SYSTEM FOR GAS COMPRESSION ON ELECTRIC HYDRAULIC FRACTURING FLEETS
1. A method of providing electric power to hydraulic fracturing equipment, the method comprising:
- releasing a natural gas stream from a main gas line to a turbine gas line, the turbine gas line including one or more natural gas turbine generators;
reducing a natural gas stream pressure so that the natural gas stream pressure is within an optimum pressure range for use in a natural gas compressor;
compressing the natural gas stream using the natural gas compressor so that the natural gas stream pressure is within an optimum pressure range for use by the one or more natural gas turbine generators;
combusting natural gas from the natural gas stream in the one or more natural gas turbine generators to generate electric power; and
providing the electric power to an electric motor to power hydraulic fracturing equipment.
Embodiments relate to hydraulic fracturing equipment powered by one or more natural gas turbine generators. Natural gas from a supply line is released via a valve into a turbine gas line. The turbine gas line includes one or more regulators to reduce the pressure of the natural gas stream in the turbine gas line to a pressure or pressure range optimum for one or more gas compressors. The gas compressors increase the pressure of the natural gas stream, which is then directed to one or more natural gas turbine generators. The natural gas turbine generators combust the natural gas to produce electricity, which powers electric hydraulic fracturing equipment.
- 1. A method of providing electric power to hydraulic fracturing equipment, the method comprising:
releasing a natural gas stream from a main gas line to a turbine gas line, the turbine gas line including one or more natural gas turbine generators; reducing a natural gas stream pressure so that the natural gas stream pressure is within an optimum pressure range for use in a natural gas compressor; compressing the natural gas stream using the natural gas compressor so that the natural gas stream pressure is within an optimum pressure range for use by the one or more natural gas turbine generators; combusting natural gas from the natural gas stream in the one or more natural gas turbine generators to generate electric power; and providing the electric power to an electric motor to power hydraulic fracturing equipment.
- View Dependent Claims (2, 3, 4, 5)
This application is a divisional of U.S. patent application Ser. No. 15/356,436, filed Nov. 18, 2016, titled “SYSTEM FOR GAS COMPRESSION ON ELECTRIC HYDRAULIC FRATURING FLEETS,” which claims priority to U.S. Provisional Patent Application Ser. No. 62/258,055, filed Nov. 20, 2015, the full disclosures of which are hereby incorporated by reference herein for all purposes.
The present disclosure relates to operations in a subterranean formation. In particular, the present disclosure relates to a hydraulic fracturing system.
Hydraulic fracturing is a technique used to stimulate production from some hydrocarbon producing wells. The technique usually involves injecting fluid into a wellbore at a pressure sufficient to generate fissures in the formation surrounding the wellbore. Typically, the pressurized fluid is injected into a portion of the wellbore that is pressure isolated from the remaining length of the wellbore so that fracturing is limited to a designated portion of the formation. The fracturing fluid slurry, whose primary component is usually water, includes proppant (such as sand or ceramic) that migrate into the fractures with the fracturing fluid slurry and remain to prop open the fractures after pressure is no longer applied to the wellbore. Other than water, potential primary fluids for the slurry include nitrogen, carbon dioxide, foam (nitrogen and water), diesel, or other fluids. The fracturing slurry may also contain a small component of chemical additives, which can include scale build up inhibitors, friction reducing agents, viscosifiers, stabilizers, pH buffers, acids, biocides, and other fluid treatments. In embodiments, the chemical additives comprise less than 1% of the fracturing slurry.
Powering hydraulic fracturing equipment is typically done with diesel engines. These and other internal combustion engines create safety issues, such as fire hazards, and produce pollution, including both noise and environmental pollution. Thus, there is a need for systems and methods of powering electric generators for use with hydraulic fracturing equipment.
