JPS59109283A - Solidifying method of solvent by evaporation - Google Patents

Abstract

PURPOSE:To solidify the largest possible amt. of a solvent by evaporation within a prescribed time by increasing successively the temp. or area of the heat transmission surface for heating of a heating element or both thereof with lapse of a heating time and retarding the decrease in the quantity of heat transmission. CONSTITUTION:An aq. NaCl soln. is flooded through a flooding pipe 13 in a solidifying vessel 1 and thereafter heating steam is fed through a control valve 5 and an inlet pipe 3 into the coil 2 of a heating tube, by which the aq. NaCl soln. is heated to form drain. The drain is discharged through a discharging pipe 6 and a trap 7. The steam evaporating from the aq. soln. is admitted through a steam chamber 8 and an outlet pipe 9 into a condenser 10, where the steam is condensed by cooling water 11 and is discharged through a discharging pipe 12 to the outside. The valve 5 is automatically controlled by a temp. indicating controller 4 in this case to increase gradually the pressure of the heating steam, by which the temp. of the coil 2 is increased and the difference in the temp. of heat transmission is increased.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for evaporating and solidifying solutions of salts, etc., and is particularly suitable for treating radioactive liquid waste such as recycled waste liquid of iosi-exchange resins from nuclear power plants. Regarding.

[Prior art]

One way to treat salt solutions, such as recycled waste fluids from iosi-exchange resins generated from nuclear power plants, is to heat these solutions to evaporate the liquid portion and reduce the volume and collect and dispose of only the solutes as assimilated substances. It is being done. However, this method has the disadvantage that as time passes, a large number of assimilated substances precipitate onto the heat transfer surface of the heating element, reducing the υ heat transfer and lowering the assimilation rate.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned drawbacks, to secure the amount of heat transfer by delaying the decrease in the amount of heat transfer as much as possible from the beginning to the end of heating of solutions such as salts, and to reduce the solidification rate as much as possible.
It is an object of the present invention to provide an efficient method for evaporating and solidifying solutions of salts, etc., which can evaporate and solidify as much solution as possible within a predetermined time.

[Summary of the invention]

Generally, in a heat transfer mechanism, the amount of heat transfer Q is the overall heat transfer coefficient U,
The heat transfer temperature difference Δ and the heat transfer area A become U·Δt−A. In the case of evaporation and solidification of solutions of salts, etc., salts, etc., which are solutes, precipitate and accumulate as assimilates on the heat transfer surface of the heating element, so the value of the overall heat transfer coefficient U essentially decreases over time. As solidification progresses, the amount of heat transfer decreases, and the overall heat transfer coefficient continues to decrease as solidification progresses. Therefore, in order to secure the amount of heat transfer required for evaporation and solidification, two other factors must be used to compensate for the decrease in the overall heat transfer coefficient: the heat transfer temperature difference △ and/or the heat transfer area A as the evaporation and assimilation progresses. It may be changed over time. The method for evaporating and solidifying a solution of salts, etc. according to the present invention is based on the above-mentioned principle, and the temperature, area, or both of the heating heat transfer surface of the heating body that heats the solution of salts, etc. supplied in the solidification container is controlled by the heating time. By gradually increasing the heat transfer coefficient with the passage of time, the reduction in the overall heat transfer coefficient is compensated for, and the desired amount of heat transfer is ensured over a long period of time during the evaporation and assimilation operation.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 shows an embodiment in which a solidified body of NaCl is produced by heating an aqueous solution of NaCl. In FIG. 1, 1 is a solidification container containing a heating tube] 2, 3 is a heating steam inlet pipe that guides heated steam as a heating medium to the heating tube coil 2, 4 is a temperature indicating regulator 5 is a control valve, and 6 is a The heating tube coil's dore discharge pipe 7 is a dore trap, 8 is a steam chamber for receiving evaporated steam from the aqueous solution in the container l, 9 is an evaporated steam outlet pipe, and 10
is a condenser, 11 is cooling water, 12 is a condensed water discharge pipe, 13t
RI aqueous solution charging tube is shown.

First, an NaC4 aqueous solution is charged into the solidification container 1 through the filling pipe 13. Next, the heated steam is sent to the heating tube coil 2 via the control valve 5 and the artificial tube 3, heats the aqueous solution, and is discharged through the drain pipe 6 and the drain rack Jj7.

On the other hand, water vapor evaporated from the aqueous solution enters the steam chamber 8 and the outlet pipe 9.
It enters the condenser 10 through the cooling water 11, is cooled and condensed, and is discharged through the discharge pipe 12. In this way, as the water in the aqueous solution evaporates, Nac7 precipitates and solidifies on the heat transfer surface of the heating tube coil, so the overall heat transfer coefficient gradually decreases, and if no measures are taken, the amount of heat transfer will decrease. It gradually decreases and the solidification rate decreases. As a measure to prevent such a situation and ensure the amount of heat transfer, in this embodiment, the temperature of the heating tube coil 2 is gradually increased as the precipitation and solidification of NaCz progresses, thereby reducing the difference in heat transfer temperature.

