The Double Contact Process For Sulfuric Acid Production

Abstract

In the usual contact plants 97-98% of the SO₂ is oxidized to SO₃ while the remaining 2-3% nonoxidized S0₂ are emitted. The stack gas generally contains 0.2-0.3% by volume SO₂.Through changing to the Bayer Double Contact process, the conversion can be raised to 99.5% or higher. The sulfuric acid can be produced at the same cost as with the single contact method, since the additional capital investment is compensated by higher yield and throughput (this applies to Germany). Based on equilibrium considerations, the rates of conversion obtainable with the contact and double contact processes are shown. The theoretical results are compared with the values obtained in practical operations. The fundamentals of the process are explained and the experience so far accumulated is discussed. The first double contact plant was started up in March 1964. By the end of 1966 as many as sixteen double contact plants were in operation and a further ten will go into production during 1967. These plants use sulfur, pyrite, zinc sulfide, or sulfates as raw materials.