Kraus reaction mechanism

Process principle of the sulfur recovery unit: The Claus process with partial combustion is employed. In this partial combustion approach, all acidic gases are sent to a combustion furnace; by controlling the amount of air supplied, 1/3 of the hydrogen sulfide in the flue gas is burned to produce sulfur dioxide, while the remaining 2/3 of the hydrogen sulfide reacts with the sulfur dioxide generated within the Claus reactor, under the action of a catalyst, to form sulfur. The main reactions are as follows: 2H2S+O2→2H2O+2/XSX↓ (instantaneous reaction) (1) H2S+3/2O2→H2O+SO2 (instantaneous reaction) (2) 2H2S+SO2→2H2O+3/XSX↓ (reversible reaction) (3) 2H2S+SO2→2H2O+3S↓ (Clausius reaction under catalysis) (4) CS2+H2O→COS+H2S (hydrolysis reaction under catalysis) (5) COS+H2O→CO2+H2S (hydrolysis reaction under catalysis) (6) Reactions 1, 2, and 3 occur in the high-temperature flue gas (1200°C) inside the acid gas combustion furnace ； Reactions 4, 5, and 6 occur on the catalysts in the first and second Claus converters, in an environment of low-temperature flue gas (210–320°C). The Claus sulfur recovery process, particularly the actual chemical reactions taking place in the high-temperature reactor, is highly complex, which in turn makes the components in the gas stream after the reaction more complex as well.