KR0131579B1 - Cooling apparatus using propane refrigerant gas in natural gas liquidification - Google Patents

Abstract

In the propane refrigerant process, which is widely used as a natural gas liquefaction process, there is provided an improved cooling device for precooling natural gas or cooling a mixed refrigerant for natural gas liquefaction. As a heat exchanger for pre-cooling natural gas or cooling a mixed refrigerant for natural gas liquefaction, propane-based refrigerants are preferably distributed in a vertical direction, preferably plate fin heat exchangers installed in parallel, and for horizontal propane-based refrigerants generally installed horizontally. By having a thermosiphon drum, the passage of natural gas or mixed refrigerant does not change with each other over the entire length, and thus high heat transfer effect can be achieved even if any of propane-based refrigerant, natural gas or mixed refrigerant is gas-liquid mixed, and the heat exchanger can be miniaturized. Can be. In particular, it is desirable from the viewpoint of economics that the thermosiphon drum also serves as a flash tank.

Description

Cooling system using propane refrigerant in natural gas liquefaction process

1 is a schematic diagram showing a natural gas precooling apparatus in a natural gas liquefaction process to which a cooling apparatus using propane according to the present invention is applied,

2 is a schematic diagram showing a liquefaction apparatus of natural gas in a natural gas liquefaction process to which a cooling apparatus using propane according to the present invention is applied,

3 is a schematic view showing the main parts of the first embodiment of the cooling apparatus according to the present invention,

4 is a schematic view showing the main parts of a second embodiment of a cooling apparatus according to the present invention,

5 is a plan view showing the arrangement of the device shown in FIG.

6 is an elevation view showing the arrangement of the device shown in FIG.

7 is a plan view showing the main parts of a third embodiment of a cooling apparatus according to the present invention;

8 is a side cross-sectional view of the embodiment shown in FIG.

9 is a side view showing a fourth embodiment of a cooling apparatus according to the present invention,

FIG. 10 is a cross sectional front view of the embodiment shown in FIG.

* Explanation of symbols for main parts of the drawings

1: heat exchanger 2: drum

3: dryer 4,5,6: heat exchanger

7: washing column 8: main heat exchanger

9,10 drum 11: pump

12,14 Compressor 13,16 Subsequent Cooler

15: internal cooler 17-20: heat exchanger

21: separation drum 31: plate fin heat exchanger

32,34,36,38: Pressure reducing valves 33,35,37,39: Thermosiphon drum

33 ', 35', 37 ', 39: flash tank 40: pipeline

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling device for precooling natural gas or cooling a mixed refrigerant for natural gas liquefaction using propane in a propane refrigerant process that is widely used in natural gas liquefaction processes. .

In the general natural gas liquefaction process, as shown in FIG. 1, high-pressure natural gas from which acidic gases such as CO2 and H2 have been removed in advance is about 20 ° C by the shell-and-tube heat exchanger 1 distributed by HHP propane. It is cooled down until most of the water is condensed and separated from the drum (2). Next, the moisture is removed from the dryer 3 to about 1 wt ppm again, the shell and tube heat exchanger 4 distributed by HP propane is cooled to 0 ° C, and the shell and tube heat exchanger 5 distributed by MP propane. Cooling to −10 ° C.) and cooling to −25 ° C. with a shell and tube heat exchanger 6 through which LP propane flows to the washing column 7 where heavy oil is removed.

Next, as shown in FIG. 2, the liquid is returned by entering the main heat exchanger 8 and cooling the heat exchange with the mixed refrigerant to -145 ° C. The fluid obtained here is washed twice with drums 9 and 10, and the pressure is removed to remove N2. Atmospheric pressure, LNG is sent to the storage facility by the pump 11.

On the other hand, in the mixed refrigerant cycle, as shown in FIG. 2, the mixed refrigerant heat-exchanged with the natural gas in the main heat exchanger 8 is sent to the LPMR compressor 12 at -30 ° C and pressurized to 13 Bar, It is cooled to room temperature in the subsequent cooler (13). Moreover, it is sent to the HPMR compressor 14, it pressurizes to 25 Bar, and it cools to normal temperature with the internal cooler 15, and it presses again to 40 Bar with the HPMRdkq accumulator 14 again. The pressurized mixed refrigerant is cooled to room temperature with a subsequent cooler 16 and then cooled to 15 ° C. by HHP propane in the shell and tube heat exchanger 17 and 0 ° C. by HP propane in the shell and tube heat exchanger 18. To -10 ° C by MP propane in the shell and tube heat exchanger 19 and to -25 ° C by LP propane in the shell and tube heat exchanger 20, respectively.

