JP5379399B2 - Storage device for sodium hypochlorite solution added to tap water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preserving a sodium hypochlorite solution utilizing ground water as a means for maintaining the quality of a sodium hypochlorite solution to be poured for disinfecting city water when it is preserved, and to provide an apparatus therefor. <P>SOLUTION: The apparatus, preserving the sodium hypochlorite solution by indirectly cooling the solution with ground water of 14 to 17&deg;C, is composed of: an outer tank flowing in/out the ground water; and a plurality of cylindrical inner tanks for storing and preserving a sodium hypochlorite solution in which the respective ones are arranged at the inside of the outer tank so as to be planarly separated each other. The apparatus is provided with an upper part communication part communicating the respective upper parts of the plurality of cylindrical inner tanks and a lower part communication part communicating the respective lower parts thereof, the upper part communication part is connected with a liquid pouring tube, and the lower part communication part is connected with a discharge tube continued to a liquid feeding pump. Each cylindrical inner tank is made of a metal and whose inside face is coated with a corrosion resistant synthetic resin film. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method and apparatus for storing a sodium hypochlorite solution added to disinfect tap water.

  Disinfection of tap water is based on chlorine according to the provisions of the Water Supply Law, and sodium hypochlorite, which is safer and easier to handle than liquefied chlorine, is mainly used as the chlorine disinfectant. Yes. However, sodium hypochlorite is a highly reactive, easy-to-degrade chemical and is added to the water that people drink, making it suitable for maintaining proper handling and properties. Maintenance is necessary. In recent years, due to inappropriate management of sodium hypochlorite, knowledge such as a decrease in available chlorine in sodium hypochlorite and an increase in chloric acid contained as impurities has become clear.

  As a conventional example, a case in which groundwater is pumped up and used as tap water is shown in the flow chart of FIG. 3, but the groundwater pumped up from the well 10 by the pump 10a enters the receiving tank 11, and is further supplied by the pump 11a. In the middle of water supply, the sodium hypochlorite solution is injected from the sodium hypochlorite solution tank 2 into the tap water, which is groundwater, by the liquid feed pump 7 for disinfection. And the water for tap water is sent to a post-processing apparatus or a demand destination with the water pump 12a.

  Usually, a commercially available sodium hypochlorite solution for water supply is a light green-yellow transparent liquid in which effective chlorine as a main component is 12 wt% or more and PH is 12 or more. In addition to sodium hypochlorite (chlorine content: 35.5 wt%), sodium chlorite and sodium chlorate as oxides of sodium hydroxide, sodium chloride and sodium hypochlorite to suppress decomposition And an aqueous solution containing bromic acid which is an impurity during production. In addition, sodium hypochlorite solution is an unstable substance, and gradually decomposes during storage to produce sodium chloride and oxygen. In this case, sodium chlorate is produced through sodium chlorite as a side reaction.

  As described above, the decomposition of sodium hypochlorite solution gradually decomposes spontaneously with an unstable compound even at room temperature, the decomposition is accelerated by sunlight, particularly ultraviolet rays, and the decomposition rate increases with increasing temperature. It is characterized by rising. Thus, sodium hypochlorite decomposes over time, available chlorine decreases, and chloric acid increases. The relationship is said to increase chloric acid by about 3,500 mg / kg when available chlorine decreases by 1%. In addition, sodium hypochlorite decomposes quickly when the storage temperature is high, the effective chlorine concentration rapidly decreases, and conversely, the chloric acid concentration increases rapidly. The effect of this temperature is, for example, when the effective chlorine 12% is reduced to 10%, and the period until the chloric acid is further increased by 7,000 mg / kg from the initial concentration is 30% when only the temperature requirement is considered. It is said to be about 20 days when stored at ℃ and about 80 days when stored at 20 ℃.

  On the other hand, tap water such as sodium hypochlorite or chemicals injected into water during the treatment process must comply with the chemical standards stipulated by the Water Supply Law. The chemical criteria items to be listed are chloric acid and bromic acid. Chloric acid was added to the water quality standard item (standard value 0.6 mg / L or less) from April 2008, based on the detection status of clean water such as tap water. Strengthened from 6 mg / L or less to 0.4 mg / L or less.

