Cooling of gas recovered from wells

Abstract

Flow from the gas well is regulated upstream of the production pipeline. A flowline is configured to connect to the gas well to receive the gas and to connect to the production pipeline to direct the received gas downstream from the production site. The flowline is located at the production site and includes a power generation system having a turbine generator. The turbine generator's inlet nozzle and turbine wheel are configured to reduce the pressure and temperature of the received gas to conditions associated with the production pipeline.

Description

[Technical Field]

[0001] (Priority Claim) This application claims priority to U.S. Patent Application No. 18 / 172,794, filed February 22, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to conditioning gas for pipelines. [Background technology]

[0003] Natural gas is one of the primary energy sources for many of our daily needs and activities. Its abundance and relatively clean properties make it an attractive fossil fuel. Natural gas is typically produced from wells located in remote areas, far from national, regional, or municipal power grids and other readily available sources of electricity. In the case of offshore natural gas wells, the well product is piped to offshore platforms far from populated areas. Therefore, when electricity is required at a production site (including an offshore platform), it is typically generated on-site by combusting a portion of the produced gas. Summary of the Invention

[0004] In one aspect, a system for cooling a flow from a gas well upstream of a production pipeline includes an inlet flowline coupled to the gas well head to receive gas produced from the gas well. The flowline is coupled to the inlet flowline to receive the gas and to the production pipeline to direct the received gas downstream from the production site. The flowline is disposed at the production site and includes a power generation system. The power generation system includes a turbine wheel configured to receive the gas and rotate in response to expansion of the gas entering the turbine wheel inlet and exiting the turbine wheel outlet. A nozzle is configured to direct the gas to the turbine wheel inlet. An electric rotor is coupled to the turbine wheel and configured to rotate with the turbine wheel within a fixed electric stator. The electric rotor and the electric stator define a generator configured to generate an electric current as the electric rotor rotates within the electric stator. In one example, the turbine wheel is configured to reduce the temperature of the received gas at the inlet to the production pipeline to below a specified temperature associated with the production pipeline. Also, in some instances, the turbine wheel may be configured to have an isentropic efficiency of 80% or less at the conditions of the received gas.

[0005] In one aspect, a method for conditioning a flow from a gas well for a production pipeline includes receiving the flow from the gas well in a flowline. The flowline includes a power generation system disposed at a production site of the gas well. The flowline includes a turbine wheel configured to receive the gas and rotate in response to expansion of the gas entering an inlet of the turbine wheel and exiting an outlet of the turbine wheel. The flowline also includes a nozzle configured to direct the gas to the inlet of the turbine wheel. An electric rotor is coupled to the turbine wheel and configured to rotate with the turbine wheel within a fixed electric stator. The electric rotor and the electric stator define a generator configured to generate an electric current as the electric rotor rotates within the electric stator. In one example, a portion of the flow from the gas well is channeled through the flowline and the power generation system, and the turbine is used to reduce the temperature of the gas at an inlet to the production pipeline to below a specified temperature associated with the production pipeline. Also in one example, a portion of the flow from the gas well is channeled through the flowline and the power generation system, and the turbine operates at an isentropic efficiency of 80% or less.

[0006] In one aspect, the system includes a flow path from the well to a production pipeline, the flow path including a nozzle and a turbine wheel coupled to a generator located at the production site of the well. The nozzle and the turbine wheel are configured to reduce the temperature of gas received through the flow path to below a specified temperature associated with the pipeline. In one example, the nozzle and the turbine wheel are configured to reduce the temperature of gas received through the flow path to no lower than a specified minimum temperature associated with the production pipeline and to operate at an isentropic efficiency of 80% or less.

[0007] The above aspects may include some, all, or none of the following features.

[0008] In one example, the turbine wheel is configured to have an isentropic efficiency of 80% or less when both of the following conditions are met: (i) At the entrance to the production pipeline, the pressure of the received gas is reduced to at least the specified maximum pressure associated with the pipeline; and (ii) At the entrance to the production pipeline, reduce the temperature of the received gas so as not to fall below the specified minimum temperature relevant to the pipeline.

[0009] The isentropic efficiency of the turbine wheel may be selected based on the conditions of the received gas, the specified maximum pressure, and the specified minimum temperature.

[0010] The turbine wheel may be configured to reduce the temperature of the received gas from above a specified maximum temperature associated with the pipeline to below the specified maximum temperature.

[0011] The nozzle and turbine wheel may be configured to reduce the temperature of the received gas at the inlet of the pipeline to a temperature no lower than that at which hydrates form in the gas.

[0012] In one example, the nozzle and turbine wheel are configured to reduce the temperature of the received gas to 38°C or less.

[0013] The flow path between the turbine wheel and the production pipeline may be provided without a heater.

[0014] The nozzle and turbine wheel characteristics may be selected based on a specified minimum temperature for the pipeline and configured to maintain temperatures above the specified minimum temperature over the operating life of the well.

[0015] The hermetically sealed housing may be configured to house the turbine wheel, the electrical rotor, and the electrical stator, and to be hermetically sealed and positioned in-line within the first-mentioned flow line, such that received flow passes through the turbine and over the electrical stator.

[0016] A flow control valve may be provided in the flow line upstream of the power generation system.

[0017] In some examples, a second flowline is coupled to the inlet flowline to receive the gas and provide an alternate flow path for the gas around the first-referenced flowline. The second flowline includes a pressure control valve, and the first-referenced flowline and the second flowline are coupled downstream of the power generation system to recombine the flow from the first-referenced flowline and the second flowline. In some examples, a nozzle and turbine wheel may be configured to cooperate with the pressure control valve in the second flowline to maintain a temperature of the received gas at the inlet to the production pipeline above a specified minimum temperature associated with the production pipeline while the well is producing gas at a pressure higher than the specified maximum pressure associated with the production pipeline. The nozzle and turbine wheel may also be configured to cooperate with the pressure control valve in the second flowline to maintain a pressure of the received gas at the inlet to the production pipeline below a specified maximum pressure associated with the production pipeline. In one example, the nozzle and turbine wheel characteristics may be selected to maximize the amount of power generated by the power generation system and, in cooperation with a pressure control valve in the second flow line, to maintain the temperature of the received gas at the inlet to the production pipeline above a specified minimum temperature associated with the production pipeline while the well is producing gas at a pressure above the specified maximum pressure associated with the production pipeline.

[0018] The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a power generation system according to the concepts disclosed herein. [Figure 2]FIG. 2 is a schematic diagram of an exemplary turboexpander system according to the concepts disclosed herein. [Figure 3] FIG. 3 is a schematic diagram of an exemplary energy recovery system including a power generation system according to the concepts disclosed herein. [Figure 4] FIG. 4 is a schematic diagram of another exemplary energy recovery system including two power generation systems according to the concepts disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0020] Like reference symbols in the various drawings indicate like elements. The drawings are not to scale.

[0021] Natural gas wells produce gas at high pressures and temperatures. Pressures can reach 9,000 PSIG (62.05 MPa) and even 15,000 PSIG (103.42 MPa). Temperatures can exceed 100°F (38°C) and even reach temperatures as high as 150°F (66°C) and higher. The pressure of the produced natural gas must be reduced before pre-processing to separate particulates and moisture from the gas, and also for transportation via pipelines. Similarly, the temperature of the gas must be reduced to the operating temperature of the pipeline. For example, pipelines transport gas from production sites (e.g., well sites) to processing facilities, and from processing facilities to regional distribution networks, such as regional, city, or district networks, or on-site industrial plant networks.

[0022] Processes at production sites and intermediate pressure reducing stations use pressure control valves (i.e., choke valves or throttle valves) to achieve the required pressure letdown. However, a significant amount of head pressure energy is lost in such processes. Additional pressure control valves may be used at other locations for pressure control in subprocesses within the processing facility, as well as in end-user processes and piping. Chillers, usually multiple chillers, are often used upstream in the pipeline (e.g., at the production site) to reduce the temperature of the produced gas to the pipeline's operating temperature. Common chillers include vapor compression cycle chillers and absorption chillers. In either case, the chillers consume electricity and are often powered by a portion of the produced natural gas.

