KR20140112496A - System and method for producing a liquefied hydrocarbon stream and method of operating a compressor - Google Patents

Abstract

At least a portion of the fluid is compressed by a compressor driven by an electric motor. The compressor includes variable inlet guide vanes capable of adjusting the angle. The electric motor is powered using a power supply network, and a signal indicative of conditions of the power supply network is monitored. From the signal, the signal is compared with a preset reference to automatically determine if additional load interruption is required. The variable inlet guide vane angle is automatically adjusted when the criterion is met and additional load blocking is required. This automatically reduces the load on the compressor. The compressor and the method of operating it may be used as part of an apparatus for producing a liquefied hydrocarbon stream and / or for producing a liquefied hydrocarbon stream, wherein the compressor is a refrigerant compressor and the fluid is a refrigerant fluid.

Description

TECHNICAL FIELD The present invention relates to a liquefied hydrocarbon stream producing apparatus and method, and a method of operating a compressor.

In one aspect, the invention is directed to a method of making a liquefied hydrocarbon stream.

In a second aspect, the invention relates to an apparatus for producing a liquefied hydrocarbon stream.

In yet another aspect, the present invention relates to a method of operating a compressor.

A common liquefied hydrocarbon stream in the industry is liquefied natural gas (LNG), which is obtained by liquefying the natural gas stream. Liquefaction of natural gas is required for many reasons. For example, natural gas can be stored more easily in the form of LNG than it is in a gaseous state, and can be transported over a long distance, because it is LNG and it is not necessary to store it at high pressure.

US Prior Art Patent Application Publication No. 2010/0257895 discloses all electrical LNG plants that produce LNG, wherein a compressor in the form of a refrigerant compressor is employed to cool the natural gas. The refrigerant compressor is driven by an electric motor. Power is supplied from the plant for these motors. The power plant includes a plurality of power generation units respectively based on a generator driven by a gas or a steam turbine.

For some reason, if the available power suddenly goes down or partly stops, the LNG production process is stopped, and it may take at least several hours for the refrigerant compressor to restart and the LNG production process to regain operational stability.

This risk can be mitigated by installing over-power plants (based on so-called N + 1 principles) in the form of standby power generators or by generating multiple generations of power below full capacity (sometimes referred to as a continuous "spinning reserve" Can be reduced by operating the units. These solutions are common in that one power generating unit may fail because one additional power generating unit is provided in accordance with the principle of N + 1, compared to the requirement of N power generating units being the minimum required to provide the total demand of LNG power generation .

In addition, US 2010/0257895 discloses that in the event of a failure of a power generation unit in a power plant, the compressor drive (rotation) speed is preferably lowered if the predetermined total preliminary load is lower than the power supplied by the power generation unit before failure I am proposing. According to the secondary load characteristic curve of the turbine compressor, the power drawn from the electric motors is reduced to a cube of rotational speed. If the actual energy demand of the LNG plant is not met even considering a reduction in the compressor drive speed, it is a solution to switch off at least one predetermined electricity consuming part of the gas liquefaction plant.

The drawback of the load interception solution proposed in US 2010/0257895 is that the response time for the load interrupting effect is limited by the total rotational inertia of the rotating parts of the motor, compressor and drive shaft. Another drawback of the US 2010/0257895 solution is that the compressor needs to be driven by a variable speed motor.

It is an object of the present invention to provide a method and apparatus for producing an improved liquefied hydrocarbon stream and a method of operating the compressor to solve the problems of the prior art.

According to one aspect,

- compressing at least a portion of the refrigerant fluid in a refrigerant compressor driven by an electric motor with variable inlet guide vanes capable of angle adjustment relative to a reference position, circulating the refrigerant fluid through the refrigerant circuit;

- removing heat from the initial vapor phase hydrocarbon stream to condense at least a portion of the initial vapor phase hydrocarbon stream to form a liquefied hydrocarbon stream, said heat removal being accomplished by at least a portion of the refrigerant fluid circulated through the refrigerant circuit Exchanging at least the portion of the initial vaporous hydrocarbon stream with respect to the portion;

- powering the electric motor using a power supply network;

- monitoring a signal indicative of a condition of said power supply network;

- comparing the signal with a preset reference to automatically determine from the signal whether additional load shedding is required;

- reducing the load of the refrigerant compressor by automatically adjusting the angle of the variable inlet guide vane when the criterion is met and additional load cut-off is required

≪ / RTI > to provide a process for producing a liquefied hydrocarbon stream.

