Methods for reducing wear on components of a heat engine system at startup

Provided herein are heat engine systems and methods for starting such systems and generating electricity while avoiding damage to one or more system components. A provided heat engine system maintains a working fluid (e.g., sc-CO2) within the low pressure side of a working fluid circuit in a liquid-type state, such as a supercritical state, during a startup procedure. Additionally, a bypass system is provided for routing the working fluid around one or more heat exchangers during startup to avoid overheating of system components.

BACKGROUND

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.

Waste heat can be converted into useful energy by a variety of turbine generator or heat engine systems that employ thermodynamic methods, such as Rankine cycles. Rankine cycles and similar thermodynamic methods are typically steam-based processes that recover and utilize waste heat to generate steam for driving a turbine, turbo, or other expander connected to an electric generator or pump. 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.

During a typical startup procedure, various components of the heat engine system begin to warm up, and the flow of the working fluid through a working fluid circuit is initiated. However, the waste heat flue is usually immediately operational at the beginning of the startup procedure. The thermal energy in the waste heat stream may cause immediate heat soaking of a heat exchanger provided to transfer heat from the waste heat stream to the working fluid. If the working fluid absorbs excess energy from the heat exchanger during the startup procedure, the properties of the working fluid may be disadvantageously altered, and one or more components of the heat engine system may be subject to damage or wear.

For example, if the working fluid absorbs excess thermal energy, then the working fluid may change to a different state of matter that is outside the scope of the system design. For further example, if a generator system requires the working fluid in a supercritical state, once overheated, the working fluid may have a subcritical, gaseous, or other state. Further, the overheated working fluid may escape by rupturing seals, valves, conduits, and connectors throughout the generally closed generator system, thus causing damage and expense. Additionally, the increased thermal stress can cause failure of fragile mechanical parts of the turbine power generator system. For example, the fins or blades of a turbo or turbine unit in the generator system may crack and disintegrate upon exposure to too much heat and stress. An overspeed situation is another expected problem upon the absorption of too much thermal energy by the turbine power generator system. During an overspeed situation, the rotational speed of the power turbine, the power generator, and/or the drive shaft becomes too fast and further accelerates the flow and increases the temperature of the working fluid and, if not controlled, generally leads to catastrophic system failure.

Additional concerns may arise during the startup procedure because the working fluid may change from a vapor phase to a liquid phase on a low pressure side of the fluid circuit, and the pressure of the liquid must be raised on the high pressure side of the circuit. Raising the pressure of a liquid phase by pumping generally requires less work per unit mass of working fluid than raising the pressure of a vapor phase by compression, and pumping also results in a higher overall cycle efficiency. Unfortunately, one consequence of pumping is that bubbles may form if the working fluid drops below the saturation temperature and pressure for the specific working fluid. Such bubbles may cause or otherwise form cavitation of the pump used to circulate the working fluid in the fluid circuit, thus leading to flow reduction and, in some cases, catastrophic damage to the pump and shutdown of the heat engine system.

Therefore, there is a need for systems and methods for generating electrical energy in which temperatures and pressures within a working fluid circuit are controlled to reduce or eliminate thermal stress on vulnerable mechanical parts of the heat engine system during a startup procedure.

SUMMARY

Embodiments of the invention generally provide heat engine systems and methods for starting heat engine systems and generating electricity. In one embodiment described herein, the method for starting a heat engine system is provided and includes circulating a working fluid within a working fluid circuit by a pump system, such that the working fluid circuit has a high pressure side containing the working fluid in a supercritical state, a low pressure side containing the working fluid in a subcritical state or a supercritical state, and the pump system may contain a turbopump, a start pump, other pumps, or combinations thereof. The method further includes transferring thermal energy from a heat source stream to the working fluid by at least a primary heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit and flowing the working fluid through a power turbine or through a power turbine bypass line circumventing the power turbine. The power turbine may be configured to convert the thermal energy from the working fluid to mechanical energy of the power turbine and the power turbine is coupled to a power generator configured to convert the mechanical energy into electrical energy. In addition, the method includes monitoring and maintaining a pump suction pressure of the working fluid within the low pressure side of the working fluid circuit upstream to an inlet on a pump portion of the turbopump via a process control system operatively connected to the working fluid circuit. Generally, the inlet on the pump portion of the turbopump and the low pressure side of the working fluid circuit contain the working fluid in the supercritical state during a startup procedure. Therefore, the pump suction pressure may be maintained at but generally greater than the critical pressure of the working fluid during the startup procedure.

In other embodiments, a method for starting a heat engine system is provided and includes circulating a working fluid within a working fluid circuit by a pump system, such that the working fluid circuit has a high pressure side containing the working fluid in a supercritical state and a low pressure side containing the working fluid in a subcritical state or a supercritical state. The method further includes transferring thermal energy from a heat source stream to the working fluid by at least a primary heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit and flowing the working fluid through a power turbine or through a power turbine bypass line circumventing the power turbine. Generally, the power turbine may be configured to convert the thermal energy from the working fluid to mechanical energy of the power turbine and the power turbine is coupled to a power generator configured to convert the mechanical energy into electrical energy.

Additionally, the method further includes monitoring and maintaining a pressure of the working fluid within the low pressure side of the working fluid circuit via a process control system operatively connected to the working fluid circuit, such that the low pressure side of the working fluid circuit contains the working fluid in the supercritical state during a startup procedure. The working fluid in the low pressure side is maintained at least at the critical pressure, but generally above the critical pressure of the working fluid during the startup procedure. In some embodiments, such as for the working fluid containing carbon dioxide and disposed within the low pressure side, the value of the critical pressure is generally greater than 5 MPa, such as about 7 MPa or greater, for example, about 7.38 MPa. Therefore, the working fluid in the low pressure side may be maintained at a pressure within a range from about 5 MPa to about 15 MPa, more narrowly within a range from about 7 MPa to about 12 MPa, more narrowly within a range from about 7.38 MPa to about 10.4 MPa, and more narrowly within a range from about 7.38 MPa to about 8 MPa during the startup procedure, in some examples.

The method may further include increasing the flowrate or temperature of the working fluid within the working fluid circuit and circulating the working fluid by a turbopump contained within the pump system during the startup procedure. In some configurations, the pump system of the heat engine system may have one or more pumps, such as a turbopump, a mechanical start pump, an electric start pump, or a combination of a turbo pump and a start pump.

The method may also include circulating the working fluid by the turbopump during a load ramp procedure or a full load procedure subsequent to the startup procedure, such that the flowrate or temperature of the working fluid sustains the turbopump during the load ramp procedure or the full load procedure. In some configurations, the heat engine system may have a secondary heat exchanger and/or a tertiary heat exchanger configured to heat the working fluid. Generally, the secondary heat exchanger and/or the tertiary heat exchanger may be configured to heat the working fluid upstream to an inlet on a drive turbine of the turbopump, such as during the load ramp procedure or the full load procedure. In some examples, at least one of the primary heat exchanger, the secondary heat exchanger, and/or the tertiary heat exchanger may reach a steady state during the load ramp procedure or the full load procedure.

In other embodiments, the method includes decreasing the pressure of the working fluid within the low pressure side of the working fluid circuit via the process control system during the load ramp procedure or the full load procedure. The method may also include decreasing the pressure of the working fluid within the low pressure side of the working fluid circuit via the process control system during the load ramp procedure or the full load procedure. In many examples, the working fluid within the low pressure side of the working fluid circuit is in a subcritical state during the load ramp procedure or the full load procedure. The working fluid in the subcritical state is generally in a liquid state and free or substantially free of a gaseous state. Therefore, the working fluid in the subcritical state is generally free or substantially free of bubbles. In many examples, the working fluid contains carbon dioxide.

In other embodiments, the method further includes detecting an undesirable value of the pressure via the process control system, wherein the undesirable value is less than a predetermined threshold value of the pressure, modulating at least one valve fluidly coupled to the working fluid circuit with the process control system to increase the pressure by increasing the flowrate of the working fluid passing through the at least one valve, and detecting a desirable value of the pressure via the process control system, wherein the desirable value is at or greater than the predetermined threshold value of the pressure.

In some examples, the method further includes measuring the pressure (e.g., the pump suction pressure) of the working fluid within the low pressure side of the working fluid circuit upstream to an inlet on a pump portion of a turbopump. The pump suction pressure may be at the critical pressure of the working fluid, but generally, the pump suction pressure is greater than the critical pressure of the working fluid at the inlet on the pump portion of the turbopump. In other examples, the method further includes measuring the pressure of the working fluid downstream from a turbine outlet on the power turbine within the low pressure side of the working fluid circuit. In other examples, the method further includes maintaining the pressure of the working fluid at or greater than a critical pressure value during the startup procedure. Alternatively, in other examples, the method may further include maintaining the pressure of the working fluid at less than the critical pressure value during the load ramp procedure or the full load procedure.

DETAILED DESCRIPTION

As described in more detail below, presently disclosed embodiments are directed to heat engine systems and methods for efficiently transforming thermal energy of a heat stream (e.g., a waste heat stream) into valuable electrical energy. The provided embodiments enable the reduction or prevention of damage to components of the heat engine systems during a startup period. For example, in one embodiment, a heat engine system is configured to maintain a working fluid (e.g., sc-CO2) within the low pressure side of a working fluid circuit in a liquid-type state, such as a supercritical state, during a startup procedure. The pump suction pressure at the pump inlet of a turbopump or other circulation pump is maintained, adjusted, or otherwise controlled at or greater than the critical pressure of the working fluid during the startup procedure. Therefore, the working fluid may be kept in a supercritical state free or substantially free of gaseous bubbles within the low pressure side of the working fluid circuit to avoid pump cavitation of the circulation pump.

For further example, in other embodiments, a bypass valve and a bypass line are provided for directing the working fluid around one or more heat exchangers, which transfer heat from the waste heat flue to the working fluid, to avoid excessively heating the working fluid while the heat engine system is warming up during startup. In some embodiments, the bypass line and the bypass valve may be fluidly coupled to the working fluid circuit upstream to the one or more heat exchangers, configured to circumvent the flow of the working fluid around at least one or more of the heat exchangers, and configured to provide the flow of the working fluid to a primary heat exchanger. One end of the bypass line may be coupled to the working fluid circuit upstream to the two or more heat exchangers and the other end of the bypass line may be coupled to the working fluid circuit downstream from the one or more of the heat exchangers and upstream to the primary heat exchanger. As the heat engine system approaches full power, the bypass line and the bypass valve are utilized to provide additional control while managing the rising temperature of the working fluid circuit in order to prevent the working fluid from getting too hot and to reduce or eliminate thermal stress on a turbopump used for circulating the working fluid.

Turning now to the drawings,FIGS. 1 and 2illustrate an embodiment of a heat engine system90, which may also be referred to as a thermal engine system, an electrical generation system, a waste heat or other heat recovery system, and/or a thermal to electrical energy system, as described in one or more embodiments below. The heat engine system90is 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 system90includes a waste heat system100and a power generation system90coupled to and in thermal communication with each other via a working fluid circuit202disposed within a process system210. During operation, a working fluid, such as supercritical carbon dioxide (sc-CO2), is circulated through the working fluid circuit202, and heat is transferred to the working fluid from a heat source stream110flowing through the waste heat system100. Once heated, the working fluid is circulated through a power turbine228within the power generation system90where the thermal energy contained in the heated working fluid is converted to mechanical energy. In this way, the process system210, the waste heat system100, and the power generation system90cooperate to convert the thermal energy in the heat source stream110into mechanical energy, which may be further converted into electrical energy if desired, depending on implementation-specific considerations.