That is, the temperature indicating regulator 4 automatically controls the regulating valve 5 to gradually increase the heating steam pressure, thereby gradually increasing the temperature of the heating tube coil. As a result, as shown in Fig. 2, the evaporation rate curve A without taking the above measures is improved to the evaporation rate curve B by taking the above measures, and the evaporation rate increases due to the increase in the amount of heat transfer. The decrease in speed is delayed over time. Along with this, the cumulative processing amount curve C increases as shown in the processing amount curve when the above measures are taken,
Premature decline in assimilation rate is prevented.

In the embodiment shown in FIG. 3, the pre-heated carp is divided into a plurality of sections (in this embodiment, it is divided into two sections), and heating steam is made to flow through each valley independently. In FIG. 3, 2 is an upper heating tube coil, and 14 is a lower pre-heating coil. Similarly to the upper heating tube coil, the 'F section heating tube coil 14 is also equipped with a temperature controller 1.
5. Control valve 16. Heating steam inlet pipe 17, dressing discharge',
4-ts, dress trap 19 is attached.

In this embodiment, at the beginning of the assimilation operation, heated steam is flowed only through the lower heating tube coil 14 to heat and evaporate the NaCt aqueous solution. If the solidification rate begins to decrease over time due to the above-mentioned reasons, heating steam is also caused to flow into the upper heating tube coil 2. In the upper heating tube carp), NaC is
Since precipitation of t has not occurred, a new heat transfer area is secured, which can contribute to maintaining the amount of heat transfer, and similarly to the above, it is possible to prevent an early decrease in the evaporation rate and increase the cumulative throughput.

In another embodiment shown in FIG. 4, the heating heat transfer surface is
The heating tube coil 2 is used, which has a large amount in 1b and a small amount in the lower part. In this example ((), heating steam is heated to 1
b) When performing evaporation assimilation operation by flowing the
Cl crystals must be deposited from the F section of the solidification container 1.
The upper heating surface is in an effective state in the latter half of the evaporation solidification operation, and a new heat transfer area is secured as a whole, which can also contribute to maintaining the amount of heat transfer. Therefore, the effects of preventing an early drop in the evaporation rate and increasing the cumulative throughput as shown in the second article can be similarly expected.

In the embodiments shown in FIGS. 3 and 4 above, the first
It is possible to use the method of gradually increasing the temperature of the heating tube coil as described with reference to the figures, and the solidification efficiency can be further increased by such a combination.

〔Effect of the invention〕

According to the present invention, it is possible to secure the amount of heat transferred from the heating heat transfer surface to the solution over a long period of time during the evaporation and solidification operation of the solution, thereby preventing a decrease in the evaporation rate and increasing the cumulative throughput. It is possible to evaporate and assimilate solutions such as salts with higher solidification efficiency than in the past.

[Brief explanation of the drawing]

Fig. 1 is a schematic illustration of one embodiment of the present invention, Fig. 2 is a performance comparison diagram of the solidification operation according to the prior art and the embodiment, and Figs. 3 and 4 are respectively other embodiments of the present invention. This is a schematic diagram. ■ ・Assimilation vessel 2... Heating tube coil 3...
Heat medium (heated steam) inlet pipe 4...Temperature indicator controller 5...Control valve 6...Do 1
Noshi discharge y 7...
Steam chamber 9... Evaporated steam outlet pipe 10... Condenser l [... Cooling water 12... Condensed water discharge pipe 13... Solution filling pipe 14... Lower heating tube coil 1
5... Temperature controller 16... Control valve 17...
・Heat medium (heated steam) inlet pipe 18...Dorol exhaust pipe
L9...do 1 nosi trap m da←θ1 song 4 m1m+
l Tsuji J11i + makeup (stomach)

Claims (1)

[Claims] l A solution of salts, etc., supplied to a solidification container is heated by a heating element installed in the container to evaporate the liquid, and only solutes such as salts are precipitated to produce a solidified product. A method for evaporating and assimilating a solution, characterized in that the temperature, area, or both of the heating heat transfer surface of a heating body is increased sequentially as the heating time elapses to delay a decrease in the amount of heat transfer. 2. The heating body is a heat exchanger tube coil through which heating steam flows, and the heating temperature is gradually increased with the elapse of heating time by changing the pressure of the heating steam flowing through the heat exchanger tube coil. A method for evaporating and solidifying a solution according to scope 1. 3. The solution according to claim 1, characterized in that the heating heat transfer surface of the heating body is divided into a plurality of parts, and the heating start time and heating time are made different for each of the divided heating heat transfer surfaces. Evaporation solidification method. 4. A method for evaporating and solidifying a solution as set forth in claim 1, characterized in that the heating heat transfer surface of the heating body is arranged more in the upper part of the assimilation container and less in the lower part, and these heating heat transfer surfaces are heated simultaneously. .