DUCT BURNER OF HRSG WITH LINER FILM COOLING

Abstract

A duct burner assembly for a HRSG having a casing that defines a combustion chamber with a liner for communicating an exhaust gas. A firing runner attaches to the liner and extends through the combustion chamber. The firing runner defines a plurality of orifices for emitting combustible gas and sustaining a flame. A flame stabilizer attaches to the firing runner and is configured to at least partially shield the plurality of orifices from the exhaust gas. A guide plate attaches to the firing runner and is configured to define a slot between the liner and the guide plate. The guide plate has an upstream end and a downstream end wherein the downstream end is closer to the lining than the upstream end to reduce turbulent flow of the exhaust gas through the slot and cool the liner.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND

This invention relates to heat recovery steam generators (HRSG), and more particular to a duct burner assembly for a liner of a HRSG.

Natural gas and to a lesser extent fuel oil are the sources of much of the electrical energy consumed today. Combined cycle power plants convert those fuels into electrical energy in a highly efficient manner. There are three major components in a combined cycle power plant: a combustion turbine or electrical generator, a Heat Recovery Steam Generator (HRSG), and a steam turbine or electrical generator. Basically, the fuel, whether it is natural gas or oil, burns within the combustion turbine, and the turbine drives an electrical generator that produces some of the electrical energy furnished by the plant. The combustion turbine also discharges exhaust gas at elevated temperatures often exceeding 1000° F. The exhaust gas flows through the HRSG which extracts heat from it to convert subcooled water into superheated steam that flows into the steam turbine, which in turn drives another electrical generator that produces more electricity.

Duct burners use supplementary firing to increase the heat energy of a gas turbine's exhaust, making it possible to increase the output of a downstream heat-recovery steam generator (HRSG). Using an HRSG with auxiliary or supplemental fuel firing in a duct burner can increase steam production, control steam superheat temperature, or meet process steam requirements. HRSG designs can also directly incorporate selective catalytic reduction (SCR) technology for nitrous oxide control.

A common problem for duct burners with heavy supplemental firing is overheating and deterioration of the liners of a combustion chamber. Thus, reliable control of the liner temperature regime is very important to prevent deterioration. This is especially true for the modern generation of combustion turbines and liquid fuels, such as oil or kerosene.

Duct burners include burner sections that produce high flame temperatures of about 1700° to about 3000° F. including significant thermal radiation. Duct liners are used to confine and protect ceramic fiber insulation behind the liners and the HRSG outer casing in the region of the burner sections. In some cases, liners are unable to withstand the elevated temperatures over extended periods of operation. The liners fail, and when they do, the ducting that they are designed to protect is damaged.

The turbine exhaust gas approaching the burner in the ducting of a HRSG, while being at an elevated temperature, is considerably cooler than the flames produced at the burner. Turbine exhaust flowing along the liners in the combustion chamber is not heated directly by the fuel combustion. As liners absorb radiant energy from the flames, they are cooled convectively by the adjacent turbine exhaust. The amount of flow along the liner and the degree of mixing of this flow with the bulk flow heated by the flame will affect the convective heat transfer from the liner.

In existing duct burners, there are no special elements which could properly form a cold or cooler gas flow over the liners. Moreover, the burner pipe and guide tube in the gap between the duct burner framework and liner generate turbulence. Additionally, some elements of the duct burner, such as flame stabilizers and gas baffles, generate strong turbulence in the gas flow. These elements together with turbulent turbine exhaust flow destroy the protective cold film over the liners. As a result, the turbulent flow decreases the heat transfer coefficient from the liner to the coolant and can increase the temperature of the liner in the vicinity of the flame. A less turbulent, non-turbulent or laminar, would increase the heat transfer coefficient from the liner to the coolant and lower the temperature of the liner.

Therefore, there is a need for effective cooling of the liner of a HRSG duct burner with less or non-turbulent turbine exhaust flow.

DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which form part of the specification:

FIG. 1 is a partial section view of a heat recovery steam generator (HRSG);

FIG. 2 is a front view of a duct burner assembly;

FIG. 3 is a top view of the duct burner assembly;

FIG. 4 is a perspective view of a duct burner liner; and

FIG. 5 is a perspective view of an alternate embodiment of a duct burner liner.

Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings.

DETAILED DESCRIPTION

The following detailed description illustrates the claimed invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the disclosure, describes several embodiments, adaptations, variations, alternatives, and uses of the disclosure, including what is presently believed to be the best mode of carrying out the claimed invention. Additionally, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

As shown in FIGS. 1-5, an embodiment constructed in accordance with the present disclosure, generally referred to as a Heat Recovery Steam Generator (HRSG) 10 having an inlet 12 for receiving a gas turbine exhaust, an outlet 14, and a casing 16 configured for housing a duct burner assembly 18 configured for providing cooling to the liner sidewalls 20.

The duct burner assembly 18 defines a generally rectangular prism shaped combustion chamber 22 configured for combustion of fuel with oxygen from a gas turbine exhaust (FIG. 1). The liner sidewalls 20 are configured within the combustion chamber 20 to withstand gas temperatures that exceed the allowable temperature of the liner material, such as about 1700° to about 3000° F.

The duct burner assembly 18 includes a plurality of gas-fired sections 24 arranged in a generally vertical plane within the casing 16 (FIG. 2-3). Each section 24 includes a firing runner pipe 26 that extends transversely through the casing 16 with each end of the running pipe 26 secured by runner guide tubes 28. The firing runner pipe 26 defines a plurality of orifices 30 that open or point generally in the direction of the turbine exhaust flow. The orifices 30 are configured for discharge of a combustible gas, such as natural gas, propane, or other suitable gas.

A flame stabilizer 32 attaches to the firing runner pipe 26, such as by welding or fasteners, and is configured to at least partially shield the combustible gas discharged from the orifices 30 from the turbine exhaust flow. In the embodiment of FIGS. 1-5, the flame stabilizer 32 is a generally semi-cylindrical panel that extends generally the length of the runner pipe 26 and is positioned on the downstream side of the runner pipe 26 to define a space therebetween for burning flames. The flame stabilizer 32 defines a plurality of openings 34. When the combustible gas is ignited, the flame stabilizer 32 allows a flame to be sustained generally along the runner pipe 26. Accordingly, flames produced by each burner section 24 provide supplemental heat for increasing the steam production in the HRSG.

A guide plate 36 is a generally square or rectangular plate that attaches near each end of the runner pipe 26, such as by welding or other suitable method (FIGS. 3-5). Alternatively, the guide plate 36 can attach to guide tubes 28. The guide plate 36 is in a generally vertical position with an inner face of the guide plate 36 abutting the end of the flame stabilizer 32 and spaced a predetermined distance from the liner sidewall 20 to define a slot 38. The guide plate 36 is positioned at an angle relative to the liner sidewall 20 with the downstream end 40 of the guide plate 36 positioned closer to the liner sidewall 20 than the upstream end 42. In other words, the slot 38 is widest at the upstream end 42 and narrowest at the downstream end 40. Preferably, the angle between the liner sidewall 20 and the guide plate 36 is between a range of about 0° and about 8° (FIG. 3). The length of guide plates 36 in the direction of exhaust flow are preferably about three times the width of the slot 38 at the downstream end 40. The configuration of the guide plates 36 stabilizes jets and enhances cooling of the liner sidewalls by increasing the colder turbine exhaust flow over the liner sidewalls 20 and decreasing turbulent mixing. This increases cooling of the liner sidewalls 20 and separates the flow by the liner sidewall 20 from contact with hot gas flow.

Additional guide plates 36 are installed along the liner sidewall 20 in the vertical spaces between the runner pipes 26 to form a generally contiguous slot 38 between the liner sidewall 20 and the guide plates 36. Preferably, the guide plates 36 are configured vertically to slightly overlap with each other so that the physical detachment and overlap accommodates thermal expansion of the guide plates 36.

