WO2014117074A1

WO2014117074A1 - Process for controlling a power turbine throttle valve during a supercritical carbon dioxide rankine cycle

Info

Publication number: WO2014117074A1
Application number: PCT/US2014/013170
Authority: WO
Inventors: Brett A. BOWAN
Original assignee: Echogen Power Systems, L.L.C.
Priority date: 2013-01-28
Filing date: 2014-01-27
Publication date: 2014-07-31
Also published as: EP2948649A1; CA2899163C; EP2948649B1; US9752460B2; KR20150122665A; US20140208751A1; CA2899163A1; EP2948649B8; EP2948649A4; AU2014209091A1; AU2014209091B2

Abstract

Embodiments of the invention generally provide a heat engine system, a method for generating electricity, and an algorithm for controlling the heat engine system which are configured to efficiently transform thermal energy of a waste heat stream into electricity. In one embodiment, the heat engine system utilizes a working fluid (e.g., sc-CO₂) within a working fluid circuit for absorbing the thermal energy that is transformed to mechanical energy by a turbine and electrical energy by a generator. The heat engine system further contains a control system operatively connected to the working fluid circuit and enabled to monitor and control parameters of the heat engine system by manipulating a power turbine throttle valve to adjust the flow of the working fluid. A control algorithm containing multiple system controllers may be utilized by the control system to adjust the power turbine throttle valve while maximizing efficiency of the heat engine system.

Description

Process for Controlling a Power Turbine Throttle Valve

During a Supercritical Carbon Dioxide Rankine Cycle

Cross -Reference to Related Applications

[001] This application claims benefit of U.S. Utility Appl. No. 1 4/164,780, filed on January 27, 201 4 and of U.S. Prov. Appl. No. 61 /757,590, filed on January 28, 201 3, the contents of both are hereby incorporated by reference to the extent not inconsistent with the present disclosure.

Background

[002] 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.

[003] Waste heat can be converted into useful energy by a variety of heat engine or turbine generator 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. 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.

[004] A synchronous power generator is a commonly employed turbine generator utilized for generating electrical energy in large scales (e.g., megawatt scale) throughout the world for both commercial and non-commercial use. The synchronous power generator generally supplies electricity to an electrical bus or grid (e.g., an alternating current bus) that usually has a varying load or demand over time. In order to be properly connected, the frequency of the synchronous power generator must be tuned and maintained to match the frequency of the electrical bus or grid. Severe damage may occur to the synchronous power generator as well as the electrical bus or grid should the frequency of the synchronous power generator become unsynchronized with the frequency of the electrical bus or grid.

[005] Turbine generator systems also may suffer an overspeed condition during the generation of electricity - generally - due to high electrical demands during peak usage times. Turbine generator systems may be damaged due to an increasing rotational speed of the moving parts, such as a turbine, a generator, a shaft, and a gearbox. The overspeed condition often rapidly progresses out of control without immediate intervention to reduce the rotational speed of the turbine generator. The overspeed condition causes the temperatures and pressures of the working fluid to increase and the system to overheat. Once overheated, the turbine generator system may incur multiple problems that lead to catastrophic failures of the turbine generator system. The working fluid with an excess of absorbed heat may change to a different state of matter that is outside of the system design, such as a supercritical fluid becoming a subcritical state, gaseous state, or other state. The overheated working fluid may escape from the closed system causing further damage. Mechanical governor controls have been utilized to prevent or reduce overspeed conditions in analogous steam-powered generators. However, similar mechanical controls are unknown or not common for preventing or reducing overspeed conditions in turbine generator systems utilizing supercritical fluids.

[006] Physical controllers and software controllers have been used to adjust independent aspects of turbine generator systems and process parameters. Such controllers may be utilized - in part - during a synchronous process or to avoid or minimize an overspeed condition. However, in the typical system, when a first controller is used to adjust a process parameter for manipulating a first variable, additional variables of the process generally become unfavorable and independent controllers are utilized to adjust different aspects of the process parameters while manipulating these variables. Such turbine generator systems that have multiple controllers are usually susceptible for failure and also suffer inefficiencies - which increase the cost to generate electricity.

[007] What is needed, therefore, is a turbine generator system, a method for generating electrical energy, and an algorithm for such system and method, whereby the turbine generator system contains a control system with multiple controllers for maximizing the efficiency of the heat engine system while generating electrical energy.

Summary

[008] Embodiments of the invention generally provide a heat engine system, a method for generating electricity, and an algorithm for managing or controlling the heat engine system which are configured to efficiently transform thermal energy of a waste heat stream into valuable electrical energy. The heat engine system utilizes a working fluid in a supercritical state and/or a subcritical state contained within a working fluid circuit for capturing or otherwise absorbing the thermal energy of the waste heat stream. The thermal energy is transformed to mechanical energy by a power turbine and subsequently transformed to electrical energy by a power generator coupled to the power turbine. The heat engine system contains several integrated sub-systems managed by an overall control system that utilizes a control algorithm within multiple controllers for maximizing the efficiency of the heat engine system while generating electricity.

[009] In one or more embodiments described herein, a heat engine system for generating electricity is provided and contains a working fluid circuit having a high pressure side, a low pressure side, and a working fluid circulated within the working fluid circuit, wherein at least a portion of the working fluid is in a supercritical state (e.g., sc- C0₂) and/or a subcritical state (e.g., sub-C0₂). The heat engine system further contains at least one heat exchanger fluidly coupled to the high pressure side of the working fluid circuit and in thermal communication with a heat source stream whereby thermal energy is transferred from the heat source stream to the working fluid. The heat engine system further contains a 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 a pressure drop in the working fluid to mechanical energy whereby the absorbed thermal energy of the working fluid is transformed to mechanical energy of the power turbine. The heat engine system further contains a power generator coupled to the power turbine and configured to convert the mechanical energy into electrical energy and a power outlet electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid or bus. The heat engine system further contains a power turbine throttle valve fluidly coupled to the high pressure side of the working fluid circuit and configured to control a flow of the working fluid throughout the working fluid circuit. The heat engine system further contains a control system operatively connected to the working fluid circuit, enabled to monitor and control multiple process operation parameters of the heat engine system, and enabled to move, adjust, manipulate, or otherwise control the power turbine throttle valve for adjusting or controlling the flow of the working fluid.

[010] In other embodiments described herein, a control algorithm is provided and utilized to manage the heat engine system and process for generating electricity. The control algorithm is embedded in a computer system and is part of the control system of the heat engine system. The control algorithm may be utilized throughout the various steps or processes described herein including while initiating and maintaining the heat engine system, as well as during a process upset or crisis event, and for maximizing the efficiency of the heat engine system while generating electricity. The control system and/or the control algorithm contains at least one system controller, but generally contains multiple system controllers utilized for managing the integrated sub-systems of the heat engine system. Exemplary system controllers of the control algorithm include a trim controller, a power mode controller, a sliding mode controller, a pressure mode controller, an overspeed mode controller, a proportional integral derivative controller, a multi-mode controller, derivatives thereof, and/or combinations thereof.

[011] In some examples, the control system or the control algorithm contains a trim controller configured to control rotational speed of the power turbine or the power generator. The trim controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to increase or decrease rotational speed of the power turbine or the power generator during a synchronization process. The trim controller is provided by a proportional integral derivative (PID) controller within a generator control module as a portion of the control system of the heat engine system.

[012] In other examples, the control system or the control algorithm contains a power mode controller configured to monitor a power output from the power generator and modulate the power turbine throttle valve in response to the power output while adaptively tuning the power turbine to maintain a power output from the power generator at a continuous or substantially continuous power level during a power mode process. The power mode controller may be configured to maintain the power output from the power generator at the continuous or substantially continuous power level during the power mode process while a load is increasing on the power generator.

[013] In other examples, the control system or the control algorithm contains a sliding mode controller configured to monitor and detect an increase of rotational speed of the power turbine, the power generator, or a shaft coupled between the power turbine and the power generator. The sliding mode controller is further configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to reduce the rotational speed after detecting the increase of rotational speed.

[014] In other examples, the control system or the control algorithm contains a pressure mode controller configured to monitor and detect a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit during a process upset. The pressure mode controller is further configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to increase the pressure of the working fluid within the working fluid circuit during a pressure mode control process. In some examples, the control system or the control algorithm contains an overspeed mode controller configured to detect an overspeed condition and subsequently implement an overspeed mode control process to immediately reduce a rotational speed of the power turbine, the power generator, or a shaft coupled between the power turbine and the power generator. [015] In one example, the control system or the control algorithm contains a trim controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to control a rotational speed of the power turbine while synchronizing the power generator with the electrical grid during a synchronization process and a power mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to adaptively tune the power turbine while maintaining a power output from the power generator at a continuous or substantially continuous power level during a power mode process while increasing a load on the power generator. The control system or the control algorithm further contains a sliding mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to gradually reduce the rotational speed during the process upset, a pressure mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to increase the pressure of the working fluid in response to detecting a reduction of pressure of the working fluid throughout the working fluid circuit during a pressure mode control process, and an overspeed mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to reduce the rotational speed during an overspeed condition.

[016] In other embodiments described herein, a method for generating electricity with a heat engine system is provided and includes circulating the working fluid within a working fluid circuit having a high pressure side and a low pressure side, wherein at least a portion of the working fluid is in a supercritical state and transferring thermal energy from a heat source stream to the working fluid by at least one heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit. The method further includes transferring the thermal energy from the heated working fluid to a power turbine while converting a pressure drop in the heated working fluid to mechanical energy and converting the mechanical energy into electrical energy by a power generator coupled to the power turbine. The power turbine is generally disposed between the high pressure side and the low pressure side of the working fluid circuit and fluidly coupled to and in thermal communication with the working fluid. The method further includes transferring the electrical energy from the power generator to a power outlet, wherein the power outlet is electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid or bus. The method further includes controlling the power turbine by operating a power turbine throttle valve to adjust a flow of the working fluid, wherein the power turbine throttle valve is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit upstream from the power turbine. The method further includes monitoring and controlling multiple process operation parameters of the heat engine system via a control system operatively connected to the working fluid circuit, wherein the control system is configured to control the power turbine by operating the power turbine throttle valve to adjust the flow of the working fluid. In many examples, the working fluid contains carbon dioxide and at least a portion of the carbon dioxide is in a supercritical state (e.g., sc-C0₂).

[017] In some examples, the method further provides adjusting the flow of the working fluid by modulating, trimming, adjusting, or otherwise moving the power turbine throttle valve to control a rotational speed of the power turbine while synchronizing the power generator with the electrical grid during a synchronization process. In other examples, the method provides adjusting the flow of the working fluid by modulating the power turbine throttle valve while adaptively tuning the power turbine to maintain a power output of the power generator at a power level that is stable or continuous or at least substantially stable or continuous during a power mode process while experiencing an increasing load on the power generator. In some examples, the method includes detecting the process upset and subsequently adjusting the flow of the working fluid by modulating the power turbine throttle valve to increase the pressure of the working fluid within the working fluid circuit during a pressure mode control process. In other examples, a sliding mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to gradually reduce the rotational speed and to prevent an overspeed condition. In other examples, the method includes detecting that the power turbine, the power generator, and/or the shaft is experiencing an overspeed condition and subsequently implementing an overspeed mode control process to immediately reduce the rotational speed. An overspeed mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to reduce the rotational speed during the overspeed condition.

Brief Description of the Drawings

[018] 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.

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

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

[021] Figure 3 illustrates a schematic diagram of an exemplary control system with a plurality of controllers for heat engine systems, according to one or more embodiments disclosed herein.

[022] Figure 4 illustrates a flow chart of an embodiment of a method for generating electricity with a heat engine system.

Detailed Description

[023] Embodiments of the invention generally provide a heat engine system, a method for generating electricity, and an algorithm for managing or controlling the heat engine system which are configured to efficiently transform thermal energy of a waste heat stream into valuable electrical energy. The heat engine system utilizes a working fluid in a supercritical state (e.g., sc-C0₂) and/or a subcritical state (e.g., sub-C0₂) contained within a working fluid circuit for capturing or otherwise absorbing the thermal energy of the waste heat stream. The thermal energy is transformed to mechanical energy by a power turbine and subsequently transformed to electrical energy by a power generator coupled to the power turbine. The heat engine system contains several integrated subsystems managed by an overall control system that utilizes a control algorithm within multiple controllers for maximizing the efficiency of the heat engine system while generating electricity.

[024] Figure 1 illustrates an exemplary heat engine system 1 00, which may also be referred to as a thermal engine system, a power generation system, a waste heat or other heat recovery system, and/or a thermal to electrical energy system, as described in one or more embodiments herein. The heat engine system 100 is generally configured to encompass one or more elements of a Rankine cycle, a derivative of a Rankine cycle, or another thermodynamic cycle for generating electrical energy from a wide range of thermal sources. The heat engine system 1 00 contains at least one heat exchanger, such as a heat exchanger 5 fluidly coupled to the high pressure side of the working fluid circuit 1 20 and in thermal communication with the heat source stream 101 via connection points 1 9 and 20. Such thermal communication provides the transfer of thermal energy from the heat source stream 1 01 to the working fluid flowing throughout the working fluid circuit 120.

[025] The heat source stream 101 may be a waste heat stream such as, but not limited to, gas turbine exhaust stream, industrial process exhaust stream, or other combustion product exhaust streams, such as furnace or boiler exhaust streams. The heat source stream 1 01 may be at a temperature within a range from about 1 00°C to about 1 ,000°C or greater, and in some examples, within a range from about 200°C to about 800°C, more narrowly within a range from about 300°C to about 600°C. The heat source stream 1 01 may contain air, carbon dioxide, carbon monoxide, water or steam, nitrogen, oxygen, argon, derivatives thereof, or mixtures thereof. In some embodiments, the heat source stream 1 01 may derive thermal energy from renewable sources of thermal energy, such as solar or geothermal sources.

[026] The heat engine system 1 00 further includes a power turbine 3 disposed between the high pressure side and the low pressure side of the working fluid circuit 1 20, disposed downstream from the heat exchanger 5, and fluidly coupled to and in thermal communication with the working fluid. The power turbine 3 is configured to convert a pressure drop in the working fluid to mechanical energy, whereby the absorbed thermal energy of the working fluid is transformed to mechanical energy of the power turbine 3. Therefore, the power turbine 3 is an expansion device capable of transforming a pressurized fluid into mechanical energy, generally, transforming high temperature and pressure fluid into mechanical energy, such as by rotating a shaft.

[027] The power turbine 3 may contain or be a turbine, a turbo, an expander, or another device for receiving and expanding the working fluid discharged from the heat exchanger 5. The power turbine 3 may have an axial construction or radial construction and may be a single-staged device or a multi-staged device. Exemplary turbines that may be utilized in power turbine 3 include an expansion device, a geroler, a gerotor, a valve, other types of positive displacement devices such as a pressure swing, a turbine, a turbo, or any other device capable of transforming a pressure or pressure/enthalpy drop in a working fluid into mechanical energy. A variety of expanding devices are capable of working within the inventive system and achieving different performance properties that may be utilized as the power turbine 3.

[028] The power turbine 3 is generally coupled to a power generator 2 by a shaft 1 03. A gearbox (not shown) is generally disposed between the power turbine 3 and the power generator 2 and adjacent to or encompassing the shaft 103. The shaft 103 may be a single piece or contain two or more pieces coupled together. In one example, a first segment of the shaft 103 extends from the power turbine 3 to the gearbox, a second segment of the shaft 1 03 extends from the gearbox to the power generator 2, and multiple gears are disposed between and couple to the two segments of the shaft 1 03 within the gearbox. In some configurations, the shaft 103 includes a seal assembly (not shown) designed to prevent or capture any working fluid leakage from the power turbine 3. Additionally, a working fluid recycle system may be implemented along with the seal assembly to recycle seal gas back into the fluid circuit of the heat engine system 1 00.

[029] The power generator 2 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 103 and the power turbine 3 to electrical energy. A power outlet (not shown) is electrically coupled to the power generator 2 and configured to transfer the generated electrical energy from the power generator 2 to power electronics 1 or another electrical circuit. The electric circuit may include an electrical grid, an electrical bus (e.g., plant bus), power electronics, and/or combinations thereof.

[030] In one example, the power generator 2 is an electric generator that is electrically and operably connected to an electrical grid or an electrical bus via the power outlet. The electrical grid or bus generally contains at least one alternating current bus, alternating current grid, alternating current circuit, or combinations thereof. In another example, the power generator 2 is an alternator and electrically that is operably connected to adjacent power electronics 1 via the power outlet. The power electronics

1 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 1 may include converters or rectifiers, inverters, transformers, regulators, controllers, switches, resistors, storage devices, and other power electronic components and devices.

[031] In other embodiments, the power generator 2 may be any other type of load receiving equipment, such as other types of electrical generation equipment, rotating equipment, a gearbox, or other device configured to modify or convert the shaft work created by the power turbine 3. In one embodiment, the power generator 2 is in fluid communication with a cooling loop 1 12 having a radiator 4 and a pump 27 for circulating a cooling fluid, such as water, thermal oils, and/or other suitable refrigerants. The cooling loop 1 12 may be configured to regulate the temperature of the power generator

2 and power electronics 1 by circulating the cooling fluid to draw away generated heat.

[032] The heat engine system 1 00 also provides for the delivery of a portion of the working fluid into a chamber or housing of the power turbine 3 for purposes of cooling one or more parts of the power turbine 3. In one embodiment, due to the potential need for dynamic pressure balancing within the power generator 2, the selection of the site within the heat engine system 100 from which to obtain a portion of the working fluid is critical because introduction of this portion of the working fluid into the power generator 2 should respect or not disturb the pressure balance and stability of the power generator 2 during operation. Therefore, the pressure of the working fluid delivered into the power generator 2 for purposes of cooling is the same or substantially the same as the pressure of the working fluid at an inlet (not shown) of the power turbine 3. The working fluid is conditioned to be at a desired temperature and pressure prior to being introduced into the housing of the power turbine 3. A portion of the working fluid, such as the spent working fluid, exits the power turbine 3 at an outlet (not shown) of the power turbine 3 and is directed to the recuperator 6.

[033] The working fluid flows or is otherwise directed from the heat exchanger 5 to the power turbine 3 via a valve 25, a valve 26, or combinations of valves 25, 26, prior to passing through filter F4 and into the power turbine 3. Valve 26 may be utilized in concert or simultaneously with valve 25 to increase the flowrate of the working fluid into the power turbine 3. Alternatively, valve 26 may be utilized as a bypass valve to valve 25 or as a redundancy valve instead of valve 25 in case of failure of or control loss to valve 25. The heat engine system 1 00 also contains a valve 24, which is generally a bypass valve, utilized to direct working fluid from the heat exchanger 5 to the recuperator 6. In one example, a portion of the working fluid in transit from the heat exchanger 5 to the power turbine 3 may be re-directed by having valves 25, 26 in closed positions and the valve 24 in an open position.

[034] At least one recuperator, such as recuperator 6, may be disposed within the working fluid circuit 1 20 and fluidly coupled to the power turbine 3 downstream thereof and configured to remove at least a portion of the thermal energy in the working fluid discharged from the power turbine 3. The recuperator 6 transfers the removed thermal energy to the working fluid proceeding towards the heat exchanger 5. Therefore, the recuperator 6 is operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit 120. A condenser or a cooler (not shown) may be fluidly coupled to the recuperator 6 and in thermal communication with the low pressure side of the working fluid circuit 120, the condenser or the cooler being operative to control a temperature of the working fluid in the low pressure side of the working fluid circuit 1 20.

[035] The heat engine system 1 00 further contains a pump 9 disposed within the working fluid circuit 1 20 and fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit 1 20. The pump 9 is operative to circulate the working fluid through the working fluid circuit 1 20. A condenser 12 is fluidly coupled to the pump 9, such that pump 9 receives the cooled working fluid and pressurizes the working fluid circuit 120 to recirculate the working fluid back to the heat exchanger 5. The condenser 12 is fluidly coupled with a cooling system (not shown) that receives a cooling fluid from a supply line 28a and returns the warmed cooling fluid to the cooling system via a return line 28b. The cooling fluid may be water, carbon dioxide, or other aqueous and/or organic fluids or various mixtures thereof that is maintained at a lower temperature than the working fluid. The pump 9 is also coupled with a relief tank 1 3, which in turn is coupled with a pump vent 30a and relief 30b, such as for carbon dioxide. In one embodiment, the pump 9 is driven by a motor 1 0, and the speed of the motor 10 may be regulated using, for example, a variable frequency drive 1 1 .

[036] In some embodiments, the types of working fluid that may be circulated, flowed, or otherwise utilized in the working fluid circuit 1 20 of the heat engine system 1 00 include carbon oxides, hydrocarbons, alcohols, ketones, halogenated hydrocarbons, ammonia, amines, aqueous, or combinations thereof. Exemplary working fluids that may be utilized in the heat engine system 100 include carbon dioxide, ammonia, methane, ethane, propane, butane, ethylene, propylene, butylene, acetylene, methanol, ethanol, acetone, methyl ethyl ketone, water, derivatives thereof, or mixtures thereof. Halogenated hydrocarbons may include hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) (e.g., 1 ,1 ,1 ,3,3-pentafluoropropane (R245fa)), fluorocarbons, derivatives thereof, or mixtures thereof.

