Patent Publication Number: US-2012039725-A1

Title: Method, system and apparatus for powering a compressor via a dam

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of U.S. patent application Ser. No. 12/854,707, filed Aug. 11, 2010. The subject matter of this earlier filed application is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     The present invention relates to a method, system and apparatus for powering a compressor. More specifically, the method, system and apparatus use potential energy from the head of a dam to power one or more stages of a compressor. 
     2. Description of the Related Art 
     In power generation systems, gas turbines are known that extract energy from a combustible fuel. For instance, a gas turbine generally has an upstream multi-stage compressor that compresses air flowing into the engine, a combustion chamber where fuel (typically gas) is ignited and combusted with the compressed air, and a turbine that harnesses the energy from the flow of the combustion gases. The combusted gas is then expelled from the rear of the engine. The rotating turbine drives an electric generator that converts mechanical energy into electrical energy, and thus creates electricity. 
     SUMMARY 
     Certain embodiments of the present invention may provide solutions to the problems and needs in the art that have not yet been fully solved by currently available gas turbine technologies. For example, certain embodiments of the present invention provide a method and system that uses head of a dam to power one or more compressor stages of a Brayton cycle heat engine, such as a gas turbine. This uses less external power to drive the Brayton cycle heat engine and delivers on-demand power more effectively and efficiently than typical Brayton cycle heat engines. 
     In one embodiment of the present invention, a system includes a power generation mechanism configured to be driven by flowing water. The system also includes a compressor water channel configured to supply flowing water from a dam to the power generation mechanism. The system further includes a heat engine including a compressor with one or more compressor stages. The power generation mechanism is configured to drive the one or more compressor stages. The flowing water in the compressor water channel is driven at least in part by gravity due to head of the dam. 
     In another embodiment of the present invention, an apparatus includes one or more compressor stages of a heat engine having one or more external blades. The apparatus also includes one or more compressor stage water conduits surrounding the one or more compressor stages. The apparatus further includes one or more compressor stage entry inlets configured to supply flowing water from a dam to the one or more compressor stage water conduits. The flowing water drives the external blades of the one or more compressor stages, causing the one or more compressor stages to rotate. The flowing water is driven at least in part by gravity due to head of the dam. 
     In yet another embodiment of the present invention, a method includes supplying flowing water from a dam to a power generation mechanism via a compressor water channel. The method also includes driving the power generation mechanism using the flowing water to generate power. The method further includes driving one or more compressor stages of a heat engine using power generated by the power generation mechanism. The flowing water in the compressor water channel is driven at least in part by gravity due to head of the dam. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of certain embodiments of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. While it should be understood that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1  is a side view of a dam system combining gas turbine power generation and hydroelectric power generation, according to some embodiments of the present invention. 
         FIG. 2  is a side view of a direct mechanical water drive powering the low pressure section of a gas turbine in a dam, according to an embodiment of the present invention. 
         FIG. 3  is a side view of a direct electrical water drive powering the low pressure section of a gas turbine in a dam, according to an embodiment of the present invention. 
         FIG. 4  is a side view of a water turbine and generator powering the low pressure section of a gas turbine in a dam, according to an embodiment of the present invention. 
         FIG. 5  is a side view of a system where the low pressure compressor section of a gas turbine in a dam is powered by water running through external blades on the compressor stages, according to an embodiment of the present invention. 
         FIG. 6  is a side view of the water feed mechanism for three fan stages of the compressor, according to an embodiment of the present invention. 
         FIG. 7  is a front view of a compressor fan stage that is driven by water flowing through external blades, according to an embodiment of the present invention. 
         FIG. 8  illustrates a flow diagram of a method for powering one or more stages of a compressor, according to an embodiment of the present invention. 
         FIG. 9  illustrates a flow diagram of another method for powering one or more stages of a compressor, according to an embodiment of the present invention. 
         FIG. 10  is a side view of a gas turbine, according to an embodiment of the present invention. 
