JP2005164092A - Vent stack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vent stack for reducing the supply amount of noncombustible gas to be mixed with combustible gas by suppressing the entry of the atmospheric air into the vent stack without any trouble in exhausting the combustible gas from the vent stack. <P>SOLUTION: The vent stack 1 is attached to a gas feed pipe through which the combustible gas G1 is fed to a combustion installation for mixing the unnecessary combustible gas G1 with the noncombustible gas G2 and then releasing it from a top opening 3 of a cylinder 2 erected on a ground to the atmospheric air during normal operation of the combustion installation. In the top opening 3, a lid 20 is provided for allowing the release of mixed gas G of the combustible gas G1 and the noncombustible gas G2 and preventing the entry of the atmospheric air into the cylinder 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vent stack that discharges unnecessary flammable gas generated in a chemical plant, a power plant, or the like to the atmosphere without burning it.

In chemical plants and power plants, when combustible gas is sent to a combustion facility, the combustion facility is left in the gas pipe due to an emergency stop etc. There is a vent stack that releases to the atmosphere.
Japanese Patent Laid-Open No. 10-318498

Such a vent stack, like a chimney, discharges gas from a vertically provided cylinder, and is a safety valve provided in a gas feed pipe that communicates with the lower end of the vent stack in normal times except for the above-mentioned emergency. Mix flammable gas such as methane (CH ₄ ) gas leaked from flammable gas with nitrogen (N ₂ ) gas or other non-flammable gas and reduce the concentration to prevent ignition. ing.
However, since the upper end of the vent stack is always open, especially in strong winds, the atmosphere penetrates deep into the vent stack, and oxygen and flammable gas in the atmosphere mix to easily burn the flammable gas. An environment is formed. In addition, the amount of air intrusion is difficult to predict because it depends on the weather. Therefore, by always setting the amount of non-combustible gas supplied to the combustible gas discharged from the vent stack to be several times the required amount, the combustible gas is ignited even when the atmosphere penetrates deep into the vent stack. Try not to be afraid.
For this reason, in the vent stack, there is a problem that a large amount of incombustible gas is always consumed, and the running cost increases.

  The present invention has been made in view of the above-described circumstances, and supplies non-combustible gas by suppressing the intrusion of air into the vent stack without hindering discharge of combustible gas from the vent stack. It is an object of the present invention to provide a vent stack that can reduce the amount of.

The vent stack according to the present invention employs the following means in order to solve the above problems.
In the present invention, it is attached to a gas feed pipe for feeding a combustible gas to a combustion facility. During normal operation of the combustion facility, an unnecessary combustible gas is mixed with a non-combustible gas and then installed on the ground. In the vent stack that is released to the atmosphere from the top opening, a lid is provided at the top opening that can release a mixed gas of combustible gas and non-combustible gas and suppress the intrusion of air into the cylinder. According to the present invention, since the intrusion of the atmosphere into the cylinder of the vent stack is suppressed, the risk of ignition by mixing the combustible gas and the oxygen in the atmosphere can be reduced.

In addition, in the case where the lid is placed on the backflow prevention plate provided on the top inner wall of the cylinder, the lid can be easily installed at the top opening even in the existing vent stack.
In addition, in the case where a vent hole through which the mixed gas flows is formed in the lid or the backflow prevention plate, the mixed gas of the combustible gas and the nonflammable gas can be easily released to the atmosphere.
In addition, in the case where an engagement part that prevents the displacement of the lid is provided on the inner wall of the top of the vent stack, there is a risk that the air may enter the cylinder of the vent stack due to the lid falling off from the backflow prevention plate during strong winds. Can be reduced.
In addition, in the case where a plurality of protrusions are provided on the upper surface of the lid, it is possible to prevent the wind flowing near the upper surface of the lid from being turbulent by the protrusions and the lid from being sucked by the wind and falling off the backflow prevention plate. .
In addition, when the lid is formed of conductive polystyrene, static electricity is difficult to be charged on the lid, and the risk of static sparks igniting combustible gas can be reduced.
Further, in the case where a ground wire is provided on the lid, the risk of static sparks igniting the flammable gas can be reduced by discharging static electricity charged on the lid through the ground wire.
In addition, when the ground wire also serves as a safety band for preventing the lid from falling, the lid can be easily prevented from falling from the top opening of the vent stack.

