KR102211431B1 - Boil-Off Gas Treatment System and Method for Ship - Google Patents

Abstract

Disclosed are a boil-off gas treatment system for a ship and a method thereof. The boil-off gas treatment system for a ship comprises: a boil-off gas supply line provided in a ship and connected from a storage tank, in which liquefied gas is stored, to a main engine in the ship; a compressor provided on the boil-off gas supply line to receive the boil-off gas generated from the liquefied gas and compress the same with the fuel supply pressure of the main engine; a reliquefaction line which is branched from the boil-off gas supply line downstream of the compressor to connect to the storage tank and cools and reliquefies compressed gas that is not supplied as fuel for the main engine; a precooler provided on the reliquefaction line to receive the compressed gas and cool the same through heat exchange with a refrigerant; a heat exchanger which is provided on the reliquefaction line and receives the compressed gas cooled by the precooler and cools the same through heat exchange with the uncompressed boil-off gas to be supplied to the compressor; a refrigerant circulation line through which the refrigerant for cooling the compressed gas in the precooler circulates; and a refrigerant heat exchanger which is provided on the refrigerant circulation line and cools the refrigerant through heat exchange with the uncompressed boil-off gas that is to be supplied to the compressor after heat-exchanged by the heat exchanger. Therefore, the boil-off gas treatment system can cool the boil-off gas more effectively, thereby increasing reliquefaction performance.

Description

Boil-Off Gas Treatment System and Method for Ship}

The present invention relates to a system and method for treating boil-off gas of a ship, and more particularly, to supply boil-off gas generated in a storage tank as fuel such as a main engine on board, and the boil-off gas not supplied as fuel is cold heat of the boil-off gas itself. It relates to a system and method for treating boil-off gas of a ship that is re-liquefied and stored in a storage tank.

In recent years, the consumption of liquefied natural gas (LNG) and other liquefied gases is increasing rapidly around the world. The liquefied gas obtained by liquefying the gas at a low temperature has an advantage of increasing storage and transfer efficiency because the volume is very small compared to the gas. In addition, liquefied gases, including liquefied natural gas, can remove or reduce air pollutants during the liquefaction process, and thus can be viewed as eco-friendly fuels with less air pollutant emissions during combustion.

Liquefied natural gas is a colorless and transparent liquid obtained by liquefying natural gas containing methane as its main component by cooling it to about -163°C, and has a volume of about 1/600 compared to natural gas. Therefore, when the natural gas is liquefied and transported, it can be transported very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -163°C, the liquefied natural gas is sensitive to temperature changes and is easily evaporated. For this reason, the storage tank that stores liquefied natural gas is insulated, but external heat is continuously transferred to the storage tank. Therefore, during the transportation of liquefied natural gas, the liquefied natural gas is continuously evaporated in the storage tank and boiled gas (Boil). -Off Gas, BOG) occurs.

Boil-off gas is a kind of loss and is an important problem in transport efficiency. In addition, if the boil-off gas accumulates in the storage tank, the internal pressure of the tank may increase excessively, and in severe cases, there is a risk of damage to the tank. Therefore, various methods for treating the boil-off gas generated in the storage tank have been studied. Recently, for the treatment of the boil-off gas, a method of re-liquefying the boil-off gas and returning it to the storage tank, and the boil-off gas as fuel such as a ship's engine. The method of using it as an energy source of the customer is being used.

As a method for re-liquefying the boil-off gas, a method of reliquefying the boil-off gas by heat exchange with the refrigerant by providing a refrigeration cycle using a separate refrigerant, a method of re-liquefying the boil-off gas itself as a refrigerant without a separate refrigerant, etc. There is this.

Meanwhile, among engines generally used in ships, gas-fueled engines such as DF engines, X-DF engines, and ME-GI engines are used as engines that can use natural gas as fuel.

DF engine (DFDE, DFGE) consists of 4 strokes, and adopts the Otto Cycle, which injects natural gas with a relatively low pressure of 5.5 barg into the inlet of the combustion air and compresses it while the piston rises. Are doing.

The X-DF engine consists of two strokes, uses 12 to 15 barg of natural gas as fuel, and adopts an auto cycle.

