Radiation furnace tube of cracking furnace and cracking furnace

Abstract

The utility model provides a cracking furnace radiation furnace tube and a cracking furnace, the cracking furnace radiation furnace tube comprises at least one group of 6-2-1-1 type radiation furnace tubes, each group of 6-2-1-1 type radiation furnace tubes comprises a first-stroke furnace tube, a second-stroke furnace tube, a third-stroke furnace tube and a fourth-stroke furnace tube which are communicated in sequence; the first-stroke furnace tube comprises six furnace tubes, and every three furnace tubes form a group; the second-stroke furnace tube comprises two furnace tubes; each of the third-stroke furnace tube and the fourth-stroke furnace tube comprises a furnace tube; according to the sequence of the first-stroke furnace tube, the second-stroke furnace tube, the third-stroke furnace tube and the fourth-stroke furnace tube, the tube spacing / outer diameter ratio of each-stroke furnace tube is sequentially increased. The radiation furnace tubes are reasonably arranged, the heat absorption area can be enlarged, heat can be quickly absorbed, the retention time can be shortened, meanwhile, the heating uniformity of each furnace tube can be ensured, side reactions are reduced, and the selectivity and the yield of ethylene are improved.

Description

Technical Field

[0001] The utility model belongs to the field of cracking furnaces, and particularly relates to a radiant furnace tube and a cracking furnace of a cracking furnace. Background Art

[0002] Ethylene is an important organic chemical raw material, mainly used for the production of downstream products such as polyethylene, ethylbenzene, ethylene oxide, vinyl acetate, etc. Among them, the main production method of ethylene is steam cracking, that is, by pyrolyzing raw materials such as naphtha, light diesel, and hydrogenated tail oil at high temperature to produce unsaturated hydrocarbons such as ethylene, propylene, and butadiene. In this process, the cracking furnace is a key device, and the radiant furnace tube is the core component of the cracking furnace. The cracking raw material and dilution steam are heated to the initial cracking temperature in the convection section furnace tubes of the cracking furnace, and then enter the radiant section furnace tubes for cracking. The configuration and structural parameters of the radiant furnace tubes have an important influence on the yield of cracking products and the coking rate.

[0003] The existing ethylene cracking technologies mainly adopt the furnace types developed by companies such as Stone&Webster, LUMMUS, Linde, Kellog&BraunRoot, and Sinopec. These furnace types usually adopt multi-pass variable-diameter or equal-diameter furnace tubes, such as W-type, M-type, 3-1-1 type, 4-2-1-1 type, 1-1-1-1 type, etc., to meet different process requirements.

[0004] The Chinese patent with the publication number CN204198680U provides a 3-1-1 type radiant furnace tube for an ethylene cracking furnace, which includes three-pass furnace tubes. The first pass uses three furnace tubes, and the second and third passes both use one furnace tube. Due to the small number of tube passes and furnace tubes, and the fact that the ethylene cracking reaction mostly occurs in the first half, with fewer furnace tubes, problems such as incomplete ethylene cracking, slow heat absorption, and generation of by-products usually occur.

[0005] However, the number of furnace tubes and the number of tube passes are not necessarily the more the better. When the number of furnace tubes is large, the furnace tubes are arranged closely, and it is easy to shield between adjacent furnace tubes, which easily leads to uneven heating of the furnace tubes. Therefore, how to provide a reasonably arranged radiant furnace tube that can absorb heat quickly, shorten the reaction time, ensure the uniformity of heating, improve the selectivity and yield of ethylene cracking, and reduce by-products is a problem to be solved.

[0006] In view of this, the present utility model is particularly proposed. Content of the Utility Model

[0007] The purpose of the present utility model is to solve the problems existing in the prior art and provide a cracking furnace radiant furnace tube and a cracking furnace. The radiant furnace tube of the present utility model has a simple structure and reasonable arrangement, can expand the heat absorption area, realize the rapid heat absorption of the raw material, shorten the residence time, ensure the uniformity of the furnace tube heating, reduce the occurrence of side reactions, and improve the selectivity and yield of ethylene.

