JPS6349717B2 - - Google Patents

Description

[Detailed description of the invention]

This invention can convert liquid or/and gaseous hydrocarbons into hydrocarbons alone or auxiliary raw materials such as water vapor, oxygen-containing gas, etc., and/or hydrogen, carbon monoxide, etc.
This invention relates to improvements in methods for conducting chemical reactions such as thermal decomposition, steam reforming, partial oxidation, or other high-temperature treatments together with reaction products such as carbon dioxide (hereinafter simply referred to as hydrocarbon-containing substances). Recently, hydrocarbon-containing materials such as those mentioned above have been thermally decomposed at high temperatures and pressures with or without catalysts.
Chemical reactions such as steam reforming, partial oxidation, or a combination of two or three of these reactions are used to produce large-scale products such as ethylene, hydrogen, and mixtures of hydrogen and carbon oxides. When performing various reactions and the high-temperature treatment of hydrocarbon-containing materials associated with these reactions, precipitation of solid carbon occurs due to thermal decomposition of the hydrocarbons, which are the main raw materials, and this precipitated solid carbon is deposited in the reactor, etc. In order to prevent carbon from accumulating in parts of the equipment that come in contact with high-temperature gases, production equipment that operates continuously is temporarily suspended and various methods are used to remove deposited carbon (so-called decoking). is well known. In most cases, nickel-containing steel is used as a material for equipment that comes into contact with high-temperature hydrocarbon-containing substances in these processes, in order to maintain sufficient strength at high temperatures. The present invention has discovered that the above-mentioned carbon deposition is promoted by the catalytic action of nickel in metal materials containing nickel, which are widely used as equipment materials at high temperatures. If the surface that comes into contact with the nickel-containing material is coated with a heat-resistant material that does not contain nickel, the catalytic action of nickel will be eliminated and carbon deposition will be reduced. This is based on the discovery that the embrittlement phenomenon of nickel-containing metals caused by diffusion into metal materials containing nickel (so-called charring phenomenon) can be significantly reduced. The content of this explanation will be specifically explained below. In this invention, the first material that can be used to coat the surface of the nickel-containing device material (hereinafter simply referred to as base material) is the following alloy or metal. (1) Steel or iron-based alloys that do not contain nickel. Here, steel refers to an iron-carbon alloy with a carbon content of 2% or less. Further, the term "iron-based alloy" refers to an alloy that has a high content of iron in its alloy components. (Hereinafter, all base alloys will be used in this sense.) Examples of these alloys include iron-chromium alloys containing 10 to 30% chromium. (2) Chromium-based alloys that do not contain chromium or nickel. An example of this alloy is an alloy consisting of 1% hafnium, 1% thallium, 0.1% yttrium, and chromium. (3) Titanium-based alloys that do not contain titanium or nickel. For example, alloys of niobium and titanium containing up to 3% niobium. (4) Copper-based alloys that do not contain copper or nickel. For example, copper-beryllium alloys containing up to 3% beryllium. It can be a single metal or an alloy, such as an alloy of. Any method may be used to coat the base material with these single metals or alloys, and there are no particular limitations. The so-called casting method in which a material is poured, the method of depositing a molten coating metal using a high temperature generating means such as an acetylene burner or an electric arc, and the injection welding of a molten coating metal such as a flame spraying method or a plasma jet method. chemical vapor deposition method, in which the vapor of these metal compounds is brought into contact with the surface of the base material and the metal is deposited on the surface of the base material through a chemical reaction; An ion deposition method in which kinetic energy is imparted to ions, the ions are guided into plasma or other locations, and the ions are attached to the surface of the base material or metal is deposited on the surface of the base material through a chemical reaction, or a separately manufactured metal coating The coating is usually carried out by the so-called cladding method, in which a molded pipe, plate, etc., is crimped onto a molded base material. When using the above-mentioned metals as coating materials, when used at high temperatures, there is a slight mixing phenomenon of components due to interdiffusion between the base material and these coating metals, resulting in long-term use. In order to withstand it, it is desirable to have a coating with a thickness of 100 microns or more. In addition, adding elements according to the types of the coating metal and base material to cause a mixing phenomenon of components by diffusion with the base metal to the coating metal is important for improving the adhesion between the coating metal and the base metal and the heat resistance of the coating metal itself. It may be desirable to improve For example, it is effective to add aluminum to the metals/alloys listed in (1) to (4) above, or to add aluminum and silicon simultaneously. By performing bending, tube expansion, welding, etc. on the thus formed and coated material, devices or parts of arbitrary shapes can