed. Table 14 shows how
dust was produced when the slag was screened with its temperature
changed. The table indicates that production of dust changed
significantly after pre-screening temperature reached 600.degree.
C. This nature can be utilized to perform a screening operation or
the like without any dust collectors. Further, Table 15 shows the
result of measurement of a decrease in temperature during the
screening operation. During screening, the temperature decreases by
about 100.degree. C., thus reducing the time required for cooling.
Further, Table 16 shows how dust was produced in the screening
facility according to the present invention and in a screening
facility that does not have the diagonal plate (14) or sliding way
(16), shown in FIG. 12.
[0202] With the screening operation according to the present
invention, even desulfurization slag that is likely to produce dust
at a temperature of 600.degree. C. or lower can be screened without
any dust collectors. The method of this example significantly
simplify a facility which is used to recycle desulfurization slag
and which adjusts the grain size of dry desulfurization slag.
Further, production of dust can be prevented during screening using
a simple facility. Furthermore, during screening, the slag
efficiently contacts with the atmosphere and is thus efficiently
cooled. Moreover, by loading the desulfurization slag onto a dump
truck using the loading method described herein, the loading
operation can be achieved while preventing production of dust
without any dust collectors.
[0203] The treatment of this example enables the desulfurizing
agent to be inexpensively and efficiently treated and reduces the
amount of desulfurization slag to be treated compared to the prior
art, thereby drastically reducing costs. Other significant effects
of this example are the possibility of recovering and recycling a
large amount of desulfurization slag and a decrease in the amount
of slag, which leads to solution of environmental problems.
EXAMPLE 7
Handling of a Recovered Desulfurizing Agent
[0204] If a recovered dry desulfurizing agent is loaded onto a dump
truck for recycling, then naturally, it is powdered faster and is
very likely to produce dust. However, the amount of dust produced
can be minimized by using a vehicle with a sucking capability
instead of the dump truck to transport the recovered desulfurizing
agent. Further, the recovered desulfurizing agent can concurrently
be screened by installing a mesh at a suction port during suction,
thereby enabling efficient handling and transportation with a
reduced amount of dust produced.
[0205] Specifically, a suction hose is connected to the vehicle
with the sucking capability to suck and load a recovered
desulfurizing agent obtained by cooling and crushing
desulfurization slag resulting from the hot metal desulfurizing
step. At this time, by installing a jig having a mesh for screening
at the suction port, the desulfurizing agent can concurrently be
screened so that the required grain size can be obtained. In this
case, the jig attached to the suction port during suction may be
selected on the basis of the required level of the sieve, i.e. the
desired grain size of the recovered desulfurizing agent.
[0206] Furthermore, if no screening operation is required during
suction, the mesh need not be installed at the suction port, and
the desulfurizing agent may be sucked using only the hose.
[0207] Moreover, if only large masses of a several tens of cm level
must be removed, the recovered desulfurization slag was
simultaneously loaded and sieved on the basis of the sucking
operation using a simple jig only having partitions arranged at the
tip thereof and formed of metal bars as shown in FIG. 11. In this
example, desulfurization slag resulting from the mechanical
agitation type desulfurizing step was used. The desulfurization
slag was left to be naturally cooled in a building for about 6
days. During this period, to facilitate cooling, the
desulfurization slag was agitated about three times a day.
[0208] The hose used for suction had a diameter of 15 cm, and the
jig 11 attached to the suction port during suction included two
nets with a 30- and 5-mm meshes and a conical jig. These jigs all
had an air suction port. Furthermore, as a comparative example, the
desulfurization slag was sucked using only the hose and without any
jigs. Further, Table 12 shows the specification of the suction
vehicle used.
[0209] Table 13 shows throughput and suction performance as results
for suction of a recovered desulfurizing agent using the various
types of suction ports previously described. These results indicate
that the recovered desulfurizing agent can be efficiently loaded at
a rate of about 1 t/min. while being simultaneously sieved,
whichever suction port is used. Further, it has been confirmed that
during suction, the temperature of the recovered desulfurizing
agent decreases by about 30.degree. C. after the treatment as a
result of the positive contact of the desulfurizing agent with the
atmosphere.
[0210] Furthermore, most of the sieved large masses and the slag on
the sieve are metal and can thus be used for another process.
[0211] It has been ascertained that with the handling method of the
present invention, even a recovered desulfurizing agent which is
composed of fine powders and which is likely to produce dust can be
simultaneously and efficiently sieved and loaded onto a transport
vehicle without using any dust collectors.
