阅读说明：本技术 处理急冷锅炉炉管内表面的方法 (Method for treating inner surface of quenching boiler tube ) 是由 王申祥 柳颖 王红霞 郏景省 王国清 张利军 于 2019-10-28 设计创作，主要内容包括：本发明涉及石油化工领域,公开了一种处理急冷锅炉炉管内表面的方法,所述方法包括以下步骤：(1)对急冷锅炉炉管内表面进行挤压研磨处理,得到预处理炉管；(2)在硫化气体存在下,对预处理炉管的内表面进行硫化处理。该方法能够在急冷锅炉炉管内表面形成致密地、厚度更薄且不易剥落的硫化物保护层,使得焦炭在急冷锅炉炉管内表面的沉积显著减少,并且采用该方法处理得到的硫化物保护层的寿命更长,能够满足急冷锅炉炉管长期使用、反复升温等的需求。(The invention relates to the field of petrochemical industry, and discloses a method for treating the inner surface of a quenching boiler tube, which comprises the following steps: (1) carrying out extrusion grinding treatment on the inner surface of the quenching boiler tube to obtain a pretreatment boiler tube; (2) and carrying out vulcanization treatment on the inner surface of the pretreatment furnace tube in the presence of a vulcanization gas. The method can form a compact sulfide protection layer with thinner thickness and difficult peeling on the inner surface of the quenching boiler tube, so that the deposition of coke on the inner surface of the quenching boiler tube is obviously reduced, the service life of the sulfide protection layer obtained by the method is longer, and the requirements of long-term use, repeated temperature rise and the like of the quenching boiler tube can be met.)

1. A method of treating an interior surface of a quench boiler tube, wherein the method comprises the steps of:

(1) carrying out extrusion grinding treatment on the inner surface of the quenching boiler tube to obtain a pretreatment boiler tube;

(2) and carrying out vulcanization treatment on the inner surface of the pretreatment furnace tube in the presence of a vulcanization gas.

2. The method of claim 1, wherein the elemental composition of the quench boiler furnace tubes comprises: 0 to 5 weight percent of chromium, 0.1 to 2 weight percent of manganese, 0 to 5 weight percent of nickel, 0.05 to 2 weight percent of silicon, 0.05 to 0.8 weight percent of carbon, 0.1 to 1.5 weight percent of molybdenum, 0 to 5 weight percent of trace elements and trace elements, and 78.7 to 99.7 weight percent of iron;

preferably, the element components of the quenching boiler furnace tube comprise: 2-5 wt% of chromium, 0.5-1.8 wt% of manganese, 0-3 wt% of nickel, 0.5-1.8 wt% of silicon, 0.05-0.6 wt% of carbon, 0.1-1 wt% of molybdenum, 0-3 wt% of trace elements and trace elements, and 82.8-96.85 wt% of iron;

preferably, the trace element is selected from at least one of niobium, titanium, tungsten, aluminum, cobalt, and rare earth elements;

preferably, the trace elements are sulphur or/and phosphorus.

3. The method according to claim 1 or 2, wherein the extrusion grinding process is carried out in the manner of: the grinding material is loaded into the quenching boiler tube, and under the action of pressure, the grinding material reciprocates in the furnace tube so as to realize the extrusion grinding of the inner surface of the quenching boiler tube.

4. The method of any of claims 1-3, wherein the extrusion milling conditions comprise: the pressure of extrusion grinding is 0.5-15MPa, preferably 1-12 MPa; the time for the extrusion-grinding is 5 to 3600 seconds, preferably 10 to 1800 seconds.

5. The method of claim 3 or 4, wherein the abrasive consists of abrasive particles and a liquid carrier;

preferably, the abrasive particles are used in an amount of 10 to 80 wt%, preferably 40 to 80 wt%, relative to the total weight of the abrasive; the amount of the liquid carrier is 20-90 wt%, preferably 20-60 wt%;

preferably, the abrasive grains are selected from at least one of tungsten oxide, cerium oxide, chromium oxide, aluminum oxide, silicon carbide, boron carbide, and diamond;

preferably, the grain size of the abrasive grains is 40-1000 meshes, preferably 200-1000 meshes;

preferably, the liquid carrier is selected from one or more of vaseline, paraffin, turpentine and oleic acid.

