JP4781032B2 - Gas replacement method and gas replacement device in piping - Google Patents

Description

  The present invention relates to a gas replacement method and a gas replacement device in a pipe for replacing flammable gas in the pipe with air.

  Fuel gas transport piping for transporting fuel gas such as blast furnace gas generated at steelworks is used while carrying out periodic inspection work and repair work. When carrying out internal inspection work, etc., for periodic inspection work and repair work, replace the fuel gas in the pipe with nitrogen gas, an inert gas, to prevent gas poisoning, fire and gas explosion. After that, the nitrogen gas is replaced with air. In particular, in the case of power generation boilers that co-fire heavy fuel oil and blast furnace gas and other steelworks by-product gases, when the power generation equipment is shut down during periodic inspection work, etc., the fuel gas in the fuel gas transport pipe is used during heavy oil combustion only to prevent explosion in the furnace. Is replaced with nitrogen gas, which is an inert gas, and then the generator is disconnected.

  FIG. 6 is a diagram showing a schematic piping system of general blast furnace gas transport piping. The blast furnace gas is sent to the boiler 3 via the U-shaped water seal valve 1 and the blast furnace gas transport pipe 2. In the middle of the blast furnace gas transport pipe 2, an emergency water seal valve 4, a preheater 5, and a flow rate control damper 6 capable of urgently shutting off the blast furnace gas are disposed. When replacing the blast furnace gas staying in the blast furnace gas transport pipe 2 with air, the nitrogen gas supply pipe 7 connected in the vicinity of one end of the blast furnace gas transport pipe 2 is used to send nitrogen gas to the blast furnace gas transport pipe 2. The blast furnace gas is discharged from the bleeder valve 8 (8a, 8b, 8c, 8d, 8e) disposed in the blast furnace gas transport pipe 2.

  While discharging the blast furnace gas with the bleeder valve 8, the sample gas is sampled with the sampling valve 9 (9a, 9b, 9c, 9d, 9e) provided in the vicinity of the bleeder valve 8, and the concentration of the blast furnace gas is not shown. Measure with a gas concentration meter. After confirming that this concentration is equal to or lower than a predetermined value, the supply of nitrogen gas is stopped, and air is supplied by the air blower 10 connected to the blast furnace gas transport pipe 2, while the bleeder valve 8 transports the blast furnace gas. The nitrogen gas in the pipe 2 is discharged, and the gas in the blast furnace gas transport pipe 2 is replaced with air. Completion of the replacement with air is performed by measuring the oxygen concentration with the sampling valve 9.

The above method is a blast furnace gas replacement method that has been commonly used in the past, but the efficiency of gas replacement is not necessarily high, the amount of nitrogen gas required for gas replacement is large, Problems such as the time required for gas replacement have been pointed out. As a method of efficiently or safely replacing the gas in the pipe or vessel, if the air in the underground storage tank is replaced with nitrogen gas once, then this nitrogen gas is replaced with methane gas. A method of efficiently replacing with gas amount is disclosed (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 11-301786

  Fuel gas transport pipes used in steelworks and the like have a large capacity such that the inner diameter of the pipe is as large as 2 to 3 m and the length exceeds 100 m. Further, the fuel gas transport pipe has a complicated shape and path such as having a bent part and a branch part. The technique described in Patent Document 1 relates to a method of efficiently substituting a small amount when replacing the nitrogen gas with methane gas after replacing the air in the underground storage tank with nitrogen gas once. In this method, the shape of the object to be replaced is simple, and gas replacement is performed by utilizing the difference in specific weight of air, nitrogen gas, and methane gas. This method is used for the gas in the fuel gas transport pipe. It cannot be used as a replacement method.

  Technology that efficiently replaces flammable gas in pipes with large capacities, long pipe lengths, complicated shapes such as bends and branches, in a short amount of inert gas There is no current situation, and development of a method for efficiently replacing the gas in these pipes in a short time and with a small amount of nitrogen gas is awaited. Especially for power generation boilers that co-fire heavy fuel oil and blast furnace gas and other ironworks by-product gases, when stopping power generation equipment during periodic inspection work, etc., blast furnace gas in fuel gas transport pipes, etc., is used as heavy oil exclusively to prevent explosion in the furnace. Since the generator is disconnected after replacing the by-product gas of the steelworks with nitrogen gas, which is an inert gas, shortening the gas replacement time is a serious problem. In addition, if technology for replacing combustible gas in piping safely and efficiently in a short time is developed, it will be used in many places without being limited to fuel gas transport piping. Not to mention deafness.

  An object of the present invention is to provide a gas replacement method and a gas replacement device in a pipe that replaces combustible gas in the pipe with air in a safe and short time and with a small amount of gas necessary for gas replacement. It is in.

The present invention is a gas replacement method in a pipe for replacing flammable gas in a pipe with air,
An inert gas replacement step in which a part of the combustible gas in the pipe is replaced with an inert gas, and an inert gas region having a high inert gas concentration is locally formed in the pipe;
After forming an inert gas region in the pipe by the inert gas replacement step, air is supplied into the pipe so as not to contact the combustible gas remaining in the pipe, and the supplied air An air replacement step of extruding the inert gas and replacing the combustible gas and the inert gas in the pipe with air;
It is the gas replacement method in piping characterized by including.

