JP2008273601A - Ventilation port structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ventilation port structure which can reduce a volatilization loss due to air. <P>SOLUTION: In this ventilation port structure, a cap 3 is installed in a manner to cover the ventilation port while ensuring air permeability at a position above the ventilation port 2 located on the distal end of a ventilation pipe 1 which communicates the space in a tank storing a volatile liquid with the outside air. In the ventilation port structure, a resisting means 5 which reduces the flow rate of the outside air flowing into the cap 3, and the flow velocity of the outside air in the cap is installed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a structure of a vent at the tip of a vent pipe that leads to outside air from a space in a tank that stores volatile liquids such as petroleum, and more particularly, a vent that reduces volatilization loss of petroleum from a tank. Concerning structure.

  Underground tanks are installed at gas stations and other facilities that handle petroleum such as gasoline and light oil. In this underground tank, since the internal pressure changes due to the entry and exit of petroleum, vaporization, etc., a vent pipe is provided to communicate the gas phase part of the underground tank with the outside air so that the inside pressure and the outside air pressure of the tank match. ing.

  Conventionally, a vent pipe is generally provided as a simple pipe, and a fire net of about 40 mesh is attached to the vent on the outside air side so that a flame does not enter the tank even if a fire occurs outside, In addition, although a cap that covers the top is attached to prevent rainwater and dust from entering, the inside of the tank and the outside air are always in communication, and harmful vapors such as gasoline continue to be released from the tank to the outside during normal times. Was in the situation.

  In recent years, due to the growing awareness of environmental problems, the release of harmful vapors to the outside air has become a problem, and the loss of liquid accompanying this release, the so-called volatilization loss, has become a problem. In particular, in recent years, the development of a highly accurate liquid level sensor such as a magnetostrictive sensor has made it possible to accurately measure the amount of liquid, and as a result, a considerable amount of volatilization loss has become apparent.

  Therefore, the inventors of the present invention have studied variously about this volatilization loss, and not only the volatilization loss due to spontaneous release from the vent, but also the volatilization loss greatly increases when “wind” hits the vent portion. found.

The problem of volatilization loss due to wind has not been recognized at all, and the influence of wind is not considered even in the volatilization loss reduction method using the valve mechanism previously disclosed by the applicant of the present application in Patent Document 1.
JP 2007-99331 A

  An object of the present invention is to provide a vent structure that can reduce volatilization loss due to wind.

  In order to solve the above problems, the present inventor has examined the cause of increase in volatilization loss due to wind. As a result, the following causes were estimated.

  As shown in FIG. 4, when wind hits the vent 2 at the tip of the vent pipe 1, part of the wind flows into the cap 3 that covers the vent 2 from above. If the amount of the inflow is large and the flow velocity is large, a vortex A is generated above the vent 2, which causes a force for sucking gas from the vent 2, thereby increasing the volatilization loss. In addition, the wind that has not flowed into the cap 3 strikes the vent pipe 1 and flows to the leeward side. At this time, the leeward side B of the vent pipe 1 becomes negative pressure, and thereby a force for sucking gas from the cap 3 acts. As a result, it is considered that the amount of wind flowing into the cap 3 and the flow velocity increase, and the volatilization loss increases.

  From the above, the inventor of the present application has completed the present invention based on the technical idea of reducing volatilization loss due to wind by reducing the amount of wind flowing into the cap 3 and the flow velocity.

  That is, according to the present invention, the vent is provided with a cap so as to cover the vent while ensuring the breathability above the vent at the tip of the vent pipe communicating with the outside air from the space in the tank storing the volatile liquid. The mouth structure is characterized by providing resistance means for reducing the flow rate of the outside air flowing into the cap and the flow rate of the outside air inside the cap.

  Since the resistance means reduces the flow rate and flow velocity of the outside air flowing into the cap, that is, the wind, the volatilization loss due to the wind can be reduced.

  As the resistance means, a resistor serving as resistance to circulation of outside air can be provided in the cap. A cover that covers the lower end opening of the cap from below can also be provided.

