Supercritical Working Fluid and

Processes Thereof

Cross -Reference to Related Applications

[0001] This application claims benefit of U.S. Utility Appl. No. 14/051 ,432, entitled "Heat Engine System with a Supercritical Working Fluid and Processes Thereof," and filed October 10, 201 3 and of U.S. Prov. Appl. No. 61 /71 2,929, entitled "Heat Engine System with a Supercritical Working Fluid and Processes Thereof," and filed October 1 2, 2012, which are both incorporated herein by reference in their entirety to the extent consistent with the present application.

Background

[0002] 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 utilize heat exchanger devices to capture and recycle waste heat back into the process via other process streams. However, the capturing and recycling of waste heat is generally infeasible by industrial processes that utilize high temperatures or have insufficient mass flow or other unfavorable conditions.

[0003] Waste heat can be converted into useful energy by a variety of turbine generator or 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 utilize waste heat to generate steam for driving a turbine, turbo, or other expander connected to an electric generator.

[0004] An organic Rankine cycle utilizes a lower boiling-point working fluid, instead of water, during a traditional Rankine cycle. Exemplary lower boiling-point working fluids include hydrocarbons, such as light hydrocarbons (e.g., propane or butane) and halogenated hydrocarbon, such as hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) (e.g., R245fa). More recently, in view of issues such as thermal instability, toxicity, flammability, and production cost of the lower boiling-point working fluids, some thermodynamic cycles have been modified to circulate non- hydrocarbon working fluids, such as ammonia.

[0005] Many heat engine systems are designed to work with a particular heat source and generally are very inefficient if used with any random heat source. The use of heat engine systems in existing facilities may also be constrained by limited available space or by limited access to waste heat sources.

[0006] Therefore, there is a need for a heat engine system and a method for recovering energy which have an optimized operating range for the heat recovery power cycle, minimized complexity, and maximized efficiency for producing mechanical energy and/or electrical energy from a wide range of thermal sources, such as a waste heat source.

Summary

[0007] Embodiments of the invention generally provide heat engine systems and methods for recovering energy, such as by producing mechanical energy and/or generating electrical energy from thermal energy. In one embodiment disclosed herein, a heat engine system for generating electricity is provided and contains a working fluid circuit with a high pressure side and a low pressure side and containing a working fluid, such that at least a portion of the working fluid circuit contains the working fluid in a supercritical state. The heat engine system further contains the power turbine disposed between the high pressure side and the low pressure side of the working fluid circuit, 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 passing or otherwise flowing between the high pressure side and the low pressure side of the working fluid circuit. The heat engine system also contains a motor-generator coupled to or with the power turbine and configured to convert the mechanical energy into electrical energy and a pump coupled to or with the power turbine. The pump may be fluidly coupled to the low pressure side of the working fluid circuit by a pump inlet configured to receive the working fluid from the low pressure side of the working fluid circuit, fluidly coupled to the high pressure side of the working fluid circuit by a pump outlet configured to release the working fluid into the high pressure side of the working fluid circuit, and configured to circulate and pressurize the working fluid within the working fluid circuit.

[0008] The heat engine system further contains a heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit, configured to be fluidly coupled to and in thermal communication with a heat source stream, and configured to transfer thermal energy from the heat source stream to the working fluid. The heat engine system also contains a recuperator fluidly coupled to a condenser (e.g., air-cooled or fluid cooled) in series on the low pressure side of the working fluid circuit. The recuperator may be fluidly coupled to the working fluid circuit downstream of the pump and upstream of the heat exchanger on the high pressure side of the working fluid circuit, fluidly coupled to the working fluid circuit downstream of the power turbine and upstream of the condenser on the low pressure side of the working fluid circuit, and configured to transfer thermal energy from the working fluid within the low pressure side to the working fluid within the high pressure side of the working fluid circuit. The condenser may be fluidly coupled to the working fluid circuit downstream of the recuperator and upstream of the pump on the low pressure side of the working fluid circuit and configured to remove thermal energy from the working fluid within the low pressure side of the working fluid circuit.

[0009] In one embodiment, the condenser is an air-cooled condenser and the air-cooled condenser generally contains cooling fins or a heat sink and the cooling fins or the heat sink may be positioned and/or configured to receive a gaseous flow from one or more fans. In another embodiment, the condenser is a fluid-cooled condenser coupled to a cooling medium circuit. The cooling medium circuit generally contains circulating chilled water. In many examples, the working fluid contains carbon dioxide (e.g., sc-C0 ₂ ).

[0010] The motor-generator may be coupled to or with the power turbine by a shaft and the pump may also be coupled to or with the power turbine by the same shaft or a different shaft. In some configurations, the motor-generator may be disposed between the power turbine and the pump and the motor-generator may be coupled to or with the power turbine and the pump by independent shafts or by one common shaft.

[0011] In some embodiments, the heat engine system further contains a power outlet or a power electronics system electrically coupled to the motor-generator and configured to transfer the electrical energy from the motor-generator to an electrical grid. In other embodiments, the heat engine system further contains a process control system operatively connected to the heat engine system. The process control system may be configured to monitor and adjust temperatures and pressures throughout the working fluid circuit. In other embodiments, the heat engine system further contains a mass management system (MMS) fluidly coupled to the working fluid circuit. The mass management system has a mass control tank configured to receive, store, and distribute the working fluid. In one example, the mass control tank may be fluidly coupled to the high pressure side of the working fluid circuit and configured to receive the working fluid from the high pressure side and may be fluidly coupled to the low pressure side of the working fluid circuit and configured to distribute the working fluid to the low pressure side. In other embodiments, the heat engine system further contains a housing at least partially encompassing the pump and the power turbine. In other embodiments, the heat engine system further contains a leak recapture system configured to transfer captured gas or fluid from the housing, through a compressor, and into the working fluid circuit at a point upstream of the recuperator and downstream of the outlet of the power turbine.

[0012] In another embodiment disclosed herein, a heat engine system for generating electricity is provided and contains a single-core condensing heat exchanger having a working fluid inlet and a working fluid outlet providing a working fluid flow channel, a recuperator inlet and a recuperator outlet providing a recuperator flow channel through the single-core condensing heat exchanger and in thermal communication with the working fluid flow channel. The single-core condensing heat exchanger further contains a condenser inlet and a condenser outlet providing a condenser flow channel through the single-core condensing heat exchanger and in thermal communication with the working fluid flow channel. The heat engine system further contains a pump having an inlet in fluid communication with the working fluid outlet and an outlet in fluid communication with the recuperator inlet, the power turbine having an inlet in fluid communication with the recuperator outlet and an outlet in fluid communication the working fluid inlet, and a motor-generator rotatably coupled to the pump and the power turbine. [0013] In another embodiment disclosed herein, a heat engine system for generating electricity is provided and contains a pump rotatably coupled to a motor-generator, the power turbine rotatably coupled to the motor-generator, and a single-core condensing heat exchanger having a working fluid inlet in fluid communication with an outlet of the power turbine and a working fluid outlet in fluid communication with an inlet of the pump. The heat engine system further contains a recuperator inlet disposed on the single-core condensing heat exchanger and in fluid communication with an outlet of the pump, a recuperator outlet disposed on the single-core condensing heat exchanger and in fluid communication with an inlet of the power turbine, and a condenser inlet and a condenser outlet disposed on the single-core condensing heat exchanger.

