Technological excellence worldwide
Metsep uses the internationally proven spray-roaster acid-regeneration process technology. Metsep has over 50 years’ experience in operating, maintaining and developing ARPs. The company has technology agreements with Amec-BKW (successors of Babcock International) being well placed to further develop the technology for the benefit of steel structures and processors. Dedicated hydrochloric acid recovery plants are used for economical, technological and environmental advantages to more than 200 major steelworks around the globe. The renowned spray-roaster process, applied successfully for more than 50 years, separates iron chloride and other metal chlorides from spent acid.
When steel is pickled with hydrochloric acid a chloride solution is produced:
FeO + 2HCl = FeCl2 = H2O
In the regeneration system, the iron chloride (FeCI2) is converted into Hydrochloric acid and iron oxide by hydrolytic decomposition.
2 FeCI2 + 2H2O + 1/2O2 = Fe2O3 = 4HCl
This reaction takes place in the reactor at temperatures ranging from 600°C to 800°C.
The iron chloride containing waste pickling acid from the pickling system is conveyed to the evaporator, where it comes into direct contact with the hot waste gases from the reactor and concentrated. This concentrated iron chloride solution is sprayed into the spray roasting reactor.
At reaction temperatures between 600°C and 800°C, the iron chloride solution is converted into hydrogen chloride and iron oxide by means of water vapour and atmospheric oxygen.
Via the cyclone, the hydrogen chloride gas, water vapour and combustion gases are routed to the evaporator and on to the absorption column, where the HCI gas is absorbed adiabatically by adding rinse water from the pickling plant.
The resulting azeotropic acid (18% of weight) is recycled to the pickling process. The gas from the column is cleaned in a scrubber stage in accordance with environmental requirements and then discharged to the atmosphere.
A fan keeps the system under vacuum, preventing the HCI gas from escaping.
Iron oxide powder in the reactor is transported to the appropriate tanks and then filled into big bags.
The many strengths…
• highly economical
• closed acid loop between the pickling plant and the regeneration system
• Si-, Zn- and Pb- containing waste pickles can be treated
• rinse water can be used as absorption water in the regeneration plant, thus pickling plant can be operated without waste water
• consistently high pickling quality due to constant iron and acid concentrations
• reactors can be heated with any gaseous or liquid fuels.
• high–purity iron oxide produced
A cleaner environment
As the acid loop between the pickling plant and the regeneration system is closed, and the rinse water from the pickling plant is re-used in the regeneration system, the pickling system can be operated largely without producing waste water.
The off–gases from the HCl regeneration system consist of water vapour and the combustion gases from reactor heating. The Cl2 and dust emission values conform to legal requirements.
High value iron oxide
On account of its specific qualities, the iron oxide produced with the spray roasting process is highly valued as a raw material. There is an increasing worldwide demand for such an oxide.
In plants where silicon–kilned steel is pickled, the portion of silicic acid in the waste pickling acid can be chemically reduced by the incorporation of a pre-process treatment stage.
Major iron oxide uses:
• Production of hard and soft ferrites
• Foundry applications
• Binder materials for refractories
• Colouring pigments