Hydrogen production using electricity generated by gas pressure reduction

Abstract

The system includes a once-through generator and an electrolytic cell. The once-through generator includes a turbine wheel, a rotor, and a stator. The turbine wheel is configured to receive natural gas from a natural gas pipeline and rotate in response to expansion of the natural gas entering an inlet of the turbine wheel and exiting an outlet of the turbine wheel. The rotor is coupled to the turbine wheel and configured to rotate with the turbine wheel. The once-through generator is configured to generate electrical power as the rotor rotates within the stator. The electrolytic cell is configured to receive a water flow and electrical power from the once-through generator. The electrolytic cell is configured to perform electrolysis on the water flow using the received electrical power to produce a hydrogen flow and an oxygen flow.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 17 / 980,191, filed November 3, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to the production of hydrogen. [Background technology]

[0003] Gas can be transported between locations through a network of pipes. Moving such gas efficiently and effectively from production areas to consumption areas requires extensive and sophisticated transportation systems. One example of such a gas is natural gas. Natural gas is one of the primary energy sources for many of our daily needs and activities. Natural gas is an attractive fossil fuel due to its abundance. When natural gas is transported through pipelines, it moves under high pressure within the pipeline.

[0004] Another example of such a gas is hydrogen, which is a rapidly expanding global energy storage market. Hydrogen is used in many manufacturing processes, from oil refining to food processing. Hydrogen is also used as a fuel source for gas turbines and in a wide range of fuel cells to generate electricity in the industrial and civilian transportation sectors. Summary of the Invention

[0005] The present disclosure relates to technology related to hydrogen production, particularly hydrogen production using electricity generated by gas expansion. Certain aspects of the subject matter of the present disclosure can be implemented as a system. The system includes a once-through generator and an electrolytic cell. The once-through generator is connected to a natural gas pipeline carrying natural gas. The once-through generator includes a turbine wheel, a rotor, and a stator. The turbine wheel is configured to receive natural gas from the natural gas pipeline and rotate in response to expansion of the natural gas flowing into an inlet of the turbine wheel and flowing out an outlet of the turbine wheel. The rotor is coupled to the turbine wheel and configured to rotate together with the turbine wheel. The once-through generator is configured to generate electricity by rotating the rotor within the stator. The electrolytic cell is electrically connected to an electrical power output of the once-through generator. The electrolytic cell is configured to receive a water flow and electrical power from the once-through generator. The electrolytic cell is configured to perform electrolysis on the water flow using the received electrical power to produce a hydrogen flow and an oxygen flow.

[0006] This and other aspects can include one or more of the following features. The system can include a natural gas pipeline. The natural gas pipeline can include an inlet flowline and a first flowline. The inlet flowline can be in fluid communication with a gas well head to receive natural gas produced from the gas well. The first flowline can be coupled to the inlet flowline to receive at least a first portion of the natural gas from the inlet flowline. A once-through generator can be coupled to the first flowline. The natural gas pipeline can include a second flowline. The second flowline can be coupled to the inlet flowline to receive at least a second portion of the natural gas from the inlet flowline and provide an alternate flow path for the natural gas bypassing the first flowline. The first and second flowlines can be coupled downstream from the once-through generator to recombine the first and second portions of the natural gas from the first and second flowlines, respectively. The system can include a pressure control valve. The pressure control valve can be coupled to the second flowline. The pressure control valve can be configured to provide an adjustable-size constriction in a second portion of the natural gas flowing through the second flow line such that the second portion of the natural gas adiabatically expands as it traverses the pressure control valve. A first outlet pressure of the first portion of the natural gas discharged from the once-through generator can be substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve. The system can include a heater. The heater can be coupled to the inlet flow line. The heater can be configured to heat the natural gas upstream of the first flow line and the second flow line. The system can include a controller communicatively coupled to the pressure control valve and the once-through generator.The controller is configured to adjust the size of the constriction provided by the pressure control valve so that a first outlet pressure of a first portion of the natural gas discharged from the once-through generator is maintained substantially equal to a second outlet pressure of a second portion of the natural gas discharged from the pressure control valve, and adjusting the size of the constriction adjusts the torque applied to the once-through generator. The once-through generator may include a hermetically sealed housing that houses a turbine wheel therein. The rotor and stator may be hermetically sealed and disposed in-line within the first flow line such that the first portion of the natural gas flows across the turbine wheel and the stator. The rotor may include a permanent magnet rotor.

[0007] Certain aspects of the presently disclosed subject matter can be implemented as a method. Natural gas is flowed from a natural gas pipeline to a turbine wheel of a once-through generator. Electricity is generated by the once-through generator as the natural gas flows across the turbine wheel. The electricity generated by the once-through generator is supplied to an electrolysis cell. The electrolysis cell uses the electricity generated by the once-through generator to perform electrolysis on a water stream to produce a hydrogen stream and an oxygen stream.

[0008] This and other embodiments can include one or more of the following features. The natural gas can be produced from a gas well. The natural gas can flow from a wellhead of the gas well to an inlet flowline of a natural gas pipeline. At least a first portion of the natural gas can flow from the inlet flowline to the first flowline of the natural gas pipeline. A once-through generator can be coupled to the first flowline. At least a second portion of the natural gas can flow from the inlet flowline to a second flowline of the natural gas pipeline. The second flowline can provide an alternative flow path for the natural gas that bypasses the first flowline. The first portion of the natural gas from the first flowline can recombine with a second portion of the natural gas from the second flowline downstream of the once-through generator. A pressure control valve can be coupled to the second flowline. The pressure control valve can provide an adjustable-size constriction in a second portion of the natural gas flowing through the second flowline such that the second portion of the natural gas adiabatically expands as it crosses the pressure control valve. A first outlet pressure of a first portion of the natural gas discharged from the once-through generator can be substantially equal to a second outlet pressure of a second portion of the natural gas discharged from the pressure control valve. A heater can be coupled to the inlet flow line. The heater can heat the natural gas upstream of the first flow line and the second flow line. The size of the constriction provided by the pressure control valve can be adjusted so that the first outlet pressure of the first portion of the natural gas discharged from the once-through generator is maintained substantially equal to the second outlet pressure of the second portion of the natural gas discharged from the pressure control valve, and adjusting the size of the constriction can adjust the torque applied to the once-through generator. The once-through generator can include a hermetically sealed housing that houses a turbine wheel therein. The rotor and stator can be hermetically sealed and positioned in-line within the first flow line such that the first portion of the natural gas flows across the turbine wheel and the stator. The rotor can include a permanent magnet rotor. The hydrogen stream may be mixed with at least one of a first portion of the natural gas downstream of the once-through generator and a second portion of the natural gas downstream of the pressure control valve.

