KR100853382B1 - Method for corrosion prevention of water distribution systems by lime slurry - Google Patents

Abstract

The present invention relates to a method of preventing corrosion of a water pipe using a slurry of lime lime, wherein the water in which the solid impurity is flocculated and precipitated in the sedimentation basin (1) is transferred to the filter media (2), and then, from the filter (2) to the purified water (3). In the conveying process, CO ₂ is injected into the water passing through the filter paper 2 in order to properly adjust the pH of the water, and then the slaked lime slurry in which the slaked lime is dissolved in water is introduced into the water supply pipe. It is characterized in that the simplification of the process and the difficulty of quantitative injection by a general pump due to the difficulty of gypsuming due to the characteristics of slaked lime make it possible to quantitatively inject the pump by a skew-type pump, and efficiently provide CO ₂ It is effective to prevent air pollution by using CO ₂ by suggesting the method of injecting

Description

Method for corrosion prevention of water distribution systems by lime slurry

1 is a process diagram of an embodiment of the present invention.

2 is an explanatory view of a CO ₂ dissolution supply apparatus of the present invention.

Figure 3 is a graph showing the change in LI in 53 days pilot scale experiment according to the present invention.

4 is a graph showing the change in LI in a 5-day pilot scale experiment according to the present invention.

5 is a graph showing the change in iron elution concentration in the pilot scale experiment for 53 days according to the present invention.

Figure 6 is a graph showing the change in iron elution concentration in a 5-day pilot scale experiment according to the present invention.

Figure 7 is a observation of calcium carbonate film formation of the tubular specimens in a pilot scale experiment for 53 days according to the present invention.

<Description of the symbols for the main parts of the drawings>

1. Settling basin

2. filter paper

3. Water Purifier

4. CO ₂ Melt Feeder

41.Tank 42.CO ₂ Supply Line

43. Transverse bulkheads 44. CO ₂ and water transfer pipes

45.Cup 46.Refill Water Supply Line

47. Excess CO ₂ discharge pipe 48. Carbonated water outlet

5. Slaked lime slurry tank

6. Smelting lime melting tank

7. Dilution Stabilization Tank

81. Flowmeter

82.CO ₂ mixing tank

According to the present invention, after the coagulation and precipitation process of the purified water treatment plant is transferred to the filter paper and the filtration process is completed on the filter paper, by injecting and discharging slaked lime slurry between the filter paper and the purified paper, the tap water forms a calcium carbonate film on the inner wall of the water supply pipe, A method of preventing corrosion of the inner wall.

Calcium hydroxide, commonly called slaked lime, is usually in the form of a white powder with a specific gravity of 2.24. These limes are very slightly soluble in water, and the solubility decreases with increasing temperature. The aqueous solution is called lime water and shows strong alkalinity. When limestone is heated to 1,200 ~ 1,300 ℃, carbon dioxide gas is released to make quicklime (CaO), and when mixed with water, it generates heat and becomes calcium hydroxide (calcite, Ca (OH) ₂ ). The slaked lime used in water purification plants so far is manufactured and transported in the form of industrial powder, which causes difficulties in use. In particular, due to the difficulty of gypsum due to the characteristics of slaked lime, it is difficult to quantitatively inject it by a general pump and cause many inconveniences such as difficulty in handling to prevent gypsum.

The only existing method for preventing corrosion of water pipes currently in use in Korea is to inject the corrosion inhibitor (rust inhibitor) of phosphate or silicate into the water tanks of apartment houses and large buildings such as apartments. This has a problem in that it is difficult to quantitatively dissolve due to uneven dissolution of solid corrosion inhibitors seasonally due to differences in temperature.