         FIG. 11  is a side view of a section of a gas turbine with non-nesting spools, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     It will be readily understood that the components of various embodiments of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of a system and method of the present invention, as represented in the attached figures, is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. 
     The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, reference throughout this specification to “certain embodiments,” “some embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in certain embodiments,” “in some embodiment,” “in other embodiments,” or similar language throughout this specification do not necessarily all refer to the same group of embodiments and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     Existing industrial gas turbine power generation systems have certain disadvantages. For instance, a drawback to gas turbine power generation systems is that on an industrial scale, it generally takes a significant amount of time and energy to spin up the compressor. This reduces the desirability of, and ability to, generate on-demand power. For instance, it may be desirable to activate certain power systems to generate on-demand power in order to satisfy a peak load on the system. Such a peak load typically occurs around 3:00 pm, particularly during summer months when much of the power demand for air conditioning occurs. 
     Accordingly, it may be beneficial to power one or more compressor stages of the gas turbine via another source. One such source may be water pressure. However, the pressure of municipal water supplies is typically too weak to power one or more stages of a compressor. Further, pressurizing municipal water by mechanical means would consume energy, and perhaps require more energy than is saved by powering one or more stages of the compressor. 
     Some embodiments of the present invention are able to overcome these disadvantages by using the far greater potential energy from the head of a dam to drive one or more stages of a compressor. Head may be defined as the difference in height between the water&#39;s source and water outflow. Some of the power generation mechanisms that may harness the potential energy from the dam include, but are not limited to, a direct mechanical water drive, a direct electrical water drive, a turbine/generator combination, or by external blades on the compressor stage(s). The number of compressor stages that are powered by embodiments of the present invention is a matter of design choice. By powering one or more stages of the compressor, a heat engine that includes the compressor may be powered up more quickly to begin generating power. 
     Driving one or more compressor stages of the heat engine reduces consumption of any fuel that may be used, and produces less pollution than conventional systems. Further, due to the powering of one or more stages of the compressor with dam head, the power generated by the heat engine is highly dispatchable (time-variable under active command), which can be a valuable secondary attribute that not all generation types possess. The commercial potential of such a system is high. Output power is in high demand, especially if dispatchable. 
     A heat engine takes advantage of heat energy to perform mechanical work. The heat engine may be any form of heat engine that is capable of expelling high velocity exhaust and generates heat from a heat source. One example of a heat engine is a Brayton cycle heat engine. A Brayton cycle heat engine may be an internal combustion engine such as a gas turbine engine or a piston engine, or an external combustion engine such as a steam engine. The engine may take any desired form and is not limited by this disclosure in any way. The heat source of the heat engine may be provided by various fuels in some embodiments. For instance, some embodiments may use gases (such as natural gas), liquids (such as petroleum fuels), sufficiently-pulverized coal, biomass, slurries, suspensions, radioisotopes, solar absorbers, geothermal transfer fluids, or any other fuel suitable for driving a heat engine. Due to an advanced pipeline infrastructure at least in the United States, natural gas may be more economical and/or cleaner than many of the other fuel alternatives for U.S. implementations at many existing or potential dam sites. 
       FIG. 1  is a side view of a system combining gas power generation and hydroelectric power generation, according to some embodiments of the present invention. The system depicted here uses exhaust gases from a gas turbine  130  to pull water and generate lower pressure in an exit channel  160 , causing the system to behave as though head  112  were higher than it mechanically is. However, some embodiments of the present invention do not take advantage of this synergy and have a gas turbine that does not interact with the water channel. Further, while often advantageous, it is not necessary for a water turbine to be present at all in some embodiments, and dam head may be used for the purpose of driving one or more stages of a compressor of a gas turbine. 
