MODELLING OF CRYSTALLINE SCALE REMOVAL

The removal of crystalline scale deposits from stainless steel surfaces has been studied experimentally using dilute solutions of hydrochloric acid to remove thin layers of calcium carbonate (calcite) in a purpose built flow cell. The initial linear removal rate decreased rapidly after a point which corresponded to the appearance of scale-free patches on the metal surface. Modelling the removal rate required reliable values of the surface-liquid mass transfer coefficient, which were obtained from heat transfer measurements. Modelling studies indicated that diffusion of H⁺ was the rate controlling step for the range of Re considered (2000 < Re < 5000). The overall cleaning behaviour was found to be dominated by the roughness and non-uniformity of the deposit.