JPS624634B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plate heat exchanger used in a seawater environment, such as for ocean temperature difference power generation.

Plate heat exchangers are in demand for heat recovery from low-temperature energy due to their excellent heat transfer performance, and are particularly widely used in applications such as ocean temperature difference power generation where one of the fluids to be heat exchanged is seawater. .

Conventionally, titanium plates have often been used as the material for heat transfer plates in plate heat exchangers used in seawater environments. The reason for this is that the heat transfer plate of a plate heat exchanger is not only structurally prone to local corrosion, but also that other heat exchangers, such as shell-and-tube heat exchangers, are required to improve its heat transfer performance. This is because a material that is thinner than the container is required to have sufficient corrosion resistance, but the use of titanium plates has the disadvantage of increasing costs.

On the other hand, Cypronickel
Although it is often used in tube heat exchangers, there are many problems in its use in plate heat exchangers, and therefore there are few examples of its use. The reason is that the surface of the heat transfer plate of a plate heat exchanger is formed into a complex waveform to improve heat transfer performance.
This is because the flow velocity in the corrugated recesses becomes extremely high in some parts, causing local erosion and adding to the local battery corrosion. There is a cathodic protection method as a method to reduce this local battery corrosion. This can be achieved by laminating two metals with different corrosion potentials, but there are many problems if the potential difference is too large, and in the case of Cypronickel, for example 9/
1Cu (copper) - Ni (nickel) and a large amount of nickel
It is recommended to use 8/2Cu-Ni or 7/3Cu-Ni.

However, there are further problems in the case of plate heat exchangers used in ocean temperature difference power generation and the like.

As shown in FIGS. 1 and 2, a plate heat exchanger is constructed by stacking and tightening a set of two heat transfer plates 1 having through holes 1a with a gasket 2 interposed between them to form a refrigerant passage A and a seawater passage B. and is formed. When such a plate heat exchanger is used for ocean temperature difference power generation, etc., the inner surface of the heat transfer plate 1 and the outer surface protruding into the gasket 2 are exposed to ammonia as a refrigerant, and the other outer surface is exposed to seawater. Cypronickel, which has a high Ni content, is highly susceptible to stress corrosion cracking due to ammonia, resulting in deep cracks, and there is a risk that ammonia may leak into seawater through these cracks, causing an accident. As a method to prevent this stress corrosion cracking, it is considered that the surface of the heat transfer plate 1 that comes into contact with ammonia, especially the outer surface that protrudes into the gasket 2, is coated with a stress corrosion cracking resistant material by means such as thermal spraying. However, for plate heat exchangers, it is preferable to use thin heat transfer plates from the viewpoint of efficiency, and the sealing performance of the contact surface between the gasket and the heat transfer plate is particularly important. It is difficult to obtain smoothness of the surface, and such a method does not sufficiently solve the problem.

The present invention has been made in view of the above circumstances, and is made of Cypronickel clad steel, in which the outer surface that comes in contact with seawater is made of Cypronickel, and the surface that comes into contact with ammonia is made of a dissimilar metal that is resistant to stress corrosion cracking. Using heat transfer plate, corrosion resistance,
The object of the present invention is to provide a plate heat exchanger that has excellent heat conductivity and is inexpensive and suitable for use in ocean temperature difference power generation.

A plate heat exchanger according to the present invention will be explained with reference to the drawings.

As shown in Fig. 2, the general structure of a plate heat exchanger is that two heat transfer plates 1 having through holes 1a are made into a set, and a large number of heat transfer plates 1 are stacked and tightened with gaskets 2 interposed between the through holes 1a. A refrigerant passage A for a refrigerant such as ammonia and a seawater passage B are formed.

As shown in an enlarged view of a part of the heat transfer plate 1, the base material 1b is a steel plate, and the intermediate material 1c is nickel in a weight ratio of 30% or more, preferably 50%.
Using an alloy of steel and nickel containing % or more,
The composite material 1d is made of a Cupronickel clad steel plate using Cupronickel.

The thickness of the Cypronickel layer, which is 1d of the composite material, varies depending on the corrosion resistance period, but for practical purposes, 0.1 mm or more is appropriate. If it is too thick, the heat transfer performance will deteriorate and local corrosion at the boundary with the intermediate material 1c will become a problem, so it is preferably 0.3 mm or less, and the thickness of the intermediate material 1c should be 0.1 mm or more for practical purposes. good. The thickness of the heat transfer plate 1 is about 0.6 mm to 1 mm, and a waveform is formed on the surface corresponding to the seawater passage B to enhance the heat transfer effect. Intermediate material 1c
The reason why the nickel content of the copper-nickel alloy is 30% or more, preferably 50% or more by weight is that the maximum susceptibility of the copper-nickel alloy to stress corrosion cracking due to contact with ammonia is the nickel-containing alloy. This is because the amount is around 30% by weight.

Furthermore, if the operating environment is one in which stress corrosion cracking is particularly likely to occur, the intermediate material 1c will expose the Cypronickel layer on the refrigerant side from the contact area between the gasket 2 and the heat transfer plate 1, as shown in FIG. As a result, stress corrosion cracking in this portion can be almost reliably prevented.

The plate heat exchanger made of Cupronickel clad steel according to the present invention has two plates having through holes.
In a plate heat exchanger made up of a set of plates stacked and tightened with a gasket interposed, the weight ratio
The heat transfer process is carried out by using a Cupronickel clad steel plate, which is a Cupronickel clad steel plate in which an alloy of nickel and copper containing 30% or more of nickel is interposed between the composite material and the base metal as an intermediate material, as the outer surface of the heat transfer plate. The Cupronickel layer on the refrigerant side of the plate in contact with the gasket was removed to expose the intermediate material.
Therefore, the following effects were produced.

(1) Since the corrosion potential difference between the composite material and the intermediate material is made sufficiently large, corrosion of the intermediate material is difficult to occur.

(2) Since the wall thickness of the composite material was set to 0.4 mm or less, local corrosion could be suppressed to the extent that it would not cause any practical problems.

(3) Since the ammonia layer on the refrigerant side was removed from the contact area of the heat transfer plate with the gasket, contact with the ammonia was eliminated, eliminating concerns about stress corrosion cracking.

(4) All surfaces of the heat transfer plate that come into contact with seawater are made of cypronickel, and by using cypronickel with a high nickel content, local battery corrosion can be suppressed.

Therefore, by using a heat transfer plate made of Cypronickel clad steel, we were able to provide a plate-type heat exchanger that has excellent corrosion resistance and heat transfer properties, and is also inexpensive and suitable for ocean thermal power generation. .

[Brief explanation of the drawing]

Fig. 1 is a front view of the plate heat exchanger, Fig. 2 is a sectional view thereof, and Fig. 3 shows the state of contact between the heat transfer plate and the gasket of the Cupronickel clad steel plate gasket according to the present invention. FIG. 1: heat transfer plate, 1a: through hole, 1b: base material,
1c: Intermediate material, 1d: Composite material (Kyupronickel), 2: Gasket, A: Ammonia passage,
B: Seawater passage.

Claims (1)

[Claims] 1. In a plate heat exchanger formed by laminating and tightening a set of two heat transfer plates having through holes with a gasket interposed, an alloy of nickel and copper containing 30% or more of nickel by weight is used. A Cypronickel clad steel plate interposed between the composite material and the base material as an intermediate material is used as the outer surface of the heat transfer plate, and the Cypronickel layer on the refrigerant side of the part of the heat transfer plate in contact with the gasket is removed. A plate-type heat exchanger made of Cypronic clad steel, characterized in that the intermediate material is exposed.