6. The method of any of claims 1-5, wherein the sulfiding gas comprises H₂And sulfide vapor;

preferably, the sulfide vapor is selected from H₂S、SO₂、SF₆、COS、CS₂、CH₃SH、CH₃CH₂SH、CH₃SCH₃、CH₃CH₂SCH₂CH₃、CH₃S-SCH₃And CH₃CH₂S-SCH₂CH₃At least one of;

more preferably, the volume percentage of sulphide vapour is between 0.01 and 0.2%, preferably between 0.03 and 0.15%, based on the total gas volume.

7. The method of any one of claims 1-6, wherein the conditions of the sulfidation process include: the temperature of the vulcanization treatment is 400-800 ℃, preferably 500-700 ℃; the time of the vulcanization treatment is 5 to 100 hours, preferably 10 to 50 hours.

8. A quench furnace tube treated by the method of any one of claims 1 to 7.

9. The quenching boiler furnace tube according to claim 8, wherein a sulfide protection layer is formed on an inner specific surface of the quenching boiler furnace tube.

10. The quench boiler tube according to claim 9, wherein the thickness of the protective layer is 0.1-20 μ ι η, preferably 5-15 μ ι η.

Technical Field

The invention relates to the field of petrochemical industry, in particular to a method for treating the inner surface of a quenching boiler tube.

Background

Ethylene is one of the most important basic raw materials in the petrochemical industry, and ethylene yield is a main mark for measuring the development level of the petrochemical industry in China. At present, the method for producing ethylene mainly adopts a tube furnace cracking technology, and coking on the inner wall of a heat exchange tube of a quenching boiler is a prominent problem in the operation process of a cracking device. In particular, when the cracking feedstock is heavy oil (such as heavy AGO, VGO, etc.), coking of the quench boiler is more severe and constitutes a major constraint factor of the operating cycle of the cracking apparatus. To ensure the smooth flow, the cracking furnace has to be shut down irregularly to decoke the quench boiler (mechanical or hydraulic decoking). This not only affects the operating rate of the cracking furnace, but also shortens the service life of the cracking furnace. In addition, the resistance drop of the quenching boiler is increased by quenching the coking of the boiler, and the partial pressure of the hydrocarbon in the radiation furnace tube is increased by increasing the upstream pressure, so that the selectivity of the cracking furnace tube to the olefin is reduced, and the yield of the olefin is reduced; and because the heat conductivity coefficient of coke scale in the quenching boiler is very small, the rising of the outlet temperature of the quenching boiler not only reduces the recovery amount of high-temperature-level heat energy, but also increases the heat load of the oil washing system, and brings difficulty to the balanced operation of the oil washing system. Therefore, how to inhibit or slow down coking of the quenching boiler becomes a problem to be solved urgently.

At present, the industry mainly adopts a novel quenching boiler or a method of adding components in the quenching boiler to slow down coking. A quenching boiler with a novel structure is developed by the cooperation of China petrochemical and Tianhua chemical machinery and automated research and design institute, a distributor of the quenching boiler is a cylinder with an inverted cone transition section, and a multi-branch pyrolysis gas conveying channel which is uniformly distributed is arranged inside the quenching boiler. The quenching boiler with the structure has short retention time of the pyrolysis gas, is quickly cooled, and effectively inhibits the secondary reaction of the pyrolysis gas, thereby slowing down the coking of the quenching boiler. Chevron Phillips chemical developed a process for injecting steam at the quench boiler inlet cone using specially made, evenly distributed nozzles to reduce coking. The flow velocity of the cracked gas is improved by injecting steam, and the cracked gas can be quenched, so that the coking of a quenching boiler is inhibited. The industrial test results show that the method prolongs the operation period of the boiler by more than 50 percent. Knightthawk engineering corporation developed a quench boiler having a "nose" cone and deflector ring mounted in the inlet head of the quench boiler to improve the uniformity of cracked gas flow distribution within the heat exchanger tubes, thereby reducing quench boiler coking.

