JPS6317117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is suitable for use in cases where hydrocarbons or derivatives thereof are thermally decomposed in the presence or absence of water vapor, such as in ethylene production equipment and delayed coking equipment, or in cases where hydrocarbons or derivatives thereof are thermally decomposed in the presence or absence of water vapor, such as in ethylene production equipment and delayed coking equipment, or in synthesis gas production equipment, etc. The present invention relates to a device that can prevent carbon deposition when handling fluid containing carbon monoxide at high temperatures.

These devices are made of materials such as austenitic steel, ferritic steel, austenitic-ferritic dual-phase stainless steel, and low-alloy steel.
Carbon precipitates in parts that are exposed to high temperatures during operation, such as piping (especially heating furnace tubes), tower tanks, etc., which often causes operational problems such as increased ΔP and decreased heating efficiency, resulting in so-called decoking. It was necessary to do this frequently. Such operations disturb the steady operation of the apparatus and are a factor in deteriorating the economic efficiency of the process, and also bring about various disadvantages to the constituent materials of the apparatus.

Conventionally, as an attempt to prevent carbon precipitation in these devices, for example, it has been reported that carbon precipitation can be suppressed to some extent by adding a small amount of H ₂ S to the raw material fluid in ethylene production equipment (BLCrynes, L.
Ind.Eng.Chem.Proc.−Design by F.Albright
and Development. 8 [1] (1969) 25).
Although it has been carried out in some cases, the actual situation is that it has not been sufficiently effective because the inside of the cracking tube in ethylene production equipment and the like is an oxidizing atmosphere to begin with. Furthermore, as part of research into materials themselves that can prevent carbon deposition, laboratory-scale coking tests using light hydrocarbons have been conducted on various pure metals.
As far as the present inventor is aware, there is currently no application to actual equipment.

In an actual device, the inner surface of the device as described above, which is the object of the present invention, is covered with oxide scale.
Preprint for the 5th
International Congress on Catalysis,
Amsterdam (1972)), carbon deposition is caused by transition metal elements such as Fe and Ni contained in the constituent materials of the device, and these atoms always float to the surface of the carbon deposit layer. It is said that precipitation continues as a result of its appearance. In fact, according to studies conducted by the present inventors, transition metal elements such as Fe and Ni are detected when coke deposited on the inner surface of equipment members are analyzed, and carbon precipitation occurs through the transition of Fe, Ni, etc. through the oxide layer on the surface. It is presumed that this is due to the fact that the metal element is diffused and supplied.

An object of the present invention is to provide a device that can prevent or significantly reduce carbon deposition in a device that processes fluids containing hydrocarbons, derivatives thereof, or carbon monoxide at high temperatures. It is a solution to the purpose.

According to the present invention, a steel material containing 1 to 10% by weight of Al in any one of an austenitic steel material, a ferritic steel material, an austenite-ferrite dual phase steel material, and a low alloy metal containing 5% or more of Cr. Al-containing oxide film is formed, and the surface is oxidized in advance by an oxidizing gas before the start of treatment, or the surface is exposed by a treatment medium or diluent fluid (hereinafter referred to as the treatment object), such as water vapor, immediately after the start of treatment, and an oxide film containing Al is formed. A carbon precipitation prevention treatment device is provided.

The process equipment targeted by the present invention processes naphtha, ethane, gas oil, etc. together with steam at 750 to 900℃.
This is a so-called ethylene production equipment whose purpose is to produce light unsaturated hydrocarbons such as ethylene by passing it through a cracking tube installed in a heating furnace at a temperature (fluid temperature) of Delayed coking equipment that heats up in advance and cokes in a coke drum, Ethylbenzene dehydrogenation equipment that produces styrene by reacting ethylbenzene with steam at high temperatures, Dealkylation equipment for various alkylbenzenes, Raw material carbonization Hydrocarbons or their derivatives, or hydrogen Conventionally, carbon precipitation (especially Examples include devices that include parts where problems such as so-called fouling, in which carbonaceous substances precipitate in a heat exchanger (same in the following specification) are problematic.

Components in these devices where carbon precipitation is a problem when exposed to high temperatures include austenitic steel, ferritic steel, austenite-ferrite dual phase steel, and low-alloy steel containing 5% or more of Cr. Use steel containing 1 to 10% by weight. These steel materials are required to have appropriate heat resistance, strength, weldability, etc. in the process equipment targeted by the present invention, and appropriate steel materials are used depending on the applied process. For example, in ethylene production equipment, SCH22 (HK-40) or
A steel material containing Al in austenitic heat-resistant cast steel such as 25% Cr-35% Ni-0.5% C cast steel (HP) is used. In addition, they can be used not only as a single unit but also as a coating on the inner wall surface of a member.

If the Al content is less than 1% by weight, an oxide film that can prevent carbon precipitation will not be formed;
If it exceeds % by weight, high temperature strength, castability, weldability, etc. will deteriorate. Preferably, Al is contained in an amount of 4.5 to 6.5% by weight. In low alloy steel containing Cr, the Cr content is 5
Even if Al is contained in the steel material at less than 5% by weight, there is no noticeable effect on suppressing carbon precipitation, so if the Cr content is 5.
% or more.

