JPH11153360A - Heat exchanger for recovering latent heat - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation and progress of corrosion for a long period of time with a simple means, by a method wherein metallic grains or metallic pieces, having an ionization tendency larger than that of the constituting material of a heat exchanger, are adhered or attached to an external surface of the heat exchanger as sacrificed anodes. SOLUTION: Metallic grains or metallic pieces, having an ionization tendency larger than that of the constituting material of a heat exchanger, are adhered or attached to the external surface of the heat exchanger constituted of stainless steel, copper, copper alloy or the like. When constituting material of the heat exchanger is steel such as the stainless steel or the like, Al, Zn or the alloys of them are employed, and when the constituting material of the heat exchanger is copper or copper alloy, Fe, Ni and the like except Al, Zn or the alloys of them are employed. Such a metallic material having a large ionization tendency is dissolved into oxidized drain water quickly and, therefore, dissolving loss or deterioration will not be generated in the constituting material of the heat exchanger. The metallic grains 27 are stuck to the external surface of tubes 236 for a cylindrical tube type heat exchanger, or wire metal 32 is suspended semiannularly around tubes 31 as the metallic pieces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latent heat recovery heat exchanger used in a water heater, a boiler, and the like, and more specifically, to a water heater and a boiler having improved corrosion resistance to acidic drain water. The present invention relates to a latent heat recovery heat exchanger used.

[0002]

2. Description of the Related Art Water supplied to a water heater, a boiler, or the like is heated by a combustion gas of a gaseous fuel or a liquid fuel via a heat exchanger, and the sensible heat of the combustion gas is mainly used for the heating. However, heating with only the sensible heat of the combustion gas cannot sufficiently recover the heat of the combustion gas.Therefore, in recent years, a heat exchanger for latent heat recovery has been installed in addition to the main heat exchanger using sensible heat, and By improving recovery of latent heat as well, the heating has been improved to achieve higher efficiency. However, corrosion of the latent heat recovery heat exchanger due to acidic drain generated in the latent heat recovery heat exchanger is a problem.

FIG. 1 is a diagram showing an example of a water heater provided with a heat exchanger having a latent heat recovery heat exchanger. In FIG. 1, 1 is a casing, 2 is a fuel gas conduit, 3 is a burner, 4 is a main heat exchanger, and 5 is a latent heat recovery heat exchanger. The fuel gas from the conduit 2 is burned in the burner 3, and the combustion gas is discharged from the exhaust gas conduit 6 via the main heat exchanger 4 and the latent heat recovery heat exchanger 5. Reference numeral 7 denotes a fan for discharging the exhaust gas. The feedwater sent from the feedwater pipe 8 enters the latent heat recovery heat exchanger 5 through the coil pipe on the side wall of the main heat exchanger 4, where it is heated by sensible heat and latent heat in the exhaust gas.

[0004] The water warmed by the latent heat recovery heat exchanger 5 is further heated to a set temperature by the heat exchanger 9, is set to the set temperature via the hot water supply pipe 10, and is supplied with hot water. If the latent heat recovery heat exchanger 5 is not provided, the combustion gas generated in the burner 3 is discharged to the outside at around 200 ° C., for example. Sensible heat and latent heat are recovered from the exhaust gas. At this time, the outer wall surface of the heat exchanger 5 for latent heat recovery is 100 ° C. or less, usually 40 to 60 ° C.
Drain water is generated because the temperature is about the same, but this drain water is discharged through the water collecting tray 11 and the drain conduit 12.
Reference numeral 13 denotes a neutralizer for discharging the acidic drain water as harmless.

By the way, the drain water contains N in the combustion exhaust gas.
Ox, SOx, or CO ₂ dissolves into HNO ₃ ,
H ₂ SO ₃ , H ₂ CO _3, etc. For this reason, the drain water becomes acidic (usually about pH = 3), which corrodes the wall surface of the latent heat recovery heat exchanger. Therefore, various corrosion prevention methods have been proposed to prevent this corrosion. The anticorrosion methods are roughly classified into two types: (1) a method of spraying water to wash out the drain, and (2) a method of coating the outer wall surface of the heat exchanger with a substance having corrosion resistance.

