Acid Regeneration for Spent Hydrochloric Pickle Liquor Sep20

Acid Regeneration for Spent Hydrochloric Pickle Liquor...

Acid Regeneration for Spent Hydrochloric Pickle Liquor  Pickling is a process which consists of chemical removal of scale (surface oxides) and other dirt from steel by immersion in aqueous acid solution. During the pickling process, acid reacts with scale as well as base steel to produce dissolved metal salts. The pickling process generates a considerable quantity of spent pickle liquor (SPL) containing the dissolved salts as well as residual free acid. This SPL is either to be disposed of after chemical neutralization with alkali or regenerated. Carbon steel is usually pickled either by sulphuric acid (H2SO4) or hydrochloric acid (HCl). But hydrochloric acid is now preferred over sulphuric acid due to the following advantages. It consistently produces a uniform light gray surface on high carbon steel. Probability of over pickling is much less. Iron concentrations can be as high as 13 %. Rinsing is facilitated because of high solubility of iron chloride. It is safer to handle when compared with sulphuric acid. Pickling is carried out at lower operating temperatures  Hydrochloric acid regeneration refers to process for the reclamation of bound and unbound HCl from metal chloride solutions such as ferrous chloride. Regenerated acid has no adverse effect on metal cleaning efficiency compared to virgin acid.  It pickles as efficiently as virgin acid. There are several processes for the regeneration of spent hydrochloric pickle liquor. A number of different process routes are available. The most widely used is based on pyrohydrolysis, hydro thermal and adiabatic absorption of hydrogen chloride in water, a process invented in the 1960s. Distillation process Distillation process has been used where there is a significant level of free acid is remaining in the SPL. Purified HCl, at the azeotropic concentration of about 15 % w/w is recovered from the ‘overs’ while the concentrated...