A quench oil system and quenching method for an ethylene cracker

Abstract

The application discloses an ethylene cracking device quenching oil system and a quenching method, and the quenching oil system is additionally provided with a precooling tower on the basis of an ethylene cracking furnace, a quenching oil tower and a viscosity reducing tower, wherein a lower discharge pipeline of the precooling tower is connected with an upper part of the viscosity reducing tower, an upper discharge pipeline of the precooling tower is connected with the quenching oil tower, a lower discharge pipeline of the quenching oil tower is connected with a middle part of the viscosity reducing tower, and the quenching oil after viscosity reduction is finally returned to the precooling tower. The system avoids the direct contact between high-temperature cracking gas and quenching oil by additionally arranging the precooling tower, and separates high-viscosity cracking heavy oil containing asphalt impurities through the viscosity reducing tower, so that the viscosity of the quenching oil is reduced, the operation cycle of the quenching oil system is increased, the ethylene cracking device plan shutdown for overhaul is prolonged from 1 year / time to 3-4 years / time, the tower kettle temperature of the quenching oil tower is increased by 5-15 DEG C, and the input of supplementary medium-pressure steam is reduced by 80-120 kg / t of ethylene product.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of ethylene cracking device quenching oil system and quenching method, especially a kind of quenching oil system and quenching method for extending system operation cycle and promoting energy utilization. BACKGROUND

[0002] Steam thermal cracking device is typical petrochemical process device, and the device is used for producing ethylene, propylene, butadiene and other olefin products and benzene, toluene, xylene and other aromatic products with naphtha, atmospheric diesel and other liquid phase fractions as cracking raw materials.Quenching oil system is applied to the first process after ethylene production cracking process, and it is an important component of ethylene device and a key equipment for recovering heat, which separates heavy components such as cracking gasoline, cracking diesel and cracking fuel oil from cracking gas in the cooling process, and further recovers heat.The temperature of cracking gas is reduced after being treated by quenching system, thereby ensuring normal operation of ethylene device and reducing power consumption of compressor.

[0003] Viscosity problem of ethylene device quenching oil system has always been a difficult problem for safe and stable operation of the device.The root cause is that a large number of unsaturated hydrocarbons and heterocyclic compounds such as olefins, diolefins and cyclic olefins are contained in quenching oil during circulation, which will generate larger compound molecules by free radical condensation when contacting with high-temperature cracking gas in quenching device, resulting in viscosity increase of quenching oil.If viscosity is not reduced in time, it will affect and harm process pipelines and equipment of ethylene production device.

[0004] The existing method for removing asphaltene in quenching oil by gas phase countercurrent extraction in extraction tower needs to set material separation tower system and gas booster compressor for gas phase solvent regeneration and gas phase solvent recovery, and the viscosity reduction process flow is complex, and a considerable amount of energy is consumed. SUMMARY

[0005] The present application aims to provide an ethylene cracking device quenching oil system for extending system operation cycle and promoting energy utilization, and another aim is to provide a quenching method realized by the quenching oil system.

[0006] Technical scheme: The ethylene cracking device quenching oil system of the present application comprises an ethylene cracking furnace, a quenching oil tower and a viscosity reduction tower, and further comprises a precooling tower, wherein the precooling tower is connected with upstream ethylene cracking furnace and quenching boiler through pipeline, the lower discharge pipeline of precooling tower is connected with the upper part of viscosity reduction tower, and the upper discharge pipeline of precooling tower is connected with quenching oil tower; the lower discharge pipeline of quenching oil tower is connected with the middle part of viscosity reduction tower; the quenching oil after viscosity reduction enters quenching oil pump and dilution steam generator through discharge pipeline of viscosity reduction tower, and then returns to precooling tower through pipeline.