The ME-GI engine is composed of two strokes, and adopts a diesel cycle in which high-pressure natural gas near 300 barg is injected directly into the combustion chamber near the top dead center of the piston.

1 schematically shows a conventional boil-off gas treatment system for ships.

In the conventional boil-off gas treatment system for ships as shown in FIG. 1, when the main engine ME and the power generation engine GE are provided, the boil-off gas discharged from the storage tank T is compressed by the compressor 10 It is supplied as fuel of the main engine, and when the fuel supply pressure of the power generation engine is lower than that of the main engine, the boil-off gas that has undergone a partial compression process of the compressor 10 is branched from the middle and supplied as fuel of the power generation engine GE.

Among the boil-off gas supplied to the compressor 10, the remaining boil-off gas is supplied as fuel for the main engine and power generation engine, and the remaining boil-off gas is supplied to the heat exchanger 20, and is cooled through heat exchange with the boil-off gas discharged from the storage tank T. .

The boil-off gas cooled in the heat exchanger 20 is depressurized by the decompression device 30 and partially re-liquefied, and the re-liquefied liquefied gas and the boil-off gas remaining in a gaseous state are supplied to the gas-liquid separator 40 and phase separated. .

The liquefied gas separated by the gas-liquid separator 40 is supplied to the storage tank T and stored again, and the gaseous evaporative gas separated by the gas-liquid separator 40 joins the boil-off gas discharged from the storage tank T. It is introduced into the heat exchanger 20 as a refrigerant.

In this way, the boil-off gas is reliquefied by using the boil-off gas itself as a refrigerant without a separate refrigerant. The boil-off gas compressed by the compressor is heat-exchanged with the boil-off gas before being compressed by the compressor to cool it, and then expand it by a JT valve. The present applicant named a system for re-liquefying a part of the boil-off gas by making it a PRS (Partial Re-liquefaction System).

The present invention further improves the PRS to more effectively cool the boil-off gas to increase the reliquefaction performance and to propose a system capable of treating the boil-off gas.

According to an aspect of the present invention for solving the above-described problem, a boil-off gas supply line provided on a ship and connected from a storage tank in which liquefied gas is stored to the ship's main engine;

A compressor provided in the boil-off gas supply line and receiving boil-off gas generated from the liquefied gas and compressing it at a fuel supply pressure of the main engine;

A reliquefaction line branched from the boil-off gas supply line downstream of the compressor and connected to the storage tank, cooling and reliquefying the compressed gas not supplied as fuel of the main engine;

A precooler provided in the reliquefaction line to receive the compressed gas and cool it by heat exchange with a refrigerant;

A heat exchanger provided in the reliquefaction line and configured to receive the compressed gas cooled by the pre-cooler and cool the uncompressed boil-off gas to be supplied to the compressor through heat exchange;

A refrigerant circulation line through which a refrigerant cooling the compressed gas circulates in the precooler; And

A refrigerant heat exchanger provided in the refrigerant circulation line and cooling the refrigerant by heat exchange with the uncompressed evaporative gas to be supplied to the compressor after heat exchange in the heat exchanger is provided.

Preferably, the refrigerant circulation line includes a refrigerant compressor for compressing the refrigerant discharged from the precooler; And a refrigerant condenser for cooling the refrigerant compressed by the refrigerant compressor; the refrigerant compressed and cooled through the refrigerant compressor and the refrigerant condenser is introduced into the refrigerant heat exchanger and further cooled, and then introduced into the precooler. .

Preferably, the reliquefaction line includes: a decompression device for further cooling by depressurizing the compressed gas cooled through the precooler and the heat exchanger; And a gas-liquid separator for gas-liquid separation by receiving the boil-off gas reduced by the decompression device.

Preferably, a flash gas line connected from the gas-liquid separator to the front end of the heat exchanger of the boil-off gas supply line, wherein the flash gas separated by the gas-liquid separator is transmitted from the storage tank through the flash gas line. The liquefied gas, which is joined to the flow of the uncompressed boil-off gas to be introduced into the heat exchanger, and separated by the gas-liquid separator, may be supplied to the storage tank.

