JPH05214568A - Method for preventing corrosion of bottom plate of low temperature tank - Google Patents

Abstract

PURPOSE:To provide a method for preventing corrosion of a bottom plate by preventing dew condensation on the lower surface of a bottom wall of an outside tank without heating a select sand layer in a low temp. tank storing the low temp. fluid liquefied petroleum gas, etc. CONSTITUTION:The outside bottom plate 3 of a double layer vessel structure tank is arranged through the select sand on the upper surface of a base structure 2. The select sand-filling recessed part 1 formed in the base structure 2 is communication-connected to a breathing tank 12. Dry nitrogen from the breathing tank 12 is continuously supplied to the select sand layer in a fine pressure condition to allow the dry nitrogen to flow through the select sand layer. By reducing the moisture of the select sand by the dry nitrogen flowing through the select sand layer, the dew condensation on the lower surface of the bottom plate is prevented, and by covering the lower surface of the bottom plate with a nitrogen atomosphere to prevent the oxidation, the corrosion of the bottom plate is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a method for preventing bottom plate corrosion in a low temperature tank for storing a low temperature fluid such as liquefied petroleum gas.

[0002]

2. Description of the Related Art A cryogenic tank for storing a cryogenic fluid such as liquefied petroleum gas has a bottom plate laid on the upper surface of a foundation structure having a select sand filling recess formed on the upper surface thereof, and is internally spaced at a certain distance above the bottom plate. A bottom plate is laid, side walls and a ceiling wall are erected from this inner bottom plate to form an inner tank, and an outer wall and an outer ceiling wall are erected from the bottom plate laid on the foundation structure to form an outer tank, It is composed of a double tank structure in which a heat insulating layer is formed between the inner tank and the outer tank, and the heat insulating layer between the inner and outer tanks is connected to the breathing tank to change the pressure or temperature of the tank with the supply and discharge of the low temperature liquid. The expansion and contraction of the tank due to changes are absorbed.

However, in the conventional cryogenic tank, water draining holes are communicated at appropriate intervals in the circumferential direction from the bottom of the select sand filling concave portion of the substructure supporting the bottom plate of the outer tank to the peripheral side wall of the substructure. Since it is formed, the select sand layer communicates with the outside air, and the humidity of this select sand layer becomes approximately the same as the outside air humidity. On the other hand, since the low temperature from the inner tank bottom plate is transmitted to the bottom plate of the outer tank via the heat insulating layer, the water content of the select sand layer is condensed on the lower surface of the bottom wall of the outer tank.

Since dew condensation on the bottom surface of the bottom wall causes corrosion of the bottom wall, conventionally, by arranging a heater in the select sand layer and raising the temperature of the select sand layer, the bottom surface temperature of the bottom plate becomes higher than the outside air temperature. By holding it, the dew condensation on the lower surface of the bottom plate is suppressed.

[0005]

However, when the heater is arranged in the select sand layer, the heat energy from the heater is transferred to the heat insulating layer arranged for keeping cold, through the bottom plate. There is a problem that not only the heating energy but also the low temperature energy in the inner tank is large, and the energy loss as a whole is large. The present invention has been made paying attention to such points, and provides a method for preventing dew condensation on the lower surface of the outer tank and preventing corrosion of the bottom wall without heating the select sand layer. To aim.

[0007]

In order to achieve the above-mentioned object, the present invention connects a select sand filling recess formed in a substructure to a breathing tank so that dry nitrogen from the breathing tank is in a slight pressure state. It is characterized in that it is continuously supplied to the select sand layer to circulate the select sand layer.

[0008]

In the present invention, the select sand filling concave portion formed in the substructure is connected to the breathing tank so that the dry nitrogen from the breathing tank is continuously supplied to the select sand layer at a slight pressure to evenly distribute the select sand layer. Since it is made to circulate, the dry nitrogen absorbs the water in the select sand tank while flowing in the select sand layer and is discharged to the outside of the select sand layer.
Moisture content in the select sand layer is significantly reduced. Therefore, even if the cold heat from the inner tank is transferred to the lower surface of the bottom plate through the heat insulation layer and the surface temperature on the lower surface of the bottom plate is lower than the outside air temperature, the humidity in the select sand layer is low, Since the dew condensation will not occur and the select sand layer will be in a nitrogen atmosphere, the lower surface of the bottom plate will not be oxidized, and corrosion of the bottom plate can be prevented.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings are schematic diagrams showing the piping system of a cryogenic tank for carrying out the method of the present invention. This low-temperature tank stores liquefied propane, and a bottom plate (3) is laid on the upper surface of a substructure (2) having a recessed portion (1) for filling select sand on the upper surface. The inner bottom plate (4) is laid on the upper side with a constant space, and the side wall (5) is laid from the inner bottom plate (4).
And the ceiling wall (6) are erected to form the inner tank (7), and the outer wall is formed from the bottom plate (3) laid on the foundation structure (2).
(8) and the outer ceiling wall (9) are erected to form an outer tank (10), and an insulating layer (11) filled with a heat insulating material is provided between the inner tank (7) and the outer tank (10). Has been formed.

A dry nitrogen supply / discharge path (13) derived from a breathing tank (12) storing dry nitrogen is connected to the heat insulating layer (11) so as to communicate with the inside tank (7). The expansion and contraction of the inner tank (7) based on the change in the internal tank pressure due to the change in the temperature of the liquefied propane and the temperature change are absorbed by the supply and discharge of dry nitrogen to the heat insulating layer (11).

