JPH11201690A - Heat exchanger and device and method for cathodically protecting heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat exchanger in which cathodic protection effectively functions even when a long time has elapsed after the combustion is stopped and the evaporation of condensed water has advanced and a method and device for cathodically protecting the heat exchanger. SOLUTION: An electrode section 60 is positioned near the cathodically protected part to be protected front corrosion by condensed water of a heat exchanger 50 for recovering latent heat and applies a prescribed voltage across the anode of the electrode section 60 and the cathodically protected part of the heat exchanger 50 which works as a cathode from a constant-voltage power source 81. The voltage is continuously applied even after the combustion is stopped. When the current value detected by means of a current detector 82 exceeds a prescribed value, a water spray control section 84 discriminates that the condensed water is concentrated and sprays water upon the heat exchanger 50 by opening a stop cock 72. Consequently, the action of cathodic protection can be maintained continuously for a long period, because the condensed water is diluted and washed away and, at the same time, the heat exchanger 50 is maintained in a wet state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal heat exchanger which absorbs heat of exhaust gas generated when fuel is burned and heats a fluid to be heated flowing through a heat receiving tube, thereby reducing the latent heat of the exhaust gas. The present invention relates to an anticorrosion device that protects against corrosion due to condensed water that forms by absorption and condensation, a heat exchanger to which the anticorrosion device is added, and an anticorrosion method.

[0002]

2. Description of the Related Art A heat exchanger that heats a fluid to be heated such as water supply by absorbing heat generated when fuel such as methane, propane, butane, petroleum, and kerosene is absorbed absorbs latent heat of exhaust gas. The resulting condensed water may form on the surface of the heat exchanger. This condensed water is formed from nitrogen oxides (NOx) generated by oxidizing combustion air at a high temperature and sulfur oxides (NOx) generated by oxidizing odorants added to the combustion gas for gas leak detection. SOx) and the like are dissolved to form acidic water drops of pH 2 to 3 in which nitric acid and sulfuric acid are melted.

In order to prevent the heat exchanger from being corroded by such condensed acidic condensed water and leaking out of the internal fluid, the surface of the conventional heat exchanger is coated with an acid-resistant paint or the like. Or by arranging an electrode in the vicinity of the heat exchanger, and applying a voltage so that the electrode becomes a positive electrode and the heat exchanger becomes a negative electrode to perform anticorrosion. In addition, the condensed water adhered to the heat exchanger was washed away with water.

[0004]

However, the acid-resistant coating film may have missing portions such as pinholes, or the coating film may be deteriorated due to long-term use, resulting in missing portions. Did not adequately protect the heat exchanger from corrosion by condensed water.

[0005] Further, since the heat exchanger has a complicated shape, it has been difficult to completely wash out the entire heat exchanger.
Since the corrosiveness is reduced only after dilution to pH 6 or more, to dilute condensed water of about pH 2 to pH 6 or more at the time of dew condensation, it is necessary to add about 1 to 10 ml of remaining condensed water.
There is a problem in that 00 liters of water is required, and a large amount of water is required in the case of anticorrosion by washing.

On the other hand, in the case of the electrolytic protection, if the appliance is not used for a long time after the combustion is stopped, the water in the condensed water condensed during the previous combustion evaporates and decreases. No anticorrosion current flows during this time, but a state occurs in which condensed water still adheres to the surface of the heat exchanger. Since the acid which is a corrosive component contained in the condensed water does not evaporate, the remaining condensed water is concentrated and has high corrosiveness. As described above, when evaporation elapses after a long time after the combustion is stopped, the cathodic protection cannot be performed, and the heat exchanger is corroded by the remaining concentrated condensed water having a high acidity. There was a problem.

[0007] The present invention has been made in view of such problems of the conventional technology, and even if the evaporation of water in the condensed water that has been formed after a long time has elapsed after the stop of combustion,
An object of the present invention is to provide a heat exchanger in which cathodic protection functions effectively, a cathodic protection method and a cathodic protection device therefor.

[0008]

The gist of the present invention to achieve the above object lies in the following inventions. [1] A metal heat exchanger that absorbs the heat of the exhaust gas generated when burning fuel and heats the fluid to be heated flowing through the heat receiving pipe (51) by absorbing the latent heat of the exhaust gas In a cathodic protection device for protecting against corrosion caused by condensed water, an electrode (60) arranged in the heat exchanger near an anticorrosion point to be protected from corrosion caused by the condensed water, and the electrode (60) is positively exposed. A power source (81) for applying a predetermined voltage between the electrode (60) so that the anticorrosion portion becomes the negative electrode (60); and a power source (81) for applying the predetermined voltage between the anticorrosion portion and the electrode (60) of the heat exchanger. Watering means for watering (84, 72, 7
0), and the power supply (81) applies a voltage between the electrode (60) and the anticorrosion portion even after the combustion is stopped, and the water sprinkling means (84, 72, 70) operates after the combustion is stopped. An anticorrosion device, wherein the evaporating water is replenished by spraying water to maintain the anticorrosion location and the electrode (60) in a wet state where the anticorrosion can be performed.

