Closed cycle inventory management

Abstract

To provide a system and method useful in controlling one or more aspects of a power production plant, and more particularly, provide a power production plant using a closed loop or semi-closed loop working fluid circuit, and operations thereof.SOLUTION: Inventory management through a working fluid circuit is performed by transfer of working fluid from a storage tank at one or more locations between a plurality of compressors based on at least one condition input to a controller located within a process facility having the working fluid circuit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The subject matter of the present disclosure relates to systems and methods for controlling various aspects of a power plant. More specifically, the systems and methods of the present disclosure may utilize a variety of signals and functions for mass management in a closed or semi-closed power cycle. [Background technology]

[0002] As the global demand for power production increases, there is a continuing need for additional power production plants to meet that demand. Closed-loop or semi-closed-loop power cycles utilizing carbon dioxide working fluids (or other working fluids) can be advantageous in terms of achievable efficiencies and the potential for little or no emissions of combustion products to the atmosphere. For example, U.S. Patent No. 8,596,075 to Allam et al. (incorporated herein by reference) provides desirable efficiencies in an oxy-fuel combustion system utilizing a recirculating CO2 stream where the CO2 is captured as a relatively pure stream at high pressure. However, closed-loop or semi-closed-loop power production cycles may require inventory management to maintain the required operating conditions, especially when variable heat inputs are utilized. Such inventory management may include functions such as mass management and / or pressure management.

[0003] Known systems for mass management may include the use of a tank capable of storing and releasing a fluid. The tank is typically fluidly connected to flow lines at the low and high pressure sides of a pressure augmentation element (e.g., a pump or compressor). Thus, fluid may be released into the low pressure side line and / or taken from the high pressure side line. The tank is therefore at a pressure between the intake and exhaust pressures of the pressure augmentation element. However, such systems may be limited in their ability to provide flexibility in operating parameters, such as when using variable heat input to the system. Thus, there is a need for additional systems and methods suitable for controlling multiple aspects of power plants, particularly power plants configured to operate in a closed or semi-closed loop power production cycle. Summary of the Invention

[0004] The present disclosure provides systems and methods for power production in which one or more control paths are utilized to control one or more behaviors. The control may be based on various manual or automatic inputs, calculated values, pre-set values, measurements, logic functions, computer algorithms, or computer program inputs.

[0005] In one or more embodiments, the present disclosure may relate to an electrical power production system. The system may include various elements effective for electrical power production utilizing a closed or semi-closed loop working fluid circuit. In some embodiments, such a system may include a working fluid circuit in which a working fluid is circulated between high and low pressures, a power generation turbine fluidly connected to the working fluid circuit to receive the working fluid at high pressure, expand the working fluid, and discharge the working fluid at an outlet at low pressure, a first compression element downstream of the power generation turbine and fluidly connected thereto, a second compression element downstream of the first compression element and fluidly connected thereto, a storage tank in fluid communication with the working fluid circuit, and a controller configured to transfer the working fluid between the tank and one or more locations in the working fluid circuit. The system may be further defined with respect to one or more of the following statements, which may be combined in any order or number:

[0006] The first compression element may be a single stage or a multi-stage compressor.

[0007] The second compression element may be a variable speed pump.

[0008] The power production system may further include at least one line configured to pass working fluid between the storage tank and the working fluid circuit.

[0009] The power production system may include at least one valve configured to control fluid flow through at least one line configured to pass the working fluid between the storage tank and the working fluid circuit.

[0010] The controller may be configured to open or close the at least one valve based on at least one condition input received by the controller.

[0011] At least one line configured to pass working fluid between the storage tank and the working fluid circuit may be configured to remove working fluid from the working fluid circuit upstream of the first compression element and downstream of an outlet of the power generation turbine.

[0012] At least one line configured to pass working fluid between the storage tank and the working fluid circuit may be configured to remove working fluid from the working fluid circuit downstream of the first compression element and upstream of the second compression element.

[0013] At least one line configured to pass working fluid between the storage tank and the working fluid circuit may be configured to introduce the working fluid into the working fluid circuit downstream of the first compression element and upstream of the second compression element.