In the present invention, the formation of the inert gas region in the inert gas replacement step may be performed by supplying the inert gas from one end of the pipe while the flammability is generated from the center and / or the other end of the pipe. Done by discharging gas,
2. The gas replacement method in a pipe according to claim 1, wherein the supply of air in the air replacement step is performed from the same end side as the end of the pipe to which the inert gas is supplied.

The present invention further includes a confirmation step for confirming that an inert gas region having a predetermined length is formed in the pipe by the inert gas replacement step,
The formation of the inert gas region is confirmed by detecting the concentration of the combustible gas in the axial direction of the pipe and confirming that the concentration of the combustible gas at a predetermined position is equal to or lower than a predetermined concentration. Item 3. A gas replacement method in a pipe according to Item 1 or 2.

  Further, in the present invention, the combustible gas has a specific weight similar to the specific weight of the inert gas, and is a gas replacement method in a pipe according to any one of claims 1 to 3.

  Further, in the present invention, the combustible gas is a blast furnace gas of a steel mill, and the inert gas is nitrogen gas, The gas in a pipe according to any one of claims 1 to 4, This is a replacement method.

  Further, in the present invention, the supply of the inert gas and the air is performed from multiple directions with respect to a cross section of the pipe, and the gas replacement in the pipe according to any one of claims 1 to 5 Is the method.

  Further, in the present invention, when an apparatus or a device is disposed in the pipe, an operation for replacing the combustible gas in the device or the apparatus with an inert gas separately from the replacement operation in the inert gas replacement step. 7. The gas replacement method for pipes according to claim 1, wherein the air replacement operation is performed thereafter.

  Further, in the present invention, when there is another pipe to be replaced in a direction different from the direction in which the inert gas is pushed out with air in the air replacement step, separately from the replacement operation in the inert gas replacement step, The pipe according to any one of claims 1 to 7, wherein an inert gas replacement operation for sufficiently reducing a combustible gas concentration in the other pipe line is performed, and then the air replacement operation is performed. This is a gas replacement method.

  Also, in the present invention, when the combustible gas is a mixed gas, the combustible gas in the pipe of the inert gas replacement process is discharged from the upper part of the pipe, and the detection of the combustible gas in the confirmation process is The gas replacement method in a pipe according to any one of claims 3 to 8, wherein a gas having a large specific weight among the mixed gas is a target.

  Further, in the present invention, when the combustible gas is a mixed gas, the combustible gas is discharged from the lower part of the pipe in the inert gas replacement process, and the detection of the combustible gas in the confirmation process is performed. The gas replacement method in a pipe according to any one of claims 3 to 8, wherein a gas having a small specific weight is a target of the mixed gas.

The present invention is also a gas replacement device in the pipe for replacing the combustible gas in the pipe with air,
An inert gas supply means connected to the pipe and capable of supplying an inert gas ;
A gas discharging means connected to the pipe and capable of discharging the gas in the pipe;
A gas concentration detecting means capable of detecting a gas concentration in the pipe;
An air supply means connected to the pipe and capable of supplying air into the pipe;
When the gas concentration detection means detects that the flammable gas concentration at a predetermined position in the pipe is not more than a predetermined value, the air supply means controls the air to be supplied to the pipe, When the gas concentration detection means detects that the flammable gas concentration at a predetermined position exceeds a predetermined value, control means for controlling air supply from the air supply means to the pipe is disabled.
It is a gas replacement apparatus in the piping used for the gas replacement method in piping of any one of Claim 1 to 10 characterized by the above-mentioned.

  The gas replacement method in a pipe according to the present invention is such that an inert gas region having a high inert gas concentration is locally formed in the pipe, and thereafter, in order to avoid direct contact with the flammable gas remaining in the pipe. Air is supplied to the air, the inert gas is extruded with the supplied air, and the combustible gas and the inert gas in the pipe are replaced with air. In the conventional gas replacement method, after the entire inside of the pipe is replaced with an inert gas, air is supplied and the inside of the pipe is replaced with air. However, the gas replacement method of the present invention is locally inert in the pipe. Since the gas replacement is performed by extruding this inert gas with air after forming a region having a high gas concentration, it is not necessary to replace the entire pipe with the inert gas as in the conventional case. For this reason, the time to replace with the inert gas is shortened, and the amount of the inert gas necessary for the gas replacement can be reduced as compared with the conventional method.

  Further, according to the present invention, the inert gas region is formed by discharging the combustible gas from the central part and / or the other end of the pipe while supplying the inert gas from one end of the pipe. In addition, the inert gas region can be formed reliably. In addition, since the supply of air in the air replacement process is performed from the same end side as the end of the pipe supplied with the inert gas, an inert gas region exists between the combustible gas and the supplied air, and the air Does not come into direct contact with the combustible gas, and the inside of the pipe can be safely replaced with air.

  Further, according to the present invention, the concentration of the combustible gas in the axial direction of the pipe is detected, and the inactive gas region is formed when the combustible gas concentration at the predetermined position is equal to or lower than the predetermined concentration. Since it confirms, formation of an inert gas area | region can be confirmed reliably. In addition, it is possible to safely replace the gas in the pipe by determining the control value of the combustible gas concentration based on the combustion range and the explosion range of the combustible gas.

  Further, according to the present invention, since the specific weight of the combustible gas approximates the specific weight of the inert gas, a blowout of the gas in which the inert gas locally flows in the pipe occurs during the replacement operation with the inert gas. Hard to do. Thereby, an inert gas area | region can be formed efficiently in a short time.

