Alloy furnace tube and method of treatment and use thereof

Abstract

The application relates to the field of ethylene cracking, and discloses an alloy furnace tube and a treatment method and application thereof. The method comprises the following steps: (1) performing first heat treatment on the alloy furnace tube in the presence of a reducing atmosphere to obtain a pretreated alloy furnace tube; and (2) performing second heat treatment on the pretreated alloy furnace tube in the presence of a low-oxygen partial pressure atmosphere to obtain an alloy furnace tube with an oxidation film on the inner surface; wherein the content of oxygen in the reducing atmosphere is 0 ppm; and the dew point of the low-oxygen partial pressure atmosphere is-40 DEG C to 40 DEG C. By performing heat treatment on the alloy furnace tube in the presence of the reducing atmosphere and the low-oxygen partial pressure atmosphere, a dense and stable oxidation film can be formed on the inner surface of the furnace tube, catalytic coking is inhibited or slowed down, the degree of carburization of the furnace tube is reduced, and the service life of the furnace tube is prolonged. The cracking furnace tube provided by the application for a hydrocarbon cracking device can adapt to various hydrocarbon raw materials, and the operation cycle of the cracking furnace is significantly prolonged compared with the prior art.

Description

Technical Field

[0001] This invention relates to the field of ethylene cracking, and more specifically, to an alloy furnace tube and its processing method and application. Background Technology

[0002] Ethylene is one of the most important basic raw materials in the petrochemical industry. Currently, the main method for producing ethylene is tubular furnace cracking technology, which is widely used worldwide. However, an unavoidable problem in ethylene production is coking and carburization of the cracking unit during operation. Coking during cracking reduces the inner diameter of the furnace tubes, increases the pressure drop inside the tubes, and shortens the operating 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 shut down for decoking. Coking on the inner wall of the furnace tubes hinders the normal progress of the cracking reaction, affects ethylene yield, reduces production efficiency, and at high temperatures, it easily promotes carburization on the inner wall of the furnace tubes, leading to a weakening of the furnace tube material properties.

[0003] Currently, to ensure the high-temperature strength of ethylene cracking furnace tubes, the materials used for the tubes are mainly composed of elements such as Fe, Cr, and Ni, while also containing trace elements such as Mn, Si, Al, Nb, Ti, W, and Mo. Existing research has 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. Therefore, "modifying" the surface state of the furnace tube by forming a protective coating layer on the inner surface, and covering the iron and nickel elements in the furnace tube alloy with other "inert" components to eliminate their catalytic coking effect, has become one of the important means to effectively inhibit coking in ethylene cracking furnace tubes.

[0004] There are two different methods for forming a protective layer on the inner surface of a pyrolysis furnace tube: one is to form a protective layer on the inner surface of the pyrolysis furnace tube through means such as thermal spraying, thermal sputtering, high-temperature sintering, chemical heat treatment, and chemical vapor deposition. The disadvantage of this method is that the protective layer is not firmly bonded to the furnace tube substrate and is easy to peel off. The other method is to generate an oxide protective layer in situ on the inner surface of the pyrolysis furnace tube through treatment in a specific atmosphere at a certain temperature. The advantage of this method is that the protective layer has a strong bond with the furnace tube substrate and is not easy to peel off.

[0005] NOVA Chemicals of Canada proposed a technical solution to obtain a chromium-manganese spinel oxide film on the inner surface of pyrolysis furnace tubes under low oxygen partial pressure using a mixture of hydrogen and water vapor as the processing atmosphere. They have applied for a number of patents based on this solution, including US5630887A, US6436202B1, US6824883B1, US7156979B2, and US7488392B2. However, this technical solution still cannot effectively solve the problems of coking and carburization in high-temperature alloy furnace tubes. Summary of the Invention