According to the present invention, the following effects can be obtained.
In the present invention, it is attached to a gas feed pipe for feeding a combustible gas to a combustion facility. During normal operation of the combustion facility, an unnecessary combustible gas is mixed with a non-combustible gas and then installed on the ground. In the vent stack that is released to the atmosphere from the top opening, a lid is provided at the top opening that can release a mixed gas of combustible gas and non-combustible gas and suppress the intrusion of air into the cylinder. According to the present invention, since the intrusion of the atmosphere into the cylinder of the vent stack is suppressed, the risk of ignition by mixing the combustible gas and the oxygen in the atmosphere can be reduced. Therefore, it is only necessary to supply the amount of incombustible gas sent into the cylinder of the vent stack in an amount corresponding to the expected amount of combustible gas leakage. Running costs can be reduced.

In addition, when the lid is placed on the backflow prevention plate provided on the top inner wall of the cylinder, the lid can be easily installed at the top opening of the existing vent stack. As a result, existing facilities can be used effectively, and generation of new facility costs can be suppressed.
In addition, in the case where a vent hole through which the mixed gas flows is formed in the lid or the backflow prevention plate, the mixed gas of the combustible gas and the nonflammable gas can be easily released to the atmosphere.
In addition, in the case where an engagement portion for preventing the displacement of the lid is provided on the top inner wall of the vent stack, the lid is prevented from slipping off from the backflow prevention plate in a strong wind. Infiltration can be suppressed. Thereby, it is avoided that combustible gas ignites in the cylinder of a vent stack, and safety of plants, such as power generation equipment, can be secured over a long period of time.
In addition, in the case where a plurality of protrusions are provided on the upper surface of the lid, it is possible to prevent the wind flowing near the upper surface of the lid from being turbulent by the protrusions and the lid from being sucked by the wind and falling off the backflow prevention plate. . As a result, the amount of incombustible gas used can be reduced and the safety of the plant can be ensured regardless of the weather.
In addition, when the lid is formed of conductive polystyrene, static electricity is difficult to be charged on the lid, and the risk of static sparks igniting combustible gas can be reduced. Thereby, the safety | security of plants, such as power generation equipment, can be ensured over a long period of time.
Further, in the case where a ground wire is provided on the lid, the risk of static sparks igniting the flammable gas can be reduced by discharging static electricity charged on the lid through the ground wire. Thereby, the safety of the plant can be further secured.
In addition, when the ground wire also serves as a safety band for preventing the lid from falling, the lid can be easily prevented from falling from the top opening of the vent stack. As a result, the amount of incombustible gas used can be reduced over a long period of time, combustion of the combustion gas in the cylinder of the vent stack can be avoided, and accidental accidents due to falling of the lid can be avoided.

Hereinafter, an embodiment of the vent stack of the present invention will be described with reference to the drawings.
FIG. 1 is a system configuration diagram of a chemical plant or a power plant, and shows a part of a system for supplying methane (CH ₄ ) gas G1 to combustion facilities A and B.
Methane gas (combustible gas) G1 is introduced into the gas feed pipe 10 from a gas tank (not shown), adjusted to an appropriate pressure by the pressure regulating valve 13, and fed to the combustion facility. Further, a gas feed pipe 11 branches from the gas feed pipe 10 and is led to the vent stack 1.
When the methane gas G1 is sent to the combustion facility, there is methane gas G1 leaking from the safety valve 15, and the leaked methane gas G1 is guided to the vent stack 1 and released to the atmosphere. Note that the expected leakage amount of the methane gas G1 is obtained based on the provisions of JIS B2007.
Here, the safety valve 15 is a valve for preventing the pressure of the methane gas G1 in the gas feed pipes 10 and 11 from exceeding a predetermined pressure, and the pressure in the gas feed pipes 10 and 11 is a predetermined pressure. Then, the methane gas G1 is led to the vent stack 1 by automatically opening the valve. The safety valve 15 may be a mechanical valve using a spring or the like, and an electric motor that detects the pressure in the gas pipes 10 and 11 with a sensor and opens the valve based on the detection result. It may be a valve of the formula.

