Abstract:
A cogenerating recuperated microturbine includes a recuperator, an air compressor and a combustor. The combustor burns a fuel along with the compressed air received from the recuperator to create products of combustion. A turbine generator operates in response to expansion of the products of combustion to generate electricity. The products of combustion then flow through the recuperator to preheat the compressed air. The products of combustion then flow out of the recuperator as an exhaust flow. A heat exchanger is movable into and out of the exhaust flow to selectively heat a fluid in the heat exchanger. The heat exchanger is actuated by a piston-cylinder type actuator that operates under the influence of compressed air selectively bled from the air compressor. The actuator may be a single-acting cylinder used in conjunction with a biasing spring, or may be a double-acting cylinder.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an articulated heat recovery heat exchanger for use on a cogenerating recuperated microturbine to selectively heat a fluid. 
     SUMMARY 
     The present invention provides a cogenerating recuperated microturbine engine as well as a method for converting a recuperated microturbine into a cogenerating recuperated microturbine. The invention also provides an apparatus and method for selectively switching the cogenerating recuperated microturbine between a cogenerating mode and a non-cogenerating mode. The cogenerating recuperated microturbine engine has a recuperator with cells and spaces between the cells, an air compressor provides compressed air to the cells, and a combustor communicates with the cells to receive the compressed air. The combustor burns a fuel along with the compressed air to create products of combustion. A turbine generator communicates with the combustor and operates in response to expansion of the products of combustion to generate electricity. The products of combustion then flow through the turbine generator and into the spaces between the recuperator cells to preheat the compressed air. The products of combustion then flow out of an exhaust side of the recuperator as an exhaust flow. A heat exchanger is movable into and at least partially out of the exhaust flow to selectively heat a fluid in the heat exchanger. 
     The microturbine engine may also include an actuator operable to move the heat exchanger into and out of the exhaust flow. The actuator preferably operates in response to receiving compressed air from the compressor. A biasing member may bias the heat exchanger toward a position either into or at least partially out of the exhaust flow. The microturbine engine may also include an exhaust manifold that substantially covers the exhaust side of the recuperator and receives the exhaust flow. Preferably, the heat exchanger is located within the exhaust manifold. The exhaust manifold may include an intake port for receiving the exhaust flow such that the heat exchanger is movable between a first position where the heat exchanger substantially covers the intake port, and a second position where the intake port is substantially unobstructed. 
     The heat exchanger may be pivotally supported near the exhaust side such that it pivots into and out of the exhaust flow about a pivot axis. Preferably, the heat exchanger includes a fluid inlet coupling that has an inlet axis, and a fluid outlet coupling that has an outlet axis. The couplings are preferably configured such that the inlet and outlet axes are substantially collinear with the pivot axis. Generally, when the heat exchanger is moved into the exhaust flow, heat is transferred from the exhaust flow to the fluid, and when the heat exchanger is moved out of the exhaust flow, a reduced amount of heat is transferred from the exhaust flow to the fluid. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a cogenerating recuperated microturbine system embodying the present invention. 
     FIG. 2 is a section view taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is an enlarged perspective view of the articulated heat recovery heat exchanger. 
     FIG. 4 is an enlarged perspective view of the articulated heat recovery heat exchanger. 
     FIG. 5 is a side view of the articulated heat recovery heat exchanger in the non-cogenerating position. 
     FIG. 6 is a side view of the articulated heat recovery heat exchanger in the cogenerating position. 
    
    
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is 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” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of “consisting of” and variations thereof herein is meant to encompass only the items listed thereafter. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order. 
     DETAILED DESCRIPTION 
     For the sake of brevity, not all aspects of heat exchanger and microturbine combustor technology are discussed herein. For additional description of that technology, reference is made to U.S. patent application Ser. No. 09/790,464 filed Feb. 22, 2001, Ser. No. 09/668,358 filed Sep. 25, 2000, Ser. No. 09/409,641 filed Oct. 1, 1999, Ser. No. 09/239,647 filed Jan. 29, 1999 (now U.S. Pat. No. 5,983,992), and Ser. No. 08/792,261 filed Jan. 13, 1997. The entire contents of these applications are incorporated by reference herein. 
     FIG. 1 illustrates a microturbine system  10  including a compressor  14 , a combustion section  18  (not shown in FIG.  1 ), a turbine  22 , a recuperator  26 , a generator  30 , a frame  34 , a heat recovery heat exchanger  38 , and a fuel supply  40 . 
     The frame  34  is constructed of steel or other known materials and should be capable of rigidly supporting the components of the system. The system  10  also includes an electrical cabinet  42  containing the system controls. 
     The generator  30  is attached to the frame  34  and is coupled to the turbine  22 . When driven by the turbine  22 , the generator  30  produces an electrical power output at a desired voltage and frequency. The system  10  can use many types of known generators  30 , however permanent magnet generators are preferred. The choice of specific generators is based on the desired power output, the output characteristics (voltage and frequency), and the expected duty cycle of the equipment. 
