JP2012511130A - Method and apparatus for cooling a hydrocarbon stream - Google Patents

Abstract

In the method and apparatus for cooling a hydrocarbon stream, the hydrocarbon stream 45 to be cooled is heat exchanged in the first heat exchanger 50 with one or more refrigerant streams 145b, 185b having a first refrigerant stream flow rate FR1, A cooled hydrocarbon stream 55 having a cooled hydrocarbon stream flow rate FR2 and one or more return refrigerant streams 105 are provided. The first refrigerant flow rate FR1 and the cooled hydrocarbon flow rate FR2 are adjusted until the first set point SP1 input for the first refrigerant flow rate FR1 is achieved. If the first set point SP1 is greater than the first refrigerant flow rate FR1, the hydrocarbon flow rate FR2 is increased before increasing the first refrigerant flow rate FR1, and the first set point SP1 is greater than the first refrigerant flow rate FR1. If it is smaller, the first refrigerant flow rate FR1 is decreased before the hydrocarbon flow rate FR2 is decreased, and if the hydrocarbon flow rate FR2 is decreased, the first refrigerant flow rate FR1 is decreased.
[Selection] Figure 1

Description

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

  An important example of a hydrocarbon stream to be cooled in this way is a natural gas stream. If the hydrocarbon stream to be cooled is a natural gas stream, the cooling includes liquefaction of the hydrocarbon stream to produce a liquefied hydrocarbon stream, such as a liquefied natural gas (LNG) stream.

  Natural gas is a useful fuel source and also a source of various hydrocarbon compounds. For many reasons, it is often desirable to liquefy natural gas at a liquefied natural gas (LNG) plant at or near the source of the natural gas stream. As an example, since liquid occupies a smaller volume than gas and does not need to be stored at high pressure, liquid can be stored and transported over a longer distance than gas.

  Natural gas, primarily containing methane, is usually pretreated to create a refined feedstock suitable for entering the LNG plant at high pressure and liquefying at cryogenic temperatures. The purified gas is processed in multiple cooling stages using a heat exchanger and gradually reduces its temperature until liquefaction is achieved. The liquid natural gas is then further cooled and expanded to a final atmospheric pressure suitable for storage and transport.

Natural gas includes, but is not limited to, methane as well as some heavier hydrocarbons and impurities such as carbon dioxide, sulfur, hydrogen sulfide and other sulfur compounds, nitrogen, helium, water, and other non-carbons. Contains hydrocarbon acid gas, ethane, propane, butane, C ₅ + hydrocarbons and aromatic hydrocarbons. These and other common or known heavy hydrocarbons and impurities interfere with or interfere with the usual known methane liquefaction processes, particularly the most efficient methane liquefaction processes. The best known or proposed method for liquefaction of hydrocarbons, especially natural gas, is based on reducing as much as possible the amount of heavy hydrocarbons and at least the majority of impurities prior to liquefaction.

  A hydrocarbon heavier than methane, usually ethane, is generally condensed and recovered as a natural gas liquid (NGL) from a natural gas stream. Methane is usually separated from NGL in a high pressure scrub column, which is then used to obtain valuable hydrocarbon products that are used as product streams themselves or as components of refrigerants for liquefaction, for example. It is rectified in a dedicated distillation tower.

On the other hand, methane from the scrub column is continuously liquefied to obtain LNG.
US patent application 2003/0046953 is available because the operator can manipulate the set point of the flow rate of one of the multiple refrigerants and the ratio of the flow rate of the heavy and light mixed refrigerants Discloses a method for controlling the amount of LNG produced, which can continuously use maximum power to drive the refrigeration cycle.

  The method cannot prevent the heat exchanger from being supercooled below its minimum temperature limit, or cannot avoid excessive mechanical stress (thermal shock) that occurs in the heat exchanger if the temperature drops rapidly. . When this happens, leakage can develop in the heat exchanger. The present invention seeks to address this problem and other problems associated with hydrocarbon stream cooling.

In the first aspect, the present invention provides:
(A) providing a hydrocarbon stream;
(B) A hydrocarbon stream having a hydrocarbon flow rate by exchanging heat between the hydrocarbon stream and one or more refrigerant streams having a stream flow rate in the first heat exchanger. And supplying one or more return refrigerant streams;
(C) inputting a first set point for the refrigerant flow rate, and (d) adjusting the refrigerant flow rate and the hydrocarbon flow rate until the set point is achieved,
(1) If the first set point is greater than the refrigerant flow rate, increase the hydrocarbon flow rate before increasing the refrigerant flow rate, 2) If the first set point is smaller than the refrigerant flow rate, decrease the refrigerant flow rate before decreasing the hydrocarbon flow rate; (3) If the hydrocarbon flow rate decreases, decrease the refrigerant flow rate The method is provided.

In a second aspect, the present invention provides:
A first heat exchanger having a first inlet for hydrocarbon stream, a first outlet for cooled hydrocarbon stream, one or more second outlets for one or more refrigerant streams, and a second outlet for return refrigerant streams;
A refrigerant that controls the flow rate of the refrigerant flow by operating a refrigerant valve to measure a signal proportional to the refrigerant flow rate of one or more refrigerant flows and to supply a refrigerant flow signal that is transmitted to the high sorter Flow controller,
Control the hydrocarbon stream flow by operating a hydrocarbon valve to measure a signal proportional to the hydrocarbon stream flow rate of the hydrocarbon stream and provide a hydrocarbon flow signal sent to the low sorter A hydrocarbon flow controller,
A flow rate setter for inputting set points and supplying set point signals to be sent to the low and high sorters;
A low selector that transmits the lowest set point signal and hydrocarbon flow rate signal to the refrigerant flow controller, and a high selector that transmits the highest set point signal and refrigerant flow rate signal to the hydrocarbon flow controller,
An apparatus for operating a heat exchanger is provided.

1 is a schematic system diagram of a hydrocarbon flow cooling device provided with means for carrying out an embodiment of the present invention. It is a figure which shows the control system of the cooling method of the hydrocarbon stream in one Embodiment of this invention. It is a figure which shows the control system of the cooling method of the hydrocarbon stream in another embodiment of this invention.

As described herein, heat exchanger subcooling can be prevented by adjusting the refrigerant flow rate and hydrocarbon flow rate until the set point is achieved according to the following method.
(1) If the first set point is greater than the refrigerant flow rate, increase the hydrocarbon flow rate before increasing the refrigerant flow rate.
(2) If the first set point is smaller than the refrigerant flow rate, reduce the refrigerant flow rate before reducing the hydrocarbon flow rate.
(3) When the hydrocarbon flow rate decreases, the refrigerant flow rate is decreased.

In this way, there is always enough hydrocarbon in the hydrocarbon stream to receive cold from the refrigerant in the refrigerant stream, thereby preventing overcooling of the heat exchanger.
These steps are preferably performed automatically after supply of the first set point, ie without human intervention or with minimal intervention, for example with a fully automated control system.

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

  Usually, the natural gas stream consists mostly of methane. Such a feed stream preferably contains methane at 60 mol% or more, more preferably 80 mol% or more.

Depending on the source, natural gas contains various amounts of hydrocarbons heavier than methane such as ethane, propane, butane and pentane and some aromatic hydrocarbons. This composition varies with the type and location of the hydrocarbon stream. Natural gas may contain non-hydrocarbons such as H ₂ O, N ₂ , CO ₂ , H ₂ S and other sulfur compounds.

If necessary, the hydrocarbon stream containing natural gas may be pretreated before use. Such pretreatment may include removal of unwanted components such as CO ₂ and H ₂ S, or other steps such as precooling or prepressurization. These steps are well known to those skilled in the art and will not be further described here.

In addition to methane, natural gas contains various amounts of ethane, propane and heavier hydrocarbons. Its composition varies depending on the type and location of the gas. Hydrocarbons heavier than methane generally can clog parts of the methane liquefaction plant for several reasons, such as in the case of C ₅ + hydrocarbons having a freezing temperature higher than the methane liquefaction temperature. It is removed from natural gas to various degrees. _C2-4 hydrocarbons can be used as a source of liquefied petroleum gas (LPG).

Accordingly, the hydrocarbon stream 45 is partly used to reduce and / or remove one or more compounds or substances including, but not limited to, sulfur, sulfur compounds, carbon dioxide, water and C ₂ + hydrocarbons. In particular, the composition is treated substantially or entirely.

  If the hydrocarbon stream contains natural gas, the hydrocarbon stream is pre-treated to make hydrocarbons heavier than methane, and including but not limited to acid gas, carbon dioxide, nitrogen, helium, water In addition, impurities such as sulfur and sulfur compounds may be separated.

  The hydrocarbon stream 45 may be precooled in a precooling stage to reduce the temperature of the hydrocarbon stream. It is known to those skilled in the art to perform the cooling in the precooling stage. Precooling may be part of the liquefaction process or separation process. The cooling of the hydrocarbon feed stream to supply the hydrocarbon stream 45 comprises the step of supplying the cooled initial hydrocarbon stream by lowering the feed stream to a temperature below 0 ° C, for example in the range of -10 ° C to -70 ° C. May include.

  This cooled hydrocarbon feed stream can be passed through a separator, such as a condensate stabilization column, which typically operates at pressures above ambient pressure, according to methods known in the art. The condensate stabilization column provides a mixed hydrocarbon overhead stream and a heavy condensate stream, preferably having a temperature below 0 ° C. The mixed hydrocarbon tower top stream is a stream rich in methane compared to the cooled hydrocarbon feed stream.

As used herein, the “mixed hydrocarbon stream” was selected from the group comprising methane (C ₁ ) and ethane (C ₂ ), propane (C ₃ ), butane (C ₄ ) and C ₅ + hydrocarbons. Relates to a stream comprising at least 5 mol% of one or more hydrocarbons. Usually, the proportion of methane in the mixed hydrocarbon stream 8 is 30-50 mol%, and the important fractions consisting of ethane and propane are each, for example, 5-10 mol%.

In NGL recovery, as in liquefaction at an LNG plant, for further cooling, methane in the mixed hydrocarbon stream is recovered and at least a C ₂ + stream and optionally a C ₂ stream, a C ₃ stream, a C ₄ stream. And at least one of the C ₅ + streams.

At least a fraction, usually all, of the mixed hydrocarbon is passed through an NGL recovery system. NGL recovery system, a mixed hydrocarbon stream typically low pressure, for example at least C ₁ stream in the range of 20 to 35 bar, such as one or more of the distillation column for separating one or more C _{2 +} stream Prefecture It has a gas-liquid separator. A preferred first gas-liquid separator is a “degasser” designed to provide a methane-rich top stream and one or more liquid streams rich in C ₂ + hydrocarbons or near the bottom. It is a “methane unit”.

  Since the mixed hydrocarbon stream 8 is typically fed from a high pressure initial hydrocarbon stream of 40-70 bar, it may need to be expanded before it is introduced into the first gas-liquid separator, for example to reduce the temperature. I don't know.

The first gas-liquid separator is adapted to separate the liquid and vapor phases to provide a C ₁ overhead stream (herein used subsequently as hydrocarbon stream 45) and a C ₂ + bottom stream. The C ₁ overhead stream (which is the hydrocarbon stream 45) may still contain small amounts of C ₂ + hydrocarbons (<10 mol%), but preferably methane is> 80 mol%, more preferably 95 mol%. C 2 ₊ bottoms stream 50 are likely to be ethane and this heavier hydrocarbons> 90 mol% or> 95 mol%, also continue be fractionated, or used according to methods known in the art it can.

  A cooling, preferably liquefaction schematic, of a hydrocarbon stream such as natural gas is shown in FIG. The hydrocarbon stream 45 passes through a main cooling stage 1 having a first heat exchanger 50 to provide a cooling, preferably a liquefied hydrocarbon stream 55, which can be liquefied natural gas.

  The main cooling stage 1 comprises one or more, preferably cryogenic, first heat exchangers 50. The first heat exchanger 50 may be a plate fin type or shell tube type heat exchanger, more preferably a multi-tube heat exchanger. The first heat exchanger 50 has a shell side 51. Three tube bundles 53, 57, 59 can be arranged on the shell side 51. The main cooling stage 1 further comprises a refrigerant circuit 100 comprising a refrigerant compressor 110, a suitable refrigerant driver 120, a refrigerant cooler 130 and a separator 140.

  In the main cooling stage 1, various arrangements are possible for the hydrocarbon stream 45 and the refrigerant stream. Such an arrangement is known in the art. These arrangements can include one or more heat exchangers 50, optionally in 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 is passed through the first tube bundle 53 in the first heat exchanger 50. The first heat exchanger 50 lowers the temperature of the hydrocarbon stream 45 to provide cooling, preferably liquefaction, hydrocarbon stream 55, for example an LNG stream. The temperature of the cooled hydrocarbon stream can be about -90 ° C or less, preferably about -120 ° C or less.

  The liquefied hydrocarbon stream 55 is passed through an expansion device, such as a cooled hydrocarbon valve 60, as a flow control valve, optionally preceded by an expansion turbine (not shown) to control the flow rate of the cooled hydrocarbon stream 55. be able to. The cooled hydrocarbon valve 60 can reduce the pressure of the cooled hydrocarbon stream 55, for example, to store the LNG stream at approximately atmospheric pressure.

  One or more refrigerant streams 145 b, 185 b are used to remove heat from the hydrocarbon stream 45 in the first heat exchanger 50. A refrigerant stream, preferably a mixed refrigerant stream, is circulated in the refrigerant circuit 100. FIG. 1 shows a closed refrigerant cycle.

  In one embodiment of the present invention, the refrigerant mixture for the refrigerant circuit 100 is selected from the group consisting of> 30 mol% of a compound selected from the group consisting of ethane and ethylene or a mixture thereof, and a group consisting of propane and propylene or a mixture thereof. Containing> 30 mol% of the resulting compound. 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 a return refrigerant stream 105 and is compressed by the refrigerant compressor 110 to provide a compressed refrigerant stream 115. The refrigerant compressor is driven by a suitable refrigerant compressor driver 120.

  The compressed refrigerant stream 115 is passed through a cooler 130, such as an air cooler, where the heat of compression is removed along with the heat absorbed in the first heat exchanger 50, thus the mixed refrigerant is partially condensed. Is supplied with a cooled compressed refrigerant stream 135. Cooling and partial condensation of the compressed refrigerant stream 115 may occur in one or more heat exchangers.

  The cooled compressed refrigerant stream 135 is passed through a separator 140 and divided into one or more fractions. FIG. 1 shows that the cooled compressed refrigerant stream 135 is divided into two fractions, an incoming refrigerant stream 143 and a second incoming refrigerant stream 147. Preferably, the separator 140 indicates that the cooled compressed refrigerant stream 135 is split into a bottom heavy mixed refrigerant (HMR) 143 and a top light mixed refrigerant (LMR) 147. If the separator 140 is a gas-liquid separator, the HMR fraction may be a liquid product and the LMR fraction may be a vapor product.

  The incoming refrigerant stream 143, which can be a first or heavy mixed refrigerant, is passed through the second tube bundle 57 in the first heat exchanger 50 where it can be supercooled. The incoming second refrigerant stream 147, which can be a second or light mixed refrigerant, is passed through a third tube bundle 59 in the first heat exchanger 50 where it can be liquefied and subcooled.

  The first or heavy mixed refrigerant exits the second tube bundle 57 as a cooling refrigerant stream 145. The cooling 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. The expanded refrigerant flow 145a can be passed through a refrigerant valve 170 that can control the flow rate of the expanded refrigerant flow 145a to supply the refrigerant flow 145b as a control flow. The refrigerant stream 145 b can pass through the second inlet 176 to the shell side 51 of the first heat exchanger 50 to cool the hydrocarbon stream 45 in the first tube bundle 53.

  Similarly, the second or light mixed refrigerant exits third tube bundle 59 as 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 can be passed through a second refrigerant valve 210 that can control the flow rate of the expanded cooling refrigerant stream 185a to supply the second refrigerant stream 185b as a control flow. The second refrigerant stream 185 b can pass through the third inlet 216 to the shell side 51 of the first heat exchanger 50 to cool the hydrocarbon stream 45 in the first tube bundle 53.

The cooling method of the hydrocarbon stream 45 is controlled by the following method.
The refrigerant flow rate FR1 corresponding to the flow rate of the refrigerant flow 145 is measured by the refrigerant flow rate controller FC1 (340). FIG. 1 shows a refrigerant flow controller 340 arranged to measure the flow rate FR1 of the cooling refrigerant flow 145. However, the flow rate controller 340 cools the hydrocarbon stream first through the second inlet 176 to cool the refrigerant flow rate FR1, which passes through the shell side 51 of the first heat exchanger 50, for example, the hydrocarbon stream 45. As long as a signal proportional to the flow rate FR1 of the refrigerant flow 145b passed through the shell side 51 of the heat exchanger 50 is supplied, the refrigerant flow controller 340 measures any flow of the flows 143, 145, 145a, 145b. Can be put in.

  The hydrocarbon flow rate FR2 corresponding to the flow rate of the cooled hydrocarbon stream 55 is measured by the hydrocarbon flow rate controller FC2 (350). FIG. 1 shows a cooled hydrocarbon flow controller 350 arranged to measure the flow rate FR2 of the cooled hydrocarbon stream 55. However, as long as the flow controller 350 provides a signal that is proportional to the flow rate FR2 of the hydrocarbon stream through the first heat exchanger 50, the hydrocarbon flow meter 350 may be the hydrocarbon stream 45 or any other hydrocarbon stream. The flow rate FR2 can also be set to measure.

  The flow rate measurement may be performed with any suitable apparatus, unit or device known in the art. Non-limiting examples include orifice plates, venturi tubes, nozzle flow meters, variable area meters, pilot tubes, calorimeters, turbine meters, Coriolis meters, ultrasonic Doppler meters and vortex meters.

  The flow controller also controls the operation of a valve, such as a valve that controls the flow of the flow, preferably pneumatically or hydraulically, or electrically.

  For the refrigerant flow rate FR1, the first set point SP1 is selected and input to the flow rate setter HC (300). The first set point SP1 is provisioned with respect to the refrigerant flow rate FR1, but the desired output of the cooled hydrocarbon stream 55, preferably the LNG stream, from the first heat exchanger 50. It corresponds to.

  If the cooling capacity (duty) from the refrigerant is supplied more than the cooling capacity required for the hydrocarbon to be cooled, the first heat exchanger 50 may be overcooled. In order to prevent overcooling of the first heat exchanger 50, the refrigerant flow rate FR1 and the hydrocarbon flow rate FR2 are adjusted according to the following cross-limiting control method.

  When the first set point SP1 for the refrigerant flow rate is larger than the measured value of the refrigerant flow rate FR1, that is, when it is necessary to increase the cooling hydrocarbon outflow amount of the first heat exchanger 50, the refrigerant flow rate FR1 is set. Before increasing, the hydrocarbon stream flow rate FR2 is increased.

  As long as the refrigerant flow rate FR1 increases after the hydrocarbon flow rate FR2 increases, overcooling of the first heat exchanger 50 can be prevented. However, to prevent overcooling of the hydrocarbon stream, the time between the increase of the hydrocarbon stream flow rate FR2 and the increase of the refrigerant stream flow rate FR1 should be as short as possible taking into account the response time of the system.

  When the first set point SP1 for the refrigerant flow rate is smaller than the measured value of the refrigerant flow rate FR1, that is, when it is necessary to reduce the cooling hydrocarbon outflow amount of the first heat exchanger 50, the hydrocarbon flow rate FR2 Before reducing the refrigerant flow, the refrigerant flow rate FR1 is reduced.

  As long as the hydrocarbon flow rate FR2 decreases after the refrigerant flow rate FR1 decreases, overcooling of the first heat exchanger 50 can be prevented. However, to prevent overcooling of the hydrocarbon stream, the time between the decrease in the refrigerant flow rate FR1 and the decrease in the hydrocarbon flow rate FR2 should be as short as possible taking into account the response time of the system.

  For example, if the hydrocarbon stream flow rate FR2 decreases during a tripping event in which the equipment using the cooled hydrocarbon stream 55 is withdrawn from operation or the feed apparatus for the hydrocarbon stream 45 is withdrawn from operation, The refrigerant flow rate FR1 should also be reduced.

  The refrigerant flow rate FR1 is preferably adjusted in proportion to the hydrocarbon flow rate FR2, so that a constant temperature is maintained for the cooled hydrocarbon stream 55.

  The refrigerant flow controller 340 can control the refrigerant flow rate FR1 by operating the refrigerant flow valve 170. In an alternative embodiment (not shown), if there is a control valve in either flow 143 or 145, this control valve will allow this to flow to the shell side 51 of the first heat exchanger 50 as long as this control valve is flowing. The refrigerant flow rate FR1 can be controlled by the presence of the control valve.

  Similarly, the cooled hydrocarbon flow rate controller FC2 can operate the cooled hydrocarbon valve 60 to control the flow rate of the cooled hydrocarbon stream 55 (and thereby the flow rate of the hydrocarbon stream 45). In an alternative 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 any second refrigerant flow flow rate FR3 needs to be controlled. FIG. 1 shows a second refrigerant flow controller FC3 (360) that operates the second refrigerant flow valve 210 to control the flow rate FR3 of the second refrigerant flow 185b. Although the second refrigerant flow valve 210 is shown after the second refrigerant expander 190, other refrigerants such as 147 or 185 may be used as long as the flow of the second refrigerant to the shell side 51 of the first heat exchanger 50 can be controlled. It can be placed in the second refrigerant.

  The flow rate FR3 of the second refrigerant flow 185b is adjusted in proportion to the flow rate of the refrigerant flow FR1. The refrigerant controller 330 can be used to adjust the position of the second refrigerant flow valve 210 based on the instruction supplied to the first refrigerant flow controller FC1. In order to ensure that the system provides accurate cooling capacity to the first heat exchanger 50, the second refrigerant flow controller FC3 measures the second refrigerant flow rate FR3.

  A cross-restricted control system that can be used in the method described herein can be automatic. FIG. 1 shows the flow controllers FC1 (340), FC2 (350), and FC3 (360) when operating the flow control valves 170, 60, and 210, respectively. A first set point SP1 for the flow rate (FR1) of the first refrigerant flow is input to the flow rate setter HC (300). The flow rate setting device 300 receives the input of the first set point SP1 and transmits it to the low selector 310 and the high selector 320.

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

  The nature and operation of the high and low sorters 310, 320 will be discussed in more detail with reference to FIG. FIG. 2 shows a control system diagram for the hydrocarbon cooling method described here. The main cooling stage 1 described with reference to FIG. 1 can be used in combination with this embodiment. For the sake of simplicity, only the cooled hydrocarbon stream 55 and the corresponding control valve 60 from FIG. 1 and only the cooling refrigerant stream 45, the refrigerant compressor 150, the compressed refrigerant stream 145a, the control valve 170 and the refrigerant stream 145b are shown in FIG. . However, other features of FIG. 1 may also exist.

  The first set point SP1 for the refrigerant flow rate FR1 is input to the flow rate setter HC (300). The flow rate setter HC generates a set point signal SPS, which is transmitted to the low and high sorters 310 and 320.

The refrigerant flow controller 340 generates a hydrocarbon flow signal FS2 that is proportional to the flow rate FR1 of the refrigerant flow 145b. The refrigerant flow signal FS1 is transmitted to the high sorter 320. High sorter 320 also receives first set point signal SPS from flow rate setter 300.
The refrigerant flow controller 340 operates the refrigerant flow valve 170 to control the flow rate of the refrigerant flow 145b.

The hydrocarbon flow controller 350 generates a refrigerant flow signal FS1 that is proportional to the flow rate FR2 of the cooled hydrocarbon stream 55. The hydrocarbon flow signal FS2 is transmitted to the low sorter 310. The low selector 310 also receives a first set point signal SPS from the flow rate setter 300.
The cooled hydrocarbon flow controller 350 operates the cooled hydrocarbon flow valve 60 to control the flow rate of the cooled hydrocarbon stream 55.

  The low sorter 310 is programmed to pass the lowest set point signal SPS and hydrocarbon flow signal FS2 to the first refrigerant flow controller 340. In this method, the increase in the first set point SPS only increases the flow rate FR1 of the refrigerant flow after the flow rate FR2 of the hydrocarbon flow increases.

  High sorter 320 is programmed to pass the highest set point signal SPS and refrigerant flow signal FS1 to hydrocarbon flow controller 350. In this method, the flow rate FR2 of the hydrocarbon stream only decreases after the flow rate FR1 of the refrigerant stream decreases due to the decrease of the set point SPS.

  Thus, since there is a cross-limiting control between the flow rate FR2 of the hydrocarbon stream and the refrigerant stream FR1, a hydrocarbon stream cooling method is provided in which overcooling of the first heat exchanger 50 is prevented.

  FIG. 3 shows a control system diagram for the hydrocarbon cooling method described here. In this method, the temperature TC2 of the cooled hydrocarbon stream 55 can be maintained by adjusting the ratio of the refrigerant stream 145b, such as the heavy mixed refrigerant stream, to the flow rate FR2 of the cooled hydrocarbon stream 55. It will be apparent that there is no means to adjust this ratio in the embodiment of FIGS. 1 and 2, and thus this means was fixed.

  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 transmits a signal TS2 proportional to this temperature.

  The temperature TC 2 of the cooled hydrocarbon stream can be adjusted by supplying a temperature set point TSP to the temperature controller 370. The temperature TC2 of the cooled hydrocarbon stream 55 can be lowered by reducing the flow rate FR2 of the cooled hydrocarbon stream 55 compared to the refrigerant flow rate FR1. Similarly, the temperature TC2 of the cooled hydrocarbon stream can be increased by increasing the flow rate FR2 of the cooled hydrocarbon stream 55 compared to the constant refrigerant flow rate FR1.

  The signal TS2 from the temperature controller 370 modulates the signal from the high selector 320 to the cooled hydrocarbon stream controller FC2 to increase or decrease the flow rate of the cooled hydrocarbon stream 55 compared to the unmodulated signal. be able to. However, the modulation performed on the signal from the cooled hydrocarbon flow rate controller FC2 to the low selector 310 is the inverse of the modulation performed on the signal from the high selector 320, resulting in a low selector. The cooled hydrocarbon flow rate signal FS2 reaching 310 corresponds to the signal from the hydrocarbon flow rate controller FC2 that occurs when not modulated by the cooled hydrocarbon flow temperature controller TC2. In this way, the operation of the low selector 310 and thus also the refrigerant flow controller FC1 is not affected by the cooled hydrocarbon flow temperature controller TC2.

  FIG. 3 shows one way in which the signal TS2 from the temperature controller 370 can modulate the signal from the high selector 320. The system has a specific flow ratio of cooled hydrocarbon stream (LNG): refrigerant stream (HMR), which provides the cooled hydrocarbon stream 55 at a specific temperature. In FIG. 3, this ratio is shown as LNG / HMR. In order to be able to adjust the temperature of the cooled hydrocarbon stream 55, the flow ratio of the cooled hydrocarbon stream: refrigerant stream must be changed from this predetermined ratio. The parameter b derived from the signal TS2 of 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 supplied to the hydrocarbon flow controller 350 includes the high selector 320 signal, the ratio of cooled hydrocarbon flow LNG: refrigerant flow HMR, ie, LNG / HMR, and temperature controller 370. As a function of parameter a derived from a scaling factor (b / 100) derived from parameter b derived from If the parameter b exceeds 100, for example in the range> 100 to 150, the parameter c of the signal supplied to the hydrocarbon flow controller 350 increases accordingly.

  Similarly, the parameter e derived from the signal supplied to the low selector 310 includes the hydrocarbon flow controller 350 signal, the refrigerant flow rate HMR: the ratio of the cooled hydrocarbon flow rate LNG, ie HMR / LNG, and temperature control. The inverse of the scaling factor (b / 100) determined from the parameter b derived from the signal of the device 370, i.e. as a function of the parameter d derived from (100 / b).

The flow rate of any second refrigerant flow FR3 can vary in proportion to the flow rate FR1 of the refrigerant flow in order to maintain a refrigerant: second refrigerant ratio, such as a HMR: LMR ratio. In another embodiment, FIG. 3 shows a refrigerant bypass stream 225 that bypasses the refrigerant expander 150. The refrigerant bypass flow 225 is controlled by the refrigerant bypass valve 230 to supply a controlled refrigerant bypass flow 225a. Control refrigerant bypass stream 225a can be blended with refrigerant stream 145b to provide blended refrigerant stream 245. The refrigerant bypass valve 230 can be operated by a signal from the refrigerant flow controller 340 and can bypass the refrigerant expander 150 with respect to the cooling refrigerant flow 145.
Those skilled in the art will readily appreciate that the present invention can be modified in many ways without departing from the scope of the appended claims.

1 main cooling stage 45 hydrocarbon stream 50 first heat exchanger 51 shell side 53 first tube bundle 55 cooling or liquefied hydrocarbon stream 57 second tube bundle 59 third tube bundle 60 cooling hydrocarbon valve 100 refrigerant circuit 105 return refrigerant stream 110 refrigerant Compressor 115 Compressed refrigerant stream 120 Refrigerant compressor driver 130 Refrigerant cooler 135 Cooled compressed refrigerant stream 140 Separator 143 Incoming refrigerant stream or tower bottom heavy mixed refrigerant (HMR)
145 Cooling refrigerant stream 145a Expanded refrigerant stream 145b Refrigerant stream 147 Second refrigerant stream, second incoming refrigerant stream or tower top light mixed refrigerant (LMR)
150 refrigerant expander 160 refrigerant expander driver 170 refrigerant flow valve 176 second inlet 185 cooling second refrigerant flow 185a expanded second refrigerant flow 185b second refrigerant flow 190 second refrigerant expander 200 second refrigerant expander driver 210 Second refrigerant flow valve 216 Third inlet 225 Refrigerant bypass flow 225a Control refrigerant bypass flow 230 Refrigerant bypass valve 245 Blended refrigerant flow 300 Flow setter 310 Low sorter 320 High sorter 330 Refrigerant controller 340 Refrigerant flow controller 350 Hydrocarbon Flow controller 360 Second refrigerant flow controller 370 Temperature controller FC1 Refrigerant flow (controller)
FC2 Hydrocarbon flow rate (controller)
FC3 Second refrigerant flow rate (controller)
FR1 Refrigerant flow rate FR2 Hydrocarbon flow rate FR3 Second refrigerant flow rate FS1 Refrigerant flow rate signal FS2 Cooling hydrocarbon flow rate signal HC Flow rate setter SP1 First set point SPS First set point signal TC2 Temperature or temperature control of cooled hydrocarbon flow Vessel TS2 temperature signal TSP temperature set point L-Sel low sorter H-Sel high sorter LNG / HMR = cooling hydrocarbon flow: flow rate ratio of refrigerant flow HMR / LMR = column bottom heavy mixed refrigerant: column top light mixed refrigerant (Second refrigerant) ratio

US Patent Application 2003/0046953

Claims (15)

(A) providing a hydrocarbon stream;
(B) heat exchanging the hydrocarbon stream with one or more refrigerant streams having a refrigerant flow rate in a first heat exchanger to provide a hydrocarbon stream having a hydrocarbon flow rate and one or more return refrigerant streams; The process of
(C) inputting a first set point for the refrigerant flow rate, and (d) adjusting the refrigerant flow rate and the hydrocarbon flow rate until the set point is achieved,
(D1) If the first set point is greater than the refrigerant flow rate, the hydrocarbon flow rate is increased before increasing the refrigerant flow rate, d2) If the first set point is smaller than the refrigerant flow rate, decrease the refrigerant flow rate before decreasing the hydrocarbon flow rate, and (d3) decrease the refrigerant flow rate if the hydrocarbon flow rate decreases. The method of letting.   The method according to claim 1, wherein the step of adjusting the refrigerant flow rate and the hydrocarbon flow rate in step (d) is automatic.   3. A method according to claim 1 or 2, wherein the ratio of [refrigerant flow] / [hydrocarbon flow] is maintained below a preselected level during step (d). The refrigerant flow rate is a refrigerant flow controller for controlling the flow rate of the refrigerant flow by operating the refrigerant flow valve, and is measured by the refrigerant flow controller that generates a refrigerant flow signal transmitted to the high sorter. And
The first set point is input to a flow setter that generates a set point signal that is sent to the low and high sorters,
The low sorter passes the lowest setpoint signal and hydrocarbon flow signal to the refrigerant flow controller, and the high sorter passes the highest setpoint signal and refrigerant flow signal to the cooled hydrocarbon flow controller,
The method according to claim 1.   5. A method according to any one of claims 1 to 4, wherein 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.   The method according to any one of claims 1 to 5, further comprising, in step (b), heat exchange of the hydrocarbon stream with a second refrigerant stream having a second refrigerant stream flow rate in the first heat exchanger. .   The method of claim 6, wherein the second refrigerant flow rate is measured as part of the refrigerant flow rate. A second refrigerant flow controller that operates the second refrigerant flow valve, thereby changing the flow rate of the second refrigerant flow, and receives the lowest set point signal and the cooled hydrocarbon flow signal from the low sorter, and A refrigerant controller that adjusts the flow rate of the second refrigerant flow relative to the flow rate of the refrigerant flow by transmitting a refrigerant controller signal to the second refrigerant flow rate controller;
The method according to claim 6 or 7, further comprising:   The second refrigerant flow is a light mixed refrigerant flow when the refrigerant flow is a heavy mixed refrigerant flow, or the second refrigerant flow is a heavy mixed refrigerant flow when the refrigerant flow is a light mixed refrigerant flow. The method according to any one of claims 6 to 8. (I) in the first heat exchanger, cooling the incoming refrigerant flow to supply a cooling refrigerant flow;
(Ii) in the refrigerant expander, expanding the cooling refrigerant flow and supplying the expanded refrigerant flow;
(Iii) supplying the refrigerant stream by passing the expanded refrigerant stream through a refrigerant valve; and (iv) passing the refrigerant stream to a second inlet of the first heat exchanger;
The method according to claim 1, further comprising: (V) passing the return refrigerant stream through a refrigerant compressor to supply the compressed refrigerant stream;
(Vi) cooling the compressed refrigerant stream in a cooler to supply a cooled compressed refrigerant stream; and (vii) separating the cooled compressed refrigerant stream in a separator to supply one or more incoming refrigerant streams. The process of
The method of claim 10, further comprising: The cooling compressed refrigerant stream separation step (vii) further generates a second incoming refrigerant stream, the method comprising:
(Viii) cooling the second incoming refrigerant stream in a first heat exchanger to provide a cooled second incoming refrigerant stream;
(Ix) expanding the cooled second incoming refrigerant stream in a second refrigerant expander to provide an expanded second incoming refrigerant stream;
(X) passing the expanded second incoming refrigerant stream through a second refrigerant valve to supply a second refrigerant stream; and (xi) passing the second refrigerant stream through a third inlet of the first heat exchanger;
The method of claim 11, further comprising:   The process according to any one of claims 1-2, wherein the hydrocarbon stream is a natural gas stream and the cooled hydrocarbon stream is an LNG stream. A first heat exchanger having a first inlet for hydrocarbon stream, a first outlet for cooled hydrocarbon stream, one or more second outlets for one or more refrigerant streams, and a second outlet for return refrigerant streams;
A refrigerant that controls the flow rate of the refrigerant flow by operating a refrigerant valve to measure a signal proportional to the refrigerant flow rate of one or more refrigerant flows and to supply a refrigerant flow signal that is transmitted to the high sorter Flow controller,
• Operate the cooled hydrocarbon stream valve to measure the signal proportional to the cooled hydrocarbon stream flow rate of the cooled hydrocarbon stream and provide a cooled hydrocarbon stream signal that is sent to the low selector. Cooling hydrocarbon flow controller to control the flow rate of the flow,
A flow rate setter for entering set points and supplying set point signals to be sent to the low and high sorters,
A low selector that sends the lowest set point signal and the cooled hydrocarbon flow rate signal to the refrigerant flow controller, and a high that sends the highest set point signal and the cooled hydrocarbon flow rate signal to the cooled hydrocarbon flow controller. Sorter,
An apparatus for operating a heat exchanger comprising at least A third inlet for the second refrigerant flow in the first heat exchanger,
A second refrigerant flow controller that changes the flow rate of the second refrigerant flow by operating the second refrigerant flow valve, and a minimum set point signal and a cooled hydrocarbon flow signal received from the low sorter, and further refrigerant control A refrigerant controller that adjusts the flow rate of the second refrigerant flow relative to the flow rate of the refrigerant flow by transmitting a vessel signal to the second refrigerant flow rate controller,
15. The apparatus of claim 14, further comprising: