Patent Application
20210190442
The invention relates to the field of fluid heat transfer technology, in particular to a heat transfer enhancement pipe as well as a cracking furnace and an atmospheric and vacuum heating furnace including the same.
The heat transfer enhancement pipe refers to a heat transfer element capable of enhancing fluid heat transfer between the interior and the outside of the pipe, that is, enabling unit heat transfer area to transfer as much heat as possible per unit time. The heat transfer enhancement pipes are used in many industries, such as thermal power generation, petrochemical, food, pharmaceutical, light industry, metallurgy, navel architecture, etc. The cracking furnace is an important equipment in petrochemical industry, therefore the heat transfer enhancement pipe has been widely used in the cracking furnace.
For a heat transfer enhancement pipe, there is a flow boundary layer between the fluid flow body and the pipe wall surface, and the heat transfer resistance is large. At the same time, due to the extremely low flow velocity in the boundary layer, coke is gradually deposited and adhered to the inner surface of the furnace pipe during the cracking process to form a dense coke layer, which coke layer is extremely large in heat transfer resistance. Therefore, the maximum resistance of the heat transfer pipe in the radiation section of the cracking furnace is in the boundary layer region of the inner wall of the pipe.
U.S. Pat. No. 5,605,400A discloses to enhance heat transfer by providing a fin on the internal wall of the heat transfer enhancement pipe. The fin not only increases surface area of the heat transfer enhancement pipe but also increases turbulent kinetic energy inside the pipe. The fin is in the form of a distorted blade. The fin is usually arranged in the interior of the heat transfer enhancement pipe to thin the boundary layer of the fluid via rotation of the fluid itself, thereby achieving the purpose of heat transfer enhancement. Although the heat transfer enhancement pipe with fin has a relatively good heat transfer enhancement effect, cracks can often occur between the fin and the pipe wall of the heat transfer enhancement pipe due to high stress at the welding site during operation, since the fin is connected with the pipe wall of the heat transfer enhancement pipe by welding. Especially in long-term operation combined with ultra-high temperature environment, it is more likely for cracks to occur between the fin and the pipe wall of the heat transfer enhancement pipe, thereby shortening service life of the heat transfer enhancement pipe.
Therefore, it is necessary to reduce thermal stress of the heat transfer enhancement pipe to increase service life of the heat transfer enhancement pipe, while ensuring heat transfer effect of the heat transfer enhancement pipe.
Objects of the present invention are to overcome issues of short service life of the heat transfer enhancement pipe existing in the prior art and to provide a heat transfer enhancement pipe capable of reducing its own thermal stress and thereby increasing service life of the heat transfer enhancement pipe.
In order to achieve the above objects, one aspect of the present invention provides a heat transfer enhancement pipe including a pipe body of tubular shape with an inlet for entering of a fluid and an outlet for said fluid to flow out, internal wall of the pipe body is provided with a fin protruding toward the interior of the pipe body, wherein the fin has one or more fin sections extending spirally in the axial direction of the pipe body, and each fin section has a first end surface facing the inlet and a second end surface facing the outlet, at least one of the first end surface and the second end surface of at least one of the rib sections is formed as a transition surface along spirally extending direction.
On the other aspect, the present invention provides a cracking furnace or an atmospheric and vacuum heating furnace comprising a radiation chamber, in which at least one furnace pipe assembly is installed; the furnace pipe assembly comprises a plurality of furnace pipes arranged in sequence and heat transfer enhancement pipe communicating adjacent furnace pipes, the heat transfer enhancement pipe is heat transfer enhancement pipe as described as above.
1—heat transfer enhancement pipe; 10—pipe body; 100—inlet; 101—outlet; 11—fin; 110—first end surface; 111—top surface; 112—side wall face; 113—smooth transition fillet; 115—second end surface; 12—interval; 120—side wall; 13—hole; 14—heat insulator; 140—straight pipe section; 141—first tapered pipe section; 142—second tapered pipe section; 15—gap; 160—first connecting piece; 161—second connecting piece; 162—connecting rod; 17—heat insulating layer; 170—metal alloy layer; 171—ceramic layer; 172—oxide layer; 2—furnace pipe.