[0009] Certain aspects of the presently disclosed subject matter can be implemented as a system. The system includes a natural gas pipeline, a once-through generator, a pressure control valve, and an electrolysis cell. The natural gas pipeline carries natural gas. The natural gas pipeline includes an inlet flowline, a first flowline, a second flowline, and an outlet flowline. The inlet flowline is in fluid communication with a gas wellhead to receive natural gas produced from the gas well. The first flowline is coupled to the inlet flowline to receive at least a first portion of the natural gas from the inlet flowline. The second flowline is coupled to the inlet flowline to receive at least a second portion of the natural gas from the inlet flowline and provide an alternative flow path for the natural gas bypassing the first flowline. The outlet flowline is coupled to the first and second flowlines to recombine the first and second portions of the natural gas from the first and second flowlines, respectively. A once-through generator is coupled to the first flowline. The once-through generator includes a turbine wheel, a rotor, and a stator. The turbine wheel is configured to receive a first portion of the natural gas from the first flow line and rotate in response to expansion of the natural gas entering the turbine wheel inlet and exiting the turbine wheel outlet. A rotor is coupled to the turbine wheel. The rotor is configured to rotate with the turbine wheel. A once-through generator is configured to generate power by rotating the rotor within the stator. A pressure control valve is coupled to the second flow line. The pressure control valve is configured to provide an adjustable-size constriction in a second portion of the natural gas flowing through the second flow line such that the second portion of the natural gas adiabatically expands as it crosses the pressure control valve. A first outlet pressure of the first portion of the natural gas discharged from the once-through generator is substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve. An electrolytic cell is electrically connected to the power output of the once-through generator. The electrolytic cell is configured to receive the water flow and the power from the once-through generator.The electrolysis cell is configured to use the received electrical power to perform electrolysis on a water stream to produce a hydrogen stream and an oxygen stream.

[0010] This and other aspects may include one or more of the following features. The system may include a heater. The heater may be coupled to the inlet flowline. The heater may be configured to heat the natural gas upstream of the first flowline and the second flowline. The system may include a controller. The controller may be communicatively coupled to the pressure control valve and the once-through generator. The controller is configured to adjust a size of a restriction provided by the pressure control valve such that a first outlet pressure of a first portion of the natural gas discharged from the once-through generator is maintained substantially equal to a second outlet pressure of a second portion of the natural gas discharged from the pressure control valve, the adjustment of the size of the restriction adjusting a torque applied to the once-through generator. The system may include a hydrogen flowline. The hydrogen flowline may couple the electrolytic cell to the outlet flowline and may provide a flow of hydrogen to the outlet flowline for combination with the natural gas flowing through the outlet flowline.

[0011] The details of one or more embodiments of the presently disclosed subject matter are set forth in the accompanying drawings and description. Other features, aspects, and advantages of the present subject matter will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a power generation system including a turboexpander. [Figure 2] FIG. 1 is a schematic diagram illustrating an example of a turboexpander system including an electrolytic cell for producing hydrogen. [Figure 3] 1 is a flowchart illustrating an example of a method for producing hydrogen using electricity generated by a pressure drop in a gas. DETAILED DESCRIPTION OF THE INVENTION

[0013] Natural gas, hydrogen, and other process gases are pressurized to facilitate efficient transportation in pipelines. To safely deliver the gas through local distribution networks, the process gas is reduced to a lower level (often using a pressure regulator). The pressure is reduced at pressure letdown (PLD) stations for delivery to industrial, commercial, and residential end users. PLD stations use regulating valves to achieve the required pressure drop, but waste a significant amount of energy in the process. A turboexpander generator can be installed in parallel with the regulating valve to recover the energy lost through the pressure drop and generate electricity. The electricity can be used, for example, to produce hydrogen through water electrolysis. By recovering the energy lost from natural gas pressure drop applications, turboexpanders can generate electricity while reducing CO2 emissions, improving overall plant efficiency, offsetting electrical costs, and generating additional revenue.

[0014] FIG. 1 is a schematic diagram of a power generation system 100. The power generation system 100 can be added to a PLD station to capture energy from the expansion of gas from the PLD process. The power generation system 100 includes a turboexpander 102 arranged in parallel with a pressure control valve 130. The turboexpander 102 is axially arranged, allowing the turboexpander 102 to be installed in-line with a pipe. The turboexpander 102 functions as a generator by generating electrical energy from the rotational kinetic energy obtained by the expansion of process gas 120 (e.g., natural gas flowing through a natural gas pipeline) via a turbine wheel 104. For example, rotation of the turbine wheel 104 can be used to rotate a rotor 108 inside a stator 110, which in turn generates electrical power.

[0015] The turboexpander 102 includes a high-performance, high-speed permanent magnet generator with an integrated radial-flow expansion turbine wheel 104 and low-loss active magnetic bearings (AMBs) 116a,b. The rotor assembly consists of a turbine wheel 104 with permanent magnets mounted directly to the rotor hub. The rotor 108 is held levitated by the magnetic bearing system, providing a frictionless (or nearly frictionless) interface between the dynamic and static components. The AMBs 116a,b enable lossless (or nearly lossless) rotation of the rotor 108.