As a method of injecting alkaline substances having pH and hardness in consideration of water quality characteristics of water supply, Korean Patent Registration No. 10-0441169 (Korean Patent Publication No. 2003-0068056) among the methods developed so far is a seasonal method of water supply. According to the factors, the CCPP value, which is the corrosive index, can be automatically adjusted to a stable range, so that the pH and calcium hardness can be adjusted to one stage before the coagulation process, and the two stage control by adjusting the pH and alkalinity in the final reservoir Disclosed is a method of controlling calcium hardness using Ca (OH) ₂ , CO ₂ , Na ₂ CO ₃ , NaOH in purified water so that it can be made. This method raises pH to 8.0 ~ 8.3 in the final reservoir, so that the pH is close to 8.5, the upper limit of drinking water quality standard, so that it is difficult to maintain stable pH, and Na component is added to the water by injecting Na ₂ CO ₃ , NaOH. It is excessively increased and poses a problem that may be very dangerous for patients with high blood pressure, heart disease and atherosclerosis.

Korean Patent Registration No. 10-0573223 relates to a water treatment system for water purification plants and a water treatment method using the same, which effectively blocks moisture and harmful air for slaked lime and effectively prevents corrosion on electrical facilities, Inject the carbon dioxide into the raw water to increase the solubility of lime, adjust the pH to 7.5 ~ 8.5 and tells you how to form a calcium carbonate film. However, this method is also difficult to properly adjust the amount of calcium and pH is a method of limiting the domestic situation of very low calcium hardness of raw water.

Japanese Patent Publication No. 1992-0002811 discloses a method of improving the LI index (corrosive index of water) by injecting calcium hydroxide and carbon dioxide gas in order to reduce the corrosiveness of tap water. The water treated by this method is also very difficult to apply to domestic sites because the pH of the final treated water is very high as 8.4.

And conventional CO ₂ injection technique and is released into the atmosphere a CO ₂ that is not using the injection method which does not consider the dissolving ability of the CO ₂ dissolved in the CO ₂ excess due doemeuro than injection amount. Therefore, in order to prevent global warming, there is a problem that acts as a technology against the efforts to reduce CO ₂ emissions that are being promoted around the world.

Accordingly, the present inventors have developed the present invention which can compensate for the difficulties of maintaining the proper pH, the difficulty of transporting and handling the powdered lime and the complexity of the process, which are disadvantages of the present invention. The present invention converts the powdered slaked lime, which has been difficult to handle in the past, into a liquid form, and avoids the past behavior of injecting slaked lime into the coagulation process of a water purification plant and injecting it into purified water to fill shortages. By injecting the slurry, the process is simplified, and the difficulty of quantitative injection by a general pump due to the difficulty of gypsum due to the characteristics of slaked lime makes it possible to quantitatively inject by a skew type pump. In addition, by combining the method of efficiently injecting CO ₂ while maintaining economic feasibility, it is intended to provide an innovative technology to prevent air pollution by using CO ₂ .

The present invention, as shown in Figure 1 of the process diagram, the step of transferring the water in which the solid impurity coagulated precipitated in the settling basin 1 to the filter paper 2, and then transfer from the filter paper 2 to the purified paper 3 in, characterized in that the injection of CO ₂ in the water passing through the filter paper (2), in a calcium hydroxide slurry which is then dissolved in the calcium hydroxide in water in order to adjust properly the water pH.

In order to maintain the injection amount appropriately when injecting CO ₂ into the water passing through the filter paper 2, the present invention substitutes CO ₂ directly with water to dissolve CO ₂ in the filtered water. It is characterized by injecting carbonated water. In order to inject carbonated water in which a certain amount of CO ₂ is dissolved into the filtered water, the CO ₂ dissolution supply device 4 installed on the filter paper 2 exit side is preferably configured to have the following configuration.

