Patent Publication Number: US-2005120719-A1

Title: Internally insulated turbine assembly

Description:
BACKGROUND  
      The present invention relates to a turbine assembly for a combustion turbine engine. More particularly, the present invention relates an internally insulated turbine assembly for a microturbine engine.  
      Microturbine engines are relatively small and efficient sources of power. Microturbines can be used to generate electricity and/or to power auxiliary equipment such as pumps or compressors. When used to generate electricity, microturbines can be used independent of the utility grid or synchronized to the utility grid. In general, microturbine engines are limited to applications requiring 2 megawatts (MW) of power or less. However, some applications larger than 2 MWs may utilize a microturbine engine.  
      Many microturbine engines employ a thick-walled turbine casing manufactured from a high-temperature alloy (e.g., nickel-based alloys, stainless steel, Inconel, Hastelloy X, and the like). Even with the use of high-temperature alloys, the casing strength is reduced at normal operating temperatures, thus requiring the relatively thick casing wall. The thick wall allows the casing to contain the high-temperature high-pressure gas within the casing.  
      As applications that use microturbine engines grow in their output requirements, larger turbines will be required. Larger turbines require larger casings that will be exposed to additional forces generated by the pressure of the gas within the casing. In addition, larger casings increase the problems associated with thermal expansion, thereby requiring greater clearances between components, which can reduce engine efficiency. The larger casings also greatly increase the cost of the engine due to the cost of the alloys used to manufacture the casing.  
     SUMMARY  
      The present invention provides a combustion turbine engine suited to operation in response to a flow of high-temperature gas. The combustion turbine engine generally includes an outer housing including walls that define an inlet, an outlet, and an inner surface. An insulation cartridge is disposed within the outer housing and defines an inner space. The insulation cartridge includes a wall and a core and is operable to at least partially thermally insulate the outer housing from the flow of high-temperature gas. A turbine rotor is disposed substantially within the inner space and is rotatable in response to the flow of high-temperature gas.  
      In another aspect, the invention generally provides a microturbine engine system operable to provide electrical power. The microturbine engine system includes a compressor that is operable to produce a flow of compressed air and a recuperator in fluid communication with the compressor to receive the flow of compressed air. The flow of compressed air is preheated within the recuperator to produce a flow of preheated compressed air. A combustor receives the flow of preheated compressed air and is operable to produce a flow of products of combustion. The flow of products of combustion have a temperature that generates thermal forces and a pressure that generates pressure forces. A turbine is driven by the flow of products of combustion. The turbine discharges the flow of products of combustion to the recuperator to preheat the flow of compressed air. A housing at least partially encloses the turbine and includes an inner surface. An insulation cartridge is positioned within the housing. The insulation cartridge at least partially isolates the housing from the flow of products of combustion such that the housing absorbs a majority of the pressure forces and the insulation cartridge absorbs a majority of the thermal forces. A generator is coupled to the turbine. The generator is driven by the turbine at a speed to output electrical power.  
      In yet another aspect, the present invention generally provides a method of assembling a turbine for use in a combustion turbine engine. The method includes providing a housing including an inlet, an outlet, and an inner surface and forming an insulation cartridge having a wall that defines a core space. The method also includes positioning an insulating material within the core space, inserting the insulation cartridge into the turbine casing, and supporting a rotor for rotation within the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The description particularly refers to the accompanying figures in which:  
       FIG. 1  is a perspective view of a portion of a microturbine engine;  
       FIG. 2  is a sectional view of a portion of the microturbine engine of  FIG. 1 ;  
       FIG. 3  is a perspective view of an insulation cartridge of  FIG. 2 ; and  
       FIG. 4  is a perspective view of an outlet half of the insulation cartridge of  FIG. 3 . 
    
    
      Before any embodiments of the invention are explained, it is to be understood that the invention 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 following drawings. The invention is capable of other embodiments and of being practiced or of 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. The use of “including,” “comprising,” or “having” and variations thereof is meant to encompass the items listed thereafter and equivalence thereof as well as additional items. The terms “connected,” “coupled,” and “mounted” and variations thereof are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected,” “coupled,” and “mounted” and variations thereof are not restricted to physical or mechanical connections or couplings.  
     DETAILED DESCRIPTION  
      With reference to  FIG. 1 , a microturbine engine system  10  that includes a turbine section  15 , a generator section  20 , and a control system  25  is illustrated. The turbine section  15  includes a radial flow turbine  35 , a compressor  45 , a recuperator  50 , and a combustor  55 .  
