Abstract:
An improved diffuser apparatus for use in connection with gas turbines that will markedly increase the fuel efficiency of the turbine. The improved diffuser apparatus improves the performance of the diffuser apparatus by insuring that the gas flow supplied by the turbine is free from unnecessary energy losses due to improperly located mechanical structures. More particularly, the prior art turbine is modified in a manner to incorporate into the diffuser itself certain of the mechanical structures that previously formed a part of the structure of the turbine.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to devices for the transformation of part of the kinetic energy of a moving fluid into pressure of the fluid. More particularly the invention concerns a diffuser for use in connection with gas turbines, where an improvement of performance is obtained at the interface between the turbine and the diffuser. 
         [0003]    2. Discussion of the Prior Art 
         [0004]    Novel and highly successful short subsonic diffusers are described in U.S. Pat. Nos. 3,599,431, 4,029,430 and 5,603,605, all issued to the present inventor. Because of the pertinence of these three patents, and because the present invention comprises an improvement over the inventions disclosed in these patents, U.S. Pat. Nos. 3,599,431, 4,029,430, and 5,603;605 are incorporated by reference as though fully set forth herein. 
         [0005]    The diffusers described in detail in the incorporated by reference patents recover a major fraction of the kinetic energy in the stream of gas issuing from the last stage of the turbine and efficiently transform it into an increment of static pressure and, therefore, results in an improvement of the thermodynamic efficiency of the turbine. However, a part of the kinetic energy of the gas at the inlet of the diffuser is not available for recovery because the original design of the turbine did not contemplate the possibility of the level of energy recovery enabled by the advanced diffuser of the present invention; hence, attention to the interface between the turbine and the diffuser permits an additional pressure recovery increment if the diffuser corrects the defects in the flow of the gas from the last stage of the turbine. 
         [0006]    Accordingly, the improved diffuser of the present invention is instantiated by transferring to the structure of the diffuser certain mechanical elements that are traditionally part of the turbine structure downstream of the last stage of the turbine. The removal of these mechanical elements from the turbine improves the gas flow to the diffuser and hence improves the energy recovery by the diffuser. As will be discussed in greater detail in the paragraphs that follow, the original function of these mechanical elements can be uniquely incorporated into the structure of the diffuser in such a way as to not affect the mechanical performance of the turbine, while at the same time relying upon the diffuser itself to provide the necessary structural support. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to provide a diffuser apparatus for use in connection with gas turbines that will markedly increase the fuel efficiency of the turbine. 
         [0008]    More particularly it is an object of the present invention to improve the performance of the diffuser apparatus by insuring that the gas flow supplied by the turbine is free from unnecessary energy losses due to improperly located mechanical structures. 
         [0009]    Another object of the invention is to modify the prior art turbine in a manner to incorporate into the diffuser itself certain of the mechanical structures that previously formed a part of the structure of the turbine. 
         [0010]    Another object of the invention is to modify the prior art turbine in the manner described in the preceding of paragraph without adversely affecting the aerodynamic function of the diffuser. 
         [0011]    Another object of the invention is to identify the stress path in the structure of the diffuser to insure adequate rigidity against deformations previously resisted by the structural elements of the turbine that were removed from the turbine and incorporated into the diffuser itself. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a side-elevational, cross-sectional view of one form of prior art diffuser structure that can be modified in accordance with the methods of the present invention. 
           [0013]      FIG. 2  is a side elevational, cross-sectional view similar to  FIG. 1 , but showing the structural elements that formed a part of the prior art diffuser structure, but were, for sake of clarity, eliminated from  FIG. 1  of the &#39;605 patent. 
           [0014]      FIG. 3  is a side-elevational, cross-sectional view of one form of the improved diffuser of the present invention. 
