Method and apparatus for adding reducing agent to secondary overfire air stream

1. A method of minimizing discharge of nitrogen oxides from a combustion boiler, the method comprising the steps of:

spraying a reducing agent into an overfire air stream;

supplying the overfire air stream with the sprayed reducing agent to the combustion boiler;

vaporizing the sprayed reducing agent at least within about 0.1 seconds of the sprayed reducing agent entering the combustion boiler;

reacting the vaporized reducing agent with the nitrogen oxides within the combustion chamber to reduce the nitrogen oxides and minimize discharge of nitrogen oxides from the combustion boiler; and

spraying the reducing agent into the overfire air stream at a discharge angle of between about 60° to about 140°.

2. A method of minimizing discharge of nitrogen oxides from a combustion boiler, the method comprising the steps of:

spraying a reducing agent into an overfire air stream;

supplying the overfire air stream with the sprayed reducing agent to the combustion boiler;

vaporizing the sprayed reducing agent at least within about 0.1 seconds of the sprayed reducing agent entering the combustion boiler;

reacting the vaporized reducing agent with the nitrogen oxides within the combustion chamber to reduce the nitrogen oxides and minimize discharge of nitrogen oxides from the combustion boiler; and

spraying the reducing agent into the overfire air stream such that a concentration of the reducing agent within the overfire air stream is between about 3 to about 5 percent.

3. The method of claim according to claim 2 , further comprising the step of using one of ammonia, ammonia salts, urea and urea prills as the reducing agent.

4. The method according to claim 2 , further comprising the steps of supplying a cooling fluid to a wall of the combustion boiler to absorb and remove heat generated within the combustion chamber, and

utilizing the heated fluid to drive a steam turbine and generate electricity.

5. A method of minimizing discharge of nitrogen oxides from a combustion boiler, the method comprising the steps of:

spraying a reducing agent into an overfire air stream;

supplying the overfire air stream with the sprayed reducing agent to the combustion boiler;

vaporizing the sprayed reducing agent at least within about 0.1 seconds of the sprayed reducing agent entering the combustion boiler;

reacting the vaporized reducing agent with the nitrogen oxides within the combustion chamber to reduce the nitrogen oxides and minimize discharge of nitrogen oxides from the combustion boiler; and

dividing at least one initial overfire air duct, for supplying an initial overfire air stream to the combustion boiler and facilitate substantially complete combustion of fuel supplied to the combustion boiler, into an initial primary overfire air stream and an initial secondary initial overfire air stream, and adding the reducing agent only to the initial secondary initial overfire air stream, but not the initial primary initial overfire air stream, prior to the secondary initial overfire air stream discharging into the combustion chamber.

6. The method according to claim 5 , further comprising the step of using at least 50 percent of the initial overfire air stream, supplied by the at least one initial overfire air duct, to form the initial primary overfire air stream and using a remainder of the initial overfire air stream, supplied by the at least one initial overfire air duct, to form the secondary initial overfire air stream.

7. The method according to claim 5 , further comprising the step of providing a reducing agent injection nozzle in the initial secondary overfire air stream for injecting the reducing agent, in liquid form, into the initial secondary air stream and vaporizing the reducing agent prior to the initial secondary overfire air stream entering the combustion chamber.

8. The method according to claim 5 , further comprising the step of heating the initial overfire air stream to a temperature of between 300 and 800 degrees F prior to the initial overfire air stream being divided into the primary and the secondary initial overfire air streams.

9. A method of minimizing discharge of nitrogen oxides from a combustion boiler, the method comprising the steps of:

spraying a reducing agent into an overfire air stream;

supplying the overfire air stream with the sprayed reducing agent to the combustion boiler;

vaporizing the sprayed reducing agent at least within about 0.1 seconds of the sprayed reducing agent entering the combustion boiler;

reacting the vaporized reducing agent with the nitrogen oxides within the combustion chamber to reduce the nitrogen oxides and minimize discharge of nitrogen oxides from the combustion boiler; and

spacing a plurality of primary combustion chamber overfire air ducts about a periphery of the combustion boiler for supplying addition air to a mid region of the primary combustion chamber and facilitating a substantially complete consumption of fuel supplied by at least one fuel supply duct to the combustion boiler.

10. A method of minimizing discharge of nitrogen oxides from a combustion boiler, the method comprising the steps of:

spraying a reducing agent into an overfire air stream;

supplying the overfire air stream with the sprayed reducing agent to the combustion boiler;

vaporizing the sprayed reducing agent at least within about 0.1 seconds of the sprayed reducing agent entering the combustion boiler;

reacting the vaporized reducing agent with the nitrogen oxides within the combustion chamber to reduce the nitrogen oxides and minimize discharge of nitrogen oxides from the combustion boiler; and

forming the reducing agent by mixing one of ammonia, ammonia salts, urea and urea prills with water in a ratio of about 3% to 15% of one of ammonia, ammonia salts, urea and urea prills with about 85% to 97% of water.

11. The method according to claim 10 , further comprising the step of spraying the reducing agent to have a particle size of between 1 micron and 40 microns.

12. A method of minimizing discharge of nitrogen oxides from a combustion boiler, the method comprising the steps of:

spraying a reducing agent into an overfire air stream;

supplying the overfire air stream with the sprayed reducing agent to the combustion boiler;

vaporizing the sprayed reducing agent at least within about 0.1 seconds of the sprayed reducing agent entering the combustion boiler;

reacting the vaporized reducing agent with the nitrogen oxides within the combustion chamber to reduce the nitrogen oxides and minimize discharge of nitrogen oxides from the combustion boiler; and

adding the reducing agent to the overfire air stream such that the reducing agent comprises generally about 1% to 25% of the overfire air stream.

