JPS6130614B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a piping system that mixes two different fluids and supplies the mixed fluid to a user, even if one fluid is allowed to flow into the other fluid. This invention relates to a backflow prevention method capable of quickly detecting signs of a risk of backflow and quickly, reliably, and automatically preventing backflow when backflow should not be allowed, and a device for implementing this method. Regardless of whether the target fluid is gas or liquid, fluids A and B, which are different from each other, are introduced into a mixing device, mixed at an appropriate mixing ratio, and the mixed fluid is supplied to the user. If fluid A is fluid B
Of course, there is no problem with fluid B getting mixed into fluid A, but there are cases where fluid B should not be allowed to flow back into fluid A. For example, even if the fluids are of the same type, fluid A is strictly required to be highly pure, while fluid B does not need to be so strictly purified, or They are completely different types, and they react with each other, so even if fluid A mixes with fluid B, it will not have a big effect, but if fluid B flows back into fluid A, it will have a slight effect. This is the case when even a small amount can cause a violent reaction and cause a major accident. By the way, in general, when an unexpected trouble occurs in a piping system at the supply source side or at the end of use, abnormal pressure fluctuations occur in the piping, and due to this, the above-mentioned problems may occur. There is a risk of causing an irreversible backflow phenomenon. Conventionally, as a measure to prevent such backflow, a check valve having a mechanical structure and function has been installed in the immediate vicinity of the pipe for fluid A led to the mixing device. However, even if check valves with such mechanical structures have a certain degree of backflow prevention effect, they are nearly impossible to completely prevent leakage, and their operation is slow, so that when there are signs of backflow, Therefore, it was impossible to detect this problem as soon as possible and expect to prevent it from occurring. There are also manual valves that can almost completely prevent backflow, but with such valves it is impossible to prevent backflow by instantaneous action in the event of an unexpected accident. The present invention has been made in view of the above-mentioned conventional problems, and has the purpose of solving the problems. The piping system of A is controlled to high pressure and the piping of fluid B is controlled to low pressure, and when the piping pressure of fluid A drops below a predetermined pressure, or when the piping pressure of fluid B rises above a predetermined pressure, or When the differential pressure between these two pipes drops below the lower limit of a predetermined range, these phenomena are detected and the check valve mechanism is activated based on the detection signal to quickly and reliably prevent backflow. A method and apparatus thereof are provided. Below, as an example of implementing the present invention, regarding the _N2 gas piping system that is often used in steel works,
This will be explained with reference to the drawings. A large amount of _N2 gas is used in steel mills, and some of the _N2 gas is of high purity, such as that used as the internal atmosphere of furnaces for annealing coils of steel strips and continuous heat treatment of steel strips. There are some materials that require relatively low purity, such as those used in the operation of converters and blast furnaces. These are delivered to the point of use through separate piping systems. In Figure 1, A is high-purity _N2
1 is the feeding side piping of A, B is low purity N ₂ gas, and 2 is the feeding side piping of B. The amount of _N2 gas used in steel plants is overwhelmingly larger than that of A.
may cause a supply shortage. In such a case, a method is used in which a part of A is diluted and mixed into B to compensate for the shortage of B supply. That is, a mixing device 6 is provided, the B side pipe 2 is connected to the mixing device 6, and the connecting pipe 4 is branched from the branch part 5 of the A side pipe 1 and connected to the mixing device 6.
A and B are mixed in the gas chamber, and the mixed gas C is distributed to each workplace through the mixing pipe 3. In this case, the amounts of A and C used at the distribution destination of the A-side piping 1 and the distribution destination of the mixing piping 3 are not necessarily constant;
Rather, it is normal for the use to be intermittent or the amount used to fluctuate, and it is not possible to always secure a constant supply amount from the supply source. Therefore, the pressure in the A-side pipe 1 may drop abnormally, or the pressure in the B-side pipe 2 and the mixing pipe 3 may rise abnormally. When such a phenomenon occurs, low-purity _N2 gas flows through the connecting pipe 4.
