CA1168875A - Powdery desulfurizer composition - Google Patents

Abstract

Title of the Invention POWDERY DESULFURIZER COMPOSITION
Abstract of the Disclosure A powdery desulfurizer composition for injection desulfurization of molten iron, said composition comprising 30 to 90% by weight of quicklime and 70 to 10% by weight of diamide lime.

Description

i 3 f~3~3~5 ~ 1 --BACKGROUND 0~ ~E~ INVEN'~I0~
1. ~ield of the Invention ~ his invention relates to a powder~ desulfuriz-ing agen-t comprising quicklime and diamide lime as main ingredie~tsO More specifically, the inven~ion pertains to a powdery desulfurizer composition comprising quicklime and diamide lime as main ingreclients, which is especially effective in injection desulfw ization of molten iron.
The diamide lime is a mixture consisting essentially of calcium carbonate and carbon~
~ he term "molten i.ron" as used herein, denotes a molten mass of pig iron, cast iron, stsel, etcO

2. Descriptio~ of the Prior Art~
As is well known, desulfurization of molten iron 15 is an impor-tant treatment for o~taini~g iro~ and steel products ha~ing excelle~t properties, and numerous desulfurizing agents and desul~urizi~g methods have been proposed heretofore.
Calcium carbide has excellent desulfurizing ability, and desulfurizers comprising calcium carbide as a main ingredient have gained widespread acceptance~
Production of calcium carbide, however, entails high electric power consumptio~, and it has been desired to re-assess calcium carbide as a desulfurizer from an economical viewpoint i~ order to cope with the recent rise in ener~y costO On the o~her ha~d, quicklime is known as one of cheaper desulfurizers9 Although ~he i~d~stry desires commercial utilizatio~ of quicklime, it8 very `~;

~ '5 low desulfurizin~ performance has made it difficul~ to meet various high-level raquirements in the present-day desulfurization of molten iron.
A method which comprises adding a powdery desulfurizing agent to molten iron and mechanically stirr-ing the mixture and a method which comprises injecting a powdery desulfurizi~g agent i~to molten iron usin~ a carrier gas are well known for desul~urizatio~ of molten iron. The injection desulfurizing me~hod has gained widespread accepta~ce because of its excellent opperational ease and desulfurizing ef~iciency. ~pecifically, the i~jection desulfurizing method comprises carrying a powdery desulfurizing agent on a stream of a carrier gas such as dry nitrogen, and injecting it into molten iron through a lance submerged in molten iron~ According to a widely accepted practice o~ injection desulfuriza~ion, a torpedo car which has received molte~ pig iro~ from a blast fur~ace, for example, is stopped for a while at a de-sulfurizing station on its way to a s~eel-making factory, and a powdery desulfurizing agent is injected into molten iron in the torpedo car during this stop. Furthermore, i~jection desulfurization in an open ladle has been put into operation in recent years in place of the mechanical-ly stirring desulfurizing method (eOgO~ the so-called ER
method in an open ladle) because of its excellent opera-tional ease and desulfurizing efficiency.
The term "injection desulfurizatio~", as used in the pre~ent application, is a term contrastive with "desulfurization methods which involve pre-addition of sulfurizers or mecha~ical stirring", and specifically de-notes a method of desulfurization which comprises inject-ing a powdery desulful7izing agent together with a carrier gas into mol~en iron beneath its surfaceO
~ he injected desulfurizing agent by the injection desulfurizi~g method escapes from the carrier ga~ in molten iron and makes contact with the molten iron, whereupon it reaots with sulfur in the molten ironO '~hen, the desulfurizing agent and/or its reaction product with sulfur rise through the molten iron and finally float as a desulfuriza-~ion slag on the surface o~ the molten ironO
~he molten iron is sufficiently moved and stirred by the carrier gas and/or gases which may be evolved from gas-~enerating substances in ~he powde~y desulfurizi~g agent, and as a result~ the chances o~ the desulfurizer to encou~ter sulfur in molten iron is enhanced, and the residual sulfur content in the molten iron is geometrically uniformedO
In this mechanism of desulfurization~ the follow-ing three factors may be recited as among the most influential upon desulfurization performance.
1. Reactivity of the powdery desulfurizi~g agent~
2. ~he area of contact between the powdery desulfurizing agent and the molte~ iron.