More specifically, in the embodiment ofFIG. 1, the waste heat system100contains three heat exchangers (i.e., the heat exchangers120,130, and150) fluidly coupled to a high pressure side of the working fluid circuit202and in thermal communication with the heat source stream110. Such thermal communication provides the transfer of thermal energy from the heat source stream110to the working fluid flowing throughout the working fluid circuit202. In one or more embodiments disclosed herein, two, three, or more heat exchangers may be fluidly coupled to and in thermal communication with the working fluid circuit202, such as a primary heat exchanger, a secondary heat exchanger, a tertiary heat exchanger, respectively the heat exchangers120,150, and130. For example, the heat exchanger120may be the primary heat exchanger fluidly coupled to the working fluid circuit202upstream to an inlet of the power turbine228, the heat exchanger150may be the secondary heat exchanger fluidly coupled to the working fluid circuit202upstream to an inlet of the drive turbine264of the turbine pump260, and the heat exchanger130may be the tertiary heat exchanger fluidly coupled to the working fluid circuit202upstream to an inlet of the heat exchanger120. However, it should be noted that in other embodiments, any desired number of heat exchangers, not limited to three, may be provided in the waste heat system100.

Further, the waste heat system100also contains an inlet104for receiving the heat source stream110and an outlet106for passing the heat source stream110out of the waste heat system100. The heat source stream110flows through and from the inlet104, through the heat exchanger120, through one or more additional heat exchangers, if fluidly coupled to the heat source stream110, and to and through the outlet106. In some examples, the heat source stream110flows through and from the inlet104, through the heat exchangers120,150, and130, respectively, and to and through the outlet106. The heat source stream110may be routed to flow through the heat exchangers120,130,150, and/or additional heat exchangers in other desired orders.

In some embodiments described herein, the waste heat system100is disposed on or in a waste heat skid102fluidly coupled to the working fluid circuit202, as well as other portions, sub-systems, or devices of the heat engine system90. The waste heat skid102may be fluidly coupled to a source of and an exhaust for the heat source stream110, a main process skid212, a power generation skid222, and/or other portions, sub-systems, or devices of the heat engine system90.

In one or more configurations, the waste heat system100disposed on or in the waste heat skid102generally contains inlets122,132, and152and outlets124,134, and154fluidly coupled to and in thermal communication with the working fluid within the working fluid circuit202. The inlet122is disposed upstream to the heat exchanger120and the outlet124is disposed downstream from the heat exchanger120. The working fluid circuit202is configured to flow the working fluid from the inlet122, through the heat exchanger120, and to the outlet124while transferring thermal energy from the heat source stream110to the working fluid by the heat exchanger120. The inlet152is disposed upstream to the heat exchanger150and the outlet154is disposed downstream from the heat exchanger150. The working fluid circuit202is configured to flow the working fluid from the inlet152, through the heat exchanger150, and to the outlet154while transferring thermal energy from the heat source stream110to the working fluid by the heat exchanger150. The inlet132is disposed upstream to the heat exchanger130and the outlet134is disposed downstream from the heat exchanger130. The working fluid circuit202is configured to flow the working fluid from the inlet132, through the heat exchanger130, and to the outlet134while transferring thermal energy from the heat source stream110to the working fluid by the heat exchanger130.

The heat source stream110that flows through the waste heat system100may 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 stream110may be at a temperature within a range from about 100° C. to about 1,000° C., or greater than 1,000° C., 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 stream110may contain air, carbon dioxide, carbon monoxide, water or steam, nitrogen, oxygen, argon, derivatives thereof, or mixtures thereof. In some embodiments, the heat source stream110may derive thermal energy from renewable sources of thermal energy, such as solar or geothermal sources.

Turning now to the power generation system90, the illustrated embodiment includes the power turbine228disposed between a high pressure side and a low pressure side of the working fluid circuit202. The power turbine228is configured to convert thermal energy to mechanical energy by a pressure drop in the working fluid flowing between the high and the low pressure sides of the working fluid circuit202. A power generator240is coupled to the power turbine228and configured to convert the mechanical energy into electrical energy. In certain embodiments, a power outlet242may be electrically coupled to the power generator240and configured to transfer the electrical energy from the power generator240to an electrical grid244. The illustrated power generation system90also contains a driveshaft230and a gearbox232coupled between the power turbine228and the power generator240.

In one or more configurations, the power generation system90is disposed on or in the power generation skid222that contains inlets225a,225band an outlet227fluidly coupled to and in thermal communication with the working fluid within the working fluid circuit202. The inlets225a,225bare upstream to the power turbine228within the high pressure side of the working fluid circuit202and are configured to receive the heated and high pressure working fluid. In some examples, the inlet225amay be fluidly coupled to the outlet124of the waste heat system100and configured to receive the working fluid flowing from the heat exchanger120and the inlet225bmay be fluidly coupled to the outlet241of the process system210and configured to receive the working fluid flowing from the turbopump260and/or the start pump280. The outlet227is disposed downstream from the power turbine228within the low pressure side of the working fluid circuit202and is configured to provide the low pressure working fluid. In some examples, the outlet227may be fluidly coupled to the inlet239of the process system210and configured to flow the working fluid to the recuperator216.

A filter215amay be disposed along and in fluid communication with the fluid line at a point downstream from the heat exchanger120and upstream to the power turbine228. In some examples, the filter215ais fluidly coupled to the working fluid circuit202between the outlet124of the waste heat system100and the inlet225aof the process system210.

Again, the portion of the working fluid circuit202within the power generation system90is fed the working fluid by the inlets225aand225b. Additionally, a power turbine stop valve217is fluidly coupled to the working fluid circuit202between the inlet225aand the power turbine228. The power turbine stop valve217is configured to control the working fluid flowing from the heat exchanger120, through the inlet225a, and into the power turbine228while in an opened position. Alternatively, the power turbine stop valve217may be configured to cease the flow of working fluid from entering into the power turbine228while in a closed position.

A power turbine attemperator valve223is fluidly coupled to the working fluid circuit202via an attemperator bypass line211disposed between the outlet on the pump portion262of the turbopump260and the inlet on the power turbine228and/or disposed between the outlet on the pump portion282of the start pump280and the inlet on the power turbine228. The attemperator bypass line211and the power turbine attemperator valve223may be configured to flow the working fluid from the pump portion262or282, around and avoid the recuperator216and the heat exchangers120and130, and to the power turbine228, such as during a warm-up or cool-down step. The attemperator bypass line211and the power turbine attemperator valve223may be utilized to warm the working fluid with heat coming from the power turbine228while avoiding the thermal heat from the heat source stream110flowing through the heat exchangers, such as the heat exchangers120and130. In some examples, the power turbine attemperator valve223may be fluidly coupled to the working fluid circuit202between the inlet225band the power turbine stop valve217upstream to a point on the fluid line that intersects the incoming stream from the inlet225a. The power turbine attemperator valve223may be configured to control the working fluid flowing from the start pump280and/or the turbopump260, through the inlet225b, and to a power turbine stop valve217, the power turbine bypass valve219, and/or the power turbine228.

The power turbine bypass valve219is fluidly coupled to a turbine bypass line that extends from a point of the working fluid circuit202upstream to the power turbine stop valve217and downstream from the power turbine228. Therefore, the bypass line and the power turbine bypass valve219are configured to direct the working fluid around and avoid the power turbine228. If the power turbine stop valve217is in a closed position, the power turbine bypass valve219may be configured to flow the working fluid around and avoid the power turbine228while in an opened position. In one embodiment, the power turbine bypass valve219may be utilized while warming up the working fluid during a startup operation of the electricity generating process. An outlet valve221is fluidly coupled to the working fluid circuit202between the outlet on the power turbine228and the outlet227of the power generation system90.

Turning now to the process system210, in one or more configurations, the process system210is disposed on or in the main process skid212and includes inlets235,239, and255and outlets231,237,241,251, and253fluidly coupled to and in thermal communication with the working fluid within the working fluid circuit202. The inlet235is upstream to the recuperator216and the outlet154is downstream from the recuperator216. The working fluid circuit202is configured to flow the working fluid from the inlet235, through the recuperator216, and to the outlet237while transferring thermal energy from the working fluid in the low pressure side of the working fluid circuit202to the working fluid in the high pressure side of the working fluid circuit202by the recuperator216. The outlet241of the process system210is downstream from the turbopump260and/or the start pump280, upstream to the power turbine228, and configured to provide a flow of the high pressure working fluid to the power generation system90, such as to the power turbine228. The inlet239is upstream to the recuperator216, downstream from the power turbine228, and configured to receive the low pressure working fluid flowing from the power generation system90, such as to the power turbine228. The outlet251of the process system210is downstream from the recuperator218, upstream to the heat exchanger150, and configured to provide a flow of working fluid to the heat exchanger150. The inlet255is downstream from the heat exchanger150, upstream to the drive turbine264of the turbopump260, and configured to provide the heated high pressure working fluid flowing from the heat exchanger150to the drive turbine264of the turbopump260. The outlet253of the process system210is downstream from the pump portion262of the turbopump260and/or the pump portion282of the start pump280, couples a bypass line disposed downstream from the heat exchanger150and upstream to the drive turbine264of the turbopump260, and configured to provide a flow of working fluid to the drive turbine264of the turbopump260.

Additionally, a filter215cmay be disposed along and in fluid communication with the fluid line at a point downstream from the heat exchanger150and upstream to the drive turbine264of the turbopump260. In some examples, the filter215cis fluidly coupled to the working fluid circuit202between the outlet154of the waste heat system100and the inlet255of the process system210. Further, a filter215bmay be disposed along and in fluid communication with the fluid line135at a point downstream from the heat exchanger130and upstream to the recuperator216. In some examples, the filter215bis fluidly coupled to the working fluid circuit202between the outlet134of the waste heat system100and the inlet235of the process system210.

In certain embodiments, as illustrated inFIG. 1, the process system210may be disposed on or in the main process skid212, the power generation system90may be disposed on or in a power generation skid222, and the waste heat system100may be disposed on or in a waste heat skid102. In these embodiments, the working fluid circuit202extends throughout the inside, the outside, and between the main process skid212, the power generation skid222, and the waste heat skid102, as well as other systems and portions of the heat engine system90. Further, in some embodiments, the heat engine system90includes the heat exchanger bypass line160and the heat exchanger bypass valve162disposed between the waste heat skid102and the main process skid212for the purpose of routing the working fluid away from one or more of the heat exchangers during startup to reduce or eliminate component wear and/or damage, as described in more detail below.

