Fouling of heat exchanger surfaces by dust particles from flue gases of glass furnaces

Abstract

Fouling by dust particles generally leads to a reduction of the heat transfer and causes corrosion of secondary heat exchangers. A deposition model, including thermodynamic equilibrium calculations, has been derived and applied to describe the deposition (i.e. fouling) process and the nature of the deposition products in a secondary heat exchanger. The deposition model has been verified by means of laboratory experiments, for the case of flue gases from soda-lime glass furnaces. Corrosion of iron-containing metallic materials, caused by the deposition products, has been briefly investigated with the same equipment. There is a close similarity between the experimental results and model calculations. The largest deposition rates from flue gases on cylindrical tubes in cross-flow configuration, are predicted and measured at the upstream stagnation point. The lowest deposition rates are determined at downstream stagnation point locations. At tube surface temperatures of approximately 520 to 550 K, the fouling rate on the tube reaches a maximum. In this temperature region NaHSO4 is the most important deposition product. This component is mainly formed at temperatures from 470 up to 540 K. The compound Na3H(SO4)2 seems to be stable up to 570 K, for even higher temperatures Na2SO4 has been found. These deposition products react with iron, SO3, oxygen and water vapour forming the complex corrosion product Na3Fe(SO4)3. NaHSO4, which is formed at tube surface temperatures below 540 K, causes more severe corrosion of iron-containing materials than Na2SO4. Maintaining temperatures of the heat exchanger surfaces above 550 to 600 Κ reduces the fouling tendency and corrosion in case of flue gases from oil-fired soda-lime glass furnaces.