The coking mechanism of quench boilers is generally divided into two categories: (1) catalytic coking, wherein pyrolysis gas at the inlet of the quenching boiler has high temperature, disordered flow and overlong retention time of partial pyrolysis gas, and Fe element on the inner surface of the quenching boiler has a remarkable catalytic effect on coking of hydrocarbon pyrolysis gas, so that the inner wall of the quenching boiler is covered by filiform catalytic coke formed by catalytic coking; (2) condensing and coking, namely condensing high-boiling-point hydrocarbons into tar droplets when polycyclic aromatic hydrocarbons and condensed ring aromatic hydrocarbons with higher boiling points in the pyrolysis gas enter the TLE and when the temperature of the inner wall is lower than the dew point of the pyrolysis gas, adsorbing the tar droplets in the pyrolysis gas easily by filiform coke formed by catalytic coking, and forming compact coke to be attached to the inner wall of the quenching boiler tube after the tar droplets are further dehydrogenated. Therefore, the catalytic coking is the basis of the quenching boiler coking, and the aim of inhibiting the quenching boiler tube coking can be achieved by reducing the Fe element content on the inner surface of the furnace tube by a coating or oxide film technology.

At present, the coating technology is used for covering Fe and Ni elements to inhibit the coking of a furnace tube mainly in crackingThe study was carried out in the radiant coils of the apparatus. The coating technology of the inner surface of the furnace tube can change the surface property of the furnace tube, and a coating (such as Al) with good mechanical property and chemical property is formed on the inner surface of the furnace tube₂O₃、SiO₂Etc.) to cover Fe and Ni elements and slow down the catalytic coking and carburization of the inner surface of the furnace tube. The anti-coking coating is prepared at home and abroad mainly by adopting methods of externally applied elements such as plasma spraying, sintering, magnetron sputtering, chemical (or physical) vapor deposition and the like. However, under the cracking conditions of high temperature, high carbon potential and strong scouring, the service life of the coating still cannot meet the requirement of long-term use.

The method for inhibiting the furnace tube from coking by covering Fe and Ni elements through an oxide film technology is mainly researched and applied to a radiant section furnace tube of a cracking device. From 1997 to 2006, Nova, canada, incorporated, disclosed a number of patents that preoxidized the inner surface of cracking furnace tubes, e.g., US5630887A, US6824883B1, US7156979B2, US2004265604a1, US2005077210a1, US2006086431a1, etc., disclosed the formation of manganese-chromium spinel protective layers on the inner surface of the tubes after preoxidation.

CN101565807A discloses a method for treating a high-temperature alloy furnace tube, which comprises the following steps: controlling the pressure of low-oxygen partial pressure gas to be 0-3 atmospheric pressures, introducing the gas into an atmosphere furnace provided with a high-temperature alloy furnace tube, heating to 600-; wherein the low oxygen partial pressure gas comprises H₂And CO, and water vapor accounting for 0.17-2% of the volume fraction of the gas with low oxygen partial pressure. CN101565808A discloses a method for treating a high temperature alloy furnace tube, which comprises the following steps: controlling the pressure of low-oxygen partial pressure gas to be 0-3 atmospheric pressures, passing through ammonia water, introducing into an atmosphere furnace provided with a high-temperature alloy furnace tube, heating to 600-.

However, the above method of forming a manganese chromium spinel oxide film on the metal surface of the furnace tube by oxidation cannot be directly applied to the quenching boiler tube.

Disclosure of Invention

The invention aims to overcome the problem of coking inside a quenching boiler tube in the prior art, and provides a method for treating the inner surface of the quenching boiler tube, which can form a compact sulfide protective layer with thinner thickness and difficult peeling on the inner surface of the quenching boiler tube, so that the deposition of coke on the inner surface of the quenching boiler tube is obviously reduced, and the sulfide protective layer treated by the method has longer service life and can meet the requirements of long-term use, repeated temperature rise and the like of the quenching boiler tube.

