JPS6239490A - Method and device for preventing oscillation of level of liquid storage tank - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and device for preventing liquid level fluctuations in a liquid storage tank, and more specifically, when an oil tank or the like is shaken by an earthquake, This relates to a device that prevents stored oil from overflowing from a tank.

"Prior Art" A conventional method or device for preventing liquid level fluctuations in oil tanks, etc. is to hang a rope over the floating roof of a floating roof type storage tank via a pulley, and attach a damper to the lobe to create a floating roof. A device for suppressing the agitation of the water, that is, the agitation of the liquid level (Special Publication Publication No. 59-2
No. 9512), a method or device for dampening liquid surface waves by floating a float on the liquid surface of a fixed roof type storage tank (Special Publication No. 59-381
No. 53.

Special Publication No. 59-29512) is known.

[Problems to be Solved by the Present Invention] The problem is that the dampers and floats used in conventional methods or devices differ depending on the type of storage tank, liquid content, etc., and cannot be commonly applied to all storage tanks. was there. In addition, dampers, floats, and equipment attached to them may become dangerous if earthquake loads are applied to them. Furthermore, all of the conventional methods passively prevent fluctuations in the liquid level, so there is a risk that they will not be as effective.

The present invention is intended to solve these problems, and its purpose is to provide a method and method for preventing liquid level fluctuations that can be applied in common, regardless of the shape, size, or type of liquid contained in the storage tank. It is an object of the present invention to provide a device that can proactively seal off overflows without causing danger due to the action of seismic loads.

[Means for Solving the Problems] In order to achieve the above object, the method of the present invention detects the pressure within the liquid storage tank at a plurality of positions along the peripheral wall, and inputs the detection signal to a computer to detect fluctuations in the liquid level. At the same time, the period and direction (mode) of the liquid level vibration are calculated, and the liquid level of the peripheral wall located in the direction of the liquid level vibration is determined in time series, and the liquid level of the peripheral wall is determined to be at the peak of the vibration. It is characterized by blowing gas bubbles onto the liquid surface to dampen fluctuations in the liquid surface. An apparatus for carrying out the method includes a gas source, pressure sensing means including pressure sensors provided at a plurality of positions along the peripheral wall of the inner bottom surface of the liquid storage tank, and a plurality of gas Suita sectors also provided along the peripheral wall. and a control value setting means including a valve that connects each gas blowing sector to a gas source, a valve that opens and closes based on a signal from the pressure detection means, and a computer that sets the opening and closing timing thereof, and a signal from the control value setting means. and control output means for opening and closing the valve set based on the set period of time.

. If a flammable liquid such as petroleum is stored in a tank, the gas source must be an explosion-proof inert gas.

[Operation] When a liquid level fluctuation occurs in the liquid in the storage tank due to seismic motion, information resulting from the liquid level fluctuation is detected by a pressure sensor installed at the bottom of the storage tank, and is input into the computer as a signal. The computer determines the mode, period, and direction of vibration based on the input signal, and then calculates the liquid level of the liquid surface of the peripheral wall located in the direction of vibration. Next, the computer controls a signal to open the valve in the gas blowing sector that blows gas to the liquid surface of the peripheral wall located in the vibration direction when the liquid level there slightly exceeds the minimum value, and closes it a little after reaching the equilibrium point. Output to output means. The control output means opens and closes the valve according to the signal from this computer, so the gas from the gas source is ejected from the gas blowing holes of the gas blowing sector located in the direction of vibration, forming a group of gas bubbles, and forming a group of gas bubbles during the antinode period of the vibration. It floats to the surface of the liquid that hits. Due to the hydrodynamic force of the gas bubble group and the disturbance of the liquid, the excitation of the liquid level oscillation is canceled out, and the liquid level oscillation is suppressed.

[Example] The method and apparatus of the present invention will be explained based on the example shown in the drawings.

As shown in FIGS. 1 and 2, eight pressure sensors IA to IH are arranged at equal arc intervals on a bottom plate 11 along the peripheral wall in a fixed roof type cylindrical η tank 10. Similarly, an annular gas blowout v9 is installed along the peripheral wall inside the storage tank 10. The gas blowing pipe 9 is divided into eight gas blowing sectors 8A by a partition wall.
It is divided into ~8H. Each gas blowing sector is ″r
! , are connected to a gas supply pipe 13 that circulates around the storage tank 10 via magnetic valves 7A to 7H, and the gas supply pipe 13 is connected to an inert gas source 18. Pressure sensors IA to IH are arranged at the center of gas blowing sectors 8A to 8H, and a large number of gas blowing holes 20 are bored in each gas blowing sector.

As shown in FIG. 3, an A/D converter 2 including a multiplexer for converting parallel analog signals coming from each pressure sensor into serial digital signals is provided. A
The output of the /D converter 2 is input to a computer 3 as control value setting means. The output of the computer 3 is input to a relay control output generator @ (PIO) 4 that operates relays EiA and E of each electromagnetic valve 7A and E.

Next, damping of liquid level fluctuation in the device of the embodiment will be explained. The liquid level in the storage tank changes due to earthquake motion (if the signal input to computer 3 exceeds the limit value,
As shown in flowchart 1 in the figure, computer 3
starts the operation. As the m1 step (PI), the period T of the first vibration of the liquid level is calculated from the diameter of the storage tank and the liquid level. Since the first-order vibration of the storage tank liquid level is predominant, the second-order and higher-order vibrations can be ignored.

In the second step (P2), the signals from each pressure sensor are input, and in the third step (P3), the direction of the liquid level fluctuation (
(with the center of the storage tank as the origin) and mode (straight line or turning)
to judge. In the fourth step (P4), the gas blowing sector and pressure sensor to be used are selected. For example, as shown in FIG. 3 and FIG.
, 8E, gas blowing sectors 8A, 8E and pressure sensors IA, IE are selected.

At the position of the pressure sensor selected in the fifth step (P5), the time O at which the pressure passes the pressure equilibrium point on the way from high to low is detected, and in the sixth step (P6), from that time O (
3/10) Count the passage of T seconds. (3/10)T
When the seconds have elapsed, as a seventh step (P7), a signal is generated to open the valve of one gas blowing sector. In the case of FIGS. 3 and 5, this signal is input from the computer 3 to the control output generator 4, and the control output generator 4 turns on the relay 6A and opens the solenoid valve 7A, so the inert gas supply source 18
Gas is supplied to the gas blowing sector 8A of the gas blowing pipe 8, and is blown into the liquid from the gas blowing hole group.

The eighth stage (P8) is a count of (2/10) T seconds, during which time the solenoid valve 7A remains open, so the gas continues to blow out from the gas blowing sector 8A, forming a group of gas bubbles. It floats to the liquid surface above the pressure sensor IA. At this time, the liquid level on the peripheral wall above the pressure sensor IA is at the antinode of the oscillation, when it changes from falling to rising, but the oscillation is attenuated by the hydrodynamic force and disturbance action of the gas bubble group. (2/10)
When T seconds have elapsed, a signal is generated to close the opened valve in the ninth step (P9). In the case of FIGS. 3 and 5, the relay 6A is turned off and the solenoid valve 7A is closed.

Then, as the 10th step (PIO), (3/10)T
Count the time ill in seconds and generate a signal to open the valve of the other gas blowing sector located on the opposite side as the 11th stage (pH). In the case of FIGS. 3 and 5, since the relay 6E is turned on and the solenoid valve 7E is opened, the inert gas is transferred to the gas blowing sector 8E with a 1/2 cycle delay from the gas blowing sector 8A.
The 12th stage (PI2) (
2/10) Since the solenoid valve 7E is open even during the counting of T seconds, the gas continues to be blown out, forming a group of gas bubbles that float to the liquid surface on the peripheral wall of the pressure sensor IA'2, causing the antrum of the vibration. Attenuates the vibration of the liquid level corresponding to the period of . The start of gas blowout was set to be (3/10) T seconds after the equilibrium point time O, which is the optimum value obtained through a model test. In addition, the blowing period was set to (2/10) T seconds, which is a time that can effectively prevent fluctuations in the liquid level without unnecessarily increasing the amount of gas consumed.