[0023] Energy recovery systems according to the concepts disclosed herein can be used in place of or in combination with one or more of the pressure control valves described above to control the pressure of gas supplied to a pipeline to the pipeline's operating pressure and reduce the temperature of the gas to the pipeline's operating temperature. Such energy recovery systems can be used to cool the gas, thereby eliminating or reducing the number of chillers (and the associated power consumption) required to cool the gas for the pipeline. Energy recovery systems can be located at production sites and / or other locations (e.g., intermediate pressure reducing stations and other locations where pressure control valves are used). The systems include turboexpanders (including generators), which can be installed inline in the flow line from the wellhead, often in parallel with a bypass flow line that includes a pressure control valve. The turboexpanders recover energy lost due to pressure and temperature reduction to generate electricity, which can then be sent to the power grid or elsewhere. For example, some or all of this electricity can be used at the production site (onshore or offshore) to meet or supplement on-site power needs, such as to power equipment at the production site. Some production sites, particularly offshore platforms, have no other source of electricity other than electricity generated on-site (e.g., by using the produced gas as fuel to run natural gas generators or diesel-fueled generators). Thus, energy recovery systems can provide power to production sites and other remote locations without burning the produced gas and generating the associated emissions. In either case, by recovering energy that would otherwise be lost from the produced natural gas, energy recovery systems can generate electricity while simultaneously reducing CO2 emissions, improving overall plant efficiency, offsetting electricity costs, and generating additional revenue.

[0024] FIG. 1 is a schematic diagram of a power generation system 100 according to an embodiment of the present disclosure, where the power generation system 100 is coupled to a power grid 140. As described in more detail below, the power grid 140 may be a municipal power grid, a microgrid, or the system 100 may be directly coupled to one or more devices powered by the output of the system 100. The power generation system 100 includes a turboexpander 102 and a pressure control valve 130 in parallel. The turboexpander 102 is axially arranged so that it can be mounted in-line within a pipe. The turboexpander 102 functions as a generator by converting kinetic energy from gas expansion into rotational energy via a turbine wheel 104 to generate electrical energy. For example, rotation of the turbine wheel 104 can be used to rotate a rotor 108 within a stator 110, thereby generating electrical energy.

[0025] 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, 116b. The rotor assembly consists of a turbine wheel 104 with permanent magnets mounted directly to a rotor hub. The rotor 108 is suspended by the magnetic bearing system, providing a frictionless (or nearly frictionless) interface between the dynamic and static components. The AMBs 116a, 116b enable lossless (or nearly lossless) rotation of the rotor 108.

[0026] 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, 116b. The rotor assembly includes a turbine wheel 104 with permanent magnets mounted directly to the rotor hub of a rotor 108. The rotor 108 is levitated by the magnetic bearing system, which provides a frictionless (or nearly frictionless) interface between dynamic and static components, for example, at the longitudinal (e.g., axial) ends of the rotor 108. The AMBs 116a, 116b enable lossless (or nearly lossless) rotation of the rotor 108.

[0027] The turboexpander 102 is designed to allow process gas to flow through the system, thereby cooling the generator section and eliminating the need for auxiliary cooling equipment. The power electronics 118 for the turboexpander 102, in some implementations, combine a variable speed drive (VSD) 206 and a magnetic bearing controller (MBC) 212 into a single cabinet. The VSD enables the turboexpander 102 to provide a steady, clean supply of generated power to the power grid 140. For example, the VSD 206 adjusts the frequency and / or amplitude of the generated current to meet the power requirements of the power grid and / or its loads. After expansion, the gas exits the turboexpander 102 along the same axial flow path for downstream processing.

[0028] The turboexpander 102 includes a flow-through configuration. This flow-through configuration allows process gas to flow from an inlet side of the turboexpander 102 to an outlet side of the turboexpander 102, with the inlet and outlet being centered on the same axis. Internally, gas enters a turbine wheel 104 through a gas inlet nozzle 154 and exits the turbine wheel 104 through an axial gas outlet 156. The gas then passes through a generator and exits through an outlet 152 before rejoining the gas pipeline 170. Generally, high-pressure process gas 120 (e.g., gas from a natural gas well) is directed into the turboexpander 102 through a flow control system 126. The flow control system 126 includes flow control or mass control valves and emergency shut-off valves. In some embodiments, the turboexpander housing 112 is hermetically sealed.

[0029] High-pressure process gas 120 expands by flowing through the turbine wheel 104, resulting in a pressure drop of the process gas. Low-pressure process gas 128 is discharged from the turboexpander 102. The expansion of the high-pressure process gas 120 as it passes through the turbine wheel 104 causes the turbine wheel 104 to rotate, which in turn rotates the rotor 108. The rotation of the rotor 108 within the stator 110 generates electrical energy. The turboexpander 102 achieves the desired pressure drop and harvests energy from the pressure drop to generate electrical power. A pressure control valve 130 (such as a conventional choke valve) may be installed in parallel with the turboexpander 102. The pressure control valve 130 may be used to control the pressure of the high-pressure process gas 120 flowing in parallel with the turboexpander 102. Excess high-pressure process gas not directed to the turboexpander may be directed through the pressure control valve 130.

[0030] The gas is cooled as it expands through the turbine wheel 104. The gas then flows through the electrical components of the turboexpander 102, cooling the generator components (e.g., the rotor 108, the stator 110, and other components). Cooling the generator components also provides heat to the gas stream exiting the turboexpander 102. In some embodiments, a heater 122 can heat the high-pressure process gas 120 before it enters the turboexpander 102. For example, if the expansion of the gas through the turbine wheel 104 reduces the temperature of the process gas to a point where moisture in the gas freezes and / or process gas components condense at or downstream from the turbine wheel or at other downstream locations in the pipeline, the pressurized process gas 120 can be heated by the heater 122 before it flows through the turboexpander 102. The heated high-pressure process gas 124 can then be directed into the turboexpander 102. Heating the process gas helps prevent freezing of moisture or condensation of components as the gas expands and its temperature drops.

[0031] The turboexpander 102 includes a fixed aerodynamic stator. The aerodynamic stator is shown as a fixed component defining a nozzle 154. While shown as converging radially at the inlet of the turbine wheel 104, other configurations, such as nozzles converging into a slanted or curved shape, are within the scope of this disclosure. The nozzle 154 increases the gas velocity and directs the gas toward the turbine wheel 104 at a given angle. Both the magnitude and direction of the gas flow exiting the nozzle 154 affect the amount of power generated. The nozzle 154, in some examples, may have multiple blades therein. The gas flow velocity exiting the nozzle 154 can be adjusted by selecting the number of blades, the blade height, and the blade profile.

[0032] The turboexpander 102 includes a turbine wheel 104. The turbine wheel 104 is shown as a radial-inlet turbine wheel, although other configurations, such as an axial-flow turbine, are within the scope of this disclosure. In this example, heated high-pressure process gas 124 is received from an inlet conduit 150 in the housing 112 and enters a nozzle 154 of the turbine wheel 104. In certain embodiments, the fluid flows through the inlet conduit 150 and is diverted by a flow diverter 158 to a radial inlet 154, which directs the fluid to the radial inlet of the turbine wheel 104. In the example turboexpander 102 of FIG. 1 , the flow diverter 158 includes a conical nose that diverges the gas flow radially outward and directs it to the nozzle 154. The flow diverter 158 may be connected to or integrally formed with the bearing 116a and sensor 117a located on the inlet side of the turboexpander 102 and a support for the bearing 116a and sensor 117a that surrounds the axial end of the rotor 108 at the inlet end of the turboexpander 102. After expansion, the low-pressure process gas exits the turbine wheel 104 through an axially oriented outlet 156 and reaches an outlet conduit 152 of the housing 112 at the outlet end of the turboexpander 102.

[0033] The turbine wheel 104 may be directly attached 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 at an axial 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 may 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, clutch mechanism, or other method.

[0034] The turbine wheel 104 includes a plurality of turbine wheel blades 106 extending outward from a hub that interact with the expanding process gases to rotate the turbine wheel 104. An unshrouded turbine wheel is shown in FIG. 1 , in which each turbine blade 106 has a generally radially exposed blade tip that extends between a nozzle 154 and an axial outlet 156. As described in more detail below, the blade tip substantially abuts and seals against a shroud 114 disposed inside a housing 112. In one example, the turbine wheel 104 is a shrouded turbine wheel.

[0035] In a configuration with an unshrouded turbine wheel 104, the housing 112 includes an inwardly disposed shroud 114 that is adjacent to the turbine wheel blades 106 but does not contact the turbine wheel blades 106 most of the time during operation. The proximity of the turbine wheel blades 106 and the shroud 114 substantially seals the passage of process gas therebetween as the process gas flows through the turbine wheel 104. While some amount of process gas may leak or pass between the turbine wheel blades 106 and the shroud 114, this leakage is negligible in the operation of the turbine wheel 104. In some instances, the leakage may be comparable to that at the interface of other similar unshrouded turbines with a shroud surface, 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 turboexpander may be optimized to reduce leakage. In some embodiments, the housing 112 is hermetically sealed to prevent process gases from escaping the nozzles 154 of the turbine wheel 104.

