The role of the air gap between copper finger coolers and refractory is examined by means of a static thermal conductivity model for different slag and meatal levels in a furnace. The objective is to determine the effect of the width of the air gap on the thickness of the frozen slag layer as a function of furnace operating conditions and cooling finger configuration. This model provides design information for the placement of copper finger coolers for a range of operating conditions. The presence of a 1 mm air gap between the copper finger and frozen slag can reduce the slag protection in front of the copper finger from 67 to 23 mm for a 50 kW m~-2 heat flux. A 2 mm gap ereduces the slag protection even further to 11 mm. Large temperature gradients found at the metal-slag -refractory triple junction are suspected to be due to the large difference in thermal conductivity between the metal and slag. This give rise to thermocapillary shear of the order of 10 N versus solutal-capillary shear of the order of 0.1-1 N; thus, thermocapillary shear is believed to be the main contributing factor to refreactory erosion at the slag-metal interface. The placement of the bottom Cu plate generally does not affect the frozen metal profile as the protective sidewall refractory in front of the Cu plate significantly limits the rate of heat loss from the furnace. This bottom plate may not be needed in the furnace, Finally, the thermal model provides quick design criteria for estiamting slag thickness as a function of ehat flux.
展开▼
