PURPOSE: To cost effectively and efficiently recover sulfur under a permissible environment reference by limiting the initial molar ratio of H2O and SO2 in a sulfur recovering apparatus and the molar ratio of the H2S and SO2 in the outflow gaseous flow flowing out of this apparatus at the time of recovering the elemental sulfur from H2S-contg. gas by a Claus process.

CONSTITUTION: The H2S-contg. gas and at least one oxygen-contg. gas which is air, molecular oxygen or SO2 are introduced into the sulfur recovering apparatus. Operating conditions are so set as satisfy the requirements to regulate the amt. of the oxygen-contg. gas to be introduced into the sulfur recovering apparatus such that the initial molar ratio of the H2S and SO2 in the sulfur recovering apparatus exceeds 2:1 and to bring the H2S-contg. gas into reaction with the oxygen-contg. gas in the sulfur recovering apparatus under the reaction conditions adequate for forming the sulfur and the effluent gaseous flow contg. H2S, CO2 and steam such that the H2S and SO2 in the effluent gaseous flow described above exceeds about 20:1.