JP3786772B2 - Corrosion prevention device for heat exchanger - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat exchanger that is mainly heated by latent heat of water vapor contained in combustion gas (hereinafter, this type of heat exchanger is referred to as a latent heat type heat exchanger).
[0002]
[Prior art]
In general, a latent heat type heat exchanger is used to improve heat efficiency by further recovering heat from, for example, a low-temperature combustion gas from which heat has been recovered in another heat exchanger. Is lower than the vaporization temperature. Therefore, during use of the latent heat type heat exchanger, water vapor contained in the combustion gas condenses on the surfaces of the water pipes and fins constituting the heat exchanger and adheres as condensed water.
In addition, although the combustion gas which heats a latent heat type heat exchanger is low temperature, it is higher temperature than a heat exchanger. Therefore, the combustion gas not only heats the heat exchanger by latent heat, but also by the heat (hereinafter referred to as sensible heat) that the combustion gas has without undergoing a phase change (phase change such that water vapor becomes water). Even heat the heat exchanger.
[0003]
When condensed water adheres to the water pipe and the fin, nitrogen oxides (NOx) and sulfur oxides (SOx) in the combustion gas are dissolved in the condensed water to generate acids such as nitric acid and sulfuric acid, respectively. These acids corrode water tubes and fins. Therefore, in the conventional latent heat type heat exchanger, the surfaces of the water pipe and the fin are coated with an organic resin such as a fluororesin and an epoxy resin or an inorganic resin such as a silicon resin, thereby preventing the water pipe and the fin from being corroded. I have to.
[0004]
[Problems to be solved by the invention]
However, it is inevitable that pinholes (holes with a small diameter) are formed in the coating layer for anticorrosion formed by coating the resin, and the outer surface of the water pipe and the fin facing the pinhole is corroded, and the corroded portion. Gradually spread. For this reason, even if the coating layer is formed, there is a problem that it is difficult to reliably prevent corrosion of the water pipe and the fin.
[0005]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 has a water pipe made of metal and a large number of fins made of metal provided on the outer periphery of the water pipe, and the water vapor contained in the combustion gas is the above. A device for preventing corrosion of the water pipe and the fin of the heat exchanger that is mainly heated by latent heat when the water pipe and the surface of the fin are in contact with condensation, and the condensation that occurs on the surface of the water pipe and the fin A positive electrode is connected to the anode disposed in close contact with the water pipe or the fin so as to be electrically connected to the water pipe or the fin, and a positive electrode is connected to the anode. And a DC power source to which a negative electrode is connected , and an insulator having water permeability is disposed between the water pipe or the fin and the anode .
[0006]
In this case, to form a through-hole arranged in along the water pipe to the fins of the upper Kio number one line, the anode is formed into a rod, in a inserted condition the anode forming the rod-like in the through holes of the fins In particular, it is desirable that the insulator be a cylindrical body, and that the cylindrical body be inserted into the through hole and that the anode be inserted into the cylindrical body. About the said cylinder, it is desirable to form by knitting glass fiber. An anticorrosion coating layer may be formed on the surfaces of the water tube and the fin.
[0007]
The corrosion prevention device includes a dew condensation water amount detection unit that detects whether or not the dew condensation water amount is a predetermined amount or less, and when the dew condensation water detection unit determines that the dew condensation water amount is a predetermined amount or less. It is desirable to further include energization stopping means for stopping energization from the DC power source to the anode and the water pipe or the fin.
In this case, the DC power source is a constant voltage circuit, and the dew condensation water amount detection means causes the dew condensation water to flow in the uncovered portion of the heat exchanger depending on whether or not the current flowing through the constant voltage circuit is equal to or less than a predetermined magnitude. The DC power supply may be a constant current circuit, and the dew condensation water detecting means may detect whether the voltage of the constant current circuit is equal to or higher than a predetermined level. It is good also as what detects whether dew condensation water has adhered to the non-coating part of a heat exchanger.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which a corrosion preventing apparatus according to the present invention is applied to a latent heat type heat exchanger of a gas hot water supply apparatus will be described with reference to FIGS. Needless to say, the present invention is also applicable to a latent heat type heat exchanger used in other combustion apparatuses other than the gas hot water supply apparatus.
