Island operation of turboexpander

Abstract

The turboexpander may operate as a microgrid generator for islanding operation. The turbo expander may recover energy lost during the pressure reduction sequence to generate electricity. The pressurized process gas may rotate the turbine, thereby rotating the rotor within the stator of the turboexpander. The power electronics may include an islanding mode inverter that outputs an alternating current including a frequency and amplitude compatible with powering the load. The power electronics may include a battery charged by the turbo-expander and may provide power to start the turbo-expander. The power electronics may include a bi-directional inverter to transmit excess power from the turboexpander to the power grid and to receive power from the power grid for startup.

Description

Priority claim

[0001] This application claims priority to U.S. patent application No. 17 / 804,265 filed on May 26, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0002] Moving gas from production areas to consumption areas effectively and efficiently uses a large and complex transportation system. Gases transported through pipelines can be pressurized and can be transported long distances through pipelines at high pressure. For example, natural gas transported through pipelines travels at high pressure in the pipelines. Natural gas is one of the main sources of energy for many of our daily needs and activities. Natural gas is an attractive fossil fuel because of its abundant reserves and relative cleanliness. As another example, hydrogen can also be transported under high pressure using pipelines. Hydrogen is a rapidly expanding global energy storage market. Hydrogen is used in many manufacturing processes from oil refining to food processing. Hydrogen is also used as a fuel source for gas turbines and is used in a wide range of fuel cells to generate electricity in the industrial and consumer transportation sectors. Other gases can also be transported through pipelines at high pressure, including propane, oxygen, carbon dioxide, and other gases. Summary of the invention

[0003] Aspects of an embodiment include an apparatus including a generator. The generator includes a turbine wheel configured to receive a process gas and to rotate in response to expansion of the process gas flowing into an inlet of the turbine wheel and flowing out of an outlet of the turbine wheel; a rotor coupled to the turbine wheel and configured to rotate with the turbine wheel; and a stationary stator, wherein the generator generates an alternating current when the rotor rotates within the stator. The apparatus includes a power converter circuit coupled to an electrical output of the generator, the power converter circuit for converting the alternating current from the generator into a direct current; and an island mode inverter circuit coupled to an electrical output of a rectifier circuit, the inverter circuit for converting the direct current from the rectifier circuit into an alternating current including a frequency and an amplitude to provide power to a load.

[0004] Aspects of an embodiment include a system including a generator and power electronics. The generator includes a turbine wheel configured to receive a process gas and rotate in response to expansion of the process gas flowing into an inlet of the turbine wheel and out of an outlet of the turbine wheel; a rotor coupled to the turbine wheel and configured to rotate with the turbine wheel; and a stationary stator, wherein the generator generates an alternating current when the rotor rotates within the stator. The power electronics include a power converter circuit coupled to an electrical output of the generator, the power converter circuit for converting the alternating current from the generator into a direct current; and an island mode inverter circuit coupled to an electrical output of a rectifier circuit, the inverter circuit for converting the direct current from the rectifier circuit into an alternating current including a frequency and an amplitude to provide power to a load.

[0005] Some aspects of an embodiment include: a brake resistor rectifier coupled to an electrical output of the generator; and a brake resistor assembly coupled to an output of the brake resistor rectifier.

[0006] In some implementations of the embodiments, the brake resistor assembly includes a speed controlled and current regulated brake resistor.

[0007] Some aspects of embodiments include a battery coupled to the generator, the battery for storing power received from the generator and providing power to rotate the rotor within the stator.

[0008] In some implementations of the embodiments, the battery is connected to the power converter circuit, which is used to: receive AC current from the generator and convert the AC current into DC current for storage in the battery; and receive DC current from the battery and convert the DC current into AC current to power the rotor.

[0009] Some aspects of the embodiments include a bidirectional inverter including the island mode inverter circuit and an active grid inverter for converting direct current to alternating current including a frequency and amplitude compatible with a grid.

[0010] In some implementations of the embodiments, the bidirectional inverter is used to provide power to the load, and to provide excess power to the grid.

[0011] In some implementations of the embodiments, the bidirectional inverter is used to supply power from the grid to the rotor to rotate the rotor within the stator before the process gas rotates the turbine wheel.

[0012] In some implementations of the embodiments, the generator comprises a three-phase permanent magnet synchronous generator.

[0013] Some aspects of the embodiments include a bidirectional inverter for directing current to the load and directing excess current to a grid.

[0014] In some implementations of the embodiments, the bidirectional inverter includes an active grid inverter for directing power to the grid and receiving power from the grid.

[0015] Aspects of an embodiment relate to a method comprising: causing a gas to flow through a turbine wheel of a generator located downstream of a flow control valve; generating current through the generator; directing the current generated by the generator to an island mode power electronic device; and directing the current from the island mode power electronic device to a load.

[0016] Some aspects of the embodiments include directing excess current generated by the generator but not directed to the load to a grid via an active grid inverter.

[0017] Some aspects of the embodiments include performing starting of the generator using power received from the grid via the active grid inverter.

[0018] Some aspects of the embodiments include directing excess current generated by the generator but not directed to the load to a battery.

[0019] Some aspects of the embodiments include performing starting of the generator using power received from the battery.

