JPS5947237B2 - How to prevent corrosion of air-cooled steam condensers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing corrosion of an air-cooled steam condenser.

In recent years, boilers have been installed in dust incineration plants for the purpose of effectively utilizing the heat of incineration, and heat has been widely used for generating electricity, heating, and hot water using steam.

However, in any application, a device is required to release the heat generated within the plant to the outside.

Air-cooled steam condensers have many advantages over traditional water-cooled condensers, and most trash incineration plants being built these days are air-cooled.

These advantages are in terms of operability, economy, and environment, but on the other hand, condenser tube corrosion accidents have occurred three to four years ago, and numerous studies and attempts have been made to find the cause.

The present invention provides a method for preventing corrosion of air-cooled steam condensers used in dust incineration plants, etc., in which a condensate-based corrosion inhibitor and deoxidizer are added to the steam in the steam inlet piping of the steam condenser using hot water. This involves spraying and mixing a chemical solution diluted with water.

One embodiment will be described below based on the drawings.

Figure 1 shows an example of a steam/condensate cycle equipped with an air-cooled steam condenser.

Raw water produced by the water purifier 1 is supplied to a condensate tank 3 by a raw water replenishment pump 2.

Condensate in the condensate tank 3 is sent to a deaerator 5 by a condensate pump 4, and dissolved oxygen (0□
) are removed.

Thereafter, the condensate is supplied to the boiler 7 by the boiler feed pump 6.

The steam generated in the boiler 7 is further heated by a super heater 8 to become dry steam, and this dry steam is sent to the power generation turbine 10 through a boiler pressure control valve 9 that keeps the internal pressure of the boiler 7 constant. It is used to generate power.

The steam that has lost most of its energy is reduced in pressure and temperature, sent to an air-cooled low-pressure steam condenser 11, and cooled there.
It becomes condensate and returns to the condensate tank 3.

On the other hand, surplus steam flows into the air-cooled high-pressure steam condenser 16 through the boiler pressure control valve 15 and becomes condensate there.
It returns to the condensate tank 3 through the drain trap 17.

The air-cooled steam condenser 11゜16 has a structure in which a large number of fin tubes 12 are arranged, and is automatically controlled by a boiler pressure control valve 9゜15 installed on the inlet side so that the pressure from the valve to the boiler side is always kept constant. has been done.

The steam that has entered the fin tube 12 is cooled by air blowing from the fan 13, becomes condensed water, and is drained from the outlet 14.

In steam and condensate systems operated in such a cycle, the fin tubes 12 near the bottom or second stage from the bottom of the air-cooled steam condensers 11 and 16 corrode, and after 3 to 4 years of use, Corrosion leakage accidents are often experienced.

In general, there are two types of corrosion on condensate lines: smooth corrosion and pitting corrosion.The former is corrosion caused by carbon dioxide gas (C02), and the latter is corrosion caused by dissolved oxygen (O2). This is due to corrosion.

Most of the corrosion that has been experienced to date is pitting corrosion, and the corrosion accidents occurred in the air-cooled low-pressure steam condenser 11 and not in the air-cooled high-pressure steam condenser 1.
6 is that the frequency is low.

In view of these facts, the present invention has succeeded in preventing this problem based on the following principle.

In other words, in order to prevent corrosion caused by carbon dioxide gas ((A)), volatile neutralized amines are dosed into the condensate, which is gasified together with steam in the boiler 7, dissolved in the condensate in the condensate line, and released into carbon dioxide. Corrosion caused by carbon dioxide (CO2) can be prevented by adjusting the dosage of amine to maintain the hydrogen ion concentration of condensate at pH 9 at the outlet 14 of the air-cooled steam condenser 11゜16. I can do it.

Moreover, such water quality management has been carried out to this day.

Therefore, the fact that the corrosion is not a smooth corrosion but pitting corrosion proves that it is not caused by carbon dioxide gas (CO2).

In order to prevent corrosion due to dissolved oxygen (0□), it can be removed in a deaerator 5 and further deoxidized with hydrazine.

Therefore, in the water quality test to determine whether deoxidation has been achieved, if a trace amount of hydrazine is detected in the canned water of the drum of boiler 7, it is proven that there is no dissolved oxygen (02) in the boiler drum.

By the way, hydrazine will combine and decompose if there is dissolved oxygen (02) in the condensate, but the residual hydrazine will not become a gas even if the condensate becomes a vapor.

Therefore, hydrazine is not present in the steam generated in the boiler drum.

These facts can be proven from the fact that even if the hydrazine concentration in the boiler can water was increased, the hydrazine concentration in the condensate water was not detected when tested at the outlet 14 of the air-cooled steam condenser ILI6.

