methodology for analyzing microelement behavior in blast furnace smelting

Methodology for analyzing and predicting the behavior of microelements in blast furnace smelting is

developed, taking account of process features, the form of microelements present in metallurgical

materials, and the method of their introduction into a blast furnace. The procedure includes experimental,

research, and calculation sections. As a result of comparing experimental data and the results of modelling,

element distribution between pig iron, slag, and the gas phase of the blast furnace process is determined.

It is established that the increase observed recently in the microelement content in blast furnace sludge is

mainly connected with features of the behavior of the proportion of these microelements within the

composition of the organic part of coke and coal dust fuel.

Keywords: microelements, blast furnace process, blast furnace sludge, blast furnace dust.

Conducting blast furnace smelting at the contemporary level is impossible without considering the behavior of

microelements that have a considerable effect on saving resources, product quality, and the condition of the environment.

Analysis and prediction methodology has been developed for the behavior of microelements in blast furnace smelting, con-

sidering features of the process, the form of impurity elements present in metallurgical materials, and the method of their

introduction into a blast furnace.

An important procedural question is the principle of separating elements into macro- and microelements. According

to a previously proposed classification [1], macroelements are those whose content in the material in question, product, or

system, exceeds 0.1 wt.%. If the content of an element is less than 0.1%, it may be conditionally referred to the category of

microelements.

As a rule, microelements are subdivided into microimpurity elements, i.e., they affect properties and qualitative char-

acteristics of a product in a marked way, and trace microelements whose content is so insignificant that their presence neither

affects any of the known user or toxic properties of a product (see Fig. 1).

Among microimpurities alloying “stray” (vagrant) and composite elements are separated. The problem of “stray”

elements in contemporary ferrous metallurgy is particularly important. Vagrant elements, as a rule, not only have an unfa-

vorable effect on pig iron quality, but also they cannot be readily removed from it during subsequent metallurgical processing.

Therefore, they gradually accumulate in finished product in a steel-metal scrap-steel recycling process. The most important

“stray” elements are currently assumed to be copper, chromium, and nickel (designated by the special abbreviation CCN),

tin, and molybdenum.

Microelements are contained in all charge materials and blast additions (within the composition of materials of nat-

ural origin and materials subjected to technogenic conversion used in blast furnace smelting). Contemporary blast furnace

Metallurgist, Vol. 55, Nos. 9–10, January, 2012 (Russian Original Nos. 9–10, September–October, 2011)

METHODOLOGY FOR ANALYZING

MICROELEMENT BEHAVIOR IN

BLAST FURNACE SMELTING

P. I. Chernousov, O. V. Golubev,and A. L. Petelin

UDC 669.162.1

National Research Technological University – Moscow Institute of Steel and Alloys (NITU MISiS), Moscow,

Russia; e-mail: [email protected]. Translated from Metallurg, No. 9, pp. 49–55, September, 2011. Original article submitted

August 4, 2010.

0026-0894/12/0910-0651 ©2012 Springer Science+Business Media, Inc. 651

smelting occurs almost entirely in a charge of previously heat-treated materials, i.e., in essence materials of technogenic ori-

gin that have passed a mineral formation stage again. In the production of agglomerate, i.e., the main component of the iron-

ore part of a charge, essentially, finely-dispersed materials enriched with impurity microelements are extensively used dur-

ing production recycling.

A particular condition occurs for microimpurities that are within the composition of coke and bituminous coal, present

within them in two basic forms. Microelements may be found within the crystal structure, formed by carbon atoms (it is assumed

that they are within the composition of the organic part of coal or coke mass). Atoms of impurity microelements are also called

“heteroatoms” of a carbon crystal lattice. In addition, microelements may be found in particles falling into a coal seam during

formation or parts of rock adjacent to coal seams, remaining in the coal concentrate after enrichment and passing subsequently

into metallurgical coke. These microelements are assumed to be within the mineral part of coal. The behavior of microimpuri-

ties of the organic or mineral part of coke or coal in blast furnace smelting as a rule has considerable differences [1].

