KR102632400B1 - Gas processing system for vessel and gas processing method using the same - Google Patents

Abstract

The present invention relates to a marine gas processing system configured to control excess pressure of a gas-liquid separator of a partial reliquefaction system in a facility equipped with a marine fuel supply system that uses gas as fuel, and a marine gas processing method using the same.
According to one embodiment of the present invention, a marine gas processing system comprising a storage tank storing liquefied natural gas and boil-off gas generated from the liquefied natural gas, and an engine using the boil-off gas discharged from the storage tank as fuel. The system includes a compressor that receives and compresses the boil-off gas generated in the storage tank; the engine receiving and using evaporative gas compressed by the compressor as fuel; a heat exchanger for cooling some of the boil-off gas compressed by the compressor that is not supplied to the engine by exchanging heat with boil-off gas before being supplied to the compressor; an expansion valve that depressurizes the boil-off gas cooled in the heat exchanger; a gas-liquid separator for separating the decompressed and at least partially liquefied boil-off gas while passing through the expansion valve into a gas component and a liquid component; A marine gas processing system may be provided, including a first controller that receives the pressure of the gas-liquid separator and compares the received pressure with a reference pressure to control a valve installed in the line between the heat exchanger and the gas-liquid separator.

Description

Marine gas processing system and marine gas processing method using the same {GAS PROCESSING SYSTEM FOR VESSEL AND GAS PROCESSING METHOD USING THE SAME}

The present invention relates to a marine gas processing system and a marine gas processing method using the same, and more specifically, to control the excess pressure of the gas-liquid separator of the partial reliquefaction system in facilities equipped with the fuel supply system of ships that use gas as fuel. It relates to a marine gas processing system and a marine gas processing method using the same.

Liquefied gas carriers such as LNG carriers are intended to carry liquefied gas on the sea and unload this liquefied gas at land-based destinations. For this purpose, they are equipped with storage tanks (commonly referred to as 'cargo holds') that can withstand the extremely low temperatures of liquefied gas. includes).

The liquefaction temperature of natural gas is extremely low at about -163°C at normal pressure, so LNG evaporates even if the temperature is only slightly higher than -163°C at normal pressure. Taking the case of a conventional LNG carrier as an example, although the LNG storage tank of the LNG carrier is insulated, external heat is continuously transferred to the LNG, so LNG is damaged during transport by the LNG carrier. LNG is continuously vaporized within the storage tank, generating boil-off gas (BOG; Boil-Off Gas) within the LNG storage tank.

The generated boil-off gas increases the pressure in the storage tank and can cause structural problems by accelerating the flow of liquefied gas due to the rocking of the ship, so it is necessary to suppress the generation of boil-off gas.

In addition, since boil-off gas is a loss of LNG, suppressing or re-liquefaction of boil-off gas is an important issue in the transportation efficiency of LNG.

Conventionally, in order to suppress and treat the boil-off gas in the storage tank of a liquefied gas carrier, there is a method of discharging the boil-off gas to the outside of the storage tank and incinerating it, or discharging the boil-off gas outside the storage tank through a re-liquefaction device. A method of re-liquefying it and then returning it to the storage tank, a method of using boil-off gas as fuel used in a ship's propulsion engine, and a method of suppressing the generation of boil-off gas by maintaining a high internal pressure of the storage tank can be used alone or It was being used in combination.

In the case of a conventional ship equipped with a boil-off gas re-liquefaction device, the boil-off gas inside the storage tank is discharged to the outside of the storage tank and re-liquefied through the re-liquefaction device in order to maintain the appropriate pressure in the storage tank. At this time, the discharged evaporation gas is reliquefied through heat exchange with a refrigerant cooled to a very low temperature in a reliquefaction device including a refrigeration cycle, such as nitrogen refrigerant or mixed refrigerant, and then returned to the storage tank.

In the case of LNG carriers equipped with the conventional DFDE propulsion system, the boil-off gas was processed only through a boil-off gas compressor and heating without installing a re-liquefaction facility, and then supplied as fuel to the DFDE to consume the boil-off gas, so the fuel requirement for the engine was reduced by boil-off gas. When the amount of gas generated was less than the amount of gas generated, there was a problem that the boil-off gas had no choice but to be burned in a gas combustion unit (GCU) or vented into the atmosphere.

In addition, although LNG carriers equipped with conventional reliquefaction facilities and low-speed diesel engines can process BOG through the reliquefaction facility, the control of the entire system is complicated due to the complexity of operating the reliquefaction device using nitrogen gas and requires a significant amount of energy. There was a problem with power consumption.

In order to solve the above-mentioned problem, the boil-off gas discharged from the storage tank is pressurized and most of it is used as fuel for the ship engine, and the remaining part is liquefied with the cold heat of the boil-off gas newly discharged from the storage tank and returned to the storage tank. , a method to efficiently use boil-off gas was proposed.

