JPH08910B2 - How to play a cracking tube - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for regenerating a cracking tube for ethylene production in the petrochemical industry.

[Prior Art] Ethylene is produced by introducing raw material naphtha and steam into a cracking tube heated to a high temperature of over 1000 ° C and decomposing the naphtha in the tube. Due to long-term operation, the inner surface of the tube is carburized, and when this amount of carburization increases, the tube swells or cracks due to material deterioration.

By the way, the cracking tube is generally a straight pipe having an inner diameter of about 50 to 150 mm, a wall thickness of about 6 to 10 mm, and a length of about 8 to 10 m, and as shown in FIG. As it is assembled, it is not easy to replace only the deformation or other defective parts of the tube. Even if the defective part is partially replaced and repaired, since the tube has already been used for a long period of operation, it is necessary to repair other parts of the tube within a short period for the same reason. Becomes Therefore, if tube deformation or the like due to carburization occurs even in one place, the entire cracking tube is replaced even if the other parts are in a sufficiently usable state.

[Problems to be Solved by the Invention] As a result of earnest research on the carburizing phenomenon of the cracking tube, the present inventor found that a stable oxide film was formed on the inner surface of the tube during the initial operation, and the operation period was within about 3 years. If it is medium (depending on operating conditions and tube material), the presence of the oxide film delays carburization on the inner surface of the tube, but if the ethylene production operation is continued, the oxide film becomes unstable, After that, it was found that carburization proceeded rapidly.

On the other hand, it was found that if the oxide film is removed and reused, a stable oxide film is formed again on the new inner surface, and the progress of carburization can be delayed.

Therefore, based on the above findings, the present invention delays the progress of carburization by removing the oxide film before the oxide film becomes unstable, exposing a new surface, and forming a new oxide film on the surface. The cracking tube is regenerated by such a method.

[Means for Solving the Problems] In order to achieve the above object, the straight pipe portion of the cracking tube is cut and removed before the oxide film formed on the inner surface of the cracking tube becomes unstable, and the straight pipe portion is removed. The inner surface is scraped off by at least 0.3 mm to remove the oxide film, returned to its original position and welded.

Although the time for removing the oxide film varies depending on the tube material and operating conditions, it is generally desirable to carry out about 2.5 to 3 years after the first operation is started.

[Operation] When the oxide film formed on the inner surface of the cracking tube is removed and then reused, a stable oxide film is newly formed on the newly exposed surface, which delays the carburization reaction.

EXAMPLE As shown in FIG. 1, the cracking tube (1) for ethylene production is assembled in a coil shape by connecting the bent portion (3) to the end of the straight pipe portion (2).

First, the straight pipe portion is cut, for example, at the positions shown in A and B of FIG. The straight pipe that has been cut and removed is then
As shown in the figure, a pair of rotating rollers (4), (4) and (5), (5) (only one of the rollers is shown in the figure, respectively) is placed on a workbench with a predetermined interval. Put on.

The rotating roller is rotated by a driving device (not shown) to rotate the straight pipe (2) on the roller. Next, a grinding means (8) in which a grindstone (7) is attached to the tip of the rotary shaft (6).
The inner surface of the straight pipe (2) is ground using. Grinding means (8)
First, it is made to enter from one end side, the inner surface of the straight pipe (2) is scraped off, and then similarly, the grinding means is made to enter from the other end to perform grinding. In addition, the straight pipe part of the cracking tube for ethylene production is usually about 8-10
Since it is a long length of m, it is desirable that the length of the rotary shaft is about half the length of the straight pipe, and as described above, one end is ground from each end side.

The thickness of the oxide film is usually about 0.1-0.2 from the surface.
mm, so grind about 0.2 mm or more, preferably about 0.3 mm or more.

The straight pipe (2) after grinding is returned to its original position and welded for use.

Next, with respect to the cracking tube used for about 3 years, a carburization test was performed for each of the case where the oxide film was removed and the case where the oxide tube was continuously used without removing the oxide film, and the progress of the carburization reaction was examined.

The test material is the cracking tube after use, 30 mm ×
It was cut into a size of about 70 mm. Sample material No.1
Is just cut out. Specimen No. 2 was obtained by cutting 0.3 mm off the portion corresponding to the inner surface of the tube. The carburizing test was carried out by a solid carburizing method using a solid carburizing agent of KG30 manufactured by Degussa Co., which was held at 1150 ° C. for 18 hours and then cooled down to 1 cycle, and this cycle was repeated 7 times. For the portion from the surface of the test piece to the depth of 4 mm, chips were collected at a pitch of 0.5 mm and the amount of carbon was analyzed. The results are shown in FIG.

As shown in FIG. 3, it can be seen that the test material in which the oxide film was removed and a new surface was exposed had a small increase in carbon and exhibited a carburizing retarding effect.

[Effects of the Invention] By repairing the cracking tube, the cracking tube can be used until its original life is reached, which is more economical than the conventional methods of use.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the assembled state of the cracking tube, FIG. 2 is an explanatory view of the grinding state of the inner surface of the cracking tube, and FIG. 3 is a graph showing the results of the carburizing test. (1) …… cracking tube (2) …… straight pipe part, (3) …… bent part (8) …… grinding means, (7) …… grinding stone

Claims (1)

[Claims] 1. Cracking at a suitable time before the stable oxide film formed on the inner surface of the cracking tube becomes unstable during the initial operation of the cracking tube used in the ethylene production process. Recycling of a cracking tube characterized by cutting and removing the straight pipe part of the tube, scraping the inner surface of the straight pipe part at least 0.3 mm to remove the oxide film, returning it to the original position and welding it again Method.