FIG. 2 is a diagram showing an example of such an anticorrosion method.
FIG. 2 (a) shows an example of the above (1) method of spraying water to wash out the drain (JP-A-6-229699), and omits the illustration of heat exchange pipes and pipes for hot water. FIG.
In (a), reference numeral 14 denotes a casing, and 15 denotes a burner. In this example, the burner 15 is burned downward, and the combustion gas is discharged from a conduit 16 as exhaust gas through heat exchange in a heat exchanger. Reference numeral 17 denotes a heat exchanger having a sensible heat exchange region and a latent heat exchange region.
8 are arranged. During operation as a water heater, water for drain flushing is supplied and sprayed from a water supply pipe 19 to a water spray nozzle 18 via a valve 20, thereby flushing drain on a heat exchanger surface in a latent heat exchange area, and then draining. It is discharged after receiving 20.

However, the method of spraying water to wash out the drain as described above requires not only a device for spraying water but also a water collecting device after spraying. A control device for adjusting the timing and the amount of water supply is also required. In addition, this method has a problem that the gaps of the heat exchanger, which is considered to be most severe against corrosion, cannot be sufficiently washed away.

In the method of (2) coating the outer surface of the heat exchanger with a substance having corrosion resistance, if the coating layer has a defect, corrosion is accelerated. To prevent the defect, the coating must be thickened. There is a need to. Then, the cost increases and the thermal conductivity is hindered. For this reason, in this method, in addition to making the coating thicker, it is necessary to consider the thermal conductivity and the like, and FIG. 2B shows an example (Japanese Patent Application Laid-Open No. 60-164167).

In FIG. 2B, reference numeral 22 denotes a metal heat transfer member composed of a heat absorbing fin and a water tube, and 23 denotes a first coating layer, which comprises an organosilicon polymer containing polyborosiloxane as a main component and a titanium organic compound. And inorganic fillers. The inorganic filler is made of Al ₂ O ₃ , SiC, TiO ₂ , stainless steel powder, etc., and is uniformly dispersed as indicated by 24 in FIG. 25 is a second coating layer made of an organic resin binder. According to the embodiment of JP-A-60-164167, the thickness of the first coating layer 23 is about 15 to 20 μm.
m, the thickness of the second coating layer 25 is about 10 to 15 μm.
m.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat exchanger for recovering latent heat disposed in a water heater, a boiler, or the like, in order to achieve corrosion prevention free from the above-mentioned corrosion problems. The purpose of the present invention is to provide a heat exchanger for recovery of latent heat capable of eliminating the occurrence and progress of corrosion over a long period of time by simple means without being affected by the acidic drain water itself. It is an object of the present invention to provide a water heater or a boiler, or a heat recovery device from exhaust gas of an absorption refrigerator, a gas engine, or a fuel cell.

[0011]

The present invention is characterized in that metal particles having a higher ionization tendency than the constituent material of the heat exchanger are attached as sacrificial anodes to the outer surface of the heat exchanger for latent heat recovery. The present invention also provides a heat exchanger for latent heat recovery, wherein a metal piece having a higher ionization tendency than the constituent material of the heat exchanger is attached to the outer surface of the heat exchanger for latent heat recovery as a sacrificial anode. A latent heat recovery heat exchanger.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, (1) metal particles having a higher ionization tendency than the constituent material of the heat exchanger are attached to the outer surface of the latent heat recovery heat exchanger, or (2).
A piece of metal having a greater ionization tendency than the material of the heat exchanger is attached. In addition, the present invention is applied to various types of water heaters, boilers, absorption refrigerators, latent heat recovery heat exchangers installed when recovering heat from exhaust gas from gas engines or fuel cells, and is applied to the case of a water heater. Speaking of
The present invention is not limited to the type shown in FIGS. 1 and 2 (a), and is applicable to any type of water heater using gaseous fuel or liquid fuel.

As the constituent material of the heat exchanger for latent heat recovery in the present invention, any metal material such as stainless steel, copper or copper alloy can be used as long as it is used as the material of the heat exchanger. In this case, metal particles having a higher ionization tendency than the constituent material of the heat exchanger are attached to the outer surface thereof, or a metal piece is attached. For example, when the constituent material of the latent heat recovery heat exchanger is iron such as stainless steel, Al, Zn or an alloy thereof is used as the metal, and the constituent material of the latent heat recovery heat exchanger is copper or a copper alloy. In
In addition to Al, Zn or alloys containing these metals, Fe, Ni, Sn, Pb or alloys containing these metals are used as the metals.