In order to achieve the above object, a first aspect of the present invention provides a method for treating an inner surface of a quench furnace tube, wherein the method comprises the steps of:

(1) carrying out extrusion grinding treatment on the inner surface of the quenching boiler tube to obtain a pretreatment boiler tube;

(2) and carrying out vulcanization treatment on the inner surface of the pretreatment furnace tube in the presence of a vulcanization gas.

The second aspect of the invention provides a quenching boiler tube obtained by the method.

Through the technical scheme, the method for treating the inner surface of the quenching boiler tube provided by the invention has the following beneficial effects:

according to the method, the step of extruding and grinding the cracking furnace tube is introduced before the vulcanization treatment, so that a large number of brittle layers and microscopic defects on the inner surface of the furnace tube are removed, the organization structure of the inner surface of the furnace tube is more compact, the crystal grains are refined, the surface roughness can be greatly improved, and further, a sulfide protective layer obtained by oxidation is more compact and difficult to peel off, and the anti-coking effect is better.

Furthermore, in the method, a small amount of sulfide steam is introduced to react with Fe element in the quenching boiler tube alloy to generate FeS, so that the catalytic coking activity is reduced, the catalytic coking in the operation process of the quenching boiler is reduced, and the operation period of a cracking device is prolonged.

Further, H is mixed into the sulfide vapor₂Can be made ofControlling chemical reactionsThe balance of (2) enables the decomposed S element to be less, so that a FeS layer formed by chemical reaction (Fe + S ═ FeS) with the Fe element is not too thick, a protective layer is not easy to peel off, and the anti-coking effect is better.

The method can be used for quenching boiler tubes in laboratory scale or quenching boiler tubes in industry, and has excellent effect. The method can reduce the coke deposited on the inner wall of the quenching boiler tube by more than 70 percent, and the sulfide protective layer formed by the method has lasting effect and can keep the anti-coking effect for a plurality of periods.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

In a first aspect of the present invention, a method for treating an inner surface of a quench furnace tube, comprises the steps of:

(1) carrying out extrusion grinding treatment on the inner surface of the quenching boiler tube to obtain a pretreatment boiler tube;

(2) and carrying out vulcanization treatment on the inner surface of the pretreatment furnace tube in the presence of a vulcanization gas.

According to the invention, before the quenching boiler tube is vulcanized, the tube is subjected to extrusion grinding treatment, under the action of the extrusion grinding, a large number of brittle layers and microscopic defects on the inner surface of the tube are removed, so that the brittle layers and the microscopic defects on the inner surface of the tube are removed, the organization structure of the inner surface of the tube is tighter, the crystal grains are refined, the surface roughness can be greatly improved, and further, the sulfide protective layer is more compact and less prone to stripping, and the anti-coking effect is better.

Meanwhile, after the furnace tube after extrusion grinding treatment is subjected to vulcanization treatment, a sulfide protective layer which is compact, thinner and not easy to peel can be obtained, the protective layer can still keep excellent bonding force with the inner surface of the furnace tube in the processes of long-term use, repeated temperature rise and the like of the furnace tube, and the furnace tube is ensured to still have excellent anti-coking capacity in the processes of long-term use, repeated temperature rise and the like.

The method of the invention can be suitable for furnace tubes with lower Cr element content, such as 15Mo, of quenching boiler tubes and the like₃And/or 5 CrMo.

Specifically, the quenching boiler tube comprises the following elements: 0 to 5 weight percent of chromium, 0.1 to 2 weight percent of manganese, 0 to 5 weight percent of nickel, 0.05 to 2 weight percent of silicon, 0.05 to 0.8 weight percent of carbon, 0.1 to 1.5 weight percent of molybdenum, 0 to 5 weight percent of trace elements and trace elements, and 78.7 to 99.7 weight percent of iron.

According to the invention, the quenching boiler tube comprises the following element components: 2-5 wt% of chromium, 0.5-1.8 wt% of manganese, 0-3 wt% of nickel, 0.5-1.8 wt% of silicon, 0.05-0.6 wt% of carbon, 0.1-1 wt% of molybdenum, 0-3 wt% of trace elements and 82.8-96.85 wt% of iron.

According to the invention, the trace elements are selected from at least one of niobium, titanium, tungsten, aluminium, cobalt and rare earth elements.

