JPH10250677A - Topping-up method in inert gas supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the burden of an engine operator by eliminating necessity for manipulation of a boiler and inert gas system even in the case where the topping-up operation has become necessary. SOLUTION: One of the water ballast tanks 9 is filled with sea water, while an inert gas is stored in the other water ballast tank 10, and the two tanks 9 and 10 are coupled together with an opening/closing valve 12 interposed, and the valve 12 is opened, and thereby the inert gas is sent into a cargo oil tank 8 with the dead load of the sea water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a topping-up method in an inert gas supply system mounted on a tanker.

[0002]

2. Description of the Related Art A combustible gas (hydrocarbon) vaporized from crude oil or the like, which is a cargo of a tanker, does not explode regardless of its concentration and presence or absence of a flammable source in an atmosphere having an oxygen concentration of 10% or less. . Applying this principle, international treaties require that tankers over 20,000 tons be equipped with an inert gas supply system.

[0003] The above inert gas supply system is a system for cooling and washing boiler combustion gas with seawater and supplying it to a cargo oil tank as inert gas when unloading crude oil or the like, which is a cargo of a tanker, onto the land.

[0004] The oxygen concentration in the boiler combustion gas is usually 5
%, And the cargo oil tank is filled with such a low oxygen concentration gas, and the pressure in the tank is constantly maintained at or above the atmospheric pressure to prevent the entry of outside air.
It becomes possible to eliminate the risk of explosion of combustible gas.

FIG. 2 is a flow chart of an inert gas supply system mounted on a tanker. The combustion gas of a boiler 1 passes through a flue 2 and is discharged out of a chimney (not shown). Part of the combustion gas in the flue 2 enters the scrubber 4 from the inert gas pipe 3. 3a is an on-off valve. In the scrubber 4, the inflowing combustion gas is cooled and washed by a large amount of seawater to become a clean inert gas.

[0006] Inert gas is supplied from an inert gas fan 5 to each cargo oil tank 8 through a deck main line 7 from a deck water seal 6 as a backflow prevention device. 7a is an on-off valve with a branch line.

In the above inert gas supply system, since the upper surface of the cargo oil tank 8 is in direct contact with the outside air, the gas temperature in the cargo oil tank 8 is easily affected by the outside air temperature. The gas pressure in 8 changes up and down.

As a matter of course, the cargo oil tank 8 has a limit in strength. For example, even if the outside air temperature rises and the gas temperature in the cargo oil tank 8 rises, the A pressure relief valve (not shown) is operated to release gas in the cargo oil tank 8 and maintain an appropriate pressure so that the pressure does not exceed an allowable limit. In addition, there is a slight leak from the pipe joint of the inert gas, and the inert gas tends to decrease from the cargo oil tank 8.

On the other hand, when the outside air temperature decreases, the gas pressure in the cargo oil tank 8 decreases. If the gas pressure falls below the atmospheric pressure, there is a possibility that the outside air is directly sucked into the cargo oil tank 8. When this happens, the oxygen concentration in the cargo oil tank 8 rises and approaches the explosion limit.

This will be described with reference to FIG. FIG.
(A) shows an example of a temporal change of the outside air temperature, and the outside air temperature constantly changes according to a change in the position of the sun, weather, and a route. On the other hand, FIG. 3B shows an example of a temporal change of the gas pressure in the cargo oil tank 8. As the outside air temperature rises, the gas pressure in the cargo oil tank 8 also rises. When the gas pressure exceeds the upper limit of 1400 mmAq, a gas pressure relief valve (not shown) operates to release gas so as not to exceed 1400 mmAq. When the release of gas is repeated, when the outside air temperature decreases, the gas pressure in the cargo oil tank 8 approaches the lower limit of 200 mmAq. 200 mmAq is the minimum pressure allowable to keep the inside of the cargo oil tank 8 always at or above the atmospheric pressure.

In order to avoid the danger that the gas pressure in the cargo oil tank 8 becomes lower than the allowable lower limit pressure,
Inert gas is additionally supplied to the cargo oil tank 8 so that the inside of the tank 8 is maintained within a normal pressure range. The operation of replenishing the inert gas in this way is generally called topping-up.

