JP6931215B2 - Detergent for dissolving and removing iron rust and oxidation scale - Google Patents

Description

The present invention relates to a method of dissolving and removing steam oxidation scale grown inside a main steam pipe system of a thermal power plant or the like and a reheated steam pipe system or the like with a chemical cleaning liquid, and particularly to a method of dissolving and removing at around room temperature.

Figure 1 shows the system diagram of the water side and steam side of the thermal power plant. 8. The steam returned from the turbine is 1. It is cooled by a condenser and condensed to supply water. Water supply is 1. 2. From the condenser through a condenser pump and a condenser pump (not shown). It is transported to a low-pressure feed water heater and heated. After that, 3. Oxygen is removed by the deaerator. Next, through a high-pressure water pump (not shown) 4. High-pressure feed water heater, 5. 6. The temperature is raised by heating with an economizer. It is carried to a boiler and heated to generate steam. Steam is 7. Further heated by a superheater 14. 10. Connected by the main steam pipe. MSV (main steam stop valve) and 11. Pass through CV (control valve), 8. It is supplied to the turbine (high pressure). 8. The steam that worked in the turbine (high pressure) is 15. 9. Connected by a low temperature reheat steam pipe. After being sent to the reheater and reheated, 16. 12. Connected by high temperature reheat steam pipe. RSV (reheat steam stop valve) and 13. Pass through the ICV (intercept valve), 8. It is sent to the turbine (medium pressure and low pressure), 8. After working with turbines (medium and low pressure), 1. Return to the condenser, cool and condense to supply water, and repeat circulation.

Superheater tubes built into superheaters of such thermal power plants, reheater tubes built into reheaters, main steam tubes, low temperature reheat steam tubes, heat transfer tubes such as high temperature reheat steam tubes, steam Heat-resistant chromium-containing steel material is used for piping and various valves, and steam oxidation scale is generated and grows on the surface on the steam side as the operation time becomes longer. If the scale becomes thicker, partial peeling will occur and it will scatter to the wake side and cause damage to the turbine, etc., so steam oxidation generated in the main steam pipe, low temperature reheat steam pipe, and high temperature reheat steam pipe. The scale is dissolved and removed by chemical cleaning.

The water vapor oxidation scale generated on the inner surface of the chromium-containing steel pipe has a two-layer structure consisting of an inner layer and an outer layer. The outer layer (steam side) scale is mainly iron oxide (magnetite), and the inner layer scale (base material side) is a chromium-rich oxide scale.

The scale generated on the inner surface of the evaporation pipe of the boiler is a scale of impurities brought into the boiler, and can be relatively easily removed by ordinary hydrochloric acid washing or citric acid washing. The scale is a strong sparingly soluble scale produced by oxidizing (self-oxidizing) the pipe material itself, and it is difficult to dissolve and remove it by a normal acid washing method.

When cleaning the steam pipe generated by the steam oxidation scale, the cleaning target part and the non-cleaning part are cut and separated, and only the cleaning target part is connected by a temporary pipe and the cleaning liquid is circulated to dissolve and remove the steam oxidation scale. There is.

As the cleaning agent used for these cleanings, a chelate cleaning agent such as an ammonium salt of EDTA or a cleaning liquid such as citric acid is used for circulating cleaning at a high temperature (around 100 ° C.) and for a long time (30 to 90 hours). It is done.

Since it is difficult to circulate and clean valves such as steam stop valves generated by steam oxidation scale, after removing them, physical removal work is performed using a grinder or the like.
Further, regarding the steam oxidation scale generated on the inner surface of the superheater tube and the reheater tube, it is structurally difficult to adjust the flow velocity in the tube (flow on average) during circulation cleaning, and it is difficult to discharge the peeling scale. Therefore, the cleaning method cannot be applied, and new pipe switching work (cutting / welding) is being carried out on a regular basis.

Since the conventional cleaning method has poor dissolving power for steam oxidation scale, it is necessary to perform cleaning at a high temperature of about 100 ° C. for a long time (20 to 100 hours), which is a problem in terms of safety and construction. ..

In order to perform cleaning at high temperature, it is necessary to configure a circulation system to raise the temperature. Construction costs such as restoration work after construction and cleaning were excessive.

Further, when cleaning a large-diameter steam pipe to be cleaned, the conventional cleaning method has a large amount of water held in the cleaning system including the temporary pipe, and the purchase cost of the cleaning liquid and the waste liquid treatment cost are excessive.

The steam pipes generated by the steam oxidation scale can be circulated and cleaned by the above method, but the valves (main steam stop valve, steam control valve and steam control valve) generated by the steam oxidation scale installed in the steam system are installed. Since it is difficult to clean a single unit (reheat steam stop valve, etc.) in the circulation system, it is removed and the scale is removed by a physical method. However, there are problems such as damage to the base material during the work, and the workability deteriorates, and the processing work takes a long time.

Therefore, in the present invention, steam oxidation of a two-layer structure including a lower layer (base material side) having a high chromium oxide content formed on the surface of a chromium-containing steel material and an upper layer (steam side) mainly composed of iron oxide. An object of the present invention is to provide a cleaning agent and a cleaning method capable of dissolving and removing scale at room temperature.

The present invention provides a cleaning agent for dissolving and removing iron rust and oxidation scale, which is characterized by containing an iodine compound, and a cleaning method using the cleaning agent.

Cleaning agent of the present invention an acid component consisting of at least one or more inorganic acids and organic acids, that formed by mixing the iodine compound and a fluorine compound, wherein.

The cleaning agent of the present invention is characterized by containing at least one selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, and sulfamic acid as the inorganic acid.

The cleaning agent of the present invention is characterized by containing at least one selected from citric acid, oxalic acid, acetic acid, formic acid, glycolic acid and tartaric acid as organic acids.

In the cleaning agent of the present invention, the iodine compounds include iodine, hydroiodic acid, potassium iodide, sodium iodide, lithium iodide, copper iodide, ammonium iodide, zinc iodide, magnesium iodide, cesium iodide, and iodine. It is characterized by containing at least one selected from strontium iodide, barium iodide, aqueous iodate, potassium iodate, sodium iodate, and calcium iodate.

The cleaning agent of the present invention is characterized by containing at least one selected from ammonium fluoride, acidic ammonium fluoride, sodium fluoride, sodium fluoride, potassium fluoride, and acidic potassium fluoride as the fluorine compound. ..

The cleaning method of the present invention is characterized in that the cleaning agent according to claim 1 is used to perform immersion or circulation cleaning at room temperature.

In the cleaning method of the present invention, when cleaning is performed using the cleaning agent according to claim 1, the cleaning speed can be increased by heating and raising the temperature of the cleaning agent.

The cleaning method of the present invention is characterized in that the cleaning agent according to claim 1 is supplied to a portion to be cleaned by utilizing the capillary phenomenon.

In the cleaning method of the present invention, a sponge-like material having coating or water retention can be impregnated with the cleaning agent according to claim 1 and supplied to a part to be cleaned for cleaning.

In the cleaning method of the present invention, the water-absorbent resin can be impregnated with the cleaning agent according to claim 1 and supplied to the part to be cleaned for cleaning.

In the scale removing method of the chromium-containing steel material of the present invention, when removing the scale of a two-layer structure having a chromium-rich lower layer and an iron oxide-based upper layer on the surface of the chromium-containing steel material, the scale is relatively at room temperature. It can be removed in a short time, which greatly improves safety and construction.

Since the steam oxidation scale having a two-layer structure can be dissolved and removed at room temperature, construction costs such as cutting of large-diameter pipes related to the circulation system configuration, temporary pipe construction, and restoration work after cleaning can be significantly reduced.

Since the work before and after cleaning, such as cutting of large-diameter pipes related to the circulation system configuration, temporary pipe construction, and restoration work after cleaning, can be omitted, the construction period can be significantly shortened.

For simple substances such as valves generated by steam oxidation scale, immersion cleaning (partial cleaning) at room temperature is possible and preparatory work is reduced, so steam oxidation of a two-layer structure takes a relatively short time. The scale can be dissolved and removed. It is also possible to use a physical treatment method together, which improves workability.

The part where the water vapor oxidation scale is generated is a mixture of the part where the scale has already peeled off and the part where the scale remains. Partial cleaning is possible for the target.
In addition, since partial cleaning is possible, simultaneous parallel work with other work is possible, which is advantageous in terms of process control.

Since partial cleaning is possible, the amount of cleaning liquid is extremely small as compared with circulating cleaning, so that the cost of cleaning liquid can be significantly reduced.

In chemical cleaning work, the ratio of waste liquid treatment cost after cleaning is large (about 50% of cleaning work), but according to the cleaning method of the present invention, the amount of cleaning waste liquid is extremely small as compared with circulating cleaning. Therefore, the waste liquid treatment cost can be significantly reduced.

This figure is a circulation system diagram on the water and steam side in a power plant for explaining the present invention. This figure is a graph showing the relationship between the weight loss associated with the removal of the black skin of the four test pieces according to Example 5 of the present invention and the mixing ratio of the 12.7% iodine solution to the 27% phosphoric acid aqueous solution. ..

As an example of the embodiment of the present invention, a cleaning method of dipping and cleaning the steam oxidation scale, a cleaning method of supplying the cleaning agent to the part to be cleaned by utilizing the capillary phenomenon, and a cleaning agent by impregnating a water-retaining material with the cleaning agent. The cleaning method and its effect and the like will be described with reference to Examples.

