MXPA00006120A - Constant turbine inlet temperature control of a microturbine power generating system - Google Patents

Abstract

A microturbine power generating system includes an electrical generator and a turbine having a fixed inlet nozzle geometry. Maximum thermodynamic efficiency of the microturbine power generating system is achieved by maintaining the turbine inlet at or near maximum temperature. When power demanded of the system is constant, power is supplied by the electrical generator. When an increase in power is demanded, the entire demand is supplied by a battery or other external storage until the electrical generator can satisfy the increased power demand.

Description

INTERNATIONAL APPLICATION PUBUSHED UNDER THE PATENT COOPERATION TRE «< TY (PCT) WO 99/32769 F02C 6/14, H02J 3/32, 7/32 Al (30) Prlorlly Data: CONSTANT TEMPERATURE CONTROL OF TURBINE ENTRY OF A MICROTURBINE ENERGY GENERATION SYSTEM BACKGROUND OF THE INVENTION The present invention relates generally to microturbine energy generating systems. More specifically, the present invention relates to modular, distributed energy generating units.

The United States Electrical Energy Research Institute (EPRI), which is the uniform research facility for domestic electrical services, predicts that up to 0% of new generation could be provided by generators distributed by 2006. In many parts of the world, the lack of electrical infrastructure (transmission and distribution lines) will greatly accelerate the commercialization of distributed generation technologies since the central plants not only cost more for ilo att, but also must have an expensive infrastructure installed for deliver the product to the consumer. Generation units with distributed, modular microturbines could help alleviate the current downturns and blackouts that prevail in many parts of the world. A concept of a simple moving part would allow maintenance with little technical skill and a low cost in general to allow its general acquisition in those parts of the world where capital is scarce. In addition, given the emphasis on electricity deregulation in the United States and the global trend in this direction, electricity consumers would not only have the right to choose the correct method of electric service but also a new, low-cost option. U.S. Patent 4, 154, 601, which is assigned to the assignee of the present invention, discloses a micro turbine power generating system suitable for applications in generation. To make these units attractive to consumers, improvements are needed in areas such as increasing fuel efficiency, reducing size and weight, and decreasing thermal signal, noise, maintenance and cost. For example: it is difficult to obtain good fuel economy and acceptable emission ranges, especially for turbines that have fixed geometry entries. The highest efficiency of the power generating units is obtained through high pressure ranges and high turbine inlet temperatures. These ranges and temperatures are obtained during full charge and when operating at full speed. However, with low partial load and no load, the Fixed geometry gas turbines are operated at reduced turbine inlet temperatures and at partial load, thereby reducing fuel efficiency. There is a need to improve fuel efficiency and the range of emissions for a micro turbine power generating system that includes a fixed input nozzle geometry. SUMMARY OF THE INVENTION The present invention optimizes the thermodynamic efficiency of a gas turbine by maximizing the inlet temperature of the turbine. The present invention can be considered as a micro turbine power generating system that includes a turbine with fixed input nozzle geometry; a power storage device and a controller to maintain the turbine inlet at or near the maximum turbine inlet temperature. The controller causes the energy storage device to supply a load when an increase in load is demanded in the system. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an illustration of a power generating system according to the present invention; and FIGURE 2 is an illustration of an engine core for the power generator system. DESCRIPTION OF THE PREFERRED MODALITY With reference to FIGURE 1, a power generating system 10 according to the present invention is illustrated. The power generating system 10 includes n compressor 12, a turbine 1 and an electric generator 16. The electric generator is flown from the compressor 16. The compressor 12, the turbine 14 and the electric generator 16 can be rotated by a single arrow 18 Although the compressor 12, the turbine 14 and the electric generator 16 can be mounted on separate arrows, the use of the common arrow 18 to rotate the compressor 12, the turbine 14 and the electric generator 16 adds compaction and reliability to the generator system. power 10. The arrow 18 can be supported by self-pressurized air bearings such as foil bearings. As shown in FIGURE 2, the arrow 18 is supported by blade support bearings 76 and 78 and blade pulse 80 bearings. The blade bearings eliminate the need for a separate bearing lubrication system and reduce the frequency of service of maintenance. The air entering through an inlet of the compressor 12 is compressed. The compressed air that comes out of the outlet of the compressor 12 circulates through cold lateral passages 20 on the cold side of the recuperator 22. In the recuperator 22, the compressed air absorbs heat, which improves the combustion. Compressed hot air exiting the cold side of the recuperator 22 is supplied to the combustion