[0036] The shroud 114 may be positioned a specified distance from the turbine wheel blades 106, and the position of the turbine wheel 104 is controlled to maintain the shroud 114 at the specified distance 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.

[0037] As described above, the turboexpander 102 generates rotational motion from the expansion of gas through the turbine wheel 104, resulting in a reduction in the pressure and temperature of the process gas 120 discharged at the outlet of the turbine wheel 104. The structures defining the aerodynamics of the nozzle 154 and shroud 114 (collectively referred to as the "aerodynamic stator"), the turbine wheel 104, the aerodynamic characteristics of the surfaces leading up to the turbine wheel 104, and the rest of the turboexpander 102 can be adjusted based on inlet temperature, inlet pressure, and inlet composition to control properties such as the power (rotational speed and / or torque) generated by the wheel and the pressure and / or temperature output from the turbine wheel 104. In other words, the configuration of the aerodynamic stator, turbine wheel 104, and other surfaces, as well as process control devices, can be utilized to meet pressure and temperature specifications downstream of the turboexpander 102, as well as other properties such as dew point. Additionally, the aerodynamic stator, turbine wheel 104, and other surfaces may be aerodynamically customized without substantially affecting other components of the turboexpander 102.

[0038] The turbine wheel 104 can be tuned by selecting the diameter of the turbine wheel, the shape and number of blades, the finish of the wheel's aerodynamic surfaces (e.g., the surfaces of the blades and between the blades), whether the wheel is shrouded, the shape of the shroud if shrouded, and the position of the blades relative to the shroud if unshrouded. The shroud 114 and inlet surfaces leading to the turbine wheel 104 can also be tuned by selecting the distance between the shroud 114 and the blades of the turbine wheel 114 and shaping the effective nozzle formed by the turbine wheel 104 and surfaces leading to the shroud 114. The wheel, shroud, and surfaces can be modeled using computational fluid dynamics (CFD) software, iteratively adjusted to achieve desired characteristics, then built and tested, and, if necessary, iteratively adjusted with CFD, followed by one or more additional builds and tests, to achieve the desired characteristics. For example, the aerodynamic stator, turbine wheel 104, and other aerodynamic paths through the turboexpander 102 can be designed to prioritize power generated by the turbine wheel 104, to prioritize pressure characteristics at the outlet of the turbine wheel 104 (and turboexpander housing 112), to prioritize temperature characteristics at the outlet of the turbine wheel 104 (and housing 112), and / or to prioritize or balance one or more of these characteristics. In some examples, the aerodynamic stator, turbine wheel 104, and other surfaces can be configured to target specific isenthalpic and isentropic efficiencies to control the outlet conditions of the turboexpander 102 for the supplied gas and the desired power generation.

[0039] 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 by the bearings 116a and 116b. In some embodiments, the turbine wheel 104 may be supported in a cantilevered manner, with the bearings 116a and 116b being positioned on one side of the turbine wheel 104. In some 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 other type of bearing.

[0040] 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 used. Bearings 116a and 116b do not have to be the same type of bearing.

[0041] 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 are directly or indirectly connected to the housing 112 and may detect axial and / or radial displacement of the rotor 108 and its connected components (e.g., the turbine wheel 104) relative to the housing 112. 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 obtain 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.

[0042] The turboexpander 102 may operate 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, 116b in the turboexpander 102 eliminates physical contact between rotating and stationary components, as well as the need for lubrication, lubrication systems, and bearing seals. In some examples, brush seals, labyrinth seals, or other types of seals are used on both sides of the rotor 106 to help balance axial thrust loads.

[0043] The turboexpander 102 may include one or more backup bearings. For example, in the event of a power outage that affects the operation of the magnetic bearings 116a and 116b, the backup bearings may be used to rotatably support the turbine wheel 104 during that period. Backup bearings may include ball bearings, needle bearings, journal bearings, etc.

[0044] As described above, the turboexpander 102 is configured to generate electrical power in response to rotation of the rotor 108. In one example, the rotor 108 may include one or more permanent magnets coupled to the rotor 108, e.g., on a radially outer surface of the rotor 108 adjacent the stator 110. The stator 110 may include, e.g., a plurality of conductive coils disposed adjacent to the magnets of the rotor 108. Rotation of the magnets within the coils of the stator 110 generates electrical current. The rotor 108 and the stator 110 may be configured as a synchronous permanent magnet multi-phase alternating current (AC) generator. The power output 160 may be, for example, a three-phase output. In one example, the stator 110 may include multiple 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 coils. At any instant in time, the magnitude of the voltage induced in the coil is proportional to the rate at which the magnetic field generated around the coil changes with time (i.e., the rate at which the magnetic field passes on both 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 electricity at that speed. Such a turboexpander 102 is referred to as a "high-speed" turbogenerator. For example, in some embodiments, the turboexpander 102 can generate up to 135 kilowatts (kW) of power at a continuous speed of the rotor 108 of 25,000 rpm. In some embodiments, the turboexpander 102 can generate approximately 315 kW of power at a certain rotational speed (e.g., around 23,000 rpm).

[0045] In some embodiments, the design of the turbine wheel 104, rotor 108, and / or stator 110 may be based on desired parameters of the exhaust gas from the turboexpander 102. For example, the design of the rotor 108 and stator 110 may be based on the expected or desired pressure and / or temperature of the gas 128 at the inlet of the turboexpander 102, the outlet of the turboexpander 102, or both.

[0046] 1, the turboexpander 102 is coupled to power electronics 118. The power electronics 118 includes a variable speed drive (VSD) 206 (or variable frequency drive) and a magnetic bearing controller (MBC) 212, as described above.

[0047] The power output 160 of the turboexpander 102 is connected to a VSD 206, which can be programmed for specific power requirements. The VSD 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 three-phase AC input current. An inverter 210 then converts the DC from the rectifier to alternating current (AC) for supply to the power grid 140 (or other load). The inverter 210 can convert the DC to 380 VAC to 480 V AC at 50-60 Hz for supply to the power grid. The specific output of the VSD 206 depends on the power grid and application. Other conversion values ​​are within the scope of this disclosure. The VSD 206 matches its output to the power grid 140 by sampling the power grid voltage and frequency and then modifying the inverter 210 output voltage and output frequency to match the sampled power grid voltage and frequency.

[0048] The turboexpander 102 is also connected to the MBC 212 within the power electronics 118. The MBC 212 constantly monitors the position, current, temperature, and other parameters of the turboexpander 102 and the active magnetic bearings 116a and 116b to ensure desired operation. For example, the MBC 212 is coupled to position sensors 117a and 117b to monitor the radial and / or 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. Synchronous cancellation control includes automatic balancing control, adaptive vibration control, adaptive vibration cancellation, and unbalance force cancellation control.

[0049] 2 is a schematic diagram of an exemplary turboexpander system 200 including a brake resistor assembly 202 according to an embodiment of the present disclosure. The turboexpander system 200 includes a turboexpander 102 and power electronics 118. The turboexpander 102 receives heated, high-pressure process gas 124, which rotates a turbine wheel 104. The rotation of the turbine wheel 104 rotates a rotor 108, which supports a number of permanent magnets. The rotation of the permanent magnets on the rotor 108 induces a current through the coils or windings of a stator 110.

[0050] The generator system acts as a brake for the rotor 108. This braking torque converts shaft power generated by the process gas flow into electrical power that can be supplied, for example, to a power grid. In the event of a power grid or load failure, inverter failure, or other fault condition, the braking torque is lost, and the rotor 108 may spin up toward an undesirable overspeed. To prevent overspeed, power can be diverted to a braking resistor assembly 202, which can temporarily absorb power until the process gas flow is reduced or cut off (e.g., by the flow control system 126) or the fault condition is resolved. The flow control system 126 may include one or a combination of flow control valves, mass control valves, or 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, if a fault condition is detected, the flow control system 126 may be signaled to close or partially close, thereby cutting off or limiting the gas supply to the turboexpander 102. By restricting or blocking gas flow to the turboexpander, the shaft power generated by the turbine wheel is reduced, resulting in a slower rotor rotational speed. In the example shown in Figures 1 and 2, a signal channel 164 from power electronics 118 can be used to open and / or close flow control system 126.

