Production methods used in sulfuric acid plants

Producing sulfuric acid from low-concentration SO₂ flue gas (expressed as a volume fraction, φ(SO₂)) presents challenges regarding heat and water balances. Regarding heat balance, a minimum SO₂ concentration-such as 1.5% (φ)-is required to maintain autothermal operation in a single-absorption conversion system. Water balance issues require controlling the moisture introduced by the gas stream; solutions include pre-drying/re-concentration processes or cryogenic methods. The pre-drying/re-concentration process was originally developed by Lurgi (Germany); in 1990, MHO (Belgium) implemented this technology at a smelter flue gas acid-making plant where the feed gas SO₂ concentration ranged from 1.5% to 1.6%.
Wet-process acid-making technologies include WSA, SNOX, MECS-Sulfox™, and SOP; among these, WSA is the most widely applied globally. In 1999, Molymet (Sonora, Mexico) adopted the WSA process to treat molybdenum smelting flue gas with an SO₂ concentration of 3%–4%. Domestically, Zhuzhou Smelter pioneered the use of this process in 2000 for lead smelting flue gas, handling concentrations of 2.2%–4.5%.
Other technologies include contact-process acid production using blended high/low-concentration SO₂ gas, low-temperature SO₂ condensation combined with the conventional contact process, and regenerative SO₂ recovery combined with the conventional contact process. The latter category encompasses regenerative amine scrubbing, regenerative inorganic solvent recovery, and activated coke (or carbon) adsorption.