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Magnesia-carbon refractories for the lining of gasification chambers: technical capabilities and limitations

M. Hampel*, P. Gehre, T. Schemmel, C.G. Aneziris

5th International Freiberg Conference on IGCC & XtL Technologies21 – 24 May 2012, Leipzig

TU Bergakademie Freiberg I Institut für Keramik, Glas- und BaustofftechnikDeutsches EnergieRohstoff-Zentrum I Agricolastraße 17 I 09596 Freiberg

Telefon +49 (0) 3731 39 - 4036 I Fax +49 (0) 3731 39 - 2419 I www.energierohstoffzentrum.de

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Gasification Chambers with brick lining

S. Stoye, 2009

T = 1200 – 1600 °C

p = 25 – 40 bar

liquid slag

alkaline corrosion

atmosphere CO, H2, CO2, H2O

C + H2O(g) CO + H2

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Why not using Magnesia-carbon refractories for the lining of gasification chambers?

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Properties of MgO-C-refractories

Raw Materials

Magnesia (sintered or fused with purity up to 98 %)

Graphite (purity up to 95 %)

Bonding agent (phenolic resin or coal tar pitch)

Additives for manipulation of properties:

Metals: Al, Mg, Si, …

Carbides and Nitrides: SiC, B4C, …

Oxides: Al2O3, ZrO2, …

Fibres: carbon, heat resisting steel

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Properties of MgO-C-refractories

Strength

Franklin et al: British Ceramic Transactions 94 (1995) 4, pp. 151-156.

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Properties of MgO-C-refractories

Thermal Conductivity

Zoglmeyer: Stahl und Eisen 100 (1980) 15, pp. 822-832.

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Properties of MgO-C-refractories

Creep under Load

Jansen et al: IAS Steelmaking Seminar, Buenos Aires (2001) pp. 315-322.

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Properties of MgO-C-refractories

Density and Porosity respectively

Porosity is caused by

manufacturing process (incomplet filled pores)

cracking of organic bonding agent (into volatiles and carbon)

expansion or shrinkage (most it is insignificant)

chemical reactions of additives

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Properties of MgO-C-refractories

Density and Porosity respectively

the average porosity of standard bricks is approx. 8…10 %

nearly no closed pores

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Wear of MgO-C-bricks in metallurgical converters and ladles

The complex interaction of brick and melt

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Magnesia brick without Carbon

good wettability of bricks

high infiltration depth of slag

pick up of iron oxide of magnesia (formation of MgO·FeO)

increasing viscosity of slag

but: creep of refratory lining

and: structural spalling due to changing the temperature

Wear of MgO-C-bricks in metallurgical converters and ladles

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Magnesia-Carbon-Brick

poor wettability of bricks

low infiltration depth of slag

reduction of iron oxide to metallic iron

CaO·FeO·SiO2 Eutectic ~ 1300°C

CaO·SiO2 + Fe Eutectic > 1650°C

increasing viscosity of slag

protective layer for preventation of oxidation of carbon

increasing of lining lifetime

Wear of MgO-C-bricks in metallurgical converters and ladles

+ Carbon

Mörtl et al: Berg- und Hüttenmännische Monatshefte 137 (1992) pp. 196.

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+ Carbon

Barthel: Stahl und Eisen 86 (1966) pp. 81.

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Refractoriness of MgO-C-bricks

is limited by carbothermic

reaction

MgO(s) + C(s) → Mg(g) + CO(g)

1830°C at atmospheric pressure

gasification of bricks

higher pressures are

advantageous for the stability

Thermodynamic stabilityof MgO-C-bricks

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The alkaline corrosion of MgO-C-bricks

1 bar

vapor-pressure

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The alkaline corrosion of MgO-C-bricks

MgO-C-Crucible height 50 mm x diameter 50 mm

Alkaline sample

Encapsulation by dense refractory castable

Test procedure

firing embedded in coke grit

100 hours at 1100°C / 1500°C

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The alkaline corrosion of MgO-C-bricks

variation of the kind of alkaline salt

coarse grain and fine grain refratories with 10 wt.-% graphite

100 hours / 1100°C

KCl

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The alkaline corrosion of MgO-C-bricks

variation of the kind of alkaline salt

coarse grain and fine grain refratories with 10 wt.-% graphite

100 hours / 1100 C

KCl K2CO3

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The alkaline corrosion of MgO-C-bricks

variation of the kind of alkaline salt

coarse grain and fine grain refratories with 10 wt.-% graphite

100 hours / 1100 C

KCl K2CO3 Na2CO3

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The alkaline corrosion of MgO-C-bricks

variation of the kind of alkaline salt

coarse grain and fine grain refratories with 10 wt.-% graphite

100 hours / 1100 C

KCl K2CO3 Na2CO3 K2SO4

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The alkaline corrosion of MgO-C-bricks

variation of temperature

coarse grain refratories with 10 wt.-% graphite

K2CO3 for 100 hours

1100 C 1500 C

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The alkaline corrosion of MgO-C-bricks

variation of graphite content

coarse grain refratory samples

K2CO3 for 100 hours / 1100 C

15 wt.-% 10 wt.-% 5 wt.-%

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Magnesia

sodium and potassium seems to be not critical

formation of sulfates < 1050 C

bursting

Graphite

potassium: formation of C8K, C16K, …

bursting

sodium: no appreciable reaction

The use of other carbon sources seems to be successfull.

The alkaline corrosion of MgO-C-bricks

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e.g.: basic electric filter ash, basicity ~ 2,0

1500°C / 10 hours / CO-atmosphere

slags with other basicities and alkaline contents

show comparably behaviour

The corrosion of MgO-C-bricks by coal slag

Oxide wt.-% Oxide wt.-%

CaO 36,0 Al2O3 2,0

SiO2 26,1 K2O 0,5

SO3 14,0 TiO2 0,2

Fe2O3 9,0 P2O5 0,2

MgO 8,5 MnO 0,1

Na2O 3,3 BaO 0,1

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Limitations of the application of MgO-C-refractories

the possible gasification of the carbon source of the bricks

depends on temperature of the lining

the formation of protective layers (glaze, slag) is possible

the hydration of the magnesia leads to bursting

depends on temperature and partial pressure of water

large crystal and grain sizes are more stable

dry installation of lining

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AcknowledgmentThis publication has been funded by the German Centre for Energy Resources, support code

03IS2021A. We would like to thank the Federal Ministry for Education and Research (BMBF) and our

partners from the industry for funding this project.