[037] In many embodiments described herein, the working fluid circulated, flowed, or otherwise utilized in the working fluid circuit 1 20 of the heat engine system 1 00, and the other exemplary circuits disclosed herein, may be or may contain carbon dioxide (C0₂) and mixtures containing carbon dioxide. Generally, at least a portion of the working fluid circuit 120 contains the working fluid in a supercritical state (e.g., sc-C0₂). Carbon dioxide utilized as the working fluid or contained in the working fluid for power generation cycles has many advantages over other compounds typical used as working fluids, since carbon dioxide has the properties of being non-toxic and non-flammable and is also easily available and relatively inexpensive. Due in part to a relatively high working pressure of carbon dioxide, a carbon dioxide system may be much more compact than systems using other working fluids. The high density and volumetric heat capacity of carbon dioxide with respect to other working fluids makes carbon dioxide more "energy dense" meaning that the size of all system components can be considerably reduced without losing performance. It should be noted that use of the terms carbon dioxide (C0₂), supercritical carbon dioxide (sc-C0₂), or subcritical carbon dioxide (sub-C0₂) 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.

[038] In other exemplary embodiments, the working fluid in the working fluid circuit 1 20 may be a binary, ternary, or other working fluid blend. The working fluid blend or combination can be selected for the unique attributes possessed by the fluid combination within a heat recovery system, as described herein. For example, one such fluid combination includes a liquid absorbent and carbon dioxide mixture enabling the combined fluid to be pumped in a liquid state to high pressure with less energy input than required to compress carbon dioxide. In another exemplary embodiment, the working fluid may be a combination of supercritical carbon dioxide (sc-C0₂), subcritical carbon dioxide (sub-C0₂), and/or one or more other miscible fluids or chemical compounds. In yet other exemplary embodiments, the working fluid may be a combination of carbon dioxide and propane, or carbon dioxide and ammonia, without departing from the scope of the disclosure.

[039] The working fluid circuit 1 20 generally has a high pressure side and a low pressure side and contains a working fluid circulated within the working fluid circuit 1 20. The use of the term "working fluid" is not intended to limit the state or phase of matter 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 system 100 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 20 of the heat engine system 1 00 (e.g., a high pressure side) and in a subcritical state over other portions of the working fluid circuit 1 20 of the heat engine system 1 00 (e.g., a low pressure side). Figure 1 depicts the high and low pressure sides of the working fluid circuit 1 20 of the heat engine system 1 00 by representing the high pressure side with " " and the low pressure side with " " - as described in one or more embodiments. 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 entire working fluid circuit 1 20 of the heat engine system 1 00. Figure 1 also depicts a mass management system 1 10 of the working fluid circuit 120 in the heat engine system 100 by representing the mass control system with "— ", as described in one or more embodiments.

[040] Generally, the high pressure side of the working fluid circuit 1 20 contains the working fluid (e.g., sc-C0₂) at a pressure of about 1 5 MPa or greater, such as about 1 7 MPa or greater or about 20 MPa or greater. In some examples, the high pressure side of the working fluid circuit 1 20 may have a pressure within a range from about 1 5 MPa to about 30 MPa, more narrowly within a range from about 16 MPa to about 26 MPa, more narrowly within a range from about 17 MPa to about 25 MPa, and more narrowly within a range from about 1 7 MPa to about 24 MPa, such as about 23.3 MPa. In other examples, the high pressure side of the working fluid circuit 1 20 may have a pressure within a range from about 20 MPa to about 30 MPa, more narrowly within a range from about 21 MPa to about 25 MPa, and more narrowly within a range from about 22 MPa to about 24 MPa, such as about 23 MPa.

[041] The low pressure side of the working fluid circuit 120 contains the working fluid (e.g., C0₂ or sub-C0₂) at a pressure of less than 1 5 MPa, such as about 12 MPa or less or about 1 0 MPa or less. In some examples, the low pressure side of the working fluid circuit 1 20 may have a pressure within a range from about 4 MPa to about 14 MPa, more narrowly within a range from about 6 MPa to about 13 MPa, more narrowly within a range from about 8 MPa to about 1 2 MPa, and more narrowly within a range from about 1 0 MPa to about 1 1 MPa, such as about 10.3 MPa. In other examples, the low pressure side of the working fluid circuit 120 may have a pressure within a range from about 2 MPa to about 1 0 MPa, more narrowly within a range from about 4 MPa to about 8 MPa, and more narrowly within a range from about 5 MPa to about 7 MPa, such as about 6 MPa.

[042] In some examples, the high pressure side of the working fluid circuit 1 20 may have a pressure within a range from about 17 MPa to about 23.5 MPa, and more narrowly within a range from about 23 MPa to about 23.3 MPa while the low pressure side of the working fluid circuit 1 20 may have a pressure within a range from about 8 MPa to about 1 1 MPa, and more narrowly within a range from about 10.3 MPa to about 1 1 MPa.

[043] Figure 1 depicts a throttle valve 150 (e.g., a power turbine throttle valve) fluidly coupled to the high pressure side of the working fluid circuit 120 and upstream from the heat exchanger 5, as described in one or more embodiments. The throttle valve 1 50 may be configured to control a flow of the working fluid throughout the working fluid circuit 120 and to the power turbine 3. Generally, the working fluid is in a supercritical state while flowing through the high pressure side of the working fluid circuit 1 20. The throttle valve 1 50 may be controlled by a control system 1 08 that is also communicably connected, wired and/or wirelessly, with the throttle valve 1 50 and other parts of the heat engine system 1 00. The control system 1 08 is operatively connected to the working fluid circuit 1 20 and a mass management system 1 1 0 and is enabled to monitor and control multiple process operation parameters of the heat engine system 1 00. A computer system, as part of the control system 1 08, contains a multi-controller algorithm utilized to control the throttle valve 1 50. The multi-controller algorithm has multiple modes to control the throttle valve 1 50 for efficiently executing the processes of generating electricity by the heat engine system 1 00, as described herein. The control system 1 08 is enabled to move, adjust, manipulate, or otherwise control the throttle valve 1 50 for adjusting or controlling the flow of the working fluid throughout the working fluid circuit 1 20. By controlling the flow of the working fluid, the control system 1 08 is also operable to regulate the temperatures and pressures throughout the working fluid circuit 1 20.

[044] Further, in certain embodiments, the control system 1 08, as well as any other controllers or processors disclosed herein, may include one or more non-transitory, tangible, machine-readable media, such as read-only memory (ROM), random access memory (RAM), solid state memory (e.g., flash memory), floppy diskettes, CD-ROMs, hard drives, universal serial bus (USB) drives, any other computer readable storage medium, or any combination thereof. The storage media may store encoded instructions, such as firmware, that may be executed by the control system 108 to operate the logic or portions of the logic presented in the methods disclosed herein. For example, in certain embodiments, the heat engine system 100 may include computer code disposed on a computer-readable storage medium or a process controller that includes such a computer-readable storage medium. The computer code may include instructions for initiating a control function to alternate the position of the throttle valve 1 50 in accordance with the disclosed embodiments.

[045] In one or more embodiments described herein, a control algorithm is provided and utilized to manage the heat engine system 1 00 and process for generating electricity. The control algorithm is embedded in a computer system as part of the control system 1 08 of the heat engine system 1 00. The control algorithm may be utilized throughout the various steps or processes described herein including while initiating and maintaining the heat engine system 100, as well as during a process upset or crisis event, and for maximizing the efficiency of the heat engine system 1 00 while generating electricity. The control algorithm contains at least one system controller, but generally contains multiple system controllers utilized for managing the integrated subsystems of the heat engine system 100. Exemplary system controllers of the control algorithm include a trim controller, a power mode controller, a sliding mode controller, a pressure mode controller, an overspeed mode controller, a proportional integral derivative controller, a multi-mode controller, derivatives thereof, and/or combinations thereof.

[046] In some examples, the control algorithm contains a trim controller configured to control rotational speed of the power turbine 3 or the power generator 2. The trim controller may be configured to adjust the flow of the working fluid by modulating the throttle valve 1 50 to increase or decrease rotational speed of the power turbine 3 or the power generator 2 during a synchronization process. The trim controller is provided by a proportional integral derivative (PID) controller within a generator control module as a portion of the control system 1 08 of the heat engine system 1 00.

[047] In other examples, the control algorithm contains a power mode controller configured to monitor a power output from the power generator 2 and modulate the throttle valve 1 50 in response to the power output while adaptively tuning the power turbine 3 to maintain a power output from the power generator 2 at a continuous or substantially continuous power level during a power mode process. The power mode controller may be configured to maintain the power output from the power generator 2 at the continuous or substantially continuous power level during the power mode process while a load is increasing on the power generator 2.

[048] In other examples, the control algorithm contains a sliding mode controller configured to monitor and detect an increase of rotational speed of the power turbine 3, the power generator 2, or the shaft 1 03 coupled between the power turbine 3 and the power generator 2. The sliding mode controller is further configured to adjust the flow of the working fluid by modulating the throttle valve 1 50 to reduce the rotational speed after detecting the increase of rotational speed.

[049] In other examples, the control algorithm contains a pressure mode controller configured to monitor and detect a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit 1 20 during a process upset. The pressure mode controller is further configured to adjust the flow of the working fluid by modulating the throttle valve 1 50 to increase the pressure of the working fluid within the working fluid circuit 1 20 during a pressure mode control process. In some examples, the control algorithm contains an overspeed mode controller configured to detect an overspeed condition and subsequently implement an overspeed mode control process to immediately reduce a rotational speed of the power turbine 3, the power generator 2, or a shaft 1 03 coupled between the power turbine 3 and the power generator 2.

[050] In one example, the control algorithm, embedded in a computer system as part of the control system 1 08 for the heat engine system 1 00, contains at least: (i.) a trim controller configured to adjust the flow of the working fluid by modulating the throttle valve 150 to control a rotational speed of the power turbine 3 while synchronizing the power generator 2 with an electrical circuit, such as an electrical grid or an electrical bus (e.g., plant bus) or power electronics 1 during a synchronization process; (ii.) a power mode controller configured to adjust the flow of the working fluid by modulating the throttle valve 150 to adaptively tune the power turbine 3 while maintaining a power output from the power generator 2 at a continuous or substantially continuous power level during a power mode process while increasing a load on the power generator 2; (iii.) a sliding mode controller configured to adjust the flow of the working fluid by modulating the throttle valve 1 50 to gradually reduce the rotational speed during the process upset; (iv.) a pressure mode controller configured to adjust the flow of the working fluid by modulating the throttle valve 1 50 to increase the pressure of the working fluid in response to detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit 1 20 during a pressure mode control process; and (v.) an overspeed mode controller configured to adjust the flow of the working fluid by modulating the throttle valve 150 to reduce the rotational speed during an overspeed condition.