[2] A metal heat exchanger for absorbing the heat of the exhaust gas generated when the fuel is burned and heating the fluid to be heated flowing through the heat receiving tube (51). An electrode (60) which is provided with an anticorrosion device for protecting against corrosion due to condensed water condensed by absorbing water, wherein the electrode (60) is disposed in the heat exchanger near the anticorrosion point to be protected from corrosion due to the condensed water. ) And said electrode (60)
A power source (8) for applying a predetermined voltage between the positive electrode (60) and the anticorrosion portion so that the anticorrosion point becomes the negative electrode (60).
1), the anticorrosion point of the heat exchanger and the electrode (6).
0) and watering means (84, 72, 70) for spraying water on the electrode (6) even after the combustion is stopped.
0) and the anticorrosion point, and the watering means (84, 72, 70) supplies water evaporating after stopping the combustion by watering to supply the water to the anticorrosion point and the electrode (60).
Characterized in that the heat exchanger is maintained in a wet state capable of cathodic protection.

[3] A metal heat exchanger for absorbing the heat of the exhaust gas generated when the fuel is burned and heating the fluid to be heated flowing through the heat receiving pipe (51). An electrode (60) which is provided with an anticorrosion device for protecting against corrosion due to condensed water condensed by absorbing water, wherein the electrode (60) is disposed in the heat exchanger near the anticorrosion point to be protected from corrosion due to the condensed water. ) And said electrode (60)
A power source (8) for applying a predetermined voltage between the positive electrode (60) and the anticorrosion portion so that the anticorrosion point becomes the negative electrode (60).
1), the anticorrosion point of the heat exchanger and the electrode (6).
0) and a water spraying means (84, 72, 70) for spraying water, wherein the anticorrosion portion is a film (53) for protecting against corrosion by the condensed water and has electrical insulation. The power supply (81) is coated and applies a voltage between the electrode (60) and the anticorrosion point even after the combustion is stopped, and the water sprinkling means (84, 72, 70) controls the moisture evaporating after the combustion is stopped. A heat exchanger for supplying water by spraying water so as to maintain the anticorrosion point and the electrode (60) in a wet state where the anticorrosion can be performed.

[4] Conductivity detecting means (82) for detecting conductivity between the electrode (60) and the anticorrosion portion is provided, and the water sprinkling means (84, 72, 70) is provided for detecting the conductivity. The cathodic protection device according to [1] or the heat exchanger according to [2] or [3], wherein water is sprayed when the conductivity detected by the means (82) is out of a predetermined range.

[5] A conductivity detecting means (82) for detecting a conductivity between the electrode (60) and the anticorrosion point is provided, and the watering means (84, 72, 70) intermittently discharges water. The electrode (6) immediately after each watering
0) and when the conductivity between the anticorrosion point falls below a predetermined termination reference value, the subsequent spraying is stopped, [1], wherein the cathodic protection device according to [4] or [4] 2], [3], the heat exchanger according to [4].

[6] The heat exchanger is a sensible heat recovery heat exchanger (40) that mainly absorbs the sensible heat of the exhaust gas, and is disposed downstream of the heat exchanger for mainly absorbing the latent heat of the exhaust gas. The cathodic protection described in any one of [1], [4] and [5], wherein the latent heat recovery heat exchanger (50) has both a latent heat recovery heat exchanger (50). An apparatus or the heat exchanger according to [2], [3], [4], or [5].

[7] A metal heat exchanger for absorbing the heat of the exhaust gas generated when burning the fuel and heating the fluid to be heated flowing through the heat receiving tube (51) absorbs the latent heat of the exhaust gas. Thus, in the method for protecting a heat exchanger from corrosion caused by condensed water condensed, the electrode (6) is provided in the heat exchanger near an anticorrosion point to be protected from corrosion caused by the condensed water.
0) is arranged, and a predetermined voltage is applied between the electrode (60) so that the anticorrosion point becomes the negative electrode (60) to the positive electrode (60) and the application of the voltage is stopped after the combustion is stopped. Characterized by maintaining the anticorrosion location and the electrode (60) in a wet state capable of cathodic protection by supplying water evaporating after the combustion is stopped by spraying water. Anticorrosion method.

The present invention operates as follows. When the latent heat is recovered from the exhaust gas generated when the fuel is burned by the heat exchanger, acidic condensed water is condensed. A voltage is applied from a power supply (81) between the anticorrosion point of the heat exchanger and the electrode (60) arranged in the vicinity thereof so that the anticorrosion point is a negative electrode and the electrode (60) is a positive electrode. Therefore, while the condensed water that has condensed adheres between the anticorrosion point and the electrode (60), current flows through the condensed water and the cathodic protection of the heat exchanger is performed.

