Patent Publication Number: US-7707818-B2

Title: Exhaust stacks and power generation systems for increasing gas turbine power output

Description:
BACKGROUND OF THE INVENTION 
   The present application relates generally to gas turbines, and more specifically to exhaust stacks and power generation systems configured to increase the power output of gas turbines. 
   A combined cycle power plant (“CCPP”) includes a gas turbine, a heat recovery steam generator (“HRSG”), a steam turbine and an exhaust stack. The gas turbine includes a turbine configured to produce a rotational power output in response to an expansion of exhaust gases. The HRSG is configured to receive the exhaust gases from the gas turbine and generate steam from heat of the exhaust gases. The steam turbine is configured to produce a rotational power output in response to an expansion of the steam. The exhaust stack is configured to pass the exhaust gases from the HRSG to the atmosphere. 
   The gas turbine includes a compressor, a combustion region and the turbine. The compressor is configured to compress an inflow of air. The combustion region is configured to receive the compressed air, combust a mixture of the compressed air and fuel, and produce a high temperature, high pressure exhaust gases. The turbine is configured to receive the exhaust gases and rotate in response to the expansion of the exhaust gases. Accordingly, the rotational power output of the turbine is proportional to the expansion of the exhaust gases and inherent pressure drop. 
   Accordingly, it is desirable to provide an exhaust stack configured to reduce the local pressure drop through the exhaust stack, such that the expansion of the exhaust gases in the gas turbine is increased and hence the power output of the gas turbine is increased. 
   BRIEF DESCRIPTION OF THE INVENTION 
   An exhaust stack in accordance with an exemplary embodiment is provided. The exhaust stack includes a junction tube. The exhaust stack further includes a flue having a silencer portion, a converging duct portion, a tubular portion, and a diverging diffuser portion. The silencer portion fluidly communicates with the junction tube. At least a portion of the silencer portion has a first hydraulic mean cross-sectional flow path, and at least a portion of the tubular portion has a second hydraulic mean cross-sectional flow path less than or equal to the first hydraulic mean cross-sectional flow path. The converging duct portion is coupled between the silencer portion and the tubular portion. The diverging diffuser portion is coupled to an end of the tubular portion opposite to the converging duct portion, such that exhaust gases flowing through the junction tube, the silencer portion, the converging duct portion, the tubular portion and the diverging diffuser portion, has a reduced localized pressure drop, at least in part due to the diverging diffuser portion, and the second hydraulic mean cross-sectional flow path being less than or equal to the first hydraulic mean cross-sectional flow path. 
   A power generation system in accordance with another exemplary embodiment is provided. The power generation system includes a gas turbine having a compressor, a combustion region and a turbine. The compressor is configured to compress air. The combustion region is configured to receive the compressed air from the compressor and combust a mixture of the compressed air and fuel, which produces exhaust gases. The turbine is configured to receive the exhaust gases from the combustion region and rotate in response to an expansion of the exhaust gases, such that a pressure of the exhaust gases decreases as the exhaust gases expands through the turbine. The power generation system further includes a heat recovery steam generator configured to receive the exhaust gases and generate steam from heat of the exhaust gases. The power generation system further includes an exhaust stack having a junction tube and a flue. The junction tube is configured to receive the exhaust gases from the heat recovery steam generator. The flue has a silencer portion, a converging duct portion, a tubular portion, and a diverging diffuser portion. The silencer portion fluidly communicates with the junction tube. At least a portion of the silencer portion has a first hydraulic mean cross-sectional flow path, and at least a portion of the tubular portion has a second hydraulic mean cross-sectional flow path less than or equal to the first hydraulic mean cross-sectional flow path. The converging duct portion is coupled between the silencer portion and the tubular portion. The diverging diffuser portion is coupled to an end of the tubular portion opposite to the converging duct portion, such that exhaust gases flowing through the junction tube, the silencer portion, the converging duct portion, the tubular portion and the diverging diffuser portion, has a reduced localized pressure drop, at least in part due to the diverging diffuser portion, and the second hydraulic mean cross-sectional flow path being less than or equal to the first hydraulic mean cross-sectional flow path. The reduced localized pressure drop in the exhaust stack increases the overall pressure differential of the exhaust gases across the turbine and hence increases the power output of the gas turbine. 