Turning now to features of the working fluid circuit202, the working fluid circuit202contains the working fluid (e.g., sc-CO2) and has a high pressure side and a low pressure side.FIG. 1depicts the high and low pressure sides of the working fluid circuit202of the heat engine system90by representing the high pressure side with “-” and the low pressure side with “”—as described in one or more embodiments. In certain embodiments, the working fluid circuit202includes one or more pumps, such as the illustrated turbopump260and start pump280. The turbopump260and the start pump280are operative to pressurize and circulate the working fluid throughout the working fluid circuit202.

The turbopump260may be a turbo-drive pump or a turbine-drive pump and has a pump portion262and a drive turbine264coupled together by a driveshaft267and an optional gearbox (not shown). The driveshaft267may be a single piece or may contain two or more pieces coupled together. In one example, a first segment of the driveshaft267extends from the drive turbine264to the gearbox, a second segment of the driveshaft230extends from the gearbox to the pump portion262, and multiple gears are disposed between and couple to the two segments of the driveshaft267within the gearbox.

The drive turbine264is configured to rotate the pump portion262and the pump portion262is configured to circulate the working fluid within the working fluid circuit202. Accordingly, the pump portion262of the turbopump260may be disposed between the high pressure side and the low pressure side of the working fluid circuit202. The pump inlet on the pump portion262is generally disposed in the low pressure side and the pump outlet on the pump portion262is generally disposed in the high pressure side. The drive turbine264of the turbopump260may be fluidly coupled to the working fluid circuit202downstream from the heat exchanger150, and the pump portion262of the turbopump260is fluidly coupled to the working fluid circuit202upstream to the heat exchanger120for providing the heated working fluid to the turbopump260to move or otherwise power the drive turbine264.

The start pump280has a pump portion282and a motor-drive portion284. The start pump280is generally an electric motorized pump or a mechanical motorized pump, and may be a variable frequency driven pump. During operation, once a predetermined pressure, temperature, and/or flowrate of the working fluid is obtained within the working fluid circuit202, the start pump280may be taken off line, idled, or turned off, and the turbopump260may be utilized to circulate the working fluid during the electricity generation process. The working fluid enters each of the turbopump260and the start pump280from the low pressure side of the working fluid circuit202and exits each of the turbopump260and the start pump280from the high pressure side of the working fluid circuit202.

The start pump280may be a motorized pump, such as an electric motorized pump, a mechanical motorized pump, or other type of pump. Generally, the start pump280may be a variable frequency motorized drive pump and contains a pump portion282and a motor-drive portion284. The motor-drive portion284of the start pump280contains a motor and a drive including a driveshaft and gears. In some examples, the motor-drive portion284has a variable frequency drive, such that the speed of the motor may be regulated by the drive. The pump portion282of the start pump280is driven by the motor-drive portion284coupled thereto. The pump portion282has an inlet for receiving the working fluid from the low pressure side of the working fluid circuit202, such as from the condenser274and/or the working fluid storage system290. The pump portion282has an outlet for releasing the working fluid into the high pressure side of the working fluid circuit202.

Start pump inlet valve283and start pump outlet valve285may be utilized to control the flow of the working fluid passing through the start pump180. Start pump inlet valve283may be fluidly coupled to the low pressure side of the working fluid circuit202upstream to the pump portion282of the start pump280and may be utilized to control the flowrate of the working fluid entering the inlet of the pump portion282. Start pump outlet valve285may be fluidly coupled to the high pressure side of the working fluid circuit202downstream from the pump portion282of the start pump280and may be utilized to control the flowrate of the working fluid exiting the outlet of the pump portion282.

The drive turbine264of the turbopump260is driven by heated working fluid, such as the working fluid flowing from the heat exchanger150. The drive turbine264is fluidly coupled to the high pressure side of the working fluid circuit202by an inlet configured to receive the working fluid from the high pressure side of the working fluid circuit202, such as flowing from the heat exchanger150. The drive turbine264is fluidly coupled to the low pressure side of the working fluid circuit202by an outlet configured to release the working fluid into the low pressure side of the working fluid circuit202.

The pump portion262of the turbopump260is driven by the driveshaft267coupled to the drive turbine264. The pump portion262of the turbopump260may be fluidly coupled to the low pressure side of the working fluid circuit202by an inlet configured to receive the working fluid from the low pressure side of the working fluid circuit202. The inlet of the pump portion262is configured to receive the working fluid from the low pressure side of the working fluid circuit202, such as from the condenser274and/or the working fluid storage system290. Also, the pump portion262may be fluidly coupled to the high pressure side of the working fluid circuit202by an outlet configured to release the working fluid into the high pressure side of the working fluid circuit202and circulate the working fluid within the working fluid circuit202.

In one configuration, the working fluid released from the outlet on the drive turbine264is returned into the working fluid circuit202downstream from the recuperator216and upstream to the recuperator218. In one or more embodiments, the turbopump260, including piping and valves, is optionally disposed on a turbo pump skid266, as depicted inFIG. 2. The turbo pump skid266may be disposed on or adjacent to the main process skid212.

A drive turbine bypass valve265is generally coupled between and in fluid communication with a fluid line extending from the inlet on the drive turbine264with a fluid line extending from the outlet on the drive turbine264. The drive turbine bypass valve265is generally opened to bypass the turbopump260while using the start pump280during the initial stages of generating electricity with the heat engine system90. Once a predetermined pressure and temperature of the working fluid is obtained within the working fluid circuit202, the drive turbine bypass valve265is closed and the heated working fluid is flowed through the drive turbine264to start the turbopump260.

A drive turbine throttle valve263may be coupled between and in fluid communication with a fluid line extending from the heat exchanger150to the inlet on the drive turbine264of the turbopump260. The drive turbine throttle valve263is configured to modulate the flow of the heated working fluid into the drive turbine264, which in turn may be utilized to adjust the flow of the working fluid throughout the working fluid circuit202. Additionally, valve293may be utilized to provide back pressure for the drive turbine264of the turbopump260.

A drive turbine attemperator valve295may be fluidly coupled to the working fluid circuit202via an attemperator bypass line291disposed between the outlet on the pump portion262of the turbopump260and the inlet on the drive turbine264and/or disposed between the outlet on the pump portion282of the start pump280and the inlet on the drive turbine264. The attemperator bypass line291and the drive turbine attemperator valve295may be configured to flow the working fluid from the pump portion262or282, around the recuperator218and the heat exchanger150to avoid such components, and to the drive turbine264, such as during a warm-up or cool-down step of the turbopump260. The attemperator bypass line291and the drive turbine attemperator valve295may be utilized to warm the working fluid with the drive turbine264while avoiding the thermal heat from the heat source stream110via the heat exchangers, such as the heat exchanger150.

In another embodiment, the heat engine system200depicted inFIG. 1has two pairs of turbine attemperator lines and valves, such that each pair of attemperator line and valve is fluidly coupled to the working fluid circuit202and disposed upstream to a respective turbine inlet, such as a drive turbine inlet and a power turbine inlet. The power turbine attemperator line211and the power turbine attemperator valve223are fluidly coupled to the working fluid circuit202and disposed upstream to a turbine inlet on the power turbine264. Similarly, the drive turbine attemperator line291and the drive turbine attemperator valve295are fluidly coupled to the working fluid circuit202and disposed upstream to a turbine inlet on the turbopump260.

The power turbine attemperator valve223and the drive turbine attemperator valve295may be utilized during a startup and/or shutdown procedure of the heat engine system200to control backpressure within the working fluid circuit202. Also, the power turbine attemperator valve223and the drive turbine attemperator valve295may be utilized during a startup and/or shutdown procedure of the heat engine system200to cool hot flow of the working fluid from heat saturated heat exchangers, such as heat exchangers120,130,140, and/or150, coupled to and in thermal communication with working fluid circuit202. The power turbine attemperator valve223may be modulated, adjusted, or otherwise controlled to manage the inlet temperature T1and/or the inlet pressure at (or upstream from) the inlet of the power turbine228, and to cool the heated working fluid flowing from the outlet of the heat exchanger120. Similarly, the drive turbine attemperator valve295may be modulated, adjusted, or otherwise controlled to manage the inlet temperature and/or the inlet pressure at (or upstream from) the inlet of the drive turbine264, and to cool the heated working fluid flowing from the outlet of the heat exchanger150.

In some embodiments, the drive turbine attemperator valve295may be modulated, adjusted, or otherwise controlled with the process control system204to decrease the inlet temperature of the drive turbine264by increasing the flowrate of the working fluid passing through the attemperator bypass line291and the drive turbine attemperator valve295and detecting a desirable value of the inlet temperature of the drive turbine264via the process control system204. The desirable value is generally at or less than the predetermined threshold value of the inlet temperature of the drive turbine264. In some examples, such as during startup of the turbopump260, the desirable value for the inlet temperature upstream to the drive turbine264may be about 150° C. or less. In other examples, such as during an energy conversion process, the desirable value for the inlet temperature upstream to the drive turbine264may be about 170° C. or less, such as about 168° C. or less. The drive turbine264and/or components therein may be damaged if the inlet temperature is about 168° C. or greater.

In some embodiments, the working fluid may flow through the attemperator bypass line291and the drive turbine attemperator valve295to bypass the heat exchanger150. This flow of the working fluid may be adjusted with throttle valve263to control the inlet temperature of the drive turbine264. During the startup of the turbopump260, the desirable value for the inlet temperature upstream to the drive turbine264may be about 150° C. or less. As power is increased, the inlet temperature upstream to the drive turbine264may be raised to optimize cycle efficiency and operability by reducing the flow through the attemperator bypass line291. At full power, the inlet temperature upstream to the drive turbine264may be about 340° C. or greater and the flow of the working fluid bypassing the heat exchanger150through the attemperator bypass line291ceases, such as approaches about 0 kg/s, in some examples. Also, the pressure may range from about 14 MPa to about 23.4 MPa as the flow of the working fluid may be within a range from about 0 kg/s to about 32 kg/s depending on power level.

A control valve261may be disposed downstream from the outlet of the pump portion262of the turbopump260and the control valve281may be disposed downstream from the outlet of the pump portion282of the start pump280. Control valves261and281are flow control safety valves and generally utilized to regulate the directional flow or to prohibit backflow of the working fluid within the working fluid circuit202. Control valve261is configured to prevent the working fluid from flowing upstream towards or into the outlet of the pump portion262of the turbopump260. Similarly, control valve281is configured to prevent the working fluid from flowing upstream towards or into the outlet of the pump portion282of the start pump280.

The drive turbine throttle valve263is fluidly coupled to the working fluid circuit202upstream to the inlet of the drive turbine264of the turbopump260and configured to control a flow of the working fluid flowing into the drive turbine264. The power turbine bypass valve219is fluidly coupled to the power turbine bypass line208and configured to modulate, adjust, or otherwise control the working fluid flowing through the power turbine bypass line208for controlling the flowrate of the working fluid entering the power turbine228.

The power turbine bypass line208is fluidly coupled to the working fluid circuit202at a point upstream to an inlet of the power turbine228and at a point downstream from an outlet of the power turbine228. The power turbine bypass line208is configured to flow the working fluid around and avoid the power turbine228when the power turbine bypass valve219is in an opened position. The flowrate and the pressure of the working fluid flowing into the power turbine228may be reduced or stopped by adjusting the power turbine bypass valve219to the opened position. Alternatively, the flowrate and the pressure of the working fluid flowing into the power turbine228may be increased or started by adjusting the power turbine bypass valve219to the closed position due to the backpressure formed through the power turbine bypass line208.

