Processes of Manufacture of Sulfuric Acid
The processes for the manufacture of sulfuric acid can be classified on the basis of raw materials used:
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Processes of Manufacture of Sulfuric Acid
2.1 Processes of Manufacture of Sulfuric Acid The processes for the manufacture of sulfuric acid can be classified on the basis of raw materials used: • elemental sulfur • Sulfide ores • Spent acid • Gases like H2S Many variants are available for each process utilizing the above-mentioned starting materials.
2.1.1 Elemental Sulfur Process description for sulfuric acid 98.5% plant (commercial grade) A typical sulfuric acid plant operating on sulfur as the main raw material consists of the following main sections: 1. Sulfur feeding section 2. Waste heat recovery section 3. SO2 conversion section 4. Acid towers section 5. Acid cooling and storage/handling section 6. Plant infrastructure (electrical/civil/water treatment, etc.)
2.1.1.1 Sulfur Burning Solid sulfur is dumped on the grids of the melter and is melted by means of the heat provided through steam coils in the melter. An agitator installed in the melter helps to melt the sulfur at a faster rate. Liquified sulfur is pumped to the pressure leaf filter and the purified sulfur stored in a separate compartment equipped with steam coils. Sulfur pumps are used to feed the liquid sulfur to the sulfur burner at a N.G. Ashar and K.R. Golwalkar, A Practical Guide to the Manufacture of Sulfuric Acid, Oleums, and Sulfonating Agents, DOI 10.1007/978-3-319-02042-6_2, © Springer International Publishing Switzerland 2013
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2 Processes of Manufacture of Sulfuric Acid
predetermined constant rate. The sulfur burner is preheated to a high temperature by an earlier oil firing and hence the sulfur being fed in ignites instantaneously, producing sulfur dioxide. Dried air is supplied to the burner by an air blower through a drying tower. The gases coming out from the burner are at temperature of 950– 1,000 °C and contain 10.0–10.5% sulfur dioxide. They are passed through a waste heat recovery boiler where high pressure steam is produced while the gases are cooled to 390–410 °C depending on the plant design and gas duct layout. The cooled gases are now passed through a multistage (four or five stage) conversion system (having three passes in the first converter and one/two passes in the second).
2.1.1.2 Conversion of SO2 into SO3 The design and operation of sulfuric acid plants are focused on the following catalytic gas phase chemical equilibrium reaction:
SO2 + 1 2 O2 ↔ SO3 ∆H = −99 kJ.mol −1 This reaction is characterized by the conversion, which is defined as follows: conversion achieved =
SO 2 in - SO 2 out ´ 100 ( % ) SO 2 in
Both thermodynamic and stoichiometric considerations are taken into account in maximizing the formation of SO3. The Le Chatelier-Braun principle is usually taken into account in deciding how to optimize the equilibrium. This states that when an equilibrium system is subjected to stress, the system will tend to adjust itself in such a way that part of the stress is relieved. These stresses are, for example, variations of temperature, pressure, or concentration of a reactant. For SO2/SO3 system
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