3 Distribution of the concentratio~ of sulfur in molten iron during desulfurization.

Methods for irnproving the desulfuri3ing ability of quicklime have been proposed, for example, in Japanese ~aid-Open Patent Publications ~os~ 38209/1979, 50414/19797 ~6416/1979, and 86417/1979 which are directed mainly to si~e reduction of CaO crystals co~stituting quicklime so as to increase its contact area and thereby improve its reactivity. It has been found, however, that when quick-lime treated by the me-thods disclosed in these prior patent ~locuments is used in injection desulfurizatiOn of molten iron, its transportability on a stream of a carrier gas is very poor, a large amount of the carrier gas is required, a~d therefore injection of the quicklime in high concentration and fine dispersion in the carrier gas is difficul-~, and consequently that the ad~antage of the finely divided CaO crystals cannot be utilized and the expected desulfurizi~g effect cannot be obtained.
It has also been found that if the particle diametex of the quicklime is further decreased, its transportability on a carrier gas is further reduced to cause various troubles in injection desulfurization. It is thus seen that although the reduction of the particle size of a desulfurizing agent has greatly to do with an increase in desulfurizing ability, its desulfuxizi~g performance is not directly governed by its particle siæe, and also it is greatly affected by the transportability of the desulfurizing agent on a carrier gasO
In the i~jection desulfurizing method, the powdery desulfurizing agent is injectcd into molten iron in a form suspended in a carrier gas~ ~hat part of the powde~ desulfurizing agent which has escaped from the gas bubbles o~ the gas stream makes dlrect contact with the molten iron and reacts with sulfur in the molten iron, but that portion of the desul~urizing agen-t which remains enclosed within the gas bubbles rises as such and floats on the surface of the molten iron without contributing to the desulfurization reaction or spuxts out of the molten iron together with the gas.
In order to increase the proportion of the desulfurizer powder which participates in the desulfuriza-tion reaction and to increase its reacti~ity, it is desirable to minimize the amount of the carrier gas~
thereby preventing the desulfurizing agent from being enclosed within the gas bubblesO ~he a~ount of the carrier gas required for injection, however depends upon the gas transportability of the powdery desulfurizing agent, and a de~ulfurizing agent which has poor gas transportability re~uires a large amount of a carrier gas for injection.
Accordingly~ even a desulfurizing agent having high reactivity cannot give the desired desulfurizi~g effect in injection desulfurization if its transportability on a carrier gas is poorO
On the other hand, if the particle size of the powdery desulfurizing a~e~t is increased, the surface area of particles per unit weight decreases a~d therefore, its desulf~rizing e~fect is also reducedO
~urthermore, w~en the desulfuriæing agent has . ~ . , i , .

poor gas tra~sportability, great fluctuations occur in the concentration of the desulfurizlng agent in the carrier gas in injection desulfurization to cause a pulsating move-ment of the desulfurizer-carrier gas stream which frequent-ly becomes an operational trouble~ For example, injectionof an excessively large amount of the powdery desulfurizing agent into molten iron at a time results in an excessively large amount of gas evolution at a time in the molten iron and thus increases vibration of a torpedo car, an open ladle, etcO q'he fluctuations in -the concentration of the desulfurizing agent also can result in the desul~urizing agent blocking up the lance and pipes, or the molten iron splashing vigorously out of the torpedo car and thus caus-ing undesirable phenomena such as the pollution of the workin~ environment.
0~
The present inventors have undertaken various in-vestigations in order to improve the performance of quick-lime in injection desulfurization with special attention to the poor gas transportability of quicklime, and unexpected-1~ found that a powdery desulfurizing composition compris-ing a specified amount o~ powdery quicklime and a specified amount of powdery diamide lime gives a complete solutio~ to the aforesaid various problems associa-ted with quicklime~
It is an object of this invention to provide a quicklime-containing powdery desulfurizer composition for use in injection desulfurization o~ molten iron, which is low in cost and fully utilizers the desulfurizing ability of quicklime.

