Patent Publication Number: US-2019178159-A1

Title: Multistage radial compressor and turbine

Description:
This patent application claims the benefit of the Aug. 10, 2016 filing date of the U.S. provisional application No. 62/372,998. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related generally to the field of heat engines designed to convert the heat energy into mechanical energy of rotation, More particularly, the present invention is related to the field of small gas turbine engines also known as microturbines. 
     BACKGROUND OF THE INVENTION 
     Gas turbine devices such as microturbine engines are known to be used to convert the thermal energy released by fuel combustion into mechanical energy of a rotating shaft. A microturbine engine typically comprises a single stage radial compressor and a single stage radial turbine attached to a common shaft. The compressed air flows from the compressor into the combustion chamber where it mixes with the fuel that burns releasing the thermal energy and increasing the gas temperature. The hot gas energy is then converted into the rotation energy of the single stage radial turbine as described in U.S. Pat. No. 6,748,742, incorporated herein by reference. Herein “radial” means the gas enters the compressor or the turbine in the direction primarily parallel to the rotating shaft and then is expelled by the rotating disk in the primarily radial direction, or the direction primarily perpendicular to the rotating shaft. Herein “Single stage” means the compressor comprises only one rotating disc and the turbine comprises only one rotating disk; “multistage” means the compressor comprises at least three rotating disks and the turbine comprises at least three rotating disks. 
     It is a common practice to have a single stage compressor and a single stage turbine positioned on the same rotating shaft which transfers a part of the energy from the turbine to power the compressor. In addition, the residual energy of the hot exhaust from the turbine is directed to a recuperator or a heat exchanger used to heat the compressed air entering the combustion chamber. 
     The efficiency of the turbine engine is the ratio of useful mechanical energy of the rotating shaft to the total thermal energy released by combusting fuel. The efficiency increases with the greater compression ratio that increases the amount of energy transferred to the turbine while the hot gas expands. The compression ratio of the compressor is limited by the rotating speed of the compressor disc and by the mechanical strength of the disc material, therefore, a one stage compressor is not sufficient to supply the compression ratio required for increased efficiency and the use of additional devices is required to capture the remaining heat energy and to return this energy into the thermal engine cycle. 
     Another important factor affecting the efficiency is the amount of thermal energy that the turbine can extract from the hot expanding gas. If the temperature of the gas entering the turbine is constant, the efficiency will be the greatest for the lowest gas temperature exiting the turbine. A single stage turbine does not effectively extract thermal energy from the hot gas, resulting in high temperature of the exiting gases and overall lower efficiency. 
     To compensate for the low efficiency of single stage compressor and single stage turbine engines, a heat exchanger or recuperator is used to utilize the thermal energy of exiting gases from the turbine to heat the compressed air entering the combustion chamber. Addition of the recuperator increases the cost and the weight of the engine while also reducing the device reliability, and increases the cost of maintenance because the recuperator is contaminated by the combustion products. The use of the recuperator also limits single stage turbines primarily to stationary applications as the application for vehicle, vessel, and aircraft propulsion is problematic due to large size, increased weight, and poor reliability. 
     A gas turbine engine with a 2-stage helical flow radial compressor is also known from U.S. Pat. No. 6,709,243, incorporated herein by reference. However, 2-stage helical flow radial compressors can suffer low efficiency and reduced reliability due to the overheating. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems described in the background section. It is an aim of this invention to greatly increase the efficiency of a radial turbine engine. 
     The present invention achieves the increased efficiency in a turbine engine comprising a multistage radial compressor and a multistage radial turbine where “multistage” means the number of stages in the compressor is at least 3 (three) and the number of stages in the turbine is at least 3 (three). 
     The present invention provides for a higher compression ratio of the air entering the combustion chamber by utilizing a multistage radial compressor wherein the air entering each stage after the first, air entry stage of the compressor is further compressing the air supplied by the previous stage. The present invention provides for a lower exhaust temperature wherein each consecutive radial turbine stage after the first turbine stage adjacent the combustion chamber further reduces the temperature of the gas exhausted by the previous stage. 
