Voluntary lecture for interested: Dolomite Refractories … Refractory-Technology Part 1...

$: Voluntary lecture for interested: Dolomite Refractories … Refractory-Technology Part 1 Refractories and Slags in the Metallurgy Dipl.-Geol. J. Hartenstein Dolomite Refractories in$
Steel Academy Steel Institute VDEh PO box 104842 40039 Düsseldorf Sohnstraße 65 40237 Düsseldorf Germany Fon +49 211 6707 454 Fax +49 211 6707 655 E-Mail: [email protected] Internet: www.steel-academy.com

Voluntary lecture for interested: Dolomite Refractories in the Steel Industry

Dipl.-Geol. Johannes Hartenstein, Magnesita Refractories GmbH, Hagen

Seminar:

Refractory Technology – Applications, Wear Mechanism, Failures

VDEh-Seminar – Refratory-Technology – Part 1 Refractories and Slags in the Metallurgy

Dolomite Refractories in the Steel Industry Dipl.-Geol. J. Hartenstein, Hagen

VDEh-Seminar IS-2015 Page 1

1. INTRODUCTION

At the end of the nineteenth century the Englishman Sidney Gilchrist Thomas used burnt lime (CaO) to line a Bessemer converter to eliminate phosphor from the pig iron. He received a patent for this new kind of lining. Due to the high porosity and affinity to moisture the burnt lime couldn’t give a satisfactory lining lifetime. The conversion from phosphor-containing pig-iron to steel in a Thomas converter was only possible after the introduction of refractories based on sintered dolomite, which has has the major components CaO and MgO. From the time of this invention on dolomite came to remarkable share in basic linings of metallurgical converters.

Horace Bénédict de Saussure Déodat de Dolomieu Sidney Gilchrist Thomas Sir Henry Bessemer

The actual global use of sintered dolomite is estimated to 300.000 t / a, whereof 90% are used in the steel industry and 10% in the cement industry. Dolomite bricks are sold according to their grades and shapes between 400 and 900 € / t. The mineral dolomite has been discovered by the French geologist Déodat de Dolomieu in the year 1791. He knew that the rock was a carbonate, but in contrast to pure limestone a test with hydrochloric-acid did not show an intense chemical reaction. One year later the chemist Horace Bénédict de Saussure made a chemical analysis and found that this mineral is a mixture of CaCO3 and MgCO3. In honour of the discoverer he named this mineral “Dolomite” (Fig. 01).

VDEh-Seminar Refractory-Technology Part 1 Refractories and Slags in the Metallurgy Dipl.-Geol. J. Hartenstein Dolomite Refractories in the Steel Industry

Page 2 VDEh-Seminar IS-2015

Fig. 01: View on the "Three Peaks", South Tyrol – Rock forming Dolomite – at noon and at dusk

2. THE GENESIS OF DOLOMITE

Dolomite CaMg(CO3)2, Calcite CaCO3 and Magnesite MgCO3 are so-called rock-forming carbonates and represent 10% of all rock-forming minerals in the solid earth crust. The total share of dolomite is approximately 1.0%, the overall content of magnesite is about 0.1%. Limestone has, without exception, organogenic roots. The first calcite has been formed 2.6 billion years ago by the photosynthesis of primitive bacteria. Later on other creatures (algae, sponges, corals) also produced calcite. The major part of the calcite productionis delivered by beacteria and algae, generally well-known is the formation by corals in reefs and flat shelf regions of tropical seas (Fig. 02, 03).

Fig. 02: View on a recent stromatolitic reef in sea water; Hamelin-Pool, Australian West Coast

Fig. 03: View on a fossile stromatolitic reef, 2.5 Billion years old; Great Slave Lake, Canada

Dolomite has two different sources: either as so-called “primary dolomite” which precipitated in the seawater or as “secondary dolomite” which is converted from limestone under the exposure of magnesia-containing solutions during the rock diagenesis. With increased pressure and temperature conditions a metamorhosis takes place. The exact conditions for the generation of dolomite are still subject of investigations.



Fig. 04: Classification of Carbonate Rocks Fig. 05: Use of Carbonate Rocks

3. DOLOMITE DEPOSITS

Dolomite can be found in many places word-wide; however, only very few of them contain dolomite which is suitable for the production of refractory materials. Examples for such ideal quarries all over the world are (Fig. 06):

[Germany Hagen closed 2009] Belgium Marche-les-Dames Brazil Contagem England Whitwell Italy Merone USA York

Fig. 06: Important Dolomite Deposits for Refractory Application in Europe and U.S.A

puremagnesite

silicate rocks

MgCO3 CaCO3

SiO2 + Al2O3 + Fe2O3

purelimestones

puredolomite

limestones

dolomitic limestones

lime dolomite stones

dolomite stones

MgCO3 CaCO3

SiO2 + Al2O3 + Fe2O3

silicate rocks

puremagnesite

purelime

puredolomite

fertilizerdolime

cement

fluxes

roadconstruction

refractoriesrefractories



Fig. 07: Aerial View on the Dolomite Quarry, Rheinkalk GmbH, Hagen Hagen-Herbeck; Germany

Fig. 08: View on the Dolomite Quarry, Magnesita Refractories; York, Pennsylvania, U.S.A.

