ENVIRONMENT FRIENDLY SAFE PICKLING (EFSP)
Introduction
In steel production, oxidation is a natural process and one of the major problems. Many hot working processesand other processes that occur at high temperatures leave a discolouring oxide layer or scale on the surface. Some method for pickling are as follows.
1) Acid Pickling:
Pickling is a popular method to remove impurities, such as strains, inorganic contaminants, rust or scale from ferrous metals. In order to remove the scale the work piece is dipped into a vat of pickle liquor. The primary acid used is hydrochloric acid, although sulfuric acid was previously more common. Hydrochloric acid is more expensive than sulfuric acid, but it pickles much faster while minimizing base metal loss. The speed is a requirement for integration in automatic steel mills that run production at high speed, speeds as high as 240 meters/min.
Disadvantages:
Acid cleaning has limitations in that it is difficult to handle because of its corrosiveness and high reactance to treatable steels, acid concentrations and solution temperatures must be kept under control to assure desired pickling rates.
Waste products:
Pickling sludge is the waste product from pickling, includes acidic rinse waters, iron chlorides, and metallic salts and waste acid. Spent pickle liquor is considered a hazardous waste by the EPA
Pickle sludge from steel processes is usually neutralized with lime and disposed of in a landfill . After neutralization the EPA no longer deems it a hazardous waste. The lime neutralization process raises the pH of the spent acid. The waste material is subject to a waste determination to ensure no characteristic or listed waste is present.
Hydrochloric pickling sludge is often treated in a hydrochloric acid regeneration system , which Environment some of the hydrochloric acid and ferric oxide . The rest (ferrous oxide) further used by paint industries.
2) Smooth clean surface (SCS):
In the SCS process, surface oxidation is removed using an engineered abrasive and the process leaves the surface resistant to subsequent oxidation without the need for oil film or other protective coating.
3) Environment pickled Surface (EPS):
EPS is a more direct replacement for acid pickling. Acid pickling relies on chemical reactions while EPS uses mechanical means. The EPS process is considered "environmentally friendly" compared with acid pickling and it imparts to carbon steel a high degree of rust resistance, eliminating the need to apply the oil coating that serves as a barrier to oxidation for acid-pickled carbon steel.
Above procedures are having its own difficulties and the better alternatives is as below. The better alternate of above pickling process is EFSP (Environment friendly safe Pickling)
Environment Friendly Safe Pickling:
Environment Friendly Safe Pickling (EFSP) is microbiology based superior replacement of existing pickling procedure where dangerous acid or high pressure mechanical system is not used.
EFSP is a new development to replace acid/ mechanical pickling of Mild steel. Like other pickling, EFSP removes mill scale from the surface of hot rolled steel. Unlike other acid pickling, EFSP is safe and completely harmless to the environment. Instead of acids, EFSP uses Microbes which as and when required recycles and re-uses.
That's why the Environmentnomics of EFSP processing are much better than acid pickling. Capital costs, variable costs of operation and space requirements of an EFSP production system are much lower than any other pickling line of the same capacity. This technology can convert existing pickling system with minor modification.
EFSP Technology for You
Steel mills, service centres and batch processors can adopt this technology EFSP gives a competitive advantage. They no longer have to purchase HRPO or outsource the pickling of hot roll steel coils. Instead, they perform their own environmentally friendly EFSP pickling, which in turn gives them a superior flat roll steel product to offer their customers.
There are three ways that you too can obtain the benefits of EFSP technology:
1) SAT (Samson Automation Technologies) offers a stand-alone EFSP Cells to be integrated into existing coil processing lines or acid pickling lines.
2) Complete turnkey batch/ coil EFSP processing lines can be purchased from SAT.
3) Existing pickling line can be converted to EFSP
Why EFSP is better:
Clearly and Cleanly, a Better Strip Steel Product process with safety than acid pickling, it produces a notably better steel product with longer life. EFSP processed steel resists rusting with no protective oil coating
The Process:
There are four part of process:
1) Dipping and cleaning, de-scaling and bushing (if required)
2) Analysis of chemical quality and sweetening
3) Draining ferrous mixed chemical
4) Re-treatment of Drained ferrous mixed chemical
Dipping and cleaning:
Raw material (MS Sheet/ Coil) dip/ pass thru microbe solution as per stipulated time and temperature, where microbes solutions react with rusty material the rust is removed from sheet and dissolve in solution. Solution level is maintained thru auto level control.
Analysis of chemical quality and sweetening:
Chemical solution is continuously monitored for quality and effectiveness to maintained process quality and recirculated and booster dose thru dosing system.
Draining ferrous mixed chemical:
Whenever ferrous level increases in chemical solution chemical solutions to be drain and stored in drain tank.
Re-treatment of Drained ferrous mixed chemical:
Drained chemical send for re-treatment and convert for other non hazardous product.
Major Component:
1) Chemical tank
2) First fill chemical
3) Drain and top-up system
4) Chemical dosing system
5) Draining system
6) Temperature control system
Automation:
1) Auto level control
2) Auto chemical quality control
3) Auto temperature control
4) Auto drain control