[0009]
1 to 4 show an embodiment of a gas hot water supply apparatus according to the present invention, and FIG. 2 shows a schematic configuration of the entire gas hot water supply apparatus. As shown in FIG. 2, the gas hot water supply apparatus includes a housing 1, in which a gas burner 2, a main heat exchanger 3, and a sub heat exchanger (heat exchanger) 4 are accommodated. .
[0010]
The gas burner 2 is disposed at a substantially central portion of the housing 1 and is connected with a gas pipe 4. The gas pipe 4 is provided with an original gas electromagnetic valve 5 and an electromagnetic proportional valve 6. The original gas solenoid valve 5 opens and closes the gas pipe 4 to supply and stop the gas to the gas burner 2. On the other hand, the electromagnetic proportional valve 6 adjusts the amount of gas supplied to the gas burner 2. The gas burner 2 has two combustion surfaces. When the electromagnetic valve 7 is opened, the gas burner 2 burns on both combustion surfaces. When the electromagnetic valve 7 is closed, the gas burner 2 burns only on one predetermined combustion surface. Reference numeral 8 denotes a blower fan for supplying combustion air to the gas burner 2.
[0011]
The main heat exchanger 3 has a plurality of water pipes 3a (only one is shown in FIG. 2) arranged in parallel with each other, and a large number of fins 3b provided on the water pipe 3a. The water pipe 3a and the fin 3b are made of metal, and are usually made of copper. The water pipes 3a are connected to each other by a U-shaped vent pipe (not shown) to constitute one pipe as a whole. A water inlet 3 c of the water pipe 3 a is connected to a water outlet 4 e of a sub heat exchanger 4 described later, and a hot water outlet 3 d is connected to a hot water pipe 9. The main heat exchanger 3 configured as described above is disposed close to and directly above the gas burner 2 and is heated by the high-temperature combustion gas generated in the gas burner 2. In this case, the surface temperature of the water pipe 3a and the fin 3b is heated to 100 ° C. or higher. Therefore, no condensation occurs on those surfaces. That is, the main heat exchanger 3 is a sensible heat type heat exchanger that is heated by the combustion gas without phase change from gas to liquid.
[0012]
Although the auxiliary heat exchanger 4 is a latent heat type heat exchanger, as shown in FIGS. 1, 3 and 4, the structure itself is the same as that of the main heat exchanger 3 which is an actual heat exchanger. That is, the auxiliary heat exchanger 4 has a plurality of water pipes 4a arranged in parallel to each other and a large number of fins that are fitted to the outer peripheral surface of the water pipe 4a so as to be separated from each other and fixed by brazing or the like. is doing. Of course, the water pipe 4a and the fin 4b are made of metal and are usually formed of copper. The ends of each water pipe 4a are connected by a U-shaped vent pipe 4c (only one is shown). Therefore, each water pipe 4a constitutes one continuous pipe as a whole. As shown in FIG. 2, the water supply pipe 10 is connected to the water inlet 4d, and the water outlet 4e is connected to the main heat exchanger 3. It is connected to the water port 3c.
[0013]
As shown in FIG. 1, the auxiliary heat exchanger 4 is installed in the exhaust passage 1 a at the top of the housing 1. Therefore, the auxiliary heat exchanger 4 is heated by the relatively low-temperature combustion gas from which heat has been removed by the main heat exchanger 3. In this case, the surface temperature of the water pipe 4a and the fin 4b of the sub exchanger 4 is less than 100 ° C. Therefore, water vapor contained in the combustion gas is condensed and attached to these surfaces. In order to prevent the water pipe 4a and the fin 4b from being corroded by acid such as nitric acid and sulfuric acid generated by dissolving nitrogen oxide and sulfur oxide in the combustion gas in the condensed water, the water pipe 4a and the fin 4 As shown in FIG. 4, the anticorrosive coating layer 11 is formed on the surface of 4b. The covering layer 11 is formed by coating an organic resin such as a fluorine resin or an epoxy resin or an inorganic resin such as a silicon-based resin.
[0014]
In addition, a dew condensation water receiver 12 for receiving dew condensation water falling from the sub heat exchanger 4 is disposed below the sub heat exchanger 4, and the dew condensation water received by the dew condensation water receiver 12 is drained. It reaches the neutralization device 14 via the pipe 13. And after neutralizing with this neutralization apparatus, it is discharged | emitted outside the hot water supply apparatus.