4. MANUFACTURING OF SINTER DOLOMITE (DOLOMA)

The pure stochiometric mineral dolomite consists 30.41% CaO, 21.87% MgO and 47.72% CO2 (Table 01, Fig. 10). On heating it decomposes in two steps into the oxides and CO2 (Fig. 09). At 800°C the MgCO3 part decomposes to MgO and CO2, the CaCO3 part is unaffected; the so-called semi burnt dolime is formed. At 1000°C the residual CaCO3 decomposes finally to CaO and and CO2, the so-called caustic dolime is formed. The caustic dolime has a very porous structure like burnt lime with approx. 55 Vol. % pores and very small crystals of CaO and MgO (less than 0.1 µm). With further increase of temperature a sintering begins, the crystal sizes increase and the porosity decreases (Table 02). At 2000°C the sintering is almost finished. A pure dolomite sinter consists now 59.56% CaO and 37.86% MgO (Fig. 11). In the figures 13 to 16 are shown fracture surfaces of raw dolomite stone, semi-burnt dolomite, caustic dolomite and dolomite sinter (in US called doloma).

Fig. 09: Thermogravimetry of Magnesite, Dolomite and Limestone



Fig. 10: Micrograph (incident light) Dolomite Rock / Raw Dolomite

Fig. 11: Micrograph (incident light) Sinter Dolomiter / Doloma Sinter

Fig. 13: Micrograph (SEM) Raw Dolomite, fracture surface

Fig. 14: Micrograph (SEM) Semi Burnt Dolomite after 800°C, fracture surface

Fig. 15: Micrograph (SEM) Caustic Dolomite after 1000°C, fracture surface

Fig. 16: Micrograph (SEM) Sinter Dolomite after 1800°C, fracture surface

The sintering of doloma is mainly controlled by volume diffusion of the oxides CaO and MgO, the impurities in the dolomite rock create also liquid phases which enhance the sintering. Above 1000°C silica (SiO2), iron/manganese oxide ((Fe,Mn)2O3) and alumina (Al2O3) begin to react with the CaO part and form Ca-Silicate (C3S), Ca-Ferrites (C2F / C4AF), Ca-Aluminate (C3A) (see Tables 03 aund 04). The molar ratio CaO / MgO of a pure doloma does not coincide exactly with the eutectic composition in the phase system CaO – MgO. Natural dolomite rocks have always an excess of CaO compared to the stochiometric composition, so that sinters made off them match very well the eutectic point with melting point of 2370°C (Fig. 17.1).



Fig. 17.1: Phase Diagram MgO – CaO Fig. 17.2: Ellingham Diagram MgO – CaO and others

A dolomite rock which is suitable for the manufacturing of doloma refractories must have a high MgO content and a good homogenity. A certain level of so-called impurities is essential to be able to sinter dolomite in a cost efficient way in a shaft or rotary kiln. The optimum lies in a very small area, the (Fe,Mn)2O3 content can vary from 0.5 - 1.6%, the Al2O3 content from 0 – 0.6%. SiO2 is, to a certain extend, indifferent. A content of 1.35% is the maximal level and is equivalent to 5.15% C3S (Table 05). CaO and MgO are the most stable oxides, which can be seen in the Ellingham diagram (Fig. 17.2). This property makes them very suitable for the production of “clean oxygen free steel”. Seen from end-user the dolomite source must be pure as possible. Unless the huge number available of dolomite deposits, only a few of them have naturally the“correct” level of impurities like quartz, pyrite, hematite and clay minerals. Such dolomite rocks are suitable for sintering in a “one-step” process (Process A in Fig. 18). The energy consumption for the firing in a rotary kiln lies around 11.5 kJ / kg. When the dolomite rock is very pure, which is the case for the majority of the American deposits, the firing process is divided into two steps. In the first step in one kiln the dolomite is decarbonated at 1000°C to a caustic dolime. This porous material is briquetted and sintered in second kiln at minimum 1800°C. This “two-step” process has a higher enery consumption of around 15 kJ / kg (Process B in Fig. 18). Besides these common but both energy consuming processes trials have been made to decrease it by direct milling of the raw dolomite stone. The carbonate meal is mixed with additions, briquetted and fired in a one-step process (Process C in Fig. 18).

sinter

dolom

ite

sinter

lime

dolom

itema

gnes

iasin

ter

magn

esia

sinter



Fig. 18A: Process Route A, Direct Manufacturing of Sinter Dolomite

Fig. 18.1: Direct Conversion of Dolomite into Doloma Rotary Kilns Ø 4.4m;110m length; 600 tpd each

