JPS6146293A - Method for converting freshwater into drinking water - Google Patents

Abstract

PURPOSE:To convert easily freshwater into drinking water by measuring the resistivity value of the water after passing through a filter, and regulating the amt. of gaseous carbon dioxide to be blown into the freshwater when freshwater is made drinkable by passing the freshwater through the filter packet with limestone, etc. CONSTITUTION:Gaseous carbon dioxide-contg. gas generated from an apparatus is blown into freshwater, which is formed in the seawater desalination apparatus by evaporation, to obtain gaseous carbon dioxide-contg. water. Then the gaseous carbon dioxide-contg. water is passed through a filter, packed with granular materials of limestone and/or dolomite, to increase the hardness. The resistivity value of the water after passing through the filter is continuously detected, and the amt. of said gaseous carbon dioxide-contg. gas to be blown in is regulated so that the resistivity value may be regulated to a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for obtaining drinking water by adding a hardness component to fresh water produced in a half-water desalination apparatus using an evaporation method.

Since the fresh water obtained by the evaporation method seawater desalination equipment is distilled water, it does not contain all kinds of ions and dissolved gases.
Hardness components such as calcium and magnesium are almost absent.

For this reason, if the fresh water mentioned above is conveyed using 11 general-purpose water conveyance equipment, corrosion of the steel pipes used in the water conveyance equipment and elution of concrete materials may occur, which may impair the function of the water conveyance equipment. There is nine. On the other hand, when used as drinking water, it has been pointed out that for the reasons mentioned above, it is tasteless and not only tastes bad, but can also cause heart disease.

[Prior Art] Therefore, in the past, for example, the document "Desalinati
On.

39 (1981) 503-520 J K, quicklime, slaked lime, dolomite, etc. have been used as hardness increasing agents, and a method of dissolving these in fresh water has been carried out, but among these, limestone and/or When using dolomite, fresh water into which carbon dioxide gas has been blown is introduced into a filter filled with granules (in drinking water production equipment, a bed of limestone and/or dolomite is usually called a filter), and calcium or magnesium is added to the filter. A common method is to increase the hardness of water by eluting it as carbonate.

As a source of carbon dioxide, methods have been proposed such as recovering carbon dioxide from exhaust gas obtained by separately burning fuel, and transporting carbon dioxide gas in carbon dioxide cylinders. The method of using it effectively is attracting attention as it is attractive from an economical point of view.

[Problem that the invention seeks to solve]

However, the carbon dioxide gas generated from desalination equipment is originally generated when bicarbonate contained in seawater is decomposed by the reaction of formula (1) below, and is 2HO (h-→Cot
+ 00g”-+ Hz O・・・・・・・・・・・・
...(1) This bicarbonate concentration is the seawater environment, that is, the temperature.

It is not necessarily constant as it depends on water temperature, wind speed, etc.

In addition, since the reaction rate of equation (1) is affected by temperature, the amount of carbon dioxide gas generated increases or decreases depending on the operating conditions of the desalination device, that is, load fluctuations.

As a result, the amount of carbon dioxide-containing gas and the concentration of carbon dioxide gas generated from the desalination device fluctuate.

If a carbon dioxide-containing gas whose amount or composition has changed is directly blown into fresh water to produce carbonated water, the carbon dioxide concentration in the water will also vary. When the carbonated water passes through a filter filled with quicklime and/or dolomite, it dissolves according to (2) and (3) 2 below, so 0a00s + OO * + HtO - Oa (HOOs) x after dissolution.
”...Song interval (21oaIIMg(OOn)* + 2
00t + 2HtOqkJa(HOOs)t +1
4g (aaoait...3) Calcium and/or magnesium in fresh water.

Both bicarbonate roots fluctuate with changes in the carbonate concentration in carbonate-containing water.

The above-mentioned fluctuations in the eluted components in the treated drinking water go against the original purpose of making the treated water into drinking water, which is to reduce and stabilize the corrosivity, and it is also incomplete from the perspective of improving the drinking taste. . Furthermore, the amount of limestone and dolomite filled in the filter varies, which is inconvenient in terms of refilling operations. Carbonic acid produced by evaporative seawater desalination equipment
The system itself that utilizes gas is relatively new, and so far no method has been found to solve the above-mentioned disadvantages.

[Means for solving problems]

The present invention was discovered as a result of intensive research to solve the above-mentioned problems of the conventional method. This is a method for producing fresh drinking water by adjusting the amount of carbon dioxide-containing gas blown into the fresh water.

Specifically, fresh water produced by a seawater desalination device using an evaporation method is made into carbonated water by blowing carbon dioxide-containing gas generated from the desalination device, and then filtered with limestone and limestone or dolomite granules. In the □ method for obtaining drinking water by passing the fresh water through the filter, the specific resistance value of the fresh water after passing through the filter is continuously detected, and the amount of the carbon dioxide-containing gas blown is adjusted so that the specific resistance value becomes a predetermined value. This paper proposes a method for converting freshwater into drinking water with its characteristics.

[Effect]

In the method of the present invention, the specific resistance value in the treated water at the filter outlet is continuously detected, and the amount of carbon dioxide-containing gas generated in the desalination equipment to be blown into the fresh water in the filter population is fed so that this value becomes a predetermined value. To adjust the parameters, first □
It has the advantage that the properties of the treated water at the filter outlet can be stably maintained even if the amount of carbon dioxide gas or the gas composition changes due to the reasons mentioned above.