[0006] To address the technical challenges of alloy coking and carburization caused by the catalytic effect of iron and nickel in alloy materials at high temperatures, this invention provides an alloy furnace tube, its treatment method, and its application. By heat-treating the alloy furnace tube in the presence of a reducing atmosphere and a low oxygen partial pressure atmosphere, a dense and stable oxide film can be formed on the inner surface of the furnace tube, inhibiting or slowing down catalytic coking, reducing the degree of carburization, and extending the service life of the furnace tube. The cracking furnace tube provided by this invention, applicable to hydrocarbon cracking units, can adapt to various hydrocarbon feedstocks, significantly extending the operating cycle of the cracking furnace compared to existing technologies.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for processing alloy furnace tubes, characterized in that the method comprises:

[0008] (1) The alloy furnace tube is subjected to a first heat treatment in the presence of a reducing atmosphere to obtain a pretreated alloy furnace tube;

[0009] (2) The pretreated alloy furnace tube is subjected to a second heat treatment in the presence of a low oxygen partial pressure atmosphere to obtain an alloy furnace tube with an oxide film on the inner surface.

[0010] The oxygen content in the reducing atmosphere is 0 ppm; the dew point of the low oxygen partial pressure atmosphere is -40°C to 40°C.

[0011] A second aspect of the present invention provides an alloy furnace tube obtained by the above method.

[0012] A third aspect of the present invention provides an application of the above-mentioned alloy furnace tube in the thermal cracking of petroleum hydrocarbons.

[0013] Through the above technical solution, the alloy furnace tube, its processing method, and its application provided by the present invention achieve the following beneficial effects:

[0014] This invention solves the problems of coking and carburizing in alloy furnace tubes by forming an oxide film on the inner surface of the tubes. Specifically, the furnace tubes are heat-treated in a reducing atmosphere and a low oxygen partial pressure atmosphere in sequence, so that an oxide film is generated on the inner surface of the furnace tubes in an in-situ growth manner. The resulting oxide film has strong adhesion to the furnace tube substrate and is suitable for long-term use.

[0015] Furthermore, this invention employs dew point to achieve precise control of low oxygen partial pressure gas, thereby forming a dense and stable oxide film on the inner surface of the alloy furnace tube, significantly inhibiting or slowing down catalytic coking, reducing the degree of carburization in the furnace tube, and extending the service life of the furnace tube. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] The first aspect of the present invention provides a method for processing alloy furnace tubes, characterized in that the method comprises:

[0018] (1) The alloy furnace tube is subjected to a first heat treatment in the presence of a reducing atmosphere to obtain a pretreated alloy furnace tube;

[0019] (2) The pretreated alloy furnace tube is subjected to a second heat treatment in the presence of a low oxygen partial pressure atmosphere to obtain an alloy furnace tube with an oxide film on the inner surface.

[0020] The oxygen content in the reducing atmosphere is 0 ppm; the dew point of the low oxygen partial pressure atmosphere is -40°C to 40°C.

[0021] In this invention, the problems of coking and carburizing of the alloy furnace tube are solved by forming an oxide film on the inner surface of the furnace tube. Specifically, the furnace tube is heat-treated in a reducing atmosphere and a low oxygen partial pressure atmosphere in sequence, so that an oxide film is generated on the inner surface of the furnace tube in an in-situ growth manner. The obtained oxide film has strong adhesion to the furnace tube substrate and is suitable for long-term use.

[0022] Furthermore, in this invention, the oxide film is tightly bonded to the inner surface of the furnace tube, which can inhibit coking on the inner wall of the furnace tube, slow down the degree of carburization of the furnace tube, and extend the coking cycle and service life of the furnace tube.

[0023] During the manufacturing process of alloy furnace tubes, residues inevitably remain on the inner surface. These residues not only affect the performance of the furnace tubes during service but also hinder the formation of an anti-coking oxide film on the inner surface during subsequent processing. The high-temperature heat treatment of the alloy furnace tubes using the reducing atmosphere of this invention can thoroughly remove these residues from the inner surface and improve the dispersion properties of the metal on the inner surface, which is beneficial for the subsequent heat treatment in a low-oxygen partial pressure atmosphere to form a dense and stable anti-coking chromium-manganese spinel oxide film.

