KR102370608B1 - Control System Of Boil Off Gas Treatment System - Google Patents

Abstract

A control system for a boil-off gas treatment system is disclosed. The control system of the boil-off gas treatment system of the present invention is a control system of a treatment system for treating BOG (Boil-Off Gas) generated in an LNG storage tank provided in a ship or an offshore structure, wherein the treatment system includes the LNG storage tank A compander (compander) comprising: an expander receiving and compressing BOG from the supply and adiabatic expansion by receiving BOG, and a BOG compressor connected to the expander and compressing the BOG by expansion force; an HD (High Duty) compressor unit for additionally compressing the BOG compressed by the BOG compressor of the compander; a precooler in which the BOG compressed in the HD compressor unit is cooled by heat exchange with the BOG to be introduced from the LNG storage tank to the BOG compressor; a main heat exchanger in which the BOG compressed through the HD compressor unit is cooled by heat exchange with the BOG adiabatically expanded from the expander of the compander; an expansion means for receiving the BOG cooled from the main heat exchanger or LNG condensed from the BOG for adiabatic expansion; and a re-liquefaction processing unit including a flash drum for gas-liquid separation by receiving the BOG or LNG from the expansion means; and a gas management system (GMS) control unit for controlling the pressure of the LNG storage tank by adjusting the reliquefaction processing amount of the reliquefaction processing unit and the fuel supply amount to the fuel consumption destination.

Description

Control System Of Boil Off Gas Treatment System

The present invention relates to a control system for a boil-off gas treatment system, and more particularly, to a precooler in which BOG compressed in an HD compressor unit is cooled by heat exchange with BOG to be introduced into a BOG compressor of a compander, and a boost compressed in the boost compressor unit. BOG controls the pressure of the LNG storage tank by controlling the BOG reliquefaction processing amount of the reliquefaction processing unit including the BOG cooled by adiabatic expansion from the expander of the compander and the main heat exchanger cooled by heat exchange and the BOG fuel supply amount to the fuel consumer It relates to a control system of a boil-off gas treatment system including a gas management system (GMS) control unit.

In recent years, the consumption of liquefied gas such as LNG (Liquefied Natural Gas) or LPG (Liquefied Petroleum Gas) is rapidly increasing worldwide. The liquefied gas obtained by liquefying the gas at a low temperature has the advantage of increasing the storage and transport efficiency because the volume is very small compared to the gas. In addition, liquefied gas, including liquefied natural gas (hereinafter referred to as "LNG"), can remove or reduce air pollutants during the liquefaction process, so it can be viewed as an eco-friendly fuel that emits less air pollutants during combustion.

For example, liquefied natural gas is a colorless and transparent liquid that can be obtained by cooling natural gas containing methane as a main component to about -162°C and liquefying it, and has a volume of about 1/600 compared to natural gas. Therefore, when transporting natural gas by liquefying it as LNG, it is possible to transport it very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -162 ℃ atmospheric pressure, LNG is sensitive to temperature changes and evaporates easily. For this reason, the LNG storage tank of the LNG carrier is insulated, but external heat is continuously transferred to the LNG storage tank, so the LNG is continuously naturally vaporized in the LNG storage tank during the LNG transportation process and boils off gas (Boil-Off Gas, BOG) occurs. This is also the case for other low-temperature liquefied gases such as ethane.

BOG is a type of loss and is an important problem in transport efficiency. In addition, when the boil-off gas is accumulated 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 BOG generated in the storage tank are being studied. Recently, for the treatment of BOG, the method of re-liquefying BOG and returning it to the storage tank, and the energy source of fuel consumption such as the engine of a ship, etc. How to use, etc. is being used.

The present applicant has proposed a reliquefaction apparatus using the cooling heat of BOG itself by using BOG as a cooling fluid in Application No. 10-2013-0081029 on July 10, 2013. The Partial Re-liquefaction System (PRS) proposed by the patent of No. 10-2013-0081029 is a device that reliquefies the BOG discharged to the outside of the storage tank using BOG itself as a refrigerant. It is evaluated as an innovative technology that can efficiently reduce the overall BOR (Boil-off Rate) of the liquefied natural gas storage tank because it can reliquefy the boil-off gas without installing a separate reliquefaction device.

1 is a schematic configuration diagram of the reliquefaction apparatus of the present applicant's application number 10-2013-0081029 invention. The process of re-liquefying boil-off gas in the re-liquefaction apparatus is briefly described with reference to FIG. 1 as follows.

BOG discharged from the storage tank 10 may be compressed through a multi-stage compressor including a plurality of compressors 30 and an intercooler (not shown). In the compressor shown in FIG. 1, five stages of compression and cooling are alternately performed while passing through the five compressors 30 and are compressed. A portion of the boil-off gas that has undergone the compression process is sent to a high-pressure fuel consumer (E1) that requires high-pressure fuel, for example, a high-pressure engine such as a ME-GI engine, and the remaining amount of the compressed gas is transferred to the heat exchanger (20). send to The boil-off gas (line A) supplied to the heat exchanger 20 through the multi-stage compression process is discharged from the storage tank 10 and exchanges heat with the boil-off gas (line B) to be introduced into the compressor in the heat exchanger 20 . Since the temperature of the BOG increases through the compression process, the BOG discharged from the storage tank 10 before compression is used as a refrigerant to cool the compressed BOG.

After compression, the boil-off gas (line C) cooled through heat exchange in the heat exchanger 20 is reduced in pressure in the pressure reducing device 40 . At least a portion of the BOG compressed while passing through the heat exchanger 20 and the pressure reducing device 40 is reliquefied. In the gas-liquid separator 50, the reliquefied liquefied natural gas and the BOG remaining in a gaseous state are separated, and the reliquefied BOG is returned to the storage tank 10, and the BOG (D line) remaining in the gaseous state is It is sent back to the heat exchanger 20 together with the boil-off gas (B line) discharged from the storage tank 10 .

