Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ he present invention is concerned with an agent
and a method for desulphurising crude iron and ra~ steel.
It is already known that a desulphuri~ing o crude
iron can be accomplished by the addition of quicklime to
the iron melt. Thus, for example, in the production of
~teel in an oxygen blow convertor, lime is added in order
to bind sulphur.
It i~ also known to blow in quicklime in powdered
form~ Thi~ take~ place, for example, in electric arc
furnaces, in oxygen blow convertors (LDAC proce~s) and
in bottom blow convertors (OBM process). When blowing
lime into crude iron transport ladle~, it i~ found to
he nece~ary to blow in a large amount of lime in order
to achieve the desired desulphuri~ing effec~. Further-
more, large amount~ of conveyor gas (about 1 litre of
gas per kg. of quicklime) are neces~ary for the pneumatic
conveyance of the lime ~ince o~herwise blockages, ~toppage
formation~ and non-unifonm pneumatic conveyance would
result. ~owever, this i~ unde~irable becau~e it give~
rise to spattering and ejection of metal from the ladle.
Consequently~ khere is a need for a de~ulphuri~ing
agent ba~ed upon quicklime which, with the use of com-
paratively ~mall amount~ of conveying gas of, for example,
10 ~l. conveying gas (10 litre~ of ga~ under normal
condition~) per ~9. of de~ulphurising agent, can be con-
veyed uniformly.
Thu~, it is an object of the pre~ent inventi~n
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to provide a highly ef~ective de~ulphuri3ing ~gent
which can be introduced into the crude iron to be
treated with the use of a comparatively ~mall amount
of conveying ga~, thus making pos~ible ~maller los~e~
of material and a considerable saving of energy due to
a reduced cooling of ~he crude iron to be de~ulphurised.
Thus, according to the pre3ent invention, ~here
is provided an agent for desulphuri~ing crude iron and
raw steel which comprises a mixtura of quicklime (CaO)
and diamide lime~
The agent according to the present invention is
preferably in powdered form, which can be obtained by
grinding the components. The agent according to the
present invention preferably has a particle ~i~e suit-
able for pneumatic conveying.
The diamide lime u~ed as a com~onent of the
agent according to the present invention i~ a chemically
produced, precipitated calcium carbonate, which prefer-
ably ha~ a car~on content of rom 5 to 4~/0 by weight.
The de~ulphuri~ing agent according to the present
invention preferably compri~es 50 to 9~ by weight and,
more preferably, 60 to 85% by weight of quicklime and
10 to 50/0 ~y weight and especially 15 to 40% by weight
of diamide lime. According to an e~pecially preferred
embodiment, the desulphuri~ing agent according to ~he
pre~ent invention contains about 40% by weight (40 ~ 3%
by weight) of diamide llme.
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The de~ulphurising agent according to ~he present
invention with a diamide lime content of about 4~/0 by
weight (with a carbon content of 40 to 5~0 by weight)
is especially ~uitable for the de~ulphurising of crude
iron in torpedo ladles. For desulphurising in open
crude iron transport and charging ladle~, the desulphur-
iqing agent according to the present invention prefer-
ably has a diamide lime content of 15 to 25% by weight.
The diamide lime present in the desulphurising
agent according to the pre~ent invention has a carbon
content of from 5 to 5~0 by weight and prefarably of
10 to 40% by weight.
Furthermore, the de~ulphurising agent according
to the present invention can also contain co~paratively
small additions of conventional adjuvant~, or example
of fluor3par, of up to loY~ by weight.
Surprisingly, we have found that the desulphur-
i~ing agent according to the present invention require~
a substantially 3maller amount of conveying gas than
the quicklime previously used for the same purpose.
Thu~, the agent according to the present invention can
be uniformly conveyed with an amount of conveyor gas of
only 7 Nlo per kg. The calcium carbonate component o
the diamide lime, after its emergence from the lance
u~ed for the introduction of the agent into the crude
iron to be desulphuri3ed, decomposes instantaneouqly
and thereby ensures an intensi~e mixing up of the ~olid
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desulphuri~ing agent with the iron melt to ~ de~ulphur~
ised. From the calcium carbonat~ component of the
diæmide lime there thereb~ ~ir~t r2sult~ quicklime,
which is highly reacti~e because it i~ freshly calcined.
Since thi~ mixture produce~ gaS in the iron melt, very
many ga9 bubbleY of small diameter are fonmed. The
re~ult of this i~ that only a very small amount of the
de3ulphuri~ing agent according to the pre3ent invention
i~ su~pended in relatively large bubble~ and is conv~yed
through the melt without the agent coming into contact
wi~h the iron. This can clearly be een by ob~erving
the surface of the iron melt during the desulphurisi~g
treatment. Thu~, when blowing quicklime into a molten
iron, bubhle~ of the conveying ga~ used reach the sur-
face and there burs~ and liberate large amount~ of fine,
dust~like ~uicklime~ Thi9 dus~ mu~t be ~ucked off and
removed from the waste ga~ with the help of a filter
or of a ~crubber, which considerably increase~ the
cost of the de~ulphurising treatment. In the case of
blowing in the de~ulphurisin~ agent according to the
pre~ent invention, no large bubble~ appear on the 9UX-
face of the molten iron and only a very ~mall amount
of dust formation is ob~erved.
