JPH11264690A - Method for preventing corrosion of high temperature high pressure water system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate a system smoothly for a long time while preventing flow out of noxious metal by cooling a mixed fluid of organic and inorganic waters in high temperature high pressure condition of water while setting specified pressure and temperature thereby preventing corrosion and elution of noxious heavy metal due to temperature drop (cooling). SOLUTION: An inner tube is made of a material containing no noxious metal in a temperature region of 271-372 deg.C where significant corrosion and elution of various noxious metals take place when the temperature is dropped from the critical point (critical temperature 374 deg.C, critical pressure 21 MPa) of water in a candidate water system down to room temperature. The inner tube of this system is not subjected to pressure. Any material may be employed for the inner tube so long as a noxious substance, e.g. titanium alloy, ceramic or glass, is not contained. The prevention system is applicable to a supercritical water reaction system and a temperature drop line of various high temperature hot water associated with a high temperature hot water processing system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing elution of harmful metals from corrosion-resistant metal materials and corrosion of lines due to a temperature drop in a system for operating a high-temperature and high-pressure hydrothermal fluid. More specifically, in the conventional corrosion-resistant metal material of high-temperature and high-pressure water, the operation of lowering the temperature causes elution of harmful metals and corrosion of specific parts. In particular, the elution of chromium used in corrosion resistant metal materials involves environmental pollution problems. Therefore, in the chemical industry plant that handles high-temperature and high-pressure water, this anticorrosion method provides a new method as a system for preventing elution and corrosion of harmful metals.

[0002]

2. Description of the Related Art Heretofore, it has been common practice to construct a system above the critical point of water by constructing a high-temperature and high-pressure system using a corrosion-resistant metal material such as Inconel or Hastelloy. However, harmful metals are eluted from the corrosion-resistant metal material and the line is corroded in a system that operates the temperature drop of the high-temperature and high-pressure hydrothermal fluid.

In the case of a line (conventional type shown in FIG. 1) constructed of a metal material that can withstand such high-temperature and high-pressure water, a high-temperature and high-pressure water having a hydrogen ion concentration of about 2 from 400.degree. (Cooling) causes elution of constituent metal elements such as nickel, chromium, and molybdenum. Such a corrosion-resistant material has nickel as a main component and chromium and molybdenum as main constituent metal elements, and such a metal element is confirmed in the eluate. In particular, the elution of chromium, a harmful heavy metal, becomes an environmental pollution problem in addition to the corrosion problem of high pressure lines.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the corrosion and the elution of harmful heavy metals due to the temperature drop (cooling) of high-temperature and high-pressure water of a corrosion-resistant metal material, thereby making the system smooth and prolonged. It is intended to provide techniques for operation and prevention of harmful heavy metal spills. A candidate for the high-temperature and high-pressure water fluid is a mixed fluid of inorganic and organic substances mainly composed of water. Specific examples of the raw materials to be candidates and the aqueous systems forming the reaction field are described below. Aqueous tap water for the candidate . Seawater. Lake water. Distilled water. Heavy water. Entrainer added water. Water added with inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and organic acids such as toluenesulfonic acid and acetic acid. Metal ion added water. Salted water. Photosensitizer added water. Water with added substances to enhance solubility. Water with added substances to increase reactivity.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have confirmed metal elements as shown in Table 1 in an eluate at a temperature drop of high-temperature and high-pressure water. . Next, when the conventional line of FIG. 1 was cut vertically after the experiment and observed under a microscope, significant corrosion damage was found in a specific temperature region. Further, the temperature distribution in the specific corrosion area was measured, and the result as shown in FIG. 3 was obtained. Figure 3 shows significant corrosion at 271
This indicates that a specific portion of the subcritical region of -372 ° C is corroded. The dielectric constant of water in this region is 14.0-2.
5.6, which is considered to be a region where the degree of ion dissociation of water is high. Therefore, it has been found that the purpose can be achieved by setting a prevention system (FIG. 2) in this specific corrosion occurrence area, and the present invention has been completed based on this finding.

That is, the present invention provides a method for remarkably corroding when the temperature of the water of the candidate water system is lowered to a room temperature from a temperature higher than the supercritical point (critical temperature: 374 ° C., critical pressure: 21 MPa). A material containing no harmful metal in a region where the harmful metal elutes, that is, in a temperature range of 271 to 372 ° C., is used as the inner tube. The inner tube in this system is kept free from pressure. As a device for the inner tube, any material that does not contain harmful metals such as titanium, titanium alloy, ceramic, and glass may be used for the system. The prevention system of the present invention provides a new method for lowering the temperature in a high temperature and high pressure chemical industrial process. As an example to which the method of the present invention can be applied, for example, supercritical water reaction systems and various high-temperature hot water temperature drop lines associated with such high-temperature hot water treatment systems can be mentioned.