According to another aspect,

- a refrigerant circuit arranged to circulate a refrigerant fluid, said refrigerant circuit comprising a refrigerant compressor for compressing at least a portion of said refrigerant fluid, and an electric motor coupled with said refrigerant compressor for driving said refrigerant compressor, The refrigerant circuit comprising variable inlet guide vanes having an adjustable angle;

A heat exchanger train comprising at least one heat exchanger arranged to remove heat from an initial vapor stream of hydrocarbons to condense at least a portion of the hydrocarbon stream on the initial vapor stream to form a liquefied hydrocarbon Wherein the at least one heat exchanger is arranged to receive at least the portion of the hydrocarbon stream on the initial vapor and at least a portion of the refrigerant fluid circulating through the refrigerant circuit in mutual heat exchange relationship, ;

A power supply network connected to the electric motor to supply power to the electric motor;

- monitoring a signal indicative of a condition of the power supply network and automatically comparing the signal with a preset reference to automatically determine from the signal whether additional load interruption is required and, A load interrupter controller arranged to adjust the angle of the variable inlet guide vane to a position where the refrigerant compressor is unloaded with respect to a load of an old condition where the angle of the variable inlet guide vane was at an old position where the reference was not satisfied, ≪ RTI ID = 0.0 > a < / RTI > liquefied hydrocarbon stream.

According to yet another aspect,

Compressing at least a portion of the fluid in a compressor driven by an electric motor having a variable inlet guide vane whose angle can be adjusted;

- powering the electric motor using a power supply network;

- monitoring a signal indicative of a condition of said power supply network;

- comparing said signal with a preset reference to automatically determine from said signal whether additional load interruption is required;

- reducing the load on the compressor by automatically adjusting the angle of the variable inlet guide vane when the above criteria are met and additional load interruption is required

And a compressor.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in more detail with reference to the accompanying non-limiting drawings,
Figure 1 schematically shows an apparatus for producing a liquefied hydrocarbon stream.
Figure 2 schematically shows a non-limiting example of an embodiment of a variable inlet guide vane of a centrifugal compressor.

In this specification, lines and streams provided in the lines are assigned a single reference number. Also, like parts, streams or lines are numbered the same.

The present invention discloses a method and apparatus for producing a liquefied hydrocarbon stream. In the process of producing a liquefied hydrocarbon stream, a compressor driven by an electric motor is used. At least a portion of the fluid in the compressor is compressed. The compressor has a variable inlet guide vane, and the angle of the vane can be adjusted. The electric motor is powered using a power supply network, and a signal indicative of the state of the power supply network is monitored. From the signal, it is automatically determined whether an additional load cutoff is required by comparing the signal with a preset reference. The angles of the variable inlet guide vanes are automatically adjusted when the reference is met and additional load cut-off is required, thereby automatically reducing the load on the compressor.

By adjusting the variable inlet guide vane angle, the power demand can be reduced without reducing the motor speed. Therefore, the method of interrupting the load proposed in the present invention can be used irrespective of whether variable speed electric driving is used or fixed speed electric driving is used.

Moreover, the inertia of the rotating mass, such as the rotating parts of the motor, the compressor and the drive shaft, does not affect the response time of the load disconnect operation. It can be expected that the inlet guide vanes will have much less inertia than the rotating parts of the motor / compressor assembly, so the response time associated with adjusting the variable inlet guide vanes may be much lower.

For example, when the monitored signal indicates that the available power falls below a predetermined value, the compressor is no-load by adjusting the variable inlet guide vane angle. Thus, the state of the power supply network indicated by the signal represents the power available in the power supply network for the power consumed, whereby a preset reference is met when the power falls below a predetermined value in accordance with the monitored signal .