[0014] In some embodiments, a portion of the single-core condensing heat exchanger within the heat engine system may be a recuperator that contains the recuperator inlet, the recuperator outlet, and the recuperator flow channel. Similarly, in other embodiments, a portion of the single-core condensing heat exchanger within the heat engine system may be a condenser that contains the condenser inlet, the condenser outlet, and the condenser flow channel. The heat engine system may also contain a condenser loop in fluid communication with the condenser inlet and the condenser outlet.

[0015] In various configurations, the heat engine system further contains at least one heat exchanger, but may contain multiple heat exchangers, such as waste heat exchanger, disposed in fluid communication with the recuperator outlet and the power turbine inlet. Also, the heat engine system contains a bypass valve providing selective fluid communication between the power turbine inlet and the power turbine outlet. The heat engine system further contains a shaft coupled to turbomachinery components, such that the pump, the power turbine, and the motor-generator are rotatably coupled by the shaft. In some examples, the single-core condensing heat exchanger contains a plurality of parallel plates. In some examples, the pump, the motor-generator, the power turbine, and the single-core condensing heat exchanger are disposed within a support structure or housing of the heat engine system.

[0016] In another embodiment disclosed herein, a method for generating electricity is provided and includes operating a motor-generator to drive a pump that circulates or otherwise transfers the working fluid from a low pressure side of a working fluid circuit to a high pressure side of the working fluid circuit, adding heat to the working fluid in the high pressure side of the working fluid circuit by passing the working fluid in thermal communication with the working fluid in the low pressure side of the working fluid circuit in a single-core condensing heat exchanger, and adding heat to the working fluid in the high pressure side of the working fluid circuit by passing the working fluid in thermal communication with a waste heat source. The method further includes introducing the working fluid into the power turbine that converts high pressure working fluid into low pressure working fluid and generates rotational energy, such that the power turbine is rotationally coupled to the motor-generator. The method also includes exhausting the working fluid from the power turbine into the single-core condensing heat exchanger where the working fluid is first cooled by passing in thermal communication with the high pressure side of the working fluid circuit and then further cooled by passing in thermal communication with a condenser loop. The method further includes operating a bypass valve to selectively control the flow of the working fluid to the power turbine.

Brief Description of the Drawings

[0017] Embodiments of the present disclosure may be 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.

[0018] Figure 1 illustrates an exemplary heat engine system, according to one or more embodiments disclosed herein.

[0019] Figure 2 illustrates another exemplary heat engine system, according to one or more embodiments disclosed herein.

[0020] Figure 3 illustrates another exemplary heat engine system, according to one or more embodiments disclosed herein.

[0021] Figure 4 illustrates a single-core condensing heat exchanger, according to one or more embodiments disclosed herein. [0022] Figure 5 illustrates an exploded view of a single-core condensing heat exchanger, according to one or more embodiments disclosed herein.

Detailed Description

[0023] Embodiments of the invention generally provide heat engine systems and methods for generating electricity. Figures 1 and 2 depict simplified schematics of heat engine systems 90 and 100, respectively, which may also be referred to as a thermal engine, a power generation device, a heat or waste heat recovery system, and/or a heat to electricity system. In one embodiment, the heat engine system 90 has a single-core condensing heat exchanger 1 18 containing a recuperator 1 14 and a fluid-cooled condenser 1 16 for condensing the working fluid within a working fluid circuit 102, as depicted in Figure 1 . In another embodiment, the heat engine system 1 00 contains the recuperator 1 14 and an air-cooled condenser 136 for condensing the working fluid within the working fluid circuit 102, as depicted in Figure 2. The heat engine systems 90 and 100 may encompass one or more elements of a Rankine thermodynamic cycle configured to produce power from a wide range of thermal sources. The terms "thermal engine" or "heat engine" as used herein generally refer to the equipment set that executes the various thermodynamic cycle embodiments described herein. The term "heat recovery system" generally refers to the thermal engine in cooperation with other equipment to deliver/remove heat to and from the thermal engine.

[0024] The heat engine systems 90 and 1 00 may operate in a closed-loop thermodynamic cycle that circulates a working fluid throughout the working fluid circuit 1 02. The working fluid circuit 1 02 contains a variety of conduits and valves adapted to interconnect the various components of the heat engine systems 90 and 100. Although the heat engine systems 90 and 100 may be characterized as closed-loop cycle systems, each of the heat engine systems 90 and 1 00, as a whole, may or may not be hermetically-sealed so to prohibit the working fluid from leaking into the surrounding environment.

[0025] In one or more embodiments, the working fluid utilized in the heat engine systems 90 and 100 may contain carbon dioxide or a mixture containing carbon dioxide and at least a portion of the working fluid circuit 102 contains the working fluid in a supercritical state (e.g., sc-C0 ₂ ). In an exemplary embodiment, the working fluid circuit 1 02 contains a working fluid that is completely carbon dioxide or substantially carbon dioxide and the working fluid is utilized in a supercritical state. It should be noted that use of the terms carbon dioxide (C0 ₂ ), supercritical carbon dioxide (sc-C0 ₂ ), or subcritical carbon dioxide (sub-C0 ₂ ) is not intended to be limited to carbon dioxide of any particular type, source, purity, or grade. For example, industrial grade carbon dioxide may be contained in and/or used as the working fluid without departing from the scope of the disclosure.

[0026] In other embodiments, the working fluid may be a binary, ternary, or other working fluid blend. For example, a working fluid combination can be selected for the unique attributes possessed by the combination within a heat recovery system, such as the heat engine systems 90 and 100. One such fluid combination includes a liquid absorbent and carbon dioxide mixture enabling the combination to be pumped in a liquid state to high pressure with less energy input than required to compress gaseous carbon dioxide. In other examples, the working fluid may be a combination or mixture of carbon dioxide and one or more other miscible fluids. In yet other examples, the working fluid may be a combination of carbon dioxide and propane, or carbon dioxide and ammonia, or other similar gases, without departing from the scope of the disclosure.

[0027] Figures 1 and 2 depict the high and low pressure sides of the working fluid circuit 1 02 of the heat engine systems 90 and 1 00 by representing the high pressure side with

" " and the low pressure side with " " - as described in one or more embodiments. The use of the term "working fluid" is not intended to limit the state or phase of matter of the working fluid or components of the working fluid. For instance, the working fluid or portions of the working fluid may be in a fluid phase, a gas phase, a supercritical state, a subcritical state, or any other phase or state at any one or more points within the heat engine systems 90 and 1 00 or thermodynamic cycle. In one or more embodiments, the working fluid is in a supercritical state over certain portions of the working fluid circuit 1 02 of the heat engine systems 90 and 100 (e.g., a high pressure side) and in a subcritical state over other portions of the working fluid circuit 1 02 of the heat engine systems 90 and 1 00 (e.g., a low pressure side). In other embodiments, the entire thermodynamic cycle may be operated such that the working fluid is maintained in either a supercritical or subcritical state throughout the working fluid circuit 102.

