Method for in-duct urea injection for selective catalytic reduction on small boilers and combustion sources
View Patent ↗A method for reducing NOx emissions from a lean burn combustor equipped with a NOx reducing exhaust catalyst, includes at least the following steps: (i) generating a computer based model of the geometry of an exhaust system of the combustor; (ii) computing at least one of flue gas velocity profiles and mass flow stream lines for exhaust gas flow through the exhaust system; (iii) inputting injector data comprising at least droplet size and velocity; (iv) modeling droplet trajectories for a plurality of injector locations; (v) modeling at least one flow conditioning device in the exhaust system; and (vi) manipulating the computer based model until an injector location is identified that provides a predicted root mean square (RMS) of reagent at the face of the catalyst that is less than 15%.
1. A method for reducing NOx emissions from a lean burn combustor equipped with a NOx reducing exhaust catalyst, said method comprising the steps of:
constructing a computer based model of the geometry of an exhaust system of the combustor with an inlet and an outlet using computational fluid dynamics modeling techniques;
computing flue gas velocity profiles and mass flow stream lines for exhaust gas flow through the exhaust system;
inputting spray lab data for known injection spray parameters, including at least droplet size and velocity;
modeling droplet trajectories for selected injector locations;
inputting at least one flow conditioning device inserted in the exhaust system into the computer based model;
integrating the computer based model until an injector location is identified that provides a predicted root mean square (RMS) of reagent at a face of the catalyst that is less than 15%;
installing at least one reagent injector on the exhaust system in a location identified in said integrating step; and
injecting an aqueous based reagent so that NOx is reduced across a downstream catalyst installed in the exhaust system of the combustor.
2. The method of claim 1 , wherein the predicted root mean square (RMS) at the catalyst face is less than 10% at a load condition on the combustor of 80% to 100% of the full load combustor capacity.
3. The method of claim 1 , wherein the injector is a solenoid pulse width reagent injector used without air assistance.
4. The method of claim 1 , wherein the injector is used with air assistance for atomization to produce a droplet of less than 50 microns Sauter mean diameter.
5. The method of claim 1 , wherein the reagent is urea.
6. The method of claim 1 , wherein the reagent is ammonia.
7. The method of claim 1 , wherein uncontrolled NOx emissions of the combustor are less than 100 ppm.
8. The method of claim 1 , wherein the injection rate of the at least one reagent injector is less than 60 gph.
9. The method of claim 1 , wherein the flow conditioning device comprises at least one of the following: a perforated plate, a turning vane, a baffle, and a swirler.
10. The method of claim 9 , wherein the flow conditioning device is located in the exhaust system upstream of a first injection point of the reagent.
11. The method of claim 9 , wherein the flow conditioning device is located in the exhaust system downstream of a first injection point of the reagent but upstream of the face catalyst of the catalyst.
12. A method for reducing NOx emissions from a lean burn combustor equipped with a NOx reducing exhaust catalyst, said method comprising the steps of:
generating a computer based model of the geometry of an exhaust system of the combustor;
computing at least one of flue gas velocity profiles and mass flow stream lines for exhaust gas flow through the exhaust system;
inputting injector data comprising at least droplet size and velocity;
modeling droplet trajectories for a plurality of injector locations;
modeling at least one flow conditioning device in the exhaust system; and
manipulating the computer based model until an injector location is identified that provides a predicted root mean square (RMS) of reagent at a face of the catalyst that is less than 15%.
13. The method of claim 12 , further comprising the step of injecting an aqueous based reagent into the exhaust system in a location identified in said integrating step.
14. The method of claim 12 , wherein the predicted root mean square (RMS) at the catalyst face is less than 10% at a load condition on the combustor of 80% to 100% of the full load combustor capacity.
15. The method of claim 13 , wherein the reagent is injected by a solenoid pulse width reagent injector used without air assistance.
16. The method of claim 13 , wherein the reagent is injected by an injector used with air assistance for atomization to produce a droplet of less than 50 microns average diameter.
17. The method of claim 13 , wherein the reagent is urea.
18. The method of claim 13 , wherein the reagent is ammonia.
19. The method of claim 13 , wherein the injection rate of the reagent is less than 60 gph.
20. The method of claim 12 , wherein the flow conditioning device comprises at least one of the following: a perforated plate, a turning vane, a baffle, and a swirler.
21. The method of claim 20 , wherein the flow conditioning device is located in the exhaust system upstream of a first injection point of the reagent.
22. The method of claim 20 , wherein the flow conditioning device is located in the exhaust system downstream of a first injection point of the reagent but upstream of the face catalyst of the catalyst.