JP5984650B2 - How to purge gas piping - Google Patents

Description

  The present invention relates to a gas pipe purging method.

  When performing gas pipe replacement work or new connection work to existing pipes, it is necessary to perform air purge (purging to replace the gas with air before repair) or gas purge (purging to replace the air with gas after repair). There is. Various methods are known for such purging. For example, Patent Document 1 discloses air in a gas supply pipe in which a plurality of branch pipes are branched and connected to a trunk pipe connected to an existing pipe. An air purge method for replacing with a replacement gas is disclosed. In one of the air purge methods disclosed in Patent Document 1, first, the supply branch pipe used for supplying city gas near the connection portion between the existing gas conduit and the main pipe is farthest from the connection portion. Several branch pipes are dug up, including a discharge branch pipe used for releasing air near the spot. Furthermore, among those digging and branching pipes, a compressor capable of supplying city gas under pressure is connected to the supply branch pipe, and the digging and branching pipes other than the discharge branch pipe and the supply branch pipe are attached to some of the digging branch pipes Replace the cap with a cap with a gas concentration sensor. Then, remove the cap blocking the end of the discharge branch pipe, and supply the end of the remaining branch pipe other than the discharge branch pipe and the supply branch pipe with the cap by operating the compressor. A city gas pressurized to a pressure higher than the working gas pressure is pressed into the trunk pipe through the supply branch pipe. As a result, the air in the trunk pipe is released from the end of the discharge branch pipe to the outside of the pipe, and after the air in the trunk pipe is replaced with city gas, the end of the discharge branch pipe is closed with a cap and sealed. When the pressure in the main pipe reaches a pressure higher than the supply gas pressure, the operation of the compressor is stopped, and the system is left for a predetermined time so that the city gas in the main pipe and the air in the branch pipe are mixed. When this replacement step is repeated and the gas concentration in the branch pipe after standing reaches a predetermined concentration, the compressor connected to the supply branch pipe is removed, and it is sealed with a cap.

  In such a purging operation, for example, an air purging operation, if the gas can be swept away without being mixed with air so much, effective purging can be performed in a short time or flow amount. When mixing occurs, it takes time to complete the purge. The same applies to a gas purge operation in which air existing in the pipe is replaced with gas.

Therefore, for example, when purging the gas pipe, for example, the purging is performed by using the flow in the pipe as a flow in a turbulent flow region exceeding the transition region. For example, by purging a pipe having an inner diameter of about 80 mm at a flow rate with a Reynolds number of 10,000 at a flow rate of air or gas so that mixing of air and gas does not occur as much as possible, The purge operation can be completed efficiently in a short time.
As a condition for performing the purge operation using such a flow as a turbulent flow, the downstream side of the piping is open to the atmosphere, and the resistance of the downstream piping portion is relatively small.
That is, when the pipe to be purged is, for example, a pipe that is buried near the ground surface and exposed by excavation work, the gas or air can be released to the atmosphere without any particular obstacles. Therefore, the purge operation can be performed using the flow of the fluid to be fed as a turbulent flow.

JP 2006-125605 A (paragraph numbers 0016-0026, FIG. 4)

However, pipes to be purged include, for example, underground pipes and the like, and the purge work for such pipes has a limited space capacity for opening the fluid as described above. Or it may be that fluid cannot be dissipated in this space.
When purging pipes with such restrictions, connect a relatively long flexible diffusion pipe to the downstream end of the pipe and guide the fluid to the outside space to dissipate it or pipe it. The gas bag is connected to the downstream end of the gas bag, and the fluid diffused by the gas bag is collected and conveyed to the outer space to be diffused.

  When these methods are adopted, in the former case, a relatively long flexible diffusion pipe is connected to the downstream end of the pipe, and the fluid is guided to the outside space to dissipate. Ascending, the flow in the pipe cannot be made turbulent, and the flow must be a laminar flow (for example, a flow having a Reynolds number of about 100). In the latter case, since a gas bag having a usable volume is connected to the downstream side, similarly, it is substantially impossible to proceed with the operation using the turbulent flow in the pipe.

