JPH1133565A - Method for preventing corrosion of water heat storage apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the corrosion of the piping, heat exchanger or the like of a water heat storage system without largely lowering the heat conductivity of the heat exchange part of the heat storage system by using slaked lime and carbon dioxide to respectively adjust the pH, Langelier index and Larson index of circulating water to specified ranges. SOLUTION: When a heat storage system is filled with water, the total alkalinity, calcium hardness, concn. of sulfate ions and concn. of chlorine ions of raw water used in filling are analyzed not only to determine an injection ratio of slaked lime setting a Langelier index to -0.5 to +0.2 and a Larson index to 0.05 to 0.2 but also to adjust the pH of intake water to 7.5 to 9. In this case, the raw water is sent to a mixing adjusting tank 4 from a filling water flow rate regulator 7 and a carbonated water making apparatus 3 and slaked lime is sent to the mixing adjusting tank 4 as a slaked lime aq. soln. by a slaked lime aq. soln. making apparatus 1 so that the amt. thereof becomes a predetermined water filling control slaked lime injection ratio by the filling water flow rate regulator 7. A carbon dioxide flow rate regulating valve 9 is controlled so that a pH value becomes a water filling control pH value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for preventing corrosion of a water heat storage system. More particularly, the present invention relates to a method for preventing corrosion of a metal surface that comes into contact with circulating water such as a water pipe or a connection device of a water heat storage system.

[0002]

2. Description of the Related Art In recent years, a heat storage system for effectively utilizing midnight power, river heat energy, urban waste heat energy, and the like for cooling and heating in a region has been increasingly installed as a system that does not emit energy or emit carbon dioxide. It is expanding. Water heat storage systems use water as a heat transport medium,
This is a heat circulation system that circulates cold or hot water between the heat storage unit and the heat use unit to cool and heat the area. This water heat storage system consists of a heat storage tank, a heat exchange unit, a water pump, piping, and a heat exchange unit (copper fin coil) for the heat utilization unit. Cold water and hot water created in the heat storage tank are sent to the heat utilization unit. It is used after heat exchange in the heat exchange section, and returns to the heat storage tank of the heat storage system.

When the structural material of the heat storage tank is concrete or mortar material, the free carbonic acid in the water of the heat storage system reacts with the slaked lime in the structural material to increase the pH and to improve the water quality by generating calcium bicarbonate. The water was non-corrosive. However, in recent heat storage tanks, concrete has been coated with a synthetic resin such as epoxy resin on concrete, and the above-mentioned water quality improvement has not been carried out. Therefore, corrosion of water pipes and heat exchange parts on the user side has occurred. Is getting more intense.

[0004] A method of improving the Langelia index by injecting slaked lime and carbon dioxide into tap water for the purpose of preventing rust of low-hardness, low-carbonate tap water (for example, see Japanese Unexamined Patent Publication (Kokai) No. 2-194893) has recently been proposed by local governments. Widely used in water supply, buildings and condominiums. In this method, slaked lime and carbon dioxide gas are injected into water to form a protective film mainly composed of calcium carbonate on the inner surface of a water pipe made of iron or the like, thereby preventing corrosion.

However, in the water heat storage system, copper is mainly used as a material of the heat exchanger. If a thick protective film is formed on the surface of the copper fin coil or the like of the heat exchanger, the thermal conductivity is reduced, and the efficiency of the heat exchanger is reduced. Corrosion of copper fin coils and the like is also a problem.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for preventing corrosion of pipes, heat exchangers and the like of a heat storage system without greatly reducing the thermal conductivity of a heat exchange section of the water storage system. The purpose is to:

[0007]

The present invention uses slaked lime and carbon dioxide gas, has a circulating water pH of 7.5 to 9, a Langerian index of -0.5 to +0.2, and a Larson index of 0.05 to 0.05.
0.2 is a method for preventing corrosion of a water heat storage system, which is set to 0.2.

