GB2143144A - Waste liquid evaporation apparatus - Google Patents

Abstract

An apparatus of the low temperature heating type for treating waste liquid, e.g. radioactive waste, in which an evaporating cell (1) is provided with a heater (3) for heating a raw liquid to a low temperature without generating splashes of the raw liquid. A structure (4) for evaporating material having an enlarged area of evaporation is provided in the evaporating cell on to which the raw liquid is supplied so that vapour is produced from this structure. An air blower (11) is provided together with an air filter (12) for blowing vapour emitted from the evaporation structure (4) into a condenser (7), so that a condensed waste liquid is obtained from the condenser. The air blower (11) is in a closed loop cell isolated from the outside atmosphere. The evaporating cell (1) is inserted in the closed loop cell. The structure (4) may be rotary discs, stationary plates. a packing of Raschig rings or porous bodies. Alternatively the liquid may be sprinkled from porous plates. <IMAGE>

Description

SPECIFICATION Waste Liquid Treatment Apparatus The present invention relates to an apparatus of the low temperature heating type for treating waste liquid which is effective for the treatment of waste liquids, in particular, liquids containing harmful substances, such as, for example, radioactive waste liquids in nuclear-powered facilities.

A nuclear-powered institution, for example, a nuclear power plant, discharges radioactive waste liquids of various concentrates ranging from high to low radioactive levels, such as, for example, cooling water of a nuclear reactor and waste liquid from cleaning various facilities and protective garments and so forth. The waste liquid of high radioactive level is usually separated by an enriching method using a heating process, an adsorptive separation method using an ion exchange resin, or a coagulative precipitation method into, for instance, radioactive fine particles and water, the radioactive fine particles are stored and only the water is drained out. With the conventional methods, however, it is difficult to prevent the separated water from containing the radioactive fine particles completely.

Consequently, the radioactive fine particle, though low in radioactive level, are accumulated, for example, on the sea bottom of the discharge region over a long period inevitably resulting in environmental disruption.

In many countries various studies and researches are now being made with a view to complete elimination of the radioactive fine particles from the water to be discharged; for instance, in connection with the enriching method by heating which is most widely employed at present, it has been clarified that the cause of such incomplete separation of the radioactive fine particles lies in the presence of splashes with the radioactive fine particles at their centres, which enter a condenser together with the vapour, and various means for removing the splashes are under study. A device in which, for example, vapour containing splashes is passed through a packed layer as of glass wool fiber and a wire gauze provided above an evaporating cell and is supplied to a condenser has been proposed. It is impossible, however, completely to remove the splashes once made.Even with an apparatus regarded as the best in performance, the decontamination coefficient is not more than 10-5 or so and no further improvement can be expected at present; accordingly, proliferation of the radioactive fine particles into environment cannot be prevented at the present stage. Furthermore, in a case in which the liquid to be treated is a washing agent, the present treatment method causes severe foaming through heating and cannot practically treat the liquid.

As a result of his study, the present inventor found that the cause of the generation of splashes was the heating temperature of the liquid to be treated and his re-study revealed, in addition, that each liquid to be treated has a particular heating temperature at which no splashes are made in its vapour. For instance, in the case of water, the presence or absence of splashes in the vapour generating atmosphere was measured by a laser grain size meter, with the heating temperature gradually lowered at ordinary pressure; the following results were obtained.As shown in Table 1, it was clarified that when the heating temperature reached 300C, no splashes were made in the vapour generating atmosphere and similar results were also obtained, for example, in connection with butyl alcohol the boiling point of which is different from that of water; namely, it was ascertained that there exists a particular temperature, though different from that in the case of water, at which no splashing is caused.