[0016] The turboexpander 102 is designed to allow the process gas 120 to flow through the system 100, thereby cooling the generator and eliminating the need for auxiliary cooling equipment. The power electronics 118 for the turboexpander 102, in some embodiments, house a power converter 206 and a magnetic bearing controller (MBC) 212 together in a single cabinet. The power converter 206 facilitates a stable supply of electrical power generated by the turboexpander 102. For example, the power converter 206 adjusts the frequency and voltage of the electrical current generated to match the local electrical grid. As another example, the power converter 206 adjusts the frequency and voltage of the electrical current generated to match usage by electrical power-using equipment, such as an electrolysis unit. After expansion, the process gas 120 exits the turboexpander 102 along the same axial path to downstream processes.

[0017] The turboexpander 102 includes a flow-through configuration that allows process gas 120 to flow from the inlet side of the turboexpander 102 to the outlet side of the turboexpander 102. The process gas 120 enters the turbine wheel 104 through a radial gas inlet 154 and exits the turbine wheel 104 through an axial gas outlet 156. The process gas 120 then passes through a generator and exits through the outlet 154 to rejoin the gas pipeline 170. Generally, the high-pressure process gas 120 is directed into the turboexpander 102 through a flow control system 126. The flow control system 126 includes flow or mass control valves and emergency shut-off valves. The flow control system 126 may be controlled by the power electronics 118 or other electrical, mechanical, or electromagnetic signals. For example, a fault condition can instruct the flow control system 126 to close or partially close, thereby cutting off or restricting the supply of gas to the turboexpander 102. When the rotor 108 is operating at a constant speed, restricting or blocking the flow of gas to the turboexpander 102 reduces the torque acting on the rotor 108, which in turn reduces the amount of current generated by the power converter 206. In the example shown in Figure 1, a signal channel 164 from the power electronics 118 can be used to open or close the flow control system 126. In some implementations, the turboexpander housing 112 is hermetically sealed.

[0018] The process gas 120 expands as it flows across the turbine wheel 104, causing a pressure drop in the process gas 120. The process gas 120 exits the turboexpander 102 at a reduced pressure. The expansion of the process gas 120 as it passes through the turbine wheel 104 causes it to rotate, which in turn rotates the rotor 108. The rotation of the rotor 108 within the stator 110 generates power. The turboexpander 102 achieves the desired pressure drop and captures the energy from the pressure drop to generate power. A pressure control valve 130, such as a conventional pressure regulator, can be installed in parallel with the turboexpander 102. Any excess high-pressure process gas 120 not directed into the turboexpander 102 can be directed through the pressure control valve 130. For example, the pressure control valve 130 is configured to provide a constriction of adjustable size so that a portion of the process gas 120 flowing through the pressure control valve 130 can expand adiabatically across the pressure control valve 130. The pressure of the portion of the process gas 120 exiting the pressure control valve 130 is equal to the pressure of the portion of the process gas 120 exiting the turboexpander 102. In this manner, the pressure control valve 130 and the flow control system 126 can cooperate to control the pressure of the process gas 120 flowing through the turboexpander, which in turn can control the amount of electrical current generated by the power converter 206.

[0019] In some embodiments, the heater 122 can heat the process gas 120 before it flows into the turboexpander 102. For example, if the process gas 120 expands through the turbine wheel 104, thereby lowering the temperature of the gas and causing moisture in the process gas 120 to freeze on the turbine wheel 104 or at another downstream location, the heater 122 can heat the process gas 120 before it enters the turboexpander 102. After heating, the process gas 120 can then be introduced into the turboexpander 102. Heating the process gas 120 can prevent moisture from freezing as the process gas 120 expands and its temperature drops.

[0020] The turboexpander 102 includes a turbine wheel 104. While the turbine wheel 104 is shown as a radial-flow turbine wheel, other configurations, such as an axial-flow turbine wheel, are within the scope of this disclosure. In this example, process gas 120 is supplied through an inlet conduit 150 in the housing 112 and enters a radially oriented inlet 154 of the turbine wheel 104. In some embodiments, the process gas 120 flows through the inlet conduit 150 and is directed by a flow diverter to the radial inlet 154, which directs the fluid to the radial inlet of the turbine wheel 104. After expansion, the process gas 120 exits the turbine wheel 104 through an axially oriented outlet 156 and is discharged into an outlet conduit 152 in the housing 112.

[0021] The turbine wheel 104 may be directly secured to the rotor 108 or an intermediate common shaft, for example, by fasteners, a rigid drive shaft, welding, or other methods. For example, the turbine wheel 104 may be received on an end of the rotor 108 and held to the rotor 108 by a shaft. The shaft threads into the rotor 108 at one end and holds the turbine wheel 104 at the other end between the end of the rotor 108 and a nut threadedly received on the shaft. The turbine wheel 104 and rotor 108 may be coupled without a gearbox and rotate at the same speed. In other examples, the turbine wheel 104 may be indirectly coupled to the rotor 108, for example, by a gear train, a clutch mechanism, or other methods.

[0022] The turbine wheel 104 includes a plurality of turbine wheel blades 106 extending outward from a hub that interact with the expanding process gases 120 to rotate the turbine wheel 104. An unshrouded turbine wheel 104 is shown in FIG. 1 , in which each turbine blade 106 has a generally radially exposed blade tip that extends between a radial inlet 154 and an axial outlet 156. As described in more detail below, the blade tip substantially seals against a shroud 114 disposed inside a housing 112. In a particular example, the turbine wheel 104 is a shrouded turbine wheel.

[0023] In a configuration with an unshrouded turbine wheel 104, the housing 112 includes an inwardly disposed shroud 114 that is in close proximity to the turbine wheel blades 106 and does not contact the blades most of the time during operation. The close proximity between the turbine wheel blades 106 and the shroud 114 substantially seals the passage of the process gas 120 between the turbine wheel blades 106 and the shroud 114 as the process gas 120 flows through the turbine wheel 104. While some amount of the process gas 120 may leak or pass between the turbine wheel blades 106 and the shroud 114, this leakage amount is negligible in the operation of the turbine wheel 104. In certain cases, the leakage amount may be comparable to the leakage amount at the interface of a similar unshrouded turbine with a shroud surface when using conventional tolerances between the turbine wheel blades 106 and the shroud 114. The amount of leakage that is considered acceptable may be predetermined. The operating parameters of the turbine generator may be optimized to reduce leakage. In some embodiments, the housing 112 is hermetically sealed to prevent the process gas 120 from escaping through the radial inlet 154 of the turbine wheel 104.