[0014] At least one line configured to pass working fluid between the storage tank and the working fluid circuit may be configured to introduce the working fluid into the working fluid circuit downstream of the second compression element and upstream of an inlet to the power generation turbine.

[0015] The power production system may further include a heater positioned upstream from the power generation turbine and having an outlet in fluid communication with an inlet of the power generation turbine.

[0016] The power production system may further include a heating / cooling element in heating / cooling communication with the storage tank and configured to heat and / or cool a working fluid present in the storage tank.

[0017] Further embodiments of the power production system described herein will be apparent from the further disclosure provided herein.

[0018] In one or more embodiments, the present disclosure may relate to a method for managing inventory in an electrical power production system utilizing a closed or semi-closed loop working fluid circuit. In some embodiments, the method may include expanding a working fluid in a closed or semi-closed loop working fluid circuit passing through a power generating turbine from high pressure to low pressure, compressing the expanded working fluid in a first compression element, further compressing the working fluid in a second compression element, and transferring the working fluid between one or more locations in the closed or semi-closed loop working fluid circuit and a storage tank. The method may be further defined with respect to one or more of the following statements, which may be combined in any order or number:

[0019] Transferring the working fluid between one or more locations of the closed or semi-closed loop working fluid circuit and the storage tank may be based on at least one condition input to at least one controller in a process facility having the working fluid circuit.

[0020] The second compression element may be a variable speed pump.

[0021] The at least one condition input to the at least one controller may include one or more of a change in operating speed of the variable speed pump, an intake pressure measured between the first compression element and the variable speed pump, and a temperature of the working fluid at an outlet of the power generation turbine.

[0022] The closed or semi-closed loop working fluid circuit may be configured to maintain an operating pressure range between the first compression unit and the second compression unit, the operating pressure range being from a minimum pressure P1 to a maximum pressure P2.

[0023] The at least one controller may be configured to pass the working fluid from the storage tank to at least one location in the closed loop or semi-closed loop working fluid circuit to maintain a pressure above a minimum pressure P1.

[0024] The working fluid may pass from the storage tank to at least one location in a closed or semi-closed loop working fluid circuit upstream of the first compression element and downstream of the outlet of the power generating turbine.

[0025] The working fluid may pass from the storage tank to at least one location in a closed or semi-closed loop working fluid circuit downstream of the first compression element and upstream of the second compression element.

[0026] The at least one controller may be configured to pass working fluid from at least one location in the closed loop or semi-closed loop working fluid circuit to the storage tank to maintain a pressure below the maximum pressure P2.

[0027] The working fluid may pass from at least one location in the closed or semi-closed loop working fluid circuit downstream of the first compression element and upstream of the second compression element to the storage tank.

[0028] The working fluid may be passed to the storage tank from at least one location in the closed or semi-closed loop working fluid circuit downstream of the second compression element and upstream of the inlet of the power generating turbine.

[0029] The working fluid may include carbon dioxide.

[0030] The working fluid may be greater than 50 mole percent carbon dioxide.

[0031] The method may further include one or both of heating and cooling the working fluid present in the storage tank.

[0032] Further embodiments of the methods described herein for managing inventory in an electricity production system will be apparent from the further disclosure provided herein.

[0033] Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a flow diagram of a closed loop power production cycle with an inventory management element according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Exemplary embodiments of the subject matter of the present disclosure are described in more detail below. These exemplary embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter of the present disclosure to those skilled in the art. Indeed, the subject matter of the present disclosure may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein, but rather, these embodiments are presented to satisfy applicable legal requirements. As used in this specification and the appended claims, the singular forms "a," "one," and "the" include plural referents unless the context clearly dictates otherwise.

[0036] The present disclosure relates to systems and methods adapted to control one or more behaviors in the operation of an electric power production plant. Accordingly, the present disclosure further relates to an electric power production plant including various elements including such a control system. Non-limiting examples of elements that may be included in an electric power production plant according to the present disclosure are described in U.S. Patent No. 8,596,075, U.S. Patent No. 8,776,532, U.S. Patent No. 8,959,887, U.S. Patent No. 8,986,002, U.S. Patent No. 9,068,743, U.S. Patent Application Publication No. 2010 / 0300063, U.S. Patent Application Publication No. 2012 / 0067054, U.S. Patent Application Publication No. 2012 / 0237881, and U.S. Patent Application Publication No. 2013 / 0213049, the disclosures of which are incorporated herein by reference.