[0028] The heat engine systems 90 and 100 generally contain a heat exchanger 1 04, such as a waste heat exchanger, in thermal communication with a heat source Q _in . One heat exchanger or multiple heat exchangers may be utilized as the heat exchanger 1 04. The temperature of the working fluid is increased as the working fluid flows through the heat exchanger 1 04 and thermal energy is transferred from the heat source Q _in to the working fluid within the working fluid circuit 1 02. The heat source Q _in may derive thermal energy from a variety of high temperature sources. For example, the heat source Q _in may be a waste heat stream such as, but not limited to, gas turbine exhaust, process stream exhaust, or other combustion product exhaust streams, such as furnace or boiler exhaust streams. Accordingly, the heat engine systems 90 and 1 00 may be configured to transform waste heat into electricity for applications ranging from bottom cycling in gas turbines, stationary diesel engine gensets, industrial waste heat recovery (e.g., in refineries and compression stations), and hybrid alternatives to the internal combustion engine.

[0029] In other embodiments, the heat source Q _in may derive thermal energy from renewable sources of thermal energy such as, but not limited to, solar thermal and geothermal sources. While the heat source Q _in may be a fluid stream of the high temperature source itself, in other embodiments the heat source Q _in may be a thermal fluid in contact with the high temperature source. The thermal fluid may deliver the thermal energy to the heat exchanger 1 04 to transfer the energy to the working fluid in the working fluid circuit 1 02. In many examples, the heat exchanger 104 is a waste heat exchanger, such that a waste heat stream or source flows through the heat exchanger 1 04 and provides thermal energy to the working fluid within the working fluid circuit 1 02.

[0030] In addition to the heat exchanger 1 04, the heat engine systems 90 and 100 generally have a power turbine 1 06 and a pump 1 10. In one embodiment, the heat engine system 90 further contains the single-core condensing heat exchanger 1 18 that includes the recuperator 1 1 4 and a fluid-cooled condenser 1 16, as depicted in Figure 1 . In another embodiment, the heat engine system 1 00 further contains the recuperator 1 14, but instead of the fluid-cooled condenser 1 1 6 (as in heat engine system 90), the heat engine system 1 00 has the air-cooled condenser 1 36, as depicted in Figure 2. In the high pressure side 101 , pressurized working fluid from the pump 1 1 0 may be provided to the recuperator 1 1 4 where the pressurized working fluid may be pre-heated by low pressure working fluid from the power turbine 106. Thereafter, the pre-heated working fluid may be provided to the heat exchanger 1 04 where the working fluid may further be heated by the heat source Q _in .

[0031] For both of the heat engine systems 90 and 1 00, the power turbine 1 06 receives and expands the heated working fluid that is discharged from the heat exchanger 1 04. The power turbine 106 may be any type of expansion device, such as an expander, a turbo, or a turbine and is rotatably coupled to a motor-generator 1 08 (e.g., a motor- power alternator/generator) and the pump 1 10 by a shaft 1 12. The power turbine 106 expands the working fluid to drive the motor-generator 1 08 and the pump 1 1 0. The recuperator 1 1 4 may be utilized to transfer thermal energy from the low-pressure, high temperature working fluid exiting the power turbine 1 06 to the high-pressure, low temperature working fluid from the pump 1 1 0.

[0032] Figure 1 depicts the heat engine system 90 with a low pressure side of the working fluid circuit 102 such that the expanded working fluid from the power turbine 1 06 is discharged into the recuperator 1 1 4 of the single-core condensing heat exchanger 1 1 8. After passing through the recuperator 1 1 4, the working fluid flows through the fluid-cooled condenser 1 1 6 of the single-core condensing heat exchanger 1 18. In the fluid-cooled condenser 1 16, a cooling medium circuit 1 20 may be utilized to further transfer heat from the working fluid and condenses the working fluid into a liquid. The cooling medium circuit 1 20 may include water, glycol, a water glycol mixture, a solvent (e.g. , organic solvent), a supercritical fluid, a subcritical fluid, air, carbon dioxide, nitrogen, or any other suitable cooling medium. The pump 1 10 receives condensed working fluid from the fluid-cooled condenser 1 1 6 and the cycle starts over.

[0033] Figure 2 depicts a conduit 134 fluidly coupled between the recuperator 1 1 4 and the air-cooled condenser 136 in the heat engine system 100, as described in one or more embodiments disclosed herein. In some examples, the air-cooled condenser 136 contains one or more fans or blowers, depicted as a fan 138, and a plurality of cooling fins 139 that are in thermal contact or communication with the conduit 1 34. The fan 138 may be utilized to blow air or another gas through and in contact with the plurality of cooling fins 139. The thermal energy may be transferred from the working fluid through the air-cooled condenser 136, and dissipated or otherwise transferred into the air or other gas flowing over the cooling fins 1 39. Therefore, the thermal energy may be removed from the working fluid within the working fluid circuit 1 02. The cooling fins 139 or other heat sinks generally have properties that include a relatively high surface area and high thermal conductivity so that thermal energy can absorb and desorb at a relatively high rate. In some examples, a finned-tube module used as the cooling fins 1 39 may be exposed to air blown from the fans 1 38, such as forced draft fans. The air- cooled condenser 136 may be utilized to condense the working fluid (e.g., C0 ₂ ) by removing thermal energy from the working fluid flowing through the conduit 134 downstream of the recuperator 1 1 4. Additionally, a conduit 132 may be fluidly coupled between the air-cooled condenser 1 36 and the pump 1 10 within the heat engine system 1 00. Therefore, the condensed working fluid may flow from the air-cooled condenser 1 36 to the pump 1 10 through the conduit 1 32.

[0034] During system start-up of the heat engine system 90 or 100, the motor-generator 1 08 may be supplied with electricity so as to act as a motor to operate the pump 1 1 0 to circulate the working fluid through the working fluid circuit 1 02. As the working fluid is circulated, the amount of energy contained within the working fluid increases to the point where the energy provided by the power turbine 1 06 is sufficient to power the pump 1 1 0 via the shaft 1 12. Once the energy is sufficient to power the pump 1 1 0, the motor- generator 1 08 may also be driven via the shaft 1 12 and utilized as a generator producing net electric power.

[0035] In another embodiment, the heat engine system 90 (Figure 1 ) and the heat engine system 1 00 (Figure 2) may contain a chamber or housing, such as a housing 1 13 at least partially, substantially, or completely encompassing the pump 1 1 0, the motor-generator 1 08, the power turbine 1 06, and/or the shaft 1 1 2. The heat engine system 1 00 may be configured to provide or otherwise deliver a gas or fluid, such as dry seal gas, bearing gas, a portion of the working fluid, air, other gas, or combinations thereof into the housing 1 1 3, for purposes of cooling one or more parts of the power turbine 1 06. In many examples, a portion of the working fluid (e.g., sc-C0 ₂ ) may be utilized in the housing 1 1 3. The housing 1 1 3 may also be utilized to prevent or capture any gas leakage, such as the working fluid, from the pump 1 10, the motor-generator 1 08, the power turbine 1 06, and/or a seal assembly (not shown) disposed along the shaft 1 1 2.