From the above, since tap water is used for drinking purposes, it is desirable that sodium hypochlorite injected into tap water is of high quality with a low impurity content. Sodium hypochlorite has different grades at the manufacturing stage, and chloric acid increases over time and the quality deteriorates.So, sodium hypochlorite for water supply is first grade, second grade, third grade in order of quality. It is set as a grade. For example, if a primary product with an effective chlorine concentration of 12% and chloric acid of 4,000 mg / kg is stored at 20 ° C. or less from the time of shipment, even if the maximum injection rate as chlorine is 10 ppm, at least 7 days later, It is supposed that the acid chemical standard of 0.4 mg / L or less can be secured. Moreover, since the secondary product has a higher chloric acid content, the maximum injection rate is as low as 4 ppm.
“Survey Report on Standards for Water Supply Chemicals” Japan Waterworks Association

  As mentioned above, maintaining and preserving the quality of the sodium hypochlorite solution injected for disinfecting tap water prevents the amount of available chlorine from decreasing and is harmful even after the storage period has elapsed. Therefore, there is no need to increase the amount of sodium hypochlorite solution injected at the time of disinfection, thus preventing an increase in the chloric acid content of tap water, The standard can be observed.

  In the above-mentioned prior literature, as a method of maintaining and maintaining the quality of the sodium hypochlorite solution, it is important to suppress degradation over time, and low temperature storage is considered simple and effective. Is effective in providing a roof to block sunlight and cooling with heat insulating material and water. In particular, in the case of indoor storage, it is said that air ventilation is improved and room cooling by an air conditioner is also good.

  The present invention has been made to solve the problem of such cold storage, in the case of storing a sodium hypochlorite solution to be injected to disinfect tap water in a facility where groundwater is used as tap water. As a means of maintaining the quality, paying attention to the fact that the amount of groundwater to be sterilized relative to the injected amount is large and the water temperature is low, a method and apparatus for storing a sodium hypochlorite solution using groundwater Is to provide.

To achieve the above object, the invention of method of storing sodium hypochlorite solution added to water canal water, in the processing of tap water to be disinfected by injecting sodium hypochlorite solution into groundwater pumped, Reduction of effective chlorine content in sodium hypochlorite solution by indirectly cooling the sodium hypochlorite solution for injection using the ground water having a water temperature of 14 to 17 ° C and storing it at 20 ° C or lower. and that to suppress the increase of the chlorate content. The invention of method of storing sodium hypochlorite solution added to the waterworks water is pre-divides the KitsugiA sodium chlorate solution accommodated in a plurality of containers, indirect respectively of the container in the ground water you cooling.

  When groundwater is pumped up and used as tap water, if the amount of sodium hypochlorite solution (hereinafter also referred to as chemical solution) injected for disinfection is 100 ppm, the amount of groundwater equivalent to this is The amount of groundwater is overwhelmingly large since it is 10,000 times the injection volume, and groundwater has little change in water temperature throughout the season, and the water temperature is 14 to 17 ° C, so the quality of the sodium hypochlorite solution changes. Since it is lower than 20 ° C., which is a difficult storage temperature, it is a storage method of a sodium hypochlorite solution that is used for indirect cooling of the sodium hypochlorite solution that stores the temperature and amount of the groundwater. When indirect cooling is used, the chemical solution and the cooling water are not in direct contact, and there is no problem of dilution of the chemical solution or contamination by the cooling water. As described above, by cooling and storing the sodium hypochlorite solution at 20 ° C. or lower, it is possible to suppress a decrease in effective chlorine content and an increase in chloric acid content in the sodium hypochlorite solution. If the amount of effective chlorine to be injected is made constant when disinfecting water for tap water, the amount of sodium hypochlorite solution injected into tap water can be small, so that the content of chloric acid can be reduced.