Further, the present invention measures the total alkalinity, calcium hardness, sulfate ion concentration, and chloride ion concentration of raw water used for filling when water is poured into the water heat storage system, and determines the Langerian index of the filled water. From -0.5 to +
0.2, the slaked lime injection rate and the pH of the impregnated water required to improve the Larson index to 0.05 to 0.2 are determined, and slaked lime is injected into the raw water so as to have the slaked lime injection rate. A method for preventing corrosion of a water heat storage system, characterized by injecting a gas and controlling an injection amount of a carbon dioxide gas so that pH after injecting slaked lime and carbon dioxide gas becomes the above-mentioned pH.

Further, the present invention is to periodically measure pH, total alkalinity, P alkalinity or total acidity, calcium hardness, sulfate ion concentration, chloride ion concentration and dissolved solid content of circulating water of the water heat storage system, The Langerian index and the Larson index are determined, and the Langerian index and the Larson index are calculated as follows: the Langerian index -0.5 to +0.2, the Larson index 0.0
If it deviates from the target value set between 5 and 0.2,
Calculate or experiment the total amount of slaked lime and carbon dioxide necessary to return the Langerian index and Larson index to the target values of the circulating water, and then add the slaked lime and carbon dioxide to a part of the circulating water The value of pH when injected at a constant injection rate is calculated or experimented, slaked lime is injected at a certain injection rate into a part of the circulating water, carbon dioxide gas is further injected, and slaked lime and carbon dioxide gas are injected. After the pH is above the pH
A method for preventing corrosion of a water heat storage system, characterized in that the injection amount of slaked lime and carbon dioxide gas is stopped when the previously injected slaked lime total injection amount is injected so that the injection amount of carbon dioxide gas is controlled so as to be as follows.

Here, the Langeria index and Larson index are defined as follows. Langelier index = pH-pHs = pH-8.313 + log [Ca 2+] + log [A] -s (1) Larson Index ^{= (2 [SO4 2-] +} [Cl -]) / [HCO 3 -] (2 Here, pH: actual pH value of water pHs: theoretical pH value log [Ca ²⁺ ]: logarithm of calcium ion concentration log [A]: logarithm of total alkalinity s: correction value [SO4 ²⁻ ] : sulfate ion concentration [Cl ^-]: chloride ion concentration [HCO ₃ ^-] - represents bicarbonate ion concentration.

[0011] The present invention uses slaked lime and carbon dioxide gas,
By keeping the pH of the circulating water of the water heat storage system, the Langeria index, and the Larson index within the above ranges, a dense protective film containing calcium carbonate as a main component is formed on the surface of the iron member to prevent corrosion, and the surface of the copper member is prevented. The purpose of the present invention is to prevent the protection film from being formed excessively and to prevent corrosion of the copper member.

The present inventors have found that the water temperature is 15 ° C., the pH is 6.8,
Calcium hardness 30mg / L, alkalinity 30mg / L
L, free carbonic acid 11 mg / L, chloride ion concentration 10 mg / L
L, at a sulfate ion concentration of 10 mg / L, the
2.2 99 g of slaked lime in water with Larson index of 0.8
L carbon dioxide gas is injected at 116 mg / L, pH 7.7 calcium hardness is 166 mg / L, alkalinity is 163 mg / L,
The water content was improved to 7 mg / L of free carbonic acid and water with a Langeria index of 0 and a Larson index of 0.15. This water was passed through a carbon steel pipe having an inner diameter of 20 mm and a length of 150 mm and a copper pipe of the same dimensions electrically insulated therefrom. Two months later, the pipe was cut and the inner surface thereof was examined. As a result, a coating mainly composed of calcium carbonate of about 150 μm was formed on the carbon steel pipe. On the other hand, only a film of about 1 μm was formed on the copper tube.

Standard electrode potential of iron and copper (based on hydrogen electrode)
Is -0.44V for iron and + 0.34V for copper. Mechanism of film formation of calcium carbonate to the metal surface, the anode portion of the metal surface: cathode part of ^{M → M + + e (A} ) metal _{surface: e + 1 / 2H 2 O} + 1 / 4O 2 → OH - (B) OH - + Ca ^{2 ++} HCO ₃ ⁻ → CaCO ₃ + H ₂ O (C) It is easy to emit the electrons represented by the formula (A), that is, iron whose electrode potential is lower than that of copper is (B),
It is considered that the calcium carbonate film represented by the formula (C) is easily formed. From this, it can be understood that the film formation on the surface of the steel pipe was 150 times larger than that of the copper pipe in the above-described experiment.

