KR20030051833A - Cylindrical tube for industrial chemical installations - Google Patents

Abstract

The present invention provides a tube for use in a furnace where gas and liquid particles are passed through a tube from one end to the other end with substantial heating and decomposition. The cylindrical tube is weight percent up to 0.08% C, 23-27% Cr, 33-37% Ni, 1.3-1.8% Mn, 1.2-2% Si, 0.08-0.25% N, 0.01-0.15% rare earth metal, And a stainless iron-nickel-chromium-based alloy containing Fe and conventional impurities. The cylindrical tube has a smooth outer surface and an inner surface, the inner surface is provided with longitudinally extending valleys or grooves having a smoothly curved bottom shape.

Description

Cylindrical tubing for industrial chemicals {CYLINDRICAL TUBE FOR INDUSTRIAL CHEMICAL INSTALLATIONS}

The present invention relates to a tube for use in a device for heating a gas or a liquid which is transferred from one end of the tube to the other end and simultaneously heated to generate a chemical reaction. The heating is for example by heating outside the wall of the cylindrical tube or by supplying heat directly through the wall.

Although specific structures and methods are referenced in the background of the invention, such references should not be considered to permit such structures and methods to be classified as prior art under applicable law. Applicant reserves the right to prove that the above referenced tasks do not constitute a prior art for the present invention.

In order to obtain acceptable products such as ethylene in ethylene crackers, it is required to use tubes that are free of cracks inside. Such a tube must also be resistant to exposure of the product produced within this tube. The use of materials in such tube arrangements often results in the formation of oxides in the tubes and the easy separation therefrom, which shortens the life of the tubes. At the same time there is a problem of carbonization, since precipitation of carbon composites is formed in these tubes. The greater the amount of precipitation formed, the smaller the amount of gas passing through the tube. At the same time, heat transfer will be reduced, resulting in lower economic efficiency.

Known furnaces for cracking hydrocarbons are typically provided with cast tubes of nickel-based alloys having large amounts of chromium. This is a disadvantage because such a tube material is very expensive and a high nickel component can be an undesirable catalyst for caulking.

In addition, the shape durability of such tubes, typically characterized by high temperature materials, becomes unsatisfactory in certain devices.

In crackers, decomposition of hydrocarbons occurs. The starting material may for example be naphtha or propane mixed with water vapor. When the material passes through the tube of the cracking furnace, the temperature rises above 800 ° C. Important products obtained are, for example, ethylene and propylene. Hydrogen gas, methane, butane and other hydrocarbons are also formed. In order to prevent undesirable reactions, heating takes place very quickly and the resulting product is required to be quenched, and the residence time in the furnace is required to be only a few tenths of a second. The temperature in the furnace can reach 1100-1200 ° C. and the tube material temperature in the furnace can exceed 1100 ° C. The heating of the furnace is made from the combustion of gases from a cracking process such as hydrogen and methane, and a number of gas burners can be placed in the furnace, which can be installed at the bottom or wall of the furnace.

Tubes used in the furnace should have good shape durability against heat and be able to withstand high temperatures. In addition, the tube must have oxidation and corrosion resistance to withstand the atmosphere in the furnace chamber. The carbon potential inside the tube in the furnace is very high and the tube material must be able to withstand carbonization and carbohydrate formation. Since small amounts of sulfur are frequently added to the starting material, the tubes should have good resistance to sulfur and sulfur compounds.

The present invention relates to a new type of finned tube made of a material which increases resistance to the environment in cracking furnaces of hydrocarbons outside the tube as well as to the unique environmental conditions occurring inside the tube. .

According to one aspect, the present invention provides a metal tube for use in a furnace, the metal tube being pressed from the inlet end to the opposite end through the tube while gas and liquid forming particles are substantially heated and decomposed, the body; Smooth exterior; And a contoured inner surface, wherein the body is, by weight, up to 0.08% C, 23-27% Cr, 33-37% Ni, 1.3-1.8% Mn, 1.2-2% Si, 0.08-0.25% N , A stainless steel-nickel-chromium group alloy comprising 0.01-0.15% rare earth metal, and conventional impurities, the contour comprising a plurality of valleys or grooves, the valleys or grooves being along the end of the tube Elongate and provide a tube with a smoothly curved bottom.