Then, as a thirteenth step (PI3), a signal is generated to close the solenoid valve that was open. In the case of Figures 3 and 5,
Close the solenoid valve 7E.

The next 14th stage (PI3) is the first stage from the 6th stage above.
The steps up to step 3 are repeated four times, and in the case of Figures 3 and 5, when the liquid level on the peripheral wall above the pressure sensors IA and IE reaches the antinode of vibration four times, the gas blown out each time It is attenuated by the damping effect of the bubble group.

As shown in FIGS. 1 and 3, the blown inert gas is released into the space 15 between the liquid level and the roof 16, and the pressure in that space increases. Since the movable It7 opens, the pressure in the space 15 is prevented from rising excessively. Although not shown in the figure, in the case of a floating roof type storage tank, a movable garment for scrap removal is attached to the outer periphery of the floating roof. The present invention can be applied in the same way as a fixed roof storage tank by dissipating the scum blown out into the atmosphere for vibration damping.

The 15th step (PI3) is to calculate the magnitude of liquid level fluctuation based on the input signals from each pressure sensor, and the calculated value is compared with the value set in advance in the 6th step (PiB). If it is smaller, the computer operation ends; if it is larger, it repeats again from the second step.

Note that when liquid level fluctuation in the swirling mode is detected, gas is blown onto the liquid surface of the peripheral wall portion in accordance with the swirling of the liquid level to suppress the vibration. - The amount of gas bubbles that are blown out from each gas blowing sector each time the solenoid valve is opened and closed is 1% of the amount of vibrating liquid in the storage tank in terms of volume.
It was confirmed through a model test that even a small amount is sufficient.

Next, a model test conducted to measure the effectiveness of the method of the present invention will be described. The model is filled with water to a depth of 24 cm and has an inner dimension of 80 cm in length and 15 cm in width.
A water tank with a height of 50 cm was used. The water tank was placed on a vibration table, and as shown in FIG. 6, sinusoidal vibration was applied in the longitudinal direction, and the pressure sensor 1 was attached to the inner bottom surface along the side wall of the tank. The signal from the pressure sensor was input to a recorder and also to a computer 3 via an A/D converter 2. Gas blow-off sectors 8A and 8E having a large number of gas blow-off holes were arranged on the inner bottom surface along both side walls of the water tank, and were connected to the surge tank 18 of the compressor via electromagnetic valves 7A and 7E, respectively. The air pressure in the surge tank was maintained at 2 atmospheres.

The solenoid valve opening/closing signal from the computer 3 is transmitted to the relay B via the output generator @PIO, and the relay 6 opens and closes the solenoid valve (7A or 7E) based on the signal. The damping effect on liquid level fluctuation was investigated by changing the gas blowout timing and gas blowout time.

The gas blowing timing is O (1/10) T seconds after the time when the liquid level of the gas blowing sector 8A reaches the equilibrium point.
(2/10) I HHHHl after T seconds (9/10) Ten conditions were tested after T seconds (T is the period of vibration). Also, the gas blowing period is (1/10) 7 seconds, (2/1
Four conditions were tested: 0) 7 seconds, (3/10) 7 seconds, and (4/10) 7 seconds. (4/10) The amount of air blown out from the gas blowing sector for 7 seconds was 2 to 3% of the amount of water in the part of the aquarium that was shaken by vibrations.

As a result of the test, the gas blowing timing was determined from the equilibrium point time (2/
10) It was confirmed that the range of T seconds to (4/10) T seconds is effective, and that gas blowing time of (2/10) T seconds or more is effective. Figure 7 is an oscilloscope showing the pressure waveform of pressure sensor l in a test under the conditions that the gas blowout timing was (3/10) T seconds after the equilibrium point time and the gas blowout period was (2/10) T seconds. However, from this figure, even if the vibration table on which the water tank is placed continues to vibrate, the fluctuation of the liquid level caused by the vibration is suppressed by the group of air bubbles blown out, and the vibration is sufficiently suppressed after one minute. Which indicates that.

The intermittent line at the top of the graph indicates the open period of the solenoid valve 7A. Although not shown, the electromagnetic valve 7E on the opposite side opens and closes in the same manner with a delay of half a cycle.

[Effects of the invention] As described above, the method and device of the present invention, when the liquid level in the storage tank is shaken due to an earthquake, causes a group of gas bubbles to float on the liquid level at the antinode of the vibration, thereby hydrodynamically controlling the liquid level. Because it attenuates fluctuations in the liquid level, unlike conventional methods that attach a damper to a floating roof or float a float on the liquid surface, it is applied as a common method regardless of the storage tank type, dimensions, content, and type of liquid. can do. Moreover, the only things added to the storage tank are the pressure sensor and the gas blowout pipe, which can be placed on the bottom 1, so unlike conventional dampers and floats, there is no risk of posing a danger due to earthquakes. The device of the present invention uses a computer to identify fluctuations in the liquid level and proactively dampens the fluctuating liquid level, so it can be said to be significantly superior to conventional vibration damping systems that passively dampen the vibrations.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a reassembled cross section of a storage tank equipped with an apparatus according to an embodiment of the present invention, and shows a state in which the liquid level is fluctuated due to earthquake motion. FIG. 2 is a schematic horizontal cross-section of the storage tank of FIG. 1; FIG. 3 is a schematic diagram showing the overall configuration of the device shown in FIG. 1. FIG. 4 is a computer flow chart. FIG. 5 is a flowchart showing the process in which the signal from the pressure sensor is processed by a computer to open and close the 'FrL magnetic valve that blows out inert gas into the storage tank liquid. FIG. 6 is a schematic diagram showing the apparatus for model testing. FIG. 7 is an oscillograph showing pressure vibrations on the inner bottom surface of the side wall of the water tank in the model test. In one sentence, the code ] is the pressure sensor, and 2 is the A/D.
Converter, 3 is a computer, 4 is a control output generator, 6 is a relay, 7 is a solenoid valve, 8 is a gas suction sector, 9
10 is a gas blowing pipe, 10 is a peripheral wall, 11 is a bottom plate, and 20 is a gas blowing hole.

Claims (1)

[Claims] 1) Detecting the pressure at a plurality of positions within the liquid storage tank and inputting the signal to a control value setting means including a computer;
The control value setting means calculates the vibration period and direction of the liquid level oscillation, and the liquid level of the liquid surface on the circumferential wall of the storage tank located in the direction of vibration, and the gas is applied to the liquid level on the circumferential wall of the storage tank at the time when the liquid level hits the antinode of the vibration. A method for preventing liquid level fluctuation in a liquid storage tank, characterized by blowing out a group of bubbles. 2) The method for preventing liquid level fluctuation in a liquid storage tank according to claim 1, wherein the pressure is detected at or near the inner bottom surface along the peripheral wall of the liquid storage tank. 3) A patent claim characterized in that gas blowing is started when the liquid level of the peripheral wall located in the vibration direction slightly exceeds a minimum value, and gas blowing is stopped when the liquid level slightly exceeds an equilibrium point. A method for preventing liquid level fluctuation in a liquid storage tank according to item 1. 4) The method for preventing liquid level fluctuation in a liquid storage tank according to claim 1, wherein the gas to be blown out is an explosion-proof inert gas. 5) A plurality of gas blowing sectors arranged along the peripheral wall of the liquid storage tank, a gas source connected to each gas blowing sector via a respective valve, and a gas blowing hole drilled in each gas blowing sector. pressure sensing means including a hole and a plurality of pressure sensors that measure pressure at positions along a peripheral wall within the liquid storage tank;
control value setting means including the valve that opens and closes based on the signal from the pressure detection means and a computer that sets the opening and closing timing thereof, and a signal from the control value setting means,
A liquid level fluctuation prevention device for a liquid storage tank, comprising control output means for opening and closing the valve. 6) The gas blowing sector is formed by dividing an annular gas blowing pipe into 6 to 8 equal parts with partition walls, and the pressure sensor is disposed at the center of each gas blowing sector. The liquid level fluctuation prevention device for the liquid storage tank described above.