Abstract:
A multi-stage refrigerant driven turbine is incorporated into a closed loop system to generate electricity. Heat transfer conduits and optional flow diverting members are disposed between the rotor blades of each stage of the turbine. The closed loop system also includes a condenser, pump, refrigerant storage container, refrigerant, and expansion valve. A heat source and heat sink are also provided. The expansion valve introduces a saturated refrigerant mist into the turbine, and the refrigerant expands as it flashes to a gas, thereby rotating the rotor blades and turbine shaft. Heat from the heat source is added between stages to increase the portion of refrigerant converted to gas. The gas is passed from the turbine, condensed, and passed as a liquid to storage or to repeat the cycle. The blending of refrigeration cycle and turbine technologies allows electricity to be generated in a closed loop system under moderate conditions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to electricity generation using a turbine and, more particularly, to electricity generation using a multi-stage turbine.  
         [0002]     There has long been a desire to find alternative sources for generating electricity. Solar power panels are known in the art but are limited in their use, because they generate DC power only. Windmills are also well known in the art and have been used for generating AC power. Still, difficulties in finding appropriate locations for windmills, and fluctuations in wind force and direction limit their use and reliability.  
         [0003]     Turbines and multi-stage turbines are known in the art. In gas turbines, compressed air is forced into an ignition chamber and combined with fuel, and the fuel is ignited. The expanding, ignited gases travel along the axis of the turbine shaft, imparting motion to rotor blades affixed to the turbine shaft, thereby rotating the shaft. Additional fuel, or after burner fuel, is sometimes added downstream of the ignition chamber to increase the power output. In steam turbines, water is boiled to generate steam, the steam is passed through a throttle valve, and the expanding steam travels along the axis of the turbine shaft, imparting motion to rotor blades affixed to the turbine shaft, thereby rotating the shaft. Additional steam is sometimes added downstream of the throttle valve to increase the power output. Gas turbines and steam turbines are capable of generating reliable A/C power but suffer from a number of disadvantages. For example, these turbines require fuels that are non-renewable or that are not readily renewable. The extreme conditions typically encountered in these turbines also adds to the cost and complexity of the equipment and materials of construction that must be used. These extreme conditions also lead to high maintenance cost, increased wear and tear, and short equipment life. The high energy input needed to maintain the extreme conditions also leads to high cost for power generation.  
         [0004]     Refrigeration cycles are also well known in the art. In a typical refrigeration cycle, a refrigerant gas is compressed and passed to a heat sink or condenser. As the heat sink removes heat from the high temperature, high pressure gas, the gas condenses to liquid form. The condensed liquid is passed through an expansion valve so that it moves from a high pressure area to a low pressure area. As the liquid moves from through the expansion valve, the liquid expands and evaporates. The expanding, evaporating gas is passed to a heat source, such as an interior of a refrigerator or freezer. The heat required to convert the liquid to gas is drawn from the heat source, thereby cooling the heat source. The refrigerant gas is then returned to the compressor to repeat the cycle. Refrigeration cycles have provided reliable cooling for years. Still, the use of a compressor in a refrigeration cycle increases the cost and complexity of the system and also increases the energy consumption and therefore operation cost of the system. Using a compressor can also add to the cost and complexity of maintaining a refrigeration cycle.  
       SUMMARY OF THE INVENTION  
       [0005]     It is therefore an object of the present invention to provide an apparatus and method for efficiently generating electricity.  
         [0006]     It is a further object of the present invention to provide an apparatus and method of the above type that is capable of using a wide variety of heat sources and heat sinks to provide a reliable source of A/C power.  
         [0007]     It is a still further object of the present invention to provide an apparatus and method of the above type that generates A/C power using solar energy.  
         [0008]     It is a still further object of the present invention to provide an apparatus and method of the above type that combines turbine technology and refrigeration cycle technology to provide a safe and efficient way of generating electricity.  
         [0009]     It is a still further object of the present invention to provide an apparatus and method of the above type that uses a refrigerant to drive a turbine.  
         [0010]     It is a still further object of the present invention to provide an apparatus and method of the above type that uses a refrigerant to drive a multi-stage turbine.  
         [0011]     It is a still further object of the present invention to provide an apparatus and method of the above type that offers an environmentally friendly way to generate electricity.  
