JPS6046321B2 - How to clean combustion gas contact surfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning deposits on surfaces that come into contact with combustion gas, such as boiler heat transfer surfaces.

In various parts of boiler furnaces that burn residual oil such as heavy oil, crude oil, and petroleum plat, deposits mainly composed of fuel ash (hereinafter simply referred to as deposits) accumulate, causing various problems as shown below. known to induce

(1) A large amount adheres to the outer surface of the heat transfer surface in the boiler furnace, inhibiting heat transfer.

(2) As a result, the exhaust gas temperature increases, which adversely affects equipment in the gas flow path.

(3) Deposits are generally highly corrosive to metals.

Table 1 Heavy oil-fired boiler sampling location Analysis item Combustion chamber '・1 ★Prison + So Oboro ”゛ Corrodes heat transfer tubes.

In other words, if the fuel contains sulfur S, it will be oxidized during fuel combustion, and some of it will turn into sulfuric acid as shown in the reaction equation below, which indicates the acidity contained in the fuel ash. Become. Furthermore, since sulfuric acid tends to condense in low temperature areas, fuel ash in low temperature areas is more acidic. S +02→502 502+11202→502 502+H2O-4, H2SO4 (4) When the amount of deposits increases, it narrows the exhaust gas flow path, making combustion itself difficult and hindering the normal operation of the boiler. As shown in Table 1, even if the same fuel is used, the chemical composition and physical properties such as hardness and adhesion to the heat transfer tube differ depending on the location where it is deposited.In general, vanadium However, at low temperatures, there is less vanadium, and the hydrogen ion concentration (hereinafter referred to as pH) of its water-soluble components tends to be low.

Example of chemical analysis of internal deposits In order to deal with the above-mentioned problems, deposits on the high-temperature pipes are removed using hammers, sandblasting, etc. when the tank is stopped, but this requires a lot of manpower and also causes noise and dust. Not only does this significantly worsen the working environment, but the latter method also has the drawback of remaining problems when removing used sand as waste, and even with this method, complete removal of deposits is not possible. It is possible.

In addition, on low-temperature pipes (e.g., energy savers), deposits are soft, but the heat transfer area is large, and the range that human power can reach is limited due to the structure, so it is difficult to remove them using methods similar to those on high-temperature pipes. I can't. As is clear from Table 1, which shows an example of chemical analysis of fuel ash adhering to a boiler, fuel ash contains a wide variety of elements (compounds), but there are many water-soluble components. , it is thought that it can be dissolved in this and removed from the heat transfer surface.

However, if water is simply applied with a rubber hose, etc., the inside of the boiler furnace becomes flooded with water, which is difficult to drain, and as is clear from Table 1, the water eluted with deposits becomes acidic. Therefore, there is a risk of corroding the boiler structural materials where it is locally concentrated. This tendency is particularly strong in low-temperature pipes where the water washing effect is considered to be large. In addition, if the heat exchanger tube is not completely washed with water and is only exposed to water splashes, the concentration of sulfuric acid will further increase, making it even more corrosive. As a result, the heat exchanger tubes will be corroded. For this reason, in actual boilers with complicated pipe structures, although it is known that fuel ash can be removed by washing with water, it is not possible to do so. For this reason, it is possible to use alkaline water as washing water, but this increases costs as well as using alkaline water that is harmful to the human body, and depending on the washing location, corrosion may occur due to insufficient neutralization of the acid. Yes, it is not a complete solution.

An object of the present invention is to efficiently and quickly remove the fuel ash deposits without causing any harm to heat exchanger tubes or other equipment.

As a result of investigating the properties of the deposits, as shown in Table 1 above, it was found that there were relatively many water-soluble components, so by devising the washing water, it was possible to remove them while preventing acid corrosion. We focused on

That is, the present invention is a method for cleaning a surface that comes in contact with combustion gas, and is characterized in that the portions other than the surface that do not require cleaning are covered with a water-impermeable sheet, and the surface is washed with cleaning water containing an acid corrosion inhibitor. The gist of this paper is a method for cleaning combustion gas contact surfaces. Although the present invention has the above-mentioned technical configuration, since the parts that do not require cleaning other than the wash area are covered with a water-impermeable sheet, there is no possibility that water splashes will fall on those parts. However, even if there is a slight amount of corrosion, as will be described later, corrosion in that area will hardly progress due to the action of the acid corrosion inhibitor added to the cleaning water. Next, the effect of the acid corrosion inhibitor added to the cleaning water will be explained. By adding a small amount of acid corrosion inhibitor to the cleaning water, even if sulfuric acid is present in the cleaning water used to clean the surface to be treated, the effect of the acid corrosion inhibitor will allow the surface to be treated to be washed away. Since corrosion of metal surfaces is suppressed, the acceleration of corrosion can be completely stopped. Any commercially available acid corrosion inhibitor can be used.