When the combustion is stopped, the water in the condensed water condensed during the combustion evaporates and gradually decreases.
4, 72, 70), water is sprayed on the anticorrosion point and the electrode (60), and these are maintained in a wet state to form a state in which anticorrosion current can flow. Thus, even if the evaporation of water in the condensed water progresses a long time after the combustion is stopped, the cathodic protection functions effectively, and the heat exchanger can be appropriately protected from corrosion by the condensed water.

Further, since the corrosion-protected portion of the heat exchanger is covered with a coating (53) for protecting the portion from corrosion by condensed water and having electrical insulation, the coating (5) is provided.
For the part covered with 3), this coating (53)
Can protect against corrosion by condensed water.
On the other hand, portions where the coating (53) is missing, such as pinholes, can be protected by cathodic protection.

By coating with the coating (53) in this manner, the cathodic protection acts only on the missing portion of the coating (53), so that the amount of current to be supplied is reduced and the size of the power supply (81) is reduced. Can be. Further, since current flows only in the missing portion, a sufficient anticorrosion effect can be obtained even if there is a missing portion relatively far from the electrode (60).

A conductivity detecting means (82) for detecting the conductivity between the electrode (60) and the anticorrosion point is provided, and the water sprinkling means (8) is provided.
4, 72, 70) spray water when the detected conductivity falls outside a predetermined range. When the condensed water is concentrated by evaporation, the conductivity of the condensed water increases and falls outside a predetermined range. Further, when all the condensed water existing between the anticorrosion point and the electrode (60) evaporates and disappears, the conductivity between the electrodes (60) rapidly decreases and falls outside a predetermined range.

For example, when a constant voltage is applied from the constant voltage power supply (81), as the concentration of the condensed water proceeds, the conductivity increases and the amount of current increases. Further, when the condensed water between the electrodes (60) completely evaporates and disappears, the conductivity sharply drops and no current flows. When the constant current power supply (81) is used, as the evaporation proceeds, the anticorrosion portion and the electrode (6) are used.
0), and when the condensed water has completely evaporated, the voltage sharply increases to the maximum voltage that can be supplied from the power supply (81).

Therefore, water is sprayed when the conductivity between the electrodes (60) (current amount in the case of the constant voltage power supply (81), voltage value in the case of the constant current power supply (81)) is out of a predetermined range. Sprinkling can be performed at a timing required for continuing the cathodic protection, such as when the concentration of the condensed water has progressed beyond a certain level or when the condensed water has evaporated and disappeared. In addition, water can be conserved because water is sprinkled only when necessary without constantly watering.

Further, when the conductivity immediately after watering falls below a predetermined termination reference value, the subsequent watering is stopped. Since the corrosive component is gradually washed away by repeating watering, after the corrosiveness has almost disappeared, there is no need to perform cathodic protection, and it is not necessary to continue watering.

By the way, as the evaporation progresses, the condensed water is concentrated to the limit, so that the condensed water adhering between the electrode (60) and the heat receiving tube (51) or the like immediately becomes completely conductive and evaporated. The rate hardly changes with repeated watering. On the other hand, immediately after watering, the electrode (60) and the heat receiving tube (5
Since there is sufficient water between 1) and 1), the absolute amount of the remaining corrosive components is substantially reflected in the concentration of condensed water, that is, the conductivity. Thus, when the conductivity immediately after watering falls below a predetermined termination reference value, it is determined that the absolute amount of the corrosive component has fallen below an allowable value, and subsequent watering is stopped. Further, it is preferable to stop the voltage application from the power supply (81) after the last sprinkling or after the last sprinkling water evaporates and stops.

A sensible heat recovery heat exchanger (40) for mainly absorbing the sensible heat of the exhaust gas and a heat exchanger for latent heat recovery arranged downstream of the sensible heat and mainly absorbing the latent heat of the exhaust gas. In the heat exchanger composed of both (50), a large amount of condensed water is generated on the side of the latent heat recovery heat exchanger (50).
What is necessary is just to apply it to the heat exchanger (50) side for the said latent heat collection.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Each drawing shows an embodiment of the present invention. In the present embodiment, a heat exchanger according to the present invention is applied to a water heater 10. As shown in FIG. 2, the water heater 10 is provided with a sensible heat recovery heat exchanger 40 that mainly absorbs sensible heat in the exhaust gas, and is disposed downstream of the sensible heat by the flow of the exhaust gas. And a latent heat recovery heat exchanger 50. Of these, the anticorrosion and watering by an external power supply are performed on the latent heat recovery heat exchanger 50 side. The heat exchange efficiency in the sensible heat recovery heat exchanger 40 is reduced to about 75%, and the latent heat recovery heat exchanger 50 is used.
The number and size of the fins are set so that the heat exchange efficiency of the fin is about 15%.

