A revamp process for modifying a sulfur abatement plant including a Claus process plant, the Claus process plant including a Claus reaction furnace and one or more Claus conversion stages, each Claus conversion stage including a conversion reactor and a means for elemental sulfur condensation, and a means of Claus tail gas oxidation configured for receiving a Claus tail gas from said Claus process plant and configured for providing an oxidized Claus tail gas, the process revamp including: a) providing a sulfuric acid producing tail gas treatment plant producing sulfuric acid, and b) providing a means for transferring an amount or all of the sulfuric acid produced in said sulfuric acid producing tail gas treatment plant to said Claus reaction furnace, wherein the moles of sulfur in the transferred sulfuric acid relative to the moles of elemental sulfur withdrawn from the Claus process plant is from 3% to 25%.

A method of treating a spent oxidizing acid is provided comprising the steps of contacting a spent acid containing peroxy acids of sulfur with a quantity of SO.sub.2 in excess of an equilibrium quantity required to convert the peroxy acids to sulfuric acid. The excess SO.sub.2 is catalytically converted to SO.sub.3, and the SO.sub.3 is absorbed into the sulfuric acid stream essentially free of H.sub.2SO.sub.5 and H.sub.2O.sub.2 to make product sulfuric acid.

A method of treating a spent oxidizing acid is provided comprising the steps of contacting a spent acid containing peroxy acids of sulfur with a quantity of SO.sub.2 in excess of an equilibrium quantity required to convert the peroxy acids to sulfuric acid. The excess SO.sub.2 is catalytically converted to SO.sub.3, and the SO.sub.3 is absorbed into the sulfuric acid stream essentially free of H.sub.2SO.sub.5 and H.sub.2O.sub.2 to make product sulfuric acid.

Apparatus and methods for treating acid gas, which utilizes multi-stage absorption cycle of ammonia desulfurization to treat acid tail gas after pre-treatment of the acid gas, thereby achieving the purpose of efficient and low-cost treatment of acid tail gas. The parameters of the acid tail gas may be adjusted by a regulatory system such that the enthalpy value of the acid tail gas is in the range of 60-850 kJ/kg dry gas, for example, 80 680 kJ/kg dry gas or 100-450 kJ/kg dry gas, to meet the requirements of ammonia desulfurization, and achieve the synergy between the acid gas pre-treatment and ammonia desulfurization. Furthermore, hydrogen sulfide may be converted into sulfur/sulfuric acid plus ammonium sulfate at an adjustable ratio.

Apparatus and methods for treating acid gas, which utilizes multi-stage absorption cycle of ammonia desulfurization to treat acid tail gas after pre-treatment of the acid gas, thereby achieving the purpose of efficient and low-cost treatment of acid tail gas. The parameters of the acid tail gas may be adjusted by a regulatory system such that the enthalpy value of the acid tail gas is in the range of 60-850 kJ/kg dry gas, for example, 80 680 kJ/kg dry gas or 100-450 kJ/kg dry gas, to meet the requirements of ammonia desulfurization, and achieve the synergy between the acid gas pre-treatment and ammonia desulfurization. Furthermore, hydrogen sulfide may be converted into sulfur/sulfuric acid plus ammonium sulfate at an adjustable ratio.

The present invention solves the existing problem of using very expensive oxidation reagents, such as H.sub.2O.sub.2 and ozone, in removal of NO.sub.x and SO.sub.x from flue gases, by performing simultaneous oxidation of NO.sub.x and SO.sub.x with atmospheric oxygen in a combined system for catalytic oxidation and wet-scrubbing of both NO.sub.x and SO.sub.x from a flue gas and manufacturing fertilisers. Two major configurations of the oxidation system are disclosed in the present invention. The first configuration operates on oxygen-enriched air to increase efficiency of the oxidation reaction and requires an additional oxygen concentrator unit. The second configuration operates on atmospheric air at ambient conditions and requires an additional catalyst activation unit. In the second configuration, the efficient oxidation process is carried out at low temperatures of about 30-90 C. in the presence of recovered and re-activated catalyst. This temperature is a result of the exothermic character of the reaction, and therefore, no heating is required in the process.

The present invention solves the existing problem of using very expensive oxidation reagents, such as H.sub.2O.sub.2 and ozone, in removal of NO.sub.x and SO.sub.x from flue gases, by performing simultaneous oxidation of NO.sub.x and SO.sub.x with atmospheric oxygen in a combined system for catalytic oxidation and wet-scrubbing of both NO.sub.x and SO.sub.x from a flue gas and manufacturing fertilisers. Two major configurations of the oxidation system are disclosed in the present invention. The first configuration operates on oxygen-enriched air to increase efficiency of the oxidation reaction and requires an additional oxygen concentrator unit. The second configuration operates on atmospheric air at ambient conditions and requires an additional catalyst activation unit. In the second configuration, the efficient oxidation process is carried out at low temperatures of about 30-90 C. in the presence of recovered and re-activated catalyst. This temperature is a result of the exothermic character of the reaction, and therefore, no heating is required in the process.

Apparatus and methods for treating acid gas, which utilizes multi-stage absorption cycle of ammonia desulfurization to treat acid tail gas after pre-treatment of the acid gas, thereby achieving the purpose of efficient and low-cost treatment of acid tail gas. The parameters of the acid tail gas may be adjusted by a regulatory system such that the enthalpy value of the acid tail gas is in the range of 60-850 kJ/kg dry gas, for example, 80-680 kJ/kg dry gas or 100-450 kJ/kg dry gas, to meet the requirements of ammonia desulfurization, and achieve the synergy between the acid gas pre-treatment and ammonia desulfurization. Furthermore, hydrogen sulfide may be converted into sulfur/sulfuric acid plus ammonium sulfate at an adjustable ratio.

Apparatus and methods for treating acid gas, which utilizes multi-stage absorption cycle of ammonia desulfurization to treat acid tail gas after pre-treatment of the acid gas, thereby achieving the purpose of efficient and low-cost treatment of acid tail gas. The parameters of the acid tail gas may be adjusted by a regulatory system such that the enthalpy value of the acid tail gas is in the range of 60-850 kJ/kg dry gas, for example, 80-680 kJ/kg dry gas or 100-450 kJ/kg dry gas, to meet the requirements of ammonia desulfurization, and achieve the synergy between the acid gas pre-treatment and ammonia desulfurization. Furthermore, hydrogen sulfide may be converted into sulfur/sulfuric acid plus ammonium sulfate at an adjustable ratio.

A process for preparing sulfuric acid may involve oxidizing sulfur to sulfur dioxide by way of dried air in a first oxidation stage. The sulfur dioxide may then be oxidized to sulfur trioxide in a second oxidation stage. The sulfur trioxide may be absorbed by sulfuric acid in at least one absorption stage. Further, heated sulfuric acid may be drawn off from the absorption stage and used for generating steam. Process gas from an intermediate absorption stage may be recycled to the second oxidation stage and, in some cases, a final absorption stage after the process gas flows through the second oxidation stage.