CA1104828A - Alkaline earth carbonate desulfurizing agents - Google Patents
Alkaline earth carbonate desulfurizing agentsInfo
- Publication number
- CA1104828A CA1104828A CA297,787A CA297787A CA1104828A CA 1104828 A CA1104828 A CA 1104828A CA 297787 A CA297787 A CA 297787A CA 1104828 A CA1104828 A CA 1104828A
- Authority
- CA
- Canada
- Prior art keywords
- alkaline earth
- desulfurizing
- metal
- mixture
- carbonate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/02—Dephosphorising or desulfurising
- C21C1/025—Agents used for dephosphorising or desulfurising
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Fine grain desulfurizing mixtures for iron based melts comprise alkaline earth carbons and a reducing metal. The metal combines with evolved CO2 exothermically, and the oxide formed in situ reacts with the melt to desulfurize it. Gas evolution is suppressed by the action of the metal. metal may be chosen to provide additional alkaline earth oxides for desulfurizing. The metal may also be chosen to increase the fluidity of the alag formed on the melt.
Fine grain desulfurizing mixtures for iron based melts comprise alkaline earth carbons and a reducing metal. The metal combines with evolved CO2 exothermically, and the oxide formed in situ reacts with the melt to desulfurize it. Gas evolution is suppressed by the action of the metal. metal may be chosen to provide additional alkaline earth oxides for desulfurizing. The metal may also be chosen to increase the fluidity of the alag formed on the melt.
Description
2l~
~ lis invention relates to fin~-grain desulEurizing mixtures Eor the treatment of lron and steel melts based on alkaline earth carbonates, and to the production and use of such mixtures.
Because of the decreasing quality of available ores and reducing agents such as coke and heavy fuel oil, the desulfurizing of pig iron and steel is becoming increasingly more important in the continued produc-tion of high quality iron based products of consistent quality.
The carbonates of the alkaline earth metals, either those which occur naturally or which are produced industria:lly in chemical reactions, are particularly suitable and inexpensive. However~ large quantities of iron are expelled from the treatment ladles when these compounds are employed because of the large quantities of gas generated when fine-grained carbonates are introduced into iron based melts at the temperatures of 1200 - 1700 C. This problem of uncontrolled gas generation renders the inexpensive alkaline earth carbonates, (otherwise environmentally unobjec-; tionable and available in sufficient quantities in the natural state) commercially unsatisfactory for desulfurizing such melts.
This is the more unfortunate, because as is generally known, thefreshly-formed alkaline earth oxides illustrated in Equations (1) and (2) are particularly reactive because of their small crystal size.
CaCO3~ CaO -~ CO2 ; L~ Hl = ~ 42,8 kcal/Mol (1) ~IgCO3~ MgO + C02 , ~ H2 = ~ 24,3 kcaljMol (2) A further disadvantage in using alkaline earth carbonates as desulfurizing agents for iron based melts results from the endothermic evolution of the carbon dioxide (see Equation (1) and (2), which causes noticeable cooling of the melt. Moreover, the resulting reaction products, e.g. calcium oxide, magnesium oxide or calcium sulphide cause hardening of the slag present on the surface on the melt, by increasing its melting temperature and thereby make slag removal from the treatment ladles more ., `30 difficult.
In all o~ the technical processes used today to deacidi~y alkaline :; -. - ~ ' :
. .
;:
. . : . - , . ,,- , : : ,
~ lis invention relates to fin~-grain desulEurizing mixtures Eor the treatment of lron and steel melts based on alkaline earth carbonates, and to the production and use of such mixtures.
Because of the decreasing quality of available ores and reducing agents such as coke and heavy fuel oil, the desulfurizing of pig iron and steel is becoming increasingly more important in the continued produc-tion of high quality iron based products of consistent quality.
The carbonates of the alkaline earth metals, either those which occur naturally or which are produced industria:lly in chemical reactions, are particularly suitable and inexpensive. However~ large quantities of iron are expelled from the treatment ladles when these compounds are employed because of the large quantities of gas generated when fine-grained carbonates are introduced into iron based melts at the temperatures of 1200 - 1700 C. This problem of uncontrolled gas generation renders the inexpensive alkaline earth carbonates, (otherwise environmentally unobjec-; tionable and available in sufficient quantities in the natural state) commercially unsatisfactory for desulfurizing such melts.
This is the more unfortunate, because as is generally known, thefreshly-formed alkaline earth oxides illustrated in Equations (1) and (2) are particularly reactive because of their small crystal size.
CaCO3~ CaO -~ CO2 ; L~ Hl = ~ 42,8 kcal/Mol (1) ~IgCO3~ MgO + C02 , ~ H2 = ~ 24,3 kcaljMol (2) A further disadvantage in using alkaline earth carbonates as desulfurizing agents for iron based melts results from the endothermic evolution of the carbon dioxide (see Equation (1) and (2), which causes noticeable cooling of the melt. Moreover, the resulting reaction products, e.g. calcium oxide, magnesium oxide or calcium sulphide cause hardening of the slag present on the surface on the melt, by increasing its melting temperature and thereby make slag removal from the treatment ladles more ., `30 difficult.
In all o~ the technical processes used today to deacidi~y alkaline :; -. - ~ ' :
. .
