1. Introduction

The reorientation of iron and steel industry on resourcessaving technologies is the basis of steady development inmany countries. Various ecological conferences showedthat the solution of environmental problems is not only ap-plication of effective clearing devices and systems, but alsointroduction of new technologies, which provide a decreaseof energy, raw materials consumption and quantity of vari-ous emissions.1)

For the iron and steel industry which influence the envi-ronment significantly, huge volumes of gases and formationof solid matters are characteristic. The dusts and/or sludgesgenerated by blast and electric furnaces, oxygen steel mak-ing and mill scale from rolling operations cause large vol-umes of waste streams.

Metallurgical sludges and dusts can contain amounts ofzinc, lead or tin. The reuse of this kind of sludges and dustsis limited, because it leads to accumulation of those ele-ments in charge materials and decrease steel quality.

Formation of ferrous containing dusts which are formedbasically in steel smelting processes is amenable to techno-logical regulation in the certain degree.

An efficient recycling process can be characterised by theseparation between the zinc and lead fraction and the ironfraction in a best suited form recycle in the steel plant.2)

One solution for further reuse of waste materials, such asferrous and/or carbon containing dusts, is the injection intovarious metallurgical aggregates.

Injection of solids into the blast furnace, BOF, EAF, ladlefurnaces, vacuum furnaces and so on, can be used for burn-ing, reacting, smelting, fluxing, refining and alloying inboth the iron and steelmaking facilities.

2. Survey of Dusts Origins in Iron and Steelmaking

All metallurgical residues can be divided by origin intointernal and external materials. Internal residues are col-

lected in dust filters and sludge processing units on site.The common dusts, sludges, other residues, and their ori-gins in the production flow are named in Fig. 1.3)

Table 1 shows the origins of the sludges and dusts of theiron and steel industry in North Rhine–Westphalia, Ger-many.4) External residues can also be carbon containingmaterial. Mainly, those are plastic residues from householdand used oil or grease. Potential materials are e.g. plasticsfrom end of life vehicle (ELV) recycling, carpets, carcassmeal, and biomass.

3. European Laws in Metallurgy

Taxes and payments, connected with preservation of theenvironment and rationalisation of nature management,have started to play an essential role in many countriessince 1960.

Recently, European domestic laws have become strict to-

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ISIJ International, Vol. 46 (2006), No. 12, pp. 1745–1751

Dust Injection in Iron and Steel Metallurgy

Dieter SENK, Heinrich Wilhelm GUDENAU, Stephan GEIMER and Elena GORBUNOVA

Department of Ferrous Metallurgy (IEHK), RWTH Aachen University, Intzestraße 1, D-52072 Aachen, Germany.

(Received on April 28, 2006; accepted on July 10, 2006 )

The occurrence of dusts in steelworks is surveyed. A brief overview of the European legislation situationis given. Current techniques of solid injection in different aggregates are presented. The investigations ofthe Department of Ferrous Metallurgy (IEHK) at RWTH Aachen University in the handling of various dusts inmetallurgical processes are introduced. The dust injection into shaft furnaces and steel melts has been cho-sen as typical treatments. Former researches and recent works are presented and the results are dis-cussed.

KEY WORDS: dust emission; solid injection; recycling; blast furnace; cupola furnace; iron and steel melts.

Review

Fig. 1. Origins of internal dusts and sludges.

wards environmental pollution.5)

In accordance with the new legislation in Germany (cir-culation bill) the main aims concerning waste of industrialprocesses are at first the avoidance, the reuse and only inlast consequence the dumping of waste materials.6) This lawadapts German legislation towards European Right so thatin the future each developed new process line should beable to recover the produced waste completely.

Council directive 1999/30/EC of April 22nd, 1999 basedon principles enshrined in Article 130r of the Treaty, theEuropean Community programme of policy and action inrelation to environment and sustainable development envis-ages in particular amendments to legislation on air pollu-tants. The aim of this directive is to reduce concentrationsof fine particles as part of the total reduction in concentra-tions of particulate matter.

The objectives of this directive are to:

– establish limit values of particulate matter to avoid, pre-vent or reduce harmful effects on human health and envi-ronment,

– assess concentrations of particulate matter in ambient air,– obtain adequate information on concentrations of partic-

ulate matter in ambient air.Table 2 shows the limit values for particulate matter

PM10, which passes through a size–selective inlet with 50%efficiency cut-off at 10 mm aerodynamic diameter.7)

4. Current Techniques of Dust Injection

Recently, powder or dust injection has been widely usedin iron and steel industry.

The technique of injecting reagents into shaft furnacesthrough the tuyeres has been developed since the beginningof the last century. Today, besides using the effect of lower

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Table 1. Origin of sludges and dusts of the iron and steel industry in North Rhine–Westphalia, Germany.

Table 2. Limit values for particulate matter (PM10).

coke consumption in the blast furnace by injecting fuels,also fine ore injection was researched without agglomera-tion, and recycling of various internal and external dustresidues was tested. Alternative fuels for injection are coal,oil, natural gas and plastic residues.

The Pulverised Coal Injection (PCI) is now a widelypractised technique in Europe and worldwide, which is be-coming increasingly important in blast furnace ironmakingas a means of cost reduction and improvement in furnaceoperation.8–10) In order to allow the maintenance of suitableraceway conditions to promote effective coal utilisation andcoke replacement, it is necessary to employ either progres-sively higher blast temperatures or greater levels of oxygenenrichment of the blast with increased coal injection rates.There are, however, technical risks and high costs associ-ated with the demonstration of very high rates of coal injec-tion on a mainstream production furnace. These relate touncertainties regarding furnace performance and the needto provide extra coal preparation, injection facilities andextra oxygen capacity, see Fig. 2.11)

Submerged injection of solids into melts, through lancesor tuyeres using a conveying gas and a submerged lance isan important operation used worldwide for smelting, flux-ing, refining and alloying since the 1970th. The main ad-vantage of injection over the earlier practice of adding solidreagents to the top of the bath is that higher reaction ratescan be achieved due to closer contact between the particlesand the melt.

In LD-AC process finely ground lime and oxygen are in-jected simultaneously through a top lance into high-phos-phorus iron. Also in OBM process lime and oxygen are in-jected simultaneously into melt, but through the bottom.

The powder injection and blowing treatment of molteniron and steel in a ladle, particularly the desulphurisation bypowder injection, has become a widely used technology.Also processes for injection of lime, calcium carbide, mag-nesium, fluorspar, synthetic slag and combinations of these,have been developed.12–17)

During the process of powder injection in a ladle, how-ever, the effectiveness of desulphurisation strongly dependson the conditions of the top slag. Some different desul-phurisation technologies using powder injection and blow-ing in the RH vacuum circulation treatment of liquid steelhave been developed. There are, for example, RH-PB (IJ),RH-PB (OB), and RH-PTB processes.18) In RH-PB (IJ)process the powder flux is injected into the ladle through alance positioned beneath the upsnorkel. In RH-PB (OB)process the powder fluxes is blown into the liquid steelfrom the oxygen blowing nozzles located in the lower partof the vacuum chamber. And in RH-PTB process the pow-der is blown through a top lance from the top of the vacuumchamber.

To improve EAF efficiency and reduce operational costsoxygen fuel burners have been successfully applied, for in-jection of carbon.19–21) The technology is based on oxygenlances and carbon injectors. Many furnaces use separatecarbon and oxygen lances and a separate oxy-fuel burner. Ithas been observed that the central oxygen jet in such aburner does not decay as rapidly as a jet exhausting intofree air. Such a jet is known as a “Coherent Jet” and main-tains its original velocity profile over a greater distance than

a conventional supersonic jet, see Fig. 3.The use of coherent jet technology in the BOF was inves-

tigated.22–23) A coherent jet can be used to inject solids, es-pecially lime, in the linked or unlinked state. With a coher-ent jet there is a possibility to inject materials without get-ting into contact with the melt. The effect of the protectingflame shroud is as if the lance is much closer to the bathand reoxidation of melt is nearly avoided. The injection ma-terial does not need to be agglomerated; it can be employedfine grained into the melt without a high off gas loss.