  When the flow in the pipe is a laminar flow, the boundary between gas and air (two types of fluids) is not clearly formed, mixing of both fluids occurs, and the original purpose is one of the fluids in the pipe It takes time to realize the state where the gas is satisfied, and in the purge operation that replaces the air in the pipe with gas, there is a problem that the amount of gas used for the purge operation increases as the work time becomes longer To do.

  Therefore, an object of the present invention is as much as possible in a working environment where it is difficult to dissipate fluid (air or gas) and it is necessary to perform a purging operation on a pipe in which the flow in the pipe becomes a laminar flow. An object of the present invention is to provide a purge method capable of efficiently completing work in a short time.

In order to solve the above-described problems, the purge method according to the present invention provides a shut-off means operable to control the outflow and stop of the fluid from the pipe on the downstream side of the pipe to be purged provided with a shut-off valve on the upstream side. Step of installing the shut-off means, step of installing the effluent fluid processing means for providing an external discharge means for collecting the fluid flowing out from the shut-off means, or filling the pipe from the upstream side of the pipe A replacement step of supplying a replacement fluid to be filled and causing the fluid to be replaced filled in the pipe to flow downstream through the blocking means, and maintaining the shut-off valve in the replacement step, The basic replacement operation step of opening the blocking means and closing the blocking means after a preset replacement fluid supply time is repeated.

That is, in the purging method according to the present application, the opening / closing of the shut-off means provided on the downstream side of the replacement section is repeated at regular intervals (“replacement fluid supply time” in the present application). When opening and closing is repeated in this way, the flow is temporarily stopped by the closing operation of the blocking means. When the shut-off means is opened again after this stop, the flow in the pipe is the boundary layer that has grown from the inner surface of the pipe with the previous replacement fluid feeding operation (if the flow velocity in the pipe is slow, this boundary If the growth of the layer promotes laminarization of the flow in the tube) and the blocking means is opened again, the flow velocity distribution is relatively uniform when viewed from the cross section of the tube, so-called turbulent flow velocity. The flow is close to the distribution. In such a flow, mixing of the upstream fluid (substitution fluid) and the downstream fluid (substitution fluid) compared to the fully developed laminar flow with a low Reynolds number (a flow velocity in the pipe is slow). The degree is low.
Therefore, in the present application, by repeating the basic replacement operation step as described above, the purge operation can be completed in a short time while avoiding mixing of the upstream fluid and the downstream fluid.

In a preferred embodiment of the present invention, the replacement fluid supply time t is set such that the pipe inner diameter of the piping is d, the kinematic viscosity coefficient of the replacement fluid is ν, and α is a constant greater than 0.1 and 6 or less.
t = α × 0.065 × d ² / ν
Has been proposed. This formula shows that the relationship between the length of the running section of the flow flowing into the pipe having a constant diameter from the open space: X and the inner diameter of the pipe: d is a dimensionless value, X / d = 0.065Re (Re is the Reynolds number) The value determined by the inventors through actual experiments in relation to this dimensionless quantity in accordance with the teaching of fluid mechanics that can be approximated by
The inventors of course have a case where α is greater than 0.1 and less than or equal to 1 and that separation of air and gas to the extent expected by the present application is possible even when the length of the run-up section is about 6 times. Was confirmed experimentally. Therefore, by using this formula, the execution time of one basic replacement operation step can be easily obtained. According to the study by the inventors, it is preferable that the waiting time from the closing operation to the opening operation of the blocking means is less than half of the replacement fluid supply time t.

