RU2424477C2 - Cooling agent circuit - Google Patents

Abstract

FIELD: machine building. ^ SUBSTANCE: cooling circuit (1) consists of cooling device (2 having inlet orifice (21) for cooling agent (10) under pressure of cooling and at least five outlet orifices (22, 23, 24, 25, 26, Ç) for vaporous cooling agent (20, 30, 40, 50, 60, Ç) evaporating at various levels of pressure. Further, cooling circuit (1) consists of first compressor (3) having one or several inlet orifices whereto vaporous cooling agent enters from the cooling device, of outlet orifice (34) connected with inlet orifice (21) of cooling device (2), of second compressor (4) having one or several inlet orifices whereto vaporous cooling agent enters from the cooling device, and of outlet orifice (44) connected with inlet orifice (21) of cooling device (2). At least five outlet orifices (22, 23, 24, 25, 26, Ç) are designed for cooling agent evaporated under conditions of pressure growing from first outlet orifice (22) to fifths outlet orifice (26) and to possible present outlet orifices with bigger numbers. ^ EFFECT: raised efficiency. ^ 7 cl, 5 dwg

Description

The present invention relates to a refrigerant circuit, in particular for use in a liquefaction plant.

Several designs of the refrigerant circuit are known. Typically, the refrigerant circuit contains a refrigeration unit (or “cooling zone”) in which the refrigerant evaporates in one or more stages, removing heat from the gas stream to be cooled, a compressor for re-compressing the vaporous refrigerant (s) and return pipes to return the re-compressed refrigerant to refrigeration unit.

The amount of cooling per unit of time in the refrigeration unit is proportional to the specific mass flow rate of the refrigerant passing through the refrigeration unit of the refrigerant circuit. With an increase in the flow to be cooled (such as natural gas to be liquefied), the specific mass flow rate of the refrigerant should be increased. Although the increase in specific mass flow rate does not affect the number of impellers in the compressor, it does affect their size, housing diameter, and speed at the inlet to the impellers. Since the latter variables increase with increasing flow velocity, an increase in flow velocity leads to an increase in compressor dimensions and inlet velocities. Moreover, increasing the diameter of the compressor housing requires thicker housing walls. As a result, the manufacturing complexity of the compressor increases, and difficulties arise when loading and unloading it.

Since natural gas liquefaction plants and other gas treatment plants are designed for ever-increasing production rates for greater economic benefits, there is a continuing need for alternative plants and methods to reduce the size and speed at the inlet to a large compressor.

WO 01/44734, which is incorporated herein by reference, describes a refrigerant circuit for use in a liquefaction plant and comprising a compression device with two compressors, each located in a separate housing. The compression device according to WO 01/44734 allows you to operate with four different flows of refrigerant, which evaporates in the refrigeration device at several pressure levels.

In the documents US 3527059 and US 6691531 described refrigerant circuits, allowing to operate with flows of refrigerant, which evaporates at three different pressure levels.

It is an object of the present invention to provide an alternative refrigerant circuit to satisfy the aforementioned need.

The specified problem and other tasks can be solved in the refrigerant circuit according to the present invention and intended, in particular, for use in a liquefaction plant, while the cooling circuit contains at least the following:

- a refrigeration device comprising an inlet for a refrigerant under cooling pressure and at least five outlet openings for vaporous refrigerant vaporizing at five different pressure levels;

- a first compressor comprising one or more inlets that receive vapor refrigerant from the refrigeration device, and an outlet that is connected to the inlet of the refrigeration device;

- a second compressor containing one or more inlets that receive vapor refrigerant from the refrigeration device, and an outlet that is connected to the inlet of the refrigeration device;

- at least five outlet openings are intended for refrigerant flows evaporating at least at four or preferably at five pressure levels increasing from the first outlet to the fifth outlet and to possibly large outlet openings.

An important advantage of the present invention is that the refrigerant circuit is surprisingly simple and allows you to operate with five or more gaseous flows of refrigerant vaporizing at four or more preferably at five or more different pressure levels in the refrigeration device.

Another advantage of the present invention is that each of the compressors can be separately protected from excessive compression, for example, using check valves or similar devices. This can significantly reduce the size of the pressure relief system.

Another advantage of the present invention is that the refrigerant is vaporized at more than four different pressure levels, which is more efficient.

It will be apparent to those skilled in the art that the design of a refrigeration device may be different. According to a most preferred embodiment of the invention, the refrigerant may vaporize at least five different pressure levels. A person skilled in the art is aware of what is meant by a refrigeration device, so it will not be described hereinafter.

The first and second compressors may be any suitable compressor. If necessary, their number may be more than two. In addition, both the first and second (and even more) compressors may contain one or more compression stages.

According to a most preferred embodiment of the invention:

- the first compressor comprises a main inlet for refrigerant exiting the first outlet, a second inlet for refrigerant exiting the third outlet, a third inlet for refrigerant exiting the fifth outlet, and an outlet that is connected to the inlet of the refrigeration devices

- the second compressor comprises a main inlet for refrigerant leaving the second outlet, a second inlet for refrigerant leaving the fourth outlet, and an outlet that is connected to the inlet of the refrigeration device.

Preferably, the odd outlets (i.e., the first, third, fifth, seventh, etc.) are connected to the first compressor, and the even outlets (i.e., second, fourth, sixth, eighth, etc.) are connected to the second compressor, however, the vapor pressure of the refrigerant increases from the first outlet to the fifth and to possibly present outlet openings with large numbers.

The advantage of the staggered design of compressor stages is that the compressor capacities can be evenly distributed between the first and second compressors, which was made possible thanks to almost equal pressure ratios of the compressor stages.

If desired, economizers may be attached to one or more of the outlet openings of the refrigeration device. Economizers are widely known in the art (see, for example, John M. Campbell /, "Gas Conditioning and Processing. - Vol.2: The Equipment Modules", 8th edition, edited by Robert A. Hubbard / Robert A. Hubbard /, 2004, page 219), therefore a description thereof is omitted. Preferably, an outlet is connected to the economizer of the refrigeration device for refrigerant evaporating at the highest pressure.

Another object of the present invention is a plant for producing a liquefied hydrocarbon product, such as liquefied natural gas, which contains a refrigerant circuit according to the present invention and designed to cool the flow of hydrocarbons, for example natural gas.

Another object of the present invention is a method of cooling, preferably liquefying, a hydrocarbon stream, wherein the hydrocarbon stream is cooled using the refrigerant circuit of the present invention.

Since methods for cooling and liquefying a hydrocarbon stream are known in the art, a description thereof is omitted. Examples of liquefaction processes are given in documents US 6389844 and US 6370910, which are incorporated herein by reference.

The hydrocarbon stream to be cooled and / or liquefied may be any suitable hydrocarbon containing stream, but it is usually a natural gas stream obtained from oil or natural gas reservoirs. Alternatively, natural gas can also be obtained from another source, including an artificial source, such as the Fischer-Tropsch process.

Typically, the hydrocarbon stream is mainly composed of methane (for example, more than 60 molar% methane). Depending on the source, the hydrocarbon stream may contain various amounts of heavier hydrocarbons, such as ethane, propane, butanes and pentanes, as well as some aromatic hydrocarbons. Also, the hydrocarbon stream may contain non-hydrocarbons such as H ₂ O, N ₂ , CO ₂ , H ₂ S and other sulfur compounds, and the like.

Prior to cooling, the hydrocarbon stream may be pretreated. This pretreatment may consist in removing undesirable components such as H ₂ O, CO ₂ , H ₂ S, and contain other steps, such as pre-cooling, pre-pressure boosting or the like. Since these steps are well known to those skilled in the art, their description is omitted.

The invention will be described in more detail by way of example with reference to non-limiting drawings.

1 schematically shows a refrigerant circuit according to the present invention, allowing operation with five flows of refrigerant vaporizing at various pressure levels;

figure 2 schematically shows the refrigerant circuit according to the present invention, allowing to operate with eight flows of refrigerant vaporizing at various pressure levels;

figure 3 schematically shows a refrigerant circuit according to the present invention with three compressors;

4 and 5 schematically show an alternative embodiment of a refrigerant circuit according to the present invention, which allows operating with five refrigerant streams.

In the following, one reference numeral denotes both the pipe and the flow passing through this pipe. The same reference numerals denote similar components.

Schematically shown in FIG. 1, the refrigerant circuit 1 comprises a refrigeration device 2 (or “cooling zone”), shown in a rectangle, a first compressor 3, a second compressor 4 and a cooling device 5, such as an air or water cooling device. Since the refrigeration device 2 is well known, for clarity, here it is shown only schematically.

The first and second compressors 3 and 4 are located in separate housings. These compressors can be any type of compressor, but it is advisable that they be centrifugal compressors.

The inlet 21 of the refrigeration device 2 is for refrigerant 10 under cooling pressure. In the refrigeration device 2, more than one inlet may be provided.

In the embodiment of the invention shown in FIG. 1, the refrigeration device 2 comprises five outlets 22, 23, 24, 25 and 26 for vapor refrigerant vaporizing at various pressure levels, the pressure increasing from the first outlet 22 to the fifth an outlet 26. For example, a first outlet 22 is for a low pressure refrigerant gas stream 20, a second outlet 23 is for a refrigerant gas stream 30 pressurized medium, a third outlet 24 for a high pressure refrigerant gas stream 40, a fourth outlet 25 for a very high pressure refrigerant gas stream 50, and a fifth outlet 26 for stream 60 gaseous refrigerant under the highest pressure.

