Cold Rolled Annealing and Pickling Line (C-APL) for Stainless Steel Strip

The entry of an APL has a small sealing followed by a Preheating Furnace (PF). The strip is heated by waste gas coming from the Direct Fired Furnace (DFF), in the DFF strip is further heated to the required annealing temperatures and hold for certain soaking time. Strip is supported inside furnace by up-down rollers. After the annealing section, the strip enters a air cooling section followed by a water quench for final cooling and a wringer roller.

In recent years Tenova has addressed its research activities to develop innovative degreasing sections, new pickling technologies aimed at reducing both the polluting effects of the chemicals used and the overall process operational costs, optimized mechanical solution for terminal equipment, Skin Pass Mill sections, design solution to minimize the fire load and other.

After the annealing operation,  Electrolytic-descaling and  Pickling  are very important process in the manufacture of  Cold Rolled stainless steel

The Electrolytic descaling process convert and partially dissolve the thin but compact layer of scale present on the strip surface. The Tenova high efficiency electrolytic tanks, operated with Sulfuric acid  at controlled Temperature, tanks also to the  optimized geometries and high turbulence, reduce the electrical consumption  and eliminate the presence of Cr6+ in the bath

The following  pickling process is  needed to  dissolve a portion of the strip surface having not the correct percentage of alloy elements (so called Chromium depleted layer) 

So generally the Descaling and Pickling processes involving a multi-step chemical reactions, and is one of the most polluting and costly chemical processes in the steel industry due to the presence of the highly corrosive acids and hazardous substances such as hexavalent chromium, nitrates  and NO_x.

Eco4 (ECOcological and ECOnomical stainless steel pickling process) is a new stainless steel pickling process developed by Tenova which avoids formation of hexavalent chromium (Cr6+) as above described, strongly improving the maintenance operator’s health and safety conditions, reduces or eliminate completely NOx and Nitrates in the waste water, reduces acid  and chemical reagent cost for acid and fumes treatments, reduces overall energy consumption and reduces the investment and operating costs for spent acid and waste waters regeneration and treatment.

Furthermore also fully re-generable acids  solution  is available for chemical tanks furtherly reducing or eliminating   cost for waste treatment and sludge disposal, recovering acid ( as HCL  or HF)  and alloy  metals  (Cr, Ni, Mn..