JPS5929512B2 - Liquid level fluctuation prevention device for liquid storage tanks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel device for preventing liquid level fluctuations in tanks for storing liquids such as heavy oil, and in particular, it reliably prevents the so-called sloshing phenomenon caused by liquid level fluctuations that occur during earthquakes, thereby improving the safety of the tank. The present invention relates to a liquid level fluctuation prevention device for a liquid storage tank that is capable of improving as much as possible.

In the field of liquid storage such as heavy oil, it is widely known that large liquid storage tanks, in particular, experience severe liquid level fluctuations, or sloshing, due to long-period large displacement amplitude components included in passive movements during earthquakes. It is being

If sloshing occurs in this type of tank, the stored liquid may collide with the tank roof and break through the roof, the stored liquid may overflow over the tank side plate, or the localized liquid pressure may increase due to agitation. As a result, the tank side plate may be subjected to excessive force, which may lead to a very dangerous situation. Therefore, there is a need for a means to effectively suppress such sloshing when it is about to occur. In order to meet the above-mentioned needs, the present applicant has developed a liquid level fluctuation prevention device for a liquid storage tank (patent application), which has a structure that reliably suppresses sloshing during an earthquake and prevents the tank from being destroyed due to the sloshing. 53-145799) and filed the application earlier.

In this liquid level oscillation prevention device (hereinafter referred to as the device of the prior application),
As shown in FIG. 2, pulleys 5, 6 and 5a, 6a are arranged adjacent to and parallel to the peripheral edge of the floating body 4 floating on the liquid storage surface in the tank T as shown in FIG. 5 and 5a and 6 and 6a are pivoted so as to face each other and form a pair. Further, on the inner wall surface of the side plate 1 of the tank T, rope upper end locking devices 8 and Ba are provided vertically above each of the pulleys 5 and 6a, and each of the upper ends of the pair of wire ropes T and 7a is attached to these locking devices. The parts are locked individually.
Then, one wire rope T is hung under the pulley 5, and then hung over the pair of pulleys 5a and suspended, and the lower end of the hanging rope is fixed to the lower end of the rope provided on the inner wall surface of the side plate 1. In the same way, the other wire rope Ta is also successively passed through the pulleys 6a to 6 of that system and is locked to the rope lower end locking device 9a. According to the device of the prior application having the structure having the rope/pulley mechanism as described above, the floating body 4 maintains a horizontal attitude and does not pose any hindrance to vertical displacement of the liquid level due to increase or decrease in the amount of liquid stored in the tank T. The wire ropes 7, 7a are smoothly followed and moved without any additional tensile load acting on the wire ropes 7, 7a.

However, in the event of an earthquake, the floating body 4 also tends to tilt due to the fluctuation of the liquid level in the tank, so a tensile load acts on one of the wire ropes 7 or 7a, which causes the floating body 4 to tilt. Tilting is suppressed. In this way, sloshing, which is likely to occur during an earthquake, is prevented and the tank is sufficiently effective to ensure safety.
In order to confirm the effectiveness of the device of the prior application, the present inventors conducted an experiment by applying horizontal vibration to a water-filled model tank equipped with the above-mentioned rope/pulley mechanism on a vibration table, and discovered the following new facts. .

First, when the rope is not tensioned, when the excitation frequency matches the free frequency (natural frequency) of the liquid surface oscillation, severe sloshing will occur and the liquid in the tank T will leak into the sealed area around the periphery of the floating body 4. It was confirmed that the sloshing was almost completely suppressed when the rope was tightened. However, in the vicinity where the excitation frequency matches the natural frequency of the liquid level fluctuation when the spring force of the rope against the floating body 4 is added to the restoring force due to the gravity of the liquid surface, sloshing newly appears. It was revealed that. This sloshing has a damping effect due to the internal friction of the ropes 7, 7a themselves, the friction between the ropes 7, 7a and the pulleys 5, 5a, 6, 6a, and the pulley bearings, and the amplitude of the sloshing is different from that of the original sloshing. An order of magnitude difference (approximately 1/1 in model experiments)
(approximately 0). However, this sloshing still places a considerable amount of tension on the rope, so
The design of the device of the prior application described above becomes difficult. This effect is 10,000K
There is almost no problem with small tanks of the 2nd class, but 10′
) When it comes to a large 5K1 class tank, it becomes necessary to use extremely thick or large numbers of wire ropes, and the area around the rope anchors 8, 8a, 9, 9a, especially the area around the upper rope anchors 8, 8a. This requires extensive reinforcement of the side plate 1 and reinforcement of the floating body 4 at the pulley attachment portion, which inevitably increases costs. As is clear from the above, the device of the prior application having a rope hanging pulley structure is very effective in preventing the original sloshing, but it is not sufficient to prevent sloshing that newly occurs due to the spring action of the rope. must be taken into account.

