Digestion of impure alumina with sulfuric acid dissolves all constituents except silica. The resulting sulfatesaluminum sulfate, ferric sulfate, titanyl sulfate, and magnesium sulfate for alumina contaminated with iron-, titanium-, and/or magnesium-containing speciesremain in solution at approximately 90 C. Hot filtration separates silica. Solution flow over metallic iron reduces ferric sulfate to ferrous sulfate. Controlled ammonia addition promotes hydrolysis and precipitation of hydrated titania from titanyl sulfate that is removed by filtration. Addition of ammonium sulfate forms ferrous ammonium sulfate and ammonium aluminum sulfate solutions. Alum is preferentially separated by crystallization. Addition of ammonium bicarbonate to an ammonium alum solution precipitates ammonium aluminum carbonate which may be heated to produce alumina, ammonia, and carbon dioxide. The remaining iron rich liquor also contains magnesium sulfate. The addition of oxalic acid generates insoluble ferrous oxalate which is thermally decomposed to ferrous oxide and carbon monoxide which is used to reduce the ferrous oxide to metallic iron. Further oxalic acid addition precipitates magnesium oxalate which is thermally decomposed to magnesium oxide.

An apparatus and a process for reducing the concentration of NOx nitrogen oxides in residual gas may be employed during shutdown and/or startup of apparatuses for preparing nitric acid. An example apparatus for reducing NOx nitrogen oxides may include a reactor that produces NOx nitrogen oxides, an absorption apparatus that absorbs at least part of the NOx nitrogen oxides produced in an aqueous composition, a residual gas purification plant that decomposes and/or reduces unabsorbed NOx nitrogen oxides, feed means for feeding the NOx nitrogen oxides to the absorption apparatus, discharge means for discharging the unabsorbed NOx nitrogen oxides from the absorption apparatus to the residual gas purification plant, and a bypass that transfers a gas mixture from the reactor to the residual gas purification plant while bypassing the absorption apparatus during startup and/or shutdown of the apparatus for preparing nitric acid.

An apparatus and a process for reducing the concentration of NOx nitrogen oxides in residual gas may be employed during shutdown and/or startup of apparatuses for preparing nitric acid. An example apparatus for reducing NOx nitrogen oxides may include a reactor that produces NOx nitrogen oxides, an absorption apparatus that absorbs at least part of the NOx nitrogen oxides produced in an aqueous composition, a residual gas purification plant that decomposes and/or reduces unabsorbed NOx nitrogen oxides, feed means for feeding the NOx nitrogen oxides to the absorption apparatus, discharge means for discharging the unabsorbed NOx nitrogen oxides from the absorption apparatus to the residual gas purification plant, and a bypass that transfers a gas mixture from the reactor to the residual gas purification plant while bypassing the absorption apparatus during startup and/or shutdown of the apparatus for preparing nitric acid.

The present invention relates to an electrolysis apparatus for collecting a nitrogen compound using ferric-ethylenediaminetetraacetic acid (Fe-EDTA), and more particularly, to an electrolysis apparatus for collecting a nitrogen compound in exhaust gas by supplying electric energy to cause a redox reaction of Fe-EDTA.

A system for producing nitric acid at reduced power consumption including an air compressor, to provide in a compressed air stream; a source of pressurized oxygen-rich gas having a pressure higher than the pressure of the compressed air stream; a mixing apparatus for mixing the oxygen-rich gas/compressed air stream mixture with an ammonia gas stream; an ammonia converter, to provide in a NO.sub.x gas/steam mixture; a water cooler/condenser for separating and condensing steam from NO.sub.x gas in the gaseous NO.sub.x gas/steam mixture; a NO.sub.x gas compressor, for compressing the gaseous NO.sub.x stream; an absorption tower downstream the water cooler/condenser, to provide in a stream of raw nitric acid-containing residual NO.sub.x gas and a tail gas including NO.sub.x gases; a mechanism for splitting the tail gas into a first tail gas stream and a second tail gas stream; and a mechanism for adjusting the amount of tail gas being split.

