JPH02175393A - Unloading method for lng ship - Google Patents

Abstract

PURPOSE:To simplify operation and save labor and energy by carrying out unloading from the tank of an LNG ship to a tank on the land and, when the inside of the ship tank becomes atmospheric pressure, feeding an LNG gas under pressure from the land tank into the ship tank by means of a blower and pressurizing the ship tank to unload a liquid into the land tank. CONSTITUTION:By opening a liquid valve 6 and preparing a liquid system, an LNG 20 in a spherical tank 3 is unloaded by means of a liquid storage pump 2. Then, as the liquid in the spherical tank 3 is reduced to approx. 90% liquid level 19, since the volume of a gas phase portion is increased causing a gas phase portion pressure to become atmospheric pressure, a gas valve 11 is opened preparing a gas system and a gas in a land tank 4 is fed under pressure into the spherical tank 3 by means of a gas returning blower 10 to pressurize the inside of the tank 3. At the same time, the unloading from the spherical tank 3 of the ship 1 is carried out by means of the liquid storage pump 2 and the system 8. By this structure, a BOG handling device and a main fuel mode switchover operation can be dispensed with to save labor and energy.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for unloading an LNG ship.

[Conventional technology]

Conventionally, ocean-going LNCs and ships have used gas-fired boilers as processing equipment for the gas (hereinafter referred to as BOG) that boils off from the LNG in the heavy oil tank 021 during LNG transportation, as shown in the vertical cross-sectional view of Figure 2. 022 is known. Here, 023 is a propeller turbine, the heavy oil tank 021 is operated under a state close to normal pressure, and unloading is performed by the ship's lifting pump.

Furthermore, as shown in the vertical cross-sectional view of FIG. 3, a BOG processing apparatus equipped with a gas-fired diesel engine 024 is also known.

However, when such an OG processing device is applied to a relatively small coastal LNG ship, the following drawbacks are expected.

(1) Since the BOG processing equipment is expensive and complicated, the construction cost and operation cost increase, and the economic efficiency of the ship decreases.

(2) The route is short, and the main engine combustion mode must be switched between gas-fired and heavy oil-fired each time the ship berths, which increases the burden of complicated work for the crew and is also problematic in terms of energy conservation.

[Problem to be solved by the invention]

The present invention was proposed in view of these circumstances, and
The purpose of the present invention is to provide an LNG unloading method for an LNG ship that does not require an expensive OG processing device or a troublesome main engine combustion mode switching operation and is excellent in economy, labor saving, and energy saving.

[Means to solve the problem]

To this end, the present invention, when pumping LNG in an LNG spherical tank, pumps LNG from an LPJG spherical tank whose internal pressure is higher than normal pressure to a land spherical tank through a pump and an LNG pumping line. The LNG is returned from the land spherical tank to the LNG spherical tank whose internal pressure has become normal pressure through the gas blower and the LNG return gas line.
The method is characterized by comprising a second step of pressurizing the LNG boat-shaped tank by pumping G gas and pumping liquid from the LNG boat-shaped tank via the liquid pump and the LNG pumping line. .

[Effect]

With the above configuration, it is possible to obtain an LNG ship unloading method that is economical, labor-saving, and energy-saving, without requiring an expensive OC treatment device or a troublesome main engine combustion mode switching operation.

〔Example〕

An embodiment in which the present invention is applied to a small coastal LNG ship will be explained with reference to the drawings. Tank type, maximum working pressure is approximately 3 ky/
'-rn'IG.

2 is a submerged pull type lifting pump installed in the spherical tank 3; 4 is a spherical tank type land tank with a maximum operating pressure of approximately 2 ky% i'G installed at the receiving base 5; 6, 7
are a liquid valve and a liquid arm installed at the tip of the liquid system 8 of the receiving tank 4, respectively.

9, 10, 11, and 12 are a gas return valve, a gas return blower, a gas valve, and a gas arm, respectively, inserted into the gas system 13 of the receiving tank 4.

14 and 15 are B inserted into the BOG processing system 17 which joins the branch port supply system 1.6 K from the gas system 13, respectively.
OG compressor, bypass valve, 18° and 19 respectively indicate the 100% liquid level of LNG20 stored in the spherical tank 3, 90
% liquid level.