[0037] In one or more embodiments, the present disclosure relates to power production systems and / or methods that utilize closed or semi-closed loop cycles. In particular, the systems and / or methods may incorporate elements beneficial to inventory management. In certain embodiments, the elements are configured to improve operation through improved management of mass and / or volumetric flow rates at one or more points in the cycle.

[0038] The power production system and / or method described herein may exhibit improved inventory management through the utilization of a combination of elements. In some embodiments, it may be useful to utilize two independent stages of compression / pumping of the fluid passing through the cycle. By having two independent compression / pumping stages, the cycle of the present disclosure is in the beneficial position of allowing the pressure between the separate and independent stages to substantially float, i.e., be within a relatively wide range defined by upper and lower limits. Multi-stage compressors / pumps are not known to exhibit such a capability, as the individual stages must be carefully balanced so that one stage is not in a surge condition and the other stage is within normal operating parameters. By utilizing the multiple independent compression / pumping stages of the present disclosure, it is possible to increase and / or decrease the pressure in the area between the stages, thereby storing excess inventory and / or supplying additional inventory to the cycle without requiring the use of additional equipment. Additionally, storage tanks can be added between the stages with simple controls to set maximum and minimum pressures to allow for much greater variation in cycle operating conditions.

[0039] Thus, the disclosed systems and methods may incorporate various components that operate under suitable conditions. For example, at least a power generating turbine and associated generator for producing electricity may be combined with multiple independent compression / pumping stages separated by piping or lines having sufficient volume to accommodate fluid storage. This may include one or more storage tanks located between the multiple compression / pumping stages. One or more coolers and / or heaters may be included at one or more points in the system, for example, to remove heat from the expanded working fluid before compression, to remove or add heat between the compression / pumping stages, and / or to add heat to the working fluid before expansion in the turbine. In some embodiments, the power generating turbine may be a combined heater / turbine unit. Alternatively, a combustor or other heating unit may be positioned upstream of the power generating turbine, particularly immediately upstream of the power generating turbine.

[0040] An exemplary embodiment of the present disclosure is shown in FIG. 1, which is a simplified diagram of a closed-loop power production cycle. However, it will be appreciated that aspects of the present disclosure may likewise be incorporated, in whole or in part, into a closed-loop or semi-closed-loop power production cycle having more or fewer components than those shown in FIG. 1. For example, aspects of the present disclosure may be incorporated into power production as described in any of the documents incorporated herein by reference. The cycle shown in FIG. 1 may be configured as a semi-closed-loop power production cycle, for example, by introducing a valve 500 as shown in FIG. 1 as an optional component. The valve 500 may allow for the withdrawal of a portion of the working fluid. Similarly, a valve 600 may be used to introduce a make-up fluid and / or fuel. The valves 500 and 600 may be positioned elsewhere in the illustrated power production cycle.

[0041] Thus, FIG. 1 illustrates an exemplary embodiment of an electrical power production system including various components. The working fluid circuit 100 may include any necessary piping, lines, valves, splitters, unions, and other components typically utilized in electrical power production systems to pass heated and / or compressed fluid. In the working fluid circuit 100, the working fluid circulates between high and low pressures. The range of high and low pressures may vary as desired. For example, the low pressure may range from ambient pressure to about 5 bar, about 4 bar, about 3 bar, or about 2 bar. The high pressure may range from about 10 bar to about 400 bar, about 15 bar to about 350 bar, or about 20 bar to about 300 bar. However, it is understood that the terms "high" and "low" are meant relative to one another and that the high pressure may be any pressure higher than the low pressure and the low pressure may be any pressure lower than the high pressure.