be manufactured. However, if the base material is a cast product, it is desirable not to perform bending, tube expansion, etc. after coating. The second materials that can be used for the coating are (5) oxide-based ceramics such as chromium oxide, alumina or silicon dioxide, (6) nitride-based ceramics such as silicon nitride or boron nitride, and (7) compounds such as silicon carbide. . In the case of oxides, the base material may be coated with these compounds using a melt injection method (so-called thermal spray method) such as a flame spray method or a plasma jet method. In the case of silicon nitride, boron nitride, and silicon carbide, a liquid or solution of a compound containing a silicon-nitrogen chemical bond, a nitrogen-boron chemical bond, or a carbon-silicon chemical bond is applied to the surface of the base material to be coated. , by performing a high-temperature chemical reaction in air or inert gas to deposit and coat, or by melting and spraying silicon carbide, boron nitride, or silicon nitride that has already been made into a powder or rod shape using a plasma jet method similar to the above. The coating can be performed by a method such as a chemical vapor deposition method, an ion deposition method, or the like. In the case of oxides, there is also a so-called baking method in which a suspension of these oxides is applied to the base material and then fired together with the base material at a high temperature, but in this case, in order to prevent the base material from melting or altering, In order to lower the melting temperature of the oxide to below the melting temperature of the base material, it is desirable to mix and bake it with a mixture of silicon oxide, alumina, boron oxide, lime oxide, zinc oxide, barium oxide, zirconium oxide, etc. with different mixing ratios. . However, the use temperature of the coating produced by this baking method is limited by the melting temperature of the coating layer. When coating the base material with such a second type of compound, a layer of metal or alloy with high heat resistance and plastic deformability is coated on the base material in advance in order to prevent the coating material from peeling off. It may be effective to do so. Examples of metals and alloys used for this purpose include metals and alloys (1) to (4) listed above as the first materials that can be used for coating. In this case, any of the above-mentioned methods can be used as a coating method for base treatment. The shape of the base material that can be used when coating the surface of the base material that requires coating with these second type of compounds is the same as for the first type of metal, such as pipes, plates, etc.
It can be applied to all other shapes. When coating with these second compounds, unlike when coating the first metal or alloy, it is necessary to provide a coating layer with a thickness of 10 microns or more, but coatings with a thickness of 1 mm or more are used in the equipment. When the heat flow passes through this coating layer during the heating process, it not only reduces the overall heat transfer coefficient but also tends to cause peeling due to the difference in thermal expansion coefficient between the base material and the coating layer. is desirable.
Furthermore, when coating with a second compound as an upper layer of a metal or alloy coating layer as a base treatment as described above, it is desirable that the total thickness of both coating layers be 1 mm or less for the same reason. . Among the base materials to be coated according to the present invention, tubular materials are particularly important. The reason for this is that the tubular base material is often used in reactors, heat exchangers, etc. and comes into contact with high-temperature hydrocarbon-containing materials. Therefore, the coating of the base material according to the present invention is not limited to one side of the base material, but may need to be coated on both the inside and outside of the base material depending on the passage of hydrocarbon-containing substances in reactors, heat exchangers, etc. There are many cases. The first feature of this invention is that, as mentioned above, when treating hydrocarbon-containing materials at high temperatures of 500°C or higher, the presence of catalysts is particularly important for chemical reactions such as thermal decomposition, steam reforming, and partial oxidation. When applied to reactors operated under or in the absence of water, precipitation and deposition of solid carbon can be significantly reduced. If solid carbon precipitation is left untreated, it will obstruct the flow of hydrocarbon-containing substances and cause an increase in pressure loss. In some cases, a significant decrease in the overall heat transfer coefficient may occur,
Continuation of operations becomes difficult. Therefore, as a countermeasure, it becomes necessary to periodically temporarily shut down the large-scale equipment and remove the deposited carbon using a number of known means. By applying this invention, the frequency of this deposited carbon removal work can be reduced to two-thirds or less of the conventional method. In this sense, the industrial effects of this invention are extremely large. The second feature of this invention is that the decarburization phenomenon for nickel-containing device materials can be greatly reduced.