TABLE 1

Heating Diameter of Number of temperature splashed splashes in (C ) particles (ym) 300 cc 100 0.1 to 10 1000 to 5000 80 0.1 to 2 700 to 4000 40 0.1 toO.3 5 to 10 30 0.05 to 0.3 0 The present invention has therefore proposed an enriching treatment method for heating a raw liquid at a temperature which causes no splashing, or at a temperature at which splashes, even if made, do not affect the treatment of the liquid.With this method, since the radioactive waste liquid is completely separated into radioactive fine particles and water, no environmental pollution is caused by the waste water, obtaining an excellent effect that has been strongly demanded in the past. Moreover, according to this method, since heating takes place at low temperatures, no bubbles are formed and, accordingly, it is possible to perform treatment of waste liquids from laundry which has been extremely difficult to treat in the known art.

On the other hand, however, this method adopts low temperature heating, and hence is defective in that the amount of vapour generated is appreciably smaller than in cases of known heating methods. Accordingly, in order to realize a treatment apparatus of a low temperature heating type capable of treating waste liquids on an industrial scale it was found necessary to increase the area of evaporation of the evaporating cell so that the amount of vapour to be generated may be at least equal to or more than those obtainable with the conventional equipment. This leads to the drawback that the evaporating cell becomes very bulky, resulting in the equipment occupying a large area.

Besides, because of low temperature heating, the pressure of vapour generated is low and its moving force is small. Therefore, even if the vapour generated is supplied to a condenser for condensation, the vapour does not actively move with its small energy, so that industrial treatment is difficult to carry out.

It is an object of the present invention to provide an apparatus of a low temperature heating type which permits industrial treatment of waste liquids while being a small size structure.

According to the present invention there is provided an apparatus for treating waste liquid comprising: evaporating cell means having first means for heating a raw liquid to a low temperature substantially without generating splashes of the raw liquid, and second means for enlarging the area of evaporation; and gas blowing means provided with a gas filter for blowing vapour emitted from the evaporating cell.

An embodiment of the present invention is characterized in that an evaporation area enlarging section comprising a large number of plates adapted to be readily wettable by a liquid to be treated is provided in an evaporating cell for markedly increasing the evaporation, and that air is blown to the vapour from the evaporating cell to absorb the vapour therein so that the vapour containing air is sent, for example, to a condenser, thereby to make up for insufficient moving force of the vapour resulting from the low temperature heating, ensuring that the industrial treatment of the waste liquids can be carried out with a small apparatus.

Embodiments of the present invention will now be described by way of example, in comparison with known arts and with reference to the accompanying drawings, in which: Fig. 1 is a sectional view showing an example of known apparatus for the treatment of waste liquid; Figs. 2A and 2B are side and top plan views, partly in section, illustrating an embodiment of the present invention; and Figs. 3, 4, 5 and 6 are side views, partly in section, illustrating other embodiments of the present invention.

To clarify the differences between the known arts and the present invention, an example of the known art is shown in Fig. 1, in which vapour containing splashes is passed through a packed layer 200 of, for example, glass wool fiber and a wire gauze 300 provided above an evaporating cell 100 and is supplied to a condenser 400. This example of the known art has above-mentioned defects.

With reference to Figs. 2A and 2B illustrating respectively a front view and a top view, partly in section, of an embodiment of the present invention, in which a liquid 2 to be treated is supplied to an evaporating cell 1 through an inlet 1 a provided on one side thereof. A heating device 3 for example, an electric heater, heats the liquid 2 to a temperature at which no splashes are made in the vapour atmosphere, for instance, to 300C in case of water. An evaporating plate assembly 4 is provided which comprises 200 discs 4a, each having a diameter of, for example, 0.6 m, i.e. a surface area of 0.28 m2 on one side, and having its surface roughened for easy wetting (for instance, a disc having its surface roughened by sandblasting, or a powder-sintered disc), which are affixed to a rotary shaft 4b at small intervals of about 5 mm.Moreover, the discs 4a are so disposed as to be partly immersed in the liquid 2 at all times and the rotary shaft 4b, mounted so as to project airtightly out of the evaporating cell 1, is slowly rotated by a motor 5, wetting the discs with the liquid 2 to increase the evaporation area. An air blowing chamber 6 and a condensing chamber 7 are disposed at the left and right of the evaporating cell 1, respectively, and interconnected through a duct 8, forming a closed treatment cell isolated from the outside atmosphere, together with the evaporating cell 1.

