How to Minimize Heat Loss through the Furnace Walls | Melting Smelting | Forum

About 30 to 40 percent of the fuel used in intermittent or continuous furnaces is used to make up for heat lost through the furnace walls. The extent of wall losses depends on:
（1） Emissivity of wall
（2） Thermal conductivity of refractories
（3） Wall thickness
（4） Whether the furnace is operated continuously or intermittently

There are several ways to minimize heat loss through the furnace skin:

(1) Choosing the appropriate refractory materials

(2) Increasing the wall thickness

(3) Installing insulating bricks. Outside wall temperatures and heat losses of a composite wall are much lower for a wall of firebrick and insulation brick compared to a wall of the same thickness that consists only of refractory bricks. The reason is that insulating bricks have a much lower conductivity.

(4) Planning operating times of furnaces. For most small furnaces, the operating periods alternate with the idle periods. When the furnaces are turn off, heat that was absorbed by the refractories during operation gradually dissipates through radiation and convection from the cold face and through air flowing through the furnace. When the furnace is turned on again, additional fuel is needed to heat up the refractories again. If a furnace is operated continuously for 24 hours in three days, practically all the heat stored in the refractories is lost. But if the furnace is operated 8 hours per day all the heat stored in the refractories is not dissipated. For a furnace with a firebrick wall of 350 mm thickness, it is estimated that during the 16 hours that the furnace is turned off, only 55 percent of the heat stored in the refractories is dissipated from the cold surface. Careful planning of the furnace operation schedule can therefore reduce heat loss and save fuel.