A Novel Model for Drying Refractory Castables
45219 Essen, Germany
Revision 09.10.2009, 22.01.2010
Volume 2, Issue 2, Pages 99-106
Abstract
Objective of this research is to optimize the time course of the temperature increase during the drying of refractory castables so as to avoid spalling as a consequence of vapour explosion. The heating rate k should be selected so that the temperature curve in the castable is as flat as possible. In the first heating period t the integral mean value of the temperature profile in the refractory castable ϑIMV should remain < 200 °C, until the cold face of the castable exceeds 110 °C. With this proviso, k can be calculated approximately: If ϑa = 30 °C (temperature at the beginning of drying), ϑIMV = 150 °C (estimated); L = 0,2 m (thickness of the castable); t = 86 400 s (24 h) (time of first heating); a = 9 ⋅ 10-7 m²/s (temperature conductivity of the castable), so according to Eq. (01) results ϑ0 = 210 °C (surface temperature after first heating). It follows from Eq. (02) that the heating rate k = 0,0021 K/s (7,5 K/h) (cf. Fig. 6 black temperature curve). With this value k heating should continue. Empirical values determined in practice should be inserted in Eqs. (01 and 02). They only apply to slow heating and times > 3 h.
Keywords
drying, spalling, refractory castables, heating rate, temperature conductivity, calculation of drying parametersrnrn
References
1] Junge, K.; Telljohann, U.: Trocknung von Ziegelrohlingen – Einfluss der Feuchteleitfähigkeit auf Schwindungsfortschritt und Trocknungsverlauf. ZI-Jahrbuch (2005) 21 ff.
[ 2] Junge, K.; Tretau, A.: Energieaufwand zur Rohlingstrocknung in Kammertrocknern. ZI-Jahrbuch (2007) 25 ff.
[ 3] Großwendt, I.: Modell zur Beschreibung der Trocknung von Feuerbetonen. Dr.-Ing. Diss. 2007, RWTH Aachen
[ 4] Akiyoshi, M.M.; Cardoso, F.A.; Innocenti, M.D.M.; Pandolfelli, V.C.: Key properties for the optimization of refractory castable drying. Refr.Applications and News 9 (2004) [4] 14–16
[ 5] Innocenti, M.D.M.; Miranda, M.F.S.; Cardoso, F.A.; Pandolfelli, V.C.: Vaporization process and pressure bild-up during dewatering of dense refractory castable. J. Am. Ceram. Soc. 86 (2003) 1500–1503
[ 6] Gerthsen, C.; Meschede, D.: Physik. Springer, 2005
[ 7] Reid, R.G.; Prausnitz, J.M.; Poling, B.E.: The properties of gases and liquids. Mc Graw-Hill, (1989) 208–209
[ 8] Junge, K.: Daten zur feuchten Luft-Trockungstechnik. ZI-Jahrbuch (1996) 128–137
[ 9] Bird, R.B.; Stewart, W.E.; Lightfoot, E.N.: Transport phenomena. J. Whiley Sons, N.Y. (1960) 541
[10] Grunewald, J.: Vorl. “Bauphysik”, TU Dresden, 2009
[11] Abe, H.: Drying mechanism of castable refractories. J. Techn. Ass. Refractories, Japan 23 (2003) [3] 164–170
[12] Abe, H.: The effect of permeability on the explosion of castables during drying. J. Techn. Ass. Refractories, Japan 24 (2004) [2] 115–119
[13] Block, F.R.; Geber, H.; Gross, C.; Pernot, J.; Zografou, C.: Temperatur und Trocknungsüberwachung bei der Herstellung monolithischer Bauteile. Proc. 37. Int. Colloquium on Refractories, Aachen,1994, pp. 210–217
[14] Schmitz, W.; Bank, H.; Block, F.R.; Geber, H.; Groß, C.; Manga, D.; Maier, H.R.; Franken, K.; Metzlaff, K.: Messtechnische Überwachung des Aufheizens und Trocknens der feuerfesten Zustellung. Proc. 38. Int. Colloquium on Refractories, Aachen,1995, 48–56
[15] Carlslaw, H.S.; Jaeger, J.C.: Conduction of heat in solids. Oxford Univ Press, 2. Ed., 1959
[16] Volmer, M.: Kinetik der Phasenbildung. Steinkopf, Dresden, 1939, S. 161
[17] Pötschke, J.: Entstehung und Verhalten von Ausscheidungen bei der Erstarrung. In: Erstarrung metallischer Schmelzen. DGM 1981, S. 221–231
[18] Routschka, G.: Refractory Materials, 2. Ed., Vulkan Verlag, Essen
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