Reference numeral 10 shows heating fins and 11 an air blower, the air-flow velocity of which is so selected as not to blow off liquid drops on the surface of each evaporating disc 4a.

Reference numeral 12 refers to a high performance air filterfor preventing the raising of dust in the treatment cell 9, 13 cooling fins, 14 a condensed liquid tank and 14a its exhaust port. In this case, the heating fins 10 heat air from the blower 11, for instance, up to 350C and supplies the heated air to the evaporating cell 1. As a result of this, the heated air absorbs vapour given off in the evaporating cell 1 from the evaporating discs 4a wetted with the liquid, thereafter being supplied to the cooling fins 13 and cooled, for example, down to 50C. At the cooling fins, only the vapour is cooled to be condensed into liquid drops, which fall into the liquid tank 14, and the air is returned by the blower 11 to the air blowing chamber 6. Thereafter the same operations are repeated.

As described above, this equipment employs the evaporating plates 4 which are wetted with the liquid to be treated and each evaporating plate has a surface area of 0.28 m2x2=0.56 m2, so that the total area is 0.56 m2x200=1 12 m2.

Accordingly, the gross area is markedly large although the area of each evaporating plate is small. For example, in the case of the evaporating cell 1 measuring 0.8 metres by 0.8 metres, when the evaporating plate assemby 4 is not provided, the evaporation area is 0.64 m2. However, when the evaporating plate assembly is used, the evaporation area, neglecting the area immersed in the liquid, is 112 m2, which is 175 times larger than the abovesaid area. According to the inventor's experiments, the quantity of water condensed in the case of only the evaporating cell being provided is about 57 cc/hour, whereas, in the case of the evaporating plate assembly being provided, the quantity of water condensed is roughly 57 cc/hourx 1 75=12220 cc/hour, that is, approximately 121/hour. Accordingly, treating equipment of large treatment capacity can be implemented in a small size.

Incidentally, when this equipment is used continuously for a long time, there is the possibility that radioactive fine particles collect on the surfaces of the evaporating discs 4a and when they collect in large quantities are dispersed by the blowing in the vapour generating atmosphere.

This can be prevented by providing an ultrasonic washer 15 as shown in Fig. 2A and incessantly cleaning the evaporating discs while in operation to wash off the radioactive fine particles into the liquid being treated. This eliminates the necessity for the troublesome operation of stopping the operation of the equipment and washing the discs.

Figs. 3 and 4 are partly sectional views illustrating other embodiments of the present invention in which the rotational part in the structure of Figs. 2A and 2B is omitted (the parts corresponding to those in Figs. 2A and 2B being identified by the same reference numerals). In the embodiment of Fig. 3, an assembly of square evaporating plates 4 with rough surfaces are provided in the evaporating cell 1 and the liquid 2 heated by the heating source 3 is circulated by a pump (not shown) to pour on the evaporating plates 4a from nozzles 16 provided above them, thereby wetting them with the liquid 2 for evaporation. In this case, the injection rate of the liquid from the nozzles 16 and the air-flow velocity are selected so that the liquid from the nozzles 16 may not enter into the condenser.

In the embodiment of Fig. 4, a number of circular Raschig rings 17 are packed in a case 18 formed by netting to provide a large evaporation area and the liquid 2 is poured on the rings 17 from above through the nozzles 16.

Fig. 5 illustrates another embodiment of the present invention in which the evaporating plates 4 are each formed by a water-absorbing material, such as felt or cloth, or a plate having the waterabsorbing material stuck thereto, and they are partly immersed in the liquid to be treated so that they are self wetting.

Fig. 6 illustrates another embodiment of the present invention in which the liquid 2 heated to a low temperature is sprinkled via a number of porous plates 19 to increase the evaporation area; this structure does not need the evaporating plates, and hence is inexpensive.

Furthermore, it is also possible in the above, to adopt such a structure in which a medium heated by the heating source of the heating fins 10, for example, Freon gas, is liquefied by compressing it using a compression pump and supplied to the cooling fins 13 for cooling them. Moreover, since the heating temperature of the liquid to be treated is close to atmospheric temperature, heating by the heater may sometimes be omitted, so that the equipment of the present invention is economical.

In the foregoing, the present invention has been described in connection with a case where generated vapour is cooled to separate the liquid to be treated into radioactive fine particles and water; according to the present invention, it is possible to reduce the radioactive fine particles in the generated vapour to zero. Therefore, the present invention does not necessitate at all the dilution of the treated liquid with water for lowering its radioactive level which is needed in the case of the conventional structure in which the radioactive fine particles are inevitably contained in the waste water to be discharged.

Accordingly, whether it is necessary or not to separate the raw liquid into a liquid form, the generated vapour can be diffused as it is into the atmosphere, so that the condenser is not needed and electric power therefore is not required, resulting in the treatment becoming economical.

Moreover, the foregoing description has been given of a case where the liquid is so heated as not to cause splashing in the vapour generating atmosphere but, in a case where the concentration of solids contained in the liquid to be treated is low and splashing to some extent does not matter, the heating temperature can be raised correspondingly.

While the foregoing description has been given of the radioactive waste liquid, it is possible, of course, that the present invention permits effective separation treatment of other waste liquids, for example, various oils, various waste liquids contaminated by various solvents, such as trichloroethylene, alcohol and so forth, and the invention is of great utility when employed in the manufacture of distilled water for medical use.

Incidentally, it is needless to say that the treatment temperature is settled in accordance with the properties of waste liquids, such as water, oil, solvent and so on.

As will be appreciated from the foregoing description, the present invention offers a treatment apparatus of a low temperature heating type of large treating capacity for small size and which permits treatment of waste liquids with no solids, such as radioactive fine particles, mixed in the treated liquids or the generated vapour and which is of particular utility when employed in the treatment of large quantities of radioactive waste liquids which has previously been difficult to carry out.

Claims (10)

1. An apparatus for treating waste liquid comprising: evaporating cell means having first means for heating a raw liquid to a low temperature substantially without generating splashes of the raw liquid, and second means for enlarging the area of evaporation; and gas blowing means provided with a gas filter for blowing vapour remitted from the evaporating cell.

2. An apparatus according to claim 1, in which the evaporating cell means further comprises third means for condensing the vapour of the raw liquid to a condensed liquid.

3. An apparatus according to claim 1 or 2, in which said blowing means is a closed loop cell isolated from the outside atmosphere.

4. An apparatus according to claim 1,2 or 3, in which said second means is composed of a number of circular plates arranged in parallel at regular intervals on a rotary shaft so that each of said circular plates is partly immersed in said raw liquid.

5. An apparatus according to claim 1, 2 or 3, in which said second means comprises a number of plates fixed in said evaporating cell means, and in which said evaporating cell means further comprises a plurality of nozzles to which said raw liquids is supplied.

6. An apparatus according to claim 1,2 or 3, in which said second means comprises a netting case packed with a number of Raschig rings, and in which said evaporating cell means further comprises a plurality of nozzles to which said raw liquid is supplied.

7. An apparatus according to claim 1,2 or 3, in which said second means comprises a block of water-absorbing material arranged for partial immersion in the raw liquid.

8. An apparatus according to claim 1,2 or 3, in which said second means comprises a number of porous plates on which said raw liquid is sprinkled.

9. An apparatus according to any preceding claim, further comprising an ultrasonic washer for said second means.

10. An apparatus for treating waste liquid substantially as herein described with reference to any of Figures 2A and 2B, 3, 4, 5 and 6 of the accompanying drawings.