Preferably, the compressor is provided as a multi-stage compressor that receives the boil-off gas and compresses it at the fuel supply pressure of the main engine through a plurality of compressors, and a fuel supply line connected to the onboard power generation engine from an intermediate stage of the multi-stage compressor; Including further, the boil-off gas compressed through a portion of the compressor of the multi-stage compressor may be supplied to the power generation engine having a lower fuel supply pressure than the main engine.

According to another aspect of the present invention, the boil-off gas generated from the storage tank in which the liquefied gas is stored in the ship is compressed by a compressor at the fuel supply pressure of the main engine in the ship,

Among the boil-off gas compressed by the compressor, the boil-off gas not supplied as fuel of the main engine is precooled by heat exchange with a refrigerant in a pre-cooler, heat-exchanged with the uncompressed boil-off gas to be introduced into the compressor in a heat exchanger to cool, and depressurize Re-liquefied by additional cooling and re-stored in the storage tank,

The refrigerant supplied to the precooler circulates along a refrigerant circulation line, and is cooled by heat exchange with the uncompressed evaporation gas to be supplied to the compressor after heat exchange in the heat exchanger. .

Preferably, the refrigerant is compressed, cooled, and condensed after passing through a precooler, and the condensed refrigerant is further cooled by heat exchange with the uncompressed evaporation gas, and then introduced into the precooler, and can be circulated along the refrigerant circulation line. .

Preferably, the boil-off gas cooled through the pre-cooler and the heat exchanger after compression in the compressor is further cooled under reduced pressure and then gas-liquid is separated, and the liquid is supplied to the storage tank to be stored again, and the separated flash gas is the It may be joined to the uncompressed boil-off gas flow to be introduced from the storage tank to the heat exchanger.

In the system of the present invention, prior to cooling the gas to be reliquefied in the main heat exchanger, it is precooled in a precooler and then transferred to a heat exchanger for stepwise cooling, so that the gas to be reliquefied can be cooled more effectively and the reliquefaction efficiency can be improved. have.

In addition, the uncompressed boil-off gas discharged from the heat exchanger is used again to cool the refrigerant supplied to the pre-cooler, so that the cold heat of the uncompressed boil-off gas can be additionally utilized. By cooling the refrigerant in this way, the amount of work required for compressing the refrigerant in the refrigerant cycle can be reduced, thereby reducing the size of the equipment.

Boil-off gas that cannot be consumed due to fuel supply and re-liquefaction should be burned out by the GCU, and the amount of boil-off gas to be burned and processed through improved re-liquid performance can be reduced to prevent energy waste and reduce the emission of carbon dioxide generated during combustion. And, it is possible to secure the safety of the ship by effectively treating the boil-off gas.

1 is a schematic diagram of a conventional boil-off gas treatment system.
2 is a schematic diagram of a boil-off gas treatment system of a ship according to an embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the object achieved by the implementation of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, the configuration and operation of a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, in adding reference numerals to elements of each drawing, it should be noted that only the same elements are marked with the same numerals as possible, even if they are indicated on different drawings.

Hereinafter, the ship in the present invention is all types of engines that can use liquefied gas and boil-off gas generated from liquefied gas as fuel for propulsion or power generation engines, or use liquefied gas or boil-off gas as fuel for onboard engines. These ships include LNG carriers, liquefied petroleum gas carriers, and ships with self-propelled capabilities such as LNG RV (Regasification Vessel), LNG Floating Production Storage Offloading (FPSO), and LNG Floating Storage Regasification (FSRU). It does not have propulsion capability like the unit), but may include offshore structures that are floating on the sea.

In addition, in the present invention, the liquefied gas may be transported by liquefying the gas at a low temperature, generating boil-off gas in a stored state, and may include all kinds of liquefied gas that can be used as fuel such as an engine. These liquefied gases are, for example, liquefied petrochemicals such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), Liquefied Ethylene Gas, and Liquefied Propylene Gas. It can be gas. However, in an embodiment to be described later, it will be described with an example that LNG, which is one of the representative liquefied gases, is applied.

Meanwhile, the fluid flowing through each line of the present embodiments may be in any one of a liquid state, a gas-liquid mixture state, a gas state, and a supercritical fluid state, depending on the operating conditions of the system.

Figure 2 schematically shows the boil-off gas treatment system of the ship according to an embodiment of the present invention.

As shown in Figure 2, the boil-off gas treatment system of this embodiment is provided on a ship and is for supplying or reliquefying boil-off gas generated from a storage tank in which the liquefied gas is stored as fuel, and the main engine on board the ship from the storage tank The boil-off gas supply line GL connected to the (ME) is provided, and the boil-off gas supply line includes a compressor 100 that receives boil-off gas generated from the liquefied gas stored in the storage tank and compresses it with the fuel supply pressure of the main engine. It is prepared.

The boil-off gas generated in the storage tank T is introduced into the compressor 100 and compressed. The compressor 100 may be provided as a multi-stage compressor in which a plurality of compressors and intermediate coolers are alternately arranged, and through these in sequence, compressing the boil-off gas to the fuel supply pressure of the main engine.

The compressor compresses the boil-off gas and uses the fuel supply pressure to the main engine, for example, 5.5 barg when a DF engine is provided, 12 to 15 barg when an X-DF engine is provided, and 300 barg when a ME-GI engine is provided. Can be compressed with The number of compressors and intermediate coolers constituting the multi-stage compressor can be changed according to the fuel supply pressure of the main engine.

A fuel supply line (SL) connected from the middle stage of the multistage compressor to the onboard power generation engine (GE) is provided, and the boil-off gas compressed through a part of the compressor of the multistage compressor can be supplied to a power generation engine with a lower fuel supply pressure than the main engine. .

For example, the main engine is a ME-GI engine, and the power generation engine that receives lower pressure fuel is DFGE (Dual Fuel Generator Engine) or TFGE (Triple Fuel Generator Engine), and a medium-pressure engine that receives fuel with lower pressure than ME-GI engine. It can be composed of.

According to ship regulations, the compressor that supplies fuel to the engine must be designed with redundancy in case of an emergency. Redundancy design means that when one cannot be used for reasons such as failure or maintenance, the other is replaced. It means designing to be usable. To this end, although only one set of compressors is shown in the drawings of the present embodiments, a plurality of compressors may be provided.

On the other hand, a reliquefaction line (RL) branched from the boil-off gas supply line (GL) downstream of the compressor (100) and connected to the storage tank is provided, cooling compressed gas not supplied as fuel of the main engine, and re-liquefying it for storage. Re-store in tank (T).

In the reliquefaction line RL, a precooler 200 and a heat exchanger 300 are sequentially provided in order to cool the compressed gas compressed by the compressor to be reliquefied.

The precooler 200 receives compressed gas branched from the compressor and then branched to the reliquefaction line and precools it by heat exchange with the refrigerant, and the heat exchanger 300 receives the compressed gas cooled through the precooler to the compressor. It is further cooled by heat exchange with the uncompressed evaporation gas to be supplied.

A closed loop refrigerant circulation line CL through which refrigerant circulates is provided to supply the refrigerant to the precooler. The refrigerant circulation line CL is characterized in that a refrigerant heat exchanger 400 is provided to cool the refrigerant in the refrigerant circulation line by heat exchange with uncompressed evaporative gas to be supplied to the compressor after heat exchange in the heat exchanger.

A refrigerant compressor 410 for compressing a refrigerant discharged from the precooler 200 and a refrigerant condenser 420 for cooling a refrigerant compressed by the refrigerant compressor are provided in the refrigerant circulation line CL.

The refrigerant compressed and cooled through the refrigerant compressor 410 and the refrigerant condenser 420 is introduced into the refrigerant heat exchanger 400, further cooled, and then introduced into the precooler 200, and heat exchanged with the compressed gas in the precooler. It is introduced into the refrigerant compressor to form a closed loop refrigerant cycle.

As a result of modeling a system comprising a refrigerant heat exchanger that additionally cools the refrigerant with uncompressed evaporative gas cooling and heat, the work of the refrigerant compressor in the refrigerant cycle is reduced by 36% compared to compression and condensation without configuring a refrigerant heat exchanger. Confirmed.

Therefore, by configuring a refrigerant heat exchanger as in this embodiment to cool the refrigerant circulating through the refrigerant cycle with cold heat of uncompressed evaporated gas to be introduced into the compressor after passing through the heat exchanger, the amount of work required for refrigerant compression in the refrigerant cycle is reduced. It is possible to reduce the size and size of the compression equipment and piping configured in the cycle and reduce the cost.

As the refrigerant in the refrigerant circulation line, preferably, a refrigerant having a boiling point of -30°C or less may be used. For example, a mixed refrigerant such as SMR (Single Mixed Refrigerant) or C3MR (Propane-precooled Mixed Refrigerant), and nitrogen may be used.

The gas to be reliquefied is precooled in the precooler 200 and then introduced into the heat exchanger 300 and cooled again by the uncompressed evaporation gas. In this way, after precooling in the precooler, it is secondarily cooled in the main heat exchanger, so that the boil-off gas to be reliquefied can be cooled more effectively, thereby improving reliquefaction performance.

Meanwhile, the heat exchanger 300 may be provided with a printed circuit heat exchanger (PCHE) or a direct contact type heat exchanger (DCHE). The boil-off gas to be introduced into the heat exchanger may be introduced into the heat exchanger after removing the lubricating oil mixed in the compression process through an oil filter (not shown).

In the reliquefaction line RL, a decompression device 500 for decompressing the compressed gas cooled through a pre-cooler and a heat exchanger for additional cooling, and a gas-liquid separator 600 for separating gas-liquid by receiving the evaporated gas depressurized from the decompression device. do.

The pressure reducing device 500 may be configured with an expander or an expansion valve such as a Joule-Thomson valve for reducing the compressed boil-off gas. Through decompression, the boil-off gas expands isentropically or adiabatically and is cooled.

The flash gas line (FL) is connected from the gas-liquid separator 600 to the front end of the heat exchanger of the boil-off gas supply line, and the flash gas separated from the gas-liquid separator passes through the flash gas line, and the uncompressed boil-off gas to be introduced from the storage tank to the heat exchanger. It joins the flow and replenishes the heat exchanger with refrigerant.

Meanwhile, the liquefied gas separated by the gas-liquid separator is supplied to the storage tank along the reliquefaction line and stored again.

As described above, in this embodiment, the boil-off gas generated from the storage tank in which the liquefied gas is stored is compressed by a compressor at the fuel supply pressure of the main engine on board, and the boil-off gas compressed by the compressor is not supplied as fuel of the main engine. The boil-off gas is pre-cooled by heat exchange with the refrigerant in a pre-cooler, and the uncompressed evaporated gas to be introduced into the compressor is heat-exchanged with the heat exchanger to cool it, and it is further cooled by decompression and then re-stored in a storage tank after gas-liquid separation. Accordingly, the refrigerant circulated and supplied to the precooler was heat-exchanged in a heat exchanger and then cooled by heat exchange with uncompressed evaporative gas to be supplied to the compressor.

Equipment for refrigerant compression by additionally cooling the compressed, cooled, and condensed refrigerant circulating along the refrigerant circulation line by heat exchange with uncompressed evaporative gas discharged from the heat exchanger and introducing it into the precooler, further cooling the refrigerant in the refrigerant cycle By reducing the amount of work, the equipment size can be reduced, and installation and operation costs can be reduced. In addition, the gas to be reliquefied can be effectively cooled by sequentially passing through a precooler and a heat exchanger to improve reliquefaction performance.

It is obvious to those of ordinary skill in the art that the present invention is not limited to the above embodiments, and can be implemented with various modifications or variations within the scope of the technical gist of the present invention. I did it.

T: storage tank
ME: main engine
GE: Power generation engine
GL: Boil-off gas supply line
RL: Reliquefaction line
CL: refrigerant circulation line
FL: flash gas line
SL: Fuel supply line
100: compressor
200: pre-cooling
300: heat exchanger
400: refrigerant heat exchanger
410: refrigerant compressor
420: refrigerant condenser
500: pressure reducing device
600: gas-liquid separator
700: heater

Claims (8)

A boil-off gas supply line provided on the ship and connected to the main engine in the ship from the storage tank in which the liquefied gas is stored;
A compressor provided in the boil-off gas supply line and receiving boil-off gas generated from the liquefied gas and compressing it at a fuel supply pressure of the main engine;
A reliquefaction line branched from the boil-off gas supply line downstream of the compressor and connected to the storage tank, cooling and reliquefying the compressed gas not supplied as fuel of the main engine;
A precooler provided in the reliquefaction line to receive the compressed gas and cool it through heat exchange with a refrigerant;
A heat exchanger provided in the reliquefaction line and configured to receive the compressed gas cooled by the pre-cooler and cool the uncompressed boil-off gas to be supplied to the compressor through heat exchange;
A refrigerant circulation line through which a refrigerant for cooling the compressed gas is circulated in the precooler; And
A refrigerant heat exchanger provided in the refrigerant circulation line and cooling the refrigerant through heat exchange with the uncompressed evaporative gas to be supplied to the compressor after heat exchange in the heat exchanger. The method of claim 1,
In the refrigerant circulation line, a refrigerant compressor compressing the refrigerant discharged from the precooler; And a refrigerant condenser for cooling the refrigerant compressed by the refrigerant compressor;
The refrigerant compressed and cooled through the refrigerant compressor and the refrigerant condenser is introduced into the refrigerant heat exchanger, further cooled, and then introduced into the precooler. The method of claim 2, wherein the reliquefaction line
A decompression device for further cooling by decompressing the compressed gas cooled through the precooler and the heat exchanger; And
A gas-liquid separator for receiving the boil-off gas reduced by the decompression device and separating the gas-liquid; The method of claim 3,
A flash gas line connected from the gas-liquid separator to a front end of the heat exchanger of the boil-off gas supply line; further comprising,
The flash gas separated in the gas-liquid separator joins the flow of the uncompressed evaporative gas to be introduced from the storage tank to the heat exchanger through the flash gas line, and the liquefied gas separated in the gas-liquid separator is supplied to the storage tank. Boil-off gas treatment system of a ship, characterized in that. The method according to any one of claims 1 to 4,
The compressor is provided as a multistage compressor that receives the boil-off gas and compresses it at a fuel supply pressure of the main engine through a plurality of compressors,
A fuel supply line connected from the intermediate stage of the multistage compressor to the onboard power generation engine; further comprising, the boil-off gas compressed through a part of the compressor of the multistage compressor is supplied to the power generation engine having a lower fuel supply pressure than the main engine. Boil-off gas treatment system of a ship, characterized in that the. The boil-off gas generated from the storage tank in which the liquefied gas is stored in the ship is compressed with a compressor at the fuel supply pressure of the main engine on board
Among the boil-off gas compressed by the compressor, the boil-off gas not supplied as fuel of the main engine is precooled by heat exchange with a refrigerant in a pre-cooler, heat-exchanged with the uncompressed boil-off gas to be introduced into the compressor in a heat exchanger to cool, and depressurize Re-liquefied by additional cooling and re-stored in the storage tank,
The refrigerant supplied to the precooler circulates along a refrigerant circulation line, and is cooled by heat exchange with the uncompressed boil-off gas to be supplied to the compressor after heat exchange in the heat exchanger. The method of claim 6,
The refrigerant is compressed, cooled, and condensed after passing through a precooler, and the condensed refrigerant is further cooled by heat exchange with the uncompressed evaporative gas, and then introduced into the precooler and circulates along the refrigerant circulation line. Boil-off gas treatment method. The method of claim 7,
After compression in the compressor, the boil-off gas cooled through the pre-cooler and the heat exchanger is further cooled by reduced pressure, and then gas-liquid is separated, and the liquid is supplied to the storage tank to be stored again, and the separated flash gas is transferred from the storage tank to the Boil-off gas treatment method of a ship, characterized in that joined to the flow of uncompressed boil-off gas to be introduced into a heat exchanger.

Images