阅读说明：本技术 两程辐射段乙烯裂解炉用导热炉管及其制备方法和应用 (Heat-conducting furnace tube for two-pass radiation section ethylene cracking furnace and preparation method and application thereof ) 是由 刘俊杰 杨士芳 王国清 张利军 周丛 张兆斌 杜志国 李晓锋 杨沙沙 郭莹 于 2019-10-29 设计创作，主要内容包括：本发明涉及用于乙烯裂解炉的导热炉管领域,公开了一种两程辐射段乙烯裂解炉用导热炉管及其制备方法和其在裂解炉中的应用。该导热炉管包括炉管主体,所述炉管主体的内侧壁设置沿炉管主体的长度方向依次重复设置多组导热构件；第一导热件和第二导热件,所述第一导热件设置为多条,沿所述炉管主体的内侧壁横截面环绕一周且向炉管主体内凸出形成；所述第二导热件沿所述炉管主体的轴向呈螺旋设置。该导热炉管具有良好的传热效果,显著提高传热炉管的传热强化综合因子达15-27％,同时能够有效降低传热炉管的结焦量和渗碳现象。(The invention relates to the field of heat-conducting furnace tubes for ethylene cracking furnaces, and discloses a heat-conducting furnace tube for a two-pass radiation section ethylene cracking furnace, a preparation method of the heat-conducting furnace tube and application of the heat-conducting furnace tube in the ethylene cracking furnace. The heat conduction furnace tube comprises a furnace tube main body, wherein a plurality of groups of heat conduction components are sequentially and repeatedly arranged on the inner side wall of the furnace tube main body along the length direction of the furnace tube main body; the first heat conducting pieces are arranged in a plurality of strips, encircle a circle along the cross section of the inner side wall of the furnace tube main body and are formed by protruding towards the inside of the furnace tube main body; the second heat conducting piece is spirally arranged along the axial direction of the furnace tube main body. The heat-conducting furnace tube has good heat transfer effect, remarkably improves the heat transfer strengthening comprehensive factor of the heat-transferring furnace tube by 15-27%, and can effectively reduce the coking amount and the carburization phenomenon of the heat-transferring furnace tube.)

1. A heat conduction furnace tube for a two-pass radiation section ethylene cracking furnace is characterized by comprising a furnace tube main body, wherein a heat conduction component is arranged on the inner side wall of the furnace tube main body along the length direction of the furnace tube main body; the heat conductive member includes a first heat conductive member and a second heat conductive member,

the first heat conducting pieces are arranged in a plurality of strips, encircle a circle along the cross section of the inner side wall of the furnace tube main body and are formed by protruding towards the inside of the furnace tube main body;

the second heat conducting piece is spirally arranged along the axial direction of the furnace tube main body.

2. The heat conducting furnace tube of claim 1, wherein the extension length H of the heat conducting member along the axial direction of the furnace tube main body satisfies: h is more than or equal to 0 and less than or equal to L/3; wherein L is the length of the furnace tube main body.

3. The heat conducting furnace tube of claim 1 or 2, wherein the rotation angle of the spiral in the second heat conducting member is 120 ° -360 °; the ratio of the axial length of the second heat-conducting piece to the inner diameter of the furnace tube is 2-3; the ratio of the area of the middle opening of the second heat conducting piece to the area of the furnace tube is 0.6-0.8: 1.

4. The heat conduction furnace tube of claim 1 or 2, wherein the diameter of the inner ring of the first heat conduction member is D, D satisfies D/D is greater than or equal to 0.4 and less than or equal to 0.7, and D is the inner diameter of the furnace tube main body.

5. The thermally conductive furnace tube of claims 1-4, wherein the set of thermally conductive members comprises a plurality of the first thermally conductive members and one of the second thermally conductive members.

6. The thermally conductive furnace tube of claims 1-5, wherein an axial distance between adjacent first thermally conductive members is between 0.3D and 0.7D.

7. The thermally conductive furnace tube of claims 1-6, wherein the ratio of the axial length of the set of thermally conductive members to the inner diameter of the furnace tube is between 9 and 11.

8. The heat conducting furnace tube of claim 1 or 2, wherein the heat conducting furnace tube is a smooth inner wall or an inner wall coated with a thermal barrier coating;

preferably, the part of the heat conducting furnace tube, on which the heat conducting component is not arranged, is a light pipe or is coated with a thermal barrier coating or is internally provided with a second heat conducting piece or any combination of the above manners.