[0042] The power generation turbine 10 is fluidly connected to the working fluid circuit 100, and receives a working fluid at high pressure, expands the working fluid, and discharges the working fluid at its outlet 10b at low pressure. The high pressure working fluid may enter the power generation turbine 10 through the inlet 10a, among other places. A first compression element (e.g., compressor 30) is positioned downstream of and in fluid communication with the power generation turbine 10 such that the working fluid enters the compressor 30 and is compressed to a pressure higher than the pressure of the working fluid at the outlet 10b of the turbine 10. The first compression element may be, for example, a single stage compressor or a multi-stage compressor. When a multi-stage compressor is used, it may be beneficial to utilize cooling between the compression stages. A second compression element (e.g., pump 20) is positioned downstream of and in fluid communication with the first compression element. As described further herein, in some embodiments, it may be useful for the second compression element to be a pump, such as a variable speed pump. This can be useful to provide controlled changes in pump speed to account for changes in working fluid inventory upstream of the pump.

[0043] A cooler 32 is positioned between the turbine 10 and the compressor 30, and a cooler 22 is positioned between the compressor 30 and the pump 20. Such coolers may be optional, but may be useful to maintain a desired pressure and / or density of the working fluid at various points within the working fluid circuit 100. As described further below, a storage tank 40 may preferably be included and positioned in fluid communication with the working fluid circuit 100. A controller 41 may be configured to transfer the working fluid between the tank 40 and one or more locations within the working fluid circuit 100. Such transfer may be automated and dependent on the input of one or more signals to the controller 41.

[0044] The cycle shown in FIG. 1 specifically illustrates the use of a controllable heat source 12, i.e., a heat source whose input can vary over a relatively wide range. The use of a controllable heat source typically introduces complications that may otherwise make inventory control unattainable. However, the present disclosure is able to achieve the necessary inventory control when using a controllable heat source or a heat source that provides a constant heat input. As shown, the heat source 12 is a controllable heat source, although it is understood that a constant heat source may also be used. The heat source 12 may be a combustor, including, for example, a flexible fuel combustor as described in U.S. Patent Application Publication No. 2018 / 0259183, the disclosure of which is incorporated herein by reference. Other types of heat sources, such as solar heaters, boilers, etc., may also be used.

[0045] Because the heat source 12 is controllable (or variable), the present disclosure includes a control element to manage the heat entering the system. As shown, the controller 1 measures the power output of the generator 11, but several possible items may be controlled by the controller 1. More specifically, the controller 1 commands the heat input to the heat source 12 to generate the required power. If the heat source is not controllable, or is otherwise controlled outside of the power loop, the controller 1 is optional and not required, and the system will simply extract the maximum amount of power from the heat added at the heat source 12. In one or more embodiments, one or more recuperative heat exchangers may be utilized, and recuperative heating may be beneficial under various conditions. If a recuperative heat exchanger is present, it may also be beneficial to include one or more additional heat sources to add heat to the cycle via the recuperative heat exchanger. Similarly, one or more heat exchangers may be used to remove heat from the cycle. This is shown in FIG. 1 by heat exchanger 14, which is optional and may be used to recuperate at least the working fluid flowing into the heater 12 by recovering heat from the working fluid stream exiting the turbine 10.

[0046] As heat is added to the system via heat source 12 (or another heat source), the temperature at various points in the cycle downstream from the heat source increases accordingly. For example, adding heat at heat source 12 increases the temperature at the inlet of turbine 10, and after expansion through turbine 10, the temperature at point 13 (after leaving the outlet of the turbine) changes as well. Controller 2 may be configured to measure the temperature at one or more points in the system and accordingly command a change in power or speed of pump 20 to maintain a constant temperature at one or more points. As shown in FIG. 1, controller 2 is coupled to the temperature measurement at point 13, so that control of pump 20 may be managed to achieve a constant temperature at point 13. However, it will be appreciated that controller 2 may be coupled to additional points in the system or may be coupled to a different point in the system. Similarly, additional controllers may be added such that control of pump 20 may be individually coupled to temperature measurements at multiple different points in the system. For example, control of pump 20 may be coupled by one or more controllers to temperature measurements at any one or more of the inlet of turbine 10, the outlet of turbine 10 (i.e., point 13), the input of heat source 12, or yet another point in the system. Additionally, use of controller 2 to manage pump 20 may be implemented in response to parameters other than (or in addition to) temperature. In general, any system parameter that can be managed based on the output at pump 20 may be automatically controlled via controller 2 by coupling the controller to a suitable parameter input location in the system. In this manner, the controller may be configured to keep the parameter substantially constant regardless of the parameter being controlled and / or may be configured to make automatic adjustments to the parameter as needed. Pump 20 may, among other things, be a variable speed pump. Thus, the outlet flow rate and pressure of pump 20 may be variable and capable of being changed to meet the requirements of the inlet of turbine 10 based on the thermal input of the turbine and / or based on the particular parameter to be managed by controller 2.For example, as shown in FIG. 1, it is possible to maintain a constant turbine exit condition at point 13 based on a controller 2 governing the operation of a pump 20 .