The power turbine bypass valve219and the drive turbine throttle valve263may be independently controlled by the process control system204that is communicably connected, wired and/or wirelessly, with the power turbine bypass valve219, the drive turbine throttle valve263, and other parts of the heat engine system90. The process control system204is operatively connected to the working fluid circuit202and a mass management system270and is enabled to monitor and control multiple process operation parameters of the heat engine system90.

In one or more embodiments, the working fluid circuit202provides a bypass flowpath for the start pump280via the start pump bypass line224and a start pump bypass valve254, as well as a bypass flowpath for the turbopump260via the turbo pump bypass line226and a turbo pump bypass valve256. One end of the start pump bypass line224is fluidly coupled to an outlet of the pump portion282of the start pump280and the other end of the start pump bypass line224is fluidly coupled to a fluid line229. Similarly, one end of a turbo pump bypass line226is fluidly coupled to an outlet of the pump portion262of the turbopump260and the other end of the turbo pump bypass line226is coupled to the start pump bypass line224. In some configurations, the start pump bypass line224and the turbo pump bypass line226merge together as a single line upstream of coupling to a fluid line229. The fluid line229extends between and is fluidly coupled to the recuperator218and the condenser274. The start pump bypass valve254is disposed along the start pump bypass line224and fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit202when in a closed position. Similarly, the turbo pump bypass valve256is disposed along the turbo pump bypass line226and fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit202when in a closed position.

FIG. 1further depicts a power turbine throttle valve250fluidly coupled to a bypass line246on the high pressure side of the working fluid circuit202and upstream to the heat exchanger120, as disclosed by at least one embodiment described herein. The power turbine throttle valve250is fluidly coupled to the bypass line246and configured to modulate, adjust, or otherwise control the working fluid flowing through the bypass line246for controlling a general coarse flowrate of the working fluid within the working fluid circuit202. The bypass line246is fluidly coupled to the working fluid circuit202at a point upstream to the valve293and at a point downstream from the pump portion282of the start pump280and/or the pump portion262of the turbopump260. Additionally, a power turbine trim valve252is fluidly coupled to a bypass line248on the high pressure side of the working fluid circuit202and upstream to the heat exchanger150, as disclosed by another embodiment described herein. The power turbine trim valve252is fluidly coupled to the bypass line248and configured to modulate, adjust, or otherwise control the working fluid flowing through the bypass line248for controlling a fine flowrate of the working fluid within the working fluid circuit202. The bypass line248is fluidly coupled to the bypass line246at a point upstream to the power turbine throttle valve250and at a point downstream from the power turbine throttle valve250.

The heat engine system90further contains a drive turbine throttle valve263fluidly coupled to the working fluid circuit202upstream to the inlet of the drive turbine264of the turbopump260and configured to modulate a flow of the working fluid flowing into the drive turbine264, a power turbine bypass line208fluidly coupled to the working fluid circuit202upstream to an inlet of the power turbine228, fluidly coupled to the working fluid circuit202downstream from an outlet of the power turbine228, and configured to flow the working fluid around and avoid the power turbine228, a power turbine bypass valve219fluidly coupled to the power turbine bypass line208and configured to modulate a flow of the working fluid flowing through the power turbine bypass line208for controlling the flowrate of the working fluid entering the power turbine228, and the process control system204operatively connected to the heat engine system90, wherein the process control system204is configured to adjust the drive turbine throttle valve263and the power turbine bypass valve219.

A heat exchanger bypass line160is fluidly coupled to a fluid line131of the working fluid circuit202upstream to the heat exchangers120,130, and/or150by a heat exchanger bypass valve162, as illustrated inFIG. 1and described in more detail below. The heat exchanger bypass valve162may be a solenoid valve, a hydraulic valve, an electric valve, a manual valve, or derivatives thereof. In many examples, the heat exchanger bypass valve162is a solenoid valve and configured to be controlled by the process control system204. Regardless of the valve type, however, the valve may be controlled to route the working fluid in a manner that maintains the temperature of the working fluid at a level appropriate for the current operational state of the heat engine system. For example, the bypass valve may be regulated during startup to control the flow of the working fluid through a reduced quantity of heat exchangers to effectuate a lower working fluid temperature than would be achieved during a fully operational state when the working fluid is routed through all the heat exchangers.

In one or more embodiments, the working fluid circuit202provides release valves213a,213b,213c, and213d, as well as release outlets214a,214b,214c, and214d, respectively in fluid communication with each other. Generally, the release valves213a,213b,213c, and213dremain closed during the electricity generation process, but may be configured to automatically open to release an over-pressure at a predetermined value within the working fluid. Once the working fluid flows through the valve213a,213b,213c, or213d, the working fluid is vented through the respective release outlet214a,214b,214c, or214d. The release outlets214a,214b,214c, and214dmay provide passage of the working fluid into the ambient surrounding atmosphere. Alternatively, the release outlets214a,214b,214c, and214dmay provide passage of the working fluid into a recycling or reclamation step that generally includes capturing, condensing, and storing the working fluid.

The release valve213aand the release outlet214aare fluidly coupled to the working fluid circuit202at a point disposed between the heat exchanger120and the power turbine228. The release valve213band the release outlet214bare fluidly coupled to the working fluid circuit202at a point disposed between the heat exchanger150and the drive turbine264of the turbopump260. The release valve213cand the release outlet214care fluidly coupled to the working fluid circuit202via a bypass line that extends from a point between the valve293and the pump portion262of the turbopump260to a point on the turbo pump bypass line226between the turbo pump bypass valve256and the fluid line229. The release valve213dand the release outlet214dare fluidly coupled to the working fluid circuit202at a point disposed between the recuperator218and the condenser274.

A computer system206, as part of the process control system204, contains a multi-controller algorithm utilized to control the drive turbine throttle valve263, the power turbine bypass valve219, the heat exchanger bypass valve162, the power turbine throttle valve250, the power turbine trim valve252, as well as other valves, pumps, and sensors within the heat engine system90. In one embodiment, the process control system204is enabled to move, adjust, manipulate, or otherwise control the heat exchanger bypass valve162, the power turbine throttle valve250, and/or the power turbine trim valve252for adjusting or controlling the flow of the working fluid throughout the working fluid circuit202. By controlling the flow of the working fluid, the process control system204is also operable to regulate the temperatures and pressures throughout the working fluid circuit202. For example, the control system204may regulate the temperature of the working fluid during startup by controlling the position of the bypass valve162to reduce or eliminate damage to one or more downstream components due to overheated working fluid.

In some embodiments, the process control system204is communicably connected, wired and/or wirelessly, with numerous sets of sensors, valves, and pumps, in order to process the measured and reported temperatures, pressures, and mass flowrates of the working fluid at the designated points within the working fluid circuit202. In response to these measured and/or reported parameters, the process control system204may be operable to selectively adjust the valves in accordance with a control program or algorithm, thereby maximizing operation of the heat engine system90.

Further, in certain embodiments, the process control system204, 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 process control system204to operate the logic or portions of the logic presented in the methods disclosed herein. For example, in certain embodiments, the heat engine system90may 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 bypass valve162during startup to route the working fluid around one or more heat exchangers, or during a fully operational mode to route the working fluid through one or more heat exchangers.

In some embodiments, the process control system204contains a control algorithm embedded in a computer system206and the control algorithm contains a governing loop controller. The governing controller is generally utilized to adjust values throughout the working fluid circuit202for controlling the temperature, pressure, flowrate, and/or mass of the working fluid at specified points therein. In some embodiments, the governing loop controller may be configured to maintain desirable threshold values for the inlet temperature and the inlet pressure by modulating, adjusting, or otherwise controlling the drive turbine attemperator valve295and the drive turbine throttle valve263. In other embodiments, the governing loop controller may be configured to maintain desirable threshold values for the inlet temperature by modulating, adjusting, or otherwise controlling the power turbine attemperator valve223and the power turbine throttle valve250.

The process control system204may operate with the heat engine system90semi-passively with the aid of several sets of sensors. The first set of sensors is arranged at or adjacent the suction inlet of the turbopump260and the start pump280and the second set of sensors is arranged at or adjacent the outlet of the turbopump260and the start pump280. 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 working fluid circuit202adjacent the turbopump260and the start pump280. The third set of sensors is arranged either inside or adjacent the working fluid storage vessel292of the working fluid storage system290to measure and report the pressure, temperature, mass flowrate, or other properties of the working fluid within the working fluid storage vessel292. Additionally, an instrument air supply (not shown) may be coupled to sensors, devices, or other instruments within the heat engine system90including the mass management system270and/or other system components that may utilize a gaseous supply, such as nitrogen or air.

In some embodiments, the overall efficiency of the heat engine system90and the amount of power ultimately generated can be influenced by the inlet or suction pressure at the pump when the working fluid contains supercritical carbon dioxide. In order to minimize or otherwise regulate the suction pressure of the pump, the heat engine system90may incorporate the use of a mass management system (“MMS”)270. The mass management system270controls the inlet pressure of the start pump280by regulating the amount of working fluid entering and/or exiting the heat engine system90at strategic locations in the working fluid circuit202, such as at tie-in points, inlets/outlets, valves, or conduits throughout the heat engine system90. Consequently, the heat engine system90becomes more efficient by increasing the pressure ratio for the start pump280to a maximum possible extent.

The mass management system270contains at least one vessel or tank, such as a storage vessel (e.g., working fluid storage vessel292), a fill vessel, and/or a mass control tank (e.g., mass control tank286), fluidly coupled to the low pressure side of the working fluid circuit202via one or more valves, such as valve287. The valves are moveable—as being partially opened, fully opened, and/or closed—to either remove working fluid from the working fluid circuit202or add working fluid to the working fluid circuit202. Exemplary embodiments of the mass management system270, and a range of variations thereof, are found in U.S. application Ser. No. 13/278,705, filed Oct. 21, 2011, 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 system270may include a plurality of valves and/or connection points, each in fluid communication with the mass control tank286. The valves may be characterized as termination points where the mass management system270is operatively connected to the heat engine system90. The connection points and valves may be configured to provide the mass management system270with an outlet for flaring excess working fluid or pressure, or to provide the mass management system270with additional/supplemental working fluid from an external source, such as a fluid fill system.

In some embodiments, the mass control tank286may be configured as a localized storage tank for additional/supplemental working fluid that may be added to the heat engine system90when needed in order to regulate the pressure or temperature of the working fluid within the working fluid circuit202or otherwise supplement escaped working fluid. By controlling the valves, the mass management system270adds and/or removes working fluid mass to/from the heat engine system90with or without the need of a pump, thereby reducing system cost, complexity, and maintenance.

In some examples, a working fluid storage vessel292is part of a working fluid storage system290and is fluidly coupled to the working fluid circuit202. At least one connection point, such as a working fluid feed288, may be a fluid fill port for the working fluid storage vessel292of the working fluid storage system290and/or the mass management system270. Additional or supplemental working fluid may be added to the mass management system270from an external source, such as a fluid fill system via the working fluid feed288. 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.