[0020] In some implementations, the island mode inverter circuit includes circuitry configured to: receive direct current on a DC bus; convert the direct current to alternating current; and regulate the alternating current to a frequency and amplitude compatible with the load.

[0021] Some aspects of the embodiments include a main controller circuit for controlling current flow to a brake resistor during a fault condition.

[0022] Some aspects of an embodiment include an active rectifier electrically connected between the generator and the brake resistor, the main controller activating the active rectifier upon detecting a fault condition to direct current from the generator to the brake resistor based on the presence of the fault condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1is a schematic diagram of a power generation system coupled to a power grid according to an embodiment of the present disclosure.

[0024] Figure 2 is a schematic diagram of an example turboexpander system supporting islanded operation without a grid source according to an embodiment of the present disclosure.

[0025] Figure 3 is a schematic diagram of an exemplary turboexpander system including a bidirectional inverter for islanded operation according to an embodiment of the present disclosure.

[0026] Figure 4A is a schematic diagram of an exemplary turboexpander converter according to an embodiment of the present disclosure.

[0027] Figure 4B is a schematic diagram of an exemplary island mode inverter according to an embodiment of the present disclosure.

[0028] Figure 5 is a process flow diagram for supporting island operations using a turboexpander according to an embodiment of the present disclosure.

[0029] Like reference numerals in the various drawings represent like elements. The drawings are not drawn to scale. DETAILED DESCRIPTION

[0030] Natural gas, hydrogen and other process gases are pressurized for efficient transportation in pipelines that are sometimes several miles long. For example, pipelines transport gas from production sites (e.g., wells) to processing facilities, and from processing facilities to local distribution networks, such as regional, city or administrative district networks or on-site industrial plant networks. In order to safely transport gas through local distribution networks and for use, the process gas is decompressed to a lower level (usually using a pressure regulator). The pressure is stepped down at the pressure letdown (PLD) station for delivery to industrial, commercial and residential end users. The PLD station uses a regulating valve to achieve the required pressure drop, but a lot of energy is also wasted in the process. Additional regulating valves can be used for pressure control in other locations, such as in pipelines between production facilities and processing facilities, in sub-processes of process facilities, and in processes and pipelines of end users. A turboexpander generator can be installed in parallel with the regulating valve to recover energy wasted due to pressure reduction and generate electricity. Electricity can be directed to the power grid or elsewhere. Similarly, a turboexpander generator may be installed at a gas storage facility upstream of one or more storage tanks to recover the high pressure gas distributed from the tanker truck to the storage tank via the turboexpander generator. The turboexpander generator is relevant in other applications, such as in the following hydrogen liquefaction process, in which the gaseous hydrogen that has been cooled and pressurized expands into a liquid state. Expansion may be performed by the turboexpander generator to recover the energy wasted by the expansion and generate electricity. As described above, the electricity may be directed to the grid or elsewhere, such as being used to power a compressor or other components of the liquefaction process. In each case, by recovering the energy lost in the pressure reduction application of natural gas and hydrogen, the turboexpander can generate electricity while also reducing CO2 emissions, improving the efficiency of the entire plant, offsetting electricity costs and generating additional revenue.

[0031] The grid to which the turboexpander may supply power (and from which it may draw power) may be a national or regional grid, a local grid for a city or administrative region, or a small grid, local grid, or microgrid, such as an on-site grid supplying power to a building, campus, industrial manufacturing or process facility, or community.

[0032] Figure 1is a schematic diagram of a power generation system 100 coupled to a grid 140 according to an embodiment of the present disclosure. The power generation system 100 can be added at a PLD station to capture energy from gas expansion from a PLD process, or added in any other application described above. The power generation system 100 includes a turboexpander 102 in parallel with a pressure control valve 130. The turboexpander 102 is arranged axially so that it can be mounted in line with the pipe. The turboexpander 102 acts as a generator that generates electrical energy from rotational kinetic energy generated from the expansion of gas through a turbine impeller 104. For example, the rotation of the turbine impeller 104 can be used to rotate a rotor 108 within a stator 110, thereby generating electrical energy.

[0033] Figure 1 1 is a schematic diagram of a power generation system 100 coupled to a grid 140 according to an embodiment of the present disclosure. The power generation system 100 can be added at a PLD station to capture energy from gas expansion from a PLD process. The power generation system 100 includes a turboexpander 102 in parallel with a pressure control valve 130. The turboexpander 102 is arranged axially so that it can be mounted in line with the pipe. The turboexpander 102 acts as a generator that generates electrical energy from rotational kinetic energy generated from the expansion of gas through a turbine impeller 104. For example, the rotation of the turbine impeller 104 can be used to rotate a rotor 108 within a stator 110, thereby generating electrical energy.

[0034] The turboexpander 102 may include a high performance, high speed permanent magnet generator. In some embodiments, the turboexpander 102 includes a radial inflow expansion turbine impeller 104. The turboexpander 102 may also include low-loss active magnetic bearings (AMB) 116a and 116b. The rotor assembly may include a permanent magnet section, wherein the turbine impeller 104 is directly mounted to the rotor hub. The rotor 108 may be suspended by a magnetic bearing system, thereby creating a frictionless (or nearly frictionless) interface between dynamic and static components. The AMBs 116a, 116b contribute to the lossless (or nearly lossless) rotation of the rotor 108.