         [0012]     It is a still further object of the present invention to provide an apparatus and method of the above type that operates under more moderate conditions than traditional turbines.  
         [0013]     It is a still further object of the present invention to provide an apparatus and method of the above type that operates without the need for the added cost and complexity of a compressor such as typically used in a refrigeration cycle.  
         [0014]     It is a still further object of the present invention to provide an apparatus and method of the above type that provides a safe, efficient closed loop system for generating electricity.  
         [0015]     It is a still further object of the present invention to provide an apparatus and method of the above type that may be constructed using less costly materials of construction because of the more moderate operating conditions.  
         [0016]     It is a still further object of the present invention to provide an apparatus and method of the above type that provides for reduced operating and maintenance expenses and for increased operating life.  
         [0017]     It is a still further object of the present invention to provide an apparatus and method of the above type that makes efficient use of waste heat from other processes.  
         [0018]     It is a still further object of the present invention to provide an apparatus and method of the above type that allows waste heat from a wide variety of sources to be used to provide a reliable source of A/C power.  
         [0019]     Toward the fulfillment of these and other objects and advantages, the present invention comprises a multi-stage, refrigerant driven turbine, a closed loop system into which it is incorporated, and a method of operating the system. A multi-stage refrigerant driven turbine is incorporated into a closed loop system to generate electricity. Heat transfer conduits and optional flow diverting members are disposed between the rotor blades of each stage of the turbine. The closed loop system also includes a condenser, pump, refrigerant storage container, refrigerant, and expansion valve. A heat source and heat sink are also provided. The expansion valve introduces a saturated refrigerant mist into the turbine, and the refrigerant expands as it flashes to a gas, thereby rotating the rotor blades and turbine shaft. Heat from the heat source is added between stages to increase the portion of refrigerant converted to gas. The gas is passed from the turbine, condensed, and passed as a liquid to storage or to repeat the cycle. The blending of refrigeration cycle and turbine technologies allows electricity to be generated in a closed loop system under moderate conditions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The above brief description, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawing, wherein:  
         [0021]      FIG. 1  is a schematic representation of a system of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     Referring to  FIG. 1 , reference numeral  10  refers in general to a refrigerant system of the present invention. The system includes an expansion valve  12 , a turbine  14 , a condenser  16 , a pump  18 , and refrigerant  20  and may include a refrigerant storage reservoir or container  22 . A heat source  24  and heat sink  26  are also provided.  
         [0023]     The expansion or throttling valve  12  of the refrigerant system  10  may take the form of any number of different commercially available throttle valves or spray nozzles. The valve  12  has speed or load governing controls, and the size and capacity of the valve depend upon a variety of system parameters, such as size and operating conditions. Multiple valves  12  may be used and may be positioned at different locations to help control load. The valve  12  may also admit refrigerant  20  directly to the turbine  14 , or may admit the refrigerant to an evaporator or heat exchanger before the refrigerant  20  is passed to the turbine  14 .  
         [0024]     In a preferred embodiment, the turbine  14  is an axial flow, multi-stage turbine. The housing or casing  28  has a front, upstream end  30  and a rear, downstream end  32 . An outer wall of the housing  28  generally diverges from front to back. A turbine shaft  34  is disposed partially within the housing  28 , and rotor blades  36   a ,  36   b ,  36   c  are affixed to the shaft  34 , positioned along the length of the shaft  34  so that they are disposed in different stages of the turbine  14 . Steam turbines operating at relatively high velocities, pressures, and temperatures are subject to blade impingement from entrained moisture in the steam, and rotor blades can be permanently damaged by the water. As a result, rotor blades in steam turbines must be of very rugged construction, placing significant restrictions on the types of materials from which the blades may be constructed. In contrast, due to the relatively modest velocities, pressures and temperatures in which the present turbine  14  should operate many fewer restrictions are placed on the materials of construction of the rotor blades  36   a ,  36   b ,  36   c  and other components. The rotor blades  36   a ,  36   b , and  36   c  may be constructed of any number of materials, including but not limited to aluminum, composites, plastics, or various blends or combinations of those and other components. For example, the blades  36   a ,  36   b , and  36   c  may comprise at least approximately 20% of a material selected from the group consisting of aluminum, composites, plastics, and combinations thereof. Further, because of the more moderate operating conditions, the rotor blades  36   a ,  36   b , and  36   c  will not require the closely machined tolerances or shrouded blade tips typically required in steam turbines. The turbine  14  stages and reduction gearing may be arranged as in any conventional turbine design, with the number of stages and the reduction ratio dependent upon the specific system flow capabilities. Due to the relatively moderate temperatures within the turbine  14 , the reduction gears may be disposed within the housing between each stage.  
