The influence of furnace wall emissivity on steel charge heating

•Spectral emissivity measurement.•Ceramic fiber insulation mat and high-temperature coatings emissivity.•Steel charge temperature measurement.•Influence of furnace wall emissivity on charge heating.

Radiation heat transfer is one of the most important heat transfer modes in high-temperature applications. It is a strongly non-linear process, which depends on the temperature and emissivity of heat exchange surfaces, their geometrical configuration and properties of the surrounding atmosphere. Heat exchange intensity between the surfaces depends mainly on their temperature differences. However, their emissivities influence significantly the radiation heat transfer process as well. Emissivity is a function of surface state or atmospheric chemical reactions, temperature and wavelengths. Because of these non-linearities, it is very complicated to evaluate such a real problem by numerical simulation, and experimental work seems to be the most reliable evaluation procedure. We applied special high-temperature coatings of different emissivities on furnace walls to evaluate the dependence between the furnace wall emissivity and steel charge heating. The emissivity analyses of the coatings used and emissivity measurement results in dependence on wavelength are presented in this paper. The dependence of the charge heating on the furnace wall emissivity, the importance of emissivity wavelength dependence and significant differences of the emissivity effect in electrical and gas heated furnaces are shown. The possible consequences and practical benefits are also discussed in this paper.