A system for producing nitric acid at reduced power consumption including an air compressor, to provide in a compressed air stream; a source of pressurized oxygen-rich gas having a pressure higher than the pressure of the compressed air stream; a mixing apparatus for mixing the oxygen-rich gas/compressed air stream mixture with an ammonia gas stream; an ammonia converter, to provide in a NO.sub.x gas/steam mixture; a water cooler/condenser for separating and condensing steam from NO.sub.x gas in the gaseous NO.sub.x gas/steam mixture; a NO.sub.x gas compressor, for compressing the gaseous NO.sub.x stream; an absorption tower downstream the water cooler/condenser, to provide in a stream of raw nitric acid-containing residual NO.sub.x gas and a tail gas including NO.sub.x gases; a mechanism for splitting the tail gas into a first tail gas stream and a second tail gas stream; and a mechanism for adjusting the amount of tail gas being split.

A production plant for producing nitric acid at reduced power, the system derived from a state-of-the art mono pressure nitric acid plant wherein the system further includes a first feature for splitting a tail gas stream into a first tail gas stream in fluid communication with an oxygen-rich gas and with compressed air and a second tail gas stream, and/or a second feature for splitting a tail gas stream into a third tail gas stream in fluid communication with an oxygen-rich gas and with compressed air and a fourth tail gas stream, a feature for pressurizing a gas downstream the absorption tower. The production plant allows for reduction of power by the air compressor. A method for operating the system, the use of the system for performing the method of the disclosure, and a method for revamping a state-of-the art mono pressure nitric acid plant into the system.

A production plant for producing nitric acid at reduced power, the system derived from a state-of-the art mono pressure nitric acid plant wherein the system further includes a first feature for splitting a tail gas stream into a first tail gas stream in fluid communication with an oxygen-rich gas and with compressed air and a second tail gas stream, and/or a second feature for splitting a tail gas stream into a third tail gas stream in fluid communication with an oxygen-rich gas and with compressed air and a fourth tail gas stream, a feature for pressurizing a gas downstream the absorption tower. The production plant allows for reduction of power by the air compressor. A method for operating the system, the use of the system for performing the method of the disclosure, and a method for revamping a state-of-the art mono pressure nitric acid plant into the system.

The invention relates to a process and apparatus for preparing nitric acid by catalytic oxidation of NH.sub.3 by means of oxygen and subsequent reaction of the NO.sub.x formed with an absorption medium in an absorption tower, which comprises a catalyst bed for N.sub.2O decomposition arranged in the process gas downstream of the catalytic NH.sub.3 oxidation and upstream of the absorption tower in the flow direction and a catalyst bed for NO.sub.x reduction and effecting a further decrease in the amount of N.sub.2O arranged in the tailgas downstream of the absorption tower in the flow direction, wherein the amount of N.sub.2O removed in the catalyst bed for N.sub.2O removal arranged in the process gas is not more than that which results in an N.sub.2O content of >100 ppmv and a molar N.sub.2O/NO.sub.x ratio of >0.25 before entry of the tailgas into the catalyst bed for NO.sub.x reduction and the catalyst bed for NO.sub.x reduction and effecting a further decrease in the amount of N.sub.2O arranged in the tailgas contains at least one iron-loaded zeolite catalyst and NH.sub.3 is added to the tailgas before entry into the catalyst bed in such an amount that an NO.sub.x concentration of <40 ppmv results at the outlet from the catalyst bed and the operating parameters are selected in such a way that an N.sub.2O concentration of <200 ppmv results.

The invention relates to a process and apparatus for preparing nitric acid by catalytic oxidation of NH.sub.3 by means of oxygen and subsequent reaction of the NO.sub.x formed with an absorption medium in an absorption tower, which comprises a catalyst bed for N.sub.2O decomposition arranged in the process gas downstream of the catalytic NH.sub.3 oxidation and upstream of the absorption tower in the flow direction and a catalyst bed for NO.sub.x reduction and effecting a further decrease in the amount of N.sub.2O arranged in the tailgas downstream of the absorption tower in the flow direction, wherein the amount of N.sub.2O removed in the catalyst bed for N.sub.2O removal arranged in the process gas is not more than that which results in an N.sub.2O content of >100 ppmv and a molar N.sub.2O/NO.sub.x ratio of >0.25 before entry of the tailgas into the catalyst bed for NO.sub.x reduction and the catalyst bed for NO.sub.x reduction and effecting a further decrease in the amount of N.sub.2O arranged in the tailgas contains at least one iron-loaded zeolite catalyst and NH.sub.3 is added to the tailgas before entry into the catalyst bed in such an amount that an NO.sub.x concentration of <40 ppmv results at the outlet from the catalyst bed and the operating parameters are selected in such a way that an N.sub.2O concentration of <200 ppmv results.