Fig. 18B: Process Route B, „two-Step“-Process of Sinter Dolomite

Fig. 18C: Process Route C, Indirect Manufacturing of Sinter Dolomite

4.1 DOLOMA MAGNESIA SINTER, CALCIA, FUSED DOLOMA AND LIME

As raw materials for refractories not only the “classic” sinter doloma is used (Fig. 19). In the system CaO–MgO also the manufacturing of magnesia enriched doloma is possible. Such co-sinters are produced in larger quantities with 55 to 65% MgO mainly in the PR of China and used for stainless steel refractories (Fig. 21). In Japan so-called synthetic doloma sinters with high purity and high density are produced. The process is derived from the “sea-water” magnesia process, instead of the normal “overliming” of the magnesia chloride brines to precipitate Mg(OH)2 only; the lime addition is so high that mix of Ca(OH)2 and Mg(OH)2 co-precipitates. These mixes are dehydrated in Herreshoff kilns, briquetted and futher sinter in high temperature shaft kilns. Such “high-lime” magnesia sinters are manufactured with MgO contents from 70 to 90%. Another special product in the system CaO – MgO can be manufactured by burning and sintering of pure limestone. This calcia sinter could be used in the near future for the lining of converters and ladles in which very pure steels are to produce (Fig. 22). For special applications in the AOD converters, in particular in the tuyere areas fused doloma magnesia is used. This material is manufactured either from a milled mix of dolomite and magnesite (carbonates), or from a milled mix of caustic dolime and caustic magnesia (oxides). These mixes are fused in electic arc furnace at minimum 2500°C. After slow cooling an oxid product with larger CaO and MgO crystals and a structure is created which is visibly different from the “normal” doloma sinter. Fused doloma magnesia products have MgO contents from 55 to 65% (Fig. 20).



Fig. 19: Micrograph (incident light) Sinter Dolomite

Fig. 20: Micrograph (incident light) Fused Doloma

Fig. 21: Micrograph (incident light) Doloma Magnesia Sinter

Fig. 22: Micrograph (incident light) Sinter Lime

5. MANUFACTURING AND PROPERTIES OF DOLOMITE BRICKS

Shaped dolomite refractories have grain size distributions which are tailor-made for the desired application. The standard process route uses kiln running dolomite sinter which is crushed and milled and screened into several fractions. Further new grain size distributions are built-up according the different recipes. For distinct applications it is favourable to replace dolomite fractions by low iron magnesia fractions. According to their different binding system dolomite (magnesia) refractory bricks are divided into two classes, which are made in two different process routes (Fig. 23): • fired direct bonded dolomite bricks • tempered carbon bonded dolomite bricks

The figures 24 and 25 show a SEM micrograph each to compare the different bond.



Fig. 23: Process Schemes for the Production Dolomite Refractories

Fig. 24: Fired direct bonded Dolomite Brick

Fig. 25: Tempered Carbon bonded Dolomite Brick

5.1 FIRED, CERAMIC BONDED DOLOMITE BRICKS

Fired direct bonded dolomite bricks in short also named as “K-bricks” are manufactured in batches in spinner mixers according the recipes together with a temporary wax binder. They are moulded on hydraulic presses with specific forces between 100 and 160 MPa. The so-called green bricks are placed on kiln cars and fired in tunnel kilns at temperatures around 1600°C. By this firing the temporary binder is removed and a ceramic bond is created by the sintering of CaO and MgO crystallites, supported by the small amounts of liquid phases of calcium ferrite and calcium silicates. In figure 25 a pure fired dolomite brick with its direct bond is shown and in figure 26 a fired dolomite magnesia brick with magnesia enrichment in the fine fraction. The typical properties of fired dolomite (magnesia) bricks are shown in the figures 28 to 32.



Fired dolomite and dolomite magnesia bricks have low porosities. Due to their rigid ceramic bond and high thermal expansion coefficient they have only little elasticity. For applications where high thermal shock resistance is needed dolomite zirconia bricks were developed. Almost a small granular addition of zirconia into the dolomite mix gives a remarkable increase of thermal shock resistance (Fig. 30). On firing the added zirconia reacts with CaO part of the dolomite sinter and forms calcium zirconate core (CaZrO3). The MgO part of the dolomite does not react with zirconia and forms a magnesia shell around this core (Fig. 33).

Fig. 26: Fired direct bonded Dolomite Brick

Fig. 27: Fired direct bonded Dolomite Magnesia Brick

Fig. 28: Thermal Properties, Linear Thermal Expansion different Basic Refractories

Fig. 29: Thermal Properties, Thermal Conductivity different Basic Refractories (steady-state Method)

Fig. 30: Hot Mechanical Properties, RuL Fired, direct bonded Dolomite (Magnesia) Bricks

Fig. 31: Hot Mechanical Properties, Creep-under-Load Fired, direct bonded Dolomite (Magnesia) Bricks



Fig. 32: Hot Mechanical Properties, Thermal Shock Resistance Fired Dolomite (Magnesia) (Zirconia) Bricks