The aforementioned problems and others are solved with the disclosed systems and methods to provide electric power to hydraulic fracturing equipment using natural gas turbine generators fueled by natural gas from the supply line of a fracturing line. In embodiments, systems can include a valve to control the release of a natural gas stream from a main gas line into a turbine gas line. The valve can include an open and closed position, or a number of intermediary positions. When the valve is closed, natural gas continues through the main supply line. When it is open, or partially open, natural gas enters the turbine gas line. The turbine gas line supplies natural gas to the natural gas turbine generators after various stages of processing.
For example, a sand trap can remove sand and other particulates from the natural gas stream, and a separator can remove water and other liquids from the natural gas stream. The natural gas stream can be directed to one or more compressors. It may be the case that gas leaves the main supply line and enters the turbine gas line at pressures that would cause damage to the compressors. A regulator in the turbine gas line can effect a pressure drop to bring the pressure of the natural gas to a pressure range that is optimum for the compressors. The optimum pressure range can be determined and set based on the specifications of the compressors and other equipment used, environmental conditions, and other factors.
In embodiments, a pressure regulator skid is used to decrease the pressure of the natural gas before it enters the compressors. The pressure regulator skid can include a system of internal valves and regulators. For instance, the pressure regulator skid can include multiple branches through which natural gas can flow. In embodiments, the pressure regulator skid includes three branches. Each branch can include an initial valve to permit or deny the flow of natural gas through that branch. Each branch can then include its own regulator downstream from the valves to independently adjust the pressure of the natural gas stream in that branch. In embodiments, additional valves can be included in one or more of the branches downstream from the regulators. Thus, individual branches can be sealed off in the event of a leak in that branch without entirely shutting down the flow of natural gas.
After the pressure of the natural gas stream decreases, the natural gas stream is routed to one or more compressors. In embodiments using more than one compressor, a compressor inlet manifold can be used to ensure natural gas is distributed evenly amongst the multiple compressors. The compressor inlet manifold can accept the natural gas stream via one or more intakes and split the stream into sub-streams corresponding to each compressor. The sub-streams may not necessarily have exactly the same volumetric flow rates or mass flow rates, but the natural gas stream will be distributed so that each compressor receives approximately the same intake of natural gas. The compressors then increase the pressure of the natural gas in their respective sub-streams.
A compressor outlet manifold can merge the sub-streams in appropriate cases. For example, a number of natural gas turbine generators will be positioned downstream from the compressors. If a compressor sub-stream were aligned one-to-one with a natural gas turbine generator, then failure of that compressor would lead to an unutilized, though otherwise operational, turbine generator. Instead, the compressor outlet manifold accepts all sub-streams from the compressor. Then, the merged stream can be directed, for example, to a second sand trap or separator. In embodiments, the stream can be divided again for an appropriate number of turbine generators. For example, two sub-streams for two compressors can be divided into four sub-streams for four turbine generators. If one compressor fails, its associated sub-stream will terminate, but the other sub-stream can still be divided amongst the four turbine generators.
In embodiments, gas discharged from the compressors can be routed to one or more filtration units. A filtration inlet manifold can similarly accept a merged stream from the compressor outlet manifold and divide the merged stream to multiple filtration units downstream from the compressors. The filtration units can remove additional particulates and liquids from the natural gas stream. Each filtration unit can have downstream from it a natural gas turbine generator, which combusts natural gas from the natural gas stream to generate electric power for electric hydraulic fracturing equipment. For example, the electric power can power an electric motor, which drives a pump that pumps hydraulic fracturing fluid into a well formation.
In embodiments, the compressors are mobile. For instance, they can be disposed on compressor trailers that can be brought to and removed from a fracturing site. The compressor trailers can carry additional equipment as well. For example, the compressor trailers can carry their own regulators to decrease the pressure of natural gas entering the compressors. Likewise, one or more additional sand traps and separators can respectively remove particulates and liquids from the natural gas streams entering the compressors. Such equipment can also operate on the exit streams from the compressors. That is, the trailers can include, for example, a separator downstream from the compressors that remove liquids from the compressor discharge streams.