     The compressor  14  is preferably a single stage radial flow compressor of known design, driven either directly or indirectly by the turbine  22 . The compressor  14  pulls in atmospheric air along its central axis, and compresses the air to a pressure in the range of 3 to 5 atmospheres. From the compressor  14 , the air flows through a duct  46  to the cold side of the recuperator  26 . 
     Referring specifically to FIG. 2, the recuperator  26  is preferably a crossflow heat exchanger having a cold gas flow path defined by a series of cells  48  within the recuperator  26 , and a hot gas flow path defined by the spaces  50  between the cells  48  of the recuperator  26 . The hot gas flow path receives hot combustion gasses from the turbine  22  via a diffuser section  52  and discharges them to the heat recovery heat exchanger  38  (not shown in FIG.  2 ). The cold gas flow path receives compressed air from the compressor  14  via the duct  46 . The compressed air is heated as it flows through the cells  48  of the recuperator  26 , finally discharging into the combustion section  18 . Preheating the combustion gas with the turbine exhaust gas before combustion results in a substantial efficiency improvement. 
     In the combustion section  18 , air and fuel are mixed. Ignition of the fuel-air mixture within the combustion chamber produces an increase in temperature and gas volume. By controlling the fuel flow to the combustion section  18 , the system  10  is capable of maintaining a desired power output and exhaust gas temperature. The hot exhaust gas exits the combustion section  18  and flows to the turbine  22 . 
     Referring again to FIG. 1, in the turbine  22 , the hot exhaust gas expands, rotating the turbine  22 , which drives the compressor  14  and the generator  30 . The turbine  22  is preferably a single stage radial flow turbine of known design capable of operating in the microturbine environment. The hot gas enters the turbine  22  at approximately 1700 F and exits at approximately 1200 F. This hot exhaust gas then flows through the diffuser section  52  to the recuperator  26 . 
     As mentioned above, the exhaust gas exits the turbine  22  at approximately 1200 F. After passing through the recuperator  26 , the exhaust gas has a temperature of approximately 420 F. This high temperature gas represents a substantial amount of thermal energy. Previously, microturbines simply discharged the exhaust gas into the atmosphere, wasting the associated thermal energy. The articulated heat recovery heat exchanger  38  provides a way to selectively heat water or other fluids by transferring a portion of the thermal energy from the hot exhaust gas to the fluid. The heated fluid may be used to heat potable water, or may be used in a hydronic heating system, for example. The microturbine therefore simultaneously generates two useful substances: electricity and heated fluid. This dual-purpose operating mode of the microturbine system  10  is termed cogeneration. 
     Referring now to FIGS. 3 and 4, the articulated heat recovery heat exchanger  38  (sometimes referred to herein as the “recovery unit”) includes an exhaust manifold or housing  54 , a heat exchanger  58 , a fluid inlet coupling  62 , a fluid outlet coupling  66 , an actuator  70 , and a tension spring  74  or other suitable biasing member. The housing  54  defines an intake opening  78  and an exhaust opening  82  and conducts the exhaust gasses expelled by the recuperator  26  from the intake opening  78  to the exhaust opening  82  where they are routed through a venting system and released to the atmosphere. The housing  54  includes a flange portion  86  including a plurality of holes  90  that may be used to secure the recovery unit  38  to a side of the recuperator  26  using bolts, screws, or other known fasteners. The housing  54  also includes a fluid drain hole  92  for the drainage of water accumulating within the housing due to condensation on the outer surfaces of the heat exchanger  58 . 
     The heat exchanger  58  is of the known tube-and-fin type although other types or styles of heat exchangers are possible. The heat exchanger  58  is pivotally mounted within the housing  54  in a manner described in more detail below. The heat exchanger  58  includes a series of tubes  94  extending across the length of the heat exchanger  58 . The tubes  94  may be oriented in a generally serpentine fashion as illustrated in FIG. 3 or there may be multiple tubes  94  arranged in parallel extending from one end of the heat exchanger  58  to the other. The tubes  94  conduct fluid from one end of the heat exchanger  58  to the other, and are preferably made of aluminum, copper, stainless steel, or another suitable heat-conducting material. A plurality of fins  98  (drawn only partially in FIG. 3) extends between the tubes  94  to enhance the heat transfer capacity of the heat exchanger  58 . The fins  98  are typically made of aluminum, copper, stainless steel, or another suitable heat-conducting material, and are brazed or otherwise thermally, structurally or metallurgically coupled to the tubes  94 . 
     The fluid inlet coupling  62  defines a fluid inlet channel that has an inlet axis  106 . The inlet coupling  62  also includes a fixed portion  110 , communicating with a fluid source  112  (see FIG.  1 ), and a rotatable portion  114  communicating with the heat exchanger  58  and adapted to rotate about the inlet axis  106 . Relatively cold fluid is received from the fluid source  112  and conducted through the fluid inlet channel into the tubes  94  of the heat exchanger  58 . The fluid then flows through the tubes  94  of the heat exchanger  58  and exits the heat exchanger at the outlet coupling  66  and continues to a fluid receptacle  116  (e.g. a water heater tank or a hydronic heating system, see FIG.  1 ). 
