JPS5815396B2 - Floating roof seal mechanism - Google Patents

Description

[Detailed description of the invention] This invention relates to a floating roof sealing mechanism.

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, even if the floating roof sealing mechanism is made highly flexible and airtight 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.

Now that the problem of pollution has become a hot topic, when the stored liquid is petroleum, even the release of hydrocarbon vapor from the sealing mechanism of the floating roof, which is technically extremely small, is considered to be one of the sources of air pollution. It has come to be monitored as one.

As a result of actually measuring the amount of emissions from floating roof oil storage tanks, the following facts were discovered.

That is, the amount of emissions differs depending on the type of seal mechanism, for example, mechanical shoe seal type (see Figure 1) or tube seal type (see Figure 2), and also depends on the seal gap actually located in the seal surface. It also varies depending on the size, wind speed, and type of oil being stored.

ii.Actual emissions amounts can be found in the American Petroleum Institute's brochure "
API Bulletin 2577 (A.D. 1962 2)
Approximately 5% of the estimated emissions listed in
It was 0-60%.

iii. There is no correlation between the amount of emissions and the seal gap in mechanical shoe seals.

In other words, even if the seal gap reaches 50 mm and can be seen with the naked eye, the amount of emissions is still 3 to 5 mm.
There was almost no difference in the amount of emissions from a place with a seal gap of about 100 m, or a place where there is no gap in engineering.

iv. Seal mechanisms that are poorly maintained emit large amounts of emissions.

V. Even if the mechanical shoe seal type seal mechanism has a considerable seal gap, the amount of emissions should be comparable to that of the tube seal type with no gap or with a small gap.

vi. The mechanical shoe 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 are v and vi.

In other words, prior to actual measurements, it seems that the tube seal type seal mechanism is superior to the mechanical shoe seal type in terms of flexibility, so it adapts well to the deformation of the tank side plate and tightly seals the side plate. It was thought that it would contact the inner wall and have an excellent sealing effect, but actual measurements showed the opposite.

Also, surprisingly, as the wind speed increases, the emission amount of the tube seal type becomes larger than that of the mechanical shoe seal type, as shown in Fig. 3.

In Figure 3, the liquid stored in the tank was gasoline.

However, in Japan, which is an earthquake-prone country, mechanical shoe seal type floating roofs have rarely been manufactured in recent years due to the fear that they would collide with the inner side walls during an earthquake and cause a fire. This is changing to flexible tube seal types.

However, from an emissions standpoint, the use of the tube seal quip's floating roof seal mechanism is desirable.

Now, in light of the above measurement results, we have considered the superiority of the conventional mechanical shoe seal type over the tube seal type in terms of emission prevention.The one shown in Figure 1 is a typical mechanical shoe seal. This type of seal mechanism has a floating roof, a tank side plate at the mouth, a seal fabric, a mechanical shoe, a Pandagraph hanger, a counterweight, and a mechanical shoe seal. In the type,
Because the shoes are sufficiently immersed in the oil, the shoes will remain intact even if the floating roof moves due to wind or other factors, forming a seal cap that induces evaporation and generates hydrocarbon emissions. 2. The hydrocarbon paper in the space A surrounded by the seal fabric and the floating roof side wall does not participate in emissions, and the gap between the tank side plate opening and shoe 2 is long, so there is no resistance to emissions. On the other hand, with the tube seal type, the roof moves due to wind etc., forming a seal cap, which induces evaporation.
In the case of a tube seal type as shown in Fig. 2, when a condition that causes hydrocarbon emission occurs, the hydrocarbon paper in the space B surrounded by the tank side plate opening, tube seal, and floating roof side wall is immediately released. In addition, the seal gap made up of the tank side plate opening and tube seal is short, so it does not provide much resistance to emissions, so the amount of evaporation progresses as the wind speed increases. It was decided that I should go.

In addition, there is a type that falls between the tube seal type and the mechanical seal type, and there is a type of Utility Model Application No. 15986/1986, which uses a liquid instead of a lining inside the tube, and uses a floating body installed at the bottom of the tube. to create a pressure in the liquid in the radial direction of the tank, and the sealing zone between the inner wall of the tank and the annular tube has upper and lower ends, respectively, a floating roof and an elastic steel piece fixed at one end to the floating body. There is one that is fixed at the end, but it has the disadvantage that the structure is extremely complicated.

In view of the above facts, this invention does not use a mechanical shoe, but applies the structure that is effective against emissions of the mechanical shoe seal type to a soft tube seal type to create a structure that is safe from ignition and has extremely low emissions. Its purpose is to provide a simple floating roof sealing mechanism.

The structure will be explained based on an embodiment shown in FIG. 4. A ring-shaped elastic body, for example, a soft synthetic resin foam such as urethane foam, is used as a core material 3 on the outer peripheral side wall 2 of the floating roof 1. A ring-shaped body 5 whose surface is covered with an oil-resistant film 4 is attached to the core material 3, and the upper surface 6 of the ring-shaped body 5 is coated with the film 4.
The upper end of a wall curtain 1 made of the same material as the above is curved into a chevron shape and fixed, and the wall curtain 7 is free without being fixed to the ring-shaped body 5 at points other than the upper end, and the outer periphery of the ring-shaped body 5 and It is made to hang down between the tank inner wall 8 and the lower surface extends to a point 1 below the oil level 9.

As shown in FIG. 5, inside the wall curtain 7, a core material 11 made of metal, for example stainless steel, and having a thickness of about 0.2 mm, for example, is preferably built in vertically.

Further, the length of l changes due to the vertical movement of the floating roof 1,
When the floating roof 1 is lowered, the wall curtain 7 is attached to the inner wall 8 of the tank.
The ring-shaped body 5 tends to remain short due to the frictional force acting between the ring-shaped body 5 and the ring-shaped body 5, which easily slides on the inner surface of the wall curtain 7.

In addition, the paper pressure of the stored liquid acts on the space C created between the upper part of the wall curtain 7 and the membrane 4, and the wall curtain 7 is slightly lifted, so the length l is
It is better to make it at least longer than the head due to the paper pressure of the stored liquid in the operating temperature range of the tank.

Since this embodiment has the above-mentioned configuration, the floating roof 1 moves due to the wind, etc., and a seal cap is formed between the wall curtain 7 and the tank inner wall 8, evaporation is induced from there, and the vapor of the built-in liquid is emitted. Even if this occurs, the steam in the space surrounded by the wall curtain 7, the lower side of the ring-shaped body 5, and the floating roof outer periphery 10 does not participate in the emission, and the wall curtain has a chevron-shaped upper end. Since the floating roof 1 is curved and fixed only on the upper surface of the ring-shaped body, and the rest is free with respect to the ring-shaped body 5, the floating roof 1 moves due to wind pressure, and even if it is separated from the tank inner wall 8, the wall curtain is fixed only on the above-mentioned chevron-shaped curved part. Therefore, it is difficult for the ring-shaped body 5 to separate from the tank inner wall 8 due to the effect of Because of this, evaporation does not proceed much, and since the ring-shaped body is covered with an oil-resistant film 4 using a weak elastic core, there is no risk of ignition even if it collides with the inner wall 8 of the tank.

Furthermore, if the metal core material 11 is provided inside the wall curtain, the floating roof 1 will not wrinkle when it is lowered, and will act as a weight, and the overall structure will be extremely simple.

Since this invention has the above-mentioned structural action, it is possible to sufficiently prevent emissions, and it is possible to safely store liquids such as hydrocarbon paper that generate flammable vapors in a floating roof tank. A roof sealing mechanism can be provided.

[Brief explanation of drawings]

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 explanatory diagram of a typical example of a tube seal type and a mechanical shoe seal mechanism. 4 is a longitudinal sectional front view of a part of two embodiments of the floating roof sealing mechanism according to the present invention, and FIG. 5 is a perspective view of the middle part of the wall curtain part. roof, 2 is the outer peripheral side wall, 3 is the core material,
4 is an oil-resistant film, 5 is a ring-shaped body, 6 is an upper surface, and 7 is a wall curtain.

Claims (1)

[Claims] 1. A ring-shaped body 5 having a ring-shaped elastic body as a core material 3 and a surface of the core material 3 covered with an oil-resistant film 4 is attached to the outer peripheral side wall 2 of the floating roof 1, and the upper surface of the ring-shaped body 5 is 6, the upper end of a wall curtain 7 made of the same material as the coating 4 is curved into a chevron shape and fixed, and the wall curtain 7 is not fixed to the ring-shaped body 5 except for the upper end, and is free to be attached to the ring-shaped body 5. A floating roof sealing mechanism characterized in that the ring-shaped body 5 is suspended between the outer periphery and the tank inner wall 8, and the lower end is long and immersed in the stored liquid.