5. Theory of Gas-powder-jet Formation and Dissolu-tion of Solids in Melt

In many metallurgical processes, tuyeres are used mainlyas gas supply devices to blow the active gases such as oxy-gen, air or nitrogen and/or the inert gases such as argon.The reliable and accurate estimation and prediction of therelative property parameters of a gas stream in a tuyere arevery important for the optimisation of tuyere design andblowing technology.24)

There are three fundamental steady-flow regimes when acompressible gas is discharged from a passage into a regionhaving a given pressure as follows at Laval nozzle:1. Adapted jets, where the passage exit pressure and am-

bient pressure are the same,2. Non-adapted under-expanded jets, where the passage

exit pressure is higher than the ambient pressure,3. Non-adapted over-expanded jets, where the passage

pressure is lower than the ambient pressure.In the non-adapted jets, steady flow only occurs when the

Mach number at the passage exit is sonic or supersonic.Pressure equalisation is achieved in multidimensional exter-nal expansion or compression waves, and consequent dis-continuities in density. The non-adapted jets can cause en-ergy loss, which reduce the momentum and produce turbu-lent flow in the jet exit, which shorten the coherent length.When the jet is adapted, an exit flow with high momentum,good uniformity and a tidy boundary is obtained.

Gas-powder-jet formation begins with introduction of adisperse phase, consisting of particles in the size dp and

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Fig. 2. Oxy/Coal injection lance.

Fig. 3. Adapted Laval nozzle and Coherent jet with solids incore jet.

density rp, in the gas flow, entering in a pipe with velocityVg, and the particles accelerate up to the velocity Vp. Atparticles acceleration in a pipe they reach a constant veloc-ity. Because of collision with the pipe walls (inner diameterD) the resistance to particles movement increases with in-creasing of Vp. As a result balance between the gas streamforce influencing on a particle and force of friction is estab-lished, from25)

.........................(1)

where rg is gas density and f is friction index.The friction index depends on a quantity of a dimension-

less index kp�rpdp/rgD and at dp>100 mm

f�7.76 ·10�4kp0.775; kp<161

f�0.04; kp>161

f�1.78kp�1.5; dp<100 mm

For the particles propulsion in a pipe, greater value ofReynolds number for a particle (see Eq. (2)) is necessary toachieve constant velocity of the particles.

................................(2)

where ng�h /r is the gas kinematic viscosity.

During solids injection into iron or steel melt processesheating, dissolution, evaporation or chemical reaction takesplace. In general total duration of heating and phase trans-formation at solids injection into melt is equal26) to

tS�th.s�td�th.l�t ev�th.g .....................(3)

where th.s is the duration of heating of solid particle, td isthe duration of dissolution, th.l is the duration of heatingliquid drop, t ev is duration of evaporation or chemical reac-tion and th.g is the duration of heating of gas bubble.

For commonly used desulphurisation agents Eq. (3) isconcretised as follows:

for Mg, Na, Ca and Na2CO3 tS�th.s�td�th.l�t ev�th.g

for CaO and CaC2 tS�th.s

According to the work of Isaev et al.27) the total durationof transformation from solid state to liquid state of alu-minium particles in radius 0.1 and 0.3 mm is equal to7.2 ·10�3 and 13.8 ·10�3 s. respectively.

Coudure and Irons28) showed that the reaction betweenCaC2 particles in size from 0.1 to 1 000 mm and sulphur dis-solved in hot metal during powder injection after an incuba-tion period takes between 20 and 40 s.

Ochotskij29) indicated that any solid particle in diameter100 mm heats up to temperature of liquid metal during10�3 s.

6. Investigation at Solid Injection of IEHK-RWTH

Several possibilities of dusts reuse, improvement of theshaft furnace and BOF process have been conducted at De-partment of Ferrous Metallurgy (IEHK), RWTH AachenUniversity.

6.1. Injection into Shaft Furnaces

At IEHK laboratory a rig was developed to investigatepulverised coal conversion during injection in detail, seeFig. 4. This rig simulates the behaviour of fines injectedinto the raceway of the blast furnace.30–37)

The rig consists of a low-pressure and a high-pressurezone. It is loaded with coal dust sample and by opening avalve of the high-pressure zone gas and dust begin to swirl.The gas for the dust injection is preheated in the low-pres-sure zone by a warming furnace up to 1 100°C. After thedust is mixed with hot oxygen from the low pressure zone itpasses the induction furnace and is heated up to 1 700°C.The product gas is accumulated in a gas-collecting con-tainer and analysed. The residues are collected in a filter.

While simulating blast furnace conditions the effect onthe ignition combustion behaviour of different coals such asporosity, particle size, content of volatile matter, carbon andash and injection rate could be tested. Further investigations

Repg p

g

�V d

ν

V

V f

p

g p g

��

1

1 ρ ρ/

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Fig. 4. Injection rig.

were performed to analyse the effect of catalysts on coalconversion, oxygen enrichment of the hot blast, preheatingof the injected coals and different lance geometries.