Streamlined plates 44 are attached to the ends of the runner pipes 26 and guide tubes 28 to improve the aerodynamic performance by reducing turbulence of the turbine exhaust and preventing generation of vortexes and separation of flow. Each streamline plate 44 is generally U-shaped to generally cover the runner pipes 26 and guide tubes 28. The streamlined plates 44 are positioned in a generally horizontal orientation or inclined orientation to follow the direction of flame. Those skilled in the art will recognize that the size and shape of the streamlined plate can vary to accommodate different geometries of runner pipes and guide tubes 28.

The duct burner assembly 12 is preferably made from a metal material, such as aluminum, steel, or composite material. However any material can be used that is capable of withstanding the elevated temperatures produced by the flames.

Changes can be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. For example, while the duct burner assembly 18 of FIGS. 1-5 are for use with the liner sidewalls, the assembly 18 can also be used with the top and bottom liners as well. Although, the duct burner assembly 12 of FIGS. 1-5 is used in a HRSG, the duct burner assembly 12 can be used in other types of burners or boilers.

Claims

1. A duct burner assembly for a HRSG having a casing that defines a combustion chamber with a liner for communicating an exhaust gas: a firing runner attached to the liner and extending through the combustion chamber, the firing runner defining a plurality of orifices for emitting combustible gas and sustaining a flame;a flame stabilizer attached to the firing runner and configured to at least partially shield the plurality of orifices from the exhaust gas; anda guide plate attached to the firing runner and configured to define a slot between the liner and the guide plate, the guide plate having an upstream end and a downstream end wherein the downstream end is closer to the lining than the upstream end.

2. The duct burner assembly of claim 1, further comprising guide tubes that secure the firing runner to the liner.

3. The duct burner assembly of claim 1, wherein the flame stabilizer is a generally semi-cylindrical shaped panel that extends generally the length of the firing runner.

4. The duct burner assembly of claim 1, wherein the guide plate is at angle of about 0° about 8° relative to the liner.

5. The duct burner assembly of claim 1, wherein the length of the guide plate is at least about three times the width of the slot at the downstream end.

6. The duct burner assembly of claim 1, further comprising a plurality of guide plates positioned along a sidewall of the liner to define a generally contiguous slot between the sidewall and the plurality of guide plates.

7. The duct burner assembly of claim 6, wherein the plurality of guide plates are configured adjacent to each other and partially overlapping to accommodate expansion of the guide plates.

8. The duct burner assembly of claim 1, further comprising a streamline plate configured to at least partially cover a section of the firing runner positioned within the slot to reduce generation of turbulence within the slot.

9. The duct burner assembly of claim 1, further comprising a streamline plate configured to at least partially cover a section of blocking gas baffles positioned within the slot to reduce generation of turbulence within the slot.

10. The duct burner assembly of claim 1, wherein the streamline plate is generally U-shaped.

11. The duct burner assembly of claim 1, wherein a geometry of streamlined plates are configured to reduce aerodynamic resistance.

12. The duct burner assembly of claim 1, wherein said the guide plate is secured to a blocking baffle runner.

13. The duct burner assembly of claim 1, wherein the slot is configured in accordance with film cooling theory.

14. A duct burner assembly for cooling a liner in a combustion chamber of a HRSG: a firing runner extending generally across the combustion chamber, the firing runner defining a plurality of orifices for emitting combustible gas and sustaining a flame;guide tubes that secure the firing runner to the liner;a flame stabilizer secured to the firing runner and configured to at least partially shield the flame from an exhaust gas; anda guide plate attached to the firing runner and configured to define an angled slot between the liner and the guide plate for reduction of turbulent flow of the exhaust gas through the slot.

15. The duct burner assembly of claim 14, wherein the guide plate comprises an upstream end and a downstream end wherein the downstream end is closer to the lining than the upstream end.

16. The duct burner assembly of claim 14, wherein the guide plate is at angle of about 0° to about 8° relative to the liner.

17. The duct burner assembly of claim 14, wherein the length of the guide plate is at least about three times the width of the slot at the downstream end.

18. The duct burner assembly of claim 14, further comprising a plurality of guide plates positioned along a sidewall of the liner to define a generally contiguous slot between the sidewall and the plurality of guide plates.

19. The duct burner assembly of claim 18, wherein the plurality of guide plates are configured adjacent to each other and partially overlapping to accommodate expansion of the guide plates.