In another embodiment described herein, bearing gas and seal gas may be supplied to the turbopump260or other devices contained within and/or utilized along with the heat engine system90. One or multiple streams of bearing gas and/or seal gas may be derived from the working fluid within the working fluid circuit202and contain carbon dioxide in a gaseous, subcritical, or supercritical state.

In some examples, the bearing gas or fluid is flowed by the start pump280, from a bearing gas supply296aand/or a bearing gas supply296b, into the working fluid circuit202, through a bearing gas supply line (not shown), and to the bearings within the power generation system90. In other examples, the bearing gas or fluid is flowed by the start pump280, from the bearing gas supply296aand/or the bearing gas supply296b, from the working fluid circuit202, through a bearing gas supply line (not shown), and to the bearings within the turbopump260. The gas return298may be a connection point or valve that feeds into a gas system, such as a bearing gas, dry gas, seal gas, or other system.

At least one gas return294is generally coupled to a discharge, recapture, or return of bearing gas, seal gas, and other gases. The gas return294provides a feed stream into the working fluid circuit202of recycled, recaptured, or otherwise returned gases—generally derived from the working fluid. The gas return294is generally fluidly coupled to the working fluid circuit202upstream to the condenser274and downstream from the recuperator218.

In another embodiment, the bearing gas supply source141is fluidly coupled to the bearing housing268of the turbopump260by the bearing gas supply line142. The flow of the bearing gas or other gas into the bearing housing268may be controlled via the bearing gas supply valve144that is operatively coupled to the bearing gas supply line142and controlled by the process control system204. The bearing gas or other gas generally flows from the bearing gas supply source141, through the bearing housing268of the turbopump260, and to the bearing gas recapture148. The bearing gas recapture148is fluidly coupled to the bearing housing268by the bearing gas recapture line146. The flow of the bearing gas or other gas from the bearing housing268and to bearing gas recapture148may be controlled via the bearing gas recapture valve147that is operatively coupled to the bearing gas recapture line146and controlled by the process control system204.

In one or more embodiments, a working fluid storage vessel292may be fluidly coupled to the start pump280via the working fluid circuit202within the heat engine system90. The working fluid storage vessel292and the working fluid circuit202contain the working fluid (e.g., carbon dioxide) and the working fluid circuit202fluidly has a high pressure side and a low pressure side.

The heat engine system90further contains a bearing housing, case, or other chamber, such as the bearing housings238and268, fluidly coupled to and/or substantially encompassing or enclosing bearings within power generation system90and the turbine pump260, respectively. In one embodiment, the turbopump260contains the drive turbine264, the pump portion262, and the bearing housing268fluidly coupled to and/or substantially encompassing or enclosing the bearings. The turbopump260further may contain a gearbox and/or a driveshaft267coupled between the drive turbine264and the pump portion262. In another embodiment, the power generation system90contains the power turbine228, the power generator240, and the bearing housing238substantially encompassing or enclosing the bearings. The power generation system90further contains a gearbox232and a driveshaft230coupled between the power turbine228and the power generator240.

Exemplary structures of the bearing housing238or268may completely or substantially encompass or enclose the bearings as well as all or part of turbines, generators, pumps, driveshafts, gearboxes, or other components shown or not shown for heat engine system90. The bearing housing238or268may completely or partially include structures, chambers, cases, housings, such as turbine housings, generator housings, driveshaft housings, driveshafts that contain bearings, gearbox housings, derivatives thereof, or combinations thereof.FIGS. 1 and 2depict the bearing housing268fluidly coupled to and/or containing all or a portion of the drive turbine264, the pump portion262, and the driveshaft267of the turbopump260. In other examples, the housing of the drive turbine264and the housing of the pump portion262may be independently coupled to and/or form portions of the bearing housing268. Similarly, the bearing housing238may be fluidly coupled to and/or contain all or a portion of the power turbine228, the power generator240, the driveshaft230, and the gearbox232of the power generation system90. In some examples, the housing of the power turbine228is coupled to and/or forms a portion of the bearing housing238.

In one or more embodiments disclosed herein, the heat engine system90depicted inFIGS. 1 and 2is configured to monitor and maintain the working fluid within the low pressure side of the working fluid circuit202in a supercritical state during a startup procedure. The working fluid may be maintained in a supercritical state by adjusting or otherwise controlling a pump suction pressure upstream to an inlet on the pump portion262of the turbopump260via the process control system204operatively connected to the working fluid circuit202.

The process control system204may be utilized to maintain, adjust, or otherwise control the pump suction pressure at or greater than the critical pressure of the working fluid during the startup procedure. The working fluid may be kept in a liquid-type or supercritical state and free or substantially free the gaseous state within the low pressure side of the working fluid circuit202. Therefore, the pump system, including the turbopump260and/or the start pump280, may avoid pump cavitation within the respective pump portions262and282.

In many embodiments described herein, the working fluid circulated, flowed, or otherwise utilized in the working fluid circuit202of the heat engine system90, and the other exemplary circuits disclosed herein, may be or may contain carbon dioxide (CO2) and mixtures containing carbon dioxide. Generally, at least a portion of the working fluid circuit202contains the working fluid in a supercritical state (e.g., sc-CO2). 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 (CO2), supercritical carbon dioxide (sc-CO2), or subcritical carbon dioxide (sub-CO2) 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.

In other exemplary embodiments, the working fluid in the working fluid circuit202may 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-CO2), subcritical carbon dioxide (sub-CO2), 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.

The working fluid circuit202generally has a high pressure side, a low pressure side, and a working fluid circulated within the working fluid circuit202. 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 system90or thermodynamic cycle. In one or more embodiments, the working fluid is in a supercritical state over certain portions of the working fluid circuit202of the heat engine system90(e.g., a high pressure side) and in a subcritical state over other portions of the working fluid circuit202of the heat engine system90(e.g., a low pressure side).

In other embodiments, the entire thermodynamic cycle may be operated such that the working fluid is maintained in either a supercritical or subcritical state throughout the entire working fluid circuit202of the heat engine system90. During different stages of operation, the high and low pressure sides the working fluid circuit202for the heat engine system90may contain the working fluid in a supercritical and/or subcritical state. For example, the high and low pressure sides of the working fluid circuit202may both contain the working fluid in a supercritical state during the startup procedure. However, once the system is synchronizing, load ramping, and/or fully loaded, the high pressure side of the working fluid circuit202may keep the working fluid in a supercritical state while the low pressure side the working fluid circuit202may be adjusted to contain the working fluid in a subcritical state or other liquid-type state.

Generally, the high pressure side of the working fluid circuit202contains the working fluid (e.g., sc-CO2) at a pressure of about 15 MPa or greater, such as about 17 MPa or greater or about 20 MPa or greater. In some examples, the high pressure side of the working fluid circuit202may have a pressure within a range from about 15 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 17 MPa to about 24 MPa, such as about 23.3 MPa. In other examples, the high pressure side of the working fluid circuit202may 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.

The low pressure side of the working fluid circuit202contains the working fluid (e.g., CO2or sub-CO2) at a pressure of less than 15 MPa, such as about 12 MPa or less, or about 10 MPa or less. In some examples, the low pressure side of the working fluid circuit202may 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 12 MPa, and more narrowly within a range from about 10 MPa to about 11 MPa, such as about 10.3 MPa. In other examples, the low pressure side of the working fluid circuit202may have a pressure within a range from about 2 MPa to about 10 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.

In some examples, the high pressure side of the working fluid circuit202may 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 circuit202may have a pressure within a range from about 8 MPa to about 11 MPa, and more narrowly within a range from about 10.3 MPa to about 11 MPa.

Referring generally toFIG. 2, the heat engine system90includes the power turbine228disposed between the high pressure side and the low pressure side of the working fluid circuit202, disposed downstream from the heat exchanger120, and fluidly coupled to and in thermal communication with the working fluid. The power turbine228is 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 turbine228. Therefore, the power turbine228is 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 (e.g., the driveshaft230).

The power turbine228may contain or be a turbine, a turbo, an expander, or another device for receiving and expanding the working fluid discharged from the heat exchanger120. The power turbine228may have an axial construction or radial construction and may be a single-staged device or a multi-staged device. Exemplary turbine devices that may be utilized in power turbine228include 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 turbine228.

The power turbine228is generally coupled to the power generator240by the driveshaft230. A gearbox232is generally disposed between the power turbine228and the power generator240and adjacent or encompassing the driveshaft230. The driveshaft230may be a single piece or may contain two or more pieces coupled together. In one example, as depicted inFIG. 2, a first segment of the driveshaft230extends from the power turbine228to the gearbox232, a second segment of the driveshaft230extends from the gearbox232to the power generator240, and multiple gears are disposed between and couple to the two segments of the driveshaft230within the gearbox232.

In some configurations, the heat engine system90also provides for the delivery of a portion of the working fluid, seal gas, bearing gas, air, or other gas into a chamber or housing, such as a housing238within the power generation system90for purposes of cooling one or more parts of the power turbine228. In other configurations, the driveshaft230includes a seal assembly (not shown) designed to prevent or capture any working fluid leakage from the power turbine228. Additionally, a working fluid recycle system may be implemented along with the seal assembly to recycle seal gas back into the working fluid circuit202of the heat engine system90.

The power generator240may be a generator, an alternator (e.g., permanent magnet alternator), or other device for generating electrical energy, such as transforming mechanical energy from the driveshaft230and the power turbine228to electrical energy. A power outlet242may be electrically coupled to the power generator240and configured to transfer the generated electrical energy from the power generator240and to an electrical grid244. The electrical grid244may be or include an electrical grid, an electrical bus (e.g., plant bus), power electronics, other electric circuits, or combinations thereof. The electrical grid244generally contains at least one alternating current bus, alternating current grid, alternating current circuit, or combinations thereof. In one example, the power generator240is a generator and is electrically and operably connected to the electrical grid244via the power outlet242. In another example, the power generator240is an alternator and is electrically and operably connected to power electronics (not shown) via the power outlet242. In another example, the power generator240is electrically connected to power electronics which are electrically connected to the power outlet242.

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, resisters, storage devices, and other power electronic components and devices. In other embodiments, the power generator240may 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., gearbox232), or other device configured to modify or convert the shaft work created by the power turbine228. In one embodiment, the power generator240is 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 generator240and power electronics by circulating the cooling fluid to draw away generated heat.

The heat engine system90also provides for the delivery of a portion of the working fluid into a chamber or housing of the power turbine228for purposes of cooling one or more parts of the power turbine228. In one embodiment, due to the potential need for dynamic pressure balancing within the power generator240, the selection of the site within the heat engine system90from which to obtain a portion of the working fluid is critical because introduction of this portion of the working fluid into the power generator240should respect or not disturb the pressure balance and stability of the power generator240during operation. Therefore, the pressure of the working fluid delivered into the power generator240for purposes of cooling is the same or substantially the same as the pressure of the working fluid at an inlet of the power turbine228. The working fluid is conditioned to be at a desired temperature and pressure prior to being introduced into the power turbine228. A portion of the working fluid, such as the spent working fluid, exits the power turbine228at an outlet of the power turbine228and is directed to one or more heat exchangers or recuperators, such as recuperators216and218. The recuperators216and218may be fluidly coupled to the working fluid circuit202in series with each other. The recuperators216and218are operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit202.