[0014]

1 and 2 show an embodiment of the present invention. An embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is an equipment diagram for initial filling of the heat storage system. The equipment includes slaked lime aqueous solution production equipment (1), carbon dioxide gas equipment (2), carbonated water production equipment (3),
It comprises a mixing adjustment tank (4), an adjustment water transfer pump (5) and the like. When water is injected into the heat storage system, the raw water (6) used for the injection is analyzed in advance for total alkalinity, calcium hardness, sulfate ion concentration, and chloride ion concentration, and the Langerian index of the injected water is -0.5. ~ + 0.
2. The slaked lime injection rate necessary for improving the Larson index to 0.05 to 0.2 (hereinafter sometimes referred to as “managed slaked lime injection rate for water impregnation”) and the pH of the impregnated water (hereinafter “water”). It may be referred to as “management pH value for intrusion.”).
The raw water (6) is adjusted so as to have a predetermined flow rate by a flow rate controller (7) for filling water, and is sent to a mixing adjustment tank (4) through a carbonated water producing device (3). Slaked lime is made into a slaked lime aqueous solution having a concentration of about 1600 mg / L by a slaked lime aqueous solution manufacturing device (1) equipped with a low-speed stirrer, and sent to the mixing adjustment tank (4). The slaked lime receives a flow signal from the flow controller (7). Then, an amount that becomes the water sludge management slaked lime injection rate determined as described above with respect to this flow rate is sent. The slaked lime aqueous solution production apparatus (1) is an overflow type tank, and a large amount of slaked lime powder is charged and stirred by a low-speed stirrer. Water for producing slaked lime aqueous solution passes through a feedwater flow rate controller (8) and is slaked lime. Aqueous solution production equipment (1)
An amount corresponding to the flow rate of the spilled water is supplied from the lower part of the apparatus to form a slaked lime ash solution (14), and a slaked lime aqueous solution production device (1)
And overflows to the mixing adjustment tank (4). The carbon dioxide gas is sent to the carbonated water production device (3) through the flow control valve (9) and mixed with the raw water (6) to become carbonated water (13) and sent to the mixing adjustment tank (4). The water is controlled and controlled by a flow rate control valve (9) so that the pH value measured by a pH controller (10) installed in a tank (4) becomes a control pH value for water impregnation. A partition wall (11) and a stirrer (12) are installed in the mixing adjustment tank (4), and the carbonated water (13) and the slaked lime aqueous solution (14) are stirred and mixed to adjust to a predetermined water quality. It is sent to the water heat storage system via (5).

In the present invention, the Langerian index of the water sent to the water heat storage system is adjusted between -0.5 and +0.2. The particles of the crystal of the protective film mainly composed of are roughened, so that the protective film does not become dense and the effect of preventing corrosion is reduced. When the Langeria index is -0.5 or less, formation of the protective film becomes insufficient. The Larson index is 0.0
The Larson index is 0.05 to 0.05.
Below, the amount of dissolved inorganic carbonic acid becomes too large, and the dissolution of copper increases, and above 0.2, the effect of suppressing corrosion (pitting) of copper is small. The water sent to the heat storage system has a pH of 7.5.
-9, total alkalinity 60-175 mg / L, preferably 75-150 mg / L, calcium hardness 60-17
It is desirably 5 mg / L, preferably 75 to 150 mg / L. If the water quality of the raw water changes during the long period of time when the water is immersed in the water heat storage system, measure the total alkalinity, calcium hardness, sulfate ion concentration, and chloride ion concentration of the raw water from time to time. Reset the management slaked lime injection rate and the water filling management pH value.