[0007] The material in the quench oil system of the ethylene plant is a dynamic balance system, fresh high-temperature cracking gas material is continuously fed in, cracking gas and cracking gasoline are continuously discharged from the top of the quench oil column, and most of the cracking gasoline is condensed and returned to the column as reflux liquid from the top of the quench oil column to maintain gas-liquid contact. The material is separated by rectification in the quench oil column, cracking diesel is continuously discharged from the middle part of the column, and cracking fuel oil is continuously discharged from the bottom part of the column.

[0008] The quench oil system of the present application adds a pre-cooling column with separation function, so that the high-temperature cracking gas is gradually cooled, avoiding direct contact with the quench oil in a single column. Because of the temperature gradient between the top and bottom of the pre-cooling column, the quench oil enters the pre-cooling column from the top with lower temperature, and the high-temperature cracking gas enters the pre-cooling column from the bottom with higher temperature, which can reduce the instantaneous increase of the quench oil temperature, thereby reducing the possibility of generating large molecular weight polymers by free radical condensation reaction, slowing down the increase of the viscosity of the quench oil, and further reducing the degree of coking and prolonging the operation cycle of the system.

[0009] Because the operating temperature of the pre-cooling column is relatively high, the light components in the quench oil are more "vaporized", and the high-viscosity heavy components in the quench oil discharged from the bottom of the column are more, so the viscosity is higher. The operating temperature of the quench oil column is relatively low, and the light components in the quench oil are more "retained", so the high-viscosity heavy components in the quench oil discharged from the bottom of the column are less, and the viscosity increases slightly. Therefore, according to the different viscosities of the materials, the material inlet is arranged at different positions of the viscosity reduction column, so that the high-viscosity quench oil separated by the pre-cooling column enters from the upper part of the viscosity reduction column, and the medium-viscosity quench oil separated by the quench oil column enters from the middle part of the viscosity reduction column, so as to adopt a differentiated viscosity reduction process, optimize the process, and improve the separation efficiency. The quench oil after viscosity reduction treatment is returned to the pre-cooling column through the quench oil pump and the dilution steam generator, realizing the recycling of the material.

[0010] Further, the quench oil system further comprises a process water pump, and the process water pumps are connected in parallel.

[0011] The quench oil system of the present application generally comprises two parallel process water pumps, one of which is in operation and the other is in standby, so as to change the natural circulation of the process water from gravity flow to forced circulation after pressurization by the process water pump, increase the circulation amount of the process water, improve the heat transfer coefficient, strengthen the heat transfer effect, further increase the production of dilution steam, reduce the input of supplementary medium-pressure steam, and reduce the discharge of process sewage. At the same time, the operation pressure of the process water side is increased, the pressure difference between the high-temperature high-pressure side quench oil and the low-temperature low-pressure side process water is reduced, the internal leakage of the dilution steam generator is slowed down, and the possibility of online switching of the dilution steam generator for emergency repair is reduced.

[0012] Further, the pre-cooling column is provided with a quench oil flow regulating device.

[0013] By adjusting the flow of quenching oil, the temperature of the pre-cooling tower bottom is controlled to ensure the distillation separation and cooling effect of high-temperature pyrolysis gas.

[0014] Further, the viscosity-reducing tower is provided with a pressure regulating device.

[0015] By adjusting the pressure of the viscosity-reducing tower, the temperature of the viscosity-reducing tower bottom is controlled to ensure the effective viscosity reduction of quenching oil with different viscosities.

[0016] Further, the pre-cooling tower, quenching oil tower or viscosity-reducing tower is provided with a tower plate, which is one of a corrugated plate, a large-pore sieve plate and a guide sieve plate.

[0017] By increasing the low-pressure drop and high-flux tower plate, the temperature difference between the top and bottom of the tower is increased to improve the separation effect of the distillation tower.