As shown in FIG. 1, the vent stack 1 discharges methane gas G1 from a circular tube 2 standing on the ground like a chimney, and includes a top opening 3 at the upper end of the tube 2, A gas feed pipe 11 and a nitrogen gas feed pipe 12 are connected to the lower end of 2.
During normal operation of the combustion facility, methane gas G1 leaking from the safety valve 15 is introduced into the cylinder 2 of the vent stack 1 through the gas feed pipe 11, and at the same time, nitrogen is introduced into the cylinder 2 through the nitrogen gas feed pipe 12. (N ₂ ) gas (nonflammable gas) G2 is introduced. Thereby, methane gas G1 and nitrogen gas G2 mix, the density | concentration of methane gas G1 is reduced to the grade which has no possibility of combustion, and it discharge | releases to the atmosphere from the top opening 3. FIG.

The methane gas G1 is colorless and odorless and has a specific gravity as low as 0.55. Combustion range is 5.0-15.0% in air (contains about 21% oxygen), 9.5% is the most intense combustion (explosion) concentration, explosion pressure is 7 kgf / cm ² , The explosion temperature is 2000 ° C. And once the concentration is reduced, it is characterized in that it does not increase in the natural state.
Therefore, as described above, when the methane gas G1 is diluted with the nitrogen gas G2 and the concentration of the methane gas G1 becomes sufficiently low and then released into the atmosphere from the top opening 3, the methane gas G1 enters the combustion range and burns. The risk of (explosion) can be reduced.
In this way, the methane gas G1 is diffused and disposed of in the atmosphere as harmless without fear of ignition or the like.
In the present embodiment, an odorant is added to the methane gas G1.

FIG. 2 is a cross-sectional view showing the vicinity of the top of the vent stack 1.
A plurality of backflow prevention plates 4 formed in an annular shape are provided on the top inner wall of the tube 2 so that the atmosphere (outside air) does not easily enter the inner bottom of the tube 2. A cylindrical lid 20 having an outer diameter smaller than the inner diameter of the cylinder 2 and larger than the inner diameter of the backflow prevention plate 4 is placed on the backflow prevention plate 4 formed in the uppermost stage. Further, the upper surface of the lid 20 is formed so as to substantially match the position of the top opening 3 of the cylinder 2.
The lid 20 is merely placed on the backflow prevention plate 4 and can move upward. This is because if the lid 20 cannot move upward, the pressure in the cylinder 2 rises abnormally and is dangerous when a large amount of mixed gas (methane gas G1 and nitrogen gas G2) G in the cylinder 2 is released. Further, when the pressure of the mixed gas G becomes equal to or higher than a predetermined value, the lid 20 is formed with a weight that can move upward due to the pressure.

The reason why the lid 20 is provided in the top opening 3 of the vent stack 1 is as follows.
Conventionally, the atmosphere always enters the cylinder 2 from the top opening 3, and there is a risk that the methane gas G <b> 1 enters the combustion range in the cylinder 2. Even when the backflow prevention plate 4 is provided, the intrusion of air cannot be reliably suppressed. Also, the amount of air intrusion depends on the weather and is unpredictable. Therefore, it is necessary to always supply the cylinder 2 with about 4 to 5 times as much nitrogen gas G2 (necessary amount) as necessary to prevent the methane gas G1 from entering the combustion range.
Therefore, a lid 20 is provided in the top opening 3 of the vent stack 1 so as to suppress the intrusion of the atmosphere into the cylinder 2.

FIG. 3 is a perspective view of the lid 20. A plurality of vent holes 21 communicating with the side surface are formed on the lower surface of the lid 20. This is because, when a small amount of the mixed gas G is released from the cylinder 2, the mixed gas G is released to the atmosphere via the vent hole 21 without moving the lid 20 upward. The vent hole 21 is formed at a position deep in the cylinder 2 from the top opening 3 of the cylinder 2, so that air hardly enters the cylinder 2 through the vent hole 21. Moreover, since the pressure in the cylinder 2 is higher than the atmospheric pressure by providing the lid 20, it is difficult for the atmosphere to enter the cylinder 2.
In addition to the case where the vent hole 21 is formed in the lid 20, a plurality of vent holes may be provided in the backflow prevention plate 4. However, when the lid 20 is placed on the existing vent stack 1, the vent hole is formed in the lid 20. Providing 21 is advantageous in terms of cost and the like because it does not involve processing of the backflow prevention plate 4 or the like.