Moreover, according to this invention, combustible gas is blast furnace gas of a steel mill, and inert gas is nitrogen gas. The blast furnace gas generally contains nitrogen gas and carbon dioxide in addition to combustible gas such as carbon monoxide and hydrogen, and the specific weight of the gas is about 1.34 (kg / m ³ N). On the other hand, the specific weight of nitrogen gas is 1.25 (kg / m ³ N), and the specific weight of blast furnace gas and nitrogen gas is similar. Therefore, the inert gas region can be formed efficiently in a short time.

  Further, according to the present invention, the supply of the inert gas and air is performed from multiple directions with respect to the cross section of the pipe, so that the supply of the inert gas and air is made substantially uniform with respect to the cross section direction of the pipe. Can do. As a result, even if the pipe has a large pipe diameter, local gas blow-off and gas mixing in the pipe can be suppressed.

  In addition, according to the present invention, when an apparatus or device is provided in the pipe, an operation for replacing the combustible gas in the device or apparatus with an inert gas is performed separately from the replacement operation in the inert gas replacement step. Do. Unlike piping, the devices and equipment arranged in the piping have complicated shapes and structures. Therefore, in the inert gas replacement operation that forms the inert gas region, the combustible gas in the devices and equipment is inert gas. May not be fully substituted. However, in the gas replacement method of the present invention, the operation of replacing the combustible gas in the apparatus and equipment with the inert gas is performed separately from the replacement operation in the inert gas replacement step. It becomes possible to perform replacement, and gas replacement of pipes and devices can be performed safely and reliably.

  Further, according to the present invention, when there is another pipe to be replaced in a direction different from the direction in which the inert gas is pushed out with air in the air replacement step, separately from the replacement operation in the inert gas replacement step, Since the inert gas replacement operation for sufficiently reducing the concentration of the combustible gas in the other pipe line is performed, and then the air replacement operation is performed, the gas replacement can be performed safely and reliably.

  Further, according to the present invention, when the combustible gas is a mixed gas, the combustible gas in the pipe of the inert gas replacement process is discharged from the upper part of the pipe, and the detection of the combustible gas in the confirmation process is performed as follows: Since the gas having a large specific weight is the target among the mixed gas, the formation of the inert gas region can be reliably detected. A gas having a large specific weight tends to stay in the lower part of the pipe. Therefore, when the combustible gas is discharged from the upper part of the pipe and a gas having a large specific weight is detected, it is highly likely that the gas having a small specific weight has already been discharged. Thereby, even if combustible gas is a mixed gas, formation of an inert gas area | region can be detected reliably.

  Further, according to the present invention, when the combustible gas is a mixed gas, the combustible gas in the pipe of the inert gas replacement process is discharged from the lower part of the pipe, and the detection of the combustible gas in the confirmation process is performed as follows: Since the gas having a small specific weight is the target among the mixed gas, the formation of the inert gas region can be reliably detected. Gas with a small specific weight tends to stay in the upper part of the pipe. Therefore, when the combustible gas is discharged from the lower part of the pipe and a gas with a small specific weight is detected, there is a high possibility that the gas with a large specific weight has already been discharged. Thereby, even if combustible gas is a mixed gas, formation of an inert gas area | region can be detected reliably.

In Rukoto using a gas replacement device in the pipe of the present invention, the combustible gas in the pipe can be replaced with air safely in a short time, also small amount of gas.

  FIG. 1 is a diagram showing a schematic configuration of a gas replacement device 20 in a pipe as one embodiment of the present invention. The fuel gas transport pipe 21 shown here is a pipe for supplying blast furnace gas to the boiler 22. An emergency water seal valve 28, a flow control damper 29, a preheater 23 for preheating fuel gas, and a burner are provided in the middle of the pipe. Burner valves 24a and 24b for shutting off the fuel. The fuel gas transport pipe 21 is equipped with a gas replacement device 20 for finally replacing the fuel gas in the pipe with air.

  The gas replacement device 20 is connected to a fuel gas transport pipe 21 for gas replacement, a gas discharge pipe 30 (30a, 30b, 30c, 30d, 30e) for discharging the gas in the pipe, and a sample connected to the gas discharge pipe. Sampling pipe 32 (32a, 32b, 32c, 32d, 32e), nitrogen gas supply pipe 40 for supplying nitrogen gas, preheater nitrogen gas supply pipe 42, and bleeder valve 31 (31a, 31b, 31c, 31d, 31e), sampling valve 33 (33a, 33b, 33c, 33d, 33e), nitrogen gas supply valve 41, preheater nitrogen gas supply valve 43, air supply means 50 for supplying air, gas concentration is measured And a control device 70 for controlling various automatic valves and the like.

  In the fuel gas transport pipe 21, gas discharge pipes 30 a and 30 b for discharging the gas in the fuel gas transport pipe 21 are provided in the vicinity of both ends 25 and 26 of the fuel gas transport pipe 21. Two gas discharge pipes 30c and 30d are disposed at the center of the fuel gas transport pipe 21. In addition, in order to discharge the gas in the preheater 23, a gas discharge pipe 30e is also provided on the top of the preheater 23. Each gas discharge pipe 30 includes a bleeder valve 31 that discharges gas in the middle of the pipe line. The bleeder valve 31 is an automatic valve that opens and closes in response to a control signal from a control device 70 described later.

