Abstract:
A Rankine cycle device includes a heat exchanger for supplying heat to a working fluid and an expansion device for expanding the working fluid. A valve is disposed between the heat exchanger and the expansion device and a cooling device is reduces a temperature of the working fluid. A pump moves the working fluid through the Rankine cycle device and a sensor is used to sense a pressure of the working fluid. A controller is operable to open the valve based upon the sensed pressure of the working fluid.

Description:
BACKGROUND OF THE INVENTION 
     The field of the present disclosure relates generally to Rankine cycle devices. More particularly, the present disclosure relates to systems and methods for cold startup of Rankine cycle devices. 
     Rankine cycle devices use a working fluid in a closed-loop cycle to gather heat from a heating source, or a heat reservoir, by generating a hot gaseous stream. The hot gaseous stream is expanded through a turbine to generate power, typically electrical power. The expanded stream is then condensed in a condenser by transferring heat from the expanded stream to a cold reservoir. The working fluid remains in a closed loop and is repeatedly sent through the Rankine cycle. 
     The efficiency of Rankine cycle devices, such as Organic Rankine Cycle (ORC) devices, in a low-temperature heat recovery application is sensitive to temperatures of the hot and cold reservoirs between which they operate. In an ORC device, the working fluid is an organic, high molecular mass fluid with a liquid-vapor phase change, or boiling point, occurring at a lower temperature than the water-steam phase change point. Typically, the temperatures of the reservoirs change significantly during the lifetime of the plant. Geothermal plants, for example, may be designed for a particular temperature of a geothermal heating fluid from the earth, but lose efficiency as the ground fluid cools over time. Air-cooled ORC plants that use an exhaust at a constant temperature from a larger plant as heating fluid deviate from their designed operating conditions as outside air temperature changes. 
     Typically, ORC plant designs encounter unreliable cold startup conditions because the working fluid condenses and settles inside the loop, rather than in the feed vessel, after the ORC plant shuts down. Plant start-up thus may become difficult, or fail altogether, with the working fluid blocking the expansion device during cold startup conditions. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect a Rankine cycle device includes a heat exchanger configured to supply heat to a working fluid and an expansion device configured to expand the working fluid. A valve is disposed between the heat exchanger and the expansion device and a cooling device is configured to reduce a temperature of the working fluid. A pump is configured to flow the working fluid through the Rankine cycle device and a sensor is configured to sense a pressure of the working fluid. A controller is configured to open the valve based upon the sensed pressure of the working fluid. 
     In another aspect a method of operating a Ranking Cycle device includes closing a valve to prevent a working fluid contained within the device from entering an expansion device and heating a working fluid contained within the Rankine cycle device until the working fluid reaches a predetermined pressure. The valve is opened and the working fluid is supplied to a feeding vessel configured to supply the working fluid to a pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an exemplary embodiment of the present disclosure. 
         FIG. 2  is a flowchart showing an exemplary method of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an exemplary embodiment of a Rankine cycle device  100  according to the present disclosure. Rankine cycle device  100  includes a heat exchanger  102  configured to receive heat from an external source  104  to heat a high pressure stream of working fluid  106 . In one embodiment, the working fluid is an organic, high molecular mass fluid. A pressure sensor  108  is disposed downstream of heat exchanger  102  and senses a pressure of working fluid  106 . Rankine cycle device  100  also includes an expansion device  110 , such as a turbine expansion device, that allows the high pressure stream of working fluid  106  to expand to expanded stream  112 . Expanded stream  112  is supplied to a cooling device  114  and a feed vessel  116 . Subsequently, the feed vessel supplies working fluid to pump  118 . 
     Upstream of expansion device  110  is a high pressure side  120  of the Rankine cycle device, and downstream of expansion device  110  is low pressure side  122 . Pump  118  is configured to pump working fluid from low pressure side  122  to high pressure side  120  via a check valve  124 . In one embodiment, check valve  124  is a one-way valve that allows the working fluid to pass therethrough in only one direction, for example, to prevent backflow into pump  118 . 
