JP2000103395A - Anticorrosive nitrogen gas feed method for ballast tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To utilize nitrogen gas disposed from a liquid nitrogen tank to atmosphere by feeding the nitrogen gas emitted from a relief valve to a ballast tank inside. SOLUTION: When the pressure in a ballast tank 2 inside and oxygen concentration are within a prescribed range, a feed valve 6 is closed so that liquid nitrogen in the liquid nitrogen tank 3 is vaporized by heat invasion and the pressure in the tank 3 is raised. When pressure reaches a prescribed pressure or more, the relief valve 18 is operated and the nitrogen gas vaporized in the tank 3 is fed from a pipe line 19 into the ballast tank 2. When the pressure in the ballast tank is raised and exceeds the specified value, a delivery valve 7 is opened and the gas in the ballast tank is emitted to the atmosphere. The gas in the ballast tank is thus substituted periodically (or, sequentially) by the nitrogen gas from the pipe line 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ballast tank for a crude oil tanker, a ballast tank mounted on a ship or a marine floating structure, or the like, which is filled with nitrogen gas to reduce the oxygen concentration in the space. The present invention relates to a method for supplying nitrogen gas to a ballast tank, which reduces the corrosion of the ballast tank by reducing the amount of nitrogen gas.

[0002]

2. Description of the Related Art Conventionally, in a crude oil tanker in which crude oil is loaded in a fuel oil tank 1, as shown in FIG. 3, the space inside each ballast tank 2 is filled with nitrogen gas for corrosion protection (ballast). The tank is partitioned by a number of partition walls in the length direction of the tanker to form a number of enclosed spaces, and one ballast tank A is shown in the drawing). The nitrogen gas supplies liquid nitrogen from the liquid nitrogen tank 3 to the evaporator 4,
Nitrogen gas is vaporized by the evaporator 4 and supplied via a supply valve 6 in the middle of a supply pipe 5 to each ballast tank. Further, a discharge pipe 8 having a nitrogen gas discharge valve 7 is installed in each ballast tank, and the pressure in each ballast tank is detected by a pressure gauge 9 provided in each ballast tank 2.
The controller 10 controls the supply valve 6 and the discharge valve 7 to control the set value. The liquid nitrogen is produced by the known liquid nitrogen production apparatus 11 and is supplied to the liquid nitrogen tank 3.
Is supplied to

[0003] The ballast water in each ballast tank 2 is supplied and drained of seawater through a valve 13 by a ballast water pump 12. That is, when unloading the crude oil in the cargo oil tank 1 by operating a cargo oil pump (not shown), the valve 13 is opened and the seawater is injected into the ballast tank 2 by the ballast water pump 12. At this time, when the gas phase portion in the ballast tank is compressed and the pressure rises, the discharge valve 7 opens according to a command from the controller 10 to release nitrogen in the gas phase portion to the atmosphere, and the pressure in the tank is adjusted to an appropriate pressure. keeping.

Next, when loading crude oil into the freight tank 1, the valve 13 is opened and the ballast water pump 12 discharges ballast water to the outside of the ship. At this time, the gas phase portion in the ballast tank 2 becomes negative pressure, so that the supply valve 6 is opened and nitrogen gas is supplied from the supply pipe 5 into the ballast tank 2, and the pressure in the tank is maintained at an appropriate pressure. During the voyage, a constant pressure of nitrogen gas (0.05 ~
The controller 10 controls the supply valve 6 and the discharge valve 7 by detecting a signal from the pressure gauge 9 so that the supply valve 6 is filled at about 0.1 atg).

Further, from the viewpoint of anticorrosion, the supply valve 6 and the discharge valve 7
Means that the oxygen concentration of the gas phase in the ballast tank 2 is 0.5
%. That is, the oxygen dissolved in the seawater in the ballast tank is released into the gas phase,
When the oxygen concentration in the gas phase increases to 0.5% or more,
When the discharge valve 7 is opened, the gas in the ballast tank 2 is released to the outside of the tank. When the pressure in the ballast tank decreases, the supply valve 6 is opened, and the nitrogen gas produced by evaporating and evaporating in the evaporator 4 is ballasted. The oxygen concentration is reduced by being supplied into the tank 2.

[0006] In order to measure the above oxygen concentration, an oxygen concentration analysis gas line R is installed in each ballast tank 2, and the measurement is performed by a known zirconia oxygen analyzer 14. In addition, in the zirconia oxygen analyzer, if a large amount of water is contained in the analysis gas, insulation failure of the sensor unit and a large measurement error occur, so that the drain separator 15 and the silica gel humidifier 16 are provided in the oxygen concentration analysis gas line. Is installed to dehydrate the analysis gas. Reference numeral 17 denotes a drain valve for the drain separator.

When the pressure and the oxygen concentration in the ballast tank are within a predetermined range, the supply valve 6 is closed, so that the liquid nitrogen tank 3 evaporates due to heat intrusion and the like. Since the internal pressure increases, a relief valve 18 is provided to release nitrogen gas to the atmosphere when the pressure exceeds a specified pressure.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a ballast tank for preventing corrosion by using nitrogen gas discarded from the relief valve 18 of the liquid nitrogen tank 3 into the atmosphere to reduce the amount of nitrogen gas used. It is an object to provide a gas supply method.

[0009]

A method for reducing the oxygen concentration in a ballast tank by supplying liquid nitrogen from a liquid nitrogen tank 3 having a relief valve 18 to a ballast tank 2 as nitrogen gas to reduce the oxygen concentration in the ballast tank. It is characterized in that the nitrogen gas released from 18 is supplied into the ballast tank 2.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for supplying a nitrogen gas for corrosion prevention to a ballast tank according to the present invention will be described with reference to the block diagram shown in FIG. The means for supplying nitrogen gas for corrosion protection into each ballast tank 2, the means for supplying and discharging ballast water in each ballast tank 2, and the oxygen concentration analysis gas line R installed in each ballast tank 2 are the same as those shown in FIG.
Are the same as those of the known means, and the same parts are denoted by the same reference numerals and detailed description thereof will be omitted. The features of this invention are:
That is, the nitrogen gas discharged from the relief valve 18 provided in the liquid nitrogen tank 3 is supplied into each ballast tank 2 through the pipe 19.

FIG. 1 shows an example in which the front end of the pipe 19 is open to the space inside the ballast tank 2, but FIG.
9 is an example in which the front end opening is opened in the ballast water of the ballast tank to perform bubbling. Further, an example is shown in which the tip end of the nitrogen gas supply pipe 5 from the evaporator 4 is also opened in the ballast water to perform bubbling. In addition, either one of the distal end of the pipe 19 and the distal end of the supply pipe 5 is located in the vacant space of the ballast tank, and the other is opened in the ballast water for bubbling. Although the case where the openings are made, or the case where both are opened in the ballast water as shown in FIG. 2 and bubbling is considered, it is most preferable to adopt the example of FIG. 2 from the viewpoint of reducing the dissolved oxygen in the water.

Next, the operation of the present invention will be described. When the pressure and the oxygen concentration in the ballast tank 2 are within a predetermined range, the supply valve 6 is closed, so that the liquid nitrogen tank 3 evaporates due to heat intrusion and the like. When the pressure rises and the relief valve 18 reaches a prescribed pressure or higher, the relief valve 18 is activated, and the nitrogen gas evaporated in the tank 3 is supplied from the pipe 19 into the ballast tank 2. Then, when the pressure in the ballast tank rises and exceeds a specified value, the discharge valve 7 opens and the gas in the ballast tank is released to the atmosphere. Therefore, line 19
The gas in the ballast tank is periodically (or continuously) replaced by nitrogen gas from the tank.

[0013]

According to the present invention, the nitrogen gas which has been evaporated in the liquid nitrogen tank 3 and discarded into the atmosphere from the relief valve 18 is used as an inert gas for corrosion prevention in the ballast tank. Regular (or continuous)
Since the gas in the ballast tank is replaced, the need for gas replacement when the oxygen concentration increases due to the release of dissolved oxygen in the ballast water is eliminated, or the frequency of replacement is drastically reduced, reducing the consumption of nitrogen gas. The effect that can be performed.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a first embodiment of a method for supplying nitrogen gas for corrosion prevention of a ballast tank according to the present invention.

FIG. 2 is an explanatory view of a second embodiment of the method for supplying nitrogen gas for corrosion prevention of a ballast tank according to the present invention.

FIG. 3 is an explanatory view of a conventionally known method of supplying nitrogen gas for corrosion prevention of a ballast tank.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cargo oil tank 2 Ballast tank 3 Liquid nitrogen tank 4 Evaporator 5 Supply pipe 6 Supply valve 7 Discharge valve 8 Discharge pipe 9 Pressure gauge 10 Controller 11 Liquid nitrogen production device 12 Ballast water pump 13 Valve 14 Zirconia oxygen analyzer 15 Drain separator 16 Silica gel moisture absorber 17 Cold trap 18 Relief valve 19 Pipe line

Claims (2)

[Claims] A method for reducing the concentration of oxygen in a ballast tank by supplying liquid nitrogen from a liquid nitrogen tank (3) having a relief valve (18) to a ballast tank (2) as nitrogen gas. A method for supplying nitrogen gas for corrosion prevention of a ballast tank, wherein the nitrogen gas released from the relief valve (18) is supplied into the ballast tank (2). 2. The method according to claim 1, wherein nitrogen gas discharged from the relief valve (18) is jetted into ballast water of the ballast tank (2).