         [0025]     An axially aligned, frustoconical inner turbine wall  38   a  diverging from front to back is positioned in close proximity to the rotor blades  36   a  in the first stage of the turbine  14 . Each rotor blade  36   a  extends a distance radially from the shaft  34 , and that distance increases with distance from the front of the stage so that an outer edge of each rotor blade  36   a  is maintained in close proximity to the diverging inner turbine wall  38   a . The rear end of the first diverging turbine wall  38   a  is aligned at or near the last rotor blade  36   a  of the first stage.  
         [0026]     A flow diverting member  40   a  is centrally positioned in the housing, disposed between the rotor blades  36   a  of the first stage and the rotor blades  36   b  of the second stage, the shaft  34  passing through an opening in the member  40   a . Front portions of the member  40   a  are disposed between the inner turbine wall  38   a  and the outer turbine wall  28 , and forward portions of the member  40   a  extend forward and downstream of the back end of the inner wall  38   a  and forward and downstream of at least one of the rotor blades  36   a  in the first stage. The flow diverting member  40   a  is affixed within the turbine  14  so that it does not move relative to the inner turbine wall  38   a.    
         [0027]     Heat transfer conduits  42   a ,  42   b , and  42   c , such as a tube bank, are disposed along or within the turbine  14  between each stage to create a regeneration area. In a preferred embodiment, tubes extend into the flow path of the refrigerant  20 , aligned generally transverse to the flow path. It is of course understood that the conduits  42   a ,  42   b , and  42   c  may take any number of forms, such as one or more tubes or jackets lining the housing or extending into the flow path within the housing  28 . The heat transfer conduits  42   a ,  42   b , and  42   c  will typically be sized and disposed to provide for greater heat transfer to later stages within the turbine  14 . The regeneration areas assist in eliminating the need for a compressor, as is typically used in convention refrigeration cycles. The use of saturated vapor and regeneration areas helps to compensate for the low enthalpy of the refrigerant  20  as compared to steam.  
         [0028]     A second axially aligned, frustoconical inner turbine wall  38   b  diverging from front to back is positioned in close proximity to the rotor blades  36   b  in the second stage of the turbine  14 . Each rotor blade  36   b  in the second stage extends a distance radially from the shaft  34 , and that distance increases with distance from the front of the stage so that an outer edge of each rotor blade  36   b  is maintained in close proximity to the diverging inner turbine wall  38   b . The rear end of the second diverging turbine wall  38   b  is aligned at or near the last rotor blade  36   b  of the second stage. The rotor blades  36   b  of the second stage generally extend a greater distance radially from the axis than do the rotor blades  36   a  of the first stage.  
         [0029]     A second flow diverting member  40   b  is centrally positioned in the housing  28 , disposed between the rotor blades  36   b  of the second stage and the rotor blades  36   c  of the third stage, the shaft  34  passing through an opening in the member  40   b . Front portions of the member  40   b  are disposed between the inner turbine wall  38   b  and the outer turbine wall  28 , and forward portions of the member  40   b  extend forward and downstream of the back end of the inner wall  38   b  and forward and downstream of at least one of the rotor blades  36   b  in the second stage.  
         [0030]     Similar to the regeneration area between the first and second stages, heat transfer conduits  42   b , such as a tube bank, are disposed along or within the turbine  14  between the second and third stages to create a second regeneration area.  
         [0031]     Additional stages are provided as needed. For example, another axially aligned, frustoconical inner turbine wall  38   c  diverging from front to back is positioned in close proximity to the rotor blades  36   c  in the third stage of the turbine  14 . Each rotor blade  36   c  in the third stage extends a distance radially from the shaft  34 , and that distance increases with distance from the front of the stage so that an outer edge of each rotor blade  36   c  is maintained in close proximity to the diverging inner turbine wall  38   c . The rear end of the third diverging turbine wall  38   c  is aligned at or near the last rotor blade  36   c  of the third stage. The rotor blades  36   c  of the third stage generally extend a greater distance radially from the axis than do the rotor blades  36   a  and  36   b  of the first and second stages. Additional flow diverting members and regeneration areas are provided for the additional stages as needed.  