      The engine  10  includes a standard Brayton cycle combustion turbine with the recuperator  50  added to improve engine efficiency. The engine shown is a single-spool engine (one set of rotating elements). However, multi-spool engines are also contemplated by the invention. The compressor  45  is a centrifugal-type compressor having a rotary element that rotates in response to operation of the turbine  35 . The compressor  45  shown is a single-stage compressor. However, multi-stage compressors can be employed where a higher pressure ratio is desired. Alternatively, compressors of different designs (e.g., axial-flow compressors, reciprocating compressors, and the like) can be employed to supply compressed air to the engine.  
      The turbine  35  is a radial flow single-stage turbine having a rotary element directly coupled to the rotary element of the compressor  45 . In other constructions, multi-stage turbines or other types of turbines may be employed. The coupled rotary elements of the turbine  35  and the compressor  45  engage a gearbox  57  or other speed reducer disposed between the turbine section  15  and the generator section  20 . In other constructions, the coupled rotary elements engage the generator section  20  directly.  
      The recuperator  50  includes a heat exchanger employed to transfer heat from a hot fluid to the relatively cool compressed air leaving the compressor  45 . One suitable recuperator  50  is described in U.S. Pat. No. 5,983,992 fully incorporated herein by reference. The recuperator  50  includes a plurality of heat exchange cells stacked on top of one another to define flow paths therebetween. The cool compressed air flows within the individual cells, while a flow of hot exhaust gas passes between the heat exchange cells.  
      During operation of the microturbine engine system  10 , the rotary element of the compressor  45  rotates in response to rotation of the rotary element of the turbine  35 . The compressor  45  draws in atmospheric air and increases its pressure. The high-pressure air exits the air compressor  45  and flows to the recuperator  50 .  
      The flow of compressed air, now preheated within the recuperator  50 , flows to the combustor as a flow of preheated air. The preheated air mixes with a supply of fuel within the combustor  55  and is combusted to produce a flow of products of combustion. The use of the recuperator  50  to preheat the air allows for the use of less fuel to reach the desired temperature within the flow of products of combustion, thereby improving engine efficiency.  
      The flow of products of combustion enters the turbine  35  and transfers thermal and kinetic energy to the turbine  35 . The energy transfer results in rotation of the rotary element of the turbine  35  and a drop in the temperature of the products of combustion. The energy transfer allows the turbine  35  to drive both the compressor  45  and the generator  20 . The products of combustion exit the turbine  35  as a first exhaust gas flow.  
      In constructions that employ a second turbine, the first turbine  35  drives only the compressor, while the second turbine drives the generator  20  or any other device to be driven. The second turbine receives the first exhaust flow, rotates in response to the flow of exhaust gas therethrough, and discharges a second exhaust flow.  
      The first exhaust flow, or second exhaust flow in two turbine engines, enters the flow areas between the heat exchange cells of the recuperator  50  and transfers excess heat energy to the flow of compressed air. The exhaust gas then exits the recuperator  50  and is discharged to the atmosphere, processed, or further used as desired (e.g., cogeneration using a second heat exchanger).  
       FIG. 2  illustrates the turbine section  15  including a turbine rotor  60 , inlet guide vanes  65 , a shroud/diffuser  70 , a scroll case  75 , an outer casing  80 , and an insulation cartridge  90 . The turbine rotor  60  includes a plurality of vanes that rotate with the rotor  60  and are arranged to provide for efficient expansion of the flow of products of combustion. The flow of products of combustion enters the turbine rotor  60  in a substantially radial direction and exits the turbine rotor  60  in a substantially axial direction parallel to the rotational axis A-A of the turbine rotor  60 . The products of combustion then exit the turbine section  15  through the shroud/diffuser  70 . In some constructions, an additional diffuser attaches to the turbine section  15  to further decelerate the flow exiting the turbine rotor  60 .  
      The inlet guide vanes  65  are positioned between the turbine scroll  75  and the shroud/diffuser  70 . The inlet guide vanes  65  are positioned to direct and accelerate the flow of products of combustion along the desired vector as the flow of products of combustion enters the turbine rotor  60 .  
