This page contains a Flash digital edition of a book.
TECHNICAL PAPER


Apart from density, the thermal conductivity is also a focal point in insulating lining concepts. The thermal conductivity of the vibration castables is given in figure 6 and for the patch mixes in figure 7. In general the thermal conductivity for all mixes is low. The higher the content of SLA-92 in the formulation, and the lower the density, the lower the thermal conductivity which is measured. The same applies for the patch mixes. Because of the 90% content of SLA-92 in PATCH SLA 1 the thermal conductivity is = 0.3 W/m·K up to 1200°C. The thermal conductivity of CA6


23


SLA-92 castables higher per-firing temperatures as applied in pevious investigations [4,5] achieved a thermal shock resistance of more than 10 cycles. Such thermal shock resistance for an insulating material is outstanding when compared to classical insulating bricks or castables.


based castables can be adjusted in the range from approximately 0.25 to 2.0 W/mK (figure 8) by blending the two aggregates SLA-92 and Bonite, and by modifications of the castable matrix.


Figure 9: Thermal shock resistance of CA6


based vibration castables Figure 6: Thermal conductivity of CA6 based vibration castables pre-fired at 1000°C/5h


A comparison of the raw material costs for the different castable concepts is shown in figure 9. Instead of cost per tonne, the cost per cubic metre of lining was calculated. This approach is more common for insulating refractory applications. Although the price level of the pure SLA-92 based castable is higher when compared to the SLA/Bonite and Bonite based ones the castable costs in relation to the material requirements are lowest.


Figure 7: Thermal conductivity of SLA-92 based patch mixes pre-fired at 1000°C/5h


Figure 10: Relative cost comparison of the different castable concepts Conclusion


The castable concepts based on different ratios of lightweight SLA-92 and dense Bonite demonstrate the flexibility with regard to castable design. The bulk density can be adjusted in a range from 1.1 to 2.7 g/cm³. The same applies for the strength which can be increased if required for a specific application. This can be important, for example, in areas where the mechanical wear is higher or in areas which are only exposed to lower temperatures and consequently strength development through sintering is hampered. The use of CA6


aggregates in patch


Figure 8: Thermal conductivity at 1000°C vs. bulk density of CA6 at 1000°C/5h


based castables pre-fired


mixes allows the use of alternative lining techniques, e.g. coating or spraying. The thermal conductivity for all castable concepts is low and therefore is beneficial when considering the overall energy efficiency of the equipment.


The thermal shock resistance was tested on samples pre-fired 1000°C/5h by air quenching from 950 °C and is shown in figure 10. For pure


NOVEMBER 2014 ISSUE


In addition to the properties discussed in the paper, synthetic calcium hexaluminate based materials exhibit a high alkali resistance, both in a test with alkali salt and with K2


CO3 the absence of Silica results in a high stability in a H2 WWW.IRENG.ORG


[2; 7]. The high chemical purity and /CO atmosphere


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36