This will flow back into the side pipe 1, reducing the purity of A. In such a case, if A is used, for example, as an annealing atmosphere gas for a steel strip coil at the distribution destination of the A-side piping 1, the quality of the steel strip will deteriorate and its commercial value will be nullified. Such accidents may occur. In the present invention, in order to prevent the above-mentioned accidents,
Basically, two measures were taken. That is, the first means is
The pressure in the A-side pipe 1, especially the pressure upstream of the branch part 5 of the connecting pipe 4, is always maintained higher than the pressure in the B-side pipe 2 by a predetermined differential pressure, and both the pipes 1,
2 to each predetermined pressure,
During steady state, this maintains a state in which backflow is difficult to occur. The second means is to provide a check valve mechanism 19 in the connecting pipe 4, and when the pressure in the A side pipe 1, the pressure in the B side pipe 2, or the differential pressure between both pipes 1 and 2 shows an abnormal value, these Check valve mechanism 1 based on the detection signal
9 is operated to interrupt and insulate the flow of A and B in the connecting pipe 4. First, the first means will be explained. A high pressure control mechanism 7 is installed in the A-side piping 1 to control the pressure on the upstream side. This high pressure control mechanism 7 includes a pressure detection section 10 that detects the pressure inside the A side piping 1;
Pressure control valve 9 that adjusts the feed rate of
It consists of a pressure regulator 8 that adjusts the opening degree of the valve, and is also equipped with a pressure indicator _P1 . The pressure detection unit 10 is provided to detect the pressure on the upstream side of the A-side piping 1 from the branching part 5 where the communication pipe 4 is branched, and the detected value Ph is input to the pressure regulator 8. Ru. A predetermined pressure value Ps ₁ is set in advance in the pressure regulator 8 so that the pressure in the A-side pipe 1 is maintained at a high pressure with a predetermined differential pressure with respect to the pressure in the B-side pipe 2. Therefore, this set pressure value Ps ₁ and the input detection value Ph are compared, and based on the obtained deviation value, an operating signal S ₁ for the pressure regulating valve 9 is output, and the pressure regulating valve 9 receives the operating signal S ₁ controls the opening/closing direction and degree of opening/closing. As mentioned above, there is a fluctuation in the amount of mixed gas C used at the distribution destination of the mixing pipe 3, and if the amount used increases, the pressure in the A side pipe 1 tends to decrease under the influence of this (in this case, The pressure in the B-side pipe 2 also shows a decreasing tendency, but this will be explained later.) This decreasing pressure Ph is input to the pressure regulator 8, and the pressure regulator 8 compares it with the set pressure value Ps ₁ . Based on the negative deviation value, a signal _S1 is issued to operate the pressure regulating valve 9 in the direction of closing it. In this case, the amount of A sent from the A-side pipe 1 to the distribution destination is limited, and the pressure inside the A-side pipe 1 is controlled so as to recover from the drop. On the contrary, in the recovery control of the tendency of pressure increase in the A-side pipe 1 when the usage amount of the mixed gas C decreases, the operation of the pressure regulating valve 9 is in the opening direction based on the positive deviation value. In this way, the detected pressure Ph in the A side pipe 1 is the set pressure.
Controlled to match Ps ₁ . On the other hand, a low pressure control mechanism 11 is installed in the B side piping 2. Similarly to the high pressure control mechanism 7, the low pressure control mechanism 11 is composed of a pressure regulator 12, a pressure regulating valve 13, and a pressure detecting section 14, and is also provided with a pressure indicator _P2 . If the amount of mixed gas C used increases at the distribution destination of the mixing pipe 3, the pressure in the B-side pipe 2 tends to decrease due to this influence. The detected pressure Pl, which is on the decline, is input to the pressure regulator 12, and the pressure regulator 12 sends a signal _S2 to open the pressure regulating valve 13 based on the negative deviation value compared with the set pressure _Ps2 . emits. Here, the set pressure Ps ₂ is a value lower than Ps ₁ set in the pressure regulator 8 of the high pressure control mechanism 7 by a predetermined differential pressure. Then, the amount of B fed to the mixing device 6 increases, and the control is performed so that the pressure drop in the B-side pipe 2 is recovered. On the contrary, in the recovery control of the tendency of pressure increase in the B-side pipe 2 when the usage amount of the mixed gas C decreases, the operation of the pressure regulating valve 13 is in the closing direction based on the positive deviation value. In this way, the detected pressure Pl in the B side pipe 2 is also set to the pressure Ps ₂
controlled to match. The pressure value Ps ₁ set in the pressure regulator 8 of the high pressure control mechanism 7 and the pressure regulator 12 of the low pressure control mechanism 11
An appropriate pressure difference is provided between the pressure value Ps ₂ and the pressure value Ps 2 set at There should be a pressure difference equal to the set pressure difference between the pressure in the B-side pipe 2 and the pressure in the B-side pipe 2, but this needs to be confirmed. Therefore, the conduit 16 is drawn out from the A-side pipe 1, and the conduit 17 is also drawn out from the B-side pipe 2, and these are connected to the differential pressure detector 15 so that the actual differential pressure value can be determined. . Note that a comprehensive pressure control device 30 is used to comprehensively control the high pressure control mechanism 7 and the low pressure control mechanism 11.
The integrated pressure control device 30 instructs the set value Ps ₂ to the low pressure control mechanism 11, and the differential pressure detector 15
The differential pressure signal Sd detected by the integrated pressure control device 30
This differential pressure signal value Sd and low pressure control mechanism 1
The set value Ps ₁ to the high pressure control mechanism 7 may be specified in relation to the set value Ps 2 to ₁ . Next, the second means, that is, the check valve mechanism 19 and its control will be explained. The check valve mechanism 19 is installed in the communication pipe 4 constructed from the branch part 5 of the A-side pipe 1 to the mixing device 6, and the upstream cutoff valve 20 is provided near the branch part 5, and the upstream cutoff valve 20 is provided near the mixing device 6. It is constituted by a downstream cutoff valve 21 and a release valve 22 that is branched from a midpoint 23 between the installation position of the upstream cutoff valve 20 and the installation position of the downstream cutoff valve 21. While the mixing device 6 is in steady operation, the upstream cutoff valve 20 and the downstream cutoff valve 21 are in an open state, and the necessary amount of fluid A flowing through the A-side pipe 1 is supplied to the mixing device 6. Diffusion valve 22 during steady operation
is kept closed. Such steady operation is performed by maintaining a predetermined differential pressure between the pressure in the A-side pipe 1 and the pressure in the B-side pipe 2, and maintaining the pressure in the A-side pipe 1 at a higher pressure. This is when the B-side pipe 2 is controlled to a low pressure. However, A
If the pressure in side pipe 1 drops below a predetermined pressure value, the pressure in B side pipe 2 rises above a predetermined pressure value, or the differential pressure between both pipes 1 and 2 becomes a predetermined difference. When the pressure decreases below the pressure value and there is a risk that fluid B or mixed fluid C may flow back toward the A-side pipe 1, the upstream shutoff valve 20 and the downstream shutoff valve 21 are closed, and the relief valve 22 is opened to prevent communication. Fluid accumulated between the upstream cutoff valve 20 and the downstream cutoff valve 21 in the pipe 4 is dissipated outside the communication pipe 4, and is connected to the A-side pipe 1, the mixing device 6, and the B-side pipe 2 or mixing pipe 3 connected thereto. The space between them is cut off. When fluids A, B and mixed fluid C are gases and the upstream shutoff valve 20 and downstream shutoff valve 21 are butterfly valves with a normal structure, fluid leakage must be completely prevented. is normally impossible, and therefore it is often impossible to completely prevent fluid B and mixed fluid C from flowing back into the A-side piping 1.
In the case of the present invention, since the discharging valve 22 is provided branching from the intermediate point 23 of the communication pipe 4, the upstream cutoff valve 20
Even if the downstream cutoff valve 21 leaks, all of the leaked fluid is radiated to the outside of the communication pipe 4 through the diffusion valve 22, so it is possible to completely prevent the above-mentioned backflow. It is. Pressure of A side piping 1 and B side piping 2 and both piping 1, 2
The operation of the check valve mechanism 19 when there is a possibility that fluid B or mixed fluid C may flow back toward the A side piping 1 due to fluctuations in the differential pressure between them is the operation issued by the backflow prevention control section 18. This is done by the signal Sc.
The backflow prevention control unit 18 includes a high pressure regulator 8 that controls the pressure inside the A side piping 1, a low pressure regulator 12 that controls the pressure inside the B side piping 2, and the pressure inside the A side piping 1 and the B side piping 1.
