Method for treating high-temperature alloy furnace tube and high-temperature alloy furnace tube
By forming a dense oxidation protective layer on the surface of the high-temperature alloy furnace tube and treating the furnace tube with a low oxygen partial pressure atmosphere, the problems of coking and carburizing of the furnace tube during ethylene cracking are solved, and the service life and coke cleaning cycle of the furnace tube are extended .
Patent Information
- Application Number
- CN202411525594.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-30
- Publication Date
- 2025-02-07
AI Technical Summary
During the ethylene cracking process, the furnace tube is prone to coking and carburizing, resulting in a shortening of the operating cycle, a decrease in ethylene yield and a decrease in production efficiency.
By forming a dense and stable oxidative protective layer on the surface of the high-temperature alloy furnace tube, the furnace tube is treated with a low-oxygen partial pressure atmosphere (containing hydrogen and 0.17-2% water vapor) to form chromium oxide and manganese oxide as The main oxidation protective layer slows down catalytic coking and carburizing.
The formed oxidative protective layer is firmly combined with the furnace tube, which can effectively inhibit catalytic coking, reduce carburizing, and extend the coking cycle and service life.
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of ethylene cracking, in particular to a method for treating a high-temperature alloy furnace tube and the high-temperature alloy furnace tube. Background Art
[0002] Ethylene is one of the most important basic raw materials in the petrochemical industry. At present, the main method for producing ethylene is tubular furnace cracking technology, which has been widely used worldwide. However, an unavoidable problem in the production process of ethylene is the coking and carburization of the cracking unit during service. Coking during the cracking process will reduce the inner diameter of the furnace tube, increase the pressure drop in the tube, and shorten the operation cycle of the cracking furnace; when the tube wall temperature reaches the allowable limit or the pressure drop reaches a certain level, the furnace must be stopped for decoking. Coking on the inner wall of the furnace tube hinders the normal progress of the cracking reaction, affects the ethylene yield, and reduces production efficiency. In addition, high temperature easily causes carburization of the inner wall of the furnace tube, resulting in weakened performance of the furnace tube material.
[0003] At present, in order to ensure the high-temperature strength of ethylene cracking furnace tubes, the materials used are mainly composed of elements such as Fe, Cr, and Ni, and also contain trace elements such as Mn, Si, Al, Nb, Ti, W, and Mo. Studies have shown that at high temperatures, Fe and Ni elements have a significant catalytic effect on the coking of hydrocarbons on the surface of FeCrNi alloy cracking furnace tubes. In addition, heavier hydrocarbon raw materials are also accompanied by a large amount of free radical coking and condensation coking during the cracking process. In existing literature, in order to reduce catalytic coking, researchers have tried to use a variety of technologies to prepare inert coatings on the inner wall surface of cracking furnace tubes to reduce the contact between hydrocarbons and Fe and Ni active components on the inner surface of cracking furnace tubes. On the other hand, researchers also use measures such as adding components inside the cracking furnace tube, reducing the pressure in the cracking tube, reducing the residence time, lowering the cracking temperature, optimizing the cracking raw materials, and adding coking inhibitors to reduce free radical coking and condensation coking during the cracking process.
[0004] NOVA of Canada proposed a technical solution of using a mixture of hydrogen and water vapor as the treatment atmosphere, and applied for a number of patents, including US5630887, US6824883, US7156979, etc. However, the weight fraction of water vapor in the atmosphere used by NOVA is 0.5-1.5%, which is equivalent to a water vapor volume fraction of 0.056%-0.169%. In the technical solution disclosed in the above patents, the water vapor content in the atmosphere used is low, and the performance of the prepared film is poor. Summary of the invention
[0005] In order to overcome the above-mentioned defects existing in the prior art, the present invention provides a method for treating a high-temperature alloy furnace tube and a high-temperature alloy furnace tube, by treating the surface of the furnace tube, a dense and stable surface oxidation protective layer is obtained, catalytic coking is inhibited or slowed down, the carburization degree of the furnace tube is reduced, and the service life of the furnace tube is extended.
[0006] The object of the present invention is also to provide a high-temperature alloy furnace tube obtained by the above method, which has a surface protective layer with good performance, can inhibit or slow down catalytic coking, and has a long coking cycle and service life.
[0007] The technical solution adopted by the present invention to solve its technical problem is: a method for treating a high-temperature alloy furnace tube and a high-temperature alloy furnace tube, which comprises the following steps: controlling the pressure of a low-oxygen partial pressure gas to be greater than 0 and less than or equal to 3 atmospheres, passing the gas into an atmosphere furnace equipped with a high-temperature alloy furnace tube, heating the gas to 650-1050 degrees Celsius, and heat-insulating the gas for 10-70 hours, so that an oxidation protective layer is formed on the surface of the high-temperature alloy furnace tube, and thus the treated high-temperature alloy furnace tube is obtained.