The steam oxidation scale attached to the steam stop valve used in the thermal power plant was physically peeled off with a hammer, and the peeled two-layer scale was used as a sample for the dissolution test.
The thickness of this two-layer scale sample was 0.47 to 0.55 mm. The thickness of the lower scale was 0.22 to 0.23 mm, and the thickness of the upper scale was 0.25 to 0.32 mm.
Six 200 ml glass beakers were prepared, and 50 ml of each of the six types of test solutions shown below was weighed and subjected to a dissolution test on a beaker scale at room temperature. The concentration of the chemical is% by weight.
CASE. 15% Hydrochloric Acid CASE. 25% citric acid CASE. 3 A mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid CASE. 4 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 9: mixed test liquid CASE 1 ratio. 5 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 8: 2 mixed test liquid CASE in proportion. 6 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 7: the steam oxidation scale samples (0.035~0.055g) was placed in test solution each test solution were mixed in a ratio of 3, the immersion dissolution test at room temperature It started.
After 16 hours from the start of the test, the appearance of the sample was confirmed. The summary of the results is as follows.
CASE. 1 Scale dissolution status: × (No change in appearance of steam oxidation scale)
CASE. 2 Scale dissolution status: × (No change in appearance of steam oxidation scale)
CASE. 3 Scale dissolution status: × (No change in appearance of steam oxidation scale)
CASE. 4 Scale dissolution status: △ (water vapor oxidation scale becomes finer)
CASE. 5 Scale dissolution status: △ (water vapor oxidation scale becomes finer)
CASE. 6 Scale dissolution status: ○ (Steam oxidation scale was almost dissolved.)
Remarks) Evaluation of scale dissolution status ×: No dissolution ability △: Dissolution ability is recognized ○: Good dissolution ability is recognized

Three locations of the valve body to which the steam oxidation scale of the steam stop valve used in the thermal power plant was attached (two-layer scale) were selected and used as the test surface (30 mm × 30 mm) for the dissolution test.
Although the scale thickness of the cleaning test surface of the valve body is unknown, the thickness of the two-layer scale sample collected from the vicinity of the cleaning test surface was about the same as the two-layer scale used in Example 1.
Three 200 ml glass beakers were prepared, and 50 ml of each of the three types of test solutions shown below was weighed and subjected to a dissolution test on a beaker scale at room temperature.
CASE. 1 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 9: mixed test liquid CASE 1 ratio. 2 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 8: 2 mixed test liquid CASE in proportion. 3 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 7: The beaker was placed with the test surface near a dissolution test provided in three places of test fluid steam stop valve in a mixing ratio of 3 test liquid, to which a suitable amount gauze Was impregnated with the test solution, the surface of the black skin was covered with one end of gauze, and the dissolution test at room temperature was started.
After 22 hours, the gauze on the test surface for the dissolution test was removed, and the dissolution status of the scale was confirmed. The summary of the results is as follows.
CASE. Dissolution status of 1 scale: △ (part of upper scale and lower scale is dissolved)
CASE. 2 Scale dissolution status: △ (Part of the upper scale and lower scale are dissolved
, A part of the material part was exposed)
CASE. 3 Scale dissolution status: ○ (Upper scale and lower scale are dissolved, test
Most of the base material on the surface was exposed)
Remarks) Evaluation of scale dissolution status ×: No dissolution ability △: Dissolution ability is recognized ○: Good dissolution ability is recognized

A carbon steel sheet with a black skin (thickness of the black skin: 20 μm) was used as a sample for the dissolution test. The surface to which the black skin was attached was the subject of the dissolution test.
Three 200 ml glass beakers were prepared, and the following three types of test solutions were added thereto and subjected to a black skin dissolution test.
CASE. 1 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 9: mixed test liquid CASE 1 ratio. 2 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 8: 2 mixed test liquid CASE in proportion. 3 With a mixed solution of 7% acidic ammonium fluoride, 9% nitric acid and 18% sulfuric acid
The 12.7% iodine solution 7: the three test solution in a mixing ratio of 3 to prepare a black unpeeled carbon steel, impregnated three test solution in gauze each of mill scale at one end of the gauze The surface was covered and a dissolution test at room temperature was started.
After 30 minutes from the start of the test, the gauze on the surface of the black skin was removed, and the dissolution status of the black skin was confirmed. The summary of the results is as follows.
CASE. Dissolution status of 1 scale: ○ (The black skin on the test surface covered with gauze is almost dissolved)
CASE. 2 scale dissolution status: ○ (The black skin on the test surface covered with gauze is almost dissolved)
CASE. Dissolution status of 3 scales: ○ (The black skin on the test surface covered with gauze is almost dissolved)
Remarks) Evaluation of scale dissolution status ×: No dissolution ability △: Dissolution ability is recognized ○: Good dissolution ability is recognized