-According to this invention, there is provideda powdery desulfurizer compositiou for use in inJection desulfurization of molte~ iron9 said composition compris-ing 30 to 90% by weight of quicklime and 70 to 10% by weight of diamide limeO
In a preferred embodiment, the composition of -this invention further comprises not more than 20 parts by weight of a carbonaceous material and/or 2 to 8 parts by weight of a desulfurization aid, particularly fluorspar, per 100 parts by weight of the quicklime and diamide lime combined~
DETAIL~D D~SCRIP~IO~ 0~ ~HE INVENTION
~ he "guicklime", as used in the present appli-cation, denotes lime containing calcium oxide in an amount of at least 60% by weight, preferably at least 70% by wei~ht, more preferably at least 80% by weight, most preferably at least 90% by weigh-tO
Quicklime is generally obtained by calcining lime materials containing calcium carbonate as a main component, such as limestone, calcite, marble and shells o~ shellfish in such a thermal decomposition device as a vertical kiln fired by heavy oil~ gases or their mixtures, or a rotary kiln, and is supplied in suitable degrees of purity and suitable extents of calcining depending upon the end uses~ For industrial use, there are, for example, quicklime ~or steel-making, quicklime for chemical industry (production of calcium carbide, bleaching age~ts and paper pulp), guicklime for agriculture, and guicklime for i7~

construction workO Usually, quicklime is marketed as special grade (CaO content 90% by weight or more), first grade (CaO content 80% or more), second grade (CaO co~tent 7~/o by weight or more), and third grade (CaO content 6~/o by weight or more). Quicklime of any of these grades can be used in the desulfurizer composition of this inventionO
However, the quick lime co~taining calcium oxide i~ an amount of at least 60% by weight, preferably at least 7~/0 by wei~lt, more preferably ,~t least 80~/o by weight, most preferably at least 9~/0 by weiæ~t can be u~ed in this inven-tionO
~ he te~m "diamide lime", as used in this irl-ventionl denotes a mixture of fine calcium carbonate and carbon precipitated from an aqueous solution or aqueous suspension by a chemical reactionO A typical example of the "diamide l~me" is a by-product filtra-tion residue in the production of dicyandiamideD In this process, an aqueous suspension of calcium cyanamide is reacted with carbon dioxide gas and cyanamide is extracted~ The filtration residue obtained generally contains 70 to 90%
by weight of calcium carbonate, 5 to l ~/o by weight of carbon and impurities such as iron oxide, aluminum oxide, silicon oxide a~d magnesium oxide~ In the production of thiourea from calcium cyanamide, a similar by-product is obtai~ed. ~hus, genexally, filtration residues obtained in the extractio~ of cyanamide from calcium cyanamide have much the same compositionO
The quicklime and diamide lime and a carbonaceous .

:

g ~ S
~ 9 _ material to be described herei~below preferably have a particle size of mainly not more than 60 microns. In the present application, the expression "mainly not more than 60 microns~' means that the proportion of particles having a particle diameter of not more than 60 microns is at least 80% by weight, preferably at least 9~/0 by weight, and in particular, the proportion of particles having a particle diameter of not more than ~ microns is ~t least 8~/o by weight,preferably at least 90% by weightO I~ the particle diameter is mainly above 60 ~icrons, the particles are too coarse to secure good gas t.ransportability, and thus, the concentration of the desulfurizing agent in the carrier gas during injection can fluctuate greatly, and the desulfurizing ability of quicklime cannot be fully utilizedO
The powdery desul~urizer composition of the in-vention comprises 30 to 9~/0 by weight of quicklime and 10 to 70% by weight of diamide lime, and preferably 50 to 90%
by weight of quicklime and 50 -to 10% by weight of diamide lime. If the amount o~ the diamide lime is less than 10%
by weight, the gas transportability of the powdery desulfurizer composition is poor, and the desulfurizing ability of quicklime cannot be fully utilizedO
When the amount of the diamide lime is at least 10% by weight7 the powdery desulfurizer composition ex-hibits good gas transportabilityO ~he transportability increases with an increase in the proportion of diacide lime added~ However, as the amount of the diamide lime ~ 10 ~
increases, the amount of the quicklime decreasesO Con-sequently, the desulfurizing ability of the powdery desulfurizer composition decreases and the amount of gases evolved increases to cause eventually splashing of the mol-ten ironG Accordingly, the amount of the dia~Dide lime should be limited to not more than 7~/0 by wei~ht. In view of the gas transportability of the desulfuxizer composi-tion and the desulfurizing per~ormance of the quicklime, the proportion of diamide lime in the compositiorl o~ the invention is preferably at least 10% by weight but no~
exceeding 5~/o by weight. ~he desulfurizer composition of the invention containing such a proportion of diamide lime shows a particularly good effec-t in injection desulfurization.
The desulfurizer composition of the invention can be injected with a carrier gas into molten iron by using known devices such as a device adapted to feed the powdery desulfurizer in specified portions down from its tank into an injection pipe line by means of a rotary valve and transport it on the carrier gas (eOgO, Japanese ~aid-Open Patent Publication No. 102515/1975), or a device adapted to fluidize the powdery desulfurizer placed in a pressure vessel and inject it by using the carrier gasO
~he desulfurizer composition of this invention is suitable ~or use in man~ injection desulfurization methods using various devices including the aforesaid devices. ~ven when a relatively large amount of the carrier gas is used as in Japanese Patent Publications 37 rj ~os. 6454/1974 and 1967/1974 in which the proportion o~
the amount of the carrier gas is about 100 N~ per kilosram of the powdery desulfurizer composition, the de~ulfurizer composition of the inv~ntion can be used by properly select~
ing the injection angles or lance declinations, -the number of injection places,the geometrical locations of injection, etc.
~ he "apparatus for dispensi~g a flowable solid material from a pressure vessel" disclosed in Japanese ~aid-Open Patent Publication ~o. 31518/1979 i8 one of especially preferred injection deveices which leads to full utilization of the effect of the powdery desulfurizer cornposition of this inventionO '~his device has gained widespread commercial acceptance because it permits in-jection into molten iron of the powdery desulfurizing agent in high concentrationsO If the amount of the carrier gas per unit amount of the powdery desulfurizer is small, : the total amount of the carrier gas required for injection can be smallu Accordingly, the degree of temperature lowering of molten iron is small, and the apparatus can be small-sizedO In injection desulfurization using this type of the device, the proportion of the carrier gas can be suitably not more than 10 NQ, preferably 2 to 10 NQl for example 5 N~, per kilogram of the powdery desulfurizer composition At such a low carrier gas propor-tion, the gas transportability of the powdery desulfurizer composi--tion is of utmost importanceO The powdery desulfuxizer composition of this inve~tion having excellent gas .