Further, an inert gas fan 5 having a capacity proportional to the capacity of the pump when unloading crude oil or the like as a cargo using a pump is provided. Since the capacity of the inert gas required for topping-up is small compared to the capacity of the inert gas fan 5, it is conventionally necessary to separately provide a small capacity inert gas fan or to obtain a small capacity and low oxygen concentration combustion gas. It was equipped with a dedicated gas generator that could be used.

[0013]

However, in a tanker propelled by a diesel engine, the boiler is normally stopped during the voyage, and not only the boiler is used only for topping up but also the inert gas is low. The oxygen concentration in the combustion gas must be kept low, even though it requires only a short time at the air volume. This requires manpower, time and experience for the engineer operating the boiler.

The present invention has been made in order to solve the above-mentioned conventional problems, and an object of the present invention is to eliminate the need for operation of a boiler and an inert gas system even if a topping-up operation is required. It is an object of the present invention to provide a topping-up method in an inert gas supply system that can reduce the burden on an engineer.

[0015]

A topping-up method in an inert gas supply system according to the present invention is characterized in that one water ballast tank is filled with seawater and the other water ballast tank stores inert gas.
The two water ballast tanks are connected via an on-off valve, and the inert gas is transferred into the cargo oil tank by its own weight by releasing the on-off valve.

[0016]

[Function] Unlike the conventional topping-up operation, the inert gas can be transferred to the cargo oil tank by the required amount only by operating the on-off valve of the pipe connecting the water ballast tank, and the cargo oil tank can be pressurized. it can.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numerals 9 and 10 denote water ballast tanks which supply or discharge seawater through a ballast water line 11. Reference numeral 12 denotes a seawater inlet / outlet opening / closing valve.
Reference numeral 3 denotes a seawater inlet / outlet opening / closing main valve. Both seawater inlet / outlet on-off valve 1
2, the water ballast tank 9 is filled with seawater and the other water ballast tank 1 is closed.
Inert gas is stored in zero.

A vent valve 14 is provided on the upper surface of the water ballast tank 9 so that outside air is introduced into or discharged from the water ballast tank 9. A branch line 15 connects between the upper surface of the water ballast tank 10 and the deck main line 7. 15a is an on-off valve.

In the system of the above embodiment, the on-off valve 7a with the branch line of each cargo oil tank 8 is normally opened, and all cargo oil tanks 8 are in the same gas pressure state. The gas pressure in the deck main line 7 is constantly monitored (not shown), and when it is determined that topping-up is necessary, the seawater inlet / outlet opening / closing valves 12 are kept closed while the seawater inlet / outlet opening / closing valves 12 are kept closed. Open.

By the above-described valve operation, seawater moves from the water ballast tank 9 only by its own weight into the water ballast tank 10 in which the inert gas is stored, and at the same time, if the ventilation valve 14 and the opening / closing valve 15a are opened,
The inert gas flows into the cargo oil tank 8 via the deck main line 7, and the gas pressure in the cargo oil tank 8 increases. These operations are monitored by a monitor connected to the deck main line 7, and if the required pressure is restored, the movement of the seawater may be stopped at that stage and the operation may be stopped.

[0021]

Advantages of the Invention 1) Even if the topping-up operation is required, the operation operation of the boiler and the inert gas system is not required. 2) There is no need for a small air volume fan dedicated to topping-up. 3) There is no need to provide a gas generator dedicated to small capacity. 4) Topping-up can be performed only by opening and closing the valve, which saves energy. 5) The burden on the crew is minimal and matches the trend of crew reduction.

[Brief description of the drawings]

FIG. 1 is a flow diagram of a system for implementing the method of the present invention.

FIG. 2 is a flowchart of a conventional inert gas system.

FIG. 3 is a graph showing a change in outside air temperature and a change in gas pressure in a cargo oil tank.

[Explanation of symbols]

 Reference Signs List 1 boiler 2 flue 3 inert gas pipe 3a open / close valve 4 scrubber 5 inert gas fan 6 deck water seal 7 deck main line 7a open / close valve 8 cargo oil tank 9, 10 water balance tank 11 water balance line 12 seawater inlet / outlet valve 13 seawater inlet / outlet open / close Main valve 14 Vent valve 15 Branch line 15a Open / close valve 5

Claims (1)

[Claims] A water ballast tank is filled with seawater and inert gas is stored in the other water ballast tank. The two water ballast tanks are connected via an on-off valve, and the on-off valve is opened. Wherein the inert gas is transferred into a cargo oil tank by the weight of the seawater.