Energy recovery from gas wells

Abstract

An energy recovery system for generating electricity from flow from a gas well, comprising: a first flow path from the well to a pipeline including a turbine wheel connected to a generator; and a second flow path from the well to the pipeline, the second flow path being spaced from the first flow path and including a valve. The first and second flow paths are at a production site of the well.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 17 / 814,597, filed July 25, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to power generation systems. [Background technology]

[0003] 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 and relative cleanliness. It is produced from gas wells, typically in remote areas, away from national, regional, or municipal power grids and other sources of electricity. In the case of offshore natural gas wells, the production from the wells is piped to offshore platforms, far from populated areas. Therefore, if electricity is required at the production site (including offshore platforms), it is common to combust some of the produced gas to generate electricity on-site. Summary of the Invention

[0004] The present disclosure describes a power generation system for generating electricity from gas well outflow. The energy recovery system includes an inlet flowline connected to a gas wellhead for receiving gas produced from the well. The energy recovery system also includes a first flowline connected to the inlet line for receiving the gas and including a power generation system at a production site of the well, the power generation system including: a turbine wheel configured to receive the gas and rotate in response to expansion of the gas entering the turbine wheel through the inlet and exiting the well through the outlet; an electric rotor connected to the turbine wheel and configured to rotate with the turbine wheel; and a fixed electric stator, the electric rotor and the electric stator defining a generator configured to generate electric current when the electric rotor rotates within the electric stator. The energy recovery system also includes a second flow line connected to the inlet line to receive the gas and provide an alternate flow path for the gas around the first flow line, the second flow line including a pressure control valve, the first flow line and the second flow line connected downstream of the power generation system to recombine flow from the first and second flow lines.

[0005] 1. An energy recovery system comprising: a housing enclosing the turbine wheel, the electric rotor, and the electric stator, the housing hermetically sealed in-line to the first flow line such that received flow passes through the turbine and over the electric stator. The electric rotor comprises a permanent magnet rotor. The energy recovery system comprises a flow control valve in the first flow line upstream of the power generation system. The energy recovery system comprises: a pressure of the flow from the gas well expected to drop from an initial pressure over the operating life of the gas well; and turbine wheel characteristics selected based on the efficiency of the turbine wheel at pressures lower than the initial pressure. The energy recovery system comprises: a first flow line and a second flow line connected upstream to a production pipeline; and a turbine wheel characteristics selected to be higher than a predetermined minimum temperature expected over the operating life of the well, based on a predetermined minimum temperature of the pipeline. The energy recovery system comprises: an offshore platform; and a power generation system connected to supply power to the offshore platform.an energy recovery system, the first and second flow lines combined at an outlet flow line receiving flow from the first and second flow lines, the energy recovery system including third and fourth flow lines connected to the outlet flow line and receiving the recombined flow from the first and second flow lines, the fourth flow line including a pressure control valve, the third flow line including a second power generation system at the production site of the well, the second power generation system receiving the gas and having it flow in through its inlet and out through its outlet; a second turbine wheel configured to rotate in response to the expansion of the gas, the second turbine wheel having characteristics that result in peak efficiency at a lower pressure than the first-mentioned turbine wheel, a second electric rotor connected to the second turbine wheel and configured to rotate with the second turbine wheel, and a second fixed electric stator, the second electric rotor and second electric stator defining a second generator configured to generate electric current as the second electric rotor rotates within the second electric stator. The energy recovery system includes: a second turbine wheel configured to rotate in response to the expansion of the gas, the second turbine wheel having characteristics that result in peak efficiency at a lower pressure than the first-mentioned turbine wheel; a second electric rotor connected to the second turbine wheel and configured to rotate with the second turbine wheel; and a second fixed electric stator, the second electric rotor and second electric stator defining a second generator configured to generate electric current as the second electric rotor rotates within the second electric stator. The energy recovery system includes: a shut-off valve in the first flow line upstream of the first-mentioned power generation system.

[0006] One general aspect includes a method for recovering energy from a gas well flow and generating electricity, comprising receiving the gas well flow through a first flowline and a second flowline, the first flowline including a power generation system including a turbine wheel at a production site of the gas well configured to receive the gas and rotate in response to expansion of the gas flowing through an inlet and outlet of the first flowline, an electric rotor connected to the turbine wheel and configured to rotate with the turbine wheel, and a fixed electric stator, the electric rotor and the electric stator defining a generator configured to generate electric current upon rotation of the electric rotor within the electric stator. The energy recovery method also includes channeling a portion of the gas well flow through the first flowline and the power generation system, and channeling a portion of the gas well flow through the second flowline, and recombining the portions downstream of the power generation system.

[0007] One general embodiment includes a system including a first flow path from a well to a pipeline that includes a turbine wheel connected to a generator, the system also including a second flow path from the well to the pipeline that is separate from the first flow path and includes a valve, the first and second flow paths being at a production site of the well.

[0008] This and other aspects can include one or more of the following features.

[0009] The details of one or more embodiments 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]

[0010] [Figure 1] 1 is a schematic diagram of a power generation system in accordance with the concepts herein; [Figure 2]FIG. 1 is a schematic diagram of an example turboexpander system according to the concepts herein. [Figure 3] 1 is a schematic diagram of an example of an energy recovery system including a power generation system according to concepts herein. [Figure 4] FIG. 2 is a schematic diagram of another example energy recovery system including two power generation systems in accordance with the concepts herein. DETAILED DESCRIPTION OF THE INVENTION

[0011] Like reference symbols in different drawings indicate like elements. The drawings are not to scale.

