JPH0631844B2 - Microwave heating device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a microwave heating device adapted to evaporate and concentrate a liquid by using microwaves.

[Prior Art] Conventionally, a liquid evaporating and concentrating device seals a liquid in a tank made of metal and uses steam or an electric heater or the like as a heat source to pass heat from the outside of the tank through a wall of the tank. It was conducted inside, and the liquid in the tank was heated and evaporated.

In this case, there is no particular problem when the composition of the liquid to be evaporated and concentrated is controlled, but when radioactive waste liquids, etc. that come out from nuclear facilities are targeted, various miscellaneous substances are dissolved in the waste liquid. In addition, the liquid composition may not be controlled, and when evaporating and concentrating the waste liquid with the above-mentioned conventional evaporative concentrator, a dissolved substance precipitates in the tank, and the deposited substance grows and adheres. Then, there is a problem that the evaporation efficiency is lowered.

[Object of the Invention]

The present invention has been made in view of the above points, and an object thereof is to prevent the growth and adhesion of precipitates even when evaporating and concentrating a radioactive waste liquid, thereby reducing the evaporation efficiency thereof. It is an object of the present invention to provide a microwave heating device which is prevented.

[Structure of Invention]

To this end, the present invention provides a microwave irradiator having a microwave radiating port and a dielectric for sealing at least the microwave radiating port of the microwave irradiating device in an apparatus for evaporating and concentrating a liquid in a tank by using microwaves. A microwave radiating section is configured with the body cover, and the microwave radiating section is inserted from the upper part of the tank to a position where it is immersed in the liquid.

〔Example〕

Examples of the present invention will be described below. FIG. 1 shows a microwave heating apparatus of the embodiment. Reference numeral 1 is a metal tank, and a discharge port 1a to which a valve (not shown) is attached is provided on the bottom. Reference numeral 2 denotes a lining material made of a chemically stable resin such as Teflon lined inside the tank 1 or a porcelain such as alumina. Reference numeral 3 denotes a metal upper lid for sealing the upper portion of the tank 1, in which the supply pipe 4, the vapor vent pipe 5, and the tank 1 are placed.
A level meter 6 for measuring the liquid level of the liquid inside and a microwave irradiation preventive body 7 made of metal are attached. A lining material similar to that of the tank 1 may be provided on the inner surface side of the upper lid 3.

A microwave irradiation unit 10 including a microwave irradiation unit 8 made of metal and a dielectric cover 9 covering the side surface and the bottom surface thereof is attached to the microwave irradiation prevention unit 7.

The microwave irradiator 8 is composed of a microwave waveguide or a cavity resonator, and a plurality of openings 8a as microwave radiating ports are formed discontinuously or continuously on the lower side wall thereof. Further, the dielectric cover 9 is made of a resin such as polypropylene or Teflon having a small microwave loss, or a porcelain such as alumina, and its surface becomes a smooth surface.
It has a lower vertical surface 9a as a non-horizontal surface that covers the opening 8a.

The upper portion of the microwave irradiator 8 is coupled to the waveguide 12 via the partition window 11. Reference numeral 13 is a discharge detector for detecting a discharge in the waveguide 12 or the microwave irradiator 8.

When evaporating and concentrating the waste liquid containing radioactivity, the waste liquid A is supplied from the supply pipe 4 and is filled up to the height defined by the level meter 6. This height is the height shown in the figure and is such that the lower end of the microwave irradiation preventive body 7 is slightly immersed.

After that, when a microwave is supplied from a microwave oscillator (not shown) connected to the waveguide 12, this microwave is transmitted into the microwave irradiator 8 via the partition window 11. . Then, this microwave passes through the opening 8a of the microwave irradiator 8 and the dielectric cover 9, and the tank 1
It is absorbed by the waste liquid A inside and the waste liquid A is heated.

The heated liquid A starts to evaporate at a certain temperature, and the vapor component is collected from the vapor vent pipe 5 into a condenser (not shown) and discharged to the outside. In addition, the remaining components are concentrated,
When the specified concentration is reached, the valve of the discharge port 1a is opened and it is transported to the next step.

In addition, when the discharge from the discharge port 1a and the vapor vent pipe 5 and the supply from the supply pipe 4 are balanced, the discharge and the supply can be continuously continued.

By the way, since the microwave irradiator 8 has the opening 8a formed in the lower portion, that is, in the side wall of the portion immersed in the liquid A, the microwave is radiated horizontally from the vertical portion to the waste liquid A in the tank 1. The other portion, that is, the upper space portion in which the liquid A is not immersed is blocked by the microwave irradiation preventing body 7 and is not irradiated, and the lower portion of the microwave irradiator 8 is not irradiated.

The microwave irradiated at this time passes through the lower vertical surface 9a of the dielectric cover 9, but since the dielectric cover 9 has a low loss, the microwave is absorbed by the waste liquid A with almost no loss and contributes to the temperature rise. To do. At this time, the lower vertical surface 9a of the dielectric cover 9 effectively blocks the waste liquid A from entering the microwave irradiator 8.