The blast furnace process is a complex subject of study, since the metallurgical system forming within a blast fur-

nace (BF) includes all forms of media: gas, liquid, solid, and it is specified by complex features of mass transfer processes

in a counterflow system over a wide temperature range (from 50 to 2500°C) and pressures (up to five atmospheres). Recently

the nature of the blast furnace process has changed considerably [2–4]:

1) there has been an increase in the intensity of processes in the furnace hearth (particularly in large volume fur-

naces), which led to a reduction in the contact time for pig iron and slag;

2) there has been an increase in the role of processes that occur at the surface of coke charge, including in “fine

films” of metal and oxide melts; and

3) processes in the BF oxidizing zone have acquired particular attention in view of the steady increase in the pro-

portion and variety of fuel additions used.

In the decades to come, transition to the extensive use in blast furnace smelting of complex ores, coal dust fuel, fuel

oil, and hard coals with an increased content of impurity microelements will be inevitable.

The following considerations have emerged in developing a new analysis procedure for the bahavior of microelement

impurities in blast furnace smelting. Since the relative amount of microimpurities is insignificant, their behavior mainly depends

on the method and location of entry into the reaction space of a metallurgical unit. If an element is distributed uniformly and is

in a reaction zone for quite a long time, then its equilibrium distribution is established between all phases. However, impurities

enter a BF in individual components of raw material in a compact way. For example, many rare and nonferrous metals are con-

centrated in the organic part of coke, halogens enter within the composition of iron-ore minerals and blast additions. With this

entry into a furnace impurities only enter locally into reaction with elements of the component within which they are found.

652

Fig. 1. Subdivision of chemical elements with respect to the degree of effect on product properties.

Entry into a BF of microelements is distributed between liquid products of the melt (pig iron and slag), blast-fur-

nace gas, and dust (bell dust and sludge). In addition, they are transferred into the composition of some particular formations,

forming within a furnace during operation, i.e., a skull, incrustations, deposits on loading devices, precipitates of some met-

als (for example lead, titanium, and lanthanoids) in the hearth lining and bottom, etc. Microelements may also form circula-

tion loops within the internal space of a furnace as a result of evaporation at high temperature and subsequent condensation

on the surface of solid charge materials at lower temperatures.

The procedure developed includes experimental, research, and calculation parts. The experimental part is based on

the knowledge of the balance for each test element, and the theoretical part is based on thermodynamic calculations of equi-

librium for all the complex chemical systems. As a result of comparing experimental data and the results of modelling, the

distribution of an element between pig iron, slag, and the gas phase is evaluated. We consider the main assumptions of the

methodology on the example of determining parameters for transfer of microelements into finely dispersed dust, forming

the blast furnace sludge.

In the first stage of the study on the basis of data about the chemical composition of metallurgical materials and fig-

ures for BF operation of Novolipetsk Metallurgical Combine (NLMK), Severstal Cherepovets Metallurgical Combine,

Tulachermet, and EKO-Stahl (Germany), typical balances were plotted for blast furnace smelting microelements. In order to

estimate the possibility of impurity element condensation from gas on the surface of dust particles carried from the furnace,

concentration coefficients were introduced for elements in the bell dust (KKbd) and blast furnace sludge (KKbs):

KKbd = [Ebd] / [Ec], KKbs = [Ebs] / [Ec],

where [Ec], [Ebd], [Ebs] are the contents of an element in the charge (taking account of all the components, including coke),

in bell dust and in the blast furnace sludge, %, respectively.

Calculations were made of indices KKbd and KKbs for elements of the base, macro- and microimpurity elements.

