A grading gradient heat exchange pressure reduction deep pulling anti-coking system and method for a conventional pressure reduction device

Abstract

The present application belongs to the field of petroleum refining atmospheric and vacuum distillation, and particularly relates to a coking prevention system and method for atmospheric and vacuum distillation unit with staged gradient heat exchange and deep vacuum distillation, which comprises an atmospheric unit, a staged gradient heat exchange unit, a sectional vacuum heating unit, a vacuum distillation unit and an intelligent control unit. The atmospheric unit comprises an atmospheric furnace and an atmospheric tower, and a discharge port at the bottom of the atmospheric tower is connected to the feed end of the low-temperature heat exchange section of the staged gradient heat exchange unit through a pipeline. The staged gradient heat exchange design fully recovers the residual heat in the unit, and the heat energy utilization rate is increased by more than 20%, thereby greatly reducing the fuel consumption of the vacuum heating furnace and reducing the comprehensive energy consumption by 12%-15%, achieving energy saving and consumption reduction. The atmospheric residue is sequentially fed into the low-temperature, medium-temperature and high-temperature heat exchange sections of the staged gradient heat exchange unit, and the staged heat exchange is performed by using the residual heat of the hot oil from each side line and the residue at the bottom of the tower, so that the atmospheric residue is gradually heated to 350-370 DEG C, the residual heat is fully recovered, and the subsequent heating load is reduced.

Description

Technical Field

[0001] This invention relates to the field of atmospheric and vacuum distillation technology in petroleum refining, and in particular to a staged gradient heat exchange vacuum deep-drain anti-coking system and method for atmospheric and vacuum distillation units. Background Technology

[0002] Atmospheric and vacuum distillation, as the first and crucial step in petroleum refining, directly determines the overall economic benefits of a refinery through its operational efficiency, product yield, and operating cycle. Deep vacuum distillation technology is a core means to improve vacuum wax oil yield, reduce heavy oil residue, and optimize crude oil utilization efficiency. However, the problem of equipment coking under high temperature and high vacuum conditions is the core bottleneck restricting the depth of deep vacuum distillation and the continuous operation of the unit.

[0003] The existing atmospheric and vacuum distillation units have the following main technical defects in their vacuum systems: First, traditional vacuum furnaces use a single-stage heating structure, where atmospheric residue oil is heated to a high temperature in one go. This results in uneven oil film temperature distribution within the furnace tubes, and localized overheating areas can easily lead to thermal cracking, condensation, and coking of heavy components. This causes a decrease in furnace tube heat transfer efficiency, an increase in tube-side pressure drop, and makes cleaning of coking material difficult, forcing frequent unit shutdowns. Second, there are dead zones where material stagnates between the vacuum distillation line and the feed section within the tower, resulting in poor mixing of the gas and liquid phases. The prolonged residence of heavy oil in the liquid phase can induce thermal cracking, condensation, and coking. Coking occurs frequently, and the entrainment of liquid droplets in the gas phase reduces the separation accuracy of the vacuum distillation tower, affecting the quality of side-stream products. Thirdly, the existing heat exchange system is a conventional countercurrent heat exchange system, which does not combine the properties of crude oil with the requirements of deep vacuum distillation for gradient control, resulting in low thermal energy utilization. Furthermore, the tendency to coke is easily aggravated by sudden temperature changes during the heat exchange of high-temperature materials. Fourthly, current technologies are mostly focused on single anti-coking or single deep-drilling optimization, lacking a synergistic design that integrates process, equipment, heat exchange, and control, making it impossible to achieve a multi-objective balance between deep-drilling efficiency, anti-coking effect, and energy consumption control.