           [0015]      FIG. 4 , is a side-elevational, cross-sectional view of an alternate form of the improved diffuser of the invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0016]    Referring particularly to  FIG. 1 , one form of prior art apparatus that can be modified in accordance with the methods of the present invention is there shown. More particularly,  FIG. 1  illustrates the apparatus shown and described in incorporated by reference U.S. Pat. No. 5,603,605 (&#39;605) that comprises a diffuser coupled with a gas turbine of conventional construction. It is to be noted that the diffuser structure of this prior art apparatus is symmetrical about the axis  34  of the turbine. The turbine portion of the apparatus includes a power shaft  36  that comprises rotating hub  38  to which a plurality of outwardly extending turbine blades  39  are affixed. Circumscribing shaft  36  is a diffuser shroud  40  having inner and outer walls  42  and  44  respectively. As indicated in  FIG. 1 , the inner open mouth  46  of the shroud  40  is disposed proximate blades  39  of the turbine and functions to receive the high velocity gas stream generated by the turbine blades. Shroud  40  also includes an outer discharge area  48  which communicates with a novel collector means shown here as a collector structure  50 . A capture means is disposed interiorly of collector structure  50  and functions to collect a portion of the gases flowing through the shroud. This capture means is here shown as a generally toroidal-shaped capture scoop  52  having an uninterrupted inlet  54 . Inlet  54  is strategically located so that it directly faces the high velocity region of the gas stream flowing through shroud  40  toward discharge area  48 . Inner wall  42  of shroud  40  is provided with a plurality of injection slots  56  while outer wall  44  is provided with a plurality of injection slots  58 . A first plenum  60  circumscribes a portion of the inner wall  42  of shroud  40  and functions to feed gases into shroud  40  through injection slots  56 . Similarly, a second plenum  62  circumscribes a portion of the outer wall  44  of shroud  40  and functions to feed gases into the shroud  40  via injection slots  58 . As indicated in  FIG. 1 , each of the injection slots  56  and  58  are constructed so as to have a sharp trailing edge  56   a  and  58   a  respectively for introducing a thin sheet of fluid tangential to the respective inner and outer walls of the shroud and into the boundary layer fluid for the purpose of preventing the detachment of the gas stream from the wall. 
         [0017]    Interconnecting first plenum  60  with toroidal structure  52  is at least a first tube or conduit  66 . Interconnecting second plenum  62  with toroidal structure  52  is at least one second tube or conduit  68 . With this novel construction conduit  66  supplies gases collected through opening  54   b  of toroidal structure  52  to injection slots  56  while conduit  68  supplies gases collected through opening  54   c  of the toroidal structure to injection slots  58 . Exhaust gas from collector  50  is exhausted to atmosphere through an exhaust stack  70 . 
         [0018]    Turning to  FIG. 2  of the drawings, this drawing shows the structural elements that formed a part of the prior art diffuser structure, but were, for sake of clarity, eliminated from  FIG. 1  of the &#39;605 patent. These important structural elements, which in the prior art apparatus functioned to maintain rigid concentricity, comprise a plurality of radial struts “RS” (typically five or six in number) that interconnect the outer wall of shroud  40  to a stationary hub generally identified as “SH” via an inner ring “IR”. Also forming a part of the prior art diffuser structure, but were, for sake of clarity, eliminated from  FIG. 1  of the &#39;605 patent is an outer ring “OR”. 
         [0019]    As illustrated in  FIG. 2 , the radial struts “RS” are directly in the path of the gas flowing between the last turbine blade  39  and the first slots  56  and  58  of the diffuser and present an undesired obstruction to the free flow of the gas. More particularly, in the prior art construction illustrated in  FIG. 2  of the drawings each radial strut “RS” creates a turbulent wake in which the stagnation pressure of the flow is reduced by a loss of momentum, thereby reducing the pressure recovery otherwise obtainable by the diffuser. In an attempt to reduce the swirl of the gas imparted to the radial struts by the last rotating blades, the radial struts in the prior art apparatus are sometimes configured to have an airfoil profile, similar to that of a stator blade. However, this approach works only at one point of RPM and load combination and for other RPM and load combinations the swirl is only partially removed generally at the cost of increased turbulence. In a conventional prior art diffuser the kinetic energy of the swirling gas is wasted and although the airfoil cross-section of the struts attempts to redirect at least part of the swirling gas in an axial direction, this approach succeeds only for a particular combination of load and RPM and, even in this case the wakes and turbulence limit the associated pressure recovery. 
         [0020]    The diffuser illustrated and described in incorporated by reference Patent No. &#39;605 re-directs the axial flow in a radial direction where any swirl present in the flow provides an added centrifugal pressure increment, regardless of the direction of the swirl. In this instance, there is no need to attempt to remove the swirl, since the diffuser itself converts the kinetic energy of the swirl into a greater pressure increment. However, as previously mentioned, the presence of the radial struts in the prior art apparatus, which are necessary for mechanical support, are detrimental to the pressure recovery by the diffuser. 
         [0021]    The thrust of the present invention is to overcome this undesirable feature of the prior art apparatus and in so doing markedly improve the performance of the diffuser without adversely affecting the mechanical performance of the turbine. As will be discussed more fully in the paragraphs which follow, this is accomplished by modifying the prior art structure to, among other things, eliminate the struts “RS”. 