[0018] The quenching method realized by the above quenching oil system comprises the following steps:

[0019] (1) the pyrolysis raw material from outside enters the ethylene cracking furnace to perform steam thermal cracking reaction and is rapidly cooled by a quenching boiler to terminate the reaction to become high-temperature pyrolysis gas;

[0020] (2) the high-temperature pyrolysis gas enters the pre-cooling tower to perform material distillation separation and primary cooling, the top separation obtains medium-temperature pyrolysis gas, and the bottom separation obtains high-viscosity quenching oil;

[0021] (3) the medium-temperature pyrolysis gas enters the quenching oil tower to perform material distillation separation and secondary cooling, the top separation obtains low-temperature pyrolysis gas, and the bottom separation obtains medium-viscosity quenching oil;

[0022] (4) the high-viscosity quenching oil and the medium-viscosity quenching oil respectively enter the viscosity-reducing tower to perform viscosity reduction treatment to obtain viscosity-reduced quenching oil;

[0023] (5) the viscosity-reduced quenching oil is pressurized by a quenching oil pump, becomes low-temperature quenching oil after the heat is removed by a dilution steam generator, and is returned to the top of the pre-cooling tower;

[0024] (6) the process water is pressurized by a process water pump and forced to circulate, is vaporized into dilution steam after obtaining heat in the dilution steam generator.

[0025] Preferably, the steam thermal cracking reaction temperature of the ethylene cracking furnace naphtha raw material is 825-865℃, the reaction pressure is 0.14-0.22MPaA, and the dilution steam mass ratio is DS:HC=0.45-0.60:1.00; the steam cracking reaction temperature of the ethylene cracking furnace atmospheric diesel raw material is 785-825℃, the reaction pressure is 0.14-0.22MPaA, and the dilution steam mass ratio is DS:HC=0.65-0.80:1.00.

[0026] Preferably, the operating pressure of the precooling tower is 0.13 to 0.21 MPa, the operating temperature at the top of the tower is 175 to 235°C, and the operating temperature at the bottom of the tower is 230 to 290°C.

[0027] Preferably, the operating pressure of the quenching oil tower is 0.12-0.20 MPaA, the operating temperature at the top of the tower is 101-121℃, and the operating temperature at the bottom of the tower is 175-235℃.

[0028] Preferably, the operating pressure of the viscosity reduction tower is 0.13 to 0.21 MPa, the operating temperature at the top of the tower is 240 to 280°C, and the operating temperature at the bottom of the tower is 260 to 300°C.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0030] (1) Extend the system operation cycle, and extend the major overhaul cycle of the ethylene cracking unit to 3-4 years; increase the bottom temperature of the quench oil tower by 5-15°C, increase the heat recovery and dilution steam generation, and reduce the external supplementary medium-pressure steam input of 80-120 kg / ton of ethylene product.

[0031] (2) Optimize the structure of the viscosity reduction tower, adopt a differentiated viscosity reduction process, optimize the process, and improve the separation efficiency;

[0032] (3) Pressurize and force the process water to circulate, improve the heat exchange efficiency of the process water, further reduce the energy consumption of the process system and reduce wastewater discharge. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the quench oil system structure of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0035] Example 1

[0036] like Figure 1 As shown, the quench oil system of the present invention mainly includes an ethylene cracking furnace 5, a precooling tower 1, a quench oil tower 2, and a viscosity-reducing tower 3. The precooling tower 1 is connected to the upstream ethylene cracking furnace 5 and the quench boiler 6 via pipeline 11. The lower discharge pipeline 13 of the precooling tower 1 is connected to the upper part of the viscosity-reducing tower 3, and the upper discharge pipeline 12 of the precooling tower 1 is connected to the quench oil tower 2. The lower discharge pipeline 14 of the quench oil tower 2 is connected to the middle part of the viscosity-reducing tower 3. The viscosity-reduced quench oil enters the quench oil pump 7 and the dilution steam generator 8 via the discharge pipeline 15 of the viscosity-reducing tower 3, and then returns to the precooling tower 1 via pipeline 17. The above-mentioned quench oil system also includes a parallel process water pump 4 at the rear of the viscosity-reducing tower 3.