As a method of attaching metal particles to the surface of the heat exchanger, any method can be used as long as metal particles can be attached to the surface of a heat exchanger having an appropriate shape such as a pipe or a pipe with fins. The method can be applied by an appropriate method such as, for example, a thermal spraying method or an aqueous suspension of metal particles together with a binder, which is applied to the surface of the heat exchanger by a spray method, and dried. In addition, as a method of attaching a metal piece to the surface of the heat exchanger, (1) the above metal (including:
(2) A metal piece made of the above-mentioned metal (including alloy) is formed in a shape corresponding to the surface of the heat exchanger. In advance, this can be performed by fitting it to the outer surface of the heat exchanger.

Since the metal material of the metal particles or metal pieces has a higher ionization tendency than the material constituting the heat exchanger, the metal material dissolves in the acidic drain water faster than the material constituting the heat exchanger. The heat exchanger constituent material does not melt. For this reason, the heat exchanger constituent material has a very effective advantage that it does not cause any melting or deterioration. Accordingly, in the present invention, defects such as gaps, holes, and cracks are allowed by attaching metal particles or attaching metal pieces to a metal material such as stainless steel, copper, or a copper alloy that constitutes a heat exchanger. The heat exchanger can be permanently protected.

The size of the metal particles in the present invention is not particularly limited, and may be an appropriate size. The amount of the heat exchanger attached to the outer surface is preferably an amount that can be maintained for a predetermined period of time, for example, until the next periodic inspection of the water heater provided with the heat exchanger. The same applies to the size of the metal piece used by being attached to the outer surface of the exchanger. In the case of metal particles, for example, it can be replenished by a simple means such as a thermal spraying method or a spraying method at the time of maintenance at regular intervals. In the case of a metal piece, its shape, thickness, width, and the like can be easily adjusted, and it is particularly advantageous because it can be easily refilled and attached.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these Examples.

FIG. 3 is a view showing an example in which metal particles are attached to the outer surface of the tube of the heat exchanger. FIG. 3A shows a case of a tubular tube type heat exchanger.
Are metal particles attached to the outer surface. FIG. 3 (b) shows a case of a tubular tube type heat exchanger with fins, 28 is a tube, 29 is a fin attached to the tube 28, and 30 is metal particles attached to the outer surface of the fin. FIG. 3B is a cross-sectional view in a direction perpendicular to the longitudinal direction of the tubular tube. In addition, the above points are the same in the case of a finned tubular tube heat exchanger in which fins are provided in the same direction as the longitudinal direction of the tubular tube or in a spiral shape.

FIGS. 4 and 5 show various examples in which a metal piece is attached to the outer surface of the tube of the heat exchanger. In the following example, one metal piece is described for convenience of description, but in the present invention, the required number of each metal piece is attached to a required portion. FIG. 4A shows a tubular tube heat exchanger in which a wire 32 is suspended as a metal piece from a tube 31. Although the wire 32 is suspended in a semi-circular shape with respect to the tube 31 in the figure, the wire 32 may be bent slightly in the direction of the arrow (→ ←) in the figure to clamp the tube 31, and further bent to the tube 31. You may make it hold | grip annularly. In addition, the cross section of the wire 32 itself can be not only circular but also square or any other appropriate shape. The same applies to the following examples.

FIG. 4B shows a finned tubular tube heat exchanger, in which 33 is a tube, 34 is a fin,
This is an example in which a wire 35 is suspended between fins 34 facing each other. The wire 32 is connected to the tube 3 as in the case of FIG.
1 may be pinched, or may be bent and held by the tube 31 in an annular shape. FIG.
(C) shows the shape of the wire when the wire is wound around a tubular tube heat exchanger or a finned tubular tube heat exchanger. This example is particularly preferably applied to a finned tubular tube heat exchanger in which fins are spirally attached to a tubular tube.