Results of calculations showed that for all groups elements KKbd is within the limits 0.5–1.5. From this it may be conclud-

ed that condensation of element sublimates on the surface of relatively large particles of bell dust does not change their com-

position in a marked fashion. In addition, for some macro- and microimpurity elements (Table 1) a marked increase was noted

653

TABLE 1. Sub-Division of Blast Furnace Microelements in Accordance with Their Distribution between the Main Process Phases

Group Microelements

Typical parameters

presence in OPC

transfer intopig iron

transfer intoslag

KKbs morethan 3 units

existence of balancediscrepancy

First

Barium, zirconium + – + – –

Lithium, rubidium + – + – +

Beryllium, yttrium, scandium lanthanoids + – + – +

Strontium + – + + –

SecondBoron, chromium + + + – –

Vanadium, arsenic, phosphorus + + + + –

ThirdCobalt, copper + + – – –

Gallium, nickel + + – + –

Fourth

Molybdenum – + – – –

Tin, antimony – + – + –

Lead – + – + +

in the value of coefficient KKbs, i.e., from 3.0 to 5.0, and in individual cases to 50–60 un., which may serve as indirect con-

firmation of the development of absorption processes for these microelements from the gas phase.

As already indicated above, the behavior of microelements in the blast furnace process depends on in what form

(compounds, surroundings) they enter a unit. We consider two main versions of entry of microelements into a BF. The first

version is IA: arrival in mineral compounds, which are a basis of iron-containing components of a charge, and also present

within coke. The second version is IB: arrival within the composition of organic compounds only present within coke, and

here the element in question is within the structure of organic molecules. In order to determine the amount of a microelement

in the organic part of coke (OPC), data in [5, 6] have been used.

The overall arrival of an element is

I = IA + IB, g/ton pig iron.

We designate the mineral part of entry of an element as ρ = IA /I, and the organic part of arrival as η = IB /I. Taking

account of the fact that each microelement in a blast furnace process is transferred into three main media, i.e., molten iron,

molten slag, and gas phase, we introduce distribution (transfer) coefficients for an element into these media: γ1, γ2, γ3 are the

proportions of transfer into pig iron, slag, and gas phase, respectively.

Transfer into each medium occurs in accordance with both versions IA and IB, and it may be accomplished by dif-

ferent mechanisms in relation to the properties of an element and its compounds, and also on the nature of the medium into

which it is transferred.

Let λi be the proportion of entry of an element from the mineral organic part, which is transferred by this mecha-

nism into one of three metallurgical media. The value of λi depends on the change in Gibbs energy ΔG:

where αi is a coefficient taking account of structural, geometric, and other factors, specifying the process of element transfer.

The overall transfer coefficient of a test element into each of the three metallurgical media is accumulated from

two terms:

γ1,2,3 = ρ∑λk + η∑λl.

The first term is the overall proportion of an element with transfer from the mineral part, and the second is the over-

all proportion with transfer from the organic part; indices k and l signify transfer mechanisms from the mineral and organic

parts, respectively.

In order to estimate the productivity of mechanisms, we need a collection of physicochemical criteria describing spe-

cific stages of element reaction with components of the blast furnace process. The following main criteria were selected:

chemical affinity of an element for an “active component” of a metallurgical system, i.e., oxygen, hydrogen, sulfur, chlorine,

and also solubility in iron. For each active component, a collection of properties was determined:

• existence of chemical compounds with a given component;

• range of temperature and chemical stability of chemical compounds;

• proportion of an element bonded in each of the possible compounds under prescribed conditions; and

• compound volatility (saturated vapor pressure).

Analysis of these characteristics makes it possible to find effective values for the change in Gibbs energy for trans-

fer mechanisms of a test microelement entering a BF by two different methods, into each of the three metallurgical media.

Basic data provided in Table 1 make it possible to subdivide the microimpurity elements of blast furnace smelting into four

groups in accordance with their distribution between the main process phases.

In three groups, there are elements entering a BF both within the composition of the mineral component and within

the organic part of coke. Elements of the first group on the whole behave similar to slag-forming (aluminum, calcium, mag-

nesium) elements, and are almost entirely transferred into the oxide melt. However, for strontium there is marked sublimation

λ αi i

G

RTE=Δ

,

654

and accumulation in sludge, and for lanthanoids and beryllium there is discrepancy in the balance. Data for lithium and rubid-

ium almost correspond to their “chemical” analogs, i.e., sodium and potassium.