;:
. . : . - , . ,,- , : : ,
2~
earth carbonates, e.g. by lime calcining or burning, the time that tlle result-ing alkaline earth oxides remain at the required deacidification temperature is,relatively speaking, several orders of magnitude greater than it is when it is air injected into a melt. Thus, industrial:Ly, calcined lime, dolomite or magnesite, because of the recrystallization of the primary resulting oxide crystallite into larger crystals, are considerably morç inert than the same alkaline earth oxides freshly formed by deacidification during pneumatic injection of the corresponding alkaline earth carbonates into a melt, which then, when rising up through the melt can react within one to five seconds with contained sulfur.
If, instead of alkaline earth carbonates, alkaline earth oxides produced industrially from such carbonates are used, it is possible to avoid the disadvantage of uncontrolled gas generation. However, the desulfurizing effect of alkaline earth oxides used in any process familiar up to now is unsatisfactory, because even when a soft-burnt alkaline earth `; oxide is used, the oxide crystals are too large and hence too unreactive.
Only part of the alkaline earth oxide reacts with the sulfur contained in the melt.
It is an object of the invention to develop new desulfurizing ; mixtures for iron based melts proceeding from products which, technically speaking, are easily accessible and available in practically unlimited quantities,which with specific additives will ensure good desulfurizing values at high reaction speeds, with scarcely increased production costs.
Here described is a process involving the use of fine-grain desulfurizing mixtures based on alkaline earth carbonates, containing a reducing metal which causes superheating oE the high]y active alkaline earth oxide formed in situ in an iron based melt and which also suppress -gas generation problems.
; It has been found that in the presence of reducing metals and at approximately 1100 - 1300 C, alkaline earth carbonates react together exothermically. Surprisingly a large quantity of carbon is formed and .
:
~ - 2 :: :
: , , ,: . : .
hardly any gas is generatecl.
When alkaline earth carbonates are injected pneumatically into iron based melts the life of the ensuing alkaline earth oxides and carbon dioxide formed by thermal disassociation is only a few seconds, even when the injecting lance is submerged to a depth of only two to four metres.
The carbon dioxide is captured in exothermic reaction by the addition of a reducing metal as here described. The resulting gas bubbles collapse almost immediately and the alkaline earth oxide which is greatly superheated in the exothermic reaction between the carbon dioxide and the metal reacts vigorously with the sulfur contained in the melt, since no recrystallization or increase in grain size takes place in the short time taken by the oxide to rise to the surface of the melt. The formation and the collapse of the gas bubbles promotes agitation and mixing of the melt.
Examples of suitable alkaline earth carbonates are calclum carbo-nate, magnesium carbonate, dolomite and semi-calcined dolomite and diamide of lime, which can occur naturally or be produced synthetically. Diamide of lime is produced as a residue, consisting in the main of calcium carbonate and graphitic carbon during the production of cyanimide or `~ dicyanadiamide from crude calcium cyanamide. On contact with the hot iron based melt which is at a minimum of approximately 1200 C the carbonates decompose into calcium oxide and carbon dioxide. At the moment of formation, - this calcium oxide is a highly effective desulfurizing agent. The evoIu- ;
tion of large quantities of carbon dioxide consumes a great amount of heat ; ~ (compare Equations (1) and (2)),which reduces the temperature of the melt.
However, this reduction in temperature is more than compensated by the addition of a metallic reducing agent. The exothermic reaction of the reducing agent - which under the conditions in question must be greater than free carbon or its combinations with hydrogen - with the carbon dioxide evolved from the carbonate,~ has a positive effect on the . .
~ thermal balance loaded negatively by -the alkaline earth carbonate (Equations
earth carbonates, e.g. by lime calcining or burning, the time that tlle result-ing alkaline earth oxides remain at the required deacidification temperature is,relatively speaking, several orders of magnitude greater than it is when it is air injected into a melt. Thus, industrial:Ly, calcined lime, dolomite or magnesite, because of the recrystallization of the primary resulting oxide crystallite into larger crystals, are considerably morç inert than the same alkaline earth oxides freshly formed by deacidification during pneumatic injection of the corresponding alkaline earth carbonates into a melt, which then, when rising up through the melt can react within one to five seconds with contained sulfur.
If, instead of alkaline earth carbonates, alkaline earth oxides produced industrially from such carbonates are used, it is possible to avoid the disadvantage of uncontrolled gas generation. However, the desulfurizing effect of alkaline earth oxides used in any process familiar up to now is unsatisfactory, because even when a soft-burnt alkaline earth `; oxide is used, the oxide crystals are too large and hence too unreactive.
Only part of the alkaline earth oxide reacts with the sulfur contained in the melt.
It is an object of the invention to develop new desulfurizing ; mixtures for iron based melts proceeding from products which, technically speaking, are easily accessible and available in practically unlimited quantities,which with specific additives will ensure good desulfurizing values at high reaction speeds, with scarcely increased production costs.
Here described is a process involving the use of fine-grain desulfurizing mixtures based on alkaline earth carbonates, containing a reducing metal which causes superheating oE the high]y active alkaline earth oxide formed in situ in an iron based melt and which also suppress -gas generation problems.
; It has been found that in the presence of reducing metals and at approximately 1100 - 1300 C, alkaline earth carbonates react together exothermically. Surprisingly a large quantity of carbon is formed and .