     The present invention provides the method to reduce the cost of manufacturing the working disks of the compressor and turbine by using Powder Injection Molding and Metal Injection Molding methods to fabricate the said parts. 
     The present invention achieves high efficiency without the use of expensive, heavy, and unreliable recuperators. 
     Further, the present invention utilizes compressor guide vanes that are movable with the respect of the rotating compressor discs to compensate for thermal expansion and stress elongation of the shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustratively shown and described in reference to the accompanying drawings, in which 
         FIG. 1  is a front view of the microturbine engine. 
         FIG. 2  is a side view of the microturbine engine. 
         FIG. 3  shows an axial section of the microturbine engine. 
         FIG. 4  is a magnified section view of the compressor. 
         FIG. 5  is a magnified section view of the turbine. 
         FIG. 6  shows a further magnified section view of the first and second stages of the compressor. 
         FIG. 7  shows an even further magnified section view of a guide vane of the compressor. 
         FIG. 8  shows the thrust unit. 
         FIG. 9  shows the position of the guide vane when the turbine is not operational. 
         FIG. 10  shows the position of the guide vane when the turbine is operational. 
         FIGS. 11 and 11   a  show an axial section of the engine at the first turbine stage. 
     
    
    
     DETAIL DESCRIPTIONS OF THE INVENTION 
     All descriptions are for the purpose of showing selected versions of the present invention and are not intended to limit the scope of the present invention. 
     The present invention resolves the problems described in the previous sections. The present invention achieves greater efficiency, lower cost and improved reliability of a turbine generator by implementing a multi-stage compressor and a multi stage turbine with the individual stages fabricated utilizing machining, powder injection molding, (PIM) and metal injection molding (MIM) technology. 
     The apparatus of the present invention, shown in  FIG. 1  (front view) and  FIG. 2  (side view), comprises a combustion chamber  1 , a rotating shaft  2 , a multistage turbine  3 , and a multistage compressor  4 . The combustion chamber  1 , the multistage turbine  3  and the multistage compressor  4  are all attached to the same shaft  2 , and are all contained in a main housing  5 . What is meant by a multistage turbine  3  is a turbine that has multiple stages where each stage is comprised of a turbine disk that rotates with the shaft  2  and a turbine guide vane that surrounds the turbine disk and does not rotate. What is meant by a multistage compressor  4  is a compressor that has multiple stages where each stage is comprised of a compressor disk that rotates with the shaft  2  and a compressor guide vane that surrounds the compressor disk and does not rotate. Multistage Turbine implementation shown in  FIGS. 1-3  has five compressor stages and five turbine stages, however, multistage implementations may have the number of stages greater than five or fewer than five and equal or greater than three. Also, in a multistage implementation, the number of stages in the compressor may be different from the number of stages in the turbine as long as the smallest of the two numbers is equal or greater than three. The operation of the apparatus of the present invention is achieved by combusting the fuel in the combustion chamber  1  and directing hot gases of combustion from the combustion chamber and into the multistage turbine  3 . The hot expanding gas exiting the combustion chamber  1  causes the turning of the multiple turbine stages of the multistage turbine  3  and converting the thermal energy into the mechanical energy of the rotating shaft  2 . Part of the mechanical energy is passed through the shaft  2  to the multistage compressor  4  which compresses the air and directs the compressed air into the combustion chamber  1  which mixes the compressed air with fuel and combusts the fuel. The hot exhaust gas from the combusted fuel is then directed into the multistage turbine  3 . Electrical generation can be achieved by connecting a generator (not shown) to the shaft  2 . 