[0212] In this example, with the desulfurizing agent treating
method used to recycle desulfurization slag, a transport vehicle
with a sucking capability can be used to load a recovered
desulfurizing agent while minimizing the amount of dust produced.
Furthermore, the recovered desulfurizing agent can be efficiently
treated by simultaneously performing a sucking and screening
operations. Moreover, the recovered desulfurizing agent efficiently
contacts with the atmosphere or suction air and is thus efficiently
cooled.
EXAMPLE 8
Measurement of the Content of CaO in Desulfurization Slag
[0213] In this example, desulfurization slag resulting from a
mechanical agitation type desulfurizing step was used. The
desulfurization slag was passed through the screening apparatus
composed of a net with a .quadrature.70-mm mesh.
[0214] The following are the results of the reuse, in a mechanical
agitation type desulfurizing facility, of the recovered
desulfurizing agent having its grain size adjusted. FIG. 14 shows
the relationship between the amount of pure CaO component and the
amount of material desulfurized .DELTA.S (the amount of sulfur
before treatment (S)-the amount of sulfur after treatment (S)). It
has been found that the amount of pure CaO component has a clear
correlationship with the amount of material desulfurized. This
nature can be utilized to easily determine the amount of
desulfurizing agent introduced depending on the amount of sulfur
before treatment (S), thereby achieving a stable desulfurization
rate.
[0215] Further, FIG. 15 shows the relationship between the bulk
density and the CaO mass %. This figure indicates that the bulk
density decreases with increasing amount of CaO. This tendency can
be utilized to estimate the CaO mass % of the recovered
desulfurizing agent by measuring the bulk density thereof.
[0216] According to this example, when desulfurization slag was
reused in the mechanical agitation type desulfurizing facility, the
required amount of desulfurizing agent could be determined
promptly, while achieving a stable desulfurization rate.
EXAMPLE 9
Example Relating to Improvement of Desulfurization Efficiency by
Addition of a Lime Source (CaO, CaCO.sub.3, Ca(OH).sub.2)
[0217] Desulfurization slag resulting from a desulfurizing step was
cooled and crushed by a natural cooling or watering treatment to
obtain a desulfurizing agent (hereinafter referred to as a
"recovered desulfurizing agent"). One or more of the
above-described desulfurizing agents were added to the recovered
desulfurizing agent, which was then used as a desulfurizing agent
according to this example. In a comparative example, only the
recovered desulfurizing agent was used. Table 18 shows the amount
of recovered desulfurizing agent added, the types of desulfurizing
agents, and the amounts of desulfurizing agents added.
[0218] These desulfurizing agents were applied to the mechanical
agitation type desulfurizing apparatus under the test conditions
shown in Table 19 to carry out hot metal desulfurization.
[0219] FIG. 19 shows the relationship between the amount of lime
component added per unit amount of hot metal and the
desulfurization rate at each desulfurization level. This figure
indicates that with an equal amount of lime added per unit amount
of hot metal, the use of the (d) recovered desulfurizing agent+lime
slightly increases the desulfurization rate compared to the use of
(a) only the recovered desulfurizing agent. The FIG. also indicates
that the use of the (b) recovered desulfurizing agent+CaCO.sub.3,
the (c) recovered desulfurizing agent+CaCO.sub.3+Ca(OH)- .sub.2, or
the (e) recovered desulfurizing agent+lime+CaCO.sub.3+Ca(OH).su-
b.2 increases both the amount of CaCO.sub.3 and Ca(OH).sub.2 added
and the desulfurization rate compared to the use of (a) only the
recovered desulfurizing agent. This is assumed to be because during
the desulfurizing treatment, decomposition of CaCO.sub.3 or
Ca(OH).sub.2 increases the reaction surface area or facilitates
agitation of hot metal to improve the desulfurization efficiency,
as previously described.
[0220] Table 20 shows the ratio of CaO to the recovered
desulfurizing agent, the amount of recovered desulfurizing agent
added, the types of desulfurizing agents, the amounts of
desulfurizing agents added, and the total amount of desulfurizing
agents which are measured if 8 kg-CaO/T of lime component is
contained in the desulfurizing agents of the compositions used in
this example. If each desulfurizing agent requires the same amount
of lime component, when only the recovered desulfurizing agent is
used, a large amount of desulfurizing agent is required if the
recovered desulfurizing agent contains only a small amount of pure
lime component. However, addition of lime and calcium carbonate or
calcium hydroxide improves the desulfurization slag rate and
reduces the amount of desulfurizing agent used. This reduces the
amount of slag discharged after the treatment. Furthermore, the
compositions of the desulfurizing agents can be freely adjusted
according to the state of the hot metal to be treated or the
required treatment conditions. Moreover, similar effects are
produced even if these desulfurizing agents are separately added to
the hot metal instead of being mixed together.
