JPH026713B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention automatically suppresses the shaking of the floating roof due to fluctuations in the liquid level when the floating roof type oil tank is subjected to seismic force. This invention relates to a sloshing suppression device for a floating roof of an oil tank.

[Prior Art] As shown in Fig. 1, a floating roof type oil tank has a floating roof c floating above the liquid level of crude oil etc. A tube d made of nitro rubber or the like and a sealing material f made by putting an elastic material e such as urethane into the tube d to make the whole elastic are attached, and the sealing material f seals the outer peripheral surface of the floating roof c and the inner periphery of the tank side plate. It is designed to be able to move up and down following fluctuations in the liquid level of crude oil, etc. b, while sealing between the surfaces, and to prevent crude oil, volatile gas, etc. b from leaking to the outside. The reason why the tube d on the surface of the sealing material f is made of rubber is that if the tube d were made of metal, the floating roof c
This is to prevent the possibility of ignition due to friction with the inner surface of the tank side plate when the seal member swings, which may cause a fire, and the surface of the sealing material f made of an elastic material should be pressed against the inner surface of the tank side plate. It is only designed to prevent the outflow of liquid and volatile gas, but does not have the function of suppressing the swinging of the floating roof. This means that the friction force is F, the friction coefficient is μ,
When the pressing force is N, there is a relationship of frictional force F = μ, and if the pressing force of the sealing material f against the inner surface of the tank side plate is increased, the frictional force will increase, and the sealing material f will move up and down due to liquid level fluctuations. Since the sealing material f wears out when the sealing material f wears out, conventionally the pressing force is reduced to reduce the frictional force, and it is clear that the sealing material f only has a sealing function.

In this way, the conventional sealing material f for floating roofs has no function to suppress sloshing of the floating roof, so when an earthquake occurs and the crude oil, etc. in tank a starts to fluctuate, the sealing material f for the floating roof starts to fluctuate as the liquid level fluctuates. Floating roof c can also swing without limit. There was a possibility that the floating roof's rocking (vertical displacement) could damage the upper structure of the tank or cause a fire due to a collision. Furthermore, since conventional floating roof sloshing cannot be suppressed, the tank has been made deep to prevent the liquid from overflowing during floating roof sloshing.
However, in the event of an unexpectedly large earthquake, there was a risk of overflow.

As a result of various studies on suppressing sloshing in floating roof oil tanks, the inventor has found that:
It was experimentally and theoretically confirmed that most of the damping that governs the sloshing response of floating roof oil tanks depends on the friction of the seal.

In other words, when considering how the friction between the sealing material around the outer circumference of the floating roof and the inner surface of the tank side plate affects the sloshing response, the damping effect due to the friction between the floating roof sealing material and the tank side plate during sloshing is equivalently Evaluate as the damping constant h _e ,
The frictional force between the sealing material and the inner surface of the tank side plate is multiplied by the rocking stroke (stroke) of the floating roof due to rocking to find the frictional work (energy dissipated by friction) E _f and calculate the sloshing movement of the internal solution. Energy K _E
The above h _e is determined by comparing with .

The energy E _f dissipated due to the friction between the seal material and the inner surface of the tank side plate during the above sloshing is: (a) Assume that the compressive repulsion force of the seal material (urethane foam) is constant when the floating roof swings. That is, the total frictional force between the sealing material and the inner surface of the tank side plate is made constant.

(b) The floating roof deck maintains the flat surface during slotting.

Assuming the conditions, it is given by the following equation for one period.

μ: Coefficient of friction between the sealing material and the inner surface of the tank side plate ηm: Maximum sloshing wave height (m): Pressing force of the sealing material against the inner surface of the tank side plate (per unit circumference) (Kgf/m) R: Tank inner radius ψ: Circumference Angle = lP l: Contact width between the sealing material and the inner surface of the tank side plate (m) P: Contact surface pressure between the sealing material and the inner surface of the tank side plate due to the repulsive force of the sealing material (urethane foam) (Kgf/m ² ) Next, the internal solution The kinetic energy K _E when causing first-order mode sloshing is given by the equation assuming the following conditions.

(c) The floating roof structure shall be rigid, and the mass of the floating roof shall be sufficiently small compared to the mass of the liquid.

(d) Replace the sloshing vibration system with a spring/mass model, and connect the periphery of the floating roof and the bottom of the tank with a sloshing gravity spring.

