JPH06146008A - Method for preventing carbon precipitation of process device and process device preventing carbon precipitation - Google Patents

Abstract

PURPOSE:To prevent the caulking which may arise in some cases in the process device handling a hydrocarbon, i.e., the precipitation and growth of carbon and to avert the trouble occurring therein. CONSTITUTION:Treatment of any among (1) using of a material contg. >=28% chromium, (2) applying of chromium plating, (3) applying of one kind of the surface treatment selected from a chromizing treatment, calorizing treatment, siliconizing treatment and sulfurizing treatment, (4) applying of a surface treatment to form a carbide layer of V, Cr, Nb or Ti by diffusion penetration of these metals, (5) applying of a coating by thermal spraying of metal carbides, for example, CrC, VC, NbC, is adopted for the device parts where fluid contg. the hydrocarbon is liable to stagnate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents the harmful effects of carbon precipitation growth which may occur in a process apparatus operated under conditions in which a fluid containing a hydrocarbon flows and carbon deposits grow on the surface. Regarding

[0002]

2. Description of the Related Art For example, structural steel is generally used as a material for constructing process equipment for petroleum refining and petrochemical plants, but for structural parts exposed to high temperatures and parts used in corrosive environments. Materials selected according to the situation, typically Cr-Mo steel and various stainless steels are used.

On the other hand, in a process device for a fluid containing hydrocarbon, a so-called coking phenomenon is known in which carbon is deposited depending on operating conditions. In the past, caulking has never been a problem, but due to changes in demand trends for petroleum or petrochemical products,
Or, in response to the fluctuation, the operating conditions of the plant have been changed variously, and as a result, coking has become a problem to some extent. Concretely, there is a phenomenon in which structural parts called reactor internals, for example, carbon precipitates and grows between the joint flanges of the catalyst transport pipe to push the flanges apart and eventually break the flange fixing bolts. Was experienced. Such troubles often lead to the need to shut down the plant for maintenance, and should be avoided as much as possible. Fear of trouble limits the process conditions that can be implemented.

As a countermeasure, it is necessary to keep the sulfur concentration in the treated fluid above a predetermined lower limit, based on the experience that coking is less likely to occur when sulfur is present in the hydrocarbon at a concentration higher than a certain concentration. Although the addition of sulfur compounds is carried out, it is not an advantageous measure.

[0005]

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a method for preventing carbon deposition in a process apparatus on the side of the apparatus and a process apparatus in which carbon deposition is prevented, as a more advanced solution to the above problems. To do.

[0006]

A method for preventing carbon deposition in a process apparatus according to the present invention is a process apparatus manufactured by using structural steel, in which a fluid containing a hydrocarbon flows and carbon is deposited on the surface. A part of the apparatus operated under growing conditions in which carbon precipitation growth is not preferable is subjected to one of the following surface treatments. 1) Chromium plating, 2) Chromize treatment, calorization treatment, siliconization treatment and one of the treatments selected from sulfurization treatment, 3) Formation of a carbide layer of these metals by diffusion and permeation of V, Cr, Nb or Ti, or 4) Metal Film formation by thermal spraying of carbide.

The process device of the present invention which prevents carbon precipitation is a process device manufactured by using structural steel, which is operated under the condition that a fluid containing hydrocarbon flows and carbon deposits and grows on the surface. In the device described above, a portion where carbon precipitation growth is not preferable is composed of any of the following materials. a) Steel containing 28% or more of Cr, b) Steel plated with chrome, c) Steel subjected to one kind of surface treatment selected from chromizing treatment, calorizing treatment, siliconizing treatment and vulcanization treatment, d) Steel having a carbide layer of these metals formed on its surface by diffusion and permeation of V, Cr, Nb, or Ti, or e) Steel having a film formed by thermal spraying of metal carbide.

A process apparatus in which the present invention is useful is a fluid containing a hydrocarbon, particularly a gas mixture containing hydrogen, a hydrocarbon fraction and carbon monoxide as a main component, and a chemical reaction is carried out at a high temperature. And various devices as described above.
Specifically, i) a plant that handles a dehydrogenation reaction at a temperature of 500 ° C or higher and a hydrogen partial pressure of 2 atm. Or higher, ii) a temperature of 450 ° C
Above, plants that handle cracking reactions with hydrogen partial pressures of 1 atm. Or less, iii) Plants that handle catalytic reforming reactions with temperatures of 450 ° C or more and hydrogen partial pressures of 5 atm. Or less, iv) Temperatures of 450 ° C or more, hydrogen partial pressures of 1 atm An example is a device that is a constituent part of a plant that handles a steam reforming reaction, such as the following.

The portion of the apparatus where carbon deposition is to be prevented is a portion where gas is likely to stay, which is represented by the above-mentioned gap between the flanges or the gap between the bolts and nuts fastening the flanges. If the operating conditions lead to carbon deposition, carbon deposition will occur in other parts as well, but accumulated growth is unlikely to be a problem on the surface where the fluid flows at a relatively high flow rate.

[0010]

The trouble caused by the caulking phenomenon occurs as shown in FIGS. 1 and 2 when the flange fixing bolt is broken. That is, carbon precipitates in the flange gap portion shown by the arrow in FIG. 1, and it grows as shown in FIG. 2 and leads to bolt breakage. When the pipes are connected by welding, carbon precipitates in the gaps also shown by the arrows in FIG. 3, and they grow to deform the ends of the inner pipes inward as shown in FIG. As a result, the cross-sectional area of the pipe channel is narrowed, which causes problems such as an increase in pressure loss.

