Corrosion Protection in Sulphuric Acid Plants

The materials used in the construction of sulphuric acid plants need to be able to withstand extreme chemical and thermal stresses. The careful use of corrosion protection systems is not only essential in protecting the structure, thus assuring the reliability of the plant and productivity, but it also helps to protect the environment from exposure to aggressive and harmful chemicals.

Steuler’s has Corrosion Protection Materials and Refractory Systems for all areas of plants used for the production of sulphuric acid:


Sulphur Combustion Furnaces and Sulphur Pits

The contact process (with single or dual catalysis) which is now commonly used to produce sulphuric acid requires sulphur dioxide (SO2). This can be obtained, for example, either from a roasting plant with a fluidised bed roaster, or by oxidizing a sulphide ore in a combustion furnace. In the wet precipitator process, the sulphur dioxide (SO2) is produced by burning hydrogen sulphide (H2S).

The fluidised bed roasters and combustion furnaces are lined with multiple layers of Steuler Refractory Systems on account of the high temperatures reached.

The sulphur pits are lined using Steuler’s own acid-resistant ceramic bricks. The bricks are laid up and pointed using Steuler’s acid-resistant mortar S 50 HF or furadur mortar, which has been used successfully for over 20 years.


Gas Scrubbers

The sulphur dioxide (SO2) gases produced as a result of the fluidised bed roaster process are cooled initially in a cooling chamber before having dust removed in a hot electrical filter, then passing to the venturi scrubber, in which they are washed out and cooled.


Venturi Scrubber

The pre-treated gases are cooled in a venturi scrubber in a direct current process.
The most problematic area in the venturi scrubber is the gas inlet which is subjected to high temperatures. The rubber lining membrane used to protect the steel from corrosion has to be protected from excessive temperatures to increase its longevity. For this, Steuler uses a suitable brick lining, depending on the temperatures that actually occur. The layered construction, built on a wealth of experience, consists of layers of heat protection and acid-resistant ceramic bricks. The bricks are laid up using Steuler’s own water glass mortar.
The nozzle roof is particularly prone to stress through changes in temperature and must also be lined with temperature-reducing layers using materials which are not affected by temperature shocks. Different types of brick are used for this including graphite, silicon carbide and other quartz bricks. The majority of roasted gases contain fluoride which produces fluid acid in the venturi washer. As the acid destroys materials containing quartz, graphite or carbon materials have to be used where fluid acid is present. This also applies to the cement and mortar. Steuler stocks all materials needed to line venturi scrubbers.


Wet electrostatic precipitator

The sulphurioxide gas is still wet when it comes out of the venturi scrubber and has to be purified in a wet electrostatic precipitator. Steuler supplies polypropylene (PP) precipitator inserts for these installations. Steuler also uses flake and laminate coatings to protect the precipitator housing from corrosion.


Absorption towers

The SO2 gas is dried in a drying tower using concentrated sulphuric acid and then fed into the contact reactor.

Depending on the choice of method (single or double contact), the SO3, formed in a catalytic process using vanadium oxide, is absorbed by an intermediate and/or final absorber into the circulating concentrated sulphuric acid. The concentration of the absorption acid is maintained at a constant value of 98.5 - 99% through the addition of water.

The combustion of pure sulphur method is not quite so laborious in its cleaning requirements. The sulphur dioxide (SO2) produced is fed into the contact reactor directly after cooling in the cooling chamber.
The next stages in the processing of the sulphur trioxide (SO3) take place as described above, in the different absorption towers.

Lining materials for towers which come into contact with sulphuric acid (drying tower, intermediate and final absorption tower)

The drying towers, intermediate and final absorption towers are all very similar in terms of operating conditions. In both case, the stress is determined by varying concentrations of sulphuric acid (95 – 98% in the drying tower, 93 – 98 % in the absorbers).
The temperature of the acid in the packing of the drying tower is app. 40 – 70°C, whereas in the intermediate and final absorption towers, the acid can reach temperatures of 70 – 90°C.


Absorption towers made of unalloyed steel

Unalloyed steel (carbon steel) does not offer long lasting resistance to flowing sulphuric acid, even if concentrations are higher, and therefore needs to be protected against corrosion. The pre-treated steel surface is lined firstly with a 2mm thick sheet of polyisobutylene or a 0.25 mm thick film of PTFE (polytetrafluorethylene). In parts of the absorption towers which are less resistant, a special ceramic paper is used before applying the acid and temperature resistant brick lining. The absorption towers are lined with acid-resistant ceramic stones and special water glass mortar. The number of layers applied may be one or more, depending on the level of stress. The service life of the lining depends on the type of material used and the quality of the lining work. Particular skill is required with the supporting dome for the packed region, for which Steuler uses specially trained personnel and sophisticated engineering technology.


Work surfaces, ducts, tanks and pipe work in sulphuric acid plants

In sulphuric acid plants the floors, pits channels and tanks also require protection. There are two types of protection to be considered: corrosion and environmental. The floor areas are protected from aggressive sulphuric acid using floor tiles which conform to DIN 28052-5. We also supply high quality coating systems, which are approved for structural use, and are preferable in the case of storage area applications.
In addition to traditional materials, Steuler uses its special thermoplastic lining system Bekaplast in ducts and pits, due to its excellent resistance to sulphuric acid in all concentrations.
A wide range of plastic materials is available for pipe and container linings.