Fig. 33: Fired direct bonded Dolomite Zirconia Brick

5.2 TEMPERED, CARBON BONDED DOLOMITE BRICKS

Tempered carbon bonded dolomite bricks in short also named as “C-bricks” are also manufactured in batches in spinner mixers according the recipes together with carbon containing bindes. They are also moulded on hydraulic presses with specific forces between 120 and 180 MPa. Further these bricks are pushed through a tempering furnace at around 300°C to remove the volatiles parts of the binders and to cure them. Carbon bonded dolomite bricks can be improved to better slagging resistance and better elasticity by addition of solid carbon carriers like carbon black or graphite as well as enrichment with high grade magnesia sinters (dolomite magnesia carbon bricks see Fig. 34). All carbon bonded bricks evolve their final carbon bond in the heating-up process in the metallurgical vessels above 600°C. After the release of the volatiles the residual carbon changes above 800°C its structure. Above 1000°C the bricks are changed to a mineral composition of dolomite (magnesia) and solid carbon. Traditionally coal tar pitch was used as binder for tempered dolomite bricks. In the 80’s also synthetic resins were established as binder. In last decade new developed synthetic pitches, either petroleum based or coal tar based, replaced more and more the classic pitch due to the demands to reduce the impacts of polycyclic aromatic hydrocarbons (PAHs) on the working environment (Fig. 35 and 36). Synthetic resins and synthetic pitches have compared to coal tar pitch different chemical structures. If the carbon binder in the bricks changed, the properties are changed as well; this can have advantages but also disadvantages depending on the field of application. The figures 37 to 39 show clearly the different properties of dolomite bricks with different carbon binders when heated-up first. Figure 40 shows the remarkably lower contents of PAHs and B[a]P (Benzo-[a]-Pyren). The lower carbon yield of resins and synthetic pitches must be compensated by the addition of solid carbons like carbon black or graphite.



Fig. 34: Micrograph (incident light) Tempered Carbon bonded Dolomite Brick

Fig. 35: Micrograph (SEM) Pitch bond on coarse Particles, fracture surface

Fig. 36: Micrograph (SEM) Resin bond on coarse Particles, fracture surface

Fig. 37: Hot Mechanical Properties, RuL, Tempered Carbon bonded Dolomite Bricks

Fig. 38: Hot Mechanical Properties, MoR Tempered Carbon bonded Dolomite Bricks



Fig. 39: Thermal Properties, Thermogravimetry Tempered Carbon bonded Dolomite Bricks

Fig. 40: Chemical Analysis, Share of Volatiles, PAHs and B(a)P Tempered Carbon bonded Dolomite Bricks

6. APPLICATION OF DOLOMITE BRICKS

Nearly 90% of the dolomite refractories are used to line metallurgical vessels in the steel industry. The remaining 10% are used in the cement, lime and dolomite industry to line rotary and shaft kilns. In the tables 06 and 07 the most important physical and chemical properties of fired direct bonded brick grades are compiled as well those of tempered carbon bonded brick grades together with their dedicated applications.

6.1 PIG IRON TRANSPORT

For a long period until the 90’s pig iron was desulphurated in the torpedo cars on its way from the blast furnaces to the BOF shops. The best adopted wear lining for this application were dolomite bricks. With the switch to desulphurate the pig iron direct in blast furnace a basic dolomite lining got obsolete, nowadays 100% of the torpedo car are lined with fired and carbon bonded alumina bricks.

6.2 PRIMÄRY METALLURGY

Despite the invention of Sir Thomas and the long use dolomite bricks in BOF shops the process development there reduced the application in the 80’s significantly. The main reasons were increased tapping temperatures and higher content of iron oxide in the slags. Further the speed-up of the BOF process by bottom purging with argon or nitrogen and finally the application foam slag. IN the 90’s still some converters in Europe were lined partially with carbon bonded dolomite bricks but today all BOF converters are lined completely with high grade magnesia carbon bricks. In EAFs carbon bonded dolomite bricks are used wall linings and monolithic dolomite (magnesia) mixes in hearth. Today the new ultra high power furnaces (UHP) the wall lining consists magnesia carbon bricks. Only in small EAFs for casting of high grade special steels dolomite is still used in the whole furnace.

Volat

iles

PAH

B[a]

P

1

10

100

1000

10000

100000

SINDOFORM T

SINDOFORM C

SINDOFORM R

shar

e/ m

g · k

g-1(p

pm)



6.3.1 SECONDARY METALLURGY, AOD CONVERTER

Stainless steel converters are usually lined with fired bricks. Since the 80’s the wear linings of European converters consist in their majority fired direct bonded dolomite and dolomite magnesia bricks. Also in USA and Japan the general trend is to switch from magnesia chrome to dolomite magnesia linings. The reason for the excellent performance of dolomite linings is in the AOD process of chrome-alloyed steels itself. The recovering of chrome from the decarburisation slag needs a strong basic environment and subsequent desulphuristion step also needs basic slags; both process steps are naturally supported by the CaO part of the dolomite (magnesia) lining. The tuyere zone is due to extreme high temperatures (above 2300°C in the decarburisation step) the part with highest specific wear. Therefore special fired dense dolomite magnesia bricks with fused grain (doloma magnesia) and zirconia addition were developed, which give nowadays a well balanced lining despite the high and different wear rates (Fig 43 and table 07). The total specific wear in AOD converters is in the range of 10 to 15 kg refractories per ton processed. The total residence times are between 80 and 130 hours.