The water heater 10 has a combustion chamber 11,
A burner 12 is arranged below the combustion chamber 11. Above the burner 12, the sensible heat recovery heat exchanger 4
0, and a latent heat recovery heat exchanger 50 is disposed further above. An electrode portion 60 for performing cathodic protection is inserted and attached to a hole formed in the fin 52 of the latent heat recovery heat exchanger 50.

Between the sensible heat recovery heat exchanger 40 and the latent heat recovery heat exchanger 50, the condensed water generated in the latent heat recovery heat exchanger 50 is received, and the condensed water is supplied to the sensible heat recovery heat exchanger 40. A tray 13 is attached to prevent the tray from dropping. The pan 13 partitions the combustion chamber 11 up and down except for a part of the right end, and the exhaust after passing through the sensible heat recovery heat exchanger 40 is discharged to the opening 14 at the right end of the combustion chamber 11 without the pan 13. Through the exhaust passage portion 15 in which the latent heat recovery heat exchanger 50 is disposed.

The receiving tray 13 is connected to the combustion chamber 1 from the opening 14 side.
1, a drain receiver 16 for temporarily storing condensed water collected by the tray 13 is provided at a lower end portion of the slope. Drain receiver 1
A discharge passage 17 for condensed water is connected to the bottom of 6, and a neutralization treatment device 18 for neutralizing acidic condensed water is attached in the middle of the discharge passage 17.

The inlet of the latent heat recovery heat exchanger 50 is connected to a feed water pipe 21 into which feed water flows, and the outlet of the latent heat recovery heat exchanger 50 is connected to the sensible heat recovery heat exchanger 40 by a connecting water pipe 22. Is connected to the input side. Heat exchanger for sensible heat recovery 4
A hot water supply pipe 23 from which the supply water after heating flows out is connected to the outlet side of 0.

A water input thermistor 24 for detecting the temperature of the supplied water is provided near the inlet of the water supply pipe 21.
On the downstream side, a water flow sensor 25 for detecting the presence or absence of water flow and the amount of water flow is attached. A hot water supply thermistor 26 for detecting the temperature of hot water to be discharged is provided near the outlet of the hot water supply pipe 23, and a water flow control valve 2 for limiting the flow rate of hot water to be discharged is provided downstream thereof.
7 are provided.

Above the latent heat recovery heat exchanger 50, a water spray nozzle 70 serving as a discharge port of water sprayed toward the latent heat recovery heat exchanger 50 is arranged. A sprinkling branch pipe 71 branched from the water supply water pipe 21 is connected to the watering nozzle 70, and in the middle thereof, a water stoppage for switching whether or not the water supply from the water supply water pipe 21 is watered from the watering nozzle 70. A valve 72 is mounted.

A combustion fan 28 for sending supply air toward the burner 12 is disposed below and to the left of the combustion chamber 11. Further, in the middle of a gas supply pipe 31 for feeding the combustion gas to the burner 12, a gas solenoid valve 32 for controlling the supply of the combustion gas on and off, an original gas solenoid valve 33, and a burner 12
Proportional valve 34 that regulates the amount of combustion gas supplied to the
Is attached.

The water heater 10 has an electric board 80 containing circuit components for controlling the operation of the water heater 10. The electric board 80 is disposed, for example, in a kitchen or the like, and is used to set a hot water temperature. And a remote controller 36 for performing various status displays. The circuit part for performing the cathodic protection and the circuit part for controlling the sprinkling are mounted on the electric board 80, and between the electrode part 60 and the electric board 80, and between the water stop valve 72 and the electric board 80. Are provided with predetermined electric wiring.

FIG. 3 shows the latent heat recovery heat exchanger 50 in more detail. Latent heat recovery heat exchangers 50 are heat receiving tubes 51 arranged in two stages, upper and lower, through which feed water to be heated passes.
And a large number of fins 52 for improving heat recovery efficiency. Here, the heat receiving tube 51 and the fin 52
Are each formed of copper. In addition, the heat receiving tube 51 and the fins 52 may be formed of stainless steel (SUS), aluminum, or an alloy thereof.

The heat receiving tube 51 and the fins 52 are coated with a coating 53 having an acid resistance and an electrically insulating property on a surface portion (corrosion preventing portion) which comes into contact with the exhaust gas. Coating 5
As 3, an organic paint such as epoxy, Teflon, acrylic or the like, or silicon, ceramic or the like can be used.

Between the upper heat receiving tube and the lower heat receiving tube, a rod-shaped electrode portion 60 is arranged along the extending direction of each heat receiving tube 51. The electrode portion 60 is composed of an electrode rod 61 obtained by plating titanium with platinum, and a glass fiber film 62 covering the periphery of the electrode rod 61. The electrode portion 60 may be made of a metal that is hardly corroded by acidic condensed water, and may be formed of, for example, a stainless steel material.