     The side section of the apparatus of present invention is shown in  FIG. 3 . With the reference to  FIG. 3  the multistage compressor  4  has five compressor stages with five rotating compressor disk stages  4   a,    4   b,    4   c,    4   d,  and  4   e  secured stationary on the shaft  2 . The multistage turbine  3  has five turbine stages with five rotating turbine disk stages  3   a,    3   b,    3   c,    3   d,  and  3   e  secured stationary on the same shaft  2 . The shaft  2  has a bearing  6  located on the left end of the shaft  2  as viewed in  FIG. 3  where air enters the multistage compressor  4 , and another bearing  7  located on the right side of the shaft  2  as viewed in  FIG. 3  where exhaust gases exit the multistage turbine  3 . The bearings  6  and  7  are of the journal kind to sustain the radial forces and prevent radial movement of the shaft  2 , and to allow axial movement of the shaft  2  along the shaft  2  axis x-x of rotation due to the thrust forces and shaft elongation at increased temperature and rotation speed. The main housing  5 , located between the multistage turbine  3  and the multistage compressor  4 , has a thrust journal bearing  5   a  that can sustain both radial and axial forces. The combustion chamber  1  is attached to the main housing  5 . Each rotating compressor disk of the compressor stages  4   a,    4   b,    4   c,    4   d,  and  4   e  has an associated non-rotating compressor guide vane  8   a,    8   b,    8   c,    8   d,  and  8   e,  respectfully. Each rotating turbine disk of the turbine stages  3   a,    3   b,    3   c,    3   d,  and  3   e  has an associated non-rotating turbine guide vane  9   a,    9   b,    9   c,    9   d,  and  9   e,  respectively. 
     With the further reference to  FIG. 3 , each rotating compressor disk  4   a,    4   b,    4   c,    4   d,    4   e  and its associated non-rotating compressor guide vane  8   a,    8   b,    8   c,    8   d,    8   e  comprises a working stage of the multi-stage compressor  4  and each rotating turbine disk  3   a,    3   b,    3   c,    3   d,    3   e  and its associated non-rotating turbine guide vane  9   a,    9   b,    9   c,    9   d,    9   e  comprises a working stage of the multistage turbine  3 . The first four stages of the multistage compressor  4  have compressor guide vanes  8   a,    8   b,    8   c,    8   d  that are moveable in the axial direction from right to left as viewed in  FIG. 3  in response to increasing pressure in the multistage compressor  4  produced by rotation of the shaft  2  and the rotation of the compressor disks  4   a,    4   b,    4   c,    4   d,    4   e  on the shaft  2 . This enables the compressor guide vanes  8   a,    8   b,    8   c,    8   d  to move axially from right to left as viewed in  FIG. 3  to compensate for movement of the respective compressor disks  4   a,    4   b,    4   c,    4   d  from right to left due to axial elongation of the shaft  2  caused by the increasing temperature of the shaft and axial forces applied to the shaft during operation of the turbine. To form a pressure seal, the first moveable compressor guide vane  8   a  has an annular seal  11   a  around the interior of a cylindrical portion of the guide vane on a downstream end of the first guide vane  8   a  from the air intake of the multistage compressor  4 . The annular seal  11   a  extends around an annular groove in the second compressor guide vane  8   b  and provides a pressure seal between the first compressor guide vane  8   a  and the second compressor guide vane  8   b.  The second compressor guide vane  8   b  has two similar annular seals  11   a  and  11   b  on opposite sides of the second compressor guide vane. The third compressor guide vane  8   c  has two similar annular seals  11   b  and  11   c  on opposite sides of the third compressor guide vane. The fourth compressor guide vane  8   d  has two similar annular seals  11   c  and  11   d  on opposite sides of the fourth compressor guide vane. The fifth compressor guide vane  8   e  has the annular seal  11   d  in an annular groove on the upstream end of the fifth compressor guide vane toward the air intake of the multistage compressor  4 . The annular seals  11   a,    11   b,  and  11   c  are also movable in the axial direction of the rotating shaft. For example, the annular seal  11   a  moves axially with the compressor guide vane  8   b,  the annular seal  11   b  moves axially with the compressor guide vane  8   c  and the annular seal  11   c  moves axially with the compressor guide vane  8   d.  Each of the annular seals  11   a,    11   b,    11   c,    11   d  has a different diameter to compensate for the increasing pressure difference between the input and output sides of each of the compressor disks  4   a,    4   b,    4   c,    4   d  with the diameter increasing from left to right as viewed in  FIG. 3  with the increasing pressure. The movable compressor guide vanes  8   a,    8   b,    8   c,    8   d,  and  8   e  each have axial keys that fit into and move along the keyways or guide channels  12  and  12   a  that are attached to the main housing  5 . The guide channels  12  and  12   a  are spatially arranged around the interior surface of the main housing and allow the compressor guide vanes  8   a,    8   b,    8   c,    8   d  to move axially through the main housing  5  while preventing their rotation. 
