JPH06123569A - Lng compulsive evaporation device of lng ship - Google Patents

Abstract

PURPOSE:To execute simply even a system control with easy LNG supplying control by arranging, at an outside of a LNG tank, a heating means which compulsorily causes LNG in its inside to evaporate. CONSTITUTION:In a case wherein a boiled off gas is supplied to a boiler 5 which is a main machinery, the boiled off gas is discharged from a compressor 4, and is supplied to the boiler 5. If a gas quantity necessary for the boiler 5, becomes large, a gas pressure in a tank becomes low, and therefore, this is detected by a gas pressure detecting means 20, and a control device 21, based on its signal executes a control to make a divergence of a control valve 15 small. Then, in a coolant circulation device 10, most of a coolant discharged from a pump 11 passes through a first heat exchanger 12 of a coolant circulation circuit 13, here is heated and flows into a second heat exchanger 9 (a heating device), heats LNG in a LNG tank 2 and forcedly generates the boiled off gas. Accordingly, a supply control of a gas becomes easy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in an LNG carrier carrying LNG (liquefied natural gas), when boil-off gas from an LNG tank is used as a main engine fuel, the LNG is forcibly vaporized to assist it. LNG forced evaporation device.

[0002]

2. Description of the Related Art Generally, in an LNG carrier carrying LNG (liquefied natural gas), boil-off gas is naturally generated from the inside of the LNG tank during full-load voyage. Therefore, this is used as fuel for the boiler that rotates the turbine of the main engine, and the boil-off gas is effectively used. This boil-off gas is
Almost 60% to 70% of the main engine fuel is used, and the remaining 40% to 30% is usually used as fuel oil. However, if fuel oil soars compared to LNG, the voyage cost may increase. It was Therefore, in order to make it possible to use less expensive LNG for all of the main engine fuel, LN forcibly evaporating LNG is used.
A G forced evaporation device has been provided.

FIG. 2 shows an LNG carrier equipped with a conventional LNG forced evaporation device. This LNG ship has a hull 10
A boil-off gas conduit 103 is connected to the upper part of the LNG tank 102 arranged in the No. 1 and a compressor 104 is provided in this conduit 103, and the end of the conduit 103 is connected to the fuel injection nozzle of the boiler. The LNG forced evaporation device 105 includes a pump 106 installed in the LNG tank 102, and an LNG forced pumping passage 107 connected to the outlet side of the pump 106 and joined to the conduit 103 outside the LNG tank 102. The LNG forced pumping path 107 includes a bypass path 110 for returning a part of the LNG pumped to the tank 102, and a forced evaporator 108 interposed in the forced pumping path 107. The evaporator 108
Then, the LNG forcibly pumped from the pump 106 is heat-exchanged with the steam 109 to raise the temperature to about −40 ° C., and is joined to the conduit 103. The temperature of the LNG in the LNG tank 102 is -163 ° C, and the temperature of the naturally evaporated boil-off gas is -1 at the inlet of the compressor 104.
It is about 20 ° C.

[0004]

However, the above-mentioned prior art has the following problems. The feed amount (pump discharge amount) to the evaporator 108 must be adjusted according to the required amount of the main engine, but this is adjusted by returning a part of the pump discharge amount to the LNG tank. Simultaneously with this control, the LN sent by the evaporator 108
In order to make the temperature of the outlet side constant for the purpose of surely gasifying all of G, the evaporator 108 performs control such as bypassing part of the LNG fed. Therefore, the control system becomes complicated. At the inlet side of the compressor 104, the boil-off gas and the gas from the evaporator 108 are mixed, and the boil-off gas is almost 100% methane, whereas the boil-off gas is almost 100%.
The gas from is the same as the composition of LNG, and the composition of LNG is
Since it contains methane, ethane, propane, etc., the boil-off gas and the evaporative gas supplied from the evaporator 108 have different compositions. Therefore, the calorific value of the gas changes depending on the mixing ratio of the two, which is not very preferable in controlling the gas supply amount to the boiler. The temperature of the vaporized gas from the evaporator 108 is high (-40
Since the boil-off gas from the LNG tank 102 and the vaporized gas from the evaporator 108 are mixed at the inlet side of the compressor 104, the temperature of the gas is
The temperature of the boil-off gas from 02 rises, and the gas expands correspondingly, and the load on the compressor 104 increases, and a large compressor 104 becomes necessary. A pump 106 is used for pumping LNG from the LNG tank 102, but for forced evaporation,
This pump 106 must be operated at all times. Conventionally, LNG ships are equipped with 3 to 5 LNG tanks, but have 1 or 2 pumps for cooling these tanks using LNG during ballast navigation. Normally, the pump 106, which is a component of the LNG forced evaporation device 105, is also used as this cooling pump. However, as described above, the forced evaporation pump 10 is used.
No. 6 always operates, so each LNG tank 102 should be replaced by another pump 106 in terms of bearing life.
There must be one pump in each. Then, the number of pumps increases and the cost increases.