This becomes an important issue, especially in the case of large tanks.
In order to solve this problem, it is necessary to reduce the resonance amplitude of the newly generated sloshing as much as possible. One possible solution to this problem is to limit the resonance amplitude of the above-mentioned new sloshing by increasing the friction by the pulley and the friction between the seal around the floating body and the inner wall surface of the tank side plate. This is not practicable because it inevitably results in hindering the free vertical movement of the floating body.

The present invention has been made in view of the above-mentioned circumstances, and its main purpose is to suppress the swinging of floating bodies on the liquid level in the tank caused by long-period large displacement amplitude components during earthquakes in the device of the prior application. By adding a hydraulic damper with a simple structure to the hanging part of the rope, it is possible to minimize the liquid level sloshing that newly occurs due to the spring action of the rope, thereby further ensuring the sloshing prevention effect. An object of the present invention is to provide a liquid level fluctuation prevention device for a liquid storage tank.

Another object of the present invention is to provide a liquid level fluctuation prevention device for a liquid storage tank that is constructed as a hydraulic damper that directly uses the liquid stored in the tank as hydraulic oil, thereby eliminating the need for maintenance.

An embodiment of the present invention will be described in detail below with reference to FIGS. 3 to 7.

The tank T shown in FIG. 3 for storing liquids such as heavy oil has a tank side plate 1 formed in a cylindrical shape on a tank bottom plate 3, and a floating body 4 as a floating roof above the liquid storage surface in the tank. It has a roof-type cylindrical tank structure. The floating body 4 has an annular seal member S between its peripheral edge and the inner circumferential wall surface of the tank side plate 1, and covers the liquid storage surface in the tank. Further, on the upper surface of the peripheral edge of the floating body 4, there are a plurality of pairs of pulleys 5, 5a arranged in the same arrangement as in the device of the prior application shown in FIGS. 1 and 2.
and 6, 6a are pivotally supported via respective pulley bearings 5' and 6', as shown in FIG. That is, as shown in FIG. 4, the pulleys 5, 5a and 6, 6a are such that 5 and 6 and 5a and 6a are adjacent to each other in parallel, and 5 and 5a and 6 and 6a are parallel to each other. They are arranged in pairs facing each other with respect to the center line of the floating body 4. On the other hand, a rope upper end stopper 8 is provided on the inner wall surface of the tank side plate 1 vertically above the pulleys 5 and 6a.
, 8a, and vertically below the other pulleys 5a and 6 are damper locking devices 9, 9a, respectively.

A pair of wire ropes 7 are attached to the rope upper end locking devices 8, 8a.
, 7a are locked. These wire ropes 7
, 7a, one of the wire ropes 7 is hooked onto the pulley 5 on the line of descent from the upper end stopper 8, and then
It hangs over a pulley 5a facing this pulley 5 and hangs down,
The lower end of the hanging rope is connected to a damper locking device 9 via a hydraulic damper 10. In the same way, the other wire rope 7a is hung on a pulley 6a located on the line of descent from the upper end stopper 8a, and then hung on the opposite pulley 6, so that the lower end of the rope is suspended under hydraulic pressure. It is connected to a damper locking device 9a via a damper 10a. In the illustrated example, the hydraulic dampers 10 and 10a are as follows:
The cylinder configuration is as shown in an enlarged view in FIG. 5, and a specific example of the configuration is as follows.

That is, as shown in the figure, the inside of the cylinder 11 serving as the damper body is partitioned by the piston 12 into a pressure chamber R on the head side and a liquid guide chamber R2 on the bottom side. communicates with the inside of the tank through a plurality of liquid inlet/outlet holes 14 provided in the bottom plate. The piston 12 receives a biasing force in the direction of contracting the liquid guide chamber R2 by a return spring 16 provided in the pressure chamber R1. In addition, the piston 12
a port 17 that communicates the liquid guide chamber R2 and the pressure chamber R1;
and 18 are provided, and these ports are opened and closed by a check valve 19 and a hydraulic pressure responsive valve 20, respectively. These check valves 19 and hydraulic response valves 20 may be of a type commonly used in general hydraulic systems;
Although no special explanation is necessary for the structure, FIG. 5 shows the basic structure for understanding their functions.