         [0032]     It is of course understood that most common turbine designs may be used, including but not limited to radial flow, axial flow, horizontal, vertical, and with or without pressure and velocity compounding. Casing or housing pressure requirements will depend on factors such as the type of refrigerant  20  used and the maximum operational pressures and temperatures expected. The casing may also be designed as a hermetic unit with an internal casing dividing the stages rated at system differential pressure, and an outer casing rated at overall system pressure.  
         [0033]     The downstream or discharge end of the multistage turbine  14  is connected to a condenser  16 . The condenser  16  may take the form of any number of commercially available condensers. The condenser  16  is sized for the expected operating parameters of the particular system to provide sufficient heat transfer to condense the refrigerant gas into liquid. The condenser  16  cooling may be of the direct type, in which the refrigerant  20  in the closed loop system is cooled directly by the heat sink  26 , or of the indirect type, in which a cooling medium such as water is used to transfer heat between the condenser  16  and the heat sink  26 . As used herein, “direct” cooling or heating is not intended to mean or imply direct contact between the refrigerant  20  and the heating or cooling fluid. Under rare circumstances, such direct contact or commingling may be used, but not in the preferred embodiment.  
         [0034]     A line  44  connects the condenser  16  to the refrigerant reservoir  22 , and a feed pump  18  is provided in the line  44  for transferring liquid refrigerant  20  to the reservoir  22  or expansion valve  12 , depending on system load requirements. The pump  18  is sized as needed to meet the pressure and flow requirements of the particular system. The refrigerant  20  may take the form of any number of different commercially available refrigerants. The refrigerant  20  preferably has a boiling point at 14.7 psi that is less than or equal to approximately 10° F. and more preferably has a boiling point at 14.7 psi that is less than or equal to approximately 32° F. The refrigerant  20  is most preferably selected from the group consisting of R- 11 , R- 12 , R- 13 , R- 134   a , R- 142   b , R- 152 A, R- 290 , R- 410   a , R- 404   a , R- 600 , R- 600   a , a hydrofluorocarbon, a chlorofluorocarbon, CO 2 , ammonia, nitrogen, freon, and combinations thereof. Because of the refrigerant or refrigerants being used, the refrigerant system  10  is preferably a closed loop system. The refrigerant system  10  may be designed as hermetic or semi-hermetic depending upon the application.  
         [0035]     The heat source or heating system  24  is preferably an indirect heat collection system  24  that uses a secondary medium, such as water, to collect and transfer heat from the heat source  24  to the refrigerant system  10 . The heating system  24  is connected to the heat transfer conduits  42   a ,  42   b , and  42   c  in the refrigerant system  10 . The heating system  24  will have relatively moderate operating conditions. For example, there are relatively low pressure requirements since the transfer medium is merely circulating. Accordingly, lower cost materials, such as plastic and PVC pipe and tubing may be used. Using this indirect heating system  24  allows great flexibility in positioning and configuring the refrigerant system  10  relative to the heat source  24 .  
         [0036]     The heat source  24  may take any number of forms ranging from solar panels to a heat exchanger used to dissipate or disperse waste heat from large-scale industrial activities. Any number of different conventional sources of heat, or combinations thereof, may be used, including heat sources  24  that have heretofore not been used for generating AC power. Water is preferably used to acquire heat from the heat source  24  and to transfer that heat to the refrigerant  20  in the refrigerant system  10 . Pump  46  circulates the water between the heat source  24  and the heat transfer conduits  42   a ,  42   b , and  42   c  of the refrigerant system  10 .  
         [0037]     The heat sink or cooling system  26  is preferably an indirect heat collection system that uses a secondary medium, such as water, to absorb heat from the condenser  16  and transfer it to the heat sink  26 . The heat sink  26  is connected to the cooling coils  48  in the condenser  16 . The cooling system  26  will have relatively moderate operating conditions. For example, there are relatively low pressure requirements since the transfer medium is merely circulating. Accordingly, lower cost materials, such as plastic and PVC pipe and tubing may be used. Using this indirect cooling system  26  allows great flexibility in positioning and configuring the refrigerant system  10  relative to the heat sink  26 .  