     The stream of working fluid leaves pump  118  and enters heat exchanger  102 . Heat exchanger  102  receives a heat input  126  from external source  104  to heat the working fluid  106 . In one embodiment, heat input  126  is a hot exhaust gas from an internal combustion engine, power plant, industrial waste gas, natural thermal sources (e.g., geothermal), or solar heating. However, heat input  126  may be any heat input that allows the Rankine cycle device to operate as described herein. Heat exchanger  102  heats the working fluid at a constant pressure (i.e., isobarically) to produce a high pressure stream of working fluid  106 . 
     High pressure stream of working fluid  106  passes through a valve  128  and enters expansion device  110  on high pressure side  120 . Expansion device  110  allows the working fluid to expand therethrough until the working fluid exits expansion device  110  on low pressure side  122 . In one embodiment, expansion device  110  is a turbine for a power plant, wherein expansion of the working fluid causes a rotation of the turbine to produce power, such as electrical power. Expansion of the working fluid through expansion device  110  decreases the pressure and temperature of the working fluid. 
     In one embodiment, expanded stream  112  of working fluid  106  is supplied to a cooling device  114 . In another embodiment, cooling device  114  is a condenser, which allows the working fluid to cool into a liquid. In one embodiment, cooling device  114  is configured to cool the working fluid using ambient air. In another embodiment, cooling device receives a refrigerant from an external source (not shown) to cool the working fluid. 
     In one embodiment, the liquid stream exiting cooling device  114  is supplied to a feed vessel  116 . Feed vessel  116  is configured to contain a quantity of working fluid such that a constant supply of working fluid may be supplied to pump  118 . In one embodiment, the Rankine cycle device is a closed loop system, and pump  118  again pumps the working fluid to heat exchanger  102  and the cycle repeats. 
     Sometimes, it is necessary to stop the operation of a Rankine cycle device. Typically, when a Rankine cycle device is shut down, the working fluid condenses and accumulates in a location of natural fluid accumulation, such as a low-point of the Rankine cycle device. The location of natural fluid accumulation is typically within heat exchanger  102  or on high pressure side  120  of expansion device  110 . Thus, typically, the working fluid accumulates outside of pump  118  and feed vessel  116 , which may cause difficulty during later attempts to start up the Rankine cycle device. 
     In one embodiment, to improve ease of startup of Rankine cycle device  100  after a shutdown, a controller  130  is configured to close valve  128  and control heat exchanger  102  to heat the working fluid. Because valve  128  is in a closed position, heating the working fluid in heat exchanger  102  increases the pressure of the working fluid. In one embodiment, controller  130  controls heat exchanger  102  to heat the working fluid until a predetermined pressure is sensed by sensor  108 . When the pressure of the working fluid reaches or exceeds the predetermined pressure level, controller  130  controls valve  128  to open abruptly, which allows for a surge of working fluid to flow from high pressure side  120  to low pressure side  122 . In one embodiment, the predetermined pressure level is selected to allow for sufficient levels of working fluid to accumulate into feed vessel  116  and/or pump  118  to facilitate startup of the Rankine cycle device  100 . 
     In another embodiment, Rankine cycle device  100  comprises a bypass valve  132 . Bypass valve  132  is installed along bypass channel  134 , which bypasses expansion device  110 . Controller  130  is configured to close valves  128  and  132  and operate heat exchanger  102  to heat the working fluid until a predetermined pressure, and/or temperature level, of the working fluid is sensed by sensor  108 . Once the predetermined pressure or temperature is met or exceeded, controller  130  sends a signal to bypass valve  132  to open, causing a surge of working fluid to flow from high pressure side  120  to low pressure side  122 . In one embodiment, bypass valve  132  is opened abruptly, causing a rapid causing a surge of working fluid to flow from high pressure side  120  to low pressure side  122 . In one embodiment, the predetermined pressure level is selected to allow for sufficient levels of working fluid to accumulate into feed vessel  116  and/or pump  118  to facilitate startup of the Rankine cycle device  100 . 
