WO1998021522A1

WO1998021522A1 - Coal combustion system with gas cooled walls, and method thereof

Info

Publication number: WO1998021522A1
Application number: PCT/US1997/018144
Authority: WO
Inventors: Ronald L. Bannister; Rhomas E. Dowdy
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1996-11-12
Filing date: 1997-10-08
Publication date: 1998-05-22
Anticipated expiration: 1999-05-12
Also published as: TW351750B; JPH10153310A

Abstract

An apparatus and method for controlling wall temperature of a coal combustion system, having a primary combustion chamber (10) connected and in pressurized communication with a secondary combustion chamber (30), are disclosed. Optionally, the coal combustion system has a separation chamber (20) disposed between the primary combustion chamber and the secondary combustion chamber. A gas, such as steam or compressed air, flows through internal gas flow passages within the wall (16, 26, 36) of at least one of the combustion system components. The flow of gas removes heat from the refractory material of the wall portion adjacent to the internal passages. Controlling wall temperature in this manner enhances slag collection and removal within the combustion system.

Description

COAL COMBUSTION SYSTEM WITH GAS COOLED WALLS, AND METHOD THEREOF

FIELD OF THE INVENTION

This invention relates to methods and apparatus for removing debris from direct coal combustion systems, and more particularly, to methods and apparatus for collecting and removing debris from such combustion systems during operation.

BACKGROUND OF THE INVENTION

The inherent problem of slag entrained in coal combustion products has limited the scope of application of coal fuel. Some applications are feasible only if fed with a low-ash, highly beneficiated coal, rather than utility grade coal. For example, a direct coal-fired combustion system has been technically and commercially incompatible with a combustion turbine, despite favorable efficiency, because of the slag entrained in the coal combustion system exit gas. Researchers have proposed numerous approaches to removing entrained slag from coal combustion products. One promising approach is a multi-stage, slagging combustor with integral particulate emissions control. U. S. Patents

4,960,056 and 4,961,389 to Pillsbury (1990), incorporated by reference in their entirety, describe a direct coal-fired combustor consisting of three stages: a primary combustion chamber for the rich burn of coal; a separator for removing molten slag and other particles from the combustion products; and, a secondary combustion chamber for the lean burn of the combustion products.

Because of the combustion reaction, combustion systems typically operate at high interior gas temperatures, typically above 3,000 °F. Walls of the combustion system traditionally have consisted of a steel shell with an interior refractory lining to protect against high temperature. The high wall interior surface temperatures, resulting from the high interior gas temperatures, tend to contribute to refractory loss. Moreover, the prospect of sudden, local refractory loss requires monitoring of the temperature of the exterior steel shell. Also, the traditional wall design results in high exterior steel shell temperatures, for example greater than 500 °F. Insulating the external steel shell surface would reduce potential harm to personnel upon physical contact and would enhance system thermal efficiency, but such insulation is infeasible with the traditional wall design because of the operating temperature limitations of the steel shell.

Maintaining proper coal viscosity is crucial to the collection and removal of the slag from the wall interior surface of the combustion system chambers. Because the slag viscosity depends upon temperature, the interior surface temperature of the wall must remain at least about 2,600 °F to maintain proper coal viscosity, depending upon the characteristics of the particular coal.

Wall interior surface temperatures below the optimal temperature may cause excessive slag build-up on the wall interior surface, harm overall system thermal efficiency, and hamper the combustion reaction by reducing the flame temperature. Maintaining proper wall temperature ensures slag of proper temperature and viscosity. At proper viscosity, slag flows down the wall by gravity and solidifies in a thin layer, which protects the surface from erosion.