According to the invention, the trace elements are sulphur or/and phosphorus.

According to the invention, the extrusion grinding process is carried out in the following manner: the grinding material is loaded into the quenching boiler tube, and under the action of pressure, the grinding material reciprocates in the furnace tube so as to realize the extrusion grinding of the inner surface of the quenching boiler tube.

In the invention, the extrusion grinding treatment comprises the following specific steps:

the grinding material is loaded in the furnace tube, the furnace tube is fixed on the machine tool, the upper grinding cylinder and the lower grinding cylinder are coaxially opposite, and the furnace tube is clamped between the upper cylinder body and the lower cylinder body by an oil pressure device. When the oil pressure piston of the lower cylinder body extrudes the grinding materials upwards, the grinding materials are forced to flow through the inner cavity of the furnace tube and enter the upper grinding cylinder. When the lower oil cylinder piston reaches the top dead center, the upper oil cylinder piston starts to downwards extrude the grinding materials, so that the grinding materials return to the lower grinding cylinder along the original channel. When the upper cylinder piston reaches the bottom dead center, the lower cylinder piston starts to move upwards again. The grinding material reciprocates in the channel and acts on the wall of the furnace tube under certain pressure, so that the grinding material can grind the inner wall of the furnace tube.

In the invention, the method further comprises the step of cleaning the pretreatment quenching boiler tube obtained by the extrusion grinding treatment.

The cleaning may be carried out in a manner conventional in the art, such as ultrasonic cleaning or the like. The solvent used for washing may be a solvent conventional in the art, such as water, ethanol, etc.

In the invention, the loading amount of the grinding material can be adjusted according to different furnace tubes.

According to the invention, the conditions of the extrusion grinding include: the pressure of extrusion grinding is 0.5-15MPa, and the time of extrusion grinding is 5-3600 seconds.

In the invention, in order to ensure the treatment effect on the inner surface of the quenching boiler tube, the inventor researches the conditions of extrusion grinding treatment, and the research shows that when the extrusion grinding pressure and time meet the requirements in the range, the extrusion grinding treatment can remove a large amount of brittle layers and micro defects on the inner surface of the furnace tube, the organization structure of the inner surface of the furnace tube becomes tighter, the crystal grains are refined, the surface roughness can be greatly improved, and the formation of a subsequent compact oxide protective layer is facilitated.

Furthermore, when the extrusion grinding pressure is 1-12MPa and the extrusion grinding time is 10-1800 seconds, the treatment effect on the inner surface of the quenching boiler tube is more excellent.

According to the invention, the abrasive consists of abrasive grains and a liquid carrier.

According to the invention, the abrasive grains are used in an amount of 10 to 80% by weight, preferably 40 to 80% by weight, relative to the total weight of the abrasive; the amount of the liquid carrier is 20 to 90 wt%, preferably 20 to 60 wt%.

According to the present invention, the abrasive grains are selected from at least one of tungsten oxide, cerium oxide, chromium oxide, aluminum oxide, silicon carbide, boron carbide, and diamond.

According to the invention, the grain size of the abrasive particles is 40-1000 meshes, preferably 200-1000 meshes.

According to the invention, the liquid carrier is selected from one or more of vaseline, paraffin, turpentine and oleic acid.

According to the invention, the sulphurization gas comprises H₂And sulfide vapor.

In the present invention, the sulfide vapor refers to vapor generated by a sulfide at high temperature and high pressure.

In the present invention, a fuel containing sulfide vapor and H is used₂The sulfuration gas carries out sulfuration treatment on the furnace tube, and Fe element in the alloy of the furnace tube can react to generate FeS, thereby reducing the activity of catalytic coking, reducing the catalytic coking in the operation process of the quenching boiler and prolonging the operation period of the cracking device.

Specifically, the inventors have found that S element contained in sulfide vapor reacts with Fe element in the furnace tube alloy to form FeS, while H element₂Can control chemical reactionsThe balance of (2) enables the decomposed S element to be less, so that a FeS layer formed by chemical reaction (Fe + S ═ FeS) with the Fe element is not too thick, a protective layer is not easy to peel off, and the anti-coking effect is better.