Elements of the second group are distributed between molten metal and slag (on the whole similar to manganese or

silicon), but for vanadium, arsenic, and phosphorus there is a significant (KKbs ≈ 3.5) transfer into the gas phase of the pro-

cess. Elements of the third group almost entirely pass into pig iron. For nickel and gallium, transfer is also noted into the gas

phase (KKbs ≈ 3.5).

For elements of the fourth group, there is typical arrival in the BF only within the composition of the mineral compo-

nent of a charge, and they are distributed between pig iron and gas phase. For tin and lead, the highest values of KKbs = 50–60

are noted, and for lead there is discrepancy in the balance at the level of 20–25 rel.%.

A description of the proposed calculations being used for determining transfer coefficients of microelements into the

gas phase (in sublimates) is provided below. We choose elements differing in chemical composition and with respect to

behavior in the blast furnace process (relating to different groups of Table 1). Some starting data and results of calculations

are provided in Table 2. Values of coefficients η and ϕ (proportion of an element passing into sludge of its total entry into a

furnace) are averaged factory data, obtained in the metallurgical enterprises mentioned above.

Analysis of the results obtained makes it possible to confirm that the procedure developed describes quite adequately

the quantitative distribution of microelements between the main phases of the blast furnace process. A short description is

Balance itemEnterprise

Severstal NLMK Tulachermet EKO-Stahl

Entry into blast furnaces:

with iron-ore part 110 130 250 400

with coke 90 270 250 110

including OPC 45 135 125 55

Total, g/ton pig iron 200 400 500 510

Transfer during blast furnace smelting:

into pig iron None None None None

into slag 195 390 480 500

into blast furnace dust 3 6 10 5

into blast furnace sludge 2 4 10 5

* KKbs within limits 0.5–1.5.

Index, wt.%Microelements

Ba Zr Sr P Cu Ga Ni Sn

η 23 7 10.2 20 13 8.5 4.7 0

ϕ 1.2 1.2 4.2 4.2 <3.1 3.0 3.6 33.6

γ3 3 ~0.5 6.7 ~15 >1.4 ~2.6 4.2 ~50

655

TABLE 2. Parameters of Microelement Transfer into the Blast Furnace Process Gas Phase

TABLE 3. Typical Balances for Barium with Smelting of Steel-Making Pig Iron, g/ton pig iron*

given below for the behavior in blast furnace smelting of some microelements based on analyzing the balance and thermo-

dynamic calculations.

Barium is hardly reduced to metal in a BF, which reduces to a minimum the possibility of its transfer into the gas

phase from the mineral part (Table 3). Its sublimation from the organic part is possible either in the form of volatile oxides,

or in the form of compounds with chlorine. Since entry of barium into a BF as a rule by far exceeds the entry of chlorine,

then transfer of it into the gas phase within the composition of compounds with chlorine is insignificant. Consideration of

this and some other criteria makes it possible for barium to obtain a proportion of transfer into the gas phase γ3Ba = 3%.





with coke 10 20 5 5




into pig iron 15 45 45 65

into slag None None None None

into blast furnace dust <1 <1 <1 <1

into blast furnace sludge <1 <1 <1 <1






with coke 30 30 120 6




into pig iron None None None None

into slag 122 43 165 80

into blast furnace dust 2 1 3 0.5

into blast furnace sludge 1 1 2 0.5


656

TABLE 4. Typical Balances for Zirconium with Smelting of Steel-Making Pig Iron, g/ton pig iron*

TABLE 5. Typical Balances for Copper with Smelting of Steel-Making Pig Iron, g/ton pig iron*

Zirconium (Table 4) has very stable oxides, which cannot entirely be reduced in the course of the blast furnace pro-

cess. Zirconium itself and its compounds are almost not gasified independent of the fact of whether they are found either in

the mineral or organic part. Very insignificant gasification of ZrO2 is only possible in an oxidizing atmosphere not below

2200°C, i.e., in the tuyere zone. Here the maximum amount of zirconium in the gas may be about γ3Zr ≈ 0.5%.