~ :~ fi~75 transportability is most effective unde.r such conditionsO
Accordingly, the powdery desulfurizer composition of the invention is suitable for use in an injection desulfurizing method particularly the one which comprises fluidizing the powdery desulfurizer composition in a pressure vessel, and injecting it into molte~ iron using a carrier gas in an amount of not more than 10 ~ per kilogram of the desulfurizer composition.
The present inventors have also found unexpected-ly that when fine quicklime is produced by calciningdiamide lime, and this quicklime is used in combination with diamide lime, the resulting composition has more improved gas transportability and further impro~ed desulfurizing abilityO
Japanese Laid-Open Patent Publications ~osO
50414~1979 and 86417/1979 cited above disclose that by calcining diamide lime under special conditions, quicklime having good desulfurizability can be obtainedO However, calcining of diamide lime -to obtain -the aforesaid quicklime does not re~uire any special calcining condi-tions althou~h no clear reason can be assigned. Quicklime obtained by calcining diamide lime until its CaO content reaches at least 6~/o by weight, preferably at least 7~/O
by weight, more preferably at least 80% by weight, most preferably at least 9~/O by weight ca~ be used with good results in i~jection desulfurization of molte~ ironO
However, fluidized calcination under ox~gen-excessive atmosphere can be used preferably to produce the quicklime for this invention, , ~:~8~i'JS

~ he quicklime obtained by calcining diamide lime may be mixed in any desired proportions with quicklimes from other more conventional lime sources. But since the quicklime obtained by calcining of diamide lime imparts better gas transport~bility and greatex desulfu-rizing ability, it is preferred to use 30 to 90% by weight of quicklime having a particle diameter of mainly not more than 60 microns obtained by calcinin~ diamide lime and 70 to 10% by weight of diamide lime havi~g a particle diameter of mainly not more than 60 microns.
In accordance with this invention~ it has also been found tha-t when not more than 20 parts by weight, preferably 3 to 15 parts by wei~ht, of a carbonaceous rnaterial is added to 100 parts by weight of a powdex~
desulfurizer composition composed of quicklime and diamide lime, the resulting mixture shows more improved gas transportability and desulfurizing ability suitable for use in desulfurization of molten ironO
Examples of the carbonaceous material are graph-ite, coal, coke, petroleum coke, and charcoal. There isno particular restriction on its kind and properties.
It is desirable however tha-t such a carbonaceous material should have a low sulfur content and a low water content so as to use it with quicklimeO Coal and coke are preferred carbonaceous materials in view of their ready availability and low cost~ ~he carbonaceous material desirably has a particle diameter of mainly not more than 60 microns as stated hereinaboveO