[0024] In this invention, the oxygen content of the reducing atmosphere being 0 ppm means that the reducing atmosphere does not contain oxygen or is a gas that can generate oxygen.

[0025] In this invention, the oxygen content in the reducing atmosphere is measured using a trace oxygen analyzer.

[0026] According to the present invention, the reducing atmosphere comprises hydrogen and at least one gas selected from nitrogen, helium and argon.

[0027] According to the present invention, the hydrogen content is 20-80 vol%, preferably 40-80 vol%, based on the total volume of the reducing atmosphere.

[0028] In this invention, by controlling the hydrogen content in the reducing atmosphere to meet the above-mentioned range, it is possible to thoroughly remove residues from the inner surface of the furnace tube, improve the dispersion performance of metals on the inner surface of the furnace tube, and facilitate the formation of a dense and stable oxide film in subsequent low oxygen partial pressure atmosphere treatment.

[0029] Furthermore, based on the total volume of the reducing atmosphere, the hydrogen content is 40-80 vol%.

[0030] In this invention, the low oxygen partial pressure gas with the aforementioned specific dew point results in a low oxygen partial pressure in the gas, thus the oxidation process is very slow, which is beneficial for forming a dense oxide film on the material surface. Oxygen partial pressure refers to the pressure occupied by oxygen in the atmosphere. Under a low oxygen partial pressure atmosphere, the oxygen in the atmosphere mainly comes from the oxygen produced by the decomposition of oxygen-containing compounds (such as H2O).

[0031] As those skilled in the art know, a low-oxygen partial pressure atmosphere is difficult to obtain, both in engineering and in the laboratory, and achieving a stable low-oxygen partial pressure atmosphere through flow control devices is extremely difficult and challenging. Through theoretical analysis and numerous experiments, the inventors of this invention ingeniously discovered that accurately controlling the low-oxygen partial pressure atmosphere can be achieved by controlling the dew point of the mixed gas.

[0032] In this invention, the dew point refers to the temperature at which saturated water vapor in the air begins to condense and form dew. At 100% relative humidity, the temperature of the surrounding environment is the dew point temperature.

[0033] In this invention, the method further includes the step of determining the dew point of the low oxygen partial pressure gas.

[0034] In this invention, the method further includes testing the dew point of the low-oxygen partial pressure gas (using a commercially available dew point meter) before treating the pretreated alloy furnace tube with the low-oxygen partial pressure gas, so that the low-oxygen partial pressure gas has the dew point defined by this invention.

[0035] Furthermore, the method also includes the step of monitoring the dew point of the low-oxygen partial pressure gas in real time using a commercially available dew point meter during the second heat treatment reaction using a low-oxygen partial pressure gas.

[0036] Furthermore, the dew point of the low-oxygen partial pressure gas is 0°C to 5°C.

[0037] According to the present invention, the low oxygen partial pressure atmosphere is a gaseous mixture of water vapor and hydrogen.

[0038] According to the present invention, the conditions for the first heat treatment reaction include: a reaction temperature of 850-1100°C and a reaction time of 10 hours or more.

[0039] Furthermore, the conditions for the first heat treatment reaction include: a reaction temperature of 900-1000℃ and a reaction time of 10-40 hours.

[0040] In this invention, in the first heat treatment reaction, the flow rate of the reducing atmosphere is 100-800 ml / min, preferably 200-600 ml / min.

[0041] In this invention, by controlling the flow rate of the reducing atmosphere to meet the above-mentioned range, it is possible to thoroughly remove residues from the inner surface of the furnace tube, improve the dispersion performance of metals on the inner surface of the furnace tube, and facilitate the formation of a dense and stable oxide film in subsequent low-oxygen partial pressure atmosphere treatment.

