JPS6335574B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for continuously producing a slaked lime aqueous solution to be injected into tap water for the purpose of adjusting the pH of tap water and protecting water pipes. This is a method of effectively using

BACKGROUND ART Conventionally, rust has sometimes formed in water pipes, resulting in red water, and there is a need to prevent this. Furthermore, the lifespan of pipes, which account for the majority of water facility costs, varies depending on the location; in some places, there is almost no rust even after nearly 80 years of use; There are some parts that need to be replaced. Such differences in the durability of pipes are due to the quality of tap water, and it is known that water with higher alkalinity and less corrosiveness has a longer lifespan.

In order to extend the life of the pipes and prevent red water from forming in the tap water, it is necessary to adjust the pH of the tap water.
For this reason, caustic soda, soda ash, slaked lime, etc. are injected, and recently caustic soda has been widely used because it is easy to handle.
However, while caustic soda only has the function of adjusting pH, when using slaked lime, it creates a calcium carbonate film on the pipe wall, which also has the function of preventing corrosion of pipes, making it more desirable to use slaked lime. It is. Despite this, slaked lime is not often used because it is difficult to dissolve and requires a large tank to store as a solution, it is difficult to continuously meter and inject powder, and undissolved lime deposits and sticks to the bottom, and it is not used as a slurry. This is because when injected, it tends to deposit in the pipes along the way, and when a cloudy slurry is injected, the tap water becomes colored.

Recently, in order to solve the above-mentioned inconvenience caused by slaked lime injection, a wire mesh is installed at the bottom of a cylindrical tank to partition the top and bottom, and a layer of slaked lime is formed on the wire mesh.
A method has been proposed in which water from a separately provided constant pressure water tank is fed at a constant flow rate from the bottom of a slaked lime storage and dissolution tank filled with water, and slaked lime saturated water is discharged from the top. According to this method, the stock slaked lime remains as it is, and the tank is extremely small compared to solution storage, and since only the amount to be injected is melted, the dissolution tank is also small, and the overall apparatus is said to be compact.

However, according to the research conducted by the present inventors, in the above method, a slaked lime aqueous solution with an expected concentration can be taken out for the first few hours, but the concentration of slaked lime gradually decreases. This is because pores are formed in the slaked lime deposit layer, and as time passes, the pores become larger, allowing water to locally pass through areas where there is no slaked lime deposit, allowing good contact between water and slaked lime. due to the fact that it no longer exists. In addition, in the case of the conventionally proposed method of forming a deposited layer of slaked lime on a wire mesh, there may be no problem in a short period of several months, but if used continuously for several years, the wire mesh will become clogged and the water passage will become blocked. It will cause a blockage. That is, the wire mesh is clogged by a trace amount of sand or insoluble matter contained in slaked lime, or by a trace amount of iron or other insoluble matter contained in tap water. Furthermore, _free carbonic acid present in water is
Since it is converted to CaCO ₃ , it causes scaling and clogging of the wire mesh.

As a result of various studies conducted by the present inventors to completely eliminate these inconveniences and obtain slaked lime saturated water stably and continuously for a long period of time, we have found that it is possible to obtain slaked lime saturated water stably and continuously for a long period of time without using a wire mesh inside the dissolution tank. The present invention has been achieved in which a saturated aqueous solution of slaked lime is obtained continuously over time.

The present invention provides a water supply pipe and an insoluble matter outlet at the bottom of a tank having a cylindrical or prismatic upper part and an inverted truncated pyramid shape at the lower part, and a stirring blade or an upper end of the tank that rotates horizontally directly above the water supply pipe. An overflow liquid receiving part having a slaked lime aqueous solution extraction pipe is provided in the tank, a deposited layer of slaked lime is formed inside the tank, and tap water is fed through the bottom water supply pipe at a constant or substantially constant rate while stirring. The blades are rotated at low speed to flow and dissolve the slaked lime, and the slaked lime aqueous solution is taken out from the overflow liquid receiving part. When the concentration of the aqueous solution taken out from the overflow liquid receiving part of the first dissolution tank starts to decrease from the concentration close to the saturation of slaked lime, the aqueous solution is introduced into the water supply pipe of the second dissolution tank, and then 2 until the concentration at the outlet of the take-out pipe of the overflow liquid receiving part of the dissolution tank 1 reaches 80 to 65% of the concentration before reduction.
The slaked lime saturated aqueous solution is continuously taken out by operating the tanks in series, then operating the second dissolving tank independently, and then repeating such serial or independent operation of the two tanks and sequentially switching them. The present invention relates to a method for producing a saturated aqueous solution of slaked lime.