In comparison with the conventionally u3ed lime,
the de3ulphuri~ing agent according to the pre~ent
inventlon po~sesse~ the considerable adva~tage of a
substantially improved reactivity. Thus, when u~ing
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the agent according to th~ present invention, for
obtaining the same desulphuri~ing effect it i~,
~urprisingly, only nece3~ary to use about half the
amount which would be necessary if carrying out the
treatment with quicklime.
This ~urpri~ing advantage of ~ubstantially
better reactivity or of increa~ed degree of action i~
also manife~ted by the fact that, because of the
reduction of t~e a~ount of desulphuriqing agent to be
blown in, a correspondingly ~maller amount of de~ulphur-
i~ing slag i9 obtained. The de~ulphurising ~lag always
contain~ a high proportion of metallic iron, which can
amount to up to ~OYO by weight. This iron contained in
the de~ulphurising 31ag is first 105t from the ladle
and can only ~e recovered ~ub~equently ~ro~ the ~olid-
ified slag with considerable expen~e. E3pecially when
the slag c0019 more considerably, for example ~hen it
is not removed immediately after the treatment, ~his
can result in a part of it remaining in the treatment
ves~el, whereb~ the transport capacity thereof for the
liquid metal melt i~ reduced.
In the following Example, which is given for
the purpo~e of illu~trating the pr2sent invention, a
compari~on i~ made between the use of the agent accord
ing to the present invention and the use of the
previously conventionally employed quicklime.
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a~ 9b~ L~L~æeaa~
160 Tonne~ crude iron were desulphuri3ed in a
torpedo ladle solely wi~h quicklime. The initial
~ulphur content of the crude iron wa~ 0.042% by weight.
A total of 1760 k~. of fine quicklime were blown into
the melt with the u~e of a lance which wa~ in~erted
into the melt to a depth of 1.6 xetres. In order to
be able to achieve a rea-~onably uniform blownng in of
the quicklime, 120 ~1. of conveying gas per kg. of
quicklime had to be u~ed. Due to this large amount
of gas, a violent bubbling of he molten metal occurred,
large amount~ of m~tal spattering out of the ladleO
Thick cloud~ of white ~moke th~reby emerged from the
mouth of the ladle. In order to prevent the spatter-
ing from becoming too violent, only 30 k~. of ~uicklime
could be blown in per minute with 3600 ~1. of conveying
ga~. The final sulphur content of the crude iron was
0.018% by weight.
b)
invention.
Sub~equently, i~ the came plant, the ~ame amount
of crude iron was desulphuri~ed using t~e agent accord-
ing to the pre~ent invention, w~ich had been produced
by grinding 60% by weight of quicklime and 4~% by weight
of diamide lime with a carbon content o~ 2~o by weight.
In order to achieve the sæme desulphurising action~ only
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4.8 kg. of desulphurising agent were needed per tonne
of crude iron and the mixture could thereby al~o be
conveyed with a ~maller amount o~ ga3. For a uniform
and di~turbance-free blowing in, it wa~ only neces~ary
to use 7 ~1. of conveying ga~ per Xg. o~ desulphurising
agent. Therefore, the rate of conveying could be
increased to 100 kg. per minute. Even in the case of
thi~ higher rate of blowing, only 700 ~1. of conveying
gas per minute were needed. Thi9 corresponds to only
about one fif~h of the amount per unit time which was
needed for conveying the quicklime. There wa~ also a
correspondingly lower turbulence of the melt. ~en
when the ladle wa~ well filled, no spattering occurred.
A further advantage of the desulphurising agent
according to the present invention, which only had to be
u~ed in smaller amounts, and of the higher conveying
rates which were po~ible, i9 the fact that the treat-
ment of 160 tonnes of crude iron i~ inished after
about 10 minutes, whereas the de~ulphurisation with
quicklime takes practically 1 hour. ~ormally, such a
long period of time i~ not available for the desulphur-
ing~ A further consequence of the laborious treatment
in which large amounts of quicklime are blown in is a
considerable cooling of the molten crude iron. Thu~,
~the temperature cf the crude iron melt de~ulphurised
with q~icXlime decreased by 42C., whereas the temper-
ature losr in the case oE using the dosu1phurising
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agent according to the present invention was only 8C.
Thus, it can be ~een that, in compari~on with
the quicklime normall.y used, the desulphurising agent
according to the present invention display~ ~urpri3ing
advantages.
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