Do we remove Sulphur from hot metal in Blast Furnace in industry? What we do to control sulphur in final products in industry?
AakashSinghCopper
Do we remove Sulphur from hot metal in Blast Furnace in industry? What we do to control sulphur in final products in industry?
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To start with this answer ,I would like to address what as the conditions required for desulphurisation,.they are; Reducing atmosphere High T High activity O2- in slag Low [wt% O] in metal. Now since we know the conditions let's answer nyour first que. Yes, most of the deoxidation is done in Blast fRead more
To start with this answer ,I would like to address what as the conditions required for desulphurisation,.they are;
Now since we know the conditions let’s answer nyour first que.
Yes, most of the deoxidation is done in Blast furnace. A very basic reason for this is a blast furnace is operated in reducing conditions. So suitable for desulphurisation.
S in B.F. comes from coke(CaS or FeS) and burden; this are either reduced in raceways or hearth as SiS usually.
However there are process in B.F. Bosh and belly which cause some SiS to break and cause disslove S in hot metal. ( SiS(g) = [Si] + [S] ).
So the conclusion is most of S is reduced in B.F. but many dissolve back and we might have more than desired level of S in hot metal.
Now several industries products require to still lower the S value whereas there are some who don’t consider S value and take the product as treated after B.F.B.F.
But for better property we require further desulphurisation. This can be done in many ways.
1) During Primary steelmaking. In BOF or EAF ; we know that here oxidising atmosphere is maintained. So several practices like Flush slag method ( where we flush oxidising slag and add reducing slag for desulphurisation) is used.
2) In modern steelmaking, industries usually does more separate process like desulphurisation in Laddles as laddle Treatment.Â
So we can conclude that most of desulphurisation in final product is done in
1) Blast furnace
2) primary steelmaking like EAF
3) Laddles.
However there may be other industries specific methods but as per my knowledge this is how it’s done.
Feedback is welcomed.
See lessYes sulphur removal is must otherwise presence of sulphur causes hotshortedness in the final products. The properties negatively affected by sulfur: Ductility; Impact toughness; corrosion resistance; Weldability. to top Desulfurization of steel by slags The most popular method of desulfurization isRead more
Yes sulphur removal is must otherwise presence of sulphur causes hotshortedness in the final products.
The properties negatively affected by sulfur:
Ductility;
Impact toughness;
corrosion resistance;
Weldability.
to top
Desulfurization of steel by slags
The most popular method of desulfurization is removal of sulfur from molten steel to the basic reducing slag. Basic slag is a slag containing mainly basic oxides: CaO, MgO, MnO, FeO.
A typical basic slag consists of 35-60% CaO + MgO, 10-25% FeO, 15-30% SiO2, 5-20% MnO.
Transition of sulfur from steel to slag may be presented by the chemical equation:
[S] + (CaO) = (CaS) + [O]
The equilibrium constant KS1 of the reaction is:
KS1 = a[O]*a(CaS)/a[S]*a(CaO)
Where:
a[O], a[S] – activities of oxygen and sulfur in the liquid steel;
a(CaS), a(CaO) – activities of CaS and CaO in the slag.
The same reaction in ionic form:
[S] + (O2-) = (S2-) + [O]
The equilibrium constant KS2 of the reaction is:
KS2 = a[O]*a(S2-)/a[S]*a(O2-)
Where:
a(S2-), a(O2-) – activities of S2- and O2- in the slag.
Capability of a slag to remove sulfur from steel is characterized by the distribution coefficient of sulfur:
LS = (S)/[S]
Where:
(S) – concentration of sulfur in slag;
[S] – concentration of sulfur in steel;
As appears from the above equations desulfurization is effective in deoxidized (low (O)) basic (high (CaO)) slags. Therefore ability of Basic Oxygen Process (BOP) to remove sulfur is low due to its highly oxidized slag.
Desulfurization may be effectively conducted in the reducing slag stage of the steel making process in Electric-arc furnace. At this stage the oxidizing slag is removed and then lime flux is added to form basic slag with high CaO content.
Deep desulfurization by slags may be achieved in ladle:
The refining (desulfurizing) slag with high content of CaO and no FeO is prepared and placed in an empty ladle.
The molten steel is poured into the ladle filled with the refining slag.
Energy of the falling steel stream causes mixing the slag with the steel, during which sulfur is removed from the steel to slag phase.
Effect of desulfurization may be enhanced by additional stirring, for which electromagnetic (induction) stirrers or argon bubbling are used.
Desulfurization of steel by injection of active agents
Injection of desulfurizing agents to a molten steel is the most effective method of sulfur removal.
Injection methods usually combine supply of a disperse desulfurizing agent (powder) with stirring by argon blowing.
Deep desulfurization by injection of active agents are achieved due to the following factors:
High chemical activity of the desulfurization agents (Ca, Mg);
High contact area between the steel and slag phases;
Stirring providing good kinetic conditions of desulfurization;
Presence of basic non-oxidized slag capable to absorb the products of the desulfurization reaction (CaS, MgS).
The following materials are used as desulfurizing agents:
Slag mixtures CaO (50-90%) + CaF2 (10-20%) + A2lO3 (0-30%);
CaSi;
CaC2;
CaC2 + Mg;
Lime (CaO) + Mg;
Ca + Al;
Ca;
Mg.
The desulfurizing agents are injected into molten steel either in form of powder transported by an argon blown to the steel through a lance or in form of a cored wire containing powder of desulfurizing agent. In the latter method stirring by argon bubbling from the porous plug mounted in the ladle bottom is used.
Chemical reactions between desulfurizing agents and sulfur dissolved in steel may be presented by the following equations:
Ca + [S] = (CaS)
Mg + [S] = (MgS)
Injection of desulfurizing agents allows to achieve ultra-low concentrations of sulfur in steel (0.0002%).
See lessIN INDUSTRIAL PRACTICE WE CAN REDUCE SULPHUR FROM HOT METAL IN BLAST FURNACE IF WE MAINTAIN THE FOLLOWING CONDITIONS:- 1. Oxygen activity in the HOT METAL should be as low as possible. 2. Carbon should be high (As it reacts with oxygen and thus reduces a[O]). 3. Silicon should be high (it reacts witRead more
IN INDUSTRIAL PRACTICE WE CAN REDUCE SULPHUR FROM HOT METAL IN BLAST FURNACE IF WE MAINTAIN THE FOLLOWING CONDITIONS:-
See less1. Oxygen activity in the HOT METAL should be as low as possible.
2. Carbon should be high (As it reacts with oxygen and thus reduces a[O]).
3. Silicon should be high (it reacts with oxygen as well and thus reduces a[O]).
4. Manganese should be high (it reacts with sulphur to form MnS).
Iron blast furnace is an ideal place for S removal. Remaining S is removed by soda ash treatment in ladle hot metal and by active mixer practice before steelmaking. MnS is more safe than FeS. [FeS]-->(FeS); (FeS) + (CaO) = (FeO) + ((CaS); (FeO) + CO = [Fe] + CO2. In this way [Fe] will come back tRead more
Iron blast furnace is an ideal place for S removal. Remaining S is removed by soda ash treatment in ladle hot metal and by active mixer practice before steelmaking. MnS is more safe than FeS.
See less[FeS]–>(FeS); (FeS) + (CaO) = (FeO) + ((CaS);
(FeO) + CO = [Fe] + CO2. In this way [Fe] will come back to bulk metal after desulphurisation in b/f. Sulphur Partition coefficient = (%S)/[%S] ie. lesser S in denominator/hot metal higher S transferred to slag phase.