[0042] According to the present invention, the conditions for the second heat treatment reaction include: a reaction temperature of 850-1100°C and a reaction time of 10 hours or more.

[0043] Furthermore, the conditions for the second heat treatment reaction include: a reaction temperature of 900-1000℃ and a reaction time of 10-40 hours.

[0044] In this invention, in the second heat treatment reaction, the flow rate of the low oxygen partial pressure atmosphere is 100-800 ml / min, preferably 200-600 ml / min.

[0045] In this invention, by controlling the flow rate of the low-oxygen partial pressure atmosphere to meet the above-mentioned range, the effect of forming a dense and stable oxide film through low-oxygen partial pressure atmosphere treatment can be achieved.

[0046] In this invention, the conditions for the first heat treatment may be the same as or different from the conditions for the second heat treatment.

[0047] According to the present invention, the oxide film comprises chromium manganese oxide and a metal element, wherein the metal element comprises iron and / or nickel.

[0048] According to the present invention, the composition of the chromium manganese oxide is Mn x Cr 3-x O4, x value is 0.5-2.

[0049] According to the present invention, the dew point of the low oxygen partial pressure atmosphere and the content of metal elements in the oxide film on the inner surface of the alloy furnace tube satisfy the following relationship:

[0050] (W1-W2) / W1=aT 2+bT+c Formula I;

[0051] In Equation I, -0.0029 ≤ a ≤ -0.0001, 0.0013 ≤ b ≤ 0.0274, 0.8126 ≤ c ≤ 0.8508, R 2 ≥0.9582;

[0052] Wherein, W1 is the total content of iron and nickel in the alloy furnace tube before the first heat treatment, wt%; W2 is the total content of metal elements in the oxide film on the inner surface of the alloy furnace tube after the second heat treatment, wt%; and T is the dew point of the low oxygen partial pressure atmosphere, ℃.

[0053] In this invention, the alloy furnace tube is heat-treated sequentially in a reducing atmosphere and a low-oxygen partial pressure atmosphere. By controlling the relationship between the dew point of the low-oxygen partial pressure gas and the content of metal elements in the oxide film on the inner surface of the alloy furnace tube, it is possible to further ensure that a dense and stable oxide film is formed on the inner surface of the alloy furnace tube through in-situ growth. The obtained oxide film is firmly bonded to the furnace tube substrate, which can significantly inhibit or reduce catalytic coking, reduce the degree of carburization of the equipment, and extend the service life of the equipment.

[0054] In this invention, the content of metal elements in the alloy furnace tube before treatment and the content of metal elements in the oxide film on the inner surface of the alloy furnace tube after treatment are determined by X-ray energy dispersive spectroscopy (EDS).

[0055] According to the present invention, the matrix composition of the alloy furnace tube, by weight percentage, includes: 12-50 wt% chromium, 20-50 wt% nickel, 0.2-3 wt% manganese, 1-3 wt% silicon, 0.1-0.75 wt% carbon, 0-5 wt% trace elements and 0-0.06 wt% ultra-trace elements, and 5-40 wt% iron.

[0056] According to the present invention, the trace element is selected from one or more of niobium, titanium, tungsten, molybdenum, aluminum and rare earth elements.

[0057] According to the present invention, the trace element is selected from sulfur and / or phosphorus.

[0058] According to the present invention, (W1-W2) / W1≥0.514.

[0059] In this invention, the content of metal elements including iron and nickel in the oxide film on the inner surface of the alloy furnace tube prepared by the above method is significantly reduced, thereby inhibiting catalytic coking in the thermal decomposition process of petroleum hydrocarbons, extending the operating cycle of the alloy furnace tube, and meeting the requirements for long-term use of the alloy furnace tube.

[0060] Furthermore, (W1-W2) / W1≥0.757.

