Before steel is cold it rolled it has to be rid of its coating of oxides called scales, rust, dirt. This is done with acid, either Sulphuric or Hydrochloric, although weighing the pros & cons of one over the others, the latter is preferred. Modern picking lines for hot rolled mild steel sheets use commercial HCL acid at high temperatures. The acid dissolves the mill scale rust along with some virgin steel. The reaction ensues into formation of ferrous and ferric chlorides (with 15% of iron ) and the waste acid after use still contains residual 1- 4% of HCL. The resultant spent acid is then neutralised by use of quick /slaked lime. The neutral slurry is then filtered and the clear liquid is sent  for solar evaporation. The sludge thus obtained is then dried & used for land filling.Certain problems associated with this mode of treatment and disposal of acid makes Acid Regeneration Plant as a more feasible and popular alternative to the above method. The process utilised is that of thermal cracking and there are different systems viz., manual, semi and totally computerised. In this process the spent acid is sprayed into the roaster at high temperatures. 

The residual acid instantly gets evaporated while the chlorides of iron break down into oxide of iron and HCL. Fumes of  HCL , steam & flue gases leave the roaster from the top while the oxide of iron settles down and is collected from the bottom. HCL thus regenerated is absorbed by water in the scrubber and  this ready acid is reused for further picking. The oxide of iron thus produced is an end products with industrial and commercial importance. 

Other advantages that the Acid Regeneration Plant has over the disposal method are enumerated below:

* Recovery of maximum usable picking acid.
* Generation of commercially viable oxide of iron as a byproduct.
* Since no waste is generated there are no disposal problems.
* Process is economically viable.
* Versatile plant designed to accept HSD, LDO & LPG  as fuel.
* Load on rinse water treatment reduces.
* Only small Inventory of HCL need be maintained to cope up with make ups.
* All problems associated with conventional lime treatment are taken care of viz., handling, large quantities of costly lime, sludge, construction & completely eliminated.
* Preservation of natural resources of Nation, and making available pollution free fertile land.

 
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