Patent Publication Number: US-2017362963-A1

Title: Passive alternator depressurization and cooling system

Description:
This application claims the benefit of U.S. Prov. Appl. No. 62/093,544, filed Dec. 18, 2015. This application is incorporated herein by reference in its entirety to the extent consistent with the present application. 
    
    
     Waste heat is often created as a byproduct of industrial processes where flowing streams of high-temperature liquids, gases, or fluids must be exhausted into the environment or removed in some way in an effort to maintain the operating temperatures of the industrial process equipment. Some industrial processes use heat exchanger devices to capture and recycle waste heat back into the process. However, the capturing and recycling of waste heat is generally infeasible by industrial processes that use high temperatures, have insufficient mass flow, or include other unfavorable conditions. 
     Waste heat can be converted into useful energy by a variety of heat engine systems that employ thermodynamic methods, such as Rankine cycles. Rankine cycles and similar thermodynamic methods are typically steam-based processes that recover and use waste heat to generate steam for driving a turbine or other type of expansion device. The turbine is then connected to an electric generator, such as an alternator, which is used to supply electricity to an electrical bus or grid (e.g., an alternating current bus) that usually has a varying load or demand over time. 
     In certain circumstances, such as, for example, peak demand, alternators and associated components thereof (e.g., rotor, stator, and bearings) may be susceptible to overheating. To eliminate or reduce such overheating, methods employed have included cooling the alternator by using a blower or a fan to circulate gas or fluid through an external heat exchanger then through the alternator. However, using such cooling components (e.g., blower/fan, heat exchanger, piping, and valves) generally incurs additional expenses, increases installation and maintenance time, and creates a larger footprint. 
     Alternators may also be susceptible to over pressurization of the alternator cavity, which may occur when additional working fluid from the expansion device leaks past the bearings and seals encasing the rotor of the alternator. Over pressurization of the alternator often results in reduced efficiency, and in some instances, complete shutdown of the alternator. 
     What is needed, then, is a system for use in a heat engine system that efficiently cools the alternator and efficiently reduces pressure within the alternator as needed. 
     In one embodiment, a pressure reduction system may include an alternator. The alternator may include a casing and a rotor positioned, at least in part, within a cavity defined by the casing. The pressure reduction system may also include a mass management system having a control tank configured to be maintained at a tank pressure lower than a cavity pressure within the cavity of the alternator, thereby forming a pressure differential therebetween. A first transfer conduit may be configured to transfer a working fluid from the cavity of the alternator to the control tank via the pressure differential. 
     In another embodiment, a cooling system may include an alternator having a casing and a rotor positioned, at least in part, in a cavity defined by the casing. The cooling system may also include a mass management system having a control tank configured to be positioned at an elevation above the alternator. The control tank may include a refrigeration loop configured to cool a working fluid contained within the control tank. The cooling system may include a first transfer conduit fluidly coupling the alternator and the mass management system, and the first transfer conduit may be configured to transfer the working fluid from the cavity to the control tank. The cooling system may also include a second transfer conduit fluidly coupling the alternator and the mass management system, and the second transfer conduit may be configured to transfer the cooled working fluid from the control tank to the cavity via gravitational force. 
     In another embodiment, a heat engine system may include an expansion device in a working fluid circuit, and the expansion device may be configured to receive a working fluid at an expansion device inlet at a high pressure. The expansion device may output the working fluid at a low pressure, and further convert a pressure drop in the working fluid to mechanical energy. The heat engine system may include an alternator fluidly coupled to the expansion device. The alternator may convert the mechanical energy to electrical energy, and include a casing and a rotor positioned at least in part in a cavity defined within the casing. The cavity of the alternator may further be configured to receive a portion of the working fluid from the expansion device. The heat engine system may include a mass management system that includes a control tank configured to be maintained at a tank pressure substantially lower than a cavity pressure within the cavity to form a pressure differential therebetween. A first transfer conduit may be configured to transfer the working fluid from the cavity of the alternator to the control tank via the pressure differential. The heat engine system may include a pump fluidly coupled to the expansion device and configured to receive the working fluid at a low pressure and output the working fluid at a high pressure. A recuperator may be fluidly coupled to the pump and configured to heat the working fluid exiting the pump. The heat engine system may further include a waste heat exchanger fluidly coupled to the recuperator. The waste heat exchanger may be configured to further heat the working fluid after exiting the recuperator and before entering the expansion device. 