  According to the present invention, it is possible to reduce volatilization loss due to wind that has not been recognized at all in the past, and to greatly reduce the absolute amount of volatilization loss.

  Embodiments of the present invention will be described below based on examples shown in the drawings.

  FIG. 1 is a cross-sectional view showing a first embodiment of the vent structure of the present invention.

  The proximal end of the vent pipe 1 communicates with a gas phase portion of an underground tank (not shown), and the distal end communicates with outside air. A cap 3 is attached to the tip of the vent pipe 1 via an adapter 1a. The cap 3 is attached by screwing to a mounting portion (not shown) partially protruding from the periphery of the adapter 1a.

  In this embodiment, the adapter 1a is separate from the vent pipe 1, but forms a part of the vent pipe 1, and its tip is the vent hole 2. And the above-mentioned cap 3 is attached so that this ventilation hole 2 may be covered from upper direction. As a matter of course, in order to ensure the function of the vent 2, the air permeability is ensured even if the cap 3 is attached. Note that a fire net 4 made of a metal net of about 40 mesh is attached to the vent 2 so as to cover the entire upper part of the vent 2.

  In the basic configuration described above, in this embodiment, as a resistance means for reducing the outside air flowing into the cap 3, that is, the flow rate of the wind and the flow velocity of the wind in the cap 3, the resistance of the wind flow in the cap 3 is obtained. A resistor 5 is provided. Specifically, the upper and lower two-stage resistors 5a and 5b are provided from the inner periphery of the cap 3 over the entire circumference so as to protrude into the wind flow path in the cap 3, and the adapter 1a (pass A resistor 5c is provided from the outer periphery of the trachea 1) over the entire periphery.

  The resistor 5 reduces the flow rate and flow velocity of the wind flowing into the cap 3 and reduces volatilization loss due to the wind. Actually, when an experiment was conducted by simulating a wind speed of 5 m, the volatilization loss of the present invention including the resistor 5 was reduced by 33% compared to the conventional vent structure not including the resistor 5.

  FIG. 2 is a sectional view showing a second embodiment of the vent structure of the present invention.

  In this embodiment, a ventilation valve 6 is provided as an intake / exhaust valve mechanism in addition to the resistor 5 as the resistance means described above.

  The vent valve 6 includes a circular exhaust port 7 provided at the upper part of the adapter 1a and a disc-shaped exhaust valve body 8. The exhaust valve body 8 normally closes the exhaust port 7 from above, When the pressure increases, the pressure rises due to the pressure, and the exhaust port 7 is opened. The specified opening pressure (pressure when the exhaust valve body 8 just rises) is 5 kPa. An O-ring 9 is provided between the exhaust valve body 8 and the exhaust port 7 in order to ensure that the exhaust port 7 is closed by the exhaust valve body 8.

  Further, a weight 10 is integrally provided below the exhaust valve body 8. The weight 10 extends so as to be positioned below the exhaust port 7. As a result, the center of gravity of the exhaust valve main body 8 becomes lower than the exhaust port 7, and the balance of the exhaust valve main body 8 is improved so that the exhaust valve main body 8 can move up and down smoothly. Further, by adjusting the weight of the weight 10, the specified opening pressure is adjusted to 5 kPa.

  The weight 10 also serves as the guide portion 11. The guide portions 11 are provided at four locations at equal intervals along the outer periphery of the exhaust valve main body 8, and each guide portion 11 is provided so as to be inscribed in the inner peripheral edge of the exhaust port 7. As a result, when the exhaust valve body 8 moves up and down, it is guided by the guide portion 11, so that the vertical movement of the exhaust valve body 8 becomes smoother. In addition, in the Example, although the guide part 11 was provided in four places, what is necessary is just to provide in at least three places or more. However, it is preferable to provide each guide part at equal intervals in which the weight is balanced.

  The ventilation valve 6 shown in FIG. 2 includes an intake valve in addition to an exhaust valve. The intake valve closes the intake port 13 provided in the exhaust valve body 8 from the lower side when the intake valve main body 12 is normal, and when the pressure in the tank decreases, the intake valve 13 decreases due to the differential pressure from the external pressure. Is configured to open. The intake valve body 12 is normally urged upward by a coil spring 14 so as to close the intake port 13, and the regulation pressure for opening (pressure when the intake valve body 12 is just lowered) is adjusted by a coil. This is done by adjusting the strength of the spring 14. In the examples, the regulation pressure for opening was adjusted to be -5 kPa.

  In the vent valve 6 of FIG. 2 provided with the exhaust valve and the intake valve as described above, when a high pressure of 5 kPa or more is generated in the tank due to an increase in the inventory amount due to unloading to the tank or the like, the viewpoint of safety The exhaust valve automatically opens to release the pressure to the outside air and maintain a high pressure range within 5 kPa, but at other times the exhaust valve with improved airtightness by the O-ring mechanism is always closed, It forms an almost enclosed space in the tank and actively reduces volatilization loss.

  In addition, if a low pressure of -5 kPa or less occurs in the tank due to a decrease in inventory due to refueling from the weighing machine to the car, etc., the intake valve automatically opens and the outside air is taken in, so that the inside of the tank is predetermined The following negative pressure is avoided, but at other times, the intake valve is always closed, forming a substantially sealed space and actively reducing volatilization loss. In addition, the tank is temporarily in a negative pressure state due to a decrease in inventory due to refueling from the weighing machine to the car, but after refueling etc., the pressure higher than atmospheric pressure is maintained within 5 kPa due to the volatilization of liquid fuel. .

  By providing such a vent valve 6 in addition to the resistor 5 as the resistance means described above, the volatilization loss can be greatly reduced. Actually, the same experiment as in Example 1 was performed. Compared to the conventional vent structure without the resistor 5 and the vent valve 6, the volatilization loss was reduced by 65%.

  FIG. 3 is a sectional view showing a third embodiment of the vent structure of the present invention.

  In this embodiment, a cover 15 that covers the lower end opening of the cap 3 from below is provided as resistance means for reducing the flow rate of the wind flowing into the cap 3 and the flow velocity of the wind in the cap 3. The cover 15 makes it difficult for the wind to flow into the cap 3, and the flow rate of the wind flowing into the cap 3 is reduced. Accordingly, the flow velocity is also reduced. As a result, volatilization loss due to wind is reduced. Actually, when the same experiment as in Example 1 was performed, the volatilization loss was reduced by 30% as compared with the conventional vent structure without the cover 15.

  The shape of the cover 15 is not particularly limited as long as it covers the lower end opening of the cap 3 from below, but in order to effectively reduce the flow rate of the wind flowing into the cap 3, as shown in FIG. In addition, it is preferable that the upper end of the cover 15 extends upward beyond the lower end opening of the cap 3. Also in this embodiment, if the vent valve 6 described in the second embodiment is applied, the volatilization loss can be further reduced.

It is sectional drawing which shows 1st Example of the vent structure of this invention. It is sectional drawing which shows 2nd Example of the vent structure of this invention. It is sectional drawing which shows 3rd Example of the vent structure of this invention. It is explanatory drawing explaining the cause which volatilization loss increases with a wind.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vent pipe 1a Adapter 2 Vent 3 Cap 4 Fire net 5 (5a-5c) Resistor 6 Vent valve 7 Exhaust port 8 Exhaust valve body 9 O-ring 10 Weight 11 Guide part 12 Intake valve body 13 Inlet port 14 Coil spring 15 cover

Claims (3)

  In the vent structure where a cap is provided above the vent at the tip of the vent pipe leading to the outside air from the space in the tank that stores volatile liquid so as to cover the vent while ensuring air permeability. A vent structure comprising resistance means for reducing the flow rate of outside air flowing into the cap and the flow rate of outside air in the cap.   The vent structure according to claim 1, wherein a resistor that provides resistance to circulation of outside air is provided in the cap as the resistance means.   The vent structure according to claim 1, wherein a cover that covers the lower end opening of the cap from below is provided as the resistance means.

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