[0061] In one specific embodiment of the present invention, based on the total volume of the reducing atmosphere, the hydrogen content is 40-80 vol%, and the dew point of the low oxygen partial pressure gas is 0°C to 5°C.

[0062] In Equation I, a = -0.0029, b = 0.0274, c = 0.8126, R 2 =1.

[0063] In this invention, the heat treatment reaction can be carried out in a conventional device capable of maintaining a certain atmosphere, for example, at least one of a tube furnace, a pit furnace, and an atmosphere box furnace.

[0064] A second aspect of the present invention provides an alloy furnace tube obtained by the above-described method.

[0065] According to the present invention, the inner surface of the alloy furnace tube contains an oxide film comprising chromium manganese oxide and metallic elements.

[0066] In this invention, the oxide film is formed by in-situ growth.

[0067] In this invention, the inventors discovered that the alloy furnace tube described herein can slow down coking and carburization because: chromium, manganese, and silicon elements in the high-temperature alloy furnace tube composition have a high oxidation tendency and can be oxidized under the stepwise heat treatment employed in this invention; while iron and nickel elements in the furnace tube alloy have a low oxidation tendency and are not oxidized or are oxidized only in very small amounts under the stepwise treatment employed in this invention. As a result, an oxide film mainly composed of chromium and manganese oxides is formed on the inner surface of the high-temperature alloy furnace tube through in-situ growth, while iron and nickel elements, which catalyze coking in the furnace tube, are covered; the oxide film is firmly bonded to the furnace tube substrate, which helps to inhibit coking on the inner wall of the furnace tube, slows down the degree of carburization, and extends the decoking cycle and service life of the furnace tube.

[0068] A third aspect of the present invention provides the application of the above-mentioned alloy furnace tube in the thermal cracking of petroleum hydrocarbons.

[0069] In this invention, the liquid feedstock used for pyrolysis is selected from at least one of naphtha, condensate oil, hydrocracking tail oil, and diesel oil.

[0070] In this invention, the liquid feedstock can be cracked using conventional cracking processes in the prior art.

[0071] The present invention will be described in detail below through embodiments. In the following embodiments,

[0072] The elemental composition of the furnace tubes was determined using X-ray energy dispersive spectroscopy (EDS).

[0073] The dew point of the low oxygen partial pressure atmosphere was measured using a commercially available dew point meter.

[0074] The oxygen content in the reducing atmosphere was measured using a trace oxygen analyzer.

[0075] The amount of coking on the furnace tubes was calculated by measuring the concentrations of CO and CO2 in the coking gas online using an infrared instrument and by measuring the volume of the coking gas online using a wet gas flow meter.

[0076] Example 1

[0077] The 35Cr45Ni pilot furnace tube was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The elemental composition of the furnace tube alloy (wt%) was: Cr: 34.15, Ni: 43.7, Mn: 1.15, Si: 1.23, C: 0.49, Fe: 18.08, Nb: 1.2.

[0078] (1) The furnace tube is subjected to a first heat treatment in a reducing atmosphere composed of H2 and N2 to obtain a pretreated alloy furnace tube. The oxygen content in the reducing atmosphere is 0 ppm, the volume percentage of H2 is 50 vol%, and the remainder is N2. The flow rate of the reducing atmosphere is 400 ml / min. The conditions for the first heat treatment are: treatment temperature is 950℃ and treatment time is 20 hours.

[0079] (2) The pretreated alloy furnace tube is subjected to a second heat treatment in a low oxygen partial pressure atmosphere composed of H2O and H2, wherein the dew point of the low oxygen partial pressure atmosphere is 5℃, the flow rate of the low oxygen partial pressure atmosphere is 400ml / min, and the conditions for the second heat treatment are: treatment temperature is 950℃ and treatment time is 30 hours.

[0080] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 7.55 wt%. The contents of iron and nickel are 2.79 wt% and 4.76 wt%, respectively. (W1-W2) / W1 = 0.878.