    
    
     
       The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  depicts an exemplary heat engine system including a system for depressurizing and cooling the alternator, according to one or more embodiments disclosed herein. 
         FIG. 2  depicts an exemplary system for depressurizing and cooling an alternator, according to one or more embodiments disclosed herein. 
         FIG. 3  is a graph depicting fluid friction loss and refrigeration work as a function of pressure in an alternator, according to one or more embodiments disclosed herein. 
     
    
    
     It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure. 
     Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. It should also be appreciated that the term “about,” as used herein, in conjunction with a numeral refers to a value that is +/−5% (inclusive) of that numeral, +/−10% (inclusive) of that numeral, or +/−15% (inclusive) of that numeral. It should further be appreciated that when a numerical range is disclosed herein, any numerical value falling within the range is also specifically disclosed. Furthermore, as it is used in the claims or specification, the term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein. 
     Embodiments of the disclosure generally provide a system for cooling and/or reducing pressure in an alternator. One or more embodiments of the disclosure also provide a heat engine system including the system for cooling and/or reducing pressure in the alternator. 
       FIG. 1  depicts a heat engine system  10  that includes a system  100  for heating and cooling an alternator  105 . The heat engine system  10  may also be referred to as a thermal engine system, an electrical generation system, a waste heat or other heat recovery system, and/or a thermal to electrical energy system, as described in one of more embodiments herein. The heat engine system  10  may include a waste heat system  12  and a power generation system  220  coupled to and in thermal communication with each other via a working fluid circuit  202 . The working fluid circuit  202  may contain the working fluid (e.g., sc-CO 2 ) and may have a high pressure side and a low pressure side, which will be described herein. A heat source stream  11  may flow through heat exchangers  20  and  30  disposed within the waste heat system  12 . Each of the heat exchangers  20  and  30 , independently, may be fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit  202 , configured to be fluidly coupled to and in thermal communication with a heat source stream  11 , and configured to transfer thermal energy from the heat source stream  11  to the working fluid within the high pressure side of the working fluid circuit  202 . Thermal energy may be absorbed by the working fluid within the working fluid circuit  202  and converted to mechanical energy by flowing the heated working fluid through one or more expanders or turbines. 
     The heat engine system  10  may further include at least one pump, such as a turbopump  260 , disposed within the working fluid circuit  202  and fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit  202 . The turbopump  260  may be configured to circulate and to pressurize the working fluid throughout the working fluid circuit  202 . The turbopump  260  may include a pump portion  262  coupled with a turbine  264 . The low pressure side of the working fluid circuit  202  extends from an outlet of the turbine  264  to the inlet of the pump portion  262  of the turbopump  260 . The high pressure side of the working fluid circuit  202  extends from the inlet of the pump portion  262  to the outlet of the turbine  264 . 
     The turbine  264  of the turbopump  260  may be fluidly coupled to the working fluid circuit  202  downstream of the heat exchanger  20  and the pump portion  262  of the turbopump  260  may be fluidly coupled to the working fluid circuit  202  upstream of the heat exchanger  20 . In one embodiment, the turbine  264  may be downstream of multiple heat exchangers, such as heat exchanger  20  and  30 , within the working fluid circuit  202 . In one example, the turbine  264  may be configured to receive and be powered by the working fluid passing through and absorbing thermal energy from the heat exchanger  20 . In one example, the turbine  264  may be configured to receive and be powered by the working fluid passing through and absorbing thermal energy from more than one heat exchanger, such as heat exchangers  20  and  30 . The turbopump  260  may further include a driveshaft  267  coupled between the turbine  264  and the pump portion  262 . 
     The turbine  264  may be fluidly coupled to and in thermal communication with the working fluid, and configured to convert thermal energy to mechanical energy by a pressure drop in the working fluid flowing between the high and the low pressure sides of the working fluid circuit  202 . An alternator  105  may be coupled to the turbine  264  and configured to convert the mechanical energy into electrical energy. A power outlet may be electrically coupled to the alternator  105  and configured to transfer the electrical energy from the alternator  105  to an electrical grid. The power generation system  220  may further include a driveshaft  230  coupled between the turbine  264  and the alternator  105 . In one embodiment, the driveshaft  267  may be integral with the driveshaft  230 , or may be a solitary driveshaft. The power generation system  220  may further contain a bearing housing  238  which substantially encompasses or encloses the bearings disposed within the power generation system  220 . 