There exists a need for an effective method for controlling wall temperature of a combustion system to enhance slag collection and removal, to promote the combustion reaction, and to control refractory erosion. SUMMARY OF THE INVENTION

A coal combustion system according to the present invention comprises a primary combustion chamber connected and in pressurized communication with a secondary combustion chamber. Optionally, a separation chamber may be disposed between the primary combustion chamber and the secondary combustion chamber. Further, at least part of the wall of any chamber contains internal gas flow passage means, such as cylindrical tubes. A gas, such as steam or compressed air, flows through the internal gas flow passage means. The flow of gas removes heat from the wall portion adjacent to the internal gas flow passage means. Controlling wall temperature in this manner enhances slag collection and removal within the combustion system.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagrammatic view of a coal-fired combustion apparatus according to the invention that includes a primary combustion chamber, a secondary combustion chamber, and an integrally disposed separation chamber with internal impaction separation means.

Figure 2 is a cross section taken through line 2-2 of Figure 1, and illustrates an exemplary chamber wall that may be employed in any of the primary combustion chamber, the separation chamber, and the secondary combustion chamber.

Figure 3 is a cross section taken through line 3-3 of Figure 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, wherein like numbers designate like components, there is shown in Fig.l, a coal combustion system comprising a primary combustion chamber 10, a separation chamber 20, and a secondary combustion chamber 30. The primary combustion chamber 10 is connected to the separation chamber 20, which is connected to the secondary combustion chamber 30, as shown. As used in this description and in the appended claims, the word "connected" includes operatively connected (e.g. by means of intervening apparatus) , and , in pressurized communication. The primary combustion chamber 10 comprises a primary chamber coal and compressed air inlet 11, a primary chamber combustion products outlet 18, and a primary chamber wall 16. The primary chamber wall 16 forms the primary combustion chamber shape, encloses the primary chamber interior 19, and has an interior surface 15 and an exterior surface 17. The separation chamber 20 comprises a separation chamber combustion products inlet 21, a separation chamber combustion products outlet 28, a debris outlet 50, and a separation chamber wall 26. The separation chamber wall 26 forms the separation chamber shape, encloses the separation chamber interior 29, and has an interior surface 25 and an exterior surface 27.

The secondary combustion chamber 30 comprises a secondary chamber combustion products inlet 31, one or more secondary chamber compressed air inlets 32, a secondary chamber combustion products outlet 38, and a secondary chamber wall 36. The secondary chamber wall 36 forms the secondary combustion chamber shape, encloses the secondary chamber interior 39, and has an interior surface 35 and an exterior surface 37. A coal and compressed air stream 14 enters the primary combustion chamber 10 through the primary chamber coal and compressed air inlet 11. The coal and compressed air mix, and at least partially burn, within the primary chamber interior 19, forming a primary chamber combustion products and debris stream 13. The primary chamber combustion products and debris stream 13 exits the primary combustion chamber 10 through the primary chamber combustion products outlet 18.

As used in this description and in the appended claims, the word "combustion products" includes gaseous products of a completed combustion reaction, gaseous products of a partially completed combustion reaction that remain combustible, and combustible carbonaceous particles. Also, as used in this description and in the appended claims, the word "debris" includes molten slag, ash, and other non- combustible particulate matter.

The primary chamber combustion products and debris stream 13 enters the separation chamber 20 through the separation chamber inlet 21. The separation chamber 20 separates at least part of the debris from the combustion products, forming a separation chamber combustion products and debris stream 23 and a debris steam 24. An internal impaction separation means 22 within the separation chamber interior 29 removes part of the debris from the separation chamber combustion products and debris stream 23. The debris stream 24 exits the separation chamber 20 through the debris outlet 50. The separation chamber combustion products and debris stream 23, from which a portion of the debris has been removed, exits the separation chamber 20 through the separation chamber combustion products and debris outlet 28.

The secondary chamber combustion products and debris stream 23 enters the secondary combustion chamber 30 through the secondary chamber combustion products and debris inlet 31. A secondary chamber compressed air stream 34 enters the secondary combustion chamber 30 through the secondary chamber compressed air inlet 32. The combustion products and debris mix with the secondary chamber compressed air 34 stream within the secondary chamber interior 39, forming a secondary chamber combustion products and debris stream 33. The unburned portion of the combustion products burn within the secondary chamber interior 39 in a fuel-lean environment. The secondary chamber combustion products and debris stream 33 exits the secondary combustion chamber 30 through the secondary chamber combustion products and debris outlet 38.