[051] In other embodiments described herein, as illustrated in Figure 4, a method 400 for generating electricity with a heat engine system 1 00 is provided and includes circulating a working fluid within a working fluid circuit 1 20 having a high pressure side and a low pressure side, such that at least a portion of the working fluid is in a supercritical state (e.g., sc-C0₂) (block 402). The method 400 also includes transferring thermal energy from a heat source stream 101 to the working fluid by at least one heat exchanger 21 0 fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit 1 20, as depicted in Figure 2 (block 404).

[052] The method 400 further includes transferring the thermal energy from the heated working fluid to a power turbine 3 while converting a pressure drop in the heated working fluid to mechanical energy (block 406) and converting the mechanical energy into electrical energy by a power generator 2 coupled to the power turbine 3 (block 408), wherein the power turbine 3 is disposed between the high pressure side and the low pressure side of the working fluid circuit 1 20 and fluidly coupled to and in thermal communication with the working fluid. The method 400 further includes transferring the electrical energy from the power generator 2 to a power outlet (block 410) and from the power outlet to the power electronics 1 and/or an electrical circuit, such as an electrical grid, an electrical bus.

[053] The method 400 further includes controlling the power turbine 3 by operating a throttle valve 150 to adjust a flow of the working fluid (block 41 2). The throttle valve 1 50 is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit 1 20 upstream from the power turbine 3. The method further includes monitoring and controlling multiple process operation parameters of the heat engine system 100 via a control system 108 operatively connected to the working fluid circuit 120, wherein the control system 1 08 is configured to control the power turbine 3 by operating the throttle valve 150 to adjust the flow of the working fluid. In many examples, the working fluid contains carbon dioxide and at least a portion of the carbon dioxide is in a supercritical state (e.g., sc-C0₂).

[054] In some examples, the method further provides adjusting the flow of the working fluid by modulating, trimming, adjusting, or otherwise moving the throttle valve 1 50 to control a rotational speed of the power turbine 3 while synchronizing the power generator 2 with the electrical grid or bus (not shown) during a synchronization process. Therefore, the throttle valve 1 50 may be modulated to control the rotational speed of the power turbine 3 which in turn controls the rotational speed of the power generator 2 as well as the shaft 103 disposed between and coupled to the power turbine 3 and the power generator 2. The throttle valve 1 50 may be modulated between a fully opened position, a partially opened position, a partially closed position, or a fully closed position. A trim controller, as part of the control system 1 08, may be utilized to control the rotational speed of the power turbine 3. The generator control module provides an output signal in relation to a phase difference between a generator frequency of the power generator 2 and a grid frequency of the electrical grid or bus. Generally, the electrical grid or bus contains at least one alternating current bus, alternating current circuit, alternating current grid, or combinations thereof. Additionally, a breaker on the power generator 2 may be closed once the power turbine 3 is synchronized with the power generator 2. In one embodiment, the trim controller for adjusting the fine trim may be activated once the generator frequency is within about +/- 10 degrees of phase of the grid frequency. Also, a course trim controller for adjusting the course trim may be activated once a phase value of the grid frequency is outside of about 1 0 degrees of a predetermined "phase window".

[055] In other examples, the method provides adjusting the flow of the working fluid by modulating the throttle valve 1 50 while adaptively tuning the power turbine 3 to maintain a power output of the power generator 2 at a power level that is stable or continuous or at least substantially stable or continuous during a power mode process, even though the power generator 2 experiences a changing demand in load. Generally, the load on the power generator 2 is increasing during the power mode process while a power mode controller adaptively tunes the power turbine 3 by modulating the throttle valve 1 50 to maintain a substantially stable or continuous power level. In some examples, the method includes monitoring the power output from the power generator 2 with the power mode controller as part of the control system 108, and modulating the throttle valve 150 with the power mode controller to adaptively tune the power turbine 3 in response to the power output.

[056] In other examples, the method provides monitoring and detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit 120 during a process upset. In some examples, the method includes detecting the process upset and subsequently adjusting the flow of the working fluid by modulating the throttle valve 1 50 to increase the pressure of the working fluid within the working fluid circuit 1 20 during a pressure mode control process. A pressure mode controller may be configured to adjust the flow of the working fluid by modulating the throttle valve 1 50 to increase the pressure during the process upset.

[057] In other examples, a sliding mode control process may be implemented to protect the power turbine 3, the power generator 2, the shaft 103, or the gearbox (not shown) from an overspeed condition. The method provides monitoring for a change in the rotational speed of the power turbine 3, the power generator 2, or a shaft 103 coupled between the power turbine 3 and the power generator 2 during the process upset. Upon detecting the increase of rotational speed during the process upset - the method includes adjusting the flow of the working fluid by modulating the throttle valve 1 50 to gradually reduce the rotational speed. A sliding mode controller may be configured to adjust the flow of the working fluid by modulating the throttle valve 1 50 to gradually reduce the rotational speed and to prevent an overspeed condition. Alternatively, upon detecting a decrease of rotational speed during the process upset - the method includes adjusting the flow of the working fluid by modulating the throttle valve 1 50 to gradually increase the rotational speed.

[058] In other examples, the method includes detecting that the power turbine 3, the power generator 2, and/or the shaft 1 03 is experiencing an overspeed condition and subsequently implementing an overspeed mode control process to immediately reduce the rotational speed. An overspeed mode controller may be configured to adjust the flow of the working fluid by modulating the throttle valve 150 to reduce the rotational speed during the overspeed condition.

[059] In some embodiments, the overall efficiency of the heat engine system 100 and the amount of power ultimately generated can be influenced by the inlet or suction pressure at the pump 9 when the working fluid contains supercritical carbon dioxide. In order to minimize or otherwise regulate the suction pressure of the pump 9, the heat engine system 1 00 may incorporate the use of a mass management system ("MMS") 1 10. The mass management system 1 10 controls the inlet pressure of the pump 9 by regulating the amount of working fluid entering and/or exiting the heat engine system 1 00 at strategic locations in the working fluid circuit 120, such as at tie-in points A, B, and C. Consequently, the heat engine system 1 00 becomes more efficient by increasing the pressure ratio for the pump 9 to a maximum possible extent.

[060] The mass management system 1 1 0 has a vessel or tank, such as a storage vessel, a working fluid vessel, or the mass control tank 7, fluidly coupled to the low and high pressure sides of the working fluid circuit 1 20 via one or more valves. The valves are moveable - as being partially opened, fully opened, and/or closed - to either remove working fluid from the working fluid circuit 120 or add working fluid to the working fluid circuit 120. Exemplary embodiments of the mass management system 1 10, 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. 2012-0047892, the contents of which are incorporated herein by reference to the extent consistent with the present disclosure. Briefly, however, the mass management system 1 1 0 may include a plurality of valves and/or connection points 1 4, 1 5, 16, 17, 1 8, 21 , 22, and 23, each in fluid communication with a mass control tank 7. The valves 14, 15, and 1 6 may be characterized as termination points where the mass management system 1 10 is operatively connected to the heat engine system 1 00. The connection points 1 8, 21 , 22, and 23 and valve 17 may be configured to provide the mass management system 1 10 with an outlet for flaring excess working fluid or pressure, or to provide the mass management system 1 1 0 with additional/supplemental working fluid from an external source, such as a fluid fill system, as described herein.

[061] The first valve 1 4 fluidly couples the mass management system 1 10 to the heat engine system 1 00 at or near tie-in point A, where the working fluid is heated and pressurized after being discharged from the heat exchanger 5. The second valve 1 5 fluidly couples the mass management system 1 10 to the heat engine system 1 00 at or near tie-in point C, arranged adjacent the inlet to the pump 9, where the working fluid is generally at a low temperature and pressure. The third valve 1 6 fluidly couples the mass management system 1 1 0 to the heat engine system 100 at or near tie-in point B, where the working fluid is more dense and at a higher pressure relative to the density and pressure on the low pressure side of the heat engine system 1 00 (e.g., adjacent tie- in point C).

[062] The mass control tank 7 may be configured as a localized storage for additional/supplemental working fluid that may be added to the heat engine system 100 when needed in order to regulate the pressure or temperature of the working fluid within the fluid circuit or otherwise supplement escaped working fluid. By controlling the valves 1 4, 1 5, and 1 6, the mass management system 1 1 0 adds and/or removes working fluid mass to/from the heat engine system 100 without the need of a pump, thereby reducing system cost, complexity, and maintenance. For example, the mass control tank 7 is pressurized by opening the first valve 1 4 to allow high-temperature, high-pressure working fluid to flow into the mass control tank 7 via tie-in point A. Once pressurized, additional/supplemental working fluid may be injected back into the fluid circuit from the mass control tank 7 via the second valve 15 and tie-in point C. Adjusting the position of the second valve 1 5 may serve to continuously regulate the inlet pressure of the pump 9. The third valve 16 may be opened to remove working fluid from the fluid circuit at tie-in point B and deliver that working fluid to the mass control tank 7.

[063] The mass management system 1 1 0 may operate with the heat engine system 1 00 semi-passively with the aid of first, second, and third sets of sensors 1 02, 1 04, and 1 06, respectively. The first set of sensors 102 is arranged at or adjacent the suction inlet of the pump 9 and the second set of sensors 104 is arranged at or adjacent the outlet of the pump 9. The first and second sets of sensors 102, 1 04 monitor and report the pressure, temperature, mass flowrate, or other properties of the working fluid within the low and high pressure sides of the fluid circuit adjacent the pump 9. The third set of sensors 106 is arranged either inside or adjacent the mass control tank 7 to measure and report the pressure, temperature, mass flowrate, or other properties of the working fluid within the tank 7.

[064] The control system 1 08 is also communicably connected, wired and/or wirelessly, with each set of sensors 1 02, 104, and 1 06 in order to process the measured and reported temperatures, pressures, and mass flowrates of the working fluid at the designated points. In response to these measured and/or reported parameters, the control system 108 may be operable to selectively adjust the valves 1 4, 15, and 16 in accordance with a control program or algorithm, thereby maximizing operation of the heat engine system 100. Additionally, an instrument air supply 29 may be coupled to sensors, devices, or other instruments within the heat engine system 100 including the mass management system 1 10 and/or other system components that may utilize a gaseous supply, such as nitrogen or air.