K _E = 1/2・2m _v R′ ²・(η/R′) ² = m _v η ² m _v : Sloshing effective mass (Kgf・s ² /m) η : Vertical velocity of mass m _v (tank side plate ) (m/s) R′: Equivalent radius of mass m _v (m) Especially when the sloshing response is sinusoidal, K _E = m _v (ω ₁ ηm) ² ω: First-order circular frequency (1/sec) ηm: Maximum amplitude (maximum response wave height (m)) Also, g: Gravitational acceleration (9.8m/s ² ) H: Liquid level height (m) Equivalent damping coefficient h due to friction between the floating roof sealing material and the inner surface of the tank side plate Since _e is given by h _e =1/2π·E _f /2K _E , substituting the formula into this gives h _e =4μNR/πm _v ω ₁ ² η _n .

From this formula, it can be seen that the equivalent damping coefficient h _e is proportional to the friction coefficient μ and the pressing force, and the friction coefficient,
Sloshing can be reduced by increasing the pressing force and increasing the equivalent damping coefficient h _e .

[Object of the Invention] Based on the above theory, the present invention aims to increase the damping force by the time the wave height increases when the liquid in the tank is shaken by an earthquake. The object of the present invention is to automatically increase the pressing force against the inner surface of the side panels to increase the frictional force and suppress the swinging of the floating roof in a short time, thereby solving the above-mentioned conventional problems.

[Structure of the Invention] In order to achieve the above object, the present invention interposes a pressurizing telescopic bag that can be expanded and contracted between the sealing material attached to the outer periphery of the floating roof and the floating roof outer peripheral surface, and the pressurizing telescopic bag is connected to the reserve tank via a pressurized fluid pipe with a valve in the middle, and in the event of an earthquake, the above valve is controlled based on the detection signal of tilting etc. caused by the shaking of the floating roof due to the shaking of crude oil etc. The pressurizing fluid is automatically injected into the pressurizing telescopic bag to inflate the pressurizing telescopic bag, and the sealing material is pressurized to increase the pressing force against the inner surface of the tank side plate and control the swinging of the floating roof. The structure is such that the sloshing of the floating roof is suppressed before the sloshing grows.

Next, embodiments of the present invention will be described.

[Embodiment] Figures 3 to 8 show an embodiment of the present invention, in which a ring-shaped structure is attached to the outer periphery of a floating roof 3 that floats on the liquid level of crude oil, etc. 2 in a flat-bottomed cylindrical oil tank 1. An elastic sealing material 4 made of an elastic body 6 such as urethane foam is supported in a rubber tube 5, and the sealing material 4 seals between the floating roof 3 and the inner surface of the tank side plate 7. In the floating roof type oil tank, pressurizing telescopic bags 8 are interposed between the outer circumferential surface of the floating roof 3 and the inner surface of the sealing material 4 at several locations in the circumferential direction as shown in the figure. 8 and a reserve tank 9 are connected via a pressurized fluid piping 10, and by opening and closing a valve 11 provided in the middle of the piping 10, fluid pressure (air pressure or oil pressure) from the reserve tank 9 can be applied to each pressurized fluid. It acts on the inside of the pressurizing telescopic bag 8 to expand or contract the pressurizing telescopic bag 8, thereby increasing or decreasing the pressing force of the sealing material 4 against the inner surface of the tank side plate 7.

A ring-shaped support frame 14 is erected on the upper surface of the peripheral part of the floating roof 3, and the tip roller 17 is always pressed against the tank side plate 7 by a spring 16 at several locations on the support frame 14 in the circumferential direction. The differential transformer displacement gauges 15 are arranged radially, each of the differential transformer displacement gauges 15 is connected to the displacement limit switch 18, and the displacement limit switch 18 is connected to the control section of the valve 11. The amount of floating roof inclination is detected by a signal from 15, and when this signal exceeds a certain level, a displacement limit switch 18 is turned on to control valve 11 open.

In response to fluctuations in the liquid level when no earthquake occurs, the roller 17 at the tip of the differential transformer displacement gauge 15, which is always pressed against the tank side plate 7 by the spring 16, freely rolls along the tank side plate 7. , the floating roof can follow fluctuations in the liquid level without any problems.

