Abstract: In a process for preparing nitric acid, nitrogen oxides are first generated in an ammonia combustion plant (2), and these are then supplied to at least one absorption tower (4, 5). In the absorption tower (4, 5), the nitrogen oxides are contacted in the water and oxygen, with at least partial reaction of the nitrogen-containing gas mixture with the water and the oxygen to form an aqueous nitric acid-containing solution which collects at the base of the absorption tower (4, 5) and is subsequently compressed and introduced via a riser line (12, 14, 21) back into the absorption tower (4, 5). In order to minimize the concentration of nitrogen oxides in the offgas from such a plant, it is proposed in accordance with the invention that oxygen be introduced in liquid form or gaseous form into a region of the riser line (12, 14, 21) that is lower in a geodetic sense. This promotes the dissolution of the oxygen and the reaction of the oxygen with likewise dissolved nitrogen oxides to give nitric acid.

Abstract: In a process for chlorine-alkali electrolysis, use is made of an oxygen depletion cathode. The process is run with a high excess of oxygen. The oxygen needed for this is provided for a device of the gas separation, for example a VPSA plant or an air fractionation plant. The large quantities of oxygen produced lead to considerable costs of the process. According to the invention, the oxygen-rich atmosphere remaining after passing through the process is fed back into the device for gas separation as input gas. The device the gas separation is therefore operated with an oxygen-rich input gas and therefore produces a larger quantity of oxygen-rich gas, which in turn is fed to the oxygen depletion cathode. As a result of the circulation of the gas, the economy of the overall process is increased considerably.

Abstract: In a process for chlorine-alkali electrolysis, use is made of an oxygen depletion cathode. The process is run with a high excess of oxygen. The oxygen needed for this is provided for a device of the gas separation, for example a VPSA plant or an air fractionation plant. The large quantities of oxygen produced lead to considerable costs of the process. According to the invention, the oxygen-rich atmosphere remaining after passing through the process is fed back into the device for gas separation as input gas. The device the gas separation is therefore operated with an oxygen-rich input gas and therefore produces a larger quantity of oxygen-rich gas, which in turn is fed to the oxygen depletion cathode. As a result of the circulation of the gas, the economy of the overall process is increased considerably.