[0035] The turboexpander 102 is shown as flowing the process gas through the system, the turboexpander 102 cooling the generator section and eliminating the need for auxiliary cooling equipment. In some embodiments, a non-flow-through overhung system may also be implemented. In some embodiments, the power electronics 118 for the turboexpander combines a variable speed drive (VSD) 166 and a magnetic bearing controller (MBC) 168 into one cabinet. The VSD allows the electricity generated from the turboexpander 102 to be delivered to the power grid 140 consistently and cleanly. The VSD 166 adjusts the frequency and amplitude of the generated current to match the local power grid. After expansion, the gas leaves the turboexpander 102 along the same axial path for use in downstream processes.

[0036] The turboexpander 102 is shown as having 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. The gas flows into the radial gas inlet 154 and flows to the turbine impeller 104, and flows from the turbine impeller 104 to the axial gas outlet 156. Then, the gas flows through the generator and flows out of the outlet 156, where the gas rejoins the gas pipeline 170. In general, the high-pressure process gas 120 is guided through the flow control system 126 to flow into the turboexpander 102. The flow control system 126 includes a flow control valve or a quality control valve and an emergency shut-down valve. The flow control system 126 can be electrically controlled from the power electronics 118 through the control line 164. In an embodiment, the turboexpander housing 112 is hermetically sealed. As described above, without departing from the scope of the present disclosure, the turboexpander can be a non-flow-through and suspended type. The high pressure process gas 120 is expanded by flowing through the turbine impeller 104, thereby causing the pressure of the process gas to drop. The low pressure process gas 128 leaves the turbo expander. The expansion of the high pressure process gas 120 through the turbine impeller 104 causes the turbine impeller 104 to rotate, which causes the rotor 108 to rotate. The rotation of the rotor 108 in the stator 110 generates electrical energy. The turbo expander 102 achieves the desired pressure drop and captures the energy from the pressure drop to generate electrical energy. A pressure control valve 130 (e.g., a conventional pressure regulator) can be installed in parallel with the turbo expander 102. The pressure control valve 130 can be used to control the pressure of the high pressure process gas 120 flowing through the turbo expander 102. Any excess high pressure process gas that is not directed into the turbo expander can be directed through the pressure control valve 130.

[0037] In some embodiments, the heater 122 may heat the high pressure process gas 120 before the gas flows into 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 at the turbine wheel or other downstream location in the pipeline, the pressurized process gas 120 may be heated by the heater 122. The heated high pressure process gas 124 may then be directed into the turboexpander 102. Heating the process gas may prevent moisture from freezing as the gas expands and the temperature of the gas decreases.

[0038] The turboexpander 102 includes a turbine wheel 104. The turbine wheel 104 is shown as a radial inflow turbine wheel, but other configurations are also within the scope of the present disclosure, such as an axial inflow turbine wheel. In this example, the heated high-pressure process gas 124 is received from the inlet duct 150 of the housing 112 and enters the radially oriented inlet 154 of the turbine wheel 104. In certain embodiments, the fluid flows through the inlet duct 150 and is diverted by the flow diverter to the radial inlet 154, which directs the flow into the radial inlet (mouth) of the turbine wheel 104. After expansion, the low-pressure process gas leaves the turbine wheel 104 from the axially oriented outlet 156 to the outlet duct 152 of the housing 112.

[0039] The turbine impeller 104 can be fixed directly to the rotor 108, or fixed to the intermediate common shaft, such as by fasteners, rigid drive shafts, welding or other means. For example, the turbine impeller 104 can be received at the end of the rotor 108 and is retained to the rotor 108 using an axle. The axle is screwed into the rotor 108 at one end, and the turbine impeller 104 is captured between the end of the rotor 108 and a nut at the other end, and the nut is received on the axle by a thread. The turbine impeller 104 and the rotor 108 can be coupled without a gearbox and rotate at the same speed. In other cases, the turbine impeller 104 can be indirectly coupled to the rotor 108, which is achieved, for example, by a gear train, a clutch mechanism or other means.

[0040] The turbine wheel 104 includes a plurality of turbine wheel blades 106 that extend outwardly from a hub and act with the expanding process gas to cause the turbine wheel 104 to rotate. Figure 1 An unshrouded turbine wheel is shown, wherein each turbine blade 106 has an exposed, generally radially oriented blade tip extending between a radial inlet 154 and an axial outlet 156. As discussed in more detail below, the blade tips are substantially sealed to the shroud 114 within the interior of the housing 112. In some cases, the turbine wheel 104 is a shrouded turbine wheel.