When an earthquake occurs and the crude oil, etc. 2 in the tank begins to oscillate, the floating roof 3 also begins to oscillate as the liquid level oscillates. Differential transformer displacement gauges 15 are attached to the floating roof 3 at symmetrical positions in the circumferential direction, so when the floating roof 3 tilts due to rocking, the displacement gauge 15 located at the lower part of the tilt as shown in FIG. Spring 1
6 is compressed and retreated, and the displacement meter 15 at the symmetrical position is expanded so as to increase the distance from the tank side plate 7. Now, when the floating roof 3 is in a horizontal state, the distance between the frame 14 and the tank side plate 7 is x ₀ ,
If the distance between the frame 14 and the tank side plate 7 when the displacement meter 15 is extended as shown in Fig. 8 is x ₁ , then
x ₁ −x ₀ =Δx, and this Δx is the product of the inclination angle θ of the floating roof 3 and the height h ₁ of the frame 14, that is, x ₁ −x ₀ =Δx=θ·h ₁ . This Δx is proportional to the amount of inclination of the floating roof 3, and this amount of inclination is detected by the displacement meter 15, and when this detected value exceeds a certain level, the displacement limit switch 18 is activated to open the valve 11.

As a result, fluid pressure is applied to each pressurizing telescopic bag 8 from the reserve tank 9 through the piping 10, and each pressurizing telescopic bag expands and strongly presses the sealing material 4 outward. The pressing force against the inner surface of the side plate 7 is increased. Due to this increase in pressing force, the frictional force between the sealing material 4 and the inner surface of the tank side plate increases, and the damping constant increases as in the above theory. Therefore, the floating roof 3 is restrained from swinging for a short time after an earthquake occurs, and sloshing is suppressed.

The displacement amplitude due to an earthquake is small at the time of the earthquake, but becomes large after a certain period of time. In the present invention, since the swinging of the floating roof 3 is restrained within a certain period of time during which the amplitude does not increase,
Sloshing of the floating roof 3 can be suppressed easily and reliably.

Furthermore, long-period earthquake motion with small ground surface acceleration may cause sloshing of the floating roof 3, and in such cases, seismometers and accelerometers cannot determine sloshing of the floating roof. Since the actual inclination of the roof 3 is detected and the pressurizing telescopic bag 8 is expanded, sloshing of the floating roof 3 can be reliably detected and prevented.

It should be noted that the present invention is not limited to the above-described embodiments, and as means for detecting the inclination of the floating roof, it is possible to detect the swinging speed in the vertical direction when the floating roof tilts due to swinging, or It is also possible to place a container filled with water on the floating roof and use a differential pressure gauge to measure the difference in water head that occurs when the floating roof is tilted.

[Effects of the Invention] As described above, according to the apparatus of the present invention, the following excellent effects can be achieved.

When an earthquake occurs, the sealing material is compressed to increase the pressing force of the sealing material against the inner surface of the tank side plate, increasing the frictional force and damping the swinging of the floating roof. It is possible to suppress the shaking of the floating roof before the sloshing grows, thereby eliminating the risk of damaging the upper structure of the tank or causing a fire due to a collision.

Since the actual inclination of the floating roof is detected and the pressurizing telescopic bag is expanded, sloshing of the floating roof can be reliably prevented even in the case of long-period earthquake motions with low ground surface acceleration.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a conventional floating roof type oil tank, Fig. 2 is an enlarged view of the part shown in Fig. 1, Fig. 3 is a schematic diagram of an embodiment of the present invention, and Fig. 4 is a schematic diagram of the part shown in Fig. 3. Fig. 5 is an enlarged view of the part shown in Fig. 3, Fig. 6 is a view taken from - direction of Fig. 3, Fig. 7 is an enlarged view of the part shown in Fig. 3, and Fig. 8 is an enlarged view of the part shown in Fig. 3. FIG. 3 is a state diagram during sloshing. 1 is an oil tank, 2 is crude oil, etc., 3 is a floating roof, 4 is a sealing material, 7 is a tank side plate, 8 is an extensible bag for pressurization, 9 is a reserve tank, 10 is piping, 11 is a valve, 14 is a support frame, 15 is a differential transformer displacement gauge, 16 is a spring, and 18 is a displacement limit switch.

Claims (1)

[Claims] 1. A pressurizing telescopic bag is provided between the sealing material supported on the outer circumferential surface of the floating roof in a floating roof type oil tank and the outer circumferential surface of the floating roof to press the sealing material against the tank side plate by being expanded. It is provided with a device for detecting the inclination of the floating roof by intervening at a plurality of locations in the circumferential direction, connecting each of the pressurizing extensible bags to a fluid pressure supply source, and based on a signal from the detection device, pressure fluid is supplied from the supply source. A sloshing suppressing device for a floating roof of an oil tank, characterized in that the device is configured to be fed under pressure to a pressurizing telescopic bag.