  Since sodium hypochlorite solution is a substance that can be easily decomposed, heat exchange between groundwater and chemicals for cooling cannot be adopted because forced stirring of chemicals may promote decomposition, and natural convection and heat transfer. It becomes heat exchange by. In order to increase the efficiency of this heat exchange, it is necessary to increase the heat transfer area of the storage container with respect to the storage capacity as much as possible. As a method for realizing this, means for dividing the storage container into n pieces and combining them was adopted. As a result, the total heat transfer area becomes √n times when divided into n, and can contribute to heat transfer, as compared with the case where the total heat transfer area is not divided. Further, it is considered that by arranging the divided storage containers individually, the heat transfer is promoted because the water flow of the groundwater is disturbed and brought into contact with each of the divided containers.

The invention of a storage device for sodium hypochlorite solution added to tap water according to claim 1 is a device for storing the sodium hypochlorite solution by indirectly cooling it with ground water at a water temperature of 14 to 17 ° C. A plurality of outer tanks that allow the groundwater to flow into and out of the tank and that stores and stores the sodium hypochlorite solution, and the outer tanks are spaced apart from each other in a plane. It is characterized by comprising a cylindrical inner tub arranged in the manner described above. The invention of a storage device for sodium hypochlorite solution added to tap water according to claim 2 is the storage device for sodium hypochlorite solution according to claim 1 , wherein the plurality of cylindrical inner tanks An upper communication part that communicates with each upper part and a lower communication part that communicates with each lower part are provided, a liquid injection pipe is connected to the upper communication part, and a discharge pipe that is connected to a liquid feed pump is provided at the lower communication part Are connected and provided. The invention of a storage device for sodium hypochlorite solution added to tap water according to claim 3 is the storage device for sodium hypochlorite solution according to claim 1 or 2 , wherein the tubular inner tank Is made of metal whose inner surface is coated with a corrosion-resistant synthetic resin film.

Be those embodying saving method of sodium hypochlorite solution added to the above-mentioned water canal water, by using the groundwater cold water temperature 14 to 17 ° C., stock solution of sodium hypochlorite solution It aims at cooling to 20 ° C. or lower, and is a facility aimed at suppressing decomposition by efficiently cooling sodium hypochlorite solution, which is easily decomposed when the temperature rises, with groundwater. The main point is that sodium hypochlorite solution passes from the container surface to the solution because it is soaking, that is, forced stirring to eliminate heat gradient and improve heat exchange cannot proceed. In order to increase the heat flow, the container was divided into a plurality of containers, the total surface area of the container was increased, and the container itself was made of metal with good heat conduction (however, the sodium hypochlorite solution was Because it is highly corrosive, a corrosion-resistant synthetic resin film was provided on the inner surface of the container), and in order to make the solution level of each divided container the same, a communication part was provided at the bottom of the container, and the last-in first-out was aimed at In addition, a communication part is provided at the upper part, so that the replenishment / injection of the solution from the upper part is uniformly supplied to each container, and can be dispensed as uniformly as possible from the lower part. In addition, by using divided containers, the inner diameter of the container is reduced, and the solution temperature can be easily uniformed in the cross-sectional direction. In addition, the outer tub from which groundwater flows in and out is basically entered from the lower part, warm effluent water is taken out from the upper part, it is introduced so as to create a swirling flow in a plane with respect to the outer tub, By providing a flow straightening plate so as not to make a shortcut, the contact between the inner tub and the groundwater flow was improved, and the heat exchange from the groundwater to the solution was advanced.

According to the apparatus of the present invention as set forth in claims 1 to 3 , an apparatus for storing and preserving a sodium hypochlorite solution for disinfection from several days to more than one month, wherein a plurality of cylindrical next The inner tanks, which are sodium chlorite solution containers, are arranged in a plane spaced from each other. In addition, since each inner tank is provided with a communication part that communicates the inner tank with each other at the upper part and the lower part, the chemical liquid height of each inner tank can be made the same when injecting or dispensing the chemical liquid into the inner tank. In addition, the injection amount or the discharge amount of each inner tank can be made the same. In addition, the outer tank is filled with groundwater for cooling in a portion other than the inner tank, and the groundwater is made to flow in from the outside in a swirling flow, and a rectifying plate is provided to replace the groundwater without stagnation. The inner tank to be cooled is immersed in the cooling water. At the same time, the surface is washed by the cooling water flowing in and out, heat exchange is performed through the inner wall of the inner tank, and the sodium hypochlorite solution is formed by the groundwater. It will be cooled efficiently.