Both the first 3 and the second 4 compressors are located in separate housings. The first compressor 3 contains three interconnected parts 51, 52 and 53, and the second compressor 4 contains two interconnected parts 61 and 62. Each part may contain one or more impellers. In this case, the impeller is sometimes called the step. Parts 51, 52, 53, 61 and 62 are called as follows: parts 51 and 61 - low pressure, part 52 - intermediate pressure and parts 53 and 62 - high pressure.

The first compressor 3 comprises a main or first inlet 31, a second inlet 32, a third inlet 33 and an outlet 34. The second compressor 4 comprises a main or first inlet 41, a second inlet 42 and an outlet 44. The main inlet 31 of the first compressor 3 leads to a low pressure part 51, and a second inlet 32 leads to an intermediate pressure part 52. A third inlet 33 leads to a high pressure portion 53. The main inlet 41 of the second compressor 4 leads to the low pressure part 61, and the second inlet 42 leads to the high pressure part 62. For clarity, the drive mechanisms of compressors 3 and 4 are not shown.

The outlets 34 and 44 of the compressors 3 and 4 are connected to the inlet 21 of the refrigeration device 2 by means of pipes 10, 10a and 10b. The first outlet 22 of the refrigeration device 2 is connected to the main inlet 31 of the first compressor 3 by a pipe 20, and the second outlet 23 is connected to the main inlet 41 of the second compressor 4 by a pipe 30. The third outlet 24 is connected to the second inlet 32 the first compressor 3 through the pipe 40, the fourth outlet 25 is connected to the second inlet 42 of the second compressor 4 through the pipe 50, and the fifth outlet 26 is connected to the third inlet from verst 33 of the first compressor 3 through the pipe 60.

During normal operation of the device, each of the two compressors 3 and 4 compresses part of the refrigerant to the cooling pressure, so that all the refrigerant enters the inlet 21 of the refrigeration device 2 through pipes 10, 10a and 10b under the cooling pressure. The refrigerant vaporizes in five heat exchangers (not shown) arranged in series in the refrigeration device 2.

In the first heat exchanger, the refrigerant partially evaporates at the highest pressure, which is lower than the cooling pressure, the liquid part of the refrigerant passes into the second heat exchanger, and the remaining steam is returned to the first compressor 3 through pipe 60. In the second heat exchanger, the refrigerant partially evaporates at a very high pressure, which is lower than the highest high pressure, the liquid part of the refrigerant passes into the third heat exchanger, and the remaining steam is returned to the second compressor 4 through the pipe 50. In the third heat exchanger, the refrigerant partially evaporates I at high pressure, which is below very high pressure, the liquid part of the refrigerant passes into the fourth heat exchanger, and the remaining steam is returned to the first compressor 3 through pipe 40. In the fourth heat exchanger, the refrigerant partially evaporates at an average pressure that is lower than the high pressure, the liquid part of the refrigerant passes to the fifth heat exchanger, and the remaining steam is returned to the second compressor 4 through pipe 30. In the fifth heat exchanger, the refrigerant evaporates at a low pressure that is lower than the average pressure, and the refrigerant leaving th heat exchanger is returned to the first compressor 3 through a pipe 20. If desired, one or more outlet openings the cooling device 2 can be attached economizers. Preferably, an outlet of the refrigeration device 2 is connected to the economizer for refrigerant evaporating at the highest pressure (i.e., the fifth outlet 26 of FIG. 1).

FIG. 2 schematically shows a refrigerant circuit 1 according to the present invention, allowing operation with eight flows of refrigerant vaporizing at various pressure levels. To this end, the refrigeration device 2 contains eight consecutive heat exchangers (not shown). The refrigeration device 2 comprises eight outlet openings, including a sixth outlet 27, a seventh outlet 28 and an eighth outlet 29.

The sixth outlet 27 and the eighth outlet 29 are connected (via pipes 70 and 90) to the third and fourth inlets 43 and 45 of the second compressor 4, and the seventh outlet 28 (through a pipe 80) is connected to the fourth inlet 35 of the first compressor 3.

In the embodiment of the invention shown in FIG. 2, the first and second compressors 3 and 4 comprise four interconnected parts 51, 52, 53, 54 and 61, 62, 63, 64, respectively.

According to the present invention, it is preferable that the odd outlets (i.e., the first outlet 22, the third outlet 24, the fifth outlet 26, etc.) of the refrigeration device 2 are connected to the first compressor 3, and the odd outlets (i.e. a second outlet 23, a fourth outlet 25, etc.) were connected to a second compressor 4 (as shown in FIGS. 1 and 2). However, the present invention also provides alternative embodiments.

As an example, FIG. 3 shows an embodiment of a refrigerant circuit 1 according to the present invention and comprising more than two compressors. The refrigerant circuit 1 in this example also comprises a third compressor 6 with a main inlet 71, an outlet 74 and a second and third inlet 72 and 73.

The embodiment shown in FIG. 3 makes it possible to operate with seven refrigerant streams 20, 30, 40, 50, 60, 70, 80, evaporating in the refrigeration device 2 at four different pressure levels: a first pressure level for vaporous refrigerant streams 50 and 80, a second pressure level for the vapor refrigerant streams 40 and 70, a third pressure level for the vapor refrigerant streams 30 and 60, and a fourth pressure level for the vapor refrigerant stream 20. The pressure level decreases from the first pressure level to the fourth pressure level, that is, stream 20 has less pressure than streams 50 or 80.

Figures 4 and 5 show examples of alternative refrigerant circuits according to the present invention and also allowing operation with five flows of refrigerant vaporizing at five different pressure levels. These options are alternatives to the design shown in figure 1. The pressure level at which the refrigerant streams 20, 30, 40, 50, and 60 evaporate decreases from 60 to 20. It is clear that pipes 20, 30, 40, 50, 60 can be connected to the first and second compressors 3 and 4 in other ways In this regard, it should be noted that many different designs can be presented in which there are more refrigerant flows and three or more compressors are used.

One skilled in the art will appreciate that the present invention can be modified in various ways without departing from the scope of the claims.

Claims (8)

1. A refrigerant circuit (1) intended, in particular, for use in a liquefaction plant, comprising a refrigeration device (2) with an inlet (21) for a refrigerant (10) under cooling pressure and with at least five discharge openings (22, 23, 24, 25, 26, ...) for vaporous refrigerant (20, 30, 40, 50, 60, ...) evaporating at various pressure levels; a first compressor (3) with one or more inlets for receiving vaporous refrigerant from the refrigeration device and with an outlet (34) connected to the inlet (21) of the refrigeration device (2); a second compressor (4) with one or more inlets for receiving vaporous refrigerant from the refrigeration device and with an outlet (44) connected to the inlet (21) of the refrigeration device (2); at least five outlet openings (22, 23, 24, 25, 26, ...) are intended for vaporous refrigerant flows evaporating at least five pressure levels increasing from the first outlet (22) to the fifth outlet (26 ) or up to possibly large outlet numbers. 2. The refrigerant circuit (1) according to claim 1, wherein the vapor pressure of the refrigerant increases from the first outlet to the fifth and to possibly large outlets, the odd outlets are connected to the first compressor, and the even outlets are connected to second compressor. 3. The refrigerant circuit (1) according to claim 1, wherein the first compressor (3) comprises a main inlet (31) for refrigerant (20) exiting the first outlet (22), a second refrigerant inlet (32) ( 40) exiting the third outlet (24), a third inlet (33) for refrigerant (60) exiting the fifth outlet (26), and an outlet (34) connected to the inlet (21) of the refrigeration device ( 2); and the second compressor (4) comprises a main inlet (41) for refrigerant (30) exiting the second outlet (23), a second inlet (42) for refrigerant (50) exiting the fourth outlet (25), and an outlet (44) connected to the inlet of the refrigeration device (2). 4. The refrigerant circuit (1) according to claim 3, in which the refrigeration device (2) comprises a sixth outlet (27) for vaporous refrigerant connected to the third inlet (43) of the second compressor (4). 5. The refrigerant circuit (1) according to any one of claims 1 to 4, in which the refrigeration device (2) contains more than six outlets (22, 23, 24, 25, 26, 27, 28, ...) for the refrigerant evaporating at different pressure levels, with odd outlets (22, 24, 26, 28, ...) connected to the first compressor (3), and even outlets (23, 25, 27, ...) connected to the second compressor (4). 6. The refrigerant circuit (1) according to any one of claims 1 to 4, in which the outlet of the refrigeration device (2) for the refrigerant evaporating at the highest pressure is connected to the economizer. 7. Installation for producing a liquefied hydrocarbon product, such as liquefied natural gas, containing a refrigerant circuit (1) according to any one of claims 1 to 6 for cooling a hydrocarbon stream, such as a stream of natural gas to be liquefied. 8. A method of cooling, preferably liquefying, a hydrocarbon stream, such as a natural gas stream, in which the hydrocarbon stream to be cooled is cooled using a refrigerant circuit (1) according to any one of claims 1 to 6.

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