JPS60161794A - Post-treatment of distilled water - Google Patents

Abstract

PURPOSE:To contrive to miniaturize equipment and to reduce equipment cost, in a method for treating distilled water obtained by a brine desalting apparatus with a Ca-salt and CO2 obtained by the decarbonation treatment of seawater, by using CO2 in extracted gas by the degassing of partially degassed seawater. CONSTITUTION:Seawater is subjected to the injection of an acid in an apparatus 3 and injected into a partial decarbonation apparatus 4 operated under atmospheric pressure and imperfectly decarbonated. CO2-gas generated herein is discharged to the open air from an exhaust port 10 along with air. Seawater containing removing CO2-gas accumulated to the bottom of the apparatus 4 is guided to a vacuum degasifier 13 to be injected thereinto. Degassed seawater enters an evaporation type brine desalting apparatus 15 and is evaporated under heating while generated steam is condensed to form distilled water which, in turn, enters a limestone bed 17. On the other hand, non-condensible gas such as O2 or N2 containing CO2 extracted by an ejector 18 from the apparatus 13 is subjected to the separation of condensed water and introduced into distilled water in a pipe 16 under pressure through a compressor 20 and absorbed thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a post-treatment method for converting distilled water produced in a desalination apparatus using an evaporation method into water quality suitable for tap water.

Distilled water obtained from salt water by evaporation method contains almost no mineral components, so it corrodes the piping materials of the water supply system and has a poor taste as drinking water. For this reason, a method is adopted in which calcium carbonate, slaked lime, and carbon dioxide gas are added to distilled water produced from salt water by evaporation. In this case, carbon dioxide gas produced by burning petroleum or fuel gas has been used, but it has the disadvantage that a large amount of equipment and operating costs are required to produce carbon dioxide gas.

Therefore, Japanese Patent Application Laid-Open No. 55-35971 as a prior art discloses that when producing distilled water from salt water using an evaporation method desalination device, the purpose is to prevent corrosion and scale formation in the evaporation method desalination device. By using the fact that carbon dioxide gas is generated when an acid such as hydrochloric acid or sulfuric acid is added to the salt water before it is supplied to the desalination equipment, decarboxylation is performed before the acid-added salt water is supplied to the desalination equipment. Carbon dioxide gas is generated under reduced pressure in the tower, which is extracted by an extraction ejector operated by high-pressure steam from the boiler, and after condensing and removing moisture from the high-pressure steam in a condenser, the water is removed from the desalination equipment. It is suggested that it be mixed with distilled water from

In this way, since carbon dioxide gas is not produced in a separate process, operating costs can be reduced accordingly, and the equipment can be made smaller compared to the conventional method, but in this method, a sufficient amount of carbon dioxide gas cannot be As stated in the specification, the inside of the decarboxylation tower must be brought to a high vacuum of 0.2 atm, that is, about -600 mmHg, using the ejector, so the drive of the decarbonation ejector requires In addition to the increased consumption of high-pressure steam, a large amount of cooling water is required to condense the steam used for this extraction, increasing operating costs.Moreover, as the extraction ejector becomes larger, Since the piping must be made quite thick, the equipment cannot be sufficiently miniaturized, and the decarbonation tower must be of a closed type, which increases equipment costs.

On the other hand, seawater contains approximately 9 carbonates in the form of bicarbonate ions.
The amount of carbon dioxide required for post-treatment of distilled water is approximately 0 ppm (as CO2), and the amount of carbon dioxide required for post-treatment of distilled water is 40%
Since it is about ppm (20 ppm of the above 90 ppn+ if the amount of seawater supplied is twice the amount of distilled water), it is not necessary to use the entire amount of carbon dioxide gas in the seawater.

Therefore, if the deaerator in the post-process can decarboxylate up to 95% of the carbonic acid components initially contained, then the decarboxylation tower will take out the carbonate components necessary for post-treatment of distilled water in the deaerator. It is necessary to suppress partial decarboxylation to about 70%.

The present invention was made with a focus on this amount of carbon dioxide gas, and after adding acid to the raw brine to prevent scale and adjust pH, partial decarboxylation is carried out in a decarboxylation device that operates at approximately atmospheric pressure. The partial pressure of carbon dioxide in the non-condensable gas to be extracted in the next step of vacuum degassing is reduced to the conventional complete This was done with the aim of increasing the amount of extracted gas when decarboxylating the water and then vacuum degassing it, and also reducing the amount of gas to be processed, making the equipment more compact, and making it possible to use carbon dioxide gas for after-treatment of distilled water to an advantage. An example of this will be described below with reference to drawings of an example apparatus in which seawater is used as raw water.