[0047] The controller 3 controls the spillback valve 31 (sometimes called a recirculation valve). The controller 3 can return flow from the high pressure side of the compressor 30 to the intake side at point 33 upstream of the cooler 32 so as not to overheat the system. In doing so, the controller 3 maintains the intake pressure of the compressor 30 at a controlled value, taking into account system losses, which becomes the exhaust pressure of the turbine 10 at point 13. By fixing the exhaust temperature and exhaust pressure of the turbine 10, the inlet conditions to the turbine will be determined by the amount of power produced in the generator 11, and these inlet conditions will necessarily be determined by the basic operation of the turbine, the turbine map, and the position of the exhaust on the turbine map, as determined by the controllers 2, 3. Similarly, temperatures or different parameters can be similarly fixed at different points in the system based on the output provided by one or both of the controllers 2, 3.

[0048] It can be seen that as the amount of heat entering the system at the heat source 12 changes, the flow through the system changes. Because the illustrated power cycle is closed loop (and therefore has a constant volume), the inventory in the system may need to change. "Inventory" can refer to a variety of different fluids that may be in different states (e.g., gas, liquid, supercritical). The inventory may be, inter alia, a CO2-containing fluid, preferably a fluid that is mostly CO2 or substantially pure CO2. For example, the inventory (i.e., working fluid) may contain more than 50 mole % carbon dioxide. Substantially pure CO2 may mean at least 98 mole %, at least 99 mole %, at least 99.5 mole %, or at least 99.9 mole % carbon dioxide.

[0049] The power production system may further comprise at least one line configured to pass the working fluid between the storage tank 40 and the working fluid circuit 100. In FIG. 1, the line 44a is configured to pass the working fluid from the working fluid circuit 100 to the storage tank 40, and the line 44b is configured to pass the working fluid from the storage tank to the working fluid circuit. However, it is understood that a single line may be utilized or multiple input and / or output lines (input and output are to the tank) may be utilized. Any input and / or output line(s) may include at least one valve configured to control the flow of fluid through the at least one line configured to pass the working fluid between the storage tank 40 and the working fluid circuit 100. In FIG. 1, the line 44a includes the valve 42 and the line 44b includes the valve 43. It is understood that the valve(s) may include a pumping element to improve the active movement of the fluid into and out of the storage tank 40. As described further herein, controller 41 may be configured to open or close at least one valve (eg, valve 42 and / or valve 43) based on at least one condition input received by the controller.

[0050] Inventory control tank 40 is used to store fluid that may be added to and / or removed from the cycle. As pump 20 changes speed and changes flow rate, the pressure in the system near point 400 changes. There is a minimum requirement for the combination of intake pressure at point 400 and temperature of the flow leaving cooler 22 for pump 20 to operate efficiently. Controller 41 uses valve 43 to add fluid at point 402 to maintain a pressure above a minimum pressure P1, which may be selected based on desired operating parameters. Also, as cycle conditions change, the pressure at point 400 increases and begins to approach a maximum pressure P2. The maximum pressure may be selected to meet any desired operating range. In certain embodiments, P2 may be selected as the pressure that would cause damage to piping and other equipment or exceed the capacity of compressor 30. Controller 41 uses valve 42 to remove fluid from the cycle at point 401 and add fluid to storage tank 40 to maintain the pressure at point 400 below the maximum pressure P2. Thus, the pressure in the tank 40 will be between P1 and P2 at the midpoint, as at point 400, but the pressure in the tank and at point 400 will be different. In this way, the tank 40 and the controls around point 400 act as an accumulator, allowing the pressure in this area to be between P1 and P2 while keeping the mass in the system constant, so that small changes in the operation of the turbine 10 do not affect the mass in the system. If the change in conditions is significant enough, the pressure at point 400 may go above or below the limits of P1 and P2. In such a case, the controller 41 reacts to maintain the pressure within the limits.