      The turbine scroll  75  is positioned as the inner most casing of the turbine section  15  and contains the flow of products of combustion as the flow enters the turbine section  15 . The flow enters the turbine scroll  75  through an inlet  95  and fills an annular chamber  100  defined by the scroll  75 . From the annular chamber  100 , the flow passes through the inlet guide vanes  65  to the turbine rotor  60 . The innermost wall  105  of the turbine shroud/diffuser  70  follows the outer contour of the turbine rotor  60  and functions to contain the flow of products of combustion within the turbine rotor  60 . The innermost wall  105  also forms a portion of, or attaches to, the shroud/diffuser  70  and cooperates with the scroll  75  to completely enclose the annular chamber  100  and define an outer flow path wall for the flow passing through the turbine rotor  60  and the shroud/diffuser  70 .  
      The turbine scroll  75  is generally formed from a thin-walled metal material (e.g., nickel-based alloys, stainless steel, Inconel, Hastelloy X, and the like). The thin wall of the scroll  75  allows it to move and flex in response to temperature changes. In addition, the thin wall is able to quickly and uniformly change temperature in response to temperature changes of its surrounding, thereby reducing the overall thermal stress applied to or built up within the turbine scroll  75 .  
      The insulation cartridge  90  is positioned between the turbine scroll  75  and the outer casing  80  and as such defines an inner gap  135  between the insulation cartridge  90  and the turbine scroll  75  and an outer gap  140  between the insulation cartridge  90  and the outer casing  80 .  
      The insulation cartridge  90  is generally manufactured from thin metal materials (e.g., less than about 0.2 inches and preferably less than about ⅛ of an inch) that react quickly and evenly to temperature changes. However, like the turbine scroll  75 , the insulation cartridge  90  is exposed to high-temperature gas. As such, an appropriate high-temperature material (e.g., nickel-based alloys, stainless steel, Inconel, Hastelloy X, and the like) should be used to form the insulation cartridge  90 .  
      Turning to  FIGS. 3 and 4 , the insulation cartridge  90  is illustrated as including an exterior  145 , an interior  150 , an inlet  155 , an outlet  160 , and a turbine opening  165 . The cartridge exterior  145  includes a cylindrical portion  170  that is centered on the rotational axis A-A (shown in  FIG. 2 ). The inlet  155  passes through the cylindrical portion  170  at an angle that is approximately perpendicular to the rotational axis A-A to provide a flow path into the cartridge interior  150 . The inlet  155  also provides space for the scroll inlet  95 , which in turn receives the flow of products of combustion from the combustor  55 .  
      The turbine opening  165  facilitates the attachment of the turbine rotor  60  to the compressor rotor  230 . The insulation cartridge outlet  160  provides clearance space for the shroud/diffuser  70  and an expansion bellows  175  that guide the exhaust gas out of the turbine section  15 .  
      To facilitate the assembly and manufacture of the engine  10  and the insulation cartridge  90 , the insulation cartridge  90  is divided into two halves, an outlet half  180  and a turbine half  185 . The outlet half  180  includes the outlet opening  160  and the turbine half  185  includes the turbine opening  165 . The halves  180 ,  185  are separated along a plane that is substantially perpendicular to the rotational axis A-A and passes through the center of the inlet opening  155 . The two halves  180 ,  185  each include an attachment flange  190  that allows for their attachment to one another. The attachment can be made using any common means, with bolts or welding being preferred. In some constructions, a slip joint exists between the halves  180 ,  185 . The slip joint allows relative movement between the two halves  180 ,  185  during engine operation.  
      As illustrated in  FIG. 4 , the insulation cartridge  90  includes an inner wall  195 , an outer wall  200 , and a layer of insulating material  205  disposed between the inner wall  195  and the outer wall  200 . The inner wall  195  attaches to the outer wall  200  to define a core space  210  that is substantially enclosed when the two halves  150 ,  155  of the insulation cartridge  90  are assembled. The layer of insulating material  205  is placed within the core space  210  to define a completed core. In most constructions, a ceramic material is used as insulating material  205 . However other constructions may use other materials (e.g., trapped gas, plastic, glass, and the like). In still another construction, an evacuated space is used as the insulating material  205 . While an outer wall  200  is illustrated herein, other constructions may eliminate the outer wall  200 .  
