RU2490565C2 - Control method and device for cooling agent compressor, and their use in hydrocarbon flow cooling method - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: control method of one or more compressors (12) used for compression of one or more gas flows (10) at normal operating temperature. At least one cooling agent compressor (12) is equipped with steam recirculation pipeline (30). Initial flow (10a) for the compressor is obtained as a result of combination of recirculation steam flow (30) from steam recirculation pipeline (30) and at least partially evaporated cooling agent flow (8). Initial flow (10a) for the compressor is passed through inlet separator (11) to obtain gas flow (10) for the compressor, which is passed through cooling agent compressor(s) (12). Inlet temperature T1 of gas flow (10) is determined for the compressor, and cooling agent flow cooling is controlled depending on temperature T1 to obtain gas flow (10) for the compressor at normal operating temperature at least of one cooling agent compressor (12).

EFFECT: use of the invention will allow independent control of temperature of the initial flow entering the compressor.

21 cl, 4 dwg, 1 tbl

Description

The present invention relates to a method and apparatus for controlling a compressor for compressing a refrigerant, and to their use in a method for cooling a hydrocarbon stream.

In other aspects, the invention relates to the use of said method and apparatus in order to avoid the surge phenomenon in such a refrigerant compressor.

The compressor (s) for the refrigerant can be used in one or more refrigerant circuits that serve to cool, at the discretion of including liquefaction, a hydrocarbon stream, for example, a natural gas stream. Therefore, according to another aspect, the invention relates to a cooling method, optionally comprising liquefying a hydrocarbon stream.

Various methods are known for cooling, usually liquefying, a natural gas stream, resulting in liquefied natural gas (LNG). Natural gas liquefaction is desirable for a number of reasons. For example, natural gas is easier to store and transport over long distances in the form of a liquid than in a gaseous state, since it occupies a smaller volume and there is no need to store it at high pressure.

As an example of liquefying natural gas, natural gas containing mainly methane is fed to the LNG plant at elevated pressures and preliminarily purified to obtain a purified feed stream suitable for liquefaction at cryogenic temperatures. The purified gas is treated using a series of cooling stages using heat exchangers, including one or more refrigerant circuits to sequentially lower the gas temperature until liquefaction is achieved.

In many cases, systems and circuits, compressors are used to compress gas flows. Typically, there is a piping line to return or recycle the vapor back to the compressor in order to avoid surging. It is said that the compressor is “in a deep surge” when the main stream passing through the compressor changes its direction of flow in the opposite direction. Usually, in this case, the pressure at the compressor outlet is less than the pressure downstream of the compressor outlet. This can lead to rapid pulsations in the flow, commonly referred to as “surge”.

Often signs of surging are excessive vibration and noise. The indicated reversal of the flow direction is accompanied by a very sharp change in energy, which leads to a change in the direction of action of the axial force. The surge process can be cyclical in nature, and if allowed to continue for some time, irreparable damage can occur in the compressor.

In the event that the compressor operates at a gas temperature appropriate to the surrounding or other non-critical conditions, the recirculation of the exhaust gas through the vapor recirculation pipe in order to avoid surging is a simple and well-known operation that is carried out without difficulty. However, any change in the temperature of the flow in the compressor is not particularly important.

When using compressors in refrigerant circuits, there are, in particular, problems associated with them, in particular when the compressors are driven by fixed speed drives, such as a gas turbine. Refrigerant circuits are used in liquefaction systems, plants and plants, for example, to produce a stream of liquefied hydrocarbons, for example, liquefied natural gas (LNG). To cool the hydrocarbon stream, the refrigerant is vaporized in refrigerant circuits in one or more stages, and one or more refrigerant compressors are used to secondary compress the evaporated refrigerant in one or more stages. Refrigerant compressors operating at substantially constant speed require a relatively constant flow of gas to their suction side. In the event that the flow of gas for some reason decreases below a certain minimum value, surge may occur.

Since the compressor inlet for the refrigerant is colder compared to the temperature of the returning or recirculating steam, in the recirculation mode there is a problem in using the conventional method of compressor operation for the refrigerant. In a system using a refrigerant, when the recirculation valve is opened, the initial flow rate increases rapidly, but then the compressor flow for the refrigerant quickly drops to a level below the initial value, and then slowly increases in time to a new higher steady-state value. However, the time period necessary for this is much longer than the typical time scale in which the surge phenomenon occurs.

Figure 4 explains the experimentally obtained result, which consists in the fact that the relationship between the flow rate of the compressor for the refrigerant and the compression ratio in the compressor for the refrigerant is different for different inlet gas temperatures.

4, the starting operating point of the refrigerant system is indicated by a triangle α. As soon as the recirculation valve is opened, the system reacts to this by increasing the initial flow rate. The indicated increase in flow rate is a consequence of the rapid increase in suction pressure, which is associated with the opening of the recirculation valve. However, opening the recirculation valve causes the warmer recirculation vapor to mix with the original cold vapor flowing through the refrigerant compressor. This leads to an increase in the temperature of the combined flow in the compressor for the refrigerant, as a result of which the compressor operates at a lower volume flow at a given pressure ratio (compression ratio), and thus, an increase in the suction temperature leads to a decrease in flow.

As soon as the suction pressure and discharge pressure are set in accordance with the new equilibrium state, a higher flow rate is obtained with a lower compression ratio in the compressor, and, finally, the goal of the regulatory action is achieved: increase the compressor flow for the refrigerant by opening the recirculation valve. However, the control action of the recirculation valve also leads to the undesirable effect of temporarily reducing the volume flow through the refrigerant compressor. The trajectory of the change in the flow rate of the refrigerant as it passes through the opening of the recirculation valve is shown in Fig. 4 by line A. It ends at the point indicated by β on the characteristic curve at a different temperature (higher, equal to 16.5 ° C). Changes that occur along line A can lead to surge, and not to prevent it.

The problem noted above will occur in cooling systems that use both a mixed and pure component (refrigerant). For cooling systems with a clean component, in particular, the compression ratio is partly selected according to the temperature of the liquid mass in the heat exchanger (s) on the inlet side and the temperature of the collection tank on the discharge side of the compressor for the refrigerant. For such a system, the compression ratio in the system compressor adapts even more slowly to changes in the valve settings or changes in the flow rate through the valve, and therefore this problem for systems with a refrigerant representing a clean component is especially serious.

US Pat. No. 4,464,720 discloses a surge control system that uses some algorithm to calculate the desired pressure difference obtained by passing the flow through the diaphragm, and which compares the calculation result with the actual pressure difference. Temperature and pressure are measured both on the suction side and on the discharge side of the centrifugal compressor, and the obtained data is input into the control system so that the actual pressure difference is made equal to the desired pressure difference. The suction temperature of the gas entering the centrifugal compressor is measured and used. However, the complex algorithm and the selected values necessary for calculation in the patent document US 4464720, do not allow to solve any of the above problems.

US Pat. No. 3,572,059 describes a method for matching the operation of a number of parallel refrigerant compressors. The known method involves recirculating a portion of the compressed gaseous refrigerant from the last compression stage to the zone of the first and to the zone of the second compression stage of each of the compressors of the system. The size of the recycle from the last compression stage to the zone of the first compression stage is controlled by maintaining the difference between the flow rates of gaseous refrigerants entering the zone of the second compression stage and leaving this zone. The amount of compressed gaseous refrigerant sent for recirculation from the last compression stage to the zone of the second compression stage is an amount that will maintain at least the minimum predetermined flow rate from the zone of the second compression stage. Compression efficiency is improved by cooling the recirculating refrigerant by passing it through irrigation or distribution devices below the liquid level in the tank containing the liquid refrigerant. Since the heated vapors of the recirculating refrigerant are in contact with the liquid refrigerant, this recirculating refrigerant leaves the tank in the form of saturated steam at a temperature corresponding to its condensation temperature.

The disadvantage of this method is that it does not allow you to independently adjust the temperature of the feed stream entering the compressor, since the temperature of the recirculation stream is set at the level of the condensation temperature.

The objective of the present invention is to eliminate the above problems inherent in known methods.

Another object of the invention is to provide an improved method for controlling one or more refrigerant compressors at normal operating temperature, in particular two or more compressors for compressing a refrigerant at many pressure levels.

The present invention provides a method for controlling one or more refrigerant compressors having a steam recirculation pipe. The specified method includes at least the stages:

(a) obtaining a compressor feed stream by combining a recirculated steam stream from a steam recirculation pipe and at least a partially vaporized refrigerant stream;

(b) passing the feed stream for the compressor through the inlet separator to obtain a gas stream for the compressor;

(c) passing a gaseous stream for the compressor through the compressor (s) for the refrigerant;

(d) measuring the temperature T1 of the gas stream for the compressor inlet of at least one refrigerant compressor; and

(e) cooling one or more of the streams from the group consisting of: a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a gaseous stream for the compressor; wherein said cooling is controlled depending on the temperature T1 in order to obtain a gas stream for the compressor at the normal operating temperature of at least one compressor.

The present invention also provides the use of the above method for cooling a hydrocarbon stream, for example, a natural gas stream. Accordingly, a method for cooling a hydrocarbon stream, for example a natural gas stream, is provided. The specified method includes at least the stages:

obtaining the initial flow of hydrocarbons;

cooling the hydrocarbon feed stream through heat exchange with a refrigerant stream to provide a cooled hydrocarbon stream and at least a partially vaporized refrigerant stream;

obtaining a feed stream for the compressor as a result of combining a recycle steam stream and at least a partially vaporized refrigerant stream;

passing the source stream for the compressor through the inlet separator to obtain a gas stream for the compressor;

passing a gas stream for the compressor through one or more compressors having a steam recirculation pipe to obtain a compressed refrigerant stream;

determining a temperature T1 of the gaseous stream for the compressor inlet of at least one refrigerant compressor; and

cooling one or more of the streams from the group including: a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a gas stream for the compressor; wherein said cooling is controlled depending on the temperature T1 in order to obtain a gas stream for the compressor at the normal operating temperature of at least one compressor.

The hydrocarbon stream may be partially or completely liquefied, for example, as a result of cooling or after cooling (the next step) in order to obtain a stream of liquefied hydrocarbons, for example, LNG.

The present invention also provides an apparatus for controlling one or more compressors for compressing one or more gas streams at normal operating temperature. The specified device, at least includes:

an inlet separator for receiving a feed stream for a compressor obtained by combining a recirculated steam stream and at least a partially vaporized refrigerant stream and to obtain a gas stream for a compressor;

at least one refrigerant compressor having an inlet for a flow of gaseous refrigerant and an outlet for a compressed flow of refrigerant;

one or more paths allowing passage of the recycle portion or the entire compressed refrigerant stream in the form of a recirculated vapor stream through the refrigerant compressor;

temperature controller for determining the temperature T1 of the gas stream at the inlet to the compressor (12) for the refrigerant, as well as for regulating:

(i) one or more chillers used to cool one or more of the streams from the group comprising a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a gas stream for the compressor, to produce a gas stream for the compressor at normal operating temperature; or

(ii) one or more streams colder than the recirculated steam stream combined with one or more streams from the group comprising a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a gas stream for the compressor, in order to obtain a gas stream for the compressor at normal operating temperature; or

(iii) one or more at least partially liquid streams combined with one or more streams from a group of streams comprising a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a gaseous compressor stream , in order to obtain a gaseous stream for the compressor at normal operating temperature; or

combinations of two or more of (i) - (iii) depending on temperature T1.

Embodiments and embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings.

1 is a diagram illustrating a method for controlling a compressor for a refrigerant in accordance with various embodiments of the present invention.

FIG. 2 is a diagram illustrating a method of controlling a series of refrigerant compressors in accordance with another embodiment of the present invention.

Figure 3 is an alternative diagram with respect to the method illustrated in figure 2.

4 is an illustration of changes in volumetric flow depending on the magnitude of the compression ratio in a compressor for a refrigerant in accordance with an analogue of the invention and in a compressor for a refrigerant controlled in accordance with one embodiment of the present invention.

For the purposes of the present description, one reference position number will be used both for designating the pipeline and for the flow transported through this pipeline. Identical circuit elements are indicated in the drawings by the same reference numbers.

The description contains references to various types of “valves”, including a flow control valve, a recirculation (bypass) valve, and an expansion valve. It is possible that some of the valves required in any circuit or process are not specifically or generally mentioned or indicated here. The person skilled in the art knows the type and arrangement of the valve or valves necessary to influence the flow in the pipeline, flow, circulation, circuit, etc.

Currently known methods and devices allow to regulate to varying degrees the cooling of one or more of the streams from the group including a recirculated steam stream, a partially vaporized refrigerant stream, an initial stream for the compressor and a gas stream for the compressor, which are regulated depending on the temperature T1 of the gas stream for the compressor at the compressor inlet for refrigerant, in order to maintain the gas flow for the compressor at normal operating temperature. This provides a more efficient control of the flow temperature at the inlet to the compressor, regardless of the flow rate of the recirculation flow.

In the present description, a gaseous stream for a compressor obtained from a source stream for a compressor is passed through a refrigerant compressor having a conduit for recirculating the steam stream. Embodiments contemplated use cooling of one or more streams, including a steam recirculation stream, a refrigerant stream, a compressor feed stream and a gaseous stream for the compressor to maintain the gas stream for the compressor at a normal operating temperature related to the refrigerant compressor.

By maintaining the temperature of the gas stream for the compressor at the inlet or on the suction side of the compressor at or near the normal operating temperature of the stream, the recirculated vapor stream is able to maintain the flow rate in the compressor for the refrigerant within its operating range, and thus surging is prevented.

The normal operating temperature of the compressor for the refrigerant is the temperature of the gaseous stream for the compressor at the inlet or at the suction side of the compressor for the refrigerant when steam is not recirculated (or the recirculation is minimal) (i.e., any recirculation valve is closed) .

In the case of using a compressor whose refrigerant is a clean component, the normal operating temperature of the gas stream for the compressor is the condensation temperature. One skilled in the art will recognize that the vapor supplied to the refrigerant compressor may be slightly superheated (less than a few degrees Celsius) due to the pressure differential between the refrigerant evaporator and the compressor inlet. In this case, in accordance with the invention, it is preferable to maintain the temperature rise relative to the condensation point of the gaseous stream for the compressor during the steam recirculation or recirculation process at a level of less than 10 ° C, more preferably less than 5 ° C.

In the case of a compressor using mixed refrigerant, the normal operating temperature may be the condensation temperature, but it may also be higher than the condensation temperature. In this case, the invention allows preferably to maintain any deviation of the temperature of the gas stream for the compressor at a level of up to 10 ° C higher or lower than the normal operating temperature, more preferably less than 5 ° C higher or lower, in the process of steam recirculation or recycling.

A compressor feed stream is obtained by combining a recirculated steam stream from a steam recirculation pipe and at least a partially vaporized refrigerant stream. Said at least partially vaporized refrigerant stream may flow from a heat exchanger in which a refrigerant stream removes heat by heat exchange with another stream (e.g., a cooled hydrocarbon stream) in a cooling zone. The recirculation pipe bypasses the cooling zone including the heat exchanger, and thus the recirculated steam stream bypasses the cooling zone and / or said heat exchanger.

The present invention is suitable, but not limited, for controlling one or more multi-stage refrigerant compressors having a number of inlets into which refrigerant enters at various pressure levels.

Accordingly, the present invention is particularly suitable, but not by way of limitation, when two or more refrigerant compressors are used for different gas flows for a compressor, in particular when these gas flows are at different pressure levels. When using multi-stage compressors for a refrigerant or compressor (s) for a refrigerant having a large number of sections and a large number of gas inlets with different pressures, and usually a large number of recirculation pipelines, simple and effective maintenance of the temperature (s) on the suction side, it is possible to avoid surging for all refrigerant compressors.

The present invention is particularly useful if the refrigerant stream is vaporized at various pressure levels, but a second compression of each vaporized portion of the stream to a single pressure is required to reuse it as a refrigerant.

Thus, in one embodiment, the described method includes two or more, preferably two or four, refrigerant compressors, and two, three, four or five gas streams for compressors.

Preferably, the present invention provides a method comprising using two or more gas streams for compressors having two or more different pressures, for example four gas streams for a compressor at four different pressures passing through two or four refrigerant compressors, which are separate compressors for refrigerant, one or more compressors for refrigerant with a large number of sections in one housing, or a combination of these types of compressors.

Maintaining the temperature on the suction side of the compressor for the refrigerant can be achieved in the process of steam recirculation, carried out using a number of ways. For example, it is possible to change the temperature of the recycle stream in the conduit to recycle the steam, usually cooled, in order to control on the compressor suction side the temperature of the gas stream, which includes the recycle stream.

Preferably, the temperature on the suction side can be maintained by adding one or more additional streams to one or more objects selected from the group including: one or more at least partially evaporated refrigerant streams, recirculated steam stream, compressor feed stream , compressor inlet separator, and gas flow for the compressor. One or more of these additional flows or has (have) a lower temperature than the stream to which it (they) are added, and / or they are fully or partially liquid flows, due to which the temperature on the suction side of the gas stream can be changed as needed. These colder and / or cooling streams can be directly introduced to change the temperature on the suction side of the gas stream as necessary. The source of one or more additional flows may be part of a cycle, circuit, or cooling system including a refrigerant compressor.

The particular or each refrigerant compressor used in the present invention may be any suitable refrigerant compressor, optionally having two or more compression stages or pressure sections. The use of the term “compressor for refrigerant” refers here to a single compressor for refrigerant having a series of pressure sections in one housing capable of sucking in two or more gas streams at different pressures. One or more other refrigerants or compressors not included in the present invention and not implementing a recirculation mode may also be used in an installation or in a plant for cooling or liquefying hydrocarbons, unlike those disclosed in the present invention.

The particular or each recycle line that can be used in the present invention can be any suitable line capable of transporting the recycle stream, which can be in a liquid, gaseous, or two-phase state, from the discharge side of the refrigerant compressor to the suction side. A particular or each recirculation pipe may be branched or split in a manner known in the art to supply a portion or a fraction of the recirculation stream to two or more refrigerant compressors.

The refrigerant stream may include a single component, for example propane or nitrogen, or may include a mixture of two or more components selected from the group consisting of nitrogen, methane, ethane, propane, butanes, pentanes.

Optionally, the present invention further includes one or more of the following additional steps:

(f) dividing the compressed refrigerant stream into at least a first constant stream and a recirculated steam stream;

(g) cooling the first constant stream to obtain at least partially condensed first constant stream;

(h) dividing the at least partially condensed first constant stream into a second constant stream and a second recycle stream;

(i) allowing evaporation of at least a portion of the second constant stream to produce at least a partially vaporized refrigerant stream of step (a); and

(j) using a second recycle stream as one or more cold streams.

1 is a simplified and general diagram 2 illustrating the implementation of various compressor control methods for compressing a refrigerant stream.

Figure 1 also illustrates a method of cooling a stream of hydrocarbons, for example, natural gas. The natural gas feed stream 5 passes through a cooling zone 21, which may contain one or more heat exchangers arranged in series or in parallel or in series-parallel to obtain a cooled hydrocarbon stream 6, for example, having a temperature below 0 ° C, for example, in the range from -10 ° C to -70 ° C, optionally partially liquefied.

The hydrocarbon feed stream 6 is cooled by heat exchange with a refrigerant stream 20e, which provides at least partially, usually a large part, and preferably a fully vaporized refrigerant stream 8. Further, it is necessary that for the most part the vaporized refrigerant stream 8 be recycled for reuse. Accordingly, the source of the compressor feed stream 10a partially or completely passes through the compressor inlet separator 11 to remove substantially any liquid that may be present in the compressor feed stream 10a, thereby obtaining a gas stream 10 for the compressor discharged from the top of the separator. (The inlet separator 11 may also provide a small liquid stream 10b discharged from the bottom of the separator).

The gas stream 10 for the compressor passes through the inlet 14 of the compressor 12 for the refrigerant. In said refrigerant compressor 12, the gas stream is compressed to produce a compressed refrigerant stream 20 discharged through outlet 16.

If desired, a first heat exchanger 26 is used, typically an environmentally cooled heat exchanger, for example, one or more water and / or air coolers placed after outlet 16 and designed to cool the compressed refrigerant stream 20 and produce a cooler compressed refrigerant stream 20a.

The compressed refrigerant stream 20 (or cooled compressed stream 20a) is separated by a separation device 18 or stream divider into a constant refrigerant stream 20b and a steam recirculation stream 30. The separation device 18 may be any device capable of dividing the flow into two or more parts or parts, for example, a block of collectors or a special device, or more simply, a tee. The steam recirculation stream 30 is preferably substantially completely in the vapor phase. A constant flow of refrigerant 20b passes through one or more coolers 17 and one or more collecting tanks 19, before expanding as it passes through expansion valve 7 and recirculating through recirculation zone 21.

In general, the separation of the compressed refrigerant stream 20 can provide any percentage, from 0 to 100%, of a 30 steam recirculation stream. That is, during the operation of the compressor 12 for the refrigerant, there may be cases in which recirculation is not required to keep the minimum flow rate at the compressor inlet 14 (i.e., the steam recirculation stream 30 corresponds to 0%). Alternative cases are possible in which 100% of the compressed refrigerant stream 20 is directed to recirculation in the form of a steam recirculation stream 30, for example, during startup of the compressor 12 for the refrigerant.

For the purposes of the present invention, a recycle stream 30 and some other recycle stream are used in the workflow and combined with at least a partially vaporized refrigerant stream 8 coming from the heat exchanger 21. For example, the steam recirculation stream 30 is some for example, 10 vol.% of the compressed refrigerant stream 20.

The steam recirculation stream 30 passes through an expansion device, for example, a recirculation valve 22, known in the prior art, to obtain an expanded first stream 30a, which can be combined with at least partially vaporized refrigerant stream 8, using a combining device 24 to obtain as a result of the source stream 10a for the compressor.

Figure 1 shows the temperature controller T1, which measures the temperature T1 of the gas stream 10 at the inlet 14 of the compressor 12 for the refrigerant. The temperature controller T1 may be any device known in the art for this purpose. The actual temperature of the gas stream 10 for the compressor inlet 14 of the compressor is not essential to the present invention. It is only essential to maintain the compressor 12 for the refrigerant at or near normal operating temperature, for example, ± 10 ° C. Thus, in one embodiment, the temperature controller T1 may determine a temperature difference between the temperature T _{1 of the} gas stream 10 for the compressor at the inlet 14 of the compressor 12 for the refrigerant and the normal operating temperature of said compressor 12 for the refrigerant.

In another embodiment, the normal operating temperature of the compressor 12 for the refrigerant may be introduced into the temperature controller T1 as an insert (a predetermined value of an adjustable parameter), or a range of a predetermined value may be entered and the temperature controller T1 seeks to maintain a measured input temperature T1 within this interval.

1, a temperature controller T1 is shown mounted on a compressor gas line 10. However, it can be placed on any pipeline through which the temperature T1 at the inlet of the compressor can be determined.

Figure 1 shows a number of possible circuits that allow you to adjust the gas flow 10 for the compressor to maintain its desired inlet temperature T1.

In one design, the first heat exchanger 26 can be used to control the temperature of the cooler compressed refrigerant stream 20a, which, therefore, will influence the temperature of the separated steam recirculation stream 30. Such temperature control can be used along the entire recirculation pipe 30 and affects the temperature of the stream obtained by combining the expanded steam recirculation stream 30a and the at least partially evaporated refrigerant stream 8 so as to maintain the desired inlet temperature T1 of the gas stream 10 for the compressor.

In a second circuit, a second heat exchanger 28 is arranged along the flow path of the source stream 10a for the compressor. This second heat exchanger 28 can control the temperature of the gas stream 28 for the compressor maintained at or near normal operating temperature.

A third possible arrangement, illustrated in FIG. 1, provides for the addition of a first cold, preferably liquid-containing, stream 32 combined by a combiner 32a with an expanded steam recirculation stream 30a. It is preferable to directly introduce the first cold, preferably liquid-containing, stream 32 into the expanded steam recirculation stream 30a. The cold stream 32 is vaporized in contact with the warmer steam recirculation stream 30a to produce a first combined recirculation stream 30b having a temperature lower than the steam recirculation stream 30a. The temperature of said last stream can be changed by changing the ratio between the cold stream 32 and the more heated steam recirculation stream 30a combined with it. Thus, the temperature of the first combined recycle stream 30b may be such as to affect the connection of this stream with an at least partially vaporized refrigerant stream 8 to produce a gas stream 10 for a compressor having a desired inlet temperature.

In a fourth possible arrangement, shown in FIG. 1, a second cold stream 34 is provided that is combined with the compressor feed stream 10a via a combiner 34a, for example, for example, by directly introducing a second cold stream 34. The temperature and / or phase of the second cold stream 34 may also be such as to affect the temperature of the gas stream 10 for a compressor having an inlet temperature corresponding to or close to its operating point.

The cooling of the stream by combining it with a cold stream or a cooling stream, as described above in the third and fourth schemes, can be called direct heat transfer. The passage of this stream and the cold stream or cooling stream through the heat exchanger, such as in the first and second schemes described above, may be called indirect heat exchange.

To influence the temperature or to control the temperature of the gas stream 10 for the compressor, two or more heat exchangers shown in FIG. 1 can be used in front of the compressor inlet 14.

The person skilled in the art is aware of the basic properties and the supply of flows to the first and second heat exchangers 26, 28, which may include one or more heat exchangers arranged in parallel, sequentially or sequentially-in parallel, as well as about the basic properties and preparation of the first and second cold streams 32, 43.

For example, the second heat exchanger 28 may be provided with a cold stream 28a, which first passes through the control / expansion valve 28b. The expansion of such flows and their use in heat exchangers are known in the art.

The first and second cold streams 32, 34 can be obtained from any suitable source, which is placed separately or included in the circuit with the refrigerant of the General circuit 2, shown in figure 1. For example, after a constant flow of refrigerant 20b has passed through one or more coolers 17 and through one or more collection tanks 19, its flow 20c can be separated using a separation device 19a or a flow divider into a second constant flow 20d (which flows through the valve 7 and becomes a refrigerant stream 20e) and a second recycle stream 40, which is preferably at least partially vaporized liquid recycle stream 40 flowing through the second recycle ruboprovod 40. The liquid recirculation stream 40 preferably includes a liquid phase or in a mixed liquid and vapor phases, or essentially a fully liquid phase.

The source (source stream) for the second cold stream 34 may be a suitable supply, at least partially, preferably completely, of the liquid stream 34b.

Preferably, the first and second feed streams 40, 34b for the first and second cold streams 32, 34 flow through the respective first and second flow control valves 40a, 34c. Optionally, one or more of the feed streams for cold streams 32, 34 may also be cooled in a separate heat exchanger (s).

Figure 1 also shows that data on the inlet temperature T1 of the compressor gas stream 10 can be transmitted, for example, to one or more expansion devices, for example, valves, which affect the flow and / or cooling of one or more streams in the general scheme 2 shown in FIG. For example, the inlet temperature T1 may be transmitted via one or more lines 9 (shown in broken lines) to one or more valves 28b, 34c and 40a. These valves then, during their operation, control the flow rate of the expanded flow, which as a result changes the degree of cooling of one or more flows passing through one or more heat exchangers, or one or more flows combined with it.

The present invention can thus provide quick control and feedback on the inlet temperature to one or more valves to maintain the temperature of the gas stream 10 for the compressor at or near normal operating temperature. In addition, a signal indicating the position of the regulator of the recirculation valve 22, or a signal coming from a regulator (not shown) that regulates the recirculation valve 22, can be directed to any of the other control valves in the circuit shown in figure 1, to increase the speed of temperature control. This provides proactive or ratio control.

Thus, cooling as a function of temperature T1 may suitably include controlling the operation of one or more valves. These valves may control the flow and / or expansion of the cold stream or cooling stream used to cool one or more of the streams determined in step (e) - appropriately due to direct or indirect heat exchange between said streams - or they may otherwise the effect on cooling of one or more of the streams determined in step (e).

The effect of maintaining the temperature T1 of the gas stream 10 for the compressor at a “constant” level, for example, within ± 10 ° C of the normal operating temperature, is that the recirculated steam stream is able to maintain the required intake flow rate of the gas stream 10 of the compressor at the inlet 14 in order to avoid surging of the compressor 12 for the refrigerant.

By maintaining the required inlet temperature T1 of the gas stream 10 for the compressor, surging of the compressor is prevented by temporarily reducing the flow rate, as shown by line A in FIG. 4. With a minimum flow rate in the recirculation pipe 30 for steam, the operation of the compressor 12 for the refrigerant, in addition, will be more efficient by reducing the unreasonably high degree of recirculation. For example, US Pat. No. 4,464,720 shows a centrifugal compressor having a recirculation pipe connected between the compressor suction and discharge sides. However, the said document does not describe the temperature control of the recirculation pipe or the flow passing through it, so that the opening and closing of the bypass anti-surge valve shown in US Pat. No. 4,464,720 leads to a change in pressure and therefore the temperature of the gas being returned back to the centrifugal compressor, so as described above with respect to line A in FIG. 4.

In the absence of any regulation of the temperature of the incoming gas during pressure changes caused by changes in the recirculation pipe (for example, when it is opened or closed), surging is possible in the compressor for the refrigerant. In addition, in the case of recirculation with a reduced output power of the drive, the compressor is forced to operate in a less efficient mode. By maintaining the inlet temperature of the gas stream 10 for the compressor at a point corresponding to normal operation, for example, less than 10 ° C above the condensation point for refrigerants comprising a clean component, and within 10 ° C of the normal operation point for mixed refrigerants, the invention avoids such changes and, thus, maintain the compressor 12 for the refrigerant when changing the flow rate of the gas stream 10 at optimal performance.

Figure 4 illustrates, by line B, how the compressor performance for a refrigerant can be significantly improved by fixing the inlet temperature of the compressor using the present invention. In particular, a refrigerant compressor does not change its performance. In addition, the temperature of the liquid volume in the system no longer changes. As shown in figure 4, there is a movement from the initial stationary state (shown by triangle a) to the new stationary state (asterisk γ) along only one compressor operating characteristic. Thus, with a decrease in the compression ratio, the flow rate through the compressor continuously increases, without following the above-described path of change along line A.

1, the refrigerant compressor 12 may be a single refrigerant compressor designed to compress a single refrigerant stream, or a series of refrigerant compressors designed to compress one or more refrigerant streams may be used, and / or one may be used a refrigerant compressor having two or more inlets for compressing one or more refrigerant streams at various pressures, optionally enclosed in a single housing.

2 illustrates another cooling circuit 3 having a cooling zone 41. Said cooling zone 41 may include two or more, for example, four separate heat exchangers, or it may include a single heat exchanger having refrigerant outlets at various pressure levels. Such schemes are well known in the art, and for example, are known from patent documents WO 01/44734 A2 and WO 2005/057110 A1.

The cooling zone 41 may serve to remove heat from the stream, for example, from one or more hydrocarbon streams 5, for example, a stream of liquefied natural gas. Examples of methods for liquefying natural gas are mentioned in patent documents US 6389844 and US 6370910 included in this description by reference. These patent documents describe a natural gas liquefaction apparatus comprising a pre-cooling heat exchanger having a natural gas inlet, a chilled natural gas outlet and a pre-cooling circuit for removing heat from natural gas in a pre-cooling heat exchanger.

The cooling zone 41 may be equivalent to the heat exchanger 21 shown in FIG. 1, or a part thereof. For example, when cooling, preferably liquefying, a hydrocarbon stream 5, two or more stages are used, for example, a first stage to lower the temperature of the hydrocarbon stream 5 below 0 ° C, and a second stage to further lower the temperature of the hydrocarbon to below -90 ° C or - 100 ° C, while the cooling zone 41 can serve as a first stage cooler.

Since the arrangement and operation of the cooling zone 41 is well known, it is shown only schematically for clarity. The specified cooling zone has an inlet 42 for the flow of refrigerant 60, which is at the pressure of the cooling process. More than one input can be used.

In the circuit shown in FIG. 2, the cooling zone 41 has first, second, third and fourth outlets 43, 44, 45, 46, respectively, for certain parts of the refrigerant that has evaporated at various pressure levels, with pressure decreasing from the first outlet 43 to the fourth outlet 46. For example, the first outlet 43 is for gaseous refrigerant discharged at very high pressure as the first vaporized stream 70, the second outlet 44 is for gaseous refrigerant discharged at high pressure as the second vaporized stream 80, the third outlet 45 is for gaseous refrigerant discharged at intermediate pressure as the third vaporized stream 90, and a fourth outlet 46 is used for gaseous refrigerant discharged at intermediate pressure as the fourth vaporized stream 100. The cooling zone 41 may also have other outlets.

Each vaporized stream 70, 80, 90, 100 is directed to a corresponding inlet separator, each of which can be made in the form of a gas-liquid separator, for example, drum separators 48a, 48b, 48c, 48d, from the top of which gas flows 70a, 80b, 90c , 100d, then sent to one or more refrigerant compressors.

The gas stream 100a leaving the fourth drum separator is directed to the first refrigerant compressor 58 to produce a compressed stream 120 that is combined with the gas stream 80a drawn from the second drum separator and fed to the second refrigerant compressor 56 to produce a first combined compressed stream 120. The first and second compressors 58, 56 can be separate compressors for the refrigerant, or they can be placed in one housing with two inlets and one or two sections to provide different pressure levels the separated streams 80a and 100a allocated from the second and fourth drum separators

Similarly, the gas stream 90a from the third drum separator is directed to the third refrigerant compressor 54, and the compressed stream 90b therein is combined with the gas stream 70 discharged from the first drum separator, sent to the fourth refrigerant compressor 52 and a second combined compressed stream 110 is obtained. As in the case described above, the third and fourth refrigerant compressors 54, 52 may be separate refrigerant compressors, or they may be in the same common housing having two inputs and different sections for the refrigerant vaporized gas flows diverted from the first and third drum separators.

Each refrigerant compressor (12, 52, 54, 56, 58) may have a steam recirculation stream (30) or part of the steam recirculation stream (150a-d). Similarly, each of one or more of the available refrigerant compressors may be provided with a vapor recirculation pipe and at least partially liquid recirculation pipe to bypass a particular or each refrigerant compressor.

The arrangement of the cooling zone 41, the gas outlet and the refrigerant compressors 52-58 are known in the art and are described, for example, in patent document WO 01/44734 A2.

The first and second combined compressed streams 110 and 120 are combined with each other to form a common compressed stream 130, which is cooled using a first cooler, for example, using the environment as a refrigerant, for example, using a water and / or air cooler known in the art technicians. The first cooler 62 may include one or more coolers connected in parallel, in series or in series-parallel, and provides a cooled compressed stream 140.

In the same manner as described above for the circuit shown in FIG. 1, the cooled compressed stream 140, using the stream divider 72, can be divided into a first constant stream 160 and a steam recirculation stream 150. The steam recirculation stream 150 can be divided into four separate parts 150a, 150b, 150c, 150d of the recirculation stream, which pass through separate respective control valves and are combined with the evaporated refrigerant flows 70, 80, 90 and 100, respectively.

The first constant stream 160 is further cooled and for the most part or completely condensed, for example, using a second cooler 64, which is one or more coolers, for example, air and / or water coolers, which provides a cooled first constant stream 170. Cooling with using the specified second cooler 64 preferably completely condenses the cooled first continuous stream 170. The specified cooled first constant stream 170 enters the collection tank 66, which may be a separate apparatus, or into a conventional divider of a first cooled constant flow 170.

The collection tank 66 provides a second constant liquid stream 190, which can be further cooled using a third cooler 68, which is one or more coolers, for example, water and / or air coolers, to obtain a recovered or improved usually liquid refrigerant stream, ready to pass through valve 77, return and use as stream 60 in cooling zone 41.

The collection tank 66 also provides a convenient source of a second usually liquid recirculation stream 180, which is colder than the first recirculation stream 150. Thus, the second recirculation stream 180 can act as a source of the cold stream 32 shown in FIG. Like the first recycle stream 150, the second recycle stream 180 can be divided into a series of partial streams, for example, into the four partial streams 180a, 180b, 180c, 180d shown in FIG. 2 for passing them through respective four-part flow control valves 150a, 150b, 150c, 150d of the flow, respectively, before the combined flow enters the drum separators 48a-48d. The colder partial streams 180a-180d (which are liquid in the circuit shown in FIG. 2, but in other circuits, possibly biphasic or even only gaseous) evaporate by contacting and combining with the warmer parts 150a-150d of the steam recirculation stream, for example by directly introducing a recirculated steam stream into the warmer parts 150a-150d, whereby the temperature of the combined streams decreases before they enter the respective refrigerant compressors 52-58.

The flow rate and temperature of the second recirculation stream 180 and the four partial flows 180a, 180b, 180c, 180d can be controlled by adjusting the flow rate of the outlet tank 66 and / or by adjusting the valves through which the four partial flows 180a, 180b, 180c, 180d before combining them with recirculation flow portions 150a, 150b, 150c, 150d. These actions are simple control actions carried out so that they influence the temperature of the various flows just combined.

Thus, the second recirculation stream 180 provides a recirculation stream having a temperature lower than the temperature of the first recirculation stream 150, so that their combination can be used to control the temperature of the combined refrigerant flows 70a, 80a, 90a and 100a before the combined flows enter 52-58 compressors for refrigerant.

Thus, maintaining the inlet temperatures of at least the first and third compressors 58, 54 indicated in FIG. 2 as the inlet temperatures T ₂ , T _3, respectively, can preferably be carried out within ± 5 ° C of their normal operating temperature. The control of the temperature and flow rate of the steam stream 150 and the second recirculation stream 180, as well as the valves for each part of the flows before combining them with the vaporized refrigerant stream 70-100, can provide optimal control accuracy for the 52-58 refrigerant compressors and their inlet temperatures T ₂ and T ₃ .

If desired or necessary, the inlet temperatures before the fourth and second refrigerant compressors 52, 56 can be maintained in a similar manner at or close to their normal operating temperature, including directly controlling the flows 70a, 80a and combining them with the compressed flows 90b and 100b.

FIG. 3 shows a second cooling circuit 4, similar to the first cooling circuit 3 shown in FIG. 2. However, in the second cooling circuit 4, the second vaporized refrigerant stream 80a is now combined with the second compressed stream 90b before supplying said combined stream to the fourth refrigerant compressor 52. In this case, the first gaseous vaporized stream 70a is combined with the first compressed stream 100b to be directed to the third refrigerant compressor 56. Such an arrangement of compressors for refrigerant and vaporized refrigerant streams flowing from the cooling zone is presented in patent document WO 2005/057110 A1.

In a circuit similar to that shown in FIG. 2, the two combined compressed streams 110a, 120a are subsequently combined to produce a common compressed stream 130, first cooled, to produce a steam recirculation stream 150 and divide it into four partial streams to combine with each of the vaporized flows of 70-100 refrigerant. The first constant stream 160 is then cooled with a second cooler 64 and sent to a collection tank 66 where a second recirculation stream 180 is obtained, which is subsequently divided into four parts 180a-180d to add them to the corresponding parts 150a, 150b, 150c and 150d of the recirculation stream as described above.

Again, controlling the temperature and flow rate of the first and second recirculation flows 150 and 180, as well as the valves for each part of the flow before combining them with 70-100 refrigerant flows, can ensure the accuracy of the optimal operation of the 52-58 refrigerant compressors in the circuit shown figure 3, to maintain their input temperature T2 and T3 within normal operating temperature or close to it.

In the circuits shown in FIGS. 2 and 3, additional recirculation of the flows and / or different separation of each of the recirculation flows can be provided in order to optimize the temperature control of the gaseous refrigerant flows entering each refrigerant compressor or to each compressor section for the refrigerant in such a way as to maintain the inlet temperature of at least one compressor corresponding to the normal operating temperature, or close to it.

Table 1 shows a comparison of the various flows in the cooling circuit that occur in the first case in the circuit used in the analogue, based on the circuit illustrated in Fig. 2, but only with a single steam recirculation, and, in the second case, according to the circuit demo the cooling circuit according to the present invention shown in figure 2, using the second recirculation stream 180.

Table 1 Recycling according to analogue Recirculation through stream 180 Flow Consumption (kg / s) P (bar) T (° C) Consumption (kg / s) P (bar) T (° C) 130 693 21.5 714 23.6 70a 5.5 20.9 5,4 7.8 80a 3,5 15.3 3.0 -8.0 90a 1.4 -5.1 1,2 -33.8 100a 1,1 10.3 0.73 -46.5 180a 20,2 180b 15.4 180c 13.3 180d 11.3 150a 144 93.1 150b 86 56.6 150c 53 26.5 150d 63 15.4

Table 1 shows a significant decrease in the temperature of the streams 70a, 80a, 90a, 100a removed from the top of the compressor inlet separators (which are then full or additional gas streams for the compressor) in the case when these streams are a combination with the cooler part 180a-180d the second recirculation stream 180. These temperature reductions allow you to maintain the combined flows 70a, 80a, 90a, 100a (and therefore also the connection of flows 90 + 70a and 100b + 80a) at normal operating temperatures of the compressors 5 2-58 refrigerant or close to it.

The methods and devices disclosed in this description can be used to prevent surge in one or more compressors.

Claims (21)

1. A method of controlling one or more refrigerant compressors designed to compress one or more gas streams at normal operating temperature, wherein at least one of the refrigerant compressors is provided with a steam recirculation pipe, said method comprising, at least stages:
(a) obtaining a feed stream for the compressor as a result of combining the recirculated steam stream from the steam recirculation pipe and at least a partially vaporized refrigerant stream;
(b) passing the feed stream for the compressor through the inlet separator to obtain a gas stream for the compressor;
(c) passing the gas stream for the compressor through the compressor (s) for the refrigerant;
(d) determining a temperature T1 of the gaseous stream for the compressor at the inlet of at least one refrigerant compressor; and
(e) cooling one or more of the streams from the group consisting of: a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a gas stream for the compressor; while the specified cooling is regulated depending on the temperature T1 in order to obtain a gas stream for the compressor at normal operating temperature of at least one compressor. 2. The method according to claim 1, comprising two or more, preferably two or four compressors for the refrigerant and two, three, four or five gas streams for the compressor. 3. The method according to claim 2, in which two or more gas streams for the compressor have different pressures relative to each other. 4. The method according to claim 3, in which four gas streams for compressors at four different pressures pass through two or four compressors for the refrigerant. 5. The method according to claim 1, in which the refrigerant stream mainly includes propane. 6. The method according to claim 1, in which at least one of the compressors has a large number of pressure sections. 7. The method according to claim 1, wherein said regulation comprises maintaining the temperature T1 of the gas stream for the compressor within ± 10 ° C, preferably within ± 5 ° C of the normal operating temperature of the compressor for the refrigerant. 8. The method according to claim 1, wherein said cooling in step (e) comprises cooling using a cold stream or a cooling stream in a heat exchanger. 9. The method according to claim 1, wherein said cooling in step (e) comprises adding one or more colder streams or cooling streams to one or more streams from said stream group. 10. The method according to claim 9, further comprising the steps of:
(f) dividing the compressed refrigerant stream into at least a first constant stream and a recirculated steam stream;
(g) cooling the first constant stream to obtain at least partially condensed first constant stream;
(h) dividing the at least partially condensed first constant stream into a second constant stream and a second recycle stream;
(i) allowing evaporation of at least a portion of the second constant stream to produce at least a partially vaporized refrigerant stream of step (a); and
(j) using a second recycle stream as one or more cold streams or cooling streams. 11. The method of claim 10, wherein the second recirculation stream is added to the recirculated steam stream. 12. The method according to claim 1, in which stage (e) includes cooling the recirculated steam stream. 13. The method according to any one of the preceding paragraphs, in which the specified cooling, depending on the temperature T1, includes regulating the functioning of one or more valves, which affects the cooling of one or more streams indicated in stage (e). 14. The method according to item 13, in which one or more valves regulate the flow and / or expansion of the cold stream or cooling stream used to cool one or more of the streams described in stage (e). 15. The use of the method according to one of the preceding paragraphs for cooling the flow of hydrocarbons, according to which
provide an initial flow of hydrocarbons;
cool the hydrocarbon feed stream by heat exchange with a refrigerant stream that passes through one or more refrigerant compressors to produce a cooled hydrocarbon stream and at least a portion of the at least partially vaporized refrigerant stream of step (a). 16. The use of claim 15, further comprising the step of liquefying the initial hydrocarbon stream to produce a liquefied hydrocarbon stream. 17. The use according to clause 16, in which the liquefied hydrocarbon stream is a stream of LNG. 18. Use according to any one of claims 15-17, wherein the hydrocarbon stream is a natural gas stream. 19. A device for controlling one or more compressors for refrigerant, designed to compress one or more gaseous streams at normal operating temperature, containing at least:
an inlet separator for receiving a feed stream for a compressor formed by combining a recirculated steam stream and at least a partially vaporized refrigerant stream and to produce a gaseous stream for the compressor;
at least one refrigerant compressor having an inlet for a gaseous refrigerant stream and an outlet for receiving a compressed refrigerant stream;
one or more paths allowing passage of the recycle portion or the entire compressed refrigerant stream in the form of a recirculated steam stream through the refrigerant compressor;
a temperature controller for determining the temperature T1 of the gaseous stream for the compressor at the inlet to the compressor for the refrigerant, and for regulating or:
(i) one or more chillers used to cool one or more of the streams from the group comprising a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a compressor gas stream, to produce a gas stream for the compressor at normal operating temperature; or
(ii) one or more streams colder than the recirculated steam stream combined with one or more streams from the group comprising a recirculated steam stream, at least partially vaporized refrigerant stream, a compressor feed stream and a gas stream for the compressor, in order to obtain a gas stream for the compressor at normal operating temperature;
(iii) one or more at least partially liquid streams combined with one or more streams from a group of streams comprising a recirculated steam stream, at least a partially vaporized refrigerant stream, a compressor feed stream and a gaseous compressor stream, in order to obtain a gaseous stream for the compressor at normal operating temperature; or
(iv) a combination of two or more of (i) to (iii) depending on the temperature T1. 20. The use of the device according to claim 19 for cooling a hydrocarbon stream, comprising cooling the initial hydrocarbon stream by heat exchange with a refrigerant stream that passes through one or more refrigerant compressors to produce a cooled hydrocarbon stream and at least a portion of at least at least partially vaporized refrigerant flow. 21. The use of claim 20, wherein the hydrocarbon stream is a natural gas stream.

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