A process for production of elemental sulfur from a feedstock gas comprising from 15 vol%, 20 vol%, 30 vol%, 40 vol% or 50 vol% to 99 vol% or 100 vol% H 2 S and a stream of sulfuric acid involving the steps of a. providing a Claus reaction furnace feed stream comprising an amount of said feedstock gas, an amount of sulfuric acid, an amount of oxygen and optionally an amount of fuel, wherein the amount of oxygen is substoichiometric with respect to the Claus reaction, b. directing said Claus reaction furnace feed stream to a reaction furnace operating at elevated temperature such as above 900°C, providing a Claus converter feed gas, c. cooling said Claus converter feed gas to provide a cooled Claus converter feed gas and optionally withdrawing elemental sulfur from the gas d. directing said cooled Claus converter feed gas to contact a material catalytically active in the Claus reaction, e. withdrawing a Claus tail gas and elemental sulfur, optionally by cooling the effluent from said material catalytically active in the Claus reaction, f. directing a stream comprising said Claus tail gas, oxygen and optionally a fuel as a feedstock gas to a means for Claus tail gas oxidation, providing a SO 2 converter feed gas g. directing said SO 2 converter feed gas to contact a material catalytically active in SO 2 oxidation to SO 3, providing an SO 3 rich gas, h. converting said SO 3 rich gas to concentrated sulfuric acid, either by absorption of SO 3 in sulfuric acid or by hydration of SO 3, cooling and condensation of sulfuric acid, i. recycling at least a part of the produced sulfuric acid to the Claus reaction furnace, characterized by the SO 2 converter feed gas being provided from an amount of combustibles, in the Claus tail gas, being oxidized in the means for Claus tail gas oxidation in the presence of a material catalytically active in sulfur oxidation at an inlet temperature below 400°C. a. providing a Claus reaction furnace feed stream comprising an amount of said feedstock gas, an amount of sulfuric acid, an amount of oxygen and optionally an amount of fuel, wherein the amount of oxygen is substoichiometric with respect to the Claus reaction, b. directing said Claus reaction furnace feed stream to a reaction furnace operating at elevated temperature such as above 900°C, providing a Claus converter feed gas, c. cooling said Claus converter feed gas to provide a cooled Claus converter feed gas and optionally withdrawing elemental sulfur from the gas d. directing said cooled Claus converter feed gas to contact a material catalytically active in the Claus reaction, e. withdrawing a Claus tail gas and elemental sulfur, optionally by cooling the effluent from said material catalytically active in the Claus reaction, f. directing a stream comprising said Claus tail gas, oxygen and optionally a fuel as a feedstock gas to a means for Claus tail gas oxidation, providing a SO 2 converter feed gas g. directing said SO 2 converter feed gas to contact a material catalytically active in SO 2 oxidation to SO 3, providing an SO 3 rich gas, h. converting said SO 3 rich gas to concentrated sulfuric acid, either by absorption of SO 3 in sulfuric acid or by hydration of SO 3, cooling and condensation of sulfuric acid, i. recycling at least a part of the produced sulfuric acid to the Claus reaction furnace,