[0024] The shroud 114 may be positioned a specific distance from the turbine wheel blades 106 and is maintained spaced apart from the turbine wheel blades 106 during operation of the turboexpander 102 by using a magnetic positioning device including active magnetic bearings and position sensors.

[0025] The bearings 116a and 116b are positioned to rotatably support the rotor 108 and turbine wheel 104 relative to the stator 110 and shroud 114. The turbine wheel 104 is supported in a cantilevered manner by the bearings 116a, 116b. In some embodiments, the turbine wheel 104 may be supported in a non-cantilevered manner, and the bearings 116a and 116b may be positioned on the outlet side of the turbine wheel 104. In certain examples, one or more of the bearings 116a or 116b may include a ball bearing, a needle bearing, a magnetic bearing, a foil bearing, a journal bearing, or the like.

[0026] Bearings 116a and 116b may be a combination radial and thrust bearing that provides radial and axial support for rotor 108. Other configurations may also be utilized. Bearings 116a, 116b do not have to be the same type of bearing.

[0027] In embodiments in which the bearings 116a and 116b are magnetic bearings, a magnetic bearing controller (MBC) 212 is used to control the magnetic bearings 116a and 116b. Position sensors 117a, 117b may be used to detect the position or change in position of the turbine wheel 104 and / or rotor 108 relative to the housing 112 or other reference point (e.g., a predetermined value). The position sensors 117a, 117b may detect axial and / or radial displacement. The magnetic bearings 116a and / or 116b may respond to information from the position sensors 117a, 117b and adjust the detected displacement as needed. The MBC 212 may receive information from the position sensors 117a, 117b, process the information, and provide control signals to the magnetic bearings 116a, 116b. The MBC 212 may communicate with various components of the turboexpander 102 via a communication channel 162.

[0028] The turboexpander 102 may be operated without the need for seals (e.g., without the need for dynamic seals) by using the magnetic bearings 116a, 116b and position sensors 117a, 117b to maintain and / or adjust the position of the turbine wheel blades 106 so that they remain in close proximity to the shroud 114. The use of active magnetic bearings 116a,b in the turboexpander 102 eliminates physical contact between rotating and stationary components, and also eliminates the need for lubrication, lubrication systems, and seals.

[0029] The turboexpander 102 may include one or more backup bearings. For example, backup bearings may be used to rotatably support the turbine wheel 104 during start-up and shutdown, or in the event of a power outage that affects the operation of the magnetic bearings 116a and 116b. Backup bearings may include ball bearings, needle bearings, journal bearings, etc.

[0030] As described above, the turboexpander 102 is configured to generate electrical power in response to the rotation of the rotor 108. In certain examples, the rotor 108 may include one or more permanent magnets. The stator 110 includes a plurality of conductive coils. Electrical power is generated by the rotation of the magnets within the coils of the stator 110. The rotor 108 and the stator 110 may be configured as a synchronous permanent magnet multi-phase alternating current (AC) generator. The electrical output 160 may be, for example, a three-phase output. In certain examples, the stator 110 may include a plurality of coils (e.g., three or six coils for a three-phase AC output). As the rotor 108 rotates, a voltage is induced in the stator 110. At any instant in time, the magnitude of the voltage induced in the stator coil is proportional to the rate at which the magnetic field surrounded by the coil changes with time (i.e., the rate at which the magnetic field passes two sides of the coil). When the rotor 108 is coupled to rotate at the same speed as the turbine wheel 104, the turboexpander 102 is configured to generate electrical power at that speed. Such turboexpanders 102 are so-called "high speed" turbine generators. For example, the turboexpanders 102 can generate up to 280 kW of power at a continuous speed of 30,000 rpm. In some implementations, the turboexpanders generate approximately 350 kW of power at higher rotational speeds (e.g., around 35,000 rpm).

[0031] In some embodiments, the design of the turbine wheel 104, rotor 108, and / or stator 110 may be based on desired parameters of the output gas from the turboexpander 102. For example, the design of the rotor and stator may be based on the desired temperature of the process gas 120 exiting the turboexpander 102.

[0032] The turboexpander 102 may be coupled to power electronics 118. The power electronics 118 may include a power converter 206 and a magnetic bearing controller (MBC) 212 (described above). The power converter 206 may be, for example, a variable speed drive (VSD) or a variable frequency drive.

[0033] The electrical output 160 of the turboexpander 102 is connected to a power converter 206 that can be programmed to specific power requirements. The power converter 206 can include an insulated gate bipolar transistor (IGBT) rectifier 208 to convert the variable frequency, high voltage output from the turboexpander 102 to direct current (DC). The rectifier 208 can be a three-phase rectifier for a three-phase AC input current. An inverter 210 then converts the DC from the rectifier 208 to AC for supply to the power grid 140. The inverter 210 can convert the DC to 380V-480V AC (50Hz-60Hz) for supply to the power grid 140. The specific output of the power converter 206 depends on the power grid 140 and the application. Other conversion values ​​are within the scope of this disclosure. The power converter 206 matches its output to the power grid 140 by sampling the grid voltage and frequency and then varying the output voltage and frequency of the inverter 210 to match the sampled grid voltage and frequency.

[0034] In some embodiments, power converter 206 is a bidirectional power converter. In such embodiments, rectifier 208 can receive alternating current from power grid 140 and convert the alternating current to direct current. Inverter 210 can then convert the direct current from rectifier 208 to alternating current and provide it to a generator. In such embodiments, power is provided from power grid 140 to the generator, which can drive rotation of rotor 108 and, therefore, turbine wheel 104, to induce a flow of process gas. In short, in embodiments where power converter 206 is a bidirectional power converter, the flow of power can be reversed and used to induce a flow of process gas by the generator (as opposed to the process gas providing expansion work to generate power).