When treating boil-off gas using this method, the boil-off gas discharged from the storage tank must be pressurized to high pressure, cooled, and then go through the process of decompressing it to low pressure. To depressurize the boil-off gas, an expansion valve (e.g. J-T valve).

After passing through the heat exchanger and expansion valve, the low-temperature liquefied fluid enters the liquid/gas separator and is separated into liquid and gas. The liquid is returned to the storage tank, and the gas is transferred from the gas-liquid separator through the gas line pipe to the heat exchanger. is delivered to the low pressure line inlet, which is also recycled to the high pressure compressor inlet.

Since the gas recycled to the high-pressure compressor inlet is supplied to the gas-liquid separator of the partial reliquefaction system, its stable control affects the stable control of the high-pressure compressor pressure.

Therefore, a system that can stably control the pressure of the liquid/gas separator of the partial reliquefaction system is required.

The purpose of the present invention is to provide a marine gas processing system configured to control the excess pressure of the gas-liquid separator of the partial reliquefaction system in facilities equipped with a fuel supply system for ships that use gas as fuel, and a marine gas processing method using the same. there is.

According to an embodiment of the present invention for achieving the above object, a storage tank storing liquefied natural gas and boil-off gas generated from the liquefied natural gas, and an engine using the boil-off gas discharged from the storage tank as fuel. A marine gas processing system comprising: a compressor that receives and compresses the boil-off gas generated in the storage tank; the engine receiving and using evaporative gas compressed by the compressor as fuel; a heat exchanger for cooling some of the boil-off gas compressed by the compressor that is not supplied to the engine by exchanging heat with boil-off gas before being supplied to the compressor; an expansion valve that depressurizes the boil-off gas cooled in the heat exchanger; a gas-liquid separator for separating the decompressed and at least partially liquefied boil-off gas while passing through the expansion valve into a gas component and a liquid component; A marine gas processing system may be provided, including a first controller that receives the pressure of the gas-liquid separator and compares the received pressure with a reference pressure to control a valve installed in the line between the heat exchanger and the gas-liquid separator.

The marine gas processing system according to an embodiment of the present invention further includes a second controller set to a maximum pressure higher than the reference pressure, and the second controller controls the gas-liquid separator when the opening degree of the valve is the maximum opening degree. By determining whether the pressure reaches the maximum pressure, the opening degree of the expansion valve can be adjusted when the pressure of the gas-liquid separator reaches the maximum pressure.

The marine gas processing system according to an embodiment of the present invention further includes a Royer selector for selecting the lowest pressure value, wherein the Royer selector selects the pressure value of the gas-liquid separator and the pressure value received from the storage tank pressure controller. The lowest pressure value selected from the pressure value of the storage tank and the pressure value of the fuel supplied to the engine received from the pressure controller of the engine may be transmitted to the expansion valve.

The expansion valve may be connected in parallel along two lines.

When the pressure of the gas-liquid separator becomes higher than the maximum pressure, the second controller may adjust the pressure of the fluid flowing into the gas-liquid separator by lowering the opening degree of the expansion valve.

The liquid component separated in the gas-liquid separator may be returned to the storage tank.

The gas component separated in the gas-liquid separator may join the boil-off gas supplied to the compressor.

According to another embodiment of the present invention, marine gas processing comprising a storage tank storing liquefied natural gas and boil-off gas generated from the liquefied natural gas, and an engine using the boil-off gas discharged from the storage tank as fuel. A marine gas processing method using a system, comprising: receiving pressure from a gas-liquid separator; A marine gas processing method using a marine gas processing system may be provided, including the step of comparing the received pressure and the reference pressure to adjust a valve installed in the line between the heat exchanger and the gas-liquid separator.

The adjusting step determines whether the pressure of the gas-liquid separator reaches the maximum pressure set higher than the reference pressure when the opening degree of the valve is the maximum opening degree, and when the pressure of the gas-liquid separator reaches the maximum pressure, the expansion valve The opening degree can be adjusted.

The adjusting step is performed by a Royer selector among the pressure value of the gas-liquid separator, the pressure value of the storage tank received from the storage tank pressure controller, and the pressure value of the fuel supplied to the engine received from the pressure controller of the engine. The opening degree of the expansion valve can be adjusted to the selected lowest pressure value.

According to another embodiment of the present invention, marine gas including a storage tank storing liquefied natural gas and boil-off gas generated from the liquefied natural gas, and an engine using the boil-off gas discharged from the storage tank as fuel. A marine gas processing method using a processing system, wherein the pressure of the gas-liquid separator of the partial re-liquefaction system, which liquefies the compressed gas delivered from a high-pressure compressor through a heat exchanger and an expansion valve, is maintained within a preset maximum pressure. Using a marine gas processing system that controls the pressure of the fluid flowing into the gas-liquid separator by transmitting the lowest pressure value among the pressure value of the gas-liquid separator, the pressure value of the storage tank, and the pressure value of the fuel supplied to the engine. A gas processing method for ships may be provided.

