Abstract:
An exhaust section for a gas turbine power plant including: an exhaust duct in fluid communication with exhaust gas from a gas turbine engine, wherein the exhaust gas flows through the exhaust duct along a flow direction; a catalyst supporting platform spanning a flow passage in the exhaust duct such that the exhaust gas passes through the platform, wherein the platform includes apertures having catalyst coated surfaces and the catalyst supporting platform has a front face which is no perpendicular to the flow direction.

Description:
BACKGROUND OF INVENTION 
       [0001]    The invention relates to a gas turbine power plant comprising an exhaust system including a transition duct, a flue gas exhaust duct, an exhaust stack outlet, and a catalyst, wherein the catalyst is arranged such that the exhaust flow encounters the catalyst in the exhaust duct. 
         [0002]    Catalysts have been inserted in exhaust ducts to remove pollutants from the exhaust of a gas turbine engine. These catalyst walls span the exhaust duct and are perpendicular to the flow of the exhaust gas through the duct. The walls cause the exhaust gas to rapidly increase in speed as the gas flows through apertures, channels, or honey comb holes in the wall. The rapid acceleration results in a large loss of pressure of up to 15 inches of water (H 2 O). 
         [0003]    The large pressure loss is not desired. To minimize the pressure drop, the flow passages of exhaust ducts have been given greater cross-sectional areas in the flow direction through the ducts. Increasing the cross section of an exhaust duct increases the cost and footprint of the ducts. 
       BRIEF DESCRIPTION OF INVENTION 
       [0004]    A novel orientation for a catalyst supported platform has been conceived in which the face of the platform is slanted in the exhaust duct. Angling the catalyst support platform, e.g., wall, increases exposed surface area of the platform and thereby permits an increase in the number of apertures through which flows the exhaust gas. The greater the number of apertures, the lower the pressure drop through the catalyst supported platform. 
         [0005]    An exhaust section for a gas turbine power plant including: an exhaust duct in fluid communication with exhaust gas from a gas turbine engine, wherein the exhaust gas flows through the exhaust duct along a flow direction; a catalyst supporting platform spanning a flow passage in the exhaust duct such that the exhaust gas passes through the platform, wherein the platform includes apertures having catalyst coated surfaces and the catalyst supporting platform includes portions arranged at an angle greater than ten (10) degrees with respect to the flow direction. 
         [0006]    The catalyst supporting platform may be substantially a conical shape with a cone axis parallel to the flow direction, wherein the conical shape has a V-cross section which converges in the flow direction. The apertures may have axes oriented in a range of ten to ninety degrees with respect to the flow direction. The cone axis may also be other than parallel to the flow direction. 
         [0007]    Further, the catalyst supporting platform may be oriented in a plane at an angle with respect to the flow direction in a range of ten to ninety degrees. Or, the catalyst support platform may include steps where each step includes a riser in a plane substantially perpendicular to the flow direction and a tread in a plane substantially parallel to the flow direction. 