Fig. 43: Principal Lining Sketch of an AOD Converters with Dolomite and Dolomite Magnesia Bricks

6.3.2 SECONDARY METALLURGY, LADLE METALLURGY AND REFINING

The steadily increasing demands for very clean steel grades and the increasing share of refined and vacuum treated melts have triggered the demand for basic ladle linings. Basic dolomite linings enable to process steel melts with low levels of oxygen, silicon and sulphur. The CaO part of a dolomite lining prevents reoxidation and resulpurisation. In transfer ladles are used to convey the steel from the EAF to the AOD converter normally no treatment takes place. The lining is exposed to hot steel with very long residence times. The wear lining is usually fired direct bonded dolomite bricks or tempered carbon bonded dolomite bricks (depending on the



carbon levels of the steel processed). In the impact area a higher lining thickness is the countermeasure for the higher specific wear rate. The same lining conception is used in argon purged teeming ladles where the steel is homogenized. In both ladle ladle types service lives from 40 to 180 melts are reached. In refining and furnace ladles (LF) the wear depends significantly on the process route applied. The very different specific wear rates in the bottom, barrel and slag line are balanced by sophicated zoned lining design. In the barrel and bottom in majority temperaed carbon bonded dolomite bricks are installed, in the slag lines adequate adopted magnesia carbon or dolomite magnesia carbon bricks are used. In steel plants where ultra low carbon steel ULCs are produced the LF ladles are lined with carbon free fired direct bonded dolomite bricks (Fig. 44 and table 06).

Fig. 44: Principal Lining Sketch of a VOD Ladle with Dolomite and Dolomite Magnesia Bricks

6.3.3 SECONDARY METALLURGY, CONTINIOUS CASTING

Steel plants producing aluminium-killed stainless or carbon steel quite often observe “clogging” in the submerged entry nozzles of the casting machine. These desposition can block the flow through the nozzle and cause severe problems. Eventually the melt gets too cold has to be re-treated. The clogging depositions are often low melting calcium aluminates (C12A7 and CA) which react with alumina of the nozzle and form high melting calcium aluminates (CA2 and CA6). To avoid this clogging mechanism doloma graphite nozzles have been developed. The CaO in dolomite changes not the low melting calcium aluminates into other mineral phases which can block the bore in the nozzle (see Fig. 45).



Fig. 45: Different SEN’s after use, left and middle alumina graphite “clogged” tubes right dolomite graphite nozzle without clogging

7.1 ADDITIONAL INFORMATIONS – PACKAGING OF DOLOMITE BRICKS

Since more than 50 years dolomite bricks are successful used in the steel and in the cement industry. This success was not only based on development of new brick grades. It was also much supported by the development of a appropriate packaging, which allows that the bricks came in perfect condition to the customer and may be stored there also for certain period of time. In the 60’s up to the 90’s of the last century fired bricks were additionally impregnated with tar to prevent the hydration of the CaO part of the dolomite sinter. For some special applications in the steel industry even a vacuum impregnation and re-tempering was done in order to create a fine pore structure which is infiltration resistant against low viscous high iron oxide slags. After the millennium this practice was given up completely due to regulations against uncontrolled release of PAHs. Today most of the dolomite products are delivered in vacuum sealed wrap foils in which allow a long term storage. Shelf lives up tp 5 years even in countries with hot and humide climate are possible when to packaging is not damaged before. When the packaging is opened once the bricks are to install promptly (Fig. 46).



Fig. 46: ALUVAC Packaging No. 16 for Bricks (LWB)

7.2 ADDITIONAL INFORMATIONS – WEAR MECHANIMS BY SLAGS ON DOLOMITE BRICKS

The wear of dolomite bricks is to deal here only in short. The second part of the seminar is dedicated to wear mechanisms in detail. The wear of dolomite bricks depend generally on the brick grade, the metallurgical process and place were the brick is used. The detailed wear mechanisms are complex due to the interaction of refractories and process. Nevertheless the wear of dolomite bricks has three main factors: • destruction of brick structure by oxidation of the carbon bond (only C–bricks) • reaction of the brick material with slags (K– and C–bricks) • mechanical overload of the bricks (K– and C–bricks)

An overview on the wear mechnisms of dolomite bricks is shown in figure 47.

Fig. 47: Wear Mechanisms of fired direct bonded Dolomie Bricks and Carbon bonded Bricks Dolomite (Magnesia) Carbon Bricks