~ ~ s ~

If the amount of the carbonaceous rnaterial ex-ceeds 20 parts by weight per lO0 parts by weight of the powdery desulfurizer composition composed of quicklime and diamide lime, the amount of the carbonaceous material in exhaust gases from, for an example, an open ladle in the injection desulfurization process increases to cause various working environmental trouble.s such as higher exhaust gas temperature, ~lushi.ng danger, and or the increase amount oP carbon monoxideO
The powdery desulfuri.zer composition for molten iron of this invention i5 inexpensive and exhibits excel-lent desulfurizing performance in injection desulfuriza-tion with effects comparable to calcium carbideO Its desulfurizing effect can be further improved by using it in combination with various conventional de3lilfurizing agents and desulfurization aidsO ~xamples O'r` these con-ventional materials include calcium carbide, calcium cyanamide, fluoride compound such as fluorspar, or cryolite, the oxides, hydroxides, carbo~ates or other compound~ of sodium, magnesium or aluminum, calcium hydroxide, powders of synthetic resins, and compounds capable of liberating water or hydrogen in the desulfuriza-tion systemO ~luors-par and cryolite are preferred, and fluorspar is especial-ly preferredO ~he amount of fluorspar and the other conve~tional materials me~tioned above is 2 to 8 parts by weight, preferably 3 to 6 parts by weight, per lO0 parts by weight of the desulfurizer composition composed of quicklime and diamide limeO In addition to increasing 3 ~ ~1 5 the desulfurizing ability of the desulfurizer composition ~urther, fluorspar permits easy removal of the slag after desulfurization. r~he reason for this ls not entirel~
clear, but it is theorized that fluorspar prevents ad-hesion of calcium silicate to the surface of the limepowder, and decreases the ViSC05i ty of the slagO
When the amount of f:Luorspar and the o-ther conve~tional materials exceeds 8 part6 by weight, re-fractories will be heavily damaged, and if it is less than 2 parts by weight, the de~ree of improvement o~
desulfurizin~ ability and slag removablility is small.
~ luorspar which may be used in this invention contains about 80 to about 98% by weight of CaF~ a~d up to about ly/o by weight of SiO2, ~e203, MgO, etcO
r~he following ~xamples and Comparative Examples illustrate the present invention more speci~ically~

In each run, the various materials shown in ~able 1 or 2 were mixed uniforml~ in an inert atmosphere to form a powdery desulfurizer compositio~O
: r~he powdery desulfurizer composition was i~aect-ed at a rate of 80 to 150 kg~minO through a lance into a torpedoladle having a capacity of 350 r~ filled with 300 to 33o r~ of molten iron having a sulfur content of OoO32 to 000~/O by means of the injectio~ device described in Japanese Laid-Open Pate~t Publication ~oO 31518/1974 using dry nitrogen g~s as a carrier gasO
~ he results of the desulfurization are shown in r~ables 1 and 20 `,. .. .

3 ~7 ~ he amounts of quicklime ~(quicklime)lDL, (quicklime)2DL, or (quicklime)~, and diamide lime i~
~ables 1 and 2 are by weight % based on the total amount o~ these two compo~ents, and the amounts o~ the carbo-naceous material a~d ~luorspar are expressed by parts byweight per 100 parts by weight of the quicklime and diamide lime combinedO
~ he material.s used in these examples were as follows:
1) Quicklime ~ uicklime suitable for calcium carbide pro~
duction, which has a CaO content of 95%.
2) Diamide lime Diamide lime obtained as a by-product in the productio~ of dicyandiamide from calcium cyanamlde. Its chemical composition is: CaC03 85% by wei~ht, C 10% by weight, SiO2 1~8% by weight, A1203 1~% by weight~ ~e203 0.8% by weight, MgO 0.~/0 by weight, and others 00~% by weight~
3) (~uicklime)lD~
Obtained by calci~ing the diamide lime mentioned in paragraph 2) above in the fluidized state at 1000C
for 30 seconds in a~ excess o~ air using CO gas as a fuelO Its chemical compositio~ is: CaO 7Z/O by weight, Ca~03 23% by weight, C 105% by weight, SiO2 10~~6 by weight, A1203 0.9% by weight, aad others 1~2?/o by weight.

4) (Quicklime)2D~
~he diamide lime mentioned in paragraph 2) , .