The present inventors believe that there is a certain correlation between the specific resistance value and the concentration of dissolved components in the liquid, such as calcium, magnesium, and bicarbonate. The present invention was developed based on the fact that continuous measurement can be carried out extremely easily simply by immersing the target in water. In other words, the properties of the treated water at the filter outlet are specifically calcium and magnesium, which increase hardness, and total alkalinity, which is mainly caused by the bicarbonate machine, and it is important to understand the correlation between the specific resistance value and these values in advance. It has been found that it is possible to continuously observe the properties of the water after the above treatment by measuring the specific resistance value.

〔effect〕

According to the method of the present invention, even when the amount of carbon dioxide gas generated in the desalination generator increases, limestone and/or dolomite dissolves in the fresh water to a level exceeding a predetermined value, increasing the consumption of limestone and dolomite more than necessary. Moreover, when the amount of carbon dioxide gas generated decreases, by increasing the amount of carbon dioxide-containing gas blown in, a predetermined amount of limestone and/or dolomite can be dissolved, and fresh water can be converted into drinking water. obtain.

〔Example〕

Next, in order to clarify the embodiment of the method of the present invention, it will be explained with reference to the drawings.

FIG. 1 shows the case where the present invention is applied to the drinking of fresh water obtained from a multi-stage flash evaporation method of seawater. Seawater is supplied to the multistage flash evaporator 1 through line a, and the produced fresh water is pumped to the carbon dioxide absorption tower 2 through line b.

On the other hand, the concentrated seawater is discharged out of the system through line 0, and among the carbon dioxide-containing gases generated as a result of evaporation, the gas used to make drinking water passes through line d and is pressurized by compressor 3, after which the flow rate After passing through the control valve 7, it is sent to the carbon dioxide absorption tower 2 via line f. Excess carbon dioxide-containing gas is discharged from ejector (not shown) K to line e.
is discharged from the system through the In the carbon dioxide absorption tower 2, a predetermined amount of carbon dioxide is dissolved in the fresh water fed through the line bK, and then fed into the filter 4 through the line h. Undissolved carbon dioxide and gases such as nitrogen and oxygen are discharged out of the system via line gJ. As the carbon dioxide absorption tower 2, a packed tower can be used.

Further, depending on the absorption conditions, a line mixer may be used instead of the absorption tower 20. The carbonated water fed through line h dissolves the limestone filled in the filter while passing through filter 4, increases hardness and total alkalinity, and is then extracted from line 1. A resistivity detection end 5 is installed in the line 1 to continuously measure the resistivity of the treated water and its output is input to a controller 6. Detection end 5
Usually, electrodes are used.

A signal corresponding to the difference from a preset specific resistance value is outputted from the controller 6 via line k, and the flow rate of the carbon dioxide-containing gas sent to the absorption tower 2 is regulated by the control valve 7. If the resistivity value measured by the end 5 is less than the set value, the regulating valve 7 is opened, and if the resistivity value is higher than the set value, the regulating valve 7 is closed. Through such control, water whose hardness, total alkali, and TDS (total dissolved solids) are set to predetermined values is taken out of the thread from the rhinoceros. The water taken out is added with alkali and adjusted (not shown) to become stable water without corrosive properties.

In Fig. 1, the entire amount of fresh water produced by the multi-stage flash evaporator IK is extracted through line b and treated to make it into drinking water, but the application of the present invention is not limited to this, and the production It is also applicable to the case where a part of the fresh water produced is treated to make it into drinking water.

Fresh water and carbon dioxide-containing gas produced by the multi-stage flash evaporation device 1 of seawater were separated and treated by the potable water conversion method shown in FIG. The amount of fresh water extracted is 20 (11'/h
r, and the carbon dioxide-containing gas is extracted from the first stage and the seventh stage, and its flow rate is regulated by the control valve 7. A Raschig ring packed tower was used as the absorption tower 7, and the filter 4 was filled with limestone having a sieve diameter of 11III to 4 wm.

Total hardness after treatment is 60wIgμ based on l calcium carbonate.
The setting value of the controller 6 was determined so that

The analysis results were as follows.

Average value standard deviation Total hardness <21P/l as oaOos) 60.31
．． 88 total power level (jlIP# as 0aOOs
) 60.4 1.38 The average flow rate of carbon dioxide-containing gas collected during the above sampling period was 4.2 NZ
/h. The total number of samples was 12.

Comparative Example: In FIG. 1, the controller 6 was set to manual, and the flow rate of the carbon dioxide-containing gas fed into the absorption tower 2 was fixed to the average value during the sampling period of the example. The other conditions were exactly the same as in the example, and the total hardness and total alkalinity of the produced water taken out from j were sampled every 2 hours as in the example.

・The analysis results were as follows.

Average value Standard deviation Total hardness <9/l aaσaoos) 58.5 6.
94 full strength level (mfll as 0aoos)
5 &8' 6.24 The total number of samplings is the same as in the example.

Comparing the Examples and Comparative Examples, the properties of the water after treatment in the Examples are very close to the target values and have little variation, which clearly shows the effects of the application of the present invention.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for explaining the method of the present invention. 1... Multi-stage flash evaporator, 2... Carbon dioxide absorption tower, 3... Compressor, 4... Filter,
5... Specific resistance detection end, 6... Controller, 7... Flow rate control valve.

Claims (1)

[Claims] Fresh water produced by a seawater desalination device using the evaporation method is made into carbonated water by blowing carbon dioxide-containing gas generated from the desalination device, and then passed through a filter filled with limestone and/or dolomite granules. In the method for obtaining drinking water, the specific resistance value of the fresh water after passing through the filter is continuously detected, and the amount of the carbon dioxide-containing gas blown is adjusted so that the specific resistance value becomes a predetermined value. A method of converting fresh water into drinking water.