Heat recovery steam generator boiler tube arrangement   

Abstract: A heat recovery steam generator includes a casing having an inlet and an outlet, a boiler tube disposed in the casing, the boiler tube defining an inner cavity and an outer surface, the boiler tube having a cross-sectional shape with a longitudinal axis and a transverse axis, wherein a length of the longitudinal axis is greater than a length of the transverse axis, and at least one fin arranged on the outer surface of the boiler tube.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to boiler tubes in heat recovery steam generators.

Gas turbine combined cycle power systems include a gas turbine engine that is mechanically connected to a generator. The gas turbine emits hot exhaust gasses that are directed through a heat recovery steam generator (HRSG). The exhaust gasses flow through an inlet duct in the HRSG and through a casing that includes a number of boiler tubes. Boiler water or steam flows through the boiler tubes and is heated by the flow of exhaust gasses resulting in heated steam that may be used to power a steam turbine.

According to one aspect of the invention, a heat recovery steam generator includes a casing having an inlet and an outlet, a boiler tube disposed in the casing, the boiler tube defining an inner cavity and an outer surface, the boiler tube having a cross-sectional shape with a longitudinal axis and a transverse axis, wherein a length of the longitudinal axis is greater than a length of the transverse axis, and at least one fin arranged on the outer surface of the boiler tube.

According to another aspect of the invention, a power system includes a gas turbine engine having an exhaust duct, and a heat recovery steam generator including a casing having an inlet connected to the exhaust duct and an outlet, a boiler tube disposed in the casing, the boiler tube defining an inner cavity and an outer surface, the boiler tube having a cross-sectional shape with a longitudinal axis and a transverse axis, wherein a length of the longitudinal axis is greater than a length of the transverse axis, and at least one fin arranged on the outer surface of the boiler tube.

According to yet another aspect of the invention, a boiler tube assembly includes a tube disposed in the casing, the tube defining an inner cavity and an outer surface, the tube having a cross-sectional shape with a longitudinal axis and a transverse axis, wherein a length of the longitudinal axis is greater than a length of the transverse axis, and at least one fin arranged on the outer surface of the tube.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a system diagram of an exemplary combined cycle power system.

FIG. 2 illustrates a side view of a portion of an exemplary embodiment of a boiler tube assembly

FIG. 3 illustrates a cross-sectional view along the line 3-3 of FIG. 2.

FIG. 4 illustrates a side view of a portion of an alternate exemplary embodiment of a boiler tube assembly.

FIG. 5 illustrates a cross-sectional view along the line 5-5 of FIG. 4.

FIG. 6 illustrates a cross-sectional view of an exemplary embodiment of an arrangement of boiler tube assemblies in a portion of the HRSG of FIG. 1.

FIG. 7 illustrates a graph showing the change in output in kilowatts versus a change in exhaust pressure.

FIG. 8 illustrates a graph showing the change in system efficiency versus a change in exhaust pressure.

FIG. 9 illustrates a cross-sectional view of an alternate exemplary embodiment of an arrangement of boiler tube assemblies in a portion of the HRSG of FIG. 1.

FIG. 10 illustrates a cross-sectional view of another alternate exemplary embodiment of an arrangement of boiler tube assemblies.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION

FIG. 1 illustrates a system diagram of an exemplary combined cycle power system 100. The system 100 includes a gas turbine engine 102 mechanically connected to a generator 104. The gas turbine engine 102 includes an air intake plenum 106, a compressor portion 108, a combustor portion 110, a turbine portion 112 and an exhaust plenum (duct) 114. The exhaust plenum 114 is connected to an inlet duct 116 of a heat recovery steam generator (HRSG) 118. The HRSG 118 includes a casing 120 that encloses boiler tubes 122. The casing 120 is connected to an outlet duct 125. The boiler tubes 122 are connected to a pump 124 and a steam turbine 126. The steam turbine 126 is mechanically connected to a generator 128. The steam turbine outputs steam to a condenser 130 that is connected to the pump 124.

In operation, air 101 flows into the air intake plenum 106 and is pressurized by the compressor 108. Fuel is added to the compressed air and ignited in the combustor 110. Hot expanding gasses flow through the turbine 112, which rotates and drives the compressor 108 and the generator 104. Exhaust gasses 103 flow from the exhaust plenum 114 and enter the inlet duct 116 and the casing 120 of the HRSG 118. The exhaust gasses 103 flow through the HRSG 118 and around the boiler tubes 122, heating the boiler water flowing through the boiler tubes 122. The boiler water is converted into steam that drives the steam turbine 126 and the mechanically connected generator 128. The steam exits the steam turbine 126 and is condensed by the condenser 130 into water that is pressurized by the pump 124.

FIG. 2 illustrates a side view of a portion of an exemplary embodiment of a boiler tube assembly 202. The boiler tube assembly 202 includes a tube 204 and fins 206 arranged in parallel on an outer surface 208 of the tube 204. The 204 and fins 206 may be fabricated from any suitable material including, for example, steel or another metallic material. The fins 206 may be secured to the outer surface 208 of the tube 204 using a suitable method such as, for example, welding, brazing, an adhesive, or a mechanical linkage.

FIG. 3 illustrates a cross-sectional view along the line 3-3 (of FIG. 2) of the boiler tube assembly 202. The boiler tube assembly 202 includes a cavity 302 defined by the tube 204 having an inner surface 304. The tube 204 is elliptically shaped, having a major axis (longitudinal axis) (y) 301 and a minor axis (transverse axis) (x) 303; where y>x.

