Sulfuric Acid Manufacturing
BACKGROUND
Sulfuric acid (H2SO4) is a strong, heavy acid with a density of 1.84 g/cc and a marked tendency to absorb moisture from the air, generating much heat. Concentrated sulfuric acid (93-98%) is used in the manufacture of fertilizers, explosives, dyes, and petroleum products. Sulfuric acid is formed during the Contact Process. The Contact Process forms sulfur trioxide (SO3) gas from sulfur dioxide (SO2) and oxygen in a catalyst tower, and sulfuric acid is formed when water is added. A mixture of H2SO4 and free SO3 is equivalent to a sulfuric acid concentration of over 100 percent. This mixture is called fuming sulfuric acid or oleum.
SULFURIC ACID PLANT
Electrical conductivity is the most cost-effective technique for both monitoring process conditions and safeguarding process equipment (a typical plant schematic is shown in Figure 1).
Elemental sulfur (or other sulfur-containing ore) is first burned in air to form hot sulfur dioxide gas. The hot gas is cooled to about 400°C (752°F) in a waste heat boiler and then, in a catalyst tower, passed through 2 to 4 stages of platinum or vanadium catalyst to form SO3 gas. The catalytic reaction generates a lot of heat and is reversible. The catalyst tower is, therefore, arranged with alternating levels of catalyst and gas coolers to prevent the reverse reaction from occurring at high temperatures.
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