Fuel staging methods for low NOx tangential fired boiler operation

1. A tangential fired boiler comprising:

a circumferential wall defining a combustion zone, said circumferential wall being generally rectangular when viewed along a generally horizontal cross-section;

a fireball disposed within the combustion zone, said fireball rotating about an imaginary axis when viewed along a generally horizontal cross-section;

a corner member disposed proximate to at least one corner of said combustion zone;

a plurality of fuel inlets disposed along said corner member, said plurality of fuel inlets injecting fuel into the combustion zone; and

wherein at least some of said plurality of fuel inlets inject fuel in a direction which is angled with respect to a normal, when viewed along a generally horizontal cross-section, of said corner member and upstream relative to a direction of rotation of said fireball.

2. The tangential fired boiler of claim 1 further comprising a plurality of air inlets disposed along said corner member, said plurality of air inlets injecting air into the combustion zone.

3. The tangential fired boiler of claim 2 wherein at least some of said plurality of air inlets inject air in a direction normal to said corner member.

4. The tangential fired boiler of claim 1 wherein said generally rectangular circumferential wall has a diagonal, and wherein said corner member is angled with respect to a normal of the diagonal and downstream relative to a direction of rotation of said fireball.

5. The tangential fired boiler of claim 4 wherein said corner member is angled with respect to the normal of the diagonal at an angle of about 6 degrees.

6. The tangential fired boiler of claim 4 wherein an angle of said corner member with respect to a normal of the diagonal is adjustable in order to fine-tune performance of said boiler.

7. The tangential fired boiler of claim 1 wherein the angle at which said plurality of fuel inlets inject fuel with respect to a normal of said corner member is greater than zero degrees and less than 45 degrees.

8. The tangential fired boiler of claim 7 wherein the angle at which said plurality of fuel inlets inject fuel with respect to a normal of said corner member is between about 15 degrees and about 25 degrees.

9. The tangential fired boiler of claim 1 wherein a corner member and a plurality of fuel inlets are disposed proximate to each corner of said combustion zone.

10. The tangential fired boiler of claim 1 wherein fuel is injected uniformly through said plurality of fuel inlets.

11. The tangential fired boiler of claim 1 wherein fuel is injected non-uniformly through said plurality of fuel inlets.

12. The tangential fired boiler of claim 1 wherein said corner member is disposed in the at least one corner of said combustion zone.

13. The tangential fired boiler of claim 1 wherein said corner member is disposed offset from, but near, the at least one corner of said combustion zone and in a sidewall of the circumferential wall for convenience in arrangement.

14. The tangential fired boiler of claim 13 wherein said corner member is offset from the at least one corner of said combustion zone downstream relative to the direction of rotation of said fireball, whereby fuel can be injected at a greater angle with respect to a normal of said corner member in order to overcome mechanical limitation or obstruction.

15. A tangential fired boiler comprising:

a circumferential wall defining a combustion zone, said circumferential wall being generally rectangular when viewed along a generally horizontal cross-section and having a diagonal;

a fireball disposed within the combustion zone, said fireball rotating about an imaginary axis when viewed along a generally horizontal cross-section;

a corner member disposed proximate to at least one corner of said combustion zone, said corner member being angled with respect to a normal of the diagonal and downstream relative to a direction of rotation of said fireball;

a plurality of fuel inlets disposed along said corner member, said plurality of fuel inlets injecting fuel into the combustion zone;

a plurality of air inlets disposed along said corner member, said plurality of air inlets injecting air into the combustion zone; and

wherein at least some of said plurality of fuel inlets inject fuel in a direction which is angled between about 15 degrees and about 25 degrees with respect to a normal, when viewed along a generally horizontal cross-section, of said corner member and upstream relative to a direction of rotation of said fireball.

16. The tangential fired boiler of claim 15 wherein at least some of said plurality of air inlets inject air in a direction normal to said corner member.

17. The tangential fired boiler of claim 15 wherein said corner member is angled with respect to the normal of the diagonal at an angle of about 6 degrees.

18. The tangential fired boiler of claim 15 wherein an angle of said corner member with respect to a normal of the diagonal is adjustable in order to fine-tune performance of said boiler.

19. The tangential fired boiler of claim 15 wherein a corner member and a plurality of fuel inlets are disposed proximate to each corner of said combustion zone.

20. The tangential fired boiler of claim 15 wherein fuel is injected uniformly through said plurality of fuel inlets.

21. The tangential fired boiler of claim 15 wherein fuel is injected non-uniformly through said plurality of fuel inlets.

22. The tangential fired boiler of claim 15 wherein said corner member is disposed in the at least one corner of said combustion zone.