[0012] Natural gas wells produce at high pressures, sometimes as high as 9,000 PSIG (62.05 MPa) or 15,000 PSIG (103.42 MPa). The pressure of the produced natural gas must be reduced before pre-treatment to separate particulates and moisture from the gas and before transportation via pipelines. Pipelines transport the gas, for example, from production sites to processing facilities, from processing facilities to local distribution networks (e.g., regional, city, or district networks), or to on-site industrial plant networks. Processes at well sites and intermediate pressure reduction stations use pressure control valves (i.e., choke or throttle valves) to achieve the necessary pressure reduction, wasting significant amounts of head pressure energy in the process. Additional pressure control valves may be used elsewhere to control pressure within processing facility subprocesses and end-user processes and piping. An energy recovery system according to the concepts herein may be used in place of or in combination with one or more of these pressure control valves. The system includes a turboexpander (with generator). Turboexpanders, placed inline with the flow line from the wellhead and often in parallel with a bypass flow line equipped with a pressure control valve, extract waste energy from the reduced pressure to produce electricity. The electricity can be routed to a power grid or elsewhere. For example, some or all of the electricity can be used at the well site (onshore or offshore) to meet or offset on-site power needs, such as powering well site or platform equipment. Some production sites, particularly offshore platforms, have no other power source besides on-site generated electricity (e.g., using produced gas to run natural gas generators or diesel-fueled generators). In this way, energy recovery systems can power the production site without flaring the produced gas and resulting exhaust gases. In either example, by recovering lost energy from the produced natural gas, the energy recovery system can simultaneously generate electricity and reduce CO2 emissions, increase overall plant efficiency, offset electricity bills, and generate additional revenue.

[0013] FIG. 1 is a schematic diagram of a power generation system 100 connected to a power grid 140 in accordance with an embodiment of the present disclosure. As described in further detail below, the grid 140 may be a municipal grid, a microgrid, or the system 100 may be directly connected to one or more devices powered from its output. The power generation system 100 includes a turboexpander 102 in parallel with a pressure control valve 130. The turboexpander 102 is axially positioned such that the turboexpander 102 is mounted in-line with piping. The turboexpander 102 functions as a generator by converting kinetic energy from gas expansion through a turbine wheel 104 into rotational energy to generate electrical energy. For example, rotation of the turbine wheel 104 can be used to rotate a rotor 108 within a stator 110, generating electrical energy.

[0014] The turboexpander 102 includes a high-performance, high-speed permanent magnet generator that integrates a radial expansion turbine wheel 104 with low-loss active magnetic bearings (AMBs) 116a,b. The rotor assembly consists of a turbine wheel 104 and permanent magnet sections mounted directly to a rotor hub. The rotor 108 is levitated by the magnetic bearing system, which provides a frictionless (or nearly frictionless) interface between the dynamic and static components. The AMBs 116a,b facilitate lossless (or nearly lossless) rotation of the rotor 108.

[0015] The turboexpander 102 includes a high-performance, high-speed permanent magnet generator that integrates a radial expansion turbine wheel 104 with low-loss active magnetic bearings 116a,b. The rotor assembly includes a turbine wheel 104 with permanent magnet sections mounted directly to a rotor hub of a rotor 108. The rotor 108 is levitated by a magnetic bearing system, for example, at the longitudinal ends (e.g., axial ends) of the rotor 108, creating a frictionless (or nearly frictionless) interface between the dynamic and static components. The AMBs 116a,b facilitate lossless (or nearly lossless) rotation of the rotor 108.

[0016] The turboexpander 102 is designed to allow process gas 120 to flow through the system, thereby cooling the generator section and eliminating the need for auxiliary cooling equipment. The power electronics 118 of the turboexpander 102, in one embodiment, integrates a variable speed drive (VSD) 206 and a magnetic bearing controller (MBC) 212 into a single cabinet. The VSD enables consistent, clean transport of generated power from the turboexpander 102 to the power grid 140. For example, the VSD 206 adjusts the frequency and / or amplitude of the generated current to match the power requirements of the grid and / or loads. After expansion, the gas exits the turboexpander 102 along the same axial path for downstream processing.

[0017] The turboexpander 102 includes a flow-through configuration. The flow-through configuration allows process gas to flow from the inlet side of the turboexpander 102 to the outlet side of the turboexpander 102, with the inlet and outlet being centered on the same axis. Internally, gas enters through a radial gas inlet 154 to the turbine wheel 104 and an axial gas outlet 156 from the turbine wheel 104. The gas then passes through a generator and exits through an outlet 152, where the gas rejoins 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. In an embodiment, the turboexpander housing 112 is sealed.

[0018] The high-pressure process gas 120 is expanded by flowing through the turbine wheel 104, resulting in a pressure reduction of the process gas 120. Low-pressure process gas 128 exits the turboexpander 102. The expansion of the high-pressure process gas 120 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 reduction and extracts energy from the pressure reduction to generate electricity. A pressure control valve 130, such as a conventional choke, 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 parallel to the turboexpander 102. Excess high-pressure process gas not directed to the turboexpander may be directed through the pressure control valve 130.

[0019] In certain embodiments, a heater 122 can heat the high-pressure process gas 120 before passing the gas to the turboexpander 102. For example, if the expansion of the gas through the turbine wheel 104 reduces the temperature of the process gas and causes moisture in the gas to freeze and / or components of the process gas to condense at or downstream of the turbine wheel or at another downstream location in the pipeline, the pressurized process gas 120 can be heated by the heater 122 before passing through the turboexpander 102. The heated high-pressure process gas 124 can then be directed to the turboexpander 102. Heating the process gas can prevent moisture from freezing and components from condensing as the gas expands and cools.