When the carbon adhering to the equipment in which such a trouble occurred was analyzed, it was found that it was generated by the decomposition of hydrocarbons in the liquid, and that the material constituting the equipment was catalytic to the decomposition. I found out that I was working. Therefore, the inventors who have advanced the research further found that the Fe and Ni components of the materials that make up the device act as a catalyst, and these actions dilute the device surface with other substances to lower the Fe and Ni concentrations. It has been found that this can be suppressed by coating with another substance or by reducing the chances of Fe or Ni coming into direct contact with hydrocarbons. The specific method is the above-mentioned various points.

That is, when steel containing 28% or more of Cr is used, the concentration of Fe (and also the concentration of Ni when Ni is present) can be increased by making Cr present in a composition of Fe-Cr-X above a certain limit. It is to lower.

The chromizing treatment, the calorizing treatment and the siliconizing treatment are so-called diffusion coating methods, and Cr, Al or Si are applied to the surface of carbon steel or low alloy steel, respectively.
Is diffused and permeated to improve corrosion resistance, especially high temperature oxidation resistance,
This is a surface treatment method that improves wear resistance and heat resistance.
These surface treatments are usually carried out according to a technique called the pack method, in which a mixture of a metal powder to be diffused and a chloride powder thereof is put in a container, and a structural component to be surface-treated therein is placed therein. For example, fill flanges, bolts, nuts, etc., in a stream of hydrogen or inert gas to 800-10
It is carried out by heating to a temperature of 00 ° C. for several hours.

The sulfurizing method is also a surface treatment technique similar to the above diffusion coating method.

Chromium plating is a technique for preventing Fe and Ni from coming into contact with hydrocarbons in a liquid by coating a problematic portion of the equipment surface with Cr. Cr is Fe
It will be understood from the use of steel containing 28% or more of Cr as described above, unlike Ni and Ni, it does not act catalytically on the precipitation of carbon due to the decomposition of hydrocarbons.

The coating of metal carbide by thermal spraying is also a technique for preventing contact between hydrocarbons and steel, similar to plating. Suitable carbides for this purpose are CrC, VC, NbC and the like.

The metal carbide is not only coated,
It is also possible to form and use this on the surface of steel. That is, it is a method in which a metal is diffused and permeated to bond carbon in steel to form a carbide thereof. This includes
It suffices to carry out a treatment in which the temperature is maintained at 850 to 1000 ° C. for a predetermined time in a salt bath containing SiO ₂ as a main component and containing salts of V, Nb, Cr or Ti.

[0018]

EFFECTS OF THE INVENTION By taking the measures according to the present invention, troubles due to the coking phenomenon can be prevented in the process equipment handling hydrocarbons. As a result, the operating conditions of the process are not constrained to avoid coking and there is no need to add a sulfur compound as an anti-coking agent to the liquid or remove it later.
Needless to say, this is preferable from the viewpoint of maintenance and operation cost savings and safety.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view illustrating an example of a process apparatus in which the present invention is useful.

FIG. 2 is a similar cross-sectional view showing a situation in which a trouble caused by the caulking phenomenon has occurred in the portion of FIG.

FIG. 3 is a partial cross-sectional view showing another example of the process apparatus to which the present invention is useful, which is different from FIG. 1;

FIG. 4 is a sectional view similar to FIG. 2, showing a situation in which a trouble caused by a caulking phenomenon has occurred in the portion of FIG. 3.

Claims (6)

[Claims] 1. A process apparatus manufactured by using structural steel, which is operated under conditions in which a fluid containing a hydrocarbon flows and carbon deposits grow on the surface of the process apparatus. A method for preventing carbon deposition in a process apparatus, which comprises subjecting an unfavorable portion to any one of the following surface treatments: 1) Chromium plating, 2) Chromize treatment, calorizing treatment, siliconizing treatment and vulcanization treatment. Seed, 3) formation of a carbide layer of these metals by diffusion and penetration of V, Cr, Nb or Ti, or 4) film formation by thermal spraying of metal carbide. 2. A process apparatus manufactured by using structural steel, which is operated under conditions in which a fluid containing a hydrocarbon flows and carbon deposits grow on the surface, Process equipment in which carbon deposition is prevented by constructing an unfavorable part by any of the following materials: a) Steel containing 28% or more of Cr, b) Chrome-plated steel, c) Chromize treatment , Steel having one kind of surface treatment selected from calorizing treatment, siliconizing treatment and sulfurizing treatment, d) steel having a carbide layer of these metals formed on the surface thereof by diffusion and permeation of V, Cr, Nb or Ti, or e) Steel having a coating formed by thermal spraying of metal carbide. 3. The apparatus according to claim 2, which is a component of a plant that handles a dehydrogenation reaction at a temperature of 500 ° C. or more and a hydrogen partial pressure of 2 atm. Or less. 4. The apparatus according to claim 2, which is a constituent part of a plant that handles a decomposition reaction at a temperature of 450 ° C. or more and a hydrogen partial pressure of 1 atm. Or less. 5. The apparatus according to claim 2, which is a component of a plant that handles a catalytic reforming reaction at a temperature of 450 ° C. or more and a hydrogen partial pressure of 5 atm. Or less. 6. The apparatus according to claim 2, which is a component of a plant that handles a steam reforming reaction at a temperature of 450 ° C. and a hydrogen partial pressure of 1 atm. Or less.