In embodiments, a heating element can be included, either on the compressor trailers or elsewhere in the process. The heating element can supply heat to the natural gas stream to prevent the natural gas stream from condensing. In embodiments, the filtration units downstream from the compressors and upstream from the natural gas turbine generators act as heating elements as well, supplying heat to the natural gas stream before the stream reaches the turbine generators.
In an embodiment system, a natural gas source can provide a natural gas stream to a turbine gas line. The natural gas source can be a natural gas supply line of a hydraulic fracturing site. As described above, a valve can selectively permit natural gas to enter a turbine gas line from the natural gas supply line, or main supply line. In embodiments, the natural gas source is a fuel storage vessel. One or more fuel transport vehicles can deliver natural gas, including for instance liquefied natural gas, to a hydraulic fracturing site. A fuel transfer manifold can route the natural gas to the fuel storage vessel. From there, a fuel storage valve, when in the open position, can permit natural gas from the fuel storage vessel to enter the turbine gas line.
As noted, in embodiments, liquefied natural gas can be supplied from the natural gas source. A vaporization skid downstream from the natural gas source in the turbine gas line can vaporize the liquefied natural gas, thus converting it to a gaseous state suitable for processing by the one or more compressors. Thus, the compressors downstream from the vaporization skid will receive a gas, rather than a liquid. As discussed above, embodiments can include heating elements to supply heat to the natural gas stream. The heat can prevent the natural gas stream from condensing back into liquid. Or, in case liquefied natural gas is not the input, the heat prevents liquid from forming in the first instance.
Regardless of the input state of the natural gas, it will reach a natural gas compressor in a gaseous state. The natural gas compressor is configured to receive the gas at a first pressure and discharge the gas at a second, higher pressure. A pressure regulator skid and other equipment upstream from the natural gas compressor can ensure that the first pressure—the pressure of the natural gas stream when it enters the compressor—is within an optimum range for operation of the natural gas compressor. The compressor can then increase the pressure of the gas to put the pressure of the gas stream in an optimum range for operation of a natural gas turbine generator downstream.
A filtration unit downstream from the natural gas compressor can remove particulates, liquids, or both from the natural gas stream to provide an additional filtering step before the natural gas stream reaches a natural gas turbine generator. The turbine generator can then combust the natural gas stream to generate electricity. In embodiments, the produced electricity powers an electric motor, which drives hydraulic fracturing equipment, such as a pump.
Methods according to various embodiments can include releasing a natural gas stream from a main gas line to a turbine gas line. The turbine gas line can include equipment to process the natural gas stream and route the natural gas stream to one or more natural gas turbine generators. Embodiments further include reducing the pressure of the natural gas stream so that the pressure is within an optimum range for use in a natural gas compressor.
The natural gas stream can then be compressed in a natural gas compressor so that the natural gas stream pressure is within an optimum pressure range for use by the one or more natural gas turbine generators. The natural gas stream can then be combusted in the one or more natural gas turbine generators to generate electric power, which is then provided to an electric motor to power hydraulic fracturing equipment.
Example embodiments further include removing particulates and liquids from the natural gas stream. These steps can occur upstream from compressors, downstream from compressors, or both. Likewise, the natural gas stream can be heated at various stages of the process to prevent the natural gas stream from condensing. If the gas stream does condense, separators can be used to remove liquids. In certain embodiments, liquefied natural gas is used as an input to the process. A vaporization skid can be used to vaporized the liquefied natural gas stream upstream from the natural gas compressor(s) so that the natural gas compressor(s) receive natural gas in a gaseous state.
Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude.
It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.