[0051] The fault condition may include a grid or load failure, a VSD failure, an inverter failure, or any other fault condition that removes or reduces the braking torque acting on the rotor 108.

[0052] The braking resistor assembly 202 is electrically connected to the power output 160 (e.g., the output of a generator) of the turboexpander 102. The braking resistor assembly 202 may have a tuned impedance to allow efficient transfer of power from the turboexpander 102 to the braking resistor assembly 202.

[0053] In some embodiments, in the event of a fault condition in the VSD 206 or the power grid 140, the contactor 204 may connect the output current of the turboexpander 102 to the braking resistor assembly 202. The contactor 204 is an electrically controlled switch for performing switching in the power circuit. The contactor 204 may receive the three-phase current output from the generator and direct the current to the braking resistor assembly 202.

[0054] In some embodiments, the contactor 204 is directly connected to the (three-phase) power output 160 of the turboexpander 102. In some embodiments, the braking resistor assembly 202 and / or the contactor 204 are not part of the power electronics and are connected to the power output 160 of the turboexpander 102 external to the power electronics 118.

[0055] The VSD 206 can provide an energizing signal 220 to the coil of the contactor 204 to operate the contactor 204 to connect the turboexpander power output 160 to the braking resistor assembly 202. Depending on the implementation choice, the contactor 204 can be a normally closed (NC) contactor or a normally open (NO) contactor.

[0056] For example, in an exemplary implementation using a normally open (NO) contactor, under normal operating conditions, the power output 160 of the turboexpander 102 is connected to the VSD 206 and supplies three-phase AC current to the VSD 206. Under a fault condition, the VSD may energize the contactor 204, connecting the contactor 204 to the power output 160 of the turboexpander 102. In some implementations, the energizing signal 220 to the contactor 204 may be provided by another source (e.g., another component of the power electronics 118 or another component external to the power electronics 118) that is responsive to the fault condition. In this implementation, if a failure of the VSD 206 is the cause of the fault condition, the contactor 204 can operate independently of the VSD 206.

[0057] If a normally closed (NC) contactor is used, under normal operating conditions, the VSD 206 (or other source) provides an energizing signal 220 to the contactor 204, maintaining the contactor switch in an open state. If a fault condition occurs, the energizing signal 220 to the contactor 204 is interrupted, causing the contactor switch to close and completing a circuit between the power output 160 of the turboexpander 102 and the braking resistor assembly 202.

[0058] 3 illustrates an exemplary energy recovery system 300 coupled to and located between a wellhead 302 and a production pipeline 320 of a well 304. The production pipeline 320 is a pipeline that transports produced fluid from the well 304 to one or more processing facilities (not shown) and ultimately to an end user. The system 300 includes a power generation system 350 that includes a turboexpander 102 (including a generator) for recovering energy from reducing the pressure of the produced fluid from the well 304, as well as associated flow lines and other equipment. In some examples, the system 300 is located at a production site 312 adjacent to the wellhead 302. In other examples, the system 300 is located upstream of the production pipeline 320, either inside or outside the production site 312. In one example of an onshore well 304, the production site 312 is a site with other equipment located upstream of the production pipeline 320 and near the well 304, and the system 300 is located at the site. In another example, multiple onshore wells 304 are located at the same production site 312 feeding the same pipeline 320, with system 300 coupled to one or more of the wells 304 and installed at the production site 312. In one example, the production site may have a surface area of ​​between one-half acre (2,000 square meters) and two acres (8,000 square meters). In one example of a subsea well 304, the production site 312 is an offshore platform, with system 300 installed on the platform. The platform may be the production platform corresponding to the well 304 (i.e., the subsea well), or it may be installed on a production platform associated with multiple subsea wells 304. For example, multiple wells 304 may be manifolded together to deliver fluid to a single production platform. In one example, system 300 may be installed on a dedicated platform separate from any production platform and connected to one or more other production platforms by flowlines.

[0059] In one example, power generation system 350 is the same as power generation system 100. Referring to FIGS. 1 and 2 , power generation system 350 includes some of the components of power generation system 100, including the aforementioned turboexpander 102 disposed within hermetic housing 112. The electrical power output of the generator of turboexpander 102 is connected to power electronics 118 (which in some examples includes VSD 206 with braking resistor assembly 202). Turboexpander 102 can be configured to respond to the conditions of the gas produced in well 304. For example, it can be configured to handle a specified amount of liquid in the gas, particulates in the gas, and to be resistant to corrosive components in the gas (e.g., hydrogen sulfide). In one example, VSD 206 can be coupled to a cooling system 352 to cool electronics in VSD 206 and maintain a temperature below a specified operating temperature. The output of VSD 206 can be electrically connected to load 354. The loads 354 may be, as described above, a power grid to supply power to a grid, a microgrid to supply power to equipment used in gas production or processing at the production site 312, and / or directly connected to and power one or more pieces of equipment used in gas production or processing at the production site 312. In some examples, the equipment may include sensors (e.g., flow, pressure, temperature, and level sensors) for various equipment, valve actuators, communications equipment to enable remote communication with the sensors, controls for other equipment and valve actuators, separators (e.g., sand separators, liquid separators), heat treatment equipment, site lighting, control trailers, and / or other types of equipment. In some examples, the power generated by the power generation system 350 may be used by other equipment at the production site 312 that is not involved in the production or processing of gas from the wells 304. For example, the power may be used to power a hydrogen electrolyzer in a process to produce hydrogen from water at the production site 312.

[0060] System 300 includes an inlet flowline 310 connected to an outlet of wellhead 302. Well product, i.e., primarily gaseous natural gas (but often containing some oil, water, moisture, and particulates), exits wellhead 302 and flows through flowline 310. Flowline 310 includes flow conditioning equipment to condition the flow to specified conditions selected based on the specifications of downstream pipelines 320 and equipment at production site 312, as well as the characteristics of turboexpander 102 in power generation system 350. In FIG. 3, the flow conditioning equipment is shown as solid-liquid separator 306 and dryer 308, although the flow conditioning equipment may include additional, different, or fewer components and types of equipment. For example, flow conditioning equipment may include separators, molecular dryers, knockout drums, two-phase coalescers, and / or other types of conditioning equipment. Returning to the example of FIG. 3 , the stream in flow line 310 flows from wellhead 302 into and through separator 306. In separator 306, solids and liquids are separated from the gas stream. The stream then flows through flow line 310 into dryer 308, where it is dried to reduce the moisture content in the stream to a specified level selected (in part or in whole) based on the specifications of turboexpander 102 of power generation system 350. From dryer 308, the stream flows through flow line 310 into pressure control valve 314. Pressure control valve 314 may 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, may be remotely controlled, for example, via an operator at a remote control panel located at production site 312 and / or elsewhere, and / or may be autonomously controlled by a control algorithm in a controller located at production site 312 and / or elsewhere.

[0061] 3 , flow from pressure control valve 314 is split into a first downstream flow line 316 with a power generation system 350 including turboexpander 102 and a second downstream flow line 318 that provides an alternate flow path around, i.e., bypasses, turboexpander 102. First downstream flow line 316 and second downstream flow line 318 reunite upstream of production pipeline 320, with the remainder of flow line 310 connected to the inlet of production pipeline 320. In other examples, second downstream flow line 318 may be omitted, in which case the only flow path to production pipeline 320 is through power generation system 350. Flow entering production pipeline 320 exits production site 312. The inlet of the airtight housing 112 is airtightly connected in series with the first flow line 316 so that all fluid in the flow line 316 is channeled into the airtight housing 112, flows through the housing 112, and returns to the remainder of the first flow line 316. In many cases, the production pipeline (e.g., pipeline 320) is provided and maintained by a production pipeline operator, an entity different from the entity that provides and maintains the equipment at the production site.

[0062] If provided, the second flow line 318 includes a pressure control valve 322 (e.g., pressure control valve 130) configured based on a correlation between a prescribed pressure drop and an operating position. The pressure control valve 322 may be controlled to regulate the pressure downstream of the pressure control valve 322 in the second flow line 318, and therefore the pressure upstream of the pressure control valve 322 (as a function of the pressure of the incoming flow from the wellbore), as well as the pressure in the first flow line 316. The first flow line 316 includes a flow control valve 324 (e.g., flow control valve 126) configured based on a correlation between a prescribed flow rate and an operating position. The flow control valve 324 may be controlled in conjunction with the pressure control valves 314, 322 to control the flow rate of fluid through the first flow line 316, thereby controlling the flow rate through the turboexpander 102.

