Imaging of hot infrared emitting surfaces obscured by particulate fume and hot gases

摘要

An apparatus is described which is capable of producing an image of a smelt bed of inorganic chemicals collected at the bottom of a kraft pulp recovery boiler. The image produced is free of interferences of fume particles and gaseous radiation which have obscured prior attempts to view hot surfaces under such environmental conditions. The apparatus includes an industrial closed circuit video camera fitted with an infrared imaging detector or vidicon tube. An objective lens obtains the image. An optical filter interposed between the lens and the vidicon is a key element of the invention and is selected to reject radiation less than about a micrometer to avoid fume interference. The filter is further selected to reject all but limited ranges of radiation to avoid gaseous species overlying the smelt bed which are strongly emitting and absorbing. As an example, a spectral filter centered at 1.68 micrometers with a band width of 0.07 micrometer is suitable for imaging a kraft recovery smelt bed.