[0036] In another embodiment, as depicted in Figure 1 , the heat engine system 90 contains a seal gas system 204 that may be utilized to provide pressurized seal gas or fluid to the motor-generator 1 08, as well as to the other components, such as the power turbine 1 06 and/or the shaft 1 12. The seal gas system 204 may be a pressurized gas/fluid system and may be external of the working fluid circuit 1 02 and/or the heat engine system 90. The seal gas or fluid may be transferred to the motor-generator 108 or into the housing 1 13 through a seal gas inlet 206 and the recovered seal gas may be transferred out of the motor-generator 108 or the housing 1 13 by a seal gas outlet 208. The seal gas inlet 206 and the seal gas outlet 208 may be disposed on the housing 1 1 3 and/or casing or other portions of the pump 1 10, the motor-generator 108, the power turbine 1 06, and/or the shaft 1 1 2. The seal gas system 204 may be fluidly coupled to the seal gas inlet 206 by a conduit 205 and may be fluidly coupled to the seal gas outlet 208 by a conduit 207. Maintaining a sufficient seal gas pressure within the motor- generator 108 can help prevent the migration of the working fluid from the pump 1 1 0 or the power turbine 106 into the motor-generator 1 08. The seal gas may contain carbon dioxide, nitrogen, argon, air, or combinations thereof and the seal gas may be in a gaseous state, a liquid state, a supercritical state, or a subcritical state. In some exemplary embodiments, the seal gas may contain a portion of the working fluid contained within the seal gas system 204. In one example, the seal gas contains carbon dioxide removed from the working fluid circuit 102.

[0037] In another embodiment, as depicted in Figure 2, the heat engine system 1 00 has a leak recapture system 150 that may be utilized to recycle leaked and captured gas. The leak recapture system 150 may be configured to flow or otherwise transfer the leaked and captured gas or fluid from the housing 1 13 back into the working fluid circuit 1 02. A conduit 1 54 may be fluidly coupled to and between the housing 1 1 3 and a compressor 152, as well as fluidly coupled to and between the compressor 152 and a point on a conduit 1 03 upstream of the recuperator 1 1 4 and downstream of the outlet of the power turbine 1 06. The compressor 1 52 may be utilized to remove the leaked and captured gas or fluid from the housing 1 1 3, to pressurize and to flow the leaked and captured gas, as a gas, a liquid, a subcritical fluid, and/or a supercritical fluid into the working fluid circuit 1 02.

[0038] The compressor 152 may be utilized to remove the leaked and captured gas or fluid from a motor-generator case (not shown) that may be within or part of the housing 1 13. The motor-generator case may be a case, a housing, or the like that completely or partially encompasses the motor-generator 108. In some examples, the pressure of the motor-generator case may be actively maintained within a range from about 0.5 MPa to about 1 0 MPa, more narrowly within a range from about 0.8 MPa to about 5 MPa, and more narrowly within a range from about 1 MPa to about 3 MPa. The pressurized state of the working fluid (e.g., sc-C0 ₂ or sub-C0 ₂ ) reduces density of the working fluid, thereby minimizing windage or fluidic frictional drag at the motor-generator rotor.

[0039] In other embodiments, a process control system 182 containing a computer system 1 84 is generally operatively connected to the heat engine systems 90 and 100. The process control system 1 82 may be configured to control and operate each of the components of the heat engine systems 90 and 100 including the power turbine 106, the motor-generator 108, the pump 1 1 0, and other components, as well as any of the valves and sensors throughout the working fluid circuit 102. The process control system 182 may be configured to monitor and adjust temperatures and pressures throughout the working fluid circuit 1 02 by controlling and adjusting each of the components of the heat engine systems 90 and 1 00. In one embodiment, the process control system 1 82 is enabled to move, adjust, manipulate, or otherwise control at least one valve, or multiple valves, for adjusting or controlling the flow of the working fluid throughout the working fluid circuit 1 02. By controlling the flow of the working fluid, the process control system 1 82 is also operable to regulate the temperatures and pressures throughout the working fluid circuit 102.

[0040] A power turbine shut-off valve 1 22 and a bypass valve 1 24, depicted in Figures 1 and 2, may be independently utilized to reduce or cease the flow of the working fluid during a system start-up process. The power turbine shut-off valve 122 is operatively coupled to a conduit 21 8 extending from the outlet of the heat exchanger 1 04, along the high pressure side of the working fluid circuit 102, and to the inlet of the power turbine 1 06. The power turbine shut-off valve 122 is configured to control the flow of the working fluid through the conduit 21 8. The bypass valve 1 24 is operatively coupled to a conduit, a bypass line 126, extending from a point downstream of the outlet of the pump 1 10 and upstream of the inlet of the recuperator 1 1 4, along the high pressure side of the working fluid circuit 1 02, and to the conduit 218. The bypass valve 1 24 is configured to control the flow of the working fluid through the bypass line 126. The power turbine shut-off valve 1 22 and the bypass valve 124 may be partially or completely closed/opened or modulated between varying opened/closed positions to control the flow of the working fluid entering the power turbine 106. The control of the working fluid circulation via the power turbine shut-off valve 1 22 and the bypass valve 1 24 provides the working fluid to be heated to the desired temperature and/or pressurized to the desired pressure for driving the power turbine 106. The power turbine shut-off valve 1 22 and the bypass valve 124 may independently be manually controlled or may be automatically controlled via the process control system 1 82.

[0041] In certain embodiments, during the operation of the heat engine systems 90 and 1 00 or other heat engine systems described herein, the pump 1 1 0 may provide the working fluid (e.g., C0 ₂ ) contained in the working fluid circuit 1 02 at a pressure within a range from about 2 MPa to about 23 MPa, more narrowly within a range from about 1 7 MPa to about 23 MPa and at a flowrate within a range from about 1 kg/s (kilogram per second) to about 1 5 kg/s, more narrowly within a range from about 2 kg/s to about 1 2 kg/s, and more narrowly within a range from about 4 kg/s to about 7 kg/s. The temperature of the working fluid, such as carbon dioxide, entering the recuperator 1 1 4 may be within a range from about -10°C to about 70°C, more narrowly within a range from about 30°C to about 50°C, and the temperature of the working fluid exiting the recuperator 1 14 may be within a range from about 50°C to about 180°C, more narrowly within a range from about 1 00°C to about 130°C.

[0042] Since the heat source Q _in may derive thermal energy from a variety of high temperature sources, the temperature of and the available energy from the heat source Q _in will also vary. Generally, the heat source Q _in may be at a temperature within a range from about 1 00°C to about 1 ,000°C, or greater than 1 ,000°C, and in some examples, within a range from about 1 00°C to about 800°C, more narrowly within a range from about 150°C to about 600°C, and more narrowly within a range from about 200°C to about 550°C. The heat source Q _in may provide available energy within a range from about 1 ,500 kWth (kilowatt thermal) to about 2,600 kWth, so as to increase the temperature of the working fluid passing through the heat exchanger 104 and provided to the power turbine 106. The temperature of the working fluid is increased as the working fluid passing through the heat exchanger 1 04 and thermal energy is transferred from the heat source Q _in to the working fluid within the working fluid circuit 1 02. In some exemplary embodiments, the working fluid passing through the heat exchanger 1 04 may have an increased temperature within a range from about 1 70°C to about 550°C, more narrowly within a range from about 190°C to about 350°C. Subsequently, once a portion of the thermal energy is removed from the heat source Q _in stream, a return temperature of the heat source Q _in stream may be within a range from about 50°C to about 250°C, more narrowly within a range from about 70°C to about 1 90°C, and more narrowly within a range from about 80°C to about 1 70°C.