[0063] This arrangement places the turboexpander 102 in parallel with the second flow line 318, providing flexibility in sizing the turboexpander 102 depending on the pressure and flow rate of the flow produced from the well 304 and the conditions of the pipeline 320, as described in more detail below. This flexibility is due in part to the fact that the second flow line 318 allows flow to selectively bypass the turboexpander 102 as it flows from the wellhead 302 to the production pipeline 320. In other words, because not all flow needs to pass through the turboexpander 102 as it flows from the wellhead 302 to the pipeline 320, the turboexpander 102 does not need to be sized to accommodate all of the flow. Additionally, the first flow line 316 includes an emergency shut-off valve 326 upstream of the turboexpander 102 to quickly shut off flow to the turboexpander 102 if necessary. When the emergency shut-off valve 326 is closed, all flow will flow through the second flow line 318. In particular, although not shown, inlet flow line 310, first flow line 316, and second flow line 318 may be additionally instrumented with sensors to monitor 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 within the flow lines).

[0064] During operation, when a new well 304 first begins production, the fluids produced from the well 304 are at or near their maximum pressure and flow rate. Over the operational life of the well 304, the pressure of the produced fluid decreases, and the flow rate of the produced fluid also decreases, eventually rendering the well inoperable. Therefore, the pressure of the produced stream is regulated to a prescribed pressure by the pressure control valve 314 in the flow line 310. The pressure control valve 322 in the second flow line 318 is then controlled to maintain the pressure in the first flow line 316 and the turboexpander 102, thereby, in cooperation with the flow control valve 324, maintaining conditions through the turboexpander 102 within the turboexpander's prescribed operating range. Excess flow exits the second flow line 318 and is directed to the pipeline 320. Flow through first flow line 316 flows through turboexpander 102 to generate power, then recombines with flow from second flow line 318 and exits into pipeline 320 .

[0065] The characteristics of the turboexpander 102 (including the turbine wheel 104 of the turboexpander 102 and the rest of the aerodynamic flow path through the turboexpander 102) are selected based on several factors, including the expected pressure, temperature, and flow rate that can be sustained by the well 304 over time, the time frame during the operating life of the well 304 during which power generated by the turboexpander 102 is desired or needed (e.g., whether power is needed early in the well's life, for as long as possible throughout the well's life, or only toward the end of the well's life), the environmental conditions at the production site 312, the efficiency / performance of the solid-liquid separator 306 and dryer 308, the conditions specified for acceptance by the pipeline 320 (including pressure, temperature, and / or flow rate, often specified by the pipeline operator), and the amount of power desired or needed to be generated by the turboexpander 102 at the production site 312. In some examples, the characteristics of the turboexpander 102 (including the characteristics of the turbine wheel 104) may be selected based on the expected drop in pressure of the wellbore fluid rather than the initial state of the fluid from the wellbore 304. As discussed above, the characteristics of the turboexpander 102, e.g., the turbine wheel 104 and other aerodynamic flow paths through the turboexpander 102, may be designed to prioritize power generated by the turbine wheel 104, to prioritize pressure characteristics at the outlet of the turbine wheel 104 (and turboexpander housing 112), to prioritize temperature characteristics at the outlet of the turbine wheel 104 (and housing 112), and / or to prioritize or balance one or more of these characteristics.

[0066] The characteristics of the turboexpander 102 can be adjusted by adjusting the design of the turbine wheel 104, as described above, as well as the aerodynamic shapes and flow area designs of other aspects of the turboexpander 102. For example, the characteristics can be adjusted by selecting the aerodynamic shapes and areas of the flow passages and nozzles leading to the turbine wheel and from the turbine wheel through the electric rotor and stator to the outlet of the turboexpander 102. The specified pressure to which the pressure control valve 314 is controlled is then selected based on several factors. These factors include the pressure, temperature, and flow characteristics of the turboexpander 102, the amount of power desired or required to be produced, and the specified pressure, temperature, and / or flow rate for acceptance by the pipeline 320. For example, in one example, the pipeline 320 is configured to operate at the specified pressure. The turboexpander 102, which creates a pressure drop while extracting energy from the flow, is configured, alone or in conjunction with one or both of the pressure control valves 314 and 322, to maintain the pressure at the inlet of the pipeline 320 (or upstream thereof, e.g., the outlet of the turboexpander 102) equal to (either exactly or approximately) the specified maximum pressure of the pipeline 320 while the well 304 is producing at a pressure higher than the specified pressure of the pipeline 320. In some instances, the pipeline 320 also has specified minimum and maximum temperatures. For example, in some instances, the specified minimum temperature may be a temperature selected to prevent freezing of condensate or hydrate formation in the gas. In some instances, the specified maximum temperature is selected based on the temperatures that the piping and equipment within the pipeline can withstand or are designed (e.g., rated) to withstand. Often, the specified pressures and temperatures are communicated by the pipeline operator to operators of the production sites that supply gas to the pipeline.The turboexpander 102, which reduces the temperature as it extracts energy from the flow, is configured, alone or in cooperation with one or both of the pressure control valves 314, 322 (which also reduce the temperature), to maintain the temperature at the inlet to the pipeline 320 (or upstream thereof, e.g., at the outlet of the turbine wheel 104 and valve 322) below a specified maximum pressure and above a specified minimum temperature. The turboexpander 102 may also be further configured, alone or in cooperation with one or both of the pressure control valves 314, 322 (which also reduce the temperature), to maintain the temperature at the inlet to the pipeline 320 (or upstream thereof, e.g., at the outlet of the turbine wheel 104 and valve 322) below a specified maximum temperature.

[0067] In most instances, turboexpander 102, alone or in conjunction with one or both of pressure control valves 314 and 322, can be configured to maintain the temperature to pipeline 320 below a specified maximum temperature without requiring a chiller or other cooling device or means to be installed in-line between well 304 and pipeline 320.

[0068] In some examples, due to the condition of the gas received by the turboexpander 102 and constraints in the energy recovery system 300, the pressure drop across the turboexpander 102 may cause the temperature at the inlet to the pipeline 320 to be higher than the specified maximum temperature for the pipeline 320. One or more chillers or other refrigeration cycles, heat exchangers, or cooling means may be provided within the energy recovery system 300 or elsewhere upstream of the inlet to the pipeline 320 to further reduce the temperature at the inlet to the pipeline 320 below the specified maximum temperature for the pipeline 320. However, because of the temperature reduction provided by the energy recovery system 300, the number and / or cooling capacity of the chillers (or other systems) may be less than would be required if the energy recovery system 300 or turboexpander 102 were not provided.

[0069] In one example, depending on the particular inlet conditions of the process gas 120 supplied to the turboexpander 102 and the specified maximum pressure of the pipeline 320, the turboexpander 102 (e.g., the aerodynamic stator defining the nozzle 154 and / or the turbine wheel 104) can be configured to have a high isentropic efficiency (e.g., 85-90%). Such a configuration allows the turboexpander 102, alone or in conjunction with one or both of the pressure control valves 314 and 322, to prioritize power generation under conditions that provide a sufficient pressure drop to bring the pressure at the inlet to the pipeline 320 below the specified maximum pressure of the pipeline. The turboexpander 102 can be configured to prioritize power generation over a specified period of the life of the well 304. For example, the turboexpander 102 can be configured to prioritize power generation for a majority of the life of the well 304, or for all or a majority of the time that the well 304 is producing gas at a pressure above a specified pressure (e.g., the specified maximum pressure of the pipeline 320, or a pressure above or below this maximum pressure). This prioritization of power generation may result in a significant pressure drop across the turboexpander 102, but may also result in a significant temperature drop that, in some instances, may fall below a specified minimum temperature for the pipeline 320 and / or may cause condensate to freeze and hydrate to form within and downstream of the turboexpander 102. Thus, the specified temperature condition for the pipeline 320 may be achieved, for example, by including one or more heaters (e.g., natural gas, electric, and / or other types) within the energy recovery system 300 or upstream of the inlet of the pipeline 320 to heat the flow from the turboexpander 102 to the specified minimum temperature for the pipeline 320.