The main component of the acid corrosion inhibitor is an organic amine compound,
n-butylamine, N,N-dimethylbutylamine, n
-hexylamine, N,N-dimethylhexylamine,
n-octylamine, N,N-dimethyloctylamine, n-dodecylamine, N,N-dimethyldodecylamine, n-hexadecylamine, N,N-dimethylhexadecylamine, cyclohexylamine, N-cyclohexyldimethylamine, Hydrofuronic acid amide, N,N-dimethylcaproic acid amine, etc., and derivatives thereof are known, and any of them including these can be used in the present invention. Further, although the corrosion inhibiting effect is recognized even when the amount of the acid corrosion inhibitor added to the washing water is 0.005%, the effect is generally further increased when it is added at 0.01%.

However, even if 0.1% is added, the amount of corrosion will decrease.
The effect does not increase compared to the case where the amount added is less than that, and the corrosion tends to be saturated, so it is economically meaningless to add more than that amount. The amount of acid corrosion inhibitor added from the viewpoint of corrosion inhibition is as shown above. However, in the washing water after cleaning, insoluble components (for example, unburned carbon) in the fuel ash, the acid corrosion inhibitor This unburned carbon still remains on the surface cleaned with cleaning water containing 0.01% of carbon.
Some roughness may be observed on the surface, but if the amount of acid corrosion inhibitor added is 0.02%, this roughness phenomenon is hardly observed, so it is not practical to inhibit acid corrosion. It is recommended that the amount of the agent added be set at 0.02% or more and 0.1% or less. The present invention further recommends adding an acid corrosion inhibitor to the wash water as well as a penetrant.

Penetrants themselves do not have a corrosion-inhibiting effect, but they do have the effect of lowering the surface tension of the cleaning water, allowing the cleaning water to penetrate well into the adhering fuel ash and promoting the peeling and falling off of the fuel ash from the boiler pipe surface. It is. Hereinafter, the present invention will be further described in detail with reference to one embodiment of the present invention. This example belongs to the low-temperature section of the boiler heat transfer device, and has a larger heat transfer area than other tubes.
This is an example of washing a fuel economizer with water, which tends to inhibit heat transfer due to deposits and has a large amount of highly corrosive fuel ash deposited on it.

Prior to this washing, a simple investigation was conducted on the deposits on this economizer, and the results are summarized in Table 2. Table 2 Survey results of economizer pipe deposits Adhesion status Upper layer black, middle layer grayish white to light edge color, lower layer light brown, 2 to 3T0n thick layer Scale adhesion amount (g/d)
1000-7000pH (1g/100Tn1H20)
2.0-3.0 Solubility (%) (Water Solubility)
11℃ approx. 45% 49℃ approx. 7
0% In the attached drawings, A is the combustion chamber, B is the combustion gas flow path, and C is the combustion chamber.
Showing the side wall.

As shown in the figure, an impermeable sheet is used to prevent wastewater from flowing into the front, left and right side walls of the economizer 1 for washing with water, the lower end of the superheater tube 2 above the economizer 1, and further into the duct section 3. 4 (a vinyl sheet was used in this example).

(In other words, a large impermeable bag covers the economizer 1 from the front and back.) This sheet 4 covers the hanging fittings and other accessories of the economizer 1, as well as the economizer 1. There were some imperfections due to the water supply 7 and drain pipe 8 introduced into the furnace from the upper and lower manholes 5 and 6 of the vessel 1, but the gaps were sealed with adhesive tape or the like. The washing nozzle 9 is movable and is installed above or below the economizer 1 depending on the washing situation, and is adapted to spray washing water onto the economizer 1. This nozzle 9 is connected to a flow meter 10, a valve 11, and a water supply pump 1 by means of a flexible water supply pipe 7.
It is connected to the water supply line 13 with 2 in between.

A drain pipe 8 for flushing water is installed at the bottom of the seat below the economizer 1, and the water is drained out of the furnace through a drain hole 14 and a lower manhole 6 by a drain pump 15.

A flow meter 16 and a pH meter 1 are installed at the outlet of the drainage pump 15.
7 is installed and is designed to operate in conjunction with the water supply pump 12 and chemical injection pump 18. The washing process begins with the nozzle 9 installed on the top of the economizer 1 moving and spraying washing water as shown in Table 3.

At this time, the washing water is heated if necessary. (Table 2
(As shown in Figure 2, the solubility increases significantly as the temperature rises.) The washing water flows down from the top of the economizer 1 while dissolving and peeling off deposits.

At this time, each wall and the superheater 2 on the upper part of the economizer 1 are covered with sheets to prevent washing water from seeping into areas other than the washing section (the economizer 1). Furthermore, since an appropriate amount of acid corrosion inhibitor is added to the washing water, corrosion in seepage and other stagnant areas is suppressed.