When there is a low-pressure fuel consumer that is supplied with gas at a lower pressure than the gas that has passed through all of the multi-stage compressors, for example, three compressors of the five compressors 30 that have passed through only a part of the multi-stage compressor are used to convert a part of the gas to such a low pressure It can be supplied as fuel to the fuel consumer E2. In addition, if the amount of BOG generated from the storage tank 10 is large, and it is supplied as fuel to high-pressure and low-pressure fuel consumers, and remains after re-liquefaction by a partial re-liquefaction device, it is vented or a gas combustion device (GCU). ; to the Gas Combustion Unit) for incineration.

The applicant's prior invention is a device that can effectively process boil-off gas generated in a storage tank. In order to configure such a device, an expensive compressor is configured, so the equipment cost is high. The operation cost was high as the power consumption was high.

The present invention intends to propose a boil-off gas treatment system capable of more effectively compressing and re-liquefying BOG by solving this problem.

According to one aspect of the present invention, in a control system of a processing system for processing BOG (Boil-Off Gas) generated in an LNG storage tank provided in a ship or an offshore structure,

The processing system may include: a re-liquefaction processing unit including a compander, a high duty (HD) compressor, a precooler, a main heat exchanger, a boost compressor, and an expansion means; a fuel consumer provided in the ship or offshore structure and supplied with compressed BOG through all or a part of the HD compressor; and a GMS (Gas Management System) control unit controlling the pressure of the LNG storage tank by adjusting the reliquefaction processing amount of the reliquefaction processing unit and the fuel supply amount to the fuel consumption destination. provided

The compander includes an expander and a BOG compressor connected to the expander to compress the BOG by expansion force, and the BOG (first stream) discharged from the LNG storage tank is a refrigerant in the precooler. The BOG compressed by the BOG compressor after being used as One stream (second stream) of the branched BOG is cooled by the pre-cooler and then expanded by the expander, and the fluid (third stream) expanded by the expander is used as a refrigerant in the main heat exchanger, The remaining flow not sent to the pre-cooler among the BOG branched into two flows after being further compressed by the HD compressor unit is compressed by the boost compressor unit, and the BOG (fourth) compressed by the boost compressor unit stream) is cooled by the main heat exchanger and then expanded by the expansion means, the precooler uses the first stream as a refrigerant to cool the second stream, and the main heat exchanger includes the third stream may be used as a refrigerant to cool the fourth stream.

Preferably, it further comprises a tank pressure control unit for controlling the pressure of the LNG storage tank so that the LNG temperature range of the LNG storage tank is in a saturated state,

By receiving a signal from the tank pressure control unit, the GMS control unit may control the amount of reliquefaction processing in the reliquefaction processing unit.

Preferably, the fuel consumer includes: a first fuel consumer provided in the ship or offshore structure and supplied with the compressed BOG as fuel through a part of the HD compressor; and a second fuel consumer provided in the ship or offshore structure and supplied with compressed BOG through all of the HD compressor unit,

a first fuel control unit configured to detect an amount of BOG supplied to the first fuel consumer; and

It may further include a second fuel control unit for detecting the amount of the BOG supplied to the second fuel consumer.

Preferably, the GMS control unit receives a signal from the tank pressure control unit, so that the BOG excluding the fuel supply amount from the first and second fuel control units from the amount of BOG generated in the LNG storage tank is reliquefied in the reliquefaction processing unit. The processing flow rate of BOG can be adjusted.

Preferably, the method further comprises a refrigerant flow control unit for controlling a flow rate of BOG that is adiabatically expanded from the expander of the compander and supplied as a refrigerant to the main heat exchanger,

The refrigerant flow control unit may control the flow rate of the refrigerant based on the reliquefaction amount of the BOG that has passed through the reliquefaction processing unit downstream of the main heat exchanger.

Preferably, the HD compressor unit comprises: a first HD compressor for compressing the BOG compressed by the BOG compressor; a first HD compressor cooler installed at the rear end of the first HD compressor to cool the BOG compressed by the first HD compressor; a second HD compressor installed at the rear end of the first HD compressor cooler to compress the BOG cooled by the first HD compressor cooler; and a second HD compressor cooler installed at the rear end of the second HD compressor to cool the BOG compressed by the second HD compressor.

Preferably, the processing system includes: a boost compressor for receiving the BOG compressed by the HD compressor and further compressing it to a pressure exceeding a critical pressure; and a boost compressor cooler provided at the rear end of the boost compressor to cool the compressed BOG;

The BOG compressed through the boost compressor may be cooled by heat exchange with the BOG cooled by adiabatic expansion from the expander in the main heat exchanger.

Preferably, the first fuel consumer is a marine engine that receives BOG compressed to 3 to 15 bar through some of the HD compressor units, and the second fuel consumer is compressed through the HD compressor unit and the boost compressor unit. It may be a marine engine supplied by additionally compressing BOG to a pressure higher than the critical pressure in a high-pressure compressor.

Preferably, it may further include a load control unit for controlling the boost compressor unit by sensing the pressure of the BOG from the rear end of the boost compressor unit.

Preferably, the first HD pressure indication control unit for sensing the pressure of the BOG compressed in the first HD compressor from the rear end of the first HD compressor cooler;

a second HD pressure indication control unit for sensing the pressure of the BOG compressed in the second HD compressor from the rear end of the second HD compressor; and

The HD control unit may further include an HD control unit for controlling the first and second HD compressors in conjunction with the first and second HD pressure indication control units.

Preferably, the treatment system further comprises a spray cooler provided upstream of the pre-cooler and cooling the BOG by spraying LNG supplied from the LNG storage tank to the BOG to be introduced into the pre-cooler,

It may further include a cooler control unit for controlling the spray cooler by sensing the temperature of the BOG introduced from the spray cooler to the pre-cooler.

By controlling the BOG treatment system through the control system of the present invention, BOG generated in the LNG storage tank can be effectively reliquefied and stored, thereby securing the safety of the tank and vessel, and increasing the transport efficiency of LNG. In particular, it is possible to re-liquefy compressed BOG using BOG without configuring a separate refrigerant system, thereby reducing costs and contributing to securing space in the ship. In addition, it is possible to realize a system with high liquefaction efficiency while simple in configuration and operation.