:
~ - 2 :: :
: , , ,: . : .
hardly any gas is generatecl.
When alkaline earth carbonates are injected pneumatically into iron based melts the life of the ensuing alkaline earth oxides and carbon dioxide formed by thermal disassociation is only a few seconds, even when the injecting lance is submerged to a depth of only two to four metres.
The carbon dioxide is captured in exothermic reaction by the addition of a reducing metal as here described. The resulting gas bubbles collapse almost immediately and the alkaline earth oxide which is greatly superheated in the exothermic reaction between the carbon dioxide and the metal reacts vigorously with the sulfur contained in the melt, since no recrystallization or increase in grain size takes place in the short time taken by the oxide to rise to the surface of the melt. The formation and the collapse of the gas bubbles promotes agitation and mixing of the melt.
Examples of suitable alkaline earth carbonates are calclum carbo-nate, magnesium carbonate, dolomite and semi-calcined dolomite and diamide of lime, which can occur naturally or be produced synthetically. Diamide of lime is produced as a residue, consisting in the main of calcium carbonate and graphitic carbon during the production of cyanimide or `~ dicyanadiamide from crude calcium cyanamide. On contact with the hot iron based melt which is at a minimum of approximately 1200 C the carbonates decompose into calcium oxide and carbon dioxide. At the moment of formation, - this calcium oxide is a highly effective desulfurizing agent. The evoIu- ;
tion of large quantities of carbon dioxide consumes a great amount of heat ; ~ (compare Equations (1) and (2)),which reduces the temperature of the melt.
However, this reduction in temperature is more than compensated by the addition of a metallic reducing agent. The exothermic reaction of the reducing agent - which under the conditions in question must be greater than free carbon or its combinations with hydrogen - with the carbon dioxide evolved from the carbonate,~ has a positive effect on the . .
~ thermal balance loaded negatively by -the alkaline earth carbonate (Equations
(3) and (~1)).
: :
~ - 3 ~ J,~ ~
CO -~ Si- -~ SiO -~ C ~H = -123,7 kcal/Mol (3) 1,5 C02 ~ 2 ~ A1203 ~ 1,5 C ~ H = -258,9 kcal/Mol (4) The purpose of the reducing agent is thus to bind the carbon dioxide, generated by the thermal decomposition of the alkaline earth carbonate, in an exothermic chemical reaction in such a manner that only intermediate gas generation takes place and that such gas generation agitates the melt but does not result in any expulslon of metal from the ladle. The overall thermal balance is also made positive. rl~he pneumat-ically injected desulfurizing agent is thereby superheated in relation to the melt, with a certain amount of desirable gas generation to ensure sufficient mixing of the melt.
Reducing agents which fulfill these conditions are, for example, silicon, aluminum, alloys of silicon and aluminum, mangagese silicide, ferrosilicon with a silicon content of 15 - 98%, as well as mixtures of ; the foregoing substances, and powdered metal containing wastes from comminution processes, aluminum grindings, etc.
The proportion of such reducing agents in the desulfurizing mixture can amount to 90%-wt. A content of 5 to 85%-wt is preferred~
A further purpose of the reducing agent, if it is oxidized by carbon monoxide and/or carbon dioxide is to form additional alkaline earth ; oxide that then has a similar desulfurizing effect.
The following reaction Equations are given as examples:
CO ~ Ca~ CaO ~ C ~ H = -125 kcal/Mol (5) C2 ~ 2 Mg---?2 MgO ~ C A H = -193 kcal/Mol (6) As examples, the following are reducing agents which meet both conditions: calcium silicide, barium calcium silicide, magnesium ferro-silicon, calcium, magnesium, strontium, barium, alIoys of calcium, .
~ magnesium, strontium and barium, magnesium calcium silicide, ferrocalcium , :: :
sillcide, aluminum calclum silicide. Mixtures of these and other substances, particularly with lron, can be used. Up to 90%-wt, preferably 10 to 25%-wt should be in the desulfurizing mixture, for effective results.
: :
~ - 3 ~ J,~ ~
CO -~ Si- -~ SiO -~ C ~H = -123,7 kcal/Mol (3) 1,5 C02 ~ 2 ~ A1203 ~ 1,5 C ~ H = -258,9 kcal/Mol (4) The purpose of the reducing agent is thus to bind the carbon dioxide, generated by the thermal decomposition of the alkaline earth carbonate, in an exothermic chemical reaction in such a manner that only intermediate gas generation takes place and that such gas generation agitates the melt but does not result in any expulslon of metal from the ladle. The overall thermal balance is also made positive. rl~he pneumat-ically injected desulfurizing agent is thereby superheated in relation to the melt, with a certain amount of desirable gas generation to ensure sufficient mixing of the melt.
Reducing agents which fulfill these conditions are, for example, silicon, aluminum, alloys of silicon and aluminum, mangagese silicide, ferrosilicon with a silicon content of 15 - 98%, as well as mixtures of ; the foregoing substances, and powdered metal containing wastes from comminution processes, aluminum grindings, etc.
The proportion of such reducing agents in the desulfurizing mixture can amount to 90%-wt. A content of 5 to 85%-wt is preferred~
A further purpose of the reducing agent, if it is oxidized by carbon monoxide and/or carbon dioxide is to form additional alkaline earth ; oxide that then has a similar desulfurizing effect.
