JP4818144B2 - High liquid level alarm device - Google Patents

Description

  The present invention relates to a high level alarm device installed in a liquid storage tank, and in particular, can prevent a spark discharge accident due to charging of stored liquid without constructing an earth wire. Is.

  The high liquid level warning device is a device that detects that the liquid stored in the tank has reached the uppermost part of the tank and issues a warning that there is a risk of overflow. There are an electromagnetic float method, an ultrasonic sensor method, etc. depending on the liquid level detection method. In addition, there are land storage tanks, marine vessels, and the like depending on the application.

  When installed on a hull, a contact-type high liquid level alarm device that detects the liquid level when the sensor comes into contact with the stored liquid detects the liquid level so that a discharge accident does not occur due to charging of the liquid that is the cargo. Therefore, it is practically obliged to connect the sensor portion attached to the tip of the alarm device and the bottom of the ship on which the tank is mounted with a ground wire.

  Examples of the liquid stored in the tank include oils and fats such as crude oil, gasoline and vegetable oil, and chemicals such as hydrochloric acid and nitric acid, and most of them are insulating. In such an insulating liquid, static electricity is generated due to friction caused by the pump and piping passing when flowing into the storage tank, and friction generated by shaking of the liquid itself, and the liquid is charged. The voltage charged to the liquid in this way can reach several thousand volts or more.

  Since the side and bottom of the storage tank are at ground potential, the storage liquid located near the side of the tank is unlikely to be charged as described above, but the storage liquid near the center of the tank that is far from the tank side is not Easily charged.

  FIG. 6 shows an example of a conventional contact type high liquid level alarm device and its installed state in a storage tank. In FIG. 6, a contact-type high liquid level alarm device 10 (hereinafter referred to as “device 10”) includes a main body 1, a vertical bar 2 attached to the main body 1, and a sensor attached to the tip of the vertical bar 2. 3. By detecting that the sensor 3 has come into contact with the stored liquid 30 and transmitting the signal to the main body 1 through the vertical bar 2, the liquid level can be detected and an alarm can be issued.

  The main body 1 is installed on the hull deck 20, and the vertical bar 2 has a predetermined length for placing the sensor 3 in the hold space 40, which is a storage tank below the hull deck 20. FIG. 6 shows an example in which two vertical rods 2 are installed in the main body 1 and the sensor 3 is arranged at the tip of each, but this detects the liquid level in a plurality of stages. In order to issue an alarm in multiple stages, the configuration of the apparatus 1 is not limited to this.

  In FIG. 6, the stored liquid 30 is stored from the ship bottom 50 to a predetermined liquid level in the hold space 40, and the charge 30 a is concentrated and charged on the liquid surface near the central portion of the stored liquid 30. The main body 1 is usually installed so that the sensor 3 comes to the center with respect to the horizontal plane position of the hold space 40. Therefore, when the liquid level rises, the liquid level on which the charges 30 a are concentrated comes into contact with the sensor 3. A large current flows at the moment when the sensor 3 comes into contact with the storage liquid 30 in which the charges 30a are concentrated and charged. This large current flows toward the ground potential of the main body 1 through the sensor 3 and the vertical bar 2.

  Since the above charging voltage may reach several thousand volts or more, there is a risk that spark discharge occurs between the sensor 3 and the stored liquid 30. Since the storage liquid 30 contains a lot of flammable liquid or highly explosive liquid, such a spark discharge causes a serious accident such as explosion or ignition.

  In order to prevent such a serious accident, a method of constructing an earth wire for preventing the charge 30a from being charged at the liquid level in advance is well known. The earth wire is a conductor that connects the vertical rod 2 and the ship bottom 50, and the ground potential of the main body 1 and the ground potential of the ship bottom 50 corresponding to the vicinity immediately below the main body 1 are made equal to each other to make the liquid level. The charge 30a is prevented from being charged.