~ 5 above was calcined u~der the same conditions as in 3) above except that the calcinirlg time was changed to 45 secondsO
me chemical compositi~n of the product was: CaO 90%
by weight, CaC03 201% by weight, C 00~/O by weight, SiO2 207% by weight, A1203 l.~/o by weight, ~e203 lo~/O by weight, and others 20 Z/o by weightO

5) (Quic~lime)~
~he diamide lime described i~ ~able 1, Example, Calcination ~o.4 of the specification of Japanese Laid-Open Patent Publication NoO 86L~17/1~79 was calcined in a nitrogen gas atmosphere at 950C for 60 seconds.

6) Carbon Obtained by pulverizing cor~ercially a~ailable coke. It has a carbon content of 86% by weight.

7) Fluorspar Obtained by pulverizing imported fluorspar in the same way as in the preparation of the carbo~aceous substanceO This fluorspar had the following chemical composition: CaF2 90% by weight, SiO2 8.5% by weight7 Fe20~ 100% by weight, and MgO 0~3% by weightO

8) Synthetic diamide lime Obtained by uniformly mixing 88% by weight of calcium carbonate pulverizad to a size of less than 60 microns and 12~/o by weight of coke pulverized to a size of 25 less than 60 micronsO
~ he particle size distributions (%~ of the quicklime, diamide lime, (quicklime)lDL, ~quicklime)2DL, (quicklime)~ and carbon used in these examples were as tabulated belowO

.

, 7 S

Quick- Diamide (Quick- (Quick-Size lime lime li~e)lD~ ll~e)?DL C~rbon 70 ~esh and2.0 1~0 1~5 005 1~0 larger si%es 70 1~5 loO 0~5 0 D 5 0O5 0.5 lL15 -- 2501.5 1~0 loO loO 1~5 250 - 350 205 0O5 0 0O5 ~5 350 mesh and93O0 97O0 97~0 9700 96~5 smaller sizes '~he particle size of (quicklime)~ was such as rqore than 85% passing a 145 mesh sieve~
~he terms used in ~ables 1 and 2 have the follow-ing meaningsO
(a) Unit consumption Weight(kg) of the powdery desulfurizercomposition injected into molten iron Weigh~ ~) o~ molten lron (b) Carrier gas ratio Flow rate (~/minD~ of_~he ca _l~r ~as Injecting rate ~kg~min~ of the powdery desulfurizer composition (c) Injecting pressure ~he pressure (kg~cm2) of the carrier gas to be connected to -the discharging exib point when the desul~u-rizer composition is carried on the carrier gas into molten ion and injected (corresponding to a relatively low pressure P3 con~ected to the discharge opening 4 in ~igure 2 of Japanese Laid-Open Patent Publication ~oO
31518/1979)o -- 19 ~
(d) Desul~urizing ability S~, - S2 (- ~S) ~ r = sulfur conten-t (%) of molten iro~ before desulfurization S2 = sulfur content (%) of molten iron after desulfurization (e) Desulfurizatio~ rate Sl - S
~ 2 x 100 (%) Comparative Example 8 Desulfurization was carried out under the same conditions as in Examples 1 to 9 excep-t that a powdery desulfurizer composition composed of 60% by weight of (quicklime)lD~ and 40% by weight of diamide lime and 25 parts b~ weight, per 100 parts by weight of the quicklime and diamide lime combined, of carbon was used. During the injection operation, the temperature of the exhaust gas became exceedingly high, and the operation was too danger-ous to perform. ~hus, this compositio~ cannot be used ~: for practical purposes.

