Thermal conductivity
Thermal conductivity of the bricks determine heat losses. Increase in porosity decreases thermal conductivity but at the same time decreases strength also.
Bulk density:
Decrease in bulk density increases volume stability, heat capacity.
Selection of refractory
Selection of a refractory is complicated. Among physico-chemical –thermal properties, cost is the most important. Broadly speaking selection may depend on
Furnace Design
How the furnace is to be heated; whether directly or indirectly. In indirect heating e.g coke oven, Pidgeon’s process for Mg production, Kroll’s process (production of Ti by reduction of TiCl2 with Mg), walls of the furnace are heated and heat is transferred from the walls to the charge. Among other properties, thermal conductivity of the refractory is important. Whereas in direct heating fuel and air mixture is supplied to the furnace and here wall of the refractory facing the reaction chamber must have high refractoriness besides other properties.
Condition of heating:
There are furnaces which operate continuously and others batchwise. For example coke oven is kept continuously at high temperature for months but a cupola operates intermittently.
Loading
Loading and unloading required/ unit time
Operating Factor
Chemistry of phases:
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