KR102614526B1 - Boil-Off Gas Reliquefaction System For Ship - Google Patents

Abstract

The ship's boil-off gas re-liquefaction system is launched. The ship's boil-off gas re-liquefaction system of the present invention includes a first compressor that receives and compresses boil-off gas generated from liquefied gas in a cargo tank provided on the ship, and a second compressor that further compresses the boil-off gas compressed in the first compressor. It includes a compression unit that compresses the boil-off gas in multiple stages; an intercooler that receives compressed boil-off gas from the first compressor, cools it, and then supplies it to the second compressor; A condenser that cools the boil-off gas compressed through the compression unit; A liquefied gas recovery line that transfers the liquefied gas cooled and condensed in the condenser to the cargo tank after recovering cold heat through the intercooler; And it may include a first temperature control line that branches off the liquefied gas from the liquefied gas recovery line and sprays it onto the upper part of the intercooler.

Description

Boil-Off Gas Reliquefaction System For Ship}

The present invention relates to a ship's boil-off gas re-liquefaction system, and more specifically, to a ship's boil-off gas re-liquefaction system that compresses, re-liquefies, and recovers boil-off gas generated from liquefied gas in a cargo tank.

Consumption of liquefied gases such as LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas) is rapidly increasing worldwide. Liquefied gas is transported in a gaseous state through gas pipes on land or at sea, or is stored in a liquefied state on a liquefied gas carrier and transported to a distant consumer. Liquefied gases such as LNG or LPG are obtained by cooling natural gas or petroleum gas to extremely low temperatures (approximately -163°C in the case of LNG), and their volume is significantly reduced compared to the gaseous state, making them very suitable for long-distance transportation by sea.

Meanwhile, conventional LPG carriers, etc., adopt a fuel supply system that uses relatively inexpensive heavy oil such as bunker C oil as propulsion fuel for ships. This heavy oil fuel supply system has the international exhaust gas emissions associated with the use of heavy oil fuel. Due to strengthened regulations, a separate low-sulfur heavy fuel fuel tank (LSHFO tank) had to be installed, and the demand for an eco-friendly fuel supply system that meets international environmental regulation standards has increased.

Recently, the application of fuel supply systems that use LPG or LNG and boil-off gas generated therefrom as propulsion fuel is increasing in LPG or LNG carriers, and in accordance with the strengthening of international exhaust gas emission regulations, LNG or LNG is used not only in LPG or LNG carriers but also in general ships. The number of ships using fuel as propulsion fuel is increasing.

In particular, LPG is easier to store than LNG, which is liquefied at extremely low temperatures, and does not fall significantly in SPECIFIC ENERGY and ENERGY DENSITY compared to existing HFO, and has excellent savings in SOX, NOX, CO2, and PM compared to existing HFO.

The liquefaction temperature of petroleum gas is low at about -42°C at normal pressure, and it can be stored in liquid form up to a temperature of about 45°C at 18 bar and up to 20°C at 7 bar. Since LPG evaporates when the atmospheric pressure is higher than -42℃, the ship's LPG storage tank is insulated. However, because external heat is continuously transferred to LPG, LPG is continuously vaporized within the LPG storage tank during the LPG transport process, generating boil-off gas within the LPG storage tank.

If evaporation gas accumulates in the LPG storage tank, the internal pressure of the storage tank may increase excessively, which may pose a threat to the safety of the ship and crew. Therefore, the LPG storage tank must be equipped with a pressure-resistant structure and evaporation gas in order to handle the evaporation gas generated within the tank. Use a gas reliquefaction device.

The present invention reliquefies the boil-off gas generated from liquefied gas such as LPG and returns it to a storage tank to control tank pressure, reduce costs by reducing the number of required equipment, and increase the price competitiveness of ships. I would like to propose a system.

According to one aspect of the present invention for solving the above-described problem, a first compressor that receives and compresses boil-off gas generated from the liquefied gas of a cargo tank provided on a ship, and a first compressor that further compresses the boil-off gas compressed in the first compressor A compression unit including a second compressor and compressing the boil-off gas in multiple stages;

an intercooler that receives compressed boil-off gas from the first compressor, cools it, and then supplies it to the second compressor;

A condenser that cools the boil-off gas compressed through the compression unit;

A liquefied gas recovery line that transfers the liquefied gas cooled and condensed in the condenser to the cargo tank after recovering cold heat through the intercooler; and

A ship's boil-off gas re-liquefaction system is provided, including a first temperature control line that branches off the liquefied gas from the re-liquefied gas recovery line and sprays it onto the upper part of the intercooler.