[0008] To solve the above technical problems, the basic concept of the technical solution adopted by the present utility model is:

[0009] The present utility model provides a cracking furnace radiant furnace tube, which includes at least one group of 6-2-1-1 type radiant furnace tubes. Each group of 6-2-1-1 type radiant furnace tubes includes a first-pass furnace tube, a second-pass furnace tube, a third-pass furnace tube, and a fourth-pass furnace tube that are connected in sequence; the first-pass furnace tube includes six furnace tubes, and every three furnace tubes are in a group; the second-pass furnace tube includes two furnace tubes; the third-pass furnace tube and the fourth-pass furnace tube each include one furnace tube; in the order of the first-pass furnace tube, the second-pass furnace tube, the third-pass furnace tube, and the fourth-pass furnace tube, the ratio of the tube spacing to the outer diameter of each pass of furnace tubes increases in sequence.

[0010] In a further scheme, each pass of furnace tubes is located in the same plane and arranged side by side in a single row, and the tube spacing between the furnace tubes in each pass is 1.5 to 2.5 times the outer diameter of the furnace tubes.

[0011] In a further scheme, in the order of the first-pass furnace tube, the second-pass furnace tube, the third-pass furnace tube, and the fourth-pass furnace tube, the inner diameters of each pass of furnace tubes increase in sequence.

[0012] In a further scheme, the inner diameter of the first-pass furnace tube is φ1, the inner diameter of the second-pass furnace tube is φ2, the inner diameter of the third-pass furnace tube is φ3, and the inner diameter of the fourth-pass furnace tube is φ4, and 40mm ≤ φ1 ≤ 150mm, 80mm ≤ φ2 ≤ 200mm, 120mm ≤ φ3 ≤ 300mm, 120mm ≤ φ4 ≤ 300mm.

[0013] In a further scheme, in the second-pass furnace tube, one end of each of the two furnace tubes is connected to each group of furnace tubes in the first-pass furnace tube through two first connectors, and the other ends of the two furnace tubes are connected to the third-pass furnace tube through a second connector.

[0014] In a further scheme, each first connector includes three inlets and one outlet. The three inlets of the first connector are respectively connected to the three outlet ends of a group of three furnace tubes in the first-pass furnace tube, and the outlet of the first connector is connected to the inlet end of one furnace tube in the second-pass furnace tube through a U-shaped bend pipe.

[0015] In a further solution, the second connecting member includes two inlets and one outlet, the two inlets of the second connecting member are respectively connected to the outlet ends of the two furnace tubes in the second-pass furnace tube, and the outlet of the second connecting member is connected to the inlet end of the third-pass furnace tube through a U-shaped bend pipe.

[0016] In a further solution, the outlet end of the third-pass furnace tube is connected to the inlet end of the fourth-pass furnace tube via a U-shaped bend pipe.

[0017] A further solution includes two groups of 6-2-1-1 type radiation furnace tubes to form a 12-4-2-2 type furnace tube configuration.

[0018] In a further solution, all radiation furnace tubes are made of high temperature heat-resistant alloy steel, which can withstand high temperature and high pressure environment.

[0019] The utility model also provides a cracking furnace, in which one or two or more groups of the above-mentioned cracking furnace radiation furnace tubes are arranged.

[0020] Compared with the prior art, the beneficial effects of the utility model are:

[0021] 1. The radiation furnace tube of the cracking furnace of the utility model comprises at least one group of 6-2-1-1 type radiation furnace tubes, and the ratio of the tube spacing / outer diameter of each furnace tube increases successively. Compared with the existing radiation furnace tube for ethylene, the first half adopts a parallel structure of multiple furnace tubes, the furnace tubes are arranged reasonably, and the tube spacing / outer diameter is set reasonably, which can not only expand the heat absorption area, so that the cracking raw material can quickly absorb heat in the first half of the radiation furnace tube, shorten the residence time, but also ensure the uniformity of heating of each furnace tube, reduce the occurrence of side reactions, thereby improving the selectivity and yield of ethylene.

[0022] 2. The radiation furnace tube of the cracking furnace of the utility model includes six furnace tubes in the first pass, and three furnace tubes form a group; the heat transfer area is larger and the heat transfer speed is faster, which is conducive to the rapid absorption of heat by the raw materials. The radiation furnace tubes of two adjacent passes are connected by appropriate connectors, the structure is simple, and the actual position and height of the connectors can be set as needed, which can further optimize the layout of the furnace tubes, so that the flow of the cracking raw materials in the furnace tubes is smoother, the reaction efficiency is improved, and it also helps to reduce the maintenance cost of the equipment.

