JPS6358762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and 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. be.

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 places that need to be converted. 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 also has the function of creating a calcium carbonate film on the pipe wall and preventing corrosion of the pipe line, making it more desirable to use slaked lime. It is. Despite this, slaked lime is not often used because it is difficult to dissolve, requires a large tank to store as a solution, it is difficult to continuously measure and inject powder, and undissolved lime deposits and adheres to the bottom, and slurry This is because if it is injected directly, it tends to deposit in the pipes along the way.

Recently, in order to solve the above-mentioned disadvantages due to slaked lime injection, a wire mesh was installed at the bottom of the tank to divide it into upper and lower parts, and a deposited layer of slaked lime was formed on the wire mesh, and a slaked lime storage and dissolution tank filled with water was installed separately from the bottom of the tank. A method has been proposed in which water is fed into a constant pressure water tank at a constant flow rate and slaked lime saturated water is taken out 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 dissolved, the dissolution tank is also small, and it is said that the overall apparatus becomes more compact.

However, according to the research conducted by the present inventors, although in the above method it is possible to take out a slaked lime aqueous solution of the expected concentration for the first few hours, the concentration of slaked lime gradually decreases.

This is because pores are formed in the slaked lime deposit layer, which become larger over time, 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, 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, resulting in water leakage. This will block the passage. 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 the water supply. Furthermore, free carbonic acid present in water is converted to _CaCO3 in the presence of Ca(OH) ₂ , so
This 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 to obtain a saturated aqueous solution of slaked lime continuously for a period of time.

The present invention provides a slaked lime dissolving tank having a cylindrical or square tube shape, or a lower part of which is an inverted truncated conical shape or an inverted truncated conical shape, and an upper part of which is a cylinder or a rectangular tube (hereinafter simply referred to as an inverted truncated conical shape). An eggplant tank is used, and a water supply port is provided at the bottom of the tank, and a part of the slurry liquid is taken out of the tank from the side wall of the tank where the slurry in which slaked lime particles are suspended is provided, and a circulation pump is installed to supply the tank to the bottom. To,
After adding a predetermined amount of slaked lime, the liquid is circulated by a circulation pump, and tap water is fed at a constant or almost constant rate from the water supply port at the bottom to fluidize and dissolve the slaked lime, while continuously pouring the slaked lime aqueous solution from the top of the tank. It relates to a device for taking out.

Next, the present invention will be explained in detail 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 liquid receiving part 4 having a slaked lime aqueous solution extraction pipe 3 is provided at the upper end, a water supply pipe 5 is provided at the bottom of the tank 1, and a circulation pump 6 is provided outside the tank 1 to Part of the slurry liquid in the tank is extracted from the middle of the inverted conical part through pipe 7 and discharged to the bottom of tank 1 through pipe 8, thereby stirring and fluidizing the slaked lime deposited at the bottom of tank 1, thereby dissolving the slaked lime. let The discharge pipe 8 connected to the circulation pump 6 can also be used as the water supply pipe 5 for fresh water. In this case, fresh water is preferably supplied to the suction side of the circulation pump 6. The discharging pipe 8 may have a single distal end, but is preferably divided into a plurality of distal ends in order to make the slaked lime deposited on the bottom of the tank 1 flow as uniformly as possible.

The slaked lime dissolving tank 1 used in the present invention may be cylindrical or prismatic, but preferably the first
As shown in the figure, an inverted truncated cone-shaped tank is used in which the cross-sectional area is different at the bottom and top of the tank. When the circulation pump 6 discharges liquid from the pipe 8 to the bottom part with a small cross-sectional area, the flow rate of the liquid decreases as it goes to the top, so a large flow rate can be given at the bottom part with a small cross-sectional area, and the discharge It is advantageous that the slaked lime particles can be strongly fluidized by the liquid, and the height at which the slaked lime particles flow can be kept relatively low.

When carrying out the present invention, 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 substantially constant rate. To supply new water at a substantially constant rate, for example, a constant pressure water tank 9
new water is introduced from pipe 10, and overflow pipe 1
1, the water is supplied from the water supply pipe 5 to the tank 1 through the water supply pipe 12 and the flow meter 13 while keeping the water level in the constant pressure water tank 9 constant. It is preferable that the flow rate of water at this time is 2 mm/sec or less at the top of the tank. Further, the larger the amount of liquid circulated by the circulation pump 6, the more vigorously the slaked lime particles can be made to flow, which is preferable, but it is determined as appropriate depending on the state of flow of the slaked lime particles. However, the height of the fluidized bed of slaked lime particles should be approximately 1/2 of the total height of the tank, and the position from which the tank slurry is extracted from the side wall of the tank should not exceed the height of the fluidized bed. desirable.
By supplying new water while circulating the liquid with the circulation pump 6, the concentration will be approximately 1500 to 1800 ppm (depending on the water temperature) until the slaked lime is almost gone.
A slaked lime aqueous solution is continuously obtained from the slaked lime aqueous solution take-out pipe 3 via the overflow liquid receiving part 4 (if you want to keep the concentration of the slaked lime aqueous solution constant, you can adjust the temperature of the water supply by installing a heater in the constant pressure water tank) ). Note that 14 is an insoluble matter removal tube.

