JPS60245787A - Heat exchanger - Google Patents

Abstract

PURPOSE:To improve durability and reliability of a heat exchanger to be used for a combustion device for hot water supply or heating by uniting a main heat exchange part and a heat exchange part for recovering latent heat to one body and forming a plating layer on the surface of a copper heat transmitting member. CONSTITUTION:The heat exchanger 3 consisting of the main heat exchange part A and the heat exchange part B for absorbing latent heat in one body is disposed below a combustion chamber 2. The copper heat transmitting member 6 constitutes heat absorbing fins 4 and a water tube 5. The plating layer consisting essentially of Ni is formed on both of the parts A and B and further the plating layer 8 consisting essentially of Sn is formed on the plating layer 7 of the part B. The compsn. of the layer 7 consists of an alloy of Ni and P, for which electroless plating is applied. The compsn. of the plating layer 8 consists of an alloy of >=1 kinds from the group of Bi, Al and Mg and Sn, for which hot dipping is applied. The corrosion of the heat exchanger is prevented by the above-mentioned constitution, by which the durability and reliability thereof are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a heat exchanger used in a combustion device for hot water supply or space heating.

Conventional configurations and their problems Recently, there has been a strong trend toward higher performance from the perspective of energy conservation in combustion equipment for hot water supply or space heating. The development of heat exchangers with the added function of recovering heat is actively underway, and some of them have already been put into practical use.

The combustion exhaust gas contains large amounts of nitrogen oxides, carbon dioxide gas, water vapor, and trace amounts of sulfur oxides, and as mentioned above, when the steam is condensed to recover latent heat, the combustion exhaust gas dissolves at a pH of 2. A large amount of acidic condensed water of ~4 is generated. Conventionally, the surface treatment material for heat exchangers has generally been a hot-dip plated lead-tin alloy containing lead as a main component. However, when this lead-tin alloy plating is applied to a heat exchanger with a latent heat recovery function, it corrodes in an extremely short period of time because the lead itself has no resistance to the acidic condensation water mentioned above, and the heat exchanger material There have been problems in that it corrodes some copper, lowering the performance of heat exchangers, or creating holes that can cause water leaks, resulting in a significant loss of durability and reliability.

In addition, the acidic condensation water is drained from the equipment, but the drainage standards for sewerage systems stipulate that the lead content is 1 ppm, and the copper content is 3 ppm or less.If the above-mentioned corrosion occurs, a large amount of lead, There was a problem that the above-mentioned wastewater standards could not be satisfied because the copper was dissolved.

On the other hand, in the parts that exchange sensible heat, corrosion occurs due to steam oxidation at high temperatures and partial dew condensation during cooling when combustion is stopped, and corrosion products accumulate between the heat-absorbing fins. There were problems such as the flow of waste gas being obstructed, resulting in incomplete combustion, and poor heat conduction, resulting in a decrease in thermal efficiency.

Purpose of the Invention The present invention solves such conventional problems, and aims to improve the durability of the heat exchanger by preventing corrosion caused by acidic condensation water in which combustion waste of the heat exchanger is dissolved and corrosion caused by high-temperature oxidation. At the same time, the purpose is to prevent incomplete combustion and a decrease in thermal efficiency, and to improve the reliability of the combustion device.

Structure of the Invention In order to achieve this object, the present invention has a structure in which a main heat exchange part and a latent heat recovery heat exchange part are integrated, which are disposed below the burner and the combustion chamber and are made of copper heat transfer members such as heat absorption fins and water tubes. and a plating layer containing nickel as a main component on the surface of the copper heat transfer member of the main heat exchange section and the heat exchange section for latent heat recovery, and a plating layer containing tin as the main component of the plating layer of the heat exchange section for latent heat recovery. A plating layer is formed.

With this configuration, even if a large amount of acidic condensation water is generated in the heat exchanger for latent heat recovery during combustion, corrosion can be significantly suppressed because the two plating layers formed on the copper heat transfer member have excellent corrosion resistance. In addition, in the main heat exchange section, the single plating layer formed on the copper heat transfer member has excellent heat resistance and corrosion resistance, so corrosion due to high temperature oxidation and dew condensation phenomenon that occurs when combustion is stopped can be prevented.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a sectional view of a combustion apparatus equipped with a heat exchanger according to the present invention, in which 1 is a burner, 2 is a combustion chamber, 3 is a heat exchanger, 4 is an endothermic fin, and 5 is a water tube. The heat exchanger 3 is arranged at the lower part of the combustion chamber 2, and includes a main heat exchange section A and a latent heat recovery heat exchange section B.
It has an integrated structure. FIG. 2 is a sectional view of a main part of a heat exchanger showing the present invention, and (a) is a main heat exchange section A.
, (bl indicates the configuration of the heat exchange part B for latent heat recovery. 6 is a heat absorption fin, a copper heat transfer member that constitutes a water tube, 7 is a plating layer mainly composed of nickel, and 8 is a plating layer mainly composed of tin. The plating layer 7 mainly composed of nickel is formed on both the main heat exchange section A and the heat exchange section B for latent heat recovery, and the plating layer 8 mainly composed of tin is formed on the heat exchange section B for latent heat recovery. is formed on the plating layer 7 of.

The composition of the plating layer 7 is an alloy of nickel and phosphorus, and electroless (chemical substitution) plating is used to form it so that a uniform film thickness can be obtained even in a complex shape. On the other hand, the composition of the plating layer 8 is an alloy of one or more selected from the group of bismuth, aluminum, and magnesium and tin, and the forming means is such that the melting point of the alloy is 300
'C or less, hot-dip plating is applied.

In this configuration, when combustion is performed using the combustion apparatus shown in FIG. In addition to being attacked by combustion exhaust gas, when combustion is stopped, the fuel is cooled, and a small amount of acidic dew condensation water is generated at the contact area between the heat absorbing fins 4 and the water pipes 5. However, since the copper heat transfer member 6 that constitutes the heat absorbing fins 4 and the water tubes 5 is coated with a plating layer 7 mainly composed of nickel, which has excellent heat resistance and corrosion resistance, it is possible to prevent deterioration due to heat and prevent high temperature oxidation. Corrosion due to dew condensation can be prevented, and accumulation of corrosion products can be significantly suppressed.

On the other hand, due to the design of the heat exchanger for latent heat recovery heat exchange section B, the temperature is always below the dew point during combustion, and the water vapor condenses, and the combustion exhaust gas is dissolved in this, producing a large amount of acidic condensed water with a pH of about 3. In the heat exchange part B for latent heat recovery, the copper heat transfer member 6 is coated with two plating layers: a plating layer 7 mainly composed of nickel, which has excellent corrosion resistance, and a plating layer 8 mainly composed of tin. Therefore, corrosion of the copper heat transfer member 6 can be significantly prevented. In particular, the plating layer 8 whose main component is tin is highly resistant to nitric acid and carbonic acid, which are the main components of the acidic condensation water, and the amount of corrosion is extremely small.

Moreover, even if corrosion factors enter through the pinholes in the plating layer 8, since the plating layer 7 whose main component is nickel is formed below the plating layer 8, the corrosion factors will not enter the copper heat transfer member 6. Invasion can be almost completely prevented, and furthermore, since the components of the plating layers 7 and 8 are more base in potential than copper, each plating layer has an inertial anode effect, and copper ions are removed from the copper heat transfer member 6. It does not dissolve into acidic condensation water and satisfies the sewer drainage standard of 3 ppm or less.

By forming 7 and 8, excellent corrosion resistance and heat resistance can be achieved, which eliminates the accumulation of corrosion products on the copper heat transfer member 6, preventing incomplete combustion, reduction in thermal efficiency, and contamination of the surrounding area. At the same time, the durability and reliability of the heat exchanger can be significantly improved.

Next, experimental results showing specific effects of the present invention will be explained.

Experimental Example 1 A copper plate with dimensions of 75 x 75 Xo and 4 mm was used as a heat transfer member, a plating layer of the alloy listed in Table 1 was formed, and a test piece was created.

(Table 1 Table 1 White) Table 1 Types of alloys in each plating layer The plating layer 7 made of an alloy of nickel and phosphorus was formed by electroless plating to a thickness of 3 to 51 tm, and The plating layer 8 of No. 5 was formed on the plating layer 7 by hot-dip plating to a thickness of 10 to 20 μm. Also, for comparison, the copper plate was made of conventional 99wt% lead.
A sample coated with hot-dip plating containing 1 wt% tin was also produced.