   An exhaust stack in accordance with another exemplary embodiment is provided. The exhaust stack includes a junction tube. The exhaust stack further includes a flue having a first tubular portion, a first diverging diffuser portion, a silencer portion, a converging duct portion, a second tubular portion, and a second diverging diffuser portion. The first tubular portion fluidly communicates with the junction tube. At least a portion of the first tubular portion has a first hydraulic mean cross-sectional flow path, and at least a portion of the silencer portion has a second hydraulic mean cross-sectional flow path. The first hydraulic mean cross-sectional flow path is less than or equal to the second hydraulic mean cross-sectional flow path. The first diverging diffuser portion is coupled between the first tubular portion and the silencer portion. At least a portion of the second tubular portion has a third hydraulic mean cross-sectional flow path less than or equal to the second hydraulic mean cross-sectional flow path. The converging duct portion is coupled between the silencer portion and the second tubular portion. The second diverging diffuser portion is coupled to an end of the second tubular portion opposite to the converging duct portion, such that exhaust gases flowing through the junction tube, the first tubular portion, the first diverging diffuser portion, the silencer portion, the converging duct portion, the second tubular portion and the second diverging diffuser portion, have a reduced localized pressure drop, at least in part due to the second diverging diffuser portion, and the third hydraulic mean cross-sectional flow path being less than or equal to the second hydraulic mean cross-sectional flow path. 
   A power generation system in accordance with another exemplary embodiment is provided. The power generation system includes a gas turbine having a compressor, a combustion region and a turbine. The compressor is configured to compress air. The combustion region is configured to receive the compressed air from the compressor and combust a mixture of the compressed air and fuel which produces exhaust gases. The turbine is configured to receive the exhaust gases from the combustion region and rotate in response to an expansion of the exhaust gases, such that a pressure of the exhaust gases decreases as the exhaust gases expands through the turbine. The power generation system further includes a heat recovery steam generator configured to receive the exhaust gases and generate steam from heat of the exhaust gases. The power generation system further includes an exhaust stack having a junction tube and a flue. The junction tube is configured to receive the exhaust gases from the heat recovery steam generator. The flue has a first tubular portion, a first diverging diffuser portion, a silencer portion, a converging duct portion, a second tubular portion, and a second diverging diffuser portion. The first tubular portion fluidly communicates with the junction tube. At least a portion of the first tubular portion has a first hydraulic mean cross-sectional flow path. At least a portion of the silencer portion has a second hydraulic mean cross-sectional flow path. The first hydraulic mean cross-sectional flow path is less than or equal to the first hydraulic mean cross-sectional flow path. The first diverging diffuser portion is coupled between the first tubular portion and the silencer portion. At least a portion of the second tubular portion has a third hydraulic mean cross-sectional flow path less than or equal to the second hydraulic mean cross-sectional flow path. The converging duct portion is coupled between the silencer portion and the second tubular portion. The second diverging diffuser portion is coupled to an end of the second tubular portion opposite to the converging duct portion, such that exhaust gases flowing through the junction tube, the first tubular portion, the first diverging diffuser portion, the silencer portion, the converging duct portion, the second tubular portion and the second diverging diffuser portion have a reduced overall pressure drop, at least in part due to the second diverging diffuser portion, and the third hydraulic mean cross-sectional flow path being less than or equal to the second hydraulic mean cross-sectional flow path. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of a combined cycle power generation system having an exhaust stack, in accordance with an exemplary embodiment; 
       FIG. 2  is a perspective view of the exhaust stack of  FIG. 1 ; 
       FIG. 3  is a flow profile for the exhaust stack of  FIG. 2 ; 
       FIG. 4  is a cross-sectional view of the exhaust stack of  FIG. 2 ; 
       FIG. 5  is an enlarged cross-sectional view of a diverging diffuser portion of the exhaust stack of  FIG. 2 ; 
       FIG. 6  is a cross-sectional view of an exhaust stack showing a top surface of a junction tube extending from a silencer portion by an angle within a range between about 90 and about 135 degrees, and a bottom surface of the junction tube extending from the silencer portion by an angle within a range between about 22.5 and about 67.5 degrees, in accordance with another exemplary embodiment; 
       FIG. 7  is a cross-sectional view of an exhaust stack showing a top surface of a junction tube extending from a silencer portion by an angle within a range between about 90 and about 135 degrees, a bottom surface of the junction tube extending from the silencer portion by an angle within a range between about 22.5 and about 67.5 degrees, and a flow guider having a planar surface positioned at an angle within a range between about 22.5 and about 67.5 degrees from a lateral axis  272  of the exhaust stack, in accordance with yet another exemplary embodiment; 
       FIG. 8  is a cross-sectional view of an exhaust stack showing a top surface of a junction tube extending from a silencer portion by an angle within a range between about 90 and about 135 degrees, a bottom surface of the junction tube extending from the silencer portion by an angle within a range between about 22.5 and about 67.5 degrees, and a flow guider having a concave surface extending from a lateral axis of the exhaust stack by an angle within a range between about 22.5 and about 67.5 degrees, in accordance with another exemplary embodiment; and 
       FIG. 9  is a cross-sectional view of an exhaust stack, in accordance with another exemplary embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Exemplary embodiments are directed to an exhaust stack configured to increase a power output of a gas turbine of a combined cycle power plant (“CCPP”). However, it is contemplated that the exhaust stack can increase the power output of gas turbines integrated in other suitable power generation systems. In these exemplary embodiments, the exhaust stack is configured to reduce the pressure drop in the exhaust stack in order to increase the pressure drop associated with the expansion of the exhaust gases in the gas turbine, such that the increased expansion of gas increases the power output of the gas turbine. 