[065] Of the connection points 1 8, 21 , 22, and 23 and valve 1 7, at least one connection point, such as connection point 21 , may be a fluid fill port for the mass management system 1 1 0. Additional/supplemental working fluid may be added to the mass management system 1 1 0 from an external source, such as a fluid fill system via the fluid fill port or connection point 21 . Exemplary fluid fill systems are described and illustrated in U.S. Pat. No. 8,281 ,593, the contents of which are incorporated herein by reference to the extent consistent with the present disclosure. [066] Figure 2 illustrates an exemplary heat engine system 200, which may also be referred to as a thermal engine system, a power generation system, a waste heat or other heat recovery system, and/or a thermal to electrical energy system, as described in one or more embodiments herein. The heat engine system 200 is generally configured to encompass one or more elements of a Rankine cycle, a derivative of a Rankine cycle, or another thermodynamic cycle for generating electrical energy from a wide range of thermal sources. The heat engine system 200 contains at least one heat exchanger, such as a heat exchanger 21 0, fluidly coupled to the high pressure side of the working fluid circuit 202 and in thermal communication with the heat source stream 1 90. Such thermal communication provides the transfer of thermal energy from the heat source stream 190 to the working fluid flowing throughout the working fluid circuit 202.

[067] The heat source stream 190 may be a waste heat stream such as, but not limited to, gas turbine exhaust stream, industrial process exhaust stream, or other combustion product exhaust streams, such as furnace or boiler exhaust streams. The heat source stream 1 90 may be at a temperature within a range from about 1 00°C to about 1 ,000°C or greater, and in some examples, within a range from about 200°C to about 800°C, more narrowly within a range from about 300°C to about 600°C. The heat source stream 1 90 may contain air, carbon dioxide, carbon monoxide, water or steam, nitrogen, oxygen, argon, derivatives thereof, or mixtures thereof. In some embodiments, the heat source stream 1 90 may derive thermal energy from renewable sources of thermal energy, such as solar or geothermal sources.

[068] The heat engine system 200 further contains a power turbine 220 disposed between the high pressure side and the low pressure side of the working fluid circuit 202, disposed downstream from the heat exchanger 210, and fluidly coupled to and in thermal communication with the working fluid. The power turbine 220 is configured to convert a pressure drop in the working fluid to mechanical energy whereby the absorbed thermal energy of the working fluid is transformed to mechanical energy of the power turbine 220. Therefore, the power turbine 220 is an expansion device capable of transforming a pressurized fluid into mechanical energy, generally, transforming high temperature and pressure fluid into mechanical energy, such as rotating a shaft. [069] The power turbine 220 may contain or be a turbine, a turbo, an expander, or another device for receiving and expanding the working fluid discharged from the heat exchanger 21 0. The power turbine 220 may have an axial construction or radial construction and may be a single-staged device or a multi-staged device. Exemplary turbines that may be utilized in power turbine 220 include an expansion device, a geroler, a gerotor, a valve, other types of positive displacement devices such as a pressure swing, a turbine, a turbo, or any other device capable of transforming a pressure or pressure/enthalpy drop in a working fluid into mechanical energy. A variety of expanding devices are capable of working within the inventive system and achieving different performance properties that may be utilized as the power turbine 220.

[070] The power turbine 220 is generally coupled to a power generator 240 by a shaft 230. A gearbox 232 is generally disposed between the power turbine 220 and the power generator 240 and adjacent or encompassing the shaft 230. The shaft 230 may be a single piece or contain two or more pieces coupled together. In one example, a first segment of the shaft 230 extends from the power turbine 220 to the gearbox 232, a second segment of the shaft 230 extends from the gearbox 232 to the power generator 240, and multiple gears are disposed between and couple to the two segments of the shaft 230 within the gearbox 232. In some configurations, the shaft 230 includes a seal assembly (not shown) designed to prevent or capture any working fluid leakage from the power turbine 220. Additionally, a working fluid recycle system may be implemented along with the seal assembly to recycle seal gas back into the fluid circuit of the heat engine system 200.

[071] The power generator 240 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 230 and the power turbine 220 to electrical energy. A power outlet 242 is electrically coupled to the power generator 240 and configured to transfer the generated electrical energy from the power generator 240 to an electrical grid 244. The electrical grid 244 may be or include an electrical grid, an electrical bus (e.g. , plant bus), power electronics, other electric circuits, or combinations thereof. The electrical grid 244 generally contains at least one alternating current bus, alternating current grid, alternating current circuit, or combinations thereof. In one example, the power generator 240 is a generator and is electrically and operably connected to the electrical grid 244 via the power outlet 242. In another example, the power generator 240 is an alternator and is electrically and operably connected to power electronics (not shown) via the power outlet 242. In another example, the power generator 240 is electrically connected to power electronics which are electrically connected to the power outlet 242.

[072] The power electronics 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 may include converters or rectifiers, inverters, transformers, regulators, controllers, switches, resistors, storage devices, and other power electronic components and devices. In other embodiments, the power generator 240 may contain, be coupled with, or be other types of load receiving equipment, such as other types of electrical generation equipment, rotating equipment, a gearbox (e.g., gearbox 232), or other device configured to modify or convert the shaft work created by the power turbine 220. In one embodiment, the power generator 240 is in fluid communication with a cooling loop having a radiator and a pump for circulating a cooling fluid, such as water, thermal oils, and/or other suitable refrigerants. The cooling loop may be configured to regulate the temperature of the power generator 240 and power electronics by circulating the cooling fluid to draw away generated heat.

[073] The heat engine system 200 also provides for the delivery of a portion of the working fluid into a chamber or housing of the power turbine 220 for purposes of cooling one or more parts of the power turbine 220. In one embodiment, due to the potential need for dynamic pressure balancing within the power generator 240, the selection of the site within the heat engine system 200 from which to obtain a portion of the working fluid is critical because introduction of this portion of the working fluid into the power generator 240 should respect or not disturb the pressure balance and stability of the power generator 240 during operation. Therefore, the pressure of the working fluid delivered into the power generator 240 for purposes of cooling is the same or substantially the same as the pressure of the working fluid at an inlet (not shown) of the power turbine 220. The working fluid is conditioned to be at a desired temperature and pressure prior to being introduced into the housing of the power turbine 220. A portion of the working fluid, such as the spent working fluid, exits the power turbine 220 at an outlet (not shown) of the power turbine 220 and is directed to one or more heat exchangers or recuperators, such as recuperators 21 6 and 218. The recuperators 216 and 218 may be fluidly coupled with the working fluid circuit 202 in series with each other. The recuperators 216 and 218 are operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit 202.

[074] In one embodiment, the recuperator 216 is fluidly coupled to the low pressure side of the working fluid circuit 202, disposed downstream from a working fluid outlet on the power turbine 220, disposed upstream from the recuperator 21 8 and/or the condenser 274, and configured to remove at least a portion of the thermal energy from the working fluid discharged from the power turbine 220. In addition, the recuperator 216 is also fluidly coupled to the high pressure side of the working fluid circuit 202, disposed upstream from the heat exchanger 210 and/or a working fluid inlet on the power turbine 220, disposed downstream from the heat exchanger 208, and configured to increase the amount of thermal energy in the working fluid prior to flowing into the heat exchanger 210 and/or the power turbine 220. Therefore, the recuperator 21 6 is a heat exchanger configured to cool the low pressurized working fluid discharged or downstream from the power turbine 220 while heating the high pressurized working fluid entering into or upstream from the heat exchanger 210 and/or the power turbine 220.

[075] Similarly, in another embodiment, the recuperator 21 8 is fluidly coupled to the low pressure side of the working fluid circuit 202, disposed downstream from a working fluid outlet on the power turbine 220 and/or the recuperator 21 6, disposed upstream from the condenser 274, and configured to remove at least a portion of the thermal energy from the working fluid discharged from the power turbine 220 and/or the recuperator 216. In addition, the recuperator 218 is also fluidly coupled to the high pressure side of the working fluid circuit 202, disposed upstream from the heat exchanger 212 and/or a working fluid inlet on a drive turbine 264 of turbo pump 260, disposed downstream from a working fluid outlet on a pump portion 262 of turbo pump 260, and configured to increase the amount of thermal energy in the working fluid prior to flowing into the heat exchanger 212 and/or the drive turbine 264. Therefore, the recuperator 218 is a heat exchanger configured to cool the low pressurized working fluid discharged or downstream from the power turbine 220 and/or the recuperator 21 6 while heating the high pressurized working fluid entering into or upstream from the heat exchanger 212 and/or the drive turbine 264.

[076] In some examples, an additional condenser or a cooler (not shown) may be fluidly coupled to each of the recuperators 21 6 and 21 8 and in thermal communication with the low pressure side of the working fluid circuit 202, the condenser or the cooler is operative to control a temperature of the working fluid in the low pressure side of the working fluid circuit 202.

[077] The heat engine system 200 further contains several pumps, such as a turbo pump 260 and a start pump 265, 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 turbo pump 260 and the start pump 265 are operative to circulate the working fluid throughout the working fluid circuit 202. The start pump 265 is utilized to initially pressurize and circulate the working fluid in the working fluid circuit 202. Once a predetermined pressure, temperature, and/or flowrate of the working fluid is obtained within the working fluid circuit 202, the start pump 265 may be taken off line, idled, or turned off and the turbo pump 260 is utilize to circulate the working fluid during the electricity generation process. The working fluid enters each of the turbo pump 260 and the start pump 265 from the low pressure side of the working fluid circuit 202 and exits each of the turbo pump 260 and the start pump 265 from the high pressure side of the working fluid circuit 202.

[078] The start pump 265 is generally a motorized pump, such as an electrical motorized pump, a mechanical motorized pump, or any other suitable type of pump. Generally, the start pump 265 may be a variable frequency motorized drive pump and contains a pump portion 266 and a motor-drive portion 268. The motor-drive portion 268 of the start pump 265 contains a motor and the drive including a drive shaft and gears. In some examples, the motor-drive portion 268 has a variable frequency drive, such that the speed of the motor may be regulated by the drive. The pump portion 266 of the start pump 265 is driven by the motor-drive portion 268 coupled thereto. The pump portion 266 has an inlet for receiving the working fluid from the low pressure side of the working fluid circuit 202, such as from the condenser 274 and/or the working fluid storage system 300. The pump portion 266 has an outlet for releasing the working fluid into the high pressure side of the working fluid circuit 202.

[079] The turbo pump 260 is a turbo-drive pump or a turbine-drive pump and utilized to pressurize and circulate the working fluid throughout the working fluid circuit 202. The turbo pump 260 contains a pump portion 262 and a drive turbine 264 coupled together by a drive shaft and optional gearbox. The pump portion 262 of the turbo pump 260 is driven by the drive shaft coupled to the drive turbine 264. The pump portion 262 has an inlet for receiving the working fluid from the low pressure side of the working fluid circuit 202, such as from the condenser 274 and/or the working fluid storage system 300. The pump portion 262 has an outlet for releasing the working fluid into the high pressure side of the working fluid circuit 202.

