CN103526210A - Method of corrosion prevention for resting boiler - Google Patents

Abstract

The present invention provides a boiler corrosion prevention method based on water-filled storage technology, which can be applied to boilers whose structure is so complex that the dry storage method cannot be implemented due to the inability to completely drain water, ensuring a high degree of safety for human beings, and re- There is no need to blow dry the whole thing or wash it thoroughly with pure water when starting to operate. Stop the running boiler supplied with dehardened water, then fill the boiler drum with stored water and store it so that the ammonia concentration in the boiler drum reaches 10 mg/L to 500 mg/L, wherein the stored water passes to It is obtained by adding ammonia to dehardened water. When the ammonia concentration or pH of the stored water in the boiler drum is detected to decrease, or the concentration of iron ions increases, a part of the stored water in the boiler drum is discharged and supplied to the boiler. Stored water to which ammonia has been added such that the ammonia concentration in the stored water in the boiler drum becomes 10 mg/L or more and 500 mg/L or less.

Description

Methods of Preventing Corrosion of Idle Boilers

This case is a divisional application with an application date of November 10, 2006 , an application number of 200680043064.3 , and an invention title of " Method for Preventing Idle Boiler Corrosion"

technical field

The present invention relates to a method for preventing corrosion of a boiler during shutdown, and more particularly, to a method for preventing corrosion of a boiler filled with water including chemical substances and preserved.

Background technique

When the boiler equipment is shut down, the temperature of boiler water drops, and the pressure becomes a negative pressure lower than atmospheric pressure to absorb external air including oxygen, thereby causing corrosion to occur. Therefore, in the event of a relatively long shutdown of the boiler (for example, more than a week), there is a need to prevent corrosion of the boiler during shutdown.

Traditionally, a method in which boiler water is completely blown dry and a desiccant such as silica gel placed inside the boiler drum (boilerdrum) is used to dry the boiler drum, and a dry storage method in which the boiler drum is sealed with nitrogen gas has been used as Methods of preventing corrosion of boiler equipment during shutdown (Japanese Industrial Standard JISB8223 established in 1999).

However, in the case where the boiler water cannot be emptied or the boiler water cannot be completely blown dry due to the complex structure of the boiler itself, it is difficult to adopt the above-mentioned dry storage method, so the wet storage method (in 1999) is used instead JIS B8223 established in 2010).

In this method, water obtained by adding hydrazine in an addition amount of 100-1000 mg/L or sodium nitrite in an addition amount of 200-500 mg/L to pure water and soft water is used as storage water (storage water) , and the boiler drum is filled with the stored water for storage.

In recent years, as an alternative to the above-mentioned wet storage methods, it has been proposed to add amines with neutralizing properties such as monoethanolamine, monoisopropanolamine, cyclohexylamine, 2- The method of amino-2-methyl-1-propanol or morpholine (Japanese Published Patent Application No. 2002-129368).

However, these conventional methods have problems as follows.

That is, according to the dry storage method, when the downtime exceeds a long period of time, the desiccant must be replaced periodically, which is troublesome.

Because hydrazine is suspected of being carcinogenic, its use can be avoided. In addition, since sodium nitrite is a solid compound, in boilers including superheaters or turbines, sodium nitrite can only be used if it can be backwashed with pure water after storage.

Although the problems as mentioned above have been solved by the wet storage method using stored water including amines having neutralizing properties, the following problems still exist in, for example, boilers operating with high-pressure or high-temperature superheaters . That is, when amines with neutralizing properties are mixed with working water (water present in the boiler drum and heated to generate steam during boiler operation), thermal decomposition of the amines produces organic acids or carbon dioxide, reducing feed water, condensate Or the pH of the boiler water, or increasing the acid conductivity of the feed water or steam, I am afraid that problems will occur in the operation of the boiler, although it depends on the recovery rate of the condensate. As a result, there arises a problem that all stored water must be blown dry, and, in the case of a space where water cannot be drained, it is necessary to sufficiently clean the inside of the drum with pure water at the time of rerunning. Also, although some kinds of amines with neutralizing properties are approved as boiler additives according to the standards of the U.S. Food and Drug Administration (FDA), they are not approved as food additives in Japan. Consequently, users are often reluctant to use these amines due to safety concerns in situations where boiler-generated steam comes into direct contact with humans or food.

