JPH0511235B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a free liquid level type vertical shaft pump in which the free liquid level is covered with a cover gas, such as a pump that handles high-temperature liquid metal, such as liquid metal sodium. Regarding the outer torso.

[Prior Art] As is well known, a free liquid level vertical shaft pump has an outer shell, and has a structure in which a submerged bearing that pivotally supports a rotating shaft is fixed to the outer shell. On the other hand, high-temperature liquid metals, such as liquid metallic sodium, have a low viscosity like water at high temperatures and a large heat capacity, so they have reached the stage of practical use as coolants for fast breeder reactors.

By the way, liquid metallic sodium is scientifically extremely unstable and reacts violently with water vapor and oxygen in the atmosphere, so in containers, pumps, purifiers, etc. that handle it, its free liquid surface is usually called the cover gas. Surrounded by inert gas.

In such devices that handle liquid metal sodium, the space filled with cover gas has a double cylindrical shape with a closed top. For example, the pump has a double structure, as seen between the inner and outer shells of the pump, or between the pump shell and the through hole in the installation floor. Therefore, the cover gas causes natural convection between the double structures, causing deformation of equipment such as the pump body due to thermal expansion.

This deformation phenomenon will be explained using an example of a pump shown in FIGS. 1 and 2. The pump outer shell 1 is arranged with a distance D from the through hole 3 of the installation floor 2 (for example, a roof slab of a nuclear reactor), and there is an upper part between the outer peripheral surface of the outer shell 1 and the wall surface of the through hole 3. An upper end closed annular gap 5 is formed which is closed with a lid body 4.
This gap 5 is filled with cover gas 7. In this state, the cover gas heated by the liquid metal sodium 6 rises as shown by arrow A. On the other hand, since the upper part where the lid body 4 is provided is much lower in temperature than the surface of the liquid metal sodium 6, the cover gas is cooled in the upper part in turn and is placed at a proper place in the gap 5 as shown by arrow B. descend. In this way, the phenomenon of natural convection of the cover gas occurs. If there is an upward flow in this way, a downward flow will also occur, and therefore, multiple pairs of circulating flows will flow through the gap 5.
formed in place. Therefore, the pump outer shell 1 that is in contact with the flow of the cover gas becomes high or low temperature, and the temperature difference may be 100° C. or more. For this reason, the pump outer shell 1 undergoes thermal expansion deformation and bends as shown by the chain line 11. As a result, the center line O of the rotating shaft 10 is displaced to position _O1 . Then, the submerged bearing 8 fixed to the outer shell 1 is also displaced, causing a misalignment between the pump rotating body including the impeller 12 and the bearing 10, which induces galling of the bearing 8.

Measures to eliminate galling of bearings or inconveniences in pump drive have been proposed in the past; for example, Japanese Utility Model Publication No. 17114/1987 discloses a system in which an impeller for stirring the cover gas is attached to the pump rotating shaft. ing. In this known example, since the cover gas is stirred by the impeller, natural convection is prevented, but the impeller is expensive and the power cost for driving the pump increases. Also, in Japanese Patent Application Laid-open No. 55-96395,
A technique for installing a baffle plate to prevent convection between the inner and outer body parts is shown. According to this technique, a large number of baffle plates are provided, which increases the cost, and furthermore, vapor of liquid metal sodium adheres to these baffle plates.
Cleaning during inspection is extremely difficult as it is contaminated with radioactivity.

Japanese Utility Model Publication No. 56-38234 discloses a technique in which a spiral groove is provided in the welded part of the internal body of the pump, but since the spiral groove is provided in the liquid, uneven flow of high-temperature fluid can be prevented. However, circumferential temperature differences due to natural convection cannot be prevented.

Furthermore, a technique for wrapping a flexible material such as metal wool around the pump body in order to prevent natural convection is disclosed in JP-A-54-1403, but as mentioned above, cleaning during inspection is difficult. be.

Further, Japanese Patent Application Laid-Open No. 12210/1983 discloses a technique in which a spiral heat shield plate forms a flow path for upward flow and downward flow due to natural convection. However, although this known technique makes the total vertical thermal expansion uniform in the circumferential direction, the cover gas does not necessarily flow in this way and is not sufficient to prevent distortion from occurring.

[Problems to be Solved] Therefore, an object of the present invention is to provide an outer shell of a free surface type vertical shaft pump that can prevent thermal deformation due to cover gas and is easy to clean during inspection.

[Means for Solving the Problems] According to the present invention, in the outer shell of a free liquid level vertical shaft pump that handles high-temperature pumped liquid whose free liquid surface is covered with a cover gas, the outer shell exposed above the liquid surface is A wire body is spirally wound around the outer periphery, a thin-walled cylinder is arranged in close contact with the wire body, a lower end of the thin-walled cylinder is connected to a bellows fixed to the outer body, and the wire body is made up of tubes.