[0043] The power turbine 106 may expand the working fluid containing carbon dioxide and may operate the motor-generator to produce or otherwise generate electricity at a power level of generally less than 1 MW (or sub 1 MW), such as within a range from about 10 kW to about 950 kW, more narrowly within a range from about 50 kW to about 800 kW, more narrowly within a range from about 100 kW to about 500 kW, and more narrowly within a range from about 1 50 kW to about 375 kW, for example, about 300 kW. Upon exiting the power turbine 106, the working fluid may be flowed to the single- core condensing heat exchanger 1 18 (Figure 1 ) or the air-cooled condenser 1 36 (Figure 2) and has a temperature within a range from about 140°C to about 350°C, more narrowly within a range from about 180°C to about 260°C, and more narrowly within a range from about 200°C to about 230°C. Once the working fluid containing carbon dioxide passes through the single-core condensing heat exchanger 1 1 8 or the air- cooled condenser 1 36, the working fluid may be provided to the pump 1 10 at a temperature within a range from about -20°C to about 40°C, more narrowly within a range from about 1 0°C to about 20°C. Figure 2 depicts the heat engine system 100 configured with the air-cooled condenser 1 36. The working fluid containing carbon dioxide that exits the recuperator 1 1 4 and is provided or otherwise delivered to the air-

is cooled condenser 1 36 may have a temperature within a range from about 5°C to about 75°C, more narrowly within a range from about 25°C to about 75°C, and more narrowly within a range from about 50°C to about 70°C.

[0044] Figure 3 illustrates an exemplary embodiment of a heat engine system 200, which may be similar in some respects to the heat engine system 90 or 1 00 and therefore, may be best understood with reference to Figures 1 and 2, where like numerals correspond to like elements that will not be described again. The heat engine system 200 has a power unit 202 containing the power turbine 1 06, the motor-generator 1 08, and the pump 1 10. Each of the power turbine 106, the motor-generator 1 08, and the pump 1 10 may be coupled to a central shaft (not shown) and integrated into a single or consolidated unit. In some configurations, the central shaft may be similar or the same as the shaft 1 1 2. Also, the power turbine 1 06 and the pump 1 10, as well as other components, such as the heat exchanger 1 04, the recuperator 1 14, and the single-core condensing heat exchanger 1 18 may be fluidly coupled to the working fluid circuit 1 02.

[0045] In certain embodiments, the power unit 202 may include a seal gas system (not shown) for isolating the motor-generator 1 08 from the power turbine 1 06 and the pump 1 10. The seal gas system, which may be the same or similar to the seal gas system 204, may be a pressurized system, external of the heat engine system 200, which provides pressurized seal gas or fluid to the motor-generator 1 08 through the seal gas inlet 206 and recovers seal gas or fluid from the seal gas outlet 208. In an alternative embodiment, the seal gas inlet 206 and the seal gas outlet 208 may be reduced to a single port located at the center of the motor-generator case, such as a case, a housing, or an enclosure 226. This single port may be part of a leak recapture system, similar to the leak recapture system 1 50 depicted in Figure 2 and discussed below.

[0046] Pressurized working fluid from the pump 1 1 0 may be provided through the conduit 21 0 to the recuperator 1 1 4, which is a portion of the single-core condensing heat exchanger 1 1 8. In the recuperator 1 1 4, the pressurized working fluid is heated by low-pressure working fluid supplied through the conduit 212 from the power turbine 1 06. The pre-heated working fluid is then provided to a waste heat exchanger (not shown) through the working fluid supply 214. The working fluid is heated by the waste heat exchanger (not shown) and returned to the heat engine system 200 via the working fluid return 21 6.

[0047] The heated, high-pressure working fluid is passed through the conduit 21 8, which may include a filter 220 and the power turbine shut-off valve 1 22, before entering the power turbine 106. The expanded working fluid is transferred from the power turbine 1 06 to the single-core condensing heat exchanger 1 1 8 via the conduit 21 2. The bypass valve 1 24 provides selective fluid communication between the conduit 21 8 and the conduit 212 via the bypass line 1 26.

[0048] The working fluid flowing or passing through from conduit 21 2 may be discharged into the single-core condensing heat exchanger 1 1 8. The recuperator 1 1 4, as a portion of the single-core condensing heat exchanger 1 18, is operable to transfer thermal energy from the low-pressure, high temperature working fluid exiting the power turbine 1 06 to the high-pressure, low temperature working fluid from the pump 1 10. In one embodiment, such as in a water-cooled configuration or a fluid-cooled configuration, after the working fluid flows through the recuperator 1 14, the working fluid flows through the fluid-cooled condenser 1 1 6 that is in fluid communication with the cooling medium circuit 1 20 and utilized to further transfer heat from the working fluid, as depicted in the heat engine system 90 (Figure 1 ) and the heat engine system 200 (Figure 3). The cooling medium circuit 1 20 may include a cooling water supply 224 and a cooling water return 225 through which a cooling-fluid, water, or other fluid may be circulated therethrough. In another embodiment, such as in an air-cooled configuration, after the working fluid flows through the recuperator 1 1 4, the working fluid flows through a conduit 134 to the air-cooled condenser 1 36, as depicted in the heat engine system 100 (Figure 2). The air-cooled condenser 1 36 is configured to further transfer heat from the working fluid and into the air - outside of the heat engine system 1 00. The pump 1 1 0 receives condensed working fluid via a conduit 222 from the fluid-cooled condenser 1 1 6 or the air-cooled condenser 1 36 and the cycle starts over.

[0049] The heat engine system 200 may be contained within a case or an enclosure 226 that also provides for easy portability of the system, as depicted in Figure 3. In certain exemplary embodiments, the enclosure 226 may have a footprint with a dimension of about 6 feet by about 1 0 feet and a height of about 8 feet, thus allowing the heat engine system 200 to be positioned in close proximity to a waste heat source or other heat sources, such as the heat source Q _in . In other embodiments, any of the waste heat systems disclosed herein may be disposed on a skid or other supporting device. The waste heat system 1 00 may be disposed on a supporting device or a skid 1 80, as depicted in Figure 2. Similarly, the waste heat system 200 may be disposed on a supporting device or a skid 280, as depicted in Figure 3. In one example, the air-cooled condenser 1 36 along with the plurality of cooling fins 1 39 and/or the fan may be located off of the skid 180.