[0035] The turboexpander 102 is also connected to the MBC 212 within the power electronics 118. The MBC 212 constantly monitors position, current, temperature, and other parameters to ensure that the turboexpander 102 and the active magnetic bearings 116a and 116b are operating as desired. For example, the MBC 212 is coupled to position sensors 117a and 117b to monitor the radial and axial positions of the turbine wheel 104 and rotor 108. The MBC 212 can control the magnetic bearings 116a and 116b to selectively vary the stiffness and damping characteristics of the magnetic bearings 116a and 116b as a function of rotational speed. The MBC 212 can also perform synchronous cancellation control, including automatic balancing control, adaptive vibration control, adaptive vibration cancellation, and unbalance force cancellation control.

[0036] 2 is a schematic diagram illustrating an example of an illustrative turboexpander system 200 including an electrolysis cell 260 for producing hydrogen. The turboexpander system 200 is for recovering energy by reducing the pressure of fluid produced from a well 204 and includes the turboexpander 102 and power electronics 118 of system 100 (described above and shown in FIG. 1 ), as well as associated flowlines and other equipment. In certain examples, the system 200 is located at a production site 213 and is located proximate to a wellhead 202. In certain examples, the system 200 is located on or off the production site 213, upstream of a production pipeline 220. In one example of an onshore well 204, both the production site 213 and the system 200 are located at the same equipment site as another nearby well 204, located upstream of the production pipeline 220. In another example, multiple onshore wells 204 are at the same production site 213 and feed the same pipeline 220, with system 200 coupled to one or more of the wells 204 and located at the site 213. In one example of a subsea well 204, the production site 213 is a surface platform and system 200 is also located on the platform. The platform may be a production platform corresponding to the well 204 (i.e., a subsea well) or may be a production platform associated with multiple subsea wells 204 (e.g., when multiple wells 204 are manifolded to supply fluids to a single production platform). In certain examples, system 200 may be located on a dedicated platform separate from any production platform and coupled to one or more other production platforms via flowlines. In certain examples, system 200 is located at a gas processing facility (e.g., a natural gas processing facility). When system 200 is not located at a production site 213, turboexpander 102 and electrolytic cell 250 are located at the same physical site. In some embodiments, the turboexpander 102 and the electrolytic cell 250 are located within 10 meters, within 50 meters, within 100 meters, or within 500 meters of each other.

[0037] In some cases, the power generation system 250 is the same as the power generation system 100. Referring to FIGS. 1 and 2 , the system 250 includes, among other things, the turboexpander 102 described above disposed within the hermetic housing 112 of the system 100. An electrical output from a generator of the turboexpander 102 is coupled to the power electronics 118, which in turn includes a VSD 206 with a brake resistor assembly 203. If included, the brake resistor assembly 203 is electrically connected to the electrical output of the turboexpander 102 (e.g., the output of the generator via the VSD 206). The brake resistor assembly 203 may have a tuned impedance to enable efficient transfer of power from the turboexpander 102 to the brake resistor assembly 203. In some embodiments, if a fault condition occurs in the VSD 206, a contactor may connect the output current of the turboexpander 102 to the brake resistor assembly 203. The contactor is an electrically controlled switch that performs switching in a power circuit. The contactor can receive the three-phase current output from the generator and direct the current to the brake resistor assembly 203. In some embodiments, the contactor is connected directly to the (three-phase) electrical output of the turboexpander 102. In some embodiments, the brake resistor assembly 203 and / or the contactor are not part of the power electronics but are connected to the electrical output of the turboexpander 102 external to the power electronics 118. The VSD 206 can provide an energization signal to the contactor coil, causing the contactor to connect the electrical output of the turboexpander to the brake resistor assembly 203. Depending on the implementation, the contactor can be a normally closed (NC) contactor or a normally open (NO) contactor.

[0038] The turboexpander 102 can be configured to respond to the conditions of the gas produced by the well 204, such as to handle certain amounts of liquids in the gas, particulates in the gas, and to be resistant to corrosive components in the gas (e.g., hydrogen sulfide). In certain examples, the VSD 206 can be coupled to a cooling system 252 to cool the electronics of the VSD 206 and maintain a temperature below a specified operating temperature. The output of the VSD 206 can be electrically coupled to a load, such as, for example, a power grid to provide power to the grid, a microgrid at the production site 213 to power equipment used to generate or process the gas at the production site 213, and / or directly connected to one or more pieces of equipment used to produce or process the gas at the production site 213 to power the equipment, as described above. In certain cases, the equipment includes flow, pressure, temperature, and level sensors for various equipment, valve actuators, communication equipment to enable remote communication with the sensors, other equipment, and controls for the valve actuators, separators (e.g., sand separators, liquid separators), heater treatment equipment, site lighting, control trailers, and / or other types of equipment. In some cases, the power generated by power generation system 250 may be used by other equipment at production site 213 that is not involved in the production or processing of gas from wells 204. For example, this power may be used to power electrolysis cell 260 in a process for producing hydrogen from water at production site 213.

[0039] System 200 includes a flowline 211 that carries production fluid (such as natural gas) from well 204. The well output, i.e., primarily gaseous natural gas (but often containing some oil, water, moisture, and particulates), exits wellhead 202 and flows through flowline 211. Flowline 211 includes flow conditioning equipment to condition the flow to selected specified conditions based on the specifications of downstream equipment in pipeline 220 and production site 213, as well as the characteristics of turboexpander 102 in power generation system 250. In FIG. 2, the conditioning equipment is shown as solid and liquid separator 207 and dryer 209, but the conditioning equipment can include additional, different, or fewer components and types of equipment. For example, the conditioning equipment can include separators, molecular dryers, knockout drums, two-phase coalescers, and / or other types of conditioning equipment. Returning to the specific example of FIG. 2 , the stream in flow line 211 enters separator 207 from wellhead 202 and passes through the separator. In separator 207, solids and liquids are separated from the gas stream. The stream then enters dryer 209 through flow line 211, where it is dried to reduce the moisture content of the stream to a specific level selected (in part or in whole) based on the specifications of turboexpander 102 of power generation system 250. From dryer 209, the stream flows through flow line 211 to pressure control valve 24. Pressure control valve 214 can be controlled to reduce the pressure of the gas stream to a specified pressure. Each of the valves herein, whether control valves, shut-off valves, or other valves, can be remotely controlled, for example, via an operator in a remote control panel located at production site 213 and / or elsewhere, and / or can be autonomously controlled by a control algorithm in a controller located at production site 213 and / or elsewhere.