CO ₂ dissolved in the supply device 4 is the tank 41 and the transverse bulkhead 43 provided on the upper portion of the CO ₂ supply pipe 42 and a CO ₂ supply pipe 42, which is installed in the aeration way to the bottom of the tank 41 and the cross The CO ₂ and the water transfer pipe 44 installed on the partition 43 and the cup 45 installed on the upper portion of the CO ₂ and the water transfer pipe 44, the supplemental water supply pipe 46 installed on the upper portion thereof, and the undissolved surplus CO ₂ are provided. It is based on the unit (A) consisting of the surplus CO ₂ discharge pipe 47 for discharging, and the unit is preferably composed of three stages as shown in the accompanying drawings, three or more stages Can be configured in series. In this unit system, CO ₂ and water Lee Dong - kwan 44 when his lower the CO ₂ is supplied into the tank 41, by protruding below the transverse bulkhead 43, the water level at a pressure of CO ₂ lower As CO ₂ is To the CO ₂ and water transfer pipe (44). Thus, the length of the CO ₂ and water transfer pipe 44 determines the pressure (Cm / H ₂ O) in the tank 41. The upper end of the CO ₂ and the water movement pipe 44 is configured to protrude to the upper portion of the transverse bulkhead 43 and a cup 45 is installed on the upper portion. The height of the lower periphery of the cup 45 is made lower than the top of the CO ₂ and the water transfer pipe 44 so that the height difference determines the discharge pressure (Cm / H ₂ O) of the CO ₂ .

When the above unit device (a) is the CO ₂ fed to the CO ₂ supply pipe 42 supplied from the tank 41 to the bubbling type, CO ₂ is continued melting in the water rises far transverse bulkheads 43, and CO _When the water level is lowered by the pressure of ₂ and the water level exceeds the lower end of the CO ₂ and the water moving pipe 44, the CO ₂ is discharged through the CO ₂ and the water moving pipe 44. Thus, the tank 41 in the CO ₂ is dissolved is promoted by the pressure, the un-dissolved CO ₂ is there is discharged through the CO ₂ and water Lee Dong - kwan 44, CO ₂ and the upper yen of water Lee Dong - kwan 44 The cup 45 is installed again to dissolve the discharged CO ₂ in water again. The carbonated water in which CO ₂ is dissolved is combined with the carbonated water outlet of each unit device (a, b, c) when the carbonated water outlet 48 (a plurality of unit devices (a, b, c) is installed in series). The concentration is constant] into the filtrate.

Increasing the pressure of the CO ₂ to be supplied to the tank 41 as described above, by the relationship between the partial pressure and solubility of CO ₂ CO ₂ is soluble in water, the carbon dioxide does not dissolve the same, go to the dissolution apparatus of the upper layer By principle, some CO ₂ is dissolved. Therefore, by installing a multi-stage dissolving device, CO ₂ can be efficiently dissolved in water to satisfy the pH range required by the present invention.

The carbonated water produced by the CO ₂ dissolution supply device 4 is introduced into the filtrate by using a device such as a pump, and the water that is insufficient due to the input to the filtrate is supplemented with a water supply pipe installed in the upper layer ( By supplying fresh water using 46), the mass balance in the tank 41 can be kept constant.

CO ₂ which is not dissolved even in the unit of the final stage is returned to the feed pump through the recovery pipe and supplied again to the tank 41. Therefore, the CO ₂ dissolution supply device 4 of the present invention can adjust the pH by supplying carbonated water to the filtered water without fear of release of CO _{2 into} the atmosphere.

The slaked lime slurry stored in the slaked lime slurry storage tank (5) is introduced into the slaked lime slaked lime dissolution tank (6) using a screw-type injection pump, and then injected into the purified water (3) directly through the dilution stabilization tank (7). Since the method of the present invention as described above is easy to quantitatively control the amount of carbonated water and the amount of lime water supplied, the pH of the purified water reaching the water purification paper 3 is adjusted to 7.5 to 8.0, and the calcium carbonate hardness is 100 The corrosion index LI can be adjusted to -0.5 to 0.5 by controlling the concentration to -200 mg / L, thereby forming a calcium carbonate film on the water supply pipe to prevent corrosion of the inner wall of the water supply pipe.