   Referring to  FIG. 1 , a CCPP  10  includes a gas turbine generator  12  and a steam turbine generator  14 . The gas turbine generator  12  is configured to generate electricity and produce exhaust gases. The steam turbine generator  14  is configured to receive the exhaust gases from the gas turbine generator  12  and generate additional electricity from waste heat of the exhaust gases. 
   The gas turbine generator  12  includes a gas turbine  16 , a first output shaft  18  and a first electrical generator  20 . The gas turbine  16  has a compressor  22 , a combustion region  24  and a turbine  26 . The compressor  22  is configured to compress an inflow of air. The combustion region  24  is configured to receive the compressed air from the compressor  22  and combust a mixture of the compressed air and fuel, which produces a high pressure, high temperature exhaust gases. The turbine  26  is configured to receive the exhaust gases from the combustion region  24  and rotate in response to an expansion of the exhaust gases. The turbine  26  is operably connected to the first electrical generator  20  by the first output shaft  18  for providing rotational power to the first electrical generator  20  and producing electricity. The turbine  26  is further configured to pass the exhaust gases to the steam turbine generator  14 . 
   The steam turbine generator  14  includes a HRSG  28  and an exhaust stack  30 . The HRSG  28  is configured to receive the exhaust gases from the gas turbine  16  and generate steam from the waste heat of the exhaust gases. The exhaust stack  30  is configured to pass the exhaust gases from the HRSG  28  to the atmosphere and reduce the local pressure drop of the exhaust gases in the stack and increase the overall pressure differential across the turbine, as described in detail below. 
   The steam turbine generator  14  further includes a steam turbine  32 , a second output shaft  34 , a second electrical generator  36 , a condenser  38 , a cooling tower  40  and a pump  42 . The steam turbine  32  is configured to receive the steam from the HRSG  28  and rotate in response to the expansion of steam. The steam turbine  32  is operably connected to the second electrical generator  36  by the second output shaft  34  for providing rotational power to the second electrical generator  36  and generating electricity. However, it is contemplated that the steam turbine  32  can instead be operably connected to the first electrical generator  20  by the first output shaft  18  in a single shaft arrangement. The condenser  38  is configured to receive the steam from the steam turbine  32  and condense the steam into water. In particular, the condenser  38  is configured to receive water from the cooling tower  40  and transfer heat from the steam to the water and condense the steam into water. It is contemplated that the condenser  38  can instead be configured to transfer heat to water from a lake, river, sea or other suitable non-limiting examples. The pump  42  is configured to pump water from the condenser  38  into the HRSG  28 . 
   Referring to  FIGS. 2-5 , the exhaust stack  30  includes a junction tube  44  and a flue  46 . The junction tube  44  is configured to fluidly communicate with the HRSG  28 . The flue  46  includes a silencer portion  48 , a converging duct portion  50 , a tubular portion  52  and a diverging diffuser portion  54 . The silencer portion  48  is configured to fluidly communicate with the junction tube  44 . At least a portion of the silencer portion  48  has a first hydraulic mean cross-sectional flow path, and at least a portion of the tubular portion  52  has a second hydraulic mean cross-sectional flow path less than or equal to the first hydraulic mean cross-sectional flow path. The converging duct portion  50  is coupled between the silencer portion  48  and the tubular portion  52 . The diverging diffuser portion  54  is coupled to an end of the tubular portion  52  opposite to the converging duct portion  50 . Accordingly, the exhaust gases flowing through the junction tube  44 , the silencer portion  48 , the converging duct portion  50 , the tubular portion  52  and the diverging diffuser portion  54 , have a reduced overall pressure drop at least in part due to the diverging diffuser portion  54  and the second hydraulic mean cross-sectional flow path being less than or equal to the first hydraulic mean cross-sectional flow path. 