  Each gas discharge pipe 30 has a branch portion in a pipe line connecting the bleeder valve 31 and the fuel gas transport pipe 21, and a sample for detecting the gas concentration in the fuel gas transport pipe 21 is provided at the branch section. A sampling tube 32 is connected. The sample collection pipe 32 has a sample collection valve 33 for collecting gas in the middle of the pipeline. The sampling valve 33 is an automatic valve that opens and closes in response to a control signal from a control device 70 described later.

  The nitrogen gas supply pipe 40 is a pipe for supplying nitrogen gas to the fuel gas transport pipe 21, and has a nitrogen gas supply valve 41 that opens and closes in response to a control signal from the control device 70. Since the nitrogen gas supply pipe 40 is for replacing the combustible gas in the fuel gas transport pipe 21 with nitrogen gas, it is connected to the vicinity of one end 25 of the fuel gas transport pipe 21. A preheater nitrogen gas supply pipe 42 is also provided to replace the blast furnace gas in the preheater 23 installed in the middle of the fuel gas transport pipe 21 with nitrogen gas.

  This is because the preheater 23 is different in size from the fuel gas transport pipe 21 and has a complicated shape, so that the gas in the preheater 23 is sufficiently replaced with nitrogen gas only by the nitrogen gas replacement operation of the fuel gas transport pipe 21. Because there is a fear of not being able to. Further, when supplying nitrogen gas to a large-diameter fuel gas transport pipe, nitrogen gas is viewed from multiple directions as shown in FIG. 2 in order to suppress the occurrence of gas bias due to a specific weight difference in the cross section of the pipe. It is desirable to supply

  The air supply means 50 includes an air blower 51 and an air supply pipe 52 that sends air from the air blower 51 to the fuel gas transport pipe 21. The air blower 51 sends air to the fuel gas transport pipe 21 and supplies air to the fuel gas transport pipe 21 through an air supply pipe 52 having an air supply valve 53 that opens and closes in response to a control signal from the control device 70. To do. Since the air supply pipe 52 is for replacing the nitrogen gas in the fuel gas transport pipe 21 with air, it is connected to the vicinity of one end 25 of the fuel gas transport pipe 21. Although the specific weight difference between nitrogen gas and air is small, there is a concern about uneven supply of air when the pipe diameter is large. Therefore, it is preferable to introduce air from multiple directions as shown in FIG.

  The gas concentration meter 60 for measuring the gas concentration collects the sample gas from the sample collection pipe 32 and measures the combustible gas concentration and the oxygen concentration. The blast furnace gas shown in this embodiment is a mixture of various gases as will be described later. The detection of the concentration of the combustible gas composed of such a mixed gas may be a method in which a specific gas contained in the fuel gas is used as a representative gas and the concentration of this gas is detected. The concentration measurement range and accuracy of the gas concentration meter 60 may be determined from a management value when the fuel gas is replaced with nitrogen gas and a management value when the nitrogen gas is replaced with air. Moreover, although the measurement principle of the gas concentration meter 60 is not particularly limited, a gas concentration meter that can be measured online is desirable.

  Based on the gas concentration signal from the gas concentration meter 60, the control device 70 controls the start / stop of the air blower 51 and the opening / closing of valves such as the bleeder valve 31, the sampling valve 33, the nitrogen gas supply valve 41, and the air supply valve 53. To do. The control device 70 is calculated by an input unit that inputs a gas concentration signal from the gas concentration meter 60, a storage unit that stores data input via the input unit, a calculation unit that calculates data in a predetermined procedure, and a calculation unit The output part which outputs the data to perform is provided. The air blower 51 is started and stopped in response to a control signal from the control device 70, and the bleeder valve 31, the sample collection valve 33, the nitrogen gas supply valve 41, the air supply valve 53, etc. open and close in response to the control signal from the control device 70. do. The control device 70 can be realized by using a computer, and the data processing procedure can be input to the computer as a program. In addition, the control device 70 is provided with an interlock function in which all the burner valves 24 operate under conditions such as closing.

  Further, the fuel gas transport pipe 21 includes a U-shaped water seal valve 80 for separation from the fuel mother pipe at the fuel gas inlet 25. The U-shaped water sealing valve 80 can block gas by filling water into the U-shaped portion. For this reason, the U-shaped water seal valve 80 has a level switch 88 (88a, 88b) for detecting the water level, a water supply pipe 81 for supplying water, and an overflow pipe 82 for discharging water overflowing from the U-shaped water seal valve 80. , And a drain pipe 83 for discharging water from the U-shaped water sealing valve 80 is connected. The water supply pipe 81, the overflow pipe 82, and the drain pipe 83 are provided with automatic valves 84, 85, 86, 87 that open and close in response to control signals from the control device 70.

  Next, the gas replacement method in the pipe of the present invention will be described. In the gas replacement method in the pipe of the present invention, when the combustible gas in the pipe is replaced with air, an inert gas region having a high inert gas concentration is locally formed in the pipe, and the combustible gas and air By placing this inert gas region (inert gas lump) between the pipes, even if flammable gas remains in the pipe, the pipe is brought into air without causing direct contact between the air and the flammable gas. Features that can be replaced. This is because the mass of inert gas is extruded with air, so that the inert gas functions as a plug in the pipe, and the flammable gas remaining in the pipe does not come into direct contact with the air. It can be extruded. Hereinafter, a method for replacing the gas in the fuel gas transport pipe 21 shown in FIG. 1 using the gas replacement device 20 of the present invention will be described.

