KR20190139724A - BOG Reliquefaction System for Vessels and Method of Discharging Lubrication Oil in the Same - Google Patents

Abstract

Disclosed is a boil off gas re-liquefying system for a ship. The boil off gas re-liquefying system for a ship includes: a multi-layered compressor compressing boil off gas; a heat exchanger heat-exchanging boil off gas compressed by a non-fueling end of the multi-layered compressor to cool the same by using low temperature boil off gas before being compressed by the multi-layered compressor as a refrigerant; a third filter installed on an upward stream of a high temperature flow path of the heat exchanger and filtering lubrication oil mixed in the boil off gas transmitted to the heat exchanger; and a decompressing device decompressing fluid cooled by the heat exchanger, wherein the multi-layered compressor includes: a non-fueling end forming a front end; a fueling end forming a back end; and a backflow preventing part installed between the non-fueling end and the fueling end. The backflow preventing part includes a first check valve preventing backflow of the boil off gas.

Description

BOG Reliquefaction System for Vessels and Method of Discharging Lubrication Oil in the Same}

The present invention relates to a system for re-liquefying the remaining boil-off gas used as the fuel of the engine of the boil-off gas generated inside the storage tank.

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 -162 ℃, and has a volume of about 1/600 compared with 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 -162 ℃, liquefied natural gas is easily evaporated because it is sensitive to temperature changes. 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. The same applies to other low temperature liquefied gases such as ethane.

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, gas engines such as DFDE (Dual Fuel Diesel Electric), DFDG (Dual Fuel Diesel Generator), and ME-GI engines are used as engines that can use natural gas as fuel. have.

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

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. Recently, there is a growing interest in ME-GI engines with better fuel efficiency and propulsion efficiency.

In the boil-off gas reliquefaction system using boil-off gas itself as a refrigerant, it is necessary to compress the boil-off gas to a high pressure of about 150 bar or more for re-liquefaction efficiency, and when a high-pressure engine such as a ME-GI engine is employed as the main engine It is necessary to compress the boil-off gas to a high pressure of approximately 300 bar in order to meet the pressure of the fuel required by the fuel cell.

In the high pressure compressor for compressing the boil-off gas to a high pressure of 150 to 300 bar, it is inevitable to use lubricating oil for preventing the wear of the cylinder and extending the life. Lubricant supplied to the cylinder is mixed with the boil-off gas compressed by the high-pressure compressor and accumulated in the pipe or the device, which can cause a breakdown.In particular, during heat exchange for re-liquefaction of the boil-off gas, the oil is condensed before the boil-off gas and the heat exchanger There is a problem that can block the flow path.

In order to prevent the lubricating oil mixed with the boil-off gas from accumulating inside the piping or the device or clogging the flow path of the heat exchanger, the lubricating oil mixed with the boil-off gas is filtered by an oil separator or an oil filter and then supplied to a heat exchanger or the like. The method was adopted.

In the present invention, in order to more fundamentally solve the problems caused by the lubricating oil mixed with the boil-off gas, to provide a marine boil-off gas reliquefaction system and lubricating oil discharge method using a multi-stage compressor including a partially oil-free cylinder.

According to an aspect of the present invention for achieving the above object, a multi-stage compressor for compressing the boil-off gas; A heat exchanger for heat-exchanging and cooling the boil-off gas compressed by the oilless stage of the multi-stage compressor by using the low-temperature evaporated gas before being compressed by the multi-stage compressor as a refrigerant; A third filter installed upstream of the high temperature flow path of the heat exchanger to filter lubricant oil mixed with the boil-off gas sent to the heat exchanger; And a decompression device for depressurizing the fluid cooled by the heat exchanger, wherein the multistage compressor includes an oilless stage constituting a front end, an oil lubrication stage constituting a rear end, and a backflow prevention unit installed between the oilless stage and the oil lubricating end. And, the backflow prevention unit is provided with a boil-off boil-off gas reliquefaction system including a first check valve for preventing the backflow of the boil-off gas.

The backflow prevention unit may further include a first filter installed upstream of the first check valve to filter out lubricating oil contained in the boil-off gas.

The backflow prevention unit may further include a second check valve installed upstream of the first filter to prevent backflow of the boil-off gas.

The ship boil-off gas reliquefaction system may further include a shutoff valve installed respectively upstream and downstream of the third filter.

The ship boil-off gas reliquefaction system may further include a first bypass line for passing the boil-off gas compressed by the oil-free stage of the multistage compressor to bypass the third filter to a high temperature flow path of the heat exchanger.

The multistage compressor may be composed of six stages.

The oilless stage may be composed of five stages.

The oilless stage may compress the boil-off gas to 100 barg to 250 barg.

The oilless stage may compress the boil-off gas to 150 barg.

The vessel boil-off liquefaction system may further include a second filter installed downstream of the oil feed stage to filter out lubricating oil contained in the boil-off gas.

The boil-off gas compressed by the oil supply stage may be supplied to the first engine.

According to another aspect of the present invention for achieving the above object, the boil-off gas used as a refrigerant in the heat exchanger at the time of re-liquefaction of the boil-off gas, by bypassing the heat exchanger by a second bypass line and supplied to the multi-stage compressor, the multi-stage The evaporated gas compressed by the oilless stage of the compressor is supplied to the hot flow path of the heat exchanger to dissolve condensed or solidified lubricant or lower the viscosity, and the evaporated gas passed through the hot flow path of the heat exchanger is a gas-liquid separator. The multi-stage compressor is provided, the lubricating oil discharge method comprising a non-lubrication stage constituting the front end, the lubrication stage constituting the rear end, and a backflow prevention portion provided between the lubrication stage and the lubrication stage.

Lubricating oil melted in the gas-liquid separator or lower in viscosity may be collected, and the lubricant oil collected in the gas-liquid separator may be discharged to the outside.

The boil-off gas passing through the high-temperature flow path of the heat exchanger and the gas-liquid separator may be sent back to the second bypass line to circulate the boil-off gas while discharging the condensed or solidified lubricant or lowering the viscosity.

Boil-off gas can be fueled in the engine while the condensed or solidified lubricant is dissolved or the viscosity is reduced.

According to the present invention, it is possible to prevent the lubricant oil supplied from the oil supply stage from flowing into the oil supply stage by including a backflow prevention portion between the oil supply stage and the oilless stage in the multistage compressor.

According to an embodiment of the present invention, by utilizing a multi-stage compressor installed for redundancy purposes, the flow rate of the re-liquefied evaporated gas and the flow rate of the evaporated gas used as the refrigerant in the heat exchanger are increased, thereby increasing the amount of reliquefaction. You can.

1 is a schematic diagram of a boil-off gas reliquefaction system according to a first preferred embodiment of the present invention.
2 is a schematic diagram of a boil-off gas reliquefaction system according to a second preferred embodiment of the present invention.
3 is a schematic view of a boil-off gas reliquefaction system according to a third preferred embodiment of the present invention.
4 is a schematic diagram of a boil-off gas reliquefaction system according to a fourth preferred embodiment of the present invention.

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.

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 to 3 are schematic views of a boil-off gas reliquefaction system according to the first to third embodiments of the present invention.

1 to 3, the vessel boil-off gas reliquefaction system of the present invention includes a heat exchanger 100, a multi-stage compressor 200, and a decompression device 300.

The heat exchanger 100 uses a low-temperature evaporated gas as a refrigerant, and heats and cools the evaporated gas compressed by the multistage compressor 200. The low temperature evaporated gas used as the refrigerant in the heat exchanger 100 may be an evaporated gas discharged from the storage tank T, and the evaporated gas used as the refrigerant in the heat exchanger 100 is sent to the multistage compressor 200. Lose.

The boil-off gas compressed by the multi-stage compressor 200 is used as the fuel of the first engine E1, and the excess boil-off gas not used as the fuel of the first engine E1 is sent to the heat exchanger 100 to perform the reliquefaction process. Going through.

The decompression device 300 depressurizes the boil-off gas cooled by the heat exchanger 100 after being compressed by the multistage compressor 200. The decompression device 300 may be an expansion valve such as a Joule-Thompson valve or may be an expander.

The evaporated gas that has undergone the compression process by the multistage compressor 200, the cooling process by the heat exchanger 100, and the pressure reduction process by the decompression device 300 is partially or completely reliquefied.

The vessel boil-off liquefaction system of the present embodiment further includes a gas-liquid separator 400 installed downstream of the decompression device 300 to separate the liquefied liquefied gas and the boil-off gas (including the flash gas) remaining as the boil-off gas. It may include. The liquefied gas separated by the gas-liquid separator 400 may be sent to the storage tank T, and the boil-off gas separated by the gas-liquid separator 400 is joined with the boil-off gas discharged from the storage tank T to exchange heat. 100 may be used as the refrigerant.

The multistage compressor 200 includes an oilless end 210, an oil supply end 220, and a backflow prevention unit 230. The boil-off gas compressed by the multi-stage compressor 200 is used as a fuel of the first engine E1, and the excess boil-off gas not used in the first engine E1 is sent to the heat exchanger 100 to undergo a reliquefaction process. .

The oilless stage 210 constitutes a front end of the multistage compressor 200 and includes an oilless cylinder 211. The oilless stage 210 may include a plurality of oilless cylinders 211 and a plurality of coolers 212 respectively installed downstream of the plurality of oilless cylinders 211 as shown in FIGS. have. In the present exemplary embodiment, the oilless end 210 includes five oilless cylinders 211, but is not limited thereto.

The oil supply stage 220 constitutes a rear end of the multistage compressor 200 and includes an oil supply cylinder 221. The oil supply stage 220 may include a cooler 222 installed downstream of the oil supply cylinder 221 as shown in FIGS. 1 to 3. In the present exemplary embodiment, the oil supply stage 220 includes one oil supply cylinder 221, but is not limited thereto. The oil supply terminal 220 may include a plurality of oil supply cylinders 221 and a plurality of oil supply cylinders as necessary. May include two coolers 222.

Each cylinder has a meaning of 'stage' of the multistage compressor 200.

In the present invention, the evaporation gas passed through the oil-free stage 210 is branched and sent to the heat exchanger 100 undergoes a reliquefaction process, after passing through the oil-free stage 210 further evaporated through the oil feed stage 220 Gas is supplied to the fuel of the first engine E1.

In the boil-off gas reliquefaction system using the boil-off gas itself as a refrigerant, in order to ensure a practically applicable level of re-liquefaction efficiency and the amount of re-liquefaction, it is about 100 barg to 250 barg, preferably about 150 barg It is necessary to compress the boil off gas.

Therefore, in the present invention, the oilless stage 210 compresses the boil-off gas to approximately 100 barg to 250 barg, preferably approximately 150 barg, and converts the boil-off gas compressed by the oil-free stage 210 into the heat exchanger 100. To re-liquefy.

In addition, in order to satisfy the pressure condition required by the first engine E1, the vaporized gas compressed by the oilless stage 210 is further compressed by the oil feed stage 220 and then supplied to the first engine E1. do. In other words, the present invention is particularly meaningful when an engine using a boil-off gas having a pressure higher than the pressure required to secure the re-liquefaction efficiency and the amount of re-liquefaction which is actually applicable is adopted. The first engine E1 may be a ME-GI engine and the oil feed stage 220 may compress the boil-off gas to approximately 250 barg to 400 barg, preferably approximately 300 barg.

In the present invention, the rear end of the multi-stage compressor 200 is configured as an oil supply stage 220, in order to compress the boil-off gas at a pressure of about 150 barg to 250 barg or more at the current technology level, to prevent wear of the cylinder and to extend the life. This is because it is necessary to supply lubricating oil.

Multi-stage compressor 200 is preferably composed of six stages, as shown in Figures 1 to 4, when the multi-stage compressor 200 is composed of six stages, five stages of the front end to the oil-free oil stage 210 It is preferable that one end of the rear end is constituted by the oil feed stage 220.

Designing a multistage compressor with fewer stages has the advantage of reducing costs, and designing a large number of stages has the advantage of reducing the compression ratio of each stage (degree of compression of each cylinder) and reducing the burden on each stage. In particular, in the case of the oil-free stage that does not supply the lubricant to the cylinder, the life is shorter than when the lubricant is supplied to the cylinder, the life of the oil-free (210) stage by reducing the burden on each stage by increasing the number of stages of the multistage compressor This shortening can be alleviated.

The inventors of the present invention have found that it is appropriate to design the multistage compressor 200 in six stages in consideration of both the cost and the lifespan according to the compression ratio of each stage.

In addition, the inventors of the present invention, the maximum pressure of the oil-free stage 210 is approximately, considering the maximum degree of compression and the re-liquefaction efficiency of the boil-off gas in order to maintain the service life of the practically applicable level in the case of oil-free cylinder It has been found that 100 to 250 barg, preferably approximately 150 barg, is appropriate.

In the case of the commonly used five-stage high-pressure compressor, the pressure of the boil-off gas after the four stages of compression is about 100 barg, and the pressure of the boil-off gas after all the five stages of compression is about 250 barg to 400 barg, it is difficult to compress the boil-off gas to approximately 150 barg, which is the optimum pressure considering the maximum degree of compression of the oil-free cylinder and the reliquefaction efficiency.

When the multistage compressor 200 is designed in six stages as in one embodiment of the present invention, the pressure of the boil-off gas which has undergone the five stages of compression is approximately 150 barg, considering the maximum degree of compression and the reliquefaction efficiency of the lubrication-free cylinder. It is possible to compress the boil-off gas at the optimum pressure.

Meanwhile, according to the present invention, the boil-off gas undergoing the reliquefaction process undergoes only a partial compression process by the oilless stage 210 of the multistage compressor 200, and only the boil-off gas used as fuel in the first engine E1. The oilless stage 210 and the oil stage 220 of the multi-stage compressor 200 are subjected to all compression processes, so that the boil-off gas not used in the first engine E1 is required of the first engine E1. Since only the pressure necessary for reliquefaction is compressed without compressing the pressure, both the boil-off gas undergoing the reliquefaction process and the boil-off gas supplied to the first engine E1 are subjected to the entire compression process of the multistage compressor 200, and then a part of the Compared to branching to undergo reliquefaction, there is an advantage in that energy for compressing the boil-off gas can be reduced.

The boil-off gas compressed by some stages of the multistage compressor 200 may be partially branched and supplied to the second engine E2, and the second engine E2 may be evaporated at a lower pressure than the first engine E1. It may be an engine using gas as a fuel, for example, a DF engine. In addition, the boil-off gas compressed by some stages of the multistage compressor 200 may be sent to the gas combustion device G for combustion as necessary.

The backflow prevention unit 230 is installed between the oil supply stage 220 and the oilless end 210 to prevent lubricating oil from flowing from the oil supply stage 220 to the oilless end 210.

The multistage compressor 200 includes a recirculation line RL and a recirculation valve RV for adjusting the pressure of each stage. 1 to 3 illustrate that the recirculation line RL and the recirculation valve RV are installed in the oil supply stage 220, and the recirculation line RL and the recirculation valve RV may also be installed in the non-lubrication stage 210. have.

The boil-off gas recycled to adjust the pressure of each stage of the multi-stage compressor 200 is reduced by the pressure of the front end by the recirculation valve RV and then recirculated by the recirculation line RL. The lubricating oil mixed in the boil-off gas may be condensed or solidified through the decompression process by the recirculation valve (RV). The inventors of the present invention have found that a problem may occur when the lubricating oil decompressed or solidified by the recirculation valve RV in the oil supply stage 220 flows into the oilless stage 210.

Referring to FIG. 2, according to one embodiment of the present invention, the backflow prevention unit 230 includes a first check valve CV1, and the lubricant oil condensed or solidified by the recirculation valve at the oil supply stage 220 is reduced. The backflow of the boil-off gas is blocked so as not to flow into the oilless stage 210.

The inventors of the present invention have found that even when the back flow of the boil-off gas is blocked by the first check valve CV1, a problem may occur in which some leakage occurs. Referring to FIG. 3, in order to prepare for a case in which a part of the boil-off gas leaks from the first check valve CV1, the backflow preventing unit 230 may include a first filter F1 installed upstream of the first check valve CV1. ) May be further included. The first filter F1 filters the lubricating oil contained in the boil-off gas leaked from the first check valve CV1 and flowed back from the oil feed stage 220.

On the other hand, when the multi-stage compressor 200 is shut down (Shut Down), the compressed boil-off gas must be discharged from each stage (Releasing), the inventors of the present invention, the process of sharing the boil-off gas of each stage for the discharge of boil It was found that the lubricant in the first filter (F1) can flow into the oil-free end 210 in the.

Referring to FIG. 3, according to an embodiment of the present invention, the backflow prevention unit 230 further includes a second check valve CV2 installed upstream of the first filter F1, and thus, the first filter F1. The internal lubricating oil was prepared in case the oil flows into the oil free end 210. The second check valve CV2 blocks the lubricating oil inside the first filter F1 from flowing into the oil free end 210.

Referring to FIG. 1, two first filters F1 may be installed in parallel, one for everyday use, and the other for the first filter F1 that is normally used. That is, the first filter F1 may be additionally installed and used for redundancy purposes. In addition to the first filter F1, the first check valve CV1 and the second check valve CV2 may be additionally installed to be used for redundancy purposes.

When additionally installing the first filter F1 for redundancy, isolation valves V1 and V2 may be installed upstream and downstream of the first filter F1 so as to operate one by one. Shut-off valves V1 'and V2' may be provided upstream and downstream of the first filter F1 ', respectively.

In addition, as shown in FIG. 1, check valves CV1 and CV2 are provided upstream and downstream of the first filter F1, respectively, and shutoff valves V1 and V2 respectively upstream and downstream of the check valves CV1 and CV2. ) Are installed, and devices F1 ', CV1', CV2 ', V1', and V2 'having the same configuration are installed in parallel, and can serve as redundancy with each other.

On the other hand, while the boil-off gas compressed by the oil feed stage 220 of the multi-stage compressor 200 is supplied to the first engine E1, the lubricating oil mixed in the boil-off gas may be mixed with dust and block the pipe or equipment. Can be. Since the lubricating oil is sent to the first engine E1, the combustion is performed in the first engine E1, so there is no big problem. However, the inventors of the present invention provide the first engine E1 when the lubricating oil is actually supplied to the first engine E1. It has been found that a problem arises in that a strainer or the like installed upstream of the engine E1 is blocked by lubricating oil. The strainer is equipment installed upstream of the engine to prevent particles such as impurities from entering the engine and damaging the engine.

1 to 3, according to one embodiment of the present invention, in order to prevent lubricating oil from entering the first engine E1 and damaging the engine, the impurities, such as a strainer, are filtered upstream of the first engine E1. The second filter F2 was installed upstream of the equipment so that the boil-off gas filtered with lubricating oil by the second filter F2 could be supplied to the first engine E1.

2 and 3, the marine boil-off gas reliquefaction system of the present invention, the lubricating oil mixed with the boil-off gas to be sent to the heat exchanger 100 after being compressed by the oil-free end 210 of the multi-stage compressor 200. The filter may further include a third filter F3. The third filter F3 serves to prevent lubricating oil mixed in the boil-off gas from the oil supply stage 220 from entering the heat exchanger 100 in preparation for a leak that may occur even when the counter flow prevention unit 230 is installed. do.

It may further include a first bypass line (BL1) for allowing the boil-off gas to bypass the third filter (F3), and when the failure, maintenance of the third filter (F3), the first bypass line ( The third filter F3 is bypassed by BL1). In addition, shut-off valves V1 and V2 are provided upstream and downstream of the third filter F3 so that the third filter F3 can be isolated at the time of failure or maintenance of the third filter F3. Can be.

4 is a schematic diagram of a boil-off gas reliquefaction system according to a fourth preferred embodiment of the present invention. The marine boil-off gas liquefaction system of the fourth embodiment shown in FIG. 4 differs from the marine boil-off gas liquefaction system of the first embodiment shown in FIG. 1 in that it utilizes the redundant multistage compressor 200 '. It exists and will be described below with emphasis on the differences. Detailed description of the same members as those of the vessel boil-off gas liquefaction apparatus of the first embodiment described above will be omitted.

According to the present embodiment, the redundancy multistage compressor 200 ′ which is configured in the same way as the multistage compressor 200 and installed in parallel with the multistage compressor 200 is utilized, and the multistage compressor 200 is also used in normal times without failure. The amount of liquefaction can be increased.

By simultaneously operating the multistage compressor 200 and the redundancy multistage compressor 200 ', the flow rate of the low-temperature evaporated gas used as the refrigerant in the heat exchanger 100 can be increased, and the multistage compressors 200 and 200' Since the flow rate of the boil-off gas cooled by the heat exchanger 100 after being compressed may also be increased, the amount of reliquefaction is increased.

According to the present invention, since the evaporated gas compressed to about 100 barg to 250 barg, preferably about 150 barg by the oil-free oil stage 210 is sent to the heat exchanger 100 to undergo a reliquefaction process, While securing the re-liquefaction efficiency and the amount of re-liquefaction, it is possible to fundamentally solve the problem that the heat exchanger 100 and other devices and piping are blocked by condensed or solidified lubricant.

According to the present invention, it is possible to solve the problem that the heat exchanger 100 and other devices and pipes are blocked by condensed or solidified lubricating oil by using a lubricated cylinder to a minimum, and to prevent wear and extend the life of the cylinder. I could do it.

In addition, according to the present invention, by appropriately utilizing the check valve (CV1, CV2) and the filter (F1, F2) to compensate for the problems that may occur while using the oil-filled cylinder, the liquefied evaporated gas efficiently and stably We have optimized the system to make it possible.

On the other hand, even if the oil-filled cylinder in the ship's boil-off gas system of the present invention is used to the minimum, and the problem that may occur while using the oil-filled cylinder is compensated for, lubricating oil may be accumulated inside the pipe and various equipment. In particular, in the heat exchanger 100, since the lubricating oil is condensed or solidified before the evaporating gas, the flow path may be blocked by the lubricating oil. In the case of adopting the micro-channel heat exchanger 100 such as PCHE, the heat exchanger 100 Since the internal flow path is narrow, the flow path may be more frequently blocked by lubricating oil.

According to the present invention, the lubricating oil in the system is discharged by utilizing the second bypass line BL2, which is conventionally installed for failure or maintenance of the heat exchanger 100.

1 to 4, when lubricating oil is discharged, the low temperature evaporated gas is not used as the refrigerant in the heat exchanger 100, but bypasses the heat exchanger 100 by the second bypass line BL2. The boil-off gas bypassing the heat exchanger 100 by the second bypass line BL2 is sent to the multistage compressor 200 (in the fourth embodiment shown in FIG. 4, the multistage compressor 200 and the multistage compressor for redundancy). (200 ') can be sent), the evaporated gas compressed by the oil-free end 210 of the multi-stage compressor 200, the temperature is raised through the high-temperature flow path of the heat exchanger 100, the heat exchanger 100 The condensation or solidified lubricant in the interior is dissolved or the viscosity is discharged.

The low temperature flow path of the heat exchanger 100 means a flow path through which the evaporative gas used as the refrigerant in the heat exchanger 100 passes, and the high temperature flow path is a multistage compressor for redundancy in the fourth embodiment shown in FIG. 4. After the compression by the compressor (200 ') also means a flow path through which the boil-off gas cooled by the heat exchanger 100 passes.

The boil-off gas passing through the heat exchanger 100 may be sent to the gas-liquid separator 400 after being decompressed by the pressure-reducing device 300, and may collect the lubricating oil melted or lowered in the gas-liquid separator 400, and the gas-liquid Lubricating oil collected in the separator 400 may be discharged to the outside.

In addition, the boil-off gas sent to the gas-liquid separator 400 is sent back to the second bypass line BL2, so that the boil-off gas while discharging the lubricating oil, the second bypass line BL2, the multistage compressor 200, shown in FIG. In the fourth embodiment, the oilless stage 210 of the multi-stage compressor 200 'for redundancy, the high temperature flow path of the heat exchanger 100, the pressure reducing device 300, the gas-liquid separator 400, and again the second bypass line The cycle connecting the BL2 can be cycled.

According to the present invention, even while the lubricating oil is discharged by utilizing the second bypass line BL2, the boil-off gas can be supplied to the engines E1 and E2. In the case of equipment failure or maintenance, it is common to refuel the engine. According to the present invention, the engine E1 and E2 may be supplied while the lubricant inside the system is discharged for the maintenance of the equipment. It is efficient.

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.

T: Storage tank E1, E2: Engine
G: Gas Combustor F1, F2, F3: Filter
CV1, CV2: Check valve V1, V2: Shut-off valve
RV: Recirculation Valve RL: Recirculation Line
BL1, BL2: Bypass Line 100: Heat Exchanger
200: multi-stage compressor 210: oil-free oil stage
211: oil-free cylinder 212, 222: cooler
220: oil supply stage 221: oil supply cylinder
230: backflow prevention unit 300: pressure reducing device
400: gas-liquid separator

Claims (15)

A multistage compressor for compressing boil-off gas;
A heat exchanger for heat-exchanging and cooling the boil-off gas compressed by the oilless stage of the multi-stage compressor by using the low-temperature evaporated gas before being compressed by the multi-stage compressor as a refrigerant;
A third filter installed upstream of the high temperature flow path of the heat exchanger to filter lubricant oil mixed with the boil-off gas sent to the heat exchanger; And
And a decompression device for depressurizing the fluid cooled by the heat exchanger.
The multistage compressor includes an oilless stage constituting a front end, an oil stage constituting a rear end, and a backflow prevention unit installed between the oilless stage and the oil stage,
The backflow prevention unit, a boil-off boil-off gas reliquefaction system including a first check valve for preventing the backflow of the boil-off gas. The method according to claim 1,
The backflow prevention unit further comprises a first filter installed upstream of the first check valve to filter out lubricating oil contained in the boil-off gas. The method according to claim 2,
The backflow prevention unit further includes a second check valve installed upstream of the first filter to prevent backflow of the boil-off gas, the vessel boil-off gas liquefaction system. The method according to any one of claims 1 to 3,
Further comprising a shut-off valve respectively installed upstream and downstream of the third filter, the vessel boil-off gas liquefaction system. The method according to any one of claims 1 to 3,
And a first bypass line for passing the boil-off gas compressed by the oil-free stage of the multistage compressor to bypass the third filter and into the high-temperature flow path of the heat exchanger. The method according to any one of claims 1 to 3,
The multistage compressor is composed of six stages, the vessel boil-off gas liquefaction system. The method according to claim 6,
The oilless stage is composed of five stages, the vessel boil-off gas liquefaction system. The method according to any one of claims 1 to 3,
The oilless stage compresses the boil-off gas to 100 barg to 250 barg, marine boil-off gas reliquefaction system. The method according to claim 8,
The oilless stage compresses the boil-off gas to 150 barg, marine boil-off gas reliquefaction system. The method according to any one of claims 1 to 3,
And a second filter installed downstream of the oil supply stage to filter out lubricating oil contained in the boil-off gas. The method according to any one of claims 1 to 3,
The boil-off boil-off gas liquefaction system is supplied to the first engine by the boil-off gas compressed by the oil supply stage. During the reliquefaction of the boil-off gas, the boil-off gas used as the refrigerant in the heat-exchanger is supplied to the multistage compressor after bypassing the heat-exchanger by the second bypass line,
By supplying the boil-off gas compressed by the oil-free stage of the multi-stage compressor to the high-temperature flow path of the heat exchanger, to dissolve the condensed or solidified lubricating oil or to lower the viscosity,
The boil-off gas passing through the high temperature flow path of the heat exchanger is sent to the gas-liquid separator,
The multistage compressor includes a lubrication stage constituting a front end, a lubrication stage constituting a rear end, and a backflow prevention unit provided between the lubrication stage and the lubrication stage. The method according to claim 12,
Lubricating oil is melted or the viscosity is lowered in the gas-liquid separator is collected,
Lubricating oil collected in the gas-liquid separator is discharged to the outside, the lubricant discharge method. The method according to claim 12 or 13,
And sending the boil-off gas passed through the high-temperature flow path of the heat exchanger and the gas-liquid separator back to the second bypass line to circulate the boil-off gas while melting the condensed or solidified lubricant or lowering the viscosity. The method according to claim 12 or 13,
A method of lubricating oil, wherein the engine is fed with boil-off gas while the condensed or solidified lubricating oil is melted or the viscosity is reduced.

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