1 schematically shows a partial reliquefaction apparatus capable of processing boil-off gas in the prior patent of the present applicant.
2 schematically shows a BOG treatment system according to a basic embodiment of the present invention.
Figure 3 shows the boil-off gas treatment system of the basic embodiment of the present invention in more detail.
Figure 4 schematically shows the boil-off gas treatment system of the first embodiment of the present invention expanded from the basic embodiment.
5 schematically shows a boil-off gas treatment system of a second embodiment of the present invention expanded from the basic embodiment.
5A schematically shows a system of a second modified example extended from the boil-off gas treatment system of the second embodiment.
Fig. 5b schematically shows a system of a second modification and a control system for controlling the same.
6 schematically shows a boil-off gas treatment system of a third embodiment of the present invention expanded from the basic embodiment.
7 schematically shows a boil-off gas treatment system of a fourth embodiment of the present invention expanded from the basic embodiment.
8 schematically shows a boil-off gas treatment system of a fifth embodiment of the present invention expanded from the basic embodiment.
9 schematically shows a boil-off gas treatment system of a sixth embodiment of the present invention expanded from the basic embodiment.

In order to fully understand the present invention, 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 present invention will be described in detail by describing preferred embodiments of the present invention with reference to the accompanying drawings. Like reference numerals in each figure indicate like elements.

First, the BOG treatment system to be described later of the present invention includes all types of ships and offshore structures installed with storage tanks capable of storing low-temperature liquid cargo or liquefied gas, that is, LNG carriers, LEG (Liquefied Ethane Gas) carriers, and LNG RVs. It can be applied for BOG treatment in offshore structures such as LNG FPSO and LNG FSRU, including the same ship.

In the embodiments to be described below, for convenience of description, LNG, which is a representative low-temperature liquid cargo, will be described as an example, but the present invention is not limited thereto, and the liquefied gas stored in such a storage tank may be any liquid cargo that can be liquefied and transported at a low temperature. For example, in addition to LNG, LEG, LPG, liquid nitrogen, liquefied gas such as ethylene, acetylene, propylene, etc. may correspond to this. This embodiment can be applied to the treatment of boil-off gas generated from such liquefied gas.

FIG. 2 schematically shows a BOG treatment system according to an embodiment of the present invention, and FIG. 3 shows the BOG treatment system in more detail.

2 and 3, in the BOG treatment system of the present embodiment system, BOG (Boil-Off Gas) generated from an LNG storage tank (T) provided in a ship or offshore structure is supplied and compressed, but BOG A compander 100 is provided, which includes an expander 110 that receives the supply and adiabatic expansion, and a BOG compressor 120 that is connected to the expander and compresses the BOG by expansion force. BOG (Boil-Off Gas) generated from the LNG storage tank is supplied to the compander 100 along the BOG reliquefaction line BL. The expander 110 of the compander may be provided, for example, of a turbine type. The expansion force obtained when the expander adiabatically expands the BOG is connected to the expander through a rotation shaft and the kinetic energy when the turbine is rotated. BOG may be compressed by transmitting it to the BOG compressor 120 .

BOG compressed by the BOG compressor of the compander is supplied to the HD (High Duty) compressor unit 200 to be further compressed. BOG supplied from the BOG compressor 120 to the HD compressor unit 200 may be cooled through the cooler 150 .

The system of the present embodiment includes a precooler 300 in which the BOG compressed in the HD compressor unit 200 is cooled by heat exchange with the BOG to be introduced into the BOG compressor of the compander. Since the temperature of BOG increases as it is compressed through the BOG compressor 120 and the HD compressor unit 200, it is generated from the LNG storage tank and supplied to the compander 100 through the BOG reliquefaction line BL. It can be cooled through heat exchange. After being compressed in the HD compressor unit, the BOG cooled through the pre-cooler 300 is introduced into the expander 110 of the compander and adiabatically expanded. BOG is cooled through adiabatic expansion, and the BOG compressor 120 can compress BOG by the expansion force during adiabatic expansion.

On the other hand, in the present embodiment system, the boost compressor unit 400 that receives the BOG compressed from the HD compressor unit and additionally compresses it to a pressure exceeding the critical pressure, and the BOG compressed in the boost compressor unit is supplied from the expander of the compander. It includes a main heat exchanger 500 cooled by heat exchange with BOG cooled by thermal expansion. From the line connected from the HD compressor unit 200 to the pre-cooler 300 , a line for supplying the compressed BOG to the boost compressor unit 400 is branched, and the BOG supplied to the boost compressor unit along the branched line is critical. After being compressed further to a pressure exceeding the pressure, it is supplied to the main heat exchanger. Since the critical pressure of methane constituting most of the BOG is about 55 bar, it is introduced into the main heat exchanger 500 after being compressed to a pressure of 70 bar or more higher than the critical pressure while passing through the boost compressor unit 400 .

The BOG compressed to a pressure exceeding the critical pressure is cooled while exchanging heat with the adiabatic expanded BOG from the expander in the main heat exchanger 500 . Since the temperature of BOG compressed to a pressure of 70 bar or higher is around 25°C, it can be re-liquefied while cooling through heat exchange with BOG at around -160°C adiabatically expanded to around 1 bar through an expander.

After compression in the boost compressor unit 400 , BOG cooled from the main heat exchanger 500 or LNG condensed from BOG is supplied to the expansion means 600 to be adiabatically expanded. The expansion means may be, for example, a J-T valve or an expander, and may be further cooled while adiabatic expansion through the expansion means. BOG or LNG, adiabatically expanded through the expansion means, is supplied to a flash drum 700, and gas-liquid is separated into gaseous and liquid phases.