[0050] In some embodiments, the motor-generator 1 08 may be a generator, an alternator (e.g., permanent magnet alternator), or other device for generating electrical energy, such as transforming mechanical energy from the shaft 1 1 2 and the power turbine 1 06 to electrical energy. Figure 2 depicts a power outlet 1 70 electrically coupled with the motor-generator 108, a power electronics system 172, and an electrical grid 1 74 via a line 176. The power outlet 170 may be configured to transfer the generated electrical energy from the motor-generator 1 08 to the power electronics system 172 and to the electrical grid 174 via the line 1 76. Also, the power outlet 170 may be configured to receive electricity from the electrical grid 1 74 through the power electronics system 1 72 and transfer the electricity to the motor-generator 1 08 - such as to run the motor- generator 1 08 to drive the pump 1 1 0 during some operational steps.

[0051] The line 1 76 may be electrical wires or cables and utilized to transfer electricity to and from the motor-generator 108, the power outlet 170, the power electronics system 1 72, and the electrical grid 1 74. The power electronics system 1 72 may be configured to convert the electrical power into desirable forms of electricity by modifying electrical properties, such as voltage, current, or frequency. The power electronics system 1 72 may include converters or rectifiers, inverters, transformers, regulators, controllers, switches, resisters, storage devices, and other power electronic components and devices. The electrical grid 1 74 may be or include an electrical power grid, an electrical bus (e.g., plant bus), other electric circuits, or combinations thereof. The electrical grid 1 74 generally contains at least one alternating current bus, alternating current grid, alternating current circuit, or combinations thereof. [0052] In some exemplary embodiments, when the motor-generator 108 is driven by the power turbine 1 06, the motor-generator 1 08 may be utilized as an electrical generator to produce and transfer electricity to the electrical grid 1 74 via the line 1 76 through the power outlet 170 and the power electronics system 1 72. In other exemplary embodiments, when the motor-generator 1 08 is powered by electricity to drive the pump 1 10, the motor-generator 1 08 may be utilized as an electrical motor to receive electricity from the electrical grid 1 74 via the line 176 through the power outlet 170 and the power electronics system 172.

[0053] In some embodiments, the overall efficiency of the heat engine systems and the amount of power ultimately generated can be influenced by the inlet or suction pressure at the pump 1 10 when the working fluid contains supercritical carbon dioxide. In order to minimize or otherwise regulate the suction pressure of the pump 1 1 0, the heat engine system 1 00 may incorporate the use of a mass management system (MMS) 140, as depicted in Figure 2. The mass management system 1 40 controls the inlet pressure of the pump 1 1 0 by regulating the amount of the working fluid entering and/or exiting the heat engine system 100 at strategic locations in the working fluid circuit 1 02, such as at tie-in points, inlets/outlets, valves, or conduits throughout the heat engine system 1 00. Consequently, the heat engine system 1 00 becomes more efficient by increasing the pressure ratio for the pump 1 1 0 to a maximum possible extent.

[0054] The mass management system 140 contains at least one vessel or tank, such as a storage vessel (e.g., working fluid storage vessel), a fill vessel, and/or a mass control tank (e.g., mass control tank 142), fluidly coupled to the low pressure side of the working fluid circuit 1 02 by one or more conduits and valves, such as one or more of the conduits 1 44a, 144b, and 144c and the valves 1 46a, 146b, and 146c. The valves 146a, 1 46b, and 1 46c are moveable - as being partially opened, fully opened, and/or closed - to either remove working fluid from the working fluid circuit 102 or add working fluid to the working fluid circuit 102 via the conduits 144a, 1 44b, and 144c.

[0055] In one exemplary configuration, the conduit 144a may be fluidly coupled to the high pressure side of the working fluid circuit 102, such that one end of the conduit 1 44a is fluidly coupled to the working fluid circuit 1 02 at a point disposed downstream of the pump 1 10 and upstream of the recuperator 1 14, and the other end of the conduit 144a is fluidly coupled to an inlet on the mass control tank 1 42. The valve 1 46a may be operably connected to and fluidly coupled to the conduit 1 44a and configured to control the flow of the working fluid from the high pressure side of the working fluid circuit 102, through the conduit 1 44a, and to the mass control tank 142. The conduit 144b may be fluidly coupled to the high pressure side of the working fluid circuit 102, such that one end of the conduit 1 44b is fluidly coupled to the working fluid circuit 1 02 at a point disposed downstream of the heat exchanger 1 04 and upstream of the power turbine 1 06, and the other end of the conduit 144b is fluidly coupled to an inlet on the mass control tank 142. The valve 1 46b may be operably connected to and fluidly coupled to the conduit 1 44b and configured to control the flow of the working fluid from the high pressure side of the working fluid circuit 102, through the conduit 144b, and to the mass control tank 142. The conduit 1 44c may be fluidly coupled to the low pressure side of the working fluid circuit 102, such that one end of the conduit 144c is fluidly coupled to an outlet on the mass control tank 1 42 and the other end of the conduit 144c is fluidly coupled to the working fluid circuit 102 at a point disposed downstream of a cooler or condenser (e.g., the single-core condensing heat exchanger 1 18 in Figure 1 and/or the air-cooled condenser 1 36 in Figure 2) the heat exchanger 1 04 and upstream of the pump 1 10. The valve 1 46c may be operably connected to and fluidly coupled to the conduit 144c and configured to control the flow of the working fluid from the mass control tank 142, through the conduit 1 44c, and to low pressure side of the working fluid circuit 1 02.

[0056] Besides the valves 1 46a, 1 46b, and 146c, the mass management system 140 may also include a plurality of connection points. Each of the valves 1 46a, 146b, and 1 46c and/or the connection points may be in fluid communication with the mass control tank 142. The valves 1 46a, 1 46b, and 146c may be considered as termination points where the mass management system 1 40 is operatively connected to the heat engine system 1 00. The connection points and valves 1 46a, 1 46b, and 146c may be configured to provide the mass management system 1 40 with an outlet for flaring excess working fluid or pressure, or to provide the mass management system 1 40 with additional/supplemental working fluid from an external source, such as a fluid fill system. [0057] In some embodiments, the mass control tank 1 42 may be configured as a localized storage tank for additional/supplemental working fluid that may be added to the heat engine system 1 00 when needed in order to regulate the pressure or temperature of the working fluid within the working fluid circuit 1 02 or otherwise supplement escaped working fluid. By controlling or otherwise operating the valves 1 46a, 1 46b, and 146c, the mass management system 1 40 adds and/or removes the working fluid to/from the heat engine system 1 00 with or without the need of a pump, thereby reducing system cost, complexity, and maintenance. Exemplary embodiments of the mass management system 1 40, and a range of variations thereof, are found in U.S. Appl. No. 1 3/278,705, filed October 21 , 201 1 , and published as U.S. Pub. No. 201 2-0047892, which are incorporated herein by reference in their entirety to the extent consistent with the present application.

[0058] In one or more embodiments disclosed herein, as depicted in Figures 1 -3, the heat engine systems 90, 100, and 200 may be utilized to produce mechanical energy and/or electrical energy from a wide range of thermal sources, such as a waste heat source. The working fluid circuit 1 02 of the heat engine systems 90, 100, and 200 contains the working fluid and has the high pressure side and the low pressure side. At least a portion of the working fluid circuit 1 02 contains the working fluid in a supercritical state, such as supercritical carbon dioxide. The heat engine systems 90, 1 00, and 200 further contain the power turbine 1 06 disposed between the high pressure side and the low pressure side of the working fluid circuit 102, 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 passing or otherwise flowing between the high and the low pressure sides of the working fluid circuit 102.