[0041] In the configuration of the turbine wheel 104 without a shroud, the housing 112 includes an inwardly directed shroud 114, which is adjacent to the turbine impeller blades 106 and does not contact the turbine impeller blades 106 for most of the time during operation. As the process gas flows through the turbine impeller 104, the close proximity of the turbine impeller blades 106 to the shroud 114 makes it essentially sealed, preventing the process gas from passing between the two. Although a certain amount of process gas may leak or pass between the turbine impeller blades 106 and the shroud 114, the leakage is not obvious in the operation of the turbine impeller 104. In some cases, using the conventional tolerances between the turbine impeller blades 106 and the shroud 114, the leakage can be comparable to other similar turbine / shroud surface interfaces without a shroud. The amount of leakage that is considered to be an acceptable leakage can be predetermined. The operating parameters of the turbine generator can be optimized to reduce leakage. In some embodiments, the housing 112 is hermetically sealed to prevent the process gas from escaping from the radial inlet 154 of the turbine impeller 104.

[0042] The shroud 114 may be located at a specified distance away from the turbine wheel blades 106 and maintained at the distance away 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.

[0043] The bearings 116a and 116b are arranged to rotatably support the rotor 108 and the turbine wheel 104 relative to the stator 110 and the shroud 114. The turbine wheel 104 is supported in a cantilever manner by the bearings 116a and 116b. In an embodiment, the turbine wheel 104 may be supported in a non-cantilever manner, and the bearings 116a and 116b may be located on the outlet side of the turbine wheel 104. In some 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 bearings.

[0044] The bearings 116a and 116b may be a combination of radial bearings and thrust bearings, supporting the rotor 108 in both radial and axial directions. Other configurations may be used. The bearings 116a and 116b need not be the same type of bearings.

[0045] In an embodiment where the bearings 116a and 116b are magnetic bearings, a magnetic bearing controller (MBC) 168 is used to control the magnetic bearings 116a and 116b. Position sensors 117a, 117b can be used to detect the position or change in position of the turbine impeller 104 and / or rotor 108 relative to the housing 112 or other reference points (e.g., predetermined values). The position sensors 117a, 117b can detect axial and / or radial displacements. The magnetic bearings 116a and / or 116b can respond to information from the position sensors 117a, 117b and adjust the detected displacements if necessary. The MBC 168 can receive information from (one or more) position sensors 117a, 117b and process the information to provide control signals to the magnetic bearings 116a, 116b. The MBC 168 can communicate with various components of the turboexpander 102 via a communication channel 162.

[0046] The use of magnetic bearings 116a, 116b and position sensors 117a, 117b to maintain and / or adjust the position of the turbine wheel blades 106 allows the turbine wheel blades 106 to remain in close proximity to the shroud 114, thereby allowing the turboexpander 102 to operate without seals (e.g., without dynamic seals). The use of active magnetic bearings 116a, 116b in the turboexpander 102 eliminates physical contact between rotating and stationary components and eliminates lubrication, lubrication systems, and seals.

[0047] The turboexpander 102 may include one or more backup bearings. For example, at startup and shutdown or in the event of a power failure that affects the operation of the magnetic bearings 116a and 116b, the bearings may be used to rotatably support the turbine impeller 104 during this time period. The backup bearings may include ball bearings, needle bearings, journal bearings, or similar bearings. As previously described, the turboexpander 102 is configured to generate electrical energy in response to the rotation of the rotor 108. In some cases, the rotor 108 may include one or more permanent magnets. The stator 110 includes a plurality of conductive coils. Current is generated by the rotation of the magnets in the coils of the stator 110. The rotor 108 and the stator 110 may be configured as a synchronous, permanent magnet, multi-phase alternating current (AC) generator. For example, the electrical output 160 may be a three-phase output. In some cases, the stator 110 may include a plurality of coils (e.g., three or six coils for a three-phase AC output). When the rotor 108 rotates, a voltage is induced in the stator coils. At any moment, the magnitude of the voltage induced in the coil is proportional to the rate at which the magnetic field enclosed by the coil changes over time (i.e., the rate at which the magnetic field passes through both sides of the coil). In the case where the rotor 108 is coupled to rotate at the same speed as the turbine impeller 104, the turboexpander 102 is configured to generate electrical energy at that speed. Such a turboexpander 102 is a so-called "high-speed" turbine generator. For example, in an embodiment, the turboexpander 102 can generate up to 280 kW at a continuous speed of 30,000 rpm. In an embodiment, the turboexpander can generate approximately 350 kW at a higher rotational speed (e.g., approximately 35,000 rpm).

[0048] In some embodiments, the design of the turbine wheel 104, rotor 108, and / or stator 110 may be based on desired parameters of the output gas from the turboexpander 102. For example, the design of the rotor and stator may be based on a desired temperature of the gas 128.

[0049] The turboexpander 102 may be coupled to power electronics 118. The power electronics 118 may include a variable speed drive (VSD) 166 (or variable frequency drive) and a magnetic bearing controller (MBC) 168 (as discussed above).

[0050] The electrical output 160 of the turboexpander 102 is connected to a VSD 166, which can be programmed for specific power requirements. The VSD 166 can include an insulated-gate bipolar transistor (IGBT) rectifier to convert the variable-frequency high-voltage output from the turboexpander 102 into a direct current (DC). The rectifier 210 can be a three-phase rectifier for a three-phase AC input current. The inverter then converts the DC from the rectifier into AC to supply the grid 140. The inverter can convert the DC to 380V AC to 480V AC at 50 Hz to 60 Hz for delivery to the grid. The specific output of the VSD 166 depends on the grid and the application. Other conversion values ​​are also within the scope of the present disclosure. The VSD 166 matches the output of the VSD 166 to the grid 140 by sampling the voltage and frequency of the grid and then changing the output voltage and frequency of the inverter to match the voltage and frequency of the sampled grid.