         [0008]    An exhaust section for a gas turbine power plant comprising: a transition duct; an exhaust duct; an exhaust exit stack; a porous catalyst supporting platform within the exhaust duct or exhaust exit stack, wherein the catalyst supporting platform extends across an exhaust air flow passage such that the exhaust air from a gas turbine engine flows through platform; and the catalyst supporting platform is arranged such that the exhaust air flow encounters the catalyst at an angle to the direction of the exhaust air flow in a range of ten to ninety degrees. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1 a    is an illustration of an exemplary conventional exhaust system;  FIG. 1 b    is an alternative view of a gas turbine system according to  FIG. 1   a;    
           [0010]      FIG. 2 a    is an illustration of a first embodiment of an exhaust system according to the invention;  FIG. 2 b    is an alternative view of a gas turbine system according to  FIG. 2   a;    
           [0011]      FIG. 3 a    is an illustration of a second embodiment of an exhaust system according to the invention;  FIG. 3 b    is an alternative view of a gas turbine system according to  FIG. 3   a;    
           [0012]      FIG. 4 a    is an illustration of a third embodiment of an exhaust system according to the invention;  FIG. 4 b    is an alternative view of a gas turbine system according to  FIG. 4   a;    
           [0013]      FIG. 5 a    is an illustration of a fourth embodiment of an exhaust system according to the invention;  FIG. 5 b    is an alternative view of a gas turbine system according to  FIG. 5   a;    
           [0014]      FIG. 6 a    is an illustration of a fifth embodiment of an exhaust system according to the invention;  FIG. 6 b    is an alternative view of a gas turbine system according to  FIG. 6   a;    
           [0015]      FIG. 7 a    is an illustration of a sixth embodiment of an exhaust system according to the invention;  FIG. 7 b    is an alternative view of a gas turbine system according to  FIG. 7   a;    
           [0016]      FIG. 8 a    is an illustration of a seventh embodiment of an exhaust system according to the invention;  FIG. 8 b    is an alternative view of a gas turbine system according to  FIG. 8   a;    
           [0017]      FIG. 9 a    is an illustration of an eighth embodiment of an exhaust system according to the invention;  FIG. 9 b    is an alternative view of a gas turbine system according to  FIG. 9 a   ; and 
           [0018]      FIG. 10  is an illustration of a ninth embodiment of an exhaust system according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1 a    is an illustration of a conventional gas turbine system  100  featuring a catalyst contained in a platform  101  within its exhaust duct  102  oriented normal to the flow  103  of exhaust gases. As  FIG. 1 a    illustrates, air exiting the turbine system  100 , which will be at a high temperature and a high velocity, enters the exhaust duct  102  via a transition stage  104  where the exhaust may be mixed with cooling air supplied by fans  106 , and/or it may have a mix of NH 3  and hot flue gases  108  introduced by a blower  109 , the NH 3    107  and hot flue gases  108  optionally passing through an evaporator/mixer  111 . The exhaust gas, which may include the NH 3    107  and hot flue gases, then is forced to pass through a catalyst  101 . The catalyst may be for removing NO x  as required by environmental laws. As is illustrated, the catalyst conventionally is arranged as a wall which is normal (perpendicular) to the flow  103  of gases through the exhaust duct  102 . In the conventional design illustrated herein, the flow  103  of exhaust gas is forced to abruptly speed up and go through the catalyst wall, resulting in an unfavorable substantial drop in pressure and resulting loss in efficiency of the gas turbine. Flow  103  may optionally pass through additional catalysts such as CO catalyst  112 .  FIGS. 1 a  and 1 b    illustrate alternative views of gas turbine system  100 . 
         [0020]      FIG. 2 a    is an illustration of a first embodiment of a gas turbine system  200  featuring an exhaust system according to the invention. In the first embodiment, the wall-like catalyst structure of  FIG. 1 a    has been replaced instead with a substantially V-shaped catalyst  201 . The V-shaped catalyst  201  may be oriented such that the tip of the V is pointed in the direction of the flow  203  of the exhaust gas. The V-shaped catalyst  201  may be arranges such that the arms of the V-shaped catalyst originate at substantially the same location or a different location on the exhaust duct as the conventional catalyst, with the V shape projecting outwardly therefrom. The V-shape may be substantially wedge-like, comprising two structures which may be identical or of different lengths. 