FIG. 4 is a flowchart showing a gas replacement procedure in the pipe of the present invention. The FIG. 5 (a) ~ FIG. 5 (d) is a diagram schematically showing the transition of the gas in the pipe. The procedure shown here is only an example, and it goes without saying that the operation and judgment may be changed. First, the burner valves 24a and 24b are closed by a command from the burner control device (boiler control device), the burner is extinguished and the conditions for gas replacement are adjusted, and then the controller 70 fills the U-shaped water seal valve 80 with water. Perform (step S1). Thereby, it is possible to prevent the fuel gas from flowing in from the upstream side (the side opposite to the boiler) of the U-shaped water seal valve 80 by a gas replacement operation described later.

5 (a) is a diagram schematically showing the status of the fuel gas transport pipe 21 in the burner ignition. During the ignition of the burner, the U-shaped water seal valve 80 is opened by the drain valve 86 provided in the drain pipe 83, and as shown in FIG. There is no water. Therefore, after the burner valves 24a and 24b are closed by a command from the boiler control device (burner control device) and the gas replacement execution condition is satisfied, the control device 70 sets the water supply pipe 81 connected to the U-shaped water seal valve 80. Control is performed so that the water supply valve 84 and the overflow valve 85 of the overflow pipe 82 are opened, and the drain valve 86 provided in the drain pipe 83 is closed. As a result, the U-shaped water seal valve 80 can be filled with water. Further, after completion of water filling with the level switch 88a for detecting the water level, the water supply valve 84 is closed and the small capacity water supply valve 87 that bypasses the water supply valve 84 is opened to constantly supply a small amount of water to prevent the water level from being lowered due to evaporation or the like. . The level switch 88b for detecting the water level is used to warn of completion of draining and a rise in the water level of the U-shaped water seal valve during burner ignition.

  After filling the U-shaped water sealing valve 80 in step S1, the fuel gas is discharged while supplying nitrogen gas into the fuel gas transport pipe 21 in step S2. Nitrogen gas is supplied through a nitrogen gas supply pipe 40 disposed near one end 25 of the fuel gas transport pipe 21. The exhaust of the fuel gas is performed by gas exhaust pipes 30d and 30e disposed in the center of the fuel gas transport pipe 21, and a gas exhaust pipe 30a located between the nitrogen gas supply pipe 40 and the U-shaped water seal valve 80. To do. The supply of nitrogen gas and the discharge of fuel gas are performed by sending control signals from the control device 70 to the nitrogen gas supply valve 41 and the bleeder valves 31a, 31d and 31e, and opening these valves. FIG. 5B shows a situation in which the fuel gas is discharged from the bleeder valves 31 d and 31 e while supplying the nitrogen gas into the fuel gas transport pipe 21.

  In the gas replacement method of the present invention, an inert gas region (a region having a high inert gas concentration) is provided between the combustible gas and air, and the combustible gas and the inert gas are extruded with air in a piston flow manner. Since the pipe is finally replaced with air, in the nitrogen gas replacement operation in step S2, it is not necessary that the fuel gas is replaced with nitrogen gas in the entire region of the fuel gas transport pipe 21. A region having a predetermined length and a high nitrogen gas concentration may be formed. For this reason, the fuel gas may be discharged from the gas discharge pipes 30d and 30e provided in the central part of the nitrogen gas supply pipe 40 and the fuel gas transport pipe 21. The reason why the fuel gas is discharged by using the gas discharge pipe 30a located between the nitrogen gas supply pipe 40 and the U-shaped water seal valve 80 is to prevent the fuel gas from remaining in this portion.

  The supply of nitrogen gas and the discharge of fuel gas, which are nitrogen gas replacement operations, are performed mainly for the purpose of providing a region with a high nitrogen gas concentration in the fuel gas transport pipe 21. It is necessary to suppress typical gas blow-through and mixing of nitrogen gas and fuel gas. Therefore, the supply speed of nitrogen gas and the discharge speed of fuel gas must be such that the nitrogen gas and the fuel gas do not blow through locally in the pipe. Almost simultaneously with the supply of the nitrogen gas and the discharge operation of the fuel gas in step S2, measurement of the combustible gas concentration in the exhaust gas is started in step S3. This is for determining the end point of the nitrogen gas replacement operation. The measurement of the combustible gas concentration is performed by opening the sampling valves 33a, 33d, and 33e, collecting the gas, and guiding it to the gas concentration meter 60.

  In this embodiment, since blast furnace gas is used, by measuring the carbon monoxide concentration using a gas representing the combustible gas as carbon monoxide, this can be used as an index of the combustible gas concentration. An example of the component ratio of blast furnace gas is shown in Table 1. As shown in Table 1, since the concentration of carbon monoxide is high as a combustible gas component contained in the blast furnace gas, it can be used as a representative gas. Moreover, when the gas discharge pipe 30 is arrange | positioned at the upper part of the fuel gas transport piping 21 like embodiment of this invention, the segregation of the gas concentration in piping is made by making gas with a large specific weight into a representative gas. Can be prevented. Further, it is desirable from the viewpoint of safety that a toxic gas is used as the representative gas. Further, as the combustible gas that represents the mixed gas, it is desirable that the combustible gas is easy to measure the concentration and can be measured accurately.