In this way, the power supply network can be protected by quickly relieving the power required from the power supply network with the compressor unloaded.

If the preset criteria are not met, no additional load interruption is required.

In a group of embodiments, the signal indicative of the state of the power supply network represents the network frequency over which the power supply network operates. The need for additional load interception can be deduced from the signal if the network frequency deviates from the predetermined nominal network frequency. Typically, if the actual network frequency is lower than the nominal network frequency, a load interruption is required to reduce the power demand for the network, which helps return the actual network frequency to the nominal network frequency. Automatically determining from the signal whether additional load blocking is required may include comparing the actual network frequency to a predetermined nominal network frequency. A predetermined criterion for determining whether additional load interception is required includes a nominal network frequency, which is met when the actual network frequency falls below a predetermined nominal network frequency.

In a preferred embodiment, the compressor is provided in the form of a refrigerant compressor, whereby the fluid is a refrigerant fluid such as used in an apparatus and / or method for producing a liquefied hydrocarbon stream. Suitably, the compressor is driven only by an electric motor.

The proposed load shutdown method may also be used to prevent overload that may result from an increase in ambient temperature. This is particularly useful when the compressor is provided in the form of a refrigerant compressor which is employed to compress at least a portion of the refrigerant fluid, such as is performed in the course of operating the manufacturing process as a liquefied hydrocarbon stream. In general, an increase in ambient temperature increases the demand for power to liquefy the hydrocarbon stream. Moreover, if the power supply network is powered through one or more gas turbines, the available power will be reduced as a result of an increase in ambient temperature.

The proposed load-unblocking method is based on the assumption that the power supply network is powered by a dedicated power plant and that an internal grid or another power consumer is powered by the incoming power supplied from the connected industrial grid Can be used in connection with compressors that depend on so-called "island-mode" power generation.

If the compressor includes a variable inlet guide vane capable of adjusting the angle, the implementation of the proposed load blocking method does not require significant facility adaptation. Implementation of the above method can be accomplished by adding a dedicated control device or by altering an existing control device that is typically already employed to control the inlet guide vane setting.

1 shows a method for producing a liquefied hydrocarbon stream and a method for operating a compressor in an apparatus. However, the teachings provided below with respect to the operation of the compressor herein are not necessarily limited or limited to the embodiment where the compressor is a refrigerant compressor and / or the fluid is a refrigerant fluid.

The apparatus shown in Figure 1 employs at least one refrigerant circuit comprising a first refrigerant circuit 100 arranged to circulate a refrigerant fluid 110. [ Each of the at least one refrigerant circuit includes a compressor in the form of a refrigerant compressor (120) to compress at least a portion of the refrigerant fluid (110) circulated in the refrigerant circuit (100). Each refrigerant compressor is connected to an electric motor 130 through an electrical motor 130 and a mechanical drive shaft 125 extending between each refrigerant compressor 120 to rotationally drive its rotor.

The electric motor 130 is connected to the electric power supply network 400 to supply electric power to the electric motor 130. The power supply network typically includes a power supply in the form of a power plant 410 and a distribution network 420 connected to that power supply. The power plant may be of the " island mode "type, or may be a dedicated power plant for powering the hydrocarbon liquefaction plant or an external power supply for powering the liquefaction plant. The distribution network 420 may be connected to a power busbar 130 arranged to supply power to at least one electric motor 130 via a transmission line 140.

In the embodiment of FIG. 1, at least one refrigerant circuit also includes an optional second refrigerant circuit 200 for circulating a second refrigerant fluid 210. The refrigerant circuit includes a second refrigerant compressor (220); A second electric motor 230; A second transmission line 240; And a second mechanical drive shaft 125, which elements are similarly interconnected as described above with respect to the first refrigerant circuit 100.

The apparatus shown in FIG. 1 also includes a heat exchanger column 300. The heat exchanger heat source 300 is shown very schematically because many different types of such heat exchanger heaters are known in the art. The heat exchanger column 300 is arranged to remove heat from the initial vaporous hydrocarbon stream 10 thereby condensing at least a portion of the initial vaporous hydrocarbon stream 10 to form a liquefied hydrocarbon stream 90 do. The heat exchanger heat exchanges heat with at least a portion of the refrigerant fluid (110) circulating through the refrigerant circuit (100) in at least one heat exchanger arranged to receive the at least a portion of the initial vapor- .

