Annealing
Referenced data includes 1180 C annealing, 6-7 seconds soaking and cooling faster than 20 C/s.
Nitric Acid Free Stainless Steel Pickling
Nitric acid free pickling line for stricter environmental projects.
This route replaces nitric acid oxidation with sulfuric acid, HF-containing additive and hydrogen peroxide chemistry, supported by electrolytic pre-pickling, counterflow rinsing and waste acid regeneration.
Overview
For new stainless steel lines with nitrate nitrogen and NOx pressure.
The workbook includes a nitric acid free continuous annealing and pickling project using neutral salt electrolytic pre-pickling and a sulfuric acid, HF and hydrogen peroxide acid system.
- Target product in the referenced project includes high-quality wide stainless steel strip.
- Designed to reduce nitric acid consumption and downstream nitrate nitrogen or NOx treatment pressure.
- Best evaluated together with acid regeneration, acid mist capture and wastewater handling.
Process Route
Neutral salt pre-pickling and nitric acid free mixed acid chemistry.
The process data below is extracted from the supplied workbook's environmental and process sheet.
Neutral salt electrolysis
Na2SO4 at 150-220 g/L and 70-90 C supports oxide removal before mixed acid pickling.
Nitric acid free pickling
H2SO4 + 704B containing HF + 704Z containing H2O2 replaces nitric acid oxidation.
Rinse and regenerate
Three-stage counterflow rinsing and online acid regeneration reduce fresh acid demand.
Parameters
Nitric acid free line data extracted from the workbook.
These figures are project-reference values and not universal guarantees.
| Item | Workbook Data | Engineering Note |
|---|---|---|
| Typical use | Continuous stainless steel annealing and pickling with lower nitrate nitrogen and NOx risk | Useful for projects with stricter environmental approvals |
| Capacity reference | 1.2 million t/a project, two phases of 600,000 t/a each | Public project reference from workbook source data |
| Acid system | H2SO4 + 704B containing 50-60% HF + 704Z containing 20-60% H2O2 | Final chemistry must be confirmed by process supplier and safety review |
| Rinsing | Three-stage counterflow rinsing, fresh water heated to 65-80 C | Supports residual acid removal and water efficiency |
| Product direction | 2B high-quality wide stainless steel strip | Reference applications include rail transit, petrochemical, medical, home appliance and electronics |
Environmental Data
Acid recovery, acid mist capture and wastewater treatment define the line boundary.
The environmental package should be specified together with the acid process, not after the mechanical line is already fixed.
Acid regeneration
Referenced ion exchange system capacity is 500 L/h with acid recovery up to 90%.
Acid mist capture
Mixed acid mist capture efficiency is referenced above 95% in the workbook.
HF removal
Referenced HF removal efficiency is above 97.5% with alkaline scrubbing.
Wastewater
Total treatment capacity reference is 25 m3/h and 300 m3/d daily volume.