EXAMPLE 10
Example Relating to Improvement of Desulfurization Efficiency by
Addition of Various Carbon Sources
[0221] Desulfurization slag resulting from a desulfurizing step was
cooled and crushed by a natural cooling or watering treatment to
obtain a desulfurizing agent (hereinafter referred to as a
"recovered desulfurizing agent"). Various C sources were added to
the recovered desulfurizing agent, which was then used as a
desulfurizing agent according to this example. Table 21 shows the
amount of recovered desulfurizing agent added, the types of
desulfurizing agents, and the amounts of desulfurizing agents
added. The C sources were composed of powders of grain size 1 mm or
smaller.
[0222] These desulfurizing agents were applied to the mechanical
agitation type desulfurizing apparatus under the test conditions
shown in Table 22 to carry out hot metal desulfurization.
[0223] FIG. 20 shows the relationship between the amount of lime
component added per unit amount of hot metal and the
desulfurization rate at each desulfurization level. This figure
indicates that with an equal amount of lime added per unit amount
of hot metal, the use of the (d) to (d) recovered desulfurizing
agent+C source increases the desulfurization rate linearly with the
amount of C source added, compared to the use of (a) only the
recovered desulfurizing agent. It has also been confirmed that
equivalent effects are produced regardless of the type of the C
source or the method of adding the C source. This is assumed to be
because the C source acts as a reducing agent during the
desulfurizing step to improve the desulfurization rate, as
previously described. Further, part of the C source dissolved in
the hot metal to increase the concentration of C in the hot metal
by 0.1 to 0.5% in each case under the conditions of this
example.
[0224] By thus adding a C source such as anthracite or coke, the
desulfurization rate can be improved while reducing the amount of
slag discharged after the treatment. Any C source may be used, such
as coal, coke, pitch coke, or plastic. Furthermore, the
compositions of the desulfurizing agents can be freely adjusted
according to the state of the hot metal to be treated or the
required treatment conditions. Moreover, similar effects are
produced even if these desulfurizing agents are separately added to
the hot metal instead of being mixed together.
[0225] As described above, the present invention provides a method
of desulfurizing hot metal, which method effectively reuses
desulfurization slag resulting from a hot metal desulfurizing
treatment in order to reduce the costs of hot metal desulfurization
and the amount of slag generated. Further, the present invention
provides a desulfurizing agent that allows a hot metal
desulfurizing treatment with a reduced amount of slag generated to
be inexpensively carried out. The present invention produces
significant effects. For example, it reduces desulfurization costs,
allows desulfurization slag to be recycled, and reduces the amount
of slag to solve environmental problems. Therefore, the present
invention has a high industrial value.
1TABLE 1 Main components of average conventional desulfurizing
agent and recovered desulfurizing agent Main component T-Fe CaO
SiO.sub.2 Al.sub.2O.sub.3 T-S CaF.sub.2 (1) Conventional -- 90.0 --
-- -- 5.0 desulfurizing agent (2) Recovered desulfurizing 19.2 53.6
9.3 4.1 1.7 2.1 agent (3) Desulfurization slag 19.7 45.0 12.0 11.0
3.2 2.2 resulting from recovered desulfurizing agent-used
defulfurizing treatment (unit: mass %)
[0226]
2TABLE 2 Test conditions Item Contents Desulfurizing method
Mechanically agitating type desulfurizing apparatus Treatment
Container Hot metal ladle Throughput 140-160 t Hot metal
temperature 1300-1450.degree. C. Hot metal [S] 0.05-0.02% Amount of
0 to 30 kg - CaO/t desulfurizing agent
[0227]
3TABLE 3 KR desulfurization treatment conditions After Before
introduction introduction of recycling of recycling Item process
process Hot metal [S] 0.05-0.02% 0.05-0.02% Amount of 8 kg/t 3-5
kg/t lime used Amount of -- 8 kg - CaO/t desulfurizing agent
used
[0228]
4TABLE 4 Changes in amount of slag generated associated with
introduction of desulfurization recycling process Amount of slag
generated (t/month) Before recycling 8000 After recycling 4000
Amount of decrease in 4000 amount of slag generated
[0229]
5TABLE 5 Main components of average conventional desulfurizing
agent and recovered desulfurizing agent Main Conventional Drying
after component desulfurizing agent watering CaO 90.0 53.6 T-Fe --
19.2 SiO.sub.2 -- 9.3 Al.sub.2O.sub.3 -- 4.1 T-S -- 1.7 CaF.sub.2
5.0 2.1 CaCO.sub.3 -- 2.3 Ca(OH).sub.2 -- 18.3 (Unit: mass %)
[0230]
6TABLE 6 Time required for desulfurizing treatment method and 40T
treatment Non-watering Watering Natural cooling Drying
Desulfurization Desulfurization Treatment Watering after slag
thickness slag thickness Mechanical method 150.degree. C.