         [0022]    Turning now to  FIG. 3  of the drawings, one form of the improved apparatus of the present invention is there shown and generally designated by the numeral  100 . This apparatus is similar in some respects to the prior art apparatus shown in  FIG. 1  of the drawings and like numbers are used in  FIGS. 1 and 2  to identify like components. As indicated in  FIG. 3 , the shaft that was designated in  FIGS. 1 and 2  by the numeral  36  has been removed from the drawing, since the same diffuser structure is equally usable in connection with a turbine having a power takeoff shaft that protrudes from the opposite, or compressor end (see column 4, line 65 of the incorporated by reference &#39;605 patent). Stationary hub “SH” houses bearings that are precisely concentric with the outer structures of the turbine and function to support the rotating parts of the turbine. 
         [0023]    As is also shown in  FIG. 3  of the drawings, the improved apparatus  100  here comprises combination conduit and structural support members  102  and  104  that take the place of the prior art conduits  66  and  68  and combination plenum and structural support members  106  and  108  that take the place of plenums  60  and  62 . As indicated in  FIG. 3 , combination conduit and structural support member  102  and  104  function to provide rigidity to the diffuser, to maintain concentricity between hub “SH” and shrouds  40  and  42  during operation and to direct a portion of the high velocity gas stream captured by said capture means toward the injector slots provided in said inner wall of the shroud. Conduits  102  and  104 , as well as plenums  106  and  108 , have relatively thick sidewalls which, unlike the prior art conduits and plenums (which provided only gas pressure containment) function to provide substantial structural support to the diffuser. Accordingly, in the improved apparatus of the invention, the combination conduit and structural support members  102  and  104  and the combination plenum and structural support members  106  and  108  comprise load bearing structures as well as comprising structures for conveying gas from capture scoop  52  to slots  56  and  58 . 
         [0024]    Also forming a part of the improved apparatus  100  are substantially larger structural rings  110  and  112  that take the place of the prior art rings “IR” and “OR”. As shown in  FIG. 3  of the drawings, structural rings  110  and  112  circumscribe and are connected to stationary hub “SH”. Additionally, the wall thickness of the generally toroidal-shaped capture scoop  52 , which is designated in  FIG. 3  by the numeral  114  has been substantially increased. With the construction thus described, combination plenum and structural support member  106  carries the stress from combination conduit and structural support member  102  to structural ring  110  which distributes the stress to the area of shroud  40  where former struts “RS” were previously anchored. Similarly, combination plenum and structural support member  108  carries the stress from combination conduit and structural support member  104  to structural ring  112 , which distributes the stress to, and supports stationary hub “SH” as was previously done by struts “RS”. 
         [0025]    The details of the design of load-bearing structures, such as combination conduit and structural support members  102  and  104  and combination plenum and structural support members  106  and  108 , are well known in the art of mechanical design and involve careful consideration of the moment of inertia of the cross-sections, the modulus of elasticity of the material, and the overall curvature of the structures. In addition, the designer must take into consideration the differential thermal expansion coefficients required by the different temperatures of the gas flowing within the structure. No further discussion of the structural design is here required beyond emphasizing that the reinforced portion of the diffuser structure, including novel members  102 ,  104 ,  106  and  108 , must be designed to maintain the required concentricity between stationary hub “SH” and shroud  40  under all operating conditions. 
         [0026]    Alternate approaches to improving the performance of the diffuser without adversely effecting the mechanical performance of the turbine comprise adding the reinforcing structure directly to conduits  66  and  68  as described in connection with the embodiment of  FIG. 3  and partially separating the load-carrying structure from the gas conveying structures in order to derive the maximum advantage from the geometry of the combined elements. One such approach is shown in  FIG. 4 , which comprises a partial external view of the reinforcing structure superimposed on the cross-sectional view of the improved diffuser, noting that the re-enforcements are mounted externally to collector structure  50  and join reinforced members  102  and  104  as shown. 
         [0027]    In this case a first generally vertically extending reinforcement plate or built-up structural member  116 , that is located in the vertical plane of symmetry of the diffuser can be connected to reinforced member  102  and extended to a ground-engaging plate  118  and can be used to support the weight of the diffuser as well as the weight of the exit section of the turbine. In this alternate embodiment, other reinforcements can be placed to the side to insure rigidity in the transverse plane. For example, a second reinforcement plate or built-up structure  120 , which is operably associated with first generally vertically extending reinforcement plate  118 , can be connected to reinforced member  102  in the manner shown in  FIG. 4  of the drawings. 
         [0028]    A mandatory requirement is that the rigidity combined with the mass of the supported elements results in a resonant frequency far from the operating RPM and its harmonics. This requirement dictates the number of reinforcing structures  120  and their location around the diffuser, with suitable spacing between them to accommodate the passage of exhaust stack  70 . 
         [0029]    Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.