Contents of the invention

problem to be solved

The object of the present invention is to provide a method for preventing corrosion of idle boilers, which can be applied to any boiler, by means of which a high degree of safety for humans and a high degree of corrosion protection over a long period of time can be obtained.

way to solve the problem

The present invention provides the following methods for preventing corrosion in idle boilers:

(1) A method for preventing corrosion of idle boilers, the method comprising:

shutting down the operating boiler, supplying said boiler with dehardness water; and then,

The drum of the boiler is filled with storage water obtained by adding ammonia to dehardened water and stored.

(2) The method for preventing corrosion of an idle boiler according to (1), wherein the dehardened water is pure water,

Water obtained by adding ammonia to boiler water in which the boiler water remains is supplied to the inside of the boiler drum as the stored water.

(3) The method for preventing corrosion of an idle boiler according to (1), wherein

draining boiler water from the interior of said boiler drum; and then,

Water obtained by adding ammonia to dehardened water was supplied to the inside of the boiler drum as the stored water.

(4) The method for preventing corrosion of an idle boiler according to any one of (1) to (3), wherein the boiler is made of steel.

(5) The method for preventing corrosion of an idle boiler according to (4), wherein the boiler has a superheater and operates with a recovery rate of 50% or more.

Invention effect

As described above, according to the present invention, since corrosion of the boiler during shutdown can be easily prevented by the method in which the boiler is filled with ammonia solution, the anticorrosion method of the present invention can be applied to any type of boiler. For example, the present invention can prevent corrosion of boilers that cannot be stored dry or that cannot be stored wet-filled (using solid anti-corrosion substances such as sodium nitrite). Moreover, even when the boiler is shut down and stored for a long time, when the boiler anticorrosion method of the present invention is applied, a high anticorrosion effect can be maintained.

In addition, because ammonia does not contain carbon, even if the storage water is not completely blown dry, or the boiler drum is not sufficiently washed after storage, it can still avoid the pH drop of the feed water, condensate or boiler water, because after restarting the boiler operation Afterwards, organic acids and carbon dioxide etc. are produced as pyrolysis products. Therefore, it is possible to avoid the obstruction of the operation of the boiler due to the increase of the acid transferability of the feed water or steam. According to the present invention, it is possible to use smaller amounts of additives for the preparation of storage water than with methods using amines with neutralizing properties, resulting in a beneficial drum storage effect.

Moreover, the ammonia used in the present invention is listed as a direct food substance (DIRECT FOOD SUBSTANCE) according to the US FDA standard, and is also recognized as a food additive with high safety for humans in Japan. Therefore, after the boiler is shut down, even if all the stored water is not dried up after the boiler is operated again, the possibility that the boiler water obtained after restarting the boiler operation will contain substances harmful to humans is very small.

Detailed ways

The dehardened water in the present invention refers to water that has been treated to remove hard components, and soft water and pure water belong to the category of dehardened water. Soft water refers to water that has been subjected to demineralization treatment, and specifically, it is preferable that the concentration of each of the hard components Ca and Mg is 1 mg CaCO ₃ /liter or less. Pure water is water from which impurities have been removed by filtration or demineralization treatment, that is, in which impurities other than hard components, such as ions other than hard components, organic substances, and the like have been removed.

The anticorrosion method of the present invention can be applied to any boiler, more specifically, a drum boiler, a water tube boiler, a through flow boiler, and a circulation boiler, and the like. These boilers can also be low pressure boilers, medium pressure boilers or high pressure boilers. In addition, the corrosion prevention method of the present invention can also be applied to a boiler having a superheater or a turbine that cannot be backwashed.

A pure water boiler or a soft water boiler in which pure water or soft water is supplied for boiler operation is suitable as the boiler used in the present invention.

The anticorrosion method of the present invention is implemented in the following manner in these types of boilers depending on differences in raw water.

First, in the case of a pure water boiler, after the boiler is shut down, the boiler is filled with stored water to which ammonia has been added. Because steam is continuously generated during boiler operation, the surface of the boiler water (working water) inside the boiler drum is close to the normal water level, and the remaining upper space of the boiler drum is composed of steam. Then, the boiler was filled by adding further water (feed water) supplied to the boiler, and at this time, stored water that had been prepared by adding ammonia to the feed water was supplied.