An object of the present invention is to provide an LNG forced evaporation device in which LNG feed control is easy and system control is easy.

[0006]

According to a first aspect of the present invention, there is provided an LNG forced evaporation device for an LNG ship, wherein the LNG ship uses boil-off gas from an LNG tank as main engine fuel.
A heating means for forcibly evaporating the LNG therein is provided outside the NG tank. LNG of claim 2
In the forced evaporation device, the heating means is composed of a heat exchanger connected to the refrigerant circulation device. In the LNG forced evaporation device according to claim 3, the refrigerant circulation device is provided with a control valve for controlling the amount of the refrigerant sent to the heat exchanger, and the LNG tank is provided with gas pressure detection means for detecting the gas pressure in the tank. A control device for adjusting and controlling the opening degree of the control valve based on a signal from the gas pressure detecting means is provided.

[0007]

In the LNG forced evaporation device according to the first aspect of the present invention, the amount of boil-off gas can be increased by forcibly evaporating the LNG inside the LNG tank by the heating means. Here, the LNG forced evaporation device according to claims 1 to 3 will be comprehensively described. When supplying the boiler-off gas to the boiler, when the gas requirement of the boiler increases, the amount of the boil-off gas becomes insufficient, and the gas in the tank is reduced. The pressure drops. This decrease in gas pressure is detected by the gas pressure detecting means, and the opening of the control valve is adjusted based on the signal to increase the amount of heat energy supplied to the heat exchanger. Then, the heating amount of the LNG tank increases, the evaporation amount of LNG increases, and the boil-off gas amount increases. On the contrary, when the gas pressure in the tank is high, the amount of heat energy supplied to the heat exchanger is reduced,
The amount of evaporation of LNG is reduced. At this time, since the gas supply amount control to the boiler uses only the gas pressure in the tank as a parameter, the control can be performed easily and easily. Further, since gas is supplied to the boiler by a single fuel (methane), the calorific value is constant, and gas supply control can be further facilitated. Furthermore, since a conventional forced evaporation pump is unnecessary, it is sufficient to have one or two cooling pumps for cooling about five LNG tanks.
Further, since the forced evaporator is not necessary, the manufacturing cost can be reduced as compared with the conventional one.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an LN of an LNG carrier according to an embodiment of the present invention.
It is a figure showing composition of a G tank and its LNG forced evaporation device. In the LNG ship, the LN arranged inside the hull 1
A conduit 3 for discharging boil-off gas is connected to the upper part of the G tank 2, a compressor 4 is provided in this conduit 3, and the end of the conduit 3 is connected to a fuel injection nozzle 6 of a boiler 5. The LNG forced evaporation device 8 is for forcibly evaporating LNG in the LNG tank 2.
Basically, it is composed of a second heat exchanger 9 as a heating means and a refrigerant circulation device 10 for circulating a refrigerant in the second heat exchanger 9. The second heat exchanger 9 is provided on the outer bottom of the LNG tank 2, strictly speaking, on the inner bottom of a heat insulating layer (not shown) formed on the outer surface of the LNG tank 2.

The refrigerant circulation device 10 includes a refrigerant circulation circuit 13 for circulating a refrigerant through the second heat exchanger 9, and a refrigerant circulation pump 11 provided in the refrigerant circulation circuit 13.
And the refrigerant circulation circuit 1 on the discharge port side of the pump 11.
3 has a first heat exchanger 12 and a pump 11
The refrigerant pressurized by is heated in the first heat exchanger 12,
It is configured to be supplied to the second heat exchanger 9 and then returned to the pump 11. Further, a bypass circuit 14 that short-circuits the discharge side of the pump 11 and the outlet side of the first heat exchanger 12 is formed in the refrigerant circulation circuit 13. This bypass circuit 14
And a control valve 15 for controlling the amount of refrigerant sent to the second heat exchanger 9.
Is provided.

When the diameter of the spherical LNG tank 2 is 40 m, the second heat exchanger 9 is installed in a ring shape with a width of 5 m via a heat insulating layer at the bottom thereof. As for the refrigerant flowing through the second heat exchanger 9, the LNG in the LNG tank 2 is −16.
Non-flammable liquid that does not solidify due to 3 ° C,
For example, a chlorofluorocarbon-based refrigerant is used, and a refrigerant of about -100 ° C flows through the second heat exchanger 9. First heat exchanger 12
Is for exchanging heat between the circulating refrigerant and the steam 17, and seawater may be used instead of steam. The pump 11 and the first heat exchanger 12 are arranged on the deck.

As the control valve 15, a valve whose opening degree can be adjusted by a proportional solenoid valve, a stepping motor or the like is used. A gas pressure detecting means 20 for detecting the gas pressure in the tank is provided above the LNG tank 2, and a control device for adjusting and controlling the opening degree of the control valve 15 based on a signal from the gas pressure detecting means 20. 21 is provided. The gas pressure detecting means 20 is a pressure sensor and is arranged closer to the LNG tank 2 side than the suction port of the compressor 4. The control device 21 is composed of a microcomputer and the like, and controls the control valve 15 based on a signal from the pressure sensor 20. In the drawing, 23 is an upper protective cover of the LNG tank 2.

In the above structure, when supplying the boil-off gas to the boiler 5 of the main engine, the boil-off gas evaporated from the upper part of the LNG tank 2 is discharged from the compressor 4 through the boil-off gas conduit 3 and the boil-off gas is heated to about 30 ° C. Is heated and supplied to the boiler 5. Since the compressor 4 supplies the required amount of gas to the boiler 5, the required gas amount of the boiler 5 becomes large, and if the boil-off gas amount becomes insufficient, the gas pressure in the tank will decrease. Detected by the gas pressure detection means 20, the control device 21 controls the opening of the control valve 15 to be small based on the signal. Then, in the refrigerant circulation device 10, most of the refrigerant discharged from the pump 11 passes through the first heat exchanger 12 of the refrigerant circulation circuit 13, is heated there, and flows into the second heat exchanger 9, where the second heat LN with exchanger 9
The LNG in the G tank 2 is heated to forcibly generate boil-off gas at about -160 ° C. Then, the feed gas amount of the compressor 4 and the boil-off gas amount generated in the tank are balanced.

On the contrary, when the required gas amount of the boiler 5 becomes small, the amount of boil-off gas supplied from the compressor 4 becomes small and the gas pressure in the tank increases, so this gas pressure is detected by the gas pressure detecting means 20. Control device 21
Increases the opening of the control valve 15 based on the signal.
Then, in the refrigerant circulation device 10, a part of the refrigerant discharged from the pump 11 returns to the second heat exchanger 9 through the bypass circuit 14 without passing through the first heat exchanger 12, so that the refrigerant circulation circuit. In 13, the heat energy supplied to the second heat exchanger 9 decreases. Therefore, the amount of boil-off gas evaporated from the inside of the LNG tank 2 is reduced, and the feed gas amount of the compressor 4 and the amount of boil-off gas generated inside the tank are balanced again.