     The depicted system includes a dam  100  holding back dammed water  102 . Water enters dam  100  via a water intake  104  and the flow of the water is controlled by control gate  106 . Control gate  106  may be raised or lowered to increase, decrease, or completely restrict water flow to a penstock  108 . While penstock  108  is depicted as a water channel here, a pipe, a conduit, or any other suitable water channel or water piping mechanism may be used. After passing control gate  106 , the water enters penstock  108  that supplies the water to a water turbine  110 . Dammed water  102  has a certain head  112 , which is the difference in height between the level of water  114  before the dam  100  and the level of water  116  after the dam  100  (i.e., water that has passed through the dam and is now downstream in the river). However, in some embodiments, the difference in height may be anywhere and not necessarily near the top of the dam. 
     The system also includes an air intake  120  that supplies air to gas turbine  130 . While gas turbine  130  is shown in this embodiment, any suitable heat engine may be used. In this embodiment, compressor water channel  140  provides water that may power one or more stages of a compressor  132  of gas turbine  130  via a power generation mechanism including, but are not limited to, a direct mechanical water drive, a direct electrical water drive, a turbine/generator combination, or by external blades on the compressor stage(s) (not shown). The stages of compressor  132  that are driven by water from compressor water channel  140  may include fewer than all of the stages of the compressor. Further, in this and other embodiments, compressor stages in multiple compressor sections, such as a low pressure compressor section and a high pressure compressor section, may be driven by water from compressor water channel  140 . The direct drive shaft uses gravity-driven potential energy from head  112  of dammed water  102  and is driven by water running through compressor water channel  140 . Keeping one or more stages of compressor  132  running may be advantageous over existing heat engine systems since compressor  132  can be spun up to generate power more quickly, and with less energy cost, than a typical gas turbine. This may allow gas turbine  130  to generate on-demand power more quickly, efficiently and effectively than existing gas turbines. 
     In some other embodiments, in lieu of a direct drive shaft, water from compressor water channel  140  runs through a second water turbine that powers another generator. In yet other embodiments, water from compressor water channel  140  may drive external blades that rotate one or more stages of the compressor  132 . 
     A power plant  150  houses a generator complex  152  that generates power for the system. Generator complex  152  may include a single generator or multiple generators. Water turbine  110  and gas turbine  130  are operably connected to generator complex  152  via shafts  154  and  156 , respectively. Shafts  154  and  156  may drive the same generator or different generators, depending on the desired implementation. The rotation of water turbine  110  and gas turbine  130  rotates shafts  154  and  156 , respectively. In some embodiments, as shafts  154  and  156  turn, a series of magnets inside generator complex  152  also turn. The magnets in such generators generally rotate past copper coils, producing current by generating moving electrons. However, some users may simply accept shaft work in other embodiments. In this embodiment, it is possible to operate water turbine  110  alone, gas turbine  130  alone, or both, at any given time to achieve the desired power output. To further facilitate this selective operation, a gate mechanism (not shown) may be included in some embodiments to prevent water spray from water entering exit channel  160  from heading up exit channel  160  towards gas turbine  130  when gas turbine  130  is not operating. 
     Exhaust gases  138  from gas turbine  130  accelerate water  162  in exit channel  160  that has passed through water turbine  110 . Accelerating water  162  in this fashion takes advantage of the Bernoulli principle and the Coand{hacek over (a)} effect to draw water into water intake  104  and through penstock  108  with greater pressure. The Bernoulli principle states that an increase in speed of a fluid occurs simultaneously with a decrease in pressure. The Coand{hacek over (a)} effect is the tendency of a rapidly moving fluid jet to be attracted to a nearby surface. In the context of these principles, a “fluid” may be a gas such as air. 
     The Bernoulli principle and the Coand{hacek over (a)} effect cause exhaust gases  138  to pull water  162 , decreasing pressure in the exit channel exit channel  160  and increasing a flow of water  162 . Further, there is some entrainment of the water stream due to viscous forces. This lower pressure environment in exit channel  160  causes the system to behave as though head  112  of dammed water  102  is greater than it mechanically is. Specifically, the system behaves as though the exit for the water is lower than it mechanically is. 