Described herein are embodiments of systems and methods that allow turbine generators to utilize field gas (natural gas from a wellhead) as a fuel source. Most well sites have a natural gas line, sometimes called a sales line, main line, or main gas supply line. In embodiments, natural gas from the sales line is accepted by one or more mobile compressors. From the compressors, the natural gas, at an elevated pressure post-compression, is fed to one or more natural gas turbine generators to provide electricity to a fleet of electric hydraulic fracturing pumps (“Clean Fleet”). The turbine generators require a fuel source to create three phase electrical power. Field gas from the sales line provides such a fuel source. Field gas is processed prior to use by the turbines. In embodiments, gas from the sales line is treated offsite as part of its preparation for sale to residential and consumer markets. However, processing can occur at various stages before gas is used by the turbines. Processing includes compressing the natural gas input to a pressure and flow rate suited for use by the turbine(s). Compressors for pressurizing the gas upstream of the turbine generators can be powered by electricity or internal combustion engines. The gas can also be further conditioned by coarse and fine particulate filters, condensate filters, or water separators. Once the turbines are running properly, they are essentially a small power plant and it is more economical, cleaner, and quieter to run as much equipment as possible from this electricity.
A black start generator (“BSG”) can be used to initially power the compressors and the electronic equipment rooms (“EER”) before the turbines are used for electricity. Each turbine can have its own EER, which will include breakers, fire suppression, instrumentation, and controls for the turbine engine and generator. The BSG can be powered by diesel, natural gas, or other hydrocarbon based combustible fuel. Before the turbines are running and producing electricity, this generator can be used to provide power to the compressors so they can provide natural gas to the turbines. Once the turbines are started and running steadily the compressors can be powered by the turbines, and the black start generator may no longer be needed, thus making the process completely independent of diesel fuel and self-sustaining from a power generation perspective. Also included in the present disclosure is the use of a make-before-break uninterrupted power transfer switch to seamlessly switch the power supply from black start power to turbine power once the turbines are running properly and producing electricity. The power supply transfer is initiated when the three phases are synchronized, which avoids severe damage to the equipment. The switch is also HOA (hand-off-auto) allowing seamless switching of the power supply for the compressors from the black start generator to the turbine generator. An HOA allows changing from black start power to turbine power after the turbines are running properly and producing electricity. In an example, the HOA does not interrupt the power supply and will not cause the compressors to shut down. That is, the compressors seamlessly switch power sources. After the compressors are being powered by the turbines only, the black start generator is no longer needed and can be shut down. The three modes of this switch are 1) hand, where the transfer and sync occurs manually; 2) off, where no transfer occurs; and 3) auto, where the transfer and sync occurs automatically.
In an example where electrically powered compressors are used, the compressor'"'"'s onboard power voltage is the same as the voltage used for the compressor motor starter. An example compressor design employs 480V three phase power for the electric motor, and for the onboard electronics and small motors. Other embodiments could include other voltages such as 600 V. The same voltage for compressor power can be used as is used on the turbine Motor Control Center (480V). Other embodiments could include using other voltages such as 600 V, or pulling the 600V from the transformers supplying 600V power to the oilfield equipment.
Optionally, PLCs (programmable logic controllers) and/or RIOs (real-time input/output controllers) can be used to monitor, record, and control the sensor information and processes of the compression units. These controllers help automate the gas compression system while relaying critical information to operators via an HMI (human machine interface) screen on the compression units, in a data van, or in the turbines. The information can be relayed using Ethernet communications. As further elaborated below, example networks utilize Ethernet switches placed on key equipment throughout the fleet to create a robust network.
In an embodiment, controls are provided, such as in the data van (control center of the entire frac site), so that a shutdown command can be initiated for deactivating the compressors. In conjunction with the shutdown command, flaps can optionally be engaged to block a feed of ambient air to one or more of the internal combustion engines that drive the compressors. Without an oxygen source the engines cannot operate, and failure of the engines turn deactivates the compressors. By blocking ambient air, the flaps provide an added safety measure because during a natural gas leak cold compression engines could continue to operate even after an ignition switch is closed or if fuel is no longer supplied to the engine. If the ambient air has a high enough content of natural gas to support combustion, the motor can potentially still run even if the resident fuel supply is stopped. Closable intake air flaps are employed to ensure that the engine shuts down in any emergency. For electric powered compressors, the system disconnects the electrical power, instantly shutting down the compressors.