The compressor may be of any type provided with variable inlet guide vanes and includes an axial compressor (e.g. AN 200 axial flow compressor manufactured by General Electric) and a centrifugal compressor.

The inlet guide vanes are often installed in commercially available refrigerant compressors to increase efficiency and extend the operating range. The inlet guide vanes are typically installed at a first stage of compression, but for example in the case of an integrated gear compressor with multiple stages of compression stages, the inlet guide vanes may also be provided at one or more subsequent stages May be installed.

The inlet guide vanes are typically provided in the form of an aerofoil positioned radially in the steam flow of the compressor. It is appropriate that the inlet guide vanes are disposed inside the suction duct. In general and under normal operating conditions, the inlet guide vanes are adapted to direct the refrigerant vapor to the vanes or impellers of the subsequent compression stage in the most efficient direction to a subsequent compression stage.

The variable inlet guide vanes can typically rotate about their mounting axis, as employed in the present invention. Under normal operating conditions, different refrigerant introduction rates can be accommodated by rotating the variable inlet guide vanes to different positions. The rotation is imparted to the variable inlet guide vanes by a vane adjustment device connected to the actuator.

The invention is not limited to any particular form of inlet guide configuration and / or vane adjustment device. There are a variety of suitable ways to operate the vanes, including rotating ring concepts, lever concepts, hydraulic piston concepts, and all that work with variable inlet guide vanes. Examples of variable inlet guide vanes and possible devices for adjusting their angles are disclosed in, for example, US Patent Application Publication No. 2010/0172745 and US Patent No. 7,520,716. In these examples, the vapor flow generally flows inward toward the axis of rotation of the compressor. US Patent Application Publication No. 2010/0329898 shows an example in which steam generally flows axially in a direction along the axis of rotation. US Patent Application Publication Nos. 2010/0172745 and 2010/0329898, and US Patent 7,520,716 refer to the disclosure of the present invention.

An embodiment of a variable inlet guide vane of a centrifugal compressor, derived from US patent application publication no. 2010/0172745, is shown in FIG. 2 as a non-limiting example. The embodiment includes a vane adjustment device employing a rotary ring 13 provided with a plurality of elongated slots 31 and an inlet guide vane 11 disposed around the circumference of the rotary ring 13. [ The inlet guide vanes 11 are pivotally secured to a base plate (not shown for simplicity of illustration) so that each of the inlet guide vanes 11 can be pivoted about the shaft 45. Each of the inlet guide vanes 11 is connected to one end of a plurality of lever arms 43 by a shaft 45. Each lever arm 43 is provided with a pin 35 projecting outwardly in a direction perpendicular to the plane of rotation of the lever arm 43 about the shaft 45. Each of the pins 35 is configured to be disposed in one slot of the elongated slots 31. As the rotary ring 13 rotates relative to the base plate, each inlet guide vane 11 is rotated in the same amount.

In FIG. 2, the vane adjustment device also includes a rack and pinion drive device 21 configured to drive one of a plurality of inlet guide vanes 11 to form a drive vane 47. The rack and pinion drive apparatus includes a pinion 53 connected to the long shaft 55 of a drive vane 47 which replaces the shaft 45 and a rack 57. The rack 57 includes a plurality of teeth 59 that are configured to engage a plurality of teeth 61 of the pinion 53 to thereby operably connect the rack 57 to the pinion 53. The end of the rack 57 is connected to a drive shaft 23, which is actuated by, for example, an inflow cylinder (not shown).

The drive shaft 23 is arranged to impart a linear motion 24 to the rack 57 and its linear motion is converted into a rotational motion 25 at the pinion 53 to thereby drive the drive vane 47 against the base plate . The drive vane 47 is configured to allow the torque of the pin 35 to be adjusted by positioning the respective pin 35 on each lever arm 43 within the associated elongated slot 31 of the rotary ring 13, To the rotary ring (13). Whereby the torque is transmitted to the remaining inlet guide vanes 11 as shown in Fig. 2, whereby each inlet guide vane 11 is synchronously changed in its angular position in the same amount. In this way, the variable inlet guide vane angle can be adjusted with respect to the reference position 16. In Fig. 2, although the radial position is taken as an example to be the reference position 16, any other suitable reference position may be selected.

Referring back to Fig. 1, the apparatus is additionally provided with a load cutoff controller (C). The load interruption controller C monitors the signal indicative of the power available in the power supply network for the power consumed and adjusts the variable inlet guide vane angle when the monitored available power falls below a predetermined value . In such a case, the angle of the variable inlet guide vane is adjusted to a position where the refrigerant compressor is unloaded with respect to the load under the old condition when the angle of the variable inlet guide vane was at the previous position. For this purpose, the controller C may cooperate with an actuator of the compressor 120. [

A suitable signal to monitor is the network frequency. When the AC power supply network is operating stably, the power supply network operates at the (nominal) preset frequency. The network frequency, defined as the frequency of the entire device associated with the power network (including all operating loads consuming power and the generator in operation), is directly proportional to the amount of power the generator can deliver to the device as compared to the power required for consumption It depends. A gradual or sudden downward change in generating capacity results in a frequency reduction. The network frequency is therefore a good guideline for the need to cut off the load, and it is particularly appropriate in combination with the development of the island mode. Preferably, the controller C cooperates with the actuator of the compressor 120 to stop the descent of the network frequency.

Particularly when operating on imported power, it is appropriate that the signal is an external signal generated by one of the power supplies or power supplies that provide power to the network to require a load cut-off.

Therefore, the angle of the variable inlet guide vanes is preferably adjusted so that the refrigerant compressor becomes unloaded by the portion of the original load which is not less than the power generation deficiency. Thus, a balance between generated power and demand for power will be restored after the power network can continue its stable operation.

The apparatus further includes a process controller (PC) for controlling the production of the liquefied hydrocarbon stream (90). The process controller may be configured to maintain the variable inlet guide vanes at an optimized target angle to optimize one or both of the operating range and efficiency of the refrigerant compressor 120 when the monitored available power is greater than or equal to a predetermined value .

The load interrupting controller C may be a separate dedicated controller unit, or may be integrated with another controller, for example a controller arranged to also control other aspects of the apparatus, or it may be a hybrid controller, The selected portions may be provided as separate controllers and the other portions may be provided integrated with the other controllers. For example, the other controller may be a process controller (PC).

The above apparatus is operated as follows.

The refrigerant fluid (110) circulates through the refrigerant circuit (100). During this cycle, at least a portion of the refrigerant fluid 100 is compressed in the refrigerant compressor 120 to form a compressed refrigerant. The refrigerant compressor (120) is driven by an electric motor (130), which transmits rotational motion to a mechanical drive shaft (125) about a longitudinal axis. The electric motor 130 receives electric power using electric power from the electric power supply network 400.

The compressed refrigerant is delivered to a heat exchanger column 300 where the refrigerant typically expands at low pressure to evaporate heat from at least the initial vaporous hydrocarbon stream 10. Although not essential for all types of heat exchanger columns 300, in many cases, the compressed refrigerant is condensed and preferably subcooled before being inflated to the aforementioned low pressure. The evaporated refrigerant is returned from the heat exchanger column (300) to the refrigerant compressor and recompressed. This completes one cycle in the refrigerant circuit (100). At the same time, heat exchange of at least a portion of the initial vaporous hydrocarbon stream (10) with respect to at least a portion of the refrigerant fluid circulating through the refrigerant circuit (100) during the cycle results in at least a portion of the vapor stream 10). ≪ / RTI > Ultimately, as a result of removing heat from the initial vapor stream (10) by the refrigerant fluid (120), the optional second and further refrigerant fluids, at least a portion of the hydrocarbon stream on the initial vapor phase is condensed and liquefied Resulting in the formation of a hydrocarbon stream 90.

Under steady, normal operation, the variable inlet guide vanes may be manually installed by an operator or automated by a process controller (PC) and / or a compressor anti-surge controller. The variable inlet guide vanes are installed at selected angles, for example, to obtain the required working window.

The available power in the power supply network 400 is monitored and variable inlet guide vanes may be maintained at a selected angle or may be moved to another selected angle as long as the monitored available power is above a predetermined value. In a preferred embodiment of operation, the variable inlet guide vanes are maintained at a target angle that is optimized to optimize either or both of the efficiency and operating range of the refrigerant compressor, as long as the monitored available power is above a predetermined value.

However, when the monitored available power drops below a predetermined value, the load cutoff controller reacts by adjusting the variable inlet guide vane angle to load the refrigerant compressor 120 without load. This is done by quickly changing the angle from the selected angle to another position. No load of the refrigerant compressor 120 is achieved by intentionally changing the variable inlet guide vane angle to deviate from the optimized target angle if the selected angle was at the optimized target angle, which is the case for the preferred embodiment operation.

Typically, the load demand by the refrigerant compressor is reduced by closing the variable inlet guide vane, such closing of the vane corresponds to increasing the position of the variable inlet guide vane by a negative angle in accordance with the art, Where 0 ° corresponds to the optimized target angle.

The heat exchanger column 300 of the present disclosure is schematically illustrated. This represents a suitable hydrocarbon liquefaction process, particularly a natural gas liquefaction process for producing liquefied natural gas, and the invention is not limited to any particular choice of heat exchanger column. Examples of suitable heat exchanger columns include a single refrigerant cycle process, a single mixed refrigerant, such as PRICO, as disclosed in KR Johnsen and P Christiansen, "LNG production on a floating platform," filed in Gastech 1998 (Dubai) Process, but a single component refrigerant such as the BHP-cLNG process also disclosed in the above-mentioned article of Johnsen and Christiansen is also possible); Mixed-refrigerant processes, such as the commonly-used propane-mixed-refrigerant processes commonly abbreviated to C3MR as disclosed in US Pat. No. 4,404,008, or double mixed refrigerant-DMR processes, such as those disclosed in US Patent 6,658,891, Or a two-cycle process in which each refrigerant cycle comprises a single component refrigerant); And a process based on three or more compressor columns for three or more cooling cycles (eg, as disclosed in US Pat. No. 7,141,351).

Other examples of suitable heat exchange columns are disclosed in US Pat. No. 5,832,745 (Shell SMR); US Patent 6,295,833; US Patent 5,657,643 (both of which are variants of Black and Veatch SMR); US Patent 6,370, 910 (Shell DMR). Another suitable example of DMR is the so-called Axens LIQUEFIN process as described in PY Martin et al., "LIQUEFIN: Innovation Process for LNG Cost Reduction", submitted at the 22nd World Gas Conference in Tokyo, Japan (2003) . Other suitable 3-cycle heat exchanger heat sources are described, for example, in US Patents 6,962,060; WO 2008/020044; US Patent 7,127,914; DE3521060A1; US Pat. No. 5,669,234 (commercially known as an optimized cascade process); US Pat. No. 6,253,574 (commercially known as a mixed fluid cascade process); US Patent 6,308,531; US Application Publication No. 2008/0141711; And Mark J. Roberts et al., "High Capacity Single Train AP-X (TM) Hybrid LNG Process", Gastech 2002, Doha, Qatar (13-16 October 2002). These suggestions are provided to illustrate the wide availability of the present invention and are not intended to be an exclusive and / or exclusive list of possibilities. Not all of the examples in the above list use an electric motor as the refrigerant compressor driving means. It is clear that any drive means other than the electric motor can be substituted for the electric motor suitable for use in the present invention.

The initial vapor phase hydrocarbon stream 10 that is cooled and ultimately preferably liquefied is drawn from any suitable gas stream to be cooled and optionally liquefied. Commonly used examples are natural gas or natural gas streams in a petroleum store or coal bed. Alternatively, the hydrocarbon stream 10 on the initial vapor phase may also be obtained from other sources, including, for example, a synthesis source such as a Fischer-Tropsch process.

When the initial vaporous hydrocarbon stream 10 is a natural gas stream, significant amounts of methane are often included. Preferably, the gaseous hydrocarbon stream 10 comprises at least 50 mol% methane, more preferably at least 80 mol% methane.

Depending on the source, the natural gas may comprise an amount of hydrocarbons in particular heavier than methane, such as ethane, propane and butane, possibly minor amounts of pentane and aromatic hydrocarbons. Such composition varies depending on the type and position of the gas.

Typically, hydrocarbons heavier than methane are removed as needed to produce a liquefied hydrocarbon product stream according to the required use. Hydrocarbons heavier than butane (C4) are removed as efficiently as possible from natural gas prior to significant cooling, for a number of reasons, such as having different freezing points or liquefaction temperatures that can cause clogging of parts of the methane liquefaction plant.

Natural gas may also include non-hydrocarbons such as H ₂ O, N ₂ , CO ₂ , Hg, H ₂ S and other sulfur compounds and the like. Thus, if desired, the initial vapor phase hydrocarbon stream 10 containing natural gas can be treated (pre-treated) before it is cooled or during cooling. This (pretreatment) treatment may involve removal and / or reduction of undesirable components such as CO ₂ and H ₂ S, or may involve other steps such as initial cooling, pre-pressurization, and the like. Since these steps are well known to those skilled in the art, the mechanism is not described in detail herein.

In the preferred embodiments disclosed herein, the initial vaporous hydrocarbon stream 10 comprises natural gas, whereby the liquefied hydrocarbon stream 90 is a liquefied natural gas stream.

A compressor such as the refrigerant compressor used in the present invention can be driven solely by an electric motor, which means that the electric motor is the only driving means for driving the compressor.

Those skilled in the art will appreciate that the present invention is particularly well suited for applications in which: < RTI ID = 0.0 > US < / RTI & US Patent 7,114,351; It will be appreciated that the present invention can be used advantageously in combination with other load cut-off techniques and / or plant design, including Fritz Kleiner and Steve Kaufmann's Gastech 2005 paper entitled "Advantages Provided by All Electric-Powered Cooling Compressors in LNG Plants ". For example, if the apparatus and method proposed in the present invention for producing a liquefied hydrocarbon stream comprises two or more refrigerant compressors (each compressor compressing a portion of the total amount of refrigerant flow), the remaining compressor One or more compressors may not operate during operation. This can be especially taken into account when extreme adjustments of the inlet guide vanes are required and / or operation under considerably reduced loads is expected over an extended period of time.

It will be understood by those skilled in the art that the present invention may be carried out in many different ways without departing from the scope of the appended claims.

Claims (16)