[0051] The turbo expander 102 is also connected to the MBC 168 in the power electronics 118. The MBC 168 continuously monitors position, current, temperature, and other parameters to ensure that the turbo expander 102 and the active magnetic bearings 116a and 116b are operating as desired. For example, the MBC 168 is coupled to position sensors 117a, 117b to monitor the radial and axial positions of the turbine impeller 104 and the rotor 108. The MBC 168 can control the magnetic bearings 116a, 116b to selectively change the stiffness and damping characteristics of the magnetic bearings 116a, 116b according to the rotational speed. The MBC 168 can also control synchronization cancellation, including automatic balancing control, adaptive vibration control, adaptive vibration suppression, and unbalanced force suppression control.

[0052] The pressure reduction system converts shaft power from the process stream. The turboexpander can support islanding operation. In the event that the grid supplying power to a location is interrupted, the turboexpander can continue to provide power to the location. The present disclosure describes components that can help load match the shaft power generated by the process gas stream to the load demand at the pressure reduction station. In this way, the turboexpander can support microgrid functionality for islanding operation.

[0053] The turboexpander 102 described above includes example features specific to the embodiment. Certain features may be changed, added, removed, or redesigned without departing from the scope of the present disclosure. For example, other types of bearings, such as ball bearings, fluid film bearings, etc., may be used instead of or in addition to the AMB. Rotors and stators of different designs may be used, such as brushless DC types, induction types, etc. Other types of stator cooling architectures may be used, such as non-circulation architectures and overhanging architectures.

[0054] Figure 2 is a schematic diagram of an example turboexpander system 200 supporting islanded operation without a grid source according to an embodiment of the present disclosure. The turboexpander system 200 includes the turboexpander 102 as described above.

[0055] The turboexpander system 200 includes a power electronics component 201 for supporting island operation. For example, the turboexpander power converter 202 electrically connects the electrical connection 160 of the turboexpander 102 to the island mode power electronics (PE) 204. The power converter can convert the AC power from the turboexpander 102 into DC, which can be stored in the battery 206 or routed to other places on the DC bus. The turboexpander power converter 202 can convert the AC output of the turboexpander into DC for transmission to the DC bus. In some embodiments, the turboexpander power converter 202 includes a rectifier circuit, which includes electrical components that can convert AC to DC. The DC from the turboexpander power converter 202 is input to the island mode PE 204. The island mode PE 204 can convert DC into AC with a frequency and amplitude compatible with the load 220.

[0056] The load 220 may be an appliance, printer, computer, lighting, telecommunication equipment, HVAC, air filtration system, or other critical system.

[0057] In an embodiment, the island mode PE 204 may include an inverter circuit. The inverter circuit may convert the DC from the turbo expander power converter 202 to AC. The inverter circuit may include, for example, circuit elements that convert the DC to AC with a frequency and amplitude (voltage) compatible with the load 220. The inverter circuit may also support multiple loads with different power requirements and parameters.

[0058] The power electronics 201 may include a battery 206. The battery 206 may be coupled to the turboexpander 102 via the turboexpander power converter 202. The battery 206 may store power output from the turboexpander 102. For example, AC from the electrical connection 160 may be converted to DC by the turboexpander power converter 202 and stored in the battery 206.

[0059] In an embodiment, the battery can facilitate a "dark start" of the turboexpander 102. In the absence of a connected grid as a source of electrical power for the turboexpander, the battery 206 can supply the power required to start the rotor rotation of the turboexpander 102 through the bidirectional electrical connection 160. In some embodiments, the battery 206 can help start the rotor when the process gas begins to flow into the turboexpander inlet. After some time, the process gas flow is sufficient to bring the rotor up to speed, and the battery 206 can be disconnected from the turboexpander bidirectional connection 160. The ability to dark start a turboexpander allows the turboexpander to act as a microgrid without the grid as a source of electrical power.

[0060] The brake resistor assembly 208 is electrically connected to the electrical output 160 of the turboexpander 102 (e.g., the output of a generator). The brake resistor assembly 208 can have a tuned impedance to allow power to be efficiently transferred from the turboexpander 102 to the brake resistor assembly 208. In an embodiment, the brake resistor assembly 208 includes a speed-controlled and current-regulated brake resistor. The brake resistor assembly 208 can receive current (AC) directly from the turboexpander or receive current (DC) through a rectifier circuit 210. The rectifier circuit 210 can convert AC from the turboexpander 102 to DC. A current monitor 212 can be connected in parallel with the rectifier to monitor the current from the turboexpander electrical output 160. In an embodiment, the rectifier circuit 210 includes an active rectifier circuit 210.

[0061] The battery 206 and the brake resistor 208 may mitigate the lag of the turbocharger to provide seamless operation during the application and removal of step loads.

[0062] Load 220 may be any electrical load, including critical loads, at the location served by turboexpander system 200. Critical loads include, but are not limited to, lighting systems, food storage systems, air conditioning / heating systems, communication systems, and other loads considered critical to the location.