[0081] Hydrocarbon steam cracking was carried out in a small-scale pilot furnace tube after stepwise treatment. The cracking feedstock was naphtha, with the following properties: distillation range 33.4-162.8℃, specific gravity d 20 0.7358 g / ml; pyrolysis conditions: pyrolysis temperature 850℃, water-oil ratio 0.5. The coking amount of the furnace tube of the present invention is reduced by 95.28 wt% compared with the coking amount of the untreated 35Cr45Ni furnace tube in the prior art.

[0082] Example 2

[0083] The same small-scale test furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the dew point of the low oxygen partial pressure atmosphere was 3°C, and the other treatment conditions were the same as in Example 1.

[0084] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 8.10 wt%. The contents of iron and nickel elements are 3.01 wt% and 5.09 wt%, respectively. (W1-W2) / W1 = 0.869.

[0085] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 92.22 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0086] Example 3

[0087] The same small-scale furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the dew point of the low oxygen partial pressure atmosphere was 0°C, and the other treatment conditions were the same as in Example 1.

[0088] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 11.58 wt%. The contents of iron and nickel elements are 4.13 wt% and 7.45 wt%, respectively. (W1-W2) / W1=0.813.

[0089] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 90.15 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0090] Example 4

[0091] The same small-scale furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the dew point of the low oxygen partial pressure atmosphere was -40°C, and the other treatment conditions were the same as in Example 1.

[0092] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 24.33 wt%. The contents of iron and nickel elements are 8.68 wt% and 15.65 wt%, respectively. (W1-W2) / W1=0.606.

[0093] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 35.77 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0094] Example 5

[0095] The same small-scale test furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the dew point of the low oxygen partial pressure atmosphere was 40°C, and the other treatment conditions were the same as in Example 1.

[0096] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 18.09 wt%. The contents of iron and nickel elements are 6.70 wt% and 11.39 wt%, respectively. (W1-W2) / W1=0.707.

[0097] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 53.85 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0098] Example 6

[0099] The same small-scale test furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the conditions for the first heat treatment in reducing atmosphere were: treatment temperature of 850°C and treatment time of 30 hours, while other treatment conditions were the same as in Example 1.

[0100] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 20.37 wt%. The contents of iron and nickel are 7.28 wt% and 13.09 wt%, respectively. (W1-W2) / W1 = 0.670.

[0101] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 50.83 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0102] Example 7

[0103] The same small-scale test furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the conditions for the first heat treatment in reducing atmosphere were: treatment temperature of 1100℃ and treatment time of 15 hours, while other treatment conditions were the same as in Example 1.

[0104] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 12.48 wt%. The contents of iron and nickel elements are 4.62 wt% and 7.86 wt%, respectively. (W1-W2) / W1 = 0.798.

[0105] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 85.78 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0106] Example 8

[0107] The same small-scale test furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the conditions for the first heat treatment in reducing atmosphere were: treatment temperature of 750°C and treatment time of 40 hours, while other treatment conditions were the same as in Example 1.

[0108] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 40.25 wt%. The contents of iron and nickel are 14.37 wt% and 25.88 wt%, respectively. (W1-W2) / W1 = 0.348.

[0109] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 18.27 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0110] Comparative Example 1

[0111] The same small-scale furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the dew point of the low oxygen partial pressure atmosphere was 50°C, and the other treatment conditions were the same as in Example 1.

[0112] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 35.16 wt%. The contents of iron and nickel elements are 12.55 wt% and 22.61 wt%, respectively. (W1-W2) / W1 = 0.431.

[0113] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 20.75% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0114] Comparative Example 2

[0115] The same small-scale test furnace tube as in Example 1 was subjected to stepwise heat treatment in reducing atmosphere and low oxygen partial pressure atmosphere. The difference was that the dew point of the low oxygen partial pressure atmosphere was -50°C, and the other treatment conditions were the same as in Example 1.