[0051] The positions of points 400, 401, and 402 relative to each other and to the cooler 22 may differ from those shown in FIG. 1 . That is, the order is not determined by the shape shown. For example, point 401 may be optionally positioned between the cooler 32 and the compressor 30 to redirect fluid from the cycle into the storage tank 40 upstream of the compressor 30 instead of downstream of the compressor 30. As a further example, point 402 may be optionally positioned between the pump 20 and the heater 12 to return fluid into the cycle downstream of the pump 20 instead of upstream of the pump 20. In addition, it is not necessary that two valves (42, 43) must be used; instead, a single valve may be used. Furthermore, the functions of the controller 41 may be realized utilizing multiple different controllers. For example, the valves 42 and 43 may be controlled by a first valve controller and a second different valve controller, respectively. It will further be appreciated that pump 20 is sometimes referred to as a compressor as the difference is purely nomenclature and is merely for convenience. In some embodiments, controller 41 may take input from one or more of pump 20 intake conditions, operating conditions, or exhaust conditions and enable calculation of P2 for equipment protection to maintain pump operation within a desired operating range.

[0052] Optionally, the temperature within the tank 40 may be controlled using a heating / cooling element 45. The heating / cooling element 45 may specifically be in heating / cooling communication with the storage tank 40 and may be configured to heat and / or cool the working fluid present within the storage tank. Heating and cooling may be accomplished by the same component, or separate heating and cooling elements may be associated with the storage tank 40.

[0053] In some embodiments, the heating / cooling element 45 may be a fluid flow that can add and / or remove fluid from the tank 40 to change the temperature conditions within the tank. Since the volume of the tank 40 is constant, this fluid flow allows additional fluid to be added to the tank 40 without increasing or decreasing the pressure beyond the P1 and P2 limits by manipulating the density within the tank 40. Alternatively, in a similar manner, for a given volume of the tank 40 containing a given mass of fluid, the pressure within the tank 40 may be manipulated by varying the density of the fluid and / or by varying the temperature of the fluid such that P1 and P2 may be increased or decreased for unsteady state cases and operations such as start-up, load following, turn-down, etc. Thus, the heating / cooling element 45 may alternatively be a heater that adds heat to the tank (or directly to the contents of the tank) or a cooler that removes heat from the tank (or directly from the contents of the tank). For example, the component 45 may be a jacket around the tank 40 configured to heat and / or cool the tank. As another example, component 45 may be heat exchange lines inside tank 40 through which heating and / or cooling fluids can be passed to heat / cool the contents of the tank without directly mixing with the fluid contained within the tank. The fill point of the tank and the pressure relief safety devices on tank 40 are not shown.

[0054] As can be appreciated from the foregoing, power production systems as described herein may be particularly useful in implementing a method of managing working fluid inventory in a power production system utilizing a closed or semi-closed loop working fluid circuit. For example, the method may include expanding a working fluid in a closed or semi-closed loop working fluid circuit passing through the power generation turbine 10 from a high pressure to a low pressure to generate power, such as electricity. The working fluid exiting the power generation turbine 10 may be compressed in multiple compression elements, such as the first and second compression elements described above. Additionally, the method may include transferring the working fluid between one or more locations in the closed or semi-closed loop working fluid circuit 100 and the storage tank 40.

[0055] As discussed above, the transfer of working fluid between one or more locations of the closed or semi-closed loop working fluid circuit 100 and the storage tank 40 may be based on at least one condition input to at least one controller in a process facility having the working fluid circuit. The controller 41 shown in FIG. 1 may be configured to, among other things, control the transfer of working fluid between the working fluid circuit 100 and the storage tank.