80.degree. C. watering 1.5 m 0.4 m crushing Amount of water 8 15 30
-- -- supplied (t) Mechanical Not required Not Not required
Required crushing required Drying Not required Required Not
required Not required Time required 30 24 10 170 70 50 to cool slag
down to 100.degree. C.
[0231]
7TABLE 7 Main components of average conventional desulfurizing
agent and recovered desulfurizing agent Conventional watered
watered Main desulfurizing agent agent component agent (150.degree.
C.) (80.degree. C.) CaO 90.0 53.6 53.6 T-Fe -- 19.2 19.2 SiO.sub.2
-- 9.3 9.3 Al.sub.2O.sub.3 -- 4.1 4.1 T-S -- 1.7 1.7 CaF.sub.2 5.0
2.1 2.1 CaCO.sub.3 -- 5.2 1.1 Ca(OH).sub.2 -- 3.3 24.1 (Unit: mass
%)
[0232]
8TABLE 8 Main components of average conventional desulfurizing
agent and recovered desulfurizing agent Non- watered and
Non-watered Conventional naturally mechanically Main desulfurizing
cooled crushed component agent agent agent CaO 90.0 53.6 53.6 T-Fe
-- 19.2 19.2 SiO.sub.2 -- 9.3 9.3 Al.sub.2O.sub.3 -- 4.1 4.1 T-S --
1.7 1.7 CaF.sub.2 5.0 2.1 2.1 CaCO.sub.3 -- 6.5 0.4 Ca(OH).sub.2 --
2.5 0.5 (Unit: mass %)
[0233]
9TABLE 9 Recovery treatment conditions for desulfurization slag
Desulfurization 600-1200.degree. C. slag temperature Sieve Made of
iron, mesh 70 mm .times. 70 mm Sieve angle 8-15.degree. Throughput
2 t/times
[0234]
10TABLE 10 Changes in composition during recovery process
Conventional Hot slag Recovered desulfurizing (before desulfurizing
agent screening) agent Weight Metal 0 20 7.2 ratio component % Slag
100 80 92.8 component % Slag CaO 90 54 53.8 composition T-Fe --
18.5 18.2 SiO.sub.2 -- 9.0 8.8 Al.sub.2O.sub.3 -- 4.1 4.1 T-S --
1.7 1.8 CaF.sub.2 5 2.1 1.8 CaCO.sub.3 -- 0.4 1.3 Ca(OH).sub.2 --
0.5 1.0 (unit: mass %)
[0235]
11TABLE 11 Test conditions Item Contents Desulfurizing Mechanically
agitating method type desulfurizing apparatus Refining Hot metal
ladle container Throughput 130-165 t Hot metal 1300-1450.degree. C.
temperature Initial [S] in 0.02-0.05% hot metal Agitation time 5 to
7 minutes Amount of 6-30 kg/t desulfurizing agent
[0236]
12TABLE 12 Specification of suction vehicle Suction air quantity 80
m.sup.3 Vacuum pressure -650 mmHg Suction tank capacity 5.5 m.sup.3
Connection hose diameter 15 cm
[0237]
13TABLE 13 Sucking method and Recovered desulfurizing agent loading
capability Amount of Sucking method recovered Suction Sucking
Diameter of Suction desulfurizing agent time capability hose used
port type sucked (t) (min.) (t/min.) 15 cm 5 mm mesh 14.2 14.7 1.00
15 cm 30 mm mesh 22.4 20.13 1.11 15 cm Cone-shaped 6.00 5.10 1.18
15 cm Cone-shaped 16.2 16.2 1.00 15 cm Cone-shaped 11.1 12.5 0.89
15 cm Cone-shaped 29.7 33.2 0.89 15 cm Cone-shaped 15.0 15.9 0.94
15 cm Only hose 13.8 9.8 1.40
[0238]
14TABLE 14 Screening temperature and dust generation Temperature
before screening Dust generation 420.degree. C. Large 610.degree.