FIG. 2 is an equipment diagram for maintaining the water quality of the water heat storage system. The equipment includes slaked lime aqueous solution production equipment (1), carbon dioxide gas equipment (2), carbonated water production equipment (3), mixing adjustment tank (4), regulated water transfer pump (5), slaked lime aqueous solution transfer pump (15), heat storage It comprises a tank (21), a heat storage tank water transfer pump (22), a heat storage tank water extraction pump (23), a heat pump (24) and the like. The circulating water of the water heat storage system is transferred to the heat exchange device at the customer by the heat storage tank water transfer pump (22) and used, and returns to the heat storage tank (21) again. Water in the water heat storage system circulates for a long time, and during operation, calcium in the circulating water precipitates on the tank wall or tube wall, separates from the circulating water as sediment, or the pump ground of the water heat storage system Replenishment of low-calcium hardness water against water leakage from the water lowers the calcium hardness. The value of the calcium hardness can be measured by collecting the circulating water and manually analyzing the calcium hardness by chelate titration analysis, or by installing a calcium ion concentration meter in the circulating water. When the calcium hardness decreases, the value of [Ca ²⁺ ] in the expression (1) decreases, so that the Langeria index decreases and deviates from the target water quality value. It is considered that slaked lime and carbonic acid react in the circulating water as shown in the following equation. Ca (HCO ₃ ) ₂ is an unstable substance, and becomes Ca (HCO ₃ ) ₂ → CaCO ₃ ↓ + CO ₂ ↑ + H ₂ O due to a rise in temperature, decomposes HCO ₃ to release carbon dioxide gas, and releases calcium carbonate. Settles. In addition, Ca (HCO ₃ ) ₂ is converted into Ca (HCO ₃ ) ₂ + OH ⁻ → CaCO ₃ ↓ + HCO ₃ ⁻ by OH ⁻ generated at a cathode portion such as a metal surface.
+ H ₂ O to precipitate calcium carbonate and decompose HCO ₃ . Therefore, the [HCO ₃ ⁻ ] value in the equation (2) decreases, and the Larson index increases, deviating from the target water quality value.

Water quality management of the water heat storage system is performed by periodically analyzing the water quality of the circulating water of the heat storage system and monitoring the change in water quality. If the water quality deviates from the management target value, the difference and the water storage amount of the heat storage system are used. The amount of calcium and carbon dioxide to be replenished is calculated and replenished by the water quality maintenance device. Specifically, the pH, total alkalinity, P alkalinity or total acidity, calcium hardness, sulfate ion concentration, chloride ion concentration, dissolved solid content, etc. of the circulating water of the heat storage system are periodically measured, and the Langerier index and Larson index are measured. Find the index. The Langerian index and the Larson index are calculated as follows:
If the values deviate from the target values set between 5 and +0.2 and the Larson index between 0.05 and 0.2, slaked lime and carbon dioxide required to return the Langerian index and Larson index of the circulating water to the target values are obtained. The total injection amount of the water is calculated or experimented in consideration of the total water storage capacity of the water heat storage system, and then slaked lime and carbon dioxide gas are injected into a part of the circulating water at a fixed injection ratio based on the total injection ratio of both. (Hereinafter sometimes referred to as "water quality maintenance management pH value") is calculated or experimented, slaked lime is injected into a part of the circulating water at the above constant injection rate, and carbon dioxide gas is further injected. Then, the amount of carbon dioxide gas injected is controlled so that the pH after injecting slaked lime and carbon dioxide gas becomes the management pH value for maintaining water quality. That is, the concentration of the slaked lime aqueous solution coming out of the slaked lime aqueous solution production apparatus (1) is approximately constant 16
Since it is 00 mg / L, the total slaked lime aqueous solution injection amount is calculated from the required calcium replenishment amount, and this value is set as an operation end point in the feedwater flow rate integrator (16) of the slaked lime aqueous solution manufacturing apparatus (1). A constant flow rate of water is extracted from the water heat storage system by a heat storage tank water extraction pump (23), carbon dioxide gas is injected into the water, and sent to the mixing adjustment tank (4). The slaked lime aqueous solution is mixed by the slaked lime aqueous solution transfer pump (15) from the slaked lime aqueous solution manufacturing apparatus (1) so that the water from the heat storage tank water extraction pump (23) has a predetermined injection rate. ). The mixing tank (4) is provided with a stirrer (12) to uniformly mix each solution, and the pH is measured by a pH controller (10). Carbon dioxide injection
The value measured by the pH controller (10) is the water quality management p
The control is performed by controlling the flow rate control valve (9) so that the H value is obtained. The conditioned water is returned to the water heat storage system by the conditioned water transfer pump (5). In consideration of safety against scaling to the heat exchanger, the water for water quality adjustment is automatically drained only when water flows from the heat exchanger toward the center of the heat storage tank, and the returned water is immediately pumped up again. Return to the downstream side of the pumping outlet so that there is no When the set value of the feedwater flow rate integrator (16) set earlier reaches the operation end point, the injection of slaked lime and carbon dioxide gas is stopped, and the water quality adjustment is completed.