  As shown in FIG. 7, the ground wire is constructed so as to connect between the ground tab 4 provided on the side surface of the vertical bar 2 and the ground fixing member 50 a provided on the ship bottom 50. As a result, even if the storage liquid 30 is charged when the cargo space 40 is filled, the charged charge always flows toward the bottom of the ship, which is the ground potential, through the ground wire 9, so that the charged potential is the same as in the prior art. A high voltage such as several thousand volts is not reached. Therefore, even when the liquid level of the storage liquid 30 rises and contacts the sensor 3, a large current does not flow toward the main body 1 as described above. Spark discharge can be prevented.

  However, when the ground wire 9 is constructed as described above, the following technical problems arise. For example, it is necessary to remove the device 10 from the hull deck 20 in order to perform periodic inspection and repair of the device 10. However, even if the main body 1 is to be removed from the outside of the hold space 40 (on the hull deck 20), the ground tab 4 is secured to the ship bottom 50 by the ground wire 9, so that it cannot be removed. It is necessary to remove the earth wire 9 from the earth fixing member 50a at the ship bottom 50. However, since the storage liquid 30 may contain a lot of harmful substances and the like, before the worker enters the hold space 40, the liquid in the hold space 40 is removed and thoroughly cleaned. It needs to be detoxified. As described above, in the configuration in which the storage liquid 30 is prevented from being charged by the ground wire 9, a great burden is required both in terms of time and cost.

  In particular, in the case of a storage tank in a ship, the storage liquid 30 greatly shakes as the hull shakes, and so-called sloshing occurs. The ground wire 9 may be broken by the sloshing stress. Thus, if the earth wire 9 is broken and floats in the hold space 40, there is a fear that other structures such as a pump (not shown) installed in the hold space 40 may be damaged. In addition, since the antistatic function by the earth wire does not work, there is a risk of accidents due to spark discharge.

  Accordingly, an invention is known that prevents spark discharge due to charging of the storage liquid 30 without using the ground wire 9 in order to solve the above-mentioned problem of maintainability and eliminate the cause of a new failure (patent) Reference 1).

Japanese Patent Laid-Open No. 08-159842

  In the spark discharge prevention structure due to charging of the stored liquid described in Patent Document 1, a connecting rod is installed at the tip of the sensor of the high liquid level alarm device, and an insulating plate having a predetermined thickness is attached to the connecting rod. Thus, an insulating layer having a minimum discharge distance is formed between the sensor and the liquid level of the stored liquid to prevent spark discharge due to static electricity. Here, the connecting bar is connected to a metal bar corresponding to the conventional vertical bar 2.

  However, even if the invention described in Patent Document 1 is used, it is not possible to completely prevent a spark discharge or the like due to the electric charge charged in the storage liquid 30. That is, the said invention makes the space | gap where static electricity is discharged by a disk shaped insulator extremely small. In such a structure, particularly when used in a storage tank that is grounded to the hull, the storage liquid 30 is shaken by the shaking of the hull, and the liquid level directly touches the metal rod beyond the thickness of the insulator. There is. In such a case, spark discharge may occur. Further, there is a risk that the insulating plate, which is a thin plate-like member, is damaged or falls off the connecting rod due to the impact of the storage liquid 30 colliding with the insulating plate due to the shaking of the stored liquid 30. That is, the above-described method of forming an insulating layer that cannot be discharged between the sensor 3 and the storage liquid 30 using an insulating plate has a structural problem.

  The present invention has been made in view of the above problems, and provides a high level liquid level alarm device that prevents a spark discharge phenomenon due to charging of the liquid level without installing a ground wire and that is excellent in maintainability. With the goal.

The present invention includes a main body, a sensor for detecting that the liquid level of the liquid stored in the tank has reached a predetermined height position, and the sensor is fixed at a predetermined height position in the tank. A high level liquid level alarm device that issues a warning when a sensor detects a liquid level, wherein a high resistance discharge bar is fixed to the vertical bar, and the liquid level of the liquid The main characteristic is that the electric charge charged in the liquid is discharged when the liquid surface of the liquid contacts the high resistance discharge rod.
The position where the liquid surface of the liquid contacts the high resistance discharge rod is lower than the sensor.

  According to the present invention, when the liquid level in the storage tank rises and the liquid level comes into contact with the high resistance discharge rod, the charge charged on the liquid level is gradually discharged through the high resistance discharge rod, Spark discharge can be prevented in advance, and the possibility of a serious accident such as explosion or ignition can be avoided. Further, since the high level alarm device is not secured to the bottom of the hull by the earth wire, it is possible to prevent a secondary disaster due to the breaking of the earth wire without losing maintenance workability.

  Hereinafter, embodiments of a high level alarm device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the appearance of an embodiment of a high level alarm device according to the present invention. In FIG. 1, a high liquid level alarm device 10 includes an apparatus body 1, two vertical bars 2A and 2B extending downward from the bottom surface of the body 1 by a predetermined length, and lower ends of the vertical bars 2A and 2B. Are provided with sensors 3A and 3B for detecting the liquid level at a predetermined height position. Further, a connection support bracket 5 is fixed to the ground tab 4 disposed between the main body 1 and the sensor 3A on the side surface of the vertical bar 2A, and the high resistance discharge rod 6 is connected to the tip of the fixed connection support bracket 5. It is fixed. One vertical bar 2A is longer than the other vertical bar 2B, and therefore one sensor 3A is at a lower position than the other sensor 3B. The sensor 3A is for high level alarm, and the sensor 3B is for overflow alarm. Whether or not the overflow warning sensor 3B is provided together with the high liquid level warning sensor 3A is arbitrary. The detection method of the sensors 3A and 3B is arbitrary, and may be, for example, a float method or an ultrasonic method. The example shown is an ultrasonic method, and has a transmitter and a receiver that face each other up and down, and when liquid exists between the transmitter and receiver, the ultrasonic wave transmitted from the transmitter propagates in the liquid. By reaching the receiving unit, it is detected that the liquid level has reached the position of the sensor 3A.

  FIG. 2 is an enlarged view of the vertical bar 2A, the high liquid level alarm sensor 3A and the components associated therewith enclosed by the dotted line in FIG. In FIG. 2, the high resistance discharge rod 6 is fixed to the connection support metal 5 by a pressure contact ring 6a. The connection support metal fitting 5 is fixed to the earth tab 4 integrally protruding from the side surface of the vertical bar 2A with a bolt or the like. Therefore, the high resistance discharge rod 6 is fixed to the ground tab 4 by the connection support metal fitting 5 and further connected to the vertical rod body 2 </ b> A via the ground tab 4. The tip (lower end) of the high resistance discharge rod 6 fixed to the ground tab 4 by the connecting support metal fitting 5 is positioned below the sensor 3A, and when the liquid level of the stored liquid 30 rises, the liquid level is higher than the sensor 3A. Also, it has a predetermined length so as to come into contact with the lower end of the high resistance discharge rod 6 first.

The high resistance discharge rod 6 is a resistor having a volume resistivity in the range of several hundreds kΩcm to several MΩcm, and the material thereof is, for example, a small amount of carbon powder in PTFE resin (Poly-Tetra-Fluoro-Ethylene). Confused materials are used. Since PTFE resin has a volume resistivity of about 10 ¹⁶ Ωcm to 10 ¹⁷ Ωcm, it is almost a material that can be called an insulator. Carbon powder is a good conductor having a volume resistivity of about several hundred Ωcm, and varies depending on the degree of compression and purity.

  By mixing a small amount of carbon powder with PTFE resin, the high resistance discharge rod 6 having a volume resistivity of about several hundred kΩcm to several MΩcm can be obtained.