Fired, direct bonded brick

brick surface slaginfiltration

densified infiltration zone

reactionslag / brick

texturaldecomposition

thermal shockrecrystallisation

facture formation

thermal shockmechanical stresses

spallingWear of 10 - 50 mm brick

Carbon bonded brick

brick surfaceburn-out byslag / gases

soft,decarburized zone

slaginfiltration

reactionslag / brick

densifiedinfiltration zone

dissolution or slabbingWear of 0.1 -1 mm brick



The CaO part in the sinter dolomite has a high basicity which drives the reaction with metal oxides in the slag. Some of mineral phases were already presented in Table 04: calcium silicates, calcium ferrites and calcium aluminates. Which mineral phases are formed depends first on the iron / manganese oxide content and on the alumina content, then on the silicate content and finally on the lime-silica-ratio in the slag. Unfavourable for dolomite bricks are always high levels of these oxides. The figures 48 and 49 show two typical wear mechanisms of dolomite bricks. Fig. 45 shows a micrograph of dolomite brick which has been in contact with a slag high in iron oxide. It is to recognize an upper reaction zone (top = hot face) and a second reaction zone underneath. In the upper reaction zone is the CaO part of sinter dolomite completely converted into calcium ferrite (C2F / C4AF), the MgO part is partially converted into magnesia ferrite (MF). The original structure of the dolomite sinter is completely destroyed. In the deeper second reaction zone the CaO part is only partially converted into calcium ferrites and calcium silicates, the MgO part is still unchanged. The micrograph in figure 46 shows the impact of a slag with high silica and high alumina content on a dolomite brick. In the thin upper section (top = hot face) the initial slag is visible, in the middle section shows a reaction zone, the lower section shows unchanged sinter dolomite. In the reaction zone the CaO part has completely reacted with the slag and formed calcium aluminates and calcium silicates, the MgO part is unchanged; nevertheless the structure of the sinter dolomite is destroyed.

Fig. 48: Micrograph (incident light) Dolomite Brick after Use, hot face section, Final BOF Slag

Fig. 49: Micrograph (incident light) Dolomite Brick after Use, hot face section, Desulphuration Slag

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8. TA

BLES

AND

ILLU

STRA

TION

S

Tabl

e 01:

Pr

oper

ties o

f raw

and

sinte

r dol

omite

ra

w do

lomite

Ha

gen /

D

min

eral

Dolo

mite

sin

ter do

loma

Hage

n / D

sin

ter d

olom

a Yo

rk / U

S sin

ter d

olom

a Na

mur

/ B

min

erals

Do

lom

a Ch

emica

l Com

posit

ion

Loss

on

Igni

tion

ma

ss %

47

,30

0,3

6 0,2

4 0,3

0

MgO

ma

ss %

32

,20

21,87

38

,96

39,94

38

,19

41,82

Ca

O

mass

%

19,90

30

,41

58,83

57

,91

59,15

58

,18

SiO 2

ma

ss %

0,1

5

0,81

0,77

0,89

(F

e,Mn)

2O3

mass

%

0,34

1,1

3 0,8

9 0,8

1

Al2O

3 ma

ss %

0,2

7

0,53

0,42

0,54

ot

her o

xides

ma

ss %

0,0

4

0,08

0,07

0,06

Mine

ralo

gica

l Com

posit

ion

M + C

+ C 3

S + C

2S

mass

%

n.a.

n.a.

96,9

97,6

97,5

100,0

C 2

F + C

4AF

+ C3A

ma

ss %

n.a

. n.

