JP-7857105-B2 - Liquid level detection device for molten salt pumps

JP7857105B2JP 7857105 B2JP7857105 B2JP 7857105B2JP-7857105-B2

Inventors

小山斎
本間陽子
牧坂光浩

Assignees

ＪＦＥプロジェクトワン株式会社

Dates

Publication Date: 20260512
Application Date: 20220111

Claims (7)

A molten salt pump comprising: a pump chamber for drawing in/discharging molten salt diluted with water; an impeller positioned in the pump chamber that draws in/discharges the molten salt by rotating around a rotating shaft that passes through the pump chamber and whose axial direction is upward; a pump chamber mechanical seal provided around the outer circumference of the part in which the rotating shaft passes through the pump chamber; and a liquid level adjustment means for filling the pump chamber with inert gas to push down the molten salt and maintain the liquid level of the molten salt in the pump chamber below the pump chamber mechanical seal, wherein a mixture of sodium nitrite, sodium nitrate, and potassium nitrate is used as the molten salt, and the heating temperature of the molten salt diluted with water is in the range of 400°C to 500 °C , wherein the liquid level detection device for a molten salt pump detects the liquid level of the molten salt in the pump chamber. A rod-shaped common electrode is provided, which is electrically grounded and protrudes downward from above the pump chamber into the interior of the pump chamber. A rod-shaped detection electrode is provided, which protrudes downward from above the pump chamber into the interior of the pump chamber, is connected to the pump chamber via an insulating member, and at least a portion of the surface exposed inside the pump chamber, excluding the lower end, is covered with an insulating layer. The pump chamber is equipped with a liquid level gauge that is electrically connected to the common electrode and the detection electrode, and detects the height of the lower end of the detection electrode in the pump chamber as the liquid level of the molten salt when the common electrode and the detection electrode are electrically connected through the molten salt, A liquid level detection device for a molten salt pump, characterized in that the insulating layer is made of alumina.
The liquid level detection device for a molten salt pump according to claim 1, wherein the insulating layer is a thermal spray film of an insulator coated on the surface of the detection electrode.
The liquid level detection device for a molten salt pump according to claim 1, wherein the insulating layer is an insulating tube, which is a tubular insulator, and the insulating layer covers the detection electrode by inserting the detection electrode through the hollow portion of the insulating tube.
The inner diameter of the insulating tube is larger than the outer diameter of the detection electrode, and a radial gap is provided between the insulating tube and the detection electrode. A cylindrical upper end cap, which is an insulator, is fitted into the gap between the upper end of the insulating tube and the detection electrode to fix the insulating tube to the detection electrode, A cylindrical lower end cap that is fitted into the gap between the lower end of the insulating tube and the detection electrode, thereby fixing the insulating tube to the detection electrode, A liquid level detection device for a molten salt pump according to claim 3, comprising:
The aforementioned detection electrode is A tubular electrode housing tube, which protrudes upward from an opening provided in the pump chamber and communicates with the pump chamber through the opening, is fixed inside the tube via an insulating sleeve, which is an insulating tube. The aforementioned insulating layer is A liquid level detection device for a molten salt pump according to any one of claims 1 to 4, wherein the device is provided in a region where the shortest distance between the outer surface of the detection electrode and the inner circumference of the opening and/or the inner circumference of the electrode housing tube is 20 mm or less.
The aforementioned insulating layer is The liquid level detection device for a molten salt pump according to claim 5, wherein the detection electrode is provided in a region where the shortest distance between the outer surface of the detection electrode and the inner circumference of the opening and/or the inner circumference of the electrode housing tube is 18 mm or less.
The aforementioned insulating layer is The liquid level detection device for a molten salt pump according to claim 5, wherein the detection electrode is provided in a region where the shortest distance between the outer surface of the detection electrode and the inner circumference of the opening and/or the inner circumference of the electrode housing tube is 8 mm or less.

