Technical Diagnostics of the State of Composite Tanks of the Evaporators of Sulfuric Acid
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TECHNICAL DIAGNOSTICS OF THE STATE OF COMPOSITE TANKS OF THE EVAPORATORS OF SULFURIC ACID О. І. Balyts’kyi,1,2 М. Kawiak,3 and P. Kawiak3
UDC 621.791
The recycling of wastes of hydrolytic sulfuric acid (concentrated and purified in special evaporators) returns them into the technological process of production of mineral fertilizers. In this case, the main structural element of the technological equipment (the tank of the evaporator) suffers intense degradation and requires efficient diagnostics. It is shown that the service life of the evaporator strengthened with glass fibers of polymeric vinyl ester laminate and operating under the conditions of variable mechanical and thermal loads manly depends on the properties of the material of wear-resistant coating protecting the inner surface of the tank against abrasion by hard precipitates of the salts of monohydrates, iron sulfates, and magnesium sulfates. Keywords: wastes of sulfuric acid, evaporator, glass-fiber-strengthened polymeric vinyl ester laminate.
The process of production of mineral fertilizers at contemporary plants is connected with the appearance of wastes. By using appropriate technological processes (recycling), these wastes can be often "restored" as valuable products. This is true, e.g., for gaseous hydrogen (up to 60 tons per year), wastes of sulfuric acid, and synthetic gas obtained from the solid domestic garbage intended for burning at local power-generating objects [1, 2]. The wastes of sulfuric acid contaminated by salts have low densities and, hence, the procedures of their cleaning and concentration are realized in evaporators. The choice of structural materials for the tanks of these installations is performed with regard for their corrosion resistance, mechanical durability, thermal conductivity, and the cost of production [3–5]. Evaporating tanks are made both of steel (for the protection against the corrosion influence of the acid, the inner surface is coated with lead or rubber) and of the polymeric laminates. In recent years, these laminates are increasingly often regarded as preferable materials due to their high chemical resistance, satisfactory mechanical strength, and the required heat-conduction coefficient. This is why, after long-term operation, steel tanks are often replaced with evaporators made of vinyl ester laminates with glass fibers. The evaporator operates under severe temperature-and-force conditions under the action of corrosive media. Thus, the acid is concentrated at a temperature of about 80°C under an overpressure of about 100 hPa. The evaporator operates in a continuous mode for a week. In the course of its operation, we observe the formation of solid precipitations of the salts of monohydrates and iron and magnesium sulfates in the concentrated acid. Under the conditions of circulation of acid, they play the role of abrasives and abrade the inner surface. After one weak of operation, the tank is emptied of acid and filled with water to wash away the deposits of these salts. The water heated to 90°C circulates in
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