In the present invention, without indicated on the contrary, words such as “up”, “down”, “left”, and “right” used herein to define orientations generally refer to and are understood as orientations in association with the drawings and orientations in actual application; “interior” and “external” is relative to the axis of the heat transfer enhancement pipe. In addition, the height of the fin refers to the height or distance between the top surface of the fin facing the central axis of the pipe body and the internal wall of the pipe body. The axial length of the fin refers to the length or distance of the fin along the central axis in the side view.
The present invention proposes to provide a heat transfer enhancement pipe in a furnace pipe assembly, to enhance heat transfer, thereby reducing or preventing formation of coke layer. As shown in
As shown in
In addition, it should be noted that the transition surface may be a curved face or a flat face. The curved face may be convex or concave. Preferably, the curved face is concave to further improve the heat transfer effect of the heat transfer enhancement pipe and to further reduce the thermal stress of the heat transfer enhancement pipe. In addition, the transition surface can also reduce the impact force of the fluid on the fins. “Transition angle” refers to the angle between the transition surface or the tangent plane of the transition surface (when the transition surface is a curved face) and the tangent plane of the pipe wall at the connection position. The transition angle extends at an angle greater than or equal to 0° and less than 90°.
As shown in
In addition, the first transition surface can be formed as a first curved face. The first curved face can be either convex or concave shape; preferably, the first curved face is of concave shape so as to further improve heat transfer effect of the heat transfer enhancement pipe 1 and further reduce thermal stress of the heat transfer enhancement pipe 1. Specifically, the first curved face can be a partial paraboloid taken from a paraboloid.
In addition, the transition angle of the first transition surface can be greater than or equal to 0° and less than 90°, so as to further reduce thermal stress of the heat transfer enhancement pipe 1 and greatly increase service life of the heat transfer enhancement pipe 1. The transition angle of the first transition surface can be 10°, 15°, 20°, 25°, 30°, 35°, 38°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°.
In order to further reduce thermal stress of the heat transfer enhancement pipe 1, the second end surface of the fin 11 closest to the outlet 101 can be formed as the second transition surface in a spirally extending direction; wherein the second end surface 110 is sloped in the spirally extending direction, so as to correspondingly increase service life of the heat transfer enhancement pipe. In addition, the second transition surface can be formed as a second curved face. The second curved face can be either convex or concave shape; preferably, the second curved face can be of concave shape. In addition, the transition angle of the second transition surface can be greater than or equal to 0° and less than 90°, so as to further reduce thermal stress of the heat transfer enhancement pipe 1 and greatly increase service life of the heat transfer enhancement pipe 1. The transition angle of the second transition surface can be 10°, 15°, 20°, 25°, 30°, 35°, 38°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°.
As shown in
Preferably, two opposite side wall faces 112 of the fin 11 gradually approach to each other in a direction from the internal wall of pipe body 10 to the center of pipe body 10; that is to say, each of the side wall faces 112 can be inclined, so as to enable fin 11 to enhance disturbance to the fluid entering into pipe body 10 and improve heat transfer effect, while further reducing thermal stress of the heat transfer enhancement pipe 1. It is also understood that the cross section of the fin 11, which is the cross section taken from a plane parallel to a radial direction of pipe body 10, can substantially be trapezoidal or trapezoidal-like. Of course, the cross section of the fin 11 can substantially be rectangular.
In order to reduce thermal stress of the heat transfer enhancement pipe 1, a smooth transition fillet 113 can be formed at the connection of at least one of two opposite side wall faces 112 of the fin 11 with the internal wall of pipe body 10. Further, the radius of smooth transition fillet 113 is greater than 0 and less than or equal to 10 mm. Setting the radius of smooth transition fillet 113 within the above range can further reduce thermal stress of the heat transfer enhancement pipe 1 and increase service life of the heat transfer enhancement pipe 1. Specifically, the radius of smooth transition fillet 113 can be 5 mm, 6 mm, or 10 mm.
In addition, the angle formed by each of the side wall faces 112 and the internal wall of pipe body 10 at the connection with each other can be 5° to 90°; that is to say, the angle between the tangential planes of each of the side wall faces 112 and the internal wall of pipe body 10 at the connection with each other can be 5° to 90°; setting the angle within the above range can further reduce thermal stress of the heat transfer enhancement pipe 1 and increase service life of the heat transfer enhancement pipe 1. The angle formed by each of the side wall faces 112 and the internal wall of pipe body 10 at the connection with each other can be 20°, 30°, 40°, 45°, 50°, 60°, 70°, or 80°.