The circuit breakers on the switchgear can open also ensuring that electrical power is not supplied to the working oilfield equipment. The fire suppression system in the compression units can include its own dedicated 120V power supply. This ensures that even in the event of a power loss from the turbines, which is likely in the event of a fire, there will still be power to the compressors for the fire suppression system only.
In the event of a fire in any turbine, the compressors which are providing fuel can automatically shut down to help suppress and control the fire and prevent the fire from spreading. Inlet and outlet valves will also be automatically closed to isolate the main gas line from the gas compression and power generation equipment. The signal can instantly cut power to the electric motor which will stop the flow of gas to the turbines shutting them down. An enclosed housing on the compression unit mitigates noise from the engine, compressor, and associated machinery. The housing also allows the use of a fire suppression system. With an enclosed environment, any fire can be automatically detected enabling the fire suppression system to replace all of the oxygen within the enclosure with a fire suppressant. The final filtration and heating units can also vent all gas trapped in the lines to atmosphere to prevent the gas lines, filters, manifolds, and separators from being fire and explosion hazards. This venting further ensures that the turbines shut down faster and that the gas lines to not add fuel to any ground level fire. In embodiments, the outlet for this emergency purge is located above the bottom of the filtration units, (e.g. about eight feet above), which is often set on the deck of a trailer. The location of the outlet here helps prevent vented gas from adding to any fire.
Noise insulation can be included on the enclosed housing on the compression units to mitigate noise. Composite noise insulation (different types of noise insulation) can be included on the compression units to mitigate noise of various frequency bands. An inner reflective noise insulation can be used to reflect noise from the compressors. The use of an outer absorbent noise insulation can absorb noise that passes through the reflective layer of insulation on the fuel compressors. In an example, a suction fan is included with the fan exhaust pointed up to help mitigate noise from the cooling package fan. An enclosure air inlet and outlet on the gas compression can provide further noise mitigation, by providing both insulation and a non-straight path for any noise produced.
One or more final filtration units can heat gas, e.g. 50 degrees over the gas dew point, can prevent dropout before the gaseous fuel hits the turbine blades. Heat trace can also be used on the fuel lines. Insulation and heat trace can be applied to the drain lines to prevent freezing during cold weather operations; and insulation and/or heating can be added to pressure regulation valves to prevent freezing during cold weather operations. In certain multiple compressor embodiments, the use of a common separator and/or manifold can ensure that all compressors can feed gas to all turbines on site.
Electric gas compression units can operate on 480V of three phase power. The requisite voltage can be supplied by the electronic equipment room (EER) once the turbine is running. In embodiments, the motor starter is external and each compressor can supply over 2,000 Mcf per day at maximum capacity. In embodiment electric fracturing fleets, compression units use natural gas fueled internal combustion engines to power the compressors to provide natural gas to the filtration skids and in turn to the turbines. These do not require a black start generator as they are not electrically driven.
In embodiments, gas can be transmitted using flexible four inch diameter steel braided hoses. In embodiments, gas can be transmitted via as 2″ steel braided flexible hoses, 2″ hardlines, and 4″ hardlines. Installing flexible lines saves time during rig in, and reduces the probability of leaks that could occur from hammer union style pipe and from angled or swiveling pipe. The flexible lines are also easier to route, and provide more line routing options. The drain lines can also be flexible, e.g. 2″ diameter, steel braided hose. The drain lines can also be insulated and heat traced to avoid having the liquid freeze during the winter. Pressurized gas from the compressors (or elsewhere) can be used to clear the drain lines.
In addition, pressure regulators can be insulated and/or heat traced to avoid freezing during winter application. In embodiments, entire lines can be insulated. Glycol heaters can also be used to prevent lines from freezing. Furthermore, methanol or other compounds can be injected into the lines during freezing conditions to help thaw the system. In embodiments, multiple sets of pressure regulators can be used to drop the pressure in multiple steps to help prevent valves from freezing.