That is, these valves 19 and 20 are attached to the piston 12 so as to communicate with the ports 17 and 18, and include a valve box 21 that is shaped like a cylinder with a lid and that projects into the pressure chamber R1, and a valve body 22 that is provided inside the valve box. and a spring 23 which is also provided in the valve box 21 and always biases the valve body 22 in the valve closing direction. 20 has an orifice 24. however,
The valve bodies 22 of the check valve 19 on the port 17 side and the hydraulic pressure responsive valve 20 on the port 18 side are closed in opposite directions. That is, the check valve 19 on the port 17 side uses the port 17 as the valve hole and the valve body 2 in the direction of closing the port.
2 is biased by a spring 23, and the hydraulic pressure responsive valve 20 on the other side of the port 18 is biased by the spring 23 so that the valve body 22 closes the orifice by using the orifice 24 in the canopy of its own valve box 21 as a valve hole. energized. Therefore, the check valve 19 on the port 17 side is pushed open by the hydraulic pressure from the liquid guide chamber R2 due to the action of the return spring 16, and the hydraulic response valve 20 on the other port 18 side is forced open by the liquid from the pressure chamber R. 0 In addition, in FIG. 5, reference numeral 13 is a piston rod, 13a is an eye ring for connecting a rope formed at the tip of the piston rod 13, and 25 is a piston rod penetrating portion of the cylinder head. The provided seal packing 26 is a mounting piece integrally provided on the bottom plate of the cylinder 11. The hydraulic dampers 10, 10a configured as described above are attached by pin-coupling the mounting pieces 26 at the bottom of each cylinder to the damper locking tools 9, 9a on the tank side plate 1.

The hanging ends of the wire ropes 7 and 7a hanging down from the pulleys 5a and 6 are stopped at the distal eye ring part 13a of the piston rod 13 of each of the attached hydraulic dampers 10 and 10a. Therefore, each of the above hydraulic dampers 10
, 10a are attached in series with respect to the spring force acting direction of the wire ropes 7, 7a. Next, the operation of the above embodiment will be explained.

Each hydraulic damper 10, 10a installed as described above
will be immersed in a liquid such as heavy oil stored in the tank T. In each of these hydraulic dampers 10, 10a, an internal pressure chamber R1 and a liquid guide chamber R2 are filled in advance with the same liquid as the liquid in the tank. In such a state, first, if the liquid level in the tank is calm, the hydraulic damper 1
The return spring 16 in the pressure chamber R1 of 0, 10a is compressed until it balances the initial tension of the wire ropes 7, 7a and maintains a state of equilibrium with that tension. At this time, the liquid pressure in the pressure chamber R1 and the liquid guide chamber R2 are equal to the liquid pressure in the tank T. If an earthquake causes a fluctuation in the liquid level in the tank from this state, As a result, the floating body 4 tends to tilt around the center in the directions indicated by arrows A and B in FIG. Attempt to pull up rope 7.

Therefore, the piston 12 of the hydraulic damper 10 connected to the hanging end of the wire rope 7 rises together with the piston rod 13 against the return spring 16. As the liquid in the pressure chamber R1 is compressed by the rising of the piston, this liquid pushes open the valve body 22 of the pressure-responsive valve 20, passes through the orifice 24 and the valve body 21 in order, and passes from the port 18 to the liquid guiding chamber. It flows out into R2. At this time, a pressure is generated in the pressure chamber R1, which acts on the piston 12 and resists the wire rope 7 from being pulled up. This force becomes the damping force of the hydraulic damper 10, and the damping force is composed of the spring force of the spring 23 in the pressure-responsive valve 20 and the orifice 2.
Depending on the shape of 4, it can be made proportional to the speed of the piston 12, or
Or it can be freely adjusted to any functional form as needed. It goes without saying that the port 17 on the check valve 19 side is closed during the above process. On the other hand, a wire rope 7a running parallel to the wire rope 7 is loosened by the movement of the floating body 4 in the directions of arrows A and B, so a hydraulic damper 10 connected to the hanging end of the wire rope 7a is
a is a return spring 16, contrary to the case of the hydraulic damper 10 described above.
acts to push down the piston 12.

At this time, the valve body 22 of the check valve 19 provided on the piston 12 is pushed up by the liquid pressure from the liquid guide chamber R2 and the port 17 opens, so the liquid in this liquid guide chamber is pushed up with almost no resistance. Flows into chamber R. Eventually, the hydraulic pressure in the pressure chamber R1 returns to the hydraulic pressure in the tank T as well as in the liquid guide chamber R2. When the rising and falling sides of the liquid level in the tank T due to sloshing are reversed to the above case, a tensile force acts on the wire rope 7a, which was on the slack side in the above case, and the wire rope 7, which was on the tension side, becomes slack. Become a side.

For this reason, the hydraulic dampers 10, 10a connected to the hanging ends of these ropes each operate in the opposite direction to that described above. Thus, each of the hydraulic dampers 10, 10
a works only when the wire ropes 7 and 7a connected to them are pulled, but since they work alternately and continuously, the wire ropes 7 and 7a work through the vibration cycle of rising and falling of the liquid level in the tank due to sloshing. , 7a alternately, which gives a spring force and at the same time a damping force to the floating body 4. As a result of the above, the rocking (tilting) of the floating body 4 due to sloshing that is likely to occur during an earthquake is prevented. Since it is effectively suppressed by the wire ropes 7, 7a, it is not only effective in preventing the original sloshing, but also especially the tensile force acting on the wire ropes 7, 7a is suppressed by the hydraulic dampers 10, 1.
Since it is attenuated by 0a, the resonance amplitude of the liquid level sloshing newly generated by the spring action of the wire ropes 7, 7a can be suppressed to be as small as possible.

Next, the operation of the above-mentioned device of the present invention will be explained from the perspective of vibration theory, in comparison with the case of a general floating roof type cylindrical tank and the device of the prior application.

In general, when the vibration system of liquid level fluctuation in a floating roof type cylindrical tank is modeled, it can be represented by a simple system of mass, spring, and damper, as shown in FIGS. 6A, B, and C. 6th
Figure A shows the vibration system in the case of only a floating roof (floating body), Figure 6B shows the vibration system in the case of the device of the prior application, and Figure C shows the vibration system in the case of the device of the present invention. In these figures, m is the equivalent mass obtained by converting the effective mass of the liquid in the tank and the floating body to the wire rope attachment point of the floating body, and KO is the restoring force due to gravity acting on the liquid in the tank, which is the same as m. Equivalent spring constant when converted to a point, k1
is the spring constant of the wire rope, C1 is the damping coefficient of the rope/pulley system, and C2 is the damping coefficient of the hydraulic damper connected to the hanging end of the rope. Further, F represents the excitation force acting on m due to the horizontal acceleration of the tank foundation due to the earthquake, and x represents the displacement of m, that is, the displacement of the liquid level oscillation. In these vibration systems, the equivalent spring constant K due to the gravity of the liquid in the tank. The damping force that should be associated with is actually extremely small, so it is omitted. Furthermore, since the spring constant of the return spring 16 built into the aforementioned hydraulic damper is much smaller than the spring constant k1 of the wire rope, this is also omitted. In these vibration systems, the excitation force is F=FOSinC! )t, the displacement of liquid level fluctuation x=asin(ωt+γ) can be obtained by simple calculation.

Here, Fo is the amplitude of the excitation force, a is the amplitude of the liquid level, ω is the circular frequency of the excitation force, and γ is the phase difference with respect to x0F.
When the resonance curve of each vibration system is drawn as described above, the diagram shown in FIG. 7 is obtained.

In this figure, the vertical axis is the amplitude a of the liquid level fluctuation, and the horizontal axis is the circular frequency ω. That is, in the case of only the floating body shown in FIG. 6A, the original liquid level sloshing frequency ω is as shown by curve A in FIG. = f A very intense resonance occurs at the 7th depth of the ball. On the other hand, in the case of the prior application device shown in FIG. 6B, which has a wire rope/pulley mechanism, the resonance at ωo disappears, as is clear from the B curve in FIG.
Resonance newly appears at ω,=f°C=TT=Z. Although the resonance amplitude of the B curve is much smaller than that of the A curve, it is still advisable to make the resonance amplitude of the B curve as small as possible, as described above. By the way, the A curve in FIG. 7 corresponds to the case where C2-0 is set in the vibration system of FIG. 6 C, that is, the case of FIG. 6 A, and the B curve corresponds to the case where C2-(1) is set, This corresponds to the case in FIG. 6B. As inferred from this, the intersection point P of both curves AB is the point through which the resonance curve of the C system in FIG. 6 necessarily passes, regardless of the value of C2.
Therefore, by appropriately selecting the value of C2, the resonance curve of this system can be made to reach a maximum at point P, as shown by curve C in FIG. That is, at this time, the resonance amplitude becomes minimum. This can be proven by simple vibration theory calculations. The optimum value of C2 based on the calculation result is expressed as follows.

