Technology
Technological excellence worldwide
Technology
Metsep uses the internationally proven spray-roaster acid-regeneration process
technology. Metsep has over 30 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 30 years, separates
iron chloride and other metal chlorides from spent acid.
The Process…
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 a chemicl reaction
with 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.
The exhaust fan keeps the system under vacuum, preventing the HCI gas from
escaping and allows changing of spray booms, while still operating.
Iron oxide powder in the reactor is transported to bunkers 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 HCl, 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