[0008] In the technical solution of the present invention, a reducing atmosphere is used as a treatment atmosphere to treat a high-temperature alloy furnace tube. The low oxygen partial pressure gas used includes hydrogen and water vapor accounting for 0.17-2% of the total volume fraction of the low oxygen partial pressure gas; the pressure of the low oxygen partial pressure gas can be controlled to be 0-3 atmospheres (in actual operation, it is controlled to be greater than 0 and less than or equal to 3 atmospheres), the treatment temperature can be controlled to be about 650-1050 degrees Celsius, and the insulation treatment time can be controlled to be about 10-70 hours; in the actual treatment process, the gas pressure is preferably controlled at about normal pressure.
[0009] In the low oxygen partial pressure gas, the volume fraction of water vapor can be controlled to be 0.25-1.9%. According to a specific embodiment of the present invention, the low oxygen partial pressure gas can also include an inactive gas, which includes one or more of carbon dioxide, nitrogen and argon, and the inactive gas can account for 0-90% of the volume fraction of the low oxygen partial pressure gas.
[0010] The atmosphere furnace used in the present invention can be a protective atmosphere treatment furnace commonly used in the art, such as a tube furnace, a pit furnace, an atmosphere box furnace, and the like.
[0011] In terms of weight percentage, the composition of the high-temperature alloy furnace tube treated by the present invention may include: 15%-50% chromium, 17-50% nickel, 0.2-3% manganese, 0-3% silicon, 0-5% trace elements (including one or more of niobium, carbon, titanium, tungsten, aluminum, rare earth and trace elements), and the balance is iron. Among them, trace elements refer to elements such as phosphorus and sulfur that are inevitably contained in high-temperature alloys.
[0012] The beneficial effects of the present invention are:
[0013] 1. This invention solves the high temperature coking and carburization problems of furnace tubes by forming a protective layer inside the high temperature alloy furnace tubes, that is, by treating the furnace tubes under a certain atmosphere, an oxidation protective layer is generated on the surface of the furnace tubes in an in-situ growth manner. The obtained oxidation protective layer has a strong bonding force with the furnace tubes and is suitable for long-term use.
[0014] 2 Among the components of the high-temperature alloy furnace tube, chromium, manganese and silicon have a high oxidation tendency and can be oxidized in the atmosphere used in the present invention; while the iron and nickel elements in the furnace tube have a low oxidation tendency and are not oxidized in the atmosphere used in the present invention, or only a very small amount is oxidized. As a result, the surface of the high-temperature alloy furnace tube forms an oxidation protective layer mainly composed of chromium oxide and manganese oxide through in-situ growth, while the iron and nickel elements are covered, and only a small amount exists in the surface oxidation protective layer. In actual use, most of the iron and nickel elements are no longer in direct contact with the atmosphere in the furnace tube. Analysis shows that the components of the obtained surface layer (oxidation protective layer) mainly include oxides and metals. Among them, the structure of the oxide can be expressed as MnxCr3-xO4, with an x value of 0.4-1.6, and the metal mainly includes iron and nickel. In the components of the surface layer, the molar fraction of oxides is about 70-99.6%, the molar fraction of iron is about 0.2-15%, and the molar fraction of nickel is about 0.2-15%. Obviously, this dense and firmly bonded surface oxide protective layer helps to inhibit coking on the inner wall of the furnace tube and slow down the carbonization tendency.
[0015] 3 In the process involved in the present invention, there are multiple key factors, among which the most influential are water vapor content and temperature, among which water vapor content directly determines the oxygen partial pressure value. After research, in order to achieve the best film performance, there is a corresponding relationship between water vapor content and temperature. The most suitable water vapor content decreases with the increase of temperature. In other words, a lower water vapor content should be used at high temperature. However, on the other hand, the temperature itself must be within a certain range. Too low a temperature will make the film grow too slowly, and too high a temperature will reduce the density of the film and seriously damage the mechanical properties of the substrate. After the research of the present invention, it is concluded that 650-1000 degrees Celsius is the best process temperature range, and the relatively suitable water vapor content range in the low oxygen partial pressure gas corresponding to this process is 0.17-2% by volume. When the water vapor content is between 0.17%-0.25% and between 1.9%-2%, a relatively satisfactory effect can be obtained; and the more preferred water vapor content range of the present invention is 0.25-1.9% by volume. The effect obtained by treating with a low oxygen partial pressure gas atmosphere containing water vapor beyond the content range provided by the present invention is relatively poor.