[080] The drive turbine 264 of the turbo pump 260 is driven by the working fluid heated by the heat exchanger 21 2. The drive turbine 264 has an inlet for receiving the working fluid flowing from the heat exchanger 21 2 in the high pressure side of the working fluid circuit 202. The drive turbine 264 has an outlet for releasing the working fluid into the low pressure side of the working fluid circuit 202. In one configuration, the working fluid released from the outlet on the drive turbine 264 is returned into the working fluid circuit 202 downstream from the recuperator 216 and upstream from the recuperator 21 8.

[081] A bypass valve 261 is generally coupled between and in fluid communication with a fluid line extending from the inlet on the drive turbine 264 and a fluid line extending from the outlet on the drive turbine 264. The bypass valve 261 may be opened to bypass the drive turbine 264 while using the start pump 265 during the initial stages of generating electricity with the heat engine system 200. Once a predetermined pressure and temperature of the working fluid is obtained within the working fluid circuit 202, the bypass valve 261 may be closed and the heated working fluid is flowed through the drive turbine 264 to start the turbo pump 260.

[082] Control valve 246 is disposed downstream from the outlet of the pump portion 262 of the turbo pump 260 and control valve 248 is disposed downstream from the outlet of the pump portion 266 of the start pump 265. Control valves 246 and 248 are flow control safety valves and generally utilized to regulate the directional flow or to prohibit backflow of the working fluid within the working fluid circuit 202. Bypass valves 254 and 256 are independently 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. Therefore, the working fluid flows through each of the bypass valves 254 and 256 from the high pressure side of the working fluid circuit 202 and exits each of the bypass valves 254 and 256 to the low pressure side of the working fluid circuit 202.

[083] A cooler or condenser 274 is fluidly coupled to the turbo pump 260 and/or the start pump 265 and receives the cooled working fluid and pressurizes the working fluid circuit 202 to recirculate the working fluid back to the heat exchanger 210. The condenser 274 is fluidly coupled with a cooling system (not shown) that receives a cooling fluid from a cooling fluid supply 278a and returns the warmed cooling fluid to the cooling system via a cooling fluid return 278b. The cooling fluid may be water, carbon dioxide, or other aqueous and/or organic fluids or various mixtures thereof that is maintained at a lower temperature than the working fluid.

[084] In some embodiments, the types of working fluid that may be circulated, flowed, or otherwise utilized in the working fluid circuit 202 of the heat engine system 200 include carbon oxides, hydrocarbons, alcohols, ketones, halogenated hydrocarbons, ammonia, amines, aqueous, or combinations thereof. Exemplary working fluids that may be utilized in the heat engine system 200 include carbon dioxide, ammonia, methane, ethane, propane, butane, ethylene, propylene, butylene, acetylene, methanol, ethanol, acetone, methyl ethyl ketone, water, derivatives thereof, or mixtures thereof. Halogenated hydrocarbons may include hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) (e.g., 1 ,1 ,1 ,3,3-pentafluoropropane (R245fa)), fluorocarbons, derivatives thereof, or mixtures thereof.

[085] In many embodiments described herein, the working fluid circulated, flowed, or otherwise utilized in the working fluid circuit 202 of the heat engine system 200, and the other exemplary circuits disclosed herein, may be or may contain carbon dioxide (C0₂) and mixtures containing carbon dioxide. Generally, at least a portion of the working fluid circuit 202 contains the working fluid in a supercritical state (e.g., sc-C0₂). Carbon dioxide utilized as the working fluid or contained in the working fluid for power generation cycles has many advantages over other compounds typically used as working fluids, since carbon dioxide has the properties of being non-toxic and nonflammable and is also easily available and relatively inexpensive. Due in part to a relatively high working pressure of carbon dioxide, a carbon dioxide system may be much more compact than systems using other working fluids. The high density and volumetric heat capacity of carbon dioxide with respect to other working fluids makes carbon dioxide more "energy dense," meaning that the size of all system components can be considerably reduced without losing performance. It should be noted that use of the terms carbon dioxide (C0₂), supercritical carbon dioxide (sc-C0₂), or subcritical carbon dioxide (sub-C0₂) 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.

[086] In other exemplary embodiments, the working fluid in the working fluid circuit 202 may be a binary, ternary, or other working fluid blend. The working fluid blend or combination can be selected for the unique attributes possessed by the fluid combination within a heat recovery system, as described herein. For example, one such fluid combination includes a liquid absorbent and carbon dioxide mixture enabling the combined fluid to be pumped in a liquid state to high pressure with less energy input than required to compress carbon dioxide. In another exemplary embodiment, the working fluid may be a combination of supercritical carbon dioxide (sc-C0₂), subcritical carbon dioxide (sub-C0₂), and/or one or more other miscible fluids or chemical compounds. In yet other exemplary embodiments, the working fluid may be a combination of carbon dioxide and propane, or carbon dioxide and ammonia, without departing from the scope of the disclosure.

[087] The working fluid circuit 202 generally has a high pressure side and a low pressure side and contains a working fluid circulated within the working fluid circuit 202. The use of the term "working fluid" is not intended to limit the state or phase of matter 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 system 200 or thermodynamic cycle. In one or more embodiments, the working fluid is in a supercritical state over certain portions of the working fluid circuit 202 of the heat engine system 200 (e.g., a high pressure side) and in a subcritical state over other portions of the working fluid circuit 202 of the heat engine system 200 (e.g., a low pressure side). Figure 2 depicts the high and low pressure sides of the working fluid circuit 202 of the heat engine system 200 by representing the high pressure side with a "— " line and the low pressure side with the combined " " and "— " lines (as shown in key on Figure

2) - as described in one or more embodiments. 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 entire working fluid circuit 202 of the heat engine system 200. Figure 2 also depicts other components or portions of the working fluid circuit 202 in the heat engine system 200 by representing the miscellaneous portions of the working fluid circuit 202 with the combined " " and "— " lines (as shown in key on Figure 2), as described in one or more embodiments.

[088] Generally, the high pressure side of the working fluid circuit 202 contains the working fluid (e.g., sc-C0₂) at a pressure of about 1 5 MPa or greater, such as about 1 7 MPa or greater or about 20 MPa or greater. In some examples, the high pressure side of the working fluid circuit 202 may have a pressure within a range from about 1 5 MPa to about 30 MPa, more narrowly within a range from about 16 MPa to about 26 MPa, more narrowly within a range from about 17 MPa to about 25 MPa, and more narrowly within a range from about 1 7 MPa to about 24 MPa, such as about 23.3 MPa. In other examples, the high pressure side of the working fluid circuit 202 may have a pressure within a range from about 20 MPa to about 30 MPa, more narrowly within a range from about 21 MPa to about 25 MPa, and more narrowly within a range from about 22 MPa to about 24 MPa, such as about 23 MPa.

[089] The low pressure side of the working fluid circuit 202 contains the working fluid (e.g., C0₂ or sub-C0₂) at a pressure of less than 1 5 MPa, such as about 12 MPa or less or about 1 0 MPa or less. In some examples, the low pressure side of the working fluid circuit 202 may have a pressure within a range from about 4 MPa to about 14 MPa, more narrowly within a range from about 6 MPa to about 13 MPa, more narrowly within a range from about 8 MPa to about 1 2 MPa, and more narrowly within a range from about 1 0 MPa to about 1 1 MPa, such as about 10.3 MPa. In other examples, the low pressure side of the working fluid circuit 202 may have a pressure within a range from about 2 MPa to about 1 0 MPa, more narrowly within a range from about 4 MPa to about 8 MPa, and more narrowly within a range from about 5 MPa to about 7 MPa, such as about 6 MPa.

[090] In some examples, the high pressure side of the working fluid circuit 202 may have a pressure within a range from about 17 MPa to about 23.5 MPa, and more narrowly within a range from about 23 MPa to about 23.3 MPa while the low pressure side of the working fluid circuit 202 may have a pressure within a range from about 8 MPa to about 1 1 MPa, and more narrowly within a range from about 10.3 MPa to about 1 1 MPa.

[091] Figure 2 further depicts a power turbine throttle valve 250 fluidly coupled to the high pressure side of the working fluid circuit 202 and upstream from the heat exchanger 21 0, as disclosed by at least one embodiment described herein. Additionally, Figure 2 depicts a drive turbine throttle valve 252 fluidly coupled to the high pressure side of the working fluid circuit 202 and upstream from the heat exchanger 212, as disclosed by another embodiment described herein. The power turbine throttle valve 250 and the drive turbine throttle valve 252 are configured to control a flow of the working fluid throughout the working fluid circuit 202 and to the power turbine 220 and drive turbine 264, respectively. Generally, the working fluid is in a supercritical state while flowing through the high pressure side of the working fluid circuit 202. The power turbine throttle valve 250 may be controlled by a control system 204 that also communicably connected, wired and/or wirelessly, with the power turbine throttle valve 250 and other parts of the heat engine system 200. The control system 204 is operatively connected to the working fluid circuit 202 and a mass management system 270 and is enabled to monitor and control multiple process operation parameters of the heat engine system 200. A computer system 206, as part of the control system 204, contains a multi-controller algorithm utilized to control the power turbine throttle valve 250. The multi-controller algorithm has multiple modes to control the power turbine throttle valve 250 for efficiently executing the processes of generating electricity by the heat engine system 200, as described herein. The control system 204 is enabled to move, adjust, manipulate, or otherwise control the power turbine throttle valve 250 for adjusting or controlling the flow of the working fluid throughout the working fluid circuit 202. By controlling the flow of the working fluid, the control system 204 is also operable to regulate the temperatures and pressures throughout the working fluid circuit 202.

[092] In some embodiments, the overall efficiency of the heat engine system 200 and the amount of power ultimately generated can be influenced by the inlet or suction pressure at the start pump 265 when the working fluid contains supercritical carbon dioxide. In order to minimize or otherwise regulate the suction pressure of the start pump 265, the heat engine system 200 may incorporate the use of a mass management system ("MMS") 270. The mass management system 270 controls the inlet pressure of the start pump 265 by regulating the amount of working fluid entering and/or exiting the heat engine system 200 at strategic locations in the working fluid circuit 202, such as at tie-in points, inlets/outlets, valves, or conduits throughout the heat engine system 200. Consequently, the heat engine system 200 becomes more efficient by increasing the pressure ratio for the start pump 265 to a maximum possible extent.