In this way, after the boiler drum is filled with water, by storing it in this state, the boiler is protected from corrosion during shutdown.

Next, in the case of a soft water boiler, after the boiler is shut down, the water inside the boiler drum is blown dry all at once. In the case of adding soft water, the soft water contains various condensed components because the soft water (boiler water) that has been supplied to the boiler drum is condensed during operation of the boiler. Therefore, if the boiler is shut down while boiler water is still in the boiler drum, it may be the cause of boiler corrosion. Therefore, the boiler water is blown dry in one go. Also, although it is preferable that the boiler water is completely blown dry, in the case where the boiler water cannot be completely blown dry, a preferable blow-dry step is one in which as much boiler water as possible is drained and then the remaining boiler water is replaced with supply water.

Even in the case of supplying pure water as described above, it may be necessary to dry the boiler water in the same manner depending on the quality of the boiler water or the conditions of the device. The following example is an example of drying boiler water even when pure water is supplied. In this case, phosphate or alkali metal hydroxide is used as a boiler scale inhibitor, and there is a fear that boiler water may enter into a superheater or the like when the boiler is filled.

Next, soft water or pure water to which ammonia has been added is supplied into the empty boiler until it is full.

In either case, the concentration of ammonia added needs to be adjusted according to water quality or storage time, but should generally be 10-500 mg/L, preferably 20-300 mg/L or more preferably about 30-100 mg/L.

Due to the introduction of ammonia, carbon dioxide or other acidic substances present in the boiler are neutralized, the pH level of the water inside the boiler drum (storage water) increases and the storage water remains alkaline. Therefore, the boiler can be prevented from being corroded for a long time.

The above-mentioned anti-corrosion effect can be achieved by adding ammonia at a concentration of 10 mg/L or higher, and the higher the added concentration is, the stronger the anti-corrosion effect is, but when economical efficiency is considered, the upper limit of the preferred concentration is about 500 mg/L , or when odor is considered, more preferably 300 mg/L.

The pH of the water to which ammonia has been added should be 9.5 or higher, or more preferably 10 or higher. Depending on the set conditions, phosphates or alkali metal hydroxides generally used as boiler scale inhibitors may be used in combination.

Ammonia can be directly added to various feed water as ammonia gas or ammonia water.

Ammonia is listed as a direct food substance (DIRECT FOODSUBSTANCE) according to FDA standards, and ammonia with the above concentration is also recognized as a food additive with high safety for humans in Japan.

Preferably, the boiler used in the present invention is made of steel because there is no need to consider the copper corrosion problem due to the high concentration of ammonia. Also, where copper is used in condensers or low-pressure feed water heaters, all stored water should be blown dry after storage in the drum, and, if there is a space where water cannot be drained, the drum should be fully filled with pure water. Scrubbing, or after the boiler is started, steam should be released until the ammonia concentration drops below a predetermined level, and then the supply of steam should begin. Also, in a boiler with a superheater and a condensate recovery rate of 50% or more, when the drum is stored with amine, the neutralized amine is mixed with working water, organic acid or carbon dioxide is generated by thermal decomposition of the amine, and the feed water The pH of the condensate or boiler water drops, and the acidity of the feed water or steam increases, which may cause boiler operation to fail. However, since these problems are not considered with the present invention, it is suitable to use the present invention.

In this way, routine inspections are preferred when ammonia-filled boilers are stored for extended periods of time. For example, the ammonia concentration, pH, or iron ion concentration of corrosive substances should be checked about once or twice a month. If the ammonia concentration or pH decreases, or the iron ion concentration increases, it is preferable to inject additional ammonia into the boiler. In this case, a part of the stored water is blown dry, and water is supplied while adding ammonia so that the ammonia concentration in the stored water in the boiler drum becomes a predetermined concentration. At this time, when a part of the stored water is extracted from the boiler, it is preferable to heat the stored water in the boiler drum and make it convect in the boiler drum so that the ammonia concentration in the stored water in the boiler drum becomes uniform.

Other known boiler water treatment additives other than ammonia may be added, depending on the need for soft or pure water to fill the boiler.