[0116] Through stepwise heat treatment in reducing and low-oxygen partial pressure atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 44.12 wt%. The contents of iron and nickel elements are 15.75 wt% and 28.37 wt%, respectively. (W1-W2) / W1=0.286.

[0117] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 15.23% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0118] Comparative Example 3

[0119] The same small-scale furnace tube as in Example 1 was used, except that the furnace tube underwent a second heat treatment only in a low-oxygen partial pressure atmosphere at a temperature of 950°C for 50 hours, with other conditions remaining the same as in Example 1. An oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium-manganese oxide in the oxide film was MnCr2O4, and the total content of iron and nickel relative to the total weight of the oxide film was 15.18 wt%. The contents of iron and nickel were 5.62 wt% and 9.56 wt%, respectively. (W1-W2) / W1 = 0.754.

[0120] Hydrocarbon steam cracking was carried out in a pilot furnace tube after treatment in a low-oxygen partial pressure atmosphere. The cracking feedstock and cracking conditions were the same as in Example 1. The amount of coke deposited in the pilot furnace tube was reduced by 82.02 wt% compared with that in the existing untreated 35Cr45Ni furnace tube.

[0121] Comparative Example 4

[0122] The same small-scale furnace tube as in Example 1 was used, except that the furnace tube underwent a first heat treatment only in a reducing atmosphere at a temperature of 950°C for 20 hours, with other conditions identical to those in Example 1. No chromium or manganese oxides were formed on the inner wall surface of the furnace tube after the reducing atmosphere treatment. The total iron and nickel content on the inner surface of the furnace tube was 51.83 wt%. The iron and nickel contents were 19.20 wt% and 32.63 wt%, respectively. (W1-W2) / W1 = 0.161.

[0123] Hydrocarbon steam cracking was carried out in a pilot furnace tube treated with a reducing atmosphere, using the same feedstock and conditions as in Example 1. The amount of coke deposited in the pilot furnace tube was reduced by 9.06 wt% compared to that in an untreated 35Cr45Ni furnace tube in the prior art.

[0124] Comparative Example 5

[0125] The pilot furnace tube was the same as in Example 1, except that it was not treated in any way. Hydrocarbon steam cracking was carried out in the pilot furnace tube, with the same cracking feedstock and conditions as in Example 1. The coking rate in the pilot furnace tube was 100%.

[0126] Comparative Example 6

[0127] The same small-scale reactor as in Example 1 was used, except that the furnace tubes were first subjected to a first heat treatment in a low-oxygen partial pressure atmosphere, and then the pretreated alloy furnace tubes were subjected to a second heat treatment in a reducing atmosphere. Other conditions were the same as in Example 1.

[0128] Through stepwise heat treatment in low-oxygen partial pressure and reducing atmospheres, an oxide film mainly composed of Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube. The chromium and manganese oxide in the oxide film is MnCr2O4. The total content of iron and nickel elements relative to the total weight of the oxide film is 30.64 wt%. The contents of iron and nickel elements are 10.94 wt% and 19.7 wt%, respectively. (W1-W2) / W1 = 0.504.

[0129] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The coking amount of the furnace tube of the present invention was reduced by 30.88 wt% compared with that of the untreated 35Cr45Ni furnace tube in the prior art.

[0130] Comparative Example 7

[0131] The same small-scale reactor as in Example 1 was used, except that the oxygen content in the reducing atmosphere was 10 ppm. All other conditions were the same as in Example 1.

[0132] An oxide film mainly composed of elements such as Cr, Mn, Ni, Fe, O, and Si was formed on the inner wall surface of the furnace tube through stepwise heat treatment in a reducing atmosphere and a low oxygen partial pressure atmosphere. The total content of iron and nickel on the inner surface of the furnace tube is 46.79 wt%. The contents of iron and nickel are 17.33 wt% and 29.46 wt%, respectively. (W1-W2) / W1 = 0.243.

[0133] Hydrocarbon steam cracking was carried out in a pilot-scale furnace tube after stepwise treatment, with the same cracking feedstock and conditions as in Example 1. The amount of coke deposited in the pilot-scale furnace tube was reduced by 12.56 wt% compared to the amount of coke deposited in the untreated 35Cr45Ni furnace tube of the prior art.

[0134] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for processing alloy furnace tubes, characterized in that, The method includes: (1) The alloy furnace tube is subjected to a first heat treatment in the presence of a reducing atmosphere to obtain a pretreated alloy furnace tube; (2) In the presence of a low oxygen partial pressure atmosphere, the pretreated alloy furnace tube is subjected to a second heat treatment to obtain an alloy furnace tube with an oxide film on the inner surface. The oxygen content in the reducing atmosphere is 0 ppm; the dew point of the low oxygen partial pressure atmosphere is -40°C to 40°C. The reducing atmosphere includes hydrogen and at least one gas selected from nitrogen, helium and argon; Based on the total volume of the reducing atmosphere, the hydrogen content is 20-80 vol%. The oxide film comprises chromium manganese oxide and metal elements, wherein the metal elements include iron and / or nickel. The dew point of the low-oxygen partial pressure atmosphere and the content of metallic elements in the oxide film on the inner surface of the alloy furnace tube satisfy the following relationship: (W1-W2) / W1=aT 2 +bT+c formula I; In Equation I, -0.0029 ≤ a ≤ -0.0001, 0.0013 ≤ b ≤ 0.0274, 0.8126 ≤ c ≤ 0.8508, R 2 ≥0.9582; (W1-W2) / W1≥0.514; Wherein, W1 is the total content of iron and nickel in the alloy furnace tube before the first heat treatment, wt%; W2 is the total content of metal elements in the oxide film on the inner surface of the alloy furnace tube after the second heat treatment, wt%; T is the dew point of the low oxygen partial pressure atmosphere, °C; The low-oxygen partial pressure atmosphere is a gas mixture of water vapor and hydrogen. By weight percentage, the matrix composition of the alloy furnace tube includes: 12-50 wt% chromium, 20-50 wt% nickel, 0.2-1.15 wt% manganese, 1-1.23 wt% silicon, 0.1-0.75 wt% carbon, 0-5 wt% trace elements and 0-0.06 wt% ultra-trace elements, and 5-40 wt% iron. The total weight percentage of the matrix components of the alloy furnace tube is 100%.

2. The method according to claim 1, wherein, Based on the total volume of the reducing atmosphere, the hydrogen content is 40-80 vol.

3. The method according to claim 1 or 2, wherein, The conditions for the first heat treatment reaction include: a reaction temperature of 850-1100℃ and a reaction time of more than 10 hours.

4. The method according to claim 1 or 2, wherein, The conditions for the second heat treatment reaction include: a reaction temperature of 850-1100℃ and a reaction time of more than 10 hours.

5. The method according to claim 1 or 2, wherein, The composition of the chromium manganese oxide is Mn x Cr 3-x O4, x value is 0.5-2.

6. The method according to claim 1 or 2, wherein, The trace elements are selected from one or more of niobium, titanium, tungsten, molybdenum, aluminum, and rare earth elements.

7. The method according to claim 1 or 2, wherein, The trace elements are selected from sulfur and / or phosphorus.

8. The method according to claim 1 or 2, wherein, (W1-W2) / W1≥0.

757.

9. The method according to claim 1 or 2, wherein, Based on the total volume of the reducing atmosphere, the hydrogen content is 40-80 vol%, and the dew point of the low oxygen partial pressure atmosphere is 0°C to 5°C. In Equation I, a = -0.0029, b = 0.0274, c = 0.8126, R 2 =1.

10. An alloy furnace tube obtained by the method described in any one of claims 1-9.

11. The application of the alloy furnace tube of claim 10 in the thermal cracking of petroleum hydrocarbons.