~' ' ' ~ ' ' 7 ~ ~8~)75 Table 1 EY- Desulfurizer cor~position Desul~u-ample _ _ _ rizin~; con-(13x.) ~ ck- ~Quick- (Qu~ck- Diamide Carbo- ditions or lime lime)1 lime) lime naceous S content Com- DL * material of molten para- iron before tive desulfu-3~{- rization arllple ( ~ ) (CEx _ __ L
___ wto% wto % wto% wt.% weig~ %
:Ex. 1 90 10 00035 Ex. 2 60 40 0.038 Ex. 3 3o 70 00032 ~XO 4 90 10 00039 Ex. 5 60 40 00034 Ex~ 7 90 10 00040 EX. 8 60 40 20 0.036 :~x. 9 60 40 5 00037 CEX.1 100 00036 C3~X.2 95 5 0Oo33 C~X~3 20 80 00040 C13X.4 95 5 00036 ~Ex.5 95 5 0~033 CEX~61 25 __ 75 0.03B
_ . _ I :J ~ ~ ~, 7 _ _ _ _ _ _ . _ :Ex~ Gas Desulfurization results ~:~ple transportability ~ __. ___ ___ (~X~ ) e __ S content Ur~it Desulfu- Desulfu-or Carrier In~ oî molten con- rizing rizing Com- gas jecting i.ron aIter sump_ ability ratio para-ratio pres- defulsu- tion tive sure ri zation a~rXnple _ 2 (S2) ___ (CEx.)N~/ ~g kg/cm % kg~ ~ S/kg %
_ _ _ _ _ Ex. 110 3.7 0 O 016 5 O 2 0 O 0037 54 Bx,, 2 6 300 0O 017 501 0O OOL~l 55 Exo 3L~r 208 00014 5O 5 000033 56 Ex. Ll, 6 209 00016 409 000047 59 Exo 55 208 OoO10 L~o8 5 71 Exo 64 207 0 O 013 5 O 1 000041 62 3~x. 7 8 306 0.018 500 000044 55 Exo 84 204 0 O 008 5O 3 53 78 Ex. 94 2~ 6 0 O 006 506 00 0055 84 CExo 1 65 703 000 26 8 O 2 000012 28 ~Exo2 60 64 7 00025 603 000013 24 CEx.3 4 207 0.031 508 000016 23 C~3x~4 6 3O4 00024 600 000020 33 CEx.5 25 4 5 023 6.,1 Oo0016 30 CE:x.6 4 2 9 0.026 5~6 00002l _ 32 Table 2 __ ~ ~
Ex- Desulfurizer compositi.on Desulfu-c~ple _ . .. ~ . ~ ~ - - rization (Exo) (Quick- Diamide Synthe- Gar~o- Fluor- conditions or lime) lime tic ~aceous spar S content Com- 2 diamide material of molten para- DL lime iron before tive desulfu Ex- rization ~n~le ($2) (aEx _ _ __ _ wto% wto% wt~% partg by parts %
_ _ _ _ _ vei~ht ~x.lO 90 10 00037 Ex,ll 60 L~ 00033 Ex.12 60 40 5 00036 Exol3 60 40 5 00036 ~X o 1 L~ 60 L~ 5 5 0.036 C~x.7 60 ~ L~0 . _ _ 0.039 . _ ~ ~ . ._ . .
Ex- Gas Desulfurization results am-Qle transPortabilit~r _ _ (Ex.) _ - S content Unit Desulfu- Desulfu or Carrler In- of molten co~- rizing rization Co~1- gas aecting ~esulfu- tuimOp- ability ratio t-ive rization ~x- (~2) an~ple ._ _ _ _ . . _ . _ (C$xo) N~/kg kgfcm2 c/o k~ Q S/kg %
__ - . _ __ __ __ .10 6 2.9 OoOl~ 408 000048 ~2 ~oll 5 208 00009 406 000052 73 ~x~12 4 2.6 0.005 5~4 0.0057 86 Exol3 5 208 00005 5~ 3 000058 86 ~x~14 4 206 00004 501 000063 $9 C~x.7 21 403 0.024 5.50.0027 3 _ 3 ~ ~ 5 As shown in ~ables 1 and 2, the powdery de-sulfurizer compositions o~ the invention in ~xamples 1 to 14 did not cause pulsating movement at relatively low inJection pressures, and exhibited excellent gas trans-portability with a carxier gas ratio of less than 10 N~/kg, and furthermore, they scarcely caused splashing of molten iron from -the torpedo ladle~ Moreover si~ce the powdery pulverizer composition could be injec-ted at high concentrations, the inherent desulfuri~ing ability of quicklime was fully utilized. The ratio of desulfuri-zation reacted about 55% to about 8~/1 and the desulfurized molten iron has a sulfur content of less than 0.01%.
These results are difficult to obtain by conventional quicklime-type powdery desulfurizer compositions.
r~he powdery desulfurizer composition of ~xample 2 is best in gas transportability and desulfurizing ability among those obtained in ~xamples 1 to 3~ The powdery desulfurizer composi~ions of ~yamples 4 to 6 prepared by using ~quicklime~lDL are better than those 2G obtained in Examples 1 to 3, and the desulfurizer com position of ~xample 5 is better in desulfuxizing ability tha~ those of ~xamples 4 and 6. ~he compositio~ of Ex ample 7 prepared by using the (quicklime)~ was inferior i~ gas transportability a~d desulfurizing ability to the composition obtained in Example 4. ~he powdery desulfuriz-ing compositions obtained in ~xamples 8 and 9 which contain carbon exhibit especially good gas transportabllity and desulfuriæi~g ability.