A carbon steel sheet with a black skin (thickness of the black skin: 20 μm) was used as a sample for the dissolution test. The surface to which the black skin was attached was the subject of the dissolution test.
Three 200 ml glass beakers were prepared, and the following three types of test solutions were added thereto and subjected to a black skin dissolution test.
CASE. 1 Mixing of 7% acidic ammonium fluoride, 9% citric acid and 18% sulfuric acid
Liquid and 12.7% iodine solution 7: mixed test liquid CASE at 3. 2 Acidic ammonium fluoride 7%, glycolic acid 9% and sulfuric acid 18%
Mixture and 12.7% iodine solution 7: 3 test solutions CASE in a mixing ratio of. 3 Acidic ammonium fluoride 7%, citric acid 4.5%, glycolic acid 4
.. A mixture of 5% and 18% sulfuric acid and a 12.7% iodine solution at a ratio of 7: 3.
Prepare the mixed test solution three black unpeeled carbon steel at a ratio, the three test solution was impregnated respectively gauze, covering the surface of the mill scale at one end of the gauze, start dissolution test at room temperature bottom.
After 60 minutes from the start of the test, the gauze on the surface of the black skin was removed, and the dissolution status of the black skin was confirmed. The summary of the results is as follows.
CASE. Dissolution status of 1 scale: 〇 (The black skin on the test surface covered with gauze is almost dissolved)
CASE. 2 scale dissolution status: 〇 (The black skin on the test surface covered with gauze is almost dissolved)
CASE. Dissolution status of 3 scales: 〇 (The black skin on the test surface covered with gauze is almost dissolved)
Remarks) Evaluation of scale dissolution status ×: No dissolution ability △: Dissolution ability is recognized 〇: Good dissolution ability is recognized

A carbon steel sheet with a black skin (thickness of the black skin: 20 μm) was used as a sample for the dissolution test. The surface to which the black skin was attached was the subject of the dissolution test.
Four 200 ml glass beakers were prepared, and the following four types of test solutions were added thereto and subjected to a black skin dissolution test.
CASE. 1 Phosphoric acid 27% aqueous solution CASE. 2 A 27% aqueous solution of phosphoric acid and a 12.7% iodine solution are mixed at a ratio of 9: 1.
The test solution CASE. 3 A 27% aqueous solution of phosphoric acid and a 12.7% iodine solution are mixed at a ratio of 8: 2.
The test solution CASE. 4 A 27% aqueous solution of phosphoric acid and a 12.7% iodine solution are mixed at a ratio of 7: 3.
And were prepared test solution four black unpeeled carbon steel, 4 types of test liquid impregnated respectively gauze, covering the surface of the mill scale gauze began dissolution test at room temperature.
After 60 minutes from the start of the test, the gauze on the surface of the black skin was removed, and the dissolution status of the black skin was confirmed.
FIG. 2 shows the results of weight reduction after the test of the carbon steel sheet with black skin. The addition of iodine to the aqueous phosphoric acid solution tended to increase the removal rate of black skin. In addition, the higher the iodine mixing ratio (iodine addition rate), the faster the black skin removal rate tended to be.

Possibility of industrial use

Since it is a powerful cleaning agent that dissolves the strong and sparingly soluble steam oxidation scale generated in the steam side pipes and valves of thermal power plants at room temperature, it is a high temperature not only in thermal power plants but also in nuclear power plants. It can be used for maintenance of plants that use steam. It can also be used to remove black skin (oxidation scale) and iron rust on steel.

1 water recovery device, 2 low-pressure feed water heater, 3 deaerator, 4 high-pressure feed water heater, 5-concrete heater, 6 boiler, 7 superheater, 8 turbine, 9 reheater, 10 MSV (main steam stop valve), 11CV (control valve), 12RSV (reheat steam stop valve), 13ICV (intercept valve), 14 main steam pipe, 15 low temperature reheat steam pipe, 16 high temperature reheat steam pipe Solid line is the piping line of the feed water system. Steam system piping line

Claims (1)

An inorganic acid consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, and sulfamic acid, and an acid consisting of at least one organic acid consisting of citric acid, oxalic acid, acetic acid, formic acid, glycolic acid, and tartaric acid. and the component,
Iodine, hydroiodic acid, potassium iodide, sodium iodide, lithium iodide, copper iodide, ammonium iodide, zinc iodide, magnesium iodide, cesium iodide, strontium iodide, barium iodide, aqueous iodic acid , potassium iodate, sodium iodate, and iodine compounds containing at least one selected from iodate calcium,
Fluorine compounds containing at least one selected from ammonium fluoride, acidic ammonium fluoride, sodium fluoride, sodium acidic fluoride, potassium fluoride, and acidic potassium fluoride .
A cleaning agent for dissolving and removing iron rust and oxide scale, which is characterized by being composed of.

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