Combustion system with precombustor

1. A precombustor comprising:

a chamber bounded by a first end, outer walls, and a second end; and

an inlet configured to deliver a substantially parallel flow of solid fuel surrounded by oxygen through the first end of the chamber,

wherein the first end of the chamber includes a recirculation step immediately downstream of the inlet and the second end of the chamber fluidly communicates with a furnace;

wherein the inlet and the recirculation step are arranged to form a recirculation zone within the chamber of at least a portion of the solid fuel and the oxygen exiting the inlet, the recirculation step having a step height h from an edge of the inlet to an edge of the chamber defined by the outer walls;

wherein the inlet is further configured to provide recycled flue gas; and

wherein the inlet is further configured to provide recycled flue gas downstream of the recirculation step.

2. The precombustor of claim 1 , wherein the inlet includes an inlet port configured to provide the solid fuel.

3. The precombustor of claim 1 , wherein the precombustor is configured such that:

1.2

≤

D

p

d

≤

2.4

wherein D p is the chamber diameter and d is the inlet diameter.

4. The precombustor of claim 1 , wherein the chamber has length (L) and that is greater than or equal to about 5 times the recirculation step height (h).

5. The precombustor of claim 1 , wherein the precombustor is configured such that:

L

≤

7.4

*

d

+

15.7

*

h

-

9.7

*

h

2

d

wherein L is precombustor length and d is the inlet diameter.

6. The precombustor of claim 1 , wherein the precombustor is configured such that:

0.1 *d≦h≦ 0.7 *d

wherein d is the inlet diameter.

7. The precombustor of claim 1 , wherein the precombustor includes a circular cross-sectional geometry.

8. The precombustor of claim 1 , wherein the precombustor includes a non-circular cross-sectional geometry.

9. The precombustor of claim 1 , wherein the inlet is configured to deliver a second oxygen stream which is at least partially surrounded by fuel.

10. A combustion system comprising:

a furnace; and

at least one precombustor, the at least one precombustor having a chamber bounded by a first end, outer walls, and a second end, and an inlet configured to deliver a substantially parallel flow of solid fuel surrounded by oxygen through the first end of the chamber, the first end further including a recirculation step immediately downstream of the inlet, the second end fluidly communicating with the furnace;

wherein the inlet and the recirculation step are arranged to form a recirculation zone within the chamber of at least a portion of the solid fuel and the oxygen exiting the inlet, the recirculation step having a step height from an edge of the inlet to an edge of the chamber defined by the outer walls;

wherein the inlet is further configured to provide recycled flue gas; and

wherein the inlet is further configured to provide recycled flue gas downstream of the recirculation step.

11. The system of claim 10 , wherein the inlet includes a inlet port configured to provide the solid fuel.

12. The system of claim 10 , wherein the precombustor is configured such that:

1.2

≤

D

p

d

≤

2.4

wherein Dp is the chamber diameter and d is the inlet diameter.

13. The system of claim 10 , wherein the chamber has length (L) and that is greater than or equal to about 5 times the recirculation step height (h).

14. The system of claim 10 , wherein the precombustor is configured such that:

L

≤

7.4

*

d

+

15.7

*

h

-

9.7

*

h

2

d

wherein L is precombustor length and d is the inlet diameter.

15. The system of claim 10 , wherein the precombustor is configured such that:

0.1 *d<=h<= 0.7 *d

wherein d is the inlet diameter.

16. The system of claim 10 , wherein the precombustor includes a circular cross-sectional geometry.

17. The system of claim 10 , wherein the precombustor includes a non-circular cross-sectional geometry.

18. The system of claim 10 , wherein the inlet is configured to deliver a second oxygen stream which is at least partially surrounded by fuel.

19. A method for operating a combustion system comprising:

providing a furnace;

providing at least one precombustor, the precombustor having a chamber bounded by a first end, outer walls, and a second end, and an inlet configured to deliver a substantially parallel flow of solid fuel surrounded by oxygen through the first end of the chamber, wherein the concentration of O 2 is at least 35%, the first end further including a recirculation step immediately downstream of the inlet, the second end fluidly communicating with the furnace; and

delivering the solid fuel and the oxygen to the inlet to form a recirculation zone within the chamber of at least a portion of the solid fuel and the oxygen exiting the inlet, the recirculation step having a step height h from an edge of the inlet to an edge of the chamber defined by the outer walls; wherein the length of the precombustor is sufficient to prevent a flame generated by the system from contacting the precombustor;

wherein the inlet provides recycled flue gas; and

wherein the inlet provides recycled flue gas downstream of the recirculation step.

20. The method of claim 19 , further comprising delivering a second oxygen stream which is at least partially surrounded by fuel.

21. The method of claim 19 wherein the recirculation zone is located within the chamber of the precombustor.