chamber 24. Fuel is also supplied to the combustion chamber 24. Gaseous and liquid fuels can be used. In the gaseous fuel mode, any suitable gaseous fuel can be used. The fuel selection includes diesel, flair gas, gas off, gasoline, naphtha, propane, JP-8, methane, natural gas and other manufactured gases. The fuel flow is controlled by the flow control valve 26. The fuel is injected into the combustion chamber 24 by means of an injection nozzle 28. Inside the combustion chamber 24 the fuel and the compressed air are mixed and ignited by a lighter 27 in an exothermic reaction. In the preferred embodiment, the combustion chamber 24 contains a suitable catalyst capable of burning the compressed high temperature air-fuel mixture at the process conditions. Some known catalysts used in the combustion chamber 24 include platinum, palladium, as well as metal oxide catalysts with active nickel and cobalt elements. After combustion, the hot expanding combustion gases are directed to an inlet nozzle 30 of the turbine 14. The inlet nozzle 30 has fixed geometry. The hot expanding gases resulting from the combustion are expanded through the turbine 14, thereby creating the power of the turbine. The power of the turbine, in turn, drives the compressor 12 and the electric machine 16. The exhaust gas is circulated through hot side passages 3 on the hot side of the recuperator 22. Inside the recuperator 22, the heat of the gas exhaust from the hot side turbine is transferred to the compressed air on the cold side. In this way, part of the combustion heat is recovered and used to increase the temperature of the compressed air en route to the combustion chamber 24. After delivering part of the heat, the combustion product leaves the recuperator 22. Additional stages of recovery can be added to the power generation system 10. The generator 16 can be a dipole 34 brushless permanent magnet machine and stator winding 36. The turbine power generated by the rotating turbine 14 is used to rotate the rotor 34. The rotor 34 is fixed to the arrow 18. When the rotor 34 is rotated by the power of the turbine, an alternating current is induced in the winding of the stator 36. The speed of the arrow 18 can be varied according to external demands of energy on the system 10. The variations in the speed of the arrow will produce a variation in the frequency of the alternating current (being this, aberrant frequencies) generated by the electric generator 16. Regardless of the frequency of the EC power generated by the electric generator 16, the power EC can be rectified to DC power by the rectifier 38, and then cut by a solid-state electronic inverter 40 to produce AC power with fixed frequency. Accordingly, when the power of the arrow is required less power, therefore, the speed of the turbine 14 can be reduced without affecting the frequency of the AC output. When the rectifier 38 extracts electrical power from the generator 16, a load is placed on the generator 16. As the amount of energy extracted increases, the load increases. When the amount of energy extracted is decreased, the load is decreased. In addition, reducing the speed of the arrow reduces air flow because the compressor operates more slowly. Consequently, the inlet temperature of the turbine remains relatively constant, thereby maintaining high efficiency at partial load. The use of the rectifier 38 and the inverter 40 allows ample flexibility to determine the electrical service to be supplied by the power generating system of the present invention. Because any inverter 40 can be selected, the frequency of the AC power can be selected by the consumer, if there is direct use for AC power at aberrant frequencies. The rectifier 38 and the inverter 40 can be eliminated. When high frequency power is used for fluorescent lamps, it only operates the lamp more efficiently, but the inductor ballasts can be replaced by capacitor ballasts. Such use of high frequency voltage used in a lighting system can result in an efficiency of 25% higher. If only DC power is desired, it is possible to eliminate the resulting direct current 40.1a inverter can be used for galvanizing, for elevator operation and for incandescent lighting. The power generating system 10 may also include a battery 46 to provide additional storage and backup power. When used in In combination with the inverter 40, the combination can provide uninterrupted power for hours after generator failure. Additionally, the controller causes the battery 46 to supply the load when a load increase is demanded. The battery 46 can be sized to handle a peak load demand on the system 10 During the operation of the power generating system 10, heat is generated in the electric generator 16 due to inefficiencies in the design of the generator. In order to extend the life of the electric generator 16, as well as capture useful heat, the compressor inlet air flows over the generator 16 and absorbs the excess heat from the generator 16. The rectifier 38 and the inverter 40 can also be placed inside. of the air flow. After the air has absorbed heat from the aforementioned sources, it is compressed in the compressor 12 and is further heated in the recuperator 22. A controller 42 controls the speed of the arrow by controlling the amount of fuel flowing into the combustion chamber. 24. The controller 42 uses sensor signals generated by a sensor group 44 to determine external demands on the power generating system 10, as well as generating control commands to operate the system 10 at maximum efficiency.