The following reaction Equations are given as examples:
CO ~ Ca~ CaO ~ C ~ H = -125 kcal/Mol (5) C2 ~ 2 Mg---?2 MgO ~ C A H = -193 kcal/Mol (6) As examples, the following are reducing agents which meet both conditions: calcium silicide, barium calcium silicide, magnesium ferro-silicon, calcium, magnesium, strontium, barium, alIoys of calcium, .
~ magnesium, strontium and barium, magnesium calcium silicide, ferrocalcium , :: :
sillcide, aluminum calclum silicide. Mixtures of these and other substances, particularly with lron, can be used. Up to 90%-wt, preferably 10 to 25%-wt should be in the desulfurizing mixture, for effective results.
- 4 After ox:idation by the carbon dioxide or carbon monoxide, preEerably the reducing agent should contribute to a reduction of the melting point of the slag from the desulfurizing reaction without increasing any erosion of the lining oE the processing vessel by added fluxes such as, for example, fluorspar or colemani~e. Thus, these compounds should be those that are present in the slag before desulfurization, e.g. in the case of pig iron, compounds such as silicon dioxide, aluminum oxide or silicates containing these or other oxides. Reducing agents which satisfy this requirement are, for example, calcium silicide, magnesium ferrosilicon, silicon, ; 10 aluminum, alloys of silicon and aluminum, manganese si]icide, manganese calcium silicide, magnesium ferrosilicon, aluminum calcium silicide, as well as mixtures of the foregoing substances and others. The composition of the reducing agent should be selected according to the type of slag on the melt prior to the desulfurizing treatment, in such a way that the slag does not harden during the treatment.
The quantity of reducing agent of the foregoing type in the desulfurizing mixture can amount to 90%-wt. It is preferable that a proportion of approximately 10 - 80%-wt be used.
All the reducing agents cited herein can be industrial grade products and contain the usual impurities associated with their manufacture.
Thus, no special requirements for purity are imposed. Iron, in particular, may be present as an impurity.
The metallic reducing agents described herein thus completely fulfill other purposes than the reduction agents in desulfurizing agents described in the prior art. Because of the liberation of hydrogen, carbon dioxide, carbon monoxide or another gas which has a reducing effect, these prior art agents merely create an atmosphere which protects the actual desulfurizing agent, e.g., calcium carbide, against oxidation.
As described herein, however, the added metallic reducing agents bind the carbon dioxide liberated durlng the decomposition of the alkaline earth carbonates in an exothermic reaction, supply additional active alkali~e .
X~2~3 earth oxide in situ, and reduce the melting point of the slag. The active superheated calcium oxide reacts in the familiar way wlth the sulfur dissolved in the melt, for example, in the case of iron according to the following Equation:
CaO ~ S (dissolved) -~ C (disso:Lved) ~CaS -~CO (7) The calcium sulfide that forms accord:Lng to Equation (7) i8 absorbed by the slag floating on the melt.
The melting points of the oxide or oxide mixtures resulting from the desulfurizing mixtures can be varied by using various metals in the alkaline earth carbonate and in the metallic reducing agent. This also makes it possible to vary the melting point and consistency of the slag floating on the melt. In addition, the desulfurizing mixtures can also contain a specific proportion of fluxes such as inorganic fluorides or borates.
In order to further increase the exothermy of the desulfurizing mixture added to thè melt and thereby increase the superheating of the desulfurizing alkaline earth oxide, chosen quantities of known thermite mixtures, containing fine-grained iron oxide and aluminum powder, can also be included.
When mixtures which consist for the most part of calcium carbonate and ferrosilicon are used, i~ can be expedient to add a few percentage ; parts by weight of a calcium magnesium or calcium silicon alloy.
Such desulfurizing agents, as here described, can be manufactured by simply mixlng the individual substances together in the appropriate proportions. However, it is preferred, after strong drying of the alkaline earth carbonate, that the components be ground together as the .~
~ resultant lumps with one or more lump size reducing agents and reduced to -` a grain size of 3 mm, preferably less than 0.3 mm. The grain size of the alkaline earth~carbonate can be coarser than that of the reducing agent, which should~be of the finest possible grain size. This fine-gralned mixture of alkaline earth carbonate snd reduc mg metal can be delivered .~ .
:~:; ' ~ . ~ : .
pneumatically and is injected into iron based melts in the blast furnace crucible in open ladles, torpedo ladIes, or mixers. It is particularly advantageous for the reaction between the released carbon dioxide and the reducing metal, for the desulfurizing mixtures to be injected through an injection lance placed as deeply as possible in the melt. The ferrostatic pressure or the applied over-pressure oE the gas atmosphere is advantageous in accelerating the reaction between the carbon dioxide and the metal.
Should it be expedient to do so, instead of producing a mixture of alkaline earth carbonate and reducing metal, the individual components can be 10 stored separately, measured separately, delivered pneumatically and then combined into a mixture shortly before entering, or when actually in, the lance.
More particularly in accordance with one aspect of the invention there is provided a fine grain cesulfurizing mixture for iron based melts, comprising an alkaline earth metal carbonate and from 10 to 90% by weight of a reducing metal for superheating of highly active alkaline earth metal oxide formed in situ from said carbonate in the melt and for suppressing attendant gas generation.