[0020] The turboexpander 102 includes a turbine wheel 104. The turbine wheel 104 is shown as a radial turbine wheel, although other configurations, such as an axial 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 radially oriented inlet 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 that directs the flow to the radial input of the turbine wheel 104. In the example turboexpander 102 of FIG. 1 , the flow diverter 158 includes a conical nose that divertes the gas flow radially outward toward the radial inlet 154. The flow divider 158 may be connected to or integrally formed with the bearing 116a and sensor 117a on the inlet side of the turboexpander 102 and the support for the bearing 116a and sensor 117a that surrounds the axial end of the rotor 108 on the inlet side of the turboexpander 102. After expansion, the low-pressure process gas exits the turbine wheel 104 through an axially oriented outlet 156 to an outlet conduit 152 in the housing 112 at the outlet end of the turboexpander 102.

[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 at one axial end of the rotor 108 and held to the rotor 108 by a shaft. The shaft may be threaded into the rotor 108 at one end and capture the turbine wheel 104 at the other end between one end of the rotor 108 and a nut threaded onto the shaft. The turbine wheel 104 and rotor 108 are connected without a gearbox and rotate at the same speed. In other examples, the turbine wheel 104 may be indirectly connected 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 that extend outward from a hub and react with the expanding process gases to rotate the turbine wheel 104. Figure 1 illustrates an unshrouded turbine wheel in which the turbine blades 106 each have an exposed, generally radially oriented blade tip that extends between a radial inlet 154 and an axial outlet 156. As described in more detail below, the blade tips are substantially sealed against a shroud 114 inside a housing 112. In certain cases, 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 facing shroud 114 that is in close proximity to the turbine wheel blades 106 but generally does not contact the turbine wheel blades 106 during operation. The close proximity of the turbine wheel blades 106 and the shroud 114 substantially blocks the passage of process gas between the turbine wheel blades 106 and the shroud 114 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 not significant to the operation of the turbine wheel 104. In certain cases, leakage may be comparable to other similar unshrouded turbine / shroud surface interfaces using conventional tolerances between the turbine wheel blades 106 and the shroud 114. The acceptable leakage amount may be predetermined. Optimizing the turboexpander's operating parameters can reduce leakage. In an embodiment, the housing 112 is sealed to prevent process gases from leaking out of the radial inlet 154 of the turbine wheel 104 .

[0024] The shroud 114 may be spaced a predetermined distance from the turbine wheel blades 106 and is maintained at that distance from the turbine wheel blades 106 during operation of the turboexpander 102 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 and 116b. In 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 cases, 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 bearing type.

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

[0027] In embodiments where the bearings 116a and 116b are magnetic bearings, a magnetic bearing controller (MBC) 212 is used to control the magnetic bearings 116a and 116b. The 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 the position sensors 117a, 117b 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, if necessary. 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 can 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 are 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, in the event of a power outage that affects the operation of the magnetic bearings 116a and 116b, the bearings may be used to rotatably support the turbine wheel 104 during that period. The backup bearings may include ball bearings, needle bearings, journal bearings, etc.

[0030] As previously described, the turboexpander 102 is configured to generate electricity in response to rotation of the rotor 108. In certain cases, the rotor 108 may include one or more permanent magnets connected to the rotor 108, for example, on a radially outer surface of the rotor 108 adjacent the stator 110. The stator 110 may include, for example, multiple conductive coils positioned adjacent to the magnets on the rotor 108. Rotation of the magnets within the coils of the stator 110 generates current. 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 cases, 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. In either case, the magnitude of the voltage induced in the coil is proportional to the rate at which the magnetic field surrounding the coil changes over time (i.e., the rate at which the magnetic field passes on both sides of the coil). When the rotor 108 is connected 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 an embodiment, the turboexpander 102 can generate up to 135 kilowatts (kW) of power at a continuous speed of the rotor 108 of 25,000 revolutions per minute (rpm). In an embodiment, the turboexpander 102 can generate in the order of 315 kW at a certain rotational speed (e.g., in the order of 23,000 rpm).

[0031] In certain 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 108 and stator 110 may be based on the desired temperature of the gas 128 at the input of the turboexpander 102, the output of the turboexpander 102, or both.

[0032] 1, the turboexpander 102 is connected 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 (discussed above).

[0033] The electrical output 160 of the turboexpander 102 is connected to a VSD 206, which can be programmed for specific power requirements. The VSD 206 may include an insulated-gate bipolar transistor (IGBT) rectifier 208 that converts the variable frequency high voltage output from the turboexpander 102 to direct current (DC). The rectifier 208 may be a three-phase rectifier for three-phase AC input current. An inverter 210 converts the DC from the rectifier to AC for supply to the power grid 140 (or other load). The inverter 210 may convert the DC to 380 VAC to 480 VAC 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. VSD 206 matches its output to power grid 140 by sampling the grid voltage and frequency and changing the output voltage and frequency of inverter 210 to match the sampled grid voltage and frequency.

[0034] 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 the turboexpander 102 and active magnetic bearings 116a and 116b are operating as desired. For example, the MBC 212 is connected to position sensors 117a and 117b to monitor the radial and / or axial position 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 spin speed. The MBC 212 can also control desynchronization, including auto-balancing control, adaptive vibration control, adaptive vibration cancellation, and unbalanced force cancellation control.

[0035] 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 and rotates a turbine wheel 104. The rotation of the turbine wheel 104 rotates a rotor 108, which supports a plurality of permanent magnets. The rotation of the permanent magnets on the rotor 108 induces current through coils or windings on a stator 110.

