JPH0258506B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a shaft seal that prevents leakage of sealed fluid from the rotating shaft of a steam turbine or pump, and which can be used even with chemically active substances. This relates to a sealing method using.

[Prior Art] Conventionally, as shaft seals for steam turbines, for example, contact-type mechanical seals and non-contact-type labyrinth seals that reduce steam pressure have been used. Since mechanical seals are contact type, the sealing pressure is high and it is possible to achieve a state close to complete sealing, but depending on the type of fluid to be sealed, such as steam, the sealing material may corrode, for example.
If the fluid to be sealed is a chemically very active substance such as metallic potassium vapor, there are considerable restrictions such as the inability to use it for a long period of time. On the other hand, since the labyrinth seal is a non-contact type, it is not so severe in terms of corrosion caused by the sealed fluid, but due to its structure, it cannot completely prevent leakage of steam and the like. On the other hand, there are almost no practical examples of opposed visco seals, and the only known examples are Na pump shaft seals for fast breeder reactors and NASA's plans to use them in space power generators. Opposing visco seals are capable of almost "complete sealing" even when the sealed fluid is a chemically very active substance, but the sealing pressure per shaft seal length is small and leakage occurs when the shaft rotation stops. There are drawbacks. When using this opposed visco seal, it has been confirmed that leakage due to rotation stoppage can be sufficiently covered by the seal system and system operating method.

[Purpose of the invention]

The present invention aims to substantially increase the sealing pressure of the opposed visco seal and to follow pressure fluctuations. Originally, with Visco Seal, the sealing pressure can be increased by reducing the gap (clearance) between the rotating shaft and the fixed part (housing) or by increasing the circumferential speed. However, in reality, there are limits and it cannot be made that large. In addition to the above method, a method of increasing the sealing pressure by increasing the pump pressure of the visco seal portion is to cause a portion of the sealant to leak. In this case, it is necessary that the fluid to be sealed and the sealant are the same substance. However, if the sealant can be separated from the fluid to be sealed, they may not be made of the same material. The present invention can be used if this is allowed. The advantage of this method is that by flowing the sealant to the sealed fluid side, the sealing pressure can be several times higher than when no sealant is flowing, so the shaft seal length can be shortened, and the cover gas pressure can be adjusted to a constant pressure. Since only pressurization is performed, there is no need to control the cover gas pressure in response to pressure fluctuations of the fluid to be sealed, and the sealing portion can be cooled by the flow of the sealant.

This method is easiest to control when the shielded chamber is almost evacuated, and is suitable for chemically very active fluids, such as shaft seals of metallic potassium steam turbines. Furthermore, since it can be used satisfactorily even at high temperatures, its range of applications is wide.

[Structure of the invention]

FIG. 1 shows an example of a sealing pressure control system for opposed visco seals in a rotating shaft seal system for a potassium steam turbine. In the figure, the turbine 1 is on the left, the generator (not shown) is on the right, and between them, there are opposing visco seals (visco seals 22 and 24 are threaded in opposite directions to each other and assembled on the rotating shaft, and they are connected to each other along the rotating shaft 16). Visco seals in which the pressure due to the pump action (pump pressure) is applied to the center part are collectively called opposed visco seals, and the center part is called the opposed part 23. This opposed part 23 is usually threaded. ) is provided. Mechanical seals 13, 15 and a bearing (not shown) are provided on the generator side of this opposing visco seal. A shielding chamber 20 is provided between the opposing visco seal and the mechanical seals 13 and 15,
On the other hand, potassium liquid is supplied as the sealant 3 from the liquid tank 4 above the facing part 23 to the visco seals 22 and 24, and the liquid level 5 of the sealant 3 in the liquid tank 4 and the shielding chamber 20 are supplied with a sealant pressurizing system. A cover gas pressure from a cover gas supply source is introduced as follows, and a gas-liquid interface 21 with the cover gas of the shielding chamber 20 exists in the visco seal 22 on the shielding chamber 20 side. The length from the opposing part 23 is determined by the height of the sealant 3 in the liquid tank 4, that is, the balance between the head h of the potassium solution, the cover gas pressure in the liquid tank 4, and the pressure in the shielding chamber 20), To ensure that the sealant 3 leaks to the turbine 1 side, the threaded portion of the left side (turbine 1 side) visco seal 24 is made shorter or the clearance is made larger than the right side visco seal 22 in the figure. The pressure sensor 29 detects the cover gas pressure in the liquid tank 4, which varies depending on the amount of leakage, and processes it in the controller 9, operating the solenoid valve 27 to maintain a constant pressure. (This is a method of keeping the pressure constant). Further, a sealant supply system is added so that the liquid head (head h) of the sealant 3 in the liquid tank 4 is constant. Liquid level 5 in this liquid tank 4
For example, the position is detected by the liquid level gauges A and B in FIG. 1, and the sealant 3 is controlled by the flow rate control valve 7 through the controller 6. The pressure in the shielding chamber 20 is equal to the pressure in the liquid tank 4.
If the internal pressure is kept the same, the position of the gas-liquid interface 21 will not change as the head h remains constant. Further, even if the pressure in the shielding chamber 20 is independently maintained at a constant pressure, the gas-liquid interface 21 does not change because the gas pressure in the liquid tank 4 is constant. However, in this case, the position of the gas-liquid interface 21 is balanced by the pressure of the head h and the shielding chamber 20 and the pressure of the liquid tank 4.