Therefore, the inside of the air-cooled steam condenser IL16 becomes negative pressure, and oxygen (02) is released from the valve seal and flange.
If hydrazine is mixed in, pitting corrosion will naturally occur because there is no hydrazine in the condensate.

In the air-cooled low-pressure steam condenser 11, it is possible to control the pressure above atmospheric pressure by equipping the condenser outlet piping 14A with some kind of resistor (such as a pressure control valve) to prevent negative pressure. There is no control over it.

Furthermore, since the turbine efficiency will be higher if the pressure at the outlet of the power generation turbine 10 is lowered to around atmospheric pressure, it is not preferable to equip the outlet pipe 14A of the air-cooled low pressure steam condenser 11 with a resistor.

Therefore, when the air-cooled high-pressure steam condenser 11 becomes negative pressure, the outlet pipe 14A is generally inserted up to the water pressure of the condensate tank 3 in order to prevent a large amount of air from entering the condensate outlet pipe 14A. The water surface is sealed.

On the other hand, air-cooled high-pressure steam condenser 1 that condenses surplus steam
6 is equipped with a drain trap 17.

This drain trap 1T allows condensate to flow, so 2 to 3 kg/cry! is inside the capacitor! Therefore, there is always positive pressure inside the capacitor.

Therefore, contamination with oxygen (0□) is rare, and pitting corrosion accidents are also less common than in the air-cooled low-pressure steam condenser 11.

In view of the above facts, the present invention has succeeded in preventing pitting corrosion based on the following principle.

In other words, as a result of analyzing condensate during long-term operation,
The condensate at the outlets of the steam condensers 11 and 16 had a pH of 9 or higher and no hydrazine was detected.

Almost no total iron ions are detected in the air-cooled high-pressure steam condenser 16, but in the air-cooled low-pressure steam condenser 11
In this case, around 0.10 ppIn was detected, which means that the corrosion of the tube is progressing little by little.

Moreover, the inlet steam pressure of the air-cooled low-pressure steam condenser 11 is 0.
．． Operating in a small pressure range of 1 to 0.3 ky/d involves heat exchange between steam and air, and the rate of heat transfer is slow, so there is a high possibility that the pressure will become negative.

Even if oxygen (0□) mixes into the steam under negative pressure, corrosion occurs because hydrazine, which combines and decomposes oxygen (02), is not present in the steam.

Therefore, it is necessary to prevent corrosion by spraying and mixing a liquid chemical into the steam at the inlet of the steam condenser 1Li6 and storing an inhibitor in the steam condensate.

Therefore, in the present invention, the chemical solution in the hydrazine solution tank 19 and the amine solution tank 20 is transferred to the chemical solution pump 21 in the piping for pumping the condensate from which dissolved oxygen (02) has been removed in the deaerator 5 using the condensate injection pump 18. A mechanism is provided for mixing the steam and the chemical with a chemical injection nozzle 24 inside the steam condenser inlet steam mixing pipe 23 through the supply pipe 22 to the steam condensers 11 and 16.

In the case of the air-cooled high-pressure steam condenser 16, by equipping it with the structure described above, it is useful for preventing corrosion when condensing excess air heated at high pressure, but also for reducing the temperature and pressure of the heated steam. This increases the margin ratio in the heat transfer area of the capacitor 16.

As a result of operation with this structure installed, almost no iron ions were detected in the condensate of the outlet condensate pipes of the air-cooled steam condensers 11 and 16, proving that the progress of corrosion had stopped. .

Furthermore, hydrazine was detected in all condensate lines, and oxygen (0
□) Since the condensate is circulated without
We successfully tried to prevent pitching corrosion on a 6-person LiLi machine using an actual machine.

Therefore, it prevents corrosion of air-cooled steam condensers used in dust incineration plants, etc., which occurs due to the difficulty of fine pressure adjustment, and also has the effect of reducing temperature and pressure in high-pressure steam condensers, making them easier to operate. However, it is advantageous in terms of economy and the practical effects are extremely large.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a cycle diagram;
Figure 2 is an enlarged view of the main parts. 3... Condensate tank, 5... Deaerator, 7
...boiler, 11 ... air-cooled low-pressure steam condenser, 12 ... fin tube, 16.
...Air-cooled high-pressure steam condenser, 18...
・Condensate injection pump, 19...Hydrazine solution tank, 20...Amine solution tank, 21.
... Chemical pump, 22 ... Supply pipe, 23
...Steam condenser inlet steam mixing pipe, 24...
...Medical liquid injection nozzle.

Claims (1)

[Claims] 1. When cooling and condensing steam using an air-cooled steam condenser, a chemical solution prepared by diluting a condensate-based corrosion inhibitor and deoxidizing agent with warm water is mixed by spraying into the steam in the steam inlet piping of the air-cooled steam condenser. A method for preventing corrosion of an air-cooled steam condenser.