(The effects of adding acid corrosion inhibitors are summarized in Table 4.) Since the quantitative effect cannot be confirmed by washing an actual boiler with water, the results in Table 4 were confirmed by the experiment described in the notes. be.

Table 4 also shows the effects not only on energy savers, but also on superheaters and reheaters. (1) In the experiment, the fuel ash adhering to each tube was dissolved in the washing water listed in Table 3 and ordinary industrial water.
35 carbon steel pipe) was immersed, and its corrosion loss ratio (using the washing water listed in Table 3 was set as 1) was determined.

(2) 50g of fuel ash dissolved in each wash water 1'
It is.

(3) The conditions under which the washing water was immersed were 40°C x 2411°C.

(4) The surface area of the test piece steel pipe is 17.2d. Washing water collected at the bottom of the seat is drained from drain pipe 8 and drain pump 1.
However, the flow rate and pH value are measured at the outlet of the drain pump 15, and the water is discharged to the outside of the furnace by the water supply pump 12.
and the chemical injection pump 18,
The amount of water used for washing and the amount of medicine dispensed can be increased or decreased depending on the washing situation. Also, as the water washing progresses, the nozzle 9 installed at the bottom of the economizer 1
As a result, the lower surface of the economizer 1 is cleaned in the same way as the upper surface.

Using the method described above, when the boiler is operated after washing the heat transfer surface of the economizer 1 with water, the temperature of the exhaust gas at the outlet of the economizer 1 decreases by approximately 70°C compared to before washing with water, and the temperature of the exhaust gas at the exit of the economizer 1 decreases by approximately 70℃ compared to before washing. It was found that the fuel ash was completely removed, and that heat recovery was sufficient.

In addition, there was little washing water seeping into each side wall, and there was little moisture in the superheater 2 above the energy saver 1, which is probably due to the effect of covering it with the vinyl sheet.

Furthermore, although there was some leakage of washing water from the seams of the sheet, as shown in Table 4, no particularly significant corrosion damage was observed due to the effect of the addition of the acid corrosion inhibitor. In this way, cover the heat exchanger tubes other than those for washing with water with a vinyl sheet,
We believe that the rinsing method using rinsing water containing additives such as acid corrosion inhibitors had a significant effect, along with the safety of the spray nozzle operation.

Next, Table 5 shows the concentration effect of the acid corrosion inhibitor added to the water saver flushing water.

This test was conducted under the same conditions as in Table 4. or,
Table 6 shows the effect of the acid corrosion inhibitor added with the penetrant.

This test was also conducted under the same conditions as in Table 4. In addition,
An example of washing the high-temperature superheater, which is a high-temperature section pipe, was also performed using the same method as the energy saver, which produced excellent results.

The boiler economizer has been described in detail as an embodiment of the present invention, but the places through which combustion gas passes, such as the air preheater, electric precipitator, flue, and chimney, are similar to the economizer. It will be readily understood that since acidic fuel ash is deposited on these areas, it is also possible to wash these areas with water in a manner similar to the embodiments described above. For the same reason, it will be obvious that the present invention can also be applied to similar locations such as gas turbines, heavy oil heating furnaces, etc., which have combustion gas passages for fuel containing sulfur. The features and effects of the present invention are listed below.

(1) For heat transfer devices intended for washing with water! , remove deposits by spraying with washing water.

(2) Cover the front, left and right side walls and upper and lower water-impermeable surfaces of heat transfer tubes that are intended for washing with water to prevent washing water from seeping into the side walls, etc., with sheets (for example, vinyl sheets).

Note that the washing water is drained from the bottom of the sheet. (3
) If the washing water seeps into the side walls, etc., or if it is difficult to wash thoroughly due to structural constraints, corrosion of the structural materials will occur due to acid eluted in the water. Since additives are added, corrosion damage caused by acidic solutions can be prevented.

(A large amount of sulfuric acid exists in the washing water, but the acid corrosion inhibitor suppresses its corrosive action and eliminates acid corrosion damage.) (4) Washing water is present even in places where washing is insufficient. Where acid corrosion is applied, the corrosion effect can be suppressed since the acid corrosion inhibitor is always present.

(5) It is believed that by performing water washing, deposits can be removed from locations that could not be removed by conventional physical peeling methods due to the action of water and the penetrant added therein. We can expect a significant increase in the removal effect and reduction in artificial labor.

[Brief explanation of the drawing]

The accompanying drawings illustrate one embodiment of the invention.

Claims (1)

[Claims] 1. A method for cleaning a surface that comes in contact with combustion gas, characterized in that the surface that does not require cleaning other than the surface is covered with a water-impermeable sheet, and the surface is washed with cleaning water containing an acid corrosion inhibitor. How to clean gas contact surfaces.