KR20230060844A - Boil Off Gas Treatment System For Ship - Google Patents

Abstract

Disclosed is an evaporation gas treatment system for a ship. The evaporation gas treatment system for a ship according to the present invention comprises: a heat exchanger through which evaporation gas generated from liquefied gas stored in the storage tank of a ship passes; a gas supply line supplying the evaporation gas to the heat exchanger; a heater which receives evaporation gas branched from the gas supply line to heat the same; a heating line which is branched from the gas supply line to be joined to the gas supply line by means of the heater; and a turning device which is disposed at the rear end of the joining point of the heating line at the gas supply line. The low-temperature evaporation gas of the gas supply line and the evaporation gas which has passed through the heating line may be mixed in the turning device to be transferred to the heat exchanger. Therefore, thermal stress may be reduced.

Description

Boil Off Gas Treatment System For Ship}

The present invention relates to an evaporation gas processing system of a ship, and more particularly, to evaporation of a ship in which boil-off gas generated in a ship is branched, heated in a heater, mixed with boil-off gas not heated in a heater in a turning device, and transferred to a heat exchanger. It relates to a gas handling system.

Natural gas (natural gas) has methane (methane) as a main component, and there is little emission of environmental pollutants during combustion, so it is attracting attention as an eco-friendly fuel. Liquefied Natural Gas (LNG) is obtained by liquefying natural gas by cooling it to about -163°C under atmospheric pressure, and since its volume is reduced to about 1/600 of that in gaseous state, it is suitable for long-distance transportation through sea. very suitable Therefore, natural gas is mainly stored and transported in the form of liquefied natural gas, which is easy to store and transport.

Since the liquefaction point of natural gas is a cryogenic temperature of about -163 ° C. at atmospheric pressure, it is common for LNG storage tanks to be insulated so that LNG can remain in a liquid state. However, although the LNG storage tank is insulated, there is a limit to blocking external heat, and since external heat is continuously transferred to the LNG storage tank, LNG is continuously stored in the LNG storage tank during the LNG transportation process. It is vaporized and boil-off gas (BOG) is generated.

When boil-off gas is continuously generated in the LNG storage tank, it becomes a factor that increases the internal pressure of the LNG storage tank. If the internal pressure of the storage tank exceeds the set safety pressure, it may cause an emergency situation such as tank rupture, so the boil-off gas must be discharged to the outside of the storage tank using a safety valve. However, boil-off gas is a kind of LNG loss, and since it is an important problem in the transportation efficiency and fuel efficiency of LNG, various methods for treating boil-off gas generated in the storage tank are used.

Recently, a method of using boil-off gas at a fuel demand place such as a ship's engine, a method of re-liquefying boil-off gas and recovering it to a storage tank, or a method of using these two methods in combination have been developed and applied.

In the case of applying a re-liquefaction cycle to re-liquefy boil-off gas in a ship, typical liquefaction methods that can be adopted include processes using an SMR cycle and a C3MR cycle. The C3MR cycle (Propane-precooled Mixed Refrigerant Cycle) is a process of cooling natural gas using a single propane refrigerant, and then liquefying and supercooling it using a mixed refrigerant. It is a process of liquefying natural gas using a mixed refrigerant composed of refrigerants.

Both the SMR cycle and the C3MR cycle are processes using mixed refrigerants. When the refrigerant leaks during the liquefaction process and the composition ratio of the mixed refrigerant changes, the liquefaction efficiency decreases. The composition of the refrigerant must be maintained by filling the components.

As another method of the re-liquefaction cycle for re-liquefying boil-off gas, a single cycle liquefaction process using a nitrogen refrigerant may be used.

Nitrogen refrigerant has a relatively low efficiency compared to a cycle using a mixed refrigerant, but has a high safety because the refrigerant is inert and is easier to apply to ships because there is no phase change of the refrigerant.

In a system that re-liquefies and processes boil-off gas, the cryogenic boil-off gas is introduced as it is to the heat exchanger that cools the boil-off gas at room temperature at the beginning of startup or before sufficient cool-down. When the temperature difference between the heat exchanger and the evaporative gas is large, as in the case of a heat exchanger, a significant thermal stress may be applied, which may cause damage to the device.

The present invention is to solve this problem, and to propose a boil-off gas treatment system capable of reducing the thermal stress applied to the heat exchanger.

According to one aspect of the present invention for solving the above problems, the heat exchanger through which the boil-off gas generated from the liquefied gas stored in the storage tank of the ship passes;

a gas supply line for supplying the boil-off gas to a heat exchanger;

a heater receiving and heating the boil-off gas branched from the gas supply line;

a heating line branching from the gas supply line and joining the gas supply line through the heater; and

Including: a turning device provided at the rear end of the joining point of the heating line in the gas supply line;

There is provided a boil-off gas treatment system of a ship, characterized in that the low-temperature boil-off gas of the gas supply line and the boil-off gas passing through the heating line are mixed in the turning device and transferred to the heat exchanger.

Preferably, the turning device includes a plate portion inserted into or flanged into a pipe of the gas supply line; and a plurality of swirl guide vanes provided inside the plate portion.

Preferably, a strainer provided downstream of the turning device in the gas supply line to filter out foreign substances in the boil-off gas and transfer them to the heat exchanger may be further included.

Preferably, a plurality of swing devices are provided in the gas supply line, and the plurality of swing devices may have different plate shapes and different numbers of swirl blades.

Preferably, a temperature sensor provided downstream of the strainer in the gas supply line to detect the temperature of the boil-off gas introduced into the heat exchanger; A first valve provided in the gas supply line; a second valve provided in the heating line; and a control unit controlling the first and second valves according to the temperature of the boil-off gas detected by the temperature sensor.

Preferably, the boil-off gas passing through the heat exchanger is compressed by a compressor and cooled while passing through the heat exchanger, and the heat exchanger may be a cryogenic heat exchanger.

Preferably, in the heat exchanger, nitrogen refrigerant circulates along a refrigerant circulation line to cool boil-off gas compressed in the compressor.

In the present invention, by allowing the temperature of the boil-off gas introduced into the heat exchanger to be adjusted, even when the temperature of the boil-off gas changes due to the start-up of the re-liquefaction system or a change in the condition of the storage tank, excessive heat is generated in the heat exchanger due to a rapid temperature change. It prevents stress from being generated, prevents device damage, and stably re-liquefies the boil-off gas for processing.

In particular, while maximizing the mixing efficiency of the boil-off gas heated by the heater and the boil-off gas that has not passed through the heater by providing a turning device, it is possible to solve the limitation of installation space.

1 schematically illustrates a boil-off gas treatment system according to a basic embodiment of the present invention.
Figure 2 schematically shows an evaporation treatment system of an extended embodiment of the present invention, which evolves the basic embodiment.
Figure 3 schematically shows the shape of the swing device provided in the system shown in Figure 2.

In order to fully understand the operational advantages of the present invention and the objects achieved by the practice 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. In adding reference numerals to the components of each drawing, it should be noted that the same components are marked with the same numerals as much as possible, even if they are displayed on different drawings.

In one embodiment of the present invention described later, the vessel may be any type of vessel provided with a storage tank for storing liquefied gas. Representatively, ships with self-propelled capabilities such as LNG carriers, liquid hydrogen carriers, and LNG RV (Regasification Vessel), as well as LNG FPSO (Floating Production Storage Offloading) and LNG FSRU (Floating Storage Regasification Unit) Offshore structures that do not have the capability but are floating on the sea may also be included.

In addition, the present embodiment can be transported by liquefying the gas at a low temperature, and can be applied to a re-liquefaction cycle of all types of liquefied gas in which boil-off gas is generated in a stored state. 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. may be gas. However, in the embodiment to be described later, it will be described as an example in which LNG, which is a representative liquefied gas, is applied.

1 schematically shows a boil-off gas treatment system of a ship according to a basic embodiment of the present invention.

As shown in FIG. 1, the boil-off gas treatment system of this embodiment compresses the boil-off gas generated from a storage tank (not shown) in which liquefied gas is stored on board with a compressor (not shown), cools it by heat exchange in a heat exchanger, and recycles it. It is a system for returning to the storage tank after liquefaction.

The boil-off gas generated from the liquefied gas stored in the storage tank of the ship is discharged to the vapor header and supplied to the compressor along the gas supply line, and the gas supply line (GL) is connected from the storage tank to the compressor through the heat exchanger 100, , the uncompressed evaporation gas generated in the storage tank supplies cold heat to the heat exchanger.

The boil-off gas compressed by the compressor is introduced into the heat exchanger 100 again and cooled by the cooling heat of the uncompressed boil-off gas passing through the gas supply line.

In addition to the uncompressed boil-off gas, a separate refrigerant circulating along the refrigerant circulation line may be additionally supplied to the heat exchanger. The refrigerant of the refrigerant circulation line may be nitrogen, and a refrigerant compressor and a refrigerant expander for compressing the nitrogen refrigerant are provided in the refrigerant circulation line. The nitrogen refrigerant in the refrigerant circulation line is compressed in the refrigerant compressor, cooled through the heat exchanger, expanded and cooled in the refrigerant expander, supplied as a refrigerant to the heat exchanger, and circulates through the refrigerant circulation line. Accordingly, in the heat exchanger 100, four flows of evaporation gas compressed in the compressor, uncompressed evaporation gas to be introduced into the compressor, refrigerant expanded and cooled in the refrigerant expander, and refrigerant compressed in the refrigerant compressor can be heat exchanged.

The boil-off gas cooled while passing through the heat exchanger is gas-liquid separated, and the separated re-liquefied gas is recovered to the storage tank.

However, when the boil-off gas is cooled and re-liquefied in the heat exchanger, the thermal stress of the heat exchanger when the temperature of the boil-off gas changes due to the start-up of the re-liquefaction system or a change in the condition of the storage tank ) can cause

In particular, even if a cryogenic heat exchanger such as a plate-fin cryogenic heat exchanger (CRYOGENIC HEAT EXCHANGER, CHE) is installed in accordance with the boil-off gas and nitrogen refrigeration cycle from cryogenic LNG, boil-off gas generated in the storage tank and introduced into the heat exchanger The temperature of is around -100℃, and evaporation gas below -130℃ can be generated in the storage tank depending on the condition of the storage tank, so the heat exchanger is subjected to significant thermal stress. In particular, the heat exchanger and the boil-off gas, such as when the cryogenic boil-off gas is introduced as it is to the heat exchanger at room temperature at the beginning of startup or before sufficient cool-down is achieved by operating the re-liquefaction system that has been stopped. The greater the temperature difference between the heat exchangers, the greater the thermal stress (thermal stress) is applied to the heat exchanger, which may cause device damage such as fatigue failure of the heat exchanger and a reduction in life.

In order to solve this problem, the present embodiment configures a heating line (PHL) capable of adjusting the temperature of the boil-off gas introduced into the heat exchanger in the gas supply line (GL) at the front end of the heat exchanger 100, thereby reducing thermal stress in the heat exchanger. make it possible to minimize

As shown in FIG. 1, the heating line (PHL) for heating all or part of the boil-off gas upstream of the heat exchanger 100 of the gas supply line (GL) and supplying it to the front end of the heat exchanger of the gas supply line (GL) is branched, and the heating A heater (or heat exchanger, 200) for heating the boil-off gas is provided in the line. As the heat source of the heater, for example, glycol water, steam, seawater, or fresh water may be used.

In the gas supply line (GL), a first valve (TV1) is provided between the branching point and the joining point of the heating line, and a second valve (TV2) is provided in the heating line (HL), so that the heat exchanger is directly introduced from the storage tank. It controls the amount of boil-off gas that is heated through the boil-off gas and the heater and introduced into the heat exchanger. In the gas supply line (GL), a temperature sensor (TE) for detecting the temperature of the boil-off gas introduced into the heat exchanger is provided at the rear end of the joining point of the heating line, and the control unit (TI, TIC) is provided according to the temperature of the boil-off gas detected by the temperature sensor. ) can control the opening and closing of the first and second valves TV1 and TV2. A strainer 300 is additionally provided in the gas supply line to filter foreign substances in the boil-off gas and transfer them to the heat exchanger.

In this way, all or part of the evaporation gas supplied from the storage tank is branched to the heating line (PHL) and heated in the heater 200, and the evaporation gas flow without passing through the heater is mixed in the mixing section (ML) of the gas supply line. It is possible to reduce the thermal stress of the heat exchanger by controlling the temperature of the boil-off gas supplied to the heat exchanger and introduced into the heat exchanger. This can prevent thermal fatigue of the heat exchanger and device damage.

FIG. 2 schematically shows a boil-off gas treatment system of an extended embodiment developed from the basic embodiment of FIG. 1, and FIG. 3 schematically shows a shape of a turning device.

In the system of the present extended embodiment, the heating line (PHL) is connected to the gas supply line (GL) so that the boil-off gas heated through the heating line and the low-temperature boil-off gas that has not passed through the heater can be effectively mixed and supplied to the heat exchanger at a more uniform temperature. ), the turning device 400 was provided at the rear end of the joining point, that is, in the mixing section (ML) of the gas supply line. Descriptions of configurations overlapping with those of the above-described basic embodiment will be omitted.

As shown in FIG. 3, the turning devices 400A, 400B, and 400C include donut-shaped plate portions 410a, 410b, and 410c inserted into or flanged into the pipe of the gas supply line, and a plurality of plates provided inside the plate portion. It may be configured in a form equipped with two swirl guide vanes 420a, 420b, and 420c.

In this way, the donut-shaped plate portion is inserted into the pipe of the gas supply line or connected by a flange between the pipe of the gas supply line, thereby solving the restriction on installation space and facilitating installation. In addition, by mixing boil-off gas heated by a plurality of swirl blades provided inside the plate and cryogenic boil-off gas, even if the pipe length of the gas supply line is short, the effectively mixed boil-off gas at a uniform temperature can be supplied to the heat exchanger.

As shown in FIG. 3, the thickness and shape of the plate part of the swirl device, the shape and number of swirl blades, etc. can be variously determined according to the required temperature of boil-off gas, the diameter and length of the gas supply line pipe in which the swirl device is installed, and the like. Accordingly, a plurality of swing devices having different plate shape and number of swing blades may be installed in the gas supply line pipe.

Boiled gas mixed in the turning device 400 may be supplied to the heat exchanger 100 after removing foreign substances through the strainer 300. In this way, by maximizing the mixing efficiency through the system of this extended embodiment and supplying the boil-off gas mixed at a uniform temperature to the heat exchanger, it is possible to prevent thermal fatigue of the heat exchanger and decrease in device life, and to perform the re-liquefaction process. It can operate more stably.

It is obvious to those skilled in the art that the present invention is not limited to the above embodiments and can be variously modified or modified without departing from the technical gist of the present invention. it did

100: heat exchanger
200: heater
300: strainer
400: turning device
GL: gas supply line
PHL: Heating Line

Claims (7)

A heat exchanger through which boil-off gas generated from liquefied gas stored in a storage tank of a ship passes;
a gas supply line for supplying the boil-off gas to a heat exchanger;
a heater receiving and heating the boil-off gas branched from the gas supply line;
a heating line branching from the gas supply line and joining the gas supply line through the heater; and
Including: a turning device provided at the rear end of the joining point of the heating line in the gas supply line;
The vessel's boil-off gas treatment system, characterized in that the low-temperature boil-off gas of the gas supply line and the boil-off gas passing through the heating line are mixed in the turning device and transferred to the heat exchanger. The method of claim 1, wherein the turning device
a plate portion inserted into or flanged into the pipe of the gas supply line; and
A plurality of swirl guide vanes provided on the inside of the plate portion: The boil-off gas treatment system of the ship, characterized in that it comprises. According to claim 2,
A ship's boil-off gas treatment system further comprising: a strainer provided downstream of the turning device in the gas supply line to filter out foreign substances in the boil-off gas and transfer them to the heat exchanger. According to claim 3,
A plurality of turning devices are provided in the gas supply line,
The boil-off gas treatment system of a ship, characterized in that the plate part shape and the number of swirl blades of the plurality of swing devices can be provided differently. According to claim 3,
a temperature sensor provided downstream of the strainer in the gas supply line to detect the temperature of the boil-off gas introduced into the heat exchanger;
A first valve provided in the gas supply line;
a second valve provided in the heating line; and
A control unit for controlling the first and second valves according to the temperature of the boil-off gas detected by the temperature sensor: Ship's boil-off gas treatment system further comprising a. According to any one of claims 1 to 5,
The boil-off gas passing through the heat exchanger is compressed in a compressor and then cooled while passing through the heat exchanger.
The heat exchanger is a ship's boil-off gas treatment system, characterized in that the cryogenic heat exchanger (Cryogenic Heat Exchanger). According to claim 6,
In the heat exchanger, nitrogen refrigerant circulates along the refrigerant circulation line and cools the boil-off gas compressed in the compressor.

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