JPH0357051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for purifying raw saline water used when producing caustic soda and chlorine by electrolyzing common salt.

Conventional technology In conventional salt electrolysis, raw salt is dissolved in water,
The resulting impurities were separated and purified before being supplied to the electrolytic cell, but as the demand for higher purity of the resulting caustic soda increased and the electrolytic method changed from the diaphragm method to the ion exchange membrane method, the purification of brine became more important. It has come to be.

If the salt water for ion-exchange membrane electrolysis contains many impurities and hard components, it will deteriorate the performance of the ion-exchange membrane and significantly shorten its life. Therefore, it has become necessary to conduct high-level purification by introducing the resin into a chelate resin packed bed. However, it has been discovered that the lifespan of such chelate resins is significantly affected by the amount of solid suspension remaining in the saline solution, and in addition to the conventional solid separation using Shitsukuna etc. Even more precise solid matter separation has become necessary. In order to meet these demands, the supernatant brine from which solids have been separated using a filter, etc., is further subjected to precision filtration to produce purified brine, but it is not possible to completely capture the solids. This requires the amount of treated liquid to be kept small and the filter to be washed and regenerated frequently, causing an increase in saline purification costs.

Problems to be Solved As described above, there is a need for a low-cost purification method that can reliably filter a large amount of salt water with high precision in ion-exchange membrane salt electrolysis, and the present invention satisfies this demand. The aim is to provide a satisfactory purification system.

Means for Solving the Problems The present invention saturates the dilute brine recovered from the salt electrolytic tank again with salt, makes it alkaline, separates the generated solids from Shitsukuna, and further performs precision filtration before applying chelate resin. The conventional salt water purification system, which passes through layers to obtain high purity salt water suitable for ion exchange membrane electrolysis, has been improved as follows. That is, a filter having a fixed filter layer is used, and when the filtration efficiency of the filter decreases, an insoluble solution containing hydrochloric acid is supplied to the filter instead of the supernatant salt water. dissolving and removing substantially all of the insoluble matter by circulating, then washing the filter using purified brine or a washing solution consisting of purified water, and filtering the supernatant brine again; Substantially all of the undissolved matter solution and washing solution used to regenerate the filter are simultaneously collected and used for dissolving salt, and as a result, substantially all of the insoluble matter is removed. Therefore, we decided to separate all of them from only Shitukuna.

By doing this, the number of man-hours and labor required to separate the salt water mud that was conventionally captured by a filter by backwashing, and further to separate and dispose of the mud from the wash water containing mud, can be reduced. On the other hand, since most of the matsudo is dissolved by the dissolving solution and returned to the raw salt dissolution tank, the number of man-hours for cleaning is significantly reduced, and the downtime for cleaning the filter is also significantly reduced. It was decided to decrease to .

In addition, the filter has a fixed filter layer, but the filter layer is fixed to the filter and does not change in shape or performance due to cleaning operations such as backwashing, for example. It consists of a filter medium that is itself fixed, such as a planar filter medium made of filter cloth or filter paper such as brushed filter cloth or non-woven fabric, or a wound string-type cylindrical filter medium, and a filter aid such as diatomaceous earth or activated carbon. In filter machines that have a filter layer obtained by coating the surface of a filtration base material or a sand filter layer, the dissolution of insoluble matter does not proceed uniformly when cleaning the filter layer, resulting in extremely low cleaning efficiency. Playback takes time. Therefore, in the present invention, since a filter having such a fixed filter layer is used, there is no need to form a filter layer such as coating with a filter aid, so that it can be used for filtration immediately after washing, and the effective operating time is shortened. It is more efficient because it can be used for a longer time.

Furthermore, in the past, it was unthinkable to recover the washing water of the filter, but the dissolving liquid and washing water of the present invention can all be used for dissolving raw salt, and can be used for washing the filter. Almost no water is discarded outside the system, and it is used as process water without any waste. On the other hand, the solid content dissolves in the washing liquid and returns to the brine saturated with raw salt, but when alkali is added, it precipitates out as a solid content again, enters the system, and is sedimented and separated, so it accumulates in the system. This will not affect the operation of the salt electrolyzer in any way.

Embodiment FIG. 1 is a diagram showing a conventional salt water purification process, in which dechlorinated salt water recovered from an electrolytic cell 14 is sent from a dechlorinated salt water tank 13 to a saturated salt water tank 1. Raw salt is added here, and if necessary, water is replenished to make saturated saline solution, which is then sent to the mixing tank 2. In the mixing tank, caustic soda or soda carbonate, etc. are mixed to produce so-called salt water mud, but the salt water containing mud is sent to Shitsukuna 3, where most of it settles and is discharged from the bottom of Shitsukuna 3 as mats out of the system. is discharged.

Since the supernatant brine discharged from the water tanker 3 usually contains a small amount of undissolved solid matter, it is once stored in the supernatant brine tank 4 and then pumped to the filter 6 by the pump 5. The filtered purified salt water is stored in a purified salt water tank 7, then sent to a chelate resin tower 8 to remove residual trace impurity ions, and further subjected to PH adjustment with hydrochloric acid in a PH adjustment tank 9, where it is electrolyzed as high-purity salt water. sent to the tank.

The present invention is an improvement of the portion including the filter 6, and the improvements as shown in FIG. 2 have been added.

In the present invention, the process in which the salt water sent from the saturated salt water tank 1 passes through the liquid filter 3 and reaches the supernatant salt water tank 4 is the same as in the prior art, but the supernatant salt water passes through the filtration pump 5 and the flow meter 15 and undergoes precision filtration. The filter is sent to a filter 6 having a fixed filter layer made of filter cloth. Filter machine 6
In order to maintain the filter layer in a state suitable for precision filtration,
The purified brine obtained by operating under stable filtration conditions once enters the storage tank 7 and then is sent to the chelate resin tower 8.