According to method of storing sodium hypochlorite solution added to the onset Ming waterworks water by performing heat exchange by utilizing the low temperature of groundwater, sodium hypochlorite solution decomposition proceeds hardly Temperature Since it can be stored and preserved, it is possible to prevent the amount of effective chlorine in the sodium hypochlorite solution from decreasing and to prevent an increase in the amount of chloric acid. This eliminates the need to increase the amount of sodium hypochlorite solution to be added when disinfecting with effective chlorine in tap water, so that the increase in chloric acid content can be reduced and the amount of harmful chloric acid can be reduced. It can be easily kept within the water quality standards. Further, since the method of the present invention is a simple method, it can be easily implemented.

Further, according to the storage device for sodium hypochlorite solution added to tap water according to claims 1 to 3 , the storage and storage temperature of the sodium hypochlorite solution is maintained at 20 ° C. or lower by utilizing low-temperature groundwater. Since it is a simple facility, the installation cost of the apparatus is low, the operation is simple, it is easy to automate, and it is a labor-saving facility. In addition, maintenance costs are not expected to be excessive. Further, the apparatus of the present invention can be applied regardless of the storage amount and handling amount of the sodium hypochlorite solution, and is therefore versatile.

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best embodiment of the present invention will be described. FIG. 1 is an explanatory view of a method and apparatus for storing a sodium hypochlorite solution added to tap water according to the best embodiment of the present invention, It is a typical flow diagram. FIG. 2 is an explanatory view of a storage device for a sodium hypochlorite solution added to tap water according to the best embodiment of the present invention. FIG. 2 (a) is a storage device for a sodium hypochlorite solution. (B) is an AA arrow directional cross-sectional view, (c) is a BB arrow directional cross-sectional view.

  Describing an embodiment of a method for storing a sodium hypochlorite solution added to tap water according to the present invention and an embodiment using the apparatus, as shown in FIG. 1, it is a tap water treatment facility 1 using groundwater as raw water. Then, groundwater with a water temperature of 14 to 17 ° C. pumped from the shallow well or deep well 10 is sent to the groundwater receiving tank 11 by the water pump 10a. Water is supplied from the groundwater receiving tank 11 to the water receiving tank 12 by the water supply pump 11 a, but a part of the water branches and passes through for cooling the sodium hypochlorite solution storage tank 2, and then goes to the water receiving tank 12. Water is supplied from the water receiving tank 12 to the destination of tap water or the final treatment facility of the water for the tap water by the water pump 12a, and the sodium hypochlorite solution storage tank 2 is added to the water for the water to be supplied near the outlet of the water pump 12a. Then, a predetermined injection amount is taken out by the liquid feed pump 7 and injected to disinfect. This injection system is a regular method, and since injection proportional control for injecting at a predetermined ratio with respect to the amount of water to be fed can be used, it is not particularly shown.

  Referring to FIG. 2, the sodium hypochlorite solution storage device according to the present invention will be described. The sodium hypochlorite solution storage tank 2 has a cylindrical outer tank 3 and a space between the outer tank 3 and each other. And six cylindrical inner tubs 4 arranged annularly in plan view. For example, if it is possible to inject 10 ppm as effective chlorine at 300 m3 / day for tap water, the injection amount of sodium hypochlorite solution (effective chlorine 10%) per day is equivalent to 30 L, and should be stored for 20 days. 600L storage tank is required. The six inner tubs 4 corresponding to this have an inner diameter of 400 mm and a height of about 900 mm. (Incidentally, the inner tank 4 having one structure has an inner diameter of 1000 mm and a height of about 900 mm.) The outer tank 3 has an inner diameter of 1600 mm and a height of about 1500 mm. These numerical values are merely examples, and are not restricted by these numbers.