[0036] 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 connected to, for example, an electrical grid. In the event of a grid or load failure, inverter failure, or other fault condition, the braking torque is lost and the rotor 108 may rotate toward an undesirable overspeed. To prevent overspeed, power may be diverted (e.g., by the flow control system 126) to a brake resistor assembly 202 that can temporarily absorb power until the process gas flow is reduced or eliminated or the fault condition is resolved. The flow control system 126 may include one or a combination of a flow control valve, a mass control valve, or an emergency shut-off valve. 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 may signal the flow control system 126 to close or partially close, cutting off or limiting the gas supply to the turboexpander 102. Restricting or eliminating gas flow to the turboexpander reduces the shaft power generated by the turbine wheel, resulting in a slowdown of the rotor. In the example shown in Figures 1 and 2, a signal channel 164 from power electronics 118 can be used to open or close flow control system 126.

[0037] Fault conditions may include grid or load failures, VSD failures, inverter failures, or other fault conditions. Fault conditions may include any condition that removes or reduces the braking torque of the rotor 108.

[0038] The brake resistor assembly 202 is electrically connected to the electrical output 160 (e.g., the output of a generator) of the turboexpander 102. The brake resistor assembly 202 may have a tuned impedance to allow efficient power transfer from the turboexpander 102 to the brake resistor assembly 202.

[0039] In an embodiment, the contactor 204 can connect the output current of the turboexpander 102 to the brake resistor assembly 202 when there is a fault condition in the VSD 206 or the power grid 140. The contactor 204 is an electrically controlled switch for switching power circuits. The contactor 204 can accommodate the three-phase current output from the generator and direct the current to the brake resistor assembly 202.

[0040] In some embodiments, the contactor 204 is directly connected to the (three-phase) electrical output 160 of the turboexpander 102. In some embodiments, the brake resistor assembly 202 and / or the contactor 204 are not part of the power electronics and are connected to the electrical output 160 of the turboexpander 102 outside of the power electronics 118.

[0041] The VSD 206 can provide an energization signal 220 to the coil of the contactor 204, causing the contactor 204 to connect the turboexpander electrical output 160 to the brake resistor assembly 202. Depending on the implementation choice, the contactor 204 can be a normally closed (NC) contactor or a normally open (NO) contactor.

[0042] For example, in an embodiment using a NO contactor, under normal operating conditions, the electrical output 160 of the turboexpander 102 is connected to the VSD 206 to provide three-phase AC to the VSD 206. Under a fault condition, the VSD can energize the contactor 204 to connect the contactor 204 to the electrical output 160 of the turboexpander 102. In some embodiments, the energization signal 220 to the contactor 204 can be provided by another source (e.g., another component in the power electronics 118 or another component external to the power electronics 118) that can respond to the fault condition. In this embodiment, if a failure of the VSD 206 is the cause of the fault condition, the contactor 204 may operate independently of the VSD 206.

[0043] If an NC contactor is used, the VSD 206 (or other source) provides an energization signal 220 to the contactor 204 to keep the contactor switch open during normal operating conditions. If a fault condition occurs, the energization signal 220 to the contactor 204 is removed, causing the contactor switch to close and completing a circuit between the electrical output 160 of the turboexpander 102 and the brake resistor assembly 202.

[0044] 3 illustrates an exemplary energy recovery system 300 connected between a wellhead 302 of a well 304 and a production pipeline 320. 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 (with a generator) for recovering energy by depressurizing the produced fluid from the well 304, as well as associated flowlines and other equipment. In certain cases, the system 300 is located at a production site 312 proximate to the wellhead 302. In certain cases, the system 300 is located at the production site 312 upstream from the production pipeline 320 or off-site from the production site 312. In one example of an onshore well 304, the production site 312 is a site where other nearby well 304 equipment is located upstream from the production pipeline 320, and the system 300 is located there. In another example, multiple onshore wells 304 are at the same production site 312 feeding the same pipeline 320, and system 300 is connected to one or more of the wells 304 and is at site 312. In one example of a subsea well 304, production site 312 is a surface platform on which system 300 resides. The platform may be the production platform corresponding to the well 304 (i.e., the subsea well), or it may be a production platform associated with multiple subsea wells 304, for example, where the wells 304 are manifolded to flow to a single production platform. In certain cases, system 300 may reside on a dedicated platform separate from any production platform and connected to one or more other production platforms by flowlines.

[0045] In certain cases, power generation system 350 is the same as power generation system 100. Referring to FIGS. 1 and 2 , system 350 includes the aforementioned turboexpander 102 of system 100 within hermetically sealed housing 112, with the electrical output of the generator of turboexpander 102 connected to power electronics 118 including VSD 206, possibly including brake resistor assembly 202. Turboexpander 102 may be configured to treat the conditions of the gas produced from well 304, for example, to treat a predetermined amount of liquid in the gas, particulates in the gas, or to be resistant to corrosive aspects in the gas (e.g., hydrogen sulfide). In certain cases, VSD 206 may be connected to a cooling system 352 to cool electronics of VSD 206 and maintain the temperature below a predetermined operating temperature. The output of VSD 206 may be electrically connected to loads 354 (such as a power grid to supply power to the grid, a microgrid at production site 312 to supply power to equipment used to produce or process gas at production site 312, as described above), and / or may be directly connected to one or more pieces of equipment used to produce or process gas at production site 312 to power the equipment. In certain cases, the equipment includes flow, pressure, temperature, and level sensors of various equipment, valve actuators, communications equipment to enable remote communication with sensors, other equipment, and controls for valve actuators, separators (e.g., sand separators, liquid separators), heat treatment equipment, site lighting, control trailers, and / or other types of equipment. In certain cases, the electricity generated by power generation system 350 may be used by other equipment at production site 312 that is not involved in the production or processing of gas from wells 304. For example, the electricity may be used to power a hydrogen electrolyzer in the production site 312 process of producing hydrogen from water.

