Integrated plants and associated processes for producing ammonia and sulfuric acid have been developed comprising air separation and water electrolysis subsystems and which make surprisingly efficient use of the products from these subsystems (i.e. oxygen and nitrogen from the former and hydrogen and oxygen from the latter). The invention is particularly suitable for use as part of an integrated fertilizer production plant.

A method for preparing an electronic grade sulfuric acid from a waste sulfuric acid solution includes the steps of: performing, in sequence, a concentration treatment, a cracking treatment, and a purification treatment; performing a first oxidation treatment on sulfur dioxide; performing a first absorption treatment and a second oxidization treatment; performing an evaporation treatment; performing a first removal treatment on an acid mist containing metal ions and anion impurities; performing a second absorption treatment; and performing a second removal treatment on residual sulfur dioxide.

A method for preparing an electronic grade sulfuric acid from a waste sulfuric acid solution includes the steps of: performing, in sequence, a concentration treatment, a cracking treatment, and a purification treatment; performing a first oxidation treatment on sulfur dioxide; performing a first absorption treatment and a second oxidization treatment; performing an evaporation treatment; performing a first removal treatment on an acid mist containing metal ions and anion impurities; performing a second absorption treatment; and performing a second removal treatment on residual sulfur dioxide.

A method for treating a spent oxidizing acid which contains at least one of H.sub.2O.sub.2 and one or more peroxy acids of sulfur comprising contacting the spent oxidizing acid with a quantity of SO.sub.2 in excess of an equilibrium quantity required to convert the H.sub.2O.sub.2 and peroxy acids of sulfur to sulfuric acid.

The invention describes a process for producing sulfuric acid by catalytic oxidation of SO.sub.2 to SO.sub.3 and subsequent absorption of the SO.sub.3 in sulfuric acid, wherein the SO.sub.3 is introduced into a first absorption stage (primary absorber) and at least partly absorbed there in concentrated sulfuric acid, wherein the SO.sub.3 not absorbed in the first absorption stage is supplied to a second absorption stage (secondary absorber) for the further absorption in concentrated sulfuric acid, and wherein the sulfuric acid is cooled after passing through the two absorption stages. The cooling of the sulfuric acid is effected in at least two heat exchangers connected in parallel, wherein one of the at least two heat exchangers is operated as partial evaporator and is cooled with boiler feed water/steam and the other one is cooled with cooling water and operated as pure acid cooler.

A method for treating a spent oxidizing acid which contains at least one of H.sub.2O.sub.2 and one or more peroxy acids of sulfur comprising contacting the spent oxidizing acid with a quantity of SO.sub.2 in excess of an equilibrium quantity required to convert the H.sub.2O.sub.2 and peroxy acids of sulfur to 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.

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 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.

A process plant for production of sulfuric acid from a process gas comprising SO2, including a process gas inlet, a first SO2 converter having an inlet and an outlet, a first condenser having a gas inlet, a gas outlet and a liquid outlet, a gas mixing device having a first inlet, a second inlet and an outlet, a process gas heater having an inlet and an outlet, a second SO2 converter having an inlet and an outlet, a second condenser having a gas inlet, a gas outlet and a liquid outlet, one or more means for cooling and storage of sulfuric acid and a purified process gas outlet.