[0015]
In the above configuration, when a hot water tap (not shown) connected to the hot water pipe 9 is opened, the gas burner 2 is ignited, and the water supplied through the water supply pipe 10 is first heated by the auxiliary heat exchanger 4. Thereafter, the main heat exchanger 3 is heated. The heated hot water is supplied to the hot water tap through the hot water discharge pipe 9 and discharged from there. In this case, the tapping temperature is adjusted by the control unit 19. That is, the control unit 19 uses the water supply temperature detected by the water supply temperature sensor 15, the water supply amount detected by the water amount sensor 16 (same as the amount of hot water), the hot water temperature detected by the hot water temperature sensor 17, and the remote controller 18. Based on the set temperature, the electromagnetic proportional valve 6, the solenoid valve 7 and the blower fan 8 are feedforward controlled and feedback controlled to adjust the tapping temperature to the set temperature.
[0016]
Here, during combustion of the gas burner 2, condensed water adheres to the water pipe 4 a and the fin 4 b of the auxiliary heat exchanger 4. Then, nitrogen oxides and sulfur oxides in the combustion gas dissolve in the condensed water, and nitric acid, sulfuric acid, and the like form acids. For this reason, when the pinhole 11a (refer FIG. 4) exists in the coating layer 11, there exists a possibility that the water pipe 4a and the fin 4b may be corroded from the location which faces the pinhole 11a. Therefore, the auxiliary heat exchanger 4 is provided with a corrosion prevention device 20.
[0017]
As shown in FIGS. 1, 3, and 4, the corrosion prevention device 20 includes a cylinder (insulator) 21, an anode rod (anode) 22, and a DC power source 23. These are provided in the heat exchanger 4 as follows.
[0018]
That is, in each fin 4b, a through hole 24 is formed at a position located between the four water pipes 4a. The through holes 24 formed in each fin 4b are a set of those arranged in a line in parallel with the water pipe 4a, and a plurality of such sets are formed. The cylinders 21 are inserted and fixed in the through holes 24 of each set. An anode rod 22 is inserted into each cylinder 21. A positive electrode of a DC power source 23 is connected to each anode rod 22. The negative electrode of the DC power supply 23 is connected to one of the water pipes 4a. Each water pipe 4a is electrically connected to each fin 4b by being in contact with each fin 4b, and is also electrically connected to another water pipe 4a via each fin 4b. Therefore, the negative electrode of the DC power supply 23 may be connected to another water pipe 4a or any one of the fins 4b.
[0019]
The cylinder 21 is for preventing the anode rod 22 from contacting the water pipe 4a or the fin 4b and being electrically connected in a short-circuited state. Therefore, the cylinder 21 is made of an electrical insulating material. Moreover, the cylindrical body 21 allows the condensed water adhering to the fins 4b to enter the cylindrical body 21, and electrically connects the anode rod 22 and the fins 4b via the condensed water that has entered the interior. It is. Therefore, the cylinder 21 needs to have water permeability. For example, a cylindrical body made of porous ceramic is used as the one having such insulating properties and water permeability. Here, a cylindrical body formed by knitting glass fibers is used. Glass fiber is not only rich in electrical insulation, but also has good anticorrosive properties against acids such as nitric acid and sulfuric acid, and when it is knitted, condensed water can enter the interior from the stitch. .
[0020]
The anode rod 22 is formed of a material that is insoluble in acids such as nitric acid and sulfuric acid. For example, it is formed of carbon, platinum, stainless steel or the like. Further, in this embodiment, the anode rod 22 is formed to have a smaller diameter than the inner diameter of the cylinder 21 and is separated from the cylinder 21 except for both ends thereof. The diameter may be substantially the same, and the outer peripheral surface of the anode rod 22 may be brought into contact with the inner peripheral surface of the cylindrical body 21. In such a case, even when the amount of condensed water is small, the anode rod 22 and the fin 4b can be reliably connected via the condensed water.
[0021]
Although the battery may be used as the DC power source 23, it is desirable to use a constant voltage circuit or a constant current circuit. The reason will be described later.
[0022]
In the gas hot water supply apparatus provided with the corrosion preventing apparatus 20 having the above-described configuration, when the gas burner 2 burns and the condensed water adheres to the water pipe 4a and the fin 4b of the auxiliary heat exchanger 4, the water pipe is inserted into the pinhole 11a into which the condensed water has entered. A local battery having the positive electrode 4a or the fin 4b is formed, and the surface of the water tube 4a or the fin 4b is corroded by the local battery. However, in this corrosion preventing apparatus 20, since the negative electrode of the DC power source 23 is connected to the water pipe 4a and the fin 4b, the electromotive force of the local battery becomes zero. Therefore, corrosion of the water pipe 4a and the fin 4b is prevented. Note that the voltage of the DC power supply 4a is set in advance to such a voltage that the electromotive force of the local voltage can be reduced to 0 by an experiment or the like.
[0023]
As the DC power source 23, it is desirable to use a constant voltage circuit or a constant current circuit.
In the case where a constant voltage circuit is used as the DC power source 23, when the condensed water is dried and disappears after the combustion of the gas burner 2 is stopped, the current flowing through the constant voltage circuit 23 gradually decreases and finally becomes 0. become. Therefore, the current value flowing through the constant voltage circuit 23 is detected and the detected value is output to the control unit 19. On the other hand, if a predetermined threshold value is set in the control unit 19, the current value is compared with the threshold value. Thus, it can be determined whether or not condensed water remains. In addition, if the control unit 19 controls the energization of the constant voltage circuit, the energization of the constant voltage circuit can be stopped when the value of the current flowing through the constant voltage circuit becomes 0 or extremely small. It can save energy.
[0024]
On the other hand, when a constant current circuit is used as the DC power supply 23, the voltage of the circuit of the DC power supply 23 increases as the dew condensation water dries out. When the voltage is detected and becomes equal to or greater than a predetermined magnitude, it is assumed that the condensed water has disappeared. By outputting the voltage value to the control unit 19, it is possible to detect whether or not the condensed water remains. it can. Further, when the voltage of the constant current circuit becomes equal to or higher than a predetermined level, the control unit 19 stops energization of the constant current circuit, thereby saving energy.
[0025]
FIG. 5 shows another embodiment of the corrosion preventing apparatus according to the present invention. In the corrosion preventing apparatus 20 ′ according to this embodiment, the through hole 24 is directly below the water pipe 4a so as to be in contact therewith. Arrangement is formed. Therefore, the cylindrical body 21 is also in contact with the water pipe 4a, and the anode rod 22 is also arranged directly under the water pipe 4a. Other configurations are the same as those in the above embodiment.
[0026]
The portion directly below the water pipe 4a is a portion that remains until the end in the process in which the condensed water adhering to the sub heat exchanger 4 is dried by a post fan or the like. Therefore, when the cylindrical body 21 and the anode rod 22 are arranged directly below the water pipe 4a, current can flow between the anode rod 22 and the heat exchanger 4 until the latest as compared with the case where the cylinder body 21 and the anode rod 22 are arranged elsewhere. Thus, corrosion in the pinhole 11a can be prevented to the end.
[0027]
In addition, this invention is not limited to said embodiment, It can change suitably.
For example, in the above embodiment, a plurality of cylinders 21 and anode rods 22 are provided, but only one may be provided. However, it is desirable to provide a plurality of potential differences in order to make the potential difference between the anode rod 22 and each part of the water pipe 4a or fin 4b as constant as possible. In particular, when the water pipe 4a and the fin 4b are covered with the covering layer 11 as in this embodiment, it is desirable to provide a plurality of pipes for the same reason.
[0028]
Further, although the cylindrical body 21 is inserted into the through hole 24 and the anode rod 22 is inserted into the cylindrical body 21, the anode rod 22 may be disposed close to the outside of the auxiliary heat exchanger 4. For example, the anode rod 22 may be disposed on the lower side of the fin 4b in close proximity thereto. In that case, it may replace with the cylinder 21 and may arrange | position the insulator which makes flat form between the lower end surface of the fin 4b, and the anode rod 22. FIG. However, if the cylindrical body 21 is inserted into the through-hole 24 and the anode rod 22 is inserted into the cylindrical body 21, the corrosion prevention device is compared with the case where the anode rod 22 is disposed outside the auxiliary heat exchanger 4. The space occupied by 20 can be reduced. Further, if the anode rod 22 does not reliably contact the fin 4b, it is not necessary to provide an insulator.
[0029]
Furthermore, if the corrosion of the water pipe 4a and the fin 4b can be sufficiently prevented by the corrosion prevention device 20, the coating layer 11 may not be formed. An oil burner may be used instead of the gas burner 2.