FIG. 4 is a schematic diagram showing the engaging portion. As shown in FIG. 4, the engaging portion 5 that prevents the displacement of the lid 20 is provided on the inner wall of the cylinder 2 and on the portion facing the side surface of the lid 20. Since the lid 20 is formed so as to open a predetermined interval without completely sealing the top opening 3 of the cylinder 2, the lid 20 can also move in the horizontal direction. However, if the amount of movement of the lid 20 increases, a part of the lid 20 may come off from the backflow prevention plate 4 and a large amount of air may enter the cylinder 2. Since the intrusion of air into the cylinder 2 increases the risk of ignition of the mixed gas G, the engagement portion 5 is provided on the inner wall of the cylinder 2 so that the lid 20 does not shift in the horizontal direction.
Specifically, as shown in FIG. 4, a plurality of leaf springs are provided on the inner wall of the cylinder 2, and the lid 20 is biased by a spring from the horizontal direction. In addition, not only a leaf | plate spring but the member spaced apart with the lid | cover 20 with a predetermined distance may be provided, and only the movement amount of the lid | cover 20 may be controlled.
In addition, the engaging part 5 only restricts the amount of movement of the lid 20 in the horizontal direction, and the lid 20 can be moved upward.

The lid 20 is made of conductive styrene. By forming the lid 20 with conductive polystyrene, the lid 20 is formed which is lightweight but is difficult to be charged with static electricity. If the lid 20 is light, the upward movement of the lid 20 is easy, which is advantageous for releasing the mixed gas G. On the other hand, if the lid 20 is difficult to be charged with static electricity, the risk of static sparks igniting the mixed gas G can be reduced.
Further, a ground wire 30 is connected to the lid 20. One end of the ground wire 30 is connected to the upper surface of the lid 20, and the other end is connected to the outer wall side surface of the cylinder 2. As a result, the static electricity charged in the lid 20 is discharged through the cylinder 2, and the risk of ignition of the mixed gas G is reduced without generating a spark due to static electricity between the lid 20 and the cylinder 2. it can.
The ground wire 30 also functions as a safety belt that prevents the lid 20 from falling. Even if a large amount of mixed gas G is released or the lid 20 jumps out of the top opening 3 due to the influence of strong wind, the lid 20 does not fall to the ground, and an accident is avoided. be able to.
In the present embodiment, one end of the ground wire 30 is connected to the upper surface of the lid 20 and the other end is connected to the outer peripheral side surface of the cylinder 2 in order to retrofit the existing vent stack 1 with the lid 20. However, when the lid 20 is provided since the vent stack 1 is constructed, one end of the ground wire 30 may be connected to the lower surface of the lid 20 and the other end may be connected to the inner wall side surface of the cylinder 2. This is because adjusting the length of the ground wire 30 can also prevent the lid 20 from jumping out from the top opening 3 of the vent stack 1.

Moreover, since the top opening 3 of the vent stack 1 in which the lid 20 is disposed is at a position higher than the ground and there are no obstacles in the periphery, the upper surface of the lid 20 is exposed to the wind. Then, when the wind speed exceeds a predetermined value, a phenomenon occurs in which the lid 20 is lifted by the wind. This is because when the fluid (air) moves along the upper surface of the lid 20, the pressure on the upper surface of the lid 20 decreases (Bernoulli's theorem), and the lid 20 is lifted upward.
In this way, when the lid 20 is lifted, the air enters the cylinder 2 at that time, mixes with the mixed gas G, and there is a risk of ignition. In addition, particularly when the wind is strong, the lid 20 may jump out of the top opening 3 and the lid 20 may not function at all.
Therefore, by providing a large number of protrusions 22 on the upper surface of the lid 20, the rise of the lid 20 is suppressed. That is, by providing a large number of protrusions 22 on the upper surface of the lid 20, the flow of gas flowing along the upper surface of the lid 20 becomes turbulent and the flow velocity decreases. This makes it difficult for the pressure on the upper surface of the lid 20 to decrease, and prevents the lid 20 from rising.
In addition, as a result of carrying out the experiment for several months by attaching the lid 20 having a large number of protrusions 22 on the upper surface and the lid 20 without the protrusions 22 to the vent stack 1, the lid without the protrusions 22 was obtained. In the case of 20, the lid frequently falls on a strong wind day, but in the case of the lid 20 having a large number of protrusions 22 on the upper surface, the lid 20 does not fall on days other than the typhoon day. It was.