Preferably, a first temperature sensor detects the temperature of the evaporation gas to be cooled in the intercooler and supplied to the second compressor; And a first temperature control valve that controls the flow rate of the liquefied gas to be branched to the first temperature control line, and controls the first temperature control valve according to the boil-off gas temperature detected by the first temperature sensor to control the liquefied gas flow rate to be branched to the first temperature control line. The inlet temperature of the boil-off gas of the second compressor can be adjusted.

Preferably, a liquid level control line branched from the liquefied gas recovery line to supply liquefied gas into the intercooler; A liquid level sensor that detects the liquefied gas liquid level inside the intercooler; And a liquid level control valve that opens and closes the liquid level control line, wherein the liquid level control valve is controlled according to the liquefied gas level detected by the liquid level sensor, so that the liquefied gas level inside the intercooler is maintained in a certain range, The boil-off gas compressed in the first compressor may be cooled by being supplied to the liquefied gas filled in the intercooler through the injection nozzle.

Preferably, a knock-out drum that receives the boil-off gas discharged from the cargo tank and supplies the gas to the first compressor of the compression unit; And a second temperature control line branched from the liquefied gas recovery line downstream of the intercooler and connected to the knockout drum, wherein the liquefied gas of the liquefied gas recovery line flows into the lower part of the knockout drum and is supplied to the compression unit. The evaporation gas can be cooled.

Preferably, a second temperature sensor detects the temperature of the evaporation gas compressed in the first compressor and introduced into the intercooler; And a second temperature control valve that controls the flow rate of the liquefied gas to be branched to the second temperature control line, and controls the second temperature control valve according to the boil-off gas temperature detected by the second temperature sensor to control the liquefied gas flow rate to be branched to the second temperature control line. The flow rate of liquefied gas flowing into the lower part of the knockout drum can be adjusted.

Preferably, the re-liquefied gas recovery line further includes a re-liquefied gas receiver provided upstream of the intercooler to receive the re-liquefied gas cooled in the condenser, and the gas can be separated from the re-liquefied gas receiver and discharged to the vent line. there is.

Preferably, the liquefied gas includes LPG (Liquefied Petroleum Gas), and the compression unit may be a three-stage centrifugal compressor or a three-stage reciprocating compressor.

In the present invention, the boil-off gas generated from the liquefied gas stored in the cargo tank is compressed, cooled, re-liquefied, and then recovered in the cargo tank, taking into account the multi-component boil-off gas with a large change in physical properties, maximizing the cooling effect of the intercooler and reducing the power of the compression unit. The reliquefaction rate can be increased while reducing consumption.

Furthermore, through the present invention, the number of required equipment can be reduced to reduce equipment installation costs and increase the price competitiveness of the ship. By re-liquefying the boil-off gas and returning it to the cargo tank, the pressure in the cargo tank can be safely maintained and the LPG transport rate can be increased. .

Figure 1 shows an example of a system for re-liquefying boil-off gas generated from LPG.
Figure 2 schematically shows a ship's boil-off gas reliquefaction system according to a basic embodiment of the present invention.
Figure 3 schematically shows a ship's boil-off gas re-liquefaction system according to an expanded embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objectives achieved by practicing 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 structure and operation of a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Here, in adding reference numerals to components in each drawing, it should be noted that identical components are indicated with the same reference numerals as much as possible, even if they are shown in different drawings.

In the embodiments of the present invention described later, the ship refers to all types of ships, representatively such as LPG carrier, VLGC (Very Large Gas Carrier), LNG carrier, liquid hydrogen carrier, and LNG RV (Regasification Vessel). In addition to ships with self-propulsion capabilities, it may also include offshore structures that do not have propulsion capabilities but are floating at sea, such as LNG Floating Production Storage Offloading (FPSO) and LNG Floating Storage Regasification Unit (FSRU).

In addition, the present embodiments can be liquefied at low temperatures and transported, and can be applied to all types of liquefied gas re-liquefaction systems 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. It may be gas, ammonia, etc. However, in the embodiments described later, the application of LPG, one of the representative liquefied gases, will be described as an example.

Figure 1 shows an example of a system for re-liquefying boil-off gas generated from LPG.

As shown in Figure 1, the boil-off gas generated in the cargo tank is sent to the compressor 20 through the KO drum 10, compressed, cooled in the condenser 50, and re-liquefied, and then re-liquefied gas container 60 and intercooler ( 30), etc., and then return it to the cargo tank.

In order to compress the boil-off gas to the pressure necessary for re-liquefaction, the compressor 20 may be configured to include multiple stages, for example, a three-stage compressor, and is usually operated at a constant speed. In order to increase compressor operation efficiency, the boil-off gas compressed in the first stage compressor is cooled through an intercooler before being introduced to the second stage compressor, and the intercooler can use the cold heat of re-liquefied LPG.

However, the boil-off gas generated from LPG in cargo tanks contains various components such as Ethane, Propylene, and Ammonia in addition to propane and butane (I-Butane/N-Butane), and the physical properties of the boil-off gas vary greatly.

In order to effectively cool the multi-component boil-off gas, which has a large change in physical properties, to increase compressor efficiency and to increase liquid efficiency, a trim cooler 40 is installed to additionally cool the boil-off gas cooled in the intercooler and introduced into the two-stage compressor. A separate intercooler may also be installed between the compressor and the 3-stage compressor.

However, due to the characteristics of the compressor that operates at a constant speed and the large variation in the inflow of multi-component boil-off gas, it is difficult to effectively control the temperature of the boil-off gas introduced into the two-stage compressor through the intercooler and trim cooler, and the boil-off gas is not cooled sufficiently. When it flows into the compressor, the compressor power consumption increases and the final liquid efficiency decreases. Accordingly, complete re-liquefaction of boil-off gas is virtually difficult, and unliquefied gas is processed through a separate vent gas system. The reliquefaction system according to an embodiment of the present invention, which will be described later, is designed to improve these problems and effectively cool multi-component boil-off gas with large changes in physical properties, thereby reducing compressor power consumption, increasing reliquefaction efficiency, and reducing device costs. .

Figure 2 schematically shows a ship's boil-off gas re-liquefaction system according to a basic embodiment of the present invention, and Figure 3 schematically shows a ship's boil-off gas re-liquefaction system according to an expanded embodiment of the present invention.

As shown in Figure 2, the boil-off gas re-liquefaction system of this embodiment includes a first compressor (100A) that receives and compresses the boil-off gas generated from the liquefied gas of the cargo tank provided on the ship, and the vapor compressed in the first compressor. It includes a second compressor (100B) that further compresses the gas, a compression unit (100) that compresses the boil-off gas in multiple stages, and an intercooler (200) that receives the compressed boil-off gas from the first compressor, cools it, and supplies it to the second compressor. , a condenser (300) that cools the boil-off gas compressed through the compression unit, a re-liquid gas recovery line (RL) that transfers the liquefied gas cooled and condensed in the condenser to a cargo tank after recovering cold heat through an intercooler, and liquefying the liquefied gas in the re-liquid gas recovery line. It includes a first temperature control line (TL1) that branches out the gas and sprays it onto the upper part of the intercooler.

Upstream of the compression section of the gas re-liquefaction line (GL), a knock-out drum (500) is provided that receives the boil-off gas discharged from the cargo tank and supplies the gas to the compression section (100). In addition to propane and butane (I-Butane/N-Butane), evaporation gas generated from cargo tanks may contain various components such as Ethane, Propylene, and Ammonia. In this way, the multi-component boil-off gas generated in the cargo tank is discharged to the knockout drum 500 along the gas re-liquefaction line (GL), and the gas is transferred from the knockout drum to the first compressor of the compression unit 100 and goes through a re-liquefaction process. After being reliquefied, it is recovered into a cargo tank.

The compression unit 100 includes a first compressor (100A) that receives and compresses the boil-off gas, a second compressor (100B) that further compresses the boil-off gas compressed in the first compressor, and a second compressor (100B) that compresses the boil-off gas compressed in the second compressor. It may be a three-stage multi-stage compressor including a third compressor (100C) that further compresses and transfers it to the condenser. The compression unit may be composed of a three-stage centrifugal compressor including first to third compressors, and may be composed of a three-stage reciprocating compressor with a reciprocating piston as in the expanded embodiment shown in FIG. 3. there is. The number of stages in the compression section may be added as needed.

The boil-off gas compressed through the compression unit is supplied to the condenser 300 and cooled.

In the condenser 300, the boil-off gas compressed in the compression unit 100 is cooled through heat exchange to re-liquefy it, and as a heat source for cooling the boil-off gas, seawater, which is easy to obtain on a ship, can be used, for example.

The re-liquefied gas cooled in the condenser 300 is received into the re-liquefied gas receiver 400 along the re-liquefied gas recovery line, and the liquid from the re-liquefied gas receiver is recovered to the cargo tank along the re-liquefied gas recovery line (RL), and the re-liquefied gas is returned to the cargo tank. Vent gas separated from the receiver is discharged through the vent line.

The liquid gas recovery line (RL) is connected to the cargo tank through the intercooler (200). In the intercooler 200, heat is exchanged between the boil-off gas compressed in the first compressor 100A and the re-liquefied gas to be transferred to the cargo tank. As shown in Figure 2, the boil-off gas compressed in the first compressor (100A) of the compression section is transferred to the intercooler (200) and intermediately cooled by the re-liquefied gas transferred from the re-liquefied gas receiver (400) to the cargo tank. It is supplied to the second compressor (100B) and compressed, further compressed again in the third compressor (100C), and then supplied to the condenser (300) to cool and re-liquefy.

A liquid level control line (LL) is provided that branches off from the liquefied gas recovery line (RL) and supplies liquefied gas into the intercooler 200, a liquid level sensor (LIC) that detects the liquefied gas level inside the intercooler, and a liquid level control line. A liquid level control valve (LV) is provided to open and close the . Depending on the liquefied gas level detected by the liquid level sensor, the liquid level controller (LIC) controls the liquid level control valve to maintain the liquefied gas level inside the intercooler within a certain range.

The boil-off gas compressed in the first compressor 100A may be supplied to the liquefied gas filled in the intercooler 200 through the injection nozzle. The liquefied gas passing through the re-liquid gas receiver and the re-liquid gas recovery line can also supply cold heat to the inside of the intercooler by passing through a heat conduction pipe filled with liquefied gas at the bottom of the intercooler, and the boil-off gas compressed in the first compressor is cooled in the intercooler.

Furthermore, in this embodiment, considering the multi-component boil-off gas with a large change in physical properties, the cooling effect of the intercooler is maximized to reduce the power consumption of the compression unit and increase the re-liquefaction rate, and the inlet temperature of the boil-off gas supplied from the intercooler to the second compressor is finely adjusted. Adjustable configurations have been added.

For this purpose, the system of this embodiment includes a first temperature control line (TL1) that branches off the liquefied gas from the liquefied gas recovery line (RL) and sprays it onto the upper part of the intercooler (200), and an evaporation gas that is cooled in the intercooler and supplied to the second compressor. It includes a first temperature sensor (TIT1) that detects the temperature, and a first temperature control valve (TV1) that controls the flow rate of liquefied gas to be branched to the first temperature control line.

According to the temperature of the boil-off gas at the rear of the intercooler detected by the first temperature sensor (TIT1), the first temperature control unit (TI1) controls the first temperature control valve (TV1) to control the first temperature of a portion of the liquefied gas in the re-liquid gas recovery line. By branching into a line and spraying it onto the upper part of the intercooler, the evaporative gas cooled at the bottom of the intercooler can be additionally cooled to control the inlet temperature of the evaporative gas into the second compressor. A spray nozzle for additional cooling may be provided at the end of the first temperature control line to spray liquefied gas.

In this way, by increasing the cooling efficiency of the boil-off gas to be introduced into the second compressor after compression in the first compressor of the compression section in the intercooler and finely controlling the temperature of the boil-off gas at the front of the second compressor, a separate intermediate gas is created between the second compressor and the third compressor. Since there is no need to install additional cooling devices, device costs can be reduced, compression unit power consumption can be reduced, and liquid efficiency can be increased.

Furthermore, through the system of this embodiment, the boil-off gas is re-liquefied and recovered into the cargo tank, thereby safely maintaining the pressure of the cargo tank and increasing the LPG transport rate.

The expanded embodiment system shown in FIG. 3 is configured to further reduce the power consumption of the compression section and increase the re-liquefaction rate by lowering the temperature of the boil-off gas introduced from the knockout drum into the first compressor of the compression section.

To this end, as shown in FIG. 3, the expanded embodiment system additionally configures a second temperature control line (TL2) branched from the liquid gas recovery line (RL) downstream of the intercooler 200 and connected to the knockout drum. , a portion of the liquefied gas from the liquefied gas recovery line can be sprayed into the knockout drum 500 to cool the boil-off gas to be supplied to the compression unit 100.

This system includes a second temperature sensor (TIT2) that detects the temperature of the evaporation gas compressed in the first compressor and introduced into the intercooler, and a second temperature control valve (TV2) that controls the flow rate of liquefied gas to be branched to the second temperature control line. ) further includes. The liquefied gas returned to the cargo tank through the liquefied gas recovery line may be in a sub-cooled state. According to the temperature of the evaporation gas at the rear end of the first compressor detected by the second temperature sensor, the second temperature control valve is controlled to branch some of the low-temperature liquefied gas in a supercooled state downstream of the liquid gas recovery line to the second temperature control line and to the bottom of the knockout drum. By cooling the boil-off gas by introducing it, the temperature of the boil-off gas inlet into the first compressor of the compression unit can be adjusted.

Descriptions of configurations that overlap with those of the basic embodiment described above will be omitted.

In this way, a part of the low-temperature liquefied gas downstream of the liquefied gas recovery line is branched to the second temperature control line and sent to the knockout drum to cool the boil-off gas to be supplied to the compression section, and a part of the low-temperature liquefied gas is sent to the upper part of the intercooler through the first temperature control line. By finely controlling the inlet temperature of the boil-off gas from the second compressor by spraying, the power consumption of the compression section can be further reduced and the final re-liquefaction rate can be increased.

It is clear to those skilled in the art that the present invention is not limited to the above-mentioned embodiments, and that it can be implemented with various modifications or variations without departing from the technical gist of the present invention. It is self-evident.

100: Compression part
200: intercooler
300: Condenser
400: Re-liquid gas receiver
500: Knockout Drum

Claims (7)

It includes a first compressor that receives and compresses boil-off gas generated from liquefied gas in a cargo tank provided on the ship, and a second compressor that further compresses the boil-off gas compressed in the first compressor, and a compression unit that compresses the boil-off gas in multiple stages. ;
An intercooler that receives compressed boil-off gas from the first compressor, cools it, and then supplies it to the second compressor;
A condenser that cools the boil-off gas compressed through the compression unit;
A liquefied gas recovery line that transfers the liquefied gas cooled and condensed in the condenser to the cargo tank after recovering cold heat through the intercooler;
A first temperature control line that branches off the liquefied gas from the liquefied gas recovery line and sprays it onto the upper part of the intercooler;
a first temperature sensor that detects the temperature of evaporation gas to be cooled in the intercooler and supplied to the second compressor; and
It includes a first temperature control valve that controls the flow rate of liquefied gas to be branched to the first temperature control line,
A ship's boil-off gas reliquefaction system, characterized in that the boil-off gas inlet temperature of the second compressor is controlled by controlling the first temperature control valve according to the boil-off gas temperature detected by the first temperature sensor. According to clause 1,
The compression unit further includes a third compressor that further compresses the boil-off gas compressed in the second compressor and transfers it to the condenser,
A ship's boil-off gas reliquefaction system, characterized in that no separate intermediate cooling device is installed between the second compressor and the third compressor by finely controlling the temperature of the boil-off gas in front of the second compressor. According to clause 2,
A liquid level control line branched from the liquefied gas recovery line and supplying liquefied gas into the intercooler;
A liquid level sensor that detects the liquefied gas liquid level inside the intercooler; and
It further includes a liquid level control valve that opens and closes the liquid level control line,
By controlling the liquid level control valve according to the liquefied gas liquid level detected by the liquid level sensor, the liquefied gas liquid level inside the intercooler is maintained within a certain range,
A ship's boil-off gas re-liquefaction system, characterized in that the boil-off gas compressed in the first compressor is supplied to the liquefied gas filled in the intercooler through a spray nozzle and cooled. According to clause 2,
A knock-out drum that receives the evaporation gas discharged from the cargo tank and supplies the gas to the first compressor of the compression unit; and
It further includes a second temperature control line branched from the liquid gas recovery line downstream of the intercooler and connected to the knockout drum,
A ship's boil-off gas re-liquefaction system, characterized in that the boil-off gas to be supplied to the compression unit can be cooled by flowing the liquefied gas from the re-liquid gas recovery line into the lower part of the knockout drum. According to clause 4,
a second temperature sensor that detects the temperature of the evaporation gas compressed in the first compressor and introduced into the intercooler; and
It further includes a second temperature control valve that controls the flow rate of the liquefied gas to be branched to the second temperature control line,
A ship's boil-off gas re-liquefaction system, characterized in that the flow rate of liquefied gas flowing into the lower part of the knockout drum is controlled by controlling the second temperature control valve according to the boil-off gas temperature detected by the second temperature sensor. According to any one of claims 1 to 5,
It further includes a re-liquefied gas receiver provided upstream of the intercooler in the re-liquefied gas recovery line to receive the re-liquefied gas cooled in the condenser,
A ship's boil-off gas re-liquefaction system, wherein the gas is separated from the re-liquid gas receiver and discharged into the vent line. According to clause 6,
The liquefied gas includes LPG (Liquefied Petroleum Gas),
A ship's boil-off gas reliquefaction system, wherein the compression unit is a three-stage centrifugal compressor or a three-stage reciprocating compressor.

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