Method of reducing nitrogen oxides in a gas stream with vaporized ammonia
View Patent ↗The present invention is a method for selective reduction of nitrogen oxides in a gas stream with ammonia wherein the ammonia is vaporized prior to contacting it with the carrying fluid. The present invention also comprises a reducing agent dispersion system for use in substantially uniformly mixing a reducing agent with nitrogen oxides in a flue gas stream comprising a header and a plurality of lances. Further, the present invention comprises a novel reactor design for use in selective reduction of nitrogen oxides in a gas stream.
1. A method for selective reduction of nitrogen oxides in a gas stream with ammonia, wherein the gas stream comprises nitrogen oxides, the method comprising:
a) vaporizing the ammonia in a heater, wherein the vaporizing uses steam and wherein the steam produces a condensate in said heater;
b) directing the condensate from said heater to a secondary heat exchanger/coil mounted in a casing containing a carrying fluid and heating the carrying fluid with the secondary heat exchanger/coil;
c) contacting the vaporized ammonia with the heated carrying fluid;
d) mixing the vaporized ammonia with the heated carrying fluid; and
e) exposing the mixture of the vaporized ammonia and the heated carrying fluid to the gas stream for selective reduction of nitrogen oxides; and
wherein a, b, c, d, and e occur in order.
2. The method of claim 1 wherein the ammonia is in an aqueous solution before the vaporizing.
3. The method of claim 2 wherein the ammonia is present at a concentration of about 29.4% by weight before the vaporizing.
4. The method of claim 2 wherein the ammonia is present at a concentration of about 19% by weight before the vaporizing.
5. The method of claim 1 wherein the carrying fluid is ambient air.
6. The method of claim 1 wherein the carrying fluid is flue gas.
7. The method of claim 1 wherein the vaporized ammonia is above about 120° F. during the contacting.
8. The method of claim 1 further comprising raising a temperature of the carrying fluid with a heat source prior to the mixing.
9. The method of claim 1 , wherein the method further comprises, before step (b) of directing the condensate from said heater to a secondary heat exchanger/coil mounted in a casing containing a carrying fluid and heating the carrying fluid with the secondary heat exchanger/coil, the step of:
heating the carrier fluid, wherein the heating uses a heat source.
10. The method of claim 9 , wherein the heat source for heating the carrier fluid is a low pressure waste steam.
11. The method of claim 9 , wherein the heat source for heating the carrier fluid is hot flue gas.
12. The method of claim 9 , wherein the heat source for heating the carrier fluid is an electric heater.
13. A method for selectively reducing nitrogen oxides in an exhaust gas comprising:
(a) indirectly heating aqua ammonia in a heater with a heating fluid comprising steam, wherein the steam is not mixed with the ammonia, to produce in said heater vaporized ammonia and a residual fluid of said heating fluid, wherein said residual fluid comprises steam, condensate, or mixtures thereof;
(b) directing said residual fluid from said heater to a secondary heat exchanger/coil and indirectly heating a carrier gas with said residual fluid to produce a heated carrier gas;
(c) mixing the vaporized ammonia with said heated carrier gas to produce a reducing agent; and
(d) contacting the reducing agent with the exhaust gas to selectively reduce at least a portion of the nitrogen oxide.
14. The method of claim 13 wherein said residual fluid is steam condensate.