A new infrared camera-based technology for the optimization of the Waelz process for zinc recycling

Today, the Waelz process using a rotary kiln is the best technology available for the pyro-metallurgical treatment of zinc-bearing residues. However, this process will only result in a good zinc recovery, if the temperature distribution in the kiln and the rheological behavior of the material are controlled. Unfortunately, these properties cannot be measured with conventional sensors. In this paper, an image processing system for the Waelz kiln process will be presented, which calculates the relevant process information from infrared camera images in an online manner. It uses a custom-built infrared camera with a spectral filter at 3.9 μm, which provides for a detailed insight into the kiln. The information that is calculated by the image processing system, including temperature distributions of the material, repose and filling angles, is directly used for closed loop control. The system presented has been in operation at an industrial plant in Germany for about 2 years.