Seawater is introduced from pipe 1 via pump 2, and acid injection device 3
After more sulfuric acid is injected, it is sent to the decarboxylation device 4 through the jet nozzle 5.
More erupts. This decarboxylation device 4 is configured to be suitable for partially performing decarboxylation under approximately atmospheric pressure,
For example, as shown in the figure, the amount of atmospheric air introduced from the bottom by a fan 6 is limited by a damper 7. This restricted atmospheric air enters the vessel through the curved opening 8, reverses upwards, and then passes through the packed bed 9, and the spouted seawater is decarboxylated by contact with the atmospheric air in the packed bed 9.
Since the amount of air is limited, partial decarboxylation, or incomplete decarboxylation, occurs. The carbon dioxide gas generated here is discharged to the atmosphere from the discharge port 10 together with the air.

Partial decarboxylation from seawater is not limited to the above-mentioned method of restricting popular air; for example, it is possible to lower the position of the jet nozzle 5 of the decarbonator 4, raise the liquid level, or open the air introduction opening 8. This can also be done by various methods such as increasing the seawater load by increasing the amount of seawater by increasing the opening degree of the valve 11 provided in the seawater introduction pipe.

Seawater containing residual carbon dioxide accumulated at the bottom of the partial decarboxylation device 4 is led to a vacuum deaerator 13 through a pipe 12 and is spouted into the vessel. The degassed water passes through the pipe 14, enters the evaporative salt water desalination device 15, is heated and evaporated, and condenses to become distilled water into the pipe 16.
and enters the limestone bed 17.

On the other hand, non-condensable gases such as oxygen and nitrogen, including carbon dioxide gas, which are suctioned and extracted from the vacuum deaerator 13 by the steam ejector 18, accompany steam and reach the condenser 19, where they are cooled by seawater and the condensed water is separated. After that, the distilled water in the pipe 16 passes through the compressor 20 and is absorbed under pressure, so that the distilled water in the pipe 16 becomes P.
I-I is lowered into the limestone bed 17 to produce calcium bicarbonate, which enhances the flavor of the distilled water and prevents corrosion of piping materials, and is removed via pipe 21 as manufactured water.

The above-mentioned compressor 20 uses, for example, a water ring type compressor that uses produced distilled water as a sealing liquid, takes out the sealing liquid in which carbon dioxide gas is stirred and dissolved, mixes it with the distilled water in the pipe 16, and then separates it from the compressor. If this carbon dioxide gas is also absorbed into the distilled water in the pipe 16, this carbon dioxide gas Φ can be effectively utilized.

In the present invention, salt water into which acid has been injected is introduced into a decarboxylation device that operates at approximately atmospheric pressure to partially decarboxylate, and some carbon dioxide gas is released while some carbon dioxide gas is still in the salt water. The remaining residue is introduced into a deaerator under reduced pressure and degassed.
Since the carbon dioxide gas in the extracted gas from the deaerator is absorbed into distilled water, the amount of carbon dioxide gas that evaporates in the deaerator under reduced pressure is small, making it possible to use thin piping, and the deaerator can be easily Vacuum generating devices such as steam ejectors and condensers can also be made smaller and operating costs can be reduced. In addition, since it is customary to perform atmospheric pressure decarboxylation and vacuum deaeration in seawater desalination plants that use acids, it can be easily applied to existing plants, and decarboxylation equipment only partially performs decarboxylation. Therefore, while this decarbonation device can be made smaller, when partial decarbonation is limited by the amount of air, the amount of air is reduced and the power is reduced.

[Brief explanation of the drawing]

The figure is a flow sheet for an apparatus according to an embodiment of the present invention. 1... Pipe, 3... Acid injection device, 4... Decarboxylation device, 13... Vacuum deaerator, 15... Evaporative salt water desalination device, 17... ...Limestone floor, 18...
・Steam ejector-120...Compressor. Patent applicant: Sasakura Machinery Co., Ltd.

Claims (1)

[Claims] In a method for post-treatment of distilled water in which salts mainly composed of calcium and carbon dioxide gas are dissolved in distilled water obtained by a salt water desalination apparatus using an evaporation method, acid is injected as carbon dioxide gas to be dissolved in the distilled water. Before supplying the salt water to the desalination equipment, it is introduced into a decarboxylation device that operates at approximately atmospheric pressure to decarboxylate approximately gl+l, and then introduced into a deaeration device that operates under reduced pressure to degas it. A method for post-treatment of distilled water, characterized in that the carbon dioxide gas in the extracted gas from the deaerator is used.