     In another embodiment, a secondary pump  135  is provided on high pressure side  120 . Controller  130  is configured to close valve  128  and bypass valve  132 . Controller  130  operates heat exchanger  102  to heat the working fluid and controls secondary pump  135  to flow the working fluid toward closed valve  128  (e.g., using a positive displacement type secondary pump  135 ) until a predetermined pressure level of the working fluid is sensed by sensor  108 . Once the predetermined pressure or temperature is met or exceeded, controller  130  sends a signal to bypass valve  132  (and/or valve  128 ) to open, causing a surge of working fluid to flow from high pressure side  120  to low pressure side  122 . In one embodiment, the predetermined pressure level is selected to allow for sufficient levels of working fluid to accumulate into feed vessel  116  and/or pump  118  to facilitate startup of Rankine cycle device  100 . 
     The above embodiments are encompassed by one or more methods.  FIG. 2  shows a block diagram of a method of operating a Rankine Device according to the present disclosure. As shown in  FIG. 2 , the Rankine cycle device is shut down  200 . During cold startup, one or more of valve  128  and bypass valve  132  are closed  204 . Heat exchanger  102  and/or secondary pump  135  are operated to increase the pressure level of the working fluid. When it is determined  206  that the pressure level has met or exceed a predetermined pressure level, one or more of valve  128  and bypass valve  132  are opened  208 . Fluid level in pump  118  and/or feed vessel  116  is measured at  210 . If it is determined that sufficient levels of working fluid are contained with pump  118  and/or feed vessel  116 , the Rankine cycle device  100  is operated to initiate startup  212 . If insufficient levels of working fluid are contained with pump  118  and/or feed vessel  116 , the process is repeated from step  202 . 
     In another embodiment a secondary cooling device  136  is provided to cool heat input  126  to heat exchanger  102 . Secondary cooling device  136  is operated to cool heat input  126  when it is determined that heat input  126  is at or exceeds a predetermined temperature. 
     Technical effects of the present disclosure allow for the possibility of one or more of controlling one or more valves and a heat exchanger to increase a pressure level of a working fluid and abruptly opening one or more valves of a Rankine cycle device to provide a surge of working fluid to a pump to facilitate startup of the device. 
     In some embodiments, the above described systems and methods are electronically or computer controlled. The embodiments described herein are not limited to any particular system controller or processor for performing the processing and tasks described herein. The term controller or processor, as used herein, is intended to denote any machine capable of performing the calculations, or computations, necessary to perform the tasks described herein. The terms controller and processor also are intended to denote any machine that is capable of accepting a structured input and of processing the input in accordance with prescribed rules to produce an output. It should also be noted that the phrase “configured to” as used herein means that the controller/processor is equipped with a combination of hardware and software for performing the tasks of embodiments of the invention, as will be understood by those skilled in the art. The term controller/processor, as used herein, refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), logic circuits, and any other circuit or processor capable of executing the functions described herein. 
     The embodiments described herein embrace one or more computer readable media, including non-transitory computer readable storage media, wherein each medium may be configured to include or includes thereon data or computer executable instructions for manipulating data. The computer executable instructions include data structures, objects, programs, routines, or other program modules that may be accessed by a processing system, such as one associated with a general-purpose computer capable of performing various different functions or one associated with a special-purpose computer capable of performing a limited number of functions. Aspects of the disclosure transform a general-purpose computer into a special-purpose computing device when configured to execute the instructions described herein. Computer executable instructions cause the processing system to perform a particular function or group of functions and are examples of program code means for implementing steps for methods disclosed herein. Furthermore, a particular sequence of the executable instructions provides an example of corresponding acts that may be used to implement such steps. Examples of computer readable media include random-access memory (“RAM”), read-only memory (“ROM”), programmable read-only memory (“PROM”), erasable programmable read-only memory (“EPROM”), electrically erasable programmable read-only memory (“EEPROM”), compact disk read-only memory (“CD-ROM”), or any other device or component that is capable of providing data or executable instructions that may be accessed by a processing system. 
     A computer or computing device such as described herein has one or more processors or processing units, system memory, and some form of computer readable media. By way of example and not limitation, computer readable media comprise computer storage media and communication media. Computer storage media include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically embody computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and include any information delivery media. Combinations of any of the above are also included within the scope of computer readable media. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.