[0016] 4 The method for treating high-temperature alloy furnace tubes provided by the present invention is used to treat furnace tubes of hydrocarbon cracking furnaces, etc., so that a dense and stable oxidation protection layer can be formed on the surface of the furnace tube, and the oxidation protection layer is formed by in-situ growth on the surface of the furnace tube, and has a strong bonding force with the furnace tube, which can meet the requirements of long-term use; the treated high-temperature alloy furnace tube can well inhibit or slow down the catalytic coking phenomenon, reduce the carburization degree of the furnace tube, and extend the coke cleaning cycle and service life of the furnace tube. The method for treating high-temperature alloy furnace tubes provided by the present invention is suitable for treating the coking of the inner wall of the furnace tube and the carburization problem of the furnace tube itself in the process of inhibiting and slowing down hydrocarbon cracking, and in similar chemical processes for treating carbon-containing atmospheres. DETAILED DESCRIPTION
[0017] The method for treating a high-temperature alloy furnace tube provided by the present invention may include the following specific steps:
[0018] The furnace tube is subjected to atmosphere treatment using a low oxygen partial pressure gas, wherein the low oxygen partial pressure gas includes H2 and H2O accounting for 0.17-2% of the total volume fraction;
[0019] Low oxygen partial pressure gas may be mixed with inactive gas with a volume fraction not exceeding 90%, such as carbon dioxide, nitrogen and argon;
[0020] The pressure of the low oxygen partial pressure gas is controlled to be about 0-3 atmospheres, and the low oxygen partial pressure gas is introduced into the atmosphere furnace;
[0021] The furnace tube temperature is raised to 650-1050 degrees Celsius, preferably 700-1000 degrees Celsius;
[0022] The heat preservation treatment is carried out for 10-70 hours, and the preferred heat preservation treatment time is 25-40 hours;
[0023] An oxidation protective layer is formed on the surface (mainly the inner surface) of the high-temperature alloy furnace tube to obtain a treated high-temperature alloy furnace tube.
[0024] Example 1
[0025] The high temperature alloy HP40-Nb furnace tube was cut into square specimens with a side length of 10 mm and a thickness of 4 mm. The material composition of the specimens was analyzed by X-ray energy dispersive spectrometer (EDS), where the Cr content was 24.1, the Ni content was 35.9, the Fe content was 33, the Mn content was 1.2, the Si content was 0.8, the Nb content was 1.2, the O content was 0, and the other contents were 0.8.
[0026] The data show that there are a lot of iron and nickel elements on the surface of the high-temperature alloy furnace tube, which is the reason for catalytic coking. Two test pieces were placed in two tubular furnaces, and hydrogen (containing 0.169% and 0.25% water vapor by volume, respectively) was introduced. The gas pressure was controlled to 1.01 atmospheres. After the atmosphere furnace was heated to 900 degrees Celsius, the heat was kept for 30 hours, and the test pieces were taken out after the furnace cooled.
[0027] The surface composition of the treated specimens was tested using an X-ray photoelectron spectroscopy (XPS).
[0028] 1. The Cr content in 0.169% water vapor treatment is 26.93, the Ni content is 13.3, the Fe content is 9.9, the Mn content is 8.09, the Si content is 0.07, the Nb content is 0.08, the O content is 40.32, and the other contents are 0.87. The thickness of the film (oxidation protection layer) is calculated to be 0.4 μm using the energy spectrum (EDS) values at different acceleration voltages;
[0029] 2. The Cr content in the 0.25% water vapor treatment is 27.89, the Ni content is 11.21, the Fe content is 8.63, the Mn content is 9.01, the Si content is 0.07, the Nb content is 0.1, the O content is 40.82, and the other contents are 0.9. The thickness of the film (oxidation protection layer) calculated by the energy spectrum (EDS) values at different acceleration voltages is 1.12μm
[0030] From the data, we can see that the film (oxidation protection layer) prepared by treating with low oxygen partial pressure gas with 0.25% water vapor content has higher chromium and manganese content and lower iron and nickel content on the surface. More importantly, the film prepared by treating with low oxygen partial pressure gas with 0.25% water vapor content is more than 1 times thicker than the film prepared by treating with low oxygen partial pressure gas with 0.169% water vapor content, and the bonding strength is also higher.
[0031] Example 2
[0032] The high-temperature alloy HP40-Nb furnace tube was cut into square specimens with a side length of 10 mm and a thickness of 4 mm.
[0033] The material composition of the test piece was analyzed by X-ray energy dispersive spectrometer (EDS), wherein the Cr content was 24.1, the Ni content was 35.9, the Fe content was 33, the Mn content was 1.2, the Si content was 0.8, the Nb content was 1.2, the O content was 0, and the other contents were 0.8.