The water returned to the water heat storage system is p
H7.5-9, Langeria index -0.5- + 0.2, Larson index 0.05-0.02, total alkalinity 60-1
75 mg / L, preferably 75 to 150 mg / L, calcium hardness 60 to 175 mg / L, preferably 75 to 1
It is desirable to be in the range of 50 mg / L. Accordingly, deviations from the target values of the Langerian index and Larson index of the circulating water of the water heat storage system and the target values that determine when to operate the water quality maintenance device are set so that the quality of the water returned to the water heat storage system falls within the above range. It is preferable to set.

[0019]

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of an apparatus for implementing the present invention.

FIG. 2 is a configuration diagram illustrating an example of an apparatus for implementing the present invention.

[0020]

[Explanation of symbols]

 1. Slaked lime aqueous solution production equipment 2. Carbon dioxide device 3. Carbonated water production equipment 4. Mixing adjustment tank 5. Regulated water transfer pump 6. Raw water 7. 7. Flow rate controller for seawater Water supply flow controller 9. Flow control valve 10. pH meter 11. Partition plate 12. Stirrer 13. Carbonated water 14. Slaked lime aqueous solution 15. Slaked lime aqueous solution transfer pump 16. Feed water flow meter 21. Thermal storage tank 22. Heat storage tank water transfer pump 23. Heat storage tank drainage pump 24. heat pump

Claims (3)

[Claims] 1. Using slaked lime and carbon dioxide gas, p of circulating water
H is 7.5 to 9, and the Langeria index is -0.5 to +0.
2. A method for preventing corrosion of a water heat storage system, wherein the Larson index is 0.05 to 0.2. 2. When water is poured into a water heat storage system, the total alkalinity, calcium hardness, sulfate ion concentration, and chloride ion concentration of raw water used for the filling are measured in advance, and the Langerian index of the filled water is set to −0. The slaked lime injection rate and the pH of the impregnated water required to improve the Larson index to 0.05 to 0.2 are determined, and slaked lime is injected into the raw water so as to have the slaked lime injection rate. And further inject carbon dioxide gas, and the pH after injecting slaked lime and carbon dioxide
A method for preventing corrosion of a water heat storage system, wherein the amount of carbon dioxide gas injected is controlled so as to be H. 3. The pH, total alkalinity, total alkalinity, total alkalinity or total acidity, calcium hardness, sulfate ion concentration, chloride ion concentration and dissolved solid content of the circulating water of the water heat storage system are periodically measured, and the Langerier index and Larson's index are measured. An index is obtained, and the Langerian index and the Larson index are calculated as
If the values deviate from the target values set between 0.5 to +0.2 and the Larson index of 0.05 to 0.2, slaked lime required for returning the circulating water to the target values of the Langeria index and the Larson index are obtained. Calculate or experiment the total injection amount of carbon dioxide gas, and then calculate or experiment the pH value when slaked lime and carbon dioxide gas are injected into a part of the circulating water at a constant injection rate at the total injection ratio of both. Injecting slaked lime at a certain injection rate into a part of the circulating water, further injecting carbon dioxide gas, controlling the amount of carbon dioxide gas injected so that the pH after slaked lime and carbon dioxide gas injection becomes the above pH, A method for preventing corrosion of a water heat storage system, wherein the injection of slaked lime and carbon dioxide gas is stopped when the obtained total amount of slaked lime is injected.