As described above, the basic replacement operation process in which the supply of the replacement fluid is limited to such an extent that the mixing of the upstream fluid and the downstream fluid does not become large can be realized by limiting the replacement fluid supply time. It is also possible to limit the supply amount of the replacement fluid. In other words, the supply of one replacement fluid is limited to such an extent that it does not exceed the run-up section length. Based on such knowledge of the inventors, the purging method according to the present invention for solving the above-described problem is that the outflow of fluid from the pipe to the downstream side of the pipe to be purged provided with a shutoff valve on the upstream side. And a blocking means installation step for providing a blocking means operable to stop the outflow, and a spilled fluid treatment means installation step for providing a collecting means for collecting the fluid flowing out from the blocking means, or for providing an external discharge means for external discharge. A replacement step of supplying a replacement fluid to be filled in the pipe from the upstream side of the pipe, and causing the fluid to be replaced filled in the pipe to flow out to the downstream side through the blocking means, and in the replacement step, The basic replacement operation step of maintaining the shut-off valve in an open state, opening the shut-off means, and closing the shut-off means after supplying a preset replacement fluid supply amount is repeated.
At that time, assuming that Re is the Reynolds number in the laminar flow formed in the pipe by continuous supply of the replacement fluid and d is the inner diameter of the pipe, the run-up section length: X is obtained by (0.065 × Re × d). be able to. Therefore, if the replacement fluid supply amount at one time is (0.065 × Re × d) × ((d / 2) 2 × π) or less, the movement distance of the supplied replacement fluid is less than the run-up section length. Limited and good purge is obtained. Therefore, in a preferred embodiment of the present invention, the replacement fluid supply amount is represented by the following equation (0.065 × Re × d) where d is the inner diameter of the pipe and Re is the Reynolds number of the fluid flowing in the pipe. ) × ((d / 2) ² × π)
Or less.

  In the above-described method for limiting the supply amount of replacement fluid, the volume of the collecting means is related to the amount of fluid that flows out in one basic replacement operation step, and the trap is collected every time one basic replacement operation step is completed. If the collecting means is discharged to the outside and emptied, the procedure of the purge operation becomes easy to understand and practical. For this reason, in one of the preferred embodiments of the present invention, in the spilled fluid treatment means installation step, the collection means having a volume equal to or less than the value obtained by the equation is used, and in the replacement step, With the opening operation of the blocking means, the blocking means is closed in a state where the collecting means is filled with fluid, and the fluid filled in the collecting means is discharged to the outside.

  It is necessary to determine the end of the repeated replacement process based on experimental and empirical knowledge of gas construction. According to the inventor's knowledge, the concentration of the replacement fluid in the final position region of the purged pipe is 95% by volume. For this reason, in a preferred embodiment of the present invention, the blocking means is opened and closed until the concentration of the replacement fluid in the portion of the piping near the blocking means reaches 95% by volume. However, the replacement step is repeated.

  When piping or the like in the basement is the target of the purge operation, it is practically impossible to dissipate the gas that flows out of the purge operation to the surroundings. In such a situation, it is advantageous to use a bag (container) that contains the gas to be discharged. From this, in one of the preferred embodiments of the present invention, the collection means is less than the pipe volume of the purge target pipe, and more than the fluid volume flowing out of the pipe in one replacement step. A bag having a capacity. Of course, since the amount of gas flowing out in the purging operation is small, it is possible to diffuse the gas to the surroundings depending on the surrounding environment. In consideration of such a situation, in one preferred embodiment of the present invention, the external discharge means is a pipe that communicates and connects the outlet of the blocking means and the external space.

It is a time chart which shows the basic flow of the purge method of this invention. It is a schematic diagram which shows the relationship between the run-up area until a laminar flow fully develops, and a laminar boundary layer. It is a schematic diagram which shows the structure of the experiment example of a purge method. It is a graph which shows the measurement result of eight density | concentration sensors obtained in the experiment example of FIG. FIG. 5 is a graph obtained by extracting only the measurement result of the first concentration sensor from the graph of FIG. 4. FIG. 5 is a graph obtained by extracting only the measurement result of the eighth density sensor from the graph of FIG. 4. FIG.

