Abstract: The invention relates to a process for eliminating nitrogen oxides and sulphur oxides from a stream of flue gas containing nitrogen oxides and sulphur oxides comprising the steps of(a) adding ammonia to the stream of flue gas and contacting the resulting stream, at a temperature of 250.degree.-450.degree. C., with a reduction catalyst for selective reduction of nitrogen oxides into nitrogen and water, the molar ratio of ammonia to nitrogen oxides being in the range of 0.6-1.8,(b) contacting the stream from step (a), at a temperature of 300.degree.-470.degree. C., with an oxidation catalyst for oxidation of unreacted ammonia into nitrogen and water and simultaneous oxidation of sulphur dioxide into sulphur trioxide, and(c) cooling the stream from step (b) for condensation of sulphur trioxide in the form of sulphuric acid.The products of the process of the invention are steam, nitrogen, and concentrated sulphuric acid of commercial quality giving no waste disposal problems.

Abstract: The invention relates to a process for preparing concentrated sulfuric acid by conducting a gas stream containing SO.sub.3 and H.sub.2 SO.sub.4 -vapor in a sulfuric acid tower in countercurrent to liquid sulfuric acid formed through a concentrating zone containing filler bodies trickled with sulfuric acid and an absorption zone where sulfuric acid vapor is absorbed in recycled sulfuric acid on filler bodies trickled therewith. A very substantial reduction in the amount of acid mist formed in conventional processes of this type is obtained by maintaining such temperature conditions in the tower that the recycle acid is withdrawn from the tower at a temperature T.sub.4 determined by the formulaT.sub.4 >140+6.alpha.+.beta.+0.2(T.sub.1 -T.sub.d)where .alpha. is the concentration of SO.sub.3 +H.sub.2 SO.sub.4 vapor in the inlet gas to the tower, .beta. the concentration of water vapor in the same inlet gas, T.sub.1 the temperature in .degree. C. of the same inlet gas and T.sub.