JPS632891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for continuously and, if necessary, intermittently 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.

Conventionally, in waterworks, rust etc. may occur in the pipes, producing 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 pipes and prevent red water from forming in tap water, it is necessary to adjust the pH of tap water.For this purpose, caustic soda, soda ash, slaked lime, etc. are injected into the water. Caustic soda is often used because it is easy to use. 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 pour powder, and the undissolved residue settles and sticks to the bottom, and because it is not used as a slurry. This is because when it is injected, it tends to deposit in the pipes along the way, and insoluble substances (for example, MgO, SiO ₂ , Fe ₂ O _3, etc.) contained in slaked lime mix into tap water.

Recently, in order to solve the above-mentioned inconvenience caused by slaked lime injection, a wire mesh was installed at the bottom of the tank to divide it into upper and lower parts.
A method has been proposed in which a deposited layer of slaked lime is formed on the wire mesh, water is fed from a separate constant pressure water tank at a constant flow rate from the bottom of the slaked lime storage and dissolution tank filled with water, and slaked lime saturated water is taken out from the top. There is.

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 dissolved, the dissolution tank is also small, and the overall apparatus is said to be compact.

However, according to 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. By disappearing. In addition, in the case of the conventionally proposed method of forming a deposited layer of slaked lime on a wire mesh, although there may be no problem in a short period of several months, the wire mesh will become clogged if used continuously for several years, and the water passage will become blocked. It will cause a blockage. That is, the wire mesh is clogged by a separate amount of sand or insoluble matter contained in slaked lime, or by iron or other minute amounts of insoluble matter contained in tap water. Furthermore, the free carbonic acid present in water is
In the presence of Ca(OH) ₂ , it is converted to CaCO ₃ , causing 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 dissolved layer. The present invention has been achieved to continuously obtain a saturated aqueous solution of slaked lime.

The present invention provides a slaked lime dissolving tank having a cylindrical or rectangular tube shape, or a lower part of which is an inverted truncated conical shape or an inverted truncated pyramidal shape (hereinafter simply referred to as an inverted truncated pyramidal shape), and the largest diameter portion of the cone. A vertical tank is used, in which a slaked lime supply port is provided on the top surface of the tank, and an overflow liquid receiving part with a slaked lime aqueous solution extraction pipe is provided at the top end of the tank. A water supply port and one or more stirring blades rotating vertically are provided at the bottom,
The present invention relates to a device that continuously takes out a slaked lime aqueous solution from the upper part of the tank while rotating the stirring blade and feeding water at a constant or substantially constant speed from the water supply port at the bottom to fluidize and dissolve the slaked lime.

In the present invention, the slaked lime dissolving tank may have a cylindrical shape with the upper and lower cross-sectional areas being the same; however, it is preferable to use a tank in which the upper and lower sections have different cross-sectional areas and at least the lower part is in the shape of an inverted truncated cone. preferable. When water is supplied from the bottom, the water flow rate decreases toward the top, so when stirring at the bottom, where the cross-sectional area is small, the height at which the slaked lime particles flow can be kept relatively low. In other words, the stirring blades can provide a strong stirring force considering the height at which the slaked lime particles flow, so the stirring blades act as a distributor to uniformly supply the water into the dissolution tank, and at the same time, they also serve as a distributor to uniformly supply water into the dissolution tank. It is possible to prevent the phenomenon that calcium carbonate produced by free carbonic acid in water and magnesium hydroxide produced from magnesium oxide present in slaked lime coat the surface of slaked lime particles and make it difficult to dissolve. This makes it possible to obtain a slaked lime aqueous solution with a substantially uniform concentration over a long period of time until almost all undissolved dissolved lime disappears.

Therefore, it is preferable to use an inverted truncated cone-shaped slaked lime dissolving tank in which the cross-sectional area of the upper part is larger than that of the lower part where the stirring blades are present. In addition, stirring blades that rotate vertically are used, for example, a stirrer with multiple notched blades attached to a horizontally arranged rotating shaft, and the stirrer cannot stir the slaked lime at the bottom of the slaked lime dissolution tank. Arrange the stirring blades so that no lumps occur. For this purpose, a single stirrer may be sufficient in some cases, but in many cases a plurality of stirrers may be provided in appropriate combinations depending on the size of the tank. The blades attached to the stirrer are often about 10 to 30 cm long.