[0056] As an example, if a variable speed pump (e.g., pump 20 of FIG. 1) is used as the second compression element, the at least one condition input to the at least one controller may include one or more of a change in the operating speed of the variable speed pump, an intake pressure measured between the first compression element (e.g., compressor 30) and the variable speed pump 20, and a temperature of the working fluid at the outlet 10b of the power generation turbine 10. The controller 41 may, for example, receive inputs related to one or all of the foregoing to automatically control the passage of working fluid between the storage tank 40 and the working fluid circuit 100. As discussed above, this may be accomplished utilizing a single line between the working fluid circuit 100 and the storage tank 40, in which case a suitable valve(s) (and optionally a pumping element(s)) may be used to effect flow from the storage tank to the working fluid circuit or from the working fluid circuit to the storage tank, as needed.

[0057] In some embodiments, such controllability may be beneficial when the closed or semi-closed loop working fluid circuit 100 is configured to maintain an operating pressure range between a first compression unit (e.g., compressor 30) and a second compression unit (e.g., pump 20). As previously described, such operating pressure range may be defined to be between a minimum pressure P1 and a maximum pressure P2. In one or more embodiments, P1 and P2 are both pressures above the low pressure and below the high pressure referred to herein for the power generating turbine. Specifically, P1 may be above the low pressure of the working fluid leaving the outlet 10b of the turbine 10 and below P2. Similarly, P2 may be above P1 and below the high pressure of the working fluid entering the inlet 10a of the turbine. The controller 41 may be programmed to perform one or more functions to maintain the pressure of the working fluid circuit 100 within the range of P1 to P2. For example, the controller 41 may be configured to pass the working fluid from the storage tank 40 to at least one location in the closed or semi-closed loop working fluid circuit 100 to maintain a pressure higher than the minimum pressure P1. The working fluid may pass from the storage tank 40 to at least one location in the closed or semi-closed loop working fluid circuit 100 that is upstream of the first compression element (e.g., compressor 30) and downstream of the outlet 10b of the power generation turbine 10. Alternatively, or in addition, the working fluid may pass from the storage tank 40 to at least one location in the closed or semi-closed loop working fluid circuit 100 that is downstream of the first compression element (e.g., compressor 30) and upstream of the second compression element (e.g., pump 20). Similarly, the controller 41 may be configured to pass the working fluid from at least one location in the closed or semi-closed loop working fluid circuit 100 to the storage tank 40 to maintain a pressure lower than the maximum pressure P2. For example, the working fluid may pass from at least one location in the closed or semi-closed loop working fluid circuit 100 downstream of a first compression element (e.g., compressor 30) and upstream of a second compression element (e.g., pump 20) to the storage tank 40.Alternatively, or in addition, the working fluid may pass to the storage tank 40 from at least one location in the closed or semi-closed loop working fluid circuit downstream of the second compression element (e.g., pump 20) and upstream of the inlet 10a of the power generation turbine 10.

[0058] In addition to the foregoing, methods of the present disclosure may include one or both of heating and cooling the working fluid present in the storage tank 40. This may be performed as otherwise described above utilizing a single heating / cooling element 45 or using a heating element and a separate cooling element.

[0059] Many modifications and other embodiments of the subject matter of the present disclosure will come to mind to one skilled in the art to which the subject matter of the present disclosure pertains having the benefit of the teachings presented in the above descriptions and the associated drawings. It is to be understood, therefore, that the present disclosure is not limited to the specific embodiments described herein, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms have been employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. 1. An electricity production system comprising: a working fluid circuit in which a working fluid circulates between high pressure and low pressure; a power generating turbine fluidly connected to the working fluid circuit, the power generating turbine receiving the working fluid at high pressure, expanding the working fluid, and discharging the working fluid at a low pressure through an outlet; a first compression element downstream from and in fluid communication with the power generation turbine; a second compression element downstream of and in fluid communication with the first compression element; a storage tank in fluid communication with the hydraulic fluid circuit; a controller configured to transfer hydraulic fluid between the tank and one or more locations in the hydraulic fluid circuit; An electric power production system comprising:

2. The electrical power production system of claim 1 , wherein the first compression element is a single stage or a multi-stage compressor.

3. The electrical power producing system of claim 1 , wherein the second compression element is a variable speed pump.

4. The electrical power production system of claim 1 , further comprising at least one line configured to pass a working fluid between the storage tank and the working fluid circuit.