[0070] Alternatively, the turboexpander 102 (e.g., the aerodynamic stator and / or turbine wheel 104 defining the nozzle 154) can be configured to have a lower isentropic efficiency at the receiving gas conditions and the outlet conditions described above. This allows for less enthalpy to be extracted from the gas. As a result, for the same pressure drop, the outlet temperature of the turboexpander 102 will be higher, and the inlet temperature of the pipeline 320 will be higher than the pipeline 320's specified minimum temperature. Using the same method, the heating requirements on the upstream side of the pipeline 320 can simply be relaxed compared to a turboexpander including a turbine wheel optimized for power generation (which has an isentropic efficiency that may cause freezing or hydrate formation). In other words, in some examples, the aerodynamic stator and turbine wheel 104 can be configured to prioritize temperature into the pipeline 320. This eliminates the need for heaters / heating means upstream or downstream of the turboexpander 102 when the turboexpander 102 operates alone or in conjunction with one or both of the pressure control valves 314 and 322, or reduces the heaters / heating means from that required for a turboexpander 102 that prioritizes power generation. The turboexpander 102 may be configured to prioritize pressure to the pipeline 320 for a specified period of time during the life of the well 304. The specified period may be, for example, a majority of the life of the well 304 or the entire or majority of the time that the well 304 is producing gas at a pressure above a specified pressure (e.g., a specified maximum pressure of the pipeline 320 or another pressure higher or lower than that maximum pressure). In some examples, the low isentropic efficiency may be less than 85%, and in some examples, the low isentropic efficiency may be less than 80%, less than 75%, less than 70%, or less than 50%. As discussed above, such low isentropic efficiency can be achieved by tuning the aerodynamic stator and turbine wheel 104.For example, for a particular pressure drop across the turbine wheel 104 under the same inlet conditions, the turbine wheel 104 may have the following configurations compared to a wheel with an isentropic efficiency of 85-90%: additional blades, differently shaped blades (e.g., less aerodynamically efficient blades), greater surface roughness on the aerodynamic surfaces of the blades and the gap surfaces between the blades, and / or blade or wheel configurations (sized to achieve a larger gap between the blade tips and the surrounding shroud). In other words, by reducing the isentropic efficiency of the turbine wheel 104, the wheel may be configured to prioritize, for a particular pressure drop, the temperature at the inlet of the pipeline 320 (or upstream thereof, e.g., the outlet of the turbine wheel 104, the outlet of the turboexpander 102, or the outlet of the power generation system) exceeding a specified minimum temperature of the pipeline 320 over the power generated by the wheel for the same pressure drop. In some examples, the aerodynamic stator may be adjusted to change the velocity and direction of gas entering the turbine wheel 104. Such adjustments can reduce aerodynamic efficiency and increase temperatures to the inlet of the pipeline 320 without affecting pressure drop. The same method can be used to simply reduce heating requirements for systems where no prioritization is performed.

[0071] In yet another configuration, the turboexpander 102 (e.g., the aerodynamic stator defining the nozzle 154 and / or the turbine wheel 102) can be configured to have an isentropic efficiency at the state of the received gas and the outlet conditions described above to extract a specified enthalpy from the received gas to balance power generation and temperature to the pipeline 320. This turboexpander 102 is configured such that, when used in combination with one or both of the pressure control valves 314 and 322, the pressure to the pipeline 320 is reduced below a specified maximum pressure in the pipeline 320 to generate a specified amount of power (e.g., a maximum or near-maximum amount) while eliminating the need for heaters / heating means upstream or downstream of the turboexpander 102 or reducing the heaters / heating means from what would be required for a turboexpander 102 prioritizing power generation. The turboexpander 102 can be configured to operate in this balanced state for a specified period of time over the life of the well 304. The specified period of time may be, for example, a majority of the life of the well 304 or all or a majority of the time that the well 304 is producing gas at a pressure above a specified pressure (e.g., a specified maximum pressure of the pipeline 320 or another pressure higher or lower than that maximum pressure). As discussed above, a low isentropic efficiency may be less than 85%, and in some examples, a low isentropic efficiency may be less than 80%, less than 75%, less than 70%, or less than 50%. Such low isentropic efficiencies may be achieved by adjusting the aerodynamic stator and turbine wheel 104.

[0072] To provide a numerical example, in one example, the well pressure may initially be greater than 9,000 PSIG (62.05 MPa) at a temperature of 150°F (66°C), and the flow is then regulated down to 1,600 PSIG (11.03 MPa) using pressure control valve 314. This 1,600 PSIG (11.03 MPa) pressure can be maintained even as the well 304 deteriorates over time and the pressure decreases, until the well pressure drops below 1,600 PSIG (11.03 MPa). While the well pressure is above 1,600 PSIG (11.03 MPa), the turboexpander 102 may be optimized to operate at its maximum design efficiency under the pressure, temperature, and flow conditions provided by the well 304 during this time, operating to generate power while also creating a further pressure drop at the inlet to the pipeline 320 (or downstream from the turboexpander 102) to and maintaining a specified pressure in the pipeline 320. Additionally or alternatively, the turboexpander 102 may be optimized to operate alone or in conjunction with one or both of the pressure control valves 314 and 322 to maintain the temperature at the inlet to the pipeline (or downstream from the turboexpander 102) above a specified minimum temperature while maintaining the temperature below a specified maximum temperature in the pipeline 320. In either example, given the same gas flow rate, minimum temperature, and minimum pressure in the pipeline 320, the hotter the well, the more energy will be available for extraction by the turboexpander 102. If the pressure in the well 304 falls below 1,600 PSIG (11.03 MPa), the efficiency of the turboexpander 102 will decrease until well conditions no longer allow the turboexpander 102 to operate satisfactorily. The first flow line 316 is then shut off, and flow is directed only through the second flow line 318. This prevents the turboexpander 102 from creating any further pressure drop. In one example, the turboexpander 102 may be configured to generate a usable amount of power until the upstream pressure approaches the pipeline's specified pressure. Often, this specified pressure is 1,000 PSIG (6.89 MPa).

[0073] FIG. 4 illustrates another exemplary energy recovery system 400 coupled to and disposed between both a wellhead 402 of a well 404 (or, in some examples, multiple wells) and a production pipeline 420. This second exemplary energy recovery system 400 is more feature-rich than the exemplary energy recovery system 300 described in connection with FIG. 3. For example, this second exemplary energy recovery system 400 is illustrated as including two power generation systems 450 and 452, each configured similarly to energy recovery system 350. Like system 300, this second exemplary system 400 is installed at a production site 412 (onshore or offshore platform) and is located proximate to the wellhead 402 and / or upstream from the production pipeline 420. In some examples, one or both of power generation systems 450 and 452 are identical to power generation system 100. However, as described in more detail below, power generation systems 450 and 452 may have the same or different operating characteristics as one another.

[0074] System 400 includes an inlet flow line 410 coupled to an outlet of wellhead 402. Produced fluid from well 402 enters inlet flow line 410. As discussed above, flow line 410 includes flow conditioning devices, which in this example are shown to include solid-liquid separator 406 and dryer 408. System 400 is further shown to include heat exchanger 416, the cold side of which is shown receiving upstream flow from dryer 408. Additional, different, or fewer numbers and types of flow conditioning devices may be provided. Pressure control valve 414 is shown between wellhead 402 and separator 406, but may be located elsewhere in the system upstream of power generation systems 450 and 452. Downstream of the dryer 408 , the flow splits into a compressed natural gas (CNG) filling station line 460 leading to a CNG filling station and a production pass line 438 leading to the entrance of the production pipeline 420 .

[0075] Line 460 to the CNG filling station includes a shutoff valve 462 and a pressure control valve 464. When shutoff valve 462 is closed, it seals line 460 and shuts off the CNG filling station line 460. This ensures that all flow is through production pass line 460 only. Pressure control valve 464 allows the pressure to the CNG filling station to be adjusted.

[0076] The production path line 438 includes two power generation systems 450 and 452. The stream enters this portion of the system through the hot side of heat exchanger 416 to recover heat (i.e., cooling) from the hotter stream upstream of the dryer 408. In FIG. 4 , the stream then splits into a first flow line 422 that includes the power generation system 450 and a second flow line 424 that bypasses the power generation system 450. The first and second flow lines 422 and 424 meet downstream of the power generation system 450 and upstream of the downstream power generation system 452. In other examples, the second flow line 424 may be omitted, in which case the only path to the downstream power generation system 452 is through the first (upstream) power generation system 450. If the second flow line 424 is included, it includes a pressure control valve 426 (e.g., pressure control valve 130). First flow line 422 includes a flow control valve 428 (e.g., flow control valve 126) upstream of flow meter 430. Downstream, first flow line 422 includes a shutoff valve 432 that can be closed to stop flow into first flow line 422 and power generation system 450. First flow line 422 also includes a pressure control valve 434. Downstream of power generation system 450, an additional shutoff valve 436 is provided that can completely shut off power generation system 450 to prevent backflow into power generation system 450.