In order to reduce thermal stress of the heat transfer enhancement pipe 1, the height of the fin 11 is preferably greater than 0 and less than or equal to 150 mm; for example, the height of the fin 11 can be 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, or 140 mm.
As shown in connection with
Preferably, at least one of two sidewalls 120 of intervals 12 is formed as the fourth transition surface. For example, as shown in
Further, a plurality of fins 11, for example, two, three, or four fins 11, can be arranged on the internal wall of pipe body 10. As viewed in the direction of inlet 100, the plurality of fins 11 can be clockwise or counterclockwise spiral. Configuring the plurality of fins 11 with the above structure not only improves heat transfer effect of the heat transfer enhancement pipe 1, but also reduces thermal stress of the heat transfer enhancement pipe 1, improves the ability of the heat transfer enhancement pipe 1 to resist high temperature, and greatly extends service life of the heat transfer enhancement pipe 1.
Preferably, as viewed in the direction of inlet 100, the plurality of fins 11 can be enclosed at the center of pipe body 10 to form a hole 13 extending in the axial direction of pipe body 10 to facilitate the flow of the fluid into pipe body 10 and to reduce pressure drop. In order to reduce pressure drop to as low as possible, the ratio d:D between diameter d of hole 13 and internal diameter D of pipe body 10 can preferably be greater than 0 and less than 1; for example, the ratio d:D can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.
In order to increase disturbance effect of fin 11 to the fluid, the rotational angle of fin 11 can preferably be 90-1080°; for example, the rotational angle of fin 11 can be 120°, 180°, 360°, 720°, or 1080°.
Generally, the ratio of the axial length of fin 11 rotated by 180° to internal diameter D of pipe body 10 is a distortion ratio that determines the length of each fin 11; while the rotational angle of fin 11 determines the degree of distortion and affects heat transfer efficiency. The distortion ratio of fin 11 can be 2.3 to 2.6; for example, the distortion ratio of fin 11 can be 2.35, 2.4, 2.5, 2.49, or 2.5.
In addition, the ratio L1:D of length L1 of fin 11 in the axial direction of pipe body 10 to internal diameter D of pipe body 10 is 1-10:1; preferably, the ratio L1:D=1-6:1.
The present invention also provides a cracking furnace comprising a radiation chamber, in which at least one furnace pipe assembly is mounted, as shown in
Effects of the present invention will be further illustrated through embodiments and comparative examples in the following.
A plurality of the furnace pipe assemblies are arranged in a radiation chamber of a cracking furnace. The heat transfer enhancement pipes 1 are arranged in three of the furnace pipe assemblies. Two heat transfer enhancement pipes 1 are arranged in each furnace pipe assembly at intervals in axial direction of the furnace pipe 2. Each heat transfer enhancement pipe 1 has an internal diameter of 65 mm. In each furnace pipe assembly, the axial length of the furnace pipe 2 between two adjacent heat transfer enhancement pipes 1 is 50 times the internal diameter of the heat transfer enhancement pipe 1. Structure of each of the heat transfer enhancement pipes 1 is as follow: two fins 11 are arranged on the internal wall of pipe body 10 with their two ends respectively formed as the first transition surface and the second transition surface of concave shapes in a spirally extending direction as shown in
Example 12 is the same as Example 11 except that: the transition angle of the first transition surface is 35°; the transition angle of the second transition surface is 35°; the cross section of each fin 11, i.e. the cross section taken from a surface in the radial direction parallel to pipe body 10, is substantially trapezoidal; the angle formed by each side wall face 112 and the internal wall of pipe body 10 at the connection with each other is 45°; and one interval is arranged on each of the fins 11. Other conditions remain unchanged.
Example 13 is the same as Example 11 except that: the transition angle of the first transition surface is 35°; the transition angle of the second transition surface is 35°; the cross section of each fin 11, i.e. the cross section taken from a surface in the radial direction parallel to pipe body 10, is substantially trapezoidal; the angle formed by each side wall face 112 and the internal wall of pipe body 10 at the connection with each other is 45°; and the top surface 111 of each fin 11 in the direction towards the central axis of pipe body 10 is a concave transition surface as shown in
The heat transfer enhancement pipe of the prior art is arranged, wherein in the pipe body is provided with only one fin that extends spirally in the axial direction of the pipe body and separates the interior of the pipe body into two mutually non-communicating chambers, with the remaining conditions unchanged.