[0037] During system operation, the pyrolysis feedstock from outside the system enters the convection section of ethylene cracking furnace 5 for preheating, and dilution steam also enters the convection section of ethylene cracking furnace 5 for preheating. The preheated pyrolysis feedstock and dilution steam are combined and mixed, and then re-enter the convection section of ethylene cracking furnace 5 for heating. They then enter the radiation section of ethylene cracking furnace 5 for steam thermal cracking reaction, producing basic organic chemical products such as ethylene, propylene, butadiene, benzene, toluene, and xylene. The cracked gas after the reaction is rapidly cooled by quench boiler 6 to terminate the steam thermal cracking reaction. The high-temperature cracked gas exiting quench boiler 6 enters the bottom of precooling tower 1 via pipeline 11, and the low-temperature quench oil enters the top of precooling tower 1 via pipeline 17. The materials undergo gas-liquid contact within precooling tower 1, resulting in heat and mass transfer, thus avoiding the phenomenon of a sudden temperature increase in the quench oil due to direct contact between the high-temperature cracked gas and the quench oil. The medium-temperature pyrolysis gas flowing from the top of precooling tower 1 enters the bottom of quench oil tower 2 via pipeline 12. Pyrolysis gasoline from outside the boundary enters the top of quench oil tower 2 via pipeline 16. The materials undergo gas-liquid contact within quench oil tower 2, resulting in heat and mass transfer. The low-temperature pyrolysis gas flowing from the top of quench oil tower 2 is then discharged outside the boundary via pipeline 18. The high-viscosity quench oil flowing from the bottom of precooling tower 1 enters the top of viscosity reduction tower 3 via pipeline 13. The medium-viscosity quench oil flowing from the bottom of quench oil tower 2 enters the viscosity reduction tower 3 via pipeline 14. The materials undergo gas-liquid contact within viscosity reduction tower 3, resulting in heat and mass transfer. The high-viscosity pyrolysis heavy oil containing asphalt impurities flowing from the bottom of viscosity reduction tower is then discharged outside the boundary via pipeline 19. The viscous quench oil flowing out from the top of the viscous reduction tower 3 first enters the quench oil pump 7 via pipeline 15 for pressurization, and then passes through the dilution steam generator 8 to vaporize process water to remove heat, becoming low-temperature quench oil, and then returns to the top of the precooling tower 1 via pipeline 17.

[0038] Fresh process water from outside the boundary enters the dilution steam drum 9. The process water flowing out of the dilution steam drum 9 is pressurized by the process water pump 4 to become circulating process water for forced circulation. It absorbs heat through the dilution steam generator 8, and part of the circulating process water vaporizes into dilution steam and enters the dilution steam drum 9. The dilution steam with water droplets removed in the dilution steam drum 9 flows out and returns to the convection section of the ethylene cracking furnace 5.

[0039] Example 2

[0040] like Figure 1 The process flow shown is for a 115,000-ton / year ethylene cracking unit using naphtha (NAP) as the cracking feedstock. Process parameters and operating results are shown in Table 1. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 8°C to 190°C. A major overhaul is planned every 3.2 years, reducing the supplementary medium-pressure steam input by 1.29 tons / hour.

[0041] Comparative Example 1

[0042] The existing technology has a production capacity of 115,000 tons / year for ethylene cracking, using naphtha (NAP) as the cracking feedstock. The process parameters and operating results are shown in Table 2. The bottom operating temperature of the quench oil tower in the quench oil system is 182℃. The planned major overhaul is once every 1.0 year. The problem is that the process flow is long, the operating energy consumption is high, and the economic benefits are poor.

[0043] Example 3

[0044] like Figure 1 The process flow shown is for a 1 million tons / year ethylene cracking unit using atmospheric diesel (AGO) as the cracking feedstock. Process parameters and operating results are shown in Table 1. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 10°C to 215°C. A major overhaul is planned every 3.0 years, reducing the supplementary medium-pressure steam input by 12.50 tons / hour.