The results of experiment are applied to a real practice inBF. In a test done parallel in the blast furnaces to get moreinformation,38,39) e.g. about the raceway, it was measured bylaser-technique, that the depth of the raceway was becom-ing shorter by injection of coal.40)

Tests and discussion about injection coal mixed with dif-ferent fine materials have started. The reasons for the com-bined injection of coal and fine iron ore or iron containingdust are different, e.g. the amount of fine ore increasessteadily due to a decreasing number of high-grade lumpores. The additional injection of fine iron ore was investi-gated in order to substitute pellets or sinter and herewith toreduce agglomeration and hot metal costs and save en-ergy.41–43)

The injection rig was steadily adapted for the differentproposes. It was found that by using a coal with a low con-tent of volatile matter mixed with iron ore the highest re-duction degree was reached. The result shows that the re-duction degree depends on the ignition and conversion be-haviour of the coal.44)

Further experiments were performed in order to analysethe effect of the particle size on the reduction degree. It wasfound out that a complete reduction of hematite iron ore tometallic iron is possible within the short residence time of10–20 ms. Therefore further experiments were performedwith blast furnace flue dust, steel plant residues and rollingmill scale. Concerning the iron and carbon content of thesematerials an injection into the blast furnace seems to bepossible. Figure 5 shows the results of the combined injec-tion of flue dust and coal.

Further researches about the raceway gave results andknowledge about different materials,42,44–47) e.g. petrol coke,mill scale, BF-sludge, activated carbon and catalyst mostlyas mixture with coals. Figure 6 shows the influence of mix-tures of different coals and mixtures of waste with coal.48)

Beside the injection into raceway of blast furnace thereare some researches with injection technique implementa-tion in the field of a newly developed shaft furnace.49) Theprinciple of the shaft furnace is based on a used Cupola fur-nace and adjusted to the task of remelting and recyclingiron bearing residues emerging from operations in the steelworks. The dusts are agglomerated in self-reducing bricksand charged with coke from top of the furnace. The subjectof investigation now is iron bearing residues which cannotbe agglomerated. The possibility of reuse these residues inthe shaft furnace would mean a decrease in landfill and areduced loss of iron. For the investigation, in a first ap-proach the above mentioned injection rig is being used.Metallic and oxide iron dusts from BOF plant are examinedand injected in the injection rig. By the time, the furnace isin production at the company ThyssenKrupp Steel (TKS).In this manner TKS will be able to recycle the most part ofits internal wastes.

Beside injection into blast furnace research was carriedout to recycle foundry dusts in cupola furnaces. The differ-ent circumstances in the tuyere level were studied and dis-cussed.50) It was possible to recycle different foundry dustsand furthermore e.g. plastics. It was found that no dioxin

appears in the off-gas.51)

To increase the injection rate of unburning material anew process was developed. Parallel to tests at a cupola fur-nace an injection-coke-bed-simulator was built up at IEHK,see Fig. 7.

In this equipment dusts are injected by a natural gas/oxy-gen-burner. Aim of this research is to study the behaviourof hot gas injection with foundry dusts in contact with thecoke and in the furnace. Tested dusts are internal foundrydust, Si–, Mn– and Fe–oxide-containing dust, SiC-dust,coke dust, iron swarf and mixture of them. It was found thatresidues with high loose density (SiC-dust, iron dust andiron swarf) show fast melting and good suitability. A hugeamount of offgas was observed with coke dust and the finefractions of mixtures. Furthermore, the Cupola furnace per-formance could be enhanced by over 40% using the addedburners.52)

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Fig. 5. Conversion behaviour of coal for different percentage offlue dust in the mixture.

Fig. 6. Conversion behaviour of pulverised coal (HVC, highvolatile coal; LVC, low volatile coal), shredder light frac-tion (SLF), unburned carbon of power station (UBC) andwaste plastics (WP).

Fig. 7. Coke-bed simulator with measurement positions at IEHK(total length is 3 350 mm).

6.2. Injection into Steel Melts

To improve the productivity of the BOF process investi-gations of solids injection in melt were done at IEHK withthe use of coherent jet technology.53)

The first researches were carried out in water modellingtests with a simulation coherent jet lance. During those teststhe bath mixing time was measured at different combina-tions of shroud and core gas pressure. It was observed thatthere is a minimum bath mixing time at each shroud pres-sure. The minimum bath mixing time increases with in-creasing shroud pressure. In all instances the total momen-tum flow for the minimum bath mixing time was the same.The minimum in the bath mixing time is as a result ofswirling in the bath, which dissipates energy.