Supernatant salt water usually contains about 10 mg of undissolved matter, which mainly consists of magnesium hydroxide, iron hydroxide, calcium carbonate, and small amounts of clay minerals, and is in the form of fine flocs. Floating. When these are captured and accumulated in the filter layer, the filtration resistance increases and the filtration pressure increases. When the filtration pressure reaches a certain limit, solid content leaks from the filter layer, so the operation of the filter is stopped and cleaning of the filter is started before this limit is reached.

When cleaning the filter 6, first wash the solution tank 16.
Prepare a solution containing hydrochloric acid at a concentration of 1% or more. The simplest composition of the dissolving solution is diluted hydrochloric acid water, or it may be a hydrochloric acid-acid saline solution, or it may be one in which the acidity of the solution used for repeated washing is adjusted with hydrochloric acid. Next, the valves V ₁ and V ₂ before and after the filter are closed, and the valves V ₃ and V ₄ are opened to circulate the liquid in the solution tank 16 into the filter by the pump 5. Although the figure shows a forward flow in the same direction as the flow of liquid during normal filtration, it may also flow in the opposite direction. By washing the filter layer with such a solution, most of the undissolved solids trapped in the filter layer are dissolved and removed, so the flow resistance of the filter layer returns to near its initial value, reducing the filtration capacity. I can see that you have recovered.

Next, the valve V ₄ is closed, and all the liquid in the filter 6 is collected into the tank 16, and then the liquid prepared in the cleaning liquid tank 17 is transferred to the filter 6 by the pump 5 by opening the valve V ₇ .
send to Since some dissolved solution remains in the filter 6, this is washed out with a cleaning solution and drained into the tank 16. At this time, open V ₃ and V ₅ to clean the inside of the filter as thoroughly as possible. The simplest cleaning liquid is water, but it may also be saline, water made alkaline with caustic soda, etc., or saline. Furthermore, purified salt water in the tank 7 that has already been filtered may be used.

When all the acidic solution in the filter 6 is washed out and collected in the tank 16, close V ₃ and V ₅ , and close V _6.
Pump 5 is opened while collecting cleaning liquid into tank 17.
Therefore, the liquid is circulated, and after the recovery of the function of the filter layer in the filter 6 is confirmed, V ₇ is closed, and the liquid in the filter 6 is recovered as completely as possible, and V ₆ is closed.
Complete all cleaning operations.

After the filter 6 has been washed in this way, V ₁ and V ₂ are opened and supernatant salt water is filtered again.

In this way, the tank 16 and the tank 17 store a solution in which insoluble matter captured by the filter is dissolved and a washing solution thereof, and the pump 18 sends it little by little to the saturated saline tank 1 to dissolve the raw salt. used.

Effects of the Invention As explained in detail above, by carrying out the method of the present invention, the number of man-hours and labor required to operate the saline water filter can be significantly reduced, and at the same time, the processing that was generated by the filter can be reduced. Waste treatment measures have become extremely simple as no difficult waste is generated and only sludge from the Sikkuna is generated.

In addition, all the water that was conventionally used for cleaning the filter and wasted can now be reused as process water, and the cleaning of the filter can be done in a short time, increasing the operating efficiency of the equipment.

Taken together, the operating costs of the equipment are greatly reduced, the increase in costs of cleaning and dissolving chemicals, etc. is negligible, and a much greater economic effect is obtained.

[Brief explanation of drawings]

FIG. 1 is a process diagram of the conventional salt water purification method, and FIG. 2 is a process diagram of the electrolytic salt water purification method according to the present invention.

Claims (1)

[Scope of Claims] 1. Salt is dissolved in dilute brine and/or purified water recovered from a salt electrolyzer to form a nearly saturated salt aqueous solution, and caustic soda and/or soda carbonate is added to the solution. The dissolved matter is separated by sedimentation, and the trace amount of undissolved matter remaining in the supernatant brine is further filtered out and purified using a filter, and then the pH is adjusted with hydrochloric acid to produce high-purity brine for salt electrolysis. In this case, a filter having a fixed filter layer is used as the filter, and when the filtration efficiency of the filter decreases, an insoluble matter solution containing hydrochloric acid is supplied to the filter instead of the supernatant salt water. Substantially all of the undissolved matter is dissolved and removed by circulating the filter, and then the filter is washed with purified salt water or a washing liquid made of purified water, and the supernatant salt water is filtered again. and a method for purifying salt water for electrolysis, characterized in that substantially all of the insoluble matter dissolving solution and washing solution used for regenerating the filter are recovered and used for dissolving the salt. 2 Salt is dissolved in the diluted saline solution and/or purified water recovered from the salt electrolytic tank to form a nearly saturated saline solution, and caustic soda and/or soda carbonate is added to this to precipitate and separate the generated insoluble matter. A trace amount of undissolved matter remaining in the supernatant brine is further removed by filtration using a filter, and the thus obtained purified brine is passed through a chelate resin layer for secondary purification, followed by pH adjustment with hydrochloric acid. In producing high-purity brine for salt electrolysis, a filter having a fixed filter layer is used as the filter, and when the filtration efficiency of the filter decreases, hydrochloric acid is added in place of the supernatant brine. Substantially all of the insoluble matter is dissolved and removed by supplying and circulating an insoluble matter solution to the filter, and then washing the filter using a cleaning solution consisting of purified salt water or purified water, filtering the supernatant salt water again, and recovering substantially all of the undissolved matter solution and washing solution used for regenerating the filter and using it for dissolving the salt. Characteristic method for purifying saline water for electrolysis.