[0045] Comparative Example 2

[0046] The existing technology has a production scale of 1 million tons / year for ethylene cracking units, using atmospheric diesel (AGO) as the cracking feedstock. The process parameters and operating results are shown in Table 2. The bottom operating temperature of the quench oil tower in the quench oil system is 205℃, and a major overhaul is planned once every 1.0 year. This results in a long process flow, high operating energy consumption, and poor economic benefits.

[0047] Example 4

[0048] like Figure 1 The process flow shown is for a 1.5 million tons / year ethylene cracking unit, currently the largest single-line cracking unit in terms of production capacity. Naphtha (NAP) is used as the cracking feedstock. The process parameters and operating results are shown in Table 1. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 10°C to 195°C. A major overhaul is planned every 4.0 years, reducing the supplementary medium-pressure steam input by 18.75 tons / hour.

[0049] Comparative Example 3

[0050] The existing ethylene cracking unit has a production capacity of 1.5 million tons / year, which is currently the largest single-line cracking unit in terms of production capacity. It uses naphtha (NAP) as the cracking feedstock. The process parameters and operating results are shown in Table 2. The bottom operating temperature of the quench oil tower in the quench oil system is 185℃. The planned major overhaul is once every 1.0 year. It has problems such as long process flow, high operating energy consumption, and poor economic benefits.

[0051] Table 1. Process parameters and operational results of Examples 2-4

[0052]

[0053]

[0054] Table 2. Process parameters and operating results of Comparative Examples 1-3

[0055] Comparative Example 1 Comparative Example 2 Comparative Example 3 Production size (kiloton / year) 11.5 100 150 Cracking feedstock: Naphtha NAP / Atmospheric Gas Oil AGO NAP AGO NAP Cracking furnace cracking reaction pressure (MPaA) 0.18 0.14 0.22 Cracking furnace cracking reaction temperature (°C) 845 785 865 Dilution steam to cracking feed mass ratio (wt:wt) 0.50：1.00 0.65：1.00 0.60：1.00 Quench oil column operating pressure (MPaA) 0.16 0.12 0.20 Quench oil column overhead operating temperature (°C) 108 106 116 Quench oil column bottom operating temperature (°C) 182 205 185 Scheduled shutdown major turnaround (year / once) 1.0 1.0 1.0

[0056] Example 5

[0057] like Figure 1 The process flow shown in this embodiment relates to a system and method for quench oil in an ethylene cracking unit. The unit has a production scale of 3 million tons / year and is considered as two parallel production lines. Atmospheric diesel (AGO) is used as the cracking feedstock. Process parameters and operating results are shown in Table 3. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 12°C to 220°C. A major overhaul is planned every 3.8 years, reducing the supplementary medium-pressure steam input by 41.25 tons / hour.

[0058] Comparative Example 4

[0059] The existing technology has a production capacity of 3 million tons / year for ethylene cracking units. Considering two parallel production lines, atmospheric diesel (AGO) is used as the cracking feedstock. The process parameters and operating results are shown in Table 4. The bottom operating temperature of the quench oil tower in the quench oil system is 208℃. The planned major overhaul is once every 1.0 year. This results in a long process flow, high operating energy consumption, and poor economic benefits.

[0060] Example 6

[0061] like Figure 1 The process flow shown in this embodiment relates to a system and method for quench oil in an ethylene cracking unit with a production scale of 1 million tons / year. Naphtha (NAP) is used as the cracking feedstock. The process parameters and operating results are shown in Table 3. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 5°C to 175°C. The planned major overhaul is carried out every 3.0 years, reducing the supplementary medium-pressure steam input by 10.00 tons / hour.