Under the above setting conditions (shaft rotation speed, internal pressure of liquid tank 4, head h: constant), a constant flow rate of sealant 3 leaks. However, this leakage amount changes according to pressure fluctuations on the turbine (sealed fluid) side, so as explained later (Figure 2), below this limit, the sealing pressure will be automatically controlled by itself. . In addition, 8, 11, 18, and 28 are manual valves, 12 is a pressure reducing adjustment valve, 14 is lubricating oil, 19 is a drain, 26 is the shaft seal end on the turbine 1 side, and 25 is the outflow part of the sealant 3. ing.

[Action of the invention]

In FIG. 1, for example, if the pressure in the shielding chamber 20 is pulled by a vacuum pump to almost 0 atmospheres, the position of the gas-liquid interface 21 of the right visco seal 22 of the opposing visco seal is determined by the pressure in the liquid tank 4 and the liquid head (head h). ) becomes stable when it balances the pump pressure of the visco seal 22. In this state, when the pressure of the sealed fluid on the turbine 1 side increases, the leakage of the sealant 3 of the left visco seal 24 decreases, and finally the leakage stops and a gas-liquid interface (not shown) is formed, and the gas-liquid interface faces the This leads to part 23. Therefore, since the gas-liquid interface 21 of the right visco seal 22 is stable until it reaches the facing portion 23, pressure changes in the fluid to be sealed during this period are allowed. Further, when the pressure on the turbine 1 side becomes low and finally reaches 0 atmospheres, the amount of leakage of the sealant 3 to the turbine 1 side becomes maximum. This principle will be explained below.

Figure 2 shows the characteristics with the vertical axis representing the amount of sealant leakage and the horizontal axis representing the pump pressure of the Visco seal. In the figure, N ₁ and N ₂ are the rotational speed of the shaft 16 _.
< _N2 . Point a is the pump pressure when the amount of leakage = 0 when the shaft rotation speed is N ₁ , and is usually called the "shutoff pressure", and when the pump pressure is below this pressure, a gas-liquid interface is formed within the visco seal. Also, sealant 3
When leakage occurs, the pump pressure has a characteristic that increases in proportion to the amount of leakage. Now, the first
Considering the opposed visco seal shown in the figure, it is assumed that the sealant 3 is leaked to the left visco seal 24 in FIG. 1 and is initially at point b in FIG. 2. At this time, it is assumed that the pressures in each part of FIG. 1 are balanced. When the pressure of the fluid to be sealed (turbine 1 side pressure) rises, the pump pressure of the left visco seal 24 must be reduced because the pressure of the opposing portion 23 is kept constant. Looking at this pressure change in Fig. 2, the pump pressure at point d, which corresponds to the amount of sealant leakage at point b, initially moves to point e, and the amount of sealant leakage decreases by that amount, resulting in the pressure at point e. Move to point g corresponding to . In this way, the pressure balance between the opposed visco seals in FIG. 1 is maintained. That is, changes in the amount of sealant leakage result in automatic adjustment of the pressure balance. However, due to this pressure change, the pressure of the sealed fluid increases and the amount of leakage becomes 0, and at point a in FIG. 2, a gas-liquid interface (not shown) occurs. As shown in FIG. 1, the pressure generated in the left visco seal 24 further increases, and when the gas-liquid interface finally reaches the opposing part 23, the pressure balance collapses, and the sealed fluid on the turbine 1 side is transferred to the left visco seal 24. It passes through the opposing part 23 to the liquid tank 4, and also to the right visco seal 22, breaking the sealing state. Therefore, a pressure increase up to this range is allowed as a pressure change in the sealed fluid. On the other hand, when the pressure of the fluid to be sealed decreases, the amount of sealant leakage increases and the pump pressure increases, as shown in Figure 2, and the pressure balance is maintained, so if the capacity of the sealant supply system is sufficient, the sealant leakage will increase. Even if the pressure of the sealing fluid drops to 0 atmospheres, the pressure balance will not collapse. Therefore, within this range of pressure fluctuations, a much greater sealing pressure can be created than in the case where the sealant 3 does not leak. However, the present invention requires a supply system or circulation system for the sealant 3. When supplying this sealant 3, in the example shown in FIG. 1, a liquid level controller 6 is required to keep the liquid head (head h) in the liquid tank 4 constant. In this liquid level sensor, electrode rods for detecting upper and lower parts are shown by A and B in Fig. 1, but liquid level detection must be done in other ways depending on the type of sealant 3. .