Copper (Table 5) should be transferred into the gas phase from the organic part of coke in the form of volatile sul-

fides and hydrides. In addition, part of the copper may be transferred into gas from the mineral part of a charge in compounds

with sulfur. This part may vary considerably depending on charge composition. The rest of the copper at above 1300°C is

reduced, and having good solubility in iron may be transferred into pig iron. The overall content of copper in the gas phase





with coke None None None None




into slag No No No No

into blast furnace dust <1 <1 <1 <1


KKbs 40.0 30.0 30.0 50.0





with coke 20 15 15 20





into slag None None None None

into blast furnace dust 1 1 1 1


KKbs ~3.5 ~3.5 ~3.5 ~3.5

657

TABLE 6. Typical Balances for Nickel with Smelting of Steel-Making Pig Iron, g/ton pig iron

TABLE 7. Typical Balances for Tin with Smelting of Steel-Making Pig Iron, g/ton pig iron

should be not less than γ3Cu > 1.4%. It is possible that the low content of copper in sludge is explained by formation within

the BF contour of circulation of copper sulfide (for example similar to lead sulfide). As a result, the main part of the gaseous

copper sulfide is absorbed by the slag phase of the process, and almost all the copper is transferred into pig iron.

Nickel (Table 6) is easily reduced under conditions of the blast furnace process, and in addition it is almost entirely

dissolved in iron, which makes it possible for all of it, contained in the mineral part, to be transferred almost entirely into pig

iron. Transfer of nickel into a gaseous form is only possible from the organic part of coke in the range from 1300°C (when

gaseous nickel hydride develops and atoms of pure nickel from the coke organic are gasified) up to 1600°C. The overall pro-

portion of nickel transferred into the gas phase is γ3Ni = 4.2%.

Tin (Table 7), which is hardly present in the organic part of coke, is moreover readily evaporated from the mineral

part at above 900°C in the form of chloride, oxide, sulfide, and in the form metal atom vapor. At above 1200–1300°C, reduced

tin may be dissolved in solid reduced iron, and it is also captured by droplets of molten metal and transferred into pig iron.

Thus, that part of tin is transferred into the gas phases that manages to be gasified up to these temperatures, i.e., γ3Sn ≈ 50%.

Conclusion. Analysis of the results obtained makes it possible to conclude that the increase observed in recent years

in the proportion of transfer of microelements in blast furnace smelting into sublimates and an increase in their content in

blast furnace sludge is mainly connected with features of the behavior of the proportion of their microelements within the

composition of the organic part of coke and coal dust fuel.

REFERENCES

1. E. F. Vegman, B. N. Zherebin, A. N. Pokhvisiev, et al., Pig Iron Metallurgy [in Russian], IKTs Akademkniga,

Moscow (2004).

2. Yu. S. Yusfin, I. G. Tovarovskii, P. I. Chernousov, and V. A. Shatlov, “Blast furnace – a unit of the 21st century,” Stal,

No. 8, 108 (1995).

3. Yu. S. Yusfin, L. I. Leontiev, P. I. Chernousov, et al., “New blast furnace functions,” Rynok Vtor. Metal., No. 4, 36–37

(2002).

4. P. I. Chernousov, Yu. S. Yusfin, and O. V. Golubev, “Low volume furnaces – the future of blast-furnace production,”

Izv. Vyssh. Ucheb. Zaved., Chern. Met., No. 10, 20–25 (2005).

5. Ya. E. Yudovich, A Gram is More Expensive than a Ton: Rare Elements in Coal [in Russian], Nauka, Moscow (1989).

6. Ya. E. Yudovich, M. P. Kertis, and A. V. Merts, Impurity Elements in Fossil Coals [in Russian], Nauka, Leningrad (1985).

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methodology for analyzing microelement behavior in blast furnace smelting

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