High temperature sub-critical boiler with steam cooled upper furnace

Patent metadata

Field	Value
Publication number	US-10429062-B2
Application number	US-201615091236-A
Country	US
Kind code	B2
Filing date	Apr 5, 2016
Priority date	Apr 5, 2016
Publication date	Oct 1, 2019
Grant date	Oct 1, 2019

Abstract

A boiler is disclosed in which the furnace is divided into a lower furnace and an upper furnace. The lower furnace uses water-cooled membrane walls, while the upper furnace uses steam-cooled membrane walls that act as superheating surfaces. A transition section is present between the lower furnace and the upper furnace. The boiler is a high temperature sub-critical natural circulation boiler which is completely top supported. The lower furnace is supported through the transition section by the upper furnace.

First claim

We claim:

1. A boiler, comprising:
a lower furnace having water-cooled membrane walls;
an upper furnace having steam-cooled membrane walls and located above the lower furnace, wherein flue gas passes from the lower furnace to the upper furnace, and wherein the steam-cooled membrane walls of the upper furnace include a front wall, a rear wall, and side walls;
a convection pass downstream of the upper furnace, the convection pass having steam-cooled convection pass membrane walls and extending downwards, wherein the steam-cooled convection pass membrane walls of the upper furnace include a front wall, a rear wall, and side walls;
wherein the upper furnace and the convection pass share a common steam-cooled membrane wall, the common steam-cooled membrane wall being both the rear wall of the upper furnace and the front wall of the convection pass;
a baffle wall that divides the convection pass into a front convection pass and a rear convection pass;
a primary superheater in the rear convection pass;
a secondary superheater disposed inside the upper furnace;
a steam separator having a fluid inlet and a dry steam outlet;
a water-cooled circuit connected to the fluid inlet of the steam separator to deliver wet steam to the steam separator, the water-cooled circuit including the water-cooled membrane walls of the lower furnace; and
a steam-cooled circuit connected to the dry steam outlet of the steam separator to receive dry steam from the dry steam outlet, the steam-cooled circuit running sequentially from the dry steam outlet through the rear wall of the convection pass, the side walls of the convection pass, the baffle wall, through the primary superheater, through the upper furnace front wall and the common steam-cooled membrane wall, then through the upper furnace side walls, and through the secondary superheater.

2. The boiler of claim 1 , wherein
the water-cooled circuit including the water-cooled membrane walls of the lower furnace comprise carbon steel; and
the steam-cooled circuit including the steam-cooled membrane walls of the upper furnace comprise alloy steel.

3. The boiler of claim 2 , wherein the pipes of the water-cooled membrane walls of the lower furnace have upper ends fluidly connected to the fluid inlet of the steam separator and have lower ends fluidly connected to a water outlet of the steam separator.

4. The boiler of claim 3 , further comprising a transition section disposed between the upper furnace and the lower furnace, wherein the upper furnace is top-supported and the lower furnace is top-supported by the upper furnace.

5. The boiler of claim 4 , wherein a horizontal cross-sectional area of the upper furnace is smaller than a horizontal cross-sectional area of the lower furnace.

6. The boiler of claim 5 , wherein the upper furnace includes a slanted surface transitioning from the larger cross-sectional area of the lower furnace to the smaller cross-sectional area of the upper furnace.

7. The boiler of claim 6 , wherein the secondary superheater disposed inside the upper furnace comprises pipes without membrane.

8. The boiler of claim 7 , wherein the steam-cooled convection pass membrane walls comprise pipes sealed by membrane disposed between and connected to the pipes.

9. The boiler of claim 8 , wherein the primary superheater disposed inside the convection pass comprises pipes without membrane.

10. The boiler of claim 9 , wherein the water-cooled membrane walls of the lower furnace comprise water pipes, the steam-cooled membrane walls of the upper furnace comprise steam pipes, and the water pipes have a diameter greater than a diameter of the steam pipes.

11. The boiler of claim 10 , wherein the boiler is a natural circulation boiler.

12. A method for generating superheated steam, comprising:
combusting a fuel in a lower furnace of a boiler, wherein an upper furnace is located above the lower furnace, and flue gas passes from the lower furnace to the upper furnace and then through a convection pass;
wherein the upper furnace includes a front wall, a rear wall, and side walls;
wherein the convection pass includes a front wall, a rear wall, and side walls;
wherein the upper furnace and the convection pass share a common wall, the common wall being both the rear wall of the upper furnace and the front wall of the convection pass;
wherein the boiler further includes a baffle wall that divides the convection pass into a front convection pass and a rear convection pass;
generating wet steam from water in water-cooled membrane walls of the lower furnace;
separating the wet steam into dry steam and water in a steam separator;
sending dry steam sequentially through the convection pass rear wall, the convection pass side walls, the baffle wall, through a primary superheater in the rear convection pass, through the upper furnace front wall and the common wall, then through the upper furnace side walls, and through a secondary superheater.

13. The method of claim 12 , further comprising top-supporting the lower furnace by suspension from the upper furnace through a transition casting.

14. The method of claim 13 , further comprising accelerating a velocity of flue gas in the upper furnace by reducing a horizontal cross-sectional area of the upper furnace compared to a horizontal cross-sectional area of the lower furnace to increase heat transfer efficiency.

15. The method of claim 12 , wherein the superheated steam has a temperature of at least 900° F.

16. The method of claim 15 , further comprising draining water separated from the wet steam by the steam separator into the lower furnace.

17. The method of claim 16 , wherein the fuel that is combusted in the lower furnace is coal.

18. The boiler of claim 1 , wherein the upper furnace does not contain water-cooled tube walls; and wherein the lower furnace does not contain steam-cooled walls.

Assignees

• Babcock & Wilcox Co

Inventors

• Wells Eric L
• Detzel Roger A
• Bennett Albert J
• Thayer Steven D

Classifications

• F22B21/34

  built-up from water tubes grouped in panel form surrounding the combustion chamber, i.e. radiation boilers · CPC title

• F22G5/20

  by combined controlling procedures · CPC title

• F22B31/04 Primary

  Heat supply by installation of two or more combustion apparatus, e.g. of separate combustion apparatus for the boiler and the superheater respectively · CPC title

• F22B37/14

  Supply mains, e.g. rising mains, down-comers, in connection with water tubes · CPC title

• F22B35/04

  during starting-up periods, i.e. during the periods between the lighting of the furnaces and the attainment of the normal operating temperature of the steam boilers · CPC title