JPS5879811A - Preparation of salt from seawater - Google Patents

Abstract

PURPOSE:To stabilize the operation of electrodialysis and to improve the yield of salt preparation from seawater, by subjecting seawater to heat exchange with warm waste water and/or salt water so that it is heated upto a fixed temperature, or heating it further with exhaust steam to give raw material seawater. CONSTITUTION:In a device for preparing salt consisting of the electrodialyzer 2, the evaporator 3, the boiler 4, etc., seawater is fed from the path 10 to the heat exchanger 5, subjected to heat exchange with warm waste water introduced from the electrodialyzer 2 through the path 12 to it so that the seawater is heated upto a fixed temperature, sent to the condenser 1 by the path 18, where the seawater is heated by the waste steam sent from the evaporator 3 through the path 15 to it to give raw material seawater, which is sent to the electrodialyzer 2. The raw material seawater is separated into warm waste water and salt water by an ion exchange membrane, the salt water is sent from the path 13 to the evaporator 3, concentrated by the heating steam from the boiler 4, salt and bittern are recovered and exhaust steam is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion exchange membrane salt production method, and more specifically, the present invention relates to an ion exchange membrane salt production method, and more specifically, seawater is heated to a certain temperature using hot wastewater and/or can water discharged from an electrodialysis device, or
This invention relates to a method for producing salt by heating skeleton temperature wastewater and/or raw material seawater to a certain temperature using can water and waste steam from an evaporator, and electrodialyzing this raw material seawater.

Conventionally, in the ion exchange membrane salt production method, as shown in Figure 1, seawater is supplied to a condenser 1, where the temperature is raised by heat exchange with waste steam from an evaporator 3, and the seawater is converted into raw material seawater. after,
This raw seawater is sent to an electrodialysis device 2, where it is subjected to electrodialysis to obtain canned water.Then, this canned water is sent to an evaporation device 3, where it is heated by heated steam sent from a boiler 4. There are methods of producing salt using salt.

However, in this method, the amount of heat of the waste steam generated in the evaporator is constant, and since the purpose is to condense the waste steam, the temperature of the seawater is varied as shown in Figure 2.
Y It is not possible to obtain raw seawater at a constant temperature that absorbs seasonal seawater temperature changes by simply increasing the temperature by a certain amount, and also because such raw material seawater has different viscosity and electrolyte diffusion state. , variations in the thickness of the limiting membrane occur during electrodialysis operations; for example, when the temperature is low, the limiting membrane thickness increases and the operating limit of current density (k/dm'') decreases, resulting in There are problems such as a decrease in production capacity and variations in the concentration of can water.

The present inventors have conducted various studies on an ion-exchange membrane salt production method that does not have the above-mentioned problems of conventional ion-exchange membrane salt production methods. By using it as a source, it is possible to obtain raw material seawater at a constant temperature that absorbs seasonal changes in seawater temperature, and also to solve various problems in electrodialysis operations, and to obtain Kansui with a constant high concentration. The present invention was completed based on this discovery.

That is, in the first aspect of the present invention, seawater is used as a raw material seawater, and then the mosquito raw material seawater is concentrated by electrodialysis to produce salt/water, and then the can water is heated to produce salt.
This is a method for producing salt from seawater in which seawater is heated to a certain temperature using hot wastewater and /l or can water from an electrodialysis device to obtain raw material seawater, and the raw material seawater is electrodialyzed.
The invention is a seawater salt production method in which the raw material seawater heated to a certain temperature in the first invention is further heated to a raw material seawater using waste steam emitted from an evaporator, and the raw material seawater is electrodialyzed.

The method of the present invention will be explained below with reference to FIGS. 3 and 4.

FIG. 3 is a flow sheet showing one embodiment of the method of the present invention, and FIG. 4 is a graph showing changes in temperature from seawater to raw material seawater in the method shown in FIG. 3.

In FIG. 3, l is a condenser, 2 is an electrodialyzer, 3 is an evaporator, 4 is a boiler, and 5 is a heat exchanger. The water is introduced from the electrodialyzer 2 into the heat exchanger gs5, heated to a constant temperature (27C') as shown in FIG. At this time, this is done by increasing or decreasing the temperature and humidity of the seawater, increasing or decreasing the heat transfer area, or increasing or decreasing the flow rate of heated wastewater or seawater.

The heated seawater sent to the condenser 1, that is, the seawater at a temperature of 27 C, is further heated (as shown in FIG. 35
C) The raw seawater is then sent to the electrodialyzer 2.

The raw seawater sent to the electrodialysis device 2 is separated into cold water and warm wastewater by desalination using an ion exchange membrane, which is usually carried out in the device, and then transferred to the heat exchanger 5. After being sent to the seawater and exchanging heat with seawater, it is discarded as wastewater. On the other hand, the can water is sent to the evaporator 3, where it is concentrated by the heating steam sent from the boiler 4 and separated into waste steam, salt, and bittern, and the waste steam is sent to the condenser 1. The heated seawater sent from the heat exchanger 5 is further heated and then discarded, and the salt and bittern are 4! I'll put it out.