     Also, the interaction between hot exhaust gases and water flowing in the exit channel generates steam. In some embodiments, the steam can be recovered for various purposes. For instance, the steam may be harnessed to drive one or more stages of compressor  132  in some embodiments. 
       FIG. 2  is a side view of a direct mechanical water drive  210  powering a low pressure section  250  of a gas turbine  230  in a dam, according to an embodiment of the present invention. While a compressor having axial (“fan”) stages is depicted in the figures of the present application, some embodiments of the present invention use compressor types that do not have fan stages, and the compressor type that may be used is not limited in any way. For instance, in some embodiments, a centrifugal, or radial, compressor is used. Among other things, stages of such compressors may use, for example, centrifugal or piston pumps or blowers to generate compression. Further, a combination of different compressor types may be used for different stages of the compressor. 
     In some embodiments, the system depicted in  FIG. 2  may be present in the system depicted in  FIG. 1 . Gas turbine  230  has a compressor  240  for compressing air that enters through air intake  220 . Compressor  240  has a low pressure section  250  and a high pressure section  260 , each including multiple fan stages. In this embodiment, low pressure section  250  includes three fan stages  252 ,  254  and  256 . 
     Water from a dam enters compressor water channel  200  and flows  202  towards direct mechanical water drive  210 . The water is driven by gravity due to head of the dam. Direct mechanical water drive  210  has fins or blades  212  that harness the flow of water  202  to rotate direct mechanical water drive  210 . After passing through direct mechanical water drive  210 , water flows  204  past direct mechanical water drive  210  and on down compressor water channel  200 . In some embodiments (not shown), at least part of the water may then be used for injection into warmer stages of compressor  240  and/or into, around, and/or inside gas turbine  230 . In some embodiments, water may be misted into a flow of exhaust gases leaving gas turbine  230  to reduce noise. 
     Direct mechanical water drive  210  is operably connected to one end of a shaft  214  that rotates with the rotation of direct mechanical water drive  210 . At the other end, shaft  214  is operably connected to fan stages  252 ,  254  and  256  of low pressure compressor stages  250 , and/or connected to a spool (not shown) that may join low pressure compressor section  250  to turbine  270 . However, a turbine is not connected to the spool in some embodiments. Gearing mechanisms (not shown) may be present so fan stages  252 ,  254  and  256  rotate at different speeds, if desired by the specific architecture of gas turbine  230 . However, in many embodiments, fan stages  252 ,  254  and  256  rotate at the same speed since they are connected to the same spool. Thus, gravity-driven water flowing through direct mechanical water drive  210  drives fan stages  252 ,  254  and  256  of low pressure compressor section  250 . 
     In some embodiments, a gate mechanism  206  may be present to regulate the flow  202  of water that drives direct mechanical water drive  210 . In some embodiments, a valve or any other suitable flow metering mechanism may be used as a gate mechanism. Gate mechanism  206  is capable of restricting, or completely shutting off, the flow of water through compressor water channel  200 . In addition to, or in lieu of, gate mechanism  206 , a braking mechanism (also not shown) may be included that serves to slow the rotation of direct mechanical water drive  210 . The operation of gate mechanism  206  and/or the braking mechanism may be controlled remotely by an electronic controller. In this manner, the speed of rotation of fan stages  252 ,  254  and  256  of low pressure compressor section  250  can be regulated. 
     While a shaft is used as a power transfer mechanism in this embodiment, any suitable mechanical means may be used as a power transfer mechanism. For instance, power may be transferred via direct gear teeth, intermediary gearing, or a hydraulic drive that uses a fluid. Further, various combinations of shafts, gearings, and hydraulic mechanisms may be used. 