  The total surface area of the six inner tanks 4 described above is approximately 2.45 times (√6 times) the surface area of one inner tank corresponding to the total of these internal capacities. As described above, even in the case of the same internal volume, the total surface area can be increased to √N times in the case of an N-divided inner tank as compared with the surface area of one inner tank. The amount of heat exchange between the groundwater for cooling and the solution in the tank can be increased by sandwiching the surface wall of the inner tank 4 by increasing the total surface area of the inner tank 4. Moreover, since the inner diameter of the inner tank 4 can be made smaller than that of one inner tank, the temperature of the solution 2a in the inner tank 4 can be easily made uniform in the cross-sectional direction.

  The material of the inner tank 4 is preferably made of a metal having good thermal conductivity from the viewpoint of heat exchange. The internal sodium hypochlorite solution 2a is highly oxidative and corrosive, so titanium is the optimum metal, but there are problems in terms of workability and cost. Therefore, it is preferable to use a steel pipe and apply a corrosion-resistant synthetic resin film on the inner surface. As the synthetic resin, vinyl chloride, polyvinylidene chloride, polyethylene, fluorine resin, or the like is preferable.

  The six inner tanks 4 are connected to each other with their lower portions connected to the lower communication portion 5. A liquid feed pump 7 is connected to the lower center of the lower communication part 5, and the solution 2 a can be extracted by the liquid feed pump 7 and used for disinfection injection. The six inner tanks 4 are connected to each other with their upper portions connected to the upper communication portion 6. A liquid injection pipe 8 is connected to the central upper part of the upper communication part 6, and the sodium hypochlorite solution is replenished through the liquid injection pipe 8 and supplied to each inner tank 4 almost evenly. The upper and lower communication portions 6, 5 are formed of a large-diameter dished cylinder, and communicate with the cylinder by connecting the upper and lower ends of the inner tank 4. Due to the presence of these communicating portions 5 and 6, even if the solution 2a is replenished or extracted, the solution level 2a of each inner tank 4 can be maintained substantially the same, and the cooling by the groundwater 3a can be evenly and evenly distributed. Since it can be performed, the temperature of the solution 2a is the same regardless of the location, and the location where the liquid temperature is locally high is prevented from appearing.

  The outer tub 3 is filled with ground water 3d having a cooling water temperature of 14 to 17 ° C., and the pipe serving as the lower ground water inlet 3a is connected to the tub 3 in a tangential direction. The groundwater flow flows in a plane. Further, the cooling drainage from the outer tub 3 overflows and flows out from the groundwater outlet 3 b provided in the upper part, and goes to the water supply / receiving tank 12. Further, in the outer tub 3, a difference shelf-shaped rectifying plate 3c having a three-stage gradient in the height direction is provided. As a result, the inflowing groundwater 3d can be efficiently cooled by flowing so as to wash the outer surface of the inner tank 4 without overflowing as a shortcut. Further, the current plate 3c can also be used as a support for fixing the six inner tanks 4 at predetermined positions. The ceiling of the outer tub 3 is provided with a spherical cover that blocks sunlight and outside air. Moreover, the main body of the outer tub 3 may be made of a steel plate or a synthetic resin, and in the case of a steel plate, heat conductivity is good. Therefore, it is preferable to insulate the outer surface.

  The sodium hypochlorite solution 2a stored in the sodium hypochlorite solution storage tank 2 at a liquid temperature of 20 ° C. or lower is extracted by the liquid feed pump 7 and supplied to the tap water from the water feed pump 12a. A predetermined amount is injected in the vicinity of the outlet of the pump 12a to disinfect tap water. Although not shown, the amount of liquid from the liquid feed pump 7 is controlled and injected so that the predetermined ratio with respect to the amount of water fed by the water feed pump 12a is equal to the set amount of solution. These injection volume control is a regular method, using a liquid volume control loop composed of a flow meter and a flow control valve, so that it is equal to the set liquid volume multiplied by the set ratio linked to the measured value of the water supply volume. This can be done in a manner that controls the injection volume. As an example of the liquid feed pump 7, a motor-driven diaphragm type digital metering pump (trade name, Grundfos Digital Metering Pump) is suitable for application of a digital control system of discharge amount.

