JPS5844200B2 - Corrosion prevention method for heat exchangers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing corrosion of heat exchangers using copper alloy tubes, such as large condensers for power generation that use seawater as cooling water.

In general, the corrosion resistance of copper alloy-based members depends on the anti-corrosion coating formed on the surface, and it is widely known that iron-based anti-corrosion coatings play a particularly important role in improving corrosion resistance.

The formation of this iron-based anti-corrosion film mainly depends on the concentration of ferrous ions contained in the cooling water. A method of supplying iron ions by injecting and mixing sulfuric acid to form an anticorrosive iron oxide film on the inner wall of the tube was used, and this method was often combined with cathodic protection using an insoluble electrode. Since ferrous iron is a hygroscopic powder, chemical management such as storage and handling is complicated, many people and time are required for dissolution and injection work, and there are problems such as discoloration of cooling water to brown. Therefore, the development of a new anti-corrosion method was desired from the viewpoint of labor saving and environmental protection.

For this reason, research and development was carried out to supply iron ions using an electrolytic method, including a method of installing a large electrolytic iron ion generator in the intake channel (No. 5244742), and a method of dissolving iron ions as electrodes for cathodic protection. A method using iron electrodes (1986)
Iron ion supply technologies such as No. 2-76523) have been developed.

However, although the former method can supply sufficient iron ions to form an anti-corrosion film, the equipment is large and consumes a lot of power, while the latter method has a small equipment and consumes a lot of power. Although the amount of iron ions supplied is small, there are some drawbacks such as insufficient supply of iron ions, and further technological development is required.

The inventors of the present invention focused on the relationship between the formation and maintenance of the anticorrosion coating on copper alloy tubes and the amount of iron ion supplied, and as a result of intensive research based on the technology and experience accumulated over the years. It has been found that there is a close relationship between the iron ion concentration in cooling water and the formation of an anticorrosive film.

That is, 0.1 to 0.5 ppm during initial film formation.
, 0.01 to 0.03 ppm when regenerating the destroyed film.
It has also been found that an iron ion concentration of 0.001 to 0.01 ppm is preferable for forming and maintaining a completed film.

This means that to maintain the formation of a corrosion-resistant film, a large amount of iron ions is required initially, a small amount for maintenance, and a medium amount for regeneration depending on the state of the film, so the iron ion supply system must be adjusted accordingly. It would be a good idea to develop

Based on the above research results, the present inventors have developed an electrolytic iron ion generator that supplies iron ions to the cooling water intake channel and a thermal A soluble iron electrode is installed as an electrode for cathodic protection in the water chamber on the water inlet side of the exchanger, and an electrolytic iron ion generator is operated according to the formation status of the tube anticorrosion coating to form a stable anticorrosion coating, and at the same time It has been discovered that supplying iron ions to maintain the anticorrosive film by electrolytic protection using electrodes is an effective iron ion supply system that satisfies the above conditions.

However, this method of controlling the anti-corrosion film based on iron ion concentration cannot respond to changes in the flow rate of cooling water, so iron ions may adhere thickly and reduce the heat transfer efficiency of the tube, or iron ions may This was not sufficient as there was a risk that the corrosion protection of the tube would be impaired due to insufficient adhesion.

From these facts, it has been found that in the corrosion protection management of copper alloy tubes, it is necessary to have a means to clearly check the corrosion protection status and to continue to supply an appropriate amount of iron ions based on this.

Conventionally, the corrosion protection status in the iron ion supply method was confirmed by supplying iron ions for a fixed period of time, then pulling out the cooling tube and cutting a part of it, or by taking out a sample piece that had been placed in a water chamber in advance and checking the corrosion protection formed on the surface. Since this method involves observing the state of the film and analyzing its components, the determination is subject to time constraints and requires a great deal of time and effort.

Based on data accumulated over many years, the present inventors have found that there is a close relationship between the cathodic polarization resistance value of the anti-corrosion protective film formed on the surface of the copper alloy member and the state of the film, as shown in the table below. I discovered that.

Based on these facts, the present invention measures the state of the anti-corrosion coating on copper alloy tubes using a cathodic polarization resistance method, for example, using a cathodic protection device installed in a water chamber, and calculates the polarization resistance value. By automatically controlling the corrosion protection current for cathodic protection and the electrolytic iron ion generator based on the It shall be managed rationally.

Next, embodiments of the anticorrosion method of the present invention will be specifically described with reference to the drawings.

The drawing is a plan view of the case where the method of the present invention is applied to a condenser of a power generation plant. Initial formation of anti-corrosion coating on the tube and supply of iron ions for regeneration.

On the other hand, an iron electrode 4 for cathodic protection installed in the water chamber of the condenser 3
From this point, an anti-corrosion current is applied and iron ions necessary for maintaining the anti-corrosion film are supplied.

The electrolytic iron ion generator 2 is supplied with DC current and controlled by a power supply device 5, and the amount of eluted iron ions is managed.

Further, direct current is supplied and controlled to the iron electrode device 4 by a cathodic protection power supply device 6, and the elution amount of iron ions and the amount of corrosion protection current are managed.

7 is a sub-electrode of a cathode polarization resistance meter installed in the water chamber of the condenser 3, which measures the potential of the copper alloy tube.
This data is input to the arithmetic processing circuit 8 to determine the cathodic polarization resistance value, and this value is used to judge the state of the anticorrosion coating on the tube, thereby determining the appropriate value of the output current for cathodic protection and the output current of the electrolytic iron ion generator. do the calculations,
Control signals are sent to each device to automatically control the corrosion protection current and iron ion supply amount.

In this embodiment, the sub-electrode 1 of the cathodic polarization resistance meter is also used as the sub-electrode of the cathodic protection electrometer, but a dedicated cathodic polarization resistance measuring device may be provided separately.

Further, the arithmetic processing circuit 8 can also be incorporated into a cathodic protection power supply device.

According to this anti-corrosion method, the electrolytic iron ion generator 2 mainly supplies iron ions for initial film formation.
Without assuming continuous long-term supply, it is sufficient to have the ability to generate iron ions commensurate with the initial film formation based on various conditions such as the area of the copper alloy tube and the amount of water. is small and has a small capacity, and can reduce power consumption.

Since a large amount of iron ions is initially supplied by this electrolytic iron ion generator 2, the concentration of iron ions constantly supplied to maintain the film only needs to be a small amount, and the electrolytic protection electrode is made of soluble iron. Sufficient supply can be achieved by using electrodes.

Even if an iron electrode is simply used as the electrode for cathodic protection, the amount of iron ion supplied is small because the applied current is limited by the corrosion protection current, and is far below the amount required for initial film formation.

Therefore, when iron electrodes are used, ferrous sulfate has conventionally been added intermittently, but according to the method of the present invention, it is possible to maintain the anticorrosive film without adding ferrous sulfate. .

In addition, according to this method, in the corrosion protection of copper alloy tubes of heat exchangers, it is possible to effectively control the corrosion protection current value of cathodic protection and the amount of supplied iron ions in a correlated manner, and also to perform appropriate and rational control. Corrosion prevention management can be performed.

Furthermore, since the state of the anticorrosive coating on the tube is constantly monitored to maintain the anticorrosive coating in an appropriate state, it is possible to prevent misalignment such as a decrease in heat transfer efficiency caused by excess or deficiency of iron ions.

[Brief explanation of drawings]

The drawing is a plan view showing an embodiment of the present invention. 1... Cooling water intake channel, 2... Electrolytic iron ion generator, 3... Condenser, 4...
・Iron electrode for cathodic protection, 5...Power supply device, 6...
...Electric protection power supply device, γ...Cathode polarization resistance meter sub-electrode, 8...Arithmetic processing circuit.

Claims (1)

[Claims] 1. In forming and maintaining an anti-corrosion coating on the copper alloy tubes of the heat exchanger, an electrolytic iron ion generator that supplies iron ions to the cooling water intake channel and an electrode for cathodic protection are installed in the water chamber on the water inlet side of the heat exchanger. A soluble iron electrode is provided as a method, and a stable anti-corrosion film is formed by the electrolytic iron ion generator, and the anti-corrosion film is maintained by the soluble iron electrode.
The state of the anti-corrosion coating on the copper alloy tube is measured using the cathode polarization resistance method, and based on this polarization resistance value, the anti-corrosion current for cathodic protection and the electrolytic iron ion generator are automatically controlled. A method for preventing corrosion of a heat exchanger, characterized by setting the amount of ion supply to an appropriate value.