The glass fiber membrane 62 has a function of preventing the electrode rod 61 from directly contacting the fins 52 and conducting. The glass fiber membrane 62 has a mesh shape, so that condensed water can come into contact with the electrode rod 61 through a gap in the mesh. When performing cathodic protection, the electrode rod 61 is brought to a positive potential, and the latent heat recovery heat exchanger 50 is turned on.
A DC voltage is applied so that the heat receiving tube 51, the fins 52, and the like attain a negative potential.

The coating 53 may have a hydrophilic property or a water repellency. In the case where the electrode rod 61 has hydrophilicity, even if a small amount of condensed water remains, the electrode rod 61 and the heat receiving tube 51 or the fin 5
2 to ensure long continuity. On the other hand, in the case of a material having water repellency, the effect that condensed water can be efficiently washed away by water sprinkling is obtained.

FIG. 1 shows an anticorrosion and sprinkling circuit for controlling corrosion and sprinkling. The anticorrosion sprinkling circuit includes a constant voltage power supply 81 that generates a constant voltage of 1 VDC.
, A current detector 82, a voltage application control unit 83, and a watering control unit 84. The negative side of the constant voltage power supply 71 is connected to the heat receiving tube 51, and the positive side is connected to each electrode rod 61. The acidic condensed water forms heat receiving tubes 51 and fins 52.
When condensation occurs between the electrode rod 61 and the electrode rod 61, the fin 52 and the like and the electrode rod 61 conduct through the condensed water, a closed circuit is formed, and a current flows from the constant voltage power supply 71.

The current detector 72 detects a current flowing in a closed circuit formed through the condensed water.
The voltage application control unit 73 is a control circuit that switches whether to apply a voltage from the constant voltage power supply 71 or not. The voltage application control unit 73 determines whether or not the burner 12 is burning based on the combustion signal 85. From the time when the combustion is started, until the time when it is determined that it is no longer necessary to apply the cathodic protection after the combustion is completed. During this time, a voltage is applied by the constant voltage power supply 81.

The watering control section 84 is provided with the latent heat recovery heat exchanger 5.
0 is always in a wet state, that is, the electrode rod 61 and the heat receiving tube 5
This is a circuit part for controlling the opening and closing of the water stop valve 72 so as to maintain a state in which water exists between the fins 52 and the fins 52 so that the water can be protected from electricity. Specifically, when the current value detected by the current detector 82 deviates from a predetermined range after the combustion is stopped (here, exceeds a predetermined watering reference value), the water stop valve 72 is turned on for a predetermined time (several seconds). When the current value after watering falls below a predetermined end reference value,
A function to stop subsequent watering is provided. More specifically, the watering operation is stopped until the next combustion is completed and the condensed water condensed during the combustion is concentrated and the current value again falls outside the predetermined range.

Next, the operation will be described. FIG. 4 shows the flow of operation when performing cathodic protection. When the combustion of the burner 12 starts (Step S101; Y), the voltage application control unit 83 recognizes this by the combustion signal 85 and applies a constant voltage between the electrode rod 61 and the heat receiving tube 51 from the constant voltage power supply 81. (Step S102). This voltage is set at about 1 volt.

The heat from the burner 12 is first absorbed by the sensible heat recovery heat exchanger 40 arranged near the burner 12. At this time, since the heat exchange efficiency of the sensible heat recovery heat exchanger 40 is suppressed to about 75 to 80%, dew condensation hardly occurs in the sensible heat recovery heat exchanger 40. The exhaust gas whose sensible heat has been recovered by the sensible heat recovery heat exchanger 40 passes through the opening 14 and the latent heat recovery heat exchanger 50.
To reach.

Since the temperature of the exhaust gas that has reached the latent heat recovery heat exchanger 50 has dropped to about 200 ° C. to 280 ° C., the latent heat recovery heat exchanger 50 mainly recovers the latent heat of the exhaust gas, Condensed water (about 50 mm / min) is condensed on the latent heat recovery heat exchanger 50. This condensed water is nitrogen oxide (NOx) generated by oxidizing combustion air at high temperature.
Sulfur oxide (SOx) and the like generated by oxidizing the odorant added to the combustion gas to detect gas and gas leaks are dissolved, and nitric acid and sulfuric acid are dissolved to form acidic water drops of pH 2-3. ing.

The condensed water that has condensed forms a latent heat recovery heat exchanger 5.
It falls from 0 and is received by the tray 13, and is discharged through the drain receiver 16, the discharge passage 17, and the neutralization device 18. Since the condensed water condensed on the latent heat recovery heat exchanger 50 is received by the tray 13, the sensible heat recovery heat exchanger 40
The condensed water does not fall on the surface of the heat exchanger, and the sensible heat recovery heat exchanger 40 is hardly corroded by the condensed water.