9. The thermally conductive furnace tube of claim 8, wherein the thermal barrier coating comprises a thermally conductive layer comprising 30-40 wt.% Cr, 2.5-6 wt.% Ni, 3-9 wt.% Fe, 8-13 wt.% Mn, 0-0.5 wt.% C, 35-40 wt.% O, 1.5-20 wt.% of at least one element selected from the group consisting of Al, Zr, Nb, and Mo, based on the total amount of the thermally conductive layer;

preferably, the thickness of the heat conducting layer is 0.1-5 μm.

10. The thermally conductive furnace tube of claim 8, wherein the interior side of the thermally conductive furnace tube further comprises a reinforcement coating over the thermally conductive layerA layer comprising SiO in weight percent based on the total amount of the reinforcement coating₂45-80% by weight, K₂10-25% by weight of O, Al₂O₃0-10 wt%, MgO 0-10 wt%, ZnO 0-20 wt%, Co₃O₄0-5 wt%, Na₂0-10 wt% of O;

preferably, the thickness of the reinforcement coating is 5-10 μm.

11. The method according to any one of claims 1 to 10, comprising heating the heat-conducting furnace tube under an atmosphere of low oxygen partial pressure to form a heat-conducting layer on the surface of the heat-conducting furnace tube.

12. The production method according to claim 11, wherein the conditions of the low oxygen partial pressure atmosphere include: the gas providing the low oxygen partial pressure atmosphere comprises CO₂、CO、H₂And water vapor, the oxygen partial pressure is less than or equal to 10^-16Pa; the conditions of the heat treatment include: the temperature of the heating treatment is 400-1100 ℃, and preferably 800-1000 ℃; the time of the heat treatment is 5 to 200 hours, preferably 10 to 100 hours.

13. The method of claim 11, further comprising spraying a reinforcement coating on the surface of the thermally conductive layer;

preferably, the preparation method of the reinforced coating comprises the following steps: mixing the raw materials with water to form slurry, spraying the slurry on the surface of the heat-conducting layer, and sintering at the temperature of 1000-1100 ℃ to form a reinforced coating;

the reinforced coating comprises SiO in percentage by weight based on the total amount of the reinforced coating₂45-80% by weight, K₂10-25% by weight of O, Al₂O₃0-10 wt%, MgO 0-10 wt%, ZnO 0-20 wt%, Co₃O₄0-5 wt%, Na₂0 to 10 weight percent of O.

14. Use of the thermally conductive furnace tube of any one of claims 1-13 in a two pass radiant section ethylene cracking furnace.

15. The use of claim 14, wherein the portion of the furnace tube not provided with the heat conducting member is a light pipe or is coated with a thermal barrier coating or is provided with a built-in second heat conducting member or any combination of the above manners.

Technical Field

The invention relates to the field of heat-conducting furnace tubes for ethylene cracking furnaces, in particular to a heat-conducting furnace tube for a two-pass radiation section ethylene cracking furnace, a preparation method of the heat-conducting furnace tube and application of the heat-conducting furnace tube in the ethylene cracking furnace.

Background

At present, the industrial production of ethylene mainly adopts a tubular reactor high-temperature steam thermal cracking method. For a cracking furnace for producing ethylene, in order to improve selectivity of cracking products, yield of cracking products and adaptability to raw materials, it is necessary to optimize the structure of the cracking furnace, especially the structure of a radiation furnace tube of the cracking furnace. In recent years, various radiant coils with different structures appear in sequence, and mainly include single-row branch reducing, mixed-row branch reducing, non-branch reducing, single-pass equal-diameter and the like. At present, high-selectivity furnace tubes with two-range (18-24m) branch diameter variation and two-range diameter variation are widely applied in mainstream cracking furnace design companies. The residence time of the reaction materials in the furnace tubes is generally controlled to be 0.15-0.25s, the furnace tubes in the first process usually adopt the furnace tubes with small diameters and large specific surface areas, which is favorable for rapid temperature rise, and the furnace tubes with large diameters are favorable for reducing the coking sensitivity of the furnace tubes in the second process. In recent decades, with the progress of engineering technology, large-scale cracking furnaces have been developed greatly, megaton-class ethylene plants have come out, and the large-scale cracking furnaces can save investment on one hand, and can reduce the number of furnaces while ensuring yield on the other hand, so that the occupied area is reduced, and the large-scale cracking furnaces are convenient to manage and maintain. For cracking furnaces of 10-20 ten thousand tons, the cracking furnace with two-pass furnace tube has the advantages of improved mechanical performance of the furnace tube, reduced thermal stress, improved ethylene yield, moderate operation period, high cracking selectivity, small furnace hearth in the radiation section, and the like. Cracking furnaces with two-pass tubes are the predominant type of cracking furnaces in current practice.