[0046] System 300 includes an inlet flowline 310 connected to an outlet of wellhead 302. Well product, primarily gaseous natural gas (but often containing some oil, water, moisture, and particulates), flows from wellhead 302 and through flowline 310. Flowline 310 includes flow conditioners for conditioning the flow to predetermined conditions selected based on the specifications of the pipeline 320 and equipment downstream of production site 312 and the characteristics of the turboexpander 102 of power generation system 350. In FIG. 3 , the conditioners are shown as solid-liquid separator 306 and dryer 308, but the conditioners may include additional, different, or fewer number and types of equipment. For example, the conditioners may include separators, molecular dryers, knockout drums, two-phase coalescers, and / or other types of conditioners. Returning to the example of FIG. 3 , the stream in flow line 310 flows from wellhead 302 to and through separator 306. In separator 306, solids and liquids are separated from the gas stream. The stream then flows through flow line 310 to dryer 308, where it is dried to reduce the moisture content in the stream to a predetermined level selected based (partially or fully) on the specifications of turboexpander 102 of power generation system 350. From dryer 308, the stream flows through flow line 310 to pressure control valve 314. Pressure control valve 314 may be controlled to reduce the pressure of the gas stream to a predetermined pressure. Each valve herein, whether a control valve, isolation valve, or other valve, may be remotely controlled, for example, via an operator at a remote control panel located at production site 312 or elsewhere, or both, and / or may be autonomously controlled by a control algorithm in a controller located at production site 312 or elsewhere, or both.

[0047] Flow from pressure control valve 314 splits into a first downstream flow line 316 that includes a power generation system 350 that includes turboexpander 102, and a second downstream flow line 318 that bypasses turboexpander 102. First downstream flow line 316 and second downstream flow line 318 recombine upstream of production pipeline 320 before exiting production site 312. The inlet of seal housing 112 is sealed in-line with first flow line 316 so that all fluid in flow line 316 is directed into seal housing 112, flows through housing 112, and returns to the remainder of first flow line 316.

[0048] The second flow line 318 includes a pressure control valve 322 (e.g., pressure control valve 130) configured to provide a predetermined pressure drop relative to an actuation position correlation. The pressure control valve 322 can be controlled to regulate the pressure in the second flow line 318 downstream of the valve 322, which in turn regulates the pressure upstream of the pressure control valve 322 and the pressure in the first flow line 316 (as a function of the pressure of the flow from the wellbore). The first flow line 316 includes a flow control valve 324 (e.g., flow control valve 126) configured to have a predetermined flow rate relative to the actuation position correlation. The flow control valve 324 can be controlled in conjunction with the pressure control valves 314, 322 to control the flow rate of the fluid through the first flow line 316, and therefore the flow rate through the turboexpander 102.

[0049] This arrangement places the turboexpander 102 in parallel with the second flow line 318, and as described in more detail below, the turboexpander 102 can be sized flexibly relative to the pressure and flow rate of the flow produced from the well 304 and the conditions of the pipeline 320. 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. However, the bottom line is that not all flow needs to pass through the turboexpander 102 as it flows from the wellhead 302 to the pipeline 320, and therefore the turboexpander 102 does not need to be sized to accommodate all flow. The first flow line 316 also includes an emergency shut-off valve 326 upstream of the turboexpander 102 to quickly shut off flow to the turboexpander 102 if necessary. In a closed state, all flow flows through the second flow line 318. Although not shown, inlet flow line 310, first flow line 316, and second flow line 318 may be additionally instrumented with sensors to monitor pressure, temperature, flow rate, and / or other flow characteristics upstream and / or downstream of each line and each component (e.g., valves, turboexpanders, other components in the flow lines).

[0050] During operation, when well 304 is new and first begins production, the fluid produced from well 304 is at or near its maximum pressure and flow rate. Over time, the pressure of the produced fluid decreases, and so does the flow rate of the produced fluid. Therefore, the pressure of the produced stream is regulated to a predetermined pressure by pressure control valve 314 in flow line 310. Pressure control valve 322 in second flow line 318 is controlled to maintain the pressure through first flow line 316 and through turboexpander 102, which, together with flow control valve 324, maintains the conditions through turboexpander 102 within the turboexpander's predetermined operating range. Excess flow exits second flow line 318 and is directed to pipeline 320. The flow through first flow line 316 flows through turboexpander 102, generates electricity, and then recombines with the flow from second flow line 318 and flows through pipeline 320.

[0051] The characteristics of the turboexpander 102 are selected based on many factors, including the expected pressure, temperature and flow rate that can be sustained by the well 304 over time, the period for which the power generated by the turboexpander 102 is desired or needed during the life of the well 304 (e.g., whether power is needed from the beginning of the well's life, for as long as practicable throughout the well's life, or only at 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 the dryer 308, the conditions, including pressure, temperature, and / or flow rate, designated for receipt by the pipeline 320 (often designated by the pipeline operator), and the amount of power desired or needed to be produced at the production site 312 by the turboexpander 102. The predetermined pressure to which the pressure control valve 314 is controlled is selected based on many factors, including the pressure, temperature, and flow rate characteristics of the turboexpander 102, the amount of power desired or needed, and the pressure, temperature, and / or flow rate designated for receipt by the pipeline 320. For example, in a particular case, the pipeline 320 is configured to operate under a predetermined pressure. The turboexpander 102, which creates a pressure drop as it extracts energy from the flow, is configured, in cooperation with the pressure control valves 314, 322, to produce an outlet pressure of the turboexpander 102 equal to the predetermined pressure of the pipeline 320. In a particular case, the pipeline 320 also has a predetermined minimum temperature, e.g., a temperature selected to prevent freezing of the fluid in the pipeline. The turboexpander 102, which creates a temperature drop as it extracts energy from the flow, is configured, in cooperation with the pressure control valves 314, 322 (which also create a temperature drop), to maintain the outlet temperature of the turboexpander 102 and the inlet of the pipeline 320 above the predetermined minimum temperature at the predetermined pressure. To provide a numerical example, in a particular case, the well pressure is initially 9,000 PSIG (62.05 MPa) or greater, and the flow is adjusted to 1,600 PSIG (11.03 MPa) using the pressure control valve 314. As well 304 ages and the pressure drops, this 1,600 PSIG (11.03 MPa) can be maintained until the well pressure falls below 1,600 PSIG (11.03 MPa).While the wellbore 304 pressure exceeds 1,600 PSIG (11.03 MPa), the turboexpander 102 can be optimized to operate at peak efficiency under the pressure, temperature, and flow conditions provided by the wellbore 304 during this time, operating to generate power while providing and maintaining an additional pressure drop downstream of the turboexpander 102 to the predetermined pressure in the pipeline 320. The hotter the wellbore, the more energy the turboexpander 102 can extract. If the wellbore 304 pressure falls below 1,600 PSIG (11.03 MPa), the efficiency of the turboexpander 102 decreases until wellbore conditions no longer allow the turboexpander 102 to operate satisfactorily. The first flowline 316 is then shut off and flow is directed only through the second flowline 318, so that the turboexpander 102 does not provide any additional pressure drop. In certain cases, the turboexpander 102 is configured to generate a usable amount of power until the upstream pressure approaches a predetermined pipeline pressure, which is often 1,000 PSIG (6.89 MPa).