  When combustible gas consists of mixed gas like this embodiment, it is as above-mentioned that a specific gas can be made into representative gas among mixed gas. When the combustible gas is discharged from the lower part of the pipe, a gas having a small specific weight should be used as the representative gas. This is because a gas with a small specific weight tends to stay in the upper part of the pipe. Therefore, when the combustible gas is discharged from the lower part of the pipe and a gas having a small specific weight is detected, it is highly likely that the gas having a large specific weight has already been discharged. Thereby, even if combustible gas is a mixed gas, the density | concentration of combustible gas is reliably detectable.

  The formation of the inert gas region is completed when the carbon monoxide concentration at the sampling valve 33d reaches the control value. The fact that the carbon monoxide concentration at the sampling valve 33d has become the control value is that the carbon monoxide concentration in the vicinity of the nitrogen gas supply pipe 40 is further lower, so that the gap between the nitrogen gas supply pipe 40 and the sampling valve 33d is thereby reduced. It can be confirmed that an inert gas region is formed. In addition, after grasping | ascertaining the nitrogen gas amount required for formation of an inert gas area | region, the time which should supply nitrogen gas, etc., the measurement of a combustible gas density | concentration can also be abbreviate | omitted by performing the operation.

  The concentration of the combustible gas that determines the completion of the formation of the inert gas region can be determined with reference to the combustion range of the fuel gas in the air. In the embodiment of the present invention, as an example of the management value of the completion of the formation of the inert gas region, it can be the time when the carbon monoxide concentration at the sampling valve 33d reaches 5% by volume or less. A state where the carbon monoxide concentration is 5% by volume or less indicates that about 80% by volume of the fuel gas has been replaced with nitrogen gas, and the combustion range in air is also narrowed to 64 to 75% by volume. Further, as the air is supplied to the piping described later, the inert gas region moves in the piping, so that the carbon monoxide concentration at the sampling valve 33d further decreases. From these facts, it can be said that the possibility that the fuel gas remaining in the pipes burns is extremely small.

  The nitrogen gas replacement operation is performed for the purpose of locally replacing the fuel gas in the pipe with nitrogen gas to form a region with a high nitrogen gas concentration. When gas can be supplied and no equipment or device is attached to the pipe, the nitrogen gas replacement operation can be terminated when the formation of the nitrogen gas region is confirmed. However, when the nitrogen gas supply pipe 40 is not connected to the end of the fuel gas transport pipe 21 to be replaced with gas or when equipment or an apparatus is attached to the pipe as in this embodiment. After confirming that the fuel gas in this portion has been sufficiently replaced with nitrogen gas, it is desirable to end the nitrogen gas replacement operation.

  In order to replace the fuel gas in the fuel gas transport pipe 27 located between the nitrogen gas supply pipe 40 and the U-shaped water sealing valve 80 with nitrogen gas, the flow of nitrogen gas for forming an inert gas region in the pipe A different gas flow is required. For this reason, even if the carbon monoxide concentration becomes a control value at the sampling valve 33d and the formation of the inert gas region is confirmed, the fuel gas in the fuel gas transport pipe 27 may not be replaced with nitrogen gas. . In the present embodiment, the remaining fuel gas is discharged while feeding the inert gas toward the larger pipe capacity, using the inert gas region as a stopper during the air replacement operation. For this reason, the nitrogen gas forming the inert gas region moves in the fuel gas transport piping section connecting the gas exhaust pipes 30c and 30d with the air replacement operation described later for supplying air to the piping. The concentration of combustible gas decreases.

  However, since the fuel gas transport pipe 27 does not supply nitrogen gas accompanying the air replacement operation after the nitrogen gas replacement is completed, the combustible gas concentration does not decrease with the air replacement operation. Therefore, it is desirable to sufficiently reduce the combustible gas concentration in this portion. For example, the nitrogen gas replacement can be completed when the carbon monoxide concentration in the sampling valve 33a is 1% by volume or less. When this value is reached, the combustion range of the fuel gas in the air is as narrow as about 73 to 76% by volume, and even if air is mixed into the fuel gas, there is almost no possibility of explosion.

  If the nitrogen gas supply pipe 40 and the air supply pipe 52 are provided at the end of the fuel gas transport pipe 21 and the gas replacement in the pipe can be performed only by flowing the gas in one direction, Needless to say, no operation is required. In piping having the fuel gas transport piping portion 27, after confirming that the formation of the inert gas region and the replacement of this portion with nitrogen gas have been completed, the operation proceeds to the air replacement operation described later. It is desirable.

  Similarly, for parts having a different shape from the fuel gas transport pipe 21 such as the preheater 23, the replacement of the fuel gas is performed by diverting a nitrogen gas replacement operation for forming an inert gas region in the fuel gas transport pipe 21. In addition to the nitrogen gas replacement operation for forming the inert gas region in the fuel gas transport pipe 21, it is desirable to perform an operation for replacing with nitrogen gas separately. This is because the shape is complicated, and the nitrogen gas replacement operation that forms the inert gas region in the fuel gas transport pipe 21 may not be sufficiently replaced with nitrogen gas. The gas replacement operation in the preheater 23 can be performed completely separately from the nitrogen gas replacement operation in which the inert gas region is formed in the fuel gas transport pipe 21, but the inert gas in the fuel gas transport pipe 21. It is efficient to follow the nitrogen gas replacement operation to form the region.