On the other hand, the heat receiving tube 5 of the heat exchanger 50 for latent heat recovery
Since the layers 1 and the fins 52 are covered with the film 53, they are not corroded by acidic condensed water unless the film 53 has a missing portion such as a pinhole. After the combustion of the burner 12 is started, the heat receiving tube 5
Since a constant voltage is applied between the electrode 1 and the electrode rod 61 from the constant voltage power supply 81, even if there is a missing portion in the coating 53, the cathodic protection works and the corrosion from the missing portion of the coating 53 does not occur. Absent.

That is, when condensed water is condensed between the electrode rod 61 and the missing portion of the coating 53 in the heat receiving tube 51 or the fin 52, the heat receiving tube 51 or the fin 52 is a negative electrode. At the negative electrode side, a reaction occurs in which hydrogen ions and electrons in the condensed water combine to generate hydrogen gas. Thereby, the heat receiving tube 51 and the fins 52 are
Is not oxidized and corroded.

On the other hand, electrons flowing out into the condensed water from the negative electrodes such as the heat receiving tube 51 and the fins 52 or anions such as nitrate ions in the condensed water gather on the side of the electrode rod 61 serving as the positive electrode, and the electrons are deprived. For example, it flows from the electrode rod 61 to the constant voltage power supply 81 side. In this manner, electrons or anions move through the condensed water to form a closed circuit, so that while the condensed water is condensed between the electrode rod 61 and the heat receiving tube 51 or the fins 52, the current is reduced. The current is detected by the detector 82.

When the combustion of the burner 12 is completed (Step S103; Y), the condensation of the new condensed water hardly occurs and the latent heat recovery heat exchanger 5
The moisture in the condensed water adhering to 0 gradually evaporates and concentrates, and the detected current value gradually increases. When the evaporation of the moisture further progresses and the current value detected by the current detector 82 exceeds the predetermined watering reference value 91 (step S104; Y), the watering control unit 84 opens the water stop valve 72, and A fixed amount of water is sprinkled from above the latent heat recovery heat exchanger 50 (step S106).

Thus, the latent heat recovery heat exchanger 50 is
The wet state, that is, the state where the cathodic protection functions effectively, is maintained. If the combustion is resumed before the watering reference value 91 is exceeded (step S104; N, step S105; Y), dew condensation starts anew, so step S
Returning to 102, the cathodic protection is continued.

FIG. 5 shows the relationship between the lapse of time after the stop of combustion and the change in the current value, and the relationship between the timings of watering. During combustion, a large amount of condensed water is condensed, so that a substantially constant current flows. After the time T1 when the combustion is stopped, only the water contained in the condensed water gradually evaporates, and corrosive components (nitrate ions and the like) remain, so that the concentration proceeds and the pH value further decreases. Accordingly, the current value 92 detected by the current detector 82 also gradually increases.

Then, the water stop valve 72 is opened and water is sprayed from time T2 when the current value detected by the current detector 82 exceeds the water spray reference value 91 to time T3 when a predetermined time has elapsed. Since the concentration of the corrosive component is reduced by the water spray and the corrosive component is washed out to some extent, the current value sharply decreases at the same time as the start of the water spray, and decreases to a current value 93 or the like immediately after the end of the water spray.

After the end of the watering, the evaporation proceeds again. As the time elapses, the current value detected by the current detector 82 increases, and when the current value exceeds the watering reference value 91, the watering is performed again. As such an operation is repeated, the absolute amount of the corrosive component remaining on the surface of the latent heat recovery heat exchanger 50 gradually decreases.
It decreases gradually with each sprinkling.

When the current value detected immediately after watering falls below the predetermined end reference value (step S107; Y), the watering control unit 84 determines that it is not necessary to water any more. Stop watering. Further, the voltage application control unit 83 stops applying the voltage when the watering control unit 84 determines to stop the subsequent watering (step S108). When the last sprinkled water completely evaporates and disappears, that is, when the current detector 8
The application of the voltage may be stopped when the current value detected by No. 2 decreases to substantially “0”.

Since a certain amount of ions are originally dissolved in the water to be sprayed, a constant current flows immediately after spraying even if all the corrosive components contained in the condensed water are washed away. In addition, since the same water as the water to be sprinkled is present in the heat receiving tube 51, even if the cathodic protection is performed after the current value has decreased to the end reference value, corrosion from the inside cannot be prevented. There is little point in providing corrosion protection.

Therefore, a current value at which the current is conducted by the ions originally dissolved in the water to be sprayed is set as an end reference value, and the water spray and the voltage after the corrosive component contained in the condensed water are almost completely washed away are set. Is stopped.
Thereby, water is not wasted. In addition,
If the combustion is restarted before the current value drops below the termination reference value, the process returns to step S102 to continue the cathodic protection.

