High temperature sub-critical boiler with common steam cooled wall between furnace and convection pass

1. A boiler, comprising:

an upper furnace having steam-cooled membrane walls, the steam-cooled membrane walls comprising pipes sealed by membrane disposed between and connected to the pipes;

a lower furnace below the upper furnace, the lower furnace having water-cooled membrane walls comprising water-cooled pipes sealed by membrane disposed between and connected to the water-cooled pipes; and

a convection pass downstream of the upper furnace, the convection pass having steam-cooled membrane walls and extending downwards;

wherein the upper furnace and the convection pass share a common steam-cooled membrane wall, the common steam-cooled membrane wall being both a rear wall of the upper furnace and a front wall of the convection pass; and

a steam separator configured to deliver dry steam to a steam-cooled circuit including the common steam-cooled membrane wall; and

wherein the upper furnace includes a side wall, the convection pass includes a side wall having a lower edge, and a seal is present at a junction of the common steam-cooled membrane wall, the upper furnace side wall, and the lower edge of the convection pass side wall;

wherein the upper furnace does not contain water-cooled tube walls; and

wherein the lower furnace does not contain steam-cooled tube walls.

2. The boiler of claim 1 , wherein the steam-cooled circuit includes the steam-cooled membrane walls of the upper furnace and the steam separator is also configured to receive wet steam from a water-cooled circuit including the water-cooled membrane walls of the lower furnace.

3. The boiler of claim 2 , further comprising one or more superheaters disposed in the upper furnace or the convection pass, the one or more superheaters comprising pipes without a membrane.

4. The boiler of claim 1 , further comprising:

burners arranged to combust fuel to generate heated flue gas that flows upward through the upper furnace and then downward through the convection pass;

wherein the common steam-cooled membrane wall is heated by the heated flue gas that flows upward through the upper furnace and by the heated flue gas that flows downward through the convection pass.

5. A boiler, comprising:

a furnace having steam-cooled membrane walls forming an upper portion of the furnace, the steam-cooled membrane walls comprising pipes sealed by membrane disposed between and connected to the pipes; and

a convection pass having steam-cooled membrane walls forming at least a portion of the convection pass, and being fluidly connected to the upper portion of the furnace;

wherein the furnace and the convection pass share a common steam-cooled membrane wall comprising a single layer of pipes sealed by a single layer of membrane disposed between and connected to the single layer of pipes, the common steam-cooled membrane wall being both a rear wall of the upper furnace and a front wall of the convection pass; and

a steam separator configured to deliver dry steam to a steam-cooled circuit including the common steam-cooled membrane wall;

wherein the furnace includes an upper furnace and a lower furnace below the upper furnace, the upper furnace having the steam-cooled membrane walls and the common steam-cooled membrane wall; and the lower furnace having water-cooled membrane walls, the water-cooled membrane walls comprising water-cooled pipes sealed by membrane disposed between and connected to the water-cooled pipes;

wherein the upper furnace does not contain water-cooled tube walls; and

wherein the lower furnace does not contain steam-cooled tube walls; and

wherein the steam-cooled circuit runs sequentially through an upper furnace front wall and the common steam-cooled membrane wall, then through upper furnace side walls, then through a secondary superheater.

6. The boiler of claim 5 , wherein the steam separator includes a saturated steam inlet connected with a water-cooled circuit including the water-cooled membrane walls of the lower furnace.

7. The boiler of claim 6 , wherein the steam-cooled circuit further includes one or more superheaters disposed in the upper furnace or the convection pass and comprising pipes without membrane.

8. The boiler of claim 7 , further comprising:

burners arranged to combust fuel to generate heated flue gas that flows upward through the upper furnace and then downward through the convection pass;

wherein the common steam-cooled membrane wall is heated by the heated flue gas that flows upward through the upper furnace and by the heated flue gas that flows downward through the convection pass.

9. A method of operating a boiler, comprising:

combusting fuel to generate heated flue gas that flows sequentially upwards through an upper furnace and downwards through a convection pass; and

sending superheated steam through a common steam-cooled membrane wall to capture heat energy from the heated flue gas and further superheat the superheated steam;

wherein the common steam-cooled membrane wall is heated both by the heated flue gas flowing upward through the upper furnace and by the heated flue gas flowing downward through the convection pass;

wherein the common steam-cooled membrane wall is both a rear wall of the upper furnace and a front wall of the convection pass;

wherein the superheated steam sent through the common steam-cooled membrane wall is generated from water that is heated in a lower furnace located below the upper furnace to obtain wet steam that is subsequently separated in a steam separator to obtain water and dry steam;

wherein the upper furnace does not contain water-cooled tube walls; and

wherein the lower furnace does not contain steam-cooled tube walls; and

wherein the steam-cooled circuit runs sequentially through an upper furnace front wall and the common steam-cooled membrane wall, then through upper furnace side walls, then through a secondary superheater.

10. The method of claim 9 , wherein the dry steam passes through at least one superheater prior to being sent to the common steam-cooled membrane wall.

11. The method of claim 10 , wherein the common steam-cooled membrane wall comprises a single layer of pipes separated by membrane therebetween.

12. The method of claim 11 , wherein the upper furnace includes a side wall, the convection pass includes a side wall having a lower edge, and a seal is present at a junction of the common steam-cooled membrane wall, the upper furnace side wall, and the lower edge of the convection pass side wall.

13. The boiler of claim 1 , wherein the water-cooled tube walls comprise carbon steel.

14. The boiler of claim 5 , wherein the water-cooled tube walls comprise carbon steel.

15. The method of claim 9 , wherein the water-cooled tube walls comprise carbon steel.

16. The boiler of claim 13 , wherein the steam-cooled tube walls comprise stainless steel.

17. The boiler of claim 14 , wherein the steam-cooled tube walls comprise stainless steel.

18. The method of claim 15 , wherein the steam-cooled tube walls comprise stainless steel.

19. The boiler of claim 1 , wherein the upper furnace comprises an arch surface.

20. The boiler of claim 5 , wherein the boiler further comprises a baffle wall that divides the convection pass into a front convection pass and a rear convection pass, the front convection pass containing a reheater and the rear convection pass containing a primary superheater.