The group of sensors 44 may include sensors such as position sensors, arrow speed sensors and various temperature and pressure sensors for measuring pressures and operating temperatures of the system 10. Using the above-mentioned sensors, the controller 42 controls the start-up and the optimal operation during stable operation. The controller 42 can also determine the direct current storage status in the battery 46 if it is included in the inverter 40, and adjusts the operation to maintain the conditions of net charge, net discharge and constant charge of the battery. The controller 42 also uses speed and temperature signals from the sensor group 44 to calculate the load demanded from the system 10. Based on the calculated load demand, the controller 42 determines whether the generator 16 must supply the load or the battery 46 must supply load. When a constant power demand is supplied, the controller 42 causes the generator 16 to supply all the load demand of the system. When the load demand increases, the controller 42 causes the battery 46 to satisfy the total load demand, but only for a short time. While the battery 46 is supplying the total charge, the generator 16 is discharged, this causes the rotor speed to increase to a new high level. Once the greater rotor speed is obtained, the controller 42 causes the generator 16 to supply the total load. Changing the load to the battery 46 allows the input of the turbine 30 to be maintained at or near the maximum temperature, which allows the system 10 to operate at maximum efficiency and reduce the range of emissions. The controller 42 commands that the fuel flow control valve 26 maintain the inlet temperature at or near the maximum. Additionally, the controller 42 controls the load of the turbine regardless of the electrical load demand on the system 10 by regulating the load on the generator 16. If the turbine speed falls below a fixed point (the set point depending on the value of the load demand of the system), the controller 42 commands that the rectifier 38 and the inverter 40 reduce the load on the generator 16.

If the speed of the turbine increases above the speed set point, the controller 4 commands the rectifier 38 and the inverter 40 to increase the load on the generator 16. When the load demand is increased, the battery 46 delivers the load, with that unloading the generator 16 and allowing the rotor 38 to increase its speed. A switch / starter control 48 can be provided off-line to start the power generating system 10. The rotation of the arrow 18 can be started using the generator 16 as the motor. During startup, the switch / starter 48 supplies an excitation current to the winding of the stator 34 of the electric generator 16. The starting power is supplied by the battery 46. In the alternative, a compressed air device can be used to drive the generator system of the generator. power 10. With reference to FIGURE 2, the "motor core" 50 of the power generating system 10 is shown. The compressor 12 includes an impeller 52 having a bore, a compressor screw 54 and a diffuser channel 56. The air that enters through the air inlet 58 is filtered by the air filter 59 and is directed to the screw of the compressor 54. The air flowing out of the screw 54 of the compressor is directed to the recuperator 22. The turbine 14 includes a turbine screw 60, a plurality of fixed nozzle fins 62 and a turbine wheel without drilling 64. Expanded hot gases exiting the combustion chamber 24 are directed into the screw of the turbine 60 already through the fins of the nozzle 62, which direct the expanding hot gas into the turbine wheel 64. The exhaust gas from the turbine leaves the turbine 14 through the exhaust diffuser 66, which reduces the temperature and the noise of the exhaust gas from the turbine. The rotor 38 of the electric generator 16 includes magnets 68 made of rare earth material such as sa cobalt. The magnets 68 are surrounded by a containment sleeve 70 made of non-magnetic material such as Inconel 718. The winding of the stator 40 is housed within a generator cover 73. The rotor 38 has a bore and an optional containment sleeve (not shown) that is in contact with a surface of the perforation. The power conductors 72 extend from the winding of the stator 40 and end in a power connector pin 74, which is secured to the cover 73 of the generator. A single arrow 18 is shown in FIGURE 2 as a link arrow 75, which extends through the perforations in the rotor 38 and the impeller of the compressor 52. The link arrow 75 is thin, having a diameter of about less. The perforations have gaps that allow the link arrow 75 extends through rotor 38 and impeller 52. However, link arrow 75 does not extend through turbine wheel 64. In contrast, link arrow 75 is secured to the turbine wheel 64. The link shaft 75 can be secured to the center of the turbine wheel by means of an inertial joint. Therefore, the wheel of the turbine 64 has no perforation because it does not take a hole through which the link arrow 75 extends. By eliminating the perforation it reduces the tension on the wheel of the turbine 64. When they are joined by the link arrow 18, the impeller of the compressor 52, the wheel of the turbine 64 and the rotor 38 rotate as a single unit. Under high operating temperatures and at high rotational speeds, however, the impeller 52, the turbine wheel 64 and the rotor 38 tend to expand and separate. To maintain contact between the faces of the impeller 52, the wheel of the turbine 64 and the rotor at high speeds of rotation (80,000 r.p.m. or more), the link arrow 75 is overloaded. For example: the connecting arrow 75 made of titanium can overload in tension up to 90% of the fracture force. During assembly, the link arrow 75 is placed in tension, the impeller 2 and the rotor 38 are slid on the link shaft 75, and a nut 77 is secured on the threaded end of the link shaft 75. The tension is maintained as the nut 77 rotates. The tension is greater in the the centers of the impeller 52 and the rotor 38. When the impeller 52 and the rotor 38 are rotated, the high stresses on the outer portion of these components is counteracted by the stress applied by the link shaft 75. The rotating unit 52, 64 , 38 and 18 are supported in a radial direction by laminar inner and outer bearings 76 and 78. The rotating unit 52, 64, 38 and 18 are supported in an axial direction by a pulse rolling bearing 80. A base 79 provides support for a fuel inlet, the air inlet 58, the compressor 12, the turbine 14, the generator 16, the recuperator 22, the combustion chamber 24, the rectifier 38 and the inverter 40, to allow the system 10 to exist as a unity package. Several cooling ports are provided for the motor core 50. Ports 82 and 84 are provided to circulate a coolant over the winding of the stator 40. Ports 86 and 88 are also provided to circulate a coolant over the bearings 76, 78 and 80. The power generating system 10 can be constructed in several main modules such as a rotating module, a heat exchanger module and an electronic module. Each of these modules is relatively light and compact. The modules can be changed without interrupting the liquid lines. The use of laminar bearings 52 and 54 eliminates the need for an oil-based lubrication system, therefore, this results in low maintenance of the power generating system 10. The scheduled maintenance would consist mainly in the change of the lighter 27, the filter 59 and catalytic elements in the combustion chamber 24. The power generating system 10 operates in a recovered Brayton cycle. The Brayton cycle can be operated at a relatively low pressure ratio (3.8) to maximize total efficiency, since, in recovered cycles, the lower pressure range, the turbine's exhaust temperature is closer to the inlet temperature . This allows to add heat to the cycle at high temperature and, according to Carnot's law, the entropic losses associated with the supply of heat to the cycle are reduced. This high temperature addition results in a general increase in the cycle. The air is compressed in a single-stage radial compressor at 3.8 bar. The compressed air can be directed to the recuperator 22 where the temperature of the compressed air is increased using the waste heat of the exhaust gas of the turbine. The exhaust gas temperature of the turbine is limited to about 1,300 ° F in order to help extend the life of the recuperator 22. For exhaust gas temperatures greater than 1,300 ° F, the recuperator 22 can be made of super alloys instead of stainless steel. The recuperator 22 can be designed either for an efficiency of 85% or 90% depending on the economic needs of the client. In the most efficient configuration, and using 90% recovery, the overall net cycle efficiency is 30%, providing a range of heating heat value of approximately 11,900 BTU / kh with diesel. After being heated in the recuperator 22, the compressed air is directed to the combustion chamber 24, where additional heat is added to increase the temperature of the compressed air to 1,650 ° F. A combustion chamber 24 designed according to a conventional design can provide a Nox level of less of 25 ppm, and a combustion chamber 24 using a catalyst can produce a range of Nox that is virtually undetectable (commercial Nox detectors are limited to a detection range between 2 and 3 ppm). The high enthalpy gas expands through the turbine 14. The compressor 12, the turbine 14, the generator 16 and the single arrow 18 - the only moving part in the motor core 50 - rotates at a high speed of approximately 80,000 r.p.m. or more. The resulting high frequency of about 1,200 hertz is reduced by the inverter 38 to a frequency compatible with the network of 50 or 60 cycles. As a result we have a high power density typified by low weight (about one third the size of a comparable diesel generator) and a small footprint (for example: approximately 3 feet by 5 feet by 6 feet high) (0.914 mx 1.524) mx 1,829 m). The high power density and low weight of the technology is made possible through the high speed components which allows large amounts of power using a minimum of materials. The unit is fully self-contained within a weatherproof enclosure. The power generator system 10 is "connect and operate" technology, requiring little more than a clean fuel supply, liquid or gas. Thus, a highly efficient power generating system 10 has been revealed. Although the turbine 14 is an inherently unstable turbine 14, it operates within a stable system 10. The turbine 14 can be operated at or near the maximum inlet temperature, but will not lose power if faced with an increase in demand. Because the turbine is operated at maximum inlet temperature, the thermodynamic efficiency of the system is maximized and emissions are reduced. When an increase in demand for the energy storage device is satisfied, the electrical output of the generator can be reduced by reducing the speed of the turbine. Therefore, the turbine load is controlled independently of the load demand of the system. The micro turbine 10 power generator system can use various fuels including natural gas, diesel and JP- (The power generator system 10 has a low thermal signature and minimal noise generation.) The use of air bearings eliminates the need of an oil-based lubrication system The electric generator system 10 has high reliability and minimum service requirements due to the design of a single moving part.