  For example, the carbon monoxide concentration at the sampling valve 33e provided in the gas discharge pipe 30e of the preheater 23 reaches 20% by the nitrogen gas replacement operation for forming an inert gas region in the fuel gas transport pipe 21. Then, if the gas is discharged from the bleeder valve 31e connected to the preheater 23 while supplying the nitrogen gas from the preheater nitrogen gas supply pipe 42 provided in the preheater 23, the inside of the previous fuel gas transport pipe 21 It can be seen that nitrogen gas has reached the preheater 23 by the nitrogen gas replacement operation for forming an inert gas region, and the nitrogen gas replacement operation can be performed efficiently.

In step S4, after it is confirmed that the carbon monoxide concentration at the predetermined position is equal to or lower than the predetermined control value, the supply of nitrogen gas and the discharge of gas are stopped (step S5), and the fuel gas continues. Air is sent into the transport pipe 21. Thereby, the inside of the fuel gas transport pipe 21 can be replaced with air. Air is supplied by opening the bleeder valve 31b of the pipe end 26, opening the air supply valve 53 provided in the air supply pipe 52, and starting the air blower 51 (step S6). The opening operation of the valve and the activation of the air blower 51 are performed based on the control signal of the control device 70. 5 (c) is a diagram showing a state of the gas in the after air replacement pipe schematically.

Simultaneously with the air supply, the gas concentration meter 60 is also switched to the measurement of the oxygen concentration, and after confirming that the oxygen concentration is equal to or higher than a predetermined control value by the sampling valve 33b of the pipe end portion 26 (step S7), the rest The bleeder valves 31a, 31c, 31d and 31e are opened and the gas is discharged (step S8). Figure 5 (d) is a diagram schematically showing a state of the gas in the near the end air displacement pipe. After opening the bleeder valves 31a, 31c, 31d, 31e, after confirming that the oxygen gas concentration is equal to or higher than the control value by the sampling valves 33a, 33c, 33d, 33e (step S9), the air blower 51 is turned on. Stop (step S10) and end the gas replacement operation. Note that a concentration of 20% by volume can be adopted as the oxygen concentration management value in step S7.

  Next, a modification of the embodiment of the present invention will be shown. Unlike the previous embodiment, the concentration of combustible gas and the concentration of oxygen gas contained in the gas collected from each sampling tube are simultaneously detected by a gas concentration meter. Of course, the gas concentration meter for measuring the gas concentration may be a separate gas concentration meter. After the inert gas region is formed, when the inside of the pipe is replaced with air, the combustible gas concentration and oxygen concentration in the gas are measured simultaneously. If it is determined from the measured oxygen gas concentration and the combustible gas concentration that the combustible gas is likely to burn, the air supply valve 53 is closed, the nitrogen gas supply valve 41 is opened, and the nitrogen gas is supplied to the fuel gas transport pipe. 21 is supplied. On the other hand, if it is determined from the measured oxygen gas concentration and combustible gas concentration that the combustible gas is not likely to burn, the air supply is continued.

  Based on the measured oxygen gas concentration and combustible gas concentration, the control device 70 determines that the combustible gas may burn or that the combustible gas does not burn. Based on these determinations, by controlling the opening and closing of the air supply valve 53 and the nitrogen gas supply valve 41, the combustible gas in the pipe can be more safely replaced with air.

  As described above, when replacing the combustible gas in the pipe with air, the gas replacement method in the pipe of the present invention forms an inert gas region between the combustible gas and the air, and the air and the combustible gas. It is characterized in that air is supplied into the pipe and the combustible gas in the pipe is discharged without directly contacting the gas. For this reason, in the operation of replacing the combustible gas with the inert gas and the operation of replacing the inert gas with the air, it is necessary to avoid mixing these gases as much as possible from the viewpoint of efficient gas replacement and safety. is important.

  In order to complete the gas replacement in a short time, it is desirable to supply an inert gas or air at a large flow rate. However, the supplied inert gas or air and the gas in the pipe should be mixed as little as possible. It is necessary to set an appropriate gas flow rate. If the flow rate of the inert gas or air to be supplied is extremely slow, mixing of the gas due to diffusion cannot be ignored, and if the flow rate of the inert gas or air to be supplied is too high, it is easy for gas to blow through in the piping. Therefore, a gas flow rate at which the gas flow in the pipe is an extrusion flow is desirable.

The control value of the combustible gas concentration at the completion of the formation of the inert gas region is preferably determined in consideration of the specific weight of the combustible gas and the specific weight of the inert gas. The specific weight of the blast furnace gas in Table 1 shown in the embodiment of the present invention is 1.34 (kg / m ³ N), the specific weight of nitrogen gas and air is 1.25 (kg / m ³ N), 1.29 (kg / m ³ N), which is close to the specific weight. In such a case, when the inert gas region is formed, it is presumed that the inert gas to be supplied hardly blows through the pipe locally or stays in the upper part or the lower part of the pipe. On the other hand, in the case of replacing gases with greatly different specific weights of gas, for example, when methane gas is replaced with nitrogen gas, the specific weights are 0.72 (kg / m ³ N), 1. Since it is very different from 25 (kg / m ³ N), it is necessary to reduce the concentration of combustible gas, which is the control value for the completion of nitrogen gas substitution, because the gas is easily blown out during the substitution operation and gas is easily mixed. I will.

  This is also true when nitrogen gas is replaced with air, but since air has almost no specific weight difference with nitrogen gas, air does not cause a difference in flow velocity at various points in the cross section of the pipe. If the gas is supplied, it is considered that the possibility of overtaking the mass of nitrogen gas in which air is formed, mixing with combustible gas, and burning or exploding is extremely low.