In the practice of the present invention, a description will be given of techniques for adjusting the supply amount of carbonated water and the supply amount of lime water. That is, as shown in Figure 1, the filtered water passing through the filter paper 2, which is the end of the flocculation settling process of the purified water treatment plant through a flow meter 81 that can quantitatively control the carbonated water by the CO ₂ dissolution supply device (4) adjusted to acid hydrolysis CO ₂ (pH is measured by the meter 1) the pH injected into the mixing chamber 82, the range of 4.5 to 6.5. In the next step, the slaked lime slurry supplied from the slaked lime slurry storage tank 5 and the filtered water adjusted to a pH range of 4.5 to 6.5 (measured by a pH meter 2) by mixing carbonated water in the slaked lime slurry tank 6 While mixing, stirring so that the carbonated water and the slaked lime slurry is sufficiently mixed, the mixed water as described above is sent to the purified water (3) through the dilution stabilization tank (7). The amount of slaked lime slurry sent to the slaked lime dissolution tank (6) is adjusted so that the water sent to the purified water (3) can have a pH of 7.5 to 8.0 and a calcium hardness of 100 to 200 mg / L as CaCO ₃ .

The present invention configured as described above not only solves the drawbacks of transport and handling difficulties by using powdered industrial slaked lime in existing water treatment plants, but also simplifies the process by directly injecting slaked lime slurry between filter paper and purified water. In addition, it is expected that the operators of the purification plant will overcome the difficulties of handling due to the use of the powdered lime in the limestone injection process, which has been avoided by the managers. In addition, by allowing the lime slurry to be injected in a quantitative manner using a screw-type injection pump, there is an advantage in that the desired pH, calcium hardness and alkalinity can be adjusted.

In order to prove this, by injecting slaked lime slurry (Ca (OH) ₂ ) and CO ₂ according to the method of the present invention for 53 days and 5 days on a pilot scale, the change in the corrosive index LI is shown in FIGS. 3 and 4. As shown, the LI of the influent water increased from -1.4 and -1.3 to LI -0.5 and 0.2 of the reaction water, and the iron elution concentration of the corrosion specimens was also shown in FIGS. Were 35.1% and 16.8%, respectively. FIG. 7 shows the surface of the tube infused with the lime slurry and the surface of the tube not injected with a scanning electron microscope. As shown in FIG. 7, it was confirmed that a fine calcium carbonate film was applied to the surface of the tube into which the slaked lime slurry was injected.

Claims (5)

delete delete In the process of transferring the water in which the solid impurity coagulated and precipitated in the sedimentation basin (1) to the filter paper (2), and then from the filter paper (2) to the purified water (3), the filter paper (2) in order to properly adjust the pH of the water Injecting CO ₂ into the water passed through, and then the slaked lime slurry in which the slaked lime was dissolved in water is introduced into the water supply pipe through the purified water, and injecting CO ₂ into the water passed through the filter paper (2), according to injecting the carbonated water by dissolving the CO ₂ in the water filtered through replaced as direct injection of CO ₂ in the water, CO ₂ dissolved in the supply to be installed on the filter paper (2), the outlet in order to input the carbonated water by dissolving the CO ₂ in the water filtered device 4 is the tank 41 and a CO ₂ supply pipe 42, and the upper transverse bulkhead 43 and the transverse bulkhead 43 provided in the CO ₂ supply pipe 42, which is installed in the aeration way to the bottom of the tank 41 CO ₂ and water transfer pipe 44 installed in the upper portion and the cup 45 installed on the CO ₂ and water transfer pipe 44 And a unit consisting of a supplementary water supply pipe 46 installed at an upper portion thereof and a surplus CO ₂ discharge pipe 47 for discharging undissolved surplus CO _2. The unit is composed of three or more stages. Corrosion prevention method of water pipe using the lime slurry slurry, characterized in that installed in series. 4. The method of claim 3, wherein the input of the slaked lime slurry is introduced into the slaked lime slurry solution tank (6) with a screw-type metering injection pump stored in the slaked lime slurry storage tank (5), and then immediately through the dilution stabilization tank (7). A method for preventing corrosion of water supply pipes using a slurry of slaked lime, characterized in that it is injected into a purified water (3). The amount of carbonated water and the amount of lime water supplied are such that the pH of the purified water reaching the purified paper 3 is 7.5 to 8.0, the calcium carbonate hardness is 100 to 200 mg / L, and the corrosion index LI is -0.5 to 0.5. Corrosion prevention method of water pipes using the lime slurry, characterized in that determined.

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