[0052] 4 illustrates another exemplary energy recovery system 400 connected between a wellhead 402 of a well 404 (or potentially multiple wells) and a production pipeline 420. This second exemplary energy recovery system 400 is more fully featured than the exemplary energy recovery system 300 described with respect to FIG. 3. For example, this second exemplary energy recovery system 400 is shown with two power generation systems 450, 452. Like system 300, this second exemplary system 400 is located at a production site 412 (onshore or offshore platform) proximate to the wellhead 402 and / or upstream from the production pipeline 420. In certain cases, one or both of the power generation systems 450, 452 are the same as the power generation system 100. However, as described in more detail below, the power generation systems 450, 452 may have the same or different operating characteristics as one another.

[0053] System 400 includes an inlet flowline 410 connected to an outlet at wellhead 402. Well production flows from wellhead 402 into flowline 410. As noted above, flowline 410 includes flow conditioning devices, which in this example include a solid-liquid separator 406 and a dryer 408. System 400 is also shown with a heat exchanger 416, the cooled side of which is shown receiving the upstream flow from dryer 408. Additional, different, or fewer 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. After dryer 408, the flow splits into a compressed natural gas (CNG) filling station line 460, which leads to a CNG filling station, and a production pass line 438, which leads to production pipeline 420.

[0054] Line 460 to the CNG filling station includes an isolation valve 462 and a pressure control valve 464. Isolation valve 462, in the closed state, seals off line 460, isolating CNG filling station line 460 and ensuring all flow is through production pass line 460. Pressure control valve 464 allows pressure to be regulated to the CNG filling station.

[0055] The production path line 438 includes two power generation systems 450, 452. The stream enters this portion of the system through the hot side of a heat exchanger 416, collecting heat (i.e., cooling) from the hot stream upstream of the dryer 408. The stream then splits into a first flow line 422, which includes the power generation system 450, and a second flow line 424, which bypasses the power generation system 450. The first and second flow lines 422, 424, converge downstream of the power generation system 450. The second flow line 424 includes a pressure control valve 426 (e.g., pressure control valve 130). The first flow line 422 includes a flow control valve 428 (e.g., flow control valve 126) upstream of a flow meter 430. The first flow line 422 then includes an isolation valve 432 that can be closed to stop flow to the first flow line 422 and the power generation system 450. The first flow line 422 also includes a pressure control valve 434. An additional isolation valve 436 follows the power generation system 450 to completely shut off the power generation system 450 and prevent backflow into the power generation system 450.

[0056] The flow then splits again into a third flow line 442, which includes a power generation system 452, and a fourth flow line 444, which bypasses the power generation system 452. The third and fourth flow lines 442 and 444 converge downstream of the power generation system 452, and the flow continues into the pipeline 420. The fourth flow line 444 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. The third flow line 442 then includes an isolation valve 456 that can be closed to stop flow to the third flow line 442 and the power generation system 452. An additional isolation valve 458 is provided after the power generation system 452 to completely shut off the power generation system 452 and prevent backflow into the power generation system 452.

[0057] The two power generation systems 450, 452 may be configured identically, although in certain cases the turboexpanders and / or electronics of the power generation systems 450, 452 may be configured differently. The same design considerations described above for the turboexpander of power generation system 350 and pressure regulation by pressure control valve 314 ( FIG. 3 ) may apply to the turboexpanders of the two power generation systems 450, 452 and pressure control valve 414. However, the power generation system 450 may take into account desired or required inlet conditions of 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 the conditions at the outlet of the turboexpander are within, preferably at or near the upper end of, the operating pressure range of the turboexpander of the downstream power generation system 452. In certain cases, the turboexpander of the upstream power generation system 450 may be configured to operate at higher pressures, temperatures, and / or flow rates more efficiently than the turboexpander of the downstream power generation system 452. Configuring the upstream turboexpander in this manner allows for more effective utilization of pressure decreases that occur throughout the life of the wellbore. For example, in the embodiment of FIG. 3 , if the pressure generated in wellbore 304 is greater than the turboexpander of power generation system 350 can handle, the pressure is adjusted to the turboexpander's efficient operating pressure range, effectively delaying the conversion of the available energy in the stream into electrical power. If the turboexpander were configured to have a higher operating pressure range, the lower end of the operating pressure range would likely also be higher. Thus, as wellbore pressure decreases, the point in the wellbore's life where it can no longer efficiently drive the turboexpander of power generation system 350 will be reached sooner. For example, by configuring the turboexpander of upstream power generation system 450 to operate under higher pressure, system 400 can generate more electricity by utilizing the higher pressure in the turboexpander of power generation system 450.Subsequently, when the well pressure drops to the point where it can no longer efficiently drive the turboexpander of power generation system 450, power generation system 450 can be isolated from the flow and power can be generated at a lower pressure using only the turboexpander of downstream power generation system 452. Note that while system 400 is described herein as having only two power generation systems, three, four, or more additional power generation systems can be provided, each with two separate flow paths and valves as described above. Two or more in a set can be of the same configuration, or all can be of different configurations. For example, each downstream power generation system can have a progressively lower operating range. In some embodiments, there can be additional power generation systems installed in parallel with one another in one or more operating regimes.