[0077] The flow then splits again into a third flow line 442 that includes the power generation system 452 and a fourth flow line 444 that bypasses the power generation system 452. The third and fourth flow lines 442 and 444 reunite downstream of the power generation system 452 and return to the production pass line 438, which is connected to the inlet of the production pipeline 420. In other examples, the fourth flow line 444 may be omitted, in which case the only path to the production pipeline 420 is through the downstream power generation system 452. If a fourth flow line 444 is provided, it includes a pressure control valve 446 (e.g., pressure control valve 130). The third flow line 442 includes a flow control valve 448 (e.g., flow control valve 126) upstream of the flow meter 454. Downstream, third flow line 442 includes a shutoff valve 456 that can be closed to stop flow into third flow line 442 and power generation system 452. Downstream of power generation system 452, an additional shutoff valve 458 is provided that can completely shut off power generation system 452 to prevent backflow into power generation system 452.

[0078] The two power generation systems 450 and 452 may be identically configured, although in some examples the turboexpanders and / or electronics of the power generation systems 450 and 452 may be differently configured. The same design considerations discussed above for pressure regulation by the turboexpander and pressure control valve 314 ( FIG. 3 ) of the power generation system 350 may also apply to the turboexpanders and pressure control valves 414 of the two power generation systems 450 and 452. As an additional note, the power generation system 450 may take into account desired or required inlet conditions for the power generation system 452. For example, the turboexpander of the upstream power generation system 450 may be configured, and the pressure control valve 414 may be controlled, such that its outlet conditions are within the operating pressure range of the turboexpander of the downstream power generation system 452, preferably at or near the upper end of that range. In some examples, the turboexpander of the upstream power generation system 450 may be configured to operate at higher pressures, temperatures, and / or flow rates, making it more efficient, than the turboexpander of the downstream power generation system 452. By configuring the upstream turboexpander in this manner, the pressure drop created by the wellbore may be more easily utilized over the life of the wellbore. For example, in the embodiment of FIG. 3 , if the pressure created by the wellbore 304 is greater than the turboexpander of the power generation system 350 can handle, the pressure is adjusted down to the turboexpander's efficient operating pressure range, thereby effectively delaying the conversion of the available energy in the stream to power. If the turboexpander is configured with a higher operating pressure range, the lower limit of the operating pressure range may also be higher. Thus, as the wellbore pressure decreases, a point may be reached earlier in the wellbore's life where the wellbore pressure can no longer efficiently drive the turboexpander of the power generation system 350. For example, by providing an upstream turboexpander of power generation system 450 configured to operate at higher pressure, system 400 can generate more power by utilizing the higher pressure with the turboexpander of power generation system 450.Subsequently, when the well pressure drops to a point where it cannot efficiently drive the turboexpander of power generation system 450, power generation system 450 is disconnected from the flow, allowing power generation at a lower pressure using only the turboexpander of downstream power generation system 452. Note that while system 400 is described herein as including only two power generation systems, three, four, or more additional power generation systems may be provided. Each of the power generation systems may have separate flow paths and valves for bypassing the power generation system described above, some of the power generation systems may have such flow paths and valves, or none of the power generation systems may have separate bypass flow paths. Two or more power generation systems in a set may be identical, or all of the power generation systems may be different, e.g., with each downstream power generation system having a progressively lower operating range. The turboexpanders of the power generation systems may be configured to operate alone or in conjunction with one or both pressure control valves in their respective bypass lines to generate a pressure at the inlet to the pipeline (or upstream thereof, e.g., at the outlet of the turboexpander) that is equal to or less than the specified pipeline pressure. The turboexpanders of the power generation system may be configured to operate alone or in conjunction with one or both of the pressure control valves in the respective bypass lines to maintain the temperature at the inlet to the pipeline (or upstream thereof, e.g., at the outlet of the turboexpander) at or above a specified minimum temperature and below a specified maximum temperature under conditions of up to a specified pressure. In some embodiments, there may be multiple power generation systems installed in parallel with one another.

[0079] During operation, the pressure of the stream from wellhead 402 is regulated down to a prescribed pressure by pressure regulating valve 414. The fluid then flows through a flow regulation system (e.g., separator 406 and dryer 408) and is cooled by the cold side of heat exchanger 416 (transferring heat to a downstream stream in the system). When the CNG filling station is operating (i.e., shutoff valve 462 is open), a portion of the stream is directed to CNG filling station line 460, while the remainder of the stream continues to production pass line 438. The pressure of the fluid supplied to the CNG filling station may be regulated to a prescribed pressure by pressure control valve 464.

[0080] Within production pass line 438, the fluid is heated (heat transferred from an upstream stream in the system) by heat exchanger 416. The flow then splits into first flow line 422 and second flow line 424 if two shutoff valves 434 and 436 within first flow line 422 are open. If one or both of shutoff valves 434 and 436 are closed, the flow bypasses first flow line 422 and continues through second flow line 424. In the example where the flow splits into first flow line 422 and second flow line 424, pressure control valve 426, pressure control valve 434, and flow control valve 428 are controlled to control the flow rate entering first flow line 422 and, therefore, the flow rate entering the turboexpander of power generation system 450. The flow exiting the turboexpander of the power generation system 450 recombines with the flow in the second flow line 424 .

[0081] When both shut-off valves 456 and 458 in third flow line 442 are open, the flow splits between third flow line 442 and fourth flow line 444. When one or both of shut-off valves 456 and 458 in third flow line 442 are closed, the flow bypasses the turboexpander of power generation system 452. In instances where the flow splits between third flow line 442 and fourth flow line 444, pressure control valve 446 and flow control valve 448 are controlled to control the flow rate entering third flow line 442 and, therefore, the turboexpander of power generation system 452. The flow exiting the turboexpander of power generation system 452 recombines with the flow from fourth flow line 444 and then enters the inlet of pipeline 420 at the pipeline's defined pressure.

[0082] When the wellbore is new and the resulting pressure is high, the turboexpanders of both power generation systems 450 and 452 can be operated. If the wellbore pressure drops, and the turboexpander of power generation system 450 is configured to operate at a higher pressure than the turboexpander of power generation system 452, the flow pressure may become too low to effectively operate power generation system 450. In this case, isolation valves 432 and 436 can be closed to bypass the flow to power generation system 452 via second flow line 424. Power generation system 452 can then continue to operate until the wellbore pressure drops to a point where the turboexpander of power generation system 452 can no longer effectively operate. Isolation valves 456 and 458 can then be closed to bypass the flow to pipeline 420 via fourth flow line 444.

[0083] To provide a numerical example, in one example, the well pressure may initially be 9,000 PSIG (62.05 MPa) or greater. The flow is then regulated down to 3,600 PSIG (24.82 MPa) using pressure control valve 414. This 3,600 PSIG (24.82 MPa) pressure can be maintained even as well 304 deteriorates over time and the pressure decreases, until the well pressure drops below 3,600 PSIG (24.82 MPa). While the well pressure is above 3,600 PSIG (24.82 MPa), both power generation systems 450 and 452 can operate to generate power while the pipeline 420 or upstream thereof can further reduce the pressure to the specified pressure of the pipeline 420 and maintain that pressure. Power generation systems 450 and 452 generate power while reducing the temperature in or upstream of pipeline 420 to between a specified maximum temperature and a specified minimum temperature for pipeline 420. In this example, upstream power generation system 450 is configured to reduce the pressure of a 3,600 PSIG (24.82 MPa) flow to 1,600 PSIG (11.03 MPa), so pressure control valve 426 is also controlled to this pressure. In one example, power generation system 450 is configured to have an isentropic efficiency of 80% or less under these conditions. Also in this example, the turboexpander of downstream power generation system 452 is configured to accept an inlet pressure of 1,600 PSIG (11.03 MPa). In one example, power generation system 452 is configured to have an isentropic efficiency of 80% or less under these conditions. If the pressure in well 404 falls below 3,600 PSIG (24.82 MPa), the efficiency of the turboexpander in the upstream power generation system 450 will decrease until well conditions no longer allow the turboexpander to operate satisfactorily. First flow line 422 is then shut off by closing isolation valves 432 and 436, and flow is directed only through second flow line 424.However, second power generation system 452 continues to operate with pressure control valve 426 (or, optionally, pressure control valve 414) maintaining the pressure on third flow line 442 and fourth flow line 444 at 1,600 PSIG (11.03 MPa). If the pressure in well 404 falls below 1,600 PSIG (11.03 MPa), the efficiency of the turboexpander in downstream power generation system 452 will decrease until well conditions no longer allow the turboexpander to operate satisfactorily. Third flow line 442 is then shut off by closing isolation valves 456 and 458, and flow is directed only through fourth flow line 444, preventing the turboexpander from further reducing the pressure. In one example, the turboexpander in downstream power generation system 452 is configured to generate a usable amount of power until the upstream pressure approaches the pipeline's specified pressure. In most cases, this specified pressure is 1000 PSIG (6.89 MPa).

