Pyrometry inside an arc furnace using a ray-tracing correction for surface emissivity

Abstract

A general method using a ray-tracing analysis has been developed to improve the accuracy of surface temperatures measured by pyrometry inside a furnace. This method allows temperature correction for enclosed non-ideal black-body surfaces, having temperature gradients, by taking into account the contributions from the reflected fraction of the pyrometer field-of-view. The development has been made possible by the recent availability of internal furnace scanning pyrometry technology for complete temperature profile measurements inside furnaces. The correction method can be expressed in terms of the solution of a square matrix having a dimension corresponding to the number of spatially resolved points in the temperature profile, with the number of non-zero elements depending on the number of field-of-view reflective surface bounce points used in the analysis. The utility of this method is demonstrated for the correction of 19-point temperature profiles measured inside a dc arc furnace. Reflective contributions from two, three, and four field-of-view surface bounce points are considered. Generally, the lower the surface emissivity and the higher the temperatures, the more bounces needed in the analysis. It is shown that there can be significant corrections to internal furnace temperatures measured by pyrometry when temperature gradients exist.