[0040] Flow from pressure control valve 214 is split into a first downstream flow line 216 that includes a power generation system 250 that includes turboexpander 102, and a second downstream flow line 218 that bypasses turboexpander 102. First downstream flow line 216 and second downstream flow line 218 reunite upstream of production pipeline 220 before exiting production site 213. The inlet of airtight housing 112 is airtightly coupled in series with first flow line 216, such that all fluid in flow line 216 is directed into airtight housing 112, flows through housing 112, and returns to the remainder of first flow line 216.

[0041] The second flow line 218 includes a pressure control valve 222 (e.g., pressure control valve 130) configured based on a specific pressure drop versus operating position. The pressure control valve 222 can be controlled to regulate the pressure in the second flow line 218 downstream of the valve 222, and thus the pressure upstream of the pressure control valve 222 and the pressure in the first flow line 216 (as a function of the pressure of the flow from the wellbore). The first flow line 216 includes a flow control valve 224 (e.g., flow control valve 126) configured based on a specific flow rate versus operating position. The flow control valve 324 can be controlled in conjunction with the pressure control valves 214, 222 to control the flow rate of the fluid through the first flow line 216, which in turn controls the flow rate through the turboexpander 102.

[0042] This arrangement places the turboexpander 102 in parallel with the second flow line 218, providing flexibility in sizing the turboexpander 102 depending on the pressure and flow rate of the flow generated from the well 204 and the conditions of the pipeline 220, as described in more detail below. This flexibility comes, in part, from the fact that the second flow line 218 allows flow to selectively bypass the turboexpander 102 as it flows from the wellhead 202 to the production pipeline 220. In short, not all flow needs to pass through the turboexpander 102 as it flows from the wellhead 202 to the pipeline 220, and therefore the turboexpander 102 does not need to be sized to accommodate all flow. Additionally, the first flow line 216 includes an emergency shut-off valve 226 upstream of the turboexpander 102 to quickly shut off flow to the turboexpander 102 if necessary. When this valve is closed, all flow will flow through the second flow line 218. In particular, although not shown, inlet flow line 211, first flow line 216, and second flow line 218 may further comprise sensors for monitoring the pressure, temperature, flow rate, and / or other characteristics of the flow within each line and upstream and / or downstream of each component (e.g., valves, turboexpanders, and other components of the flow lines).

[0043] During operation, when well 204 begins new production, the fluid produced from well 204 is at or near its peak pressure and flow rate. Over time, the pressure and flow rate of the produced fluid decrease. Therefore, the pressure of the produced stream is regulated to a specified pressure by pressure control valve 214 in flow line 211. Pressure control valve 222 in second flow line 218 is then controlled to maintain pressure through first flow line 216 and turboexpander 102, so that, in conjunction with flow control valve 224, conditions through turboexpander 102 are maintained within the turboexpander's specified operating range. Excess flow exits second flow line 218 and is directed to pipeline 220. Flow through first flow line 216 flows through turboexpander 102 to generate power, then recombines with flow from second flow line 218 and enters pipeline 220.

[0044] The characteristics of the turboexpander 102 are selected based on several factors, including the expected pressure, temperature, and flow rate that the well 204 can sustain over time, the time frame during the life of the well 204 during which power generation by the turboexpander 102 is desired or required (e.g., whether power is needed early in the well's life, for as long as possible during the well's life, or only at the end of the well's life), the ambient conditions at the production site 213, the efficiency / performance of the solids and liquids separator 207 and dryer 209, the conditions, including pressure, temperature, and / or flow rate, specified for acceptance by the pipeline 220 (often specified by the pipeline operator), and the amount of power desired or required to be generated by the turboexpander 102 at the production site 213. The designated pressure to which pressure control valve 214 is controlled is then selected based on several factors, including the pressure, temperature, and flow characteristics of turboexpander 102, the amount of power desired or needed to be produced, and the designated pressure, temperature, and / or flow rate for acceptance by pipeline 220. For example, in certain instances, pipeline 220 is configured to operate at a designated pressure. Turboexpander 102, which creates a pressure drop as it extracts energy from the flow, is configured to operate in conjunction with pressure control valves 214, 222 to create an outlet pressure of turboexpander 102 equal to the designated pressure of pipeline 220. In certain instances, pipeline 220 has a particular minimum temperature (e.g., a temperature selected to prevent freezing of fluid within the pipeline). The turboexpander 102 induces a temperature drop as it extracts energy from the flow and is configured to cooperate with pressure control valves 214, 222 (which also induce a temperature drop) to maintain the outlet temperature of the turboexpander 102 and the inlet temperature of the pipeline 220 above a specified pressure and a specified minimum temperature. To provide a numerical example, in a particular example, the well pressure may initially be above 9000 PSIG (62.05 MPa), and the pressure control valve 214 is used to regulate the flow to 1600 PSIG (11.03 MPa).As the wellbore 204 ages and pressure drops, this regulated pressure of 1600 PSIG (11.03 MPa) may be maintained until the wellbore pressure drops below 1600 PSIG (11.03 MPa). While the wellbore pressure remains above 1600 PSIG (11.03 MPa), the turboexpander 102 can be optimized to operate at its highest efficiency under the pressure, temperature, and flow conditions of the wellbore 204 during this period, operating to generate power while simultaneously providing additional pressure drop downstream of the turboexpander 102 to the specified pressure in the pipeline 220 to maintain the specified pressure. The higher the wellbore temperature, the more energy the turboexpander 102 can extract. As the wellbore 204 pressure falls below 1600 PSIG (11.03 MPa), the efficiency of the turboexpander 102 decreases until the wellbore conditions no longer support the turboexpander 102's operation. Thereafter, first flow line 216 is shut off and flow is directed only through second flow line 218, resulting in no additional pressure drop through turboexpander 102. In a particular example, turboexpander 102 is configured to produce a usable amount of power until the upstream pressure approaches the pipeline's specified pressure, which is often 1000 PSIG (6.89 MPa).