  First, the basic flow of the purge method of the present invention will be described with reference to FIG. Here, the purge target pipe is the branch pipe 1 branched from the gas supply pipe 2. Air remains in the branch pipe 1 due to construction or the like. As a pre-purging operation (blocking means installation step), a first cutoff valve 1A is attached to the upstream end of the branch pipe 1, and a second cutoff valve (an example of a cutoff means) 1B is attached to the downstream end. Yes. During the purge operation, the gas / air mixture flowing through the branch pipe 1 flows out from the outlet of the second shut-off valve 1B. As an outflow fluid treatment means installation step, gas flows into the outlet of the second shut-off valve 1B. A bag 3 (an example of an external discharge means) is attached, and the air-fuel mixture flowing out is temporarily stored in the gas bag 3.

  Substantial gas purging is performed by using city gas (a type of replacement fluid, hereinafter simply referred to as gas) that supplies air (a type of fluid to be replaced) filled in the branch pipe 1 via the gas supply pipe 2 on the downstream side. This is a replacement process in which it is swept away and replaced. Next, this replacement step will be described with reference to the time chart of FIG.

(1) First, the first shutoff valve 1A is opened to allow gas to flow from the gas supply pipe 2 to the branch pipe 1. At this time, the second shutoff valve 1B is kept closed.
(2) First purge start command.
(3) By opening the second shutoff valve 1B in response to the start command, the purge of the air staying in the branch pipe 1 by the gas from the gas supply pipe 2 starts. Thus, by opening the 2nd cutoff valve 1B, the air located downstream from the said cutoff valve is pushed away downstream by gas. If the flow in the pipe is maintained while the second shutoff valve 1B is kept open, the flow rate of the gas is small (the Reynolds number cannot be increased beyond the critical Reynolds number). As indicated, the development of the boundary layer from the tube wall creates a so-called laminar flow which is not preferred in the present application. When such a laminar flow is formed and flows in a section where the flow is constantly long, air that is the fluid to be replaced is distributed near the tube wall, and gas that is the fluid to be replaced is distributed near the tube center. If a relatively long mixing zone of fluid is formed and this laminar flow state is maintained, it takes a long time for the gas concentration in the entire pipe to reach a predetermined concentration (95% by volume) or more.
Therefore, in the present application, the opening operation of the second shutoff valve 1B and the closing operation subsequent to the opening operation are repeated for a certain time (this time is referred to as “replacement fluid supply time” in the present application). When the opening operation and the closing operation are sequentially repeated in this way, the flow is intermittently stopped, and the formation of a laminar flow in the pipe can be suppressed. That is, the run-up section shown in FIG.
In the study by the inventors, such a “substitution fluid supply time t” is set such that the pipe inner diameter of the pipe is d, the kinematic viscosity coefficient of the substitution fluid is ν, α is a constant greater than 0.1 and less than or equal to 6. Let t = α × 0.065 × d ² / ν.
(4) In order to accurately measure the purge time, the timer is started in response to the opening operation of the second shut-off valve 1B. The timer is set to the previously calculated purge time: t.
(5) In response to the time-up of the timer, the second shut-off valve 1B is closed and the purge operation is completed. After the purge operation is completed, if the gas bag 3 does not have enough room to accommodate the amount of air-fuel mixture sent in at least one more purge operation, the air-fuel mixture filled in the gas bag 3 is collected in another container. Or release it in a place where the release of the air-fuel mixture is not a problem and empty it.
(6) After the purge operation is completed, the concentration measurement result by the densitometer 4 disposed in the branch pipe 1 in the vicinity of the second shutoff valve 1B is evaluated, and it is checked whether or not a predetermined determination threshold value has been reached. The As an example of this determination threshold, a gas concentration value of 95% by volume is employed.
(7) Unless the measured gas concentration value reaches the determination threshold value, the second, third,... Purge start command is issued, and the purge operation (from (1) to (6) above) Is repeated.
(8) When the measured gas concentration value reaches the determination threshold value after the completion of the several purge operations, the purge operation is completed.

  When the air-fuel mixture can be sent from the second shut-off valve 1B to a place where the air-fuel mixture emission does not matter by the gas discharge pipe (a kind of external discharge means), the gas bag 3 can be used for recovery. Instead, such a gas discharge pipe may be provided.

Next, an experimental example of the purge method according to the present invention will be described with reference to FIGS.
In this experimental facility, the purge target pipe is a straight pipe 1 connected to a supply pipe 2 for city gas (low pressure 13A gas) via a shutoff valve 1A. A gas meter is connected to the downstream end of the pipe 1, and a gas bag 3 is connected to an outlet tube of the gas meter via a shutoff valve 1B. The length of the tube 1 is 8 m. In order to measure the internal concentration of the tube 1, eight concentration sensors S1 to S8 are equally arranged from the upstream side to the downstream side. The first concentration sensor S1 is disposed at a position of 0.5 m from the first shutoff valve 1A, and thereafter the second concentration sensor S2 to the eighth concentration sensor S8 are disposed at an interval of 1 m. The tube 1 is filled with atmospheric air. The capacity of the gas bag 3 is 5 liters.

This purge experiment is performed in accordance with the purge method of the present invention described with reference to FIG. That is, the following (1) to (4), that is, (1) the first shut-off valve 1A is opened and gas flows into the pipe 1,
(2) Opening the second shut-off valve 1B and storing the purge gas purged in the gas bag 3;
(3) Close the second shutoff valve 1B, remove the gas bag 3 from the shutoff valve 1B, and dissipate the purge gas to the atmosphere.
(4) Reattach the gas bag 3 to the shutoff valve 1B.
As a single purge (purge time of about 1 minute), the measurement values of the concentration sensors S1 to S8 are acquired continuously in 8 while repeating this 15 times.

  FIG. 4 shows the concentration measurement results of the eight concentration sensors S1 to S8 in 15 purges over about 17 minutes. In the graph of FIG. 4, the vertical axis represents the gas concentration expressed in volume%, and the horizontal axis represents the experimental elapsed time expressed in minutes. In FIG. 4, the density measurement results of the eight density sensors S1 to S8 are indicated by independent graph lines, and S1 is appended to the graph line indicating the density measurement results of the density sensor S1. A graph line indicating the density measurement result of the density sensor is attached with a figure number assigned to the density sensor. FIG. 5 is a graph in which only the measurement result of the first density sensor S1 is extracted from the graph of FIG. 4, and FIG. 6 is a graph in which only the measurement result of the eighth density sensor S8 is extracted from the graph of FIG. is there.

  The vertical arrows indicate the end points of the first to eighth purges, respectively. In particular, as apparent from the comparison between FIG. 5 and FIG. 6, the concentration change at the position on the most upstream side of the tube 1 due to the repetition of the purge operation described above rises rapidly and rises gradually, whereas the most downstream. The density change at the side position increases at a substantially constant rate. For example, the measurement result of the first concentration sensor S1 indicating the concentration at the most upstream position at the end of the first purge exceeds 60% by volume, whereas the concentration at the most downstream position is The measurement result of the eighth density sensor S8 showing is only a few volume%. In addition, the measurement result of the first concentration sensor S1 indicating the concentration at the most upstream position at the end of the tenth purge has already reached 100% by volume, whereas at the most downstream position, The measurement result of the eighth density sensor S8 indicating the density is 90% by volume at most.

  A preferable end state in the purge operation is that the concentration at the most downstream position of the pipe 1 to be purged reaches 95% by volume. From this experimental example, the measurement result of the eighth concentration sensor S8 reaches 95% by volume at the end of the 12th purge. Therefore, in this experimental example, it is considered that the air in the tube 1 is sufficiently eliminated by repeating the purge for about 1 minute per time 12 times.

  The concentration of the air-fuel mixture stored in the gas bag 3 at the end of the 12th purge was 80% by volume. Further, by purging three times, the concentration of the gas bag 3 was 95% by volume. Therefore, if the purging operation is performed until the concentration of the gas bag 3 reaches 95% by volume, several more purges may be performed after the concentration by the concentration sensor S8 at the most downstream position reaches 95% by volume. .

In the above-described embodiment, a form in which the supply of the replacement fluid in one replacement step is limited by time is adopted. However, although it is substantially similar, a form in which this is limited by the supply amount of the replacement fluid is used. It may be adopted. In order to suppress mixing of the upstream fluid and the downstream fluid, in this alternative embodiment, the amount of the replacement fluid supplied in one replacement stroke is set to (0.065 × Re × d) × ((d / 2) Limit to the set replacement amount set to ² × π) or less. That is, the shutoff valve 1B is closed when the replacement fluid supply amount or the fluid outflow amount from the shutoff means reaches the set replacement amount in the replacement step. This set replacement amount can be measured using a flow meter. Further, when the gas bag 3 having a set replacement amount is used, the shut-off valve 1B is closed when the gas bag 3 becomes full, the gas bag 3 is detached from the shut-off valve 1B, and the purge gas is discharged to the outside. By doing so, an effective purge operation can be performed. Of course, the capacity of the gas bag 3 may be an integral multiple of the set replacement amount, and the purge gas may be discharged to the outside every time the basic replacement operation process is completed a predetermined number of times.

  The purge method according to the present invention can be applied to various purges including gases other than city gas that need to be performed with mixed gas in a laminar flow state.

1: Branch pipe (pipe to be purged)
1A: 1st cutoff valve 1B: 2nd cutoff valve 2: Gas supply pipe 3: Gas bag

Claims (8)

A shut-off means installation step for providing shut-off means operable to flow out and stop the outflow of fluid from the pipe on the downstream side of the pipe to be purged provided with a shut-off valve on the upstream side ;
An outflow fluid treatment means installation step for providing a collection means for collecting the fluid flowing out from the blocking means, or for providing an external discharge means for external discharge;
A replacement step of supplying a replacement fluid to be filled in the pipe from the upstream side of the pipe, and causing the fluid to be replaced filled in the pipe to flow out to the downstream side through the blocking means,
A purge method that repeats a basic replacement operation step of maintaining the shut-off valve in the open state, opening the shut-off means, and closing the shut-off means after a preset replacement fluid supply time in the replacement step. T = α × 0.065 × d ² / wherein the replacement fluid supply time t is defined as d where the pipe inner diameter is d, the kinematic viscosity coefficient of the replacement fluid is ν, and α is a constant greater than 0.1 and less than or equal to 6. The purge method according to claim 1, wherein ν is used. A shut-off means installation step for providing shut-off means operable to flow out and stop the outflow of fluid from the pipe on the downstream side of the pipe to be purged provided with a shut-off valve on the upstream side ;
An outflow fluid treatment means installation step for providing a collection means for collecting the fluid flowing out from the blocking means, or for providing an external discharge means for external discharge;
A replacement step of supplying a replacement fluid to be filled in the pipe from the upstream side of the pipe, and causing the fluid to be replaced filled in the pipe to flow out to the downstream side through the blocking means,
A purge method that repeats a basic replacement operation step of maintaining the shut-off valve in the replacement step, opening the shut-off means, and closing the shut-off means after supplying a preset replacement fluid supply amount. The replacement fluid supply amount is represented by the following formula (0.065 × Re × d) × ((d / 2) ² × π, where d is the pipe inner diameter of the pipe and Re is the Reynolds number of the fluid flowing in the pipe. )
The purging method according to claim 3, wherein the purge method is equal to or less than a value obtained by the above. In the spilled fluid treatment means installation step, the collection means having a volume equal to or less than the value obtained by the above formula is used, and in the replacement step, the collection means is fluid with the opening operation of the blocking means. The purging method according to claim 4, wherein the shutting means is closed in a full state to discharge the fluid filled in the collecting means to the outside.   The purge according to any one of claims 1 to 5, wherein the basic replacement operation step of the blocking means is repeated until a concentration of the replacement fluid in a portion of the pipe in the vicinity of the blocking means reaches 95% by volume. Method.   The purging method according to claim 1 or 2, wherein the collecting means is a bag having a capacity equal to or less than a pipe volume of the purge target pipe and having a capacity equal to or larger than a fluid volume discharged from the pipe in one replacement step. .   The purge method according to claim 1 or 2, wherein the external discharge means is a pipe that communicates and connects the outlet of the blocking means and the external space.

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