[0059] The heat engine systems 90, 1 00, and 200 also contain the motor-generator 108 coupled to the power turbine 1 06 and configured to convert the mechanical energy into electrical energy and the pump 1 1 0 coupled to the power turbine 1 06. The pump 1 1 0 may be fluidly coupled to the low pressure side of the working fluid circuit 102 by the pump inlet of the pump 1 1 0 which is configured to receive the working fluid from the low pressure side of the working fluid circuit 102. Also, the pump 1 10 may be fluidly coupled to the high pressure side of the working fluid circuit 102 by the pump outlet of the pump 1 10 which is configured to release the working fluid into the high pressure side of the working fluid circuit 1 02. The pump 1 10 may also be configured to circulate and/or pressurize the working fluid within the working fluid circuit 1 02; therefore, the pump 1 1 0 may be utilized to increase or decrease the flowrate of the working fluid and the pressure at which the working fluid is maintained within the working fluid circuit 1 02.

[0060] The heat engine systems 90, 100, and 200 further contain the heat exchanger 1 04 fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit 1 02, configured to be fluidly coupled to and in thermal communication with a heat source stream, such as the heat source Q _in , and configured to transfer thermal energy from the heat source stream to the working fluid. The heat engine systems 90, 1 00, and 200 also contain the recuperator 1 1 4 fluidly coupled to a condenser (e.g., the fluid-cooled condenser 1 16 (Figures 1 and 3) or the air-cooled condenser 1 36 (Figure 2)) in series on the low pressure side of the working fluid circuit 1 02. The recuperator 1 1 4 may be fluidly coupled to the working fluid circuit 102 downstream of the pump 1 1 0 and upstream of the heat exchanger 1 04 on the high pressure side of the working fluid circuit 1 02, fluidly coupled to the working fluid circuit 1 02 downstream of the power turbine 106 and upstream of the condenser 1 1 6 or 1 36 on the low pressure side of the working fluid circuit 1 02, and configured to transfer thermal energy from the working fluid within the low pressure side to the working fluid within the high pressure side of the working fluid circuit 1 02. The condenser 1 1 6 or 1 36 may be fluidly coupled to the working fluid circuit 102 downstream of the recuperator 1 1 4 and upstream of the pump 1 10 on the low pressure side of the working fluid circuit 102 and configured to remove thermal energy from the working fluid within the low pressure side of the working fluid circuit 102.

[0061] In one embodiment, as depicted in Figure 1 , the fluid-cooled condenser 1 1 6 is coupled to and in thermal communication with the cooling medium circuit 120 and the working fluid circuit 102. The cooling medium circuit 1 20 generally may contain circulating chilled water or another liquid medium. In another embodiment, as depicted in Figure 2, the air-cooled condenser 1 36 generally contains cooling fins 139 or a heat sink and the cooling fins 1 39 or the heat sink may be positioned and/or configured to receive a gaseous flow from one or more fans 138. In many examples disclosed herein, the working fluid within the working fluid circuit 1 02 disposed in the heat engine systems 90, 100, and 200 contain carbon dioxide (e.g., sc-C0 ₂ ).

[0062] For the heat engine systems 90, 1 00, and 200, the motor-generator 108 may be coupled to or with the power turbine 106 by the shaft 1 1 2 and the pump 1 10 may also be coupled to or with the power turbine 1 06 by the shaft 1 1 2 or an independent shaft (not shown). The motor-generator 1 08 is generally disposed between the power turbine 1 06 and the pump 1 1 0 and the motor-generator 1 08 may be coupled to or with the power turbine 1 06 and the pump 1 1 0 by independent shafts or by one common shaft, such as the shaft 1 12. In some examples, the pump 1 1 0, the power turbine 1 06, and the motor-generator 108 are rotatably coupled by the shaft 1 1 2 within the heat engine systems 90, 1 00, and 200.

[0063] In some embodiments, as illustrated in Figure 2, the heat engine system 100 further contains a power outlet or the power electronics system 1 72 electrically coupled to the motor-generator 108 and configured to transfer the electrical energy from the motor-generator 108 to the electrical grid 1 74. In other embodiments, the mass management system 140 may be fluidly connected to the working fluid circuit 1 02 via a mass control tank 142. The mass control tank 1 42 is configured to receive or remove the working fluid from the working fluid circuit 102, store the working fluid, and distribute the working fluid back into the working fluid circuit 1 02. In one exemplary configuration, the mass control tank 1 42 may be fluidly coupled to the high pressure side of the working fluid circuit 1 02 and configured to receive the working fluid from the high pressure side. Also, the mass control tank 142 may be fluidly coupled to the low pressure side of the working fluid circuit 102 and configured to distribute the working fluid to the low pressure side.

[0064] The heat engine systems 90 and 100 may contain the housing 1 1 3 to at least partially encompass the pump 1 1 0, the motor-generator 1 08, and the power turbine 1 06, as depicted in Figures 1 and 2. Similarly, Figure 3 depicts the heat engine system 200 containing the motor-generator 1 08, the power turbine 106, and the single-core condensing heat exchanger 1 18 disposed on a support structure, such as the skid 280 and encompassed partially, substantially, or completely by a housing or an enclosure 226. [0065] In another embodiment disclosed herein, a heat engine system 90 may be utilized to generate electricity and contains the single-core condensing heat exchanger 1 18. Generally, the single-core condensing heat exchanger 1 1 8 has a working fluid inlet and a working fluid outlet that provides a working fluid flow channel. The inlet and the outlet of the recuperator 1 1 4 provide the recuperator 1 14 a flow channel through the single-core condensing heat exchanger 1 18 and provide thermal communication with the working fluid flow channel. Also, a condenser inlet and a condenser outlet provide a condenser flow channel through the single-core condensing heat exchanger 1 18 and provide thermal communication with the working fluid flow channel.

[0066] The heat engine systems 90, 100, and 200 further contain the pump 1 10 which has an inlet in fluid communication with the working fluid outlet and an outlet in fluid communication with the inlet of the recuperator 1 1 4. The power turbine 106 has an inlet in fluid communication with the outlet of the recuperator 1 14 and an outlet in fluid communication the working fluid inlet. The motor-generator 1 08 may be rotatably coupled to the pump 1 1 0 and the power turbine 1 06.

[0067] In another embodiment disclosed herein, as depicted in Figures 1 and 3, the heat engine systems 90 and 200 may be utilized to generate electricity and contain the pump 1 10 rotatably coupled to the motor-generator 1 08, the power turbine 1 06 rotatably coupled to the motor-generator 108, and the single-core condensing heat exchanger 1 18 having a working fluid inlet in fluid communication with an outlet of the power turbine 106 and a working fluid outlet in fluid communication with an inlet of the pump 1 10.