      With continued reference to  FIG. 2 , the outer casing  80 , or turbine housing is positioned outside of the insulation cartridge  90  and defines an inlet opening  215 , an outlet opening  220 , and a turbine opening  225 . The turbine opening  225  provides for the coupling of the turbine rotor  60  to a compressor rotor  230  when the outer casing  80  is attached to a compressor casing  235 . The inlet  215  is positioned to provide space for the passage of flow components that guide the flow of products of combustion from the combustor  55  to the turbine scroll  75 . In some constructions, the recuperator  50  attaches directly to the outer casing  80  adjacent the inlet  215 . In other constructions, an additional housing connects the outer casing  80  to the recuperator  50 . A pipe or duct connects to the outer casing  80  adjacent the outlet  220  to receive the flow of exhaust gas exiting the shroud/diffuser  70  and direct that flow to the recuperator  50 .  
      The walls that make up the outer casing  80  are generally thicker than the walls that make up the turbine scroll  75  and the insulation cartridge  90 . In some constructions, the outer casing  80  may be cast from a lower-temperature alloy (e.g., low-alloy cast steel, cast iron, high-temperature cast iron, and the like) and then machined as required. In other constructions, the outer casing  80  is machined from a single piece of material, such as a forging. In many constructions, cast iron (e.g., NiResist Cast Iron) is the preferred material.  
      During engine operation the flow of products of combustion exits the combustor  55  and flows into the turbine scroll  75 . A substantially sealed path between the combustor  55  and the turbine scroll  75  inhibits the entry of products of combustion into the inner gap  135  or the outer gap  140 . From the turbine scroll  75 , the flow of products of combustion passes through the remainder of the turbine section  15  as has been described. The products of combustion within the turbine scroll  75  have a temperature and a pressure. The temperature is quite high (e.g., 1400 degrees F. or higher), thus making the use of thin-walled high-temperature materials appropriate. However, the pressure within the turbine scroll  75  is also high (e.g., 2-30 times atmospheric pressure or higher). To reduce the pressure load on the scroll  75 , recuperator discharge air is provided to the inner gap  135 . Recuperator discharge air is preheated compressed air that has not been heated within the combustor  55 . As such, recuperator discharge air has a lower temperature (e.g., about 1200 degrees F.) than the products of combustion. Furthermore, the pressure of the recuperator air is substantially equal to the pressure of the products of combustion. Thus, the pressure forces applied to the inside of the turbine scroll  75  are substantially equal to the pressure forces applied to the outside of the scroll  75 . As such, a thick pressure-containing wall is not necessary for the turbine scroll  75 .  
      The outer gap  140  is substantially sealed and provides little more than clearance between the outer casing  80  and the insulation cartridge  90 . However, during engine operation, recuperator air typically leaks into the outer gap  140  and fills the space. Thus, the outer gap  140  is maintained at a pressure that is substantially equal to the pressure within the inner gap  135 . However, because the outer gap  140  is substantially sealed, little flow between the inner gap  135  and the outer gap  140  will actually occur once the pressures equalize. As such, the gas trapped within the outer gap  140  will cool somewhat during engine operation. The substantially equal pressure within the inner gap  135  and outer gap  140  apply substantially equal pressure forces on either side of the insulation cartridge  90 . As such, the overall pressure forces applied to the insulation cartridge  90  are small, thereby allowing for the use of thin-walled materials for its manufacture.  
      The insulation cartridge  90  does provide a significant thermal barrier between the products of combustion and the outer casing  80 . As such, the outer casing  80  operates at a temperature that is lower than outer casings used in turbines that do not include an insulation cartridge  90 . The lower temperature allows for the use of lower temperature materials to manufacture the casing  80 . However, the pressure within the outer gap  140  is still approximately equal to the pressure of the flow of products of combustion. As such, the casing  80  must be strong enough to contain the forces generated by the difference in pressure between the interior of the casing  80  and the outer atmosphere. Typically, a thicker wall is used to provide the necessary strength. However, other constructions may employ higher-grade materials to achieve the desired strength. For example, one construction may substitute stainless steel for low-alloy steel to achieve the desired strength at the elevated operating temperature.  
      The strength of the casing  80  is a function of the thickness of the material, the operating temperature, and the particular material used. As such, different constructions may require different wall thicknesses. Generally, an outer casing  80  with a wall thickness of about one-half inch or more is well suited for use with the present invention. However, one of ordinary skill in the art will realize that thinner walls could be employed in constructions having suitable operating conditions, and thicker walls may be required under other conditions.  
      The insulation cartridge  90  functions to reduce the operating temperature of the outer casing  80 . The lower operating temperature allows for the reduction in the wall thickness of the casing  80  and/or the reduction in the grade of material used to form the casing  80 .  
      Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.