   Referring to  FIG. 4 , the junction tube  44  has a top surface  56  and a bottom surface  58  extending from an outer surface  60  of the silencer portion  48 , such that the junction tube  44  provides a uniform flow distribution into the silencer portion  48  for reducing a localized pressure drop into the silencer portion. In particular, the top surface  56  extends from the outer surface  60  of the silencer portion  48  by 135 degrees, and the bottom surface  58  extends from the outer surface  60  by 45 degrees. Accordingly, the junction tube  44  directs the exhaust gases through the silencer portion  48  towards the converging duct portion  50 , with a substantially uniform flow profile for reducing pressure drop in the silencer section. In this regard, the junction tube  44  also reduces a turning loss at a closed end  62  of the silencer portion  48  and enhances the pressure recovery in the diverging diffuser portion  54 . 
   It is contemplated that the top surface  56  and the bottom surface  58  of the junction tube  44  can extend from the outer surface  60  of the silencer portion  48  by various suitable angles, as exemplified in the embodiments of  FIGS. 6-9 . 
   Referring to  FIG. 5 , the diverging diffuser portion  54  is configured to diverge from the tubular portion  52 , such that the diverging diffuser portion  54  recovers exit pressure loss. Examples of a divergence angle α include 5 degrees, 15 degrees and suitable angles in the range therebetween, in order to recover pressure in the range between about 1.5 and 2.0 centimeters of water for a velocity range between about 18 and about 22 meters per second. It is contemplated that the divergence angle can be greater or less than this range, utilizing a suitable pressure recovery device. 
   The diverging diffuser portion  54  further includes a first end  64  with a diameter of 6 meters and a second end  66  with a diameter of 9 meters. It is understood that the diameters of the first end  64  and second end  66  can be greater or less than 6 and 9 meters, respectively. The diverging diffuser portion  54  has a length of 15 meters from the first end  64  to the second end  66 . However, the diverging diffuser portion  54  can have a length greater or less than 15 meters. 
   Referring to  FIG. 6 , an exhaust stack  130  having a junction tube  144  and a flue  146  with a silencer portion  148 , a converging duct portion  150 , a tubular portion  152  and a diverging diffuser portion  154 , is substantially similar to the exhaust stack  30  having the junction tube  44  and the flue  46  with the silencer portion  48 , the converging duct portion  50 , the tubular portion  52  and the diverging diffuser portion  54  of  FIGS. 1-4 . However, the junction tube  144  has a top surface  156  that can extend from an outer surface  160  of the silencer portion  148  by an angle within the range between about 90 and about 135 degrees. In addition, the junction tube  144  has a bottom surface  158  that extends from the outer surface  160  by an angle within a range between about 22.5 and about 67.5 degrees. 
   Referring to  FIG. 7 , an exhaust stack  230  having a junction tube  244  and a flue  246  with a silencer portion  248 , a converging duct portion  250 , a tubular portion  252  and an diverging diffuser portion  254  is substantially similar to the exhaust stack  30  respectively having the junction tube  44  and the flue  46  with the silencer portion  48 , the converging duct portion  50 , the tubular portion  52  and the diverging diffuser portion  54  of  FIGS. 1-4 . However, the junction tube  244  has a top surface  256  that extends from the outer surface  260  by an angle within the range between about 90 and about 135 degrees. Moreover, the junction tube  244  has a bottom surface  258  that extends from the outer surface  260  by an angle within a range between about 22.5 and about 67.5 degrees. Furthermore, the flue  246  further includes a flow guider  268  configured to reduce turning loss at a closed end  262  of the silencer portion  248  and to provide a substantially uniform velocity flow profile upstream of silencer portion  248  and diffuser portion  246 . The flow guider  268  is a plate having a planar surface extending from the bottom surface  258  of the silencer portion  248  and across a cavity  270  of the silencer portion  248 . The planar surface of the flow guider  268  is positioned at an angle within a range between about 22.5 and about 67.5 degrees from a lateral axis  272  of the flue  246 . In that regard, a significant portion of exhaust gases is directed away from the closed end  262  of the silencer portion  248  and towards the converging duct portion  250 . 
   The silencer portion  248  is configured to allow for the expansion of the exhaust gases and reduce the velocity and the turbulence of the exhaust gases, such that high energy noise is dissipated in the silencer portion  248 . The silencer portion  248  is configured to have a first mean velocity of exhaust gases flowing therethrough and the tubular portion  252  is configured to have a second mean velocity of exhaust gases flowing therethrough. The first mean velocity is equal to at least one-half the second mean velocity. 