[0058] During operation, the flow from wellhead 402 is regulated to a predetermined 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 in the cooling side of heat exchanger 416 (transferring heat to downstream flow in the system). When the CNG filling station is operational (i.e., isolation valve 462 is open), a portion of the flow is directed to CNG filling station line 460, and the remaining flow continues to production pass line 438. The pressure of the fluid supplied to the CNG filling station may be regulated to a predetermined pressure by pressure control valve 464.

[0059] In the production pass line 438, a heat exchanger 416 heats the fluid (transferring heat from an upstream stream in the system). The flow then splits into the first flow line 422 and the second flow line 424, provided that two isolation valves 434, 436 in the first flow line 422 are open. If one or both of the isolation valves 434, 436 are closed, the flow bypasses the first flow line 422 and continues through the second flow line 424. In the example where the flow splits into the first flow line 422 and the second flow line 424, the pressure control valve 426, the pressure control valve 434, and the flow control valve 428 are controlled to control the flow rate into the first flow line 422 and, therefore, into the turboexpander of the power generation system 450. The flow exiting the turboexpander of the power generation system 450 is recombined with the flow in the second flow line 424.

[0060] When both isolation valves 456, 458 on the third flow line 442 are open, the flow is split between the third flow line 442 and the fourth flow line 444. When one or both of the isolation valves 456, 458 on the third flow line 442 are closed, the flow bypasses the turboexpander of the power generation system 452. In instances where flow is split between the third flow line 442 and the fourth flow line 444, the pressure control valve 446 and the flow control valve 448 are operated to control the flow entering the third flow line 442 and, therefore, the turboexpander of the power generation system 452. The flow exiting the turboexpander of the power generation system 452 is recombined with the flow from the fourth flow line 444 and continues to the pipeline 420 at the predetermined pressure of the pipeline 420.

[0061] When the well is new and production pressure is high, both turboexpanders of both power generation systems 450, 452 can be operated. If the well 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 be too low to effectively operate power generation system 450. In this case, isolation valves 432, 436 are closed and the flow is diverted to power generation system 452 through second flow line 424. Power generation system 452 can then continue to operate until the well pressure drops to a point where the turboexpander of power generation system 452 can no longer operate effectively. Isolation valves 456, 458 may then be closed and the flow diverted to pipeline 420 through fourth flow line 444. To provide a numerical example, in a particular case, the well pressure is initially 9,000 PSIG (62.05 MPa) or greater, and the pressure control valve 414 is used to regulate the flow to 3,600 PSIG (24.82 MPa). As the well 404 ages and the pressure drops, the 3,600 PSIG (24.82 MPa) can be maintained until the well pressure drops below 3,600 PSIG (24.82 MPa). While the well exceeds 3,600 PSIG (24.82 MPa), both power generation systems 450, 452 can operate to generate power while simultaneously providing and maintaining a further pressure drop to the predetermined pressure in the pipeline 420. In this example, the upstream power generation system 450 is configured to reduce the 3,600 PSIG (24.82 MPa) flow to 1,600 PSIG (11.03 MPa), so the pressure control valve 426 is also regulated to this pressure. Also in this example, the turboexpander of the downstream power generation system 452 is configured to receive an inlet pressure of 1,600 PSIG (11.03 MPa). If the pressure in the well 404 falls below 3,600 PSIG (24.82 MPa), the efficiency of the turboexpander of the upstream power generation system 450 will decrease until well conditions no longer allow the turboexpander to operate satisfactorily. The first flow line 422 is then shut off by closing the isolation valves 432 and 436, and flow will flow only through the second flow line 424.However, the second power generation system 452 continues to operate with pressure control valve 426 (or optionally pressure control valve 414) maintaining the pressure to the third flow line 442 and the fourth flow line 444 at 1,600 PSIG (11.03 MPa). If the pressure in the well 404 falls below 1,600 PSIG (11.03 MPa), the efficiency of the turboexpander in the downstream power generation system 452 decreases until well conditions no longer allow the turboexpander to operate sufficiently. The third flow line 442 is then shut off by closing isolation valves 456 and 458, and flow is directed only through the fourth flow line 444, so that the turboexpander does not provide any additional pressure drop. In certain cases, the turboexpander 102 in the downstream power generation system 452 is configured to generate a usable amount of power until the upstream pressure approaches the predetermined pipeline pressure. In most cases, this predetermined pressure is 1000 PSIG (6.89 MPa).

[0062] Although the foregoing specification has been described in detail with reference to certain exemplary embodiments, it will be apparent, however, 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. An energy recovery system for generating electricity from flow from a gas well, comprising: an inlet flowline connected to a wellhead of the gas well for receiving gas produced from the gas well; a first flow line connected to the inlet line for receiving the gas, the first flow line including a power generation system, the power generation system being at the production well site; a turbine wheel configured to receive the gas and rotate in response to expansion of the gas flowing through the inlet and exiting through the outlet; an electric rotor connected to the turbine wheel and configured to rotate with the turbine wheel; a fixed electric stator, the electric rotor and the electric stator defining a generator configured to generate an electric current upon rotation of the electric rotor within the electric stator; a first flow line including: a second flow line connected to the inlet line to receive the gas and provide an alternate flow path for the gas around the first flow line, the second flow line including a pressure control valve, the first flow line and the second flow line connected downstream of the power generation system to recombine flow from the first flow line and the second flow line; Energy recovery system including.