[0034] The test piece was placed in a tube furnace, and hydrogen containing 1.9% water vapor by volume was introduced, and the gas pressure was 1.01 atmospheres. After the atmosphere furnace was heated to 1000 degrees Celsius, the temperature was kept for 40 hours, and the test piece was taken out after the furnace cooled.
[0035] The surface composition of the treated specimens was tested using an X-ray photoelectron spectroscopy (XPS).
[0036] The Cr content is 30.15, the Ni content is 2.96, the Fe content is 3.13, the Mn content is 14.66, the Si content is 0.07, the Nb content is 0.03, the O content is 48.86, and the other contents are 0.85. The energy spectrum (EDS) values of different accelerating voltages are used to calculate the thickness of the film (oxidation protection layer) to be 6.9μm. It is found that the oxidation protection layer is mainly composed of elements such as manganese, chromium, oxygen, iron and nickel, among which the iron and nickel contents are much lower than before treatment.
[0037] Example 3
[0038] The high-temperature alloy HP40-Nb furnace tube was cut into square specimens with a side length of 10 mm and a thickness of 4 mm.
[0039] The material composition of the test piece was analyzed by X-ray energy dispersive spectrometer (EDS), wherein the Cr content was 24.1, the Ni content was 35.9, the Fe content was 33, the Mn content was 1.2, the Si content was 0.8, the Nb content was 1.2, the O content was 0, and the other contents were 0.8.
[0040] The test piece was placed in a tubular furnace and a mixture of hydrogen and argon was introduced, wherein the volume fraction of argon was 75%, the volume fraction of water vapor in the mixture was 1.55%, and the gas pressure was 1.01 atmospheres. The atmosphere furnace was heated to 1000 degrees Celsius, and the temperature was kept for 45 hours. After the furnace cooled, the test piece was taken out.
[0041] The surface composition of the treated specimens was tested using an X-ray photoelectron spectroscopy (XPS).
[0042] The Cr content is 32.26, the Ni content is 3.88, the Fe content is 3.25, the Mn content is 13.19, the Si content is 0.01, the Nb content is 0, the O content is 45.82, and the other contents are 0.99. The thickness of the film (oxidation protection layer) is calculated to be 6.1 μm using energy spectrum (EDS) values at different acceleration voltages.
[0043] The surface (oxidation protective layer) composition of the test piece was tested using an X-ray photoelectron spectroscopy (XPS) and it was found that it was mainly composed of manganese, chromium and oxygen, and the content of iron and nickel was reduced to a very low level.
Claims
1. A method for treating a high temperature alloy furnace tube, comprising the following steps: The pressure of the low oxygen partial pressure gas is controlled to be greater than 0 and less than or equal to 3 atmospheres, and the gas is introduced into an atmosphere furnace equipped with a high temperature alloy furnace tube, and the temperature is raised to 650-1050 degrees Celsius, and the temperature is kept for 10-70 hours, so that an oxidation protective layer is formed on the surface of the high temperature alloy furnace tube, thereby obtaining a treated high temperature alloy furnace tube; The low oxygen partial pressure gas includes hydrogen and water vapor accounting for 0.17-2% of the volume fraction of the low oxygen partial pressure gas; the components of the high temperature alloy furnace tube include, by weight percentage: 15%-50% chromium, 17-50% nickel, 0.2-3% manganese, greater than 0% and less than or equal to 3% silicon, greater than 0% and less than or equal to 5% trace elements, and the balance is iron; the trace elements include one or more of niobium, carbon, titanium, tungsten, aluminum, rare earth and trace elements, and the trace elements refer to phosphorus and sulfur elements inevitably contained in high temperature alloys.
2. The method of claim 1, wherein: The low oxygen partial pressure gas also includes an inactive gas, which includes one or more of carbon dioxide, nitrogen and argon. The volume fraction of the low oxygen partial pressure gas in the inactive gas is no more than 90%.
3. The method of claim 1, wherein: The volume fraction of the water vapor is 0.25-1.9%.
4. A high temperature alloy furnace tube, characterized in that: An oxidation protection layer is formed on the surface of the high-temperature alloy furnace tube by in-situ growth, and the oxidation protection layer is formed after being treated by the method described in any one of claims 1 to 3.
5. The high temperature alloy furnace tube according to claim 4, wherein: The oxidation protection layer comprises oxides and metals.
6. The high temperature alloy furnace tube according to claim 5, wherein: The structure of the oxide is MnxCr3-xO4, the value of x is 0.6-1.4, and the metal includes iron and nickel.
7. The high temperature alloy furnace tube according to claim 6, wherein: Among the components of the oxidation protection layer, the molar fraction of the oxide is 70-99.6%, the molar fraction of the iron is 0.2-15%, and the molar fraction of the nickel is 0.2-15%.