C. Small 940.degree. C. Very little
[0239]
15TABLE 15 Decrease in temperature during screening Before After
Decrease in screening screening temperature 1 930.degree. C.
790.degree. C. .DELTA. 140.degree. C. 2 940.degree. C. 880.degree.
C. .DELTA. 60.degree. C. 3 940.degree. C. 860.degree. C. .DELTA.
80.degree. C.
[0240]
16TABLE 16 Dust generation observed when present facility is used
Slag Dust temperature generation Present screening 450.degree. C.
Little facility Screening facility 480.degree. C. Very large
without diagonal plate or sliding way
[0241]
17TABLE 17 Average desulfurizing agent composition used when both
recovered desulfuring agent and lime are used Recovered
desulfurizing agent + 50% lime Conventional Recovered Recovered
(introduced Recovered desulfurizing Recovered desulfurizing
desulfurizing through desulfurizing agent desulfurizing agent + 25%
agent + 50% different agent + 80% (Comparative agent lime lime
system) lime example (Example a) (Example b) (Example c) (Example
d) (Example e) Slag composition % CaO 90 53.8 65.4 75.8 75.8 90.1
T-Fe -- 18.2 14.0 9.3 9.3 4.2 SiO.sub.2 -- 8.8 6.8 4.6 4.6 2.1
Al.sub.2O.sub.3 -- 4.1 3.2 2.2 2.2 1.0 T-S -- 1.8 1.4 1.0 1.2 0.5
CaF.sub.2 5 1.8 1.4 1.1 1.2 0.6 CaCO.sub.3 -- 1.3 1.1 0.7 0.8 0.6
Ca(OH).sub.2 -- 1.0 0.8 0.6 0.7 0.6 (Unit: mass %)
[0242]
18TABLE 18 Average desulfurizing agent composition used when both
recovered desulfurizing agent and lime source Recovered
desulfurizing Example agent Lime CaCO.sub.3 Ca(OH).sub.2 a 100 --
-- -- b 70 -- 30 -- c 60 -- 20 20 d 50 50 -- -- e 30 50 10 10
(Unit: mass %)
[0243]
19TABLE 19 Test conditions Item Contents Desulfurizing Mechanically
agitating type method desulfurizing apparatus Treatment Hot metal
ladle container Throughput 140-160 t Hot metal 1300-1450.degree. C.
temperature Hot metal [S] 0.05-0.02%
[0244]
20TABLE 20 Amounts of recovered desulfurizing agent and lime source
added when 8.0 kg/T of CaO component is required in desulfurizing
agent Recovered desulfurizing agent Added desulfurizing agent Total
Cao Amount of Ca(OH).sub.2 amount component recovered Lime
CaCO.sub.3 Amount of of in desulfurizing Cao Amount of Amount of
Ca(OH).sub.2 desulfurizing desulfurizing agent added component lime
added CaCo.sub.3 added added agent agent wt % kg/T wt % wt % kg/T
wt % kg/T wt % kg/T kg/T kg/T 100 11.4 70 -- -- -- -- -- -- 11.4
8.0 20.0 40 -- -- -- -- -- -- 20.0 70 12.5 40 -- -- 30 5.4 -- --
17.9 60 9.5 40 -- -- 20 3.2 20 3.2 15.9 50 5.7 40 50 5.7 -- -- --
-- 11.4 30 3.2 40 50 5.3 10 1.1 10 1.1 10.6 (Unit: mass %)
[0245]
21TABLE 21 Average desulfurizing agent composition used when both
recovered desulfurizing agent and C source are used C source Amount
Recovered of C desulfurizing source Adding agent Type added method
Example 100 -- 0 -- a 95 Coke 5 Mixture b 95 Anthracite 5 Mixture c
80 Coke 20 Mixture d 70 Coke 30 Separate addition (Unit: mass
%)
[0246]
22TABLE 22 Test conditions Item Contents Desulfurizing Mechanically
agitating method type desulfurizing apparatus Treatment Hot metal
ladle container Throughput 140-160 t Hot metal 1300-1450.degree. C.
temperature Hot metal [S] 0.05-0.02%
* * * * *