As a boiler water treatment additive, you can use alone or choose two or more of the following additives and add them: For example, diethylhydroxylamine, isopropylhydroxylamine (isoprohydroxylamine), 1-aminopyrrolidine, 1-amino-4 - Methylpiperazine, carbohydrazide, trisodium phosphate, disodium hydrogen phosphate, sodium tripolyphosphate and sodium hydroxide.

When restarting the operation of the boiler after the shutdown period, all or a portion of the stored water is blown dry as required, and then the boiler is filled with water and the operation is started. At this time, boiler anti-scaling agent or deoxidizer can also be added as needed.

The dried stored water is discharged after treatment so that it meets certain water discharge standards.

Furthermore, preferably no hydrazine or sodium nitrite is used.

Example 1

The present invention will be explained in further detail below using specific examples. However, the present invention is not limited to these examples. In Examples 1-7, the chemical substances shown in Table 1 were added to pure water to make 500ml, the mixture was added to a 500ml resin beaker, and two steel test pieces (1mm×30mm×50mm) were immersed in To this mixture, the upper part of the beaker was sealed with a resin sheet, and the beaker was allowed to stand at room temperature. After the time shown in Table 1 had elapsed, the test pieces were taken out and visually inspected for the presence of rust. The results are shown in Table 1. In this table, MEA means monoethanolamine, MIPA means monoisopropanolamine, and CHA means cyclohexylamine.

Comparative Example 1 was carried out under the same conditions as in Examples, except that the chemical reagents used for the anti-corrosion test were not added. Comparative Examples 2-12 were carried out under the same conditions as in Examples, except that a known amine having neutralizing properties was used instead of ammonia.

(Table 1)

From the results shown in Table 1, in Examples 1 to 7 using the ammonia of the present invention, it was found that the same or better anti-corrosion properties could be obtained with a smaller amount of additives compared to the amines with neutralizing properties of the comparative examples. corrosion effect.

The operation method of the idle boiler proposed by the present invention can be applied to any boiler, such as a cylindrical boiler, a water tube boiler, a tubular boiler and a circulation boiler. In addition, because the chemical agent used is ammonia, which is approved as a food additive, it can be applied even when the steam comes into direct contact with the human body or food.

Claims (6)

1. for preventing a method for idle boiler corrosion, described method comprises:

The boiler that is supplied with the running of hard-off degree water is shut down; then, will in the drum barrel of described boiler, fill to store water and store, the ammonia concentration in described boiler drum is reached below above 500 mg/litre of 10 mg/litre; wherein said storage water by adding ammonia to obtain in hard-off degree water

In the situation that detect ammonia concentration or pH reduction or the iron concentration increase of the described storage water in described boiler drum,

A part for described storage water in described boiler drum is discharged, in described boiler, supply with the storage water that has added ammonia, the ammonia concentration in the described storage water in described boiler drum is become below above 500 mg/litre of 10 mg/litre.

2. for preventing a method for idle boiler corrosion, described method comprises:

The boiler that is supplied with the running of hard-off degree water is shut down; then, will in the drum barrel of described boiler, fill to store water and store, the ammonia concentration in described boiler drum is reached below above 500 mg/litre of 10 mg/litre; wherein said storage water by adding ammonia to obtain in hard-off degree water

In the situation that detect ammonia concentration or pH reduction or the iron concentration increase of the described storage water in described boiler drum,

A part for described storage water in described boiler drum is discharged, heat the described storage water in described boiler drum and make this storage water convection current in described boiler drum, make the ammonia concentration in the described storage water in described boiler drum become even, and, in described boiler, supply with the storage water that has added ammonia, the ammonia concentration in the described storage water in described boiler drum is become below above 500 mg/litre of 10 mg/litre.

It is 3. according to claim 1 and 2 that for preventing the method for idle boiler corrosion, wherein said hard-off degree water is pure water,

To add the described hard-off degree water of ammonia to append in the feedwater being supplied in described boiler drum as described storage water.

4. according to claim 1 and 2 for preventing the method for idle boiler corrosion, wherein

From the inside of described boiler drum, discharge feedwater, the inside that then water by adding ammonia to obtain is supplied to described boiler drum in hard-off degree water is as described storage water.

5. according to claim 1 and 2 for preventing the method for idle boiler corrosion, wherein said boiler is formed from steel.

6. according to claim 5 for preventing the method for idle boiler corrosion, wherein said boiler has superheater, and the rate of recovery of running is more than 50%.