In one embodiment, the recuperator216is fluidly coupled to the low pressure side of the working fluid circuit202, disposed downstream from a working fluid outlet on the power turbine228, and disposed upstream to the recuperator218and/or the condenser274. The recuperator216is configured to remove at least a portion of thermal energy from the working fluid discharged from the power turbine228. In addition, the recuperator216is also fluidly coupled to the high pressure side of the working fluid circuit202, disposed upstream to the heat exchanger120and/or a working fluid inlet on the power turbine228, and disposed downstream from the heat exchanger130. The recuperator216is configured to increase the amount of thermal energy in the working fluid prior to flowing into the heat exchanger120and/or the power turbine228. Therefore, the recuperator216is operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit202. In some examples, the recuperator216may be a heat exchanger configured to cool the low pressurized working fluid discharged or downstream from the power turbine228while heating the high pressurized working fluid entering into or upstream to the heat exchanger120and/or the power turbine228.

Similarly, in another embodiment, the recuperator218is fluidly coupled to the low pressure side of the working fluid circuit202, disposed downstream from a working fluid outlet on the power turbine228and/or the recuperator216, and disposed upstream to the condenser274. The recuperator218is configured to remove at least a portion of thermal energy from the working fluid discharged from the power turbine228and/or the recuperator216. In addition, the recuperator218is also fluidly coupled to the high pressure side of the working fluid circuit202, disposed upstream to the heat exchanger150and/or a working fluid inlet on a drive turbine264of turbopump260, and disposed downstream from a working fluid outlet on the pump portion262of turbopump260. The recuperator218is configured to increase the amount of thermal energy in the working fluid prior to flowing into the heat exchanger150and/or the drive turbine264. Therefore, the recuperator218is operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit202. In some examples, the recuperator218may be a heat exchanger configured to cool the low pressurized working fluid discharged or downstream from the power turbine228and/or the recuperator216while heating the high pressurized working fluid entering into or upstream to the heat exchanger150and/or the drive turbine264.

A cooler or a condenser274may be fluidly coupled to and in thermal communication with the low pressure side of the working fluid circuit202and may be configured or operative to control a temperature of the working fluid in the low pressure side of the working fluid circuit202. The condenser274may be disposed downstream from the recuperators216and218and upstream to the start pump280and the turbopump260. The condenser274receives the cooled working fluid from the recuperator218and further cools and/or condenses the working fluid which may be recirculated throughout the working fluid circuit202. In many examples, the condenser274is a cooler and may be configured to control a temperature of the working fluid in the low pressure side of the working fluid circuit202by transferring thermal energy from the working fluid in the low pressure side to a cooling loop or system outside of the working fluid circuit202.

A cooling media or fluid is generally utilized in the cooling loop or system by the condenser274for cooling the working fluid and removing thermal energy outside of the working fluid circuit202. The cooling media or fluid flows through, over, or around while in thermal communication with the condenser274. Thermal energy in the working fluid is transferred to the cooling fluid via the condenser274. Therefore, the cooling fluid is in thermal communication with the working fluid circuit202, but not fluidly coupled to the working fluid circuit202. The condenser274may be fluidly coupled to the working fluid circuit202and independently fluidly coupled to the cooling fluid. The cooling fluid may contain one or multiple compounds and may be in one or multiple states of matter. The cooling fluid may be a media or fluid in a gaseous state, a liquid state, a subcritical state, a supercritical state, a suspension, a solution, derivatives thereof, or combinations thereof.

In many examples, the condenser274is generally fluidly coupled to a cooling loop or system (not shown) that receives the cooling fluid from a cooling fluid return278aand returns the warmed cooling fluid to the cooling loop or system via a cooling fluid supply278b. The cooling fluid may be water, carbon dioxide, or other aqueous and/or organic fluids (e.g., alcohols and/or glycols), air or other gases, or various mixtures thereof that is maintained at a lower temperature than the temperature of the working fluid. In other examples, the cooling media or fluid contains air or another gas exposed to the condenser274, such as an air steam blown by a motorized fan or blower. A filter276may be disposed along and in fluid communication with the cooling fluid line at a point downstream from the cooling fluid supply278band upstream to the condenser274. In some examples, the filter276may be fluidly coupled to the cooling fluid line within the process system210.

FIG. 3illustrates one configuration of the working fluid systems in accordance with disclosed embodiments. In the illustrated embodiment, the working fluid may flow through the working fluid circuit202from a turbopump supply125and into the turbo pump inlet line259of the pump portion262of the turbopump260. Once the working fluid has passed through the pump portion262, the working fluid may flow through the turbopump bypass line226along the turbopump bypass126, through the turbopump discharge line136along the turbopump discharge138, and/or though the bearing gas supply line142to the bearing housing268of the turbopump260. In some examples, a portion of the working fluid may combine with the bearing gas or other gas along the bearing gas supply line142. The drive turbine264of the turbopump260may be fed by the heat exchanger discharge157that contains heated working fluid flowing from the heat exchanger150through the drive turbine inlet line257. Once the heated working fluid passes through the drive turbine264, the working fluid flows though the drive turbine outlet line258to the drive turbine discharge158.

FIG. 4illustrates an embodiment of a method300for starting a heat engine system90while reducing or preventing the likelihood of damage to one or more components of the system. The method300includes circulating a working fluid within a working fluid circuit202by a pump system such that the working fluid is maintained in a supercritical state on at least one side of the working fluid circuit (block302). For example, in one embodiment, the working fluid is circulated such that the working fluid circuit202has a high pressure side containing the working fluid in a supercritical state and a low pressure side containing the working fluid in a subcritical state or a supercritical state. The pump system used to circulate the working fluid may contain a turbopump, a start pump, a combination of a turbopump and a start pump, a transfer pump, other pumps, or combinations thereof, as described in detail above. However, in some embodiments, the pump system may include at least a turbopump, such as the turbopump260.

The method300further includes transferring thermal energy from a heat source stream110to the working fluid (block304), for example, by utilizing at least a primary heat exchanger, such as the heat exchanger120, fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit202. The method300further includes flowing the working fluid through a power turbine228or through a power turbine bypass line208circumventing the power turbine228(block306). The power turbine228may be configured to convert the thermal energy from the working fluid to mechanical energy of the power turbine228and also the power turbine228may be coupled to a power generator240configured to convert the mechanical energy into electrical energy.

In addition, the method300includes monitoring and/or maintaining a pump suction pressure of the working fluid within the low pressure side of the working fluid circuit202upstream to an inlet on the pump portion262of the turbopump260via the process control system204operatively connected to the working fluid circuit202(block308). Generally, the inlet on the pump portion262of the turbopump260and the low pressure side of the working fluid circuit202contain the working fluid in the supercritical state during a startup procedure. Therefore, in some embodiments, the pump suction pressure may be maintained at but generally greater than the critical pressure of the working fluid during the startup procedure.

In another embodiment, a method for starting the heat engine system90includes circulating a working fluid within a working fluid circuit202by a pump system, such that the working fluid circuit202has a high pressure side containing the working fluid in a supercritical state and a low pressure side containing the working fluid in a subcritical state or a supercritical state. As before, this embodiment of the method further includes transferring thermal energy from a heat source stream110to the working fluid by at least a heat exchanger120fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit202and flowing the working fluid through a power turbine228or through a power turbine bypass line208circumventing the power turbine228. Generally, the power turbine228may be configured to convert the thermal energy from the working fluid to mechanical energy of the power turbine228and also the power turbine228may be coupled to a power generator240configured to convert the mechanical energy into electrical energy.

Additionally, as before, the method further includes monitoring and maintaining a pressure of the working fluid within the low pressure side of the working fluid circuit202via the process control system204operatively connected to the working fluid circuit202, such that the low pressure side of the working fluid circuit202contains the working fluid in the supercritical state during a startup procedure. However, in this embodiment, during step308, the working fluid in the low pressure side is maintained at least at the critical pressure, but generally above the critical pressure of the working fluid during the startup procedure. In some embodiments, such as for the working fluid containing carbon dioxide and disposed, flowing, or circulating within the low pressure side of the working fluid circuit202, the value of the critical pressure is generally greater than 5 MPa, such as about 7 MPa or greater, for example, about 7.38 MPa. Therefore, in some examples, the working fluid containing carbon dioxide in the low pressure side may be maintained at a pressure within a range from about 5 MPa to about 15 MPa, more narrowly within a range from about 7 MPa to about 12 MPa, more narrowly within a range from about 7.38 MPa to about 10.4 MPa, and more narrowly within a range from about 7.38 MPa to about 8 MPa during the startup procedure.

The method may further include increasing the flowrate or temperature of the working fluid within the working fluid circuit202and circulating the working fluid by a turbopump, such as the turbopump260contained within the pump system during the startup procedure. In some configurations, the pump system of the heat engine system90or200may have one or more pumps, such as a turbopump, such as the turbopump260, and/or a start pump, such as the start pump280. In some examples, the pump system may include a turbopump, a mechanical start pump, an electric start pump, or a combination of a turbopump260and a start pump, as described in more detail above.

The method may also include circulating the working fluid by the turbopump260during a load ramp procedure or a full load procedure subsequent to the startup procedure, such that the flowrate or temperature of the working fluid sustains the turbopump260during the load ramp procedure or the full load procedure. In some configurations, the heat engine system90may have a secondary heat exchanger and/or a tertiary heat exchanger, such as the heat exchangers150,130, configured to heat the working fluid. Generally, the heat exchanger150or another heat exchanger may be configured to heat the working fluid upstream to an inlet on a drive turbine of the turbopump260, such as during the load ramp procedure or the full load procedure. In some examples, one or more of the heat exchanger120, the heat exchanger130, and/or the heat exchanger150may reach a steady state during the load ramp procedure or the full load procedure.

In other embodiments, the method includes decreasing the pressure of the working fluid within the low pressure side of the working fluid circuit202via the process control system204during the load ramp procedure or the full load procedure. The method may also include decreasing the pressure of the working fluid within the low pressure side of the working fluid circuit202via the process control system204during the load ramp procedure or the full load procedure. In many examples, the working fluid within the low pressure side of the working fluid circuit202is in a subcritical state during the load ramp procedure or the full load procedure. The working fluid in the subcritical state is generally in a liquid state and free or substantially free of a gaseous state. Therefore, the working fluid in the subcritical state is generally free or substantially free of bubbles. In many examples, the working fluid contains carbon dioxide.

In other embodiments, as illustrated inFIG. 5, a method400further includes maintaining the pressure of the working fluid at or above a predetermined threshold. For example, an embodiment of the method400includes measuring a pressure of the working fluid (block402) and inquiring as to whether the measured pressure is below a predetermined threshold (block404). In this way, the method400provides for detecting an undesirable value of the pressure via the process control system204. If the pressure is below the threshold, the method400includes modulating at least one valve fluidly coupled to the working fluid circuit202with the process control system204to increase the pressure (block406), for example, by increasing the flowrate of the working fluid passing or flowing through the at least one valve. Following an adjustment of the valve, the pressure is again measured (block402) to determine if the adjustment raised the pressure above the predetermined threshold. In this way, the method400provides for detecting a desirable value of the pressure via the process control system204, wherein the desirable value is at or greater than the predetermined threshold value of the pressure.