[0023] 3. The radiation furnace tube of the cracking furnace of the present invention can include a single group of 6-2-1-1 type radiation furnace tubes, or two groups of 12-4-2-2 type furnace tubes can be arranged side by side, or multiple groups of 6-2-1-1 type radiation furnace tubes or 12-4-2-2 type furnace tubes. The design of this furnace tube configuration and structural parameters can adapt to different raw material processing amounts and process conditions, improve the use flexibility and economy of the equipment, and have stronger adaptability.

[0024] The following further describes in detail the specific embodiments of the present utility model in conjunction with the accompanying drawings. Description of the Drawings

[0025] Figure 1 is a schematic structural diagram of the four-pass 6-2-1-1 type furnace tube of the present utility model.

[0026] Figure 2 is a schematic structural diagram of the four-pass 12-4-2-2 type furnace tube of the present utility model.

[0027] Figure 3 is another schematic structural diagram of the 6-2-1-1 type furnace tube of the present utility model.

[0028] Figure 4 is yet another schematic structural diagram of the 6-2-1-1 type furnace tube of the present utility model.

[0029] Figure 5 is still another schematic structural diagram of the 6-2-1-1 type furnace tube of the present utility model.

[0030] In the figure: 1 - the first-pass furnace tube; 2 - the three-way tube; 3 - the first U-shaped elbow; 4 - the second-pass furnace tube; 5 - the Y-shaped tube; 6 - the second U-shaped elbow; 7 - the third-pass furnace tube; 8 - the third U-shaped elbow; 9 - the fourth-pass furnace tube.

[0031] It should be noted that these drawings and textual descriptions are not intended to limit the scope of the concept of the present utility model in any way, but rather to illustrate the concept of the present utility model to those skilled in the art by reference to specific embodiments. Specific Embodiments

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present utility model clearer, the following will clearly and completely describe the technical solutions in the embodiments in conjunction with the accompanying drawings in the embodiments of the present utility model. The following embodiments are used to illustrate the present utility model but are not used to limit the scope of the present utility model.

[0033] In the description of the present utility model, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present utility model.

[0034] In the description of the present utility model, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0035] As Figure 1 shown, the present utility model provides a cracking furnace radiant furnace tube, including at least one group of 6-2-1-1 type radiant furnace tubes. Each group of 6-2-1-1 type radiant furnace tubes includes a first-stage furnace tube 1, a second-stage furnace tube 4, a third-stage furnace tube 7, and a fourth-stage furnace tube 9 that are sequentially connected in series. The first-stage furnace tube 1 includes six furnace tubes, and every three furnace tubes form a group; the second-stage furnace tube 4 includes two furnace tubes; the third-stage furnace tube 7 and the fourth-stage furnace tube 9 each include one furnace tube; in the order of the first-stage furnace tube 1, the second-stage furnace tube 4, the third-stage furnace tube 7, and the fourth-stage furnace tube 9, the ratio of the tube pitch to the outer diameter of each stage of furnace tubes increases in sequence.

[0036] The cracking furnace radiant furnace tube of the present utility model includes at least one group of 6-2-1-1 type radiant furnace tubes, and the ratio of the tube pitch to the outer diameter of each stage of furnace tubes increases in sequence. Compared with the existing radiant furnace tubes for ethylene, a parallel structure of multiple furnace tubes is adopted in the first half of the furnace tubes. The arrangement of the furnace tubes is reasonable, and the tube pitch to outer diameter gradually increases. Such a setting is reasonable, which can not only expand the heat absorption area, enable the cracking raw materials to quickly absorb heat in the first half of the radiant furnace tubes, shorten the residence time, but also ensure the uniformity of heat absorption of each furnace tube, reduce the occurrence of side reactions, thereby improving the selectivity and yield of ethylene.

[0037] Each furnace tube in the first-stage furnace tube 1, the second-stage furnace tube 4, the third-stage furnace tube 7, and the fourth-stage furnace tube 9 is a straight tube, and the cross-section of the furnace tube is circular.

[0038] It should be noted that the tube pitch refers to the shortest distance between the outer walls of two adjacent furnace tubes arranged side by side in the same stage.

[0039] Inside the same stage, the tube pitch between adjacent furnace tubes is the same; inside the same stage, the outer diameter of the furnace tubes is the same.

[0040] Each stage of furnace tubes is located in the same plane and arranged side by side in a single row. The tube pitch between the furnace tubes in each stage is 1.5 to 2.5 times the outer diameter of the furnace tubes.