According to the invention, the sulphide vapour is selected from H₂S、SO₂、SF₆、COS、CS₂、CH₃SH、CH₃CH₂SH、CH₃SCH₃、CH₃CH₂SCH₂CH₃、CH₃S-SCH₃And CH₃CH₂S-SCH₂CH₃At least one of (1).

In addition, the inventor researches the volume percentage of sulfide steam in the sulfide gas, and the research shows that when the volume percentage of the sulfide steam is 0.01-0.2% based on the total gas volume, the quenching boiler tube is vulcanized, so that the Fe element in the alloy of the furnace tube can be ensured to fully react with the sulfide steam, the inner surface of the furnace tube can be covered by the formed FeS layer, meanwhile, the formed FeS layer is not too thick, the protective layer is not easy to peel off, and the excellent anti-coking effect is obtained.

Furthermore, when the volume percentage of the sulfide vapor is 0.03-0.15% based on the total gas volume, the anti-coking effect of the quenching boiler tube obtained through treatment is more excellent.

In the present invention, the inventors have conducted extensive studies and found that the conditions of the vulcanization treatment include: the temperature of the vulcanization treatment is 400-800 ℃, and the time of the vulcanization treatment is 5-100h, so that the sulfide steam in the sulfide gas reacts with Fe element in the furnace tube alloy more fully, the vulcanization treatment effect of the sulfide gas on the inner surface of the furnace tube is more excellent, and the quenching boiler tube obtained after the treatment has an excellent anti-coking effect.

Further, the vulcanization treatment temperature is preferably 500-700 ℃; the vulcanization treatment time is preferably 10 to 50 hours.

According to the invention, when the volume percentage of sulfide steam in the sulfide gas and the vulcanization treatment condition simultaneously satisfy the range defined by the invention, the treatment effect on the quenching boiler tube is more excellent, and the obtained sulfide protective layer has a more compact structure, is not easy to peel off, and has a better anti-coking effect.

The second aspect of the invention provides a quenching boiler tube obtained by the method.

According to the invention, a sulfide protection layer is formed on the inner specific surface of the quenching boiler tube.

According to the invention, the thickness of the protective layer is 0.1 to 20 μm, preferably 5 to 15 μm.

The present invention will be described in detail below by way of examples.

The composition of the inner surface of the quenching boiler tube is analyzed by an X-ray Energy Dispersive Spectrometer (EDS for short).

The thickness of the oxide protective layer can be determined by measuring the cross section of the inner surface of the cracking furnace by using an XL-30 field emission environment Scanning Electron Microscope (SEM) of FEI company, and the acceleration voltage is 15 kv.

The cracking material was an industrial naphtha, and its physical properties are shown in table 1;

examples and comparative examples all other materials were commercially available.

TABLE 1

Test example

The furnace tube is used for carrying out cracking coking evaluation experiments on a laboratory device with the feeding amount of 200g/h by taking naphtha as a cracking raw material. After cracking, air is used for burning, and CO in the burnt gas are burnt₂The concentration is measured on line by an infrared instrument, the volume of the scorching gas is recorded on line by a wet flowmeter, and finally the carbon content in the scorching gas is calculated to be the coking content in the cracking process.

The cleavage experimental conditions were as follows:

raw materials: industrial naphtha (physical properties are shown in Table 1)

Cracking time: 2 hours; temperature of the preheater: 600 ℃; temperature of the cracking furnace: 850 ℃; water-oil ratio: 0.5; residence time: 0.35 second.

Comparative example 1

Has a size ofThe 15Mo3 alloy furnace tube has bright and non-oxide scale inner surface after mechanical processing, and the surface composition of the furnace tube is analyzed, and the results are shown in Table 2. And (3) carrying out 10 times of cracking and scorching circulation experiments on the furnace tube subjected to air steam pre-oxidation according to the cracking conditions, wherein the coking amounts of different cracking times are shown in Table 3.