   Referring to  FIG. 8 , an exhaust stack  330  having a junction tube  344  and a flue  346  with a silencer portion  348 , a converging duct portion  350 , a tubular portion  352  and an diverging diffuser portion  354 , is substantially similar to the exhaust stack  30  having the junction tube  44  and the flue  46  with the silencer portion  48 , the converging duct portion  50 , the tubular portion  52  and the diverging diffuser portion  54  of  FIGS. 1-4 . However, the junction tube  344  has a top surface  356  that extends from an outer surface  360  of the silencer portion  348  by an angle within a range between about 90 and about 135 degrees. In addition, the junction tube  344  has a bottom surface  358  that extends from the outer surface  360  by an angle within a range between about 22.5 and about 67.5 degrees. Furthermore, the flue  346  further includes a flow guider  368  configured to reduce turning loss at a closed end  362  of the silencer portion  348  and provide substantially uniform velocity profile at the silencer inlet and diffuser inlet section ensuring maximum pressure recovery. The flow guider  368  is a plate having a concave surface extending from the bottom surface  358  of the silencer portion  348  and across a cavity  370  of the silencer portion  348 . The concave surface has a radius of curvature equal to one-half of the first diameter of the silencer portion  48 . However, the concave surface can instead have other suitable radii of curvatures. The flow guider  368  is positioned at an angle within a range between about 22.5 and about 67.5 degrees from a lateral axis  372  of the flue  346 . 
   Referring to  FIG. 9 , an exhaust stack  400  is configured to limit the pressure drop of the exhaust gases to approximately 0.5 inches of water. In particular, the exhaust stack  400  includes a junction tube  402  and a flue  404 . The junction tube  402  fluidly communicates with the HRSG  28  and is configured to receive steam from the HRSG  28 . The flue  404  includes a first tubular portion  406 , a first diverging diffuser portion  408 , a silencer portion  410 , a converging duct portion  412 , a second tubular portion  414 , and a second diverging diffuser portion  416 . The first tubular portion  406  fluidly communicates with the junction tube  402 . The first tubular portion  406  has a first hydraulic mean cross-sectional flow path, and the silencer portion  410  has a second hydraulic mean cross-sectional flow path. The first hydraulic mean cross-sectional flow path is less than or equal to the second hydraulic mean cross-sectional flow path. The first diverging diffuser portion  408  is coupled between the first tubular portion  406  and the silencer portion  410 . The second tubular portion  414  has a third hydraulic mean cross-sectional flow path less than or equal to the second hydraulic mean cross-sectional flow path. The converging duct portion  412  is coupled between the silencer portion  410  and the second tubular portion  414 . The second diverging diffuser portion  416  is coupled to an end of the second tubular portion  414  opposite to the converging duct portion  412 , such that exhaust gases flowing through the junction tube  402 , the first tubular portion  406 , the first diverging diffuser portion  408 , the silencer portion  410 , the converging duct portion  412 , the second tubular portion  414  and the second diverging diffuser portion  416  has a reduced overall pressure drop, at least in part due to the second diverging diffuser portion and the third hydraulic mean cross-sectional flow path being less than or equal to the second hydraulic mean cross-sectional flow path. The reduced localized stack pressure drop increases an overall pressure differential of the exhaust gases through the gas turbine  16  and increases a power output of the gas turbine  16 . 
   The first tubular portion  406 , silencer portion  410  and second tubular portion  414  are configured to have first, second, and third mean velocities, respectively, of exhaust gases flowing therethrough. The first mean velocity is at least equal to an average of the second and third mean velocities. Further, the second mean velocity is equal to at least one-half the third mean velocity. The silencer portion  410  is further configured to allow for the expansion of the exhaust gases and reduce the velocity and the turbulence of the exhaust gases, such that high-energy noise is dissipated in the silencer portion  410 . 
   The flue  404  further includes a flow guider  468  configured to reduce turning loss at a closed end  462  of the silencer portion  410  and to provide a substantially uniform velocity profile upstream of the silencer section and diffuser section. The flow guider  468  is a plate having a planar surface extending from the bottom surface  462  of the silencer portion  410  and across a cavity  470  of the silencer portion  410 . The flow guider  468  is positioned at an angle within the range of about 22.5 degrees and about 67.5 degrees from a lateral axis  472  of the flue  404 . 
   The exhaust stacks and methods described herein provide a substantial advantage over other devices and methods. In particular, the exhaust stacks provide a technical effect of reducing a pressure drop of exhaust gases and increasing an amount of power output by a gas turbine. In one exemplary embodiment, the terms hydraulic mean cross-sectional flow path refers to a mean or average cross-sectional size of a flow path. 
   While the invention has been described with reference to an exemplary embodiment, various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed herein, but that the invention will include all embodiments falling within the scope of the appended claims.