The liquid LNG separated from the flash drum 700 is supplied to the LNG storage tank along the LNG line LL and stored again, and the gaseous flash gas separated from the flash drum is transferred from the upper part of the flash drum to the gas line (GL). ) from the LNG storage tank to the BOG reliquefaction line (BL). The combined flash gas is introduced into the BOG compressor 120 of the compander through the pre-cooler 300 together with the BOG. Flash gas can be fueled on board or sent to the GCU for treatment or venting.

In the system as described above, the flow of BOG supplied from the LNG storage tank to the BOG compressor of the compander is the first stream, the flow of BOG compressed from the BOG compressor is further compressed and then the flow supplied to the expander of the compander is the second stream, The flow in which the adiabatic expanded BOG from the expander is supplied to the front end of the BOG compressor is branched from the third stream and the second stream, and the stream in which the additionally compressed BOG is compressed to a pressure exceeding the critical pressure and then cooled and reliquefied is the fourth stream If referred to, the first stream and the second stream, and the third stream and the fourth stream are mutually heat-exchanged. Through such a configuration, the system of the present embodiment can cool and reliquefy BOG through heat exchange between BOG and BOG compressed to different pressures without providing a separate refrigerant system.

Since there is no need to provide a separate refrigerant system, system configuration costs can be reduced, and the system is simple because BOG can be reliquefied using only BOG itself. In addition, the BOG generated from the LNG storage tank has a low temperature and a large temperature difference from the compressed BOG, so the liquefaction efficiency is high. By re-liquefying BOG and re-storing it to an LNG storage tank for transport, transportation efficiency can also be improved.

Meanwhile, as shown in FIG. 3 , the HD compressor unit includes a plurality of HD compressors 210a and 210b for additionally compressing the BOG compressed by the BOG compressor of the compander, and a plurality of HD compressors provided at the rear end of the HD compressor to cool the compressed BOG. of HD compressor coolers 220a and 220b may be included. The plurality of HD compressors and HD compressor coolers are arranged in such a way that one HD compressor cooler is provided at the rear end of one HD compressor as shown in FIG. 3 , and the compressors and coolers are alternately provided.

The boost compressor unit 400 also receives the compressed BOG from the HD compressor unit and additionally compresses it to a pressure exceeding the critical pressure, and a boost compressor cooler provided at the rear end of the boost compressor to cool the compressed BOG. 420 , and may include a plurality of compressors and a cooler similar to the above-described HD compressor unit.

Next, FIG. 4 schematically shows the BOG treatment system of the first embodiment of the present invention expanded from the basic embodiment.

As in the above-described embodiment, also in the first embodiment, the HD compressor unit 200A includes a plurality of HD compressors 210aA and 210bA for additionally compressing the BOG compressed by the BOG compressor of the compander, and is provided at the rear end of the HD compressor. It consists of a plurality of HD compressor coolers (220aA, 220bA) for cooling the compressed BOG, and the plurality of HD compressors and HD compressor coolers are provided with one HD compressor cooler behind one HD compressor, so that the compressor and the cooler are arranged in a form in which they are alternately provided, and the BOG is compressed in multiple stages.

The first embodiment is characterized in that the BOG compressed through a part of the HD compressor unit can be supplied to a fuel consumer E, such as an onboard engine, through a fuel supply line FL. The fuel consumer E may be, for example, an engine for power generation of a ship, and more specifically, a Dual Fuel Diesel Engine (DFDE).

When the fuel consumer E is DFDE, the discharge port pressure at the rear end of the set of the first HD compressor 210aA and the HD compressor cooler 220aA of the HD compressor unit 200A is 3 to 15 bar, as shown in FIG. 4 , More preferably, it is designed to be 5 to 7 bar, and from it, compressed BOG can be supplied to the DFDE through a fuel supply line.

By providing a gas combustion line (RML) at the front end of the HD compressor unit 200A, the BOG at the rear end of the BOG compressor 120A of the compander may be supplied to a GCU provided in a ship or an offshore structure. In the GCU, the supplied BOG can be burned and removed, or the inert gas generated by combustion can be supplied to the equipment that requires it on board.

As such, the system of the first embodiment is configured to supply BOG that has passed through only a part of the multi-stage HD compressor unit as fuel to a fuel consumer or send it to the GCU from the front end of the HD compressor unit. These configurations can be supplied. Therefore, it is possible to reduce the amount of BOG to be liquefied while supplying the fuel required in the ship, thereby reducing the load of the devices and increasing the energy efficiency.

Since other configurations are similar to those of the above-described basic embodiment, redundant descriptions are omitted.

5 schematically shows a boil-off gas treatment system of a second embodiment of the present invention expanded from the basic embodiment.

The second embodiment shown in FIG. 5 is configured so that compressed BOG can be supplied to all of these devices when there is a fuel consumer using high-pressure gas as fuel and a fuel consumer using low-pressure gas as fuel in the ship. It is an extension from the first embodiment described above.

The first fuel consumer receiving the low pressure gas may be a marine engine, for example, DFDE, supplied with BOG compressed to 3 to 15 bar through only a part of the HD compressor unit, and the second fuel consumer is the HD compressor unit and the boost. It may be a marine engine supplied with compressed BOG through the compressor unit, for example, a ME-GI engine that is a marine propulsion engine.

In this embodiment, two fuel supply lines are provided for supplying fuel to these consumers. First, the first fuel supply line FL1B for supplying fuel to the first fuel consumer E1 is the first HD compressor 210aB and the HD compressor cooler of the HD compressor unit 200B as in the first embodiment described above. A second fuel supply line FL2B for supplying fuel to the second fuel consumer E2 is provided at the rear end of the boost compressor unit 400B.

If the second fuel consumer is a ME-GI engine, high-pressure gas of about 150 to 400 bar, more preferably 300 bar, is supplied. In order to supply according to fuel supply conditions, BOG is additionally compressed in the second fuel supply line (FL2B). A high-pressure compressor (800B) and a high-pressure compressor rear end heat exchanger (810B) are provided. Since the critical pressure of methane, which constitutes most of the BOG, is about 55 bar, it is compressed to a pressure higher than the critical pressure through the boost compressor unit 400B, and then goes through the high pressure compressor 800B again to the supercritical state of around 300 bar ME. -Can be supplied to the GI engine.

This second embodiment is configured to supply the fuel necessary to both low-pressure and high-pressure gas fuel consumers in the ship using BOG as fuel, thereby reducing the amount of BOG to be liquefied, reducing the load of devices for this, and energy efficiency can be increased. In addition, BOG can be supplied as fuel or liquefied to each engine according to the amount of BOG generated or the level of fuel required by fuel consumers on board, which has the advantage of enabling flexible system operation.

Since other configurations are similar to those of the above-described basic and first embodiments, redundant descriptions are omitted.

FIG. 5A schematically shows a system of a second modified example extended from the BOG treatment system of the second embodiment described above.

As shown in FIG. 5A , the system of this modified example supplies the LNG pumped from the LNG storage tank to the BOG introduced from the LNG storage tank to the precooler, cools it, and then supplies the precooler to the precooler 300B'. An LNG cooling unit (1010B', 1020B') is provided upstream.

As in the initial operation of the system, when the temperature of the BOG generated in the LNG storage tank is relatively high and the temperature of various facilities including pipelines is relatively high, when the cooling and heat of the BOG supplied to the pre-cooler is not sufficient, from the initial operation Time is delayed until the system can be operated stably, and the liquefaction efficiency of BOG may decrease, resulting in energy wastage.

In this modified example, in order to solve this problem, the LNG cooling unit 1000B' is configured.

The LNG cooling unit includes an LNG supply pump (1010B') provided in an LNG storage tank to pump LNG, and a spray cooler (1020B') for cooling by spraying the LNG pumped by the LNG supply pump to the BOG supplied from the LNG storage tank. do. LNG and BOG sprayed through the spray cooler 1020B' come into contact with each other, and the BOG is cooled. The LNG supply pump 1010B' may be provided in the lower part of the storage tank as an in-tank type, and the LNG pumped from the LNG supply pump is supplied to the spray cooler 1020B' through an LNG cooling line (LCL). Since the liquefaction temperature of LNG is a cryogenic temperature of around -160°C, the BOG can be cooled by injecting the LNG in the lower part of the LNG storage tank to the BOG from the spray cooler 1020B'. In addition to the initial operation, if necessary, by injecting LNG to the BOG to be used as a refrigerant for the pre-cooler, the temperature of the BOG can be kept constant, so that the system can be stably driven.

Since other configurations are similar to the above-described embodiments, a redundant description will be omitted.

5B schematically shows the system of the second modification described above and a control system for controlling the same.

As shown in Fig. 5B, the present system is a control system for controlling the BOG processing in the system of the second modification.

This control system regulates the reliquefaction processing amount of the reliquefaction processing unit capable of reliquefying BOG, including the precooler 300B' and the main heat exchanger 500B', and the fuel supply amount to the fuel consumers E1 and E2. Thus, a gas management system (GMS) control unit (GPC) that controls the pressure of the LNG storage tank is included.

The purpose of controlling the reliquefaction system for BOG treatment is to secure the safety of the LNG storage tank and increase the LNG transport rate by basically treating the BOG generated from the LNG storage tank. That is, the control of the boil-off gas treatment system is connected to the pressure control of the LNG storage tank. To this end, the system of this embodiment further includes a tank pressure control unit (TPC) that controls the pressure of the LNG storage tank so that the LNG temperature range of the LNG storage tank is in a saturated state, and receives a signal from the tank pressure control unit to receive the GMS The control unit controls the amount of reliquefaction processing in the reliquefaction processing unit.

The fuel consumer includes a first fuel consumer E1 such as a DFDE that receives compressed BOG as fuel through a part of the HD compressor unit as described in the above-described embodiments, all of the HD compressor unit, a boost compressor, and a high-pressure compressor and a second fuel consumer E2, such as a propulsion engine supplied with compressed BOG via the like.

In order to control the supply of BOG fuel to these fuel consumers, the present control system includes a first fuel control unit F1C that detects and controls the amount of BOG supplied to the first fuel consumer, and the amount of BOG supplied to the second fuel consumer. A second fuel control unit (F2C) for detecting and controlling is provided, the GMS control unit (GPC) receives a signal from the tank pressure control unit, The BOG processing flow rate of the reliquefaction processing unit is adjusted so that the remaining BOG is reliquefied except for the amount of fuel supplied to the first and second fuel consumers.

As described in the above embodiment, the adiabatic expanded BOG from the expander 110B' of the compander is used as a refrigerant for cooling the compressed BOG through the HD compressor unit in the main heat exchanger 500B'. A refrigerant flow control unit ALC2 for controlling the flow rate of BOG supplied as a refrigerant to the main heat exchanger is provided in the present control system. In the refrigerant flow control unit, the BOG refrigerant to be supplied to the main heat exchanger 500B' through the expander 110B' based on the reliquefaction amount of the BOG that has passed through the reliquefaction processing unit downstream of the main heat exchanger, that is, the amount of reliquefied LNG. flow rate can be controlled. If the inlet temperature set point of the expander is set to -50 to -60 ℃ through the control unit (CC), two-phase flow is prevented, and sufficient refrigerant temperature is obtained for BOG cooling in the main heat exchanger. can

On the other hand, in the present system, the first HD pressure command control unit (H1C) that senses the pressure of the BOG compressed by the first HD compressor from the rear end of the first HD compressor cooler, and the second HD compressor from the rear end of the second HD compressor cooler A second HD pressure indication control unit (H2C) for sensing the pressure of the BOG is provided, and the first and second HD compressors ( 210aB', 210bB'). It is preferable to operate the BOG discharge pressure from the first HD compressor through the HD control unit ALC1 as the fuel supply pressure of the first fuel consuming destination. For example, when the first fuel consuming destination is DFDE, BOG discharge of the first HD compressor It can be operated by maintaining the pressure at about 6 bara. Accordingly, fuel may be smoothly supplied from the downstream of the first HD compressor to the first fuel consumer, and the density of the gas inlet of the second HD compressor may be constantly maintained. The BOG discharge pressure from the second HD compressor through the HD control unit ALC1 is operated appropriately to achieve a cryogenic temperature at the rear end of the expander after pre-cooling of the BOG refrigerant. For example, the discharge pressure of the second HD compressor may be maintained at 28 to 30 bara.

As described in the second modification described above, when a spray cooler 1020B' for cooling the BOG by spraying LNG supplied from the LNG storage tank to the BOG to be introduced into the pre-cooler is provided upstream of the pre-cooler, from the spray cooler A cooler control unit BC for controlling the spray cooler by sensing the temperature of the BOG introduced into the precooler may be provided in the control system.

A load control unit LC1 for controlling the boost compressor unit by sensing the pressure of the BOG from the rear end of the boost compressor unit may be further included. Through the load control unit, the boost compressor maintains the set pressure above the critical pressure, for example, 80 bar or more to increase the BOG heat exchange efficiency in the main heat exchanger 500B'. In order to increase the liquefaction efficiency in the main heat exchanger 500B', a filter 450B' for removing N ₂ from BOG to be introduced into the main heat exchanger may be provided downstream of the boost compressor 410B'. For example, when a membrane filter is provided, N ₂ having a heavy molecular weight may be separated from methane to be removed.

The high-pressure compressor 800B' may also be provided with a BOG load control unit LC2 capable of controlling the BOG load.

Since the boil-off gas treatment system is similar to the above-described embodiments, a redundant description thereof will be omitted.

6 schematically shows a boil-off gas treatment system of a third embodiment of the present invention expanded from the basic embodiment.

In the system of the third embodiment, in case the amount of BOG generated in the LNG storage tank is not large or the temperature is not low enough, in case the cold energy by the BOG in the precooler 300C is insufficient. , it is configured to sufficiently supply cooling heat to the pre-cooler by composing a refrigerant cycle together with BOG.

To this end, the refrigerant is circulated, and a refrigerant circulation unit 900C for cooling the compressed BOG through heat exchange in the pre-cooler is provided, which includes a refrigerant compressor 910C that compresses the refrigerant, and a refrigerant compressor that cools the refrigerant compressed in the refrigerant compressor. It includes a refrigerant compressor cooler 920 and a refrigerant expansion means 930C for further cooling by adiabatic expansion thereof. The refrigerant may be ethane.

The BOG compressed through the HD compressor is cooled to a temperature of 0 to -70 ℃, preferably 50 ℃ or less through heat exchange with the BOG to be introduced from the pre-cooler to the BOG compressor and the refrigerant circulating in the refrigerant circulation unit, and is then heated to the expander 110C. can be introduced.

Since the present embodiment can lower the temperature of the compressed BOG introduced into the expander 110C to an appropriate range, the BOG further cooled through adiabatic expansion can be used as an effective refrigerant in the main heat exchanger 500C. This can increase the liquefaction efficiency of the system.

Since other configurations are similar to those of the above-described basic embodiment, redundant descriptions are omitted.

7 schematically shows a BOG treatment system of a fourth embodiment of the present invention expanded from the basic embodiment.

In the embodiments of the present invention, as described above, BOG is directly used as a refrigerant in the precooler. As in the initial operation of the system, the temperature of BOG generated in the LNG storage tank is relatively high, and the temperature of BOG generated in the LNG storage tank is relatively high, and When the temperature is relatively high, the cooling heat of the BOG supplied to the pre-cooler may not be sufficient. In this case, time is delayed from the initial operation until the system can be operated stably, and the liquefaction efficiency of BOG may decrease, resulting in energy wastage.

In this embodiment, in order to solve this problem, the LNG cooling unit 1000D is provided upstream of the pre-cooler 300D, and the LNG pumped from the LNG storage tank is supplied to the BOG introduced from the LNG storage tank to the pre-cooler. After cooling, it was configured to be supplied to the pre-cooler.

The LNG cooling unit 1000D includes an LNG supply pump 1010D provided in an LNG storage tank to pump LNG, and a spray cooler 1020D for cooling by spraying the LNG pumped by the LNG supply pump to BOG supplied from the LNG storage tank. includes LNG injected through the spray cooler 1020D and BOG are cooled while in contact with the inside of a drum (not shown). The LNG supply pump 1010D may be provided in the lower part of the storage tank as an in-tank type. The LNG pumped from the LNG supply pump is supplied to the spray cooler 1020D through the LNG cooling line (LCL). Since the liquefaction temperature of LNG is a cryogenic temperature of around -160°C, the BOG to be supplied to the pre-cooler 300D can be cooled by injecting the LNG in the lower part of the LNG storage tank to the BOG from the spray cooler 1020D. In addition to the initial operation, if necessary, by injecting LNG to the BOG to be used as a refrigerant for the pre-cooler, the temperature of the BOG can be kept constant, so that the system can be stably driven.

Since some of the supplied LNG may be vaporized while the injected LNG and BOG come into contact, vaporized gas and cooled BOG are supplied to the pre-cooler 300D, and the liquid LNG is separated from the liquid LNG in the flash drum 700D and Together, they are re-stored to the LNG storage tank (T) along the LNG line (LLD).

Since other configurations are similar to the above-described embodiments, a redundant description will be omitted.

8 schematically shows a boil-off gas treatment system of a fifth embodiment of the present invention expanded from the basic embodiment.

In particular, the system of the fifth embodiment shown in Fig. 8 adds the configuration of the fifth embodiment to the above-described second embodiment, and can supply LNG as fuel for smooth fuel supply to the first and second fuel consumers. It is a system to which a system for supplying fuel is added.

As in the second embodiment described above, as the first fuel consumer E1 supplied with the low-pressure gas, a marine engine receiving BOG compressed to 3 to 15 bar through only a part of the HD compressor 200E, for example, It may be DFDE, and the second fuel consumer E2 is a marine engine that receives compressed BOG through the HD compressor unit 200E and the boost compressor unit 400E, for example, a ME-GI engine that is an engine for propulsion of a vessel. can be

In order to supply BOG fuel to these consumers, the first fuel supply line FL1E for supplying fuel to the first fuel consumers E1 is the first HD compressor 210aE and the HD compressor cooler of the HD compressor unit 200E. A second fuel supply line FL2E for supplying fuel to the second fuel consumer E2 is provided at the rear end of the boost compressor unit 400E.

If the second fuel consumer is a ME-GI engine, a high-pressure compressor ( 800E) and a high-pressure compressor rear end heat exchanger (810E) are provided. Since the critical pressure of methane, which makes up most of the BOG, is about 55 bar, it is compressed to a pressure higher than the critical pressure through the boost compressor unit 400E, and then goes through the high pressure compressor 800E again to the supercritical state of around 300 bar ME. -Can be supplied to the GI engine.

In addition to this, in this embodiment, a fuel supply unit 1100E capable of supplying compressed BOG or LNG pumped from an LNG storage tank as fuel is provided.

The fuel supply unit 1100E includes a low-pressure vaporizer 1110E that receives LNG from an LNG supply pump, vaporizes it and supplies it to a first fuel consumer, and receives LNG from an LNG supply pump and compresses it to the fuel supply pressure of a second fuel consumer. It may include a high-pressure pump 1120E, and a high-pressure vaporizer 1130E that receives compressed LNG from the high-pressure pump, vaporizes it, and supplies it to a second fuel consumer. If the first fuel consumer E1 is a DFDE, the LNG supplied from the LNG supply pump 1010E may be vaporized by the low pressure vaporizer 1110E and supplied at a pressure of about 5 bar. When the second fuel consumer E2 is an ME-GI engine, the high-pressure pump 1120E compresses the LNG to a high pressure of about 300 bar, then vaporizes it in the high-pressure vaporizer 1130E and supplies it to the ME-GI engine. However, since gas and liquid cannot be distinguished in the supercritical state, the expression 'compressed LNG is forcibly vaporized' increases the temperature by supplying thermal energy to the compressed LNG (or, in a supercritical state with high density, change to a critical state).

Also, the fuel supply unit 1100E may further include a recondenser 1150E that receives compressed BOG through a part of the HD compressor unit and mixes and liquefies the LNG supplied from the LNG supply pump 1010E. To this end, the recondenser line RCLE for supplying the compressed BOG to the recondenser 1150E may be branched from the first fuel supply line FL1B. The LNG liquefied in the recondenser 1150E may be supplied to a low-pressure vaporizer or a high-pressure pump, and may be vaporized and supplied as fuel to the first and second fuel consumers E1 and E2.

As such, the LNG pumped from the LNG storage tank from the LNG supply pump may be branched and supplied to a spray cooler, a recondenser, a low-pressure carburetor, or a high-pressure pump.

In the system of this embodiment, as in the above-described embodiments, the devices for compressing BOG are composed of multi-stages such as a multi-stage HD compressor unit and a boost compressor unit, so that BOG can be liquefied with little energy, and it is necessary for fuel consumption in the ship. According to the pressure condition, BOG compressed through all or part of the multi-stage configuration may be branched and supplied as fuel.

In addition, in the ballast voyage state of the vessel in which the amount of BOG generation is not large, LNG can be vaporized through the fuel supply unit 1100E and supplied to a fuel consumer, so that a smooth fuel supply can be achieved.

In this embodiment, by providing a recondenser in the fuel supply unit, using BOG as a refrigerant, the HD compressor unit, the boost compressor unit, the precooler, the main heat exchanger, the expansion means, and the flash drum do not operate the liquid loop of the recondenser. Since BOG can be processed to a certain extent using LNG, BOG can be processed with less energy than when operating the entire ash loop.

Even when the temperature of the BOG is not high during the initial operation of the system, the BOG can be cooled through the LNG cooling unit and supplied as a refrigerant to the pre-cooler. there is.

As such, the present embodiment can be driven effectively in response to various operating conditions, and thus BOG can be efficiently processed.

Since other configurations are similar to the above-described embodiments, a redundant description will be omitted.

9 schematically shows a boil-off gas treatment system of a sixth embodiment of the present invention expanded from the basic embodiment.

The system of this embodiment is configured so that the BOG compressed from the ship or offshore structure can be supplied to the offshore consumer or offshore consumer. The ship or offshore structure of this embodiment may be, for example, a Floating Storage and Regasification Unit (FSRU) or a Regasification Vessel (RV).

In the system of this embodiment, a vaporization supply unit 1200F for vaporizing LNG from an LNG storage tank and supplying it to an onshore or offshore consumer is provided.

The vaporization supply unit 1200F includes an LNG discharge pump 1210F provided in an LNG storage tank for pumping LNG, an LNG booster pump 1220F that receives LNG from the LNG discharge pump and compresses it to the required pressure of a land consumer, and an LNG booster It includes a vaporizer (1230F) that vaporizes the LNG compressed in the pump and supplies it to an onshore consumer. The LNG pumped from the LNG storage tank (T) is compressed to a pressure above the critical pressure, for example, around 100 bar, in the LNG booster pump (1220F) through the outboard supply line (SLF), and the compressed LNG is again in the vaporizer ( 1230F) and then supplied overboard.

On the other hand, if the amount of BOG generated is large, it may be liquefied and stored, or it may be compressed through the HD compressor unit 200F and the boost compressor unit 400F and directly supplied overboard. To this end, a first outboard supply line SL1F capable of supplying the compressed BOG overboard is provided at the rear end of the boost compressor unit 400F.

On the other hand, the vaporization supply unit 1200F receives the compressed BOG through a part of the HD compressor unit 200F, and a recondenser 1240F for mixing and liquefying the LNG supplied from the LNG discharge pump 1210F is provided, LNG liquefied from the recondenser can be supplied to an LNG booster pump, compressed and then vaporized to be supplied overboard. Instead of re-liquefying all of the BOG, all or part of it is compressed to a low pressure, for example, around 6 bar through the HD compressor unit 200F, and then supplied to the recondenser 1240 through the second outboard supply line (SL2F) to LNG It is mixed with the LNG supplied from the storage tank and supplied overboard through the LNG booster pump 1220F and the carburetor 1230F. BOG can be re-liquefied or supplied as onboard fuel when overboard supply is not required.

Through this configuration and operation, it is possible to effectively operate the system and process BOG according to the amount of BOG generated and the demand for gas onboard.

The present invention is not limited to the above embodiments, and it is apparent to those of ordinary skill in the art that various modifications or variations can be implemented without departing from the technical gist of the present invention. did it

T: LNG storage tank
100: compander
200: HD compressor unit
300: pre-cooler
400: boost compressor
500: main heat exchanger
600: expansion means
700: flash drum

Claims (11)

In the control system of a processing system for processing BOG (Boil-Off Gas) generated from an LNG storage tank provided in a ship or an offshore structure,
The processing system is
Reliquefaction processing unit including a compander, HD (High Duty) compressor unit, pre-cooler, main heat exchanger, boost compressor unit and expansion means;
a fuel consumer provided in the ship or offshore structure and supplied with compressed BOG through all or a part of the HD compressor; and
A gas management system (GMS) control unit that controls the pressure of the LNG storage tank by adjusting the reliquefaction processing amount of the reliquefaction processing unit and the fuel supply amount to the fuel consumption destination;
The compander includes an expander and a BOG compressor connected to the expander and compressing the BOG by expansion force,
BOG (first stream) discharged from the LNG storage tank is compressed by the BOG compressor after being used as a refrigerant in the pre-cooler,
BOG compressed by the BOG compressor is further compressed by the HD compressor unit and then is branched into two streams,
After being further compressed by the HD compressor unit, one flow (the second stream) of the boil-off gas branched into two flows is cooled by the pre-cooler and then expanded by the expander,
The fluid (third stream) expanded by the expander is used as a refrigerant in the main heat exchanger,
After being further compressed by the HD compressor unit, the remaining flow not sent to the pre-cooler among the boil-off gas branched into two flows is compressed by the boost compressor unit,
BOG (fourth stream) compressed by the boost compressor unit is cooled by the main heat exchanger and then expanded by the expansion means,
The precooler cools the second stream using the first stream as a refrigerant,
The main heat exchanger, using the third stream as a refrigerant to cool the fourth stream, the control system of the boil-off gas treatment system. The method of claim 1,
Further comprising a tank pressure control unit for controlling the pressure of the LNG storage tank so that the LNG temperature range of the LNG storage tank is in a saturated state,
A control system of the BOG treatment system for receiving a signal from the tank pressure control unit to control the amount of reliquefaction processing in the reliquefaction processing unit in the GMS control unit. 3. The method of claim 2,
The fuel consumer may include: a first fuel consumer provided in the ship or offshore structure and supplied with the compressed BOG as fuel through a part of the HD compressor; and a second fuel consumer provided in the ship or offshore structure and supplied with compressed BOG through all of the HD compressor unit,
a first fuel control unit configured to sense an amount of BOG supplied to the first fuel consumer; and
The control system of the boil-off gas treatment system further comprising a second fuel control unit for detecting the amount of BOG supplied to the second fuel consumer. 4. The method of claim 3,
The GMS control unit receives a signal from the tank pressure control unit, and the BOG processing flow rate in the re-liquefaction processing unit so that the BOG excluding the fuel supply amount from the first and second fuel control units is reliquefied from the amount of BOG generated in the LNG storage tank. The control system of the boil-off gas treatment system, characterized in that for adjusting the. The method of claim 1,
Further comprising a refrigerant flow control unit for controlling the flow rate of the third stream,
The refrigerant flow control unit, downstream of the main heat exchanger, controls the flow rate based on the re-liquefaction amount of the BOG passing through the re-liquefaction processing unit, the control system of the boil-off gas treatment system. The method of claim 1,
The HD compressor unit,
a first HD compressor for compressing the BOG compressed by the BOG compressor;
a first HD compressor cooler installed at the rear end of the first HD compressor to cool the BOG compressed by the first HD compressor;
a second HD compressor installed at the rear end of the first HD compressor cooler to compress the BOG cooled by the first HD compressor cooler; and
and a second HD compressor cooler installed at the rear end of the second HD compressor to cool the BOG compressed by the second HD compressor. The method of claim 1,
The boost compressor unit,
a boost compressor for additionally compressing the BOG compressed by the HD compressor unit to a pressure exceeding the critical pressure; and
A boost compressor cooler installed at the rear end of the boost compressor to cool the BOG compressed by the boost compressor. 4. The method of claim 3,
The first fuel consumer is a marine engine that receives BOG compressed to 3 to 15 bar through some of the HD compressor units, and the second fuel consumer is a high-pressure compressor for BOG compressed through the HD compressor unit and the boost compressor unit. A control system for a boil-off gas treatment system, characterized in that it is a marine engine supplied by additional compression at a pressure higher than the critical pressure. The method of claim 1,
The control system of the boil-off gas treatment system further comprising a load control unit for controlling the boost compressor unit by sensing the pressure of the BOG from the rear end of the boost compressor unit. 7. The method of claim 6,
a first HD pressure indication control unit for sensing the pressure of the BOG compressed in the first HD compressor from the rear end of the first HD compressor cooler;
a second HD pressure indication control unit for sensing the pressure of the BOG compressed in the second HD compressor from the rear end of the second HD compressor; and
The control system of the boil-off gas treatment system further comprising an HD control unit for controlling the first and second HD compressors in conjunction with the first and second HD pressure indication control units. The method of claim 1,
The treatment system further includes a spray cooler provided upstream of the pre-cooler and cooling the BOG by spraying LNG supplied from the LNG storage tank to the BOG to be introduced into the pre-cooler,
The control system of the boil-off gas treatment system further comprising a cooler control unit for controlling the spray cooler by sensing the temperature of the BOG introduced from the spray cooler to the pre-cooler.

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