In some examples, the method further includes measuring the pressure (e.g., the pump suction pressure) of the working fluid within the low pressure side of the working fluid circuit202upstream to an inlet on a pump portion of a turbopump, such as the turbopump260. The pump suction pressure may be at the critical pressure of the working fluid, but generally, the pump suction pressure is greater than the critical pressure of the working fluid at the inlet on the pump portion262of the turbopump260. In other examples, the method further includes measuring the pressure of the working fluid downstream from a turbine outlet on the power turbine228within the low pressure side of the working fluid circuit202. In other examples, the method further includes maintaining the pressure of the working fluid at or greater than a critical pressure value during the startup procedure. Alternatively, in other examples, the method may further include maintaining the pressure of the working fluid at less than the critical pressure value during the load ramp procedure or the full load procedure. Indeed, it should be noted that the pressure may be measured at any desirable location or locations within the working fluid circuit, not limited to those mentioned above, depending on implementation-specific considerations.

FIG. 6is a simplified embodiment of the heat engine system90depicted inFIG. 1and illustrates the placement and function of the bypass line160and bypass valve162in detail. More particularly,FIG. 6depicts a bypass line160fluidly coupled to a fluid line131of the working fluid circuit202upstream to the heat exchangers120,130, and140by a bypass valve162. During operation, the bypass valve162may be adjusted to multiple positions for controlling the flow of the working fluid within the working fluid circuit202during various segments of the electricity generation processes described herein. By adjusting the flow of the working fluid, the temperature of the working fluid may be regulated, for example, during startup to reduce or eliminate the likelihood of wear or damage to system components due to excess thermal heat.

In a first position, the bypass valve162may be configured to flow the working fluid from the throttle valve250, through the fluid line131, through the bypass valve162, through the bypass line160while avoiding the heat exchangers130and140and the fluid line133, through the fluid line135, and then through the recuperator216, the heat exchanger120, the inlet of the power turbine228, and the fluid lines therebetween. In a second position, the bypass valve162may be configured to flow the working fluid from the throttle valve250, through the fluid line131, through the bypass valve162, through the heat exchangers130and140and the fluid line133while avoiding the bypass line160, through the fluid line135, and then through the recuperator216, the heat exchanger120, the inlet of the power turbine228, and the fluid lines therebetween. In a third position, the bypass valve162may be configured to stop the flow the working fluid at the bypass valve162while avoiding the bypass line160and avoiding the heat exchangers130and140and the fluid line133. In this way, the bypass line160and bypass valve162may be controlled to reduce or prevent the likelihood of damage to components of the heat engine system90during startup due to overheated working fluid.

In one embodiment disclosed herein, during the startup process, the working fluid initially does not flow or otherwise pass through the heat exchangers120,130,140, and150and the temperature of the waste heat steam110(e.g., a gas turbine exhaust) may reach about 550° C. or greater. Therefore, the heat exchangers120,130,140, and150—generally composed of metal—absorb the thermal energy from the waste heat steam110and become heated, such that the temperatures of the heat exchangers120,130,140, and150may approach the temperature of the waste heat steam110. Generally, during the startup process, the bypass valve162may already be positioned to divert the working fluid around and avoid the heat exchangers130,150, and the optional heat exchanger140if present, such that the working fluid is flowed through the bypass line160.

In some examples, if the heat exchangers130,140, and150are not bypassed at the startup, the low mass flowrate of the working fluid (e.g., CO2) that initially flows through the fluid lines133and135disposed between the heat exchangers130and140and the recuperator216may result in the working fluid being heated to a temperature of about 550° C. at a pressure within a range from about 4.7 MPa to about 8.2 MPa. Therefore, in these examples, the inlet temperature of the recuperator216along the fluid line135may be maintained at a temperature of about 175° C. or less, such as about 172° C. or less. Failure to bypass the heat exchangers130,140, and150via the bypass line160during the startup process may cause overheating and possible damage to the recuperator216and/or other components.

It should be noted that the position of the bypass line160and the bypass valve162within the heat engine system may be varied in certain embodiments, depending on implementation-specific considerations.FIGS. 7-9illustrate suitable positions for the bypass line160and bypass valve162in accordance with some embodiments, but the illustrated positions are merely examples and are not meant to limit the positions possible in other embodiments. Indeed, the bypass line160and/or the bypass valve162may be positioned in any location that enables the bypass valve162to redirect the flow of the working fluid to place one or more of the heat exchangers120,130,140, and150in or out of the working fluid flow path.

In the embodiment ofFIG. 7, the heat engine system90contains the bypass line160and the bypass valve162disposed within the main process skid212. In this embodiment, the bypass valve162is fluidly coupled to the fluid line131extending between the throttle valve250and the heat exchanger130, more specifically, fluidly coupled to a segment of the fluid line131extending between and in fluid communication with the throttle valve250and the outlet231of the main process skid212. The fluid line131further extends through and is in fluid communication with the inlet132of the waste heat skid102. One end of the bypass line160may be fluidly coupled to the fluid line131by the bypass valve162. The other end of the bypass line160may be fluidly coupled to the fluid line135at a point downstream from the heat exchanger130, upstream to the recuperator216, and within the main process skid212.

More specifically, the other end of the bypass line160may be fluidly coupled to a segment of the fluid line135extending between and in fluid communication with the inlet235of the main process skid212and the recuperator216. In one embodiment, the fluid line135extends between and in fluid communication to the heat exchanger140and the recuperator216, as depicted inFIG. 7. In another embodiment, the heat exchanger140and the fluid line133are omitted, the fluid line135extends between and in fluid communication to the heat exchanger130and the recuperator216, and the other end of the bypass line160may be fluidly coupled to a segment of the fluid line135extending between and in fluid communication with the inlet235of the main process skid212and the recuperator216(not shown).

In other embodiments, the heat engine system90contains the bypass line160and the bypass valve162disposed within the waste heat skid102, as depicted inFIG. 8. The bypass valve162may be fluidly coupled to the fluid line131extending between the throttle valve250and the heat exchanger130, more specifically, fluidly coupled to a segment of the fluid line131extending between and in fluid communication with the inlet132of the waste heat skid102and the heat exchanger130. One end of the bypass line160may be fluidly coupled to the fluid line131by the bypass valve162. The other end of the bypass line160may be fluidly coupled to the fluid line135at a point downstream from the heat exchanger130, upstream to the recuperator216, and within the waste heat skid102.

More specifically, the other end of the bypass line160may be fluidly coupled to a segment of the fluid line135extending between and in fluid communication with the heat exchanger140and the outlet134of the waste heat skid102. In one embodiment, the fluid line135extends between and in fluid communication to the heat exchanger140and the recuperator216, as depicted inFIG. 8. In another embodiment, the heat exchanger140and the fluid line133are omitted, the fluid line135extends between and in fluid communication to the heat exchanger130and the recuperator216, and the other end of the bypass line160may be fluidly coupled to a segment of the fluid line135extending between and in fluid communication with the heat exchanger130and the outlet134of the waste heat skid102(not shown).

In the embodiment ofFIG. 9, the heat engine system90includes the bypass line160and the bypass valve162disposed between the waste heat skid102and the main process skid212. The bypass valve162may be fluidly coupled to the fluid line131extending between the throttle valve250and the heat exchanger130, more specifically, fluidly coupled to a segment of the fluid line131extending between and in fluid communication with the outlet231of the main process skid212and the inlet132of the waste heat skid102. One end of the bypass line160may be fluidly coupled to the fluid line131by the bypass valve162. The other end of the bypass line160may be fluidly coupled to the fluid line135at a point downstream from the heat exchanger130, upstream to the recuperator216, and between the waste heat skid102and the main process skid212. More specifically, the other end of the bypass line160may be fluidly coupled to a segment of the fluid line135extending between and in fluid communication with the outlet134of the waste heat skid102and the inlet235of the main process skid212. In one embodiment, the fluid line135extends between and is in fluid communication with the heat exchanger140and the recuperator216, as depicted inFIG. 1. In another embodiment, the fluid line135extends between and is in fluid communication with the heat exchanger130and the recuperator216, as depicted inFIG. 9.

In some embodiments, as depicted inFIG. 9, the heat exchangers130,140, and150may be bypassed from initial start through power turbine part power until the working fluid flow through the heat exchangers120and150reaches full design flow rate. Once the full design flow rate of the working fluid has been achieved, the temperature of the waste heat steam110exiting the heat exchanger120will be low enough to allow additional heat recovery from the heat exchangers130,140, and150without overheating the recuperator216. At this point, the bypass valve162may be switched to allow the working fluid to flow through the heat exchanger130, resulting in additional heat recovery and higher power turbine output without damage to the recuperator216.

Further, provided herein are methods for managing the “thermal transients” present as the heat engine system90approaches full power during an electricity generation process. For example, the methods may include controlling the bypass valve162such that the working fluid may be by-passed around to avoid one or more heat exchangers (e.g.,130,140,150) during startup until the process is ready to handle the increased thermal energy imparted to the working fluid within the working fluid circuit202by the waste heat stream. Implementation of one or more of the following methods may reduce or eliminate the likelihood of damage to components of the heat engine system during startup due to the high temperature of the waste heat flue.

In the embodiment ofFIG. 10, a method500is provided for rerouting the working fluid to avoid flow through one or more heat exchangers, for example, during startup of the heat engine system90. The method500includes circulating a working fluid through a working fluid circuit (block502) and inquiring as to whether bypass of the heat exchanger is desired (block504). For example, a controller may receive feedback from one or more temperature or pressure sensors within the system90to determine whether it is desirable to raise the temperature of the working fluid by flowing the working fluid through the heat exchangers, or to reduce or maintain the working fluid temperature by bypassing the heat exchangers.

If it is desirable to raise the working fluid temperature, then the working fluid is directed through the heat exchanger (block506). However, if bypass is desired, for example, during startup, then the position of the bypass valve is controlled to effectuate routing of the working fluid around the heat exchanger (block508) and to the power conversion device, such as power turbine228(block510).

In another embodiment shown inFIG. 11, a method600is provided for routing of the working fluid to or around one or more heat exchangers in a manner that reduces or eliminates the likelihood of damage to one or more components in the heat engine system90. The method600includes circulating a working fluid (e.g., sc-CO2) within a working fluid circuit202having a high pressure side and a low pressure side (block602) and flowing a heat source stream110through two or more heat exchangers disposed within the waste heat system100(block604).

In some examples, the one or more heat exchangers include a primary heat exchanger and a tertiary heat exchanger, such as the heat exchangers120and130, respectively. In other examples, a plurality of heat exchangers includes at least the primary and tertiary heat exchangers (e.g., heat exchangers120and130, respectively), as well as a secondary heat exchanger, such as the heat exchanger150, and/or an optional quaternary heat exchanger, such as the heat exchanger140. Each of the heat exchangers120,130,140, and150may be fluidly coupled to and in thermal communication with the heat source stream110, and independently, fluidly coupled to and in thermal communication with the working fluid within the working fluid circuit202.