The alkaline earth metal carbonate may be selected from calcium carbonate, magnesite, dolomite and diamide of lime with the reducing metal being selected from calciumJsilicon~aluminum, magnesium and mixtures or alloys of these.
In accordance with a second aspect of the invention there is provided the process of desulfurizing an iron based melt comprising the step of injectinga mixture of an alkaline earth metal carbonate and from 10 to 90% by weight of a reducing metal through a lance pneumatically into said melt, highly active alkaline earth metal oxide being formed in situ from said carbonate, said metal effecting superheating and suppressing attendant gas generation. The steps may be included of separately measuring chosen quantities of the alkaline earth metal carbonate ancl the metal reducing agent, individually delivering these .
- ~
.
.- -, . : . - - . ~ ~
2~3 quantities pneumatically to the lance, and combining the qu~ntities to form the mixture at the lance.
The following examples illustrate embodiments of the invention in greater detail without in any way being restrictive to the specific compositions of the mixtures, their manufacture or use.
EXAMPLE N0. 1 Desulfurization of pig iron, using a mixture consisting of magnesium powder and calcium carbonate.
The desulfurizing mixture was manufactured in a tube mill by simultaneously grinding limestone previously, reduced to 0 - 5 mm, with magnesium powder with a grain size of less than 1 mm, using nitrogen as a protective atmosphere.
'L'wo hundred and three tons of pig iron were treated in a 230-ton torpedo ladle, using a mixture of 40%-wt magnesium powder and 60æ-wt ground limestone; the mixture was pneumatically injected at 1.85 m depth through a dip lance, using argon as the carrier gas.
The iron melt was at a temperature of 1310 C. The delivery rate throttled down until no significant flaming caused by the burning magnesium could be observed on the surface. This occurred at 17 kg/min.
The pig iron melt had an initial sulfur content of SA = 0.042%.
After treatment lasting ll mlDuteS, 198 kg of desulfurizing agent had been , : ~ ~
- 7a -: :
~, I ,:
- ' f~
pneumatically injected. This corresponds to 0.98 kg/t pig iron. AEter treatment the sulfur content was S~ = 0.005%.
This amounts to a total conversion factor of 46% of the calcium oxide (formed from the calcium carbonate) to calcium sulfide, the magnesium oxide (freshly formed during the reaction) to magnesium sulfide and the excess magnesium to magnesium sulfide.
EX~PLE N0. 2 Desulfurization of a steel melt us:ing a mixture of calcium carbonate, calcium silicide and aluminum.
The steel at a temperature of 1620 C contained 0,07%-wt carbon 0.13%-wt silicon 0.35%-wt manganese with a sulfur content 0.024 - 0.033%-wt, to be reduced to an average 0.005%-wt by desulforization treatment.
In order to reduce the oxidizing effect on the steel bath a desulfurizing mixture with a deficiency of calcium carbonate was selected.
The small amount of aluminum supplement content was to assure the desired aluminum content of the steel and bring aluminum oxide into the slag by partial reaction with the calcium carbonate.
~ A desulfurizing mixture consisting of ; 37%-wt calcium carbonate 60%-wt calcium silicide 30%-wt aluminum in combination with a low-oxide slag cover containing fluorspar was injected pneumatically into the steel melt in a 70-ton ladle. Six to ten litres of argon per kilogram of desulfurizing mixture was used as the carrier gas. The following table shows the results of the individual treatments.
:
; ~ , ~ ~ - 8 : ' :
. .
~ ~ -- ~
Quantity of Treatmen~ Initial Final Change Mixture No. S~ SE ~S kg/t c~
. _ . - -'-'I
1 0.031 0.005 0.026 2.~ 0.55 2 0.027 0.003 0.02~ 2.4 0.60 3 0.030 0.002 0.028 2.7 0.58 4 0.019 0.003 0.016 2.1 0.78 0.013 0.002 0.011 2.0 1.09 6 0.016 0.002 0.014 2.1 0.9 7 0.033 0.008 0.025 2.2 0.84 0.032 0.0l1 0.0ZI 1.8 0.86 ~ is a coefficient representing the specific consumption oE desulfurizing mixture in kg per ton oE iron and per 0.01% reduction of S content.
Ihe consumption of an average oE 2.2 kg desulfurizing mixture per ton of steel indicates 50 - 60% better utilization of the desulfur:izing mixture in comparison with those mixtures usually employed.
Desulfurization of pig iron using a mixture consisting of powdered calcium silicide and calcium carbonate. A mixture of 28.6% industrial grade calcium silicide and 71.4% calcium carbonate was made. The industrial grade calcium silicide contained 30.1% calcium and 60.3% silicon.
The calcium carbonate was a precipitated product produced synthetically.
Ihe mixture was made in a 3-chamber tube mill. The grain size of the mixture of calcium carbonate and industrial grade calcium silicide leaving .
the mill was 98% less than 0.1 mm.
One hundred and ninety-six tons of pig iron in a torpedo ladle was treated with this mixture. Air was used as the injection gas.
The ch rge was 12 Nl air/kg mixture. 325 kg of the mixture was injected pneumatically iD 9.5 min.