Respective test results of the cracking furnaces in the examples and the comparative example after operating under same conditions are shown in Table 1 below.
It can be known from the above that arranging the heat transfer enhancement pipe provided by the present invention in the cracking furnace increases heat transfer load maximally by 6620w, significantly increases heat transfer efficiency, and significantly reduces pressure drop, while increasing service life of the heat transfer enhancement pipe due to maximum thermal stress reduction of the heat transfer enhancement pipe being over 50%.
In addition, according to another example, a height of the fin 11 gradually increases from one end in at least a part extension of the fin. In the example shown in
In order to further reduce thermal stress of the heat transfer enhancement pipe 1, a ratio of the height of the highest part of the fin 11 to the height of the lowest part of the fin 11 is 1.1-1.6:1. For example, the ratio of the height of the highest part of the fin 11 to the height of the lowest part of the fin 11 is 1.2:1, 1.3:1, 1.4:1 or 1.5:1.
Effects of the present invention will be further illustrated through Examples and comparative Examples in the following.
Example 21 is the same as Example 11, except that: the height of each fin 11 gradually increases in the extending direction from the inlet 100 to the outlet 101, the ratio of the height of the highest part of the fin 11 and the height of the lowest part of the fin 11 is 1.4:1. The heat transfer enhancement pipes 1 are used in atmospheric and vacuum heating furnaces. The inner diameter of each heat transfer enhancement pipe 1 is 75 mm, the transition angle of the first transition surface is 60°, and the second transition of the second transition surface is 60°, and the outlet temperature of the heating furnace is 406°.
Comparative Example 21 is the same as Example 21, except that: the structure of the enhanced heat transfer tube is changed, that is, the heat transfer enhancement pipe of the prior art is arranged, wherein in the pipe body is provided with only one fin that extends spirally in the axial direction of the pipe body and separates the interior of the pipe body into two mutually non-communicating chambers, with the remaining conditions unchanged.
Respective test results of the atmospheric and vacuum heating furnaces in the Example 21 and the comparative example 21 after operating under same conditions are shown in Table 2 below.
It can be known from the above that applying the heat transfer enhancement pipe provided by the present invention in the atmospheric and vacuum heating furnace, makes the atmospheric and vacuum heating furnace to have better heat transfer effect, and makes the heat transfer enhancement pipe to have less thermal stress.
According to another example, the outside of the pipe body 10 is provided with a heat insulator 14 at least partially surrounding the external circumference of the pipe body 10. By providing the outside of the pipe body 10 with heat insulator 14 at least partially surrounding the external circumference of the pipe body 10, heat transfer between high-temperature gas and the external wall of the pipe body 10 is impeded to reduce temperature of the external wall of the pipe body 10, thereby reducing temperature difference between the pipe body 10 and the fin 11, so as to effectively reduce thermal stress of the heat transfer enhancement pipe 1, extend service life of the heat transfer enhancement pipe 1, and correspondingly increase the allowable temperature of the heat transfer enhancement pipe 1. When applying the aforementioned heat transfer enhancement pipe 1 to a cracking furnace, long-term stable operation of the cracking furnace can be ensured. Since the fins 11 are arranged in the interior of the pipe body 10, the fluid entering into pipe body 10 can turn into a swirling flow; due to its tangential velocity, the fluid can destroy the boundary layer and reduces the rate of coking. It is to be understood that the heat insulator 14 can completely surround the external circumference of the pipe body 10 at the circumference of the pipe body 10, i.e. at 360° around the external circumference of the pipe body 10; the heat insulator 14 can also partially surround the external circumference of the pipe body 10 at the circumference of the pipe body 10, e.g. at 90° around the external circumference of the pipe body 10; of course, the heat insulator 14 can surround the external circumference of the pipe body 10 with a suitable angle according to actual needs; it should be noted that, when applying the aforementioned heat transfer enhancement pipe 1 to a cracking furnace and providing the heat insulator 14 that partially surrounds the external circumference of the pipe body 10 at the outside of the pipe body 10, it is preferable to provide the heat insulator 14 at a heated surface of the pipe body 10. In addition, the heat insulator 14 can preferably be arranged at the outside of the pipe body 10 that is provided with the fins, so that the fins are not easily cracked away from pipe body 10, and service life of the heat transfer enhancement pipe 1 can be increased.
As shown in
In addition, the manner in which the heat insulator 14 is disposed is also not specifically limited, as shown in
In order to further improve structural stability of the heat transfer enhancement pipe 1, a connector that connects heat insulator 14 and pipe body 10 can be arranged there-between, wherein the structural form of the connector is not specifically limited as long as it can connect heat insulator 14 with pipe body 10. As shown in
As shown in
Further, the angle formed between the horizontal surface and the external wall surface of the first tapered pipe section 141 is preferably 10-80°; specifically, the angle formed between the horizontal surface and the external wall surface of the first tapered pipe section 141 can be 20°, 30°, 40°, 50°, 60°, or 70°. The angle formed between the horizontal surface and the external wall surface of the second tapered pipe section 142 is preferably 10-80°; similarly, the angle formed between the horizontal surface and the external wall surface of the second tapered pipe section 142 can be 20°, 30°, 40°, 50°, 60°, or 70°.
Further, the extension length of the heat insulator 14 in the axial direction of the pipe body 10 is preferably 1-2 times the length of the pipe body 10. Setting the axial length of the heat insulator 14 within the above range can further decrease temperature of the pipe wall of the pipe body 10 in use and further reduces thermal stress of the pipe body 10.
Effects of the present invention will be further illustrated through examples and comparative Examples in the following.
Example 31 is the same as Example 11, except that: a heat insulator 14 of cylindrical shape is arranged on the outside of the pipe body 10; heat insulator 14 completely surrounds the external circumference of the pipe body 10 and leaves gap 15 with the external wall of the pipe body; heat insulator 14 is connected with pipe body 10 through connecting rod 162.
Example 32 is the same as Example 31 except that: heat insulator 14 is elliptical; the transition angle of the first transition surface is 35°; the transition angle of the second transition surface is 35°. Other conditions remain unchanged.
Example 33 is the same as Example 31 except that: heat insulator 14 is attached to the external wall of the pipe body 10; the transition angle of the first transition surface is 40°; the transition angle of the second transition surface is 40°. Other conditions remain unchanged.
Comparative Example 31 is the same as Comparative Example 11, that is, a heat transfer enhancement pipe of the prior art is arranged, wherein the outside of the pipe body is not provided with a heat insulator; the interior of the pipe body is provided with only one fin 11 that extends spirally in the axial direction of the pipe body and separates the interior of the pipe body into two mutually non-communicating chambers, with the remaining conditions unchanged.
Respective test results of the cracking furnaces in the examples and the comparative Example after operating under same conditions are shown in Table 3 below.
It can be known from the above that providing the heat transfer enhancement pipe provided by the invention in the cracking furnace increases heat transfer load, significantly increases heat transfer efficiency, and significantly reduces pressure drop, while reducing maximum thermal stress of the heat transfer enhancement pipe and significantly increasing service life of the heat transfer enhancement pipe.
According to another example of the present invention, a heat insulating layer 17 is provided on the external surface of the pipe body 10. By providing the heat insulating layer 17 on the external surface of the pipe body 10, heat transfer between high-temperature gas and the pipe wall of the pipe body 10 is impeded to reduce temperature of the pipe wall of the pipe body 10, thereby reducing temperature difference between the pipe body 10 and the fin 11, so as to effectively reduce thermal stress of the heat transfer enhancement pipe 1, extend service life of the heat transfer enhancement pipe 1, and also improve high temperature resistance performance, thermal shock performance, and high-temperature corrosion resistance performance of the heat transfer enhancement pipe 1 because of the arrangement of the heat insulating layer 17. When applying the aforementioned heat transfer enhancement pipe 1 to a cracking furnace, long-term stable operation of the cracking furnace can be ensured. In addition, heat insulating layer 17 can preferably be arranged at the outside of the pipe body 10 that is provided with the fins, so that the fins are not easily cracked away from pipe body 10, and thermal stress of the heat transfer enhancement pipe 1 can be reduced.
Preferably, heat insulating layer 17 can include a metal alloy layer 170 arranged on the external surface of the pipe body 10 and a ceramic layer 171 arranged on the metal alloy layer 170. Through providing metal alloy layer 170 on the external surface of the pipe body 10 and ceramic layer 171 on the metal alloy layer 170, the heat insulating effect of the heat insulating layer 17 can be improved to further decrease thermal stress of the heat transfer enhancement pipe 1.
It is to be understood that metal alloy layer 170 can be prepared and formed by metal alloy materials including M, Cr, Al, and Y, wherein M is selected from one or more of Fe, Ni, Co, and Al; when M is selected from two or more metals therein, such as Ni and Co, metal alloy layer 170 can be prepared and formed by metal alloy materials including Ni, Co, Cr, Al, and Y; when metal alloy layer 170 contains Ni and Co, heat insulating ability of the heat insulating layer 17 can be further improved, and oxidation resistance and hot corrosion resistance of the heat insulating layer 17 are improved. As for the content of each metal in the metal alloy materials, it can be configured according to actual needs with no particular requirement. For example, the weight fraction of Al can be 5-12%, and the weight fraction of Y can be 0.5-0.8%, so that the robustness of the heat insulating layer 17 can be improved, while reducing oxidation rate of metal alloy layer 170; the weight fraction of Cr can be 25-35%. In addition, it should also be noted that the metal alloy materials can be sprayed on the external surface of the pipe body 10 to form metal alloy layer 170 by employing low pressure plasma, atmospheric plasma, or electron-beam physical vapor deposition. Thickness of metal alloy layer 170 can be 50 to 100 μm; specifically, thickness of metal alloy layer 170 can be 60 μm, 70 μm, 80 μm, or 90 μm.
In order to further improve oxidation resistance of the heat insulating layer 17 and extend service life of the heat insulating layer 17, additive materials can be added to the metal alloy materials for preparing metal alloy layer 170, that is, metal alloy layer 170 can be prepared and formed after mixing the metal alloy materials with the additive materials, wherein the metal alloy materials include M, Cr, Al, and Y, wherein M is selected from one or more of Fe, Ni, Co, and Al; the additive materials are selected from Si, Ti, Co, or Al2O3; as for the amount of addition of the additive materials, it can be added according to actual needs with no particular limitations, wherein the metal alloy materials have already been described in the above, and will not be described in details herein again.
In addition, ceramic layer 171 can be prepared and formed by one or more materials from yttria-stabilized zirconia, magnesia-stabilized zirconia, calcia-stabilized zirconia, and ceria-stabilized zirconia. When ceramic layer 171 is formed by two or more materials from the above, any two or more of the above materials can be mixed and then form into ceramic layer 171 after mixing. Specifically, when selecting yttria-stabilized zirconia as the material for ceramic layer 171, ceramic layer 171 can have a relatively high thermal expansion system, for example, it can reach up to 11×10−6 K−1; ceramic layer 171 can also have a relatively low thermal conductivity coefficient of 2.0-2.1Wm−1K−1; while ceramic layer 171 also has good thermal shock resistance. It should also be noted that when selecting yttria-stabilized zirconia as ceramic layer 171, the weight fraction of yttrium oxide is 6-8%. In order to further improve heat insulating performance of the heat insulating layer 17, cerium oxide can also be added to the above materials forming ceramic layer 171; specifically, the amount of addition of cerium oxide can be 20-30% of the total weight of yttria-stabilized zirconia; further, the amount of addition of cerium oxide can be 25% of the total weight of yttria-stabilized zirconia. Similarly, one or more materials of yttria-stabilized zirconia, magnesia-stabilized zirconia, calcia-stabilized zirconia, and ceria-stabilized zirconia can be sprayed onto the external surface of metal alloy surface 170 to form ceramic layer 171 by employing methods of low pressure plasma, atmospheric plasma, or electron-beam physical vapor deposition. In addition, the thickness of ceramic layer 171 can be 200-300 μm; for example, the thickness of ceramic layer 171 can be 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, or 290 μm. It should be noted that when the heat transfer enhancement pipe 1 is in use, the Al in metal alloy layer 170 reacts with the oxygen in ceramic layer 171 to form a thin and dense aluminum-oxide protective film, thereby protecting pipe body 10.
In order to improve peeling resistance of the heat insulating layer 17, an oxide layer 172 can be arranged between metal alloy layer 170 and ceramic layer 171, wherein oxide layer 172 is preferably prepared and formed by alumina, silica, titania, or a mixture of any two or more materials from alumina, silica, and titania. Preferably, alumina is selected for preparing and forming oxide layer 172 to improve heat insulating performance of the heat insulating layer 17. Similarly, the above oxide materials can be sprayed onto the surface of metal alloy layer 170 to form oxide layer 172 by employing methods of low pressure plasma, atmospheric plasma, or electron-beam physical vapor deposition. In addition, the thickness of oxide layer 172 can be 3-5 μm; for example, the thickness of oxide layer 172 can be 4 μm.
Additionally, the porosity of the heat insulating layer 17 can be 8 to 15%.
In order to effectively reduce temperature of the pipe wall of the pipe body 10 and to make temperature variation in the axial direction of the pipe body 10 relatively uniform while also to reduce thermal stress of the heat transfer enhancement pipe 1, heat insulation layer 17 can include a straight section, and a first tapered section and a second tapered section that are connected to the first end and the second end of the straight section, respectively, wherein the first tapered section is tapered in a direction from close to the first end to away from the first end; the second tapered section is tapered in a direction from close to the second end to away from the second end. It is to be understood that the thickness of the heat insulating layer 17 is thinner near the ends; the thickness of the heat insulating layer 17 can gradually decrease by a value of 5-10%. In order to further reduce thermal stress of the heat transfer enhancement pipe 1, heat insulating layer 17 is thicker at positions corresponding to the fins.
Effects of the present invention will be further illustrated through Examples and comparative Examples in the following.
Example 41 is the same as Example 11, except that: the heat insulating layer 17 is disposed on the external surface of the pipe body 10, the heat insulating layer 17 includes a 70 μm thick metal alloy layer 170, a 4 μm thick oxide layer 172, and a 240 μm thick ceramic layer 171 sequentially arranged at the external surface of the pipe body 10; wherein the metal alloy layer 170 is spray-formed from metal alloy materials having weight fraction of 64.5% Ni, 30% Cr, 5% Al, and 0.5% Y via atmospheric plasma spray method; the oxide layer 172 is formed by spraying aluminum oxide to the surface of metal alloy layer 170 by a selected method of low pressure plasma spray; the ceramic layer 171 is formed by spraying yttria-stabilized zirconia mixed with cerium oxide of 25% weight fraction of the yttria-stabilized zirconia; in the yttria-stabilized zirconia, the weight fraction of cerium oxide is 6%, the transition angle of the first transition surface is 35°; the transition angle of the second transition surface is 35°; the cross section of each fin 11, i.e. the cross section taken from a surface in the radial direction parallel to pipe body 10, is substantially trapezoidal; the angle formed by each side wall face 112 and the internal wall of the pipe body 10 is 45°.
Example 42 is the same as Example 41, except that: in heat insulating layer 17, metal alloy layer 170 is prepared and formed by metal alloy materials having weight fraction of 64.2% Ni, 30% Cr, 5% Al, and 0.8% Y, respectively; ceramic layer 171 is formed by yttria-stabilized zirconia; in the yttria-stabilized zirconia, the weight fraction of yttrium oxide is 8%. Other conditions remain unchanged.
Comparative Example 41 is the same as Comparative Example 11, i.e.: the heat transfer enhancement pipe of the prior art is arranged (the external surface of the pipe body is not provided with heat insulating layer), wherein the outside of the pipe body is not provided with heat insulating layer; the interior of the pipe body is provided with only one fin that extends spirally in the axial direction of the pipe body and separates the interior of the pipe body into two mutually non-communicating chambers, with the remaining conditions unchanged.
Respective test results of the cracking furnaces in the Examples and the comparative Example after operating under same conditions are shown in Table 4 below.
It can be known from the above that providing the heat transfer enhancement pipe provided by the invention in the cracking furnace increases heat transfer load, significantly increases heat transfer efficiency, and significantly reduces pressure drop, while reducing maximum thermal stress of the heat transfer enhancement pipe and significantly increasing service life of the heat transfer enhancement pipe.
Preferred embodiments of the present invention have been described in detail above in association with the drawings; however, the present invention is not limited thereto. Various simple alterations of the technology of the present invention including combinations of each specific technological feature in any suitable ways can be made in the scope of the technology contemplated in the present invention. To avoid unnecessary repetitions, the present invention will not illustrate further on various possible combinations. However, these simple alterations and combinations should be regarded as contents disclosed by the present invention and fall into the scope protected by the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201711023424.X | Oct 2017 | CN | national |
| 201711027588.X | Oct 2017 | CN | national |
| 201711029500.8 | Oct 2017 | CN | national |
| 201711056794.3 | Oct 2017 | CN | national |
| 201711057043.3 | Oct 2017 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2018/111795 | 10/25/2018 | WO | 00 |