The method600further includes flowing the working fluid through one or more heat exchangers (block606) and through a pump that circulates the working fluid through the working fluid circuit (block608). Additionally, the method600provides for flowing the working fluid through a bypass valve and/or bypass line to bypass one or more of the remaining heat exchangers (block610) to avoid overheating the working fluid, for example, during a startup procedure. It should be noted that the foregoing steps may be performed in any desired order, not limited to the order in which they are presented inFIG. 11. For instance, one or more of the heat exchangers may be bypassed prior to flowing the working fluid through another one of the heat exchangers.

For example, in one embodiment, the method600may include flowing the working fluid through the fluid line131and then through a bypass valve162and a bypass line160while avoiding the flow of the working fluid through the heat exchanger130and the fluid line133. The bypass line160may be fluidly coupled to the working fluid circuit202upstream to the heat exchanger130via the bypass valve162, fluidly coupled to the working fluid circuit202downstream from the heat exchanger130, and configured to circumvent the working fluid around the heat exchanger130and the fluid line133. Subsequently, the method600may include flowing the working fluid from the bypass line160, through the fluid line135, through other lines within the working fluid circuit202, and then to the heat exchanger120. The working fluid flows through the heat exchanger120while thermal energy is transferred from the heat source stream110to the working fluid within the high pressure side of the working fluid circuit202via the heat exchanger120.

In one aspect, both the temperature of working fluid and the power demand increase as the heat engine system200initially starts an electricity generation process. As the heat engine system200approaches full power, the bypass valve162and the bypass line160are utilized to provide additional control while managing the rising temperature of the working fluid within the working fluid circuit202. The bypass valve162and the bypass line160are configured and adjusted to circumvent the flow of the working fluid around at least one or more of the heat exchangers, such as the heat exchangers130and140, and to provide the flow of the working fluid upstream of the heat exchanger120. By avoiding the heat exchanger130and/or the heat exchanger140during the initial stage of the electricity generation process, the working fluid is prevented from absorbing too much thermal energy and damaging the recuperator216, and other components of the working fluid circuit202. Therefore, the additional controllability of the temperature of the working fluid via the bypass valve162and the bypass line160provides improved and safer maintenance of the working fluid in a supercritical state and also provides a reduction or elimination of thermal stress on mechanical parts of the heat engine system200, such as the turbo unit or turbine unit in the turbopump260and/or the power turbine228.

Additionally, the method600includes monitoring and receiving feedback regarding at least one process condition (e.g., a process temperature, pressure, and/or flowrate) of the working fluid within the high pressure side of the working fluid circuit202(block612) and inquiring as to whether the process condition is at or above a predetermined value (block614). Once the predetermined value is detected for at least one of the process conditions of the working fluid, a subsequent adjustment is made to the bypass valve162to divert the working fluid to avoid the bypass line160while directing the flow towards the heat exchanger130(block616).

In some embodiments, the predetermined value of the process temperature of the working fluid may be within a range from about 150° C. to about 180° C., more narrowly within a range from about 165° C. to about 175° C. during the startup process, as detected at the point on the working fluid circuit202disposed downstream from the (tertiary) heat exchanger130and upstream to the recuperator216. The working fluid containing carbon dioxide and at least a portion of the working fluid may be in a supercritical state within the high pressure side of the working fluid circuit202. Generally, during the startup process, the predetermined pressure of the working fluid as detected at the point on the working fluid circuit202may be within a range from about 4 MPa to about 10 MPa.

The heat exchanger130is generally fluidly coupled to the working fluid circuit202upstream to the heat exchanger120via line133, line135, and other fluid lines therebetween. Once the predetermined value for the process condition of the working fluid is detected and the bypass valve162is adjusted, the working fluid flows from the bypass valve162serially through the heat exchanger130and the heat exchanger120while thermal energy is transferred from the heat source stream110to the working fluid within the high pressure side of the working fluid circuit202.

For example, once the heat engine system200drawing thermal energy from the heat exchanger120achieves full power or substantially full power during the electricity generation process, additional thermal energy may be provided by bringing the heat exchanger130, the heat exchanger140, and/or the heat exchanger150into fluid and thermal communication with the working fluid. The bypass valve162and the fluid line133are configured to circumvent the flow of the working fluid around the bypass line160and provide the flow of the working fluid through the heat exchanger130, the heat exchanger140, and/or the heat exchanger150prior to flowing the working fluid through the heat exchanger120.

Thereafter, the method600includes flowing the working fluid from the heat exchanger120to a power turbine228, transforming thermal energy of the working fluid to mechanical energy of the power turbine228by a pressure drop in the working fluid, and converting the mechanical energy into electrical energy by a power generator240coupled to the power turbine228(block618). The power turbine228may be disposed between the high pressure side and the low pressure side of the working fluid circuit202and fluidly coupled to and in thermal communication with the working fluid.

In some examples, the method600further includes flowing the working fluid through the heat exchanger150(e.g., the secondary heat exchanger) while thermal energy is transferred from the heat source stream110to the working fluid within the high pressure side of the working fluid circuit202via the heat exchanger150, and subsequently flowing the heated working fluid through the turbopump260configured to circulate the working fluid within the working fluid circuit202.

In one embodiment, both the temperature of working fluid and the power demand increase as the heat engine system90initially starts an electricity generation process. As the heat engine system90approaches full power, the bypass valve162and the bypass line160are utilized to provide additional control while managing the rising temperature of the working fluid within the working fluid circuit202. The bypass valve162and the bypass line160are configured and adjusted to circumvent the flow of the working fluid around at least one or more of the heat exchangers, such as the heat exchangers130and140, and to provide the flow of the working fluid upstream of the heat exchanger120. By avoiding the heat exchanger130and/or the heat exchanger140during the initial stages of the electricity generation process (e.g., a startup process), the working fluid is prevented from absorbing too much thermal energy and damaging the recuperator216, and other components of the working fluid circuit202. Therefore, the additional controllability of the temperature of the working fluid via the bypass valve162and the bypass line160provides improved and safer maintenance of the working fluid in a supercritical state and also provides a reduction or elimination of thermal stress on mechanical parts of the heat engine system90, such as the turbo unit or turbine unit in the pump279and/or the power turbine228.

Again, certain embodiments of the heat engine systems provided above may enable a reduction or elimination of wear or damage to one or more system components. For example, in embodiments described herein, cavitation of pumps may be avoided by maintaining the working fluid containing carbon dioxide as a liquid. During startup, in a heat-saturated heat exchanger situation (e.g., where the waste heat flue is already operational), the low pressure of the working fluid containing carbon dioxide may be subjected to additional pressurization, which will tend to push the working fluid containing carbon dioxide towards a liquid-type state, such as a supercritical fluid state. The working fluid containing carbon dioxide may be utilized in a supercritical state (e.g., sc-CO2) and disposed on the low pressure side during system startup to reduce the likelihood that pump cavitation will occur.

More particularly, embodiments of the invention include a heat engine system and process that employs additional pressurization to maintain the working fluid containing carbon dioxide on the low pressure side in supercritical state. This is counter-intuitive to most systems, as power is derived from the pressure ratio. Therefore, movement in the low pressure side has a large effect on the efficiency and power of the system. However, providing the working fluid containing carbon dioxide in supercritical state reduces or removes the possibility of cavitation in the pump. Once the main pump (e.g., turbopump) may be ramped up to self-sustaining levels and the temperature of the heat exchangers reaches steady state, the working fluid containing carbon dioxide on the low pressure side may be reduced back into normal low pressure liquid phase, such that at least a portion of the working fluid is in a subcritical state.

Further, in order to manage the “thermal transients” as the heat engine system approaches full power during an electricity generation process and avoid damage to system components, the working fluid may be by-passed around to avoid one or more heat exchangers (e.g.,130,140,150) until the process is ready to handle the increased thermal energy imparted to the working fluid within the working fluid circuit. To that end, as discussed in detail above, a bypass valve may be disposed along an output line from a start pump and/or a turbopump and used to divert the flow of the working fluid through a bypass line and past the heat exchangers to introduce the working fluid at a location upstream to the inlet of a power conversion device, such as a power turbine.

In such embodiments, thermal energy imparted into the working fluid in a supercritical state is greatly reduced by circumventing the working fluid around and avoiding the passage of the working fluid through one, two, three, or more waste heat exchangers, such as the heat exchangers130,140, and150. In one embodiment, a single heat exchanger, such as the heat exchanger120, may be utilized to heat the working fluid flowing through the working fluid circuit202. The working fluid may be circulated multiple times through the single heat exchanger120by recirculating the working fluid through the working fluid circuit202. In certain embodiments, additional control for managing the increasing temperature of the working fluid without introducing “thermal shock” may be accomplished by only using the heat exchanger120.

In another embodiment described herein, the heat exchangers are pre-heated by the already-running main heat source during a heat saturated startup and the recuperators cannot handle the high temperature and flow of the working fluid. Therefore, the working fluid may be rerouted around the recuperators.

In another embodiment described herein, during the operation of a gas turbine, which acts as a heat source for the present heat engine system, there are times when the gas turbine is operated at reduced flow rates. At such times, full running of the heat engine system results in an insufficient heating of the working fluid (e.g., sc-CO2). Therefore, one or more recirculation lines are used to reduce the flow rate of the working fluid within the working fluid circuit. The pump has an optimal efficiency, so simply reducing flow is generally not the most efficient option. To reduce the flow rate, the recirculation lines connect the main pump to a point upstream of the condenser to shunt flow around the waste heat exchangers and expanders and route the working fluid back to the cold side.

In one or more embodiments, a gas turbine is utilized as a heat source for providing the heat source stream110flowing through the waste heat system100. There are times when the gas turbine is operated at less than full capacity and the heat source stream110has a reduced flowrate. At such times, full running of the heat engine system200results in an insufficient heating of the working fluid (e.g., sc-CO2). Therefore, one or more recirculation or fluid lines, such as fluid lines244and/or226, are utilized to reduce the flow rate of the working fluid within the working fluid circuit202. Again, the turbopump260has an optimal efficiency, so simply reducing flow is generally not the most efficient option. The relative flow rate of the working fluid is decreased by increasing the distance the working fluid flows while at the same actual flowrate. A fluid line226and bypass valve256may be fluidly coupled to the working fluid circuit202between the pump portion262of the turbopump260and a point on the fluid line229between the recuperator218and the condenser274. Such point on the fluid line229is downstream from the recuperators216and218and upstream of the condenser274. Also, a fluid line224and bypass valve254may be fluidly coupled to the working fluid circuit202between the pump portion282of the start pump280and the same point on the fluid line229between the recuperator218and the condenser274.

The passageway through the fluid lines226and229or the fluid lines224and229provides a bypass around the heat exchangers120,130,140, and/or150and the expanders, such as the power turbine228of the power generation system220and/or the drive turbine264of the turbopump260. Instead, the working fluid is recirculated through the cold or low pressure side of the working fluid circuit202.