Differential pressure detector 1 that detects the differential pressure with the internal pressure of side pipe 2
5, the signals Sh, corresponding to the respective detected values,
Sl and Sd are entered. The backflow prevention control unit 18 is set with a lower limit value of the internal pressure of the A-side pipe 1, an upper limit value of the internal pressure of the B-side pipe 2, and a lower limit value of the differential pressure between the two pipes 1 and 2. signal
Sh, Sl, and Sd are constantly compared with their respective set values. The backflow prevention control unit 18 causes the value of the signal Sd to change to a value corresponding to the value of the signal Sd when the value of the signal Sh decreases below the corresponding set value and when the value of the signal Sl increases to the corresponding set value or more. When the value falls below the set value, it is determined that this is abnormal, and an operation signal Sc for the check valve mechanism 19 is issued, the upstream cutoff valve 20 and the downstream cutoff valve 21 are closed, and the release valve 22 is opened. . All of these valve operations may be performed at the same time, but the operation of the relief valve 22 may be delayed by a short period of time required for the upstream cutoff valve 20 and the downstream cutoff valve 21 to be completely closed. The purpose of the present invention is to prevent the fluid B in the B-side piping 2 from flowing back into the A-side piping 1. The higher the pressure in the side pipe 1 is made, that is, the higher the set value is given to the pressure regulator 8 of the high pressure control mechanism 7, the greater the backflow prevention effect becomes, but the higher the pressure, the higher the equipment cost. Normally, it is necessary to consider the pressure balance with other fluid destinations. Taking these circumstances into consideration, in the embodiment of the present invention, the control pressure of the A-side pipe 1, the control pressure of the B-side pipe 2 during steady operation,
The control differential pressure between both pipes 1 and 2 and the reference pressure for determining that the signals Sh, Sl, and Sd input by the backflow prevention control unit 18 are abnormal are set to the values shown in Table 1, respectively. We are getting good results.

[Table] As described above, in the two piping systems provided to mix mutually different fluid A into fluid B, the pressure in the A side piping is lowered by a predetermined differential pressure than the pressure in the B side piping. If any of the pressure in the A-side pipe, the pressure in the B-side pipe, or the differential pressure between the two pipes deviates from the abnormality judgment reference value, the The upstream shutoff valve, the downstream shutoff valve, and the relief valve installed at the midpoint between the two shutoff valves are operated to automatically and completely shut off the space between the two pipes. Therefore, if there is a risk that fluid B may flow back to fluid A side, this can be detected quickly and the backflow can be quickly and reliably prevented.
Therefore, accidents and economic losses caused by backflow can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a control system block diagram showing a basic embodiment of the present invention. 1... A side piping, 2... B side piping, 3... Mixing pipe, 4... Connecting pipe, 6... Mixing device, 7... High pressure control mechanism, 11... Low pressure control mechanism, 15... Difference Pressure detector, 18... Backflow prevention control unit, 19... Check valve mechanism, 20... Upstream cutoff valve, 21... Downstream cutoff valve, 22... Discharge valve, 30... Comprehensive pressure control device.

Claims (1)

[Claims] 1 In a two-system piping system in which a connecting pipe is installed between the two in order to mix fluid A with fluid B, a predetermined differential pressure is maintained between the A-side piping and the B-side piping. The pressure in the A-side piping is controlled to be high and the pressure in the B-side piping is controlled to be low, so that if the pressure in the A-side piping drops below a predetermined pressure, the pressure in the B-side piping will rise above the predetermined pressure. In either case, when the differential pressure increases or when the differential pressure decreases below a predetermined pressure, a check valve mechanism provided in the connecting pipe is operated based on a signal that detects these cases. , 2 above
A method for preventing backflow between two fluid pipes, characterized by completely blocking the system pipes. 2 In a two-system piping system in which a connecting pipe is installed between the two in order to mix fluid A with fluid B, in order to maintain a predetermined differential pressure between the A-side piping and the B-side piping, a A high pressure control mechanism is provided, a low pressure control mechanism is provided in the B side piping, and a differential pressure detector is provided to detect the differential pressure between the A and B piping. A check valve mechanism consisting of a discharging valve branching from a point is provided, and each pressure signal from the high pressure control mechanism, low pressure control mechanism, and differential pressure detector is inputted, and when the signal from the high pressure control mechanism becomes below a predetermined value, If the signal from the low pressure control mechanism exceeds a predetermined value or the signal from the differential pressure detector falls below a predetermined value, a backflow prevention control section is provided that issues a signal to operate the check valve mechanism. A backflow prevention device between two fluid pipings.