Patent ID: 7520946

Claim:
A dry descaling process for the removal of a scale on the surface of a metal product, which is carried out with a dry pickling apparatus comprising: at least one heating area for heating the metal product, at least one reducing area for performing a reaction between a metal-oxide reducing gas and the scale, at least one area for cooling the metal product, first heating means for heating the metal product, second heating means for heating the reducing gas, means for removing reaction products from the reducing gas after reaction, means for removing reaction products which are left on the surface of the metal product after treatment, and means for cooling the metal product, the process comprising the following steps: a) providing a metal-oxide reducing gas, b) heating the metal product to a first temperature greater than ambient temperature without reducing and without oxidizing the specific surface of the material to be treated, c) heating the reducing gas to a second temperature greater than ambient temperature, d) introducing the metal product in the reducing area, e) performing the reaction between said metal-oxide reducing gas and said scale, f) cooling the metal product, g) removing the reaction products from the reducing gas after the reaction with the scale, h) removing the reaction products from the surface of the treated metal product, the process being characterized by: i) controlling fluid dynamics of boundary layer of the flow of the reducing gas over the surface of the metal product by means of first control means ( 16 , 17 , 19 , A 1 , B 1 , C 1 ) whereby there are provided pressure oscillations and amplitude of pressure having the features: gas-solid velocity greater than 5 m/s, shear stress between 0.03 and 5 Pa, high turbulent kinetic energy; and homogeneous gas concentrations adequate to the amount of the scale found on said surface and sufficient for removing the reaction products from said reducing gas, j) providing a blowing stage of the heated reducing gas to the surface of said metal product at a predetermined flow rate in the range from 4 to 100 Nm 3 /(min kg scale ), k) providing a reaction time comprised in the range from 20 to 90 sec. to remove oxygen from the scale, of magnitude greater than +2 Pa, l) providing, by means of the boundary layer fluid dynamic control means, an evacuation flow of said reducing gas, after it has reacted in accordance with stage k), whereby said evacuation flow is associated with a corresponding depression area on the surface of said metal product, m) performing stages j) and l) cyclically in regular succession along the entire surface of said metal product, n) removing the reaction products from the reducing gas after the reaction with the scale.