JP2000103390A - Dehydration method for gas to be analyzed oxygen concentration in ballast tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with installation of a silicagel moisture absorber or, if installed, to reduce the frequency of exchanging the silicagel by installing a cold trap in an oxygen concentration analysis gas line of a ballast tank and by dehydrating water in the oxygen concentration analysis gas. SOLUTION: A valve 20 of an entrance side refrigerant pipe line of a heat transfer part 17' of a cold trap 17 is opened so that liquid nitrogen from a liquid nitrogen tank 3 is fed to the heat transfer part 17' and cools it. On the other hand, gas to be analyzed in a ballast tank 2 is water separated by a drain separator 15 to be fed to the cold trap 17. The analysis gas is cooled down to the dew point or less on the heat transfer surface of the heat transfer part 17' to condense dew, the water content in the gas is condensed, and the gas to be analyzed having little water content is sent to a zircoinia type oxygen analyzer to be measured. Two systems of the cold traps 17 are arranged in parallel and alternatively used so that so-called regenerative cycle can be realized.

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 technique for preventing a ballast tank from being corroded by reducing it, and more particularly to an improvement in an oxygen concentration analysis line in a ballast tank.

[0002]

2. Description of the Related Art Conventionally, in a crude oil tanker in which crude oil is loaded in a cargo oil tank 1, as shown in FIG. 2, a space inside each ballast tank 2 is filled with nitrogen gas as an inert gas for corrosion protection. (The ballast tank is partitioned by a number of partition walls in the longitudinal 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 the liquid nitrogen from the liquid nitrogen tank 3 to the evaporator 4, vaporizes the nitrogen gas into the nitrogen gas by the evaporator 4, and supplies the gas through the supply valve 6 in the middle of the supply pipe 5 to each ballast tank. I have. A discharge pipe 8 having a nitrogen gas discharge valve 7 is installed in each ballast tank. The pressure in each ballast tank is sensed by a pressure gauge 9 provided in each ballast tank 2, and is controlled by a controller 10. Supply valve 6, discharge valve 7
Is controlled to the set value. In addition,
Liquid nitrogen is produced by a known liquid nitrogen production device 11 and supplied to the liquid nitrogen tank 3. Reference numeral 22 denotes a relief valve provided in the liquid nitrogen tank 3.

[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 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 into the atmosphere,
The pressure in the tank is maintained at an appropriate level.

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, the nitrogen gas in the ballast tank is maintained at a constant pressure (0.05 to 0.1 atg).
The supply valve 6 and the discharge valve 7 are controlled by the controller 10 by detecting a signal from the pressure gauge 9 so that the pressure is filled.

Further, from the viewpoint of anticorrosion, the supply valve 6 and the discharge valve 7 are controlled so that the oxygen concentration in the gas phase in the ballast tank 2 becomes 0.5% or less. That is, when the oxygen dissolved in the seawater in the ballast tank is released into the gas phase and the oxygen concentration in the gas phase increases to 0.5% or more, the discharge valve 7 is opened to open the ballast tank 2. The gas inside is released to the outside of the tank, and the supply valve 6 is opened due to a decrease in the pressure in the tank, whereby nitrogen gas is supplied into the tank and the oxygen concentration is reduced.

An oxygen concentration analysis gas line R is installed in each ballast tank 2 to measure the oxygen concentration, and a known zirconia oxygen analyzer 14 is used to measure the oxygen concentration quickly and accurately. Have been. The zirconia oxygen analyzer is susceptible to moisture, and if a large amount of moisture is contained in the analysis gas, the zirconia oxygen analyzer has a defect that insulation failure of the sensor portion and a large measurement error occur. Therefore, conventionally, when the hull of the hull is severe during ballast voyage, seawater may enter the oxygen concentration analysis gas line. In this method, silica gel is frequently exchanged and a large amount of silica gel is required. In addition, high temperature gas is required for regeneration of silica gel. Reference numeral 23 denotes a drain valve of the drain separator 15.

[0007]

SUMMARY OF THE INVENTION The present invention is based on the assumption that a silica gel moisture absorber is installed in an oxygen concentration analysis gas line for controlling the oxygen concentration in a ballast tank using a zirconia oxygen analyzer. Another object of the present invention is to provide a method for dehydrating an oxygen concentration analysis gas line which can reduce the frequency of silica gel exchange.

