JPS6317711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sealing mechanism for a floating roof of a tank.

Floating roof type liquid storage tanks are used to store evaporable liquids, and in order to minimize the amount of evaporation, various improvements have been made to the sealing mechanism of the floating roof.

However, when it comes to large-diameter tanks made of thin plates, the floating roof sealing mechanism is made highly flexible, and even if airtightness is achieved between the tank side wall and the surrounding wall of the floating roof, there is no loss due to the release of vapor from the stored liquid. I have not yet succeeded in doing so.

Nowadays, the issue of pollution has become more and more prominent.
When the storage liquid became petroleum, even the technically small emission of hydrocarbon vapor from the sealing mechanism of a floating roof came to be monitored as a source of air pollution.

As a result of actually measuring the amount of emissions in floating roof oil storage tanks, the following facts were discovered. In other words, the amount of emission depends on the type of seal mechanism, for example, the mechanical seal type (see Figure 1) and the tube seal type (see Figure 2).
It also varies depending on the size of the seal gap actually formed on the seal surface, the wind speed, and the type of oil stored.

The actual amount of emissions can be found in the American Petroleum Institute's booklet "API Bulletin 2577 (published February 1962)"
Approximately 50~ of the estimated emission amount listed in
It was 60%.

For mechanical show seals, there is no correlation between the amount of emission and the seal gap. In other words, the seal gap reaches 50mm,
Even if it is actually visible, the amount of emission is almost the same as that of a normal seal gap of about 3 to 5 mm, or an area that is considered to have no gap in engineering terms.

Seal mechanisms that are poorly maintained have a large amount of emissions.

The mechanical seal type seal mechanism has a considerable seal gap, and the tube seal type has no gap.
Or the amount of emission should be comparable to that of a microgap.

The mechanical seal type seal mechanism has a more effective evaporation prevention effect than the tube seal type.

That's what I was saying. Of the above, the most noteworthy is: In other words, before actual measurements, the tube seal type seal mechanism was more effective.
It seems to be superior in terms of flexibility than the mechanical show-seal type, so it is thought to adapt well to the deformation of the tank side plate and come into close contact with the inner wall of the side plate, resulting in an excellent sealing effect. However, the actual measurement results were the opposite.

Also, surprisingly, as the wind speed increases, the amount of emission becomes larger in the tube seal type than in the mechanical show seal type, as shown in FIG. In Figure 3, the liquid stored in the tank was gasoline.

However, in Japan, which is an earthquake-prone country, mechanical show-seal type floating roofs are rarely manufactured in recent years due to the risk of them colliding with the inner side walls and catching fire during an earthquake. This has given way to flexible tube seal types.

However, from the point of view of the amount of emission, the use of a tube seal type floating roof seal mechanism requires consideration.

Now, in light of the above measurement results, we consider the superiority of the conventional mechanical shoe seal type over the tube seal type in terms of preventing emissions.The one shown in Figure 1 is a typical mechanical shoe. - It is a seal type seal mechanism, where A is the floating roof, B is the tank side plate, C is the sealing cap, D is the mechanical shoe, E is the pantograph type hanger, F is the counterweight, and G is the oil level. However, in the mechanical show seal type, the show unit is fully immersed in oil, so the floating roof moves due to wind, etc., creating a seal gap, which induces evaporation and emits hydrocarbon vapor. Even in such a situation, the hydrocarbon vapor in space A surrounded by the tank, the seal flop, and the floating roof side wall does not participate in the emission, and the gap consisting of the tank side plate and the floating roof does not participate in the emission. Since the tube seal type is long, there is resistance to the emission, so evaporation does not progress much. In contrast, with the tube seal type, the roof moves due to wind etc., forming a seal cap and evaporation is induced from there, which prevents the emission of hydrocarbon vapor. In the case of tube seal type as shown in Fig. 2, when the condition occurs, the hydrocarbon vapor in the space B surrounded by the tank side plate RO, the tube seal ri, and the floating roof side wall immediately participates in the emission. In addition, the seal gap, which consists of the tank side plate and the tube seal, is short and does not provide much resistance to the emitters, so the amount of evaporation will increase as the wind speed increases. It was judged.

In view of the above facts, this invention does not use a mechanical shoe, but incorporates a structure that is effective for ejection in a mechanical shoe seal type into a soft-touch tube seal type, and a part of the tube seal portion is in contact with the stored liquid. In addition, even if the floating roof moves due to wind etc. and the seal gap between the tank side wall and the tube seal increases, a part of the tube seal will not increase immediately. It is an object of the present invention to provide a sealing mechanism for a floating roof of a tank, which functions to cover the liquid level of a seal gap and prevent evaporation of stored liquid.