     Exemplary structures of the bearing housing  238  may completely or substantially encompass or enclose the bearings as well as all or part of turbines, generators, pumps, driveshafts, or other components shown or not shown for the heat engine system  10 . The bearing housing  238  may completely or partially include structures, chambers, cases, housings, such as turbine housings, generator housings, driveshaft housings, driveshafts that contain bearings, gearbox housings, derivatives thereof, or combinations thereof.  FIG. 1  depicts the bearing housing  238  containing all or a portion of the turbine  264 , the alternator  105 , the driveshafts  230  and  267 , and the pump portion  262  of the power generation system  220 . In some examples, the housing of the turbine  264  may be coupled to and/or forms a portion of the bearing housing  238 . 
       FIG. 2  shows the alternator  105  in more detail, and also depicts the system  100  for depressurizing and cooling the alternator  105 . The alternator  105  may include a casing  110  defining a cavity  115  in which, at least in part, a rotor  125  is positioned and configured to spin at high speed. The rotor  125  may be integral with the driveshafts  230  or  267 , or the rotor  125  may form a solitary driveshaft with the driveshafts  230  and/or  267 . In one embodiment, the rotor  125  may have a rotational speed between about 20,000 RPM and about 40,000 RPM. The cavity  115  may contain a working fluid, which in one embodiment, may be or include carbon dioxide. Further, in one embodiment, the working fluid may be carbon dioxide and at least a portion of the working fluid may be in a supercritical state. However, other working fluids including, but not limited to ammonia and a combination of working fluids, are contemplated. The working fluid in the cavity  115  may be contained within the alternator  105  by a shaft seal  120  positioned between the rotor  125  and the casing  110  at one end of the alternator  105 . The shaft seal  120  may be a labyrinth seal, a double seal, a dynamically pressure balanced seal, a dry gas seal, or any other sealing mechanism configured to reduce leakage flow of the working fluid into or out of the casing  110 . 
     The system  100  for depressurizing and cooling the alternator  105  may include a mass management system  150  configured to control the pressure and temperature within the cavity  115  of the alternator  105 . As discussed in more detail below, the mass management system  150  may include a control tank  155  configured to receive and store working fluid from the alternator  105  and, in addition, to disperse working fluid to the alternator  105 . The control tank  155  may be maintained at a relatively low pressure, such as, for example, about 0.5 MPa to about 2 MPa. 
     The mass management system  150  may include a closed refrigeration loop  160  positioned, at least in part, within the control tank  155  in order to maintain a low pressure of the working fluid within the control tank  155 . The refrigeration loop  160  may include a cool fluid source  161 , which may be water, seawater, nitrogen, or any other fluid, that may flow through a conduit into the control tank  155 . The cooled fluid may flow through a condenser  162  to further condense the cooled fluid. After condensing the cooled fluid, the cooled fluid may flow through a heat exchanger  163 , wherein heat is transferred from the working fluid to the cooled fluid, and wherein the fluid flows into a compressor  164  and out to the cooled fluid source. The closed refrigeration loop  160  may therefore cool the working fluid contained within the control tank  155 . The pressure of the control tank  155  may be lower than the pressure within the alternator  105 , which may be, for example, around about 0.5 MPa to about 11 MPa. In one embodiment, the control tank  155  may be positioned at an elevation above the alternator  105 . 
     The system  100  may include a first transfer conduit  130  fluidly coupling the alternator  105  and the mass management system  150 , thereby forming a first fluid passageway therebetween. More specifically, the first transfer conduit  130  may fluidly couple the cavity  115  of the alternator  105  and the control tank  155 . In one embodiment, the first transfer conduit  130  may provide the first fluid passageway between a lower portion of the alternator  105  and an upper portion of the control tank  155 . 
     The first transfer conduit  130  may include a valve  135  positioned within the first fluid passageway between the alternator  105  and the control tank  155  and configured to control fluid flow therebetween. As such, the valve  135  may prevent or throttle the flow of working fluid between the alternator  105  and the control tank  155 . In one embodiment, the valve  135  may be a check valve to prevent working fluid from flowing from the control tank  155  to the alternator  105  via the first transfer conduit  130 . The system  100  may also include a heat exchanger  140  fluidly coupled with the first transfer conduit  130  and configured to cool the working fluid moving from the alternator  105  to the control tank  155  prior to the working fluid entering the control tank  155  in order to reduce the cooling duty of the closed refrigeration loop  160 . 