         [0021]    In this novel system, the improved catalyst gives the exhaust air additional cross sectional area to go through as compared with the conventional design. The catalyst  201  itself may be a honeycomb design comprising an array of holes, which may be for removal of pollutants and especially NON. The exhaust flow  203 , as it reaches the novel catalyst arrangement, will encounter the catalyst  201  at angles other than ninety degrees, which will mitigate the energy loss and thus also mitigate the pressure loss to the system. The cooling flow  206  may mix with flue gas  203  and reduce the temperature of  203 , as the catalyst  201  may have improved function at the reduced temperature. The mixed flue gas  203  and cooling air  206  flow through catalyst  201  with angle relative the flow direction. This process gives the system more residence time and cross section area to allow catalytic reactions of ammonia and NOx. In contrast, in a conventional system, the smaller cross sectional area and lower/diminished residence time would result in a large drop in pressure and correspondingly a large drop in efficiency of the gas turbine.  FIGS. 2 a  and 2 b    illustrate views of gas turbine system  200 . Flow  203  may optionally pass through additional catalysts such as CO catalyst  212 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0022]      FIG. 3 a    is an illustration of a second embodiment according to the invention. In this embodiment, the V-shape of  FIG. 2 a    is replaced with a cone-shape catalyst  301  oriented to point in the direction of the flow  303  of the exhaust gases. Instead of the substantially flat sections comprising the V-shape of the embodiment of  FIG. 2 a   ,  FIG. 3 a    illustrates a cone shape located within the exhaust duct  302  performing the same function as the V-shaped catalyst of  FIG. 2 a   . The cone originates around the edges of the exhaust duct and narrows in the direction of the flow  303  of exhaust gas. In an alternative embodiment, the catalyst may be configured as a hollow pyramidal structure. The shape of the perimeter of the catalyst structure will be determined by the shape of the corresponding exhaust duct  302 . The cone may be oriented such that its central axis aligns with the flow  303  of exhaust gas. The cone may alternatively be oriented such that the cone has a central axis oriented at an angle greater than zero relative to the flow direction of the exhaust gas. The circular (or rectangular) edge defining one end of the cone may be arranged concentrically within the section in which the cone is located, or may be offset or angled relative to the exhaust section and the flow of gases passing therethrough.  FIGS. 3 a  and 3 b    illustrate views of gas turbine system  300 . Flow  303  may optionally pass through additional catalysts such as CO catalyst  312 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0023]      FIG. 4 a    is an illustration of a third embodiment according to the invention. In this embodiment the conventional flat wall oriented perpendicularly to the flow of exhaust gases has been replaced with an angled catalyst wall  401 . The catalyst will be anchored to the exhaust duct and extend backwards towards the exhaust stack, where its more downstream end will also be configured to substantially contact the exhaust duct and require exhaust gases to pass through the catalyst structure  401  before exiting the system. The angled wall embodiment may be arranged within an exit stack instead or in addition to being within the exhaust duct  402 .  FIGS. 4 a  and 4 b    illustrate views of gas turbine system  400 . Flow  403  may optionally pass through additional catalysts such as CO catalyst  412 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0024]      FIG. 5 a    is an illustration of a fourth embodiment according to the invention. In this embodiment, the angled catalyst has been modified to be structured as a substantially stair step configuration  501 . Such an embodiment can be oriented such that the stair step consists of segments which are normal to the flow  503  of exhaust gas and other segments which are parallel to the flow  503  of exhaust gas. In another configuration, the stair step catalyst  501  consists of segments which are neither perpendicular nor parallel to the direction of flow  503  of the exhaust gases. The segments may all be of the same length or the segments may vary in length. The segments may all be oriented with the same pair of angles relative to each other or the segments may be oriented using a range of angles. The angles chosen specifically will be dependent on the particular exhaust duct  502  structure utilized.  FIGS. 5 a  and 5 b    illustrate views of gas turbine system  500 . Flow  503  may optionally pass through additional catalysts such as CO catalyst  512 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0025]      FIG. 6 a    is an illustration of a fifth embodiment according to the invention.  