The cracking of petroleum hydrocarbons to ethylene is a highly endothermic process at high temperatures, and therefore requires not only heating of the reaction mass to relatively high temperatures to initiate the cracking reaction, but also continuous supply of sufficient heat during the reaction to achieve the desired conversion. By optimizing the structure of the cracking furnace tube, the higher heat transfer efficiency of the furnace tube can be realized, and in the prior art, the furnace tube of the cracking furnace commonly used in the petrochemical industry generally has the following structure:

(1) one or more ribs on the inner surface of the tube wall of one or more regions or all regions are arranged in the cracking furnace tube from the inlet end to the outlet end of the furnace tube along the axial direction of the furnace tube, and the ribs extend spirally on the inner surface of the tube wall along the axial direction of the furnace tube. For example, the reinforced heat transfer tube disclosed in CN2144807Y includes a tube body, in which single-blade rotating fins are fixed, and although the fins can achieve the purpose of stirring the fluid to reduce the thickness of the boundary layer as much as possible, as the service time of the furnace tube increases, the coking on the inner surface of the furnace tube will make the fins have weaker functions, and the function of reducing the boundary layer will also be reduced correspondingly.

(2) The fins, which are discretely disposed on the inner surface of the furnace tube, also reduce the boundary layer thickness, but also play a smaller and smaller role as the amount of coking on the inner surface of the furnace tube increases.

(3) The cracking furnace tube is additionally provided with a twisted piece reinforced heat transfer tube, such as the heat transfer tube disclosed in CN104560111A, the twisted piece extends spirally along the axial direction of the heat transfer tube, although the twisted piece reinforced heat transfer tube has good effects of reinforcing heat transfer and inhibiting coking, in the long-time operation process, because the tube is often over-temperature in the operation process, and because the cracking furnace tube inevitably generates phenomena such as carburization in the use process, the twisted piece reinforced heat transfer tube cracks, and the twisted piece reinforced heat transfer tube fails.

Therefore, the problem to be solved in the field is how to further slow down coking and carburization in the heat transfer pipe while ensuring the heat transfer effect of the heat transfer pipe, and to increase the temperature of the cracking material in a short time.

Disclosure of Invention

The invention aims to solve the problems that the inner wall of a heat transfer furnace tube in the prior art is easy to coke and carburize and has poor heat transfer effect, and provides the heat transfer furnace tube for the two-pass radiation section ethylene cracking furnace, the preparation method and the application in the cracking furnace.

In order to achieve the above object, a first aspect of the present invention provides a heat conduction furnace tube for a two-pass radiation-section ethylene cracking furnace, wherein the heat conduction furnace tube comprises a furnace tube main body, and a heat conduction member is disposed on an inner side wall of the furnace tube main body along a length direction of the furnace tube main body; the heat conducting components comprise a first heat conducting piece and a second heat conducting piece, the first heat conducting pieces are arranged in a plurality of pieces, and the first heat conducting pieces surround the cross section of the inner side wall of the furnace tube main body for a circle and are formed by protruding towards the inside of the furnace tube main body; the second heat conducting piece is spirally arranged along the axial direction of the furnace tube main body.

A second aspect of the present invention provides a method for manufacturing the heat conducting furnace tube of the first aspect, including heating the heat conducting furnace tube in an atmosphere with a low oxygen partial pressure to form a heat conducting layer on the surface of the heat conducting furnace tube.

The third aspect of the invention provides an application of the heat conducting furnace tube of the first aspect in a two-pass radiation section ethylene cracking furnace.

The heat conducting components in the heat conducting furnace tube prepared by the invention are matched with each other, so that the heat transfer performance of the heat conducting furnace tube can be obviously improved, the coking amount in the heat conducting furnace tube prepared by the invention is greatly reduced, and the service life of the heat conducting furnace tube is prolonged; and the carburization phenomenon of the heat conduction furnace tube can be reduced.

Drawings

Fig. 1 is a schematic structural view of a heat conductive member according to the present invention;

fig. 2 is a schematic structural view of a two-pass 2-1 type radiant coils.

Description of the figures

1: a first heat-conducting member;

2: a second heat-conducting member;

3: a first pass furnace tube;

4: a second pass furnace tube.

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.