[0068] The heat engine systems 90 and 200 further contain the inlet of the recuperator 1 14 disposed on the single-core condensing heat exchanger 1 1 8 and in fluid communication with an outlet of the pump 1 10, the outlet of the recuperator 1 1 4 disposed on the single-core condensing heat exchanger and in fluid communication with an inlet of the power turbine 106, and a condenser inlet and a condenser outlet disposed on the single-core condensing heat exchanger 1 1 8. The heat exchanger 104 (e.g., a waste heat exchanger) may be disposed in fluid communication with the outlet of the recuperator 1 14 and the inlet of the power turbine 106. The heat engine systems 90 and 200 also contain a condenser loop, such as the cooling medium circuit 1 20, in fluid communication with the condenser inlet and the condenser outlet. The heat engine systems 90 and 200 have the bypass valve 1 24 providing selective fluid communication between the inlet and the outlet of the power turbine 106. In some examples, the single- core condensing heat exchanger 1 18 contains a plurality of parallel plates or fins.

[0069] In another embodiment disclosed herein, the heat engine systems 90 and 200 may be utilized to perform a method for generating electricity that includes operating the motor-generator 1 08 to drive the pump 1 10 that circulates or otherwise transfers the working fluid from a low pressure side of the working fluid circuit 102 to a high pressure side of the working fluid circuit 102, adding heat to the working fluid in the high pressure side of the working fluid circuit 102 by passing the working fluid in thermal communication with the working fluid in the low pressure side of the working fluid circuit 1 02 in the single-core condensing heat exchanger 1 1 8, and adding heat to the working fluid in the high pressure side of the working fluid circuit 1 02 by passing the working fluid in thermal communication with a waste heat source, such as the heat source Q _in . The method further includes introducing the working fluid into the power turbine 1 06 that converts high pressure working fluid into low pressure working fluid and generates rotational energy, such that the power turbine 1 06 is rotationally coupled to the motor- generator 1 08. The method also includes exhausting the working fluid from the power turbine 1 06 into the single-core condensing heat exchanger 1 18 where the working fluid is first cooled by passing in thermal communication with the high pressure side of the working fluid circuit 1 02 and then further cooled by passing in thermal communication with a condenser loop, such as the cooling medium circuit 1 20. The method further includes operating the bypass valve 124 to selectively control the flow of the working fluid to the power turbine 1 06, such as for operating the power turbine 106 and the motor-generator 1 08 to generate electricity.

[0070] In another embodiment disclosed herein, the heat engine system 1 00 may be utilized to perform a method for generating electricity that includes operating the motor- generator 1 08 to drive the pump 1 10 that circulates or otherwise transfers the working fluid from a low pressure side of the working fluid circuit 102 to a high pressure side of the working fluid circuit 1 02 and transferring thermal energy from the heat source Q _in (e.g., waste heat source or heat source stream) to the high pressure side of the working fluid circuit 1 02 by flowing the working fluid through the heat exchanger 104 thermally coupled to the heat source Q _in . The method further includes transferring thermal energy from the low pressure side to the high pressure side of the working fluid circuit 1 02 by flowing the working fluid through the recuperator 1 14.

[0071] The method further includes introducing the working fluid into the power turbine 1 06 and converting a high pressure working fluid into a low pressure working fluid and generating mechanical or rotational energy. The mechanical or rotational energy formed by the power turbine 1 06 may be utilized to rotate or otherwise operate the motor-generator 108 for generating electrical energy and to rotate or otherwise operate the pump 1 10 for circulating and pressurizing the working fluid within the working fluid circuit 1 02.

[0072] The method also includes exhausting the working fluid from the power turbine 1 06 through the recuperator 1 14 where the working fluid is first cooled by passing in thermal communication with the high pressure side of the working fluid circuit 102 and then further cooled by passing in thermal communication with and the air-cooled condenser 1 36. The method further includes operating the bypass valve 1 24 to selectively control the flow of the working fluid to the power turbine 1 06, such as for operating the power turbine 1 06 and the motor-generator 108 to generate electricity.

[0073] Figure 4 depicts an exemplary single-core condensing heat exchanger 300 that contains a recuperator 302 and a condenser 304. The single-core condensing heat exchanger 300 may include a working fluid inlet 306 and a working fluid outlet 316 that provide a working fluid flow channel through the single-core condensing heat exchanger 300. The recuperator 302 may include a recuperator inlet 308 and a recuperator outlet 314 that provide a recuperator flow channel that passes in thermal communication with the working fluid flow channel. The condenser 304 may include a condenser inlet 31 0 and a condenser outlet 31 2 that provide a condenser flow channel that passes in thermal communication with the working fluid flow channel. The single-core condensing heat exchanger 300 may include additional recuperators and/or condensers as desired by a particular process. In some embodiments, the single-core condensing heat exchanger 300 and the single-core condensing heat exchanger 1 18 may have the same components or may be configured with different components. The single-core condensing heat exchanger 300 may be utilized in the heat engine systems 90 and 200 as a substitute for the single-core condensing heat exchanger 1 1 8.

[0074] The single-core condensing heat exchanger 300 may be constructed using any of a variety of types of heat exchangers, including, but not limited to shell and tube heat exchangers, plate heat exchangers, plate fin heat exchangers, and spiral heat exchangers. Figure 5 illustrates an exploded view of a single-core condensing heat exchanger 400 constructed from a plurality of thin metal plates containing flow passages formed on one or both sides thereof. In certain embodiments, the plates may have a thickness within a range from about 0.5 millimeters to about 5.0 millimeters, more narrowly within a range from about 1 .0 millimeters to about 3.5 millimeters, and more narrowly within a range from about 1 .6 millimeters to about 2.0 millimeters. The flow passages may be formed onto the plates through a variety of processes, such as machining, chemical-etching, photo-etching, or stamping, as well as by other techniques or processes.

[0075] The heat exchanger 400 may include one or more longitudinal flow plates 402 interleaved with one or more cross-flow plates 404. Each longitudinal flow plate 402 may include flow passages forming a working fluid flow passage that directs flow from a working fluid inlet 306 to a working fluid outlet 316. Each cross-flow plate 404 may include recuperator flow passages 406 that form a recuperator flow passage between a recuperator inlet 308 and a recuperator outlet 31 4. Each cross-flow plate 404 may also include condenser flow passages 408 that form a condenser flow passage between a condenser inlet 31 0 and a condenser outlet 31 2.

[0076] The longitudinal flow plates 402 and the cross-flow plates 404 are disposed between opposing cover plates 41 0 and formed into a unitary structure (as shown in Figure 5). The plates (e.g., the cover plates 410, longitudinal flow plates 402, and the cross-flow plates 404) may be formed into a unitary structure by a brazing or welding process or in a diffusion bonding oven that compresses the plates together under conditions that cause the grain structure in adjacent plates to bond. Headers and/or nozzles are then coupled to the heat exchanger 400 at the inlets 306, 308, and 310 and the outlets 312, 31 4, and 31 6 from each flow passage or group of flow passages. [0077] It is to be understood that the present disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the disclosure. Exemplary embodiments of components, arrangements, and configurations are described herein 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 present disclosure 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 described herein may be combined in any combination of ways, e.g., any element from one exemplary embodiment may be used in any other exemplary embodiment without departing from the scope of the disclosure.

[0078] Additionally, certain terms are used throughout the written 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 disclosure, 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. Further, in the written description and in the claims, the terms "including", "containing", 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. 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. [0079] 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.