In this way, the gas pressure in the tank is detected by the gas pressure detecting means 20, the control valve 15 is feedback-controlled to adjust the heat energy sent to the second heat exchanger 9, and a predetermined gas pressure is maintained. By doing so, the amount of boil-off gas sent from the compressor 4 follows the amount of gas required by the boiler 5, and the fuel of the boiler 5 can be covered by 100% boil-off gas. Further, the boil-off gas sent to the compressor 4 is methane gas at about -120 ° C, and its composition is close to that of a single fuel unlike the conventional forced evaporator shown in Fig. 2, and therefore gas supply control is easy. You can do it. Further, in the fuel supply control to the boiler 5 including the forced evaporation device 8, since the control valve 15 is feedback-controlled with only the gas pressure as a parameter, the control can be easily and surely performed. Furthermore, in the conventional forced evaporation device shown in FIG.
The load of the compressor 4 was increased because the forced evaporative gas of −40 ° C. was mixed with the natural evaporative gas of 120 ° C. and the gas of which the temperature was raised was supplied, but in the present embodiment, the load is always low (−120 Since the gas of (° C.) is supplied, the load on the compressor 4 can be reduced and a small compressor can be used.

The second heat exchanger 9 as a heating means
It is also possible to directly supply the steam generated by the combustion of the boiler 5, but when the engine is stopped, such as when moored, no steam is generated and the temperature of the LNG tank 2 is a low temperature of about -163 ° C. , The water in the heat exchanger may freeze, and the circulation pipe may be damaged. In this respect, if a CFC-based refrigerant that does not solidify even at a low temperature is used as in this embodiment, there is no risk of freezing of the circulation pipe.

The present invention is not limited to the above embodiment, and it goes without saying that many modifications and changes can be made within the scope of the present invention. For example, although the control valve is arranged in the bypass circuit 14 in the above embodiment, the control valve may be directly provided in the refrigerant circulation circuit without providing the bypass circuit, and the rotation speed of the pump 11 may be controlled. You may comprise. Further, although steam was used as the heat source of the heat exchanger of the refrigerant circulation device in the above-mentioned embodiment, the heat source is not limited to this, and it is also possible to use solar heat.

[0017]

As described above, the L according to claim 1
According to the NG forced evaporating apparatus, the heating means for forcibly evaporating the LNG in the LNG tank is provided outside the LNG tank, so that the conventional forced evaporative pump is not necessary and the cooling pump has five pumps. In the case of, it is sufficient to use about two pieces and the manufacturing cost can be reduced. Moreover, the gas supplied to the compressor of the gas discharge path is close to a single fuel, and the gas supply control can be easily performed. Further, unlike the conventional case, the boil-off gas sent to the compressor is a low-temperature evaporative gas, so the load on the compressor can be reduced, a compact compressor can be used, and further cost reduction can be realized. In the LNG forced evaporation device according to claim 2, since the heat exchanger is used as the heating means, the thermal energy of the steam generated from the seawater or the boiler can be effectively used, and the energy saving effect is large without using new energy. Is. According to the LNG forced evaporation device of the third aspect, the fuel supply control to the main engine is performed by feedback control of the control valve using only the gas pressure as a parameter, so that the excellent effect that the control can be performed easily and reliably is achieved. is there.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an LNG tank of an LNG ship and its LNG forced evaporation device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional LNG forced evaporation device for an LNG ship.

[Explanation of symbols]

 2: LNG tank 3: Conduit 4: Compressor 5: Boiler 8: LNG forced evaporation device 9: Second heat exchanger (heating means) 10: Refrigerant circulation device 11: Pump 12: First heat exchanger 13: Refrigerant circulation circuit 14: Bypass circuit 15: Control valve 20: Gas pressure detection means 21: Control device

Claims (3)

[Claims] 1. A LNG forcible evaporation system, wherein a heating means for forcibly evaporating the LNG inside is provided outside the LNG tank in an LNG ship that uses boil-off gas from the LNG tank as a main engine fuel. apparatus. 2. The LNG forced evaporation device according to claim 1, wherein the heating means is a heat exchanger connected to a refrigerant circulation device. 3. The refrigerant circulation device is provided with a control valve for controlling the amount of refrigerant sent to a heat exchanger, and gas pressure detection means for detecting gas pressure in the tank is provided above the LNG tank.
The LNG forced evaporation device according to claim 2, further comprising a control device that adjusts and controls the opening degree of the control valve based on a signal from the gas pressure detection means.