When carbon-containing substances such as carbon hydrocarbons and carbon oxides come into contact with carbon steel or alloy steel containing nickel, chromium, iron, etc. at temperatures of 700°C or higher, the carbon content of these steels undergoes the so-called decarburization phenomenon. It is known that a percolation-diffusion phenomenon occurs within the structure, weakening the strength of these steels and rendering them unusable. This decarburization phenomenon is said to be caused not only by the diffusion of deposited carbon into the microstructure of the steel, but also by gaseous carbon-containing substances. This invention effectively blocks direct contact of deposited carbon and gaseous carbon-containing substances to the base material.
The above-mentioned charring phenomenon can be significantly reduced. This effect makes it possible to extend the life of members such as the reaction tubes, which normally need to be replaced with new ones every 2 to 3 years. This invention applies to parts, members, etc. made of heat-resistant steel containing nickel that are used at temperatures of 500°C or higher.
It is possible to achieve a remarkable effect by applying it to the surface of equipment that comes into contact with a flow of hydrocarbon-containing materials, and the members and equipment in this case may be manufactured in any shape, but in particular, the above-mentioned reactor It is important to apply this to tubular members used in The reason is that during a series of processes in which hydrocarbon-containing substances are treated at temperatures above 500°C, the flow of hydrocarbon-containing substances in the reactor usually reaches a maximum temperature, and at this time a large amount of reaction heat needs to be removed or supplied. Therefore, carbon deposition is most likely to occur, and a decrease in the overall heat transfer coefficient due to the deposited carbon causes the greatest problem. Any type of hydrocarbon can be treated with this invention. Even in the case of hydrocarbons with a small number of carbon atoms such as methane, ethane, etc., when the content of auxiliary raw materials such as water vapor and oxygen-containing gas is small, or when the hydrocarbon has a high boiling point, that is, carbon contained in one molecule. When the number of atoms is large, it becomes particularly effective when treating heavy oils such as distillate oil obtained by further vacuum distillation of residual oil from atmospheric distillation of crude oil. Furthermore, this invention
In the above cases, a single stream of gaseous or liquid hydrocarbons, a mixture of these hydrocarbons with auxiliary raw materials such as water vapor, oxygen-containing gas, etc., or cases containing hydrogen, carbon monoxide, carbon dioxide, etc. produced as a result of the reaction It is also effective when hydrocarbons are contained as a component. Such hydrocarbon processing is usually carried out at pressures above atmospheric pressure of about 100 kg/cm ² , and such high temperature and pressurized conditions require the use of nickel-containing equipment materials under harsh conditions. Therefore, the practical effects of this invention are best exhibited. Example 1 Steel specimens coated with various materials listed in Table 1 were used as test materials (width and depth 20 mm each, thickness 2 mm),
This was placed on a porcelain boat in a test reaction tube heated by an electric heater, and exposed to a mixed flow of ethane and water vapor at a molar ratio of 1:1.5 at a temperature of 800°C. Changes due to precipitation were investigated by weight increase. The coating was applied by plasma spraying, especially for materials No. 6 and 7, by vacuum plasma spraying in a reduced pressure argon atmosphere, and the metal material was coated to a thickness of 300 μm, and the compound material was first coated with 20% Cr, 0.05% C, and the remainder Ni.
50 μm of the alloy was applied on top of the 80 μm of alloy. The steel material is an alloy consisting of 80% Ni, 18% Cr, 0.8% Si, 0.5% C, and the balance is Fe.The steel material is an alloy consisting of 80% Ni, 18% Si, 0.8% Si, 0.5% C, and the balance is Fe. to f are comparative examples. The results are shown in Table 2. Example 2 The carburizability of each sample material used in Example 1 was tested using the solid carburizing method. That is, a steel container is filled with carburizing agent (main ingredient: charcoal) together with the test material, sealed, and then heated at 600 to 1000℃ (in 100℃ steps) in an electric furnace for 24 hours.
After heating for a period of time, the external appearance of the specimen and changes in the structure of the cut surface were examined. As a result, the test materials No. 3 and 4 showed some oxidation loss and coarsening of the crystals at temperatures above 900°C.
Further, in Nos. a to c and the control, there was no change other than carburization. From the above examples, it can be seen that in Ni alloys, the higher the Ni content, the better the carburizing properties, but carbon precipitation (coking)
It can be seen that while there are problems in this respect, the present invention is good in all respects.

[Table] Alloys

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Claims (1)

[Scope of Claims] 1. Hydrocarbons alone or together with auxiliary raw materials such as steam and oxygen-containing gas and/or reaction products such as hydrogen, carbon monoxide, and carbon dioxide at high temperatures.
When processing at temperatures above 500°C, the surfaces of equipment made of nickel-containing steel that come into contact with the hydrocarbon component must be (1) nickel-free steel or iron-based alloys (2) chromium- or nickel-free steel. Chromium-based alloys (3) Titanium-based alloys without titanium or nickel (4) Copper-based alloys without copper or nickel (5) Chromium oxide, alumina or silicon dioxide (6) Silicon nitride or boron nitride (7) Silicon carbide A method for treating hydrocarbons, characterized in that the treatment is carried out by coating with a material selected from the group consisting of: