KR20110061615A - Method of cooling a hydrocarbon stream and an apparatus therefor - Google Patents

Abstract

In a method and apparatus for cooling a hydrocarbon stream, the hydrocarbon stream 45 to be cooled has a first heat exchanger (50) for at least one refrigerant stream (145b, 185b) having a flow rate (FR1) of the first refrigerant stream. Heat exchange at to provide a cooled hydrocarbon stream 55 and at least one return refrigerant stream 105 having a flow rate FR2 of the cooled hydrocarbon stream. The flow rate FR1 of the first refrigerant stream and the flow rate FR2 of the cooled hydrocarbon stream are adjusted until the input first set point SP1 for the flow rate FR1 of the first refrigerant stream is obtained. If the first set point SP1 is greater than the flow rate FR1 of the first refrigerant stream, the flow rate FR2 of the cooled hydrocarbon stream is increased before the flow rate FR1 of the first refrigerant stream is increased; If the first set point SP1 is less than the flow rate FR1 of the first refrigerant stream, the flow rate FR1 of the first refrigerant stream is reduced before the flow rate FR2 of the cooled hydrocarbon stream is reduced; If the flow rate FR2 of the cooled hydrocarbon stream is reduced, the flow rate FR1 of the first refrigerant stream is also reduced.

Description

METHOD OF COOLING A HYDROCARBON STREAM AND AN APPARATUS THEREFOR}

The present invention relates to a method and apparatus for cooling a hydrocarbon stream.

An important example of the hydrocarbon stream to be cooled is the natural gas stream. Such cooling may include liquefying the hydrocarbon stream to produce a liquefied natural gas (LNG) stream if the liquefied hydrocarbon stream, eg, the hydrocarbon stream to be cooled, is a natural gas stream.

Natural gas is not only a useful source of fuel, but also a source of various hydrocarbon compounds. For many reasons, it is often desirable to liquefy natural gas in a liquefied natural gas (LNG) plant at or near the source of the natural gas stream. For example, natural gas can be easily stored and transported over long distances in the liquid phase rather than in the gas phase because the liquid phase occupies a small volume and does not need to be stored at high pressure.

Typically, natural gas, mainly including methane, is pretreated to enter the LNG plant at elevated pressure and produce a purified feed stream suitable for liquefaction at cryogenic temperatures. The purified gas is processed through a number of cooling stages using a heat exchanger to drastically lower its temperature until a liquefaction is obtained. The liquid natural gas can then be further cooled and expanded to the final atmospheric pressure suitable for storage and transportation.

In addition to methane, natural gas typically contains some weight hydrocarbons and impurities such as carbon dioxide, sulfur, hydrogen sulfide and other sulfur compounds, nitrogen, helium, water, other non-hydrocarbon acid gases, ethane, propane, butane, C ₅ + Hydrocarbons and aromatic hydrocarbons include, but are not limited to. These and any other common or known weight hydrocarbons and impurities prevent or hinder the usual known methods of liquefying methane, in particular the most effective way of liquefying methane. Most known or proposed methods of liquefying hydrocarbons, in particular liquefied natural gas, are based on reducing the levels of hydrocarbons and impurities of at least most of the weight as much as possible before the liquefaction process.

Hydrocarbons heavier than methane and usually ethane are typically condensed and recovered from the natural gas stream as natural gas liquids (NGL). The methane is usually separated from the NGL in a high pressure scrub column, which is then used to produce the expensive hydrocarbon product as a component of the product stream itself or as a product stream for liquefaction, for example a refrigerant, In a number of dedicated distillation columns.

On the other hand, the methane from the scrubbing column is then liquefied to provide LNG.

U.S. Patent Application 2003/0046953 describes a method for controlling the production of LNG to continuously use the maximum power available to drive a refrigeration cycle, which allows the operator to set the light weight and the set point of the flow rate of one of the refrigerants. The ratio of the flow rate of the mixed refrigerant of the weight to the mixed refrigerant of can be adjusted.

The aforementioned method cannot prevent overcooling of the heat exchanger below the minimum temperature limit or prevent excessive mechanical stress (thermal shock) of the heat exchanger caused when the temperature drops too rapidly. If this happens, leakage from the heat exchanger may proceed.

The present invention seeks to address the above and other problems associated with cooling hydrocarbon streams.

In a first aspect, the present invention provides a method of cooling a hydrocarbon stream in a heat exchanger, wherein the method comprises at least:

(a) providing a hydrocarbon stream,

(b) in a first heat exchanger, heat exchange with said hydrocarbon stream for at least one refrigerant stream having a flow rate of a refrigerant stream to provide a cooled hydrocarbon stream and at least one return refrigerant stream having a flow rate of a hydrocarbon stream; ,

(c) entering a first set point for the flow rate of said refrigerant stream, and

(d) adjusting the flow rate of the refrigerant stream and the flow rate of the hydrocarbon stream until the set point is obtained,

(1) if the first set point is greater than the flow rate of the refrigerant stream, the flow rate of the hydrocarbon stream is increased before the flow rate of the refrigerant stream is increased,

(2) if the first set point is less than the flow rate of the refrigerant stream, before the flow rate of the hydrocarbon stream is reduced, the flow rate of the refrigerant stream is reduced,

(3) When the flow rate of the hydrocarbon stream is reduced, the flow rate of the refrigerant stream is reduced.

In a second aspect, the present invention provides an apparatus for operating a heat exchanger, the apparatus comprising at least:

A first heat exchanger having a first inlet for a hydrocarbon stream and a first outlet for a cooled hydrocarbon stream, at least a second inlet for at least one refrigerant stream and a second outlet for a return refrigerant stream,

A refrigerant stream flow controller measuring a signal proportional to the flow rate of the refrigerant stream of the at least one refrigerant stream and providing a refrigerant flow signal sent to the high selector and operating the refrigerant valve to control the flow rate of the refrigerant stream,

Measure a signal proportional to the flow rate of the cooled hydrocarbon stream of the cooled hydrocarbon stream to provide a cooled hydrocarbon flow signal sent to the row selector and also operate the cooled hydrocarbon stream valve to control the flow rate of the cooled hydrocarbon stream. Cooled hydrocarbon stream flow controller,

A flow setter that inputs a set point to provide a set point signal sent to the low selector and high selector,

A row selector for transmitting the smallest of said set point signal and the cooled hydrocarbon stream flow signal to a refrigerant flow controller, and

A high selector for transmitting the largest of the set point signal and the refrigerant stream flow signal to the cooled hydrocarbon stream flow controller.

Embodiments and examples of the present invention are described by way of example only with reference to the attached non-limiting drawings.

1 is a schematic flow diagram of an apparatus for cooling a hydrocarbon stream provided with means for implementing one embodiment of the present invention;
2 is a control diagram for a method of cooling a hydrocarbon stream according to one embodiment of the invention, and
3 is a control diagram for a method of cooling a hydrocarbon stream according to another embodiment of the present invention.

As described herein, subcooling of the heat exchanger can be prevented by adjusting the flow rate of the refrigerant stream and the flow rate of the hydrocarbon stream in the following manner until the set point is obtained:

(1) If the first set point is greater than the flow rate of the refrigerant stream, the flow rate of the hydrocarbon stream is increased before the flow rate of the refrigerant stream is increased:

(2) If the first set point is less than the flow rate of the refrigerant stream, the flow rate of the refrigerant stream is reduced before the hydrocarbon stream is reduced:

(3) When the flow rate of the hydrocarbon stream is reduced, the flow rate of the refrigerant stream is reduced.

In this way, it is ensured that there is always enough hydrocarbon in the hydrocarbon stream to obtain cooling from the refrigerant in the refrigerant stream.

The steps are performed automatically, ie with or without minimal human intervention after the first set point has been established, for example in a fully automatic control system.

1 provides an apparatus for cooling, preferably liquefying, a hydrocarbon stream 45. This hydrocarbon stream may be any suitable gas stream to be cooled, but is a natural gas stream typically obtained from natural gas or petroleum reservoirs. As an alternative, the natural gas stream may be obtained from other sources, including synthetic sources such as the Fischer-Tropsch process.

Typically, the natural gas stream consists essentially of methane. Preferably, the feed stream comprises at least 60 mol% methane, more preferably at least 80 mol% methane.

Depending on the source, natural gas may include various amounts of hydrocarbons heavier than methane, such as ethane, propane, butane and pentane as well as some aromatic hydrocarbons. Natural gas may also include non-hydrocarbons such as H ₂ O, N ₂ , CO ₂ , H ₂ S and other sulfur compounds.

If necessary, the hydrocarbon stream comprising natural gas may be pretreated before use. Such pretreatment may include removing desired components such as CO ₂ and H ₂ S or pre-cooling, pre-pressurizing and the like. Since these steps are well known to those skilled in the art, they are not described herein.

In addition to methane, natural gas includes varying amounts of ethane, propane and weight hydrocarbons. This composition varies depending on the type and location of the gas. Hydrocarbons that are heavier than methane are generally removed from natural gas for a variety of reasons, for example for C ₅ + hydrocarbons with freezing temperatures above the methane liquefaction temperature, which can block part of the methane liquefaction plant. Because. C _2-4 hydrocarbons can be used as a source of liquefied petroleum gas (LPG).

Thus, the hydrocarbon stream 45, the sulfur, sulfur compounds, carbon dioxide, water and C ₂ + one or more compounds or material containing the hydrocarbon, but not limited to, in part in order to reduce and / or eliminate substantially or entirely Refers to the composition to be treated.

If the hydrocarbon stream 45 includes natural gas, it may be pretreated to separate any weight of hydrocarbons and impurities such as carbon dioxide, nitrogen, helium, water, sulfur and sulfur compounds, including but not limited to acidic gases. .

The hydrocarbon stream 45 may be precooled in the preliminary cooling step to reduce the temperature of this hydrocarbon stream. Cooling in the preliminary cooling step is known to those skilled in the art. Precooling may be part of the liquefaction process or a separate process. Cooling the hydrocarbon feed stream to provide a hydrocarbon stream 45 reduces the temperature of the feed stream to 0 ° C. or less, eg, −10 ° C. to -70 ° C., to provide a cooled initial hydrocarbon stream. It may include.

 The cooled hydrocarbon feed stream may go to a separator, such as a condensate stabilization column, typically operating above atmospheric pressure, as is known in the art. This condensate stabilization column provides an overhead mixed hydrocarbon stream having a temperature of preferably 0 ° C. or less and a heavy condensate stream. The overhead mixed hydrocarbon stream is a methane rich stream as compared to the cooled hydrocarbon feed stream.

The term "mixed hydrocarbon stream" as used herein is selected from the group comprising methane (C ₁ ) and ethane (C ₂ ), propane (C ₃ ), butane (C ₄ ), and C ₅ + hydrocarbons. A stream comprising at least 5 mol% of at least one hydrocarbon. Typically, the ratio of methane in the mixed hydrocarbon stream (8) is 30 to 50 mol% and significant fractions of ethane and propane are each for example 5 to 10 mol%.

Upon NGL recovery, the methane of the mixed hydrocarbon stream to be further cooled, such as liquefaction of the LNG plant, is recovered and at least C ₂ + streams, optionally one or more C ₂ streams, C ₃ streams, C ₄ streams and C ₅ + It is desirable to provide a stream.

At least some, typically all, of the mixed hydrocarbon streams are passed into an NGL recovery system. The NGL recovery system is typically at least one gas, such as a distillation column, to separate the mixed hydrocarbon stream into at least a C ₁ stream and at least one C ₂ + stream, typically at low pressure, for example in the range from 20 to 35 bar. / Liquid separator. Examples of suitable first gas / liquid separator, a "de-methanation unit (demethanizer)" consisting of the overhead stream and a methane-rich, so that C ₂ + hydrocarbons to provide a rich bottom or in the vicinity of one or more liquid streams.

Since a mixed hydrocarbon stream 8 is usually provided from a high pressure initial hydrocarbon stream of 40 to 70 bar, it may be necessary to expand, for example, to reduce the temperature before the first gas / liquid separator.

A first gas / liquid separator is suitable to separate (the hydrocarbon as a stream 45 to be used later herein) C ₁ overhead stream and a C + _2, liquid phase and the gas phase to provide a bottom stream. C ₁ overhead stream (hydrocarbon stream 45) is still a small amount of (<10 mol%) C ₂ + in comprising a hydrocarbon, but preferably 80 mol% excess, more preferably greater than 95 mole% And methane. ₂ C + bottoms stream 50, may be greater than 90 mol% of ethane and heavy hydrocarbons, or of more than 95 mol%, may also be used otherwise than as known in the art that after the classification or for the NGL stream.

A method of cooling, preferably liquefying, a hydrocarbon stream such as natural gas is shown in FIG. 1. The hydrocarbon stream 45 passes through the main cooling stage 1 with the first heat exchanger 50 to provide a cooled, preferably liquefied hydrocarbon stream 55 which can be liquefied natural gas. do.

The main cooling step 1 comprises at least one, preferably cryogenic first heat exchanger 50. The first heat exchanger 50 may be a plate and fin or shell and tube heat exchanger, more preferably a kettle heat exchanger. The first heat exchanger 50 has a shell side 51. On the shell side three tube bundles 53, 57, 59 can be arranged. The main cooling step 1 further comprises a refrigerant circuit 100 having a refrigerant compressor 110, a suitable refrigerant driver 120, a refrigerant cooler 130, and a separator 140.

In the main cooling stage (1) there can be various devices for the hydrocarbon stream 45 and the refrigerant stream. Such a device is known in the art. Such a device may optionally include one or more heat exchangers 50 at different pressure levels and optionally in one vessel, such as the illustrated cryogenic heat exchanger.

In the embodiment shown in FIG. 1, the hydrocarbon stream 45 passes through a first heat exchanger 50 of the first tube bundle 52. The first heat exchanger 50 reduces the temperature of the hydrocarbon stream 45 to provide a cooled, preferably liquefied hydrocarbon stream 55, such as an LNG stream, and is near or below −90 ° C., preferably It may be at a temperature below -120 ° C.

The liquefied hydrocarbon stream 55 is optionally followed by an expansion turbine (not shown) followed by an expansion device such as a cooled hydrocarbon stream valve 60 which is a flow control valve to control the flow rate of this cooled hydrocarbon stream 55. I can go. The cooled hydrocarbon stream valve 60 can reduce the pressure of the cooled hydrocarbon stream 55, for example to store the LNG stream near atmospheric pressure.

At least one refrigerant stream 145b, 185b is used to remove heat from the hydrocarbon stream 45 in the first heat exchanger 50. Refrigerant, preferably a mixed refrigerant, is circulated in the refrigerant circuit 100. 1 shows a closed refrigerant circuit.

In one embodiment of the present invention, the mixed refrigerant for the refrigerant circuit 100 includes:

More than 30 mole percent of a compound selected from the group consisting of ethane and ethylene or mixtures thereof; And

More than 30 mole percent compound selected from the group consisting of propane and propylene or mixtures thereof.

In general, the second refrigerant may be any suitable mixture of components including two or more of nitrogen, methane, ethane, ethylene, propane, propylene, butane, pentane and the like.

The gaseous refrigerant is withdrawn from the shell side 51 of the first heat exchanger 50 as return refrigerant stream 105. This refrigerant is compressed by the refrigerant compressor 110 to provide a compressed refrigerant stream 115. The refrigerant compressor 110 is driven by a suitable driver, refrigerant compressor driver 120.

The compressed refrigerant stream 115 is directed to a cooler, such as an air cooler, in which the heat of compression is removed together with the heat absorbed in the first heat exchanger 50, so that the mixed refrigerant receives the cooled compressed refrigerant stream 135. It may be partially condensed to provide. Cooling and partial condensation of the compressed refrigerant stream 115 may be carried out in one or more heat exchangers.

The cooled compressed refrigerant stream 135 goes to separator 140, which separates the cooled compressed refrigerant stream 135 into one or more fractions. 1 shows a cold compressed refrigerant stream 135 separated into two fractions of an inlet refrigerant stream 143 and a second inlet refrigerant stream 147. Preferably, separator 140 separates cold compressed refrigerant stream 135 into bottom-weight mixed refrigerant (HMR) 143 and overhead lightweight mixed refrigerant (LMR) 147. If such separator 140 is a gas / liquid separator, the HMR fraction may be a liquid product and the LMR fraction may be a gas product.

Inlet refrigerant stream 143, which may be a first or weighted mixed refrigerant, passes through first heat exchanger 50 in second tube bundle 57 and may be sub-cooled therein. Inlet second refrigerant stream 147, which may be a second or lightweight mixed refrigerant, passes through first heat exchanger 50 in third tube bundle 59, where it can be liquefied and differentially cooled.

The first or weighted mixed refrigerant exits the second tube bundle 57 as a cooled refrigerant stream 145. The cooled refrigerant stream 145 is expanded in the refrigerant expander 150 to provide an expanded refrigerant stream 145a. The refrigerant expander 150 can be driven by a suitable refrigerant expander driver 160. Expanded refrigerant stream 145a may pass through refrigerant valve 170, which may control the flow rate of expanded refrigerant stream 145a to provide refrigerant stream 145b, which is a controlled stream. have. Refrigerant stream 145b enters shell side 51 of first heat exchanger 50 through second inlet 176 to cool hydrocarbon stream 45 in first tube bundle 53.

Similarly, the second or light mixed refrigerant exits the third tube bundle 59 as a cooled second refrigerant stream 185. The cooled second refrigerant stream 185 is expanded in the second refrigerant expander 190 to provide an expanded second refrigerant stream 185a. The second refrigerant expander 190 can be driven by a suitable second refrigerant expander driver 200. The expanded second refrigerant stream 185a is capable of controlling the flow rate of the expansion cooled second refrigerant stream 185a to provide a controlled second stream of refrigerant 185a. Can pass through The second refrigerant stream 185b is directed to the shell side 51 of the first heat exchanger 50 through the third inlet 216 to cool the hydrocarbon stream 45 in the first tube bundle 53. .

The method of controlling the hydrocarbon stream 45 is controlled in the following manner:

The flow rate FR1 of the refrigerant stream corresponding to the flow rate of the refrigerant stream 145b is measured by the refrigerant flow controller FC1 310. 1 shows a refrigerant flow controller 340 arranged to measure the flow rate FR1 of the cooled refrigerant stream 145. Refrigerant flow controller 340, however, does not allow the flow controller 340 to flow into the shell side 51 of first heat exchanger 50, for example FR1, so that flow controller 340 cools hydrocarbon stream 45. As long as it provides a signal proportional to the flow rate FR1 of the refrigerant stream 145b going to the shell side 51 of the first heat exchanger 50 via the second inlet 176 to cool the hydrocarbon stream 45. It is adapted to measure the flow rate of any stream 143, 145, 145a, 145b.

The flow rate FR2 of the hydrocarbon stream corresponding to the flow rate of the cooled hydrocarbon stream 55 is measured by the hydrocarbon flow controller (FC2) 350. 1 shows a cooled hydrocarbon flow controller 350 arranged to measure the flow rate FR2 of the cooled hydrocarbon stream 55. However, the hydrocarbon flow controller 340 is a signal proportional to the flow rate FR2 of the hydrocarbon stream 45, or the flow rate FR2 of the hydrocarbon stream through which the flow controller 350 passes through the first heat exchanger 50. It is suitable for measuring the flow rate of any other hydrocarbon stream so long as.

The measurement of the stream flow can be carried out by any suitable device, unit or device known in the art. Non-limiting examples include orifice plates, venturi tubes, flow nozzles, variable area meters, pilot tubes, calorimetry meters, turbine meters, Coriolis meters, ultrasonic Doppler meters, and vortex meters.

The flow controller also controls the operation of the means for controlling the flow of the stream, preferably a valve, for example a pneumatic, hydraulic or electrically operated valve.

A first set point SP1 for the flow rate FR1 of the refrigerant stream is set and input to the flow setter HC 300. The first set point SP1 corresponds to the desired output of the cooled hydrocarbon stream 55, preferably the LNG stream, from the first heat exchanger 50, even if provided in terms of the flow rate FR1 of the refrigerant stream. do.

Overcooling of the first heat exchanger 50 may occur when more cooling duty is supplied from the refrigerant than is required for the hydrocarbon to be cooled. In order to prevent subcooling of the first heat exchanger 50, the flow rate FR1 of the refrigerant stream and the flow rate FR2 of the hydrocarbon stream are adjusted in accordance with the following cross-limiting control method.

If the first set point SP1 for the flow rate of the refrigerant stream is greater than the measured flow rate FR1 of the refrigerant stream, ie when the cooled hydrocarbon output of the first heat exchanger 50 is increased, then the hydrocarbon stream The flow rate FR2 is increased before the flow rate FR1 of the refrigerant stream is increased.

As long as the flow rate FR1 of the refrigerant stream is increased after the flow rate of the hydrocarbon stream FR2 is increased, subcooling of the first heat exchanger 50 can be prevented. However, any period between increasing the flow rate FR2 of the hydrocarbon stream and increasing the flow rate FR1 of the refrigerant stream should be as short as possible in terms of system reaction time to prevent undercooling of the hydrocarbon stream.

If the first set point SP1 for the flow rate FR2 of the hydrocarbon stream is smaller than the flow rate FR1 of the measured refrigerant stream, that is, when the cooled hydrocarbon output of the first heat exchanger 50 is reduced, then The flow rate FR1 of the refrigerant is reduced before the flow rate FR2 of the hydrocarbon stream is reduced.

As long as the flow rate FR2 of the hydrocarbon stream is reduced after the flow rate FR1 of the refrigerant stream is reduced, subcooling of the first heat exchanger 50 can be prevented. However, any period between the decrease in the flow rate FR1 of the refrigerant stream and the decrease in the flow rate FR2 of the hydrocarbon stream should be as short as possible in terms of system reaction time to prevent differential cooling of the hydrocarbon stream.

When the flow rate FR2 of the hydrocarbon stream is reduced, for example, a user of the cooled hydrocarbon stream 55 is withdrawn from the operation or a supplier of the hydrocarbon stream 45 is withdrawn from the operation. In the case of a tripping, then the flow rate FR1 of the refrigerant stream must also be reduced.

Preferably, the flow rate FR1 of the refrigerant stream is adjusted in proportion to the flow rate FR2 of the hydrocarbon stream so as to maintain a constant temperature with respect to the cooled hydrocarbon stream 55.

The refrigerant flow controller 340 can control the flow rate FR1 of the refrigerant stream by operating the refrigerant stream valve 170. In another embodiment (not shown), the flow rate FR1 of the refrigerant stream controls any stream 143, 145 as long as the control valve causes the refrigerant flow into the shell side 51 of the first heat exchanger 50. It can be controlled by the presence of a valve.

Similarly, the cooled hydrocarbon flow controller FC2 can control the flow rate of the cooled hydrocarbon stream 55 (and thus the flow rate of the hydrocarbon stream 45) by operating the cooled hydrocarbon valve 60. In another embodiment (not shown), the flow rate of the cooled hydrocarbon stream 55 can be controlled by the presence of a control valve in the hydrocarbon stream 45.

It will be apparent from the system of FIG. 1 that the flow rate of any second refrigerant stream FR3 must be controlled. In FIG. 1, a second refrigerant flow controller (FC3) 360 is shown that operates the second refrigerant flow valve 210 to control the flow rate FR3 of the second refrigerant stream 185b. The second refrigerant flow valve 210 is shown after the second refrigerant expander 190, but as long as the flow rate of the second refrigerant to the shell side 51 of the first heat exchanger 50 can be controlled. Two refrigerant streams (147 or 185).

The flow rate FR3 of the second refrigerant stream 185b is adjusted in proportion to and also in proportion to the flow rate of the refrigerant stream FR1. The refrigerant controller 330 can be used to adjust the position of the second refrigerant flow valve 210 in accordance with instructions provided to the first refrigerant stream flow controller FC1. The second refrigerant flow controller FC3 measures the second refrigerant flow rate FR3 to ensure that the system provides the correct cooling duty to the first heat exchanger 50.

Cross-limiting control systems that can be used in the methods described herein can be automatic. 1 shows flow controller FC1 340, FC2 350, and FC3 360 in operation of each of flow control valves 170, 60, 210. The first set point SP1 for the flow rate FR1 of the first refrigerant stream is input to the flow setter HC 300. The flow setter 300 receives the input of the first set point SP1 and also sends it to the row selector 310 and the high selector 320.

Row selector 310 receives the flow rate of the cooled hydrocarbon stream as a signal from the cooled hydrocarbon stream flow controller 350. The high selector 320 receives the flow rate of the refrigerant stream as a signal from the refrigerant stream flow controller FC1.

The nature and operation of the high and low selectors 310, 320 are described in greater detail below with reference to FIG. 2. 2 shows an exemplary control method for the method of cooling hydrocarbons as described herein. The main cooling step 1 shown in FIG. 1 can be used in this embodiment. 1, only the cooled hydrocarbon stream 55 and the corresponding control valve 60, the cooled refrigerant stream 45, the refrigerant compressor 150, the compressed refrigerant stream 145a, the control valve 170 and the refrigerant Stream 145b is shown similarly in FIG. However, there may be additional features of FIG. 1.

The first set point SP1 for the flow rate FR1 of the refrigerant stream is a flow setter (HC) 300 which generates a set point signal SPS which is transmitted to the low selector 310 and the high selector 320. Is entered.

The refrigerant flow controller 340 generates a refrigerant flow signal FS1 that is proportional to the flow rate FR1 of the refrigerant stream 145b. The refrigerant flow signal FS1 is sent to the high selector 320. The high selector 320 also receives a first set point signal SPS from the flow setter 300.

Refrigerant flow controller 340 operates refrigerant stream valve 170 to control the flow rate of refrigerant stream 145b.

The hydrocarbon flow controller 350 generates a hydrocarbon flow signal FS2 that is proportional to the flow rate FR2 of the cooled hydrocarbon stream 55. The hydrocarbon flow signal FS2 is sent to the row selector 310. Row selector 310 also receives a first set point signal SPS from flow setter 300.

The cooled hydrocarbon flow controller 350 operates the cooled hydrocarbon stream valve 60 to control the flow rate of the cooled hydrocarbon stream 55.

The row selector 310 is programmed to pass the smallest of the set point signal SPS and the hydrocarbon flow signal FS2 to the first refrigerant flow controller 340. In this way, the increase in the first set point SPS increases only the flow rate FR1 of the refrigerant stream after the flow rate FR2 of the hydrocarbon stream is increased.

The high selector 320 is programmed to pass the largest of the set point signal SPS and the refrigerant flow signal FS1 to the hydrocarbon flow controller 350. In this way, the reduction of the first set point SPS only reduces the flow rate FR2 of the hydrocarbon stream after the flow rate FR1 of the refrigerant stream is reduced.

Thus, a method is provided for cooling a hydrocarbon stream with cross-limiting control between the flow rate FR2 of the hydrocarbon stream and the flow rate FR1 of the refrigerant stream so that subcooling of the first heat exchanger 50 is prevented.

3 shows a control method for the method of cooling the hydrocarbons described herein, wherein the temperature TC2 of the cooled hydrocarbon stream 55 is compared to the flow rate FR2 of this cooled hydrocarbon stream 55. Can be maintained by adjusting the ratio of the flow rate FR1 of the refrigerant stream 145b, such as heavy mixed refrigerant. In the embodiment of FIGS. 1 and 2, it is evident that there is no means for adjusting the ratio and it is thus constant.

The cooled hydrocarbon stream 55 is provided with a temperature controller (TC2) 370. The temperature controller 370 measures the temperature of the cooled hydrocarbon stream 55 and also transmits a signal TS2 in proportion to this temperature.

The temperature of the cooled hydrocarbon stream TC2 can be adjusted by providing a temperature set point TSP to the temperature controller 370. The temperature TC2 of the cooled hydrocarbon stream 55 can be reduced by reducing the flow rate FR2 of the cooled hydrocarbon stream 55 relative to the flow rate FR1 of the refrigerant stream. Similarly, the temperature TC2 of the cooled hydrocarbon stream 55 can be increased by increasing the flow rate FR2 of the cooled hydrocarbon stream 55 relative to the flow rate FR1 of the constant refrigerant stream.

The signal TS2 from the temperature controller 370 sends the signal from the high selector 320 to the cooled hydrocarbon stream to increase or decrease the flow rate of the cooled hydrocarbon stream 55 compared to the unmodulated signal. Can be modulated However, the modulation carried out on the signal from the cooled hydrocarbon stream flow controller FC2 to the row selector 310 is such that the cooled hydrocarbon stream flow signal FS2 reaching the row selector 310 is cooled. In contrast to the modulation performed on the signal from the high selector 320, so as to correspond to the signal from the hydrocarbon flow controller FC2 that occurs when not modulated by TC2. In this way, the operation of the row selector 310 and thus the refrigerant flow controller FC1 are not affected by the cooled hydrocarbon stream temperature controller TC2.

3 shows one way in which the signal TS2 from the temperature controller 370 can adjust the signal from the high selector 320. This system has a predetermined ratio of the flow rate of the cooled hydrocarbon stream (LNG) to the refrigerant stream (HMR), which provides the cooled hydrocarbon stream 55 at a specific temperature. This ratio is represented by (LNG / HMR) in FIG. 3. In order to be able to adjust the temperature of the cooled hydrocarbon stream 55, the flow rate ratio of the cooled hydrocarbon stream 55 to the refrigerant stream must be changed from a predetermined ratio. The parameter (b) derived from the signal TS2 from the temperature controller 370 can be used to scale the signal from the high selector 320.

For example, the parameter (c) derived from the signal provided to the hydrocarbon flow controller 350 is the parameter (a) derived from the signal from the high selector 320, the ratio of the cooled hydrocarbon flow rate to the refrigerant flow rate (HMR). Ie, (LNG / HMR), and a function of the scaling factor (b / 100) determined from parameter (b) derived from the signal from temperature controller 370. If parameter b exceeds 100, for example, if parameter b exceeds 100 and is in the range of 150 or less, parameter c of the signal provided to hydrocarbon flow controller 350 will increase accordingly.

Similarly, the parameter (e) derived from the signal provided to the row selector 310 is the parameter (d) derived from the signal from the hydrocarbon flow controller 350, the refrigerant flow rate (HMR) for the cooled hydrocarbon flow rate (LNG). ), I.e. (HMR / LNG), and the inverse of the scaling factor (b / 100) determined from the parameter (b) derived from the signal from the temperature controller 370, i.e. as a function of (100 / b) Can be determined.

The flow rate FR3 of any second refrigerant stream can be changed in proportion to the flow rate FR1 of the refrigerant stream such that the ratio of the refrigerant to the second refrigerant is maintained, such as the ratio of HMR to LMR. In another embodiment, FIG. 3 shows a refrigerant bypass stream 225 that bypasses refrigerant expander 150. The refrigerant bypass stream 225 is controlled by the refrigerant bypass valve 230 to provide a controlled refrigerant bypass stream 225a. Controlled refrigerant bypass stream 225a may be combined with refrigerant stream 145b to provide a combined refrigerant stream 245. The refrigerant bypass valve 230 can be actuated by a signal from the refrigerant flow controller 340 such that the cooled refrigerant stream 145 bypasses the refrigerant expander 150.

Those skilled in the art will readily appreciate that the present invention may be modified in many ways without departing from the scope of the appended claims.

Claims (15)

A method of cooling a hydrocarbon stream in a heat exchanger, the method comprising:
(a) providing a hydrocarbon stream,
(b) in a first heat exchanger, heat exchange with said hydrocarbon stream for at least one refrigerant stream having a flow rate of a refrigerant stream to provide a cooled hydrocarbon stream and at least one return refrigerant stream having a flow rate of a hydrocarbon stream; ,
(c) entering a first set point for the flow rate of said refrigerant stream, and
(d) adjusting the flow rate of the refrigerant stream and the flow rate of the hydrocarbon stream until the set point is obtained,
(d1) if the first set point is greater than the flow rate of the refrigerant stream, the flow rate of the hydrocarbon stream is increased before the flow rate of the refrigerant stream is increased,
(d2) if the first set point is less than the flow rate of the refrigerant stream, the flow rate of the refrigerant stream is reduced before the flow rate of the hydrocarbon stream is reduced,
(d3) the flow rate of the hydrocarbon stream is reduced, the flow rate of the refrigerant stream is reduced. The method of claim 1,
In step (d), the adjustment of the flow rate of the refrigerant stream and the flow rate of the hydrocarbon stream is automatic. The method according to claim 1 or 2,
During the step (d), the ratio of [flow rate of refrigerant stream] / [flow rate of hydrocarbon stream] is kept below a preselected level. The method according to any one of claims 1 to 3,
The flow rate of the refrigerant stream is measured by a refrigerant flow controller that generates a refrigerant flow signal sent to a high selector, the refrigerant flow controller operating a refrigerant stream valve to control the flow rate of the refrigerant stream,
The flow rate of the hydrocarbon stream is measured by a hydrocarbon flow controller that generates a hydrocarbon flow signal sent to a row selector, the hydrocarbon flow controller operating the hydrocarbon stream to control the flow rate of the hydrocarbon stream,
The first set point is input to a flow setter which generates a set point signal sent to the low selector and the high selector,
The row selector sends the smallest of a set point signal and a hydrocarbon flow signal to the refrigerant flow controller,
The high selector sends the largest of a set point signal and a refrigerant flow signal to the cooled hydrocarbon flow controller. The method according to any one of claims 1 to 4,
The refrigerant stream is selected from the group comprising a heavy mixed refrigerant stream and a light mixed refrigerant stream, preferably a heavy mixed refrigerant stream. 6. The method according to any one of claims 1 to 5,
And in step (b), heat exchange with the hydrocarbon stream for a second refrigerant stream having a flow rate of a second refrigerant stream in a first heat exchanger. The method according to claim 6,
The flow rate of the second refrigerant stream is determined in proportion to the flow rate of the refrigerant stream. The method according to claim 6 or 7,
A second refrigerant flow controller operating the second refrigerant stream valve to change the flow rate of the second refrigerant stream;
Receiving the smallest of the set point signal and the cooled hydrocarbon flow signal from the row selector and transmitting the signal of the refrigerant controller to the second refrigerant flow controller to adjust the flow rate of the second refrigerant stream relative to the flow rate of the refrigerant stream; Further comprising a refrigerant controller. The method according to any one of claims 6 to 8,
The second refrigerant stream is a lightweight mixed refrigerant stream when the refrigerant stream is a heavy mixed refrigerant stream, or the second refrigerant stream is a heavy mixed refrigerant stream when the refrigerant stream is a lightweight mixed refrigerant stream; Way. The method according to any one of claims 1 to 9,
(i) cooling the refrigerant stream entering the first heat exchanger to provide a cooled refrigerant stream,
(ii) expanding the cooled refrigerant stream in a refrigerant expander to provide an expanded refrigerant stream,
(iii) passing the expanded refrigerant stream through a refrigerant valve to provide a refrigerant stream, and
(iv) passing said refrigerant stream through a second inlet of a first heat exchanger. The method of claim 10,
(v) passing the return refrigerant stream through a refrigerant compressor to provide a compressed refrigerant stream,
(vi) cooling the compressed refrigerant stream in a cooler to provide a cooled compressed refrigerant stream, and
(vii) separating the cold compressed refrigerant stream in a separator to provide at least one inlet refrigerant stream. The method of claim 11,
In step (vii), the second inlet refrigerant stream is further generated by separating the cold compressed refrigerant stream, the method further comprising:
(viii) cooling the second inlet refrigerant stream in a first heat exchanger to provide a cooled second refrigerant stream,
(ix) expanding the cooled second refrigerant stream in a second refrigerant expander to provide an expanded second refrigerant stream,
(x) passing said expanded second refrigerant stream through a second refrigerant valve to provide a second refrigerant stream, and
(xi) passing said second refrigerant stream through a third inlet of a first heat exchanger. The method according to any one of claims 1 to 12,
Wherein said hydrocarbon stream is a natural gas stream and said cooled hydrocarbon stream is an LNG stream. Apparatus for operating a heat exchanger, at least,
A first heat exchanger having a first inlet for a hydrocarbon stream and a first outlet for a cooled hydrocarbon stream, at least a second inlet for at least one refrigerant stream and a second outlet for a return refrigerant stream,
A refrigerant stream flow controller measuring a signal proportional to the flow rate of the refrigerant stream of the at least one refrigerant stream and providing a refrigerant flow signal sent to the high selector and operating the refrigerant valve to control the flow rate of the refrigerant stream,
Measure a signal proportional to the flow rate of the cooled hydrocarbon stream of the cooled hydrocarbon stream to provide a cooled hydrocarbon flow signal sent to the row selector and also operate the cooled hydrocarbon stream valve to control the flow rate of the cooled hydrocarbon stream. Cooled hydrocarbon stream flow controller,
A flow setter that inputs a set point to provide a set point signal sent to the low selector and high selector,
A row selector for transmitting the smallest of said set point signal and the cooled hydrocarbon stream flow signal to a refrigerant flow controller, and
A high selector for transmitting the largest of said set point signal and refrigerant stream flow signal to a cooled hydrocarbon stream flow controller. The method of claim 14,
A third inlet for a second refrigerant stream of the first heat exchanger,
A second refrigerant flow controller operating the second refrigerant stream valve to change the flow rate of the second refrigerant stream, and
A refrigerant that receives the smallest of a set point signal and a cooled hydrocarbon flow signal from the row selector and sends a refrigerant controller signal to the second refrigerant flow controller to regulate the flow rate of the second refrigerant stream relative to the flow rate of the refrigerant stream The apparatus further comprises a controller.

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