Alitizing by metallization of internal surfaces of gas flues. Wear-resistant, anti-corrosion, heat-resistant internal coatings.

Wear-resistant, corrosion-resistant heat-resistant internal coatings for gas flues. Alitizing by metallization of the internal surfaces of gas flues by flame spraying aluminum. Coatings withstand temperatures up to 800^oC, work in vapors of sulfuric acid.

Contact devices are the main link in the chain of sulfuric acid production. At this stage, the dry purified gas enters the contact oxidation of SO2 to SO3, which occurs by a reversible exothermic reaction that occurs with a decrease in the volume of gas. To achieve the maximum rate of oxidation of SO₂ to SO₃, the process begins at a temperature of about 600^oC and ends at 400^oC. Heated SO₂, passing between the tubes of heat exchangers located in the contact apparatus between the shelves with the contact mass, heats up to 450^oC and enters the upper catalyst layer, where the reaction heats up to 600^oC. The gas passes through several lattice shelves with a contact mass and heat exchangers located between them, with the result that 97 ... 98% of SO₂ is converted to SO₃. At the sulphuric acid plants of our country as the catalyst use mainly vanadic contact masses with the maintenance of V₂O₅ of about 7% and also the including oxides of alkaline metals and high-porous aluminosilicates as the carrier. Contact catalytic weight can keep activity for several years. But at contact of SO₂ with steel there is a formation of sulfates of iron and its subsequent "peeling" from walls of ceilings and the bearing beams of the contact device. For catalysts, sulfate of iron is one of the main "contact" poisons. Thus, for increase in service life of the expensive catalyst, it is necessary to provide protection of steel structures of the contact device against influence of SO₃. To protect the steel of the walls, ceiling and power beams of the contact apparatus from SO₃ exposure, an aluminum gas-thermal coating, indicated in the project documentation, was used.