FIG. 4 illustrates a side view of a portion of an alternate exemplary embodiment of a boiler tube assembly 402. The boiler tube assembly 402 includes a tube 404 and fins 406 arranged in parallel on an outer surface 408 of the tube 404.

FIG. 5 illustrates a cross-sectional view along the line 5-5 (of FIG. 4) of the boiler tube assembly 402. The boiler tube assembly 402 includes a cavity 502 defined by the tube 404 having an inner surface 504. The tube 404 is pill shaped having a longitudinal axis (a) 501 and transverse axis (b) 503; where a>b. The tube 404 includes parallel longitudinal segments 510 and end segments 512 forming a continuous shape. The end segments 512 of the boiler tube assembly 402 are rounded having a radius (r) 505.

FIG. 6 illustrates a cross-sectional view of an exemplary embodiment of an arrangement of boiler tube assemblies 202 in a portion of the HRSG 118 (of FIG. 1). The flow path of the exhaust gasses 103 from the gas turbine engine 102 is shown. In operation, boiler water flows through the cavity 204 of the boiler tube assemblies 202. The exhaust gasses 103 transfer heat to the boiler water via the fins 206 and the tube 204. The elliptical shape of the boiler tube assembly 202 improves the flow of the exhaust gasses 103 by extending and flattening the surface area of each tube assembly 202 in the direction of the flow path of the exhaust gasses 103; and decreases the pressure loss through the HRSG 118. The elliptical shape of the tube 204 and fins 206 increases the surface area of the boiler tube assembly 202 (as opposed to a circular shaped tube and fin assembly) and increases the heat transfer per tube to the boiler water. The improved heat transfer of the boiler tube assembly 202 may also allow the spacing (intervals) (indicated by the arrow 601) of the boiler tube assemblies 202 to be relatively greater (than an arrangement of circular tubes) while maintaining the desired heat transfer specifications (heat exchanger effectiveness) of the HRSG 118. Increased spacing of the boiler tube assemblies 202 further reduces pressure loss and improves the flow rate of the exhaust gasses 103 as they flow through the HRSG 118. For example, referring to FIG. 1, the exhaust gasses 103 have a pressure P1 at the inlet duct 114 of the HRSG 118 and a pressure P2 at the outlet duct 125. The difference in pressure may be expressed as: ΔP=P2-P1. In the illustrated embodiment the ΔP is less than a ΔP for an HRSG having tubes that are spaced at smaller intervals (e.g., an arrangement of circular boiler tubes). The reduction of ΔP in the illustrated embodiment increases the efficiency of the gas turbine engine 102 (of FIG. 1) by lowering a back pressure on the turbine 112. The increased efficiency of the gas turbine engine 102 increases the overall efficiency of the system 100.

Another advantage of the increased heat transfer of the boiler tube assembly 202 is that the number of boiler tube assemblies 202 in the HRSG 118 may be reduced; thereby; decreasing the overall size (and cost) of the HRSG 118 while maintaining a desired heat exchanger effectiveness value.

FIG. 7 illustrates a graph showing the change in output in kilowatts (kW) of a combined cycle system (CCkW) similar to the system 100 described above and a simple cycle (SCkW) versus a change in exhaust pressure dP (ΔP) (in inches of water) of a turbine engine. In this regard, a reduction in exhaust pressure results in an increase in output.

FIG. 8 illustrates a graph showing the change in efficiency of a combined cycle system (CCeff) and a simple cycle (SCeff) versus a change in exhaust pressure dP (ΔP) (in inches of water) of a turbine engine. A reduction in exhaust pressure results in an increase in efficiency.

The improved flow rate of the exhaust gasses 103 improves the heat transfer of the boiler tube assemblies 202 by more evenly transferring heat to the boiler tube assemblies 202 as the exhaust gasses 103 flow through the HRSG 118. For example, referring to FIG. 6, the tubes along the row 602 receive exhaust gasses 103 at a higher temperature and flow rate than the boiler tube assemblies 202 along the row 604 due to the loss of heat in the exhaust gasses 103 as the gasses pass through the HRSG 118. The improved flow path of the illustrated embodiment reduces the difference between the heat transferred to the boiler tube assemblies 202 in the row 602 and the boiler tube assemblies 202 in the row 604. The more uniform transfer of heat to the boiler tube assemblies 202 along the flow path of the exhaust gasses 103 increases the efficiency of the HRSG 118 and the system 100, and may allow for the number of boiler tube assemblies 202 to be reduced in the HRSG 118 while maintaining a desired heat exchanger efficiency value. The reduced number of boiler tube assemblies 202 in the HRSG 118 may allow for a reduction in the size of the HRSG 118.

FIG. 9 illustrates a cross-sectional view of an alternate exemplary embodiment of an arrangement of boiler tube assemblies 402 in a portion of the HRSG 118 (of FIG. 1). The boiler tube assemblies 402 are arranged in a similar manner as the arrangement illustrated in FIG. 6.

FIG. 10 illustrates a cross-sectional view of another alternate exemplary embodiment of an arrangement of boiler tube assemblies 202 in a portion of the HRSG 118 (of FIG. 1) The boiler tube assemblies 202 are arranged in rows that are staggered.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.