As shown in fig. 1, the heat conduction furnace tube for the two-pass radiation-section ethylene cracking furnace provided by the invention comprises a furnace tube main body, wherein the inner side wall of the furnace tube main body is provided with a heat conduction member along the length direction of the furnace tube main body; the heat conducting component comprises a first heat conducting piece 1 and a second heat conducting piece 2, wherein the first heat conducting pieces 1 are arranged in a plurality of strips, encircle a circle along the cross section of the inner side wall of the furnace tube main body and are formed by protruding towards the interior of the furnace tube main body; the second heat conducting piece 2 is spirally arranged along the axial direction of the furnace tube main body.

The heat conduction furnace tube for the two-pass radiation section ethylene cracking furnace provided by the invention can be a double-U-shaped tube structure shown in figure 2.

According to the invention, the heat conduction member formed by the first heat conduction piece 1 and the second heat conduction piece 2 is arranged in the furnace tube main body, so that the tangential speed of fluid is improved, the boundary layer near the wall surface of the furnace tube is damaged, the heat transfer effect is improved, the coking phenomenon on the inner wall of the furnace tube is reduced, and the decoking period and the service life of the furnace tube are effectively prolonged.

The heat conducting furnace tube can be a nickel-chromium furnace tube, and the composition of the nickel-chromium furnace tube comprises Cr, Ni, Fe, Mn, C and at least one element selected from Al, Zr, Nb and Mo.

The extension length H of the heat conducting component along the axial direction of the furnace tube main body meets the following requirements: h is more than or equal to 0 and less than or equal to L/3, in order to further improve the heat transfer performance of the heat-conducting furnace tube, preferably, the extension length H of the heat-conducting component along the axial direction of the furnace tube main body meets the following requirements: h is not less than 1/4L and not more than 1/3L; wherein L is the length of the furnace tube main body.

The extension length H of the heat conduction member along the axial direction of the furnace tube main body in the invention refers to the extension length of the heat conduction member composed of the first heat conduction piece 1 and the second heat conduction piece 2 along the axial direction of the furnace tube main body.

In order to further improve the heat transfer effect and simultaneously reduce the coking amount of the furnace tube, the diameter of an inner ring of the first heat conducting piece 1 is D, D satisfies D/D is more than or equal to 0.1 and less than or equal to 0.9, and D is the inner diameter of the main body of the furnace tube; preferably, 0.4. ltoreq. D/D. ltoreq.0.7.

Preferably, the angle of rotation of the spiral in the second heat-conducting member 2 is 90 ° -1080 °, preferably 120 ° -360 °. In addition, the extension length H1 of the second heat conduction member 2 along the axial direction of the furnace tube main body satisfies: 1D ≦ H1 ≦ 10D, more preferably satisfying: 2D is less than or equal to H1 and less than or equal to 8D, and particularly preferably 2.5D, and the extension length H1 of the second heat conduction piece 2 along the axial direction of the furnace tube main body is the extension length of only one second heat conduction piece 2 in a spiral shape along the axial direction of the furnace tube main body.

In the invention, a group of heat conducting members consists of a plurality of first heat conducting pieces 1 and a plurality of second heat conducting pieces 2 which are parallel, and the ratio of the axial length of the group of heat conducting members to the inner diameter of the furnace tube is 8-12, preferably 9-11, and particularly preferably 10. The diameter D of the inner ring of the first heat conduction member 1 is the diameter of the inner ring formed by the highest point of the first heat conduction member 1 protruding out of the inner side of the furnace tube main body, and the axial distance between the adjacent first heat conduction members 1 is 0.01D-2.5D, preferably 0.3-0.7D, and particularly preferably 0.5D. The inner spiral of the second heat conduction member 2 can rotate clockwise or counterclockwise, and the spiral directions of the second heat conduction member 2 can be the same or opposite.

The first heat conducting piece 1 and the second heat conducting piece 2 are arranged according to the structure, and particularly under the condition that the first heat conducting piece 1 and the second heat conducting piece 2 are matched with each other, the heat transfer effect of the heat conducting furnace tube can be greatly improved, the flow resistance of fluid in the heat conducting furnace tube is reduced, and the coking phenomenon of the inner wall of the heat conducting furnace tube is reduced.

In order to further improve the heat transfer performance of the heat-conducting furnace tube and reduce the coking phenomenon of the inner wall of the heat-conducting furnace tube, the inner side of the heat-conducting furnace tube also comprises a heat-conducting layer, and the heat-conducting layer comprises 30-40 wt% of Cr, 2.5-6 wt% of Ni, 3-9 wt% of Fe, 8-13 wt% of Mn, 0-0.5 wt% of C, 35-40 wt% of O and 1.5-20 wt% of at least one element selected from Al, Zr, Nb and Mo based on the total weight of the heat-conducting layer.