[0041] In the present utility model, the first-stage furnace tubes 1 are designed as six straight tubes connected in parallel, with three tubes in each group. The second stage consists of straight tubes connected in parallel. In this way, the heat absorption area is increased, enabling the cracking raw materials to rapidly absorb heat in the first half of the radiant furnace tubes, shortening the residence time. At the same time, the tube spacing between the furnace tubes in each stage is controlled to be 1.5 to 2.5 times the outer diameter of the furnace tubes. Thus, while increasing the number of furnace tubes, it also avoids being too closely arranged and prevents shielding between adjacent furnace tubes, ensuring that each furnace tube can be evenly heated, avoiding coking blockage, further reducing the generation of side reactions, and improving the selectivity and yield of ethylene.

[0042] In the order of the first-stage furnace tubes 1, the second-stage furnace tubes 4, the third-stage furnace tubes 7, and the fourth-stage furnace tubes 9, the ratio of the tube spacing to the outer diameter of the furnace tubes in each stage increases successively. For example, the ratios of the tube spacing to the outer diameter of the furnace tubes in each stage can be 1.5, 1.6, 1.8, and 2.0 in sequence.

[0043] In a further embodiment, in the order of the first-stage furnace tubes 1, the second-stage furnace tubes 4, the third-stage furnace tubes 7, and the fourth-stage furnace tubes 9, the inner diameters of the furnace tubes in each stage increase successively.

[0044] In the flow direction of the raw materials, the cracking raw materials converge from the six furnace tubes of the first-stage furnace tubes 1 to the two furnace tubes of the second stage, and then successively enter one furnace tube of the third-stage furnace tubes 7 and the fourth-stage furnace tubes 9. The inner diameters of the furnace tubes in each stage increase successively. This can better adapt to the heat absorption ratio at different stages and achieve a better cracking effect.

[0045] In a further embodiment, the inner diameter of the first-stage furnace tubes 1 is φ1, the inner diameter of the second-stage furnace tubes 4 is φ2, the inner diameter of the third-stage furnace tubes 7 is φ3, and the inner diameter of the fourth-stage furnace tubes 9 is φ4, and 40mm ≤ φ1 ≤ 150mm, 80mm ≤ φ2 ≤ 200mm, 120mm ≤ φ3 ≤ 300mm, 120mm ≤ φ4 ≤ 300mm.

[0046] For example, as a specific embodiment, the inner diameter φ1 of the first-stage furnace tubes 1 is 63mm, the inner diameter φ2 of the second-stage furnace tubes 4 is 108mm, the inner diameter φ3 of the third-stage furnace tubes 7 is 158.8mm, and the inner diameter φ4 of the fourth-stage furnace tubes 9 is 200mm.

[0047] In a further embodiment, in the second-stage furnace tubes 4, one end of the two furnace tubes is respectively connected to each group of furnace tubes in the first-stage furnace tubes 1 through two first connectors, and the other ends of the two furnace tubes are connected to the third-stage furnace tubes 7 through a second connector.

[0048] In a further embodiment, each first connector includes three inlets and one outlet. The three inlets of the first connector are respectively connected to the three outlet ends of a group of three furnace tubes in the first-stage furnace tubes 1, and the outlet of the first connector is connected to the inlet end of one furnace tube in the second-stage furnace tubes 4 through a U-shaped elbow.

[0049] The first connecting member described above may be a three-way pipe 2. The outlet ends of the two groups of furnace tubes of the first-stage furnace tube 1 are each connected to a three-way pipe 2, and the outlet end of each three-way pipe 2 is connected to a U-shaped elbow. The other end of each U-shaped elbow is connected to the inlet end of one of the furnace tubes in the second-stage furnace tube 4.

[0050] In a further embodiment, the second connecting member includes two inlets and one outlet. The two inlets of the second connecting member are respectively connected to the outlet ends of two of the furnace tubes in the second-stage furnace tube 4, and the outlet of the second connecting member is connected to the inlet end of the third-stage furnace tube 7 through a U-shaped elbow.

[0051] The second connecting member described above may be a Y-shaped pipe 5. The outlet ends of two of the furnace tubes in the second-stage furnace tube 4 are connected to the Y-shaped pipe 5. The outlet end of the Y-shaped pipe 5 is connected to a U-shaped elbow, and the other end of the U-shaped elbow is connected to the inlet end of the furnace tube in the third-stage furnace tube 7.

[0052] In a further embodiment, the outlet end of the third-stage furnace tube 7 is connected to the inlet end of the fourth-stage furnace tube 9 through a U-shaped elbow.

[0053] In a further embodiment, it includes two groups of 6-2-1-1 type radiant furnace tubes, forming a 12-4-2-2 type furnace tube configuration.

[0054] In a further embodiment, the material of all radiant furnace tubes is high-temperature heat-resistant alloy steel, which can withstand high-temperature and high-pressure environments.

[0055] The present utility model also provides a cracking furnace, in which one group, two groups or multiple groups of the above-mentioned cracking furnace radiant furnace tubes are arranged.

[0056] According to the raw material processing capacity, multiple groups of furnace tubes can be set in the cracking furnace. The multiple groups of furnace tubes can be set in multiple groups of 6-2-1-1 type structures or multiple groups of 12-4-2-2 type structures.

[0057] As a specific implementation manner, each group of radiant furnace tubes in the cracking furnace adopts a 6-2-1-1 type structure, and two groups adopt a 12-4-2-2 type structure.

[0058] The pyrolysis feedstock enters the first-pass furnace tubes 1 from the inlet of the radiant coil. The outlet of the first-pass furnace tubes 1 is connected to the tee tube 2, and the tee tube 2 is connected to the first U-shaped bend 3. The first U-shaped bend 3 is connected to the inlet of the second-pass furnace tubes 4. The outlet of the second-pass furnace tubes 4 is connected to the Y-shaped tube 5, and the Y-shaped tube 5 is connected to the second U-shaped bend 6. The second U-shaped bend 6 is connected to the inlet of the third-pass furnace tubes 7. The third-pass furnace tubes 7 are connected to the third U-shaped bend 8, and the third U-shaped bend 8 is connected to the inlet of the fourth-pass furnace tubes 9. The mixture of the pyrolysis feedstock and the dilution steam flows through the tube passes 1 - tube pass 2 - tube pass 3 - tube pass 4 in sequence, and then flows out of the radiant chamber. At this time, the mixture has completed the pyrolysis reaction in the furnace tubes.

[0059] Through the above steps, the pyrolysis feedstock can quickly absorb heat in the first half of the radiant furnace tubes, shorten the residence time, thereby reducing the occurrence of side reactions and improving the selectivity of ethylene. At the same time, the design of this furnace tube configuration and structural parameters can adapt to different feedstock throughput and process conditions, improving the flexibility and economy of equipment use.

[0060] In a set of embodiments of the present utility model (as Figure 2 shown), radiant furnace tubes with a 12 - 4 - 2 - 2 type structure are adopted. Two groups of 6 - 2 - 1 - 1 type four-pass furnace tubes are arranged side by side, expanding the heat absorption area, enabling the pyrolysis feedstock to quickly absorb heat in the first half of the radiant furnace tubes, shortening the reaction time, reducing the occurrence of side reactions, and thus improving the selectivity of ethylene.

[0061] In addition, in the present utility model, the connection position of the tee tube 2 and the first-pass furnace tubes 1 in the radiant furnace tubes can be adjusted according to the needs of the actual production process, and the connection position of the Y-shaped tube 5 and the second-pass furnace tubes 4 can be adjusted.

[0062] For example:

[0063] As Figure 3 shown, the connection position of the tee tube 2 and the first-pass furnace tubes 11 is adjusted.

[0064] Compared with the basic 6 - 2 - 1 - 1 type furnace tubes (as Figure 1 ), the connection position of the tee tube 2 and the first-pass furnace tubes 1 is raised by 1 - 6 m. When the feedstock is relatively easy to pyrolyze and a too fast reaction rate is not required in the first pass, the position of the tee tube can be appropriately raised to reduce the heat absorption area in the first pass.

[0065] As Figure 4 shown, the connection position of the Y-shaped tube 5 and the second-pass furnace tubes 4 is adjusted.

[0066] Compared with the basic 6 - 2 - 1 - 1 type furnace tubes (as Figure 1), the connection position of the Y-shaped tube 5 and the second-stage furnace tube 4 is lowered by 1-6 m. When the raw material is relatively easy to crack and a too fast reaction rate is not required in the second stage, the position of the Y-shaped tube 5 can be appropriately lowered to reduce the endothermic area of the second stage.

[0067] As Figure 5 shown, the connection position of the three-way tube 2 and the first-stage furnace tube 1 and the connection position of the Y-shaped tube 5 and the second-stage furnace tube 4 are adjusted simultaneously.

[0068] Compared with the basic version of the 6-2-1-1 type furnace tube (as Figure 1 ), the connection position of the three-way tube 2 and the first-stage furnace tube 1 is raised by 1-6 m and the connection position of the Y-shaped tube 55 and the second-stage furnace tube 44 is lowered by 1-6 m. When the raw material is extremely easy to crack and too fast reaction rates are not required in both the first stage and the second stage, the positions of the three-way tube and the Y-shaped tube 5 can be lowered simultaneously to reduce the endothermic areas of the first stage and the second stage.

[0069] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of this patent, without departing from the scope of the technical solution of the present invention, can make some changes or modifications using the technical content prompted above into equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A cracking furnace radiant furnace tube, characterized in that, It includes at least one set of 6-2-1-1 type radiant furnace tubes. Each set of 6-2-1-1 type radiant furnace tubes includes a first-pass furnace tube, a second-pass furnace tube, a third-pass furnace tube, and a fourth-pass furnace tube that are connected in sequence. The first-pass furnace tube includes six furnace tubes, and every three furnace tubes are a group. The second-pass furnace tube includes two furnace tubes. The third-pass furnace tube and the fourth-pass furnace tube each include one furnace tube. In the order of the first-pass furnace tube, the second-pass furnace tube, the third-pass furnace tube, and the fourth-pass furnace tube, the ratio of the tube pitch to the outer diameter of each pass of furnace tubes increases in sequence.

2. The cracking furnace radiant furnace tube according to claim 1, wherein Each pass of furnace tubes is located in the same plane and arranged side by side in a single row. The tube pitch between the furnace tubes in each pass is 1.5 to 2.5 times the outer diameter of the furnace tubes.

3. The cracking furnace radiant furnace tube according to claim 1, wherein In the order of the first-pass furnace tube, the second-pass furnace tube, the third-pass furnace tube, and the fourth-pass furnace tube, the inner diameters of each pass of furnace tubes increase in sequence.

4. The cracking furnace radiant furnace tube according to claim 3, characterized in that, The inner diameter of the first-pass furnace tube is φ1, the inner diameter of the second-pass furnace tube is φ2, the inner diameter of the third-pass furnace tube is φ3, and the inner diameter of the fourth-pass furnace tube is φ4, and 40mm ≤ φ1 ≤ 150mm, 80mm ≤ φ2 ≤ 200mm, 120mm ≤ φ3 ≤ 300mm, 120mm ≤ φ4 ≤ 300mm.

5. The cracking furnace radiant furnace tube according to any one of claims 1-4, characterized in that In the second-pass furnace tube, one end of each of the two furnace tubes is connected to each group of furnace tubes in the first-pass furnace tube through two first connectors respectively, and the other ends of the two furnace tubes are connected to the third-pass furnace tube through a second connector.

6. The cracking furnace radiant furnace tube according to claim 5, wherein Each first connector includes three inlets and one outlet. The three inlets of the first connector are respectively connected to the three outlet ends of a group of three furnace tubes in the first-pass furnace tube, and the outlet of the first connector is connected to the inlet end of one furnace tube in the second-pass furnace tube through a U-shaped elbow.

7. The cracking furnace radiant furnace tube according to claim 5, characterized in that, The said second connector includes two inlets and one outlet. The two inlets of the second connector are respectively connected to the outlet ends of the two furnace tubes in the second-pass furnace tube, and the outlet of the second connector is connected to the inlet end of the third-pass furnace tube through a U-shaped elbow.

8. The cracking furnace radiant furnace tube according to any one of claims 1-4, characterized in that The outlet end of the third-pass furnace tube is connected to the inlet end of the fourth-pass furnace tube through a U-shaped elbow.

9. The cracking furnace radiant furnace tube according to any one of claims 1-4, characterized in that, It includes two sets of 6-2-1-1 type radiant furnace tubes, forming a 12-4-2-2 type furnace tube configuration.

10. A cracking furnace, characterized in that, One set or two sets or multiple sets of the cracking furnace radiant furnace tubes described in any one of claims 1-9 are arranged in the cracking furnace.

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