Figure 2 shows a cross section of a typical chamber wall 40, as found in the primary chamber wall 16, the separation chamber wall 26, and the secondary chamber wall 36. Figure 3 shows section view 3-3 of the typical chamber wall. The typical chamber wall 40 is formed from cylindrical steel tubes 42, which are joined by fin-welds 47. The typical chamber wall 40 is constructed to withstand continuous operation at elevated internal chamber pressures typical of gas turbine systems. Refractory material 46 is attached to the typical chamber wall 40 forming the interior surface of the respective chamber. The methods for connecting the refractory material 46 to the typical chamber wall 40 are well known in the art . According the preferred embodiment of the invention, steam enters the typical chamber wall tubes 42 through a steam inlet valve, not shown, flows through the typical chamber wall tubes 42, and exits through a steam outlet valve, not shown. As used in this description and in the appended claims, the word "steam" includes saturated steam and superheated steam.

In the preferred embodiment, the primary combustion chamber wall 16, the separation chamber wall 26, and the secondary chamber wall 36 are constructed similarly to the typical chamber wall 40.

In other embodiments of the invention, the coal combustion system lacks a separation chamber 20, wherein the primary combustion chamber 10 is directly connected to the secondary combustion chamber 30, not shown. In further embodiments of the invention, at least a portion of the primary chamber wall 16, the separation chamber wall 26, and the secondary chamber wall 36, or any combination thereof, are formed by fin-welded, cylindrical steel tubes 42. In further embodiments of the invention, wall internal gas flow passages of different shapes, arrangements, and fabrication methods, not shown, may be used in place of cylindrical tubes 42 to suitably cool the walls of the components as described below. In further embodiments of the invention, alternative steam inlet valve and steam outlet valve arrangements, not shown, may be used. In further embodiments of the invention, a gas, such as compressed air, may be used in place of steam. In further embodiments of the invention, not shown, at least a portion of the primary chamber wall 16, the separation chamber wall 26, or the secondary chamber wall 36 lack the refractory lining 46. In further embodiments of the invention, not shown, the separation chamber 20 lacks the internal impaction separation means 22. According to the invention, there is also provided a method of controlling wall temperature in a coal combustion system. The method comprises the step of flowing steam through tubes 42 disposed between the interior surface and the exterior surface of the primary chamber wall 16, the separation chamber wall 26, and the secondary chamber wall 36, respectively. Within the primary chamber 10 and the secondary chamber 30, the coal and combustion products mix with compressed air and burn. The resulting combustion products and debris often reach temperatures above 3000 °F, depending upon the operating characteristics. Heat is transferred from the combustion products and debris streams of the primary chamber 13, the separation chamber 23, and the secondary chamber 33 to the respective refractory surface of primary chamber wall 16, the separation chamber wall 26, and the secondary chamber wall 36. The refractory material conducts heat from the refractory surface to the tubes . Steam flowing through the tubes removes heat from the refractory material, thereby removing heat from the wall portion adjacent to the tubes. The heat transfer rate from the tubes to the flowing steam may be controlled by varying the steam flow rate, steam pressure, and steam quality of the steam feed to the steam inlet valve means, not shown.

The herein disclosed apparatus and method for controlling wall temperature in a coal combustion system permits the wall interior surface to operate at a temperature advantageous for slag collection and removal, i.e. above 2600 °F, while keeping the steel tube temperature within the safe operating range for steel. The advantageous refractory or wall surface temperature ensures proper slag viscosity such that the slag flows by gravity down the wall and such that a thin layer of slag may solidify on the wall, thereby reducing refractory loss due to erosion.