[0062] Comparative Example 5

[0063] The existing technology is for an ethylene cracking unit with a production capacity of 1 million tons / year, using naphtha NAP as the cracking feedstock. The process parameters and operating results are shown in Table 4. The bottom operating temperature of the quench oil tower in the quench oil system is 170℃, and a major overhaul is planned once every 1.0 year. This results in a long process flow, high operating energy consumption, and poor economic benefits.

[0064] Example 7

[0065] like Figure 1The process flow shown in this embodiment relates to a system and method for quench oil in an ethylene cracking unit with a production scale of 1 million tons / year. Atmospheric diesel (AGO) is used as the cracking feedstock. Process parameters and operating results are shown in Table 3. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 15°C to 235°C. A major overhaul is planned every 4.0 years, reducing the supplementary medium-pressure steam input by 15.00 tons / hour.

[0066] Comparative Example 6

[0067] The existing technology has a production scale of 1 million tons / year for ethylene cracking units, using atmospheric diesel (AGO) as the cracking feedstock. The process parameters and operating results are shown in Table 4. The bottom operating temperature of the quench oil tower in the quench oil system is 220℃, and the planned major overhaul is once every 1.0 year. This results in a long process flow, high operating energy consumption, and poor economic benefits.

[0068] Table 3. Process parameters and operational results of Examples 5-7

[0069]

[0070]

[0071] Table 4. Process parameters and operating results of comparative examples 4-6

[0072] Comparative Example 4 Comparative Example 5 Comparative Example 6 Production size (kiloton / year) 300 100 100 Cracking feedstock: Naphtha NAP / Atmospheric Gas Oil AGO AGO NAP AGO Cracking furnace cracking reaction pressure (MPaA) 0.17 0.14 0.22 Cracking furnace cracking reaction temperature (°C) 805 825 825 Dilution steam to cracking feed mass ratio (wt:wt) 0.75：1.00 0.45：1.00 0.80：1.00 Quench oil column operating pressure (MPaA) 0.15 0.12 0.20 Quench oil column overhead operating temperature (°C) 114 101 121 Quench oil column bottom operating temperature (°C) 208 170 220 Scheduled shutdown major turnaround (year / once) 1.0 1.0 1.0

[0073] Example 8

[0074] like Figure 1 The process flow shown in this embodiment relates to a system and method for quench oil in an ethylene cracking unit. The unit has a production scale of 1 million tons / year and uses 10% naphtha (NAP) and 90% atmospheric diesel (AGO) as cracking feedstocks. Process parameters and operating results are shown in Table 5. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 13°C to 210°C. A major overhaul is planned every 3.3 years, reducing the supplementary medium-pressure steam input by 13.75 tons / hour.

[0075] Comparative Example 7

[0076] The existing technology has a production scale of 1 million tons / year for ethylene cracking units, using 10% naphtha (NAP) and 90% atmospheric diesel (AGO) as cracking feedstocks. The process parameters and operating results are shown in Table 6. The bottom operating temperature of the quench oil tower in the quench oil system is 197℃, and a major overhaul is planned once every 1.0 year. This results in a long process flow, high operating energy consumption, and poor economic benefits.

[0077] Example 9

[0078] like Figure 1The process flow shown in this embodiment relates to a system and method for quench oil in an ethylene cracking unit. The unit has a production scale of 1 million tons / year and uses 50% naphtha (NAP) and 50% atmospheric diesel (AGO) as cracking feedstocks. Process parameters and operating results are shown in Table 5. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 10°C to 205°C. A major overhaul is planned every 3.5 years, reducing the supplementary medium-pressure steam input by 12.50 tons / hour.

[0079] Comparative Example 8

[0080] The existing technology is for an ethylene cracking unit with a production capacity of 1 million tons / year, using 50% naphtha (NAP) and 50% atmospheric diesel (AGO) as cracking feedstocks. The process parameters and operating results are shown in Table 6. The bottom operating temperature of the quench oil tower in the quench oil system is 195℃, and a major overhaul is planned once every 1.0 year. This results in a long process flow, high operating energy consumption, and poor economic benefits.