Comparative example 2

The size and the material of the furnace tube adopted by the comparative example are the same as those of the comparative example 1, the furnace tube is treated according to the method of the patent CN106591845A, hydrogen passes through a chromic acid aqueous solution with the concentration of 30 percent at the temperature of 10 ℃, and then enters a high-temperature furnace tube with the temperature of 900 ℃ for constant temperature treatment for 30 hours. After cooling, the composition of the inner surface of the furnace tube was analyzed and the thickness of the oxide layer on the inner surface was measured, the results are shown in Table 2.

The furnace tube was subjected to 10 cycles of cracking and scorching using the cracking conditions described in the test examples, and the coke quantities for different cracking times are shown in Table 3.

Comparative example 3

The size and the material of the furnace tube adopted by the comparative example are the same as those of the comparative example 1, and the furnace tube is extruded and ground according to the following conditions: (1) abrasive formulation, 15% alumina (800 mesh) + 35% boron carbide (400 mesh) + 35% paraffin + 15% oleic acid; (2) extrusion grinding pressure, 5 MPa; (3) extrusion milling time, 60 seconds. After extrusion grinding, the composition of the inner surface of the furnace tube was analyzed and the thickness of the oxide layer on the inner surface was measured, the results are shown in Table 2.

The furnace tube was subjected to 10 cycles of cracking and scorching using the cracking conditions described in the test examples, and the coke quantities for different cracking times are shown in Table 3.

Comparative example 4

The furnace tube adopted by the comparative example has the same size and material as those of the comparative example 1, and adopts H₂-H₂S(H₂S volume concentration 0.1%) gas was sulfided at 600 c for 20 hours. After cooling, the composition of the inner surface of the furnace tube was analyzed and the thickness of the inner surface vulcanizate was measured and the results are shown in Table 2.

The furnace tube was subjected to 10 cycles of cracking and scorching using the cracking conditions described in the test examples, and the coke quantities for different cracking times are shown in Table 3.

Example 1

The size and material of the furnace tube adopted in the embodiment are the same as those of the comparative example 1, the furnace tube is extruded and ground according to the method of the comparative example 3, and then H is adopted₂-H₂S(H₂S volume concentration 0.1%) gas was sulfided at 600 c for 20 hours. After cooling, the composition of the inner surface of the furnace tube was analyzed and the thickness of the inner surface vulcanizate was measured and the results are shown in Table 2.

The furnace tube was subjected to 10 cycles of cracking and scorching using the cracking conditions described in the test examples, and the coke quantities for different cracking times are shown in Table 3.

Example 2

This example adoptsThe size and material of the used furnace tube are the same as those of the comparative example 1, and the furnace tube is extruded and ground according to the following conditions: (1) abrasive formulation, 83% silicon carbide (400 mesh) + 17% petrolatum; (2) extrusion grinding pressure is 2 MPa; (3) extrusion milling time, 500 seconds. Then using H₂-CH₃SH(CH₃SH vapor volume concentration 0.05%) gas was sulfided at 550 c for 30 hours. After cooling, the composition of the inner surface of the furnace tube was analyzed and the thickness of the inner surface vulcanizate was measured and the results are shown in Table 2.

The furnace tube was subjected to 10 cycles of cracking and scorching using the cracking conditions described in the test examples, and the coke quantities for different cracking times are shown in Table 3.

Example 3

The size and material of the furnace tube adopted in the embodiment are the same as those of the comparative example 1, and the furnace tube is extruded and ground according to the following conditions: (1) abrasive formula, 76% boron carbide (1000 mesh), 12% paraffin, 10% oleic acid and 2% turpentine; (2) extrusion grinding pressure, 10 MPa; (3) extrusion milling time, 15 seconds. Then using H₂-CH₃S-SCH₃(CH₃S-SCH₃Steam concentration 0.15%) gas was sulfided at 650 c for 40 hours. After cooling, the composition of the inner surface of the furnace tube was analyzed and the thickness of the inner surface vulcanizate was measured and the results are shown in Table 2.

The furnace tube was subjected to 10 cycles of cracking and scorching using the cracking conditions described in the test examples, and the coke quantities for different cracking times are shown in Table 3.

TABLE 2

Elemental content (wt%)	Cr	Fe	Mn	S	O	Others	Thickness, μm
								Comparative example 1	/	95.99	0.65	/	1.27	2.09	/
Comparative example 2	43.25	4.71	18.19	/	24.48	9.37	25.4
								Comparative example 3	/	97.56	0.81	/	0.42	1.21	0
Comparative example 4	/	79.36	0.29	9.45	9.27	1.63	27.3
								Example 1	/	70.19	0.43	23.55	4.71	1.12	13.5
Example 2	/	69.89	1.22	22.56	2.55	3.78	9.5
								Example 3	/	72.54	1.41	23.71	1.88	0.46	16.1

TABLE 3

From table 2, we can find that the S element content on the inner surface of the furnace tubes of the treated comparative example and the example is remarkably increased, while the Fe element with catalytic coking activity is greatly reduced, and the Fe element content in the example is lower compared with the comparative example.

From Table 3 we can see that the average coke charge for 10 cracks in comparative example 1 (blank value) is 1.55 grams; the coking amounts of the first times in the comparative examples 2, 3 and 4 are very low, but the coking amounts gradually increase along with the increase of the cracking and burning times; the coke amount in examples 1, 2 and 3 was low, and was reduced by 70% or more on average from the blank value, and the coke amount did not increase significantly as the cracking and burning times increased.

Comparative example 5

The material of the furnace tube in the comparative example 1 is changed to 15CrMo, other conditions are unchanged, and the elemental composition and the coking amount of the inner surface of the furnace tube are shown in tables 4 and 5.

Comparative example 6

The material of the furnace tube in the comparative example 2 is changed to 15CrMo, other conditions are unchanged, and the elemental composition and the coking amount of the inner surface of the furnace tube are shown in tables 4 and 5.

Comparative example 7

The material of the furnace tube in the comparative example 3 is changed to 15CrMo, other conditions are unchanged, and the elemental composition and the coking amount of the inner surface of the furnace tube are shown in tables 4 and 5.

Comparative example 8

The material of the furnace tube in the comparative example 4 is changed to 15CrMo, other conditions are unchanged, and the elemental composition and the coking amount of the inner surface of the furnace tube are shown in tables 4 and 5.

Example 4

The material of the furnace tube in example 1 was changed to 15CrMo, the other conditions were not changed, and the elemental composition and the coking amount of the inner surface of the furnace tube are shown in tables 4 and 5.

Example 5

The material of the furnace tube in example 2 was changed to 15CrMo, the other conditions were not changed, and the elemental composition and the coking amount of the inner surface of the furnace tube are shown in tables 4 and 5.

Example 6

The material of the furnace tube in example 3 was changed to 15CrMo, the other conditions were not changed, and the elemental composition and the coking amount of the inner surface of the furnace tube are shown in tables 4 and 5.

TABLE 4

Elemental content (wt%)	Cr	Fe	Mn	S	O	Others	Thickness, μm
								Comparative example 5	0.93	93.81	0.54	/	1.91	2.81	/
Comparative example 6	40.58	2.18	17.92	/	32.21	7.11	20.2
								Comparative example 7	5.21	92.26	0.75	/	1.22	0.56	0
Comparative example 8	5.36	71.26	0.52	9.89	11.23	1.74	29.5
								Example 4	2.47	69.23	0.55	21.36	4.75	1.64	14.1
Example 5	3.58	70.56	1.17	22.13	1.98	0.58	9.3
								Example 6	2.13	68.95	0.68	23.25	3.58	1.41	16.9

TABLE 5

From table 4, we can find that the S element content on the inner surface of the furnace tubes of the treated comparative example and the example is remarkably increased, while the Fe element with catalytic coking activity is greatly reduced, and the Fe element content in the example is lower compared with the comparative example.

From Table 5 we can see that the average coke charge for 10 cracks in comparative example 6 (blank value) is 1.17 grams; in the comparative examples 5-8, the coking amount in the first times is very low, but the coking amount gradually increases along with the increase of the cracking and the coking times; the coke amount in examples 4, 5 and 6 was low, and was reduced by 70% or more on average from the blank value, and the coke amount did not increase significantly as the cracking and burning times increased.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.