_ ~L~ _ The desulfurizer powder of Comparative Example 1 which consists solely of (quicklime)~ has very bad gas transportability and ~aused vigorous pulsating movement and the splashing of the molten iron, and its desul~uriz-ing ability is so poor as is not feasible in practicalapplicationsO With regard to the po~dery desulfurizer compositions of Comparative Examples 2, 4 and 5 consi~t-ing of 95% by weight of quickl:ime, (quicklime)lDL or (quicklime)~ respectively and 5% by weight of diamide lime, some improvement is seen in the occurrence of pulsating movement as a result of incorporation of the diamide lime~ ~ut the amount of the diamide lime is too small, and pulsatin~ movement still occursl Moreover, their desulfurizing ability is poor~ Hence, the composi~
tiOrlS of E~amples 2, 4 and 5 are neither feasible for practical application. The powdery desulfurizer com-positions obtained in Comparative ~xamples 3 and 6 which contain a large amount of the diamide lime have excellent gas transportability. ~ut the proportion of the quicklime is small, and their desulfurizing ability is much inferior to those of the desulfurizer compositions of Examples 1 -to 90 ~urthermore, since splashing of the molten iron is vigorous, a large amount of the molten iron is lost.
The desulfuri~er compositions containing (quick-lime)2DL as in Examples 10 and 11 show better desulfuriza-tion results than the co~positio~ containing (quicklime~lDL, and the compositions of Examples 12 to 14 which further contain a carbonaceous material and/or fluorspar show ~till better desulfurization results, On the other hand, the composition of Comparative E.xample 7 contai~ing the syn-thetic diamide lime instead of diamide lime has poor gas transportability, and gives poor desulfuriz.ation results<, Desulfurization was performed by using the same desulfurizer composition as i~ Example 9 under the conditions shown in Table 30 ~he results are shown in ~able 30 ., 3 ~3 7 ;~

__ ~ a __ U~ N
a~ h ~d ' ~ bD ~ O O O
~D ~ rl r-~ O O O
h u~ N- ~O O O
o ~_ _ N .rl ~ ~ ~9 0 ~
r~J ____ _ ____ R . ~
h h q O N N

P¦ M ~ u ~a ~h C' ~ ~

r-l ~ rl a o r~ 4~ O O O
:1 ~a ~ o ~ ~ o ~ ~
~ N a ~ h ~-rl O O O
P~ h 1 )~r~ rl ~ h __.
S~D ~ ~D ~ Cl) O ~~i OJ 01 P~ ~ ~4 ~

~rl h rl ;i~
CQ ~ h a~
~ $ ~3 r l'--oh r~$ O ~

r~ ~;

It is seen from ~able 3 that the powdery desulfu~
rizing composition obtained in ~xample 9 which is used at a small carrier gas ra~io shows the best desulfurizing performance. As stated hereinabove, the powdery de-sulfurizing composition shows especially good desulfuriz~ing performance when the carrier gas ratio is not more than 10 N~ per kg of the desulfurizer composition, and this ~alue is suitable for goocl injection desulfurizatio~.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A powdery desulfurizer composition for injection desulfurization of molten iron, said composition comprising 30 to 90% by weight of quicklime and 70 to 10% by weight of diamide lime.

2. The composition of claim 1 wherein the quicklime is obtained by calcining diamide lime.

3. The composition of claim 1 which further contains not more than 20 parts by weight of a carbonaceous material per 100 parts by weight of the compo-sition of claim 1 or 2.

4. The composition of claim 1, 2 or 3 wherein the quicklime, diamide lime and carbonaceous material have particle diameters of substantially not more than 60 microns.

5. The composition of claim 1, 2 or 3 which further contains 2 to 8 parts by weight of a desulfurization aid per 100 parts by weight of the composition of claim 1, 2 or 3.

6. The composition of claim 1, 2 or 3 which further contains 2 to 8 parts by weight of fluorspar per 100 parts by weight of the composition of claim 1, 2 or 3.

7. A process for injection desulfurization of molten iron which comprises fluidizing a powdery desulfurizer composition as claimed in claim 1, 2 or 3 in a pressure vessel, and injecting said powdery desulfurizer composition into molten iron using a carrier gas in an amount of not more than 10 N? per kilogram of the powdery desulfurizer composition.