Next, the pressure of the cover gas in the liquid tank 4 and the shielding chamber 20 will be described.

In FIG. 1, in order to keep the pressure in the liquid tank 4 constant, the pressure is detected by a pressure sensor 29,
The signal is judged and processed by the controller, and the electromagnetic valve 27 is operated to control the pressure inside the liquid tank 4. On the other hand, when the shielding chamber 20 maintains a constant pressure instead of 0 atmospheres, the pressure is detected by the pressure sensor 30, judged and processed by the controller 9, and the solenoid valve 10 or 17 is operated to shield the chamber. The pressure in the chamber 20 is kept constant. At this time, as for the pressure relationship in the liquid tank 4 and the shielding chamber 20, either the pressures in both parts are made equal (this method is not shown, but the pressure control becomes one series, making the control easier), or Should the pressure in tank 4 be made higher?
can be lowered. However, as shown in the figure, there is a method that requires two series of control and is more complicated. In any case, the gas-liquid interface 21 inside the right visco seal 22
The liquid tank 4 and the shielding chamber 20 are
The pressure inside must be controlled.

The explanation so far has been made under the condition that the shaft rotation speed is constant, but when the shaft rotation speed changes, that is, when there are large load fluctuations, starting and stopping operations, etc., the cover gas pressure must be controlled. No.
To do this, the rotation speed sensor (tachometer) 35 shown in FIG. What is necessary is to control the pressure of the cover gas inside and always maintain it at the pressure of the opposing part 23 corresponding to the number of rotations. However, since the relationship between the shaft rotation speed that keeps the position of the gas-liquid interface 21 constant and the pressure of the opposing part 23 is uniquely determined by the shape and dimensions of the visco seal, the sealant temperature, the position setting of the gas-liquid interface, etc., the controller 9 must be memorized in advance.

The present invention relates to a rotary shaft seal, and is not limited to turbine steam. For example, when the inside of the turbine casing 2 in FIG. Can be sealed.

FIG. 3 shows another example of a method for causing the sealant 3 to flow out to the sealed fluid side, similar to that shown in FIG. In this case, a pressure sensor 30 detects pressure fluctuations in the facing portion 23, and the controller 9 judges and processes the pressure fluctuations to operate an electromagnetic pump 32 to keep the pressurizing force constant.The electromagnetic pump 32 is used as a sealant supply system. It constitutes both parts of the sealant pressurizing system. In the figure, an accumulator 31 absorbs pressure noise in this system. In this case, the liquid tank (service tank: 3
The head of the interface in 4) does not need to be constant, unlike in FIG. 33 is a manual valve.

〔Effect of the invention〕

The present invention has the advantage that it can be applied even in cases where the pressure difference between the sealed fluid and the sealed fluid is large and sealing cannot be achieved with only the pump pressure of the opposed visco seal. It has advantages such as relatively easy adjustment of the head, and because the sealant flows out to the sealed fluid side, it is easy to cool the heat transmitted to the seal portion and the shaft.

[Brief explanation of the drawing]

Fig. 1 is a piping diagram showing an example of the shaft sealing device used in carrying out the present invention, Fig. 2 is an explanatory diagram showing the pressure characteristics of the Visco seal, and Fig. 3 is a piping diagram showing another example of the shaft sealing device. It is. 1... Turbine, 2... Turbine casing,
3...Sealant, 4...Liquid tank, 5...Liquid level, 6
...Liquid level controller, 7...Flow rate control valve, 8, 11,
18, 28, 33...Manual valve, 9...Controller, 1
0, 17, 27... Solenoid valve, 12... Pressure reducing adjustment valve, 13, 15... Mechanical seal, 14...
Lubricating oil, 16... Rotating shaft, 19... Drain, 20
... Shielding chamber, 21 ... Gas-liquid interface, 22 ... Right side Visco seal, 23 ... Opposing part, 24 ... Left side Visco seal, 25 ... Outflow sealant, 26 ... Turbine side shaft seal part end, 29, 30... Pressure sensor, 31... Accumulator, 32... Electromagnetic pump, 34... Service tank, 35... Rotation speed sensor.

Claims (1)

[Claims] 1 A pair of visco seals with threads cut in opposite directions are combined axially on the same rotating shaft, and sealant is supplied from a sealant supply system to the opposing parts of both visco seals, and the sealant is applied to the visco on the side of the fluid to be sealed. The sealant is applied to the sealant so that the sealant leaks from the seal, and the fluctuation in the pressure applied by the sealant pressure system to the sealant in the facing part due to the sealant leakage is detected, and based on the detected value, the sealant is applied so that the sealant pressure in the facing part is constant. A sealing method using a visco seal characterized by controlling a pressure system and a sealant supply system.