5. 5. The electrical power production system of claim 4, further comprising at least one valve configured to control fluid flow through at least one line configured to pass working fluid between the storage tank and the working fluid circuit.

6. The power production system of claim 5 , wherein the controller is configured to open or close the at least one valve based on at least one condition input received by the controller.

7. 5. The electrical power production system of claim 4, wherein at least one line configured to pass working fluid between the storage tank and the working fluid circuit is configured to remove working fluid from the working fluid circuit upstream of the first compression element and downstream of an outlet of the power generating turbine.

8. 5. The electrical power production system of claim 4, wherein at least one line configured to pass working fluid between the storage tank and the working fluid circuit is configured to remove working fluid from the working fluid circuit downstream of the first compression element and upstream of the second compression element.

9. 5. The electrical power production system of claim 4, wherein at least one line configured to pass working fluid between the storage tank and the working fluid circuit is configured to introduce working fluid into the working fluid circuit downstream of the first compression element and upstream of the second compression element.

10. 5. The electrical power production system of claim 4, wherein at least one line configured to pass working fluid between the storage tank and the working fluid circuit is configured to introduce working fluid into the working fluid circuit downstream of the second compression element and upstream of an inlet of the power generating turbine.

11. The electrical power production system of claim 1 , further comprising a heater positioned upstream of the power generating turbine and having an outlet in fluid communication with an inlet of the power generating turbine.

12. 10. The power production system of claim 1, further comprising a heating / cooling element in heating / cooling communication with the storage tank and configured to heat and / or cool a working fluid present in the storage tank.

13. 1. A method for managing working fluid inventory in an electrical power production system utilizing a closed or semi-closed loop working fluid circuit, the method comprising: Expanding a working fluid in a closed or semi-closed loop working fluid circuit through a power generating turbine from a high pressure to a low pressure; compressing the expanded working fluid in a first compression element; further compressing the working fluid in a second compression element; transferring hydraulic fluid between one or more locations in the closed or semi-closed loop hydraulic circuit and a storage tank; A method comprising:

14. 14. The method of claim 13, wherein transferring working fluid between one or more locations of the closed or semi-closed loop working fluid circuit and the storage tank is based on at least one condition input to at least one controller in a process facility having the working fluid circuit.

15. The method of claim 14 , wherein the second compression element is a variable speed pump.

16. 16. The method of claim 15, wherein the at least one condition input to the at least one controller includes one or more of a change in operating speed of the variable speed pump, an intake pressure measured between the first compression element and the variable speed pump, and a temperature of the working fluid at an outlet of the power generating turbine.

17. 15. The method of claim 14, wherein the closed or semi-closed loop working fluid circuit is configured to maintain an operating pressure range between the first compression unit and the second compression unit, the operating pressure range being from a minimum pressure P1 to a maximum pressure P2.

18. 20. The method of claim 17, wherein the at least one controller is configured to pass working fluid from the storage tank to at least one location in the closed or semi-closed loop working fluid circuit to maintain a pressure above the minimum pressure P1.

19. 20. The method of claim 18, wherein working fluid passes from the storage tank to at least one location in the closed or semi-closed loop working fluid circuit upstream of the first compression element and downstream of an outlet of the power generating turbine.

20. 20. The method of claim 18, wherein working fluid passes from the storage tank to at least one location in the closed or semi-closed loop working fluid circuit downstream of the first compression element and upstream of the second compression element.

21. 18. The method of claim 17, wherein the at least one controller is configured to pass working fluid from at least one location in the closed or semi-closed loop working fluid circuit to the storage tank to maintain a pressure below the maximum pressure P2.

22. 22. The method of claim 21, wherein working fluid passes from at least one location in the closed or semi-closed loop working fluid circuit downstream of the first compression element and upstream of the second compression element to the storage tank.

23. 22. The method of claim 21, wherein working fluid passes to the storage tank from at least one location in the closed or semi-closed loop working fluid circuit downstream of the second compression element and upstream of an inlet to the power generating turbine.

24. The method of claim 13 , wherein the working fluid comprises carbon dioxide.

25. The method of claim 13 , wherein the working fluid is greater than 50 mole percent carbon dioxide.

26. The method of claim 13 , further comprising one or both of heating and cooling the working fluid present in the storage tank.

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