[0045] As the natural gas flows through the turboexpander 102, it expands, rotating the turbine wheel 104. The rotation of the turbine wheel 104 rotates the rotor 108, which supports a number of permanent magnets. The rotation of the permanent magnets on the rotor 108 induces current through coils or windings on the stator 110, generating electrical power. An electrolytic cell 260 is electrically connected to the electrical output of the turboexpander 102. In some embodiments, as shown in FIG. 2 , the power electronics 118 is configured to steadily supply electrical power generated by the turboexpander 102 to the electrolytic cell 260. In some embodiments, the power electronics 118 is configured to steadily supply electrical power generated by the turboexpander 102 to an electrical grid, and the electrolytic cell 260 is electrically connected to the electrical grid and configured to receive electrical power from the electrical grid. In such an embodiment, even though the electrolytic cell 260 is not directly connected to the turboexpander 102, the electrolytic cell 260 can still be considered to be electrically connected (albeit indirectly) to the electrical output of the turboexpander 102, i.e., the power grid connects the electrolytic cell 260 to the electrical output of the turboexpander 102.

[0046] The electrolysis cell 260 includes an anode 262, a cathode 264, and a membrane 266. The membrane 266 can conduct protons from the anode 262 to the cathode 264 while electrically insulating the electrodes (262, 264). The electrolysis cell 260 can be, for example, a polymer electrolyte membrane (PEM) electrolysis cell, an alkaline water electrolysis cell, a solid oxide electrolysis cell, or an anion exchange membrane (AEM) electrolysis cell. The half-reaction occurring on the anode 262 side is also referred to as the oxygen evolution reaction (Equation 1). The half-reaction occurring on the cathode 264 side is also referred to as the hydrogen evolution reaction (Equation 2). 2H2O→O2+4H + +4e - (1) 4H + +4e - →2H2(2)

[0047] Water 268 is introduced into electrolysis cell 260. Electrolysis cell 260 splits water 268 into hydrogen and oxygen. The produced hydrogen and oxygen are separated from each other and exit electrolysis cell 260 as hydrogen stream 270 and oxygen stream 272, respectively. For example, membrane 266 can be permeable to hydrogen, such that hydrogen passes through membrane 266 and is separated from oxygen, while oxygen remains on the other side of membrane 266. Oxygen stream 272 exits electrolysis cell 260 from the anode 262 side, and hydrogen stream 270 exits electrolysis cell 260 from the cathode 264 side. Hydrogen stream 270 and / or oxygen stream 272 can be processed (e.g., compressed) for transportation. In some embodiments, at least a portion of hydrogen stream 270 is mixed with natural gas exiting turboexpander 102, natural gas exiting pressure control valve 222, or both.

[0048] 3 is a flowchart of an exemplary method 300 for producing hydrogen by supplying electrical power generated by the expansion of gas to an electrolytic cell. Method 300 may be performed, for example, by an embodiment of turboexpander system 200. In block 302, natural gas flows into a turbine wheel (e.g., turbine wheel 104) of a generator (e.g., turboexpander 102). In some embodiments, the natural gas is heated (e.g., by heater 122) before flowing into turbine wheel 104 of turboexpander 102 in block 302. In block 304, electrical power is generated by turboexpander 102 in response to the natural gas flowing across turbine wheel 104. In block 306, the electrical power (generated by turboexpander 102 in block 304) is supplied to an electrolytic cell (e.g., electrolytic cell 260). The power provided to the electrolysis cell 260 in block 306 may be provided through a power converter 206, which converts the power generated by the turboexpander 102 in block 304 so that it is suitable for use by the electrolysis cell 260. In block 308, the electrolysis cell 260 uses the power generated by the turboexpander 102 to perform electrolysis on a water stream (such as water 268) to produce a hydrogen stream (such as hydrogen stream 270) and an oxygen stream (such as oxygen stream 272).

[0049] As used in this disclosure, the term "substantially" refers to a majority or majority, such as at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

[0050] Accordingly, the specification and drawings should be regarded in an illustrative rather than a restrictive sense. Moreover, the foregoing use of the terms "embodiment" and "other exemplary" does not necessarily refer to the same embodiment or the same example, but can refer to different, distinct embodiments, as well as potentially the same embodiment. In the foregoing specification, a detailed description has been given with reference to certain exemplary embodiments. However, it will be apparent that various modifications and changes can be made without departing from the broader spirit and scope of the present disclosure as set forth in the claims.

Claims

1. A once-through type generator connected to a natural gas pipeline through which natural gas flows, a turbine wheel configured to receive the natural gas from the natural gas pipeline and to rotate in response to expansion of the natural gas flowing into an inlet of the turbine wheel and flowing out an outlet of the turbine wheel; a rotor coupled to said turbine wheel and configured to rotate with said turbine wheel; and - a stator, a once-through generator configured to generate electrical power by rotating the rotor inside the stator; an electrolysis cell electrically connected to the electrical power output of the once-through generator, the electrolysis cell configured to receive a water flow and the electrical power from the once-through generator, and configured to perform electrolysis on the water flow using the received electrical power to produce a hydrogen stream and an oxygen stream; Including, the system.

2. The natural gas pipeline includes: an inlet flowline in fluid communication with the gas well wellhead for receiving natural gas produced from the gas well; a first flowline coupled to the inlet flowline to receive at least a first portion of the natural gas from the inlet flowline, the once-through generator coupled to the first flowline. The system of claim 1 .