[0007] The prevention system of the method of the present invention, the temperature range of 250-450 ° C in the process of lowering the temperature of high-temperature high-pressure water
In this case, the progress of corrosion due to a temperature drop can be prevented. The temperature at this time varies slightly depending on the flow speed of the line, but the temperature region does not change. The pressure can be in a system in the range of 21 MPa or more.

Usually, tap water, well water, river water and the like are used as the water system for forming the high-temperature hot water state of the present invention, but distilled water and ion-exchanged water can also be used. Furthermore, various substances can be added to these waters to increase the solubility or the reactivity. A typical example is given as the water system of the above-mentioned candidate object. An object is not limited to this.

The method of the present invention can be used or applied to the operation of lowering the temperature of any high-temperature high-pressure line.

[0010]

According to the present invention, it is possible to prevent corrosion at the time of a temperature drop in a high-temperature and high-pressure line, and prevent elution of harmful metals from expensive materials such as Hastelloy and Inconel generated due to the corrosion. Therefore, the present invention eliminates the need for replacing expensive materials by preventing corrosion and elution of harmful heavy metals due to the temperature drop (cooling) of the high-temperature and high-pressure water of the corrosion-resistant metal material, and has an economic advantage. This is useful in that long-term smooth operation of the high-temperature and high-pressure system is expected, and harmful heavy metals can be prevented from flowing out.

[0011]

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Comparative Example Here, the reaction temperature shown in FIG.
An example of the condition a will be described. The inner diameter of the Hastelloy C-276 high-temperature and high-pressure line is about 4 millimeters, the total length of the pipe in the heating furnace is about 40 centimeters, and the temperature is about 25 centimeters from 2-3 centimeters onwards. A cooling device for descent is provided. The temperature in the tube was measured at intervals of about 8 millimeters. Here, a high-temperature and high-pressure fluid of water having a hydrogen ion concentration of about 2 is used for about 1.
The operation was continuously performed at 5 milliliter / minute for 336 hours. The effluent is a pale yellowish aqueous solution. The results of ICP analysis of the metal elements in the aqueous solution are as shown in Table 1, and are almost the same as the metal elements constituting the Hastelloy C-276 piping used. Further, FIG. 3 shows a corrosion observation part and a temperature change. FIG. 3 shows Hastelloy C at 271-372 ° C.
Corrosion in a specific area of the -276 pipe was indicated. This result is consistent with the metal element analysis of the eluate. Table 1 Eluate of FIG. 1 (Results of ICP analysis) Hastelloy composition Eluent Element Metal element ratio (%) Metal concentration (ppm) Fe 6.0 2.3 W 4.0 Not detected Ni 57.0 100.0 Mo 16 0.0 17.0 Cr 15.5 27.0 V 0.3 0.01 Co 1.1 C 0.01 * Cobalt is detected as an impurity of nickel.

EXAMPLE An example of the conditions in FIG. 2 at a reaction temperature of 600 degrees and a reaction pressure of 30 MPa will be described. The inner diameter of the Hastelloy C-276 high-temperature and high-pressure line is about 4 millimeters, and the total length of the pipe in the heating section of the electric furnace is about 40 centimeters, which is about 25 centimeters from 2-3 centimeters onwards. A circulation port of a cooling device for cooling from the outside is installed in the apparatus. The inner tube was set so that the alumina ceramic tube could be set in a temperature range of 200 to 450 degrees, that is, the temperature range in question was about 8 cm when the injection rate was 1.2 milliliter / minute. , So as to cover the area. The outer diameter of the inner tube is about 2 millimeters and the inner diameter is about 1 millimeter. The fixing portion of the inner tube is supported by a fixing union provided at the room temperature portion. As shown in Fig. 2, an inlet for cooling water in the inner pipe is installed in the outer pipe of the double pipe so that cooling water (about 17 degrees) can be injected at 0.5-4 milliliters at the same pressure as the internal pressure. did. The main fluid is water, about 1.2
It is injected at a rate of milliliters / minute, but by injecting chloride from the upper part of the heating furnace, it moves as a high-temperature high-pressure fluid of water having a hydrogen ion concentration of about 2. In the continuous operation for 336 hours, the main fluid flow was about 1.2 milliliter / minute, and the injection water for cooling the inner tube was 1 milliliter / distilled water containing no salt or the like.
Injected in minutes. As shown in FIG. 2, the water injected between the inner tube and the outer tube rises toward the heating furnace, is mixed with the main fluid, and passes through the inside of the inner tube. At this time, the passing fluid is gradually cooled by the water injected into the inner pipe and the outer pipe. The effluent is a clear, colorless aqueous solution. As a result of ICP analysis of the metal element in the aqueous solution, the constituent metal element of Hastelloy C-276 was 1 ppm or less. In addition, as a result of cutting and observing the tube after the experiment, local corrosion unlike the conventional type was not observed. In addition, the temperature of these high-temperature and high-pressure lines is raised to a set temperature and raised to a set pressure. For cooling the line, a cooling device for circulating water at about 15 ° C. was used.