In the invention, the heat conduction layer is arranged in the heat conduction furnace tube, and the heat conduction layer and the heat conduction component are matched with each other, so that the heat transfer performance and the wear resistance of the heat conduction furnace tube can be effectively improved, the coking phenomenon of the inner wall of the heat conduction furnace tube can be effectively inhibited, the anti-permeability performance of the heat conduction furnace tube is improved, the decoking period of the heat conduction furnace tube is prolonged, and the service life of the heat conduction furnace tube is prolonged.

Preferably, the thickness of the heat conducting layer is 0.1-5 μm. The heat conduction layer is within the thickness range, the coking amount of the heat conduction furnace tube can be effectively reduced, and the heat transfer performance of the heat conduction furnace tube cannot be influenced.

Preferably, the inner side of the heat conducting furnace tube further comprises a reinforcing coating positioned above the heat conducting layerThe reinforcing coating comprises SiO in percent by weight based on the total amount of the reinforcing coating₂45-80% by weight, K₂10-25% by weight of O, Al₂O₃0-10 wt%, MgO 0-10 wt%, ZnO 0-20 wt%, Co₃O₄0-5 wt%, Na₂0 to 10 weight percent of O.

According to the invention, the reinforcing coating, the heat conduction layer and the heat conduction member arranged on the inner wall of the heat conduction furnace tube are matched with each other, so that the coking phenomenon of the inner wall of the heat conduction furnace tube can be further inhibited, and the service life of the furnace tube is prolonged.

Preferably, the thickness of the reinforcement coating is 5-10 μm. In the invention, the reinforced coating is in the thickness range, so that the coking amount of the heat-conducting furnace tube can be effectively inhibited, the carburization phenomenon of the heat-conducting furnace tube is reduced, and the service life and the heat transfer efficiency of the heat-conducting furnace tube are improved. The reinforced coating and the heat conduction layer are mutually matched, so that the strong impact effect of air flow on the heating furnace tube in the decoking process can be effectively reduced, and the service life and the decoking period of the furnace tube can be further prolonged.

In the invention, the part of the heat conducting furnace tube not provided with the heat conducting component can be a light pipe, or a heat barrier coating is coated, or a second heat conducting piece is arranged in the heat conducting furnace tube, or any combination of the above modes. Preferably, the part of the heat conducting furnace tube, which is not provided with the heat conducting component, is coated with a thermal barrier coating or internally provided with a second heat conducting piece or a combination of the above modes. Particularly, the part of the heat conducting furnace tube, which is not provided with the heat conducting component, is a combination of two ways of coating a thermal barrier coating and internally arranging a second heat conducting piece. The heat conducting furnace tube is characterized in that the heat conducting furnace tube is provided with a heat conducting component, and the heat conducting component is arranged on the heat conducting furnace tube.

A second aspect of the present invention provides a method for manufacturing the heat conducting furnace tube of the first aspect, including heating the heat conducting furnace tube in an atmosphere with a low oxygen partial pressure to form a heat conducting layer on the surface of the heat conducting furnace tube.

In the process of preparing the heat-conducting furnace tube, at least one metal selected from Al, Zr, Nb and Mo is added into the nickel-chromium alloy containing Cr, Ni, Fe, Mn and C elements according to the conventional manufacturing process of the cracking furnace tube (such as a centrifugal casting method, the temperature is 900-1000 ℃, the rotating speed is 1000-1300r/min, and the forming time is 3-4h) to prepare the tube, and then the tube is heated under the environment of low oxygen partial pressure to form a heat-conducting layer on the surface of the tube. The heat conductive layer comprises 30-40 wt% of Cr, 2.5-6 wt% of Ni, 3-9 wt% of Fe, 8-13 wt% of Mn, 0-0.5 wt% of C, 35-40 wt% of O, and 1.5-20 wt% of at least one element selected from the group consisting of Al, Zr, Nb and Mo, based on the total weight of the heat conductive layer. The method is more convenient to form the heat conduction layer on the surface of the heat conduction furnace tube, reduces the thermal interface between the heat conduction furnace tube and the heat conduction layer, and improves the heat conduction performance of the heat conduction furnace tube.