Sand traps, three phase separators, and final filtration units typically collect water, condensate, and solid particulates. In order to clear these unwanted contaminants from the system, a drain line is connected. This drain line allows for open collection reservoirs on the various filtering vessels, and allows for the dump of the contaminates into the drain line. The drain line can then be pressurized by the natural gas line so that the contaminates are blown back to the well owner through the well owner'"'"'s drain line for larger natural gas distribution and compression system. This system allows for nonstop operating of filtering vessels and prevents any flammable liquids or gases from being exposed at the well site. In embodiments, the diameter of the drain line size is 2″. This line returns unwanted liquids to the well owner. High pressure, such as 350 psi, is used to pressurize the holding vessels on the filtration units, and the liquids are then purged back to the main line to be captured by associated processing equipment. If sales quality gas is used, there will typically be very little liquid returned. Alternatively, unwanted liquids and particulates can be drained into plastic totes instead of using a drain line. The plastic totes can then be disposed when full. One advantage of using drain lines instead of totes is to avoid storing flammable liquids onsite.
A number of example schematic diagrams are provided illustrating potential arrangements of compressors, turbines, and associated components for systems and methods to supply natural gas from a sales line to natural gas turbines for powering an electric hydraulic fracturing fleet.
Gas leaving the main supply line 102 typically has a pressure of between 60 psi and 180 psi, though the pressure can be higher, such as 400 psi. At very high pressures, such as 3000 psi, a regulator may be installed in the main supply line itself to effect a pressure drop before gas leaves the line. In an embodiment, the regulator 106 maintains pressure to the compressor inlet at around 100 psi. Thus, the regulator 106 can effect a pressure drop if the incoming gas pressure is greater than 100 psi. The maintenance pressure can be selected based on ground conditions, and the regulator 106 can be configured to maintain pressure at that level. Downstream from the regulator 106, gas is fed to a compressor 108. The compressor 108 compresses the gas it receives, thus increasing the pressure of the gas in the line. At the compressor discharge, gas pressure can be elevated up to around 300 psi; however, in embodiments, the turbines safely handle fuel at a pressure of 150 psi to 380 psi. As with the regulator 106, the compressor 108 can be configured to discharge gas at a desired pressure or range of pressures, based on the conditions on the ground and/or the natural gas turbine generators 112 being used. In embodiments, the compressor 108 is powered by electricity, which further decreases overall emissions and noise pollution and brings the entire process closer to being powered by turbine-produced electricity. In embodiments, the incoming gas pressure from the main supply line can be high enough to supply the turbines directly. However, when the turbines reach a higher load, the supply pressure decreases as extra gas volume is drawn from the line, which causes the turbines to shut down. Additionally, many supply lines are inconsistent and fluctuate between higher and lower pressure, regardless of the fuel demand of the turbines. Thus, compressors ensure a reliable stream of gas at a consistent pressure for operation of the turbines, which avoids costly well damage and downtime.
In the example embodiment of
A compressor inlet manifold 214 can receive gas that exits the pressure regulator skid 206. The compressor inlet manifold 214 can evenly distribute the gas stream it receives, such that each of multiple compressors 218 receives a portion of the gas stream. Parallel regulators 216 can regulate the pressure of gas entering each respective compressor 218. Thus, the pressure of the gas stream entering each compressor 218 can be individually raised or lowered as appropriate even if the compressor inlet manifold 214 unevenly distributes gas to each compressor 218. Gas leaving the compressors 218 can exit via a compressor outlet manifold 220, which ensures that the multiple incoming streams in the illustrated embodiments are merged and directed to a series of gas filtration units 222. This manifold ensures that every natural gas turbine generator 224 receives a consistent flow of natural gas regardless of whether one or more compressors 218 fail. For example, if Compressor 1 fed natural gas directly to Turbine 1, then the failure of Compressor 1 would render Turbine 1 inoperative. Using one or more manifolds, the failure of any one compressor 218 does not prevent the natural gas turbine generators 224 from continuing to operate by receiving natural gas that passes through other compressors. Separate filtration units 222 can be provided for each natural gas turbine generator 224. The filtration units 222 can catch liquids, such as water and condensate (i.e. flammable natural gas liquids), as well as solids, such as sand.
