JPS58223481A - Method for controlling ph of tap water - Google Patents

Abstract

PURPOSE:To control the pH of water of waterworks, by supplying water to the 1st dissolution tank until >=80wt% the supplied slaked lime is dissolved, removing the soln. therefrom, transferring the undissolved slaked lime into the 2nd dissolution tank, controlling the pH thereof to <=10 and supplying the soln. continuously to a trough. CONSTITUTION:Slaked lime of the amt. corresponding to the consumption in continuous operation of, for example, two days, is charged beforehand into the 1st dissolution tank 1, and water is introduced continuously therein from a supply pipe 3. The slaked like is dissolved under stirring and the approximately satd. aq. slaked lime soln. is removed from an outflow pipe 4. Slaked lime charged beforehand into the tank 1 is dissolved with <=80wt% thereof and to the extent that the pH of the outflow liquid does not decrease down to 12 or below. The undissolved slaked lime in the tank 1 is transferred in the form of slurry into the 2nd dissolution tank 2, where water is introduced continuously from a water supply pipe 5 and the aq. slaked lime soln. of <=10pH is obtd. from an outflow pipe 6. The aq. slaked lime solns. to be flowed from the 1st dissolution tank and the 2nd dissolution tank are supplied to a trough 7, whereby the pH of tap water is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting the pH of tap water using slaked lime.

Conventionally, in water supply systems, rust has sometimes formed in pipes, resulting in red water, and it is necessary to prevent this. Furthermore, the lifespan of pipes, which account for the majority of water facility costs, varies depending on the location, with some places showing almost no rust even after nearly 80 years of use, while others require replacement after just two years. There are some things you have to do. The difference in durability of these five types of pipes is due to the quality of tap water, and it is known that water pipes with high alkalinity and low corrosivity have a long lifespan.

In order to extend the life of pipes and prevent red water from forming in tap water, it is necessary to adjust the pH of tap water, and for this purpose injection of caustic soda, soda ash, slaked lime, etc. Caustic soda is often used because it is easy to use. However, caustic soda is simply 7)H
While slaked lime only has an adjustment function, it is more desirable to use slaked lime because it also has the function of forming a calcium carbonate film on the pipe wall and preventing corrosion of the pipe.

There are powder injection methods, slurry injection methods, and solution injection methods for injecting slaked lime into tap water to adjust pH, but powder injection has problems with dust and difficulty in quantitative injection, and slurry injection has problems. Although it varies depending on the slurry concentration, it causes scaling inside the stock tank and piping, making it difficult to operate. On the other hand, solution injection is a method in which slaked lime is continuously dissolved and discharged in a dissolution tank, and is extremely superior in terms of fluid transfer.

However, with this solution injection method, undissolved substances remain in the dissolution chamber,
There was a problem in processing this insoluble matter.

The present inventors investigated this residual insoluble material and found that its components are carbonic acid produced by the reaction of slaked lime with carbonic acid, etc. in raw water, and slaked lime that is prevented from dissolving due to the presence of this calcium carbonate. In addition, I learned that this substance hardly dissolves while the pH of the slaked lime aqueous solution is maintained at 12 to 13 in the dissolution tank, and furthermore, it takes a very long time to dissolve it. .

Therefore, the present inventors have made full use of slaked lime, that is, without leaving any undissolved calcium compounds, and have
The present invention was achieved by studying a method for stably performing HH adjustment.

The present invention is provided with a dissolving tank for slaked lime powder and a dissolving tank for further dissolving the undissolved content in the dissolving tank, and the dissolving tank is used until at least 80 weight of the slaked lime charged in advance in the first dissolving tank is dissolved. After taking out a roughly saturated aqueous solution of slaked lime while supplying water, the undissolved portion is transferred to a second dissolution tank, and dissolved while supplying water to this tank, and a slaked lime aqueous solution with a pH of 10 or less is continuously taken out. This is a method for adjusting the pH of tap water by continuously supplying a slaked lime aqueous solution obtained from a dissolution tank to a receiving well.

Next, the present invention will be specifically explained with reference to the accompanying drawings.

In the attached diagram, 1 is the first dissolving tank, and 2 is the second dissolving tank. Both dissolving tanks have a stirrer inside, and the raw water is poured from the bottom of the tank in the first tank and from the bottom or top in the second tank. The slaked lime aqueous solution is taken out from the top. A considerable amount of slaked lime for continuous operation, for example, for two days, is charged into this first dissolution tank in advance, and water is continuously introduced from the water supply pipe 3 at the bottom, and the slaked lime is dissolved under gentle stirring to obtain a substantially saturated slaked lime aqueous solution. is taken out from the upper outflow pipe 4. In this first dissolving tank, the slaked lime charged in advance is dissolved to an extent of 80% or less and the pH of the effluent does not fall below 12. The undissolved content in the first dissolution tank is transferred to the second dissolution tank in the form of slurry, water is continuously introduced from the water supply pipe 5, and water is continuously introduced from the outflow pipe 6 (p) (1
A slaked lime aqueous solution with a concentration of 0 or less is obtained. The slaked lime aqueous solution flowing out from the first and second dissolution tanks is sent to the receiving well T and is used for PK adjustment of tap water.

The undissolved content in the first dissolution tank may be transferred to the second dissolution tank at once, and the operation may be performed so that only water is continuously introduced into the second dissolution tank, but in another embodiment, the first The undissolved content in the dissolution tank may be temporarily stored in the sudock tank 8 and then quantitatively and continuously supplied to the second dissolution tank by the pump 9.

When carrying out the present invention, the first dissolution tank and the second dissolution tank are operated in parallel, so that a slaked lime aqueous solution with a substantially constant pH is obtained continuously and quantitatively, and the 7) H adjustment of tap water is stabilized. It can be done by

[Brief explanation of drawings]

The accompanying drawing shows an example of an apparatus used to carry out the present invention. 1...First dissolution tank, 2...Second dissolution tank, 3゜5
... Water supply pipe, 4, 6 ... Outflow pipe, 7 ... Water landing well,
8...Stock tank, 9...Pump.

Claims (1)

[Claims] In a method of adjusting the pH of tap water by injecting a substantially saturated aqueous solution of slaked lime, water is supplied to the nuclide until 80% by weight or more of the supplied slaked lime is dissolved in the first dissolution tank, and after the substantially saturated aqueous solution of slaked lime is taken out. The undissolved content is transferred to a second dissolution tank and dissolved while supplying water to the nuclide to form a slaked lime aqueous solution with a pH of 10 or less, and the slaked lime aqueous solution obtained from both bath dissolution tanks is continuously supplied to the receiving well. How to adjust the pIi of tap water.