[0081] Example 10

[0082] like Figure 1 The process flow shown in this embodiment relates to a system and method for quench oil in an ethylene cracking unit with a production scale of 1 million tons / year. The unit uses 80% naphtha (NAP) and 20% atmospheric diesel (AGO) as cracking feedstock. Process parameters and operating results are shown in Table 5. The bottom operating temperature of the quench oil tower in the quench oil system is increased by 7°C to 200°C. A major overhaul is planned every 3.7 years, reducing the supplementary medium-pressure steam input by 11.25 tons / hour.

[0083] Comparative Example 9

[0084] The existing technology is for an ethylene cracking unit with a production capacity of 1 million tons / year, using 80% naphtha (NAP) and 20% atmospheric diesel (AGO) as cracking feedstocks. The process parameters and operating results are shown in Table 6. The bottom operating temperature of the quench oil tower in the quench oil system is 193℃, and a major overhaul is planned once every 1.0 year. This results in a long process flow, high operating energy consumption, and poor economic benefits.

[0085] Table 5. Process parameters and operational results of Examples 8-10

[0086] Example 8 Example 9 Example 10 Production size (kiloton / year) 100 100 100 Cracking feedstock: Naphtha NAP / Atmospheric Gas Oil AGO 10% N + 90% A 50% N + 50% A 80% N + 20% A Cracking furnace cracking reaction pressure (MPaA) 0.16 0.19 0.20 Cracking furnace cracking reaction temperature (°C) 820 825 830 Dilution steam to cracking feed mass ratio (wt:wt) 0.70：1.00 0.65：1.00 0.55：1.00 Pre-cooling column operating pressure (MPaA) 0.15 0.18 0.19 Pre-cooling column overhead operating temperature (°C) 210 205 200 Pre-cooling column bottom operating temperature (°C) 265 260 255 Quench oil column operating pressure (MPaA) 0.14 0.17 0.18 Quench oil column overhead operating temperature (°C) 113 111 109 Quench oil column bottom operating temperature (°C) 210 205 200 Visbreaker column operating pressure (MPaA) 0.15 0.18 0.19 Visbreaker column overhead operating temperature (°C) 265 260 255 Visbreaker column bottom operating temperature (°C) 285 280 275 Scheduled shutdown major turnaround (year / once) 3.3 3.5 3.7 Increase quench oil column bottom temperature (°C) 13 10 7 Reduce make-up medium pressure steam input (tons / hour) 13.75 12.50 11.25

[0087] Table 6. Process parameters and operating results of comparative examples 7-9

[0088]

[0089]

Claims

1. A quench oil system for an ethylene cracking unit, comprising an ethylene cracking furnace (5), a quench oil tower (2), and a viscosity-reducing tower (3), characterized in that, It also includes a precooling tower (1), wherein the precooling tower (1) is connected to the upstream ethylene cracking furnace (5) and the quench boiler (6) via a pipeline (11), the lower discharge pipeline (13) of the precooling tower (1) is connected to the upper part of the viscosity reduction tower (3), the upper discharge pipeline (12) of the precooling tower (1) is connected to the quench oil tower (2); the lower discharge pipeline (14) of the quench oil tower (2) is connected to the middle part of the viscosity reduction tower (3); the quench oil after viscosity reduction enters the quench oil pump (7) and the dilution steam generator (8) via the discharge pipeline (15) of the viscosity reduction tower (3) and then returns to the precooling tower (1) via a pipeline (17); The material flow direction of the quench oil system is as follows: (1) The cracking feedstock from outside the boundary enters the ethylene cracking furnace (5) for steam thermal cracking reaction and then is rapidly cooled by the quench boiler (6) to terminate the reaction and become high temperature cracking gas. (2) The high-temperature cracked gas enters the precooling tower (1) for material distillation and separation and primary cooling. The top of the tower separates to obtain medium-temperature cracked gas, and the bottom of the tower separates to obtain high-viscosity quench oil. (3) The medium-temperature cracked gas enters the quench oil tower (2) for material distillation and separation and secondary cooling. The low-temperature cracked gas is obtained from the top of the tower and the medium-viscosity quench oil is obtained from the bottom of the tower. (4) High viscosity quench oil and medium viscosity quench oil are respectively fed into viscosity reduction tower (3) for viscosity reduction treatment to obtain viscosity-reduced quench oil; (5) The reduced viscosity quench oil is pressurized by the quench oil pump (7) and the heat is removed by the dilution steam generator (8), and then it becomes low temperature quench oil and returns to the top of the precooling tower (1).