The economics of such tubes and furnaces are greatly improved by forming tubes from high strength stainless steel with good resistance to oxidation flaking and carbonization. Thus it is possible to produce tubes with very good heat transfer properties while substantially increasing the resistance to the rapid occurrence of carbonization, carbonization and oxidation flaking due to the by-products generated during the transport of the material in the tube. .

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings in which like numbers are used for like elements.

1 shows a cylinder formed according to the invention.

FIG. 2 shows a cross section of the cylinder embodiment shown in FIG. 1.

3 shows the weight change during oxidation at 1000 ° C. with air as a function of exposure time of the tube.

4 schematically shows how the carbonization form is measured in rod-shaped specimens for analyzing the carbohydrate content.

5 shows the measurement results of carbonation as a function of the area of carbohydrates.

1 shows a tube 10 having an inlet end that is directed toward the outlet end while gaseous media such as hydrocarbons and steam pass through and undergo a chemical reaction.

In the illustrated embodiment, as shown in FIG. 2, the inner surface 11 of the tube 10 is provided with grooves 13 and ridges 14 having a sinusoidal contour, the outer surface of the tube being substantially As soft or arched. The ridges 14 and the grooves 13 are provided in a rounded shape to prevent fatigue cracks.

According to an alternative embodiment, the groove 13 provided inside the cylinder 10 may be provided helically in the longitudinal direction of the cylinder.

Alternatively, the tube can be conical from its inlet end to its outlet end rather than spiraling over its entire length.

U.S. In the manner as described in patent no. 4,095,447, it has been found that the shape durability against heat is increased by the use of tubes as described above if the tubes are produced by pilger rolling onto the mandrel. Alternatively, however, such tubes may be U.S. It may be prepared in the manner described in Patent No. 5,016,460. Instead of rolling onto the mandrel, the drawing onto the mandrel may be applied.

The steel material to be selected for such a cylinder 10 is a stainless iron-nickel-chromium alloy having an austenitic structure or, on the one hand, a strictly controlled and optimized alloying component. The alloy is up to 0.08% C by weight, 23-27% Cr, 33-37% Ni, 1.3-1.8% Mn, 1.2-2% Si, 0.08-0.25% N, 0.01-0.15% rare earth metal (rare earth) metals) and Fe and conventional impurities. The amount of rare earth metal is preferably 0.03-0.1% to improve the production of thin flexible adhesive oxide films when the metal is exposed to an oxidizing environment at high temperatures. The amount of nitrogen is preferably 0.13-0.18% and the amount of silicon is preferably 1.3-1.8%.

By the above selection of materials, it is possible to achieve unexpectedly superior substantially longer service times without interruption for tube exchange while substantially reducing the amount of carbon compound precipitated inside the tube and also having less sediment in the tube. This occurs, for example, so that higher amounts of hydrocarbons and vapors can be transported through the tubes in the manufacture of ethylene, thereby increasing economic utilization.

Further improvements can be made by providing a chromium oxide layer on the inner surface of the tube, which prevents carbon from dispersing into the material by oxidation of the tube prior to use of the tube.

3 is a study of the tendency of oxidation flaking of tubes made of Sanicro 39 type material according to the present invention for some conventional materials used in corresponding applications. As a reference these studies are often used for example for cracker tubes of ethylene furnaces, for example, materials sold by International Nickel Corporation with the INCO 803 designation, materials sold by Sumitomo Metals Ltd. with the HK4M designation and HP45-Nb. It includes both forging and casting alloys, such as casting alloys of markings. Analysis of various reference substances is given in the table below.

alloy Cr Ni Si Mn C N Nb Ti Al HP45-Nb 23.6 36.9 1.4 1.22 0.17 0.046 1.2 - - Inco 803 25.8 35.3 0.65 0.90 0.075 0.013 - 0.55 0.52 HK4M 25.3 24.5 0.41 1.12 0.21 0.017 - 0.46 0.33 Sanicro 39 24.9 34.8 1.5 1.4 0.048 0.166 - - - REM = 0.05

The diagram of FIG. 3 shows the weight change as a function of the exposure time of the tube during oxidation in 1000 ° C. air.