In such a system, the LNG carrier 1 accumulates BOG that has naturally evaporated during the voyage in the spherical tank 3, and the LNG carrier 1 carries it to the receiving terminal 5 in a relatively high-pressure state where the internal pressure is generally about 3 ky/cm'G. After arriving at the berth, the related pipelines are connected to the liquid arm 7 and gas arm 12 of the receiving base 5, respectively.

In this state, as a first step, the liquid valve 6 is opened and the liquid system is lined up, and then the LNG 20 in the spherical tank 3 is unloaded from the state of 100% liquid level 18 by the unloading pump 2 of the LNG ship 1. .

Next, when the inside of the spherical tank 3 reaches a 90% liquid level of about 19, the volume of the gas phase increases, and the pressure of the gas phase becomes normal pressure according to Boyleschard's law.

Therefore, as a second step, after opening 1 gas valve II and lining up the gas system, as is done in the unloading of known ocean-going LNG ships, the internal pressure of the spherical tank 3 is maintained at normal pressure. In order to
10 into the spherical tank 3 of the LNG ship 1 to pressurize the inside thereof, and pump liquid from the spherical tank 3 of the LNG ship 1 through the lifting pump 2 and liquid system 8. .

In addition, even in an emergency situation where the gas valve 11 is opened while the spherical tank 3 is under relatively high pressure, the land tank 4 is a spherical tank, so the design pressure of about 2 ky/cm I G is sufficient. It is safe for practical use because it can withstand it.

In addition, as an alternative measure for the above emergency situation, BOG compressor 1
It is also possible to transfer the gas directly to the supply system 16 by adjusting the bypass valve 15 and the gas return valve 9 of 4.

According to this method, even if the internal pressure of the LNG spherical tank is higher than the internal pressure of the land spherical tank at the start of unloading, LNG can be unloaded to the land spherical tank, so the following effects can be achieved. It will be done.

(1) In the case of small coastal LNG ships, the voyage days are short and the spherical tank σ diameter is not as large as the one on the left, so BOG can be stored as is in the current spherical tank, making it expensive to process the OG. The equipment and its complicated handling become unnecessary, improving the economic efficiency, labor saving, and energy saving of the LNG ship.

(2) At the start of unloading, the internal pressure of the LNG spherical tank is high, so the pushing head of the unloading pump acts conveniently, thus shortening the unloading time.

〔Effect of the invention〕

In short, according to the present invention, the LNG in the LNG spherical tank
When pumping G, a pump pumps liquid from an LNG spherical tank whose internal pressure is higher than normal pressure.

A first step of unloading LNG to the land spherical tank through the LNG lifting line, and a gas blower returning the LNG from the land spherical tank to the LNG ship spherical tank whose internal pressure has become normal pressure.
Pressurizing the LNG tank by pressurizing the LNG gas through the LNG return gas line, and
By comprising a second step of pumping liquid into the LNG spherical tank via the liquid pump and the LNGI liquid line,
Economical as there is no need for expensive OG processing equipment or troublesome main engine combustion mode switching work.

The present invention is industrially extremely useful because it provides an LNG ship unloading method that is excellent in labor-saving and energy-saving properties.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment in which the present invention is applied to a small coastal LNG ship. FIG. 2 and FIG. 3 are longitudinal cross-sectional views showing different BOG processing devices of a known ocean-going LNG ship, respectively. 1... LNG ship, 2... Lifting pump, 3... Spherical tank, 4... Land tank, 5... Receiving base, 6...
...Liquid valve, 7...Liquid arm, 8...Liquid system, 9...
・Gas return valve, 10...Gas return blower 11...
Gas valve, 12... Gas arm, 13... Gas system,
14... BOG compressor, 15... Bypass valve, 16
... Supply system, 17... BOG processing system, 18...
・100% liquid level, 1.9-90% liquid level, 2O-LNG,

Claims (1)

[Claims] When pumping LNG in an LNG spherical tank, the first step is to unload LNG from the LNG spherical tank, where the internal pressure is higher than normal pressure, to the land spherical tank through the pump and the LNG pumping line. Then, the LNG ship tank is pressurized by pressure-feeding LNG gas from the land tank to the LNG ship tank whose internal pressure has become normal pressure through the return gas blower and the LNG return gas line, and A method for unloading an LNG ship, comprising a second step of pumping liquid into an LNG spherical tank via a liquid pump and an LNG liquid lifting line.