As described above, since the heat exchanger 50 for latent heat recovery is maintained in a wet state while being diluted by water sprinkling before the concentration progresses, the cathodic protection can be effectively operated for a long period of time. The heat receiving tube 51 and the fins 52 are not corroded by the condensed water whose concentration has advanced. In addition, since it is only necessary to perform water spraying to such an extent that the cathodic protection can be effectively continued, the amount of water to be sprinkled is significantly reduced as compared with a case where the cathodic protection is not performed and the corrosive component is simply washed away to prevent corrosion. be able to. For example, in order to dilute condensed water of about pH 2 to pH 6, about 100 liters of water is required for 10 ml of condensed water, but it is possible to reliably prevent corrosion with an extremely small amount of water by using the electrolytic protection together. .

In the embodiment described above, a constant voltage is applied by the constant voltage power supply 81 and watering is controlled based on the flowing current value. However, a constant current is supplied from the constant current power supply and the voltage at that time is controlled. Watering may be controlled by the value. That is, when the voltage value falls below the watering reference voltage, watering may be performed, and when the voltage immediately after watering rises above the termination reference voltage, the subsequent watering may be stopped.

In the embodiment, watering is started when the watering reference value 91 is exceeded. However, water between the electrode rod 61 and the heat receiving tube 51 or the fins 52 completely disappears, and current flows. When it runs out, watering may be performed. However, when water is sprinkled at a stage where the concentration has progressed to some extent, corrosion due to the condensed water whose concentration has progressed can be accurately prevented. Further, one sprinkling may be stopped at a fixed amount or for a fixed time, or may be stopped when the current value decreases to a certain value or when the voltage value increases to a certain value. .

It should be noted that the value of the watering reference value 91 may be gradually reduced every time watering is repeated. That is, if the amount of water adhering to the latent heat recovery heat exchanger 50 is reduced, the portion where the cathodic protection is not effective, that is, the electrode rod 61
, The probability of the presence of isolated condensed water on the heat receiving tubes 51 and the fins 52 increases. Therefore, it is desirable to sprinkle water when the amount of adhesion drops below a certain level. However, even if the amount of water adhering to the latent heat recovery heat exchanger 50 decreases to the same extent, the smaller the absolute amount of the remaining corrosive components, The current value decreases. So, every time you spray water,
Next time, if the watering reference value 91 at the time of watering is lowered, when the water adhering to the latent heat recovery heat exchanger 50 has decreased to a certain amount, watering can be performed, and the cathodic protection can be performed more appropriately. It can be carried out.

In the embodiment, when the current value drops below the watering reference value 91, watering is performed. However, watering may be performed periodically every predetermined time. . Further, it is desirable to determine whether to stop watering based on the current value immediately after watering. However, when water reaches a predetermined upper limit, watering may be stopped thereafter.

In addition, in the embodiment, in the water heater 10 provided with both the sensible heat recovery heat exchanger 40 and the latent heat recovery heat exchanger 50, the anti-corrosion and water spraying are performed on the latent heat recovery heat exchanger 50 side. However, for example, only one heat exchanger may be provided so that both the sensible heat and the latent heat of the exhaust gas are recovered, and the anticorrosion and the water spray may be applied. In the embodiment, the combustion gas is used as the fuel, but may be a type that burns liquid combustion such as petroleum or kerosene.

[0063]

According to the heat exchanger, the cathodic protection device and the cathodic protection method of the heat exchanger according to the present invention, the condensed water, whose water content has been reduced by evaporation and concentrated, is diluted by the water spray from the water spray means. , So that the space between the anticorrosion point and the electrode is kept wet by spraying water, so that even if a long time elapses after the combustion is stopped, the anticorrosion works effectively and the heat exchanger is properly protected from corrosion by condensed water. can do.

Further, when the conductivity immediately after watering falls below a predetermined termination reference value, watering is stopped thereafter, so that watering is continued even after the corrosive components are almost washed off, and water is wasted. Consumption can be prevented and water can be saved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit for anticorrosion sprinkling provided in a heat exchanger according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a water heater using the heat exchanger according to one embodiment of the present invention.

FIG. 3 is a perspective view showing a heat exchanger for latent heat recovery and an electrode unit of the water heater shown in FIG. 2;

FIG. 4 is a flowchart showing a flow of an operation when performing cathodic protection and watering.