FIG. 4D shows an example of a metal piece suspended from the tubular tube. This applies to both the tubular tube heat exchanger and the finned tubular tube heat exchanger. As shown in the drawing, the wire has a tip portion 36 formed in a semi-annular shape, and is suspended by this portion from the tubular tube. Since this piece is made of metal and has elasticity, it can be easily attached to the tube. Since the metal piece has the rod-shaped portion 37, the metal piece can be attached to the tubular tube while grasping this portion. Further, after the attachment, it can have a role of promoting the flow of the acidic drain water through the rod-shaped portion 37.

FIG. 5 is a view showing an example in which a metal piece is attached to an adjacent tubular tube. FIG. 5A shows a case of a tubular tube type heat exchanger. As shown in the drawing, a wire 39 is suspended and attached to adjacent tubes 38, 38. The end portion 40 of the wire 39 may hold the tube 38 as in the case of FIG. 4A, or may be bent and held by the tube 38 in an annular shape. FIG. 5B shows a case of a tubular tube type heat exchanger with fins, in which 42 are fins. Wire 43 as shown
Is suspended and attached to adjacent tubes 41, 41. The end 44 of the wire 43 is shown in FIG.
It may be the same as the case of (a).

[0023]

According to the present invention, in a latent heat recovery heat exchanger applied to a water heater, a boiler, etc., it is possible to eliminate the generation and progress of corrosion for a long time without being affected by the acidic drain water itself. it can. Further, when a metal piece is used in the present invention, its shape, thickness, and the like can be easily adjusted, and it is particularly advantageous because its replenishment, replacement, and attachment are easy.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a water heater provided with a heat exchanger having a latent heat recovery heat exchanger.

FIG. 2 is a diagram illustrating a conventional method for preventing corrosion of a latent heat recovery heat exchanger.

FIG. 3 is a diagram showing an example in which metal particles are attached to the outer surface of a tube of a heat exchanger.

FIG. 4 is a view showing various examples in which a metal piece is attached to an outer surface of a tube of a heat exchanger.

FIG. 5 is a diagram showing another example in which a metal piece is attached to the outer surface of the tube of the heat exchanger.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 14 Casing 2 Fuel gas conduit 3, 15 Burner 4 Main heat exchanger 5 Latent heat recovery heat exchanger 6 Exhaust gas conduit 7 Fan for exhaust gas discharge 8 Water supply pipe 9 Heat exchanger 10 Hot water supply pipe 11 Water collecting tray 12 Drain pipe DESCRIPTION OF SYMBOLS 13 Neutralizer 16 Exhaust gas conduit 17 Heat exchanger (consisting of sensible heat exchange area and latent heat exchange area) 18 Water spray nozzle 19 Water supply pipe 20 Valve 21 Drainage receiver 22 Heat absorbing fin 23 First coating layer 24 Second coating layer 25 inorganic filler 26, 28, 31, 33, 38, 41 tube 27, 30 metal particle 29, 34, 42 fin 32, 35, 39, 43 wire (metal piece) 36 tip of metal piece 37 rod shape of metal piece Part 40 end of wire 39 44 end of wire 43

Claims (5)

[Claims] 1. A latent heat recovery heat exchanger comprising a sacrificial anode and a metal particle having a higher ionization tendency than a constituent material of the heat exchanger attached to an outer surface of the latent heat recovery heat exchanger. 2. A latent heat recovery heat exchanger characterized in that a metal piece having a higher ionization tendency than a constituent material of the heat exchanger is attached as a sacrificial anode to an outer surface of the latent heat recovery heat exchanger. 3. The heat exchanger for latent heat recovery is made of copper,
It is a copper alloy, and the metal of the metal particles and metal pieces is Al, Zn,
3. The heat exchanger for latent heat recovery according to claim 1, wherein the heat exchanger is Fe, Ni, Sn, Pb or an alloy containing these metals. 4. The material of the latent heat recovery heat exchanger is stainless steel, and the metal particles and metal pieces are made of Al, Zn.
3. The heat exchanger for latent heat recovery according to claim 1, wherein the heat exchanger is an alloy containing these metals. 5. The latent heat recovery heat exchanger according to claim 1, wherein the latent heat recovery heat exchanger is a water heater, a boiler, an absorption refrigerator, a gas engine, or a latent heat recovery heat exchanger in a heat recovery device from exhaust gas of a fuel cell. A latent heat recovery heat exchanger according to any of the claims.