  In order to maintain the temperature of the solution 2a stored in the sodium hypochlorite solution storage tank 2 at a set temperature of 20 ° C. or less, the liquid temperature of each inner tank 4 is measured and the set liquid temperature is set. On-off control or flow rate control that turns on and off the flow rate of the cooling groundwater 3d can be used.

  When disinfecting tap water using the method and apparatus for storing sodium hypochlorite solution added to tap water according to the present invention, when a large amount of effective chlorine is required, the effective chlorine concentration is 12 to Injecting a solution as high as 13% requires only a small amount of injection, so that the chloric acid concentration in tap water can be easily suppressed to a regulated value within 0.4 mg / L. In this case, it is important not to increase the concentration of chloric acid contained in the sodium hypochlorite solution during storage.

  As shown in Table 1, when the sodium hypochlorite solution is stored at a storage temperature of 20 ° C., the decrease in effective chlorine concentration that tends to decrease with the elapsed days is reduced as compared with the storage temperature of 30 ° C. However, the increase in the concentration of chloric acid accompanying the decrease can be extremely reduced. For example, in the case of a sodium hypochlorite solution with a storage temperature of 30 ° C., the effective chlorine concentration decreases with the number of days elapsed. Therefore, for the disinfection of tap water that requires a certain amount of effective chlorine, the amount of solution injected However, on the other hand, the chloric acid concentration accompanying it may increase excessively in the tap water and exceed the regulation value, and eventually the injection amount of the solution must be reduced. The purpose of disinfection will not be achieved.

  Also from these viewpoints, the method and apparatus for storing a sodium hypochlorite solution added to tap water according to the present invention can easily and reliably store the sodium hypochlorite solution at 20 ° C. or lower. It is preferable because it has a better effect on the disinfection work of tap water and can suppress an increase in harmful chloric acid concentration.

  Regardless of industrial or commercial facilities, it can be widely used for storage related to sodium hypochlorite solution to be injected for disinfection of tap water even in residential facilities.

It is explanatory drawing of the preservation | save method of the sodium hypochlorite solution added to the water for tap water which is the best embodiment of this invention, and its apparatus, Comprising: It is a typical flowchart. It is explanatory drawing of the preservation | save apparatus of the sodium hypochlorite solution added to the tap water which is the best embodiment of this invention, Comprising: (a) is typical sectional drawing of the preservation | save apparatus of a sodium hypochlorite solution, (B) is AA arrow sectional drawing, (c) is BB arrow sectional drawing. A method and apparatus for storing a sodium hypochlorite solution added to conventional tap water. It is explanatory drawing of this, Comprising: It is a typical flowchart.

Explanation of symbols

1: Water treatment facility for tap water 2: Sodium hypochlorite solution storage tank 2a: Solution 3: Outer tank 3a: Groundwater inlet 3b: Groundwater outlet 3c: Rectifier 3d: Groundwater 4: Inner tank 5: Lower communication part 6: Upper part Communication part 7: Liquid feed pump 8: Injection pipe
10: Well 10a: Water pump 11: Groundwater receiving tank 11a: Water pump 12: Water receiving tank 12a: Water pump

Claims (3)

In the processing of tap water to be disinfected by injecting sodium hypochlorite solution into groundwater pumped, a device for storing and indirect cooling by groundwater of the sodium hypochlorite solution from the water temperature 14 17 ° C., the A plurality of outer tanks that allow groundwater to flow into and out of the tank and that stores and stores the sodium hypochlorite solution, and that are spaced apart from each other in a plane. A storage device for a sodium hypochlorite solution to be added to tap water, comprising a cylindrical inner tank provided . An upper communication part that communicates each upper part of the plurality of cylindrical inner tanks and a lower communication part that communicates each lower part are provided, and a liquid injection pipe is connected to the upper communication part. 2. A storage device for a sodium hypochlorite solution added to tap water according to claim 1 , wherein a discharge pipe connected to a liquid feed pump is connected and provided . The apparatus for storing a sodium hypochlorite solution added to tap water according to claim 1 or 2, wherein the cylindrical inner tank is made of metal whose inner surface is coated with a corrosion-resistant synthetic resin film. .

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