Gas turbine with articulated heat recovery heat exchanger

[0002] The invention relates to an articulated heat recovery heat exchanger for use on a cogenerating recuperated microturbine to selectively heat a fluid.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] FIG. 1 is a perspective view of a cogenerating recuperated microturbine system embodying the present invention.

[0008] FIG. 2 is a section view taken along line 2—2 of FIG. 1.

[0009] FIG. 3 is an enlarged perspective view of the articulated heat recovery heat exchanger.

[0010] FIG. 4 is an enlarged perspective view of the articulated heat recovery heat exchanger.

[0011] FIG. 5 is a side view of the articulated heat recovery heat exchanger in the non-cogenerating position.

[0012] FIG. 6 is a side view of the articulated heat recovery heat exchanger in the cogenerating position.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.