       FIG. 3  is a side view of a direct electrical water drive  310  powering a low pressure section  350  of a gas turbine  330  in a dam, according to an embodiment of the present invention. In some embodiments, the system depicted in  FIG. 3  may be present in the system depicted in  FIG. 1 . Gas turbine  330  has a compressor  340  for compressing air that enters through air intake  320 . Compressor  340  has a low pressure section  350  and a high pressure section  360 , each including multiple fan stages. In this embodiment, low pressure section  350  includes three fan stages  352 ,  354  and  356 . 
     Water from a dam enters compressor water channel  300  and flows  302  towards direct electrical water drive  310 . The water is driven by gravity due to head of the dam. Direct electrical water drive  310  has fins or blades  312  that harness the flow of water  302  to rotate direct electrical water drive  310 . After passing through direct mechanical water drive  310 , water flows  304  past direct electrical water drive  310  and on down compressor water channel  300 . In some embodiments (not shown), at least part of the water may then be used for injection into warmer stages of compressor  340  and/or into, around, and/or inside gas turbine  330 . In some embodiments, water may be misted into a flow of exhaust gases leaving gas turbine  330  to reduce noise. 
     The rotation of direct electrical water drive  310  generates electrical current. Direct electrical water drive  310  is operably connected to a power cable  314  that transmits the electrical current generated by direct electrical water drive  310 . Power cable  314  is also operably connected to gas turbine  330  and delivers power thereto. Gas turbine  330  uses the power from power cable  314  to run fan stages  352 ,  354  and  356  of low pressure compressor section  350 . The rotation speed of fan stages  352 ,  354  and  356  may be controlled by an electronic controller. Thus, gravity-driven water flowing through direct electrical water drive  310  provides power that drives fan stages  352 ,  354  and  356  of low pressure compressor section  350 . Naturally, in embodiments where some or all of the stages are not fan stages, the power may be used to drive another suitable mechanism for such stages, such as centrifugal or piston pumps or blowers. 
     In some embodiments, a gate mechanism  306  may be present to regulate the flow  302  of water that drives direct electrical water drive  310 . Gate mechanism  306  is capable of restricting, or completely shutting off, the flow of water through compressor water channel  300 . Gate mechanism  306  may be used to regulate the amount of electricity generated by direct electrical water drive  310 . The operation of gate mechanism  306  can also be controlled by an electronic controller. However, rather than regulating the electricity, some embodiments may harness extra electricity for other purposes, such as providing some power to the dam. 
       FIG. 4  is a side view of a water turbine  410  and generator  414  for powering a low pressure section  450  of a gas turbine  430  in a dam, according to an embodiment of the present invention. In some embodiments, the system depicted in  FIG. 4  may be present in the system depicted in  FIG. 1 . Gas turbine  430  has a compressor  440  for compressing air that enters through air intake  420 . Compressor  440  has a low pressure section  450  and a high pressure section  460 , each including multiple fan stages. In this embodiment, low pressure section  450  includes three fan stages  452 ,  454  and  456 . 
     Water from a dam enters compressor water channel  400  and flows  402  towards water turbine  410 . The water is driven by gravity due to head of the dam. Water turbine  410  has fins or blades  412  that harness the flow of water  402  to rotate water turbine  410 . After passing through water turbine  410 , water flows  404  past water turbine  410  and on down compressor water channel  400 . In some embodiments (not shown), at least part of the water may then be used for injection into warmer stages of compressor  440  and/or into, around, and/or inside gas turbine  430 . In some embodiments, water may be misted into a flow of exhaust gases leaving gas turbine  430  to reduce noise. 
     The rotation of water turbine  410  rotates a shaft  414  that is operably connected to both water turbine  410  and generator  416 . As shaft  414  turns, a series of magnets inside generator  416  also turn. The magnets in such generators generally rotate past copper coils, producing current by generating moving electrons. A power cable  418 , which is operably connected to both generator  416  and gas turbine  430 , transmits the generated power from generator  416  to gas turbine  430 . Gas turbine  430  uses the power from power cable  418  to run fan stages  452 ,  454  and  456  of low pressure compressor section  450 . The rotation speed of fan stages  452 ,  454  and  456  may be controlled by an electronic controller. Thus, gravity-driven water flowing through water turbine  410  creates power in generator  416  that drives fan stages  452 ,  454  and  456  of low pressure compressor section  450 . Naturally, in embodiments where some or all of the stages are not fan stages, the power may be used to drive another suitable mechanism for such stages, such as centrifugal or piston pumps or blowers. 
     In some embodiments, a gate mechanism  406  may be present to regulate the flow  402  of water that drives water turbine  410 . Gate mechanism  406  is capable of restricting, or completely shutting off, the flow of water through compressor water channel  400 . Gate mechanism  406  may be used to regulate the amount of electricity generated by generator  416  via speeding, slowing or stopping the rotation of water turbine  410 . The operation of gate mechanism  406  can also be controlled by an electronic controller. However, rather than regulating the electricity, some embodiments may harness extra electricity for other purposes, such as providing some power to the dam. 
       FIG. 5  is a side view of a system where a low pressure section  550  of a gas turbine  530  in a dam is powered by water running through external blades on the compressor stages, according to an embodiment of the present invention. In some embodiments, the system depicted in  FIG. 5  may be present in the system depicted in  FIG. 1 . Gas turbine  530  has a compressor  540  for compressing air that enters through air intake  520 . Compressor  540  has a low pressure section  550  and a high pressure section  560 , each including multiple fan stages. In this embodiment, low pressure section  550  includes three fan stages. 
     Water from a dam enters compressor water channel  500  and flows  502  towards entry inlets  510 ,  512  and  514 , which compressor water channel  500  branches into. The water is driven by gravity due to head of the dam. The water enters entry inlets  510 ,  512  and  514  and drives the respective fans via external blades (not shown). This mechanism is shown in more detail in  FIGS. 6 and 7 . Gates (not shown) may be present for each of entry inlets  510 ,  512  and  514  to regulate the flow of water into each inlet. 
     The water pushes the external blades and causes each fan stage to rotate. Each fan may be closely joined to the next such that water is not able to flow into the fan stages. Or, the fans may have small gaps therebetween to allow water to enter low pressure section  550  of gas turbine  530  and increase the mass of the air flowing therethrough. A further option is to have small valves or gates on the outside of each fan that allows a desired amount of water to flow into low pressure section  550  of gas turbine  530 , or restricts the flow thereof. 
     After passing through the fan stages of low pressure section  550 , water flows through the respective exit outlets  570 ,  572  and  574 , and then merges back into compressor water channel  500 . The water then flows  504  further down compressor water channel  500 . In some embodiments (not shown), at least part of the water may then be used for injection into warmer stages of compressor  540  and/or into, around, and/or inside gas turbine  530 . In some embodiments, water may be misted into a flow of exhaust gases leaving gas turbine  530  to reduce noise. 
     In some embodiments, a gate mechanism  506  may be present to regulate the flow  502  of water in water channel  500 . Gate mechanism  506  is capable of restricting, or completely shutting off, the flow of water through compressor water channel  500 . This gate mechanism may be in addition to, or in lieu of, gate mechanisms within entry inlets  510 ,  512  and  514 . Where entry inlets  510 ,  512  and  514  do not have water flow regulating mechanisms, the diameter of each entry inlet may be sized such that the desired amount of water feeds and spins the fan stages of low pressure section  550  at the desired speed. Further, each exit outlet may be designed so as to carry the appropriate flow of water away from the respective fan stage. 
     While the fan stages of low pressure compressor section  550  may spin at the same speed due to their connection to a common school in some embodiments, different relative fan speeds may be possible in some embodiments, particularly where fan stages do not share a spool. For instance, the diameter may be designed such that for three fan stages, the second fan stage spins 1.5 times as quickly as the first fan stage and the third fan stage spins twice as fast as the first fan stage. Naturally, the specific speeds would vary with the desired turbine performance and implementation. 
       FIG. 6  is a side view of the water feed mechanism for three fan stages  630 ,  632  and  634  of a compressor, according to an embodiment of the present invention. In some embodiments, the water feed mechanism may be present in the system of  FIG. 5 . Water may be provided to the water feed mechanism via a compressor water channel, for instance. 
     Water enters each of entry inlets  600 ,  610  and  620 . Gate mechanisms  602 ,  612  and  622  meter respective water flows  604 ,  614  and  624  for entry inlets  600 ,  610  and  620 , respectively. Water flows  604 ,  614  and  624  then enter each respective fan stage  630 ,  632  and  634 , pushing external blades (not shown) on the fan stages that cause fan stages  630 ,  632  and  634  to rotate. After the water passes through fan stages  630 ,  632  and  634 , respective water flows  634 ,  642  and  644  enter and flow through respective exit outlets  650 ,  652  and  654 . 
       FIG. 7  is a front view of a compressor fan stage that is driven by water flowing through external blades, according to an embodiment of the present invention. In some embodiments, the compressor fan stage of  FIG. 7  may be present in  FIGS. 5  and/or  6 . 
     Water flows through entry inlet  700  and into water conduit  710 . There, the water contacts and rotates blades, such as blade  720 . The compressor fan stage rotates about shaft  740 , spinning compressor fan blades  730 . The rotation of compressor fan blades  730  pressurizes air and pushes the air through the compressor. Once water has rotated around water conduit  710 , the water exits water conduit  710  and flows into exit outlet  750 . The design of the water inlet system and the number of blades engaged between entry inlet  700  and exit outlet  750  is a matter of design choice. In this embodiment, each fan stage has its own entry inlet, water conduit and exit outlet. However, in some embodiments, multiple fan stages may share a single water conduit, or all fan stages of a given compressor section may share a common water conduit. Further, the inner wall of a water conduit may serve as a mounting surface for the blades. 
     In the embodiments discussed in  FIGS. 5-7 , the externally-driven blades may improve efficiency over other configurations, such as an internal blade configuration. Also, the water flow in the water conduits acts as coolant for the gas turbine. Further, in some embodiments, the internal air blades are also “shrouded” (i.e., no significant gap between the blade tip of each fan blade to the outer casing). This may reduce air losses due to blow-by. 
       FIG. 8  illustrates a flow diagram of a method for powering one or more stages of a compressor, according to an embodiment of the present invention. The method begins by regulating water flow in a compressor water channel at  800 . The water flow may be regulated by a gate mechanism, including any suitable water flow control mechanism such as a valve. The flowing water in the compressor water channel is driven at least in part by gravity due to head of the dam. The operation of a power generation mechanism and a heat engine are controlled at  810  via an electronic controller. The operation may be adjusted based on the desired power to be generated by the power generation mechanism and the desired operation of the heat engine. 
     Flowing water is supplied from a dam to the power generation mechanism via the compressor water channel at  820 . The flowing water drives the power generation mechanism at  830 . Power generated by the power generation mechanism is then used to drive one or more compressor stages of the heat engine at  840 . If desirable for the operation of the heat engine, the one or more compressor stages may be operated at different speeds or powers at  850 . 
       FIG. 9  illustrates a flow diagram of another method for powering the one or more stages of a compressor, according to an embodiment of the present invention. The method begins by regulating water flow in one or more entry inlets at  900 . The water flow may be regulated by gate mechanisms, including any suitable water flow control mechanism such as a valve. The flowing water in one or more entry inlets is driven at least in part by gravity due to head of the dam. The operation of a power generation mechanism and a heat engine are controlled at  910  via an electronic controller. The operation may be adjusted based on the desired power to be generated by the power generation mechanism and the desired operation of the heat engine. 
