JPS5836676B2 - High temperature corrosion inhibitor for heat transfer surfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a corrosion inhibitor for preventing high-temperature corrosion damage to equipment used at high temperatures, such as boilers.

In boiler furnaces that burn heavy (crude) oil and residual oil from petroleum plants, deposits mainly consisting of these fuel ash accumulate, and in high-temperature pipes (high-temperature superheaters, high-temperature reheaters), there is a significant amount of deposits. Corrosion and thinning may occur (high temperature corrosion).

Generally, fuel ash containing sodium, sulfur, and vanadium as main components adheres to high-temperature pipes, but its melting point is 700%.
Most of the tube surface temperature is ~900℃ (550~6000℃).
In C), it has solidified.

There are various possible causes of the above-mentioned high-temperature corrosion, but the one with the greatest influence is Na2S.
This is the production of a low melting point compound by the O4-Na・■・0 system compound.

As shown in Table 1, these Na-v-O compounds have low melting points to begin with, and they tend to form a eutectic composition with Na2SO4, further lowering the melting point.

(Ash with a low melting point of around 500°C has been confirmed in fuel ash in actual cans.)

The in-furnace deposits, which are mainly composed of fuel ash, contain large amounts of highly corrosive Na・■・O and Na2SO4-Na-v-O compounds, which are in a solid state and cannot be deposited on heat exchanger tubes. When they are adhered, there is solid-to-solid contact (adhesives and heat transfer tubes), so no corrosion reaction occurs.

However, when the deposit becomes molten, it becomes a liquid-solid relationship, and a rapid corrosion reaction occurs.

C as a method of preventing high temperature corrosion caused by these low melting point compounds.
a, Mg compounds are added, and these are heated to 2000 ml in the boiler.
CaO, M.C. having a high melting point of ℃ or higher. It is known to increase the melting point of fuel ash by reacting with deposits in a molten state to increase the melting point of the fuel ash, thereby suppressing corrosive effects.

M. 19.Ca compounds are added to fuel or directly into the furnace, but according to experience with conventional use in actual cans, it takes a long time, from six months to a year, for the effects of these additives to become apparent. ing.

Furthermore, if the amount of these additives is increased at an early stage in order to enhance their effectiveness, not only will the economic burden increase, but also the amount of adhesion to the amount of heat transfer will become excessive, resulting in a decrease in heat absorption and a decrease in the efficiency of the boiler. Adverse effects are recognized.

In addition, if a large amount of additive is injected, NOx in the exhaust gas will increase, which is not desirable from the viewpoint of exhaust gas pollution.

The present inventors have proposed a method for preventing high-temperature corrosion damage caused by fuel ash. 9. Research has been carried out to improve the delayed effect when adding compounds such as Ca, but after cleaning the surface of the heat exchanger tube by washing with water, etc.
Ca,M. 9. When an emulsion in which compounds such as Si are finely dispersed and suspended is applied to the surface of the target heat transfer steel pipe, it was discovered that it exerts high-temperature corrosion prevention effects for a long period of time, starting shortly after the start of operation. This invention has been achieved.

The Ca, Mg, and Si compounds used in the present invention include C
Ca(OH)2, Mg(OH), etc., which do not generate toxic gas in the fuel atmosphere and eventually become the oxides, including a O t MgO, S t 02, etc.
)2, CaCO3, MgCO3, etc. are used,
As water-soluble resins, acrylic ester (co)polymers,
Polyvinyl acetate, polystyrene, styrene-butadiene copolymer, etc. are used.

In making an emulsion, these substances are finely dispersed and suspended using water as a solvent.
It is preferable to use a surfactant that does not leave behind toxic gases such as SO2 or HC7 or corrosive residues upon pyrolysis.

These surfactants include nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene fatty acid ester, cationic surfactants such as trimethylaminoethyl alkylamide halogenide, and amphoteric surfactants such as alkyl betaine. can be given.

Anionic surfactants are not preferred because most of them are sulfates.

Application of these emulsions to the tube surface is done by spraying.
It can be applied by brushing or any other method, and it can be applied not only to heat transfer surfaces after cleaning, but also to areas where fuel ash has already adhered, to reduce its corrosive properties. Can be suppressed.

The method of the present invention provides the following effects.

(1) Compounds such as Ca, Mg, and Si applied to the surface of the steel pipe react with flying fuel ash after the boiler is restarted to form high-melting point compounds and suppress the occurrence of high-temperature corrosion.

(2) The processing agent can be freely diluted with water,
Therefore, there is no danger of fire, and after drying, it forms a water-impermeable and elastic film on the treated surface.

(3) Since the processing agent contains resin components, Ca, Mg,
Unlike simply dissolving or dispersing compounds such as Si in water, it is possible to form a thick film on the tube surface (the amount of Ca, Mg, and Si per unit area increases), and There is also less chance of it falling off due to thermal shock during startup.

(4) During construction, since the treatment agent is in liquid form, it can freely penetrate into complex structures that cannot be reached by human power, and exhibit its anticorrosion effect.

(5) Since the resin component in the treatment agent is composed of an organic compound consisting of elements such as carbon, hydrogen, and oxygen, it will burn after the boiler is restarted (emitting CO, CO2, H20, etc.), and will not only damage the treated steel pipes. , there will be no adverse effect on the inside of the furnace.

The method of the present invention can be applied to boilers, heating furnaces, garbage incinerators, gas turbines, etc.

This is a suspended type high-temperature recycler, which belongs to the high-temperature pipes on the heat transfer surface of the boiler, and where a large amount of highly corrosive fuel ash tends to adhere. The method of the present invention was applied to a heating device.

Note that, prior to this treatment, fuel ash had been almost completely removed from the reheater by washing with water.

A treatment agent having the following composition was prepared and evenly applied to the high-temperature reheater after washing with water using a sprayer used for spraying agricultural chemicals.

A white film is formed almost uniformly on the surface of the reheater coated with this treatment agent, and after being left for about 12 hours, this film dries completely and does not come off even if it comes into contact with foreign matter during subsequent work inside the furnace. There was no.

Approximately six months after the boiler was restarted, fuel ash adhering to the high-temperature reheater was collected during a weekend shutdown and its properties were investigated.

The results are shown in Table 2 in comparison with the properties of the fuel ash that had adhered before this treatment.

As is clear from Table 2, the proportion of Mg in the high-temperature reheater deposit after treatment was higher than before treatment, and it was confirmed that the melting point was also increased by about 100°C.

Also, based on the results of outer diameter and wall thickness measurements conducted at the same time, the
The amount of corrosion (amount of thinning) for 1 month is 0. 1 mm or less, and when compared with the corrosion amount before treatment, which was 0.4 to 0.5 mm/year, it is considered that this treatment was sufficiently effective in preventing high-temperature corrosion.

It should be noted that no particular change was observed in the gas temperature or NOx value after this treatment compared to before treatment, and therefore it is judged that this treatment has no effect on the inside of the furnace.

In addition, when CaO, SiO, etc. are used in place of the MgO mentioned above, the following increase in melting point has been confirmed, so it is thought that it can be put to practical use, and even if these are added at the same time, the effect will not disappear. Multiple additions are also possible.

Addition of Cab (15%) 120°C Melting point increase S102 (15%) addition 900C
〃MgO (5%) + CaO (5%) 105°C
〃+S i02 (5%)

Claims (1)

[Claims] I Prevention of high-temperature corrosion on heat transfer surfaces of equipment used at high temperatures, consisting of an emulsion in which at least one compound selected from the group consisting of Mg, Ca, and Si and a water-soluble synthetic resin are dispersed and suspended in water. agent.