     As previously discussed, the control tank  155  may be maintained at a lower pressure than the cavity  115  of the alternator  105 . Therefore, working fluid may flow through the first transfer conduit  130 , from the alternator  105  to the control tank  155 , based on a positive pressure differential. Such flow may be passive, or in other words, without aid of a pump or other like equipment. In addition, the positive pressure differential may allow working fluid to be transferred from the alternator  105  to the control tank  155  to optimize the operation of the alternator  105 . For example, the pressure within the cavity  115  may increase as working fluid from the turbine  264  leaks past the shaft seal  120  into the cavity  115 . As shown in  FIG. 3 , a higher fluid pressure within the cavity  115  results in greater power loss within the alternator  105 . However, in embodiments of the system  100  described herein, as working fluid leaks past the turbine  264  shaft seal  120  and into the cavity  115 , working fluid may flow from the alternator  105  to the control tank  155  via the first transfer conduit  130  based on the pressure differential between the cavity  115  and the control tank  155  to prevent additional power loss. In one embodiment, the flow rate of the working fluid from the cavity  115  to the control tank  155  may be about 600 grams per second. The flow rate may be dependent on, amongst other factors, the leak rate of working fluid from the turbine  264  to the alternator  105 . 
     The system  100  further includes a second transfer conduit  165  fluidly coupling the mass management system  150  and the alternator  105 . More specifically, the second transfer conduit  165  may fluidly couple the control tank  155  and the cavity  115  of the alternator  105  to form a second fluid passageway therebetween. In one embodiment, the second transfer conduit  165  may form the second fluid passageway between a lower portion of the control tank  155  and an upper portion of the alternator  105 . The second transfer conduit  165  may include a valve  170  positioned within the second fluid passageway between the control tank  155  and the alternator  105  and configured to control fluid flow therebetween. As such, the valve  170  may prevent or throttle the flow of working fluid between the control tank  155  and the alternator  105 . In one embodiment, the valve  170  may be a check valve to prevent fluid from flowing from the alternator  105  to the control tank  155  via the second transfer conduit  165 . 
     As discussed, the control tank  155  may be positioned at an elevation above the alternator  105 , such that working fluid may be gravity fed via the second transfer conduit  165  from the control tank  155  to the cavity  115  of the alternator  105 . In one embodiment, the working fluid may exit the control tank  155  at a flow rate of about 500 grams per second. In other embodiments, the flow rate of the working fluid exiting the control tank  155  may be greater or lesser depending on, amongst other factors the windage within the cavity  115  and the elevation of the control tank  155  above the alternator  105 . Further, because the working fluid within the control tank  155  may be cooled by the refrigeration loop  160 , the working fluid flowing from the control tank  155  to the alternator  105  may cool the alternator  105 , which may be heated by the fluid friction (windage) generated by the rotation of the rotor  125  within the cavity  115  of the alternator  105 . Because the control tank  155  may be vertically positioned at an elevation above the alternator  105 , the cooling of the alternator  105  may be accomplished in a passive manner. 
     The system  100  may also include a return conduit  175  fluidly coupled with the second transfer conduit  165  at a location  185  between the control tank  155  and the alternator  105 . The return conduit  175  may be configured to transfer working fluid from the second transfer conduit  165  to the heat engine system  10 . A transfer pump  180  may be fluidly coupled with the return conduit  175  and configured to maintain a relatively constant amount of mass in the heat engine system  10  by transferring the working fluid from the mass management system  150  to the heat engine system  10  at a flow rate relatively equal to the flow rate of the working fluid entering the alternator  105  through the shaft seal  120  from the heat engine system  10 . In one embodiment, the flow rate of the working fluid through the return conduit  175  may be about 100 grams per second. In other embodiments, the flow rate of the working fluid through the return conduit  175  may be greater or lesser depending, amongst other factors, on the leak rate of working fluid from the turbine  264  to the alternator  105 . 
     In operation, the rotor  125 , which may be driven by the turbine  264 , may rotate at a high speed, e.g., about 20,000 RPM to about 40,000 RPM, within the cavity  115  at least partially filled with working fluid. In operation, as the rotor  125  rotates, working fluid may leak past the shaft seal  120  and into the cavity  115  from the turbine  264  of the heat engine system  10 . The additional working fluid entering the cavity  115  may result in an increase of pressure within the cavity  115 . Further, the rotation of the rotor  125  may induce fluid friction which leads to heating, or windage. As shown in  FIG. 3 , power loss within the alternator  105  increases as fluid pressure increases within the cavity  115  inducing windage. Accordingly, if the rotor  125  continues to rotate within the cavity  115  without intervention, the temperature within the alternator  105  will increase, which may lead to overheating. However, in the system  100  provided herein, as working fluid leaks into the cavity  115 , working fluid may flow from the alternator  105  to the control tank  155  via the first transfer conduit  130  based on the pressure differential between the cavity  115  and the control tank  155 . 
