Used double-absorption sulfuric acid plant designed by MECS (Monsanto Enviro-Chem System, Inc.) to process an acid stream from an acid gas removal unit (AGR), an ammonia acid gas stream from an ammonia stripper, and a sulfur dioxide stream from a hot gas cleanup unit (HGCU). The acid gas removal unit is a conventional amine unit using MDEA. The ammonia stripper unit is a steam stripping system that removes the hydrogen sulfide, carbon dioxide, ammonia and other gases from sour water. The hot gas cleanup unit uses a solid reactant to remove sulfur compounds from a gas stream and is then regenerated with dry air. The plant produced industrial grade 98% sulfuric acid. The plant consists of 4 process sections: (1) Formation of sulfur dioxide (SO2) gas in the decomposition furnace with the combustion of H2S gas. (2) Cooling and purification of the SO2 process gas. (3) Convention of the SO2 to sulfur trioxide (SO3) gas. (4) Absorption of the SO3 in sulfuric acid.