It is a figure which shows schematic structure of the gas replacement apparatus 20 in piping as one Embodiment of this invention. It is a figure which shows an example of arrangement | positioning of the nitrogen gas supply pipe | tube 40 which comprises the gas replacement apparatus 20 in piping as one Embodiment of this invention. It is a figure which shows an example of arrangement | positioning of the air supply pipe | tube 52 which comprises the gas replacement apparatus 20 in piping as one Embodiment of this invention. It is a flowchart which shows the procedure of the gas substitution method in piping of this invention. Figure 5 (a) ~5 (d) are views for explaining a gas replacement method in the pipe of the present invention is the gas in the pipe that shown schematically. It is a figure which shows the schematic piping system of the conventional general blast furnace gas transport piping.

Explanation of symbols

20 Gas Displacement Device 21 Fuel Gas Transport Pipe 23 Preheater 25 One End of Fuel Gas Transport Pipe 26 Other End 27 of Fuel Gas Transport Pipe 30 Fuel Gas Transport Pipe 30 Located Between Nitrogen Gas Supply Pipe and U-shaped Water Seal Valve 30 Gas Discharge pipe 31 Breeder valve 32 Sampling pipe 40 Nitrogen gas supply pipe 41 Nitrogen gas supply valve 42 Preheater nitrogen gas supply pipe 50 Air supply means 51 Air blower 52 Air supply pipe 53 Air supply valve 60 Gas concentration meter 70 Controller 80 U Water seal valve 84 Water supply valve 85 Overflow valve 86 Drain valve

Claims (11)

A gas replacement method in a pipe for replacing flammable gas in a pipe with air,
An inert gas replacement step in which a part of the combustible gas in the pipe is replaced with an inert gas, and an inert gas region having a high inert gas concentration is locally formed in the pipe;
After forming an inert gas region in the pipe by the inert gas replacement step, air is supplied into the pipe so as not to contact the combustible gas remaining in the pipe, and the supplied air An air replacement step of extruding the inert gas and replacing the combustible gas and the inert gas in the pipe with air;
A gas replacement method in a pipe characterized by comprising: The inert gas region is formed in the inert gas replacement step by discharging the combustible gas from the center and / or the other end of the pipe while supplying the inert gas from one end of the pipe. Done in
2. The gas replacement method in a pipe according to claim 1, wherein the supply of air in the air replacement step is performed from the same end side as the end of the pipe to which the inert gas is supplied. And a confirmation step for confirming that an inert gas region having a predetermined length is formed in the pipe by the inert gas replacement step.
The formation of the inert gas region is confirmed by detecting the concentration of the combustible gas in the axial direction of the pipe and confirming that the concentration of the combustible gas at a predetermined position is equal to or lower than a predetermined concentration. Item 3. A gas replacement method in a pipe according to Item 1 or 2.   The method for replacing a gas in a pipe according to any one of claims 1 to 3, wherein the combustible gas has a specific weight approximate to a specific weight of the inert gas.   The gas replacement method in a pipe according to any one of claims 1 to 4, wherein the combustible gas is a blast furnace gas of a steel mill, and the inert gas is nitrogen gas.   6. The gas replacement method in a pipe according to claim 1, wherein the inert gas and the air are supplied from multiple directions with respect to a cross section of the pipe.   When an apparatus or a device is disposed in the pipe, an operation for replacing the combustible gas in the device or the device with an inert gas is performed separately from the replacement operation in the inert gas replacement step, and then The gas replacement method in a pipe according to any one of claims 1 to 6, wherein an air replacement operation is performed.   When there is another pipe to be replaced with gas in a direction different from the direction in which the inert gas is pushed out by the air in the air replacement process, the other pipe is separate from the replacement operation in the inert gas replacement process. The gas replacement method in a pipe according to any one of claims 1 to 7, wherein an inert gas replacement operation for sufficiently reducing a combustible gas concentration in the inside is performed, and then the air replacement operation is performed.   When the combustible gas is a mixed gas, the combustible gas in the pipe of the inert gas replacement process is discharged from the upper part of the pipe, and the concentration of the combustible gas in the confirmation process is detected by the mixed gas. The gas replacement method for pipes according to any one of claims 3 to 8, wherein a gas having a large specific weight is used as a target.   When the combustible gas is a mixed gas, the combustible gas in the pipe of the inert gas replacement process is discharged from the lower part of the pipe, and the detection of the combustible gas in the confirmation process is performed in the mixed gas. The gas replacement method in a pipe according to any one of claims 3 to 8, wherein a gas having a small specific weight is a target. A gas replacement device in a pipe for replacing flammable gas in a pipe with air,
An inert gas supply means connected to the pipe and capable of supplying an inert gas ;
A gas discharging means connected to the pipe and capable of discharging the gas in the pipe;
A gas concentration detecting means capable of detecting a gas concentration in the pipe;
An air supply means connected to the pipe and capable of supplying air into the pipe;
When the gas concentration detection means detects that the flammable gas concentration at a predetermined position in the pipe is not more than a predetermined value, the air supply means controls the air to be supplied to the pipe, When the gas concentration detection means detects that the flammable gas concentration at a predetermined position exceeds a predetermined value, control means for controlling air supply from the air supply means to the pipe is disabled.
The gas replacement apparatus in a pipe used for the gas replacement method in a pipe according to any one of claims 1 to 10 , characterized by comprising:

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