As described above, according to the vent stack 1 of the present invention, the mixed gas G of the methane gas G1 and the nitrogen gas G2 can be released into the top opening 3 and can be discharged into the cylinder 2 during normal operation of the combustion facility. Since the lid 20 that suppresses the intrusion of the atmosphere is provided, the risk of ignition by mixing the methane gas G1 and the oxygen in the atmosphere can be reduced. Further, since it is difficult for the atmosphere to enter the tube 2 of the vent stack 1, it is sufficient to supply the amount of nitrogen gas G2 to be supplied according to the amount of methane gas G1, and the consumption of nitrogen gas G2 is reduced. The running cost of plants such as power generation facilities can be reduced.
FIG. 5 is a diagram comparing the oxygen concentration in the cylinder 2 when the lid 20 is provided at the top opening 3 of the vent stack 1 and when the lid 20 is not provided. This is a case where the same amount of methane gas G1 and nitrogen gas G2 are supplied.
As shown in FIG. 5, when the lid 20 is provided, the oxygen concentration in the cylinder 2 can obviously be suppressed lower than when the lid 20 is not provided. That is, the intrusion of the atmosphere is kept low. Therefore, the risk of ignition of the methane gas G1 can be effectively reduced by the nitrogen gas G2. In other words, the risk of ignition of the methane gas G1 can be reduced with a small amount of nitrogen gas G2.

  Further, by accurately measuring the amount of methane gas G1 in the cylinder 2, the amount of nitrogen gas G2 can be further reduced. That is, the amount of leakage of methane gas G1 is obtained based on the provisions of JIS B2007 as described above. The obtained leak amount is often larger than the actual leak amount. Therefore, the supply amount of the nitrogen gas G2 is always excessive. Therefore, by providing a gas pipe 11 with a sensor (flow rate sensor) that measures the amount of methane gas G1, the supply amount of nitrogen gas G2 can be more accurately defined, and the consumption of nitrogen gas G2 can be suppressed. It is.

Note that the shapes, combinations, and the like of the constituent members shown in the above-described embodiments are merely examples, and various changes can be made based on process conditions, design requirements, and the like without departing from the spirit of the present invention.
For example, in the above-described embodiment, the case where methane gas is used as the combustible gas has been described. However, the present invention is not limited thereto, and hydrogen (H ₂ ) gas, acetylene (C ₂ H ₂ ) gas, ethylene (C ₂ H ₄ ) It may be gas, ethane (C ₂ H ₈ ) gas, propane (C ₃ H ₈ ) gas, or the like.
Further, there has been described a case where nitrogen gas was used as the noncombustible gas, not limited to this, carbon dioxide (CO ₂₎ gas may be used helium (He) gas or the like.

Plant configuration diagram Sectional view showing the vicinity of the top of the vent stack Surface showing the lid The figure which shows an engaging part Figure comparing oxygen concentration in the vent stack cylinder

Explanation of symbols

A, B combustion facility, 1 vent stack, 2 cylinders, 3 top opening, 4 backflow prevention plate, 5 engaging part, 10, 11 gas feed pipe, 15 safety valve, 20 lid, 21 vent hole, 22 protrusion, 30 ground Wire (safety zone), G mixed gas, G1 methane gas (flammable gas), G2 nitrogen gas (nonflammable gas)

Claims (8)

Attached to a gas pipe for sending flammable gas to a combustion facility, and mixed with unnecessary nonflammable gas during normal operation of the combustion facility, then released to the atmosphere from the top opening of a cylinder standing on the ground In the vent stack,
A vent stack, characterized in that a lid is provided at the top opening so that a mixture of the combustible gas and the non-combustible gas can be released and the atmosphere is prevented from entering the cylinder.   2. The vent stack according to claim 1, wherein the lid is placed on a backflow prevention plate provided on an inner wall of a top portion of the cylinder.   The vent stack according to claim 1 or 2, wherein a vent hole through which the mixed gas flows is formed in the lid or the backflow prevention plate.   The vent stack according to any one of claims 1 to 3, wherein an engagement portion that prevents a displacement of the lid is provided on a top inner wall of the vent stack.   The vent stack according to any one of claims 1 to 4, wherein a plurality of protrusions are provided on an upper surface of the lid.   The vent stack according to any one of claims 1 to 5, wherein the lid is made of conductive polystyrene.   The vent stack according to claim 6, wherein a ground wire is provided on the lid. 8. The vent stack according to claim 7, wherein the ground wire also serves as a safety belt for preventing the lid from falling.

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