This present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims

CLAIMS :

1. A coal combustion system comprising: a. a primary combustion chamber having a primary chamber coal and compressed air inlet, a primary chamber combustion products outlet, and a primary chamber wall defining a primary chamber interior; and b. a secondary combustion chamber having a secondary chamber compressed air inlet, a secondary chamber combustion products inlet, and a secondary chamber wall defining a secondary chamber interior; the secondary chamber combustion products inlet being connected to the primary chamber combustion products outlet; at least one of the primary chamber wall and the secondary chamber wall having internal gas flow passage means for flowing a gas therein for transferring heat from at least one of the primary chamber wall and the secondary chamber wall to the gas; the internal gas flow passage means being operatively connected to gas inlet means and gas outlet means.

2. The combustion system of claim 1 wherein the primary chamber wall has a primary chamber wall interior surface, the primary chamber wall further comprising a primary chamber refractory lining attached to at least a portion of the primary chamber wall interior surface.

3. The combustion system of claim 1 wherein the secondary chamber wall has a secondary chamber wall interior surface, the secondary chamber wall further comprising a secondary chamber refractory lining attached to at least a portion of the secondary chamber wall interior surface.

4. The combustion system of claim 1 wherein the internal gas flow passage means comprises cylindrical tubes.

5. The combustion system of claim 1 wherein the gas inlet means and the gas outlet means comprise each of steam inlet means and steam outlet means, or compressed air inlet means and compressed air outlet means, respectively.

6. The combustion system of claim 5 wherein both the primary chamber wall and the secondary chamber wall each have the internal gas flow passage means, and the primary chamber wall and the secondary chamber wall each have a primary chamber wall interior surface and a secondary chamber wall interior surface, respectively, the system further comprising a primary chamber refractory attached to at least a portion of each of the primary chamber wall interior surface and the secondary chamber wall interior surface.

7. A coal combustion system comprising: a. a primary combustion chamber having a primary chamber coal and compressed air inlet, a primary chamber combustion products outlet, and a primary chamber wall defining a primary chamber interior; b. a secondary combustion chamber having a secondary chamber compressed air inlet, a secondary chamber combustion products inlet, and a secondary chamber wall defining a secondary chamber interior; and c. a separation chamber disposed between the primary combustion chamber and the secondary combustion chamber and having a separation chamber combustion products inlet, a separation chamber combustion products outlet, a debris outlet, and a separation chamber wall 5 defining a separation chamber interior; the separation chamber combustion products inlet being connected to the primary chamber combustion products outlet, and the separation chamber combustion products outlet being 10 connected to the secondary chamber combustion products inlet; at least one of the primary chamber wall, the secondary chamber wall or the separation chamber wall having internal gas flow passage means for flowing a gas therein for 15 transferring heat from at least one of the primary chamber wall, the secondary chamber wall or the separation chamber wall to the gas; the internal gas flow passage means being operatively connected to gas inlet means and gas outlet means.

8. The combustion system of claim 7 wherein the 20 separation chamber comprises one of a cyclone separator or an impact separator.

9. The combustion system of claim 7 wherein the separation chamber comprises a cyclone separator having internal impaction separation means.

25 10. The combustion system of claim 7 wherein the separation chamber wall has a separation chamber wall interior surface, the separation wall further comprising a separation chamber refractory lining attached to at least a portion of the separation chamber wall interior surface.

30 11. The combustion system of claim 7 wherein the internal gas flow passage means comprises cylindrical tubes .

12. The combustion system of claim 7 wherein the gas inlet means and the gas outlet means comprise one of steam inlet means and steam outlet means, or compressed air inlet means and compressed air outlet means, respectively.

13. The combustion system of claim 12 wherein each of the primary chamber wall, the secondary chamber wall, and the separation chamber wall each have the internal gas flow passage means, and the primary chamber wall, the secondary chamber wall and the separation chamber wall each have a primary chamber wall interior surface, a secondary chamber wall interior surface, and a separation chamber wall interior surface, respectively; the system further comprising a primary chamber refractory lining, a secondary chamber refractory lining, and a separation chamber refractory lining attached to at least a portion of the primary chamber wall interior surface, the secondary chamber wall interior surface, and the separation chamber wall interior surface, respectively.