According to an embodiment of the present invention, a marine gas processing system configured to control excess pressure of a gas-liquid separator of a partial reliquefaction system in a facility equipped with a fuel supply system for a vessel that uses gas as fuel can be provided. Maintaining and improving reliquefaction performance can be expected through stable pressure control of such a gas-liquid separator.

1 is a schematic configuration diagram of a marine gas processing system according to a preferred embodiment of the present invention.
Figure 2 is a diagram for explaining a marine gas processing method using a marine gas processing system according to a preferred embodiment of the present invention.

The marine gas processing system according to the present invention can be applied to marine structures equipped with a storage tank capable of storing liquefied gas inside the hull.

Examples of offshore structures equipped with storage tanks capable of storing liquefied gas at extremely low temperatures include, in addition to liquefied gas carriers, ships such as LNG RV (Regasification Vessel), LNG FSRU (Floating Storage and Regasification Unit), LNG FRU (Floating and Regasification Unit), These include plants such as LNG FPSO (Floating, Production, Storage and Off-loading), FSPP (Floating Storage Power Plant), and BMPP (Barge Mounted Power Plant).

The LNG RV is an LNG regasification facility installed on a liquefied natural gas carrier capable of sailing and floating under its own power, and the LNG FSRU stores liquefied natural gas unloaded from an LNG carrier in a storage tank at sea far from land and then regasifies it as needed. It is a structure that vaporizes liquefied natural gas and supplies it to onshore customers. LNG FRU is a structure that vaporizes liquefied natural gas at sea and supplies it to onshore customers while omitting the storage function and is used in cooperation with a separate storage tank. LNG FPSO is a structure used to purify mined natural gas at sea, liquefy it directly, store it in a storage tank, and transfer the LNG stored in this storage tank to an LNG transport ship when necessary. FSPP is a structure used to produce electricity at sea by mounting an LNG storage tank and power generation facilities on a hull floating at sea, and BMPP is a structure used to produce electricity at sea by mounting power generation facilities on a barge. .

In this specification, a ship is a concept that includes all liquefied gas carriers such as LNG carriers, LNG RVs, etc., as well as structures such as LNG FPSO, LNG FSRU, LNG FRU, FSPP, and BMPP.

Hereinafter, the structure and operation of a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Additionally, the following examples may be modified into various other forms, and the scope of the present invention is not limited to the following examples.

Figure 1 shows a schematic configuration diagram of a marine gas processing system according to a preferred embodiment of the present invention.

Figure 1 shows an example of the marine gas processing system of the present invention being applied to an LNG carrier equipped with a high-pressure natural gas injection engine, such as a MEGI engine, as a marine engine that can use natural gas as fuel. However, the marine gas processing system of the present invention is shown. The treatment system can be applied to all types of ships equipped with liquefied gas storage tanks, such as LNG carriers, LNG RVs, etc., as well as offshore plants such as FSPP, BMPP, LNG FRU, LNG FPSO, and LNG FSRU.

According to the marine gas processing system according to the first embodiment of the present invention, the boil-off gas (NBOG) generated and discharged from the storage tank 111 for storing liquefied gas is transported along the boil-off gas supply line (L1). After being compressed in the compressor 113, it is supplied to the main engine 101 (eg, a high-pressure natural gas injection engine such as a MEGI engine). The boil-off gas may be compressed to a high pressure of approximately 150 to 400 bara by the compressor 113 and then supplied as fuel to the main engine 101.

Storage tanks are equipped with sealing and insulating barriers to store liquefied gases such as LNG at extremely low temperatures, but they cannot completely block heat transmitted from the outside. Accordingly, evaporation of the liquefied gas continues within the storage tank 111, and in order to maintain the pressure of the evaporation gas at an appropriate level, the evaporation gas inside the storage tank 111 is discharged through the evaporation gas discharge line (L1). I order it.

A discharge pump 112 is installed inside the storage tank 111 to discharge LNG to the outside of the storage tank when necessary. One or more storage tanks 111 may be included in the ship, and any type, such as a membrane type or an independent type, may be used as long as it can store liquefied gas in a cryogenic state.

The compressor 113 may include one or more compression stages 114 and one or more intermediate coolers (not shown) for cooling the boil-off gas whose temperature has risen while being compressed. For example, the compressor 113 may be configured to compress boil-off gas to a high pressure of about 150 to 400 bara. In Figure 1, a multi-stage compressor including five compression stages 114 is illustrated, but the number of compression stages and intercoolers may be changed as needed. Additionally, in addition to having a structure in which a plurality of compression cylinders are arranged within one compressor, it can also be changed to have a structure in which a plurality of compressors are connected in series.

The boil-off gas compressed in the compressor 113 is supplied to the main engine 101 through the boil-off gas supply line (L1). Depending on the amount of fuel required by the main engine, all of the compressed boil-off gas may be supplied to the main engine. Also, only part of the compressed evaporation gas can be supplied to the main engine.