[Operations and Effects of the Invention] As mentioned above, natural convection circulation flow inevitably occurs,
A thin-walled cylinder such as the pump shell itself generates a temperature difference. However, according to the present invention, the wire body is spirally wound around the outer periphery of the pump outer body, and the thin-walled cylinder is arranged in close contact with the wire body, so that the thin-walled cylinder receives from the convective cover gas. For heat,
Only a small amount of heat conducted through the wire bodies in contact with each other and heat transmitted by convection of the cover gas existing between the spirally wound wire bodies are transferred to the outer shell. Moreover, convective heat transfer between the wire bodies to the cover gas is natural convection, but since the vertical distance is limited by the wire bodies, the development of natural convection is hindered. Furthermore, since the cover gas, which is locally heated by the spiral structure of the wire body, spirals upward in a spiral manner, heat is evenly transmitted to the outer shell without locally heating the outer shell. Therefore, no temperature difference occurs in the circumferential direction of the outer shell, and thermal deformation is suppressed.

Further, according to the present invention, since the cylinder constituting the shell is thin, thermal stress is small, and therefore, no undue stress is applied to the outer shell.

[Example] An example of the present invention will be described below with reference to FIGS. 3 and 4. Note that the same parts as in the conventional example shown in FIGS. 1 and 2 are given the same reference numerals, and redundant explanation will be omitted.

3 and 4, a wire body, that is, a tube 20 in the illustrated embodiment, is spirally wound around the outer periphery of the pump outer body 1, which also functions as a spacer. A thin cylinder 21 constituting a heat insulating shell is disposed in close contact with this spirally wound tube 20 so that the outer shell surrounds it. The lower end of the thin cylinder 21 is connected to a bellows 22, and the end of the bellows 22 is tightly fixed to the outer periphery of the outer shell 1 by means such as welding 23.

During operation, the cover gas 7 heated by the surface S of the liquid metal sodium 6 rises and descends through the gap 5 between the thin cylinder 21 and the wall of the through hole. Therefore, a temperature difference occurs in the thin cylinder 21 in the circumferential direction. However, since this thin cylinder has a small thermal stress, its thermal deformation does not extend to the outer shell 1. The heat transferred to the outer shell 1 is the conduction heat transferred through the tube 20 as described above, and the heat due to the convection of the cover gas existing in the gap 5, but the conduction heat is a small amount, and moreover, Since the vertical distance H between the tubes 20 is small, the development of convection is hindered, and furthermore, due to the spiral structure of the tubes 20, heat is evenly transferred to the outer shell 1. Therefore, the outer shell 1 will not be deformed due to local thermal stress.

[Effects of the Invention] As described above, the present invention provides the following excellent effects.

(i) By combining a spiral tube and a thin cylinder, the temperature of the cover gas is hardly transmitted to the pump outer body with a simple structure.

(ii) Since the vertical distance between the thin-walled cylinder and the pump shell is limited by the tube, the development of natural convection between them is hindered.

(iii) Even if the cover gas is locally heated during this time, the outer shell is evenly heated while it is swirling upward.

(iv) The spiral tube makes it difficult for heat outside the thin cylinder to be transferred to the pump outer body, and even if localized heating occurs, it can be heated evenly by natural convection as described above.

(v) No strain stress is applied to the pump outer shell due to the thin cylinder.

(vi) As a result, no temperature difference occurs in the circumferential direction, and thermal deformation of the pump outer shell is suppressed.

(vii) Cleaning work is easy because the surfaces of the parts are smooth.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams for explaining the flow of cover gas due to natural convection in a free-level vertical pump, with Figure 1 being a transparent perspective view, Figure 2 being a sectional view, 3 and 4 are views showing one embodiment of the present invention, in which FIG. 3 is a sectional view corresponding to FIG. 2, and FIG. 4 is a sectional view of the main part thereof. 1...Outer body of free liquid level vertical shaft pump, 6...High temperature pumped liquid (liquid metal sodium), 7...Cover gas, 2
0... Wire body (tube), 21... Thin cylinder, 22...
Bellows.

Claims (1)

[Claims] 1. The outer shell of a free liquid level vertical shaft pump that handles high-temperature pumped liquid whose free liquid surface is covered with a cover gas is equipped with a wire body spirally wound around the outer circumference of the outer shell exposed above the liquid surface, A thin-walled cylinder is disposed in close contact with the wire body, a lower end of the thin-walled cylinder is connected to a bellows fixed to the outer body, and the wire body is composed of a tube. Outer body of liquid level vertical shaft pump.