By rotating the stirring blade vertically, the rotating shaft penetrates from the top of the tank to the bottom and the stirring blade rotates horizontally. Since there is no rotating body, the upward flow of the liquid in the tank is not disturbed.
Separation of slaked lime particles becomes easier. Furthermore, since the rotating shaft inserted into the tank can be shortened, the pedestal supporting the rotating shaft can also be made smaller, which is advantageous. There is also a method of vertically penetrating the rotating shaft into the tank from the bottom of the tank, but in this case, due to the solid slaked lime particles and undissolved substances present at the bottom of the tank, it is difficult to use a rotary seal that does not leak. accompanied by difficulties. When the rotary shaft of the present invention penetrates horizontally into the tank from the side wall, there is an advantage that the use of the rotary seal is relatively easier than when the rotary shaft penetrates vertically.

The stirrer is rotated from the beginning of operation, but when the slaked lime used contains a large amount of easily soluble fine particles, an aqueous slaked lime solution with a near saturated concentration can be obtained from the upper part of the tank without stirring. Therefore, in such a case, the stirrer may be rotated from the time when most of the slaked lime fine particles are dissolved and the concentration of the obtained slaked lime aqueous solution begins to decrease. Of course, there is no problem in rotating the agitator from the beginning of the operation.

The rotational speed of the stirrer should be within a range where the slaked lime particles flowing through stirring do not overflow from the top of the tank, but if the stirring speed is too high, the slaked lime particles will flow to a higher height, making it difficult to increase the height of the dissolution tank. This is not preferable because it requires a higher power consumption and the power consumption also increases.

Next, the apparatus used in the present invention will be explained with reference to the accompanying drawings.

FIG. 1 shows a specific example of the device used in the present invention,
A slaked lime supply port 2 on the top surface of the slaked lime dissolving tank 1, the tank 1
An overflow receiver 4 having an aqueous slaked lime solution outlet 3 is provided at the upper end of the tank 1, and a water supply pipe 5 and one or more stirrers 6 are provided at the bottom of the tank 1.
The stirrer 6 is attached from the side of the lower part of the tank, and is provided within the tank so that the stirring blade rotates vertically at the end of a horizontal shaft. The opening of the water supply pipe 5 is preferably directed downward to prevent backflow of the slaked lime slurry. Further, the opening of the water supply pipe 5 may be divided into a plurality of parts. Further, the upstream part of the tank 1 needs to be horizontal so as not to disturb the flow in the tank when the liquid overflows, and preferably a notch is provided.

In such an apparatus, a predetermined amount of slaked lime is put into the slaked lime dissolving tank 1 from the slaked lime supply port 2, and fresh water is supplied from the water supply pipe 5 at a constant or substantially constant rate. To supply new water at a constant or substantially constant rate, for example, a constant pressure water tank 7 is provided, new water is introduced through a pipe 8, and water is supplied while maintaining the water level in the constant pressure water tank 7 constant through an overflow pipe 9. Pipe 10, flow meter 11
The water is supplied to the tank 1 from the water supply pipe 5 through the water supply pipe 5. At this time, it is preferable that the flow rate of water be 2 mm/sec or less at the top of the tank.

When fresh water is supplied while slaked lime is fluidized and dissolved by the stirrer, the slaked lime aqueous solution with a concentration of approximately 1500 to 1800 ppm (depending on the water temperature) passes through the overflow liquid receiver until the slaked lime is almost gone. It can be obtained continuously from the outlet 3. In order to keep the concentration of the slaked lime aqueous solution constant regardless of the temperature, a heater may be installed in the constant pressure water tank to control the temperature of the water supply to be constant. Note that 12 is an insoluble matter removal tube.

In addition, when carrying out the present invention, as shown in FIG. , 5', and when the concentration of slaked lime in the solution obtained from one dissolution tank begins to decrease, this aqueous solution is further passed through the other dissolution tank and used in series to continuously provide a high concentration slaked lime aqueous solution. It is preferable to obtain the slaked lime by substantially completely utilizing the raw material slaked lime.