The manner in which the oxide film containing Al is formed on the inner wall surface of the device differs depending on the applied process. In other words, if the process system contains water vapor as a diluting medium or heat medium, such as in the cracking tube of an ethylene production plant or in the dehydrogenation reaction of ethylbenzene, and an oxidized state is reached at the processing temperature or reaction temperature, the material to be processed may itself be oxidized. After the start of treatment or reaction, Al on the inner wall surface of the member is oxidized and a dense film is formed, without requiring any treatment. If the material to be treated does not have or has little oxidizing property to the steel material at the treatment temperature or reaction temperature, the inner wall surface should be oxidized by an appropriate means before introducing the material into the process system, or the surface of the inner wall should be oxidized. Measures are taken to allow an appropriate amount of aqueous fluid to flow through the process or before the start of the reaction to form an oxide film containing Al.

Thus, in the present invention, an oxide film containing Al is formed on the surface of the component where carbon precipitation conventionally occurs, and this film is extremely dense and robust, and once formed on the steel surface, it is physically and chemically stable. Various transition metals in the steel material that have properties and induce carbon precipitation are covered by the oxide film and do not permeate onto the surface of the film, and carbon precipitation is prevented or significantly reduced.

Therefore, according to the present invention, periodic decoking operations are not required and continuous operation is guaranteed, thereby stabilizing product quality. In addition, unnecessary equipment and utilities for decoking are omitted, and it is expected that equipment costs and decoking costs will be significantly reduced. Furthermore, no increase in ΔP occurs and healthy operation is guaranteed. Furthermore, in heating furnaces, etc., the heat insulation effect of precipitated carbon on the inner surface of the tube is eliminated, so it is possible to ensure heating of the internal fluid without gradually increasing the temperature on the outer surface of the tube, and it is also possible to save fuel. become.

Examples of the present invention are shown below.

Example 1 Base steel type: SCH22 (HK-40), 25% Cr-
35%Ni-0.5%C centrifugal cast steel (HP), an austenitic steel of SUS304, was added with Al in a range of 1 to 10% by weight, vacuum melted, and ingot formed in a mold to prepare a test piece. SCH22 and centrifugally cast steel (HP) without Al added were cut from commercially available centrifugally cast pipes, and SUS304 was cut from commercially available plate material. Each specimen has dimensions of 4 x 10 x 45 mm, #120
The surface was finished with emery paper, and pretreatment was performed by oxidizing it in the air at 1100°C for 1 hour and then cooling it in air. Each of these test pieces was placed in the center of a reaction tube of a coking experimental apparatus, and subjected to a test in which raw material gas and carrier gas were introduced from one end under the conditions shown below and flowed out from the other end.

Raw material gas Benzene 0.52lig.cc/hr (room temperature) Carrier gas Ar 16.0Nml/min Temperature and time 700°C x 3hr The results are shown in Figure 1. The 〇 mark in the diagram is
SCH22, × mark is 25%Cr-35%Ni-0.5%C cast steel,
The △ mark indicates the result for SUS304. The amount of carbon deposited was calculated by dividing the weight difference between the test piece before and after the test by the surface area.

From FIG. 1, it can be seen that when Al is contained in an amount of 1% by weight, the amount of carbon precipitation is drastically reduced, and when Al is about 4% by weight, carbon precipitation hardly occurs.

Example 2 As the base steel type, the Al content was 1 to 10 as in Example 1 to ferritic steel types such as SUS405 and STPA25.
The test pieces were prepared by varying the weight percentage within a range.
Al-free test pieces were cut from commercially available plate materials for SUS405, and from commercially available pipe materials for STPA25. These test pieces were pretreated in the same manner as in Example 1, and then tested under the same conditions in the same apparatus.

The results are shown in FIG. The □ mark in the diagram is
SUS405, ◇ indicates STPA25.

From FIG. 2, it can be seen that carbon precipitation is significantly reduced by containing Al, and almost no precipitation is observed in SUS405 at 5% Al and in STPA25 at 10% Al.

In addition, STPA26 (7Cr−1/2
Similar tests were conducted on Mo).
It showed the same tendency as STPA25 (5Cr−1/2Mo), but STPA24 (2 1/4Cr−
1Mo), even when the Al content was 10% by weight, no significant effect of suppressing carbon precipitation could be obtained.

[Brief explanation of the drawing]

FIG. 1 shows the results of a carbon precipitation test on austenitic steel types, and is a diagram showing the relationship between the amount of carbon precipitation and the added Al content. FIG. 2 shows the results of a carbon precipitation test on ferritic steel types, and is a diagram showing the relationship between the amount of carbon precipitation and the added Al content.

Claims (1)

[Scope of Claims] 1. An apparatus for treating a fluid containing hydrocarbons or derivatives thereof, or carbon monoxide at high temperatures,
At least 1 to 10 parts exposed to high temperatures are made of steel.
1. A treatment device for preventing carbon precipitation, comprising a member in which % by weight of Al is present and an oxide film containing Al is formed on the surface during treatment. 2. Carbon precipitation prevention treatment according to claim 1, wherein the steel material is any one of an austenitic steel material, a ferritic steel material, an austenite-ferrite dual phase steel material, and a low alloy steel containing 5% or more of Cr. Device. 3. The carbon precipitation prevention treatment apparatus according to claim 1 or 2, wherein the oxide film is formed with an oxidizing gas before the start of the treatment. 4. The carbon precipitation prevention treatment apparatus according to claim 1 or 2, wherein the oxide film is formed by the object to be treated immediately after the start of treatment.