         [0038]     The heat sink  26  may take any number of forms such as reservoirs, streams, bodies of water, the atmosphere, buried pipes, cooling towers, other things and systems typically used to dissipate or disperse heat, and combinations thereof. Water is preferably used to absorb heat from the condenser  16  and to transfer that heat to the heat sink  26 . Pump  50  circulates the water between the heat sink  26  and the condenser  16  of the refrigerant system  10 .  
         [0039]     In operation, pump  46  passes a heating medium, such as water, through line  52  and through the heat source  24 . The water absorbs heat and passes through line  54  to the heat transfer conduits  42   a ,  42   b , and  42   c , located in the regeneration areas of the refrigerant system  10 , to transfer heat to the refrigerant  20  passing through the turbine  14 . The water then passes through line  56  and back through the pump  46  to begin another cycle. It is of course understood that any number of heating systems  24  and heating mediums may be used and that any number of things may serve as the heat source  24 .  
         [0040]     Refrigerant  20  passes through the expansion or throttling valve  12  and expands through the diverging inner turbine wall  38   a  as it flashes to a gas, thereby rotating the first set of rotor blades  36   a  and the turbine shaft  34 . The refrigerant  20  exits this first stage in the form of a heavily saturated mist. A first flow diverting member  40   a  redirects the refrigerant  20  so that it passes downstream of but forward of at least one of the first set of rotor blades  36   a , through a first regeneration area. Heat transfer conduits  42   a  in the first regeneration area transfer heat to the gas, increasing the portion of the refrigerant  20  that is converted to gas. Some of the entrained refrigerant droplets boil, or flash off into vapor before being directed through the second diverging inner turbine wall  38   b  and through the second set of turbine blades  36   b . A second flow diverting member  40   b  redirects the refrigerant  20  so that it passes downstream of but forward of at least one of the second set of rotor blades  36   b , through a second regeneration area. Heat transfer conduits  42   b  in the second regeneration area transfer additional heat to the gas, increasing the portion of the refrigerant  20  that is converted to gas. The refrigerant  20  is then directed through the third diverging inner turbine wall  38   c  and third set of turbine blades  36   c . Additional stages are used as desired. The rotating shaft  34  is used to perform work, such as to generate AC power. It is of course understood that the system may be used to generate DC power or to perform work in any number of different forms.  
         [0041]     Upon leaving the final turbine stage, the refrigerant  20  is in the form of a high temperature, high pressure gas. The refrigerant  20  is then directed to the condenser  16 . In the condenser  16 , the water in the cooling coils  48  absorbs heat from the refrigerant  20  and transfers it to the heat sink  26 . Sufficient heat is removed to cause the refrigerant  20  to condense into liquid form and gather at the bottom of the condenser  16 . Feed pump  18  then transfers the liquid refrigerant  20  via line  44  to the reservoir  22  or back to the throttle valve  12 , depending upon the load on the refrigerant system  10 .  
         [0042]     Pump  50  passes a cooling medium, such as water, through line  58  and through the cooling coils  48  of the condenser  16 . The water absorbs heat in the condenser  16  and then passes through line  60  to the heat sink  26  for cooling. The water then passes through line  62  and back through the pump  50  to begin another cooling cycle. It is of course understood that any number of cooling systems  26  and cooling mediums may be used and that any number of things may serve as the heat sink  26 .  
         [0043]     Other modifications, changes and substitutions are intended in the foregoing, and in some instances, some features of the invention will be employed without a corresponding use of other features. For example, the heating system  24  and cooling system  26  may be open loop, closed loop, or hybrids of the same. Although it is preferred that the refrigerant system  10  be closed loop, it is understood that the refrigerant system  10  may also be open loop, closed loop, or hybrids of the same. Further, the heating system  24 , refrigerant system  10 , and cooling system  26  may but are not required to have associated reservoirs for accommodating fluctuating loads. Further still, the turbine  14  may or may not include flow diverter members disposed therein, and, if included, any number of different shapes, configurations, and flow patterns may be used. It is of course understood that all quantitative information is given by way of example only and is not intended to limit the scope of the present invention.