     The outlet coupling  66  is similar to the inlet coupling and includes a fixed portion  118  mounted to the housing  54  and a rotatable portion  122  communicating with the heat exchanger  58 . The rotatable portion  122  rotates about a fluid outlet axis  126  that is substantially collinear to the inlet axis  106 . The couplings  62 ,  66  provide rotational motion about their respective axes  106 ,  126  while maintaining a fluid-tight seal between the heat exchanger  58  and the fluid source  112  and fluid receptacle  116 . The inlet coupling  62  and the outlet coupling  66  also serve as bearings, pivotally supporting the heat exchanger  58  for pivotal movement about a pivot axis that is substantially collinear with the inlet and outlet axes  106 ,  126 . 
     Referring now also to FIGS. 5 and 6, the actuator  70  is mounted on one end to a fixed arm  130 . The fixed arm  130  is mounted to the housing  54  by welding or other known fastening methods. The fixed arm  130  extends from one side of the housing  54  and includes a depending portion  134  to which the actuator  70  is pivotally mounted by a first pivot pin  138 . The other end of the actuator  70  is pivotally mounted to an actuator arm  142  by a second pivot pin  146 . The actuator arm  142  is fixed to the rotatable portion  114  of the inlet coupling  62 . The illustrated actuator  70  is a piston-cylinder type actuator having a piston  150  and a cylinder  154 , and is moveable between an extended position (FIG. 6) and a retracted position (FIG.  5 ). The tension spring  74  is interconnected between the first and second pivot pins  138 ,  146  and biases the actuator  70  toward the retracted position. The illustrated tension spring  74  is a helical spring, however other known springs such as elastic cords or bands are possible. 
     To move the actuator  70  to the extended position, compressed air is bled from the compressor  14  into the cylinder  154  of the actuator  70  by way of a high-pressure conduit  158 . The pressure within the cylinder  154  creates a force on the piston  150  of the actuator  70  that overcomes the biasing force of the spring  74  and moves the actuator  70  toward the extended position. Once in the extended position, the pressure in the cylinder  154  is maintained, preventing the spring  74  from returning the actuator  70  to the retracted position. When it is desired to return the actuator  70  to the retracted position the compressed air is bled from the cylinder  154  and the force provided by the spring  74  moves the actuator  70  back toward the retracted position. 
     Because the actuator  70  is operated under the influence of the compressed air from the compressor  14 , efficiency may be improved over systems using an external or dedicated electric motor to actuate the heat exchanger  58 . More specifically, to actuate the heat exchanger  58 , the illustrated construction requires only a small amount of electricity to intermittently actuate a solenoid that opens and closes a flow path for the compressed air to the cylinder  154 . Once the flow path is pressurized by the compressed air, the compressor  14  will maintain such pressure continuously until the solenoid closes the flow path. By contrast, a system using an electric motor would have to constantly supply electricity to the motor to operate against the bias of the spring  74 . 
     The heat exchanger  58  is movable between a non-cogenerating, disengaged position (FIG. 5) and a cogenerating, engaged position (FIG.  6 ). In the disengaged position, the heat exchanger  58  is positioned substantially adjacent one of the walls of the housing  54 , allowing the exhaust gasses to enter the housing at the intake opening  78  and flow substantially unrestricted out of the housing  54  through the exhaust opening  82 . When the heat exchanger  58  is in the disengaged position, very little exhaust gas flows across the tubes  94  and fins  98  of the heat exchanger  58 , as a result, very little heat is transferred from the exhaust gasses to the fluid flowing through the heat exchanger  58 . 
     When it is desired to heat the fluid flowing through the heat exchanger  58 , air is bled from the compressor  14  to move the actuator  70  toward the extended position as described above. Moving the actuator  70  toward the extended position pivots the heat exchanger  58  by way of the actuator arm  142 , and positions the heat exchanger  58  in the engaged position where it substantially covers the intake opening  78 . When the heat exchanger  58  is in the engaged position, substantially all of the exhaust gasses flow across the tubes  94  and fins  98  of the heat exchanger  58 , transferring a maximum amount of heat from the exhaust gasses to the fluid flowing through the heat exchanger  58 . After passing through the heat exchanger  58 , the exhaust gasses exit the housing  54  through the exhaust opening  82 . When it is no longer desired to heat the fluid flowing through the heat exchanger  58 , the compressed air is bled from the cylinder  154  of the actuator  70  as described above, the spring  74  then returns the actuator  70  to the retracted position, thus returning the heat exchanger  58  to the disengaged position. 
     It should be apparent that the operation of the spring  74  and actuator  70  may be reversed such that the spring  74  biases the heat exchanger  58  toward the engaged position and the actuator  70  is used to move the heat exchanger  58  to the disengaged position. Alternatively, a dual-action actuator may be used that is capable of positively moving the heat exchanger  58  toward either position, thus eliminating the need for the spring  74 .