In order to further improve the heat conductivity of the heat conducting furnace tube, the conditions of the low oxygen partial pressure atmosphere comprise: the gas providing the low oxygen partial pressure atmosphere comprises CO₂、CO、H₂And water vapor, the oxygen partial pressure is less than or equal to 10^-16Pa; the conditions of the heat treatment include: the temperature of the heating treatment is 400-1100 ℃, and preferably 800-1000 ℃; the time of the heat treatment is 5 to 200 hours, preferably 10 to 100 hours.

Preferably, the gas providing the low oxygen partial pressure atmosphere comprises CO₂Gas mixture with CO, gas mixture of water vapor and CO, H₂And water vapor.

The heat conduction layer formed on the surface of the heat conduction furnace tube by the method has a stable structure and excellent heat transfer performance, and can reduce the coking amount of the inner wall of the heat conduction furnace tube.

In order to further improve the anti-coking performance of the heat conduction furnace tube and prolong the service life of the heat conduction furnace tube, the method also comprises the step of spraying a reinforcing coating on the surface of the heat conduction layer.

Preferably, the preparation method of the reinforced coating comprises the following steps: mixing the raw materials with water to form slurry, spraying the slurry on the surface of the heat-conducting layer, and sintering at the temperature of 1000-1100 ℃ to form a reinforced coating;

based on the total weight of the reinforced coating, the reinforced coating comprisesSiO in percent by weight₂45-80% by weight, K₂10-25% by weight of O, Al₂O₃0-10 wt%, MgO 0-10 wt%, ZnO 0-20 wt%, Co₃O₄0-5 wt%, Na₂0 to 10 weight percent of O.

The reinforced coating is arranged on the surface of the heat conducting layer according to the method, so that the interface thermal resistance between the heat conducting layer and the reinforced coating is reduced, the heat transfer performance of the heat conducting furnace tube is improved, and the coking amount of the inner wall of the heat conducting furnace tube is effectively reduced.

In a third aspect, the invention provides the use of the heat conducting furnace tube of the first aspect in a two-pass radiant section ethylene cracking furnace.

Preferably, the part of the furnace tube not provided with the heat conducting component is a light pipe or is coated with a thermal barrier coating or is internally provided with the second heat conducting piece 2 or any combination of the above modes.

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

In the following examples and comparative examples,

the heat transfer enhancement integration factor is defined as follows:

wherein, Nu_sNu represents the Nussel number of the untreated smooth heat transfer furnace tube and the high-performance heat transfer furnace tube added with the inner member, f_sF represents the resistance coefficient of the untreated smooth heat transfer furnace tube and the high-performance heat transfer furnace tube added with the inner member, d represents the inner diameter of the furnace tube, Δ p represents the pressure drop of the furnace tube, L represents the length of the furnace tube, ρ represents the density of fluid in the tube, and u represents the flow velocity of the fluid in the tube. In the above, the untreated smooth heat transfer furnace tube means that the heat conducting member, the heat conducting layer and the reinforcing coating are not arranged in the heat transfer furnace tube.

The untreated smooth heat transfer furnace tube means that the heat transfer furnace tube is internally provided with no heat conducting component, no heat conducting layer and no reinforcing coating.

The variation of the heat transfer enhancement factor in the examples and the comparative examples was determined by measuring the heat transfer enhancement factor η 1 of the heat conductive furnace tubes, the heat transfer enhancement factor η 0 of the untreated smooth heat transfer furnace tubes, and the variation of the heat transfer enhancement factor ═ η 1- η 0)/η 0 × 100% in one operating cycle.

The variation of the coking amount is detected in one operation cycle, the coking thickness h1 of the inner wall of the heat-conducting furnace tube in the following examples and comparative examples, the coking thickness h0 of the heat-conducting furnace tube without the heat-conducting component, the heat-conducting layer and the reinforcing coating inside, and the variation of the coking amount is (h0-h1)/h0 x 100%. Wherein, the operation periods of different heat conduction furnace tubes are not necessarily the same.

Example 1

The present embodiment is used to provide a heat conducting furnace tube, which is a two-pass radiant-section cracking furnace tube including a first-pass furnace tube 3 and a second-pass furnace tube 4, as shown in fig. 2.

The inner diameter D of the tube body is 50mm, the length L of the tube body is 13m, as shown in fig. 2, 8 sets of heat conducting members are uniformly arranged at the two top ends of the U-shaped tube along the axial direction of the tube, and the extension length H of the 8 sets of heat conducting members along the axial direction of the tube body is 4 m.

The first heat conducting piece 1 is a circular ring formed by surrounding a circle along the cross section of the inner wall of the furnace tube main body, and the diameter d of the inner ring of the first heat conducting piece 1 is 12.5 mm. A group of heat conduction members comprises 15 first heat conduction members 1, and the axial distance between every two adjacent first heat conduction members 1 is 0.5D.

The second heat conduction pieces 2 are arranged in parallel, the rotation angle of the second heat conduction pieces 2 along the spiral of the inner wall of the furnace tube main body is 180 degrees, and the two second heat conduction pieces 2 are spiral along the clockwise direction. The length H1 of the second heat conduction member 2 extending along the length direction of the furnace tube main body is 2.5D, and the ratio of the area of the middle opening of the second heat conduction member to the area of the furnace tube is 0.65: 1.

And only the second heat-conducting piece 2 is arranged at the position where the axial length of the furnace tube main body is H-4 m-13m and the position of the two-pass tube.

The heat conducting furnace tube is used in a cracking furnace, the operation period is 90 days, and the heat transfer enhancement comprehensive factor eta is improved by 23 percent.

Example 2

The present embodiment is used to provide a heat conducting furnace tube, which is a two-pass radiant-section cracking furnace tube including a first-pass furnace tube 3 and a second-pass furnace tube 4, as shown in fig. 2.

The inner diameter D of the tube body is 50mm, the length L of the tube body is 13m, as shown in fig. 2, 8 sets of heat conducting members are uniformly arranged at the two top ends of the U-shaped tube along the axial direction of the tube, and the extension length H of the 8 sets of heat conducting members along the axial direction of the tube body is 4 m.

The first heat conducting piece 1 is a circular ring formed by surrounding a circle along the cross section of the inner wall of the furnace tube main body, and the diameter d of the inner ring of the first heat conducting piece 1 is 12.5 mm. A group of heat conduction members comprises 15 first heat conduction members 1, and the axial distance between every two adjacent first heat conduction members 1 is 0.5D.

The second heat conduction pieces 2 are arranged in parallel, the rotation angle of the second heat conduction pieces 2 along the spiral of the inner wall of the furnace tube main body is 180 degrees, and the two second heat conduction pieces 2 are spiral along the clockwise direction. The length H1 of the second heat conduction member 2 extending along the length direction of the furnace tube main body is 2.5D, and the ratio of the area of the middle opening of the second heat conduction member to the area of the furnace tube is 0.65: 1.

And no heat conducting component or thermal barrier coating is arranged at the position where the axial length of the furnace tube main body is H-4 m-13m and the position of the two-pass tube.

The heat conducting furnace tube is used in a cracking furnace, the operation period is 60 days, and the heat transfer enhancement comprehensive factor eta is improved by 15 percent.

Example 3

The present embodiment is used to provide a heat conducting furnace tube, which is a two-pass radiant-section cracking furnace tube including a first-pass furnace tube 3 and a second-pass furnace tube 4, as shown in fig. 2.

The inner diameter D of the tube body is 50mm, the length L of the tube body is 13m, as shown in fig. 2, 8 sets of heat conducting members are uniformly arranged at the two top ends of the U-shaped tube along the axial direction of the tube, and the extension length H of the 8 sets of heat conducting members along the axial direction of the tube body is 4 m.

The first heat conducting piece 1 is a circular ring formed by surrounding a circle along the cross section of the inner wall of the furnace tube main body, and the diameter d of the inner ring of the first heat conducting piece 1 is 12.5 mm. A group of heat conduction members comprises 15 first heat conduction members 1, and the axial distance between every two adjacent first heat conduction members 1 is 0.5D.

The second heat conduction pieces 2 are arranged in parallel, the rotation angle of the second heat conduction pieces 2 along the spiral of the inner wall of the furnace tube main body is 180 degrees, and the two second heat conduction pieces 2 are spiral along the clockwise direction. The length H1 of the second heat conduction member 2 extending along the length direction of the furnace tube main body is 2.5D, and the ratio of the area of the middle opening of the second heat conduction member to the area of the furnace tube is 0.65: 1.

The inner wall of the furnace tube is provided with a thermal barrier coating at the position where the axial length of the furnace tube main body is H-4 m-13m and the position of the two-pass tube.

The preparation method of the heat conduction furnace tube comprises the following steps:

(1) and carrying out low-oxygen partial pressure gas atmosphere treatment on the nickel-chromium furnace tube. The method comprises the steps of treating a nickel-chromium furnace tube containing Cr, Ni, Fe, Mn, C and Nb for 4 hours at the temperature of 1000 ℃ and the rotating speed of 1000r/min by adopting a centrifugal casting method, and then carrying out heat treatment under low oxygen partial pressure to form a heat conduction layer on the surface of the nickel-chromium furnace tube.

The low oxygen partial pressure gas used in the low oxygen partial pressure condition is H₂And water vapor, the water vapor accounts for 10% of the gas mixture by volume, the oxygen partial pressure is less than or equal to 10^-16Pa. The heating temperature is 800 ℃, the heating treatment time is 100h, and the heat conduction layer with the thickness of 5 μm is formed on the surface of the nickel-chromium furnace tube by the treatment of the method. The heat conductive layer was analyzed by energy spectroscopy and comprised, in weight percent, 30% Cr, 3% Ni, 3% Fe, 8% Mn, 0.3% C, 38% O, and 17.7% Nb, based on the total weight of the heat conductive layer.

(2) And coating a reinforced coating on the surface of the heat-conducting furnace tube. Mixing SiO₂、K₂O、Al₂O₃、MgO、Co₃O₄、Na₂Mixing O and water uniformly to form slurry, spraying the slurry on the surface of the heat-conducting layer uniformly, and sintering at the temperature of 1000 ℃ to form a reinforcing coating with the thickness of 10 mu m, so that the reinforcing coating comprises the following components in percentage by weight based on the total amount of the reinforcing coating: SiO 2₂70% by weight, K₂O10 wt%, Al₂O₃5% by weightMgO 5 wt%, Co₃O₄5% by weight and Na₂O5 wt.%.

The heat-conducting furnace tube is used in a cracking furnace, the operation period is 80 days, the coking amount is reduced by 30 percent, and the heat transfer enhancement comprehensive factor eta is improved by 18 percent.

Example 4

The present embodiment is used to provide a heat conducting furnace tube, which is a two-pass radiant-section cracking furnace tube including a first-pass furnace tube 3 and a second-pass furnace tube 4, as shown in fig. 2.

The inner diameter D of the tube body is 50mm, the length L of the tube body is 13m, as shown in fig. 2, 8 sets of heat conducting members are uniformly arranged at the two top ends of the U-shaped tube along the axial direction of the tube, and the extension length H of the 8 sets of heat conducting members along the axial direction of the tube body is 4 m.

The first heat conducting piece 1 is a circular ring formed by surrounding a circle along the cross section of the inner wall of the furnace tube main body, and the diameter d of the inner ring of the first heat conducting piece 1 is 12.5 mm. A group of heat conduction members comprises 15 first heat conduction members 1, and the axial distance between every two adjacent first heat conduction members 1 is 0.5D.

The second heat conduction pieces 2 are arranged in parallel, the rotation angle of the second heat conduction pieces 2 along the spiral of the inner wall of the furnace tube main body is 180 degrees, and the two second heat conduction pieces 2 are spiral along the clockwise direction. The length H1 of the second heat conduction member 2 extending along the length direction of the furnace tube main body is 2.5D, and the ratio of the area of the middle opening of the second heat conduction member to the area of the furnace tube is 0.65: 1.

The second heat-conducting member 2 was disposed along the axial length H of the furnace tube main body at 4m to 13m and the second pass tube, and the thermal barrier coating was applied to the inner wall of the furnace tube (the thermal barrier coating was prepared in the same manner as in example 3).

The heat conducting furnace tube is used in a cracking furnace, the operation period is 120 days, and the heat transfer enhancement comprehensive factor eta is improved by 27 percent.

Comparative example 1

This comparative example provides a two-pass heat transfer tube, the same structure as the heat transfer tube in example 2, with the difference that: the heat transfer pipe is not provided with a heat conduction component inside. When the two-pass heat transfer pipe is used in a cracking furnace, the heat transfer enhancement comprehensive factor eta is improved by 0 percent.

Comparative example 2

Compared with the heat transfer pipe in embodiment 2, the difference is that: only the first heat-conducting member 1 is disposed inside the two-pass heat transfer tube. When the heat conduction furnace tube is used in a cracking furnace, the heat transfer enhancement comprehensive factor eta is improved by 7 percent.

Comparative example 3

Compared with the heat transfer pipe in embodiment 2, the difference is that: only the second heat-conducting member 2 is arranged inside the two-pass heat transfer tube. When the heat conduction furnace tube is used in a cracking furnace, the heat transfer enhancement comprehensive factor eta is improved by 6 percent.

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.