As shown in the diagram of FIG. 3, the oxides produced when compared to the material sac 39 selected according to the invention are more easily separated from these reference materials.

The carbonization test was conducted to be similar to the ethylene environment present in the above cracker applications by providing a moving carbonization and oxidation environment. The carbonization takes place in a gas mixture comprising carbon monoxide, hydrogen gas and methane of a mixture given an oxygen potential corresponding to a temperature of 1050 ° C. and 10-15 atm and greater than 1 carbon activity. The coke formed after 120 hours of exposure to this carbonization environment is withdrawn by introducing air to combust the coke. The time for the carbonation / oxidation cycle varies between 135-140 hours. As described above, the total test time corresponding to 8 cycles was 1104 hours. The temperature was kept constant at 1050 ° C. during the entire first test. The shape of the specimen was 8 mm x 8 mm x 20 mm.

After the test was completed, the cross section of the test rod was studied by observing how the specimen was pulled out and how the area fraction of the carbides changed along the selected line. The cross section of the specimen had a rectangular outer surface, and in this specimen shape the degree of carbonization was highly dependent on where the measurement was made. The area closer to the edges and edges than the outer surface of the plane appeared to be more sensitive to carbonization. In FIG. 4 the position of the line analyzed in the cross section of the test piece is shown. A first line (Prof 10) is arranged along the outer surface at 0,8 mm (10% of edge length) into the material. The second line (Prof 50) is placed 4 mm from the edge while extending to the center of the test piece.

4 schematically shows whether the degree of carbonization changes depending on whether the position is close to the edge or extends into the outer surface of the plane.

This figure also schematically shows how the degree of carbonization depth varies with distance from the edge. The gray areas represent carbonized areas and white areas represent non-carbonized areas. It should be noted that the carbonization depth is greater at the edge of the specimen.

In FIG. 5 an area fraction analysis of carbohydrate is shown. The x axis represents the distance (0-8 mm) from the starting point on one outer surface and the y axis represents the area fraction of the measured carbohydrate (%). The diagram shows that Sancro 39 and HP45-Nn are not affected by carbonization from a planar surface (Prof 50), and from these two Sancro 39 in the area close to the edge or edge (Prof 10). It seems to be the most resistant. The alloy 803 was affected by the collective carbonization in the corner region and showed strong carbonization in the plane. The alloy HK4M showed maximum carbonization throughout the entire material.

Although the present invention has been described with reference to the above embodiments, certain modifications and variations will be apparent to those skilled in the art. Therefore, the invention is limited only by the scope and spirit of the appended claims.

Claims (9)

A metal tube used in a furnace, which is a metal tube pressurized through the tube from the inlet end to the opposite end while the gas and liquid medium is substantially heated and decomposed, Body; Smooth exterior; And a contoured inner surface, wherein the body is weight percent, 0.08% C max, 23-27% Cr, 33-37% Ni, 1.3-1.8% Mn, 1.2-2% Si, 0.08-0.25% N, 0.01-0.15% rare earth metals, And stainless iron-nickel-chromium group alloys containing conventional impurities, The contour includes a plurality of bones or grooves, the bones or grooves extending along the longitudinal direction of the tube and having a smoothly curved bottom. The tube of claim 1, wherein each of the plurality of valleys or grooves is straight, extending longitudinally along the cylinder. The tube of claim 1, wherein each of the plurality of valleys or grooves and each of the plurality of peaks spirally extend from the inlet end to the opposite end of the tube. The tube of claim 1 further comprising a chromium oxide layer on the inner surface. Hydrocarbon cracking furnace comprising a tube according to claim 1. The metal tube according to any one of claims 1 to 5, wherein the amount of the rare earth metal is 0.03% -0.10%. The metal tube according to any one of claims 1 to 6, wherein the amount of silicon is 1.3-1.8%. 8. Metal tube according to any of the preceding claims, characterized in that the amount of nitrogen is 0.13-0.18%. Use of a metal tube according to any of the preceding claims in a furnace for producing ethylene.