KR102016379B1 - Boil-Off Gas Reliquefaction Method and System for LNG Vessel - Google Patents

Abstract

An evaporative gas reliquefaction system for LNG carriers is disclosed.
The boil-off gas reliquefaction system of the LNG carrier, the compressor for compressing the boil-off gas; A heat exchanger configured to heat the boil-off gas compressed by the compressor with a boil-off gas, thereby cooling the boil-off gas; And expansion means for expanding the fluid cooled by the heat exchanger, wherein the heat exchanger comprises: a core in which heat exchange between the high temperature fluid and the low temperature fluid occurs; And fluid dispersing means for dispersing the fluid flowing into the core or the fluid discharged from the core, wherein the core includes a plurality of diffusion blocks.

Description

Boil-Off Gas Reliquefaction Method and System for LNG Vessel

The present invention relates to a method and system for reliquefaction of excess evaporated gas remaining in the engine among the evaporated gas generated inside the storage tank of the LNG carrier using the evaporated gas itself as a refrigerant.

Recently, the consumption of liquefied gas such as liquefied natural gas (Liquefied Natural Gas, LNG) is increasing worldwide. Liquefied gas liquefied gas at low temperature has the advantage that the storage and transport efficiency can be improved because the volume is very small compared to the gas. In addition, liquefied gas, including liquefied natural gas can remove or reduce air pollutants during the liquefaction process, it can be seen as an environmentally friendly fuel with less emissions of air pollutants during combustion.

Liquefied natural gas is a colorless and transparent liquid obtained by liquefying natural gas containing methane as a main component at about -163 ℃ and having a volume of about 1/600 compared to natural gas. Therefore, when liquefied and transported natural gas can be transported very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -163 ℃ at normal pressure, liquefied natural gas is sensitive to temperature changes and easily evaporated. As a result, the storage tank storing the liquefied natural gas is insulated. However, since the external heat is continuously transferred to the storage tank, the natural gas is continuously vaporized in the storage tank during the transport of the liquefied natural gas. -Off Gas, BOG) occurs.

Boil-off gas is a kind of loss and is an important problem in transportation efficiency. In addition, when boil-off gas is accumulated in the storage tank, the internal pressure of the tank may be excessively increased, and there is also a risk that the tank may be damaged. Accordingly, various methods for treating the boil-off gas generated in the storage tank have been studied. In recent years, for the treatment of the boil-off gas, a method of re-liquefying the boil-off gas to return to the storage tank, and returning the boil-off gas to a fuel such as an engine of a ship The method used as an energy source of a consumer is used.

As a method for reliquefaction of the boil-off gas, a refrigeration cycle using a separate refrigerant is used to re-liquefy the boil-off gas by exchanging the boil-off gas with the refrigerant, and a method of re-liquefying the boil-off gas itself as a refrigerant without a separate refrigerant. There is this. In particular, a system employing the latter method is called a Partial Re-liquefaction System (PRS).

On the other hand, among the engines generally used in ships as a fuel that can use natural gas as a fuel gas engines such as DFDE, X-DF engine, ME-GI engine.

DFDE is composed of four strokes and adopts the Otto Cycle, which injects natural gas with a relatively low pressure of 6.5 bar into the combustion air inlet and compresses the piston as it rises.

The X-DF engine consists of two strokes, uses about 16 bar of natural gas as fuel, and employs an auto cycle.

The ME-GI engine is composed of two strokes and employs a diesel cycle that directly injects high pressure natural gas near 300 bar into the combustion chamber near the top dead center of the piston.

The present invention is to provide a method and system for reliquefaction of boil-off gas of LNG ship, which can stabilize the reliquefaction performance and increase the overall reliquefaction efficiency and reliquefaction amount.

According to an aspect of the present invention for achieving the above object, a compressor for compressing the boil-off gas; A heat exchanger configured to heat the boil-off gas compressed by the compressor with a boil-off gas, thereby cooling the boil-off gas; And expansion means for expanding the fluid cooled by the heat exchanger, wherein the heat exchanger comprises: a core in which heat exchange between the high temperature fluid and the low temperature fluid occurs; And fluid dispersion means for dispersing the fluid flowing into the core or the fluid discharged from the core, wherein the core includes a plurality of diffusion blocks.

The fluid dispersing means may disperse the fluid by resisting the fluid.

The fluid dispersing means may be a porous plate.

The heat exchanger, the hot fluid inlet header to distribute the hot fluid flowing into the heat exchanger to the core; A high temperature fluid discharge header configured to collect the high temperature fluid discharged from the core and discharge the high temperature fluid to the outside of the heat exchanger; A low temperature fluid inlet header which disperses the low temperature fluid introduced into the heat exchanger and sends it to the core; And a low temperature fluid discharge header configured to collect the low temperature fluid discharged from the core and discharge the external fluid to the outside of the heat exchanger. The porous plate may include the hot fluid discharge header and the hot fluid discharge header between the core and the core. It may be installed between at least one of the core, between the low temperature fluid inlet header and the core, and between the low temperature fluid discharge header and the core.

The hole formed in the porous plate has a small cross-sectional area near the pipe into which the fluid is introduced or discharged, and the larger the cross-sectional area is from the pipe.

The hole formed in the porous plate has a low forming density near the pipe into which the fluid is introduced or discharged, and may have a higher forming density as it moves away from the pipe.

The distance between the porous plate and the core may be 20 to 50 mm.

The heat exchanger may further include one or more partition walls, and the partition walls may be installed between the porous plate and the core to prevent the fluid dispersed by the porous plate from gathering again.

The partition wall may have a shape of dividing an internal space into a plurality of regions.

The partition wall may prevent the refrigerant from gathering again within one diffusion block as well as between the plurality of diffusion blocks.

The partition wall may allow the porous plate to be spaced apart from the core.

The barrier rib may have a shape in which one or more unidirectional gratings and one or more other directional gratings cross each other to divide an internal space.

The evaporative gas reliquefaction system of the LNG carrier may further include a gas-liquid separator installed at the rear end of the expansion means to separate the liquefied liquefied gas and gas components.

The gas component separated by the gas-liquid separator may be combined with the boil-off gas and used as a refrigerant of the heat exchanger.

The boil-off gas compressed by the compressor may be in a supercritical state.

The pressure of the boil-off gas compressed by the compressor may be 100 to 400 bara.

The pressure of the boil-off gas compressed by the compressor may be 150 to 400 bara.

The pressure of the boil-off gas compressed by the compressor may be 150 to 300 bara.

According to another aspect of the present invention for achieving the above object, a compressor for compressing the boil-off gas; A heat exchanger configured to heat the boil-off gas compressed by the compressor with a boil-off gas, thereby cooling the boil-off gas; And expansion means for expanding the fluid cooled by the heat exchanger, wherein the heat exchanger includes a core through which heat exchange between the high temperature fluid and the low temperature fluid occurs, and the core includes a plurality of diffusion blocks. An evaporation gas reliquefaction system for an LNG carrier is provided, characterized in that the temperature difference between the diffusion blocks is within 40-50 degC.

According to another aspect of the present invention for achieving the above object, a compressor for compressing the boil-off gas; A heat exchanger configured to heat the boil-off gas compressed by the compressor with a boil-off gas, thereby cooling the boil-off gas; And expansion means for expanding the fluid cooled by the heat exchanger, wherein the heat exchanger includes a core through which heat exchange between the high temperature fluid and the low temperature fluid occurs, and the core includes a plurality of diffusion blocks. Among the fluids supplied to the diffusion blocks, the flow rate (a) of the flow with the highest flow rate is less than four times (a <4b) of the flow rate (b) of the flow with the least flow rate, and is respectively discharged from the plurality of diffusion blocks. Boiler gas reliquefaction system of the LNG carrier, characterized in that the flow rate (a ') of the highest flow rate of the fluid is less than four times (a' <4b ') of the flow rate (b') of the least flow rate flow. This is provided.

According to the present invention, the reliquefaction performance can be stably maintained even if the flow rate of the reliquefaction target evaporation gas varies.

According to one embodiment of the present invention, a phenomenon in which a refrigerant is concentrated in one diffusion block may be alleviated by dispersing a fluid supplied to or discharged from the heat exchanger.

According to an embodiment of the present invention, the refrigerant may be evenly distributed between not only a plurality of diffusion blocks but also within one diffusion block, and the porous plate and the core may be spaced apart from each other. In particular, it is possible to prevent the case where the flow of the fluid to the core is prevented by contacting the porous plate and the core to block the flow path.

According to an embodiment of the present invention, since the porous plate is combined with a heat exchanger to enable thermal expansion and contraction, the porous plate does not bend or break even when it contracts due to contact with cryogenic evaporative gas, and the connection portion of the porous plate is It is not broken.

According to an embodiment of the present invention, since the heat exchanger includes a channel having a shape capable of resisting the fluid, it is possible to alleviate the concentration of the refrigerant in one diffusion block without adding a separate member for dispersing the fluid. You can prevent it.

1 illustrates a basic model for explaining the concept of boil-off gas reliquefaction according to an embodiment of the present invention.
Figure 2 shows the process calculation program of the reliquefaction performance evaluation experiment according to the re-liquefaction target boil-off gas pressure of the present invention.
FIG. 3 is a view illustrating an example of a high temperature fluid and a low temperature fluid when the pressure of the boil-off gas to be reliquefied is 39 bara and 50 bara to 120 bara increased by 10 bara in the evaporation gas reliquefaction system according to an embodiment of the present invention. It is a graph showing the temperature change according to the heat flow amount.
4 is a heat flow amount of the hot fluid and the low temperature fluid in the case of the 130bara to 200bara and the 300bara pressure of the evaporation gas to be reliquefied in the evaporation gas re-liquefaction in accordance with an embodiment of the present invention is increased by 10bara It is a graph showing the temperature change according to.
5 is a schematic diagram of an evaporation gas reliquefaction system according to an embodiment of the present invention when the evaporation gas pressure to be reliquefaction is 39 bara.
Figure 6 is a schematic diagram of an evaporation gas reliquefaction system according to an embodiment of the present invention when the re-liquefaction target evaporation gas pressure is 150 bara.
7 is a schematic diagram of an evaporation gas reliquefaction system according to an embodiment of the present invention when the re-liquefaction target evaporation gas pressure is 300 bara.
8 and 9 are graphs showing the “reliquefaction amount” of Table 1 in the pressure range from 39 bara to 300 bara.
10 is a schematic diagram of a conventional PCHE.
11 is a schematic diagram of a heat exchanger according to a first preferred embodiment of the present invention.
12 is a schematic diagram of a first partition wall or a second partition wall included in a heat exchanger according to a second embodiment of the present invention.
13 is a schematic view of a first partition wall and a first porous plate included in a heat exchanger according to a second preferred embodiment of the present invention.
14 is a schematic diagram of a second partition wall and a second porous plate included in a heat exchanger according to a second embodiment of the present invention.
15 is a schematic diagram of a third or fourth partition wall included in a heat exchanger according to a second embodiment of the present invention.
16 is a schematic diagram of a third partition wall and a third porous plate included in a heat exchanger according to a second embodiment of the present invention.
17 is a schematic view of a fourth partition wall and a fourth porous plate included in a heat exchanger according to a second preferred embodiment of the present invention.
Figure 18 (a) is a schematic diagram showing the refrigerant flow of the conventional heat exchanger, (b) is a schematic diagram showing the refrigerant flow of the heat exchanger according to the first preferred embodiment of the present invention, (c) is A schematic diagram showing a refrigerant flow of a heat exchanger according to a second preferred embodiment of the invention.
(A) is a schematic diagram showing the position of the temperature sensor installed to measure the internal temperature of the heat exchanger, (b) is the temperature inside the heat exchanger respectively measured by the temperature sensor at the position shown in (a) It is a graph showing the distribution.
20 is a schematic view showing a part of a heat exchanger according to a third preferred embodiment of the present invention.
FIG. 21 is an enlarged schematic view of a portion A of FIG. 20.
22 is a schematic view showing a part of a heat exchanger according to a fourth preferred embodiment of the present invention.
FIG. 23 is an enlarged schematic view of a portion B of FIG. 22.
(A) is a schematic diagram of the whole shape of a heat exchanger, (b) is a schematic diagram of a diffusion block, (c) is a schematic diagram of a channel plate.
FIG. 25A is a schematic view of the low temperature fluid channel plate shown in FIG. 24C as viewed from the C direction, and FIG. 25B is a schematic view of the channel of the low temperature fluid channel plate of the conventional heat exchanger. , (c) is a schematic diagram of the channel of the low-temperature fluid channel plate of the heat exchanger according to the fifth preferred embodiment of the present invention, and (d) is a low-temperature fluid channel of the heat exchanger according to the sixth preferred embodiment of the present invention. Schematic diagram of the channels of the plate.

Hereinafter, the configuration and operation of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The present invention can be applied to various applications, such as a ship equipped with an engine using natural gas as a fuel and a ship including a liquefied gas storage tank. In addition, the following examples may be modified in many different forms, and the scope of the present invention is not limited to the following examples.

The systems for treating boil-off gas of the present invention described below are all types of vessels and offshore structures, such as LNG carriers and liquefied ethane gas carriers, which are equipped with storage tanks capable of storing low temperature liquid cargo or liquefied gas. Carriers, LNG RVs, as well as offshore structures such as LNG FPSO, LNG FSRU, and the like. However, in the embodiments to be described later, for the sake of convenience of explanation, liquefied natural gas, which is a representative low temperature liquid cargo, will be described as an example, and the term “LNG ship” is a concept encompassing LNG carriers, LNG RVs, LNG FPSOs, and LNG FSRUs.

In addition, the fluid in each line of the present invention may be in any one of a liquid state, a gas-liquid mixed state, a gas state, and a supercritical fluid state, depending on the operating conditions of the system.

1 illustrates a basic model for explaining the concept of boil-off gas reliquefaction according to an embodiment of the present invention.

Referring to Figure 1, in the present invention, the evaporated gas (①) discharged from the storage tank is sent to the heat exchanger to be used as a refrigerant and then compressed by a compressor, the compressed boiled gas by the compressor is used as the fuel of the engine (② ), The surplus evaporated gas (③) remaining after satisfying the requirements of the engine is sent to the heat exchanger, and the evaporated gas (①) discharged from the storage tank is cooled by heat exchange with a refrigerant.

After being compressed by the compressor, the re-liquefaction target evaporated gas cooled by the heat exchanger is separated into a liquid component and a gas component by a gas-liquid separator after passing through a decompression means (for example, an expansion valve or an expander). The liquid component separated by the gas-liquid separator is returned to the storage tank, and the gas component separated by the gas-liquid separator is combined with the boil-off gas (①) discharged from the storage tank and supplied to the heat exchanger again as a refrigerant.

The present invention is characterized by re-liquefying the boil-off gas by using the boil-off gas itself discharged from the storage tank as a refrigerant, rather than using a separate additional cycle to re-liquefy the boil-off gas. In some cases, of course, a separate refrigeration cycle may be provided to ensure re-liquefaction of all boil-off gases. The provision of a separate cycle requires the need for additional equipment or additional power, but it can guarantee reliquefaction of almost all boil-off gases.

In the system for reliquefaction of the boil-off gas by using the boil-off gas itself as the refrigerant, the re-liquefaction performance is largely dependent on the pressure of the boil-off gas (hereinafter referred to as 're-liquefaction target boil-off gas'). The difference is that the experiment to know the reliquefaction performance according to the pressure of the boil-off gas to be reliquefaction (hereinafter referred to as 'Experiment 1') results are as follows.

< Experiment 1  >

First, the conditions of the reliquefaction performance evaluation experiment according to the pressure of the re-liquefaction target boil-off gas is as follows.

1. Target vessel: LNG carrier containing high pressure gas injection engine as a propulsion engine and low pressure engine as a power generation engine

2. Process calculation program: Aspen HYSYS V8.0 (shown in Figure 2)

3. Property calculation formula: Peng-Robinson equation

4. Amount of boil-off gas: Since boil-off gas of approximately 3500 kg / h to 4000 kg / h is generated for 170,000 CBM (cubic meter) LNG carrier, 3800 kg / h is applied in this experiment.

5. Composition of boil-off gas: The composition of 10% of nitrogen (N ₂ ) and 90% of methane (CH ₄ ) is applied to the boil-off gas discharged from the storage tank and the boil-off gas compressed by the compressor.

6. Temperature and pressure of boil-off gas discharged from storage tank: 1.06 bara pressure and -120 degC temperature.

7. Fuel consumption in the engine: In actual ship operation, the engine is operated at a low load in consideration of economic efficiency. In this experiment, the total amount of evaporated gas used in the propulsion engine and the power generation engine is evaporated from the storage tank. Assume 2,660 kg / h, which is 70% of gas (3800 kg / h).

8. Compressor capacity: Normally, compressor capacity does not exceed 150% of the evaporated gas generated from the storage tank. In this calculation, 120% of the evaporated gas generated from the storage tank based on the compressor suction flow rate (3800 kg / h × 120% = 4650 kg / h).

9. Heat exchanger performance: Logarithmic Mean Temperature Difference (LMTD) 13 degC or more, Minimum Approach 3 degC or more.

When designing a heat exchanger, the temperature and heat flow rate of the low temperature fluid and the high temperature fluid flowing into the heat exchanger are fixed, respectively, so that the temperature of the fluid used as the refrigerant is not higher than the temperature of the fluid to be cooled (that is, the temperature according to the heat flow amount is shown. In the graph, the logarithmic mean temperature difference (LMTD) is minimized as much as possible, so that the graph of the low temperature fluid and the graph of the high temperature fluid do not cross each other.

Logical mean temperature difference (LMTD) is a heat exchange method in which the hot fluid and the low temperature fluid are injected in opposite directions and discharged from the opposite side, and the temperature before the low temperature fluid passes through the heat exchanger is tc1 and the low temperature fluid passes through the heat exchanger. When the temperature after tc2 and the high temperature fluid pass through the heat exchanger is th1, and the temperature after the high temperature fluid passes through the heat exchanger is th2, and d1 = th2-tc1 and d2 = th1-tc2, (d2- d1) / ln (d2 / d1), the smaller the logarithmic mean temperature difference, the higher the efficiency of the heat exchanger.

In the graph showing the temperature according to the heat flow amount, the logarithmic mean temperature difference (LMTD) is expressed as the interval between the low temperature fluid used as the refrigerant and the high temperature fluid cooled by heat exchange with the refrigerant. It means that the temperature difference LMTD is small, and that the logarithmic mean temperature difference LMTD is small means that the efficiency of the heat exchanger is high.

The thermodynamic calculations under the experimental conditions of 1 to 9 were performed to quantitatively show the effect of the high pressure compression of the reliquefaction target boil-off gas on the reliquefaction performance. In order to verify the reliquefaction performance according to the pressure of the boil-off gas and the cooling curve characteristics of the heat exchanger, the pressure of the boil-off gas to be reliquefied was re-liquefied at each pressure of 39 bara, 50 bara to 200 bara in increments of 10 bara, 250 bara and 300 bara. The amount of liquefaction and the cooling curve of the heat exchanger were calculated thermodynamically.

FIG. 3 is a view illustrating an example of a high temperature fluid and a low temperature fluid when the pressure of the boil-off gas to be reliquefied is 39 bara and 50 bara to 120 bara increased by 10 bara in the evaporation gas reliquefaction system according to an embodiment of the present invention. 4 is a graph showing a change in temperature according to the heat flow rate, and FIG. 4 is a case in which the pressure of the boil-off gas for reliquefaction is 130 bara to 200 bara increased by 10 bara and 300 bara in the boil-off gas reliquefaction system according to an embodiment of the present invention. Is a graph showing the temperature change according to the heat flow amount of each of the hot fluid and the cold fluid.

5 is a schematic diagram of an evaporation gas reliquefaction system according to an embodiment of the present invention when the re-liquefaction target evaporation gas pressure is 39 bara, and FIG. 6 is a case where the reliquefaction target evaporation gas pressure is 150 bara. FIG. 7 is a schematic diagram of a boil-off gas reliquefaction system according to an embodiment of the present invention, and FIG. 7 is a schematic diagram of a boil-off gas reliquefaction system according to an embodiment of the present invention when the pressure of re-liquefaction target boil-off gas is 300 bara.

Table 1 below shows the calculated value of the reliquefaction performance according to the pressure of the re-liquefaction target boil-off gas in the boil-off gas reliquefaction system according to an embodiment of the present invention.

Pressure of boil-off gas subject to reliquefaction
(bara) Cooling temperature before expansion
(degC) Reliquefaction amount
(kg / h) Reliquefaction Relative Rate
(%) 39 -97.7 563.8 100.0 50 -96.1 712.8 126.4 60 -99.6 821.6 145.7 70 -103.8 909.3 161.3 80 -107.8 979.9 173.8 90 -111.5 1036.4 183.9 100 -114.6 1080.5 191.7 110 -117.0 1113.8 197.6 120 -119.0 1137.9 201.9 130 -120.4 1154.7 204.8 140 -121.4 1165.9 206.8 150 -122.1 1173.8 208.1 160 -122.4 1174.6 208.4 170 -122.4 1172.7 208.0 180 -122.4 1170.7 207.7 190 -122.4 1168.6 207.3 200 -122.4 1166.3 206.9 250 -122.5 1153.4 204.6 300 -122.6 1138.2 201.9

8 and 9 are graphs showing the "reliquefaction amount" of Table 1 in the pressure range of 39 bara to 300 bara.

Referring to FIGS. 3 to 9 and Table 1, the result shows that the latent heat section shown when the compression pressure of the boil-off evaporation gas is 39 bara in the 50 bara to 100 bara section even though the compression pressure of the boil-off gas is a supercritical state section. It can be seen that the horizontal section, which is similar to, gradually decreases, but still exists, and the maximum liquefaction (compression temperature -122.4 ° C, reliquefaction 1174.6kg / h, relative liquefaction rate 208.4%) at a compression pressure of 160 bara It was confirmed to appear.

The largest difference between the low evaporation gas and the high evaporation gas is the cooling temperature before expansion. As can be seen in Figure 9 due to the difference in the cooling curve according to the pressure in the case of low pressure occurs a limit at the cooling temperature before expansion can not lower the cooling temperature much, while in the case of high pressure the temperature of the evaporated gas discharged from the storage tank Cooling down to near.

The difference is that latent heat section exists below the critical pressure (about 47 bara for pure methane) due to the property of methane (CH ₄ ), the main component of the boil-off gas, and similar to the latent heat section above the critical pressure. But you can see that it is reduced. Therefore, from the viewpoint of the amount of reliquefaction, it is preferable to carry out at 47 bar or more which is a critical pressure when re-liquefying the boil-off gas.

Meanwhile, the ME-GI engine has a supply pressure of fuel gas in a range of 150 bara to 400 bara (mainly operated at 300 bara). As shown in FIG. 8 and Table 1, the pressure of the boil-off gas for reliquefaction is 150 to 170 bara. Reliquefaction amount shows the maximum value in the vicinity, and there is little change in the amount of liquefaction between 150 and 300 bara.In case of reliquefaction of the boil-off gas while supplying fuel to the ME-GI engine, control related to reliquefaction or fuel supply There is an easy advantage.

The 'reliquefaction amount' of Table 1 is the reliquefaction liquefaction separated by the gas-liquid separator 40 after passing through the compressor 10, the heat exchanger 20, and the pressure reduction device 30 in Figs. The flow rate of natural gas is shown, and the "relative amount of reliquefaction amount" shows the relative ratio of the amount of reliquefaction at each pressure as a percentage with respect to the amount of reliquefaction when the reliquefaction target evaporation gas is 39 bara.

On the other hand, 'reliquefaction rate' may represent the reliquefaction performance. The reliquefaction rate represents the value obtained by dividing the flow rate of the reliquefied liquefied natural gas by the flow rate of the entire boil-off gas to be reliquefied. That is, the 'reliquefaction amount' represents the absolute amount of the liquefied natural gas re-liquefied, the 'reliquefaction rate' represents the ratio of the liquefied liquefied natural gas out of the total re-liquefied liquefied natural gas.

For example, when the speed of the vessel is low and the amount of the boil-off gas in the propulsion engine decreases, the amount of the boil-off gas to be reliquefied increases, and the 'reliquefaction amount' may also increase. However, under the conditions of Experiment 1, the 'reliquefaction rate' may decrease because the sum of the evaporated gas discharged from the storage tank, the fluid used as the refrigerant, and the gaseous components separated by the gas-liquid separator are almost constant due to the capacity limitation of the compressor. Can be.

In Experiment 1, the flow rate of the refrigerant flowing into the compressor was 4560 kg / h, which is 120% of the 3800 kg / h of evaporated gas generated in the storage tank, and the amount of engine used was 2660 kg / h (ME-GI engine 2042 kg / 1900 kg / h, excluding h + DFDG 618 kg / h), is the boil off gas for reliquefaction.

In the experiment of raising the pressure of the reliquefaction target boil-off gas to 400 bara, there was no significant difference from the case of 300 bara, and the difference of the reliquefaction flow rate at 150 bara and 400 bara was within 4%.

Meanwhile, in each of the graphs of FIGS. 3 and 4, the high temperature fluid indicated by red (above) means the evaporation gas to be reliquefied, and the low temperature fluid indicated by blue (below) indicates the evaporated gas discharged from the storage tank, that is, the refrigerant do.

In the graphs of FIGS. 3 and 4, the straight line section having no temperature change even in the change of the heat flow rate is a latent heat section, and in the supercritical fluid state, the latent heat section does not appear, and thus the amount of reliquefaction depends on whether or not it is a supercritical fluid. The difference appears. That is, when the evaporation target gas to be reliquefaction is a supercritical fluid, the latent heat section does not appear during heat exchange, so the reliquefaction flow rate and reliquefaction rate are high.

Summarizing the above results, the reliquefaction performance is high when the evaporation gas to be reliquefied is in a supercritical state, particularly in the range of 100 bara to 400 bara, preferably in the range of 150 bara to 400 bara, more preferably It can be seen that the reliquefaction performance is high at 150 bara to 300 bara.

Considering that the required pressure of the ME-GI engine is 150 bara to 400 bara, high reliquefaction performance is achieved by using the compressed evaporation gas as the evaporation target gas to be reliquefied to meet the required pressure of the ME-GI engine. Therefore, it can be seen that there is a very advantageous advantage of linking the system for supplying fuel to the ME-GI engine and the boil-off gas reliquefaction system using the boil-off gas itself as a refrigerant.

On the other hand, the 'Experiment 1' described above is to evaluate the reliquefaction performance according to the boil-off gas pressure of the reliquefaction by a simulation program, in order to see if these results show the same results in the actual reliquefaction apparatus using a heat exchanger Experiment using PCHE (Printed Circuit Heat Exchanger) (hereinafter referred to as 'Experiment 2').

< Experiment 2  >

In actual operating conditions, the amount of boil-off gas is constant, but the amount of boil-off gas used in the engine changes, so the flow rate of the boil-off gas for reliquefaction that is used in the engine changes. Therefore, in Experiment 2, the reliquefaction performance of the actual reliquefaction apparatus was evaluated while changing the flow rate of the reliquefaction target boil-off gas. For the convenience of experiments, instead of explosive methane, commonly used nitrogen was used, and the temperature of nitrogen used as a refrigerant was controlled to be the same as that of the evaporated gas discharged from the storage tank. Was adjusted in the same manner as in the 1 to 9 conditions.

In addition, the fuel consumption of the ME-GI engine used varies depending on the operating conditions. Under the conditions of 'Experiment 1', the LNG carrier's ME-GI engine was assumed to be 25 MW (two 12.5 MW units) and operated at full speed, at about 19.5 knot (engine fuel consumption of about 3800 kg / h). It can be operated, and at economical speeds it will operate at about 17 knots (about 2660 kg / h of engine fuel consumption). Therefore, considering the actual operating conditions, the maximum operating speed of 19.5 knots, the economical operating speed of 17 knots and the anchored state (0 fuel consumption of the ME-GI engine, 618 kg / h fuel consumption of the DFDG) will be the most operating conditions. . In Experiment 2, the reliquefaction performance was tested under these conditions.

When nitrogen was used as the refrigerant and the evaporation gas to be reliquefied, the reliquefaction performance was confirmed to be almost the same as the calculated value in 'Experiment 1' regardless of the flow rate of the reliquefaction gas to be reliquefied. That is, since the consumption of boil-off gas in the propulsion engine varies according to the operating speed of the LNG carrier, the flow rate of the boil-off gas to be reliquefied is also changed. Reliquefaction performance remained stable regardless of flow rate.

However, in an actual boil-off gas reliquefaction system, when methane (ie, boil-off gas generated in an actual storage tank) is used instead of nitrogen as a refrigerant and a boil-off gas for re-liquefaction, when the LNG carrier is at anchor or near the maximum operating speed. (At maximum operating speed, most of the boil-off gas from LNG storage tanks can be used as fuel.) The reliquefaction performance is almost the same as the calculated value of 'Experiment 1', but at the highest operating speed. When operating a vessel at 70% of fuel consumption or when operating a vessel at a speed lower than that, the reliquefaction performance is less than 70% of the theoretical expected value, and depending on the operating speed range, Lower cases were also identified. That is, when methane (ie, an evaporated gas generated in an actual storage tank) is used instead of nitrogen as a refrigerant and an evaporated gas to be reliquefied, the reliquefaction performance does not reach the theoretical calculated value depending on the flow rate of the evaporated gas to be reliquefied. There was a missing section.

Specifically, an example in which the reliquefaction performance of the actual boil-off gas reliquefaction system does not meet the theoretical calculation value is as follows.

1. An LNG Carrier using a 25 MW ME-GI engine operates at speeds of 10 to 17 knots.

2. Assuming that the flow rate of the boil-off gas from the storage tank is 3800 kg / h, the flow rate of the boil-off gas used as fuel in the engine (the ME-GI engine as the propulsion engine + the DFDG as the power generation engine) is 1100 to For 2660 kg / h

3. Assuming that the flow rate of boil-off gas from the storage tank is 3800 kg / h, if the flow rate of boil-off gas to be reliquefaction is 1900 to 3300 kg / h

4. The ratio of the flow rate of the boil-off gas to be reliquefied to the flow rate of the boil-off gas (which may be separated by the gas-liquid separator) used as the refrigerant is in the range of 0.42 to 0.72.

According to the operating conditions of the ship or the flow rate of the boil-off gas to be reliquefied, the amount of reliquefaction actually measured is very different from the theoretical calculated value. If the reliquefaction performance is low and there are a lot of evaporative gases that cannot be reliquefied, there is a problem that additional measures are required, such as discharging or burning the evaporated gas to waste energy or reliquefying by a separate reliquefaction cycle. have. Thus, unlike the nitrogen, the reliquefaction performance of the boil-off gas is significantly different from the theoretical expected value, seems to be due to the difference in the properties of nitrogen and boil-off gas.

From the above results, it can be seen that it is necessary to stably maintain the reliquefaction performance even if the operating conditions of the LNG carrier change, that is, the flow rate of the boil-off gas for reliquefaction changes.

Thus, according to one aspect of the invention, the step of compressing the boil-off gas discharged from the storage tank to a high pressure, branching all or part of the high-pressure compressed boil-off gas to heat exchange with the boil-off gas discharged from the storage tank and heat exchanged high pressure compression A method of reliquefaction of an LNG carrier having a high pressure gas injection engine, comprising the step of reducing the boil-off gas, wherein the reliquefaction performance is stably maintained even if the operating conditions of the LNG carrier are changed or the flow rate of the re-liquefaction target evaporation gas is changed. It provides a method for re-liquefying the boil-off gas of the LNG carrier having a high-pressure gas injection engine, characterized in that it comprises a step of maintaining.

On the other hand, if the engine mounted on the LNG carrier is not a high-pressure gas injection engine but an engine that uses relatively low-pressure evaporative gas as fuel, such as an X-DF engine, The present invention is advantageous in the case of repressurizing after further pressurizing the excess evaporated gas undergoing the liquefaction process.

In the reliquefaction method, the LNG vessel operates at a speed of 10 to 17 knots, the flow rate of the boil-off gas used as fuel in the engine (propulsion engine + power generation engine) is 1100 to 2660 kg / h, The flow rate of the boil-off gas to be liquefied is 1900 to 3300 kg / h, or the flow rate of the boil-off gas to be reliquefied compared to the flow rate of the boil-off gas (which may include a gas component separated by a gas-liquid separator) used as a refrigerant. The ratio is in the range of 0.42 to 0.72.

The step of stably maintaining the reliquefaction performance is characterized in that the reliquefaction performance is stably maintained even when the heat capacity ratio of the heat exchanger becomes 0.7 to 1.2.

The heat capacity ratio is CR, the flow rate of the high temperature fluid (in this invention evaporation gas to be reliquefaction) m1, the specific heat of the high temperature fluid c1, the flow rate of the low temperature fluid (evaporation gas used as refrigerant in the present invention) m2, When the specific heat is called c2, the following equation is satisfied.

CR = (m1 × c1) / (m2 × c2)

In 'Experiment 2', the amount of boil-off gas (which may also include gaseous components generated from the gas-liquid separator) used as the refrigerant is kept constant and when the amount of boil-off gas to be reliquefied changes, that is, m 2 in the above formula is constant. It was found that the reliquefaction performance did not reach the calculated value when m1 was changed and m1 was changed, but not only that, but also the amount of evaporated gas (which may include gaseous components generated from the gas-liquid separator) used as a refrigerant changed. That is, it was confirmed that the reliquefaction performance does not reach the calculated value even when m2 is changed in the above equation.

Therefore, the step of stably maintaining the reliquefaction performance of the present invention, at least one of the amount of the boil-off gas (which may also include a gas component generated from the gas-liquid separator) used as the refrigerant, and the amount of the boil-off gas to be reliquefed In the case of fluctuation, the reliquefaction performance is maintained stably even when the heat capacity ratio of the heat exchanger becomes 0.7 to 1.2.

In addition, the step of stably maintaining the reliquefaction performance is characterized in that the reliquefaction amount is maintained at 50% or more of the calculated value under the calculation conditions of 'Experiment 1'. Preferably it is maintained to be 60%, more preferably 70% or more of the calculated value. When the amount of reliquefaction is less than 50% of the calculated value, there is a problem that the gaseous combustion apparatus (GCU) has to burn off the remaining boil-off gas depending on the operating conditions when the LNG carrier operates.

Therefore, it can be seen from the above result that a step of stably maintaining the reliquefaction performance is required even if the operating conditions of the LNG carrier change, that is, the flow rate of the reliquefaction target boil-off gas is changed.

In addition, one of the reasons that the reliquefaction performance is significantly different from the theoretical expected value was found to be caused by a heat exchanger of a combination of two or more blocks.

The heat exchanger applied to the boil-off gas reliquefaction system of LNG carriers is a PCHE which has an advantage when the boil-off gas to be reliquefied is high pressure, manufactured by KOBELCO, ALfa Laval, Heatric, etc. (Diffusion Block) is limited, so it is necessary to use two or more diffusion blocks in combination.

10 is a schematic diagram of a conventional PCHE.

Referring to FIG. 10, the conventional PCHE includes a hot gas inlet pipe 110, a hot gas inlet header 120, a core core 190, and a hot fluid discharge header. Gas Outlet Header (130), Hot Gas Outlet Pipe (140), Low Temperature Fluid Inlet Pipe (Cold Gas Inlet Pipe, 150), Low Temperature Fluid Inlet Header (Cold Gas Inlet Header, 160), Low Temperature Fluid Outlet Header (Cold Gas Outlet Header, 170), and cold gas outlet pipe (Cold Gas Outlet Pipe, 180).

The high temperature fluid supplied to the heat exchanger is introduced into the heat exchanger through the high temperature fluid inlet pipe 110 and then dispersed by the high temperature fluid inlet header 120 and sent to the core 190. The high temperature fluid sent to the core 190 is cooled by heat exchange with the low temperature fluid in the core 190, and then collected in the high temperature fluid discharge header 130 and discharged to the outside of the heat exchanger through the high temperature fluid discharge pipe 140.

The low temperature fluid supplied to the heat exchanger is introduced into the heat exchanger through the low temperature fluid inlet pipe 150 and then dispersed by the low temperature fluid inlet header 160 and sent to the core 190. The low temperature fluid sent to the core 190 is used as a refrigerant for heat exchange to cool the high temperature fluid in the core 190, and then gathered from the low temperature fluid discharge header 170 to the outside of the heat exchanger through the low temperature fluid discharge pipe 180. Discharged.

The low temperature fluid used as the refrigerant in the heat exchanger of the present invention is the evaporated gas (which may include gaseous components separated by the gas-liquid separator) discharged from the storage tank, and the high temperature fluid cooled in the heat exchanger is compressed Evaporative gas for reliquefaction.

Meanwhile, the core 190 may include a plurality of diffusion blocks (FIG. 10 illustrates a case of including three diffusion blocks. Hereinafter, the core of the heat exchanger may include three diffusion blocks. If the core of the heat exchanger includes two or more diffusion blocks, a space exists between the diffusion blocks, and air filled in the spaces between the diffusion blocks is formed in the insulating layer. As a result, the thermal conductivity between the diffusion blocks is reduced.

In addition, in the case of using the evaporation gas as the refrigerant, when the refrigerant is first introduced into any one of the diffusion block, the phenomenon that the refrigerant supplied thereafter is concentrated to the diffusion block into which the refrigerant is introduced first, and the diffusion block into which the refrigerant is introduced first. The temperature of is lower than that of other blocks.

When the phenomenon that the refrigerant is concentrated in the block into which the refrigerant is introduced first and the phenomenon of the thermal conductivity between the blocks are engaged with each other, the temperature difference between the blocks increases, resulting in lower reliquefaction performance.

11 is a schematic diagram of a heat exchanger according to a first preferred embodiment of the present invention.

Referring to FIG. 11, in addition to the configuration included in the conventional PCHE illustrated in FIG. 10, the heat exchanger of the present embodiment may include a first porous plate 210 installed between the high temperature fluid inflow header 120 and the core 190. ), A second porous plate 220 installed between the high temperature fluid discharge header 130 and the core 190, a third porous plate 230 installed between the low temperature fluid inflow header 160 and the core 190, And a fourth porous plate 240 installed between the low temperature fluid discharge header 170 and the core 190.

The heat exchanger of the present embodiment is characterized by including means for dispersing the fluid supplied to or discharged from the heat exchanger, and means for resisting the flow of the fluid to disperse the fluid. The porous plates 210, 220, 230, and 240 of the present embodiment are examples of means for dispersing the fluid or means for resisting the flow of the fluid, and the heat exchanger of the present embodiment is not limited to include the porous plate.

The porous plates 210, 220, 230, and 240 of the present embodiment are thin plate members having a plurality of holes, and the first porous plate 210 has the same size and shape as the cross section of the high temperature fluid inflow header 120. Preferably, the second porous plate 220 has the same size and shape as that of the cross section of the high temperature fluid discharge header 130, and the third porous plate 230 has a cross section of the low temperature fluid inlet header 160. It is preferable to have the same size and shape, and the fourth porous plate 240 preferably has the same size and shape as the cross section of the low temperature fluid discharge header 170.

The plurality of holes formed in the porous plates 210, 220, 230, and 240 of the present embodiment may all have the same cross-sectional area, and have a small cross-sectional area near the pipes 110, 140, 150, and 180 through which fluid is introduced or discharged. As the distance from the pipes 110, 140, 150, 180 increases, a hole having a larger cross-sectional area may be formed.

In addition, the plurality of holes formed in the porous plates 210, 220, 230, and 240 of the present embodiment may have a uniform forming density, and are formed near the pipes 110, 140, 150, and 180 through which fluid is introduced or discharged. The density is low, and the further away from the pipes 110, 140, 150, and 180, the higher the forming density. Low formation density means that fewer holes are formed in the same area, and high formation density means that more holes are formed in the same area.

In addition, the porous plates 210, 220, 230, and 240 of the present exemplary embodiment may allow the fluid passing through the first porous plate 210 and the third porous plate 230 to be effectively dispersed and introduced into the core 190. Alternatively, the fluid discharged from the core 190 may be effectively spaced apart from the core 190 so that the fluid may be effectively dispersed to pass through the second porous plate 220 and the fourth porous plate 240. The distance between the porous plates 210, 220, 230, 240 and the core 190 may be, for example, about 20 to 50 mm.

According to the heat exchanger of the present embodiment, since the fluid is dispersed by one or more of the first to fourth porous plates 210, 220, 230, and 240, the phenomenon in which the refrigerant is concentrated in one of the diffusion blocks can be alleviated.

The heat exchanger according to the second preferred embodiment of the present invention is, in addition to the configuration included in the heat exchanger of the first embodiment shown in FIG. 11, the first partition wall installed between the first porous plate 210 and the core 190. 310, a second partition wall 320 installed between the core 190 and the second porous plate 220, a third partition wall 330 installed between the third porous plate 230 and the core 190, And a fourth partition 340 disposed between the core 190 and the fourth porous plate 240.

FIG. 12 is a schematic view of a first partition wall or a second partition wall included in a heat exchanger according to a second preferred embodiment of the present invention, and FIG. 13 is a first partition wall and a second partition included in a heat exchanger according to a second preferred embodiment of the present invention. 1 is a schematic diagram of a porous plate, and FIG. 14 is a schematic diagram of a second partition wall and a second porous plate included in a heat exchanger according to a second preferred embodiment of the present invention.

The first to fourth partitions 310, 320, 330, and 340 of the present embodiment prevent the fluid dispersed by the first to fourth porous plates 210, 220, 230, and 240 from being collected again.

12 and 13, the first partition wall 310 of the present exemplary embodiment may have a shape of enclosing an edge of the first porous plate 210 at a predetermined height and dividing the surrounding inner space into a plurality of regions. 12 and 13 (a) shows a shape divided into four inner spaces surrounding the edge of the first porous plate 210 at a predetermined height, and (b) shows a shape divided into eight.

12 and 13 (b) is a first partition 310, the inner space surrounding the edge of the first porous plate 210 to a certain height, as shown in (a) in a one-way grid Not only by dividing, but also by other grids. That is, in the first partition 310 illustrated in FIGS. 12 and 13A, if the member for dividing the internal space surrounding the edge of the first porous plate 210 at a predetermined height is referred to as the vertical member 1, The first partition wall 310 illustrated in (b) includes not only a plurality of vertical members 1 but also a plurality of horizontal members 2 dividing a space between the vertical members 1, and thus, a direction different from a one-way grid. The grids intersect and divide the interior space.

As shown in FIG. 12 and FIG. 13B, when the internal space of the first porous plate 210 is divided once more in another direction, the fluid may be more dispersed, particularly among the plurality of diffusion blocks. In addition, it is possible to prevent the refrigerant from being collected again in one diffusion block.

In addition, when the internal space of the first porous plate 210 is further divided in another direction, there is an advantage that the first porous plate 210 and the core 190 can maintain the separation better. In particular, the first porous plate 210 may be prevented from contacting the core 190 due to the pressure of the fluid passing through the first porous plate 210. When the first porous plate 210 is in contact with the core 190, the fluid may not be properly supplied to the contacted portion, and the heat exchange efficiency may be lowered.

11 and 13, the high temperature fluid introduced through the high temperature fluid inflow pipe 110 may sequentially include the high temperature fluid inflow header 120, the first porous plate 210, and the first partition wall 310. Gina is introduced into the core 190.

12 and 14, the second partition wall 320 according to the present exemplary embodiment may surround the edge of the second porous plate 220 at a predetermined height and divide the surrounding inner space into a plurality of regions. 12 and 14 (a) shows a shape divided into four inner spaces surrounding the edge of the second porous plate 220 at a predetermined height, and (b) shows a shape divided into eight.

The second partition wall 320 illustrated in FIGS. 12 and 14 (b) has an inner space surrounding the edge of the second porous plate 220 at a predetermined height, as shown in (a). Not only by dividing, but also by other grids. That is, in the second partition 320 illustrated in FIGS. 12 and 14 (a), if the member for dividing the internal space surrounding the edge of the second porous plate 220 at a predetermined height is referred to as the vertical member 1, The second partition wall 320 illustrated in (b) includes not only a plurality of vertical members 1, but also a plurality of horizontal members 2 that divide a space between the vertical members 1, and thus a direction different from a one-way grid. The grids intersect and divide the interior space.

As shown in FIG. 12 and FIG. 14B, when the inner space of the second porous plate 220 is divided once more in another direction, the fluid may be more dispersed, particularly between the plurality of diffusion blocks. In addition, it is possible to prevent the refrigerant from being collected again in one diffusion block.

In addition, when the inner space of the second porous plate 220 is further divided in another direction, there is an advantage that the second porous plate 220 and the core 190 may be better maintained at a separation. In particular, the second porous plate 220 may be prevented from contacting the core 190 due to the pressure of the fluid passing through the second porous plate 220. When the second porous plate 220 and the core 190 contact, the fluid may not be properly discharged to the contacted portion, and the heat exchange efficiency may be lowered.

11 and 14, the hot fluid discharged from the core 190 sequentially passes through the second partition wall 320, the second porous plate 220, and the hot fluid discharge header 130 to discharge the hot fluid. It is discharged through the pipe 140.

15 is a schematic diagram of a third partition or a fourth partition included in a heat exchanger according to a second preferred embodiment of the present invention, and FIG. 16 is a third partition and a third partition included in a heat exchanger according to a second preferred embodiment of the present invention. 3 is a schematic diagram of a porous plate, and FIG. 17 is a schematic diagram of a fourth partition wall and a fourth porous plate included in a heat exchanger according to a second preferred embodiment of the present invention.

15 and 16, the third partition wall 330 of the present exemplary embodiment may have a shape that surrounds the edge of the third porous plate 230 at a predetermined height and divides the surrounding inner space into a plurality of regions. 15 and 16 (a) shows a shape divided into four inner spaces surrounding the edge of the third porous plate 230 at a predetermined height, and (b) shows a shape divided into eight.

The third partition 330 illustrated in FIGS. 15 and 16 (b) has an inner space surrounding the edge of the third porous plate 230 at a predetermined height, as shown in (a). Not only by dividing, but also by other grids. That is, in the third partition 330 illustrated in FIGS. 15 and 16A, if the member for dividing the internal space surrounding the edge of the third porous plate 230 at a predetermined height is referred to as the vertical member 1, The third partition wall 330 illustrated in (b) includes not only a plurality of vertical members 1 but also a plurality of horizontal members 2 that divide a space between the vertical members 1, and thus, a direction different from a one-way grid. The grids intersect and divide the interior space.

As shown in FIG. 15 and FIG. 16B, when the internal space of the third porous plate 230 is divided once more in another direction, the fluid may be more dispersed, particularly among the plurality of diffusion blocks. In addition, it is possible to prevent the refrigerant from being collected again in one diffusion block.

In addition, when the internal space of the third porous plate 230 is further divided in another direction, the third porous plate 230 and the core 190 may have better separation. In particular, it may be possible to prevent the third porous plate 230 from contacting the core 190 due to the pressure of the fluid passing through the third porous plate 230. When the third porous plate 230 is in contact with the core 190, the fluid may not be properly supplied to the contacted portion, and the heat exchange efficiency may be lowered.

Referring to FIGS. 11 and 16, the low temperature fluid introduced through the low temperature fluid inlet pipe 150 may sequentially include the low temperature fluid inlet header 160, the third porous plate 230, and the third partition wall 330. Gina is introduced into the core 190.

15 and 17, the fourth partition 340 of the present exemplary embodiment may surround the edge of the fourth porous plate 240 at a predetermined height and divide the surrounding inner space into a plurality of regions. 15 and 17 (a) shows a shape divided into four internal spaces surrounding the edge of the fourth porous plate 240 at a predetermined height, and (b) shows a shape divided into eight.

The fourth partition 340 illustrated in FIGS. 15 and 17 (b) has an inner space surrounding the edge of the fourth porous plate 240 at a predetermined height, as shown in (a). Not only by dividing, but also by other grids. That is, in the fourth partition 340 illustrated in FIGS. 15 and 17A, if the member dividing the internal space surrounding the edge of the fourth porous plate 240 at a predetermined height is referred to as the vertical member 1, The fourth partition wall 340 illustrated in (b) includes not only a plurality of vertical members 1 but also a plurality of horizontal members 2 that divide a space between the vertical members 1, and thus, a direction different from the one-direction grid. The grids intersect and divide the interior space.

As shown in FIG. 15 and FIG. 17B, when the inner space of the fourth porous plate 240 is divided once more in another direction, the fluid may be more dispersed, particularly among the plurality of diffusion blocks. In addition, it is possible to prevent the refrigerant from being collected again in one diffusion block.

In addition, when the inner space of the fourth porous plate 240 is further divided in another direction, there is an advantage that the fourth porous plate 240 and the core 190 can be better maintained at a separation. In particular, the case in which the fourth porous plate 240 is bent to contact the core 190 may be prevented due to the pressure of the fluid passing through the fourth porous plate 240. When the fourth porous plate 240 and the core 190 contact, the fluid may not be properly discharged to the contacted portion, and the heat exchange efficiency may be lowered.

11 and 17, the low temperature fluid discharged from the core 190 sequentially passes the fourth partition 340, the fourth porous plate 240, and the low temperature fluid discharge header 170 to discharge the low temperature fluid. It is discharged through the pipe 180.

Figure 18 (a) is a schematic diagram showing the refrigerant flow of the conventional heat exchanger, (b) is a schematic diagram showing the refrigerant flow of the heat exchanger according to the first preferred embodiment of the present invention, (c) is A schematic diagram showing a refrigerant flow of a heat exchanger according to a second preferred embodiment of the invention.

Referring to FIG. 18A, in the case of the conventional heat exchanger, it can be seen that the low temperature fluid introduced into the low temperature fluid inlet pipe 150 is concentrated and supplied to the diffusion block in the vicinity of the low temperature fluid inlet pipe 150. Can be. In the case of the conventional heat exchanger having three diffusion blocks, about 70% of the refrigerant is supplied to the diffusion block in the middle near the low temperature fluid inlet pipe 150, and about 15% of the refrigerant is supplied to the other diffusion blocks, respectively. It was found that the refrigerant flow rate difference between the blocks is more than four times.

Referring to FIG. 18B, in the heat exchanger according to the first embodiment of the present invention, the low temperature fluid introduced into the low temperature fluid inlet pipe 150 is dispersed by the third porous plate 230, and thus, the conventional heat exchanger. It can be seen that evenly introduced into a relatively large number of diffusion blocks, respectively. However, it can be seen that the phenomenon in which the low temperature fluid is concentrated in the diffusion block remains in close proximity to the low temperature fluid inflow pipe 150 to some extent.

Referring to (c) of FIG. 18, in the heat exchanger of the second embodiment of the present invention, the third partition wall after the low temperature fluid introduced into the low temperature fluid inlet pipe 150 is dispersed by the third porous plate 230. Passing through 330, it can be seen that not only is evenly introduced into the plurality of diffusion blocks, respectively, compared to the conventional heat exchanger, but also more evenly compared to the heat exchanger of the first embodiment.

The heat exchanger of this embodiment is characterized in that the flow rate difference of the fluids respectively supplied to the plurality of diffusion blocks or the fluids respectively discharged from the plurality of diffusion blocks is less than four times.
That is, among the fluids supplied to each of the plurality of diffusion blocks, the flow rate a of the highest flow rate is less than four times (a <4b) of the flow rate b of the lowest flow rate, and the plurality of diffusion blocks Among the fluids discharged from each of the fluids, the flow rate a 'of the flow with the highest flow rate is less than four times (a'<4b') of the flow rate b' of the flow with the least flow rate.

(A) is a schematic diagram showing the position of the temperature sensor installed to measure the internal temperature of the heat exchanger, (b) is the temperature inside the heat exchanger respectively measured by the temperature sensor at the position shown in (a) It is a graph showing the distribution. In addition, (1) graph shown in Figure 19 (b) shows the temperature distribution inside the conventional heat exchanger, (2) graph shows the temperature distribution inside the heat exchanger according to a second preferred embodiment of the present invention It is shown.

Referring to (b) of FIG. 19, in the case of the conventional heat exchanger, the temperature of the central diffusion block is very low compared to the temperature of the other diffusion blocks, and it can be confirmed that a large temperature difference between the plurality of diffusion blocks remains. In the case of the conventional heat exchanger, the temperature difference between the lowest temperature part and the highest temperature part was found to be approximately 130 to 140 degC.

On the other hand, in the case of the heat exchanger of the second embodiment, it can be seen that the temperature difference between the plurality of diffusion blocks remains relatively small. In the case of the heat exchanger of this embodiment, it was confirmed that the temperature difference between the lowest temperature portion and the highest temperature portion is approximately 40 to 50 degC, and the temperature difference between the diffusion blocks is reduced compared to the conventional heat exchanger.

According to the present invention, even if the evaporation gas is used as the refrigerant of the heat exchanger, and the heat exchanger includes a plurality of diffusion blocks, the flow rate of the refrigerant supplied to each diffusion block can be maintained relatively evenly, and the temperature difference between the diffusion blocks is reduced. The heat exchange efficiency can be improved, and stable reliquefaction performance can be secured even when the flow rate of the re-liquefaction target boil-off gas is changed.

On the other hand, the porous plate may be made of SUS material, and contracted due to contact with the cryogenic evaporation gas may be returned to its original state after the refrigerant passes. The thinner perforated plate has much less heat capacity than the heat exchanger. When the perforated plate is welded to the heat exchanger, the heat exchanger with the large heat capacity is less likely to contract even when it comes into contact with the evaporating gas, and the porous plate with the smaller heat capacity is in contact with the evaporating gas. If the shrinkage is large, the porous plate may be broken.

Therefore, it is necessary to combine the porous plate with the heat exchanger to enable thermal expansion and contraction, and an example of the porous plate coupled to enable thermal expansion and contraction in the fourth and fifth preferred embodiments of the present invention will be described.

20 is a schematic view showing a part of a heat exchanger according to a third preferred embodiment of the present invention, and FIG. 21 is an enlarged schematic view of part A of FIG.

The heat exchanger of the present embodiment also has a first porous plate installed between the hot fluid inflow header 120 and the core 190 in addition to the configuration included in the conventional PCHE shown in FIG. 210, a second porous plate 220 installed between the high temperature fluid discharge header 130 and the core 190, and a third porous plate 230 installed between the low temperature fluid inflow header 160 and the core 190. And at least one of a fourth porous plate 240 installed between the low temperature fluid discharge header 170 and the core 190.

20 and 21, the fourth porous plate 240 of the present embodiment is installed in the low temperature fluid discharge header 170, the fourth porous plate 240 is directly welded to the low temperature fluid discharge header 170. Rather, two support members 420 are spaced at regular intervals to be welded 410 to the low temperature fluid discharge header 170, and the fourth porous plate 240 is sandwiched between the two support members 420.

Since the fourth porous plate 24 is sandwiched between the two supporting members 420 and is not completely fixed, the fourth porous plate 24 is not bent or broken even when it is contracted due to contact with the cryogenic evaporation gas, and the connection part is broken. It doesn't work.

The support member 420 is preferably the minimum size that the fourth porous plate 240 can accommodate the contraction, and the interval between the support members 420 also slightly moves due to the contraction of the fourth porous plate 240. It is preferred that it is the minimum distance possible.

Similar to the fourth porous plate 240, the first to third porous plates 210, 220, and 230 of the present embodiment are also welded by being spaced apart from the hot fluid inflow header 120 at a predetermined interval. The second support plate 220 is sandwiched between the two support members, which are spaced apart from the hot fluid discharge header 130 at regular intervals and welded, and the third porous plate 230 is The low temperature fluid inlet header 160 is sandwiched between two support members spaced apart at regular intervals.

FIG. 22 is a schematic view showing a part of a heat exchanger according to a fourth preferred embodiment of the present invention, and FIG. 23 is an enlarged schematic view of part B of FIG.

The heat exchanger of the present embodiment also has a first porous plate installed between the hot fluid inflow header 120 and the core 190 in addition to the configuration included in the conventional PCHE shown in FIG. 210, a second porous plate 220 installed between the high temperature fluid discharge header 130 and the core 190, and a third porous plate 230 installed between the low temperature fluid inflow header 160 and the core 190. And at least one of a fourth porous plate 240 installed between the low temperature fluid discharge header 170 and the core 190.

22 and 23, the fourth porous plate 240 of the present embodiment is installed in the low temperature fluid discharge header 170 as in the third embodiment, but directly welded to the low temperature fluid discharge header 170. It is not.

However, unlike the third embodiment, the fourth porous plate 240 of the present embodiment has a shape in which both ends extend in parallel with the core 190 and are stepped in a direction away from the core 190. It is not sandwiched between the members 420, but is sandwiched between one support member 420 and the core 190.

That is, one support member 420 is spaced apart from the core 190 at a predetermined interval by welding 410 to the low temperature fluid discharge header 170, and the fourth porous plate 240 extending in parallel with the core 190. The both ends of the is sandwiched between the support member 420 and the core 190, the fourth porous plate 240 is separated from the core 190 from both ends sandwiched between the support member 420 and the core 190. It is formed to be stepped in the direction.

Since the fourth porous plate 24 of the present embodiment is sandwiched between the support member 420 and the core 190 and is not completely fixed, the fourth porous plate 24 is not bent or damaged even if it contracts due to contact with cryogenic evaporation gas. And the connection is not broken.

The support member 420 of this embodiment is preferably the minimum size that the fourth porous plate 240 can accommodate the contraction, and the interval between the support member 420 and the core 190 is also the fourth porous plate 240. ) Is preferably the minimum distance at which some movement is possible due to contraction. In addition, both ends of the fourth porous plate 240 extending in parallel with the core 190 may be inserted between the support member 420 and the core 190 and have a minimum length to accommodate deformation and movement due to contraction. Is preferably.

Similar to the fourth porous plate 240, the first to third porous plates 210, 220, and 230 of the present embodiment also have both ends extending in parallel with the core 190 and stepped in a direction away from the core 190. The first porous plate 210 has both ends sandwiched between the support member welded to the hot fluid inflow header 120 and the core 190, and the second porous plate 220 has the hot fluid discharge header 130. Both ends are inserted between the support member welded to the core and the core 190, and the third porous plate 230 is inserted between the support member welded to the low temperature fluid inflow header 160 and the core 190. Lose.

(A) is a schematic diagram of the whole shape of a heat exchanger, (b) is a schematic diagram of a diffusion block, (c) is a schematic diagram of a channel plate.

Referring to FIG. 24, the core 190, in which heat exchange between the low temperature fluid and the high temperature fluid occurs, is composed of a plurality of diffusion blocks 192, and the diffusion block 192 is composed of a plurality of low temperature fluid channel plates 194. The high temperature fluid channel plates 196 are configured in such a way that they are alternately stacked. Each channel plate 194, 196 is engraved with a plurality of channels through which fluid flows.

FIG. 25A is a schematic view of the low temperature fluid channel plate shown in FIG. 24C as viewed from the C direction, and FIG. 25B is a schematic view of the channel of the low temperature fluid channel plate of the conventional heat exchanger. , (c) is a schematic diagram of the channel of the low-temperature fluid channel plate of the heat exchanger according to the fifth preferred embodiment of the present invention, and (d) is a low-temperature fluid channel of the heat exchanger according to the sixth preferred embodiment of the present invention. Schematic diagram of the channels of the plate.

Referring to FIG. 25, the channel 198 engraved on the channel plate is generally uniform in width and straight as shown in (a). The heat exchange according to the fifth and sixth exemplary embodiments of the present invention is performed. The group includes a channel shaped to resist a fluid.

Referring to FIG. 25C, the heat exchanger of the fifth embodiment includes a plurality of channels 198 that are narrower than the widths of other portions of the inlet portion. In other words, the channel 198 of the present embodiment has a smaller cross-sectional area when the channel plate is viewed in the direction C of FIG.

When the cross-sectional area of the inlet of the channel 198 is formed small, the incoming fluid is resisted to distribute the flow, and the phenomenon of concentrating the fluid in any one of the plurality of diffusion blocks may be alleviated or prevented.

Referring to FIG. 25D, the heat exchanger of the fifth embodiment includes a plurality of zigzag channels 198. When the channel 198 is formed in a zigzag shape, the fluid is resisted and the flow is dispersed, thereby mitigating or preventing the fluid from being concentrated in any one of the plurality of diffusion blocks.

According to the heat exchanger of the fourth and fifth embodiments of the present invention, since the channel includes a channel shaped to resist the fluid, the refrigerant is concentrated in one diffusion block without adding a separate member for dispersing the fluid. There is an advantage that the phenomenon can be alleviated or prevented.

The present invention is not limited to the above embodiments, and various modifications or changes may be made without departing from the technical spirit of the present invention, which will be apparent to those of ordinary skill in the art. It is.

10 compressor 20 heat exchanger
30: decompression device 40: gas-liquid separator
110: high temperature fluid inlet pipe 120: high temperature fluid inlet header
130: high temperature fluid discharge header 140: high temperature fluid discharge pipe
150: low temperature fluid inlet pipe 160: low temperature fluid inlet header
170: low temperature fluid discharge header 180: low temperature fluid discharge pipe
190: core 192: diffusion block
194: Channel Plate for Low Temperature Fluid 196: Channel Plate for High Temperature Fluid
198: channel 210, 220, 230, 240: porous plate
310, 320, 330, 340: partition 420: support member

Claims (13)

A compressor for compressing the boil-off gas discharged from the LNG storage tank;
A heat exchanger that heats and cools the boil-off gas compressed by the compressor using the boil-off gas discharged from the LNG storage tank as a refrigerant; And
Expansion means for expanding the fluid cooled by the heat exchanger;
The heat exchanger,
As PCHE,
A core in which heat exchange between the hot fluid and the cold fluid occurs; And
And fluid dispersing means for dispersing the fluid flowing into the core or the fluid discharged from the core.
The core includes a plurality of diffusion blocks,
Characterized in that the space existing between the plurality of diffusion blocks to form a heat insulating layer,
The fluid dispersing means resists the flow of the fluid flowing into the core or the fluid flowing out of the core, so that the fluid does not concentrate on any one of the plurality of diffusion blocks, even when the flow rate varies. An LNG carrier evaporative gas reliquefaction system, dispersed between a plurality of diffusion blocks and within one diffusion block, such that the reliquefaction performance is at least 50% of theoretical expectations. delete delete The method according to claim 1,
Evaporation gas reliquefaction system of the LNG carrier, the distance between the fluid dispersing means and the core is 20 to 50 mm. The method according to any one of claims 1 and 4,
And a gas-liquid separator installed at the rear end of the expansion means to separate the liquefied liquefied gas and gas components. The method according to claim 5,
The gas component separated by the gas-liquid separator is combined with the boil-off gas is used as a refrigerant of the heat exchanger, the boil-off gas reliquefaction system of the LNG carrier. The method according to any one of claims 1 and 4,
The boil-off gas reliquefaction system of the LNG carrier, the boil-off gas compressed by the compressor is in a supercritical state. The method according to any one of claims 1 and 4,
The boil-off gas reliquefaction system of the LNG carrier, the pressure of the boil-off gas compressed by the compressor is 100 to 400 bara. The method according to claim 8,
The boil-off gas reliquefaction system of the LNG carrier, the pressure of the boil-off gas compressed by the compressor is 150 to 400 bara. The method according to claim 9,
The boil-off gas reliquefaction system of the LNG carrier, the pressure of the boil-off gas compressed by the compressor is 150 to 300 bara. The method according to any one of claims 1 and 4,
Evaporation gas reliquefaction system of the LNG carrier, characterized in that the temperature difference between the plurality of diffusion blocks within 40 to 50 degC. The method according to any one of claims 1 and 4,
Among the fluids supplied to the plurality of diffusion blocks, the flow rate (a) of the flow with the highest flow rate is less than four times (a <4b) of the flow rate (b) of the flow with the least flow rate, and from the plurality of diffusion blocks. Among the fluids discharged from each of the fluids, the flow rate a 'of the most flow is less than four times (a'<4b') of the flow rate b' of the least flow. Reliquefaction System. The method according to claim 4,
And the fluid dispersing means is a perforated plate.

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