[0004] A search of domestic and international patents and technical literature reveals that existing patents primarily focus on improvements to single feed distributor structures, localized furnace tube modifications, and single steam injection for coking prevention. However, no integrated system technology solution combining graded gradient heat exchange, segmented temperature control, cyclone gas-liquid pre-separation, and intelligent online coking prevention has been disclosed. There is a significant gap in the synergistic control technology for heavy crude oil depressurization and deep extraction combined with long-term coking prevention, failing to meet the industrial demands for efficient, low-consumption, and long-term operation of existing large-scale atmospheric and vacuum distillation units. Therefore, this invention proposes a graded gradient heat exchange depressurization and deep extraction system and method for coking prevention in atmospheric and vacuum distillation units, addressing many shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a graded gradient heat exchange decompression deep-drawing anti-coking system and method for atmospheric and vacuum distillation devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A graded gradient heat exchange and vacuum distillation system for preventing coking in an atmospheric and vacuum distillation unit includes an atmospheric unit, a graded gradient heat exchange unit, a segmented vacuum heating unit, a vacuum distillation unit, and an intelligent control unit. The atmospheric unit includes an atmospheric furnace and an atmospheric tower. The bottom outlet of the atmospheric tower is connected to the feed end of the low-temperature heat exchange section of the graded gradient heat exchange unit via a pipeline. The graded gradient heat exchange unit sequentially includes a low-temperature heat exchange section, a medium-temperature heat exchange section, and a high-temperature heat exchange section. The three heat exchange sections are independently set up with progressively increasing temperature differences. The heat source for the low-temperature heat exchange section is the side-stream hot oil of the atmospheric tower, the heat source for the medium-temperature heat exchange section is the side-stream wax oil of the vacuum tower, and the heat source for the high-temperature heat exchange section is the high-temperature residue oil at the bottom of the vacuum tower, thereby achieving a stepped temperature increase of the atmospheric residue oil. The segmented pressure-reducing heating unit includes a primary pressure-reducing heating furnace and a secondary pressure-reducing heating furnace, which are connected in series. The feed end of the primary pressure-reducing heating furnace is connected to the discharge end of the high-temperature heat exchange section of the graded gradient heat exchange unit, and the discharge end of the secondary pressure-reducing heating furnace is connected to the feed inlet of the cyclone gas-liquid pre-separation system. The primary pressure-reducing heating furnace adopts a radiation-convection composite heating structure, and the secondary pressure-reducing heating furnace adopts a uniform temperature-controlled spiral tube heating structure. Both heating furnaces are equipped with temperature sensors and multi-point steam injection modules. The vacuum distillation unit includes a vacuum tower, a cyclone gas-liquid pre-separation system, a vacuum system, and a bottom circulation module. The vacuum tower is equipped with high-efficiency packing and a side-stream discharge assembly. The cyclone gas-liquid pre-separation system includes a pre-separation cylinder, a cyclone guide assembly, a gas-liquid splitting baffle, and a collection cone. The inner wall of the pre-separation cylinder is equipped with spiral cyclone guide vanes. The gas-liquid splitting baffle is located above the cyclone guide assembly, and the surface of the baffle has uniformly distributed gas phase through holes. The bottom of the collection cone is connected to the feed section of the vacuum distillation unit. The top of the pre-separation cylinder is equipped with a gas phase guide pipe, which is connected to the vacuum tower vertically. The vacuum system adopts a combination structure of a steam jet pump and a mechanical vacuum pump to achieve gradient vacuum in the vacuum tower. The bottom circulation module includes a circulation pump, a filter, and an online anti-coking agent injection system. Part of the bottom residue oil is returned to the feed end of the secondary vacuum heater via the circulation pump, and the other part is sent out through the filter. The online anti-coking agent injection system is connected to the circulation pipeline. The intelligent control unit includes a PLC controller, a temperature acquisition module, a pressure acquisition module, a flow acquisition module, and a coking monitoring module. All sensors and actuators are electrically connected to the PLC controller to realize automatic control of parameters throughout the process and anti-coking early warning.

[0007] Preferably, in the graded gradient heat exchange unit, the heat exchange temperature difference in the low-temperature heat exchange section is controlled at 30-45℃, and the atmospheric pressure residue oil is heated to 180-220℃; the heat exchange temperature difference in the medium-temperature heat exchange section is controlled at 50-65℃, and the residue oil is heated to 260-300℃; the heat exchange temperature difference in the high-temperature heat exchange section is controlled at 70-85℃, and the residue oil is heated to 350-370℃. All three heat exchange sections use shell-and-tube heat exchangers, and anti-eddy current baffles are provided on both the shell side and the tube side.

[0008] Preferably, the outlet temperature of the primary pressure-reducing heating furnace is controlled at 380-395℃, the outlet temperature of the secondary pressure-reducing heating furnace is controlled at 400-415℃, and the spiral tube of the secondary pressure-reducing heating furnace adopts a variable diameter structure, the material flow velocity inside the tube is maintained at 1.2-1.8m / s, the steam injection volume of the multi-point steam injection module is 2%-4% of the total material feed volume, and the steam injection temperature is 320-350℃.

[0009] Preferably, the spiral angle of the cyclone guide vanes in the cyclone gas-liquid pre-separation system is 35°-45°, the diameter of the gas phase through hole is 8-12mm, the inner wall of the liquid collecting cone is a smooth polished surface with a roughness Ra≤0.8μm, and the pre-separation cylinder is sealed to the feed section of the pressure reducing tower, with no dead corners where materials are stuck.

[0010] Preferably, the vacuum gradient inside the pressure reducing tower is 1-3 kPaA at the top of the tower, 2-4 kPaA at the feed section, and 3-5 kPaA at the bottom of the tower. The vacuum system is linked with the PLC controller to achieve real-time fine adjustment of the vacuum level. The anti-scorching agent is a nano-silica composite anti-scorching agent with an injection concentration of 60-100 ppm.

[0011] A method for preventing coking in a staged gradient heat exchange decompression deep-drawing vacuum system in an atmospheric and vacuum distillation unit includes the following steps: S1. After pretreatment, crude oil is fed into an atmospheric furnace for heating, and then enters an atmospheric distillation tower for atmospheric distillation to separate light components such as gasoline, kerosene, and diesel. Atmospheric residue oil is obtained at the bottom of the atmospheric distillation tower. S2. Atmospheric residue oil is sequentially fed into the low-temperature, medium-temperature, and high-temperature heat exchange sections of the graded gradient heat exchange unit. The residual heat of the side hot oil and the bottom residue oil in the unit is used for graded heat exchange to gradually raise the temperature of the atmospheric residue oil to 350-370℃, fully recover the residual heat, and reduce the subsequent heating load. S3. After heat exchange, the atmospheric residue oil enters the primary vacuum furnace and the secondary vacuum furnace for staged heating. The temperature is gradually increased to 400-415℃ through the two-stage heating furnace. Superheated steam is injected by the multi-point steam injection module to reduce the partial pressure of the material in the furnace tube, inhibit the splitting and coking of the heavy batch, and maintain the turbulent state in the material tube to eliminate local overheating. S4. The material after segmented heating is fed into the cyclone gas-liquid pre-separation system. Under the action of the cyclone guide vanes, a cyclone field is formed. The gas and liquid phases are rapidly separated under the action of centrifugal force. The gas phase enters the distillation section of the vacuum tower through the gas phase guide pipe, and the liquid phase is evenly fed into the feed section of the vacuum tower through the liquid collection cone to avoid gas-liquid entrainment and material retention. S5. Gradient vacuum distillation is used in the vacuum tower to separate side products such as vacuum wax oil. Part of the residue oil at the bottom of the tower is recycled to the secondary vacuum heater for further deep distillation, and the other part is sent out of the unit. At the same time, anti-coking agent is injected in timed and quantitatively through the online anti-coking agent injection system to inhibit coking at the bottom of the tower and the heater tubes. S6. The intelligent control unit collects real-time temperature, pressure, flow rate and coking monitoring data of each node, and automatically adjusts the heating furnace temperature, steam injection rate, vacuum degree, circulation rate and anti-coking agent injection rate through the PLC controller to achieve stable operation and anti-coking early warning throughout the process.

[0012] Preferably, in S3, the flow velocity inside the material pipe is maintained at 1.2-1.8 m / s.

[0013] Preferably, in S5, the concentration of the anti-scorching agent is 60-100 ppm, and the vacuum degree of each section of the pressure reducing tower is finely adjusted in real time.

[0014] The beneficial effects of the graded gradient heat exchange decompression deep-drawing anti-coking system and method of the present invention are as follows: 1. The staged gradient heat exchange design fully recovers the waste heat in the device, improves the thermal energy utilization rate by more than 20%, significantly reduces the fuel consumption of the vacuum heating furnace, and reduces the overall energy consumption by 12%-15%, achieving energy saving and consumption reduction; 2. Segmented pressure reduction heating combined with multi-point steam injection avoids one-time high-temperature heating of atmospheric residue oil, eliminates local overheating areas in furnace tubes, shortens material residence time, reduces coking rate by more than 70%, and extends the continuous operation cycle of the unit from 8-10 months to 18-24 months; 3. The cyclone gas-liquid pre-separation system achieves efficient gas-liquid pre-separation, reducing the amount of liquid droplets entrained in the gas phase to below 50 ppm, improving the separation accuracy of the vacuum tower, reducing the overlap of the distillation range of side-stream products by 50%, increasing the yield of vacuum wax oil by 3%-5%, and demonstrating significant vacuum deep-drawing effect. 4. The combination of gradient vacuum and bottom circulation optimizes the gas-liquid phase distribution in the vacuum tower, increases the depth of deep drawing, avoids excessive cracking, and ensures stable product quality. 5. The intelligent control unit realizes full-process automated control and online anti-coking early warning, reduces human operation error, is suitable for processing various heavy crude oils with high residual carbon, has strong versatility, can be used for new plants, and can also be adapted to the renovation of existing old plants, with low renovation cost and short payback period. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a graded gradient heat exchange decompression deep-drawing anti-coking system and method for atmospheric and vacuum distillation devices proposed in this invention.

[0016] In the diagram: 1. Atmospheric furnace; 2. Atmospheric tower; 21. Side-stream hot oil of atmospheric tower; 3. Low-temperature heat exchange section; 4. Medium-temperature heat exchange section; 5. High-temperature heat exchange section; 6. Primary vacuum furnace; 7. Secondary vacuum furnace; 8. Vacuum tower; 82. Side-stream wax oil of vacuum tower; 9. Cyclone gas-liquid pre-separation system; 92. Pre-separation cylinder; 93. Spiral cyclone guide vane; 94. Gas-liquid diversion baffle; 95. Liquid collecting cone; 96. Gas phase guide pipe; 10. Combined vacuum system; 11. Tower bottom circulation module; 111. Circulation pump; 112. Filter; 113. Online anti-coking agent injection system; 114. High-temperature residue oil at the bottom of vacuum tower. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1

[0018] Reference Figure 1 A staged gradient heat exchange and decompression deep-drain anti-coking system for atmospheric and vacuum distillation includes an atmospheric unit A, a staged gradient heat exchange unit B, a segmented decompression heating unit C, a decompression distillation unit D, and an intelligent control unit E. Atmospheric unit A includes atmospheric furnace 1 and atmospheric tower 2. The bottom outlet of atmospheric tower 2 is connected to graded gradient heat exchange unit B. Graded gradient heat exchange unit B is sequentially set with independent low temperature heat exchange section 3, medium temperature heat exchange section 4, and high temperature heat exchange section 5. The temperature difference of the three heat exchange sections increases step by step. The heat source of low temperature heat exchange section 3 is hot oil 21 from the side of atmospheric tower. The heat source of medium temperature heat exchange section 4 is wax oil 82 from the side of vacuum tower. The heat source of high temperature heat exchange section 5 is high temperature residue oil 114 from the bottom of vacuum tower. The segmented vacuum heating unit C includes a primary vacuum heater 6 and a secondary vacuum heater 7 connected in series. Both heaters are equipped with temperature sensors and multi-point steam injection modules. The discharge end of the secondary vacuum heater 7 is connected to the cyclone gas-liquid pre-separation system 9 inside the vacuum tower 8. The vacuum distillation unit D includes a vacuum tower 8, a cyclone gas-liquid pre-separation system 9, a combined vacuum system 10, and a bottom circulation module 11. The bottom circulation module 11 includes a circulation pump 111, a filter 112, and an online anti-scorching agent injection system 113. The cyclone gas-liquid pre-separation system 9 includes a pre-separation cylinder 92, a cyclone guide assembly, a gas-liquid splitting baffle 94, and a liquid collecting cone 95; the inner wall of the pre-separation cylinder 92 is provided with a spiral cyclone guide plate 93, the gas-liquid splitting baffle 94 is located above the cyclone guide assembly, the baffle has a gas phase passage hole, the top of the pre-separation cylinder 92 is provided with a gas phase guide pipe 96, and the liquid collecting cone 95 is connected to the vacuum distillation unit D; The intelligent control unit E includes a PLC controller and multiple sets of data acquisition sensors, and each actuator is electrically connected to the PLC controller.

[0019] In this embodiment, in the graded gradient heat exchange unit B, the low-temperature heat exchange section 3 has a heat exchange temperature difference of 30-45℃, and the residual oil is heated to 180-220℃; the medium-temperature heat exchange section 4 has a heat exchange temperature difference of 50-65℃, and the residual oil is heated to 260-300℃; the high-temperature heat exchange section 5 has a heat exchange temperature difference of 70-85℃, and the residual oil is heated to 350-370℃; the low-temperature heat exchange section 3, the medium-temperature heat exchange section 4, and the high-temperature heat exchange section 5 are all shell and tube type, and anti-eddy current baffles are installed in both the shell side and the tube side.

[0020] In this embodiment, the outlet temperature of the primary vacuum heating furnace 6 is 380-395℃, and the outlet temperature of the secondary vacuum heating furnace 7 is 400-415℃. The secondary vacuum heating furnace 7 adopts a variable diameter spiral tube with a material flow velocity of 1.2-1.8m / s inside the tube. The steam injection rate of the multi-point steam injection module is 2%-4% of the total material feed rate, and the steam injection temperature is 320-350℃.

[0021] In this embodiment, the spiral guide vane 93 has a helix angle of 35-45°, the gas phase through hole diameter is 8-12mm, and the inner wall roughness Ra of the liquid collecting cone 95 is ≤0.8μm.

[0022] In this embodiment, the gradient vacuum inside the pressure reducing tower 8 is 1-3 kPaA at the top of the tower, 2-4 kPaA at the feed section, and 3-5 kPaA at the bottom of the tower; the anti-scorching agent is a nano-silica composite anti-scorching agent with an injection concentration of 60-100 ppm.

[0023] This embodiment also proposes a method for preventing coking in a atmospheric and vacuum distillation unit through staged gradient heat exchange and deep-drawing, including the following steps: S1. After being heated, crude oil enters atmospheric distillation tower 2 for distillation, and atmospheric residue is obtained at the bottom of the tower. S2. The atmospheric residue oil is successively heated to 350-370℃ through the low-temperature heat exchange section 3, medium-temperature heat exchange section 4, and high-temperature heat exchange section 5 of the graded gradient heat exchange unit B. S3. After heat exchange, the residual oil is heated to 400-415℃ in stages by the primary vacuum heater 6 and the secondary vacuum heater 7, while superheated steam is injected simultaneously to suppress coking and maintain the turbulent state of the material. S4. After heating, the material enters the cyclone gas-liquid pre-separation system 9 of the vacuum tower 8. After cyclone separation, the gas phase is sent to the rectification section of the vacuum tower 8, and the liquid phase is sent to the feed section of the vacuum tower 8. S5, Gradient vacuum distillation in pressure reducing tower 8, part of the residue oil at the bottom of the tower is recycled and further extracted, part is sent out of the unit, and anti-coking agent is injected online at the same time. S6 and the intelligent control unit E collect parameters in real time and automatically adjust the operating parameters of each node to achieve anti-scorching early warning and stable operation.

[0024] In this embodiment, during step S3, the flow velocity inside the material pipe is maintained at 1.2-1.8 m / s.

[0025] In this embodiment, in step S5, the concentration of the anti-scorching agent is 60-100 ppm, and the vacuum level of each section of the pressure reducing tower is finely adjusted in real time. Example 2

[0026] A 6 million tons / year atmospheric and vacuum distillation unit in an oil refinery processes Middle Eastern heavy crude oil (11.5% residual carbon, 7.8% asphaltene content). The system and method of this invention were used for its modification and operation. Atmospheric residue oil undergoes staged gradient heat exchange, with the low-temperature section heated to 200℃, the medium-temperature section to 280℃, and the high-temperature section to 360℃. The outlet temperature of the primary vacuum heater is 390℃, and the outlet temperature of the secondary vacuum heater is 408℃. The steam injection rate is 3% of the feed rate, and the steam injection temperature is 330℃. The spiral angle of the swirl guide vanes is 40°. The vacuum degree at the top of the vacuum tower is 2 kPaA, at the feed section it is 3 kPaA, and at the bottom it is 4 kPaA. The concentration of the anti-coking agent is 80 ppm.

[0027] Operating results: The unit operated continuously for 22 months without significant coking, the yield of vacuum wax oil increased by 4.3%, the content of light components below 500℃ in the residue oil decreased to 3.6%, the overall energy consumption decreased by 13.8%, and the annual economic benefits increased by more than 90 million yuan. Example 3

[0028] A newly built 4 million tons / year atmospheric and vacuum distillation unit is designed and installed using the system of this invention. The feedstock is naphthenic heavy crude oil. The operating parameters are as follows: residual oil temperature after staged gradient heat exchange is 355℃, primary heater outlet temperature is 385℃, secondary heater outlet temperature is 405℃, steam injection rate is 2.5%, vacuum degree at the top of the vacuum tower is 2 kPaA, and anti-coking agent injection concentration is 70 ppm.

[0029] Operating results: The unit operated stably, with no coking in the furnace tubes and vacuum tower. The yield of vacuum wax oil increased by 3.8%, and the thermal energy utilization rate increased by 22% compared with the traditional unit, achieving the goal of long-term, high-efficiency operation.

[0030] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A graded gradient heat exchange and decompression deep-drawing anti-coking system for atmospheric and vacuum distillation devices, characterized in that, It includes an atmospheric pressure unit (A), a graded gradient heat exchange unit (B), a segmented vacuum heating unit (C), a vacuum distillation unit (D), and an intelligent control unit (E). The atmospheric pressure unit (A) includes an atmospheric pressure furnace (1) and an atmospheric pressure tower (2). The bottom outlet of the atmospheric pressure tower (2) is connected to the graded gradient heat exchange unit (B). The graded gradient heat exchange unit (B) is provided with independent low temperature heat exchange section (3), medium temperature heat exchange section (4), and high temperature heat exchange section (5) in sequence. The temperature difference of the three heat exchange sections increases step by step. The heat source of the low temperature heat exchange section (3) is the hot oil (21) on the side of the atmospheric pressure tower. The heat source of the medium temperature heat exchange section (4) is the wax oil (82) on the side of the vacuum tower. The heat source of the high temperature heat exchange section (5) is the high temperature residue oil (114) at the bottom of the vacuum tower. The segmented pressure-reducing heating unit (C) includes a first-stage pressure-reducing heating furnace (6) and a second-stage pressure-reducing heating furnace (7) connected in series. Both heating furnaces are equipped with temperature sensors and multi-point steam injection modules. The discharge end of the second-stage pressure-reducing heating furnace (7) is connected to the cyclone gas-liquid pre-separation system (9) inside the pressure-reducing tower (8). The vacuum distillation unit (D) includes a vacuum tower (8), a cyclone gas-liquid pre-separation system (9), a combined vacuum system (10), and a bottom circulation module (11). The bottom circulation module (11) includes a circulation pump (111), a filter (112), and an online anti-scorching agent injection system (113). The cyclone gas-liquid pre-separation system (9) includes a pre-separation cylinder (92), a cyclone guide assembly, a gas-liquid splitting baffle (94), and a liquid collecting cone (95); the inner wall of the pre-separation cylinder (92) is provided with a spiral cyclone guide plate (93), the gas-liquid splitting baffle (94) is located above the cyclone guide assembly, the baffle has a gas phase passage hole, the top of the pre-separation cylinder (92) is provided with a gas phase guide pipe (96), and the liquid collecting cone (95) is connected to the vacuum distillation unit (D); The intelligent control unit (E) includes a PLC controller and multiple sets of acquisition sensors, and each actuator is electrically connected to the PLC controller.

2. The staged gradient heat exchange and decompression deep-drawing anti-coking system for atmospheric and vacuum distillation devices according to claim 1, characterized in that, In the graded gradient heat exchange unit (B), the low temperature heat exchange section (3) has a heat exchange temperature difference of 30-45℃, and the residual oil is heated to 180-220℃; the medium temperature heat exchange section (4) has a heat exchange temperature difference of 50-65℃, and the residual oil is heated to 260-300℃; the high temperature heat exchange section (5) has a heat exchange temperature difference of 70-85℃, and the residual oil is heated to 350-370℃; the low temperature heat exchange section (3), the medium temperature heat exchange section (4), and the high temperature heat exchange section (5) are all shell and tube type, and anti-eddy current baffles are installed in both the shell side and the tube side.

3. The staged gradient heat exchange and decompression deep-drawing anti-coking system for atmospheric and vacuum distillation devices according to claim 2, characterized in that, The outlet temperature of the primary pressure-reducing heating furnace (6) is 380-395℃, and the outlet temperature of the secondary pressure-reducing heating furnace (7) is 400-415℃. The secondary pressure-reducing heating furnace (7) adopts a variable diameter spiral tube with a material flow rate of 1.2-1.8m / s inside the tube. The steam injection amount of the multi-point steam injection module is 2%-4% of the total material feed amount, and the steam injection temperature is 320-350℃.

4. The staged gradient heat exchange and decompression deep-drawing anti-coking system for atmospheric and vacuum distillation devices according to claim 3, characterized in that, The swirling guide vane (93) has a helix angle of 35-45°, a gas phase through-hole diameter of 8-12 mm, and an inner wall roughness Ra≤0.8 μm for the liquid collecting cone (95).

5. The staged gradient heat exchange and decompression deep-drawing anti-coking system for atmospheric and vacuum distillation devices according to claim 4, characterized in that, The vacuum gradient inside the pressure reducing tower (8) is 1-3 kPaA at the top of the tower, 2-4 kPaA at the feed section, and 3-5 kPaA at the bottom of the tower; the anti-scorching agent is a nano-silica composite anti-scorching agent with an injection concentration of 60-100 ppm.

6. A method for preventing coking in a staged gradient heat exchange and decompression deep-drawing vacuum device based on any one of the systems described in claims 1-5, characterized in that, Includes the following steps: S1. After being heated, crude oil enters the atmospheric distillation tower (2) for distillation, and atmospheric residue oil is obtained at the bottom of the tower. S2. The atmospheric residue oil is heated to 350-370℃ by passing through the low temperature heat exchange section (3), medium temperature heat exchange section (4), and high temperature heat exchange section (5) of the graded gradient heat exchange unit (B). S3. After heat exchange, the residual oil is heated to 400-415℃ in stages by the first-stage vacuum heater (6) and the second-stage vacuum heater (7), and superheated steam is injected simultaneously to suppress coking and maintain the turbulent state of the material. S4. After heating, the material enters the cyclone gas-liquid pre-separation system (9) of the pressure reducing tower (8). After cyclone separation, the gas phase is sent to the rectification section of the pressure reducing tower (8), and the liquid phase is sent to the feed section of the pressure reducing tower (8). S5. Gradient vacuum distillation in the pressure reducing tower (8), the bottom residue oil is partially recycled and further extracted, and part of it is sent out of the device. At the same time, anti-coking agent is injected online. S6, the intelligent control unit (E) collects parameters in real time and automatically adjusts the operating parameters of each node to achieve anti-scorching early warning and stable operation.

7. The method for preventing coking in a staged gradient heat exchange and decompression deep-drawing vacuum device according to claim 6, characterized in that, In S3, the flow velocity inside the material pipe is maintained at 1.2-1.8 m / s.

8. The method for preventing coking in a staged gradient heat exchange and decompression deep-drawing vacuum device according to claim 6, characterized in that, In S5, the concentration of the anti-scorching agent is 60-100ppm, and the vacuum level of each section of the pressure reducing tower is finely adjusted in real time.

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