In addition, when carrying out the present invention, as shown in FIG. , 5',
When the concentration of slaked lime in the liquid obtained from one dissolution tank begins to decrease, this aqueous solution is passed through the other dissolution tank to continuously obtain a highly concentrated slaked lime aqueous solution, which makes almost complete use of the raw slaked lime. It is preferable that it can be done.

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 1, and there is no need to intentionally introduce it into the second dissolving tank 1', and the liquid flows directly into the slaked lime aqueous solution. It may also be taken out from the take-out 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 dissolving tank 1 is introduced into the second dissolving tank 1' by the switching valve 15. 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 9 is switched to the second dissolving tank 1' by a switching valve 16. 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 substantially saturated concentration. During this time, the insoluble matter in the first dissolution tank 1 is removed from the insoluble matter removal pipe 14, and a predetermined amount of slaked lime is newly added and water is filled. Then, before the concentration of the slaked lime aqueous solution obtained from the second dissolving tank 1' begins to decrease, the aqueous solution is introduced from the second dissolving tank into the first dissolving tank using the switching valve 15', and the first dissolving tank is operated 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.

As a stirring means, the inventions disclosed in Japanese Patent Application No. 54-36614 (Japanese Unexamined Patent Publication No. 55-10819) and Japanese Patent Application No. 54-121665 (Unexamined Japanese Patent Application No. 56-59650) use horizontal stirring blades. Although it is installed at the bottom of the tank, the pump circulation of the present invention is better than the one using stirring blades.
This is an excellent means for preventing slaked lime fine particles from floating up.

That is, as follows: (a) In the invention related to the above-mentioned published application, a rotating shaft is inserted vertically from the top of the dissolving tank in order to provide a horizontal stirring blade at the bottom. induces floating of undissolved lime particles. In the case of a relatively small dissolution tank, the agitation rotating shaft is also thin, so even if the problem of particle flotation does not occur, if the dissolution tank is large, the diameter of the shaft will naturally become large, which tends to induce the flotation of fine particles. In the pump circulation according to the present invention, there is no rotating shaft in the dissolution tank, so there is no need to worry about this.

(b) According to the pump circulation of the present invention, the slaked lime deposited layer forms a fluidized bed, and the slaked lime fine solid particles at the top of the fluidized bed are sucked as a slurry liquid from the tank side wall that does not exceed the height of the fluidized bed. Since it is recirculated into the tank from the water supply port at the bottom, it is possible to suppress the floating and outflow of slaked lime fine particles to the upper part of the dissolution tank, which has an effect that the stirring blade method does not have.

(c) In the present invention, since there is no complicated structure such as an agitator inside the dissolution tank, not only the equipment cost can be reduced, but also inspection and repair of the inside of the tank are extremely easy, which is industrially significant in this field. It is.

Example Bottom inner diameter 334mmφ, top inner diameter 625mmφ, height 2800
In the dissolving device shown in Figure 1, where the height of the lower inverted truncated cone section is 1640 mm and the upper part is cylindrical, slaked lime particles are allowed to float up to the maximum diameter of the inverted cone section. The device used a pump to draw out the liquid from slightly below the center of the layer, feed it to the lower part, and circulate it. Fill this dissolution tank with water and 20 kg of slaked lime (contains 80% by weight of fine particles of 63μ or less)
(equivalent to approximately 4 days of continuous operation) and maintained at a constant pressure in a constant pressure water tank.
The solution is fed at a flow rate of 0.4 to 0.8 mm/sec, and the liquid in the dissolving tank is sucked in from the upper part by a circulation pump, circulated to the lower part, and slaked lime is extracted from the overflow pipe at the upper end of the tank. The aqueous solution was taken off continuously. The resulting aqueous solution is heated until almost all undissolved lime is gone.
It was a slaked lime aqueous solution with a constant concentration of 1500 to 1800 ppm. The height of the fluidized bed portion of the slaked lime particles at this time was 1600 to 1800 mm.

[Brief explanation of drawings]

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 dissolution tank, 2, 2'... Slaked lime supply port, 3, 3'... Slaked lime aqueous solution outlet, 4,
4'... Overflow liquid receiving part, 5, 5'... Water supply pipe, 6,
6'...Circulation pump, 7, 8, 10...Pipe, 9...
... constant pressure water tank, 11 ... overflow pipe, 12 ... water supply pipe,
13...Flowmeter, 14...Insoluble matter removal pipe.

Claims (1)

[Claims] 1. The slaked lime dissolving tank has a cylindrical shape or a lower part has an inverted truncated cone shape, and an upper part has a cylindrical shape, and has a slaked lime supply port on the top surface of the tank, and an overflow liquid receiving part having a slaked lime aqueous solution extraction pipe at the upper end of the tank. Either one slaked lime dissolving tank equipped with a slaked lime aqueous solution or two slaked lime dissolving tanks each having a slaked lime aqueous solution outlet pipe connected to the water supply pipe of the other tank by a switching valve, and a water supply port and a slaked lime disposed at the bottom of the tank. A part of the slurry liquid in the tank is taken out from the side wall of the tank in the area where the slurry exists where particles are suspended, and a conduit and a circulation pump are installed to supply it to the bottom of the tank. 1. An apparatus for continuously producing a slaked lime aqueous solution, characterized in that it is connected to a means for feeding tap water at a constant or substantially constant rate.