Dual pressure plant for the production of nitric acid and method for operating same

A method for operating a high pressure bleacher unit in a plant comprising:

• an air compressor, operable to pressurize air to a pressure ranging from 2 bar to 6 bar (low pressure, LP);
• a converter, operating at the low pressure (LP), operable to be fed with a stream of an ammonia/pressurized air mixture at the low pressure (LP), to oxidize the ammonia and to produce an LP gaseous NOx gas/steam mixture, comprising water and NO;
• a NOx gas compressor, operable to elevate the pressure of a gaseous NOx stream from the low pressure (LP) to a pressure ranging from 9 bar to 16 bar (high pressure, HP), resulting, at its downstream side, in an HP gaseous NOx stream;
• an absorber unit, operating at the high pressure (HP), operable to react the nitrogen oxides contained in the high pressure (HP) gaseous NOx stream with water, wherein the absorber unit-provides an output product stream containing nitric acid and dissolved nitrogen oxides, and a tail gas;
• and
• a bleacher unit, operable to strip dissolved nitrogen oxides away from the output product stream with a stripping medium, providing a stripped nitric acid stream and a NOx-loaded stripping gas;
• wherein
• the bleacher unit operates at the high pressure (HP), which is about equal to the pressure at which the absorber unit is operating;
• the bleacher unit is in fluid communication with a source of high pressure (HP) oxygen-rich gas, for providing the bleacher unit with the high pressure (HP) oxygen-rich gas as a stripping medium;
• the plant comprising means for directing the NOx-loaded stripping gas to the downstream side of the NOx gas compressor;
• the plant being characterised in that it further comprises:
• a high pressure (HP) water electrolyzer, operating at a gas pressure of at least 9 bar, in fluid communication with the bleacher unit for providing the high pressure (HP) oxygen-rich gas at a pressure ranging from 9 bar to 16 bar to be used as the stripping medium, alone or mixed with pressured air or any other suitable gas, the method comprising steps of:
• a) operating the bleacher unit at the high pressure (HP), which is about equal to the pressure at which the absorber unit is operating;
• b) providing the bleacher unit with the high pressure (HP) oxygen-rich gas as the stripping medium at the pressure ranging from 9 bar to 16 bar, wherein the high pressure (HP) oxygen-rich gas is provided by the high pressure (HP) water electrolyzer;
• and
• c) directing the NOx-loaded stripping gas to downstream of the NOx gas compressor.