From the above, the waste liquid A in the tank 1 is heated particularly strongly at the portion of the lower vertical surface 9a where the opening 8a of the dielectric cover 9 is formed, and boils there. Then, as the waste liquid A evaporates, the substance dissolved in the waste liquid A gradually precipitates, and this precipitation is particularly violent in the boiling portion.

Therefore, it is conceivable that the deposited substance adheres to the dielectric cover 9, further absorbs microwaves and rises in temperature, and burns the dielectric cover 9.

However, since the waste liquid A boils in the vertical direction, the precipitate generated in the boiling part is exposed to a violent upflow accompanying the boiling.

Here, if the surface of the dielectric cover 9 is uneven, an upward flow pocket may be formed, and precipitates may accumulate in the pocket and grow, but as described above, the dielectric cover 9
Since the surface of is formed to be a smooth surface, the deposit that has just adhered is stripped off by the upward flow.

Further, in the lining material 2 portion on the inner surface of the tank 1, the microwave reaching the portion is absorbed and weakened before reaching, so that no large boiling occurs in the portion of the lining material 2, so that No dissolved material is deposited.

Therefore, the deposit of the substance dissolved in the waste liquid A is prevented from adhering to the inside as much as possible, and it is possible to avoid the deterioration of the evaporation efficiency and the corrosion due to the deposit and to operate for a long period of time.

FIG. 2 shows a microwave heating apparatus of another embodiment. In this embodiment, the microwave irradiator 8'of the microwave irradiator 10 is of an electromagnetic horn type in which the tip of the waveguide is simply cut, and a slight gap 8a '(microwave radiation port) is provided from the tip. The reflection plate 14 is arranged via the above, and the reflection plate 14 is held by the dielectric cover 9.

In this embodiment, microwaves are radiated from the gap 8a ', pass through the lower vertical surface 9a of the dielectric cover 9, and heat the waste liquid A. This structure is extremely simple and easy to manufacture.

In addition, in the above, when the microwave radiation port formed by the portion (vertical portion) where the opening 8a of the microwave irradiator 8 is formed or the gap 8a ′ between the microwave irradiator 8 ′ and the reflector 14 is too long. In addition, when the bubbles of the waste liquid A are spread in a film shape and the bubbles cover the surface of the dielectric cover 8, the deposit stripping action by the above-described upward flow is reduced and the deposit adhesion becomes dominant. Therefore, a precipitate may grow in the space within the film and cover the surface of the dielectric cover 8.

Therefore, it is preferable that the vertical length of the microwave irradiation port is not too long. Further, even when the microwave output is increased, the problem due to the foams similarly occurs, so that the microwave output also needs to be appropriate.

FIG. 3 shows a microwave heating apparatus of still another embodiment. In this embodiment, the lower end portion of the microwave radiator 8'is covered with a conical dielectric cover 9'having a lower conical sloped surface 9a 'as a non-horizontal surface, and a reflector is not used. Is.

In this embodiment, the microwave is also radiated downward, but the upward flow is generated along the inverted conical slope 9a 'of the dielectric cover 9', so that the deposit adheres to the dielectric cover 9 '. Is prevented.

In addition, although the microwave radiators 8 and 8'are configured by the waveguides or the resonators in the above-described embodiment, they may be configured by the coaxial lines. In this case, by arranging the short-circuit plates at a certain distance at the tip of the core wire exposed from the tip and by arranging as shown in FIG. 2, the microwave is radiated only from the side surface. Therefore, it is possible to achieve the same effects as the above-described embodiment.

〔The invention's effect〕

As described above, according to the present invention, since the microwave is irradiated to the liquid from the inside of the liquid, the heating effect is improved, and a strong upward flow is formed to the liquid during the heating. Therefore, even if a substance dissolved in the liquid is deposited, it is prevented from adhering to the microwave irradiation part as much as possible,
It is possible to prevent a decrease in heating efficiency and endure long-term use.

[Brief description of drawings]

FIG. 1 is a sectional view of a microwave heating apparatus according to an embodiment of the present invention, and FIGS. 2 and 3 show a microwave heating apparatus according to another embodiment. 1 ... Tank, 2 ... Lining material, 3 ... Top cover, 4 ...
… Supply pipe, 5 …… Steam vent pipe, 6 …… Level gauge, 7 ……
Microwave irradiator, 8 ... Microwave irradiator, 9 ...
… Dielectric cover, 10 …… Microwave irradiation part, 11 ……
Partition window, 12 ... Waveguide, 13 ... Discharge detector.

Claims (1)

[Claims] 1. A device for evaporating and concentrating a liquid in a tank by using microwaves, the dielectric cover comprising a microwave irradiator having a microwave radiating port and a dielectric cover for sealing the microwave irradiator. The microwave irradiating part is configured so that the portion covering the microwave irradiating port in is a non-horizontal plane, and the microwave irradiating part is inserted from the upper part in the tank to a position where it is immersed in the liquid. Microwave heating device.