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

Transcription

1 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 Technologies May 2012, Leipzig TU Bergakademie Freiberg I Institut für Keramik, Glas- und Baustofftechnik Deutsches EnergieRohstoff-Zentrum I Agricolastraße 17 I Freiberg Telefon +49 (0) I Fax +49 (0) I 1

2 Gasification Chambers with brick lining C + H 2 O (g) CO + H 2 T = C p = bar liquid slag alkaline corrosion atmosphere CO, H 2, CO 2, H 2 O S. Stoye,

3 Why not using Magnesia-carbon refractories for the lining of gasification chambers? 3

4 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, B 4 C, Oxides: Al 2 O 3, ZrO 2, Fibres: carbon, heat resisting steel 4

5 Properties of MgO-C-refractories Strength Franklin et al: British Ceramic Transactions 94 (1995) 4, pp

6 Properties of MgO-C-refractories Thermal Conductivity Zoglmeyer: Stahl und Eisen 100 (1980) 15, pp

7 Properties of MgO-C-refractories Creep under Load Jansen et al: IAS Steelmaking Seminar, Buenos Aires (2001) pp

8 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 8

9 Properties of MgO-C-refractories Density and Porosity respectively the average porosity of standard bricks is approx % nearly no closed pores 9

10 Wear of MgO-C-bricks in metallurgical converters and ladles The complex interaction of brick and melt 10

11 Wear of MgO-C-bricks in metallurgical converters and ladles 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 11

12 Wear of MgO-C-bricks in metallurgical converters and ladles Magnesia-Carbon-Brick poor wettability of bricks low infiltration depth of slag reduction of iron oxide to metallic iron CaO FeO SiO 2 Eutectic ~ 1300 C + Carbon CaO SiO 2 + Fe Eutectic > 1650 C increasing viscosity of slag protective layer for preventation of oxidation of carbon increasing of lining lifetime Mörtl et al: Berg- und Hüttenmännische Monatshefte 137 (1992) pp

13 + Carbon Barthel: Stahl und Eisen 86 (1966) pp

14 Thermodynamic stability of MgO-C-bricks 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 14

15 The alkaline corrosion of MgO-C-bricks vapor-pressure 1 bar 15

16 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 16

17 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 17

18 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 K 2 CO 3 18

19 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 K 2 CO 3 Na 2 CO 3 19

20 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 K 2 CO 3 Na 2 CO 3 K 2 SO 4 20

21 The alkaline corrosion of MgO-C-bricks variation of temperature coarse grain refratories with 10 wt.-% graphite K 2 CO 3 for 100 hours 1100 C 1500 C 21

22 The alkaline corrosion of MgO-C-bricks variation of graphite content coarse grain refratory samples K 2 CO 3 for 100 hours / 1100 C 15 wt.-% 10 wt.-% 5 wt.-% 22

23 The alkaline corrosion of MgO-C-bricks Magnesia sodium and potassium seems to be not critical formation of sulfates < 1050 C bursting Graphite potassium: formation of C 8 K, C 16 K, bursting sodium: no appreciable reaction The use of other carbon sources seems to be successfull. 23

24 The corrosion of MgO-C-bricks by coal slag e.g.: basic electric filter ash, basicity ~ 2, C / 10 hours / CO-atmosphere Oxide wt.-% Oxide wt.-% CaO 36,0 Al 2 O 3 2,0 SiO 2 26,1 K 2 O 0,5 SO 3 14,0 TiO 2 0,2 Fe 2 O 3 9,0 P 2 O 5 0,2 MgO 8,5 MnO 0,1 Na 2 O 3,3 BaO 0,1 slags with other basicities and alkaline contents show comparably behaviour 24

25 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 25

26 Acknowledgment This publication has been funded by the German Centre for Energy Resources, support code 03IS2021A. WewouldliketothanktheFederalMinistry for Education and Research (BMBF) and our partners from the industry for funding this project. 26