Method for the catalytic oxidation of ammonia gas
View Patent ↗A process for catalytic oxidation of ammonia gas by way of an oxygen-containing gas in a presence of a noble metal-containing catalyst may be employed to give nitrogen monoxide. A temperature of an ammonia/air mixed gas may be optimized in respect of nitrogen monoxide selectivity of the reaction before contact with the catalyst. Examination of catalytic NH 3 oxidation according to 4NH 3 +5O 2 →4NO+6H 2 O revealed that an optimum mode of operation of an NH 3 burner in an HNO 3 plant is not to be achieved by maintenance of a constant gauze temperature of the catalyst gauze by automatic setting of the NH 3 :air ratio. Rather, there is an optimum temperature for each process condition that should be set not by changing the NH 3 :air ratio but instead by altering the temperature of the NH 3 /air mixed gas before contact with the catalyst gauzes.
1. A process for catalytic oxidation of ammonia gas by way of an oxygen-containing gas in a presence of a catalyst to give nitrogen monoxide in an oxidation reactor, the process comprising regulating a reaction temperature at the catalyst to an optimum value with respect to nitrogen monoxide selectivity of a reaction of catalytic oxidation of ammonia gas, wherein the regulating is effected by way of measures upstream of the oxidation reactor, wherein the oxygen-containing gas is air, the process comprising directly heating or cooling the air and/or the ammonia gas/air mixed gas before contact with the catalyst, wherein the process further comprises introducing upstream of the addition of the ammonia gas a first fuel gas that influences the reaction temperature, with combustion of the fuel gas occurring at the catalyst.
2. The process of claim 1 wherein the oxygen-containing gas is air, the process comprising indirectly heating or cooling the air and/or the ammonia gas/air mixed gas before contact with the catalyst.
3. The process of claim 2 comprising indirectly heating the air and/or the ammonia gas/air mixed gas by way of steam or other heat transfer medium.
4. The process of claim 2 wherein the catalytic oxidation occurs in a plant comprising a process air compressor with an intermediate cooler and a regulated process air-side bypass around the intermediate cooler for setting an exit temperature of air exiting from the process air compressor, wherein the process air compressor provides said air.
5. The process of claim 4 wherein the catalytic oxidation occurs in a plant comprising a process air compressor, the process comprising mixing a process air stream with a hot medium and/or a cold medium upstream or downstream of the process air compressor.
6. The process of claim 5 wherein the cold medium comprises at least one of demineralized water, liquid nitrogen, or water from NH 3 vaporization.
7. The process of claim 5 wherein the ammonia gas is mixed with primary air prior to or during the catalytic oxidation of the ammonia gas to form the nitrogen monoxide, wherein the nitrogen monoxide is thereafter mixed with secondary air for oxidation to form nitrogen dioxide, wherein a total air stream includes the primary air and the secondary air, the process comprising mixing the hot medium or the cold medium with a total air stream or only with the primary air.
8. The process of claim 5 comprising heating by mixing in steam upstream of the process air compressor.
9. The process of claim 5 comprising heating or cooling the ammonia gas/air mixed gas by mixing in steam downstream of the process air compressor.
10. A process for catalytic oxidation of ammonia gas by way of an oxygen-containing gas in a presence of a catalyst to give nitrogen monoxide in an oxidation reactor, the process comprising regulating a reaction temperature at the catalyst to an optimum value with respect to nitrogen monoxide selectivity of a reaction of catalytic oxidation of ammonia gas, wherein the regulating is effected by way of measures upstream of the oxidation reactor, wherein the oxygen-containing gas is air, the process comprising directly heating or cooling the air and/or the ammonia gas/air mixed gas before contact with the catalyst, wherein the process further comprises heating the air and/or the ammonia gas/air mixed gas before contact with the catalyst via a fuel gas for increasing a burner temperature, wherein the fuel gas is introduced into an air stream in a region of a conduit upstream of an addition of the ammonia gas with combustion of the fuel gas.
11. The process of claim 1 comprising introducing a second fuel gas or a second medium that influences the reaction temperature downstream of the addition of the ammonia gas.
12. The process of claim 1 wherein the oxygen-containing gas is air, the process comprising indirectly heating or cooling the air and/or the ammonia gas/air mixed gas before contact with the catalyst, the process comprising at least one of:
indirectly heating or cooling the air by way of a first indirect heat transfer before adding the ammonia gas; or
indirectly heating or cooling the ammonia gas/air mixed gas by way of a second heat transfer after adding the ammonia.
13. The process of claim 1 wherein a change in temperature of combustion occurs via changing a setting parameter of a process air compressor and wherein the process air compressor provides said air.
14. The process of claim 1 comprising determining a value of a temperature of a catalyst gauze as a function of an NH 3 concentration, a plant load, and/or a burner pressure by performing closed loop control and setting an amount of heating or cooling medium fed upstream of the oxidation reactor and/or adjusting a setting of a process air compressor, wherein the process air compressor provides said air.
15. The process of claim 14 comprising performing cascade control whereby an output of a temperature regulator for the temperature of the catalyst gauze provides the value of a temperature setting for a flow regulator for the heating or cooling medium.
16. The process of claim 14 comprising operating a plant in which the process is practiced by varying amounts of the heating or cooling medium and/or changing settings of the process air compressor using data measured during plant operation and performing a feed-forward control with feedback trim.
17. A process for catalytic oxidation of ammonia gas by way of an oxygen-containing gas in a presence of a catalyst to give nitrogen monoxide in an oxidation reactor, the process comprising regulating a reaction temperature at the catalyst to an optimum value with respect to nitrogen monoxide selectivity of a reaction of catalytic oxidation of ammonia gas, wherein the regulating is effected by way of measures upstream of the oxidation reactor, wherein the oxygen-containing gas is air, the process comprising directly heating or cooling the air and/or the ammonia gas/air mixed gas before contact with the catalyst, wherein the process further comprises introducing a first fuel gas or a first medium that influences the reaction temperature downstream of the addition of the ammonia gas, with combustion of the fuel gas occurring at the catalyst in an ammonia burner.