Acid Regeneration Plants (ARP)

Acid-Regeneration-LinesYOGIJI-DIGI and ASPCON have formed an association to provide customers integrated solutions for acid regeneration plants. The aim is to integrate ASPCON’s ARP technology in YOGIJI DIGI’s Pickling Lines at affordable price with quick payback period.

Regeneration of HCl Acid as well as Iron oxide as byproduct from Waste Pickling Liquor.

The proven economic way of regeneration of hydrochloric acid from Waste Pickling Liquor is by pyrohydrolysis. It minimizes the need to neutralize, hauling of waste acid and reduces water consumption. It also produces a saleable iron oxide as by product.

The spray pyrohydrolysis ARP technology is a proven and established since many years. The process regenerates HCl from pickling lines with 99% recovery rate. The ARP is specially designed to minimize the Capital cost, Operating cost, Maintenance cost with minimized spare parts. Neutralisation of waste acid, maintaining the pollution control standards for water/land/air, sludge handling/disposal and water consumption involves high level of cost apart from the maintenance and manpower. Why to waste above costs year after year with dissatisfaction of Pollution control board and the society? With ASPCON ARP, the payback period varies from 1 to 3 years depending on the waste acid discharge.

In Carbon Steel Pickling line, the Iron chloride solution in the pickling baths needs to be controlled either by discarding the bath or by regeneration of Iron free acid. For regeneration of hydrochloric acid from these waste pickling solutions, a number of regeneration processes are known. The most economic and ecologically advantageous process is the pyrohydrolysis of spent pickling solutions. We discuss Spray type pyrohydrolysis technology whose operating cost is lower than Sintered (Fluidised bed) technology.

The process

The dissolved Iron Oxide scale in Hydrochloric Acid (HCl) is separated into free HCl and Ferric oxide powder.
When Carbon steel is pickled with HCl, Ferrous chloride solution is produced:
FeO + 2HCl = FeCl2 + H2O
In the Spray Pyrohydrolysis Process, the ferrous chloride (FeCl2) is hydrolytically decomposed into HCl and Ferric oxide.                                                    4 FeCl2 + 4H2O + O2 = 2Fe2O3 + 8HCl

Pre-concentration: The Iron chloride solution in the waste pickling solution is fed to the venturi evaporator, where direct mass and heat exchange with the hot roast gas from the roaster takes place. The separator separates the gas and liquid phase of the venturi evaporator product. The liquid phase is re-circulated back to the venturi evaporator to increase mass and heat exchange performance.

  • Approx. 25 to 30% of the waste acid (H2O, HCl) are evaporated and gets pre-concentrated.
  • Roast gas is cooled down to approx. 90 to 95 °C
  • Any residual Iron oxide dust particles are also removed from the roast gas

Roasting: Pre-concentrated waste acid is then injected into the “Reactor Roaster” by means of one or more spray booms bearing one or more injection nozzles each. Injection takes place at reactor top at high pressure. The Roaster is directly fired by tangentially mounted burners that create a hot swirl. Temperatures inside the reactor vary between 700 °C (burner level) and 400 °C (roast gas exit duct). In the reactor the conversion of droplets of pre-concentrated waste acid into iron oxide powder and hydrogen chloride gas takes place. Hydrogen Chloride leaves the Roaster through the top, while iron oxide powder is removed from the Roaster bottom by means of mechanical extraction devices. A cyclone in the roast gas duct ensures separation and feed back of larger oxide particles carried by the roast gas.

Absorption: In the specially designed absorption column, the hydrogen chloride compound of the roast gas is absorbed in rinse water from pickling line. Regenerated acid (typical strength: 18% wt/wt) is collected at absorption column bottom.

Scrubbing: In another scrubber, similar as before, remaining hydrogen chloride and dust are removed.

Exhaust gas Cleaning: The roast gas is conveyed through the system by means of an exhaust gas fan. Fan, with pressure and feedback-controlled, is to maintain a relative pressure between reactor and atmosphere to avoid any overpressure-related leaking of acid gas. To rinse the impeller and cool the gas as well as to remove remaining traces of HCl (if any) from the roast gas, the exhaust gas fan’s impeller is sprayed with fresh water, which is separated from the exhaust gas stream by means of a mist eliminator at the pressure side of the fan.

Oxide transportation: Ferric oxide powder in the reactor is transported to the Oxide storage bin which can be filled into bags for transportation. This bagging machine keeps the area completely dust free.


Justification and Benefits.

A Pickling line and an Acid Regeneration Plant are logically an integrated process for many reasons and are considered as one pickling system and operated as such. ARP cost should be as minimum as possible.

  • Consistently high pickling quality due to constant iron and acid concentrations,
  • Huge savings from reduced hazardous neutralization or difficult disposal costs,
  • Savings from reduced acid purchases,
  • Profit from Iron Oxide by-product which is on increasing demand,
  • Elimination of production downtime associated with the dumping and refilling of acid baths,
  • Minimization of direct operator contact with hazardous Acid,
  • Improved environmental impact,
  • Waste Rinse water of Pickling Plant can also be used in Acid Recovery Plant.