[093] The mass management system 270 has a vessel or tank, such as a storage vessel, a working fluid vessel, or the mass control tank, fluidly coupled to the low and high pressure sides of the working fluid circuit 202 via one or more valves. In some examples, a working fluid storage vessel 31 0 is part of a working fluid storage system 300. The valves are moveable - as being partially opened, fully opened, and/or closed - to either remove working fluid from the working fluid circuit 202 or add working fluid to the working fluid circuit 202. The mass management system 270 and exemplary fluid fill systems that may be utilized with the heat engine system 200 may be the same as or similar to the mass management system 1 10 and exemplary fluid fill systems that may be utilized with the heat engine system 100 described herein.

[094] The control system 204 is also communicably connected, wired and/or wirelessly, with each set of sensors in order to process the measured and reported temperatures, pressures, and mass flowrates of the working fluid at the designated points. In response to these measured and/or reported parameters, the control system 204 may be operable to selectively adjust the valves in accordance with a control program or algorithm, thereby maximizing operation of the heat engine system 200.

[095] The control system 204 and/or the mass management system 270 may operate with the heat engine system 200 semi-passively with the aid of several sets of sensors. The first set of sensors is arranged at or adjacent the suction inlet of the pumps 260, 265 and the second set of sensors is arranged at or adjacent the outlet of the pumps 260, 265. The first and second sets of sensors monitor and report the pressure, temperature, mass flowrate, or other properties of the working fluid within the low and high pressure sides of the fluid circuit adjacent the pumps 260, 265. The third set of sensors is arranged either inside or adjacent the working fluid storage vessel 31 0 of the working fluid storage system 300 to measure and report the pressure, temperature, mass flowrate, or other properties of the working fluid within the working fluid storage vessel 31 0.

[096] In one or more embodiments described herein, a control algorithm is provided and utilized to manage the heat engine system 200 and process for generating electricity. Figure 3 depicts an exemplary scheme 350 of the control algorithm that may be utilized to manage, operate, adjust, modulate, or otherwise control the throttle valve 1 50 disposed within the heat engine system 1 00 (Figure 1 ), as well as the power turbine throttle valve 250 and the drive turbine throttle valve 252 disposed within the heat engine system 200 (Figure 2).

[097] The control algorithm may be embedded in the computer system 206 as part of the control system 204 of the heat engine system 200. The control algorithm may be utilized throughout the various steps or processes described herein including while initiating and maintaining the heat engine system 200, as well as during a process upset or crisis event, and for maximizing the efficiency of the heat engine system 200 while generating electricity. The control system 204 or the control algorithm contains for at least one system controller, but generally contains multiple system controllers utilized for managing the integrated sub-systems of the heat engine system 200. Exemplary system controllers include a trim controller, a power mode controller, a sliding mode controller, a pressure mode controller, an overspeed mode controller, a proportional integral derivative controller, a multi-mode controller, derivatives thereof, and/or combinations thereof.

[098] In some examples, the control system 204 or the control algorithm contains a trim controller configured to control rotational speed of the power turbine 220 or the power generator 240. The trim controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to increase or decrease rotational speed of the power turbine 220 or the power generator 240 during a synchronization process. The trim controller is provided by a proportional integral derivative (PID) controller within a generator control module as a portion of the control system 204 of the heat engine system 200.

[099] In other examples, the control system 204 or the control algorithm contains a power mode controller configured to monitor a power output from the power generator 240 and modulate the power turbine throttle valve 250 in response to the power output while adaptively tuning the power turbine 220 to maintain a power output from the power generator 240 at a continuous or substantially continuous power level during a power mode process. The power mode controller may be configured to maintain the power output from the power generator 240 at the continuous or substantially continuous power level during the power mode process while a load is increasing on the power generator 240.

[0100] In other examples, the control system 204 or the control algorithm contains a sliding mode controller configured to monitor and detect an increase of rotational speed of the power turbine 220, the power generator 240, or the shaft 230 coupled between the power turbine 220 and the power generator 240. The sliding mode controller is further configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to reduce the rotational speed after detecting the increase of rotational speed.

[0101] In other examples, the control system 204 or the control algorithm contains a pressure mode controller configured to monitor and detect a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit 202 during a process upset. The pressure mode controller is further configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to increase the pressure of the working fluid within the working fluid circuit 202 during a pressure mode control process. In some examples, the control system 204 or the control algorithm contains an overspeed mode controller configured to detect an overspeed condition and subsequently implement an overspeed mode control process to immediately reduce a rotational speed of the power turbine 220, the power generator 240, or a shaft 230 coupled between the power turbine 220 and the power generator 240.

[0102] In one example, the control algorithm, embedded in the computer system 206 as part of the control system 204 for the heat engine system 200. The control system 204 and/or the control algorithm contains at least: (i.) a trim controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to control a rotational speed of the power turbine 220 while synchronizing the power generator 240 with the electrical grid 244, such as an electrical grid, an electrical bus (e.g., plant bus), power electronics, or other circuit during a synchronization process; (ii.) a power mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to adaptively tune the power turbine 220 while maintaining a power output from the power generator 240 at a continuous or substantially continuous power level during a power mode process while increasing a load on the power generator 240; (iii.) a sliding mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to gradually reduce the rotational speed during the process upset; (iv.) a pressure mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to increase the pressure of the working fluid in response to detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit 202 during a pressure mode control process; and (v.) an overspeed mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to reduce the rotational speed during an overspeed condition.

[0103] In other embodiments described herein, a method for generating electricity with a heat engine system 200 is provided and includes circulating a working fluid within a working fluid circuit 202 having a high pressure side and a low pressure side, wherein at least a portion of the working fluid is in a supercritical state (e.g., sc-C0₂) and transferring thermal energy from a heat source stream 190 to the working fluid by at least one heat exchanger 21 0 fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit 202. The method further includes transferring the thermal energy from the heated working fluid to a power turbine 220 while converting a pressure drop in the heated working fluid to mechanical energy and converting the mechanical energy into electrical energy by a power generator 240 coupled to the power turbine 220. The power turbine 220 is generally disposed between the high pressure side and the low pressure side of the working fluid circuit 202 and fluidly coupled to and in thermal communication with the working fluid.

[0104] The method further includes transferring the electrical energy from the power generator 240 to a power outlet 242 and from the power outlet 242 to the electrical grid 244, such as an electrical grid, an electrical bus, power electronics, or other electrical circuits. The power outlet 242 is electrically coupled to the power generator 240 and configured to transfer the electrical energy from the power generator 240 to an electrical grid 244. The method further includes controlling the power turbine 220 by operating a power turbine throttle valve 250 to adjust a flow of the working fluid. The power turbine throttle valve 250 is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit 202 upstream from the power turbine 220. In another example, the drive turbine throttle valve 252 is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit 202 upstream from the drive turbine 264 of the turbo pump 260.

[0105] The method further includes monitoring and controlling multiple process operation parameters of the heat engine system 200 via a control system 204 operatively connected to the working fluid circuit 202, wherein the control system 204 is configured to control the power turbine 220 by operating the power turbine throttle valve 250 to adjust the flow of the working fluid. In many examples, the working fluid contains carbon dioxide and at least a portion of the carbon dioxide is in a supercritical state (e.g., sc-C0₂).

[0106] In some examples, the method further provides adjusting the flow of the working fluid by modulating, trimming, adjusting, or otherwise moving the power turbine throttle valve 250 to control a rotational speed of the power turbine 220 while synchronizing the power generator 240 with the electrical grid or bus (not shown) during a synchronization process. Therefore, the power turbine throttle valve 250 may be modulated to control the rotational speed of the power turbine 220 which in turn controls the rotational speed of the power generator 240 as well as the shaft 230 disposed between and coupled to the power turbine 220 and the power generator 240. The power turbine throttle valve 250 may be modulated between a fully opened position, a partially opened position, a partially closed position, or a fully closed position. A trim controller, as part of the control system 204, may be utilized to control the rotational speed of the power turbine 220. The generator control module provides an output signal in relation to a phase difference between a generator frequency of the power generator 240 and a grid frequency of the electrical grid or bus. Generally, the electrical grid or bus contains at least one alternating current bus, alternating current circuit, alternating current grid, or combinations thereof. Additionally, a breaker on the power generator 240 may be closed once the power turbine 220 is synchronized with the power generator 240. In one embodiment, the trim controller for adjusting the fine trim may be activated once the generator frequency is within about +/- 1 0 degrees of phase of the grid frequency. Also, a course trim controller for adjusting the course trim may be activated once a phase value of the grid frequency is outside of about 1 0 degrees of a predetermined "phase window".

[0107] In other examples, the method provides adjusting the flow of the working fluid by modulating the power turbine throttle valve 250 while adaptively tuning the power turbine 220 to maintain a power output of the power generator 240 at a power level that is stable or continuous or at least substantially stable or continuous during a power mode process, even though the power generator 240 experiences a changing demand in load. Generally, the load on the power generator 240 is increasing during the power mode process while a power mode controller adaptively tunes the power turbine 220 by modulating the power turbine throttle valve 250 to maintain a substantially stable or continuous power level. In some examples, the method includes monitoring the power output from the power generator 240 with the power mode controller as part of the control system 204, and modulating the power turbine throttle valve 250 with the power mode controller to adaptively tune the power turbine 220 in response to the power output.

[0108] In other examples, the method provides monitoring and detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit 202 during a process upset. In some examples, the method includes detecting the process upset and subsequently adjusting the flow of the working fluid by modulating the power turbine throttle valve 250 to increase the pressure of the working fluid within the working fluid circuit 202 during a pressure mode control process. A pressure mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to increase the pressure during the process upset.

[0109] In other examples, a sliding mode control process may be implemented to protect the power turbine 220, the power generator 240, the shaft 230, and/or the gearbox 232 from an overspeed condition. The method provides monitoring for a change in the rotational speed of the power turbine 220, the power generator 240, or a shaft 230 coupled between the power turbine 220 and the power generator 240 during the process upset. Upon detecting the increase of rotational speed during the process upset, the method includes adjusting the flow of the working fluid by modulating the power turbine throttle valve 250 to gradually reduce the rotational speed. A sliding mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to gradually reduce the rotational speed and to prevent an overspeed condition. Alternatively, upon detecting a decrease of rotational speed during the process upset, the method includes adjusting the flow of the working fluid by modulating the power turbine throttle valve 250 to gradually increase the rotational speed.

[0110] In other examples, the method includes detecting that the power turbine 220, the power generator 240, and/or the shaft 230 is experiencing an overspeed condition and subsequently implementing an overspeed mode control process to immediately reduce the rotational speed. An overspeed mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to reduce the rotational speed during the overspeed condition. [0111] In other examples, the method provides monitoring and detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit 202 during a process upset. In some examples, the method includes detecting the process upset and subsequently adjusting the flow of the working fluid by modulating the power turbine throttle valve 250 to increase the pressure of the working fluid within the working fluid circuit 202 during a pressure mode control process. A pressure mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to increase the pressure during the process upset.

[0112] In other examples, a sliding mode control process may be implemented to protect the power turbine 220, the power generator 240, the shaft 230, or the gearbox 232 from an overspeed condition. The method provides monitoring for a change in the rotational speed of the power turbine 220, the power generator 240, or a shaft 230 coupled between the power turbine 220 and the power generator 240 during the process upset. Upon detecting the increase of rotational speed during the process upset, the method includes adjusting the flow of the working fluid by modulating the power turbine throttle valve 250 to gradually reduce the rotational speed. A sliding mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to gradually reduce the rotational speed and to prevent an overspeed condition. Alternatively, upon detecting a decrease of rotational speed during the process upset, the method includes adjusting the flow of the working fluid by modulating the power turbine throttle valve 250 to gradually increase the rotational speed.

[0113] In other examples, the method includes detecting that the power turbine 220, the power generator 240, and/or the shaft 230 is experiencing an overspeed condition and subsequently implementing an overspeed mode control process to immediately reduce the rotational speed. An overspeed mode controller may be configured to adjust the flow of the working fluid by modulating the power turbine throttle valve 250 to reduce the rotational speed during the overspeed condition.

[0114] In some embodiments of the heat engine system 200 described herein, the power turbine throttle valve 250 is fluidly coupled to the working fluid circuit 202 and is utilized to control the power turbine 220 for driving the power generator 240. The computer system 206, as part of the control system 204, contains a multi-controller algorithm utilized to control the power turbine throttle valve 250. The multi-controller algorithm has multiple modes to control the power turbine throttle valve 250 for efficiently executing the processes of generating electricity by the heat engine system 200, as described herein. Exemplary modes include precise speed control of the power turbine 220 and the power generator 240 to achieve generator synchronization between the frequencies of the power generator 240 and the electrical grid 244, power control or megawatt control of the heat engine system 200 to achieve maximum desired "load" or power and pressure control in the event of a process upset.

[0115] The multi-controller algorithm may be utilized for controlling the power turbine throttle valve 250 with the various desired modes of control by using multiple process variables based on the control mode for managing the working fluid circuit 202 containing at least a portion of the working fluid in a supercritical state (e.g., sc-C0₂ advanced cycle). As the system pressure and flowrate within the working fluid circuit 202 is brought to full load (e.g., full power), the power turbine throttle valve 250 may be first modulated to control the rotational speed of the power turbine 220 and the power generator 240 to achieve synchronization with the electrical grid 244. In one or embodiments, a power turbine speed controller, for controlling the power turbine 220 via the power turbine throttle valve 250, utilizes a fine "trim control" provided by a proportional integral derivative (PI D) controller in an Allen-Bradley combined generator control module that provides an output in relation to the phase difference of the generator frequency and the "plant bus" or "grid" frequency, for example, the phase difference of the frequency of the power generator 240 and the frequency of the electrical grid 244.

[0116] In another embodiment described herein, after achieving synchronization and the generator breaker is closed, the heat engine system 200 - and therefore the power turbine throttle valve 250 - operates in megawatt mode or power mode. A second controller - the power mode controller - utilizes generator power as a process variable for modulating the power turbine throttle valve 250. The power mode controller utilizes the advance control technique of adaptive tuning to maintain stable megawatt control as the demand for load and/or power is increased. In the event of a process upset and the heat engine system 200 is still connected to the electrical grid 244, a pressure mode controller adjusts the power turbine throttle valve 250 to increase the system pressure during a pressure mode control process. The increased pressure is generally within the high pressure side of the working fluid circuit 202 and helps to gain control or partial control to the working fluid in a supercritical state (e.g., sc-C0₂ process).

[0117] In another embodiment described herein, a sliding mode control may be implemented to protect the power turbine 220, the gearbox 232, and the power generator 240 from an overspeed condition. In the event that an overspeed is detected, a sliding mode controller will assume control of the power turbine throttle valve 250 to immediately reduce the rotational speed of the turbo machinery, such as the power turbine 220, the shaft 230, and the power generator 240.

[0118] It is to be understood that the present disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. 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, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment without departing from the scope of the disclosure. [0119] Additionally, certain terms are used throughout the present disclosure 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. Further, in the present disclosure 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.

[0120] 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.

Claims

Claims:

1 . A method for generating electricity with a heat engine system, comprising:

circulating a working fluid within a working fluid circuit having a high pressure side and a low pressure side, wherein at least a portion of the working fluid is in a supercritical state;

transferring thermal energy from a heat source stream to the working fluid by a heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit;

transferring the thermal energy from the working fluid to a power turbine while converting a pressure drop in the working fluid to mechanical energy, wherein the power turbine is disposed between the high pressure side and the low pressure side of the working fluid circuit and fluidly coupled to and in thermal communication with the working fluid;

converting the mechanical energy into electrical energy by a power generator coupled to the power turbine;

transferring the electrical energy from the power generator to a power outlet, wherein the power outlet is electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid;

controlling the power turbine by operating a power turbine throttle valve to adjust a flow of the working fluid, wherein the power turbine throttle valve is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit upstream from the power turbine; and

monitoring and controlling process operation parameters of the heat engine system via a control system operatively connected to the working fluid circuit, wherein the control system is configured to control the power turbine by operating the power turbine throttle valve to adjust the flow of the working fluid.

2. The method of claim 1 , wherein a control algorithm is embedded in a computer system as part of the control system, and the control algorithm comprises one or more system controllers selected from the group consisting of a trim controller, a power mode controller, a sliding mode controller, a pressure mode controller, an overspeed mode controller, a proportional integral derivative controller, a multi-mode controller, derivatives thereof, and combinations thereof.

3. The method of claim 1 , further comprising adjusting the flow of the working fluid by modulating the power turbine throttle valve to control a rotational speed of the power turbine while synchronizing the power generator with the electrical grid during a synchronization process.

4. The method of claim 3, wherein the electrical grid contains at least one alternating current bus, alternating current circuit, alternating current grid, or combinations thereof.

5. The method of claim 3, wherein the working fluid comprises carbon dioxide and at least a portion of the carbon dioxide is in a supercritical state.

6. The method of claim 3, further comprising controlling the rotational speed of the power turbine by a trim controller as part of the control system.

7. The method of claim 6, wherein the trim controller is provided by a proportional integral derivative (PID) controller within a generator control module.

8. The method of claim 6, wherein the generator control module provides an output signal in relation to a phase difference between a generator frequency of the power generator and a grid frequency of the electrical grid.

9. The method of claim 3, further comprising closing a breaker on the power generator once the power turbine is synchronized with the power generator.

1 0. The method of claim 1 , further comprising adjusting the flow of the working fluid by modulating the power turbine throttle valve while adaptively tuning the power turbine to maintain a power output from the power generator at a continuous or substantially continuous power level during a power mode process.

1 1 . The method of claim 10, further comprising increasing a load on the power generator while maintaining the power output from the power generator at the continuous or substantially continuous power level during the power mode process.

1 2. The method of claim 10, further comprising:

monitoring the power output from the power generator with a power mode controller as part of the control system; and

modulating the power turbine throttle valve with the power mode controller to adaptively tune the power turbine in response to the power output.

1 3. The method of claim 1 , further comprising monitoring and detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit during a process upset.

1 4. The method of claim 1 3, further comprising detecting the process upset and subsequently adjusting the flow of the working fluid by modulating the power turbine throttle valve to increase the pressure of the working fluid within the working fluid circuit during a pressure mode control process.

1 5. The method of claim 1 4, wherein a pressure mode controller is configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to increase the pressure during the process upset.

1 6. The method of claim 1 , further comprising monitoring and detecting an increase of rotational speed of the power turbine, the power generator, or a shaft coupled between the power turbine and the power generator during a process upset.

1 7. The method of claim 16, further comprising detecting the increase of rotational speed and subsequently adjusting the flow of the working fluid by modulating the power turbine throttle valve to reduce the rotational speed.

1 8. The method of claim 16, further comprising detecting the increase of rotational speed and subsequently implementing a sliding mode control process to reduce the rotational speed.

1 9. The method of claim 18, wherein a sliding mode controller is configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to gradually reduce the rotational speed during the process upset.

20. The method of claim 18, further comprising detecting an overspeed condition and subsequently implementing an overspeed mode control process to immediately reduce the rotational speed.

21 . The method of claim 20, wherein an overspeed mode controller is configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to reduce the rotational speed during the overspeed condition.

22. A control algorithm for controlling the heat engine system of claim 1 , wherein the control algorithm is embedded in a computer system as part of the control system, and the control algorithm comprises:

a trim controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to control a rotational speed of the power turbine while synchronizing the power generator with the electrical grid during a synchronization process;

a power mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to adaptively tune the power turbine while maintaining a power output from the power generator at a continuous or substantially continuous power level during a power mode process while increasing a load on the power generator;

a sliding mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to gradually reduce the rotational speed during the process upset;

a pressure mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to increase the pressure of the working fluid in response to detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit during a pressure mode control process; and

an overspeed mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to reduce the rotational speed during an overspeed condition.

23. A heat engine system for generating electricity, comprising:

a working fluid circuit having a high pressure side, a low pressure side, and a working fluid circulated within the working fluid circuit, wherein at least a portion of the working fluid is in a supercritical state;

a heat exchanger fluidly coupled to the high pressure side of the working fluid circuit and in thermal communication with a heat source stream whereby thermal energy is transferred from the heat source stream to the working fluid;

a 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 whereby the power turbine is configured to convert a pressure drop in the working fluid to mechanical energy and the thermal energy is transferred from the working fluid to the power turbine;

a power generator coupled to the power turbine and configured to convert the mechanical energy into electrical energy;

a power outlet electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid; a power turbine throttle valve fluidly coupled to the high pressure side of the working fluid circuit and configured to control a flow of the working fluid in the supercritical state with the working fluid circuit; and

a control system operatively connected to the working fluid circuit, enabled to monitor and control process operation parameters of the heat engine system, and enabled to move the power turbine throttle valve for controlling the flow of the working fluid.

24. The heat engine system of claim 23, wherein the control system comprises a control algorithm embedded in a computer system, and the control algorithm comprises one or more system controllers selected from the group consisting of a trim controller, a power mode controller, a sliding mode controller, a pressure mode controller, an overspeed mode controller, a proportional integral derivative controller, a multi-mode controller, derivatives thereof, and combinations thereof.

25. A control algorithm for controlling the heat engine system of claim 23, wherein the control algorithm is embedded in a computer system as part of the control system, and the control algorithm comprises:

a sliding mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to gradually reduce the rotational speed during the process upset; a pressure mode controller configured to adjust the flow of the working fluid by modulating the power turbine throttle valve to increase the pressure of the working fluid in response to detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit during a pressure mode control process; and