However, K=k1/ko. Using this equation, the required damping coefficient C2 of the hydraulic damper of the device of the present invention can be determined. Therefore, the above-mentioned hydraulic damper may be selected using a commonly used method. In the above embodiments, the operation was explained only when the liquid level in the tank fluctuated due to an earthquake. It goes without saying that the floating body 4 can smoothly move up and down in accordance with the above without any hindrance.

At this time, the hydraulic dampers 10 and 10a are in the state when the liquid level is calm, that is, the return spring 16 is
, 7a, and maintains a state of equilibrium with the initial tension, and no tensile force greater than the initial tension acts on each wire rope 7, 7a. It should be noted that the liquid storage tank T in the above embodiment may have a closed tank configuration in which the upper end opening is covered with the roof 2, as in the case of the device of the prior application shown in FIG. . Furthermore, although the check valve and the pressure responsive valve of the hydraulic damper are shown as being provided on the piston, they may also be provided on the cylinder head. As described above, according to the device of the present invention, the swinging of the floating body on the liquid surface due to the fluctuation of the liquid level in the tank that occurs during an earthquake is suppressed using a simple rope/pulley mechanism, thereby almost completely suppressing sloshing. In addition to the effects of the prior-application device, the following new and remarkable effects can be obtained.

(1) A hydraulic damper that generates a drooping force only when the rope that suppresses the rocking of the floating object is pulled is newly installed at the hanging part of the rope, so the hydraulic damper Due to the damping effect, new springs generated by the spring action of the rope are
The resonance amplitude of lossing can be suppressed to a minimum.

(2) In order to prevent excessive tension from being applied to the rope due to slotting during an earthquake, it is possible to make the rope diameter extremely thick, or to use a large number of ropes. There is almost no need for extensive reinforcement of the nearby tank side plates or the pulley attachment part of the floating body.

Therefore, the device of the present invention has a simplified design and is advantageous in terms of cost, and is also highly practical as it can be easily applied to existing tanks. (3) On the other hand, the above-mentioned hydraulic damper is equipped with a pressure chamber and a liquid guiding chamber that are partitioned by a piston, and this liquid guiding chamber is provided with a liquid inlet and outlet hole that opens while the liquid is stored in the tank, so that the liquid can be kept in the tank at all times. Since it is immersed in the liquid stored in the tank, the liquid stored in the tank that flows into and out of the liquid guide chamber and pressure chamber from the liquid inlet/output hole is used as the working fluid. This is extremely advantageous because there is no need to worry about oil leakage, which eliminates the need for damper maintenance.

(4) In addition, a return spring is provided in the pressure chamber of the hydraulic damper to urge the piston toward the liquid guiding chamber, and the action of this return spring provides an appropriate initial tension to the wire rope. This allows the wire rope pulley system to operate smoothly and increases safety in terms of strength and strength. do.

(5) Therefore, in the device of the present invention, the sloshing prevention effect achieved by the device of the prior application can be made even more reliable, and its reliability can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the device of the prior application, FIG. 2 is a view taken along the - line in FIG. is a view taken along the - line in FIG. 3, FIG. 5 is an enlarged sectional view of the hydraulic damper, and FIGS. 6 A, B, and C are for a general cylindrical tank with only a floating roof, and for the device of the prior application, FIG. 7 is an explanatory diagram of each vibration system comparing the cases of the apparatus of the present invention, and FIG. 7 is a resonance curve diagram of each vibration system in each of the above cases. In the figure, T is the tank, 1 is the tank side plate, 4 is the floating body, 5, 5
a, 6, 6a are pulleys, 7, 7a are ropes, 10, 10a
is a hydraulic damper.

Claims (1)

[Claims] 1. A floating body floated to cover the liquid storage surface of a tank storing heavy oil, etc., pulleys that are pivoted on the upper part of the peripheral edge of the floating body and run adjacent to each other in parallel, and those pulleys. A pair of pulleys facing each other, and the upper end portions are locked at opposite positions near the upper edge of the tank side plate, and while hanging down, the pulley is stretched from one pulley to the other pulley of the pair, and is passed along the tank inner plate. a hanging rope, one end of which is locked to the hanging end of the rope, and the other end of which is locked near the lower edge of the tank inner plate;
A liquid level oscillation prevention device for a liquid storage tank, characterized by comprising a hydraulic damper that operates to attenuate the tensile force of the rope and uses liquid stored in the tank as working fluid.