The method of the present invention will be explained below with reference to the accompanying drawings.

As shown in FIG. 1, the present invention uses a device in which two slaked lime dissolving tanks each having horizontally rotating stirring blades are connected to each other to continuously obtain a saturated aqueous solution of slaked lime by almost completely utilizing the raw material slaked lime. It's a method.

Water supply pipes 2, 2' and insoluble matter outlet ports 3, 3' are provided at the bottom of the dissolution tanks 1, 1', stirring blades 4, 4' are provided above the water supply pipes 2, 2', and the upper ends of the tanks 1, 1' Two slaked lime dissolving tanks each having an overflow liquid receiving part 6, 6' having a slaked lime aqueous solution extraction pipe 5, 5' are connected to each other, and each slaked lime solution extraction pipe 5, 5' is connected to a water supply pipe by a switching valve 7, 7'. 2 and 2' is used.

Using such a device, slaked lime can be supplied into the dissolution tanks 1 and 1' through the slaked lime supply ports 10 and 10' by an appropriate method, but in order to prevent the slaked lime powder from scattering, a slaked lime bag or container is used. It is preferable that a pipe 13 connected to a bag filter 12 is connected to the bag 11, the absorption fan 14 absorbs the lime, and the slaked lime is supplied through the bag filter 12, the rotary valve 15, and the slaked lime supply ports 10, 10'. 16 is a compressor for backwashing and dropping powder adhering to the bag filter. A predetermined amount of slaked lime may be put into the slaked lime dissolving tank before operation, and when the slaked lime is almost completely used up and the concentration of the produced slaked lime aqueous solution has decreased, it may be supplied again. Water is supplied to the dissolution tanks 1 and 1' at a constant or approximately constant rate. For this purpose, for example, a constant pressure water tank 8 is provided, tap water is introduced through a pipe 17, and the constant pressure water tank is introduced through an overflow pipe 18. The liquid is supplied from the water supply pipe 2 through the water supply pipe 19 and the flow rate controller 20 while keeping the water level of 8 constant, and the stirring blade 4 is rotated at low speed to fluidize and dissolve the slaked lime, and the liquid is taken out from the slaked lime aqueous solution extraction pipe 5 at the upper end of the tank. The slaked lime aqueous solution is introduced into another dissolution tank 1' through the pipe 21' via the water supply pipe 2' using the switching valve 7, and in the same way, the slaked lime aqueous solution is continuously taken out from the slaked lime aqueous solution extraction pipe 5' at the upper end of the tank 1'. It is. In this case, the liquid flowing out from the first dissolving tank 1 is almost a saturated aqueous solution when there is sufficient slaked lime in the dissolving tank 1, so there is no need to intentionally introduce it into the second dissolving tank 1', and it can be taken out as it is. However, if the dissolution tank 1 is operated for a long period of time, the amount of slaked lime in the dissolution tank 1 decreases, and the concentration of the slaked lime aqueous solution obtained from the slaked lime aqueous solution extraction pipe 5 gradually decreases. At least at the point when the concentration of this slaked lime aqueous solution starts to decrease, the first
The solution obtained from the dissolution tank 1 is transferred to the second dissolution tank 1'.
(Start of serial use). By doing so, the slaked lime saturated aqueous solution can be continuously obtained while substantially completely utilizing the slaked lime in the first dissolution tank 1. After slaked lime in the first dissolving tank 1 is consumed, the water supply from the constant pressure water tank 8 is switched to the second dissolving tank using the valve 9 (single use resumes. (This is when the concentration of the obtained slaked lime aqueous solution reaches 80 to 65% of the concentration at the time when the concentration starts to decrease.) At this time, there is enough slaked lime in the second dissolution tank 1', and the slaked lime aqueous solution The aqueous solution obtained from the take-out tube 5' has a substantially saturated concentration. During this time, the insoluble matter in the first dissolution tank 1 is removed from the insoluble matter outlet 3, a predetermined amount of slaked lime is newly added and water is filled, and the concentration of the slaked lime aqueous solution obtained from the second dissolution tank is At the point when the aqueous solution starts to drop, the aqueous solution coming out of the second dissolving tank 1' is introduced into the first dissolving tank 1 by the switching valve 7',
The same operation is carried out to obtain a saturated lime saturated aqueous solution from the aqueous solution take-out pipe 5 of the first dissolution tank. By sequentially switching and using the slaked lime in this manner, it is possible to continuously produce a saturated aqueous solution of slaked lime while substantially completely utilizing the raw slaked lime.