[0030]
【The invention's effect】
As described above, according to the inventions according to claims 1 to 8, there is an effect that the corrosion of the water pipe and the fin of the latent heat type heat exchanger can be prevented.
According to the invention which concerns on Claim 2, corrosion of a water pipe and a fin can be prevented still more reliably.
According to the invention which concerns on Claim 3, the effect that the space which a corrosion prevention apparatus occupies can be made as small as possible is acquired.
According to the invention which concerns on Claim 4, the effect that it can prevent that an anode contacts a water pipe and a fin and is short-circuited to them is acquired.
According to the invention which concerns on Claim 5, the effect that durability of a corrosion prevention apparatus can be improved is acquired.
According to the invention which concerns on Claim 6, the effect that corrosion of a water pipe and a fin can be prevented still more reliably is acquired.
According to the invention which concerns on Claim 7, the effect that energy saving can be achieved is acquired.
According to the invention which concerns on Claim 8, 9, the effect that it can detect that dew condensation water dried and was lose | eliminated is acquired.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a heat exchanger according to the present invention.
FIG. 2 is a diagram showing a schematic configuration of the entire gas water heater in which the heat exchanger shown in FIG. 1 is used.
3 is a partially omitted enlarged sectional view taken along line XX of FIG.
4 is a partially omitted enlarged cross-sectional view taken along line YY in FIG. 3;
FIG. 5 is a cross-sectional view similar to FIG. 3 showing another embodiment of the corrosion preventing apparatus according to the present invention.
[Explanation of symbols]
4 Sub heat exchanger (heat exchanger)
4 'Sub heat exchanger (Heat exchanger)
4a Water pipe 4b Fin 11 Cover layer 19 Control unit 20 Corrosion prevention device 21 Tubular body (insulator)
22 Anode rod (anode)
23 DC power supply 24 Through hole

Claims (8)

It has a water pipe made of metal and a large number of fins made of metal provided on the outer periphery of the water pipe, and the water vapor contained in the combustion gas is mainly caused by latent heat generated when the water pipe contacts with the surface of the water pipe and the fins to condense. An apparatus for preventing corrosion of the water pipe and the fin of the heat exchanger to be heated, wherein the water pipe is electrically connected to the water pipe and the condensed water generated on the surface of the fin. or an anode disposed proximate a non-contact state to the fin, the anode a positive electrode connected to, a DC power supply negative electrode is connected to the water pipe or the fin, the water pipes or the An anti-corrosion device for a heat exchanger, wherein a water-permeable insulator is disposed between the fin and the anode . The plurality of fins are formed with through-holes arranged in a line along the water pipe, the anode is formed in a rod shape, and the rod-shaped anode is arranged in an inserted state in the through-hole of each fin. The corrosion prevention device for a heat exchanger according to claim 1 . The corrosion of the heat exchanger according to claim 2 , wherein the insulator is a cylinder, and the cylinder is disposed in the through hole and the anode is inserted into the cylinder. Prevention device. The corrosion prevention device for a heat exchanger according to claim 3 , wherein the cylindrical body is formed by knitting glass fibers. The corrosion prevention device for a heat exchanger according to any one of claims 1 to 4 , wherein a coating layer for anticorrosion is formed on the surface of the water pipe and the fin. Condensed water amount detecting means for detecting whether or not the amount of condensed water is less than or equal to a predetermined amount; and when the condensed water detecting means determines that the amount of condensed water is less than or equal to a predetermined amount, The corrosion prevention device for a heat exchanger according to any one of claims 1 to 5 , further comprising energization stopping means for stopping energization of the anode and the water pipe or the fin. The DC power source is a constant voltage circuit, and the dew condensation water amount detection means causes the dew condensation water to adhere to the non-covered portion of the heat exchanger depending on whether or not the current flowing through the constant voltage circuit is a predetermined magnitude or less. It is detected whether it is, The corrosion prevention apparatus of the heat exchanger of Claim 6 characterized by the above-mentioned. The DC power source is a constant current circuit, and the dew condensation water detection means causes the dew condensation water to adhere to the non-covered portion of the heat exchanger depending on whether the voltage of the constant current circuit is equal to or higher than a predetermined level. It is detected whether it exists, The corrosion prevention apparatus of the heat exchanger of Claim 6 characterized by the above-mentioned.

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