2. 2. The energy recovery system of claim 1, including a housing that encloses the turbine wheel, the electric rotor, and the electric stator and is hermetically sealed in-line with the first flow line such that received flow passes through the turbine and over the electric stator.

3. The energy recovery system of claim 1 , wherein the electrically driven rotor comprises a permanent magnet rotor.

4. The energy recovery system of claim 1 , including a flow control valve in the first flow line upstream of the power generation system.

5. 2. The energy recovery system of claim 1, wherein the pressure of the flow from the gas well is expected to drop from an initial pressure over the operating life of the gas well, and the turbine wheel characteristics are selected based on the efficiency of the turbine wheel at pressures lower than the initial pressure.

6. 6. The energy recovery system of claim 5, wherein the first flow line and the second flow line are connected upstream to a production pipeline, and the turbine wheel characteristics are selected to be greater than a predetermined minimum temperature expected over the operating life of the well based on a predetermined minimum temperature of the pipeline.

7. 10. The energy recovery system of claim 1, wherein the production site is an offshore platform and the power generation system is connected to provide electrical power to the offshore platform.

8. the first flow line and the second flow line are joined by an outlet flow line that receives flow from the first flow line and the second flow line, and the energy recovery system comprises: third and fourth flow lines connected to the outlet flow line and receiving the recombined flows from the first and second flow lines, the fourth flow line including a pressure control valve, and the third flow line including a second power generation system at the production site of the well, the second power generation system including: a second turbine wheel configured to receive the gas and rotate in response to the expansion of the gas flowing through its inlet and outlet, the second turbine wheel having a characteristic such that its efficiency peaks at a lower pressure than that of the first turbine wheel; a second electric rotor connected to the second turbine wheel and configured to rotate with the second turbine wheel; a second fixed dynamo stator, the second dynamo rotor and the second dynamo stator defining a second generator configured to generate an electric current upon rotation of the second dynamo rotor within the second dynamo stator; Including, The energy recovery system of claim 1 .

9. 9. The energy recovery system of claim 8, wherein the second turbine wheel is configured based on the characteristics of the first turbine wheel mentioned.

10. 10. The energy recovery system of claim 8, including a shut-off valve in the first flow line upstream of the first of the power generation systems mentioned.

11. 1. A method for recovering energy from a gas well flow and generating electricity, comprising: receiving a flow from the gas well into a first flow line and a second flow line, the first flow line being at a production site of the gas well; a turbine wheel configured to receive gas and rotate in response to expansion of the gas flowing through the inlet and exiting through the outlet; an electric rotor connected to the turbine wheel and configured to rotate with the turbine wheel; a fixed electric stator, the electric rotor and the electric stator defining a generator configured to generate an electric current upon rotation of the electric rotor within the electric stator; a power generation system including: directing a portion of the flow from the gas well into the first flow line and into the power generation system, directing a portion of the flow from the gas well into the second flow line, and recombining the portions downstream of the power generation system; A method comprising:

12. 12. The method of claim 11, wherein directing a portion of the flow to the first flow line and directing a portion of the flow to the second flow line comprises controlling a flow control valve in the first flow line and a pressure control valve in the second flow line.

13. directing a portion of the recombined flow into a third flow line and a fourth flow line including a second power generation system, the second power generation system being at the production site of the well; a second turbine wheel configured to receive the gas and rotate in response to expansion of the gas flowing through its inlet and exiting its outlet; a second electric rotor connected to the second turbine wheel and configured to rotate with the second turbine wheel; a second fixed dynamo stator, the second dynamo rotor and the second dynamo stator defining a second generator configured to generate an electric current upon rotation of the second dynamo rotor within the second dynamo stator; including, shedding, passing a portion of the recombined flow through the third flow line and to a second power generation system, passing a portion of the recombined flow through a fourth flow line, and recombining the portion downstream of the second power generation system; 12. The method of claim 11, comprising:

14. The method of claim 13 , further comprising operating a first power generation system to generate electricity while operating the second power generation system to generate electricity.

15. 14. The method of claim 13, wherein the first turbine wheel is configured to operate under a higher pressure than the second turbine wheel.

16. 14. The method of claim 13, comprising operating the second power generation system to generate electricity while completely bypassing the first power generation system referred to in claim 1 by closing a valve in the first flow line.

17. 13. The method of claim 12, wherein the power generation system includes a sealed housing that encloses the turbine wheel, the electric stator, and the electric rotor and is sealed to a remainder of the first flow line, and wherein channeling the portion of the flow from the gas well through the first flow line and the power generation system includes channeling the flow around the electric stator.

18. a first flow path from the well to the pipeline including a turbine wheel connected to a generator; a second flow path from the well to the pipeline, the second flow path being separate from the first flow path and including a valve, the first and second flow paths being at a production site of the well; A system including:

19. The system of claim 18 , wherein the turbine wheel and generator are within an enclosed housing that defines a portion of the flow path.

20. the first flow path and the second flow path converge upstream of the pipeline, and the system: a third flow path downstream of the convergence to the pipeline, the third flow path including a second turbine wheel and a second generator, the second turbine wheel having different flow characteristics than the first turbine wheel; and a fourth flow path separate from the third flow path downstream of the convergence to the pipeline, the fourth flow path including a second valve; Including, 20. The system of claim 18.

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