[0084] While certain illustrative embodiments have been described in detail in the foregoing specification, it will be apparent that various modifications and changes can be made thereto without departing from the broader spirit and scope of the present disclosure as set forth in the appended claims.

Claims

1. 1. A system for cooling a flow from a gas well upstream of a production pipeline, comprising: an inlet flowline connected to the gas well head for receiving gas produced from the gas well; a flowline connected to the inlet flowline to receive the gas and connected to the production pipeline to direct the received gas downstream from a production site, the flowline being located at the production site and including a power generation system; Equipped with The power generation system comprises: a turbine wheel configured to receive the gas and rotate in response to expansion of the gas entering an inlet of the turbine wheel and exiting an outlet of the turbine wheel; a nozzle configured to direct gas to an inlet of the turbine wheel; an electric rotor coupled to the turbine wheel and configured to rotate with the turbine wheel; a fixed electric stator, wherein the electric rotor and the electric stator define an electric generator configured to generate an electric current by rotation of the electric rotor within the electric stator; the turbine wheel is configured to reduce the temperature of the received gas at an inlet to the production pipeline to below a specified temperature associated with the production pipeline; system.

2. 2. The system of claim 1, wherein the pressure of the flow from the gas well is expected to decrease from an initial pressure over the operating life of the gas well, and the characteristics of the nozzle and turbine wheel are selected to maintain the temperature of the received gas at the inlet to the production pipeline above a specified maximum pressure associated with the production pipeline while the gas well is producing gas at a pressure above the specified maximum pressure.

3. 3. The system of claim 1 or claim 2, wherein the specified temperature is a specified maximum temperature for gas supplied to the production pipeline.

4. The system of any one of claims 1 to 3, wherein the nozzle and turbine wheel are configured to reduce the temperature of the received gas to 38°C or less.

5. The system of claim 4 , wherein the turbine is configured to reduce the temperature of the received gas and maintain the temperature of the gas at an outlet of the turbine wheel above a hydrate formation temperature.

6. The system of claim 5 , wherein there is no heater between the turbine wheel and the production pipeline.

7. 7. The system of claim 1, further comprising a second flow line coupled to the inlet flow line to receive the gas and provide an alternate flow path for the gas around the first-referenced flow line, the second flow line comprising a pressure control valve, and the first-referenced flow line and the second flow line coupled downstream of the power generation system to recombine flow from the first-referenced flow line and the second flow line.

8. 8. The system of claim 7, wherein the nozzle and the turbine wheel are configured to cooperate with the pressure control valve in the second flow line to maintain a temperature of the received gas at an inlet to the production pipeline above a specified minimum temperature associated with the production pipeline while the gas well is producing gas at a pressure above a specified maximum pressure associated with the production pipeline.

9. 9. The system of claim 8, wherein the nozzle and the turbine wheel are configured to cooperate with the pressure control valve in the second flow line to maintain a pressure of the received gas at an inlet to the production pipeline below a specified maximum pressure associated with the production pipeline.

10. 9. The system of claim 8, wherein characteristics of the nozzle and turbine wheel are selected to maximize the amount of power produced by the power generation system and, in cooperation with the pressure control valve in the second flow line, to maintain a temperature of the received gas at an inlet to the production pipeline above a specified minimum temperature associated with the production pipeline while the gas well is producing gas at a pressure above a specified maximum pressure associated with the production pipeline.

11. 11. The system of claim 1, comprising a hermetically sealed housing that houses the turbine wheel, the electrical rotor, and the electrical stator and is arranged in-line and hermetically sealed within the first-mentioned flow line to allow received flow to pass through the turbine and over the electrical stator.

12. The system of any preceding claim, wherein the electric rotor comprises a permanent magnet rotor.

13. The system of any preceding claim, comprising a flow control valve in the flow line upstream of the power generation system.

14. 1. A method for regulating flow from a gas well for a production pipeline, comprising: receiving flow from the gas well in a flow line, the flow line comprising a power generation system located at the production site of the gas well; The flow line a turbine wheel configured to receive the gas and rotate in response to expansion of the gas entering an inlet of the turbine wheel and exiting an outlet of the turbine wheel; a nozzle configured to direct gas to an inlet of the turbine wheel; an electric rotor coupled to the turbine wheel and configured to rotate with the turbine wheel; a fixed electric stator, wherein the electric rotor and the electric stator define a generator configured to generate an electric current by rotation of the electric rotor within the electric stator; receiving flow from the gas well in a flow line; directing at least a portion of the flow from the gas well through the flow line and the power generation system and using the turbine to reduce the temperature of the gas at an inlet to the production pipeline to below a specified temperature associated with the production pipeline; A method comprising:

15. 15. The method of claim 14, wherein the specified temperature is a specified maximum temperature of gas supplied to the production pipeline.

16. 16. The method of claim 14 or claim 15, comprising maintaining a minimum temperature of the gas at the outlet of the flow line above a hydrate formation temperature of the gas.

17. receiving flow from the gas well in a second flowline; flowing a portion of the flow from the gas well through the second flowline and a portion of the flow from the gas well through the first-mentioned flowline; then combining the portions of the flows downstream of the power generation system; The method according to any one of claims 14 to 16, comprising:

18. 18. The method of claim 17, wherein flowing a portion of the flow from the gas well through the second flowline and flowing a portion of the flow from the gas well through the first-mentioned flowline comprises controlling a flow control valve in the first-mentioned flowline and a pressure control valve in the second flowline to reduce the temperature of the recombined flow to 38°C or less.

19. 20. The method of claim 18, comprising controlling the pressure control valve in the second flow line to maintain a temperature of the received gas at an inlet to the production pipeline above a specified minimum temperature associated with the production pipeline while the gas well is producing gas at a pressure above a specified maximum pressure associated with the production pipeline.

20. 20. The method of claim 19, comprising controlling the pressure control valve in the second flow line to maintain a pressure of the received gas at an inlet to the production pipeline above a specified maximum pressure associated with the production pipeline.

21. 20. The method of claim 19, wherein the nozzle and turbine wheel characteristics are selected to maximize the amount of power produced by the power generation system and, in cooperation with the pressure control valve in the second flow line, to maintain a temperature of the received gas at an inlet to the production pipeline above a specified minimum temperature associated with the production pipeline while the gas well is producing gas at a pressure above a specified maximum pressure associated with the production pipeline.

22. 22. The method of claim 14, wherein the power generation system comprises a hermetically sealed housing that houses the turbine wheel, the electric stator, and the electric rotor and is hermetically sealed to a remainder of the flow line, and wherein channeling the portion of the flow from the gas well through the flow line and the power generation system comprises channeling the flow around the electric stator.

23. a flow path from the well to a production pipeline, the flow path including a nozzle and a turbine wheel connected to a generator located at the production site of the well; the nozzle and the turbine wheel configured to reduce the temperature of gas received through the flow path to below a specified temperature associated with the pipeline; A system comprising:

24. The system of claim 23 , wherein the turbine wheel and the generator are disposed within a hermetically sealed housing that defines a portion of the flowpath.

25. 25. A system according to claim 23 or claim 24, wherein the generator comprises a permanent magnet rotor.

26. The system according to any one of claims 23 to 25, wherein the specified temperature is 38°C.

27. 24. The system of claim 23, further comprising a second flow path between the well and the pipeline, the first-mentioned flow path and the second flow path meeting upstream of the pipeline.

28. 28. The system of claim 27, wherein the second flow path includes a pressure control valve, and the nozzle and turbine wheel are configured to cooperate with the pressure control valve to reduce the pressure of gas received from the well below a specified maximum pressure associated with the production pipeline.

29. 30. The system of claim 28, wherein the specified temperature is a specified maximum temperature associated with the pipeline.

30. 30. The system of claim 29, wherein the nozzle and the turbine wheel are configured to maximize power production by the generator.

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