Description

This invention relates to a liquid level detection device for a molten salt pump. Molten salts are salts composed of cations and anions that solidify at room temperature but melt and become molten at temperatures above a certain level. Among molten salts, there are substances called HTS (Heat Transfer Salts) that act as sensible heat transfer fluids, storing/releasing heat without phase change, and are used to heat heat exchangers, reactors, etc. An example of an HTS is a mixture of sodium nitrite, sodium nitrate, and potassium nitrate. This mixture is also called niter, derived from the English name of potassium nitrate crystals. When using molten salt such as HTS as a heat transfer medium, a molten salt pump is required to deliver the HTS from a heating device to the object to be heated or kept warm. A centrifugal pump can be an example of the structure of a molten salt pump. On the other hand, since HTS is a material that solidifies below a certain temperature, the molten salt drawn in/discharged by the molten salt pump that delivers the HTS will come into contact with components of the pump, such as mechanical seals, and solidify below that temperature. In this state, the solidified molten salt can stick to the mechanical seal, causing the drive shaft supported by the mechanical seal to become immobile, or the stuck molten salt can damage the mechanical seal, causing lubricating oil to leak from the damaged area. Therefore, the molten salt pump needs a structure that prevents such components from coming into contact with the HTS. For example, in Patent Document 1, gas is filled into the molten salt pump to pressurize the molten salt downwards, pushing the liquid level of the molten salt inside the pump below the mechanical seal, which is the bearing of the impeller's rotating shaft, thereby preventing the molten salt from coming into contact with the mechanical seal. More specifically, the liquid level of the molten salt is measured using a level switch inside the pump, and the amount of gas filled is adjusted based on the measurement result. The liquid level height is adjusted by maintaining the internal pressure of the pump at a pressure midway between the head pressure between the tank liquid level and the pump and the pump circulating fluid pressure. Japanese Patent Publication No. 2007-231874 This is a schematic diagram of a molten salt circulation system using a molten salt pump equipped with a liquid level detection device according to the first embodiment of the present invention.Figure 1 is a longitudinal cross-sectional view showing the molten salt pump, with the motor and rotating shaft shown in the front view.This is an enlarged view of the vicinity of the detection electrode in Figure 1, with the detection electrode and terminals shown in a side view.This figure shows a molten salt pump equipped with a liquid level detection device according to a second embodiment of the present invention, and corresponds to Figure 3 in the first embodiment. Hereinafter, preferred embodiments of the present invention will be described in detail based on the drawings. First, with reference to Figures 1 and 2, a schematic configuration of a molten salt circulation system 100 using a molten salt pump 104 equipped with a liquid level detection device 1 according to the first embodiment of the present invention will be described. Here, the circulation system 100 illustrates a system in which a water-diluted molten salt, HTS (a type of molten salt), is circulated, and the water-diluted HTS is used to heat and maintain the temperature of the HTS-using equipment 103. As shown in Figure 1, the circulation system 100 includes an HTS tank 101, a molten salt pump 104, HTS usage equipment 103, and an expansion tank 105. The HTS tank 101 stores the water-diluted HTS and is a device that adjusts the temperature and concentration of the water-diluted HTS by heating it or diluting it with water. The HTS tank 101 shown in Figure 1 includes a storage tank 102, a heater 115, a power supply 117, a water injection pipe 119, and a vent pipe 121. The storage tank 102 is a container for storing water-diluted HTS, and in Figure 1, it is illustrated as a horizontally placed cylindrical container with hemispherical ends. The heater 115 is a device for heating the water-diluted HTS and is placed inside the storage tank 102. The heater 115 can use any known heating method as long as it can raise the water-diluted HTS to the desired temperature. In Figure 1, a resistance heating type is illustrated as the heater 115. The power supply 117 is a power supply that drives the heater 115, and if the heater 115 is a resistance heating type, it is the power supply that energizes the heater 115 to heat it. The water injection pipe 119 is a pipe that injects the dilution water used to dilute the water-diluted HTS into the storage tank 102, and in Figure 1, it is connected to the upper end of the storage tank 102. The vent pipe 121 is a pipe that r