A method of making a liquefied hydrocarbon stream comprising:
- compressing at least a portion of the refrigerant fluid in a refrigerant compressor driven by an electric motor with variable inlet guide vanes capable of angle adjustment relative to a reference position, circulating the refrigerant fluid through the refrigerant circuit;
- removing heat from the initial vapor phase hydrocarbon stream to condense at least a portion of the initial vapor phase hydrocarbon stream to form a liquefied hydrocarbon stream, said heat removal being accomplished by at least a portion of the refrigerant fluid circulated through the refrigerant circuit Exchanging at least the portion of the initial vaporous hydrocarbon stream with respect to the portion;
- powering the electric motor using a power supply network;
- monitoring a signal indicative of a condition of said power supply network;
- comparing the signal with a preset reference to automatically determine from the signal whether additional load shedding is required;
- reducing the load of the refrigerant compressor by automatically adjusting the angle of the variable inlet guide vane when the criterion is met and additional load cut-off is required
≪ / RTI > The method of claim 1, further comprising maintaining the variable inlet guide vanes at an optimized target angle to optimize either or both of the efficiency and the operating envelope of the refrigerant compressor when the criterion is not met Lt; RTI ID = 0.0 > of: < / RTI > 3. The method of claim 2, wherein adjusting the angle of the variable inlet guide vane includes deliberately changing the angle of the variable inlet guide vane to deviate from the optimized target angle . 4. The method of any one of claims 1 to 3, wherein the condition of the power supply network represents power available in the power supply network for consuming power, ≪ / RTI > is satisfied when the possible power falls below a predetermined value. 5. A method as claimed in any one of claims 1 to 4, characterized in that the power supply network operates at a network frequency and the signal indicative of the conditions of the power supply network represents a network frequency at which the power supply network operates ≪ / RTI > 6. Process according to any one of claims 1 to 5, characterized in that the initial vapor-phase hydrocarbon stream comprises a natural gas and the liquefied hydrocarbon stream is a liquefied natural gas stream . A system for producing a liquefied hydrocarbon stream comprising:
- a refrigerant circuit arranged to circulate a refrigerant fluid, said refrigerant circuit comprising a refrigerant compressor for compressing at least a portion of said refrigerant fluid, and an electric motor coupled with said refrigerant compressor for driving said refrigerant compressor, The refrigerant circuit comprising variable inlet guide vanes having an adjustable angle;
A heat exchanger train comprising at least one heat exchanger arranged to remove heat from an initial vapor stream of hydrocarbons to condense at least a portion of the hydrocarbon stream on the initial vapor stream to form a liquefied hydrocarbon Wherein the at least one heat exchanger is arranged to receive at least the portion of the hydrocarbon stream on the initial vapor and at least a portion of the refrigerant fluid circulating through the refrigerant circuit in mutual heat exchange relationship, ;
A power supply network connected to the electric motor to supply power to the electric motor;
- monitoring a signal indicative of a condition of the power supply network and automatically comparing the signal with a preset reference to automatically determine from the signal whether additional load interruption is required and, A load interrupter controller arranged to adjust the angle of the variable inlet guide vane to a position where the refrigerant compressor is unloaded with respect to a load of an old condition where the angle of the variable inlet guide vane was at an old position where the reference was not satisfied, ≪ / RTI > 8. The apparatus of claim 7, further comprising a process controller arranged to maintain the variable inlet guide vanes at an optimized target angle to optimize either or both of the efficiency and operating range of the refrigerant compressor when the criterion is not met ≪ / RTI > 9. The method of claim 7 or 8, wherein the condition of the power supply network represents the power available in the power supply network for the power consumed, and the predetermined criterion is based on the monitored signal, Is met when it falls below a set value. ≪ Desc / Clms Page number 13 > 10. A method according to any one of claims 7 to 9, wherein the power supply network operates at a network frequency, the signal indicative of the conditions of the power supply network represents a network frequency at which the power supply network operates, Wherein the established criterion is satisfied when the network frequency falls below a predetermined nominal network frequency. Compressing at least a portion of the fluid in a compressor driven by an electric motor having a variable inlet guide vane whose angle can be adjusted;
- powering the electric motor using a power supply network;
- monitoring a signal indicative of a condition of said power supply network;
- comparing said signal with a preset reference to automatically determine from said signal whether additional load interruption is required;
- reducing the load on the compressor by automatically adjusting the angle of the variable inlet guide vane when the above criteria are met and additional load interruption is required
Lt; / RTI > 11. The method of claim 10, further comprising maintaining the variable inlet guide vanes at an optimized target angle to optimize either or both of the efficiency and operating range of the refrigerant compressor when the criteria is not met How the compressor works. 13. The method of claim 12, wherein adjusting the angle of the variable inlet guide vane includes deliberately changing the angle of the variable inlet guide vane to deviate from an optimized target angle. 14. A method according to any one of claims 11 to 13, wherein said condition of said power supply network represents power available in said power supply network for consumed power, And when the available power drops below a predetermined value. 15. The method according to any one of claims 11 to 14, wherein the power supply network operates at a network frequency, the signal indicative of the condition of the power supply network indicates a network frequency at which the power supply network operates, Wherein the established criterion is satisfied when the network frequency falls below a predetermined nominal network frequency. 16. A method according to any one of claims 11 to 15, wherein the compressor is a refrigerant compressor and the fluid is a refrigerant fluid.

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