In this case, partial condensation starts in the shell and tube heat exchanger 17, and partial condensation of about 3/4 of the whole is performed in the shell and tube heat exchanger 20 to enter the separation drum 21. Here, each of the separated gas liquids enters the main heat exchanger 8 to liquefy natural gas.

Here, for the LNG plant production of 2.6 million tons per year for example, shell-and-tube type heat exchanger that is cooled by propane (Kane forming frame: 1,4,5,6) is large cake forming frame heat date of each 1,000m ² to 2,000m ² There is a need, and the shell and tube type heat exchanger (kettle type ^{17, 18,} 19, 20) is required to be a large kettle type heat exchanger of about 2,000 m ² x 2 sets respectively. Since these heat exchangers are huge, land transportation is difficult, the cost of each heat exchanger is high, and the cost of a base structure and local construction cost arises.

In the shell and tube type heat exchangers 5, 6, 18, 19, and 20, the natural gas or mixed refrigerant is multiphase at the inlet of these heat exchangers. It is inevitable that the gas-liquid ratio for the tube will be out of theory and that the performance of the heat exchanger will be significantly reduced.

In view of the problems of the prior art, the main object of the present invention is an improved cooling apparatus for precooling natural gas or cooling a mixed refrigerant for natural gas liquefaction in a propane refrigerant process that is widely used in a natural gas liquefaction process. To provide.

This object is an apparatus for precooling natural gas or cooling a mixed refrigerant for natural gas liquefaction using a propane-based refrigerant in a natural gas liquefaction process. Plate fin type heat exchangers, which are installed in a plurality in parallel, preferably horizontally arranged so that passages are generally separated from each other over the entire length thereof, and the propane-based refrigerant is circulated in a vertical direction. It is achieved by providing an apparatus comprising a thermosiphon drum for propane-based refrigerant connected to the plate fin type heat exchanger at the same time as the tank of the cabinet. In particular, it is desirable from the viewpoint of economics that the thermosiphon drum also serves as a flash tank.

Thus, by using a plate fin type heat exchanger having a heat transfer area of 10 times that of the shell and tube type heat exchanger per unit volume, the unit cost can be reduced, and the heat exchanger can be integrated by omitting the pipe during the heat exchange period of the shell and tube type heat exchanger. By using a plate fin type heat exchanger, the required heat transfer area can be obtained without enlarging the heat exchanger. An example of the plate fin heat exchanger which can be used for such a use is disclosed by Unexamined-Japanese-Patent No. 58-55432. In addition, the problem of the prior art that a natural gas or a mixed refrigerant is mixed to obtain a desired heat transfer effect can be avoided by not changing the passage over the entire length in the plate fin heat exchanger. In addition, it is preferable that natural gas or a mixed refrigerant uses vertical down flow or horizontal flow, and propane uses vertical up flow in consideration of maintaining its performance even in the plant's weight reduction operation.

Example

3 shows the main part of the propane cooling apparatus according to the present invention using the plate fin type heat exchanger 31 to be used instead of the heat exchangers 17, 18, 19, and 20 in FIG. 2. 33, 35, 37, and 39 are thermosiphon drums, and 33 ', 35', 37 'and 39' are for making low pressure propane refrigerants. It's a flash tank. In the present embodiment, four thermosiphon drums are provided for a set of plate fin heat exchangers 31.

Liquefied propane under conditions of 15 Bar and 43 ° C. becomes HHP propane at 7 Bar and 10 ° C. by the pressure reducing valve 32, becomes gas-liquid mixed, introduced into the flash tank 33 ′, and gas-liquid separation. The liquid is then returned to the compressor of the propane cooling system, and the liquid component must be circulated in the heat exchanger 31, which is first sent to the thermosyphon drum 33, and partly 5 bar,-by the pressure reducing valve 34. It becomes HP propane of 5 degreeC, and becomes gas-liquid mixture, and is supplied to the next flash tank 35 '. Propane circulated in the heat exchanger 31 is evaporated by heat exchange with the mixed refrigerant in the heat exchanger 31 to form a gas-liquid mixture and returned to the thermosiphon drum 33. In the thermal siphon drum 33, the vaporized powder separated from the gas-liquid is also returned to the propane cooling system by the conduit 40. Hereinafter, the functions of the thermosiphon drums 35, 37, 39, flash tanks 35 ', 37', 39 'and the pressure reducing valves 36, 38 of the respective stages are also the same. The detailed description thereof will be omitted.

In the case of using a plate fin type heat exchanger instead of the heat exchangers 4, 5, and 6 in FIG. 1, in which the medium to be cooled is natural gas, HHP propane is almost the same as above. It is preferable not to heat exchange with a plate fin type heat exchanger. In the shell and tube heat exchanger of FIG. 1, it is necessary to strictly control the temperature of HHP propane to prevent hydrate generation, which is advantageously done by a control valve installed in the gas phase line. It is because it is preferable to carry out by a shell and tube type heat exchanger separately from (31).

When a plant with a capacity of 2.6 million tons per year is produced in a conventional base load LNG LNG plant, theoretically, such plate fin heat exchangers 31 are required to use 6-8 even if the largest ones can be manufactured. If a separation drum such as a thermosyphon drum is installed in each unit, the number of separation drums increases and the unit price increases. Therefore, a large vertical separation drum is installed in each level of propane, and the liquid is exchanged from the header for each plate fin type heat exchanger. The gas-liquid mixed propane distributed to the gas and exiting from each plate fin type heat exchanger can be considered to return each piping to the header and return to the separation drum.

In addition, according to the inventors' knowledge, in the fluid introduction portion of the thermosiphon drum, for example, by installing a horizontal baffle to prevent bubbles from sinking in the liquid, the role of the flash tank in the gas-liquid separator of the thermosiphon. The cost can be reduced by combining. A schematic of the propane flow of an embodiment based on this knowledge is shown in FIG.

However, since the refrigerant is gas-liquid mixed, it is difficult to uniformize the pressure loss from each plate fin heat exchanger to the separation drum, and the pressure loss is also large, so that it cannot be prevented from adversely affecting the heat transfer performance of the plate fin heat exchanger. One reason why plate fin heat exchangers have not been used so far has been the reduction in heat transfer performance resulting from this unbalanced pressure loss. Therefore, according to the present invention, the separation drum as the thermal siphon drum is made horizontal and lengthened, the role of the header is provided to the separation drum, and the return pipe from the plate fin heat exchanger to the separation drum is directly connected to each other. The heat transfer performance of each plate fin type heat exchanger is improved by entering a single pipe so that the pressure loss is uniform and small.

That is, as shown in FIGS. 5 and 6, five vertical plate fin heat exchangers 31 are installed in parallel, and thermal siphon drums 33, 35, 37, 39 ) Is arranged horizontally to the left and right, and forms a common header for each plate fin heat exchanger 31. In the present embodiment, the thermosiphon drums are installed in two stages above and below, respectively, and four thermosiphon drums are used per set of fin fin heat exchanger 31. In this case, propane is a vertical flow, in particular a vertical up flow, which allows passages that are separated from each other over the entire length, reducing pressure loss and mixing pressure in each passage of the plate fin heat exchanger, even though it is mixed. Equalization is possible. On the other hand, natural gas or mixed refrigerant is a vertical down flow or horizontal flow, and in view of the fact that this is a mixed phase, the heat transfer effect is lowered by preventing the passage of natural gas or mixed refrigerant in the plate fin type heat exchanger over the entire length. It is desirable to avoid this.

7 and 8 show a third embodiment of the present invention. The same code | symbol is attached | subjected to the part corresponding to the said Example. In the present embodiment, the plate fin heat exchanger 31 is arranged horizontally, natural gas or mixed refrigerant flows in the horizontal direction, and propane refrigerant flows upward as a vertical rising thermosiphon. As shown in FIG. 7, the plate fin heat exchanger 31 is formed by combining a plurality of long segments, and the segments are arranged in parallel with each other along the longitudinal direction. Separation drums 33, 35, 37 and 39, each functioning as a thermosiphon drum, are each configured as a horizontal tank, so as to be orthogonal to the long heat exchanger segment as in the case of the second embodiment, And the heat exchanger is arrange | positioned so that it may transverse from right to left. In this case, each separation drum also has the function of a header, and each pipeline from the separation drum to each segment of the plate fin heat exchanger and one channel from each segment of the plate fin heat exchanger to the separation drum each have one pipe line. It is connected directly through. Thus, the pressure loss due to these pipelines is reduced, and the pressure is evenly distributed in the other pipelines of the plate fin heat exchanger. Thereby, the heat exchange efficiency of a heat exchanger can be improved.

In this embodiment, the natural gas or mixed refrigerant flows horizontally in the heat exchanger, but the condensate resulting from the cooling of those streams is separated at the bottom of the heat exchanger, and the plate is used to avoid damaging the heat transfer effect of the heat exchanger. As the fin heat exchanger, it is necessary to use a straight fin plate fin heat exchanger. Platerate fins have slightly lower heat transfer effects than commonly used through fins for condensing upstream or downstream streams, but they do not require space for distributing the stream at each level of propane. Can actually increase.

9 and 10 show a fourth embodiment of the present invention. In this embodiment, the separation drum and the plate fin heat exchanger are provided separately, whereas in the present embodiment, the separation drum and the plate fin heat exchanger. We integrate group. That is, each of the separation drums 33, 35, 37, and 39 is formed by dividing one long tank by partition walls, and the plate fin heat exchanger 31 passes through these partition walls. It is intended to extend in the separation drum.

As shown in FIG. 10, in each separation drum, the liquid level of the propane is determined so that the heat exchanger is almost submerged in the liquid propane, and the propane circulates upward in the heat exchanger as a vertically rising thermosiphon by convection.

According to the present embodiment, the internal structure of the separation drum is slightly complicated, but the piping is greatly unnecessary, so that the cost of manufacturing is expected to decrease, and the overall pressure loss can be reduced. In addition, by arranging a plurality of such configurations in parallel, the required capacity can be secured. Further, if necessary, a plurality of long heat exchanger segments may be arranged in parallel in the same separation drum as in the case of the above embodiment, although separated by isolation.

In a cooling device for precooling natural gas or cooling a mixed refrigerant for natural gas liquefaction, a plate fin type heat exchanger is used instead of a shell and tube heat exchanger, and a passage of propane, natural gas or mixed refrigerant passage in the heat exchanger is used. By not changing over, the non-uniformity of the gas-liquid ratio for every channel | path is reduced. This achieves a high heat transfer effect to reduce the unit cost. Further, propane in a plate fin type heat exchanger is vertically up, and by installing a thermosiphon drum attached to the side, even if propane is mixed with gas and liquid, pressure loss can be reduced and equalized.

Claims (6)

In a device for precooling natural gas using a propane-based refrigerant in a natural gas liquefaction process or for cooling a mixed refrigerant for natural gas liquefaction, a plurality of passages of the natural gas or the mixed refrigerant are generally applied to the entire length. A plate fin heat exchanger installed in such a manner as to be separated from each other over each other, and installed such that the propane refrigerant is distributed in a vertical direction, and a separation drum for the propane refrigerant connected to the plate fin heat exchanger; A plurality of segments each disposed in parallel with each other to define at least one passage separated from each other, wherein each segment is divided into a plurality of stages along its entire length, and the separation drum is a plurality of separation drums, respectively. The horizontal tank is installed horizontally, Each separation drum is arranged to serve as a common header for the plurality of segments. The plate fin heat exchanger of claim 1, wherein each of the segments is arranged vertically and the plurality of separation drums are arranged horizontally so as to cross the segment transversely on at least one surface of the plate fin heat exchanger. And vertically arranged. 2. The plate fin heat exchanger of claim 1 wherein the plate fin heat exchanger is arranged such that each segment is arranged horizontally and the plurality of separation drums are arranged in a horizontal direction to cross transversely with the segment of the plate fin heat exchanger. Device arranged. In the natural gas liquefaction process, in the apparatus for precooling natural gas using a propane type refrigerant | coolant, or cooling the mixed refrigerant for natural gas liquefaction, the source of propane type refrigerant | coolant and the said propane type refrigerant | coolant sent from the said source. Natural gas or natural gas by means of an expansion device for reducing the pressure, a separation drum for gas-liquid separation of the propane-based refrigerant consisting of a mixture of vapor and liquid obtained from the expansion device, and the propane-based refrigerant as a boiling point obtained from the separation drum. A heat exchanger for cooling the gas liquefied mixed refrigerant and returning the propane-based refrigerant consisting of a mixture of steam and liquid after heat exchange to the separation drum, and extracting a part of the propane-based refrigerant as a liquid obtained from the separation drum; Expansion device of the next stage to depressurize, Natural gas or gas by means of a separation drum of the next stage for gas-liquid separation of the propane-based refrigerant consisting of a mixture of vapor and liquid obtained from an expansion device of the next stage, and the propane-based refrigerant as a boiling point obtained from the separation drum of the next stage. The next stage heat exchanger which cools the mixed refrigerant for natural gas liquefaction, and returns the said propane type refrigerant | coolant which consists of a mixture of the steam and a liquid after heat exchange to the next stage separation drum, and the steam obtained from the said separation drum of each stage. And a steam pipe for returning the propane-based refrigerant to the supply source, wherein the heat exchanger extends in a state in which a plurality of passages of the natural gas or the mixed refrigerant are separated from each other over the entire length thereof, and the propane-based refrigerant is Plate fin heat exchanger installed for vertical flow And said separation drum is comprised of a horizontally horizontal tank which is generally horizontally installed as said thermosiphon drum for said propane-based refrigerant connected to said plate fin type heat exchanger. The apparatus of claim 1 wherein said separation drum also serves as a flash tank. An apparatus according to claim 5, wherein said separation drums are each thermosyphon drums.