     A more detailed side section view of the multistage compressor  4  is shown in  FIG. 4 . To provide registration of movable compressor guide vanes  8   a,    8   b,    8   c,    8   d,  and  8   e  when rotating compressor disks  4   a,    4   b,    4   c,    4   d,  and  4   e  move in the axial direction with elongation of the loaded shaft  2 , each compressor disk  4   a,    4   b,    4   c,    4   d  and  4   e  has a bi-directional thrust bearing  10   a,    10   b,    10   c,    10   d,  and  10   e,  respectively. The compressor guide vane  8   a  in the first stage of the multistage compressor  4  has a radial seal  11   a  that joins it to the next stage compressor guide vane  8   b.  The compressor disk  4   a  in the first stage of the multistage compressor  4  has a two-sided thrust bearing  10   a  that provides precise axial registration with the respect of compressor disk  4   a  as the shaft  2  elongates. The opposite side of the first guide vane  8   a  has an elastic thrust element  13   a  with the stiffness designed and calibrated to compensate the difference of input and output pressure on the guide vane and taking into account the section area of annular seal  11   a.  The elastic element  13   a  could be a single spring assembly that extends around the shaft  2  and biases the first compressor guide vane  8   a  to the right as viewed in  FIG. 4 , or could be multiple spring assemblies arranged around the shaft  2 . On the other side the elastic element  13   a  is set against the housing  13 . Housing  13  has a nozzle assembly  14  of the first stage compressor disk  4   a,  air intake  15 , and front journal bearing  6 . The housing  13  is connected to the guide channel  12 . 
     A more detailed side section of the multistage turbine  3  is shown in  FIG. 5 . The expanding gas sequentially passes the turbine stages comprising the rotating disks  3   a,    3   b,    3   c,    3   d,  and  3   e  and stationary guide vanes  9   a,    9   b,    9   c,    9   d,  and  9   e.  The radial positioning of the shaft  2  is achieved by journal bearing  7  at the exhaust of the turbine. The position of the rotating turbine disks with the respect of the turbine guide vanes does not affect the turbine efficiency as much as the position of the compressor guide vanes. Therefore, the axial position of the turbine guide vanes is fixed and the turbine guide vanes are not movable in any direction. 
       FIG. 6  shows further details of first two compressor stages comprising rotating disks  4   a,    4   b  and guide vanes  8   a,    8   b.    
       FIG. 7  shows even further details of the position of two compressor guide vanes  8   a  and  8   b  including a movable annular seal  11   a  and a flexible spring bellows seal  11 - 1   a.  The movable annular seal  11   a  and the flexible spring bellows seal  11 - 1   a  extend completely around the first compressor guide vane  8   a  and the second compressor guide vane  8   b  to seal a required working gap  4 - 1  that must be maintained between the rotating compressor disk  4   b  and the compressor guide vane  8   b  as the shaft is expanding and elongating under the temperature and thrust load. Here  4 - 1  is the gap formed between the working disk surface of the compressor disk  4   b  and the compressor guide vane  8   b.  This working gap requirement applies to all 5 stages of the compressor and is critical for optimizing the compressor efficiency. The choice of material for the compressor seals depends on the stage number as the operating temperature increases with the stage number. 
     The multistage compressor and turbine engine requires a shaft much longer than the shaft used for a single stage turbine. The shaft elongates during the turbine operation due to the axial loads at elevated temperatures with a longer shaft in the multistage engine having greater absolute elongation than a shorter shaft in a single stage engine. Therefore, a multistage compressor requires an additional element to compensate for shaft elongation during the engine operation. 
       FIG. 8  shows the pre-tension module positioned on the shaft  2  that comprises the thrust ring  16 , truss bushing  17 , and adjustment screws  18  having threaded connection to the bushing  17 , and having the ends  18   a  set against the compensating thrust bushing  19 . Compensating bushing  19 , together with calibrated torque of adjustment screws  18  compensates for the elongation and stress of the engine shaft  2 . The compensating bushing  19  is constructed of a resilient material. Prior to operation of the apparatus, the adjustment screws are screw threaded into the truss bushing, from left to right as viewed in  FIG. 8 . This causes the ends  18   a  of the adjustment screws  18  to compress the compensating bushing  19 . On operation of the apparatus, the temperature of the shaft increases and the shaft  2  elongates. The elongation of the shaft  2  relieves the compression load on the compensating bushing allowing the compensating bushing  19  to expand. The expanding compensating bushing remains in contact with the ends  18   a  of the adjustment screws  18  and the bearing  6 , maintaining the positioning of the bearing  6  in the apparatus. The calibrated torque depends on the thermal and mechanical properties of the materials used in the compressor and turbine and is set during the engine assembly. 
       FIG. 9  and  FIG. 10  show the position of the guide vanes  8   a  and  8   b  next to each other and movable along the shaft.  FIG. 9  shows the position of the guide vanes when the turbine is stopped while  FIG. 10  shows the position of the guide vanes when the turbine is operational. When the turbine is operating the working gap increases from Zo to Zo+Zt+Zsigma due to the shaft elongation under the axial load at increased temperature. The entire stack of movable guide vanes is spring-loaded by the elastic element  13   a  shown in  FIG. 4  that returns the reduces Zsigma distance as the operating speed of the engine is reduced and returns the guide vanes in the original position in  FIG. 9  when the engine is stopped. 
       FIGS. 3 and 4  show the positions of the compressor disks  4   a,    4   b,    4   c,    4   d,    4   e  and their respective compressor guide vanes  8   a,    8   b,    8   c,    8   d  and  8   e  in the main housing  5  prior to combustion taking place in the combustion chamber  1 . As combustion is initiated in the combustion chamber  1 , the shaft  2  begins to rotate and begins to increase in temperature. As the temperature of the shaft  2  increases, the shaft  2  begins to elongate from right to left as viewed in  FIGS. 3 and 4 . As the shaft  2  begins to elongate from right to left, the compressor disks  4   a,    4   b,    4   c,    4   d,    4   e  secured on the shaft  2  begin to move from right to left. 
     As the shaft  2  in the multistage compressor  4  rotate the compressor disks  4   a,    4   b,    4   c,    4   d,    4   e,  the compressor disks pull air into the multistage compressor  4  through the nozzle assembly  14  and the air intake  15 . The rotating compressor disks  4   a,    4   b,    4   c,    4   d,    4   e  push the air from left to right as viewed in  FIGS. 3 and 4 . As the air flows through the multistage compressor  4  from left to right, the rotating compressor disks  4   a,    4   b,    4   c,    4   d,    4   e  increase the pressure of the air flowing through the multistage compressor  4 . The increasing air pressure increases in each successive stage of the multistage compressor  4  as the air moves through the compressor from left to right. For example, the air traveling through the first stage by the rotation of the first compressor disk  4   a  will be at a first pressure. The air traveling through the second stage by rotation of the second compressor disk  4   b  will be at a second pressure that is greater than the first pressure. The air traveling through the third compressor stage by the rotation of the third disk  4   c  will have a third pressure that is greater than the second pressure. The air traveling through the fourth stage of the multistage compressor  4  by the rotation of the fourth compressor disk  4   d  will be at a fourth pressure greater than the third pressure. The air traveling through the fifth stage of the multistage compressor  4  by the rotation of the fifth compressor disk  4   e  will be at a fifth pressure that is greater than the fourth pressure. 
     The increasing air pressure in each stage of the multistage compressor  4  acts on the compressor guide vane in that stage and moves the guide vane to a position in the main housing  5  where the guide vane is substantially centered relative to the compressor disk rotating in that stage. For example, rotation of the compressor disk  4   a  in the first stage of the multistage compressor  4  increases the air pressure in that stage and the increasing air pressure causes the compressor guide vane  8   a  to move from right to left slightly where the compressor guide vane  8   a  is substantially centered relative to the rotating compressor disk  4   a.  The rotating compressor disk  4   b  in the second stage of the multistage compressor  4  increases the air pressure in the second stage which acts on the compressor guide vane  8   b  of the second stage and causes the compressor guide vane  8   b  to move slightly from right to left to a substantially centered position of the compressor guide vane  8   b  relative to the compressor disk  4   b.  Rotation of the compressor disk  4   c  in the third stage of the multistage compressor  4  increases the air pressure in the third stage which acts on the compressor guide vane  8   c  in the third stage and causes the compressor guide vane  8   c  to move from right to left slightly to a position where the compressor guide vane  8   c  is substantially centered relative to the compressor disk  4   c.  The rotation of the compressor disk  4   d  in the fourth stage of the multistage compressor  4  increases the air pressure in the fourth stage which acts on the fourth compressor guide vane  8   d  moving the fourth compressor guide vane  8   d  from right to left slightly where the fourth compressor guide vane  8   d  is substantially centered relative to the fourth compressor disk  4   d.  The rotation of the fifth compressor disk  4   e  in the fifth stage of the multistage compressor  4  increases the air pressure in the fifth stage which acts on the fifth compressor guide vane  8   e  in the fifth stage which moves the compressor guide vane  8   e  from right to left slightly where the fifth compressor guide vane  8   e  is substantially centered relative to the fifth compressor disk  4   e.    
     The movement of the compressor guide vanes  8   a,    8   b,    8   c,    8   d,    8   e  from right to left as viewed in  FIGS. 3 and 4  is resisted by the compression of the elastic thrust element  13   a.    
     When combustion in the combustion chamber  1  is halted, the rotation of the shaft  2  slows and the shaft is eventually stopped. The pressure in the multistage compressor  4  by the rotation of the compressor disk  4   a,    4   b,    4   c,    4   d,    4   e  is relieved. The shaft  2  begins to cool and contract from right to left as viewed in  FIGS. 3 and 4 . The cooling shaft  2  moves the compressor disk  4   a,    4   b,    4   c,    4   d,    4   e  from left to right as viewed in  FIGS. 3 and 4  as the shaft cools. With the pressure relieved in the multistage compressor  4 , the elastic thrust element  13   a  pushes the compressor guide vanes  8   a,    8   b,    8   c,    8   d,    8   e  from left to right as viewed in  FIGS. 3 and 4 , to substantially centered positions of the compressor guide vanes  8   a,    8   b,    8   c,    8   d,    8   e  relative to their respective compressor disks  4   a,    4   b,    4   c,    4   d,    4   e.    
     The combination of pre-tensioned shaft, movable guide vanes and elastic elements compensates for the shaft elongation and improves the efficiency of compressor operation at different speeds and while starting from the complete stopped position. 
       FIG. 11  is the engine section along the direction  11   a  at the first turbine stage showing four combustion chambers  1  positioned perpendicular to the shaft  2  and utilizing gaseous or liquid fuel. 
     This invention is not limited to the embodiment described and can be implemented by one skilled in the art with some modifications and alterations within the spirit and scope of the embodiment as disclosed.