     The working fluid in the control tank  155  may be cooled by the mass management system  150  via the refrigeration loop  160 . Because the control tank  155  may be positioned at an elevation above the alternator  105 , the cooled working fluid may be transferred to the alternator  105  via the second transfer conduit  165  by gravitational force, thereby cooling the alternator  105 . In addition, as working fluid is added to the system  100  from leakage through the shaft seal  120 , working fluid may be returned back to the heat engine system  10  via the return conduit  175  and the transfer pump  180  as the working fluid flows out of the control tank  155 . 
     Turning back to the heat engine system  10  illustrated in  FIG. 1 , the heat engine system  10  may further include at least one recuperator  216  fluidly coupled to the working fluid circuit and operative to transfer thermal energy between the high and low pressure sides of the working fluid circuit  202 . In some examples, the recuperator  216  may be configured to transfer the thermal energy from the low pressure side to the high pressure side. The heat engine system  10  may further include a cooler  274  in thermal communication with the working fluid contained in the low pressure side of the working fluid circuit  202  and configured to remove thermal energy from the working fluid in the low pressure side. In some examples, the cooler  274  may be a condenser configured to control a temperature of the working fluid in the low pressure side of the working fluid circuit  202  by transferring thermal energy from the working fluid in the low pressure side to a cooling loop outside of the working fluid circuit  202 . 
     In one embodiment, the cooler  274  may circulate a coolant from a cooling circuit  200  to cool the working fluid contained in the low pressure side of the working fluid circuit  202 . In one embodiment, the coolant circulating through the cooling circuit  200  may be water, such as freshwater. A pump  210  may be disposed within the cooling circuit  200  to circulate the coolant through the cooling circuit  200 . A cooler  215  may also be disposed within the cooling circuit  200  to transfer thermal energy from the coolant moving through the cooling circuit  200 . In one embodiment, the cooler  215  may circulate seawater to transfer thermal energy from the coolant to the seawater. For example, seawater may enter the cooler  215  via an inlet line  212 , and seawater may exit the cooler  215  via an outlet line  214 . 
     The heat engine system  10  may also include another mass management system (MMS)  270  fluidly coupled to the working fluid circuit  202 . The MMS  270  may include a mass control tank  286  fluidly coupled to the low pressure side of the working fluid circuit  202  and configured to receive, store, and deliver the working fluid. The mass control tank  286  and the working fluid circuit  202  may share the working fluid (e.g., carbon dioxide) such that the mass control tank  286  may receive, store, and disperse the working fluid during various operational steps of the heat engine system  10 . In one embodiment, the mass control tank  286  may receive additional working fluid via a feed line inlet  288 . 
     The MMS  270  may include an inventory return line  72  fluidly coupled to and between the mass control tank  286  and the low pressure side of the working fluid circuit  202 , such as downstream of the condenser  274 . As depicted in  FIG. 1 , a fluid line  68  may be fluidly coupled with and extend from the outlet of the condenser  274 , and the inventory return line  72  may be fluidly coupled to and extend from the fluid line  68  to the mass control tank  286 . The MMS  270  may also include a pump  70  fluidly coupled to the mass control tank  286  and configured to transfer the working fluid from the mass control tank  286  to the low pressure side of the working fluid circuit  202  by an inventory supply line  82 . Accordingly, the MMS  270  may receive the working fluid from the working fluid circuit  202 , store the working fluid for subsequent use, and deliver the working fluid into the working fluid circuit  202 . 
     It is contemplated that the mass management system  270  for use with the pump portion  282  of the heat engine system  10  may be combined with the mass management system  150  for use with the alternator  105 , as described above. To that extent, the mass control tank  286  of the heat engine system  10  for use with the pump portion  282  and the control tank  155  of the mass management system  150  for use with the alternator  105  may be combined into a single tank. The single tank may control the addition and/or removal of working fluid to the high pressure side of the heat engine system  10 , the low pressure side of the heat engine system  10 , and/or the alternator cavity  115 . 
     The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.