13. A method of minimizing discharge of nitrogen oxides from a combustion boiler, the method comprising the steps of:

spraying a reducing agent into an overfire air stream;

supplying the overfire air stream with the sprayed reducing agent to the combustion boiler;

vaporizing the sprayed reducing agent at least within about 0.1 seconds of the sprayed reducing agent entering the combustion boiler;

reacting the vaporized reducing agent with the nitrogen oxides within the combustion chamber to reduce the nitrogen oxides and minimize discharge of nitrogen oxides from the combustion boiler; and

adding the reducing agent to the overfire air stream such that the reducing agent comprises generally about 2.5% to 7.5% of the overfire air stream.

14. A combustion boiler for combustion of fuel and generating heat, the combustion boiler comprising:

a housing defining an internal combustion chamber therein;

at least one fuel supply duct connected to the combustion boiler for supplying fuel to the combustion chamber; and

at least one initial overfire air duct for supplying an initial overfire air stream to the combustion chamber to facilitate complete combustion of the fuel supplied to the combustion boiler;

wherein the at least one initial overfire air duct is divided into an initial primary overfire air stream and an initial secondary initial overfire air stream, and a reducing agent is added only to the initial secondary initial overfire air stream, but not the initial primary initial overfire air stream, prior to the secondary initial overfire air stream discharging into the combustion chamber; and

the housing comprises a base wall, a sidewall and a top wall with an exit section formed in the sidewall adjacent the top wall, and an indentation is formed in the sidewall of the housing to form a throat which accelerates combustion byproducts and the over-fire air and any residual reducing agent as the combustion byproducts, the overfire air and any residual reducing agent flow from a primary combustion chamber toward a secondary combustion chamber located above the indentation in the combustion boiler.

15. The combustion boiler according to claim 14 , wherein the reducing agent injection nozzle has a discharge spray angle of between about 60° to about 140° and a plurality of fuel supply ducts supply fuel to the combustion chamber where the fuel ignites and is consumed upon operation of the combustion boiler.

16. A combustion boiler for combustion of fuel and generating heat, the combustion boiler comprising:

a housing defining an internal combustion chamber therein;

at least one fuel supply duct connected to the combustion boiler for supplying fuel to the combustion chamber; and

at least one initial overfire air duct for supplying an initial overfire air stream to the combustion chamber to facilitate complete combustion of the fuel supplied to the combustion boiler;

wherein the at least one initial overfire air duct is divided into an initial primary overfire air stream and an initial secondary initial overfire air stream, and a reducing agent is added only to the initial secondary initial overfire air stream, but not the initial primary initial overfire air stream, prior to the secondary initial overfire air stream discharging into the combustion chamber; and

the reducing agent added to the initial secondary initial overfire air stream is selected from the group comprising ammonia, ammonia salts, urea and urea prills.

17. A combustion boiler for combustion of fuel and generating heat, the combustion boiler comprising:

a housing defining an internal combustion chamber therein;

at least one fuel supply duct connected to the combustion boiler for supplying fuel to the combustion chamber; and

at least one initial overfire air duct for supplying an initial overfire air stream to the combustion chamber to facilitate complete combustion of the fuel supplied to the combustion boiler;

wherein the at least one initial overfire air duct is divided into an initial primary overfire air stream and an initial secondary initial overfire air stream, and a reducing agent is added only to the initial secondary initial overfire air stream, but not the initial primary initial overfire air stream, prior to the secondary initial overfire air stream discharging into the combustion chamber; and

the initial overfire air stream is heated to a temperature of between 300 and 800 degrees F. prior to the initial overfire air stream being divided into the primary and the secondary initial overfire air streams.

18. A combustion boiler for combustion of fuel and generating heat, the combustion boiler comprising:

a housing defining an internal combustion chamber therein:

at least one fuel supply duct connected to the combustion boiler for supplying fuel to the combustion chamber; and

at least one initial overfire air duct for supplying an initial overfire air stream to the combustion chamber to facilitate complete combustion of the fuel supplied to the combustion boiler;

wherein the at least one initial overfire air duct is divided into an initial primary overfire air stream and an initial secondary initial overfire air stream, and a reducing agent is added only to the initial secondary initial overfire air stream, but not the initial primary initial overfire air stream, prior to the secondary initial overfire air stream discharging into the combustion chamber;

the housing comprises a base wall, a sidewall and a top wall with an exit section formed in the sidewall adjacent the top wall, and an indentation is formed in the sidewall of the housing to form a throat which accelerates combustion byproducts and the overfire air and any residual reducing agent as the combustion byproducts, the overfire air and any residual reducing agent flow from a primary combustion chamber toward a secondary combustion chamber located above the indentation in the combustion boiler;

the reducing agent added to the initial secondary initial overfire air stream is selected from the group comprising ammonia, ammonia salts, urea and urea prills;

the reducing agent injection nozzle has a discharge spray angle of between about 60° to about 140° and a plurality of fuel supply ducts supply fuel to the combustion chamber where the fuel ignites and is consumed upon operation of the combustion boiler; and

the initial overfire air stream is heated to a temperature of between 300 and 800 degrees F. prior to the initial overfire air stream being divided into the primary and the secondary initial overfire air streams.