3. 3. The system of claim 2, wherein the natural gas pipeline includes a second flowline coupled to the inlet flowline to receive at least a second portion of the natural gas from the inlet flowline and to provide an alternate flow path for the natural gas that avoids the first flowline, the first and second flowlines joining downstream of the once-through generator to recombine the first and second portions of the natural gas from the first and second flowlines, respectively.

4. 4. The system of claim 3, further comprising a pressure control valve coupled to the second flow line, the pressure control valve configured to provide an adjustable-size constriction in the second portion of the natural gas flowing through the second flow line such that the second portion adiabatically expands as it traverses the pressure control valve, and wherein a first outlet pressure of the first portion of the natural gas discharged from the once-through generator is substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve.

5. 5. The system of claim 4, further comprising a heater coupled to the inlet flow line, the heater configured to heat the natural gas upstream of the first flow line and the second flow line.

6. 6. The system of claim 5, further comprising a controller communicatively coupled to the pressure control valve and the once-through generator, the controller configured to adjust a size of the restriction provided by the pressure control valve such that a first outlet pressure of the first portion of the natural gas discharged from the once-through generator is maintained substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve, and adjusting the size of the restriction adjusts a torque applied to the once-through generator.

7. 7. The system of claim 6, wherein the once-through generator comprises a hermetically sealed housing that houses the turbine wheel therein, the rotor and the stator being hermetically disposed in-line within the first flow line such that the first portion of the natural gas flows across the turbine wheel and the stator.

8. The system of claim 7 , wherein the rotor comprises a permanent magnet rotor.

9. flowing natural gas from a natural gas pipeline to a turbine wheel of a once-through generator; generating electrical power with the once-through generator in response to the natural gas flowing across the turbine wheel; supplying the electrical power generated by the once-through generator to an electrolysis cell; electrolyzing a water stream using the electrical power generated by the once-through generator in the electrolysis cell to produce a hydrogen stream and an oxygen stream; A method comprising:

10. The natural gas is produced from a gas well, and the method comprises: flowing the natural gas from the gas wellhead to an inlet flowline of the natural gas pipeline; flowing at least a first portion of the natural gas from the inlet flowline into a first flowline of the natural gas pipeline, the once-through generator coupled to the first flowline; 10. The method of claim 9, comprising:

11. flowing at least a second portion of the natural gas from the inlet flowline to a second flowline of the natural gas pipeline, the second flowline providing an alternate flow path for the natural gas that avoids the first flowline; recombining the first portion of the natural gas from the first flowline and the second portion of the natural gas from the second flowline downstream of the once-through generator; The method of claim 10, comprising:

12. 12. The method of claim 11, comprising providing a constriction of adjustable size in the second portion of the natural gas flowing through the second flow line with a pressure control valve coupled to the second flow line such that the second portion adiabatically expands as it traverses the pressure control valve, wherein a first outlet pressure of the first portion of the natural gas discharged from the once-through generator is substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve.

13. The method of claim 12 , comprising heating the natural gas upstream of the first flowline and the second flowline with a heater coupled to the inlet flowline.

14. 14. The method of claim 13, comprising adjusting a size of the restriction provided by the pressure control valve so that a first outlet pressure of the first portion of the natural gas discharged from the once-through generator is maintained substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve, and adjusting the torque applied to the once-through generator by adjusting the size of the restriction.

15. 15. The method of claim 14, wherein the once-through generator comprises a hermetically sealed housing that houses the turbine wheel therein, a rotor and a stator hermetically disposed in-line within the first flow line such that the first portion of the natural gas flows across the turbine wheel and the stator.

16. 16. The method of claim 15, comprising mixing the hydrogen stream with at least one of the first portion of the natural gas downstream of the once-through generator and the second portion of the natural gas downstream of the pressure control valve.

17. A natural gas pipeline for flowing natural gas, an inlet flowline in fluid communication with the wellhead of the gas well for receiving natural gas produced from said gas well; a first flowline coupled to the inlet flowline to receive at least a first portion of the natural gas from the inlet flowline; a second flow line coupled to the inlet flow line to receive at least a second portion of the natural gas from the inlet flow line and to provide an alternative flow path for the natural gas that avoids the first flow line; and a natural gas pipeline including an outlet flowline coupled to the first flowline and the second flowline, the outlet flowline recombining the first and second portions of the natural gas from the first and second flowlines, respectively; a once-through generator coupled to the first flow line, a turbine wheel configured to receive the first portion of the natural gas from the first flow line and to rotate in response to expansion of the natural gas entering an inlet of the turbine wheel and exiting an outlet of the turbine wheel; a rotor coupled to said turbine wheel and configured to rotate with said turbine wheel; and - a stator, a once-through generator configured to generate electrical power by rotating the rotor inside the stator; a pressure control valve coupled to the second flow line, the pressure control valve configured to provide an adjustable-size constriction in the second portion of the natural gas flowing through the second flow line such that the second portion expands adiabatically as it traverses the pressure control valve, wherein a first outlet pressure of the first portion of the natural gas discharged from the once-through generator is substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve; an electrolysis cell electrically connected to the electrical power output of the once-through generator, the electrolysis cell configured to receive a water flow and the electrical power from the once-through generator, and configured to perform electrolysis on the water flow using the received electrical power to produce a hydrogen stream and an oxygen stream; Including, the system.

18. 20. The system of claim 17, comprising a heater coupled to the inlet flow line, the heater configured to heat the natural gas upstream of the first flow line and the second flow line.

19. 20. The system of claim 18, further comprising a controller communicatively coupled to the pressure control valve and the once-through generator, the controller configured to adjust a size of the restriction provided by the pressure control valve such that a first outlet pressure of the first portion of the natural gas discharged from the once-through generator is maintained substantially equal to a second outlet pressure of the second portion of the natural gas discharged from the pressure control valve, and adjusting the size of the restriction adjusts the torque applied to the once-through generator.

20. 20. The system of claim 19, further comprising a hydrogen flow line coupling the electrolytic cell to the outlet flow line and flowing the hydrogen stream into the outlet flow line for combination with the natural gas flowing through the outlet flow line.

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