An Integrated Concept for the Application of High-Temperature Granular Bed Filters in the Aluminum Industry

Abstract

Granular bed filters can be used for the simultaneous collection of fine particles and gaseous pollutants in a wide temperature range up to 1300 K. A concept for flue-gas cleaning in the secondary aluminum industry has been developed based on the results of theoretical and experimental investigations of granular bed filters in the laboratory, as well as on the characterization of the flue-gas and under consideration of the industrial process. The cleaning concept with granular bed filters provides two independently regenerated granular beds, separating the solids and acid gaseous components, respectively. The dust particles are collected in the first fixed bed at a temperature of around 973 K using quartz collectors with diameters smaller than 0.5 mm. In the second stage, the sorption of the gaseous pollutants can be realized with either CaO- or NaHCO₃-pellets in a counter-current bed. The supply of NaHCO₃ enables the recovery of the reaction products, thus minimizing the residues. The proposed concept was verified with the aid of a test-rig which was installed in the secondary aluminum plant. The emission standards were easily satisfied. With this concept it is possible to use the heat content of the flue-gases for the operation of a crystallization unit.