The use of a solid-state inverter allows the system 10 to provide a variable AC output. Installation is easy due to the modular self-contained design, and service is easy because the system 10 has a single moving part and the main parts are easily accessible. The width, long and high core motor 50 can be adjusted to meet a variety of dimensional requirements. The 10 power generator system is smaller, lighter, more fuel efficient and has a low thermal signature, low noise, maintenance and cost than comparable internal combustion engines. Therefore, due to its low initial cost, low installation costs, high efficiency, high reliability and simple low cost maintenance, the 0 power generator system provides lower operating and fixed costs than generation technologies of comparable size. The potential applications of the power generator system 10 are many and varied. The applications include in off-network applications for independent power, in applications within the network for peak savings, for load tracking service or for load service, emergency backup and for non-interruptible power supply, Main movement applications (example: pumping, air conditioning) and for hybrid automotive vehicles. The invention is not limited to the modalities mentioned above. For example, a flywheel can be used as a storage device instead of a battery 46. When peak power is demanded, the moment of the flywheel allows additional power to be delivered and an additional load to be placed on the electric generator 16, all without deprive turbine 16 of movement. Accordingly, the present invention is defined according to the following Claims.

Claims (11)

1. CLAIMS A micro turbine power generator system comprising: a turbine with fixed inlet nozzle; an energy storage device; and a controller to maintain the turbine inlet at or near the turbine inlet maximum temperature, the controller causes the energy storage device to supply a load when an increase in load is required in the system.
2. The system of claim 1, wherein the system further includes an electric generator driven by turbine power, wherein the energy storage device includes a battery, wherein the controller causes the electrical power to be supplied by the electric generator. until the power demand is increased, where the controller causes the electrical power to be supplied by the battery.
3. The system of claim 2, wherein the controller causes the battery to supply the total power demand when the power demand increases, wherein the turbine speed is increased while the battery supplies the load.
4. The system of claim 1, further comprising an electronic power unit in communication with the engine control unit for adjusting the generator load to control the engine speed, the energy storage device supplying the load when the demand for load is increased.
5. An apparatus for controlling a micro turbine power generating system, the system includes a turbine, the system responds to a load demand during operation, the apparatus comprises: a controller for monitoring the temperature of the motor and the speed of the motor; an electric generator; an energy storage device; means, which respond to the controller to regulate the flow of fuel to maintain the temperature of the motor constant, even when the load demand changes on the system; and the controller further determines whether it is necessary to transfer a part of the load demand from the generator to the energy storage device when the load demand changes.
6. The apparatus of claim 5, wherein the engine speed is controlled by regulating a load in the generator in order to maintain the speed at a fixed point.
7. The apparatus of claim 6, wherein the set point of the motor speed is determined by the load demand and produced by controlling the generator load independently of the load demand in the system.
8. The apparatus of claim 5, wherein the controller causes the load on the generator to increase when the speed of the turbine increases above the fixed speed point.
9. The apparatus of claim 5, wherein the controller causes the regulation means to maintain the temperature of the motor constant regardless of the speed of the turbine.
10. 10. The apparatus of claim 5, wherein the energy storage device is sized to meet the peak load demand on the system.
11. 11. A method for controlling a micro turbine power generating system, the system includes an electrical generator, a turbine having a fixed input nozzle geometry and an external storage device, the method comprising: maintaining the temperature of the nozzle of entry constant; use the electric generator to satisfy the power demanded in the system until the power demanded is increased; and using the external storage device to satisfy the power demanded when the power demanded is increased; the temperature of the inlet nozzle is maintained at a constant temperature while the power demand is being satisfied by the external storage device. . The method of claim 11, wherein the external energy storage device is used to satisfy the total power demand when the demanded power of the system is increased.