Further, the foundation structure (2) is provided with a drainage hole (14) from the peripheral side wall toward the bottom of the select sand filling recess (1) which is recessed in the upper surface of the foundation structure (2). Communication is formed at appropriate intervals in the direction. Then, in the central portion of the select sand filling concave portion (1) of the substructure (2), a nitrogen releasing ring is provided.
(15) is arranged, and a plurality of nitrogen releasing holes (16) toward the center of the tank are formed inside the ring circumference of the nitrogen releasing ring (15).

The nitrogen discharge ring (15) arranged in the select sand filling recess (1) is connected to the dry nitrogen supply / discharge passage through one of the plurality of drain holes (14) formed in the substructure (2). A dry nitrogen piping (17) branched from (13) is connected. A pressure reducing mechanism (18) consisting of a pressure adjusting valve and a flow rate adjusting valve is provided in the dry nitrogen piping (17), and by the action of the pressure reducing mechanism (18), the dry nitrogen in the breathing tank (12) is The pressure 5
Under the conditions of 0 mmAq and a flow rate of 5 to 7 liters / min, the selective sand filling concave portion (1) is continuously fed.

In the figure, reference numeral (19) is a nitrogen separation and purification device for producing dry nitrogen to be supplied to the breathing tank (12).
The dry nitrogen stored in the breathing tank (12) has a dryness of DP 200K or less.

In the above embodiment, the nitrogen releasing ring (15) having a plurality of nitrogen releasing holes (16) facing the center of the tank is arranged in the select sand filling recess (1) when the tank is newly installed.
When using an existing tank, one of the drain holes (14) is formed so that the select sand filling recess (1) and the outer peripheral surface of the substructure (2) communicate with each other. May be communicatively connected to the breathing tank (12), and dry nitrogen from the breathing tank (12) may be supplied to the select sand layer through the water drain hole (14).

In the cryogenic fluid storage tank configured as described above, since the dry nitrogen is fed at a slight pressure to the select sand which is in contact with the bottom plate of the outer tank, the water content of the select sand is greatly reduced. In addition, even if the temperature of the bottom plate becomes lower than the outside air temperature, the moisture contained in the select sand does not condense on the lower surface of the bottom plate.
Since the lower surface of the bottom plate which is in contact with the select sand is covered with the nitrogen atmosphere, the lower surface of the bottom plate is prevented from being oxidized and the bottom plate can be prevented from being corroded.

[0016]

According to the present invention, the select sand filling recess formed in the substructure is connected to the breathing tank, and dry nitrogen from the breathing tank is continuously supplied to the select sand layer at a slight pressure to form the select sand layer. Since it is made to circulate, the dry nitrogen absorbs the water in the select sand tank and is discharged to the outside of the select sand layer while flowing in the select sand layer. The rate drops significantly. Therefore, even if the cold heat from the inner tank is transferred to the lower surface of the bottom plate through the heat insulation layer and the surface temperature on the lower surface of the bottom plate is lower than the outside air temperature, the humidity in the select sand layer is low, Since the dew condensation is eliminated and the select sand layer is in a nitrogen atmosphere, the bottom surface of the bottom plate is not oxidized and corrosion of the bottom plate can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a piping system of a cryogenic tank.

FIG. 2 is a cross-sectional plan view of a substructure portion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Recessed portion for filling with select sand, 2 ... Foundation structure, 3 ... Bottom plate,
4 ... inner bottom plate, 5 ... side wall,
6 ... Ceiling wall, 7 ... Inner tank,
8 ... outer wall, 9 ... outer ceiling wall,
10 ... Outer tank, 11 ... Insulation layer,
12 ... breathing tank, 14 ...
Drainage hole, 15… Nitrogen release ring.

Claims (3)

[Claims] 1. A recess (1) for filling a select sand on an upper surface thereof
Laying the bottom plate (3) on the upper surface of the substructure (2) formed with
An inner bottom plate (4) is laid on the upper side of the bottom plate (3) at regular intervals, and a side wall (5) and a ceiling wall (6) are erected from the inner bottom plate (4) to form an inner tank (7). In addition, the outer wall (8) and the outer ceiling wall (9) are erected from the bottom plate (3) laid on the foundation structure (2) to form the outer tank (10), and the inner tank
A low temperature tank in which a heat insulating layer (11) is formed between the outer tank (10) and the outer tank (10) and the heat insulating layer (11) and the breathing tank (12) storing dry nitrogen are connected in communication. In, the select sand filling recess (1) formed in the substructure (2)
Is connected to the breathing tank (12), and the dry nitrogen from the breathing tank (12) is continuously supplied to the select sand layer in a slight pressure state so that the select sand layer is circulated. Bottom plate corrosion prevention method. 2. Breathing of one of a plurality of drainage holes (14) for communicating the select sand filling recess (1) formed in the substructure (2) with the outer peripheral surface of the substructure (2). tank
The method for preventing corrosion of a bottom plate of a low temperature tank according to claim 1, wherein the bottom plate is corroded to the (12) and dry nitrogen is supplied to the recess (1) for filling the select sand. 3. A nitrogen releasing ring (15) is arranged in the select sand filling recess (1) formed in the substructure (2), and this nitrogen releasing ring (15) is connected to the breathing tank (12) for communication. The method for preventing bottom plate corrosion of a cryogenic tank according to claim 1, wherein dry nitrogen is supplied to the select sand filling recess (1).