Before treatment, the sulfur content was 0.047%, and after treatment it was 0.013%. Thus, 0.034% sulfur was removed; this corresponds . ~
to 72% desulfurization. The yield of the reaction of the desulfurizing agent to the calcium sulfide, related to the total weight of calcium, was ` 30 59.8%. The consumption of desulfurizing agen-t amounted to 0.5 kg/t pig iron and 0.01~ of sulfur removed.
g :
, ~ - ~
The quantity of reducing agent of the foregoing type in the desulfurizing mixture can amount to 90%-wt. It is preferable that a proportion of approximately 10 - 80%-wt be used.
All the reducing agents cited herein can be industrial grade products and contain the usual impurities associated with their manufacture.
Thus, no special requirements for purity are imposed. Iron, in particular, may be present as an impurity.
The metallic reducing agents described herein thus completely fulfill other purposes than the reduction agents in desulfurizing agents described in the prior art. Because of the liberation of hydrogen, carbon dioxide, carbon monoxide or another gas which has a reducing effect, these prior art agents merely create an atmosphere which protects the actual desulfurizing agent, e.g., calcium carbide, against oxidation.
As described herein, however, the added metallic reducing agents bind the carbon dioxide liberated durlng the decomposition of the alkaline earth carbonates in an exothermic reaction, supply additional active alkali~e .
X~2~3 earth oxide in situ, and reduce the melting point of the slag. The active superheated calcium oxide reacts in the familiar way wlth the sulfur dissolved in the melt, for example, in the case of iron according to the following Equation:
CaO ~ S (dissolved) -~ C (disso:Lved) ~CaS -~CO (7) The calcium sulfide that forms accord:Lng to Equation (7) i8 absorbed by the slag floating on the melt.
The melting points of the oxide or oxide mixtures resulting from the desulfurizing mixtures can be varied by using various metals in the alkaline earth carbonate and in the metallic reducing agent. This also makes it possible to vary the melting point and consistency of the slag floating on the melt. In addition, the desulfurizing mixtures can also contain a specific proportion of fluxes such as inorganic fluorides or borates.
In order to further increase the exothermy of the desulfurizing mixture added to thè melt and thereby increase the superheating of the desulfurizing alkaline earth oxide, chosen quantities of known thermite mixtures, containing fine-grained iron oxide and aluminum powder, can also be included.
When mixtures which consist for the most part of calcium carbonate and ferrosilicon are used, i~ can be expedient to add a few percentage ; parts by weight of a calcium magnesium or calcium silicon alloy.
Such desulfurizing agents, as here described, can be manufactured by simply mixlng the individual substances together in the appropriate proportions. However, it is preferred, after strong drying of the alkaline earth carbonate, that the components be ground together as the .~
~ resultant lumps with one or more lump size reducing agents and reduced to -` a grain size of 3 mm, preferably less than 0.3 mm. The grain size of the alkaline earth~carbonate can be coarser than that of the reducing agent, which should~be of the finest possible grain size. This fine-gralned mixture of alkaline earth carbonate snd reduc mg metal can be delivered .~ .
:~:; ' ~ . ~ : .
pneumatically and is injected into iron based melts in the blast furnace crucible in open ladles, torpedo ladIes, or mixers. It is particularly advantageous for the reaction between the released carbon dioxide and the reducing metal, for the desulfurizing mixtures to be injected through an injection lance placed as deeply as possible in the melt. The ferrostatic pressure or the applied over-pressure oE the gas atmosphere is advantageous in accelerating the reaction between the carbon dioxide and the metal.
Should it be expedient to do so, instead of producing a mixture of alkaline earth carbonate and reducing metal, the individual components can be 10 stored separately, measured separately, delivered pneumatically and then combined into a mixture shortly before entering, or when actually in, the lance.
More particularly in accordance with one aspect of the invention there is provided a fine grain cesulfurizing mixture for iron based melts, comprising an alkaline earth metal carbonate and from 10 to 90% by weight of a reducing metal for superheating of highly active alkaline earth metal oxide formed in situ from said carbonate in the melt and for suppressing attendant gas generation.
The alkaline earth metal carbonate may be selected from calcium carbonate, magnesite, dolomite and diamide of lime with the reducing metal being selected from calciumJsilicon~aluminum, magnesium and mixtures or alloys of these.
In accordance with a second aspect of the invention there is provided the process of desulfurizing an iron based melt comprising the step of injectinga mixture of an alkaline earth metal carbonate and from 10 to 90% by weight of a reducing metal through a lance pneumatically into said melt, highly active alkaline earth metal oxide being formed in situ from said carbonate, said metal effecting superheating and suppressing attendant gas generation. The steps may be included of separately measuring chosen quantities of the alkaline earth metal carbonate ancl the metal reducing agent, individually delivering these .
- ~
.
.- -, . : . - - . ~ ~
2~3 quantities pneumatically to the lance, and combining the qu~ntities to form the mixture at the lance.
The following examples illustrate embodiments of the invention in greater detail without in any way being restrictive to the specific compositions of the mixtures, their manufacture or use.
EXAMPLE N0. 1 Desulfurization of pig iron, using a mixture consisting of magnesium powder and calcium carbonate.
The desulfurizing mixture was manufactured in a tube mill by simultaneously grinding limestone previously, reduced to 0 - 5 mm, with magnesium powder with a grain size of less than 1 mm, using nitrogen as a protective atmosphere.