As noted above, the compressor units 218 (Compressors 1-3) can use a natural gas fueled combustion engine to power the compressor. Other embodiments include using a diesel fueled engine, gasoline engine, dual fuel engine, or electric motor to power the compressor. An advantage of using the regulators 216 to reduce the pressure of the feed to the compressor units 218 is that a wider range of gas pressures can be accommodated. For example, the pressure regulator skid 206 can be used to achieve a first pressure drop, and the one or more regulators 216 immediately upstream from the compressors 218 can be used to achieve a second pressure drop. Moreover, regulating the gas pressure upstream of the compressors 218 protects the compressor components. In one example, gas pressure regulation is performed in two steps, which allows for separate and sequential pressure drops, which can help prevent valves from icing or reaching a critical pressure drop, thus damaging the valves.
In addition, a compressor inlet manifold 512 can split the gas stream to direct gas to multiple compressors 516, each of which can include an associated regulator 514. The gas stream can be merged at a compressor outlet manifold 518, and the merged stream can be directed to a second three phase separator 520, from which the gas stream can be directed to a filtration inlet manifold 522. In the illustrated embodiment, the filtration inlet manifold 522 splits the gas stream in two, and the two streams are directed to separate gas filtration trailers 524a, 524b, each of which can have one or more filtration units. The streams from the first gas filtration trailer 524a can be directed to one or more natural gas turbine generators 526a, and the streams from the second gas filtration trailer 526b can be directed to separate natural gas turbine generators 526b.
The aforementioned black start generator can be used to power the compressors 516 before the turbines 526a, 526b are producing electricity. Gas pressure as low as 35 psi can be compressed to over 400 psi by these compressors 516. However, if pressure is that low, they may not be able to provide the required gas volume to the turbines. In an example, if pressure coming out of the compressors 516 is over 380 psi the turbines 526a, 526b will automatically shut down to prevent damage. Due to this, inlet pressure can be regulated to around 100 psi and outlet pressure can be set at around 300 psi. When the gas reaches the natural gas turbine generators 526a, 526b, the gas flows into the turbine inlets for use in a multi stage combustion chamber to rotate a three phase electric generator. These electric compression units can be a viable option wherever gas compression is required for electricity generating turbines. This is especially true on Clean Fleet hydraulic fracturing fleets where low noise and low emissions are of high importance.
An advantage of the system of
The natural gas being provided to the compressors and gas compression system can be from a pipeline (sales line, main gas line, producing wellhead) or it can be shipped to the well site via tankers as LNG (liquid natural gas) or CNG (compressed natural gas). As shown fuel transport vehicles 802 provide fuel to a fuel transfer manifold 804, which routes gas to a fuel storage vessel 806. A valve 808 and regulator 810 can then control the flow of natural gas to the vaporization skid 812 and other downstream components. Other gaseous or liquid fuels can be used as well. In an example, the amount of filtration largely depends on the quality of natural gas that the well owner can provide. If the gas is expected to contain large amounts of water, three phase separators can be added, starting at one, and adding more anywhere in the gas lines as needed. If the natural gas is unfiltered and will contain sediments, one or more sand traps can be added to capture the particulates to prevent them from reaching the turbines. Each turbine can also have a specialized filtration unit that is able to clean out finer particles as well as any water or condensate that is still in the gas. However, if the natural gas is cleaned and pre-filtered enough from the well owner, it is possible to omit them from the layout of the gas compression system.