[0063] Figure 3 is a schematic diagram of an exemplary turboexpander system 300 including a bidirectional inverter for islanded operation according to an embodiment of the present disclosure. Figure 3 The illustrated embodiment is supported by the grid 140. For the system coupled to the grid 140, the power electronics use a bidirectional inverter system 304 described below. The bidirectional inverter system 304 facilitates powering the turboexpander 102 from the grid 140, and also facilitates directing excess power generated by the turboexpander 102 beyond the load requirements of the load 220 back to the grid 140. In some embodiments, the turboexpander 102 can act as a microgrid or backup power station to supply power to the load 220 if the grid 140 is lost.

[0064] The turboexpander system 300 includes power electronics 302. Figure 2 Similar to the system 200 shown, the turboexpander system 300 includes a turboexpander 102 that can generate electricity from the rotation of a rotor in a stator using, for example, a process gas flow at a pressure reduction station. Also similar to the system 200, the turboexpander system 300 includes a brake resistor assembly 208 coupled to the electrical output 160 of the turboexpander 102. The brake resistor assembly 208 can have a tuned impedance to allow power to be effectively transmitted from the turboexpander 102 to the brake resistor assembly 208. In an embodiment, the brake resistor assembly 208 includes a speed-controlled and current-regulated brake resistor. The brake resistor assembly 208 can receive current (AC) directly from the turboexpander or receive current (DC) through a rectifier circuit 210. The rectifier circuit 210 can convert AC from the turboexpander 102 to DC. A current monitor 212 can be connected in parallel with the rectifier to monitor the current of the electrical output 160 from the turboexpander.

[0065] The power electronics 302 may include a battery 206. The battery 206 may be coupled to the turboexpander 102 via the turboexpander power converter 202. The battery 206 may store power output from the turboexpander 102. For example, AC from the electrical output 160 may be converted to DC by the turboexpander power converter 202 and stored in the battery 206. In an embodiment, the battery may facilitate a “dark start” of the turboexpander 102.

[0066] In an embodiment, the power electronics 302 (and the power electronics 201) may include different types of power storage devices. The power storage device may be charged using AC or DC. The power storage device may typically store power from the turboexpander 102, and in some embodiments, may store power from the grid. In an embodiment, when process gas flow is established during a pressure reduction sequence or other gas flow process, the power storage device may be used to start the rotation of the rotor within the stator of the turboexpander 102.

[0067] To support the use of power from and delivery of power to the grid 140, the power electronics 302 include a bidirectional inverter system 304. The bidirectional inverter system 304 includes an island mode inverter 204 and a grid converter 308. The island mode inverter 204 may receive DC from the turboexpander power converter 202 and convert the DC to compatible AC for the load 220 (or multiple loads).

[0068] The bidirectional inverter system 304 also includes a grid converter 308. The grid converter 308 can direct excess power not used by the load 220 to the grid 140. An active grid inverter can include electrical components that can convert DC from the turboexpander power converter 202 to AC having a frequency and amplitude compatible with the grid 140.

[0069] The grid inverter 308 can also receive AC from the grid and convert the AC from the grid 140 to DC for transmission to the power converter 202 via the DC bus. The power converter 202 can then convert the DC from the grid inverter 308 to AC compatible with the turboexpander 102 to start the rotation of the rotor within the stator during the startup procedure. In an embodiment, the battery 206 can also be charged using power from the grid 140.

[0070] The battery 206 of the turboexpander system 200 can act as an uninterruptible power supply in a similar manner to continue to provide power to the load 220 if the turboexpander 102 fails. Figure 3 In the embodiment of the present invention, if the grid 140 fails, the turboexpander 102 and the battery 206 can supply power to the load 220. If both the grid 140 and the turboexpander 102 fail, the battery 206 can supply power to the load 220. In any case, the island mode inverter 204 can adjust the DC input to simulate the AC power of the grid 140 or the turboexpander 102, thereby seamlessly supplying power to the load 220.

[0071] In any of the above cases, the power supplied by the battery 206 to the load 220 should simulate the grid power provided to the load. Therefore, the island mode inverter 204 includes electronic devices for shaping the power from the battery to simulate the grid power. In this way, even if the grid 140 and the turboexpander 102 fail, the turboexpander system can use the battery 206 to support seamless operation of the load. Similarly, the battery 206 and the grid 140 can be supplied by the turboexpander 102. The electrical components described herein facilitate the ability to supply power to the battery 206 and the grid 140 through the turboexpander 102, while also ensuring that the load 220 continues to receive power during a grid failure and / or a turboexpander failure.

[0072] Furthermore, the battery 206 should have sufficient charge or capacity to supply power to the load 220 for an amount of time to allow the grid 140 or the turboexpander 102 to come back online.

[0073] The main controller 230 can provide power management control to various components, including output voltage shaping, output voltage control, reactive and active load compensation, and other power control features. The main controller 230 can activate, deactivate or otherwise control active rectifiers, inverters, converters, etc., so as to provide power to the correct components based on operating conditions. The main controller can connect and control the turboexpander power converter 202, the island mode inverter 204, the brake resistor 208, the active rectifier 210, and the grid converter 308. For example, a tripped circuit breaker can indicate that the load 220 is lost. In order to prevent an overspeed condition at the turboexpander 102, the main controller 230 can activate the active rectifier 210 to direct power from the turboexpander 102 to the brake resistor assembly 208. After the overspeed or other fault conditions have been resolved, the main controller 230 can also redirect power to the power electronics. For example, if a circuit breaker is tripped at the output of the power electronics, the master controller 230 may route power from the turboexpander 102 to the active rectifier 210 to allow power to be dissipated by the brake resistor assembly 208. After the circuit breaker is reset, the master controller 230 may reroute power from the turboexpander 102 to the power electronics for delivery to the load.

[0074] Figure 4A is a schematic diagram 400 of an exemplary turboexpander converter according to an embodiment of the present disclosure. Figure 4A, the turboexpander 102 is simplified as a three-phase permanent magnet synchronous AC generator 402. Although not shown, a current monitor can be connected in parallel to the brake resistor assembly to monitor the current flowing into the (one or more) brake resistors. A turboexpander power converter 404 similar to the turboexpander power converter 202 is shown. The turboexpander power converter 404 can be used to convert the AC power from the generator 402 to DC power to supply the DC bus. The DC power can be stored in the battery 206, or sent to the island mode inverter 204 or the grid converter 308.

[0075] The turboexpander power converter 404 may also convert DC power from the battery 206 or from the grid converter 308 to AC power to drive the turboexpander during startup operations. The main controller 230 may be used to control the turboexpander power converter 404 to drive current into or out of the generator 402 based on operating conditions. For example, the main controller 230 may receive power management control information that causes the main controller 230 to control the turboexpander power converter 404 to drive current from the battery 206 or the grid 140 to the generator 402 during startup. The main controller 230 may receive power management control information that causes the main controller 230 to control the turboexpander power converter 404 to drive current from the generator 402 to the DC bus to supply power to the battery 206, the grid 140, or the load 220. For example, the main controller 230 may activate a rectifier in the turboexpander power converter 404 based on the presence or absence of a fault condition at the load 220 or the grid 140.

[0076] Figure 4B 4 is a schematic diagram 450 of an exemplary island mode inverter 454 according to an embodiment of the present disclosure. The island mode inverter 454 is similar to the island mode inverter 204. The island mode inverter 454 can change a DC current into an AC current to supply the AC current to the load 220. The island mode inverter 454 can regulate the power output from the island mode inverter 454 to simulate grid power. For example, the island mode inverter can include electrical components for regulating the AC power, including a sine filter 456. The power output to the load 220 is similar to the power provided to the load 220 by the grid 140 or the generator 402, so that if the grid is lost, the load 220 can continue to operate.

[0077] In one example embodiment, the master controller 230 may receive information 458 that signals the master controller 230 to send battery power to the loads via the island mode inverter 454. A tripped circuit breaker may signal that there is a fault on the grid or elsewhere, which causes the master controller to cause the battery 206 to provide power to the loads 220.

[0078] Figure 5 500 is a process flow diagram for using a turboexpander to support islanded operation according to an embodiment of the present disclosure. In some embodiments, a power source may be used to initiate rotation of a rotor within a stator of a turboexpander (502). The power source may be a battery connected to the turboexpander, or an electrical grid connected to the turboexpander. When the process gas flow is accumulating sufficient flow or mass to rotate the rotor at a desired speed to produce a desired output power, the power source may help the rotor reach speed (504).

[0079] The load can be disconnected from the grid. The turboexpander provides power to the load during islanded operation, thereby acting as a microgrid. The turboexpander power electronics may include island mode power electronics (e.g., an island mode inverter) to convert current originating from the turboexpander into current having a frequency and amplitude compatible with the load (506). The output current of the turboexpander may be used to power the load (508). Excess power not used by the load may be output to a battery (or other power storage device) or a grid. If the grid is connected to the turboexpander, an active grid inverter may convert current originating from the turboexpander into current having a frequency and amplitude compatible with the grid.

[0080] Therefore, the description and drawings should be regarded as illustrative rather than restrictive. In addition, the embodiments and other exemplary language used in the foregoing do not necessarily refer to the same embodiment or the same example, but may refer to different and distinct embodiments, as well as to the same embodiment. In the foregoing description, a detailed description has been given with reference to specific exemplary embodiments. However, it is apparent that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present disclosure set forth in the claims.

Claims

1. A device comprising: A generator, comprising: - a process gas inlet configured to be coupled to a process gas line and to receive a high pressure process gas from the process gas line; - a turbine wheel configured to receive a high pressure process gas from the process gas inlet and to rotate in response to expansion of the process gas flowing into an inlet of the turbine wheel and out of an outlet of the turbine wheel, the outlet of the turbine wheel being coupled to a downstream process gas line for conveying a low pressure process gas downstream of the generator; - a rotor coupled to the turbine wheel and configured to rotate together with the turbine wheel; and - a stationary stator, wherein the generator generates an alternating current when the rotor rotates within the stator; a power converter circuit coupled to the electrical output of the generator, the power converter circuit converting alternating current from the generator to direct current; an island mode inverter circuit coupled to the electrical output of the power converter circuit, the inverter circuit for converting direct current from the power converter circuit to alternating current including a frequency and an amplitude to provide power to an electrical load; The generator is connected in parallel to the electrical load and a power grid that supplies power to the electrical load, and the device further comprises: A main controller, the main controller is used for: - determining that the electrical grid is no longer supplying power to the electrical load; and - based on determining that the grid is no longer supplying power to the electrical load, causing the island mode inverter to direct power generated by the generator from expansion of the high pressure process gas received by the process gas line to the load.

2. The device according to claim 1, further comprising: a brake resistor rectifier coupled to an electrical output of the generator; and A brake resistor assembly is coupled to the output of the brake resistor rectifier.

3. The device according to claim 2, wherein: The brake resistor assembly includes a speed controlled and current regulated brake resistor.

4. The apparatus of claim 1 further comprising a battery coupled to the generator, the battery for storing power received from the generator and for providing power to rotate the rotor within the stator.

5. The device according to claim 4, wherein: The battery is coupled to the power converter circuit, the power converter circuit being configured to: receiving alternating current from the generator and converting the alternating current into direct current for storage in the battery; as well as A direct current is received from the battery and converted into an alternating current to power the rotor.

6. The apparatus according to claim 1, comprising a bidirectional inverter, the bidirectional inverter comprising: The island mode inverter circuit; and An active grid inverter is used to convert direct current into alternating current including a frequency and amplitude compatible with a grid.

7. The device according to claim 6, wherein: The bidirectional inverter is used to provide power to the load and to provide surplus power to the power grid.

8. The device according to claim 6, wherein: The bidirectional inverter is used to supply power from the grid to the rotor to rotate the rotor within the stator before the process gas rotates the turbine wheel.

9. The device according to claim 1, wherein: The island mode inverter circuit comprises a circuit, wherein: receiving direct current on a DC bus; converting the direct current into an alternating current; as well as The alternating current is adjusted to a frequency and amplitude compatible with the load.

10. The apparatus of claim 1, further comprising a main controller circuit for controlling current flow to the brake resistor during a fault condition.

11. The apparatus of claim 10, further comprising an active rectifier electrically connected between the generator and the brake resistor, the master controller activating the active rectifier upon detecting the fault condition to direct current from the generator to the brake resistor based on the presence of the fault condition.

12. The device according to claim 1, wherein: The generator comprises a three-phase permanent magnet synchronous generator.

13. A method comprising: receiving high pressure process gas from a process gas line into an inlet of a turbine wheel of a generator located downstream of a flow control valve of the process gas line, the generator being coupled in parallel to an electrical load and a grid supplying electrical power to the electrical load; causing the high pressure gas to flow through the turbine wheel of the generator, wherein the flow of the high pressure gas through the turbine wheel causes a rotor coupled to the turbine wheel to rotate within a stator of the generator and causes the high pressure gas to expand; generating electric current by rotation of the rotor within the stator of the generator; directing the expanded process gas from an outlet of the generator to a downstream portion of the pipeline; directing current generated by the generator to island mode power electronics; determining that the power grid has stopped providing power to the electrical load; as well as Based on determining that the grid has ceased providing power to the electrical load, current is directed from the island mode power electronics device to the electrical load.

14. The method according to claim 13, comprising: Excess current generated by the generator but not directed to the load is directed to the grid via an active grid inverter.

15. The method according to claim 14, comprising: Starting of the generator is performed using power received from the grid via the active grid inverter.

16. The method according to claim 13, comprising: Excess current generated by the generator but not directed to the load is directed to a battery.

17. The method according to claim 16, comprising: Starting of the generator is performed using power received from the battery.

18. A system comprising: A generator, comprising: - a process gas inlet configured to be coupled to a process gas line and to receive a high pressure process gas from the process gas line; - a turbine wheel configured to receive a high pressure process gas from the process gas inlet and to rotate in response to expansion of the process gas flowing into an inlet of the turbine wheel and out of an outlet of the turbine wheel, the outlet of the turbine wheel being coupled to a downstream process gas line for conveying a low pressure process gas downstream of the generator; - a rotor coupled to the turbine wheel and configured to rotate together with the turbine wheel; and - a stationary stator, wherein the generator generates an alternating current when the rotor rotates within the stator; and A power electronic device system, the power electronic device system comprising: - a power converter circuit coupled to the electrical output of the generator, the power converter circuit for converting alternating current from the generator into direct current; and - an island mode inverter circuit coupled to the electrical output of the rectifier circuit, the inverter circuit for converting direct current from the rectifier circuit into alternating current including frequency and amplitude for providing power to an electrical load; The power electronic device system is connected in parallel to the electric load and a power grid that supplies power to the electric load, and the power electronic device system further comprises: A main controller, the main controller is used for: - determining that the electrical grid is no longer supplying power to the electrical load; and - based on determining that the grid is no longer supplying power to the electrical load, causing the island mode inverter to direct power generated by the generator from expansion of the high pressure process gas received by the process gas line to the load.

19. The system of claim 18, further comprising a bidirectional inverter for directing current to the load and directing excess current to a grid.

20. The system according to claim 19, wherein: The bidirectional inverter includes an active grid inverter for directing power to the grid and receiving power from the grid.

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