a. 3,1

2,4

2,5

0,0

Phys

ical P

rope

rties

tru

e den

sity

g / cm

³ 2,8

5 2,8

6 3,4

2 3,4

2 3,4

2 3,4

2 bu

lk de

nsity

g /

cm³

2,76

3,2

2 3,2

5 3,2

3

appa

rent

por

osity

vo

lume %

1,6

5,8

5,0

5,6

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-Sem

inar I

S-20

15

Tabl

e 02

Chem

ical P

roce

sses

on

Firin

g an

d Si

nter

ing

of R

aw D

olom

ite

Raw

Dolo

mite

Ca

Mg(C

O 3) 2

800°

C ⇒

Se

mi B

urnt

Dol

omite

Ca

CO3 +

MgO

+ CO

2 Se

mi B

urnt

Dol

omite

Ca

CO3 +

MgO

10

00°C

⇒

Ca

ustic

Dol

omite

Ca

O + M

gO +

CO2

Caus

tic D

olom

ite

CaO

+ MgO

18

00°C

⇒

Si

nter

Dol

omite

Ca

O + M

gO

Tabl

e 03

Mine

ral C

onve

rsio

ns o

n Si

nter

ing

of R

aw D

olom

ite

CaO,

SiO

2 , 12

00°C

⇒

Ca2S

iO4

Ca3S

iO5

C 2S

C 3S

CaO,

Fe 2

O 3

CaO,

Al 2O

3, Fe 2

O 3

CaO,

Al 2O

3 , 14

00°C

⇒

Ca2F

e 2O 5

Ca

4Al 2F

e 2O 1

0 Ca

3Al 2O

6

C 2F

C 4AF

C 3

A Ca

O, M

gO

1800

°C ⇒

Ca

O, M

gO

C, M

VDEh

-Sem

inar

Refra

ctory-

Tech

nolog

y Pa

rt 1

Refra

ctorie

s and

Slag

s in t

he M

etallu

rgy

Di

pl.-G

eol. J

. Har

tens

tein

Dolo

mite

Ref

ract

ories

in th

e Ste

el In

dust

ry

VDEh

-Sem

inar I

S-20

15

Page

21

Tabl

e 04

Mine

rals

in S

inte

r Dol

omite

– Pr

oper

ties

Nam

e Ch

emica

l For

mul

a Se

ger

Form

ula

Melti

ng

Poin

t (°C

) Mo

rpho

logy

Ma

ss S

hare

(%

) Pe

riclas

e Mg

O M

2800

idi

omor

phic,

roun

ded

38 -

42

Lim

e Ca

O C

2570

idi

omor

phic,

roun

ded

55 -

62

Alite

3 C

aO ·

SiO 2

C 3

S 20

70

lamell

ar, x

enom

orph

ic 0 -

10

Dica

lcium

ferri

te

2 CaO

· Fe

2O3

C 2F

1445

xe

nomo

rphic

0 -

5 Br

ownm

illerit

e 4 C

aO ·

Al2O

3 · F

e 2O 3

C 4

AF

1395

xe

nomo

rphic

0 -

5 Tr

icalci

umalu

min

ate

3 CaO

· Al

2O3

C 3A

1535

xe

nomo

rphic

0 -

1

Tabl

e 05

Fact

ors f

or S

inte

rabi

lity o

f Raw

Dol

omite

Sto

ne

Typi

cal D

epos

it Mg

O-Sh

are

> 18

.0 %

Im

purit

y Con

tent

0.5

%<

( SiO

2 + F

e 2O 3

+ A

l 2O3

) < 1.

5 %

Impu

rity D

istrib

utio

n ho

moge

ne; n

o con

centr

ation

s; no

veins

Cr

ysta

l Size

s ho

moge

ne; <

0,20

0 mm

Poro

sity

< 10

Vol.