  FIG. 3 shows an enlarged view of the connection support metal fitting 5. FIG. 3A is a front view of the flat portion 5a having the bolt fixing portion 5d for fixing to the ground tab 4 as shown in FIG. 2, and FIG. 3B shows the flat portion 5a. It is the figure seen from the side. As shown in FIG. 3A, the connection support metal fitting 5 has a flat portion 5a at the upper end and a cylindrical portion 5b below it. A hole serving as a bolt fixing portion 5d is provided near the center of the flat portion 5a. At least the upper end portion of the high resistance discharge rod 6 is formed in a cylindrical shape so that the high resistance discharge rod 6 fits on the outer periphery of the cylindrical portion 5b, and the inner diameter of the cylindrical portion of the high resistance discharge rod 6 is the connecting support fitting. 5 is slightly larger than the outer shape of the cylindrical portion 5b. The outer periphery of the high resistance discharge rod 6 is fitted with a press contact ring 6a at two locations on the upper and lower sides, and the press contact ring 6a is caulked so that the high resistance discharge rod 6 fitted to the cylindrical portion 5b of the connection support metal fitting 5 is connected and supported. It is fixed to the metal fitting 5. When the crimping ring 6a for fixing the high-resistance discharge rod 6 is caulked, the high-resistance discharge rod 6 bites into the connection support bracket 5 so that the high-resistance discharge rod 6 is firmly fixed to the connection support bracket 5; A circumferential groove 5c is formed at a position corresponding to the pressure contact ring 6a of the connection support fitting 5 so that the high resistance discharge rod 6 does not fall off from the connection support fitting 5. The high resistance discharge rod 6 extends in the vertical direction in parallel with the vertical rod 2A.

  As shown in FIG. 3 (b), the upper end of the flat portion 5a of the connection support metal fitting 5 is fixed to the ground tab 4 with a bolt or the like by engaging with the upper end of the ground tab 4, and then the bolt is centered. A folded portion 5e is provided for preventing rotation.

  FIG. 4 shows a state where the device 10 is installed in a storage tank. As shown in FIG. 4, the apparatus 10 installs the main body 1 on the hull deck 20 so that the sensors 3A and 3B are positioned at a predetermined height in the hold space 40 that is a storage tank. A high resistance discharge rod 7 is fixed to the connection support fitting 5 of the ground tab 4 provided on the side surface of the vertical rod 2A. When the liquid level of the storage liquid 30 rises, the liquid level comes into contact with the high resistance discharge rod 6 before coming into contact with the sensor 3A, and the charge 30a charged on the liquid level can be discharged. In FIG. 4, in order to focus on the configuration of the high liquid level alarm device 10, the dimensions from the high liquid level alarm device 10 to the ship bottom 50 are extremely different from the vertical dimension of the high liquid level alarm device 10. It is drawn small.

  When the charging potential by the electric charge 30a is 5000 volts, the volume resistivity of the high resistance discharge rod 6 is 500 kΩcm, and the length below the press contact fitting 6 of the high resistance discharge rod 6 is 200 mm (resistance value is 10 MΩ), the above potential A current of 0.5 milliamperes flows at the moment when the liquid surface charged to the high resistance discharge rod 6 comes into contact. If the instantaneous current is about 0.5 milliamperes, no spark discharge will occur.

When the discharge proceeds with a current of 0.5 milliamperes, the charging potential due to the charge 30a gradually decreases, and the liquid surface potential finally becomes the ground potential. In this way, by using the high resistance discharge rod 6 without using the ground wire, the electric charge 30a charged on the liquid surface of the storage liquid 30 is gradually discharged according to the principle of corona discharge, thereby causing a sudden spark discharge. The cause of serious accidents such as explosion and ignition can be eliminated.
When the liquid level further rises and reaches the position of the sensor 3A, the sensor 3A outputs a detection signal, and the detection signal is transmitted to the main body 1. The main body 1 transmits a detection signal to a control room, for example, and a high liquid level alarm is issued from the control room. Based on this alarm, the supply of liquid to the tank is stopped. In the unlikely event that an alarm is overlooked and the liquid supply continues, the overflow alarm sensor 3B detects the liquid level and issues an emergency alarm.

  According to the embodiment described above, since it is not necessary to tie the device 1 to the bottom of the ship with a conventional earth wire, the maintainability of the contact-type high liquid level alarm device is not impaired, and the hull is shaken. Problems such as ground wire breakage and damage to other equipment can be solved.

  Even if PFA resin is used instead of PTFE resin as the material of the high resistance discharge rod 6, a high resistance discharge rod exhibiting the same effect can be obtained. Even when metal powder, which is a similar conductive material, is used instead of carbon powder, a high-resistance discharge rod that exhibits the same effect can be obtained.

  In the above-described embodiment, the high resistance discharge rod 6 is fixed at a predetermined position by fixing the connection support fitting 5 to the ground tab 4 formed in advance on the vertical rod body 2, but without using the ground tab 4. The high resistance discharge rod 6 can be fixed. The embodiment will be described with reference to FIG.

  In FIG. 5, the connecting support fitting 8 has a flat surface portion extending in a direction perpendicular to the cylindrical portion, and a hole serving as a bolt fixing portion 8a is formed. A dedicated mounting bracket 7 is attached to the tip of the sensor 3, and this is fixed through a bolt fixing portion 8a. With this configuration, even the device 10 that does not have the ground tab 4 can prevent spark discharge using the high resistance discharge rod 6.

  The high-level liquid level alarm device according to the present invention can be installed in a tank that stores powerful drugs and the like, and can take advantage of the ease of maintenance and inspection.

It is a front view which shows the external appearance of the Example of the high level liquid level alarm apparatus which concerns on this invention. It is an enlarged front view which expands and shows the characteristic part of the said Example. It is an enlarged front view of the connection support metal fitting used for the said Example. It is a front view which shows the state which installed the high level liquid level alarm apparatus concerning the said Example in the storage tank. It is a front view which shows the principal part of the other Example of the high level liquid level alarm apparatus concerning this invention. It is a front view shown in the state where the conventional high level alarm device was installed in the storage tank. It is a front view which shows the state which constructed the earth wire in the said conventional high level liquid level alarm apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body 2 Vertical bar | burr 3 Sensor 4 Ground tab 5 Connection support metal fitting 6 High resistance discharge rod 6a Pressure welding metal fitting 7 Dedicated attachment metal fitting 8 Connection support metal fitting 10 Device

Claims (8)

A main body, a sensor for detecting that the liquid level of the liquid stored in the tank has reached a predetermined height position, and a vertical bar for fixing the sensor to a predetermined height position in the tank and connecting to the main body A high-level liquid level alarm device that issues a warning when the sensor detects the liquid level level,
A high level liquid level alarm characterized in that a high resistance discharge rod is fixed to the vertical rod body, and the electric charge charged on the liquid level of the liquid is discharged by the liquid level of the liquid coming into contact with the high resistance discharge rod. apparatus.   The high level liquid level alarm device according to claim 1, wherein the position where the liquid level of the liquid contacts the high resistance discharge rod is lower than the sensor.   2. The high level liquid level alarm device according to claim 1, wherein the upper high resistance discharge rod is a substance obtained by mixing carbon powder with synthetic resin.   4. The high level alarm device according to claim 3, wherein the upper synthetic resin is PTFE resin.   4. The high level alarm device according to claim 3, wherein the synthetic resin is a PFA resin.   The high level liquid level alarm device according to any one of claims 3 to 5, wherein the high resistance discharge rod uses a metal powder instead of carbon powder.   7. The high liquid level alarm device according to claim 1, wherein the high resistance discharge rod is fixed to an earth tab formed on a side surface of the vertical rod body. The high-level liquid level alarm device according to any one of claims 1 to 6, wherein the high-resistance discharge rod is fixed via a dedicated metal fitting attached to the tip of the sensor.

Images