In addition, according to a preferred embodiment of the present invention, when the boil-off gas discharged from the storage tank 111 and compressed in the compressor 113 (i.e., the entire boil-off gas discharged from the storage tank) is referred to as the first stream, the boil-off gas The first stream may be divided into a second stream and a third stream after compression, the second stream may be supplied as fuel to a high-pressure natural gas injection engine, and the third stream may be liquefied and returned to the storage tank.

At this time, the second stream is supplied to the main engine 101 through the boil-off gas supply line (L1), and the third stream is returned to the storage tank 111 through the boil-off gas return line (L3). A heat exchanger 121 is installed in the boil-off gas return line (L3) to liquefy the third stream of compressed boil-off gas and return it to the storage tank 111. In the heat exchanger 121, the third stream of compressed boil-off gas is discharged from the storage tank 111 and then exchanges heat with the first stream of boil-off gas supplied to the compressor 113.

The third stream of compressed boil-off gas may be cooled by receiving cold heat from the first stream of boil-off gas before compression. In this way, the heat exchanger 121 exchanges heat between the extremely low temperature boil-off gas immediately discharged from the storage tank 111 and the high-pressure and high-temperature boil-off gas compressed in the compressor 113 to cool the high-pressure and high-temperature boil-off gas. I order it.

The boil-off gas (LBOG) cooled in the heat exchanger 121 is depressurized while passing through the expansion valves (V06, V07) and the isolation valves (V08, V09, V10, and V11) and is supplied to the gas-liquid separator 123 in a gas-liquid mixed state. . The LBOG in a high pressure state (e.g., 300 to 350 barg) may be reduced to a low pressure state (e.g., 2 to 10 barg) while passing through the expansion valves (V06, V07) and the isolation valves (V08, V09, V10, and V11). Expansion valves (V06, 07) are connected in parallel along two lines.

The first controller 151 receives the pressure of the gas-liquid separator 123 measured by the pressure measurement sensor 150, which measures the pressure of the gas-liquid separator 123, and uses the received pressure and a preset reference pressure (e.g. 3.5barG) to determine whether the received pressure is higher than the reference pressure. The reference pressure can be set at 2 barG to 10 barG, and is preferably set at 3.5 barG.

The first controller 151 can control the opening degree of the fourth valve (V04) installed in the evaporation gas recirculation line (L5).

The first controller 151 opens the fourth valve (V04) when the pressure of the gas-liquid separator 123 is higher than the reference pressure, and closes the fourth valve (V04) when it is lower.

The second controller 152, which is set to a maximum pressure (for example, 4.5 barG) higher than the reference pressure of the first controller 151, operates when the pressure of the gas-liquid separator 123 reaches the maximum pressure to lower the pressure.

During normal operation, the first controller 151 controls the pressure of the gas-liquid separator 123, but if the amount of gas produced inside the gas-liquid separator 123 increases, the pressure continues to rise, and the fourth valve (V04) cannot be opened 100%. there is. In this way, when the fourth valve (V04) is opened 100%, the fourth valve (V04) can no longer control the gas pressure, so the pressure continues to increase and reaches the maximum pressure of the second controller (152). The second controller 152 operates to lower the pressure.

That is, when the second controller 152 operates, the second controller 152 sends the pressure value of the gas-liquid separator 123 to the lower selector (LS).

The Royer selector (LS) sends the lowest pressure value among the pressure value of the gas-liquid separator 123, the pressure value of the storage tank 111, and the pressure value of the fuel supplied to the MEGI engine 101 to the expansion valves (V06, V07). deliver it to The expansion valves (V06, V07) are pre-selected by the selector (S) so that only one of them is used as a redundancy concept. The pressure value of the storage tank 111 may be received by the storage tank pressure controller 111a installed around the storage tank 111, and the pressure value of the fuel supplied to the MEGI engine 101 may be received around the MEGI engine 101. It can be received by the MEGI engine pressure controller 153 installed in.

Therefore, when the internal pressure of the gas-liquid separator 123 becomes higher than the internal set pressure (maximum pressure) of the second controller 152, the second controller 152 lowers the opening degree of the expansion valves (V06 and V07). This can reduce the amount of gas produced in the gas-liquid separator 123 by reducing the pressure of the fluid flowing into the gas-liquid separator 123.

As the boil-off gas is at least partially liquefied as it cools and depressurizes, the gas and liquid components are separated in the gas-liquid separator 123, and the liquid component, that is, LNG, is transferred to the storage tank 111 through the boil-off gas return line (L3). , The gas component, that is, the boil-off gas, can be discharged from the storage tank 111 through the boil-off gas recirculation line (L5) and join the boil-off gas supplied to the compressor 113. More specifically, the boil-off gas recirculation line (L5) extends from the top of the gas-liquid separator 123 and can be connected to the upstream or downstream side (not shown) of the heat exchanger 121 in the boil-off gas supply line (L1). .

In addition to being configured to return to the storage tank 111, the liquid component may be configured to be supplied and stored in a separate tank (not shown). In addition, without separating the gas component and the liquid component in the gas-liquid separator 123, the expanded boil-off gas is directly sent to the storage tank 111 without passing through the gas-liquid separator 123 (i.e., without including the gas-liquid separator in the system). The system may be configured to revert.

Above, for convenience of explanation, the heat exchanger 121 was described as being installed in the boil-off gas return line (L3), but in reality, the heat exchanger 121 is used to connect the first stream of boil-off gas being transported through the boil-off gas supply line (L1) and the heat exchanger 121. Since heat exchange occurs between the third stream of boil-off gas being transported through the boil-off gas return line (L3), the heat exchanger 121 is also installed in the boil-off gas supply line (L1).

On the other hand, if the amount of boil-off gas generated in the storage tank 111 is greater than the amount of fuel required by the high-pressure natural gas injection engine, and excess boil-off gas is expected to be generated, it is compressed or step-wise compressed in the compressor 13. The boil-off gas in transit can be branched through the boil-off gas branch lines (L7, L8) and used in the boil-off gas consumption means. As a means of consuming boil-off gas, an auxiliary engine 103 or a GCU 105 that can use natural gas at a relatively low pressure as fuel compared to the main engine 101 may be installed. As the auxiliary engine 103, a DF engine (DFDG), a gas turbine, etc. may be used.

The boil-off gas branch line (L8) is branched from the boil-off gas supply line (L1) so as to branch off the boil-off gas that is being multistage-compressed in the compressor (113). For example, the two-stage compressed BOG can be branched and supplied to the auxiliary engine 103, but this is only an example and does not limit the present invention. For example, the boil-off gas branch line L8 may be configured to branch BOG compressed in one or three stages, or may be configured to branch BOG that has passed through all compression stages of a multi-stage compressor. However, since the required pressure of the DF engine, which is an auxiliary engine, is lower than that of the MEGI engine, which is the main engine, when the BOG compressed at high pressure is branched off at the rear end of the compressor (113), the pressure of the BOG is lowered again and then applied to the auxiliary engine. It can be inefficient because it has to be supplied.

According to the marine gas processing system according to a preferred embodiment of the present invention as described above, the boil-off gas generated when transporting cargo (i.e., LNG) of an LNG carrier is used as fuel for an engine or is re-liquefied and returned to the storage tank. Because it can be stored, it is possible to reduce or eliminate the amount of boil-off gas consumed and discarded in GCU, etc., and to re-liquefy and process the boil-off gas without the need to install a re-liquefaction device using refrigerants such as nitrogen. do.

In addition, according to the marine gas processing system and processing method according to a preferred embodiment of the present invention, a reliquefaction device (for example, a nitrogen refrigerant refrigeration cycle or a mixed refrigerant refrigeration cycle, etc.) using a refrigerant such as a nitrogen refrigerant or a mixed refrigerant may be installed. Since there is no need to install additional equipment to supply and store refrigerant, the initial installation and operating costs for constructing the entire system can be reduced.

So far, some configurations of the gas processing system for processing the liquefied gas stored in the storage tank 111, that is, the boil-off gas generated from LNG, have been described. Hereinafter, the gas processing system for processing the liquefied gas stored in the storage tank 111 will be described. The remaining configuration is explained.

The marine gas processing system of the preferred embodiment shown in FIG. 1 includes a high-pressure natural gas injection engine, such as a MEGI engine, as the main engine 101, and a DF Generator (DFDG) as the auxiliary engine 103. can do. Normally, the main engine is used for propulsion to operate the ship, and the auxiliary engine is used for power generation to supply power to various devices and facilities installed inside the ship. However, the present invention is based on the use of the main engine and the auxiliary engine. It is not limited. Multiple main engines and multiple auxiliary engines may be installed.

The marine gas processing system according to the present invention uses natural gas (i.e., gaseous boil-off gas (BOG)) stored in the storage tank 111 for the engines (i.e., the MEGI engine, which is the main engine, and the DF engine, which is the auxiliary engine). ) and liquid liquefied gas (LNG)) as fuel.

As described above, in order to supply gaseous boil-off gas as fuel gas, the marine gas processing system of the present invention uses a BOG main supply line that supplies BOG contained in the storage tank 111 to the main engine 101. It includes a boil-off gas supply line (L1) and a boil-off gas branch line (L8) as a BOG sub-supply line that branches off from the boil-off gas supply line (L1) and supplies boil-off gas to the auxiliary engine (103).

In addition, in order to supply liquefied gas (e.g., LNG) in a liquid state as fuel gas, the marine gas processing system of the present invention uses an LNG main supply line ( L23) and an LNG secondary supply line (L24) that branches off from the LNG main supply line (L23) and supplies liquefied gas to the auxiliary engine (103).

According to the present invention, a compressor 113 for compressing BOG is installed in the boil-off gas supply line (L1), and a high-pressure pump 143 for compressing LNG is installed in the LNG main supply line (L23). Two high pressure pumps 143 may be installed in parallel to meet redundancy requirements.

The LNG main supply line (L23) includes a discharge pump 112 installed inside the storage tank 111 to discharge LNG to the outside of the storage tank 111, and primary compression in the discharge pump 112. A high-pressure pump 143 is installed to secondarily compress the LNG to the pressure required by the MEGI engine. One discharge pump 112 may be installed inside each storage tank 111.

As described above, the fuel gas pressure required by the MEGI engine is high pressure of about 150 to 400 bara (absolute pressure).

LNG discharged from the storage tank 111 for storing liquefied gas through the discharge pump 112 is transported along the LNG main supply line (L23) and supplied to the high pressure pump 143. Subsequently, the LNG is compressed to high pressure in the high pressure pump 143 and then supplied to the temperature controller 144 to be heated. LNG, heated to the temperature required by the main engine, is supplied as fuel to the main engine, such as the MEGI engine. Because the pressure required by the MEGI engine is higher than the critical pressure of natural gas (LNG and BOG), i.e. methane (approximately 50 bara), natural gas compressed to high pressure is in a supercritical state, that is, neither a gas nor a liquid.

The secondary LNG supply line (L24) for supplying fuel gas to the DF engine, which is an auxiliary engine, branches off from the main LNG supply line (L23). More specifically, the secondary LNG supply line (L24) branches off from the main LNG supply line (L23) so as to branch off LNG before being compressed in the high pressure pump (143).

A heater 145 is installed in the secondary LNG supply line (L24), so that the temperature of LNG supplied as fuel can be adjusted to the value required by the DF engine. During this process, LNG may be vaporized.

According to the present invention, there are two paths for supplying fuel gas to the engines (main engine 101 and auxiliary engine 103). That is, the evaporation gas as fuel gas may be supplied to the engine after being compressed through the compressor 113, and the liquefied gas as fuel gas may be compressed and heated through the high pressure pump 143 and the temperature controller 144 and then supplied to the engine. may be supplied.

In particular, ships such as LNG carriers and LNG RVs are used to transport LNG from production sites to consumption sites, so when sailing from production sites to consumption sites, they operate in a Laden state with the storage tank fully loaded with LNG, and then unload the LNG. When returning to the production site, the storage tank is operated in an almost empty ballast state. In the Raiden state, the amount of LNG is large, so the amount of boil-off gas generated is relatively high, and in the ballast state, the amount of LNG is small, so the amount of boil-off gas generated is relatively small.

There are some differences depending on conditions such as storage tank capacity and external temperature, but for example, when the LNG storage tank capacity is approximately 130,000 ㎥ to 350,000 ㎥, the amount of boil-off gas generated is approximately 3 to 4 tons in Raiden. /h, and is approximately 0.3 to 0.4 ton/h during ballast. Additionally, the amount of fuel gas required by the engines is approximately 1 to 4 ton/h (average approximately 1.5 ton/h) for MEGI engines and approximately 0.5 ton/h for DF engines (DFDG). Meanwhile, recently, as the insulation performance of storage tanks has improved, BOR (Boil Off Rate) has been gradually decreasing, so the amount of BOG generation is also decreasing.

Therefore, in the case where a compressor line (i.e., L1 and L8 in FIG. 1) and a high-pressure pump line (i.e., L23 and L24 in FIG. 1) are equipped together as in the gas processing system of the present invention, a large amount of evaporation gas is generated. It is desirable to supply fuel gas to the engines through a compressor line in a ballast state, and to supply fuel gas to the engines through a high-pressure pump line in a ballast state with low evaporation gas generation.

In general, the energy required to compress gas (BOG) by a compressor to the high pressure of 150 to 400 bara (absolute pressure) required by a MEGI engine is significantly more than the energy required to compress liquid (LNG) by a pump. Since energy is required and the compressor for compressing gas to high pressure is quite expensive and takes up a lot of volume, it may be considered economical to use only the high pressure pump line without the compressor line. For example, 2MW of power is consumed to drive a set of multi-stage compressors to supply fuel to the MEGI engine, but when a high pressure pump is used, only 100kW of power is consumed. However, when fuel gas is supplied to engines using only the high-pressure pump line in a raided state, a re-liquefaction device to re-liquefy the BOG is necessary to deal with the BOG continuously generated in the storage tank, and this re-liquefaction device is required. When considering the energy consumed together, it may be advantageous to install a compressor line and a high-pressure pump line together to supply fuel gas through the compressor line in a raid state and supply fuel gas through a high-pressure pump line in a ballast state.

On the other hand, when the amount of boil-off gas generated in the storage tank does not reach the amount of fuel required by the MEGI engine, such as in the ballast state, the boil-off gas is not compressed in the multi-stage compressor to the high pressure required by the MEGI engine, and evaporates during multi-stage compression. It can be efficient to branch off the boil-off gas through the gas branch line (L8) and use it as fuel in the DF engine. That is, for example, if evaporative gas is supplied to the DF engine through only the second stage compression cylinder of a five-stage compressor, the remaining third stage compression cylinders idle. If the entire 5-stage compressor is driven to compress the evaporation gas, the power required is 2MW, whereas if only the 2nd stage is used and the remaining 3rd stage is left idling, the power required is 600kW, and fuel can be supplied to the MEGI engine through a high-pressure pump. In this case, the required power is 100kW. Therefore, in cases where the amount of BOG generated is less than the fuel requirement in the MEGI engine, such as in a ballast state, it may be advantageous in terms of energy efficiency to consume the entire amount of BOG in the DF engine and supply LNG as fuel through a high pressure pump.

However, if necessary, even when the amount of BOG generated is less than the fuel requirement in the MEGI engine, BOG can be supplied as fuel to the MEGI engine through a compressor and the insufficient amount of LNG can be forcibly vaporized and supplied. Meanwhile, in the ballast state, the amount of BOG generated is small, so instead of discharging and consuming BOG whenever it is generated, BOG is collected without being discharged until the storage tank reaches a certain pressure, and then discharged intermittently to be used in the DF engine or MEGI engine. It can also be supplied as fuel.

Additionally, on ships where it is not easy to repair or replace equipment, it is required to install two important facilities in consideration of emergencies (redundancy; i.e., dual design). In other words, on a ship, extra equipment that can perform the same function as the main equipment is installed, and when the main equipment is operating normally, the spare equipment is placed on standby, and when the main equipment fails, it takes over the function. It is required to design important facilities overlapping to enable this. Equipment that requires dual design mainly includes rotationally driven equipment, such as compressors and pumps.

In this way, on ships, various facilities need to be installed in duplicate in order to satisfy only the dualization requirements while not being used in normal times. A gas processing system using two compressor lines requires a lot of cost and space for compressor installation. There is a problem that a lot of energy is consumed when using this gas, and a gas processing system using two high-pressure pump lines may have a problem that a lot of energy is consumed in processing (i.e., reliquefaction) evaporation gas. In contrast, the gas processing system of the present invention, which installs one compressor line and one high-pressure pump line together, can continue normal operation through the other supply line even if a problem occurs in one supply line, and can eliminate expensive compressors. It is possible to select and operate the optimal fuel gas supply method appropriately according to the amount of evaporative gas generated while using less, thereby reducing not only the initial drying cost but also the operating cost.

As shown in FIG. 1, when using the marine gas processing system of the present invention, the boil-off gas generated when transporting cargo (i.e., LNG) of an LNG carrier is used as fuel for an engine or is re-liquefied and returned to the storage tank. Because it can be stored, it is possible to reduce or eliminate the amount of boil-off gas consumed and discarded in the GCU, etc., and the boil-off gas can be re-liquefied and treated without the need to install a re-liquefaction device that uses a separate refrigerant such as nitrogen. There will be.

According to the present invention, despite the recent trend of increasing the capacity of the storage tank, increasing the amount of evaporative gas generated and reducing the amount of fuel required as engine performance is improved, the evaporative gas remaining after being used as engine fuel is re-liquefied and reused. Since it can be returned to the storage tank, waste of evaporative gas can be prevented.

In particular, according to the present invention, there is no need to install a reliquefaction device using a separate refrigerant (i.e., a nitrogen refrigerant refrigeration cycle or a mixed refrigerant refrigeration cycle, etc.), so there is no need to install additional equipment for supplying and storing the refrigerant. Therefore, the initial installation and operating costs for configuring the entire system can be reduced.

Non-explanatory code: LIT-A is a gas-liquid separator level control measurement sensor, LIT-B is a gas-liquid separator level high measurement sensor, LIC-A is a gas-liquid separator level controller, V01 is the first valve, V02 is the second valve, and V03 is the third. Valve, V05 is the 5th valve, V12 is the 12th valve.

Figure 2 shows a diagram for explaining a method of treating marine gas using a marine gas processing system.

According to a preferred embodiment of the present invention, the first controller 151 receives the pressure of the gas-liquid separator 123 measured by the pressure measurement sensor 150 that measures the pressure of the gas-liquid separator 123.

The first controller 151 compares the received pressure of the gas-liquid separator 123 with a preset reference pressure and determines whether the received pressure is higher than the reference pressure.

The first controller 151 controls the fourth valve (V04) installed in the evaporation gas recirculation line (L5) to close when the pressure of the received gas-liquid separator 123 is less than the standard pressure, and the received gas-liquid separator 123 If the pressure is greater than the standard pressure, the fourth valve (V04) is controlled to open.

In this way, while the pressure of the gas-liquid separator 123 is controlled by the first controller 151, the pressure of the gas-liquid separator 123 is increased even though the fourth valve (V04) is opened to the maximum by the first controller 151. If it is greater than the standard pressure, the second controller 152, which controls the pressure by setting a maximum pressure higher than the standard pressure of the first controller 151, determines whether the pressure of the gas-liquid separator 123 has reached the maximum pressure. do.

When the pressure of the gas-liquid separator 123 reaches the maximum pressure by the second controller 152, the second controller 152 sends the pressure value of the gas-liquid separator 123 to the lower selector (LS).

The Royer selector (LS) sends the lowest pressure value among the pressure value of the gas-liquid separator 123, the pressure value of the storage tank 111, and the pressure value of the fuel supplied to the MEGI engine 101 to the expansion valves (V06, V07). deliver it to

The pressure of the fluid flowing into the gas-liquid separator 123 can be reduced according to the lowest pressure value applied to one of the two expansion valves (V06, V07) selected. Accordingly, the amount of gas generated in the gas-liquid separator 123 can be reduced, and ultimately, the internal pressure of the gas-liquid separator 123 can be stably controlled. Such stable pressure control of the gas-liquid separator 123 not only affects the stable control of the high pressure compressor pressure, but can also be expected to maintain and improve reliquefaction performance.

As such, in the detailed description of the present invention, specific embodiments have been described, but of course, various modifications are possible without departing from the technical spirit of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims described below as well as equivalents to these claims.

101: main engine 111: storage tank
121: heat exchanger 123; gas liquid separator
150: pressure meter 151: first controller
152: Second controller 153: MEGI engine pressure controller
LS: lower selector S: selector

Claims (11)

A marine gas processing system comprising a storage tank storing liquefied natural gas and boil-off gas generated from the liquefied natural gas, and an engine that uses the boil-off gas discharged from the storage tank as fuel,
A compressor that receives the boil-off gas generated in the storage tank through a boil-off gas supply line and compresses it;
the engine receiving and using evaporative gas compressed by the compressor as fuel;
a heat exchanger for cooling some of the boil-off gas compressed by the compressor that is not supplied to the engine by returning it through a boil-off gas return line and exchanging heat with the boil-off gas before being supplied to the compressor;
an expansion valve that depressurizes the boil-off gas cooled in the heat exchanger;
a gas-liquid separator for separating the boil-off gas that is depressurized and at least partially liquefied while passing through the expansion valve into a gas component and a liquid component;
a boil-off gas recirculation line extending from the top of the gas-liquid separator and connected to the boil-off gas supply line;
a first controller that receives the pressure of the gas-liquid separator and compares the received pressure with a reference pressure to adjust the opening degree of the valve installed in the boil-off gas recirculation line;
a second controller set to a maximum pressure higher than the reference pressure;
Including,
The second controller determines whether the pressure of the gas-liquid separator reaches the maximum pressure when the opening degree of the valve is the maximum opening degree, and lowers the opening degree of the expansion valve when the pressure of the gas-liquid separator becomes higher than the maximum pressure. A gas processing system for ships that regulates the pressure of fluid flowing into the gas-liquid separator. delete In claim 1,
Further comprising a Royer selector for selecting the lowest pressure value,
The Royer selector selects the lowest pressure value selected from among the pressure value of the gas-liquid separator, the pressure value of the storage tank received from the storage tank pressure controller, and the pressure value of fuel supplied to the engine received from the pressure controller of the engine. A gas processing system for ships that delivers to the expansion valve. In claim 3,
A marine gas processing system in which the expansion valve is connected in parallel along two lines. delete In claim 1,
The liquid component separated in the gas-liquid separator is returned to the storage tank. In claim 1,
A gas processing system for ships, wherein the gas component separated in the gas-liquid separator joins the boil-off gas supplied to the compressor. A vessel using a marine gas processing system including a storage tank storing liquefied natural gas and boil-off gas generated from the liquefied natural gas, and an engine using the boil-off gas discharged from the storage tank to the boil-off gas supply line as fuel. As a gas processing method,
Receiving the pressure of the gas-liquid separator;
Comparing the received pressure and the reference pressure in a first controller to adjust the opening degree of a valve installed in a boil-off gas recirculation line extending from the top of the gas-liquid separator and connected to the boil-off gas supply line; and
When the opening degree of the valve is the maximum opening degree, the second controller determines whether the pressure of the gas-liquid separator reaches the preset maximum pressure, and when the pressure of the gas-liquid separator becomes higher than the maximum pressure, the opening degree of the expansion valve is lowered to Step of controlling the pressure of the fluid flowing into the gas-liquid separator
A marine gas processing method using a marine gas processing system, including. delete In claim 8,
Lowering the opening degree of the expansion valve is determined by selecting the pressure value of the gas-liquid separator, the pressure value of the storage tank received from the storage tank pressure controller, and the pressure value of the fuel supplied to the engine received from the pressure controller of the engine. A marine gas processing method using a marine gas processing system, wherein the opening degree of the expansion valve is adjusted to the lowest pressure value selected by a selector. delete

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