[0008]

The present invention is characterized in that a cold trap 17 is provided in an oxygen concentration analysis gas line R of a ballast tank to dehydrate water in an oxygen concentration analysis gas. Further, a plurality of cold traps 17 are installed in parallel, and the refrigerant supplied to the heat transfer section 17 'of the cold trap 17 is liquid nitrogen.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a dehydration method 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 prevention to the space inside 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 as shown in FIG. The same components are denoted by the same reference numerals and detailed description is omitted. A feature of the present invention is that a cold trap 17 is provided in the oxygen concentration analysis gas line R provided in each ballast tank 2.

The cold trap 17 is a known one, and is installed on the oxygen concentration analysis gas line R on the downstream side of the drain separator 15. In the illustrated example, two cold traps 17 are installed in parallel. Although one cold trap may be used, it is desirable to install two or more cold traps. The cold trap 17 has a multi-surface area heat transfer section 17 ′ cooled by liquid nitrogen from the liquid nitrogen tank 3. FIG. 1 shows an example in which a silica gel moisture absorber 16 is provided downstream of the cold trap 17, but the silica gel moisture absorber 16 is not necessarily required.

Reference numerals 18 and 19 denote valves installed on the gas lines on the inlet side and the outlet side of the cold trap 17 of the oxygen concentration analysis gas line R, respectively. Reference numerals 20 and 21 denote valves provided on the refrigerant pipes on the inlet and outlet sides of the heat transfer section 17 'of the cold trap 17, respectively. The outlet side refrigerant pipe of the heat transfer section 17 'is connected to the nitrogen gas supply pipe 5 to the ballast tank. Reference numeral 24 denotes a drain valve provided in the cold trap 17.

Next, the operation of the present invention will be described below. The valve 20 of the refrigerant pipe on the inlet side of the heat transfer section 17 'of the cold trap 17 is opened to supply liquid nitrogen from the liquid nitrogen tank 3 to the heat transfer section 17' to cool the heat transfer section. On the other hand, the gas to be analyzed in the ballast tank 2 is supplied to the drain separator 15.
Is separated into steam and water and supplied to the cold trap 17. The gas to be analyzed is cooled below the dew point on the heat transfer surface of the heat transfer section 17 'to form dew, and the moisture in the gas is condensed.

The nitrogen gas evaporated by heat exchange in the heat transfer section 17 'is supplied into the ballast tank 2 via the nitrogen gas supply pipe 5 through the valve 21 of the outlet side refrigerant pipe. By using two cold traps 17 arranged side by side as shown in the figure and using them alternately, a so-called regeneration cycle in which the condensed water in the cold traps is discharged outside the system by natural temperature rise when the cold traps are stopped can be performed. .

In the method of the present invention, the gas to be analyzed is the heat transfer section 1
Since it is cooled to the temperature of liquid nitrogen on the heat transfer surface 7 ', the dew point of water in the gas to be treated is lower than that in the case of adsorption by silica gel, so that the zirconia oxygen concentration analyzer can be operated without any trouble. Therefore, the silica gel moisture absorber 1
6 is unnecessary, but it is more effective if installed as a double protection measure. In this case, the replacement frequency of silica gel can be drastically reduced.

[0015]

According to the present invention, the silica gel is frequently replaced by using a silica gel moisture absorber. However, the use of a cold trap eliminates the need to use a silica gel moisture absorber. In addition, even if it is used, it has an effect that the exchange frequency of silica gel can be drastically reduced. In addition, the liquid nitrogen to be supplied to the cold trap can share the liquid nitrogen for supplying the ballast tank, so that the operation cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of a method for dehydrating an oxygen concentration analyte gas in a ballast tank according to the present invention.

FIG. 2 is an explanatory view of a conventionally known method for dehydrating an oxygen concentration analyte gas in 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 17 'Heat transfer section 18, 19, 20, 21 Valve 22 Relief valve 23, 24 Drain valve R Oxygen concentration analysis line

Claims (5)

[Claims] An oxygen concentration in a ballast tank is characterized in that a cold trap (17) is installed in an oxygen concentration analysis gas line (R) of a ballast tank (2) to dehydrate water in an oxygen concentration analysis gas. Method for dehydrating gas to be analyzed. 2. The method according to claim 1, wherein a drain separator (15) is provided upstream of the cold trap (17). 3. The method according to claim 1, wherein a silica gel moisture absorber (16) is installed downstream of the cold trap (17). 4. The method according to claim 1, wherein a plurality of cold traps (17) are installed in parallel with each other. 5. A heat transfer section (1) of a cold trap (17).
5. The method according to claim 1, wherein the refrigerant supplied to 7 ') is liquid nitrogen.