The slaked lime dissolving tanks 1, 1' used in the present invention have a cylindrical or prismatic upper part, preferably an inverted truncated tank with different cross-sectional areas at the bottom and the upper part. If you use a tank with an inverted truncated conical bottom,
When water is supplied from the bottom, the flow rate of water decreases toward the top, so when stirring at the bottom, which has a small cross-sectional area, the height at which slaked lime particles flow can be kept relatively low. In other words, it is possible to apply a strong stirring force to the height at which the slaked lime particles flow, so the stirring blades serve as a distributor that uniformly supplies the supply water into the dissolution tank, and at the same time, they also serve as a distributor to uniformly supply the water into the dissolution tank. This is convenient because it allows for effective contact.

The stirring blades 4 may have any shape such as a paddle shape, but it is preferable to use a turbine type so that the slaked lime slurry layer does not accumulate too much on the bottom surface. Try not to give as much as possible. In other words, the slaked lime fine particles should not be entrained in the slaked lime aqueous solution overflowing from the upper end of the tank, and for this purpose, at least no fluidized bed of slaked lime particles should be observed in the upper cylinder of the tank. The upper limit of the height of the inverted cone part is based on the results of many experiments.If the tank height is fixed at approximately 2500 mm, the upper limit of the height of the slaked lime particles is It has been confirmed that the height of the flow is 1,600 to 1,800 mm from the bottom of the tank, which is approximately 2/3 of the total height of the tank from the bottom.

As for the lower limit, it will not have a big effect unless the minimum diameter of the bottom cone is increased, but it should be about 1/3 of the total tank height from the bottom. Regardless of whether the slaked lime particles used are fine particles or coarse particles, the stirring blades are rotated from the beginning of operation, but the rotation speed of the stirring blades only needs to be within a range where the slaked lime particles flowing due to stirring do not overflow from the top of the tank. If the stirring speed is too high, the slaked lime particles will flow to a higher height, making it necessary to unnecessarily increase the height of the dissolving tank, and also increasing power consumption, which is not preferable. The stirring speed varies depending on the size of the dissolution tank and the shape of the stirring blade, but according to experimental results, a circumferential speed of 1 m/sec or less is sufficient.
Preferably, the flow rate of water supplied from the bottom of the dissolution tank should be set to 2 mm/sec or less, preferably 1 mm/sec or less, to avoid unnecessarily increasing the height of the dissolution tank.

In carrying out the present invention, the water temperature changes depending on the season, and the solubility of slaked lime may change slightly, but if it is necessary to maintain a constant concentration of the obtained slaked lime aqueous solution, a dissolution tank or a constant pressure water tank is used. A stable slaked lime aqueous solution can be obtained by heating the water by installing a heater inside it, or by cooling it to maintain a constant water temperature.

Furthermore, the method of the present invention can be effectively used when minerals are supplied to drinking water obtained by desalinating seawater.

Example 1 Bottom inner diameter 334 mm, upper inner diameter 625 mm, height 2830
The device as shown in Fig. 1 is equipped with two melting tanks each equipped with a turbine-type stirring blade with an outer diameter of 175 mm inside a transparent vinyl chloride tank whose lower part has an inverted truncated pyramid shape as shown in Fig. 1. Using.