'L'wo hundred and three tons of pig iron were treated in a 230-ton torpedo ladle, using a mixture of 40%-wt magnesium powder and 60æ-wt ground limestone; the mixture was pneumatically injected at 1.85 m depth through a dip lance, using argon as the carrier gas.
The iron melt was at a temperature of 1310 C. The delivery rate throttled down until no significant flaming caused by the burning magnesium could be observed on the surface. This occurred at 17 kg/min.
The pig iron melt had an initial sulfur content of SA = 0.042%.
After treatment lasting ll mlDuteS, 198 kg of desulfurizing agent had been , : ~ ~
- 7a -: :
~, I ,:
- ' f~
pneumatically injected. This corresponds to 0.98 kg/t pig iron. AEter treatment the sulfur content was S~ = 0.005%.
This amounts to a total conversion factor of 46% of the calcium oxide (formed from the calcium carbonate) to calcium sulfide, the magnesium oxide (freshly formed during the reaction) to magnesium sulfide and the excess magnesium to magnesium sulfide.
EX~PLE N0. 2 Desulfurization of a steel melt us:ing a mixture of calcium carbonate, calcium silicide and aluminum.
The steel at a temperature of 1620 C contained 0,07%-wt carbon 0.13%-wt silicon 0.35%-wt manganese with a sulfur content 0.024 - 0.033%-wt, to be reduced to an average 0.005%-wt by desulforization treatment.
In order to reduce the oxidizing effect on the steel bath a desulfurizing mixture with a deficiency of calcium carbonate was selected.
The small amount of aluminum supplement content was to assure the desired aluminum content of the steel and bring aluminum oxide into the slag by partial reaction with the calcium carbonate.
~ A desulfurizing mixture consisting of ; 37%-wt calcium carbonate 60%-wt calcium silicide 30%-wt aluminum in combination with a low-oxide slag cover containing fluorspar was injected pneumatically into the steel melt in a 70-ton ladle. Six to ten litres of argon per kilogram of desulfurizing mixture was used as the carrier gas. The following table shows the results of the individual treatments.
:
; ~ , ~ ~ - 8 : ' :
. .
~ ~ -- ~
Quantity of Treatmen~ Initial Final Change Mixture No. S~ SE ~S kg/t c~
. _ . - -'-'I
1 0.031 0.005 0.026 2.~ 0.55 2 0.027 0.003 0.02~ 2.4 0.60 3 0.030 0.002 0.028 2.7 0.58 4 0.019 0.003 0.016 2.1 0.78 0.013 0.002 0.011 2.0 1.09 6 0.016 0.002 0.014 2.1 0.9 7 0.033 0.008 0.025 2.2 0.84 0.032 0.0l1 0.0ZI 1.8 0.86 ~ is a coefficient representing the specific consumption oE desulfurizing mixture in kg per ton oE iron and per 0.01% reduction of S content.
Ihe consumption of an average oE 2.2 kg desulfurizing mixture per ton of steel indicates 50 - 60% better utilization of the desulfur:izing mixture in comparison with those mixtures usually employed.
Desulfurization of pig iron using a mixture consisting of powdered calcium silicide and calcium carbonate. A mixture of 28.6% industrial grade calcium silicide and 71.4% calcium carbonate was made. The industrial grade calcium silicide contained 30.1% calcium and 60.3% silicon.
The calcium carbonate was a precipitated product produced synthetically.
Ihe mixture was made in a 3-chamber tube mill. The grain size of the mixture of calcium carbonate and industrial grade calcium silicide leaving .
the mill was 98% less than 0.1 mm.
One hundred and ninety-six tons of pig iron in a torpedo ladle was treated with this mixture. Air was used as the injection gas.
The ch rge was 12 Nl air/kg mixture. 325 kg of the mixture was injected pneumatically iD 9.5 min.
Before treatment, the sulfur content was 0.047%, and after treatment it was 0.013%. Thus, 0.034% sulfur was removed; this corresponds . ~
to 72% desulfurization. The yield of the reaction of the desulfurizing agent to the calcium sulfide, related to the total weight of calcium, was ` 30 59.8%. The consumption of desulfurizing agen-t amounted to 0.5 kg/t pig iron and 0.01~ of sulfur removed.
g :
, ~ - ~
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A fine grain desulfurizing mixture for iron based melts, comprising an alkaline earth metal carbonate and from 10 to 90% by weight of a reducing metal for superheating of highly active alkaline earth metal oxide formed in situ from said carbonate in the melt and for suppressing attendant gas generation.
2. A desulfurizing mixture as defined in claim 1, characterized in that the metal is chosen for effecting a reduction of the melting point of slag on said melt after oxidation of said metal.
3. A desulfurizing mixture as defined in claim 1, the alkaline earth metal carbonate being selected from calcium carbonate, magnesite, dolomite and diamide of lime.
4. A desulfurizing mixture as defined in claim 1, the reducing metal being selected from calcium, silicon, aluminum, magnesium, mixtures or alloys of these, and containing iron, manganese or chromium as optional impurities.
5. A desulfurizing mixture as defined in claim 1, the reducing metal being selected from alloys of silicon, namely, silicocalcium, silicocalcium magnesium, ferrosilicon, silicomanganese, magnesium ferrosilicon, aluminum silicocalcium.
6. A desulfurizing mixture as defined in claim 1, consisting of 20 - 80%-wt alkaline earth metal carbonate and corresponding 80 - 20%-wt reducing metal, balance impurities.
7. A desulfurizing mixture as defined in claim 1, consisting of 30 - 70%-wt calcium carbonate and corresponding 70 - 30%-wt silicon, balance impurities.
8. A desulfurizing mixture as defined in claim 1, consisting of 30 - 70%-wt alkaline earth metal carbonate and corresponding 70 - 30%-wt silicon alloy, balance impurities.
9. A desulfurizing mixture as defined in claim 1, consisting of 35 - 70%-wt diamide of lime as alkaline earth metal carbonate and corresponding 65 - 30%-wt magnesium ferrosilicon as the reducing metal, balance impunities.
10. The process of desulfurizing an iron based melt comprising the step of injecting a mixture of an alkaline earth metal carbonate and from 10 to 90% by weight of a reducing metal through a lance pneumatically into said melt, highly active alkaline earth metal oxide being formed in situ from said carbonate, said metal effecting superheating and suppressing attendant gas generation.
11. The process as defined in claim 10, comprising the steps of, separately measuring chosen quantities of said alkaline earth metal carbonate and said metal reducing agent, individually delivering said quantities pneumatically to said lance, and combining said quantities into said mixture at said lance.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19772708424 DE2708424A1 (en) | 1977-02-26 | 1977-02-26 | Desulphurisation agent for iron melts - consists of alkaline earth carbonate(s) contg. a metal or alloy |
| DEP2708424.8 | 1977-02-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104828A true CA1104828A (en) | 1981-07-14 |
Family
ID=6002249
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA297,787A Expired CA1104828A (en) | 1977-02-26 | 1978-02-27 | Alkaline earth carbonate desulfurizing agents |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS53131216A (en) |
| CA (1) | CA1104828A (en) |
| DE (1) | DE2708424A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2432550A1 (en) * | 1978-08-04 | 1980-02-29 | Sueddeutsche Kalkstickstoff | PROCESS FOR THE MANUFACTURE OF AN EASILY FLOWABLE PULVERULATED DESULFURIZATION MIXTURE |
| JPS5953611A (en) * | 1982-09-22 | 1984-03-28 | Kawasaki Steel Corp | Desulfurizing method of molten iron |
| US4462823A (en) * | 1982-12-11 | 1984-07-31 | Foseco International Limited | Treatment agents for molten steel |
| DE3831831C1 (en) * | 1988-09-20 | 1989-11-02 | Skw Trostberg Ag, 8223 Trostberg, De | |
| DE102008031294A1 (en) * | 2008-07-02 | 2010-01-07 | Alzchem Trostberg Gmbh | Producing calcium carbonate pellets useful for producing quicklime products comprises homogenizing a mixture of calcium carbonate and carbon and granulating or pelletizing the mixture with a binder |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS51110413A (en) * | 1975-03-25 | 1976-09-30 | Sumitomo Metal Ind |
-
1977
- 1977-02-26 DE DE19772708424 patent/DE2708424A1/en active Granted
-
1978
- 1978-02-27 CA CA297,787A patent/CA1104828A/en not_active Expired
- 1978-02-27 JP JP2196378A patent/JPS53131216A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS53131216A (en) | 1978-11-15 |
| DE2708424A1 (en) | 1978-08-31 |
| DE2708424C2 (en) | 1987-03-19 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR100694012B1 (en) | A slag conditioner composition, process for manufacture and method of use in steel production | |
| AU579275B2 (en) | Magnesium calcium oxide composite | |
| US4209325A (en) | Desulphuration of metals | |
| CA1104829A (en) | Treatment of iron based melts with agents containing alkaline earths by gas injection | |
| JP3557910B2 (en) | Hot metal dephosphorization method and low sulfur and low phosphorus steel smelting method | |
| JPS5942725B2 (en) | Composition for desulfurization and nodularization | |
| US4014684A (en) | Manufacture of steel | |
| CA1104828A (en) | Alkaline earth carbonate desulfurizing agents | |
| US4154606A (en) | Composition and method for the desulfurization of molten iron | |
| US4154605A (en) | Desulfurization of iron melts with fine particulate mixtures containing alkaline earth metal carbonates | |
| JPS63195209A (en) | Steel making method | |
| US3897244A (en) | Method for refining iron-base metal | |
| JPH0733534B2 (en) | Method for producing desulfurization mixture | |
| JPS6315326B2 (en) | ||
| US3376130A (en) | Process for dephosphorization of pig iron particularly pig iron rich in phosphorus | |
| US3579325A (en) | Steel-making process employing an auxiliary composition | |
| US4988387A (en) | Agent and process for desulfurizing molten metals | |
| US3666445A (en) | Auxiliary composition for steel-making furnaces | |
| JPS58167711A (en) | Refining agent for steel melt | |
| JP3769875B2 (en) | Desulfurization method and desulfurization agent for iron-based molten alloy | |
| US4786322A (en) | Magnesium and calcium composite | |
| JPS6393813A (en) | Steel making method | |
| JP2757707B2 (en) | Hot metal dephosphorization slag treatment method | |
| CA1239797A (en) | Method for steel manufacture | |
| JPH1036148A (en) | Treatment of molten iron dephosphorized slag and slag |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |