KR101277952B1 - A fuel gas supply system of liquefied natural gas - Google Patents

Abstract

PURPOSE: A system for supplying LNG is provided to prevent cavitations by collecting evaporation gas so that the gas doesn't move into a pump. CONSTITUTION: A system for supplying LNG comprises a fuel supply line(21), a boosting pump(31), a high pressure pump(32), a return line(40), and a differential pressure flow meter. The fuel supply line is connected to an engine from an LNG storage tank(10). The boosting pump is installed in the fuel supply line. The high pressure pump pressurizes LNG discharged from the boosting pump at 200 to 400 bar. The return line is installed at the front side of the high pressure pump. The differential pressure flow meter measures the pressure of the LNG which is collected along the return line. [Reference numerals] (10) LNG storage tank; (20) Engine; (60) Heat exchanger

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an LNG fuel supply system,

The present invention relates to an LNG fuel supply system.

A ship is a means of transporting large quantities of minerals, crude oil, natural gas, or more than a thousand containers. It is made of steel and buoyant to float on the water surface. ≪ / RTI >

Such a vessel generates thrust by driving the engine. In this case, the engine uses gasoline or diesel to move the piston so that the crankshaft is rotated by the reciprocating motion of the piston, so that the shaft connected to the crankshaft is rotated to drive the propeller It was common.

In recent years, however, LNG fuel supply systems for driving an engine using LNG as a fuel have been used in an LNG carrier carrying Liquefied Natural Gas (LNG) It is also applied to other ships.

Generally, it is known that LNG is a clean fuel and its reserves are more abundant than petroleum, and its usage is rapidly increasing as mining and transfer technology develops. This LNG is generally stored in a liquid state at a temperature of -162 ° C. or below under 1 atm. The volume of liquefied methane is about one sixth of the volume of methane in a gaseous state, The specific gravity is 0.42, which is about one half of that of crude oil.

However, the temperature and pressure required to drive the engine may be different from the state of the LNG stored in the tank. Therefore, in recent years, research and development have been made on the technology of controlling the temperature and pressure of the LNG stored in the liquid state and supplying the engine to the engine.

The present invention was created to solve the problems of the prior art as described above, an object of the present invention is provided with a suction drum downstream of the LNG storage tank, by recovering the boil-off gas so that the boil-off gas does not flow into the pump, It is to provide an LNG fuel supply system that can prevent the phenomenon from occurring.

It is another object of the present invention, a recovery line is connected between the boosting pump and the high pressure pump, and the boosting pump supplies the maximum flow rate to the high pressure pump, but the surplus flow rate that is not received from the high pressure pump is recovered to the suction drum, thereby providing a high pressure pump. It is to provide an LNG fuel supply system that can satisfy the required flow rate.

Still another object of the present invention is to provide an orifice in a recovery line connected to a suction drum to monitor the pressure of the recovered LNG to control the supply flow rate of the boosting pump, thereby optimizing power consumption and LNG recovery flow rate. It is for providing a fuel supply system.

LNG fuel supply system according to an aspect of the present invention, the fuel supply line connected to the engine from the LNG storage tank; A boosting pump provided on the fuel supply line to pressurize the LNG discharged from the LNG storage tank; A high pressure pump pressurizing the LNG discharged from the boosting pump to a high pressure; A recovery line connected between the boosting pump and the high pressure pump to recover the LNG upstream; And a differential pressure flow meter provided in the recovery line to measure the pressure of the LNG recovered along the recovery line, wherein the boosting pump varies the supply flow rate of the high pressure pump according to the differential pressure measured by the differential pressure flow meter. It is characterized by.

Specifically, the differential pressure flow meter may be an orifice.

Specifically, the boosting pump may vary the supply flow rate according to the differential pressure measured by the differential pressure flow meter at a predetermined time or in real time.

In detail, the recovery line may be connected to the LNG storage tank to recover the LNG to the LNG storage tank.

Specifically, further comprising an auxiliary storage tank provided on the fuel supply line downstream of the LNG storage tank, the recovery line is connected to the auxiliary storage tank may recover the LNG to the auxiliary storage tank. .

Specifically, the auxiliary storage tank may be a suction drum for separating the boil-off gas from the LNG discharged from the LNG storage tank.

Specifically, the high pressure pump may pressurize the LNG to 200 bar to 400 bar.

In the LNG fuel supply system according to the present invention, the suction drum provided downstream of the LNG storage tank separates the boil-off gas from the LNG discharged from the LNG storage tank, thereby preventing the gas from flowing into the pump and preventing a failure of the pump. Can be.

In addition, the LNG fuel supply system according to the present invention, by connecting the suction drum to the recovery line between the boosting pump and the high pressure pump, the boosting pump to provide the maximum flow rate to the high pressure pump to satisfy the required flow rate of the high pressure pump However, the surplus flow rate can be recovered to the suction drum to enable a smooth pump operation.

In addition, the LNG fuel supply system according to the present invention, by installing an orifice in the recovery line connected to the suction drum between the boosting pump and the high pressure pump to determine the recovery pressure, by varying the supply flow rate of the boosting pump according to the recovery pressure, The power consumption by the boosting pump can be reduced.

1 is a conceptual diagram of a conventional LNG fuel supply system.
2 is a conceptual diagram of an LNG fuel supply system according to an embodiment of the present invention.
3 is a cross-sectional view of an LNG storage tank in an LNG fuel supply system according to an embodiment of the present invention.
4 is a conceptual diagram of an LNG fuel supply system according to another embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual diagram of a conventional LNG fuel supply system.

As shown in FIG. 1, the conventional LNG fuel supply system 1 includes an LNG storage tank 10, an engine 20, a pump 30, and a heat exchanger 60. At this time, the pump 30 may include a boosting pump 31 and a high pressure pump 32. In the present specification, LNG can be used to encompass both NG, which is a liquid state, and NG, which is a supercritical state, for the sake of convenience.

In the conventional LNG fuel supply system 1, after the boosting pump 31 pressurizes LNG discharged from the LNG storage tank 10 to several to several tens of bar, the high pressure pump 32 requests the engine 20. The LNG is pressurized at a pressure (for example, 200 bar to 400 bar) to be supplied to the heat exchanger 60. Thereafter, the heat exchanger 60 may increase the temperature of the LNG supplied from the pump 30 and allow the LNG in the supercritical state to be supplied to the engine 20. In this case, the LNG supplied to the engine 20 may have a pressure of 200 to 400 bar and a supercritical state having a temperature of 40 to 60 degrees.

At this time, the high pressure pump 32 must be supplied with a constant flow rate of LNG, and the flow rate required by the high pressure pump 32 is expressed by NPSHr (Net Positive Suction Head). If a predetermined amount of LNG does not flow into the high pressure pump 32, cavitation may occur and the high pressure pump 32 may be damaged. Therefore, it is very important to satisfy the required flow rate of the high pressure pump 32.

Therefore, in order to continuously satisfy the required flow rate of the high pressure pump 32, the boosting pump 31 is disposed in front of the high pressure pump 32, and the boosting pump 31 is discharged from the LNG storage tank 10. The LNG was pressurized and then delivered to the high pressure pump 32 to prevent breakage of the high pressure pump 32.

In this case, however, it is considerably difficult to control the operation of the boosting pump 31 to keep the required flow rate of the high-pressure pump 32 constant. When the discharge flow rate of the boosting pump 31 is different from the NPSHr of the high- There is a problem that the risk of breakage of the battery 32 still exists.

FIG. 2 is a conceptual diagram of an LNG fuel supply system according to an embodiment of the present invention, and FIG. 3 is a sectional view of an LNG storage tank in an LNG fuel supply system according to an embodiment of the present invention.

As shown in FIG. 2, the LNG fuel supply system 2 according to an embodiment of the present invention includes an LNG storage tank 10, an engine 20, a pump 30, a recovery line 40, and auxiliary storage. Tank 50, heat exchanger 60. In an embodiment of the present invention, the LNG storage tank 10, the engine 20, the pump 30, the heat exchanger 60, and the like refer to the same reference numerals for convenience of each configuration in the conventional LNG fuel supply system 1. Used, but not necessarily the same configuration.

The LNG storage tank 10 stores the LNG to be supplied to the engine 20. The LNG storage tank 10 must store the LNG in a liquid state, and the LNG storage tank 10 may have a pressure tank form.

As shown in FIG. 3, the LNG storage tank 10 includes an outer tank 11, an inner tank 12, and an insulator 13. The outer tank 11 is formed as an outer wall of the LNG storage tank 10, and may be formed of steel, and may have a polygonal cross section.

The tanks 12 are provided inside the tanks 11 and can be supported and supported inside the tanks 11 by means of a support 14. At this time, the support 14 may be provided at the lower end of the inner tank 12, and may be provided at the side of the inner tank 12 in order to suppress the lateral movement of the inner tank 12. [

The bath tank 12 may be made of stainless steel and designed to withstand a pressure of 5 bar to 10 bar (for example 6 bar). The reason why the inner tank 12 is designed to withstand such a constant pressure is that the inner pressure of the inner tank 12 can be raised as the LNG provided in the inner tank 12 is evaporated to generate the evaporation gas Because.

A baffle 15 may be provided in the inner tank 12. [ The baffle 15 means a plate in the form of a lattice and the baffle 15 is installed so that the pressure inside the tank 12 can be evenly distributed to prevent the tank 12 from being subjected to concentrated pressure .

The heat insulating portion 13 is provided between the inner tank 12 and the outer tank 11 and can prevent the external heat energy from being transmitted to the inner tank 12. [ At this time, the heat insulating portion 13 may be in a vacuum state. By forming the adiabatic portion 13 in a vacuum, the LNG storage tank 10 can more efficiently withstand higher pressures as compared to a conventional tank. For example, the LNG storage tank 10 may sustain a pressure of 5 to 20 bar through the vacuum insulation 13.

As described above, the present embodiment uses the pressure tank LNG storage tank 10 having the vacuum insulation unit 13 between the outer tank 11 and the inner tank 12 to minimize the generation of the evaporated gas And it is possible to prevent the LNG storage tank 10 from being damaged even if the internal pressure is increased.

The engine 20 is driven through the LNG supplied from the LNG storage tank 10 to generate thrust. In this case, the engine 20 may be a MEGI engine or a dual fuel engine.

When the engine 20 is a dual fuel engine, LNG and oil may be selectively supplied without being mixed with the LNG. This is to prevent the mixture of two materials having different combustion temperatures from being mixed and to prevent the efficiency of the engine 20 from being lowered.

As the piston 20 (not shown) in the cylinder (not shown) reciprocates due to the combustion of the LNG, the engine 20 rotates the crank shaft (not shown) connected to the piston, (Not shown) can be rotated. Therefore, as the propeller (not shown) connected to the shaft finally rotates when the engine 20 is driven, the hull is moved forward or backward.

Of course, in the present embodiment, the engine 20 may be an engine 20 for driving a propeller, but it may be an engine 20 for generating electricity or an engine 20 for generating other power. That is, the present embodiment does not specifically limit the type of the engine 20. However, the engine 20 may be an internal combustion engine that generates a driving force by combustion of the LNG.

A fuel supply line 21 for transmitting LNG may be installed between the LNG storage tank 10 and the engine 20, and the pump supply line 21 may include a pump 30, an auxiliary storage tank 50, and a heat exchanger. 60 may be provided to allow LNG to be supplied to the engine 20.

At this time, the fuel supply line 21 is provided with a fuel supply valve (not shown), the supply amount of LNG can be adjusted according to the opening degree of the fuel supply valve.

The pump 30 is provided on the fuel supply line 21 and pressurizes the LNG discharged from the LNG storage tank 10 to a high pressure. The pump 30 includes a boosting pump 31 and a high-pressure pump 32.

The boosting pump 31 may be provided on the fuel supply line 21 between the LNG storage tank 10 and the high pressure pump 32 or in the LNG storage tank 10 and may be sufficient for the high pressure pump 32 So that positive LNG is supplied to prevent cavitation of the high-pressure pump 32. Also, the boosting pump 31 can extract the LNG from the LNG storage tank 10 and pressurize the LNG within several to several tens of bars.

The LNG stored in the LNG storage tank 10 is in a liquid state. At this time, the boosting pump 31 may pressurize the LNG discharged from the LNG storage tank 10 to slightly increase the pressure and the temperature, and the LNG pressurized by the boosting pump 31 may still be in a liquid state.

In this embodiment, the boosting pump 31 may supply the maximum flow rate to the high pressure pump 32. The maximum flow rate means the flow rate that the boosting pump 31 can discharge as much as possible. In this case, since a larger amount of LNG than the required flow rate of the high pressure pump 32 is transferred from the boosting pump 31 to the high pressure pump 32, smooth driving of the high pressure pump 32 is possible.

However, the processing of the surplus LNG may be a problem, but in the present embodiment, the surplus LNG may be recovered to the auxiliary storage tank 50 or the LNG storage tank 10 through the recovery line 40. This will be described later.

The high-pressure pump 32 pressurizes the LNG discharged from the boosting pump 31 to a high pressure so that the LNG is supplied to the engine 20. The LNG is discharged at a pressure of about 10 bar from the LNG storage tank 10 and then pressurized primarily by the boosting pump 31, and the high pressure pump 32 receives the liquid LNG pressurized by the boosting pump 31. It pressurizes secondary and supplies to the heat exchanger 60 mentioned later.

At this time, the high-pressure pump 32 may pressurize the LNG to the engine 20 at a pressure required by the engine 20, for example, 200 to 400 bar, thereby causing the engine 20 to produce thrust through the LNG .

The high pressure pump 32 is capable of phase-changing the LNG discharged from the boosting pump 31 to a supercritical state having a higher temperature and a higher pressure than the LNG at a high pressure have. At this time, the temperature of the supercritical LNG may be lower than -20 ° C, which is relatively higher than the critical temperature.

Or the high-pressure pump 32 can pressurize the LNG in a liquid state to a super-cooled liquid state by pressurizing it with a high pressure. Here, the LNG in the subcooled liquid state is a state in which the pressure of the LNG is higher than the critical pressure and the temperature is lower than the critical temperature.

Specifically, the high-pressure pump 32 pressurizes the liquid LNG discharged from the boosting pump 31 to a high pressure of 200 to 400 bar so that the temperature of the LNG becomes lower than the critical temperature, Phase change. Here, the temperature of the LNG in the subcooled liquid state may be -140 캜 to -60 캜, which is relatively lower than the critical temperature.

The recovery line 40 is connected between the boosting pump 31 and the high pressure pump 32 to recover LNG upstream. The recovery line 40 may be connected to the LNG storage tank 10 to recover LNG to the LNG storage tank 10, or may be connected to the auxiliary storage tank 50 to recover LNG to the auxiliary storage tank 50. Can be.

In this embodiment, since the boosting pump 31 supplies the maximum flow rate to the high pressure pump 32, an excess flow rate exceeding the required flow rate of the high pressure pump 32 may be supplied to the high pressure pump 32 side. In this case, if the surplus flow rate is left, some flow rates may flow back to the boosting pump 31 or the supply flow from the boosting pump 31 to the high pressure pump 32 may be lowered.

Therefore, in this embodiment, the recovery line 40 is connected between the boosting pump 31 and the high pressure pump 32 so that an excess flow rate exceeding the required flow rate of the high pressure pump 32 flows into the recovery line 40. can do. At this time, the surplus flow rate may be introduced into the LNG storage tank 10 along the recovery line 40 or into the auxiliary storage tank 50 and then introduced into the boosting pump 31 again.

The auxiliary storage tank 50 is provided on the fuel supply line 21 downstream of the LNG storage tank 10, and receives the LNG recovered along the recovery line 40 and delivers the LNG to the boosting pump 31 again. have. Through this, the present embodiment can prevent a problem such as backflow due to the excess flow rate that may remain between the boosting pump 31 and the high pressure pump 32.

The auxiliary storage tank 50 may be a suction drum separating the boil-off gas from the LNG discharged from the LNG storage tank 10. That is, the auxiliary storage tank 50 is disposed on the fuel supply line 21 connected from the LNG storage tank 10 to the boosting pump 31, and after separating the boil off gas from the LNG, only the LNG in the liquid state is boosted by the pump. By supplying to (31), it is possible to prevent cavitation from occurring in the boosting pump (31).

In addition, the auxiliary storage tank 50, when the internal pressure of the LNG storage tank 10 is excessively increased and the abnormal amount of LNG is transferred to the boosting pump 31 direction, by temporarily storing the LNG by boosting the pump 31 Overload can be prevented.

The heat exchanger 60 is provided on the fuel supply line 21 between the engine 20 and the pump 30, and heats LNG supplied from the pump 30. The pump 30 for supplying LNG to the heat exchanger 60 may be a high pressure pump 32, and the heat exchanger 60 may be a pressure at which the LNG of the supercooled liquid state or the supercritical state is discharged from the high pressure pump 32. By heating while maintaining 200 bar to 400 bar, it can be converted to LNG in a supercritical state of 40 degrees to 60 degrees and then supplied to the engine 20.

Depending on the state in which the high pressure pump 32 changes the phase of LNG, the amount of heat supplied to the LNG by the heat exchanger 60 may vary. That is, when the high pressure pump 32 phase changes the LNG to a supercritical state, the heat exchanger 60 must heat the LNG from -20 degrees to 40 to 60 degrees, while the high pressure pump 32 causes the LNG to be supercooled liquid. When the phase change to the state, the heat exchanger 60 should heat the LNG from -60 degrees to 40 to 60 degrees.

The heat exchanger 60 may heat LNG using a steam heater supplied through a boiler (not shown) or a glycol heater supplied from a glycol heater (not shown), or heat LNG using electric energy. Alternatively, the LNG may be heated by using waste heat generated from a generator or other facilities provided in the vessel.

As such, the present embodiment operates the boosting pump 31 to the maximum so that a sufficient flow rate may be supplied to the high pressure pump 32, but the excess flow rate that does not flow into the high pressure pump 32 may cause the recovery line 40 to recover. Accordingly, the LNG storage tank 10 or the auxiliary storage tank 50 can be recovered, thereby enabling smooth operation of the high pressure pump 32.

In addition, the present embodiment, by using the suction drum as the auxiliary storage tank 50, by allowing the boil-off gas to be separated from the LNG supplied to the boosting pump 31, such as damage to the pump 30 by the inlet of the boil-off gas Problems can be prevented from occurring.

4 is a conceptual diagram of an LNG fuel supply system according to another embodiment of the present invention.

As shown in FIG. 4, the LNG fuel supply system 3 according to another embodiment of the present invention includes an LNG storage tank 10, an engine 20, a pump 30, a recovery line 40, and a differential pressure flow meter. 41, an auxiliary storage tank 50, and a heat exchanger 60. Except for the pump 30 and the differential pressure flow meter 41 in the present embodiment is similar to the configuration described in the above embodiment, a detailed description thereof will be omitted.

The pump 30 includes a boosting pump 31 and a high pressure pump 32. Since the high pressure pump 32 in the present embodiment is the same as the high pressure pump 32 in the above-described embodiment, the following will focus on the boosting pump 31.

In the present embodiment, the boosting pump 31 is driven within a range capable of matching the required flow rate of the high pressure pump 32. Unlike the embodiment described above, the present embodiment does not operate the boosting pump 31 to the maximum so that the maximum flow rate flows into the high pressure pump 32, but the recovery line 40 through the differential pressure flow meter 41. ) To determine the pressure of the LNG to be recovered, thereby controlling the boosting pump 31.

When the boosting pump 31 is operated at maximum and the excess flow rate is recovered, the power consumption by the boosting pump 31 increases and the internal pressure of the LNG storage tank 10 is increased due to the LNG recovered to the LNG storage tank 10. Problems may arise.

However, in the present embodiment, the boosting pump 31 detects the excess flow rate recovered by the recovery line 40 and increases or decreases the supply flow rate of the boosting pump 31, thereby increasing the high pressure pump 32 by the boosting pump 31. Power consumption can be optimized by ensuring that a sufficient flow rate is supplied).

At this time, the boosting pump 31 may vary the supply flow rate according to the differential pressure measured by the differential pressure flow meter 41 at a predetermined time or in real time. This is to prepare for the case where the required flow rate of the high pressure pump 32 changes according to external conditions.

The differential pressure flow meter 41 is provided in the recovery line 40 to measure the pressure of LNG recovered along the recovery line 40. The differential pressure flow meter 41 may be an orifice and measure the differential pressure at the front and rear ends.

Therefore, in the present embodiment, the pressure of the LNG flowing along the recovery line 40 is measured by the differential pressure flow meter 41, and the measured value is transmitted to the boosting pump 31, so that the measured pressure of the LNG is over the preset value. If so, the supply flow rate of the boosting pump 31 is reduced, and if the measured pressure of the LNG is less than the preset value, the supply flow rate of the boosting pump 31 is increased, so that the LNG of less than the required flow rate flows into the high pressure pump 32. This can be prevented from occurring.

As described above, the present embodiment measures the LNG pressure of the recovery line 40 with the differential pressure flow meter 41, and varies the supply flow rate of the boosting pump 31 based on the differential pressure flow meter 41, thereby causing excessive power consumption by the boosting pump 31. It is possible to prevent the increase and increase the operating efficiency of the system by reducing the recovery flow rate of LNG.

1: conventional LNG fuel supply system 2, 3: LNG fuel supply system of the present invention
10: LNG storage tank 11: outer tank
12: inner tank 13:
14: Support 15: Baffle
20: engine 21: fuel supply line
30: Pump 31: Boosting pump
32: high pressure pump 40: return line
41: differential pressure meter 50: auxiliary storage tank
60: heat exchanger

Claims (7)

A fuel supply line connected from the LNG storage tank to the engine;
A boosting pump provided on the fuel supply line and configured to pressurize the LNG to several to several tens of bar;
A high pressure pump for pressurizing the LNG discharged from the boosting pump to 200 bar to 400 bar;
A recovery line provided at the front side of the high pressure pump to recover surplus LNG upstream when an amount of LNG greater than a required flow rate of the high pressure pump is transferred from the boosting pump to the high pressure pump; And
It includes a differential pressure flow meter for measuring the pressure of the LNG recovered along the recovery line,
When the high pressure pump is driven, the boosting pump reduces the supply flow rate to the high pressure pump when the differential pressure measured by the differential pressure flow meter is equal to or greater than a preset value, and supplies the supply flow rate when the measured differential pressure is less than the preset value. By increasing the, by continuously satisfying the required flow rate of the high pressure pump to prevent the occurrence of the cavitation in the high pressure pump to enable smooth operation of the high pressure pump and LNG, characterized in that to optimize the power consumption of the boosting pump Fuel supply system. According to claim 1, wherein the differential pressure flow meter,
LNG fuel supply system, characterized in that the orifice. The booster pump according to claim 1,
The LNG fuel supply system, characterized in that the supply flow rate is varied according to the differential pressure measured by the differential pressure flow meter at a predetermined time or in real time. The method of claim 1, wherein the recovery line,
The LNG fuel supply system, characterized in that connected to the LNG storage tank to recover the LNG to the LNG storage tank. The method of claim 1,
Further comprising a secondary storage tank provided on the fuel supply line downstream of the LNG storage tank,
The recovery line is connected to the auxiliary storage tank LNG fuel supply system, characterized in that for recovering the LNG to the auxiliary storage tank. The method of claim 5, wherein the auxiliary storage tank,
The LNG fuel supply system, characterized in that the suction drum for separating the boil-off gas from the LNG discharged from the LNG storage tank. delete

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