JPS6358763B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus 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.

Conventionally, in waterworks, rust etc. may occur in the 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 purpose, caustic soda, soda ash, slaked lime, etc. are injected into the water, which is easy to handle these days. Caustic soda is often used for this reason. 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 remains settle and adhere to the bottom, and because it is not used as a slurry. This is because, when injected, it tends to deposit in the pipes along the way, and impurities contained in slaked lime (for example, MgO, SiO ₂ , Fe ₂ O _3, etc.) mix into tap water.

Recently, in order to solve the above-mentioned inconveniences due to slaked lime injection, a wire mesh is installed at the bottom of the tank to separate the upper and lower parts, and a deposited layer of slaked lime is formed on the wire mesh. A device 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 device, the stock slaked lime remains as it is, so 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 device as a whole 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, and making good contact between water and slaked lime. This is due to the fact that it no longer occurs. 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 trace amounts of sand or insoluble matter contained in slaked lime, or trace amounts of iron or other insoluble matter contained in tap water. Furthermore, free carbonic acid present in water is converted to CaCO ₃ in the presence of Ca(OH) ₂ , causing scaling and clogging of the wire mesh.

As a result of various research 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 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 maximum diameter of the conical portion is A tank with a cylindrical upper part connected to the upper part is used, and a water supply port is provided at the bottom of the tank from which water is ejected from a water ejector. A slurry liquid in the tank consisting of an aqueous slaked lime solution and slaked lime is connected to a means for maintaining the water level in the constant pressure water tank at a constant level and feeding tap water to the water ejector at a constant or substantially constant rate. This invention relates to a device for continuously taking out an aqueous solution of slaked lime from a take-out pipe of an overflow liquid receiving part at the top of the tank while circulating the slaked lime at the bottom of the tank with a jet liquid.

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

FIG. 1 shows a specific example of the device of the present invention, in which a slaked lime supply port 2 is provided on the top surface of a slaked lime dissolving tank 1, an overflow liquid receiving part 4 having a slaked lime aqueous solution extraction pipe 3 is provided at the upper end of the tank 1, and A part of the slurry consisting of slaked lime and an aqueous solution is extracted from the water supply port 6 spouted from the water ejector 5 at the bottom of the tank 1 and the side wall of the tank in the area where the slurry in which slaked lime particles are suspended is present in the tank 1 and connected to the water ejector 5. An extraction pipe 7 is provided to
The slaked lime deposited on the bottom of the tank is stirred and fluidized by the jet water discharged by the water ejector to dissolve the slaked lime. The number of water ejectors 5 may be one, but depending on the size of the tank used, a plurality of water ejectors 5 may be provided so that the entire slaked lime at the bottom of the tank can be stirred and fluidized.

The slaked lime dissolving tank 1 used in the present invention may be cylindrical or prismatic, but as shown in Figure 1, an inverted truncated pyramid-shaped tank with different cross-sectional areas at the top and bottom is used. is preferable. When water is jetted from the water inlet 6 through the water ejector 5 at the bottom with a small cross-sectional area, the flow velocity of the water decreases as it goes to the top where the cross-sectional area is large. Even if the slaked lime is vigorously stirred and fluidized by the water jet, the height at which the slaked lime particles flow can be kept relatively low, which is advantageous. It is desirable to prevent slaked lime microparticles from being entrained in the slaked lime aqueous solution overflowing from the upper end of the tank using the device of the present invention, and as a result of many experiments, the upper limit of the height of the inverted cone is set at 280 mm. It has been confirmed that when fixed, the height at which slaked lime particles flow is 1,600 to 1,800 mm from the tank bottom within the desired range of upward flow rate of tap water during continuous operation. This indicates that the height of the fluidized bed is approximately 2/3 of the total tank height from the bottom of the tank. It is preferable that the height of the fluidized bed is less than this so that fine slaked lime particles are not entrained in the overflowing slaked lime aqueous solution, but in order to avoid excessively increasing the capacity of the dissolution tank, the height of the fluidized bed must be adjusted as described above. The height should be about 2/3 of the tank height.

This corresponds to the upper limit of the height of the lower cone portion of the inverted truncated cone-shaped tank (see embodiments of the present invention).