The same injection facility and flow meters were used forhot laboratory tests. The experiments were carried outusing the induction furnaces at IEHK, as shown in Fig. 8.Initial safety tests were carried out at low gas speed, whichwas gradually increased for the experiments.

The following experiments were carried out:– Injection of fine-grained manganese and FeSi mixture for

steel alloying.– Injection of coarse-grained recarburisation agent.– Injection of desulphurisation slag

(50% CaO, 40% Al2O3 and 10% SiO2).– Silicon carbide injection, aiming the increase of the car-

bon and silicon content in melt.– Injection of iron ore and filter dust consisting of FeO.

The injection experiments showed that no general state-ment about solid injection in melt using coherent jet tech-nology can be made. There is a conflict between injectinglarge amounts of material and injection efficiency. Injectinga large amount of material in a short time supports bathmixing, but the material cannot be transferred to the bath insufficient quantities. Injecting solids in the unlinked stategives a much better transfer of material to the bath, but thequantity of gas to support mixing is not as great as it is inthe linked state. Increasing the gas flow rate to create an un-linked injection state would solve this problem. Additionalenergy would be transferred into fluid motion at the bathsurface and have a negative effect on bath mixing in thevolume.

Basically it is possible to inject solids using coherent jettechnology avoiding a contact between the lance and themelt with low off gas and deeper penetration of materials.Furthermore it is necessary to consider every injectionagent beforehand, in accordance with environment condi-tions.

Tests with utilisation of residues of nickel production socalled “tailings” in EAF steelmaking route were carried outin an induction furnace at IEHK with capacity of 50 kg,equipped with porous plug for bottom gas stirring, inert at-mosphere and injection of cored wire. The materials weretechnical pure iron or low-alloyed steel, tailings from Cuba,slag (CaO/Al2O3) and Ca–Al-alloy, anthracite or metallicaluminium as reducing agents. The results of experimentsshowed, that Fe, Ni and Cr from tailings can be recycled toa steel melt up to 90%, see Fig. 9.54)

Present work55,56) is carried out at IEHK related to the di-rect alloying of steel with Mn-ore injection into the steel

melt. The purposes of this investigation is to study the re-duction of Mn-ore with use of various reducing agents suchas C, Al or Si in the crucible, as well as to get high yield ofmetallic manganese in the melt. Analysis of the injection, areduction mechanism of MnO and a process modelling isunder progress.

7. Conclusion

According to new tendencies of iron and steel industrydevelopment the investigations on injection of various dustsinto BF, shaft furnace, cupola furnace and steel melt havebeen carried out in the Department of Ferrous Metallurgy(IEHK) at RWTH Aachen University. With the aim of reuseof metallurgical residues and improvement of BF processvarious dusts such as pulverised coal, mixture of coal andfine iron ore or iron containing dust, blast furnace flue dust,steel plant residues and rolling mill scale, petrol coke, BF-sludge, activated carbon and catalyst mostly as mixturewith coals have been used in experiments with injection rig,which simulates the behaviour of fines injected into theraceway of the blast furnace. The results showed that the in-jection of these materials into the blast furnace is possible.

Beside injection into blast furnace research was carriedout to recycle foundry dust, plastics, Si–, Mn– andFe–oxide containing dust, SiC-dust, coke dust and ironswarf in cupola furnaces with the use of the naturalgas/oxygen burners. The experiments showed a clear im-provement of the melt process by an increase of the furnacecapacity and possibility to utilise dusts which have not beenutilised before.

To improve the productivity of the BOF process investi-gations of solids injection into melt were done with the useof coherent jet technology. The following solids were used:

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Fig. 8. Coherent jet lance and induction furnace at IEHK.

Fig. 9. Summary of the experiments with utilisation of residuesof nickel production (tailings) with different mixings.

fine-grained manganese and FeSi mixture, coarse-grainedrecarburisation agent, desulphurisation slag (50% CaO,40% Al2O3 and 10% SiO2), silicon carbide, iron ore andfilter dust consisting FeO. The injection experimentsshowed that it is possible to inject solids using coherent jettechnology avoiding a contact between the lance and themelt, with low offgas and deeper penetration of materials.

Tests with utilisation of residues of nickel production socalled “tailings” in EAF by injection of cored wire showedthat Fe, Ni and Cr from colas can be recycled to a steel meltup to 90%.

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