2. The quench oil system according to claim 1, characterized in that, The quench oil system also includes process water pumps (4), which are connected in parallel.

3. The quench oil system according to claim 1, characterized in that, The precooling tower (1) is equipped with a quench oil flow rate regulating device.

4. The quench oil system according to claim 1, characterized in that, The viscosity reduction tower (3) is equipped with a pressure regulating device.

5. The quench oil system according to claim 1, characterized in that, The precooling tower (1), quench oil tower (2) or viscosity reduction tower (3) is equipped with a tray, which is one of corrugated plate, large aperture sieve plate or guide sieve plate.

6. A quenching method using the quenching oil system described in any one of claims 1-5, characterized in that, The rapid cooling method includes the following steps: (1) The cracking feedstock from outside the boundary enters the ethylene cracking furnace (5) for steam thermal cracking reaction and then is rapidly cooled by the quench boiler (6) to terminate the reaction and become high temperature cracking gas. (2) The high-temperature cracked gas enters the precooling tower (1) for material distillation and separation and primary cooling. The top of the tower separates to obtain medium-temperature cracked gas, and the bottom of the tower separates to obtain high-viscosity quench oil. (3) The medium-temperature cracked gas enters the quench oil tower (2) for material distillation and separation and secondary cooling. The low-temperature cracked gas is obtained from the top of the tower and the medium-viscosity quench oil is obtained from the bottom of the tower. (4) High viscosity quench oil and medium viscosity quench oil are respectively fed into viscosity reduction tower (3) for viscosity reduction treatment to obtain viscosity-reduced quench oil; (5) The viscous quenching oil is pressurized by the quenching oil pump (7), and the heat is removed by the dilution steam generator (8), and then it becomes low temperature quenching oil and returns to the top of the precooling tower (1). (6) The process water is pressurized and forced to circulate by the process water pump (4), and enters the dilution steam generator (8) to obtain heat and then vaporizes into dilution steam.

7. The quenching method according to claim 6, characterized in that, The naphtha feedstock steam thermal cracking reaction temperature of the ethylene cracking furnace (5) is 825-865℃, the reaction pressure is 0.14-0.22MPaA, and the mass ratio of the diluted steam cracking feedstock is 0.45-0.60:1.00; the atmospheric diesel feedstock steam cracking reaction temperature of the ethylene cracking furnace (5) is 785-825℃, the reaction pressure is 0.14-0.22MPaA, and the mass ratio of the diluted steam cracking feedstock is 0.65-0.80:1.

00.

8. The quenching method according to claim 6, characterized in that, The operating pressure of the precooling tower (1) is 0.13 to 0.21 MPa, the operating temperature at the top of the tower is 175 to 235°C, and the operating temperature at the bottom of the tower is 230 to 290°C.

9. The quenching method according to claim 6, characterized in that, The operating pressure of the quench oil tower (2) is 0.12-0.20 MPaA, the operating temperature at the top of the tower is 101-121℃, and the operating temperature at the bottom of the tower is 175-235℃.

10. The quenching method according to claim 6, characterized in that, The operating pressure of the viscosity reduction tower (3) is 0.13-0.21 MPaA, the operating temperature at the top of the tower is 240-280℃, and the operating temperature at the bottom of the tower is 260-300℃.

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