%

Stre

ngth

of R

aw S

tone

hig

h St

reng

th o

f Cau

stic

mat

erial

su

fficien

t

Typi

cal P

roce

ss

Kiln

Typ

e Ro

tary K

iln

Shaft

Kiln

Fu

el Co

al Du

st / O

il Ga

s / O

il Si

ngle

Firin

g 20

to 50

mm

or 6

to 20

mm

20 to

50 m

m or

6 to

20 m

m Do

uble

Firin

g Ca

ustic

Briq

uette

s Ca

ustic

Briq

uette

s Si

nter

ing

Prom

otio

n Ad

mix o

f Impu

rities

hig

h Ash

Coa

l

VDEh

-Sem

inar

Refra

ctory-

Tech

nolog

y Pa

rt 1

Refra

ctorie

s and

Slag

s in t

he M

etallu

rgy

Di

pl.-G

eol. J

. Har

tens

tein

Dolo

mite

Ref

ract

ories

in th

e Ste

el In

dust

ry

Page

22

VDEh

-Sem

inar I

S-20

15

Tabl

e 06.1

: Pr

oper

ties o

f fire

d, ce

ram

ic bo

nded

dol

omite

-mag

nesia

bric

ks

main

appl

icatio

n

Ladl

e AO

D / V

OD

lower

cone

ba

rrel

AOD

lower

cone

ba

rrel

AOD

/ VOD

sla

g zon

e AO

D tuy

ere p

ad

AOD

tuyer

e pad

AO

D tuy

ere b

rick

AOD

/ VOD

sla

g zon

e

mat

erial

s use

d sin

ter d

olom

a sin

ter d

olom

a sin

ter m

agne

sia

sinte

r dol

oma

fuse

d m

agne

sia

fuse

d do

lom

a fu

sed

mag

nesia

Chem

ical C

ompo

sitio

n Mg

O

mass

%

40,0

40,0

55,0

59,0

64,0

65,5

65,0

74,0

CaO

ma

ss %

58

,0 58

,0 43

,0 39

,0 33

,0 32

,5 33

,0 24

,0 Si

O 2

mass

%

0,8

0,8

0,7

0,6

0,8

0,5

0,7

0,6

(Fe,M

n)2O

3 ma

ss %

0,6

0,6

0,6

0,5

0,6

0,5

0,7

0,6

Al

2O3

mass

%

0,5

0,5

0,4

0,4

0,4

0,5

0,5

0,5

Phys

ical P

rope

rties

bu

lk de

nsity

g /

cm³

2,850

2,9

00

2,925

2,9

50

2,975

3,0

00

3,000

3,0

00

appa

rent

por

osity

vo

lume %

15

,0 13

,5 13

,0 13

,0 12

,5 12

,0 13

,0 13

,0 co

ld cr

ushi

ng st

reng

th

MPa

60

60

70

60

70

70

70

80

perm

eabi

lity

µm²

1,5

0,4

0,2

0,3

0,2

0,3

0,3

0,2

Ther

mo

Mech

anica

l Pro

perti

es

refra

ctor

ines

s-un

der-l

oad

T 05

°C

1400

14

30

1540

15

70

1650

16

80

> 170

0 > 1

700

cree

p-in

-com

pres

sion

Z 10 @

1500

°C

%

12

10

7,5

5 4

3 2

2

VDEh

-Sem

inar

Refra

ctory-

Tech

nolog

y Pa

rt 1

Refra

ctorie

s and

Slag

s in t

he M

etallu

rgy

Di

pl.-G

eol. J

. Har

tens

tein

Dolo

mite

Ref

ract

ories

in th

e Ste

el In

dust

ry

VDEh

-Sem

inar I

S-20

15

Page

23

Tabl

e 06.2

: Pr

oper

ties o

f uns

hape

d do

lom

a and

dol

oma-

mag

nesia

pro

duct

s

main

appl

icatio

n

EAF

botto

m

EAF

botto

m

EAF

repa

ir co

nver

ter-l

adle-

fla

nge

how

to u

se

dry f

ill dr

y fill

dry f

ill dr

y fill

ramm

ing

plasti

c ra

mming

dr

y fill

bond

ing

ce

rami

c ce

rami

c ce

rami

c ce

rami

c ce

rami

c or

ganic

ca

rbon

ce

rami

c

mat

erial

s use

d

sinte

r dol

oma

sinte

r dol

oma

sinte

r mag

nesia

sin

ter d

olom

a sin

ter d

olom

a

Chem

ical C

ompo

sitio

n Mg

O

mass

%

38,0

54,0

74,0

77,0

36,0

40,0

39,0

39,0

CaO

ma

ss %

58

,0 42

,0 23

,0 17

,5 49

,0 56

,0 58

,0 58

,5 Si

O 2

mass

%

2,0

1,0

0,9

3,0

1,5

2,0

1,0

1,0

(Fe,M

n)2O

3 ma

ss %

1,0

2,0

0,6

2,0

8,0

1,0

1,0

0,8

re

sidua

l car

bon

cont

ent

mass

%

1,5

Phys

ical P

rope

rties

gr

ain si

ze

mm

0 - 4

0 - 8

0 - 8

0 - 8

0 - 4

0 - 5

0 - 8

0 - 4

requ

ired

mat

erial

kg

/ m³

1600

22

00

2400

24

00

2000

28

00

2700

16

00

VDEh

-Sem

inar

Refra

ctory-

Tech

nolog

y Pa

rt 1

Refra

ctorie

s and

Slag

s in t

he M

etallu

rgy

Di

pl.-G

eol. J

. Har

tens

tein

Dolo

mite

Ref

ract

ories

in th

e Ste

el In

dust

ry

Page

24

VDEh

-Sem

inar I

S-20

15

Tabl

e 07:

Pr

oper

ties o

f car

bon

bond

ed d

olom

a and

dol

oma-

mag

nesia

bric

ks

main

appl

icatio

n lad

le - b

arre

l / bo

ttom

co

nver

ter -

upp

er co

ne

ladle

- bar

rel /

botto

m

conv

erte

r - b

otto

m

ladle

- slag

zone

lad

le - b

arre

l

mat

erial

s use

d sin

ter d

olom

a sin

ter d

olom

a gr

aphi

te

sinte

r dol

oma /

sint

er m

agne

sia

grap

hite

carb

on ca

rrier

co

ked

bind

er

coke

d bi

nder

ca

rbon

blac

k co

ked

bind

er

grap

hite

co

ked

bind

er

grap

hite

co

ked

bind

er

grap

hite

co

ked

bind

er

carb

on b

lack

coke

d bi

nder

gr

aphi

te

coke

d bi

nder

gr

aphi

te

Chem

ical C

ompo

sitio

n Mg

O

mass

%

39,0

39,0

58,0

39,0

39,0

58,0

56,0

64,0

CaO

ma

ss %

59

,0 59

,0 39

,0 59

,0 59

,0 39

,0 41

,0 33

,0 Si

O 2

mass

%

0,8

0,8

0,9

0,8

0,8

0,9

1,0

0,8

(Fe,M

n)2O

3 ma

ss %

0,8

0,8

0,9

0,8

0,8

0,9

0,7

0,8

Al

2O3

mass

%

0,5

0,5

0,5

0,5

0,5

0,3

0,3

0,2

resid

ual c

arbo

n co

nten

t ma

ss %

2,5

4,0

5,0

7,0

9,0

5,0

9,0

8,0

Phys

ical P

rope

rties

– as

ship

ped

= (A

) bu

lk de

nsity

(A

) g /

cm³

2,900

2,9

10

2,920

2,8

90

2,880

2,9

60

2,940

2,8

90

cold

crus

hing

stre

ngth

(A

) MP

a 40

40

40

30

25

30

25

30

Phys

ical P

rope

rties

– af

ter c

okin

g 2h

@ 10

00°C

= (V

) bu

lk de

nsity

(V

) g /

cm³

2,860

2,8

40

2,890

2,8

70

2,850

2,9

50

2,900

2,8

60

appa

rent

por

osity

(V

) vo

lume %

12

,0 13

,0 10

,5 10

,5 11

,0 11

,0 10

,0 11

,0 co

ld cr

ushi

ng st

reng

th

(V)

MPa

50

45

50

40

30

40

35

30

Voluntary lecture for interested: Dolomite Refractories … Refractory-Technology Part 1...

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Transcript of Voluntary lecture for interested: Dolomite Refractories … Refractory-Technology Part 1...