14. A method for combusting coal comprising the steps of: a. providing a primary combustion chamber having a primary chamber coal and compressed air inlet, a primary chamber combustion products outlet, and a primary chamber wall defining a primary chamber interior; b. providing a secondary combustion chamber having a secondary chamber compressed air inlet, a secondary chamber combustion products inlet, and a secondary chamber wall defining a secondary chamber interior; the secondary chamber combustion products inlet being connected to the primary chamber combustion products outlet; at least one of the primary chamber wall and the secondary chamber wall having internal gas flow passage means for flowing a gas therein for transferring heat from at least one of the primary chamber wall and the secondary chamber wall to the gas; the internal gas flow passage means being operatively connected to gas inlet means and gas outlet means; c. flowing coal and compressed air through the primary chamber coal and compressed air inlet into the primary chamber interior, and at least partially burning the coal therein to produce combustion products and debris; d. enabling the combustion products and debris to flow through the primary chamber combustion products outlet, through the secondary chamber combustion products inlet, and into the secondary chamber interior, further burning the combustion products therein; and e. flowing a gas through the wall internal gas flow passage means for transferring heat to the gas .

15. The method of claim 14 wherein the step of flowing the gas through the internal gas flow passage means further comprises the step of flowing steam or compressed air through the internal gas flow passage means.

16. The method of claim 15 wherein both the primary chamber wall and the secondary chamber wall each have the internal gas flow passage means; the system further comprising a primary chamber refractory lining and a separation chamber refractory lining attached to at least a portion of each of the primary chamber wall interior surface and the secondary chamber wall interior surface .

17. A method for combusting coal comprising the steps of: a. providing a primary combustion chamber having a primary chamber coal and compressed air inlet, a primary chamber combustion products outlet, and a primary chamber wall defining a primary chamber interior; b. providing a secondary combustion chamber having a secondary chamber compressed air inlet, a secondary chamber combustion products inlet, and a secondary chamber wall defining a secondary chamber interior; c. providing a separation chamber disposed between the primary combustion chamber and the secondary combustion chamber, having a separation chamber combustion products inlet, a separation chamber combustion products outlet, a debris outlet, and a separation chamber wall defining a separation chamber interior; the separation chamber combustion products inlet being connected to the primary chamber combustion products outlet, and the separation chamber combustion products outlet being connected to the secondary chamber combustion products inlet; at least one of the primary chamber wall, the secondary chamber wall, and the separation chamber wall having internal gas flow passage means for flowing a gas therein for transferring heat from at least one of the primary chamber wall, the secondary chamber wall, and the separation chamber wall to the gas; the internal gas flow passage means being operatively connected to gas inlet means and gas outlet means ; d. flowing coal and compressed air through the primary chamber coal and compressed air inlet into the primary chamber interior, and at least partially burning the coal therein to produce combustion products and debris; e. enabling the combustion products and debris to flow through the primary chamber combustion products outlet and through the separation chamber combustion products inlet and into the separation chamber interior, and separating at least a portion of the debris from the combustion products therein, and at least a portion of the debris exiting through the debris outlet; and f . enabling the combustion products and debris to flow through the separation chamber combustion products outlet and through the secondary chamber combustion products inlet and into the secondary chamber interior, and further burning the combustion products therein; and g. flowing a gas through the wall internal gas flow passage means for transferring heat to the gas .

18. The method of claim 17 wherein the step of flowing the gas through the internal gas flow passage means further comprises the step of flowing steam or compressed air through the internal gas flow passage means.

19. The method of claim 18 wherein each of the primary chamber wall, the secondary chamber wall, and the separation chamber wall each have the internal gas flow passage means; the primary chamber wall, the secondary chamber wall, and the separation chamber wall have a primary chamber wall interior surface, a secondary chamber wall interior surface, and a separation chamber wall interior surface, respectively; the system further comprising a primary chamber refractory lining, a secondary chamber refractory lining, and a separation chamber refractory lining attached to at least a portion of each of the primary chamber wall interior surface, the secondary chamber wall interior surface, and the separator chamber wall interior surface, respectively.