FIG. 5 is an explanatory diagram showing a relationship between a lapse of time after the combustion is stopped and a change in the amount of current, and a relationship between timings of watering.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Water heater 12 ... Burner 13 ... Receiving tray 21 ... Water supply water pipe 40 ... Heat exchanger for sensible heat recovery 50 ... Heat exchanger for latent heat recovery 51 ... Heat receiving pipe 52 ... Fin 53 ... Coating 60 ... Electrode part 61 ... Electrode rod 62 ... glass fiber membrane 70 ... watering nozzle 71 ... watering branch pipe 72 ... water stop valve 81 ... constant voltage power supply 82 ... current detector 83 ... voltage application controller 84 ... watering controller 85 ... combustion signal

Claims (7)

[Claims] 1. A metal heat exchanger, which absorbs heat of exhaust gas generated when burning fuel and heats a fluid to be heated flowing through a heat receiving tube, absorbs latent heat of the exhaust gas to form dew condensation. An electrode provided in the heat exchanger near the anticorrosion point to be protected from corrosion by the condensed water, wherein the electrode is a positive electrode and the anticorrosion point is a shadow. A power supply for applying a predetermined voltage between the electrodes so as to form electrodes, and water spraying means for spraying water on the anticorrosion points and the electrodes of the heat exchanger, wherein the power supply keeps the electrodes even after combustion stops. And applying a voltage between the anticorrosion point and the water spraying means, by supplying water evaporating after stopping the combustion by water spraying, and maintaining the anticorrosion point and the electrode in a wet state capable of cathodic protection. Characteristic cathodic protection device. 2. A metal heat exchanger that absorbs heat of exhaust gas generated when burning fuel and heats a fluid to be heated flowing through a heat receiving tube, by absorbing latent heat of the exhaust gas. An electrode provided with an anticorrosion device for protecting against corrosion due to condensed water condensed, wherein an electrode disposed in the heat exchanger near an anticorrosion point to be protected from corrosion due to the condensed water, and the electrode is positively exposed. A power supply for applying a predetermined voltage between the electrodes so that the anticorrosion portion becomes a negative electrode, and watering means for watering the anticorrosion portion and the electrode of the heat exchanger; After the combustion is stopped, a voltage is applied between the electrode and the anticorrosion portion, and the water spraying means supplies water evaporating after the combustion is stopped by spraying water to wet the anticorrosion portion and the electrode so that the anticorrosion can be performed. To maintain Heat exchanger and butterflies. 3. A metal heat exchanger for absorbing heat of exhaust gas generated when burning fuel and heating a fluid to be heated flowing through a heat receiving tube, by absorbing latent heat of the exhaust gas. An electrode provided with an anticorrosion device for protecting against corrosion due to condensed water condensed, wherein an electrode disposed in the heat exchanger near an anticorrosion point to be protected from corrosion due to the condensed water, and the electrode is positively exposed. A power supply for applying a predetermined voltage between the electrodes so that the anticorrosion portion becomes a negative electrode; and a water sprinkling means for watering the anticorrosion portion and the electrode of the heat exchanger. Is a coating for protecting against corrosion by the condensed water and is coated with an electrically insulating material.The power supply applies a voltage between the electrode and the anticorrosion portion even after the combustion is stopped, The sprinkling means is provided after the combustion is stopped. A heat exchanger for supplying water that evaporates to the surface by spraying water to maintain the anticorrosion location and the electrode in a wet state capable of cathodic protection. 4. An electric conductivity detecting means for detecting electric conductivity between the electrode and the anticorrosion point, wherein the water spraying means has an electric conductivity detected by the electric conductivity detecting means out of a predetermined range. 4. The anticorrosion device according to claim 1, wherein water is sprayed when the water is sprayed. 5. An electric conductivity detecting means for detecting electric conductivity between the electrode and the anticorrosion point, wherein the water sprinkling means intermittently sprinkles water and the electrode and the anticorrosion point immediately after watering each time. When the conductivity between the water drops below a predetermined termination reference value, water spraying after that is stopped, and the cathodic protection device according to claim 1 or 4, or claim 2, 3, or 4, Heat exchanger. 6. A heat exchanger for recovering sensible heat, which mainly absorbs sensible heat of exhaust gas, and a heat exchanger for recovering latent heat, which is disposed downstream of the exhaust passage and mainly absorbs latent heat of exhaust gas. A heat exchanger for recovering the latent heat in a system having both the heat exchanger and the heat exchanger.
The cathodic protection device according to claim 5, or the heat exchanger according to claim 2, 3, 4, or 5. 7. A metal heat exchanger that absorbs heat of exhaust gas generated when burning fuel and heats a fluid to be heated flowing through a heat receiving tube is condensed by absorbing latent heat of the exhaust gas. In a method for protecting a heat exchanger from corrosion by condensed water, an electrode is disposed in the heat exchanger near an anticorrosion point to be protected from corrosion by the condensed water, wherein the electrode is a positive electrode and the anticorrosion point is A predetermined voltage is applied between these electrodes so that the electrode becomes a negative electrode, and the application of the voltage is continuously performed after the combustion is stopped. And a method for maintaining the wet state of the heat exchanger.