23 kg of slaked lime was put into each of the two dissolving tanks, water was filled, and water was introduced from the bottom of one dissolving tank 1 at a speed of 0.4 mm/sec to the bottom part with an inner diameter of 334 mm.
From the start, rotate the stirring blade at a circumferential speed of 0.5 m/sec, and from the slaked lime aqueous solution extraction pipe 5 at the upper end of the tank, approx.
A slaked lime aqueous solution of 1800 ppm was obtained, but the concentration of the slaked lime aqueous solution started to decrease after 90 hours had passed, so the liquid in the slaked lime aqueous solution extraction pipe 5 was introduced into the second dissolution tank 1' using the switching valve, and the slaked lime aqueous solution extraction pipe 5 About 1800 ppm slaked lime aqueous solution was continuously obtained from '.

After 120 hours, the concentration of slaked lime in the liquid coming out of the first dissolving tank reached 1400 ppm, so the water from the constant pressure water tank was directly supplied to the second dissolving tank 1'.
The insoluble matter inside was removed from the insoluble matter extraction pipe, 23 kg of slaked lime was added, and water was filled. After 190 hours, the concentration of slaked lime in the liquid coming out of the second dissolving tank 1' began to decrease, so when the liquid coming out of the second dissolving tank was introduced into the first dissolving tank 1 using the switching valve 7', it continued. A slaked lime aqueous solution of about 1800 ppm was obtained.

Example 2 The dissolution tank of the apparatus used in Example 1 had an inner diameter of 146 mm,
A device was used in which the stirring blade was replaced with a turbine-type stirring blade with an external diameter of 50 mm in a cylindrical non-chloride tank with a height of 2350 mm and a baffle inside. When 0.4 kg of slaked lime was put into this dissolution tank and the operation was performed in the same manner as in Example 1 at a water flow rate of 0.2 mm/sec, a stable slaked lime aqueous solution was obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an apparatus for producing a slaked lime aqueous solution used in the present invention. 1, 1'...dissolution tank, 2, 2'...water supply pipe, 3,
3'... Insoluble matter outlet, 4, 4'... Stirrer, 5,
5'... Slaked lime aqueous solution extraction pipe, 6, 6'... Overflow liquid receiver, 7, 7'... Switching valve, 8... Constant pressure water tank, 9... Switching valve, 10, 10'... Slaked lime supply Mouth, 11... Container bag, 12... Bag filter, 14... Suction fan, 15...
Rotary valve, 16...Compressor, 1
8... Overflow pipe, 19... Water supply pipe, 20... Flow rate controller.

Claims (1)

[Claims] 1. A water supply pipe and an insoluble matter outlet are installed at the bottom of a tank whose upper part is cylindrical or prismatic and whose lower part is an inverted truncated pyramid.
A stirring blade that rotates horizontally right above the water supply pipe and an overflow liquid receiver having a slaked lime aqueous solution extraction pipe are provided at the upper end of the tank, and a layer of slaked lime is formed inside the tank, and the water is removed from the bottom water supply pipe. Two slaked lime dissolving tanks are provided, in which the aqueous slaked lime solution is taken out from the overflow liquid receiving part, while the stirring blades are rotated at low speed while water is fed at a constant or substantially constant speed, and the slaked lime is fluidized and dissolved. Each slaked lime aqueous solution extraction pipe is connected to the water supply pipe of another tank by a switching valve, and the concentration of the aqueous solution taken out from the overflow liquid receiving part of the first dissolution tank starts to decrease from a concentration close to the saturation of slaked lime. After introducing the water into the water supply pipe of the second dissolution tank at the point in time, the two tanks are fed until the concentration at the outlet of the take-out pipe of the overflow liquid receiving part of the first dissolution tank reaches 80 to 65% of the concentration before reduction. are operated in series, and then the second dissolution tank is operated independently.
A method for producing a slaked lime saturated aqueous solution, which is characterized in that the slaked lime saturated aqueous solution is subsequently taken out continuously by repeatedly operating the two tanks in series or singly or by successively switching them.