That is, 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, and there is no need to introduce it into the second dissolving tank 1', and the slaked lime aqueous solution can be taken out as it is. It may also be taken out from tube 3. However, when operating 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 3 gradually decreases. At least before the concentration of the slaked lime aqueous solution begins to decrease, the solution obtained from the first dissolution tank 1 is introduced into the second dissolution tank 1' by the switching valve 13. 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 the slaked lime in the first dissolving tank 1 is consumed, the water supply from the constant pressure water tank 7 is switched to the second dissolving tank 1' by the switching valve 14. At this time, there is sufficient slaked lime in the second dissolution tank 1', and the slaked lime aqueous solution extraction pipe 3'
The resulting aqueous solution has a concentration of about 1500-1800 ppm. During this time, the insoluble matter in the first dissolution tank 1 is removed from the insoluble matter removal pipe 12, and a predetermined amount of slaked lime is added to the tank and water is filled. Then, before the concentration of the slaked lime aqueous solution obtained in the second dissolution tank 1' begins to decrease, the aqueous solution is introduced from the second dissolution tank into the first dissolution tank using the switching valve 13', and the operation is continued in the same manner. A slaked lime aqueous solution is obtained from the aqueous solution take-out pipe 3 of the dissolution tank. By sequentially switching and using the slaked lime in this manner, the slaked lime aqueous solution can be produced while making almost complete use of the raw slaked lime.

Example Bottom inner diameter 334mmφ, top inner diameter 625mmφ, height 2800
The melting apparatus shown in Fig. 1 has a lower inverted truncated conical part with a height of 1400 mm and a cylindrical upper part. A device with a turbine-type stirring blade with an outer diameter of 175 mmφ that rotates in the same direction was used. This dissolution tank was filled with water, 20kg of slaked lime (containing 80% by weight of fine particles of 63μ or less) (equivalent to about 4 days of continuous operation) was added, and tap water maintained at a constant pressure in a constant pressure water tank was poured into a tank with an inner diameter of 334mmφ at the bottom. The slaked lime aqueous solution was continuously taken out from the take-out pipe at the upper end of the tank by feeding the tank at a flow rate of 0.4 to 0.8 mm/sec and rotating the stirrer at a circumferential speed of 0.5 to 1.0 m/sec. The resulting aqueous solution was a slaked lime aqueous solution with a constant concentration of 1,500 to 1,800 ppm until almost all undissolved dissolved lime disappeared. The height of the fluidized bed portion of the slaked lime particles at this time was 1600 to 1800 mm.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one example of the apparatus of the present invention, and FIG. 2 is a schematic diagram showing another embodiment of the present invention. 1, 1'... Slaked lime dissolving tank, 2... Slaked lime supply port, 3, 3'... Slaked lime aqueous solution extraction pipe, 4... Overflow liquid receiver, 5, 5'... Water supply pipe, 6... Stirring machine,
7... Constant pressure water tank, 9... Overflow pipe, 10... Water supply pipe, 11... Flow meter, 12... Insoluble matter removal pipe, 1
3, 13', 14...Switching valve.

Claims (1)

[Claims] 1 The slaked lime dissolving tank has a cylindrical shape or an inverted truncated cone shape at the bottom, and the largest diameter part of the cone is connected to the cylindrical upper part, and a slaked lime supply port is provided on the top surface of the tank, and a slaked lime supply port is provided at the top of the tank. One slaked lime dissolving tank equipped with an overflow liquid receiving part with a slaked lime aqueous solution extraction pipe in the section, or two slaked lime dissolving tanks arranged so that each slaked lime aqueous solution extraction pipe is connected to the water supply pipe of the other tank by a switching valve. The water tank is equipped with a water inlet and one or more agitators rotating in the vertical direction at the bottom of the tank, and tap water is supplied at a constant or almost constant speed while maintaining a constant water level in the constant pressure water tank. 1. An apparatus for continuously producing a slaked lime aqueous solution, characterized in that the slaked lime aqueous solution is connected to a means for feeding the slaked lime aqueous solution into the slaked lime dissolving tank.