As described above, warm wastewater and 1114 which are one embodiment of the method of the present invention
Salt production method using M gas t - As explained above, in the method of the present invention, ti is warm waste water alone (Fig. 5.6), ti is cold waste water alone, warm waste water and cold water, and cold water and waste steam. Alternatively, it is also possible to raise the temperature of seawater using three types: hot wastewater, boiling water, and waste steam.

The types of heat exchangers and condensers used in the present invention include multi-tube type, grate type, double-pipe type, non-contact types such as those using heat pipes, and contact types such as vapor absorption condensation type. Any type or combination thereof may be used.

According to the method of the present invention, raw seawater at a constant high temperature can be obtained throughout the year, and by using this raw seawater, electrolyte diffusion and the viscosity of the raw seawater are reduced in electrodialysis, resulting in a reduction in film thickness. The operating limit of the current density f (mu/d♂) is raised, which improves the production capacity per unit number of ion exchange membranes. At the same time, the amount of dissolved air in the raw seawater decreases, which increases the current flow. The generation of bubbles is eliminated, and the amount of wear and tear on the ion exchange membrane due to troubles based on this is reduced.

It also becomes possible to increase the freshness of the produced can water.

Furthermore, the electrodialysis and evaporation steps can be operated under constant conditions throughout the year, which simplifies the control and regulation of the entire plant and allows for increased efficiency.

Examples 1 to 4 and Comparative Examples The seawater shown in Table 1 was supplied to a heat exchanger according to the flow sheet shown in Figure 3, and the temperature shown in Table 1 was reached by heated waste water discharged from an electrodialysis device in the carpet. This warm seawater is sent to a condenser, and heated to the temperature shown in Table 1 using waste steam sent from the evaporator, and used as raw material seawater.

Next, this raw seawater is sent to an electrodialysis device, where it is desalinated at the current density shown in Table 1. The desalted hot wastewater is sent to a heat exchanger, where it is heat exchanged with seawater in the dialysis device. On the other hand, the concentrated can water is supplied to the evaporator, where it is heated and evaporated by the heating steam sent from the boiler, and the evaporated waste steam is sent to the condenser and heated into warm seawater. It was used to raise the temperature of the battery and was later discarded. The results are shown in Table-1.

For comparison, the flow sheet shown in FIG. 1 was followed. That is, a method was implemented in which seawater was heated in a condenser to produce raw material seawater, and this raw material seawater was used to perform electrodialysis and evaporation of can water to produce salt. The results are also shown in Table 14C.

Table-l Examples 5 to 8 Seawater shown in Table-2 was supplied to the heat exchanger according to sheet 70 in Figure 5, and heat exchanged with heated wastewater whose temperature was raised by Joule heat in the electrodialysis device. The temperatures shown in Table 2 and the pear raw material seawater were used.

Next, this raw seawater is sent to an electrodialysis device, where l! Desalination is carried out at the current density shown in -2, and the desalinated hot waste water whose temperature has been raised by Joule heat is sent to a heat exchanger, where it exchanges heat with seawater and is then disposed of.

The result is 1! -2.

Table-2

[Brief explanation of drawings]

Figure 1 shows a flow sheet for the conventional ion-exchange membrane salt production method, Figure 2 shows a graph of the temperature change of the raw seawater used in the process from seawater to raw seawater, and Figure 3 shows the flow sheet for the method of the present invention. FIG. 4 is a flow sheet showing one embodiment of the ion-exchange membrane salt production method, FIG. The flow sheet showing the embodiment, FIG. 6, is a graph of the temperature change from the raw seawater used in FIG. 5 to one volume of raw seawater. In the figure, 1 is a condenser, 2 is an electrodialyzer, /3 is an evaporator, 4 is a boiler, 5 is a heat exchanger, IO is a seawater passage, 1
1 is a passage for raw seawater, 12 is a passage for waste hot water, 13 is a passage for can water, 14 is a passage for heating steam, 15 is a passage for waste steam, 16 is a bittern extraction passage, and 17 is a salt extraction passage. , 18 indicate the passage of heated seawater. Patent applicant Shin Nihon Chemical Co., Ltd. Patent applicant Asahi Kasei Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] 1. Seawater is used as a raw material seawater, the raw material seawater is concentrated by electrodialysis to produce salt water, and then the seawater is heated to produce salt. Salt production method from seawater characterized by raising the temperature to a certain temperature with hot waste water and/or can water from an electrodialysis device to obtain raw material seawater, and electrodialyzing the raw material seawater. Afterwards, the raw seawater is concentrated by electrodialysis to produce kansui, and then, when the kansui is heated to produce salt, the seawater is heated to a certain temperature using warm wastewater and/or kansui discharged from the electrodialyzer. A method for producing salt from seawater, which is characterized in that after raising the temperature, the temperature is further raised using waste steam emitted from an evaporator to obtain raw seawater, and the raw seawater is subjected to electrodialysis.