When producing a slaked lime aqueous solution using the apparatus of the present invention, a predetermined amount of slaked lime is introduced into the slaked lime dissolving tank 1 through the slaked lime supply port 2, and new water is supplied through the water ejector 5 at a substantially constant rate. To supply new water at a substantially constant rate, for example, a constant pressure water tank 8 is provided, new water is introduced through a pipe 9, and the water level in the constant pressure water tank 8 is maintained constant through an overflow pipe 10, while the water supply pipe 11 is , water ejector 5 through flow meter 12
The water is supplied to tank 1 as water in which slaked lime is dissolved. At this time, the flow rate of water in the tank is preferably set to 2 mm/sec or less in the upper part of the tank, which has a large cross-sectional area. Generally, the height of the slaked lime fluidized bed, including the cylindrical dissolving tank of the present invention, is set to be in the middle of the total tank height.
It is desirable that the position from which the slurry liquid in the tank is drawn out from the side wall of the tank does not exceed the height of the fluidized bed. In this way, the liquid drain pipe 7 and the water ejector 5
When a part of the liquid in the tank is circulated and new water is jetted into the tank by the water ejector 5, the concentration is about 1500~ until the slaked lime in the tank is almost gone.
A slaked lime aqueous solution of 1800 ppm (varies depending on the water temperature) is continuously obtained from the slaked lime aqueous solution extraction pipe 3 via the overflow liquid receiver 4. In order to keep the concentration of the obtained slaked lime aqueous solution constant regardless of the temperature, a heater may be provided in the constant pressure water tank to keep the water temperature constant. Sho 13
is an insoluble matter extraction tube.

Further, when carrying out the present invention, as shown in FIG. 2, the two slaked lime dissolving tanks 1 and 1' are switched between each other's slaked lime aqueous solution outlet pipes 3 and 3' by switching valves 14 and 14' to the water supply port 6 of the other dissolving tank. , 6', and when the concentration of slaked lime in the liquid obtained from one dissolution tank begins to decrease, this aqueous solution is further passed through the other dissolution tank to continuously obtain a high concentration slaked lime aqueous solution. This is preferable because the raw material slaked lime can be used almost completely.

In other words, 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'. The liquid may be taken out from the liquid take-out pipe 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 14. 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 8 is switched to the second dissolving tank 1' by a switching valve 15. 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 through the insoluble matter removal pipe 13, a predetermined amount of slaked lime is added and water is filled, and the slaked lime aqueous solution obtained from the second dissolution tank 1' Before the concentration of water begins to decrease, the aqueous solution is introduced from the second dissolution tank into the first dissolution tank using the switching valve 14', and the slaked lime aqueous solution is obtained from the aqueous solution take-out pipe 3 of the first dissolution tank by operating in the same manner. . By sequentially switching and using the slaked lime in this way, the slaked lime aqueous solution can be continuously produced while substantially completely utilizing the raw slaked lime.

As a stirring means, the inventions disclosed in Japanese Patent Application No. 54-36614 (Japanese Unexamined Patent Publication No. 55-130819) and Japanese Patent Application No. 121665 (Sho 56-59650) disclose horizontal stirring blades. Although it is provided at the bottom of the tank, the water ejector circulation of the present invention is superior to the one using stirring blades as a means of preventing fine slaked lime 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 water ejector circulation according to the present invention, there is no rotating shaft in the dissolution tank, so
There is no need to worry about that.

(b) According to the ejector 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 top of the dissolution tank, which has an effect not found in the stirring method.

(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.

(d) In ejector circulation, the water is circulated by the pressure of the water supply itself (tap water pressure), so there is no need for a motor like a stirring blade.

Example Bottom inner diameter 334mmφ, top inner diameter 625mmφ, height 2800
The height of the lower inverted truncated conical part is 1850 mm, and the melting device shown in Fig. 1 with a cylindrical upper part is used to create a slaked lime fluidized bed in which slaked lime particles are allowed to float up to the maximum diameter part of the inverted conical part. The device was designed to suck out the liquid using an ejector below the height of the upper part, feed it to the lower part, and circulate it. This dissolving tank was filled with water and 20 kg 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 the water was maintained at a constant pressure in a constant pressure water tank and passed through a water ejector with an inner diameter of 334 mmφ at the bottom. The flow velocity at the part is 0.4
The solution was fed at a rate of ~0.8 mm/sec, and the solution in the dissolution tank was sucked from the upper part by an ejector and circulated through the lower water supply pipe, and the slaked lime aqueous solution was continuously taken out from the take-out pipe at the upper end of the tank. The resulting aqueous solution was a slaked lime aqueous solution with a constant concentration of 1500 to 1800 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 dissolution tank, 2, 2'... Slaked lime supply port, 3, 3'... Slaked lime aqueous solution extraction pipe, 4,
4'... Overflow liquid receiver, 5, 5'... Water ejector, 6, 6'... Water supply port, 7, 7'... Outlet pipe, 8
... constant pressure water tank, 10 ... overflow pipe, 11 ... water supply pipe, 12 ... flow meter, 13, 13' ... insoluble matter removal pipe, 14, 14', 15 ... 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 in which each slaked lime aqueous solution extraction pipe is connected to the water supply pipe of the other tank by a switching valve. A slurry liquid circulation system is provided in which a water supply port is provided at the bottom of the tank and is ejected from a water ejector, and the water ejector is connected to an extraction pipe extending from the side wall of the tank in an area where slurry in which slaked lime particles are suspended is present. 1. An apparatus for continuously producing a slaked lime aqueous solution, characterized in that the water ejector is connected to a means for maintaining the water level of the constant pressure water tank at a constant level and feeding tap water at a constant or substantially constant rate.