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[Procedure amendment]

[Submission date] June 17, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

[Brief description of the drawings]

Fig. 1 Plan view Cooling line via conventional reactor

[Explanation of Signs] 400-600 ° C .: Represents a temperature range from 400 ° C. to 600 ° C., and 30 MPa represents pressure (about 300 atm). The reaction zone represents the area that has been exposed to the aforementioned temperature contained in the furnace. The corroded area represents the corroded area shown in FIG. Cooling part: represents a cooling part by cooling water reflux. FIG. 1 shows that the fluid flows from the upper end to the lower end.

Fig. 2 Plan view Prevention system for specific corrosion occurrence area

[Explanation of Signs] 400-600 ° C .: Represents a temperature range from 400 ° C. to 600 ° C., and 30 MPa represents pressure (about 300 atm). The reaction zone represents the area that has been exposed to the aforementioned temperature contained in the furnace. The corroded area represents the corroded area shown in FIG. Inner pipe inclined cooling section: Represents a cooling section whose temperature is inclined by injection of cooling water. FIG. 2 shows that the fluid flows from the upper end to the lower end. The ceramic inner tube is inside the reaction tube, which is supported below the cooling water inlet,
The pressure is not applied to the ceramic tube itself.

FIG. 3 Diagram of specific corrosion caused by corrosion observation part and temperature change

[Explanation of Symbols] The scale on the left side of FIG. 3 is a temperature, and a square point plots a temperature change at a distance from the center of the cooling T union at the upper end. The right side of FIG. 3 shows the dielectric constant of water, and the triangular points similarly show changes in the dielectric constant. The lines in the table show the plan view from the reactor to the cooling unit according to the distance in the table. Corroded area: Corroded area (372-
271 degrees). εr = 15 indicates the vicinity of the dielectric constant 15 of water.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

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[Procedure amendment 3]

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[Correction target item name] Figure 2

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[Procedure amendment 4]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

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Continued on the front page (72) Inventor Osamu Sato 3-chome, 2-chome, Miyagino-ku, Sendai-shi, Miyagi 8-10-102 (72) Inventor Takashi Aizawa 68 Kameoka-cho, Kawauchi-cho, Kawauchi-cho, Aoba-ku, Miyagi Pref. District 2-45

Claims (9)

[Claims] (1) Compressing the mixed aqueous solution to a pressure of 21 MPa or more; (2) Making the mixed aqueous solution a high temperature of 374 ° C. or more. (3) cooling the mixed aqueous solution; and a method for preventing corrosion associated with a temperature drop comprising the mixed aqueous solution. 2. The method according to claim 1, wherein the anticorrosion system is incorporated in a temperature range of 250 ° C. to 400 ° C. during the temperature drop of the high temperature fluid of 374 ° C. or more. 3. The method of claim 1 wherein said aqueous phase is provided in tap, sea, lake, or distilled water streams. 4. The method according to claim 1, wherein the mixture of the aqueous phase is supplied as an organic substance and an inorganic substance. 5. During the temperature drop of the high temperature fluid of 374 ° C. or more, a 250 ° C. to 450 ° C. range including a temperature range of 250 ° C. to 400 ° C. is combined with an inner pipe to prevent harmful metals and corrosion. Claim 1
The method described in the section. 6. During the temperature drop of the high-temperature fluid of 374 ° C. or more, a 250 ° C. to 450 ° C. area including a temperature range of 271 ° C. to 372 ° C. is combined with an inner pipe to prevent harmful metals and corrosion. Claim 1
The method described in the section. 7. The method of claim 5, wherein the inner tube of the corrosion protection system is selected from the group consisting of titanium, titanium alloy, ceramic, glass, or a combination thereof. 8. The method of claim 6, wherein the inner tube of the anticorrosion system is ceramic. 9. The method according to claim 6, wherein a plurality of inner pipes of the anticorrosion system are set.