CEE Jul-Sep-2012

to the lining. Dynamic upset process conditions can also-for example be a result of equipment failures, malfunctioning top sprays, (unscheduled) shut-downs, burden slips, casting deficiencies and 'gas-jets'. Local, incidental upset process conditions can result in loadings that are ten times higher compared to average conditions. An example is illustrated in Figure 1: this dynamic temperature development has often been reported to reflect 'loss of solidified protection layer' and rapid solidification of new protection layer due to high-efficiency cooling system. We believe, however, that it is more likely that this reflects the consequences of a high-temperature 'gas-jet' impinging on the lining. roil loOO ~~ c ~ Table 2: Maximum peak heat load capabilities Cooling ..... Refractories Maximum Peak Dense Pattern Plate Coolers Copper Stave Coolers Medium to low Dense Pattern Plate Coolers Dense Pattern Plate Coolers Third Generation Cast Iron Stave Coolers Dense Pattern Plate Coolers First Generation Cast Iron Stave Coolers Wide Pattern Plate Coolers Graphite SIC/Gunnite Graphite SiC bricks SiC/ Castable Alumina/Chamotte Alumina 1 Chamottee Alumina/Chamotte Heat Load Capability (W/m 2 ) 500.000 500.000 320.000 180.000 170.000 110.000 110.000 35.000 3 I? ~ •OO ;:kc I I \ , · I I i ""--/'- ~~ lining material grades and actual temperature fluctuations for 3 different raw material compositions. It is clear that only high-conductive, ductile lining material such as copper and (semi) graphite will survive (irregular) high productivity, particularly with high pellet operations. Lining designs are often an 'assembly' of metal cooling members and refractory components. The design and engineering of the cooling system and refractory components may have been executed by different companies and consequentially may not match each other. For example, the application of low conductivity ceramics and high density plate coolers systems introduces opposing philosophies with regards to thermal fatigue. ~ 200 I _.,./ I L/ / ..../ ,_________ ~--~-=========== ------ ---- 0 16011 1?.00 Timeofday (hn) --- _ ___; 22.00 Figure 1: (Lower) Stack temperature measurements Table 1: Temperature fluctuations Material Fatigue Limits °C/min °F/min Graphite Semi Graphite Silicon Carbide Cast Iron 85%Ab03 45%Ab03 Chrome Corundum Observed Temperature Fluctuations Sinter Burden >90% Mixed Burden 50%/ 50% Pellet Burden >70% 500 250 50 50 5 5 4 50 150 180 900 450 90 90 9 9 7 90 270 320 Process conditions have been monitored at many plants and temperature fluctuations have often been observed exceeding > 100°C 1 minute. Table 1 summarizes actual 'fatigue limits' of various It is our philosophy to evaluate the 'integrated lining design' as one system: this system includes mechanical (shell and cooling members), refractory and process engineering (cooli ng system) components. Customized systems can be developed to meet specific blast furnace requirements and loading conditions. Maximum peak heat load capabilities of typical bosh and stack lining designs are summarized in Table 2 (shown above). It is noticed that the blast furnace bosh and stack design imposes conflicting requirements • Minimize fuel consumption/ minimize heat loss – minimum cooling • Minimize shell temperatures - maximum cooling. The heat load is a consequence of specific process conditions and lining design. History has proven that high-efficiency designs using high– conductivity materials are required to secure low 12