It is also possible to bypass the compressors 822 in certain conditions. For example, if the gas pressure flowing from the main line is above 150 psi and holding steady, the turbines 832a, 832b would be able to use the natural gas straight from the line. However any fluctuation in pressure could cause the turbines to shut down, and it may not be a reliable solution. The compressors, filtering units, three phase separators, sand traps, and regulation skids can be skid mounted, trailerized, or bodyload units. For the purpose of clarification, the gas manifolds 804, 818, 824, 828 are shown separate from the equipment in
In embodiments, an electric starter for the motor can be integrated into the compressors 822, or it can be mounted externally with power cables connecting it to the unit. It can be externally mounted into the EER (electronic equipment room) or auxiliary unit. With the motor starter mounted on the compression unit 822 itself, one set of three phase power cables can be connected to the unit. If the starter is external to the unit, in the EER for example, there could be two sets of power cables running to the unit; power for the motor from the starter, and power for onboard electronics and small motors.
In the fueling system, the connectors can be of different sizes and flange ratings, some of which include 4″ 300# RF Flanges. Adaptors can be used to couple together different sized/type connectors to make up connections between pieces of equipment and to assemble the system. In an example, supply side connectors could be 4″ 300# RF Flange, thereby allowing connection between braided stainless steel hoses. Also, multiple sections of hose can be used to add lengths, instead of having a single braided hose between each section. One example of a segment length of hose is a length of 20 feet.
Fire Stop analog signal cables from the turbines 920a, 920b, 920c, 920d to shut down the compressors 918a, 918b in the case of a turbine fire are represented by single headed arrows. These signal cables shut down the compressors if the turbines 920a, 920b, 920c, 920d detect a fire, so fuel will not be continuously pumped into the fire. The Fire Stop analog signals are directed from Turbine 1 920a to Gas Compressor 1 918a, from Turbine 2 920b to Gas Compressor 1 918a, from Turbine 3 920c to Gas Compressor 2 918b, and from Turbine 3 920c to Gas Compressor 2 918b. The Fire Stop analog signal of
Still referring to
Auxiliary Trailer 1 904, Auxiliary Trailer 2 906, Gas Compressor 1 918a, Gas Compressor 2 918b, Turbine 1 920a, Turbine 2 920b, Turbine 3 920c, Turbine 920d, and data van(s) 902 can all contain Ethernet switches to create a single communications network. In the example of
The information relayed through the network of
Incorporated onto the same trailer as the compressors can be the gas pressure regulators, sand traps, water separators, and gas filtration components, all described in more detail herein. These components can be added before the gas inlet and/or after the gas outlet of the compressor for pre-compressed and post-compressed filtering of the natural gas. The voltage transformer for the power supply can have several different configurations including being on the unit itself or external and being connected by DLO (diesel locomotive cables). Overhead power lines can also be used such as All Aluminum Alloy Conductor (AAAC), All Aluminum Conductor (AAC), Aluminum Conductor Steel Reinforced (ACSR), Aluminum Conductor Steel Supported (ACSS), Aluminum Conductor Alloy Reinforced (ACAR), Aluminum Conductor Composite Reinforced (ACCR) or Aluminum Conductor Composite Core (ACCC). This can be a stand alone transformer (skidded, trailerized, body mounted), a transformer that is part of a turbine, an EER (electronic equipment room), or auxiliary unit such as the one designed to run the electric frac blender. The compression unit can be designed to be powered from a 120V, 208V, 240V, 277V, 480V, 600V, 4,160V, 13.8 kV, or any other common three phase AC electric supply in either a wye or delta transformer configuration. It could also be powered from a single phase or DC power supply. The electric motor can be an AC induction motor (asynchronous motor) in either a squirrel cage rotor or wound rotor configuration, a synchronous motor which can be self-excited or directly excited (like permanent magnet motors), or a DC motor that contains either brushes or is brushless. Steel braided hoses or rigid iron pipe could be used to contain and transport natural gas between components of the compression system.
The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.