     Water is supplied from the one or more entry inlets to one or more water conduits at  920 . The water flowing through the one or more water conduits drives external blades of the one or more compressor stages at  930 , causing the one or more compressor stages to rotate. Water is then directed out of the one or more water conduits through one or more exit outlets at  940 . If desirable for the operation of the heat engine, the one or more compressor stages may be operated at different speeds or powers at  950 . 
       FIG. 10  is a side view of a gas turbine, according to an embodiment of the present invention. In some embodiments, the gas turbine of  FIG. 10  may be present in one or more of  FIGS. 1-5 . In  FIG. 10 , the gas turbine has three spools—a turboshaft spool  1000 , a low pressure spool  1010 , and a high pressure spool  1020 . While three spools are shown in this embodiment, more or fewer spools may be present, and the number of spools and compressor stages that are used is a matter of design choice. 
     Low pressure spool  1010  is nested within high pressure spool  1020 , and turboshaft spool  1000  is nested within low pressure spool  1010 . Further, the upper and lower portions of the spools depicted in this side view are all part of the same cylindrical spool. The gas turbine also has a cylindrical burner  1030 . In some embodiments, rather than a single burner, multiple burners may be used. The gas turbine depicted in this embodiment is an aeroderivative gas turbine, but in some embodiments, non-aeroderivative gas turbines may be used. Aeroderivative gas turbines are based on aircraft engines. 
     Each spool has a respective turbine  1002 ,  1012  and  1022 . Low pressure spool  1010  has a low pressure compressor section  1014  including a series of fan stages and high pressure spool  1020  has a high pressure compressor section  1024  that also includes a series of fan stages. Rotation of turbines  1012  and  1022  also causes respective compressor sections  1014  and  1024  to rotate due to sharing of a common spool. 
     Air is compressed by low pressure compressor section  1014  and high pressure compressor section  1024 , and then passed through burner  1030 . The air is mixed with fuel, which is then combusted, creating hot exhaust gases. The hot exhaust gases then flow through turbines  1002 ,  1012  and  1022 , causing the turbines to rotate. Rotation of turbine  1002  rotates turboshaft spool  1000 , which causes shaft  1004  to rotate. The rotation of shaft  1004  can be used to do work, such as drive a generator. The hot exhaust gases then exit the gas turbine via a nozzle (not shown). 
       FIG. 11  is a side view of a section of a gas turbine with non-nesting spools, according to an embodiment of the present invention. In some embodiments, the gas turbine of  FIG. 11  may be present in one or more of  FIGS. 1-5 . Air enters the gas turbine through air intake  1100 . The gas turbine includes two non-nested spools, low pressure spool  1110  and high pressure spool  1120 . Low pressure spool  1110  has a low pressure compressor  1112 , a shaft  1114 , and a turbine  1116 . High pressure spool  1120  has a low pressure compressor  1122 , a shaft  1124 , and a turbine  1126 . Unlike with  FIG. 10 , low pressure spool  1110  is not nested within high pressure spool  1120 . While the drawing shows space between compressors  1112  and  1122  and the sides of the turbine, such space is not typically present in order to encourage air to flow through the compressors without a path around. Further, the number of spools and the location thereof, as well as which spool is actually driven, is a matter of design choice. Additionally, the spool that is being driven may not have a turbine, or at least have a turbine with a reduced size, power, and flow. Such a partial spool may thus be placed anywhere, which may improve packaging, flow, maintenance, etc. 
     Some embodiments of the present invention take advantage of dam head to supply flowing water that either directly or indirectly drives one or more stages of a compressor of a heat engine. The flowing water may either drive a power generation mechanism that drives the one or more compressor stages, or directly drive the one or more compressor stages via external blades on the compressor stages. In this manner, a virtually perpetual, and non-polluting, source of energy may be provided to power the one or more stages of the compressor, saving fuel and facilitating highly dispatchable power from the heat engine. 
     It should be noted that reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. 
     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
     One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.