The gist of the present invention is to form an annular sealed chamber 4 with a storage liquid resistant coating 3 on the outer peripheral side wall 2 of a floating roof 1 of a tank, and to form a separate coating 5 on the side wall 2 in the upper part of the sealed chamber 4. A cushion part 7 made by covering the elastic bed material 6 with
is fixed, and the lower part of the sealed chamber 4 is filled with a liquid 8 having a specific gravity equal to or lower than the storage liquid 10 in the tank,
Moreover, the sealing mechanism of the floating roof of the tank is characterized in that the bottom part 9 of the sealed chamber 4 is always immersed in the stored liquid 10.

The structure of the sealing mechanism of the floating roof of this tank will be explained based on an embodiment shown in FIG. With an oil-resistant film,
An annular sealed chamber 4 is formed. In the illustrated embodiment,
Both sides of a long rectangular membrane 3 are put together and fixed to the outer peripheral side wall 2 of the floating roof 1 with bolts and nuts 12 to form a sealed chamber 4.

A cushion part 7 made by covering an elastic bed body 6 with a separate membrane 5 is placed on top of the sealed chamber 4 and fixed to the side wall 2 of the sealed chamber 4.
The interior of the sealed chamber 4 is filled with a liquid 8 having a specific gravity equal to or lower than that of the stored liquid, such as kerosene or naphtha if the stored liquid is petroleum, and the bottom 9 of the sealed chamber 4 is filled with a liquid 8 having a specific gravity equal to or lower than that of the stored liquid. It is designed to be immersed in the storage liquid 10 of the tank.

Since this embodiment has the configuration as described above,
When the bottom part 9 of the annular sealed chamber 4 is installed so as to be partially immersed in the storage liquid 10, the floating roof 1 will move in the direction of the arrow x due to wind, etc., as shown in FIG. , when the seal gap m between the tank side wall 11 and the side wall 2 of the floating roof 1 increases, liquid 8
Since the fluid is filled with liquid, the liquid tends to spread between the seal gaps m due to the fluidity of the liquid, and as shown in FIG. Film 3 in sealed chamber 4
Since a part of the tube is necessarily in contact with the inner wall of the tank side plate 11, there is no gap between the inner wall of the tank side plate and the tube seal, as well as a place where the vapor of the stored liquid 10 accumulates. This is similar to the effect that occurs because the seal in a mechanical seal mechanism is always forced into contact with the inner wall of the tank side plate and is immersed in the stored liquid.

This invention has the structure and operation as described above, and since the bottom part 9 of the sealed chamber 4 is always immersed in the storage liquid 10, there is no place where the vapor of the storage liquid 10 accumulates, and the seal gap m As the liquid 8 increases, the liquid 8 existing on the surface of the stored liquid via the film 3 increases.
Due to the fluidity of the liquid, the bottom of the sealed chamber 4 expands and stops until it reaches the inner wall of the tank side plate 11, so there is no gap between the inner wall of the tank side plate 11 and the tube seal, so the vapor of the stored liquid is prevented. There is a remarkable effect that the release of is completely prevented.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a typical example of a mechanical shoe seal mechanism, Fig. 2 is an explanatory diagram of a typical example of a tube seal mechanism, and Fig. 3 is an illustration of a typical example of a tube seal type and a mechanical shoe seal mechanism. An evaporation amount diagram, FIG. 4 is a longitudinal sectional front view of a part of an embodiment of the floating roof sealing mechanism according to the present invention, and FIG.
The figures each show an explanatory view of the action, 1 is a floating roof, 2 is a floating roof outer peripheral side wall, 3 is a storage liquid resistant coating, 4 is a sealed chamber, 5 is a coating, 6 is an elastic cushion, 7 is a cushion part, 8 represents the liquid, 9 represents the bottom, and 10 represents the storage liquid.

Claims (1)

[Claims] 1. An annular sealed chamber 4 is formed on the outer circumferential side wall 2 of the floating roof 1 of the tank with a storage liquid-resistant coating 3, and in the upper part of the sealed chamber 4, an elastic cushion 6 is formed on the side wall 2 with a separate coating 5.
The lower part of the sealed chamber 4 is filled with a liquid 8 having a specific gravity equal to or lower than the stored liquid 10 in the tank, and the bottom part 9 of the sealed chamber 4 is not necessarily filled. A sealing mechanism for a floating roof of a tank, characterized in that it is immersed in a storage liquid 10.