FIG. 6 a    inverts the V-shape of  FIG. 2 a   . In this embodiment, the catalyst wedge  601  is pointed in the direction opposite the flow  603  of exhaust gases. In this configuration, exhaust gases are split and forced outward before passing through the catalyst. The V-shape here provides the benefit of splitting the exhaust flow  603  before it passes through the catalyst, unlike the V-shape of  FIG. 2 a   , which corrals the airflow within its wedge. Both configurations provide benefits over the conventional designs in that additional residence time and surface area are provided to the exhaust flows.  FIGS. 6 a  and 6 b    illustrate views of gas turbine system  600 . Flow  603  may optionally pass through additional catalysts such as CO catalyst  612 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0026]      FIG. 7 a    is an illustration of a sixth embodiment according to the invention.  FIG. 7 a    inverts the cone shape of  FIG. 3 a   . In this embodiment, the catalyst cone  701  is pointed in the direction opposite the flow  703  of exhaust gases. In this configuration, exhaust gases are split and forced outward before passing through the catalyst. The cone shape here provides the benefit of splitting the exhaust flow before it passes through the catalyst, unlike the cone shape of  FIG. 3 a   , which corrals the airflow within its cone. Both configurations provide benefits over the conventional designs in that additional time and surface area are provided to the exhaust flows.  FIGS. 7 a  and 7 b    illustrate views of gas turbine system  700 . Flow  703  may optionally pass through additional catalysts such as CO catalyst  712 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0027]      FIG. 8 a    is an illustration of a seventh embodiment according to the invention.  FIG. 8 a    provides a catalyst  801  with a stair step configuration added to the V-shape of  FIGS. 2 a  and 6 a   . Utilizing a stair step as illustrated in  FIG. 5 a    applied to the V shape of  FIGS. 2 a  and 6 a    further provides additional surface area to assist in passing more exhaust gas through the catalyst  801  as well as reducing the effects of the pressure drop.  FIGS. 8 a  and 8 b    illustrate views of gas turbine system  800 . Flow  803  may optionally pass through additional catalysts such as CO catalyst  812 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0028]      FIG. 9 a    is an illustration of an eighth embodiment according to the invention.  FIG. 9 a    provides a catalyst  901  with a stair step configuration added to the cone shape of  FIGS. 3 a  and 7 a   . Utilizing a stair step as illustrated in  FIG. 5 a    applied to the cone shape of  FIGS. 3 a  and 7 a    further provides additional surface area to assist in passing more exhaust gas through the catalyst  901  as well as reducing the effects of the pressure drop.  FIGS. 9 a  and 9 b    illustrate views of gas turbine system  900 . Flow  903  may optionally pass through additional catalysts such as CO catalyst  912 , which may be of conventional design arranged according to any of the nonlimiting embodiments described herein. 
         [0029]      FIG. 10  is an illustration of a ninth embodiment according to the invention.  FIG. 10  illustrates the alternative configuration for the catalyst  1001  provided in the stacks  1010  rather than the exhaust duct  1002 . Any of the alternative structures for the catalyst discussed and illustrated in association with  FIGS. 2 a -9 a    may be configured and arranged to be placed in the stacks  1010  or the exhaust duct  1002 . Moving the catalyst further downstream, i.e., into the stack and past the exhaust duct, provides the gas more time to cool and slow down without interference. The additional time helps to reduce the pressure loss associated with conventional designs. 
         [0030]    The delaying of the interaction of the flue and/or exhaust gas with the catalyst structure provides the flue and/or exhaust gas with a slower velocity when it passes through the catalyst, whereby the catalyst may remove NO x  or another pollutant. The slower velocity is accomplished using any of a number of catalyst structure designs which are not available conventionally, whereby the front surface of the catalyst is intentionally misaligned with the flow direction of the exhaust and/or flue gases. The alternative configuration and arrangement effectively creates a much larger cross sectional area for pollutant, i.e., NO x , reduction. 
         [0031]    The additional surface area serves to better catalyze pollutants in the exhaust gas, therefore being a more efficient and more effective system for removing pollutants, while also significantly reducing the pressure drop associated with conventional systems. Experimentally, the alternative designs were found to reduce the pressure drop by more than 70%. Correspondingly, according to gas turbine models, the alternative arrangements described herein also can lead to an increased power output of the associated gas turbine by at least 5 MW (megawatts). Further, by minimizing the need to increase the size of the exhaust duct, costs were reduced by up to 20%. 
         [0032]    For the purposes of this application, “flue gas” and “exhaust gas” may be used interchangeably, meaning that the invention has beneficial effects when discussing catalyst structures played in the path of the flow of exhaust and/or flue gases associated with a gas turbine power plant. 
         [0033]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.