A corrosion test was conducted on the test piece prepared as described above by immersion in acidic dew water.

The acidic condensed water was collected from the condensed water generated during combustion in the combustion device shown in Figure 1, and was heated to iodine at 6°C.
Corrosion resistance was evaluated by corrosion loss after immersion for a time. The results are shown in Table 2.

Table 2 Corrosion resistance evaluation using acidic condensation water *Plating of lead-tin alloy As is clear from Table 2, sample 1' in which plating layers 7 and 8 were formed on the surface of the copper heat transfer member of the present invention! : It was confirmed that test pieces of 12 to 5 exhibited good corrosion resistance. Furthermore, the plated layer 7 made of nickel and phosphorus alloy only has relatively good corrosion resistance, and can be applied to the main heat exchange section A, which has a weaker corrosive environment than the latent heat recovery heat exchange section B. .

In addition, copper ions were analyzed using an atomic absorption spectrophotometer in the acidic dew water after the corrosion test, but no copper ions were detected in any of samples Nos. 1 to 5.

Experimental Example 2 Next, using the combustion device and heat exchanger shown in FIGS. 1 and 2, using sample No. 1 described in Experimental Example 1 as the plating layer 7 and sample holes 2 to 5 as the plating layer 8, As a result of conducting 50,000 cycles of repeated tests of burning for 1 minute and extinguishing for 1 minute, slight corrosion products were observed in plating layers 7 and 8, but there was no incomplete combustion or decrease in thermal efficiency. Furthermore, no copper ions were found in the acidic condensation water, confirming that it satisfies sewerage drainage standards.

From the perspective of corrosion resistance, is it possible to further improve corrosion resistance by forming the plating layer 8 also on the main heat exchange part A?
The alloy mainly composed of tin in plating layer 8 has a melting point of 300°.
Since the temperature is low, below C, it cannot be applied to the main heat exchange section A in terms of temperature. On the other hand, the plating layer 7 mainly composed of nickel has a very high melting point of about 900"C (it has excellent heat resistance and also shows excellent resistance to steam oxidation, so it is used in the main heat exchange section A. It is best to form only a plating layer mainly composed of nickel.

Effects of the Invention As described above, the heat exchanger of the present invention provides the following effects.

(1) Corrosion of the heat transfer member can be significantly suppressed, so there is no accumulation of corrosion products between the heat absorbing fins, and the flow of combustion waste is not inhibited, so incomplete combustion can be prevented.

(2) No more holes or falling off due to corrosion of heat transfer members.
The durability as a heat exchanger is greatly improved, and the reliability as a combustion device is improved.

(3) Since an alloy plating layer is formed on the surface of the copper heat transfer member, the excellent thermal conductivity of copper is not significantly impaired, and the occurrence of corrosion can be significantly suppressed.
The initial excellent thermal efficiency can be maintained over a long period of time.

(4) Even if the acidic condensation water is drained, it does not contain copper ions, so it can meet sewer drainage standards.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a combustion device to which the present invention is applied, and FIGS. 2(a) and 2(b) are sectional views showing essential parts of a heat exchanger according to an embodiment of the present invention. 3°° ・Heat exchanger, 4... Endothermic fin, 5.
...Water pipe, 6...Copper heat transfer member, 7...
Plated layer, 8... Plated layer, A... Main heat exchange section, B... Heat exchange section for latent heat recovery. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2

Claims (3)

[Claims] (1) A main heat exchange section is arranged below the burner and the combustion chamber, and is composed of copper heat transfer members such as heat absorption fins and water tubes, and a heat exchange section for latent heat recovery is integrated, and the main heat exchange section and the latent heat A heat exchanger in which a plating layer containing nickel as a product is formed on the surface of a copper heat transfer member of a heat exchanger for recovering latent heat, and a plating layer containing tin as a main component on the plating layer of the heat exchanger for latent heat recovery. vessel. (2) The heat exchanger according to claim 1, wherein the plating layer containing nickel as a main component is an alloy of nickel and phosphorus. (3) The heat exchanger according to claim 1, wherein the plating layer containing tin as a main component is an alloy of tin and one or more selected from the group of bismuth, aluminum, and magnesium.